Clean Energy Technology

In an integrated gasification combined-cycle biomass power plant, biomass is gasified into a synthesis gas, consisting of hydrogen and carbon monoxide. The synthesis gas is shifted in a water-gas-shift (WGS) reaction to produce additional hydrogen and convert the carbon monoxide into carbon dioxide. The CO2 is then captured from the shifted syngas using physical separation processes, such as adsorption, and afterward, the remaining hydrogen (H2) is combusted in a combined-cycle gas turbine that generates power.

At a coal-fired power plant with post-combustion capture using chemical absorption, the CO2 is separated from the combustion flue gas by using a chemical solvent (e.g. amine-based). The CO2 is released at elevated temperatures, the solvent regenerated and recycled back for further operation.

In an integrated gasification combined-cycle coal power plant, coal is gasified into a synthesis gas, consisting of hydrogen and carbon monoxide. The synthesis gas is shifted in a water-gas-shift (WGS) reaction to produce additional hydrogen and convert the carbon monoxide into carbon dioxide. The carbon dioxide is then captured from the shifted syngas using physical separation processes, such as adsorption, and afterwards, the remaining hydrogen (H2) is combusted in a combined-cycle gas turbine that generates power.

Direct lithium extraction (DLE) from brine at concentrations from 50 to over 500 mg/l using adsorption (acid solution required for exchange), ion exchange or solvent extraction (organic liquid exchange). Proven pilot projects in Canada, France, United States, Germany and Argentina. Columbia and UK projects 2022/23 (UK deployment 2022). Traditional geothermal lithium brine extraction involves evaporative brine processing. Brine is pumped into a series of large ponds at the surface, occupying large tracts of land (1 000 m2) where water evaporates leaving a highly concentrated lithium brine (>6 000 mg/kg) that is then sent onwards for processing.

Chemical looping is a technology that involves CO2 capture at high temperatures using two main reactors. Chemical looping systems use small particles of metal (e.g. iron, manganese) to bind oxygen from the air to form a metal oxide (1st reactor), which is then transported to the other reactor where it releases the oxygen for the combustion of the fuel, thus generating energy and a concentrated stream of CO2 (2nd reactor). The metal is then looped back to the first reactor. A main benefit of solid looping is the potentially lower overall process energy consumption. Challenges include reducing the cost and degradation of the metal carrier (IEAGHG, 2019).

At a coal-fired power plant with post-combustion capture using chemical absorption, the CO2 is separated from the combustion flue gas by membranes, which are polymeric films and act as a selective barrier able to separate CO2 from a stream. They can also act, in a non-selective way, as a contacting device between the gas stream and the liquid solvent (i.e. membrane absorption).

While in conventional power plants flue gas or steam is used to drive one or multiple turbines, in supercritical CO2 (sCO2) cycles supercritical CO2 is used, i.e. CO2 at or above its critical temperature and pressure, where liquid and gaseous phases of CO2 are indistinguishable. sCO2 cycles offer many potential advantages, including higher plant efficiencies, lower air pollutant emissions, lower investment costs and high CO2 capture rates. In some cases, they could also allow for reduced water consumption. sCO2 cycles typically use nearly pure oxygen to combust the fuel gas in order to create a flue gas stream comprised primarily of CO2 and water vapour.

Dry steam plants, which make up about a quarter of geothermal capacity today, directly utilise dry steam that is piped from production wells to the plant and then to the turbine.

An oxy-fuelling coal-fired power plant involves the combustion of coal using nearly pure oxygen instead of air, resulting in a flue gas composed of CO2 and water vapour, which can be dehydrated to obtain a high-purity CO2 stream. Typically, oxygen is commercially produced via low-temperature air separation. Lowering the energy consumption and cost for oxygen production (via improved low-temperature air separation or air-separating membranes, or by generating oxygen during periods of low-cost power, e.g. during night time), and the overall oxyfuel process, are key factors in reducing capture costs.

In solid adsorption, the carbon dioxide is separated from the combustion flue gas by using a solid sorbent (e.g. zeolites, metal organic framework). Compared to amine-based chemical absorption, solid adsorbents can have lower regeneration energy and greater adsorption selectivity.

Closed-loop geothermal systems cover a range of new, closed or partially closed-loop (hybrid) technology trials for power generation. These trials largely rely on thermal conduction in rock (a poor conductor) along long wellbores and often rely on the use of supercritical CO2 or other new working fluids. CLGS allows for applications in low-temperature sedimentary resources with from about 100 °C to 180 °C. This allows expansion of geothermal from a limited conventional geothermal supply into sedimentary basins leading to a growth in geothermal supply of several magnitudes and locations.

Enhanced or engineered geothermal systems aim at using the heat of the Earth where no or insufficient steam or hot water exists and where permeability is low. EGS technology is centred on engineering and creating large heat exchange areas in hot rock. The process involves enhancing permeability by opening pre-existing fractures and/or creating new fractures. Heat is extracted by pumping a transfer medium, typically water, down a borehole into the hot fractured rock and then pumping the heated fluid up another borehole to a power plant, from where it is pumped back down (recirculated) to repeat the cycle.