Adding gas from biomass to the gas grid - SGC

Comparing efficiency data is a difficult task. The availability of data is poor and often these data lackin a clear definition of the system border. The most important efficiency is the total efficiency of thewhole chain between the input of renewable primary energy and the end-use by the consumer. Anydissipation of energy to the environment reduces the energy efficiency. By narrowing the systemborders essential parts of the chain are omitted and too high or low efficiency data are reported.Figure 1 gives a survey of the process from the input of solar radiation to the end-use of energy.This process follows the flow of materials and also the flow of energy. An important aspect is the‘balance of plant’ indicating the exchange of energy (and often also mass) between partialprocesses. The ‘balance of plant’ is an important tool to improve the total process efficiency. Theintegrated gasification combined cycle (IGCC) biomass power plant is an example with anelaborated balance of plant approach. This figure indicates also the partial processes: biomassproduction, biomass treatment, production of gas, conversion, distribution and finally the end-use.For each step a partial efficiency can be defined, in which care should be taken for the effects of thebalance of plant the input of energy from outside and losses to the environment. Often usedefficiency definitions are: total efficiency, gasification efficiency, efficiency heat production, efficiencypower production and distribution efficiency. The efficiency is always given by the ratio of totaluseful energy output divided by the total energy input, expressed as a percentage. The totalefficiency of the process is built from partial efficiencies in the chain from input to product.Subsystem: biomass production, collection and transportRadiation energy from the sun is collected and stored in biomass. All human activity later in thechain introduces losses. The addition of fertilisers, energy use in the collection and transport ofbiomass can do this. The balance of plant may be improved by using the ash from the gasificationprocess as fertiliser and by the use of bio fuel in the collection and transport apparatus.A practical limit is the diameter of the collection area. A 30 - 50 km diameter area seems to be themaximum.When organic waste, either liquid or solid, is used as the source of energy this subsystem is of no,or minor, importance.Subsystem: biomass pre-treatmentSome biomass conversion processes require some energy using facilities before the biomass canbe used. The facilities often include drying and grinding facilities. The energy needed by thesefacilities should be accounted for in the amount of primary energy.In the balance of plant the heat from the conversion subsystem can be used for drying.Subsystem: gas productionpage: 10