Cement Energy and Environment

After carrying outlhe above upgradations in all the ESP's, an engineering audit for funher reduction of emission was conducted by M/s. Precipcare, Pune, specia list consultants on ESP's. Their recommendations have led to extraordinary resu lts and an enormous improvement in the efficiency of ESP's and fall in stack emissions. The three key factor identified by the consultants. as affecti ng the du st coll ection and ESP efficiency. were as under : 1. Residence time u. Energisation 111. Cleaning of electrodes The time available for treatment of gas inside the ESP. The electrical energy available for collecting the dust. The effec ti veness of du st removal from the electrodes. These factors, in turn. are influenced by a whole range of operating conditions as briefly described below : Res idence time gets reduced owing to a variet)' of '-' '-' operating conditions resulting. in turn, from augmentation in productioncapacity, and manifesting by larger volumes of gas, increased sneakage and main ly poor gas disu·ibution. a) Larger gas volume : With increase in production capacity. the volume and velocity of the gas inside the ESP increases, which shortens the residence time. Owing to this, the finer dust particles acquire lesser electrical charge and hence do not experience the de. ired pull toward~ the co llecting plates . Consequently, such fine patticles escape the ESP. b) Increased sneakage : The gas flowing above and below the treatment zone is known as sneakage. With increased gas volume. the gas profile changes too. The effect of changed gas profile can be seen in a precipitator where the gas entry is either from the top or from the bottom. The high velocity of the ga can direct it either to the hopper or towards the roof. The portion of the gas that sneaks from outside the treatment zone carries away with it substantial dust load which adds to a higher stack emission. 2 c) Poor gas distribution : Proper gas distribution is the most important factor as it ensures equal usage of the entire ESP volume. Poor gas distribution overloads one portion of the ESP leaving the rest un/under-utilised. The poor ga distribution cau. es uneven dust accumulation on the collecting plates whereby the c lean ing ab ility of the rapp ing mechanism is affected. The electrical energisation suffers as the voltage-current (V-1) characteristic is grossly dominated by the ESP's under-utilised pot1ion. Case Stud~ Following is the detailed case study in respect of the ESP of kiln No.2 of tbe works carried out in the light of the aforementioned aspects, and the corrective measures worked out to eliminate the identified problems. Process parameters Gas volume ESP inlet temperature I,65,000 Nm 3 /hr. at ll5°C ESP inlet dust concentration 42g/ Nm 3 (approx.) ESP outlet dust emission 120 mg/ Nm 3 ESP design details Make ABB(formerly Flakt fndia Ltd.) No. of chambers Single No. of electrical fields Two No. of mechanical fields Two Gas passages 27 Gas passage width 250 mm Height of collecting plates 8000 mm Length of collecting plates 4000mm Cleaning mechanism Tumbling hammer T/R set 48 KV average/ 700M Amps. Rapping Timing through + programmable logic controller