Near-Isothermal Hydraulically Actuated Compressor for CO2 compression

Gas compression is an energy intensive process. Industrial gas compression alone uses 8 to 12 Quads per year (8 to 12% of the US annual energy use). Almost every compressor runs in a near-adiabatic regime, as they do not cool the gas as it is compressed. Compression is more efficient if the gas is maintained at ambient temperature, in a near-isothermal process. Compared to an adiabatic process, for a 11:1 pressure ratio (industrial air), a near-isothermal process would save 30% of energy used. At a 70:1 pressure ratio (piped natural gas or supercritical CO2) it would save 49% energy used, and at 200:1 (hydrogen creation and storage) it would save 57%. The current trend in gas compression is to use oil-free compressors, to avoid polluting the gas with oil. Most compressors use a near-adiabatic regime, with some variations to try to cool the process. Oiled compressors inject oil in the gas stream to cool and lubricate the components. Oil-free compressors may use external liquid cooling to keep their component temperature at acceptable working conditions but cannot cool the gas. Some oil-free screw compressors use water injections, creating reliability issues. Recent efforts have been done trying to mix air and water in reciprocal or centrifugal compressors, creating contamination issues. At large pressure ratios, compressors use a multistage approach, cooling the gas between stages, only approaching a near-isothermal process at the cost of complexity. Otherlab is developing a true near isothermal compressor that maintains gas purity. It is using compliant polymer bladders and hydraulic actuation. The hydraulic fluid acts both as the mechanical source and the heat sink. With large surface area to volume ratio bladders, the gas is maintained close to ambient temperature during the whole compression process, allowing for large energy gains. Otherlab demonstrated a near isothermal compressor at commercial scale (1 hp) and machine shop working pressure (90 psig), and is currently working at increasing the power and pressure of a laboratory scale compressor (2 hp, 145 psig). Phase I will study the technical viability of CO2 compression (specific polymer development and valving). The first application we are exploring is in industrial air compression, where the energy usage exceeds the upfront plus maintenance cost of typical compressors, so that any efficiency gain is welcome. Energetical and monetary cost of compression is even more of a problem for other applications, such as hydrogen creation and storage, or CO2 capture and sequestration.