Electric Power Generation from Wood Waste - American Chemical

23 Electric Power Generation from Wood Waste A Case Study RICHARD T. SHEAHAN

Downloaded by CORNELL UNIV on October 21, 2016 | http://pubs.acs.org Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

Hennington, Durham & Richardson, 5454 Wisconsin Avenue, Washington, D C 20015

The current "Energy Crisis" being experienced worldwide has directed attention to the development of alternate sources of energy. One of those alternatives is wood. Wood appears to have numerous attractive advantages; it is available and renewable, a "clean" fuel, and has potential positive impacts on the enhancement of good forest management practice. The availability of wood residue exists in all forested areas of the United States, including "Urban" wooded areas. It is renewable because it regenerates in a relatively short time after each harvest cycle unlike fossil fuels. Wood is a relatively "clean" fuel because it contains virtually no sulfur. Most forested areas in the United States are currently not properly managed. Typical harvesting operations will "high-grade" a forest, or cut mostly the strong and marketable specimens, leaving the weak and "weedy" tree behind. As any gardener knows, if you do not "weed" your garden it will eventually become a weedpatch. This phenomenon occurs in numerous forested areas throughout the country. In most of these areas, there is no environmentally sound method of disposing of the rough and rotten wood residue, nor are there economic incentives for its removal. Utilizing this residue as an energy source can create an environmentally sound and economically viable motivation for "culling-out" and disposing of this

0097-6156/81/0144-0465$05.00/0 © 1981 American Chemical Society

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

466

BIOMASS AS A NONFOSSIL F U E L SOURCE

material. C o m b u s t i o n t e c h n o l o g y for g e n e r a t i n g e l e c t r i c i t y f r o m w o o d w a s t e s is w e l l e s t a b l i s h e d ; t h e major p r o b l e m area is t h e g a t h e r i n g a n d t r a n s p o r t i n g of t h e w o o d material in an e c o n o m i c a l l y a c c e p t a b l e fashion.


A general o v e r v i e w of t h e r e q u i r e m e n t s necessary t o i m p l e m e n t a w o o d residue e n e r g y p r o g r a m is presented in t h i s article. A case s t u d y of a n a c t u a l 5 0 m e g a w a t t ( M W ) w o o d - f i r e d electric g e n e r a t i n g p l a n t in B u r l i n g t o n . V e r m o n t w i l l be p r e s e n t e d as a m o d e l . Each c o m p o n e n t necessary t o m a k e u p t h e entire w o o d e n e r g y s y s t e m w i l l be d i s c u s s e d in s u f f i c i e n t detail t o assist t h e reader in u n d e r s t a n d i n g t h e r e q u i r e m e n t s necessary t o e v a l u a t e a n y w o o d e n e r g y p r o g r a m , be it t h e r m a l , s t e a m , or e l e c t r i c g e n e r a t i o n . T h e e x p e r i e n c e of t h e B u r l i n g t o n p r o j e c t is based o n t h e results o f a c o n c e p t u a l e n g i n e e r i n g s t u d y c o n d u c t e d by H e n n i n g s o n . D u r h a m & Richardson. Inc.O) T h e a v a i l a b i l i t y of w o o d residue a n d s u p p l y , its e n e r g y c h a r a c t e r i s t i c s , harvesting methodology, transportation and handling, combustion equipment, institutional and environmental concerns, and economic considerat i o n s are d i s c u s s e d . W O O D SUPPLY Due t o t h e relative sparsity of t i m b e r i n v e n t o r y data it is d i f f i c u l t t o a c c u r a t e l y d e t e r m i n e the t o t a l a m o u n t of w o o d residue available in t h e U n i t e d States. H o w e v e r , e s t i m a t e s i n d i c a t e t h a t a p p r o x i m a t e l y t h r e e p e r c e n t of t h e t o t a l U n i t e d States e n e r g y d e m a n d c o u l d possibly be s u p p l i e d by w o o d residues (2). There are several sources of w o o d residues s u i t a b l e for f u e l . A p r i m a r y criteria is t h a t t h e material be of a n o n - c o m m e r c i a l nature a n d have a l o n g t e r m a n d reliable s u p p l y . The p r i m a r y sources of w o o d residue are forest a n d mill residue. T h e U.S. Forest Service publishes statistics w h i c h c a n p r o v i d e t h e basis for e s t i m a t i n g t h e p o t e n t i a l a m o u n t s of available w o o d residues. O t h e r state a n d regional organizations also p u b l i s h d a t a w h i c h are useful in e s t i m a t i n g t h e q u a n t i t y of available material(3). Forest Residue There are several sources of available w o o d residues f r o m c o n v e n t i o n a l l o g g i n g opearations t h a t are n o r m a l l y n o t utilized o n a c o m m e r c i a l basis. A large v o l u m e of material c a n be d e r i v e d f r o m t o p s , b r a n c h e s , leaves, roots, s t u m p s , etc. w h i c h are usually left on t h e forest floor f o l l o w i n g a t y p i c a l s a w log h a r v e s t i n g o p e r a t i o n . This material can represent f r o m 3 5 t o 4 5 p e r c e n t of t h e v o l u m e , a n d therefore t h e e n e r g y c o n t e n t , of a tree. It c a n be c h i p p e d in t h e forest as an a d j u n c t t o a n o r m a l h a r v e s t i n g o p e r a t i o n . Removal of s o m e of this w a s t e material c a n reduce forest fire risk a n d e n h a n c e w i l d life habitat. N o n - c o m m e r c i a l species of trees are also available for fuel. These i n c l u d e



23.

SHEAHAN

Electric Power Generation

467

t y p i c a l small size, poor f o r m , or inferior q u a l i t y trees w h i c h have little h o p e o f m a t u r i n g or d e v e l o p i n g into trees suitable f o r industrial a p p l i c a t i o n . These plants c o m p e t e f o r m o i s t u r e a n d n u t r i e n t s w i t h t h e p r i m a r y forest. Therefore, p r u d e n t removal o f t h i s m a t e r i a l , w h i c h o f t e n is categorized as w a s t e , c a n e n h a n c e t h e health o f an overall forest. A n o t h e r source o f w o o d w a s t e is cull i n c r e m e n t a n d r o u g h a n d r o t t e n trees. Cull i n c r e m e n t refers t o t h e q u a n t i t y of w o o d w h i c h a n n u a l l y b e c o m e s n o n - c o m m e r c i a l , or " c u l l " material, d u e t o i n s u f f i c i e n t c u t t i n g or o v e r m a t u r e t i m b e r stands. A c e r t a i n n o n g r o w i n g p o r t i o n o f trees in a n y forested area is classified as s t a n d i n g r o u g h - a n d r o t t e n . This material is n o n - c o m m e r c i a l because it is either r o t t e n , b r o k e n , or d e a d . A s in a n y aspect of life, g o i n g t o e x t r e m e s is generally incorrect. Likewise, in a forest harvest o p e r a t i o n , c u t t i n g o u t t o o m u c h o f t h e n o n m e r c h a n t a b l e material is also incorrect. A certain a m o u n t o f t h e material m u s t be left b e h i n d t o replenish t h e soil n u t r i e n t s t o ensure f u t u r e forest health a n d vitality. Therefore, in a n y w o o d p r o c u r e m e n t o p e r a t i o n , g o o d forest m a n a g e m e n t practices m u s t be f o l l o w e d t o ensure t h a t t h e proper a m o u n t of w a s t e w o o d material is left t o m a i n t a i n t h e forest e c o l o g i c a l balance. M i l l Residue M i l l residue is a s o u r c e o f w o o d w a s t e w h i c h c a n be d e r i v e d f r o m t h e w o o d p r o d u c t s industry. D e p e n d i n g o n t h e e f f i c i e n c y o f a m i l l , u p t o f i f t y p e r c e n t o f t h e i n c o m i n g material c a n b e c o m e w a s t e material in t h e f o r m o f bark, s a w d u s t , c u t slabs, etc. (4). This residue is a n e x c e l l e n t source o f f u e l ; h o w e v e r , f o r a l o n g - t e r m s u p p l y , it m a y d w i n d l e as m o r e e m p h a s i s is p l a c e d on utilizing it f o r " i n - h o u s e " e n e r g y uses by t h e w o o d p r o d u c t s industries. Supply Evaluation W h e n e v a l u a t i n g a w o o d residue s u p p l y , c e r t a i n a s s u m p t i o n s m u s t be m a d e t o q u a n t i f y t h e availability. Data p u b l i s h e d b y t h e U.S. Forest Service a n d o t h e r organizations are a g o o d s t a r t i n g p o i n t f o r f o r m u l a t i n g w o o d residue q u a n t i t y . H o w e v e r , a t h o r o u g h u n d e r s t a n d i n g of t h e local h a r v e s t i n g t e c h n i q u e s a n d c u s t o m s , access t o t r a n s p o r t a t i o n , p e r c e n t grade o f local t e r r a i n , land o w n e r a t t i d u e s , seasonal w e a t h e r c o n d i t i o n s a n d o t h e r c o n s i d e r a t i o n s m u s t be e v a l u a t e d . A s an e x a m p l e of t h e latter i t e m , t h e City of B u r l i n g t o n w i l l have t o s t o c k p i l e s u f f i c i e n t w o o d residue in t h e s p r i n g a n d fall d u e t o a s h u t d o w n of h a r v e s t i n g operations. In t h e s p r i n g , t h e " m u d s e a s o n " makes l o g g i n g roads impassable d u e t o m e l t i n g s n o w s . In t h e fall, t h e h u n t i n g season closes d o w n t h e forest t o m o s t h a r v e s t i n g operations. Culling o u t of t h e n o n - m e r c h a n t a b l e material s h o u l d a c t u a l l y increase t h e a n n u a l g r o w t h rate o f a forest because t h e residual-stock is healthier a n d


468


faster g r o w i n g . H o w e v e r , it is m o s t i m p o r t a n t t h a t t h e a n t i c i p a t e d a n n u a l r e m o v a l rate of w o o d residue does not exceed t h e a n n u a l n e w g r o w t h rate of a forest. Burlington W o o d Supply


Based o n a reasonable e n e r g y balance a n d load f a c t o r for a 5 0 M W w o o d fired p o w e r plant, it w a s e s t i m a t e d t h a t t h e City of B u r l i n g t o n requires a p p r o x i m a t e l y 4 7 0 . 0 0 0 g r e e n t o n s of w o o d r e s i d u e / y e a r t o o p e r a t e t h e i r p o w e r plant. Several a s s u m p t i o n s w e r e m a d e t o d e t e r m i n e if t h a t q u a n t i t y of m a t e r i a l is available t o t h e City. •

T h e s u p p l y area w a s a s s u m e d t o be c i r c u l a r a n d a p p r o x i m a t e l y 8 0 miles in d i a m e t e r . B u r l i n g t o n is s i t u a t e d in t h e w e s t e r n regions of t h e c i r c u l a r area.

•

M i n i m u m parcel size for t h e h a r v e s t i n g o p e r a t i o n w a s a s s u m e d t o be 5 0 acres. This is a very c o n s e r v a t i v e e s t i m a t e since m a n y h a r v e s t i n g o p e r a t i o n s take place o n h o l d i n g s b e l o w 3 0 acres in size.

•

Timberland that was owned

by t h e forest i n d u s t r y w a s

considered

unavailable for c o m p e t i t i v e p u r c h a s e of w o o d . •

A n n u a l g r o w t h o n state a n d national forests w a s c o n s i d e r e d available.

•

It w a s a s s u m e d t h a t w o o d in t h e i m m e d i a t e v i c i n i t y of B u r l i n g t o n w a s not available; likewise, it w a s a s s u m e d t h a t no s u b s t a n t i a l s u p p l y of w o o d f r o m Canada or across Lake C h a m p l a i n is available.

Based o n these a s s u m p t i o n s , it w a s d e t e r m i n e d t h a t t h e total w o o d d e m a n d by B u r l i n g t o n Is m o r e t h a n a d e q u a t e l y s u p p l i e d f r o m t h e a s s u m e d area. W O O D FUEL C H A R A C T E R I S T I C S W h e n e v a l u a t i n g w o o d as a f u e l , c h a r a c t e r i s t i c s of t h e delivered material m u s t be e s t i m a t e d relative t o t h e w e i g h t e d average of energy c o n t e n t s for t h e v a r i o u s a n t i c i p a t e d species of w o o d . I m p o r t a n t c o m b u s t i o n c h a r a c teristics of w o o d are its h e a t i n g value, w h i c h is a f u n c t i o n of its m o i s t u r e c o n t e n t a n d d e n s i t y , a n d its ash c o m p o s i t i o n . F l u c t u a t i o n s of these values are p r i m a r i l y d u e t o d i f f e r e n t c o n c e n t r a t i o n s of l i g n i n a n d t h e presence of e x t r a c t i v e s in t h e w o o d s u c h as resins a n d t a n n i n s . H a r d w o o d s (i.e., oak, m a p l e , etc.) generally have an average h i g h h e a t i n g v a l u e b e t w e e n 8 5 0 0 and 8 6 0 0 B t u / o v e n dry p o u n d of w o o d . Resin has a m u c h greater h e a t i n g value



23.

SHEAHAN


469

t h a n w o o d ( a p p r o x i m a t e l y 1 7 , 0 0 0 B t u / l b ) . Therefore, soft w o o d s (i.e., m o s t l y pines) w h i c h have h i g h e r resin c o n t e n t s a n d p r o p o r t i o n s of l i g n i n have h i g h e r e n e r g y c o n t e n t s t h a n hard w o o d s a n d average a p p r o x i m a t e l y 9 0 0 0 B t u / o v e n d r i e d p o u n d o f w o o d . These average values vary o n l y 5 t o 8 p e r c e n t d e p e n d i n g o n specific w o o d s (5). Bark also has a higher e n e r g y c o n t e n t t h a n w o o d . T h e a c t u a l h e a t i n g value f o r w o o d decreases as m o i s t u r e increases, since w a t e r has no h e a t i n g value. T h e m o i s t u r e c o n t e n t o f " g r e e n " w o o d , or w o o d r e c e n t l y harvested a n d c h i p p e d , is a p p r o x i m a t e l y 5 0 p e r c e n t (on a w e t basis). Based o n this m o i s t u r e c o n t e n t , t h e average h i g h h e a t i n g values are approximately 4 3 0 0 Btu/lb for hardwoods and approximately 4 5 0 0 Btu/lb for s o f t w o o d s . The ash c o m p o n e n t is generally c o n s i d e r e d undesirable since it is inert a n d n o t c o m b u s t i b l e . A s h e i t h e r remains in t h e c o m b u s t i o n c h a m b e r or is e n t r a i n e d w i t h stack gases w h i c h m a y create p a r t i c u l a t e air e m i s s i o n p r o b l e m s . T h e average ash c o n t e n t of m o s t w o o d s ranges f r o m 0.1 t o 3 percent, w i t h m o s t species a v e r a g i n g less t h a n o n e percent. A possible increase in t h e ash c o n t e n t o f w o o d can c o m e f r o m t h e s k i d d i n g of harvested trees in t h e forest w h i c h o f t e n results in t h e c o l l e c t i o n of s o m e dirt and sand on t h e bark. Unless t h i s material is r e m o v e d , it c a n increase t h e t o t a l ash c o n t e n t o f t h e fuel. A s a p o i n t o f c o m p a r i s o n , m o s t coals have an average ash content substantially above 5 percent w i t h some reaching t h e 25 percent level. B u r l i n g t o n ' s Fuel C h a r a c t e l s t i c s Based o n a w e i g h t e d average o f t h e w o o d specie m i x in t h e s u p p l y area, it w a s e s t i m a t e d t h a t t h e average h i g h h e a t i n g value of t h e w o o d fuel t o B u r l i n g t o n w o u l d be a p p r o x i m a t e l y 4 7 5 0 B t u / l b . HARVESTING TECHNIQUES N u m e r o u s c o m b i n a t i o n s of h a r v e s t i n g scenarios are possible. A l l basically involve t h e t r a d i t i o n a l steps o f a n o r m a l h a r v e s t i n g a n d delivery process w h i c h includes f o u r separate a c t i v i t i e s : f e l l i n g , s k i d d i n g , y a r d i n g , a n d hauling. Felling — This step involves t h e c u t t i n g o f i n d i v i d u a l trees. T h e p r e v a i l i n g f e l l i n g e q u i p m e n t is t h e c h a i n s a w ; h o w e v e r , m o r e m e c h a n i z e d devices are available a n d b e i n g d e v e l o p e d . T h e fellerb u n c h e r is a m a c h i n e t h a t uses a h y d r a u l i c s y s t e m t o h o l d t h e s t a n d i n g tree w h i l e c u t t i n g it near g r o u n d level w i t h a m e c h a n i c a l shear. O n c e c u t , t h e trees are i n d i v i d u a l l y laid side by side.


470


Skidding— The s k i d d i n g o p e r a t i o n involves d r a g g i n g t h e logs or trees f r o m their felled p o s i t i o n t o a general c o l l e c t i o n site called a l a n d i n g . T h i s is usually d o n e by large f o u r - w h e e l e d d r i v e , r u b b e r - t r i e d skidders. T o a l i m i t e d e x t e n t s k i d d i n g is d o n e by steel t r a c k e d c r a w l e r s or by horses. Skidders usually pull m o r e t h a n one log or tree at a t i m e , h o l d i n g t h e leading e n d s of t h e logs off t h e g r o u n d by use of steel cables a n d a


w i n c h , or by h y d r a u l i c g r a p p l e devices. Yarding— O n c e t h e logs or trees have been s k i d d e d t o t h e l a n d i n g , t h e y are prepared for s h i p m e n t t o t h e w o o d y a r d . This process is called y a r d i n g . A n i n t e g r a t e d o p e r a t i o n t h a t s u p p l i e s w o o d for a p o w e r p l a n t w o u l d p r o b a b l y skid either long logs or entire trees. A t t h e l a n d i n g , q u a l i t y s a w logs w o u l d be c u t . sorted a n d piled for s u b s e q u e n t l o a d i n g o n large t r u c k s for delivery t o t h e a p p r o p r i a t e m i l l . T h e balance of t h e trees or logs m a y t h e n be c h i p p e d a n d b l o w n i n t o e n c l o s e d trailers by w h o l e - t r e e c h i p p e r s . A w h o l e - t r e e c h i p p e r c a n be t o w e d by t r u c k t o t h e l a n d i n g area a n d q u i c k l y set up for o p e r a t i o n . A m e c h n i c a l a r m picks up t h e w h o l e tree or log a n d feeds one e n d i n t o a m o t o r i z e d c o n v e y o r s y s t e m w h i c h t h e n pushes t h e material t o w a r d s a set of h i g h s p e e d , r o t a t i n g knives. T h e w o o d c h i p s t h a t result are generally a b o u t t h e size of m a t c h b o o k s . If w h o l e - t r e e c h i p p e r s are n o t used, t h e logs w o u l d be c u t into c o n v e n i e n t l e n g t h s for loading i n t o t r u c k s . In a n o n c h i p p i n g o p e r a t i o n , t h e t o p s a n d b r a n c h e s w o u l d be left b e h i n d as w a s t e m a t e r i a l . Hauling — T h e c h i p s are t r a n s p o r t e d f r o m a l a n d i n g t o a p o w e r p l a n t b y tractor-trailer. S a w logs o n t h e o t h e r h a n d c a n be h a u l e d by e i t h e r s t r a i g h t t r u c k s or tractor-trailers. These log t r u c k s m a y be e q u i p p e d w i t h self-loading e q u i p m e n t . Burlington Harvesting Scenario In e v a l u a t i n g t h e c o s t of h a r v e s t i n g w o o d f u e l , t h e r e are i n f i n i t e c o m b i n a t i o n s of labor a n d e q u i p m e n t w h i c h c o u l d be utilized in p r o c u r i n g t h e w o o d w a s t e . M a n y factors m u s t be c o n s i d e r e d ; these i n c l u d e h a r v e s t i n g e q u i p m e n t , m a n p o w e r r e q u i r e m e n t s , slope of terrain, access t o l o g g i n g trails and t r a n s p o r t a t i o n roads, haul d i s t a n c e t o u l t i m a t e use, land o w n e r a t t i t u d e s a n d n u m e r o u s o t h e r c o n s i d e r a t i o n s . In e v a l u a t i n g t h e c o s t of fuel d e l i v e r e d t o B u r l i n g t o n , t h r e e w o o d fuel p r o d u c t i o n m o d e l s w e r e e x a m i n e d . T h e p r o d u c t i o n m o d e l s selected for e v a l u a t i o n w e r e j u d g e d t o be fairly representative of m e t h o d s c u r r e n t l y e m p l o y e d in t h e N e w England region. Model Number 1 — Traditional Round Wood - This m o d e l e x e m p l i f i e s m a n y small w o o d h a r v e s t i n g operations a n d consists of t w o m e n a n d one skidder. One m a n is responsible for felling a n d c u t t i n g t h e tree t o


23.

SHEAHAN

471


desired lengths. T h e o t h e r l u m b e r m a n skids t h e tree o u t t o a l a n d i n g . This h a r v e s t i n g s y s t e m requires a m o d e s t c a p i t a l i n v e s t m e n t a n d offers o p e r a t i n g f l e x i b i l i t y t o c o n f o r m t o local c o n d i t i o n s . It is t h e p r e d o m i n a n t h a r v e s t i n g s y s t e m c u r r e n t l y utilized in V e r m o n t ' s forest. Model

Number

2 — Chip Harvesting

(Moderate

Mechanization)-

This

represents a p o p u l a r e m e r g i n g h a r v e s t i n g t e c h n o l o g y in N e w England. " I n - t h e - w o o d s " c h i p p i n g offers a d v a n t a g e s of greater resource utilizat i o n a n d r e d u c e d t r a n s p o r t a t i o n cost. W h o l e trees are felled b y c h a i n s a w s a n d s k i d d e d t o a m e d i u m size (18 in.) c h i p p e r at t h e l a n d i n g area.


Chips are b l o w n into tractor-trailers f o r t r a n s p o r t t o t h e p o w e r plant. Model Number 3 — Whole Tree Harvesting (Highly Mechanized)This s y s t e m utilizes a m e c h a n i c a l f e l l e r - b u n c h e r t o c u t trees utilizing m u l t i p l e skidders t o m o v e t h e m t o a large (22 in.) c h i p p e r located at t h e l a n d i n g area. T h e increased capital i n v e s t m e n t a n d higher o p e r a t i n g costs c o m b i n e d w i t h p r o b l e m s presented b y r u g g e d terrain have t o date e x c l u d e d t h e general use o f f e l l e r - b u n c h e r s in V e r m o n t . Generally, t h e y are restricted t o terrain h a v i n g slopes of 15 p e r c e n t or less (6). It is d o u b t f u l t h a t f e l l e r - b u n c h e r o p e r a t i o n s w i l l b e c o m e w i d e s p r e a d in V e r m o n t ' s forests d u e t o h i g h capital costs, u n c e r t a i n t y a b o u t p r o d u c t i v i t y in certain c u t s , a n d t h e i r l i m i t e d a d a p t a b i l i t y t o small a n d m e d i u m size parcels w h i c h are very c o m m o n in V e r m o n t . H o w e v e r , its p o t e n t i a l is very s i g n i f i c a n t in less r u g g e d a n d sloped terrain a n d large parcels of forested land. Economic

assumptions

a n d capital

and operating

costs

f o r t h e three

p r o d u c t i o n m o d e l s are p r e s e n t e d in Tables I a n d II. T o realistically evaluate t h e cost of p r o d u c i n g w o o d fuel f o r t h e B u r l i n g t o n plant, it w a s a s s u m e d t h a t o n l y p r o v e n h a r v e s t i n g t e c h n o l o l g y w o u l d be utilized. T h u s , a f e l l e r - b u n c h e r o p e r a t i o n , a l t h o u g h t e c h n i c a l l y possible, w a s not c o n s i d e r e d t o be a m a j o r c o n t r i b u t o r . It w a s a s s u m e d t h a t t h e p r e d o m i n a n t p o r t i o n o f t h e w o o d fuel w o u l d be s u p p l i e d by t r a d i t i o n a l r o u n d w o o d a n d m o d e r a t e l y m e c h a n i z e d c h i p h a r v e s t i n g operations. It w a s f u r t h e r a s s u m e d t h a t 7 0 p e r c e n t o f t h e fuel r e q u i r e m e n t s w o u l d be s u p p l i e d b y " i n t h e - w o o d s " c h i p p i n g a n d 3 0 p e r c e n t b y t r a d a t i o n a l r o u n d w o o d subseq u e n t l y c h i p p e d at a satellite facility or c o n c e n t r a t i o n y a r d . T h e w e i g h t e d average o f w o o d fuel cost (prior t o c h i p p i n g o f t h e r o u n d w o o d p o r t i o n a n d t r a n s p o r t a t i o n of t h e t o t a l p o r t i o n of t h e w o o d fuel) w a s e s t i m a t e d t o be $ 8 . 0 6 / t o n (1977 dollars).


472


T A B L E I. P R O D U C T I O N M O D E L A S S U M P T I O N S (All c o s t s e x p r e s s e d in 1 9 7 7 dollars) Productivity: Estimate based on m a n u f a c t u r e r ' s i n f o r m a t i o n a n d national averages revised t o reflect V e r m o n t c o n d i t i o n s . A s s u m e 1,800 h r / y r o p e r a t i o n . Labor: Based o n 4 5 w e e k s per year at $ 2 2 0 / w e e k per person plus 2 5 % payroll


benefits. Fuel a n d O i l : Fuel Diesel @ $ 0 . 5 0 / g a l Skidders Feller-buncher, c r a w l e r t r a c t o r Chipper — M e d . 1 8 " Lg. 2 2 "

Consumption 5.0 g a l / h o u r 6.0 g a l / h o u r 10.0 g a l / h o u r 12.0 g a l / h o u r

3 0 % of Fuel Cost M a i n t e n a n c e a n d Repair: Hourly D e p r e c i a t i o n (HD) = Purchase P r i c e / E x p e c t e d Life A s s u m e .70 x HD x 1 8 0 0 h r / y r = M a i n t e n a n c e a n d Repair Skidders — Dovers — Chippers —

7 , 5 0 0 hr e x p e c t e d life 10,000 hr e x p e c t e d life

$0.50/ton

Financing: A s s u m e 7 5 % Debt — 2 5 % Equity

12%, 5 years

Depreciation: A s s u m e 5 years s t r a i g h t line S t u m p a g e : (Payment to l a n d o w n e r for w o o d removed) A s s u m e average $ 0 . 7 5 / t o n Taxes: State a n d Federal Federal i n c l u d e s i n v e s t m e n t tas c r e d i t a m o r t i z e d over 5 years. Profit: Reflects o n assessment of r i s k - r e w a r d f a c t o r s a n d varies a c c o r d i n g t o size of capital i n v e s t m e n t , m a r g i n s are c o n s i d e r e d reasonable t o a c h i e v e desired p r o d u c t i o n levels.


23.

SHEAHAN

473


TABLE II. PRODUCTION MODELS -

CAPITAL A N D OPERATING COST

SUMMARY


(All c o s t s e x p r e s s e d in 1 9 7 7 dollars)

P r o d u c t i v i t y (tons/year) Labor (Men)

Moderately

Highly

Mechanized

Mechanized

Traditional Roundwood

Chip Harvesting

Chip Harvesting

8.440 2

33.750 6

54,000 9

1 1

2

$44,000

$242,000

1 2 2 1 1 $509,000

$67,112

$273,316

$526,639

$24,750 5.850 6.700 2.550 9.350 6.330

$74,250 23,000 29.000 14,000 48,500 25,000 7,825 21,676

$111,375 43.000 51.000 29.600

Equipment C r a w l e r Tractor Cable Skidders Grapple Skidders Feller-Buncher Chipper Capital I n v e s t m e n t

1

Revenues A n n u a l W o o d Sales Costs Labor Fuel & Oil M a i n t e n a n c e & Repair Interest Depreciation Stumpage Miscellaneous Taxes Net Profit Profit o n Sales (%) Return o n I n v e s t m e n t (%) U n i t Cost ($/ton)

2.775 3.706 5.371 8 12

30.065 11 12

7.95

8.10

100.000 38.000 12.000 62.733 78,931


15 15 9.75

474



T R A N S P O R T A T I O N , H A N D L I N G A N D PROCESSING There are e s t i m a t e s t h a t indicate o n a net zero e n e r g y basis for electric g e n e r a t i o n (i.e.. e n e r g y i n p u t r e q u i r e m e n t t o p r o d u c e a c o m p a r a b l e electrical o u t p u t derived f r o m w o o d chips), " g r e e n " w o o d c h i p s can be hauled by t r u c k for a p p r o x i m a t e l y 5 0 t o 100 miles d e p e n d i n g o n t h e average heat a n d m o i s t u r e c o n t e n t of t h e w o o d fuel (7). T h e c o m p a r a b l e d i s t a n c e for rail haul is m u c h greater. H o w e v e r , o n an e c o n o m i c basis, rail haul p r o v e d t o be u n a c c e p t a b l y m o r e e x p e n s i v e d u e t o t h e a d d i t i o n a l costs associated w i t h l o a d i n g a n d u n l o a d i n g of railroad cars. It w a s a s s u m e d t h a t all w o o d c h i p s w o u l d be hauled t o t h e p o w e r p l a n t b y t r u c k s . T r u c k i n g costs for r o u n d w o o d a n d c h i p s w e r e d e t e r m i n e d t h r o u g h analysis of rate s c h e d u l e s of w o o d haulers in t h e B u r l i n g t o n area. Generally, r o u n d w o o d is m o r e c o s t l y t o t r a n s p o r t t h a n c h i p s d u e t o r e d u c e d v e h i c l e p a y loads a n d h a n d l i n g p r o b l e m s . Therefore, a c o m p o s i t e average t r u c k i n g cost r e f l e c t i n g r o u n d w o o d a n d c h i p t r a n s p o r t w a s used. Rates w e r e s t r u c t u r e d t o p r o v i d e i n c e n t i v e s for utilization of efficient vehicles a n d t o a t t r a c t d i s t a n t supplies. It w a s a s s u m e d t h a t v e h i c l e s w o u l d average 3 5 m i l e s - p e r - h o u r a n d carry a p a y l o a d of f r o m t w e n t y t o t w e n t y five tons. T h e t r u c k t r a n s p o r t a t i o n costs w e r e d e t e r m i n e d by a p p l y i n g u n i t haul costs per m i l e t o t h e w e i g h t e d d i s t r i b u t i o n of w o o d e d area w i t h i n t h e s u p p l y area. T h e average t r u c k i n g c o s t w a s d e t e r m i n e d t o be $ 3 . 4 3 / t o n ( 1 9 7 7 dollars) f r o m t h e forest t o p o w e r plant. A n a d d i t i o n a l cost of $ 1 . 6 7 / t o n w a s d e t e r m i n e d for t h e cost of c h i p p i n g t h e plant's w o o d fuel r e q u i r e m e n t s d e r i v e d f r o m t h e r o u n d w o o d o p e r a t i o n . This cost w a s a p p l i e d t o 3 0 p e r c e n t of t h e t o t a l w o o d s u p p l y per t h e p r e v i o u s assumption. T h e f o l l o w i n g f i g u r e s indicate t h e t o t a l e s t i m a t e d c o s t in 1 9 7 7 dollars for w o o d fuel p r o c u r e m e n t for t h e B u r l i n g t o n P o w e r Plant. W o o d P r o d u c t i o n Costs Trucking C h i p p i n g of R o u n d W o o d (applied t o 3 0 p e r c e n t of w o o d supply)

$8.06/ton 3.43 0.50 $11.99/ton

FUEL H A N D L I N G A N D STORAGE Chip t r u c k s a r r i v i n g at t h e p o w e r p l a n t are w e i g h e d a n d t h e n u n l o a d e d by h y d r a u l i c t r u c k d u m p e r s . Chips f l o w by g r a v i t y f r o m t h e t r u c k s into liveb o t t o m receiving h o p p e r s ; a n d f r o m there, o n t o i n c l i n e d belt c o n v e y o r s w h i c h t r a n s p o r t t h e c h i p s t o storage. A m e c h a n i c a l - b e l t pile-builder d i s t r i b u t e s the chips evenly a r o u n d the p e r i m e t e r of t h e storage pile. A disk


23.

SHEAHAN


475


screen a n d w o o d pulverizer are p r o v i d e d t o reduce oversized material t o p r e v e n t j a m m i n g o f material h a n d l i n g systems. Also, a m a g n e t i c ferrous recovery s y s t e m is necessary t o recover t r a m p m e t a l parts w h i c h c a n cause d a m a g e t o t h e c o n v e y i n g a n d c o m b u s t i o n systems (8.9). D u r i n g w i n t e r m o n t h s , vehicles a r r i v i n g at t h e u n l o a d i n g area m u s t be carefully i n s p e c t e d t o ensure t h a t massive loads o f frozen chips are n o t d u m p e d o n t o t h e r e c e i v i n g hoppers t h e r e b y c r e a t i n g a b o t t l e neck t o s u b s e q u e n t u n l o a d i n g operations. The e x p e r i e n c e o f c h i p h a n d l i n g facilities in Canada indicates t h a t t h e o n l y sure p r e v e n t i o n is t o establish a f i r m policy against delivery of frozen chips. M o s t freezing p r o b l e m s o c c u r w h e n c h i p s are loaded i n t o vans a n d left t o s t a n d over long periods o f t i m e prior t o delivery. Chips p r o d u c e d in t h e w o o d s a n d b r o u g h t p r o m p t l y t o t h e p o w e r plant s h o u l d n o t arrive solidly frozen. The a n t i c i p a t e d w o o d storage pile f o r t h e p o w e r plant is s e m i - c i r c u l a r in shape a p p r o x i m a t e l y 3 8 0 feet in d i a m e t e r w i t h a h e i g h t of 4 0 feet. It c o n t a i n s a p p r o x i m a t e l y 4 2 . 5 0 0 t o n s o f c h i p s o r a p p r o x i m a t e l y 21 days o f fuel s u p p l y for t h e p o w e r plant. T w o c h i p dozers w o r k t h e pile a n d share responsibility f o r m a n a g i n g t h e pile a n d r e c l a i m i n g w o o d . Chip pile m a n a g e m e n t is a n i m p o r t a n t task w h i c h i n c l u d e s responsibility f o r r o t a t i o n o f c h i p i n v e n t o r y , c h i p m i x i n g , d u s t c o n t r o l , a n d fire p r e v e n t i o n . T h e relatively h i g h m o i s t u r e c o n t e n t of w o o d fuel d i c t a t e s t h a t material be reclaimed o n a " f i r s t - i n firsto u t " basis t o m a i n t a i n freshness a n d i n h i b i t c h i p d e c o m p o s i t i o n . Chip i n v e n t o r y s h o u l d be c o m p l e t e l y rotated at least o n c e a year t o m i n i m i z e d e c o m p o s i t i o n . A c e r t a i n degree o f natural d e c o m p o s i t i o n w i l l o c c u r a n d t h e p o t e n t i a l f o r s p o n t a n e o u s c o m b u s t i o n fires exists. C o m p a c t i o n of t h e entire pile, especially a l o n g t h e o u t e r perimeter, reduces air f l o w w h i c h c a n feed " h o t s p o t s " in t h e pile. " H o t - s p o t s " , i d e n t i f i e d b y t h e presence of smoke, s h o u l d be u n c o v e r e d a n d a p p r o x i m a t e l y a t r u c k load of d r y ice a p p l i e d a n d the area r e c o m p a c t e d . Carbon d i o x i d e gas is d r a w n into t h e " h o t " area a n d causes it t o be e x t i n g u i s h e d . Before large w o o d c h i p inventories are a c c u m u l a t e d , a q u a n t i t y supplier o f d r y ice s h o u l d be i d e n t i f i e d . W o o d c h i p s are r e c l a i m e d f r o m t h e storage pile b y c h i p dozers and d e p o s i t e d in r e c l a i m hoppers a d j a c e n t t o t h e w o o d pile. Steel grates a b o v e t h e hoppers p r e v e n t frozen c h i p s or oversized o b j e c t s f r o m j a m m i n g c o n v e y o r s or o t h e r w i s e f o u l i n g h a n d l i n g e q u i p m e n t . Draft c o n v e y o r s installed beneath t h e hoppers discharge c h i p s t o i n c l i n e d belt c o n v e y o r s w h i c h elevate t h e w o o d fuel t o storage bunkers s i t u a t e d above t h e p o w e r plant boilers. Chips are c o n t i n u o u s l y f e d t o t h e boiler feeders t o provide a d e q u a t e fuel s u p p l y .


476


ELECTRIC G E N E R A T I O N S Y S T E M W o o d is basically a cellulose fiber a n d its c o m b u s t i o n t e c h n o l o g y is w e l l e s t a b l i s h e d . T h e p a p e r a n d p u l p i n d u s t r y for years has been b u r n i n g bark; t h e l u m b e r i n d u s t r y b u r n s s a w d u s t ; a n d m a n y f o o d p r o c e s s i n g industries have years of e x p e r i e n c e in t h e c o m b u s t i o n of cellulosic fiber. T h e r e f o r e t h e


p r i m a r y p r o b l e m in t h e large scale g e n e r a t i o n of e l e c t r i c i t y f r o m w o o d w a s t e is n o t c o m b u s t i o n , b u t t h e g a t h e r i n g a n d t r a n s p o r t a t i o n of t h e w o o d f u e l . T h e p r i m a r y c o n c e r n of w o o d fuel c o m b u s t i o n is t h a t it has a h i g h m o i s t u r e c o n t e n t w h i c h reduces h e a t i n g values a n d i n f l u e n c e s c o m b u s t i o n t e m p e r a tures a n d o t h e r f u r n a c e p a r a m e t e r s . T h e basic f u n d a m e n t a l s of w o o d w a s t e c o m b u s t i o n entail three c o n s e c u t i v e stages: t h e e v a p o r a t i o n of m o i s t u r e , t h e d i s t i l l a t i o n a n d b u r n i n g of volatile m a t t e r , a n d t h e c o m b u s t i o n of t h e f i x e d c a r b o n . In t h e f u r n a c e c o m b u s t i o n c h a m b e r , r a d i a t i o n a n d c o n v e c t i v e heat i n p u t evaporates t h e w o o d ' s m o i s t u r e a n d distills t h e v o l a t i l e matter. T h e e v a p o r a t i o n of m o i s t u r e t o s t e a m takes a p p r o x i m a t e l y 1 1 0 0 B t u / l b of m o i s t u r e . O n c e m o i s t u r e has been e v a p o r a t e d , heat is a b s o r b e d by t h e fuel particles t h u s d r i v i n g off v o l a t i l e matter. T h e v o l a t i l e m a t t e r b u r n s in a s e c o n d a r y c o m b u s t i o n r e a c t i o n w i t h i n t h e f u r n a c e c h a m b e r , b u t e x t e r n a l t o t h e a c t u a l w o o d fiber. Finally, t h e f i x e d c a r b o n of t h e w o o d b u r n s in t h e p r i m a r y c o m b u s t i o n reaction in c o n j u n c t i o n w i t h c o m b u s t i o n air. T h e m o s t e f f i c i e n t m e t h o d of w o o d w a s t e c o m b u s t i o n in t h e 5 0 M W p o w e r p l a n t size p r o p o s e d for B u r l i n g t o n is by use of a t r a v e l l i n g - g r a t e spreaderstoker boiler. A single u n i t is m o r e e f f i c i e n t t h a n m u l t i p l e units. Boiler m a n u f a c t u r e r s i n d i c a t e t h a t t h e largest stoker size available limits t h e i n p u t of b u r n i n g w o o d in a single u n i t t o a p p r o x i m a t e l y 7 5 t o n / h r or 1 8 0 0 t o n / d a y . A s s u m i n g a 7 5 p e r c e n t p o w e r p l a n t c a p a c i t y factor, t h i s fuel i n p u t e q u a t e s t o a n o m i n a l 5 0 M W c a p a c i t y . T h e c a p a c i t y f a c t o r of 7 5 p e r c e n t m e a n s t h a t t h e u n i t w i l l operate o n an average of 7 5 p e r c e n t of its rated c a p a c i t y o n an a n n u a l basis. T h u s the p l a n t w o u l d average 3 7 , 5 0 0 k W on an a n n u a l basis. A c t u a l l y t h e p o w e r plant w o u l d p r o d u c e on an average over 4 0 , 0 0 0 k W / h r for j u s t over 8 , 0 0 0 hr of t h e year. This a l l o w s for 3 0 days of d o w n t i m e for m a i n t e n a n c e d u r i n g t h e year. T h e e n e r g y i n p u t r e q u i r e d t o s u p p l y t h i s e l e c t r i c g e n e r a t i o n c a p a c i t y e q u a t e s on a Btu basis t o a p p r o x i m a t e l y 4 7 0 , 0 0 0 t o n s of " g r e e n " w o o d c h i p s per year. The p r o p o s e d B u r l i n g t o n p l a n t i n c l u d e s a 5 0 M W c o n d e n s i n g t u r b i n e generator u n i t ; a 5 2 5 , 0 0 0 I b / h r boiler; a c o m p l e t e c o m p l e m e n t of s t a t i o n auxiliary, m e c h a n i c a l , a n d electrical e q u i p m e n t ; a n d a p o w e r t r a n s m i s s i o n s u b s t a t i o n . S t e a m f r o m t h e boiler is s u p p l i e d t o t h e t u r b i n e at a pressure of 1,250 p o u n d s a n d t e m p e r a t u r e of 9 5 0 ° F . A h y d r a u l i c ash h a n d l i n g s y s t e m c o n v e y s t h e ash f r o m t h e stoker s i t t i n g s a n d ash h o p p e r to a s y s t e m w h e r e it is d e w a t e r e d and t r u c k e d to


23.

SHEAHAN

All



landfill. W o o d has a n inherently l o w sulfur c o n t e n t a n d therefore poses n o p r o b l e m as a source o f sulfur d i o x i d e air emission. W o o d b u r n s at a l o w e r t e m p e r a t u r e t h a n fossil f u e l s ; a n d likewise, has a n i n h e r e n t l y l o w e r n i t r o g e n c o n t e n t t h a n fossil fuels. A s a result, w o o d c o m b u s t i o n p r o d u c e s l o w e r q u a n t i t i e s of n i t r o g e n oxides. T h e p r i m a r y air e m i s s i o n c o n c e r n f o r t h e w o o d fired p l a n t is p a r t i c u l a t e matter. M e c h a n i c a l c o l l e c t i o n a n d e l e c t r o s t a t i c p r e c i p i t a t i o n e q u i p m e n t is e x p e c t e d t o ensure c o m p l i a n c e w i t h p a r t i c u l a t e a n d s m o k e e m i s s i o n s t a n d a r d s (12.13). T h e s y s t e m operates o n a closed c o o l i n g s y s t e m a n d therefore t h e r e is n o t h e r m a l w a t e r d i s c h a r g e t o t h e a d j a c e n t river or nearby Lake C h a m p l a i n . COST ESTIMATES Estimates o f t h e c a p i t a l , o p e r a t i n g , a n d m a i n t e n a n c e costs of t h e p r o p o s e d 5 0 M W w o o d - f i r e d p o w e r p l a n t are p r e s e n t e d in Table III a n d are based o n c o n c e p t u a l d e s i g n c o n c e p t s . A l l costs are expressed in 1 9 7 7 dollars. The t o t a l c o n s t r u c t i o n cost e s t i m a t e w a s $ 4 6 , 2 2 7 , 0 0 0 .

T A B L E III. C A P I T A L C O S T E S T I M A T E FOR 50 M W WOOD-FIRED POWER PLANT A T BURLINGTON, VERMONT (All c o s t s e x p r e s s e d as $ 1 , 0 0 0 in 1 9 7 7 ) S t e a m Boiler

$8,820

Turbine System Mechanical Equipment

3,870 3,660

Electrical E q u i p m e n t Piping Site D e v e l o p m e n t Building - Structural W o o d Handling System

3,300 2,900 1,275 10,500 2,039

Chimney Substation, Interconnect

1.200 1,010

C o n t i n g e n c i e s , E n g i n e e r i n g , Legal T o t a l Capital Cost

7,653 $46,227


478


The p r o p o s e d p o w e r plant w i l l p r o d u c e a gross of 3 2 8 , 5 0 0 M W - h r a n n u a l l y or a net of 3 0 2 , 2 0 0 M W - h r (8 p e r c e n t i n - p l a n t use) o p e r a t i n g at a 7 5 p e r c e n t c a p a c i t y factor. It w i l l c o n s u m e a p p r o x i m a t e l y 4 7 0 , 0 0 0 green tons of w o o d c h i p s w h i c h is 100 p e r c e n t of t h e energy input. Based on t h e p r e v i o u s l y d e r i v e d cost of f u e l of $ 1 1 . 9 9 / t o n , t h e t o t a l a n n u a l fuel cost w i l l be a p p r o x i m a t e l y $ 5 , 6 3 5 , 0 0 0 . Plant o p e r a t i o n w a s e s t i m a t e d t o require a staff of 4 2 w i t h an a n n u a l payroll of $ 7 1 4 , 0 0 0 . A n n u a l m a i n t e n a n c e , c h e m i c a l a n d s u p p l y costs, a n d o p e r a t i o n a n d m a i n t e n a n c e for t h e fuel off l o a d i n g a n d h a n d l i n g s y s t e m w a s e s t i m a t e d t o be $ 7 2 7 , 0 0 0 / y r . T h e e s t i m a t e d t o t a l o p e r a t i n g a n d m a i n t e n a n c e c o s t for t h e p o w e r plant is $ 7 , 0 7 6 , 0 0 0 / y r .


Annual Cost Projection It w a s a s s u m e d t h a t t h e p o w e r p l a n t w i l l be f i n a n c e d f r o m revenue b o n d i n g . Therefore, reasonable e s t i m a t e s w e r e m a d e for interest o n b o n d s , interest earned a n d e x p e n d e d d u r i n g c o n s t r u c t i o n , a n d b o n d d i s c o u n t s . W o r k i n g capital a n d t h e d e b t reserve f u n d w e r e a s s u m e d t o be capitalized. By p r o j e c t i n g all c a p i t a l a n d o p e r a t i n g costs w i t h reasonable escalation f a c t o r s , a life-cycle cost analysis w a s p e r f o r m e d . Results of t h a t analysis s h o w n b e l o w indicate an e s t i m a t e of required revenues t o offset all costs. These p r o j e c t e d costs are favorable w h e n c o m p a r e d t o a l t e r n a t i v e fossil fuel u n i t costs p r o j e c t e d for t h e N e w England region.

Year Unit Cost (cents/kWhr) 1982 1984 1986 1988 1990

5.1 5.5 5.9 6.4 6.9

INSTITUTIONAL CONSIDERATIONS A c c o r d i n g t o o u r analysis, t h e g e n e r a t i o n of e l e c t r i c i t y f r o m w o o d w a s t e is t e c h n i c a l l y feasible a n d e c o n o m i c a l l y a t t r a c t i v e . The m o s t d i f f i c u l t p r o b l e m in i m p l e m e n t i n g a w o o d - f i r e d p o w e r plant is perceived as being of i n s t i t u t i o n a l nature. These c o n c e r n s are p r i m a r i l y associated w i t h forest m a n a g e m e n t , t h e economy, and environmental considerations.


23.

SHEAHAN


479


Forest M a n a g e m e n t A forest is like a g a r d e n w h i c h needs t o be w e e d e d t o p r o m o t e a s o u n d a n d h e a l t h y s t a n d o f t i m b e r . Currently, there is no large-scale m e t h o d o l o g y t o remove n o n - c o m m e r c i a l w e e d trees w h i c h c o m p e t e f o r t h e s u p p l y o f w a t e r , n u t r i e n t s , a n d s u n l i g h t w i t h i n t h e forest. D e v e l o p m e n t o f a l o n g - t e r m w a s t e w o o d d e m a n d f o r electric g e n e r a t i o n c o u l d create a w a y t o better m a n a g e t h e forest's t i m b e r . A basic c o n c e r n t h a t a l w a y s a c c o m p a n i e s t h e d e v e l o p m e n t of any large forest-based i n d u s t r y is t h e p o t e n t i a l f o r abuse. It is therefore m a n d a t o r y t h a t a p o w e r plant n o t be s u p p l i e d w i t h w o o d at t h e expense of d e g r a d i n g or d e n u d i n g t h e forest. T o alleviate this c o n c e r n , it is r e c o m m e n d e d t h a t t h e personnel responsible f o r w o o d a c q u i s i t i o n m u s t be qualified professional foresters. In a d d i t i o n t o being in c h a r g e of w o o d w a s t e a c q u i s i t i o n , t h e y c o u l d also be available f o r private land o w n e r c o n s u l t a t i o n . This is p a r t i c u l a r l y i m p o r t a n t in V e r m o n t , since 9 0 p e r c e n t of t h e c o m m e r c i a l forest acreage is in private o w n e r s h i p . This t y p e of personnel a r r a n g e m e n t is similar t o t h e c o o p e r a t i v e assistance p r o g r a m s w h i c h are c o m m o n p l a c e in t h e p u l p a n d paper industry. T h e a c q u i s i t i o n personnel w o u l d be responsible for m o n i t o r i n g w o o d w a s t e deliveries t o a v o i d w a s t e f u l operations. T h e y w o u l d have t w o p r i m a r y c o n c e r n s . T h e first is t o ensure t h a t d i f f e r e n t i a t i o n is m a d e b e t w e e n h i g h q u a l i t y a n d l o w q u a l i t y material so t h a t q u a l i t y s a w t i m b e r a n d veneer logs are n o t c h i p p e d f o r fuel w o o d . T h e s e c o n d c o n c e r n is t o m a n d a t e t h a t small trees be carefully e v a l u a t e d before m a r k e t i n g f o r harvest. M a n y y o u n g trees m a y b e c o m e v a l u a b l e stock if g i v e n s u f f i c i e n t t i m e . In V e r m o n t , t h e p r i m a r y o w n e r s h i p o b j e c t i v e s o f t i m b e r land are recreation a n d place of residence; t i m b e r p r o d u c t i o n ranks t h i r d (14). Therefore, personnel responsible f o r w o o d w a s t e p r o c u r e m e n t s h o u l d recognize t h i s f a c t a n d p r e s c r i b e a n d e n c o u r a g e forest m a n a g e m e n t p r o c e d u r e s w h i c h m i n i m i z e a n y d i s r u p t i o n s t o t h e o w n e r s ' values a n d objectives. Economy T h e o p e r a t i o n o f a 5 0 M W w o o d - f i r e d p o w e r plant c o u l d have s i g n i f i c a n t a n d positive i m p a c t s o n V e r m o n t a n d t h e City of B u r l i n g t o n . The f o l l o w i n g are a f e w of t h e potential impacts: • The creation of a long-term and consistent demand for non-merchantable w o o d w a s t e c o u l d result in d r a m a t i c a l l y higher y i e l d f o r land parcels; therefore m a n y areas w h i c h previously h a d m a r g i n a l h a r v e s t i n g p o t e n t i a l c o u l d b e c o m e f i n a n c i a l l y viable.


480


• T h e e x i s t i n g forest p r o d u c t i n d u s t r y c o u l d e x p e r i e n c e a l o n g - t e r m general u p g r a d i n g , faster g r o w i n g a n d healthier forest d u e t o t h e r e m o v a l of nutrient-depleting waste wood.


• Private land o w n e r s c o u l d realize an i n c o m e f r o m t h e s t u m p a g e (price p a i d for t h e r e m o v a l of t h e w o o d ) w h i c h c o u l d help offset t h e effects of p r o p e r t y taxes. • V e r m o n t a n d t h e City of B u r l i n g t o n w o u l d b e c o m e m o r e self-sufficient in t h e i r e n e r g y resources, t h u s o f f s e t t i n g t h e r e q u i r e m e n t s for p r e d o m i n a n t l y i m p o r t e d fossil fuels. L i k e w i s e t h e s t a t e w i d e balance of p a y m e n t s w o u l d be i m p r o v e d by t h e r e d u c t i o n of i m p o r t e d energy. • T h e e c o n o m i c m u l t i p l i e r effect a p p l i e d t o t h e m o n e y kept in V e r m o n t , plus t h e general e x p a n s i o n of t h e forest-based i n d u s t r y c o u l d result in a s u b s t a n t i a l i m p a c t o n t h e City a n d State e c o n o m i e s . Environmental Concerns S o m e of t h e p r i m a r y e n v i r o n m e n t a l c o n c e r n s associated w i t h t h e h a r v e s t i n g of w o o d w a s t e f r o m a forested area i n c l u d e , b u t are not l i m i t e d t o , soil erosion, n u t r i e n t d e p l e t i o n , a e s t h e t i c d e g r a d a t i o n , r e d u c e d w a t e r q u a l i t y , a n d d e t e r i o r a t i o n of w i l d l i f e habitat. W i t h p r u d e n t h a r v e s t i n g m a n a g e m e n t p r o c e d u r e s , s u c h d a m a g e need n o t h a p p e n , a n d in fact, t h e e n v i r o n m e n t c o u l d be e n h a n c e d by t h e process. T h e forest is a l w a y s s u b j e c t t o insect a t t a c k s , disease infestations, a n d w i l d fire. Dense s t a n d s of o v e r m a t u r e trees are h i g h l y s u s c e p t i b l e t o insect or disease outbreaks. O n c e e s t a b l i s h e d , t h e y c a n spread easily t h r o u g h s u c h stands. Resistance of t h e forest d e p e n d s d r a m a t i c a l l y o n t h e species c o m p o s i t i o n , size d i s t r i b u t i o n , d e n s i t y , a n d general health of t h e tree. If trees are l a b o r i n g u n d e r o l d age a n d severe n u t r i e n t c o m p e t i t i o n caused by h i g h d e n s i t y , t h e general forest w i l l m o s t likely be seriously d a m a g e d . O n c e a s u b s t a n t i a l p o r t i o n of t h e t i m b e r is d e a d or r o t t e n , dry s u m m e r days c a n t r a n s f o r m t h e forest i n t o a h a v e n for disease o u t b r e a k a n d spread of fire. P r o v i d i n g a m a r k e t for l o w q u a l i t y m a t e r i a l c a n p r o v i d e a m e c h a n i s m for u p g r a d i n g t h e h e a l t h of t h e residual trees. F u r t h e r m o r e , l o g g i n g roads p r o v i d e access for p r o t e c t i o n as w e l l as recreation. W i l d l i f e needs an a d e q u a t e f o o d s u p p l y as w e l l as p r o t e c t i v e cover. Dense, o v e r m a t u r e trees m a y p r o v i d e p r o t e c t i o n a n d f o o d for s o m e b u t n o t m o s t of the w i l d l i f e species because t h e r e is relatively little p r o t e c t i o n of f o o d at g r o u n d level. S t u m p s , tree t o p s , a n d l i m b s w h i c h a c c o m p a n y c o n v e n t i o n a l h a r v e s t i n g o p e r a t i o n s are h a v e n s of p r o t e c t i o n for m a n y w i l d l i f e species. N e w g r o w t h t h a t f o l l o w s h a r v e s t i n g o p e r a t i o n s also represents an a b u n d a n t a n d c o n v e n i e n t f o o d source for w i l d l i f e . Therefore, it is i m p o r t a n t


23.

SHEAHAN


481

t h a t in a h a r v e s t i n g o p e r a t i o n , a balance be p r o v i d e d b e t w e e n n e w g r o w t h a n d m a t u r e stands w i t h a s u b s t a n t i a l a m o u n t o f t r a n s i t i o n b e t w e e n t h e t w o . This is a desired w i l d l i f e m a n a g e m e n t o b j e c t i v e .


T h e nature o f t h e w o o d d e m a n d o f a p o w e r plant is likely t o result in more m e c h a n i z e d harvesting operations, a n d e x p a n s i o n as a n t i c i p a t e d in t h e p u r c h a s e a n d use o f w h o l e tree c h i p p e r s , a n d t o a lesser e x t e n t , m e c h a n i c a l h a r v e s t i n g e q u i p m e n t . Care m u s t be a p p l i e d in t h e selection a n d use o f this t y p e o f e q u i p m e n t o t h e r w i s e t h e large r u b b e r w h e e l s or tracks c o u l d b e c o m e a serious source of soil erosion. T h e n e g a t i v e c o n n o t a t i o n s associated w i t h t h i s t y p e o f p r o b l e m c o u l d q u i c k l y d i s c o u r a g e t h e c o o p e r a t i o n of private l a n d o w n e r s in a l l o w i n g w o o d w a s t e removal. SUMMARY Generation of e l e c t r i c i t y f r o m w a s t e w o o d is t e c h n i c a l l y , e c o n o m i c a l l y , a n d e n v i r o n m e n t a l l y feasible. A brief o v e r v i e w of p r i m a r y c o n c e r n s w h i c h a n y o r g a n i z a t i o n or c o m m u n i t y s h o u l d c o n s i d e r in i m p l e m e n t i n g s u c h a f a c i l i t y is presented. A s a n e p i l o g u e , t h e City of B r u l i n g t o n c o n d u c t e d a successful b o n d i n g r e f e r e n d u m f o r c o n s t r u c t i o n of t h e 5 0 M W w o o d - f i r e d p o w e r plant. By t h e s u m m e r o f 1 9 7 9 , d e s i g n w a s w e l l u n d e r w a y a n d plans f o r implementing construction were being formulated.

REFERENCES

1.

Henningson, Durham & Richardson, Inc. "Burlington, Vermont Refuse-Wood Power Plant, Aquaculture, Greenhouse - A Conceptual Study"; Washington D.C.; 1977.

2.

Ellis, T. Paper presented at the Forest Products Research Society Energy Workshop; FPRS Proceedings P-75-13; Denver, Colo., 1976.

3.

North Central Forest Experiment Station Forest Service; U.S. Department of Agriculture. Forest Residue Energy Program; St. Paul, Minn., 1978. Christensen, G. Paper presented at the Forest Products Research Society Energy Workshop; FPRS Proceedings P-75-13; Denver, Colo., 1976.

4.

5.

Corder, S. "Fuel Characteristics of Wood and Bark and Factors Affecting Heat Recovery"; ibid.



482

BIOMASS AS A NONFOSSIL FUEL SOURCE

6.

Hewett, C. DSD No. 114; Thayer School Engineering, Dartmouth College: Hanover, NH, 1978.

7.

Blankenhorn, P.; Bowersox, T.; Murphey, W. Tappi 1978 61, 4.

8.

Towne, R. Paper presented at Forest Products Research Society Energy Workshop; FPRS Proceedings P-75-13; Denver, Colo. 1976.

9.

Hoff, E. "Abstracts of Papers:, the Conference on Energy and the Wood Products Industry sponsored by the Forest Products Research Society, Atlanta, Ga., 1976.

10.

Fernandes, J. "Wood Energy Systems, State of the Art and Developing Technologies"; Paper presented at the Future of Wood as an Energy Source Conference, Gorham, Maine, 1976.

11.

Johnson, N. "Wood Waste Burning on a Traveling Grate Spreader Stoker"; Paper presented at conference Hardware for Energy Generation in the Forest Products Industry, Seattle, Washington, 1979.

12.

Costle, D. "Standards of Performance for New Stationary Sources, Wood Residue-Fired Steam Generators"; 40 CFR Part 60; Federal Register 44, 12, Jan. 17, 1979.

13.

Phelan, J. "Review of Particulate Equipment for Power Plant Effluents"; Tappi 1977 60, 9.

14.

Kingsley, N.; Birch, T. "The Forest-Lane Owners of New Hampshire and Vermont. USDA Forest Service Resource Bulletin 1977, NE-51.

RECEIVED M A Y 12, 1980.


Electric Power Generation from Wood Waste - American Chemical

Recommend Documents