Condensing streams, expansion

Radial inflow turboexpanders are the best equipment for this application because they handle condensing streams, provide a high expansion ratio in a single stage, and are custom-built to accommodate the plant s process conditions. 

The product stream leaving the stripper goes through an expansion valve to the low-pressure section, the operating pressure there being 5 bar. In a steam-heated rectifier, further ammonia and carbon dioxide are removed and, with some water vapour, are condensed to give a weak carbamate solution. This is pumped back to the high-pressure condenser. 

Condensate is normally considered the entrapped liquids in process or production gas streams due to temperature or pressure, in the typically in the range of C3, C4, C5 or heavier hydrocarbon liquids. It is also known as natural gasoline C5 plus and pentanes plus, and as a liquid at normal temperatures and pressures it generally consists of a mixture of the C5 (pentanes) and heavier hydrocarbons. It is normally condensed (i.e., by expansion and cooling of the gas) out of the process stream in primary separation processes, where it is then sent to other refinery processes to further separate the condensate into its primary fractions, i.e., propane, butane, and liquids constituents. 

Direct sampling and analysis of the effluent stream may be used to determine the solubility of the heavy phase in the volatile component (often a supercritical fluid). Alternatively, the composition can be determined from the total volume of gas (i.e., of the supercritical fluid after expansion) passed through the saturator, and from the known mass of solute extracted during die sample-collecting period. The efflluent stream is expanded to atmospheric pressure via an expansion valve. Then it passes through a cold trap, where the extract is quantitatively precipitated or condensed, and finally proceeds to a dry-test or a wet-test gas meter or other device, where the total amount of the passed gas is measured. The amount of extracted solute... 

It is necessary to avoid the precipitation or condensation, and subsequent deposition of the extracted solute, from the effluent stream during the expansion in the expansion valve or in the section of tubing before the stream reaches the collecting trap. Weighing the valve can overcome this problem. 

The need to recover increasing amounts of valuable hydrocarbon feedstocks from natural gas streams has resulted in expanded use of low-temperature processing of these streams. The majority of such natural gas processing is now accomplished using a turboexpander in a modified isentropic expansion cycle with feed gas normally available from 1 to 10 MPa. The first step is to dry the gas to dew points of 200 K and lower. After drying, the feed gas is cooled with cold residue gas. Liquid produced at this point is separated before entering the expander and sent to the condensate stabilizer. The gas from the separator... 

After cooling at an appropriate temperature, the mixture is separated in gas and liquid, both operations simulated by a single flash unit FLASH. The gas phase contains most of methane, with a significant amount of C2, and small C3+. The liquid phase collects most of ethane and C3+ components. The gas is submitted to expansion in the unit EXP, in order to get low temperature and eventually the condensation of C2 and C3+ components. The liquid from the flash is depressurised by means of a valve and sent to separation in a reboiled absorption unit COL, together with the stream issued from expander. The top product is a methane gas, while the bottom product collects ethane and heavier components. Note that the unit COL has 8 trays, with the feeds on top and above the third stage. The column pressure is 22.5 bar. Finally the top gas product is compressed by the unit COMP and sent to the consumer. 

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