Thermal Conversion of Solid Wastes and Biomass - ACS Publications

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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 14, 2016 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch005

Mass Burning of Municipal Solid Waste -Worldwide PHILIP R. BELTZ Battelle Columbus Laboratories, 505 King Avenue, Columbus, OH 43201

Municipal, commercial and light industrial waste is converted to energy daily in about 450 mass burning facilities worldwide. Of these, less than 20 operate in the U.S.A. Realizing this fact, Steve Levy and David Sussman of the U.S. EPA Office of Solid Waste developed a study program titled, "Evaluation of European Refuse Fired Energy Systems Design Practices." This paper presents research conclusions. World Wide Inventory of Waste-to-Energy Systems The " B a t t e l l e Worldwide Inventory of Waste-to-Energy Systems" shows (as of March 1979) 522 l o c a t i o n s where d a i l y opera t i n g p l a n t s have, a r e or w i l l process waste i n t o energy . A l s o included a r e s e v e r a l l a r g e p i l o t and demonstration p l a n t s . Of these about 450 are c u r r e n t l y operating mass burning u n i t s . Over 99 percent of the world's m u n i c i p a l s o l i d waste that i s converted to energy i s processed i n a "Mass Burning Refuse F i r e d Energy System". Very few of the p l a n t s opened s i n c e World War I I have c l o s e d . Plants t y p i c a l l y operate f o r 25 to 40 y e a r s . Hamburg has been producing e l e c t r i c i t y from household refuse s i n c e 1896. Other e a r l y refuse f i r e d energy systems were Chicago (1877), P a r i s (1903), Z u r i c h (1904) New York (1903), e t c . Many of these systems have been replaced by a succession of r e f u s e to energy systems. Japan has more systems and processes more waste than any other country. However, due to the h i g h moisture and p l a s t i c s content (causing high temperature c h l o r i d e c o r r o s i o n ) , very l i t t l e u s e f u l energy i s produced f o r s a l e . The C e n t r a l European count r i e s of West Germany, France and Switzerland have concentrated on high temperature steam systems f o r e l e c t r i c a l production and d i s t r i c t heating. Many Scandinavians produce high pressure hot water f o r d i s t r i c t heating. Sewage sludge i s d r i e d and u s u a l l y i s destroyed by the energy i n refuse i n 34 c o - d i s p o s a l systems worldwide.

0-8412-0565-5/80/47-130-059$05.00/0 © 1980 American Chemical Society Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

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In the U.S., we have t r i e d to develop new advanced chemical systems w h i l e the remainder of the world has continued to b u i l d mass burning energy recovery systems. At one p l a n t , odors that are c o l l e c t e d i n a new rendering p l a n t are piped 100 f e e t to the r e f u s e f i r e d steam generator f o r d e s t r u c t i o n . At other p l a n t s , f l u e gases from i n c i n e r a t i n g i n d u s t r i a l and hazardous waste are blown i n t o the f u r n a c e / b o i l e r thus p r o v i d i n g s u f f i c i e n t residence time at h i g h temperatures. In other words, a r e f u s e f i r e d steam generator can be an a f t e r b u r n e r — s a v i n g n a t u r a l gas or f u e l o i l . Composition of Refuse While there w i l l be excursions below and above t h i s range, the moisture content normally v a r i e s from a low average of 22 percent to a h i g h average of 32 percent. The average among s i x f a c i l i t i e s was 27 percent. European r e f u s e has been r a p i d l y approaching the composition of American waste as Europe has continued to "modernize" i t s way of l i f e . The heating v a l u e s , which have r i s e n d r a m a t i c a l l y s i n c e 1945, are expected to begin s t a b i l i z i n g as c i t i z e n s become more cons e r v a t i o n conscious, as petroleum becomes more precious and as m a t e r i a l needs become s a t i s f i e d . The dramatic r i s e i n heating values has adversely a f f e c t e d f a c i l i t y performance. B o i l e r tube c o r r o s i o n has i n c r e a s e d . Downtime i s up as w e l l as maintenance c o s t s . Many u n i t s have e v e n t u a l l y been derated. Some 10 to 15 year o l d p l a n t s have d i s c o n t i n u e d r e c e i v i n g " h o t t e r " i n d u s t r i a l waste i n an attempt to reduce the o v e r a l l average heating value to o r i g i n a l design v a l u e s . Refuse Generation and Burning Rates Per Person Most f a c i l i t i e s viewed accept household, commercial and l i g h t i n d u s t r i a l waste f o r burning: at a r a t e of 2.2 pounds per person per day. Development of V i s i t e d Systems The primary m o t i v a t i o n f o r c o n s t r u c t i n g r e f u s e to energy p l a n t s i n Europe has been to r e p l a c e an e x i s t i n g l a n d f i l l , compost p l a n t or i n c i n e r a t o r or to add a d d i t i o n a l i n c i n e r a t i o n with heat recovery c a p a c i t y . However, dramatic changes i n the world energy supply w i l l a f f e c t f u t u r e a t t i t u d e s about waste-to-energy. At none of the 15 major and 15 minor v i s i t e d p l a n t s d i d anyone i n d i c a t e to these authors that the primary m o t i v a t i o n was connected with energy, i . e . cost savings from f r e e f u e l , energy c o n s e r v a t i o n or u n a v a i l a b i l i t y or other energy forms. C i t i z e n and e l e c t e d l o c a l o f f i c i a l ' s p e r c e p t i o n of harmful e f f e c t s from l a n d f i l l s i s greater i n Europe than America. This U.S. p e r c e p t i o n may be changing due to r e v e l a t i o n s about

Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

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"Love Canal", "The V a l l e y of the Drums," e t c . Revelations that 60 to 80 percent of the American municipal waste l a n d f i l l s have accepted hazardous waste are a l s o bound t o increase the American c i t i z e n s p e r c e p t i o n of the hazards of u n c o n t r o l l e d l a n d f i l l i n g . For many years, European f e d e r a l governments have energeti c a l l y supported r e f u s e - f i r e d energy p l a n t s a t the same time that the U.S. P u b l i c Health S e r v i c e and USEPA were i n n o v a t i v e l y d e v e l oping and encouraging the s a n i t a r y l a n d f i l l concept. Regarding p o t e n t i a l leachate, the U.S. approach has been to " c o r r e c t " the problem by operating a b e t t e r l a n d f i l l . Europe's approach has been to "avoid" the problem by burning the refuse and r e c y c l i n g the ash i n t o u s e f u l products. Many European equipment vendors have not j o i n e d the American t h r u s t towards c o - f i r i n g and hence such t e c h n i c a l options have not been r e a d i l y a v a i l a b l e i n Europe. On both c o n t i n e n t s , net operating costs per ton, a f t e r s a l e of resources recovered, have always been two to four times g r e a t er i n a refuse to energy p l a n t than i n a l a n d f i l l of p r e v a i l i n g p r a c t i c e a t the time. Composting, very f a s h i o n a b l e i n Europe 10 to 20 years ago, has f a l l e n as a chosen a l t e r n a t i v e because l a r g e volume, cons i s t e n t product markets could not be maintained.


1

Ownership O r g a n i z a t i o n

and Personnel

Each o f the 30 systems v i s i t e d i n Europe was owned by e i t h e r the l o c a l m u n i c i p a l i t y or a not f o r p r o f i t a u t h o r i t y . Of the 15 p l a n t s studied i n d e t a i l , c i t i e s own 8, p u b l i c a u t h o r i t i e s own 6, and a n a t i o n a l i z e d e l e c t r i c company owns one. Private enterprise owns few d a i l y operating resource recovery systems i n Europe consuming municipal waste. P o t e n t i a l economics o f s c a l e f o r l a r g e p l a n t s were o f t e n negated by e s t a b l i s h i n g too many job c a t e g o r i e s and p l a c i n g too many people i n t o them. The program of education, t r a i n i n g and experience v a r i e s among c o u n t r i e s . The Germans have a very r i g o r o u s program of s c h o o l i n g , shipboard b o i l e r room experience, landbased powerplants experience, e t c . Other c o u n t r i e s , however, emphasize on-the-job training. C a p i t a l Investment C a p i t a l investment costs per d a i l y ton of system c a p a c i t y have increased 5 f o l d during "'the past 10 years. The 1960-1968 " c a p i t a l cost per d a i l y ton" ranged from $13,000 to $15,000 a t three surveyed p l a n t s . The average f o r a l l 15 p l a n t s was about $35,000. Three l a t e r p l a n t s b u i l t i n 1975 and 1976 averaged about $70,000. P l a n t s i n the e a r l y 1980's could i n i t i a l l y cost over $100,000 per d a i l y ton c a p a c i t y .



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Among the reasons f o r t h i s extreme cost growth i s that the American vendors of mass burning systems do not have as many " b e l l and w h i s t l e " design features as the European systems. The American purchaser has not p r e v i o u s l y feared c o r r o s i o n enough to demand p r o t e c t i v e f e a t u r e s . The American buyer o f t e n concent r a t e s more on the lowest b i d while the European buyer p r e f e r s a r e l i a b l e system of which he and the community can be proud. The e s s e n t i a l d i f f e r e n c e , however, i s momentum. With 275 European systems to v i s i t and observe f e a t u r e s , the European buyer knows and a p p r e c i a t e s h i s o p t i o n s . To some extent, there may be peer pressures to have an e x c e l l e n t system. We Americans have not been exposed to enough f a c i l i t i e s to have developed the same C o n t i n e n t a l a p p e t i t e . Expenses, Revenues and Net D i s p o s a l Costs Communities that have i n s i s t e d on e x t r a "chute-to-stack" design and o p e r a t i n g f e a t u r e s to i n c r e a s e r e l i a b i l i t y have bene f i t e d by having low net d i s p o s a l c o s t s . The p l a n t s averaged $27 per ton f o r t o t a l gross expenses. With the exception of one very small p l a n t , there seems to be l i t t l e e f f e c t of p l a n t capaci t y on t o t a l expenses per ton of r e f u s e processed, i . e . , there seems to be l i t t l e i f any economy of s c a l e . Buyers, vendors, designers, c i t i z e n groups, e t c . seem unable to r e s i s t the temptat i o n to "spend" p o t e n t i a l economies of s c a l e on personnel, e l e v a t o r s , b i g o f f i c e s , conference rooms, a r c h i t e c t u r e , landscaping, m u l t i p l e energy c o n f i g u r a t i o n s , e t c . Revenues from s a l e of energy averaged about $7.50 per ton throughput. A l l 5 of the 15 systems r e c e i v i n g the highest revenue per r e f u s e input ton are p r o v i d i n g energy to d i s t r i c t h e a t i n g systems. T h e i r average revenue i s $9.76 per ton. A l l 5 of the 15 systems r e c e i v i n g the lowest revenue per r e f u s e input ton are adversely a f f e c t e d by very competitive f o s s i l f u e l or nuclear e l e c t r i c a l power s t a t i o n s . T h e i r revenue averaged $5.30 per ton. Net d i s p o s a l costs per ton ranged from $6.27 up to $48.25 with the average being $16.38 per ton. Refuse Handling For furnace feeding, a l l p l a n t s observed have the system of " p i t crane mixing and l o a d i n g i n t o the feed hopper". No p l a n t observed has the American i n n o v a t i o n of dumping r e f u s e onto the f l o o r , moving i t by front-end loader onto conveyors, e t c . Crane operators are s i t u a t e d i n the s t a t i o n a r y c o n t r o l rooms along the front, s i d e or back of the p i t . T h i s i s i n c o n t r a s t to many American systems where the cab i s l o c a t e d on the crane. European designers have concern f o r operator s a f e t y should there be a p i t f i r e and disease prevention from dusty p a t h o l o g i c atmospheres.


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Source s e p a r a t i o n programs f o r newspaper, cardboard, b o t t l e s , cans, e t c . w i l l not s u b s t a n t i a l l y d e t r a c t from energy production. Most systems have doors between the truck t i p p i n g f l o o r and the p i t (1) to keep odors i n s i d e when the system i s c l o s e d , (2) to permit a higher negative pressure and thus b e t t e r odor c o n t r o l when operating and (3) to i n c r e a s e the e f f e c t i v e volume of the p i t f o r r e f u s e storage against a few of the c l o s e d doors. The only commercially operating m u n i c i p a l r e f u s e systems i n Europe known to these r e s e a r c h e r s which a r e not mass burners are i n England. One i s a suspension f i r e d b o i l e r at the IMI p l a n t i n Birmingham, England. Another i s a P o r t l a n d Cement k i l n i n England. Most European grate vendors a r e s k e p t i c a l regarding the long-term commercial v i a b i l i t y of suspension f i r e d systems i n s t e a d of mass burning grate systems. One concern i s the a d d i t i o n a l costs of preparing the r e f u s e d e r i v e d f u e l (RDF). Another concern expressed by many vendors i s the high temperatures u s u a l l y experienced when c o - f i r i n g w i t h a c o n v e n t i o n a l f u e l such as c o a l , o i l or gas. The f l u e gas temperature causes s t i c k y d e p o s i t s to form on b o i l e r tubes. T h i s can reduce heat t r a n s f e r e f f i c i e n c y and o c c a s i o n a l l y can b l o c k sections of b o i l e r s . When these deposits are f i n a l l y blown o f f , the unprotected surfaces s u f f e r increased "high-temperature corrosion". Observed grate c a p a c i t i e s ranged from 3.33 tonnes (3.7 tons) to 24.6 tonnes (27 tons) per hour. Other furnaces, not viewed, can process as much as 50 tonnes per hour. Concentrated amounts of high energy-containing m a t e r i a l may (1) melt the cast i r o n grates or (2) cause f i r e underneath the g r a t e s . Examples are magnesium c h i p s , aluminum, p l a s t i c f i l m , b u t t e r , e t c . Progress i v e p l a n t managers have suggested i n d u s t r i a l waste sources s e p a r a t i o n programs. Furnace Wall P r i o r to 1957, a l l European r e f u s e furnaces were l i n e d with r e f r a c t o r y and not w i t h water tube w a l l s , beginning i n 1957 with the Berne, Switzerland p l a n t , the use o f water tube w a l l s as the furnace e n c l o s u r e has i n c r e a s e d s u b s t a n t i a l l y . R e f r a c t o r y w a l l furnaces w i t h waste heat b o i l e r s , being l e s s expensive, are o f t e n a p p r o p r i a t e f o r hot water or low temperature steam a p p l i c a t i o n s . Water tube w a l l f u r n a c e / b o i l e r s producing high temperature steam a r e u s u a l l y chosen f o r h i g h temperature steam systems producing e l e c t r i c i t y e f f i c i e n t l y . The remarkable i n c r e a s e i n r e f u s e heating value s i n c e 1945 has exerted substant i a l i n f l u e n c e on furnace w a l l design. Even c o n t r o l l e d a i r i n j e c t i o n or f l u e gas r e c i r c u l a t i o n alone was not enough to lower f l u e gas temperature so that o l d e r equipment would s u r v i v e .



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Secondary

(Overfire) A i r

To o b t a i n complete combustion and to abate smoke and c o r r o s i v e carbon monoxide formation, the unburned v o l a t i l e (or p y r o l y s i s ) gases r i s i n g from the f u e l bed must be mixed r a p i d l y w i t h ample oxygen. T h i s mixing must be done r e l a t i v e l y near the f u e l bed with the a s s i s t a n c e of h i g h v e l o c i t y secondary a i r j e t s .


Boilers At t h i s time, 1977-1978, i t appears that the current " b e s t " b o i l e r - f u r n a c e design i n use f o r l a r g e , high pressure u n i t s i s the completely water-tube-walled furnace and r a d i a n t s e c t i o n , studded and coated with t h i n p l a s t i c r e f r a c t o r y i n the intense burning zone, followed by one or more long, open, v e r t i c a l r a d i a t i o n passes preceding a convention-type superheater and b o i l e r - c o n v e c t i o n passes and economizer. An emerging newer b o i l e r design i s to f o l l o w the t a i l water-tube-walled combustion chamber by a long superheater, b o i l e r convection s e c t i o n and economizer. This i s c a l l e d the "dacha" b o i l e r ( a f t e r the female dashund dog) because of i t s extended h o r i z o n t a l c o n f i g u r a t i o n with s e v e r a l f l y a s h hoppers. This permits tube c l e a n i n g by mechanical rapping and eases the labor of tube replacement when needed. Above some ash deposit temperature, perhaps 744 C (1300 F ) , the p r o t e c t i v e deposit becomes chemically a c t i v e and c o r r o s i o n begins. There are s e v e r a l t h e o r i e s of c o r r o s i o n causes. Three causes stand out: high temperature, HC1 and CO. Investigators do not agree among themselves as to the " r e a l " phenomena. I n t e r e s t i n g l y , the s u c c e s s f u l systems (those producing high temperature steam w i t h l i t t l e or no c o r r o s i o n of b o i l e r tubes) have design features and o p e r a t i n g p r a c t i c e s c o n s i s t e n t with a l l the theories. Recent work f o r EPA by the B a t t e l l e Columbus L a b o r a t o r i e s p o s t u l a t e that c o r r o s i o n can be lessened due to an i n t e r e s t i n g chemical phenomena. S u l f u r ( i n c o a l , o i l , sewage sludge or contaminated methane gases from l a n d f i l l s ) has the e f f e c t of forming r e l a t i v e l y harmless d e p o s i t s that prevent c h l o r i n e from being so c o r r o s i v e . The r e p o r t i d e n t i f i e s over 33 design features and o p e r a t i n g p r a c t i c e s that reduce c o r r o s i o n . A prudent d e s i g n / o p e r a t i o n a l w i l l s e l e c t i v e l y use more than 10 f e a t u r e s and p r a c t i c e s but not waste money by u t i l i z i n g a l l of them. E x c e s s i v e us of high-pressure steam soot blowers i s a common source of tube e r o s i o n - c o r r o s i o n . Other b o i l e r c l e a n i n g methods l e s s t h r e a t i n g to b o i l e r tubes are a v a i l a b l e such as mechanical rapping, shot c l e a n i n g , and compressed a i r soot blowing.


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Supplementary F i r i n g and C o - F i r i n g of F u e l O i l , Waste O i l , Solvents and Coal Supplementary f i r i n g of f u e l o i l , waste o i l , or s o l v e n t s i s p r e f e r r e d when there i s a need f o r emergency backup, r o u t i n e weekend uses, preheating upon s t a r t u p , p r e v e n t i o n of dew p o i n t c o r r o s i o n , l e g a l l y d e s t r o y i n g pathogens and other hydrocarbons, and f o r r o u t i n e energy uses when the r e f u s e f i r e d energy p l a n t i s down. However, supplementary f i r i n g may not be necessary when the energy user has h i s own a l t e r n a t i v e energy supply, when e l e c t r i c i t y i s f e d to a l a r g e e l e c t r i c a l network, when treatment of refuse or sewage sludge can be postponed s e v e r a l days or when a r e g i o n a l p l a n mandates waste o i l treatment and burning at another facility. Many European vendors suggest that i f r e f u s e and a f o s s i l f u e l a r e to be f i r e d i n the same system they be f i r e d i n separate combustion chambers. Flue gases can l a t e r be u n i t e d before e n t e r i n g the b o i l e r convection s e c t i o n . Air Pollution Control The development of the modern water-tube w a l l f u r n a c e / b o i l e r was i n part due to the need f o r proper a i r p o l l u t i o n c o n t r o l of incinerators. F l u e gases can be cooled w i t h massive a i r d i l u t i o n , water spray o r b o i l e r . Energy recovery i n b o i l e r s i s the p r e f e r r e d c o o l i n g method i f a reasonable market can be assured or anticipated. The almost u n i v e r s a l l y accepted method f o r part i c u l a t e removal i s the e l e c t r o s t a t i c p r e c i p i t a t o r . Scrubbers alone have u s u a l l y f a i l e d to meet the p a r t i c u l a t e standards. R e l i a b i l i t y of e l e c t r o s t a t i c p r e c i p i t a t o r s (ESP) has been e x c e l l e n t except where the i n l e t gases have been too c o l d o r too hot. E n t e r i n g f l u e gas temperatures must be kept above 177 C (350 F) to prevent dew p o i n t c o r r o s i o n of e l e c t r o s t a t i c p r e c i p i t a t o r s (ESP). But e n t e r i n g f l u e gas temperatures a l s o must be kept below 260 (500 F) to prevent h i g h temperature c h l o r i d e corrosion. The most s t r i n g e n t a i r p o l l u t i o n c o n t r o l standards have been set f o r Japan and West Germany. T h e i r standards a r e much more s t r i n g e n t than i n the U.S. Many persons questioned the h e a l t h j u s t i f i c a t i o n f o r the standards. Other European F e d e r a l e n v i r o n mental agencies have c a r e f u l l y viewed the standards and have e i t h e r accepted the p a r t i c u l a t e but r e j e c t e d the t i g h t gaseous (HC1, HF) c o n t r o l o r have adopted a wait and see a t t i t u d e . T e c h n i c a l l y , the U.S. standard f o r p a r t i c u l a t e s of 0.08 grains per standard cubic foot adjusted to 12 percent C 0 ?


66



J

(180 mg/nM ) i s b e t t e r e d by many p l a n t s a c h i e v i n g 0.03 to 0.05 g/SCF. Some Janapese p l a n t s and the N a s h v i l l e Thermal T r a n s f e r C o r p o r a t i o n achieve even o.Ol g/SCF. The requirement of scrubbers f o r HC1 removal f o r new p l a n t s g r e a t l y i n c r e a s e s o r i g i n a l c a p i t a l investment and has g r e a t l y slowed commercialization of resources recovery i n Germany. Of the German p l a n t s v i s i t e d having scrubbers, none was yet working adequately and without c o r r o s i o n . The Europeans seem to be more concerned with heavy metals and organics i n l a n d f i l l leachate and groundwater than they are w i t h t r a c e s of heavy metal oxides from the r e f u s e f i r e d energy p l a n t s t a c k . Water p o l l u t i o n c o n t r o l i s o f t e n not an i s s u e except at p l a n t s with scrubbers. D i r t y process water can normally be d i s posed of i n the ash chute quenching system. Conclusion The major c o n c l u s i o n i s that the mass burning of unprepared m u n i c i p a l s o l i d waste i n heat recovery b o i l e r s i s w e l l establ i s h e d , and can be a t e c h n i c a l l y r e l i a b l e , environmentally acceptable and economic s o l u t i o n to the problem of d i s p o s a l of s o l i d wastes. I t i s not as cheap as i s c u r r e n t l y a v a i l a b l e l a n d filling. However, when the cost i s considered of upgrading current l a n d f i l l s and e s t a b l i s h i n g new l a n d f i l l s i n accordance with the expected Resource Conservation and Recovery Act (RCRA) p r o v i s i o n s , these mass burning waste-to-energy systems are expected to compare more economically with t r u e s a n i t a r y l a n d fills. Many c o n d i t i o n s i n the U.S. have been d i f f e r e n t , hence waste-to-energy has not advanced as r a p i d l y as i n Europe. Some of these d i f f e r e n c e s w i l l continue, but we are moving r a p i d l y to s i m i l a r c o n d i t i o n s i n most of our m e t r o p o l i t a n areas. Hence the lessons that have been learned i n 80 years of r e f u s e f i r e d energy p l a n t (RFEP) experience i n Europe can be e f f e c t i v e l y u t i l i z e d by many U.S. communities. RECEIVED November 20,

1979.


Thermal Conversion of Solid Wastes and Biomass - ACS Publications

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