Monday, May 11, 2020

Flashing up and Raising ste procedure on a shutdown boiler

  • Check that the boiler is properly closed-up after repairs (if any). Cheek that all boiler mountings and equipments are in place and properly connected to tile boiler.
  • Check that all the appropriate valves are shut such as steam stop, blow down valve, chemical injection etc;
  • Open air vent completely.
  • Open auxiliary feed cheek valve and fill boiler with pure water up to 1/4 of the gauge glass level. Do not fill the boiler up to the normal operating level, since the water will expand when heated and so cause the level to rise.
  • Start forced draft fan with dampers opened correctly to purge the furnace and combustion space off any foul gases. If such gases are present, a ‘blow back’ is possible. Some times a ‘blow back’ may occur due to very dirty uptakes. 'Blow back' is a very rapid combustion of inflammable gases and is, in reality, all explosions, which can cause serious damage to equipment and personnel.
  • Check must he made to ensure that there is no deposited oil in the furnaces. The oil burners to he cleaned of any cold heavy oil and a light diesel oil re-circulation is started with fuel oil pump running and re-circulating valve open and all burner valves shut. The initial light-up is normally done on diesel oil, which may later he changed over to heavier oil. Most boilers can also start up on heavy oil.
  • Ascertain that the exhaust duct is clear and the burner system is operational.
  • Select the smallest size burner tip and light-up the burner (normally center one), with a lighted torch, after closing the re-circulating valve.
  • For a stable flame condition, the air register sleeves may be operated to reduce the airflow to a minimum at the start so that a flame can he established, which is then adjusted to give a smoke-less combustion. Too much air gives a colour less to whitish flue discharge through the funnel. If air is too less the boiler starts issuing black smoke. The right combustion condition is established when a brown hazy discharge issues from the stack. A periscope type of arrangement is normally provided to cheek the condition of the exhaust flue gas.
  • For initial warming of the boiler, the burner, is to he operated at low firing rate and the firing has to he intermittent, i.c.5 minutes on and 10 minutes off, until a steady whiff of steam keeps coming from the boiler air vent.
  • Close the air vents and allow the boiler pressure to build up slowly and steadily.
  • Steady firing can now be continued.
  • Start heating up the fuel oil in the heater provided. As the fuel temperature approaches about 90*C, a change over from diesel oil to heavy oil can then be made.
  • A bigger burner tip is chosen to go with the heavy oil and the steam pressure comes up quite quickly.
  • The gauge glass are blown through and checked for proper water level indication.
  • As the pressure comes up to the working pressure, the boiler safety valves can be operated by means of the easing gear, to ensure that they are in good order.
  • The main steam stop valve is opened after opening its by-pass valve and after draining the steam lines sufficiently to avoid water hammer. The stop valve must he opened very slowly, only when pressure equalization has been achieved by the opening of the by-pass valve.
  • The auxiliary feed cheek is closed, the main feed cheek valves are opened and the main feed pump started up to maintain boiler water level.
  • If the boiler is geared for automatic running, this is the time to change over the system to auto-control, when both the water level and the steam pressure would he maintained with in a predetermined range. If the system is on hand operation, close watch on water level, steam pressure and the fuel oil pressure, plus the condition of flue gas through the funnel has to be maintained and regulated manually.

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