CN213475843U - Device for separating three dry gases rich in carbon dioxide and carbon dioxide - Google Patents

Abstract

A device for separating three dry gases rich in carbon and carbon dioxide comprises a dry gas pretreatment system, a dry gas precooling heat exchanger, a multi-stage absorption tower, a high-pressure zone flash tank, a low-pressure zone flash tank, a carbon dioxide desorption tower, a carbon three desorption tower, a carbon two concentration gas compressor system and a lean solvent cooling heat exchanger; the outlet of the dry gas pretreatment system is communicated with a dry gas precooling heat exchanger; the outlet of the dry gas precooling heat exchanger is communicated with the bottom of the multistage absorption tower; and the tower kettle of the multi-stage absorption tower is communicated with the first-stage flash tank of the high-pressure area. The utility model discloses a process flow is simple, and the lean solvent quantity is few, and the energy consumption is low, and the investment is little, and carbon dioxide carbon recovery rate is high, handles carbon dioxide and three components of carbon respectively, improves the economic benefits of product.

Description

Device for separating three dry gases rich in carbon dioxide and carbon dioxide

Technical Field

The utility model belongs to the technical field of the refinery dry gas is retrieved, specifically say so, relate to a separation is rich in device of three dry gases of carbon two.

Background

The dry gas is from oil refining devices and chemical devices in refineries, at present, most of dry gas generated by refineries in China is burnt as fuel, and some dry gas is even burnt by putting a torch, so that the utilization value is low, and serious waste of resources and environmental pollution are caused. The main components of the refinery dry gas are methane, ethane, ethylene, propylene, propane, butane and the like, wherein the content of the carbon-two components is the largest, ethylene in the carbon-two after the recovery of the dry gas can be used as the production raw material of devices such as ethylbenzene, ethylene oxide and the like, and ethane is an ideal cracking raw material, and the ethane in the refinery is recovered and sent to an ethylene production device, so that the cost of the cracking raw material is reduced. The three carbon components can be sent to an alkane dehydrogenation device for further recycling, so that the economic benefit is greatly improved.

At present, methods for recovering a carbon dioxide component from refinery dry gas mainly comprise a cryogenic separation method, a cold oil absorption method, a Pressure Swing Adsorption (PSA) method and the like, and various methods have advantages and disadvantages. The cryogenic separation method is developed and improved for decades, has mature technology, perfect process and high product purity and recovery rate, and is a common method for cracking ethylene. However, the method generally needs to carry out gas separation at a low temperature of about-100 ℃, has large cold load and complex refrigeration process, and also needs to carry out pretreatment on raw material gas, thus leading to large investment of the device. In addition, the cryogenic separation method is generally suitable for areas with centralized refineries and large dry gas byproduct quantity, and the method has poor economy under the condition that the refineries in China are relatively small in scale and relatively dispersed. The pressure swing adsorption method can realize normal temperature operation, has high automation degree, simple operation, low energy consumption and environmental protection, but the method has huge equipment, more complex control system, lower purity of the obtained ethylene and low recovery rate, and usually needs to adopt multi-stage pressure swing adsorption to obtain polymerization-grade ethylene, thereby increasing the occupied area and equipment investment.

The cold oil absorption method belongs to physical absorption, and realizes the separation of dry gas by utilizing the solubility difference of each component in the dry gas in an absorbent, wherein the absorbent is generally mixed carbon four, mixed carbon five, liquefied gas and the like, firstly, non-condensable gas components such as methane, hydrogen and the like are absorbed and removed, and then, components C2 and C3 are recovered by a desorption method. The cold oil absorption method comprises an intermediate cold oil absorption method (-40 to-20 ℃) and a shallow cold oil absorption method (more than 0 ℃), and the existing cold oil absorption method has the problems of large circulation quantity of a poor solvent, high energy consumption and the like because desorption is separated by thermal desorption.

The patent CN 109553504A provides a method and a device for recovering refinery saturated dry gas by adopting a shallow cold oil absorption technology, the process comprises the steps of compression, absorption, desorption, reabsorption desorption and the like, the absorption temperature is 5-15 ℃, the operation condition is mild, but the absorption temperature is high, so that the solvent circulation is high, the device energy consumption is high, and the contents of C3 and heavy components in the absorbed methane hydrogen are high, so that two sets of absorption-desorption systems are required, and the process is complicated.

The patent CN 109912379A, CN 111320522A, CN 111320523A, CN 111320521A, CN 111320524A obtains products of each component such as carbon two, carbon three and the like by expanding a subsequent product separation sequence on the basis of the patent CN 109553504A, realizes the effective utilization of each component, but the core of the method is still a shallow cold oil absorption heating desorption mode, and does not solve the problems of large solvent consumption and high device energy consumption.

Patent CN 104892340 a discloses a three-tower apparatus and method for recovering ethylene and ethane from oil absorption dry gas, which increases the recovery rate of methane and reduces the methane content in the ethylene product by increasing the cooling and flashing modes and reducing the absorption operation temperature in front of the desorption tower, but the cooling and flashing technology is essentially equivalent to adding a dephlegmator system at the top of the desorption tower, the flash tank is equivalent to a gas-liquid buffer tank behind the dephlegmator, and is finally equivalent to performing secondary methane and ethylene separation in the dephlegmator mode, thereby achieving the purpose of improving the recovery rate of methane, but not solving the problem of high process energy consumption.

Patent CN 101063048A discloses a method for separating refinery dry gas by inter-cold oil absorption method, the process comprises steps such as compression, dry gas pretreatment, absorption, desorption, cold recovery and rough separation, the utility model discloses a liquefied gas of refinery is used as absorbent, set up cold box-expander system and retrieve absorbent and the carbon two that run away the loss, have absorbent with low costs, the loss is low, the carbon two rate of recovery is high, do not need ethylene refrigeration compressor advantage such as, however, this process absorbent is whole with the poor solvent of desorption tower bottom circulation, it is whole to obtain by desorption tower thermal desorption, lead to the poor solvent circulation volume great, the desorption load is big, the device energy consumption is high, and the equipment investment is great.

Patent CN 107987885 a proposes an apparatus and method for recovering carbon two and carbon three from catalytic dry gas, the apparatus includes a first absorption tower, a first desorption tower, a second absorption tower and a second desorption tower, the method is that the first absorption tower absorbs C3+, the first desorption tower recovers C3, the second absorption tower absorbs C2, and the second desorption tower recovers C2, thereby realizing the recovery of carbon two and carbon three components from catalytic dry gas. The process has the advantages of simple device structure, high recovery rate of carbon three and no need of a propylene refrigeration system, etc., but the process needs a large amount of absorbent to be absorbed and regenerated in the system, and the C3C2 recovered by the first desorption tower and the second desorption tower is completely separated by thermal desorption, so that the four equipment towers of the process have large treatment capacity, high equipment investment and high energy consumption.

In conclusion, the existing process for recovering the carbon three from the refinery dry gas generally has the problems of large solvent circulation amount and high energy consumption. Therefore, in order to solve the problems, a new energy-saving process for recovering refinery dry gas is developed.

SUMMERY OF THE UTILITY MODEL

In order to realize the reliable recycling of the refinery dry gas and solve the problems of large investment, high energy consumption and the like, the utility model provides a method and a device for separating the dry gas rich in carbon dioxide and carbon dioxide. The method adopts an intercooled oil absorption technology, recovers three components of carbon and carbon from refinery dry gas in a multi-stage absorption and high-low pressure area multi-stage flash evaporation mode, obtains a carbon three-concentrated product, can directly send the carbon three-concentrated product to an ethylene device cracking furnace, obtains a carbon three-concentrated product, can send the carbon three-concentrated product to an alkane dehydrogenation device, has high recovery rate of carbon two and carbon three, has low consumption of an absorbent, simple flow and low energy consumption of the device, and realizes respective recovery processing of carbon two and carbon three.

The utility model provides a method for separating three dry gases rich in carbon dioxide, which comprises the following steps:

(1) the refinery dry gas rich in carbon three is subjected to deacidification drying and compression treatment by a dry gas pretreatment system, wherein the content of carbon two components in the dry gas is 10-50 mol%, the content of carbon three components in the dry gas is 2-20 mol%, particularly the dry gas with the loosely controlled content of carbon three in an upstream device is cooled and then sent into a multistage absorption tower for treatment, the gas phase at the top of the tower obtained by the treatment of the multistage absorption tower is subjected to cold energy recovery and then sent into a fuel gas pipe network or a PSA device, and the liquid phase at the bottom of the tower obtained by the treatment of the multistage absorption tower is sent into a high-pressure flash evaporation area for treatment;

(2) the high-pressure flash evaporation area is provided with a multi-stage high-pressure flash evaporation tank, the gas phase obtained by flash evaporation is returned to the compression section of the dry gas pretreatment system, part of the obtained liquid phase is used as a semi-lean solvent to circularly return to the multi-stage absorption tower, and the other part of the obtained liquid phase is sent to the low-pressure flash evaporation area for treatment;

(3) the low-pressure flash evaporation area is provided with a multi-stage low-pressure flash evaporation tank, the gas phase obtained by flash evaporation is sent to the inlet of a carbon dioxide concentration gas compressor, part of the obtained liquid phase is used as a secondary lean solvent to circularly return to the multi-stage absorption tower, and the other part of the obtained liquid phase is sent to a carbon dioxide desorption tower for treatment;

(4) mixing the gas phase obtained by the treatment of the carbon two desorption tower with the pressurized gas phase in the low-pressure flash evaporation area, and sending the mixture to a cracking furnace of an ethylene device, and sending the liquid phase obtained by the carbon two desorption tower to a carbon three desorption tower for treatment;

(5) and (3) sending the gas phase at the top of the carbon-III desorption tower to an alkane dehydrogenation device, returning most of the liquid phase obtained at the bottom of the tower to the multistage absorption tower as a lean solvent, taking a small part of the liquid phase as extracted carbon-IV, sending the extracted carbon-IV out of a boundary region, and supplementing a fresh carbon-IV absorbent.

The specific working principle is as follows:

the utility model discloses a front end flow is unanimous with cryrogenic technology and well cold oil absorption technology, and the dry gas gets into the separation element after preliminary treatment, drying, pressurization. The process is used for treating the refinery dry gas (3-5 MpaG) after pretreatment, drying and pressurization, wherein the content of carbon two components in the dry gas is 10-50 mol%, the content of carbon three components in the dry gas is 2-20 mol%, and particularly the dry gas in an upstream device, which is not strict in controlling the content of carbon three components, is treated.

The utility model discloses select mixed carbon four as the absorbent, the poor solvent composition carbon four 80 ~ 95 mol% of circulation, all the other are a small amount of carbon three and carbon five, and the poor solvent composition of circulation inferior is carbon four 50 ~ 80 mol%, and the half poor solvent composition of circulation is carbon four 30 ~ 70 mol%.

The absorbent used in the utility model is not limited to carbon four-fraction, and can be various absorbents commonly used in the field and meeting the absorption requirements. Specifically, it may be a carbon three cut, a carbon four cut or a carbon five cut commonly used in the art, preferably alkane components in the carbon three, carbon four and carbon five cuts, and more preferably a carbon four cut containing n-butane and isobutane or a liquefied gas containing a saturated carbon three cut and carbon four cut. The carbon three absorbent and the carbon four absorbent can be refinery liquefied gas or mixed carbon four components, the utility model discloses do not have special restriction to the quantity of absorbent, and the person skilled in the art can confirm according to the actual conditions, and this is known by the person skilled in the art, and the no longer repeated description here.

In the step (1), the compressed dry gas is cooled to-15 to-40 ℃, propylene refrigeration is adopted in the cooling treatment, and primary refrigeration to tertiary refrigeration is adopted in combination with the operation temperature of other equipment in the process.

In the step (1), the theoretical plate number of the multistage absorption tower is preferably 30-60, the operation pressure is 3-5 MpaG, the tower top temperature is preferably-15 ℃ to-35 ℃, and the tower kettle temperature is preferably-10 ℃ to-30 ℃. The multi-stage absorption tower is not provided with a reboiler and a condenser, a plurality of intercoolers, preferably two intercoolers, are arranged at the upper section and the lower section of the tower, the intercoolers at the upper section are respectively used for recovering liquid phase cold energy from a low-pressure area flash tank to a carbon dioxide desorption tower, and the intercoolers at the lower section adopt propylene at the temperature of minus 40 ℃ for refrigeration.

The technology is understood that the refinery dry gas after pretreatment and pressurization is precooled, then enters the bottom of a multi-stage absorption tower to be in countercurrent contact with a secondary lean solvent, a semi-lean solvent and a lean solvent in sequence to absorb carbon dioxide and heavier components in materials, hydrogen and methane gas which are not absorbed are mainly obtained at the top of the multi-stage absorption tower, and the obtained gas is sent to a fuel gas pipe network or a PSA device for hydrogen recovery after cold recovery.

In the step (2), one or more flash tanks can be arranged in the high-pressure zone flash tank, the flash tanks are sequentially connected in series under reduced pressure, and the pressure of the last flash tank is 0.1-0.3 MpaG. And (3) feeding the gas phase obtained by treatment of each flash tank in the high-pressure flash zone into each stage of a corresponding compressor of the dry gas pretreatment system according to pressure to obtain a liquid phase, wherein the liquid phase entering the low-pressure flash zone is the liquid phase of the last flash tank, the semi-lean solvent can be the liquid phase of each flash tank, the semi-lean solvent enters the lower section of the multistage absorption tower, the feeding plate is preferably 20-45, and the temperature of the semi-lean solvent is-10 ℃ to-40 ℃.

The partial technology is understood as that light components such as methane and hydrogen absorbed are separated through reduced pressure flash evaporation, the light components are sent into a dry gas compression system to be mixed with feed and then return to a multi-stage absorption tower, the recovery rate of the methane and the hydrogen can be improved, the content of the methane and the hydrogen in the final carbon dioxide concentrated gas can be reduced, the recovery rate of the methane and the hydrogen can be regulated and controlled through flash evaporation pressure, the content of the methane and the hydrogen is low and controllable, and the carbon dioxide concentrated gas can be directly used as a raw material for ethylene cracking. By pumping the semi-lean solvent out of the high-pressure flash evaporation area, the dosage of the lean solvent can be greatly reduced, the treatment capacity of a subsequent carbon two desorption tower and a subsequent carbon three desorption tower is reduced, and finally the energy consumption is reduced.

In step (3), the low-pressure zone flash tank can be provided with one or more flash tanks, and the flash tanks are sequentially connected in series under reduced pressure, the pressure of the last flash tank is 0-0.1 MpaG, the gas phase obtained by processing the low-pressure flash zone is used as a part of the carbon dioxide concentrated gas, and enters a carbon dioxide concentrated gas compressor to be pressurized and sent out of a boundary zone, and the obtained liquid phase is: the liquid phase fed into the carbon dioxide desorption tower is the liquid phase of the last flash tank, the secondary lean solvent can be the liquid phase of each flash tank, the secondary lean solvent enters the middle part of the multistage absorption tower, the feeding plate is preferably 5-25 ℃, and the temperature of the secondary lean solvent is-30 ℃ to-70 ℃.

The partial technology is understood as that partial carbon dioxide components are recovered by pressure reduction flash evaporation instead of thermal desorption, and the content of the carbon quadruple components in the recovered carbon dioxide product gas and the carbon dioxide flash evaporation amount are controlled by regulating the flash evaporation pressure, so that the desorption amount of a subsequent carbon dioxide desorption tower is reduced, and the energy consumption is reduced. By setting the secondary lean solvent circulation, the consumption of the lean solvent can be continuously reduced, the treatment capacity of the subsequent carbon two desorption tower and the subsequent carbon three desorption tower is reduced, and the energy consumption is continuously reduced.

In the step (4), the residual carbon dioxide component is recovered by a thermal desorption mode of a carbon dioxide desorption tower, the theoretical plate number of the carbon dioxide desorption tower is 20-60, the operation pressure is 0.8-4 MpaG, the tower top temperature is-35-45 ℃, and the tower kettle temperature is 50-150 ℃.

The partial technology is understood to mean that after a part of carbon dioxide products are recovered by reduced pressure flash evaporation, the residual carbon dioxide component is recovered by means of thermal desorption of a carbon dioxide desorption tower, and the carbon dioxide concentrated product gas obtained at the top of the tower is mixed with the carbon dioxide concentrated gas recovered by reduced pressure flash evaporation and then sent to an ethylene cracking furnace as final carbon dioxide concentrated gas.

In the step (5), recovering the carbon three components through a carbon three desorption tower, wherein the theoretical plate number of the carbon three desorption tower is 20-60, the operation pressure is 0.5 MpaG-1.5 MpaG, the tower top temperature is-35-45 ℃, and the tower kettle temperature is 60-120 ℃.

The partial technology is understood to be that the recovery of the carbon three components is carried out by a carbon three desorption tower, and carbon three concentrated gas is obtained at the top of the tower and enters alkane dehydrogenation. Most of the liquid phase obtained from the tower bottom is used as a poor solvent, is cooled to-15 to-40 ℃ through heat recovery, returns to the top of the multi-stage absorption tower, and the rest part is sent out of a battery limit. In order to ensure the flow rate of the lean solvent in the system, it is further preferred that the fresh carbon tetra-absorbent is replenished during the cooling of the lean solvent, and the utility model has no special requirement on the temperature of the replenished fresh carbon tetra-absorbent itself.

This part of technique should be understood, the utility model discloses in, take out three desorber tower cauldron of carbon partial liquid phase and send out the boundary region to the purpose of replenishing four absorbents of fresh carbon prevents the accumulation of heavy ends in the four absorbents of circulation carbon, thereby leads to three desorber tower cauldron temperatures of carbon too high. The extraction amount of the tower kettle of the carbon three-desorption tower and the supplement amount of the fresh carbon four-absorbent are different according to different compositions of dry gas raw materials, more heavy components above C4 in a plurality of gas raw materials need to be extracted and supplemented in a large amount, and if the heavy components are less, the extraction amount is less or only intermittent extraction is needed.

In the steps (3) and (4), the obtained carbon dioxide concentrated gas mainly contains 60 mol% -95 mol% of carbon dioxide, the content of carbon III is less than 5 mol%, the content of methane is less than 5 mol%, and the carbon dioxide concentrated gas is controllable and can be directly used as a raw material for ethylene cracking. The carbon three concentrated gas obtained in the step (5) mainly contains 50-95% of carbon three components, and the carbon content is less than 5 mol%.

The utility model discloses in, carbon two desorption towers and three desorption towers in carbon set up the reboiler to the carbon two concentrated product that obtains at the top of the tower and three concentrated product rate of recovery in carbon and purity reach the technological requirement, and the heating medium of reboiler can adopt low pressure steam, also can adopt low temperature hot oil or low temperature hot water of refinery.

The utility model also provides a device that the separation is rich in three dry gases of carbon two carbon:

the device comprises a dry gas pretreatment system, a dry gas precooling heat exchanger, a multi-stage absorption tower, a high-pressure zone flash tank, a low-pressure zone flash tank, a carbon-two desorption tower, a carbon-three desorption tower, a carbon-two concentration gas compressor and a lean solvent cooling heat exchanger.

The outlet of the dry gas pretreatment system is communicated with a dry gas precooling heat exchanger;

the outlet of the dry gas precooling heat exchanger is communicated with the bottom of the multistage absorption tower;

the tower kettle of the multi-stage absorption tower is communicated with the first-stage flash tank of the high-pressure area;

the top of the high-pressure zone flash tank is communicated with the dry gas pretreatment system, the bottom of each stage of flash tank in the high-pressure zone is connected with the inlet of the next stage of flash tank, the pipeline at the bottom of the first stage or multi-stage flash tank is connected with the lower part of the multi-stage absorption tower, and the bottom of the last stage of flash tank is connected with the inlet of the first stage of flash tank in the low-pressure zone flash tank;

the top of the low-pressure zone flash tank is communicated with a carbon dioxide concentration gas compressor system, the bottoms of the flash tanks in all stages of the low-pressure zone flash tank are connected with the inlet of the next flash tank, the pipeline at the bottom of the flash tank in one stage or multiple stages is connected with the middle part of the multiple-stage absorption tower, and the bottom of the flash tank in the last stage is connected with the inlet of the carbon dioxide desorption tower;

the top of the carbon dioxide desorption tower is connected with a carbon dioxide concentrated gas product extraction pipeline, and a tower kettle is communicated with the middle part of the carbon three desorption tower;

the top of the carbon three desorption tower is connected with a carbon three concentrated gas product extraction pipeline, the tower kettle pipeline is divided into two branches, one branch is communicated with the lean solvent cooling heat exchanger, the other branch is an extracted carbon four pipeline, and a fresh carbon supplementing four pipeline is connected with the lean solvent pipeline;

the outlet of the lean solvent cooling heat exchanger is communicated with the top of the multistage absorption tower;

the utility model discloses an in the device, the mode that communicates each other and be connected between each equipment and between pipeline and the equipment can set up as required, and each equipment is not limited to the connected mode of above-mentioned description.

The utility model discloses a method and device for separating three dry gases rich in carbon dioxide, compared with the prior art, have following advantage:

(1) in the utility model, the high-pressure flash evaporation and low-pressure flash evaporation are utilized, so that the circulation volume of the lean solvent is reduced, the desorption load is reduced, the total energy consumption of the device is finally reduced, and the impurity content of the product gas is controllable;

(2) in the utility model, a multistage absorption mode is adopted, the semi-poor solvent, the sub-poor solvent and the poor solvent are fully utilized, and the circulation volume of the poor solvent is reduced, so that the energy consumption of the device and the equipment investment are reduced;

(3) in the utility model, the recycling and respective treatment of the carbon two and the carbon three components are realized, and the economic benefit of the device product is improved;

(4) in the utility model, the amount of the absorbed agent carried in the methane and hydrogen light component gas at the top of the multi-stage absorption tower is small, and a cold box-expander system or a reabsorption system is not needed, thereby greatly reducing the equipment investment;

drawings

Fig. 1 is a schematic structural diagram of a device for separating three dry gases rich in carbon dioxide.

In the figure: 1, a dry gas pretreatment system; 2, a dry gas precooler; 3, a multi-stage absorption tower; 4, a high-pressure zone flash evaporation tank; 5a low-pressure zone flash tank; 6 carbon two concentrated gas compressor system; 7, a carbon two desorption tower; 8 carbon three desorption tower; 9 lean solvent cooling heat exchanger; a, refinery dry gas; b, absorbing tail gas; c, adding carbon dioxide to extract concentrated gas; d, a lean solvent; e lean solvent; f, semi-lean solvent; g, extracting carbon four; h, fresh make-up solvent; and (4) concentrating the M carbon III.

Detailed Description

The technical solution of the present invention will be clearly and completely described below. It is obvious that the described embodiments are only some of the embodiments of the present invention, and not all of them. All other embodiments which are based on the embodiments of the present invention, modified or adjusted by a person skilled in the art, belong to the protection scope of the present invention.

Use figure 1 for the example description the utility model provides a pair of method and device of three dry gas of carbon two are richened in separation, wherein dry gas precooling heat exchanger, multistage absorption tower intercooler, carbon two concentration gas compressor progression, high-pressure region flash tank, the low-pressure region flash tank can set up a plurality ofly according to the demand, dry gas precooling heat exchanger in this embodiment, multistage absorption tower intercooler, high-pressure region flash tank, the low-pressure region flash tank sets up two, carbon two concentration gas compression system sets up threely, and only set up inferior lean solvent circulation according to optimizing the result in this embodiment, do not set up half lean solvent circulation:

the utility model is explained by taking the dry gas recovery after compression and drying in a certain refinery as an example, the composition of the dry gas in the refinery is shown in the table 1:

TABLE 1

The method and the device for separating the three dry gases rich in carbon and carbon are adopted to separate and recycle the carbon and the carbon. The specific process comprises the following steps:

each device dry gas gets into after preliminary treatment, compression, dry mixing in the refinery the utility model discloses technology, the dry gas pressure that gets into this technology is 3.75 MpaG. And (2) cooling the dry gas to-23 ℃ through a 2A/B dry gas precooling heat exchanger, sending the cooled dry gas into the bottom of a 3-stage absorption tower, wherein in the multi-stage absorption tower 3, an absorbent is a mixed carbon four absorbent, the total absorbent dose is 58t/h, the lean solvent dose of D is 23t/h, the lean solvent dose of E is 35t/h, the lean solvent of D is sprayed from the top of the 3-stage absorption tower, and the lean solvent of E is sprayed from the middle of the 3-stage absorption tower and is in countercurrent contact absorption with the dry gas. The theoretical plate number of the multistage absorption tower 3 is 30, the operation pressure is 3.6MpaG, the tower top temperature is-27.9 ℃, and the tower kettle temperature is-16.9 ℃. Liquid phase materials from the tower bottom of the multistage absorption tower 3 are sent to a high-pressure zone flash tank 5a-b for treatment, cold energy recovery is carried out on gas phase materials from the tower top of the multistage absorption tower 3 by heat exchange with dry gas to 33 ℃, the gas phase materials mainly comprise unabsorbed methane, hydrogen and the like and are sent to a fuel gas pipe network or a PSA device for treatment, and if the gas phase materials are sent to the fuel gas pipe network, throttling depressurization is preferably carried out until the gas phase materials reach 0.9MpaG, and then the gas phase materials are subjected to heat exchange with the dry gas to carry out.

Liquid phase materials from the tower bottom of the multistage absorption tower 3 are preferably depressurized to 1MpaG and are fed into a high-pressure-area first-stage flash tank 4a, liquid phase at the bottom of the high-pressure-area first-stage flash tank 4a is preferably depressurized to 0.3MpaG and is fed into a high-pressure-area second-stage flash tank 4b, gas phase (rich in hydrogen and methane) at the top of the high-pressure-area flash tanks 4a-b is fed into a dry gas compression system for different stages according to different pressures, and liquid phase at the bottom of the high-pressure-area second-stage flash tank 5b is fed into.

The liquid phase from the high-pressure zone secondary flash tank 4b is preferably depressurized to 0.13MpaG and is fed into the low-pressure zone primary flash tank 5a, the liquid phase returning to the low-pressure zone primary flash tank 5a is preferably depressurized to 0MpaG and is fed into the low-pressure zone secondary flash tank 5b, the gas phase at the top of the low-pressure zone primary flash tank 5a is fed into the 6a carbon concentrated gas primary compressor, the gas phase at the top of the low-pressure zone secondary flash tank 5b is fed into the 6b carbon concentrated gas secondary compressor, and the C carbon concentrated gas (1MpaG) pressurized by the 6a-C carbon concentrated product compression system is fed into the ethylene plant cracking furnace. The liquid phase at the bottom of the secondary flash tank 5B of the low-pressure area is divided into two branches, one branch is used as E-time lean solvent (35t/h and 58.6 ℃) for circular absorption, and the other branch is sequentially subjected to cold energy recovery through a multi-stage absorption tower intercooler and a dry gas pre-cooling heat exchanger 2B to 33 ℃ and enters a carbon dioxide desorption tower 7.

The liquid phase from the bottom of the second flash tank 6b of the low-pressure area is sent to the middle part of a 7-carbon desorption tower after cold recovery and pressurization, the theoretical plate number of the 7-carbon desorption tower is 30, the operation pressure is preferably 2.2MpaG, the temperature of the top of the tower is-0.26 ℃, and the temperature of the bottom of the tower is 118.4 ℃. The condenser at the top of the carbon dioxide desorption tower 7 is refrigerated to-0.26 ℃ by propylene at the temperature of-6 ℃, and the reboiler at the bottom of the tower is heated by low-pressure steam or hot oil. The gas phase (rich in carbon) at the top of the carbon dioxide desorption tower 7 is mixed with the carbon dioxide concentrated gas recovered by the reduced pressure flash evaporation and then sent to the cracking furnace of the ethylene device. The liquid phase at the bottom of the carbon two desorption tower 7 is sent to a carbon three desorption tower 8 for treatment.

And the gas phase at the top of the carbon triple desorption tower 8 is used as carbon triple concentrated gas M and sent to a mixed alkane dehydrogenation device, and most of liquid phase at the bottom of the tower is used as a D lean solvent (23t/h) for cyclic absorption after a fresh solvent is supplemented. The lean solvent D is cooled to 0 ℃ by a-6 ℃ propylene refrigerant through a lean solvent cooling heat exchanger 9A, cooled to-35 ℃ by a-40 ℃ propylene refrigerant through a lean solvent cooling heat exchanger 9B and then sent to the top of the multistage absorption tower 3. The theoretical plate number of the carbon-III desorption tower 8 is 30, the operation pressure is preferably 1.3MpaG, the tower top temperature is 40.69 ℃, and the tower kettle temperature is 101.08 ℃. The condenser at the top of the carbon desorption tower 8 is refrigerated to 40.69 ℃ by wet air cooling or circulating cooling water, and the reboiler at the bottom of the tower is heated by low-pressure steam.

In the present embodiment, the compositions of the carbon two concentrate gas and the carbon three concentrate product are shown in table 2, and the compositions of the lean solvent and the second lean solvent are shown in table 3.

TABLE 2

In this example, the carbon two recovery was 91.1%, the ethane recovery was 94.8%, and the carbon three recovery was 98.8%.

TABLE 3

Name (R)	Lean solvent	Sub-lean solvent
			Mass flow rate, t/hr	23	35
Molar flow, kmol/hr	659	376
			Composition in mol%
Methane	0.00	0.04
			Ethane (III)	0.00	20.81
Ethylene	0.00	0.89
			Propane	0.44	8.36
Propylene (PA)	0.02	0.91
			N-butane	48.60	34.41
Isobutane	27.11	16.46
			1-butene	0.54	0.41
Isobutene	0.33	0.25
			Butene of trans-butene	0.06	0.04
Cis-butenediol	0.52	0.40
			N-pentane	19.92	15.14
Isopentane	2.16	1.64

The embodiments of the present invention have been described above, where the lean solvent circulation amount is only 1/4 of the total solvent amount, and half of the carbon dioxide stripping gas is recovered by means of flash desorption, resulting in a large reduction in the carbon dioxide desorber throughput at the main energy consumption, and a large reduction in the total energy consumption. And the purposes of saving energy and reducing investment are achieved by optimizing the process flow.

This description is intended to be exemplary rather than a complete description, and all other embodiments which may be modified or adapted by those skilled in the art are intended to be within the scope of the present invention.

Claims (1)

1. The device for separating the three dry gases rich in carbon and carbon is characterized by comprising a dry gas pretreatment system, a dry gas precooling heat exchanger, a multistage absorption tower, a high-pressure zone flash tank, a low-pressure zone flash tank, a carbon two desorption tower, a carbon three desorption tower, a carbon two concentration gas compressor system and a lean solvent cooling heat exchanger;

the outlet of the dry gas pretreatment system is communicated with a dry gas precooling heat exchanger;

the outlet of the dry gas precooling heat exchanger is communicated with the bottom of the multistage absorption tower;

the tower kettle of the multi-stage absorption tower is communicated with the first-stage flash tank of the high-pressure area;

the top of the high-pressure zone flash tank is communicated with the dry gas pretreatment system, the bottom of each stage of flash tank in the high-pressure zone is connected with the inlet of the next stage of flash tank, the pipeline at the bottom of the first stage or multi-stage flash tank is connected with the lower part of the multi-stage absorption tower, and the bottom of the last stage of flash tank is connected with the inlet of the first stage of flash tank in the low-pressure zone flash tank;

the top of the low-pressure zone flash tank is communicated with a carbon dioxide concentration gas compressor system, the bottoms of the flash tanks in all stages of the low-pressure zone flash tank are connected with the inlet of the next flash tank, the pipeline at the bottom of the flash tank in one stage or multiple stages is connected with the middle part of the multiple-stage absorption tower, and the bottom of the flash tank in the last stage is connected with the inlet of the carbon dioxide desorption tower;

the top of the carbon dioxide desorption tower is connected with a carbon dioxide concentrated gas product extraction pipeline, and a tower kettle is communicated with the middle part of the carbon three desorption tower;

the top of the carbon three desorption tower is connected with a carbon three concentrated gas product extraction pipeline, the tower kettle pipeline is divided into two branches, one branch is communicated with the lean solvent cooling heat exchanger, the other branch is an extracted carbon four pipeline, and a fresh carbon supplementing four pipeline is connected with the lean solvent pipeline;

and the outlet of the lean solvent cooling heat exchanger is communicated with the top of the multistage absorption tower.

Images