Helium recovery unit in natural gas
Technical Field
The invention relates to the field of helium recovery, in particular to a device for recovering helium in natural gas.
Background
Helium is present in air in very small amounts, mainly in natural gas, from a few thousandths to a few percent, so extraction of helium from natural gas is still the main industrial source of nitrogen. Currently, the common methods for recovering and purifying helium in industry mainly comprise low-temperature condensation, pressure swing adsorption, chemical separation and membrane separation.
The most applied low-temperature condensation (cryogenic separation) is to liquefy almost all methane and most nitrogen under the cryogenic condition by utilizing the characteristic of extremely low helium liquefying temperature, separate crude helium by low-temperature rectification, condense residual methane and nitrogen in the crude helium at high pressure and low temperature, and obtain pure helium by adsorption. The low-temperature condensation method has high product purity and recovery rate of helium extraction, but has low operation flexibility and large equipment investment and operation cost.
Compared with the traditional low-temperature condensation method for extracting helium, the membrane technology does not need to be separated after low-temperature condensation phase change, and the energy consumption is obviously lower than that of the low-temperature condensation method, so that the method has better application and development prospects in the field of natural gas helium extraction. However, how to ensure high yield and purity of helium is still a problem.
Disclosure of Invention
The invention aims at solving the problems and researches and designs a device for recovering helium in natural gas. The technical means adopted by the invention are as follows:
the utility model provides a helium recovery unit in natural gas, including compressor I, cooler I behind the machine, the filter before the membrane, membrane separator I, compressor II, cooler II behind the machine, membrane separator II and membrane separator III, the feed gas passes through compressor I, get into membrane separator I behind cooler I and the filter before the membrane after the machine, the infiltration side export of membrane separator I links to each other with the entry of compressor II, the side export of holding back of membrane separator I links to each other with the entry of membrane separator III, the side export of holding back of membrane separator II links to each other with the entry of membrane separator I, the infiltration side export of membrane separator III links to each other with the entry of compressor I.
Further, the pre-membrane filter is arranged between the after-machine cooler I and the membrane separator I.
Further, the membrane separator I, the membrane separator II and the membrane separator III all comprise at least one membrane separation assembly.
Further, the structure of the membrane separation module is selected from one or more of the group consisting of spiral wound, plate and frame, and hollow fiber.
Furthermore, the machine aftercooler I and the machine aftercooler II are both water coolers.
Compared with the prior art, the device for recovering helium from natural gas provided by the invention realizes efficient recovery of helium by setting a three-stage membrane separation process. The helium recovery rate can be more than 99 percent, the purity is more than 95 percent, the equipment investment is low, the operation is simple and convenient, and the energy consumption for operation is low.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of the present invention.
Detailed Description
As shown in fig. 1, a device for recovering helium from natural gas sequentially comprises, along a material flow direction: the system comprises a compressor I1, an after-machine cooler I2, a pre-membrane filter 3, a membrane separator I4, a compressor II 5, an after-machine cooler II 6, a membrane separator II 7 and a membrane separator III 8; the permeation side outlet of the membrane separator I4 is connected with the inlet of a compressor II 5; the outlet at the interception side of the membrane separator I4 is connected with the inlet of a membrane separator III 8; the interception side outlet of the membrane separator II 7 is connected with the inlet of the membrane separator I4; the permeate side outlet of membrane separator III 8 was connected to the inlet of compressor I1.
The membrane separator I4, the membrane separator II 7 and the membrane separator III 8 are all internally provided with at least one membrane separation component with preferential permeability to helium. The structure of the membrane separation module is selected from one or more of a combination of spiral wound type, plate frame type and hollow fiber type, preferably the hollow fiber type.
The working flow of this embodiment is:
the raw material gas (such as BOG flash evaporation gas of an LNG plant, the helium content is about 13%) firstly enters a compressor i 1 through an air inlet pipeline 10, the pressure is increased to about 2MPaG, and then enters an after-machine cooler i 2 through a first connecting pipeline 11 to be cooled to 40 ℃ through water, and then enters a pre-membrane filter 3 through a second connecting pipeline 12 to remove impurities, and the adjustment of the temperature and the removal of the impurities are beneficial to improving the membrane separation efficiency and prolonging the service life. The treated gas enters the membrane separator I4 through a third connecting pipeline 13. In the membrane separator I4, helium permeates through the membrane preferentially, is enriched and concentrated to about 30% on the permeation side, enters the compressor II 5 through the fourth connecting pipeline 14 to increase the pressure to about 2.1MPaG, enters the after-cooler II 6 through the fifth connecting pipeline 15, is cooled by water, and enters the membrane separator II 7 through the sixth connecting pipeline 16. Helium with the concentration of 97% is obtained at the permeation side of the membrane separator II 7 and is conveyed out of the boundary area through a first gas outlet pipeline 17; the tail gas at the trapped side returns to the inlet of the membrane separator I4 through a seventh connecting pipeline 18 to be continuously recovered. Tail gas at the interception side of the membrane separator I4 enters a membrane separator III 8 through an eighth connecting pipeline 19, wherein helium enriched at the permeation side returns to an inlet of the compressor I1 through a ninth connecting pipeline 21 to be continuously recovered so as to improve the recovery rate of the helium to 99%; the tail gas at the trapped side is conveyed out of the boundary area through a second gas outlet pipeline 20 and is sent to a fuel gas pipe network to be used as fuel gas.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.