JPH0524844B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides hydrocarbons (or hydrocarbon derivatives)
A hydrocarbon (or hydrocarbon derivative) feedstock is produced by reacting the feedstock with a free oxygen-containing oxidant gas (e.g. air, oxygen, oxygen enriched air) and optionally steam and/or carbon dioxide in the presence of a catalyst. The present invention relates to a catalytic reaction process for the production of gas streams containing hydrogen and carbon oxides from hydrogen, in particular to the start-up of such a process.

Such catalytic reaction methods are well known and include so-called catalytic partial oxidation methods and secondary reforming methods.

In these processes, which are operated continuously and are usually carried out at elevated pressure, the feed stream is partially combusted and the combustion products are then catalyzed by a catalyst (hereinafter referred to as reaction catalyst, or equilibrium catalyst) to drive it towards equilibrium. (sometimes referred to as a chemical reaction catalyst). If used, steam and/or carbon dioxide are included in one or both of the reactant streams;
Alternatively, it may be supplied as a separate stream.

For example, autothermal reforming in which combustion is carried out under catalytic action by providing a combustion catalyst bed upstream of a conversion (equilibrium) catalyst is described in, for example, "Chemical Engineering" (January 3, 1966). , 24th
26, UK Pat. No. 1,137,930 and U.S. Pat. No. 4,522,894. The disadvantage is that there is a risk of deactivation due to There is also a risk that the feedstock will self-ignite and the resulting flame will damage the combustion catalyst and/or the container.

Therefore, it is more common to employ non-catalytic combustion methods by feeding each reactant to a burner. In this case, a flame is formed in the burner.

Initiation (i.e. start-up) of such catalytic partial oxidation processes intended to be operated at high pressures
This is typically carried out by feeding the feedstock and oxidizer to a burner at atmospheric pressure and igniting the feedstock/oxidizer gas mixture to produce a flame. However, igniting the mixture requires the use of an oxygen-rich mixture, whereas normal operation requires a feedstock-rich mixture (i.e., an oxygen-deficient mixture) so that only partial combustion occurs. . This means that, after ignition, the burner used must be changed from a burner suitable for operation with an oxidant-rich mixture to a burner suitable for operation with a rich feedstock mixture. Not only does the need for such a burner change increase the time required to start the process, but it is also nontrivial and somewhat dangerous due to the high temperature burner handling involved.

Also, performing an oxidant-rich operation early means that the gases resulting from that operation often have to be vented if there is an oxygen-sensitive downstream catalyst.

The secondary reformer feedstock in secondary reforming is the primary reformed gas stream.
For example, European Patent No. 124226 and US Patent No.
In some reforming methods, such as that described in No. Supplied.
In such a reforming method, its initiation involves the same problems as the partial oxidation process described above.

In the present invention, the above problems are overcome by self-ignition in the burner. The reactants are heated by a hot gas stream produced by catalytic combustion.
Heated directly or indirectly to autoignition temperatures.

According to the invention, therefore, a plurality of reactant streams comprising: (a) a stream containing a gaseous hydrocarbon or hydrocarbon derivative feed; and (b) a stream containing an oxidant gas comprising free oxygen. hydrogen and carbon oxides by feeding them separately under increased pressure to one burner, causing partial combustion in that burner, and feeding the combustion products to a catalyst to drive the combustion products toward equilibrium. A method of initiating a process for continuous production of a gas stream comprising: (i) producing a hot gas stream by carrying out at least partial combustion of a stream of gaseous combustible material and a free oxygen-containing oxidizing gas; wherein the hot gas stream is at least initially produced by catalytic combustion by passing the combustible material and the oxidizing gas over a combustion catalyst; (ii) at least one of the plurality of reactant streams; heat the two directly or indirectly with the hot gas stream to a temperature above the autoignition temperature of the reactants, and feed the reactant streams to the one burner, thus (iii) terminating the production of the hot gas stream while directing the plurality of reactant streams to the burner; continue supply,
The above starting method is provided.

In one embodiment of the invention, a hot gas stream is passed over a conversion catalyst to heat the conversion catalyst and a reactant stream is passed over it. When the autoignition temperature is reached, the flame produced by autoignition ignites the burner. The combustion catalyst may be present in bed form in the same vessel as the conversion catalyst, or preferably in a separate vessel. When the combustion catalyst is in the same vessel as the conversion catalyst, it may be located upstream or downstream of the burner. Particularly if the combustion catalyst is upstream of the burner, e.g. in a separate container, the combustion catalyst may be removed from service when startup is complete, such as by isolating or bypassing the combustion catalyst. can. Alternatively,
As discussed below, the combustion catalyst may remain in one line of the reactant stream, or if the combustion catalyst is downstream of the burner, it may remain in the line and the combusted gas from the burner may be passed through the combustion catalyst.

In another aspect of the invention, the combustion catalyst is in the same container as the conversion catalyst or in a separate container, but is downstream of the conversion catalyst such that exhaust gases from the conversion catalyst pass through the combustion catalyst. Do it like this.
In this embodiment, a hot gas stream from the combustion catalyst is used to heat one or more of the incoming reactant streams by indirect heat exchange such that after such heating the reactant streams are fed to the burner. heating one or more of the incoming reactant streams by heating and/or recycling a portion of the hot gas stream leaving the combustion catalyst to the burner. Such recirculation can occur if the combustion catalyst is upstream of the conversion catalyst.
It is also desirable to increase the heating rate. It will be clear that once autoignition is complete, such recirculation may be reduced or stopped.

If the combustion catalyst is downstream of the conversion catalyst,
The combustion catalyst may remain in the same line as the effluent stream from the conversion catalyst, especially when the combustion catalyst is in a separate container, it may be bypassed after autoignition is complete, or it may be isolated from the line. May be released from service.

The process reactants may be preheated by indirect heat exchange with a hot gas stream produced from a separate vessel containing the combustion catalyst, but during the start-up period it is preferred that:

Either the hot gas stream from the combustion catalyst is passed through the conversion catalyst, or the effluent gas from the conversion catalyst is passed through the combustion catalyst, preferably along with additional oxidant gas and/or combustible material.

The supply of combustible material and/or oxidant gas to the combustion catalyst is separate from the supply of feedstock and oxidant reactants to the burner. In this way, the combustion catalyst can be taken out of service by ceasing the supply of combustible material and/or oxidant gas to the combustion catalyst, but the combustion catalyst does not contain one of the reactants, the combusted gas, or remain in line with the exhaust stream from the conversion catalyst. However, even without such a separate supply, and even if the combustion catalyst remains in the line, it is possible to discontinue combustion at the combustion catalyst, thereby reducing the Generation of hot gas flow can be stopped. This is accomplished by supplying the reactant stream to the burner such that after self-ignition is complete and self-sustaining combustion has been established in the burner, there is no oxygen in the mixture supplied to the combustion catalyst. , to be sufficiently enriched with feedstock.

Whether or not the combustion catalyst is downstream of the conversion catalyst, at least one of the reactant streams is preferably preheated by indirect heat exchange from the conversion catalyst with the exhaust gas stream. In a preferred embodiment of the invention, the feed stream to the burner comprises a gaseous stream of a primary steam reforming agent, and the endothermic reaction heat required to carry out the primary reforming is It is supplied by heat from the exhaust gas from the catalyst.

The hydrocarbon (or hydrocarbon derivative) feedstock may in principle be any hydrocarbon or derivative thereof that can be vaporized. Typically, the feedstock has a boiling point below 220° C. at atmospheric pressure and is preferably gaseous at ambient temperature and pressure. The feedstock is preferably natural gas or naphtha, or a derivative such as methanol, or a pre-formed gas derived from natural gas, naphtha or methanol. If the feedstock contains sulfur, it is preferably desulfurized before being fed to the burner. When carrying out a preliminary first steam reforming step, the feed stream fed to the burner is preferably a gas stream obtained from the first steam reforming of natural gas, naphtha or methanol; Examples include hydrogen, methane, steam and carbon oxides.
Preferably, the combustible material is natural gas, naphtha, or a hydrogen-containing gas stream (eg, a primary reformed gas stream, ammonia synthesis gas, methanol synthesis gas, or purge gas from an ammonia or methanol synthesis).

The oxidizing gas supplied to the burner is preferably the same as that flowing to the combustion catalyst, preferably air. As mentioned above, one or more of the reactant streams may contain steam, and preferably at least one contains steam. Steam may be present in one or both of the gas streams fed to the combustion catalyst.

The combustion catalyst is preferably a platinum group metal on a suitable ceramic or metal support, especially platinum, rhodium and/or palladium. The support preferably has a large geometrical surface area per unit volume of the combustion catalyst bed and may be, for example, a honeycomb of corrugated metal plates or one or more coils, directly impregnated with the catalytically active substance. Good too. Alternatively, the catalytically active material may be present in a wash coat applied to the support.

When a combustible material (eg, natural gas) and an oxidizing gas (eg, air) are passed over the combustion catalyst, a combustion reaction proceeds, resulting in an increase in the temperature of the product gas stream and the combustion catalyst. If the gas velocity is not too high and/or the inlet temperature is not too low, for a gas mixture of a given composition, the maximum amount of combustion of that gas mixture will occur at a certain distance within the combustion catalyst bed (e.g. honeycomb). This causes a rapid temperature rise. Depending on the combustible material: oxidizer gas ratio (which also influences the maximum temperature peak value and thus also the combustion catalyst outlet temperature), this can correspond to partial or complete combustion. Initially, even at low gas velocities, this maximum temperature peak value may not be established as a result of too low inlet temperature. The gas inlet temperature generally depends on the degree of preheating of the combustible material (if carried out, for example, as a result of a desulfurization step) and the preheating of the oxidant gas (eg, as a result of compression). In some cases, external available heat sources may be used that are not sufficient to heat the reactant streams to autoignition temperatures as well. However, such an external heat source can be utilized to heat the gas stream and often one or more of the reactant streams that are fed to the combustion catalyst. If the preheating of the gases supplied to the combustion catalyst does not heat the combustion catalyst sufficiently to produce the desired temperature rise of the combustion catalyst, some of the gas leaving the combustion catalyst is recirculated to the combustion catalyst inlet. This effectively increases the inlet temperature. The inlet gas composition and the degree of recirculation (if performed) should be selected such that the aforementioned peak temperature is achieved before autoignition occurs in the burner.

If the stream containing combustible material fed to the combustion catalyst also contains steam, the gas stream leaving the combustion catalyst will be partially reformed, as the combustion catalyst will generally exhibit some reforming activity. and therefore will contain some hydrogen. Recirculating such gases leaving the combustion catalyst to the combustion catalyst inlet then has the advantage of introducing hydrogen into the combustible material fed to the combustion catalyst. The presence of hydrogen in the combustible material that is fed to or recycled to the combustion catalyst is advantageous. This is because the inlet temperature at which the hydrogen can be combusted by the combustion catalyst is relatively low, thus making it easier to achieve the peak temperature at the start of catalytic combustion. For this reason, it is advantageous to use a hydrogen-containing gas stream, such as ammonia synthesis gas, methanol synthesis gas or purge gas, as at least part of the combustible material.

When passing the hot gas stream from the combustion catalyst through the conversion catalyst, which is the preferred embodiment, if the hot gas stream passed through the conversion catalyst also contains hydrogen (e.g. (as a result of only partial combustion of the combustible material containing or steam) is preferred. Therefore, if the conversion catalyst is a freshly charged conversion catalyst precursor and it is to be reduced and made available as an active catalyst, passing a hot hydrogen-containing gas stream through the conversion catalyst is recommended. , some of the necessary reduction has been made,
This will thus reduce the overall start-up time.

In some cases, especially if a portion of the gas stream leaving the combustion catalyst is recirculated to the inlet, autoignition of the combustible material fed to the combustion catalyst is caused by a mixture of the combustible material and the oxidizing gas. and the true inlet of the combustion catalyst, with the formation of a flame. In this case, the combustion catalyst is in fact largely ineffective in the combustion producing a gas stream that is used to directly or indirectly heat one or more of the reactant streams fed to the burner. may not be shown. In this case, therefore, a hot gas stream is only initially produced by catalytic combustion.

Typically, the flow rate of gas in the burner must be above a certain minimum value, depending on the burner configuration, to ensure that a stable flame is formed when ignition occurs. The amount of combustion catalyst should be selected so that an appropriate amount of hot gas is produced to provide the desired direct or indirect heating of the reactant stream fed to the burner.

Achieving sufficiently rapid start-up when the combustion catalyst is upstream of the conversion catalyst and there is no indirect or direct heat recirculation to the combustible material fed to the combustion catalyst. In this case, the volume of the combustion catalyst bed is between 1 and 50% of the volume of the conversion catalyst bed, especially 2
~20% is typical.

If the heat from the gas leaving the combustion catalyst and/or the gas leaving the conversion catalyst is recycled directly or indirectly to the combustible material fed to the combustion catalyst (this is the preferred embodiment), the combustion catalyst bed volume is Generally less than 10% of the conversion catalyst bed volume, typically 0.1-3%.

The amount of combustion catalyst used is generally considerably greater than that required to effect the desired degree of partial combustion of the reactants fed to the burner at the design flow rate of the reactants in normal operation of the continuous process. few.

As mentioned above, combustion catalysts may exhibit some activity as some types of conversion catalysts. Indeed, in some cases both the combustion and conversion catalysts may consist of a platinum group metal supported on a suitable support as described above. However, combustion catalysts typically have a fairly high platinum group metal loading, expressed as the amount of active metal per unit geometric surface area of the support.

Typically, autoignition in a burner occurs by combining the feedstock reactant stream with the hot gas stream and/or the feedstock until the temperature of the feedstock reactant stream or the temperature of its mixture with the hot gas stream is above the autoignition temperature. This is accomplished by preheating the reactant stream by heat exchange with a hot gas stream before feeding it to the burner. The supply of oxidant reactant (preferably preheated) is then started and autoignition ensues. In this way, when there is a catalyst affected by the oxidizing agent downstream of the conversion catalyst, there is no need to discharge the exhaust stream from the conversion catalyst to the outside of the system.

The feed rate of reactant stream to the burner should be gradually increased until the desired flow rate is achieved. The composition of the reactants, ie, the proportions of the components in the reactant stream, may be modified as the start-up operation progresses.

At a suitable point after self-ignition and self-sustaining partial combustion has been established in the burner, the generation of the hot gas stream by partial combustion of at least the combustible material and the oxidizing gas is stopped. If the supply of combustible material and/or oxidizer to the combustion catalyst is separate from the supply of reactants to the burner, such cessation of generation of the hot gas stream shall be effected by cutting off this separate supply. This can be done by isolating or bypassing the combustion catalyst at an appropriate time after self-ignition in the burner has occurred, especially if the combustion catalyst is in a separate container. Stopping the feed and isolation or diversion as appropriate may, however, be carried out before the desired flow rate of the reactants is fully achieved. If the combustion catalyst remains in the process line and is downstream of the burner and the oxidizer is not separately supplied to the combustion catalyst, after autoignition has been achieved, the high temperatures resulting from the combustion of the combustible material and the oxidizer gas It will be appreciated that the cessation of gas flow production occurs naturally due to partial combustion in the burner using substantially all of the available oxidant. After autoignition is achieved in this case, the combustion catalyst has little or no effect. However, often the combustion catalyst exhibits some activity as a conversion catalyst and thus may assist the conversion catalyst. The invention will be further explained with reference to the drawings.

The drawings and related processes assume that the basic feedstock is desulfurized natural gas and that the oxidant gas is air.

In FIG. 1, a combustion catalyst 1 is placed in a vessel 2 upstream of a vessel 3 containing a conversion catalyst 4 for the desired reaction process. The conversion catalyst is typically supported on a suitable support, such as a ceramic ring or a monolith such as a honeycomb.
It is nickel supported on top. During normal operation, natural gas was supplied to the burner in vessel 3 via line 6 and air was supplied to the burner via line 7, with the combusted gas stream being directed to equilibration over conversion catalyst 4. It later leaves the container 3 via line 8.

During the start-up period, the oxidizing gas (e.g. air) and the combustible material (shown in the drawing as being the same as the feed to burner 5) are
The hot gases from vessel 2 are fed to vessel 2 via lines 9 and 10 respectively, and the hot gas from vessel 2 is passed via line 11 to the feed inlet 6 of the burner of vessel 3.
supplied to Initially some natural gas may be fed directly to the burner 5 (via line 12 bypassing the vessel 2). The amount of air supplied to vessel 2 via line 9 is such that incomplete combustion occurs in the combustion catalyst. The gas fed to the burner 5 via line 6 is therefore a hot partially combusted exhaust stream from line 11;
as well as natural gas bypassing vessel 2 via line 11 (if such natural gas exists)
It is. The supply of natural gas to the burner 5 via the bypass 12 is then started or increased as necessary. The flow rate is such that a stable flame is formed in the burner 5 when air is supplied to the burner 5. The supply of air to the burner 5 begins when the temperature of the mixture of natural gas and hot gas stream supplied to the burner 5 rises to a temperature above the autoignition temperature. Self-ignition will then occur and a flame will be established at burner 5. Then,
The flow rate of the natural gas (to which steam may be added by humidification) supplied to the burner 5 can be gradually increased to the desired level. The air flow rate may or may not need to be increased.

To increase the rate at which the exhaust stream from vessel 2 reaches the desired temperature, a portion of the hot gas leaving vessel 2 via line 11 is recycled via line 13 to feed inlet 10 of vessel 2. (This line 11 may be a recirculation duct within the vessel 2, as described below).

After the flame is established in burner 5, line 10
The supply of natural gas via line 9 and air via line 9 is stopped and vessel 2 is completely bypassed via lines 7 and 12. Alternatively, in some cases it may be desirable to have all feedstock pass through the combustion catalyst 1, except for the bypass line 12. In this case, after autoignition has been established in burner 5, the combustion catalyst is completely removed from service by closing line 9 so that air is only supplied to burner 5 via line 7, The generation of a hot gas stream by combustion of natural gas in the vessel 2 can be stopped.

In each embodiment of FIGS. 2 and 3, the combustion catalyst 1
is placed in a separate vessel 2 downstream of the conversion catalyst 4 and the gas is passed through a heat exchanger 14 via line 8 and its heat is supplied to the burner via line 6. feedstock.

In the embodiment of FIG. 2, vessel 2 is placed before heat exchanger 14 in line 8 so that the gas leaving conversion catalyst 4 provides the feed to combustion catalyst 1. Air is supplied to container 2 via line 9. As in the embodiment of FIG. 1, a recirculation line 13 (indicated by dotted lines in FIG. 2) may be provided and, when autoignition is established in burner 5, the combustion catalyst via line 9. Remove the combustion catalyst from service by stopping the air supply to the combustion catalyst.

In the embodiment of FIG. 3 (which is less preferred), the combustion catalyst 1 is not in the same line as the process stream, but is connected to the high temperature gas stream leaving the conversion catalyst via line 8 before the heat exchanger 14. There is a combustion catalyst in a separate equipment unit that supplies the gas. In this example, the feed to the combustion catalyst 1 is shown as a separate stream 15. That is, it is not part of the feedstock fed to burner 5 via line 6.
Feed stream 15 therefore does not have to be chemically identical to that fed to burner 5.

In the embodiment of FIG. 4, interposed in the natural gas/steam supply line to burner 5 includes a primary reforming catalyst disposed in a tube through which a mixture of steam and feedstock passes. 1st
The tubes are heated by the gas leaving the conversion catalyst 4. Although the primary reformer may be of conventional type and in a separate vessel from the vessel containing the conversion catalyst, in the illustrated embodiment an integrated primary/secondary reformer is used. . In this embodiment, the primary reformer tubes (two shown, but in practice more tubes would be used) are placed inside the vessel 3 and the conversion catalyst 4 (here the The gas leaving the secondary steam reforming catalyst (secondary steam reforming catalyst) heats these tubes. Each rehoming tube is
It consists of an outer tube 17 closed at its upper end and having a concentric inner tube 18 which extends inside the outer tube 17 over substantially its entire length. A primary reforming catalyst 16 is filled in the annular space between the inner tube and the outer tube. Feedstock is fed to vessel 3 via line 19 and enters the open end of outer tube 17. Then it is the catalyst 16
rises in the annular space filled with
Descending within 8. It is then fed via line 6 to burner 5. The line 6 may be on the outside of the container 3 as shown, but is preferably
A suitable duct within the container 3.

The gas leaving the secondary reforming catalyst 4 is transferred to the tube 1
7 leaves the vessel 3 via line 8 after heating, passes through a heat exchanger 20 and flows via heat exchanger 20 from source 21 to line 19.
Preheat the steam mixture.

In this embodiment, the combustion catalyst 1 is in a separate container 2
It is arranged within and is supplied with air via line 9 and with a natural gas/steam mixture via line 10 from a source 21. The hot gas stream produced by the catalytic combustion of natural gas/steam and air in vessel 2 is fed via line 11 to burner 5 of the secondary reformer. After self-ignition has occurred in burner 5 and a flame has been established, the supply of air and/or natural gas to vessel 2 via lines 9 and 10 is stopped. Similar to the embodiment of FIGS. 1 and 2, a portion of the gas leaving the combustion catalyst may be recycled via line 13 to its inlet. In this embodiment, the gas flowing within the primary reforming catalyst in the annular space between the inner tube 18 and the outer tube 17 is substantially unreformed before autoignition occurs in the burner. I hope you understand. As tubes 17 and catalyst 16 become heated, reforming will begin and the feed to burner 5 will therefore change from a natural gas/steam mixture to a first reformed gas mixture.

The combustion catalyst 1 in FIG. 5 is in the same container as the conversion catalyst 4, but on the downstream side.
In this case, it is necessary to recirculate a portion of the gas leaving the vessel 3 via line 8 to the feed inlet 6 via line 22 in order to effect heating to the autoignition temperature. Alternatively, instead of providing such recirculation, one or more heat exchangers may be used to transfer the heat in the gas leaving the vessel via line 8 to the air supplied via line 7. and/or may be transferred to the feedstock supplied via line 6.

In the embodiment of FIG. 5, the flammable material is in line 1
0 to the inlet of the combustion catalyst. The system supplies air to the burner 5 via line 7 and natural gas (preferably also containing steam).
The combustion catalyst 1 is started by supplying it via the line 10 to the combustion catalyst 1. The amount of air is such that incomplete combustion occurs in the combustion catalyst and the hot gas containing some combustible material is recirculated via line 22. When the recycle gas is hot enough, autoignition of the combustible material in the recycle gas occurs in burner 5 and a flame is established. Before or after the flame is established in burner 5, the supply of fresh feedstock to burner 5 is started. The supply to the combustion catalyst via line 10 is then cut off. Combustion catalyst 1 as in the previous embodiments
A portion of the gas leaving the can be recycled via line 13 to its inlet.

Alternatively, instead of supplying air to the burner via line 7 and natural gas to the burner via line 10 during start-up, natural gas to the burner and air between the burner and the combustion catalyst. It may also be fed via a line (not shown) to an intermediate location. As before, partial combustion takes place in the combustion catalyst 1 and a hot gas is obtained, which is transferred to the burner 5.
recycled to When this recirculated stream is hot enough to heat the mixture of it and the natural gas supplied to burner 5 above the autoignition temperature, at the beginning of the supply of air to burner 5, Self-ignition occurs. After such self-ignition, the supply of air to the position between the burner and the combustion catalyst is stopped.

In some cases, a separate supply of combustible material and/or oxidant gas to a location between the burner and the combustion catalyst may not be necessary.

It will be appreciated that in a similar arrangement, the combustion catalyst may be upstream of the conversion catalyst but downstream of the burner. In this case it is not necessary to carry out a separate supply of combustible material to the combustion catalyst, and self-ignition at the burner can be achieved simply by flashback from the surface of the combustion catalyst to the burner. However, after starting, the flame tends to become hot enough to damage the combustion catalyst and prevent further starting. This can be prevented by sandwiching the combustion catalyst within the conversion catalyst, with the combustible material preferably being fed separately to the inlet of the combustion catalyst. This way, after a flame has been established in the burner, an endothermic reaction, such as a reforming reaction between the feedstock and steam, can cool the gases and remove damage to the combustion catalyst before it reaches the combustion catalyst. can. Since there is little or no such endothermic reaction upstream of the combustion catalyst prior to autoignition, and almost no endothermic reaction downstream thereof, starting is not unduly disturbed.

Combustion catalyst containing container 2 as shown in Figures 1 to 4
The sixth preferred form of device for use as
and shown in Figure 7.

In the embodiment of Figures 6 and 7, the device consists of an outer cylindrical shell 30 designed to withstand process pressures (typically 5 to 60 bar absolute). At one end of the shell 30 there is an inlet hole 32 for a first gas stream consisting of a steam/natural gas mixture and an outlet hole 34 for a product gas stream. At the other end of the shell 30 there is an inlet hole 38 for air. Disposed within and sealed to the shell 30 at the end adjacent the inlet hole 32 is a lining 4.
It is 0. The lining 40 extends almost to the other end 36 of the shell 30, thus defining an annular conduit 42 between the inner surface of the shell 30 and the outer surface of the lining 40. The inlet hole 32 is connected to this annular conduit 42 . At the end 36 of the shell 30, an inner side 40 extends laterally from the shell 30 and terminates in a cylindrical portion 44. This cylindrical portion 44 has air inlet holes 38
It surrounds a pipe 46 which serves as a means for supplying air from the air, but there is a gap between it and the pipe 46. The end of the cylindrical portion 44 remote from the end 36 of the shell 30 is provided with an inwardly enlarged portion 48 (see FIG. 7), thus making the cylindrical portion 4
A limiting portion is provided between the end of the pipe 4 and the pipe 44 to function as an ejector.

The conduit 42 defined by the lining 40, the wall of the shell 30, the cylindrical portion 44 and the outer surface of the pipe 46 thus forms a supply means for distributing natural gas from the inlet hole 32. This construction is therefore of the hot-wall type and relatively reduces the amount of refractory insulation required, if any, on top of the shell 30, since the gas flowing within the conduit 42 acts as an insulator. It can be reduced.

Disposed within the lining 40 is a hollow elongate member 50 of circular cross section. This hollow member has an open, flared end 54, a combustion area 56 of a larger cross-section than the inlet area 52, adjacent to the ejector terminating in the natural gas supply means;
and includes a combustion catalyst 58 at its end remote from the inlet region 52;
6 and an inlet region 52 . Beneath the combustion catalyst, the lower end 62 of the hollow member 50 is supported on the end of the shell 30. For example, by providing a hole 64 through the wall of the hollow member 50 adjacent the end 62, gases exiting the combustion catalyst 58 can enter the space 66 between the outer surface of the hollow member 50 and the inner surface of the lining 40. It's meant to fit in. A portion of the gas leaving the catalyst can thus enter space 66, while the remaining portion leaves the shell via outlet hole 34. The combustion catalyst consists of a number of honeycomb members 68, on the surface of which a suitable combustion-active metal is deposited. Openings 70 are also provided in the walls of the hollow members 50 between adjacent members of the honeycomb, so that a portion of the gas flow may enter the spaces 66 without passing through the entire combustion catalyst. .

The air introduction pipe 46 extends along the length of the inlet region 52 of the hollow member 50 and ends where its combustion region 56 begins. A nozzle 72 is provided at the outlet of the inlet hole 38.

In operation, natural gas and steam are supplied under pressure to the inlet holes 32 and air is supplied under pressure to the inlet holes 38. The natural gas/steam mixture flows upwardly through the gap between the shell 30 and the lining 40, exits the evacuator formed by the restriction 48, and then flows downwardly through the inlet region 52 and transition region 60 of the hollow member 50. , where it is mixed with the air exiting from the nozzle 72. The resulting mixture is
It then passes through a combustion zone 56 and a combustion catalyst 58 therein. A portion of the gas flow leaving combustion catalyst 58 flows out through outlet hole 34, while the remaining portion passes through holes 64 and 70 and connects hollow member 50 and lining 4.
It enters the space 66 between 0 and 0. The gas in this space 66 flows upwardly towards the upper end 36 of the shell 30;
The effect of the natural gas/steam mixture exiting the ejector formed by the restriction 48 is then drawn into the inlet region 52 of the hollow member 50 . In this way, the recirculated gas mixes with the natural gas/steam mixture and flows down through the hollow member 50.

Initially, some reactions occur as the gas stream passes through the combustion catalyst 58, thereby creating a heated gas stream. A portion of the gas flow that enters the space 66 via the holes 64 and 70 and returns to the inlet region 52 of the hollow member 50 heats the natural gas/steam mixture flowing within the conduit 42 and increases its temperature so that combustion occurs. The gas entering the catalyst is preheated. This recirculated gas also heats the air as it flows through the air inlet pipe 40, which extends into the inlet region 52 and transition region 60 of the hollow member 50. With continued operation, the temperature of the gases entering the combustion zone increases to the autoignition temperature, at which time a flame is formed at nozzle 72. Because of the reforming activity that the combustion catalyst has to some extent as mentioned above, the gas stream leaving the combustion region 56 of the hollow member 50, and thus the recycled gas mixture, will contain some hydrogen; The gas mixture that mixes with the air at nozzle 72 contains hydrogen, which allows a flame to be established at nozzle 72 more quickly.

When a flame is established, the recirculating gas flowing upwardly through that portion of the space 66 between the combustion zone of the hollow member 50 and the inner surface of the lining 40 undergoes heat exchange through the walls of the combustion zone 56. At the same time, the shell 3
conduit 42 between the inner surface of 0 and the outer surface of lining 40
It will be appreciated that the natural gas/steam mixture flowing within the corresponding portion of the gas/steam mixture will be heated. When recirculating gas flows within that portion of the space 66 between the outer surfaces of the transition region 60 and inlet region 52 of the hollow member 50 and the inner surface of the lining 40, In addition to heating the natural gas/steam mixture flowing through conduit 42, hollow member 5
0 inlet and transition regions 52, 60 will also be heated.

In another embodiment, the lining 40 is not used and a refractory insulation layer is provided on the outer surface of the shell. In this embodiment, the natural gas supply means is coaxial with the air supply pipe 56, the end of which is provided with an enlarged section (corresponding to enlarged section 48 in Figure 7) from a tube which creates a restriction to serve as an ejector. configured. In this embodiment, therefore, the natural gas stream is not preheated by the recycle gas before it leaves the supply pipe, but a heated mixture of the natural gas stream and the recycle gas is provided. is created by simply mixing both gas streams. This mixed gas is then mixed with air leaving pipe 46.

In either embodiment, suitable protrusions may be provided on the outer surface of the hollow member 50 to position the hollow member in a desired distance relationship from the lining 40 in the embodiment of FIG. The hollow member can be placed in a desired distance relationship from the inner lining. Similarly, suitable spacers may be provided between the inner surface of the inlet region 52 of the hollow member 50 and the air pipe 46 to maintain them in the desired distance relationship.

One advantage of recirculation in processes with only partial combustion and where one or both of the oxidizer and combustible streams include steam is that after achieving autoignition at nozzle 72, the hot gases leaving the combustion catalyst are It is to have a temperature somewhat lower than the maximum temperature in the upstream combustion zone. This is because the combustion catalyst exhibits some steam reforming activity.
This is because such steam reforming, which is an endothermic reaction, occurs upon passage of gas through the catalyst. The recirculated product gas, which is cooler than the gas inside the combustion zone, thus acts to maintain the hollow member at an acceptable temperature, and therefore the hollow member 50 must be constructed of a material that can withstand very high temperatures. do not have.

The catalytic combustion apparatus of FIGS. 6 and 7 provides natural gas at or near the design flow rate and then starts the air flow at a low flow rate and then gradually increases the air flow rate. It can be conveniently started by itself. At low air flow rates, virtually all combustion occurs within the first section of the combustion catalyst. The gas recirculated through the holes 70 (if such holes are provided) is therefore at a higher temperature than the product gas passing through the entire catalyst (after all, such product gas is cooled by the cold combustion). (lower temperatures result from heat transfer to the catalyst and/or endothermic reforming reactions that occur). The recirculated gas is therefore hotter than it would be without the holes 70. By mixing the recirculated gas with the incoming natural gas stream and as shown in FIGS.
0, the natural gas is preheated before it comes into contact with the incoming air due to heat exchange through such a lining. Such preheating allows catalytic combustion to occur earlier in the catalyst-containing region and thus allows the air flow rate to be increased more quickly. In a short time, the air flow rate can be increased to a level such that the product gas has the desired flow rate and temperature. It will generally be appreciated that for a given installation and a given flow rate of a natural gas stream of a given composition, the product gas outlet temperature will depend on the feed rate of air to the combustion zone. Therefore, the process can be easily controlled by adjusting the air flow rate.

As the air flow rate is increased, the amount of recirculation decreases. After all, the addition of airflow increases the mass of gas flowing through the system, but the "driving force" for recirculation, the mass of the natural gas flow,
This is because the product of the natural gas inlet pressure and the product gas outlet pressure difference remains substantially constant. Furthermore, as the recirculated gas becomes hotter, the efficiency of the effluent decreases.

It will be appreciated that autoignition normally involves the formation of a flame at the nozzle supplying air to the combustion catalyst. To prevent damage to the combustion catalyst caused by such flames, it is recommended that the air supply means terminate significantly upstream of the catalyst so that the flame is generated in a space upstream of the catalyst that does not contain the catalyst. preferable.

In the above discussion, catalytic combustion initiation was described with the assumption that the flow rate of the natural gas stream was held substantially constant. However, this is not necessarily the case.
I hope you understand. In fact, if autoignition is established in the catalytic combustion vessel upstream of the combustion catalyst, the feed flow rate of the natural gas and/or air stream will be
It can increase considerably after self-ignition. This is because their flow rates are no longer limited by the need to obtain combustion within the catalyst.

The catalytic combustion apparatus of Figures 6 and 7 is particularly useful when the natural gas and air supplied thereto are relatively cold. During the first stage of the starting (starting) operation, the gases supplied to the device are approximately 150~
It will be appreciated that it is possible to carry out the process using reactants at low temperature (eg ambient temperature) by providing a small heater, eg an electric heater, for heating to 200°C. However, usually sufficient heating can be achieved to achieve starting without the need for such a heater.
It can be obtained from steam and/or an external heat source, for example as a result of the heating that occurs when compressing natural gas or air to the desired process operating pressure. As previously mentioned, catalytic combustion is facilitated by the presence of hydrogen in the combustible stream that is fed to the combustion catalyst. Therefore, if a hydrogen source, for example purge gas from an ammonia synthesis plant, is available, it is advantageous to add such a hydrogen-containing gas to the combustible gas, at least at the start-up of the catalytic combustion. be.

Rather than conducting catalytic combustion to only partially burn the combustible material fed to the combustion catalyst, thereby producing a hot fuel-rich stream as described above, catalytic combustion It can also be implemented to create a hot air-rich gas stream from "cold" reactants.

An example of using a device such as that shown in FIGS. 6 and 7 but without the aperture 70 is shown. The device is dimensioned such that at the design flow rate the proportion of product gas recycled after autoignition is achieved at nozzle 72 is approximately 50% of the gas leaving the combustion catalyst. The cylindrical shell is approximately 3 m long and 40 cm in diameter.
If a natural gas/steam mixture with a steam:carbon ratio of 2.5 is supplied as the first gas stream at a rate of 162 Kg mol/h at a temperature of 200 °C and a pressure of 12 bar absolute, and air is supplied as the second gas stream at 240 Kg mol/h. temperature in °C and
When fed at 146 Kg mol/h at a pressure of 12 bar absolute, the product gas leaving the shell via outlet hole 34 is
The temperature is 750°C, and the following composition is obtained by calculation.

Nitrogen and argon 31.7% v/v Carbon dioxide 7.0% v/v Steam 29.9% v/v Hydrogen 25.8% v/v Carbon monoxide 4.8% v/v Methane 0.8% v/v Under these conditions, natural gas The /steam mixture is heated to about 330°C by the time it leaves the effluent formed by restriction 48, and the natural gas/steam/recycle gas mixture entering the transition region has a temperature of about 550°C. It is calculated that
It is calculated that autoignition and steady state in the catalytic combustion vessel can be achieved within 5-10 minutes from the start of reactant flow. 750°C leaving outlet hole 34
A hot gas stream at a temperature of 1000 Hz allows the autoignition temperature of the natural gas/steam mixture fed to the inlet of the burner (eg, the configuration of FIG. 4) to be quickly achieved.
Once that autoignition temperature is achieved, the air supply to the burner is started to establish a flame. Thereafter, the catalytic combustor unit may be closed by stopping the air supply to holes 38 and/or the natural gas/steam supply to holes 32. This unit can then be isolated by closing hole 34 if desired. For this application, the volume of the combustion catalyst in the form of an alumina honeycomb support impregnated with a platinum group metal as an active catalyst need only be about 2.4% of the volume of the secondary reforming catalyst. is calculated.

As a comparison, a similar arrangement but with no recirculation of the product gas and therefore with heat returning to the combustion zone through the catalyst to increase the temperature of the natural gas fed to the combustion catalyst to the auto-ignition temperature. In experiments using a placement system that relied on the movement of , the time required to achieve autoignition upstream of the combustion catalyst was over an hour.

[Brief explanation of the drawing]

Figures 1-4 are schematic diagrams of exemplary arrangements in which two catalysts are housed in separate containers. FIG. 4 shows an application to first/second reforming, in which the first reformer is heated by the second reformer discharge stream. FIG. 5 is a schematic diagram of an arrangement in which the combustion catalyst is located downstream of the conversion catalyst, but both catalysts are housed in the same container. FIG. 6 is a schematic longitudinal sectional view of a preferred embodiment of the portion of the apparatus of FIGS. 1-4. FIG. 7 is a partially enlarged view of FIG. 6. Combustion catalyst...1, Conversion (reaction) catalyst...4.

Claims (1)

[Scope of Claims] 1 (a) a stream containing a gaseous hydrocarbon or hydrocarbon derivative feedstock; and (b) a stream containing an oxidizing gas containing free oxygen;
separately feeding a plurality of reactant streams under elevated pressure to a burner to cause partial combustion in the burner, and feeding the combustion products to a catalyst to drive the combustion products to equilibrium. A method for initiating a process for the continuous production of a gas stream, possibly containing hydrogen and carbon oxides, comprising: (i) carrying out at least partial combustion of a stream of gaseous combustible material with an oxidizing gas containing free oxygen; (ii) producing a hot gas stream, the hot gas stream being at least initially produced by catalytic combustion by passing the combustible material and the oxidizing gas over a combustion catalyst; heating at least one of the plurality of reactant streams directly or indirectly with the hot gas stream to a temperature above the autoignition temperature of the reactants, and directing the reactant streams to the one burner; (iii) terminating the production of the hot gas stream while the continuing to feed multiple reactant streams to the burner;
The above starting method consists of: 2. The supply of combustible material to the combustion catalyst is separate from the supply of raw reactant streams to the burner, and/or the supply of oxidant gas to the combustion catalyst is separate from the supply of oxidant gas to the burner. and producing a hot gas stream by combustion of the combustible material and oxidant gas is at least one of the combustible material and oxidant gas to the combustion catalyst while continuing to supply the reactant stream to the burner. The method according to claim 1, wherein the method is stopped by stopping one of the supplies. 3. Self-ignition by heating the feed reactant stream to a temperature above the autoignition temperature of the feed reactant stream by direct or indirect heat exchange with a hot gaseous fluid and then initiating the feed of oxidant reactant to the burner. 3. A method according to claim 1 or 2, wherein ignition occurs. 4. (a) passing a hot gas stream from a combustion catalyst through the equilibration reaction catalyst; or (b) passing an exhaust stream gas from the reaction catalyst through the combustion catalyst. The method described in any of the above. 5. The combustion catalyst is upstream of the burner and the hot gas stream from the combustion catalyst is supplied to the burner separately from the reactant stream or as part of one of the reactant streams. The method described in paragraph 4. 6. The combustion catalyst is in a separate vessel from that containing the equilibration reaction catalyst, and once autoignition is achieved producing a flame in the burner,
6. A method as claimed in any one of claims 1 to 5, in which the container containing the combustion catalyst is bypassed or isolated. 7. After cessation of the production of a hot gas stream by combustion of the combustible material and oxidizing gas, the combustion catalyst remains in service and the reactants; the combusted gases from the burner; and the gases leaving the equilibration reaction catalyst; 6. A method according to any one of claims 1 to 5, in which one of the catalysts continues to pass through the combustion catalyst. 8 Recirculating a portion of the hot gas stream leaving the combustion catalyst to its inlet, at least until autoignition of the reactants in the burner is achieved.
The method described in any of Section 7. 9. A method according to any one of claims 1 to 8, wherein the exhaust stream from the equilibration reaction catalyst is subjected to indirect heat exchange with at least one of the reactants to heat the adsorbent. 10 The feedstock fed to the burner is a primary steam reforming product of a hydrocarbon or hydrocarbon derivative, and the endotherm required for the primary steam reforming reaction is combined with the exhaust stream from the equilibration reaction catalyst. 10. The method according to claim 9, wherein the method is provided by heat exchange. 11 (a) a feed reactant stream fed to the burner; (b) an oxidant gas reactant stream fed to the burner; (c) a combustible material fed to the combustion catalyst; and (d) a feed to the combustion catalyst. 11. A method according to any one of claims 1 to 10, wherein at least one of the oxidizing gas streams comprises steam. 12. A method according to any of claims 1 to 11, wherein the combustible material stream fed to the combustion catalyst comprises hydrogen.