AU2002300519B2 - Process for removal of carbon dioxide for use in producing direct reduced iron - Google Patents

Description

P/00/011 28/5/91 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: PROCESS FOR REMOVAL OF CARBON DIOXIDE FOR USE IN PRODUCING DIRECT REDUCED IRON The following statement is a full description of this invention, including the best method of performing it known to us "PROCESS FOR REMOVAL OF CARBON DIOXIDE FOR USE IN PRODUCING DIRECT REDUCED IRON" BACKGROUND OF THE INVENTION [0001] The present invention relates to the removal of carbon dioxide from spent reducing gas in a process for the direct reduction of iron.

[0002] Direct reduced iron (DRI) production produces steel by the actual reduction of the iron ore in a direct reduction reactor in the presence of a reducing gas comprising hydrogen and carbon monoxide. The DRI process removes carbon dioxide produced in the reduction reaction with the spent reducing gas, or reactor off-gas. The reactor off-gas includes unreacted hydrogen, carbon monoxide, carbon dioxide and water. After cooling, the reactor off-gas is vented or reprocessed to remove the carbon dioxide and enrich the hydrogen and carbon monoxide content before returning the enriched off-gas to the direct reduction reactor as the reducing gas. Flow arrangements may use a reforming step to provide more hydrogen and carbon monoxide and/or a water gas shift step to enhance the recycle gas to provide the reducing gas. All arrangements must remove carbon dioxide to maintain the reduction process.

[0003] The direct reduction of iron ore reduces iron oxides by reaction with carbon monoxide, hydrogen and/or solid carbon through successive oxidation states to metallic iron. The iron oxide and a carbonaceous material, e.g. coal, typically enter a furnace that receives heat by the combustion of fuel with air which generates, inter alia, carbon monoxide and delivers reduced metallic iron while a flue or exhaust conduit removes furnace gases. Effective reduction temperatures range from 7500 to 1050 0

C.

[0004] US-A-5,238,487 B 1 discloses passing the reducing gas into a cooler/scrubber, a CO 2 removal unit, a gas heater to heat the gas to a temperature between 2000 and 500'C, and a partial combustion chamber to heat the gas to a temperature between 7500 and 850'C, before being returned to the second reactor.

[0005] US-A-5,882,579 B1 discloses a method and an apparatus for utilizing in a second reduction reactor the excess exhausted gas from a first reduction reactor fed with a reducing gas produced in a melter-gasifier. Carbon dioxide is removed from the reducing gas thus producing a reducing gas stream with a hydrogen content above percent and utilizing the reducing gas in a second reduction reactor.

[0006] US-A-5,858,057 B 1 discloses a process arrangement for the production of direct reduced iron, wherein the DRI process controls the amount of carbon by modifying the relative amounts of water, carbon dioxide and oxygen in the composition of the reducing gas returned to the reduction reactor.

[0007] US-A-4,363,654 B 1 relates to a DRI process for producing a hydrogen reducing gas wherein that partially oxidizes oil and/or coal to produce a reducing gas that treats the reducing gas to remove essentially all gases other than hydrogen.

[0008] The DRI reactor generally produces reactor off-gas at low pressure and high temperature. Employing separation methods such as pressure swing adsorption (PSA) or liquid absorption require cooling of the reactor off-gas and raising of its pressure to drive the separation. Processes are sought which provide carbon dioxide removal from DRI reactor off-gas at low operating pressure without the danger of explosion.

SUMMARY OF THE INVENTION [0009] Applicant discovered that a PSA process using an external purge step following a depressurization step provides an effective way of carrying out the separation of carbon dioxide from DRI spent reducing gas at very low adsorption pressures without requiring a substantial lowering of desorption pressure. The present invention solves the -2- 00 O above problems by using natural gas to purge and desorb CO 2 from an adsorption zone.

SThe present invention advantageously uses a particular cycle in the PSA zone to

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surprisingly avoid the need for subatmospheric regeneration of the adsorbent. Natural gas, instead of reducing gas, first purges most of the CO 2 and water from the adsorption zone.

S 5 A small amount of product purge may be used after the natural gas purge step to remove Ssome methane and additional CO 2 from the adsorption zone. Recycle of the reducing gas to the reactor recovers a portion of the natural gas that provides the external purge gas.

CCombining the remaining portion of the natural gas with a C0 2 -rich stream provides fuel gas. Preferably, the external purge step is combined with an internal purge step wherein a portion of the product stream is used to purge the adsorbent bed either prior to, or following the external purge step. Using the external purge step at the lowest pressure in the pressure swing cycle surprisingly strips the adsorbent of adsorbed species to a point which increases carbon dioxide removal rates relative to conventional pressure swing or vacuum swing adsorption units, sufficiently to overcome need for vacuum equipment or large blowers. The external purge step of the present invention more completely sweeps the adsorbent beds of carbon dioxide than conventional PSA processes. This unexpectedly enhances carbon dioxide removal and improves effective working capacity of the adsorbent relative to a conventional PSA process.

According to the first aspect of the present invention there is provided a process for the production of direct reduced iron comprising: a) contacting an iron oxide stream at effective reducing conditions with a reducing gas stream comprising hydrogen and carbon monoxide in a reaction zone and recovering a direct reduced iron product and a reactor 00 off-gas stream and cooling the reactor off-gas stream to provide a cooled Nreactor off-gas stream; b) passing a portion of the cooled reactor off-gas stream as a feed stream to a pressure swing adsorption zone comprising at least two adsorbent beds, s 5 each adsorbent bed undergoing a cyclic process consisting of an adsorption step, a co-current depressurization step, a counter-current depressurization step, an external purge step and a repressurization step wherein the external Spurge step is conducted following the counter-current depressurization step to provide a reducing gas product stream comprising hydrogen and carbon monoxide during said adsorption step and to provide a tail gas stream during the counter-current depressurization and external purge steps; and c) heating the reducing gas product stream in a furnace to provide a heated reducing gas stream and directly oxidizing a portion of the heated reducing gas stream to provide the reducing gas stream.

In one embodiment, the present invention is a process for the production of direct reduced iron. The process contacts an iron ore stream with a reducing gas stream comprises hydrogen and carbon monoxide at effective reducing conditions in a reaction zone and recovers a direct reduced iron product and a reactor off-gas stream. Cooling the reactor off-gas stream provides a cooled reactor off-gas stream, at least a portion of which passes as a feed stream to a PSA zone. The PSA zone comprises at least two adsorbent beds. Each adsorbent bed undergoes cyclic process steps of adsorption, co-current depressurization, counter-current depressurization, external purge step and repressurization step to provide a reducing gas product stream and a tail gas stream. In the cyclic PSA process, the external purge step follows the depressurization step. The adsorption step produces the reducing gas product stream comprises hydrogen and carbon 4a 00oo monoxide. The tail gas stream is produced during the depressurization and external purge Nsteps. A furnace heats the reducing gas product stream to provide the heated reducing gas stream that passes to the DRI reactor as reducing gas stream.

N In another embodiment, the present invention is a low pressure DRI process. In addition to the process steps as described above cooling and quenching of the reactor offgas stream provides the cooled off-gas stream comprising hydrogen, carbon monoxide, carbon dioxide and water. Admixing a water stream with a remaining portion of the Scooled off-gas stream and a hydrocarbon stream provides a reforming zone feed stream.

The reforming zone feed stream passes to a reforming zone that receives heat indirectly by combustion of a fuel mixture containing at least a portion of the tail gas stream an oxygen containing stream and a fuel stream. The reformer effluent stream and the reducing gas product stream are admixed to provide the reducing stream.

Comprises/comprising and grammatical variations thereof when used in this specification are to be taken to specify the presence of stated features, integers, steps or components or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the present invention schematically.

FIG. 2 schematically illustrating the invention with a steam reforming zone.

DETAILED DESCRIPTION OF THE INVENTION PSA efficiently and economically separates a gas stream containing at least two gases having different adsorption characteristics. The more strongly adsorbable gas separated from the less strongly adsorbable gas can constitute either an impurity or the desired product which is. In PSA, a feed gas typically enters one of a plurality of adsorption zones at an elevated pressure effective to adsorb at least one component, while at least one other component passes through. At a defined time entry of the feed gas to the adsorber terminates and one or more co-current depressurization steps depressurizes the adsorption zone to a defined level which draws off the separated, less strongly adsorbed component or components remaining in the adsorption zone without significant concentration of the more strongly adsorbed components. (PSA terminology refers to the flow as either co-current (in the same direction) or counter-current (in a direction opposite) to the direction of the feed stream passing through the adsorbent bed.) Then, a counter-current depressurization step depressurizes the adsorption zone to further reduce adsorption zone pressure by withdrawing desorbed gas counter-currently to the direction of the feed stream. Finally, the adsorption zone is purged and repressurized.

[0015] According to the present invention, the adsorption zone is purged with at least a portion of an internal purge gas stream from another adsorption zone undergoing a provide-purge step and an external purge gas stream supplied at a purge gas pressure.

The external purge step of providing the external purge gas stream to the adsorption zone can occur prior to or following an internal purge step. The term "tail gas stream" typically refers to the combined gas stream produced during the counter-current depressurization step and the purge step. The final stage of repressurization typically introduces slipstream of product gas. This final stage of repressurization is often referred to as product repressurization. In multi-zone systems, there are typically additional steps and those noted above may be done in stages. US-A-3,176,444, US-A-3,986,849, US-A- 3,430,418 and US-A-3,703,068 B describe multi-zone, adiabatic PSA systems that may include additional steps to those described.

[0016] The PSA process employs at least two adsorbent beds containing the selective adsorbent and arranged in parallel for conducting adsorption and desorption steps in a cyclic manner. Cycling the beds out-of-phase provides a continuous PSA process. In this invention the adsorption step terminated prior to breakthrough of carbon dioxide and the first adsorption bed is co-currently depressurized in a provide-purge step to provide a purge gas stream to another adsorbent bed undergoing an internal purge step.

[0017] The adsorbent contained in the adsorbent beds may comprise powdered solid, crystalline compounds capable of adsorbing and desorbing the adsorbable compound.

Examples of such adsorbents include silica gels, activated aluminas, activated carbon, molecular sieves and mixtures thereof. Molecular sieves include zeolite molecular sieves.

The adsorbents can be employed individually or in combination. Preferably, an adsorbent bed contains a plurality of layers including a bottom water removal layer comprising activated carbon or alumina and a CO 2 adsorption layer including silica gel or zeolite at the top of the adsorbent bed. The CO 2 adsorption layer can comprise only silica gel or it can comprise a lower silica gel layer and an upper zeolite layer. Preferably, the zeolite layer comprises a zeolite X or a zeolite Y. More preferably, the top zeolite layer comprises a zinc or sodium exchanged zeolite X or a sodium exchanged zeolite Y.

Preferably, the zeolite layer comprises from 0.01 to 40 volume percenf of the adsorbent bed and the water adsorption layer comprising activated carbon or alumina comprises from 1 to 80 volume percent of the adsorbent bed and the CO 2 adsorption layer comprising silica gel and/or zeolite comprises from 0 to 90 volume percent of the adsorbent bed. More preferably, the water removal layer comprising activated carbon or alumina comprises 5 to 10 volume percent and the zeolite layer comprises from 1 to volume percent and the silica gel layer comprises from 0 to 70 volume percent of the total adsorbent bed. The adsorbent of the present invention is preferably incorporated -6into solid particles. Solid particles comprising the molecular sieve and a binder may be formed into shapes such as pills, pellets, granules, rings, spheres, etc. The solid particles comprise an adsorptively effective amount of the adsorbent and at least one matrix material, preferably selected from the group consisting of binder materials, filler materials and mixtures thereof to provide a desired property or properties, e.g., mechanical strength and the like to the solid particles. Filler and binder materials include synthetic and naturally occurring substances such as metal oxides, clays, silicas, aluminas, silica-aluminas, silica-magnesias, silica-zirconias, silica-thorias, silicaberylias, silica-titanias, silica-alumina-thorias, silica-alumina-zirconias, aluminophosphates, mixtures of these and the'like.

[0018] FIG. 1 describes a direct reduction system having moving bed reactors, but the system can be adapted to schemes with fixed bed or fluidized reactors. In FIG. 1, iron ore enters a direct reduction reactor 66 via line 42 and the iron ore contacts a reducing gas introduced via line 24 in an upper reduction zone 68. The reducing gas comprises hydrogen and carbon monoxide. The reduction reaction temperature typically varies from 7500 to 1050 0 C. and more preferably from 950°and 1050 0 C. A line 46 removes the reduced iron ore from a lower cooling zone 70 of reactor 66. A line 28 removes a top gas stream, or a reactor off-gas stream, comprising unreacted hydrogen, carbon monoxide, water and carbon dioxide from reactor 66 at a temperature of from 3500 to 500 0 C. A first cooler 74 cools the top gas by indirect heat exchange with a preheated reducing gas stream in line 20 to provide a first cooled top gas stream in line 30 and a further preheated reducing gas stream in line 22. A line 30 passes the first cooled top gas stream to a second cooler 76 that exchanges heat with a first water stream in line 80 to provide a second cooled top gas stream in line 32 and a heated first water stream in line 82. Lines 32, 34 and 33 pass at least a portion of the second cooled top gas stream at a temperature -7of 300 to 60'C. A compressor 86 compresses the second cooled top gas stream to a recycle pressure of 200 to 1500 kPa. Preferably, the cooled top gas temperature ranges between 350 and 50'C, and the recycle pressure ranges from 275 to 1240 kPa. Lines 36 and 38 and a valve 88 vent a portion of the second cooled top gas stream to maintain pressure control of the system and to purge from the system a portion of undesirable components such as carbon dioxide and nitrogen. Lines 48 and 52 pass at least a portion of the compressed top gas stream to a PSA zone 90 containing at least two adsorbent beds. Each of the adsorbent beds contains an adsorbent selective for the adsorption of carbon dioxide from a mixture of components including hydrogen, carbon monoxide and water as previously described. The PSA zone 90 operates in a continuous cycle comprising an adsorption step at an adsorption pressure varying from 200 to 1500 kPa, to produce an adsorption effluent stream in line 60. The continuous cycle includes a cocurrent depressurization step, a counter-current depressurization step which reduced the pressure of the first adsorption bed to a desorption pressure, a purge step, and a repressurization step to return the adsorbent bed to the adsorption pressure. The purge step of the present invention consists of a combination of an internal purge employing provide-purge gas from another adsorbent bed which is undergoing the adsorption step or the co-current depressurization step, and an external purge using an exiemrnal purge gas stream. Preferably, the external purge gas stream comprises a non-adsorbable gas component such as a natural gas stream passed to the PSA zone 90 via lines 10, 12 and 14. The counter-current depressurization and the purge steps produce a desorption effluent stream that a line 58 withdraws from the PSA zone 90 via line 58. The external purge stream flows less than 10 volume percent of the top gas stream and, more preferably, between 2 to 8 volume percent of the top gas stream from line 28. The use of natural gas as an external purge gas stream in the PSA zone advantageously returns the -8desorption effluent comprising the external purge stream for admixing with a second natural gas stream in lines 10, 12 and 16 to produce a gas admixture in line 18. The gas admixture passes to first gas preheater 78 that indirectly heats the gas admixture with the first heated water stream in line 82 to provide the preheated reducing gas stream in line 20 and a second heated water stream in line 84.

[0019] A line 60 combines the adsorption effluent with a fuel gas stream, or a third natural gas stream in line 64 to produce a fuel admixture in line 62. The fuel admixture passes to a gas heater 72 that heats reducing gas stream in line 22 to a pre-oxidation temperature between 2000 and 500'C by combustion of the fuel admixture in the gas heater 72. A line 24 withdraws a heater effluent stream from the gas heater 72. A line 26 introduces an oxygen-containing stream to line 24 via line 26 to at least partially combust the gas heater effluent stream to provide a reducing gas stream in line 27 at a reduction temperature between 7500 and 850'C, to carry out the reduction reaction in reactor 66. The major reduction gas loop passes a portion of the compressed top gas stream to the lower cooling zone of reactor 66 via lines 48, 50 and 56, along with a fourth water stream in line 53. The present invention maintains an effective reducing gas concentration by removing at least a portion of the carbon dioxide from the reducing gas loop to carry out the direct reduction of the iron ore.

[0020] The invention may also withdraw an intermediate gas comprising hydrogen, carbon monoxide, water and carbon dioxide stream from lower cooling zone 70 via a line is withdrawn from the lower cooling zone 70. Line 40 admixes its contents with the cooled top gas stream in line 33 for venting through lines 34, 36, valve 88 and line 38 as required to remove inerts and control the pressure of the reactor.

[0021] FIG. 2 shows a direct reduction of iron ore process of this invention integrated with a steam reforming zone. This type of DRI process employs a natural gas -9feed steam reformer to produce the reducing gas comprising hydrogen and carbon monoxide and enrich a circulating reducing gas loop. The PSA zone of the present invention removes at least a portion of the carbon dioxide produced in the direct reduction reactor. According to FIG. 2, a line 104 passes an iron ore stream to a direct reduction reactor 162. A reducing gas comprising hydrogen and carbon monoxide from line 106 contacts the iron ore in an upper reduction zone 162a. A line 160 withdraws a reduced iron stream from a lower cooling zone 162b. A line 108 withdraws a top gas stream from the upper reduction zone 162a and passes it to a quench zone 164 for cooling. The cooled top gas stream passes through lines 110 and 116 for admixture with a first natural gas stream in line 118 to provide a feed gas admixture in line 120 which passes to a first compressor 158. Lines 122 and 126 pass a compressed reformer feed gas to a steam reforming zone 148. Steam reforming zone 148 contains a conventional reforming catalyst disposed in indirect thermal contact with a combustion zone 150.

Lines 138, 140 and 142 introduce fuel stream for combustion with oxygen from line 144 to heat steam reforming zone 148. A line 124 may mix additional natural gas with the compressed reformer feed gas in line 126 to provide additional carbon monoxide in the steam reforming effluent in line 146. A line 100 mixes a further amount of natural gas with the steam reforming effluent in line 146 to provide the reducing gas stream in line 102. The direct reduction reaction produces carbon dioxide and water. According to the present invention, a portion of the cooled top gas stream in line 110 passes to a second compressor 156 via line 114 which raises the top gas stream to an effective adsorption pressure of 345 to 276 kPa to produce an adsorption feed stream.

[0022] A line 128 passes the adsorption feed stream to a PSA zone 154 having at least two adsorbent beds containing an adsorbent selective for the adsorption of carbon dioxide. Each adsorbent bed undergoes a cyclic process similar to that described in conjunction with Fig. 1. Counter-currently depressurization of the first adsorption to a desorption pressure provides a first desorption effluent. A line 136 withdraws an adsorption effluent stream from the first adsorbent bed. An external purge stream in line 132 and an internal purge stream from another adsorbent bed undergoing a providepurge step purge the first adsorption bed to produce a second desorption effluent stream comprising carbon dioxide and methane. A portion of the adsorption effluent countercurrently repressurizes the first adsorbent bed to return the first adsorbent bed to the adsorption pressure. Line 136 passes the net adsorption effluent stream to a heater 152 that provides a heated adsorption effluent stream in line 168 depleted of carbon dioxide relative to the top gas stream. The effluent in line 168 mixes with the reducing gas stream in line 102 and then passes to the direct reduction reactor 162 via line 106. The first desorption effluent stream in line 130 admixes with the fuel stream in lines 138 and 140 and passes to the fuel stream to the combustion zone 150 via lines 134, 140 and 142.

Line 134 mixes the second desorption effluent stream with the fuel stream in line 138 prior to its entering the combustion zone 150.

[0023] The PSA zone 154 preferably reduces the carbon dioxide concentration in the adsorption effluent to less than 7.5 mole percent while maintaining the recoveries of hydrogen and carbon monoxide at least 93 and 81, respectively. Preferably, the adsorption pressure ranges from 200 to 1000 kPa. More preferably, the adsorption pressure ranges from 300 to 600 kPa. The external purge unexpectedly provides desired recoveries without using a vacuum pump or a compressor, which results in lower capital cost and operating cost. Preferably, the external purge stream in line 132 ranges from to 25 percent of the top gas stream in line 108.

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EXAMPLES

EXAMPLE I [0024] The following example is based on data obtained from the operation of a PSA pilot plant on a feedstock for the evaluation of adsorbents and PSA cycles. The pilot plant consisted of a single adsorbent chamber 3 meters long and 3.8 centimeters in diameter and containing 3400 cc of silica gel adsorbent along with the ancillary vessels, valves and connecting piping required to simulate multi-bed PSA cycles. The feed to the pilot plant comprised carbon dioxide, hydrogen, nitrogen, carbon monoxide and methane. The external purge stream comprised essentially pure methane. The chamber operated in a cyclic adsorption and desorption sequence over a range of operating pressures from an adsorption pressure of 1.14MPa to a desorption pressure of 186 kPa.

The basic cycle consisted of an adsorption step, a co-current equalization step, a cocurrent depressurization step to provide purge gas, a counter-current depressurization step to produce a portion of the tail gas stream, a constant pressure purge step to produce the remainder of the tail gas and a repressurization step. The gas stream produced during the provide-purge step was used to purge another bed during the purge step. The external methane purge step of the present invention was added at a point in the cycle prior to the constant pressure purge step. The feed temperature averaged 43 0 C. The temperature of the adsorbent chamber remained within 6'C of the feed temperature, with little variation during the adsorption time in the cycle. The adsorption time of the PSA cycle ranged from 2 minutes to 4 minutes. Thus, the total cycle time ranged from 4 minutes to 8 minutes. Chromatographic means measured the tail gas composition and demonstrated that the composition of the feed to the PSA unit averaged 13 volume percent carbon -12dioxide. Table I presents the average feed composition for the pilot plant determinations.

Table 2 presents a series of pilot plant runs.

TABLE 1 Average Feed Composition Average Composition, Component Mole Percent Carbon Dioxide 12.7 Hydrogen 50.1 Methane 20.2 Carbon Monoxide 16.0 TABLE 2 Pilot Plant Results Component Base Case 3% External 5% External Recoveries, No External Purge Purge Purge Carbon Dioxide 29.0 29.6 28.7 Hydrogen 93.0 93.6 95.1 Purge/Feed 0.0 3.0 Relative Bed Size 100 90 Tail Gas Pressure, kPa 160 190 190 [0025] The pilot plant results demonstrate that the use of an external methane purge provided essentially the same carbon dioxide recovery or removal rate as the base case which did not employ the external methane purge stream. At an external purge rate of 3 percent of the feed rate, the overall efficiency of the process increased by 10 percent as indicated by the reduction in bed size factor and, at an external purge rate of 5 percent of the feed rate, the overall efficiency of the process increased by 20 percent as indicated by the reduction in bed size factor.

EXAMPLE II [0026] The results of the pilot plant study in Example I, indicate that a commercial PSA cycle of this invention having two equalization steps and operating at the same -13adsorption pressure and cycle times can achieve a cost savings over a base case without an external purge stream. This example analyzed a 12 bed cycle, containing 12 adsorbent beds with three adsorbent beds undergoing an adsorption step at any time and each adsorbent bed undergoing two equalization steps without the methane purge step and with the methane purge step and found that both can achieve the same carbon dioxide rejection. The cases differed in the pressure level to which the tail gas must be reduced to achieve the desired recovery of carbon dioxide. The process without the methane purge step produces a tail gas stream at a pressure of 130 kPa which requires a blower to raise the tail gas stream to an acceptable discharge pressure. With the methane purge tail gas pressure remains at 184 kPa and above that which would require an additional blower to raise the tail gas pressure. For a plant processing 340,000 Nm 3 /hr of feed, this represents percent capital saving and an additional operation cost advantage of 360,000 dollars per year by use of the present invention.

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Claims (9)

1. A process for the production of direct reduced iron comprising: a) contacting an iron oxide stream at effective reducing conditions with a reducing gas stream comprising hydrogen and carbon monoxide in a reaction zone and recovering a direct reduced iron product and a reactor off-gas stream and cooling the reactor off-gas stream to provide a cooled reactor off-gas stream; b) passing a portion of the cooled reactor off-gas stream as a feed stream to a pressure swing adsorption zone comprising at least two adsorbent beds, each adsorbent bed undergoing a cyclic process consisting of an adsorption step, a co-current depressurization step, a counter-current depressurization step, an external purge step and a repressurization step wherein the external purge step is conducted following the counter-current depressurization step to provide a reducing gas product stream comprising hydrogen and carbon monoxide during said adsorption step and to provide a tail gas stream during the counter-current depressurization and external purge steps; and c) heating the reducing gas product stream in a furnace to provide a heated reducing gas stream and directly oxidizing a portion of the heated reducing gas stream to provide the reducing gas stream.

2. The process of claim 1 wherein the external purge step comprises counter- currently passing an external purge stream comprising a non-adsorbable component to the adsorbent bed.

3. The process of claim 2 wherein the non-adsorbable component comprises methane, nitrogen, and mixtures thereof. L

4. The process of any of claims 1 3 wherein a ratio of the external purge stream to the feed stream comprises between 0.02 to The process of any of claims 1 4 wherein the counter-current depressurization step comprises counter-currently depressurizing each adsorbent bed in the cyclic process to a purge pressure greater than atmospheric pressure.

6. The process of any of claims 1 5 further comprising combining at least a portion of the tail gas stream with a fuel stream to produce a fuel admixture and burning the fuel admixture in the furnace.

7. The process of any of claims 1 6 wherein an internal purge step is performed before or after the external purge step.

8. The process any of claims 1 7 wherein the adsorbent bed contains an adsorbent selected from the group consisting of activated carbon, activated alumina, silica gel, zeolites, and mixtures thereof.

9. The process of any of claims 1 9 wherein each of the adsorbent beds contains a total adsorbent bed having a plurality of adsorbent layers, including a water adsorption layer comprising alumina or activated carbon at a bottom end, and a carbon dioxide adsorption layer at a top end comprising silica gel, zeolite, and mixtures thereof. The process of any of claims 1 9 wherein the cyclic pressure swing adsorption process comprises: a) passing the feed stream comprising hydrogen, carbon monoxide and carbon dioxide in the adsorption step to a first adsorption bed of the at least two adsorption beds, each adsorbent bed containing a carbon dioxide selective adsorbent, to provide the reducing gas product stream comprising hydrogen and carbon monoxide; -16- 17 00 O b) co-currently depressurizing the first adsorbent bed in the at least one Sequalization step with another adsorbent bed; Sc) further co-currently depressurizing the first adsorbent bed in the provide-purge step to provide a provide-purge stream to the other adsorbent bed undergoing c 5 an internal purge step; d) counter-currently depressurizing the first adsorbent bed to provide a first portion of a tail gas stream; (,1 e) counter-currently purging the first adsorbent bed with an external purge stream to provide a second portion of the tail gas stream; f) counter-currently purging the first adsorbent bed with the provide-purge stream to provide a third portion of the tail gas stream; g) repressurizing the first adsorbent bed; and h) combining the first, second and third portions of the tail gas stream to provide the tail gas stream.

11. A process for the production of direct produced iron as herein above described with reference to the accompanying drawings. UOP LLC WATERMARK PATENT TRADE MARK ATTORNEYS P21759AU00