As cooler weather approaches, your facility operating engineers may be preparing boilers that have been off-line for normal seasonal operation. Some boilers will have been laid up dry; others will have been stored wet. Regardless of the off-line storage, certain procedures need to be followed for a well-planned, safe start-up of off-line boilers. We encourage all engineers to closely review and follow the boiler manufacturer's start-up procedures, as each boiler is different. This article outlines generic, basic start-up practices for a small to medium size package boiler. Larger high pressure boilers will have start-up procedures with greater detail.
Boilers that have been laid up dry will need to be opened and inspected for any obvious signs of corrosion or scale blockages. Remove any desiccants (if used) for maintaining a dry environment. Both steam and mud drums should be cleaned of any chip scale. For boilers that have been wet stored, it is good practice to drain the boiler and inspect the internals and water level control devices to make certain no blockages or debris will restrict the operation.
Boiler operating engineers are trained to survey and inspect the details of a boiler system before moving the power switch to ON. Once a boiler has been refilled with treated feedwater, the engineer should carefully perform the start-up checks. During start-up checks, verify all lockout/tagout locks have been removed, all ventilation and combustion air openings and louvers are clean and free of debris, and the water level in the boiler is correct. Test the low water fuel cutoff and check that all stack dampers are open. Examine the boiler furnace for foreign material, and the furnace and flue passes for fuel accumulation. Also verify the fuel train valve position and operation of the feed/condensate systems.
After completing the start-up checks, close the operating switch and commence the normal start-up sequence. A typical starting sequence includes operating the controls closed and interlocks (safety controls) closed. Start the fans and purge the boiler, and confirm the purge requirements have been met. Within 10 seconds of energizing the main fuel valve and igniter, prove the ignition flame. Establish and monitor the main flame, then de energize the ignition. Release the fire rate (combustion) control to demand.
Once the unit has warmed, turn power switch to OFF. Verify the shut down cycle. Then restart. Let it come up to full firing rate and open isolation/stop valves to release steam into the system. Have the operating engineer monitor it throughout the day, looking at the flame, stack outlet, controls, and linkage as well as verify gasket tightness for both water side and fire side.
If your facility is in the process of starting up a boiler from layup, make certain the engineers are closely following the boiler manufacturer safety checks and startup procedures. When first starting an off line boiler from long term layup, understand that steaming at low-load or no-load (undercycling) is when corrosion will be accelerated. It is important that boiler engineers keep adequate chemical residuals during this startup period, failure to maintain residuals will increase the internal corrosion rates of the boiler, leading to unplanned outages or costly repairs.
For low to medium pressure boilers during the first few weeks after startup, maintain the oxygen scavenger residual 15-20% higher than normal winter operation and supplement the alkalinity as necessary to maintain a hydroxyl alkalinity above 250 ppm. Inspect and verify all chemical feed equipment is operational and the treatment program is appropriate for the boiler feedwater quality and operating pressure.
For additional information regarding boiler start-up, contact your U.S. Water representative.