14 Densification Systems for Agricultural Residues
Downloaded by PURDUE UNIV on September 15, 2017 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch014
THOMAS R. MILES and THOMAS R. MILES, JR. T. R. Miles, Consulting Engineers, 5475 S. W. ArrowWood Lane, Portland, OR 97225
The marketing and utilization of many agricultural residues can be significantly expanded by densification into bales, cubes or pellets. End uses and supply logistics usually determine their particular requirements of physical form and "packaging". Densification itself is only one of a sequence of operations which always includes collection, storage and transport - and can also involve treating, grinding and drying. Because residue is a waste, one obviously limits processing to the minimum. Since residue utilization is essentially a series of materials handling operations, not only these steps but also the shaft and thermal energy required must be kept to a minimum. If truck transport and storage are the only criteria, there is no need to densify to a greater compaction than 16 Lb/CF (256 Kg/m3), since at this density a truck reaches both its volume and weight limits. Nearly all stalks and straws can be field baled in one step to this density with currently available equipment. Densification is accomplished in several quite different ways: stalks, stems and leafy materials can be chopped or ground; stalks, stems and chips can be aligned or "laminated" to substantially increase bulk density; mechanical vibration and pressure can be used in combination with the above methods for higher densities. To maintain achieved density, the material must be bonded, or restrained (as in wire-bound bales) or not disturbed (as in the aligned or laminated states). The "Bulk Density" (B. Dens.) resulting from a process is more significant than the specific particle density. Significant factors controlling densification are moisture, particle size, form, fibrous or nonfibrous nature, leafy legumes vs. stiff waxy resilient straws, and binders, starch or sugar content, type and quantity of binder. 0-8412-0565-5/80/47-130-179$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.
Downloaded by PURDUE UNIV on September 15, 2017 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch014
180
THERMAL CONVERSION OF SOLID WASTES AND BIOMASS
In our e x p e r i e n c e , the use of COMBINATIONS o f m a t e r i a l s to f a c i l i t a t e d e n s i f i c a t i o n - p a r t i c u l a r l y f o r c u b i n g and p e l l e t i n g - cannot be o v e r - e m p h a s i z e d . The f o l l o w i n g must be borne i n mind when c o n s i d e r i n g d e n s i f i c a t i o n : (a) S o l u t i o n s are always s p e c i f i c to a p a r t i c u l a r m a t e r i a l , s i t e and end u s e . (b) The use of a g i v e n r e s i d u e i s always a f f e c t e d by the m a t e r i a l i t can r e p l a c e or the a v a i l a b i l i t y of other r e s i d u e s and many s p e c i a l crops or p r o d u c t s competing i n the same market, (c) S e l e c t i o n of d e n s i f i c a t i o n systems must take i n t o account the e n t i r e process from p r o d u c t i o n of the r e s i d u e to i t s d e l i v e r y and use i n i t s f i n a l form, (d) P h y s i c a l l y h a n d l i n g a r e s i d u e w i l l account f o r h i g h er c o s t s and more energy than the i n d i v i d u a l d e n s i f i c a t i o n systems. Most of the d a t a and c o n c l u s i o n s f o l l o w i n g are the r e s u l t of our nationwide e x p e r i m e n t a l and p r o d u c t i o n e n g i n e e r i n g i n the h a r v e s t , p r o c e s s i n g and t r a n s p o r t systems f o r a g r i c u l t u r a l and wood r e s i d u e s over the p a s t 31 y e a r s . S i n c e these m a t e r i a l s are a l l n a t u r a l and thus v a r i a b l e - v a l u e s are p r e s e n t e d i n r a n g e s . C h a r a c t e r i s t i c s of
Residues
Crop Residues : Straws, S t a l k s , V i n e s , S h e l l s , P i t s , F i b e r s 7500 B T U / L b , 10-20$ M, 2 T / A , B . Dens. 10-16 L b / C F b a l e d Must bear c o l l e c t i o n c o s t s a s i d e from c r o p . M u l t i - u s e s as f e e d s , f i b e r s , f u e l s , f e r t i l i z e r s . Seasonal s u p p l y , l i m i t e d h a r v e s t p e r i o d . Most are p e r i s h a b l e w i t h o u t covered s t o r a g e . Do not produce c l e a n b u r n i n g f u e l s without p r o c e s s i n g * Straws do not d e n s i f y without b i n d e r s . Best u t i l i z e d a t A r e a - I n t e g r a t e d - C o n v e r s i o n - C e n t e r s . Manure : F e e d l o t s and D a i r i e s , P o u l t r y and Hog Farms 6500 BTU/Lb DM, 80-90$ M, 1-8 Lb DS/Animal/Day 60 L b / C F s l u r r y v e r y p e r i s h a b l e , u s e - a t - s i t e s p e c i f i c . Low s o l i d s (12-15$) make d r y i n g c o s t l y . Twice BTU y i e l d as Biogas (methane) vs d r y / d i r . combust. R e l a t i v e l y few l a r g e c o n c e n t r a t i o n s of a n i m a l s . Has o n - f a r m , s m a l l s c a l e p o t e n t i a l . Forest Residues: M a t u r e , D i s e a s e d or Fire-damaged Trees 4500 B T U / L b , 50$ M, 2 0 - 5 0 T / A , Β Dens 18-22 L b / C F chipped Storage on stump, t h i n n i n g s , u n d e s i r a b l e s p e c i e . High c a p i t a l c o s t of r o a d s , a c c e s s , r i g h t - o f - w a y . Other c h a r a c t e r i s t i c s s i m i l a r to l o g g i n g r e s i d u e s .
Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
14.
MILES AND MILES
Densification Systems for Agricultural Residues
1 8 1
Downloaded by PURDUE UNIV on September 15, 2017 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch014
Logging R e s i d u e s : Limbs, Tops, S h a t t e r , Chunks 4500 B T U / L b , 50$ M, 2 0 - 5 0 T / A , Β Dens 18-22 L b / C F chipped C o l l e c t i o n costs vary widely with s i t e . Must be c h i p p e d a t l a n d i n g to a l l o w b u l k h a u l i n g , h a n d l i n g and s t o r a g e , w i t h added c a p i t a l c o s t . Chips ready f o r b o i l e r , to g a s i f y or c o n v e r t . P o t e n t i a l domestic f u e l t h r u d i s t r i b u t o r s . Q u a n t i t i e s per acre depend on s p e c i e and age. S t o r e o u t s i d e , low d e g r a d a t i o n . Competing f i b e r u s e s : pulp, board. Vhole-harvest chipping for f u e l / f i b e r . Sawmill R e s i d u e s : S h a v i n g s , B a r k , Sawdust 4500 B T U / L b , 50$ M, 2T/MFBM, Β Dens 16-22 L b / C F "hogged" C o l l e c t i o n and t r a n s p o r t s u b s i d i z e d by lumber. A l r e a d y reduced to usjable form. Ready f o r d i r e c t combustion or g a s i f i c a t i o n . Convenient to c o n v e r t to other forms at m i l l s i t e . At or near o t h e r l o g i c a l Energy C o n v e r s i o n s i t e s . Steady year-round supply, stores w e l l o u t s i d e . Sawdust/bark mix good domestic f u e l ( i n use up to 1950). Burns w e l l w i t h o u t d r y i n g (4500 BTU/Lb n e t ) . MSW, RDF: C o l l e c t e d M u n i c i p a l S o l i d Wastes, Refuse D e r i v e d F u e l 5000 B T U / L b , 30-40$ M, 5 L b / C a p / D a y , Β Dens 12-20 L b / C F Generated i n c i t i e s - near energy need. S u b s i d i z e d c o l l e c t i o n and t r a n s p o r t - low c o s t . S e p a r a t i o n and r e c o v e r y o f m e t a l s , etc. S u p p l y c o n s t a n t and p r o p o r t i o n a l to p o p u l a t i o n . S t o r e o n l y under c o v e r . L o g i s t i c s demand prompt s e p a r a t i o n and use i n l a r g e facilities. I n s t i t u t i o n a l and economic c o n s t r i n g e n c i e s abound. Residue Combustion S e v e r a l furnaces (1 to 6 M B T U / H ) to use b u l k or b a l e d r e s i d u e s are b e i n g developed here and abroad f o r on-farm or s m a l l commercial use f o r g r a i n or seed d r y i n g - ours among them. Proven s m a l l s l o p i n g g r a t e d e s i g n s f o r domestic and s m a l l commercial furnaces (200-1000 Κ BTU/H - 211-1055 M J / H ) use sawdust p e l l e t s and s m a l l cubes. L a r g e r i n d u s t r i a l dutch ovens, s l o p i n g or p i n h o l e g r a t e s or c e l l s can be e f f i c i e n t l y f i r e d w i t h wet (>40$ M) r e s i d u e f u e l s i n c l u d i n g wood hog f u e l , cubed RDF or s t r a w , s h e l l s and p i t s i n v a r i ous mixes - and i n combination w i t h c o a l - w i t h
Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Figure 1. Spectrum of values and densities for various products
Downloaded by PURDUE UNIV on September 15, 2017 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch014
%
Downloaded by PURDUE UNIV on September 15, 2017 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch014
14.
MILES AND MILES
Densification Systems for Agricultural Residues
183
pneumatic or r o t o s t o k e r s . Suspension f i r i n g , e i t h e r t a n g e n t i a l c y c l o n i c or l i n e a r , i s r e s t r i c t e d to low moisture (
