# US 4,398,927 A · Cyclic adsorption process

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- Number: US 4,398,927 A
- Document ID: US4398927A
- Status: Granted
- Kind: A
- Application number: 06/324,463
- Filed: 1981-11-24
- Granted: 1983-08-16
- Earliest claimed: 1980-07-30
- Assignees: Exxon Research & Engineering Co.
- Inventors: William J. Asher; Agustin F. Venero
- Web page: https://patentgrep.com/patent/US4398927A

## CPC

- B01D 53/04: with stationary adsorbents {(B01D53/025 takes precedence)}
- B01D 53/261: {by adsorption}
- F24F 3/1411: {by absorbing or adsorbing water, e.g. using an hygroscopic desiccant}
- F24F 3/1423: {with a moving bed of solid desiccants, e.g. a rotary wheel supporting solid desiccants}
- B01D 53/06: with moving adsorbents, e.g. rotating beds {(B01D53/025 takes precedence)}
- B01D 2259/40088: by heating
- B01D 2259/4009: using hot gas
- F24F 2203/1016: combined with another type of cooling principle, e.g. compression cycle
- F24F 2203/1036: Details
- F24F 2203/104: Heat exchanger wheel
- F24F 2203/1056: comprising a reheater
- F24F 2203/1072: comprising two rotors
- F24F 2203/108: comprising rotor parts shaped in sector form
- F24F 2203/1084: comprising two flow rotor segments
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- F24F: AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING (removing dirt or fumes from areas where they are produced B08B15/00; vertical ducts for carrying away waste gases from buildings E04F17/02; tops for chimneys or ventilating shafts, terminals for flues F23L17/02)

## Abstract

A cyclic adsorption process is provided in which two zones are employed--an adsorption zone and a heat storage zone. A fluid stream containing a solute to be removed therefrom is passed through the adsorption zone and the effluent is then passed through heat storage zone. The conditions under which the stream is passed through the adsorption zone are selected so that the rate of progression of the heat transfer front and mass transfer front are substantially equal. This results in an optimum temperature of the effluent stream for efficient heat recovery in the heat storage zone. During regeneration of the adsorbent, a fluid regenerating stream is passed through the heat storage zone where it is partially heated. At a point between the adsorption zone and the heat storage zone the regenerating fluid stream is further heated, via an additional heat source, and passed through the adsorbent zone. The amount of additional heat is sufficient to effectively desorb the adsorbent. Alternatively, of course, a pressure reduction and a combination of heat addition and pressure reduction may be employed to desorb the adsorbent.

## Claims

### Claim 1

An improved cyclic adsorption process comprising:
passing a fluid stream containing an adsorbate to be removed therefrom through an adsorption zone and then through a heat storage zone, said fluid being passed through said adsorption zone under conditions sufficient to provide that the velocity of the heat transfer front and the velocity of the mass transfer front through said adsorption zone are substantially equal; and
regenerating said adsorbent by passing a regeneration stream through said heat storage zone and then through said adsorption zone whereby said regeneration stream is heated in said heat storage zone.

### Claim 2 (depends on 1)

The process of claim 1 wherein desorption of said adsorption zone is achieved by a technique selected from the group of:
(a) adding an incremental amount of heat to said regeneration stream at a point between said heat storage zone and said adsorption zone, said incremental amount of heat being sufficient to raise the temperature of said regeneration stream to a point sufficient for removing said solute from said adsorbent in said adsorption zone whereby said adsorbent is regenerated; and
(b) decreasing the pressure in said adsorption zone when said regeneration stream is passed through said adsorption zone, said decrease in pressure being in an amount sufficient to remove solute from said adsorbent in said adsorption zone; and
(c) adding an incremental amount of heat to said regeneration stream at a point between said heat storage zone and said adsorption zone by simultaneously reducing the pressure in said adsorption zone, said incremental amount of heat and said pressure decrease being sufficient for removing said solute from said adsorbent in said adsorption zone whereby said adsorbent is regenerated.

### Claim 3 (depends on 2)

The process of claim 2 wherein said fluid stream being passed through said adsorption zone is at a predetermined operating temperature and concentration of adsorbate whereby the velocity of the heat and mass transfer fronts through said adsorption zone are substantially equal.

### Claim 4 (depends on 3)

The process of claim 3 wherein a heat capacity material is added to said adsorption zone whereby said velocity of said heat transfer and mass transfer fronts are substantially equal.

### Claim 5

A method of improving the thermal efficiency of a cyclic adsorption process of the type wherein a fluid stream containing an adsorbate to be removed therefrom is passed through an adsorption zone and then through a heat storage zone during the adsorption cycle and wherein a regenerating stream is passed through said heat storage zone and then through said adsorption zone during the regeneration cycle, the improvement comprising adjusting the relative rate of velocity of the heat transfer front and mass transfer front through said adsorption zone so as to be substantially equal.

### Claim 6 (depends on 5)

The method of claim 5 wherein said relative velocities are adjusted by selecting operating conditions under which the ratio .DELTA.q.sub.o /.DELTA.C.sub.o is substantially equal to the ratio C.sub.s /C.sub.f wherein .DELTA.q.sub.o is the change in adsorbed phase concentration expressed as moles per unit total volume of solid, .DELTA.c.sub.o is the difference in fluid phase concentrations between the end and the beginning of the adsorption step expressed as moles per unit fluid volume, C.sub.f is the heat capacity of the fluid in calories per unit fluid volume per degree and C.sub.s is the average heat capacity of the solid material in the adsorbent zone.

### Claim 7 (depends on 6)

The method of claim 6 wherein the relative velocity of the heat and mass transfer fronts are adjusted by the addition of a heat capacity material to the adsorption zone in an amount sufficient that the ratio C.sub.s /C.sub.f is substantially equal to the ratio .DELTA.q.sub.o /.DELTA.c.sub.o.

### Claim 8

An improved cyclic adsorption process comprising:
passing a fluid stream containing an adsorbate to be removed therefrom through an adsorption zone and then through a heat storage zone, said adsorption zone containing an adsorbant and heat capacity material, said heat capacity material being present in an amount sufficient to provide a temperature in said adsorption zone under operating conditions which is higher than the temperature that otherwise would exist in said adsorption zone under operating conditions;
regenerating said adsorbent by passing a regeneration stream through said heat storage zone and then through said adsorption zone whereby said regeneration stream is heated in said heat storage zone; and
adding an incremental amount of heat to said regeneration stream at a point between said heat storage zone and said adsorption zone, said incremental amount of heat being sufficient to raise the temperature of said regeneration stream to a point sufficient for removing said adsorbate from said adsorbent in said adsorption zone whereby said adsorbent is regenerated.

### Claim 9 (depends on 8)

The process of claim 8 wherein the amount of heat capacity material contained in said adsorption zone is sufficient to provide a temperature which will desorb from 90% to 95% of the solute adsorbed by the adsorbent.

### Claim 10 (depends on 9)

The process of claim 9 wherein the amount of heat capacity material per pound of adsorbent in said adsorption zone is such that the mass of heat capacity material times its heat capacity is in the range of from about 0.2 to 50 Btu's/.degree.F/lb of adsorbent.

### Claim 11 (depends on 10)

The process of claim 10 wherein the fluid stream is air and where said adsorbent is a desiccant.

### Claim 12 (depends on 11)

The process of claim 11 wherein the desiccant is silica gel and the ratio of heat capacity material per pound of silica gel in said adsorption zone is such that the product of mass of the heat capacity material times the heat capacity of such material is in the range of from about 0.2 to 6.0 Btu/.degree.F/lb of silica gel.

### Claim 13 (depends on 12)

The process of claim 12 wherein the desiccant is silica gel and the ratio of heat capacity material per pound of silica gel in said adsorption zone is such that the product of mass of the heat capacity material times the heat capacity of such material is in the range of from about 0.5 to 2.0 Btu/.degree.F/lb of silica gel.

### Claim 14 (depends on 13)

The process of claim 13 wherein the product of the specific heat and the mass of the regeneration stream used is not more than 15% greater than the product of the specific heat and mass of fluid stream used.

### Claim 15

An improved cyclic adsorption process comprising:
passing a fluid stream containing a solute to be removed therefrom through an adsorption zone and then through a heat storage zone whereby a heat transfer front and a mass transfer front are generated and progress through said adsorption zone and said heat storage zone, said adsorption zone containing an adsorbent and a heat capacity material, said adsorbent and said heat capacity material being present in a weight ratio sufficient to provide for a rate of progression of said heat transfer front through said adsorption zone which is substantially equal to the rate of progression of said mass transfer front through said adsorption zone;
regenerating said adsorbent by passing a regeneration stream through said heat storage zone and then through said adsorption zone, whereby said regenerating stream is heated in said heat storage zone; and
promoting desorption of said adsorbent by the technique selected from
(a) adding an incremental amount of heat to said regeneration stream at a point between said heat storage zone and said adsorption zone, said incremental amount of heat being sufficient to raise the temperature of said regeneration stream to a point sufficient for removing said solute from said adsorbent in said adsorption zone; (b) decreasing the pressure of said adsorbent zone in an amount sufficient to remove solute from said adsorbent: and (c) adding an incremental amount of heat to said regeneration stream and reducing said pressure in said adsorption zone in combined amounts sufficient to remove solute from said adsorbent whereby said adsorbent is regenerated.

### Claim 16 (depends on 15)

The process of claim 15 wherein the product of the specific heat and the mass of the regeneration stream used is not more than 15% greater than the product of the specific heat and mass of fluid stream used.

### Claim 17 (depends on 16)

The process of claim 16 wherein said fluid stream is air and where said adsorbent is a desiccant.

### Claim 18 (depends on 17)

The process of claim 17 wherein the amount of heat capacity material per pound of adsorbent in said adsorption zone is such that the mass of heat capacity material times its heat capacity is in the range of from about 0.2 to 50 Btu's/.degree.F/lb of adsorbent.

### Claim 19 (depends on 18)

The process of claim 18 wherein the desiccant is silica gel and the ratio of heat capacity material per pound of silica gel in said adsorption zone is such that the mass of heat capacity material times its heat capacity is in the range of from about 0.2 to 6.0 Btu/.degree.F/lb of silica gel.

### Claim 20 (depends on 19)

The process of claim 19 wherein the ratio of heat capacity material per pound of silica gel in said adsorption zone is such that the means of heat capacity material times its heat capacity is in the range of from about 0.5 to 2.0 Btu/.degree.F/lb of silica gel.

### Claim 21

A desiccant cooling process including the steps of:
passing ambient air through a desiccant zone to produce relatively dry air, said desiccant zone containing a silica gel and heat capacity material therein, the ratio of said heat capacity material per pound of desiccant being such that the mass of heat capacity material times its heat capacity is in the range of from about 0.2 to about 6.0 Btu/.degree.F;
passing said relatively dry air through a heat storage zone to produce relatively cool dry air for use in an enclosed conditioned space;
withdrawing a stream of exhaust air from said conditioned space through an evaporative pad whereby said exhaust air is cooled;
passing said cooled exhaust air stream through said heat storage zone whereby said heat storage zone is cooled when said exhaust air is heated;
adding additional heat to said exhaust gas by heating means;
passing said heated exhaust air through said adsorption zone, whereby said adsorbent is regenerated.

### Claim 22 (depends on 21)

The process of claim 21 wherein said adsorption zone and said heat storage zone are in the form of a continuously rotating segmented wheel.