Cement Energy and Environment

Rapping Cycles of ESP A commo n phenomenon observed in many ESP's is fluctuation in the vis ible emission or opacity. This is commonl y known as puffing. Puffing is an indication of over-rapping of the co llecting plates or poo r gas distri bution, or both. The effect of gas distributio n has already been explained. Puffing on account of over– rapping can be minimised by proper fine-tuning of the rapping cycles. J.K. Cements encountered thi s probl em in the ir ESP. As there is no set program for the rapping cycles, which may e nsure the des ired result at once, the following guide !ines we re evolved for the purpose. After 7 to I0 days of continuous trials, the desired result was achieved. Guidelines for fine-tuning the rapping i) Rapping frequency of the emitting frame needs to be kept at the highest possible value to avoid any build-up of material on the emitting electrodes (whi c h m ay c au se loss of corona ). While continuous rapping of the emitting electrodes helps corona generatio n, it may at the same time damage the high-tension frame, so the rapping frequency needs to be gradually brought down, say, starting from 1-minute-on and ]-minute- off to !-minute– on and 5-minutes-off. The on-time can be made equa l to one revolution of the rapper shaft. ii) Rapping of the collecting plate can be switched off where upon the stack opacity can be seen falling. The duration can be clocked from the mome nt the collecting pl ate rappers ar e switched off and the stack opac ity starts increasing once again. Thi s is the off-time required for the first fie ld. iii) The second f ield requires an off-time 4 to 8 times the first fi e ld . T his is becau se the fin e r dust particles, which escape the first field, require some accumulation on the plates to dig themselves in . iv) The excessive build-up on the plates may cause back-coro na. Thi s can be de tected f rom the controllers whe reupon the rapping frequency can be increased. The off-time can then be reduced in steps o r 15 minutes . Gas Distribution Problem Orig inally, the layout of ESP ducting had an acute ' U' tum at its inle t and the inlet transition of the ESP was not f itted with diffusing turning vanes . So, it was suspected that the gas distribution was getting severe ly hampe red and would assume the course indicated in Fig./. But in spection revealed that the d istribution pattern was its exact mirTor image as in Fig.2. I Fig 1 Anticipated air distribution pattern (see shaded portion at right) Fig 2 Actual air distribution pattern (See shaded portion at left) 3