Replenishable Organic Energy for the 21st Century - ACS Symposium

15 Replenishable Organic Energy for the 21st Century JOHN L. STAFFORD and ANDREW D. LIVINGSTON

Downloaded by TUFTS UNIV on June 3, 2018 | https://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch015

Guaranty Fuels, Inc., P.O. Box 748, Independence KS 67301

During the past several years, the "Economic Feasibility" and the "Technical Feasibility" of a biomass derived fuel source has been argued and generally concluded. Certainly the "Technical Feasibility", limited in definition to the answer to the question, "Can i t be done with existing techniques?", is established. Many studies have been exercised to address the question of the economic justification of a commercial operation for the purpose of producing a specification fuel derived from biomass raw material. The answers assembled by these studies have differed because the assumptions used to define the question have been different. A recently encountered expression, used in description of an entirely different human effort, is nevertheless appropriate in the context of human effort in general; "...while not perfect...is probably as near to perfection as possible." There must come a time in the development of an enterprise when an end to study is called and the proposal subjected to a test. The feasibility of the densification/refinement of fuels from residual biomass sources is currently being tested. The Guaranty companies are engaged in this "Feasibility" test. The quotation marks used are for the emphasis that the technical feasibility and economic feasibility are for this discussion separated, when in truth they cannot be. There are natural laws which govern the behavior of materials and processes of science. These laws are not invented nor created but are discovered. There are within our economic system a set of analogous "natural laws". Efficient production and delivery of goods is provided by one of these natural laws of the economic system. A statement of this law is: "Nothing happens until something is sold." Sold means that the two or more parties involved in the proposal are satisfied and agreed that i t is to their mutual benefit to consumate the proposal. The "Feasibility Test" is not to examine the conclusion drawn from specific hypotheses, but to test the existence of those pretexts. Guaranty Fuels, Inc., was formed to test the feasibility of a commercial enterprise producing densified biomass fuels. The companion company, Guaranty Performance Co., Inc., having determined to the limits of its own definition of the diminishing return of investigative study, that 0-8412-0565-5/80/47-130-195$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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the process i s " T e c h n i c a l l y F e a s i b l e " . Ultimate t e c h n o l o g i c a l development of the r e f i n i n g of biomass f u e l s i s a long way from c o n c l u s i o n . I t can and i s being done. The f i r s t commercial embodiment by n e c e s s i t y has adapted many e x i s t i n g process t e c h n o l o g i e s . The d r y i n g and suspension burning of biomass are two examples of proven technology that have been immediately i n c o r p o r a t e d . S i z e r e d u c t i o n by hammermill and densi f i c a t i o n by p e l l e t e x t r u s i o n are current techniques. Improvement and o p t i m i z a t i o n of these consecutive steps are under development. Our entry i n t o the business of r e f i n e d biomass f u e l s i s i n h i n d s i g h t viewed ingenuous. How e l s e could we attempt to produce a s p e c i f i c a t i o n , r e f i n e d f u e l product with no r e c e i v i n g s p e c i f i c a t i o n f o r raw m a t e r i a l s ? The r e f i n i n g process removes the more troublesome v a r i a b l e s of moisture, d e n s i t y , and p a r t i c l e s i z e , but energy w i l l not be contained i n the product unless i t was f i r s t i n the raw m a t e r i a l . The raw m a t e r i a l source has a pronounced e f f e c t on the o v e r a l l system production c a p a c i t y and the product q u a l i t y . B e n e f i t s of the Use of D e n s i f i e d Biomass Fuels Burning r e f i n e d , woodbased f u e l s i n e x i s t i n g b o i l e r s allows immediate b e n e f i t to the operator by reduced emission of p a r t i c u l a t e that f o r stoker f i r e d systems has demonstrated to be w i t h i n s t a t e a i r q u a l i t y l i m i t s . No c o s t l y conversion i s r e q u i r e d s i n c e e x i s t i n g stoker systems are used unchanged and p u l v e r i z e d c o a l systems r e q u i r e minimal change. The inconvenience of "hog f u e l " or green wood chips mainly derives from m a t e r i a l handling problems that r e s u l t from a minimally s p e c i f i e d f u e l . Refined f u e l p e l l e t s provide a convenient, uniform f u e l which meets property l i m i t s s p e c i f i e d by the f u e l supply c o n t r a c t . Thus the operator may a n t i c i p a t e the f u e l p r o p e r t i e s and burning c h a r a c t e r i s t i c s . I t has been estimated that 50% of the energy needs of large i n d u s t r i a l users, t y p i f i e d by c u r r e n t l y c o a l - f i r e d 250,000 pound per hour steam generators, could be s a t i s f i e d by wood sources that are now wastes, an environmental burden. The use of these wood f u e l sources i n s u b s t i t u t i o n f o r the c o a l now burned would reduce s u l f u r dioxide emission i n p r o p o r t i o n to the degree of s u b s t i t u t i o n without i n c r e a s i n g smog forming n i t r o u s - o x i d e or p a r t i c u l a t e emission. These waste wood sources may be c o l l e c t e d , processed by r e f i n i n g , and conveniently s u p p l i e d . Atmospheric p o l l u t a n t s are reduced by the l a r g e s c a l e employment of the biomass r e f i n e d f u e l program through f i r s t - and second-order e f f e c t s . The r e d u c t i o n of f u e l burning source emissions has been c i t e d and i s the primary e f f e c t . The waste materi a l s that without the program would have remained an environmental burden, would a l s o have been allowed to be destroyed by decomposit i o n , r o t , or combustion. The only c o n t r o l s imposed of these processes are so as to c o n t a i n them w i t h i n an assigned area. The c o n t r i b u t i o n of these processes to atmospheric p o l l u t i o n are being s t u d i e d by others and thus f a r have exposed at l e a s t one i n t e r e s t ing datum: Carbon monoxide c o n t r i b u t i o n by the minimally c o n t r o l led combustion of biomass has been much greater than would be

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

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p r e d i c t e d by data r e c e n t l y published by the EPA. This CO i n the atmosphere reacts r a p i d l y with the hydroxyl r a d i c a l , OH. Since OH reacts with n e a r l y a l l p o l l u t a n t s , and thereby " c l e a n s e s " the atmosphere, the r o l e of CO i s then to "use up" the a v a i l a b l e OH and allow the accumulation of other p o l l u t a n t s . The c o n t r o l l e d combustion of biomass r e f i n e d f u e l s , derived from these otherwise waste sources, completes the o x i d a t i o n of carbon, and t h i s i s the second-order e f f e c t . The conversion of wastes to r e f i n e d biomass f u e l s b e n e f i t s the atmosphere's n a t u r a l f u n c t i o n of c l e a n s i n g itself.


D e n s i f i c a t i o n P l a n t Processes Basic process steps i n the production of ROEMMC® f u e l p e l l e t s are DRYING of the wet raw m a t e r i a l , SIZE REDUCTION of the dry mate r i a l , and DENSIFICATION of the dry, f i n e m a t e r i a l . The thermal energy f o r the d r y i n g process i s derived from the combustion of f i n e s separated from the dry, f i n e m a t e r i a l . The only e x t e r n a l energy input t o the production of p e l l e t s i s e l e c t r i c a l . The hardware embodiment of these processes i s described i n these paragraphs, as employed i n the S t i l l w a t e r , Minnesota, p l a n t . This p l a n t was designed to have an output production r a t e of 150 tons per day, continuous o p e r a t i o n . D e n s i f i c a t i o n i s accomplished by a 300 HP C a l i f o r n i a P e l l e t M i l l Model 7162-3. The p e l l e t s are formed by e x t r u s i o n through nominally 3/8 i n c h diameter r a d i a l holes i n a c y l i n d r i c a l d i e . Pressure i s exerted on a "pad" of the m a t e r i a l t o be d e n s i f i e d by r o l l s which have f i x e d s h a f t s . The p e l l e t d i e r o t a t e s about the pressure r o l l s . P e l l e t length i s c o n t r o l l e d by a " c u t - o f f " k n i f e p o s i t i o n e d to c l i p the p e l l e t s as they e x i t the r o t a t i n g d i e . The e x i t i n g m a t e r i a l stream from the p e l l e t m i l l i s mechanically l i f t ed to a p e l l e t c o o l e r , which discharges to a screen to remove under-size p e l l e t pieces and f i n e s . The f i n e s and pieces are r e c y c l e d to the p e l l e t m i l l i n f e e d system. F i n i s h e d p e l l e t s are conveyed by high pressure a i r system t o tank storage. Size Reduction i s by g r i n d i n g through a screen using a 300 HP Champion Model 18304 "Magnum" hammermill. Screen opening s i z e s ranging from 5/64 i n c h diameter to 1/4 inch diameter have been used. Ground m a t e r i a l from the hammermill i s conveyed by a i r t o a cyclone r e c e i v e r on the p e l l e t m i l l i n f e e d system. Fines are separated from t h i s m a t e r i a l stream by screening to be used as dry fuel. Drying of the wet raw m a t e r i a l i s performed i n a Guaranty Performance Co. 10 f e e t diameter by 32 f e e t long, three-pass r o t ary drum dryer. Dry m a t e r i a l i s conveyed i n the dryer exhaust gases to a cyclone r e c e i v e r which discharges i n t o the hammermill i n f e e d system. Drying i s accomplished p r i m a r i l y by convection heat t r a n s f e r between the hot dryer gas and the drying medium ( s o l i d s ) . The hot dryer gas i s produced by the combustion of the f i n e m a t e r i a l screened from the hammermill output, i n a c y c l o n i c suspension ROEMMC burner system. The burner i n t h i s a p p l i c a t i o n i s a wood-fired a i r heater.


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Heterogenous Biomass Raw

BIOMASS

Materials

The nature of the raw m a t e r i a l s f o r biomass residue derived f u e l s i s c e r t a i n l y heterogenous. This i s somewhat demonstrated by the s i z e d i s t r i b u t e d f u e l p r o p e r t i e s of Peanut H u l l s . Table I l i s t s the f u e l analyses of samples prepared by s i e v e s e p a r a t i o n . This m a t e r i a l leaves the peanut processing plant with a r e l a t i v e l y low moisture content, average value f o r the reference sample i s 7.83%. Weather p r o t e c t i o n during t r a n s p o r t a t i o n and storage would preserve t h i s low moisture and may e v e n t u a l l y , but cannot c u r r e n t l y be assured. O c c a s i o n a l l y a simple process step can be employed to s i g n i f i c a n t l y upgrade the product. In t h i s i n s t a n c e , by screen s e p a r a t i o n , a major p o r t i o n of the non-combustible f r a c t i o n (ash) can be removed while s a c r i f i c i n g a small p o r t i o n of the f u e l heati n g value. A three-way screening operation i s i n v i s i o n e d that would separate the raw m a t e r i a l stream i n t o : 1) Large s i z e f o r d e n s i f i c a t i o n processing, 2) Intermediate s i z e f o r process (dryer) f u e l , and 3) Undersize to be discarded. The components, from an i d e a l screening process would r e s u l t i n the m a t e r i a l streams l i s t e d i n Table I I . D i s c a r d i n g h a l f the raw m a t e r i a l ash content may be accomplished f o r 5% of the heating value. Although higher moisture, the intermediate "cut i s s t i l l an acceptable dryer f u e l . 11

TABLE I PEANUT HULLS, FUEL ANALYSIS DISTRIBUTION BY SIZE Heat Fraction Value Retained Total Passing BTU/LB Ash Moisture US No. US No. Weight 8015 .0277 .0676 .710 8 7920 .0311 .102 .0689 8 16 8110 .0498 .061 .0669 16 30 6971 .1928 .1585 30 50 .068 5026 .4521 .0367 .051 50 100 3385 .6375 .0313 100 .008 7750 .0672 .0783 Average TABLE I I THREE-WAY SPLIT, PROCESS MATERIAL STREAMS Stream Component Stream A n a l y s i s F r a c t i o n T o t a l A n a l y s i s F i n a l Use Moisture Ash Heat Value Mass Ash Heat Value Product .07 .03 7970 .778 .325 .800 Dryer F u e l .11 .08 8070 .143 .175 .150 Discard .07 .43 4970 .079 .500 .050 D e n s i f i e d biomass f u e l i n the form of extruded p e l l e t s have been produced from a v a r i e t y of raw m a t e r i a l s and by systems that vary the sequence of process steps from that described h e r e i n . These v a r i a t i o n s i n the processes should have l i t t l e e f f e c t on the composition of the combustible f r a c t i o n of the product p e l l e t s , A survey of f u e l p r o p e r t i e s of a number of these f u e l p e l l e t s i s i l l u s t r a t e d i n F i g u r e 1. When the moisture and ash are removed





Figure 1. Pellet fuel analyses


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from the f u e l , the balance i s combustible m a t e r i a l . As the moisture + ash f r a c t i o n of the f u e l i n c r e a s e s , the " a s - f i r e d " h e a t i n g value on a "moisture-free and ash-free b a s i s " might be expected to be f a i r l y constant on the assumption of a simple mixing theory. The data of F i g u r e 1 would suggest, however, that the a d d i t i o n of moisture and ash content i s accompanied by a l o s s i n the moisture- and ash-free h e a t i n g v a l u e . This e f f e c t would r e s u l t f o r the degradation of the f u e l raw m a t e r i a l by p a r t i a l o x i d a t i o n of the combustibles. Some of the samples analyzed f o r the F i g u r e 1 survey were of p e l l e t s produced from sawdust raw m a t e r i a l taken from the bottom of the sawdust d i s c a r d p i l e of a saw m i l l . These had obviously s u f f e r e d some decomposition. F u e l analyses of these samples support the p a r t i a l o x i d a t i o n hypothesis. Process Equipment C a p a c i t i e s The dryer a i r - h e a t e r system was somewhat o v e r - s i z e d f o r the evaporation load imposed by the average 45% moisture wet raw m a t e r i a l . The s i g n i f i c a n t adjustments made were those r e q u i r e d so that the dryer would be able to induce a l l of the " l o w - f i r e " products of combustion. A fundamental p r i n c i p l e of the burner design i s the c o n t r o l of the combustion chamber gas temperature i n order to prevent the m e l t i n g or f u s i o n of the s o l i d non-combustible (ash). The burner system i n c l u d e s a r e f r a c t o r y - l i n e d cyclone furnace from which the dry ash i s removed. The c o n t r o l of the gas temperature to avoid s l a g g i n g i s accomplished by the use of large amounts of "excess" combustion a i r . Although there i s no thermal e f f i c i e n c y l o s s f o r t h i s a i r - h e a t e r a p p l i c a t i o n , there r e s u l t s a l a r g e q u a n t i t y of gaseous combustion products that the dryer system must be able to t o t a l l y induce f o r there to be no thermal l o s s . The dryer exhaust fan was sped-up to f u r t h e r a i d the system i n using a l l the product gases. A necessary compromise has been suggested f o r the optimum boundary c o n d i t i o n s to impose on the hammermill and p e l l e t m i l l systems. Hammermill horsepower should be reduced by drying the m a t e r i a l to a lower moisture and by the use of a l a r g e r hammermill screen opening. Both of these adjustments are expected to reduce the q u a l i t y and production throughput capacity of the p e l l e t m i l l . The o r i g i n a l arrangement of the p l a n t was to dry the i n f e e d biomass, g r i n d i t , and accumulate the ground m a t e r i a l i n a surge b i n . M a t e r i a l was metered from t h i s b i n to the p e l l e t m i l l and as f u e l to the dryer a i r - h e a t e r . I t i s g e n e r a l l y accepted that the ground m a t e r i a l f o r p e l l e t i n g should be produced by g r i n d i n g through a screen with openings l e s s than the p e l l e t diameter, and that extreme f i n e s are not s u f f i c i e n t l y compacted i n the p e l l e t mill. Smaller p a r t i c l e s i z e production from the hammermill may by v i r t u e of the g r e a t e r s p e c i f i c energy input produce a greater moisture r e d u c t i o n a s s o c i a t e d with the s i z e r e d u c t i o n and t h i s may c o n t r i b u t e to the f a i l u r e to compact the extreme f i n e s . Production experiments were performed to demonstrate the e f f e c t of ground m a t e r i a l s i z e on the p e l l e t i n g o p e r a t i o n . P e l l e t



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q u a l i t y was determined by judgement of p e l l e t d e n s i t y , hardness, d u r a b i l i t y , and f l o w a b i l i t y . P e l l e t approximate length and v i s u a l appearance i n d i c a t e combinations of d e s i r a b l e p r o p e r t i e s . "Good" p e l l e t s appear shiny, s l i c k , or smooth, while "Bad" p e l l e t s are d u l l f i n i s h e d , rough, or s c a l y . Near optimum p e l l e t length i s 3 to 4 times the p e l l e t diameter. Ground m a t e r i a l p a r t i c l e s i z e was adjusted i n steps by r e p l a c i n g the g r i n d i n g screen i n the hammermill. Screen opening diameters of 5/64, 1/8, 3/16, and 1/4 inch were used. P e l l e t diameter was 3/8 i n c h . In general an optimum hammermill screen opening s i z e was not demonstrated. Although an optimum of 3/16 i n c h diameter was i n d i c a t e d f o r one species of bark m a t e r i a l , most m a t e r i a l s demonstrated continuously improved p e l l e t q u a l i t y and horsepower economy f o r l a r g e r screen opening size. The p a r t i c l e s i z e experiments demonstrated p e l l e t q u a l i t y was improved by l a r g e r s i z e d p a r t i c l e s . The dryer energy source, c y c l o n i c suspension burner, p r e f e r s s m a l l s i z e p a r t i c l e s with r a p i d i g n i t i o n and short residence requirement f o r complete comb u s t i o n . Therefore, the best m a t e r i a l f o r each process, p e l l e t i n g and suspension burning, i s produced by screening the ground material. C u r r e n t l y the dry m a t e r i a l i s ground through a 1/4 i n c h diameter hammermill screen opening and separated by a 22 mesh screen i n t o dryer f u e l and p e l l e t m i l l feed streams. Some f u r t h e r r e l i e f of the hammermill would be achieved by performing t h i s s e p a r a t i o n before the hammermill. A second u n i t or a replacement u n i t of greater c a p a c i t y may have to be the s o l u t i o n of what now appears to be the p l a n t "bottle-neck". This arrangement of p e l l e t m i l l i n f e e d p r o p e r t i e s permits the p e l l e t m i l l to operate s l i g h t l y i n excess of the p l a n t design throughput rate f o r the short p e r i o d allowed by the surge b i n feeding the pellet mill. I t i s b e l i e v e d that the p e l l e t m i l l would be capable of maintaining very near the design production r a t e on a d a i l y average b a s i s . An average r a t e of 120 tons per day i s used i n the cost references to f o l l o w . User Experience with D e n s i f i e d Biomass Fuels D e n s i f i e d f u e l p e l l e t s may be used as b o i l e r f u e l i n place of c o a l i n s t o k e r - f i r e d furnaces. D i r e c t s u b s t i t u t i o n of f u e l p e l l e t s was demonstrated i n two i n f o r m a l l y reported instances with no furnace adjustments. The p a r t i c u l a t e emission from each of these i n s t a l l a t i o n s were monitored with the emission r a t e r e s u l t s shown i n Figure 2. As a comparison, the North C a r o l i n a A d m i n i s t r a t i v e Code allowable p a r t i c u l a t e emission r a t e schedule (a f u n c t i o n of heating rate) i s a l s o shown. The environmentally acceptable p a r t i c u l a t e emission c o n t r i b u t e s to the economic j u s t i f i c a t i o n of the conversion of small-to-medium s i z e steam generators to the use of p e l l e t e d biomass f u e l s . Two such i n s t a l l a t i o n s are now using p e l l e t e d f u e l s on a r o u t i n e b a s i s , and a t h i r d has concluded the economic b e n e f i t by e n t e r i n g i n t o a contract agreement to purchase pelleted fuel.



202

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CHARGING R A T E * M I L L I O N

Figure 2.

100

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Stoker fired boiler emissions grate burning pelleted fuels

D hCQ Ζ Ο BURNING GROUND B I O M A S S FUEL

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CHARGING RATE • M I L L I O N B T U / H R

Figure 3.

Demonstration unit roemmc burner emission rate


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P u l v e r i z e d c o a l - f i r e d steam generators should experience simi l a r emission r a t e s as the ROEMMC burner which i s a c y c l o n i c suspension burning system. S e v e r a l emission t e s t s have been performed on the demonstration burner u n i t i n Independence, Kansas. The r e s u l t s of these t e s t s are shown i n F i g u r e 3. F o r these t e s t s the burner system was operated without the recovery of energy from the gaseous products of combustion. Emission sampling was done i n the r e l a t i v e l y high temperature gas stream e x i t i n g the cyclone furnace.


Production Costs Considerations The " F e a s i b i l i t y T e s t " being conducted must demonstrate f o r success that a market may be e s t a b l i s h e d f o r the raw m a t e r i a l that competes with the a l t e r n a t i v e uses or d i s p o s i t i o n of the m a t e r i a l . This market w i l l d e f i n e a schedule of raw m a t e r i a l p r i c e s such as i s i n d i c a t e d by Table I I I . At the same time, a s u c c e s s f u l t e s t r e s u l t w i l l demonstrate that the product d e n s i f i e d f u e l competes with a l t e r n a t i v e f u e l s , e s t a b l i s h i n g a product s a l e s p r i c e on the order of the Table IV i n v i t a t i o n . Between these schedules, there must be the money t o accomplish the p h y s i c a l p r o c e s s i n g and a t t r a c t the f i n a n c i n g . The " t e s t " i s not to presume e i t h e r of these schedules, but t o demonstrate the t h r e e - f o l d mutual b e n e f i t : 1) A market f o r the raw m a t e r i a l , 2) An a t t r a c t i v e investment, and 3) An acceptable p r i c e f o r the product energy. TABLE I I I RAW MATERIAL Guaranty F u e l s , Inc. s h a l l purchase s i z e d wood and other biomass m a t e r i a l s on the f o l l o w i n g c o n d i t i o n s : 1. Must be d e l i v e r e d i n s e l f - u n l o a d i n g trucks (5 ton or o v e r ) . 2. NO metal, g l a s s , rocks, or d i r t s h a l l be i n m a t e r i a l s . 3. A l l m a t e r i a l must be 3 i n c h a l l s i d e s or l e s s . 4. Moisture i n m a t e r i a l must not be over 55% 5. A s c a l e t i c k e t must come with each l o a d . 6. P r i c e p e r ton: Sawdust (wet) $5.00 Whole t r e e chips $6.00 Bark (hogged) $3.00 Dry hogged wood $6.00 Sawdust (dry) $6.00 7. Terms: Invoiced, p a i d weekly. _ The production cost break-down i t e m i z a t i o n i n c l u d e s , i n a d d i t i o n t o the above i n d i c a t e d cost of raw m a t e r i a l and cost of f i n a n c i n g , the cost of energy f o r the process, l a b o r , maintenance and r e p a i r s , insurance, taxes and r o y a l i t i e s . These costs have been v a r i o u s l y l i s t e d i n the study r e p o r t s . Estimates range from approximately 15 d o l l a r s per ton t o over 20 d o l l a r s per ton of f i n i s h e d product. I t i s not the purpose here t o present a d e t a i l ed balance sheet o r income statement. There has been f a r too l i t t l e operating time of the S t i l l w a t e r p l a n t to e s t a b l i s h the long-term costs y e t . The replacement of machine p a r t s has been a


204

THERMAL CONVERSION OF SOLID WASTES AND

BIOMASS

r e s u l t of speed changes to evaluate c a p a c i t y , system rearrangements , and so f o r t h i n a d d i t i o n to the replacement of worn or broken p a r t s . The production status of the p l a n t has been dependent on the status of the n e g o t i a t i o n s r e q u i r e d to e s t a b l i s h the balance suggested by the p r i c e schedules of Table I I I and Table IV. This aspect of the operation has s e t t l e d down a b i t and a longer run of experience operation i s now under way.


TABLE IV SALE OF ROEMMC FUEL PELLETS Specifications : BTU per pound Moisture Ash Density (LB/CF) Fines (by weight) Price : Are F.O.B. Bayport, Minnesota On Contract, 10 ton or more per day NO Contract, 1 to 10 ton

8,200 Average 10% Maximum 5% Maximum 38 Average 5%

$31.00 per $35.00 per

ton ton

The energy c o s t s , f o r the p l a n t as defined, are more e a s i l y e s t a b l i s h e d . A long run of operation i s not required to y i e l d a f a i r l y good idea of the production capacity of the given equipment arrangement. I t was s t a t e d before that the production capacity of the p l a n t , dependent to a degree on the s p e c i f i c raw m a t e r i a l , i s 120 tons per day sustained operation. Thermal energy requirement f o r the process i s s u p p l i e d by the combustion of f i n e s separated from the process. The e x t e r n a l l y s u p p l i e d energy i s e l e c t r i c a l power. A t o t a l of 1114 connected horsepower i s d i s t r i b u t e d among the production subsystems (Table V ) . TABLE V HORSEPOWER DISTRIBUTION Connected Horsepower Dryer System 140.5 Burner System 88.5 Hammermill System 378. P e l l e t M i l l System 378.2 Storage T r a n s f e r 87.5 A i r Q u a l i t y System 16. U t i l i t y Systems 25.3 TOTALS 1114.0

Running Amperes 161.5 103. 423.5 413.5 47.5 15,2 32.5 1196.7

A i r q u a l i t y i n f l u e n c e i s a c t u a l l y somewhat greater s i n c e the c o l l e c t i o n equipment imposes a d d i t i o n a l pressure l o s s on the a i r systems. The l i s t e d running amperes are f o r a normal load on each of the a f f e c t e d motors. As such they represent a t y p i c a l motor current t o t a l , adding to about 90% of the nameplate amperes. E l e c t r i c a l energy demand represents an energy account of 2.5 m i l l i o n BTU per hour. On a s p e c i f i c u n i t of production b a s i s using


15.



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the 120 tons per day capacity, this i s :


222.8 HP hours/finished ton, or 0.5 million BTU/finished ton. Two significant differences exist between densification processes available today. Pelleting and Cubing are extrusion processes relying on the forces of f r i c t i o n at the extrusion die surface to compact the material. Another process of Briquetting uses the force between opposed roll-dies to compact the material. Comparison production tests were performed using the r o l l - d i e , briquetting machine. Two series of briquetting machine runs were performed, one on a small sample shipped to the machine manufacturer, and a more extensive test with the machine on-loan at the Stillwater plant. Energy costs were no greater per ton of finished product. Further tests may demonstrate less energy cost than for the pellet m i l l operation. The finished product was acceptable for air system transfer and tank storage. Maintenance and wear costs require considerable conjecture for comparison at this stage. The urgency of conversion from fossil-based energy sources is in order to prepare for the inevitable depletion of these nonrenewable sources. Preparation and orderly conversion to renewable energy sources may forestall the panic-stricken scramble for depleted sources within the next decade. The United States Cent r a l Intelligency Agency projects world demand for o i l to reach production capacity i n the next few years. Sharply rising price w i l l effectively ration available supplies without regard for Middle-East p o l i t i c s or balance-of-payment. The supply of biomass to support the process densification/refinement described herein w i l l not support the energy needs of a l l the steam production of this country. The use of these fuel pellets may not prove to be the best alternative source for everybody. The direct combustion of biomass fuel pellets may eventually be opposed as a poor use of the feedstock, supported by second-law arguments. The course we take as individuals must be according to our visionary aptitudes. For the present, for the economic conditions and technology existing as the depletion of f o s s i l sources is f e l t , Densified Biomass fuels have been and are gaining in acceptance as a means of l i m i t ing the ever escalating cost of energy with environmental acceptance . References "Burn Trees Not Coal to Reduce SO2", SCIENCE NEWS, March 17, 1979. "Plant Burning is Major CO Source", SCIENCE NEWS, March 17, 1979. "The International Energy Situation: Outlook to 1985", U. S. Government Printing Office, S/N 041-015-00084-5, 1977.


Replenishable Organic Energy for the 21st Century - ACS Symposium

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