1. Field of the Invention (Technical Field)
Embodiments of the present invention relate to a method, system, and apparatus for controlling the gas temperature of the gas flowing between compression stages so that the temperature of the gas always remains above the dew-point and hydrate temperature of the gas. A further embodiment of the present invention provides a method for controlling inner stage compression temperatures that can be part of a new compressor assembly or retrofitted to compressors already installed and operating.
2. Description of Related Art
To collect gases that are commonly vented by process equipment used at natural gas locations, including but not limited to well sites and processing plants, a flash gas compressor is commonly used. The flash gas compressors operate at pounds of suction pressure (usually 25 to 100 pounds per square inch gauge (“psig”) and discharge pressures generally above 100 and less than 1500 psig). The compressors generally have from one to four compression stages and the gas entering and leaving the inner compression stages is cooled by flowing through a radiator utilizing air, driven by a fan, as the heat sink.
During cool weather, the air circulating through the gas cooler radiator can cool the gas to a temperature below the hydrocarbon dew-point of the gas as well as cooling the gas to a temperature that causes gas hydrates to form.
Cooling the gas below its dew-point results in hydrocarbon liquids forming in the gas stream. The hydrocarbon liquids are separated from the gas by scrubbers installed between the compression stages. The hydrocarbon liquids that condense and are separated by the scrubbers are commonly called “recycle loops”. Depending upon the British Thermal Units of heat (“BTU”) of the gas, how low the ambient temperature is, and how high the inner stage compression pressures are, the recycle loops, when dumped back to the storage tank, can create a volume of hydrocarbon vapors that will overload the vapor recovery system or require installation of a pressurized storage tank or flaring.
Cooling the gas below the hydrate formation temperature causes ice crystals to form in the radiator, potentially blocking the flow of gas. There is thus a present need for a method, system, and apparatus which can consistently cool the gas between multiple stages of compression so that the gas temperature remains above the dew-point of the gases and below a temperature which would cause thermal damage to the compressor when the vapors are compressed in a subsequent stage of compression.
Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.