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
  • 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
  • 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
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/81—Solid phase processes

Definitions

• This invention relates to a method and a device for separating gaseous pollutants, such as sulphur dioxide and hydrogen chloride, from flue gases generated upon the combustion of fossil fuel, such as coal, in an atmospheric or pressurised fluidised bed in the temperature range of 700-900°C.
• gaseous pollutants such as sulphur dioxide and hydrogen chloride
• An absorbent containing burnt lime and/or substances that, in this temperature range, are converted to burnt lime is added in excess to the bed in order to react with these gaseous pollutants in the form of sulphur dioxide and convert them to separable, particulate pollutants.
• the particles entrained by the flue gases from the bed are hereby separated from the gases and then recycled to the bed.
• Certain pollutants such as nitrogen oxides, can be resolved into harmless substances, such as nitrogen gas and water vapour, by a catalytic process in which ammonia is added as reducing agent. These pollutants may also be reduced to a certain extent by optimising the combustion process, thereby to prevent or render more difficult their formation.
• sulphur-oxide compounds chiefly consist of sulphur dioxide, they will in the following be referred to as sulphur dioxide.
• the absorbent is added in the hearthcombustion chamber or in a special flue-gas-cleaning system.
• FBC and PFBC here refer to furnaces of the type atmos ⁇ pheric or pressurised fluidised bed.
• limestone in the form of a finely-ground or slightly coarser powder is usually added along with the coal already in the hearthcombustion chamber in order to bind the pollutants formed upon the combustion of coal, especially sulphur dioxide, hence preventing or reducing the discharge of these pollutants.
• sulphur is in this manner bound as sulphate in accordance with the reaction
• thermodynamics provide much poorer conditions for binding chlorine in the form of calcium chloride in the hearthcombustion chamber, since the calcium chloride formed at the temperatures (700-900°C) prevailing in the hearth is not stable but disintegrates in the presence of water vapour in accordance with the reaction
• coal has a chlorine content in the range of 0.05-0.2% by weight, corresponding to a discharge of 50-200 mg of HCl/Nm 3 of flue gas, which often exceeds current emission standards. In Germany, for instance, there is a maximum limit of 100 mg of HCl/Nm 3 of flue gas for plants having a thermal effect exceeding 300 MW.
• DE 35 36 899 discloses a method for separating first sulphur dioxide and then hydrogen chloride from the flue gases generated upon the combustion of coal in an atmospheric or pressurised fluidised bed (Wirbel Anlagenung).
• sulphur dioxide is first separated by the addition of an additive, such as limestone, in a reaction channel arranged downstream from a first dust separator.
• hydrogen chloride is separated by the addition of e.g. fresh limestone, the flue gases passing through a heat-recovery stage in which the additive reacts with hydrogen chloride.
• the hereby formed reaction products and the unreacted additive are then separated in a subsequent dust separator.
• the reaction takes place in the temperature range of 400-500°C.
• One object of this invention is, therefore, to provide a simple and inexpensive method for effective separation of gaseous pollutants, preferably hydrogen chloride, without resorting to the addition of a fresh and costly absorbent, such as calcium hydroxide or limestone, besides the absorbent added to the hearthcombustion chamber in order to bind sulphur dioxide.
• gaseous pollutants preferably hydrogen chloride
• a fresh and costly absorbent such as calcium hydroxide or limestone
• Another object of the invention is to provide a device of simple design, which is suitable for implementing the above method.
• the above problem concerning the achievement of satisfactory separation of gaseous pollutants, such as sulphur dioxide and hydrogen chloride, from flue gases generated upon the combustion of fossil fuel, such as coal, in an atmospheric or pressurised fluidised bed in the temperature range of 700-900°C, is solved by adding in excess to the bed an absorbent containing burnt lime and/or substances that, in this temperature range, are converted to burnt lime, with a view to achieving a reaction with these gaseous pollutants in the form of sulphur dioxide and a conversion thereof to separable, particulate pollutants.
• the particles entrained by the flue gases from the bed are separated from the gases and then recycled to the bed.
• This method is characterised in that a partial amount of the particles separated from the flue gases and containing burnt lime is not recycled to the bed but instead supplied to the flue gases in the temperature range of 90-200°C, preferably 120- 150°C, in order to react with the remaining gaseous pollutants in the form of hydrogen chloride in the flue gases, so as to convert these pollutants to particulate pollutants, whereupon the resulting particles are separated.
• the basic idea behind the invention thus is to utilise the fine-grained ash accompanying the combustion gases from the hearthcombustion chamber.
• the partial amount of fine-grained ash drawn off preferably makes up at least 1% of the separated particles and preferably contains 2-30% by weight of burnt lime, depending on the dosage of limestone, the ash content and composition of the coal, and so forth.
• the particles of this partial amount are supplied to the flue gases in finely-divided pulverulent form, the particle size preferably being in the range of 0-70 mm, and constitute a dust load preferably falling in the range of 0.5-10 g/Nm 3 of flue gas.
• the burnt lime is disintegrated, which is of special importance when the dust employed is fairly coarse, as is the case when use is made of cyclone dust.
• the resulting dust product has, after hydration, a water content of 5-20% by weight. It is essential that the water content should not be too high, but that the dust product should retain its pulverulent character.
• the present invention further provides a device which is suited for use in the implementation of the above method and which comprises a first dust separator in which the particles entrained from the bed are separated from the flue gases and then recycled to the bed.
• This device is characterised in that a partial amount of the particles separated from the flue gases and containing burnt lime is not recycled to the bed but instead supplied to a contact reactor, in which they are mixed with the flue gases in the temperature range of 90-200°C, preferably 120-150°C, in order to react with the remaining gaseous pollutants in the form of hydrogen chloride in the flue gases, whereupon the resulting particulate pollutants are separated in the first dust separator and/or in a second dust separator.
• the contact reactor which preferably is arranged upstream from the first dust separator, or arranged downstream from the first dust separator and upstream from the second dust separator, a large amount of the hydrogen-chloride gas found in the flue gases will react with the burnt lime forming part of the amount of particles supplied, thereby forming particulate and separable pollutants in the form of calcium chloride.
• the contact reactor achieves an even distribution of the supplied lime-containing dust product in the flue-gas channel upstream from the dust separator.
• the contact reactor prolongs the contact time and enhances the possibilities of a reaction between the lime-containing dust and the hydrogen chloride, thereby enabling an effective bonding of hydrogen chloride.
• the contact reactor and the following dust separator operate in the temperature range of 90-200°C.
• the first dust separator consists of a cyclone or several successive cyclones
• the second dust separator preferably consists of a bag filter or an electrostatic precipitator.
• the lime-containing particles fed to the contact reactor which are supplied to the flue gases in the contact reactor in dispersed pulverulent form, are preferably hydrated in the contact reactor and/or in a separate moistening unit.
• coal 2 is, besides limestone 3, added to the fluidised bed in order to bind the pollutants formed upon the combustion of coal, primarily sulphur dioxide, resulting in an approximately 90% separation in form of solid stable compounds, such as calcium sulphate.
• the acidifying gaseous pollutants formed upon the combustion of coal, such as hydrogen chloride and remaining sulphur dioxide, are, along with particles entrained from the bed, conducted through a channel 4 to a first dust separator 5.
• This separator is connected to the furnace 1 and, in the embodiment illustrated, consists of a cyclone, in which the particles entrained by the flue gases from the combustion are separated in a first stage.
• the flue gases are here compelled to perform a movement of rotation, such that at least the larger particles collide with the walls and drop towards the narrow end of the cyclone under the action of the centri- fugal force.
• the flue gases then leave the cyclone and are conducted, via a channel 6, through an energy-recovery stage 7 in the form of a heat exchanger, while being cooled and conducted to a contact reactor which, in the embodiment illustrated, consists of an elongate tube reactor 8.
• a partial amount of the particles separated in the cyclone which chiefly consist of burnt lime as absorbent, fly ash and calcium sulphate formed upon the combustion, is, in finely-divided pulverulent form supplied to the tube reactor 8 and there mixed with the flue gases, such that the lime-containing particles react with the gaseous pollutants, converting them to particulate, separable pollutants.
• the particulate pollutants formed upon the reaction, the unreacted absorbent particles and the fly ash remaining in the flue gases are then separated in a bag filter 9 arranged downstream from the tube reactor 8.
• the flue gases thus cleaned of particulate and gaseous pollutants are then conducted through a channel 10 to a flue-gas fan 11, which feeds the cleaned flue gases through a channel 12 to a chimney 13, where they are discharged into the surrounding atmosphere.
• the particles separated in the dust separator 9 are collected in hoppers 14 and 15 arranged at the bottom of the separator. These particles are, via a conduit, conducted to a storage silo (not shown), as indicated by the arrow 16.
• a partial amount of the separated, particulate dust accumulated in the cyclone 5 and containing burnt lime is drawn off to be used for separating the gaseous pollutants remaining in the flue gases, primarily hydrogen chloride.
• the remainder of the cyclone dust is recycled to the fluidised bed via a sluice 17 and a conduit, as indicated by the arrow 18.
• the partial amount of lime-containing dust drawn off is then conducted by a conveyor, as indicated by the arrow 19, to a moistening unit 20, in which the burnt lime in the dust is hydrated, resulting in the formation of fine-grained, pulverulent slaked lime (calcium hydroxide).
• the moistened lime-containing dust is thereafter conducted through a conduit, as indicated by the arrow 21, to the tube reactor 8, where the dust is dispersed in the flue gases with the aid of pressurised air and hence is effectively mixed with the flue gases from the heat exchanger 7 arranged upstream.
• the tube reactor 8 achieves an even distribution of the absorbent particles supplied, resulting in a prolonged contact time and enhanced possibilities of a reaction between these particles, i.e. the moistened dust containing burnt lime, and the gaseous pollutants found in the flue gases, preferably the hydrogen chloride.
• a partial amount of the particles separated in the second dust separator 9 may be supplied to the contact reactor 8, preferably after hydration and optionally in combination with a partial amount of the particles separated in the first dust separator 5. This can be done instead of using only a partial amount of the particles separated in the first dust separator 5.
• the contact reactor 8 may be arranged upstream from the first dust separator 5, in which case use need only be made of this first dust separator, instead of be arranged downstream from the first dust separator 5 and upstream from the second dust separator 9.
• the first dust separator 5 may consist of several successive cyclones, instead of but a single cyclone.
• the second dust separator 9 may consist of an electrostatic precipitator instead of a bag filter.
• a bag filter instead of an electrostatic precipitator, owing to the fact that the absorption and the reaction between the gaseous pollutants and the lime-containing dust may continue during the passage of the gases through the dust cake formed on the outside of the filter bags in operation.
• the lime-containing particles of the separated partial amount may be hydrated in the contact reactor 8, instead of in a separate moistening unit 20.
• the partial amount of separated particles may be supplied to the flue gases directly at the inlet to the second dust separator 9, in which case the latter serves as the only contact reactor, instead of be supplied to the tube reactor 8.
• the energy-recovery stage 7 may consist of a steam or hot-water boiler.
• lime-containing dust can be drawn off and utilised, primarily for separating hydrogen chloride from the flue gases in the same manner as the cyclone dust, as has been described above in connection with the proposed embodiment.
• coal to which was added limestone in an excess of 100%, i.e. with a Ca/S ratio of 2 was burnt.
• the coal had a sulphur content of approximately 1% by weight and a chlorine content of approximately 0.12% by weight.
• the amount of flue gas was approximately 100,000 Nm 3 /h, and the first dust separator of the plant consisted of a cyclone.
• the bed ash chiefly consisted of 21.5% of unreacted limestone, 15.0% of burnt lime and 16.2% of calcium sulphate, while the cyclone dust contained 14.0% of burnt lime, 20.8% of calcium sulphate, non-analysable amounts of limestone, and a total of approximately 65% of ash (SiO 2 , Al 2 O , etc.) containing certain amounts of unbumt material.
• the flue gases still contained approximately 180 mg of SO 2 /Nm 3 of flue gas and 120 mg of HCl/Nm 3 of flue gas (approximately 12 kg of HCl/h).

Landscapes

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

Applications Claiming Priority (3)

Publications (1)

Family

ID=20396466

Family Applications (1)

Country Status (7)

Families Citing this family (3)

Family Cites Families (4)

• 1994
  • 1994-12-23 SE SE9404505A patent/SE504755C2/sv not_active IP Right Cessation
• 1995
  • 1995-12-21 WO PCT/SE1995/001557 patent/WO1996020038A1/en not_active Application Discontinuation
  • 1995-12-21 AU AU43602/96A patent/AU4360296A/en not_active Abandoned
  • 1995-12-21 PL PL95320879A patent/PL320879A1/xx unknown
  • 1995-12-21 CA CA 2207733 patent/CA2207733A1/en not_active Abandoned
  • 1995-12-21 JP JP8520405A patent/JPH10511599A/ja active Pending
  • 1995-12-21 EP EP95942354A patent/EP0799084A1/en not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events