GB2115130A - Process and heat exchanger for the progressive cooling of a hot gas stream - Google Patents

Abstract

The casing 2 constructed e.g. as a reactor has an inner area 3, which is bounded by an inner jacket 6 which, whilst forming an intermediate area 7, is surrounded by an outer jacket, on which is arranged a heat exchanger for cooling fluid (eg water) with an inlet connection 12 and an outlet connection 13. The mixture e.g. of air and oil entering through mixing chambers 20 is ignited and an exothermic reaction takes place. The heat liberated during the reaction must be removed in controlled manner in order to ensure at outlet A a temperature which is within a relatively narrow temperature range. This is achieved by the series connection of two radiation processes, i.e. from reaction gas to the inner jacket 6 and from there to the outer wall 4. The temperature peaks occurring with different mixing ratios having only a limited influence on the temperature profile towards the reactor outlet and there is no need for external action, e.g. via a cooling system control. <IMAGE>

Description

SPECIFICATION Process and heat exchanger for the progressive cooling of a hot gas stream The invention relates to a process for the progressive cooling of a hot gas stream in a casing using a cooling medium provided art a boundary of the casing and to a casing equipped to perform such process.

Within the context of the present invention, the term casing is considered to cover lines and vessels, particularly reaction vessels, whose operation takes place under overpressure or underpressure and in which high temperatures occur.

For the purpose of dissipating heat from a casing, it is known to provide heat exchange devices in the casing wall, for instance jackets welded thereto as a function of the operating conditions in the casing.

Heating or cooling ducts welded to the casing wall, lines in the casing wall, and thin or diaphragm walls, are also known. If it is necessary to remove different quantities of heat and if it is necessary to maintain a given outlet temperature at the casing outlet, special measures have to be taken, and the cooling circuit control system must be constructed in such a way that it can be ensured that the temperature does not drop below the desired outlet temperature. This more particularly applies if the casing is used for performing reactions, and if the maintainance of the outlet temperature influences the quality of a product obtained.

If the casing is designed for performing exothermic reactions, large and varying quantities of heat are produced in the reaction zone requiring an intense cooling of said zone. In the case of known heat exchangers this cannot be ensured or can only be ensured by considerable expenditure and effort, so that other solutions have been sought. A direct cooling process is known, in which a cooling medium is introduced directly into the reaction zone.

This process is, for example, used in the production of carbon black by substoichoimetric combustion of hydrocarbons. The cooling medium used is water.

However, this process suffers from the disadvantage that the carbon black produced partly agglomerates to black grit, which must be ground in a further treatment operation to permit it to be used.

The aim of the invention is to provide a process and apparatus which enable better control of outlet temperature.

According to the present invention there is provided a process for cooling a hot gas stream passing through a casing, wherein a cooling medium to receive heat dissipated from the gas is provided at a boundary of the casing, and wherein a radiant surface arranged between the gas stream and the cooling medium is used to radiate heat from the gas stream towards the cooling medium.

The present invention also provides a casing to conduct and cool a hot gas stream including means to conduct a cooling medium to receive heat dissipated from the gas at a boundary of the casing, and a member having a radiant suface positioned so as, in use, to radiate heat from the gas stream towards the cooling medium.

The invention will be more clearly understood from the following description which is given by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic longitudinal section through a reactor for producing carbon black; and Figure 2 is a temperature gradient diagram for a reactor according to the invention for two different operating conditions.

Figure 1 diagrammatically shows a casing 2 constructed as a reactor 1. The casing 2 has an inner area 3 with a cross-section, which can for example be circular, rectagonal or polygonal. E and A desig nate the inlet and outlet sides of casing 2. The reactor shown in Figure 1 is used for producing carbon black from hydrocarbons with the aid of which the process according to the invention is explained. Casing 2 has an outer wall 4, on whose outside is arranged a heat exchanger 5 in the form of a jacket welded to said wall 4. However, the heat exchanger 5 can also be constructed in some other way, for example in the form of one of the previously described, known constructions.

The inner area 3 is peripherally bounded by an inner jacket 6, made of a heat-resistant material, e.g.

metal, which is spaced from the outer wall 4 and with the latter forms an annular intermediate area 7.

On the outlet side intermediate area 7 is separated by a seal 8 from inner area 3. Intermediate area 7 is also closed on the inlet side E by a cover plate 9, to which inner jacket 6 is fixed by means of a flange 10 and which extends up to the outer wall 4, which is connected by a flange 11 to the edge of cover plate 9.

A connecting piece 12 is provided on outlet side A and a further connecting piece 13 on inlet side E. The direction of the arrows indicate the cooling medium entry at connecting piece 12 and the cooling medium exit at connecting piece 13. Below and connected to outer wall 4 is a terminating cone 14, whose outlet port 15 is connected to further, not shown, means required for treating the carbon black produced.

On cover plate 9 are diagrammatically shown those parts of the reactor with which the oxygen carrier, usually air, and the hydrocarbons are introduced into the inner area 3. The oxygen carried is fed from an oxygen source 16, via a line 17 into a distributor 18 having on the casing side openings 19, through which the oxygen carrier is introduced into mixing chambers 20. In the latter the oxygen carrier is mixed with the hydrocarbons injected through a nozzle 21, which are supplied thereto by means of lines 23 from a diagrammatically represented stoage container 22 and the mixture is fed into inner area 3.

In the latter, the mixture is continuously ignited and there is a more or less powerful exothermic reaction.

The heat liberated during the reaction must be removed in controlled manner, in order to ensure an outlet temperature within a narrow temperature range and the successful mantainance of this temperature has a considerable influence on the product quality obtained. Thus, the gas outlet temperature must be largely independent of the quantity of heat released.

The heat transfer from the reaction gas and reaction product takes place by means of radiation to the inside of inner jacket 6. The temperature on the outside of inner jacket 6 is increased by heat conduction. Inner jacket 6 forms a radiant surface and by means of said radiation supplies the heat to outer wall 4. As the heat transfer increases by radiation with the fourth powerofthetemperature, very little importance is attached to convective and conductive heat transfer of the gas in the immediate area. The heat absorption taking place in outer wall 4 is taken up by a suitable cooling medium, e.g.

boiling water.

Figure 2 shows the action of the cooling process according to the invention comprising the series connection of two radiation processes, initially of the gas in inner area 3 to inner jacket 6 and from there to outer wall 7.

Figure 2 represents two reactions for producing two different carbon black qualities. The continuous lines show the temperature gradient in the gas over the length L of inner area 3, whilst the broken lines show the temperature of inner jacket 6 for the two operating cases and the dot-dash line the wall temperature of heat exchanger 5. In operating case I with the highest gas temperature of approximately 1900"C it is a question of producing a black quality in which the oxygen proportion is relatively high, whereas in the second operating case II with the much lower maximum gas temperature of approximately 1000"C it is a question of producing a black quality in which the oxygen proportion is relatively low.However, it is apparent from Figure 2 that the temperature gradient at the outlet A of the reactor is largely independent of the temperature peak reached at the reactor inlet E. On modifying the operating conditions in the production of different carbon black types by varying the oil/air ratio widely varying temperature peaks are obtained, but have only a limited influence on the temperature profile towards reactor outlet A, so that no action has to be taken from the outside, i.e. via the cooling system control. Thus, the desired reaction conditions towards the reactor outlet A are obtained largely independently of what happens at the reactor inlet E without any external action being required.

Thus, the cooling process described has the advantage that the temperature peaks occurring during the reaction rapidly drop to a relatively low temperature when, compared with the high reaction temperature, further cooling only takes place slowly.

Due to this selective heat dissipation, the quantity of heat liberated during the reaction and dependent on the specific reaction heat and the through quantity only has a very limited influence on the outlet temperature of the reaction gases. In addition, the temperature of the cooling medium and outer wall 4 has virtually no influence on the temperature gradient in the reaction gas. Thus, the choice of the cooling medium can be adapted to other requirements, e.g. for a particularly appropriate further use of the heat.

Claims (13)

1. A process for cooling a hot gas stream passing through a casing, wherein a cooling medium to receive heat dissipated from the gas is provided at a boundary of the casing, and wherein a radiant surface arranged between the gas stream and the cooling medium is used to radiate heat from the gas stream towards the cooling medium.

2. A process according to claim 1, wherein the radiant surface is arranged adjacent the casing wall.

3. A process according to claim 1 or 2, wherein the radiant surface is one surface of a member of which the other surface is in contact with the hot gas stream.

4. A casing to conduct and cool a hot gas stream including means to conduct a cooling medium to receive heat dissipated from the gas at a boundary of the casing, and a member having a radiant surface positioned so as, in use, to radiate heat from the gas stream towards the cooling medium.

5. A casing according to claim 4, wherein the radiant surface is arranged adjacent the casing wall.

6. A casing according to claim 4 or 5, wherein the other surface of the member from the radiant surface is, in use, in contact with the hot gas stream.

7. A casing according to any one of claims 4 to 6, wherein the means to conduct cooling medium are at the outer wall of the casing and the member is inwards of said outer wall.

8. A casing according to claim 7, wherein the intermediate area between the outer wall and the member is sealed both with respect to the interior of casing and with respect to the atmosphere.

9. A casing according to any one of claims 4 to 8, wherein the heat exchanger is integrated into the boundary wall of the casing in the form of a thin or diaphragm wall.

10. A casing according to any one of claims 4 to 9, wherein the member is made from a heat-resistant metal.

11. A casing according to any one of claims 4 to 10 including means to supply media for elevated temperature reactions.

12. A process for cooling a hot gas stream substantially as hereinbefore described with reference to the accompanying drawings.

13. A casing to conduct and cool a hot gas stream constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.