Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
  • B01D53/06—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds
  • B01D53/10—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds with dispersed adsorbents
  • B01D53/12—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds with dispersed adsorbents according to the "fluidised technique"
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/48—Sulfur compounds
  • B01D53/50—Sulfur oxides
  • B01D53/508—Sulfur oxides by treating the gases with solids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/68—Halogens or halogen compounds
  • B01D53/685—Halogens or halogen compounds by treating the gases with solids
• • 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

Definitions

• the invention relates to a method for cooling and cleaning flue gases according to the preamble of claim 1.
• Waste incineration plants now have the function of waste treatment.
• the waste is largely mineralized using the thermal energy contained in the waste.
• hydrochloric acid HC1 and CI2 from the incineration of waste containing PVC
• sulfur dioxide SO2 from the incineration of rubber
• sewage sludge paper and dyes.
• Coal very large amounts of HCl.
• a typical waste incineration plant is constructed as follows: The waste materials are burned in a furnace with an afterburner. The flue gases produced during combustion flow through the waste heat boiler downstream of the furnace for heat recovery and then enter the downstream flue gas cleaning devices, where the pollutants are separated at low temperatures.
• the most common method used for flue gas cleaning is "wet processes", i.e. the treatment of the flue gases in a single or multi-stage wet scrubber. In some cases “dry processes” are also used, in which the gaseous pollutants are sorbed on fine-grained, solid sorbents. For this purpose, these solids are brought into contact with the flue gas stream in a suitable manner.
• the dry separation of SO2 and HC1 is known.
• the substances contained in natural limestone are calcium carbonate CaC-03 and dolomite CaMg (003) 2, as well as calcium oxide CaO and calcium hydroxide Ca (OH> 2) and the analogous alkaline earth metal compounds (e.g. MgO, Mg (0H) 2 etc.).
• the products of the separation are CaS04 and CaCl2.
• Typical concentrations of the pollutants in the unpurified flue gas are 1000 mg / Nm 3 HCl and 300 mg / Nm 3 SO2.
• a typical flue gas composition for domestic waste incineration is 70% 2, 11% CO2, 7 % O2 and 12% H2O.
• the equilibrium temperature of the reaction of HCl with the sorbents at 5 to 20% water content in the flue gases is between 570 ° C and 540 ° C. Adequate separation is therefore no longer possible at higher temperatures.
• the deposition of SO2 takes place at temperatures below 600 ° C with an insufficient reaction rate.
• DE 3023480 discloses a process for hot desulfurization of fuel or reducing gases with lime or dolomite or the corresponding fired products (desulfurizing agent), in which the fuel or reducing gases are used as fluidizing gas in a fluidized bed reactor which contains the desulfurizing agents , initiates.
• a temperature of 700 ° C. to 1100 ° C. and a stoichiometric ratio of 1.2 to 2.0 (calculated as Ca: S) are set in the fluidized bed reactor.
• the solids discharged from the fluidized bed reactor with the flue gases are separated in a dust separator and returned to the fluidized bed reactor, so that a circulating fluidized bed is created.
• This method has the disadvantage that, at the selected temperature and the selected stoichiometric ratio, only an amount of HC1 which is insufficient for the incineration of household waste could be separated.
• Concentrations of 1000 mg / Nm 3 HCl and 300 mg / Nm 3 SO2 in the flue gas correspond to the stoichiometric ratio of 2.0 calculated as Ca: S and a stoichiometric ratio of 0.5 calculated as Ca: (S + 0.5C1 ), ie there would be far too little sorbent available for the combined separation of SO2 and HCl.
• the unfavorable equilibrium position of the sorption reaction which shifts to the side of the gaseous reactant HCl at higher temperatures, prevents sufficient HCl separation.
• the equilibrium concentration of HCl in the gas phase at 700 ° C and 5% water content is already 450 mg / Nm 3 , ie only an insignificant amount of HCl is separated.
• DE 33 07 848 discloses a process for the post-combustion and purification of process exhaust gases containing combustible constituents in metallurgy, in which the process exhaust gas and the oxygen-containing gases required for the combustion are introduced separately into the fluidized bed reactor of a circulating fluidized bed, in which the process gas simultaneously burns and is cleaned.
• a temperature of 700 ° C. to 1100 ° C. and a stoichiometric ratio of 1.2 to 3.0 (calculated as Ca: S) is set in the fluidized bed reactor.
• the solids discharged from the fluidized bed reactor with the flue gases are separated in a dust separator and returned to the fluidized bed reactor, so that a circulating fluidized bed is created.
• This method also has the disadvantage that far too little HCl is deposited at the selected temperature and the selected stoichiometric ratio.
• WO 88/08 741 it is known to cool hot process exhaust gases in a circulating fluidized bed, the process gas being cooled in a mixing chamber with recirculated cooled solid and recirculated cooled process gas.
• the gas recirculation increases the amount of flue gas, which is disadvantageous because it means an increase in the volume of the downstream apparatus.
• An increase in the amount of flue gas also means a reduction in the amount of heat that can be recovered in the boiler, since the exhaust air heat loss increases. This reduces the boiler efficiency.
• EP-A-0 328 874 it is known to gradually cool exhaust gases from waste incineration in a plurality of exhaust gas coolers arranged one behind the other and designed as tube bundle heat exchangers by indirect heat transfer and clean at the same time. In each of the at least three stages, a partial amount of sorbent is introduced into the exhaust gas stream which is substoichiometric in relation to the amount of pollutant present in the exhaust gas.
• the present invention is based on the object of proposing a method of the type mentioned at the outset which enables both optimal flue gas cleaning and more efficient flue gas cooling, at the same time largely eliminating the risk of corrosion on heat transfer surfaces.
• the advantages achieved by the invention are to be seen in particular in the fact that the two-stage gas purification means that the first stage takes place in a circulating fluidized bed and the predetermined temperature control ensures optimal separation of both SO2 and HCl with simultaneous optimal utilization of the sorbents is achieved.
• the combination of dry gas cleaning and fluidized bed boiler also enables very efficient heat extraction. As a result, the construction volume of the boiler can be greatly reduced compared to a conventional system.
• the walls are designed as heat transfer surfaces and possibly additional heat transfer surfaces are arranged directly in the fluidized bed.
• the design as a circulating fluidized bed enables the corrosion problems to be solved.
• the errosive effect of the gas-solid flow prevents the formation of corrosive deposits on the heat transfer surfaces in the fluidized bed.
• sticky fly dusts introduced into the fluidized bed reactor already combine with the circulating solid before they come into contact with the heat transfer surfaces.
• part of the heat transfer surface of the first stage is removed from the flue gas path into an external fluid bed cooler.
• the solid particles serve as an intermediate medium for heat transfer from the fluidized bed reactor to the fluid bed cooler: A part of the circulating solid is passed into the fluid bed cooler.
• the cooled solid matter from the fluid bed cooler is conveyed back into the fluidized bed reactor, where it absorbs heat from the flue gas stream.
• the heat transfer surfaces most affected by corrosion are now preferably arranged in the fluidized bed cooler, ie outside the flue gas path. These are the hottest heat transfer surfaces, i.e.
• FIG. 1 shows a flow diagram of a first method variant
• FIG. 3 shows a flow diagram of a third method variant.
• hot flue gases are introduced into a fluidized bed reactor 6 (indicated by an arrow 5) from a furnace of a plant for the thermal treatment of waste, not shown in the drawing, as fluidizing gases.
• the walls of the fluidized bed reactor 6 are designed as heat transfer surfaces; possibly further heat transfer surfaces can be arranged directly in the fluidized bed. These cooling surfaces are symbolically designated 7 overall in FIG. 1.
• the fluidized bed reactor 6 is operated at such a high gas velocity that at least some of the solid particles are discharged from the fluidized bed reactor 6 together with the flue gas stream. Arrived via a line 9 in a dust separator 10, which can be designed, for example, as a cyclone, a dust filter or as an electrostatic filter, the solid particles are separated from the flue gas stream.
• Part of the solids is in the fluidized bed reactor 6 returned so that a circulating fluidized bed is formed; the solids can be returned via a line 11 directly or at least partially via line 12, an external fluid bed cooler 15 and a line 14 into the fluidized bed reactor 6.
• the part of the solids passed over the fluidized bed cooler 15 is cooled in a stationary fluidized bed (fluidized bed) by direct or indirect heat transfer; corresponding heat transfer surfaces are symbolically designated 16.
• a fluidizing gas required for the operation of the fluidized bed cooler 15 is fed to the fluidized bed cooler 15 via a line 17 and withdrawn above the fluidized bed for further use (line 18).
• a first stage of the method according to the invention takes place in the fluidized bed reactor 6 and the dust separator 10 and fluid bed cooler 15 assigned to it, which is denoted by 1 in the fluidized flow diagram according to FIG.
• Fine-grained dry sorbents are introduced into the fluidized bed reactor 6 via a line 8 and mixed with the solid particles of the fluidized bed.
• the circulating fluidized bed of the first stage 1 is characterized by very good gas-solid mixing.
• the recirculated solid causes a very homogeneous temperature distribution in the entire fluidized bed reactor 6. These conditions create optimal conditions for good SO 2 separation, which is carried out at a temperature above 600 ° C.
• the first stage is preferably operated at a temperature between 600 ° C. and 1200 ° C.
• the first stage 1 is operated with a stochiometric D ratio of at least 1.0 calculated as Ca: (S + 0.5Cl).
• S + 0.5Cl a stochiometric D ratio of at least 3.9 calculated as Ca: S, ie in a large excess of sorbent based on the mainly occurring in this stage S ⁇ 2 ⁇ deposition. This enables excellent S ⁇ 2 ⁇ deposition.
• the flue gases leaving the dust separator 10 are introduced into a second stage 2a of the method by being fed via line 21 to a second fluidized bed reactor 20 as fluidization gases, where HCl separation and further cooling of the flue gases take place.
• the fluidized bed reactor 20 is equipped with heat transfer or cooling surfaces 22, the walls again being designed as heat transfer surfaces or additional heat transfer surfaces being arranged directly in the fluidized bed.
• the fluidized bed reactor 20 is also operated at such a high gas velocity that at least some of the solid particles together with the flue gases are discharged from the fluidized bed reactor 20 and fed to a dust separator 24 via a line 23. There, the solid is separated from the gas stream and recirculated into the fluidized bed reactor 20 via a line 25. Basically, there is also the possibility to use an external fluid bed cooler.
• a smaller part of the solid separated in the dust separator 10 of the first stage 1 is not recirculated, but is fed via a line 19 to the fluidized bed reactor 20 of the second stage 2a. With this solid, a large proportion of unused is also obtained Sorbent from the first stage 1 to the second stage 2a.
• the sorbent requirement of the second stage 2a is covered in this way, since the first stage is operated with a large excess in terms of SO2 separation.
• the circulating fluidized bed of the second stage 2a creates good conditions for the HCl separation with the very good gas-solid mixing and long residence times of the sorbents. This stage is operated at temperatures below 600 ° C, so that sufficient separation of HCl is guaranteed. Since no solids from the second stage 2a can get back to the first stage 1, the risk is also eliminated that HCl which has already been deposited is released again as a result of the reversible HCl sorption.
• the cleaned and cooled flue gases are fed via line 26 to a conventional boiler (not shown in the drawing), in which they are cooled to the desired temperature (preferably about 200 ° C.) with heat recovery, before they reach a chimney (also not shown) be fed. If there is sufficient cooling in the second stage, the conventional boiler can be dispensed with at all.
• the first stage 1 of the method is carried out in the same way as already described.
• the known and constant elements of the flow diagram from FIG. 1 are designated in FIG. 2 with the same reference numerals.
• the fluidized bed reactor 20 is expanded by an external fluid bed cooler 27, in which at least part of the solid separated in the dust separator 24 and fed via a line 28 is cooled. Over a Line 29 is then returned to part of the cooled solid in the fluidized bed reactor 20.
• a fluidizing gas required for the operation of the fluidized bed cooler 27 is fed to the fluidized bed cooler 27 via a line 41 and withdrawn again via a line 42 above the fluidized bed.
• the additional cooling surfaces in the fluidized bed can be dispensed with, since the solid cooled in the fluidized bed cooler 27 absorbs the heat from the still hot flue gases from the first stage 1 and provides cooling.
• the dust separator 24 is followed by a preferably multi-stage floating gas cooler 30 which has a plurality of dust separator stages 31, 32, 33.
• the individual dust separator stages 31, 32, 33 can be cyclones, dust filters, electrostatic filters, etc. act; in the embodiment shown in Fig. 2, for the last dust separator stage 33 e.g. see an electrostatic filter.
• the flue gases flow from the dust separator 24 via a line 35 to the first dust separator stage 31; the further connecting lines between the dust separator stages 31, 32 and 32, 33 are denoted by 36, 37.
• a portion of the solid cooled in the fluidized bed cooler 27 is removed from the fluidized bed cooler 27 and introduced into the flue gas stream via a line 38 immediately before the last dust separator stage 33.
• the the solid particles that cool the flue gases are entrained by the flue gas flow and conveyed via line 37 into the dust separator stage 33, separated from the flue gases there and introduced into line 36, where they are again carried along by the flue gas flow and conveyed to the penultimate dust separator stage 32. Separated there, they in turn pass with the flue gas stream via line 35 into the dust separator stage 31, from where they are led back via line 39 into the fluidized bed reactor 20.
• the second fluidized bed reactor 20 known from FIGS. 1 and 2 is omitted.
• a fluidized bed cooler 27c and a floating gas heat exchanger 30c are present.
• the floating gas heat exchanger 30c is again preferably designed in several stages.
• three dust separator stages 31, 32, 33 are shown analogously to FIG. 2; however, the number and design of the individual stages can also be freely selected as required.
• the dust separator 10 of the first stage 1 can be designed such that the proportion of sorbents discharged from the first stage 1 with the flue gases via the line 21 is sufficient for the HCl separation in the second stage 2c.
• Another possibility is to transfer part of the solid separated in the dust separator 10, including the unused sorbent, to the fluid bed cooler 27c 3 (this solid feed is shown in dashed lines in FIG. 3 and designated 43). Also in the suspended gas heat exchanger 30c according to FIG.
• the flue gas velocity in line 21 also ensures that no solid particles get back into the first stage 1, so that HCl that has already been separated cannot be released again in this variant.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Analytical Chemistry (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• General Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Environmental & Geological Engineering (AREA)
• Dispersion Chemistry (AREA)
• Organic Chemistry (AREA)
• Combustion & Propulsion (AREA)
• Treating Waste Gases (AREA)

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• 1995
  • 1995-01-10 CH CH00054/95A patent/CH689633A5/de not_active IP Right Cessation
• 1996
  • 1996-01-08 US US08/702,552 patent/US5878677A/en not_active Expired - Fee Related
  • 1996-01-08 PL PL96316169A patent/PL316169A1/xx unknown
  • 1996-01-08 WO PCT/CH1996/000008 patent/WO1996021504A1/de not_active Application Discontinuation
  • 1996-01-08 CZ CZ962593A patent/CZ259396A3/cs unknown
  • 1996-01-08 JP JP8521349A patent/JP3009926B2/ja not_active Expired - Fee Related
  • 1996-01-08 EP EP96900075A patent/EP0749349A1/de not_active Withdrawn
  • 1996-01-08 CA CA002184087A patent/CA2184087A1/en not_active Abandoned
  • 1996-09-09 FI FI963527A patent/FI963527A/fi unknown
  • 1996-09-09 NO NO963774A patent/NO963774L/no unknown

Non-Patent Citations (1)

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