Saturday, February 8, 2020

Start sequence for burner and fuel/air regulation in Marine low pressure boiler

Oil/air regulation

The oil and air regulation for the burner are handled by two servomotors. The oil flowis regulated bya valve, which is regulated by a servomotor. The air damper is regulatedby a second servomotor.Figure 1 illustrates the regulator system.The servomotorsare controlled by the control system during start-up/stop and operationof the burner.

The oil quantity burned is determined by nozzle size and oil pump pressure. The oilregulator regulates the return oil flow according to the capacity demand. At partial loadthe oil regulator is open so that the oil throughput in the valve is at maximum and thereturn oil flow pressure at minimum. At full load the oil regulator is closed whereuponthe oil throughput is at minimum and the pressure at maximum.

The  air  quantity  is  matched  to  the  fired  oil  quantity  by  means  of  the  control  system, which controls the servomotor for the air dampers.

Start sequence for burners with microprocessor control systems.



1) Pre-purge  takes  place  with  the  air  quantity  of  full  load.  During  pre-purge  period  solenoid  valves  (4),  (5),  and  (8)  are  closed  and  solenoid  valve  (15)  is  open,  see  Figure  1 and Figure 2.



2) Flushing period-At the end of the purging period the servomotors turn to the position of ignition  load,  solenoid  valve  (5)  and  (8)  opens  and  a  flushing  sequence  will  take  place, the  nozzle  valve  is  purged  (pre-heated)  during  this  period.  The  oil  temperature  regulation  controls  that  the  oil  temperature  is  adequate  during  purging  and  atomising  periods.



3)Atomizing period-After  the  flushing  period  is  completed  the  solenoid  valve  (5)  will  close  and  the  oil  in the  pre-heater  will  be  heated.  The  burner  will  then  go  into  the  ignition  step;  solenoid valves  (4)  and  (5)  are  opened  and  solenoid  valve  (3)  closed.  The  electric  arc  between the ignition electrodes ignites the oil spraying from the nozzle.

4)Burner operation- The  oil  quantity  to  be  fired  is  regulated  by  means  of  the  oil  regulator  (12)  by  throttling the  return  flow.  At  partial  load  the  oil  regulator  is  open  and  at  full  load  closed.  During burner  operation  the  control  system  drives  the  servomotors,  which  again  drives  the  oil regulator  and  the  air  dampers  between  partial  load  and  full  load  according  to  the  steam demand.

5)Shut down-  If  the  burner  shuts  down,  solenoid  valves  (4),  (5),  and  (8)  close,  and  solenoid valve (3) opens. The oil pressure is released from the nozzle valve. The  nozzle  valve  spring-back  closes  the  needle  valve  in  the  nozzle  and  closes  the  oil flow  in  the  nozzle.  At  full  load  the  atomising  pressure  is  approx.  20-25  bar  when operating  on  MDO  or  MGO  and  approx.  25-30  bar  on  heavy  fuel  oil.  The  return  pressure  of  the  oil  measured  at  manometer  position  2  can  vary  from  the  lowest  possible  for the  nozzle  at  low  load  and  up  to  max  30  bar(g)  at  full  load.  The  return  flow  pressure is determined according to the position of the oil regulator.

No comments:

Post a Comment

OVERHAULING OF CYLINDER UNIT of auxiliary engine IN SHIP

THE PROCEDURE FOR DISMANTLING OF CYLINDER UNIT FROM THE ENGINE ARE AS FOLLOWS: 1.Safety precautions -Stopped engine -Shut...