GB1589290A

GB1589290A - Process and apparatus for the production of carbon monoxide

Info

Publication number: GB1589290A
Application number: GB3512777A
Authority: GB
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1976-08-23
Filing date: 1977-08-22
Publication date: 1981-05-07
Also published as: FR2362918B1; DE2737669A1; DE2737669B2; DE2737669C3; FR2362918A1

Description

(54) PROCESS AND APPARATUS FOR THE PRODUCTION OF CARBON MONOXIDE (71) We, PHILLIPS PETROLEUM COMPANY, a corporation organised and existing under the laws of the State of Delaware, United States of America, of Bartlesville, Oklahoma, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates broadly to the gasification of carbon sources.

The conversion of solid carbon sources to a gas has been known for many years. One process contacts coal and steam under elevated temperature conditions to produce a gas consisting essentially of carbon monoxide and hydrogen (synthesis gas). The coal gasification processes are of great interest since they generally have the advantage of providing an environmentally clean process for coal utilisation, of producing a high heating value gas which can substitute for natural gas and of producing a low heating value gas suitable for use as synthesis gas for subsequent conversion to hydrocarbons or chemicals or as boiler fuel.

The introduction of air into contact with coal in a coal gasification process is generally undesirable since large volumes of nitrogen have to be handled in the process. These nitrogen gases have no function in the process and add to the process costs, as well as to the equipment size. It would therefore, be desirable to have available a process for the conversion of coal into carbon monoxide that can be carried out essentially without the direct use of air.

In accordance with this invention, a cyclic process is provided in which a solid carbon source is reacted with ZnO to produce Zn and carbon monoxide and wherein the Zn is reoxidized to ZnO which is then recycled to the reaction with carbon source. This process avoids the use of air in the main reaction. The carbon monoxide produced, therefore, does not have to be separated from large volumes of nitrogen.

The main reaction between the carbon source and ZnO is carried out at a temperature of from 1665" to 280() F and preferably under slightly super-atmospheric pressure. The time required for the reaction will generally be from 5 minutes to 2 hours. This reaction time depends upon the temperature employed, the size range of the carbon source particles and the Zno particles, and the degree of mixing in the reactor. In the drawings, Figure 1 is a flow sheet illustrating the fundamental features of the present invention.

Figure 2 is a flow sheet illustrating an advantageous heat balance system in connection with the present invention.

Figure 3 is a flow diagram showing a heat balance system which is a variant of that shown in Figure 2.

Figure 4 is a flow diagram illustrating a modification of the present invention.

Figure 5 is a flow diagram illustrating a further process variant of the present invention.

Figure 6 is a flow diagram illustrating a modification of the present invention in which a novel temperature control system is used.

Figure 7 is a variant of the system shown in Figure 6.

Figure 8 illustrates a further process variation of the invention in which certain by-product recovery features and waste elimination features are shown.

Figure 9 illustrates a process modification of the present invention involving an advantageous preheating step.

Figure 10 illustrates a variant of the process shown in Figure '9.

Figure 11 is a flow diagram illustrating a further variant of the process shown in Figure 9.

The zinc oxide is preferably employed in finely divided particle form. These particles can have a size such as to pass entirely through a 45-mesh (U.S. Standard) screen (ASTM method D 293-29). Smaller particles can readily be used. Larger particles tend to slow down the reaction. Since the reaction between the carbonaceous source and the zinc oxide is endothermic. high temperatures will generally result in shorter reaction times.

The reactions involved in the process are generally solid/solid reactions so that the pressure is not critical. Preferably however, the pressure will be slightly above atmospheric pressure, e.g., in the range of 0.1 to 50 psig (102-446 kPa).

Solid carbon sources used in this invention are those that are solid under temperatures of up to 2500"F (1373"C) and include solid carbonaceous material such as coal, coke, char. The solid carbon source materials are preferably employed in finely divided form. Advantageously the solid carbon source consists of particles having a diameter of less than 0.4 mm. The particle size refers to the longest dimension of the individual particle.

The process of this invention can be advantageously used to gasify and convert to carbon monoxide even those solid carbon sources that are solid residues from other gasifications or liquefactions of other carbon sources such as coal, shale, oil and residual oil. Examples for coal pyrolysis processes resulting in a solid char residue are the COED processes (developed by FMC Corporation), the Garrett process, the Synthane process and the Toscoal process. Under this aspect of the invention, char is the preferred solid source for the process of this invention.

The relative quantities of solid ZnO and carbon source can be varied in fairly broad ranges. Generally the ZnO oxygen donor is used in such a quantity that a slight surplus of available oxygen atoms per available carbon atoms is achieved. A range of 0.9 to 1.2 moles of ZnO, preferably about 1 mole of ZnO, per gram atom of carbon in the carbon source can be employed.

In the zinc oxidizer zinc is combusted with an oxygen source in an exothermic reaction to form ZnO. Examples of such oxygen sources are air, steam, oxygen-enriched air, oxygen.

Air is the preferred oxygen source. Generally the oxygen source is used in quantities above the stoichiometric requirement. Preferably about 1.05 to about 1.25 atoms of available oxygen per atom of Zn are utilized in the oxidation mixture of Zn and the oxygen source.

The process of this invention preferably. and in accordance with the preferred embodiment of this invention, is carried out as follows. The carbon source and the zinc oxide are both admixed in finely divided form in a reactor to form a reaction mixture. The reaction mixture is heated to a temperature in the range of 1700"C to 280()0C (928-1540"C).

The reaction mixture is continuously stirred either mechanically or by means of a fluidizing gas, which preferably is carbon monoxide and equilibrium quantities of carbon dioxide.

From the reactor a gas comprising carbon monoxide, zinc and an equilibrium amount of CO2 is withdrawn. The relative quantities of CO and CO2 in the gas depend upon the reaction condition and the relative quantities of carbon source and ZnO introduced into the reactor. By "equilibrium amount" or ''equilibrium quantities" of CO2, a concentration of CO2 is referred to which is present in the gaseous effluent from the reactor at the specific conditions. From the bottom of the reactor. solids containing ash are withdrawn. The gas mentioned above is separated into a gas stream consisting essentially of carbon monoxide and a liquid zinc stream, preferably by cooling the stream sufficiently to condense the zinc.

The zinc stream then is contacted in a zinc oxidizer with oxygen to form zinc oxide and the zinc oxide formed is reintroduced into the reaction zone. The reaction mixture is heated during the entire process in the reactor, preferably by circulating a heating fluid into indirect heat exchange with the reaction mixture. The heating can, however, also be achieved by utilizing a heated fluidized gas such as carbon monoxide.

The embodiment just described is particularly advantageous because the temperature conditions at which a very good yield of carbon monoxide is achieved are above the boiling point of zinc so that the process results in gaseous zinc, which is readily separated from the effluent, reoxidized and recirculated to the reaction mixture.

The reoxidation of zinc can be carried out by contacting the zinc with air under elevated temperature conditions. In this variation the process utilizes oxygen from air without introducing the nitrogen into the CO forming reaction zone. The zinc oxide serves as the oxygen carrier.

The gaseous effluent after the removal of zinc therefrom consists essentially of carbon monoxide with minor amounts of carbon dioxide, hydrogen and light hydrocarbons admixed thereto. This gas eventuallv after admixture with further hydrogen can be utilized for many processes. e.g.. the Fischer-Tropsch process for producing liquid hydrocarbons.

In a further embodiment of this invention. a non-volatile carbon source such as coke and char containing a considerable amount of sulfur. e.g.. up to 8 wt. % can be used in connection with zinc oxide as the oxygen donor. The carbon monoxide gas produced is essentially sulfur-free since the sulfur contained in the carbon source is converted to sulfides of zinc. possibly in combination with components of the ash, and withdrawn from the reactor with the ash. The zinc thus introduced into the ash can be recovered therefrom readily by conventional roasting techniques.More efficiently yet, the reaction to form CO is carried out when utilizing a sulfur-rich carbon source at a temperature above the sublimation temperature of ZnS. which is 2165"C (1185"C). Then the gaseous effluent from the reactor comprises ZnS in addition to Co and Zn. This ZnS can be removed from the gas stream by condensing (subliming) it at a temperature between the boiling temperature of the zinc and the sublimation temperature of the ZnS. Recovery of the Zn from this ZnS can then be carried out without the dilution of ash.

Figure 1 is a schematic flow diagram for a basic process for converting a carbon source into carbon monoxide. The carbonaceous feed material is introduced into the main reactor l through a heat exchanger 2 via line 3. Zinc oxide is introduced into the main reactor 1 via line 4. The solid materials are mixed in the reactor 1 by a fluidizing carbon monoxide stream introduced via two rings 5 and 6. Carbon monoxide gas is introduced to these rings 5 and 6 via line 7 from a carbon monoxide source 20. The carbon monoxide gas has been heated in furnace 8 so that this gas introduces the necessary heat for the reaction. Ash accumulates in the lower section of the reactor 1 and is withdrawn via line 9.Carbon monoxide and zinc. as well as gaseous by-products. pass through a cyclone separator 10. which separates entrained solids from the gaseous effluent. and the gases freed of solids are withdrawn via line 11 from the reactor I. The entrained solids separated in the cyclone separator 10 fall back into the reactor bed.

The gas consisting essentially of carbon monoxide and zinc is passed from main reactor 1 via line I I to a zine condenser 12 in which this gas is brought into indirect heat relationship with an air stream introduced vii line 13. In zinc condenser 12 the gaseous zinc is liquefied and separated from the CO gas which is recovered via line 14 as the product of the process.

The liquid zinc obtained in the zinc condenser l2 is withdrawn via line 22 and introduced into a zinc oxidizer 23. In this zinc oxidizer. the liquid zinc is contacted with an air stream that has been preheated in the zine condenser 12. together with additional air introduced via line 24. The zinc is oxidized to solid zinc oxide in the zinc oxidizer 23 and the remaining gas, essentially nitrogen, is withdrawn from the zinc oxidizer 23 via line 25. This gas is passed through indirect heat exchanger 2 in order to preheat the carbonaceous feedstock.

This heat exchange may also be carried out directly by contacting a bed of carbonaceous feed 3 with hot gas stream 25. preferably in a countercurrent manner. Solid zinc oxide in a finely divided state is withdrawn from the bottom of the zinc oxidizer 23 via line 4 and is introduced into the main reactor l.

EXAMPLE I Three runs were carried out in which 1.32 grams of char from the COED process (developed by the FMC Corp. and utilizing a series of fluid beds) corresponding to 1 gram of carbon were introduced into a tubular quartz reactor. An oxygen donor. zinc oxide. was also introduced into the quartz reactor. Both the char and the oxygen donor were used in finely divided form. namely having a particle size of -45 mesh. The weight ratio of oxygen donor to char was chosen so that about l atom of oxygen was available per atom of carbon.

The reactor was in opcn communication with a gas collector and analyzer. The reactor was then heated to the temperatures indicated in the table and kept at that temperature by continuing the heating until the evolution of gas ceased, which took about 45 minutes. Zinc passing out of the reactor in the gas stream was collected. oxidised into ZnO and recycled.

The results of the analysis of the gaseous effluent are shown in the following table: Reactor Temp.. ZnO Char CO/CO2 CO Production, ZnO Char Mol Ratio in liters CO per "F "C Weight Katio Product Gas gram char 19)3 1(14(1 5.13 2().3 1.54 IX5 I()S5 5.13 37.4 1.0i7 2()7() 1132 r 3'.3 1.84 * Theoretical CO yield is 1.87 liters per gram of char.

From the above-shown data. it is apparent that char can efficiently be gasified utilizing the solid ZnO oxygen donor shown in the table above. The results. also show that a higher reaction temperature results in an improved quantity of carbon monoxide production.

Figure 2 illustrates an embodiment of the invention in which a heat-exchange loop comprising indirect heat exchange means in the reactor and in the zinc oxidizer are connected to each other. In this heat exchange loop, a heat exchange fluid is circulated to transfer heat generated in the zinc oxidizer to the reactor in which the endothermic reaction between the carbon source and zinc oxide takes place. The zinc oxide produced in the zinc oxidizer is introduced into the reactor for further reaction with the carbon source.

Particularly useful heat exchange fluids in this process are those that can be readily kept liquid under the temperature of the carbon monoxide forming reaction between the carbon source and the zinc oxide and that can be kept in vapour phase at the temperature of the zinc oxidation. Molten metals and salts can be used. The preferred group of heat exchange fluids consists of zinc. sodium. potassium and mixtures of sodium and potassium.The pressures under which the heat exchange loops are preferably operated to achieve the advantageous result that these fluids are liquid at the temperature of the carbon monoxide forming reaction and in vapour phase at the temperature of the zinc oxidation are given in the following table: Pressure Range Heat Exchange Fluid psia kPa Zn 25-50 170-345 Na 25-50 17()-345 K 8()-130 55()-895 Na + K (.5(V5() weight ratio) 4()-1()0 275-69t) The preferred heat exchange fluid is zinc. To use this metal is particularly advantageous since it is totally compatible with every stage of the overall process.Any small leaks in the heat exchange loop which might occur in the main reactor in which the carbon monoxide is formed or in the zinc oxidizer do not substantially influence the performance or result of the overall process.

The heat exchange fluid flowing from the heat exchange means in the zinc oxidizer to the heat exchange means in the reactor can be passed through a third heat exchange means and into indirect heat exchange relationship with at least a portion of the zine separated from the gas withdrawn from the reactor. The third heat exchange means serve, e.g., to completely evaporate liquid zinc before the further use thereof.

The zinc stream that is separated from the gas leaving the reactor is generally present as a liquid having a temperature lower than but near the boiling point of zinc. Preferably this liquid zinc is vaporized before it is further used. For achieving this a part or all of the liquid zine can be passed into indirect heat exchange relationship with the gas withdrawn from the reactor and/or with the heat exchange fluid flowing from the heat exchange means arranged in the zinc oxidizer to the heat exchange means arranged in the reactor and/or with an extraneous heating fluid.

In case a completely separated heat exchange loop between the reactor and the zinc oxidizer is used. the liquid zinc stream separated from the gas leaving the reactor preferably is passed through indirect heat exchange relationship with the gas leaving the reactor and thereafter with the heat exchange fluid leaving the heat exchange means arranged in the zine oxidizer.

The stream of evaporated zine is introduced into the zinc oxidizer to be oxidized to zinc oxide. Optionally a carrier portion of this zinc vapor stream, instead of being introduced into the zinc oxidizer, can be injected into the line for transporting the zinc oxide of the zinc oxidizer to the reactor. Also optionally. a fluidizing portion of this zinc vapor stream can be injected into the lower portion of the reactor such as to fluidize the reaction mixture comprising a solid carbon source and the solid zinc oxide.

If zinc itself is the heat exchange fluid in the heat exchange loop the preferred heat exchange loop between the reactor and the zinc oxidizer is not completely separated from the other process. For this embodiment it is preferred to separate liquid zinc at two stages from the gas leaving the reactor such as to fOI lil a first and a second liquid zinc stream. Each of these separation stages is generally carried out by passing the gas through condenser and separator. The first liquid zinc strcanl is split into an oxidizer portion and a carrier portion.

The oxidizer portion is conducted through an evaporator into the zinc oxidizer. The carrier portion is combined with a circulating heat exchange zinc fluid and passed therewith through the heat exchange means in the zinc oxidizer. Essentially the same quantity of zinc is added to the heat exchange zinc fluid loop is withdrawn therefrom downstream of the heat exchange means associated with the zinc oxidizer and before the zinc enters the heat exchange means in the reactor. The separated zinc vapors are used as the carrier gas for carrying the zinc oxide from the zinc oxidizer to the reactor. The second liquid zinc stream is passed into indirect heat exchange relationship with the gas leaving the reactor to evaporate this second liquid zinc stream. The resulting zinc vapor stream eventually after compression is also passed into the zinc oxidizer.

In Figure 2 a schematic flow diagram for the process of this invention with a completely separated heat exchange loop is shown. Into a reactor 1 a carbon source from a carbon source supply 30 is introduced via line 31. Zinc oxide is also introduced into the main reactor 1 via line 32. The main reactor 1 is equipped with a first indirect heat exchange coil 33. The reaction mixture in reactor 1 is fluidized by zinc vapours injected into the reactor via a fluidizing ring 34. The reaction of the carbon source with the zinc oxide produces a gaseous effluent that is withdrawn via line 35 and comprises carbon monoxide and zinc. The reaction also produces a solid residue comprising ash which is withdrawn via line 36 from the bottom of reactor 1. The gaseous effluent is passed through a heat exchanger 37 and a condenser 38 to a gas-liquid separator 39.From separator 39 a gas comprising carbon monoxide essentially free of zinc is withdrawn via line 40. From the bottom of the gas-liquid separator 39 a liquid zinc stream is withdrawn via line 41. This liquid stream is passed through heat exchanger 37 into indirect heat exchange relationship with the gas withdrawn via line 35 from the reactor 1. Thus this gas is cooled and the zinc is at least partially condensed and the liquid zinc in line 41 is heated and at least partially evaporated.

The zinc stream leaving heat exchanger 37 is passed via line 42 to indirect heat exchanger 43 in which the zinc is completely evaporated by indirect heat exchange with the heat exchange fluid circulating in the heat exchange loop explained in the following. This evaporated zinc stream leaving the heat exchanger 43 is split in three ways. The main portion is passed via line 44 into zinc oxidizer 23. A second or carrier portion is passed via line 45 into contact with the zinc oxide in line 46 and carries the zinc oxide via line 32 back into reactor 1. A third or fluidizing portion of the zinc vapor is passed via line 47 into the ring 34 from which it is injected upward into contact with the solid materials in reactor 1 to fluidize them.

The zinc vapour stream introduced via line 44 into oxidizer 23 is contacted with an oxidizing agent introduced via line 48. This oxidizing agent can be any suitable oxidizing agent that converts zinc into zinc oxide and is preferably air or steam. In oxidizer 23, solid zinc oxide in finely divided form is produced and is transferred via line 49 into zinc oxide surge tank 50. A gaseous effluent. consisting essentially of nitrogen in case air is used as the oxidizing agent, leaves zinc oxidizer 23 via line 51.

In accordance with this embodiment of the invention, a closed heat-exchange loop between the reactor 1 and zinc oxidizer 23 is provided. In the zinc oxidizer a second heat exchange coil 52 is arranged that is connected into a loop with the first heat exchange coil 33 in reactor 1 via pump 53. Part of this heat exchange loop is the heat exchanger 43. In coil 52 a heat exchange fluid. preferably a liquid metal, introduced via line 54, is evaporated by the heat developed during the zinc oxidation taking place in zinc oxidizer 23. The evaporated heat exchange fluid is passed via line 55 through heat exchanger 43, via line 56 into heat exchance coil 33. In this coil the heat exchange fluid is condensed and delivers both latent heat and sensible heat to the carbon monoxide forming reaction in reaction 1.The liquid heat exchange fluid is withdrawn from coil 33 via line 57 and recycled to coil 52 by pump 53.

In the heat exchange loop comprising the heat exchange coils 33 and 52, zinc or any other heat exchange fluid can be utilized. The heat exchange loop may contain a heat balance heat exchanger that is not shown in the drawing. This heat balance heat exchanger serves to add or remove heat such as to maintain the system in heat and temperature balance. In the flow diagram shown in Figure 3, on the other hand, zinc has to be used as the heat exchange fluid in the heat exchange loop since the system is not a closed loop heat exchange but there is a flow of zinc into the heat exchange loop and out of this loop as will be explained.

The basic system shown in Figure 3 is the same as that shown in Figure 2. The same numerals refer to the same elements. The gas leaving the reactor 1 via line 35 is passed through heat exchanger 37/37', the two heat exchange paths of which are shown at different locations in the drawing. These two portions of the heat exchanger 37 are in reality in close contact with each other so that the heat exchange between the liquid zinc stream and the gas can be achieved. The gas leaving heat exchanger 37 is passed through a first condenser 38' and a first gas/liquid separator 39'.The gas leaving the first gas/liquid separator 39' is passed through a second condenser 38" and a second gas/liquid separator 3')". The gas leaving gas/liquid separator 39" finally is passed to a water quench and washing unit 58 via line 59 in which this gas stream is quenched and washed with water, introduced through inlet 59' to cool the gas and to remove traces of zinc. The carbon monoxide-comprising gas leaves the water quench and washing unit 58 via line 60, and water containing traces of zinc leaves the unit 58 via line 61. The liquid zinc stream leaving the bottom of the first gas/liquid separator 39' via line 41' is pumped via pump 62 for further processing. This liquid zinc stream leaving the pump 62 is split into an oxidizing portion in line 63 and a carrier portion in line 63'.

The liquid zinc line 63 is passed through an evaporator 64. The evaporator 64 may receive its heat by being submerged in oxidation reactor 23. Similarly, the liquid zinc stream in line 41", having passed through the heat exchanger 37' in indirect heat exchange relationship with the gas leaving the reactor 1 via line 35, leaves this heat exchanger 37' as a zinc vapour.

The two zinc vapour streams in lines 65 and 65' are combined in line 44 and injected into the zinc oxidizer 23. The zinc vapour stream in line 65' is passed through a zinc vapour compressor 66 so that both zinc vapour streams in lines 65 and 65' are at the same pressure.

The carrier portion of the liquid zinc stream in line 63' is passed into a liquid zinc vessel 67. The liquid zinc leaving the heat exchange coil 33 is also passed into this vessel 67.

Furthermore, make up zinc is introduced into this vessel 67 via line 68. The liquid zinc is removed from this vessel via line 69 by pump 70 and passed through the heat exchange coil 52 via line 71. From the zinc vapour stream leaving the heat exchange coil 52 in line 55, a carrier portion is withdrawn via line 45. The quantity of zinc vapour withdrawn via line 45 from the heat exchange loop is essentially the same as the sum of the zinc streams introduced into the liquid zinc vessel 67 via lines 68 and 63'. The zinc vapour stream in incline 45 serves as a carrier gas for carrying the zinc oxide from zinc oxide surge tank 50 back into reactor 1. Thus the carrier portion of the liquid zinc from line 63' is evaporated in contact with the heat exchange fluid in the heat exchange loop.

In the embodiments of Figures 2 and 3, the liquefied zinc recovered from the gasification reactor effluent is reevaporated to produce a zinc vapour stream which is contacted with an oxidizing agent in a zinc oxidation zone to produce zinc oxide. This zinc oxide then is reintroduced into the main reactor as the oxygen source for the main reactor for forming carbon monoxide.

Reevaporating the liquefied zinc for converting it into zinc oxide has the advantage of a fast and complete oxidation of the zinc and an easy separation of zinc oxide from the gas stream leaving the zinc oxidation zone by passing the mixture of zinc oxide and gas through gas/solid separating means such as filters, centrifuges or cyclones, centrifuges being presently preferred. Furthermore, no problems from buildup of zinc oxide on zinc droplet surfaces occur.

A further embodiment employing this principle is illustrated in Figure 4. In this embodiment the gaseous effluent comprising carbon monoxide and zinc from the reactor is passed in indirect heat exchange relationship with the separated liquid zinc which is at least partially reevaporated thereby with consequential cooling of the effluent. The reevaporated zinc is then passed into indirect heat exchange relationship with the mixture of zinc and oxidizing agent in the zinc oxidation zone. Thereby the remaining liquid zinc is evaporated and zinc vapours are withdrawn from this indirect heat exchange relationship and are injected into the zinc oxidation zone.In this way the sensible and latent heat of the gaseous reactor effluent, as well as the heat generated in the exothermic zinc oxidation step, are effectively utilized. reducing the amount of external energy needed for the process to a minimum.

Referring in detail to Figure 4. carbon from a carbon source 30 is introduced via line 31 into reactor 1. Zinc oxide is introduced into the reactor 1 via line 4. Ash is withdrawn via line 36. The gaseous effluent consisting essentially of carbon monoxide and zinc is withdrawn from the reactor 1 via line 11. Since the reaction between zinc oxide and carbon to form carbon monoxide and zinc is an endothermic reaction, heating means such as a heating coil 80 is provided.

The gaseous effluent in line 11 is passed through indirect heat exchanger 81, condenser 82, and gas-liquid separator 83. In heat exchanger 81, as well as the condenser 82, the zinc vapours are essentially completely liquefied. In the separator 83, the liquid zinc is separated from the carbon monoxide-comprising gas. which is withdrawn via line 84. Liquid zinc is withdrawn from the bottom of gas/liquid separator 83 via line 85. By means of pump 86, the liquid zinc is passed through heat exchanger 81, line 87 and heat-exchange coils 88, where it is vaporized, and finally into zinc oxidizer 23. An oxidizing agent such as air is also passed into the zinc oxidation zone 23 via line 24.

In zinc oxidizer 23, the zinc that has been reevaporated by means of the heat exchanger 81 and heat-exchange coils 88 is reacted with oxygen to form zinc oxide. Some of the heat developed during this oxidation reaction is utilized for evaporating zinc in heat exchange coil 88. A gas is withdrawn from the zinc oxidizer 23 via line 89. This gas consists essentially of nitrogen in case air is used as the oxidizing agent introduced via line 24. Finely divided solid zinc oxide is withdrawn from the zinc oxidizer 23 via line 4. This zinc oxide is reintroduced into reactor 1.

In accordance with another embodiment of this invention, the oxidation reaction mixture, zinc vapour plus oxidizing gas, is passed in indirect heat exchange relationship with the reaction mixture of carbon and zinc oxide, thereby to transfer heat from the exothermic oxidation of the zinc vapour to the endothermic reaction of the carbon with zinc oxide. Such an embodiment is illustrated in Figure 5.

As shown in Figure 5, carbon is introduced via line 31 into reactor 1 from a carbon source 30. Zinc oxide, in finely divided form, is also introduced into reactor 1 via line 90. Ash is withdrawn via line 36. The gaseous effluent consisting essentially of carbon monoxide and zinc is withdrawn from the reactor via line 11. This gaseous effluent stream is split into a product stream 91 and recycle stream 92. The recycle stream 92 is reintroduced into the lower portion of the reactor 1 via pump 93 and serves as a fluidizing gas for the reaction mixture.

The product stream 91, consisting essentially of carbon monoxide and zinc, is exchanged in heat exchanger 94 with liquid zinc whereby it is cooled and the gaseous zinc is partially condensed. In order to condense all the zinc, the effluent of the reactor is passed from the heat exchanger 94to a cooler 95 in which most of the zinc that is still in vapour form is condensed. In separator 96 liquid zinc is separated from the gaseous effluent which is withdrawn via line 97. The liquid zinc is withdrawn via line 98 and passed through pump 99 via line 100, through heat exchanger 94. in which the zinc is at least partially evaporated, and via line 101 into contact with an oxidizing agent such as air or steam, introduced through inlet 102.The zinc/oxidizer mixture is reacted to form zinc oxide while passing through heat exchange coils 103 'located inside main reactor 1. Thus the heat development during the reaction of the zinc with the oxidizer to form zinc oxide is effectively utilized to heat the reaction mixture in reactor 1. The mixture of solid zinc oxide and gas is passed from the heat exchange coils 103 into a cyclone 1()4 from which a gaseous effluent freed of zinc oxide particles is removed via line 1()5: From the lower portion of the cyclone 104, the solid, finely divided zinc oxide is withdrawn and passed via line 90 into reactor 1. Makeup zinc oxide is introduced via line 106.

In accordance with another embodiment of this invention, the amount of heat generated by the reoxidation of zinc to zinc oxide becomes controllable, without changing the quantity of zinc oxide circulated, by reoxidizing a first portion of the zinc with air and a second portion of the zinc with H2O. In a process in which zinc is reoxidized into zinc oxide with air alone, this reoxidation furnishes essentially a constant amount of heat per unit of Zn reoxidized. Without changing the quantity of ZnO produced, the quantity of heat produced cannot be changed. Thus the temperature in the carbon monoxide-forming reaction cannot be controlled without changing the quantity of ZnO that is produced by the zinc oxidation in heat exchange with the CO-forming reaction.In accordance with the present embodiment, this type of control is possible because the heat developed per mole of zinc oxide formed is dependent upon whether air or H,O is utilized as the oxygen source. The amount of heat developed by the oxidation of a given quantity of zinc with air is higher than the amount of heat developed by the oxidation of the same quantity of zinc with H,O. Thus depending upon the relative sizes of the first and second portions of zinc, the total amount of heat developed by oxidizing a given quantity of zinc can be adjusted, changed or controlled without changing the total amount of zinc oxidized and thereby provide a thermally neutral system in which the heat liberated in the exothermic zinc oxidations essentially balances the heat requirements of endothermic carbon oxidation reaction plus the system heat leak when the reactions are carried out in indirect heat exchange relationship with each other.

Another advantage of this embodiment of the invention resides in the production of relatively pure hydrogen as a by-product. This hydrogen can be combined with part of the CO produced to make methanol or methane. The hydrogen can also be used or sold as such.

The relative quantities of zinc that are reoxidized with air and with H,O depend upon the efficiency of the heat transfer from these exothermic oxidation reactions to the endothermic carbon monoxide-forming reaction. Typically, the ratio of the portion of the total zinc to be reoxidized with air to the portion of the total zinc to be reoxidized with H2O is in the range of 1.1:1 to 6.0:1.

Most preferably. the zinc-zinc oxide reactions of this invention are carried out in a cyclic manner in which the zinc oxide formed both by oxidation of zinc with air and with H2O is reintroduced into the main carbon monoxide-forming reaction. The two zinc oxide streams can be introduced separately or can be combined and introduced together into the carbon monoxide-forming reaction.

The splitting of the zinc stream to provide the two streams for the two separate reoxidations can be achieved anywhere downstream of the main carbon monoxide-forming reaction. The gaseous effluent from the reactor can be split into two streams which are individually separated into a carbon monoxide and zinc stream to provide a first and a second zinc stream for the two reoxidation reactions. Alternatively the total gaseous effluent is first separated into a gaseous carbon monoxide stream, the product of the process, and a liquid zinc stream. This liquid zinc stream is then split into two liquid streams that are individually utilized for reoxidation with air on the one hand and H2O on the other hand.

Thus in accordance with a preferred embodiment of this invention, the gaseous effluent stream is fractionated to form one stream of liquid zinc and one carbon monoxide stream.

The zinc stream is split into a first and a second portion. The first portion of the zinc stream is oxidized in a first oxidation zone with air. The second portion of thi: zinc stream is oxidised in a second oxidation zone with H2O. An indirect heat exchange is established between the reaction and both the first and the second oxidation zone.

A particularly efficient heat exchange can be achieved if at least a portion both of the first and of the second oxidation zone is arranged in indirect heat exchange relationship with the reaction zone mentioned above. This can be done by arranging the first and second oxidation zones as such within the reactor in which the carbon monoxide-forming reaction is carried out.

One of the main advantages of this embodiment of the present invention resides in the possibility of controlling the temperature of the reaction forming the carbon monoxide. To carry out this temperature control, it is presently preferred to determine the heat required for the carbon monoxide-forming reaction and to manipulate the ratio of the two zinc streams responsive to the heat requirement. More particularly, the ratio of the zinc stream oxidized with air to the zinc stream oxidized with H,O is increased when the heat required for the carbon monoxide-forming reaction is increased and vice versa.

In accordance with a preferred embodiment. the temperature of the reaction between the carbon source and zinc oxide is sensed and a reaction temperature signal is generated responsive thereto. Then the flow of the first portion of zinc or the flow of the second portion of zinc or both are manipulated responsive to this control signal to control the temperature in the reaction by controlling the quantity of heat developed in the overall oxidation of the zinc. Thereby without changing the quantity of total zinc flowing in the system, the heat developed in the exothermic reactions of the cyclic operation can be readily adjusted.

In accordance with a further embodiment of this invention, there is also provided an apparatus for the production of carbon monoxide from carbonaceous materials in which the process of this invention can be carried out. This apparatus comprises a reaction section having first inlet means and second inlet means and outlet means connected thereto, a source of carbonaceous materials connected to the first inlet means and a source of zinc oxide connected to the second inlet means. A separating means for separating zinc from the gaseous effluent from the reactor is connected to the outlet means and from these separating means a carbon monoxide-comprising stream can be withdrawn via one conduit and a liquid zinc stream can be withdrawn from another conduit. A first oxidizing unit in the apparatus of this invention is provided for the conversion of zinc to zinc oxide.This first oxidizing unit has a first zinc inlet connected to the separating means for introducing a portion of this zinc into the first oxidizing unit. The first oxidizing unit also has an air source connected to an air inlet of the oxidizing unit so that air can be injected into the first oxidizing unit and the zinc that is in this unit can be oxidized. The first oxidizing unit finally comprises a zinc oxide outlet means and a first gas outlet means. The apparatus of this invention further is provided with a second oxidizing unit having essentially the same function as the first oxidizing unit with the difference, however, that instead of an air source there is provided an H2O source and an H,O inlet to this second oxidizing unt so that zinc in this second oxidizing unit is contacted with H2O and converted into zinc oxide. The second oxidizing unit is also provided with a second zinc oxide outlet and a second gas outlet means. Both the first oxidizing unit and the second oxidizing unit are in indirect heat exchange relationship with the reaction section such as to transfer at least a portion of the heat developed in the two oxidizing units to the reaction section. The first and second zinc oxide outlets of the first and second zinc oxidizing units are operatively connected to the reaction section and to the second inlet means for the introduction of zinc oxide. Thus a gasification operation that is readily controllable can be carried out for converting carbonaceous materials into carbon monoxide.

Most preferably the reaction section consists of one reactor vessel and the two oxidizing units are at least partially arranged inside of this reactor vessel for indirect heat exchange between the Interior of the oxidizing units and the interior of the reactor vessel. It is advantageous to provide means in both oxidizing units to separate the zinc oxide formed from the gas consisting essentially of nitrogen in the first oxidizing unit and from the gas consisting essentially of hydrogen in the second oxidizing unit. The zinc oxide produced in the two units and leaving the two cyclones is preferably combined and injected into the reaction section as a combined zinc oxide stream.

For an accurate, fast control of the apparatus. it is preferred to provide means for sensing the temperature in the reaction section and for generating a control signal responsive thereto. Flow manipulating means. such as a three-way valve in the zinc stream. are operatively connected to this temperature-sensing means to increase or decrease the flow rate of zinc into the first oxidizing unit and correspondingly decrease or increase the flow rate of zinc into the second oxidizing unit responsive to the control signal if the temperature in the reaction section is below or above a setpoint temperature.

In Figure 6 a main reaction vessel 1 is provided into which carbonaceous material is introduced via line 31 from a source 30. Zinc oxide is introduced into the reaction vessel 1 via line 4. The gaseous effluent leaving reactor vessel 1 via line 110 is essentially composed of carbon monoxide and zinc. A portion of this gaseous effluent is recycled directly into the reactor vessel 1 by means of pump 111 through line 112 to fluidize the materials in the reactor 1. A first oxidation unit 113 and a second oxidation unit 114 are arranged within the reaction vessel 1 in indirect heat exchange relationship with the materials in the vessel. The balance of the gaseous effluent from line 110 is passeed via line 115 into a condensing and separating unit 116.This condensing and separating unit 116 comprises an indirect heat exchange means 117 and a gas/liquid separating unit 118, as well as a pump 119. In heat exchanger 117, the liquid zinc precools the gaseous effluent in line 115 and thereby the liquid zinc is at least partially reevaporated. Gas consisting essentially of carbon monoxide leaves separating means 118 by way of line 120.

Liquid zinc is pumped from separating means 118 by means of pump 119 through the heat exchanger 117. Optionally, a further evaporating means to evaporate zinc can be provided (not shown in the drawing) and arranged downstream of the heat exchange means 117 in the zinc line 121. The zinc stream is then passed through a three-way valve 122 where it is split into a first stream 123 and a second stream 124. The first stream 123 is mixed with air from an air source 125 and the mixture of zine and air is passed via line 126 into oxidizing unit 114. In this oxidizing unit the zinc and air react to form essentially zinc oxide and nitrogen. The effluent from the oxidizing unit 114 is passed via line 127 to a separating means 128 such as a cyclone.In this cyclone 128 the solid zinc oxide is collected in the bottom and the gas consisting essentially of nitrogen leaves cyclone 128 via line 129.

Similarly, the second portion of the zinc stream flowing in line 124 is mixed with H2O, preferably in the form of steam, that comes fron an HO source 130. The mixture of steam and zinc is passed via line 131 into the second oxidizing unit 113 where this mixture is converted exothermically into zinc oxide and hydrogen. The zinc oxide/hydrogen mixture is passed via line 132 into a gas/solid separating means such as a cyclone 133. The gaseous effluent consisting essentially of hydrogen leaves the cyclone via line 134.

Zinc oxide leaving the two cyclones 128 and 133 via lines 135' and 135, respectively, are combined in line 4 and injected into the reactor vessel 1 as the oxygen donor for the carbon monoxide-forming reaction.

A sensing means 136, such as a thermocouple, measures the temperature and generates a signal responsive thereto. A controller 137 compares this reaction temperature signal with a setpoint signal from a setpoint signal source 138 and generates a control signal via line 139 responsive thereto. This control signal operates the three-way valve 122 in such a manner that the relative quantity of zinc flowing into the first oxidizing unit 114 increased when'ever the temperature sensed by the thermocouple 136 is below the setpoint and correspondingly increases the relative quantity of zinc flowing through the second oxidizing unit 113 whenever that temperature is above the setpoint.

Another embodiment of the apparatus for carrying out the present invention is shown in Figure 7. In this system, instead of one reactor there are provided two reactors, la and lb, in which carbon-containing material from source 3()a or 3()b is reacted with zinc oxide introduced via line 4a or 4b to form carbon monoxide and zinc vapour which gas mixture is withdrawn via lines 11()a and limb. Similarly. there is provided a direct recycle stream of effluent gas which is injected by means of pump Illa and 111b via lines 112a and 112b as a fluidizing gas.In reactor la the oxidizing unit 114 is arranged whereas the oxidizing unit 113 is arranged within the reactor ib. The balance of the gaseous effluents from the two reactors in lines 115a and 1 15b are combined and separated in the separating unit 116 which is the same as that shown in Figure 6. into a gas stream consisting essentially of carbon monoxide in line 120 and a zinc stream in line 121. This zinc stream is then split into a first stream 123 for the reoxidation with air from air source 125 and a second stream in line 124 for the reoxidation with an H2O stream from H2O source 130. Two valves 122a and 122b are provided to control the relative amounts of zinc flowing into the two oxidation units.

The two zinc oxide outlets of the two cyclones 133 and 128 are interconnected by a line 140.

Since the heat generated by oxidizing zinc with H,O per mole of zinc is less than the amount of heat consumed by the production of 1 mole of zinc and 1 mole of carbon monoxide, a larger quantity of zinc has to be oxidized in reoxidation unit 113 than that which is chemically necessary in the reactor lb. Therefore, the difference of zinc oxide produced in the reoxidation unit 113 is transferred via line 140 and line 4a into the reactor la.

In accordance with another modification of this invention, zinc values, which are otherwise lost in the ash by-product when using zinc oxide as the oxygen source for the conversion of a carbonaceous source to carbon monoxide in a primary reaction zone, are readily recovered by treating the ash containing zinc values with hot air whereby the zinc values are converted to zinc oxide. The resulting zinc oxide in admixture with ash is thereafter used as the oxygen source for conversion of additional carbon source to carbon monoxide in a secondary reaction zone wherefrom a carbon monoxide and zinc metal mixture is removed. Zinc is separated from the carbon monoxide, reconverted to zinc oxide and thereafter returned to the primary reaction zone.

The reaction in the secondary reaction zone, wherein the zinc values in the form of zinc oxide are utilised for the conversion -of additional carbon source to carbon monoxide, is also carried out at elevated temperature. The reaction in both reaction zones is conducted at a temperature in the range of 910"C to 1540"C. To assure high zinc oxide conversion, the second reaction is preferably operated at a higher temperature and for a longer reaction time than that employed in the first reaction zone. An average reaction time of from 5 minutes to 2 hours is satisfactory.

The zinc oxide in the second reaction zone is preferred to be in a finely divided state, as employed in the first reaction zone. If necessary, the ash-zinc oxide mixture can be passed through a grinder before introduction into the second reaction zone.

Since it is desired to avoid loss of zinc in the secondary reactor by further entrainment of zinc values in the ash, carbon sources for the secondary reactor are preferably those having a very low sulfur content, below 0.01 weight percent. or those which are essentially free of sulfur.

Zinc values entrained in ash from the first reaction zone are contacted at a temperature in the range 1093 to 16500C in a second oxidation zone with oxygen to form a second quantity of zinc oxide. This recovered or regenerated zinc oxide in admixture with ash is introduced to a secondary reaction zone wherein a quantity of low-sulfur or sulfur-free carbon source is converted to carbon monoxide at a temperature in the range of 910 to 15400C. Heating of the reaction mixture is achieved by indirect heat exchange with the oxidation reaction mixture wherein the entrained zinc values are converted to zinc oxide. From the reactor a gas comprising essentially carbon monoxide and zinc vapour is withdrawn. From the bottom of the reactor solids containing ash which is essentially free of zinc values are withdrawn.The carbon monoxide-zinc gas may be combined with product gas from the first reactor which is then cooled and separated into a gas stream consisting of carbon monoxide and a liquid zinc stream. The zinc stream, representing the recovered zinc values, is then reoxidized to zinc oxide for return to the primary reactor.

As shown in Figure 8, hot char at a temperature of about 2000"F is introduced into the primary reactor 150 via line 151. Particulate zinc oxide is introduced into the primary reactor via line 152. The solid materials are mixed in the reactor 150 by a fluidizing stream of carbon dioxide, carbon monoxide or a mixture of carbon monoxide and carbon dioxide which is introduced into the reactor via line 153. The initial charge of zinc oxide as oxygen source to reactor 150 is made by passing make-up zinc oxide through lines 154 and 155, through reaction zone 156 and ultimately line 152.

Ash accumulates in the lower section of the reactor 150 and is withdrawn via line 157.

Carbon monoxide and zinc. as well as any other gaseous by-products, are removed free of entrained solids from reactor 150 via line 158. A cyclone, not shown, can be provided in reactor 150 to separate entrained solids from the gaseous reactor effluent and return thereof to the reactor bed.

Effluent gas, consisting essentially of carbon monoxide and zinc, is passed via line 158 to heat exchanger 159 wherein gas is condensed through indirect heat exchange with liquid zinc from phase separator 160. In phase separator 160 the liquid zinc is separated from the CO gas. Product gas is removed via line 161.

The condensed liquid zinc in phase separator 160 is withdrawn via line 161, passed through heat exchanger 159 to revaporize the zinc by indirect heat exchange with the reactor produced gases, and introduced into line 162. In line 162, the zinc vapour is admixed with hot air (90() to 16500C) via conduit 163. The resulting admixture is then passed to reaction zone 156 via line 155 wherein the zinc is oxidized to zinc oxide. Following oxidation, the reaction mass is passed via line 164 to separator 165 wherein the gaseous content, consisting essentially of nitrogen and excess oxygen, is removed via line 166. Zinc oxide is withdrawn from the bottom of separator 165 via line 152 and introduced into reactor 150.

The gaseous product stream consisting essentially of carbon monoxide and some carbon dioxide recovered via line 161 from separator 160 can be treated in a heat recovery unit 167 to remove heat therefrom for further use. Thereafter the gaseous stream is passed to a carbon dioxide absorber-stripper 168 via line 169 wherein any CO, present is removed, thereby providing a product stream 170 which is essentially pure carbon monoxide. CO, removed in absorber-stripper 168 can be returned via lines 171 and 153 to the main reactor 150 for further use in the fluidizing of the reactor bed or can be vented.

Ash containing entrained zinc values, generally in the form of zinc sulfide, is removed via line 157 from reactor 150 and passed via line 172 into heat exchange relationship with the interior of secondary reactor 173. Hot air (900 to 16500C) is introduced via line 174 into line 172 in an amount to effect conversion of the zinc values in line 172 to the oxide. Heat generated during this exothermic reaction is provided via heat-exchange section 175 to assist in maintaining the contents of secondary reactor 173 at the desired level.Following heat exchange of the reactants moving in heat exchange zone 175, the reactants, principally zinc oxide, ash and nitrogen along with some air and CO2, are passed via line 176 to separator 177 wherefrom gaseous portions consisting essentially of nitrogen, air and carbon dioxide are removed via line 178 and solid particles consisting essentially of a mixture of zinc oxide and ash and further oxidized char are removed via line 179 and introduced into secondary reactor 173. A second char charge having a low sulfur content is introduced via line 180 into secondary reactor 173, which is operated in a manner similar to that of primary reactor 1 but generally at higher temperature and longer reaction time. Ash now essentially free of zinc values accumulates in the lower section of reactor 173 and is withdrawn via line 181.Gaseous zinc and CO are withdrawn free of entrained solids overhead via line 182 and are combined in conduit 158 with the gaseous effluent from primary reactor 150.

Gaseous effluent removed from separator 177 via line 178 is'passed to heat recovery unit 183. The resulting cooled gas is thereafter passed via line 184 to CO, absorber-stripper 185 wherein a stream consisting essentially of CO2 is separated and removed via line 186 for recycle via lines 187 and 188 to reactors 150 and 173 or is vented. A further gaseous stream 189 which consists essentially of nitrogen and air is withdrawn from absorber-stripper unit 185.

In the event SO, is present in the system. a sulfur removal unit 190 can be employed in line 186 whereby an essentially pure CO, stream is provided in line 187 with sulfur oxides or sulfur and oxygen being removed from unit 190 via line 191.

According to another embodiment of the invention, the carbon source is contacted in a preheating step with at least a portion of the gas produced in the gasification zone. The carbon source is thereby preheated and any zinc present in this portion of the gas is condensed on the carbon source. The carbon source together with zinc is exposed to steam for oxidizing the zinc to zinc oxide thus forming a mixture of the carbon source with zinc oxide. In the final gasification step the carbon source and zinc oxide are reacted to form a gas comprising carbon monoxide and zinc.

The process of this embodiment provides several important advantages. The carbon source is preheated by the direct countercurrent contacting with at least a portion of the product gases so that a considerable portion of the sensible heat of these gases above the temperature of the carbon source feedstock is recovered. All the volatiles such as water, light hydrocarbons and even some coal tar products are volatilized and stripped from the carbon source in this preheating step. This is of particular advantage in cases where the carbon source contains a significant amount of these materials, as in the case of coal.

Furthermore, any uncondensed zinc in the gases utilised to contact the carbon source is recovered by condensation of this zinc onto the carbon source particles. This advantage is significant because molten zinc has an appreciable vapour pressure at temperatures far below its boiling point of 907"C. For example, at 730"C the vapour pressure of zinc is still about 100 mm Hg.

In one form of this embodiment. the carbon monoxide and zinc comprising gas leaving the gasification zone is split into two streams and one of these streams is directly contacted with the carbon source in the preheating zone. In this method the gas stream contacting the carbon source is a zinc-rich stream. The remaining stream is introduced into a zinc separation zone in which the zinc is removed from this gas stream. The zinc-lean gas stream preferably is also contacted with the carbon source.

In another form of this embodiment. the carbon monoxide and zinc-comprising gas stream from the gasification zone is passed to a zinc separation zone where the major portion of the zinc is separated from this gas stream, e.g., by condensation. The remaining zinc-lean gas stream is passed into contact with the carbon source resulting in a zinc-free carbon monoxide comprising product gas stream. Zinc is condensed on the carbon source.

The zinc from the zinc separation zone can be introduced as such into the oxidation zone where the zinc in contact with the carbon source and in the presence of steam is reacted into zinc oxide and hydrogen. A portion of the zinc can also be converted to zinc oxide in a zinc combustion zone by contacting the zinc with a free oxygen-containing gas such as air.

Preferably, the thermal energy of this zinc combustion zone is utilised to supply at least a portion of the heat consumed in the endothermic gasification reaction between the carbon source and the zinc oxide.

It is desirable to have as much of the zinc condensed on the feed solids as possible. In practice this quantity will be limited by the heat balance and the desired operating temperature in the zinc oxidation zone. The maximum amount of zinc introduced into this zinc oxidation zone is limited to the stoichiometric quantity which can be oxidized by the steam. Zinc oxide deposited on the feed solids via condensation will be present in a very finely divided state and very uniformly distributed over the surface of the solids. The subsequent conversion of zinc oxide and carbon into carbon monoxide and zinc will, therefore, be very efficient.

This modification of the invention minimizes the use of indirect heat exchangers and reduces the size of zinc separation zones. Thus, the investment costs for such a plant are reduced while at the same time the thermal efficiency of the process is in'creased. Some or all of the steam required may be generated by heat exchange with gasifier effluent.

Depending upon the operating conditions, a fraction of the carbon source may be already gasified in the zinc oxidation zone. This is, however, not detrimental to the process because the gas produced in this section of the process is essentially of the same composition as the gas desired.

The temperature and pressure conditions in the three zones preferably are as follows: Preferred Operating Conditions Temperature Reference Numeral "C in Figures 9-11 Preheating zone: Feed temperature Ambient 200 Zone outlet temperature 150-970 201 Oxidation zone 500-1200 205 Gasification zone 910-1540 209 Zn-combustion zone 1200-1800 217 Residence Time Preheating zone 1-30 min. 201 Oxidation zone 2-30 min. 205 Gasification zone 10 min.-2 hrs. 209 Zn-combustion zone 0.1-10 sec. 217 To move the materials through the various zones the contacting and reactions are carried out at slightly superatmospheric pressure. If desired, however, the reactions can be carried out at higher pressures, and high pressure carbon monoxide can be produced as the product of the process. The preferred operating pressure range for the process is 1 to 4 atmospheres (101 to 401 kPa).

The beds for preheating steam oxidation of the zinc. gasification and zinc combustion may be moving beds or agitated beds. The preheating bed is preferably operated as a moving bed in order to achieve a particularly efficient heat and zinc recovery in this bed. If the preheating zone, the zinc oxidation zone and the gasification zone are operated in separate vessels, the gasification zone is preferably operated as a fluidized bed. The zinc oxidation zone, too, is in this case preferably operated as a fluidized bed.

As shown in Figure 9, a carbon source such as coal or char is fed via line 20() to preheater 201. In preheater 201 the carbon source is countercurrently contacted with a gas stream from line 202. This gas stream is a carbon monoxide and hydrogen-containing gas stream but also contains zinc. Zinc is condensed on the carbon source particles and these particles containing some zinc are removed from the preheater 201 via line 203. Product gas stream that is free of zinc is removed from the preheater 201 via line 204.

The zinc-containing carbon source particles are introduced via line 203 to zinc oxidation zone 2()5. Into zinc oxidation zone 205 steam is introduced via line 206. Zinc is introduced into this zone via line 207. In zone 205 the zinc on the carbon source is reacted with steam, producing zinc oxide in finely divided form on the carbon source and hydrogen. which leaves the zinc oxidation zone via line 202. The carbon source together with zinc oxide is passed from the zinc oxidizing zone 205 via line 208 to gasification zone 209. In this gasification zone the carbon source and the zinc oxide are reacted to form gaseous effluent comprising carbon monoxide and zinc. which leaves the gasifier 209 via line 210. The zinc oxide utilised as the oxygen source in this reaction is introduced in part via line 2()8 from zinc oxidizer 205 and in part via line 211.Ash is removed from the gasification section 209 via line 245.

The gaseous effluent comprising carbon monoxide and zinc is passed via line 210 to a cooler 212 and a zinc separator 213. Zinc is removed from this zinc separator 213 via line 214. A portion of this zinc removed via line 214 is introduced into the zinc oxidizer via line 207. Another portion of the zinc is passed via line 215 together with air introduced via line 216 into a zinc combustion unit 217. In this zinc combustion unit 217 zinc and air are converted to zinc oxide and a gas consisting essentially of nitrogen. The zinc combustion zone 217 is located in indirect heat exchange relationship inside of the gasification zone.

The zinc oxide suspension is passed via line 218 to a zinc oxide separator such as a cyclone or filter 219. The solid zinc oxide is removed from separator 219 via line 211 and introduced into the gasifier as explained above. Zinc oxide-free offgas consisting essentially of nitrogen is removed from the separator 219 via line 22(). Carbon monoxide-containing gas containing only a small quantity of zinc is removed from the zinc separator 213 via line 221. This gas is introduced into the zinc oxidizer where part of the zinc is oxidized to zinc oxide. A small portion of zinc remains in the gas stream 202 and is consensed onto the carbon source in the preheater 2()1. Alternatively, a portion of the carbon monoxide and zinc-comprising gas in line 21() can be passed directly to the zinc oxidizer. The quantity of this gas is controlled by valve 222.

Figure 1(1 shows an embodiment of the present invention in which the preheating zone, the zinc oxidation zone and the gasification zone are all arranged within one long.

preferably vertically arranged housing 25(). The feed lines and the product withdrawal lines have been given the same reference numerals as in Figure 9 so that a detailed explanation of these lines can be avoided. In this embodiment no separation of zine and no handling of zinc is necessary. Rather, the zinc in vapour form is removed from the lower section of the housing 25() as a gas. is partly oxidized in the central portion to form a solid and the remainder is condensed as metal in the upper portion on the carbon source feed and moved back down with this feed where it is finallv oxidized with steam. In this embodiment it is necessary to provide an external heating fluid in order to supply the heat necessary for the overall process. In return for this additional heat a higher relative quantity of hydrogen is produced in this embodiment.Any heating fluid can be used for the purpose of supplying the heat necessary for the gasification reaction in the gasification zone 2()9. The heating coils 217 transmit this heat to the carbon source and the zinc oxide and the cooled heating fluid leaving the coils 217 can be reseated. e.g. in a gas-firer burner (not shown).

A further embodiment of this invention is schematically illustrated in the flow diagram of Figure 11. From a coal reservoir I a coal is introduced via line 20() into the preheater 201.

Zinc-free carbon monoxide and hydrogen comprising product gas is removed from preheater 2()1 via line 2(14. A product gas stream containing a small quantity of zinc is introduced countercurrently via line 2()2 into preheating zone 201. The coal particles remove the zinc from this stream. These coal particles containing condensed thereon some zinc are passed via line 2()3 to a vessel 23() in which both the zinc oxidation zone 205 and the gasification zone 2()9 are arranged. From this vessel 230 a zinc, carbon monoxide and hydrogen-containing stream is withdrawn via line 231, and passed through two indirect heat exchangers 232 and 232' to zinc separator 233. A portion of this stream can be passed directly via line 2()2 controlled by valve 234 into preheated 2()1.Generally () to about 25 percent of the stream leaving the zinc oxidizer and containing Zn, CO and H2 is passed via line 2()2' to the preheater. From the zinc separator the carbon monoxide-containing gas stream. being lean in zinc. is withdrawn via line 202 and introduced into preheater 201. Zinc is removed from the zinc separator via line 235. The reheated zinc leaving the heat exchanger 232 is in part introduced via line 236 into zinc oxidation zone 2()5 where this zinc reacts with steam. introduced into the vessel 23() from a water or steam source 2a via line 237 through the heat exchanger 232' and. in part. is introduced via line 238 into admixture with air, supplied from air source 55a via line 239 to a zinc combustion zone 217.Zinc combustion zone 217 is in indirect heat exchange relationship with the carbon source and the zinc oxide and supplies the thermal energy consumed during the endothermic gasification reaction. A zinc oxide suspension is removed from the zinc combustion zone 217 via line 240. Zinc oxide is removed from this suspension in separator 241 and reintroduced via line 242 into the gasification zone as explained in connection with Figure 9.

Gas comprising essentially nitrogen is vented via line 243.

EXAMPLE II Flow quantities in kilogram moles per hour are shown in the following table for a case assuming 100% conversion of the char, entrance and exit of all reactants and products at 77 F (25 C) and an operation temperature of the gasifier reactor 1 at 2077 F (1137 C) under a pressure of between 1 and 4 atmospheres. The following table shows a material balance for these materials.The figures shown in parenthesis refer to Figure 6. TABLE Char (31) Water (130) Air (125) Product Zinc Hydrogen Nitrogen Oxides (121) (134) (129) (120) Carbon (C) 6.36 Hydrogen (H) 0.80 Nitrogen (N) 0.04 Sulfur (S) 0.11 Oxygen (O2) 1.91 Nitrogen (N2) 7.22 7.22 CO 6.12 CO2 0.24 NO 0.04 SO2 0.11 Zn 7.27 Ash 0.18 Water 3.45 0.40 Hydrogen (H2) 3.45 Totals 7.49 3.45 9.13 6.91 7.27 3.45 7.22 If an overall efficiency of only 70neo is assumed allowing for heat leakage, heat exchange losses and the like, the corresponding feed rates would be 1.13 kilogram moles per hour of water and 3.07 kilogram moles per hour of oxygen.

The 7.27 kilogram moles of zinc circulating in the system in case of a 100% conversion under the conditions given above, would be split into 3.45 kilogram moles in line 124 and 3.82 kilogram moles in line 123. Correspondingly, for only a 70% efficient process as indicated, the 7.27 kilogram moles of zinc circulating in the system would be split into 1.13 kilogram moles in line 124 and 6.14 kilogram moles in line 123.

WHAT WE CLAIM IS: 1. A process for the production of carbon monoxide, which comprises reacting a solid carbon source with zinc oxide in a reaction zone at a temperature in the range 1665 to 2800"F to produce a gas stream containing zinc and carbon monoxide, oxidizing the zinc, with or without prior separation from said gas stream, to form zinc oxide, recovering and recycling the zinc oxide to the reaction zone, and recovering said carbon monoxide as the process product.

2. A process according to claim 1, wherein the carbon source and the zinc oxide are reacted in finely divided form in the presence of a fluidizing gas.

3. A process according to claim 1 or 2, wherein the zinc oxide and the carbon source are reacted at a ratio of from 0.9 to 1.2 moles per gram atom of carbon in the carbon source.

4. A process according to any one of the preceding claims, wherein the zinc is separated from said gas stream by condensation and then oxidized.

5. A process according to any one of the preceding claims, wherein the carbon source contains up to 8% by weight of sulfur.

6. A process according to claim 5, wherein the carbon source and zinc oxide are reacted at a temperature above 2165"F and by-product zinc sulfide is condensed from the gaseous product stream for recovery of the zinc therefrom.

7. A process according to any one of the preceding claims, wherein the carbon source is a solid residue from a coal gasification or liquefaction process.

8. A process according to claim 2, wherein the fluidising gas comprises carbon monoxide.

9. A process according to claim 1, when carried out substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

10. A process according to any one of claims 1-7, wherein heat of reaction is transferred from the zinc oxidation process to the carbon source/zinc oxide reaction using a heat exchange fluid circulating in indirect heat exchange relationship with the two reaction mixtures.

11. A process according to claim 10, wherein there is used as said heat exchange fluid a compound which is in vapour phase at the temperature of the zinc oxidation reaction and in liquid phase at the temperature of the carbon source/zinc oxide reaction.

12. A process according to claim 11, wherein the heat exchange fluid is elemental sodium, potassium, zinc or a mixture of sodium and potassium.

13. A process according to claim 10 or 11, wherein the zinc separated from the product gas stream is at least partially revapourised by indirect heat exchange with the product gas stream and the revapourised zinc is split into three streams, the first of which is fed as reactant to the zinc oxidation stage, the second of which is used as a carrier stream for the recycle zinc oxide and the third of which is fed to the carbon source/zinc oxide reaction as a fluidising gas.

14. A process according to claim 10 or 11. wherein the heat exchange fluid is zinc and wherein the zinc is separated from the product gas stream by condensation into liquid phase, a first part of said separated zinc in liquid phase being used to provide at least part of the said heat exchange fluid and a second part being fed as reactant to the zinc oxidation stage, with a side stream of zinc in vapour phase being withdrawn from the heat exchange fluid circuit and used as a carrier stream for the recycle zinc oxide.

15. A process according to claim 14, wherein said second part of the condensed zinc is revapourised by indirect heat exchange with the product gas before feeding as reactant to the zinc oxidation stage.

16. A process according to claim 10, substantially as described with reference to Figure 2 or 3 of the accompanying drawings.

17. A process according to any one of claims 1-7, wherein zinc recovered from the product gas is at least partially reevaporated by indirect heat exchange with the product gas stream and the reevaporated zinc stream fed in indirect heat exchange with the zinc oxidation reaction mixture prior to feed as reactant zinc vapour to the zinc oxidation stage.

18. A process according to claim 17, when carried out substantially as described with reference to Figure 4 of the accompanying drawings.

19. A process according to any one of claims 1-8, wherein the zinc oxidation reaction is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. If an overall efficiency of only 70neo is assumed allowing for heat leakage, heat exchange losses and the like, the corresponding feed rates would be 1.13 kilogram moles per hour of water and 3.07 kilogram moles per hour of oxygen. The 7.27 kilogram moles of zinc circulating in the system in case of a 100% conversion under the conditions given above, would be split into 3.45 kilogram moles in line 124 and 3.82 kilogram moles in line 123. Correspondingly, for only a 70% efficient process as indicated, the 7.27 kilogram moles of zinc circulating in the system would be split into 1.13 kilogram moles in line 124 and 6.14 kilogram moles in line 123. WHAT WE CLAIM IS:

1. A process for the production of carbon monoxide, which comprises reacting a solid carbon source with zinc oxide in a reaction zone at a temperature in the range 1665 to 2800"F to produce a gas stream containing zinc and carbon monoxide, oxidizing the zinc, with or without prior separation from said gas stream, to form zinc oxide, recovering and recycling the zinc oxide to the reaction zone, and recovering said carbon monoxide as the process product.

carried out in indirect heat exchange relation with the carbon source/zinc oxide reaction.

20. A process according to claim 19. wherein zinc is recovered from the product gas stream by condensation, the condensed zinc being at least partially revaporised by indirect heat exchange with the product gas, and the vapourised zinc thereafter being reoxidized with air or steam in indirect heat exchange relation with the carbon source/zinc oxide reaction.

21. A process according to claim 19, when carried out substantially as described with reference to Figure 5 of the accompanying drawings.

22. A process according to any one of claims 1-8, wherein a first portion of said separated zinc is reoxidized by reaction with air and a second portion is reoxidized with steam, and wherein at least a portion of the heat produced in those oxidation processes is transferred to the carbon source/zinc oxide reaction.

23. A process according to claim 22, wherein the zinc is recovered from the product gas by condensation into the liquid phase. and the liquid phase zinc at least partially revapourised by indirect heat exchange with the product gas before reoxidation with said steam or air.

24. A process according to claim 22 or 23, wherein the oxidation reactions are carried out in reaction zones which are at least partially in indirect heat exchange relation with the carbon source/zinc oxide reaction mixture.

25. A process according to claim 22, 23 or 24, wherein the temperature of the carbon source/zinc oxide reaction is monitored and the relative proportions of the zinc passed for oxidation by said air and steam respectively adjusted in response thereto.

26. A process according to claim 22, 23 or 24, wherein the heat required for the reaction of the carbon source and zinc oxide is determined, a control signal generated responsive thereto, and the ratio of the proportions of zinc passed for oxidation by said air and steam respectively adjusted in response thereto.

27. A process according to claim 22, 23 or 24, wherein the reaction between the carbon source and the zinc oxide is carried out in two reaction zones in parallel, and wherein the zinc oxidation reactions between said zinc and said air and steam respectively are carried our in indirect heat exchange relation each with a different one of said zones.

28. A process according to claim 27. wherein all the zinc oxide produced by oxidation of said zinc with air is introduced into the carbon source/zinc oxide reaction zone with which that oxidation reaction is in indirect heat exchange relation, and the zinc oxide produced by the other of the oxidation reactions is divided between said zones.

29. A process according to claim 22, when carried out substantially as described with reference to Figure 6 or 7 of the accompanying drawings.

30. A process according to any one of claims 1-8, wherein ash withdrawn from the carbon source/zinc oxide reaction is separately oxidized to convert zinc values therein to zinc oxide and the zinc oxide so produced reacted with additional carbonaceous material to produce a secondary product gas stream containing carbon monoxide and zinc from which the carbon monoxide is recovered as additional carbon monoxide product and the zinc is recovered for oxidation to zinc oxide which is recycled.

31. A process according to claim 30. wherein the carbonaceous material used as carbon source in the recovery of the zinc values from said ash is substantially sulfur-free.

32. A process according to claim 30 or 31, wherein the zinc values in the ash are oxidized by treating the ash with air, the oxidation taking place in indirect heat exchange relation with the reaction mixture comprising the reconverted zinc oxide and said additional carbonaceous material.

33. A process according to any one of claims 30-32, wherein the zinc is recovered from the primary and secondary product gas streams by condensation into liquid form, and wherein the liquid zinc is at least partially vapourised by indirect heat exchange with the primary product gas stream, the zinc vapour so formed being oxidized by reaction with an oxidizing gas in indirect heat exchange relation with the primary reaction mixture comprising said carbon source and said zinc oxide.

34. A process according to claim 30. when carried out substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.

35. A process according to claim 1. which comprises passing the carbon source sequentially through a preheater, a zinc oxidizing zone and a gasification zone: contacting the carbon source in said preheater with hot gas from the gasification zone; introducing steam and zinc into the oxidation zone to form a reaction mixture containing said zinc, steam and said carbon source and reacting said mixture to form a solids mixture containing said carbon source and zinc oxide, and a gaseous product stream containing hydrogen, reacting said solids mixture in said gasification zone to produce said product gas stream and passing at least a portion of said product gas stresam through said preheater in countercurrent contact with the carbon source thereby to heat the carbon source and form a deposit of zinc thereon from the product gas stream.

36. A process according to claim 35, wherein a major portion of the zinc in said product gas stream is separated therefrom on leaving the gasification zone for conversion into zinc oxide and recycling as reactant to the gasification zone, and minor portion is carried in the product carbon monoxide stream into countercurrent contact with the carbon source in said preheter via the zinc oxidizing zone.

37. A process according to claim 36, wherein part of the separated zinc is fed to the oxidizing zone for oxidation therein into zinc oxide in the presence of the carbon source and wherein the rest of the separated zinc is separately oxidized into zinc oxide for recycle direct to the gasification zone.

38. A process according to claim 37, wherein the rest of said separated zinc is oxidized to zinc oxide in a reaction zone in indirect heat exchange relation with said gasification zone.

39. A process according to claim 35, wherein at least a portion of the product gas leaving the gasification zone is passed directly into the zinc oxidation zone from which an oxidation zone off gas is withdrawn and passed to the preheater in countercurrent contact with the carbon source.

40. A process according to claim 39, wherein the whole of the product gas leaving the gasification zone is passed directly into the oxidizing zone and at least part of the off gas from the oxidizing zone is fed to a zinc separator before passing to the preheater, the zinc recovered from said separator being reoxidized and recycled as zinc oxide to the gasification zone. 'A

41. A process according to claim 35, when carried out substantially as described with reference to Figure 9, 10 or 11 of the accompanying drawings.

42. A process according to claim 1, substantially as hereinbefore described in Example I.

43. A process according to claim 22, substantially as hereinbefore described in Example II.

44. Apparatus for carrying out the process of claim 22, comprising at least one reaction vessel having feed inlets for the carbon source and zinc oxide, an outlet for the product gas, a separator connected to the outlet for the recovery of zinc from the product gas, first and second oxidation reactors positioned in indirect heat exchange relation with said vessel or vessels, said first and second reactors each being connected to the separator for the supply of recovered zinc thereto and having an inlet for the separate supply of oxidizing gases thereto and having an outlet connected to the reaction vessel or vessels for the recycle of the zinc oxide produced therein to said vessel.

45. Apparatus according to claim 44, wherein the two oxidation reactors are at least partially located within said reaction vessel or vessels in indirect heat exchange relation with the reactants when in said vessel(s).

46. Apparatus according to claim 44 or 45, including means for sensing the reaction temperature in said vessel or at least one of said vessels and for generating a control signal in response thereto, and a flow control means operatively connected to said sensing means for increasing or decreasing the relative amounts of zinc fed to said two oxidation reactors, depending-on whether the sensed temperature in said vessel is above or below a set point temperature.

47. Apparatus according to claim 44, 45 or 46. wherein the two oxidation reactors are both positioned within the same reaction vessel.

48. Apparatus according to claim 44, substantially as described with reference to Figure 6 or 7 of the accompanying drawings.