CN112516781A - Three-section type dry-wet combined jet removal method suitable for CFB boiler - Google Patents

Three-section type dry-wet combined jet removal method suitable for CFB boiler Download PDF

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CN112516781A
CN112516781A CN202011492097.4A CN202011492097A CN112516781A CN 112516781 A CN112516781 A CN 112516781A CN 202011492097 A CN202011492097 A CN 202011492097A CN 112516781 A CN112516781 A CN 112516781A
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dioxin
flue gas
concentration
limestone
activated carbon
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赵元财
王慧青
王昭
赵帅
查琼亮
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Xian Thermal Power Research Institute Co Ltd
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Abstract

The invention discloses a three-section dry-wet combined jet removal method suitable for a CFB boiler, which comprises the following steps: the first section is limestone powder, and is subjected to preliminary dechlorination and desulfurization, and the specific injection amount is controlled according to the control of SO at the outlet of the hearth2The concentration is 3000-4000 mg/m3Determining that the injection position is a conventional limestone injection port and is close to a coal injection point; the second stage is that in the range of flue gas temperature 650-750 deg.C, the flue with several forms is drawn out, and the slaked lime slurry is atomized and sprayed for dechlorinationEliminating precursors of PCDDs/PCDFs and avoiding the synthesis of dioxin in the range of 250-450 ℃; the third section is activated carbon powder, and the spraying position is in front of a bag type dust collector, so that dioxin and heavy metals are mainly adsorbed. The invention is based on the generation mechanism of dioxin, adopts the technology of combining source control and removal after combustion, and firstly controls SO by spraying limestone and slaked lime slurry2And key parameters influencing the generation of the dioxin, such as a chlorine source and the like, so as to reduce the generation amount of the dioxin, and then an activated carbon injection technology is adopted to simultaneously remove the dioxin and heavy metals.

Description

Three-section type dry-wet combined jet removal method suitable for CFB boiler
Technical Field
The invention belongs to the field of thermal power generation, and particularly relates to a three-section dry-wet combined jet removal method suitable for a CFB boiler.
Background
At present, sludge treatment modes in China mainly comprise modes of landfill, composting, natural drying, incineration and the like, and the incineration can effectively remove harmful substances in the sludge at a high temperature, so that reduction, stabilization, harmlessness and resource utilization of the sludge are realized. Sludge incineration is the most thorough sludge treatment technology from the aspect of treatment effect, and the circulating fluidized bed sludge incinerator has the characteristics of uniform heat conduction in the incinerator, high heat storage, good fuel adaptability, easiness in realizing control of harmful gas and the like, and has become a development trend of sludge treatment internationally. Conventional pollutants such as CO, SOx, NOx and HCl generated by sludge incineration can be effectively controlled through the existing mature pollution control technology, however, the sludge incineration can generate harmful pollutants such as dioxin, heavy metals and the like which are rarely combusted by other fuels. In recent years, with the increasing awareness of environmental protection of people and the gradual improvement of requirements on environmental quality, environmental hazards possibly caused by substances such as dioxin, heavy metals and the like in flue gas discharged after sludge incineration become a focus of attention, and therefore higher requirements are put forward on environmental management of incineration facilities. The factors influencing the generation of dioxin during sludge incineration are many, and mainly comprise a carbon source, a chlorine source, temperature, a catalyst and SO2And the like. Currently, dioxin control is mainly divided into 2 parts: 1. controlling the generation of dioxin in the sludge incineration process, and adopting corresponding measures mainly according to the influence factors of the generation of the dioxin to control the concentration of a chlorine source and sulfur dioxide; 2. after the incineration, the waste gas is removed by using an adsorbent such as activated carbon. Hg. Migration of heavy metals such As Cd, Pb, As and NiMainly undergoes three processes of evaporation, gas phase and surface reaction, condensation, nucleation, agglomeration, fly ash adsorption and the like. The control of heavy metal pollutants in the sludge incineration process can be divided into control before incineration, control in the incineration process and control after incineration. Before incineration, the control is mainly to sort the garbage in a classified way, so that the content of heavy metals in the garbage entering the furnace is reduced; the control in the incineration mainly is a heavy metal capture technology in the incineration process, and the emission of heavy metals is inhibited through the addition of a solid adsorbent, the change of the operation condition, the use of flue gas purification equipment and the like; the control after incineration is mainly realized by adopting a control technology on heavy metals in the fly ash. The technology for jointly removing dioxin and heavy metal generated by incineration is very important.
To control the emission of dioxins and heavy metals, various common processes and combinations thereof are:
1) electrostatic precipitator + wet scrubber;
2) a cyclone dust collector, a dry lime absorbent injection system and a bag type dust collector;
3) wet scrubber + activated carbon
However, researches show that the main removing effect on dioxin is activated carbon, the mechanism of the activated carbon is the adsorption effect of the activated carbon, other process combinations can achieve better removing efficiency only when being combined with an activated carbon injection technology in different modes, and meanwhile, the activated carbon can also effectively remove heavy metals generated after incineration.
Disclosure of Invention
The invention aims to provide a three-stage dry-wet combined jet removal method suitable for a CFB boiler aiming at the defects of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a three-section dry-wet combined jet removal method suitable for a CFB boiler comprises the following steps: the first stage is limestone (calcium carbonate) powder, and preliminary dechlorination and desulfurization are carried out; in the second stage, in the range of the flue gas temperature of 650-750 ℃, a zigzag flue is led out, slaked lime slurry (calcium hydroxide) is atomized and sprayed for dechlorination, precursors of PCDDs/PCDFs (polychlorinated dibenzo-dioxin/furan) are eliminated, and the dioxin is prevented from being synthesized in the range of 250-450 ℃; the third section is activated carbon powder, and the spraying position is in front of a bag type dust collector, so that dioxin and heavy metals are mainly adsorbed.
The invention is further improved in that the specific injection quantity of the first section is controlled according to the control of the outlet SO of the hearth2The concentration is 3000-4000 mg/m3And determining that the injection position is a conventional limestone input port and is close to a coal input point.
A further improvement of the invention is that the first stage limestone injection is given by the following equation:
Figure RE-GDA0002922161420000021
Figure RE-GDA0002922161420000031
in the formula: omegas,ar-mass fraction of sulphur in the in-furnace fuel,%;
mFuel-mass flow of fuel to the furnace, kg/h;
Figure RE-GDA0002922161420000032
the addition amount of the desulfurized limestone is kg/h;
Figure RE-GDA0002922161420000033
the addition amount of dechlorinated limestone is kg/h;
ηSO2-desulfurization efficiency,%, of limestone addition;
Figure RE-GDA0002922161420000034
in the formula:
Figure RE-GDA0002922161420000035
SO in the furnace Outlet flue gas2Concentration, mg/m3；
ωs,ar-mass fraction of sulphur in the in-furnace fuel,%;
Vfg,dvolume of dry flue gas generated per kilogram of fuel, m3；
Figure RE-GDA0002922161420000036
Figure RE-GDA0002922161420000037
In the formula: m isFuel-the input of fuel, kg/h;
VHClconcentration of HCl in the furnace exit flue gas, mg/m3；
ωs,ar-mass fraction of sulphur in the in-furnace fuel,%;
the total limestone injection amount is obtained from the equations (1), (2) and (3).
The invention is further improved in that sulfur is converted into SO when fuel is taken and combusted2At a ratio of 90%, spraying a predetermined amount of limestone to make SO at the hearth outlet2The concentration is kept between 3000 and 4000mg/m3I.e. VSO2＝3000～4000mg/m3And calculating the limestone desulfurization efficiency in the formula (5).
The invention is further improved by taking
Figure RE-GDA0002922161420000038
Calculate the corresponding VHCl。
In a further improvement of the present invention, the injection amount of the second-stage slaked lime slurry is obtained by the following formula:
Figure RE-GDA0002922161420000041
in the formula: m isSlaked limeThe amount of sprayed slaked lime in unit time is kg/h;
ωCa(OH)2——Ca(OH)2accounts for mass fraction of slaked lime,%;
Vfgvolume flow of flue gas, m3/h。
The present invention is further improved in that the injection amount of the third stage activated carbon is determined by the concentrations of dioxin and heavy metals.
The invention further improves that the toxicity equivalent concentration of dioxin is obtained by a prediction model, and the toxicity equivalent concentration is shown as a formula (7):
Figure RE-GDA0002922161420000042
in the formula: dioxins-dioxin toxicity equivalent, ng I-TEQ/Nm3；
T0-furnace temperature, ° c;
Tb-boiler outlet temperature, deg.c;
Tf-the temperature of the outlet of the cloth bag, deg.c;
Cw-water content of flue gas,%;
Cc-CO in flue gases2Content,%;
Cs-SO in flue gas2Content, mg/m3；
CHClConcentration of HCl in the flue gas, mg/m3；
The required amount of activated carbon injection is determined by the following equation:
FC＝FC,dioxins+FC,Hg (8)
Figure RE-GDA0002922161420000043
FC,Hg＝rC/Hg·(CHg+CAs+CPb+CCd) (10)
in the formula: f is the injection amount of the active carbon, mg/min;
Sdioxin-specified by the standardLimit, ng I-TEQ/Nm3；
Eta, the efficiency of the activated carbon for removing dioxin,%;
rC/Hgthe mass of the sprayed activated carbon in unit time is equal to the mass ratio of the elemental mercury generated in unit time;
CHgelemental mercury concentration, mg/m3；
CAsArsenic concentration in flue gas, mg/m3；
CPbConcentration of lead in the fumes, mg/m3；
CCdConcentration of Cd in flue gas, mg/m3；
The efficiency eta of removing dioxin by the active carbon is 92 to 97 percent, and r is takenC/Hg＝3×103～4×104，CHgObtained by OHM method flue gas sampling test, CAs、CPbAnd CCdObtained by sampling and testing method EPA 29.
Compared with the prior art, the invention has at least the following beneficial technical effects:
the invention provides a three-section dry-wet combined spraying removal method suitable for a CFB boiler, which adopts a three-section dry-wet combined spraying technology, wherein the first section is that limestone is sprayed at a limestone feeding port, and the spraying amount of the limestone is measured by flue gas SO at an outlet of the CFB boiler2The concentration is 3000-4000 mg/m3Determining, performing preliminary desulfurization and dechlorination, and maintaining a high-sulfur low-chlorine atmosphere to reduce the generation of dioxin; in the second stage, in the range of the flue gas temperature of 650-750 ℃, a zigzag flue (as shown in the attached figure) is led out, slaked lime slurry is atomized and sprayed for dechlorination, PCDDs/PCDFs precursors are eliminated, and the dioxin is prevented from being synthesized in the range of 250-450 ℃; the third section is activated carbon powder, the spraying position is in front of a bag type dust collector, dioxin and heavy metal are mainly adsorbed, and the spraying amount is calculated according to the concentration of the heavy metal in the flue gas. The invention is based on the generation mechanism of dioxin, adopts the technology of combining source control and removal after combustion, and reduces SO by spraying limestone at the first stage2Concentration and preliminary dechlorination, certain sulfur-chlorine ratio is maintained, and atmosphere energy of high sulfur and low chlorine is maintainedEffectively inhibiting the generation of dioxin PCDDS/F, and dechlorinating the slaked lime slurry sprayed at the second stage so as to reduce the generation of precursors of the PCDDS/F. The first two steps adopt a dry-wet combined injection technology based on a dioxin generation mechanism to inhibit the generation of dioxin from the source. Secondly, the activated carbon spraying technology is adopted to simultaneously remove dioxin and heavy metals in the flue gas.
Further, in order to improve the economy, the injection amounts of the respective additives are calculated by an empirical formula or the like.
Drawings
FIG. 1 is a schematic diagram of a three-stage dry-wet combined spray removal method suitable for CFB boilers.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, the invention provides a three-stage dry-wet combined spray removal method suitable for a CFB boiler, comprising: three-stage spraying, the first stage is limestone powder, a certain sulfur-chlorine ratio is maintained, preliminary dechlorination and desulfurization are carried out, and the specific spraying amount is controlled according to the control of SO at the outlet of the hearth2The concentration is 3000-4000 mg/m3The injection position is determined to be a conventional limestone input port and is close to a coal input point; in the second stage, in the range of the flue gas temperature of 650-750 ℃, a zigzag flue (as shown in the attached figure) is led out, slaked lime slurry is atomized and sprayed for dechlorination, PCDDs/PCDFs precursors are eliminated, and the dioxin is prevented from being synthesized in the range of 250-450 ℃; the third section is activated carbon powder, and the spraying position is in front of a bag type dust collector, so that dioxin and heavy metals are mainly adsorbed.
For a further understanding of the invention, reference will now be made to the principle.
Many domestic and foreign circulating fluidized bed incineration studies have shown SO2The method can effectively inhibit the generation of dioxin. Cl needed for forming dioxin in incineration process of municipal solid waste and sludge2Mainly through Cu2+Obtained by catalytic reaction of Deacon of the formula (11), SO2Not only will consume Cl in the atmosphere2，SO2May also be present in the catalyst Cu2+Poisoning to produce CuSO with low catalytic activity4Inhibition of Deacon reaction to reduce Cl2Formation, in addition, studies have shown that SO2The thiosulfonate phenol precursor can be formed by sulfonating the phenol precursor, thereby inhibiting the formation of dioxin.
Figure RE-GDA0002922161420000061
Research shows that organic and partial inorganic chlorine in the garbage is almost completely released in the form of HCl in the local anoxic process, and HCl removal can not only reduce corrosion to equipment, but also prevent HCl and organic components in the garbage from generating harmful substances such as PCDDs/PCDFs and the like. In conclusion, the high-sulfur low-chlorine atmosphere can effectively inhibit the generation of dioxin, and the generation of dioxin is reduced in the combustion process. The production of dioxin can be effectively inhibited from the source by keeping a certain sulfur-chlorine ratio, and the production amount of dioxin tends to decrease when the sulfur-chlorine molar ratio is gradually increased from 1, so that a certain sulfur-chlorine molar ratio r needs to be keptS/ClHerein is taken as rS/ClThe primary purpose of limestone injection in the first stage is therefore to initially desulfurize and dechlorinate, maintaining a sulfur to chlorine ratio of 10.
The possible ways for generating dioxin in the incineration process of municipal solid waste, sludge and the like are mainly three: the method comprises the following steps that firstly, dioxin contains part before municipal solid waste is incinerated; secondly, precursor synthesis is carried out, namely the dioxin precursor is subjected to a complex condensation reaction under the action of catalytic metal to generate dioxin, and the precursor mainly has two sources: the dioxin precursor contained in the municipal solid waste and the organic precursor which is generated by incomplete combustion and exists in a gas phase react with the activated material on the surface of the fly ash; and part of fly ash is synthesized from the beginning, namely a certain amount of fly ash is generated in high-temperature combustion, the fly ash contains macromolecular carbon, incompletely combusted carbon particles and catalytic substances (mainly transition metal), the fly ash can react with hydrogen chloride in flue gas at 250-400 ℃, and dioxin is generated through gasification, chlorination and condensation reaction. The dechlorination process usually adopts a semi-dry process which is low in cost, simple and easy to use, and the semi-dry process is to spray slaked lime slurry into a flue gas pipeline through a spraying system to contact and react with hydrogen chloride to generate a solid compound. Because the dechlorination calcium conversion rate is high at high temperature, the second stage injection position is in a zigzag flue with the flue gas temperature of 650-750 ℃, as shown in the attached drawing, the main purpose is dechlorination, PCDDs/PCDFs precursors are eliminated, and the synthesis of dioxin at the temperature of 250-450 ℃ is avoided.
Activated carbon adsorption is standard configuration for flue gas purification of incineration plants, and the activated carbon has a porous structure and has a strong adsorption effect on dioxins and heavy metals. The total amount of the activated carbon sprayed is determined by the contents of dioxin and heavy metals. The amount of dioxin produced is calculated by a prediction model, and thus the amount of activated carbon required for dioxin removal can be calculated. The research shows that: in the incineration process, most (78% -98%) of metal components (such As Cd, Cr, Cu, Ni, Pb, Zn and the like) contained in the sludge are fixed in fly ash, only a few of Hg, As and the like with high volatility enter flue gas and are discharged to the atmosphere along with the flue gas, and the generation amount of Pb and Cd is increased when the chlorine content in the sludge is high during incineration, so that the removal of elemental Hg, As, Pb and Cd by activated carbon is mainly considered when the amount of the heavy metal removal activated carbon for injection is calculated. The mercury in the incineration flue gas exists mainly in 3 types: granular mercury HgpHg of bivalent mercury2+Elemental mercury Hg0The granular mercury and the bivalent mercury are easy to be captured by a dust remover, wet desulphurization and the like, and the elemental mercury is difficult to remove by the existing dust removing equipment due to high volatility and water insolubility of the elemental mercury. The adsorption method based on activated carbon is the most studied mercury removal technology, and usually activated carbon is sprayed into flue gas at the upstream of a dust removal device, and oxidizing groups on the surface of the activated carbon can remove Hg in the flue gas0Oxidation to Hg2+Then the adsorption and desorption are carried out, and the efficiency of adsorbing the element state can be greatly improved by spraying the active carbon. Research shows that when the carbon-mercury ratio is 3000-40000, the activated carbon demercuration efficiency is high, the amount of the demercuration activated carbon is determined accordingly, and the ratios of As, Pb and Cd in the activated carbon and flue gas are the same.

Claims (8)

1. A three-section type dry-wet combined jet removal method suitable for a CFB boiler is characterized by comprising the following steps: the first section is limestone powder, and preliminary dechlorination and desulfurization are carried out; in the second stage, in the range of the flue gas temperature of 650-750 ℃, a zigzag flue is led out, slaked lime slurry is atomized and sprayed for dechlorination, PCDDs/PCDFs precursors are eliminated, and the dioxin is prevented from being synthesized in the range of 250-450 ℃; the third section is activated carbon powder, and the spraying position is in front of a bag type dust collector, so that dioxin and heavy metals are mainly adsorbed.
2. The method for removing by combined dry and wet injection in three stages suitable for CFB boiler in accordance with claim 1, wherein the specific injection amount in the first stage is controlled according to the SO at the outlet of the furnace2The concentration is 3000-4000 mg/m3And determining that the injection position is a conventional limestone input port and is close to a coal input point.
3. The method of claim 2, wherein the limestone injection amount of the first stage is given by the following equation:
Figure FDA0002840996260000011
Figure FDA0002840996260000012
in the formula: omegas,ar-mass fraction of sulphur in the in-furnace fuel,%;
mFuel-mass flow of fuel charged into the furnace, kg/h;
Figure FDA0002840996260000013
the addition amount of the desulfurized limestone is kg/h;
Figure FDA0002840996260000014
dechlorinated limeThe addition amount of stones is kg/h;
ηSO2-desulfurization efficiency,%, of limestone addition;
Figure FDA0002840996260000015
in the formula:
Figure FDA0002840996260000016
SO in the furnace Outlet flue gas2Concentration, mg/m3；
ωs,ar-mass fraction of sulphur in the in-furnace fuel,%;
Vfg,dvolume of dry flue gas generated per kilogram of fuel, m3；
Figure FDA0002840996260000017
Figure FDA0002840996260000021
In the formula: m isFuel-the input of fuel, kg/h;
VHClconcentration of HCl in the furnace exit flue gas, mg/m3；
ωs,ar-mass fraction of sulphur in the in-furnace fuel,%;
the total limestone injection amount is obtained from the equations (1), (2) and (3).
4. The method of claim 3, wherein the sulfur is converted into SO by burning fuel2At a ratio of 90%, spraying a predetermined amount of limestone to make SO at the hearth outlet2The concentration is kept between 3000 and 4000mg/m3I.e. VSO2＝3000～4000mg/m3And calculating the limestone desulfurization efficiency in the formula (5).
5. The method of claim 3, wherein the method comprises a dry-wet combined jet stripping process
Figure FDA0002840996260000022
Calculate the corresponding VHCl。
6. The method of claim 1, wherein the amount of the slaked lime slurry injected into the second stage is obtained by the following formula:
Figure FDA0002840996260000023
in the formula: m isSlaked limeThe amount of sprayed slaked lime in unit time is kg/h;
ωCa(OH)2——Ca(OH)2accounts for mass fraction of slaked lime,%;
Vfgvolume flow of flue gas, m3/h。
7. The method of claim 1, wherein the amount of activated carbon injected in the third stage is determined by the concentration of dioxin and heavy metals.
8. The method of claim 7, wherein the toxicity equivalent concentration of dioxin is obtained from a predictive model, as shown in formula (7):
Figure FDA0002840996260000024
in the formula: dioxins-dioxin toxicity equivalent, ng I-TEQ/Nm3；
T0-furnace temperature, ° c;
Tb-boiler outlet temperature, deg.c;
Tf-the temperature of the outlet of the cloth bag, deg.c;
Cw-water content of flue gas,%;
Cc-CO in flue gases2Content,%;
Cs-SO in flue gas2Content, mg/m3；
CHClConcentration of HCl in the flue gas, mg/m3；
The required amount of activated carbon injection is determined by the following equation:
FC＝FC,dioxins+FC,Hg (8)
Figure FDA0002840996260000031
FC,Hg＝rC/Hg·(CHg+CAs+CPb+CCd) (10)
in the formula: f is the injection amount of the active carbon, mg/min;
Sdioxin-the limit specified by the Standard, ng I-TEQ/Nm3；
Eta, the efficiency of removing dioxin from the activated carbon,%;
rC/Hgthe mass of the sprayed activated carbon in unit time is equal to the mass ratio of the elemental mercury generated in unit time;
CHgelemental mercury concentration, mg/m3；
CAsArsenic concentration in flue gas, mg/m3；
CPbConcentration of lead in the fumes, mg/m3；
CCdConcentration of Cd in flue gas, mg/m3；
The efficiency eta of removing dioxin by the active carbon is 92 to 97 percent, and r is takenC/Hg＝3×103～4×104，CHgObtained by OHM method flue gas sampling test, CAs、CPbAnd CCdObtained by sampling and testing method EPA 29.
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