CN109748771B - Method for recovering carbon dioxide in refinery dry gas - Google Patents
Method for recovering carbon dioxide in refinery dry gas Download PDFInfo
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- CN109748771B CN109748771B CN201711057353.5A CN201711057353A CN109748771B CN 109748771 B CN109748771 B CN 109748771B CN 201711057353 A CN201711057353 A CN 201711057353A CN 109748771 B CN109748771 B CN 109748771B
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Abstract
The invention relates to the field of dry gas treatment, and particularly discloses a method for recovering carbon dioxide in refinery dry gas, wherein the method comprises the following steps: 1) sequentially carrying out compression treatment and cooling phase splitting treatment on the aromatic dry gas; 2) feeding the coking dry gas into a coking dry gas compressor for compression treatment, and feeding the gas phase obtained by the cooling phase-splitting treatment in the step 1) into a coking dry gas compressor section or an outlet; 3) cooling the mixed dry gas collected at the outlet of the coking dry gas compressor, and then absorbing the mixed dry gas in an absorption tower by using the carbon four-fraction as an absorbent; and 4) feeding the liquid phase obtained by the cooling phase separation treatment in the step 1) and the tower bottom material flow of the absorption tower into a desorption tower for desorption treatment. The recovery method of the invention has high recovery rate of carbon two, does not need a propylene refrigeration system and a drying system, has lower content of more than three carbon components in the product gas, and has the advantages of low energy consumption and less investment.
Description
Technical Field
The invention relates to the field of dry gas treatment, in particular to a method for recovering carbon dioxide in refinery dry gas.
Background
Refinery dry gas, such as delayed coker dry gas, aromatics complex dry gas, etc., is derived from the secondary processing of crude oil. The dry gas typically contains a significant amount of ethane, e.g., from about 10 to about 24 mole percent ethane in the coker dry gas, and from about 25 to about 70 mole percent ethane in the aromatics complex dry gas, e.g., PX plant dry gas. At present, refinery dry gas is mainly used as fuel to be burnt, and the utilization value is low. If the ethane component in the dry gas is concentrated and sent to an ethane cracking furnace of an ethylene device to be used as a raw material, the economic benefit and the social benefit are very obvious. Because the cracking performance of the ethane component in the raw material of the ethane cracking furnace of the ethylene unit is better than that of the propane component, the ethane purity of the ethane-rich gas obtained by recovery is improved as much as possible, and the content of the three components of hydrogen, methane and carbon is reduced.
At present, methods for recovering a carbon dioxide component from refinery dry gas mainly comprise a cryogenic separation method, a pressure swing adsorption method, a shallow cold oil absorption method and the like, and various methods have characteristics. The cryogenic separation method has mature process, high ethylene recovery rate and purity, but large investment, and higher energy consumption for recovering the dilute ethylene; the pressure swing adsorption method has simple operation, low energy consumption, low product purity, low ethylene recovery rate and large occupied area.
The shallow cold oil absorption method mainly separates gas mixture by utilizing different solubility of absorbent to each component in gas, generally, heavy components above C2 and C2 are absorbed by the absorbent firstly, noncondensable gases such as methane, hydrogen and the like are separated, and then each component in the absorbent is separated by a rectification method. The method has the characteristics of high recovery rate of C2 and C3, safe production, reliable operation, strong adaptability to raw material gas and the like, and is one of the existing competitive technologies. However, the carbon content of the product carbon two concentrated gas obtained by separation by the shallow cold oil absorption method is generally higher due to the influence of the composition of the raw material gas. If the content of the carbon three in the product gas is further reduced, a method of adding an ethylene rectifying tower is adopted to separate out propane and propylene. In the process, the operation temperature of part of process material flow is lower than 0 ℃, a propylene refrigeration compressor is required to provide low-temperature cold energy, and a dryer is also required to be arranged in the process flow to prevent freezing and blocking, so that the equipment investment and the device energy consumption are high.
CN101063048A discloses a method for separating refinery dry gas by adopting an intercooled oil absorption method, which comprises the steps of compression, acid gas removal, drying and purification, absorption, desorption, cold quantity recovery, rough separation and the like, and has the advantages of low absorbent cost, low loss and the like. However, the process needs to cool the dry gas to-30 ℃ to-40 ℃, which belongs to an intercooling separation process, so the investment is large and the energy consumption is high.
CN101759518B discloses a device and a method for separating dry gas by an oil absorption method, wherein the method comprises the steps of carbon four absorption, carbon four desorption, gasoline absorption and the like, carbon four is adopted as an absorbent, and carbon two and carbon three fractions in the dry gas are recovered. And recovering carbon four in the tail gas by adopting a gasoline absorbent. The carbon dioxide recovery rate of the process is high, but the pressure of the desorption tower is low, the carbon dioxide and the carbon three components cannot be separated within the operation range (the temperature is above 0 ℃), the concentration of the carbon three in the product gas is influenced by the relative content of the carbon three in the raw material, the circulation amount of the carbon four absorbent is large, and the energy consumption of the device is influenced.
CN103588604B discloses a system and a method for recovering carbon two in refinery dry gas by a combined absorption method, which comprises a compressor, a pretreatment unit, a refinery dry gas cooling unit, a combined absorption unit and a rectification unit. In the process, mixed carbon four or mixed carbon five is used as an absorbent for carbon two absorption, and the desorbed carbon two concentrated gas is sent to an ethylene rectifying tower for separation to obtain an ethylene product and an ethane product. The process can control the content of C three and above components in ethylene products, but needs a propylene refrigeration compressor to provide propylene cold energy at the temperature of-40 ℃, and needs a drying system to remove water in dry gas to prevent freezing and blocking because the process material flow temperature is lower than-35 ℃.
Therefore, when the carbon two components in the refinery dry gas are recovered and purified, in order to reduce the content of the carbon three in the product gas, the existing refinery dry gas recovery process needs a propylene refrigeration compressor unit to provide low-temperature cold energy, and needs a drying system to remove moisture in the dry gas or the intermediate product gas to prevent freezing and blocking, so that the investment is large and the energy consumption is high.
In conclusion, the existing method for recovering the refinery dry gas is not easy to separate the carbon dioxide and the carbon in the dry gas, and low-temperature cold energy is needed, so that the problems of high investment, high energy consumption and large circulation amount of the carbon four absorbent are caused.
Disclosure of Invention
The invention aims to overcome the problems that the existing method for recovering the refinery dry gas is not easy to separate three components of carbon and carbon in the dry gas, low-temperature cold energy is required to be used, the investment is large, the energy consumption is high, and the circulating amount of a carbon four absorbent is large, and provides a method for recovering the carbon in the refinery dry gas, wherein the method comprises the following steps:
1) sequentially carrying out compression treatment and cooling phase splitting treatment on the aromatic dry gas;
2) feeding the coking dry gas into a coking dry gas compressor for compression treatment, and feeding the gas phase obtained by the cooling phase-splitting treatment in the step 1) into a coking dry gas compressor section or an outlet;
3) cooling the mixed dry gas collected at the outlet of the coking dry gas compressor, and then absorbing the mixed dry gas in an absorption tower by using the carbon four-fraction as an absorbent; and
4) and (3) feeding the liquid phase obtained by the cooling phase separation treatment in the step 1) and the tower bottom material flow of the absorption tower in the step 3) into a desorption tower for desorption treatment.
The method for recovering the carbon dioxide in the refinery dry gas has the following advantages:
(1) the compression condensation method is matched with the oil absorption method to recover refinery dry gas, the aromatic dry gas with higher carbon content is compressed and condensed, light components such as methane, hydrogen and the like and a part of carbon components enter an absorption tower along with the gas phase of a liquid separating tank, and the coking dry gas with lower carbon component content directly enters the absorption tower. Through the oil absorption-desorption process, the separation of the methane and the hydrogen in the aromatic hydrocarbon dry gas and the coking dry gas from the carbon dioxide component is realized. Due to the characteristics of high separation efficiency of C1 and C2 and high recovery rate of C2 in the oil absorption process, the process can ensure the carbon two yield and the methane-hydrogen separation efficiency.
(2) Partial carbon two and more than three carbon components in the aromatic hydrocarbon dry gas are directly sent into the desorption tower in a condensate form, and compared with a typical shallow cold oil absorption process that the dry gas in CN101759518B completely enters the absorption tower, the circulating carbon four and the load of a reboiler of the absorption tower are reduced without a carbon four absorption process.
(3) Compared with the typical shallow cold oil absorption process of CN101759518B, the pressure of the desorption tower is increased to 3.0-4.0MPaG, the temperature of the tower top can be controlled to be above 10 ℃, the carbon and the carbon are separated, the condenser at the tower top is cooled by refrigerant water, and a propylene refrigeration system or a pre-separation tower is not used. The pressure of a desorption tower in the CN101759518B process is low (2.0-3.0 MPaG), carbon dioxide and carbon cannot be completely separated at the temperature of 5-15 ℃ at the top of the tower, a lower-temperature refrigerant such as a propylene refrigerant is needed, and a dryer is needed.
(4) The carbon four-fraction is used as an absorbent to absorb the carbon two in the dry gas in the absorption tower, and the raw material of the absorbent is easy to obtain and the cost is low;
(5) in the method, the minimum temperature of the absorption and rectification operation is 5-15 ℃, a propylene refrigeration compressor is not needed, a lithium bromide refrigeration unit can be selected to provide cold energy, a drying system is not needed, the cost is reduced, the operation is simple, and the energy consumption is low;
(6) in the method, the molar content of a carbon two component in the ethane-rich gas is higher than 94%, the molar content of a hydrogen and methane component is lower than 5%, and the content of a heavy component with more than three carbon atoms is lower than 1.5%, so that the ethane-rich gas can be used as a raw material of an ethane cracking furnace of an ethylene plant.
(7) In the method, the recovery rate of carbon in the coking dry gas and the arene dry gas is more than 92 percent.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
FIG. 1 is a schematic flow diagram of a process for recovering carbon dioxide from refinery dry gas according to the present invention.
Description of the reference numerals
1 coking dry gas and 2 coking dry gas compressor section
Two-stage 4-arene dry gas of 3 coking dry gas compressor
5 arene dry gas compressor 6 lithium bromide absorption type refrigerator
7 divide liquid jar 8 coking dry gas compressor intersegmental buffer tanks
9 coking dry gas cooler 10 absorption tower
11 desorption tower 12 absorbent circulating pump
13 absorbent cooler 14 methane hydrogen tail gas
15 ethane-rich gas 16 absorbent
17 light hydrocarbon 18 condensate
Detailed Description
The present invention will be described in detail with reference to the following embodiments. It should be understood that the detailed description and specific examples, while indicating the present invention, are intended for purposes of illustration and explanation only and are not intended to limit the scope of the invention.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
As shown in fig. 1, the present invention relates to a method for recovering carbon dioxide from refinery dry gas, wherein the method comprises:
1) sequentially carrying out compression treatment and cooling phase splitting treatment on the aromatic hydrocarbon dry gas 4;
2) feeding the coking dry gas 1 into a coking dry gas compressor for compression treatment, and feeding a gas phase obtained by cooling phase splitting treatment into a coking dry gas compressor section or an outlet;
3) cooling the mixed dry gas collected at the outlet of the coking dry gas compressor, and then absorbing the mixed dry gas in an absorption tower 10 by using carbon four-fraction as an absorbent; and
4) sending the liquid phase obtained by the cooling phase separation treatment in the step 1) and the tower bottom material flow of the absorption tower 10 into a desorption tower 11 for desorption treatment.
In the present invention, the dry gas can be a coking dry gas 1 and an aromatic dry gas 4, preferably a coking dry gas from a delayed coking unit of a refinery and an aromatic dry gas 4 from an aromatic complex of a refinery.
In the present invention, preferably, the compression treatment in step 1) is operated by increasing the pressure of the aromatic hydrocarbon dry gas 4 to 2 to 4.5 MPaG;
preferably, the compression process is a multi-stage compression process, more preferably a two-stage or three-stage compression process. The compression process is close to the isothermal compression process by adopting the operation of multi-stage compression treatment, and the more the number of stages is, the more the compression process is close to the isothermal compression process, the more the saved work is, and the defect of single-stage compression is overcome.
In the present invention, it is preferable that the cooling phase separation treatment in the step 1) is carried out by cooling the aromatic hydrocarbon dry gas 4 to 5 to 15 ℃, preferably 10 to 15 ℃. In this operation, the process stream temperature ranges from 5 to 15 ℃ and remains above 5 to 15 ℃ in subsequent operations, thereby eliminating the need for low temperature propylene refrigeration and the use of propylene refrigeration and drying systems.
Preferably, the cooling phase-separating treatment comprises cooling by using cold water prepared by a lithium bromide absorption refrigerator as a refrigerant and phase-separating in a liquid-separating tank (7). More preferably, the lithium bromide absorption refrigerator 6 cools the dry aromatic hydrocarbon gas 4 to 5 to 15 ℃ using water as a refrigerant.
In the present invention, preferably, the compression treatment in step 2) is operated so that the pressure of the mixed dry gas collected at the outlet of the coker dry gas compressor section 3 is 3-5 MPaG.
Preferably, when the pressure of the gas phase obtained by the cooling phase separation treatment in the step 1) is 3-5MPaG, the gas phase obtained by the cooling phase separation treatment is sent to the outlet of the second section 3 of the coking dry gas compressor.
Preferably, the coking dry gas compressor comprises multi-stage compression, more preferably two-stage or three-stage compression, the compression process is close to the isothermal compression process by adopting multi-stage compression treatment, the more the stages are, the more the saved work is, and the energy consumption is further reduced.
Preferably, the coking dry gas compressor comprises a coking dry gas compressor section 2 and a coking dry gas compressor section 3, more preferably, an inter-section buffer tank 8 of the coking dry gas compressor is arranged between the coking dry gas compressor section 2 and the coking dry gas compressor section 3, and when the pressure of the gas phase obtained by the cooling phase separation treatment in the step 1) is lower than 3MPaG, the gas phase obtained by the cooling phase separation treatment is sent to the inter-section buffer tank 8 of the coking dry gas compressor.
In the present invention, preferably, the cooling treatment in step 3) is performed by cooling the mixed dry gas to 5 to 15 ℃, preferably 10 to 15 ℃; in this operation, the temperature of the mixed dry gas is in the range of 5 to 15 ℃ and is maintained at 5 to 15 ℃ in the subsequent absorption and desorption operations, so that the cold energy of propylene at a low temperature level is not required, and a propylene refrigeration system and a drying system are not required.
Preferably, the refrigerant used in the cooling process is cold water prepared by a lithium bromide absorption refrigerator.
In the present invention, preferably, in step 3), the mixed dry gas is fed to the middle part of the absorption tower 10, and the carbon four-fraction is injected at the top part of the absorption tower 10, so that the mixed dry gas and the carbon four-fraction are in countercurrent contact. By adopting the absorption mode, the mixed dry gas is fully contacted with the carbon four fraction, and the recovery rate of C2 in the mixed dry gas is further improved.
In the present invention, it is preferable that the number of theoretical plates of the absorption column 10 is 25 to 50, the operation pressure is 3 to 5MPaG, the overhead temperature is 10 to 30 ℃, and the bottom temperature is 70 to 130 ℃. In the absorption operation of the invention, the temperature range is 5-15 ℃, so that a propylene refrigeration compressor is not needed, a lithium bromide refrigeration unit can be selected to provide cold energy, a drying system is not needed, the operation is further simplified, and the energy consumption is reduced.
In the present invention, preferably, the carbon four fraction is at least one of n-butane, isobutane and post-etheric carbon four from a refinery.
In a preferred embodiment, the liquid phase material (i.e. the material rich in C2 component) from the bottom of the absorption tower 10 is supplied to the middle of the desorption tower 11, and the gas phase material obtained at the top of the desorption tower 11 is an ethane-rich gas product in which the molar content of the carbon two component is higher than 94%, the molar content of the hydrogen and the methane component is lower than 5%, and the content of the heavy component of more than three carbon is lower than 1.5%, and it can be supplied to the cracking furnace of the ethylene plant as the raw material of the ethane cracking furnace.
In the present invention, preferably, in the step 4), the theoretical plate number of the desorption tower 11 is 20 to 60, the operation pressure is 3.0 to 4.0MPaG, the tower top temperature is 10 to 40 ℃, and the tower bottom temperature is 90 to 130 ℃.
Preferably, the refrigerant used in the top cooling process of the desorption tower 11 is cold water prepared by a lithium bromide absorption refrigerator. In the desorption operation of the invention, the temperature range is 5-15 ℃, so that a propylene refrigeration compressor is not needed, a lithium bromide refrigeration unit can be selected to provide cold energy, a drying system is not needed, the operation is further simplified, and the energy consumption is reduced.
In the present invention, preferably, the method for recovering carbon dioxide in refinery dry gas further comprises: and returning the lean absorbent obtained in the desorption treatment process to the absorption tower 10 for recycling, specifically, the liquid-phase material obtained at the bottom of the desorption tower 11 is a carbon-lean four-absorbent, the pressure of the carbon-lean four-absorbent is increased by an absorbent circulating pump 12, and the carbon-lean four-absorbent is returned to the absorption tower 10 for recycling after being cooled to 15 ℃ by an absorbent cooler 13.
According to a preferred embodiment of the present invention, as shown in fig. 1, the method for recovering carbon dioxide from refinery dry gas comprises the following steps:
the pressure of the dry aromatic gas 4 is increased to 2.0-4.5MPaG by an aromatic dry gas compressor 5, the compressed dry gas is cooled to 5-15 ℃ by a lithium bromide type refrigerator 6, and gas-liquid phase separation is carried out in a liquid separating tank 7;
the gas phase at the top of the liquid separation tank 7 is sent to an intersegmental buffer tank 8 of a coking dry gas compressor or the outlet of a second section 3 of the coking dry gas compressor, and the condensate 18 at the bottom of the liquid separation tank 7 is sent to a desorption tower 11;
the pressure of the coking dry gas 1 is boosted to 3.0-5.0MPaG through a coking dry gas compressor section 2 and a coking dry gas compressor section 3, the outlet gas of the coking dry gas compressor is cooled to 5-15 ℃ through a coking dry gas cooler 9, and the outlet gas is sent into an absorption tower 10;
in the absorption tower 10, the carbon four fraction is used as an absorbent 16 and is sprayed from the top of the absorption tower 10 to absorb the carbon two fraction and heavier components in the feed gas, the gas 14 which is not absorbed at the top of the tower is sent to a fuel gas pipe network or other uses, and the absorption tower bottoms are sent to a desorption tower 11 for subsequent treatment;
the material flow from the tower bottom of the absorption tower 10 enters the middle part of the desorption tower 11 by pressure difference, and the condensate 18 from the bottom of the liquid separation tank 7 is also sent to the middle part of the desorption tower 11; the top of the desorption tower 11 obtains ethane-rich gas 15 which is sent into an ethane cracking furnace of an ethylene device; the tower bottom liquid of the desorption tower 11 is pressurized by an absorbent circulating pump 12, and returns to the absorption tower 10 for recycling after being cooled by an absorbent cooler 13, and a strand of absorbent is pumped out to be used as a light hydrocarbon product 17 and sent out of a battery compartment.
The invention will be described in more detail below with reference to examples, but the invention is not limited to these examples, by means of fig. 1.
In the following examples and comparative examples, the compositions of coke dry gas and aromatic dry gas from refineries are shown in table 1.
TABLE 1
| Dry gas of coking | Dry gas of aromatic hydrocarbon | |
| Temperature, C | 40 | 10.0 |
| Pressure, MPaG | 0.80 | 0.25 |
| Mass flow, t/h | 20 | 50 |
| Composition in mol% | ||
| H2 | 11.00 | 6.00 |
| CO | 0.00 | 0.00 |
| CO2 | 0.00 | 0.00 |
| N2 | 0.30 | 0.00 |
| O2 | 0.20 | 0.00 |
| CH4 | 59.80 | 2.00 |
| C2H6 | 22.00 | 70.01 |
| C2H4 | 3.00 | 0.00 |
| C3H8 | 0.50 | 18.02 |
| C3H6 | 0.50 | 0.00 |
| n-C4H10 | 0.50 | 1.54 |
| i-C4H10 | 0.50 | 1.19 |
| C4H8 | 0.50 | 0.00 |
| n-C5H12 | 0.25 | 0.40 |
| i-C5H12 | 0.25 | 0.00 |
| Benzene and its derivatives | 0.00 | 0.84 |
| H2O | 0.70 | 0.00 |
Example 1
This example illustrates the method of recovering carbon dioxide from refinery dry gas according to the present invention.
PX plant dry gas (pressure 0.25MPaG) from a refinery aromatics complex is fed to the aromatics dry gas compressor 5, raising the pressure to 2.5 MPaG. The pressurized dry gas is cooled to 15 ℃ by a lithium bromide type refrigerator 6, gas-liquid phase separation is carried out in a liquid separation tank 7, and the gas phase at the top of the liquid separation tank 7 is sent into a coking dry gas compressor interstage buffer tank 8.
The coking dry gas 1 (pressure 0.80MPaG) from a delayed coking device of a refinery is boosted to 2.0MPaG by a coking dry gas compressor section 2, then is supplied to a buffer tank 8 between coking dry gas compressor sections together with the gas phase at the top of a liquid separation tank 7, and the gas phase at the top of the buffer tank 8 is boosted to 4.0MPaG by a coking dry gas compressor section 3, is cooled to 15 ℃ by a coking dry gas cooler 9, and then is supplied to an absorption tower 10.
In the absorption tower 10, refinery n-butane is used as an absorbent 16 (flow rate 80t/h), and is sprayed from the top of the tower to absorb the carbon dioxide fraction and heavier components in the dry gas. The number of theoretical plates of the absorption tower 10 is preferably 40, the operation pressure is 3.8MPaG, the tower top temperature is 36 ℃, and the tower bottom temperature is 79 ℃. The tower bottom of the absorption tower 10 is heated by low-pressure steam, tail gas which is not absorbed at the top of the tower is discharged into a fuel gas pipe network, and rich absorbent in the tower bottom is sent into a desorption tower 11 for treatment.
The material from the bottom of the absorption tower 10 enters the middle part of the desorption tower 11 by pressure difference, and the condensate 18 from the liquid separation tank 7 enters the middle part of the desorption tower 11. The theoretical plate number of the desorption tower 11 is 50, the operation pressure is 3.3MPaG, the tower top temperature is 17 ℃, and the tower bottom temperature is 119 ℃. The condenser at the top of the desorption tower 11 is cooled by refrigerant water, the refrigerant water is provided by a lithium bromide refrigerating unit, a reboiler at the bottom of the desorption tower is heated by low-pressure steam, ethane-rich gas 15 is obtained at the top of the tower and is sent to an ethane cracking furnace of an ethylene device, the pressure of the bottom liquid of the desorption tower is increased by an absorbent circulating pump 12, the bottom liquid is returned to the absorption tower 10 for recycling after being cooled to 15 ℃ by an absorbent cooler 13, and simultaneously one absorbent is extracted to be used as a light hydrocarbon 17 product and sent out of a district. The composition of the product after isolation is shown in table 2. In this example, the carbon recovery rate was 92.9%.
TABLE 2
| Ethane-rich gas | |
| Temperature, C | 15.0 |
| Pressure, MPaG | 3.30 |
| Mass flow, t/h | 38.8 |
| Content of Components (mol%) | |
| H2 | 0.22 |
| CO | 0.00 |
| CO2 | 0.00 |
| N2 | 0.00 |
| CH4 | 1.31 |
| C2H6 | 95.66 |
| C2H4 | 1.59 |
| C3H8 | 1.12 |
| C3H6 | 0.08 |
| C4+ | 0.00 |
| H2O | 0.02 |
Example 2
This example illustrates the method of recovering carbon dioxide from refinery dry gas according to the present invention.
PX plant dry gas (pressure 0.25MPaG) from a refinery aromatics complex is fed to the aromatics dry gas compressor 5, raising the pressure to 4.5 MPaG. The pressurized dry gas is cooled to 15 ℃ by a lithium bromide type refrigerator 6, gas-liquid phase separation is carried out in a liquid separation tank 7, and the gas phase at the top of the liquid separation tank 7 is sent into a coking dry gas compressor interstage buffer tank 8.
The coking dry gas 1 (pressure 0.80MPaG) from a delayed coking device of a refinery is boosted to 2.0MPaG by a coking dry gas compressor section 2, then is supplied to a buffer tank 8 between coking dry gas compressor sections together with the gas phase at the top of a liquid separation tank 7, and the gas phase at the top of the buffer tank 8 is boosted to 5.0MPaG by a coking dry gas compressor section 3, is cooled to 10 ℃ by a coking dry gas cooler 9, and then is supplied to an absorption tower 10.
In the absorption tower 10, refinery n-butane is used as an absorbent 16 (flow rate 50t/h), which is sprayed from the top of the tower to absorb the carbon dioxide fraction and heavier components in the dry gas. The theoretical plate number of the absorption tower is 50, the operation pressure is 4.2MPaG, the tower top temperature is 28.3 ℃, and the tower kettle temperature is 92 ℃. The tower bottom of the absorption tower 10 is heated by low-pressure steam, tail gas which is not absorbed at the top of the tower is discharged into a fuel gas pipe network, and rich absorbent in the tower bottom is sent into a desorption tower 11 for treatment.
The material from the bottom of the absorption tower 10 enters the middle part of the desorption tower 11 by pressure difference, and the condensate 18 from the liquid separation tank 7 enters the middle part of the desorption tower 11. The theoretical plate number of the desorption tower 11 is 40, the operation pressure is 4.0MPaG, the tower top temperature is 20 ℃, and the tower bottom temperature is 124 ℃. The condenser at the top of the desorption tower 11 is cooled by refrigerant water, the refrigerant water is provided by a lithium bromide refrigerating unit, a reboiler at the bottom of the desorption tower is heated by low-pressure steam, ethane-rich gas 15 is obtained at the top of the tower and is sent to an ethane cracking furnace of an ethylene device, the pressure of the bottom liquid of the desorption tower is increased by an absorbent circulating pump 12, the bottom liquid is returned to the absorption tower 10 for recycling after being cooled to 15 ℃ by an absorbent cooler 13, and simultaneously one absorbent is extracted to be used as a light hydrocarbon 17 product and sent out of a district. The composition of the product after isolation is shown in Table 3. In this example, the carbon recovery rate was 97.3%.
TABLE 3
| Ethane-rich gas | |
| Temperature, C | 20.0 |
| Pressure, MPaG | 4.00 |
| Mass flow, t/h | 40.32 |
| Content of Components (mol%) | |
| H2 | 2.90 |
| CO | 0.00 |
| CO2 | 0.00 |
| N2 | 0.00 |
| CH4 | 1.86 |
| C2H6 | 92.90 |
| C2H4 | 1.51 |
| C3H8 | 0.77 |
| C3H6 | 0.05 |
| C4+ | 0.00 |
| H2O | 0.01 |
Example 3
This example illustrates the method of recovering carbon dioxide from refinery dry gas according to the present invention.
PX plant dry gas (pressure 0.25MPaG) from a refinery aromatics complex is fed to the aromatics dry gas compressor 5, raising the pressure to 3.0 MPaG. The pressurized dry gas is cooled to 5 ℃ by a lithium bromide type refrigerator 6, gas-liquid phase separation is carried out in a liquid separation tank 7, and the gas phase at the top of the liquid separation tank 7 is sent into a coking dry gas compressor interstage buffer tank 8.
The coking dry gas 1 (pressure 0.80MPaG) from a delayed coking device of a refinery is boosted to 2.0MPaG by a coking dry gas compressor section 2, then is supplied to a buffer tank 8 between coking dry gas compressor sections together with the gas phase at the top of a liquid separation tank 7, and the gas phase at the top of the buffer tank 8 is boosted to 3.5MPaG by a coking dry gas compressor section 3, is cooled to 10 ℃ by a coking dry gas cooler 9, and then is supplied to an absorption tower 10.
In the absorption tower 10, refinery n-butane is used as an absorbent 16 (flow rate 85t/h), and is sprayed from the top of the tower to absorb the carbon dioxide fraction and heavier components in the dry gas. The theoretical plate number of the absorption tower is 30, the operation pressure is 3.4MPaG, the tower top temperature is 25 ℃, and the tower kettle temperature is 80 ℃. The tower bottom of the absorption tower 10 is heated by low-pressure steam, tail gas which is not absorbed at the top of the tower is discharged into a fuel gas pipe network, and rich absorbent in the tower bottom is sent into a desorption tower 11 for treatment.
The material from the bottom of the absorption tower enters the middle part of the desorption tower 11 by pressure difference, and the condensate 18 from the liquid separating tank 7 enters the middle part of the desorption tower 11. The theoretical plate number of the desorption tower 11 is 30, the operation pressure is 3.1MPaG, the tower top temperature is 11 ℃, and the tower kettle temperature is 110 ℃. The condenser at the top of the desorption tower 11 is cooled by refrigerant water, the refrigerant water is provided by a lithium bromide refrigerating unit, a reboiler at the bottom of the desorption tower is heated by low-pressure steam, ethane-rich gas 15 is obtained at the top of the tower and is sent to an ethane cracking furnace of an ethylene device, the pressure of the bottom liquid of the desorption tower is increased by an absorbent circulating pump 12, the bottom liquid is returned to the absorption tower 10 for recycling after being cooled to 15 ℃ by an absorbent cooler 13, and simultaneously one absorbent is extracted to be used as a light hydrocarbon 17 product and sent out of a district. The composition of the product after isolation is shown in Table 4. In this example, the carbon recovery rate was 98.8%.
TABLE 4
| Ethane-rich gas | |
| Temperature, C | 11.0 |
| Pressure, MPaG | 3.10 |
| Mass flow, t/h | 41.0 |
| Content of Components (mol%) | |
| H2 | 1.15 |
| CO | 0.00 |
| CO2 | 0.00 |
| N2 | 0.00 |
| CH4 | 1.90 |
| C2H6 | 94.26 |
| C2H4 | 1.71 |
| C3H8 | 0.92 |
| C3H6 | 0.05 |
| C4+ | 0.00 |
| H2O | 0.01 |
Comparative example 1
The operation was carried out in accordance with the procedure of example 1 except that the operating pressure of the desorber 11 was 2.20MPaG, which is not within the range of 3.0-4.0MPaG of the present invention, and the overhead temperature was 15.0 ℃ at the time, the condenser at the top of the desorber 11 was cooled with refrigerant water supplied from a lithium bromide refrigerator group, and the composition of the product after separation was as shown in Table 5. In this example, the carbon recovery was 92.80%.
TABLE 5
| Ethane-rich gas | |
| Temperature, C | 15.0 |
| Pressure, MPaG | 2.20 |
| Mass flow, t/h | 47.76 |
| Content of Components (mol%) | |
| H2 | 0.00 |
| CO | 0.00 |
| CO2 | 0.00 |
| N2 | 0.00 |
| CH4 | 1.22 |
| C2H6 | 82.58 |
| C2H4 | 1.48 |
| C3H8 | 13.16 |
| C3H6 | 0.25 |
| C4+ | 1.28 |
| H2O | 0.03 |
Comparative example 2
Taking the coking dry gas from the delayed coking unit of the refinery and the aromatic dry gas from the aromatics complex as examples, the process is compared with the typical shallow cold oil absorption process of CN101759518B and the flow of the shallow cold oil absorption + pre-fractionating tower process under the same feeding conditions (see example 1) and the requirement of carbon two recovery, and is summarized in Table 6 in combination with comparative example 1.
TABLE 6
As can be seen from Table 6, the minimum temperature of the process stream in the process is 5-15 ℃, the propylene refrigeration capacity at a low temperature position is not needed, a propylene refrigeration system and a drying system are not needed, and the content of more than three carbon components in the product gas is low. Compared with the typical shallow cold oil absorption process, the method reduces the circulation amount of the carbon four absorbent and the reboiler load of the absorption tower, and has low energy consumption and low equipment investment in the whole process.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (19)
1. A method of recovering carbon dioxide from refinery dry gas, the method comprising:
1) sequentially carrying out compression treatment and cooling phase splitting treatment on the aromatic hydrocarbon dry gas (4);
2) feeding the coking dry gas (1) into a coking dry gas compressor for compression treatment, and feeding the gas phase obtained by the cooling phase-splitting treatment in the step 1) into a coking dry gas compressor section or an outlet;
3) cooling the mixed dry gas collected at the outlet of the coking dry gas compressor, and then absorbing the mixed dry gas in an absorption tower (10) by using carbon four-fraction as an absorbent; and
4) sending the liquid phase obtained by the cooling phase separation treatment in the step 1) and the tower bottom material flow of the absorption tower (10) into a desorption tower (11) for desorption treatment;
in the step 1), the cooling phase-splitting treatment is carried out by cooling the aromatic hydrocarbon dry gas (4) to 5-15 ℃;
in the step 4), the theoretical plate number of the desorption tower (11) is 20-60, the operation pressure is 3.0-4.0MPaG, the tower top temperature is 10-40 ℃, and the tower bottom temperature is 90-130 ℃.
2. The process according to claim 1, characterized in that, in step 1), the compression treatment is operated by increasing the pressure of the dry aromatic hydrocarbon gas (4) to 2-4.5 MPaG.
3. The method of claim 1, wherein the compression process is a multi-stage compression process.
4. A method according to claim 3, characterized in that the compression process is a two-or three-stage compression process.
5. The method according to claim 1, characterized in that in the step 1), the cooling phase separation treatment is carried out by cooling the aromatic hydrocarbon dry gas (4) to 5-15 ℃.
6. The method according to claim 1, characterized in that in the step 1), the cooling phase separation treatment is carried out by cooling the aromatic hydrocarbon dry gas (4) to 10-15 ℃.
7. The method according to claim 1, wherein in step 1), the cooling phase separation treatment comprises cooling with cold water produced by a lithium bromide absorption refrigerator as a refrigerant and phase separation in a phase separation tank (7).
8. The method according to claim 1, characterized in that in step 2) the compression process is operated so that the pressure of the mixed dry gas collected at the outlet of the coke dry gas compressor is between 3 and 5 MPaG.
9. The method according to claim 8, characterized in that when the pressure of the gaseous phase obtained from the cooling phase separation treatment in the step 1) is 3-5MPaG, the gaseous phase obtained from the cooling phase separation treatment is sent to the outlet of a coking dry gas compressor.
10. The method of claim 8, wherein the coker dry gas compressor comprises multi-stage compression.
11. The method of claim 8, wherein the coker dry gas compressor is a two-stage or three-stage compression.
12. The method according to claim 1, wherein in step 3), the cooling treatment is performed by cooling the mixed dry gas to 5-15 ℃.
13. The method according to claim 1, wherein in step 3), the cooling treatment is performed by cooling the mixed dry gas to 10-15 ℃.
14. The method according to claim 1, wherein in step 3), the refrigerant used in the cooling process is cold water produced by a lithium bromide absorption refrigerator.
15. A process according to any one of claims 1 to 14, wherein in step 3) the dry mixed gas is fed to the middle of an absorber column and the carbon four fraction is injected at the top of the absorber column (10) to counter-currently contact the dry mixed gas with the carbon four fraction.
16. The method of claim 15, wherein the carbon four fraction is at least one of n-butane, isobutane, and post-ethereal carbon four from a refinery.
17. The process according to any one of claims 1 to 14, wherein the absorption column (10) has a theoretical plate number of 25 to 50, an operating pressure of 3 to 5MPaG, an overhead temperature of 10 to 40 ℃ and a bottom temperature of 70 to 130 ℃.
18. The method according to any one of claims 1 to 14,
the refrigerant adopted for the tower top cooling treatment of the desorption tower (11) is cold water prepared by a lithium bromide absorption refrigerator.
19. The method of claim 18, further comprising: and returning the lean absorbent obtained in the desorption treatment process to the absorption tower (10) for recycling.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101759518B (en) * | 2008-12-25 | 2012-08-29 | 中国石油化工股份有限公司 | Method for absorbing and separating refinery catalytic dry gas by adopting oil |
| CN106608802A (en) * | 2015-10-26 | 2017-05-03 | 中国石油化工股份有限公司 | Method for separating dry gas by-produced in preparation of aromatic hydrocarbons from coal (MTA dry gas) |
| CN106608795A (en) * | 2015-10-26 | 2017-05-03 | 中国石油化工股份有限公司 | Method for separating coking dry gas |
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| CN106609161B (en) * | 2015-10-26 | 2018-08-17 | 中国石油化工股份有限公司 | A kind of method of separating plant saturation dry gas |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101759518B (en) * | 2008-12-25 | 2012-08-29 | 中国石油化工股份有限公司 | Method for absorbing and separating refinery catalytic dry gas by adopting oil |
| CN106608802A (en) * | 2015-10-26 | 2017-05-03 | 中国石油化工股份有限公司 | Method for separating dry gas by-produced in preparation of aromatic hydrocarbons from coal (MTA dry gas) |
| CN106608795A (en) * | 2015-10-26 | 2017-05-03 | 中国石油化工股份有限公司 | Method for separating coking dry gas |
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