1. Operational modelling of a green gas supply chain
J. Bekkering Msc
From biomass to injection into the gas grid
Biogas production from codigestion of cattle manure and biomass can have a significant contribution to a sustainable gas supply. Besides technological knowledge on processes, knowledge about the possibilities for biogas production are usually only available on a macrolevel, when the potential of a certain region, often at the size of a country or larger, for supplying biomass or generating renewable energy is investigated. However, in order to meet the ambitions of a future sustainable gas supply, questions should be answered like:
Where to build digesters and upgrading installations?
Where to inject green gas into the gas grid?
What scale level is optimal?
Therefore, an operational calculation model is under development to explore these questions. Our primary focus is on the northern three provinces of the Netherlands. Preliminary results are presented here. Future developments concern the implementation of matching supply and demand.varying the required gas quality (or blending) en upscaling the model to a regional approach.
3 northern provinces: ha land (32% farming, 33% grassland, 35% remaining)
Costprice as a function of scale level (preliminary results):
Sustainability criteria
Theme
Indicator
Greenhouse gas balance
Reduction in the chain should be at least 50% when compared to fossil energy, incl. application
Competition with food, local energy supply, medicine and construction materials
Availability of biomass for food, local energy supply, construction materials or medicine should not decrease
Biodiversity
No deterioration of protected areas or valuable ecosystems
Profit
No negative effects on local and regional economy
Prosperity
No negative effects on the well-being of employees and local population
Environment
No negative effects on the environment (waste, chemicals, erosion, emissions, etc.)
Costprice for 300 nm3/hr biogas production and injection (178 nm3/hr green gas):
Costprice (€/nm3 green gas)
Percentage
Biomass & Manure
0,095
12,7
Transport & Storage
0,073
9,8
Digester
0,172
23,0
Digestate
0,121
16,1
Cleaning & Upgrading
0,144
19,3
Injection
19,2
Total
0,750
100,0
Based on: combined farming (88 Dutch cows, 65 ha land, 25% of land used for energy maize), total land requirement 284 ha, upgrading PSA, 500 m gas pipeline for injection, digestate used as chemical fertilizer replacement.
The required gas quality may strongly influence the possibilities for green gas usage. Injection in a high pressure gas
grid may require strict specifications of the gas. Local usage of biogas might only need cleaning of the gas after which
it can f.i. be used in a gas engine. The scale levels in between might have their own challenges. The possibilities of blending biogas with natural gas is explored as well. The possibilities for blending depend on specifications of biogas as well as natural gas, and the flow in the gas grid. A project is in preparation to explore these possibilities (Flexigas).
With operations research techniques optimal transport movements and locations
for digesters, upgrading installations and storage can be calculated.
Usually cost prices are calculated in a static way, i.e. the prices are based on production amounts (see also above). It is interesting to see what optimisation can be achieved when the dynamic character of a green gas chain is considered. Therefore the characteristics of supply and demand are investigated.