AU2016201267B2 - A plant and process for simutaneous recovering multiple gas products from petrochemical offgas - Google Patents

Abstract

A PLANT AND PROCESS FOR SIMUTANEOUS RECOVERING MULTIPLE GAS PRODUCTS FROM PETROCHEMICAL OFFGAS Abstract The present invention relates to a combined-integrated process and plant for the simultaneous recovery of carbon dioxide, hydrogen and calorific fuel gas from a stream of, such as low-pressure tail gas from a hydrogen steam 10 reforming pressure swing adsorption(PSA) unit of a refinery plant or similar. The invention utilizes at least one of the following adsorbent materials, which may include but not limited to, zeolite x, zeolite A, silica gel, activated carbon, activated alumina and other nano 15 micro porous materials. The invention integrates two or more than two stages of adsorption separation processes. The invented process can produce high purity hydrogen, high purity carbon dioxide and high heat value fuel gas, as a result of separation.

Description

A PLANT AND PROCESS FOR SIMUTANEOUS RECOVERING MULTIPLE GAS PRODUCTS FROM PETROCHEMICAL OFFGAS

FIELD OF THE PRESENT INVENTION

The present invention relates to a process and plant for the simultaneous recovery of high purity carbon dioxide, high purity hydrogen and high calorific fuel gas, from the tail gas from a hydrogen stream reforming pressure swing adsorption (PSA) unit of a refinery plant or similar. The invention utilizes at least one of the following adsorbent materials, which may include but not limited to, zeolite x, zeolite A, silica gel, activated carbon, activated alumina and other nano-micro-porous materials. The invention integrates two or more than two stages of adsorption separation processes. The invention produces high purity hydrogen, high purity carbon dioxide and high heat value fuel gas, as a result of separation.

BACKGROUND OF THE PRESENT INVENTION

Refinery industry consumes a great amount of hydrogen in hydrogen reforming, hydrogen cracking, hydrogen addition and other processes. Steam methane reforming has become a major hydrogen production method since the introduction of pressure swing adsorption into syngas separation in the early 1980s. Such hydrogen fabrication process produces a great amount of carbon dioxide. In addition, the PSA tail gas contains significant amount of hydrogen gas which is generally burned in a furnace to provide heat for the steam reforming process. However, hydrogen, as a high value energy carrier and chemical product, may generate much more economic benefits than simple combustion heat procurement. Furthermore, as is well known, carbon dioxide is a major greenhouse gas contributor to climate change and global warming. There are both environmental and financial benefits to recovering the carbon dioxide and hydrogen contained in the petrochemical tail gas. The world is currently in a great transition period towards a low carbon emission planet and many countries are introducing or have introduced carbon tax/carbon trading scheme to abate carbon dioxide emission and increase energy efficiency. There are many technologies, including cryogenic, liquid absorption, solid adsorption, and membrane, for various separation/purification scenarios and each of them has its own strength and weakness. Pressure/vacuum swing adsorption, due to its commonly recognised energy advantage and material handling simplicity, has been applied in many situations and in different forms. In these cyclic adsorption techniques, a stream of feed gas containing carbon dioxide and other gases is passed through an adsorbent-packed fixed-bed/moving-bed to adsorb CO2/N2/CH4/H2O onto the adsorbent. The C02-rich gas is then produced through a reduction in pressure while on the other end of the adsorption column, a H2-rich gas stream is generated. In these processes, it is usual to employ multi-stage compressor(s) to pressurize the tail gas to > 6 bar.a before further separation can be started. A high pressure PSA system is usually used here to recover/remove the carbon dioxide.

Alternatively, some other processes may use the outlet gas stream from water gas shift reactor, which is often at high pressure, as the feed gas in a high pressure PSA system to remove C02 before sending the processed hydrogen-rich gas stream to the standard hydrogen PSA for high purity hydrogen production. For instance, U.S. Patent Application 2010/0287981 A1 describes various processes for hydrogen and carbon dioxide recovery for a steam reforming system. The target gas stream in that invention is the water gas shift effluent. After the conventional H2 PSA for H2 recovery, the tail gas is firstly compressed to certain pressure before sending to a C02 PVSA and membrane system for C02 recovery. However, this literatures contains no examples, no specific processes (cycles) and no detailed performances. Similarly, in U.S. Patent Application US 2008/0072752 A1, a process based on Pressure Vacuum Swing Adsorption (PVSA) and PSA was employed to first separate C02 then separate hydrogen. The process used in this prior art targets water gas shift effluent gas. U.S. Patent Application 2010/010449 A1 describes a high thermal efficiency hydrogen plant with C02 recovery. The patent application indicates a selection of solvent wash system or a PSA system for C02 removal, though the description is very superficial without the details of actual removal process. Hydrogen containing gas is recycled back to the system with zero steam export. U.S. Patent Application 2011/0011128 A1 describes a single process for recovering carbon dioxide and hydrogen from a steam reformer unit. A co-feed/co-purge is used in the PSA unit to produce higher concentration C02 while producing high purity H2 product. It also describes conceptual C02 purification. A research paper entitled "Recovery of Carbon Dioxide and Hydrogen from PSA Tail Gas", i.e. S Reddy, S Vyas, Energy Procedia 1(2009) 149 -154, mentioned a branded process C02LDSepSM which utilizes a two-stage separation process to recovery carbon dioxide and hydrogen from PSA tail gas. In Stage 1, the tail gas is firstly compressed to relatively high pressure and a cryogenic process is applied to produce liquid carbon dioxide. Stage 2 is a PSA process to purify hydrogen. For PSA Off-Gas scenario, a C02 recovery of 63.1% and a H2 recovery of 74.8% are achieved by the process in discussion. U.S. Patent Application 2010/0111784 A1 describes a liquid scrubbing process to remove carbon dioxide and to purify hydrogen for steam reforming process. U.S. Patent 7,695,545 B2 describes a PSA process for separating hydrogen from 5-50% hydrogen containing gas stream. The process uses multiple columns to perform gas separation with certain cyclic pressure profiles. The process contains one adsorption step, at least two pressure equalization steps(gas withdraw), a providing purge step, a blowdown step, a purge step, at least pressure equalization steps(gas introduction) and a repressurization step.

Based on these literature review, it is found that our simultaneous recovery of carbon dioxide and hydrogen from the tail gas of a refinery stream reforming hydrogen PSA unit, is intrinsically different from the known techniques mentioned above.

First, prior arts generally use the water gas shift effluent gas stream as feed gas. The present invention specifically focuses on the processing of the tail gas from a standard hydrogen PSA unit equipped at a steam methane reforming hydrogen production unit(referred to as 'SMR-H2PSA' in order to differentiate from the H2PSA employed in this system.)

Secondly, in this particular situation, the carbon dioxide concentration is high (~50%)but not significantly high enough for a simple process as mentioned in the patent AU2008-001831 / US 20110005389, and the gas is saturated with moisture at low temperatures. The hydrogen concentration is low (~20%), whereas, a typical hydrogen PSA feed gas contains more than 70% hydrogen.

Thirdly, the feed gas pressure (from SMR-H2PSA) is low (~40kPa.g), whereas the reported PSA C02/Hydrogen separation processes typically require >6 bar.a pressure. In order for the gas product to obtain high commercial value, the gases will require purification to a high quality of >99% CO2 and 99.99% H2. The prior art techniques described above put forward some superficial concepts and none of them include a specific H2PSA and C02VSA recovery hybrid system to achieve high purity hydrogen and high purity carbon dioxide simultaneously from the SMR-H2PSA tail gas.

Therefore, the present invention is to provide a specific process/plant suitable for this application to recover high purity hydrogen, high purity carbon dioxide and high calorie fuel gas at the same time with a low energy penalty.

SUMMARY OF THE INVENTION

The present invention relates to a process and plant for the simultaneous recovery of high purity carbon dioxide, high purity hydrogen and high calorific fuel gas, from a low pressure gas stream such as the tail gas from a hydrogen stream reforming pressure swing adsorption(PSA) unit of a refinery plant or similar. The invention utilizes at least one of the following adsorbent materials, which may include but not limited to, zeolite x, zeolite A, silica gel, activated carbon, activated alumina and other nano-micro-porous materials. The invention may include at least two stages of adsorption separation processes. The present invention provides a specific process/plant suitable for this application to recover high purity hydrogen, high purity carbon dioxide and high calorie fuel gas at a low energy penalty.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, of which:

Figure 1 is a brief representation of process for the invention;

Figure 2 is the detailed flow diagram example of process and plant;

Figure 3 is a schematic chart illustrating eight operating sequences of the vessels of Stage 1 (C02-VSA) shown in Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a low energy cost process for recovery of high purity carbon dioxide, high purity hydrogen and high calorie fuel gas at the same time. As depicted in Figure 1, the present invention comprises two stages: a CO2 vacuum swing adsorption (VSA) stage and a H2 pressure swing adsorption (PSA) stage.

The first stage, is a vacuum swing adsorption process for recovering carbon dioxide from a SMR-H2PSA tail gas ('referred to as the Feed Gas to the process in this invention'), the process including the steps of: a) adsorbing C02 onto an adsorbent from the feed gas stream at a particular or known pressure so as to convert the feed gas stream into a stream lean in carbon dioxide but rich in hydrogen; and b) reducing adsorber pressure through at least one co-current pressure equalizations. C02 gets further concentrated in the columns. C02 lean gas enters other columns counter-currently from the top to pressurize columns. c) introducing product carbon dioxide into the column as a purge step ('C02 product purge or heavy reflux'). Other light components are pushed out of the column and C02 gets further concentrated. Effluent of the step has two ways to treat: one is to send the stream to 002 lean stream; the other is to send the stream to another column for a 002-lean gas counter-current purge to improve the recovery of hydrogen and carbon dioxide. d) reducing adsorber pressure through at least one co-current pressure equalizations. C02 gets further concentrated in the columns. C02 lean gas enters other columns counter-currently from the top to pressurize columns. e) reducing adsorber pressure by connecting the column to a vacuum pump to recover the adsorbed carbon dioxide from the adsorbent ('Evacuation step'). Water vapour is removed simultaneously. f) introducing C02 lean gas counter-currently into the adsorber column from the top while the vacuum pump is still connected to the adsorber ('light reflux' ). As aforementioned, such C02 lean gas may be from C02 purge effluent or from the H2-rich gas generated during adsorption step. g) pressurizing adsorber through at least one counter-current pressure equalizations. H2 reenters the columns . h) re-pressurizing adsorber by introducing H2-rich gas or feed gas into the column.

The C02 lean gas generated in Step a) is compressed to a certain pressure before sending to the second stage for further processing ('referred to as the intermediate gas') .

The second stage, is a pressure swing adsorption process for recovering high purity hydrogen from the hydrogen-rich gas generated during Step a). The H2PSA stage itself is not meant to be limited by the H2PSA process shown in this invention. Accordingly, standard PSA unit for hydrogen production known in prior arts may be used in the process. The process including the steps of: i) adsorbing adsorptive gas components onto an adsorbent from a feed gas stream at a particular or known pressure so as to convert the feed gas stream into a stream rich in hydrogen (which is non-adsorptive); ii) reducing adsorber pressure through at least one co-current pressure equalizations. Adsorptive gas components gets further concentrated in the columns. Relatively H2-enriched gas enters other columns counter-currently from the top to pressurize columns. iii) introducing adsorptive gas streams back into the column as a purge step co-currently. H2 gas is further pushed out of the column to increase H2 recovery. Effluent of the step has two ways to treat: one is to send the stream to H2 product; the other is to send the stream to another column for a hydrogen product counter-current purge to improve the recovery and productivity of hydrogen. iv) reducing adsorber pressure through at least one co-current pressure equalizations. Relatively H2-enriched gas enters other columns counter-currently from the top to pressurize columns. v) reducing adsorber pressure by connecting the column to a vacuum pump to remove the adsorbed gas components from the adsorbent. Water vapour, if any, is removed simultaneously. vi) introducing H2-rich gas counter-currently into the adsorber column from the top while the low pressure H2-lean gas tank is still connected to the adsorber. As aforementioned, such H2-rich gas may be from heavy purge effluent or from the H2 product gas generated during adsorption step. vii) pressurizing adsorber through at least one counter-current pressure equalizations. H2 reenters the columns . viii) re-pressurizing adsorber by introducing H2-rich gas or feed gas into the column.

The term "high purity gas stream" throughout this specification means a gas stream containing at least 90% C02 by weight and suitably at least 97 or 99% C02 by weight.

In an embodiment, the feed gas for Stage 1 contains C02 at an amount equal to or greater than 30 - 50% by weight.

The feed gas for Stage 1 may also contain any one or a combination of moisture (H20) , CH4 , H2, CO, N2, 02 or any other trace elements. In the situation where the feed gas stream contains moisture, suitably the feed gas is saturated with water vapour.

In an embodiment for Stage 1, the adsorbent is contained in an adsorber vessel and the gas feed is supplied to the adsorber vessel at a pressure ranging from atmospheric pressure to 0.5 bar gauge.

In an embodiment for Stage 2, the adsorbent is contained in an adsorber vessel and the gas feed is supplied to the adsorber vessel at a pressure ranging from 5 bar gauge to 11 bar gauge.

In an embodiment for Stage 1, the feed gas exposed to the adsorbent is at a temperature of less than or equal to 60°C and suitably, in the range from 10 to 40°C.

The adsorbent may be any suitable adsorbent including zeolites, aluminas, silica gels, activated carbons, or any other solid granular material that can selectively adsorb C02 over non-C02 species in the gas stream for Stage 1. For Stage 2, the adsorbent may be any suitable adsorbent including zeolites, aluminas, silica gels, activated carbons, or any other solid granular material that can selectively adsorb CH4/C0/N2/02 in the gas stream. Many adsorbents such as zeolites or aluminas or silica gel will also adsorb water from the gas stream. A multiple-layering may be needed for Stage 1 considering high relative humidity and other trace impurities.

Throughout this specification the terms "column" and "vessel" are used synonymously and also embrace a reactor and chamber.

In the situation where two or more vessels contain the adsorbents, suitably, the process also includes a further step of interconnecting the vessels in fluid communication after Steps a) and b), or immediately after Steps a) and b) have been carried out on either one of the respective vessels. For example, in the situation where the first vessel is subject to Step a) and the second vessel is subject to Step b), connecting the vessels in fluid communication will result in an initial pressure reduction in the first vessel by gas flowing from the first vessel to the second vessel. Similarly in the situation where the first vessel is subject to Step b) and the second vessel is subject to Step a), connecting the vessels in fluid communication will result in an initial pressure reduction in the second vessel by gas flowing from the second vessel to the first vessel and, in turn, desorbing C02 from the absorbent in the second vessel and absorbing C02 onto the adsorbent in the first vessel. One of the advantages of this preferred aspect of the present invention is that interconnecting the vessels in this manner is that it lowers the energy load on the vacuum pumps or blowers that are used to depressurize vessels containing loaded adsorbent. In addition, interconnecting the vessels in this manner avoids loss of C02 that has been adsorbed onto the adsorbent to the atmosphere and, therefore, maximizes C02 recovery.

In an alternative embodiment in which two or more vessels are provided, the process includes interconnecting the vessels in fluid communication in which at least one of Steps a) and b) is at the end of being carried out (or has been completed), whereby when Step a) has or is being carried out in one of the vessels, communication between the vessels facilitates at least partial depressurization of the respective vessel from the operative pressure of Step a), and when Step b) has or is being carried out in one of the vessels, communication between the vessels facilitates at least partial repressurization of the respective vessel from the operative pressure of Step b).

In an embodiment, the vessels are connected in the fluid communication between each cycle of adsorbing and desorbing of C02 for a period of at least 1 second, and suitably in the range of the 1 to 4 seconds and even more suitably approximately 2 seconds.

In an embodiment, Step a) is carried out for a period of at least 5 seconds and suitably in the range of 5 to 15 seconds and even more suitably approximately 10 seconds .

In an embodiment, Step b) is carried out for a period of at least 5 seconds and suitably in the range of 5 to 15 seconds and even more suitably approximately 10 seconds .

In an embodiment, Step c) is carried out for a period of at least 15 seconds and suitably in the range of 5 to 25 seconds and even more suitably approximately 10 seconds.

In an embodiment, Step i) is carried out for a period of at least 5 seconds and suitably in the range of 5 to 15 seconds and even more suitably approximately 10 seconds .

In an embodiment, Step ii) is carried out for a period of at least 5 seconds and suitably in the range of 5 to 15 seconds and even more suitably approximately 10 seconds .

In an embodiment, Step iii) is carried out for a period of at least 15 seconds and suitably in the range of 5 to 25 seconds and even more suitably approximately 10 seconds.

In another configuration as shown in Figure 2, a multiple-step carbon dioxide vacuum swing adsorption process is used.

The first step, also known as the feed step, is to introduce the C02-containing gas (with moisture) Stream 100 emitted from the process into an adsorber column or vessel(11a,lib,12a,12b,13a,13b,14a,14b) through switch valves, such as 101a, at a pressure above ambient pressure in the range 0-0.50 kPa.g but typically 0.30- 0.40 kPa.g. The adsorber vessel contains at least one adsorbent that can preferably adsorb carbon dioxide at the feed pressure and temperature. These adsorbents include zeolites, aluminas, silica gels, activated carbons, or any other solid granular material which is selective for C02 over the non-C02 species in the gas stream. The effluent gas Stream 200 from the adsorption step, also known as the C02-lean gas here, is sent into waste tank 33 then sent to downstream for further processing. Many adsorbents such as zeolites or aluminas or silica gel will also adsorb water from the gas stream.

The adsorption step is followed by one or more cocurrent depressurization step, where the flow to the adsorber is stopped by switching off the solenoid valve, such as 101a, and effluent gas flows out into a second adsorption vessel which just finished its pressure reduction step (either evacuation or pressure let-down) through pressure equalization line switch valves, such as lOld or lOle, hence is at a low pressure. In this step, the vessel is depressurized and the overall gas purity is increased.

The next step is to introduce C02 product gas from product tank 36 back into the adsorption column counter-currently under low pressure through switch valves, such as 101b. Weakly adsorbed gas species will be pushed out when the C02-rich product gets re-adsorbed onto the adsorbent. The effluent gas is either sent to waste gas stream entering tank 33 or sent to another column as C02-lean gas stream purge, depending on cycle configurations, as depicted in Figure 3.

This C02-rich product gas purge step may be followed by one or more co-current depressurization step, where the flow to the adsorber from the bottom is stopped by switching off the valves, such as 101a. The effluent gas flows out into a second adsorption vessel which just finished its pressure reduction step (either evacuation or pressure let-down) and hence is at a low pressure.

The next step is to remove the C02 from the adsorbent by a reduction in pressure through connecting vacuum pump 35 to the bottom of the column and opening column bottom valves, such as 101c. This is done counter-currently to the feed direction by means of a vacuum blower or vacuum pump. The C02 rich product gas is stored in a product gas tank .

The next step is a counter-current light reflux step. C02-lean gas stream may be sourced from adsorption effluent stream (such as stream 200) or from C02-rich product purge step effluent. The C02-lean gas stream helps to push out residual C02 in the adsorbent void and adsorbed on the adsorbent. During this step, the vacuum pump 35 is still connected to keep the system under certain vacuum pressure.

The light reflux step is then followed by one or more counter-current pressurization (this is the complementary step to the co-current depressurization) to receive effluent gas from the adsorption vessel in the co-current depressurization step and this step not only increases the pressure but also cleans the top of the vessel by low concentration carbon dioxide effluent.

Finally, a feed pressurization (stream 100) or waste pressurization (stream 200) is added to raise the vessel pressure to its feed value before repeating the cycle.

These steps are repeated alternatively in a cyclic manner using multiple beds from 1 to 8. Importantly, unlike all previous C02 capture cycle which doesn't have a unique combination of light reflux purge step and heavy purge under vacuum pressure, the process described does utilize these. Surprisingly, we are able to produce > 99% C02 product stream and >86% C02 recovery with such combination. This is a great improvement in performances and it could generate great savings for possible C02 purification. Even better, in certain situations, further purifications are not needed for the production of industry grade carbon dioxide.

In a variation of the first embodiment, the feed gas stream contains C02, CH4, N2, 02, CO, H2 and moisture at a pressure of approximately Obar.g~0.5bar.g and a temperature of 10°C to 40°C, where C02 is the strongly adsorbed component. The adsorbent is selected from X or Y type zeolites.

In another variation of the first embodiment, the adsorption step has a duration of around 10 seconds, the co-current depressurization and the coupled counter-current pressurization have duration of around 2 seconds each, the C02 product purge step has duration of around 5 seconds, the evacuation step has duration of around 10 seconds, the light reflux step has duration of around 5 seconds and the repressurization step has duration of around 2 seconds .

In another variation of the first embodiment, the flow direction in the depressurization step is co-current to the feed gas flow direction and the flow direction in the pressurization is counter-current to the feed gas flow direction.

In another variation of the first embodiment, the flow direction in the evacuation step is counter-current to the feed gas flow direction. The evacuation pressure is in the range of 2-50 kPa absolute.

As shown in Figure 3, the embodiments include unique combinations of a C02-rich heavy product reflux and a C02-lean light reflux and this process can be successfully utilized to separate and recover the carbon dioxide from refinery SMR-H2PSA tail gas. The feed gas stream processed contains a certain amount of moisture which is closed to saturated level at the ambient conditions. Furthermore, this invention can also be easily applied to other C02 recovery/removal applications with similar feed gas conditions, especially in the food and beverage industry and oil/gas industry.

The effluent gas 200 during Step a) is firstly compressed by a multiple-stage compressor to certain pressure before sending to a hydrogen PSA for further processing, which is a known practice for those skilled in the art. However, different from U.S. Patent 7,695,545 B2 which claims a pressure delta ratio ΔΡ2/ΔΡ1 (ΔΡ1: pressure reduction from pressure equalization to provide purge; ΔΡ2: pressure reduction from provide purge step to blowdown step) of >2.0 and >4.0, this invention used a ΔΡ2 /ΔΡ1 is ~1.75. In the configuration depicted in Figure 2, the H2PSA in this invention has 8 columns, three pressure equalizations and two column simultaneous feed cycle. However, for those skilled in this art, many variations based on conventional H2PSA may be utilized.

Another beneficial advantage for this invention is that the feed SMR-H2PSA tail gas 100 is usually burned in the steam reformer to provide heating energy and its heat value is relatively low, 2475 kcalorie/Nm3. Through the removal of C02, the fuel gas stream 500 generated in this invention has a high heat value of ~ 5400 kcalorie/Nm3. Such high heat value stream, mainly methane and carbon monoxide, may be used as fuel in the steam reformer or other scenarios requiring energy injection.

In summary, through the process in this invention, low value SMR-H2PSA tail gas are split into three product gas streams: H2, C02 and fuel gas. The overall carbon footprint has been greatly reduced and the high purity may be sold directly as an industry grade C02, though further purification may produce high value food grade C02 . The utilization of vacuum swing technology in the invention avoids the energy-intensive compressing of the tail gas as conventional C02 separation needed. Great energy savings are achieved here. The recovery of H2 from tail gas greatly improved the overall H2 production efficiency (8-10% increase of overall recovery) and generates great economic value. The large stream of high heat value fuel gas may be used a good energy provider in various scenarios. This invention improves the SMR-H2 process efficiency, reduce carbon emissions and provides great economic benefits.

Example

The present invention will now be described with reference to the non-limiting examples.

Example 1 A separation plant having the configuration shown in Figure 1 was constructed numerically. Each vessel Stage 1 had a diameter of 300 cm, a working length of 150 cm and was packed with silica gel and zeolite NaX adsorbent with a volume ratio of 1:5. After obtaining simulation data, the process was scaled up with the following parameters set:

Feed pressure: 0.40 bar. absolute

Vacuum pressure: 0.10 bar. absolute C02 Product Purity: 96 -99% C02 Recovery: 90% C02VSA adsorber number: 8 H2PSA adsorber number: 8 H2PSA pressure: 8 bar.a H2 recovery: 86% H2 purity: 99.99%

Refinery H2PSA recovery (assumed): 90%

Overall H2 recovery in this invention: 98.60%

Increase of H2 recovery: 9.56% A simple cost-benefit would reveal the environmental and financial benefits of this invention, as this invention produces three value products from low value SMR-H2PSA tail gas: high purity hydrogen, high purity carbon dioxide and high heat value fuel gas.

Those skilled in the art of the invention will appreciate that many variations and modifications may be made to the specific embodiment and examples without departing from the spirit and scope of the invention.

It should be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims (18)

1. A PLANT AND PROCESS FOR SIMUTANEOUS RECOVERING MULTIPLE GAS PRODUCTS FROM PETROCHEMICAL OFFGAS Claims The invention claimed is:

   1. A combined-integrated process for separating hydrogen and carbon dioxide and generating a high heat value stream from refinery steam methane reforming Hydrogen PSA (SMR-H2PSA) tail gas in a multiple stage adsorption process each containing a plurality of adsorption columns packed with adsorbents selective for at least one more strongly absorbable component. Each of the plurality of adsorption beds in each stage operates in a cyclic manner. The process comprising: (a) a low pressure carbon dioxide vacuum swing adsorption (C02VSA) process for producing high purity C02 from steam methane reforming hydrogen PSA (SMR-H2PSA) tail gas; (b) compressing the C02-lean gas generated from C02VSA to certain pressure; (c) a hydrogen pressure swing adsorption (H2PSA) process for producing high purity H2 from the C02-lean gas generated from C02VSA; (d) producing high heat value fuel gas for steam reformer or other energy-demanding situations.
2. 2. The process of Claim 1 wherein the feed gas for the overall combined process is the hydrogen-lean low pressure tail gas from a typical hydrogen PSA system, typically installed at a refinery steam methane reforming-based hydrogen production unit.
3. 3. The process of Claim 1 wherein the feed gas has a pressure of 0-50kPa.g and a temperature of 10-50C°.
4. 4. The process of Claim 1 wherein the process comprised at least two-stage integrated adsorption processes (at least one VSA and one PSA).
5. 5. The process of Claim 1 where the C02 lean gas from the C02VSA system is compressed to a pressure of 2-12 bar.a, which is then sent to the H2PSA unit.
6. 6. The process of Claim 1, wherein the H2PSA is a process for selectively separating hydrogen from at least on more strongly absorbable component in a pressure swing adsorption process comprising multiple adsorption columns, each packed with adsorbent adsorbing at least one strongly adsorbable component. Though a conventional H2PSA may be applied, the process in this invention comprising (a) a providing purge step, a step pressure drop ΔΡ1; (b) a blowdown step, a step pressure drop ΔΡ2; (c) ΔΡ2/ ΔΡ1 < 2, preferably between 1.5 - 2.0, more preferably between 1.7 - 2.0.
7. 7. A process for selectively separating carbon dioxide from SMR-H2PSA tail gas stream that contains hydrogen, carbon monoxide, carbon dioxide, nitrogen, methane and water vapour, said process comprising the following steps: (a) an adsorption step introducing the tail gas into the C02VSA process to generate a C02-lean gas stream effluent; (b) one or more co-current pressure reduction steps in the form of pressure equalization with other adsorption columns; (c) a C02-rich product purge step introducing C02-rich product gas stream back into the adsorption column to improve C02 purity; (d) a C02-rich product purge step generating C02-lean effluent gas stream to be put in waste streams or to be used as light reflux source gas; (e) an evacuation step to reduce the adsorption column total pressure to produce high purity C02 product; (f) a C02-lean light reflux/purge step introducing C02-lean gas streams under vacuum pressure to further clean the columns after evacuation step; (g) a light reflux stream sourced from C02-adsorption step effluent or from C02-rich product purge step effluent; (h) one or more counter-current pressurisation steps in the form of pressure equalization with other adsorption columns; (i) a re-pressurisation step introducing feed gas (tail gas from SMR-H2PSA) or the intermediate C02-lean gas coming out of the top of the C02VSA columns to re-pressurize the columns before commencing an adsorption step.
8. 8. The process of Claim 7, wherein the adsorbents selectively for carbon dioxide adsorption, include zeolite A, zeolite X, zeolite Y, activated carbon, activated alumina, metal organic framework, silica gel.
9. 9. The process of Claim 7, wherein the adsorption step pressure is in the range of atmospheric pressure to 0.5bar gauge..
10. 10. The process of Claim 7, wherein the evacuation step pressure is in the range of 2-50kPa.a.
11. 11. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, C02 purge, co-current pressure equalization, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, CQ2-lean gas repressurization.
12. 12. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, co-current pressure equalization, C02 purge, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, C02-lean gas repressurization.
13. 13. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, C02 purge 2, co-current pressure equalization, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, C02-lean gas repressurization.
14. 14. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, co-current pressure equalization, C02 purge 2, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, C02-lean gas repressurization.
15. 15. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, C02 purge, co-current pressure equalization, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, feed gas repressurization.
16. 16. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, co-current pressure equalization2, C02 purge, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, feed gas repressurization.
17. 17. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, C02 purge 2, co-current pressure equalization2, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, feed gas repressurization.
18. 18. The process of Claim 7, wherein the step sequences are adsorption, co-current pressure equalizationl, co-current pressure equalization, C02 purge 2, evacuation, light reflux, counter-current pressure equalization 1, counter-current pressure equalization 2, feed gas repressurization.