Synthetic Natural Gas (SNG) Production via Gasification Process with Blend of Coal and Wood Chip as Feedstock

The price of natural gas is relatively higher than that of coal and the capacity factor of NGCC (natural gas combined-cycle) unit is low in Taiwan. Synthetic natural gas (SNG) from solid fuel via gasification is possible to provide a relative lower price than that of natural gas to NGCC units and to decrease the costof electricity. The commercial chemical process simulator, Pro/II® V8.1.1, is implemented to build theanalysis model in the study. The four major blocks, consisted of air separation unit (ASU), gasification island, gas clean-up unit, and methanation processes, were built in the SNG production system model. The biomass, wood chip, is introduced to blend with kaltim prima coal (KPC) from Indonesia to investigate the effect of system efficiency and CO2 emission. The flow rate of feedstock is set as 2,000 t/d for a typical commercial gasifier with pure KPC feed. It is assumed that the total energy in feedstock is set as the same and 10 % flow rate increase is acceptable for the gasifiser. The percentages of wood chip in blended cases are introduced as 5 % and 10 %. Simulation results show that the cold gas efficiency of pure KPC, 5% wood chip blend and 10 % wood chip blend are 77.64 %, 76.10 % and 74.35 %, respectively. It means the gasification performance is slightly decreased due to the blend of wood chip. The system efficiency for SNG production of KPC, 5 % blend and 10 % blend are 61.02 %, 60.10 % and 58.86 %, respectively. In order to adjust the syngas content with a specific ratio of CO to H2, the amount of 63.51 %, 64.28 % and64.97 % CO2, respectively, is captured in the clean-up unit before entering the methanation processes. It means the CO2 emission could be lower than 450 g/kWh, based on the situation that CO2 is captured in the coal to SNG process. The biomass could further reduce the CO2 emission due to the advantage of carbon neutral.