Diagnostics of the Optimal Operating Modes of Gas Turbine Compressor Stations Based on the Analysis of Technological Processes

Abstract

The article is dedicated to the analysis of the influence of the seasonally changing ambient temperature on the technological parameters of the compression process at a gas turbine compressor station for the transportation of natural and associated gas collected from oil and gas fields by an offshore subsea gas pipeline. As a result of the analysis, indicators of suction and discharge pressure, compressor capacity, ambient temperature during the summer and winter months were collected at each stage of a multi-unit two-stage compressor station. The indicators were divided into intervals, the number of measurements in the interval was determined, and graphs of the dependence of the number of measurements on the average value of the interval were built. As a result of the analysis of the graphs, the complex influence of technological parameters and ambient temperature on the performance of gas turbine compressors was evaluated. To compare the results and study the effect of the parameters on the operating mode and efficiency of the compressor station, the numerical value of the criterion as the ratio of the maximum number of measurements to the average value of the corresponding interval for each parameter was calculated. For both 1st- and 2nd-stage compressors, the value of this criterion for productivity was found to be almost twice as low in winter compared to summer. For this reason, there is a need to develop measures that can ensure the operation of the compressor station in the optimal operating mode. As a result of the analysis, it was found that in the 1st stage gas turbine compressors, due to increase of the inlet pressure, which is a positive factor for the compressor, by 16.4% (from 58 psi to 67.5 psi) in summer compared to winter, and due to the increase of the outlet pressure, which is the negative factor, by 0.9% (from 285 psi to 288 psi) and an increase in ambient temperature of 36o F (from 42o F to 80.5o F), the productivity is decreased by 15.2% (from 40.15 MMSCFD to 34.05 MMSCFD) to). In 2nd-stage gas turbine compressors, due to no change of the inlet pressure, which is a positive factor for the compressor, in summer, compared to winter (273 psi in both cases), and due to the decrease of the outlet pressure, which is a negative factor, by 0.2% (from 807.5 psi to 805.5 psi. ) and an increase in ambient temperature of 36o F (from 42o F to 80.5o F), productivity decreased by 10.1% (from 49.05 MMSCFD to 44.05 MMSCFD). Thus, 10.1% of the 15.2% decrease in the productivity of gas turbine compressors in the summer season is due to the increase in ambient temperature, while the remaining 5.1% is due to the organization of technological processes. Taking into account this factor in the field, the selection of the correct technological mode in the gas transportation system allows to prevent the loss of large amounts of gas. Taking into account the design features of gas turbine compressor units, it is concluded that the 10.1% decrease in productivity in the 2nd stage gas turbine compressors in the background of the constant no-change of compressor inlet and outlet pressures in summer and winter is due to automatic decrease in RPM of gas turbines from nominal 15000 cycles/min and thus the decrease of the power of gas turbines due to the overload in summer. Considering the fact that each turbine consumes 30,000 m3 of fuel gas per day, the 360,000 m3 gas per day for fuel at the station is taken from the outlet of the 2nd stage gas turbine compressors, and these turbines are overloaded, the fuel gas is considered to be taken from another source. By feeding all the turbines of the station from the outlet of the 1st stage compressors, it is possible to reduce the load on the interstage collector of the station, increase the productivity of the 1st stage compressors and direct the gas compressed by the 2nd stage compressors to the whole outlet pipeline. As a result of this technological operation, an additional 200,000-250,000 m3 of gas per day can be transported through the compressor station. This technique is recommended for multivariate analysis of various technological processes. As a result of the study, a technological scheme was proposed for increasing the productivity of a gas turbine compressor station by 3-4% by changing the source of fuel gas extraction. Keywords: gas turbine, compressor, natural gas pressure, ambient temperature, productivity, fuel gas, statistical method.