Economics Associated with Waste or Biomass Pyrolysis Systems

2

Economics Associated w i t h Waste or Biomass Pyrolysis

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Systems RICHARD BAILIE Chemical Engineering Department, West Virginia University, Morgantown, WV 26505 C. A. RICHMOND Wheelabrator Incineration, Inc., 600 Grant Street, Pittsburgh, PA 15219 In the early dats of the i n d u s t r i a l revolution, wood was used as the primary f u e l . In the highly developed i n d u s t r i a l nations wood was soon replaced by fossil fuels. Wood could not compete economically with these fossil fuels. U n t i l recent times, these fossil fuels were low in cost and available i n what seemed to be an endless supply. Recently, costs have risen and are expected to rise even further in the future. I t i s becoming more apparent that this supply of fuel is limited. Wood remains an alternative f u e l . Unlike fossil f u e l , wood i s not found i n large amounts i n concentrated areas. I t is available i n limited amounts spread over a wide area and is renewable. Consideration is being given to once again making more use of wood as a fuel source. In addition to wood, all plant life (biomass) can be used for its f u e l value. In the discussion to follow, wood represents but one type of biomass that may soon see use as a fuel. During the time that has elapsed since wood was widely used, several important changes have occurred. Two of these changes are: 7.

Energy consumption (both t o t a l and per capita) has increased dramatically.

2.

Size of energy conversion systems have increased. These large systems have achieved "economies of scale."

In terms of e l e c t r i c power generation, a 50 Mw power station i s extremely small and cannot achieve the thermal e f f i c i e n c i e s and economics that are attributed to larger systems. Even this size u t i l i t y would require 1,000 tons/day of biomass or 365,000 tons per year on a continuing basis. The Department of Energy has a study underway (1) to determine i f this amount of fuel can be obtained on a continuing basis i n a l o c a l area i n the Northeast. Wood may be burned d i r e c t l y to provide for generation of steam or e l e c t r i c i t y or i t may be converted to a more attractive fuel form such as gas or l i q u i d that may be transported to a central 0-8412-0434-9/78/47-076-021$05.75/0 © 1978 American Chemical Society Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

22

SOLID WASTES AND RESIDUES

s i t e where generation of steam or e l e c t r i c i t y occurs. The f i n a l judgement as to what form biomass can most e f f e c t i v e l y be used as a f u e l must r e s t on economics. I t i s not l i k e l y t h a t there i s a s i n g l e conversion process that w i l l be p r e f e r r e d f o r a l l biomass f u e l s i n a l l s i t u a t i o n s . The most common process f o r conversion i s d i r e c t combustion of biomass. Burning of wood and bagasse to produce steam has been an e s t a b l i s h e d p r a c t i c e . There are many s i t u a t i o n s where d i r e c t combustion may not be the most a t t r a c t i v e a l t e r n a t i v e . This paper d e s c r i b e s one a l t e r n a t i v e to d i r e c t combustion of biomass. Biomass may be converted to a medium energy f u e l gas t h a t i s l a t e r burned. The paper makes the case f o r c o n s i d e r a t i o n of generating medium energy f u e l gas, desc r i b e s a system that can accomplish the conversion of gas at a moderate s c a l e , d i s c u s s e s the economics of t h i s system, and p r o v i d e s some examples as to how the medium energy gas compares to d i r e c t combustion. Reasons to Consider Medium Energy Gas I f a power p l a n t operator were given a choice of n a t u g a l gas, petroleum, or c o a l as a f u e l ( a l l at the same cost i n $/10 Btu); n a t u r a l gas would be p r e f e r r e d . Some of the reasons f o r t h i s preference are: 1.

N a t u r a l gas can be burned i n an environmentally acceptable manner without a i r p o l l u t i o n c o n t r o l equipment.

2.

The s i z e of the furnace i s s m a l l e r . B e c h t e l i n a r e p o r t f o r the e l e c t r i c power i n d u s t r y (2) gave the r a t i o of 1.0/1.35/1.85 f o r gas, o i l and c o a l f u e l systems.

3.

There i s a lower maintenance f o r the gas systems.

fired

F i g u r e 1 i s a schematic that compares s o l i d f u e l and gas f u e l b o i l e r s . The area of the furnace b l o c k represents the s i z e . The n a t u r a l gas furnace r e q u i r e s no p o l l u t i o n c o n t r o l equipment. Both of these f a c t o r s r e l a t e d i r e c t l y to c o s t s . I t i s cheaper to conv e r t n a t u r a l gas than s o l i d f u e l to steam or e l e c t r i c i t y i n a u t i l i t y b o i l e r . In a d d i t i o n to these f a c t o r s , f a v o r i n g gas f i r e d systems, the hog f i r e d b o i l e r s and bagasse b o i l e r s have a lower t h e r mal e f f i c i e n c y . The s i z e of these biomass b o i l e r systems are much l a r g e r than these f o r f o s s i l f u e l s of the same c a p a c i t y . Based on these f a c t s , i t can be seen that n a t u r a l gas i s much more v a l u a b l e (on a Btu b a s i s ) than i s biomass f u e l . Biomass may be converted to a medium Btu f u e l gas. B e c h t e l Corporation i n t h e i r r e p o r t to the E l e c t r i c Power Industry (2) prov i d e d curves of the thermal e f f i c i e n c y , the a i r r e q u i r e d and the

Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

Economics Associated with Waste

23

combustion products produced f o r gases of v a r y i n g f u e l v a l u e s . They are shown i n Figures 2 and 3. These curves show that a 300 Btu gas has a higher e f f i c i e n c y , lower a i r requirements and pro duce l e s s combustion product. This i n d i c a t e s that a 300 Btu gas could be burned as e f f e c t i v e l y as n a t u r a l gas. I f a 300 Btu gas can be exchanged f o r a n a t u r a l gas, then the statement regarding the d e s i r a b i l i t y of n a t u r a l gas can apply to t h i s f u e l gas. I t f o l l o w s that a 300 Btu gas would be p r e f e r r e d over biomass f u e l s i n their natural state. Figure 4 provides a r e p r e s e n t a t i o n of the f u e l costs and a l l other y e a r l y costs to o b t a i n steam or e l e c t r i c i t y from wood, c o a l , or a 300 Btu gas. The costs of o p e r a t i n g a wood f i r e d p l a n t i s higher than a c o a l f i r e d p l a n t . To produce e l e c t r i c i t y at the same c o s t , the b a s i c f u e l cost must be l e s s as shown i n Figure 4. The y e a r l y cost of o p e r a t i n g a gas p l a n t i s considerably l e s s (about 1/2) than f o r a c o a l p l a n t . I f the conversion of wood to gas i s equal to Δ i n Figure 4 then wood to gas to e l e c t r i c i t y would produce e l e c t r i c i t y at the same p r i c e as c o a l . The s u b s t i t u t i o n of biomass f o r f o s s i l f u e l i n an e x i s t i n g f a c i l i t y i s seldom p o s s i b l e . The s i z e of a furnace i s l a r g e r f o r systems using a biomass f u e l than f o r f o s s i l f u e l s . Figure 5 shows a h i e r a r c h y of s u b s t i t u t i o n s that are p o s s i b l e . Gas may be s u b s t i t u t e d f o r petroleum, c o a l , and wood; p e t r o leum may be s u b s t i t u t e d f o r c o a l and wood; and c o a l may be sub s t i t u t e d f o r wood. S u b s t i t u t i o n s cannot normally be made i n the reverse d i r e c t i o n without major r e t r o f i t and/or d e r a t i n g of the boiler. N a t u r a l gas i s p r e d i c t e d to be the f i r s t form of f o s s i l f u e l to become depleted (estimates p r e d i c t as l i t t l e as eleven years of n a t u r a l gas remain). Industry has already f e l t c u r t a i l m e n t and i t may be s a f e l y p r e d i c t e d that i t w i l l be i n d u s t r y that w i l l be f i r s t to f e e l any e f f e c t s o f dwindling s u p p l i e s . Experience over the l a s t two years shows i n d u s t r y i s the f i r s t to f e e l the e f f e c t s o f c u r t a i l m e n t . What w i l l happen to i n d u s t r i a l and u t i l i t y b o i l e r s b u i l t to f i r e gas? Many of these are r e l a t i v e l y new and many were i n s t a l l e d to meet environmental r e g u l a t i o n s . They are h i g h l y e f f i c i e n t and are i n e x c e l l e n t o p e r a t i n g c o n d i t i o n , but cannot be switched to o i l o r c o a l . In such a s i t u a t i o n a customer w i l l be w i l l i n g to pay a premium p r i c e f o r a gas that may be sub s t i t u t e d f o r n a t u r a l gas and use t h i s f a c i l i t y . The a l t e r n a t i v e would be to r e t i r e the present system and commit the c a p i t a l t o b u i l d a new (and expensive) furnace. In such a s i t u a t i o n , a 300 Btu gas becomes an a t t r a c t i v e f u e l . Economics of Medium Energy Gas

Production

2 Two processes are a v a i l a b l e that can produce a 300-400 Btu/ f t f u e l gas from biomass that have been demonstrated i n p i l o t plant s i z e operations.



Clean-Up

Solid Fuel

Furnace

Natural Gas ,

- • Steam or Electricity

Furnace

Figure 1.

- Steam or Electricity

Comparison of solid and gas fired

1,000

800

Flue Gas per 10,000 Btu of Fuel Fired

Theoretical Air Required to Burn 10,000 Btu of Fuel

ο 600h

05 400

200 J 0

2

4

J 6

I 8

I 10

I 12

L 14

16

Pounds

Figure 2.

Theoretical air and flue gas


2.

BAILIE AND RICHMOND

25


100 h

90

80

70 I

J_ 200

400

600

800

J 1000

Figure 3.

Gas Fuel Btu/Cu. Ft.

Wood-Gas

Wood

Unit efficiency

Coal

Unit Cost of Electricity (KWH)

Basic Fuel Cost I All other yearly costs.

J

Figure 4.

Cost breakdown for electricity from coal, wood, or wood^gas

Gas

i Petroleum

c

°

a l

I

Wood or Bagasse

Figure 5. Fuel substitution hierarchy


26


1.

Purox - Union Carbide has operated a 200 ton/day p i l o t f a c i l i t y i n I n s t i t u t e , West V i r g i n i a ( 3 ) . The major system components are a s h a f t k i l n and an Oxygen p l a n t .

2.

Pyrox - K i k a i K u n i i has operated a 50 ton/ day p i l o t f a c i l i t y i n Japan. Some r e s u l t s have been reported by K u n i i ( 4 ) .

Both of these systems have used m u n i c i p a l waste to produce an i n t e r mediate Btu gas and the Pyrox u n i t has been operated on biomass. Since the organic p o r t i o n of m u n i c i p a l waste i s p r i m a r i l y c e l l u l o s e , comparable performance should be expected from s o l i d waste or biomass. Both processes p y r o l y z e the organic p o r t i o n present i n the s o l i d f u e l . To produce an i n t e r m e d i a t e Btu gas, i t i s necessary that the gas i s not d i l u t e d w i t h N i t r o g e n . In the Purox Process t h i s i s accomplished by s e p a r a t i n g the Oxygen from the N i t r o g e n i n an a i r s e p a r a t i o n p l a n t . In the s i n g l e s h a f t k i l n r e a c t o r , both a combustion r e a c t i o n and p y r o l y s i s occur. In the Pyrox Process the combustion r e a c t i o n and the p y r o l y s i s take p l a c e i n separate f l u i d i z e d bed r e a c t o r s . S o l i d s c i r c u l a t e between the two beds to prov i d e the heat needed f o r the p y r o l y s i s r e a c t i o n . In the United States market, the p y r o l y s i s process developed by B a i l i e and a v a i l a b l e through Wheelabrator I n c i n e r a t i o n , I n c . , i s comparable to the Pyrox system. This process was the one sel e c t e d f o r t h i s paper because the authors are more f a m i l i a r w i t h the process economics and i t i s more compatible w i t h the modest s i z e d f a c i l i t y needed f o r most biomass conversion s i t e s . In a recent r e p o r t by B a t t e l l e i n a study of sugar cane as a f u e l crop (5) the f o l l o w i n g comment was made: Commercialization of r e l a t i v e l y s m a l l s y n t h e s i s gas p l a n t s needs a process such as P r o f e s s o r R. C. B a i l i e (1972) has suggested so t h a t the expense of an oxygen f a c i l i t y can be avoided. . . .The process i s admittedly s p e c u l a t i v e but i t s t r i k e s d i r e c t l y at a major drawback of the processes d i s c u s s e d a b o v e — t h e need f o r an e n e r g y - i n t e n s i v e oxygen p l a n t . F i g u r e 6 i s the b a s i c schematic of the two f l u i d i z e d bed process. The s o l i d f u e l i s fed i n t o a p y r o l y s i s r e a c t o r at about 1500 F. This r e a c t o r i s composed of hot i n e r t sand. Heat t r a n s f e r to the s o l i d feed i s r a p i d and p y r o l y s i s occurs. The r a p i d heat t r a n s f e r leads to h i g h gas y i e l d s ( 6 ) . The f u e l gas goes to a cyclone where the char i s removed. The char i s fed along w i t h a i r to a second f l u i d bed h e l d at about 1800 F. Combustion takes p l a c e and provides the energy needed f o r the p y r o l y s i s r e a c t i o n . This energy i s t r a n s f e r r e d to the p y r o l y s i s bed by a sand c i r c u l a t i o n system between the two r e a c t o r s .



Figure 6.

CHAR

SAND

FUEL GAS + CHAR

PYROLYZER

1500°F

FUEL GAS

.

SOLID WASTE OR BIOMASS

FUEL GAS RECYCLE

Schematic flow diagram of two-reactor system: temperature—1800°F, 1500°F; feed—char —unsorted waste or biomass; products—fuel gas + char + solid waste

COMBUSTOR

1800°F

COMBUSTION GASES

- •

28


Stanford Research I n s t i t u t e r e c e i v e d a c o n t r a c t from West V i r g i n i a U n i v e r s i t y to make an economic e v a l u a t i o n of the two f l u i d bed system to produce an intermediate Btu f u e l gas from s o l i d waste ( 7 ) . B e c h t e l Corporation working f o r the C i t y of C h a r l e s t o n , West V i r g i n i a , i n preparing a grant a p p l i c a t i o n to EPA provided a second economic e v a l u a t i o n of the two f l u i d bed system ( 8 ) . They confirmed the economics and process flow sheet given i n the SRI study. These s t u d i e s were made i n 1972 at a C. E. cost index of 135. For t h i s paper, the c o s t s are updated to a C. E. index of 210. The process flow sheet provided by Stanford Research I n s t i t u t e i s d i v i d e d i n t o three s e c t i o n s : f u e l p r e p a r a t i o n , p y r o l y s i s , and gas clean-up and a d e t a i l e d equipment l i s t . The totajL c a p i t a l i n v e s t ment i n 1977 d o l l a r s i s estimated to be 18.2 χ 10 as shown i n Table 1. The annual opergting c o s t s were taken as 1.5 times the costs i n 1972 or $3.0 χ 10 /year. Using these f i g u r e s , the cost of gas produced from m u n i c i p a l s o l i d waste i s estimated i n Table 2. The product gas composition developed by S.R.I, i s given i n Table 3 and the m a t e r i a l balance i n Table 4. The energy y i e l d i s defined as: Energy Value = Higher Heating Value of Gas Higher Heating Value of F u e l g y

was

77%. Chiang, Cobb and K l i n z i n g (11) have j u s t completed a study f o r Resources of the Future where they estimate the cost of f u e l gas from refuse u s i n g m u n i c i p a l waste. They based t h e i r values on the same S.R.I, study p r e v i o u s l y c i t e d ( 7 ) . These authors assumed t h a t between 1972 and 1977, the c a p i t a l costs e s c a l a t e d by a f a c t o r of 4 and the o p e r a t i n g costs doubled. Under these assump t i o n s and using economic c r i t e r i a s i m i l a r to "low debt economics" they c a l c u l a t e d t h a t the gas would cost $6.14/10 Btu w i t h no drop charge. The S.R.I, study cost estimate was made based upon s i z i n g and c o s t i n g a l l of the major equipment items. I t would seem t h a t the C. E. cost index between 1972 and 1977 (210/135 = 1.56) would be a more a p p r o p r i a t e procedure to update the c a p i t a l c o s t . I f a f a c t o r of 1.56^were used i n p l a c e of 4.00, the f u e l gas cost be comes $2.60/10 Btu which i s i n s u b s t a n t i a l agreement w i t h the cost of $2.28/10 Btu shown i n Table 2. In a more recent cost estimate by B a t t e l l e (5) the cost of gas produced i n a two f l u i d bed system i s given i n Table 5. In c o n v e r t i n g t o t a l c a p i t a l c o s t s to annualized c a p i t a l charges the r a t i o of annualized c a p i t a l costs to c a p i t a l c o s t s obtained from the c o s t s of the two bed system f o r the p y r o l y s i s of bagasse obtained by B a t t e l l e were used. The r a t i o s used were: (1) 0.167 f o r low debt economics and (2) 0.09 f o r high debt economics.


BAILIE AND RICHMOND


Table I . Estimated C a p i t a l Investment (lOOO ton/day Dry Ash Free M u n i c i p a l Waste) D o l l a r Amounts i n M i l l i o n s Feed P r e p a r a t i o n Pyrolysis Product Recovery Total Utilities General F a c i l i t i e s Total Land Start-up Working C a p i t a l Total T o t a l Working C a p i t a l

^-8 6.1 2· j+ 13-5 2.2 0*8 3.0 2

· .8 «8 1-8 18.2


30


Table I I . Annual Operating Costs and Gas Costs Low Debt* Economics Operating Costs Annualized C a p i t a l Charge Total (

$3.0xl0 2.8 T75

6

High Debt* Economics (l.l8) (l.lO) (2.28)

3-0 1.6 Ο

(l.l8) (0*63) (1.81)

) φ per 10 B t u

* These are t h e economics developed and used by B a t t e l l e i n t h e i r r e c e n t study f o r D.O.E. and g i v e n i n Appendix A.

Table I I I .

Composition o f Product Gas from Two-Reactor System ( i n Mole P e r c e n t )

CO

co

H

2

Dry, C0 -Free

27.1# 1^.7

31.TS6 0.0

kl.J

2

c%

C2 unsaturates C H6 C3 unsaturates 3 8 Total 2

C

Dry Gas

H

7.7 7.1 0.7 0.6 0Λ 100.0$

h3.9 9.0 8.3 0.9 0.7

°Λ

100.0$ 529

Gross h e a t i n g value ( B t u / s c f ) Y i e l d o f gas, s c f / l b dry r e f u s e

2

9-3

8.0



Depreciation Schedule

Investment Tax C r e d i t

0.0142 0.2355 Ο.Ο683

0.0261 0.2355 0.1052

3.0

0.2k

3.0

0.2k

O.3O O.7O Ο.Ο85 0.15 O.5O 20.0 11.0

Other

0.30 0.70 Ο.Ο85 0.15 O.5O 25.Ο 25.Ο

Steam P l a n t

Low Debt Economics

, t

Values f o r Economic Parameters

0.1k

0.0191 0.1645 O.067O

0.50 25.0 25.0 0.24 3.0

0.60 0.40 0.0875

Steam P l a n t

TT

0.0329 0.1645 0.1029

0.60 0.40 0.0875 0.l4 O.5O 20.0 11.0 0.24 3.0

Other

High Debt Economics

a

2k

12

1

0.05tL 0.0906 SL Ο.Ο889 0.0535 SL 0.1052 O.067O 0.1029 Ο.Ο683 SYD 12 0.0729 0.1047 0.1077 0.0715 0.0871 0.1224 Ο.Ο85Ο SYD 2k 0.1187 0.1046 0.0688 0.1046 0.0681 DDBSL 12 0.0829 0.1192 0.0823 DDBSL 2k 0.1173 A s t r a i g h t l i n e d e p r e c i a t i o n (SL) schedule was assumed f o r the values presented i n the upper p o r t i o n of Table A - I . I f a sum-of-the-year s d i g i t s (SYD) d e p r e c i a t i o n schedule and/or a 12 percent i n v e s t ment t a x c r e d i t had been assumed the impact on t h e "Constant f o r ( F ) b e a r i n g the symbol L" would be t a b u l a t e d as i n the lower p o r t i o n o f Table A - I . S i m i l a r l y , values a r e shown f o r computations u s i n g a double d e c l i n i n g balance w i t h a s h i f t t o s t r a i g h t l i n e ( i n t h e n/2 year) d e p r e c i a t i o n schedule DDBSL i n the lower p o r t i o n o f Table A - I . (Constants f o r (Τ-W) and (τ) a r e n o t s u b j e c t t o change.)

A

J Κ L

Constant f o r (Τ-W) Constant f o r (τ) Constant f o r ( F )

E/T

i I R Ν η Ρ Y

D/T

Symbol

Debt f r a c t i o n Equity f r a c t i o n Interest rate Return on e q u i t y Tax r a t e P r o j e c t l i f e , years D e p r e c i a t i o n l i f e , years Investment t a x c r e d i t Years f o r t a x c r e d i t

Term

Table A - I .


2

2

3

H

8

6

Note:

Total

C

2

2

H CJ% C2H C % C H 3 6 C H Liquids Ash Char

co

Feed CO

3.81* vt#

—

values.

22.32 -Wtfo

--

(0.12)

--

22.32 Wt/o 10.68 11.52

3.81* wt#

2.05 0.76 0.27 0.l6 0.11 (0.09) (0.O8) (O.32)

0

H

Parentheses i n d i c a t e estimated

30.85 vtjt

7.35

2.25 3.22 0.95 0.1*3 (0.52) (0.35) 3^5

—

3Ο.85 vtjt 8.01 1+.32

c

(0.1) (O.l) Wt/o

(ô~3)

( ο Λ ) vt/o

--

—

--

—

—

---

( O . l ) Vt/o

s

(0.1)

—

---

--

—

--

( 0 Λ ) wt/o

Ν

Table IV. Y i e l d s from P y r o l y s i s o f Refuse (Dry B a s i s - Weight Percent)

1+2.1*9 Μή$

--

—

1*2.1*9

--

—

--

—

1*2Λ9 wt#

ASH

100.00vt$

100.00vt$ I8.69 15.81* 2.05 3.01 3.^9 1.11 0.5^ 0.61 0.1*3 3.99 1*2.1*9 7.75

Total

to

2.

BAILIE AND RICHMOND

Table V.

Product Cost f o r a P l a n t of 1530 Tons/day

Raw M a t e r i a l Costs ( $ 1 . 0 0 / l 0 Operating Costs Annualized C a p i t a l Charge

($/l0

6

Btu)

Low Debt Economics

High Debt Economics

7-9 3.9 3.6

7-9 ( l . 2 ) 3.9 ( 0 . 6 ) 2.0 ( 0 . 3 )

15 Λ

Total 6

33


(l.2) (0.6) (0.6) (2Λ)

13-8

Btu)


(2.l)


34

These same r a t i o s were used throughout t h i s paper to convert t o t a l c a p i t a l cost to annualized c a p i t a l c o s t s . The b a s i s B a t t e l l e used f o r these two cases i s given i n Appendix A. The values provided by B a t t e l l e (5) were modified to r e f l e c t an energy y i e l d of 80% r a t h e r than the 62% used i n that study. Wheelabratog I n c i n e r a t i o n , Inc. (9) r e c e n t l y provided an estimate of $2.00/10 Btu f o r producing a gas from wood waste i n a p l a n t of 250 tons c a p a c i t y . In p r e p a r i n g the cost e s t i m a t e , B a t t e l l e used the gas compositions shown i n Table 6. The cost of f u e l produced i s not s e n s i t i v e to p l a n t s i z e . The cost a n a l y s i s f o r both SRI and B a t t e l l e were f o r dual t r a i n s fed 500 to 750 tons/day of s o l i d feed and there i s l i t t l e cost d i f f e r e n t i a l i n s i z e s above 500 tons/day. The cost estimates given above provide evidence that biomass can be^converted to a medium Btu gas at a cost of $2.00 to $2.50 per 10 Btu w h i l e m u n i c i p a l waste w i l l produce e g s e n t i a l l y the same q u a l i t y gas f o r about $1.75 to $2.25 per 10 Btu. These estimates assume that the feed was d e l i v e r e d to the p l a n t s i g e . The cost at the s i t e was zero f o r m u n i c i p a l waste and $1.00/10 Btu f o r biomass. For m u n i c i p a l waste there would be a drop charge. This would decrease the cost of the gas produced. For biomass, there i s a cost a s s o c i a t e d w i t h t r a n s p o r t i n g the biomass from the l o c a t i o n i t was harvested to the p l a c e where i t i s to be converted to a gas. The cost a s s o c i a t e d w i t h the t r a n s p o r t a t i o n of the b i o mass and f u e l gas are not considered i n these estimates. System A p p l i c a t i o n s In t h i s s e c t i o n s e v e r a l a p p l i c a t i o n s u s i n g intermediate energy gas made from biomass are described and some economics developed. Application 1 The Department of Energy i s supporting a study on the f u e l i n g of a 50 Mw e l e c t r i c p l a n t w i t h wood. The most s t r a i g h t forward approach i s to burn the f u e l i n a power p l a n t . An a l t e r n a t i v e to t h i s approach i s to produce a gas (to be c a l l e d wood-gas) and f i r e t h i s gas i n a gas f i r e d power p l a n t . There are s e v e r a l advantages to t h i s approach. These i n c l u d e : a)

Lower power p l a n t c o s t s - A gas f i r e d power p l a n t costs about one h a l f as much as a s o l i d f u e l e d plant.

b)

Higher combustion e f f i c i e n c y - A gas f i r e d system uses l e s s excess a i r and combustion i s more complete than i n a wood f i r e d system.

c)

E n v i r o m e n t a l l y a t t r a c t i v e - A gas f i r e d p l a n t needs no s t a c k clean-up to meet environmental standards.


BAILIE AND RICHMOND

Table V I .


Estimated Composition o f Output Gas — Process from P y r o l y s i s o f Bagasse (5)

Bailie

Mole Percent Dry B a s i s Bagasse co co Ho C% C hydrocarbons C3 hydrocarbons H2O ( i f wet) Net Heating Value 2

2

23.29 23.01* 35.38 8.53 8.66 1.10 (25.56) lk.96 MJ per scm (1*01 B t u per s c f ) (dry)



36 d)

Lower maintenance - A gas f i r e d p l a n t has much l e s s maintenance than a s o l i d f u e l e d p l a n t .

The disadvantages i n c l u d e the cost of the p l a n t needed to generate the f u e l gas and the l o s s of heating value r e s u l t i n g from the a d d i t i o n a l processing. In comparing the d i r e c t wood f i r e d system to the wood-fuel g a s - e l e c t r i c p l a n t , the f o l l o w i n g assumptions were made: 1.

C a p i t a l cost and operating cost of a wood f i r e d e l e c t r i c generating p l a n t i s twice that of a n a t u r a l gas f i r e d system.

2.

To produce 1 Kw-hr o f e l e c t r i c i t y from wood r e q u i r e s 12,750 B t u and from n a t u r a l gas i s 11,000 Btu. This i s f o r a 55 Mw system.

3.

F u e l gas can s u b s t i t u t e d i r e c t l y f o r n a t u r a l gas.

A study by M i t r e (9) estimated the c a p i t a l cost of a 55 Mw b o i l e r f i r i n g wood i s $55 χ 10^ and the operating cost i s $3.6 χ 10 /year. The previous s e c t i o n provided estimates of f u e l costs from wood t o be 2.1 χ 1 0 Btu and 2.4 χ χ 1 0 Btu f o r low debt and high debt economics. Using these values and the assumptions given above, i t i s p o s s i b l e to compare d i r e c t wood f i r e d systems to woodgas f i r e d systems. The r e s u l t s are summarized i n Table 7. The r e s u l t s shown i n Table 7 i n d i c a t e : 6

6

a)

The cost of e l e c t r i c i t y from d i r e c t wood f i r i n g are equal t o or more expensive than wood gas f i r i n g systems.

b)

The cost i s s t r o n g l y a f f e c t e d by the method of financing.

c)

For low debt f i n a n c i n g e l e c t r i c i t y from wood gas i s about 20% l e s s than d i r e c t wood f i r i n g . For high debt f i n a n c i n g the cost i s comparable.

F i g u r e 7 shows the e f f e c t of the raw m a t e r i a l costs ( b a s i c wood cost) on the cost of e l e c t r i c i t y . The d i f f e r e n t i a l between the two a l t e r n a t i v e s remains constant w h i l e the percentage d i f f e r ence decreases w i t h f u e l c o s t . Application 2 I t was suggested e a r l i e r that the conversion of wood to a f u e l gas would be p a r t i c u l a r l y important i f there was an e x i s t i n g f a c i l i t y that would be shut down i f n a t u r a l gas was c u r t a i l e d . The i n d u s t r y would not only pay the cost of a new wood burning


2.

BAILIE AND RICHMOND

Table V I I .


37

Comparison o f E l e c t r i c Costs f o r Wood-Electric and Wood-Gas-Electric Systems

6

F u e l Costs (Wood @ $ l / l 0 ) Operating Costs ($106/yr) Annualized C a p i t a l Costs Mlll/Kw-hr

Wood-- E l e c t r i c

Wood-• G a s - E l e c t r i c

High Debt

High Debt

k.l 3-6 k.Q 12.5 m

Low Debt

k.l 3-6 8.5 1ÏÏT2 (58)

8Λ 1.8 2.k 1275" (ko)

Low Debt

8.k 1.8 k.2 1O (k6)


SOLED WASTES AND RESIDUES

38

f a c i l i t y , but would be f o r c e d to pay the annualized c a p i t a l cost f o r the i d l e n a t u r a l gas p l a n t . Figure 8 shows the e l e c t r i c c o s t s f o r a new wood f i r e d p l a n t and f o r wood-gas used i n an e x i s t i n g n a t u r a l gas p l a n t as a f u n c t i o n of wood f u e l c o s t . The only d i f f e r e n c e i n t h i s f i g u r e and that shown i n F i g u r e 7 i s the annuali z e d c a p i t a l cost f o r the i d l e gas p l a n t i s added to the cost of a new wood burning p l a n t . For e i t h e r f i n a n c i n g scheme, the wood gas p l a n t provides e l e c t r i c i t y a t a s i g n i f i c a n t l y lower cost than the d i r e c t f i r e d ^ s y s t e m . For the case where the b a s i c wood f u e l c o s t s are $1.00/10 B t u , the d i f f e r e n t i a l s are 15.6 and 35.7%, r e s p e c t ively. Application 3 The economies of s c a l e are s i g n i f i c a n t i n u t i l i t y power s t a t i o n s . The M i t r e report (10) provides cost estimates f o r p l a n t s using 850, 1700 and 3400 tons of wood per day. These values were converted to annualized c a p i t a l costs i n the same manner as p r e v i o u s l y d e s c r i b e d . I n comparing c o s t s i t was assumed that the cost of the wood to gas conversion f a c i l i t y d i d not b e n e f i t from economies of s c a l e . This i s not true f o r other types of convers i o n f a c i l i t i e s . For example, the Union Carbide Process b e n e f i t s g r e a t l y from an i n c r e a s e i n s c a l e . This i s because the economies r e s u l t i n g from the l a r g e r oxygen p l a n t needed i n t h i s process. There are some s m a l l economies of s c a l e that would lower the curves f o r the wood gas systems a t l a r g e r c a p a c i t y . The curves i n F i g u r e 9 r e f l e c t the i n c r e a s e i n t r a s n p o r t a t i o n c o s t s f o r l a r g e r p l a n t s . In e v a l u a t i n g the t r a n s p o r t a t i o n costs the f o l l o w i n g assumptions were made: 1.

Cost of t r a n s p o r t a t i o n i s $0.10 per t o n m i l e .

2.

The average d i s t a n c e t r a v e l e d f o r v a r i o u s s i z e p l a n t s were: 850 tons/day 1700 tons/day 3400 tons/day

35 m i l e s 46.7 m i l e s 66 m i l e s

In F i g u r e 9 the cost of e l e c t r i c i t y i n d i r e c t f i r e d p l a n t s are seen t o cross the wood-gas f i r e d curves f o r h i g h c a p a c i t y . This i s a d i r e c t r e s u l t of not b e n e f i t i n g from economies of s c a l e for the wood-gas generators. Since there i s no cost advantage i n l a r g e r gas generating f a c i l i t i e s , i t would be more a t t r a c t i v e to l o c a t e the p l a n t s c l o s e r t o the wood source and p i p e l i n e the gas to a l a r g e c e n t r a l gas f i r e d u t i l i t y . This would reduce the d i s tance the wood i s hauled and the cost a s s o c i a t e d w i t h moving the wood t o a c e n t r a l p l a n t . This would reduce the cost below those shown i n F i g u r e 9 f o r the gas f i r e d systems. I n Figure 9 the wood-gas curves do not r e f l e c t e i t h e r the s m a l l but r e a l economies


BAILIE

A N D RICHMOND


Figure 7. Electric cost comparison between woodfiredand wood gasfired:( ) woodfired;( ) wood/gas fired

Debt Economics

Economics

$1.00

$3.00

$2.00 6

Basic Cost of Wood $ / 1 0 Btu

Figure 8. Cost comparison of electricity betweenfiringwood gas in existing plants and building new directfiredplants: ( ) new woodfiredphnts; ( ) existing plantfiredwith wood gas


SOLED

40

Figure 9.

WASTES

AND

Economies of scale


RESIDUES

2.

BAILIE

A N D RICHMOND


41

of s c a l e o r the lower t r a n s p o r t a t i o n c o s t s . The s i t u a t i o n f o r wood gas would be b e t t e r than that shown i n F i g u r e 9. Application 4 The f i n a l h y p o t h e t i c a l s i t u a t i o n considers the use of m u n i c i p a l waste t o provide a f u e l gas t o a l a r g e m a l l , group of commerc i a l establishments o r i n d u s t r i a l park. Table 2 provided e s t i mates f o r the cost of f u e l gas from m u n i c i p a l waste. I n t h i s t a b l e no charge was made f o r the f u e l . For the case of m u n i c i p a l waste, a drop charge i s imposed i n order t o leave the waste a t the f a c i l i t y . E i g h t d o l l a r s per ton i s considered t o be a reasonable charge. I f four d o l l a r s of t h i s could be assigned t o s u b s i d i z e the wasteto-gas process, a c r e d i t of $0.79 per 10^ Btu i s r e a l i z e d . This reduces the gas cost to $1.06 t o $1.53 per m i l l i o n Btu. A t t h i s p r i c e i t becomes a h i g h l y c o m p e t i t i v e f u e l . This f u e l gas can be transported by p i p e l i n e t o the user to burn i n commercial gasf i r e d equipment. This becomes important because the comparative c a p i t a l cost between gas f i r e d equipment t o s o l i d f i r e d equipment i s o f t e n as low as 1/6 f o r s m a l l commercial u n i t s . Conclusions 1.

Biomass and m u n i c i p a l waste can be converted t o an intermediate energy gas.

2.

The gas produced i n the twin f l u i d i z e d bed can s u b s t i t u t e f o r n a t u r a l gas i n e x i s t i n g equipment.

3.

The energy l o s t i n the biomass t o gas conversion system i s l a r g e l y made up i n higher combustion e f f i c i e n c y i n the power p l a n t .

4.

The cost of the wood-gas i s i n the p r i c e range of $2.00 t o $3.00 per 1 0 B t u . 6

5.

The economic choice between d i r e c t f i r e d o r wood gas f i r e d i s h i g h l y dependent on the method of f i n a n c i n g . I f there i s an advantage, i t would appear t o be w i t h wood-gas.

6.

Wood gas systems producing intermediate gas have not seen commercial o p e r a t i o n and has no t r a c k r e c o r d . D i r e c t f i r e d systems are o p e r a t i n g commercially but have a s p o t t y r e c o r d .

7.

When o p e r a t i n g n a t u r a l gas f i r e d u n i t must be r e p l a c e d by a wood f i r e d u n i t , i t becomes more a t t r a c t i v e t o convert wood t o gas and use the existing f a c i l i t y .


42

SOLID

WASTES

AND

RESIDUES

8.

For power generating systems, economies of s c a l e are s i g n i f i c a n t f o r d i r e c t f i r e d systems. The wood gas to e l e c t r i c system i s l e s s s e n s i t i v e to s c a l e because the wood gas generating system i s i n s e n s i t i v e t o s c a l e . M u l t i p l e u n i t s are b u i l t f o r l a r g e s i z e a p p l i c a t i o n s . For the Union Carbide Purox system economies of s c a l e are achieved and t h i s c o n c l u s i o n would not apply i f t h i s u n i t were s e l e c t e d to produce wood-gas.

9.

M u n i c i p a l waste can produce a f u e l gas a t a lower cost because there i s no charge f o r the feed and the system w i l l r e c e i v e a subsidy through a drop charge.

The paper has emphasized wood which was s e l e c t e d to represent biomass. Other biomass sources may a l s o be used. The f l u i d i z e d bed system w i l l more r e a d i l y accept other biomass m a t e r i a l s w i t h d i f f e r i n g p h y s i c a l c h a r a c t e r i s t i c s than the Purox system or d i r e c t f i r e d b o i l e r s . I f i t i s not p o s s i b l e to provide assurances of the economic advantages that may be obtained from wood gas there i s l i t t l e doubt that the economics of today show t h i s o p t i o n i n a more f a v o r a b l e l i g h t than the economics of a few years ago. The longest c o a l s t r i k e i n h i s t o r y i s underway. I t shows how dependent the n a t i o n i s on c o a l . The cost of c o a l w i l l without q u e s t i o n r i s e s i g n i f i c a n t l y under any new c o n t r a c t . This w i l l see a f u r t h e r s h i f t toward f a v o r a b l e economics f o r biomass u t i l i z a t i o n


2.

BAILIE AND RICHMOND


43

REFERENCES 1Study for the United States Department of Energy, prepared by Wheelabrator Clean Fuels Corporation. 2E.P.R.I., "Fuels from Municipal Refuse for Utilities: Tech n i c a l Assessment." E.P.R.I. Report 261-1, March 1975 (Prepared by Bechtel Corporation). 3Fisher, T. F., Kasbohn M. L. and J . R. Riverο, "The Purox System," presented at the 80th National Meeting of the American Institute of Chemical Engineers, September 9, 1975. 4Hasegawa, Μ., Fukuda, J. and D. Kunii, "Research and Develop ment of Circulating System Between Fluidized Beds for Application of Gas-Solid Reactions," Second P a c i f i c Chemical Engineering Congress, Denver, August 18 - 31, 1977. 5

B a t t e l l e Columbus, "Fuels from Sugar Crops," BMI Report 1957A, Volume 1 through 5, March, 1977. 6Douglas, Ε., M. Webb and E. Daborn, "The Pyrolysis of Waste and Product Assessment," paper presented at Symposium on Treatment and Recycling of Solid Wastes, Manchester, England, January, ]974. (Available through Warren Spring Laboratory, Department of Industry.) 7

A l b e r t , S. B., et. al., "Pyrolysis of Solid Waste: A Techni c a l and Economic Assessment," P.B. 218-231, September, 1972. 8Bechtel Corporation, "West V i r g i n i a Recycle Resource Recov ery Center," Technical and Economic Review for City of Charleston, July 15, 1972. 9 B a i l i e , R. C. and C. A. Richmond, "New Technology and Pyroly s i s of Wood and Wood Waste." paper presented at the 1978 Regional Tappi Conference i n Portland, Oregon. 10Mitre Corporation, "Siloculture Biomass Farm," Mitre Techni c a l Report Number 7347, Volume 1 through 5, May 1977. 11Chiang, S. H., J . T. Cobb and G. E. Klinzing, "A Critical Analysis of the Technology and Economics for the Production of Liquid and Gaseous Fuels from Wastes," paper presented at the 85th National Meeting of the American Institute of Chemical Engineers, Atlanta, Georgia, February 27, through March 2, 1978. APRIL 7,

1978.


Economics Associated with Waste or Biomass Pyrolysis Systems

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