Hydride compressor

Hydride Compressors using reversible metal hydride alloys offer an economical alternative to traditional mechanical compressors for GH2. The simplicity and passive operation of the hydride compression process offers many advantages over mechanical compressors. Hydride compressors are compact, silent, do not have dynamic seals, require very little maintenance, and can operate unattended for long periods. However, they are a very new and may be difficult to be built at the scale required for GH2 transmission pipeline service. 

R.C. BowmanJr., B.D. Freeman, J.R. Phillips, Evaluation of metal hydride compressors for applications in Joule-Thomson cryocoolers, Cryogenics 32 (1992) 127-137. 

Many of the design principles of a hydride tank also hold for a hydride compressor. It must be an effective heat exchanger. The more effective the heat exchange, the shorter is the cycle time and consequently the smaller the hydride inventory required. Ideally, the hydride should have a high slope to the Van t Hoff plot to produce maximum compression with minimum temperature excursion. Beds of different hydrides can be coupled in series to provide staged compression and thus achieve very high overall compression ratios with modest temperatures. The ability to tailor hydrides, as shown earlier, is very helpful to compressor optimization for specific applications (i.e., available heat sources, H2 input pressure, and desired output pressure). 

Bowman, R.C., et al.. Performance testing of a vanadium hydride compressor, Zeitschrift Eur Physikalische Chemie - International Journal of Research in Physical Chemistry Chemical Physics, 1994, 183 p. 245-250. 

Construct a single stage hydride compressor that employs miniature hydride heat exchangers and three purification technologies (passive purification for water vapor and diatomic oxygen [O2], inert gas purification, and elevated temperature desorption for carbon monoxide [CO] and carbon dioxide [CO2]). 

Complete construction of a single stage hydride compressor and compressor test stand. The compressor includes hydrogen purification capabilities and the test stand includes fast response, continuous impurity monitors for the gathering of real-time operating information. 

Quantify the hydride compressor s tolerance to impurities in tests occuring in the Fall of 2002. 

During the course of hydride compressor development, a number of additional insights have been gained regarding requirements for commercial hydride compressor viability. These insights are important for the overall success of the project and have been included in the project scope ... 

Figure 1. A Single stage Hydride Compressor Boosts Outlet Pressure to over 5,000 psi (350 bar) for Vehicular Storage...

Hydride compressors can compress hydrogen to the very high pressures under consideration for vehicular storage (5,000 to... 

The hydride compressor is a form of "heat engine" based on the Carnot cycle. Its energy efficiency is about 50% of Carnot efficiency. Carnot efficiency is based on the temperature difference between the hot energy source and the cold heat sink. Efficiency plotted as a function of hot water (energy source) temperature appears in Figure 2. 

Waste heat is usually available in the 80 to OO C range. With a 30°C cooling water temperature, Carnot efficiency is from 13 to 16 percent and hydride compressor efficiency is from 4 A to 6 A percent. If waste heat is free, cycle economics can endure this level of efficiency. 

By using a traditional form of heat energy, such as natural gas, cycle economics will benefit from an increase in hot water temperature. Using a heat transfer fluid from a gas fired heater at 130°C, Carnot efficiency is almost 25 percent, and hydride compressor efficiency increases to 15 percent. While 15 percent is about 1/2 that for a mechanical compressor, electricity is about 6 times costlier than natural gas, so the hydride compressor will enjoy a 67% lower energy cost. A simplified schematic of a natural gas powered hydride compressor appears in Figure 3. 

Unfortunately, when hydride alloys traditionally used for compressors are cycled at temperatures over 100 C, their performance can deteriorate through a process termed "disproportionation." In relatively few cycles, reversible hydrogen absorption capacity is lost, which would cause a hydride compressor to stop working. 

Starting with the alloy family used in the catalytic converter heater, Ergenics modified alloy formulations to adjust the pressure-temperature performance. A correlation was developed between the formulations and pressure-temperature performance to permit the engineering of alloys appropriate for the different pressure stages in a hydride compressor. The alloys were then tested for resistance to disproportionation. 

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