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 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.

In this patent we disclose, for the first time, detailed methods of our newly invented state-of-the-art cryogenic technology for the cost effective energy efficient capture of each known component of entire emissions (nearly 100%) such as carbon dioxide (CO.sub.2), sulfur oxides (SO.sub.x), nitrogen oxides (NO.sub.x), carbon monoxide(CO), any other acid vapor, mercury, steam and unreacted nitrogen from industrial plants (coal and natural gas fired power plants, cement plants etc.), in a liquefied or frozen/solidified form, such that each of the components is captured separately and is industrially useful. This new technology includes a novel NH.sub.3 power plant to generate auxiliary electrical power from the heat energy of the flue gas to further improve the energy efficiency and cost effectiveness of the capture processes. It is the most cost effective of all existing emission capture technologies. It does not require use of any chemicals/reagents/external cryogens, unlike the current technologies. It uses only a fixed amount of water needed for the cooling process which can be used repeatedly. We present detailed methods of operations, together with scientific and economic analysis of the energy needed and cost involved for the said capture in two specific examples, and advantages of the new technology over the existing ones.

A method for separating hydrogen and nitrogen from a gas mixture, including a) thereby partially condensing a hydrogen and nitrogen gas mixture and producing a two-phase stream, b) phase separating the two-phase stream, producing a nitrogen-enriched liquid fraction and a hydrogen-enriched gaseous fraction, c) expanding the nitrogen-enriched liquid fraction, producing a lower-pressure nitrogen-enriched liquid or two-phase stream, d) adding heat to the lower-pressure nitrogen-enriched liquid stream, producing a warm nitrogen enriched gaseous stream, and e) adding heat to the hydrogen-enriched gaseous fraction, producing a hydrogen-rich product stream. Wherein, at least a portion of the heat added in step d) is removed in step a), at least a portion of the heat added in step e) is removed in step a), or at least a portion of the heat added in step d) and at least a portion of the heat added in step e) is removed in step a).

One or more specific embodiments disclosed herein includes a method for separating hydrogen from an olefin hydrocarbon rich compressed effluent vapor stream, employing a single heat exchanger, multiple gas-liquid separators, multiple expander/compressor sets, and a rectifier attached to a liquid product drum.

Systems and methods for separation of a component from a mixed gas stream by a combination of direct contact heat and material exchange in an indirect contact heat exchanger are disclosed. A contact liquid stream wets an interior surface of the process channel of the indirect contact heat exchanger and the mixed gas stream passes through the process channel, contacting the contact liquid stream for heat and mass exchange. A refrigerant in the refrigerant channel of the indirect contact heat exchanger is used for heat exchange with the contact liquid.

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.

One or more specific embodiments disclosed herein includes a method for separating hydrogen from an olefin hydrocarbon rich compressed effluent vapor stream, employing a single heat exchanger, multiple gas-liquid separators, multiple expander/compressor sets, and a rectifier attached to a liquid product drum.

Methods and systems for recovering alkene (e.g., C.sub.2-C.sub.4 alkene) gas as well as producing pressurized alkene (e.g., C.sub.2-C.sub.4 alkene) gas from process gas streams including higher concentrations of alkenes are provided herein.