An Analysis of Gasohol Energetics - American Chemical Society

20 An Analysis of Gasohol Energetics

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WILLIAM A . SCHELLER Department of Chemical Engineering, University of Nebraska, Lincoln, NB 68588

The question of energy utilization and energy efficiency in the gasohol program has generated much discussion and considerable controversy. The purpose of this paper is to present a detailed energy balance associated with the components of the gasohol program, i.e., grain production, fuel alcohol production and the replacement of gasoline with ethanol to produce gasohol. The overall energy balance involves a comparison of a gasohol fuel economy with a gasoline fuel economy including the energy impact of the distillers dried grain which becomes available to the livestock feeding industry. ENERGY FOR CORN PRODUCTION Energy requirements for the production of agricultural products vary considerably from country to country. In less developed areas, the energy expended per unit of production is usually considerably lower than in highly developed areas of the world. On the other hand, the product production per unit of land is usually related to the energy expenditure and in those areas where less energy is expended, less product yield is obtained. Table I compares the energy consumption and product production in Mexico with hand labor and with oxen power with that for a modern U.S. farm. The corn production with hand labor is very energy efficient requiring only 35,000 Btu's per bushel, but the grain yield is only 31 bushels per acre. When the farmer adds an ox to assist in the corn production, not only does the energy expended per bushel of grain increase, but the net grain yield per acre is cut

0097-6156/81/0144-0419$05.75/0 © 1981 American Chemical Society

Klass; Biomass as a Nonfossil Fuel Source ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

420

BIOMASS AS A NONFOSSIL F U E L SOURCE

a l m o s t in half because of t h e need to feed t h e ox. On a m o d e r n U.S. f a r m , t h e e n e r g y e x p e n d i t u r e per bushel of c o r n is a b o u t 3.5 t i m e s t h a t for c o r n p r o d u c t i o n w i t h h a n d labor in M e x i c o . H o w e v e r , t h e y i e l d of c o r n per acre is increased by a f a c t o r of 2.8. If large q u a n t i t i e s of g r a i n are t o be p r o d u c e d , it is i m p o r t a n t t h a t t h e p r o d u c t i o n per u n i t of land be m a x i m i z e d . T a b l e I. C O M P A R I S O N O F E N E R G Y R E Q U I R E M E N T S FOR C O R N P R O D U C T I O N * b

Mexico Hand Oxen Labor Power 1000Btu/Acre Bushels/Acre Btu/Bushel a

b

U.S.A. Modern Farm

1084

1572

10,510

31 35,000

15 104,800

86 122.200

Excludes e n e r g y for m a n u f a c t u r e of f a r m m a c h i n e r y . Data f r o m Reference 1.

Table II s h o w s t h e e v o l u t i o n of e n e r g y r e q u i r e m e n t s for t h e p r o d u c t i o n of c o r n in t h e U n i t e d States b e t w e e n 1 9 5 0 a n d 1 9 7 5 . T o t a l e n e r g y c o n s u m p t i o n per acre i n c l u d i n g t h e e n e r g y for f u e l , fertilizer, pesticides, herbicides, m a n p o w e r , etc., b u t not i n c l u d i n g energy for the m a n u f a c t u r e of t h e f a r m m a c h i n e r y , increased f r o m 3.8 m i l l i o n Btu's per acre in 1 9 7 5 t o 10.51 m i l l i o n Btu's per acre in 1 9 7 5 (a f a c t o r of 2.8). T h e y i e l d per acre in t u r n increased f r o m 3 8 bushels per acre t o 8 6 bushels per acre or a f a c t o r of a b o u t 2.3. D u r i n g t h i s same p e r i o d , t h e e n e r g y c o n s u m e d per bushel of c o r n increased o n l y 22.2%. In all cases, t h e e n e r g y c o n s u m p t i o n expressed as e q u i v a l e n t gallons of oil c o n s u m e d per bushel of c o r n w a s less t h a n 1. T a b l e I I . E N E R G Y R E Q U I R E M E N T S FOR C O R N P R O D U C T I O N IN THE U.S.A.' b

1000 Btu/Acre Bushels/Acre Btu/Bushel Gal E q u i v a l e n t O i l / Bushel a

b

1960

1969

1970

1975

3800 38 100,000

6030 54 111.600

9760 81 120.500

10.510 86 122.200

0.67

0.74

0.80

0.81

Excludes e n e r g y for t h e m a n u f a c t u r e of f a r m m a c h i n e r y , 1 gal of e q u i v a l e n t oil equals 1 5 0 , 0 0 0 Btu. Data f r o m References 1 a n d 2.


20.

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Gasohol Energetics

W h i l e detailed f u e l , fertilizer, a n d c h e m i c a l c o n s u m p t i o n s are n o t y e t available f o r 1 9 7 9 , these w i l l p r o b a b l y be s o m e w h a t higher t h a n t h e 1 9 7 5 figures. O n t h e o t h e r h a n d , it is e s t i m a t e d t h a t t h e average yield of c o r n in 1 9 7 9 w i l l exceed 1 0 0 bushels per acre. Because t h e figures in Table II are average f i g u r e s f o r t h e n a t i o n , t h e y i n c l u d e t h e e n e r g y r e q u i r e m e n t s f o r a n average a m o u n t of irrigation. U n i r r i g a t e d c o r n w i l l require less e n e r g y per acre f o r p r o d u c t i o n w h i l e c o r n p r o d u c e d in arid areas w i l l require m o r e e n e r g y per unit of land area. For purposes of t h e energy c o m p a r i s o n s c o n t a i n e d in this paper, t h e e n e r g y f i g u r e f o r 1 9 7 5 w a s used. E N E R G Y R E Q U I R E M E N T S FOR F U E L A L C O H O L P R O D U C T I O N W h e n corn is f e r m e n t e d t o p r o d u c e a l c o h o l , a n u m b e r of p r o d u c t s are p r o d u c e d . The most desirable p r o d u c t is p r o b a b l y t h e grain a l c o h o l (ethanol). However, small a m o u n t s of heavier alcohols k n o w n c o l l e c t i v e l y as fusel oil are also p r o d u c e d in t h e f e r m e n t a t i o n . In t h e beverage i n d u s t r y , t h e fusel oil is c o n s i d e r e d t o be undesirable a n d a large a m o u n t of energy is e x p e n d e d in r e m o v i n g it f r o m t h e g r a i n a l c o h o l . W h e n o n e is m a n u f a c t u r i n g a fuel grade a l c o h o l f o r use in g a s o h o l , t h e fusel oil is a desirable c o m p o n e n t a n d s h o u l d r e m a i n m i x e d w i t h t h e g r a i n alcohol rather t h a n b e i n g r e m o v e d . Fusel oil p r o d u c t i o n is a b o u t 0.5% of t h e e t h a n o l . Table III c o n t a i n s a material balance s h o w i n g t h e c o m p o s i t i o n of t h e c o r n used f o r t h e c a l c u l a t i o n s a n d t h e p r o d u c t s p r o d u c e d . In a d d i t i o n t o fuel a l c o h o l , a h i g h - p r o t e i n c a t t l e feed called distillers dark g r a i n (DDG) is also p r o d u c e d in t h e f e r m e n t a t i o n process. A s w i l l be seen later, i n c l u s i o n of DDG in t h e c a t t l e ration p r o v i d e s m o r e w e i g h t gain t h a n if t h e c a t t l e had been f e d t h e original c o r n w h i c h w a s used t o p r o d u c e t h e fuel alcohol a n d DDG. Carbon d i o x i d e is a s e c o n d b y p r o d u c t p r o d u c e d in t h e f e r m e n t a t i o n , b u t f o r purposes of this analysis, it has been a s s u m e d t o be v e n t e d t o t h e atmosphere. Table III. M A T E R I A L B A L A N C E PRODUCTION OF FUEL A L C O H O L Corn C o m p o n e n t

Ib/bu

Starch

34.07

Protein Other Moisture

4.73 8.52 8.68

Total

56.00

Product, unit/bu Fuel A l c o h o l , 2 . 6 1 3 3 g a l DDG (10% H 0 ) , 18.0161b Carbon Dioxide, 16.8861b A l c o h o l Losses, 0.0531 g a l R e m a i n i n g H 0 , 3 . 4 4 9 2 lb 2

2


422


T h e recovery of a l c o h o l by d i s t i l l a t i o n is very efficient w i t h a t y p i c a l t o t a l loss of a l c o h o l b e t w e e n t h e f e r m e n t o r and t h e a n h y d r o u s p r o d u c t of o n l y 2%. It is also i n t e r e s t i n g t o n o t e t h a t there is s u f f i c i e n t m o i s t u r e c o n t a i n e d in t h e g r a i n t o s u p p l y t h e c h e m i c a l needs for c o n v e r s i o n of s t a r c h t o a l c o h o l a n d t o a c c o u n t for t h e 1 0 % m o i s t u r e c o n t e n t in t h e distillers grains. A l l a d d i t i o n a l w a t e r a d d e d t o t h e s y s t e m is s i m p l y t o s u p p l y a p p r o p r i a t e c o n c e n t r a t i o n s a n d s t r e a m s of a p p r o p r i a t e f l u i d i t y . In t h e last f e w years, t h e r e has been a d r a m a t i c r e d u c t i o n in t h e energy r e q u i r e m e n t s for grain a l c o h o l p r o d u c t i o n m a i n l y t h r o u g h m o r e e f f i c i e n t heat recovery in t h e plant. T a b l e IV c o m p a r e s t h e e n e r g y c o n s u m p t i o n in a beverage a l c o h o l p l a n t o f 1 9 7 3 w i t h fuel a l c o h o l p l a n t s d e s i g n e d in early 1 9 7 8 a n d late 1 9 7 9 . T h e beverage a l c o h o l p l a n t c o n s u m e d a b o u t 1 7 2 , 0 0 0 Btu's per g a l l o n of a l c o h o l p r o d u c e d . By early 1 9 7 8 , w i t h t h e realization t h a t there w a s n o need t o p r o d u c e a h i g h l y p u r i f i e d n e u t r a l spirits for f u e l alcohol a n d w i t h t h e i n t r o d u c t i o n of m o d e s t heat recovery facilities, t h e e n e r g y r e q u i r e m e n t s d r o p p e d t o 1 2 5 , 0 0 0 Btu's per g a l l o n . In a late 1 9 7 9 p l a n t d e s i g n w h i c h i n c l u d e d use o f f u r n a c e stack gases t o d r y t h e distillers g r a i n a n d d e v e l o p m e n t of a pressure profile in t h e p l a n t t o increase p o t e n t i a l heat recovery, t h e e n e r g y r e q u i r e m e n t d r o p p e d t o 6 9 , 6 0 0 Btu's per g a l l o n of a l c o h o l p r o d u c e d . T h e h i g h heat of c o m b u s t i o n of one g a l l o n of a n h y d r o u s fuel grade a l c o h o l is a b o u t 8 4 , 2 0 0 Btu's. T a b l e IV. E V O L U T I O N O F G R A I N A L C O H O L P L A N T ENERGY REQUIREMENTS

1 9 0 ° Proof Spirits Anhydrous Alcohol Subtotal DDG P r o d u c t i o n Total Gal Equivalent O i l / Gal A l e .

Beverage Plant

Early 1 9 7 8 Fuel Plant

Late 1 9 7 9 Fuel Plant

109.000 None 109.000 63.000 172.000

68.000 14.000 82.000 43.000 125.000

52.900 Included 52.900 16.700 69.600

1.15

0.82

0.46

T h e e n e r g y c o n s u m p t i o n s in Table IV i n c l u d e t h e fossil fuel c o n s u m p t i o n associated w i t h t h e g e n e r a t i o n of the electrical needs for the a l c o h o l plant as w e l l as t h e fossil fuel b u r n e d in g e n e r a t i n g s t e a m for t h e plant. For t h e overall g a s o h o l energy analysis, t h e late 1 9 7 9 fuel a l c o h o l p l a n t energy c o n s u m p t i o n is u s e d .


20.

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BASIS

423

Gasohol Energetics

FOR ENERGY C O M P A R I S O N

OF GASOLINE

A N D GASOHOL

FUEL S Y S T E M S In m a k i n g a c o n s i s t e n t a n d valid c o m p a r i s o n of the energy c o n s u m p t i o n in a gasohol fuel s y s t e m a n d in a gasoline fuel s y s t e m , there are a n u m b e r of factors t h a t m u s t be c o n s i d e r e d . These factors i n c l u d e a n y difference in fuel c o n s u m p t i o n (miles p e r gallon) b e t w e e n t h e t w o s y s t e m s , a n y d i f f e r e n c e in fuel o c t a n e n u m b e r b e t w e e n t h e t w o systems, a n y c h a n g e in fuel v o l u m e b e t w e e n t h e t w o s y s t e m s w h i c h m a y result f r o m b l e n d i n g of t h e fuel c o m p o n e n t s , and a n y c h a n g e in c o r n r e q u i r e m e n t s t h a t w o u l d be necessary to m a i n t a i n equal q u a n t i t i e s o f beef p r o d u c t i o n in b o t h systems. Research has been c o n d u c t e d t o p r o v i d e i n f o r m a t i o n a b o u t each of these factors. In Nebraska, a t w o m i l l i o n mile road test p r o g r a m w a s c o n d u c t e d over a 3 4 - m o n t h p e r i o d in w h i c h t h e fuel e c o n o m y of u n l e a d e d gasoline w a s c o m p a r e d w i t h t h e fuel e c o n o m y o f gasohol. Data f r o m this test indicate t h e g a s o h o l - f u e l e d cars o b t a i n e d o n t h e average 6.7% more miles per gallon t h a n the cars fueled o n u n l e a d e d gasoline. For purposes of t h e e n e r g y c o m p a r i s o n in this paper, it has been a s s u m e d t h a t t h e gasohol cars w o u l d o b t a i n o n l y 3 % more miles per g a l l o n . M e a s u r e m e n t s b y i n d e p e n d e n t laboratories have s h o w n t h a t w h e n a m i x t u r e is p r e p a r e d c o n t a i n i n g 1 0 % a n h y d r o u s e t h a n o l a n d 9 0 % u n l e a d e d gasoline, t h e average o c t a n e , [(R + M ) / 2 ] , is three n u m b e r s higher f o r gasohol t h a n f o r t h e u n l e a d e d gasoline used as t h e base stock. In t h i s paper, a three o c t a n e n u m b e r increase is used in t h e energy c o m p a r i s o n . In b l e n d i n g 1 0 % a n h y d r o u s e t h a n o l w i t h 9 0 % u n l e a d e d gasoline, laboratory m e a s u r e m e n t s have s h o w n t h a t t h e total v o l u m e of t h e m i x t u r e is 0.23% greater t h a n t h e s u m of t h e v o l u m e o f t h e c o m p o n e n t s . For this paper, t h i s excess v o l u m e of m i x i n g has been a s s u m e d t o be zero. Finally, f e e d i n g trials i n v o l v i n g distillers dark grain have s h o w n t h a t beef c a t t l e r e c e i v i n g this c o m p o n e n t in their diet s h o w increased w e i g h t gain over cattle n o t receiving t h i s material. Tests carried o u t in K e n t u c k y indicate t h a t beef c a t t l e receiving distillers dark grains f r o m t h e f e r m e n t a t i o n of 2 0 % of t h e corn fed t o the a n i m a l s g a i n e d 12.9% more w e i g h t t h a n those c a t t l e receiving t h e t o t a l ration of c o r n . Tests c o n d u c t e d in Nebraska s u p p o r t t h e c o n c l u s i o n t h a t distillers dried grains are a better feed c o m p o n e n t t h a n t h e w h o l e c o r n f r o m w h i c h t h e y are p r o d u c e d . For purposes of this paper, it has been a s s u m e d t h a t t h e increased w e i g h t gain associated w i t h f e e d i n g distillers dark g r a i n s is 6 % rather t h a n t h e 12.9% r e p o r t e d f r o m K e n t u c k y . The results of e x p e r i m e n t a l o b s e r v a t i o n s a n d t h e e v a l u a t i o n basis used in this paper are c o n t a i n e d in Table V.


424

BIOMASS AS A N O N F O S S I L F U E L

SOURCE

T a b l e V. C O M P A R I S O N OF E X P E R I M E N T A L G A S O H O L D A T A W I T H ENERGY E V A L U A T I O N B A S I S

Increased M P G . % Excess V o l u m e of M i x , % Increased O c t a n e , (R + M ) / 2 Increased Beef W e i g h t Gain W i t h DDG. %

Experimental Observation

Evaluation Basis

6.7 0.23

3.0 0

3

3

12.9

6

CRUDE OIL S A V I N G S A S S O C I A T E D W I T H G A S O H O L B L E N D I N G W h e n o n e g a l l o n of a n h y d r o u s grain a l c o h o l is b l e n d e d w i t h 9 gallons of gasoline t o p r o d u c e 10 g a l l o n s of g a s o h o l . there w i l l be a r e d u c t i o n in c r u d e oil r e q u i r e m e n t s for t h e m a n u f a c t u r e of a u t o m o t i v e f u e l . T h e m o s t o b v i o u s reason for t h i s is t h a t g r a i n a l c o h o l has replaced gasoline in t h e m i x t u r e . O t h e r factors also affect t h e a m o u n t of c r u d e oil u s e d i n c l u d i n g t h e f a c t t h a t t h e 9 gallons of u n l e a d e d gasoline can be p r o d u c e d at a l o w e r o c t a n e n u m b e r because t h e a d d i t i o n of g r a i n alcohol w i l l raise t h e o c t a n e n u m b e r of t h e b l e n d t o meet t h e market s p e c i f i c a t i o n . F u r t h e r m o r e , because a car w i l l travel f u r t h e r o n one g a l l o n of g a s o h o l t h a n it w i l l o n o n e g a l l o n of gasoline a n d since t h e a u t o m o t i v e fuel m a r k e t is a d e m a n d t o d r i v e a t o t a l n u m b e r of miles, less g a s o l i n e w i l l be n e e d e d t o m e e t t h i s d e m a n d . T h e q u a n t i t a t i v e effect o f t h e s e factors expressed as c r u d e oil savings is s h o w n in Table V I . By r e p l a c i n g one g a l l o n of gasoline o u t of t e n w i t h one g a l l o n of e t h a n o l , w e save n o t o n l y one g a l l o n of c r u d e oil b u t also a s l i g h t a m o u n t m o r e because e n e r g y is not required t o refine t h a t g a l l o n of c r u d e oil. T h i s s a v i n g by r e p l a c e m e n t a m o u n t s t o 1.014 gal of c r u d e oil per g a l l o n of g r a i n a l c o h o l . The r e q u i r e m e n t s of a l o w e r o c t a n e n u m b e r for the 9 gallons of u n l e a d e d gasoline w i l l save 0.286 gal of c r u d e oil per g a l l o n of grain a l c o h o l , a n d o b t a i n i n g 3 % m o r e miles per g a l l o n w i t h gasohol w i l l save 0.300 gallons of c r u d e oil per g a l l o n of g r a i n a l c o h o l for a t o t a l c r u d e oil s a v i n g of 1.6 gallons. I n f o r m a t i o n related t o these c r u d e oil savings w a s o b t a i n e d f r o m refinery s i m u l a t i o n studies c a r r i e d o u t by Bonner a n d M o o r e A s s o c i a t e s , Inc. of H o u s t o n , Texas for t h e U.S. D e p a r t m e n t of Energy.


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Table V I . CRUDE OIL SAVINGS ASSOCIATED W I T H GASOHOL PRODUCTION Gal/Gal Alcohol 1.014

R e p l a c e m e n t of Gasoline W i t h Ethanol L o w e r A v e r a g e O c t a n e N u m b e r of Gasoline 3 % M o r e M i l e s / G a l l o n w i t h Gasohol

0.286 0.300 1.600

Crude Oil Savings GRAIN

SAVINGS

ASSOCIATED

WITH

FEEDING

DISTILLERS

DARK

GRAINS Feeding trials at t h e U n i v e r s i t y of K e n t u c k y have d e m o n s t r a t e d t h a t i n c l u s i o n of distillers dark g r a i n in a c a t t l e ration results in increased w e i g h t gain. Specifically, their results indicate an increased gain of 12.9%. A s m e n t i o n e d previously, it is a s s u m e d f o r p u r p o s e s o f t h i s s t u d y t h a t t h e increased w e i g h t g a i n w o u l d be o n l y 6%. F u r t h e r m o r e , beef p r o d u c t i o n is geared to m e e t i n g a m a r k e t d e m a n d f o r a certain n u m b e r of t o t a l p o u n d s . This m e a n s t h a t w i t h t h e i n c l u s i o n o f DDG in t h e a n i m a l r a t i o n , f e w e r total bushels of c o r n are required t o b r i n g t h e c a t t l e t o full w e i g h t . This c o m p a r i s o n is illustrated in Figure 1. W h e n 2.03 b u of c o r n are f e d w i t h an a p p r o p r i a t e a m o u n t of r o u g h a g e (hay), t h e beef c a t t l e s h o w a w e i g h t g a i n of 9.63 lb. O n t h e o t h e r h a n d , if 2 0 % of 1.91 b u of c o r n (0.38 bu) are d i v e r t e d t o a g r a i n alcohol plant, one g a l l o n of g r a i n alcohol is p r o d u c e d . If t h e b y p r o d u c t DDG f r o m t h e a l c o h o l plant is c o m b i n e d w i t h t h e r e m a i n i n g 1.53 b u of c o r n a n d f e d w i t h t h e s a m e a m o u n t of hay t o t h e beef cattle, t h e y w i l l also g a i n 9.63 lb b u t w i t h a reduced c o n s u m p t i o n 0.12 b u of c o r n . T h i s saving of c o r n also represents a s a v i n g of energy. COMPARISON

OF ENERGY

REQUIREMENTS

FOR G A S O L I N E A N D

GASOHOL T h e e n e r g y r e q u i r e m e n t s f o r t h e p r o d u c t i o n of gasoline a n d gasohol w i t h p r o d u c t i o n of a n e q u i v a l e n t a m o u n t of beef in each case are p r e s e n t e d as gallons of e q u i v a l e n t oil in Table VII. T h e basis f o r this c o m p a r i s o n is also i n c l u d e d in Table VII. One g a l l o n of f e r m e n t a t i o n fuel e t h a n o l is a s s u m e d t o be m i x e d w i t h 9 g a l l o n s of u n l e a d e d gasoline in t h e gasohol case, a n d f o r t h e gasoline case, a s u f f i c i e n t a m o u n t of u n l e a d e d gasoline is a s s u m e d t o m o v e t h e c a r t h e s a m e d i s t a n c e as in t h e gasohol case. A l l o t h e r p e t r o l e u m p r o d u c t s p r o d u c e d in t h e refinery are t h e same in b o t h cases. The q u a n t i t y of c o r n in t h e t w o cases is as d i s c u s s e d in t h e p r e c e d i n g s e c t i o n a n d is s u f f i c i e n t t o p r o d u c e 9.63 lb o f beef w e i g h t g a i n . The energy r e q u i r e m e n t f o r p r o d u c i n g this c o r n is presented in Table II f o r 1975.



426

2.03 Bu Corn

Hay

1.91 Bu Com

0.38 Bu 1.53

Alcohol Plant

Bu DDG

I Beef I

I Beef I

9.63 l b Gain

9.63 l b Gain

Ψ Grain I Alcoholj 1 Gal

Figure 1.

Making grain alcohol reduces grain production


20.

SCHELLER

Gasohol Energetics

427

Item 1 in Table VII i n d i c a t e s t h a t f o r t h e gasoline case, 10.74 gal of c r u d e oil m u s t be refined t o p r o d u c e t h e base q u a n t i t y of gasoline. In t h e gasohol case, only 9.14 g a l of c r u d e oil are refined t o p r o d u c e t h e needed gasoline. T h e difference in these t w o q u a n t i t i e s is t h e 1.6 gal of c r u d e oil savings d e t a i l e d in Table VI. T h e s e c o n d i t e m in Table VII deals w i t h c o r n p r o d u c t i o n f o r c a t t l e feed. In t h e gasoline case, this is 2.03 b u of corn as s h o w n in Figure 1 w i t h a n associated energy e x p e n d i t u r e o f 1.65 gal of e q u i v a l e n t oil. In t h e gasohol case, 1.53 b u of corn w e r e f e d d i r e c t l y t o he cattle. This c o r n has associated w i t h it a n energy c o n s u m p t i o n o f 1.25 gal o f e q u i v a l e n t o i l . Item 3 is t h e energy c o n s u m p t i o n associated w i t h p r o d u c i n g corn f o r e t h a n o l m a n u f a c ture. In t h e gasoline case, there is n o c o r n used for e t h a n o l . In t h e gasohol case, as s h o w n in Figure 1.0.38 b u of corn are associated w i t h t h e p r o d u c t i o n of 1 gal of grain a l c o h o l . Energy f o r t h e p r o d u c t i o n of this c o r n is 0.31 g a l of e q u i v a l e n t oil. A t this p o i n t , t h e t o t a l p e t r o l e u m c o n s u m p t i o n is 12.39 g a l of e q u i v a l e n t oil in t h e gasoline case a n d 10.70 gal o f e q u i v a l e n t oil in t h e g a s o h o l case. In t h e gasohol case, w e m u s t n o w a d d t h e e n e r g y c o n s u m p t i o n associated w i t h a l c o h o l p r o d u c t i o n a n d t h e DDG p r o d u c t i o n . Using t h e figures f r o m Table IV, t h e e n e r g y c o n s u m p t i o n f o r a late 1 9 7 9 fuel alcohol plant is 0.35 gal of e q u i v a l e n t oil for t h e a l c o h o l p r o d u c t i o n a n d 0.11 gal of e q u i v a l e n t oil f o r t h e DDG p r o d u c t i o n . This e n e r g y w o u l d p r o b a b l y be s u p p l i e d by coal, so t h e s u b t o t a l plant e n e r g y f o r t h e a l c o h o l a n d c a t t l e feed p r o d u c t i o n is i n d i c a t e d as coal w i t h a n e n e r g y c o n t e n t e q u i v a l e n t of 0.46 gal of o i l . S u m m i n g t h e t w o s u b t o t a l s , e n e r g y e q u i v a l e n t t o 12.39 gal e q u i v a l e n t oil w a s c o n s u m e d in t h e gasoline case w h i l e in t h e gasohol case, e n e r g y e q u i v a l e n t t o o n l y 11.16 g a l of e n e r g y e q u i v a l e n t oil w a s c o n s u m e d . T h u s , there is a fossil fuel saving e q u i v a l e n t t o 1.23 gal of oil f o r every g a l l o n of grain a l c o h o l t h a t is b l e n d e d w i t h 9 gal of u n l e a d e d gasoline. This is a very s u b s t a n t i a l saving.


428


Table V I I . G A S O H O L REDUCES FOSSIL FUEL C O N S U M P T I O N Gasoline Case Qal Equiv. Oil

Gasohol Casa Gal Equiv. Oil

1. Crude Oil Refining 2. C o m P r o d u c t i o n for Feed

10.74

9.14

1.65

3. Corn P r o d u c t i o n for Ethanol

0.00 12.39

1.25 0.31 10.70

0.00 0.00 0.00

0.35 0.11 0.46

12.39

11.16 1.23

Subtotal —

Petroleum

4 . A l c o h o l Plant O p e r a t i o n 5. DDG Plant O p e r a t i o n S u b t o t a l — Coal 6. T o t a l Energy C o n s u m p t i o n Fossil Fuel S a v i n g w i t h Gasohol Basis: a. b. c. d. e.

1 gal of fuel e t h a n o l m i x e d w i t h 9 gal of u n l e a d e d gasoline. U n l e a d e d gasoline t o m o v e a car as far as t h e gasohol in " a " above. A l l o t h e r p e t r o l e u m p r o d u c t s are t h e same in b o t h cases. Corn a n d c o r n + DDG t o p r o d u c e 9.63 lb of beef w e i g h t g a i n . 1 gal of e q u i v a l e n t oil is e q u a l t o 1 5 0 , 0 0 0 B t u .

Even if gasohol d i d n o t s h o w t h e 3 % increase in fuel e c o n o m y a n d even if t h e DDG d i d not p r o d u c e a 6% w e i g h t g a i n in beef cattle, t h e gasohol case w o u l d still s h o w an e n e r g y s a v i n g of 0.84 gal of e q u i v a l e n t oil over t h e gasoline case. These e n e r g y s a v i n g s exist w h e t h e r t h e a l c o h o l p l a n t is f u e l e d w i t h c o a l , o i l , or n a t u r a l gas. If i n d e e d , t h e a l c o h o l p l a n t is f u e l e d w i t h c o a l , t h e n t h e a c t u a l savings in p e t r o l e u m is 1.69 gal per g a l l o n of a l c o h o l b l e n d e d . T h e U.S. D e p a r t m e n t of Energy has e s t i m a t e d t h a t t h e p o t e n t i a l exists for p r o d u c i n g a b o u t 4.5 billion gallons of g r a i n alcohol f r o m a g r i c u l t u r a l stocks in t h e near f u t u r e if a l c o h o l p l a n t s t o m a t c h t h i s c a p a c i t y are built. A t a s a v i n g of 1.69 gal of p e t r o l e u m per g a l l o n of g r a i n a l c o h o l , t h e r e is t h e p o t e n t i a l of s a v i n g over 1 8 0 m i l l i o n barrels per year of i m p o r t e d c r u d e oil. This in t u r n w o u l d r e d u c e t h e o u t f l o w of dollars by at least $ 5 billion per year, w h i c h w o u l d be a s i g n i f i c a n t p e r c e n t a g e decrease in our trade deficit. CONCLUSIONS Based o n t h i s analysis, it has been d e m o n s t r a t e d t h a t r e p l a c e m e n t of gasoline w i t h g a s o h o l in t h e a u t o m o t i v e fuel m a r k e t w i l l result in a r e d u c t i o n of fossil fuel c o n s u m p t i o n . This r e d u c t i o n is p r e s e n t w h e t h e r or n o t gasohol provides greater fuel e c o n o m y t h a n gasoline a n d w h e t h e r or not beef c a t t l e g a i n a d d i t i o n a l w e i g h t w h e n distillers dark grains (DDG) are i n c l u d e d in their diet. T h e saving in p e t r o l e u m t h a t results f r o m t h e p r o d u c t i o n a n d use of gasohol has t h e p o t e n t i a l to r e d u c e s i g n i f i c a n t l y our trade deficit.


20.

SCHELLER

429

Gasohol Energetics

REFERENCES

1.

P i m e n t e l , D.; T e r h u n e , E. C., Ann. Rev. Energy

2.

P i m e n t e l , D., et al., Science

2, 1 7 1 - 9 5 (1977).

1 8 2 , 443-49 (1973).

APPENDIX Table II c o n t a i n s a s u m m a r y o f e n e r g y r e q u i r e m e n t s f o r 1 9 7 5 c o r n p r o d u c t i o n in t h e U n i t e d States. T h e i n d i v i d u a l e n e r g y c o m p o n e n t s in 1 9 7 5 c o r n p r o d u c t i o n are listed in Table A - 1 . This table s h o w s t h a t t h e three largest sources o f e n e r g y c o n s u m p t i o n are fuel, fertilizer, a n d irrigation. Table A - 2 c o n t a i n s t h e e n e r g y c o n t e n t o f t h e c o r n g r a i n a n d associated biomass material (stover a n d cobs). T h e e n e r g y p r o d u c t i o n (810,000 B t u / b u corn) is a b o u t 6.6 t i m e s t h e energy used in p r o d u c i n g t h e c o r n . Table IV lists t h e energy r e q u i r e m e n t s f o r p r o d u c i n g fuel grade e t h a n o l a n d distillers dark g r a i n s in a late 1 9 7 9 p l a n t d e s i g n . Table A - 3 c o n t a i n s a d e t a i l e d listing of t h e u t i l i t y r e q u i r e m e n t s for this late 1 9 7 9 d e s i g n . U s i n g t h e relationship s h o w n in Figure A - 1 , these u t i l i t y r e q u i r e m e n t s w e r e c o n v e r t e d t o a total e n e r g y r e q u i r e m e n t of 6 9 , 6 0 0 B t u per g a l l o n of fuel a l c o h o l p r o d u c e d a n d i n c l u d e s t h e e n e r g y f o r DDG p r o d u c t i o n . The energy c o n t e n t of t h e grain stover f r o m Table A - 2 is a b o u t 2.6 t i m e s t h e energy r e q u i r e m e n t f o r p r o d u c i n g e t h a n o l a n d DDG. From Table A - 4 , it is a p p a r e n t t h a t t h e energy c o n t e n t of t h e p r o d u c t s f r o m t h e g r a i n alcohol p l a n t is a p p r o x i m a t e l y equal t o t h e e n e r g y c o n t e n t o f t h e c o r n used (Table A-2) even t h o u g h t h e mass of t h e p r o d u c t s is only 6 3 % of t h e mass of t h e c o r n used (Table III).


430


T a b l a A - 1 E N E M Y C O N S U M P T I O N IN C O R N F A R M I N Q Ca—joaawt 1. 2. 3. 4. 5. 6. 7. & 9.

Seed Com Fertilizer Herbicides Insecticides Fuel Electricity Irrigation Drying Transportation Total Energy

1975

Btu/bu Corn

Btu/gal EtOH

2.700 43.900 2.700 1.500 39.300 7.100 14.600 7.000 3.400 122.200

1.040 16.800 1.040 580 15:030 2.720 5.580 2.680 1.290 46.760

a

* Reference 1. Table A - 2 . E N E R G Y PRODUCTION IN C O R N F A R M I N Q C Electric. kVYhr Cold Water. Gal 1. Milling and Propagation 2. C o o k i n g & S a c charification 3. Fermentation 4. Distillation 5. Thin Stillage Concen. 6. DDG Drying and Other Total

Total Bti

0.22

0.349

2.7

4.000

11.56 0.06 20.46 3.00 1.18 36.48

0.034 0.053 0.021 0.357 0.503 1.317

41.4 19.0 54.8 3.4 45.4 166.7

18.030 650 31.500 8.340 7.080 69.600

* Calculated using the listed utilities and Figure A-1.


20.

SCHELLER

431

Gasohol Energetics

Table A 4 . ENERGY PRODUCTION F R O M A GRAIN ALCOHOL PLANT Component

Btu/Gal EtOH

1. Fuel Ethanol, H H V

84,200

2. D D G . Digestible Energy

45,000

T o t a l Energy

129,200

STEAM BOILER

TOTAL FUEL

PROCESS _ S 5 > STEAM (LB/HR) n u

REQUIRED POWER :

MAKE-UP.

1 kwh/1000 l b stm LABOR: 2 S h . P o s .

WATER

STM

Blowdown 5%

POWER COND

POWER PLANT STM: 8 . 4 2 lb/kwh

PROCESS,

C.W: 0.5 3 gpm/kw

POWER

LABOR: 2 Sh.

Pos. POWER

C.W.

1 COOLING TOWER

P R O C E S S ^ CW

0

COOLING'

MAKE-UP

REQUIRED POWER:

WATER

0 (KW)

(GPM)

60 kw/1000 g p m Losses 15'-

Total

Power P

Total

T

Fuel

Figure A-1.

(kw) - 1 - 0 5 ( P

r

Q

+ .001C S ^

(Btu/Hr) - 10,000P

Q

T

.0706CW ) Q

+ 1.32S AH Q

Blockflowdiagram: utility-fuel relationship

RECEIVED M A Y 2 0 , 1 9 8 0 .


An Analysis of Gasohol Energetics - American Chemical Society

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