A liquefaction system is capable of sequentially or simultaneously liquefying multiple feed streams of hydrocarbons having different normal bubble points with minimal flash. The liquefying heat exchanger has separate circuits for handling multiple feed streams. The feed stream with the lowest normal boiling point is sub-cooled sufficiently to suppress most of the flash. Feed streams with relatively high normal boiling points are cooled to substantially the same temperature, then blended with bypass streams to maintain each product near its normal bubble point. The system can also liquefy one stream at a time by using a dedicated circuit or by allocating the same feed to multiple circuits.

A process for recovering valuables from vent gas in polyolefin production is disclosed. The process includes a compression cooling separation step, a heavy hydrocarbon separation step, a light hydrocarbon separation step, a N.sub.2 purification step, and a turbo expansion step in sequence. The N.sub.2 purification step comprises a membrane separation procedure. The light hydrocarbon separation step comprises at least one gas-liquid separation procedure. A first gas, which is obtained by the gas-liquid separation procedure and is heated through heat exchange with multiple streams in the light hydrocarbon separation step, enters the heavy hydrocarbon separation step and is further heated; the heated first gas then enters the N.sub.2 purification step; a first generated gas, which is obtained by the membrane separation procedure of the N.sub.2 purification step, enters the heavy hydrocarbon separation step and the light hydrocarbon separation step in sequence, and is cooled through heat exchange with multiple streams in the heavy hydrocarbon separation step and the light hydrocarbon separation step; and then the cooled first generated gas enters the turbo expansion step. The energy consumption of a compressor can be greatly reduced. An external cooling medium with a temperature lower than an ambient temperature is not needed. The purity and recovery of N.sub.2 and hydrocarbons can be improved, which can facilitate reduction of energy consumption of a whole system, an investment, and a material consumption.

A system used to recycle exhaust gas during olefin polymer production, comprising: a compression cooling mechanism (101); a hydrocarbon membrane separation mechanism (102) and a hydrogen membrane separation mechanism (103), both connected to a first outlet (202) of the compression cooling mechanism; and a deep cooling mechanism (104) connected to a first outlet (208) of the hydrogen membrane separation mechanism. A method used to recycle exhaust gas during olefin polymer production, comprising a compression cooling step, a hydrocarbon membrane separation step, a hydrogen membrane separation step and a deep cooling step.

A method for cryogenically separating a natural gas supply stream into a gas containing the most volatile compounds of the supply stream, and a liquid product containing the heaviest compounds at least including the following. Introducing an at least partially condensed stream into an absorption column at an introduction stage in the lower part of said absorption column, thus producing, at the top, a gaseous stream that contains the most volatile compounds and, the bottom, a liquid product. Introducing the liquid product into a fractionation column in order to obtain, in the bottom of the fractionation column, a liquid product that contains the heaviest compounds of the supply stream and, at the top of the fractionation column, a distillate that is at least partially condensed in a second heat exchanger system

A system (102; 302) for recovering natural gas liquid from a low pressure gas source (110; 310), comprising a gas/gas heat exchanger (104; 304), fluid from the gas source flowing therethrough; at least one separator (108; 308) for receiving the fluid from the gas/gas heat exchanger (104; 304) and separating liquid from the gas, the gas being directed via a connecting pipe (116; 316) to the gas/gas heat exchanger (104; 304) where it cools the fluid from the gas source; characterised in that the connecting pipe (116; 316) includes expansion means (106; 322) for cooling the gas therein and liquid injection means (120; 320) for saturating the gas with liquid.

A gas recovery system separates a mixed gas including a process gas and an inert gas. The gas recovery system includes a cooling section for cooling and liquefying the process gas contained in the mixed gas by cooling the mixed gas at a temperature higher than a condensation temperature of the inert gas and lower than a condensation temperature of the process gas, a separating section for separating the cooled mixed gas into the process gas in a liquid state and the inert gas in a gas state, and a process gas recovery line that is connected to the separating section which circulates and gasifies the liquid-state process gas and then supplies the process gas into the a compressor. The mixed gas is formed by mixing the process gas, which is compressed by the compressor, and the inert gas, which is supplied to a seal portion of the compressor.

A heat exchanger with a uniquely designed header system which allows tubes carrying independent products to exchange heat with a product in one common shell. Multiple tube sheets provide for tubes carrying different independent products to exchange heat with the product passing through the shell side of the exchanger. The design advantages to this heat exchanger system are threefold, this exchanger design eliminates the need for multiple heat exchangers that perform the same task, it greatly reduces the size and footprint of a traditionally designed multiple heat exchanger systems, which rely on multiple independent heat exchangers to perform the same task, and lastly this new designed heat exchanger reduces the high cost of having to use multiple exchangers to obtain the same results.

An improved method for separating hydrocarbons for separating feed LNG into product LNG and a liquid fraction enriched in C3+ components is provided. Feed LNG is heated and partially vaporized by a heat exchanger to obtain a vapor-liquid two-phase stream; the whole or a liquid phase of the vapor-liquid two-phase stream is separated into first overhead vapor enriched in methane and first bottom liquid enriched in ethane and C3+ components at a first distillation column; the first bottom liquid is separated into second overhead vapor enriched in ethane and second bottom liquid enriched in C3+ components by the second distillation column; the second overhead vapor is cooled and wholly or partially condensed to obtain condensed liquid; one of two or more streams obtained by dividing the condensed liquid is mixed with the first overhead vapor; the mixed stream is totally condensed to obtain a liquid stream by heat exchange with feed LNG by the heat exchanger; the whole or a part of the liquid stream is discharged as product LNG; another of the divided streams is refluxed to the second distillation column; and the second bottom liquid is discharged as the liquid fraction enriched in C3+ components.

A liquefaction system is capable of sequentially or simultaneously liquefying multiple feed streams of hydrocarbons having different normal bubble points with minimal flash. The liquefying heat exchanger has separate circuits for handling multiple feed streams. The feed stream with the lowest normal boiling point is sub-cooled sufficiently to suppress most of the flash. Feed streams with relatively high normal boiling points are cooled to substantially the same temperature, then blended with bypass streams to maintain each product near its normal bubble point. The system can also liquefy one stream at a time by using a dedicated circuit or by allocating the same feed to multiple circuits.

An expander and motor-compressor unit is disclosed. The unit includes a casing and an electric motor arranged in the casing. A compressor is arranged in the casing and drivingly coupled to the electric motor through a central shaft. Furthermore, a turbo-expander is arranged for rotation in the casing and is drivingly coupled to the electric motor and to the compressor through the central shaft.