CN112410070B - Energy-saving process and device for recovering carbon dioxide from refinery dry gas - Google Patents

Abstract

An energy-saving process and a device for recovering carbon dioxide from refinery dry gas, the process comprises the following steps: cooling the dry gas and then sending the cooled dry gas into a multi-stage absorption tower for treatment; gas phase of the multi-stage absorption tower is sent into a fuel gas pipe network or a PSA device, and liquid phase is sent into a high-pressure flash evaporation area for treatment; the gas phase in the high-pressure flash evaporation zone returns to the compression section of the dry gas pretreatment system, one part of the liquid phase is used as a semi-lean solvent to circularly return to the multi-stage absorption tower, and the other part of the liquid phase is sent to the low-pressure flash evaporation zone for treatment; the gas phase in the low-pressure flash evaporation area is sent into a carbon dioxide concentration gas compressor system, one part of the liquid phase is used as a secondary lean solvent to circularly return to the multi-stage absorption tower, and the other part of the liquid phase is sent into a desorption tower for treatment; and mixing the gas phase of the desorption tower with the gas phase obtained in the low-pressure flash evaporation area, and sending the mixture as a carbon dioxide concentrated gas product to an ethylene device cracking furnace, wherein most of the liquid phase is used as a lean solvent and returns to the multistage absorption tower, and the small part is used as extracted carbon four and is sent out. The process of the invention has the advantages of simple flow, greatly reduced consumption of the lean solvent and energy consumption, small investment, high recovery rate of carbon two and carbon three, and the like.

Description

Energy-saving process and device for recovering carbon dioxide from refinery dry gas

Technical Field

The invention belongs to the technical field of refinery dry gas recovery, and particularly relates to an energy-saving process and device for recovering carbon dioxide from refinery dry gas.

Background

The dry gas is from oil refining unit and chemical equipment in refinery, wherein the dry gas is mainly from primary and secondary processing of crude oil, such as atmospheric and vacuum distillation unit, catalytic cracking unit, delayed coking unit, etc., and the dry gas is mainly from alkane dehydrogenation unit, PSA unit, light hydrocarbon recovery unit, ethylbenzene-styrene unit, etc. At present, most of dry gas generated by refineries in China is used as fuel to be burnt, and some dry gas is even put into a torch to be burnt, so that the utilization value is low, and the serious waste of resources and the 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 dioxide component is the largest, and if the ethane and the ethylene in the dry gas are recycled, huge economic benefits can be brought, and the environmental pollution can be effectively prevented. Ethylene in the carbon dioxide recovered by the dry gas can be used as a production raw material of devices such as ethylbenzene, ethylene oxide and the like, and ethane is an ideal cracking raw material, so that the ethane in a refinery is recovered and sent to an ethylene production device, the cost of the cracking raw material is reduced, and 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.

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.

The invention discloses a method for separating refinery dry gas by an intercooling oil absorption method, which comprises the steps of compression, dry gas pretreatment, absorption, desorption, cold energy recovery, rough separation and the like, wherein liquefied gas in a refinery is used as an absorbent, a cold box-expander system is arranged for recovering lost absorbent and carbon dioxide, and the method has the advantages of low absorbent cost, low loss, high carbon dioxide recovery rate, no need of an ethylene refrigeration compressor and the like.

Patent CN 102382680A proposes a combined process of a catalytic cracking absorption stabilization system and cold oil absorption in carbon III, and through the combination of devices, continuous circulation of carbon III and carbon II in a large amount of desorbed gas between absorption and desorption is avoided, but the complexity of the process is increased through the coupling between the devices, and the problems of large solvent consumption and high device energy consumption are not fundamentally solved.

Patent CN 101371966A proposes a new pressure swing adsorption process for recovering ethylene and hydrogen from dry gas in an oil refinery, the process consists of units of desulfurization, decarburization, drying, pressure swing adsorption for recovering ethylene, pressure swing adsorption for purifying hydrogen and the like, the process has the advantages of low energy consumption, simple operation and environmental friendliness, however, the problems of high impurity content in products, incapability of realizing complete and clear separation of main components of the dry gas in the oil refinery, huge investment occupation and the like exist by adopting a pressure swing adsorption mode.

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.

Disclosure of Invention

In order to realize reliable recycling of refinery dry gas and solve the problems of large solvent circulation amount, high energy consumption and the like, the invention provides an energy-saving process and device for recycling carbon dioxide from refinery dry gas. The process adopts an intercooling oil absorption technology, recovers the carbon dioxide component from the refinery dry gas in a multi-stage absorption-high and low pressure area multi-stage flash evaporation-desorption mode, obtains a carbon dioxide concentrated gas which can be directly sent to an ethylene device cracking furnace, has high recovery rate, low absorbent dosage and simple flow, and can reduce the total investment and energy consumption of the device by more than 20 percent compared with the traditional oil absorption process, thereby greatly reducing the economic cost of the refinery gas recovery process.

The invention provides an energy-saving process for recovering carbon dioxide from refinery dry gas, which comprises the following steps:

(1) the refinery dry gas after deacidification, drying and compression treatment by the dry gas pretreatment system is cooled and then sent to a multi-stage absorption tower for treatment, the gas phase at the top of the tower obtained by the multi-stage absorption tower treatment is recycled and then sent to a fuel gas pipe network or a PSA device, and the liquid phase at the bottom of the tower obtained by the multi-stage absorption tower treatment is sent to a high-pressure flash evaporation area for treatment;

(2) the high-pressure flash evaporation area is provided with a multi-stage high-pressure area flash evaporation tank, and the gas phase obtained by flash evaporation is returned to the compression section of the dry gas pretreatment system; one 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 a low-pressure flash evaporation zone for treatment;

(3) the low-pressure flash evaporation area is provided with a multi-stage low-pressure flash evaporation tank, the gas phase carbon dioxide concentrated gas obtained by flash evaporation is sent to a carbon dioxide concentrated gas compressor system, one 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 desorption tower for treatment;

(4) mixing the gas phase obtained by the treatment of the desorption tower with the gas phase in the low-pressure flash evaporation area to be used as carbon dioxide concentrated gas, sending the carbon dioxide concentrated gas to a cracking furnace of an ethylene device, returning most of the liquid phase obtained by the desorption tower to a multistage absorption tower as a lean solvent, extracting carbon four from a small part of the liquid phase, sending the extracted carbon four out of a boundary area, and supplementing a fresh carbon four absorbent.

The specific working principle is as follows:

the front-end flow of the invention is consistent with the deep cooling process and the middle cooling oil absorption process, and dry gas enters the separation unit after pretreatment, drying and pressurization. The process is used for treating (3-5 MpaG) pretreated (deacidified, dried and compressed) refinery dry gas, wherein the dry gas can be a byproduct from devices such as atmospheric and vacuum distillation, hydrogenation, reforming, coking and the like, and the source of the dry gas is not particularly limited.

The invention selects mixed carbon four as an absorbent, the circulating poor solvent comprises 80-95 mol% of carbon four, the balance is a small amount of carbon three and carbon five, the circulating sub-poor solvent comprises 50-80 mol% of carbon four, and the circulating semi-poor solvent comprises 30-70 mol% of carbon four.

The absorbent used in the present invention is not limited to the carbon four-cut fraction, and may be any of various absorbents commonly used in the art that satisfy the above-mentioned 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 dosage of the absorbent is not particularly limited in the invention, and can be determined by those skilled in the art according to actual conditions, which are well known by those skilled in the art and will not be described herein again.

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 zone flash tank to a 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 semi-lean solvent, a sub-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), at least one flash tank is arranged in the high-pressure zone flash tanks, when a plurality of flash tanks are arranged, the flash tanks are connected in series under reduced pressure, and the pressure of the last flash tank is 0.1-0.3 MpaG. And (2) feeding the gas phase obtained by processing in each flash tank of the high-pressure flash area into each stage of a corresponding compressor of a compression section of the dry gas pretreatment system according to pressure, wherein one part of the obtained liquid phase is used as a semi-lean solvent to circulate to the multistage absorption tower, and the other part of the obtained liquid phase is fed into the low-pressure flash area, wherein the liquid phase entering the low-pressure flash area 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 preferred material feeding plate is 20-45, and the temperature.

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 zone, the dosage of the lean solvent can be greatly reduced, the treatment capacity of a subsequent desorption tower is reduced, and the energy consumption is finally reduced.

In the step (3), at least one flash tank is arranged in the low-pressure flash tank, when a plurality of flash tanks are arranged, the flash tanks are connected in series in a decompression mode in sequence, and the pressure of the last flash tank is 0-0.1 MpaG. The gas phase obtained by the treatment of the low-pressure flash evaporation zone is used as a part of carbon dioxide concentrated gas, enters a carbon dioxide concentrated gas compressor for pressurization and is sent out of a boundary zone, a carbon dioxide concentrated gas compression system is multi-stage compression, a part of the obtained liquid phase is used as a secondary lean solvent to circulate to a multi-stage absorption tower, a part of the obtained liquid phase is sent to a desorption tower, the liquid phase sent to the 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 multi-stage absorption tower, a feeding plate is preferably 5-25, and the temperature of the secondary lean solvent is-.

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 a subsequent carbon dioxide desorption tower is reduced, and the energy consumption is continuously reduced.

In the step (4), the residual three components of carbon dioxide are 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 0.5 MpaG-4 MpaG, the tower top temperature is-35-45 ℃, and the tower kettle temperature is 60-160 ℃.

The partial technology is understood that after a part of carbon dioxide products are recovered by reduced pressure flash evaporation, the residual three components of carbon dioxide are recovered by a thermal desorption mode of a desorption tower, and carbon dioxide concentrated gas obtained at the top of the tower is mixed with the carbon dioxide concentrated gas recovered by reduced pressure flash evaporation and then is sent to an ethylene cracking furnace as final carbon dioxide concentrated gas. 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 present invention has no particular requirement on the temperature of the replenished fresh carbon tetra-absorbent itself.

The partial technology is understood that in the invention, part of liquid phase extracted from the tower kettle of the desorption tower is sent out of a boundary region, and the fresh carbon four absorbent is supplemented, so that the aim of preventing the accumulation of heavy components in the solvent is fulfilled, the tower kettle temperature of the desorption tower is overhigh, and the absorption effect and the stable operation of the device are influenced. The extraction amount of the tower kettle of the 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 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 30-90 mol% of carbon dioxide, 10-50 mol% of carbon III, and the content of methane is lower than 5 mol%, is controllable, and can be directly used as a raw material for ethylene cracking.

In the invention, the desorption tower is provided with a reboiler to ensure that the recovery rate and the purity of the carbon dioxide concentrated product obtained from the top of the tower meet the process requirements, and the heating medium of the reboiler can adopt low-pressure steam, and can also adopt low-temperature hot oil or low-temperature hot water of a refinery.

The invention also provides an energy-saving device for recovering carbon dioxide from refinery dry gas, which comprises the following steps:

the device comprises a dry gas pretreatment system, a dry gas precooler, a multi-stage absorption tower, a high-pressure zone flash tank, a low-pressure zone flash tank, a desorption tower, a carbon dioxide 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 precooler;

the outlet of the dry gas precooler is communicated with the bottom of the multi-stage absorption tower;

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

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 desorption tower;

the top of the desorption tower is connected with a carbon dioxide 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 a carbon extraction four pipeline, and a fresh carbon supplement four pipeline is connected with the lean solvent pipeline;

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

In the device of the present invention, the communication and connection between the equipments and between the pipelines and the equipments can be set according to the requirement, and the equipments are not limited to the connection described above.

The invention has the beneficial effects that:

(1) in the invention, the high-pressure flash evaporation is utilized to recover the methane and hydrogen components in the rich solvent, thereby improving the recovery rate of methane and hydrogen, reducing the contents of methane and the like in the carbon-two concentrated gas, leading the content of methane in the carbon-two concentrated gas to be low and controllable, and being directly used as an ethylene cracking raw material;

(2) in the invention, partial thermal desorption is replaced by low-pressure flash evaporation, so that the subsequent extraction amount at the top of the carbon dioxide desorption tower is reduced, and the load of the carbon dioxide desorption tower is reduced;

(3) in the invention, a multistage absorption mode is adopted, the semi-lean solvent, the sub-lean solvent and the lean solvent are fully utilized, and the circulation quantity of the lean solvent is reduced, so that the energy consumption of a device and the equipment investment are reduced;

(4) in the invention, the amount of the absorbed agent carried in the light component gas of methane and hydrogen at the top of the multi-stage absorption tower is less, and a cold box-expander system or a reabsorption system is not required to be arranged, thereby greatly reducing the equipment investment;

(5) in the invention, the lowest operation temperature of other systems except the secondary lean solvent circulating pipeline is not lower than-40 ℃, so that the equipment and pipelines of the systems can be made of common low-temperature carbon steel, and the equipment investment is saved.

Drawings

FIG. 1 is a schematic structural diagram of an energy-saving process and an apparatus for recovering carbon dioxide from refinery dry gas according to the present invention.

FIG. 2 is a schematic diagram of the application of the energy-saving process and apparatus for recovering carbon dioxide from refinery dry gas.

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; 7a desorption tower; 8 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 carbon four absorbent.

Detailed Description

The technical solution of the present invention will be clearly and completely described below. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments that can be modified or adapted by one of ordinary skill in the art based on the embodiments of the present invention are within the scope of the present invention.

Fig. 2 is an example of an energy-saving process and an apparatus for recovering carbon dioxide from refinery dry gas, where a plurality of dry gas pre-cooling heat exchangers, a multi-stage absorption tower intercooler, a carbon dioxide concentration gas compressor stage, a high-pressure region flash tank, and a low-pressure region flash tank may be provided according to requirements, in this embodiment, two dry gas pre-cooling heat exchangers, two multi-stage absorption tower intercoolers, two high-pressure region flash tanks, and two low-pressure region flash tanks are provided, a carbon dioxide concentration gas compression system is provided with three stages, and in this embodiment, only a secondary lean solvent cycle is provided according to an optimization result, and a semi-lean solvent cycle is not provided:

the dry gas obtained after the dry gas of the refinery is pretreated and dried by the dry gas pretreatment device 1 and is processed by a compressor system enters the separation unit provided by the invention, and the specific flow is as follows: the refinery dry gas after raw material purification, dehydration and pressurization enters a 2A/B dry gas precooling heat exchanger for precooling and then enters a multistage absorption tower 3, the tower kettle liquid phase of the multistage absorption tower 3 enters a first-stage flash tank 5a of a high-pressure zone, the first-stage flash tank 5a of the high-pressure zone is sequentially connected with a second-stage flash tank 5B of the high-pressure zone, the gas phase rich in hydrogen and methane at the top of the tower is sent to a dry gas compression system 1 with different stages according to different pressures, the tank bottom liquid phase is sent to a first-stage flash tank of a low-pressure zone of 6a, the flash tank 6a of the low-pressure zone is sequentially connected with the second-stage flash tank 6B of the low-pressure zone, the gas phase at the top of the tank is sent to a carbon dioxide concentration gas compression system 7a-C according to different pressures, the liquid phase at the bottom of the tank is divided into two branches, one branch is taken as E times of lean solvent to be recycled to the multistage absorption tower 3, the other branch is sent to the desorption tower after cold energy recovery to be taken as carbon dioxide three, the top gas at the desorption tower, the top of the desorption tower is taken as carbon dioxide concentration gas to be mixed with the carbon dioxide concentration gas recovered at reduced pressure to be taken as C carbon dioxide concentration gas And (3) sending the mixture to an ethylene cracking device, 8 desorbing partial liquid phase extracted from the tower bottom phase of the tower to extract carbon IV G, supplementing a fresh solvent liquid phase H, mixing the fresh solvent liquid phase H with the residual liquid phase, cooling the mixture by a 12AB lean solvent cooling heat exchanger, and circularly absorbing the mixture by a lean solvent D.

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

TABLE 1

Name (R)	Refinery dry gas
		Temperature, C	40
Pressure, MpaG	3.77
		Mass flow rate, kg/hr	30542
The molar flow rate of the mixture is controlled,kmol/hr	2010
		composition in mol%
Hydrogen gas	41.73
		Carbon monoxide	0.58
Oxygen gas	0.59
		Nitrogen is present in	7.18
Methane	28.29
		Ethane (III)	14.82
Ethylene	2.05
		Propane	2.65
Propylene (PA)	0.30
		N-butane	1.13
Isobutane	0.06
		1-butene	0.02
Isobutene	0.01
		Cis-butenediol	0.02
N-pentane	0.49
		Isopentane	0.06
N-hexane	0.01
		Total up to	100.00

The energy-saving process and the device for recovering the carbon two from the refinery dry gas are adopted to separate and recover the carbon two and the carbon three from the refinery dry gas. The specific process comprises the following steps:

the dry gas of each device in the refinery enters the process of the invention after pretreatment, compression, drying and mixing, and the pressure of the dry gas entering the process 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-28.4 ℃, and the tower kettle temperature is-17.2 ℃. 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 cold energy recovery to 33 ℃.

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 5a, liquid phase at the bottom of the high-pressure-area first-stage flash tank 5a is preferably depressurized to 0.3MpaG and is fed into a high-pressure-area second-stage flash tank 5b, gas phase (rich in hydrogen and methane) at the top of the high-pressure-area flash tanks 5a-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 a low-pressure-area first-stage flash tank 6 a.

The liquid phase from the high-pressure zone secondary flash tank 5b is preferably depressurized to 0.13MpaG and is fed into the low-pressure zone primary flash tank 6a, the liquid phase returning to the low-pressure zone primary flash tank 6a is preferably depressurized to 0MpaG and is fed into the low-pressure zone secondary flash tank 6b, the gas phase at the top of the low-pressure zone primary flash tank 6a is fed into a 7a carbon concentrated gas primary compressor, the gas phase at the top of the low-pressure zone secondary flash tank 6b is fed into a 7b carbon concentrated gas secondary compressor, and the C carbon concentrated gas (1MpaG) pressurized by a 7a-C carbon concentrated product compression system is fed into an ethylene plant cracking furnace. The liquid phase at the bottom of the second-stage flash tank 6B in the low-pressure area is divided into two branches, one branch is used as E-time lean solvent (35t/h and-59 ℃) for circular absorption, and the other branch sequentially passes through a intercooler 4a of a multi-stage absorption tower and a dry gas precooling heat exchanger 2B for cold recovery to 33 ℃ and enters a carbon dioxide desorption tower 8.

The liquid phase from the bottom of the second-stage flash tank 6b in the low-pressure area is sent to the middle part of a 8 desorption tower after cold recovery and pressurization, the theoretical plate number of the desorption tower is 30, the operation pressure is preferably 3.5MpaG, the temperature of the top of the tower is 40.8 ℃, and the temperature of the bottom of the tower is 152 ℃. The tower top condenser 9 of the desorption tower 8 is subjected to wet air cooling or circulating cooling water condensation to 40.8 ℃, and the tower kettle reboiler 11 is heated by low-pressure steam or hot oil. The gas phase (rich in carbon two and carbon three) at the top of the desorption tower 8 is mixed with the carbon two concentrated gas recovered by the reduced pressure flash distillation and then sent to the ethylene device cracking furnace. Most of the liquid phase at the bottom of the desorption tower 8 is circularly absorbed as a D lean solvent (23t/h) after being supplemented with fresh solvent. The lean solvent D is cooled to 0 ℃ by a-6 ℃ propylene refrigerant through a lean solvent cooling heat exchanger 12A, and is cooled to-35 ℃ by a-40 ℃ propylene refrigerant through a lean solvent cooling heat exchanger 12B, and then is sent to the top of the multistage absorption tower 3.

In the present embodiment, the composition of the carbon dioxide rich gas is shown in table 2, and the composition of the lean solvent and the second lean solvent is shown in table 3.

TABLE 2

Name (R)	Carbon two concentrated gas
		Temperature, C	40
Pressure, MpaG	1.06
		Mass flow rate, t/hr	12456
Molar flow, kmol/hr	389
		Composition in mol%
Hydrogen gas	0.01
		Oxygen gas	0.02
Nitrogen is present in	0.02
		Methane	4.01
Ethane (III)	73.22
		Ethylene	6.80
Propane	12.13
		Propylene (PA)	1.43
N-butane	1.18
		Isobutane	1.05
1-butene	0.02
		Isobutene	0.01
Cis-butenediol	0.01
		N-pentane	0.08
Isopentane	0.01

In this example, the carbon recovery was 91.4% and the ethane recovery was 94.9%.

TABLE 3

In this example, the energy-saving process and apparatus for recovering carbon from refinery dry gas and the conventional intercooled oil absorption process (patent CN 101063048A) and shallow cold oil absorption process (CN 109553504a) both use the dry gas feed provided by the present invention, and the energy consumption pairs are shown in table 4, wherein the electric power already includes the electric power consumed by refrigeration.

TABLE 4

The above describes an embodiment of the invention in which the lean solvent is circulated in an amount of only 1/4 parts of the total solvent amount and half of the carbon dioxide concentrate gas is recovered by means of flash desorption, resulting in a large reduction in the carbon dioxide desorber throughput where there is mainly energy consumption, and a large reduction in the total energy consumption. And through the optimization of the process flow, the goals of saving energy and reducing investment are achieved, as can be seen from table 4, compared with the traditional intercooling oil technology and the existing shallow cold oil absorption technology flow, the process of the invention can reduce the comprehensive total energy consumption by 33.5 percent and 36.65 percent respectively, and the number of main equipment towers of the invention is only 2, the equipment size is smaller, and the total investment cost is reduced.

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 (12)

1. An energy-saving process for recovering carbon dioxide from refinery dry gas is characterized by comprising the following process flows:

(1) the refinery dry gas after deacidification, drying and compression treatment by the dry gas pretreatment system is cooled and then sent to a multi-stage absorption tower for treatment, the gas phase at the top of the tower obtained by the multi-stage absorption tower treatment is sent to a fuel gas pipe network or a PSA device after cold energy recovery, and the liquid phase at the bottom of the tower obtained by the multi-stage absorption tower treatment is sent to a high-pressure flash evaporation area for treatment;

(2) the high-pressure flash evaporation area is provided with a multi-stage high-pressure area flash evaporation tank, and the gas phase obtained by flash evaporation is returned to the compression section of the dry gas pretreatment system; one 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 a low-pressure flash evaporation zone for treatment; the high-pressure area is provided with a plurality of flash tanks, 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;

(3) the low-pressure flash evaporation area is provided with a multi-stage low-pressure flash evaporation tank, the gas phase carbon dioxide concentrated gas obtained by flash evaporation is sent to a carbon dioxide concentrated gas compressor system, one 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 desorption tower for treatment; the low-pressure flash evaporation area is provided with a plurality of flash evaporation tanks, the flash evaporation tanks are sequentially connected in series under reduced pressure, and the pressure of the last flash evaporation tank is 0-0.1 MpaG;

(4) mixing the gas phase obtained by the treatment of the desorption tower with the gas phase obtained by compression of a carbon dioxide concentration gas compressor system to be used as carbon dioxide concentration gas and sending the carbon dioxide concentration gas to a cracking furnace of an ethylene device, returning most of the liquid phase obtained by the desorption tower to a multistage absorption tower as a lean solvent, taking a small part of the liquid phase as extracted carbon four and sending the extracted carbon four out of a boundary region, and supplementing a fresh carbon four absorbent.

2. The energy-saving process for recovering carbon dioxide from refinery dry gas according to claim 1, characterized in that the method of multi-stage absorption tower treatment comprises: and (3) supplying the cooled refinery dry gas into a multistage absorption tower to enable the refinery dry gas to be in contact with the mixed carbon four absorbent, wherein the theoretical plate number of the multistage absorption tower is 30-60, the operating pressure is 3-5 MpaG, the temperature of the top of the tower is-15 ℃ to-35 ℃, and the temperature of the bottom of the tower is-10 ℃ to-30 ℃.

3. An energy saving process for carbon recovery from refinery dry gas according to claim 1, characterized by the fact that in the liquid phase obtained from the high pressure flash: the liquid phase entering the low-pressure flash evaporation zone is the liquid phase of the last flash evaporation tank, the semi-lean solvent is the liquid phase of each flash evaporation tank, the feeding plate of the semi-lean solvent is 20-45 ℃, and the temperature of the semi-lean solvent is minus 10 ℃ to minus 40 ℃.

4. An energy saving process for carbon recovery from refinery dry gas according to claim 1, wherein the low pressure flash zone produces in the liquid phase: the liquid phase fed into the desorption tower is the liquid phase of the last flash tank, the secondary lean solvent is the liquid phase of each flash tank, the feeding plate of the secondary lean solvent is 5-25 ℃, and the temperature of the secondary lean solvent is minus 30 ℃ to minus 70 ℃.

5. The energy-saving process for recovering carbon dioxide from refinery dry gas as claimed in claim 1, 2, 3 or 4, wherein the processing method of the carbon dioxide concentrated gas compressor system comprises: increasing the pressure of the gas phase obtained in the low-pressure flash evaporation zone to 0.5-2 MPaG.

6. The energy efficient process for carbon recovery from refinery dry gas as claimed in claim 5, wherein the carbon concentration gas is a multi-stage compression.

7. An energy-saving process for recovering carbon from refinery dry gas as claimed in claim 1, 2, 3, 4 or 6, wherein the cooling treatment method comprises: and cooling the treated refinery dry gas to-15 to-40 ℃, wherein the cooling treatment adopts propylene refrigeration, and the propylene refrigeration adopts first-stage to third-stage refrigeration in combination with the operation temperature of other equipment of the process.

8. The energy-saving process for recovering carbon from refinery dry gas as claimed in claim 7, wherein the carbon four absorbent is a carbon four-cut containing n-butane and isobutane, or a saturated liquefied gas containing a saturated carbon three-cut and a carbon four-cut.

9. The energy efficient process for carbon recovery from refinery dry gas as claimed in claim 8, wherein in the carbon four absorbent: the circulating lean solvent comprises 80-95 mol% of carbon four and the balance of carbon three and carbon five; the composition of the circulating sub-lean solvent is 50-80 mol% of carbon four, and the composition of the circulating semi-lean solvent is 30-70 mol% of carbon four.

10. An energy-saving process for recovering carbon from refinery dry gas as claimed in claim 1, 2, 3, 4, 8 or 9, wherein the method of desorber treatment comprises: and (3) supplying the liquid phase material obtained by the treatment of the low-pressure flash evaporation zone into a carbon dioxide desorption tower for separation, wherein the theoretical plate number of the desorption tower is 20-60, the operating pressure is 0.5 MpaG-4 MpaG, the tower top temperature is-35-40 ℃, and the tower kettle temperature is 60-130 ℃.

11. The energy-saving process for recovering carbon from refinery dry gas as claimed in claim 10, wherein the lean solvent returned to the multistage absorption tower for recycling is cooled to-15 to-40 ℃, and returned to the top of the multistage absorption tower for recycling as the lean absorbent.

12. An energy-saving device for recovering carbon from refinery dry gas is characterized by comprising a dry gas pretreatment system, a multi-stage absorption tower, a high-pressure zone flash tank, a low-pressure zone flash tank, a desorption tower, a carbon 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 precooler;

the outlet of the dry gas precooler is communicated with the bottom of the multi-stage absorption tower;

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

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 desorption tower;

the top of the desorption tower is connected with a carbon dioxide 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 a carbon extraction four pipeline, and a fresh carbon supplement four pipeline is connected with the lean solvent pipeline;

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

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