Equation of state for wet gas in a steam injected gas turbine (Stig) cycle plant fit for burning gases Che （Teaching and Research Department of Thermal Engineering, Harbin Institute of Technology, Harbin, China, Post Code 150001）The wet gas in a gas-fired steam injected gas turbine cycle plant is treated as a real gas. Set up is the wet gas status equation by utilizing the corresponding status mode of a two-term Virial equation. The thermodynamic properties of the wet gas have been calculated by the use of the above-cited status equation and a complementary function correction method. Moreover, a comparison was conducted of the wet gas thermodynamic properties with those calculated on the basis of an ideal gas.
key words: gasification, steam injected gas turbine cycle, wet gas, status equation1 introduction the relatively advanced coal-fired power generation technology being developed in the world is the integrated coal gasification combined cycle and pressurized fluidized bed combined cycle . The Stig cycle burning coal gas is a new cycle combining coal gasification technology with Stig cycle. It not only has the excellent average performance of Stig cycle, but also solves the problem of environmental pollution caused by coal combustion. Fig. 1 is a diagram of the closed Stig cycle system for burning gas. Coal forms crude gas in the gasifier, which is cooled and exothermic through the heat exchanger to heat the feed water to generate steam for reinjection, and then becomes clean gas after desulfurization and dust removal, and enters the combustion chamber as the fuel for circulation. In the combustion chamber, the gas and air are burned and mixed with the injected steam to reach the inlet temperature of the gas turbine, and then expand in the turbine to do work. The waste heat boiler uses gas turbine exhaust to heat the treated water, turn it into superheated steam and inject it into the combustion chamberThe thermodynamic properties of the working medium in the cycle are the basis of the cycle analysis. The conversion and utilization of energy in the cycle must be calculated according to the thermodynamic properties of the working medium. In the closed Stig cycle of burning gas, the working medium that works in the gas turbine and is discharged into the waste heat boiler is composed of the combustion products of gas and steam, which is referred to as wet gas for short. The accuracy of its thermodynamic properties will directly affect the analysis and calculation of the cycle. Usually, the thermodynamic properties of the wet gas are calculated by superposition of the thermophysical properties of each component according to the composition of the ideal gas mixture. However, if the wet gas is considered as the actual gas, it is difficult to calculate the diameter and tensile strength of its hot products in line with the national standard force properties, so the state equation of wet gas is required. Therefore, the state equation of wet gas is established in this paper, and the thermodynamic properties of wet gas are calculated by using this state equation. Fig. 1 closed Stig cycle system for gas burning Fig. 2 Establishment of wet gas equation of state it is assumed that the molar percentages of seven components H2, Co, CO2, N2, AR, CH4 and H2O in the clean gas generated after coal gasification are M1, M2, m3, M4, M5, M6 and M7 respectively. When the GMP (2) 002 feeding system in the combustion chamber is β ( β＜ 1) When the steam injection ratio is x, after the fuel is completely burned, the wet gas has five components: CO2, H2O, O2, N2, AR; The molar percentages of the five components are R1, R2, R3, R4 and R5 respectively. For the calculation method of R1 ~ R5, see reference  The contrast form of the practical formula of the two term virial equation is: z = 1 +, which is applicable to ρ＜ρ c／2。 However, the maximum pressure of wet gas in gas-fired Stig cycle gas turbine is generally not more than 5 MPa, and the temperature in waste heat boiler is not less than 90 ℃, meeting ρ＜ρ C/2, which conforms to the applicable range of the two term virial equation. Therefore, if the equation of state of wet gas is established in the form of two term virial equation, the key is to find out the. The wet gas consists of five components, which are CO2, H2O, O2, N2 and ar. for non-polar or weak polar substances O2, N2, AR and CO2, it can be given by tsonopoulos' modified formula , that is, (1) (1-1) (1-2) for polar substances H2O, tsonopoulos' recommended formula , that is, a correction term F2 (TR) is directly added to the right of formula (1):