Commercial Emulsion Breaking - Advances in ... - ACS Publications

9 Commercial Emulsion Breaking Downloaded by NORTH CAROLINA STATE UNIV on December 7, 2012 | http://pubs.acs.org Publication Date: May 5, 1992 | doi: 10.1021/ba-1992-0231.ch009

Richard Grace Nalco Canada Inc., 3464 78th Avenue, Edmonton, Alberta, Canada T6B 2X9

This chapter’s purpose is to share the qualitative perspective of emulsion breaking held by the petroleum industry at the production or refining operations level. Incorporation of site-specific data is avoided in favor of broader conceptual information to emphasize that each commercial facility must be viewed as unique when developing emulsion-breaking goals and methods. Theories of emulsions and demulsification, variability of applied chemicals, and limitations of present demulsifier selection techniques are presented. This chapter reinforces the belief that a qualitative view of emulsion breaking is essential at this time for the petroleum industry, unless the number of variables is reduced, typically by studying each commercial facility or crude oil as a unique case. If such study is economically feasible, valid models for predicting emulsion-breaking performance may be developed and applied on a wider scale.

E l MULSIONS O F OIL A N D WATER are o n e o f m a n y p r o b l e m s d i r e c t l y associ ated w i t h t h e p e t r o l e u m i n d u s t r y , i n b o t h o i l - f i e l d p r o d u c t i o n a n d r e f i n e r y e n v i r o n m e n t s . W h e t h e r these e m u l s i o n s are c r e a t e d i n a d v e r t e n t l y o r are u n a v o i d a b l e , as i n t h e o i l - f i e l d p r o d u c t i o n area, o r are d e l i b e r a t e l y i n d u c e d , as i n refinery desalting operations, t h e e c o n o m i c necessity to e l i m i n a t e e m u l s i o n s o r m a x i m i z e o i l - w a t e r separation is present. F u r t h e r m o r e , t h e e c o n o m i c s o f o i l - w a t e r separation dictate t h e labor, resources, a n d m o n i e s d e d i c a t e d to this issue. B e f o r e w e describe t h e methods a n d e c o n o m i c s o f e m u l s i o n b r e a k i n g at c o m m e r c i a l facilities, w e w i l l restate several k e y c o n cepts c o n c e r n i n g e m u l s i o n s a n d t h e p e t r o l e u m i n d u s t r y .

Emulsions and Demulsification Theory of Emulsions. A n e m u l s i o n is a m i x t u r e o f t w o i m m i s c i b l e l i q u i d s , o n e o f w h i c h is d i s p e r s e d as d r o p l e t s i n t h e other. F o r t h e p e t r o l e u m 0065-2393/92/0231-0313 $07.75/0 © 1992 American Chemical Society

In Emulsions; Schramm, L.; Advances in Chemistry; American Chemical Society: Washington, DC, 1992.

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Downloaded by NORTH CAROLINA STATE UNIV on December 7, 2012 | http://pubs.acs.org Publication Date: May 5, 1992 | doi: 10.1021/ba-1992-0231.ch009

i n d u s t r y , the t w o l i q u i d s are usually c r u d e oils o r r e f i n e d h y d r o c a r b o n p r o d ucts a n d water. T h e p r e s e n c e o f w a t e r i n c r u d e - o i l systems is a part o f the production f r o m o i l wells. M o s t p r o d u c i n g wells w i l l produce water and o i l s i m u l t a n e o u s l y at some p o i n t i n t h e i r l i f e spans, e i t h e r as a result o f n a t u r a l f o r m a t i o n c o n d i t i o n s o r as an effect o f secondary o r tertiary p r o d u c t i o n m e t h o d s . W i t h i n the r e f i n i n g i n d u s t r y , w a t e r is e i t h e r present as a result o f w a t e r c o n t a m i n a t i o n present i n the c r u d e o i l , i n d u c e d i n t o the c r u d e o i l to " w a s h " contaminants f r o m it, o r the result o f steam i n j e c t i o n to i m p r o v e f r a c t i o n a t i o n . T h r o u g h a v a r i e t y o f m e c h a n i s m s an e m u l s i o n m a y f o r m f r o m this o i l - w a t e r m i x t u r e . E m u l s i o n s f o r m e d i n the p e t r o l e u m i n d u s t r y are p r e d o m i n a n t l y wateri n - o i l o r r e g u l a r e m u l s i o n s , i n w h i c h the o i l is the c o n t i n u o u s o r external phase a n d the d i s p e r s e d w a t e r droplets f o r m the d i s p e r s e d o r i n t e r n a l phase. R e v e r s e e m u l s i o n s , or o i l - i n - w a t e r e m u l s i o n s , are f o r m e d w h e n w a t e r c o n stitutes the c o n t i n u o u s phase a n d o i l constitutes the d i s p e r s e d phase. It is not u n u s u a l to find b o t h r e g u l a r a n d reverse e m u l s i o n s o c c u r r i n g together. M o r e c o m p l e x e m u l s i o n s have also b e e n n o t e d w h e n reverse e m u l s i o n s exist w i t h i n the i n t e r n a l phase o f a r e g u l a r e m u l s i o n . T h e c o m p l e x i t y o f these e m u l s i o n s m a y a l l o w m a n y a l t e r n a t i n g i n t e r n a l - e x t e r n a l phases, a l t h o u g h these are v e r y rare. A stable e m u l s i o n is o n e that is u n a b l e to resolve i t s e l f i n a d e f i n e d t i m e p e r i o d w i t h o u t some f o r m o f m e c h a n i c a l o r c h e m i c a l treatment. T h r e e basic c o n d i t i o n s m u s t exist b e f o r e the f o r m a t i o n o f a stable e m u l s i o n o c c u r s : 1. T w o i m m i s c i b l e l i q u i d s must b e present. T h i s c o n d i t i o n is m e t b y the simultaneous p r e s e n c e o f o i l a n d w a t e r i n m a n y p e t r o leum industry environments. 2. A n e m u l s i f y i n g agent m u s t be present to f o r m stable o i l - a n d w a t e r e m u l s i o n s (in m u c h the same m a n n e r that the n o r m a l l y i m m i s c i b l e c o m b i n a t i o n o f o i l a n d vinegar is e m u l s i f i e d b y egg whites to f o r m the stable e m u l s i o n , mayonnaise). T h e type o f o i l a n d w a t e r e m u l s i o n f o r m e d is d e p e n d e n t o n the type o f e m u l s i f y i n g agents present. E m u l s i f y i n g agents that are m o r e s o l u b l e , d i s p e r s i b l e , o r wettable i n o r b y o i l favor the d e v e l o p m e n t o f o i l as the external phase a n d h e n c e a w a t e r - i n - o i l e m u l s i o n . E m u l s i f y i n g agents that are m o r e s o l u b l e , dispers i b l e , o r wettable i n w a t e r favor the d e v e l o p m e n t o f o i l - i n w a t e r e m u l s i o n s . C o m m o n l y o c c u r r i n g e m u l s i f y i n g agents f o u n d i n p e t r o l e u m e m u l s i o n s are asphaltenes, resinous s u b stances, o i l - s o l u b l e organic acids (such as n a p h t h e n i c acid), finely d i v i d e d carbonate scales, s i l i c a , clays, m e t a l sulfates, m e t a l sulfides, o r c h e m i c a l additives. T h e s e substances u s u ally stabilize d r o p l e t interfaces b e t w e e n external a n d i n t e r n a l phases o f the e m u l s i o n .


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3. M i x i n g energy o r agitation must b e s u p p l i e d to t h e m i x t u r e o f o i l a n d w a t e r to disperse o n e l i q u i d w i t h i n the other. I n g e n e r a l , the greater the agitation o r energy a p p l i e d , the m o r e stable the e m u l s i o n . T h i s stability is a result o f the r e d u c t i o n i n d r o p l e t size o f the i n t e r n a l phase. E a c h o f these factors is v a r i a b l e . T h e c o m p o s i t i o n a n d p r o p e r t i e s o f o i l , water, a n d associated c o n t a m i n a n t s vary w i d e l y f r o m source t o source. T h e type a n d a m o u n t o f e m u l s i f y i n g agents present w i t h i n d i f f e r e n t oils a n d waters also vary w i d e l y . T h e a m o u n t o f agitation o r energy that a n o i l - w a t e r m i x t u r e is subjected to is d e p e n d e n t o n the fluid types, pressures, velocities, and m e c h a n i c a l parameters present at each c o m m e r c i a l p e t r o l e u m facility. A l t h o u g h t h e variations o f e a c h c o m p o n e n t are c o n s i d e r a b l e , the s u m total o f t h e i r effects p r o d u c e s a n almost i n f i n i t e variety o f e m u l s i o n s a n d e n v i r o n ments i n w h i c h to " b r e a k " e m u l s i o n s . A s a result, d e t e r m i n i n g t h e most costeffective m e t h o d o f b r e a k i n g a n e m u l s i o n is g e n e r a l l y a site-specific v e n t u r e . T h e o r i e s a n d m e t h o d s o f d e m u l s i f i c a t i o n are u s e d as a base f r o m w h i c h to d e v e l o p a t a i l o r - m a d e e m u l s i o n - b r e a k i n g p r o g r a m that addresses the goals o f e i t h e r t h e o i l p r o d u c e r o r the r e f i n e r i n the most cost-effective m a n n e r .

Theories of Demulsification. W i t h i n c o m m e r c i a l e m u l s i o n b r e a k i n g , a n u m b e r o f g e n e r a l rules h e l p to f o r m the basic p h i l o s o p h y o f h o w e m u l s i o n s behave: 1. P e t r o l e u m e m u l s i o n s are c o m p o s e d p r i m a r i l y o f i m m i s c i b l e l i q u i d s . S e p a r a t i o n s h o u l d b e t h e n a t u r a l t e n d e n c y o f these l i q u i d s , p r o v i d i n g a density d i f f e r e n t i a l b e t w e e n t h e l i q u i d s exists. T h e rate o f gravitational settling o r r i s i n g is d e p e n d e n t o n the surface t e n s i o n o f the droplets that f o r m the i n t e r n a l phase o f the e m u l s i o n . L a r g e droplets have less surface t e n s i o n as a f u n c t i o n o f mass t h a n s m a l l d r o p l e t s ; t h e r e f o r e , a n y t h i n g that can b e d o n e to increase d r o p l e t size, o r coalescence, w i l l increase t h e rate o f separation. A n e m u l s i o n is stable w i t h i n a g i v e n e n v i r o n m e n t . A l t e r i n g the e n v i r o n m e n t m a y affect the stability o f a n e m u l s i o n a n d thus a l l o w separation o f the phases. A stable e m u l s i o n exists o n l y w h e n e m u l s i f y i n g agents are present. E l i m i n a t i o n , alteration, o r n e u t r a l i z a t i o n o f the e m u l sifying agents w i l l a l l o w i m m i s c i b l e l i q u i d s to separate. F r o m these f o u r generalizations i t b e c o m e s apparent that a n u m b e r o f options exist i n e m u l s i o n b r e a k i n g . A n y single change i n these areas m a y


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result i n t h e r e s o l u t i o n o f a n e m u l s i o n . H o w these various factors affect


e m u l s i o n stability is p r e s e n t e d i n b r i e f as f o l l o w s . Viscosity. A n o i l w i t h a h i g h viscosity has t h e a b i l i t y t o h o l d u p m o r e a n d larger w a t e r droplets t h a n a n o i l w i t h a l o w e r viscosity. T h e viscosity o f an o i l can b e r e d u c e d b y the a p p l i c a t i o n o f heat, t h e a d d i t i o n o f a d i l u e n t , o r the a d d i t i o n o f c h e m i c a l s . L o w e r i n g t h e viscosity increases b o t h t h e rate at w h i c h w a t e r d r o p l e t s settle a n d t h e m o b i l i t y o f w a t e r droplets a n d t h e r e b y leads t o c o l l i s i o n s , coalescence, a n d a f u r t h e r increase i n t h e rate o f separa tion. Density Differential. T h e d i f f e r e n c e i n densities o f t h e t w o l i q u i d phases m a y b e i n c r e a s e d . H e a t i n g t h e e m u l s i o n t y p i c a l l y decreases t h e d e n s i t y o f the o i l at a greater rate t h a n that o f water a n d thus allows m o r e r a p i d settling o f the water. H e a v i e r o i l is t y p i c a l l y m o r e d i f f i c u l t t o d e h y d r a t e t h a n l i g h t o i l , as its density is closer to that o f water. T h e density o f the w a t e r is also i m p o r t a n t ; fresh water w i l l t e n d t o separate f r o m o i l at a s l o w e r rate t h a n salt water. Water Percentage. T h e relative p r o p o r t i o n o f o i l a n d w a t e r affects the stability o f an e m u l s i o n . I n a r e g u l a r e m u l s i o n , t h e m a x i m u m stability o f an e m u l s i o n w i l l o c c u r at a set ratio o f w a t e r t o o i l . T y p i c a l l y this m a x i m u m is f o u n d at l o w w a t e r percentages as these droplets have a m u c h s m a l l e r c h a n c e o f c o l l i d i n g w i t h o t h e r w a t e r droplets a n d coalescing. I n c r e a s i n g t h e w a t e r p e r c e n t a g e m a y destroy t h e stability o f an e m u l s i o n . Age of Emulsion. Stabilities o f e m u l s i o n s generally increase w i t h age. O x i d a t i o n , p h o t o l y s i s , e v a p o r a t i o n o f l i g h t ends, o r b a c t e r i a l a c t i o n m a y increase the ratio o f e m u l s i f y i n g agents w i t h i n a n o i l . ( L i g h t ends are l o w m o l e c u l a r - w e i g h t , l o w - d e n s i t y h y d r o c a r b o n s , s u c h as pentane, hexane, a n d b u t a n e , that w i l l v a p o r i z e xylene significantly over t i m e . ) B r e a k i n g e m u l sions as soon as possible after e m u l s i o n f o r m a t i o n w i l l e l i m i n a t e o r r e d u c e the effects o f aging. Control of Emulsifying Agents. E m u l s i f y i n g agents are necessary t o create e m u l s i o n s . T h e e l i m i n a t i o n , alteration, o r n e u t r a l i z a t i o n o f these materials allows f o r r e s o l u t i o n o r p r e v e n t i o n o f e m u l s i o n s . E l i m i n a t i o n o f e m u l s i f y i n g agents may i n c l u d e c o r r o s i o n i n h i b i t i o n p r o g r a m s to r e d u c e t h e a m o u n t o f i r o n sulfide available, c a r e f u l selection o f c o r r o s i o n i n h i b i t o r s t o a v o i d e m u l s i f i c a t i o n tendencies, o r e l i m i n a t i o n o f i n c o m p a t i b l e c r u d e oils f r o m c r u d e - o i l b l e n d s . A n i n c o m p a t i b l e c r u d e - o i l b l e n d is o n e that, w h e n b l e n d e d , results i n t h e p r e c i p i t a t i o n o f asphaltenes. T h i s p r e c i p i t a t i o n most c o m m o n l y occurs w h e n a n asphaltic c r u d e o i l is b l e n d e d w i t h a paraffinie c r u d e o i l . A l t e r a t i o n o f e m u l s i f y i n g agents w o u l d i n c l u d e s u c h measures as


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the a d d i t i o n o f an asphaltene dispersant to " t i e u p " asphaltene p o l a r sites, a d d i t i o n o f paraffin crystal m o d i f i e r s to p r e v e n t large p a r a f f i n crystals f r o m s t a b i l i z i n g e m u l s i o n s , o r r a i s i n g treating temperatures above the paraffin c l o u d p o i n t o f a c r u d e o i l . N e u t r a l i z a t i o n o f e m u l s i f y i n g agents g e n e r a l l y relates to the n e u t r a l i z a t i o n o f p o l a r charges associated w i t h the film o f e m u l s i f y i n g agents f o r m e d a r o u n d the e m u l s i f i e d droplets. N e u t r a l i z a t i o n is the f u n c t i o n c a r r i e d out b y c o m m e r c i a l e m u l s i o n breakers o r coagulants that p r o m o t e coalescence a n d t h e r e b y accelerate settling b y gravity. Agitation Control. M e a s u r e s that r e d u c e o r e l i m i n a t e agitation o f an o i l - a n d - w a t e r m i x t u r e w i l l r e d u c e e m u l s i o n stability o r p r e v e n t e m u l s i o n formation.

Performance Parameters in Production and Refining Operations W i t h i n the p e t r o l e u m i n d u s t r y , e m u l s i o n o f o i l a n d water m a y be associated w i t h every stage o f p r o d u c t i o n , t r a n s p o r t a t i o n , o r r e f i n i n g . T h e extent o f e m u l s i f i c a t i o n a n d the e c o n o m i c i m p a c t o f contaminants associated w i t h e m u l s i o n s i n h y d r o c a r b o n - p r o c e s s i n g e q u i p m e n t w i l l d e t e r m i n e w h a t treat i n g m e t h o d s , i f any, are necessary to p r o d u c e d e s i r e d h y d r o c a r b o n specifica tions. A n u n d e r s t a n d i n g o f the i m p a c t o f o i l contaminants a n d i n c o m p l e t e d e m u l s i f i c a t i o n o n k e y h y d r o c a r b o n p r o c e s s i n g areas is r e q u i r e d . T h e p r i m e areas o f c o n c e r n are t y p i c a l l y 1. h y d r o c a r b o n d e h y d r a t i o n 2. i n o r g a n i c solids a n d salt r e m o v a l 3. effluent o r p r o d u c e d - w a t e r q u a l i t y 4. o i l - w a t e r interface c o n t r o l 5. treating

temperatures

I n a b r o a d e r sense, these areas o f c o n c e r n c a n b e d i v i d e d i n t o p r o d u c t q u a l i t y issues, o p e r a b i l i t y issues, a n d energy conservation. A l t h o u g h these c o n c e r n s are v a l i d f o r b o t h the o i l p r o d u c e r a n d refiner, the p r o d u c t q u a l i t y goals o f each p o r t i o n o f the o i l i n d u s t r y m a y not be synergistic. P r o d u c e r s a n d refiners t e n d to v i e w d e m u l s i f i c a t i o n p e r f o r m a n c e p a rameters f r o m the f o l l o w i n g p e r s p e c t i v e .

Oil Dehydration. O i l p r o d u c t i o n c o m p a n i e s must b e able to b r i n g t h e i r p r o d u c t to m a r k e t . F o r most large-scale p r o d u c t i o n , this goal r e q u i r e s e n t r y i n t o a c r u d e - o i l p i p e l i n e system. P r o d u c e d o i l must m e e t o r e x c e e d p i p e l i n e specifications. I n C a n a d a , the o i l m a y not c o n t a i n m o r e t h a n 0 . 5 %


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basic s e d i m e n t a n d w a t e r ( B S & W ) as d e t e r m i n e d b y a standard B S & W test ( A S T M D 96) o r a v a r i a t i o n o f this test. P i p e l i n e specifications f o r w a t e r c o n t e n t are n e e d e d f o r a v a r i e t y o f reasons. A m o n g these are the refiner's n e e d for a p r e d i c t a b l e a n d h i g h q u a l i t y o f r a w materials, the desire o f the p i p e l i n e c o m p a n y to r e d u c e c o r r o s i o n p o t e n t i a l b y e l i m i n a t i n g the electrolyte (water) f r o m the c o r r o s i o n process, a n d the desire o f the p i p e l i n e c o m p a n y to c o n s t r u c t p i p e l i n e s o n the basis o f t h e i r capacity to d e l i v e r m a r k e t a b l e h y d r o c a r b o n p r o d u c t s r a t h e r t h a n waste materials. F a i l u r e b y the o i l p r o d u c e r to m e e t p i p e l i n e specifica tions f o r any e x t e n d e d p e r i o d o f t i m e w i l l result i n the p i p e l i n e c o m p a n y r e f u s i n g to accept p r o d u c e d o i l . T h i s o u t c o m e alone forces the o i l p r o d u c e r to ensure that e m u l s i o n s are r e s o l v e d to r e d u c e B S & W i n o i l to 0 . 5 % o r less. P r o d u c e r s p a y p i p e l i n e tariffs a c c o r d i n g to t h e i r B S & W content, so that r e d u c t i o n s i n B S & W b e l o w 0 . 5 % r e d u c e the cost o f t r a n s p o r t i n g t h e i r p r o d uct to m a r k e t . I f e a c h r e d u c t i o n i n B S & W b e l o w 0 . 5 % is less t h a n the costs necessary to achieve the n e w B S & W standard, the o i l p r o d u c e r w i l l p u r s u e that s t a n d a r d . W i t h i n the r e f i n i n g e n v i r o n m e n t , the field o f c r u d e - o i l d e h y d r a t i o n is v i e w e d s o m e w h a t d i f f e r e n t l y . T h e first process a c r u d e o i l (or b l e n d o f c r u d e oils) is subjected to is the d e s a l t i n g process. T h i s process was d e v e l o p e d w i t h the expectation that a c r u d e o i l w i l l have a k n o w n w a t e r c o n t e n t (less t h a n 0.5%) a n d a s o l u b l e i n o r g a n i c c h l o r i d e salts c o n t e n t associated w i t h this w a t e r ( f o r m a t i o n waters f r o m o i l - f i e l d p r o d u c t i o n m a y have salt contents a p p r o a c h i n g 300,000 mg^L). Salts m a y also o c c u r i n crystalline f o r m dis p e r s e d w i t h i n the o i l . A s these salts have c o n s i d e r a b l e negative effects i n the d o w n s t r e a m processes o f the refinery, it is d e s i r a b l e to r e m o v e t h e m . T h i s salt r e m o v a l is a c c o m p l i s h e d b y i n j e c t i n g a r e l a t i v e l y f r e s h w a t e r (typically 3 - 8 % o f the c r u d e - o i l v o l u m e ) i n t o the c r u d e - o i l charge l i n e to extract the salt o r " w a s h " t h e o i l . ( T h e charge l i n e is the l i n e that transfers c r u d e o i l f r o m storage o r p i p e l i n e t h r o u g h p r e h e a t exchangers to the d e salter vessel.) T h e m o r e t h o r o u g h the contact o f the w a t e r w i t h the c r u d e o i l , the h i g h e r the p o t e n t i a l f o r extracting salts. H e n c e , agitation is u s u a l l y a p p l i e d w i t h m i x valves o r i n - l i n e static mixers to p r o m o t e t h o r o u g h m i x i n g . T h i s agitation u s u a l l y creates an e m u l s i o n . T h e separation o f the o i l a n d w a t e r phases t h e n takes p l a c e i n a d e s a l t i n g vessel o r treater. A p r o b l e m m a y o c c u r h e r e i n that the separation o f o i l a n d w a t e r m a y not b e c o m p l e t e b y the t i m e the o i l exits the desalter o n its w a y to an a t m o s p h e r i c f r a c t i o n a t i o n u n i t . A n y w a t e r that r e m a i n s w i t h the c r u d e o i l w i l l have to be h e a t e d to a t m o s p h e r i c f r a c t i o n a t o r i n l e t t e m p e r a t u r e , t y p i cally 2 9 0 - 3 7 0 °C. T h i s r e q u i r e m e n t p r o v i d e s a significant cost i n f u e l gas to heat the w a t e r . A t a 20,000-m /day r e f i n e r y w i t h a desalter o u t l e t t e m p e r a t u r e o f 100 °C a n d a c r u d e - o i l h e a t e r outlet t e m p e r a t u r e o f 315 °C, each t e n t h o f a p e r c e n t o f w a t e r c a r r y o v e r w i l l result i n 20,000 k g o f w a t e r b e i n g h e a t e d 215 °C to f o r m 3


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s u p e r h e a t e d steam. I f v e r y h i g h amounts o f w a t e r c a r r y o v e r are present, the expansion o f the steam, once it enters the fractionator, m a y damage the vessel. I n c o m p l e t e d e h y d r a t i o n w i l l also r e d u c e d e s a l t i n g efficiency as the salts are c a r r i e d i n t o the system w i t h the excess water. Refiners t y p i c a l l y attempt to l i m i t w a t e r c a r r y o v e r to 0.2% i n l i g h t c r u d e oils a n d 0.4% i n heavy c r u d e oils b y a t t e m p t i n g to f u l l y resolve e m u l s i o n s w i t h i n the desalter.

Inorganic Solids and Salt Removal. F o r the o i l p r o d u c e r , the d r i v i n g force f o r the r e m o v a l o f i n o r g a n i c solids a n d salts f r o m p r o d u c e d o i l is to achieve p i p e l i n e specifications. A n y c o m b i n a t i o n o f basic sediments ( p r i m a r i l y i n o r g a n i c solids) a n d w a t e r greater t h a n 0 . 5 % w i l l p r e v e n t s h i p m e n t o f p r o d u c t . T h e r e m o v a l o f a majority o f salts is u s u a l l y a c c o m p l i s h e d as a side-effect o f r e m o v i n g excess w a t e r f r o m the c r u d e o i l . T h i s r e m o v a l necessitates disposal o f the p r o d u c e d w a t e r b y the p r o d u c e r . T y p i c a l l y , disposal is a c c o m p l i s h e d t h r o u g h d e e p disposal wells or w a t e r - f l o o d injec t i o n w e l l s . D e e p - w e l l d i s p o s a l is viable o n l y i n c e r t a i n regions because o f e n v i r o n m e n t a l concerns or regulations. T h e r e m o v a l o f solids s u c h as sands, silts, clays, a n d c o r r o s i o n p r o d u c t s must also o c c u r i f these are present i n significant quantities. H e a v y - o i l p r o d u c t i o n t y p i c a l l y contains far greater quantities o f i n o r g a n i c solids t h a n does l i g h t - o i l p r o d u c t i o n . P i p e l i n e r e q u i r e m e n t s f o r r e d u c i n g i n o r g a n i c solids c o n t e n t are n e e d e d f o r a variety o f reasons. A g a i n , the r e f i n e r wishes to receive a p r o d u c t o f p r e d i c t a b l e a n d h i g h q u a l i t y . T h e p i p e l i n e c o m p a n y wishes to transport o i l , not i n o r g a n i c solids, a n d c a n r e d u c e m a i n t e n a n c e costs b y c o n t r o l l i n g ero sion o f m e c h a n i c a l parts c a u s e d b y solids. C o n t r o l l i n g solids also helps to mitigate u n d e r d e p o s i t types o f c o r r o s i o n w i t h i n a p i p e l i n e . T h e o i l p r o d u c e r , o n the o t h e r h a n d , m u s t dispose o f any solids r e m o v e d f r o m an e m u l s i o n - t r e a t m e n t system b y l a n d f a r m i n g ( p l a c e m e n t o f waste solids i n an a p p r o v e d l a n d f i l l area), s h i p m e n t to an a p p r o v e d waste facility, r e - i n j e c t i o n t h r o u g h a d i s p o s a l w e l l or w a t e r - f l o o d system, o r s h i p m e n t to p i p e l i n e . T h e s e options are g o v e r n e d b y the a m o u n t o f o i l associated w i t h the solids, w h i c h is d i r e c t l y r e l a t e d to e m u l s i o n - b r e a k i n g capabilities a n d the a m o u n t o f solids present. I n m a n y cases it m a y b e desirable f o r a n o i l p r o d u c e r to b l e n d a p o r t i o n o f o i l - w e t solids i n t o s h i p m e n t s f o r p i p e l i n e i f the specification o f less t h a n 0 . 5 % B S & W is not e x c e e d e d . T h i s m e t h o d o f solids disposal m a y b e the most cost-effective available to the p r o d u c e r . T h e refiner's p o s i t i o n o n i n o r g a n i c solids a n d salt r e m o v a l is that as m u c h o f these contaminants (as is cost-effective) s h o u l d b e r e m o v e d f r o m the i n c o m i n g c r u d e o i l i n t o the w a s h w a t e r b y the d e s a l t i n g process. Excess c h l o r i d e salts b e c o m e catalyst poisons that p r o m o t e excessive catalyst c o n s u m p t i o n o r r e d u c e c o n v e r s i o n i n the c r a c k i n g a n d t r e a t i n g processes. C h l o r i d e salts also c o m p r o m i s e the r e l i a b i l i t y o f r e f i n e r y overheads w h e r e , b e cause o f hydrolysis u p o n h e a t i n g , they f o r m h i g h l y corrosive h y d r o c h l o r i c a c i d i n the o v e r h e a d system. ( T h e r e f i n e r y o v e r h e a d is the e q u i p m e n t , s u c h


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as exchangers, a c c u m u l a t o r s , reflux e q u i p m e n t , a n d l i n e s , that is u s e d to condense hydrocarbons and water vaporized i n a fractionation c o l u m n and e x i t i n g f r o m the top o f the c o l u m n . ) C h l o r i d e salts also cause f o u l i n g , w h i c h restricts refinery r u n lengths o r aggravates c o r r o s i o n . T h e e c o n o m i c s o f salt r e m o v a l are v e r y c o m p l i c a t e d . A salt c o n t e n t o f less t h a n 2.85 g % i (1 lb/1000 barrels) is a c o m m o n refinery target for desalted c r u d e o i l , a l t h o u g h this target varies c o n s i d e r a b l y f r o m site to site. P r i m e modifiers to this target are d e s a l t i n g e q u i p m e n t available a n d type o f c r u d e - o i l stock processed. Downloaded by NORTH CAROLINA STATE UNIV on December 7, 2012 | http://pubs.acs.org Publication Date: May 5, 1992 | doi: 10.1021/ba-1992-0231.ch009

3

T h e r e m o v a l o f i n o r g a n i c solids is also i m p o r t a n t to the refiner. B y efficient e m u l s i o n b r e a k i n g at the desalter, the refiner c a n expect to signifi cantly r e d u c e the a m o u n t o f solids c a r r i e d t h r o u g h the desalter i n t o the d o w n s t r e a m r e f i n i n g units. I n o r g a n i c solids r e m o v a l o f 8 0 % or greater is a t y p i c a l base standard, a l t h o u g h this a m o u n t varies greatly w i t h each refiner, the type o f separation e q u i p m e n t available, a n d the c r u d e oils i n v o l v e d . I n o r g a n i c solids have n u m e r o u s d e t r i m e n t a l effects o n the refiner. A s w i t h c h l o r i d e salts, m a n y solids (especially m e t a l - c o n t a i n i n g solids) may p o i s o n catalysts a n d t h e r e b y increase catalyst c o n s u m p t i o n o r r e d u c e c o n v e r s i o n o f h y d r o c a r b o n s . Solids m a y act as foulants o r p r o m o t e reactions that create f o u l i n g , w h i c h restricts heat transfer o r r u n lengths i n exchangers a n d furnaces. Excess solids m a y r e d u c e the p r o d u c t q u a l i t y o f r e s i d u a l fuels o r coke. Solids m a y also p r o m o t e f o a m i n g a n d f o u l i n g i n fractionators, w h i c h i n t u r n m a y restrict t h r o u g h p u t o r i n d u c e use o f antifoams. A l l o f these effects u s u a l l y o c c u r s i m u l t a n e o u s l y i n an i n t e g r a t e d refinery. A c c u r a t e calculations o n the e c o n o m i c i m p a c t o f i n o r g a n i c solids are extremely c o m p l i c a t e d a n d d i f f i c u l t to p e r f o r m , a l t h o u g h s u c h calculations can b e the p r i m e justifica t i o n for i m p r o v i n g desalter o p e r a t i o n . Refiners may dispose o f r e m o v e d i n o r g a n i c solids b y l a n d f a r m i n g , s h i p m e n t to a p p r o v e d waste-disposal f a c i l i ties, o r disposal to the w a t e r - h a n d l i n g system.

Effluent Water Quality, W h e n r e s o l v i n g e m u l s i o n s i n the p e t r o l e u m i n d u s t r y , water is always p r o d u c e d . I n some areas the goals o f the r e f i n e r a n d o i l p r o d u c e r are i d e n t i c a l i n effluent w a t e r quality. B o t h r e f i n e r a n d p r o d u c e r w a n t to m i n i m i z e the a m o u n t o f o i l i n the water systems, as this represents e i t h e r lost p r o d u c t , i n c r e a s e d capital, o r i n c r e a s e d o p e r a t i n g costs to r e c o v e r the o i l f r o m the water. T h e costs o f not a c h i e v i n g c o m p l e t e o i l - w a t e r separation the first t i m e i n a desalter or o i l - f i e l d treater are re flected b y the n e e d f o r e q u i p m e n t s u c h as w a t e r - s k i m tanks, w a t e r - f i l t r a t i o n e q u i p m e n t , various flotation u n i t s , clarifiers, settling p o n d s , biox u n i t s , a n d a c c u m u l a t e d - o i l treating facilities i n w a t e r - d i s p o s a l systems. E a c h o f these units w i l l have significant o p e r a t i n g costs above a n d b e y o n d the c a p i t a l costs. (A biox u n i t is a b a s i n , p o n d , o r vessel w h e r e b i o l o g i c a l activity digests organic materials s u c h as h y d r o c a r b o n s c a r r i e d w i t h the w a t e r c h a r g e d to the unit.)


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O i l p r o d u c e r s w i l l t y p i c a l l y set standards f o r o i l - i n - w a t e r content r a n g i n g f r o m less t h a n 10 p p m i n v e r y l i g h t c r u d e oils to several h u n d r e d parts p e r m i l l i o n i n v e r y heavy c r u d e o i l s . T h e s e specifications are u s u a l l y sitespecific a n d are d e p e n d e n t o n e q u i p m e n t available a n d c r u d e - o i l type. O i l p r o d u c e r s i n C a n a d a u s u a l l y have the advantage o f disposal w e l l s o r waterflood schemes i n w h i c h p r o d u c e d w a t e r is d i s p o s e d . F a i l u r e to m e e t selfi m p o s e d o i l - i n - w a t e r l i m i t s u s u a l l y results i n loss o f h y d r o c a r b o n p r o d u c t back to the f o r m a t i o n . F o r an o i l p r o d u c t i o n f a c i l i t y that disposes o f 1000 m o f w a t e r p e r day w i t h an o i l c o n t e n t o f 1000 p p m , 365 m o f o i l is lost p e r year. A t $25 ( C a n a d i a n ) p e r b a r r e l , this a m o u n t o f o i l translates to a p r o d u c t loss w o r t h a p p r o x i m a t e l y $57,000 p e r year, p l u s any m a i n t e n a n c e costs a n d w e l l s t i m u l a t i o n costs to restore injectivity lost as a result o f f o r m a t i o n p l u g g i n g f r o m o i l - w e t solids. O i l - w e t solids i n w a t e r - f l o o d systems m a y damage f o r m a t i o n p e r m e a b i l i t y a n d r e d u c e recovery.


3

I n the C a n a d i a n r e f i n i n g i n d u s t r y , o n l y refineries i n the w e s t e r n p r o v inces have access to disposal w e l l s f o r p r o d u c e d water. T h e i r c o n c e r n s are s i m i l a r to those m e n t i o n e d w i t h the o i l p r o d u c e r s . I n o t h e r areas o f the c o u n t r y , effluent waters must be treated to a standard that w i l l a l l o w f o r discharge to the e n v i r o n m e n t . T h e t y p i c a l s t a n d a r d f o r a l l o w a b l e o i l - i n w a t e r content is less t h a n 10 p p m . F a i l u r e to consistently achieve this s p e c i fication m a y result i n fines, s h u t d o w n , a n d p o o r p u b l i c p e r c e p t i o n o f the o f f e n d i n g refiner.

Oil-Water Interface Control. I n any p e t r o l e u m p r o c e s s i n g u n i t i n w h i c h e m u l s i o n s are r e s o l v e d , an interface b e t w e e n o i l a n d w a t e r m u s t o c c u r . T h e q u a l i t y o f this interface is d i r e c t l y r e l a t e d to the efficiency o f d e m u l s i f i c a t i o n i n e i t h e r a r e f i n e r y desalter o r an o i l - f i e l d f r e e - w a t e r k n o c k o u t o r treater. T h e sharper the t r a n s i t i o n b e t w e e n c l e a n w a t e r a n d c l e a n o i l (or the tightness o f the interface), the b e t t e r the a b i l i t y to c o n t r o l o i l a n d w a t e r r e t e n t i o n times a n d q u a l i t y a n d operate the vessel. B r o a d transitions b e t w e e n o i l a n d w a t e r are u s u a l l y the result o f (1) i n c o m p l e t e r e s o l u t i o n o f the e m u l s i o n , (2) f a i l u r e o f an e m u l s i o n - t r e a t i n g p r o g r a m to resolve e m u l s i o n s c a u s e d b y o n e o r m o r e specific e m u l s i f y i n g agents, (3) excess o r i n c o m p a t i b l e t r e a t i n g c h e m i c a l s , (4) b u i l d u p s o f o i l - w e t solids, (5) b u i l d u p s o f i n s o l u b l e organic materials s u c h as paraffins o r asphaltenes, o r (6) any c o m b i n a t i o n thereof. W i t h a b r o a d interface ( " r a g " , " c u f f ' , o r " p a d " layer) present, l e v e l - s e n s i n g e q u i p m e n t a n d w a t e r d u m p s m a y operate i n c o r r e c t l y or m a l f u n c t i o n , a n d t h e r e b y d i v e r t w a t e r to c l e a n - o i l outlets a n d o i l to w a t e r outlets. E l e c t r o s t a t i c grids may short out i f the p a d (usually h i g h i n w a t e r content) makes contact w i t h the g r i d s . E m u l s i o n pads also o c c u p y space w i t h i n a t r e a t i n g vessel a n d p r o m o t e c h a n n e l i n g , w h i c h affects the r e t e n t i o n t i m e o f a vessel. C o n c e n t r a t i o n o f p o l a r h y d r o c a r b o n s , e m u l s i f y i n g agents, a n d solids u s u a l l y occurs i n interface " p a d s " . T h e s e


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m o l e c u l e s have a h i g h t e n d e n c y to be d i s p e r s e d i n the w a t e r phase, b e c o m e c o n c e n t r a t e d t h r o u g h o i l - i n - w a t e r recovery processes, a n d i f r e c y c l e d , upset the vessel to f u r t h e r aggravate e m u l s i o n treatment. I n g e n e r a l , e m u l s i o n pads l i m i t the p e r f o r m a n c e o f e m u l s i o n - b r e a k i n g e q u i p m e n t a n d c h e m i c a l s . B o t h refiners a n d o i l p r o d u c e r s v i e w large e m u l s i o n pads as s y m p t o m s o f i n e f f i c i e n t e m u l s i o n treatment. I f the e m u l s i o n p a d c a n be e l i m i n a t e d , p e r f o r m a n c e i n a l l aspects o f e m u l s i o n b r e a k i n g should improve.

Treating Temperature. T r e a t i n g t e m p e r a t u r e s m a y have signifi cant impacts o n b o t h r e f i n e r y a n d o i l p r o d u c t i o n e m u l s i o n - b r e a k i n g p r o cesses. I n general, the h i g h e r the t e m p e r a t u r e , the greater the a b i l i t y to resolve e m u l s i o n s ; h o w e v e r , increases i n t r e a t i n g t e m p e r a t u r e affect m a n y o t h e r factors negatively. I n the r e f i n e r y desalter the range o f t r e a t i n g t e m peratures available is l i m i t e d b y p l a n t d e s i g n . H e a t i n g o f the c r u d e o i l u p to d e s a l t i n g t e m p e r a t u r e s is the result o f exchanger efficiencies, t h r o u g h p u t s , and plant design. T r e a t i n g t e m p e r a t u r e s are almost always d e s i g n e d to surpass p a r a f f i n crystal m e l t i n g p o i n t s ( 5 0 - 6 5 °C) a n d g e n e r a l l y a p p r o a c h the b o i l i n g p o i n t o f w a t e r at the specific u n i t pressures. T h e t r e a t i n g t e m p e r a t u r e s are u s u a l l y set to p r o v i d e the greatest a m o u n t o f d e h y d r a t i o n p o s s i b l e . A s t e m p e r a t u r e s increase, the a b i l i t y to resolve e m u l s i o n s increases, b u t so does the s o l u b i l i t y o f w a t e r i n h y d r o c a r b o n s . T e m p e r a t u r e s that w i l l p r o v i d e the greatest m e a sure o f c r u d e - o i l d e h y d r a t i o n m u s t be selected. T h i s t e m p e r a t u r e c h o i c e w i l l vary w i t h the c o m p o s i t i o n o f e a c h c r u d e o i l a n d w i t h t r e a t i n g vessel p r e s s u r e . W i t h i n the o i l - f i e l d p r o d u c t i o n facilities, m u c h greater c o n t r o l o f t e m p e r a t u r e m a y be exercised. T h e e n d goal o f the p r o d u c e r is to select a t r e a t i n g t e m p e r a t u r e that, i n c o m b i n a t i o n w i t h other factors, p r o v i d e s the most cost-effective m e t h o d o f m e e t i n g p i p e l i n e specifications a n d any sitespecific standards w i t h respect to o i l - i n - w a t e r a n d interface q u a l i t y . I n g e n e r a l , the less heat is a p p l i e d the greater the cost savings. A s heat is a p p l i e d at p r o d u c t i o n facilities b y f u e l - g a s - f i r e d heaters, any increase i n heat is r e f l e c t e d i n fuel-gas c o n s u m p t i o n . T h e a d d i t i o n o f heat also b o i l s l i g h t e r h y d r o c a r b o n fractions f r o m the c r u d e o i l ; less p r o d u c t at a l o w e r A P I gravity ( d e f i n e d i n the Glossary) results. A d d i t i o n o f heat also accelerates rates o f c o r r o s i o n a n d increases the l i k e l i h o o d o f scale f o r m a t i o n o n vessel internals, p a r t i c u l a r l y the fire tubes.

Methods of Emulsion Breaking T o m a x i m i z e the cost-effectiveness o f p e t r o l e u m p r o d u c t i o n a n d r e f i n i n g processes a n d to achieve r e q u i r e d q u a l i t y parameters o f o i l , water, a n d c r u d e - o i l c o n t a m i n a n t s , it is o f t e n necessary to resolve e m u l s i o n s to p r o m o t e c o m p l e t e separation o f the o i l , water, a n d i n o r g a n i c solids present. B r e a k i n g


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e m u l s i o n s i m p l i e s b r e a k i n g e m u l s i f y i n g films a r o u n d d r o p l e t s o f w a t e r o r o i l so that c o a l e s c i n g a n d gravitational settling m a y o c c u r . A n y o r a l l o f the f o l l o w i n g methods o f a i d i n g this process m a y b e e m p l o y e d : 1. P r o v i d i n g l o w - t u r b u l e n c e a n d l o w - v e l o c i t y e n v i r o n m e n t s (treating vessels) that a l l o w gravitational separation a n d r e m o v a l o f o i l , water, a n d solids. G a s m a y also b e r e m o v e d .


2. I n c r e a s i n g the t e m p e r a t u r e o f t h e e m u l s i o n . 3. A p p l y i n g c h e m i c a l s d e s i g n e d to b r e a k e m u l s i o n s . 4. A p p l y i n g e l e c t r i c a l fields that p r o m o t e coalescence. 5. C h a n g i n g the p h y s i c a l characteristics o f an e m u l s i o n b y the a d d i t i o n o f d i l u e n t s o r water. B e c a u s e o f the w i d e variety o f p o t e n t i a l e m u l s i o n a n d c r u d e - o i l types, m e c h a n i c a l configurations, t r e a t i n g c h e m i c a l s , t h r o u g h p u t s , a n d p r o d u c t s p e c i fications, each i n d i v i d u a l e m u l s i o n - b r e a k i n g a p p l i c a t i o n is g e n e r a l l y u n i q u e i n its selection o f specific e m u l s i o n - b r e a k i n g m e t h o d s a n d e n v i r o n m e n t s . F u r t h e r m o r e , a l l e m u l s i o n s change i n c o m p o s i t i o n w i t h t i m e , a n d h u m a n beings c o n t r o l t h e process o f e m u l s i o n b r e a k i n g ; these t w o factors r e - e m phasize this p o i n t . T h e selection o f m e c h a n i c a l e q u i p m e n t type is b a s e d p r i m a r i l y o n p r e v i ous experience. W i t h i n the r e f i n e r y d e s a l t i n g process t h e s e l e c t i o n o f m e c h a n i c a l e q u i p m e n t usually falls w i t h i n t w o b r o a d areas, one-stage desalters ( F i g u r e 1) a n d multistage desalters ( F i g u r e 2). E a c h desalter vessel is s i z e d

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to p r o v i d e a k n o w n c r u d e - o i l m i x t u r e w i t h a set r e t e n t i o n t i m e at a g i v e n rate o f c r u d e - o i l charge to w a t e r w a s h . T h i s r e t e n t i o n t i m e is d e e m e d to be adequate to a l l o w e m u l s i o n b r e a k i n g to p r o c e e d to a d e s i r e d e n d p o i n t o r o i l quality. T h e p r e h e a t exchange system w i l l heat the c r u d e - o i l to the d e s i r e d t r e a t i n g t e m p e r a t u r e . T h e d e s a l t i n g t e m p e r a t u r e is u s u a l l y d e t e r m i n e d f r o m p r e v i o u s experience w i t h s i m i l a r c r u d e oils o r f r o m s i m u l a t i o n runs u s i n g p r o p o r t i o n a l l y s m a l l e r vessels a n d flows. E x p e r i e n c e w i t h s i m i l a r c r u d e oils and any s i m u l a t i o n runs p e r f o r m e d w i l l h e l p to d e t e r m i n e the r e q u i r e m e n t s o f electrostatic grids; c r u d e - o i l d i s t r i b u t i o n systems; d e s a n d - d e s l u d g e equipment; oil-in-water removal equipment; level control equipment; washw a t e r i n j e c t i o n p o i n t s ; m i x i n g e q u i p m e n t ; a n d i n i t i a l t r e a t i n g c h e m i c a l injec t i o n p o i n t s , type, a n d dosage. E x p e r i e n c e m a y dictate that some o f this e q u i p m e n t a n d capabilities m a y not b e necessary w i t h c e r t a i n c r u d e - o i l types. M o s t m o d e r n desalters have a l l o f these capabilities. O n c e o p e r a t i o n a l , the process o f o p t i m i z i n g the d e s a l t i n g system for m a x i m u m p e r f o r m a n c e o r cost-effectiveness begins. T h r o u g h p l a n n e d m a n i p u l a t i o n o f system parameters c o n c u r r e n t w i t h m o n i t o r i n g o f the q u a l ity o f o i l , w a t e r , a n d solids p r o d u c e d , o p e r a t i o n a l data are g a i n e d . F r o m these data, o p t i m u m set p o i n t s f o r t e m p e r a t u r e , interface l e v e l , t r e a t i n g c h e m i c a l s , a d d i t i o n , w a s h - w a t e r rates a n d p l a c e m e n t , mix-valve p r e s s u r e d i f f e r e n t i a l s , a n d d e s a n d - d e s l u d g e f r e q u e n c y a n d rates are d e t e r m i n e d . T h i s process m a y take several m o n t h s . I f i n i t i a l specifications o n p r o d u c t q u a l i t y cannot be met, t h e n changes m a y be m a d e to m e c h a n i c a l e q u i p m e n t present, c h e m i c a l s a p p l i e d , rate o f c r u d e - o i l charge, type o f c r u d e o i l p r o cessed, o r p r o d u c t q u a l i t y specifications. T h e process o f o p t i m i z i n g the d e s a l t i n g p r o g r a m t h e n starts again. O n p a r t i c u l a r l y d i f f i c u l t c r u d e oils this process m a y last m a n y years, as is the case i n refineries p r o c e s s i n g heavy crude oil. W i t h i n o i l - f i e l d p r o d u c t i o n , t r e a t i n g e q u i p m e n t is s e l e c t e d i n a s i m i l a r m a n n e r . A s the a m o u n t o f w a t e r p r o d u c e d w i l l vary over the l i f e span o f an o i l field, e q u i p m e n t is o f t e n a d d e d as n e e d e d to an o i l - f i e l d t r e a t i n g facility. T h e d e s i g n o f existing facilities w i l l a l l o w the a d d i t i o n o f e q u i p m e n t to o c c u r w i t h m i n i m a l d i s r u p t i o n d u r i n g p e r i o d i c m a i n t e n a n c e shutdowns (or " t u r n a r o u n d s " ) i f p r o p e r c o n s i d e r a t i o n has b e e n g i v e n to the p o t e n t i a l o f c h a n g i n g p r o d u c t i o n fluids. T h e e q u i p m e n t variations w i t h i n o i l - f i e l d t r e a t i n g e q u i p m e n t are greater t h a n those f o u n d i n r e f i n e r y d e s a l t i n g a p p l i c a t i o n s . T h e three basic types o f m o d e r n vessels are gas separators, free-water k n o c k o u t s ( F W K O s ) , a n d treaters. G a s separators a l l o w f o r early exit o f gas f r o m the o i l , w h i c h helps to r e d u c e the a m o u n t o f agitation a n d h e n c e reduces the e m u l s i f i c a t i o n t e n d e n c i e s . T r e a t i n g c h e m i c a l s m a y be i n j e c t e d u p s t r e a m o f a gas separator. T h e F W K O is t y p i c a l l y a vessel d e s i g n e d to r e m o v e free w a t e r b e f o r e the o i l is t r a n s f e r r e d to a treater, a n d u s u a l l y allows a d d i t i o n a l re m o v a l o f gas. T h e F W K O m a y be h e a t e d b y fire tubes o r exchangers; h o w -


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ever, its t e m p e r a t u r e is u s u a l l y m u c h l o w e r t h a n that o f a treater. T h i s l o w e r t e m p e r a t u r e allows for r e m o v a l o f w a t e r f r o m a t r e a t i n g system w i t h o u t h a v i n g to heat the w a t e r to m a x i m u m system t e m p e r a t u r e s . Substantial f u e l gas savings result. T h e treater is the vessel that attempts to d e l i v e r p i p e l i n e - s p e c i f i c a t i o n c r u d e o i l as its h y d r o c a r b o n p r o d u c t . H e a t e r treaters t y p i c a l l y a i d i n resolv i n g e m u l s i o n s b y the a d d i t i o n o f heat, the use o f electrostatic grids, o r the use o f m e c h a n i c a l c o a l e s c i n g aids s u c h as hay o r baffle systems. O p t i m i z a t i o n o f o i l - f i e l d t r e a t i n g p e r f o r m a n c e parameters is a c c o m p l i s h e d i n a s i m i l a r m a n n e r to that d e s c r i b e d for r e f i n e r y desalting a p p l i c a tions.

Thermal Methods. I n b o t h r e f i n e r y a n d o i l - f i e l d e m u l s i o n break i n g , the a d d i t i o n o f heat u s u a l l y occurs to e n h a n c e e m u l s i o n b r e a k i n g . O n l y r a r e l y does the a d d i t i o n o f heat alone p r o v i d e adequate e m u l s i o n r e s o l u t i o n . I n the o i l - f i e l d e n v i r o n m e n t , r e s o l u t i o n m a y o c c u r w i t h l i g h t oils i n w h i c h p a r a f f i n f o r m s the p r i m e e m u l s i f y i n g agent. A n increase i n t e m p e r a t u r e above the p a r a f f i n m e l t i n g p o i n t ( 5 0 - 6 5 °C) may c o m p l e t e l y destabilize an e m u l s i o n . I n r e f i n e r y desalting applications a n d h e a v y - o i l p r o d u c t i o n a p p l i cations, the h i g h t r e a t i n g t e m p e r a t u r e s u s u a l l y r e m o v e p a r a f f i n as an active e m u l s i f y i n g agent. H e a t a d d i t i o n i n e m u l s i o n b r e a k i n g is u s u a l l y b a s e d o n the o v e r a l l e c o n o m i c p i c t u r e o f a t r e a t i n g facility. Excess heat is not a d d e d w h e n it is m o r e cost-effective to a d d c h e m i c a l o r i n s t a l l electrostatic grids. I n refinery d e s a l t i n g , the t e m p e r a t u r e o f the c r u d e o i l must far surpass the t e m p e r a tures present i n the desalter as the c r u d e o i l approaches the a t m o s p h e r i c f r a c t i o n a t i o n u n i t . T h u s , m i n i m i z i n g heat i n the desalter is not a k e y issue p r o v i d i n g w a t e r present i n the desalter does not b o i l , temperatures are not h i g h e n o u g h to significantly elevate w a t e r s o l u b i l i t y i n a specific c r u d e o i l , a n d h i g h t e m p e r a t u r e s d o not cause significant amounts o f asphaltenes to b e c o m e i n s o l u b l e i n the c r u d e o i l a n d f o r m an interface p a d . W i t h i n o i l - f i e l d e m u l s i o n b r e a k i n g , the e c o n o m i c s u s u a l l y favor m i n i m a l heat i n p u t because light ends are not lost to the gas phase a n d fuel-gas c o n s u m p t i o n is m i n i m i z e d . O t h e r significant effects c a u s e d b y the a d d i t i o n o f heat are an i n c r e a s e d t e n d e n c y t o w a r d scale d e p o s i t i o n o n fire tubes, an i n c r e a s e d p o t e n t i a l for c o r r o s i o n i n treating vessels, a n d a t e n d e n c y to r e n d e r asphaltenes i n s o l u b l e (because o f loss o f l i g h t a r o m a t i c c o m p o n e n t s ) , w h i c h m a y p r o d u c e an interface p a d p r o b l e m .

Electrical Methods. T h e p r i n c i p l e o f electrostatic d e h y d r a t i o n i n e m u l s i o n b r e a k i n g f o r b o t h r e f i n e r y d e s a l t i n g a n d o i l - f i e l d p r o d u c t i o n is essentially the same. T h e e l e c t r i c field p r o d u c e d disturbs the surface t e n s i o n o f e a c h d r o p l e t , p r o b a b l y b y c a u s i n g p o l a r m o l e c u l e s to r e o r i e n t themselves. T h i s r e o r i e n t a t i o n weakens the film a r o u n d e a c h d r o p l e t because the p o l a r


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m o l e c u l e s are n o l o n g e r c o n c e n t r a t e d at the droplet's surface. I n a d d i t i o n , a m u t u a l attraction o f adjacent e m u l s i o n particles receives i n d u c e d a n d o r i e n t e d charges f r o m the a p p l i e d e l e c t r i c field. T h i s m u t u a l attraction places o p p o s i t e l y c h a r g e d particles i n close p r o x i m i t y to each other. A s the film is w e a k e n e d a n d the droplets are e l e c t r i c a l l y attracted to each other, coales cence occurs. T h i s process does not u s u a l l y resolve e m u l s i o n s c o m p l e t e l y b y itself, a l t h o u g h it is an effective a n d o f t e n necessary a d d i t i o n to the use o f c h e m i cals o r heat. E l e c t r i c d e h y d r a t i o n does have l i m i t a t i o n s as w e l l . Excess w a t e r , t y p i c a l l y greater t h a n 6%, w i l l cause s h o r t i n g i n m a n y treater g r i d systems. T h u s , w h e n a d d i t i o n a l d e m u l s i f y i n g p o w e r is r e q u i r e d d u r i n g system upsets, the grids m a y cease to f u n c t i o n . T h i s f a i l u r e occurs w i t h greatest f r e q u e n c y i n l i g h t - o i l d e m u l s i f i c a t i o n w h e n r e s i d e n c e times are v e r y short a n d the percentage o f w a t e r w i t h i n the c r u d e o i l m a y b e u p to 9 0 % . A h i g h p e r c e n t age o f w a t e r m i n i m i z e s r e t e n t i o n t i m e o f the o i l phase i f d e m u l s i f i c a t i o n is not o c c u r r i n g r a p i d l y e n o u g h .

Chemical Methods. T h e most c o m m o n m e t h o d o f e m u l s i o n reso l u t i o n i n b o t h o i l - f i e l d a n d r e f i n e r y applications is a c o m b i n a t i o n o f heat a n d a p p l i c a t i o n o f c h e m i c a l s d e s i g n e d to e l i m i n a t e o r n e u t r a l i z e the effects o f e m u l s i f y i n g agents. A d d i t i o n o f suitable c h e m i c a l s w i t h d e m u l s i f y i n g p r o p erties specific to the c r u d e o i l to b e treated w i l l g e n e r a l l y p r o v i d e q u i c k , cost-effective, a n d flexible r e s o l u t i o n o f e m u l s i o n s . Success o f c h e m i c a l d e m u l s i f y i n g m e t h o d s is d e p e n d e n t u p o n the f o l l o w i n g : 1. A n adequate q u a n t i t y o f a p r o p e r l y selected c h e m i c a l m u s t e n t e r the e m u l s i o n . 2. T h o r o u g h m i x i n g o f the c h e m i c a l i n the e m u l s i o n m u s t o c c u r . 3. A d e q u a t e heat may b e r e q u i r e d to facilitate or f u l l y resolve an emulsion. 4. Sufficient r e s i d e n c e t i m e m u s t exist i n t r e a t i n g vessels to p e r m i t settling o f d e m u l s i f i e d w a t e r d r o p l e t s . F o r the o i l p r o d u c e r , the use o f c h e m i c a l s i n e m u l s i o n b r e a k i n g is attractive for a variety o f reasons. T h e c a p i t a l costs o f i m p l e m e n t i n g o r c h a n g i n g a c h e m i c a l e m u l s i o n - b r e a k i n g p r o g r a m are r e l a t i v e l y s m a l l a n d c a n be a c c o m p l i s h e d w i t h o u t a s h u t d o w n . T h i s feature is attractive because it means that e m u l s i o n - b r e a k i n g c h e m i c a l p r o g r a m s c a n be a l t e r e d " o n the fly" to react to changes i n e m u l s i o n characteristics o r c r u d e - o i l slate changes. ( C r u d e - o i l slate is a m i x t u r e o f c r u d e - o i l types that the r e f i n e r wishes to process.) C h e m i c a l e m u l s i o n - b r e a k i n g p r o g r a m s also i m p l y a ser v i c e c o m m i t m e n t f r o m the s u p p l y i n g c o m p a n y , w h i c h is an asset. T y p i c a l l y the s u p p l y i n g c h e m i c a l c o m p a n y m o n i t o r s the o v e r a l l cost p e r f o r m a n c e o f


328



an e m u l s i o n - b r e a k i n g p r o g r a m o n an o n g o i n g basis a n d reports the findings to the c u s t o m e r . I m p r o v e m e n t s i n c h e m i c a l a p p l i c a t i o n a n d adjustments to system o p e r a t i n g parameters s h o u l d also be p e r f o r m e d o n an o n g o i n g basis. I n a l l b u t the largest installations, the o i l - p r o d u c t i o n c o m p a n y o r r e f i n e r w i l l not have access to a d e s i g n a t e d expert i n this field, or, i f an i n - h o u s e expert is available, the e c o n o m i c j u s t i f i c a t i o n f o r d e s i g n a t i n g the l a b o r a n d resources to cost r e d u c t i o n s i n e m u l s i o n b r e a k i n g w o u l d not exist year after year. T h u s , the c h e m i c a l service c o m p a n y fills a t e c h n o l o g i c a l n e e d not r e a d i l y a d d r e s s e d b y the o i l p r o d u c e r o r refiner. T h e cost-effectiveness o f c h e m i c a l e m u l s i o n - b r e a k i n g p r o g r a m s is d e p e n d e n t o n p r o p e r c h e m i c a l s e l e c t i o n a n d a p p l i c a t i o n . Systems that have w i d e variations i n e m u l s i o n types a n d charge rates t y p i c a l l y r e q u i r e c h e m i cals that are effective o v e r b r o a d dosage ranges. A h y p o t h e t i c a l p e r f o r m a n c e c u r v e o f t w o d e m u l s i f i e r s c o m p a r i n g t r e a t e d - o i l B S & W q u a n t i t y versus dos age is p r o v i d e d i n F i g u r e 3. I f a p p l i e d c h e m i c a l s d o not have a b r o a d t r e a t i n g range, fluctuating overtreat a n d u n d e r t r e a t c o n d i t i o n s w i l l r e d u c e the p e r formance considerably. T h e c o n d i t i o n o f an overtreat (in w h i c h excess c h e m i c a l actually stabi lizes o r creates n e w e m u l s i o n types) is o f t e n v e r y d i f f i c u l t to detect. T h i s situation c a n be sharply aggravated b y i n e x p e r i e n c e d c h e m i c a l c o m p a n i e s and p e t r o l e u m c o m p a n y operations staff. C h e m i c a l a p p l i c a t i o n i n e m u l s i o n b r e a k i n g has a large h u m a n e l e m e n t i n v o l v e d i n its a p p l i c a t i o n a n d i n t e r p r e t a t i o n a n d is t h e r e f o r e subject to m i s a p p l i c a t i o n d u e to h u m a n e r r o r .

1.61

Treated Oil BS&W

0

20

40

60

80

100

ppm Demulsifier —— Demulsifier A

—^ Demulsifier Β

Figure 3. Hypothetical performance curve of two

demulsifiers.


120

9.

GRACE

Commercial Emulsion

Breaking

329


Chemical Applications in Commercial Emulsion Breaking In processing petroleum emulsions, chemical treating compounds may be a d d e d to a c r u d e - o i l e m u l s i o n to p r o d u c e desirable o i l q u a l i t y a n d r e m o v e w a t e r o r i n o r g a n i c solids. T h e most c o m m o n types o f t r e a t i n g c o m p o u n d s are r e f e r r e d t o as e m u l s i o n breakers. V a r i o u s m e c h a n i s m s are p o s t u l a t e d as to h o w e m u l s i o n breakers f u n c t i o n , b u t i t is clear that a n e m u l s i o n b r e a k e r m u s t r e a c h t h e interface o f a n e m u l s i f i e d d r o p l e t a n d t h e s u r r o u n d i n g l i q u i d . A t that p o i n t , an e m u l s i o n b r e a k e r d i s r u p t s t h e i n t e r f a c i a l tensions b e t w e e n o i l a n d w a t e r a n d allows t h e d r o p l e t s to coalesce a n d settle b y gravity. T h e concepts i n v o l v e d i n h o w a n e m u l s i o n b r e a k e r p e r f o r m s this f u n c t i o n are as v a r i e d as t h e c h e m i s t r i e s that constitute t h e b u l k o f c o m m e r c i a l e m u l s i o n breakers. A l l concepts m a y b e c o r r e c t i n specific cases. E m u l s i o n breakers are t y p i c a l l y specific f o r site o r c r u d e - o i l type. C o n v e n t i o n a l e m u l s i o n breakers are most c o m m o n l y f o r m u l a t e d f r o m t h e f o l l o w i n g types o f c h e m i s t r i e s : p o l y g l y c o l s a n d p o l y g l y c o l esters, ethoxylated alcohols a n d amines, ethoxylated resins, ethoxylated p h e n o l f o r m a l d e h y d e resins, ethoxylated n o n y l p h e n o l s , p o l y h y d r i c alcohols, a n d s u l f o n i c a c i d salts. C o m m e r c i a l e m u l s i o n breakers m a y c o n t a i n b u t o n e type o f active i n g r e d i e n t o r i n t e r m e d i a t e o r a v a r i e t y o f i n t e r m e d i a t e types. W i d e c h e m i c a l v a r i a t i o n is possible w i t h i n t h e i n t e r m e d i a t e types as w e l l . T h e ethoxylated r e s i n g r o u p demonstrates v a r i a b l e m o l e c u l a r w e i g h t o n its r e s i n base w i t h d i f f e r e n t amounts a n d p l a c e m e n t o f ethoxylated groups. T h e s e s t r u c t u r a l variations p r o v i d e a c o m p l e t e range o f s o l u b i l i t i e s , charge n e u t r a l i z a t i o n t e n d e n c i e s , s o l i d s - w e t t i n g characteristics, a n d costs. T o affix any d e f i n i t i v e q u a l i t y to any one type o f i n t e r m e d i a t e is u n r e a l i s tic, w i t h t h e possible e x c e p t i o n o f t h e s u l f o n i c a c i d salts, w h i c h e x h i b i t fast w a t e r d r o p ( r a p i d d e h y d r a t i o n ) a n d g o o d solids w e t t i n g . H o w e v e r , because o f the h i g h dosages r e q u i r e d , t h e y are not u s u a l l y cost-effective e n o u g h to b e u s e d i n a n y major c o m m e r c i a l e m u l s i o n - b r e a k i n g process, w i t h t h e excep t i o n o f w a s t e - o i l treatment. U s u a l l y , each i n t e r m e d i a t e has a d i f f e r e n t effect i n each c r u d e o i l tested. O n e i n t e r m e d i a t e m a y have a synergistic effect w i t h a n o t h e r i n t e r m e d i a t e that m a y far exceed t h e s u m o f the t w o i n d i v i d u a l i n t e r m e d i a t e s . T h e s e i n t e r m e d i a t e mixtures p l u s solvent systems (usually a r o m a t i c solvents a n d alcohols) are t h e i n g r e d i e n t s i n most e m u l s i o n breakers. T w o examples o f c o m m e r c i a l e m u l s i o n - b r e a k i n g p r o d u c t s s u p p l i e d b y one c h e m i c a l c o m p a n y are p r o v i d e d i n T a b l e I. P r o d u c t 1 i n T a b l e I was f o u n d to b e a p p l i c a b l e i n some p a r a f f i n i c c r u d e oils o f m e d i u m to h i g h A P I gravity. P r o d u c t 2 was f o u n d to b e a p p l i c a b l e i n some heavy asphaltic c r u d e oils w i t h significant amounts o f i n o r g a n i c solids present. F o r most c o m m e r c i a l e m u l s i o n - b r e a k i n g a p p l i c a t i o n s , c h e m i c a l c o m p a -


330


Table I. Composition of Two Commercial Emulsion-Breaking Products Component

Total Product (wt%)

Chemical Type


Product 1 Intermediate A

25

Intermediate Β

20

Intermediate C

5

Carrier solvent A

45

Carrier solvent Β

5

Ethoxylated resin (10% ethylene oxide, 40% propylene oxide) Polyglyeol ester (low ethylene oxide con tent, high propylene oxide ester compo nent, polyglyeol of mol. wt. 4000) Modified polyglyeol (polyglyeol of mol. wt. 6000 cross-linked with epon resin) Heavy aromatic naphtha (to maintain i n termediate solubility) 2-Methylpropyl alcohol (to provide prod uct with low pour point)

Product 2 Intermediate A

10

Intermediate Β Intermediate C

5 25

Intermediate D

2

Carrier Solvent A Carrier Solvent Β

53 5

Polyglyeol oxide component, - » 40% ethyl ene oxide, 60% propylene oxide Ethylene oxide resin, 45% ethylene oxide Modified polyglyeol ester, polyglyeol of mol. wt. 8000 cross-linked with epon resin Ethoxylated nonylphenol resin, 20% ethyl ene oxide, 10% propylene oxide Heavy aromatic naphtha 2-Propyl alcohol

nies are able to p r o v i d e e m u l s i o n breakers that p r o v i d e p i p e l i n e - s p e c i f i c a t i o n c r u d e o i l o r acceptable w a t e r contents i n desalted c r u d e oils. T h e s e c o m p o u n d s are most c o m m o n l y u s e d at dosages o f 1 - 2 0 0 p p m i n o i l - f i e l d p r o d u c t i o n a n d 5 - 2 0 p p m i n refinery desalting. L i g h t oils are generally treated i n the l o w e r dosage ranges, a n d heavy c r u d e oils r e q u i r e the h i g h e r dosages. E x c e p t i o n s to these dosage r e q u i r e m e n t s c a n be f o u n d . I n m a n y c o m m e r c i a l e m u l s i o n - b r e a k i n g applications, c o n v e n t i o n a l e m u l s i o n - b r e a k i n g chemistries w i l l also achieve d e s i r e d o i l - i n - w a t e r c o n tents a n d acceptable interface q u a l i t y . H o w e v e r , these results are not always a c c o m p l i s h e d . Reverse e m u l s i o n s are not u s u a l l y r e s o l v e d b y c o n v e n t i o n a l e m u l s i o n - b r e a k i n g c h e m i s t r i e s . T h e a d d i t i o n o f a specific r e v e r s e - e m u l s i o n b r e a k e r , e i t h e r to the c r u d e - o i l stream o r to the w a t e r - h a n d l i n g system, m a y b e r e q u i r e d to p r o d u c e d e s i r e d water q u a l i t y parameters. Reverse e m u l s i o n - b r e a k i n g chemicals are usually s o l u t i o n o r latex p o l y mers r a n g i n g i n m o l e c u l a r w e i g h t f r o m 10,000 to 30 m i l l i o n , a n d m a y be classified as e i t h e r coagulants o r flocculants. A l t h o u g h the classification o f coagulant or flocculant c a n b e a s s u m e d f r o m m o l e c u l a r w e i g h t (flocculants h a v i n g the h i g h e r m o l e c u l a r weights), the most accurate categorization is


9.

GRACE

Commercial Emulsion

Breaking

331

b a s e d o n the p o l y m e r s effect w i t h i n a system. M a n y o t h e r types o f reversee m u l s i o n breakers s u c h as z i n c c h l o r i d e , w a t e r - s o l u b l e ethoxylated resins, n o n y l p h e n o l resins, a n d a l u m are available. C o n c e p t s a p p l i e d t o r e g u l a r e m u l s i o n s still a p p l y w i t h reverse e m u l sions. E m u l s i f y i n g agents or charges must be n e u t r a l i z e d to p e r m i t coales c e n c e o f the o i l . A d e q u a t e s e t t l i n g t i m e f o r the o i l to rise o u t o f the w a t e r


phase m u s t be available. S k i m tanks a n d A P I separators are u s e d f o r this p u r p o s e . A variety o f flotation units w i l l a c c o m p l i s h the same goals at an accelerated rate. Dosages o f r e v e r s e - e m u l s i o n breakers w i l l v a r y w i d e l y w i t h each a p p l i c a t i o n . A 1 0 - 1 0 0 - p p m dosage o f r e v e r s e - e m u l s i o n breakers w o u l d i n c l u d e most applications b u t exclude h i g h - m o l e c u l a r - w e i g h t p o l y m e r s . H i g h - m o l e c u l a r - w e i g h t p o l y m e r dosages are usually less t h a n 10 p p m i f i n j e c t e d i n t o a w a t e r system a n d less t h a n 5 p p m i f i n j e c t e d i n t o an o i l system. I n o i l systems, h i g h - m o l e c u l a r - w e i g h t p o l y m e r s are u s u a l l y a d d e d to separate h y d r o c a r b o n s f r o m i n o r g a n i c solids ( p r i m a r i l y sands, clays, a n d i r o n sulfides). T h i s separation reduces interface pads a n d o i l - i n - w a t e r concentrations. I f a c c u m u l a t e d oils f r o m w a t e r systems are to be r e c y c l e d i n t o o i l t r e a t i n g systems, it is c r u c i a l to ensure that the a c c u m u l a t e d o i l (or slop) a n d associated c h e m i c a l s are c o m p a t i b l e w i t h the o i l - t r e a t i n g p r o g r a m . T h i s n e e d f o r c o m p a t i b i l i t y is p a r t i c u l a r l y true o f h i g h - m o l e c u l a r - w e i g h t p o l y mers w h e n a p p l i e d to systems that c o n t a i n large amounts o f asphaltenecoated solids. Dosages as l o w as 2 p p m may be excessive u n d e r these c o n d i tions a n d p r o m o t e a v e r y stable (essentially untreatable) e m u l s i o n i n oils a c c u m u l a t e d f r o m the w a t e r - h a n d l i n g system. H i g h - m o l e c u l a r - w e i g h t p o l y mers s h o u l d not b e e x p e c t e d to resolve t r e a t i n g p r o b l e m s a r i s i n g f r o m the p r e s e n c e o f asphaltenes a n d i n o r g a n i c solids. I n some c r u d e oils, h i g h amounts o f i n s o l u b l e asphaltenes a n d i n o r g a n i c solids w i t h h i g h surface charges (chiefly clays) w i l l c o m b i n e to f o r m a stable " s o l i d s " interface p a d . T h i s interface p r o b l e m is usually a c c o m p a n i e d b y p o o r w a t e r q u a l i t y a n d excessive c o n s u m p t i o n o f e m u l s i o n breakers. T h i s type o f interface p a d is t y p i c a l l y r e m o v e d f r o m a t r e a t i n g vessel b y de s an d d e s l u d g i n g operations to f o r m u n e c o n o m i c a l l y treatable slop oils. D i s p o s a l costs o f this slop m a y be h i g h f o r e i t h e r the o i l p r o d u c e r o r refiner. T h i s p r o b l e m occurs p r i m a r i l y i n t r e a t i n g heavy c r u d e oils a n d l i g h t asphaltic c r u d e oils p r o d u c e d b y m i s c i b l e flooding. T h e a d d i t i o n o f an asphaltene dispersant to the c r u d e o i l to p r e v e n t a c c u m u l a t i o n o f i n s o l u b l e asphaltenes m a y resolve this p r o b l e m . T h e selection o f asphaltene dispersant c h e m i s t r y a n d dosages r e q u i r e s c a r e f u l c o n s i d e r a t i o n . M o s t asphaltene dispersants are e i t h e r l i g h t a r o m a t i c c o m p o u n d s w i t h p o l a r groups (e.g., cresylic acid) o r h i g h l y w a t e r - d i s p e r s i b l e o r w a t e r - s o l u b l e surfactants. T h e s e materials w i l l p r e v e n t i n s o l u b i l i t y o f asphaltenes, b u t t h e y also t e n d to adversely affect the d e h y d r a t i o n o f e m u l sions a n d to increase o i l - i n - w a t e r concentrations.



332


S u c c e s s f u l s e l e c t i o n o f asphaltene dispersant c h e m i s t r i e s a n d dosages w i l l p r o v i d e r e d u c t i o n s i n interface pads, e m u l s i o n - b r e a k e r c o n s u m p t i o n , and o i l - i n - w a t e r concentrations a n d p r o v i d e o i l - f r e e i n o r g a n i c solids. E m u l s i o n s s t a b i l i z e d b y p a r a f f i n are u s u a l l y r e s t r i c t e d to l i g h t c r u d e oils i n o i l - f i e l d p r o d u c t i o n . I f p a r a f f i n d e p o s i t i o n that restricts p r o d u c t i o n is o c c u r r i n g u p s t r e a m o f a n o i l - t r e a t i n g facility, i t m a y be feasible to a p p l y a p a r a f f i n crystal m o d i f i e r to t h e c r u d e o i l to p r e v e n t p a r a f f i n d e p o s i t i o n a n d to e l i m i n a t e p a r a f f i n as a n e m u l s i f y i n g agent. A paraffin crystal m o d i f i e r m u s t e n t e r a n o i l system at a t e m p e r a t u r e greater t h a n t h e c l o u d p o i n t o f the c r u d e o i l a n d u p s t r e a m o f the p r o b l e m area. T o select c h e m i c a l p r o g r a m s f o r an o i l - t r e a t i n g facility, e a c h facility must b e e x a m i n e d o n an i n d i v i d u a l basis. T h e selection o f a c h e m i c a l o r g r o u p o f c h e m i c a l s f o r e m u l s i o n b r e a k i n g must be p r e c e d e d b y v a l i d test p r o c e d u r e s a n d a t h o r o u g h u n d e r s t a n d i n g o f t h e t r e a t i n g system a n d p e t r o l e u m c o m p a n y objectives.

Demulsifier-Auxiliary Chemical Selection T h e s e l e c t i o n o f c h e m i c a l s that w i l l p r o v i d e t h e r e f i n e r o r o i l p r o d u c e r w i t h a cost-effective e m u l s i o n - b r e a k i n g p r o g r a m that meets o r exceeds a l l p e r f o r m a n c e parameters is usually t h e f u n c t i o n o f a c h e m i c a l service c o m p a n y . T h e s e l e c t i o n process has h i s t o r i c a l l y b e e n v i e w e d as a " b l a c k a r t " that p r o d u c e s as m a n y failures as successes. T h i s assessment o f the situation has b e e n realistic. H o w e v e r , w i t h a n e v e r - i n c r e a s i n g u n d e r s t a n d i n g o f e m u l s i o n s and e m u l s i o n - b r e a k i n g c h e m i c a l s , t h e d e v e l o p m e n t o f n e w test p r o c e d u r e s and devices, a n d a w e l l - o r g a n i z e d m e t h o d o f c h e m i c a l selection, m a n y o f the failures c a n b e e l i m i n a t e d .

Characterization of Crude Oils and Containants. T h e first step i n s e l e c t i o n o f e m u l s i o n breakers is to o b t a i n as c o m p l e t e a n u n d e r s t a n d i n g as possible about the c r u d e o i l o r e m u l s i o n . D e n s i t y (or A P I gravity) a n d B S & W ranges s h o u l d b e d e t e r m i n e d . T h e c r u d e o i l s h o u l d b e classified as asphaltic o r p a r a f f i n i c , a n d t h e asphaltene a n d p a r a f f i n content s h o u l d b e d e t e r m i n e d . I f treatment w i l l o c c u r at a t e m p e r a t u r e b e l o w the p a r a f f i n m e l t i n g p o i n t , t h e c l o u d p o i n t o f the c r u d e o i l s h o u l d b e d e t e r m i n e d . T h i s information w i l l a i d i n selecting the treating temperature. T h e i n o r g a n i c solids content o f the c r u d e o i l s h o u l d b e k n o w n , a n d the types o f solids present s h o u l d b e i d e n t i f i e d . I f a t r e a t i n g system is o p e r a t i o n a l , the interface s h o u l d b e e x a m i n e d to d e t e r m i n e its c o m p o s i t i o n . F r o m this i n f o r m a t i o n , m a n y o f the k e y c r u d e - o i l emulsifiers w i l l b e i d e n t i f i e d , a n d a k n o w l e d g e o f w h i c h contaminants r e q u i r e a d d i t i o n a l treatment w i l l b e derived.


9.

GRACE

Commercial Emulsion

Breaking

333


I n r e f i n e r y d e s a l t i n g operations, the a m o u n t a n d type o f salts ( i o n i z e d o r crystalline) present i n the c r u d e o i l s h o u l d b e d e t e r m i n e d . I n a l l t r e a t i n g applications, the c h e m i s t r y o f the w a t e r s h o u l d b e k n o w n so that the i m p a c t o f c h a n g i n g t r e a t i n g t e m p e r a t u r e s a n d pressures o n s c a l i n g a n d c o r r o s i o n p o t e n t i a l c a n be c o n s i d e r e d . Past o p e r a t i n g experiences w i t h the same o r s i m i l a r c r u d e oils s h o u l d b e r e v i e w e d . I f p o s s i b l e , these s h o u l d b e c o m p a r e d w i t h the results o b t a i n e d f r o m any p r e v i o u s e m u l s i o n - b r e a k e r selection tests. T h i s c o m p a r i s o n w i l l give a n i n d i c a t i o n o f the v a l i d i t y o f p r e v i o u s test w o r k , e l i m i n a t e m a n y t r e a t i n g c o m p o u n d s f r o m the selection process, a n d p r o v i d e i n f o r m a t i o n as to w h i c h c h e m i s t r i e s m a y be r e q u i r e d to c o m p l e m e n t a c o n v e n t i o n a l e m u l sion b r e a k e r . T h i s i n f o r m a t i o n w i l l also a l l o w changes i n e m u l s i o n charac teristics to b e n o t e d v e r y q u i c k l y a n d p r e d i c t w h e t h e r an existing e m u l s i o n b r e a k i n g p r o g r a m s h o u l d be r e v i e w e d f o r p o s s i b l e i m p r o v e m e n t s .

System Mechanical Parameters and Operating Data. B e fore the selection o f e m u l s i o n - b r e a k i n g c h e m i c a l s , a c o m p l e t e u n d e r s t a n d i n g o f the e q u i p m e n t a n d o p e r a t i n g p r o c e d u r e s at a t r e a t m e n t f a c i l i t y s h o u l d b e o b t a i n e d . K e y c o m p o n e n t s w i l l i n c l u d e the f o l l o w i n g : • rates o f p r o d u c t i o n • t r e a t i n g vessel r e t e n t i o n times • t r e a t i n g vessel capabilities (i.e., e l e c t r i c a b i l i t y , t e m p e r a t u r e l i m i t a t i o n s , etc.) • r e c e n t t r e a t i n g t e m p e r a t u r e s a n d pressures • existing c h e m i c a l a d d i t i o n p o i n t s , m e t h o d s , a n d e q u i p m e n t • s a m p l i n g p o i n t locations • o p e r a t i n g p r o c e d u r e s f o r d e s a n d - d e s l u d g e cycles a n d slop o i l r e c y c l i n g w i t h a p p r o p r i a t e f r e q u e n c i e s , rates, a n d t i m e frames • type o f l e v e l c o n t r o l l e r s • schedules a n d o p e r a t i n g p r o c e d u r e s f o r w e l l treatments, e q u i p m e n t c l e a n i n g , a n d a d d i t i o n o f the c h e m i c a l s • water-handling equipment and procedures • p r o b l e m c r u d e - o i l sources • o v e r a l l cleanliness o f system i n t e r n a l c o m p o n e n t s • d i l u e n t o r w a s h - w a t e r rates a n d q u a l i t y E m u l s i o n - b r e a k i n g p e r f o r m a n c e data s h o u l d also b e g a t h e r e d . A r e a s o f p r i m e c o n c e r n are the f o l l o w i n g :


334


• o i l , w a t e r , salt, a n d solids content o f the fluids b e f o r e a n d after each t r e a t i n g vessel o r process. T e s t p r o c e d u r e s s h o u l d also b e known. • c o m p o s i t i o n a n d q u a l i t y o f interface

fluids

• a l l o p e r a t i n g a n d c h e m i c a l costs associated w i t h e m u l s i o n b r e a k i n g at that f a c i l i t y


• a m o u n t o f waste o i l , solids, a n d w a t e r generated • d o w n s t r e a m effects o f the e m u l s i o n - b r e a k i n g process

F r o m this i n f o r m a t i o n the e c o n o m i c s o f the present e m u l s i o n - b r e a k i n g p r o g r a m c a n b e c a l c u l a t e d as a standard f r o m w h i c h to evaluate changes i n the p r o g r a m . A d e t e r m i n a t i o n o f w h e t h e r c h e m i c a l , m e c h a n i c a l , o r o p e r a t i o n a l changes w i l l p r o v i d e the greatest i m p r o v e m e n t to e m u l s i o n b r e a k i n g c a n be m a d e . I f a change i n c h e m i c a l s is r e q u i r e d , the i n f o r m a t i o n c a n b e u s e d to d e s i g n a c h e m i c a l - t e s t i n g p r o c e d u r e that is most representative o f the o i l - t r e a t i n g i n s t a l l a t i o n .

Prioritization of Performance and Cost Issues. A l l p e r s o n n e l i n v o l v e d i n a t t e m p t i n g to i m p r o v e an e m u l s i o n - b r e a k i n g p r o g r a m m u s t have a clear u n d e r s t a n d i n g o f w h i c h areas r e q u i r e the greatest i m p r o v e m e n t a n d h o w m u c h i m p r o v e m e n t is r e q u i r e d f o r the exercise to b e successful. T h e i m p r o v e m e n t s to an e m u l s i o n - b r e a k i n g p r o g r a m m a y o c c u r b y a l l o w i n g c o m p l i a n c e to a p r o d u c t o r waste-stream q u a l i t y specification, i n c r e a s i n g t h r o u g h p u t , d e c r e a s i n g o v e r a l l t r e a t i n g a n d o p e r a t i o n costs, r e d u c i n g e n v i r o n m e n t a l hazards, i m p r o v i n g system r e l i a b i l i t y , o r p r o v i d i n g o p e r a t i n g i n f o r m a t i o n . A n y one o r a l l o f these areas m a y r e q u i r e i m p r o v e m e n t . I f re q u i r e m e n t s f o r successful p r o b l e m r e s o l u t i o n are not m u t u a l l y agreed to b y all parties i n v o l v e d b e f o r e b e g i n n i n g to attempt to i m p r o v e e m u l s i o n break i n g , it is u n l i k e l y that the e n d goals w i l l b e a c h i e v e d . Emulsion-Breaker Selection. I f a c h e m i c a l change m u s t be m a d e o r investigated to p r o v i d e i m p r o v e m e n t s i n the e m u l s i o n - b r e a k i n g p r o g r a m , a m e t h o d o f selecting n e w c h e m i c a l s must b e available. I n a l l cases, the test m e t h o d m u s t simulate the c o n d i t i o n s o f a t r e a t i n g system as c l o s e l y as possible. C a n d i d a t e c h e m i c a l s must t h e n b e c o m p a r e d w i t h c h e m i c a l s o f k n o w n o p e r a t i n g p e r f o r m a n c e w i t h i n the t r e a t i n g system. I f c h e m i c a l treatment was not p r e v i o u s l y u s e d , a c h e m i c a l that p e r f o r m s w e l l i n a s i m i l a r c r u d e o i l a n d system s h o u l d be selected f o r use as a standard. T h e relative i m p r o v e m e n t i n p e r f o r m a n c e over the standard must b e the c r i t e r i o n f o r s e l e c t i o n o f n e w c a n d i d a t e c h e m i c a l s . I n larger installa tions that are e x p e r i e n c i n g severe e m u l s i o n p r o b l e m s , m a n y (possibly h u n dreds) o f c o m m e r c i a l i z e d e m u l s i o n - b r e a k i n g p r o d u c t s o r e x p e r i m e n t a l


9.

GRACE

Commercial Emulsion

Breaking

b l e n d s o f e m u l s i o n - b r e a k e r i n t e r m e d i a t e s m a y b e tested. T h e

335 selection

process f o r e m u l s i o n - b r e a k i n g c h e m i c a l s c a n b e c o n f i r m e d o n l y b y a p p l i c a t i o n w i t h a t r e a t i n g system. A s a result, selection m a y b e a s l o w process.


I n the s e l e c t i o n process, various g e n e r a l testing p r o c e d u r e s are available to d e t e r m i n e a p p r o p r i a t e c h e m i c a l s . A l l test p r o c e d u r e s w i l l have l i m i t a tions. I n a l l cases, these l i m i t a t i o n s c a n b e m i n i m i z e d b y u s i n g o n l y f r e s h fluid samples that are representative o f the t r e a t i n g system o r slip streams o f system fluids, b y u s i n g consistent a n d a p p r o p r i a t e analytical p r o c e d u r e s , b y e n s u r i n g that test fluids c o n t a i n o n l y the e m u l s i o n - b r e a k i n g c h e m i c a l s to b e tested, a n d b y u s i n g test p r o c e d u r e s that subject the e m u l s i o n to c o n d i t i o n s as close as possible to those f o u n d i n the testing system o f study. H i s t o r i c a l l y , the c h e m i c a l s e l e c t i o n process has b e e n p e r f o r m e d o n a b e n c h - t o p scale. B o t t l e tests ( i n c l u d i n g ratio, e l i m i n a t i o n , a n d c o n f i r m a t i o n test), j a r tests, a n d p o r t a b l e e l e c t r i c desalter tests f a l l i n t o this test category. N o effort w i l l be m a d e to d e s c r i b e these tests o r the associated analytical p r o c e d u r e s i n d e t a i l , as t h e y are d e s c r i b e d i n C h a p t e r s 3 a n d 10. F u r t h e r m o r e , significant v a r i a t i o n i n testing p r o c e d u r e s w i l l exist b e t w e e n various c h e m i c a l c o m p a n i e s , o i l p r o d u c e r s , a n d refiners. E a c h test p r o c e d u r e is also t a i l o r e d to each t r e a t i n g facility. B e n c h - t o p testing w i l l a l l o w v a r i a t i o n i n c h e m i c a l type a n d dosage, t e m p e r a t u r e , pressure, agitation, t r e a t m e n t t i m e , e l e c t r i c a l i n p u t (portable e l e c t r i c desalters o n l y ) , a n d w a s h - w a t e r o r d i l u e n t a d d i t i o n . V a r i a t i o n s i n t e m p e r a t u r e a n d pressure w i l l not a l l o w s i m u l a t i o n o f h i g h pressures a n d t e m p e r a t u r e s . T h e bench-scale tests i m p l y that a b a t c h t r e a t m e n t o f the e m u l s i o n is u s e d to d e t e r m i n e t r e a t i n g c h e m i c a l s f o r a d y n a m i c c o n t i n u o u s t r e a t i n g system. T h u s , results w i l l have l i m i t a t i o n s e v e n i f the parameters o f the test p r o c e d u r e are as accurate as p o s s i b l e . Q u a n t i t a t i v e i n f o r m a t i o n o n the B S & W a n d salt content o f o i l as a w h o l e o r at selected levels i n the o i l c o l u m n can be c o l l e c t e d f r o m the bottle a n d p o r t a b l e e l e c t r i c desalter tests. T h i s i n f o r m a t i o n is u s u a l l y accurate w h e n a p p l i e d w i t h i n a system, a l t h o u g h the c h e m i c a l dosages necessary to achieve the results n o t e d i n the tests is u s u a l l y significantly l o w e r . Q u a n t i t a t i v e i n f o r m a t i o n o n the nature o f the o i l - w a t e r interface c a n b e o b t a i n e d f r o m a l l b e n c h - t o p tests. C h e m i c a l s that p r o d u c e a p o o r interface i n b e n c h - t o p tests w i l l almost c e r t a i n l y p r o d u c e a p o o r interface i n a t r e a t i n g facility. C h e m i c a l s that p r o d u c e a g o o d interface i n b e n c h - t o p tests w i l l not always p r o d u c e a g o o d interface i n a t r e a t i n g facility. T h e b e n c h - t o p tests have d i f f i c u l t y p r o d u c i n g a c c u m u l a t i o n s o f e m u l s i o n s , solids, a n d i n s o l u b l e h y d r o c a r b o n s that u s u a l l y p r o d u c e p o o r interfaces. T h i s d i f f i c u l t y results because they are small-scale b a t c h tests, not d y n a m i c tests that a l l o w the a c c u m u l a t e d effects o f materials present i n s m a l l quantities to be n o t e d . O i l - i n - w a t e r c o n t e n t c a n b e m e a s u r e d o n l y o n a qualitative basis i n a l l b e n c h - t o p testing. W a t e r q u a l i t y is o f t e n d i r e c t l y associated w i t h the q u a l i t y o f the interface w i t h i n a system. I f the q u a l i t y o f the interface is not f u l l y



336


p r e d i c t a b l e , t h e n n e i t h e r is w a t e r q u a l i t y . W a t e r q u a l i t y is also greatly af f e c t e d b y a t r e a t i n g system's flow d y n a m i c s . T h e a b i l i t y to accurately p r e d i c t trace quantities o f o i l i n w a t e r i n a system f r o m a small-scale b a t c h b e n c h test does not exist. I n an effort to e l i m i n a t e the l i m i t a t i o n s o f b e n c h - t o p testing, various g r o u p s a n d c o m p a n i e s are a t t e m p t i n g to d e v e l o p d y n a m i c simulators that are actually s c a l e d - d o w n t r e a t i n g facilities. T h e s e t r e a t i n g s i m u l a t i o n units p r o v i d e d y n a m i c c o n t i n u o u s flow o f e m u l s i o n s o n a s m a l l e r scale t h a n the actual t r e a t i n g facility. T h e charge o f e m u l s i o n m a y b e t r a n s p o r t e d to the s i m u l a t o r f o r test r u n s . T h i s process has b e e n u s e d f o r m a n y years to size treaters a n d desalters a n d select start-up c h e m i c a l s f o r a t r e a t i n g facility. T h e same variations possible i n a b e n c h - t o p test are u s e d ; h o w e v e r , the range o f v a r i a t i o n is m u c h greater. M a n u f a c t u r e r s o f treaters a n d desalters as w e l l as large, w e l l - f u n d e d p e t r o l e u m research groups use this m e t h o d o f testing to p r o v i d e m o r e accurate s e l e c t i o n o f m e c h a n i c a l e q u i p m e n t a n d c h e m i c a l s . T h i s system has a m u c h greater a b i l i t y to accurately p r e d i c t t r e a t e d - o i l q u a l i t y , w a t e r q u a l i t y , a n d interface q u a l i t y . A l i m i t a t i o n i n this m e t h o d is that the c r u d e o i l o r e m u l s i o n suffers f r o m aging as it is trans p o r t e d to the s i m u l a t o r . P o r t a b l e simulators c a n b e t r a n s p o r t e d to the field a n d receive t h e i r c r u d e - o i l charge d i r e c t l y f r o m the t r e a t i n g system b y d i v e r t i n g a slip-steam t h r o u g h the u n i t . T h i s step eliminates the aging effect o n the test fluids w h i l e m a i n t a i n i n g the same capabilities n o t e d i n stationary o i l - t r e a t i n g simulators. A flow d i a g r a m o f a p o r t a b l e o i l - t r e a t i n g s i m u l a t o r d e v e l o p e d b y N a l c o C a n a d a Inc. is s h o w n i n F i g u r e 4. Regardless o f the test m e t h o d u s e d to select c h e m i c a l s , the t r u e c a p a b i l ities o f the t r e a t i n g c h e m i c a l s must be d e t e r m i n e d b y c o m m e r c i a l a p p l i c a t i o n i n the t r e a t i n g system o f c o n c e r n . A l l test w o r k i n c h e m i c a l s e l e c t i o n is m e r e l y a m e t h o d o f r e d u c i n g the risk o f f a i l u r e an o i l treater is s u b j e c t e d to w h e n c h a n g i n g e m u l s i o n - b r e a k i n g c h e m i c a l s o r testing a n e w facility. O n c e n e w e m u l s i o n - b r e a k i n g c h e m i c a l s are e n t e r e d i n t o a t r e a t i n g sys t e m , they are evaluated b y the m e t h o d s n o t e d i n the system m e c h a n i c a l a n d o p e r a t i n g data section. C o n f i r m a t i o n that the goals o f the o i l - p r o d u c t i o n c o m p a n y o r refiner are b e i n g m e t is t h e n o b t a i n e d . I f the goals are not b e i n g met, the areas r e q u i r i n g i m p r o v e m e n t are d e t e r m i n e d , a n d an a p p r o p r i a t e course o f investigation a n d m a n i p u l a t i o n o f system parameters is c o n d u c t e d to achieve these goals.

Summary I n the p e t r o l e u m i n d u s t r y , mixtures o f o i l a n d water w i l l o c c u r as e m u l s i o n s i n b o t h p r o d u c t i o n a n d r e f i n i n g segments. T h e types o f e m u l s i o n s w i l l vary w i d e l y , a l t h o u g h a l l e m u l s i o n s w i l l b e the result o f n o r m a l l y i m m i s c i b l e o i l


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337

Breaking

(Well, Satellite, Header, Truck Pit)


Variable Speed Pump

Charge TanK

Oil Tank

Gas Out

>

Degasser #i

, To FWKO, (Next Pagel From Treater

Figure 4. Oil-treating simulator fluid path.

a n d w a t e r subjected to agitation a n d s t a b i l i z e d b y a w i d e variety o f e m u l s i f y i n g agents. T o achieve d e s i r e d p r o d u c t q u a l i t y , m e e t e n v i r o n m e n t a l c o n c e r n s , a n d i m p r o v e e q u i p m e n t r e l i a b i l i t y , it is o f t e n necessary f o r o i l p r o d u c e r s o r refiners to resolve e m u l s i o n s a n d e l i m i n a t e c o n t a m i n a n t s . T h e s e goals c a n b e a c c o m p l i s h e d w i t h m a n y m e t h o d s to r e a c h acceptable standards i n d e h y d r a t i o n o f o i l , r e m o v a l o f solids a n d c o n t a m i n a n t s , o i l - i n - w a t e r interface c o n t r o l , a n d energy i n p u t . M o s t commonly, a combination of electrical, thermal, chemical, and t i m e factors is a p p l i e d to an e m u l s i o n i n a t r e a t i n g f a c i l i t y d e s i g n e d specifi cally f o r that e m u l s i o n a n d f o r that facility. T h e e c o n o m i c s o f e m u l s i o n b r e a k i n g d e t e r m i n e s w h i c h m e t h o d s a n d to w h a t degree e a c h m e t h o d is u s e d to achieve the e n d goals at that facility. C h e m i c a l p r o g r a m s a p p l i e d i n c o m m e r c i a l e m u l s i o n b r e a k i n g are se l e c t e d f r o m a w i d e variety o f e m u l s i o n - b r e a k i n g c h e m i s t r i e s a n d auxiliary c h e m i c a l s that c o n t r o l v e r y specific agents w i t h i n the e m u l s i o n . T h e s e c h e m i c a l s are s e l e c t e d o n the basis o f a variety o f tests, b o t h b e n c h - t o p a n d


338

EMULSIONS IN THE PETROLEUM INDUSTRY From Free Water

From Degasser #1

^

/Γ Downloaded by NORTH CAROLINA STATE UNIV on December 7, 2012 | http://pubs.acs.org Publication Date: May 5, 1992 | doi: 10.1021/ba-1992-0231.ch009

Γ

_ To Heat Exchanger

Blowdown f

Water Tank*

Figure 4. Continued.

s i m u l a t o r , that w i l l p r o v i d e a m e a s u r e o f the p e r f o r m a n c e o f t r e a t i n g c h e m i cals w i t h a specific c r u d e - o i l a n d t r e a t i n g system. T h e results m u s t

be

c o n f i r m e d b y use o f the c h e m i c a l at a t r e a t i n g facility. T h e factors that i n f l u e n c e e m u l s i o n f o r m a t i o n a n d e m u l s i o n b r e a k i n g s h o w w i d e v a r i a t i o n f r o m site to site. A s a result, n o u n i v e r s a l rules exist f o r applying emulsion-breaking technology.

E a c h emulsion-breaking

facility

m u s t b e v i e w e d as a n i n d i v i d u a l o r u n i q u e case. I f this a p p r o a c h is t a k e n , the t h e o r i e s o f d e m u l s i f i c a t i o n m a y t h e n b e a p p l i e d to a specific situation i n a c a r e f u l l y o r g a n i z e d , d o c u m e n t e d , a n d d i r e c t e d a t t e m p t to p r o v i d e t h e most cost-effective m e t h o d s o f a c h i e v i n g the goals i n e m u l s i o n b r e a k i n g o f the producer and refinery.

Bibliography Jones, T. J.; Neustrader, E . L . ; Whittingham, K . P. “Water i n Crude O i l Emulsion Stability and Emulsion Destabilization by Chemical Demulsifiers”, J. Can. Pet. Technol. 1978, 100-107. Kronenberger, D . L . ; Pattison, D . A . Mater. Perform. 1986, 7, 9-17. Lissant, Κ. J. Demulsification;

Dekker: N e w York, 1983.


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Mackay, D . “Formation and Stability of Water-in-Oil Emulsions”, Report E E 9 3 ; Environment Canada: Ottawa, Ontario, Canada, 1987. Impurities in Petroleum; Petrolite Corporation: St. Louis, M O , 1981. Speight, J. G . The Chemistry and Technology of Petroleum; Dekker: N e w York, 1981. Speight, J. G . The Structure of Petroleum Asphaltenes: Current Concepts; Informa tion Series no. 51, Alberta Research Council: Alberta, Canada, 1981.


Strassner, J. E. J. Pet. Technol. 1968, 243, 303. Treating Oilfield Emulsions, 3rd ed.; American Petroleum Institute: Austin, T X , 1974. RECEIVED for review December 18, 1990. ACCEPTED revised manuscript July 9, 1991.


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