Patent Application
20070294943
Aspects of the present invention relate to an improved gasification reactor and systems for preparing a mixture comprising carbon monoxide and hydrogen from a carbonaceous stream using an oxygen containing stream.
In another aspect, the invention relates to a process of preparing a mixture comprising carbon monoxide and hydrogen. Such a process may be performed in said reactor and in said system.
Methods for producing synthesis gas are well known from practice. An example of a method for producing synthesis gas is described in EP-A-400740. Generally, a carbonaceous stream such as coal, brown coal, peat, wood, coke, soot, or other gaseous, liquid or solid fuel or mixture thereof, is partially combusted in a gasification reactor using an oxygen containing gas such as substantially pure oxygen or (optionally oxygen enriched) air or the like, thereby obtaining a.o. synthesis gas (CO and H2), CO2 and a slag. The slag formed during the partial combustion drops down and is drained through an outlet located at or near the reactor bottom.
The hot product gas in the reactor of EP-A-400740 flows upwardly. This hot product gas, i.e. raw synthesis gas, usually contains sticky particles that lose their stickiness upon cooling. These sticky particles in the raw synthesis gas may cause problems downstream of the gasification reactor where the raw synthesis gas is further processed. Undesirable deposits of the sticky particles on, for example, walls, valves or outlets may adversely affect the process. Moreover such deposits are hard to remove.
Therefore, the raw synthesis gas is quenched in a quench section. In such a quench section a quench gas is injected into the upwardly moving raw synthesis gas in order to cool it.
EP-A-662506 describes a process to cool synthesis gas by injecting downwardly a cooling gas into said hot synthesis gas at the interface of a combustion chamber and a tubular part fluidly connected to the top of the combustion chamber.
A similar reactor as in EP-A-400740 is described in WO-A-2004/005438 of the same applicant. This publication describes a gasification combustion chamber and a tubular part fluidly connected to an open upper end of said combustion chamber. Both combustion chamber and tubular part are located in a pressure shell defining an annular space between said pressure shell and the combustion chamber and tubular part respectively. According to this publication, measures are required to avoid dust laden raw synthesis gas as prepared in the combustion chamber to enter the annular space. This publication also describes a syngas cooler having three heat exchanging surfaces located one above the other as present in a separate pressure vessel.
U.S. Pat. No. 5,803,937 describes a gasification reactor and a syngas cooler within one pressure vessel. In this reactor a tubular part is fluidly connected to an open upper end of a combustion chamber, both located within a pressure shell. At the upper end of the tubular part the gas is deflected 180° to flow downwardly through the annular space between the tubular part and the wall of the pressure shell. In said annular space heat exchanging surfaces are present to cool the hot gas.
The afore discussed gasification reactors have in common that the synthesis gas as produced flows substantially upwards and the slag flows substantially downwards relative to the gasification burners as present in said reactors. Thus, all these reactors have an outlet for slag, which is separate from the outlet for synthesis gas. This in contrast to a class of gasification reactors as for example described in EP-A-926441 where both slag and synthesis gas flow downwardly and wherein both the outlet for slag and synthesis gas are located at the lower end of the reactor.
The present invention is directed to an improved reactor of the type where slag and synthesis gas are separately discharged from said reactor as in e.g. WO-A-2004/005438 and U.S. Pat. No. 5,803,937. A problem with the syngas cooler of WO-A-2004/005438 and also with the apparatus of U.S. Pat. No. 5,803,937 is that the heat exchanging surfaces introduce a large complexity to the design of said apparatuses. Another problem with the syngas cooler of WO-A-2004/005438 and also with the apparatus of U.S. Pat. No. 5,803,937 is that the heat exchanging surfaces are vulnerable to fouling from feedstocks with for instance a high alkaline content. There is thus a desire to process high alkaline feedstocks as well as a desire to provide more simple gasification reactors. These and other objects are achieved with the reactor as described below.
The present invention provides a gasification reactor and systems for preparing a purified mixture comprising carbon monoxide and hydrogen.
The gasification reactor comprises:
Applicants found that by using such a gasification reactor, the use of complicated heat exchange surfaces could be avoided and high alkaline and high chlorine containing feedstocks could be processed. Other advantages and preferred embodiments will be discussed hereafter.
The invention is also directed to the following systems for preparing a purified mixture comprising carbon monoxide and hydrogen comprising of gasification reactor as described above.
In one such system, the outlet for synthesis gas is fluidly connected to an inlet of a wet gas scrubber and wherein the wet gas scrubber is provided with an outlet for purified mixture comprising carbon monoxide and hydrogen.
The above system is advantageous because a dry solid removal process step can be omitted and the overall system can be made more simple.
In another such system, the outlet for synthesis gas is fluidly connected to an inlet of the dry solids removal unit and wherein an inlet of the wet gas scrubber is fluidly connected to the gas outlet of the dry solids removal unit and wherein the wet gas scrubber is provided for an outlet for purified mixture comprising carbon monoxide and hydrogen.
According to another aspect, the invention further provides a process to prepare a mixture comprising carbon monoxide and hydrogen by partial oxidation of a solid carbonaceous feed in a gasification reactor according to the present invention or in a system according to the present invention. In such a process a solid carbonaceous feed is partially oxidized in the gasification chamber with an oxygen comprising gas to form an upwardly moving gas mixture having a temperature of between 1200 and 1800° C. preferably between 1400 and 1800° C. This mixture is first cooled in the tubular part to a temperature of between 500 and 900° C. and subsequently further cooled in the annular part to below 500° C. by injecting a mist of liquid droplets into the gas flow.
It has been found that the raw synthesis gas is cooled very efficiently, as a result of which the risk of deposits of sticky particles downstream of the gasification reactor is reduced.
The invention will now be described by way of example in more detail, with reference to the accompanying non-limiting drawings.
In the accompanying drawings:
The same reference numbers are used below to refer to similar structural elements.
Disclosed is an improved gasification reactor and systems for preparing a synthesis gas comprising CO, CO2 and H2 from a carbonaceous stream using an oxygen containing stream.
The gasification reactor according to the present invention is suitably used to prepare a mixture comprising carbon monoxide and hydrogen by partial oxidation of a solid carbonaceous feed in a gasification reactor according to the present invention or in a system according to the present invention. In such a process a solid carbonaceous feed is partially oxidized in the gasification chamber with an oxygen comprising gas to form an upwardly moving gas mixture having a temperature of between 1200 and 1800° C. preferably between 1400 and 1800° C. This mixture is cooled, in a first cooling step, in the tubular part to a temperature of between 500 and 900° C. and subsequently further cooled, in a second cooling step, in the annular part to below 500° C. by injecting a mist of liquid droplets into the gas flow.
The solid carbonaceous feed is partially oxidized with an oxygen comprising gas. Preferred carbonaceous feeds are solid, high carbon containing feedstocks, more preferably it is substantially (i.e. >90 wt. %) comprised of naturally occurring coal or synthetic (petroleum)cokes, most preferably coal. Suitable coals include lignite, bituminous coal, sub-bituminous coal, anthracite coal, and brown coal.
In general, this so-called gasification is carried out by partially combusting the carbonaceous feed with a limited volume of oxygen at an elevated temperature in the absence of a catalyst. In order to achieve a more rapid and complete gasification, initial pulverisation of the coal is preferred to form fine coal particulates. The term fine particulates is intended to include at least pulverized particulates having a particle size distribution so that at least about 90% by weight of the material is less than 90 μm and moisture content is typically between 2 and 8% by weight, and preferably less than about 5% by weight.
The gasification is preferably carried out in the presence of oxygen and optionally some steam, the purity of the oxygen preferably being at least 90% by volume, nitrogen, carbon dioxide and argon being permissible as impurities. Substantially pure oxygen is preferred, such as prepared by an air separation unit (ASU).
If the water content of the carbonaceous feed, as can be the case when coal is used, is too high, the feed is preferably dried before use. The oxygen used is preferably heated before being contacted with the coal, preferably to a temperature of from about 200 to 500° C.
The partial oxidation reaction is preferably performed by combustion of a dry mixture of fine particulates of the carbonaceous feed and a carrier gas with oxygen in a suitable burner as present in the gasification chamber of the reactor according to the invention. Examples of suitable burners are described in U.S. Pat. No. 4,888,7962, U.S. Pat. No. 4,523,529 and U.S. Pat. No. 4,510,874. The gasification chamber is preferably provided with one or more pairs of partial oxidation burners, wherein said burners are provided with supply means for a solid carbonaceous feed and supply means for oxygen. With a pair of burners is here meant two burners, which are directed diametric into the gasification chamber. This results in a pair of two burners in a substantially opposite direction at the same horizontal position. The firing direction of the burners may be slightly tangential as for example described in EP-A-400740.
Examples of suitable carrier gasses to transport the dry and solid feed to the burners are steam, nitrogen, synthesis gas and carbon dioxide. Preferably nitrogen is used when the synthesis gas is used for power generation and as feedstock to make ammonia. Carbon dioxide is preferably used when the synthesis gas is subjected to downstream shift reactions. The shifted synthesis gas may for example be used as feed gas to a Fischer-Tropsch synthesis or to prepare hydrogen, methanol and/or dimethyl ether.
The synthesis gas discharged from the gasification reactor comprises at least H2, CO, and CO2. The suitability of the synthesis gas composition for the methanol forming reaction is expressed as the stoichiometric number SN of the synthesis gas, whereby expressed in the molar contents [H2], [CO], and [CO2], SN=([H2]-[CO2])/([CO]+[CO2]). It has been found that the stoichiometric number of the synthesis gas produced by gasification of the carbonaceous feed is lower than the desired ratio of about 2.05 for forming methanol in the methanol forming reaction. By performing a water shift reaction and separating part of the carbon dioxide the SN number can be improved. Preferably hydrogen separated from methanol synthesis offgas can be added to the synthesis gas to increase the SN.
In one embodiment of the present invention the raw synthesis gas is cooled in the first cooling step in the tubular part to a temperature below the solidification temperature of the non-gaseous components before performing the second cooling step. The solidification temperature of the non-gaseous components in the raw synthesis gas will depend on the carbonaceous feed and is usually between 600 and 1200° C. and more especially between 500 and 1000° C., for coal type feedstocks. The first cooling step in the tubular part may be performed by injecting a quench gas. Cooling with a gas quench is well known and described in for example EP-A-416242, EP-A-662506 and WO-A-2004/005438. Examples of suitable quench gases are recycle synthesis gas and steam. More preferably this first cooling is performed by injecting a mist of liquid droplets into the gas flow as will be described in more detail below. The use of the liquid mist as compared to a gas quench is advantageous because of the larger cooling capacity of the mist. The liquid may be any liquid having a suitable viscosity in order to be atomized. Non-limiting examples of the liquid to be injected are a hydrocarbon liquid, a waste stream etc. Preferably the liquid comprises at least 50% water. Most preferably the liquid is substantially comprised of water (i.e. >95 vol %). In a preferred embodiment the wastewater, also referred to as black water, as obtained in a possible downstream synthesis gas scrubber is used as the liquid. Even more preferably, the process condensate of an optional downstream water shift reactor is used as the liquid.
With the term ‘raw synthesis gas’ is meant the gas mixture as directly obtained in the gasification reactor. This product stream may—and usually will—be further processed, for example in a dry solids removal system, wet gas scrubber and/or a shift converter.
With the term ‘mist’ is meant that the liquid is injected in the form of small droplets. If water is to be used as the liquid, then preferably more than 80%, more preferably more than 90%, of the water is in the liquid state.
Preferably the injected mist has a temperature of at most 50° C. below the bubble point at the prevailing pressure conditions at the point of injection, particularly at most 15° C., even more preferably at most 10° C. below the bubble point. To this end, if the injected liquid is water, it usually has a temperature of above 90° C., preferably above 150° C., more preferably from 200° C. to 230° C. The temperature will obviously depend on the operating pressure of the gasification reactor, i.e. the pressure of the raw synthesis gas specified further below. Hereby a rapid vaporization of the injected mist is obtained, while cold spots are avoided. As a result the risk of ammonium chloride deposits and local attraction of ashes in the gasification reactor is reduced.
Further it is preferred that the mist comprises droplets having a diameter of from 50 to 200 μm, preferably from 100 to 150 μm. Preferably, at least 80 vol. % of the injected liquid is in the form of droplets having the indicated sizes.
To enhance quenching of the raw synthesis gas, the mist is preferably injected with a velocity of 30-90 m/s, preferably 40-60 m/s.
Also it is preferred that the mist is injected with an injection pressure of at least 10 bar above the pressure of the raw synthesis gas as present in the gasification reactor, preferably from 20 to 60 bar, more preferably about 40 bar, above the pressure of the raw synthesis gas. If the mist is injected with an injection pressure of below 10 bar above the pressure of the raw synthesis gas, the droplets of the mist may become too large. The latter may be at least partially offset by using an atomization gas, which may e.g. be N2, CO2, steam or synthesis gas, more preferably steam or synthesis gas. Using atomization gas has the additional advantage that the difference between injection pressure and the pressure of the raw synthesis gas may be reduced to a pressure difference of between 5 and 20 bar.
Further it has been found especially suitable when the mist is injected in a direction away from the gasification reactor, or said otherwise when the mist is injected in the flow direction of the raw synthesis gas. Thus preferably the mist is injected in a partially upward direction when applied in the tubular part or in a downwardly direction when applied in the annular space. Hereby no or less dead spaces occur which might result in local deposits on the wall of the annular space and the tubular formed part of the quenching section. Preferably the mist is injected under an angle of between 30-60°, more preferably about 45°, with respect to a plane perpendicular to the longitudinal axis of the tubular part. In the annular part the mist is preferably directed in a vertical downwardly direction.
According to a further preferred embodiment, the injected mist is at least partially surrounded by a shielding fluid. Herewith the risk of forming local deposits is reduced. The shielding fluid may be any suitable fluid, but is preferably selected from the group consisting of an inert gas such as N2 and CO2, synthesis gas, steam and a combination thereof.
According to an especially preferred embodiment, the amount of injected mist is selected such that the raw synthesis gas leaving the quenching sections comprises at least 40 vol. % H2O, preferably from 40 to 60 vol. % H2O, more preferably from 45 to 55 vol. % H2O.
In another preferred embodiment, the amount of water added relative to the raw synthesis gas is even higher than the preferred ranges above if one chooses to perform a so-called overquench. In an overquench type process the amount of water added, preferably the amount added in the annular space, is such that not all liquid water will evaporate and some liquid water will remain in the cooled raw synthesis gas. Such a process is advantageous because a downstream dry solid removal system can be omitted. In such a process the raw synthesis gas leaving the gasification reactor is saturated with water. The weight ratio of the raw synthesis gas and water injection can be 1:1 to 1:4.
It has been found that herewith the capital costs can be substantially lowered, as no further or significantly less addition of steam in an optional downstream water shift conversion step is necessary. With capital costs is here meant the capital costs for steam boilers which are required to generate steam needed to be injected into the feed to the water shift conversion step. It has been further found that by omitting the dry solid removal system the capital costs can be substantially lowered as well. The dry solid removal system can be omitted in the overquench operation. The dry solids removal system can also be omitted in a process embodiment wherein the synthesis gas temperature at the outlet of the reactor downstream of the annular space is below 500° C.
In a preferred method of the present invention, the raw synthesis gas, and especially the synthesis gas as saturated with water, leaving the quenching section is preferably shift converted whereby at least a part of the water is reacted with CO to produce CO2 and H2 thereby obtaining a shift converted synthesis gas stream. As the person skilled in the art will readily understand what is meant with a shift converter, this is not further discussed. Preferably, before shift converting the raw synthesis gas, the raw synthesis gas is heated in a heat exchanger against the shift converted synthesis gas stream. Herewith the energy consumption of the method is further reduced. In this respect it is also preferred that the liquid is heated before using the liquid injecting it as a mist in the process of the present invention. Preferably heating of this liquid is performed by indirect heat exchange against the shift converted synthesis gas stream.
Any desired molar ratio of H2/CO may be obtained by subjecting one part of the synthesis gas to a water shift reaction obtaining a CO depleted stream and by-passing the water shift unit with another part of the synthesis gas and combining the CO depleted stream and the by-pass stream. By choosing the ratio of by-pass and shift feed one may achieve most desired ratios for the preferred downstream processes.
Reference is made to
The ash components as are present in most of the preferred feeds will form a so-called liquid slag at these temperatures. The slag will preferably form a layer on the inner side of the wall of reactor 2, thereby creating an isolation layer. The temperature conditions are so chosen that the slag will create on the one hand such a protective layer and on the other hand will still be able to flow to a lower positioned slag outlet 7 for optional further processing.
The produced raw synthesis gas is fed via line 5 to a quench zone in the form of a quenching section 6. Both the reactor 2 and the quenching section 6 are depicted inside a pressure shell 31. The raw synthesis gas in the quenching section 6 is typically cooled to below 500° C., for example to about 400° C. Liquid water is injected into the quenching section 6 via line 17, in the form of a mist, as will be further discussed in
The amount of mist to be injected in the quenching section 6 will depend on various conditions, including the desired temperature of the raw synthesis gas leaving the quenching section 6. According to a preferred embodiment of the present invention, the amount of injected mist is selected such that the raw synthesis gas leaving the quenching section 6 has a H2O content of from 45 to 55 vol. %.
As shown in the embodiment of
After the dry solids removal unit 9 the raw synthesis gas may be fed via line 10 to a wet gas scrubber 11 and subsequently via line 12 to a shift converter 13 to react at least a part of the water with CO to produce CO2 and H2, thereby obtaining a shift converted gas stream in line 14. As the wet gas scrubber 11 and shift converter 13 are already known per se, they are not further discussed here in detail. Waste water from gas scrubber 11 is removed via line 22 and optionally partly recycled to the gas scrubber 11 via line 23. Part of the wastewater, black water, from gas scrubber 11 may be preferably used as liquid water as injected via line 17. This is advantageous because any solid compounds present in the black water will be removed from the process via the dry solids removal unit 9.
Further improvements are achieved when the raw synthesis gas in line 12 is heated in a heat exchanger 15 against the shift converted synthesis gas in line 14 that is leaving the shift converter 13.
Further it is preferred according to the present invention that energy contained in the stream of line 16 leaving heat exchanger 15 is used to warm up the water in line 17 to be injected in quenching section 6. To this end, the stream in line 16 may be fed to an indirect heat exchanger 19, for indirect heat exchange with the stream in line 17.
As shown in the embodiment in
The stream leaving the indirect heat exchanger 19 in line 20 may be further processed, if desired, for further heat recovery and gas treatment.
If desired the heated stream in line 17 may also be partly used as a feed (line 21) to the gas scrubber 11.
Reference is made to
A carbonaceous stream and an oxygen containing stream are fed via lines 103, 104, respectively to a combustion chamber 102 provided inside a pressure shell 131 and thereby obtaining a raw synthesis gas and a slag.
As in
The amount of mist to be injected in the quenching section 106 relative to the raw synthesis gas is higher than in the process of
As shown in the embodiment of
At the lower end of the tubular part 36 injecting means 39 are present for injecting a liquid or gaseous cooling medium. Preferably the direction of said injections are as described earlier in case liquid mist injections are applied. In the annular space 37 injecting means 40 are present to inject a liquid in the form of a mist, preferably in a downwardly direction, into the synthesis gas as it flows through said annular space 37.
Preferably the quench zone is provided with cleaning means 42 and/or 43, which are preferably mechanical rappers, which by means of vibration avoids and/or removes solids accumulating on the surfaces of the tubular part and/or of the annular space respectively.
The advantages of the reactor according to
One or several burners (schematically denoted at 26) are present in the gasification reactor 2 for performing the partial oxidation reaction. For reasons of simplicity, two burners 26 are shown here but a different number may be provided.
Further, the gasification reactor 2 comprises an outlet 25 for removing the slag formed during the partial oxidation reaction via line 7.
Also, the gasification reactor 2 comprises an outlet 27 for the raw synthesis gas produced, which outlet 27 is connected with the quenching section generally depicted at 6. The skilled person will readily understand that between the outlet 27 and the quenching section 6, some additional connecting tubing may be present such as depicted at 5 in
The quenching section 6 comprises a first injector 28 that is adapted for injecting a water containing stream in the form of a mist in a quenching section 6. The first injector 28 is connected to line 17. The person skilled in the art will readily understand how to select the first injector to obtain the desired mist. Also more than one first injector may be present.
The first injector injects the mist in a direction away from the gasification reactor, usually in a partially upward direction. As shown in
As shown in the embodiment of
Also in this case the person skilled in the art will readily understand how to adapt the second injector to achieve the desired effect. For instance, the nozzle of the first injector may be partly surrounded by the nozzle of the second injector. As shown in the embodiment of
The quenching section 6, wherein the liquid mist is injected, may be situated above, below or next to the gasification reactor, provided that it is downstream of the gasification reactor 2. Preferably the quenching section 6 is placed above the gasification reactor 2; to this end the outlet of the gasification reactor 2 may be placed at the top of the gasification reactor.
The person skilled in the art will readily understand that the present invention may be modified in various ways without departing from the scope as defined in the claims. Features in each claim may be combined with features of any other claim.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/EP06/61951 | May 2006 | EP | regional |
| 06123312.8 | Nov 2006 | EP | regional |
The present application is a continuation in part of U.S. application Ser. No. 11/416,432 filed 2 May 2006, incorporated herein by reference. The present application also claims priority under 35 USC § 119(e) of U.S. Provisional application No. 60/865,137 filed 9 Nov. 2006, incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60865137 | Nov 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11416432 | May 2006 | US |
| Child | 11742473 | Apr 2007 | US |
