polyethylene electrostatic test

8/13/2019 Polyethylene Electrostatic Test

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Bureau of Mines Report of Investigations/l986

Tri boelectric Effects on PolyethyleneMethane Drainage Pipelinesy A. A. Campoli J. Cervik and R L King

UNITED STATES DEPARTMENT OF THE INTERIOR


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Report of Investigations 9017

Tri boelectric Effects on PolyethyleneMethane Drainage PipelinesBy A A Campoli J. Cervik and R L King

UNITED STATES DEPARTMENT OF THE INTERIORDonald Paul Hodel SecretaryBUREAU OF MINESRobert C. Horton Director


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Library of Congress Cata login g in Pub l icat i on Da ta

C a m p o l i , A A ( A l a n A,)Triboelectr ic effec ts on polyethylene methane dra inage pipel ines .Report of inves tigat ions 9017)

Bibliography: p. 13- 14Supt. of Docs. no.: 28 .21 : 9017.1. Coalbed methane drainage. 2 Gas-Pipe line s. 3. Poly ethy-

lene. 4 Mine dusts. 5 Electr ic charge . 1. Lervik, Joseph. 11.King, Roger I*. 111 Title. IV. Seri es: Keport of inves tiga tionsUnited State s. Bureau of Mines) 9017.

TN2 3 ,U4 3 [ TN8 4 4 ,5 ] 6 2 2 s [ 6 2 2 .3 3 4 ] 8 6 - 6 0 0 0 0 3


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CONTENTS

AcknowledgmentsS t a t i c e l e c t r i c i t y and g as p ip in g s y s t e mLaboratory equipmentE l e c t r o s t a t i c t e s t p ro ce du re s~ a b o r a t o r ~e s u l t s~ i e l de s t ssummary and conc lus ions

ILLUSTRATIONSP i t o t t u b e b e i n g us e d t o m e as ur e g a s s tr e am v e l o c i t yRe la t iv e humidi ty and t empe ra ture be ing measured wi th psychromete rsHumidity chamberRock dust chamberM u lt ir an g e e l e c t r o s t a t i c v o lt m e t erG e ner a l c on f i gu r a t i on of p r obeAveraging d a t a f o r t h r e e e l e c t r o s t a t i c t e s t s

odel of c ap ac it an ce of measurement syste mComparison of pi pe da t a

f f e c t of v e l o c i t y v a r i a t i o nf f e c t of e xp os ur e t im e v a r i a t i o n

E f f e c t of d u s t s i z e v a r i a t i o nComparison of Pi t t sb ur gh and Coalburg CoalbedsC o n fi g ur a ti o n f o r e lbo w t e s tR e s u l t s of e lb ow t e s tE f f e c t o f hu m i di t y v a r i a t i o n sR e s u l t s o f g r ou n di ng e v a l u a t i o nR e s u l t s o f r oc k d u st i ng t e s tReal t ime ae ro so l moni torS in g le r an g e e l e c t r o s t a t i c v o l tm e t e r

T BLES

E f f e c t of w a l l t h i c k n e s s o n r e d u c t i o n o f i n t e r n a l c h a r g e u s i n g w et r agt e c hn i queC o a l a n a l y s i s

a r t i c l e s i z e d i s t r i b u t i o n of P i t t s b u r g h Co alb ed s am p le soc k dus t a na l y s i su st c on t a m ina t i on d a t a f o r m et ha ne d r a i na g e p i p e l i ne sRe s u l t s of r e a l t i m e e va l ua t i on of m et ha ne d r a i na ge p i pe l i ne s


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UNIT OF MEASURE ABBREVIATIONS USED N THIS REPORTc e n t i m e t e rd e g r e e C e l s i u sa n g u l a r d e g r e ede g r e e F a h r e nhe i tf o o tf o o t p e r m i n u t ec u b i c f o o t p e r d a yc u b i c f o o t p e r m i n u t egramgram per minutehorsepoweri n c hk i l og r a mk i l o \ . o l tk i l o p a s c a lk i l o w a t t

l b pound we ightl b f / i n 2 pound f o r c e pe r s qua r e i nc hm meterPm micrometermg/m3 mi l l ig ram per cu bi c mete rmin minutem m i l l i l i t e rmmMMPlFlft3/dm3m3/sPCtr a dv

m i l l i m e t e rm i l l i on c u b ic f e e tm i l l i o n c u b i c f e e t p e r d a yc ub i c m e t e rcubi c mete r pe r s econdpe r c e n tr a d i a nv o l t


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TRIBOELECTRIC EFFECTS ON POLYETHYLENE METHANE DRAINAGE PIPELINESB y A A Campol i , J ~ e r v i k ~nd R L in^^

ABSTRACTThe Bure au o f Mines pe rf o rm e d l a b o r a t o r y e xpe r i m e n t s t o e v a l ua t e t h e

t r i b o e l e c t r i c e f f e c t of p a r t i c u l a t e - l a d e n g a s s t r e a m s o n p o l y e t h y l e n ep i p e a t v a r i o u s v e l o c i t y , h u m i d i ty , d u s t - s i z e , and du s t- lo a d c o n d i t i o n s .Charges i n exce ss of 10 k w er e p r oduce d on t h e ou t s i d e a nd i n s i des u r f a c e s of l a b o r a t o r y p i p e s a m p le s , when ex p os ed t o 4 0 p c t r e l a t i v e hu-m i d i t y RH) gas s t rea m con ta in ing co a l du s t . However , no char ges werep ro du ce d i n l a b o r a t o ry t e s t s t h a t d u p l i c a t e d t h e o v e r 7 5 p c t RH anddu s t - f r e e ga s s t r e am s f ound i n w or k ing unde r gr ound p i pe l i n e s . Bar e c op -pe r w i r e , w hi ch i s wound a round th e po ly e thy lene p i pe i n a 1- f t 31-cm)s p a c i n g a nd g ro u nd ed , e l i m i n a t e d t h e c h a r g e on t h e o u t s i d e s u r f a c e oft h e p i p e , b u t n o t on t h e i n s i d e of t h e p i p e s u r fa c e ,

inin in e ng i ne e r .2 ~ u p e r v i s o r y e o p h y si c is t .3 ~ e s e a r c h u p e r v i so r .

P i t t s bu r gh Re s e ar c h Ce n t e r , Bur ea u of M i n e s , P i t t s b u r g h , PA .


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INTRODUCTIONThe Bureau o f Mines e s t ima tes tha t

a s much a s 766 t r i l l i o n c u b i c f e e t7 . 1 2 ~ 0 Om3) of co alb ed g a s , predomi-

n a n t l y m e t h a n e , i s c o n t a in e d i n t h e c o al -b e d s o f t h e U n i te d S t a t e s ( 1 ) . 4 T h i s g a si s b o th a n a t u r a l r e s o u r c e and a h i n-d r a n c e t o m in i ng . M et ha ne d r a i n a g e sy s -tems have been employed i n most majorc o a l r e g i o n s o f t h e U ni te d S t a t e s t o r e-move g a s f ro m t h e c o a l b ed p r i o r t o m i ni n ga n d /o r c a p t ur e t h e c o al be d g as f o r f u e l .

Methane d r a in ag e sys t ems employ ho r i -z o n t a l , v e r t i c a l , an d c r os s -m e as u re b or e-h o l e s . V e r t i c a l b o r eh o l e s y st em s 2)c o n s i s t o f h o l e s d r i l l e d f ro m t h e s u r f a c ei n t o t h e g a s- be ar in g c o a l s t r a t a . Theb o r e h o l e s a r e c a s e d w i t h m e t a l p i p e ,w hi ch p r o v i d es t h e c o n d u it f o r t h e f l owo f g a s f ro m t h e g as - be ar in g s t r a t a t ot h e s u r f a c e . H o r i z o n t a l (3) and c ross -measure 4 ) s y s te o s r e q u i r e t h e d r i l l i n go f b or e h o i es i n t o t h e co a lb e d o r a s s o c i -a t e d s t r a t a f ro m u nd er gr ou nd l o c a t i o n s .T he b o r e h o l e s a r e c n n n e c t ed t o a n u n de r-gr ou nd p i p e l i n e t h a t c a r r i e s t h e g a s t ot h e s u r f a c e.

Methane, which i s piped th rough minep ass ag ew ays i n q u a n t i t i e s s u f f i c i e n t t oc o n t a m in a t e l a r g e a r e a s of t h e m i ne , j u s -t i f i e s c a u t i o n an d co nc er n i n t h e d e s i g n ,i n s t a l l a t i o n , p r o t e c t i o n , and m a in te n an ce

o f t h e u n d er g ro u nd p i p e l i n e . B ot h t h eBureau (5 ) and t h e Mine S a fe ty and Hea l t h~ d m i n i s t r a t i o nMSHA) , U S Department ofLab or ( 6 ) , o u t l i n e d p r oc ed u re s f o r t h es a f e o p e r a t i o n o f u n de rg r ou n d m et ha ned r a i n a g e p i p e l i n e s . T he se r e p o r t s s h o u l db e c o n su l t e d f o r a g e n e r a l o v e rv i e w o fp i p e l i n e p r o t e c t i o n r e qu i re m e nt s .

The Bu re au s t u d y ( 5 ) p r o v i d e d t h e b a s i sf o r t h e p i p e l i n e m a t e r i a l s e l e c t i o n .P o l y e t h yl e n e p i p e b e s t m ee ts t h e d e s i g nc r i t e r i o n b ec au s e of i t s s u p e r io r r e s i s t -a n c e t o c o r r o s i o n an d i mp a ct f o r c e s . I ta l s o i s a t t r a c t i v e t o mine o p e r a t o r s be-c a u s e t i s l ig h tw e ig h t , e a s y t o i n s t a l l ,a nd s i g n i f i c a n t l y c he ap e r t h a n m e ta lp i p i n g .

I n a n a t t e m p t t o n e g a t e a ny h a z a r dp ro du ce d by t h e t r i b o e l e c t r i f i c a t i o n o fpol yet hyl ene pi pe , MSHA recommends th a t ag ro un de d b a r e c o pp er w i r e b e s p i r a l l ywound a r ou n d a l l p o l y e t h y l e n e p i p i n g .The recommendat ion was in co rp or a te d i nmany of t h e methane dr ai na ge syst ems nowi n p l a c e a c r o s s t h e U n it ed S t a t e s . Theo b j e c t i v e s o f t h i s s t u d y were t o o b t a i n ab e t t e r u nd er s ta n di ng o f t h e t r i b o e l e c t r i -f i c a t i o n p r oc es s a s i t r e l a t e s t o t h e un-de rground po lye thy len e me thane d r a in ag ep i p e l i n e a nd t o e v a l u a t e t h e r ecommendedg r o un d i ng s a f e t y p r o ce d u re .

ACKNOWLEDGMENTSThe au t ho rs wi sh t o than k Dona ld D uva l l

o f P l ex c o P i p e , J o h n M e r id e th of P h i l l i p sDr i s c o P i p e , a nd Jo se p h Uh l e r o f t h eE q u i t a b l e Gas Co. f o r t h e p i p e s a m pl e st h e y p ro v id e d f o r l a b o r a t o r y t e s t i n g .

J a c k Workman of Workman De vel opm ent sa n d R o be r t R e i f , f o r m e r ly of t h e B a t t e l l eM em or ia l I n s t i t u t e , d o n a t e d much a p p r e c i -a t e d t e c h n i c a l a s s i s t a n c e on po l y e th y l e n e

p i p e m a nu f ac tu re a nd s t a t i c c h ar g e t e s t -i n g , r e s p e c t i v e l y .

The e f f o r t s o f Jo hn S t e ve n son o f J i mW a l t e r R e sou r c es I n c . , Dave F i t z p a t r i c kof Bec kle y Mini ng Co., and Dan Weaver oft h e BethEnergy Mines In c . were inst rumen-t a l i n t h e pe rf o rm a nc e o f me th an e d r a i n -a ge p i p e li n e e v a l u at i o n s i n t h e f i e l d .

STATIC ELECTRICITY AND GAS-PIPING SYSTEMSTo t h e a v e r a g e p e r so n t h e wo r d s, s t a t - w al ki ng a c r o s s a c a r p et e d f l o o r , n o i s e i n

i c e l e c t r i c i t y , mean t h e s ho ck e x pe r i- a r a d i o r e c e i v e r , o r t h e t en de nc y f o renced when touch ing a doorknob a f t e r c l o t he s t o c l i n g o r s t i c k t i g h t l y . Near-

l y eve ryone recog nizes t h a t t h es e phenom-4 ~ n d e r l i n e d umbers i n p a r e n th e s e s re ena a r e more i n t en se when wea the r i s d r y .

f e r t o i t e m s i n t h e l i s t of r ef e r en ce s a t I n most s i t u a t i o n s , s t a t i c e l e c t r i c i t y i st h e e nd o f t h i s r e p o r t . s i m pl y a n a nn oy an ce .


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The t er m e l e c t r i c i t y s de r i ve d f r omt h e an c i en t Greek word e l ec t r on meaning

amber, because t w as w i t h t h i s s ub -s t a n c e t h a t t h e phenomenon o f e l e c t r i -f i c a t i o n was f i r s t o b s er v ed . F or c en -t u r i e s , t h e t e rm m ean t o n l y w ha t s nowc a l l ed s t a t i c e l e c t r i c i t y , t h e p ro pe rt ye x h i b i t e d by some s u b s t a n c e s a f t e r b e i n gr ub be d w i t h m a t e r i a l l i k e s i l k o r woolo f b ei ng a b l e t o a t t r a c t o r r e p e l l i g h t -w e i gh t ob j e c t s . M e c han i z at i on pr oduc eds t ro n g er e l e c t r i f i c a t i o n t h a t was f i r s to b s er v e d a b o u t 300 y e a r s a go ( 7 ) , a nd i nc om pa r a t i ve ly r e c e n t t i m e s , tGe p r oper -t i e s o f f lo wi ng e l e c t r i c i t y w er e d i s -c ove r e d ; t h e word s t a t i c t he n came i n t ou s e a s a means of d i s t i n g u i s h i n g t h e twof or ms . The i m p l i c a t i o n t h a t s t a t i c e l e c -t r i c i t y s alw ay s a t r e s t s e r r o n e o u s ,b e ca u se s u c h e l e c t r i c i t y ca u s e s t h e m ostconcern when t c ea se s t o r e s t .

F o r t h e s a ke o f s i m p l i c i t y , one mayi ma gin e e l e c t r i c i t y t o be a w e i g h t l e s sa nd i n d e s t r u c t i b l e f l u i d t h a t c an movef r e e l y t h ro u gh some s u b s t a n c e s , s u c h a sm e t a l s , t h a t a r e c a l l e d c o nd u ct o rs , b u tc an f low w it h d i f f i c u l t y o r n ot a t a l lt h ro u gh o r o v e r t h e s u r f a c e of a c l a s s ofs u b s t a n c e s c a l l e d n o nc o nd u ct o rs o r i n -s u l a t o r s . T hi s l a t t e r g ro up i n c lu d e sg a s e s , g l a s s , r u b b e r , a mb er, r e s i n , s u l -f u r , p a r a f f i n , most d r y p et ro le um o i l s ,a n d many p l a s t i c m a t e r i a l s s u c h a s p ol y-e t h y l e n e p i p e . When e l e c t r i c i t y s pr e s -e n t on t h e s u r f a c e of a nonc onduc ti vebody, where t s prevented f rom escap-i n g , t s c a l l e d s t a t i c e l e c t r i c i t y .E l e c t r i c i t y o n a c o n d uc t in g body t h a t si n c o n t a c t o nl y w i th i n s u l a t o r s s a l s op r e ve n t e d fr om e s c a p i ng a nd s t h e r e f o r en onm obile o r s t a t i c . I n e i t h e r c a s e , t h ebody on wh ich t h i s e l e c t r i c i t y s e v i d e n ts s a i d t o be c h ar g ed ( 7 ) .

S t a t i c c h a r g es o n p o l y e t h yl e n e g a s d i s -t r i b u t i o n p i p e l i n e s h av e lo n g be en a con-c e r n t o n a t u r a l g as u t i l i t i e s and p i p ema nuf act ure rs (8-9) . Of pr imary conc erns t h e b e l l h o le f i r e c au se d by s t a t i c

e l e c t r i c i t y . b e l l h o l e s dug arounda damaged s e c t i o n o f a bu r i e d ga s t r a ns -m i s si o n p i p e t o p r o v id e a c c e s s f o r r e -p a i r . S p ar k s f ro m t h e p i p e c a n i g n i t ee x p l o s i v e m i x t u re s of t h e n a r u r a l g a s a nda i r when t h e w ork er e n t e r s t h e b e l l

h o l e w i t h a t o o l t o s q ue e ze o f f t h ep l a s t i c p ip e .

In th e prec edin g example , cha r ges wereg e n e r a t e d by t h e e x t re m e ly h i g h v e l o c i t yga s f l ow t h r ough a r up t u r e . Char ge s a l s oo c c ur a t l ow er v e l o c i t i e s by t h e a d d i t i o nof a p a r t i c u l a t e m a t t e r 9) . Whetherg e n e r a t e d by r u p t u r e l e a k s o r d u s t - l a d eng as f l o ws , t h e s t a t i c ch a rg e s a r e t h e r e -s u l t o f t r i b o e l e c t r i f i c a t i o n . Gas mole-c u l e s a nd p a r t i c u l a t e s v i g o r o u sl y r u b t h es u r f a c e o f t h e p i p e c a u si n g a t r a n s f e r o fe l e c t r o n s t o t h e n o nc o nd u ct iv e p i p e .Conduct i ve p i pe u s e d i n t h e s ame a pp l i c a -t i o n w ou ld no t c hange t h e c ha r g i ng p ro -ces s ; however , t would provide a pa t hf o r t h e t r i b o e l e c t r i c i t y t o g round.

The wet-rag tec hni qu e s a c c e p t e d a st h e b a s i c s a f e t y p r o ce d u r e f o r r em ov alof s t a t i c e l e c t r i c i t y p r i o r t o r e p a i r ofpo l ye t hy l e ne ga s p i p e l i ne s . Wet r a g s a r ew ra pp ed a r ou n d t h e p i p e t o i n c r e a s e t h es u r f a c e c o n d u c t i v i t y . T h i s i n c r e a s e i nc o n d u c t i v i t y c a us ed by t h e a d d i t i o n o fm o i s t u r e d o e s n o t e l i m i n a t e t h e c ha rg e-generat ion mechanism; t o n l y p r o v i d e s ap a th t o ground f o r t h e s t a t i c e l e c r i c i t y .The technique s q u i t e e f f e c t i v e i n r e-m ov ing t h e c ha r ge f rom t h e ou t s i de s u r -fa ce (9 ) . However , t s e f f e c t i v e n e s s i nrem oviZg c h a r g e s f ro m t h e i n s i d e s u r f a c es a d v e r s e l y e f f e c t e d by p i p e w a l l t h i c k -n e s s . T a b l e 1 sho ws t h a t a s w a l l t h i c k -

ne s s i n c r e a s e s , t h e w e t- r ag t e c hn i que be-comes l e s s e f f e c t i v e i n rem oving s t a t i cc h a rg e s f ro m t h e i n s i d e s u r f a c e of t h ep i pe 9) . Most methane dr ai na ge pipe-l i n e s a r e 4 i n ( 1 0 cm) o r l a r g e r . A lt ho u gh n o d a t a a r e p r e s e n t ed o n t h e 4 i n

TABLE 1. E ff ec t of wa l l th ic kn es son r e d u c t i o n of i n t e r n a l c h a rg eus i ng we t -r a g t e c hn i que

W a l l I n t e r n a lP ip e s i z e , i n t h i c k n e s s , d i s c h a r g e ,

B .76 NANA N ot a va i l a b l e .


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1 0 cm) o r l a r g e r p i p e s i z e s , t h e g e n e r a lt r e n d i s a r e d uc t i o n i n e f f e c t i v e n e s s o fou t s i de g rounding i n r em ov ing i n s i de su r -f ace charges .

The polyethylene pipe employed i n c o almine methane drainage i s th e same a sth e p ipe u sed by t h e na tu r a l gas i ndus -t r y ; how eve r, t h e g a s f lo w v e l o c i t i e sa nd p i p e l i n e e nv ir on me nt a r e d i f f e r e n t .Coalbed methane dra i nag e systems u t i l i z eth e na tu ra l coa lbed p res su re t o move t h eg a s , and p i p e l i n e p r e s s u re s a r e g e n e r a l l y5 l b f / i n 2 3 4 k Pa ) o r l ess compared withm ore t han 30 l b f / i n 2 207 kPa) i n na tu ra lgas t ransmiss ion sys tems . Consequent ly ,much h i g h e r v e l o c i t i e s a nd t h e p o s s i b i l -i t y of e x tr em e v e l o c i t i e s d ue t o p i n h ol e

LABORATORYLaboratory app ara tus was assembled t o

s i m u l a t e a v a r i e t y of v e l o c i t y , d u s t c on-c e n t r a t i o n , and h um id it y c o n d i t i o n s i nand around poly eth ylen e pipe samples . A50-hp 37-kW) , 7 4 0 4 3/mi n 0.35-m3/s)wa te r- ri ng vacuum pump was use d t o gen-e r a t e t he a i r s t r ea m th rough t he p ipe sam-pl es . Gas-st ream v e lo c i t ie s were mea-s u r e d w i th a p i t o t t u be f i g . l , andr e l a t i v e hum idi t y and t em pera tu re weremeasured wi th psychrometers f i g . 2)Pi pe samples were connected t o t h e pumpwi t h 6- in 15-cm) f l e x i b l e suc t io n tub-i n g . P a r t i c u l a t e s were hand- fed i n to t h ei n l e t end of t he p ipe s amples.

Four ty pe s of medium-density polyet hy-l e n e p i p e u se d f o r g a s t r a n s i s s i o n we rete st ed : DuPont type 2, Drisco type 2,Dris co typ e 3, and Plexco type 3. Type 2p i p e i s orange . Type 3 i s black owing t oth e ad di t i on of carbon b lac k , which pre-ven ts t h e development of b r i t t l e ne ss whent h e p i pe i s exposed t o u l t r a v i o l e t l i g h t .Thus, ca r e must be t aken i n t h e s t o r ageo f t h e t y p e 2 p i p e b ec au se s t r u c t u r a ldegrada t ion may re su l t . Owing t o th epr op r i e t ar y natu re of th e chemical con-s i s t of po lye thy l ene p ipe , no fu r t h e r i n -fo rm ation cou ld be ob t a ined r ega rd ing t hecomposi t ion of th e pipe samples .

The p a r t i c u l a t e s u se d i n t h e l a b o r a t o r yt e s t s were c rushed co a l f rom th e P i t t s -burgh and Coalburg Coalbeds, l ime ston erock dus t . i ro n f i l i n gs . and s and. Tabl e

l e a k s e x i s t i n n a t u r a l g a s s ys te ms . Thep a r t i c u l a r m a t t e r of co nc er n i n n a t u r a lgas sys tems i s r u s t s c a l e t h a t i s car-r i e d f ro m m e t a l l i n e s i n t o p o l ye t h y le n el i nes . R us t i s no t a concern i n coa lbedmethane drai nage because th e pi pe i s a l lp l as t i c . However, coa l dus t f rom hor i -z o n t a l b o re h ol e s o r r oc k p a r t i c l e s f ro mcross-measure boreholes ar e a pos s ib i l -i t y . F i n a l l y , t h e p o ly e th y le n e p i p e i sbur i ed i n na tu ra l gas sys tem s and i s ex-posed i n m ethane d ra inage app l i ca t i ons .Thus, e l ec t r o s t a t i c haza rds a r e pa ramoun ti n r e p a i r s i t u a t i o n s o nly i n n a t u r a l g a ssystems , but could be a concern through-o u t t h e l i f e of a p i p e l i n e us ed f o r c oa l-bed me thane dra inage.

EQUIPMENTre ct an gu la r wooden frame, 8 by 8 by

24 f t 2.4 by 2.4 by 7.3 m), was co ve re dw i th c l e a r p l a s t i c t o p ro vi de f o r ava r i a b l e humid it y env ironment f i g . 3 ) .

.2 shows th e proximate and u l t im ate analy- F I G U R E 1 P i to t tu b e b e in g u sed to m easu re g ass i s of t h e two crushed coa l samples . s t re a m v e l o c i t y .


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Steam and a i r were drawn i n t o th e chamberby th e p a r t i a l vacuum genera ted by th epump. The s team and a i r in ta ke fo r th ec hamb er w er e l o c a t e d a t t h e f a r c o r n e rfrom t h e pi pe sample int ak e. The humid-i t y and tem peratu re i n s i de and sur round-in g t h e p ipe s am ple were i d e n t i c a l d u r -i n g o p e r a t i o n f i g . 3 ).The rock dust i s blown i n t o r e t u r n a i r -ways i n c o a l m in es t o r e n d er l o o s e c o a ldu s t incombus t ib le . To determine i f rockd u s t i n g p r oc e du r es c o ul d i m pa r t a s t a t i ccharge t o a po lyeth ylene methane dra inag ep i p e l i n e , a 2- by 2- by 8- ft 0.6- by0.6- by 2.4-m) chamber was co ns tr uc te d t os im u la t e such p rocedures f i g . 4 ) . Thechamber provided f o r t h e movement of roc kdu s t over and around th e p ip el i ne . Ve-l o c i t y wi th in th e chamber was measuredw it h a vane anemometer. A door was lo-ca t e d on t h e t op pane l of t h e rock dus t

TABLE 2 C oal ana lys i s , pe rcen t

chamber no t shown on f ig u re 4) t o pro-v i d e a c c e s s t o t h e chamber f o r s u r f a c echa rge measurement. S t a t i c cha rge mea-surements were made with a high-impedance5x1015-ohm) vo ltm et er f ig . 5). The me-

t e r i s vo l t age opera t ed .

Scale ft inlet

P i t t s b u r g h2.9

35.753.7

7.7100.0

5.375.51.51.18.97.7

100.0

Analys i sProximate:

Moisture.........V o l a t i l e m a tt e r. .Fixed carbon.....Ash..............Tota l . .

Ul t imate:.........ydrogenCarbon...........

Nitrogen.........Sulfur...........Oxygen...........ASh

Total.........

FIGURE 2 Rel ati ve humidity and temperature being measured with psychrometers.

Coalburg3.227.0

39.430.4

100.04.0

54.58110.2

30.4100.0

FIGURE 3 Humid ity chamber.

ock dust andair inlet 0 I

pumpFIGURE 4 Rock dust chamber.


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ELECTROSTATIC TEST PROCEDURESEven th ou gh t h e e l e c t r o s t a t i c v o l t -

me te r consumed ver y l i t t l e c u r r e n t d u et o i t s high impedance, a charg e co ll ec -t i o n d e v i c e was r e q u i r e d t o p r o vi d e s u f -f i c i e n t ch arge t o a c t i v a t e t h e i n s t r u -m e n t . I n i t i a l l y , t e s t s w e r e performedw it h a 4-in (10-cm) wid e, 1164-in (0.4-mm) t h i c k aluminum band wrapped aro undt h e p i p e ( f i g . 5). Aluminum was selectedf o r i t s low co s t and eas e of hand l ing ;however, copper o r any ot h er hig hly con-d u c t i v e metal co ul d have been used. Dur-in g th e t e s t in g , we f ound th a t t h e bandsbehaved a s charge si nk s. They gave er ro -ne ously h igh r e a d ings a t t h e po in t ofmeasurement. Thus, a probe was pu t i nc o n t a c t w i t h t h e p i p e sa mp le a f t e r i t wasc ha rge d ( f i g . 6 ) . n i n s u l a t ed h an dl e a tl eas t 3 f t (0 .9 m) l o n g i n s u r e d t h a t t h epe r son t a k ing th e r e a d ing d i d no t comec l o s e en ough t o t -i e p i p e t o d i s t u r b t h ee l e c t r i c f i e l d . The p r obe hea ds we refashi oned f rom aluminum she e t i ng , 1 /64 i n(0 .4 m) th ic k , and so l i d copper wi re ,3/16 i n (4.8 mm) i n diam eter. They wereshaped t o cover one-hal f of t h e c i rcum-fe re nc e of t h e pi pe over a 4- in (10-cm)wide band. The heads were th en glu edi n t o 4- in (10-cm) long s ec ti on s of 2- in(5-cm) round s o l i d polyv inyl ch lo r ide .An i n s u l a t e d w ir e, recommended by t h evo ltm ete r manufacturer , was connectedd i r e c t l y f ro m t h e p r ob e hea d t o t h egrounded voltmeter .

A s i m i l a r p ro be was b u i l t f o r i n t e r -n a l cha rge measurement. The pro be wasc o n s t r u c t e d o f t h e same m a t e r i a l a s t h ep ro be d es c r i b e d e a r l i e r ( f i g . 6 and con-ta c t ed a 4-in-wide ha l f cy l i nd er on t h ein s i de su r f a c e o f th e 6 -in- diam eter p ip esamples.

The ge n e r a l p r oce dure f o r th e l a bor a -t o r y e x p er i m en t s was i n i t i a t e d by e st a b -l i s h i n g t h e g a s- st re am v e l o c i t y , a l o n gwi th th e t e m pe r a tu re a nd r e l a t i ve humid-i t y o f t he ga s s t r e a m a nd of t he a m bie nta i r . D u s t w a s t h e n h an d- fe d i n t o t h e i n -l e t o f t h e p i p e s am pl e as c o n s i s te n t l y a spo ss ib le over a prede te rmined t ime of ex-posure . Measurement of the s t a t i c chargewas accomplished by pl ac in g t h e p robeh ea d o n t h e p i p e i mm ed ia te ly a f t e r t h eflow was sh u t o f f . The probe was removedf rom th e p ipe a nd g rounde d t o e l i m in a teany b ia s on subseque nt measurements.Subsequ ent measurements were made i n d i -v idu a l ly . The t o t a l e l a pse d t im e betwe enth e f i n a l measurement and when th e fa nwas s h u t of f was no more th an 2 min f o ra l l t h e t e s t s . A t t h e c onc lus ion of e a c ht e s t t h e i n t e r n a l and o u t s i d e s u r f a c e sof th e pip e sample were wet ragged, anda charg e measurement was made t o i n s u r eth a t no c ha r ge re ma ined on th e p ipe p r i o rt o t h e n e xt t e s t .

A l l t e s t s w ere r e p ea t e d t h r e e t i m e s ,a nd th e r e s u l t s we re the n a ver age d. F ig -u r e 7 shows th r e e se p a r a te t e s t s con-duc te d under id e n t i c a l c ond i t ions . Thes t a t i c c h ar g e g e n e r a l ly d e c re a s es fr omt h e i n l e t t o t h e e x ha u st e nd of t h e p i p ef o r e a ch t e s t . Var ia t ions be tween t e s t

4-in-wide aluminumsheet on copper-wire frame

2-in solid PV

pipe handle

FIGURE 5. Multirange electrostatic voltmeter FIGURE 6. General configuration of probe


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10 1 I 1 I8 o Trial Io Trial 2

A Trial 3

I 1 I I I I I 1 12 4 6 8 10 2 14 6 18DISTANCE FROM INLET, f tF I G U R E 7 Averaging data for three electrostatic

tests. Velocity 5 000 ft/min, temperature = 65 Frelative humidity = 48 pct, Pittsburgh Coalbed dust,DuPont type 2 pipe, exposuretime 3 rnin, dust con-centration = 5 500 mg/m3, dust size = minus 200mesh.

r u n s r a n g e t o kV; t h e c a u s e s f o r t h o s ev a r i a t i o n s a r e n o t known.

M ea su ri ng e l e c t r o s t a t i c c h a r ge on a no b j e c t i s a d i f f i c u l t t a s k due t o t h e e f -f e c t s of t h e c a p a c i t a n c e o f t h e m easu re -ment equipment. t i s a well-known s c i -e n t i f i c p r i n ci p le t h a t t h e e l e c t r o s t a t i cch a r g e i s s t or e d i n t h e e l e c t r i c f i e l d o ft h e s y s t em s c a p a c i t a n c e ( C) . T h e r e f o r e ,when a measur ing de vi ce i s b r o u g h t i n t ot h e v i c i n i t y of t h e o b j e ct of i n t e r e s t ,a n e f f e c t on t h e e l e c t r i c f i e l d c an bed e t e c t e d . T h is e f f e c t i s a f u n c t io n o ft h e r e l a t i v e s i z e of t h e c a p a ci t an c es a ndt h e c o n fi g ur at i on of t h e e l e c t r i c c i r c u i ta f t e r t h e m ea su ri ng d e v i c e i s connected.

I n t h e c a s e of m e as ur in g t h e e l e c t r o -s t a t i c v o l t a g e on a m e th an e dr a i n ag ep i p e l i n e , t h e f ol lo w in g c i r c u i t r e l a t i o n -s h i p s c a n b e d e r iv e d f ro m t h e t e s t s e t u p .A ssumin g th a t t h e p ip e l i n e i s i s o l a t e df ro m g ro u nd , t h e a c t u a l v o l t a g e t o wh ic ht h e p i p e l i n e i s charged i s a s f o l lo w s :

where V = t h e a c t u a l p i p e l i n e v o l ta g e ,Qo = t h e c h a rg e s t o re d i n t h e

p i p e l i n e s c a p a c it a n c e,and C p = t h e c a p a c i t a n c e of t h e

p i p e l i n e .To make an a c t u a l measurement, th e

p i p e l i n e i s i s o l a t e d and a q u a n t i t y o f

F I G U R E 8 Model of capacitance of measurementsystem.

p a r t i c u l a t e m a t e r i a l i s d r iv en th r o u g ht h e p i p e l i n e by a c e r t a i n v e l o c i t y a i r -s tream . The measur ing system i s t h e nb ro ug ht i n t o c o n t a c t w i t h t h e i n s i d e s u r -f a ce o f t h e p i p e l i n e t o make a measu re -ment . Figure 8 shows t h a t th e measur ingc i r c u i t c o n t a i n s two c a p a c i t o r s , o ne f o rth e cap ac i t an c e of t h e p r ob e ( C ) and th eo t h e r f o r t h e c a p a c it a n c e of t h e meter( C ) Because t h e cha rge w i l l r e d i s t r i ku t e i t s e l f between t h e t h r e e c a p a c i t o r swhen th e swi t ch i s c lo se d ( i e. a mea-s ur em en t t a k e n ) , t h e e q u a ti o n r e l a t i n gth e r ead in g on th e me ter (V,) w i th t h ea c t u a l v o l t a g e (V,) t h a t was i n i t i a l l y ont h e p i p e l i n e i s a s f o l lo w s :

T h i s e q u a t i o n shows t h a t i f t h e c a p a c i -t an ce o f t h e o b j ec t b e in g measu red ( Cp )i s much g r e a t e r t h a n t h e c a p a c i t a n c e o ft h e m ea su ri ng c i r c u i t (C an d Cm) , t h emeter r e a d i n g i s e q u i va l e n t t o t h e a c t u a lvo l t ag e (V ,). Second, i f th e measur ingc i r c u i t d o es ha ve a n e f f e c t on t h e a c t u a lr e ad i ng , t h e e r r o r w i l l b e s uc h t h a t t h er eco r d ed r ead in g i s l e s s t ha n t h e a c t u a lr e ad i ng . T h e r e fo r e , i f a l l o f t h e c ap ac -i t a n c e s w er e e i t h e r m easu re d o r c a l c u -l a t e d , a means t o c o r r e c t t h e r e a d i n g sf o r t h e e f f e c t of t h e m easuring c i r c u i tco uld be made. However, becau se th e ca-p a c i t a n c e o f t h e p i p e l i n e was l a r g e w i t hr e s p e c t t o t h e m ea su ri ng c i r c u i t an d


13/19

b ecau se t h e p u rp o se o f t h e p ro j ec t m easu r in g c i r c u i t was deemed s u i t ab l ewas n o t t o a s c e r t a i n a c t u a l v o l t a g e num- f o r t h e p r o j e c t .b e r s b ut r e l a t i v e o ne s, t h e f a b r i c a t e d

LABORATORY RESULTSC l ean , d ry a i r eq u i v a l en t t o 1 MMft3/d

(0.33 m3/s) was pu t thr oug h a 2-in-diam(5-cm) Dupont ty pe 2 p ip e sample a t a ve-l o c i t y of 3 3 ,0 00 f t / m i n (16 8 m / s ) . T h i sv e l o c i t y s 22 t i m e s th e maximum v el oc i t ymeasured i n underground methane pipe-l i n e s . The t em p era t u re and r e l a t i v e hu -mi d i t y of th e gas s t ream were 63 F(17 C) and 22 p c t , re sp ec t i ve ly . Whi let h e t e m p e r a t u r e s normal f o r an under-g round co a l mine, th e humid i ty s v e rylow. No charge was de te c t ed over a 3-hop er a t i ng per iod . , Thus , even a t low hu-m i d i t i e s , g a s s tr ea m s f r e e of p a r t i c u l a t em a t t e r h av e no s t a t i c ch a rg e p o t e n t i a l .

S ix - foo t (1 .8 -m) long se c t io ns o f 6 - in(15-cm) diam Dupont ty pe 2, Dr isc o ty pe2 , D r i sco type 3 , and P lexco type 3 werecom pared f o r t h e i r c h a rg e s u s c e p t i b i l i t y .Pi t t sb ur gh Coalbed d us t , minus 28 mesh(6 0 0 um) ( t a b l e 3 ) , was f ed i n t o a 5 , 00 0-ft /m in (25-1s) ai rs t r ea m. Each samplewas exposed t o a 5, 500-mg/m3 d us t concen-t r a t i o n f o r 2 m in e The t em p era t u re andt h e r e l a t i v e h u m i d i t y of t h e g a s s t re a mwere 59 F (15 C) and 40 p c t , respec -t i v e l y . F i g u r e 9 shows t h a t t h e t y p e 2p i p e c ha r ge d t o a g r e a t e r v o l t a g e t h and i d t h e t y p e 3 p i p e , w hi ch c o n t a i n s c a r -bon b lack .

Plexco type 3 v Drisco type 3

The e f f e c t of g a s v e l o c i t y o n s t a t i ccharge ge ne ra t io n was de te rmined by feed-i n g 2.6 l b ( 1 , 2 00 g ) of d u s t i n t o a p i p ef o r 3 min . F igure 10 shows t h a t a 5 ,000f t/ m in (2 5 m/s) a maximum c ha rg e of 3.2kV s g en er at ed c l o s e t o t h e i n l e t of t h ep i p e a nd d e c r e a s e s t h e r e a f t e r . t 2,500f t / m i n ( 1 3 m / s ) , t h e c h a rg e b u i l d s t o amaximum of 2.0 kV ab ou t 5 f t (1.5 m) fr omt h e i n l e t , and a t 1 ,0 00 f t / m i n (5 m/s) amaximum c ha rg e of ab ou t 1.6 kV o c c u r sab o u t 1 1 f t (3. 4 m) f ro m t h e i n l e t . Nomeasurab le charge s d e t e c t e d a l o n g t h ef i r s t 1 1 f t (3 .4 m) of t h e p i p e when t h eg a s v e l o c i t y s 1,000 f t /min (5 m/s)Ap p arent l y a t 1 , 0 0 0 f t / m i n (5 m / s) and t oa l e s s e r e x t e n t a t 2 ,5 00 f t / m i n ( 1 3 m / s ) ,t h e d u s t p a r t i c l e s r e q u i r e more t i m e t or e a c h t h e v e l o c i t y o f t h e g a s s tr e a m , a nd

TABLE 3. - P a r t i c l e - s i z e d i s t r i b u t i o nof P i t t s bur gh Coalbed samples ,p e r c e n t

Minus28 mesh

N PNAP1.6

64.626.7

7.1

P r a t i c l e s i z e ,mesh-318 in , +8. .

-8, +28.... . . .-28, +48.. ..a-48, l o o . . . . .-100, +200.. e .-200. .

Minus200 mesh

NAPNAPNAPN PNAP100.0

Minus318 i n31.0

39.713.4

7.84.33.8

NAp Not a p p l i c a b l e .

DISTANCE FROM I NL E T f t DISTANCE FROM INLET iFI GU RE 9. Comparison of pipe data. V e l o c i t y F IGURE 10. E f fec t o f ve l oc i t y va r i a t i on . Tem-

- 5,000 ft min, temp erat ure = 59- F re la t i ve hu- perature = 6 7 O F re l a t i ve humid i ty = 60 pc t , P i t t s -mid i ty = 40 pct , P i t tsb urgh Coa lbed dust, exposure burgh Coalbed dust, DuPon t type 2 pipe, exposuretime = 2 min, dust concentrat ion = 5 500 mg/m 3 t ime = 3 min, dus t load 400 g/min, dust s ize = mi-dus t s i ze = minus 28 mesh. nus 28 mesh.


14/19

c onse que n t ly the c ha r g ing p r oc e ss oc c ur sf u r t h e r from t h e i n l e t .

F igu re 11 shows th a t th e magni tude oft h e s t a t i c c h ar g e on t h e p i p e i n c r e a s e sa s t h e e xp os ur e t im e t o p a r t i c l e s i n-c rea ses . Only about 13 f t (4 .0 m) of th e20- ft (6 .1-m) le ng th of p ipe i s charged.N ote t h a t t h e p i p e i s not charged uni -formly a long i t s leng th. The charg e i sz e r o n e a r t h e i n l e t , i n c r e a s e s t o a maxi-mum a t a bou t 5 f t ( 1.5 m ), a nd the n de-c r e a s e s t o z er o . T h i s i s c o n s i s t e n t w i t ht h e 2 ,5 00 -f t/ mi n ( 1 3 1n / s ) v e l o c i t y t e s t( f i g . 1 0 ) .

P a r t i c l e s i z e h a s a marked e f f e c t o nt h e m ag ni tu de o f t h e s t a t i c c h a rg e gen-e r a t e d on p o l y et h y le n e p i p e ( t a b l e 3 ) .Fi gu re 12 shows t h a t minus 200 mesh (75ym) du s t produces a h ig her charge th ando es minus 28-mesh (600 ym) du st . Appar-e n t l y , t h e f i n e r d u s t h a s a l a r g e r s u r -fa ce a r ea f rom which charges can bes t r i p p e d . The c h a rg i n g c h a r a c t e r i s t i c s

DISTANCE FROM INLET ftFIG URE 11. Eff ect of exposure-t ime variation.

Vel oci tyl 2,50Oft/min, temperature 60 F, re la-t ive humid i ty 55 pct, Pitts burgh Coalbed dust,DuPont type 2 pipe, dust concentration 32,000mg/m3, du st si ze minus 28 mesh.

of th e Pi t t sb ur gh and Coalburg Coalbeds( t a b l e 2) were compared us in g minus 200-mesh (7 5 ym) du st . Fig ure 13 shows t h a tth e Coalburg Coalbed dus t im parted ag r e a t e r c h a rg e t h a n d i d t h e P i t t s b u r g hCoalb ed d u s t o ve r a bo ut t h e f i r s t 6 f t(1.8 m) of pip e downstream of t h e i n l e tand a lower charg e downstream of t h e 9-f t(2.7-m) measurement po in t. A pp are ntl y,t h e d i f f e r e n c e i n c h a rg i n g c h a r a c t e r i s -t i c s i s d ue t o t h e h i g h e r a s h c o n t e n t ofth e C oalbur g dus t ( t a b le 2 ) . B oth t s t scompared equa l weight du st samples.

Plex co ty pe 3 pi p e, 4-in (10-cm) diam,was assembled i n t o a 24-ft (7.3-m) lo ng,doub le 90 ( 1.57 r a d ) bend t e s t s e c t io n( f i g . 14 ) . The c i r c l e d num ber s r e p r e se n tth e e ig h t s t a t i c c ha rge m ea su re me ntpoi n ts . P i t t sb urg h Coalbed du s t [minus

10 I-KEYPittsburgh

o Coalbura

4 6 8 10 12 14 16 18DISTANCE FROM INLET f tFlGlJRE 13. Comparison of Pittsb urgh and Coal-

burg Coa Ibeds. Vel oci ty 5,000 ft/min, temperature65 F, re lat i ve humidity 48 pct, DuPont type 2

pipe, expos ure time 3 min, dust concentration5,500 mg/m3, dus t si ze minus 200 mesh.

KEYMeasurement point

4-in pipeDISTANCE FROM INLET f t I

FIGURE 12. Effect of dust-size var iat ion. Ve- dust ~nletloc i ty 5,000 f t lmin, temperature 65O F, re la t ive L Ihumid ty 48 pct, Pitts burgh Coa lbed dust, D uPonttype 2 pi pel exposure t ime 3 mint dus t concentra- FIGUR E 14. Config uratio n for elbow test. P lexot ion 5,500 mg/m3. type 3 pipe.)


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28 mes h 6 0 0 u rn )] , d eg r e a se d i r o n f i l i n g s[minus 40 mesh 425 urn)], and sa nd [min us12 mesh 1.4 mm)] were fe d t o a 10,000-f t / m i n 5 1- m/ s) v e l o c i t y airstream. A200-mL volume of co a l d us t , sand , andi r o n f i l i n g s o r 0 .4 4, 0 .6 0, a nd 1.12 l b2 0 0 , 2 70 , an d 5 10 g ) , r e s p e c t i v e l y , was

a d de d o v e r s e p a r a t e 3 m in e x p o su r e t i m et e s t s F i g u r e 1 5 shows t h a t f o r c o a ld u s t , t h e maximum s t a t i c c h a r g e o c c u r r e dn e a r t h e i n l e t s t a t i o n s 1 a nd 2) a nd d e-c r e a s e d t o wa rd s t a t i o n 3 . t t h e e l b o w s ,t h e c h a rg e o n t h e p i p e i n c r e a s e d s t a -t i o n s 4 an d 7 ) . A p p a re n t ly , t h e e lb ow sc a u s e c o a l - p a r t i c l e d e g r a d a t i o n w hi ch ex-p o s e s new s u r f a c e s t o t h e e l e c t r o n ex-c h an g e p r o c e s s . F or t h e i r o n a nd s a ndp a r t i c l e s , no c ha r ge oc c ur r ed o n t h e i n i -t i a l s t r a i g h t p o r t i o n o f t h e p i p e s t a -t i o n s 1 , 2 , and 3) u n t i l t h e p a r t i c l e si m pa c te d t h e p i p e a t t h e f i r s t e lbow

s t a t i o n 4 ) . The c h a rg e was g r e a t e s t a tt h e e l bo w , an d t h e n d e c r e a s e d a l o n g t h es t r a i g h t p o r t i o n o f t h e p i p e s t a t i o n s 5a n d 6 ) u n t i l t h e n e x t e lb ow was r e a ch e dw he re t h e c h a rg e i n c r e a s e d a g a i n s t a t i o n7 ) . The s a nd an d i r o n p a r t i c l e s d i d n o tc h a rg e t h e f i r s t 10 f t 3.1 m) o f t h ep i p e l i n e s t a t i o n s 1 , 2 , an d 3 ) . T he sea r e much h e a v i e r t h a n c o a l p a r t i c l e s a ndm a y r e q u i r e a l o n ge r p i p e l e n g t h t o r e a c ht h e s pe ed o f t h e airs t ream on a muchh i g h e r v e l o c i t y ai rs t ream.

E x p e r i e n c e sho ws t h a t when t h e re la-t i v e h u m id i ty i s l o w i n s i d e a b u i l d i n g ,w a l k i n g a c r o s s a c a r p e t e d f l o o r c a ng e n e r a t e s t a t i c c h ar g es o f c o n si d e ra b l e

I IElbow I Elbow 2

A Pi t t sburgh Coal

m a gn i tu d e, b u t w hen t h e r e l a t i v e h um i d it yi s h i g h , t h e s t a t i c charge annoyance i sm in im al o r e l i mi n a te d . S i m i l a r r e s u l t sh a v e b e e n o b se r v e d f o r p o l y e t h y l e n e p i p e .A 20-f t 6.1-m) le ng th of pi pe was pla cedi n a c ha mb er f i g . 2 ) , a n d steam was in-j e c t e d t o c o n t r o l h u m id it y. F i g u r e 1 6sh ow s t h a t when t h e r e l a t i v e h u m i di t y oft h e ai rs t ream i s i n c r e a s e d f ro m 3 8 t o8 0 p c t , t h e s t a t i c c h a r g e o n t h e p i p e d e-c r e a s e d d r a m a t i c al l y . T hu s, t h e r e l a t i v eh u m i di t y o f t h e airs t ream i s a n i m p o r t a n tf a c t o r c o n t r o l l i n g t h e s t a t i c c h a r g e o nt h e p i p e.

Ge n e r a l l y , b a r e c o p p er w i r e i s s p i r a l l ywound o n p o l y e t h y l e n e p i p e , a nd a t i n t e r -v a l s o f a b o u t 5 00 f t 1 5 2 m ), t h e c o pp e rw i r e i s c o n n e c t e d t o a b u r i e d c o p p e rground rod . Labora to ry t e s t s were con-d u ct ed t o e v a l u a t e t h e e f f e c t i v e n e s s oft h i s g r o u nd i n g p r o ce d u r e on t h e s t a t i cc h a rg e s o n t h e i n s i d e and t h e o u t s i d e o fth e p ipe . F ig ure 17 shows t h a t when noground w i r e i s p r e s e n t , t h e c h ar g e on t h ei n s i d e s u r f a c e of t h e p i p e r a ng e s f ro ma b o u t 1 0 kV n e a r t h e i n l e t t o 6 kV a b o u t7 f t 2 . 1 m) f r om t h e i n l e t . When t h ec o p p e r w i r e i s s p i r a l l y wound i n 1 - ft30-cm) o r 2-f t 61-cm) sp aci ng, t h e

s t a t i c c ha rg e on t h e i n s i d e s u r f a c e i sr e d u ce d b u t n o t e l i m i n a t e d . On t h e o u t -s i d e s u r f a c e of t h e p i p e , no c h a rg e i smeasured when t h e p i pe i s sp i r a l l y wo u n dw i t h b a r e c o pp e r wire i n a 1-ft 30-cm)spac ing . For a 2-f t 61-cm) sp ac in g, as t a t i c ch ar ge of ab ou t 2 kV i s measuredbe tween t h e winds o f copper wi re . Thus ,

K E Y8 pct RH(gas stream and a mbient)80 pc t RH (gas st ream and ambient)3 6 - o 8Opct RH gas stream and 37 pc t

3rxa 4 --

4 6 8 10 12 14 16 18I 3 4 5 6 7 8 DISTANCE FROM INLET, f t

MEASUREMENT STATION F I G U R E 16. Ef fe c t o f humid i ty var ia t ions . Ve-F I G U R E 15. Resul ts of e lbow tes t . Ve loc i t y l oc i t y 5,000 ft/min temperature 69 F, Coalburg10,000 ft/min temperature 68 F, re at ve humid- Coalbed dust DuPont type 2 pipe exposure t ime

i t y = 46 pct exposure t ime 2 min contaminate 2 min dus t concent ra t ion 11,000 mg/m3 dust s iz evolume 200 mL. minus 200 mesh.


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K E YU No qround wireGround wire 2-ft spaced spiralGround wire I-ft spaced spiral

I I I I2 4DISTANCE FROM INLET f t

FIGURE 17. Resul ts of grounding evaluat ion. Ve-loc i t y = 5 00Oft/min temperature = 62 F re la t ive hu-mid i t y = 40 pct Coalburg Coalbed dust DuPont type2 pipe exposure t ime 2 min dust concentrat ion =11 000 mg/m 3 dust s ze minus 200 mesh.

a s p i r a l l y wound, g rounded copper wi re se f f e c t i v e i n r e du c in g t h e c ha rg e o n t h eo u t s i d e a n d i n s i d e s u r f a c e s o f t h e p i pe .

Underground methane p i pe l i ne s a r e lo -c a t e d i n r e t u r n a i r wa y s, which a r e r o ckd u st e d p e r i o d i c a l l y u s in g f o r c e d a i r t oblow t h e r oc k d u s t i n t o t h e e n t r y . T h isp r oc e d ur e was s i m u l a t e d i n t h e l a b o r a t o r yt o d et er m in e t h e st a t i c -c h a r g e e f f e c t oft h e r oc k d u s t p a r t i c l e s on t h e p i p e l i n e

f i g . 4 ) . Air v e l o c i t y a ro un d t h e p i p ei n t h e dus t chamber was abou t 200 f t / m i n

1 m/s) and ov er a 5-min peri od, 25 l b

2 4 5DISTANCE FROM INLET f t

FIGURE 18. Results of rock-dust ing test . Ve loc -i t y = 210 ft/rnin temperature = 57O F re la t iv e humid-i ty 30 pct l imestone dust dust weigh t = 25 IbDuPont type 2 pipe feed t im e = 5 min.

TABLE 4. - Rock d u s t a n a l y s i s , p e r c e n t

11 kg) o f rock du s t was d rawn over t h ep i p e t a b l e 4 ) . Rock d u s t co a t ed t h ep i p e , and no m eas u rab l e s t a t i c ch a rg e wasd e t e c t e d on t h e o u t s i d e s u r f a c e of t h ep ipe . However, a s t a t i c charg e of abou t2 kV was measured on th e i ns i de su rf ac eof t h e p i p e f i g . 1 8 ). The r e l a t i v e hu-m i d i t y d u r i n g t h e t e s t was a b o u t 3 0 p c t ,which s low compared with an undergroundenv ironment and may have co n t r i bu t ed t ot h e g e n e r a t i o n o f s t a t i c c ha rg e.

CaO.......... 91.5S102.... . . . . . 4.8d 7O 3 1.3

FIELD TESTS

Fe202........ 1.2MgO.......... 1.1S............ .1

T h r ee u nd er gr ou nd p i p e l i n e s w ere d i s c o l o r a t i o n , s c a r r i n g , o r d e p o s i t s o fd i sma nt led and examined f o r contamina- du s t o r d i r t were found. One o f thet io n . Tab le 5 shows th a t th e vo lume o f p i pe l i ne s was used i n a c ross -measurem et hane t r an s p o r t ed by t h e s e p i p e l i n e s s y st em , wh ich s more prone t o produceran ged f rom 1 00 m i l l i o n t o 400 m i l l i o n d u s t b ecau s e o f s t r a t a movement.f t 3 2 .8 m i l l i o n t o 1 1.3 m i l l i o n m3). No

TABLE 5 . Dust con tamina t i on d a t a f o r methane d ra ina ge p i pe l i ne s

S i t e Drainagesys tem tra ns - Ev idence o fm a t e r i a lipe p o r t ed , co n t am i n a t i o n

Beckley Mining Co. Beckley MineNoneNone

BethEnergy Mines Inc.Cambria 33 Hn e . . ..............Mari anna Mine.... . . . . .. . . . . .. . .

o r i zo n t a l . .c ross -measureHor izon ta l . . .

Po l y e t h y l en e.. do.. ..... J J iMetal... . . . .

~ M f t 3200 None


17/19

-*A - ..F I G U R E 19 Re a l t i m e a e r o s o l m o n i to r .To f u r t h e r i n v e s t i g a t e t h e d u s t l e v e l s

i n working methane dra in age sys tems, ac ross-measure su r f ace borehole and twov e r t i c a l gob b o r e h o l e s w er e i n s p e ct e d . Area l - t ime ae ro so l moni tor f i g . 19) wasused t o measure th e conc entra t ion ofminus 20-um du st pa r t ic le s i n th emethane-ai r gas f lows f rom th e thr eeboreholes . The measured du s t le v e l s werec om par ab le t o l e v e l s i n a c l e a n a i r e nv i -ronment , which produced no s t a t i c chargeon t h e p ip e i n t h e l a b or a to r y t s t s eventhough th e ve l oc i t y o f th e ga s s t r e a m was33,000 f t / mi n 168 m/s) and re l a t i v e hu-mid i ty was low 22 pc t )

F I G U R E 20. S i n g l e r a n g e e l e c t r o s t a t i c v o l t m e t e r .TABLE 6. Re su lt s of re al -t im e

e va lua t io n o f m e thane d r a ina gep i p e l i n e s

St at ic -c ha rg e measurements were con-duct ed on two underground methane dr ai n-a ge p i p e l i n e s t a b l e 6 ) . 4-in 10-cm)wide band of aluminum was wrapped arou nde ac h p i p e l i n e t o c o l l e c t s t a t i c c ha rg esa nd a 0- t o 300-V e l e c t r os t a t i c vo l t m e te rwas use d t o m ea su re th e s t a t i c c ha rge

f i g . 20) For b o t h p i p e l i n e s , t h e r e l a -t i ve hum idi ty of the ga s s t r e a m a nd th ee n t r y c o n t a i n i n g t h e p i p e l i n e wer e 7 8 p c to r g r e a t e r . D ust c o n c e n t r at i o n s i n t h egas stre ams were comparable t o a c l ea na i r e nv ir on me nt . No s t a t i c ch a rg e wasde te c te d on the two p ipe l ine s .

Gas stream:eloci ty. . .f t /min. .ust con c.. .mg/m3..

R e la t ive hum id i ty , pc t :as stream..

Entry.................ethane conc.. pc t.emperature.. .OF .harge measured.. V

J i mWalterNo. 5Mine1,4500.06

10098

100770

BeckleyMine

1,0400.05

788397630


18/19

SUMMARY AND CONCLUSIONSV e l o c i t i e s up t o 3 3 ,0 00 f t / m i n 1 68

m/s) i n po lye thylene p ipe produced nos t a t i c c ha r ge s when th e ga s s t r e a m wasf r e e o f pa r t i c u l a t e m a t t e r . When pa r t i c -u l a t e m a t t e r i s pr e se n t , t h e m a gn i tude o fs t a t i c c ha rg e i s d i r e c t l y p r o p or t i on a l t ot he gas-s t ream ve lo c i ty and du s t concen-t r a t i o n and i n v e r s el y p r o p o r t io n a l t os i z e of t h e d u s t p a r t i c l e s and r e l a t i v ehumidi ty .

Type 2 polye thy lene p ipe charged t o ag r e a te r m a gn i tude tha n d i d type 3 , whichc on ta i ns c a r bon b la c k and i s presumablymore con duc t ive t han t yp e 2 .

F i e l d measurements showed t h a t t he re l -a t i v e h um id it y of t h e g as t r a n s p o r te d i nunderground methane dra inag e p i pe l i ne s i s78 pc t o r g r e a t e r , a nd th e dus t c once n-t r a t i o n i s n e g l i g i b l e 0.06 mg/m3). Nos t a t i c c ha r ge was m e a su r a b le on th e un-de rg r ound p ip e l i ne s unde r the se c ond i -t i o n s . I n l a b o r a t or y t e s t s where ther e l a t i v e h u mi d it y was 78 p c t o r g r e a t e rand du s t con cen tra t io ns were 11 ,000 mg/m3 a s t a t i c charge of only 2 kV was gen-e r a t ed . Where r e l a t i v e humidi ty was 22p c t and p a r t i c u l a t e c o n c e n t r at i o n s w er en e g l i g i b l e , no m ea su ra bl e s t a t i c c h ar g ewas generated even though gas-stream ve-l o c i t y was a s h igh a s 33,000 f t /m i n 168m /s ) . Thus , r e l a t i ve hum idi ty and du s t

be preven ted by wrapping ba re copp er wi rearound th e pip e i n a 1-f t 30-cm) spac-ing . When a 2-ft 61-cm) s p i r a l wrappingi s u s ed , s t a t i c c h ar g es e x i s t between t h ewraps . However, t he s t a t i c charge on th ei n s i d e p i p e s u r f a ce i s reduced but no te l im ina t ed f o r both th e 1- f t 30-cm) and2-ft 61-cm) spa cin gs.

The low-ve loc i ty f low [200 f t / min 1m/s) J of rock du s t a round polye thylen ep i p e g e n e r a t ed a s t a t i c c h a rg e of a b o u t2 kV on t h e in si d e su rf ac e and no mea-s u r a b l e c h a rg e o n t h e o u t s i d e s u r f a c e ,which was coa ted w it h rock du st . Ther e l a t i v e h um id it y d u r in g t h e t e s t was 30pc t compared wi th f i e l d measurement a t78 pc t o r g r e a t e r , which wou ld lowe r th es t a t i c c ha rg e on t h e i n s i d e s u rf a c ec ons ide r a b ly .

F i e l d measurements show t h a t t h e re la -t i v e h u m i d i t i e s i n t h e mine e n t r y and t h eg a s s t r ea m a r e h i g h 7 8 p c t o r g r e a t e r ) ,and t h e l e v e l o f p a r t i c u l a t e matter i nt h e g a s s t r e am i s c om pa ra ble to th a t o f ac l e a n a i r e nvi r onm en t . The se c ond i t ion sa re no t conduc ive t o th e development ofs t a t i c c ha r ge s on under gr ound po lyethy -l e n e p i p e l i n e s .

Because o f t h e p o s s i b i l i t y of s t a t i c -c ha r ge bu i ldup on under gr ound p i pe l i ne s ,t h e wet-rag tech niqu e should be employed

c o n c e n t r a t i o n c o n d i t i o n s would h av e t o t o remove s t a t i c c h a rg e s f ro m t h e o u t s i d ec ha ng e r a d i c a l l y f o r t h e d ev el op me nt o f p i p e s u r f a c e an d t o r ed uc e t h e s t a t i cs i z a b l e s t a t i c c h a rg e s o n un de rg ro un d c h a rg e on t h e i n s i d e s u r f a c e b e f o r e am e tha ne p ipe l ine s . p o l y e t h y l e n e p i p e l i n e i s r e p a i r e d o r

The bu i ldup o f s t a t i c c ha r ge s on th e d i sm an t l ed .o u t s i d e s u r f a c e o f p o l y et h y l en e p i p e c a n

REFERENCES1. Diamond, W e P. S i te -Sp ec i f ic and

Regiona l Geologic Co nsidera t ions f o rCoalbe d Gas Drai nag e. BuMines I C 8898,1982, 24 pp.2. Maksim ovic, S. D . and F. N K i s -s e l l . Three Coal Mine Gob Deg as i f ic a t i onSt ud ie s Using Surf ace Boreholes and aBl ee de r System. BuMines R I 8459, 1980,10 PP.

3 Cervik , J Experience With MethaneCo ntr ol From Ho ri zo nt al Boreholes . Pa-per i n Proceedings of t he Second In te r na-t i o n a l Mine Ven t i l a t i on Congress , Reno,NV Nov. 4-8, 1979. Soc. Min. Eng. AIME1980, pp. 257-264.

4. Campoli, A . A . J Cervik, andS. J Sch atz el. Co ntr ol of Longwall GobGas With Cross-Methane Bor eho les up per


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Ki t t an ni ng Coalbed) . BuMines RI 8841,1983, 17 pp.

5 . Ene rgy App l i ca t ion , Inc . Des ignand Recommended Sp ec i f i c a t io ns f o r a S a feMethane Gas Pi p i n g Sy st em c o n t r a c t501 551 45) . BuMines OFR 109-76, 197 7, 8 0pp .; NTIS PB 2593 408s .

6 . T i s d a l e , J E . D. W. M i t c h e l l ,R. A. E l a m M. J Lawless, and B. E . Tay-lo r . P ip ing Methane i n Underground Coa lMin es . MSHA IR 10 94 , 19 78 , 34 pp.

7. N a t i o n a l F i r e P r o t e c t i o n A s so ci a-t ion. Recommended P r ac t i ce on S t a t i cE l e c t r i c i t y . ANsI/NFPA 77, Dec. 7, 1982,58 PP.

8 . Davi s , G. W . and I K. DeBlieu.S t a t i c E l e c t r i c i t y and L i gh t ni n g E f f e c t so n P l a s t i c Pi pe . P a pe r i n P ro c. AGAD i s t r . Conf. , Los Ang eles , CA May 1975.AGA 197 5, pp. 175-177.

9 . Gr e n i e r , G . and R. Cald wel l .S t a t i c E l e c t r i c i t y on P o ly e th y le n e P ip e.P a pe r i n P ro c. 4 t h AGA P l a s t i c P i peSymp., Denver, CO Nov. 1972 . AGA, 1972,pp. 84-86.

10. Al l egheny Mine ra l Corp . Pr iv a t ecommunica tions , 1985; av a i l a b l e upon re-q u e s t f r o m A. A. Campol i, BuMines , P i t t s -burgh, PA.

U S GOVERNMENT PRINTING OFFICE: 1986-605-017140 022

polyethylene electrostatic test

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