Methods for thermalsiphoning supercritical CO.sub.2 within a geothermal formation includes providing a geothermal energy system that includes an underground hot rock reservoir, a production well, and an injection well that together form a fluid path suitable for circulating supercritical CO.sub.2. The supercritical CO.sub.2 flows by thermosiphoning. Thermosiphoning is maximized by maintaining a pressure between 1400-4000 psia, an injection temperature in a range from 50-200 C and a production temperature in a range from 150-600 where injection temperature and the production temperature differ by at least 50° C.

The present disclosure relates to systems and methods wherein a dilute hydrocarbon stream can be oxidized to impart added energy to a power production system. The oxidation can be carried out without substantial combustion of the hydrocarbons. In this manner, dilute hydrocarbon streams that would otherwise be required to undergo costly separation processes can be efficiently utilized for improving the power production system and method. Such systems and methods particularly can utilize dilute hydrocarbon stream including a significant amount of carbon dioxide, such as may be produced in hydrocarbon recovery process, such as enhanced oil recovery or conventional hydrocarbon recovery processes.

Power is produced by operating first and second nested cycles utilising CO.sub.2 as working fluid without mixing of working fluid between the nested cycles. The first cycle comprises a semi-open loop operating under low pressure conditions in which CO.sub.2 is sub-critical. The second cycle comprises a closed loop operating under higher pressure conditions in which CO.sub.2 is supercritical. The first cycle operates in a Brayton cycle including oxycombustion of hydrocarbons, preferably LNG, in a combustion chamber under low pressure conditions, expansion for power production to provide a first power source, cooling in a recuperator, compression, reheating by counter-current passage via the recuperator, and return of working fluid heated by the recuperator back to the combustion chamber. Water and excess CO.sub.2 resulting from the oxycombustion step are separated from the first cycle. The first cycle serves as a source of heat for the second cycle by gas/gas heat exchange in a gas/gas heat exchanger which results in cooling of the products of combustion and circulating working fluid in the first cycle and heating of working fluid in the second cycle. The second cycle is operated in a Brayton cycle including heating of working fluid in the second cycle by the gas/gas heat exchanger, expansion for power generation to provide a second power source, cooling in two-stages by first and second recuperator steps, compression, reheating by counter-current passage via the first recuperator step, and return of working fluid heated by the first recuperator step back to the gas/gas heat exchanger. Working fluid in the first cycle following the compression step is heated by working fluid in the second cycle by counter-current passage via the second recuperator step.

A subcritical pressure high-temperature steam power plant includes a combustion boiler system, steam turbine generator system, and condensate and feedwater system and wherein the conditions of steam generated in the boiler system and supplied to the steam turbine generator system are subcritical pressure and high temperature (turbine inlet temperature of 593° C. or more).

A carbon dioxide cycle power generation system includes storage collectively storing portions of carbon dioxide liquid and gas and a transfer connection selectively directing flow of the carbon dioxide through a turbine. The system cycles between different seawater depths in order to employ at least one of seawater pressure and seawater temperature in creating the carbon dioxide flow. Inlet/outlet control valves on variable volume tanks, positioned below movable pistons within the respective tank, selectively allow seawater into or out of a lower portion of the respective tank below the piston to pressurize the carbon dioxide therein relative to the carbon dioxide within the other tank when at depth rather than near the surface. Inhibited versus uninhibited heat transfer between storage portions and the seawater allows different seawater temperatures at depth and near the surface to create the carbon dioxide flow. Acoustic communications may be driven concurrent with the turbine.

Various technologies pertaining to tuning composition of a fluid mixture in a supercritical Brayton cycle power generation system are described herein. Compounds, such as Alkanes, are selectively added or removed from an operating fluid of the supercritical Brayton cycle power generation system to cause the critical temperature of the fluid to move up or down, depending upon environmental conditions. As efficiency of the supercritical Brayton cycle power generation system is substantially optimized when heat is rejected near the critical temperature of the fluid, dynamically modifying the critical temperature of the fluid based upon sensed environmental conditions improves efficiency of such a system.

An improved heat engine that includes an organic refrigerant exhibiting a boiling point below −35° C.; a heat source having a temperature of less than 82° C.; a heat sink; a sealed, closed-loop path for the organic refrigerant, the sealed, closed-loop path having both a high-pressure zone that absorbs heat from the heat source, and a low-pressure zone that transfers heat to the heat sink; a positive-displacement decompressor providing a pressure gradient through which the organic refrigerant in the gaseous phase flows continuously from the high-pressure zone to the low-pressure zone, the positive-displacement decompressor extracting mechanical energy due to the pressure gradient; and a positive-displacement hydraulic pump, which provides continuous flow of the organic refrigerant in the liquid phase from the low-pressure zone to the high-pressure zone, the hydraulic pump and the positive-displacement decompressor maintaining a pressure differential between the two zones of between about 20 to 42 bar.

Provided is a waste heat recovery power generation system, including: a compressor configured to compress a working fluid; a heat exchanger configured to recover waste heat from waste heat gas supplied from a waste heat source, the recovered waste heat heating the working fluid; a turbine configured to be driven by the working fluid heated by the recovered waste heat; and a recuperator configured to exchange heat between an output fluid of the turbine and an output fluid of the compressor to cool the output fluid of the turbine in which the output fluid of the compressor is branched into a first output fluid and a second output fluid of the compressor.

The present invention relates to the supercritical CO.sub.2 generation system applying plural heat sources. The supercritical CO.sub.2 generation system applying plural heat sources includes a pump circulating a working fluid; a plurality of heat exchangers heating the working fluid using an external heat source and including a plurality of constrained heat sources having an emission regulation condition of an outlet end thereof and a plurality of general heat sources without the emission regulation condition; a plurality of turbines operated by the working fluid heated by passing through the heat exchangers; and a plurality of recuperators cooling the working fluid passing through the turbines by heat exchange between the working fluid passing through the turbines and the working fluid passing through the pump, wherein the working fluid passing through the turbine is branched into the recuperators, respectively.

The present invention relates to a supercritical CO.sub.2 generation system applying plural heat sources. According to the present invention, each heat exchanger is effectively disposed according to conditions such as an inlet and outlet temperature, capacity, the number, etc. of the heat source, such that it is possible to use the same or smaller number of recuperators as compared to the number of heat sources, thereby simplifying the system configuration and implementing effective operation.