Flue gas dust recovery in electrostatic precipitators improved with an additive to the fuel oil

Abstract

The performance of electrostatic precipitators depends in large measure on the specific electrical resistance (i.e., resistivity) and the degrees of dispersion and cohesion of the dust, aswell as on the type of fuel.Investigations carried out by the State Scientific-Research Institute for Gas Purification in Industry and Sanitation (IGP) at the Magnezit Plant and the Dokuchaev Flux-Dolomite Plant showed that when rotary kilns are fired with sulfurous fuel oil the electrostatic precipitators do not function efficiently owing to the formation of a solid layer of dust on the electrodes [1].The resistivity of the dust from magnesite and dolomite is high, i.e., up to 1013-1014 ~ ~ cm.As a result of this high resistivity, the layer of magnesite and dolomite dust on the precipitation electrodes acts as insulator so that the current decreases sharply and an "inverse corona" is formed. The outcome is that dust entrapment becomes less efficient and the precipitators have to be disconnected so that the electrodes can be cleaned. Experiments carried out over a period of 25 days in 1970 by the IGP on the precipitators of kilns Nos. 7 and 8 in Metallurgical Powder Section No. 3 (MPS-3) of the Magnezit Plant showed that the conversion of the kilns to oil firing resulted in the efficiency of dust recovery decreasing from 91.8 to 57.7~.Trial firings of well-brine magnesia and Satkin magnesite carried out by the Institute for Gas Purification in Ferrous Metallurgy (IGPFM) on experimental installations of the Iodobrom Association and an establishment of the Ukrainian Trust for Iron Ore [2, 3] also showed that solid dust deposits are formed on the elements of gas purification installations and on the electrodes of electrostatic precipitators and sharply reduce the efficiency of dust extraction.The formation of the solid deposit is attributable not only to the sulfur in the fuel oil but also to the sulfurous and chlorous compounds in the material being fired. It was established that an effective method of reducing dust deposits and increasing the efficiency of the dust extraction process consists of using the fuel additive VNIINP-106. The results of experiments carried out by the IGPFM formed the basis for the design of an installation for introducing the additive into the fuel oil. The installation was subsequently constructed at the Magnezit Plant.The experiments were conducted on rotary kiln No. 7 in MPS-3.* The fuel gases pass from the kiln to the dust chamber, then to a waste-heat boiler in which their temperature falls to 270-300~ after which they pass to TsN-24-type cyclones and then to an AP-73-3-type twosection electrostatic dust precipitator modified to match the design of the PGDS type.