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CPOTE2020 logo
6th International Conference on
Contemporary Problems of Thermal Engineering
Online | 21-24 September 2020

Abstract CPOTE2020-1210-A

Book of abstracts draft
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Analysis a high efficiency supercritical CO2 power process integrated with Organic Rankine cycle

Wojciech NOWAK, AGH University of Science and Technology, Poland
Mikołaj ZŁOTKOWSKI, AGH University of Science and Technology, Poland

Historically, CO₂ capture has been expensive, whether using air to combust or oxy combustion. In conventional air combustion, the capture of CO2 from flue gas is a complicated process due to the low partial pressure of CO2 and large amount of nitrogen in the flue gases. Since air contains 79% of nitrogen, all of nitrogen in different chemical forms is emitted to atmosphere during the combustion process. The CO2 concentration in the flue gases is only in a range of 13-16% vol. Oxy-fuel combustion is a process whereby oxygen is separated from the air and used directly to burn the fuel in order to increase the CO2 concentration in the flue gases to 90% vol., or greater. The Allam cycle employs oxy-fuel combustion of hydrocarbons in a supercritical CO2 environment with subsequent expansion in a hybrid gas-steam turbine. The most notable feature of the Allam cycle is that it employs carbon dioxide as its “working fluid. Consequently, the size of all the system components such as the turbine and heat exchangers can be considerably reduced. The operation of the Allam cycle requires the control of three fuel components (mixture of methane + hydrogen) of the oxidant (pure oxygen) and ballast (CO2). It becomes possible to control the exhaust gas outlet temperature regardless of the changing load. The hot exhaust gas drives the turbine and leaving it gas still has a temperature of around 800oC. This heat should be used in the secondary cycle. After passing through the turbine stage the steam parameters are 2MPa and 220oC and the enthalpy drop is 550 kJ/kg. Then, in the condenser, water gives 1900 kJ/kg of heat to the lower source. The use of a secondary and a third circuit has increased the total primary efficiency from 33% to 53%. The Allam cycle makes oxy combustion economic by relying on a more efficient core power cycle, recycling heat within the system to reduce O2 and CH4 consumption, and associated costs of the air separation unit (ASU). This cycle presents a new approach to combine low-cost power generation with complete CO2 separation at a high-efficiency. Calculations of system parameters are carried out using the IPSEpro. It is a highly flexible environment for modelling, simulation, analysis and design of components and processes for energy and chemical engineering. The article describes the behavior of a micro oxy gas turbine work in the closed loop gas cycle (Allam cycle).

Keywords: Allam cycle, Oxy combustion, Gas turbine, CO2 capture, utilization and storage, Organic Rankine cycle (ORC)