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Study of Using Mixed Discharge Electrodes and Mixed ... - isesp

Study of Using Mixed Discharge Electrodes and Mixed ... - isesp

Study of Using Mixed Discharge Electrodes and Mixed ... -

8411th International Conference on Electrostatic PrecipitationStudy of Using Mixed Discharge Electrodes andMixed Spacing of Pole to Pole for Electrostatic PrecipitatorFANG Qixian, ZHANG Binxin(Lanzhou Electric Power Equipment Manufacturer, Lanzhou, China)Abstract: In order to increase the collecting efficiency of ESP and to meet requirements of saving energy and reducing emission,the new ESP design technology, according to the need of high efficient operation, is proposed under the full consideration of coalcomponent and content, ash chemical component and content. Namely, use this technology of mixed wires and mixed same–polardistance for ESP. Through several years’ operation, the present technology by approved is good and its performance is good, reliableand stable.Keywords: Chemical component, Mixed wire, Mixed spacing of pole to pole, Collecting efficiency1 INTRODUCTIONAt present, most of ESPs for coal fired boilers havebeen adopted by power stations, its main merits are thatthere are the smaller operation resistance, the longer usinglife, the lower maintenance cost and the higher bearinghigh-temperature performance. However, the coal qualitiesand boiler conditions are the big influence on performanceof ESP. When the coals are changed for boiler, thecollecting efficiency will be subjected to serious effects dueto the changes of boiler fly-ash performance and thechanges of particle resistivity and its size etc. After,especially issuing the “emission standard of atmospherepollutant for coal fired power plants”(GB13233–2003),more and more serious emissions standards were stipulatedby state for dust emissions in different period of time,among that the highest emissions at third time period isunder 50mg/Nm3. If hitting this requirement, the mostoperating ESPs should need to carry out the retrofit so as toincrease the efficiency of ESPs such as the ESPs of boilersfiring the special coals, of CFB boilers and flue gas processafter FGD etc., like this, the conventional technologies ofESPs could already not meet the requirements for collectingefficiency of special conditions, therefore, the newtechnique research, optimizing design and testing selectingtechnology for ESPs are imperative under the situation, sousing the mixed discharge electrodes and mixed spacing ofpole to pole for electrostatic precipitator is a new directionof developing ESP’ technologies.2 COAL AND ITS ASH FEATURES FOR COALFIRED POWER PLANTSAlthough, the ESP is the high effective equipment, it isoften subjected to the effect of physicals and chemicalscharacteristics from dusts collected, which are as follows:1. Low sulfur content, there are only 0.2–0.3 for mostcoal in power stations. In national standard, if the sulfurcontent from coal is lower than 1.5%, it belongs to lowsulfur coal. When a coal has the high sulfur content, theconductivity of dusts may be increased and it can have theconditioning action for dusts with high resistivity that canrise the collecting efficiency of ESP. When the sulfurcontent is lower than 1%, the gas conditioning actionalmost zero2. The AL 2 O 3 content in dusts, according to nationalstandard, should not exceed the 50%, but AL 2 O 3 content insome of coals is up to 55.66%. The ratio of true specificgravity for this kind of ash to volume specific gravity hasthe big difference, exceeding the 1: 10 and the melting pointof AL 2 O 3 is 2100, therefore, this is a difficult coal withhigh melting point, high resistivity, light gravity, fineparticulates and large viscosity to cause the chargingdifficulty and dusts re–entrainment as well as back corona,it is adverse to the dusts collection for ESP.3. The sum of contents for SiO 2 , AL 2 O 3 , Fe 2 O 3 , CaO inthe dusts is too big and the some over 90%. Tests indicatethat when this value reaches the 90%, the collectingefficiency will be subjected to great influence. CaO in dustsis such an ash which has the high resistivity, difficultcharging, light gravity, fine particulate and big viscosity aswell as uneasy rapping from collecting plate and causingeasily back corona.4. The resistivity of dusts is higher. When flue gastemperature is up to 120, the resistivity can hitn×10 11 Ω·cm—10 13 Ω·cm. Meanwhile, the collecting efficiencyis reduced due to back corona.5. Content of K 2 O andNa 2 O in fly-ash is lower. K 2 O isas with Na 2 O, has the conductive action, but it is a littleweak comparing with Na 2 O. The content of Na 2 O in dustsis 0.22%–1.8% and the content of K 2 O 0.12%3.2% .3 BASIC PRINCIPLEThe basic principle of mixed wires and mixed polespacing is as follow: in order to reach the collectingefficiency, 4 or 5 fields, in general, should be adopted,aiming to the coal performance and ash feature, and each

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