CA2036746A1 - Process and apparatus for absorption/adsorption material injection - Google Patents
Process and apparatus for absorption/adsorption material injectionInfo
- Publication number
- CA2036746A1 CA2036746A1 CA 2036746 CA2036746A CA2036746A1 CA 2036746 A1 CA2036746 A1 CA 2036746A1 CA 2036746 CA2036746 CA 2036746 CA 2036746 A CA2036746 A CA 2036746A CA 2036746 A1 CA2036746 A1 CA 2036746A1
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- Canada
- Prior art keywords
- mercury
- sulfur
- process according
- absorbent
- additive
- 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.)
- Abandoned
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Abstract
ABSTRACT OF THE INVENTION
An apparatus and method for removing mercury from flue gases produced by power generation or waste incineration. Mercury is removed from the hot waste gases, in a first embodiment, by distributing carbon and sulfur into the hot waste gas stream and then subsequently separating the mercury adsorbed or adsorbed by the carbon and sulfur particles downstream in the spray dryer absorber and baghouse filter. In a second embodiment, elemental sulfur, in particulate form, is sprayed directly into the flue gas stream. Other absorbents/adsorbents are discussed including diatomaceous earth, silica gel, activated aluminum oxide, aluminum or re-hydrate, zeolite or boiler fly ash. An apparatus is disclosed for conveying the absorbent/adsorbent by means of a screw conveyor having a plurality of spiral slots in-the screw conveyor housing. As a result, the conveyed adsorbent/absorbent is equally divided to flow through a plurality of distributor pipes connected to the flue gas passages. The distributor pipes are arranged to be respectively aligned below each of the spiral slots. Flow can be adjusted by axially sliding sleeves located adjacent each of the slots to partially or fully cover a respective slot.
An apparatus and method for removing mercury from flue gases produced by power generation or waste incineration. Mercury is removed from the hot waste gases, in a first embodiment, by distributing carbon and sulfur into the hot waste gas stream and then subsequently separating the mercury adsorbed or adsorbed by the carbon and sulfur particles downstream in the spray dryer absorber and baghouse filter. In a second embodiment, elemental sulfur, in particulate form, is sprayed directly into the flue gas stream. Other absorbents/adsorbents are discussed including diatomaceous earth, silica gel, activated aluminum oxide, aluminum or re-hydrate, zeolite or boiler fly ash. An apparatus is disclosed for conveying the absorbent/adsorbent by means of a screw conveyor having a plurality of spiral slots in-the screw conveyor housing. As a result, the conveyed adsorbent/absorbent is equally divided to flow through a plurality of distributor pipes connected to the flue gas passages. The distributor pipes are arranged to be respectively aligned below each of the spiral slots. Flow can be adjusted by axially sliding sleeves located adjacent each of the slots to partially or fully cover a respective slot.
Description
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BACKGROUND OF THE INVEN'I'ION
The present invention relates to a process for adsorbing or absorbing mercury from contaminated flue gases and an apparatus for conveying and distributing the adsorbing material.
It has long been recognizecl that mercury poses a danger to the environment and health. In power plants and in the incineration of waste materials, mercury compounds contained in the fuel or waste materials end up in the gas phase as a result of combustion or incineration. If mercury is released into the atmosphere, it can be carried through the nutrition cycle and end up causing sev~re health problems. The maximum concentration of mercury in the air that can be tolerated for a long period of time without causing health related damage is about 0.1-0.2 mg/m3. Numerous techniques have been proposed for purifying gases to reduce the presence of mercury. These systems have drawbacks including cost, complexity, efficiency, safety and effectiveness.
U.S. Patent No. 3,194,629, for example, discloses impreg-nating activated carbon with sulfur and then passing the mercury-containing gases over a bed of the impregnated activated carbon to remove the mercury. However, carbon is a costly material that is not economical for use in large scale systems. Moreover, the method of applying the activated carbon by leaving it in a bed would require frequent removal and replacement of the spent material by a relatively complex handling system. If the handling ~' system is avoided, frequent shut-downs would be necessary to remove the spent carbon at various clean-out points.
Various techniques also involve spraying activated carbon into flue gas passages to adsorb mercury vapor. However, rela-tively large quantities of activated carbon are needed, and the cost of activated carbon is high.
Another method outlined in U.S. Patent No. 3,838,190 pro-vides for washing gases containing mercury with sulfuric acid having a temperature between 60 and 180 and a concentration of at least 50%. However, this process is not suitable for boiler or incinerator opération since the treatment of hot sulfuric acid is costly, technically complex and relatively unsafe.
Anotner way of removing mercury from hot flue (waste) gases is proposed in U.S. Patent No. 4,273,747. This method involves atomizing an aqueous liquid such as water or a lime slurry into the hot flue gases in the presence of fly ash suspended in the gas stream. Subsequently, the fly ash is separated from the gas stream. It is claimed that a substantial part of the mercury originally present in the gas stream is adsorbed or absorbed by the fly ash so that the flue gases can be safely discharged into the atmosphere. However, tests conducted on numerous plants by Applicants and others do not support this result. One hypothesis is that the technique requires the presence of unburned carbon particles in the fly ash. When the boiler or incineration system does not produce adequately large :-.
quantities of unburned material, the aqueous injection techniqueis effective.
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SUMMARY AND OBJECTS OF TliIE INVENTION
In view of the foregoing, it should be apparent that there still exists a need in the art for a method and apparatus for adsorbing or absorbing mercury flue gases that i5 realized in a simple and effective manner and that is practical, economical and safe to use in a large scale system.
Ik is an object of this invention therefore to provide a method for adsorbing or absorbing mercury vapor and other toxic vapors contained in flue gases that is simple, reliable and economical, does not require frequent adjustment, costly materials or equipment, and is highly effective.
Still more particularly, it is an object of this invention to provide ~or an apparatus for treating mercury contained in flue gases produced by the combustion of refuse, waste or fossil fuels and, which provides for the distribution of the additive into the flue gases evenly and continuously with minimal operator intervention.
Another ob~ect of the invention is to provide for a mer-cury treating additive which is found to significantly reduce mercury in boiler or incinerator flue gases and that is cost effective.
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It is yet a further object of the invenkion to provide a mercury reduction apparatus easily controlled by an operator while the system is operating.
Briefly described, these and other objects of the inven-tion are accomplished in accordance with its apparatus aspecks by providing an apparatus for injecting dry additive into the flue gas passages of an incinerator. The injecting mechanism includes a screw conveyor driven by a variable speed DC motor connected mechanically through a high-ratio gear box. The screw conveyor housing has a plurality o~ spiral slots located on its base and sleeves mounted adjacent to each slot. Each sleeve extends about the circumference of the screw feeder housing and is adapted to slide axially along the housing in order to cover a respective spiral slot.
A trough hopper communicates with the screw conveyor at one end and a plurality of distribution pipes are located below each respective spiral slot. Each of the distribution pipes has a funnel connected to its top end and the funnel is aligned directly below the spiral slot to receive the dry additive. The operation of the screw conveyor causes the dry additive, placed in the trough hopper, to be mechanically conveyed by the screw conveyor and equally divided through the spiral slots. Material is then caused to drop into the flue gas passages through the distribution pipes.
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The method of the present invention is carried out by mix-ing particulate sulfur with carbon and then injecting the particulated mixture into the flue gas passages causing the removal of mercury from the flue gases. Mercury is subsequently separated from the system in the spray dryer absorber and baghouse filter located downstream from the point where the absorbing/
adsorbing particulate mixture is injected.
In a second embodiment, the process for removing mercury involves spraying sulfur dust into the flue gas passages.
With these and other objects, advantages and features of the invention ,that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block schematic diagram showiny the adsorption material injection system of the present invention;
FIG. 2 is a plan view of the injection apparatus used in the injection system of FIG. l;
FIG. 3 is a cut-away side view of the control sleeve used with the apparatus shown in FIG. 2;
FIG. 4 is a cross-sectional view taken alony lines IV-IV
~, of FIG. 3; and FIG. 5 is a cut-away side-view showing the feeder distri-bution and control sleeve arrangement under a plastic shield of : the apparatus shown in FIG. 2.
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DET~ILED DESCRIPTION OF THE PRE~ERRED EMBODIMENTS
Referring now in detail to the dra~ings wherein like parts are designated by like reference numerals throughout, there is illustrated in FIG. 1 the adsorption material injection s~stem 10 embodying the present invention. The system consists o~ an incin-erator 20 of any conventionally known design. The present invention is not solely designed to operate on incinerators but can also be applied to any conventionally known combustion device, including power genëration systems that produce stack gasses containing mercury.
The incinerator shown in Fig. 1 represents one type of an incinerator design, but it can be replaced with an~ other known incinerator. The incineration device, exemplified in this Figure, consists of a stoker grate, a boiler furnace/combustion chamber 20 constructed of gas-tight and continuously welded water walls extending down to the grate surface. Combustion takes place in the lower part of furnace 20 wher~ closely spaced high-pressure overfire air jets connected to a fan through line 27 creates turbulence along the front and rear walls of the incinerator causing intense localized turbulence. Complete combustion of the unburned gases occurs before the gases pass into a boiler bank and the subsequent heat transfer sections of the incinerator.
The incinerator also includes a stoker grate located below the combustion chamber which inclines downward from the furnace ' ' . , ' ' ' . . . ' , . , :
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feed hoppar 22 towards a discharge chute 30. A series of plenum chambers underneath the stoker grate admit primary combustion air supplied from the primary combustion fan 28. The burned out mate-rial from the stoker grate will then fall through the residue discharge chute 30 into an optional quench bath (not shown).
Combustion gases fl~w throllgh a first pass where NOx emis-sions are controlled b~ combustion control and by optional selective non-catalytic removal using N~3. The mercury containing gas stream is then introduced into duct 32 where it is treated by a mercury abatement system 100 located downstream from the steam generating equlpment and upstream from the pollution control system. Details of the apparatus 100 and the proceqs ~or treating mercury form the remaining parts of this specification.
Treated flue gases are introduced into a spray dryer absorber 36 via an appropriate disbursing device tnot shown). In the spray dryer, a liquid, such as Ca~OH)2 + H20, is atomized into small droplets causinq the fluid to evaporate after contacting the hot flue gases. As a result, a cooling of the gases and mercury suspended in those gases takes place. Fly ash and contained mer-cury is then removed by centrifugal force in the spray absorber cyclone. Ths mercury is then collected at the conically shaped base of the absorber and may then be removed through an exit 38.
The cooled gas stream exits the spray dryer through duct 39 con-nected to the fabric filter baghouse collector 40.
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In one embodiment, a pulse~jet type fabric filter arrangement is used. Alternatively, the system can be used in combination with dif~erent air pollution control equipment, such as a reverse air-type fabric filter or an electrostatic precipitator. In the baghouse 40, the particulate residues are separated from the gas stream whereupon the residues including mercury, fly ash and other materials are removed via exit 42 through the baghouse hoppers.
The treated gases from which the particulate residues in the mercury are separated, exits the baghouse filter through duct 43. The gases are then blown via induced draft fan 44 through main smoke stack 46 and out into the atmosphere. At this point, the concentration of mercury is so low as to be within safe levels.
Referring now to FXG. 2, the injection apparatus for mercury abatement 100 is illustrated. The distribution device is located adjacent a flue gas duct 32. The distribution system 100 consists o~ a screw feeder housing 102 mounted on legs 128 and 130 which is adapted to slowly convey material in accurate quantities using a single flight screw (not shown). The screw feeder 100 operates at a feed rate of 1 to 100 times the amount of mercury contained in the flue gases. An example of a feed rate for a conventional incinerator burning 400 tons per hour of refuse is 1 to 20 lbs. per hour split equally amongst the three distribution points arranged at equal distances along the feeder shaft.
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For increased rigidity, the screw shaft i5 hollow. In the prPferred embodiment, the screw feeder is made of a stainless steel construction using high temperature bearings and seals enabling it to handle corrosive materials and operate in high temperature environments. However, other conventional materials can be substituted.
Located at one end of the screw feeder shaft is a trough type feeder hopper 110. In this embodiment, the hopper has a four cubic foot capacity equivalent to 100 pounds of material with a density of 25 lbs. per foot3. It is contemplated that any conventional construction or size for the screw, the hopper 110 and the screw housing 102 may be substituted for those described above.
The screw shaft (not shown) is driven by a variable speed DC motor 104 and reducer gear (not shown) connected to the screw shaft by a chain and sprocket arrangement contained in a split type chain guard 106. A plurality of spiral slots 112 are cut into the screw housing 102. The spacing of the cut slots is based upon the requirements of the system. Parameters affecting the slot size and arrangement of slots include the size of the flue duct, the flow rate of the gases in the flue duct and the degree of mercury contained in the flue gases.
In the preferred embodiment, three spiral slots 111, 112 and 113 are used. The slots are 3/4 of an inch wide, with the ~ , 2 ~3 3 ~
exception of the end slot 111. In order to prevent build-up of the additives at the end bearing and bearing protector 139, the end-most slot 111 is cut wider than upstream slots 112 and 113.
The increased width of the slot 111 insures that all remaining material conveyed by the screw exits housing 102. In the preferred embodiment, the spiral slot is one inch wide. It is, however, contemplated that any spacing of the slots and any slot dimensions may form part of this invention.
Adjacent each slot is a respective sleeve 114, 115 or 116 mounted circum~erentially around the screw feeder housing 102.
Each sleeve is adapted to slide axially along the housing 102.
The purpose o each sleeve is to allow partial or full covering of a respective spiral slot 111, 112 and 113 so as to control the flow of additive out of the slot. For example, the sleeve position can be adjusted to accommodate the different flow characteristics or densities of the absorption/adsorption materials or any other pertinent change in conditions or materials. Located below each slot is a respective distributor pipe 117, 118 and 120 connected at a respective end to the gas passage 32. A funnel 122, 124 and 126 is attached to an opposite end of each respective distributor pipe and is oriented so that substantially all of the material flowing from each spiral slot 111, 112 and 113 will be received by each aligned distributor pipe.
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The system also includes plastic covers 134, 136 and 138 which are placed over the screw feeder shaEt 102 in order to cover the spiral slots 111, 112 and 113 and the funnels 122, 124 and 126 aligned below the slots. The plastic covers seal the area between each funnel and each aligned spiral slot so that additive flowing from the slot will not spray onto the floor. The plastic covers also minimize air leakage into the duct 32. The plastic covers are held in place as a result of negative pressure created in gas passage 32 causing the distributor pipes to pull the covers toward the duct opening. Additionally, an operator is able to monitor the flow of additive from the slots into the distributor pipes.
The material injecition rate is controlled by adjusting the variable speed drive set-point. For commercial application, a different type of seal will have to be used, to minimize the air in leakage into the duct.
FIG. 3 is a side view showing the arrangement of a spiral slot and a sliding sleeve~ As shown, the sliding sleeve 115 is mount,ed circumferentially around the screw feeder housing 102.
The sleeve further includes a flanged portion 142 having a pair of bolts 140 connecting opposite ends of the flanges 142a and 142b together (see FIG. 4). The sleeve is adapted to slide axially in the direction of arrows A-A.
The screw conveyor sleeve arrangement is shown in cross-section in FIG. 4. The screw conveyor has a plurality of vanes " ~ .
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146 mounted about a hollow screw shaft 14~ in order to convey material located inside the screw feeder housing shaft 102.
FIG. 5 illustrates the arrangement of the spiral slot distributors and plastic cover as illustrated previously in FIG.
2.
The profess of the instant invention will now be described in more detail. It has been found that either a combination of carbon particles mixed with dusting sulfur or sulfur alone effectively absorbs and/or adsorbs mercury vapor and or mercury particles. However, other materials may be employed instead of or in addition to sulfur including diatomaceous earth, silica gel, activated aluminum oxide, aluminum re-hydrate, zeolite and boiler fly ash.
The activated carbon consists typically of a particle size that has sixty to eighty-five percent that passes through #325 screen mesh (44 microns). The carbon can be lignite based having greater absorbative/adsorbative capacity as needed to remove toxic compounds. The moisture content of the carbon is between two percent to four percent max. and has a mass molasses decolorizing efficiency between 80 min. to 190 min. The pore size is ap-proximately 900 min. and the ash content is 14% max. The dusting sulfur is 98% sulfur and 2% inert. It is contemplated that any other properties of activated carbon and dusting sulfur not described above would form part of this invention. For example, .
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other types of carbon may be used depending upon the temperature and humidity environment inside the flue gas duct.
Example 1 The pilot plant 10 is an 800 ton per day resource recovery plant having two mass burn units sized for four hundred tpd.
refuse at 5200 Btu per lb. The plant generates approximately 100,000 pounds of superheated steam per hour. The flue gas temperatures in the gas passage 32 is typically 400~450 Fahrenheit having a concentration of mercury of up to 1000 micrograms/meter3. Pilot tests were run on-site. Mercury tests were performed simultaneously at inlets and outlets using an EPA
multimetals train with a filter. The first inlet was located immediately downstream of the additive injection point 100 (Fig.
e. between the economizer outlet and spray dryer inlet. A
valid measurement of total mercury can be made at this point.
However, the ratio between the solid and vapor state may be altered. The second inlet measures treated gas in the main gas stack 46 (FIG. 1). Although not ~orming a part of this invention, the multimetals train includes first and second impingers containing 5% HN03/10% H202 and third and fourth impingers containing 4% KMnO4/10% H2S04.
In this example, a mixture of 50~ activated carbon and 50%
sulfur was used. As shown in Table 1 below, the Hg "inlet"
content constituted (microgram/meter3) the particle concentration measured at the inlet. The content was 171 ug/NM (at 12% C02~V) , , . : ; ~, ", ::. ,:.' '. ,.
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and in vapor form 662 ug/NM3 (at 12% CO2DV). Using an injection rate of 6.0 lbs. per hour, the resulting particle outlet measure-ment was 1.3 ug/NM3 Hg particles and 203 ug/NM3 for the mercury vapor. The removal efficiency was 99.3% for mercury particles and 69.4% for mercury vapor. The average removal efficiency was 75.5%.
INLET OUTLET REMOVAL EFFICIENCY INJECT
Hg (ug/NM3) Hg (ug/NM3) Hg (%) LBS/HR
FRONT BACK TOTAL FRONT BACK TOTAL FRONT BACK TOTAL RATE
171 662 ~33 1.3 203 204 99.3 69.4 75.5 6.0 , Example 2 A 100% sulfur dust adsorbent/absorbent was injected at a rate of 7.5 lbs. per hour through conveyor 100. A higher throughput for the conveyor was found to be necessary due to the higher density and different flow characteristics of the absorbent/adsorbent. The inlet measurements of mercury Hg(ug) particles were 50 ug/NM3 and 444 ug/NM3 for vapor. Following treatment, the particle and vapor measurements were respectively 1.2 Hg(ug/NM3) and 228 Hg(ug/NM3). A removal efficiency of 97.2%
was found for particles and 40.5% for vapor yielding a total ef-ficiency percentage of 46.3%. The results are outlined in more detail below in Table 2.
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INLETOUTLET REMOVAL EFFICIE~CY INJECT
Hg (ug/NM3)Hg (ug/NM3) Hg (~) LBS/HR
, FRONT BACK TOTAL FRONT BACK TOTAL _FRQNT BACK TOTAL RATE
444 4941.4 264 265 97.2 40.5 46.3 7.5 .~
Although only a preferred embodiment is specifically il-lustrated and described herein, it will be appreciated that many ~ modifications and variations of the present invention are possible ; in light of the above teachings and within the purview of the ap-pended claims without departing from the spirit and scope of the invention.
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BACKGROUND OF THE INVEN'I'ION
The present invention relates to a process for adsorbing or absorbing mercury from contaminated flue gases and an apparatus for conveying and distributing the adsorbing material.
It has long been recognizecl that mercury poses a danger to the environment and health. In power plants and in the incineration of waste materials, mercury compounds contained in the fuel or waste materials end up in the gas phase as a result of combustion or incineration. If mercury is released into the atmosphere, it can be carried through the nutrition cycle and end up causing sev~re health problems. The maximum concentration of mercury in the air that can be tolerated for a long period of time without causing health related damage is about 0.1-0.2 mg/m3. Numerous techniques have been proposed for purifying gases to reduce the presence of mercury. These systems have drawbacks including cost, complexity, efficiency, safety and effectiveness.
U.S. Patent No. 3,194,629, for example, discloses impreg-nating activated carbon with sulfur and then passing the mercury-containing gases over a bed of the impregnated activated carbon to remove the mercury. However, carbon is a costly material that is not economical for use in large scale systems. Moreover, the method of applying the activated carbon by leaving it in a bed would require frequent removal and replacement of the spent material by a relatively complex handling system. If the handling ~' system is avoided, frequent shut-downs would be necessary to remove the spent carbon at various clean-out points.
Various techniques also involve spraying activated carbon into flue gas passages to adsorb mercury vapor. However, rela-tively large quantities of activated carbon are needed, and the cost of activated carbon is high.
Another method outlined in U.S. Patent No. 3,838,190 pro-vides for washing gases containing mercury with sulfuric acid having a temperature between 60 and 180 and a concentration of at least 50%. However, this process is not suitable for boiler or incinerator opération since the treatment of hot sulfuric acid is costly, technically complex and relatively unsafe.
Anotner way of removing mercury from hot flue (waste) gases is proposed in U.S. Patent No. 4,273,747. This method involves atomizing an aqueous liquid such as water or a lime slurry into the hot flue gases in the presence of fly ash suspended in the gas stream. Subsequently, the fly ash is separated from the gas stream. It is claimed that a substantial part of the mercury originally present in the gas stream is adsorbed or absorbed by the fly ash so that the flue gases can be safely discharged into the atmosphere. However, tests conducted on numerous plants by Applicants and others do not support this result. One hypothesis is that the technique requires the presence of unburned carbon particles in the fly ash. When the boiler or incineration system does not produce adequately large :-.
quantities of unburned material, the aqueous injection techniqueis effective.
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SUMMARY AND OBJECTS OF TliIE INVENTION
In view of the foregoing, it should be apparent that there still exists a need in the art for a method and apparatus for adsorbing or absorbing mercury flue gases that i5 realized in a simple and effective manner and that is practical, economical and safe to use in a large scale system.
Ik is an object of this invention therefore to provide a method for adsorbing or absorbing mercury vapor and other toxic vapors contained in flue gases that is simple, reliable and economical, does not require frequent adjustment, costly materials or equipment, and is highly effective.
Still more particularly, it is an object of this invention to provide ~or an apparatus for treating mercury contained in flue gases produced by the combustion of refuse, waste or fossil fuels and, which provides for the distribution of the additive into the flue gases evenly and continuously with minimal operator intervention.
Another ob~ect of the invention is to provide for a mer-cury treating additive which is found to significantly reduce mercury in boiler or incinerator flue gases and that is cost effective.
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It is yet a further object of the invenkion to provide a mercury reduction apparatus easily controlled by an operator while the system is operating.
Briefly described, these and other objects of the inven-tion are accomplished in accordance with its apparatus aspecks by providing an apparatus for injecting dry additive into the flue gas passages of an incinerator. The injecting mechanism includes a screw conveyor driven by a variable speed DC motor connected mechanically through a high-ratio gear box. The screw conveyor housing has a plurality o~ spiral slots located on its base and sleeves mounted adjacent to each slot. Each sleeve extends about the circumference of the screw feeder housing and is adapted to slide axially along the housing in order to cover a respective spiral slot.
A trough hopper communicates with the screw conveyor at one end and a plurality of distribution pipes are located below each respective spiral slot. Each of the distribution pipes has a funnel connected to its top end and the funnel is aligned directly below the spiral slot to receive the dry additive. The operation of the screw conveyor causes the dry additive, placed in the trough hopper, to be mechanically conveyed by the screw conveyor and equally divided through the spiral slots. Material is then caused to drop into the flue gas passages through the distribution pipes.
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The method of the present invention is carried out by mix-ing particulate sulfur with carbon and then injecting the particulated mixture into the flue gas passages causing the removal of mercury from the flue gases. Mercury is subsequently separated from the system in the spray dryer absorber and baghouse filter located downstream from the point where the absorbing/
adsorbing particulate mixture is injected.
In a second embodiment, the process for removing mercury involves spraying sulfur dust into the flue gas passages.
With these and other objects, advantages and features of the invention ,that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block schematic diagram showiny the adsorption material injection system of the present invention;
FIG. 2 is a plan view of the injection apparatus used in the injection system of FIG. l;
FIG. 3 is a cut-away side view of the control sleeve used with the apparatus shown in FIG. 2;
FIG. 4 is a cross-sectional view taken alony lines IV-IV
~, of FIG. 3; and FIG. 5 is a cut-away side-view showing the feeder distri-bution and control sleeve arrangement under a plastic shield of : the apparatus shown in FIG. 2.
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DET~ILED DESCRIPTION OF THE PRE~ERRED EMBODIMENTS
Referring now in detail to the dra~ings wherein like parts are designated by like reference numerals throughout, there is illustrated in FIG. 1 the adsorption material injection s~stem 10 embodying the present invention. The system consists o~ an incin-erator 20 of any conventionally known design. The present invention is not solely designed to operate on incinerators but can also be applied to any conventionally known combustion device, including power genëration systems that produce stack gasses containing mercury.
The incinerator shown in Fig. 1 represents one type of an incinerator design, but it can be replaced with an~ other known incinerator. The incineration device, exemplified in this Figure, consists of a stoker grate, a boiler furnace/combustion chamber 20 constructed of gas-tight and continuously welded water walls extending down to the grate surface. Combustion takes place in the lower part of furnace 20 wher~ closely spaced high-pressure overfire air jets connected to a fan through line 27 creates turbulence along the front and rear walls of the incinerator causing intense localized turbulence. Complete combustion of the unburned gases occurs before the gases pass into a boiler bank and the subsequent heat transfer sections of the incinerator.
The incinerator also includes a stoker grate located below the combustion chamber which inclines downward from the furnace ' ' . , ' ' ' . . . ' , . , :
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feed hoppar 22 towards a discharge chute 30. A series of plenum chambers underneath the stoker grate admit primary combustion air supplied from the primary combustion fan 28. The burned out mate-rial from the stoker grate will then fall through the residue discharge chute 30 into an optional quench bath (not shown).
Combustion gases fl~w throllgh a first pass where NOx emis-sions are controlled b~ combustion control and by optional selective non-catalytic removal using N~3. The mercury containing gas stream is then introduced into duct 32 where it is treated by a mercury abatement system 100 located downstream from the steam generating equlpment and upstream from the pollution control system. Details of the apparatus 100 and the proceqs ~or treating mercury form the remaining parts of this specification.
Treated flue gases are introduced into a spray dryer absorber 36 via an appropriate disbursing device tnot shown). In the spray dryer, a liquid, such as Ca~OH)2 + H20, is atomized into small droplets causinq the fluid to evaporate after contacting the hot flue gases. As a result, a cooling of the gases and mercury suspended in those gases takes place. Fly ash and contained mer-cury is then removed by centrifugal force in the spray absorber cyclone. Ths mercury is then collected at the conically shaped base of the absorber and may then be removed through an exit 38.
The cooled gas stream exits the spray dryer through duct 39 con-nected to the fabric filter baghouse collector 40.
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In one embodiment, a pulse~jet type fabric filter arrangement is used. Alternatively, the system can be used in combination with dif~erent air pollution control equipment, such as a reverse air-type fabric filter or an electrostatic precipitator. In the baghouse 40, the particulate residues are separated from the gas stream whereupon the residues including mercury, fly ash and other materials are removed via exit 42 through the baghouse hoppers.
The treated gases from which the particulate residues in the mercury are separated, exits the baghouse filter through duct 43. The gases are then blown via induced draft fan 44 through main smoke stack 46 and out into the atmosphere. At this point, the concentration of mercury is so low as to be within safe levels.
Referring now to FXG. 2, the injection apparatus for mercury abatement 100 is illustrated. The distribution device is located adjacent a flue gas duct 32. The distribution system 100 consists o~ a screw feeder housing 102 mounted on legs 128 and 130 which is adapted to slowly convey material in accurate quantities using a single flight screw (not shown). The screw feeder 100 operates at a feed rate of 1 to 100 times the amount of mercury contained in the flue gases. An example of a feed rate for a conventional incinerator burning 400 tons per hour of refuse is 1 to 20 lbs. per hour split equally amongst the three distribution points arranged at equal distances along the feeder shaft.
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For increased rigidity, the screw shaft i5 hollow. In the prPferred embodiment, the screw feeder is made of a stainless steel construction using high temperature bearings and seals enabling it to handle corrosive materials and operate in high temperature environments. However, other conventional materials can be substituted.
Located at one end of the screw feeder shaft is a trough type feeder hopper 110. In this embodiment, the hopper has a four cubic foot capacity equivalent to 100 pounds of material with a density of 25 lbs. per foot3. It is contemplated that any conventional construction or size for the screw, the hopper 110 and the screw housing 102 may be substituted for those described above.
The screw shaft (not shown) is driven by a variable speed DC motor 104 and reducer gear (not shown) connected to the screw shaft by a chain and sprocket arrangement contained in a split type chain guard 106. A plurality of spiral slots 112 are cut into the screw housing 102. The spacing of the cut slots is based upon the requirements of the system. Parameters affecting the slot size and arrangement of slots include the size of the flue duct, the flow rate of the gases in the flue duct and the degree of mercury contained in the flue gases.
In the preferred embodiment, three spiral slots 111, 112 and 113 are used. The slots are 3/4 of an inch wide, with the ~ , 2 ~3 3 ~
exception of the end slot 111. In order to prevent build-up of the additives at the end bearing and bearing protector 139, the end-most slot 111 is cut wider than upstream slots 112 and 113.
The increased width of the slot 111 insures that all remaining material conveyed by the screw exits housing 102. In the preferred embodiment, the spiral slot is one inch wide. It is, however, contemplated that any spacing of the slots and any slot dimensions may form part of this invention.
Adjacent each slot is a respective sleeve 114, 115 or 116 mounted circum~erentially around the screw feeder housing 102.
Each sleeve is adapted to slide axially along the housing 102.
The purpose o each sleeve is to allow partial or full covering of a respective spiral slot 111, 112 and 113 so as to control the flow of additive out of the slot. For example, the sleeve position can be adjusted to accommodate the different flow characteristics or densities of the absorption/adsorption materials or any other pertinent change in conditions or materials. Located below each slot is a respective distributor pipe 117, 118 and 120 connected at a respective end to the gas passage 32. A funnel 122, 124 and 126 is attached to an opposite end of each respective distributor pipe and is oriented so that substantially all of the material flowing from each spiral slot 111, 112 and 113 will be received by each aligned distributor pipe.
/~ ~t'~
The system also includes plastic covers 134, 136 and 138 which are placed over the screw feeder shaEt 102 in order to cover the spiral slots 111, 112 and 113 and the funnels 122, 124 and 126 aligned below the slots. The plastic covers seal the area between each funnel and each aligned spiral slot so that additive flowing from the slot will not spray onto the floor. The plastic covers also minimize air leakage into the duct 32. The plastic covers are held in place as a result of negative pressure created in gas passage 32 causing the distributor pipes to pull the covers toward the duct opening. Additionally, an operator is able to monitor the flow of additive from the slots into the distributor pipes.
The material injecition rate is controlled by adjusting the variable speed drive set-point. For commercial application, a different type of seal will have to be used, to minimize the air in leakage into the duct.
FIG. 3 is a side view showing the arrangement of a spiral slot and a sliding sleeve~ As shown, the sliding sleeve 115 is mount,ed circumferentially around the screw feeder housing 102.
The sleeve further includes a flanged portion 142 having a pair of bolts 140 connecting opposite ends of the flanges 142a and 142b together (see FIG. 4). The sleeve is adapted to slide axially in the direction of arrows A-A.
The screw conveyor sleeve arrangement is shown in cross-section in FIG. 4. The screw conveyor has a plurality of vanes " ~ .
' 2 ~ 3 ~
146 mounted about a hollow screw shaft 14~ in order to convey material located inside the screw feeder housing shaft 102.
FIG. 5 illustrates the arrangement of the spiral slot distributors and plastic cover as illustrated previously in FIG.
2.
The profess of the instant invention will now be described in more detail. It has been found that either a combination of carbon particles mixed with dusting sulfur or sulfur alone effectively absorbs and/or adsorbs mercury vapor and or mercury particles. However, other materials may be employed instead of or in addition to sulfur including diatomaceous earth, silica gel, activated aluminum oxide, aluminum re-hydrate, zeolite and boiler fly ash.
The activated carbon consists typically of a particle size that has sixty to eighty-five percent that passes through #325 screen mesh (44 microns). The carbon can be lignite based having greater absorbative/adsorbative capacity as needed to remove toxic compounds. The moisture content of the carbon is between two percent to four percent max. and has a mass molasses decolorizing efficiency between 80 min. to 190 min. The pore size is ap-proximately 900 min. and the ash content is 14% max. The dusting sulfur is 98% sulfur and 2% inert. It is contemplated that any other properties of activated carbon and dusting sulfur not described above would form part of this invention. For example, .
"
: ' ' ~ ~ é~
other types of carbon may be used depending upon the temperature and humidity environment inside the flue gas duct.
Example 1 The pilot plant 10 is an 800 ton per day resource recovery plant having two mass burn units sized for four hundred tpd.
refuse at 5200 Btu per lb. The plant generates approximately 100,000 pounds of superheated steam per hour. The flue gas temperatures in the gas passage 32 is typically 400~450 Fahrenheit having a concentration of mercury of up to 1000 micrograms/meter3. Pilot tests were run on-site. Mercury tests were performed simultaneously at inlets and outlets using an EPA
multimetals train with a filter. The first inlet was located immediately downstream of the additive injection point 100 (Fig.
e. between the economizer outlet and spray dryer inlet. A
valid measurement of total mercury can be made at this point.
However, the ratio between the solid and vapor state may be altered. The second inlet measures treated gas in the main gas stack 46 (FIG. 1). Although not ~orming a part of this invention, the multimetals train includes first and second impingers containing 5% HN03/10% H202 and third and fourth impingers containing 4% KMnO4/10% H2S04.
In this example, a mixture of 50~ activated carbon and 50%
sulfur was used. As shown in Table 1 below, the Hg "inlet"
content constituted (microgram/meter3) the particle concentration measured at the inlet. The content was 171 ug/NM (at 12% C02~V) , , . : ; ~, ", ::. ,:.' '. ,.
~3Ç~,t"'~
and in vapor form 662 ug/NM3 (at 12% CO2DV). Using an injection rate of 6.0 lbs. per hour, the resulting particle outlet measure-ment was 1.3 ug/NM3 Hg particles and 203 ug/NM3 for the mercury vapor. The removal efficiency was 99.3% for mercury particles and 69.4% for mercury vapor. The average removal efficiency was 75.5%.
INLET OUTLET REMOVAL EFFICIENCY INJECT
Hg (ug/NM3) Hg (ug/NM3) Hg (%) LBS/HR
FRONT BACK TOTAL FRONT BACK TOTAL FRONT BACK TOTAL RATE
171 662 ~33 1.3 203 204 99.3 69.4 75.5 6.0 , Example 2 A 100% sulfur dust adsorbent/absorbent was injected at a rate of 7.5 lbs. per hour through conveyor 100. A higher throughput for the conveyor was found to be necessary due to the higher density and different flow characteristics of the absorbent/adsorbent. The inlet measurements of mercury Hg(ug) particles were 50 ug/NM3 and 444 ug/NM3 for vapor. Following treatment, the particle and vapor measurements were respectively 1.2 Hg(ug/NM3) and 228 Hg(ug/NM3). A removal efficiency of 97.2%
was found for particles and 40.5% for vapor yielding a total ef-ficiency percentage of 46.3%. The results are outlined in more detail below in Table 2.
. .
,, .
~ ~ ~3 ~
INLETOUTLET REMOVAL EFFICIE~CY INJECT
Hg (ug/NM3)Hg (ug/NM3) Hg (~) LBS/HR
, FRONT BACK TOTAL FRONT BACK TOTAL _FRQNT BACK TOTAL RATE
444 4941.4 264 265 97.2 40.5 46.3 7.5 .~
Although only a preferred embodiment is specifically il-lustrated and described herein, it will be appreciated that many ~ modifications and variations of the present invention are possible ; in light of the above teachings and within the purview of the ap-pended claims without departing from the spirit and scope of the invention.
~. , , '^. :,', j ~ i :
~ .
. . .:.. :. .
::. . :-
Claims (33)
1. A process for removal of mercury from flue gases comprising the steps of:
providing a particulate absorbent/adsorbent material, injecting said particulate absorbent/adsorbent material into a flue gas passage; and removing mercury from said flue gases downstream from the spraying point.
providing a particulate absorbent/adsorbent material, injecting said particulate absorbent/adsorbent material into a flue gas passage; and removing mercury from said flue gases downstream from the spraying point.
2. The process according to claim 1, wherein said absorbent/adsorbent material comprises sulfur.
3. The process according to claim 1, wherein said absorbent/adsorbent material comprises diatomaceous earth.
4. The process according to claim 1, wherein said absorbent/adsorbent material comprises silica gel.
5. The process according to claim 1, wherein said absorbent/adsorbent material comprises aluminum oxide.
6. The process according to claim 1, wherein said absorbent/adsorbent material comprises aluminum re-hydrate.
7. The process according to claim 1, wherein said absorbent/adsorbent material comprises zeolite.
8. The process according to claim 1, wherein said absorbent/adsorbent material comprises boiler fly ash.
9. The process according to claim 1, further comprising the step of mixing the particulate absorbent/adsorbent material with carbon.
10. The process according to claim 9, wherein said particulate absorbent/adsorbent material comprises sulfur.
11. The process for removing mercury of claim 1, wherein the removing step involves spray drying and absorbing/adsorbing said flue gases such that particles containing mercury drop out of a spray drying device.
12. The process according to claim 11, wherein said removing step further involves filtering said flue gases following said spray drying step such that said mercury is further removed via a filter.
13. The process according to claim 12, wherein said filter comprises a baghouse filter.
14. The process according to claim 11, wherein said removing step further involves removing said particulates from said flue gases using electrostatic precipitation.
15. The process according to claim 9, wherein said carbon is activated with a particle size of 60-85% through 325 mesh screen, has a moisture content between 2%-4% max., and has a molasses decolorizing efficiency between 80-190 min.
16. The process according to claim 9, wherein said carbon is fine particulate matter with a particle size of 50-90% through 325 mesh screen.
17. The process according to claim 2, wherein said sulfur comprises sulfur dust having a 2% inert component and 90% active sulfur ingredients.
18. The process for removing mercury in claim 1, wherein the removing step involves particulate control equipment, including a baghouse filter or an electrostatic precipitator.
19. The process for removing mercury according to claim 9, wherein said mixing step mixes carbon with sulfur in order that each constitutes 50% of said particulate mixture.
20. The process for removing mercury according to claim l, wherein said injecting step involves injecting said particulate mixture into a flue gas passage at a rate within the range of 5 to 100 times the amount of mercury contained in the flue gases.
21. The process for removing mercury according to claim l, wherein said injecting step occurs downstream of an incinerator or any conventional combustion system and upstream from a spray dryer absorber or particulate control equipment.
22. A process for removing mercury from gases comprising steps of:
injecting sulfur into a flue gas passage; and removing said mercury from said flue gases as a particulate.
injecting sulfur into a flue gas passage; and removing said mercury from said flue gases as a particulate.
23. The process according to claim 22, wherein said sulfur comprises sulfur dust having 2% inert and 90% active sulfur ingredients.
24. The process for removing mercury according to claim 22, wherein said sulfur is conveyed to a injector and injected into said flue gas passages at a rate within the range of 5 to 100 times the amount of mercury contained in the flue gas passages.
25. An apparatus for providing additive into a flue gas passage comprising:
a screw conveyor including a screw feeder housing, said screw conveyor having a plurality of spiral slots cut into said screw feeder housing;
a supply hopper communicating with said screw con-veyor; and a plurality of distribution pipes each having a first end in communication with said flue gas passage and a second end in alignment with a respective spiral slot such that dry additive provided to said hopper is conveyed through said screw feeder housing by said screw conveyor wherein said additive equally flows through each of said spiral slots into said mutually aligned distribution pipes and into said flue gas passage.
a screw conveyor including a screw feeder housing, said screw conveyor having a plurality of spiral slots cut into said screw feeder housing;
a supply hopper communicating with said screw con-veyor; and a plurality of distribution pipes each having a first end in communication with said flue gas passage and a second end in alignment with a respective spiral slot such that dry additive provided to said hopper is conveyed through said screw feeder housing by said screw conveyor wherein said additive equally flows through each of said spiral slots into said mutually aligned distribution pipes and into said flue gas passage.
26. The apparatus for injecting additive according to claim 25, wherein said screw conveyor is driven by a variable speed DC motor connected to said screw conveyor.
27. The apparatus for injecting additive according to claim 25, wherein said variable speed DC motor is connected to said screw conveyor via a high ratio gear box coupled to a chain sprocket drive.
28. The apparatus for injecting additive according to claim 25, further comprising a plurality of sleeves located adjacent each of said spiral slots and circumferentially surrounding said screw feeder housing wherein said plurality of sleeves are adapted to slide axially along said screw feeder housing in order to partially or fully cover a respective spiral slot.
29. The apparatus according to claim 25, wherein said supply hopper comprises a trough hopper located at one end of said screw conveyor.
30. The apparatus according to claim 25, wherein said distribution pipes have a funnel located at said end below said spiral slot.
31. The apparatus for injecting additive according to claim 25, wherein said additive comprises a mixture of carbon and sulfur.
32. The apparatus for injecting additive according to claim 25, wherein said additive comprises elemental sulfur.
33. The apparatus for injecting additive according to claim 25, wherein said additive comprises either diatomaceous earth, zeolite, silica gel, activated aluminum oxide or aluminum re-hydrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US56074190A | 1990-07-31 | 1990-07-31 | |
| US560,741 | 1990-07-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2036746A1 true CA2036746A1 (en) | 1992-02-01 |
Family
ID=24239170
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2036746 Abandoned CA2036746A1 (en) | 1990-07-31 | 1991-02-20 | Process and apparatus for absorption/adsorption material injection |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2036746A1 (en) |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999002243A1 (en) * | 1997-07-11 | 1999-01-21 | Advanced Fuel Research, Inc. | SIMULTANEOUS MERCURY, SO2, AND NOx CONTROL BY ADSORPTION ON ACTIVATED CARBON |
| DE102007020422B4 (en) * | 2007-04-27 | 2010-10-21 | Rwe Power Ag | Method for the dry cleaning of mercury-laden exhaust gases |
| US8198208B2 (en) | 2008-10-03 | 2012-06-12 | EPCOR Power Generation Services, Inc. | Bromination process |
| US20120330060A1 (en) * | 2010-02-12 | 2012-12-27 | Stamicarbon B.V. | Removal of ammonia in urea finishing |
| US20130202504A1 (en) * | 2008-06-10 | 2013-08-08 | Calgon Carbon Corporation | Enhanced adsorbents and methods for mercury removal |
| US8906140B2 (en) | 2011-10-26 | 2014-12-09 | W.L. Gore & Associates, Inc. | Filtration module |
| US9308518B2 (en) | 2013-02-14 | 2016-04-12 | Calgon Carbon Corporation | Enhanced sorbent formulation for removal of mercury from flue gas |
| US9321032B1 (en) | 2008-06-10 | 2016-04-26 | Calgon Carbon Corporation | Inherently concrete-compatible carbon sorbents for mercury removal from flue gas |
| US9550148B2 (en) | 2015-06-02 | 2017-01-24 | Paragon Waste Solutions, Llc | Heavy metal removal |
| US10220369B2 (en) | 2015-08-11 | 2019-03-05 | Calgon Carbon Corporation | Enhanced sorbent formulation for removal of mercury from flue gas |
| US11857942B2 (en) | 2012-06-11 | 2024-01-02 | Calgon Carbon Corporation | Sorbents for removal of mercury |
-
1991
- 1991-02-20 CA CA 2036746 patent/CA2036746A1/en not_active Abandoned
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999002243A1 (en) * | 1997-07-11 | 1999-01-21 | Advanced Fuel Research, Inc. | SIMULTANEOUS MERCURY, SO2, AND NOx CONTROL BY ADSORPTION ON ACTIVATED CARBON |
| DE102007020422B4 (en) * | 2007-04-27 | 2010-10-21 | Rwe Power Ag | Method for the dry cleaning of mercury-laden exhaust gases |
| US7923397B2 (en) * | 2007-04-27 | 2011-04-12 | Rwe Power Aktiengesellschaft | Sorbent for the dry cleaning of waste gases charged with mercury and process for the production thereof |
| US9321032B1 (en) | 2008-06-10 | 2016-04-26 | Calgon Carbon Corporation | Inherently concrete-compatible carbon sorbents for mercury removal from flue gas |
| US20130202504A1 (en) * | 2008-06-10 | 2013-08-08 | Calgon Carbon Corporation | Enhanced adsorbents and methods for mercury removal |
| US8834606B2 (en) * | 2008-06-10 | 2014-09-16 | Calgon Carbon Corporation | Enhanced adsorbents and methods for mercury removal |
| US8198208B2 (en) | 2008-10-03 | 2012-06-12 | EPCOR Power Generation Services, Inc. | Bromination process |
| US20120330060A1 (en) * | 2010-02-12 | 2012-12-27 | Stamicarbon B.V. | Removal of ammonia in urea finishing |
| US9493408B2 (en) * | 2010-02-12 | 2016-11-15 | Stamicarbon B.V. | Removal of ammonia in urea finishing |
| US8906140B2 (en) | 2011-10-26 | 2014-12-09 | W.L. Gore & Associates, Inc. | Filtration module |
| US11857942B2 (en) | 2012-06-11 | 2024-01-02 | Calgon Carbon Corporation | Sorbents for removal of mercury |
| US9308518B2 (en) | 2013-02-14 | 2016-04-12 | Calgon Carbon Corporation | Enhanced sorbent formulation for removal of mercury from flue gas |
| US9550148B2 (en) | 2015-06-02 | 2017-01-24 | Paragon Waste Solutions, Llc | Heavy metal removal |
| US10220369B2 (en) | 2015-08-11 | 2019-03-05 | Calgon Carbon Corporation | Enhanced sorbent formulation for removal of mercury from flue gas |
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