Development and calculation of a scheme for a combined gas-steam plant with deep utilization of heat and moisture

Abstract

Relevance. Saving natural gas, reducing heat and steam emissions into the environment through deep utilization of heat from exhaust gases in a waste heat boiler and heat and moisture in a condensation waste heat boiler. Aim. Development of a combined gas-steam plant scheme and its calculation methods. Objects. Combined gas-steam plant with the introduction of water vapor into the combustion chamber of a gas turbine and deep heat recovery in a waste heat boiler and a condensing heat and moisture recovery unit from the exhaust gases. Methods. Numerical methods based on material and energy balances of systems and elements of gas-steam plants. Results. The authors have developed the thermal scheme of a combined gas-steam plant with water vapor introduction into the combustion chamber of a gas turbine and deep heat recovery in a waste heat boiler and heat and moisture from exhaust gases in a condensing waste heat boiler. Rhey developed as well the algorithm for calculating this scheme. Based on this scheme the authors written the calculation program in the EXCEL spreadsheet package using the Coolprop database of functions for calculating thermodynamic and thermal physical parameters of substances. This program allows calculating indicators with changes in the outside air parameters, the fuel burned composition, the air compression degree in the compressor, the flow rate of steam introduced into the combustion chamber, the temperature of combustion products at the inlet of the gas turbine, the electrical load on the gas turbine generator, and the exhaust gases temperature at the outlet of the heat recovery unit. The paper introduces the example of the circuit calculation for one variant of the initial data. This example showed that with the given initial data, when using the heat leaving in the waste heat boiler and condensing heat recovery unit in additional Rankine cycles, it is possible to obtain, relative to the electric power of the gas turbine of 100 MW, an increase in power of 12.34 MW: of which 8.94 MW in the steam turbine and 3.40 MW in the turbine on a low-boiling working fluid. The electrical efficiency of the combined gas-steam plant was 57.68%: while the efficiency of the gas turbine was 51.35%, the efficiency of the steam turbine was 83.48% and the efficiency of the turbine on a low-boiling working fluid was 4.86%.

Keywords

• combined gas-steam plant
• combustion chamber
• steam input
• combustion products
• compressor compression ratio
• combustion chamber outlet gas temperature