Integration of Alkaline electrolysers with District Heating Networks in Sweden

Abstract: Abstract Hydrogen as an alternative energy carrier has been up for discussion over decades. Perhaps this time, however, the political momentum and global technical context could be advantageous enough for the hydrogen economy to finally materialize. Despite investments from the EU commission up to €470 billion in renewable hydrogen, there are economical challenges in the way of decarbonisation of different sectors. Introducing hydrogen to different sectors is rather expensive and the cost of green hydrogen production technologies (with electrolysers) need to be lowered. One way of increasing the income is by taking advantage of the by-products (heat and oxygen) from water electrolysis processes. This study aims to investigate the latest technologies available for, recovering waste heat as district heat and taking advantage of the hydrogen and oxygen. Each District Heating Network (DH network) has different requirements (regarding heat quality and quantity), in order to take advantage of the surplus heat. However for many DH networks 1 MW is the minimum quantity. This demand is not hard to fulfil with a 17 MW Alkaline electrolyser since the amount of heat that can be delivered varies from 3-6 MW from the start to end of life of the electrolyser. Suitable placements of the electrolyser in order to take advantage of the waste heat are presented in chapter 6. The variation in requirements (from the DH networks) is due to: geographical placement, infrastructure and experience of taking advantage of waste heat etc. For DH networks that allow 78 °C or lower temperature, three plate heat exchangers are required to recover heat from the electrolyser. If a higher temperature is required, a high temperature heat pump (HTHP) will be needed. In order to take advantage of the hydrogen and oxygen both gases need to be purified and compressed. Latest purification technology is membrane separation and some benefits from other purification technologies such as pressure swing absorption, are low energy consumption, higher efficiency and flexible operation. Latest compression technology is electrochemical compression. Some benefits of this technology is low energy demand and high efficiency. Regarding waste heat recovery, heat exchangers are preferred due to two facts. First, their capex is lower than HTHPs. Second, the increasing trend of lowering the forward flow temperature enables easier integration with low temperature waste heat. The future compressors for compressing hydrogen and oxygen will most likely be none-mechanical. Electrochemical compressors with high efficiency have great potential to penetrate the market and they are already used in PEM electrolysers from NEL to compress the hydrogen. A purifier and a compressor for hydrogen are often included in an electrolyser's capex, but in order to take advantage of the oxygen they need to be added to the system. Taking advantage of the oxygen is an option in the future when the price of effective compression technologies are decreased.