IE41408B1 - Improvements in or relating to a process and apparatus for carrying out an endothermic chemical reaction - Google Patents

Abstract

1469902 Controlling endothermic reactions FRIED KRUPP HUTTENWERKE AG 18 March 1975 [23 March 1974] 11299/75 Heading B1X [Also in Division F4] In the carrying out of an endothermic chemical reaction, a heated inert gas (e.g. nitrogen) is used as the heating-up medium passed alternately first through one and then through the other or others of regenerator chambers such as 1, 1', and the heat from the chamber or chambers not at the time being heated by the gas is used in the carrying out of the endothermic chemical reation; the inert gas flowing in a circuit 2 in which it receives its heat in a heat exchanger 3/4 forming part of the coolant circuit 5 for a heat source such as a nuclear reactor 6. The chemical reaction may be carried out in the regenerator chamber itself or, as in the form shown, in a reaction chamber 10 (or 10') connected by a passage 12 (or 12') with the regenerator chamber 1 (or 1'). In Fig. 2 reactant gases entering at 11 (or 11') are preheated in the regenerator chamber 1 (or 1') before passing to the reaction chamber 10 (or 10') into which solid, liquid or gaseous reactants are charged at 13 (or 13') and 14 (or 14') whilst consumed reactants and reaction products are discharged respectively at 15 (or 15') and 16 (or 16'). In a modification of Fig. 2, the inert gas heats up only the regenerator chamber 1 (or 1') and by-passes the reaction chamber 10 (or 10'). Gas purifiers 7 and 9 are included in the inert gas circuit 2 and may be used particularly in the event that the inert gas becomes contaminated e.g. during the change-over period. If more than two regenerators are utilized, at any one time one may be in the heating-up phase, another in the change-over phase, whilst others are in the heat utilization period for the chemical reaction. Emergency heating means (e.g. electric or fossilized fuel) may be provided for heating- up the regenerator in the event that the original heat source cannot be maintained. The regenerator casing may be electrically heated to avoid condensation thereon. Gaseous, liquid, sublimating, vapourising or pulverized catalysts may be supplied to the reaction either continuously or periodically. Or, when appropriate, a catalyst can be applied to the regenerator lining or heat storing material.

Description

The present invention relates to a reactor, in particular an apparatus for carrying out endothermic chemical reactions in which a nuclear reactor cooled by a cooling medium is used to produce the necessary process heat, and to a process for operating the device.

As is known endothermic chemical reactions can be carried out in heat exchangers. One type of heat exchanger is a regenerator where a single regenerator is firstly heated and is subsequently available for the endothermic chemical reaction. Because of this periodic mode of operation the regenerative process needs at least two regenerators. For example, one endothermic chemical reaction in a regenerator is described in the form of the Wulff process in Ollmanns Encyklop&die der Technischen Chemie, 4th Edition, Volume, 3, Pages 338—339.

Another type of heat exchanger is called a recuperator in metallurgy. The channels for the hot media are separated spaced from one another and from the channels for the media to be heated in the recuperator, whereby the media are guided in the A.C./D.C. or cross current so that uninterrupted operation is possible with - 2 41408 a recuperator.

The heating up of the above-mentioned heat exchanger is normally effected with the combustion gases of fossilized (gaseous, liquid or solid) fuels or simply with hot waste gases; in individual cases electrical heating is also effected.

It is desirable to replace the fossilized energy by nucleargenerated heat. Certain suggestions have already been made. For example, a device has been described in the document ChemieIngenieur-Technik 42, No. 7 (1970), Pages 429—433. The heat exchanger in connection with nuclear-generated heat is of the type called in the metallurgical industry a recuperator. In connection with a nuclear reactor the recuperator has the advantage that the cooling medium circulating in the nuclear reactor remains isolated in itself so that a source of danger resulting from the nuclear reactor is reduced.

In the above-named document Chemie-Ingenieur-Technik two solutions are shown for utilising the nuclear-generated heat. According to page 430, right-hand column, paragraph 4 in a changing, oxidising and reducing atmosphere a heat exchanger element is envisaged on the secondary side which consists of silicon carbide with a retracted ferrite sealing pipe. In the document this solution is not considered to be optimal, as it is expensive in construction and does not necessarily bring about sufficient heat transfer. Because of these difficulties, in the document the right way is considered to be taking liquid lead as the circulating medium for the secondary circuit. This circulating lead is illustrated in diagrams in various embodiments. On the one hand the circulating lead presents technical problems since at high temperatures the lead has a considerable vapour pressure. Special safety measures have to be taken in order to prevent poisonous lead fumes escaping when faults occur.

A further problem consists in that the circulating lead can dissolve aggressive components which then lead to uncontrollable damage in the recuperators.

According to the present invention there is provided an apparatus for carrying out endothermic chemical reactions, in which a nuclear reactor cooled by a cooling medium is used to produce the necessary process heat, whereby the cooling medium of the primary circuit pf the nuclear reactor transmits heat in a heat exchanger to a medium flowing in a secondary circuit, the medium of the secondary circuit being an inert gas and the secondary circuit having at least two regenerators in an arrangement in which each regenerator alternately forms a part of the secondary circuit to be heated by the inert gas and thereafter is available for heating one or more reactants. This apparatus may allow large amounts of heat caused by the primary circulation to be available without any danger for effecting an endothermic chemical reaction.

The invention also provides a process for conducting an endothermic reaction by introducing reactants into the heated reaction zone of an apparatus as defined in the preceding paragraph, and the reaction product of such a reaction.

By an inert gas is understood any gas harmless to the materials in the conditions existing in the apparatus, e.g. nitrogen, and especially the inert gases in the strict sense of the word. It is essential that no aggressive substances are brought to the recuperator (heat exchanger)with the secondary circulation.

The regenerator itself can be the reaction chamber or a special reaction chamber can be connected to the regenerator to receive the preheated reactant from the regenerator but through which reaction chamber the heating inert gas does not pass. - 4 41408 Therefore should corresponding harmful substances be carried along from the regenerators it is advantageous to change over to a gas purifier in the inert gas circuit. In a preferred embodiment a further small gas purifier is provided which can form a diversion via conduits between the outlet of the respective regenerator and the inlet of the recuperator.

This small gas purifier is used in order to wash the regenerator firstly with the inert gas in the change-over process from the chemical reaction operation to the heating up state. The advantage of this construction lies in that the total flow of inert gas is not subject to purification and that the purification takes place in high concentrations before mixing with the main stream and for this reason the gas purifying apparatus can be small.

The small gas purifier is only necessary to counteract the maximal content of aggressive components which can be introduced into the secondary circuit immediately after the change over of the regenerator.

Particular embodiments of the invention will now be described by way of example only with reference to the accompanying schematic drawings, in which :Fig. 1 is a first embodiment, and Fig. 2 is a second embodiment.

In the Figures the same parts are given the same reference numbers. The Figures show two regenerators 1, 1'; however this number can be increased if desired. Each regenerator can be inserted and removed (diverted) into the circuit conduit 2 via valves or sliders, so that the regenerators are brought alternately into the circuit, that regenerator which is not in the circuit 2 being used for an endothermic reaction stage. When change-over is effected the reaction chamber of the regenerator to which the change-over has been made again forms a part of the circuit conduit 2. Highly heated inert gas, preferably nitrogen circulates in this circuit conduit 2. Another part of the circuit conduit 2 forms the secondary part of a recuperator 3, 4. The primary part of this recuperator is a section of a cooling medium circuit conduit 5 of a nuclear reactor 6, for heating the inert gas.

As shown in embodiment of Fig. 2, the regenerators 1, 1' have inlets 11, 11' and outlets 12, 12' respectively for the gaseous phases which are to participate in an endothermic chemical reaction. According to Fig. 2 the outlets 12, 12' lead into a special reaction chamber 10, 10'. The special reaction chambers 10, 10' each have inlets 13, 13' and 14, 14' respectively Which are intended for the reactants. The reaction chambers 10, 10' have at the lower end outlets 15, 15' which are intended for reactants which have not been consumed in the reaction. On the other hand the outlets 16, 16' are intended for the desired reaction product.

In an exemplified embodiment which is not shown the circuit conduit 2 is preferably not connected at the lower end of the reaction chamber 10, 10' but directly at the outlets 12, 12' between the upper part of the regenerators and the reaction chambers. By'this is achieved the advantage that the heating secondary circuit has no contact with the reaction chamber 10.

In this case the reaction gases led in through the inlets 11, 11' take the heat from the regenerators 1, 1' into the special reaction chambers 10, 10'.

A gas purifier 9 is provided in the circuit 2 and can be introduced in the case of the inert gas circuit 2 being contaminated. A further gas purifier 7 is provided in conduits 8 between an outlet 17, 17' of the respective generator and the inlet of the heat exchanger (recuperator 3), preferably in front of the gas 4140® purifier 9 with respect to the inert gas flow, and can be introduced into the circuit if necessary.

During operation one of the regenerators (or at least one if a series is provided) is heated up by the highly heated inert gas, while the other (or at least one other) is used for the chemical reaction, as is preferably operated in regeneratively operated systems. The changeover of the regenerators occurs periodically, as known in regenerative systems.

An apparatus like those described above firstly offers the possibility of also supplying conversions with nuclear energy which can only be effected in regenerative systems.

Moreover the apparatus also offers special advantages in cases which work can be done recuperatively; for, in contrast to purely recuperative systems, in the above-described apparatus there is a greater range of possibilities for the special selection of materials for the parts of the apparatus.

Normally metal materials are suggested for recuperators. The materials must be resistant to erosion against the reaction gases at sufficient rupture strength. Also they should only be capable of slight diffusion for hydrogen and helium. Finally for economic reasons they should be easily workable.

With devices according to the prior art it can be very difficult to meet these requirements with metal materials.

In the present apparatus, as there are no corrosive gas components in the recuperator which has to transfer the nuclear heat from the cooling medium circuit of the nuclear reactor to the inert gas, known high temperature materials having good rupture, behaviour can be used; however they do not also need to havo prominent corrosion properties. Such materials are, for example: 1. Less than 0.15% C, 15% Cr, 4% Mo, 14.5%, Co, 5% Al, 4% Ti, 60S Remainder Fe. 2. Less than 0.10% C, 21% Cr, 32% Ni, 0.4% Al, 0.4% Ti, Remainder Fe. 3. Less than 0.15% C, 15% Cr, 5% Mo, 18.5% Co, 4.3% Al, 3.5% Ti. Remainder Fe.

In recuperative systems in which the heat is transferred by the metal exchange surface at the chemical reaction, it is also to be ensured that the material of the recuperator in the reaction chamber has to withstand agressive media. In the reaction chamber in the present apparatus however this consideration is not needed as there is no recuperative separation wall which is subjected both to heat transmission and aggressive chemical substances. The material for the separating wall of the recuperator is selected according to heat transmission properties, whereas the material for the reaction chamber of the regenerator is selected according to the conditions applicable to regenerators, such as the heat storage ability of the, preferably ceramic, substances for the lining.

As a special embodiment catalysts for the chemical reaction can be applied (when appropriate) to the regenerator lining of the present apparatus. Alternatively, it is equally possible to continually or periodically supply gaseous, liquid, sublimating or vaporizing or even pulverized catalysts either to the gaseous phases which enter the regenerator or through the inlets to the reaction chamber.

When using the present apparatus basically the process is carried out so that, periodically after heating up an inert gas and diverting the inlet gas circuit to another regenerator to be heated, the gaseous phase to participate in the reaction is introduced into the highly heated regenerator and the reaction with another reactant which is gaseous, liquid or solid, is effected in the chamber of this regenerator or in a special reaction chamber connected to the regenerator (as described later). in the change-over from the chemical reaction operation to the heating up stage and vice versa it is expedient to firstly wash the regenerator with a portion of the inert gas if it is to be expected that inert gas brings aggressive media with it from the regenerator. Gas purifiers as described earlier are supplied for this purpose.

The cooling medium circuit of the nuclear reactor will generally be under a high pressure because of the high heat transfer. The secondary circuit can also just as well be under the same pressure as the first circuit or under a higher or lower pressure. A higher pressure is advantageous because If there is a leak in the recuperator little cooling medium can then flow directly from the nuclear reactor into the other circuit.

When the regenerator is operated under a different pressure during the chemical reaction than during the passage of the heating inert gas, it is expedient to provide several phases for the periodic change-over operation, the pressures firstly being built up or reduced, as required.

For a constant rate of flow through the gas purification plant during the change-over operation it is advantageous to make a diversion via a buffer container.

If reactions with hydrogen and oxygen or water vapour occur in the regenerator, water can possibly condense on the inner side of the outer casing of the regenator or in the masonry in the proximity of the outer casing. A special embodiment therefore provides an additional outer heating of the regenerator if HjO could be formed and condense. This additional heating can be done with an electric - 9 42.40® current or with the hot nitrogen after leaving the other regenerators. Finally condensation can also be avoided by use of appropriate masonry.

If three or more regenerators are used in series the first can be in the heating up phase, the second in the change-over operation and the third in the heat-utilisation period for the chemical reaction. The regenerator which is the change-over phase can divert the hot inert gas under overpressure into the third regenerator in order to repress water condensation which might otherwise occur. The inert gas conveyed in this way can be mixed with the original inert gas stream, possibly after an intermediate purification.

Conduits for supplying and removing the gases can be included in the outer casing of the regenerator or in a special case arranged beside it and connected with it.

The formation of the inert gas conduit as a combustion chamber or the supply of additional heating is advantageous. With this a flexible use of temperature and the satisfaction of peak loads is possible.

If the nuclear reactor breaks down a regenerator which has a stand-by heat supply derived from fossilized fuel or electrical energy can still be heated up and a constant operation of the chemical side can therefore be maintained.

The use of fossilized fuel or electric energy can however be used to attain higher temperatures than can be attained simply with the waste heat of the respective nuclear reactor. For this purpose devices allowing the heating up of the regenerator directly or of the inert gas can be provided.

In the regenerator heating up can take place from the exterior via the casing or in the interior by electrical heating - 10 41408 devices or with fossilized fuel which is burnt in the regenerator or in a separate burner and the combustion gasea led through the regenerator.

Electrical or combustion devices for fossilized fuel which heat up the inert gas in its conduit can be arranged between the recuperator and the regenerator.

A special advantageous embodiment for an additional heating process with combustion gas is as in a Cowper (blast preheater) With a fuel shaft next to it.

The present apparatus is suitable for example for chemical and metallurgical processes carried out in a mill race. Here the regenerators can be constructed internally as cyclones, reaction tubes or other reaction chambers.

Feed devices for dust-like solids or spray devices for liquids may be provided and arranged in the known way.

Another use is the production of reduction gases from natural gas, methane, crude oil or naphtha or other crude oil products and by-products as well as hydrocarbons attainable from other fossilized fuels as well as the coupling of nuclear power plants with central heating plants or producers via circuit controlling gases and gas mixtures which contain, for example, CH^, H2f H20, CO and C02· Instead of individual regenerators arranged in series next to one another there can be used one or several regenerators which are annular and subdivided into individual chambers allowing a phased heating up of the regenerative plant and also a phased heat removal.

The present apparatus can also be used to heat up regenerators through which the gas components of chemical and metallurgical processes are guided in the heat removal period, whereby the reaction of these heated gases occurs with other phases in reaction chambers connected at the outside of the regenerator part (e.g. as mentioned above in connection with a modified form of the embodiment of Fig. 2). In such cases the special reaction chambers which are connected at the outside to the regenerators are included within the present invention. Then they can contain the installations such as cyclones, reaction tubes, instead of the regenerators.

In the process the inert gas passes in indirect heat exchange with the cooling fluid in the heat exchanger but in direct Exchange in the reactors where the content thereof becomes heated and heat is stored therein for commencement of the endothermic process. When the desired temperature has been obtained, the flow of inert gas is changed over to a second reactor similarly free of reactants which reaction zone is heated up for a subsequent endothermic process while the first reaction zone is used to carry out the process. The gas continually passes through the second reaction zone where the heat is stored until it is time to utilize the same for the endothermic process.

The inert gas flow can thereafter be rediverted to the first reaction zone or to another or third reaction zone where the heat is stored. In all instances the inert gas is in direct heat exchange with the contents of the reactor where heat is caused to be stored. However, it passes in indirect heat exchange with the cooling fluid in the heat exchanger.

If the reactor were contaminated during the endothermic process there would be the danger that after finishing the endothermic process and rediverting the inert gas flow into this reactor the inert gas flow could be contaminated by reactants remaining within the reactor. Under these conditions a gas purifier can be put into circuit returning tbe inert gas “from the reactor to the heat exchanger.

Claims (15)

1. Apparatus for carrying out an endothermic chemical reaction, in which a nuclear reactor cooled by a cooling medium is used to produce the necessary process heat, whereby the cooling medium of the primary circuit of the nuclear reactor transmits heat in a heat exchanger to a medium flowing in a secondary circuit, the medium of the secondary circuit being an inert gas and the secondary circuit having at least two regenerators in an arrangement in which each regenerator alternately forms a part of the secondary circuit to be heated by the inert gas and thereafter is available for heating one or more reactants.

2. Apparatus according to claim 1, including a gas purifier which can be introduced into the inert gas circuit.

3. Apparatus according to claim 1 or claim 2 including a small gas purifier which can be introduced into a conduit between the outlet of the respective regenerator and the inlet of the heat exchanger.

4. Apparatus according to any one of the preceding claims including a heat supply derived from fossilized fuel or electrical energy for additional supply of heat to or in each regenerator.

5. Apparatus according to any one of the preceding claims including heating devices for the secondary circuit between the heat exchanger and each regenerator.

6. Apparatus according to any one of the preceding claims wherein a reaction chamber for the reactants is within a regenerator.

7. Apparatus according to any one of claims 1 to 5 wherein a reaction chamber is connected to the part of a respective regenerator which is heated by the secondary circuit, the heated reactant passing from the regenerator to the reaction chamber for - 13 reaction.

8. Apparatus according to claim 6 or claim 7 wherein each regenerator has an inlet and an outlet for the reactant to be heated and the respective reaction chamber has an inlet and outlet for other reactants and an outlet for the reaction product.

9. Apparatus for carrying out an endothermic chemical reaction substantially as herein described with reference to and as illustrated in Pig. 1 or Fig. 2 of the accompanying drawings.

10. A process for operating an apparatus as claimed in any one of the preceding claims including heating up a regenerator by circulating therethrough the heated inert gas, diverting the inert gas circuit to another regenerator to be heated, introducing one or more gaseous phase reactants to be heated into the heated regenerator and carrying out the desired reaction with the heated reactant within the regenerator or in a reaction chamber connected to the regenerator.

11. A process according to claim 10 wherein nitrogen is used as the inert gas.

12. A process according to claim 10 or claim 11 wherein the inert gas circuit is under a pressure which is higher than the pressure in the reactor cooling medium circuit.

13. A process for conducting an endothermic reaction which includes heating an inert gas by indirect heat exchange with recirculating cooling fluid from a nuclear reactor, passing the heated inert gas alternately through a first reaction zone free of reactant and thereafter removing the inert gas from said first reaction zone and returning it to indirect heat exchange relationship with the said cooling fluid, introducing reactant into the said first reaction zone, -

14. 41408 diverting the inert gas into a further reaction zone free of reactant, returning it to indirect heat exchange with the said cooling fluid and supplying reactant into the said second reaction zone. 5 14. A process according to claim 10 or claim 13 substantially as any herein described.

15. A reaction product of an endothermic chemical reaction carried out in an apparatus as claimed in any one of claims 1 to 9 or by a process as claimed in any one of claims 10 10 to 14.