Subject area: Hydrogen Compressors
Whenever we are talking about transporting or storing gaseous hydrogen, we know that this can only be done by compressing it.
One pillar of the ongoing energy transition to reach the ambitious CO2 reduction goals is using green hydrogen, which electrolyzers produce in the power-to-gas process, for transportation, industrial processes and as an energy storage medium.
»For all applications that require pure and not contaminated gases NEA can profit from its long experience with dry-running hydrogen compressors for pressures of more than 250 bar.«Jens Wulff, Managing Director Operations, NEUMAN & ESSER GROUP
Current examples for such power to gas projects are the 5,000 ton per year annual tenders in Germany or mega projects for 2 to 10 GW wind farms like NortH2 at the Dutch coast or the Danish-led North Sea Wind Power Hub project.
The idea is to mostly use the existing natural gas pipeline network for transporting hydrogen, initially by mixing it into the gas and in later steps by converting existing natural gas pipelines to pure hydrogen usage. Most of the big natural gas pipelines have a diameter DN of 800 to 1,200 mm and a PN of up to 100 bar, mostly operating at around 70-85 bar. Smaller regional natural gas pipelines mostly operate at 20-30 bar.
5,000 tons of hydrogen per year require about 150 MW onshore or 70 MW offshore wind farm capacity. With the typical fluctuation around 1,400 kg/h or 15,000 Nm3/h hourly peak production capability are needed for the offshore solution.
For projects like NortH2 with 3-4 GW wind power by 2030 and 10 GW by 2040 we are talking about 240,000 to 320,000 tons per year in 2030 and 800,000 tons per year in 2040. This means a peak hydrogen production of around 73,000 kg/h or 800,000 Nm3/h in 2030 and 183,000 kg/h or 2,000,000 Nm3/h in 2040.
The required electrolyzers can be installed both on- and offshore. As the sizing of the required compressors depends very much on the inlet pressure, the layout of the electrolyzers plays an important role. The main types which are nowadays in use are alkaline electrolyzers and polymer electrolyte membrane electrolyzers (PEM). They both exist with atmospheric outlet pressure and as pressurized systems. At around 20-30 bar outlet pressure we can find a sweet spot of efficiency and costs for the electrolyzers and the connected compressor systems. For all these applications that require pure and uncontaminated gases NEA can profit from its long experience with dry-running hydrogen compressors for pressures of more than 250 bar. For even higher pressures far exceeding 1,000 bar NEA Group member Andreas Hofer Hochdrucktechnik offers hydraulic driven piston or diaphragm compressors.
For the 5,000 tons of hydrogen per year case with 25 bar inlet pressure we would recommend using two smaller NEA two-stage compressors with 2 x 50 % capacity. This ensures a low invest while still ensuring high availability. The drive power of each compressor for the compression of 8,000 Nm3/h of hydrogen from 25 to 85 bar is only around 400 kW. This means that only 1,7 % of the energy contained in the 8,000 Nm3 of hydrogen (calculated with the lower heating value) are used for compression to fill the hydrogen into a pipeline with a pressure of 85 bar. Such a compressor plant can be installed on steel base frame with a footprint of around 7 x 4 meters.
In order to feed the year 2030 hydrogen peak production of NortH2 into the hydrogen grid under the same pressure conditions as mentioned above three large scale compressors with 13 MW drive power are needed. For 2040 eight of these machines will be needed. This means that again only 1.6 % of the energy stored in the hydrogen is used for compressing it into the pipeline system. The footprint of each compressor system will be around 20 x 25 meters.
The energy transportation capability of a hydrogen pipeline is huge. A DN 1,000 pipeline operated at 85 bar with a moderate gas speed of 15 m/s can transport 3,600,000 Nm3/h. Multiplied with the lower heating value of hydrogen (2.995 kWh/Nm3) we can transfer for more than 10 GW of power with a single pipeline. That means that just six pipelines would be enough to transfer the current electric power production of Germany. Compared to natural gas pipeline transportation the pressure drop of hydrogen is only at around one tenth, allowing higher gas speeds while still saving significantly on transport compressor stations.