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
  • B01D53/34—Chemical or biological purification of waste gases
• • 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
  • B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C1/00—Ammonia; Compounds thereof
  • C01C1/16—Halides of ammonium
  • C01C1/164—Ammonium chloride
• • 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
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency
  • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Definitions

• This invention relates to the effective and efficient removal of chloride values from desulfurization (FGD) systems, and is more particularly concerned with limiting the chloride content in the FGD system to prevent the known adverse impact on the system performance.
• FGD flue gas desulfurization
• chloride can accumulate to levels which cause general corrosion of process equipment and piping, or, if the designers anticipate high chloride levels, equipment must be constructed of expensive alloys to prevent such corro ⁇ sion.
• the solid waste produced is converted entirely to calcium sulfate dihydrate (gypsum) and sold for the manufacture of wallboard.
• gypsum calcium sulfate dihydrate
• a blowdown stream is required to purge chloride from the system.
• a purge stream contains expensive sodium-containing reagent.
• special process equipment is installed upstream of the FGD sys ⁇ tem to remove HC1 by aqueous scrubbing.
• Bradley U.S. 1,291,745 uses ammonia for treating gas from a smelter in connection with an electric precipitator.
• the ammonia is used to react with the sulfur dioxide in the smelter fume.
• the ammonia is converted into ammonium bisulfite, then into normal ammonium sulfite, and finally into sulfate by atmos ⁇ pheric oxidation.
• Williams U.S. 2,356,717 is also concerned with elec ⁇ tric precipitation and adds ammonia or ammonia-yielding com ⁇ pounds' to the gases or vapors from a catalytic petroleum crack ⁇ ing operation to increase the efficiency of the electric preci- pitator.
• the gas contains suspended particles and is at a tem ⁇ perature of 400-450°F.
• Humbert U.S. 3,523,407 has a similar objective and adds ammonia and water to a particle-laden gas stream. Optimum precipitation is said to occur when ammonia is added at the rate of 10 to 20 parts per million parts of gas and water is added at the rate of 4-8 gallons per 100,000 cubic feet of gas and the gas temperature is above 400°F.
• Russell U.S. 3,956,532 discloses the use of ammonia to treat a gas stream containing metal chlorides such as stannic chloride, TiCl4, VOCI3, and methyltricholorosilane, used in the coating of glass, all at a temperature ranging from 70° to 350°F «
• metal chlorides such as stannic chloride, TiCl4, VOCI3, and methyltricholorosilane
• Japanese publications 147137/80 and 78619/81 discuss the removal of HC1 from incinerator effluents in a system directed to the removal of nitrogen>oxides but no conditions regarding HC1 removal are disclosed except that a table in the latter Japanese publication shows temperatures ranging from 235°F (113°C) to 392°F (200°C) for HC1 removal, the best removal apparently being at 235°F with an NH3/HCI ratio of 2:1.
• Japanese publication 52-054276 proposes the treat ⁇ ment of PVC-containing wastes by introducing gaseous ammonia into the smoke resulting from the combustion of PVC-containing wastes when at temperatures of 500°C to form NH4CI. Subsequently the waste smoke is cooled to 250°C to collect the NH4CI formed.
• Japanese publication 58-045721 describes a method of adding ammonia to a waste combustion gas containing NO x , SO x , and HC1 to convert the NO x to 2 and H2O, the equivalent amount of ammonia added being 5-12 times as much as that of the NO x in the gas.
• Reaction with HC1 or SO x in the gas obtains a reaction product which is then contacted with- water to absorb the product from the gas and to obtain an aqueous solution of the product.
• An alkali or alkaline earth metal compound is added to the aqueous solution to generate ammonia which is recycled to the waste combustion gas.
• Japanese publication 58-174222 shows, in the purifi ⁇ cation of combustion waste gas containing dust and SO3, etc., e.g., a discharge from a coal-fired boiler, the improvement of passing the waste gas through a first dust collector to remove dust, thereafter injecting ammonia into the waste gas at an appropriate temperature, e.g., 130°-180°C, to form a reaction product, collecting the reaction product in a secondary dust collector, and supplying the collected reaction product to a furnace from which the waste gas to be treated is discharged.
• Russian Patent No. 590005 of January 31, 1978 in the name of V. Baryshev, discloses the removal of oxides of sulfur and nitrogen and of HC1 from flue gases produced by burning sul ⁇ fur-containing fuels.
• the flue gases are first cooled to 150-200°C and then treated with gaseous ammonia in the amount of 1.6 to 5 weight percent in relation to the weight of fuel burned. Deposition of ammonium salts is said to be prevented in the Russian process.
• the example shows a flue gas treated with 0.3% ammonia. No salt deposits were formed.
• Ammonia may be injected as an aqueous spray or mist or as a gas in an amount twice as great as needed stoichiometrically to react with any sulfur trioxide and any sulfuric acid present and may also be in a further amount to react with at least some of the chloride (Cl ⁇ ) present.
• the injection of the aqueous stream from the FGD system controls the buildup of dissolved chloride in the FGD system.
• the aqueous fraction of the stream so injected as an atomized mist will vaporize, leaving behind as*jdried particles the dissolved solids, including chlorides, which were contained in this stream.
• Ammonia injection must occur at the air pre ⁇ heater exit, typically at 400°F or less, e.g., at 250-400°F. Injection upstream of the preheater will cause the preheater to plug with ammonium sulfate salts and eventually to corrode.
• Ammonia may be added in an amount above that amount required to react effectively with sulfur trioxide and sulfuric acid to achieve a reduction in the chloride concentration in the FGD system streams by removing at least some HC1 from the flue gas as ammonium chloride before the flue gas enters the FGD system, upon injection of the aqueous stream from the FGD system the flue gas is cooled to 180°F to 240°F, preferably to about 210°F.
• the ammonia is added either before or during the second cooling step.
• the ammonia must be added before the particulate removal and desulfurization steps.
• the second cooling is brought about by the above-mentioned injection of the aqueous stream from the FGD
• the quantity of the FGD stream is selected so that, as mentioned, the aqueous fraction of the stream in atomized form will completely vaporize, as it cools down the flue gas to the desired temperature, leaving behind as dried particles any * dissolved solids, including chloride, which were contained in this stream.
• Solid particles consisting of the dissolved chloride which remains after the aqueous stream is vaporized, and the reaction product ammonium chloride resulting from the gas phase reaction of ammonia and HC1, are subsequently removed in the particulate collection device which may be either an electro- static precipitator (ESP) or a fabric filter. Therefore, the injection of the ammonia and the aqueous stream must occur before the particulate collection device. In this way the chloride is removed from the system along with any fly ash solids collected in the particulate collection device.
• ESP electro- static precipitator
• the present invention utilizes, in combination, the addition of ammonia and the injection of an aqueous stream from the FGD system ahead of the particulate collection device to speci ⁇ fically remove chlorides from the FGD system.
• ammonia must be added to react with all sulfur trixoxide or sulfuric acid. This prevents damage of ductwork due to condensation of the corrosive sulfuric acid compound on the flue gas duct walls after the aqueous FGD system stream is injected.
• additional ammonia may be added to react with at least some of the HCl in the flue gas to accomplish an even lower chloride concentration in the FGD system as long as the flue gas temperature is lowered to 180°F to 240°F by the injection of the aqueous stream from the FGD system.
• This invention allows the practical and economical removal of HCl from a flue gas upstream of an aqueous-based FGD system.
• a particulate control device e.g. ESP
• HCl removal is accomplished through the injection of an aqueous stream from the wet scrubber system into the hot flue gas stream ahead of the particulate control device.
• the aqueous phase of the stream is evaporated by the hot gas, leaving behind the dissolved species which are made up partially of various chloride salts such as calcium chloride, magnesium chloride, and sodium chloride, as well as ammonium chloride.
• the aqueous stream would most typically come from the solids dewatering area of the FGD system such as the overflow stream from the thickener or other primary solid/liquid separation device or the filtrate or centrate stream from the final dewatering step.
• Ammonia must be added prior to or with the aqueous stream injection point to react with all sulfur trioxide or sulfuric acid present in the flue gas, but not upstream of the boiler air preheater. This must be done to prevent the conden ⁇ sation of sulfuric acid on the flue gas ductwork after the aqueous stream is injected and the flue gas temperature lowered by the evaporation of the water in the aqueous stream. The reduction in temperature results in the condensation of sulfuric acid. Without the addition of ammonia, significant corrosion of the ductwork would be expected causing severe damage.
• the solid NH4CI formed by this reaction may precipi ⁇ tate on fly ash particles or it may nucleate to form NH4CI crys ⁇ tals. In either case, the NH4CI formed will be collected in the particulate control device and is thus prevented from entering the FGD system.
• the process of the invention avoids the prob- lems associated with the presence of undesired amounts of chlorides in the FGD system.
• the aqueous stream from the FGD system is atomized into very fine droplets. This is an important feature of the invention. It prevents wetting and corrosion of the flue gas duct where the water is injected, facilitates temperature reduction and ensures optimum operation.
• the preferred atomiza- tion devices are two fluid-type spray nozzles in which air or some other gas (e.g., steam, compressed nitrogen, and the like) is used to cause the water to form fine droplets, or rotary-type atomizers in which a rapidly-rotating disc is used to effect the same formation of fine droplets. Water mists in other environ ⁇ ments are known, but such mists are not concerned with desulfuri- zation and chloride removal.
• Polyhala 2,740,693 shows spraying hot flue gases with a fine mist of water without pre- cooling for the purpose of removing insoluble gases such as nitrogen in a process for providing a source of nitrogen for the manufacture of synthetic nitrogen by the Haber process.
• ammonium bisulfate is a very corrosive species and would severely damage this equipment.
• Ammonium sulfate does not possess corrosive characteristics to this equipment, however. For example, for a sulfur trioxide concentration of 15 ppmv in the flue gas, at least 30 ppmv of ammonia must be added to the flue gas to react with the sulfur trioxide to insure that no ammonium bisulfate is formed.
• the reaction between ammonia and HCl in the flue gas is enhanced as the temperature is lowered.
• cooling the flue gas to a temperature of about 210° F. is optimum. Therefore, the rate of addition of the aqueous stream must be closely regulated to achieve a constant tempera ⁇ ture of no higher than 240 F and preferably 210° F. while ensuring complete vaporization of the aqueous fraction of the stream.
• the point of ammonia addition is also important.
• the ammonia is added either upstream of the point where the aqueous stream from the FGD system is added, and after the flue gas exits the air preheater, or it is injected at the point the cooling water is injected, either separately or in solution with the aqueous stream.
• the preferred point is upstream of the point at which the aqueous stream is added.
• flue gas in line 10 from a coal-fired boiler 12 typically is cooled to between 250°F. to 400°F in a combustion air preheater 14 by heat-exchange.
• Ammonia in line 16 is injected at the air heater exit at a rate to provide at least twice the the amount, on a molar basis, of the sulfur trioxide and H2SO4 in the flue-gas stream being treated.
• the ammonia injection rate is controlled on the basis of the load of the boiler.
• clear liquor in line 18 from the FGD system 20 is atomized at 22 into the flue gas using two-fluid type nozzles (not shown) and compressed air from line 23.
• the water-injection rate is adjusted so that the water is completely evaporated by the flue gas and the desired chloride removal rate from the FGD system is maintained, the contained chloride com ⁇ pounds depositing as the water evaporates. Cooling of the flue gas results in precipitation of solid ammonium chloride which, along with the deposited compounds from the FGD stream, are separated in solid form from the flue gas in separator 24, which may be an electrostatic precipitator (ESP), fabric filter, or the like, subsequently removed through line 26, while the flue gas passes via lines 28 to the FGD system 20.
• separator 24 may be an electrostatic precipitator (ESP), fabric filter, or the like
• ammonia is injected after initial cooling of the gas, which is effected by passage through the air preheater in the embodiment illustrated, but it will be under ⁇ stood from the foregoing description that standard items of equipment can be used for cooling, solids removal, and the like, such as the equipment described and used in the above-mentioned prior art. Similarly, various changes and modifications in the invention may be made without departing from the scope of the appended claims.

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• 1988
  • 1988-03-18 WO PCT/US1988/000897 patent/WO1988007022A1/en not_active Application Discontinuation
  • 1988-03-18 AU AU16846/88A patent/AU1684688A/en not_active Abandoned
  • 1988-03-18 EP EP19880904020 patent/EP0305512A4/de not_active Withdrawn
  • 1988-11-10 KR KR1019880701439A patent/KR890700390A/ko not_active Application Discontinuation
  • 1988-11-16 FI FI885299A patent/FI885299A0/fi not_active Application Discontinuation

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