In many offshore oil and gas installations, the gas compressors are directly driven by the gas turbines which uses fuel gas that can be monetized if the gas turbines fuel gas consumption is reduced; both from operating the compressors at higher efficiency and optimized compressor operating envelope to operate as close to surge region, thus avoiding gas recycling at the compressor. This paper shows every molecule savings on the fuel gas consumption can derive substantial commercial value for the end users.
The presenter list prerequisites for the gas compressor operating points optimization and surge control optimization. The methods used will guide end users to operate multiple gas compressors by taking advantage of their best efficiency operating points based on either polytrophic or isentrophic efficiency calculated. Simple algorithm and easy to measure parameters from the field to derive the monetized values of the fuel savings to see if it is worth to adjust the operating points can be determined. The incipient surge test can be conducted to determine the surge region to ensure we operate the compressors without gas recycling which is waste of energy during capacity turndown for the compressor, thus this also yields return on investment.
By operating the compressor at better efficiency points, the compressor absorbs lesser brake horsepower (bhp) or shaft power, in turn, the gas turbines fuel is consumed at optimized flowrate, resulting in reduction of fuel gas that can be monetized instead of being burned in combustion chamber of the gas turbine and emitted as Green House Gas (GHG) from the gas turbine exhaust stacks. Operating the gas turbine efficiently means we are truly embarking on GREENER environment, not just by words but this is also a practical way to embrace Paris climate change initiatives. The Paris Agreement, Paris climate accord or Paris climate agreement is an agreement within the United Nations Framework Convention on Climate Change dealing with greenhouse gas emissions mitigation.
It is also common that we recycle gas to avoid surging the compressors for low flowrate scenarios in our compression operations which is an inefficient way of compression as recycling gas means energy is wasted by compressing gas then its pressure is killed via capacity recycle or anti surge control valve which in turn dissipates as heat and noise during gas recycling. Therefore, one of the desired solution is to push compressors closest to the surge region by conducting incipient surge test at site conditions to define the actual surge boundary, allowing the compressor to operate without recycling at lower flowrates, thus recycling is minimized or/and some cases avoided. This paper presents the incipient surge test done offshore with risk mitigated whilst some OEM's do not recommend this test. The author has personally conducted such test offshore, and presents risks and values proposition for end users.