Abstract
Traditional high-pressure mechanical compressors account for over half of the car station’s cost, have insufficient reliability, and are not feasible for a large-scale fuel cell market. An alternative technology, employing a two-stage, hybrid system based on electrochemical and metal hydride compression technologies, represents an excellent alternative to conventional compressors. The high-pressure stage, operating at 100–875 bar, is based on a metal hydride thermal system. A techno-economic analysis of the metal hydride system is presented and discussed. A model of the metal hydride system was developed, integrating a lumped parameter mass and energy balance model with an economic model. A novel metal hydride heat exchanger configuration is also presented, based on minichannel heat transfer systems, allowing for effective high-pressure compression. Several metal hydrides were analyzed and screened, demonstrating that one selected material, namely (Ti0.97Zr0.03)1.1Cr1.6Mn0.4, is likely the best candidate material to be employed for high-pressure compressors under the specific conditions. System efficiency and costs were assessed based on the properties of currently available materials at industrial levels. Results show that the system can reach pressures on the order of 875 bar with thermal power provided at approximately 150 °C. The system cost is comparable with the current mechanical compressors and can be reduced in several ways as discussed in the paper.
Highlights
One of the main hurdles to be overcome for a large-scale hydrogen economy is related to the H2 delivery
Valid alternative processes are represented by hybrid systems comprised of electrochemical hydrogen compressor (EHC) systems, operating at lower pressures (10–100 bar), integrated with thermal compression systems, operating at pressures on the order of 100–875 bar
The techno-economic model was applied to different metal hydride (MH), which were downselected based upon constraints and initial degrees of freedom assumed on the basis of the compressor configuration and operating conditions
Summary
One of the main hurdles to be overcome for a large-scale hydrogen economy is related to the H2 delivery. Among the other targets for hydrogen compression systems, DOE identified the uninstalled cost target for the year 2020 at $275,000, the energy requirement at 1.6 kWh/kg, availability equal to 85%, and annual maintenance cost equal to 4% of the uninstalled cost (the targets are for: inlet pressure of 100 bar, hydrogen flow rate of 100 kg/h [1]). Valid alternative processes are represented by hybrid systems comprised of electrochemical hydrogen compressor (EHC) systems, operating at lower pressures (10–100 bar), integrated with thermal compression systems, operating at pressures on the order of 100–875 bar. One of the main advantages of a hybrid system over other alternative solutions is in the possibility of recovering the available waste heat from the EHC to pressurize and discharge the hydrogen from the thermal compression system, based on metal hydrides
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