2.2. Water Usage in Hydrogen or Ammonia Synthesis Scenarios

The foregoing discussion related to power generation scenarios. When coal gasification is the basis for production of hydrogen 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.

Hydrogen

NETL recently compared cost and performance of commercial technologies for hydrogen production from fossil fuels. The cases included natural gas reforming, as well as coal/biomass gasification-based hydrogen production with and without carbon capture. Analyses included a water balance for each case, in which raw water withdrawal, process discharge, and raw water consumption were quantified and compared. The results are provided in the figure below:

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 Raw water consumption accounted for as the portion of the raw water withdrawn that is evaporated, transpired, incorporated into products or otherwise not returned to the water source it was withdrawn from.

The following key observations were made:

• Steam methane reforming without capture (Case 1) had the lowest water demand of all cases (1.9 gal/lb H₂ raw water consumption), while the coal/biomass co-gasification plant with capture (Case 6) had the highest water demands of all cases (4.0 gal/lb H₂ raw water consumption).
• Carbon capture imposes a significant water demand on all technologies. The capture technologies have significant cooling water demands that result in increased raw water consumption because of increased cooling tower blowdown and cooling tower evaporative losses. Raw water consumption increased by 53 percent for both natural gas reforming cases with capture, 12 percent for the coal-only gasification plant with capture, and 60 percent for the coal/biomass co-gasification plant with capture.

These observations serve to show that water usage in gasification-based systems will remain a relatively important consideration in future hydrogen production systems, particularly for decarbonized hydrogen production.

Ammonia

A recent study¹ compared water consumption, carbon intensity, energy input, efficiency, and capital cost for conventional ammonia production and renewable ammonia production. Although CO₂ emissions of renewable ammonia production are negligible as would be expected, a surprisingly larger water consumption figure is incurred than the conventional ammonia route. At the same time, energy input and capital cost of the renewable ammonia are both higher:

Notwithstanding the higher water consumption of coal/biomass gasification with capture compared to conventional natural gas reforming for ammonia synthesis, a water consumption advantage over renewable ammonia should persist for all fossil fuel options.

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.

PIEMSA IGCC Project Environmental and Economical Benefits

1. Ghavam S, Vahdati M, Wilson IAG and Styring P (2021) “Sustainable Ammonia Production Processes.” Front. Energy Res. 9:580808. doi: 10.3389/fenrg.2021.580808

Water

• Water Usage in Coal to Power Applications
• Water Use in Hydrogen or Ammonia Synthesis Scenarios
• Coal to Liquids and Water Use
• Gasification Process Aqueous Effluents/Wastewater
• Operating Experience and Plant Data on Waste Water Discharges