Lake Kivu contains ˜50 million tonnes (MT) dissolved biomethane. Efficient use is problematic from massive associated CO.sub.2: ˜600 MT. Conventional extraction scrubs CO.sub.2 with ˜50% overall CH.sub.4 loss, and returns ˜80% CO.sub.2 into the deep lake, preserving a catastrophe hazard threatening >2 M people. Methods and systems are disclosed coupling: (1) efficient CH.sub.4+CO.sub.2 degassing; (2) optional oxyfuel power generation and CO.sub.2 power cycle technologies; and (3) CO.sub.2 capture, processing, storage and use in a utilization hub. The invention optimally allows power production with >2× improved efficiency plus cryo-energy storage and large-scale greentech industrialization. CO.sub.2-utilizing products can include: Mg-cements/building materials, algal products/biofuels, urea, bioplastics and recycled materials, plus CO.sub.2 for greenhouse agriculture, CO.sub.2-EOR/CCS, off-grid cooling, fumigants, solvents, carbonation, packaging, ores-, biomass-, and agro-processing, cold pasteurization, frack and geothermal fluids, and inputs to produce methanol, DME, CO, syngas, formic acid, bicarbonate and other greentech chemicals, fuels, fertilizers and carbon products.

A thermal power generation system includes a combustor burning oxygen and fuel with supercritical CO.sub.2, a turbine driven by the supercritical CO.sub.2 and water vapor fed from the combustor, a low-pressure supercritical CO.sub.2 storage storing low-pressure supercritical CO.sub.2 from the turbine, a compressor compressing the low-pressure supercritical CO.sub.2, a high-pressure supercritical CO.sub.2 storage storing high-pressure supercritical CO.sub.2 from the compressor, and a high-pressure supercritical CO.sub.2 feeder supplying between the high-pressure supercritical CO.sub.2 storage and the combustor, in which the high-pressure supercritical CO.sub.2 feeder supplies the high-pressure supercritical CO.sub.2 to the combustor at a constant pressure. Thus, the thermal power generation system can perform adjustment of an electric power supply required to use unstable renewable energy sources such as solar and wind power, can achieve high efficiency power generation with high temperature working fluid, and can reduce emissions of environmental load substances such as NO.sub.x and CO.sub.2.

A plant for storing energy comprises a casing for the storage of a working fluid other than atmospheric air, in gaseous phase and in equilibrium of pressure with the atmosphere; a tank for the storage of said working fluid in liquid or supercritical phase with a temperature close to the critical temperature. The plant is configured to perform a closed cyclic thermodynamic transformation, first in one direction in a charge configuration and then in an opposite direction in a discharge configuration, between said casing and said tank. In the charge configuration the plant stores heat and pressure and in the discharge configuration the plant generates energy. The plant is also configured to define a closed circuit and to perform a closed thermodynamic cycle in the closed circuit with at least a part of the working fluid.

A compander comprises a bull gear connected to a generator a first pinion member comprising at least one first pinion provided on one side of the bull gear; and a second pinion member comprising at least one second pinion provided on the other side of the bull gear, wherein a first compressor and a first expander are mounted on the first pinion of the first pinion member, and a second compressor and a second expander are mounted on the second pinion of the second pinion member.

Systems and methods for variable pressure inventory control of a closed thermodynamic cycle power generation system or energy storage system, such as a reversible Brayton cycle system, with at least a high pressure tank and an intermediate pressure tank are disclosed. Operational parameters of the system such as working fluid pressure, turbine torque, turbine RPM, generator torque, generator RPM, and current, voltage, phase, frequency, and/or quantity of electrical power generated and/or distributed by the generator may be the basis for controlling a quantity of working fluid that circulates through a closed cycle fluid path of the system.

A heat exchanger has arcuate inlet and outlet manifolds and a plurality of tube banks, each tube bank coupling one of the inlet manifold outlets to an associated one of the outlet manifold inlets. Each tube bank partially nests with one or more others of the tube banks and has: a first header coupled to the associated inlet manifold outlet and the associated the outlet manifold inlet; a second header; and a plurality of tube bundles each having a first end coupled to the associated first header and a second end coupled to the associated second header. A flowpath from the each inlet manifold outlet passes sequentially through flowpath legs formed by each of the tube bundles in the associated tube bank to exit the tube bank to the associated outlet manifold inlet.

Aspects of the invention generally provide a heat engine system and a method for activating a turbopump within the heat engine system during a start-up process. The heat engine system utilizes a working fluid circulated within a working fluid circuit for capturing thermal energy. In one exemplary aspect, a start-up process for a turbopump in the heat engine system is provided such that the turbopump achieves self-sustained operation in a supercritical Rankine cycle. Bypass and check valves of a start pump and the turbopump, a drive turbine throttle valve, and other valves, lines, or pumps within the working fluid circuit are controlled during the turbopump start-up process. A process control system may utilize advanced control techniques of the control sequence to provide a successful start-up process of the turbopump without over pressurizing the working fluid circuit or damaging the turbopump via low bearing pressure.

Aspects of the invention disclosed herein generally provide a heat engine system, a turbopump system, and methods for lubricating a turbopump while generating energy. The systems and methods provide proper lubrication and cooling to turbomachinery components by controlling pressures applied to a thrust bearing in the turbopump. The applied pressure on the thrust bearing may be controlled by a turbopump back-pressure regulator valve adjusted to maintain proper pressures within bearing pockets disposed on two opposing surfaces of the thrust bearing. Pocket pressure ratios, such as a turbine-side pocket pressure ratio (P1) and a pump-side pocket pressure ratio (P2), may be monitored and adjusted by a process control system. In order to prevent damage to the thrust bearing, the systems and methods may utilize advanced control theory of sliding mode, the multi-variables of the pocket pressure ratios P1 and P2, and regulating the bearing fluid to maintain a supercritical state.

Described herein is a working fluid for a thermodynamic cycle that includes CO.sub.2 as main component and one or more of the compounds selected from the group including: TiCl.sub.4, TiBr.sub.4, SnCl.sub.4, SnBr.sub.4, VCl.sub.4, VBr.sub.4, GeCl.sub.4, metal carbonyls, by way of example Ni(CO).sub.4.

Aircraft power plants including combustion engines, and associated methods for recuperating waste heat from such aircraft power plants are described. A method includes transferring the heat rejected by the internal combustion engine to supercritical CO.sub.2 (sCO.sub.2) used as a working fluid in a heat engine. The heat engine converts at least some the heat transferred to the sCO.sub.2 to mechanical energy to perform useful work onboard the aircraft.