MINLP PROCESS SYNTHESIS FOR BIOGAS

PRODUCTION FROM ORGANIC AND ANIMAL

WASTE

Rozalija Drobež, Zorka Novak Pintarič,

Bojan Pahor, Zdravko Kravanja

Scientific research centre Bistra Ptuj

University of Maribor Faculty of Chemistry and Chemical Engineering

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Outlay Outlay

Introduction Biogas process superstructure Aggregated mathematical model Mass balance and biogas production Logical and other constraints Heat balance of biogas production Objective function Solution of the industrial case study

Waste from slaughterhouse and other animal wastes are often mishandled and underutilized

Leading to many serious environmental and economic problems:

Efficient, economical and sustainable solution is needed, preferably one which converts waste into valuable products and

Biogas production is one: Significantly reduce impact on greenhouse gas emissions Preventing the accumulation of organic and animal waste Used for heat, electricity and liguid fuel production

Introduction Introduction

Industry for the operation need a lot of energy, which is still mainly produced from fossil fuels

Process integration is an efficient tool which enables the reducing consumption of heat, electricity, as well as freshwater and other resources

An aggregated mathematical model - mixed-integer nonlinear programming (MINLP) problem

Applied to a large-scale existing meat company in order to optimize the biogas production

Introduction Introduction

Biogas process superstructure Biogas process superstructure

Optimal choice for the processing of animal and organic waste from the large-scale meat company:

Biogas production by anaerobic fermentation at mesophilic or thermofilic condition

With or without a combination of the rendering plant Reconstruction of existing production plant:

Reconstruct the existing pig farm – continue with pork meat production

Adapt the existing pig farm to new poultry farm – start producing poultry as the company’s main activity

Biogas process superstructure Biogas process superstructure

Existing pig farm is adapted - necessary to provide an additional water source to fulfill all the production requirements

Water demands can be satisfied:As freshwater from a local well orFrom the another meat industrial plants as an industrial

wastewater Transportation of industrial wastewater:

By cisterns orA pressurized sewage pipeline

Wastewater treatment processes:Open water system – treated in a central treatment unit orClosed water system – treated by ultrafiltation and reverse

osmosis

Biogas process superstructure Biogas process superstructure

Aggregated form as a mixed-integer nonlinear programming (MINLP) problem for the selection of an optimal process for processing animal and other bio-waste

Maximizes the net present worth (NPW) as an objective function:Concave investment cost correlations,Subject to simultaneous mass and heat balances,Simplified design equationsSimplified relationship without reaction kinetics and time

constraints andDaily available quantities of substrates - given as mean values

Aggregated mathematical modelAggregated mathematical model

For simultaneous heat integration of continuous processes we had used a modified model, developed by Duran and Grossmann (1986): Allow the determination of minimum utility consumption (cost) in

an optimal process scheme Basic model is based on a pinch point location method for the

consumption of hot and cold utilities in the nonlinear optimization problem

We have modified basic nonlinear model to linear model: Have a constant temperature process streams Heat capacity of hot and cold process stream flows are variable Avoid nonconvexity and model can obtain global optimal solutions

Aggregated mathematical modelAggregated mathematical model

Definition of sets and binary variables: Set presented the inlet substrates and water supply

slaughterhouse waste of category III inlet substrates from the pig farm potential inlet substrates from the new poultry farm freshwater industrial wastewater substrates purchased on the market other inlet organic substrates

Set presented the solid product from the rendering plant1 = meat meal2 = animal fat3 = bone meal

Aggregated mathematical modelAggregated mathematical model

25,...,1I 11,...,41 I 3,2,12 I

16,..,123 I

164 I

15,145 I

23,166 I

25,...,177 I7I6I

2I

3I

4I

5I

1II

3,2,1KK

1I

2I

3I

7I

4I5I

6I

Data for inlet waste material, other substrates and water supply

Aggregated mathematical modelAggregated mathematical modelDefinition of sets and binary variables: Set presented the production processes

anaerobic conversion process rendering plant processes – can utilized the slaugh. waste of category III

1 = thermophilic proces 2 = mesophilic process + sterilization unit 3 = mesophilic process 4 = rendering plant

Set presented the cold processes streams Set presented the hot processes streams

J 4,3,2,1J 3,2,11 J

42 J

4,2,13 J

1J

2J

3J

C 20,....,1C

H 5,....,1H

Aggregated mathematical modelAggregated mathematical modelDefinition of sets and binary variables: Set presented the remeining background alternatives

alternatives – some additional investment existing pig farm new poultry farm water supply – freshwater waster supply – industrial wastewater transportation – industrial wastewater wastewater treatment closed water system open water system

Binary variable for the selection of optimal process and background alternatives: selection of optimal production process selection of optimal remaining background amternative selection of sterilization unit

8,....,1LL 7,5,2,11 L

12 L

23 L

34 L

45 L

6,56 L

8,77 L

78 L

89 L

1L2L3L4L5L6L

7L8L9L

PjyBlySy

Mass balance and biogas productionMass balance and biogas production

Mass balance for biogas production:

1RBGBGRWW

8

,,Jjqqqq

jjljji mvLl

mIi

m

1BGVSSBG

,JjSwqfq ii

Iimjv jij

Mass balance for the production of solid product :

2R

,,Jjqqq

jkjji mKk

SPm

Iim

Production of solid product:

KkJjqwqIi

mkm jikj

, 2SPSP

1

,,

Mass flow – rate of substrates:

IiqqJj

mm jii

,

S

(1)

(2)

(3)

(4)

(5)

Biogas volume flow – rate production:

RWW – recirculated wastewaterBG – biogasR – residueVSS – volative suspended solidSP – solid productS - total substrates

Mass balance and biogas productionMass balance and biogas production

71WWOWWCWW ,

,,,LlJjqqq

ljljlj mmm

Mass balance for wastewater:

(6)

1RWWDMC,

,RWWDMCWWWW 11

8

,,

7

,Jjwqwqwq lj

Llmi

Iim

Llm ljjilj

Mass flow rate of wastewater:

(7)

81OFRWWWWC ,

,,,LlJjqqq

ljljlj mmm

Mass flow rate of wastewater to closed water network:

81WWCRWWRWW ,

,,LlJjqwq

ljlj mlm

Mass flow rate of the recirculated wastewater :

(8)

(9)

Mass balance for industrial wastewater:

5TS

6

,Iiqq

Llmm lii

(10)

WW – wastewaterWWC – wastewater to closed water networkWWO– wastewater to open water networkDMC – dry matter contentOF – organic fertilizerT - transported industrial wastewater

Logical and other constraints Logical and other constraints Constraints for substrates: Limited by the available daily amount of the substrates

JjIiyqq

JjIiyqq

jmm

jmm

jiji

jiji

,

,

PUP

PLO

,,

,, (11)

Constraint for the inlet substrates from the pig farm and new poultry farm

212BUP ,,

,,LlJjIiyqq lmm jiji

(12)

313BUP ,,

,,LlJjIiyqq lmm jiji

(13) Constraint for the water supply as freshwater and industrial wastewater

414BUP ,,

,,LlJjIiyqq lmm jiji

(14)

515BUP ,,

,,LlJjIiyqq lmm jiji

(15)

Constraint for the residue

Jjyqq jmm jj PUPR,R

(16)

LO – lower bounds UP – upper bounds

Production of solid product is limited by the daily capacity of the process

2PUPSP,

,Jjyqq j

Kkm

Kk

SPm kkj

(17)

Logical and other constraints Logical and other constraints Constraints for biogas production:

1PUPBG,BG

1PLOBG,BG

Jjyqq

Jjyqq

jvv

jvv

jj

jj

(18)

Constraints for wastewater:

7,1PUPWW,WW

,,LlJjyqq jmm ljlj

(19)

Constraint for the recirculated wastewater

8,1BUPRWW,RWW

,,LlJjyqq jmm ljlj

(20)

Constraint for an organic fertilizer

8,1BUPOF,OF

,,LlJjyqq jmm ljlj

(21)

Constraint for transported industrial wastewater

6,5BUPT,T

,,LlJiyqq jmm lili

(22)

Constraint for dry matter content

1RWWm

RDMCRWWDMC,,

RWWm

DMC 8

lj,,

8

lj,,Jjqqwwqwq

LlIimlj

Lli

Iim jiji

(23)

Logical and other constraints Logical and other constraints Constraints for the selection of process and background alternatives:

1P3

P2

P1 yyy (24)

Existence/non – existence of background alternatives in the optimal solution

1B2

B1 yy (25)

If the new poultry is selected – necessary to supply some process water

B2

B4

B3 yyy (26)

If industrial wastewater is selected – transportation B4

B6

B5 yyy (27)

Selection between wastewater treatment

1B8

B7 yy (28)

Selection between processes

Heat balance of biogas productionHeat balance of biogas productionHeat capacity flow rate for cold and hot streams in the processes: Slaughterhouse waste of category III

d1m

KO

c1

3 1

, fcqCFJj Ii

pji

Substrates and water supply

1d1

m,c 1,

JjfcqCFIi

pj ji

Recirculation wastewater

8d1

RWWm

RWWc ,1 1

,LljfcqCF plj

Slaughterhouse waste of category III which can used for biogas production

3d1

mh, 11

,JjfcqCF

Iipj ji

Wastewater which we treated in the treatment unit

7d1

WWm

WWh ,1 1

,LljfcqCF plj

Biogas production

1d1

BGBGBGv

BGh fcqCF pj

Total heat combustion of cogeneration system

1d2

BGTBGv

SPTE 11

JjfeqJj

jj

1 KOc cFCF c

4,....,0),31( 1jc, jcFCF c

17 RWWc cFCF c

3h, jhFCF hj

3 WWh hFCF h

4 BGh hFCF h

)5 PORAB hFh

(29)

(30)

(31)

(32)

(33)

(34)

(35)

Heat balance of biogas productionHeat balance of biogas production In this model, it was assumed:

two hot utility – steam and heat from cogeneration system one cold utility – cooling water inlet/out let temperatures of hot and cold streams – fixed specific heat capacity of substrates – fixed heat recovery approach temperature – 20K

Heat loss of anaerobic fermentation – is considered

Cc

c

C

Hhh

COLDHOTH

USEDSOLDCHP Total heat balance for the cogeneration system :

Total heat balance of heat integrated process :

HhTTF hhhh OUTINHOT

CcTTF cccc INOUTCOLD

110m

m0izg ,17

ji,

, JjjcFq

qc

ji

(36)

(37)

(38)

(39)

(40)

Heat balance of biogas productionHeat balance of biogas production Upper bound for the heat excange of hot streams:

PpTTTTF

TTTTTTF

hhhh

cccc

,0max,0max -

,0max,0max

5

1

POUTPIN

20

1min

PINmin

POUTH

Pinch temperatures

stream cold is p candidate if

streamhot is p candidate if

minIN

INP

TT

hTT

c

h

Upper bound for the heat excange of cold streams:

Hhhhh

Ccccc

H

TTTTTTF

TTTTF

)(,0max)(,0max -

,0max,0max

minPOUT

minPIN

PINPOUT

If the process is not heat integrated

Hh

hHOTH

Cc

cCOLDC

(41)

(42)

(43)

(44)(45)

The objective function maximizes the net present worth (NPW), in which investment cost is subtracted from discounted cash flows

Objective functionObjective function

ct

t

Frr

rIW

D

D

)1(

1)1( max

dd

dNP

Investment for the processes

BBPR,0BG,0

BG

0

121

lLl

ljJj

j

n

v

v

Jjj yIyI

q

qII

j

j

Cash flow is defined by the following substitutive equation

DrERrF ttc 1

Incomes – revenue from selling electricity, heat, solid product, organic fertilizer

d4

OF

m

OFSP

m

SPPRODTSEBGBG

v

ES )(1 8

,

2

,

1

fqcqcceqcRJj Ll

lJj Kk

kJj

j ljkjj

Expenses – cost for purchasing electricity, substrates, treating and transport , utility

d4d3CHPS

HVPST

mTWW

mmS

0,

mR,0v

PR,0fBG,0

v

BGv0E ))( )((

5 6

,

1 9

,

6 1

,

2

2

1 2

,

1

ffQcQcqcqcqcq

q

cycq

qpcE

Ii Lll

Jj Ll

Pl

Ii Jji

JjJj

Rm

Ii Jjj

Jjj liljji

j

ji

j

j

(46)

(47)

(48)

(49)

(50)

Solution of the industrial case studySolution of the industrial case study

The results of economical analysis indicate that the optimal solution is:Biogas production under thermophilic conditions without a

rendering plantIncludes potential substrates from the new poultry farmAll slaughterhouse wastes of category IIIProcess scheme comprises a freshwater source from a local

wellAdditional closed water network with the re-use of purified

wastewater and by-product as an organic fertilizer

Economic evaluation of results for mass and heat integration of biogas production

Results for mass and heat integration of biogas production

Solution of the industrial case studySolution of the industrial case study

Net present worth (NPW) is 11.80 MEUR and payback period 3.59a.

Almost complete consumption of hot 889 kW and 1/2 of cold utiliy 349 kW

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4.1MW3.5MW

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Solution of the industrial case studySolution of the industrial case study

Net present worth (NPW) is 7.31 MEUR and payback period 4.23a.

Almost complete consumption of hot 681 kW and 1/2 of cold utiliy 151 kW

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2.8MW 2.4MW

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THANK YOU FOR YOUR ATTENTION

zdravko.kravanja@uni-mb.si

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