Heat Exchanger For Cooling Gases

Abstract

A heat exchanger for cooling gases and having a number of fire tubes for conducting hot gases through a cooling chamber whereby all the tubes will be subjected to substantially the same conditions with regard to the temperature and flow conditions of a cooling medium in the cooling chamber.

Description

The invention relates to an apparatus for the cooling of fresh cracking or other gases.

Cracking gases are ordinarily produced at high temperatures and under appropriate pressure in so-called tube furnaces. Then the gases must be cooled down in an extremely short time to a temperature at which a chemical synthesis reaction or re-formation is no longer possible, that is to say the generated chemical condition is frozen.

Using conventional heat exchangers, this is effected in that the fresh cracking gases are conducted through a plurality of water-cooled tubes, called fire tubes. For reasons of flow-line pattern and to save space, the known fire tubes are bundled and arranged as close as possible. Moreover the known fire tubes are arranged on the inlet side in one common floor and enclosed by a common jacket.

Between the diameter of the crack pipe conducting the fresh cracking gas and the external diameter of the bundle of fire tubes as a rule there is a considerable difference which is compensated by a suitable funnel-shaped tube piece or a conical widening of the crack pipe. With the high speed of flow of the cracking gas in modern production plant, this is the reason for heavy eddying of the cracking gas upstream of the common floor. As a result of the ordinarily very incomplete diffusing action of the conical widening, the flow of cracking gas breaks away in the conical widening with high speed of flow, and return eddies occur at this point. The return eddies cause an additional flow resistance and involved therewith an increased time of sojourn of the cracking gas before entering the fire tubes, which often is already sufficient to render a chemical synthesis reaction or re-formation possible for the cracking gas.

However not only do the return eddies before the common floor of the fire tubes involve the danger of re-formation of the cracking gas, but at the same time a varying thermal loading of the fire tubes and their common floor occurs, the heaviest heating, that is the heaviest loading, occurring in the centre of the common floor and in the centre of the bundle of fire tubes. However, at this point, in the case of water cooling, the cooling action of the water in the conventional heat exchangers is particularly weak, since the water supplied in general from the periphery of the jacket must overcome the flow resistance of many fire tubes in order to pass into the centre of the bundle and to the centre of the common floor. There is also the fact that steam bubbles rising from the common floor and the fire tubes interfere with the water circulation in the cooling chamber and thus further reduce the cooling action of the water.

The irregular flow conditions of the water have the result that, at a temperature below or equal to 570.degree.C and a pH value higher than or equal to seven, magnetite (Fe.sub.3 0.sub.4) forms on the water-charged surfaces of the fire tubes which are produced exclusively from iron. Furthermore, at a temperature greater than or equal to 570.degree.C and a pH value lower than or equal to seven, a ferrous oxide (FeO) layer forms on the water-charged surfaces between the magnetite and the iron of the fire tube wall, which layer is very brittle and therefore easily chips away together with the magnetite. Thus the iron of the fire tube wall again comes directly into contact with the cooling water, and again magnetite is produced. This corrosion shortens the life of the fire tubes very considerably and is further reinforced by an electrochemical corrosion as a result of the different so-called electric valencies of iron and magnetite and the cooling water penetrating between the iron and the magnetite.

Moreover due to the chipping magnetite and ferrous oxide in the middle on the common floor of the fire tubes there are formed thermally insulating deposits which cause varying floor temperatures, that is to say in the case of an elevated temperature in the centre of the floor involve a corresponding distortion of the floor which in the extreme case leads to damage which puts the heat exchanger out of action.

The irregular flow conditions of the gas and the high times of sojourn involved therewith have the result that cracking gas consisting for example of C.sub.2 H.sub.2 re-forms into C.sub.2 H.sub.6 (ethane) and the free carbon atoms are deposited as a graphite-type mass on the inner wall of the fire tubes. The graphite-type mass could per se easily be removed, if in the cracking gas there were not at the same time constituents with heavy C-fraction, that is high-boiling hydrocarbons, which as a result of their high condensation point condense in the case of a relatively long time of sojourn and likewise are deposited on the inner wall of the fire tubes. The deposit of free carbon atoms and of the condensate of the high-boiling hydrocarbons on the inner wall of the fire tubes then on the one hand diminishes the efficiency of the heat exchanger. On the other hand the deposits on the inner wall of the fire tubes, as a result of the now reduced or deflected cooling of the surfaces and the high inherent temperature involved therewith, cake with heavy dehydration of the condensed hydrocarbons into an especially unpleasant increasing dirt coating (petroleum coke), for the removal of which mostly then a kind of water spray with a water pressure of 300 atmospheres is necessary.

With such wearing and soiling phenomena, what is called the tour time of conventional heat exchangers, used for the cooling of fresh cracking gas, is correspondingly short.

The invention is therefore based upon the problem of providing an apparatus for the cooling especially of fresh cracking gases which ensures a constant uniform cooling effect with any desired construction size, that is to say gas throughput, gas temperatures and gas pressure of any desired magnitude.

This is achieved according to the invention, using a heat exchanger with a number of fire tubes each having substantially the same cooling effect upon the cracking gas and for this purpose the fire tubes of the heat exchanger are arranged each in a cooling medium current which is equal as regards the temperature and the flow conditions. This results in a relative limitation of the number of fire tubes, which together with the arrangement of the fire tubes characteristic for the equal cooling action, surprisingly also leads to the existence of equal flow conditions for the cracking gas in all fire tubes.

Favourable operating conditions are present in the case of an annular arrangement of the fire tubes and supply of the cooling medium through a central descending pipe. In the extreme case a limitation of the number of fire tubes to one row of fire tubes is provided here. From the one row of fire tubes then arranged in a circle it is clear that the necessary equal operating conditions are obtained for all fire tubes. This includes both equal cooling conditions due to overall equal flow resistance opposing the flow of the cooling medium, and equal gas flows in the fire tubes. The equal gas flows in the fire tubes in the case of circular arrangement of the fire tubes, and the ordinary hot gas inlet widening conically towards the fire tubes, is explained by the fact that the flow conditions in the inlet are substantially rotation-symmetrical in relation to the central axis. The inlet openings of the circularly arranged fire tubes are charged from a gas supply aligned with the fire tubes only with gas of equal flow behaviour, so that with equal tube dimensions and surface qualities in the fire tubes, equal flow conditions establish themselves.

The rotation-symmetrical flow conditions in the widening of the gas supply circuit may be assisted by a baffle which is situated in the inlet upstream of the fire tubes. The baffle is preferably made conical and adapted in such a way to the widening, that is to say fills the widening to such extent, that the latter with a gas pressure of 1.6 to 1.8 atm.abs. produces a chamber loading which amounts at maximum to 125 mg/sec/cu.m and at least 90 kg/sec/cu.m.

As a result of its relatively large volume and its form adapted to the inlet, the baffle directs the gas directly into the fire tubes and thus advantageously prevents the return eddies which occur in conventional cracking gas supply systems, so that diffusor angles between 60.degree. and 100.degree. easily become possible for the conical widening of the gas inlet. This property makes the baffle, irrespective of the particular arrangement of the fire tubes, likewise suitable for conventional gas supply conduits and cooling devices for gas.

However the displacement body is also particularly advantageous for cooling devices with fire tubes which are retained at their inlet ends in one common upstream floor. In this case the baffle has the additional effect that it imparts to the upstream floor a larger heat-emitting area than heat absorbing area and thus extra-ordinarily good cooling. For this purpose the baffle is preferably so formed that the heat-emitting area of the upstream floor is at least twice as large as its heat absorbing area. Furthermore the baffle reinforces the common floor of the fire tubes in such a way that it can be extremely thin. In this case a bending resistance is imparted to the upstream floor which prevents unacceptable bulging out of the floor under the action of the cooling medium pressure and on heating. Optionally a cup-shaped thickening of the floor on its side facing the coolant supply pipe will contribute to this bending resistance. Apart from increasing the bending resistance, the thickening of the floor then has the additional advantage that it improves the distribution of the cooling medium, issuing from the supply pipe, to the individual fire tubes.

The equal cooling effect upon the fire tubes is kept constant by an unambiguous and stable circulation of the cooling medium. As cooling medium there serves according to choice liquid lead, liquid sodium and especially water in natural circulation. For the cooling with water in natural circulation the fire tubes, as known per se, are held at their inlet ends and at their outlet ends in common upstream and downstream floors and with an intermediate floor which encloses the coolant supply pipe and is spaced from the upstream floor. The intermediate floor may conduct the cooling medium issuing from the supply pipe against and according to choice over the entire upstream floor and/or in case of need even to a particular extent upon heavily heated surfaces of the upstream floor.

The intermediate floor may provide guide tubes which surround each fire tube in the region of maximum heat-flux density. The guide tubes ensure that the rising cooling medium flows securely along on the fire tubes and intensively cools them. Moreover, when the fire tubes are arranged upright with their inlet ends lowermost, the guide tubes together with the intermediate floor form dirt pockets in which scale and the like impurities can collect, so that these are not deposited in thermally insulating manner on the upstream, that is the lower, floor.

The dirt pockets are of such size that their cleaning is not necessary during what is called the tour time of the apparatus. As well as the dirt pockets, according to choice a regular washing off of the interspace between the upstream floor of the fire tubes and the intermediate floor is optionally also provided, in order to prevent deposits on the upstream floor and thus deterioration of the heat transmission to the cooling water. Then a washing and water drain-off system is arranged between the lower floor and the intermediate floor for the washing.

The fire tubes may be formed over a part of their length as double walled tubes, the cavity between the inner and outer walls being sealed off both against the cooling medium and against the hot gas. Thus the thermal conductivity in the tube wall of the fire tubes, with appropriate formation and arrangement of the double wall, is reduced to such an extent that the temperature of the internal wall lies above the maximum occurring condensation point of the gas, while the temperature of the outer wall lies substantially below the temperature pertaining to the maximum condensation point, and depositing of gas leading, say, to petroleum-coke separations is prevented. With the formation as double walled tubes there is optionally at the same time also involved a reduction of the free throughflow cross-section in the fire tubes, which then preferably amounts to 20 to 35 percent and in the end part of the fire tubes effects as regards the gas a higher throughflow of mass, that is to say advantageously opposes soiling of the fire tubes.

Each cooling device according to the invention, especially in the case of only one row of fire tubes arranged in circular form, has a limited cooling performance which is taken into consideration in modern cracking gas generators such for example as pyrolysis furnaces by a parallel connection of several heat exchangers. This has the additional advantage that the inflowing cracking gas is distributed to the individual heat exchangers and thus the flow conditions are already favourably influenced.

Along these lines, in contrast to conventional pyrolysis furnaces or the like cracking gas generators having several tubes which conduct away the so-called moist cracking gas, each of these tubes is provided with at least one heat exchanger. In the case of delivery quantities of 3,000 to 8,000 kg/h per tube, each tube is preferably provided with four heat exchangers connected in parallel with one another and together forming a cooler section. Moreover a horizontal or especially slightly inclined arrangement of the fire tubes is optionally foreseen. The horizontal and slightly inclined arrangement permits, for example in the case of pyrolysis furnaces, of setting up the entire apparatus for the cooling of the fresh cracking gas, hereinafter called cracking gas cooler, beneath the cracking furnace. Furthermore the horizontal arrangement of the fire tubes is much simpler in production and maintenance than a vertical arrangement.

In the case of the use of water in natural circulation and the deliberate generation of steam to boost the cooling effect and the natural circulation, in the approximately horizontal arrangement of the fire tubes a separation of the steam-water current is prevented by the fact that the fire tubes are provided each with a double jacket through which the cooling water flows. Thus its own cooling water forced circulation is advantageously allocated to each individual fire tube.

A further development of the apparatus according to the invention consists in the provision of at least two series-connected heat exchangers with a gas exit temperature of below 500.degree.C. for the first heat exchanger. In this case the construction style of the second heat exchanger is of subordinate importance, for below 500.degree.C the cracking gas no longer reforms, so that several heat exchangers connected in parallel can be provided with one series-connected common heat exchanger, and this may possibly also take place even in the case of an over-long time of sojourn of the cracking gas in the series-connected heat exchanger. In this case however precipitation of the cracking gas in the series-connected heat exchanger is prevented in that the thermal conductivity of the fire tubes of the series-connected heat exchanger is reduced, at least in the exit region, by the use of a thermally insulating double jacket, in such a way that the temperature on the inner wall of the fire tube lies above the maximum condensation point of the cracking gas, even in the case of a temperature on the outer wall of the fire tubes lying below the minimum cracking gas condensation point.

Some examples of apparatus constructed in accordance with the invention are illustrated in the accompanying drawings, wherein:

FIG. 1 shows the overall side view of an apparatus;

FIG. 2 shows a partial elevation, partial longitudinal section, of the apparatus of FIG. 1;

FIG. 3 is a section taken on the line III--III in FIG. 2;

FIG. 4 is a section showing a fire tube of another apparatus;

FIG. 5 is a section taken on the line V--V in FIG. 1;

FIG. 6 shows in diagrammatic representation a part of an overall production plant for cracking gas;

FIG. 7 shows the fire tube of a third apparatus;

FIG. 8 shows a fourth apparatus for the cooling of fresh cracking gases having several parallel-connected heat exchangers and one series-connected common heat exchanger, in plan view;

FIG. 9 shows the apparatus according to FIG. 8 in a view in the direction IX--IX in FIG. 8; and,

FIG. 10 shows a heat exchanger according to FIG. 8 in an individual view.

In FIGS. 1 and 5 a cooling apparatus is shown which consists of four heat exchangers 1 connected in parallel with one another. The heat exchangers 1 are at the same time arranged three-dimensionally parallel with one another and connected with one another through lugs 2 and bolts 22 at two positions lying one above the other in each case, for assembly. In the operational condition the heat exchangers 1 are suspended on suitable connectors, cables or the like devices and the lower bolts 22 are released in each case, so that the heat exchangers 1 with adequate freedom of movement are mounted for swinging in the upper lugs 2 and bolts 22. Thus displacements and variations of dimension of the heat exchangers occurring as a result of thermal expansion are very simply compensated.

For the connection with the connectors or cables the heat exchangers 1 are provided in the upper and especially in the lower region with tie-bolts 23. The arrangement of the tie-bolts 23 in the lower region here has the advantage that on heating the heat exchangers expand upwards and thus bending of the transfer conduits leading to the heat exchangers 1, which are subject to a substantially higher thermal stressing than the transfer conduits leading away from the heat exchangers 1, is prevented.

The four heat exchangers 1 together form a so-called cooler section. According to FIG. 6, in a pyrolysis furnace 24 generating a cracking gas, to each so-called cracking gas pipe 25 conducting away cracking gas there is allocated a cooler section. The fresh cracking gas is here fed within a cooler section to the heat exchangers 1 at a temperature of between 830.degree. and 850.degree.C and a pressure of between 1.6 and 1.8 atm.abs. by way of a distributor device 3 and pipes 4 from the associated cracking gas pipe 25.

The distributor device 3 consists of an inlet flange 6 which is connected with a corresponding flange 5 of the cracking gas pipe 25, and of a dome 7 adjoining the inlet flange 6 and connecting the pipes 4 with the inlet flange 6.

The pipes 4 open or widen into gas-distributor cones 8. The gas distributor cones 8 terminate according to FIG. 2 in each case in a cylindrical recess 9 of a container 10 and are connected with the container 10 in sealed manner by means of a sealing ring 11 and a bellows 12, which at the same time has the task of compensating thermal expansions and possibly also production tolerances. The bellows 12 is here connected with a conduit 21 which conducts away the so-called leakage gas which penetrates past the sealing ring 11 into the bellows 12.

The container 10 consists essentially of a tubular pressure jacket 13, two floors 14 and 15 and five to twelve cooling pipes, designated as fire tubes 16, which as shown in FIG. 3 are arranged in uniform distribution with one another, parallel with the longitudinal axis of the container 10 and in circular form. The fire tubes 16 are welded into the floors 14 and 15 so that the cracking gas flowing out of the associated distributor cone 8 flows through passage holes 17 of the floor 14, which connect the fire tubes 16 with the distributor cone 8, into the fire tubes 16 at the rear end, in the direction of flow, of the container 10.

In this action a uniform flow of the cracking gas into the fire tubes 16 is ensured by a baffle body 18. For this purpose the baffle body 18 is arranged in the distributor cone 8 and in the direction flow of the cracking gas before the floor 14 and has a form conducting the cracking gas to the passage holes 17, which form in the present case is that of a cone with circular base area pointing with its apex into the distributor cone 8.

In the case of a distributor cone 8 of 60.degree. to 100.degree. angle and with a displacement body 18 causing a chamber loading in the distributor cone 8 of 90 to 125 kg. per second and cubic metre, especially favourable flow conditions are achieved.

The cracking gas flows through the fire tubes 16, and by contact with the cooled tube wall of the fire tubes 16, within 15 to 20 milliseconds, loses so much heat that a temperature of 500.degree. to 550.degree.C is reached and the chemical condition of the cracking gas is frozen, that is to say re-formation of the cracking gas is prevented.

The cooling of the fire tubes 16 takes place according to FIG. 2 in a manner in which cooling medium, in this case water, is conducted through a central, supply pipe 19 between the floors 14 and 15, which form a closed space with the pressure jacket 13 of the container 10. At the end facing the floor 14 the supply pipe 19 is connected with an intermediate floor 20 which surrounds the fire tubes 16 with guide tubes 31 with an interval adequate for the water throughflow for their cooling.

The water flows in natural circulation upwards through the container formed by floors 14 and 15 and the pressure jacket 13, that is to say when the space formed by the floors 14 and 15 and the pressure jacket 13 is filled with water, the water is warmed on the common floor 14 and on the fire tubes 16. Thus the water experiences a corresponding upward thrust so that it flows along the vertically arranged fire tubes 16 through the guide tubes 31 and continuously cools the tubes 16. Since the water is introduced in the boiling condition, the heating of the water on the common floor 14 and the fire tubes 16 leads to steam formation. As a result of the steam formation the water takes up very large quantities of heat on the fire tubes 16 and the floor 14. Moreover the steam formation reinforces the flow on the fire tubes 16, in contrast to the known cooling devices.

Particularly favourable cooling conditions are present on the floor 14 if with adequate base area of the distributor cone 8 the ratio of the heat emitting surface to the heat absorbing surface is greater than 2. The heat emitting surface is the surface of the floor 14 charged with cooling medium, while the heat absorbing surface is the surface of the floor 14 charged with cracking gas.

The guide tubes 31 together with the intermediate floor 20 at the same time act as dirt pockets in which scale and the like impurities can collect. This prevents these impurities from settling in thermally insulating manner on the floor 14 to be cooled and deteriorating the heat transmission between floor 14 and cooling medium.

The cooling medium rising as a water-steam mixture is fed through overflow pipes 32, which are connected in the direction of flow of the cracking gas directly upstream of the floor 15 to corresponding openings in the pressure jacket 13, to a known evaporation drum 51, while at the same time boiling water fills up from the evaporation drum through the supply pipe 19.

For the maintenance and cleaning of the space formed by the floors 14 and 15 in the pressure jacket 13 a washing and drainage outlet 33 is fitted to the pressure jacket 13 between the floor 14 and the intermediate floor 20, which outlet consists of a pipe and a shut-off slide valve or cock (not shown).

The cooled cracking gas issuing from the heat exchanger 1 at 360.degree. to 450.degree.C flows into a gas collector hood 34 flanged to the pressure jacket 13 and converging in the direction of flow of the cracking gas, which hood continues in a conduit 35. The conduit 35 opens with the conduits 35 of the other three heat exchangers 1 into a collector device 36 which is assembled similarly to the distributor device 3 and recombines the cracking gas current previously divided by the distributor device 3, in order to feed it to a further cooler section or to a processing apparatus.

In a further example of the heat exchangers shown in FIG. 4, between the lower floor 40 and the upper floor 41, fire tubes are welded in as partially double tubes, namely with an inner tube 42 and an outer tube 43. In this case the fire tubes are formed as double tubes especially in the upper part and over two-thirds of their length.

At the point where the fire tubes merge into double tubes, the inner tubes 42 and the outer tubes 43 are tightly connected with one another, for example by welding, with a common transition part 44. While the fire tubes then are connected in the same way as according to FIGS. 1 to 3 with the lower floor 40, which is upstream in the direction of flow of the cracking gas, the fire tubes are tightly connected at their other ends only at by outer tube 43 to the upper floor 41. The inner tubes 42 of the fire tubes are conducted out through the upper floor 41 and are tightly connected with a corresponding flange or floor 45 of the gas collector hood, which is not further illustrated in this case. Since the pressure jacket 46 and forming with the floors 40 and 41 a container for the cooling medium, is not connected with the floor 45 but terminates with the floor 41, thus atmospheric air can penetrate into the cavity between the inner tube 42 and the outer tube 43. This formation of the fire tubes, with the same operation as in the heat exchangers 1 according to FIGS. 1 to 3, has the advantageous consequence that by reducing the passage of heat the temperature on the inner wall of the fire tubes, especially in their upper region, always lies above the maximum condensation point of the cracking gas, although the temperature on the outer wall of the outer tube 43 lies substantially below the temperature pertaining to the maximum condensation point.

The heat exchanger according to FIG. 4 differs otherwise from the heat exchangers 1 according to FIGS. 1 to 3, apart from in the fire tubes, essentially only by the supply of the cooling medium, that is to say in the formation of the supply pipe. According to FIG. 4 the descending pipe 47, consists of a short pipe piece which, with similar intermediate floor 20 and guide tubes 31, is provided with an additional floor 48 at the end remote from the floor 40. With an entry opening 49 for the cooling medium arranged adjacent to the floor 41 in the pressure jacket 46 and with an exit opening 50 arranged in the direction of flow of the cracking gas immediately upstream of the entry opening 49 in the pressure jacket 46, the additional floor 48 serves to separate the heated cooling medium from the inflowing cooling medium and thus to prevent intermixing of the two media.

In FIG. 7, similarly to FIG. 4, a fire tube formed as double tube is shown. In distinction from the double tube according to FIG. 4, in the case of this double tube the inner tube 42 is pushed into the outer tube 43 and rolled thereto at its lower end to such extent that at this point it is firmly and at the same time sealingly connected with the outer tube 43.

Furthermore in this example, similarly to the case of the heat exchangers 1 according to FIGS. 1 to 3, the gas collector hood 34 is tightly connected with the container 10, while the inner tube 42, with outer tube 43 firmly and sealingly welded with the upper floor 15, extends out beyond the upper floor 15 and is displaceably mounted in a further floor 53 which is arranged above the upper floor in the gas collector hood 34. The displaceable mounting of the inner tube 42 in the further floor 53 serves for the compensation of its thermal expansion, while the floor 53 in turn serves to protect a sealing composition, which fills out the interspace between the floors 53 and 15 and in doing so encloses the inner tube 42, against the inflow of the cracking gas.

According to FIGS. 8 and 9, three cracking gas pipes 60, 61 and 62 of the pyrolysis furnace 24 open into three cooler sections 63, 64 and 65 each of which consists of four parallel-connected heat exchangers 66 slightly inclined towards the cracking gas flow, so that to each cracking gas pipe 60, 61, 62 there is allocated a heat exchanger 66. The heat exchangers 66 in turn all open into a gas collector 67 which feeds cracking gas issuing from the heat exchangers 66 and cooled to 450.degree.C to a subsequently placed heat exchanger 68. One common cooling water circulation 70 represented in dot-and-dash lines is provided for all the heat exchangers 66 and 68.

According to FIG. 10 the heat exchangers 66 and the heat exchanger 68, constructed analogously with the heat exchanger 1, consist each of a number of fire tubes 75 arranged in annular form around a central supply pipe 71 and provided with a triple jacket 72, 73, 74, and of two cylindrical housing chambers 76 and 77.

Of the housing chambers 76 and 77, the housing chamber 77 is situated at the upstream end, in the direction of flow of the cracking gas, of each heat exchanger 66 and 68. The housing chamber 77 has two end walls, of which the rear wall encloses the tubes 74 of the fire tube jacketing and the supply pipe 71 as a common floor 78, while the forward end wall 79 has the same function as the floor 14 of the heat exchanger 1.

The housing chamber 76 is situated at the rear end of the heat exchangers 66 and 68 and is further divided by an intermediate wall 80 into a forward chamber 90 and a rear chamber 91. In this case the tubes 74 of the fire tube jacketing open into the forward chamber 90 and the descending pipe 71 opens into the rear chamber 91, while the tubes 73 are conducted through the rear chamber 91. Thus in the case of an adequate seal between the tubes 73, 74 and 71 and the wall of the housing chamber 76, water can flow from the chamber 91 by way of the supply pipe 71 to the housing chamber 77 and from the housing chamber 77 through the cavity between the tubes 73 and 74 to the housing chamber 90.

This water flow occurs, with a suitable water supply 92 to the chamber 91 and a corresponding water outlet 93 at the chamber 90, when the tubes 73 are warmed by throughflowing fresh cracking gas. Then steam forms on the hot tubes 73, which causes a strong water flow even in the case of an inclination of the heat exchanger of only a few degrees, for example 3.degree.. Thus the end wall 79, similar to the floor 14, and the fire tubes 75 are adequately cooled as in the heat exchanger 1.

At the same time however the tubes 12, in the region of the housing chamber 76, that is to say in the region of the cooling water entering the heat exchanger 66 or 68, with the tubes 72 prevent condensation of the cracking gas on the fire tube inner wall, in that analogously with the FIG. 7 example they correspondingly reduce the thermal conductivity of the fire tubes 7 in the region of the housing chamber 76.

Otherwise the heat exchangers 66 and 68 differ from the heat exchanger 1 only in that the intermediate space between the gas distributor cone and the bellows is partially filled with a sealing composition. A leakage conduit 84 is connected to the remaining free part of the interspace between the gas distributor cone and the bellows. Steam can be injected additionally through the leakage conduit 84, preventing escape of cracking gas at the point of contact, additionally sealed by a packing ring 85, between the gas distributor cone and the end wall 79 if the packing ring 85 should be damaged.

The water drainage and washing outlet, designated in this case by 86, is expediently situated at the lowermost point of the housing chamber 77.

Likewise the tie-rods or constant suspensions necessary for the swinging and expansion-compensating mounting of the heat exchangers 66 and 68 are secured with the aid of straps and supports to the heat exchangers 66 and 68 in such a way that each heat exchanger 66 or 68 is suspended at two points.

In assembly the heat exchangers 66 are connected with one another in the individual cooling sections 63, 64 and 65 through lugs 94 and bolts 95 which are removed after assembly.

Claims

We claim:

1. A heat exchanger for cooling cracking gases comprising a single annular row of vertically arranged laterally spaced fire tubes for conducting hot cracking gases therethrough, first means for enclosing said row of fire tubes and forming a cooling passageway for passing a cooling medium over the exterior of said fire tubes, said first means comprising a vertically arranged jacket laterally enclosing said row of fire tubes, an upstream floor extending transversely of and secured to said jacket and the lower ends of said fire tubes secured to and communicating through said upstream floor, a downstream floor extending transversely of and secured to said jacket and the upper ends of said fire tubes secured to and communicating through said downstream floor, an intermediate floor extending transversely of said jacket between said upstream and downstream floors and located adjacent said upstream floor, said fire tubes extending through said intermediate floor, second means including a supply pipe for supplying the cooling medium for flow over said fire tubes, said supply pipe being vertically arranged and disposed centrally within said row of fire tubes, said supply tube extending downwardly through said downstream floor and having its outlet end extending through and terminating at the lower face of said intermediate floor, said upstream floor intermediate floor and said jacket forming a cooling medium inlet chamber arranged to receive the cooling medium from said supply pipe, third means attached to the lower end of said jacket for introducing hot gases into said fire tubes and for assuring uniform temperature and flow conditions in the gases as they flow through said fire tubes in indirect heat transfer relationship with the cooling medium, said third means includes a conically shaped baffle located located centrally on and projecting downwardly from the lower face of said upstream floor, the diameter of said baffle at said upstream floor being smaller than the inside diameter of said row of fire tubes, fourth means forming an annular passage through said intermediate floor about each said fire tube for conducting the cooling medium from the cooling medium inlet chamber into the space between said intermediate and downstream floors for upward flow over said fire tubes extending therethrough, an overflow pipe extending through said jacket and communicating with the upper end of the space between said intermediate and downstream floors for removing the cooling medium after its upward flow over said fire tubes, and said fourth means comprises a sleeve-like guide tube located about each said fire tube and having an inside diameter slightly larger than the outside diameter of said fire tubes, said guide tube secured to and extending upwardly from the upper face of said intermediate floor and said intermediate floor forming an annular opening about each said fire tube affording communication between the cooling medium inlet chamber and the annular space between each said guide tube and said fire tube which it encloses.

2. A heat exchanger, as set forth in claim 1, wherein said third means for introducing hot gases into said fire tubes includes a gas supply pipe spaced axially from and below the inlet ends of said fire tubes, walls forming a closed inlet chamber extending from said gas inlet pipe to the inlet ends of said fire tubes in the lower face of said upstream floor, said gas inlet pipe having its axis disposed centrally of the axes of said fire tubes, said walls forming the inlet chamber include a frusto-conically-shaped member connected at its smaller diameter end to said gas inlet pipe and having its wider diameter end connected to said upstream floor encircling the outside diameter of said row of fire tubes at their inlet ends, and said conically-shaped baffle spaced radially inwardly from said frusto-conically-shaped member and extending downwardly from said upstream floor for only a portion of the axial length of said frusto-conically-shaped member.

3. A heat exchanger according to claim 2, in which the conical widening of said frusto-conically shaped member is such that with a hot gas pressure of between 1.6 and 1.8 atm.abs., there is produced a chamber loading which amounts to between 90 and 125 kg/sec./cu.m.

4. A heat exchanger, as set forth in claim 2, wherein the effective heat-emitting area of the upper face of said upstream floor is at least twice as large as its effective heat-absorbing area on the lower face of said upstream floor.

5. A heat exchanger according to claim 4, in which the upstream floor has said cup-shaped thickening on its side facing a supply pipe for the cooling medium.

6. A heat exchanger according to claim 4, in which a washing and drainage outlet is arranged between the upstream flow and the intermediate floor.

7. A heat exchanger according to claim 1, in which the fire tubes are formed at least partially at their downstream ends with double walls.

8. A heat exchanger according to claim 1, in which the fire tubes are formed with double walls over at most two-thirds of their length.

9. A heat exchanger according to claim 7, in which the annular space between inner wall and the outer wall of a fire tube is filled with air.

10. A heat exchanger according to claim 7, in which the inner wall of the double walled tube is connected by rolling or welding with the associated outer wall.

11. A heat exchanger according to claim 7, in which the inner wall reduces the free throughflow cross-section of the fire tubes by between 20 and 35 percent.

12. Gas cooling apparatus comprising several heat exchangers constructed substantially as described with reference to claim 1, the several heat exchangers being connected in parallel and/or in series.

13. Apparatus according to claim 12, in which there are at least two parallel-connected heat exchangers with a common heat exchanger connected thereafter.

14. Apparatus according to claim 12, in which, in the final heat exchanger, the fire tubes consist of several tubes of which two tubes form a double jacket through which cooling medium flows and/or two tubes form a thermally insulating jacket.

15. Apparatus according to claim 12, in which the heat exchangers are suspended in a manner enabling them to swing.

16. A plant comprising a furnace for producing hot gases and a number of pipes which lead the hot gases away from the furnace for cooling, each of such pipes being connected to a separate heat exchanger according to claim 1, or to a separate gas cooling apparatus according to claim 12.

17. A heat exchanger, as set forth in claim 7, wherein the outer wall of said double wall fire tube is sealed to said means for enclosing said fire tubes and said inner wall extends out of the cooling passageway, and a gas collector hood arranged to receive the end of said inner wall which extends outwardly from the cooling passageway.

18. A heat exchanger according to claim 17, in which the inner wall is slidingly arranged in a floor of the gas collector hood and a heat-proof seal is provided between the floor of the gas collector hood and the inner wall.