Friday, February 21, 2020

Electric fuel oil preheater in low pressure boiler

Electric pre-heater

The  electric  oil  pre-heater,  is  placed  on  the  burner  housing  and is  used  for  preheating  the  fuel  oil.  The  pre-heater  is  provided  with  electric  heating elements,  which  conduct  the  produced  heat  to  the  heavy  fuel  oil.  Depending  on  the  oil throughput  and  viscosity  the  burner  can  be  equipped  with  one  or  more  pre-heaters. Irrespective of the number of pre-heaters there is only one common temperature controller. However, each pre-heater is provided with its own limit thermostat.

Temperature limit thermostat

 The  temperature  limit  thermostat  (6)  has  a  fixed  temperature  limit  of  180˚C  and  it  is fitted  with  a  reset  button.  If  the  oil  temperature  becomes  too  high,  the  temperature  limit thermostat stops the burner. The shut down is indicated in the control system. In case of  failure,  the  fault  has  to  be  repaired.  Before  the  pre-heater  can  be  taken  into  service again,  the  reset  button  on  the  temperature  limit  thermostat  must  be  activated  and  the shut down in the control system must be reset.
Note: Reset must be carried out when the thermostat is not under voltage.

Temperature controller for pre-heater 

The  desired  fuel  oil  temperature  can  be  set  in  the  control  system  together  with  alarm set  points  and  shut  down  set  points.  The  fuel  oil  temperature  in  the  pre-heater  is  registered  by  a  Pt  100  resistance  temperature  sensor  and  supplied  to  the  control  system.Fluctuations  in  oil  temperature  are  minimized  by  the  Pt  100  sensor  which  is  placed directly  on  the  heating  plate.If  the  oil  temperature  becomes  too  low  or  too  high  during operation,  e.g.  if  the  heater  elements  are  faulty,  the  control  system  stops  the  burner  and actuates a shut down indication. Furthermore,  the  pre-heater  is  equipped  with  an  additional  Pt  100  resistance  temperature  sensor  with  transmitter,  which  handles  remote  indication  of  the  oil  temperature

Test of the functions
The  function  of  the  temperature  limit  thermostat  can  be  tested  by  dismantling  one  of the  wires  at  the  terminals  to  the  temperature  limit  thermostat.  The  burner  stops  immediately. The  low  oil  temperature  shut  down  can  be  tested  by  disconnecting  the  electric  power to  the  pre-heater.  When  the  oil  temperature  drops  below  the  shut  down  limit  the  burner stops.

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