Natural gas purification system and purification process capable of utilizing excess pressure

Abstract

The invention provides a natural gas purification system and a natural gas purification process capable of utilizing excess pressure so as to improve the utilization rate of natural gas pressure energy and reduce the energy consumption of the system. The natural gas purification system comprises desulfurization equipment, a condenser, a first heater, a second heater, a heavy hydrocarbon membrane separator, an expansion generator and a primary membrane separator for removing carbon dioxide gas, a gas inlet of the primary membrane separator is connected with a gas outlet of the desulfurization equipment through a first heater and a condenser in sequence, a gas inlet of the heavy hydrocarbon membrane separator is connected with a permeated gas outlet of the primary membrane separator through a second heater, and a residual gas outlet of the heavy hydrocarbon membrane separator is connected with a gas inlet of the condenser; a gas inlet of the expansion generator is connected with a residual gas outlet of the first-stage membrane separator, and a gas outlet of the expansion generator is connected with a cooling medium inlet of the condenser. According to the invention, greater economic benefits can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of natural gas purification, and in particular to a natural gas purification system and purification process utilizing residual pressure. Background Art

[0002] Natural gas is a high-quality fuel stored in underground porous rock formations, including oilfield gas, gas field gas, coalbed methane, mud volcano gas and biogas, etc. It can also be used as a chemical raw material. Since traditional fossil energy sources such as coal and oil are non-renewable and will cause serious environmental pollution, natural gas, as a low-carbon clean energy, produces almost zero emissions of sulfur dioxide and dust during combustion. Its development scale is getting larger and larger, and it is becoming a fossil fuel with an increasing proportion. It will play a supporting role in the future low-carbon transformation. The natural gas produced by natural gas wells is called "wet gas" in the oil field before it is refined. The "wet gas" is directly input into the chemical plant to produce liquefied gas or other various chemical products. This natural gas is called "raw natural gas."

[0003] Since the raw natural gas contains hydrogen sulfide, heavy hydrocarbons, water, etc., it needs to be treated by purification process before it can be used as fuel or chemical raw material. The raw natural gas contains high pressure energy. Membrane separation is a widely used method in the current raw natural gas purification process, but the existing natural gas purification membrane separation system has high energy consumption, and the pressure energy in the raw gas is not fully utilized, resulting in a large waste of energy. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a natural gas purification system and purification process for utilizing excess pressure, so as to improve the utilization rate of natural gas pressure energy and reduce system energy consumption.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a natural gas purification system using excess pressure, comprising a desulfurization device, a condenser, a first heater, a second heater, a heavy hydrocarbon membrane separator, an expansion generator and a primary membrane separator for removing carbon dioxide gas;

[0006] The air inlet of the desulfurization equipment is connected to the raw gas pipe, the air inlet of the primary membrane separator is connected to the air outlet of the desulfurization equipment via the first heater and the condenser in sequence, the air inlet of the heavy hydrocarbon membrane separator is connected to the permeate gas outlet of the primary membrane separator via the second heater, and the residual gas outlet of the heavy hydrocarbon membrane separator is connected to the air inlet of the condenser;

[0007] The air inlet of the expansion generator is connected to the residual gas outlet of the primary membrane separator, the air outlet of the expansion generator is connected to the cooling medium inlet of the condenser, and the cooling medium outlet of the condenser is connected to the gas pipeline.

[0008] Furthermore, the flow direction of the product gas entering the condenser through the gas outlet of the expansion generator in the condenser is opposite to the flow direction of the raw gas in the condenser.

[0009] Furthermore, the desulfurization equipment is an activated carbon desulfurization equipment.

[0010] Furthermore, it also includes a first filter arranged between the desulfurization equipment and the condenser for filtering particulate matter in the raw gas.

[0011] Furthermore, the first filter is a coalescing filter.

[0012] Furthermore, the invention further includes a particulate filter arranged between the condenser and the first heater.

[0013] Furthermore, it also includes an adsorption system arranged between the first filter and the condenser for adsorbing water and acidic gas.

[0014] Furthermore, the condensation temperature of the condenser is controlled at -10°C to 0°C.

[0015] Furthermore, the temperature of the product gas flowing out of the outlet of the expansion generator is controlled at -10°C to 0°C.

[0016] A natural gas purification process utilizing excess pressure adopts the above-mentioned natural gas purification system utilizing excess pressure.

[0017] The beneficial effects of the present invention are:

[0018] The invention discloses a natural gas purification system and purification process for utilizing excess pressure. The two-stage membrane separation is used to not only improve the recovery rate of hydrocarbons in the raw gas, but also the membrane separation system can utilize the excess pressure of the product gas for power generation by using an expansion generator after purifying the carbon-containing raw gas. The cold energy after the product gas is utilized for power generation can be used to condense the raw gas through a condenser, thereby increasing the temperature of the product gas, realizing the complementary utilization of cold, heat and electricity, improving the utilization rate of the natural gas pressure energy of the purification system, reducing the energy consumption of the system, and obtaining greater economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the natural gas purification system of the present invention;

[0020] As shown in the figure: desulfurization equipment 1, first filter 2, adsorption system 3, condenser 4, first heater 5, primary membrane separator 6, second heater 7, heavy hydrocarbon membrane separator 8, expansion generator 9, gas pipeline 10, oil-gas separator 11. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0022] like Figure 1 As shown, a natural gas purification system for utilizing excess pressure of the present invention comprises a desulfurization device 1, a condenser 4, a first heater 5, a second heater 7, a heavy hydrocarbon membrane separator 8, an expansion generator 9 and a primary membrane separator 6 for removing carbon dioxide gas. The air inlet of the desulfurization device 1 is connected to the raw gas pipe, and the air inlet of the primary membrane separator 6 is connected to the air outlet of the desulfurization device 1 via the first heater 5 and the condenser 4 in sequence. That is, the air inlet of the primary membrane separator 6 is connected to the air outlet of the first heater 5, the air inlet of the first heater 5 is connected to the air outlet of the condenser 4, and the air inlet of the condenser 4 is connected to the air outlet of the desulfurization device 1. The air inlet of the heavy hydrocarbon membrane separator 8 is connected to the permeate gas outlet of the primary membrane separator 6 via the second heater 7, and the residual gas outlet of the heavy hydrocarbon membrane separator 8 is connected to the air inlet of the condenser 4. The air inlet of the expansion generator 9 is connected to the residual gas outlet of the first-stage membrane separator 6 , the air outlet of the expansion generator 9 is connected to the cooling medium inlet of the condenser 4 , and the cooling medium outlet of the condenser 4 is connected to the gas pipeline 10 .

[0023] When the natural gas purification system of the present invention purifies natural gas, the raw gas enters the desulfurization device 1, and the desulfurization device 1 first removes hydrogen sulfide in the raw gas, and then the condenser 4 condenses the raw gas to -10°C to 0°C to remove heavy hydrocarbons and water in the raw gas. The heavy hydrocarbons and water are discharged from the liquid outlet at the bottom of the condenser 4. The raw gas with heavy hydrocarbons removed enters the first heater 5 and is heated to about 30°C to prevent the raw gas from ice blockage and other hazards due to too low temperature. The heated raw gas enters the primary membrane separator 6, and the primary membrane separator 6 removes acidic gases such as carbon dioxide. Acidic gases such as carbon dioxide are discharged from the permeate gas outlet of the primary membrane separator 6, and the remaining gas, i.e., the product gas, is discharged from the residual gas outlet of the primary membrane separator 6 and enters the expansion generator 9. When the carbon dioxide content in the raw gas is high, a large amount of hydrocarbons will pass through the membrane of the primary membrane separator and be lost, and the hydrocarbon loss rate of the system is high. For this reason, a heavy hydrocarbon membrane separator 8 is provided. Since the permeate gas after the primary membrane separation will have a pressure drop, a second heater 7 is set to heat the permeate gas flowing out of the primary membrane separator 6 to about 30°C to ensure that its pressure meets the permeate pressure requirement of the heavy hydrocarbon membrane separator 8. After the permeate gas flowing out of the primary membrane separator 6 enters the heavy hydrocarbon membrane separator 8, the hydrocarbon substances therein can be separated by the heavy hydrocarbon membrane separator 8, and the separated hydrocarbon substances are discharged from the residual gas outlet of the heavy hydrocarbon membrane separator 8 into the inlet of the condenser 4, and condensed and separated by the condenser 4, so that the hydrocarbon recovery rate can be improved. After the product gas enters the expansion generator 9, the expansion generator 9 converts the pressure energy generated during the product gas decompression process into mechanical energy to drive the generator to generate electricity. The electric energy generated by the expansion generator 9 can be used for heating the purification plant or the heater. The product gas after power generation is discharged from the outlet of the expansion generator 9 and enters the condenser 4. The temperature of the product gas will decrease due to the expansion work, and its temperature can be controlled by controlling the expansion amount of the product gas using the expansion generator 9. The temperature of the product gas is controlled at about -10°C to 0°C through the expansion generator 9, and then enters the cooling medium inlet of the condenser 4 after being discharged, so that the cold energy of the product gas is used to cool the raw gas entering the condenser 4, and at the same time, the temperature of the product gas is increased to above 0 degrees, thereby avoiding ice blockage and other hazards due to low temperature in the downstream pipeline (gas pipeline 10).

[0024] The power generation potential of product gas can be assessed in the following ways:

[0025] General use To describe the maximum energy that can be recovered from natural gas pressure energy. Considering the natural gas pipeline network as an open system, the specific enthalpy of natural gas during the process of changing from the state before pressure regulation to the stable state after pressure regulation. for:

[0026]

[0027] Where: e x,hThe specific enthalpy of natural gas , unit is kJ / kg; h1, h2 represent the specific enthalpy of natural gas before and after pressure regulation, unit is kJ / kg; c p represents the specific heat capacity of natural gas at constant pressure, in kJ / (kg·K); T1, T2, T0 represent the temperature of natural gas before and after pressure regulation and the ambient temperature, in K; P1, P2 represent the absolute pressure of natural gas before and after pressure regulation, in MPa; Rg represents the gas constant of natural gas, in kJ / (kg·K), R g Its expression formula is:

[0028] R g =ω1R g1 +ω2R g2 +ω3R g3 +ω4R g4 +ω5R g5

[0029] Where: ω1, ω2, ω3, ω4, ω5 represent the mass fractions of CH4, C2H6, C3H8, CO2, and N2 in natural gas respectively; R g1 , R g2 , R g3 , R g4 , R g5 They represent the gas constants of CH4, C2H6, C3H8, CO2, and N2 respectively.

[0030] In the final formula above, the first term is the specific temperature , the second term is the specific pressure Generally speaking, the temperature Much smaller than the specific pressure , ignoring the specific temperature , multiplied by the currently mature pressure energy output coefficient, the output model of the expansion generator set is obtained as follows:

[0031]

[0032]

[0033] In the formula, e x,P Indicates specific pressure , unit is kJ / kg; P t Indicates the actual power generation, in kW; q v Indicates the volume flow rate of natural gas under standard conditions, in m 3 / h; ρ represents the density of natural gas under standard conditions, in kg / m 3 , η e Pressure can generate electricity ratio.

[0034] In order to maximize the use of the pressure energy of the product gas, the connection pipes between the equipment in the purification system should preferably use high-quality pipes and fittings to avoid gas leakage and loss. The layout of the pipeline should be as smooth as possible, that is, dead corners and inclinations should be avoided in the pipeline during gas transportation to ensure smooth gas flow. At the same time, the pipeline should be checked regularly for leaks and maintained and repaired in a timely manner.

[0035] The gas flowing out from the permeate outlet of the heavy hydrocarbon membrane separator 8 is mainly composed of carbon dioxide, but also contains some hydrocarbon substances. The gas can enter the flare system for treatment.

[0036] In the present invention, the primary membrane separator 6 and the heavy hydrocarbon membrane separator 8 are both existing membrane separators, and their membrane materials can be existing organic silicon membrane materials, inorganic membrane materials or high molecular polymer membrane materials. Organic silicon membrane materials have the advantages of oxidation resistance and arc resistance, but there is a lack of selectivity. Inorganic membrane materials can be divided into aluminum oxide, zinc oxide, titanium oxide, silicon oxide, silicate materials and zeolite materials according to their different components. They have the advantages of good thermal stability, resistance to organic solvents and not being degraded by microorganisms, and good mechanical properties; but they also have the disadvantages of fragile membranes, high processing costs (about 10 times that of polymer membranes), small filling area, difficulty in manufacturing large-area and defect-free membranes, and difficulty in high-temperature sealing. High molecular polymer membrane materials are widely available, easy to process and shape, and have good gas separation performance and mechanical stability, and are preferred membrane materials. High molecular polymer materials are specifically cellulose acetate (CA), polyimide (PI), etc. The membrane structure can be selected from circular tube type, plate frame type, spiral roll type, hollow fiber type, etc.

[0037] The natural gas purification system adopts two-stage membrane separation, which can not only improve the recovery rate of hydrocarbons in the raw gas, but also use the expansion generator to generate electricity from the residual pressure of the product gas after the membrane separation system purifies the carbon-containing raw gas. The cold energy after the product gas is used for power generation can be used to condense the raw gas through the condenser to remove heavy hydrocarbons and other substances in the raw gas, so that the temperature of the product gas is increased. The system realizes the complementary utilization of cold, heat and electricity, improves the utilization rate of the natural gas pressure energy of the purification system, and reduces the energy consumption of the system.

[0038] The flow direction of the product gas introduced into the condenser 4 through the outlet of the expansion generator 9 may be the same as the flow direction of the raw gas in the condenser 4, that is, a cooling medium inlet is provided on the air inlet side of the condenser 4, and a cooling medium outlet is provided on the air outlet side. Of course, the flow direction of the product gas introduced into the condenser 4 through the outlet of the expansion generator 9 may also be opposite to the flow direction of the raw gas in the condenser 4, that is, a cooling medium outlet is provided on the air inlet side of the condenser 4, and a cooling medium inlet is provided on the air outlet side. In order to maximize the utilization of the cold energy in the product gas, it is best that the flow direction of the product gas introduced into the condenser 4 through the outlet of the expansion generator 9 in the condenser 4 is opposite to the flow direction of the raw gas in the condenser 4. That is, a cooling medium outlet is provided on the air inlet side of the condenser 4, and a cooling medium inlet is provided on the air outlet side.

[0039] The desulfurization equipment 1 in the present invention can adopt various existing desulfurization equipment, such as: N-methyldiethanolamine (MDEA) solution desulfurization equipment. In the embodiment of the present invention, the desulfurization equipment 1 is an activated carbon desulfurization equipment. The activated carbon desulfurization equipment can absorb both hydrogen sulfide and water in the raw gas.

[0040] In order to improve the service life of the membrane separator, the present invention is provided with a first filter 2 for filtering particulate matter in the raw gas between the desulfurization equipment 1 and the condenser 4. In this way, the particulate matter in the raw gas can be filtered by the first filter 2, so as to prevent the particulate matter from damaging the filter membrane in the membrane separator, thereby improving the service life of the membrane separator. The first filter 2 can be various existing filters. Preferably, the first filter 2 is a condensation filter that can filter both liquid and particulate matter, so as to remove liquid, especially water, in the raw gas when filtering particulate matter.

[0041] The natural gas purification system is provided with a particle filter 11 between the condenser 4 and the first heater 5. The particle filter 11 has a membrane pore size of 0.2-1 um, which can filter fine dust larger than 0.1 um in the raw gas to further ensure the efficiency and service life of the subsequent membrane separator.

[0042] The natural gas purification system of the present invention also has an adsorption system 3 for adsorbing water, acidic gases, mercury, etc. between the first filter 2 and the condenser 4 to further reduce the acidic gases, gaseous water, etc. in the raw gas. The adsorption system 3 can adopt various existing adsorption systems that can adsorb water and acidic gases, such as: UOP's MemGuard regenerative adsorption system. The system uses regenerative adsorbents to effectively remove heavy hydrocarbons and other harmful components in the gas, thereby greatly extending the service life of the membrane assembly and ensuring the continuous and reliable operation of the entire membrane separation system.

[0043] The present invention also provides a natural gas purification process for utilizing excess pressure, which adopts the above-mentioned natural gas purification system for utilizing excess pressure. After the natural gas purification process adopts the above-mentioned purification system, since the natural gas purification system adopts two-stage membrane separation, it can not only improve the recovery rate of hydrocarbons in the raw gas, but also the membrane separation system can use the expansion generator to generate electricity for the excess pressure of the product gas after purifying the carbon-containing raw gas, and the cold energy after the product gas is used for power generation can be used to condense the raw gas through the condenser to remove heavy hydrocarbons and other substances in the raw gas, so that the temperature of the product gas is increased, realizing the complementary utilization of cold-heat-electricity multi-energy, improving the utilization rate of natural gas pressure energy, and reducing the energy consumption of natural gas purification.

[0044] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0045] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A natural gas purification system utilizing excess pressure, characterized in that: It comprises a desulfurization device (1), a condenser (4), a first heater (5), a second heater (7), a heavy hydrocarbon membrane separator (8), an expansion generator (9) and a primary membrane separator (6) for removing carbon dioxide gas; The air inlet of the desulfurization device (1) is connected to the raw gas pipe, the air inlet of the primary membrane separator (6) is connected to the air outlet of the desulfurization device (1) via the first heater (5) and the condenser (4) in sequence, the air inlet of the heavy hydrocarbon membrane separator (8) is connected to the permeate gas outlet of the primary membrane separator (6) via the second heater (7), and the residual gas outlet of the heavy hydrocarbon membrane separator (8) is connected to the air inlet of the condenser (4); The air inlet of the expansion generator (9) is connected to the residual gas outlet of the primary membrane separator (6), the air outlet of the expansion generator (9) is connected to the cooling medium inlet of the condenser (4), and the cooling medium outlet of the condenser (4) is connected to the gas pipeline (10).

2. A natural gas purification system utilizing excess pressure as claimed in claim 1, characterized in that: The flow direction of the product gas entering the condenser (4) through the gas outlet of the expansion generator (9) in the condenser (4) is opposite to the flow direction of the raw gas in the condenser (4).

3. A natural gas purification system utilizing excess pressure as claimed in claim 1, characterized in that: The desulfurization equipment (1) is an activated carbon desulfurization equipment.

4. A natural gas purification system utilizing excess pressure as claimed in claim 1 or 2, characterized in that: It also includes a first filter (2) disposed between the desulfurization device (1) and the condenser (4) for filtering particulate matter in the raw gas.

5. A natural gas purification system utilizing excess pressure as claimed in claim 4, characterized in that: The first filter (2) is a coalescing filter.

6. A natural gas purification system utilizing excess pressure as claimed in claim 4, characterized in that: The invention also includes a particulate filter (11) arranged between the condenser (4) and the first heater (5).

7. A natural gas purification system utilizing excess pressure as claimed in claim 4, characterized in that: It also includes an adsorption system (3) arranged between the first filter (2) and the condenser (4) for adsorbing water and acidic gas.

8. A natural gas purification system utilizing excess pressure as claimed in claim 1, characterized in that: The condensation temperature of the condenser (4) is controlled at -10°C to 0°C.

9. A natural gas purification system utilizing excess pressure as claimed in claim 1 or 8, characterized in that: The temperature of the product gas flowing out of the gas outlet of the expansion generator (9) is controlled at -10°C to 0°C.

10. A natural gas purification process using excess pressure, characterized in that: A natural gas purification system utilizing excess pressure as claimed in any one of claims 1 to 9 is adopted.

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