The sustainability of clean coal technology: IGCC with/without CCS

Integrated gasification combined cycle power generation (IGCC) is one of the emerging clean coal technologies for reducing greenhouse emissions in coal-fired electricity generation. IGCC technology, both with and without CO2 capture and storage (CCS) is compared with conventional super-critical power generation based on pulverized coal. The comparison is based on an equal consumption rate of Queensland black coal. The sustainability parameters being investigated are: thermal efficiency, environmental performance, inherent safety and economics.The IGCC processes have been modeled using commercial steady-state mass and energy balance software. Both the gross and net thermal efficiencies of the IGCC power station are reduced when the plant is configured for CCS. The net efficiency is reduced from 32.1% to 26.1%, when 81% of the CO2 is captured. This delivers an overall reduction in CO2 emissions per unit of electrical energy output of 73.2% compared to the reference plant. However, environmental performance in other areas suffers as a result of switching to IGCC-CCS, particularly fresh water consumption is increased by 2.5 tonne/MWh for both coastal and inland locations. Inherent safety risks associated with IGCC are also greater with the gasifier being the highest risk unit in the facility with a Dow fire and explosion index of 168 compared with an index of 107 for a conventional boiler. Toxicity hazard also increases with carbon monoxide present at concentrations several thousand times higher than the TWA limit. The minimum viable selling price of electricity for a 7% IRR is calculated to increase from USD80 MWh−1 for a conventional power station to USD101 MWh−1 for IGCC and to USD145 MWh−1 for IGCC-CCS.It is concluded that the application of IGCC-CCS is highly effective in reducing carbon dioxide emissions, the highest-profile problem associated with coal-fired electricity. There is an economic penalty which has been previously documented. However, there are also drawbacks concerning inherent safety and other environmental factors apart from CO2 emissions, which until now have been under emphasized.

Research highlights▶ The IGCC without CCS has a lower net efficiency (32%) compared to conventional power generation (37%). ▶ IGCC has considerably higher water demands than conventional coal power generation for both inland and coastal locations. ▶ The IGCC process reduces the atmospheric emissions of SOx and NOx. However, this is done by transferring the environmental burden to the wastewater system. ▶ The risk associated with fire and explosion is increased in probability for IGCC due to the increased number of process units, and in severity due to the process conditions. ▶ Risk associated with toxicity are almost nil in a conventional modern power station, but are significant in an IGCC process due to high concentrations of CO and H2S. ▶ The cost differential between the conventional plant and the IGCC-CCS plant is around USD100/tonne CO2.