|Compression is a major contributor to the cost of hydrogen fueling. Source: Elgowainy et al. Click to enlarge.|
Southwest Research Institute (SwRI) will begin work in August on a $1.8-million contract awarded by the US Department of Energy DOE to develop, to fabricate and to test a linear motor reciprocating compressor (LMRC). The contract is one of 10 awarded by DOE for projects that will advance hydrogen production and delivery technologies for this fuel source. (Earlier post.)
In its 2012 Multi-Year Research, Development and Demonstration Plan, DOE notes that hydrogen fueling station compressor flow rates may be 5 - 100 kg/hr and require compression pressures as high as 90 MPa (900 bar). (Consumer vehicles will likely require gaseous hydrogen compressed to 70 MPa to meet acceptable range targets.) At present, hydrogen delivery (which includes compression) and storage is an expensive operation. Capital costs are high, and the equipment used is often inefficient and unreliable, leading to costly routine maintenance, repairs and downtime.
Currently, high-pressure diaphragm compressors are used at hydrogen fueling stations (although small reciprocating and intensifier compressors are also used). Ionic liquid compressors are beginning to be commercialized for use in low-to-moderate flow rate and high-pressure gas compression operations.
The project’s objective is to meet DOE’s goals of increasing efficiency and reducing cost for hydrogen compression, paving the way toward more economical hydrogen storage. The targets are reducing the cost of compression, storage and dispensing (CSD) of hydrogen from central production plants at the forecourt to <$1.60/gge by 2015 and <$0.70/gge by 2020.
|DOE analysis shows CSD cost reduction is key to achieving its delivery targets. Source: DOE. Click to enlarge.|
The LMRC is based on an SwRI-patented concept of driving a permanent magnet piston inside a hermetically sealed compressor cylinder through electromagnetic winding, thus minimizing mechanical part count, reducing leakage and ensuring better reliability.
SwRI’s researchers expect the LMRC system will be able to achieve the required compression ratio with efficiency greater than 95%, greatly exceeding current equipment capabilities with efficiencies that are typically only about 73%.
The SwRI design is more efficient than traditional compressors, and thus will require less energy. The simplified design should also be more reliable, requiring less maintenance, and it can easily be modularized for installation in the field.—Eugene Broerman, SwRI manager of the DOE project