AU652204B2 - Method and apparatus for controlling temperature in a circulating fluidized bed reactor - Google Patents

Method and apparatus for controlling temperature in a circulating fluidized bed reactor

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Publication number
AU652204B2
AU652204B2 AU90439/91A AU9043991A AU652204B2 AU 652204 B2 AU652204 B2 AU 652204B2 AU 90439/91 A AU90439/91 A AU 90439/91A AU 9043991 A AU9043991 A AU 9043991A AU 652204 B2 AU652204 B2 AU 652204B2
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Australia
Prior art keywords
fluidized bed
bed reactor
reactor
particles
recited
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Ceased
Application number
AU90439/91A
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AU9043991A (en
Inventor
Olli Arpalahti
Matti Hiltunen
Kurt Westerlund
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Amec Foster Wheeler Energia Oy
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Ahlstrom Corp
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Assigned to FOSTER WHEELER ENERGIA OY reassignment FOSTER WHEELER ENERGIA OY Alteration of Name(s) in Register under S187 Assignors: A. AHLSTROM CORPORATION
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
    • B01J8/1836—Heating and cooling the reactor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
    • B01J8/24—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
    • B01J8/26—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with two or more fluidised beds, e.g. reactor and regeneration installations
    • B01J8/28—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with two or more fluidised beds, e.g. reactor and regeneration installations the one above the other
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
    • B01J8/24—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
    • B01J8/38—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with fluidised bed containing a rotatable device or being subject to rotation or to a circulatory movement, i.e. leaving a vessel and subsequently re-entering it
    • B01J8/384—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with fluidised bed containing a rotatable device or being subject to rotation or to a circulatory movement, i.e. leaving a vessel and subsequently re-entering it being subject to a circulatory movement only
    • B01J8/388—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with fluidised bed containing a rotatable device or being subject to rotation or to a circulatory movement, i.e. leaving a vessel and subsequently re-entering it being subject to a circulatory movement only externally, i.e. the particles leaving the vessel and subsequently re-entering it
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/0033—In fluidised bed furnaces or apparatus containing a dispersion of the material
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B5/00—General methods of reducing to metals
    • C22B5/02—Dry methods smelting of sulfides or formation of mattes
    • C22B5/12—Dry methods smelting of sulfides or formation of mattes by gases
    • C22B5/14—Dry methods smelting of sulfides or formation of mattes by gases fluidised material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B31/00—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus
    • F22B31/0007—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus with combustion in a fluidized bed
    • F22B31/0084—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus with combustion in a fluidized bed with recirculation of separated solids or with cooling of the bed particles outside the combustion bed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C10/00—Fluidised bed combustion apparatus
    • F23C10/02—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed
    • F23C10/04—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone
    • F23C10/08—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone characterised by the arrangement of separation apparatus, e.g. cyclones, for separating particles from the flue gases
    • F23C10/10—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone characterised by the arrangement of separation apparatus, e.g. cyclones, for separating particles from the flue gases the separation apparatus being located outside the combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B15/00—Fluidised-bed furnaces; Other furnaces using or treating finely-divided materials in dispersion
    • F27B15/02—Details, accessories, or equipment peculiar to furnaces of these types
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B15/00—Fluidised-bed furnaces; Other furnaces using or treating finely-divided materials in dispersion
    • F27B15/02—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B15/18—Arrangements of controlling devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
    • B01J2208/00008—Controlling the process
    • B01J2208/00017—Controlling the temperature
    • B01J2208/00026—Controlling or regulating the heat exchange system
    • B01J2208/00035—Controlling or regulating the heat exchange system involving measured parameters
    • B01J2208/00044—Temperature measurement
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
    • B01J2208/00008—Controlling the process
    • B01J2208/00017—Controlling the temperature
    • B01J2208/00106—Controlling the temperature by indirect heat exchange
    • B01J2208/00115—Controlling the temperature by indirect heat exchange with heat exchange elements inside the bed of solid particles
    • B01J2208/00132—Tubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
    • B01J2208/00008—Controlling the process
    • B01J2208/00017—Controlling the temperature
    • B01J2208/0053—Controlling multiple zones along the direction of flow, e.g. pre-heating and after-cooling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C2206/00—Fluidised bed combustion
    • F23C2206/10—Circulating fluidised bed
    • F23C2206/101—Entrained or fast fluidised bed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C2206/00—Fluidised bed combustion
    • F23C2206/10—Circulating fluidised bed
    • F23C2206/103—Cooling recirculating particles
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/10—Reduction of greenhouse gas [GHG] emissions
    • Y02P10/134—Reduction of greenhouse gas [GHG] emissions by avoiding CO2, e.g. using hydrogen
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Dispersion Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)

Description

METHOD AND APPARATUS FOR CONTROLLING TEMPERATURE IN A CIRCULATING FLUIDIZED BED REACTOR
The present invention relates to a method and apparatus for controlling the temperature of exothermic processes, e.g. roasting of sulphide ores or burning processes, arranged to take place in a particle suspension in a circulating fluidized bed reactor. The circulating fluidized bed reactor comprises: - a fluidized bed reactor, into which process feed material and gas are introduced, the gas being introduced through a grate provided at the bottom of the fluidized bed reactor, so that the solid material particles form a fast fluidized bed in the fluidized bed reactor, from which bed a considerable portion of the solid material particles is conveyed with the gas as a particle suspension into the upper portion of the fluidized bed, and is then withdrawn from the fluidized bed reactor via an outlet arranged at the upper portion of the fluidized bed reactor, - a particle separator, connected to the outlet at the upper portion of the fluidized bed reactor to separate solid material particles from gases and
- a recycling condu.it for recycling particles from the particle separator to the fluidized bed reactor to maintain a circulating fluidized bed in the circulating fluidized bed reactor.
The product can be withdrawn from the circulating fluidized bed reactor either continuously from the grate of the reactor or it is separated as fine dust from the flow of gas with e.g. an electrostatic precipitator.
The utilization of fluidized bed technology has become common in metallurgical processes, bringing about a considerable improvement in e.g. roasting of sulphide concentrates, and presently fluidized bed technology is being commonly used for e.g. roasting of iron and zinc sulphides. It is typical to a fluidized bed that the solid material introduced therein is effectively and rapidly mixed with the bed material and gas in the fluidized bed. Thus the solid material introduced into the reactor will - because of the good conditions for mixing - instantaneously reach the temperature of the fluidized bed. Air is often used as the fluidizing gas, and acts thus often simultaneously as the oxidizing gas. Thus in e.g. a roasting reactor the fluidizing air will oxidize the sulphide concentrate. The aim of the correct control of temperature and air-to- concentrate ratio is to effect the preferred reactions for forming of metal oxides or sulphates.
Thus, zinc concentrate is roasted in e.g. a longitudinally elongated horizontal reactor, in which the roasting takes place in a slow or bubbling fluidized bed. The coarse solid material is separated from flue gases in a cyclone and the fine dust in an electrostatic precipitator. The roasted product from the reactor is cooled in a separate fluidized bed reactor. Also, a so-called vertical bubbling bed reactor is used for this purpose.
As the concentrates are often very finely ground, a portion of the oxidized particles will flow out from the fluidized bed reactor with the Sθ2~containing gases and will be sulphatized outside the roasting reactor. This is thermodynamically possible at lower temperatures, but not desired, as it leads to an excess of H2SO4 when processing the roasted product electolytically after the roasting stage. The roasted product can naturally be recycled to the bubbling bed in order to decompose the sulphate again, thus improving the roasting result.
The fast fluidized bed technology, based on the principle of circulating mass in a circulating fluidized bed, has emerged aside the previously known slow fluidized bed or bubbling fluidized bed technology. For example, roasting of zinc concentrate can be effected better than previously in a circulating fluidized bed reactor. Structurally a circulating fluidized bed reactor is smaller than a conventional reactor utilizing a bubbling fluidized bed, and thus also structurally more economical.
It is known that reactions between sulphide concentrates and air in a fluidized bed are exothermic, i.e. roasting produces excess heat, the amount of which varies depending on process conditions. Temporary fluctuations in introduc¬ tion of air or in the supply of concentrate as well as other operating conditions, e.g. humidity of the concentrate, can have a considerable effect on the amount of excess heat. When oxidizing concentrate in a fluidized bed, the excess heat formed will rapidly be evenly distributed in the bed material, but still it must be withdrawn from the fluidized bed so that the temperature for optimal chemical reactions can be maintained. Withdrawing heat is therefore an essential part of the roasting process, and it has an important effect on the structure of the roasting plant. The cooling of SO2 gases formed in the roasting process and recovering of heat therefrom is naturally economically profitable as such, even if it did not have an effect on the actual roasting process.
Usually, it would be advantageous to be able to regulate the temperature within a relatively narrow range so that e.g. the following could be avoided:
- an incomplete burning, and as a result of this residual sulphides in the roasted product, caused by too low temperature,
- sintering of the bed, caused by too high temperature, and
- wear of the structures caused by too high temperature.
The amount of excess heat released during roasting, i.e. oxidizing combustion, of zinc sulphide is so considerable that it is usually recovered as pressurized superheated steam, which is then converted into electricity with a steam turbine and a generator. The roasting temperature in a fluidized bed reactor is typically 900 - 1000°C. Utilizing e.g. the following' alternative methods, this temperature can be maintained in a fluidized bed reactor: - providing the reactor with cooling surfaces in a way similar to the furnace of a conventional boiler. It has been suggested that cooling tubes be provided both in the fluidized bed itself as well as in the free board area above it; - utilizing the circulating fluidized bed technology, in which case the cooling surfaces can be arranged in the reactor as above, but also in communication with the external circulating mass, thereby continuously recycling externally cooled circulating material back into the fluidized bed. In an extreme case the entire cooling can take place in the circulating mass, in an apparatus outside the reactor, thus eliminating any need for cooling surfaces in the reactor.
- using such an excess amount of air during the roasting or combustion that no cooling surfaces are needed. Thus the excess heat will be absorbed by the excess air;
- regulating the water content of the concentrate or
- introducing water directly into the fluidized bed.
If an economical roasting plant structure is desired, it is advantageous to provide the reactor with cooling surfaces and to practise the roasting or combustion with as small an excess amount of air as possible. Using an excess amount of air is naturally disadvantageous.
If a non-cooled roasting plant structure is utilized, the necessary cooling will have to be arranged elsewhere, which increases the apparatus costs. Further, external cooling requires more heat transfer surface area than cooling in the reactor because the heat transfer potential, i.e. the temperature difference between the medium transmitting heat and the medium receiving heat, is at its greatest in the roasting reactor. The costs would further be increased by the necessity of providing a non-cooled reactor with fire-proof brickwork.
In this kind of roasting or combustion, the desired temperature range for the process can be achieved with heat transfer surfaces. Usually it is not possible to use heat transfer surfaces for actual temperature regulation.
Controlling the temperature by adding water leads to _.n increase in the amount of steam and thus also to an increase in the amount of sulphuric acid in the flue gases, which is detrimental to e.g. electrostatic precipitators and also limits the heat recovery and necessitates the use of too expensive materials.
In conventional solutions the roasting temperature is not usually regulated, but the air coefficient is utilized to achieve the desired roasting or combustion result. In those cases the roasting temperature can not be optimized, but it is allowed to vary. In practice the result of this is that the plant will have to be run in a limited efficiency range, so that the temperature will be neither under nor above the limits for the practical combustion temperature range. As a result of this way of operating the process, in which the combustion temperature cannot be accurately controlled, an optimal roasting or combustion result is achieved "by chance", and when other process conditions change (e.g. changes in the humidity of the concentrate, irregularities in the supply of material, changes in the composition of the concentrate), the result will also change. If both the air coefficient of the combustion and the combustion temperature could simultaneously be held constant, an optimal and uniform roasting result could be achieved at all times.
The object of the present invention is to provide for a method and apparatus, superior to the above, for simultaneously regulating both the air coefficient of the combustion and the combustion temperature.
Another object of the present invention is to provide for a method for essentially decreasing the above disadvantages in present roasting and combustion technology.
A further object of the present invention is to provide for an apparatus, advantageous both in function and size, for accomplishing and regulating roasting reactions.
The method for controlling the temperature in exothermic processes in a circulating fluidized bed reactor to ac¬ complish the above objects is characterized in that - the particle suspension flowing upwards in the fluidized bed reactor is arranged to flow through a venturi portion, thereby forming an upper fluidized bed above the venturi portion, the upper fluidized bed having a circulation of mass in common with the lower fluidized bed, situated below the venturi portion;
- the upper fluidized bed is additionally provided with a circulation of mass of its own by recycling a portion of the particles separated in the particle separator to the fluidized bed reactor above the venturi portion while a second portion of the particles is recycled to the lower fluidized bed below the venturi portion;
- the exothermic reactions in the fluidized bed reactor are arranged to take place in the lower fluidized bed, i.e. the main reaction chamber; - the particle suspension is cooled in the upper fluidized bed, i.e. the cooling chamber, with heat transfer surfaces arranged therein and that
- the cooled particle suspension is directed from the upper fluidized bed to the particle separator.
The portion of separated and cooled particles recycled from the particle separator to the upper fluidized bed or cooling chamber is preferably sufficient to cool the flow of gas/solid material suspension from the lower reaction chamber, or the main reaction chamber, to a desired temperature before the flow 'reaches the heat transfer surfaces disposed in the cooling chamber. The particle suspension can, when for example roasting sulphide ores, be cooled in the cooling chamber with circulating material to < 500°C and, subsequently, with heat transfer surfaces disposed in the cooling chamber, to < 350°C.
Preferably also the portion of cooled solid material particles recycled to the lower fluidized bed, or the main reaction chamber, is sufficient to maintain a desired temperature in the reaction chamber. Thus, for example, a roasting reactor can be regulated so that the temperature is kept suitable, at about 800 - 1000°C.
An apparatus according to the invention for controlling the temperature in a circulating fluidized bed reactor is characterized in that - a throttle means is arranged in the fluidized bed reactor to restrain the flow of particle suspension at the venturi portion when the particle suspension flows from the bottom portion of the fluidized bed reactor to the upper portion of the fluidized bed reactor and to divide the fluidized bed reactor into lower and upper portions;
- a first recycling conduit is connected to the upper portion of the fluidized bed reactor for recycling solid particles from the particle separator to the upper portion of the fluidized bed reactor; - a second recycling conduit is connected to the lower portion of the fluidized bed reactor for recycling particles from the particle separator to the lower portion of the fluidized bed reactor and that
- a heat transfer surface is arranged in the upper portion or cooling chamber of the fluidized bed reactor to recover heat from the fluidized bed in the upper portion. The velocity of the gas in the circulating fluidized bed reactor is 2 - 10 m/s, preferably 5 - 10 m/s, so that a considerable portion of the particles in the fluidized bed reactor flows with the gas through the venturi portion to the upper portion of the fluidized bed reactor and from there further to the particle separator.
A fluidized bed reactor according to the invention is especially suitable for metallurgical processes, such as roasting of sulphidic concentrates. The roasting temperature can then be regulated by the recycling of particles and with heat transfer surfaces to about 800 - 1000°C so that an optimal roasting result is achieved. The final cooling of the flue gases after the roasting (or combustion), typically to about 200 - 500°C, takes place in a chamber above the venturi, i.e. the cooling chamber, the end temperature depending on e.g. the dewpoint of sulphur compounds. A very fast first cooling to a temperature of e.g. < 500°C is achieved with the recirculation of the cooled mass, by which meta-stable stages of equilibrium can be achieved, e.g. the detrimental sulphatizing of the roasted product can be avoided. The gases are subsequently cooled to e.g. a temperature < 350°C with the heat transfer surfaces. The still hot roasted product is withdrawn straight from the lower portion of the reaction chamber. It can also be withdrawn from the recycling conduit, from the cooled circulating material flow. A portion of the roasted product, especially the finest particles thereof, is conveyed with the flow of flue gases to a final dust separation to e.g. an electrostatic precipitator where it can be recovered.
When the flue gases of the roasting (combustion) are cooled in a circulating fluidized bed reactor, the solid material agglomerates, which further improves dust separation by centrifugal separators. Flue gas withdrawn from a roasting reactor according to the invention is therefore often cleaner, with less dust, than flue gases from conventional roasting plants, as the portion of the finest particulate solid material, formed especially by condensation of vaporous components during 'cooling, is substantially reduced. These vaporous components are to a considerable degree condensated onto the surface of the cooled particles returning from the particle separator. Thus also the load of separators, e.g. electrostatic precipitators, can be greatly reduced during the final cleaning of the gases from the reoasting process.
To enable the above agglomeration of dust, the cooling of the particle suspension in the cooling chamber is preferably arranged to take place in two stages, so that
- firstly, cooled particles recycled from the particle separator are mixed with the particle suspension flowing from the reaction chamber to the upper portion to rapidly lower the temperature to e.g. under 550°C, after which
- the particle suspension is directed via the heat recovering surfaces provided in the cooling chamber, so that the suspension is cooled to the temperature at which the final dust separation is to take place, typically about 350°C.
The excess heat released during roasting is recovered with heat transfer surfaces arranged in both the reaction chamber and the cooling chamber. Heat can also be recovered with heat transfer surfaces arranged in the recycling conduit.
A preferable way to integrate the combustion or roasting stage with the gas cooling stage is to construct the chamber for cooling flue gases on top of the reaction chamber, the two chambers forming an integrated construction. The throttle means separating the chambers from each other can be structurally like e.g. a conventional gas dividing grate or only one single opening connecting the chambers, the shape and cross-section of which are so chosen as to prevent the circulation of mass in the upper chamber from flowing directly down into the lower, i.e. reaction chamber, during the operation of the reactor.
In a solution according to the invention the temperature is controlled with a combination of heat transfer surfaces and circulation of mass, so that necessary heat transfer surfaces are arranged in a reactor with an appropriately sized circulation of mass. The circulation of mass can mainly be used for regulating the temperature in the reactor and the main of cooling, i.e. heat recovery, can be effected by heat transfer to the heat transfer surfaces in the reactor, unless the kinetics of the roassting reaction prevents this.
When the temperature is controlled with the circulation of mass, roasting can always be practised with an optimal air coefficient and the efficiency of roasting can also be controlled when needed. In a solution according to the invention, when both the air coefficient and the temperature are optimal, the oxidation reactions have time to take place mainly completely in the roasting reactor. If the reaction time has to be increased, it can within the scope of this solution be accomplished by decreasing the cooling effect of the heat transfer surface in the reaction chamber and increasing the cooling effect of the circulation of mass, thus increasing the reaction time with circulation of mass.
A solution according to the invention also makes it possible to eliminate a separate cooler for the roasting. In this case the roasted product can be withdrawn from the circulation of mass through the recycling conduit, the roasted product having the same temperature as the flue gas, typically about 350°C . Thus a separate hot separator is not needed in the roasting reactor, as the particles are separated and recycled only after being cooled in the cooling reactor. The separator can be manufactured of steel, because the temperature of the gas is low enough, under 400°C.
In the cooling chamber the so-called mixing temperature can be regulated to a desired level, e.g. 500°C, with its own circulation of mass. The mixing temperature is the temperature of the incoming particle suspension in the cooling chamber after the particle suspension has been mixed with the circulation of mass in the cooling chamber and before it contacts the heat transfer surfaces. The gas coming from the roasting stage can be cooled to this temperature very rapidly, which essentially decreases the risk of the roasted product being sulphatized, as has been disclosed above.
In the following the invention is described isclosed more in detail with reference to the following schematic drawing illustrating a system according to the invention for controlling the temperature of roasting of zinc concentrate in a circulating fluidized bed reactor.
The figure illustrates a circulating fluidized bed reactor comprising a double-staged fluidized bed reactor 10, a particle separator 12 and a recycling conduit 14. Fluidizing gas, in this case air, is introduced into the reaction chamber through a grate 16 arranged at the bottom of the reaction chamber from airbox 18 with nozzles 20. Fluidizing gas is introduced so that the velocity of the gas in the reaction chamber is about 2 - 10 m/s. A fluidized bed is formed in the reaction chamber by introducing therein zinc concentrate through conduit 22 and circulating particles, separated at the particle separator, through recycling conduit 24.
Thus the lower portion, i.e. reaction chamber 26, forms a roasting reactor, where the zinc concentrate is roasted in oxidizing conditions. The cross-section of the flow in the reaction chamber is chosen to be such that a considerable portion of the solid material is conveyed with the flue gases formed therein into the upper portion of the fluidized bed reactor, i.e. the cooling chamber 28. The particle suspension formed by the gases and solid material flows into the upper portion via a narrow venturi or opening 32 defined by throttle means 30. The throttle means is arranged in the reactor so that the gases flowing upwards have to flow via an opening, the cross-section of which is smaller than that of the rest of the reactor.
The velocity of the gas in the opening 32 is so high that no particles can flow downwards through the venturi back to the reaction chamber 26. As the velocity of the gas flow decreases after the venturi, a second, upper fluidized bed is formed into the upper portion 28. However, the velocity of the gas is so high, 2 - 10 m/s, also in this fluidized bed that a considerable portion of particles is conveyed with the gas out from the fluidized bed reactor via an opening 33 arranged in the uppermost part of the reactor and further into the particle separator 12. The particle separator illustrated in the figure is a vertical cyclone. Other kinds of separators, such as a horizontal cyclone or a filter, can naturally also be utilized.
In the particle separator the main portion of the solid material conveyed with the gas is separated from the gas, and the gas is directed via conduit 34 to the final particle separation to e.g. an electrostatic precipitator. The separated particles are recycled via recycling conduit 14, partly through conduit 36 to the cooling chamber 28, partly through conduit 38 to the roasting reactor 26. The roasted product is withdrawn through conduit 42 straight from the grate. The roasted product can also, if desired, be withdrawn straight from the recycling conduit 14.
A heat transfer surface 44 is arranged in the roasting reactor 26 for recovering the heat formed in the reactor. A second heat transfer surface 46 is correspondingly arranged in the cooling chamber 28 for cooling the particle suspension before the particle separator. Heat transfer surfaces 44 and 46 can be connected to the same heat recovery system. If desired, heat transfer surfaces 48 and 50 can also be arranged in the recycling conduit 14.
Controlling means 52 and 54 are arranged in recycling conduits 36 and 38 for controlling the recycling of solid material to the roasting reactor 26 and to the cooling chamber 28. When needed, the temperature in the roasting reactor can be decreased by increasing the circulation of mass into the roasting reactor. The temperature can correspondingly be increased by decreasing the amount of recycled circulating mass.
In a solution according to the invention, two fluidized beds 26 and 28 have simply been arranged in an integrated vertical structure. Thus an inexpensive and small integration of a roasting reactor and a cooling chamber can be formed. This results in two partly separately controllable circulating fluidized bed reactors having a particle separator in common.
There is no intent to limit the invention to the embodiment exemplified above, but it can be modified and applied within the inventive step defined in the appended claims.
The control system according to the invention can be utilized e.g. in the combustion of waste material or other halogen-containing fuel. The combustion is arranged to take place in the combustion chamber in the first portion of the reactor and the resulting flue gases are then cooled quickly in the cooling chamber to minimize the amount of organic halogenized compounds. This is to minimize the "de novo" synthesis, i.e. the re-formation of dioxines, furans and other toxic 'chlorine compounds on the cooling surfaces. Toxic chlorine compounds such as dioxines and furans form from chlorine compounds especially easily in the temperature range of 250 - 400°C. The gases are therefore cooled quickly over this temperature range.
The invention can also be applied to cooling of flue gases of other metallurgical process, having gases in which chlorinated organic compounds can form during the cooling phase. The aim is especially to avoid the forming of so- called super-toxins, i.e. polychlorinated dioxins and furans.
Emissions are further decreased by the condensation of the compounds in question on the surface of the particulate bed material, caused by the cooling. When the process is running continuously, a 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 recycling a portion of the material circulating in the cooling chamber to the lower reactor, acting as the combustion chamber. The organic compounds condensated on the surface of the circulating material are combusted in the combustion chamber and the recycled material is cleaned. The cleaned circulating material is returned to the cooling chamber, where it replaces the contaminated material, thus reducing the concentration of detrimental materials in the cooling chamber. This is desirable e.g. on the standpoint of further treatment of the material withdrawn from the reactor.

Claims (16)

WE CLAIM :
1. A method of controlling the temperature in exothermic processes, arranged to take place in a particle suspension in a circulating fluidized bed reactor, the reactor comprising
- a fluidized bed reactor into which solid process feed material and gas are introduced, the gas being introduced through a grate arranged at the bottom of the fluidized bed reactor so that the solid material particles form a fast fluidized bed, a considerable portion of which flows with the gas as a particle suspension into the upper portion of the fluidized bed reactor and is withdrawn from the fluidized bed reactor via an outlet arranged at the top portion of the reactor,
- a particle separator, connected to the outlet, for separating solid material particles from the gases and
- a recycling conduit for recycling particles from the particle separator to the fluidized bed reactor for maintaining a circulating fluidized bed in the fluidized bed reactor, characterized in that
- the particle suspension, while flowing upwards in the fluidized bed reactor, is caused to flow through a venturi, thereby forming an upper fluidized bed in the fluidized bed reactor above the venturi, the upper fluidized bed having a common circulation of mass with the lower fluidized bed, situated under the venturi; - a separate mass circulation is additionally arranged in the upper fluidized bed by recycling a portion of the particles separated in the particle separator into the fluidized bed reactor above the venturi, while a second portion of the particles is recycled to the lower fluidized bed, situated under the venturi;
- the exothermic reactions in the fluidized bed reactor are mainly arranged to take place in the lower fluidized bed, i.e. in the main reaction chamber; - the particle suspension is cooled in the upper fluidized bed, i.e. in the cooling chamber, with heat transfer surfaces arranged therein and that
- the cooled particle suspension is directed from the upper fluidized bed into the particle separator.
2. A method as recited in claim 1, characterized in that sulphide-containing metal concentrate is roasted in the lower portion of the fluidized bed reactor, in the reaction chamber, and that the heat from the hot gases resulting from the reaction is recovered with heat transfer surfaces in the upper portion of the fluidized bed reactor, in the cooling chamber.
3. A method as recited in claim 1, characterized in that a portion of the cooled particles, separated in the particle separator, is recycled to the cooling chamber, the portion being sufficient for cooling the particle suspension, flowing from the reactor chamber, to a desired temperature before the suspension contacts the heat transfer surfaces.
4. A method as recited in claim 3, characterized in that the particle suspension flowing from the reaction chamber is cooled in the cooling chamber to < 550°C by mixing it with cooled particles separated in the particle separator.
5. A method as recited in claim 1, characterized in that a portion, sufficient for maintaining the desired temperature in the reaction chamber, of the particles separated in the particle separator, is recycled to the reaction chamber.
6. A method as recited in claim 5, characterized in that the temperature in the reaction chamber of the roasting reactor is maintained at 800 - 1000°C by recycling cooled particles, separated in the particle separator, to the reaction chamber.
7. A method as recited in claim 2, characterized in that the roasted product is recovered from particles flowing in the recycling conduit.
8. A method as recited in claim 1, characterized in that heat is recovered with heat transfer surfaces in the reaction chamber.
9. A method as recited in claim 1, characterized in that heat is recovered with heat transfer surfaces from the solid material flowing in the recycling conduit.
10. A method as recited in claim 1, characterized in that a gas velocity of 2 - 10 m/s is maintained in the reaction chamber.
11. A method as recited in claim 1, characterized in that solid fuel is combusted in the reaction chamber and that the temperature of both the upper and lower fluidized bed is controlled by recycling the cooled particles so as to be suitable for reduction of sulphur and nitrogen emissions.
12. A method as recited in claim 1, characterized in that waste material or other halogen-containing fuel is combusted in the lower portion of the fluidized bed reactor and that the flue gases resulting from the combustion are quickly cooled in the upper fluidized bed reactor to avoid forming of toxic compounds.
13. A system for controlling the temperature in exothermic reactions arranged to take place in a circulating fluidized bed reactor, the system comprising
- a fluidized bed reactor with a fast fluidized bed arranged therein, formed of solid material particles, the bed being fluidized with fluidizing gases introduced through the bottom of the f-luidized bed reactor so that a considerable portion of the solid material particles is conveyed as particle suspension with the gases from the lower portion of the fluidized bed reactor to the upper portion of the reactor and is withdrawn from the fluidized bed reactor via an outlet arranged at the top of the reactor,
- a particle separator, connected to the outlet at the top portion of the fluidized bed reactor, for separating the particles from the gases and
- a recycling conduit for recycling particles from the particle separator to the fluidized bed reactor, characterized in that - a throttle means (30) is arranged in the fluidized bed reactor for restraining the flow of particle suspension at the venturi when the particle suspension flows from the lower portion (26) of the fluidized bed reactor to the upper portion (28) thereof and for dividing the fluidized bed reactor into a lower and upper portion;
- a first recycling conduit (14, 36) is connected to the upper portion of the fluidized bed reactor for recycling solid material particles to the upper portion of the fluidized bed reactor; - a second recycling conduit (14, 38) is connected to the lower portion of the fluidized bed reactor for recycling solid material particles to the lower portion of the fluidized bed reactor and that
- a heat transfer surface (46) is arranged in the upper portion, i.e. cooling chamber, of the fluidized bed reactor for recovering heat from the fluidized bed in the upper portion.
14. An apparatus as recited in claim 13, characterized in that the particle separator is a cyclone (12).
15. An apparatus as recited in claim 13, characterized in that a heat transfer surface (44) is arranged in the lower portion (26), i.e. the reaction chamber, of the fluidized bed reactor for recovering heat from the fluidized bed.
16. An apparatus as recited in claim 13, characterized in that a heat transfer surface (48, 50) is arranged in the recycling conduit (14) for cooling the particles.
AU90439/91A 1990-12-21 1991-12-13 Method and apparatus for controlling temperature in a circulating fluidized bed reactor Ceased AU652204B2 (en)

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FI906347A FI89944C (en) 1990-12-21 1990-12-21 Method and apparatus for controlling the temperature of a reactor with circulating fluidized bed
PCT/FI1991/000384 WO1992011499A1 (en) 1990-12-21 1991-12-13 Method and apparatus for controlling temperature in a circulating fluidized bed reactor

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CA2095480C (en) * 1993-05-04 1995-02-14 Paulo Goes Koeberle Multistage turbulent circulating fluidized bed reactor
FI20010676A0 (en) * 2001-04-02 2001-04-02 Einco Oy CSC reactor
FR2937886B1 (en) * 2008-10-30 2011-05-20 Jean Xavier Morin FAST FLUIDIZED FLUIDIZED BED DEVICE WITH SATURATED FLOW OF CIRCULATING SOLIDS
CN101579601B (en) * 2009-06-12 2011-05-18 山西晋丰环保工程设计有限公司 Venturi ring efficient mass transfer layer absorption tower
PL2642199T3 (en) * 2012-03-20 2017-11-30 General Electric Technology Gmbh Circulating fluidized bed boiler
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FI89944B (en) 1993-08-31
WO1992011499A1 (en) 1992-07-09

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