PROJECT: RAMAGUNDAM UNIT - 7 PROBLEM:ESP HOPPER HEATERS WERE CONTINUOUSLY

ENERGISED ON ACCOUNT OF INSULATION PROBLEM. All ESP hoppers are provided with insulation. Panel type of heaters are provided upto 1/3rd height of the hoppers and the panel type of heaters are covered by insulation. The arrangement of insulation for heaters are critical and if the hopper heater panels are not insulated, there will be enormous heat loss, leading to more power consumption. The heater space in between the stiffeners is also to be insulated such that there is no heat leakage through the space. The insulation of ESP hoppers of Ramagundam unit – 7, is carried out as per the drawing given by BHEL/Trichy, no.4 –00-231-48574 and Ranipet drawing no.1-78-378-00983 revision-00. It was observed that all heaters of ESP hoppers were continuously energized, since the temperature of ash inside the hopper is not reaching beyond 120 deg.C., which is the set point, set for thermostats, meant for switching off the power supply to hopper heaters. The temperature was measured with a digital indicator and it was coming around 95 deg.C. only. On investigation along with BHEL/Ranipet Engineers, it was observed that the insulation air gap from the hopper plate to the mineral wool is to the tune of 250 mm throughout the slant portion of ESP hoppers. Because of the large gap and flow of air from bottom to top, the hopper is getting cooled and it is not allowing the temperature to raise in spite of hopper heaters and fluidizing air.

Ranipet has given modified drawing no.1-78-378-00983 revision-01 and 4-00-114-30750-00, which provides variable gap from 250 mm to 75 mm with a closed portion at the bottom of the hopper. On an experimental basis, insulation of two nos. of hoppers were modified, as per the above revised drawings given by Ranipet. It was observed that the temperature is reaching around 130 deg.C. instead of 95 deg.C., as seen earlier. Heaters are cutting in for fifteen minutes and getting switched off through thermostats for thirty minutes, in sequence. Further observations with different loading of ESP are going on. The relevant drawings are as shown below: Based on the above, Ranipet was asked to decide about modification of insulation of all the 144 numbers of hoppers, which will resolve the problem of hopper heaters getting continuously energized.