anaerobic digestor design

8/17/2019 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+

7

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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10/36"6


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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

"7

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:


25/36

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)


29/36

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)


30/36

=*

> " 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')


31/36

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

=

−

⋅+××=

−

⋅=


32/36

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,)


33/36

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.*:+=

−

×⋅

××=


34/36

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.

anaerobic digestor design

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