Among the major advantages hydrogen enjoys over other fuels is that it can be rapidly refueled in just a couple of minutes and has a range of many hundreds of kilometers. The best option would depend on the final cost, carbon mitigation potential, and consumer needs in each case. In the current context, experts believe that a major chunk of the hydrogen economy would actually come from blue hydrogen and not green hydrogen.

 “There are only a few options to develop electricity from carbon free sources. These are green hydrogen with sources being wind, solar or hydrogen derived from nuclear sources. Hydrogen is of many types such as blue hydrogen which originates from fossil fuels and natural gas, green hydrogen from electrolysis of water and red hydrogen from nuclear source. Most of the processes require carbon capturing,” said Dr Klaus Brun, Director-Research & Development, Elliot Group.

 Dr Brun shared his insights through a presentation on ‘Hydrogen Compressor & Flex-op’ at the ‘NextGen Chemicals & Petrochemicals Summit 2022’ organized by Indian Chemical News last month.

“There are two major areas, one is green hydrogen and another is blue hydrogen. In the case of green hydrogen, the sources are wind, solar and water. Hydrogen economy is based on alternative energy curtailment and need for storage. Electrolysis is very expensive, first and maintenance cost. It is often cheaper to idle a plant than to give the power away. In terms of storage, green hydrogen has a round trip efficiency of 40%. It requires blending of hydrogen into the natural gas pipeline or new hydrogen system,” said Dr Brun. 

“Blue hydrogen can be produced from natural gas with carbon sequestration. It uses methane steam reforming process or partial oxidation gasification. About 10 kg of Co2 is created for every 1 kg of hydrogen produced. That requires a new Co2 transport system,” he added. 

“Even if electricity is free, the green hydrogen is significantly more expensive than blue hydrogen that will dominate the scene for the foreseeable future. Blue hydrogen based on fossil fuels, is derived mostly from natural gases.  This is produced at the fossil production site and at the end use side. In the likely hydrogen scenario, blue hydrogen will dominate for at least 25-30 years, until electrolysis price is significantly lowered. Natural gas will be continued to be transported using existing pipeline infrastructure. Conversion from natural gas to hydrogen is most economical near or at the end user,” said Dr Brun.

“The hydrogen transport options include blending with natural gas in the existing pipeline network. It utilizes the existing infrastructure and operational safety impact on infrastructure is unknown. Hydrogen will be everywhere, including in domestic distribution, in often unknown compositions and percentages. Second option is to develop a pure hydrogen distribution network. Here too we have two ways, either blended hydrogen which is an obvious solution but has significant safety and infrastructure issues that need to be addressed.  Another way is pure hydrogen with manageable technical and safety challenges but high cost and long term development. However, both of these aren’t feasible. This begets the question that why not use the existing natural gas pipeline infrastructure,” said Dr Brun.

Sharing his thoughts on the compressor design challenge, Dr Brun said: “Among the design challenges for hydrogen compressors are light gas compression including low pressure ratio. In terms of coatings and safety, there is embrittlement which means loss of ductility due to H2 penetration. There is also a loss of coating and dis-bonding. In terms of safety, there are challenges such as explosivity, wide range of flammability, dispersion and impact radius, leak detection.”

“Hydrogen compression requires specific impellers and special coating. The high speed pure hydrogen compression requires 1200 fps tip speed impellers for conventional compressors and 2400 fps tip speed impellers for high speed compressors. However, here the problem is with the materials, seals and bearings,” he added.

Outlining the company’s role in providing the technology for hydrogen compression, Dr Brun said: “Elliot has been building hydrogen compressors since 1955. Over hydrogen rich compressor trains produced from 2001-2021.The company has built compressors for a wide range of applications from pure hydrogen to hydrogen rich process applications. For advanced impeller materials for hydrogen service, aluminium is the most probable solution among options including titanium which has embrittlement.”

 “To prevent the hydrogen embrittlement, coatings may improve the erosion and corrosion resistance. But these are not the long-term solutions as all coatings will eventually be worn away, spalled, or dis-bonded. We need advanced impeller designs for higher tip speeds wheels which are being worked upon by most of the manufacturers,” said Dr Brun.

“At this moment, the high speed design is 15 years away and therefore, it is prudent to use the available conventional solution, the Flex-Op compressor arrangement. It has 3-4 integral barrel arrangements with casing optimized speed. It has got high flow, high ratio and high efficiency. Compressor is compact with ease of access for maintenance and repair. It can process gas free from contamination. It has multiple side streams or extractions,” concluded Dr Brun.