Anaerobic Digestor Design
Transcript of Anaerobic Digestor Design
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AnaerobicDigester Design
Jae K. (Jim) Park, Professor
Dept. of Civil and Environmental Engineering
University of Wisconsin!adison"
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Information Checklists for Design ofSludge Stabilization Facility
". #elect t$e %ltimate sl%dge disposal met$od as t$e degree ofsl%dge sta&ili'ation ill depend on t$e re%irements of t$edisposal practice.
*. Develop t$e c$aracteristics of t$ickened sl%dge t$at ill reac$t$e sl%dge sta&ili'ation facility.
+. #elect t$e sl%dge sta&ili'ation met$od t$at is compati&le it$t$e infl%ent sl%dge c$aracteristics, deatering, and %ltimatedisposal met$od.
. Develop design parameters (organic loading, $ydra%lic loading,c$emical dosage, reaction period, etc.) for t$e selected sl%dgesta&ili'ation facility.
-. &tain t$e design criteria from t$e concerned reg%latory agency.
/. &tain necessary man%fact%rers0 catalogs and e%ipmentselection g%ides.
*
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Design Criteria forAnaerobic Digester Design (1)
". #elect anaero&ic sl%dge digestion for sta&ili'ation of organic solids.*. Provide to completelymi1ed, $ig$rate anaero&ic $eated digesters
it$ digestion temperat%re of +-2C.
+. 3$e design flo to t$e sl%dge digester s$all &e e%al to t$ickenedsl%dge %nder t$e daily design flo condition.
. 3otal volatile solids loading to t$e digester s$all not e1ceed +./kg4m+5day %nder e1treme $ig$ loading condition.
-. 3$e solids retention time at e1treme $ig$flo condition s$all not &eless t$an "6 days.
/. 3$e digester mi1ing s$all &e ac$ieved &y internal gas mi1ing.
7. 3$e solids content in digested sl%dge is -8 and #.9. is ".6+.
:. 3$e 3## content in t$e s%pernatant is ,666 mg4;.
6.7", ? > 6.6- g =## prod%ced4g @D- %tili'ed,E > 6.:, and k d > 6.6+ "4day.
+
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"6. 3$e digester $eating s$all &e ac$ieved &y recirc%lation of sl%dge t$ro%g$ e1ternal $eat e1c$anger. 3$e sl%dgerecirc%lation system s$all also &e designed to provide digester mi1ing.
"". Provide floating digester cover for gas collection.
"*. 3$e $eat loss from t$e digester cover, side alls, and floor s$all &e calc%lated %sing t$e standard $eat transfer
coefficients for t$e digester constr%ction material.
"+. Provide gasfired $ot ater &oiler for e1ternal $eat e1c$anger.
". E1plosion prevention devices s$all &e provided to minimi'e t$e possi&ility of an e1plosive mi1t%re &eing developed
inside t$e floating covers. Proper flame traps s$all &e provided to ass%re protection against t$e passage of flame into
t$e digester, gas storage sp$ere, and s%pply lines.
"-. 3$e digester design s$all incl%de s%pernatant it$draal system, sig$t glass, sampler, man$ole, etc.
"/. Arrangement s$all &e provided to &reak t$e sc%m t$at may form on t$e sl%dge s%rface.
Design Criteria for
Anaerobic Digester Design (2)
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Characteristics of Sludgeeaching Anaerobic Digester
Average E1treme E1treme
Bactors flo lo flo $ig$ flo
#l%dge prod%ction, kg4day :,":6 /,
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Design !"am#le (1)
A$ Digester Ca#acity and Dimensions
". Comp%te digester capacity at average flo condition %sing "- days digestion period
Ass%me average flo to t$e digester > "+* m+4day
Digester vol%me > "+* m+4day "- days > ", *.- kg4m+5day ( +./) 3otal =# reac$ing t$e digester > :,":6 6.7" > -,:6: kg4day
Digester vol%me > -,:6: kg4day *.- kg4 m+5days > *,+*+ m+
+. Comp%te digester capacity %sing vol%me per capita alloance
Ass%me 6.6+ m+ digester capacity per capita
Pop%lation served > :6,666Digester capacity > :6,666 6.6+ m+ > *,66 m+
. Comp%te digester capacity %sing vol%me red%ction met$od (/78)
=ol%me of t$e digested sl%dge > "+* m+4day (A# Design #lide F*)
Digester capacity > G"+* H 6./7 ("+* H
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-. #elect digester capacity
#elect active digester capacity of *,-66 m+.
%$ Digester Dimensions and &eometry
". Correct for vol%me displaced &y grit and sc%m acc%m%lations, and floating cover level
Provide "m dept$ for grit acc%m%lation
Provide 6./m dept$ for sc%m &lanket
Provide 6./m min. space &eteen floating cover and ma1. digester level
3otal displaced $eig$t > " 6./ 6./ > *.* m
Ass%me t$at t$e active side ater dept$ is : m (*/.+ ft). additional vol%me ill &e availa&le in t$e cone.
=ol%me of eac$ digester > ",*-6 m+
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Design !"am#le (2)
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Area of eac$ digester > ",*-6 m+ ÷ : m > "-/.+ m*
Diameter of eac$ digester > (4π "-/.+ m*)6.- > "." m
@eca%se floating covers come in -ft (".-m) diameter increments, provide digesters it$ -ft ("+.7 m)
diameter.
evised side ater dept$ > ",*-6 m+ ÷ Gπ4 ("+.7 m)*I
> :.- m (*7.< ft)
Provide to digesters eac$ "+.7 m (- ft) diameter and :.- m (*: ft) side ater dept$.
*. C$eck t$e active vol. of t$e digesters, incl%ding vol. of cone
3$e floor of t$e digester is sloped at " vertical to + $ori'ontal.
" (vertical)L+ ($ori'ontal) > $L("+.74*) M $ > *.*: m N *.+ m
3$e &ottom cone dept$ of *.+ m adds additional vol%me.
Active digester vol%me > (=ol. of active cylindrical portion)
(3otal vol. of t$e cone) (Alloance for grit
acc%m%lation) > π4 ("+.7 m)* 7.+ mO "4+ π4
("+.7 m)* *.+ m "4+ π4 (/.6 m)* " m
> "67/." m+ ""+ m+ ","7 7.+ m:
Design !"am#le (')
*.+ m
" m
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Active vol. of to digesters > * ","7 *,+- * (π4 "+.7 m* :.- m
""+ m+) > *,7+* m+
Active vol. ratio incl%ding cone > *,+- 6.:/
C$ Actual Solids etention ime and Solids oading
". Comp%te act%al digestion period at average, e1tremely lo, and e1tremely $ig$ flos
Digestion period at average flo > *,+- *,+-
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#olids loading at ave. loading condition > :,":6 kg 3#4day 6.7" =#43# ÷ *,+- *.- kg
=#4m+5day
#olids loading at ave. loading condition > /, :,/:" kg4day 6.7"
=# ÷ *,+- *./ kg =#4m+5day
D$ &as +roduction
". Calc%late gas prod%ction
@D- in t$e t$ickened sl%dge (#tream "6) > ,*-+ kg4d (A# Design #lide F*)
@D;
in sl%dge > ,*-+ kg4d @D-
46./: @D;
> /,*- kg4d
Ass%me /-8 solids are &iodegrada&le and " g of &iodegrada&le solids > ".* g @D;
, ? > 6.6-, k d > 6.6+
"4day, and E > 6.:.
"*
Design !"am#le (,)
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= > 6.+- m+4kg (EQ6
#6
"6+ kg4g ".* P1) > 6.+- m+4kg
(6.: "+* m+4day /,*- g4m+ "6+ kg4g H ".*
"/+ kg4day > ",/76 m+4day
f met$ane is //8 in t$e digester gas,
Digester gas prod%ction > ",:6 m+4day ÷ 6.// > *,-+" m+4day*. Estimate gas prod%ction from ot$er r%les of t$%m&
a. @ased on =# loading %sing =# > 6.7- of 3# and gas prod%ction rate of 6.- m+4kg =#
9as prod%ced > :,":6 kg4day 6.7" 6.- m+4kg
> *,
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Ass%me average =# red%ction of -*8 and gas prod%ction of 6. :,":6 6.7" 6.-* > +,6*6 kg4day
9as prod%ced > +,6*6 kg4day 6. *,:+< m+4day
c. @ased on per capita
3otal pop%lation served > :6,666
Used gas prod%ction rate of 6.6+* m+4capita
9as prod%ced > :6,666 persons 6.6+* m+4person5day
> *,-/6 m+4day
@ased on t$e a&ove analysis, ass%me a conservative gas prod%ction rate of *,--6 m+4day at standard
conditions (62C and " atm).
!$ Digested Sludge +roduction
". Comp%te t$e %antity of solids in digested sl%dge 3=# > :,":6 kg4day 6.7" > -,:67 kg4day 3=# destroyed > -,:67 kg4day 6.-* > +,6*6 kg4day
"
Design !"am#le (.)
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3# remaining after digestion > Sonvolatile solids =#
remaining > (:,":6 -,:67) kg4day 6.: -,:67 kg4day
> -,"-< kg4day
*. Comp%te total mass reac$ing t$e digester
3otal solids reac$ing t$e digester > :,":6 kg4day (A# Design F*)
3otal solids in t$ickened sl%dge > /8 &y t
3otal mass reac$ing digester > :,":6 kg4day ÷ 6.6/ kg4kg
> "+/,+"7 kg4day
+. Comp%te vol%me and 3## in digested sl%dge and t$e digester s%pernatant
Ass%me t$at no li%id vol%me c$ange occ%rs in t$e digester
=ol. of infl%ent t$ickened sl%dge (=inf
) > =ol. of digested
sl%dge removed from digester (=sl%dge
) =ol. of digester
s%pernatant (=s%pernatant
)
=sl%dge
> "+* m+4dT Wremaining
> -,"+< kg4d
=sl%dge
> Wsl%dge
4(6.6- g4; "6+ kg4g "6+ ;4m+ ",6+6)
> "-
Design !"am#le (/)
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Ws%pernatant
> 3otal solids remaining after digestion in digested
sl%dge H Wsl%dge
> -,"-< kg4d Wsl%dge
Wsl%dge
> -,6*" kg4dT Ws%pernatant
> "+: kg4dT =sl%dge
> +- m+4d (similar to mass &alance)
. Determine t$e mass and concentration of t$e components in digested sl%dge and s%pernatant
Parameter Digested sl%dge, kg4d (#tream "*) #%pernatant (#tream "+)kg4d mg4;
a comp%ted"/
Blo, m+4d3##@D-rg.S
SS
S+ V S
3S SPPPP3P3=##43## ratio@iodeg. solids43##rg.S43=##
SPP43=##
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-. #elect a s%pernatant selector system
3o it$dra li%id from t$e top.
a. Allo direct vis%al inspection of sl%dge
&. Allo removal of clear li%id from t$e top
c. Permit operation &y one person
d. @e e1tremely relia&le
e. !inimi'e t$e danger of alloing air
to enter t$e digester
f. @e easy to service in
case of &lockage
grease, sc%m or
&y sl%dge
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Design !"am#le (1)
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F$ Influent Sludge ine to the Digester
ntermittent p%mp operation at 6.:- m+4min for eac$ t$ickener controlled &y a timer.
"-cm (/in) diameter
":
Design !"am#le (11)
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&$ Digester eating e3uirements
". Comp%te $eating re%ired for ra sl%dge
> Q6 C
p (3
* H 3
")
$ere
> $eat re%ired, J4dayT C p
> specific $eat of sl%dge (same as for ater > ,*66 J4kg52C or "
@3U4l&52C)T 3*
> digestion temperat%re, 2CT and 3"
> temperat%re of t$e t$ickened sl%dge, 2C.
3$e critical $eat re%irement for ra sl%dge is reac$ed $en sl%dge flo is ma1im%m and infl%ent
temperat%re is loestL
eat re. > :,/:" kg4day ,*66 J4kg52C (+- H "*)2C ÷ 6.6+- kg4kg > *.+< "6"6 J4day
*. Comp%te $eat loss from t$e digester
;
> UA (3* H 3
")
$ere ; > $eat loss, J4$rT U > overall coefficient of $eat transfer, J4sec5m*52C (@3U4$r5ft*52B)T A > areat$ro%g$ $ic$ $eat loss occ%rs, m* (ft*)T 3
* > digester operating temperat%re, 2C (2B)T and 3
" > o%tside air
temperat%re, 2C (2B)O.
O Critical average air and gro%nd temperat%res are 6 and -2C, respectively."<
Design !"am#le (12)
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eat losses from t$e digester occ%r from t$e roof, &ottom, and side alls
a. Comp%te area of roof oof slope > "-L" > ("+.74*) mL6./ m
oof area > πD(slant lengt$)4*
oof area > (π "+.7 m /.:7 m)÷* > "7.< m*
&. Comp%te area of side allsArea of side all a&ove gro%nd level > πD E1posed $eig$tAss%me -68 side all is e1posed
#ide all area a&ove gro%nd > π"+.7 m:.- m4*>":*.< m*
*6
Design !"am#le (1')
m/.:7m)(6./*
m"+.7
cover)of rise(=ertical*
D$eig$t#lant
*
*
*
*
=+
=
+ =
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Area of side all &elo gro%nd > ":*.< m*
c. Comp%ted &ottom area
Digester &ottom is sloped at " vertical to + $ori'ontal.
3otal drop of t$e &ottom slope at t$e center > D ÷ (* +) > "+.7 m ÷ (* +) > *.+ m @ottom area > π "+.7 m √("+.7 m4*)* (*.+ m)*
> "--.- m*
d. #elect overall coefficients of $eat transfer for different areas
Digester floating covers and roofing consist of /.-mm ("4in.) plate steel, 7/mm (+in.) rigid foam
ins%lationX, inside air space, and &%ild%p roofing ",*+/ kg4m* (76 l&4ft*) H UO > 6.
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E1posed digester side +66mm ("*in.) concrete, 7/mm (+in.) %ret$ane foam ins%lation, "66mm (in.)
&rick siding H U > 6./: J4sec5m* 52C
@%ried digester side +66mm ("*in.) concrete s%rro%nded &y moist soil H U > 6.: J4sec5m* 52C
Digester &ottom s%rro%nded &y moist soil H U > 6./* J4sec5m* 52C
e. Comp%ted $eat loss from t$e digester
eat loss from t$e cover and roofing > "7.< m* 6.<
J4sec5m* 52C (+- H 6)2C :/,66 sec4day > .6+ "6: J4day
eat loss from e1posed all > ":*.< m* 6./: J4sec5m* 52C
(+- H 6)2C :/,66 sec4day
> +.7/ "6: J4day
eat loss from &%ried all > ":*.< m* 6. : J4sec5m* 52C
(+- H 6)2C :/,66 sec4day
> .+ "6: J4day
**
Design !"am#le (1,)
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eat loss from &ottom > "--.- m* 6./* J4sec5m* 52C
(+- H -)2C :/,66 sec4day
> *.-6 "6: J4day
3otal $eat loss from eac$ digester > ".7* "6: J4day
3otal $eat loss from &ot$ digesters, incl%ding *68 minor
losses, and *-8 emergency condition > ".7* "6: J4day
* ".- > -.6< "6< J4dayf. Comp%te t$e $eating re%irements for t$e digester
eat re%irements for ra sl%dge
%nder critical condition > *.+< "6"6 J4day
eat loss from t$e digester > *./< "6: J4day
3otal $eating re%irement > *.:* "6"6 J4day
> "."7- "6< J4$r
> "."7- "6/ kJ4$r
*+
Design !"am#le (1-)
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$ Selection of eating 4nits and !nergy %alance
". #elect e1ternal $eat e1c$anger
Provide to $eating %nits eac$ rated as ".*- "6/ kJ4$r ("."< "6/ @3U4$r) it$ nat%ral gas. 3$e
digester gas $as appro1. /-8 of t$e $eating val%e of t$e nat%ral gas (+7,+66 kJ4m+). 3$erefore, eac$ %nit
ill &e derated at ".*- 6./- (≈6.:"+) "6/ kJ4$r (6.77 "6/ @3U4$r). 3otal $eat provided &y to%nits > * 6.:"+ "6/ > "./*/ "6/ kJ4$r.
3$e act%al average $eat re%irements are s%&stantially less.
*. Comp%te digester gas re%irements
At 7-8 efficiency of $eating %nits
*
Design !"am#le (1.)
+:8"6"."7-
"66)"6"."7-"6("./*/
availa&le
capacitye1tra8/
//
=×
××−×=
4daym*,""4$r m:
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3otal %antity of digester gas prod%ced > *,--6 m+4day
3$is gives appro1. *68 e1cess gas %nder t$e most critical condition $en t$e digester $eating demand is
greatest. E1cess gas ill &e %sed to prod%ce $eated ater for ot$er plant %ses.
+. Design make%p $eat e1c$angers for e1ternal sl%dge $eating
a. Comp%te average temperat%re rise of t$e sl%dge t$ro%g$ t$e e1ternal e1c$angers
Provide *+cm (
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Average sl%dge temperat%re entering t$e e1ternal $eat e1c$anger > +-2C
Ass%me average sl%dge temperat%re increase after passing t$ro%g$ t$e $eat e1c$anger > ∆32CAss%me specific $eat of sl%dge is ,*66 J4kg⋅2C (same as for ater)
3otal $eat re%ired from eac$ digester > *.:* "6"6 J4d (F**) > "."
"6"6 J4d.
f t$e efficiency of t$e $eat e1c$anger is :68.
".-+: "6"6 ∆3 J4day 6.: > "." "6"6 J4day
*/
Design !"am#le (10)
J4day3["6".-+:
kg4day"6+.//*C3[Ckg
J,*66sl%dget$etos%pplied$eat3otal
"6
/
××=
××°×°⋅=
C"."-6.:J4day"6".-+:
J4day"6"."[3
"6
"6
°=××
×=
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Average temp. of t$e sl%dge entering $eat e1c$anger > +-2C
Ave. temp. of t$e sl%dge leaving $eat e1c$anger > +/."-2C
#l%dge recirc%lation of +,- "." "6"6 J4day
f *-8additional $eating is provided to acco%nt for $eat losses,
3otal $eat re%ired per digester > "." "6"6 J4day ".*-
> ".7/ "6"6 J4day
3otal $eat re%ired for &ot$ digesters > +.-* "6"6 J4day
3otal $eat availa&le in digester gas > *+,666 kJ4m+ "."/* kg4m+ *,--6 m+4d ",666 J4kJ > /.:*
Using specific $eat of ater > ,*66 J4kg52C
eating val%e of digester gas > *+,666 kJ4m+*7
Design !"am#le (2)
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3otal $eat s%pplied &y ater > ,*66 J4kg52C +-2C
> "7,666 J4kg
ot ater recirc%lation rate t$ro%g$ t$e common $eat
e1c$anger > +.-* "6"6 J4day ÷ "7,666 J4kg
> *.6 "6- kg4day
=ol%me of ater recirc%lated > *. "6- kg4day ",666
g4kg
÷ (" g4cm+ "6/ cm+4m+) > *6 m+4day
c. Comp%te t$e lengt$ of sl%dge pipe in $eat e1c$anger Yacket
Average temp. of t$e sl%dge in t$e $eat e1c$anger
> (+- +/."-)2C ÷ * > +-.-:2CAverage temp. of t$e $eating ater in t$e $eat e1c$anger
> ( 77.-2C
Ass%me $eat transfer coefficient of e1ternal ater Yacketed
$eat e1c$anger > ,666 kJ4$r5m* 52C (" (77.- +-.-:)2C ,666 kJ4$r5m* 52C * $r4day
> .6* "6/ kJ4day5m*
*:
Design !"am#le (21)
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3otal area of t$e sl%dge pipe for eac$ $eat e1c$anger
> ".7/ "6"6 J4day ÷ (.6* "6/ kJ4day5m* ",666 J4kJ) > .+: m*
;engt$ of *+cm ( .+: m* ÷ (π 6.*+ m) > / mProvide /m long, *+cm diameter $eat e1c$anger sl%dge pipe per digester into a common $ot ater Yacket.
I$ &as Storage and Com#ressor e3uirements
". Comp%te t$e diameter of t$e gas storage sp$ere
Provide a total of +day gas storage to serve t$e digester $eating re%irements and ot$er plant %ses
3otal gas stored > + day *,--6 m+4day
> 7,/-6 m+ (standard condition, 62C and " atm)
#torage press%re > -." atm (ass%me) #torage temperat%re > -62C s%mmer
#torage vol%me, =*
> P"
="
3*
4P*3
"#%&script " stands for gas prod%ced and * for gas stored.
*<
Design !"am#le (22)
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=*
> " atm 7,/-6 m+ (*7+ -6)K ÷ G-." atm (*7+
6)IK > ",77.7 m+
Provide a $ig$ vol%me gas storage sp$ere
=ol%me of sp$ere > π4/ (diameter)+Diameter of sp$ere > (",77.7 m+ /4 π)"4+ > "- m (< ft)
Provide "- m (< ft) diameter sp$ere for gas storage
*. Comp%te si'e of $ig$press%re gas compressors
Compressors are %sed to compress t$e digester gas into t$e gas storage sp$ere.
3otal eig$t of digester gas prod%ced %nder standard conditions > *,-: kg4day (#tep E.+)
Ass%ming eig$t of gas compressed is *668 of prod%ction rate, t$en
> * *,-: kg4day "4:/,666 day4sec > 6.6-< kg4sec
> :.+" kJ4kmol5K e > compressor efficiency of 7-8
36 > inlet temperat%re > (*7+ +-)2C
+6
Design !"am#le (2')
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P6
> ".6+ atm (gas press%re inside t$e floating cover is
normally less t$an 6. m of ater)
P > -." atm
Provide to constantspeed compressors eac$ driven &y 7.- kW ("6$p) electric motor.
5$ Digester &as 6i"ing
". Comp%te poer re%irements for gas mi1ing
Poer re%irements for gas mi1ing of t$e digester
P > 9*\=
$ere 9 > velocity gradient, "4sec.
+"
Design !"am#le (2*)
-$p)"+.7kW("7."".6+
-."
6.7-:."
+-)(*7+:.+"6.6-<
"P
P
e:."
3P
6.*:+
6.*:+
6
6
=
−
⋅+××=
−
⋅=
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3$e vol%me of eac$ digester, = > ","7 * times t$e viscosity of ater at +-2C
> * 6.7+ "6+ S5sec4m* > "./ "6+ S5sec4m*
=elocity gradient for sl%dge a&ove -8 solids is over 7- "4sec. Use 9 > :- "4sec.
P > :-* ",/ "6+ S5sec4m* ","7 "*. S5m4sec ( "/./ $p
3otal poer re%ired for to digesters > * "*. kW> *.: kW > ++.* $p
Provide t$ree compressors eac$ driven &y "-k (*6$p) motor.
3otal poer provided for mi1ing > - k (/6 $p)
3o compressors ill deliver t$e re%ired poer, $ile t$e t$ird compressor ill &e a stand&y, serving
&ot$ digesters.
*. Comp%te gas flo3$e digester gas flo rate for mi1ing, , can &e calc%lated %sing t$e e%ation in t$e previo%s slide.
+*
Design !"am#le (2,)
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3$e vol%me of eac$ digester, = > ","7 * times t$e viscosity of ater at +-2C
> * 6.7+ "6+ S5sec4m* > "./ "6+ S5sec4m*
9as flo per digester > 6." kg4s ÷ ("."/* kg4m+ 6.:/) > 6." m+4s
+. #elect digestermi1ing arrangement3$e digester mi1ing ill &e ac$ieved &y flo recirc%lation, ra sl%dge, and internal gas mi1ing.
3$e sl%dge recirc%lation of +,- :/8 of air ("."/* kg4m+) ++
Design !"am#le (2-)
kg4sec6."
"".6+
*.K +6:K kJ4kmole:.+"
6.7-kg4kmole:."kW"-
6.*:+=
−
×⋅
××=
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Digester Startu#
". a%l appro1. *-6 m+ seed and transfer it into one digester.
*. Bill t$e digester it$ ra asteater.
+. #tart $eating and mi1ing, and &ring to operating temperat%re.
. @egin feeding ra sl%dge at a %niform rate appro1. *-8 of daily feed per digester. ncrease t$eloading grad%ally.
-.!aintain t$e folloing records
a. Q%antity of 3=# fed daily
&. 3=#, =#4Alk ratio, and p
c. 3emperat%re, gas prod%ction, and C* content in gas
/.At lo feeing rate, it is possi&le to &ring normal operation it$o%t adding c$emicals for p control.
f =A4Alk ratio rises to ≥ 6.:, and p is &elo /.-, addition of c$emicals s%c$ as lime or soda as$may &e considered.
7. Bairly sta&le conditions s$o%ld &e reac$ed in +6]6 days if loading is kept &elo " kg =#4m+5day.
+
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Common 7#erating +roblems
". A rise in =A4Alk ratio ( 6.+), increase in C*
content, decrease in p, rancid or
*
# odors are
indication of $ydra%lic or organic loading, e1cessive it$draal of digested sl%dge, or incoming to1ic
materials.
*. Poor s%pernatant %ality may &e d%e to e1cess mi1ing, ins%fficient settling time &efore sl%dgeit$draal, too lo s%pernatant draoff point, and ins%fficient sl%dge it$draal rate.
+.
Boam in s%pernatant may &e %se to sc%m &lanket &reaking %p, e1cessive gas recirc%lation, and organic
loading.
. 3$in digested sl%dge may &e d%e to s$ort circ%iting, e1cessive mi1ing, or too $ig$ sl%dgep%mpingrate.
-. 3ilting floating cover may &e d%e to %neven distri&%tion of load, t$ick sc%m acc%m%lation aro%nd t$eedges, rollers or g%ide &roken or rollers o%t of adY%stment.
/. @inding cover (even $en rollers and g%ides are free) may &e d%e to damaged internal g%ides or g%yires.
+-
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7#eration and 6aintenance
8ey 7#erational &oals
!inimi'e e1cess ater
Control organic loading
Control temperat%re
Control mi1ing
ed%ce acc%m%lation of sc%m
Wit$dra s%pernatant t$at is lo in solids
outine Digester 7#eration and 6aintenance Checklist
C$eck digester gas press%re.
Drain daily t$e condensate traps.
Drain daily sediment traps.
C$eck daily gas &%rner for proper flame.
ecord daily floating cover position, c$eck cover g%ides, and c$eck for gas leaks.
ecord daily digester and nat%ral gas meter readings.
C$eck daily and record f%el oil.
C$emical daily gasmi1ing e%ipment for flo and gas.
C$eck daily press%re relief and vac%%m &reaker valves.