Modelling of Biogas Supply Chains Ida Græsted Jensen Department of Management Engineering, Systems Analysis e-mail: idje@dtu.dk
What is biogas? Biogas is gas based on waste or other methane sources, e.g.: Animal manure Deep litter Household waste Waste water Crops Biogas can be produced by: Thermal gasification Anaerobic digestion 2 / 21
Why do we want to use biogas in Denmark? 3 / 21
Why do we want to use biogas in Denmark? 3 / 21
Motivation for using biogas - energy High share of wind energy need of an alternative, renewable electricity source 4 / 21
Why biogas? Biogas production has several advantages: Renewable energy - storage opportunities Reduction on GHG emissions Improved fertiliser Redistributions of nutrients Reduced smell Possible use of waste products Job creation in rural areas 5 / 21
Introduction Modelling the chain Results Biogas in Denmark Biogasproduktion pr kommune 0 1-50 51-100 Biogasproduktion pr kommune (TJ/år) 0 25 50 Kilometers Kortet er opdateret 12 2015 100 101-200 201-500 Biogasanlæg 6 / 21
Biogas plants in Denmark 7 / 21
Goal In 2020, 50% of all manure must be used for biogas production - corresponding to approximately 13 PJ 8 / 21
The BioChain project We want to help with reaching the goal 9 / 21
The plant level model Objective: Optimise the production of biogas while respecting constraints of production and considering economy of scale Waste/ wastewater Upgrade Demand Farmer Pretreatment Plant Demand 10 / 21
The plant level model Objective: Optimise the production of biogas while respecting constraints of production and considering economy of scale INPUT SIDE MODEL Week Hour ENERGY SIDE MODEL Waste/ wastewater Upgrade Demand Farmer Pretreatment Plant Demand 10 / 21
Introduction Modelling the chain Results Maabjerg Bioenergy Plant Size: approximately 650,000 tonnes input and theoretically 18 m3 of biogas 11 / 21
Input side More complicated than the output side: Flow of different biomasses Both mass and energy potential must be accounted for: Mass needed for capacities and fertiliser output Energy potential needed for the final biogas yield - changes during storage and pretreatment 12 / 21
Energy side Main problems: many possibilities through the chain and time resolution Flaring Upgrading Water scrubbing Pressure regulation 7 to 40 Organic physical scrubbing Propane addition 1 to 40 Final use NG distribution grid (40 bar) Biogas storage Desulfurisation Iron adsorption Pressure swing absorption Chemical scrubbing Methanation Bio-scrubbing Boiler Heat storage Heat CHP SCGT Bio-thrickling CCGT Electricity Gas engine 13 / 21
Flow model A 3D/2D graph network: Dimensions are process p, time t and energy level e (only on input side) Small example segment of the model - shown in 2D: Farmer 1 2 3 4 5 6 7 8 9 10 Storage1SB Ensilage 14 / 21
Constraints I - general For each process: Flow: includes mass loss for each process Capacity: restriction of amount of flow through each process Process time: process time of each process must be respected 15 / 21
Constraints II - for specific processes For farmers: Input: what biomasses are available in each time step For biogas plant: Maximum biomass type: restrictions on percentage energy crop of total mix Input to energy side model: equal to output from input side divided by number of hours in a week 16 / 21
Transportation of biomass Transported amount equals flow on transport edges Transported amount from each circle around the plant cannot exceed available amount within the circle 17 / 21
Modelling scale effects on transportation The resulting cost function: 18 / 21
Constraints IV - economy of scale on plant Economy of scale on biogas plant: Capacity: production cannot exceed capacity Bounds on plant size satisfied 19 / 21
Results I have been running the model purely on manure and sugar beet to determine if the model works and I find: Build as big as possible Upgrading biogas to bio natural gas seems most favourable Production of 8.6 million m 3 bio natural gas - seems low compared to data from real biogas plants: potential in manure is low All the available sugar beet is used, meaning up to a radius of 80 km Sugar beet is stored in order to use it throughout the year 20 / 21
Conclusion Biogas plants should be feasible energy plants but prefers to substitute the natural gas The model can help with deciding on type of input to use The model is sensitive to small changes in input data The input side of the model can be used for any other type of biomass plant (transportation) but the output side must be modified according to the plant type 21 / 21