JPH0754235B2 - Indirect heat exchange method and device between flowing particles and heat exchange fluid - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention broadly relates to a method and a heat exchanger for heating or cooling fluidized particles, and more specifically, the present invention heats or cools thermal particles by indirect heat exchange. The present invention relates to a method and a novel heat exchanger used therein.

[Background of the Invention]

It is well known to heat or cool fluidized granular materials or fine materials by indirectly contacting them with a heating or cooling fluid. This type of heat exchanger keeps the particulate material in a fluidized state by means of a flowing medium which passes upwards through the bed of granular material. tube,
A piping system such as channels or coils is arranged in the fluidized bed. The fluid adds or removes heat from this flowing solid through indirect heat exchange through the pipe. Fluidized solids are fed to the fluidized bed and continuously removed from the bed. The method of supplying or removing the fluidized solids to the bed by an exchanger is
ow through) and reverse mixing heat exchanger are included. There are two basic types of flow subcoolers. One is a gravity feed type in which particles enter through the upper inlet and exit through the lower outlet.
The other is a fluid transfer type in which particles are moved from a lower inlet through a cooling pipe to an upper outlet. In the back mixing operation, the particles circulate through conventional inlets and outlets which allow the particles to be exchanged through the rest of the process unit.

Heat exchangers for the indirect heating or cooling of fluidized particulate materials have found widespread use in numerous industrial processes. These processes include mineral processing, metal ore processing, petrochemical manufacturing, hydrocarbon conversion and the like. Many exchanger structures have been developed to meet the needs of these different processes.

Indirect heat exchangers of the type described above have been used extensively as particle coolers for regenerators in fluidized catalytic conversion processes for hydrocarbons. The fluidized catalytic cracking process (FCC) is widely used to convert hydrocarbon streams such as vacuum gas oil and other relatively heavy oils to light, valuable products. In the FCC process, the feedstock hydrocarbons come into contact with the finely divided catalyst which is fluidized by gas or steam. As this particulate material catalytically acts on the cracking reaction, cracking reaction by-products called coke are deposited on the catalyst surface. FC
The regenerator, an integral part of the C process, removes coke from the catalyst surface by oxidation. A large amount of heat is released during the oxidation of coke. Part of the heat is the heat input required for the decomposition reaction. Since FCC units are used to process relatively heavy feedstocks, large amounts of coke must be removed during the regeneration zone as the amount of heat generated increases. This added heat poses many problems for the FCC process. This excess heat upsets the heat balance of the process, thereby reducing the circulation of hot catalyst from the regenerator to the reactor and, as a result, reducing the yield of valuable product. In addition, excess heat can raise the temperature to the point of damaging the equipment and catalyst particles. Therefore, it would be advantageous to have a means of reducing the temperature of the regenerator. Due to temperature control and process flexibility, heat exchangers with cooling tubes outside the regenerator were the method of choice.

An important consideration in the FCC process is the transfer of particulate material, as with other processes that handle particulate material. It is often difficult to include a heat exchanger of the required size to provide the desired degree of particle heat transfer within the constraints of the process arrangement. These constraints mainly provide an exchanger of sufficient length to fit the required surface area of the exchanger tubing and the inlet and outlet for the movement of particles between this exchanger and the rest of the process unit. Is to provide. FCC
In the case of a process unit, with a particle heat exchanger,
In order to meet the design requirements of the exchanger, it may be necessary to either increase the overall structure or add extra piping or fluidizers. Such an increase in height when attaching the particle heat exchanger to the newly designed FCC unit, the addition of piping and a fluidizing device, and the like increase cost and complicate the unit structure. It is also usual to retrofit the existing FCC process unit with a granular heat exchanger. In these cases, structural restraints not only add to the cost of the unit, but they also make it impossible to introduce a particle exchanger with the desired heat transfer capacity.

Using a back-mixing exchanger as described above, one inlet /
Introducing a particle heat exchanger into any process is simple as it only requires outlet piping. However, the total heat exchange capacity of this type of equipment is limited by the circulation rate of the catalyst which cannot be obtained beyond the vertical length of the equipment. Moreover, the total heat transfer per length of cooling tube that can be used in a backmixing cooler is lower than in a flow-through type exchanger where the catalyst flows from the inlet at one end of the heat exchanger to the outlet at the other end. In the end, the additional layout constraint of the back-mixing cooler requires piping with very large inlet / outlet to allow sufficient circulation of fluidized particles between the heat exchanger and the area where particles are removed and recovered. And Therefore, back-mixing type exchangers cannot solve many layout problems caused by putting remote particle heat exchangers into processes that require heating or cooling of particulate material.

The problem of indirect heat exchange of fluidized particles has been described in many prior art documents. The following discussion deals with this issue.

Lomas et al., U.S. Pat. No. 4,439,533, shows a back-mixed particle heat exchanger that exchanges FCC catalyst between a heat exchanger and a retention zone for catalyst particles in the regenerator. Here, the FCC process uses a back-mixed catalyst cooler.

Lomas et al., U.S. Pat. No. 4,434,245, uses a particle heat exchanger in an FCC process having a catalyst free zone and a separate combustion zone. The hot catalyst particles are removed from the free zone and transferred downward through the cooler, with indirect heat exchange with the cooling fluid, and then removed from the bottom of the heat exchanger to raise the catalyst to transfer to the combustion zone. Reach the lift riser.

This is an FC with a combustion zone below and a catalyst retention zone above.
A particle heat exchanger is used in the C process.

In U.S. Pat.No. 4,396,531, the thermal catalyst from the FCC regenerator retention zone feeds the granular catalyst to a heat exchanger that cools the granular catalyst by indirect contact with water and transfers the cooled catalyst to the FCC reactor. . This reference shows the removal of cooled particulate material from the FCC regeneration zone.

U.S. Pat. No. 4,238,631 to Daviduk et al. Has a thermal catalyst inlet in the center of the heat exchanger, also at the bottom, a catalyst outlet for returning the catalyst to the regenerator, and also at the top discharges gas from the heat exchanger to the regenerator. 2 shows a heat exchanger for cooling the granular catalyst from the FCC regenerator with piping for.

The operation of the exchanger is also simplified by such a design, as it can be varied by adjusting the amount of fluid gas or vapor entering the backmixing section. The rate of heat removal from the backmixing section can be increased to a maximum or reduced to zero by varying the amount of fluid gas used from a maximum to essentially no amount.

The object of the present invention is to increase the heat transfer capacity of a particle heat exchanger.

Yet another object of the present invention is to provide a method for cooling particles and a particle heat exchanger having improved heat transfer capability and flexibility.

Another object of the present invention is to provide a particle heat exchanger that can be easily adapted to the apparatus and structure for supplying particles.

Yet another object of the present invention is to provide a method of regulating heat transfer in indirect heat exchange of particles by a heat exchange fluid. Accordingly, one embodiment of the present invention is a method of heating or cooling particles. The method involves collecting relatively hot or cold particles, transferring them from a particle inlet to a heat exchange zone, and then recovering relatively hot or cold particles from the heat exchange zone through a particle outlet. Heating or removing heat in the heat exchange zone by indirect heat exchange with the heat transfer fluid in the first part where particles flow from the inlet to the outlet and the second part below the inlet and outlet where all particles do not flow To do. The fluid gas is introduced into the heat removal zone to heat at least a portion of the fluidizing medium that enters the heat removal zone.

A further embodiment of the present invention is a method of cooling a hot fluidized catalyst.
This method oxidizes the coke contained in the catalyst by passing the coke-deposited catalyst particles through the combustion zone and contacting the catalyst with an oxygen-containing gas, removing the thermal catalyst from the regeneration zone and then catalytically reacting the thermal catalyst. It consists of passing through a remote heat removal zone from the inlet. Relatively cold catalyst particles are recovered from the heat removal zone through the catalyst outlet. Heat is removed from the catalyst by indirect heat exchange with the cooling fluid in the upper portion of the heat removal zone and in the lower portion of the heat removal zone. There is a total catalytic particle flow in the upper part of the heat removal zone, while there is no total catalyst particle flow in the lower part of the heat removal zone. The catalyst in the heat removal zone is fluidized by the passage of the fluid gas.

Still further embodiments of the present invention relate to heating or cooling devices for fluidized particles. The apparatus includes a vertically extending heat exchanger for indirectly contacting fluidized particles with a heat transfer fluid, upper and lower heat removal portions, a plurality of heat exchange tubes each having a substantial surface area at each of said portions, and A combination of a particle inlet and a particle outlet located at opposite ends of the upper heat removal zone for loading and unloading particles in the exchanger.

Other embodiments, descriptions and arrangements of the invention are described in the detailed description below.

[Detailed Description of the Invention]

The method of the present invention comprises the steps of indirectly heating or cooling a fluidized particulate solid. Although the method and apparatus of the present invention can be used to either heat or cool the particles, for simplicity only cooling of the particles will be mentioned. A major use of the present invention involves introducing oxygen-containing combustion gas and fluidized solid particles into a combustion zone maintained at a temperature sufficient to oxidize the combustible material from the fluidized solid particle-containing combustible material. The method of burning combustible materials is.

The combustion zone may be in a dilute phase or in a rich phase with hot particles transferred to a disengaging zone where hot particles are collected and maintained as a bed as described above. , Also the first floor itself.

A particular important embodiment of the present invention is the process of performing regenerative combustion within the regeneration zone of the coke-containing FCC catalyst from the reaction zone producing hot flue gas and heat regeneration catalyst, heat regeneration catalyst release.
ngagement) and collection step, cooling of the heat-regenerated catalyst in a heat removal zone comprising the heat exchanger of the invention, i.
And a step of returning the cooled regenerated catalyst for controlling the temperature of the catalyst in the regeneration zone. As used in the FCC process, "heat regenerated catalyst" is the temperature at which the combustion zone leaves the combustion chamber [about 1300-14
00 ° C (704-760 ° C)] means a regenerated catalyst, and "cold regenerated catalyst" means the temperature when leaving the cooling zone (lower than the temperature of the heat regenerated catalyst, up to 200 ° F (110 ° C). Temperature].

Hereinafter, the particle heat exchanger and the method of the present invention will be described with reference to FIG. In FIG. 1, regeneration gas (which may be air or other oxygen containing gas) enters combustion zone 10 through line 11 and is distributed by dome shaped distribution grid 12. Air leaving the grid mixes with coke added catalyst particles which enter the combustion zone through line 13. Although these streams are shown to flow separately in combustion zone 10, each stream can be run together in the mixing piping prior to entering combustion zone 10. Coke addition catalysts typically contain about 0.1-0.5 wt% carbon as coke. Coke consists mainly of carbon, but about 5 to about
It may contain materials such as 15 wt% hydrogen and sulfur. The regeneration gas and the catalyst carried therein flow upward from the bottom of the combustion zone 10 to the top of the lean phase. As used herein, "dilute phase" means a mixture of catalyst particles and a gas having a density of less than 30bs / ft ³ (480kg / m ³ ), and "rich phase" means such 30bs / ft ³ It means a mixture of (480 kg / m ³ ) or more. Dilute phase conditions, ie less than ³⁰ bs / ft ³ (480 kg / m ³ ), typically 2-10 bs / ft ³ (32-160 kg / m ³ ) are most effective for coke oxidation. As the catalyst / gas mixture rises in the combustion zone 10, the heat of combustion of the coke is liberated and is now absorbed by the relatively carbon-free catalyst, in other words the regenerated catalyst.

The ascending catalyst / gas stream flows through the ascending line 14 and strikes the top of the lateral line 15. This collision diverts the flow direction and directs the catalyst / gas mixture towards the outlet 16. The impingement of the catalyst / gas stream in the side pipe 15 and the change of direction to the outlet 16 causes the majority of the heat-regenerated catalyst from the combustion zone to be released from the flue gas, leaving the free zone with the hot or fluid particle collection chamber. Drop it to the bottom. Zone 20 is a free zone, but the term also includes the possibility of additional regeneration or combustion in this zone.
The free zone catalyst collection region may be an annular vessel as shown, or any shape suitable for collecting catalyst particles. The catalyst at the bottom of the collection zone is retained as a dense phase 26 with an upper level 27. Gaseous products of coke oxidation and excess regenerated gas, ie flue gas and uncollected portion of thermally regenerated catalyst particles, rise in the free zone 20 to the cyclone.
An inlet 22 enters a catalyst / gas separator such as 21. The catalyst particles separated from the flue gas fall from the cyclone through immersion legs 23 and 24 to the bottom of free zone 20. This flue gas exits the free zone 20 through line 25. An energy recovery system may be connected to the pipe 25.

Thermal catalyst particles are removed from the free zone and either transferred to the FCC reactor via line 44 or returned to the combustion zone via line 46.
Valve 48 regulates the flow of catalyst through line 46. The catalyst particles are returned to the combustion zone and continue in the conventional path through the cooling zone.

Still referring to FIG. 1, the cooling zone has a catalyst in the shell side and a heat exchanger 30 fed and withdrawn by lines 32 and 33 and having a heat exchange medium through the tube bundle 31 and extending vertically. It is composed of. The preferred heat exchange medium is water, which more preferably only partially changes from liquid to gas phase (vapor) as it passes through the tube. The heat exchanger is also preferably operated so that the exchange medium circulates through the tube at a constant rate. The tube bundle in the heat exchanger is preferably of the "plug-in tube" type, which is not fixed at one end, which reduces the problems due to tube expansion and contraction when exposed to the high temperatures of the regenerated catalyst and released. The heat transfer reaches the heat transfer medium from the catalyst through the tube wall. The upper part of the heat exchanger 30 has a piping part 34 and a dense floor 26.
It is in sealed communication with the bottom of the free zone via an inlet 35 which serves as a removal point for removing catalyst from the. The cooled catalyst is removed from the central portion of exchanger 30 and returned to combustion zone 10.
The catalyst is withdrawn from the outlet 37 in the central part (1/3 of the exchanger) and is sent to line 38 with a flow control valve 39.
Valve 39 regulates the flow of catalyst particles in pipe 38. The part connected at the inlet 35 and the outlet 37 of the heat exchanger is called the flow-through part or the first part and operates the entire catalyst flow through this part. The portion of the exchanger below outlet 37 is referred to as the backmixing portion or second portion. The lower part or back-mixing part of the exchanger accounts for at least 10% of the heat removal capacity of the exchanger, and preferably has a heat removal capacity equal to at least 25% of the total heat removal capacity of the exchanger.

A fluid gas, preferably air, is passed through lines 36 and 40 to the bottom of the outer wall of the exchanger, thereby maintaining the fluidized bed in the outer wall in a rich phase. Lines 36 and 40 are respectively valves 36 'and 4 arranged transversely to regulate the flow of the fluent gas.
Has 0 '. The fluent gas undergoes turbulent backmixing in the backmixing portion of the heat exchanger to transfer catalyst particles through the flowthrough portion of the exchanger. In this case, it is only necessary to add fluid gas to the exchanger from the lower fluid gas line 36. When the fluid gas flows upwards, it performs the necessary backmixing for heat transfer in the backmixing part of the heat exchanger, and when it enters the flow-through part of the heat exchanger of the heat exchanger, the gas forms catalyst particles. Fluidization for the transfer of Heat removal, or in other words heat exchanger duty, can also be controlled by adjusting the flow rate of the additive gas through line 36. Higher flow velocity improves heat transfer,
Also, the exchanger duty increases. It is only necessary to add fluent gas to the bottom of the heat exchanger, but fluent gas can be added at any of a number of locations. First
Addition of the flowable gas at the position shown in the figure allows unique control of the exchanger duty in the back mixing section. A minimum amount of fluid gas is required to maintain good transfer of catalyst in the flow through part of this cooler. Line 40 is used to heat all or part of this minimum amount of flue gas when heat removal requirements require little or no duty from the backmixing section of the exchanger. This makes the line
It is possible to adjust the flow of flue gas through 36 to zero, but if necessary, a minimum amount of flue gas equal to less than 5% of the total is added from the bottom nozzle during operation of the exchanger.

The tube bundle shown in the exchanger is of the plug-in type, in which all of the tubes are fixed in a single tube sheet located at the bottom of the heat exchanger. The typical construction of the plug-in tube bundle is such that each inlet tube rises from the inlet manhold 42 of the exchanger head through a relatively long outer tube having a sealed top and into the outer shell. Each inlet tube extends into the outer tube and is just below the sealed end of the outer tube. A liquid, such as water, is directed upward into the inlet tube and into the outer tube, which removes heat from the thermal catalyst that passes through the wall of the outer tube as it passes downward into the annular space formed between the inlet and outlet tubes. Is absorbed and then at least partially evaporated and discharged from the outlet manifold 43 of the heat exchanger. In the FCC process, it is important that the heat particles entering heat exchanger 30 be sufficient to maintain a depth of the dense phase fluidized catalyst bed that substantially submerges the tube in the dense phase bed. Sinking the tube can prevent it from overheating when the cooling fluid circulation is temporarily interrupted. If the tubing is made of carbon steel or other low temperature metallurgy, there will be heating problems.

The flow through portion of the exchanger is used to transfer cooled catalyst particles from the exchanger to the combustion zone. The cooled catalyst entering the combustion zone reduces the temperature of the combustion zone and the free zone as a whole. Flow-through operation is characterized by high heat transfer rates with high degree of catalyst cooling.

In addition, the backmixing portion of the exchanger reduces the temperature of the catalyst once it has passed through the flow-through portion. It is known that backmixing is obtained in the heat exchanger at a reasonable surface gas velocity that circulates the catalyst down the length of the backmixing section. The addition of the fluid gas directly affects the surface velocity on the heat exchanger tubes and indirectly affects the degree of mass flow of the catalyst through the backmixing portion of the heat exchanger, thereby increasing the heat transfer coefficient. Affect. Also, the higher the mass flow, the higher the heat exchanger duty. This is probably because the average temperature of the catalyst in the back-mixing portion is high, and thus the amount of heat transfer gives a large temperature difference in direct proportion. Details regarding the operation of the backmixing cooling zone can be found in US Pat. No. 4,439,533.

Using the back-mixing section below and the flow-through section above,
It simplifies the design of the heat exchanger and allows it to be held at long lengths not available in stand-alone heat exchangers.
With a flow-through heat exchanger with gravity feed of particles, the length of the exchanger is limited by the height between the catalyst removal point 35 and the outlet 37. Although the total height is sufficient to use the back-mixing type cooler of the length shown in FIG. 1, when the catalyst is back-mixed and circulated over such a long length, an excessive amount of fluidizing gas is required. , The overall heat transfer performance will be low.

FIG. 2 shows an example in which different types of FCC regenerators are combined with the particle heat exchanger of the present invention. The regenerator has one room in container 50. Spent catalyst containing 0.1-5 wt% coke enters the regenerator via line 52. Lower tubing 54 distributor 56 directs air to a regenerator that is distributed across the cross section of vessel 50. The air passing through the catalyst oxidizes the coke on the surface of the catalyst, maintaining it as a dense fluidized bed 57 with level 58. The regenerated gas and the catalyst carried in it all flow upwards into the cyclone via inlet 62. The cyclone dip leg 64 returns the catalyst particles to the bed 57. Nozzle 66
Carries the regenerated gas from the cyclone 60 to the container 50. The regenerated catalyst having a reduced coke concentration exists in the lower portion of the container 50, and enters the reaction zone again through the pipe 68 (not shown).

The heat exchanger 70 is in communication with the catalyst bed 57 via a pipe 72.
The heat exchanger 70 operates much the same as the exchanger 30 shown in FIG. 1, but differs primarily in the plug-in tube and means and method for returning the catalyst to the regenerator. The exchanger 70 has a plurality of plug-in tubes consisting of an inner tube that receives the heat exchange medium at the inlet manifold 74 and an outer sealed end tube that returns the heat exchange medium to the outlet manifold 76. line
Reference numerals 78 and 78 'supply and remove the heat exchange medium to and from the cooler 70. An outlet 80 located in the center of the exchanger carries the cooled catalyst particles out of the exchanger and divides it into an upper part operating in flow-through mode and a lower part operating in backmixing mode. The fluidizing gas may enter the exchanger through either or both of two fluid gas inlets 82 and 84 located beneath and at the bottom of the exchanger outlet 80, respectively. The pipe 86 takes in the cooled catalyst from the outlet 80 at a rate adjusted by the control valve 88. The cooling catalyst flows from the pipe 86 to the outer rising pipe 90. Line 92 introduces fluidizing gas into riser tube 90 which contacts the relatively cold catalyst and returns it to enriched bed 57.

The heat exchanger of the present invention is particularly useful in an FCC arrangement such as that shown in FIG. In these arrangements, the horizontal portion of line 92 is very close to ground level. Therefore, the length of the flow-through type cooler cannot be increased unless the entire regeneration container 50 is raised. The present invention increases the length of the cooler and the corresponding heat transfer area without increasing the height of the entire vessel by utilizing the space under the outlet and the area of the exchanger which are each unused. Is. The arrangement of inlet and outlet manifolds on the cooler top allows the tube bundle to be lifted from the exchanger top, thus facilitating tube bundle removal.

The examples below illustrate the advantages of using the exchanger of the present invention to reduce the temperature of the catalyst entering the reaction zone when treating medium heavy FCC feedstocks. These examples are based in part on engineering calculations and industrial experience with similar operating units. The raw material in this example is a blend of vacuum gas oil and residual oil having the properties shown in Table 1.

Table 1 Density kg / m ³ 0.87 (26.2 ° API) Sulfur yellow Wt.% 1.2 Conradson carbon Wt.% 1.74 Nickel Wt.-ppm 1 Vanadium Wt.-ppm 2 Vol% [1050 ° F (566 ° C)] 10 Practical example In this example, the FCC raw material is the FCC with riser under the processing conditions shown in Table
Processed in FCC reaction-regenerator with reaction zone. In addition, here, the particle heat exchanger designed according to the method of the present invention is
It was used as an FCC unit with the structure shown. The exchanger has a back mixing surface area of 975 ft ² (90.6 m ² ) and a flow-through area of 975 ft ¹² (90.6 m ² ). The fluidizing gas was added only at the bottom of the exchanger at a rate of 166,000 standard ft ³ / kr (4691m ³ / kr). Table 2 shows the addition yield of the raw materials and the conditions at predetermined positions of this unit.

The FCC embodiments described in the above figures and examples are only one of the most possible uses of the method of the invention in the widest sense for heating or cooling fluidized particles for any purpose. The device of the present invention in the broadest sense can also be confirmed in the drawings as described above.

[Brief description of drawings]

FIG. 1 is a front view of an FCC regenerator having a particle heat exchanger of the present invention, and FIG. 2 is another view having a modified heat exchanger of the present invention.
It is a front view of an FCC regenerator. 10 ...... Combustion zone, 2 ...... Free zone 21 ...... Cyclone, 30 ...... Heat exchanger (or cooler) 35 …… Inlet, 37 …… Outlet 50 …… Regeneration vessel, 60 …… Cyclone 70 …… Heat Exchanger (or cooler), 80 ... outlet

Claims (6)

[Claims] 1. A) collecting hot particles in a particle collection zone [20] at a first height, and b) gravitationally flowing the particles from the particle collection zone [20] to a second height lower than the first height. Heat exchange zone located at a high place [30]
Flow through the heat exchange zone [30], and at least part of the particles in the heat exchange zone [30] are flowed by introducing a flowing gas [40, 36] into the heat exchange zone [30]. D) removing heat from the particles in the heat exchange zone by indirect heat exchange with a heat transfer fluid [32], and e) recovering relatively cold particles from the heat exchange zone through an outlet [37], When transferring the particles to the first elevation, the outlet [37] is located in the exchange zone [30], whereby the heat exchange zone is between the inlet [35] and the outlet [37]. And a second portion located below the outlet [37] and having a heat removal capacity of at least 25% of the total heat removal capacity of the heat exchange zone, and Through the first part of the outlet [37] from the inlet [35] and there is no net flow of particles in the second part Performing an indirect heat exchange method between a fluidized particle and a heat exchange fluid. 2. The method of claim 1 wherein hot particles enter the top of said first portion and exit from the bottom of said first portion. 3. The hot particles pass through the bottom of the first portion,
Particles are transported upward through the first portion and returned from above the first portion to the collection zone.
the method of. 4. A vertically extending heat exchanger [30] for indirectly contacting the fluidized particles and the cooling fluid, b) a plurality of heat exchange tubes [31], and c) hot particles. And a particle outlet [35] and a particle outlet [37] for removing cooling particles from the heat exchanger.
D) having means [36] for admitting a fluid gas into the bottom of the heat exchanger [30], the outlet [37] being located at 1/3 of the heat exchanger [30] For cooling the fluidized particles, whereby the heat exchanger comprises a first part between the inlet [35] and the outlet [37] and a second part below the outlet [37]. Heat exchange device for fluid catalytic cracking equipped with a device. 5. Apparatus according to claim 4, characterized in that it comprises means (40) for feeding a flowing gas into the bottom of the first part. 6. Apparatus according to claim 4 or 5, characterized in that the inlet (35) is located at the top of the first part and the outlet (37) is located at the bottom of the first part.