Sulfur Recovery from Oil Sands - American Chemical Society

5 Sulfur Recovery from Oil Sands A . W. H Y N D M A N , J. K. L I U , and D. W. D E N N E Y

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Syncrude Canada Limited, PO Box 5790, Postal Station L , Edmonton, Alberta, Canada T6C 4G3

Syncrude Canada Limited has been producing synthetic crude oil from the Athabasca oil sand deposit since 1978. In place reserves of this deposit are estimated at 118 x 10 m . Oil sands in this deposit have bitumen saturation up to 18 w/w% and average 1012%. The bitumen is a heavy oil, API gravity 8.3, characterized by high sulphur, 3.5-5.0 w/w%. Chemical and physical modifications during recovery produce a synthetic crude with API gravity in the 30-35 range with less than 2000 wppm sulphur. At design capacity, 20,500 m/day of synthetic crude, Syncrude's Upgrading f a c i l i t i e s w i l l process 28,000 tonnes of bitumen containing 1375 tonnes sulphur. The sour water and sour gas streams are treated individually to produce H S rich streams as sulphur recovery unit feed. More than 96% of sulphur entering the recovery unit is recovered as elemental sulphur which is in a molten state for shipment. Recovered sulphur as a by-product represents less than 1% of synthetic crude value. Coke burner off-gas and sulphur recovery unit tail gas are incinerated in CO boilers to convert all forms of sulphur to SO before emission. Syncrude's Upgrading is designed so that no more than 292 tonnes SO /day leave the 180 m stack ensuring ground level concentrations prescribed by Alberta Clean A i r Regulations are not exceeded. This represents a minimum 89.4% containment of incoming sulphur feed. Regulation compliance is recorded by stack monitors, five continuous and forty static ground level stations. Minute readings from the stack monitors and continuous ground level monitors are transmitted to the Data Acquisition Centre. Violations must be documented and reported to Alberta Environment within 72 hours. Monthly and yearly summaries must also be f i l e d . 9

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0097-6156/82/0183-0069505.00/ 0 © 1982 American Chemical Society

In Sulfur: New Sources and Uses; Raymont, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

SULFUR: NEW SOURCES A N D USES

In a d d i t i o n to conventional crude oil and n a t u r a l gas, the Province of A l b e r t a , Canada, possesses s u b s t a n t i a l deposits o f oil sands. The l o c a t i o n of these d e p o s i t s are i n d i c a t e d in Figure 1. These major deposits are estimated t o c o n t a i n 158 Gm (967 GBBL) of bitumen. The Athabasca dep o s i t is the world's l a r g e s t deposit covering an area roughly the s i z e o f Belgium and contains 118 Gm . The other major deposit is Cold Lake w i t h estimated reserves o f 26.2 Gm . Of these d e p o s i t s , the Athabasca deposit has r e c e i v e d the most a t t e n t i o n from s c i e n t i s t s and commercial developers s i n c e it is the l a r g e s t and f o r t u n a t e l y a l s o has the shallowest overburden thus p e r m i t t i n g surface mining. Again, because o f the shallow overburden, the Athabasca oil sands deposit is the only deposit in the world to have a t t r a c t e d l a r g e - s c a l e commercial development. Smaller developments have taken place in Venezuela, T r i n i d a d , A l b a n i a , Rumania and in the U.S.S.R. The Athabasca deposit is the s i t e of two operational f a c i l i t i e s : Suncor, Inc. w i t h a d a i l y production of 8600 m o f s y n t h e t i c crude and Syncrude Canada L i m i t e d w i t h a design production o f 20,500 m per day o f s y n t h e t i c crude. Plans have been made f o r the Alsands P r o j e c t which would have a design c a p a c i t y of 22,220 m /day of s y n t h e t i c crude. Other oil sand p l a n t s are in p r e l i m i n a r y planning stages. The g e o l o g i c a l s t r a t i f i c a t i o n of the Athabasca deposit is presented in Figure 2. As w i t h most r i v e r s in t h i s r e g i o n of Western Canada, the Athabasca R i v e r has gouged a deep r i v e r v a l l e y , exposing the oil sands deposits along i t s banks. On warm days the bitumen oozes from the r i v e r banks and e v e n t u a l l y works i t s way to the water l i n e . Native Indians used t h i s bitumen, mixed w i t h spruce gum, to patch t h e i r canoes. The f i r s t white man to see the Athabasca oil sands was f u r t r a d e r Peter Pond in 1778. I n 1889 the c h r o n i c l e r of the government sponsored L a i r d e x p e d i t i o n wrote: "That t h i s region is stored w i t h a substance of great economic value is beyond a l l doubt, and, it w i l l , I b e l i e v e , prove to be one of the wonders of Western Canada." 3

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Sulfur Recovery from Oil Sands


HYNDMAN ET AL.

Figure 1. Location of Albertaoilsands deposits.


SULFUR:


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Figure 2.

NEW SOURCES AND USES

Geological stratification of Athabasca region.



HYNDMAN ET AL.


The Athabasca deposit is r e l a t i v e l y r i c h w i t h bitumen s a t u r a t i o n up to 18% by weight. The bitumen in i t s raw s t a t e has an API g r a v i t y of 8.3 andisc h a r a c t e r i z e d by low hydrogen to carbon r a t i o s , 1.5, and high sulphur content, 4.0-5.5 w/w%. Chemical and p h y s i c a l m o d i f i c a t i o n s employed during recovery and upgrading operations y i e l d a s y n t h e t i c crude w i t h API g r a v i t y in the range 30-35 w i t h l e s s than 2,000 wppm s u l p h u r . Elemental sulphur is produced as a by-product of s y n t h e t i c crude product i o n and as w i t h the other l a r g e source in A l b e r t a production from sour n a t u r a l gas t r e a t i n g - i t is produced a t a r a t e not i n f l u e n c e d by demand f o r sulphur. Sulphur D i s t r i b u t i o n The Syncrude o p e r a t i o n employs surface mining techniques. Oil sand is removed from the d e p o s i t u s i n g d r a g l i n e s and placed in windrows where it is reclaimed and t r a n s f e r r e d to conveyor b e l t s by bucketwheel r e c l a i m e r s . Theoilsand is transported from the mine area, v i a the 17.7 km of conveyor b e l t s , to the E x t r a c t i o n facility. The mine has an annual c a p a c i t y to move 83.7 m i l l i o n tonnes o f oil sand c o n t a i n i n g 8.6 m i l l i o n tonnes o f bitumen w i t h approximately 0.4 m i l l i o n tonnes of contained s u l p h u r . Bitumen is recovered u s i n g a c a u s t i c a s s i s t ed hot water f l o t a t i o n process and d i l u t e d w i t h naphtha to f a c i l i t a t e the removal of r e s i d u a l s o l i d s and water. D i l u e n t naphtha is removed by d i s t i l l a t i o n p r i o r to feeding bitumen to the Upgrading f a c i l i t i e s . The primary o b j e c t i v e in the Upgrading process is to convert the heavy oil i n t o a lower b o i l i n g product w i t h low sulphur and n i t r o g e n content. Sulphur is a by-product of t h i s process. F i g u r e 3 presents a schematic of Syncrude s Upgrading and w i l l be used to d e s c r i b e the d i s p o s i t i o n of sulphur and i t s recovery a t v a r i o u s stages in the process. Bitumen feed to the f l u i d cokers contains approximately 4.9% sulphur. During c o k i n g , the sulphur is r e d i s t r i b u t e d i n t o sour gas, sour water, coke and hydrocarbon streams. Figure 3 i n d i c a t e s a c i r c u l a t i n g coke stream between the coker and coke burner. 1


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SULFUR: NEW SOURCES AND USES

SULrUH

SULFUR PLANT

SOUR VWASH


\C

Figure 3.

Simplified bitumen upgrading schematic.


Ί

HYNDMAN ET AL.


Off-gas from the coke burner (CO-Gas) contains n i t r o g e n , sulphur d i o x i d e ( S O 2 ) , hydrogen s u l phide ( H 2 S ) , carbon monoxide (CO), carbon d i o x i d e ( C 0 ) , water vapour and other t r a c e contaminants. The CO-Gas is d i r e c t e d to the CO B o i l e r f o r inc i n e r a t i o n where sulphur compounds are converted to S O 2 . The B o i l e r f l u e gas is passed through electrostatic precipitators for particulate c o n t r o l and then emission to atmosphere. The CO B o i l e r a l s o serves as the Sulphur P l a n t t a i l gas i n c i n e r a t o r . Maximum sulphur emissions are 146 tonnes/day o r 10.6% o f sulphur contained in bitumen feed to the cokers. Figure 3 a l s o i n d i c a t e s coke product from the coke burner. The f l u i d cokers are net coke producers and the product coke is s u l p h u r - r i c h a n a l y z i n g a t 6.9% sulphur. T h i s product accounts f o r roughly 253 tonnes sulphur/day o r 18.4% of input sulphur. P r e s e n t l y t h i s coke is being contained on s i t e but i n v e s t i g a t i o n s are being conducted i n t o o n - s i t e o r o f f - s i t e use w i t h acceptable sulphur recovery. P o s s i b i l i t i e s a r e f l u i d bed combustion f o r steam generation, b o i l e r f u e l w i t h f l u e gas scrubbing, hydrogen production from p a r t i a l o x i d a t i o n o r u t i l i z a t i o n as a f u e l in the cement i n d u s t r y . Sulphur a l s o leaves the coking stage in three hydrocarbon product streams: gas oil a n a l y z i n g a t approximately 3.5% S; naphtha a n a l y z i n g a t approximately 1.7% S and sour f u e l gas a n a l y z i n g a t approximately 6.2% S. Sulphur is removed from the l i q u i d products during hydrot r e a t i n g . H 2 Sisrecovered from the sour f u e l gas and the h y d r o t r e a t e r gas streams by convent i o n a l (DEA) t r e a t i n g . The e q u i v a l e n t s u l p h u r , removed as H 2 S from these streams in the Amine P l a n t is 1007 tonnes or 73.2% of i n p u t sulphur. Syncrude's Sulphur Recovery U n i t s are two p a r a l l e l t r a i n s of the c o n v e n t i o n a l Claus p l a n t c o n s i s t i n g o f thermal conversion and three c a t a l y t i c r e a c t o r s in s e r i e s . A i riss u p p l i e d to the furnace to o x i d i z e s u f f i c i e n t H2S to SO2 such t h a t an H S : S 0 r a t i o o f 2.1:1 is e f f e c t e d ( 1 ) . The sulphur recovery e f f i c i e n c y is designed f o r approximately 95% (2); however, experience to date, a t near design c a p a c i t y , has i n d i c a t e d 98% H 2 S conversions and 97% sulphur r e c o v e r i e s (1).


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SULFUR: NEW

SOURCES AND USES

Continuous t a i l gas analyzers provide i n f o r m a t i o n on flow r a t e s and H 2 S : S 0 2 r a t i o s which is used to c o n t r o l o p e r a t i o n . As i n d i c a t e d p r e v i o u s l y , the t a i l gases are routed to the CO B o i l e r f o r i n c i n e r a t i o n before emission to atmosphere v i a the main stack. Elemental sulphur from the final condensers flows to the sulphur p i t where it is a v a i l a b l e in a molten s t a t e f o r shipment by truck t r a n s p o r t or t r a n s f e r to a storage b l o c k . Sulphur which is removed from s i t e t r a v e l s south to the Edmonton area. A s i g n i f i c a n t p o r t i o n is used f o r f e r t i l i z e r production. F i g u r e 4 presents a sulphur d i s p o s i t i o n d i a gram based on design case w i t h 4.9% sulphur in the bitumen feed to the f l u i d cokers. The data i n d i c a t e 18.4% to product coke, 69.6% recovered elemental sulphur, 1 0 . 6 % S 0 emissions and 1 . 4 % in the s y n t h e t i c crude oil. Increased recovery of sulphur from processing of bitumen is p o s s i b l e w i t h new technology such as F l e x i c o k i n g o r Hydrocracking. F l e x i c o k i n g i n t e g r a t e s coke g a s i f i c a t i o n w i t h f l u i d c o k i n g . Product coke is converted to low heat content f u e l gas reducing net coke production. Sulphur d i o x i d e emissions are comparatively low. Hydrocracking has the p o t e n t i a l f o r s i g n i f i c a n t l y i n c r e a s i n g net s y n t h e t i c crude y i e l d s from bitumen, from approximately 85 LV% to perhaps 90 LV% o r more. I t is i n t e r e s t i n g to note the r e d u c t i o n in p e r m i s s i b l e and planned S O 2 emissions o f the two commercial ventures, Suncor, Inc. and Syncrude Canada L i m i t e d and the proposed Alsands P r o j e c t . These data are presented in F i g u r e 5 as w e l l as the t a r g e t S O 2 emission l e v e l proposed by A l b e r t a Environment. Data are in Long Tons S 0 / 1 0 0 0 b a r r e l s o f s y n t h e t i c crude product. The proposed Alsands r a t e is approaching the t a r g e t l e v e l of A l b e r t a Environment but implementation of new technology w i l l be r e q u i r e d to meet these obj e c t i v e s in the f u t u r e . Along w i t h p r o c e s s i n g changes to achieve higher s y n t h e t i c crude y i e l d s , the employment o f f u t u r e technology w i l l r e s u l t in greater q u a n t i t i e s of sulphur production. 2

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HYNDMAN ET AL.



Tar Sand

Tailings

4.9 %S CO-Gas 96 Τ

FLUID COKER

9.0 %S Hydrotreatingj Sour Liquids Plant

Sour Fuel Gas

CO Boiler

I

1007 Τ

Electrostatic Precipitator

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Amine Plant

ΐ4βτ

Main Stack

Sulphur Recovery Plant

I

957 Τ

Elemental Sulphur

Figure 4. Syncrude'ssulfurbalance (numbers are in tonnes equivalent sulfur per day).




SUNCOR (PERMIT)

w

. SYNCRUDE \ (PERMIT)

V ALSANDS ^· (EIA)

ALBERTA ENVIRONMENT TARGET 1965 Figure 5.

1970

1975 1980 YEAR

1985

1990

Comparison of licensed and proposed S0 emissions for the Athabasca region. 2


HYNDMAN ET AL.



Table I i n d i c a t e s a comparison o f s y n t h e t i c crude y i e l d s and product sulphur using v a r i o u s processing schemes. Should s y n t h e t i c crude production r i s e to 500,000 b a r r e l s / d a y from the Athabasca r e g i o n in the N i n e t i e s , by-product sulphur could exceed 1.5 m i l l i o n tonnes annually. I n comparison, Canadian sulphur s a l e s f o r 1979 were reported a t 6.3 m i l l i o n tonnes ( 3 ) .

Table I Comparison of Bitumen Upgrading

Process LV%

F l u i d Coking

(SCO/BIT) 2

(1)

Processes

F l e x i c o k i n g LC F i n i n g

85

85

% S Recovery

(

)

69.6

95.6

% S Emission

( 3 )

10.6

2.2

89 92 1.4

1 - Net l i q u i d volume y i e l d on net bitumen feed 2 - Elemental sulphur by-product 3 - SO2 emission e q u i v a l e n t

Emission

Monitoring

As noted in F i g u r e 4, maximum SO2 emissions represent 146 tonnes e q u i v a l e n t sulphur as the d a i l y r a t e . Besides t a k i n g measures to r e s t r i c t atmospheric sulphur e m i s s i o n s , the main s t a c k was designed and constructed in accordance w i t h A l b e r t a Environment r e g u l a t i o n s which s e t a maximum h a l f hour average ground l e v e l c o n c e n t r a t i o n o f 150 yg/ m (approximately 0.06 ppm) . T h i s l e v e l was set to a l l o w f o r a d d i t i o n a l oil sands p l a n t s in t h i s area. A computational procedure s u p p l i e d by A l b e r t a Environment determined a s t a c k height o f 183 m would meet these requirements. The p e r m i s s i b l e ambient c o n c e n t r a t i o n s o f S O 2 and H S are i n d i c a t e d in Table I I . To monitor ambient c o n c e n t r a t i o n s , Syncrude e s t a b l i s h e d an extensive network o f monitoring s t a t i o n s ( 4 ) . 3

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F i v e continuous ambient a i r monitoring s t a t i o n s are i n d i c a t e d in Figure 6. A t one minute i n t e r v a l s data on these parameters are t r a n s m i t t e d by r a d i o telemetry o r land l i n e to a minicomputer in the Operations Laboratory. Data manipulation is performed by the minicomputer and a l l data a r e t r a n s m i t t e d to a l a r g e computer in Edmonton on a d a i l y b a s i s . I n a d d i t i o n to these f i v e s t a t i o n s , the monitoring network contains 40 s t a t i c ("Candle") s t a t i o n s . The l o c a t i o n of these s t a t i o n s are a l s o given in F i g u r e 6. The s t a t i c s t a t i o n s have been in operation s i n c e May, 1977, one year before s t a r t - u p , and provide monthly i n f o r m a t i o n on t o t a l s u l p h a t i o n and hydrogen s u l p h i d e . A l l data c o l l e c t e d from the network are summarized in a p r e s c r i b e d format and submitted to A l b e r t a E n v i r o n ment on a monthly and y e a r l y b a s i s . Syncrude Canada L i m i t e d operates i t s oil sand e x t r a c t i o n f a c i l i t i e s to maximize recovery of resources w h i l e m a i n t a i n i n g compliance w i t h government r e g u l a t i o n s . Table I I P e r m i s s i b l e Ambient Concentrations

Sulphur Dioxide

3

Measure

Ug/m

ppm

30

0.01

24 Hour Average

150

0.06

1 Hour Average

450

0.17

525

0.2

Annual A r i t h m e t i c Mean

h

Hour Average

Hydrogen Sulphide

Measure

yg/m

3

£pm

24 Hour Average

4

0.003

1 Hour Average

14

0.009

17

0.011

%

Hour Average




H Y N D M A N ET AL.

Figure 6. Syncrude's ambient air quality network (not all Candle stations are indicated).



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Sulphur by-product represents l e s s than 1% of the corresponding s y n t h e t i c crude value but it is an in-place resource to be recovered. One of the challenges f o r f u t u r e generations of oil sand recovery p l a n t s w i l l be the development of more e f f i c i e n t technologies i n c r e a s i n g y i e l d s of s y n t h e t i c crude and r e c o v e r i e s of sulphur w h i l e reducing sulphur emissions.


Literature Cited 1.

2.

3. 4.

Vink, K. "From Black Sand to Yellow Sulphur." Paper presented a t 7th Canadian Symposium on C a t a l y s i s , Edmonton, A l b e r t a , October 19-22, 1980. Syncrude Canada Limited."Environmental Impact Assessment, Addendum to the 1973 Report, Volume B - B i o - P h y s i c a l Aspects." October, 1978. " S p r i n g Review and Forecast 1981." Oilweek, April 27, 1981, p. 56. Kumar, Ashok. E n v i r o n . Sci. Tech. 1979, 13, 650654.

RECEIVED October 5,

1981.


Sulfur Recovery from Oil Sands - American Chemical Society

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