Page 88 - Boiler_Operators_Handbook,_Second_Edition

Boiler Plant Operations 73

valve at the steam header is closed the free blow drain low water cutoff tests if it’s necessary to shut the burner
valve should be open. down to control the rate of heating of the boiler.
Set firing rate controls to manual and low fire. Close the boiler vent valves when the pressure is
Make one quick trip around the boiler to be certain it up on heating boilers or 25 psig on power boilers. If the
isn’t open and all valves are in the proper positions non-return valve on a high pressure boiler is closed,
before starting it. Open the fuel block valves slowly to open it so steam will flow to the free blow drain. If the
ensure you don’t upset fuel supply to operating boil- second steam stop valve was left open, open the free
ers. When firing oil, check an oil burner assembly then blow drain to drain the boiler header and leave the non-
and insert in the burner. If oil is steam atomized, open return closed.
isolating valves to admit steam to the inlet of the burner Allow the pressure to increase while observing it
steam shut-off valve. If oil is air atomized, start compres- closely. The burner should shut down when the operat-
sor and admit air to the inlet of the burner air shut-off ing pressure or temperature control setting is reached.
valve. Check to be certain normal operating fuel supply Once that operation is proven, test the high pressure or
pressures have been established. Blow down the gauge high temperature limit switch by temporarily installing
glass and water column while observing the water level a jumper on the terminals of the control switch. The
in the glass to assure yourself the boiler contains water. high limit should shut the boiler down before the safety
Turn the burner management control on to allow a valves open or the temperature of a heating boiler ex-
burner to start. On multiple burner boilers and in older ceeds 250°F. It should also lock out to prevent continued
single burner plants it may be necessary to initiate a operation. Allow the pressure to fall until it is below the
purge and burner ignition. When the pilot flame is prov- operating pressure then reset the controls so the burner
en, gradually open the atomizing steam or atomizing air can be started again. Remove the jumper from the con-
shut-off valve at the burner. This ensures that any fuel trol switch terminals.
oil that may be transported to the burner by the atomiz- Once you’ve proven operation of the low water
ing medium will be exposed immediately to the ignition cutoff and the boiler pressure or temperature control
energy of the ignitor and burned at nearly a normal rate. and limit switches you can run through successive tests
Opening the valves earlier can inject a slug of oil into the of each combustion air and fuel limit switch. Proving
furnace that would subsequently vaporize to produce the operation of the low combustion air flow switch can
an explosive mixture in the furnace and ignite when the produce a condition of flammable mixtures in the boiler
pilot comes on. Open the fuel shut-off valve, if the atom- so you must be careful with that one. In some cases you
izing medium didn’t produce a fire, to start the main will have to simply adjust the switch setting to simulate
burner. If the atomizing medium dumped in some fuel a condition, not the best of tests, but at least you will
that produced a fire it’s best to repeat the purge. Some- have done something to ensure it operates. I’ve attended
times you’re so slow at opening the steam or air valve testing programs where many of the fuel and air limit
that you don’t have time to get fuel on. That’s okay, wait switches didn’t function when the operator thought
until it has purged again. This is a normal start-up and they would.
you aren’t in a hurry.
Shortly after the burner has started and is operat- • With the firing rate set at minimum fire, reduce
ing normally, close the burner manual valve. The burner combustion air flow by slowly sliding a blank over
management system should detect a flame failure and the inlet of the forced draft fan while someone
initiate a boiler shutdown. Only if the boiler shut down, watches the fire. The minimum air flow switch
reset the burner management system for another start. should trip before the fire gets smokey or unstable.
Open the burner manual valve after the burner manage- Take care that the blank doesn’t affect the switch
ment system indicates an ignitor flame is proven. Hav- sensing the air flow, use another method of reduc-
ing restored operation, check the low water cutoffs by ing air if it does.
blowing each one down and confirming the burner man-
agement system shuts the boiler down. Do not use any • Increase gas pressure to the burner while watching
bypass push-button while testing the cutoffs at this time, the fire, again at minimum fire. The high gas pres-
you want a full operational test. Once the boiler is up and sure switch should trip before the fire gets smokey.
operating it may not shut down for months; this is the one
and only, best and truest time to confirm that the flame • Decrease gas pressure to the burner while watch-
failure and low water safety systems all work. Repeat the ing the fire, again at minimum fire. The low gas