The foregoing discussion related to power generation scenarios. When coal gasification is the basis for production of hydrogen, synthetic natural gas, or ammonia, water usage is expected to change as a function of the many process differences between power generation and fuels, chemicals, or fertilizer synthesis. One of the recent Cost and Performance Baselines for Fossil Energy Power Plants, "Volume 2 - Coal to Synthetic Natural Gas and Ammonia (Various Coal Ranks)" establishes performance and cost data for coal fueled plants producing synthetic natural gas, and coproduction of synthetic natural gas (SNG) and ammonia, based on a dry-feed entrained-flow gasifier and include cases using bituminous, sub-bituminous, and lignite coals, and in configurations with and without carbon sequestration.
A water balance was performed for each case on the major water consumers in the process. The total water demand for each subsystem was determined and internal recycle water available from various sources like boiler feedwater (BFW) blow-down and condensate from syngas was applied to offset the water demand. The difference between demand and recycle is raw water withdrawal. Raw water withdrawal is the water removed from the ground or diverted from a surface-water source for use in the plant. Raw water consumption is also accounted for as the portion of the raw water withdrawn that is evaporated, transpired, incorporated into products or otherwise not returned to the water source it was withdrawn from. Results of the water balance for the various cases are shown in the following graph:
The primary observations that were drawn are:
Biomass Gasification and Water Use
Although IGCC is the application of gasification for which water use is most significant, the technology can offer water use advantages in some biomass energy applications. Biomass power plants have similar water use characteristics to coal plants. In addition, in some industrial processes, particularly in the paper and sugar industries, gasification can replace combustion technologies. The technology allows for the conversion of both biomass solids and black liquor into a gas that can fuel various processes or turn a gas turbine to provide electricity.