FORM 2
THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10, rule 13) 1. Title of the invention: HYBRID GAS PURIFICATION
2. Applicant(s)
NAME NATIONALITY ADDRESS
HINDUSTAN PETROLEUM Indian Hindustan Petroleum Corporation
CORPORATION LIMITED Ltd., Petroleum House, 17,
Jamshedji Tata Road, Churchgate, Mumbai 400020, India
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.

TECHNICALFIELD
[0001] The present subject matter relates, in general, to gas purification
and, in particular, to purification of a mixed gas feed to produce a product gas.
BACKGROUND
[0002] Gases, such as hydrogen, oxygen and nitrogen are widely used in
fertilizer industries, chemical processing plants, refineries, and steel industries. For example, pure hydrogen is used for desulfurization of petroleum products in refineries, in fertilizer industries, and for fats and oil hydrogenation. The gases are generally produced at industrial scale by utilizing gas purification techniques. One such gas purification technique is Pressure Swing Adsorption (PSA). The PSA technique is used for separation and purification of hydrogen from a mixed gas feed containing one or more undesirable gases as impurities.
[0003] The PSA technique generally includes subjecting the mixed gas
feed to a cyclic process of adsorption, desorption, and regeneration through sequential valve operations. During adsorption, the mixed gas feed is introduced at high pressure to adsorption beds within a PSA unit. The high pressure of the mixed gas feed facilitates loading of gas molecules of the impurities on adsorbent surface to separate the impurities from the mixed gas feed and provide hydrogen gas. Desorption is performed by decreasing pressure of the adsorption beds and separating the impurities from the adsorption materials to obtain regenerated adsorption beds.

BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The detailed description is described with reference to the
accompanying figures. In the figures, the left-most digit of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference the same elements.
[0005] FIG. 1 illustrates a gas purification system, in accordance with an
implementation of the present subject matter; and
[0006] FIG. 2 illustrates a flowchart of a method of purifying a mixed gas
feed to produce hydrogen, in accordance with an implementation of the present subject matter.
DETAILED DESCRIPTION
[0007] Generally, product gases are obtained at industrial scale by
utilizing gas purification units installed in industries and chemical processing plants to purify large volume of gases. The gas purification units may have multiple vessels or adsorption beds having adsorption materials through which a mixed gas feed having other gases and particles as impurities is passed. During supply of the mixed gas feed to the multiple adsorption beds, the adsorption materials adsorb the impurities from the mixed gas feed and provide a pure form of a product gas. The multiple adsorption beds are used for purifying large volumes of mixed gas feed and therefore, with time, may become saturated and show reduced adsorption efficiency.
[0008] To regain the adsorption efficiency, the adsorption materials are
generally regenerated at a positive pressure. The regeneration of the multiple adsorption beds may separate the impurities from the adsorption material such that the adsorption beds may regain adsorption efficiency and can be used for subsequent cycles of purification.
[0009] However, regenerating the adsorbent materials at the positive
pressure may have lower efficiency of regeneration and reduced desorption efficiency of the regenerated adsorption materials. Therefore, such regenerated

adsorption materials may have decreased efficiency of separating the impurities from the mixed gas feed and may have to be regenerated in short intervals, thereby reducing overall efficiency of the process.
[0010] Also, the product gas supplied by such gas purification units is
generally impure and includes traces of impurities in form of other gases and particles. Such impurities in the product gas may alter properties of the product gas and may affect usage and application of the product gas. For instance, the impurities may reduce calorific value of the product gas, thereby reducing burning efficiency of the product gas in furnaces.
[0011] Further, the gas purification units utilize large adsorption beds
having bulk amount of adsorption materials to treat the mixed gas feed and supply the product gas. Such large adsorption beds and bulk amount of adsorption materials occupy large space and incur high capital and running expenses for the industries.
[0012] The present subject matter describes a gas purification system to
purify a mixed gas feed and provide a product gas. In an implementation, the gas purification system may include a Rotating Packed Bed (RPB) unit and a Pressure Swing Adsorption (PSA) unit coupled to the RPB unit. The RPB unit may include a gas inlet, a solvent inlet, a solvent outlet, and a gas outlet. The PSA unit may include an inlet, multiple adsorption beds, a product gas outlet and an impure gas outlet. In an implementation, the inlet of the PSA unit may be coupled to the gas outlet of the RPB unit to receive a gas treated by the RPB unit.
[0013] In an implementation of the present subject matter, the gas inlet of
the RPB unit may receive a mixed gas feed. The mixed gas feed may include multiple impurities, such as bulk impurities and finer impurities. For example, the bulk impurity may include heavy hydrocarbons, and carbon dioxide gas Finer impurities may include light hydrocarbon impurities, inert gases like Nitrogen, Argon, , and carbon monoxide. The solvent may be utilized to eliminate a first set of impurities from the mixed gas feed in the RPB unit to obtain an enriched gas. The enriched gas may then be supplied through the gas outlet to the PSA unit. It

would be noted that the first set of impurities may include one or more impurities present in the mixed gas feed, such as heavy hydrocarbons, light hydrocarbons, and carbon dioxide gas.
[0014] The inlet of the PSA unit may receive the enriched gas through the
gas outlet of the RPB unit. The enriched gas may then be passed through multiple adsorption beds in the PSA unit. In an aspect, the multiple adsorption beds may adsorb a second set of impurities from the enriched gas to obtain a product gas. The product gas may then be supplied through the product gas outlet of the PSA unit. The second set of impurities may include one or more impurities present in the enriched gas, such as one or more finer impurities and may be removed from the PSA unit through the impure gas outlet.
[0015] Thus, the gas purification system purifies a mixed gas feed to
produce a product gas efficiently by removing bulk impurities in the RPB unit and the finer impurities in the PSA unit. The gas purification system facilitates a compact PSA unit having reduced quantities of adsorbent materials for purification of the gas. Further, the gas purification system facilitates purification of the mixed gas feed and regeneration of the adsorption beds at lower or negative pressures. Therefore, the gas purification system is space and process efficient and saves capital and running expenses. Further, the gas purification system reduces amount of hydrocarbon gas processed in a given time in a given space thereby enhancing safety of a user operating the gas purification system.
[0016] The following detail description describes the gas purification
system and its uses in detail. While aspects of the gas purification system can be implemented in any number of different applications, the gas purification system as per the present subject matter is described in the context of the following exemplary implementations.
[0017] FIG. 1 illustrates a gas purification system 100, in accordance with
an implementation of the present subject matter. The gas purification system 100 may include a Rotating Packed Bed (RPB) unit 102 and a Pressure Swing Adsorption (PSA) unit 104 coupled to the RPB unit 102. In an example, multiple

RPB units may be used instead of single RPB unit 102. The multiple RPB units may be connected in either series or in parallel to each other. In an implementation, the RPB unit 102 may include a gas inlet 106, a gas outlet 108, a rotor 110 housed in a rotor vessel (not shown in the figure) and a shaft 112.
[0018] The gas inlet 106 may be coupled to the rotor vessel to receive a
mixed gas feed. In an example, the gas inlet 106 may either be an inlet nozzle or a central hollow pipe to receive the mixed gas feed and the gas outlet 108 may be a central hollow pipe to supply an enriched gas. The rotor 110 may be a movable part of the RPB unit and may include one or more sets of concentric rings of packing elements 114, stacked together in a manner as shown in the figure. The rotor 110 may also include one or more sets of metallic rings (not shown in the figure). In an implementation, the sets of metallic rings may be placed in between the sets 114 of the concentric rings at regular or variable intervals. Placement of the metallic rings in between the sets of the concentric rings 114 helps in achieving a desired stiffness or mechanical strength of the rotor 110 thereby reducing fatigue in the rotor 110.
[0019] In an example, the rotor 110 may be housed inside a rotor vessel
(not shown in the figure). The rotor 110 may further include one or more metallic plates 116-1 and 116-2, individually referred to as the metallic plate 116 and collectively referred to as the metallic plates 116, hereinafter. In an example, the metallic plates 116 may be circular in shape. In an example, the metallic plates 116, the sets of the concentric rings 114 and the metallic rings may be stacked together using a plurality of fasteners, such as a tie-rod. Further, the metallic plate 116 may have a gap 118 for facilitating inflow of a solvent and outflow of a product gas.
[0020] In an implementation, the shaft 112 may be a low weight metallic
shaft with one end of the shaft 112 connected to a motor (not shown in the figure) through a removable coupling. The motor may facilitate rotation of the shaft 112 and thereby rotation of the rotor 110. On the other end, the shaft 112 may be connected to the metallic plate 116-1 through a flange (not shown in the figure).

In an example, mechanical seals may be connected to the shaft 112 and the rotor vessel for averting any leakage of the solvent and the mixed gas feed from inside the rotor vessel to outside environment. A solvent inlet pipe 120 may be close to the gas outlet 108 for facilitating inflow of a solvent. Further, the solvent may outflow from the RPB unit 102 through a liquid outlet 122. The solvent may include bulk impurities. In an implementation, the RPB unit 102 may include a solvent distribution system to uniformly distribute and contact of gas and liquid inside the RPB unit (102).
[0021] In an implementation of the present subject matter, the PSA unit
104 may include an inlet 124, and multiple adsorption beds 126-1, 126-2, …… 126-n. For ease of explanation, four adsorption beds 126-1, 126-2, 126-3, and 126-4 have been described in the figure. However, it would be noted that there may be more than four adsorption beds in the PSA unit 104 based on amount of gas to purify. The multiple adsorption beds 126-1,…., 126-n have been collectively referred to as adsorption beds 126 and individually as adsorption bed 126. Further, the PSA unit 104 may include a product gas outlet 128, and an impure gas outlet 130. The inlet 124 may be a feed inlet line coupled to the gas outlet 108 of the RPB unit 102 to receive the enriched gas from the gas outlet 108 and supply the enriched gas to the adsorption beds 126.
[0022] The adsorption beds 126 may include adsorption materials having
porous solids with high surface area to adsorb finer impurities remaining in the enriched gas. In an implementation, one of the adsorption beds 126-1 may include different layers of adsorbent materials. For instance, the adsorption bed 126-1 may include a mixture of aluminum and silicon based adsorbent material as first layer 132-1 placed at the bottom of the adsorption bed 126-1, followed by a second layer 134-1 of carbon based adsorbent material above the first layer 132-1, followed by a third layer 136-1 of zeolite based adsorption material above the second layer 134-1 and followed by a fourth layer 138-1 of cation exchanged zeolite based adsorbent material above the third layer 136-1. In a similar manner, the adsorbent bed 126-2 may include four layers 132-2, 134-2, 136-2, and 138-2,

adsorbent bed 126-3 may include 132-3, 134-3, 136-3, and 138-3, and adsorbent bed 126-4 may include the four layers of adsorbent materials 132-4, 134-4, 136-4, and 138-4. In an example, the multiple layers of adsorption material may be selected based on type of impurities which are to be eliminated by adsorption beds 126 within each zone.
[0023] In an example, the different adsorbent materials may adsorb
different types of impurities from the enriched gas. For example, the aluminum silicon mixture may adsorb moisture and heavy hydrocarbon impurities, the carbon based adsorbent material may adsorb light hydrocarbon impurities and carbon dioxide. Further, the zeolite based adsorbent material may adsorb dilute impurities as light hydrocarbons and carbon monoxide and the cation exchanged zeolite based adsorbent material may adsorb inorganic impurities such as carbon monoxide, Oxygen, Nitrogen, and Argon.
[0024] The adsorption beds 126 may be arranged within the PSA unit 104
such that one or more adsorption beds 126 may be removed from the PSA unit 104 and one or more adsorption beds may be added to the PSA unit 104, while the unit is operating, with a smooth switching over algorithm intended for ease of operation and enhanced intrinsic safety of the plant. Further, the dimensions, such as length, capacity and diameter may be determined based on amount of enriched gas feed to be purified by the adsorption beds 126.
[0025] In an implementation, a pure product gas may outflow through the
product gas outlet 128, and impurities may be removed in form of an impure gas through the impure gas outlet 130. In another implementation, a vacuum regeneration unit (not shown in the figure) may be coupled to the PSA unit 104. In an example, the vacuum regeneration unit may be a vacuum pump to apply a negative pressure on the multiple adsorption beds 126 for regenerating the adsorption beds 126 at considerably lower pressures for enhancing the extent of regeneration.

[0026] In operation, the gas inlet 106 may receive a mixed gas feed. The
mixed gas feed may include the product gas, for instance hydrogen, along with other gases as impurities.
[0027] In an example, the hydrogen may be present in about 10 to 95 mole
percentage (%) within the mixed gas feed. In an example implementation, composition of the mixed gas feed may be as given in table 1.

Composition Kg/hr Kmol/hr Mole %
H2 1800 900 68
CO 900 32 2
CO2 15000 341 26
H2O 200 11 1
CH4 600 38 3
Total Gas 18500 1322 100
Table 1
[0028] Table 1 illustrates the composition of the mixed gas feed provided
to the RPB unit 102. The left most column describes the product gas and the other gases present as impurities within the mixed gas feed. The remaining columns describe proportion of the gases in weight within the mixed gas feed, As an example, the right most column describes the weight in mole % of the gases. As shown in the table, hydrogen gas may be present in 68 mole %, Carbon monoxide (CO) may be present in 2 mole %, carbon dioxide (CO2) in 26 mole %, water (H2O) in 1 mole %, and methane (CH4) in 3 mole %.
[0029] In an example, the mixed gas feed may be supplied radially inward
to the rotor -110 with a pressure. For instance, the mixed gas feed may be supplied at a pressure of about 20 kg/cm2. In another example, the pressure of the mixed gas feed may be a value within the range 5 kg/cm2 to 120 kg/cm2. In an implementation, the mixed gas feed may flow through the set of packed elements 114 and the solvent such that the first set of impurities, referred to as bulk amount of impurities, such as carbon dioxide may be eliminated from the mixed gas feed. In an example, up to 90 % of weight of the impurities are eliminated from the mixed gas feed after flowing through the packed elements 114 and the solvent.

[0030] The gas so obtained after removal of the bulk impurities may have
second set of impurities or remaining impurities, and may be referred to as the enriched gas. Thereafter, the enriched gas may be supplied through the gas outlet 108. In an example, the solvent with the bulk impurities may be supplied out into the outside environment through the liquid outlet 122 in the RPB unit 102. The enriched gas may have a higher proportion of the product gas, for instance hydrogen in the enriched gas.
[0031] In an example implementation, the composition of the enriched gas
may be as shown in table 2.

Composition Kg/hr Kmol/hr Mole %
H2 1800 900 93
CO 900 32 2
CO2 500 11 1
H2O 200 11 1
CH4 600 38 3
Total Gas 4000 992 100
Table 2
[0032] As shown in table 2, the enriched gas may include hydrogen in 93
mole %, CO in 2 mole %, CO2 in 1 mole %, H2O in 1 mole %, and CH4 in 3 mole %. Therefore, in the enriched gas the proportion of hydrogen increases.
[0033] In an implementation, the enriched gas may be received by the
inlet124 of the PSA unit 104. The enriched gas may then be introduced to the multiple adsorption beds 126 one after another. The adsorption beds 126 may include adsorbent materials to adsorb the remaining impurities from the enriched gas. In an example, the impurities may be eliminated when molecules of the adsorbent material form bonds with molecules of the impurities. The bonding of the molecules on the adsorbent materials may trap the impurities on the surface of adsorbent materials thereby separating the impurities from the enriched gas. The feeding of the enriched gas to the multiple adsorption beds 126 may eliminate the remaining impurities from the enriched gas to provide a product gas. In an example, the product gas may be hydrogen gas. The product gas is obtained at the

product gas outlet 128 of the PSA unit 104 and the remaining impurities may be removed from the PSA unit 104 in form of impure gas through the impure gas outlet 130. In an example, the hydrogen so purified as a product gas may be 99.999 pure.
[0034] In an example, the bulk impurities may be removed by the RPB
unit 102, and the multiple adsorption beds 126 may have to eliminate the remaining impurities which may be very less in amount compared to original mixed gas feed. Therefore, the adsorption beds used for eliminating the remaining impurities may have reduced dimensions.
[0035] Thereafter, applying a vacuum regeneration unit may enhance the
performance of the PSA unit by higher level of desorbing of the impurities from the multiple adsorption beds 126. In an example, the adsorbent materials may be desorbed by releasing bonds of the molecules of the remaining impurities and the surface molecules of the adsorbent materials. In a scenario, desorption may be performed at a negative pressure having any value in between the range of -0.1 kg/cm2g to -0.9 kg/cm2g. After desorption of the adsorbent materials the adsorbent materials are regenerated with enhanced capacity to adsorb the impurities in subsequent cycles of operation.
[0036] FIG. 2 illustrates method 200 in accordance with implementations
of the present subject matter. The order in which the method 200 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 200 or an alternative method.
[0037] FIG. 2 illustrates a method for purifying a mixed gas feed to
produce a product gas, according to an implementation of the present subject matter. At block 202, a mixed gas feed is received by a RPB unit. In an implementation, the mixed gas feed is received by the gas inlet 106 of the RPB unit 102. Thereafter, at block 204, the first set of impurities is adsorbed to obtain an enriched gas. In an implementation, a solvent within the RPB unit 102 adsorbs the first set of impurities from the mixed gas feed.

[0038] At block 206, the enriched gas is supplied to a pressure swing
adsorption unit through a gas outlet. The PSA unit includes multiple adsorption beds to purify the enriched gas. Thereafter, at block 208, the enriched gas is fed to the multiple adsorption beds to eliminate the second set of impurities from the enriched gas to obtain a product gas. In an implementation of the present subject matter, the enriched gas is passed through multiple adsorption beds 126 of the PSA unit 104. Thereafter, the product gas may be provided through the outlet of the PSA unit.
[0039] It would be noted that as the mixed gas feed is purified in the RPB
unit 102, the amount of adsorbent material used in the multiple adsorption beds 126 may be reduced and adsorption beds with reduced dimensions may be used within a compact PSA unit 104 to purify the enriched gas. Therefore, the gas purification system 100 is space and cost efficient.
[0040] Thus, the gas purification system 100 may have increased
purification efficiency in producing the product gas thereby enhancing overall processing capacity. Further, the product gas so obtained through the gas purification system 100 may have high purity which can be used for any applications irrespective of the sensitiveness of consumer plant unit towards low levels of impurities in the product gas stream.
[0041] Although implementations for the rotating packed bed assembly
as per the present subject matter have been described in a language specific to structural features and/or applications, it is to be understood that the present subject matter is not necessarily limited to the specific features or applications described. Rather, the specific features and applications are disclosed as exemplary implementations.

I/We Claim:
1. A gas purification system (100) comprising:
at least one rotating packed bed (RPB) unit (102) comprising:
a gas inlet (106), to receive a mixed gas feed comprising a plurality of impurities;
a solvent to eliminate a first set of impurities from amongst the plurality of impurities within the mixed gas feed to obtain an enriched gas; and
a gas outlet (108), to supply the enriched gas; and
a pressure swing adsorption (PSA) unit (104) coupled to the RPB unit (102), comprising:
an inlet (124) coupled to the gas outlet (108) of the RPB unit (102), to receive the enriched gas;
a plurality of adsorption beds (126), to eliminate a second set of impurities from the enriched gas; and
a product gas outlet (128), to provide a product gas.
2. The gas purification system (100) as claimed in claim 1, wherein each adsorption bed from amongst the plurality of adsorption beds (126) comprises multiple layers of adsorbent material, to adsorb the second set of impurities of the enriched gas.
3. The gas purification system (100) as claimed in claim 1 further comprising a vacuum regeneration unit coupled to the PSA unit (104), to desorb the

second set of impurities from adsorbent materials of the plurality of absorption beds (126) for regeneration of the adsorbent materials.
4. The gas purification system (100) as claimed in claim 3, wherein the vacuum regeneration unit applies a negative pressure on the plurality of absorption beds (126) for desorbing the second set of impurities.
5. The gas purification system (100) as claimed in claim 1, wherein the plurality of adsorption beds (126) are placed across a plurality of zones within the PSA unit (104), wherein each zone from amongst the plurality of zones is classified based on type and composition of impurities eliminated in the zone.
6. The gas purification system (100) as claimed in claim 1, wherein the RPB unit (102) further comprises:
a solvent inlet (120) to receive a solvent, wherein the solvent absorbs the first set of impurities from the mixed gas feed;
a liquid outlet (122) to eject the solvent including the absorbed first set of impurities; and
a solvent distribution system to distribute and contact gas and liquid inside the RPB unit (102).
7. The gas purification system (100) as claimed in claim 1 is to purify the
mixed gas feed to provide hydrogen gas.

8. The gas purification system (100) as claimed in claim 1, wherein the first set of impurities comprises large amount of impurities in the mixed gas feed and the second set of impurities comprises low amount of impurities in the mixed gas feed
9. A method comprising:
receiving, by a gas inlet (106) of a rotating packed bed (RPB) unit (102), a mixed gas feed comprising a plurality of impurities;
absorbing, by a solvent, a first set of impurities of the mixed gas feed to obtain an enriched gas;
supplying, by a gas outlet (108) of the RPB unit (102), the enriched gas to an inlet (124) of a pressure swing adsorption (PSA) unit (104);
feeding the enriched gas to a plurality of adsorption beds (126) for eliminating a second set of impurities from the enriched gas; and
providing, by a product gas outlet (128) of the PSA unit (104), a product gas.
10. The method as claimed in claim 9, wherein each adsorption bed from amongst the plurality of adsorption beds (126) comprises multiple layers of adsorbent materials, to adsorb the second set of impurities of the enriched gas.
11. The method as claimed in claim 9, wherein the plurality of adsorption beds (126) are placed across a plurality of zones within the PSA unit (104), wherein each zone from amongst the plurality of zones is classified based on a type and composition of impurities eliminated in the zone.

12. The method as claimed in claim 9 further comprising desorbing, by a vacuum regeneration unit, the second set of impurities from adsorbent materials of the plurality of absorption beds (126) to regenerate the adsorbent materials.
13. The method as claimed in claim 12, wherein the desorbing comprises applying a negative pressure on the plurality of absorption beds (126).
14. The method as claimed in claim 12 comprising purifying the mixed gas feed to provide a hydrogen gas.