Hydrogen Production
Existing as either a gas or a liquid, hydrogen is used in a wide range of processes including semiconductor manufacture, laboratory analysis, welding, energy storage and balancing of the electrical grid. It is also used as a fuel for vehicles such as trains, ships, forklifts and even spacecraft. Between 80-95% of hydrogen is sourced from fossil fuels, particularly from natural gas. Hydrogen is produced from natural gas by reacting the gas with high temperature steam. Because of this green hydrogen, hydrogen made using renewable energy and feed sources, has been increasing in importance. One method of green hydrogen is hydrogen production via biomass related processes. These can include fermentation of waste organic matter or using photosynthesis and a combination of algae and cyanobacteria to produce hydrogen. However, the biomass sector makes up only 1% of global hydrogen production.
The second largest segment for hydrogen production is water electrolysis. Although this sector makes up a small proportion of global hydrogen production, it has the advantage that it can be entirely powered using renewable energy. Hydrogen electrolysers work by using electricity to split water into hydrogen and oxygen. Typically hydrogen electrolysers require 50 kWh per kg of hydrogen produced although innovations have reduced this to 41.5 kWh/kg. When the electricity is sourced from renewable sources (such as solar, wind or hydroelectric power), the resulting hydrogen is termed “green hydrogen”. Green hydrogen acts more as energy storage medium and not a fuel source. This allows for its use during periods of low renewable generation, evening out power supplies.
Ultrapure Water for Hydrogen ELectrolysers
Alkaline and Proton Exchange Membrane (PEM) electrolysers make up 80% of the current hydrogen by water electrolysis market. Both Alkaline and PEM electrolysers require ASTM Type 1 ultrapure water to ensure correct operation. High purity feedwater is also required to produce hydrogen of acceptable purity. ASTM type 1 water has a conductivity of 0.056 µS/cm, silica levels below 3 ppb and TOC levels less than 50 ppb. 9 L of ultrapure water is required to produce each kg of hydrogen. As a rule of thumb, 200 L/hr of water is required for each MW of electrolyser capacity. So a 10 MW hydrogen electrolyser will require a feed of 2000 L/hr of ultrapure water.
There are two widely used technologies for the bulk demineralisation of water – ion exchange and reverse osmosis. Ion exchange, which uses high concentration acid and base to regenerate the resin, has fallen out of use over the last two decades. In addition to the handling and storage issues of hazardous chemicals, ion exchange also required speciality resins and lacked flexibility. The development of Reverse Osmosis in the 1980s and 1990s, offered a viable alternative. Reverse osmosis (either single or two pass) can remove 98-99% of salt from a wide range of feedwater types. Additionally, a wide range of different membrane chemistries can be used to deliver high purity water.
Following Reverse Osmosis treatment, to achieve ASTM Type 1 water, the water needs to go through a final polishing stage. Polishing is mainly performed by mixed bed ion exchange or electrodeionisation. Mixed bed resins are cheaper but are often discarded as they are exhausted (instead of undergoing regeneration). Electrodeionisation, an electrical polishing method, is more expensive upfront but provides lower maintenance costs.
GReen Hydrogen
Once the ultrapure water is created, nitrogen is used to stop carbon dioxide from redissolving in the water (and increasing the conductivity). Ion exchange resins are also used in the recirculation loops in electrolysers to remove conductive species that are dissolved by the ultrapure water. If the electrolyser is producing green hydrogen, then the water treatment system that produces the ultrapure water feed also needs to be powered using renewable energy.
Moerk Water are experts in both the design of water treatment systems for hydrogen electrolysers and supporting water treatment systems with renewable energy. Contact Moerk Water today to find out more.
