Methodology and results of calculating a low-tonnage medium-pressure cycle with a turbo-expander operating at a differential pressure for the production of liquefied natural gas
DOI: 10.17586/1606-4313-2021-20-1-22-27
UDC 621.592.3
Vizgalov S. V., Khisameev I. G.
Keywords: LNG production, medium pressure expander cycle, liquefaction ratio, thermal design, cycle characteristics
UDC 621.592.3
Methodology and results of calculating a low-tonnage medium-pressure cycle with a turbo-expander operating at a differential pressure for the production of liquefied natural gas
For citation: Vizgalov S.V., Khisameev I.G. Methodology and results of calculating a low-tonnage medium-pressure cycle with a turbo-expander operating at a differential pressure for the production of liquefied natural gas. Journal of International Academy of Refrigeration. 2021. No 1. p. 22-27. DOI: 10.17586/1606-4313-2021-20-1-22-27
Abstract
A method for thermodynamic calculation of a subcritical expansion cycle of medium pressure, operating at a differential pressure, which is used in small-scale LNG production, is presented. A description of the setup and the thermodynamic cycle is given. The technique is based on the equations of the heat balance of the cycle contours, which are converted to the final form and solved by the iteration method. As the analysis of this cycle shows, the pressure on the forward flow, the expander flow, the location of the entry point to the expander, and the liquefaction coefficient are interdependent quantities. The independent parameters are flow pressures, adiabatic efficiency of the expander and DKA compressor stages, specific heat gain from the environment, and underrecovery at the warm end of the heat exchanger. The calculation results are presented in the form of graphical characteristics of the cycle versus the pressure of the incoming flow of natural gas, the efficiency of the turboexpander, and the temperature of the forward flow after the compressor at various pressures on the return flows. The analysis of the influence of the parameters is carried out and conclusions are drawn. It is shown that, with an increase in the pressure of the inlet gas and the efficiency of the turboexpander, the expander flow, while remaining significant in general, decreases to 64%, which leads to an increase in the liquefaction coefficient up to 15%; a decrease in the pressure on the reverse gas flow is effectively used at low pressures of the inlet flow.
Abstract
A method for thermodynamic calculation of a subcritical expansion cycle of medium pressure, operating at a differential pressure, which is used in small-scale LNG production, is presented. A description of the setup and the thermodynamic cycle is given. The technique is based on the equations of the heat balance of the cycle contours, which are converted to the final form and solved by the iteration method. As the analysis of this cycle shows, the pressure on the forward flow, the expander flow, the location of the entry point to the expander, and the liquefaction coefficient are interdependent quantities. The independent parameters are flow pressures, adiabatic efficiency of the expander and DKA compressor stages, specific heat gain from the environment, and underrecovery at the warm end of the heat exchanger. The calculation results are presented in the form of graphical characteristics of the cycle versus the pressure of the incoming flow of natural gas, the efficiency of the turboexpander, and the temperature of the forward flow after the compressor at various pressures on the return flows. The analysis of the influence of the parameters is carried out and conclusions are drawn. It is shown that, with an increase in the pressure of the inlet gas and the efficiency of the turboexpander, the expander flow, while remaining significant in general, decreases to 64%, which leads to an increase in the liquefaction coefficient up to 15%; a decrease in the pressure on the reverse gas flow is effectively used at low pressures of the inlet flow.
Keywords: LNG production, medium pressure expander cycle, liquefaction ratio, thermal design, cycle characteristics
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