Modelling of Biogas Supply Chains · I The model can help with deciding on type of input to use I...

Modelling of Biogas Supply ChainsIda Græsted JensenDepartment of Management Engineering, Systems Analysis

e-mail: [email protected]

DTU Management Engineering, Technical University of Denmark

Introduction Modelling the chain Results

What is biogas?

Biogas is gas based on waste or other methane sources, e.g.:

I Animal manure

I Deep litter

I Household waste

I Waste water

I Crops

Biogas can be produced by:

I Thermal gasification

I Anaerobic digestion

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Why do we want to use biogas in Denmark?

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Motivation for using biogas - energy

I High share of wind energy ⇒ need of an alternative,renewable electricity source

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Why biogas?

Biogas production has several advantages:

I Renewable energy - storage opportunities

I Reduction on GHG emissions

I Improved fertiliser

I Redistributions of nutrients

I Reduced smell

I Possible use of waste products

I Job creation in rural areas

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Biogas in Denmark

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Biogasproduktion pr kommune (TJ/år)01 - 5051 - 100101 - 200201 - 500

! Biogasanlæg

0 50 10025Kilometers

Biogasproduktion pr kommune

Kortet er opdateret 12 2015

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Biogas plants in Denmark

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Goal

I In 2020, 50% of all manure must be used for biogasproduction - corresponding to approximately 13 PJ

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The BioChain project

We want to help with reaching the goal!

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The plant level model

Objective:I Optimise the production of biogas while respecting

constraints of production and considering economy of scale

Waste/wastewater

FarmerPre-

treatmentPlant

Upgrade Demand

Demand

Week Hour

Week Hour

INPUT SIDE MODEL ENERGY SIDE MODEL

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The plant level model

Objective:

I Optimise the production of biogas while respectingconstraints of production and considering economy of scale

Waste/wastewater

FarmerPre-

treatmentPlant

Upgrade Demand

Demand

Week HourINPUT SIDE MODEL ENERGY SIDE MODEL

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Maabjerg Bioenergy Plant

Size: approximately 650,000 tonnes input and theoretically 18m3 of biogas

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Input side

More complicated than the output side:

I Flow of different biomassesI Both mass and energy potential must be accounted for:

I Mass needed for capacities and fertiliser outputI Energy potential needed for the final biogas yield -

changes during storage and pretreatment

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Energy side

Main problems: many possibilities through the chain and timeresolution

Desulfurisation

CHP

Upgrading Pressure regulation

Final use

Biogas storage

Water scrubbing

Organic physical scrubbing

Pressure swing absorption

Chemical scrubbing

Methanation

Boiler

SCGT

CCGT

Gas engine

Iron adsorption

Flaring

Bio-scrubbing

Bio-thrickling

7 to 40

Propane addition

1 to 40

Heat storage

Electricity

NG distribution grid (40 bar)

Heat

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Flow model

I A 3D/2D graph network: Dimensions are process p, time tand energy level e (only on input side)

Small example segment of the model - shown in 2D:

Farmer

Storage1SB

Ensilage

1 2 3 4 5 6 7 8 9 10

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Constraints I - general

For each process:

I Flow: includes mass loss for each process

I Capacity: restriction of amount of flow through eachprocess

I Process time: process time of each process must berespected

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Constraints II - for specific processes

For farmers:

I Input: what biomasses are available in each time step

For biogas plant:

I Maximum biomass type: restrictions on percentage energycrop of total mix

I Input to energy side model: equal to output from inputside divided by number of hours in a week

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Transportation of biomass

I Transported amount equals flow on transport edges

I Transported amount from each circle around the plantcannot exceed available amount within the circle

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Modelling scale effects on transportation

The resulting cost function:

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Constraints IV - economy of scale on plant

Economy of scale on biogas plant:

I Capacity: production cannot exceed capacity

I Bounds on plant size satisfied

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Results

I have been running the model purely on manure and sugar beetto determine if the model works and I find:

I Build as big as possible

I Upgrading biogas to bio natural gas seems most favourable

I Production of 8.6 million m3 bio natural gas - seems lowcompared to data from real biogas plants: potential inmanure is low!

I All the available sugar beet is used, meaning up to a radiusof 80 km

I Sugar beet is stored in order to use it throughout the year

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Conclusion

I Biogas plants should be feasible energy plants but prefersto substitute the natural gas

I The model can help with deciding on type of input to use

I The model is sensitive to small changes in input data

I The input side of the model can be used for any other typeof biomass plant (transportation) but the output side mustbe modified according to the plant type

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Modelling of Biogas Supply Chains · I The model can help with deciding on type of input to use I...

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