Decarbonisation Technology - February 2024 Issue

Haber-Bosch ammonia synthesis reactor

Steam generation

Purge gas

Hydrogen and nitrogen feed

Condenser

Feed compressor

Liquid ammonia

Cooling water

Phase separator

Recycle compressor

Figure 2 The Haber-Bosch Ammonia synthesis process

The AMEA Power project involves USD $2 billion of investment and will be located close to the port of Ain Sokhna in the Suez Canal Economic Zone. It will produce 390,000 tonnes of green ammonia per annum to predominantly serve export markets. The hydrogen electrolysis scheme will require more than a million cubic metres of water per year. Fresh water from the Nile is required for other purposes, such as crop irrigation and to serve population centres, which are built up along the banks of the river. Therefore, major desalination facilities will be required to support the AMEA Power project and other green hydrogen projects in the Suez Canal Economic Zone. Ultrapure water comes at a cost, but reliable supply is mission-critical With freshwater feed, the capital cost of the equipment for ultrapure water supply for a typical green hydrogen project will be around 4-8% of the electrolyser scheme. Where desalination is also required, the capital cost of the whole water processing facility may represent 10-15% of the total equipment Capex for a green hydrogen electrolyser scheme. To put this level of capital expenditure into context, the power management system involving the transformer and rectifier to provide direct current (DC) electricity for the electrolyser would be around 20% of the total project Capex. So, water treatment is an essential element of

the scheme but is unlikely to be the dominant fraction of the green hydrogen project budget. With a freshwater feed, the operating cost of the ultrapure water plant will generally be less than 1% of the total green hydrogen plant Opex. This is a combination of dosing chemical costs and electrical power for high-pressure water pumps. The cost of the freshwater procurement may be 1-2% of the total operating cost if it is withdrawn from a local pipeline supply or brought in by road tanker. With seawater supply, that operating cost may rise to be around 3% of a green hydrogen scheme due to additional complexity. The capital and operating costs of ultrapure water are a small proportion of the project total, but the consequences of failure can be very high; reliability is therefore key. An interruption to the water supply would mean the electrolyser must shut down. For a PEM system, that is unlikely to result in equipment damage. However, for alkaline or solid oxide electrolysers, an unplanned shutdown may result in degradation of the electrolyser’s performance and a reduction in its efficiency. Impure water can be extremely damaging to the valuable electrolysers. Calcium or magnesium cations in the water will rapidly damage a proton exchange membrane (PEM) electrolyser membrane due to interaction with the water-splitting catalyst that coats the