A thermal storage subsystem may include at least a first storage reservoir configured to contain a thermal storage liquid at a storage pressure that is greater than atmospheric pressure. A liquid passage may have an inlet connectable to a thermal storage liquid source and configured to convey the thermal storage liquid to the liquid reservoir. A first heat exchanger may be provided in the liquid inlet passage and may be in fluid communication between the first compression stage and the accumulator, whereby thermal energy can be transferred from a compressed gas stream exiting a gas compressor/expander subsystem to the thermal storage liquid.

A thermal storage subsystem may include at least a first storage reservoir configured to contain a thermal storage liquid at a storage pressure that is greater than atmospheric pressure. A liquid passage may have an inlet connectable to a thermal storage liquid source and configured to convey the thermal storage liquid to the liquid reservoir. A first heat exchanger may be provided in the liquid inlet passage and may be in fluid communication between the first compression stage and the accumulator, whereby thermal energy can be transferred from a compressed gas stream exiting a gas compressor/expander subsystem to the thermal storage liquid.

A method for building an underground storehouse by dissolving limestone with carbon dioxide, the method comprising the following steps: a.) drilling two wells extending from the ground surface (1) to a limestone layer (2), building a channel (5) allowing the two wells to communicate, and installing casing pipes (3, 4) respectively in the two wells; b.) introducing CO.sub.2 gas having at least 1 MPa of pressure into a CO.sub.2 absorbing solution having the same pressure to form a CO.sub.2 solution, flowing the CO.sub.2 solution into underground via the casing pipe (3) to react with the limestone to form a calcium bicarbonate solution, forming a cavern in the meanwhile, and discharging the calcium bicarbonate solution via the other casing pipe (4); c.) decompressing the discharged calcium bicarbonate solution to decompose the calcium bicarbonate contained in the solution into CO.sub.2, water and calcium carbonate, and recycling the separated CO.sub.2 absorption solution and the CO.sub.2; repeating steps b.) and c.) until a cavern meeting design requirements is formed, and discharging the solution from the cavern to form the underground storehouse (6). Also disclosed is a device for building an underground storehouse by dissolving limestone with carbon dioxide, the device comprising a CO.sub.2 storage tank (7), an absorption tower (8), a crystallizer (11), a pressure relief valve (9), a gas-liquid separator (10), a vacuum pump (13), a buffer (14) and booster pumps (12, 15, 16).

A method for building an underground storehouse by dissolving limestone with carbon dioxide, the method comprising the following steps: a.) drilling two wells extending from the ground surface (1) to a limestone layer (2), building a channel (5) allowing the two wells to communicate, and installing casing pipes (3, 4) respectively in the two wells; b.) introducing CO.sub.2 gas having at least 1 MPa of pressure into a CO.sub.2 absorbing solution having the same pressure to form a CO.sub.2 solution, flowing the CO.sub.2 solution into underground via the casing pipe (3) to react with the limestone to form a calcium bicarbonate solution, forming a cavern in the meanwhile, and discharging the calcium bicarbonate solution via the other casing pipe (4); c.) decompressing the discharged calcium bicarbonate solution to decompose the calcium bicarbonate contained in the solution into CO.sub.2, water and calcium carbonate, and recycling the separated CO.sub.2 absorption solution and the CO.sub.2; repeating steps b.) and c.) until a cavern meeting design requirements is formed, and discharging the solution from the cavern to form the underground storehouse (6). Also disclosed is a device for building an underground storehouse by dissolving limestone with carbon dioxide, the device comprising a CO.sub.2 storage tank (7), an absorption tower (8), a crystallizer (11), a pressure relief valve (9), a gas-liquid separator (10), a vacuum pump (13), a buffer (14) and booster pumps (12, 15, 16).

Systems for underground energy storage and methods for their construction. Methods include forming a plurality of chambers underground connected to a plurality of multiple flow conduits, the plurality of chambers including an upper chamber and a lower chamber each containing a working fluid, each multiple flow conduit of the plurality of multiple flow conduits comprising an inner tubular segment having a flowbore interior to the inner tubular segment configured to flow the working fluid, and an outer tubular segment containing the inner tubular segment, wherein each multiple flow conduit defines an annulus between the outer tubular segment and the inner tubular segment configured to flow a compressed gas, by drilling a borehole in the earth formation, installing an outer tubular segment in the borehole, cementing the outer tubular segment at a target location, and installing the inner tubular segment inside the outer tubular segment.

Systems for underground energy storage and methods for their construction. Methods include forming a plurality of chambers underground connected to a plurality of multiple flow conduits, the plurality of chambers including an upper chamber and a lower chamber each containing a working fluid, each multiple flow conduit of the plurality of multiple flow conduits comprising an inner tubular segment having a flowbore interior to the inner tubular segment configured to flow the working fluid, and an outer tubular segment containing the inner tubular segment, wherein each multiple flow conduit defines an annulus between the outer tubular segment and the inner tubular segment configured to flow a compressed gas, by drilling a borehole in the earth formation, installing an outer tubular segment in the borehole, cementing the outer tubular segment at a target location, and installing the inner tubular segment inside the outer tubular segment.

An apparatus for storing large quantities of compressed gas at high pressure underground.

An apparatus for storing large quantities of compressed gas at high pressure underground.

A method for disposing of biomass waste. The method includes locating an abandoned mine having a first well drilled into or through the abandoned mine. Water is removed from a mine cavity through a second well drilled into or through the abandoned mine. The water from the mine is combined with a biomass waste that is at least 70 wt. % carbon to provide biomass waste entrained in the water. The biomass waste entrained in the water is pumped through the first well into the mine cavity to fill the mine cavity. As the biomass waste settles in the mine cavity, the water used to entrain the biomass waste is recirculated to combine with additional biomass waste.

A method for disposing of biomass waste. The method includes locating an abandoned mine having a first well drilled into or through the abandoned mine. Water is removed from a mine cavity through a second well drilled into or through the abandoned mine. The water from the mine is combined with a biomass waste that is at least 70 wt. % carbon to provide biomass waste entrained in the water. The biomass waste entrained in the water is pumped through the first well into the mine cavity to fill the mine cavity. As the biomass waste settles in the mine cavity, the water used to entrain the biomass waste is recirculated to combine with additional biomass waste.