Advantages of Gasification – High Efficiency
Comparison of Gasification and Pulverized Coal Power Plants
In general, integrated gasification combined cycle (IGCC) power plants offer similar, if not better, efficiencies to other coal-based power plants. In a detailed comparison study performed by the NETL of various IGCC and pulverized coal (PC) power plant systems, expected plant efficiencies for IGCC averaged just above 40%, whereas PC plant efficiencies were 39.3 and 36.8% (supercritical and subcritical PC, respectively).
These efficiencies, however, are without carbon dioxide (CO2) capture and storage (CCS), a technology that is expected to be important—perhaps mandated—in the near future. In a CCS application, energy must be expended to separate, capture and then transport CO2 to a storage site. The NETL study showed that with CCS, IGCC is expected to achieve 31.6% plant efficiency versus 28.4 and 26.2% for supercritical and subcritical PC, respectively. Adding CCS technology reduces IGCC plant efficiency by 8.7%, but it decreases PC plant efficiency by almost 11%.
The main reason for this is that the CO2 in IGCC synthesis gas (syngas) is much more concentrated and pressurized than the CO2 in the flue gas of a PC power plant. Both concentration and pressure aid in separating CO2 from the syngas. The high CO2 partial pressure allows for the use of physical separation processes, whereas the PC gas separation must use a chemical absorption process because of low CO2 partial pressure. Chemical absorption and regeneration is relatively more energy intensive.
Gasification power can also offer efficiency benefits in the use of water. Raw water use in IGCC plants is lower than in pulverized coal plants. Without CCS, PC plants have a much higher steam turbine output, requiring more cooling water and condenser duties (typical raw water use ratio of 1.7:1.0). With carbon capture, the difference in water use is even more dramatic (2.5:1.0), as the chemical absorption process for CO2 capture in PC plants (amine) requires even more cooling water. In terms of raw water increase, CO2 capture increases raw water use by 37% for IGCC plants, versus a 95% increase for PC plants. For further discussion on water use in gasification, see the environmental benefits section.