Such an apparatus is known in practice and is used in numerous situations in which the transfer of heat between a primary medium stream and a secondary medium stream is to be realised.

Such an apparatus concerns, for example, a chemical reactor in which an exothermic or endothermic reaction is carried out.

The energy required for an endothermic reaction may, for example, be supplied with the primary medium stream, whilst the reaction itself takes place in the secondary me- dium stream. Of course, the function of the primary and the secondary medium stream may also be interchanged.

Exothermic reactions also may advantageously take place in such an apparatus since the reaction heat can then be absorbed directly by a heat-removing medium stream. Some catalysts are less effective or even become unstable at in- creasing temperatures, and then it is very useful to be able to directly remove the reaction heat that has developed with an exothermic reaction.

Such an apparatus embodied as heat exchanger is known from NL-A-298 579.

Both the primary medium stream and the secondary me- dium stream may be a liquid stream, a gas stream or a mixture thereof.

A problem of the known apparatus is that in prac- tice, the temperature difference between the housing whose temperature is wholly determined by the secondary stream and the tube bank whose temperature is determined by both streams must not be greater than approximately 50°C. The expansion

differences resulting from greater temperature differences increase the loads on the tube bank, on tube plates in which the tubes of the tube bank are lodged, and the housing. Even if thicker tube plates, tube banks and housing were the an- swer to these increased loads, in consideration of its manu- facture, such a heat exchanger would be of little interest.

In practice the load problem is resolved by embody- ing the apparatus with bellows, which deals with the expan- sion differences. However, bellows are fragile and often have a limited mechanical life.

Another solution concerns a construction wherein the tube bank is U-shaped. However, this has the disadvantage that the thermal efficiency of such an apparatus is less fa- vourable and that internal mechanical cleaning of the tube bank is difficult or impossible.

A further solution is known wherein the apparatus is embodied with a so-called floating head or moveable end plate. However, this is complex, expensive and susceptible to leakage.

The object of the invention is to provide a rela- tively simple, inexpensive and effective apparatus while avoiding the disadvantages of the known apparatus.

To this end the apparatus according to the invention is characterized in that the wall is embodied with tubes in- corporated therein or mounted thereon, through which a por- tion of the medium supplied to the tube bank flows. This pro- vides a very simple and effective construction for achieving that during operation, the wall acquires substantially the temperature of the tube bank.

An important advantage of the apparatus according to the invention is that there are no limitations with respect to the allowable temperature difference between the primary medium stream and the secondary medium stream.

The temperature of the wall may be raised to that of the tube bank by optionally using co-active heating means that are incorporated in or mounted onto this wall.

The apparatus should preferably be constructed such that the tubes of the wall have a predetermined diameter and

a predetermined mutual distance, such that during operation the wall acquires substantially the temperature of the tube bank.

A suitable construction of the apparatus according to the invention is characterized in that at their ends, the tubes that are mounted in or onto the wall and the tubes of the tube bank are lodged in tube plates that connect to, re- spectively, an inlet pipe connector or outlet pipe connector for the primary medium stream, and in that the housing at said ends possesses an inlet or outlet, respectively, for the secondary medium stream. This construction has the additional advantage that it allows the tube length of the tube bank to be used more effectively, due to which a sought effective heat-exchanging surface can be realised with a tube bank of a shorter length than that of the known apparatus.

The advantage just mentioned can be achieved in par- ticular by embodying the apparatus such that the inlet or outlet, respectively, for the secondary medium stream is em- bodied as an inlet or outlet conduit surrounding the tube bank like a housing, and that over approximately the width of this inlet or outlet conduit, between adjacent tubes of the wall surrounding the tube bank, gaps are provided for, re- spectively, the inlet or outlet of the secondary medium stream.

The invention will now be further elucidated by way of an exemplary embodiment of an apparatus embodied as heat exchanger and with reference to the drawing, without limiting the claims.

In the drawing: - Fig. 1 shows a schematic cross-sectional view of the heat exchanger according to the invention, and - Fig. 2 shows a cut-away schematic view of an end of the heat exchanger according to the invention.

Identical reference numerals in the figures refer to similar components.

With reference first to Fig. 1, reference numeral 1 indicates the heat exchanger according to the invention.

Said heat exchanger 1 has a housing 2, within which

housing 2 a tube 3 is accommodated. The figures do not show the individual tubes of the tube bank 3. However, to the per- son skilled in the art it is clear how such a tube bank 3 is constructed, so that it does not need to be shown in the fig- ure.

The tube bank 3 possesses a first end with a con- necting means 4 for the inlet of a primary medium stream 6 and a second end with a connecting means 5 for the outlet of said primary medium stream 6. In-and outlet of a secondary medium stream 7 also takes place via said connecting means 4 and 5, usually this occurs in counter-flow with respect to the primary medium stream 6. The connecting means 5 provided at the second end thus serves for the inlet of the secondary medium stream 7, whereas the connecting means 4 provided at the first end, serves for the outlet of the second medium stream 7.

The housing 2 further possesses a wall 8 extending in the longitudinal direction of the tube bank 3, which wall according to the invention is equipped such that during op- eration it acquires substantially the temperature of the tube bank 3.

To this end the wall 8 is preferably embodied with tubes 9 incorporated therein or mounted thereon, through which a portion of the medium supplied to the tube bank 3 flows. This is clearly visible in the cut-away view of an end of the heat exchanger 1 as illustrated in Fig. 2.

In the construction of the wall 8 shown in Fig. 2 the tubes 9 are incorporated in said wall 8.

Expediently, the tubes 9 of the wall 8 are embodied with a predetermined diameter and a predetermined mutual dis- tance such that during operation, the wall 8 substantially acquires the temperature of the tube bank 3. It will be obvi- ous that the diameter and the distance of the tubes 9 to the wall 8 are in part determined by the diameter of the tubes of the tube bank 3 and the resistance caused by said pipes for the medium flowing through said pipes.

Fig. 1, but even more so Fig. 2, shows that the ends of the tubes 9 of the wall 8 as well as the tubes of the tube

bank 3 are lodged in tube plates 10,11. Said tube plates are provided at both sides of the heat exchanger 1, and connect to an inlet pipe connector 12 or an outlet pipe connector 13, respectively, for the primary medium stream 6.

The Figs. 1 and 2 further show that at said inlet pipe 12 and outlet pipe 13, the housing 2 is provided with an inlet 14 and outlet 15 for the secondary medium stream 7.

The inlet 14 and outlet 15 for the secondary medium stream 7 are embodied as an inlet conduit or outlet conduit, respectively, surrounding the tube bank 3 like a housing.

Expediently, over approximately the width of said inlet and outlet conduit 14,15, between adjacent tubes of the wall 8 surrounding the tube bank 3, gaps 16,17 are pro- vided for, respectively, the inlet or outlet of the secondary medium stream 7. This is clearly shown in Fig. 2. The secon- dary medium stream 7 is thus able to flow around the tubes of the tube bank 3 in the manner known as such, allowing the heat-exchanging contact via the walls of the tubes of the tube bank 3 with the primary medium flowing through the tubes to be realised.

As already explained, the invention is not limited to the above exemplary embodiment of an apparatus embodied as heat exchanger, but can also be employed, for example, as re- actor for an endothermic chemical reaction.

To carry out such an endothermic chemical reaction it is possible, for example, to provide a catalyst in the space surrounding the tubes of the tube bank 3, through which the secondary medium stream 7 can flow. This secondary medium stream 7 then needs to contain the reaction mixture for the formation of the desired chemical product. The reaction heat necessary for the endothermic reaction may be obtained from the primary medium stream 6 flowing through the pipes of the tube bank 3. The construction of a chemical reactor embodied in this manner is such as to allow a fast and high conversion ratio for the formation of the desired chemical product, while it suffices that the reaction mixture stays for a rela- tively short time in the reactor 1.

It is also possible to provide the catalyst in the

tubes of the tube bank 3 and/or the tubes 9 of the wall 8, and to obtain the necessary reaction heat from the secondary medium 7 flowing around the tube bank 3. Thus the primary me- dium stream 6 carries the mixture of chemicals for forming the desired chemical product.

In an exothermic chemical reaction it may be desir- able to be able to remove the developed reaction heat immedi- ately. This may be effected in a manner similar to that used with the apparatus intended for endothermic reactions. If the reaction takes place in the primary stream, the secondary stream serves for the removal of heat and if the reaction takes place in the secondary stream, the primary stream serves for the removal of heat.

Furthermore, it should be noted that as a rule when the apparatus 1 is embodied as reactor, its dimensioning may well differ greatly from the dimensioning of the apparatus when used as heat exchanger. Moreover, if the apparatus is used as chemical reactor, additional measures may be neces- sary. For example, in order to prevent the catalyst being washed out, it will be necessary to close off the space in which the catalyst is introduced by means of a semi-permeable sieve or gauze. However, such measures are completely within the capabilities of the person skilled in the art and there- fore require no further explanation.