FI89944B - FREQUENCY REQUIREMENTS FOR THE CONTROL OF TEMPERATURES IN A REACTOR WITH CIRCULAR FLUIDISERAD BAEDD - Google Patents

Description

89944

METHOD AND APPARATUS FOR CONTROLLING THE TEMPERATURE IN A CIRCULAR FLUID REACTOR

RELEASE OF THE CIRCULAR FLUIDISERAD BÄDD

The present invention relates to a method and apparatus for controlling the temperature in heat transfer processes, such as, for example, sulphide ore roasting or combustion processes arranged to take place in a particulate suspension in a circulating fluidized bed reactor. The circulating fluidized bed reactor comprises - a fluidized bed reactor fed with a process feed solids and gas, the gas being fed through a grate arranged at the bottom of the fluidized bed reactor so that the fluidized bed reactor a particle separator connected to the outlet 15 at the top of the fluidized bed reactor to separate the solid particles from the gases, and - to return the particles of the return pipe from the particle separator to the fluidized bed reactor to maintain the circulating fluidized bed.

; 20 !!! The product can be continuously removed from the fluidized bed reactor either directly from the fluidized bed from the reactor grate or it is separated as a fine dust from the gas stream, e.g. by an electrostatic precipitator.

25

The use of fluidized bed technology has become more common in metallurgical processes and has brought considerable improvement to the roasting of sulphide concentrates, for example, and is now widely used for roasting iron and zinc sulphides.

The fluidized bed is characterized in that the solid fed to it is rapidly and efficiently mixed with the bed material and gas in the fluidized bed. The solid fed to the reactor then reaches the temperature of the fluidized bed in an instant due to the good mixing conditions. Air is often used as the fluidizing gas 5, in which case it may at the same time act as an oxidizing gas in the reactor. Thus, e.g. in a roasting reactor, oxidation of the sulphide concentrate fed to the reactor is effected by fluidizing air. With proper temperature control and air-to-concentrate ratio, the desired reactions are achieved to provide metal oxides or sulfates.

Thus, for example, an elongated horizontal reactor is used for roasting the zinc concentrate, in which roasting takes place in a slow or bubbling fluidized bed. Coarse solids in a cyclone and fine dust in an electrostatic precipitator are separated from the gases leaving the reactor 15. The roasting product from the reactor is cooled in a separate fluidized bed reactor. Also the so-called. a vertical bubble bed reactor is used for this purpose.

20

Because concentrates are often very finely ground, some of the oxidized particles flow out of the fluidized bed reactor with SO 2 -containing gases and sulfate outside the roasting reactor. At lower temperatures, this is thermodynamically possible, but not desirable, as it results in excess H 2 SO 4 in the post-roasting product of the roasting product. The roasting product can, of course, be returned to the bubble bed and thus decompose the sulfate again, thereby improving the roasting result.

30

Alongside the previously more generally known slow fluidized bed technology, i.e. the bubble bed technology, the fast fluidized bed technology based on the circulating pulp principle has emerged. For example, roasting of zinc concentrate can be made to work even better in a rotary 35 fluidized bed reactor. The circulating fluidized bed reactor is smaller in structure than a conventional fluidized bed reactor and thus more advantageous in structure.

3,89944

It is known that the reactions between sulphide concentrates and air in a fluidized bed are exothermic, i.e. an excess of heat is generated during roasting, which varies depending on the conditions. Both temporary fluctuations in air supply or concentrate charge and operating conditions, such as concentrate humidity, can have a significant effect on excess heat. In the fluidized bed, the excess heat generated by the oxidation of the concentrate is rapidly equalized in the bed material, 10 but it must still be removed from the fluidized bed in order to maintain the temperature required for optimal chemical reactions in the reactor. Heat removal is therefore an essential part of the roasting process and has an important effect on the structure of the roast. Of course, the cooling and heat recovery of the hot SO2 gas generated in the roasting process 15 is in itself economically viable, even if it is not relevant to the roasting process.

In general, it would be advantageous to be able to adjust the roasting temperature 20 within relatively narrow limits in order to avoid e.g.

- incomplete combustion due to too low a temperature and consequent sulphide residue in the roast, - sintering of the bed at too hot a temperature, 25 - wear due to excessive heat of the equipment.

The excess heat released during the roasting of zinc sulphide, i.e. the oxidative combustion of zinc sulphide, is so considerable that it is usually always recovered as pressurized superheated steam, from which electricity is generated by means of a steam turbine and a generator. In a fluidized bed reactor, the roasting temperature is typically 900 to 1000 ° C. This temperature can be maintained in the reactor, e.g. by the following alternative methods: 35 - the reactor is provided with cooling by the clerotic fluidized bed reactor technique, in which cooling heating surfaces can be built into the reactor as above, but also in connection with a mass circulation outside the reactor, whereby the circulating material cooled outside the reactor is continuously recycled to the fluidized bed.

10 - so much excess air is used for roasting or combustion that no cooling surfaces are required. In this case, the excess heat is bound to excess air; - adjusting the water content of the concentrate, or - introducing water directly into the fluidised bed.

15

If a low-cost roasting structure is desired, it is advisable to equip the reactor with cooling heating surfaces and run the roasting or combustion with as little excess air as possible. The use of excess air is, of course, uneconomical.

When using an uncooled roasting structure, the required cooling capacity has to be built elsewhere, which increases equipment costs. In addition, external cooling requires more heat surface, because the heat transfer potential, i.e. the temperature difference from the heat transfer state to the heat receiving state, is greatest in the roasting reactor. The cost would be further increased by the fact that the uncooled roasting reactor would have to be equipped with refractory masonry.

With the help of heating surfaces, in such combustion or roasting, the temperature range in which the process is intended to operate can be achieved. For the actual temperature control, they 35 usually cannot be used.

Temperature control by the addition of water leads to an increase in the amount of steam and thus also to an increase in the sulfuric acid content.

II

5 39944 tea in flue gases, which is harmful eg with electrostatic precipitators And also restricts heat recovery or causes the use of too expensive materials.

5 In conventional solutions, the roasting temperature is usually not regulated, but the air factor is used to achieve the desired roasting or combustion result. In this case, the roasting temperature cannot be optimized, but is allowed to vary. In practice, the plant has to be operated in a limited power range, usually of course with the highest possible power, so as not to exceed or fall below the limits of the usable combustion temperature range. As a result of this mode of operation, in which the combustion temperature cannot be precisely controlled all the time, an optimal roasting or combustion result is achieved "by chance" and as other process conditions change (e.g. concentrate moisture variations, feed unevenness, concentrate analysis variations). If the combustion air coefficient and the combustion temperature could be standardized at the same time, the optimal roasting result could be achieved at all times and kept constant.

It is therefore an object of the present invention to provide a better method and apparatus than the above for simultaneously controlling both the combustion air factor and the combustion temperature.

::: 25

It is a further object of the present invention to provide a method by which the disadvantages described above which occur in the present roasting and firing technique can be substantially reduced.

30

It is also an object of the present invention to provide a device of preferred function and size for carrying out and controlling roasting reactions.

In order to achieve the above-mentioned purposes, the method according to the invention for controlling the temperature in heat transfer processes in a circulating fluidized reactor is characterized in that - the particulate suspension with the lower fluidized bed; - the upper fluidized bed is further provided with its own mass circulation by returning part of the particles separated in the particle separator to the fluidized bed reactor above the throttling point, while the other part of the particles is returned to the lower fluidized bed below the throttling point; - the heat transfer reactions are arranged in the fluidized bed reactor mainly to take place in the lower fluidized bed, i.e. in the actual reaction chamber; - the particle suspension is cooled in the upper fluidized bed, i.e. in the cooling chamber, with thermal surfaces arranged therein, and - the cooled particulate suspension is passed from the upper 20 fluidized bed to the particle separator.

Preferably, a large part of the separated cooled solid particles is returned from the particle separator to the upper fluidized bed, i.e. the cooling chamber, so that the gas and solid suspension stream from the lower fluidized bed, i.e. the actual reaction chamber, can be cooled to the desired temperature before the cooling chamber. For example, when roasting sulphide ores, the particle suspension can be cooled first in the cooling chamber with a circulating material to <500 ° C and then to <350 ° C with the heating surfaces arranged in the cooling chamber.

The lower fluidized bed, i.e. the actual reaction chamber, is preferably also returned with such a large proportion of cooled solid particles that the desired temperature can be maintained in the reaction chamber. In this way, for example, the roasting reactor can be adjusted so that the temperature in the reaction chamber remains suitable at about 800 to 1000 ° C.

Il 7 89944

The device according to the invention for controlling the temperature in a circulating fluidized bed reactor is characterized in that - a throttling means is arranged in the fluidized bed reactor for restricting the particle-5 suspension flow at the constriction point as the particulate suspension flows from the bottom to the top and the fluidized bed reactor. - a first return pipe 10 is connected to the top of the fluidized bed reactor for returning solid particles from the particle separator to the top of the fluidized bed reactor; - a second return pipe is connected to the lower part of the fluidized bed reactor for returning particles from the particle separator to the lower part of the fluidized bed reactor and that a heat surface is arranged in the upper part of the fluidized bed reactor to recover heat from the upper fluidized bed.

In a circulating fluidized bed reactor, the gas velocity is maintained at 2-10 20 m / s, preferably 5-10 m / s, so that a considerable part of the particles in the fluidized bed reactor flows with the gas through the throttling point to the upper of the fluidized bed reactor and from there to the particle separator.

The fluidized bed reactor according to the invention is particularly suitable for use in metallurgical processes, such as roasting of sulphate concentrates. The roasting temperature in the reaction chamber can then be adjusted to about 800 eC to 1000 eC by means of particle recovery and heating surfaces, so that an optimal roasting result is achieved. In the chamber above the choke, i.e. the cooling chamber, the final cooling of the roasting (or combustion) exhaust gases takes place, typically to a temperature of 200 to 500 eC, depending on e.g. the dew point of the sulfur compounds. By means of the cooling pulp circulation 35, a very fast first cooling to a temperature of <500 ®C is achieved before the heating surfaces, by means of which metastable equilibrium states can be achieved, e.g. harmful sulphation of the roasting product can be avoided.

8 39944 On the heating surfaces, the gases are then cooled e.g.

To a temperature of <350 ° C. The roasting product is hot taken out directly from the bottom of the reaction chamber. It can also be taken out of a return tube in which cooled circulating-5 material flows. Part of the roasting product, namely its finest material, is transported from the exhaust gas stream to the final dust separation, e.g. to an electrostatic precipitator, where it can be recovered.

When the roasting (combustion) exhaust gases are cooled in a circulating fluidized bed reactor, agglomeration of the solids takes place, which in turn improves the dust separation by centrifugal separators. The gas leaving the roasting reactor according to the invention is therefore often cleaner, less dusty than the gases from conventional roasting, but in particular has a lower proportion of the finest solids formed, especially when the material in the vapor phase condenses during gas cooling. You see, such material condenses to a considerable extent on the surface of the cooled pulp circuit returning from the particle separator. In this way, it is also possible to reduce the load on the separator used for the final cleaning of the roasting gases, e.g. an electrostatic precipitator.

In order to enable the above-mentioned dust agglomeration phenomenon, the cooling of the particle suspension in the cooling chamber is preferably arranged in two steps, so that the particulate suspension 30 flowing from the reaction chamber to the top is first mixed with cooled particles below C50 to rapidly lower the particle suspension temperature. , after which - the particle suspension is directed to pass through heat-recovering heating surfaces located in the cooling chamber 35 so that the temperature of the suspension drops to the temperature at which the final dust separation is to take place, typically to about 350 ° C.

9 39944

The excess heat released during roasting is recovered by heating surfaces arranged in both the reaction chamber and the cooling chamber. In addition, heat can be recovered by heating surfaces fitted to the Palau-5 tube.

By constructing the reaction chamber and the exhaust gas cooling chamber located above it into a unitary structure, the combustion-10 or roasting part and the gas cooling part are advantageously combined. The throttle member between the chambers, by which they are separated from each other, can be of e.g. e.g. a gas distribution arc made for hot gases or only one opening connecting the chambers, the shape and cross-section of which is chosen so that the upper chamber mass flow does not flow into the lower chamber during operation.

In the solution according to the invention, the temperature is thus controlled by a combination of a heating surface and a pulp circulation, in which case the required amount of heating surface is arranged in a reactor with a pulp circulation of a suitable size. The pulp circulation can be used mainly for controlling the temperature of the reactor, and most of the cooling, i.e. heat recovery, can be provided by heat transfer to the heating surfaces of the reactor, unless the kinetics of the roasting reaction are hindered.

By adjusting the temperature with the help of the pulp circulation, the roasting can always be driven with an optimal air factor and, if necessary, the roasting power can also be adjusted. In the solution 30 according to the invention, with an optimal air coefficient at an optimal temperature, the oxidation reactions of roasting have time to take place substantially completely already in the roasting reactor. If the reaction delay has to be increased, this is done within the framework of this solution by reducing the cooling effect of the heating surface of the reaction chamber and increasing the cooling effect of the mass cycle, whereby the reaction delay is prolonged by the mass cycle.

10 39944

The solution according to the invention also offers the possibility of eliminating a separate roaster cooler. In this case, the roast can be taken out of the pulp cycle from the return line at the exhaust gas temperature, which is thus typically n.

5 350eC. In this case, a separate heat separator in the roasting reactor is also not required, as the separation and recovery of the particles takes place only after the cooling reactor. The separator equipment can be made of steel because the gas temperature is low enough, below 400 ° C.

10 In the cooling chamber, its so-called the mixing temperature is adjusted to the desired level, e.g. 500 ° C by its own mass circulation. Stirring temperature means the temperature of the incoming particle suspension in the cooling chamber after the particle suspension 15 has been mixed into the pulp circuit therein before contact with the heating surfaces. The cooling of the gas from the roasting from the roasting temperature to this mixing temperature can take place very quickly, which substantially reduces the risk of sulphation of the roast, as described above.

20

The invention will now be described in more detail with reference to the accompanying schematic drawing, which shows a system according to the invention for controlling the temperature of roasting zinc concentrate in a circulating mass reactor.

25

The figure shows a circulating fluidized bed reactor comprising a two-part fluidized bed reactor 10, a particle separator 12 and a return pipe 14. Fluidizing gas, i.e. air in this case, is fed to the reaction chamber through a grate 16 arranged at its bottom from an air cabinet 18 with nozzles 20. Fluidizing gas is 2 - 10 m / s. A fluidized bed is formed in the reaction chamber by feeding a zinc concentrate together 22 and circulating particles separated in a particle separator by a recovery compound 35.

The lower part of the fluidized bed reactor, i.e. the reaction chamber 26, thus forms a roasting reactor in which the zinc concentrate is roasted

II

11 89944 in oxidative combustion. The cross-sectional area of the reaction chamber flow is selected so that a substantial portion of solids enters the top of the fluidized bed reactor, i.e., the cooling-chamber 5, with the combustion gases formed therein. The suspension of gases and solids flows into the top through a constriction 30 or a narrow throat. The throttle member is tightly fitted to the reactor so that the upwardly flowing gases have to pass through an opening smaller than its cross-section formed in the reactor.

The velocity of the gas in the orifice 32 is so high that particles cannot flow down through the throat back into the reaction chamber 26. A second upper fluidized bed is formed in the upper part 28 as the gas flow rate 15 slows down after the throat. However, even in this fluidized bed the velocity of the gas is arranged so high, 2-10 m / s, that a considerable part of the particles travels with the gas out of the fluidized bed reactor through an opening 33 arranged in its upper part and further into the particle separator 12. The particle separator shown in the figure is a vertical cyclone. Other separators, such as a horizontal cyclone or filter, can of course be considered.

In the particle separator, most of the solids 25 entrained in the gas are separated from the gases and the gas is passed together via 34 to a final particle separation, e.g. to an electrostatic precipitator. The separated particles are returned via the return pipe 14 partly with connection 36 to the cooling chamber 28, partly with connection 38 to the roasting reactor 26. The roasting product 30 is taken out directly from the grate with connection 42. If desired, the roasting product can also be taken out directly from the return pipe 14.

A roasting reactor 26 is provided with a heating surface 44 to recover heat from the heat transfer reactor. Correspondingly, a second heating surface 46 is arranged in the cooling chamber 28 to cool the particle suspension before the particle separator. The heating surfaces 44 and 46 can be connected to the same recovery system. If desired, the heating surfaces 48 and 50 can also be fitted to the return pipe 14.

Arranged in the return connections 36 and 38 are control means 52 and 5 54 by means of which the return of solids between the roasting reactor 26 and the cooling chamber 28 can be controlled. By adding a pulp cycle to the roasting reactor, it is possible to lower the temperature of the roasting reactor, if necessary. Correspondingly, the temperature can be raised by reducing the 10 circulating masses from the return.

In the solution according to the invention, the two fluidized beds 26 and 28 are simply arranged as a single vertical structure. In this way, an inexpensive and space-saving integrator of the roasting reactor and the cooling chamber is formed. Two partially separately controllable circulating mass reactors with a common particle separator are obtained.

The invention is not intended to be limited to the exemplary embodiment, but can be modified and applied within the scope of the inventive idea defined by the claims.

The control principle according to the invention can be utilized, for example, in the combustion of waste or other halogen-containing fuel. Combustion is arranged to take place in the combustion chamber in the first part of the reactor and the flue gases generated are rapidly cooled in the cooling chamber to minimize the amount of organic halogenated compounds. This is to minimize the synthesis of "de Novo", i.e. the regeneration of dioxins, furans and other toxic chlorine compounds, on cooling surfaces. Toxic chlorine compounds such as dioxins and furans are particularly sensitive to chlorine compounds in the temperature range of 250 to 400 ®C. The gases are therefore cooled rapidly above this temperature range in the cooling chamber.

Il 13 89944

The invention can also be applied to the cooling of the exhaust gases of a metallurgical process, gases to which chlorinated organic compounds can also be formed in the cooling step. In particular, the so-called prevention of the formation of super toxins, ie 5 polychlorinated dioxins and furans.

Emissions are also reduced by cooling. condensation of the compounds on the surface of the fine bed material circulating in the cooling chamber. While the process is operating in a continuous state, some concentration level of the above and other organic compounds is formed in the bed material of the cooling chamber. This level can be controlled by returning some of the material circulating in the cooling chamber to the lower reactor acting as the combustion chamber 15. Organic compounds condensed on the surface of the circulating material burn in the combustion chamber and the removed circulating material is cleaned. The purified circulating material is returned to the cooling chamber, where it replaces the removed contaminated material, thus reducing the contaminant content of the circulating material in the cooling chamber. This is an advantage e.g. for further processing of the material to be removed from the reactor.

Claims (16)

3 9 944 A method for controlling temperature in heat transfer processes arranged to take place in a particulate suspension in a circulating fluidized bed reactor, comprising - a fluidized bed reactor fed with process feed solids and gas, the gas being fed from the fluidized bed reactor to a fluidized bed grate a rapid fluidized bed in which a substantial portion of the solid particles enters with the gas as a particulate suspension at the top of the fluidized bed reactor and exits the fluidized bed reactor through an outlet fitted to the top thereof; in a circulating fluidized bed reactor, characterized in that the 20th particle suspension is brought in the bed reactor to flow through the throttling point, whereby an upper fluidized bed is formed in the fluidized bed reactor above the throttling point, which is in common mass circulation with the lower fluidized bed below the throttling point; - the upper fluidized bed is further provided with its own mass circulation by returning part of the particles separated in the particle separator to the fluidized bed reactor above the throttling point, while the other part of the particles is returned to the lower fluidized bed below the throttling point; - the heat transfer reactions are arranged in the fluidized bed reactor to take place mainly in the lower fluidized bed, i.e. in the actual reaction chamber; - the particle suspension is cooled in the upper fluidized bed, i.e. in the cooling chamber, with heating surfaces arranged therein, and - the cooled particulate suspension is led from the upper fluidized bed to the particle separator. It is 0 9 9 4 4 Process according to Claim 1, characterized in that the sulphide-containing metal concentrate is roasted in the lower part of the fluidized bed reactor, in its reaction chamber, and the heat of the hot gases generated during roasting is recovered by thermal surfaces in the upper part of the fluidized bed reactor. A method according to claim 1, characterized in that such a large part of the cooled particles separated in the particle separator is returned to the cooling chamber such that the particle suspension coming from the reaction chamber cools to the desired temperature before coming into contact with the heating surfaces. Process according to Claim 3, characterized in that the particle suspension from the reaction chamber is cooled in the cooling chamber to <550 ° C by mixing with it the cooled particles separated in the particle separator. A method according to claim 1, characterized in that such a large part of the cooled particles separated in the particle separator is returned to the reaction chamber so that the desired temperature can be maintained in the reaction chamber. Process according to Claim 5, characterized in that the temperature in the reaction chamber of the roasting reactor is maintained at 800 to 1000 ° C by returning to the reaction chamber the cooled particles separated in the particle separator. Method according to Claim 2, characterized in that the roasting product is recovered from the particles of 35 μm 89944 flowing in the return pipe. Process according to Claim 1, characterized in that the heat is recovered on the heating surfaces in the reaction chamber. A method according to claim 1, characterized in that the heat is recovered on the heating surfaces from the solid flowing in the return pipe 10. Method according to Claim 1, characterized in that a gas velocity of 2 to 10 m / s is maintained in the reaction chambers. 15 A method according to claim 1, characterized in that solid fuel is combusted in the reaction chamber and the temperature of the lower and upper fluidized bed is adjusted by the return of the cooled particles to suit the minimization of sulfur and nitrous oxide emissions. A method according to claim 1, characterized in that waste or other halogenated fuel is incinerated in the lower part of the fluidized bed reactor and the flue gases generated during the incineration are rapidly cooled in the upper fluidized bed reactor to avoid the formation of toxic compounds. 13. A system for controlling the temperature in heat transfer processes arranged to take place in a circulating fluidized bed reactor, comprising - a fluidized bed reactor (10) and a high speed fluidized bed of solids particles fluidized therewith with fluidized gas fed through the bottom of the fluidized bed reactor. part of the solid particles passes as a particle suspension with the upwardly flowing gases from the lower part (26) of the fluidized bed reactor to its upper part (28) II 17 '69944 and exits the fluidized bed reactor through an outlet arranged at its top, and - a return pipe (14) for returning the particles from the particle separator to the fluidized bed reactor, characterized in that - a throttling member (30) 10 is arranged in the fluidized bed reactor for restricting the flow of the particulate suspension. in which the particulate suspension flows from the lower part (26) of the fluidized bed reactor to its upper part (28) and to divide the fluidized bed reactor into lower and upper parts; - a first return pipe (36) is connected to the top of the fluidized bed reactor for returning solid particles from the particle separator to the top of the fluidized bed reactor; - a second return pipe (38) is connected to the lower part of the fluidized bed reactor for returning particles from the particle separator to the lower part of the fluidized bed reactor and a heat surface (46) is provided in the upper part of the 20 fluidized bed reactor to recover heat from the upper fluidized bed. Device according to Claim 13, characterized in that the particle separator (12) is a cyclone. Device according to Claim 13, characterized in that a heating surface (44) is arranged in the lower part of the fluidized bed reactor, i.e. in the reaction chamber, for recovering heat from the fluidized bed. Device according to Claim 13, characterized in that a heating surface (48, 50) is arranged in the return pipe (14) for cooling the particles. > 39944