Thermal Conversion of Solid Wastes and Biomass

46 Studies on the Practical Application of Producer Gas from Agricultural Residues as Supplementary Fuel for Diesel Engines IBARRA E. CRUZ

Downloaded by UNIV OF ARIZONA on June 19, 2017 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch046

College of Engineering, University of the Philippines, Diliman, Zuezon City, Philippines 3004 The P h i l i p p i n e s is an a g r i c u l t u r a l country where c r o p i r r i g a t i o n h a s b e c o m e e s s e n t i a l to a c c e l e r a t e food p r o d u c t i o n . Manyirrigation systems use diesel engines. In r i c e p r o d u c t i o n , f o r instance, a government-supported cooperative-type f a r m based o r g a n i z a t i o n h a s i n s t a l l e d s i n c e 1975 a t o t a l of 334 d i e s e l e n g i n e d r i v e n p u m p s o f s i z e s r a n g i n g f r o m 15 to 150 h o r s e p o w e r (1 h o r s e p o w e r i s 746 w a t t s ) w h i c h e n a b l e d f a r m e r s to h a r v e s t t w o a n d even three crops in a year. W i t h the c o n t i n u i n g i n c r e a s e i n p r i c e c o u p l e d w i t h the s c a r c i t y of f u e l o i l s , p a r t i c u l a r l y d i e s e l f u e l , i t is b e c o m i n g m o r e and m o r e d i f f i c u l t to continue o p e r a t i n g these diesel engine-driven pumps. T h e o b j e c t i v e of t h e s e s t u d i e s t h e r e f o r e i s to a s s u r e the c o n t i n u e d o p e r a t i o n of e x i s t i n g d i e s e l e n g i n e s , p a r t i c u l a r l y t h o s e u s e d i n c r o p i r r i g a t i o n , b y c o n v e r t i n g t h e m to d u a l - f u e l e n g i n e s w i t h m i n i m u m m o d i f i c a t i o n s and u s i n g p r o d u c e r gas as s u p p l e m e n t a r y f u e l . It i n c l u d e s t h e d e s i g n o f a s i m p l e g a s p r o d u c e r that c a n be f a b r i c a t e d i n e x p e n s i v e l y . A d i e s e l engine w i t h a l i t t l e m o d i f i c a t i o n , c a n be o p e r a t e d as a d u a l - f u e l e n g i n e , that i s , an engine that u s e s both g a s e o u s fuel and liquid injection f u e l . N o r m a l l y , a d i e s e l engine a s p i r a t e s a i r d u r i n g the i n t a k e s t r o k e of the p i s t o n a n d c o m p r e s s e s t h i s to a h i g h p r e s s u r e and t e m p e r a t u r e . The c o m p r e s s i o n ratio of the d i e s e l e n g i n e i s h i g h e n o u g h s o that the t e m p e r a t u r e of the a i r i n s i d e the e n g i n e c y l i n d e r a f t e r the c o m p r e s s i o n s t r o k e a t t a i n s a s u f f i c i e n t l y h i g h l e v e l s o as to i g n i t e the d i e s e l f u e l that i s i n j e c t e d i n t o i t . In d u a l - f u e l o p e r a t i o n , a m i x t u r e of g a s e o u s f u e l a n d a i r i n the p r o p e r p r o p o r t i o n i s a s p i r a t e d i n t o the e n g i n e a n d c o m p r e s s e d d u r i n g the c o m p r e s s i o n s t r o k e . The gaseous f u e l - a i r m i x t u r e i s o n the l e a n s i d e s o that it does not p r e - i g n i t e d u r i n g the c o m p r e s s i o n s t r o k e . O n l y the i n j e c t i o n of the l i q u i d f u e l i n i t i a t e s i g n i t i o n and f i n a l c o m b u s t i o n of both g a s e o u s and 0-8412-0565-5/80/47-130-649$05.25/0 © 1980 American Chemical Society

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

THERMAL CONVERSION OF SOLID WASTES AND

650

BIOMASS


l i q u i d f u e l s . S i n c e c o m b u s t i o n of the g a s a s p i r a t e d w i t h a i r p r o v i d e s p o w e r , a m u c h l e s s a m o u n t of l i q u i d f u e l , c o m p a r e d to s t r a i g h t d i e s e l o p e r a t i o n , n e e d be i n j e c t e d to p r o d u c e a g i v e n power output. T h u s a s i g n i f i c a n t s a v i n g s i n the l i q u i d i n j e c t i o n fuel (diesel oil) is effected. T h e e c o n o m i c s of d u a l - f u e l o p e r a t i o n b e c o m e s f a v o r a b l e i f the g a s e o u s f u e l c a n be o b t a i n e d f r o m i n d i g e n o u s s o u r c e s . One such gaseous fuel is producer gas f r o m a g r i c u l t u r a l r e s i d u e s . S t u d i e s on the p r o d u c t i o n of g a s f r o m a g r i c u l t u r a l w a s t e s h a v e e a r l i e r b e e n r e p o r t e d (1). Experimental

Work With a Single-Cylinder

Engine

I n i t i a l e x p e r i m e n t a l w o r k o n the u s e of p r o d u c e r g a s f r o m c o c o n u t s h e l l c h a r c o a l w a s done w i t h the s u p p o r t of the P h i l i p p i n e C o c o n u t A u t h o r i t y (2). C h a r c o a l as fuel was c h o s e n because t h e c l e a n i n g of t h e g a s f r o m c h a r c o a l w a s s i m p l e r d u e t o l e s s t a r i n the g a s . F i g u r e 1 s h o w s the e x p e r i m e n t a l l a y - o u t f o r s t u d y i n g the p e r f o r m a n c e of a s i n g l e - c y l i n d e r d i e s e l engine when u s i n g p r o d u c e r gas as its m a i n f u e l . T h e e n g i n e h a d a b o r e of 4 . 5 i n c h e s a n d a s t r o k e o f 4 . 25 i n c h e s (1 i n c h i s 2 . 54 c e n t i m e t e r s ) . The engine was manufactured by L i s t e r - B l a c k s t o n e . I n F i g u r e 1, i t i s s e e n t h a t t h e p r o d u c e r g a s i s a s p i r a t e d i n t o the engine t o g e t h e r w i t h the a i r . T h e r e f o r e , the o n l y m o d i f i c a t i o n n e c e s s a r y to a l l o w the d i e s e l e n g i n e to u s e p r o d u c e r g a s i s a g a s p i p e l i n e c o n n e c t i o n t o the a i r i n t a k e p i p e of the e n g i n e w i t h a p p r o p r i a t e c o n t r o l v a l v e s f o r p r o p o r t i o n i n g the a i r - g a s mixtures. The gas p r o d u c e r w a s mounted on a p l a t f o r m s c a l e to a l l o w w e i g h t m e a s u r e m e n t s of the c h a r c o a l c o n s u m e d d u r i n g a t e s t run. F r o m d e r i v e d r e l a t i o n s , the w e i g h t r a t e of p r o d u c e r g a s u t i l i z e d i n the engine w a s c a l c u l a t e d . The l i q u i d f u e l tank, c o n taining d i e s e l o i l was l i k e w i s e mounted on a w e i g h i n g s c a l e . A r o t a m e t e r o r f l o w m e t e r w a s a l s o i n s t a l l e d i n the l i q u i d f u e l l i n e to s e r v e a s a c h e c k o n the r a t e of f u e l c o n s u m p t i o n . T h e e n g i n e w a s s t a r t e d i n the n o r m a l w a y b y h a n d c r a n k i n g , w i t h the a i r intake v a l v e f u l l y open and the p r o d u c e r gas v a l v e f u l l y c l o s e d . T h u s the engine w a s r u n on d i e s e l f u e l a l o n e at the start. The engine torque output w a s m e a s u r e d b y a p r o n y b r a k e mounted on another p l a t f o r m s c a l e , and the engine R P M b y hand tachometer. The b r a k e h o r s e p o w e r output i n e a c h r u n was thus determined.



Experimental layout for studying the use of producer gas from solid waste fuels in a diesel engine

(I) platform scale; (2) gas producer; (3) cyclone filter; (4) scrubber; (5) water outlet; (6) water inlet; (7) drain; (8) gas filter (coconut fiber); (9) control valve (gas); (10) control valve (air); (11) air filter; (12) gas analyzer; (13) diesel engine; (14) prony brake; (15) platform scale; (16) flowmeter; (17) liquid fuel; (18) weighing scale

Figure 1.



652

THERMAL CONVERSION OF SOLID WASTES AND

BIOMASS

The gas p r o d u c e r was a s u c t i o n - t y p e , downdraft r e a c t o r with 12 a i r h o l e s a r o u n d t h e m i d - s e c t i o n o f t h e c y l i n d r i c a l b o d y , a n d a s i n g l e gas o u t l e t at the b o t t o m . C o n n e c t e d to the g a s o u t l e t w a s a c y c l o n e s e p a r a t o r (3) t o r e m o v e e n t r a i n e d d u s t a n d c h a r c o a l f i n e s o u t of t h e g a s b e f o r e i t w e n t t o t h e e n g i n e . The gas s c r u b b e r (4) a n d f i l t e r (8) w e r e l a t e r a d d i t i o n s w h e n f u e l s w i t h high t a r and volatile m a t t e r contents w e r e u s e d . A t s t a r t - u p , the g a s p r o d u c e r w a s i n i t i a l l y f i l l e d w i t h c h a r c o a l c r u s h e d to a b o u t 1 - i n c h s i z e , u p to the l e v e l of the a i r - h o l e s . F e e d i n g o f f u e l w a s d o n e b y o p e n i n g t h e t o p of t h e r e a c t o r . A b u r n i n g z o n e w a s s t a r t e d o n the t o p of the c h a r c o a l b e d b y i g n i t i n g s m a l l p i e c e s of w o o d a n d w h e n the c h a r c o a l w a s b u r n i n g e v e n l y a t a l l l e v e l s o f t h e a i r - h o l e s ( t h i s t o o k a b o u t 10 m i n u t e s to o c c u r f r o m the t i m e the f i r e w a s lighted), the p r o d u c e r w a s c h a r g e d with m o r e c h a r c o a l u n t i l it was f u l l . The top of the r e a c t o r w a s t h e n c l o s e d a n d the g a s i n t a k e v a l v e to the e n g i n e s l o w l y opened. The engine w o u l d now a s p i r a t e g a s f r o m the r e a c t o r and speed up. S i n c e the engine w a s c o n t r o l l e d b y a s p e e d g o v e r n o r a d j u s t e d to about 1000 R P M , the l i q u i d f u e l i n take w o u l d be a u t o m a t i c a l l y r e d u c e d as m o r e p r o d u c e r gas w a s a s p i r a t e d into the e n g i n e , u n t i l a m i n i m u m u s e of l i q u i d f u e l , that which was r e q u i r e d only for ignition, was reached. T h e i n i t i a l d e s i g n of the g a s p r o d u c e r w a s s u c h that i t c o u l d be c o n v e r t e d r e a d i l y to operate e i t h e r as a downdraft o r as an updraft reactor. A l s o , the a i r intake c o u l d e i t h e r be b y s u c t i o n f r o m the e n g i n e o r b y f o r c e d d r a f t f r o m a c o m p r e s s e d a i r t a n k . T h e r e w a s o n l y a s i n g l e a i r i n l e t at the s i d e of t h e p r o d u c e r w h e n i t w a s o p e r a t e d a s a d o w n - d r a f t r e a c t o r , s o that the c o m b u s t i o n z o n e w a s c o n c e n t r a t e d i n the v i c i n i t y of t h i s s i n g l e a i r i n l e t . W h e n o p e r a t e d a s a n u p d r a f t r e a c t o r , the a i r e n t e r e d f r o m b e l o w the r e a c t o r a n d p a s s e d u p u n i f o r m l y t h r o u g h a b a r g r a t e . The q u a l i t y of t h e g a s t h u s p r o d u c e d w a s b e t t e r i n t h e u p d r a f t p r o d u cer. However, downdraft operation produced a cleaner gas, particularly when fuel with high volatile matter was used. Theref o r e a f t e r about h a l f of the e x p e r i m e n t a l r u n s w e r e f i n i s h e d , the p r o d u c e r w a s r e d e s i g n e d to o p e r a t e p e r m a n e n t l y as a s u c t i o n , downdraft r e a c t o r . R e d e s i g n i n g the r e a c t o r i n v o l v e d p r o v i d i n g f o r a d d i t i o n a l a i r i n l e t s s o that a i r d i s t r i b u t i o n to the c o m b u s t i o n z o n e c o u l d be more uniform. A l s o to i n c r e a s e the depth of the c o m b u s t i o n z o n e , the a i r h o l e s w e r e d i s t r i b u t e d a r o u n d t h r e e c i r c u m f e r e n t i a l p l a n e s (4 h o l e s t o a p l a n e ) s p a c e d 3 i n c h e s a p a r t t h u s e x t e n d i n g the b u r n i n g z o n e to a d e p t h of at l e a s t 6 i n c h e s . Furthermore, the c r o s s - s e c t i o n a l a r e a of t h i s c o m b u s t i o n z o n e w a s r e d u c e d to


46.

CRUZ

653

Producer Gas from Agricultural Residues


6 i n c h e s d i a m e t e r f r o m t h e o r i g i n a l 10 i n c h e s a n d t h e l o n g i t u d i n a l c r o s s s e c t i o n of the r e a c t o r now exhibited a c o n s t r i c t i o n o r a " t h r o a t " at the c o m b u s t i o n zone. The purpose of this throat w a s to m a k e c o m b u s t i o n m o r e i n t e n s e at this z o n e . Combustion rate p e r unit o r c r o s s - s e c t i o n a l a r e a would now be h i g h e r and hence temperature higher. T h u s , the c o m b i n a t i o n of h i g h e r t e m p e r a t u r e s a n d a deeper c o m b u s t i o n zone w o u l d l e n d to m o r e e f f i c i e n t c r a c k i n g of the v o l a t i l e a n d t a r r y m a t e r i a l i n the f u e l and to t h e p r o d u c t i o n of m o r e c o m b u s t i b l e g a s e s . A m a s s of data w a s obtained i n evaluating the p e r f o r m a n c e of the engine a s a d u a l - f u e l engine u s i n g p r o d u c e r g a s f r o m c h a r coal. The p a r a m e t e r s used f o r evaluating performance a r ethe b r a k e - h o r s e p o w e r ( B H P ) output, the b r a k e t h e r m a l e f f i c i e n c y (e^) o f t h e e n g i n e , a n d t h e p e r c e n t a g e e n e r g y f r o m p r o d u c e r g a s ( E P G ) u t i l i z e d i n the e n g i n e . E P G i s d e f i n e d a s the r a t i o of the heat r e l e a s e d b y the c o m b u s t i o n of p r o d u c e r gas a s p i r a t e d into the e n g i n e t o t h e t o t a l h e a t r e l e a s e d b y b o t h l i q u i d i n j e c t i o n f u e l ( d i e s e l ) a n d p r o d u c e r g a s , m u l t i p l i e d b y 100 t o e x p r e s s a s a p e r centage. D e r i v a t i o n of the equation f o r E P G a n d b r a k e t h e r m a l e f f i c i e n c y i s found i n the A p p e n d i x . T o o b t a i n a m o r e c o n v e n i e n t f o r m , the m a s s of d a t a w a s r e d u c e d to m u l t i p l e l i n e a r r e g r e s s i o n equations to g i v e the f o l l o w ing relationships: BHP

= 7. 2 5 - 1 . 90 χ 10

_Q

( R P M ) - 3 . 2 2 χ 10

_3

(CVn)

(1)

ο C o e f f i c i e n t of c o r r e l a t i o n , R

- 0 . 48

eb

= 2 5 . 63 - 1 . 3 4 χ 1 θ " 2 ( R P M ) • 8 . 60 χ 1 0 2 ( C V n )

R2

= 0 . 41

EPG R2

= 2 2 . 75 - 1 3 . 3 4 ( B H P ) + 1 . 0 3 ( C V n )

(2)

(3)

= 0 . 53

C V n i n the above equations i s the n e t c a l o r i f i c value of the gas i n B t u / f t 3 at N T P , i . e . , at n o r m a l t e m p e r a t u r e a n d p r e s s u r e of 2 7 3 Κ a n d 1 a t m o s p h e r e . (One B t u / f t 3 i s 37. 25913 k j / m 3 ) . T h e r a n g e of v a l u e s of the p a r a m e t e r s u s e d i n o b t a i n i n g t h e above equations a r e as follows:


654

THERMAL

(1) Engine speed: (2) Brake-horsepower: (3) Net c a l o r i f i c value in B t u / f t (4) Percent energy f r o m producer gas:


3

CONVERSION OF SOLID WASTES AND BIOMASS

900 4

<

Thermal Conversion of Solid Wastes and Biomass

Recommend Documents