Cryogenic Air Separation Oxygen Concentrator Spare Parts Turbo Expansion Turbine

Cryogenic Air Separation Oxygen Concentrator Spare Parts Turbo Expansion Turbine

1. description

It is to use adiabatic expansion inside the machine to create coldness in order to start up air separation units and make up the coldness loss, thus stablize the heat balance.

The expander is a mechine that when gas is expanded and depressurized, turbo outputs mechinical work in order to reduce the temperature of the gas so as to obtain the energy. . Expander is often used in cryogenic equipment, such as liquid oxygen plant, liquid nitrogen plant,etc.

2. application

Raw natural gas consists primarily of methane (CH₄), the shortest and lightest hydrocarbon molecule, as well as various amounts of heavier hydrocarbon gases such as ethane (C₂H₆), propane (C₃H₈), normal butane (n-C₄H₁₀), isobutane (i-C₄H₁₀), pentanes and even higher-molecular-mass hydrocarbons. The raw gas also contains various amounts of acid gases such as carbon dioxide (CO₂), hydrogen sulfide (H₂S) and mercaptans such as methanethiol (CH₃SH) and ethanethiol (C₂H₅SH).

When processed into finished by-products (see Natural-gas processing), these heavier hydrocarbons are collectively referred to as NGL (natural-gas liquids). The extraction of the NGL often involves a turboexpander^[7] and a low-temperature distillation column (called a demethanizer) as shown in the figure. The inlet gas to the demethanizer is first cooled to about −51 °C in a heat exchanger (referred to as a cold box), which partially condenses the inlet gas. The resultant gas–liquid mixture is then separated into a gas stream and a liquid stream.

The liquid stream from the gas–liquid separator flows through a valve and undergoes a throttling expansion from an absolute pressure of 62 bar to 21 bar (6.2 to 2.1 MPa), which is an isenthalpic process (i.e., a constant-enthalpy process) that results in lowering the temperature of the stream from about −51 °C to about −81 °C as the stream enters the demethanizer.

The gas stream from the gas–liquid separator enters the turboexpander, where it undergoes an isentropic expansion from an absolute pressure of 62 bar to 21 bar (6.2 to 2.1 MPa) that lowers the gas stream temperature from about −51 °C to about −91 °C as it enters the demethanizer to serve as distillation reflux.

Liquid from the top tray of the demethanizer (at about −90 °C) is routed through the cold box, where it is warmed to about 0 °C as it cools the inlet gas, and is then returned to the lower section of the demethanizer. Another liquid stream from the lower section of the demethanizer (at about 2 °C) is routed through the cold box and returned to the demethanizer at about 12 °C. In effect, the inlet gas provides the heat required to "reboil" the bottom of the demethanizer, and the turboexpander removes the heat required to provide reflux in the top of the demethanizer.

The overhead gas product from the demethanizer at about −90 °C is processed natural gas that is of suitable quality for distribution to end-use consumers by pipeline. It is routed through the cold box, where it is warmed as it cools the inlet gas. It is then compressed in the gas compressor driven by the turboexpander and further compressed in a second-stage gas compressor driven by an electric motor before entering the distribution pipeline.

The bottom product from the demethanizer is also warmed in the cold box, as it cools the inlet gas, before it leaves the system as NGL.