FI54160C - FOERFARANDE FOER BEHANDLING AV MATERIAL I EN VIRVELBAEDDREAKTOR - Google Patents

Description

- - Jl, D, .... WHEN ULUTUSJ ULISHIS -, 4 - - ^ 11 UTLÄGG NI NGSSKRI FT 54160 (45) (51) K ».ik. '/ Int.ci. · D 21 C 11/12 B 01 J 8/24 P 23 D 19/00 FINLAND —FINLAND (21) P »exam application - Patenumöknlng 762695 (22) Hikemitpilvl - AnsSknlngidag 22.09.76 ^ (23) Alkuplivi - Giltlghttsdag 22.09.76 (41) Has become public - Bllvlt offentg 23/3/78

National Board of Patents and Registration of Finland Nihtivikslpanon and k «ut. | U.ka.sun date. - "

Patents and registration "'Ansökan utlagd och utl.skrlften publlcerad 3U. Uu. fo (32) (33) (31) Claim claimed privilege — Begird priorltet (71) A. Ahlström Osakeyhtiö, Noormarkku, Finland-Finland (FI) (72) Folke Engström, Karhunkatu lU F, U8600 Karhula, Jorma Juhani Nieminen, Linjurinkatu k B 12, 78200 Varkaus 20, Suomi-Finland (Fl) (5b) Method for treating substances in a fluidised bed reactor - Förfarande för behandling av material i en virvelbäddreaktor

The present invention relates to a process for treating substances, and in particular various sludges and waste liquors, in a fluidized bed reactor. The method is suitable for use, for example, in the drying, incineration, pyrolysis or chemical reactions of substances.

It is known that a fluidized bed reactor can be used for the above-mentioned purposes. In this case, the substance to be treated is fed to the reactor bed, where it comes into contact with the floating granular substance. As an example of such an application, reference is made to U.S. Patent No. 3,319,586, which discloses the incineration of waste sludges containing organic components. Because the the water content of the sludges after the mechanical dewatering treatment is still relatively high, so there are some problems with their incineration.

By mechanical treatment, for example, so much water can be removed from the municipal sludge that its dry matter content is about 20. If suitable chemicals, such as lime and ferric chloride, are added to the sludge, about k5 ° / o 'can be achieved. n dry matter content, 2,54160 where combustion in the fluidized bed reactor occurs almost autogenously.

If the dry matter content is lower, auxiliary fuel must be fed to the furnace to maintain combustion. Many industrial waste sludges can only be mechanically removed with water with a dry matter content of less than 20 ° fo. The incineration of all these sludges results in high operating costs, which increase as the water content of the sludge increases.

To improve the thermal economy of the combustion process, the heat of the flue gases can be used to pre-dry the sludge by either direct or indirect heat transfer. In the direct method, the flue gases come into direct contact with the sludge and, as a result, the exhaust gases contain odorous gases. Due to the large amounts of gas, the afterburning of odorous components causes significant additional costs. The indirect method requires large heat transfer surfaces, so equipment costs are high.

An exemplary method of pre-drying a slurry by contacting it with flue gases is disclosed in Canadian Patent Publication No. 524,796.

According to a commonly used method, the chemicals and heat from the sulphate pulp industry effluents are recovered by incineration in a steam boiler, whereby the organic constituents are combusted and the inorganic constituents are recovered by dissolving the melt obtained in water. The combustion of waste liquors takes place in those three stages: drying, reductive combustion and oxidative combustion. As a result, it is difficult to control the “different stages of the combustion process so that the desired result is achieved. For small pulp mills, the solution becomes too expensive. The steam boiler is also not completely safe to operate, as evidenced by several devastating boiler explosions.

Waste liquors have also been proposed for treatment in rotary kilns. U.S. Patent 3 · 787 · 283 discloses a method of recovering chemicals in which concentrated sodium-based waste liquor and reactive aluminum hydrate are mixed and pelletized by the addition of sodium aluminate ash. The pellets are fed to a rotary kiln where a temperature below the melting point of sodium aluminate is maintained.

A portion of the sodium aluminate ash formed in the reaction is dissolved and contacted with furnace flue gases containing sulfur dioxide to give a solution containing sodium sulfite, from which 3,54160 of precipitated sodium hydrate is separated by filtration. The remaining part of the formed sodium aluminate ash is mixed with the waste liquor during the formation of pellets.

However, there are several disadvantages to using a rotary kiln. It is an expensive and maintenance-intensive device. Its thermal economy is disadvantageous because a support fuel must be used to maintain the temperature required for the reaction. The heat transfer from the gas to the substance to be treated is known to be poor in rotating baths, so the furnace must be dimensioned large. To reduce dust losses, the material must be treated as a pellet, which - 'requires additional equipment both before and after swimming. Due to the pelletization, the dry matter content of the material fed to the furnace must also be high, which requires considerable operating costs.

Waste liquors have also been proposed to be incinerated in a fluidized bed reactor. As an example of such a solution, reference may be made to U.S. Patent Publication No. 3-635,790. Since the combustion temperature must be lower than the melting temperature of the chemicals, for example, in the case of sodium-based cooking chemicals at most about 750 ° C, combustion takes place in an area where it is difficult to maintain a stable combustion. The temperature can be limited by feeding the waste slurry with a low dry matter content to the furnace or by cooling the process with a large excess of air. In both cases, the oven becomes large and difficult to control.

In order to eliminate the above-mentioned drawbacks, it has been proposed that the material to be treated in the mixer is brought into contact with the hot material obtained from the fluidized bed before it is fed to the reactor bed. Such a solution is disclosed in German patent application 25 32 99 ^ · However, its disadvantages are e.g. the transport of circulating petimate material to and from the reactor and the associated control problems with varying amounts or moisture of material to be treated. In addition, wear of the bedding material and equipment causes problems. Since the thermal energy of the evaporation is taken from the bed, a corresponding amount of heat must also be introduced into the bed, i.e. combustion must take place in the bed, which must therefore be relatively large and the feed to the bed must be divided into several different lines.

The object of the invention is to provide a method which has several advantages over the prior art, as will be described in more detail below. 54160

The gases leaving the combustion chamber of the fluidized bed reactor contain finely divided material which can be separated, for example, in a cyclone separator. The separated material contains ash, fine-grained petima material and usually also useful chemicals. Its heat content can also be considerable.

According to the invention, the substance to be treated is contacted with solid particles separated from the gases leaving the fluidized bed reactor, which are most preferably mixed before the substance is fed to the reactor. In this context, chemical and / or thermal reactions may occur in the substance. From the vapors and gases which may be generated during the treatment, the useful constituents can be recovered using known techniques.

The main advantages of the invention are the good thermal economy and efficiency of the method. In addition, the equipment used to apply it requires less space than previously used equipment. With the method according to the invention, the substance fed to the reactor can be preheated and pre-dried by means of hot particles separated from the flue gases, whereby less steam is generated in the reactor and the amount of flue gas is reduced. By mixing a suitable amount of solid particles with the substance to be treated, its composition and consistency can be changed so that it can be easily fed to the reactor evenly distributed over the entire cross-section of the reactor. As the reactor load increases, the temperature or amount of particles separated from the exhaust gases increases. The operation of the reactor is thus easily adjustable. Depending on the velocity of the gas flowing through the reactor and its fluidized bed, its behavior is different. If the flow rate is high, the gas entrains so much fluid that no clear boundary is formed between the bed and the gas space. This also increases the amount of particles in the gases leaving the reactor.

The invention will now be described with reference to the accompanying drawings, in which Figure 1 shows an embodiment of the method, Figure 2 shows a second embodiment and Figure 3 shows a third embodiment.

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In Fig. 1, which shows a system for incinerating sludges, a fluidized bed reactor comprising an air cabinet 2, a grate 3 and a combustion chamber k is indicated by reference numeral 1. On top of the grate is a reactor bed The air required for fluidization and combustion is supplied to the air cabinet via a line 6 connected to it. The additional air required for combustion is supplied to the combustion chamber via lines 7, 8 and 9. The gases generated in the combustion and other chemical reactions are removed from the upper end of the reactor through an outlet duct 10, from which the flue gases flow to a dust separator 11, an air preheater 12 and a flue gas scrubber 13. Through line 15, bed material is added to the reactor in mixer 16.

In the dust separator, the solid particles of the exhaust gases are separated from the gases and passed to a mixer, where they come into contact with the slurry fed to it via line 17. The mixer has two screws that rotate in opposite directions and thus ensure efficient mixing of the slurry and hot particles with each other while conveying them to the other end of the mixer, from where the substances are passed through the feed line 18 to the reactor. The mixer preheats and dehydrates the slurry fed to the reactor, generating steam which is passed through line 19 to a dust separator 20 and further to condenser 21. Condensate is removed from the bottom, for example to a water treatment plant, and non-condensable gases are bad-smelling components. Some of the particles separated in the separator 11 are removed via line 22 to control the amount of material recycled.

When using the apparatus according to Fig. 1 for the gasification of moist organic substances, the wet fuel 17 is fed to a mixer 16, where it is mixed with a shaky stream of particles separated in a dust separator 11. The water evaporates and exits with any volatile combustible substances to a dust separator 20, where dust is separated from the gases. From here, the gases travel to the condenser, where the water vapor mainly condenses. The remaining gases are directed to the fluidized bed reactor 1. The dried fuel and the heat-generating particles are fed to a fluidized bed reactor where the fuel is partially combusted and the non-combustible part is passed mainly in gaseous form 10 to a cyclone separator 11 from where the gases are fed. Thus

. S

In the flue gases developed, the amount of inert gas is substantially lower than if the fuel had been fed directly into the wet fluidized bed because the water contained in the fuel has been removed before the actual gasification. If the fuel had been dried directly with hot gases, some of the fuel would have been removed with the drying gases. The fuel gas thus obtained is thus clearly better and produced by simple equipment.

Figure 2 shows a system for the artistic recovery of waste liquor chemicals from so-called soda ash, in which NaOH is used as the cooking chemical, in which sodium is recovered in the form of a NaCO 2 solution, from which a cooking solution is obtained by causticization.

In Fig. 2, reference numeral 2k denotes a fluidized bed reactor to which the air required for fluidization and combustion is fed via line 25. The waste liquor is fed via line 26 to the mixer 27, to which the alumina hydrate separated in the filter 28 is also fed, and via line 29 as reactive Al (OH) 2 as a replenishing chemical. Alumin hydrate, together with the sodium in the waste liquor, forms sodium aluminate compounds which are fed via line 30 as a slurry with a dry matter content of 30 to 70 to a mixer 31. · Some of the flue gas dust settles to a temperature of about 300 ° C and cools to the bottom of the boiler, from where it is passed via line Jk to the mixer 31 and some separates in the flue gas scrubber.

A portion of the sodium aluminate-containing dust separated in the waste heat boiler 32 is passed to solvent 39 · The aluminate suspension is fed from the solvent via line kO to scrubber 33 »whereby it is neutralized to a pH of about 8 by precipitation of carbon dioxide in flue gases. From the solvent, the suspension is passed through a ripper 41 where the aluminum hydrate crystallizes to a filter 28 where the dissolved sodium salt is separated from the aluminum hydrate. The second sodium solution is passed via line k2 to the broth preparation compartment and the aluminum hydrate via line k1 to the mixer 27.

Figure 3 shows a system for recovering soda broth chemicals in which sodium is recovered in the form of a NaOH solution.

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In Fig. 3, reference numeral 44 denotes a fluidized bed reactor to which preheated air is fed via line 45. The waste liquor is fed via line 46 to a mixer 47, to which the aluminum hydrate separated in the filter 48 is also fed, and via line 49 as reactive Al (OH) 2 as a replenishing chemical. The formed sodium aluminate broth is fed to the mixer 51 by means of line 50. · Part of the flue gases of the fluidized bed reactor, from the hot, sodium aluminate-containing dust separated in the dust separator 52, is also passed through line 53. The evaporator generated in the mixer is removed via line 54 and water vapor can be separated from it in a manner known per se, which is removed as condensate via line 55. Non-condensable gases are introduced into the reactor for combustion via line 56. The pre-dried slurry is fed from the mixer via line 57 to the reactor. The gases generated in the combustion and other chemical reactions are removed from the upper end of the reactor through an outlet duct 58, from which the flue gases flow to a dust separator 52, a waste heat boiler 59 and a flue gas scrubber 60.

A portion of the sodium aluminate-containing dust separated in the dust separator 52 is passed to a solvent 62 to which water is added via line 61. If the sodium aluminate is sparingly soluble, the solvent 62 acts as an autoclave at a pressure of about 2-4 MPa, corresponding to a dissolution temperature of 160-190 ° C. The steam used as heating medium in the autoclave is fed through line 63. The resulting suspension is passed to a precipitation tank 64, at which the impurities are separated at a temperature of about 90 ° C. The impurities as well as the aluminate liquor are fed via line 65 to a second precipitation tank 66 where the final separation takes place. Contaminants are removed through line 67 to filter 69, where contaminants are separated from the aluminate account liquor using wash water from line 71. · Contaminants are removed through line 72 and diluted aluminate liquor is fed to precipitation tank 66 via line 70. From the precipitation tank 66, most of the aluminate solution is returned to the precipitation tank 64 via line 68.

The aluminate liquor separated in the first precipitation tank 64 is fed through a conduit 73 to a cooler 74. The refrigerant inlet and outlet lines are 75 and 76. The aluminate solution cooled to about 50 ° C is passed to a ripening tank 77, where Al (OH) 2 crystallizes ^ * 6H 2 O -3> 6NaOH + 2A1 (.OH) 3

Na 2 O * Al 2 O 3 * 4H 2 O - ^ 2NaOH + 2Al (0H) 3 8 54160

Filter 48 separates the doped Al (oh) 2, which is washed with water from line 78 and fed through line 80 to mixer 47. Sodium chemicals are removed via line 79 for reuse in cooking solution.

The invention is further illustrated by a few examples.

Example 1.

Municipal sludge incineration Sludge dry matter content $ 20

Ash content 30% calculated on the dry matter Calorimetric calorific value 16 Mj / kg dry matter Preheated air temperature 500 ° C

The slurry was mixed with dust separated from flue gases at a temperature of 800 ° C and the dried slurry was fed to the reactor at a temperature of 100 ° C.

Amount of dust mixed with sludge kg / kgKA 13 »7

Energy demand Kj / kgKA 1440

Excess air 30

Flue gas amount kg / kgKA 8.75

Flue gas composition: - 02 io 4.5 - CO2 "12.0 - N2" 72.7 - H2O "10.8

Energy input: - additional energy $ 6.5 _ - sludge "73.5 - air" 20.0

Energy output: - flue gases from the furnace $ 45.9 - steam from the mixer "47.7 - flue gas ash" 1.2 - heat loss "5.2

As can be seen from the example, in the process according to the invention, in which water is removed from the slurry before it is fed to the reactor, combustion occurs almost autogenously.

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Claims (8)

9 54160 Example 2 Combustion of soda broth effluent and chemical recovery 1.24 kg / s of effluent with a dry matter content of about 45% is fed to a mixer 27 (Fig. 2) to which 0.2 kg / s of aluminum hydrate is fed. The alumina broth mixture is fed to a mixer 31, to which 5.8 kg / s of sodium aluminate dust is fed from the waste heat boiler. Approximately 0.53 kg / s of water evaporates and the dried aluminum waste liquor with recyclable cyclone dust is fed to the vortex bed reactor. Combustion takes place at a temperature of about 1000 ° C. Sodium aluminum compounds react to form sodium aluminates, which are largely eliminated with the flue gases. Approximately 1.8 kg / s of steam is generated in the waste heat boiler. ~ Part of the sodium aluminate = 0.2 kg / s is passed to solvent 39, where the neutralization takes place by means of flue gases, whereby a Na 2 CO 3 solution is formed. In the maturing tank 41, crystallization of Al (OH) 2 occurs, after which the aluminum hydrate is separated in the filter 28, and the 0.22 kg / s sodium carbonate solution formed is used in the preparation of the cooking solution. 0.8 kg / s of water is introduced into the venturi scrubber. A method for treating water vapor and / or other gases at elevated temperature in a fluidized bed reactor, characterized in that the substance to be treated is contacted with solid particles separated from the flue gases of the fluidized bed reactor before it is fed to the fluidized bed reactor. Method according to Claim 1, characterized in that the particles separated from the flue gases are mixed with the substance to be treated. Method according to Claim 1 or 2, characterized in that at least some of the solid particles in the flue gases are cooled before they are brought into contact with the substance to be treated. Method according to Claim 1, 2 or 3, characterized in that the particles separated from the flue gases are used to dry and heat the substance to be treated. Process according to Claim 1, 2 or 3, characterized in that the thermal decomposition or pyrolysis of the substance to be treated is effected by means of particles separated from the flue gases. Process according to Claim 1, 2 or 3, characterized in that the particles separated from the flue gases and the substance to be treated are chemically reacted with each other before the substance is fed to the fluidized bed reactor. Process according to Claim 4, 5 or 6, characterized in that the vapors and / or gases generated are separated from the substance before it is fed to the fluidized-bed reactor. Process according to one of the preceding claims, characterized in that the substance to be treated is a sodium-based pulp broth effluent containing aluminum hydrate and that solid particles containing sodium aluminate separated from the flue gases of the fluidized bed reactor are mixed with the effluent and fed to a fluidized bed furnace.