Decarburization method in natural gas ethane recovery project

Abstract

The invention provides a decarburization method in a natural gas ethane recovery project, and aims to solve the problems of high energy consumption and large investment in a decarburization process of a small and medium-sized natural gas ethane recovery device in an alcohol amine decarburization method. Pressure swing adsorption decarburization, direct output of decarburized ethane and carbon dioxide rich gas pressurization circulation are adopted to form a low-energy-consumption and low-cost ethane decarburization process, pressure swing adsorption is used for ethane decarburization, the process flow is short, and the automation degree is high; and the whole decarburization process is in a deep drying environment, and medium corrosion prevention of equipment does not need to be considered. The method provided by the invention has the advantages of low energy consumption and no exhaust emission in the whole decarburization process, can be widely applied to most light hydrocarbon recovery devices, and has a better application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas, and is applied to natural gas ethane recovery devices. Specifically, it relates to a process method for decarbonization in natural gas ethane recovery projects. Background Art

[0002] Natural gas generally contains carbon dioxide, with a content range of 0.1% - 1%. In natural gas ethane recovery devices, most of the carbon dioxide will condense into the ethane product. In the Chinese petroleum enterprise standard "Technical Indicators for Natural Gas Ethane Recovery" Q / SY 01027 - 2019, it is stipulated that the carbon dioxide content (mole fraction) in the second-class gas ethane used as raw material for ethylene production ≤ 3%. Other ethane receiving plants also have clear quality requirements for the carbon dioxide content in ethane. Therefore, for natural gas ethane recovery devices with carbon dioxide in the raw material gas, an ethane decarbonization device needs to be built to ensure the quality of the ethane product.

[0003] Currently, the alcohol amine method is mostly selected for ethane decarbonization. Its working principle is that, due to the alkaline characteristics of the alcohol amine solution, it can react with carbon dioxide gas at a relatively low temperature, and then be regenerated by heating and depressurizing to desorb the absorbed carbon dioxide, and the solution is recycled. Its advantages are high purification degree, capable of completely removing carbon dioxide, and having rich industrial experience, being widely used in large-scale natural gas ethane recovery devices and the decarbonization process for producing liquid ethane.

[0004] However, the alcohol amine method for ethane decarbonization also has certain limitations. First, since the decarbonization reaction occurs under aqueous solution conditions, the supporting equipment (especially the equipment for solution regeneration) needs to consider the problem of carbon dioxide corrosion, resulting in a relatively high overall cost of the equipment; the alcohol amine solution needs to be heated during the regeneration stage, leading to high energy consumption; second, the ethane gas after decarbonization needs to be dehydrated twice (deep dehydration has already been carried out before the ethane production process itself), and heating regeneration is also required during the dehydration stage, further increasing the investment and energy consumption of the entire ethane decarbonization device; finally, the compound formed by the reaction of carbon dioxide generated during the decarbonization process of ethanol amine method with ethanol amine will reduce the concentration of the ethanol amine solution, increasing energy consumption, and the ethanol amine solution also has an absorption effect on other waste gas components such as nitrogen oxides and sulfides, which may lead to a decrease in the purity of carbon dioxide. Therefore, in small and medium-sized natural gas ethane recovery devices, the applicability of the alcohol amine method for decarbonization is relatively low.

[0005] In the prior art, CN 102675248 A discloses a method for removing carbon dioxide from the synthesis recycle gas of ethylene oxide / ethylene glycol. An aqueous solution composed of potassium carbonate and an inorganic activator is used; a two-stage absorption process with appropriate flow rate distribution and temperature control is adopted; pressure swing regeneration desorption is used. By using the suction effect of an adjustable supersonic steam ejector on the atmospheric pressure regeneration tower, a pressure difference is formed between the pressurized regeneration tower and the atmospheric pressure regeneration tower, and a mixed gas containing a large amount of water vapor is sucked out for stripping and regeneration of the pressurized regeneration tower. However, in order to remove carbon dioxide, this method requires a large amount of energy for the regeneration process, which increases the energy consumption of the entire process.

[0006] The prior art CN219072546U discloses a decarbonization system for ethylene oxide production. A recycle gas inlet is arranged at the lower part of the carbon dioxide absorption tower of the decarbonization system, and a carbon dioxide absorption liquid spray port is arranged at the upper part of the carbon dioxide absorption tower; the absorption liquid outlet of the carbon dioxide absorption tower is communicated with the liquid inlet of the flash tank, and the liquid outlet of the flash tank is communicated with the feeding port of the carbon dioxide removal tower; a reboiler is connected to the bottom of the carbon dioxide removal tower, and a steam outlet is arranged at the top of the carbon dioxide removal tower. The decarbonization system can effectively remove carbon dioxide in the ethylene oxide production system through the absorption liquid removal of the carbon dioxide absorption tower, flash removal of light components in the flash tank, and steam removal in the carbon dioxide removal tower. The decarbonization system can operate safely, energy-efficiently and highly efficiently. However, this decarbonization system has problems such as carbon dioxide corrosion, resulting in a relatively high overall cost of the equipment and a large investment.

[0007] In the practical application of decarbonization, factors such as equipment investment, operating cost, and energy consumption also need to be comprehensively considered. These factors have an important impact on the economy and feasibility of the pressure swing adsorption technology. Therefore, there is an urgent need in the art for a highly efficient and low-cost decarbonization process. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the present invention aims to solve the problems of high energy consumption and large investment existing in the decarbonization process of the amine method in small and medium-sized natural gas ethane recovery plants, and provides a decarbonization method in the natural gas ethane recovery project.

[0009] The inventive concept of the present invention is: adopting pressure swing adsorption for decarbonization, directly exporting the decarbonized ethane, and pressurizing and circulating the carbon dioxide-rich gas to form a set of ethane decarbonization process with low energy consumption and low cost. Using pressure swing adsorption for ethane decarbonization has a short process flow and high automation; and the entire decarbonization process is in a deeply dry environment, and there is no need to consider the corrosion of the equipment medium.

[0010] The technical solution of the present invention is as follows:

[0011] A decarbonization device in a natural gas ethane recovery project specifically comprises a natural gas ethane recovery device connected to a pressure swing adsorption decarbonation device, and the pressure swing adsorption decarbonation device is connected to a compressor and a dry gas transmission system of the natural gas ethane recovery device.

[0012] A decarbonization method in a natural gas ethane recovery project comprises the following steps:

[0013] S1. The gas phase of ethane gas from the reflux tank at the top of the deethanizer tower of the natural gas ethane recovery unit is heated and heated to a temperature above 30°C;

[0014] S2. The heated ethane gas enters the pressure swing adsorption decarbonation device, and after passing through the adsorbent, ethane product gas with a carbon dioxide content of ≤3% and desorbed gas with a carbon dioxide content of >60% are obtained; after the adsorption is completed, each adsorption tower undergoes the stages of equalizing pressure reduction, reverse placement, vacuuming, equalizing pressure increase, and product gas pressure increase in sequence to complete the regeneration of the adsorbent, thereby entering the adsorption state again;

[0015] S3. The gas desorbed by the adsorbent regeneration in step S2 is pressurized, and the pressurized gas enters the dry gas transmission system of the natural gas ethane recovery device.

[0016] The selection of adsorbent is crucial to the effect of ethane decarbonization. Commonly used adsorbents include activated carbon, molecular sieves, silica gel, etc. They have different adsorption properties and characteristics and need to be selected according to actual conditions. As a preferred embodiment of the present invention, the adsorbent preferably uses a silica gel adsorbent. Carbon dioxide will undergo physical adsorption with the adsorbent and be adsorbed by the adsorbent, while other components are not affected and continue to flow out of the adsorption tower. Silica gel adsorbents have better adsorption properties for carbon dioxide, and the separation of carbon dioxide and ethane gas components is achieved to obtain ethane product gas with a carbon dioxide content of ≤3% and a desorbed gas with a carbon dioxide content of >60%. As a preferred embodiment of the present invention, the compressor uses a screw compressor or a reciprocating compressor.

[0017] Regeneration is one of the key steps in pressure swing adsorption technology. During the regeneration process, the pressure of the adsorption tower is reduced to desorb carbon dioxide from the adsorbent and restore the adsorption capacity of the adsorbent. Pressure swing adsorption technology is flexible and variable, and can be adjusted and optimized according to production needs and changes in the composition of the raw gas. For example, by changing the type of adsorbent or process conditions, effective separation and purification of different components can be achieved.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Compared with the conventional alkanolamine method, the decarbonization method provided by the present invention does not involve any solution, and the ethane product itself is in a state of deep dehydration. Therefore, there is no need to consider corrosion problems for the equipment, nor is there a need for secondary dehydration. The cost of the entire equipment is significantly lower than that of the alkanolamine method for decarbonization.

[0020] (2) The energy consumption of the decarbonization method of the present invention is significantly lower than that of the alkanolamine method for decarbonization. Taking an ethane decarbonization device with a capacity of 5×10 4 m 3 / d as an example, the energy consumption can be saved by more than 200 kW.

[0021] (3) The tail gas generated by the decarbonization of the present invention can be directly pressurized and transported to the dry gas export system, and there is no waste gas emission in the entire decarbonization process.

[0022] (4) The decarbonization device of the present invention has the advantages of less floor space and high degree of operation automation.

[0023] (5) The decarbonization method and device of the present invention can be widely applied to most light hydrocarbon recovery devices and have good application prospects. Description of the Drawings

[0024] Figure 1 The pressure swing adsorption ethane decarbonization process of the present invention. Detailed Embodiments

[0025] The embodiments of the present invention will be described in detail below. The embodiments described below are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention. The endpoints and any values disclosed in this document are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered specifically disclosed in this document.

[0026] To make it easier to understand the present invention, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by those of ordinary skill in the art to which the present invention pertains.

[0027] The solution of the present invention will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those embodiments where specific techniques or conditions are not indicated, the techniques or conditions described in the literature in this field or according to the product instructions are followed. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial procurement.

[0028] A decarbonization device in a natural gas ethane recovery project in the present invention specifically includes a connection between a natural gas ethane recovery device and a pressure swing adsorption carbon dioxide removal device, and a connection between the pressure swing adsorption carbon dioxide removal device, a compressor, and the dry gas export system of the natural gas ethane recovery device. In the present invention, the functions and roles of each device are as follows:

[0029] Natural gas ethane recovery device: used to recover ethane components in natural gas.

[0030] Pressure swing adsorption carbon dioxide removal device: includes equipment such as pressure swing adsorption towers, vacuum pumps, and pressure equalization buffer tanks, used for the adsorption, separation, purification of carbon dioxide and ethane gas components, and the regeneration of adsorbents. The number of settings is several, and it is specifically adjusted according to the production scale of ethane.

[0031] Compressor: used to boost the pressure of the desorbed gas.

[0032] Example 1

[0033] A decarbonization method in a natural gas ethane recovery project includes the following steps:

[0034] S1. Ethane gas is heated through heat exchange from the gas phase part of the reflux tank at the top of the deethanizer in the natural gas ethane recovery device, raising its temperature to above 30°C.

[0035] S2. The heated ethane gas enters the pressure swing adsorption carbon dioxide removal device, and the adsorption pressure is the pressure of the gas coming from the deethanizer. After passing through the adsorbent, ethane product gas with a carbon dioxide content ≤ 3% and desorbed gas with a carbon dioxide content > 60% are obtained; after each adsorption tower completes adsorption, it successively experiences the stages of pressure equalization pressure reduction, countercurrent release, vacuum pumping, pressure equalization pressure increase, and product gas pressure increase to complete the regeneration of the adsorbent, and then enters the adsorption state again;

[0036] In the adsorption stage, the pressure swing adsorption tower is filled with silica gel - type adsorbents that can adsorb impurities and carbon dioxide in the gas. When the adsorbent reaches the saturation state, it needs to be regenerated.

[0037] In this example, the regeneration process in the pressure swing adsorption tower generally includes the following steps:

[0038] S2.1 Pressure equalization pressure reduction: By reducing the pressure in the pressure swing adsorption tower, the substances adsorbed on the adsorbent and part of the gas start to desorb, realizing separation from the adsorbent. The number of equalization times and the pressure of each equalization are determined by the adsorption pressure and the carbon dioxide concentration at both ends of the adsorption tower outlet after adsorption ends.

[0039] S2.2 Countercurrent release: After pressure equalization pressure reduction, the gas is reduced to 0.1 MPa(A) against the adsorption direction to further clean and regenerate the adsorbent.

[0040] S2.3 Vacuum pumping: Use a vacuum pump to extract the carbon dioxide on the adsorbent, and further reduce the pressure in the adsorption tower to 0.015 MPa(A) by vacuum pumping to promote the desorption and discharge of the adsorbed carbon dioxide, and this stage promotes the regeneration of the adsorbent.

[0041] S2.4 Equalization pressure boosting: This step corresponds to the equalization pressure reduction. The gas discharged by the equalization pressure reduction is used to boost the pressure in the adsorption tower by equalization, gradually increasing the pressure in the adsorption tower after vacuum pumping so that the next round of adsorption process can proceed normally.

[0042] S2.5 Product gas pressure boosting: Boost the pressure of the desorbed gas to meet the usage requirements of the product gas.

[0043] After the above steps, the adsorbent is regenerated and can be used again for the adsorption process. This workflow is cycled, enabling the adsorption tower to continuously perform gas treatment and purification. After the regeneration of the adsorbent is completed, the adsorption tower can start a new adsorption process again. At this time, the adsorbent in the adsorption tower has been fully regenerated and can effectively adsorb carbon dioxide in ethane.

[0044] In addition, to improve the regeneration efficiency of the adsorbent, methods such as thermal regeneration and microwave regeneration can also be used for the adsorption tower itself to promote the desorption and discharge of the adsorbed substances and improve the regeneration efficiency of the adsorbent.

[0045] In summary, the regeneration process of the adsorption tower is one of the important links in the operation of the adsorption tower, and reasonable control and management are required. By optimizing the regeneration process, controlling energy consumption, strengthening safety control, monitoring the regeneration effect, and dealing with environmental protection and waste issues, the normal operation and long-term stability of the adsorption tower can be ensured, providing a reliable solution for industrial production and gas treatment.

[0046] S3. Boost the pressure of the gas desorbed and regenerated from the adsorbent in step S2, and the pressurized gas enters the dry gas export system of the natural gas ethane recovery unit.

[0047] Example 2

[0048] S1. The ethane gas is heated to above 30°C after heat exchange from the gas phase of the reflux drum at the top of the deethanizer in the natural gas ethane recovery unit.

[0049] S2. The heated ethane gas enters the pressure swing adsorption carbon dioxide removal device, and the adsorbent selected is silica gel adsorbent, obtaining ethane product gas with a carbon dioxide content ≤ 3% and desorbed gas with a carbon dioxide content > 60%. After each adsorption tower completes adsorption, it successively experiences the stages of equalization pressure reduction, reverse release, vacuum pumping, equalization pressure boosting, and product gas pressure boosting to complete the regeneration of the adsorbent and then enter the adsorption state again.

[0050] S3. The gas desorbed by the adsorbent regeneration is pressurized, and the compressor is a screw compressor or a reciprocating compressor. The pressurized gas enters the dry gas transmission system of the natural gas ethane recovery unit.

[0051] Application Example 1

[0052] The ethane decarbonization device of the present invention is applied to the 800,000 cubic meters / day light hydrocarbon recovery device of Liaohe Oilfield Company. The ethane product of the 800,000 cubic meters / day light hydrocarbon recovery device is processed, and the fuel gas consumption saved due to the reduction of heating load is 25×10 4 m 3 / a, and the investment is only half of that of the amine method, with a 5×10 4 m 3 Taking the ethane decarbonization unit with a capacity of 1000MW / d as an example, it can save more than 200kW of energy.

[0053] It can be seen from the above embodiments that the decarbonization device and decarbonization method in a natural gas ethane recovery project provided by the present invention can effectively solve the problems of high energy consumption and large investment in the decarbonization process of small and medium-sized natural gas ethane recovery devices, and has the advantages of simple operation, low energy consumption, strong adaptability, high efficiency and low cost.

[0054] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A decarbonization method in a natural gas ethane recovery project, characterized in that, The steps are as follows: S1. The ethane gas is heated through heat exchange from the gas phase part of the reflux drum at the top of the deethanizer in the natural gas ethane recovery unit, raising its temperature to above 30°C. S2. The heated ethane gas enters the pressure swing adsorption carbon dioxide removal unit. After passing through the adsorbent, ethane product gas with a carbon dioxide content ≤ 3% and desorbed gas with a carbon dioxide content > 60% are obtained. After each adsorption tower completes adsorption, it successively experiences the steps of equal pressure reduction, countercurrent release, vacuum pumping, equal pressure boosting, and product gas boosting to complete the regeneration of the adsorbent, and then enters the adsorption state again. S3. The gas desorbed and regenerated from the adsorbent in step S2 is pressurized, and the pressurized gas enters the dry gas export system of the natural gas ethane recovery unit.

2. The method according to claim 1, wherein In the adsorption stage, the pressure swing adsorption tower is filled with silica gel adsorbents that can adsorb impurities and carbon dioxide in the gas. When the adsorbent reaches the saturation state, it needs to be regenerated.

3. The method according to claim 1, characterized in that, The regeneration process in the pressure swing adsorption tower generally includes the following steps: S2.1 Equal pressure reduction: By reducing the pressure in the pressure swing adsorption tower, the substances adsorbed on the adsorbent and part of the gas start to desorb, achieving separation from the adsorbent. S2.2 Countercurrent release: After equal pressure reduction, the gas is reduced to 0.1 MPa(A) against the adsorption direction, further cleaning and regenerating the adsorbent. S2.3 Vacuum pumping: Use a vacuum pump to extract carbon dioxide from the adsorbent, and further reduce the pressure in the adsorption tower to 0.015 MPa(A) by vacuum pumping to promote the desorption and discharge of the adsorbed carbon dioxide. This stage promotes the regeneration of the adsorbent. S2.4 Equal pressure boosting: This step corresponds to equal pressure reduction. The gas discharged during equal pressure reduction is used to boost the pressure in the adsorption tower, gradually increasing the pressure in the adsorption tower after vacuum pumping so that the next round of adsorption process can proceed normally. S2.5 Product gas boosting: The desorbed gas is boosted to meet the usage requirements of the product gas.

4. The method according to claim 3, characterized in that In S2.1, the number of equal pressure times and the equal pressure of each time are determined by the adsorption pressure and the carbon dioxide concentration at both ends of the adsorption tower outlet after adsorption ends.

5. The method according to claim 3, characterized in that, In step S2, after the regeneration of the adsorbent is completed, the adsorption tower can start a new adsorption process again. At this time, the adsorbent in the adsorption tower has been fully regenerated and can effectively adsorb carbon dioxide in ethane.

6. The method according to claim 3, wherein In step S3, a screw compressor or a reciprocating compressor is selected for the compressor.

7. The method according to claim 1, wherein In the decarbonization unit of this natural gas ethane recovery project, the natural gas ethane recovery unit is connected to the pressure swing adsorption carbon dioxide removal unit, and the pressure swing adsorption carbon dioxide removal unit is connected to the compressor and the dry gas export system of the natural gas ethane recovery unit.

8. The method according to claim 7, characterized in that The pressure swing adsorption carbon dioxide removal unit includes pressure swing adsorption towers, vacuum pumps, and equal pressure buffer tanks, which are used for the adsorption, separation, purification of carbon dioxide and ethane gas components, and the regeneration of the adsorbent. The number of installations is several, and it is specifically adjusted according to the production scale of ethane.

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