CN108310909B

CN108310909B - Method for extracting H2 from CO-containing purified terephthalic acid tail gas through pressure swing adsorption

Info

Publication number: CN108310909B
Application number: CN201710031972.0A
Authority: CN
Inventors: 钟雨明; 刘开莉; 陈运; 叶建红; 汪兰海; 蔡跃明
Original assignee: Sichuan Techairs Co ltd
Current assignee: Sichuan Techairs Co ltd
Priority date: 2017-01-17
Filing date: 2017-01-17
Publication date: 2020-06-19
Anticipated expiration: 2037-01-17
Also published as: CN108310909A; TWI629240B; TW201827334A

Abstract

The invention discloses a method for extracting hydrogen (H2) from Purified Terephthalic Acid (PTA) tail gas containing carbon monoxide (CO) by pressure swing adsorption, which comprises the step of enabling the raw material gas containing CO and rich in hydrogen after a primary purification process to enter a Pressure Swing Adsorption (PSA) system, wherein the PSA system adopts a multi-tower series or parallel or series and parallel process, the PSA system is alternately and circularly operated, the operation temperature is 10-120 ℃, the operation pressure is normal pressure to 5.0MPa, normal pressure flushing or vacuum desorption regeneration is carried out, and the pressure equalizing frequency is not more than 3 times. The PSA system is suitable for hydrogen-rich raw material gas with CO concentration of 0.1-15% (volume ratio, the same as below). The product H2 obtained from the PSA system has the purity of more than 99-99.9%, wherein the content of CO and carbon dioxide (CO 2) is less than 1-10 ppm, and the yield of the product H2 is more than 85-97%.

Description

Method for extracting H2 from CO-containing purified terephthalic acid tail gas through pressure swing adsorption

Technical Field

The invention belongs to the field of gas purification and separation, and particularly relates to a method for extracting hydrogen (H2) from Purified Terephthalic Acid (PTA) tail gas containing carbon monoxide (CO) through Pressure Swing Adsorption (PSA).

Background

In the PTA production process, more tail gas is generated, typical components of the tail gas include CO, volatile organic compounds (VOCs, acetic acid, benzoic acid, terephthalic acid, PT acid and other organic acids, aldehydes, ketones, alcohol ether esters volatile compounds), nitrogen (N2), methane (CH 4), carbon dioxide (CO 2), alkali, other inorganic components, water and H2, and the tail gas is often high in temperature or pressure and directly discharged, so that secondary pollution is caused, and the resource of the effective component H2 is wasted. This situation sometimes occurs during other petrochemical and like processes like PTA tail gas composition. Therefore, the recovery of H2 from PTA tail gas has become one of the important means for energy saving, consumption reduction and emission reduction in the PTA industry.

The methods for recovering H2 from PTA tail gas mainly include condensation, absorption, cryogenic cooling, adsorption, and membrane separation. In practical industrial application, the conventional pressure swing adsorption method is generally adopted to extract H2 with high purity. However, since the PTA tail gas contains a certain amount of VOCs, CO2, CO, N2, O2 and a large amount of water and other impurity components, and the presence of these impurities at high temperature or high pressure greatly affects the purity and yield of the H2 product for PSA extraction of H2. For example, the separation ratio of CO to H2 is relatively small, less than 3, which results in a decrease in the efficiency of conventional PSA separation of H2/CO, and the recovered H2 needs to be returned to the PTA refining process, with severe restrictions on the amount of CO contained therein, such as less than 10ppm, which in turn requires increased equipment investment and energy consumption in conventional PSA processes. Therefore, before entering the PSA H2 extraction process, CO is removed or converted as much as possible so as to reduce the load on the PSA H2; for another example, the VOCs in the PTA tail gas, which contain some acetic acid, xylene (PX), p-xylene aldehyde, Crude Terephthalic Acid (CTA) required in the PTA production process, and some organic matters harmful to the adsorbent in the PSA system, need to be treated by methods such as water washing, alkali washing, neutralization, condensation, chemical absorption, etc.; for water, it is treated by evaporation, condensation, drying, etc. Among them, the treatment of CO as an impurity becomes a key.

Patent CN101301570A discloses a PTA tail gas treatment method, which mainly converts VOCs and CO in tail gas into CO2 by a catalytic combustion method, and then directly separates CO2 from H2 by an absorption or adsorption method to obtain an H2 product; or directly discharging without recycling H2, thereby meeting the requirement of environmental protection. The method has the advantages that the separation coefficient of CO2 and H2 is large, separation is easy to realize by absorption or adsorption and other methods, or the waste gas is directly discharged after reaching the standard without being recycled; in addition, the defects of large fuel consumption, low combustion value, ineffective CO conversion, high cost and the like of high-pressure incineration (HPCCU) or Regenerative Thermal Oxidation (RTO) are overcome. But the method consumes a large amount of the active ingredient H2, so that the subsequent H2 product yield is greatly reduced; at the same time, additional CO2 is produced, increasing the greenhouse gas effect; the catalyst (catalyst) required by catalytic oxidation combustion is noble metal serving as an active component, the cost is high, the temperature of a reaction outlet is high and reaches 200-750 ℃, and the energy consumption waste of the subsequent recovery of normal-temperature H2 is increased; in addition, the method also introduces air (N2 and O2) in the treatment process, so that the load of a subsequent H2 separation and extraction section is increased.

Patent CN1093114C discloses a PTA tail gas treatment method, which comprises the steps of carrying out water washing, alkali washing and other pretreatments on PTA tail gas, removing impurities such as VOCs, CO2, water and the like, introducing a methanation catalyst (catalyst), converting CO and H2 in the tail gas into methane (CH 4) and CO2, and then carrying out an adsorption process to extract H2. The process has obvious disadvantages including, firstly, that the CO content in the off-gas cannot be too high, since too much CO leads to severe temperature runaway and deactivation of the methanation catalyst. The reaction temperature is increased to 30-50 ℃ every time the CO is reduced by 1%, so that methanation is generally suitable for the working condition of low CO content in the raw material gas, for example, CO removal of methane hydrogen gas containing less than 1% of CO generated in an ethylene cracking gas cooling box; secondly, more H2 is consumed, and the yield of the product H2 is reduced; thirdly, due to the imperfect pretreatment, a small amount of VOCs impurity components enter a methanation system, so that the methanation catalyst is subject to deactivation or incomplete methanation, and some residual CO enters an adsorption system to influence the adsorption efficiency and the purity of a product H2, thereby causing the deactivation of the H2 recycled to the PTA refining catalyst (catalyst); fourthly, methanation still consumes the effective component H2 in the raw material gas to additionally generate CO2, and the greenhouse gas effect is increased; fifth, the cost is high. In addition, there is no specific description of the adsorption process in this patent.

Patents TW I391372B1 and CN 101475462B disclose a CO conversion method in a PTA tail gas hydrogen extraction process, the flow is similar to patent CN1093114C, except that methanol vapor is introduced into the PTA tail gas after pretreatment and purification, CO conversion is performed in a copper catalyst (catalyst) at a temperature of 200 to 300 ℃ to generate H2 and CO2, and then hydrogen extraction is performed in an adsorption process, which has the advantages that the conversion temperature is lower than methanation, no effective component H2 in the raw gas is consumed, and the process is relatively mature. The disadvantages of extra CO2 generation, high CO conversion temperature, increased load of the subsequent H2 process due to newly introduced methanol vapor medium in the system, easy deactivation of the conversion catalyst, high investment and operation cost and the like still exist, the subsequent PSA process is not specially described, and the CO content in the feed gas actually entering the PSA process is basically close to about 0.1% (obtained from the examples).

Disclosure of Invention

The invention provides a method for extracting H2 from PTA tail gas PSA containing CO, which is characterized in that a PSA separation technology is taken as a core, CO in the PTA tail gas is not required to be converted, the differences of adsorption separation coefficients and physicochemical properties of components of CO and H2 carried by the PTA tail gas in the temperature range of 10-120 ℃ and the pressure range of normal pressure to 5.0MPa are utilized, a Pressure Swing Adsorption (PSA) method that multiple towers are connected in series and parallel and pressure equalization is carried out for a few times and an adsorbent loaded with active components can be not activated is adopted, and the adsorption and desorption regeneration in a pressure swing adsorption cycle process are adjusted by coupling water washing, alkali washing or Temperature Swing Adsorption (TSA) and the like of a pretreatment unit and a two-stage PSA or membrane separation method, so that the adsorption and desorption in the adsorption process are easy to match and balance to separate and purify the PTA tail gas and extract qualified product hydrogen. Therefore, the problems of the prior patent and the method, such as high content of CO, high investment and cost, easy inactivation of a CO conversion catalyst, high CO conversion temperature, low hydrogen purity or yield, greenhouse gas effect caused by CO2 byproduct, and the like, are solved.

In order to solve the problems of the method for recovering H2 from PTA tail gas, the invention adopts the following technical scheme:

a method for extracting H2 from CO-containing Purified Terephthalic Acid (PTA) tail gas through pressure swing adsorption comprises the steps of feeding Purified Terephthalic Acid (PTA) tail gas containing carbon monoxide (CO) and hydrogen (H2) as raw material gas into an adsorption tower in a Pressure Swing Adsorption (PSA) system with the operation temperature of 10-120 ℃ and the operation pressure of normal pressure to 5.0MPa after primary purification, and is characterized in that the PSA system adopts a multi-tower series or parallel series process of more than 2 adsorption towers, and performs adsorption-average pressure drop-forward-reverse discharge-vacuumizing/flushing-average pressure rise-final filling alternating cycle operation through a program control valve, an adjusting valve and a PSA time sequence control program in the PSA system, a vacuum pump, a buffer tank, a product tank, a process pipeline and related equipment, wherein the adsorption operation temperature is 10-120 ℃, the operation pressure is normal pressure to 5.0MPa, the pressure equalizing times (the average pressure drop and the average pressure rise times in one operation cycle of adsorption-desorption among a plurality of adsorption towers) adopted among the adsorption towers are set to be not more than 3, the H2 product which meets the requirement and has the purity of more than 99-99.9% (v/v) and the CO content of less than 1-10 ppm flows out from the top of the PSA system, and the desorption gas generated by reverse discharge and vacuum-pumping/flushing is used as byproduct-fuel gas or further recovers CO and H2 in the desorption gas.

Furthermore, the raw material gas is tail gas containing CO, H2 and other components, which is generated in the production process of Purified Terephthalic Acid (PTA), and enters the raw material gas of a PSA system after a primary purification process, wherein the concentration of CO is 0.01-15% (v/v), the concentration of volatile organic compounds (VOCs, including acetic acid, benzoic acid, terephthalic acid, PT acid and other organic acid, aldehyde, ketone and alcohol ether ester volatile compounds) is less than 0.01-2% (v/v), the concentration of nitrogen (N2), methane (CH 4) and carbon dioxide (CO 2) is less than 0.01-15% (v/v), the content of water, alkali and other inorganic components is less than 0.01-3% (v/v), and the concentration of H2 is more than 60-65% (v/v); the feed gas may also include other gases containing CO, H2 similar to the PTA tail gas component for PSA hydrogen extraction, such as coke oven gas, raw coke oven gas, syngas, methanol purge gas, acetic acid tail gas, xylene tail gas, styrene tail gas, oxo alcohol vent gas, biomass gasification gas (including straw gas), and one or more gas mixtures of various refinery tail gases and steelmaking tail gases.

Furthermore, the raw gas after the preliminary purification process is composed of one or more pretreatment devices and processes including a raw gas chiller, a primary cooler, a water scrubber, an acid gas removal tower, an alkaline washing tower, a neutralization tower, a VOCs removal scrubber, a VOCs removal activated carbon adsorption tower, a cold oil absorption tower for removing carbon and the above components (C2 +), a heat exchanger, a condenser, an air cooler and a compressor according to the composition and process conditions (temperature, pressure and flow) of the raw gas, wherein the raw gas after the pretreatment process has the temperature of 10-120 ℃, the pressure of normal pressure to 5.0MPa and the main components of hydrogen-rich gas of CO and H2 and is used as the raw gas directly entering the Pressure Swing Adsorption (PSA) system.

Further, in the Pressure Swing Adsorption (PSA) system, one or more columns are always in the adsorption step, while the remaining columns are in the desorption regeneration step consisting of pressure equalization-cocurrent discharge-countercurrent discharge-evacuation/flushing-pressure equalization-final filling.

Furthermore, the adsorption tower in the Pressure Swing Adsorption (PSA) system is filled with one or more adsorbents of active carbon, active component-loaded active carbon, silica gel, activated alumina, molecular sieve and active component-loaded molecular sieve, wherein the active component-loaded active carbon can be subjected to adsorption separation within the operating temperature and pressure ranges of the adsorption tower in the PSA system without being activated.

Furthermore, the pressure equalizing times (which refers to the times of pressure equalizing and pressure equalizing in an operation cycle of adsorption-desorption among a plurality of adsorption towers) adopted among the adsorption towers are set to be not more than 3 times, the pressure equalizing times are realized by parallelly controlling the valve opening through the program control valves and the regulating valves among the multiple adsorption towers to be not more than 3 times when the pressure of the raw material gas and the operation pressure of the adsorption towers of a Pressure Swing Adsorption (PSA) system are within the range of 1.0-5.0 MPa, and the increase of the number of the adsorption towers caused by more pressure equalizing times due to overlarge fluctuation of airflow in the adsorption towers caused by the overlarge pressure equalizing pressure drop in the operation process of the medium-high pressure PSA system is avoided.

Furthermore, the desorbed gas generated by the reverse release and the vacuum/flushing is used as a byproduct, namely fuel gas, and is required to be pressurized to the grid-connected pressure specified by a fuel gas pipe network.

Further, the desorbed gas generated by the reverse discharging and vacuumizing/flushing or further recovering CO and H2 is pressurized to the operating pressure of an adsorption tower of a Pressure Swing Adsorption (PSA) system, the desorbed gas is sent to another Pressure Swing Adsorption (PSA) system, namely a two-stage PSA system, hydrogen-rich gas with the hydrogen concentration close to that of the raw material gas entering the Pressure Swing Adsorption (PSA) system flows out of the adsorption tower top of the two-stage PSA system and is mixed with the hydrogen-rich gas to enter the Pressure Swing Adsorption (PSA) system, and more qualified hydrogen products flow out of the adsorption tower top of the two-stage PSA system, namely, effective hydrogen components are further recovered from the desorbed gas; and (2) desorbing gas flowing out of the two-stage PSA system, directly discharging, or discharging by combustion, or pressurizing and merging into a fuel gas pipe network, or using the enriched CO as a raw material required by the carbonylation reaction when the concentration of the enriched CO reaches more than 60-90% (v/v), namely further recovering the CO. The two-stage PSA system comprises an adsorption tower, a first-stage PSA system, a second-stage PSA system and a third-stage PSA system, wherein one or more adsorbents of active carbon, active component-loaded active carbon, silica gel, activated alumina, a molecular sieve and an active component-loaded molecular sieve are filled in the adsorption tower of the second-stage PSA system, and the active component-loaded active carbon can be subjected to adsorption separation within the operating temperature and pressure ranges of the adsorption tower in the PSA system without being activated.

Furthermore, the desorbed gas generated by reverse release and vacuumizing/flushing or further recovering CO and H2 is pressurized to 3.0-5.0 MPa, and then sent into a hydrogen permeable membrane system, the permeated hydrogen-rich gas is mixed with the raw material gas entering a Pressure Swing Adsorption (PSA) system and enters the system, and qualified hydrogen products with more quantity flow out of the top of the adsorption tower, namely, effective hydrogen components are further recovered from the desorbed gas; the non-permeable gas is directly merged into a fuel pipe network by regulation without pressurization or is sent out of a boundary area for carbonylation reaction or other required raw materials, namely, CO is further recovered from desorption gas.

Furthermore, the raw material gas after the primary purification process and before entering a Pressure Swing Adsorption (PSA) system can be additionally provided with a deoxidizing device containing a palladium catalyst to remove trace oxygen (O2) in the raw material gas.

Compared with the prior art, the invention has the beneficial effects that:

(1) the method is suitable for the working condition that the concentration range of CO contained in the PTA tail gas is wide, namely, the concentration range of CO can reach 0.01-15% (v/v) according to the components of the raw material gas after pretreatment and purification, various catalytic conversion means are not needed, the effective component H2 in the raw material gas is not needed to be consumed, high temperature is not needed, the method is simple, the adaptability is strong, and the investment and operation cost is low;

(2) the temperature, pressure and the like carried by the feed gas as well as the difference between the separation coefficient and the physicochemical property of each component are fully utilized, PSA operation can be carried out in a wider temperature and pressure range, the pressure equalizing frequency under medium and high pressure is less than 3 times, the adsorbent loaded with active components in the system is also suitable for activation under the operating temperature and pressure, independent activation is not needed, the system energy is utilized in a cascade way, and the energy consumption of the device is lower;

(3) the method can adopt a flexible coupling means of a pretreatment process and a PSA system according to the feeding working condition of the PTA tail gas, has strong adaptability to the composition and working condition fluctuation of the PTA tail gas, does not generate the deactivation problem of a catalyst and an adsorbent caused by the imperfect pretreatment process, is stable, safe and reliable, and is suitable for obtaining a high-purity H2 product from hydrogen-rich gas containing impurities such as CO, VOCs, N2, O2, CO2 and the like under the similar PTA tail gas composition condition;

(4) in the operation of the PSA system, particularly under the working condition of medium-high pressure feeding, the pressure equalizing technology with a few times is adopted, so that the service life of the adsorbent filled in the adsorption tower is ensured not to be shortened due to overlarge pressure change of the system, and on the contrary, the service life of the adsorbent is shortened due to the avoidance of incomplete deep adsorption and desorption, and the stability and the reliability of the device are further improved;

(5) the method can be used for further recovering H2 and CO in the desorption gas of the PSA system by adopting a flexible method of coupling a two-stage PSA or externally hung membrane system with the PSA system for the PTA tail gas with high CO content, so that the yield of the product H2 can be improved by 3-5%;

(6) the method is environment-friendly, and in the tail gas treatment process, compared with the existing method, other substances outside the system are not introduced, and additional CO2 is not generated to cause secondary pollution and emission;

(7) the process for extracting high-purity H2 with low content of CO and other impurities from PTA tail gas and similar industrial tail gas can realize the double high of yield and purity of H2 products under the double low of energy consumption and material consumption.

Drawings

FIG. 1 is a schematic flow chart of example 1.

FIG. 2 is a schematic flow chart of example 2.

FIG. 3 is a schematic flow chart of example 7.

FIG. 4 is a schematic flow chart of example 8.

Detailed Description

In order to make those skilled in the art better understand the present invention, the technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the drawings in the embodiments of the present invention.

Example 1

As shown in figure 1, the method for extracting H2 from CO-containing purified terephthalic acid tail gas by pressure swing adsorption sequentially comprises the following operations:

(1) primary purification:

the typical composition of each tail gas from the PTA production process after mixing is 85% (v/v, the same applies below); 13 percent of H2; 0.6 percent of N2; 0.3 percent of CO; 0.2 percent of CO 2; 0.01 percent of O2, and 0.69 percent of other materials including VOCs, methane and the like; the pressure of the tail gas is more than 2.0MPa, the temperature is more than 200-250 ℃, and the flow rate is 3,000Nm 3/h. Thus forming the feed gas of PTA tail gas, and entering the working procedure. The PTA tail gas pressure is stabilized to 2.0MPa (the pressure requirement of hydrogen product is 2.0 MPa). The raw material gas is cooled by boiler water for recovering the part of heat, and simultaneously, 0.5MPa saturated steam is byproduct. The raw material gas after primary heat exchange is separated from condensate, the temperature of the raw material gas is respectively reduced to 40 ℃ by using circulating cooling water, then the condensate is separated in a separator, the rest gas enters from the bottom of a soda ash washing tower and is in countercurrent contact with soda ash sprayed on the surface of a filler from the top of the tower, various VOCs components in tail gas, such as terephthalic acid, benzoic acid, p-toluic acid, acetic acid and the like, are absorbed by the soda ash, and the concentration of the liquid absorbing organic acid at the initial stage is low due to the low content of VOCs (mainly organic acid) in the tail gas, and the tail gas is pressurized by a soda ash circulating liquid pump, is cooled by a heat exchanger and then is sent into the soda ash washing tower for recycling. And after the concentration of the circulating liquid is saturated, discharging the circulating liquid to a sewage treatment system. Absorbing a small amount of soda ash solution contained in the tail gas of the organic acid, then washing in a pure water tower, and discharging the washing solution out of an outside sewage treatment system. The purified tail gas contains a certain amount of oxygen, which cannot meet the requirement of entering a PSA system and needs to be purified. Heating the crude tail gas to a post-deoxygenation tower by using partial byproduct low-pressure steam of 0.5MPa, reacting trace oxygen with hydrogen in the raw material gas to generate water under the catalysis of a novel normal-temperature palladium catalyst filled in the tower, cooling the water to about 40 ℃ by a cooler (the temperature of a hydrogen product is 40 ℃), buffering the water by a buffer tank, and then entering a PSA system. Thus, the feed gas composition entering the PSA system is constituted, the feed gas amount is about 420Nm3/H, H2: 91.2% (v/v, the same applies below); 2.4 percent of CO; 4.6 percent of N2; 0.7 percent of CO 2; 0.2 percent of CH 4; others, including small amounts of water, alkali, VOCs, etc., 0.9%; the temperature was 40 ℃ and the pressure was 2.0 MPa. The feed gas, referred to as a CO-containing hydrogen-rich feed gas, enters the PSA system.

(2) Pressure Swing Adsorption (PSA) systems:

introducing the CO-containing hydrogen-rich feed gas into a Pressure Swing Adsorption (PSA) system for alternative cycle operation, wherein the Pressure Swing Adsorption (PSA) system comprises a program control valve, an adjusting valve, a pipeline assembly and 5 adsorption towers connected in parallel, the operation temperature is 40 ℃, the operation pressure is 2.0MPa, and the CO-containing hydrogen-rich feed gas is subjected to vacuum desorption; the adsorption tower comprises a plurality of adsorption materials which are compounded and filled in a bed layer, such as activated alumina, activated carbon loaded with active components, silica gel and molecular sieves; each adsorption tower is controlled by a valve to respectively undergo the following processes of adsorption, pressure equalizing drop, evacuation, pressure equalizing rise, final filling and the like in one circulation period, wherein the process is 5-1-3V, namely, in 5 towers, 1 tower is always in the adsorption step, and the other 4 towers are in each step of the desorption process, pressure equalizing is carried out for 3 times, and vacuum pumping desorption is carried out:

a. adsorption: and (3) introducing CO-containing hydrogen-rich raw material gas subjected to temperature reduction treatment in the primary purification process into an adsorption tower from the bottom of a high-end adsorption bed in the PSA system through an air inlet pipe, selectively adsorbing high-boiling-point components (CO 2, water and VOCs) in the raw material gas by an adsorbent, and delivering unadsorbed low-boiling-point (hydrogen) serving as product gas to a buyer from the top of the adsorption tower. Wherein, the CO impurity component also belongs to a lower boiling point substance, and the lower boiling point CO component is adsorbed by the filled active component-loaded active carbon and the CO special molecular sieve adsorbent, thereby achieving the separation with the same low boiling point effective component H2. The CO content of the H2 product is less than 1-10 ppm, the CO2 content is less than 1-10 ppm, the pressure of the H2 product is 2.0MPa, and the temperature is 40 ℃;

b. pressure equalizing and reducing: after the adsorption process is completed, the pressure of the adsorption tower is higher, and the dead space in the adsorption tower also contains much hydrogen. Therefore, the pressure of the adsorption tower with the uniform pressure drop is reduced by carrying out pressure averaging for multiple times with other adsorption towers, and simultaneously, the hydrogen content in the tower is reduced. That is, the gas is discharged from the discharge end of one or more adsorption columns to the feed end of the corresponding other adsorption column or columns, and the pressure is reduced until the pressures of the two or more columns are equalized. When pressure equalization is implemented, a program control valve is adopted;

c. reverse amplification: after the completion of the adsorption process, the impurity components adsorbed in the adsorption column are released, and the part of the gas is discharged from the bottom of the adsorption column against the direction of adsorption. Reducing the impurity partial pressure through a reverse discharge step to ensure that the adsorbent obtains partial regeneration, wherein reverse discharge gas and air extraction form learned gas;

d. pressure equalization and rise: after the evacuation is completed, the pressure of the adsorption column is negative, there is a large pressure difference with the adsorption, the pressure equalization is raised to the adsorption pressure by the pressure averaging with the adsorption column which is otherwise in the desorption process, and the effective component is recovered (H2). Not only reduces the usage amount of final pressurized product gas, but also improves the total yield of hydrogen. Performing pressure equalization and rising, and reversely introducing gas discharged from the corresponding pressure equalization tower from the discharge end of one or more adsorption towers through a program control valve connected among the towers until the bed layer pressures of two or more towers are equal;

e. final charging: after the pressure equalizing step is finished, the pressure of the adsorption tower is different from the system operation pressure. In order to ensure the safe and stable operation of the system, product hydrogen is needed to be used for pressurizing, the pressure of the adsorption tower is close to the system pressure, and the instability of the system when the adsorption tower is switched is avoided. It is also possible to use a CO-containing hydrogen-rich feed gas instead of product H2 for the final filling step, which is equivalent to performing a pre-adsorption, i.e. when performing an adsorption-pressure drop-reverse discharge/evacuation-pressure rise-final fill cycle, a small amount of the adsorbate is already adsorbed on the adsorbent during the adsorption step, rather than being non-adsorbate on the adsorbent during the adsorption step after the final filling with product H2. The raw material gas is filled finally, so that the product H2 can be saved, and the product yield of H2 is higher.

In the primary purification step, in the alkaline washing step, the temperature of the crude raw material gas as the PTA tail gas is reduced from 200 to 250 ℃ to 40 ℃, the pressure is stabilized at 2.0MPa, and a large amount of water and a small amount of VOCs are removed. The crude raw material gas after temperature reduction and pressure reduction/pressure stabilization enters a deoxygenation reactor again to remove O2 impurities in the crude raw material gas, the formed CO-containing hydrogen-rich gas enters a Pressure Swing Adsorption (PSA) system consisting of a valve, a pipeline component and 5 parallel adsorption towers to perform PSA5-1-3V adsorption and desorption cyclic operation, the operation temperature is 40 ℃, the adsorption pressure is 2.0MPa, the adsorption towers are filled with active alumina, silica gel, active carbon, active component-loaded active carbon, CO special molecular sieves and other combinations, the desorption effect is good, bed regeneration can be rapidly realized, and the service life of the bed is greatly prolonged. And (3) an H2 product with the purity of more than 99.9% flows out from the top of the adsorption tower of the PSA system, wherein the contents of CO and CO2 are both less than 1-10 ppm, and the yield of the H2 product is more than 85-88%. This embodiment does not need to be as in other patents: CO (2.4%) in the hydrogen-rich raw material gas containing CO is firstly converted to about 0.1% by catalytic conversion and then enters the PSA system, so that the catalytic conversion step is saved, the extra increased CO2 discharge caused by CO conversion is not required, the consumption of an effective component H2 in the raw material gas is saved, and the yield of a product H2 is improved.

Example 2

As shown in fig. 2, on the basis of example 1, a method for extracting H2 by pressure swing adsorption of CO-containing purified terephthalic acid tail gas, wherein the composition and feeding conditions of CO-containing hydrogen-rich raw gas entering a PSA system are unchanged, the PSA system is formed by connecting 4 columns in parallel, and PSA cycle operation is performed in a 4-1-1V manner, i.e. 1 column is always in an adsorption state, the remaining 3 columns are respectively in each step of desorption, and pressure equalization is performed for 1 time. In order to prevent the influence on the mass transfer efficiency in the adsorption-desorption cycle process possibly caused by overlarge system pressure change and pulverization caused by overlarge pressure stress borne by an adsorbent due to overlarge pressure difference, a regulating valve and a program control valve are additionally arranged on a pressure equalizing pipeline between adsorption towers and are in parallel connection with each other to control the pressure equalizing speed and time between the towers, thereby realizing the slow equalizing process. The advantages of this are that, firstly, the same raw material gas, the number of adsorption towers of the adopted PSA system is reduced, the number of corresponding program control valves and pipelines is also reduced, the investment is reduced, the stability and reliability of the device are increased, and the energy consumption of the system is further reduced; secondly, the residual effective components in the dead space (dead volume) inherent in the adsorption tower are further recovered, and the yield of the effective components (namely products) is improved. However, the dead space in the adsorption column is constant, which means that there is a limit in recovering the active components in the dead space by means of pressure equalization many times. For example, the dead space ratio of activated carbon of several commonly used adsorbents is high, generally reaching about 70%, while the ratio of silica gel, molecular sieve and the like is low, about 50-60%. The pressure equalizing times are increased in the PSA process of the adsorption tower of the activated carbon adsorbent, and the marginal efficiency of further recovering effective components from the dead space is relatively high. And for an adsorption tower filled with other adsorbents, the pressure equalizing frequency is increased, and the marginal contribution to the yield of effective components is reduced. For PSA hydrogen extraction of PTA tail gas, four to five adsorbents are generally filled in an adsorption tower, so that when the pressure equalizing frequency reaches 3-4 times, the marginal contribution to the yield of H2 is a negative value, namely the pressure equalizing frequency is increased, and the yield improvement of effective components is limited; thirdly, preventing the adsorbent pulverization caused by overlarge pressure drop (change) in unit time and overhigh differential pressure stress born by the adsorbent when the PSA cycle operation process is desorbed, and influencing the service life of the adsorbent: any adsorbent has a certain pressure-resistant range, if the pressure change in the PSA tower is too large, the adsorbent can be caused to frequently bear the pressure difference stress change, and after a long time, the adsorbent can be aged or pulverized, so that the service life and the adsorption efficiency of the adsorbent are influenced, and more importantly, in the PSA circulating process, if the adsorbent is pulverized, the potential safety hazard of dust explosion is brought to the operation of extracting hydrogen from PSA. Without pressure-equalizing PSA, adsorbent powdering problems, especially high pressure adsorption conditions, can occur; similarly, the problem is also caused by less pressure equalizing times, and the embodiment adopts a slow equalizing mode, so that possible pulverization of the adsorbent caused by overlarge system pressure change can be avoided, and meanwhile, the yield of the product H2 can be improved; fourthly, a pressure equalizing mode is adopted, so that the phenomenon of uneven air flow distribution caused by overlarge pressure change in the circulating operation process of the PSA system is prevented, unstable mass transfer and poor efficiency in the adsorption-desorption circulating process are caused, and the product purity and yield are directly influenced: during most PSA operations, it is generally assumed that the distribution of fluid within the adsorption column is uniform, meeting the desired fluid requirements. If the pressure change in the unit operation time of the adsorption tower is overlarge, the fluid distribution in the tower can be caused to generate a mixed flow phenomenon, so that the adsorption mass transfer efficiency is reduced, and the product purity and yield index can be reduced; fifth, the choice of the number of pressure equalizations is also limited by the adsorption-desorption cycle time: since the adsorption and desorption times during a PSA cycle need to be matched to one another, a complete operating cycle can be formed. The general PSA adsorption time is 100-400 seconds(s), the time is too short, the adsorption is insufficient, and the efficiency is low; the long time is easy to cause deep adsorption or supersaturation, and the product purity is reduced and the service life of the adsorbent is shortened due to incomplete desorption or penetration of adsorption. Because the adsorption time is certain, namely the cycle operation time is certain, the pressure equalizing times are too many, and the pressure equalizing time is short every time, so that the desorption is insufficient, the expressed pressure curve is too steep, particularly in the last stage of the desorption, namely in the low pressure or normal pressure or negative pressure range, the most effective desorption stage is caused by the corresponding pressure change, the pressure equalizing times are mostly wasted in the range of higher pressure change, and the pressure equalizing times are another important factor which limits the product yield improvement due to the increase of the pressure equalizing times; sixth, the pressure equalization frequency increases, the reverse impurity (adsorbate) concentration gradient phenomenon also increases, affecting the product purity: during operation of the PSA cycle, the flow direction of the adsorption column receiving the equalization pressure (compensating for the pressure drop) providing the equalization pressure (providing column) is opposite to the flow direction of the product stream receiving the equalization pressure column. The upper section of the tower for receiving the product flowing out of the tower is generally provided with a reserved space, so that trace impurity components carried by the pressure-equalizing downstream gas provided by the tower can be stored; also, in the cyclic operation, the column providing pressure equalization becomes the column receiving pressure equalization, and there is also a problem of a reverse impurity concentration gradient. The longer the cycle operation, the more severe the problem of cumulative reverse concentration gradients, which directly affects product purity and also affects the adsorption efficiency and regeneration of the uppermost adsorbent. This embodiment is through combining together governing valve and programmable valve, adjusts the pressure variation in the PSA cycle process for the pressure curve presents the continuity change, and the pressure curve that avoids traditional PSA voltage-sharing mode to lead to presents the jump type shape: not only has the advantages brought by pressure equalization, but also can avoid the defects brought by excessive pressure equalization times. Namely, through the slow mode of equalling, for example 2 times slow is equalling to the efficiency of 5~6 times voltage-sharing of tradition, can overcome the negative problems that the voltage-sharing brought many times again, for example invest in too high, reverse concentration gradient etc.. The purity of the product H2 obtained in the embodiment is 99.9%, wherein the contents of CO and CO2 are both less than 1-10 ppm, and the yield of the product H2 is more than 85-88%.

Example 3

As shown in FIG. 1, on the basis of example 1, a method for extracting H2 from CO-containing purified terephthalic acid tail gas by pressure swing adsorption, wherein each tail gas generated in the PTA production process is mixed with tail gas generated in the production of other petrochemical products, such as coke oven gas, and the typical component of the mixture is 80% (v/v, the same applies below); 15% of H2; 0.6 percent of N2; 0.6 percent of CO; 0.2 percent of CO 2; 0.01 percent of O2, and 2 percent of other components including VOCs, methane and the like, wherein the VOCs contain various organic acids in the PTA tail gas, benzene, naphthalene, H2S and the like, the pressure of the mixed raw material gas is more than 2.0MPa, the temperature is more than 200-250 ℃, and the flow rate is 3,000Nm3/H, so that the raw material gas of the embodiment is formed and enters the primary purification process. Different from the primary purification process of example 1, a benzene-removing naphthalene-removing column and a disposable Temperature Swing Adsorption (TSA) column are added in the original process so as to remove benzene naphthalene and H2S in the raw material gas. The operation temperature of the debenzolization and naphthalene removal tower and the TSA tower is 70-80 ℃, and the raw material gas directly enters the deoxidation reactor at the temperature. After passing through a deoxidizing device, the alloy has the temperature of 70-80 ℃, the pressure of 2.0MPa, the composition of H2: 89% (v/v, the same below), CO of 7.0% and N2: 1.2%; 0.6 percent of CO2, 1.2 percent of CH4, and 1.0 percent of other CO-containing hydrogen-rich raw material gas comprising a small amount of water, alkali, VOCs and the like, wherein the CO content reaches 7.0 percent. The raw material gas is cooled to 40 ℃ through heat exchange, and enters a PSA system to extract H2, the purity of a product H2 reaches more than 99.5%, wherein the contents of CO and CO2 are both less than 10ppm, and the yield of the product H2 is more than 85%.

Example 4

According to the embodiments 1 and 3, the CO-containing hydrogen-rich raw material gas subjected to the primary purification process (including after deoxidation) is at the temperature of 70-80 ℃ and the pressure of 2.0MPa, and is directly fed into a PSA system for 5-1-3V PSA extraction of H2 without being cooled to 40 ℃ by heat exchange. The PSA system is filled with activated alumina, activated carbon loaded with active components (without additional activation equipment for activation), silica gel, molecular sieves loaded with active components and the like. The PSA system carries out adsorption-desorption alternate cycle operation under the conditions that the adsorption pressure is 2.0MPa and the adsorption temperature is 70-80 ℃, hydrogen with the temperature of 70-80 ℃ and the pressure of 2.0MPa is obtained from the top of the tower, and a product H2 with the temperature of 40 ℃, the pressure of 2.0MPa and the hydrogen purity of more than 99.9% is obtained through heat exchange, wherein the contents of CO and CO2 are less than 1ppm, and the yield of the product H2 is more than 85-88%. Compared with the embodiment 3, the embodiment has the advantages that firstly, the CO-containing hydrogen-rich raw material gas does not need to be cooled first, but the proposed product H2 is subjected to heat exchange, so that the energy consumption is saved; secondly, the PSA system can perform adsorption at the temperature of 70-80 ℃, so that the adsorption and desorption operation processes are easier to match, the incomplete desorption problem caused by deep adsorption is prevented, and the service life of the adsorbent is prolonged; thirdly, the loaded active component-loaded activated carbon adsorbent does not need to be activated by other equipment, and the molecular sieve loaded with the active component can also play a role in selectively adsorbing CO at the temperature, so that the CO concentration in the product H2 is lower, the level of less than 1ppm can be reached, and the quality of the product H2 is higher.

Example 5

According to the embodiments 1 and 2, the CO-containing hydrogen-rich raw material gas subjected to the primary purification process (including after deoxidation) enters a PSA system at the temperature of 10-30 ℃ and the pressure of 4.0-5.0 MPa, wherein an adsorption tower in the PSA system is filled with one or more of activated alumina, activated carbon loaded with active components, silica gel and a CO-specific molecular sieve, and the activated carbon loaded with the active components needs to be filled after activation; the adsorption tower in the PSA system is alternately operated circularly and still adopts a5-1-3V operation mode; through the two-phase control of the program control valve and the regulating valve, the pressure equalizing frequency is 3 times, which is equivalent to the pressure equalizing effect of 6 times, and the hydrogen yield is improved. The product H2 with the temperature of 10-30 ℃ and the pressure of 4.0MPa is generated from the PSA system, the purity is 99.9%, the contents of CO and CO2 are less than 1-10 ppm, and the yield of the product H2 is greater than 85-88%. This embodiment can provide a high pressure product H2.

Example 6

According to the embodiments 1 and 2, the CO-containing hydrogen-rich raw material gas enters a PSA system at the flow rate of 10 kilo-square/hour, the temperature of 40 ℃ and the pressure of 2.0MPa, wherein the PSA system adopts a 10-2-2V operation mode, namely, 10 towers, 2 towers are always in an adsorption state, the rest 8 towers are in each desorption step stage, and the pressure equalization is realized for 2 times by the two-phase control of a program control valve and an adjusting valve, so that the yield of the product H2 is improved, the number of the towers, the valves and the like is reduced, and the investment and the energy consumption are saved. The product H2 with the temperature of 40 ℃ and the pressure of 2.0MPa is generated from the PSA system, the purity of the product H2 is more than 99.9%, the contents of CO and CO2 are both less than 1-10 ppm, and the yield of the product H2 is more than 85-88%.

Example 7

As shown in fig. 3, in order to further recover CO and H2, the desorbed gas generated by the reverse desorption and evacuation/flushing is sent to another Pressure Swing Adsorption (PSA) system, i.e., a two-stage PSA system, by pressurizing (compressor) to the operating pressure of the adsorption tower of the PSA system, and hydrogen-rich gas with a hydrogen concentration close to that of the raw gas entering the PSA system flows out from the top of the adsorption tower of the two-stage PSA system and is mixed with the hydrogen-rich gas to enter the PSA system, so that a greater amount of qualified hydrogen product flows out from the top of the adsorption tower, i.e., further recovering effective hydrogen components from the desorbed gas; the desorbed gas flowing out of the two-stage PSA system is not pressurized, or is directly discharged, or is discharged by combustion, or is merged into a fuel gas pipe network by pressurization, or is used as a raw material required by the carbonylation reaction when the concentration of the enriched CO reaches more than 60-90% (v/v), namely, the CO is further recovered. Wherein, the adsorption tower of the two-stage PSA system is filled with one or more adsorbents of active carbon, active component-loaded active carbon, silica gel, active alumina, molecular sieve and active component-loaded molecular sieve, wherein the active component-loaded active carbon can be subjected to adsorption separation within the operating temperature and pressure ranges of the adsorption tower in the PSA system without being activated; the product H2 from the PSA system has a purity of greater than 99.9% and has a CO and CO2 content of less than 1 ppm. The yield of the product H2 is more than 90-95%.

Example 8

As shown in fig. 4, in order to further recover CO and H2 in the desorbed gas generated by the reverse desorption and evacuation/flushing, the desorbed gas is pressurized to 3.0-5.0 MPa, and is sent to a hydrogen permeable membrane system, the permeated hydrogen-rich gas is mixed with the raw material gas entering a Pressure Swing Adsorption (PSA) system and enters the system, and a larger amount of qualified hydrogen product flows out of the top of the adsorption tower, i.e., effective hydrogen components are further recovered from the desorbed gas; the non-permeable gas is directly merged into a fuel pipe network by regulation without pressurization or is sent out of a boundary area for carbonylation reaction or other required raw materials, namely, CO is further recovered from desorption gas. The purity of the product H2 flowing out of the PSA system is more than 99.9%, wherein the content of CO and CO2 is less than 1-10 ppm. The yield of the product H2 is more than 93-97%.

It should be apparent that the above-described embodiments are only some, but not all, of the embodiments of the present invention. All other embodiments and structural changes that can be made by those skilled in the art without inventive effort based on the embodiments described in the present invention or based on the teaching of the present invention, all technical solutions that are the same or similar to the present invention, are within the scope of the present invention.

Claims

1. CO-containing purified terephthalic acid tail gas pressure swing adsorption H extraction₂The method comprises, as a raw material gas, a gas containing carbon monoxide (CO) and hydrogen (H)₂) After the Purified Terephthalic Acid (PTA) tail gas is subjected to a primary purification process, the CO concentration is 0.01-15% (v/v), the Purified Terephthalic Acid (PTA) tail gas enters an adsorption tower in a Pressure Swing Adsorption (PSA) system with the operation temperature of 10-120 ℃ and the operation pressure of normal pressure to 5.0MPa, and the PSA system is characterized in that the PSA system adopts a multi-tower series or parallel series process of more than 2 adsorption towers, and the alternating cycle operation of adsorption-uniform pressure drop-sequential discharge-reverse discharge-vacuumizing/flushing-uniform pressure rise-final charging is carried out through program control valves, regulating valves and PSA time sequence control program setting in the PSA system, a vacuum pump, a buffer tank, a product tank, a process pipeline and related equipment, wherein the adsorption operation temperature is 10-120 ℃, the operation pressure is normal pressure to 5.0MPa, the pressure equalizing frequency adopted between the adsorption towers is set to be not more than 3 times, vacuumizing or flushing at normal pressure for desorption and regeneration, and allowing the H with purity of more than 99-99.9% (v/v) and CO content of less than 1-10 ppm to flow out from the top of the PSA system₂The product is desorbed gas generated by reverse discharge and vacuum pumping/flushing and is used as byproduct-fuel gas, or CO and H in the desorbed gas are further recovered₂。

2. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂Characterized in that the raw material gas is a CO and H-containing gas produced in the production process of Pure Terephthalic Acid (PTA)₂And tail gas of other components enter raw material gas of a PSA system after a primary purification process, and except that the concentration of CO is 0.01-15% (v/v), the concentration of Volatile Organic Compounds (VOCs) is less than 0.01-2% (v/v), and nitrogen (N)₂) Methane (CH)₄) Carbon dioxide (CO)₂) The concentration of (A) is less than 0.01-15% (v/v), the content of water, alkali and other inorganic components is less than 0.01-3% (v/v), H₂The concentration is more than 60-65% (v/v); the raw material gas may also contain CO and H₂Other gases include coke oven gas, crude gas, synthesis gas, methanol purge gas, acetic acid tail gas, xylene tail gas, styrene tail gas, oxo-alcohol exhaust gas, biomass straw gas,and one or more of various refining off-gases and steelmaking off-gases.

3. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂The method is characterized in that the raw material gas is subjected to a primary purification process, and the raw material gas comprises a raw material gas chiller, a primary cooler, a water washing tower, an acid gas removal tower, an alkaline washing tower, a neutralization tower, a VOCs removal washing tower, an active carbon adsorption tower for removing VOCs, carbon dioxide and the components (C) according to the composition of the raw material gas and the process conditions including the operation temperature, the pressure and the flow rate₂ ⁺) The one or more pretreatment equipment and the process of the cold oil absorption tower, the heat exchanger, the condenser, the air cooler and the compressor comprise that raw material gas subjected to the pretreatment process has the temperature of 10-120 ℃ and the pressure of normal pressure to 5.0MPa, and the main components of the raw material gas are CO and H₂As a direct feed gas to the PSA system.

4. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂The method of (2), wherein one or more columns are always in the adsorption step and the remaining columns are in the desorption regeneration step consisting of pressure equalization, forward discharge, reverse discharge, evacuation/flushing, pressure equalization and final filling.

5. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂The method is characterized in that the adsorption tower in the PSA system is filled with one or more adsorbents of active carbon, active component-loaded active carbon, silica gel, activated alumina, molecular sieve and active component-loaded molecular sieve, wherein the active component-loaded active carbon can be subjected to adsorption separation within the operating temperature and pressure ranges of the adsorption tower in the PSA system without being activated.

6. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂The method is characterized in that the pressure equalizing times adopted among the adsorption towers are not more than 3, the pressure equalizing times are realized by controlling the valve openings of the program control valves and the regulating valves among a plurality of adsorption towers in parallel in the range that the pressure of raw material gas and the operating pressure of the adsorption towers of the PSA system are 1.0-5.0 MPa, and the increase of the number of the adsorption towers caused by more pressure equalizing times which are adopted for preventing overlarge fluctuation of airflow in the adsorption towers due to overlarge pressure equalizing pressure in the operation process of the medium-high pressure PSA system is avoided.

7. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂The method is characterized in that desorption gas generated by reverse release and vacuumizing/flushing is used as byproduct-fuel gas and needs to be pressurized to the grid-connected pressure specified by a fuel gas pipe network.

8. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂The method is characterized in that the desorption gas generated by reverse discharge and vacuumizing/flushing or further recovering CO and H₂The desorption gas is sent to another PSA system, namely a second-stage PSA system, hydrogen-rich gas with the hydrogen concentration close to that of the raw material gas entering the PSA system flows out from the top of the adsorption tower of the second-stage PSA system and is mixed with the hydrogen-rich gas to enter the PSA system, and more qualified hydrogen products flow out from the top of the adsorption tower, namely effective hydrogen components are further recovered from the desorption gas; desorbed gas flowing out of the two-stage PSA system is directly discharged or discharged by combustion, or is pressurized and merged into a fuel gas pipe network, or is used as a raw material required by the carbonylation reaction when the concentration of the enriched CO reaches more than 60-90% (v/v), namely, the CO is further recovered, wherein one or more adsorbents of active carbon, active carbon loaded with active components, silica gel, activated alumina, molecular sieves and molecular sieves loaded with the active components are filled in an adsorption tower of the two-stage PSA system, wherein,the activated carbon loaded with active components can be subjected to adsorption separation within the operating temperature and pressure ranges of the adsorption tower in the PSA system without being activated.

9. The process of claim 1, wherein the CO-containing purified terephthalic acid tail gas is subjected to pressure swing adsorption to extract H₂The method is characterized in that the desorption gas generated by reverse discharge and vacuumizing/flushing or further recovering CO and H₂Pressurizing to 3.0-5.0 MPa, sending the hydrogen-rich gas into a hydrogen permeable membrane system, mixing the permeated hydrogen-rich gas with the raw material gas entering a PSA system, and flowing out more qualified hydrogen products from the top of an adsorption tower, namely further recovering effective hydrogen components from desorption gas; the non-permeable gas is directly merged into a fuel pipe network by regulation without pressurization or is sent out of a boundary area for carbonylation reaction or other required raw materials, namely, CO is further recovered from desorption gas.

10. The process for extracting H from CO-containing purified terephthalic acid tail gas by pressure swing adsorption as claimed in claim 1₂The method is characterized in that a deoxidizing device containing a palladium catalyst can be additionally arranged on the raw material gas after the primary purification process and before the raw material gas enters a PSA system so as to remove trace oxygen (O2) in the raw material gas.