A heightened awareness for global warming and sustainability has been steadily changing the energy market. Solutions are sought to substitute fossil fuels by more renewable sources of energy and to mitigate GHG emissions associated with combustion of fuels. One way of decreasing emissions is to improve the efficiency of the power generation processes. A large part of electricity is still generated in thermal powerplants (eg. gas, coal, nuclear). The heat produced by burning fuel is conventionally converted to by heating pressurised steam and then using that to drive a turbine connected to a generator. The vapor cycle used here is a variant of the Rankine cycle. They have a cycle efficiency of lower than 40%.
A possibility for increasing cycle efficiencies is by using supercritical CO2 instead of steam. The supercritical state is the state above the critical point (T ≈ 300K and P≈70 bar), here the gas behaves approximately as a fluid. Efficiency gains up to 10% can be obtained with respect to steam. CO2 has a high heat capacity, Cp, so that the energy density is higher than steam, which can lead to fewer turbine stages and thus a smaller and more simple installation. The supercritical CO2 cycle can be applied with a variety of heat sources, such as: waste heat from a gas turbine, nuclear reactors, coal or gas plants, geothermal, solar thermal, etc.There is already a small turbine in use, developed by Echogen and GE, that utilises the waste heat of a gas turbine to drive a secondary turbine with CO2. A company in the US, NetPower, has developed a new cycle, the Allam cycle, for a coal or natural gas combined cycle power plant based on supercritical CO2. They combined it with a pre-treatment carbon capture technique (oxy-fuel combustion) to achieve zero-emissions.
During the academic year 2019 – 2020 a first thesis 'Carbon capture, by means of oxy-combustion, in a gas turbine power plant, an assessment of the Allam cycle', was performed. A major conclusion of the thesis stresses on the importance of the heat exchangers on the cycle efficiency (the heat exchanger layout hasn’t been studied firmly in the first thesis; the importance of the heat exchangers, within the Allam-Fetvedt power cycle, was an outcome). The heat exchangers will operate under severe circumstances (high temperature and pressures), “polluted” CO2 with a minimum of O2 and vaporized water). The focus of this thesis is on the heat exchangers.
The outcome of the thesis should allow Engie – Laborelec to:
Engie – Laborelec offers the students the possibility to create a scale model of the designed heat exchanger(s) (by means of 3D printing). This model could open the pathway for some practical tests in a consecutive thesis work.