EP0765187A1 - Improved wet scrubbing method and apparatus for removing sulfur oxides from combustion effluents - Google Patents
Improved wet scrubbing method and apparatus for removing sulfur oxides from combustion effluentsInfo
- Publication number
- EP0765187A1 EP0765187A1 EP95925239A EP95925239A EP0765187A1 EP 0765187 A1 EP0765187 A1 EP 0765187A1 EP 95925239 A EP95925239 A EP 95925239A EP 95925239 A EP95925239 A EP 95925239A EP 0765187 A1 EP0765187 A1 EP 0765187A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- slurry
- calcium carbonate
- reaction tank
- calcium
- tower
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
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
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J15/00—Arrangements of devices for treating smoke or fumes
- F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
- F23J15/04—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material using washing fluids
-
- 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
-
- 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
- B01D53/502—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound characterised by a specific solution or suspension
-
- 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
- B01D53/504—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound characterised by a specific device
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J15/00—Arrangements of devices for treating smoke or fumes
- F23J15/006—Layout of treatment plant
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2215/00—Preventing emissions
- F23J2215/20—Sulfur; Compounds thereof
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2217/00—Intercepting solids
- F23J2217/10—Intercepting solids by filters
- F23J2217/102—Intercepting solids by filters electrostatic
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2219/00—Treatment devices
- F23J2219/40—Sorption with wet devices, e.g. scrubbers
Definitions
- the invention relates to improvements enabling the removal of sulfur oxides (SO x ) from combustion effluents with greater efficiency and with economies in capital and operating costs.
- the technology for wet scrubbing combustion effluents to remove SO x provides gas-liquid contact in a number of different configurations. Among the most prominent are the single- and double-loop countercurrent spray towers and towers which employ both cocurrent and countercurrent sections.
- the single-loop, open-tower systems employing calcium carbonate to react with the SO x are the simplest in construction and operation. These systems are often preferred because they can be operated with low pressure drop and have a low tendency to scale or plug.
- the advantages of their simplicity and reliability have, however, been offset in some situations by their large size. For example, because they do not employ any trays or packings to improve contact between the effluent and the scrubbing liquid, tower heights are typically high and many levels of spray nozzles have been employed to assure good contact.
- Open spray towers i.e., those not having packings, trays or other means for facilitating gas-liquid contact
- Open spray towers are simple in design and provide high reliability. They are especially useful in coal-fired power stations where the evolution of chlorides has caused a number of problems, including reduced reactivity of the scrubbing solution and severe corrosion of scrubber internals.
- Another factor favoring the use of open spray towers is their inherent low pressure loss and resulting fan power economy.
- Calcium carbonate (commercially available in a number of forms including limestone) is a material of choice because it meets these criteria and, when properly processed, yields process byproducts that can be easily disposed of as landfill or sold as gypsum.
- the height of the spray contacting zone in these towers is not given, but typical values will be on the order of from about 6 to about 15 meters, historically considered an important factor in engineering an efficient system which can be expected to reliably remove at least 95% of the SO x from combustion effluents.
- the ratio of the quantity of slurry to the quantity of gas (L/G) is said to be arguably the single most significant design parameter.
- the L/G affects the cost of pumping, the cost of holding tanks and other operational and economic factors.
- the cost of pumping the limestone slurry increases proportionally with the tower height. It would be desirable to decrease L/G requirements and height for open spray towers.
- Sulfur oxides (SO x ), principally SO 2 , are absorbed in the descending scrubbing slurry and collected in a reaction tank where solid calcium sulfite and solid calcium sulfate are formed.
- the reaction tank is oxygenated to force the production of the sulfate. Once the crystals of sulfate are grown to a sufficient size, they are separated from the slurry in the reaction tank. ln a paper by K. R.
- a scrubbing tower is depicted as including a hydrocyclone loop which separates a gypsum slurry from a wet scrubber into a coarse solids stream and a fine solids stream, with the fine solids stream being returned to the scrubber.
- a hydrocyclone loop which separates a gypsum slurry from a wet scrubber into a coarse solids stream and a fine solids stream, with the fine solids stream being returned to the scrubber.
- a scrubbing slurry composed of calcium carbonate, calcium sulfate, calcium sulfite, and other non-reacting solids flows downwardly while the SO x -laden effluent gas flows upwardly.
- the SO x principally SO 2 , is absorbed in the descending scrubbing slurry and is collected in a reaction tank where calcium sulfite and calcium sulfate are formed.
- the reaction tank is oxygenated to force the production of sulfate over sulfite.
- blow down stream It is known to reduce the chloride content of the scrubbing slurry by the use of a blow down stream.
- the blow down is taken from the reaction tank or from water recovered from gypsum recovered from the process.
- the invention improves a single-loop, open-tower, counter ⁇ current limestone wet scrubbing process for reducing the concentration of SO x (principally SO 2 ) in flue gases.
- SO x principally SO 2
- the invention provides an improved apparatus capable of achieving the noted improvements and will be described in detail in the following description.
- the process comprises: (a) directing a flow of flue gas containing SO x upwardly through a vertical scrubbing tower at a bulk flow velocity of greater than about 4.5, and preferably up to about 6, meters per second; (b) introducing into a vertical scrubbing section within said tower, a spray of droplets of an aqueous slurry of finely divided calcium carbonate, calcium sulfate, calcium sulfite, and other non-reactive solids, the calcium carbonate preferably having a weight median diameter of 6 ⁇ or less with 99% by weight less than 44 ⁇ , and a total molar ratio of calcium-containing to sulfur-containing compounds in the solids of at least 1.1 to 1.2, to contact the flue gas while descending through the tower countercurrently to the flow of flue gas; (c) collecting the slurry in a reaction tank after contact with the flue gas; (d) withdrawing slurry from the reaction tank, preferably after an average residence time of eight hours or less; (e) subject
- the slurry be introduced from spray nozzles, alternating between upward and downward orientation from two spray levels spaced from about 1 to about 2 meters apart. It is also preferred that the total tower height in the spray contacting zone be less than about 6, and preferably less than about 4, meters in height, as it has been determined that height is not so important for reliably removing 95% or more of the SO x from combustion effluents. It is an advantage of the invention that the tower diameter can be relatively small, so that the operating bulk velocity of flue gas passing vertically through the spray contacting zone, based only on the cross sectional area and neglecting the area taken up by spray headers and nozzles, be no less than 4.5 and preferably up to 6 meters per second.
- This higher velocity provides a means of suspending liquid in the tower without increasing tower height and without adding packing or trays for liquid holdup, and the liquid so suspended is more reactive due to the increased time for dissolution of the calcium carbonate.
- a distinct advantage of the invention is to increase tower contacting time without adding tower height, while at the same time maintaining the simplicity of design, construction, operation, and maintenance of an open spray tower.
- the median size of the calcium carbonate particles in the reaction tank is maintained within the range of from about 2 to about 6 ⁇ , and the weight median particle size of the finely-divided calcium carbonate as introduced is less than about 8 ⁇ , with at least 99% (e.g., 99.5 %) by weight of the particles being less than 44 ⁇ .
- the molar ratio of calcium-containing to sulfur- containing compounds in the solid phase of the scrubber slurry be high. High ratios make more alkalinity available for SO x removal, thus improving the absorptive capacity of the liquid.
- a high ratio is not economical because valuable calcium-containing compounds, specifically calcium carbonate, will be wasted with the removal of sulfur compounds via the dewatering system.
- the invention permits operation with a scrubbing slurry in the spray tower for which the solid calcium carbonate concentration is much higher than economically viable for other systems.
- the hydrocyclone is effective in increasing the relative concentration of available calcium and alkalinity in the tank.
- the scrubbing tower comprises at least a first entrainment separator to remove a significant amount of the entrained moisture and to turn the direction of flow of the flue gases by at least 30° from the vertical axis of the tower.
- the majority of droplets having diameters less than about 100 ⁇ are eliminated either by dropping them out of the effluent or consolidating them to form larger droplets which can more easily be removed by a downstream mist eliminator.
- the first entrainment separator is preferably followed by a generally vertical mist eliminator.
- the invention provides an improved wet scrubbing process for reducing the concentration of SO x in a flue gas, comprising: (a) directing a flow of flue gas upwardly through a scrubbing tower; (b) introducing a spray of an aqueous slurry of finely-divided calcium carbonate, calcium sulfate, calcium sulfite, and non-reactive solids to descend through the tower countercurrently to the flow of flue gas, the weight median size of the calcium carbonate particles being within the range of from about 2 to about 6 ⁇ ; (c) following contact with the flue gas, collecting the slurry in a reaction tank; (d) maintaining a high reactivity in the slurry by withdrawing slurry from the reaction tank and subjecting slurry withdrawn to treatment in a hydrocyclone to provide a recycle stream rich in fine particles of calcium carbonate and non-reactive solids and another stream rich in calcium sulfate, both of said streams containing dissolved chlorides, and dis
- the process permits operation at pH values that also enhance reactivity.
- the pH of the slurry in the reaction tank is within the range of from about 5.0 to about 6.3, and most preferably in the range of from about 5.8 to about 6.3.
- the molar ratio of calcium-containing to sulfur-containing compounds in the recycle stream is maintained at a value greater than about 1.3, preferably above about 1.4. Also, it is preferable to maintain a suspended solids concentration of less than about 15%, and most preferably less than about 5%, in the recycle stream.
- the process further includes determining the chloride content of the slurry, and discharging a portion of the recycle stream should the value exceed a predetermined maximum allowable chloride content. Even more preferably, the process includes determining the solids density of the recycle stream, and discharging a portion of the recycle stream whenever the solids density exceeds a predetermined control value. In this last matter, the fraction of non-reactive solids are controlled.
- the invention provides an improved wet scrubbing apparatus for reducing the concentration of SO x in flue gases, comprising: (a) a scrubbing tower comprising a gas inlet duct, a gas outlet duct, and a vertical scrubbing section, configured to direct a flow of flue gas containing SO x upwardly through said scrubbing section; (b) an array of spray devices positioned within said scrubbing section configured to introduce a spray of an aqueous slurry of finely-divided calcium carbonate, calcium sulfate, calcium sulfite, and non-reactive solids to descend through the tower countercurrently to the flow of flue gas; (c) a reaction tank located below said array of spray devices to enable collection of the slurry after a period of contact with said flue gas within said vertical scrubbing section, said reaction tank being of a size suitable to permit reaction of the SO x with the calcium carbonate to form crystals of gypsum having a weight
- Figure 1 is a schematic view of a preferred embodiment of the process of the invention employing a single-loop, open-tower, countercurrent limestone wet scrubber;
- FIG 2 is a more detailed schematic view of a scrubbing tower of the type shown in Figure 1 ;
- Figure 3 is a partial side elevational view of the arrangement of spray nozzles in two spray levels shown in the tower of Figure 2;
- Figure 4 is a bottom plan view of the spray nozzles in the two spray levels for a spray tower of the type shown in Figure 2;
- Figure 5 is a perspective view of the entrainment separator shown in the spray tower of Figures 1 and 2.
- the improvements of the invention have preferred application to coal-fired utility boiler flue gases, and in some aspects are particularly effective for high chloride operations such as incinerators. While the advantages may be the greatest in these types of operations, the invention is by no means limited to them. Effluents from the combustion of all types of carbonaceous materials can be treated, also including natural gas, synthetic gas, fuel oils, bitumens and residual fuel oils, domestic and industrial solid or other combustible waste, and the like.
- Figure 1 is a single-loop, open-tower, countercurrent limestone wet scrub- bing operation for removing sulfur oxides, principally as SO 2 , from combustion effluents.
- Limestone is the preferred form of calcium carbonate but can be replaced with another form, if desired.
- other forms of calcium carbonate include oyster shells, aragonite, calcite, chalk, marble, marl, and travertine. It can be mined or manufactured. In this description, the terms calci ⁇ um carbonate and limestone are used interchangeably.
- the limestone is finely divided, preferably by grinding as described below, to achieve a weight median diameter of about 10 ⁇ or less, with 99% below 44 ⁇ . This is extremely fine for wet scrubbing in an open tower with a countercurrent flow of limestone slurry.
- the more typical grind size of the prior art is a weight median diameter of 15 ⁇ or less with no more than 95% of the particles less than 44 ⁇ .
- the preferred grind size of the invention will yield particles with a weight median particle size of less than about 8 ⁇ , with 90% (e.g., 99.5%) by weight of the particles being less than 44 ⁇ .
- the use of a grind of the preferred size has several advantages.
- FIG. 1 shows an effluent, such as from a coal-fired industrial or utility boiler, entering a suitable means 10 for removing particulates, such as an electrostatic precipitator or fabric filter, which removes entrained solids to a practical extent.
- a suitable means 10 for removing particulates such as an electrostatic precipitator or fabric filter, which removes entrained solids to a practical extent.
- the cleaned flue gas is then passed via duct 20 to wet scrubbing tower 100 wherein it flows upwardly, countercurrent to a spray of an aqueous slurry which contains finely-divided limestone discharged within a vertical scrubbing section 110 from two levels of spray nozzles. From the scrubbing section 110, the gas continues through gas outlet duct 120.
- the tower is configured to direct a flow of flue gas upwardly through the vertical scrubbing section.
- reaction tank 130 The scrubbing slurry falling through the vertical scrubbing section 110 is collected in reaction tank 130.
- the reaction tank 130 is preferably of a size suitable to permit reaction of the SO 2 with the calcium carbonate to form crystals of gypsum having a weight median diameter at least 2, and preferably from 5 to 10, times as large as the particles of calcium carbonate added as feed.
- the vertical scrubbing section 110 contains an array of spray devices positioned within it.
- the array is configured to introduce a spray of an aqueous slurry of finely-divided calcium carbonate to descend through the tower countercurrently to the flow of flue gas.
- the Figure illustrates a bank of spray nozzles which is shown to include two levels 112, 112'of nozzles. Each of the nozzles 114 (see Figure 2) is fed slurry from a header 116, 116', or 116". It is typical to also include a third level to permit one level to be off line for repair or cleaning while two remain in operation.
- the nozzles are preferably arranged with a spacing between levels of from about 1 to less than about 2 meters and with the direction of flow from adja- cent nozzles in a given level alternating between upward and downward.
- the preferred embodiments of the invention reduce the spacing between the nozzles, reduce the number of levels in use at any time (preferably to 2), and increase the rate of gas flow upwardly through the vertical scrubbing section.
- the preferred flow patterns of both the slurry being sprayed and the effluent passing upward through the tower are illustrated in Figure 4.
- nozzle is a centrifugal nozzle which forms a spray at an angle ⁇ of within the range of from about 90 to about 140°, preferably about 120°.
- nozzle is a Whirljet 300 gallon per minute nozzle available from Spraying Systems Co., Wheaton, Illinois. Droplet sizes are preferably in the range of from about 100 to about 6000 ⁇ , typically about 2000 ⁇ , Sauter mean diameter as measured by a Malvern Particle Analyzer.
- Each of the headers 116 is oriented at an angle with respect to the header in the next upper or lower rack.
- the angle is preferably 90° when two or three racks are employed.
- the resi ⁇ dence time in the reaction tank is reduced from the typical commercial value of about 15 hours or more down to less than about 8 hours, more typically about 6 hours. This is facilitated by the improved dissolution rate of fine calcium carbonate particles and, to some extent, the relatively fast precipitation rate of calcium sulfate to form gypsum particles.
- the reactive properties of the slurry are, in turn, enhanced by the separation of calcium sulfate from calcium carbonate in the slurry and recycling the calcium carbonate to the slurry as very fine particles which dissolve rapidly in the reaction tank.
- the reduction of the residence time in the reaction tank has a positive impact on overall process efficiency as well as a number of advantages in terms of processing ease, equip ⁇ ment sizing and quality of the byproduct gypsum.
- the bulk gas velocities of the flue gas moving through the vertical scrubbing section 110 are above 4.5, and preferably up to about 6, meters per second. These gas velocities are high in the context of single-loop, open-tower wet limestone scrubbers and are employed by the invention preferably in combination with other innovative approaches to improve overall process efficiency.
- the preferred scrubbing towers of the invention enable the treatment of flue gases with practical, low pressure drops and lower relative amounts of aqueous slurry, e.g. lower L/G ratios.
- the sulfur oxides in the effluent are absorbed into the aqueous phase of the slurry, forming bisulfite and hydrogen ions. Some bisulfite oxidizes to sulfate, releasing even more hydrogen ions. As the droplets become saturated with hydrogen ions, calcium carbonate begins to dissolve at an increasing rate, thus forming calcium ions and bicarbonate. The finely-pulverized calcium carbonate is very effective at absorbing hydrogen ions, thereby improving the absorptive capacity of the aqueous phase in the tower spray zone.
- the high gas velocities employed according to the preferred embodiments, and the preferred spray pattern tend to maintain the slurry droplets suspended with a degree of fluidization to achieve enhanced contact.
- Figure 1 shows limestone being finely divided in a mill 170, classified by cyclone 172, captured by bag house 174 and metered through air lock 176 into the pressurized flow of air in line 178.
- the limestone which is introduced into the reaction tank to replenish the calcium carbonate can be made within well-defined particle size ranges, free from large particles, those greater than about 44 ⁇ .
- the exclusion of the large particles from the limestone introduced into the reaction tank is a principal feature permitting the reaction tank of the invention to be made substantially smaller than is presently employed in conventional scrubbers.
- the air in line 178 facilitates supplying oxygen for the oxidation of sulfite and bisulfite ions to sulfate ions.
- the tank is preferably stirred by conventional means which are not illustrated in the Figure.
- slurry is withdrawn from reaction tank 130 for concentrating the reactive calcium carbonate for recycle and reducing the level of solids, principally by removing gypsum.
- Figure 1 shows slurry being withdrawn from reaction tank 130 via line 183 and passed to hydrocyclone 181.
- the hydrocyclone is especially effective in the operation of the invention because it can rapidly and effectively separate the very fine particles of limestone from the larger particles of calcium sulfate.
- the particles of the calcium sulfate preferably have a weight average diameter of from about 25 to about 55 ⁇ .
- the separation of the smaller particles of limestone provides a recycle stream 174 rich in calcium carbonate and a discharge stream 176 rich in calcium sulfate.
- the weight average particle size of the calcium carbonate in the reaction tank and therefore in the recycle stream 184 is in the range of from about 2 to about 6 ⁇ .
- Figure 1 shows the preferred form of the invention wherein the recycle stream is concentrated in terms of calcium carbonate and useful process water in hydrocyclone 181.
- the preferred sizes for the calcium carbonate particles will have a weight median diameter in the range of from about 2 to about 6 ⁇ .
- the calcium sulfate particles will have a weight median diameter within the range of from about 25 to about 55 ⁇ .
- Reaction tank 130 is located below the array of spray devices to enable collection of the slurry after a period of contact with the flue gas within the vertical scrubbing section 110.
- the reaction tank 130 is of a size suitable to permit reaction of the SO 2 with the calcium carbonate to form crystals of gypsum having a weight median diameter at least 2, and preferably from 5 to 10, times as large as the particles of calcium carbonate added as feed.
- the solids concentration of calcium carbonate can be increased by about 20 to about 50% above the concentrations attainable in countercurrent designs of the prior art. It is a further advantage of the invention that the slurry will have a higher stoichiometric ratio of calcium-containing to sulfur-containing compounds than prior art systems, typically being at least 1.3 and preferably being about 1.4 or greater.
- This system includes at least one pump 182 and associated conduit 183 for withdrawing slurry from the reaction tank and delivering slurry to the hydrocyclone.
- the sulfur oxides in the effluent are absorbed into the aqueous phase of the slurry in vertical scrubbing section 110 and react with available alkalinity in ' the form of hydroxide ions to form bisulfite, which can be partially oxidized in the scrubbing section 110 and almost fully oxidized in the reaction tank 130 to form sulfate.
- the alkalinity is principally derived from the dissolution of calcium carbonate to form bicarbonate and hydroxide ions, which occurs both in the scrubbing section 110 and in the reaction tank 130.
- An oxygen sparge as conventional in the art, is preferably employed to assure sufficient reaction, although some oxygen can be obtained from the flue gas itself in the scrubbing section 110.
- reaction tank 130 which collects the slurry. It is one of the novel and improved features of the invention that the residence time in the reaction tank is reduced from the typical commercial value of about 15 hours down to about 6 hours. The reduction of the residence time in the reaction tank has a number of advantages in terms of processing ease, equipment sizing and quality of the byproduct gypsum.
- the pH of the slurry in the reaction tank 130 is preferably in the range of from about 5.0 to about 6.3, most preferably from about 5.8 to about 6.3. Higher pH indicates a higher available alkalinity in the slurry liquid and a correspondingly higher capacity of the liquid to absorb SO 2 . It is an advantage of the invention that, because the calcium carbonate is supplied as fine particles and is recycled as will be explained later, also in the form of fine particles, a higher available alkalinity is possible. Low pH is typically employed on systems of prior art to increase the rate of reaction of calcium carbonate, but this normally reduces the absorption of SO 2 in the scrubbing section because the decreased available alkalinity.
- the small particle size of the present invention offers increased available alkalinity even at lower than desired pH, thereby offsetting to a large extent the impact of low pH on the scrubbing capacity of the slurry.
- a spray slurry supply means comprising at least one pump 122 and associated conduit 124 for withdrawing slurry from the reaction tank 110 and delivering slurry to the array of spray devices positioned within the scrubbing section.
- Figure 1 shows limestone being finely divided in a mill 170, classified by cyclone 172, captured by bag house 174 and metered through air lock 176 into the pressurized flow of air in line 178, which in turn is injected directly into the scrubber 100 or into the duct 20 immediately upstream of the scrubber.
- the limestone from the baghouse 174 may be mixed in a tank and pumped to the reaction tank 130.
- the size of the pulverized material can be closely controlled.
- the size of the particles is particularly critical to the invention.
- the makeup stream of calcium carbonate has a weight median particle size of about 8 ⁇ or less with 99% or more of the particles less than 44 ⁇ , as fed to replenish the calcium carbonate lost to the reaction with SO x and to the byproduct gypsum and with soluble chlorides as will be explained later.
- the air in line 178 facilitates supplying oxygen for the oxidation of calcium sulfite to calcium sulfate.
- the tank is preferably stirred by conventional means which are not illustrated in the Figure.
- a slurry quality maintenance system depicted generally as 180.
- calcium carbonate is supplied as finely-divided particles as described, and a hydrocyclone 181 is employed to remove a portion of the slurry in reaction tank 130 for the purposes of concentrating fine particles of calcium carbonate for recycle as well as for discharging gypsum.
- the hydrocyclone 181 separates the slurry from the reaction tank into a recycle stream 184 rich in small particles of calcium carbonate and non-reactive solids and another containing a majority of relatively larger particles of calcium sulfate.
- the preferred sizes for the calcium carbonate and non-reactive solids particles will have a weight median diameter in the range of from about 1 to about 8 ⁇ , preferably from about 2 to about 6 ⁇ .
- the calcium sulfate particles will have a weight median diameter within the range of from about 25 to about 55 ⁇ .
- the weight median diameters of particles of calcium sulfate will be at least 2, and more preferably from 5 to 10, times greater than those of calcium carbonate.
- This system includes at least one pump 182 and associated conduit 183 for withdrawing slurry from the reaction tank and delivering slurry to the hydrocyclone.
- a recycle conduit 184 is shown to lead from the hydrocyclone 181 to the reaction tank 130 to carry a recycle stream rich in calcium carbonate from the hydrocyclone.
- An important feature of the system is achieving blow down from the recycle overflow, namely from recycle stream 184.
- a discharge conduit 185 in communication with the recycle conduit 184 which is adapted to remove a portion of the recycle stream from the recycle conduit. It is preferred to provide a monitor for the chloride content of the slurry in line 183 or elsewhere, and to control the amount of slurry to blow down from line 185 to control the chloride content in the slurry within reasonable values, e.g., below about 30,000 mg/l, and preferably below 20,000 mg/l.
- Stream 185 has the highest concentration of chlorides, being equal to the concentration in the reaction tank, and therefore is the best source of chloride purge in the system.
- non-reactive solids in the reaction tank 130 which enter the system with the calcium carbonate or as entrained solids in the gas stream 20 and are composed of relatively small particles, with weight median sizes ranging from about 4 to about 12 ⁇ , will tend to accumulate preferentially in the recycle stream 184, with their concentration growing in the recycle tank 130.
- Monitoring of these non-reactive solids in the recycle stream can be accomplished by chemical means (i.e., analysis for a characteristic specie, e.g., silica, iron, or others) or by physical means (i.e., either by particle size distribution analysis , total solids concentration, or some other suitable method).
- the preferred means of control is to adjust the rate of stream 185 up or down as required to meet the most stringent limit for either chlorides or non-reactive solids. It is desirable to maintain the level of non-reactive solids generally below about 20% by weight, and preferentially below 15% of the total solids in the reaction tank 130. Solids thus removed from the reaction tank via conduit 185 may be disposed with the blow down liquid, separated from the liquid, or in some other way treated and made suitable for disposal or other uses. The blow down liquid may also be treated in some manner to make the stream suitable for disposal or for some other use.
- blow down stream 185 It is not the intention of this invention to limit in any way the possible dispositions for the blow down stream 185, but rather to acknowledge that there are numerous methods for treating the stream, separating it into fractions, recycling all or a portion of it, and so forth. Such methods and means for treating stream 185 are beyond the scope of the present invention.
- a calcium sulfate slurry recovery conduit 186 leading from the hydrocyclone to remove calcium sulfate slurry from the hydrocyclone wherein the calcium sulfate is present as particles larger in size than the particles of calcium carbonate.
- Figure 1 shows the preferred form of the invention wherein the recycle stream 184 is fed back to the reaction tank 130.
- An advantage of operating in this manner according to the invention is the ability to greatly increase the available alkalinity in the liquid droplets which come into contact with the SO x - laden effluent.
- the stoichiometric ratio of calcium-containing to sulfur- containing compounds in recycle stream 184 will be in the range of from about 1.2 to about 2.0, most preferably from about 1.3 to about 1.4.
- the concentration of suspended solids in the recycle stream will typically be in the range of from about 1 to about 10%, by weight, most typically from about 2 to about 6%. Separation of the majority of the calcium sulfate from the limestone by hydrocyclone 182, in addition to raising the noted stoichiometric ratio and the available alkalinity, also decreases the solids content of the slurry.
- reaction tank has a high stoichiometric ratio of calcium-containing to sulfur-containing compounds, e.g. on the order of from about 1.1 to about 1.6, preferably from about 1.2 to about 1.3.
- Preferred solids content of stream 183 coming from the reaction tank 130 is preferably within the range of from about 10 to about 20%, preferably between about 13 to about 17%. And, the solids content of stream 186 is preferably within the range of from about 30 to about 55%.
- Stream 186 is fed to filter 188 or other suitable device to dewater the slurry.
- the solid gypsum is of high quality and can be utilized for building materials.
- the filtrate is drawn off by line 189 and can be recycled to the reaction tank 130 or any portion can be discharged as blow down, but it is an advantage of the invention that this stream need not be discharged to control the buildup of chloride in the system.
- the scrubbed effluent is significantly freed of entrained droplets of liquid and diverted in direction of flow by entrainment separator 140.
- problems of encrustation of the roof 102 of the tower and of mist eliminators of conventional construction would be experienced unless measures were taken.
- the use of a more efficient mist eliminator in lieu of the entrainment separator 140 is not feasible, since at operating bulk velocities of 4.5 to 6 meters per second, no practical, high- efficiency mist eliminators are available, and commercial units which could be specified for this location tend to drain poorly and flood, thus increasing the potential for pluggage and low reliability.
- the entrainment separator 140 is designed for the specific purposes required by this invention.
- the entrainment separator 140 removes a significant amount of the entrained moisture and turns the direction of flow of the flue gases by at least 30° from the vertical axis of the tower, also producing a more uniform velocity profile into the vertical mist eliminator 150.
- the majority (by weight) of droplets having diameters less than about 100 ⁇ are eliminated either by dropping them out of the effluent or consolidating them to form larger droplets which can more easily be removed by a downstream mist eliminator.
- the entrainment separator 140 is preferably followed by a generally vertical mist eliminator, shown in the Figures as 150.
- the bulk of the effluent flow is changed from vertical to near horizontal by the entrainment separator 140.
- This has several advantages including the reduced impingement of slurry onto the roof 102 of the scrubbing tower, with prevention of the formation of deposits there which tend to grow larger in time, to an extent that they can break off in large pieces, often as much as a meter or more in diameter, and either damage the nozzle headers or fall through to the reaction tank 130 and ultimately cause plugging of the spray nozzles in 112 and 112'. Also, and importantly, it permits high-efficiency demisting of an essentially horizontal flow by vertical mist eliminator 150.
- the high-efficiency horizontal flow mist eliminator 150 inherently drains well, thus allowing operation at higher velocities than for a similarly designed, vertical flow mist eliminator. It also achieves superior demisting in the horizontal flow orientation.
- a high degree of demisting is an important feature of the invention, although not necessarily unique, since horizontal flow mist eliminators are commonly used in FGD systems and other industries where high- efficiency demisting is required.
- the combination of the entrainment separator 140 with the high-efficiency mist eliminator 150 provides superior demisting by providing a relatively uniform velocity profile into the mist eliminator and by consolidating the majority of smaller droplets into larger droplets in the entrainment separator prior to final demisting in the high-efficiency mist eliminator.
- Figure 5 illustrates a preferred form of an improved entrainment separator 140 which can effectively remove or consolidate a majority of the smaller droplets (i.e., less than 10O ⁇ diameter) and redirect the vertical flow of the effluent away from the upper wall surfaces of the tower.
- Entrainment separator 140 is illustrated in Figure 2 as oriented at an angle y relative to the horizontal in scrub ⁇ bing tower 100. This angle will preferably be within the range of from about 10 to about 45°, e.g. about 20°.
- the separator 140 utilizes single pass separator blades 142 to collect droplets by impingement and to turn the gas in a direction most suitable for further mist elimination.
- the individual blades 142 are oriented at an angle ⁇ with regard to the lower surface of assemblies 144, 144', 144", etc., of the blades 142.
- a blade of this type will be a parallelogram-shaped piece of from about 0.15 to about 0.23 meters in minor dimension and from about 0.6 to about 1.5 meters in major dimension. Spacing between individual blades will typically be from about 40 to about 70% of the minor dimension of the individual blades.
- Angle ⁇ will preferably be within the range of from about 20 to about 40°, the exact value depending on the angle ⁇ and the desired degree of flow ' direction of the effluent stream.
- the assemblies 144, etc. are constructed and oriented in a fashion that facilitates excellent drainage.
- the individual assemblies are arranged in a pattern of chevrons as illustrated.
- the assemblies 144, efc, are preferably oriented with respect to one another at an angle ⁇ , typically in the range of from about 125 to about 145°, and preferably about 140°.
- the entrainment separator structure is supported by members 146 which run the lengths of each of the assemblies. Other arrangements of supporting structures are possible.
- the structure of the entrainment separator 140 permits direct contact washing of the blades by means of fixed nozzle lances 147 having spray nozzles 148 capable of spraying wash water directly onto the blades from both the top and the bottom.
- Washing is typically done by operating each washer header separately and sequentially with the others.
- the wash water is of sufficient quality and is used in sufficient quantity to reduce the level of saturated, dis ⁇ solved salts on the separator surfaces. Together with the good drainage afford ⁇ ed by the chevron-shaped arrangement of assemblies 144, etc., the use of high quality wash water and frequent washing affords practically deposit-free opera- tion.
- the separation efficiency of the first entrainment separator 140 need not be as high as multipass separators employed in the prior art because the ability to redirect the flow from vertical to horizontal enables the use of a high-efficiency, vertically-oriented mist eliminator 150.
- the entrainment separator causes very low pressure drops, e.g. less than about 0.15 inches water column, and has other advantages in terms of cleanability, drainage, high bulk gas velocities, and direction of the gas flow from the upper wall surfaces of the tower and toward a highly-efficient, vertical mist eliminator 150.
- the mist eliminator 150 is preferably of the baffle type, e.g. a zig-zag baffle.
- the scrubbed and demisted effluent can then be discharged to the air such as by stack 160.
- the demisted effluent is heated prior to discharge such as in a gas-to-gas heat exchanger in a vertical configuration as described in copending, commonly-assigned U.S. Patent Application S.N. 08/257,158 (attorney's docket number 1930-P0020), filed on June 9,1994, filed in the names of the inventors named herein.
- the effect of the improvements of the invention in combination is to enable construction of a single-loop, wet-scrubbing, open spray tower which is about one half the empty weight of current open spray towers.
- Total process efficiency is measured by the value of all resources expended to remove a unit of SO x from the untreated gas. These include both capital and operating resources.
Abstract
Description
Claims
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US257698 | 1981-04-27 | ||
US25716094A | 1994-06-09 | 1994-06-09 | |
US257160 | 1994-06-09 | ||
US08/257,698 US5635149A (en) | 1994-06-09 | 1994-06-09 | Wet scrubbing method and apparatus for removing sulfur oxides from combustion effluents |
PCT/US1995/007167 WO1995033547A1 (en) | 1994-06-09 | 1995-06-07 | Improved wet scrubbing method and apparatus for removing sulfur oxides from combustion effluents |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0765187A1 true EP0765187A1 (en) | 1997-04-02 |
EP0765187A4 EP0765187A4 (en) | 1997-09-10 |
Family
ID=26945826
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP95925239A Withdrawn EP0765187A4 (en) | 1994-06-09 | 1995-06-07 | Improved wet scrubbing method and apparatus for removing sulfur oxides from combustion effluents |
Country Status (17)
Country | Link |
---|---|
EP (1) | EP0765187A4 (en) |
KR (1) | KR970703798A (en) |
AU (1) | AU2943295A (en) |
BG (1) | BG63154B1 (en) |
BR (1) | BR9507951A (en) |
CA (1) | CA2190868A1 (en) |
CZ (1) | CZ353396A3 (en) |
FI (1) | FI964891A0 (en) |
GE (1) | GEP20002319B (en) |
HU (1) | HU221181B1 (en) |
PH (1) | PH31493A (en) |
PL (1) | PL317931A1 (en) |
RU (1) | RU2149679C1 (en) |
SI (1) | SI9520071A (en) |
SK (1) | SK151696A3 (en) |
TW (1) | TW349876B (en) |
WO (1) | WO1995033547A1 (en) |
Cited By (1)
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CN102000481B (en) * | 2009-08-31 | 2012-10-10 | 宝山钢铁股份有限公司 | Method for treating desulfurization ash |
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US6190630B1 (en) | 1996-02-21 | 2001-02-20 | Mitsubishi Heavy Industries, Ltd. | Flue gas treating process and apparatus |
JP3354828B2 (en) * | 1996-02-21 | 2002-12-09 | 三菱重工業株式会社 | Smoke exhaust treatment method and apparatus |
DE19652482A1 (en) * | 1996-12-17 | 1998-06-18 | Steag Ag | Process for reducing the solids content of a suspension |
DE19758526B4 (en) * | 1997-08-23 | 2004-07-15 | Lechler Gmbh + Co. Kg | Drallsprühdüse |
KR100303388B1 (en) * | 1999-06-02 | 2001-09-24 | 세 영 모 | Aaaaa |
DE102005055550A1 (en) * | 2005-11-18 | 2007-05-24 | Merkl, Rupert, Dipl.-Ing. | Apparatus and method for cleaning the exhaust gases in heating systems with simultaneous heat recovery and dust removal |
US7524473B2 (en) | 2007-03-23 | 2009-04-28 | Alstom Technology Ltd | Method of mercury removal in a wet flue gas desulfurization system |
IT1392986B1 (en) * | 2009-02-23 | 2012-04-02 | Eberle | ENERGY RECOVERY DEVICE. |
CN102179126B (en) * | 2011-04-06 | 2013-01-23 | 上海华畅环保设备发展有限公司 | Flue gas cyclone dedusting and dewatering method for flue gas carbon dioxide gathering system and device thereof |
DK2638952T3 (en) | 2012-03-12 | 2022-10-17 | Andritz Ab | Method for controlling a gas purification system by measuring a parameter of an absorbent material |
US20140314651A1 (en) | 2013-02-27 | 2014-10-23 | Fuel Tech, Inc. | Process and Apparatus for Improving the Operation of Wet Scrubbers |
RU2484890C1 (en) * | 2012-04-10 | 2013-06-20 | Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Казанский государственный энергетический университет" (ФГБОУ ВПО "КГЭУ") | Use of sludge formed at water treatment plant as sorbent for treatment of thermal power plant gas emissions |
ITTV20120153A1 (en) * | 2012-08-02 | 2014-02-03 | Giorgio Eberle | ENERGY RECOVERY PLANT. |
CN103406017B (en) * | 2013-08-19 | 2015-04-01 | 武汉龙净环保工程有限公司 | Desulfurizing absorption tower and desulfurizing absorption method |
CN103990374A (en) * | 2014-05-12 | 2014-08-20 | 孙立刚 | Novel desulfurization, denitrification, decarburization and dust removal purification combined device for coal-fired flue gas |
CN105536399A (en) * | 2015-12-15 | 2016-05-04 | 浙江百能科技有限公司 | Flue gas purifying apparatus |
US10161630B2 (en) | 2016-12-01 | 2018-12-25 | General Electric Technology Gmbh | Systems and methods for testing flue gas cleaning systems |
RU169760U1 (en) * | 2016-12-20 | 2017-03-31 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Волгоградский государственный технический университет" (ВолгГТУ) | ABSORBER |
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- 1995-06-07 BR BR9507951A patent/BR9507951A/en not_active Application Discontinuation
- 1995-06-07 KR KR1019960707118A patent/KR970703798A/en active IP Right Grant
- 1995-06-07 HU HU9603356A patent/HU221181B1/en not_active IP Right Cessation
- 1995-06-07 AU AU29432/95A patent/AU2943295A/en not_active Abandoned
- 1995-06-07 SI SI9520071A patent/SI9520071A/en unknown
- 1995-06-07 GE GEAP19953524A patent/GEP20002319B/en unknown
- 1995-06-07 RU RU97100158A patent/RU2149679C1/en not_active IP Right Cessation
- 1995-06-07 PL PL95317931A patent/PL317931A1/en unknown
- 1995-06-07 EP EP95925239A patent/EP0765187A4/en not_active Withdrawn
- 1995-06-07 CA CA002190868A patent/CA2190868A1/en not_active Abandoned
- 1995-06-08 PH PH50689A patent/PH31493A/en unknown
- 1995-06-09 TW TW084105890A patent/TW349876B/en active
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Also Published As
Publication number | Publication date |
---|---|
CZ353396A3 (en) | 1997-05-14 |
TW349876B (en) | 1999-01-11 |
WO1995033547A1 (en) | 1995-12-14 |
FI964891A (en) | 1996-12-05 |
BG101099A (en) | 1997-10-31 |
EP0765187A4 (en) | 1997-09-10 |
HU221181B1 (en) | 2002-08-28 |
HUT77896A (en) | 1998-09-28 |
SK151696A3 (en) | 1997-08-06 |
CA2190868A1 (en) | 1995-12-14 |
AU2943295A (en) | 1996-01-04 |
PH31493A (en) | 1998-11-03 |
PL317931A1 (en) | 1997-04-28 |
RU2149679C1 (en) | 2000-05-27 |
GEP20002319B (en) | 2000-12-25 |
BR9507951A (en) | 1997-09-02 |
KR970703798A (en) | 1997-08-09 |
BG63154B1 (en) | 2001-05-31 |
SI9520071A (en) | 1997-06-30 |
HU9603356D0 (en) | 1997-02-28 |
FI964891A0 (en) | 1996-12-05 |
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