Analysis On Condensation Flow Characteristics Of H₂O/CO₂ Gas Mixture

The clean and efficient utilization of coal is the basis for the better and faster development of national economy.At present,direct combustion is the most common way of coal utilization,which has low efficiency and will cause serious environmental pollution.In order to improve this situation,academician Guo Liejin put forward a new idea of hydrogen production by coal and supercritical water gasification and H₂O/CO₂ gas mixture power generation.Firstly,based on the innovative way and the experimental data of coal and supercritical water gasification,a new power generation system of H₂O/CO₂ gas mixture is developed.The condensing turbine and the four-stage regenerative extraction cycle are used.Under the premise of controlling the equipment cost,the temperature difference of heat transfer is reduced,and the balance of heat absorption and discharge of the system is ensured without introducing external pollution.The reaction products are oxidized before working,which meets the operation safety requirements,and the system efficiency reaches 43.72%.Secondly,the temperature characteristics of gas mixture condensation and the optimum exhaust pressure of gas mixture turbine are studied.The results show that the gas mixture condensation can be approximated to an isobaric cooling process,so the determination of exhaust pressure is related to ambient temperature and steam condensation ratio.With the increase of steam condensation ratio and ambient temperature,the exhaust pressure increases when the outlet end difference is fixed.In the working condition studied in this paper,the optimal exhaust pressure of the gas mixture turbine is higher than that of the condensing steam turbine to some extent,with a maximum difference of more than 40kPa.Thirdly,the condensation models of single/two-component gas are established and its accuracy is verified,of which maximum relative error is less than 4%.The condensation flow characteristics of steam and H₂O/CO₂ binary gas with different component concentrations in Laval nozzle is studied in this paper.The results show that the initial condensation position moves backward,the maximum degree of supercooling increases,and the outlet temperature and velocity decreases because of the existence of CO₂,which affects the fluid working ability.On the other hand,it makes the wetness and droplet size smaller,which is beneficial to reduce the moisture loss.The initial condensation zone moves backward,the wetness and droplet radius decrease with the increase of CO₂ concentration,and the parameters will change accordingly,such as degree of supercooling,Mach number and velocity.Finally,the condensation flow characteristics of gas mixture and pure steam in stator cascade are compared.The results show that the distribution of pressure and Mach number of them is basically the same?except for the initial condensation section?,the initial condensation position of the gas mixture moves backward and the maximum wetness decreases,but the increase of CO₂ concentration brings security risks.The average velocity of gas mixture in the downstream plane of the cascade outlet is 6%lower than that of the pure steam,which has an impact on the working capacity of the working medium and the aerodynamic design of the blade.However,the average wetness and droplet radius are decrease,which will be beneficial to the efficiency improvement and the operation safety of the subsequent moving cascade.In conclusion,the research on the condensation flow of gas mixture in this paper has reference significance for the design and strength analysis of the gas turbine with mixed gas.