EP0222433A1 - Process to obtain high-temperature reactions - Google Patents

Abstract

1. Process for carrying out high-temperature reactions between hot gas and previously heated solids, which during the high-temperature treatment lose their ability to flow freely, in a substantially vertical conveyor passage with subsequent cooling and separation from gas, characterized in that the heated solids are supplied from below and in the direction of conveyance trough a burner flame located in the lower region of the conveyor passage (17), they are caused to pass through a sufficiently long reaction zone and after the reaction has been completed they are coded to at least the temperature at which the ability to flow freely is achieved with an unchanged direction of flow by the separate addition of cooling agent downstream in the direction of flow.

Description

The invention relates to a method for carrying out high-temperature reactions between hot gas and previously heated solids, which lose their free-flowing properties in the high-temperature treatment, in a substantially vertical conveying path with subsequent cooling and separation from the gas.

In high-temperature reactions, solids are heated to temperatures above the temperature at which these solids lose their free-flowing or flowing properties. The individual particles tend to stick together, adhere to one another and / or form deposits on the inner wall of the reactor or in pipelines. The causes of the loss of flow or flowability can be the reaction processes of the solids with the gas phase or with other types of constituents. The problems mentioned above can occur when burning or sintering e.g. Alumina, lime, dolomite, magnesite and raw cement flour occur.

Numerous methods and devices are known with the aim of solving the process-related difficulties.

For example, the method according to DE-AS 23 50 768 provides, inter alia, for the material preheated in a first zone into a to heat the second zone to a final temperature by passing a flame, an air stream surrounding the flame being introduced into the second zone, which is intended to protect the wall of the flame space from formation of deposits. This measure has the disadvantage, in particular, that the unavoidable mixture of the air flow introduced into the second zone and the gas / solid suspension initially heated to sufficiently high temperatures result in cooling before the high-temperature reaction is complete. This means that there is no guarantee that the residence time required for the reaction will actually be available at the high temperature.

In the method and device for the heat treatment of fine-grained material according to DE-PS 28 46 584 with preheating zone, calcining zone, sintering zone designed as a suspension reaction zone and cooling zone, at least part of the largely calcined material is subjected to a separate heat treatment to evaporate the melt-phase-forming components before entering the sintering zone. This prior art is of course only applicable to those cases in which the free-flowing properties can be obtained by volatilizing components which form the melt phase. In other cases, this does not prevent the formation of deposits during sintering in the suspension reaction zone as a result of deflection of the gas / solid suspension. An additional reaction zone is also disadvantageous.

The object of the invention is to provide a method for carrying out high-temperature reactions between hot gas and previously heated solids, which does not have the known, in particular the aforementioned disadvantages, allows a faultless procedure and moreover can be used universally and is easy to carry out.

The object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the heated solids are introduced from below and in the conveying direction through a burner flame located in the lower region of the conveying path 17, and are passed through a sufficiently long reaction zone and after completion the reaction with unchanged flow direction cools at least to the temperature at which flowability is achieved by separate addition of coolant downstream in the flow direction.

Through the entry of the solid from below and in the direction of conveyance as well as through the subsequent separate addition of coolant with the flow direction unchanged, the gas / solid suspension goes through the critical reaction phase between heating to high temperature and cooling to a temperature which makes the gas / solid suspension easy to handle allowed, without redirection and thus without the possibility of forming an approach. The subsequent separate addition of coolant allows the dwell time at the required high temperature, which meets the respective requirements, to be set precisely.

The average gas velocity to be set in the conveyor section is to be dimensioned such that high relative velocities occur between the solid and the wall. The average gas velocity is usually in the range of 2 and 10 m / sec (indicated as empty tube velocity).

The entry of the preheated solid into the conveyor The route is expediently carried out in the form of a gas / solid suspension through the center of an annular burner which is operated, for example, with gas as the fuel. This type of solids supply ensures practically instantaneous heating to the desired temperature. Depending on the feed material and the desired result, it is approximately in the range from 1,300 to 1,700 ° C, preferably between 1,400 and 1,500 ° C.

The length of the conveyor line is measured according to the required dwell time depending on the reaction type. As a rule, a few seconds are sufficient, so that the length of the conveyor line is max. 20 m, generally 5 to 15 m, should be.

The cooling required after the high-temperature reaction has ended can be carried out using gaseous, liquid or solid coolants. Your entry should be done in such a way that a rapid intermingling with the gas / solid suspension takes place and contact with the wall of the conveyor line is avoided. An entry in the tangential direction at high speed perpendicular to or at an angle up to 60 ° against or with the flow direction is particularly expedient.

After cooling below the critical temperature, the gas / solid separation takes place in a conventional manner, e.g. in a cyclone separator.

The solids to be subjected to the high-temperature reaction can be heated in any desired manner. The heating, which is generally also associated with a chemical reaction, takes place particularly advantageously in a so-called circulating fluidized bed. The circulating fluidized bed is characterized in that - in contrast to the "classic" fluidized bed, in which a dense phase is separated from the gas space above it by a clear density jump - there are distribution states without a defined boundary layer. A leap in density between the dense phase and the dust space above it does not exist, but the solids concentration within the reactor decreases continuously from bottom to top. For details on the operation of circulating fluidized beds, L. Reh et al describes "fluidized bed processes for the chemical and metallurgical industry, energy conversion and environmental protection", Chem. Ing. Techn. 55 (1983), No. 2, pages 87-93 and DE -PS 17 67 628 or the US-PS 3 579 616 referenced.

The advantage of the circulating fluidized bed lies in the high throughput per reactor area and in the possibility of being able to set the residence time of the solid to be heated so high that the chemical reaction associated with the heating is practically complete. Only the actual high-temperature reaction then has to be carried out within the process according to the invention, i.e. there are practically no reactions that can also be carried out at a lower temperature level.

After separation of the solids emerging from the conveyor line, further cooling is usually carried out. Conventional coolers, but in particular fluidized bed coolers, can serve this purpose.

A preferred embodiment of the invention consists in integrating the high-temperature treatment according to the invention into the overall process with solid heating and final cooling in such a way that the individual gas streams can be used mutually. For example, oxygen-containing gas can be preheated in the cooler, which is then entered in the heating and / or high-temperature treatment stage. Furthermore, the exhaust gas from the conveyor line can be entered in the heating zone.

An optimal management of the overall process consists in heating the feed material in a circulating fluidized bed, which in turn has preheaters operated with the exhaust gases, and the final cooling in a fluidized bed cooler with several cooling chambers flowing through one after the other. The solid can be cooled directly and / or indirectly with oxygen-containing gases which are then fed to the conveying section as conveying gas and / or the circulating fluidized bed as fluidizing gas. The fluidizing gases used in the fluidized bed cooler can finally serve as a cooling medium for the conveying section, and the exhaust gases of the conveying section of the circulating fluidized bed can serve as secondary gas.

The invention is explained in more detail and, for example, using the figure and the example.

The figure shows a flow diagram of a composite circuit of the aforementioned type.

The material to be treated is fed to a last Venturi exchanger 2 on the gas side via a metering device 1, heated by the sensible heat of the exhaust gas and separated from the gas in the cyclone separator 3. A conveying device 4 then leads to a further preheating system, which consists of a Venturi exchanger 5 with an associated cyclone separator 6 and a Venturi exchanger 7 Cyclone separator 8 exists. By means of a bypass line 9, conveyed solid can be fed directly to the venturi exchanger 7 bypassing a preheating stage.

From the cyclone separator 8, the solid is introduced into a circulation system consisting of a fluidized bed reactor 10, return cyclone 11 and return line 12. The fluidized bed reactor 10 is supplied via line 13 with fuel, via line 14 with fluidizing gas and via line 15 with secondary gas.

After a sufficiently long dwell time, the heated material passes via line 16 to the lower region of the conveyor section 17 and is introduced from below into the burner flame generated from fuel (line 18) and oxygen-containing gas (line 19). During the upward movement of the gas / solids suspension in the lower part of the conveyor section 17, the high-temperature reaction takes place, after which it is cooled by gases supplied via line 20. After sufficient cooling with the flow direction unchanged, the gas / solid suspension is discharged via line 21 and separated in the cyclone separator 22. The solid enters the fluidized bed cooler 23, the gas via line 15 as secondary gas into the fluidized bed reactor 10.

The fluidized bed cooler 23 is divided into a plurality of cooling chambers through which the solid flows successively and has a total of three cooling sections. In the first hottest section - seen in the solids flow - oxygen-containing gas is heated, which is then fed via line 19 to the conveyor section 17. In the second section, the heating of the oxygen bed to be fed to the fluidized bed reactor 10 via line 14 is carried out term gas. In the third cooling section, the final cooling of the solid takes place by means of cooling water, which is supplied or discharged via lines 24 and 25. The cooled product is discharged via device 26. The fluidizing gas streams used in the fluidized bed cooler 23 are collected and fed via line 20 to the conveyor path 17 as a cooling medium.

Example:

Filter-moist aluminum hydroxide is to be converted into high-fired aluminum oxide.

Aluminum hydroxide with a moisture content of 12% by weight and a temperature of 60 ° C is fed in an amount of 8.69 t / h via the metering device 1 to the Venturi exchanger 2. By exchanging heat with the gases from the cyclone separator 6 brought to 390 ° C., the aluminum hydroxide is heated to 160 ° C. and the gas is cooled to approximately the same temperature.

The preheated aluminum hydroxide in the Venturi exchanger 5 is brought into contact with the 510 ° C. hot exhaust gases of the cyclone separator 8 by means of the conveying device 4. This heats up the solid or cools the gas to approx. 390 ° C. After gas / solid separation in the cyclone separator 6, the solid enters the Venturi exchanger 7, which is charged with the exhaust gases of 1,150 ° C. from the circulating fluidized bed. The intimate mixing results in a gas / solid suspension with a temperature of 510 ° C. After another gas / solid separation in the cyclone separator 8, the solid gets into the circulating fluidized bed.

The fluidized bed reactor 10 of the circulating fluidized bed is via line 14 with 2,000 Nm ³ / h of fluidizing air of 580 ° C (originating from the second section of the fluidized bed cooler 23), via line 15 with 4,800 Nm ³ / h of secondary air of 1,020 ° C (from the cyclone separator 22 originating) and supplied via line 13 with 390 Nm ³ / h of natural gas. This results in a temperature of 1,150 ° C., which is practically constant over the entire circulation system formed from fluidized bed reactor 10, return cyclone 11 and return line 12.

After an average residence time of about 20 minutes, during which the aluminum oxide has been completely calcined, a solid stream corresponding to the feed quantity is fed continuously via line 16 to the conveying path 17 and heated to 1,400 ° C. by the burner flame or the burner exhaust gases. The burner is fed with 110 Nm ³ / h natural gas and 1,200 Nm ³ / h air at 650 ° C (originating from the first section of the fluidized bed cooler 23).

The high-temperature reaction is complete after approx. 4 sec. The gas / solid suspension is cooled by introducing 3,500 Nm ³ / h of air at a temperature of 470 ° C. (originating from the fluidized bed cooler 23). As a result, the suspension cools down to a temperature of 1,020 ° C, at which sufficient flowability of the solid is ensured. The gas / solid suspension is then separated in the cyclone separator 22, the gas (4,800 Nm ³ / h) to the fluidized bed reactor 10 as secondary gas, and the solid to the fluidized bed cooler 23.

In the fluidized bed cooler 23, the solid is cooled in several sections to a final temperature of 80 ° C. For this purpose - seen in the direction of flow of the solid - in the first section 1,200 Nm ³ / h of air heated to 650 ° C, in the second section 2,000 Nm ³ / h of air heated to 580 ° C and in the third section 2 ₀ m ³ / h of water at 35 ° C is warmed to 65 ° C. As mentioned above, the gas streams are returned to the process. The production is 5 t / h aluminum oxide with a BET surface area of 3 m ² / g.

Claims (6)

1. A process for carrying out high-temperature reactions between hot gas and previously heated solids, which lose their free-flowing properties in the high-temperature treatment, in a substantially vertical conveying path with subsequent cooling and separation from the gas, characterized in that the heated solids are passed from below and in the conveying direction enters a burner flame located in the lower region of the conveying section (17), passes through a sufficiently long reaction zone and, after completion of the reaction with unchanged flow direction, cools at least to the temperature at which flowability is obtained by adding coolant separately in the flow direction. 2. The method according to claim 1, characterized in that the solids are heated in a circulating fluidized bed (10, 11, 12) operated by oxygen-containing fluidizing gas and oxygen-containing secondary gas. 3. The method according to claim 1 or 2, characterized in that the solids are heated using the exhaust gases of the conveyor section (17). 4. The method according to claim 1, 2 or 3, characterized in that the solids separated from the gas are cooled in a fluidized bed cooler (23). 5. The method according to one or more of claims 1 to 4, characterized in that the solids are cooled by heat exchange with oxygen-containing gases, which after heating in the solid heating stage (10,11,12) and / or the high-temperature reaction (17th ) are used. 6. The method according to one or more of claims 1 to 5, characterized in that for heating the solid in the circulating fluidized bed (10, 11, 12) as fluidizing gas (14) in the fluidized bed cooler (23) indirectly heated oxygen-containing gas and as oxygen-containing Secondary gas (15) uses exhaust gas from the conveyor line (17).

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