Boiler Startup – Courtesy of Rentech Boilers
It must be recognized that all boilers and auxiliary equipment require operator attention during start up. Special care must be exercised in the manipulation of feedwater and fuel systems to protect against damaging the unit and to insure personnel safety.
Check and close the manual blow-off valves, the continuous blowdown valves, the gage cocks and the water column and gage glass drain valves. Open the drum vent valve, the water column shutoff valves (if provided), the gage glass shutoff valves and the steam pressure gauge valve.
The unit should be slowly filled with properly treated feedwater using the level control valve bypass valve. The filling rate depends on the temperature of the feedwater. The feedwater should be as close as possible to the metal temperature to prevent excessive temperature stresses that could cause tube leakage. The minimum recommended feedwater temperature is 70°F. Fill slowly and vent fully to prevent any pressure buildup from the flashing of warm feedwater. The level should be set and manually maintained at just below the normal water level so that there is room for expansion when water is heated. Blowdown the gauge glass and observe the return of liquid to insure that the glass is clear and functioning properly.
When the unit is filled and the level is stabilized, start the purge cycle of the combustion controls as specified by the combustion equipment manufacturer. Allow adequate time to completely purge the entire boiler, duct work, etc.
The drum vent valve should be initially open to vent generated steam while purging air from the system. Close the steam drum vent at 15 psig. (Refer to table entitled "Summary of valve positions").
The start-up rate of the boiler is limited by the following items:
1. Allowable heat up rate of refractory, to achieve acceptable refractory life.
2. Elimination of temperature stress that could cause leaking tube joints.
3. If sulfur or HCl is present in normal fuel effluent, start the heating process on clean fuel until the dewpoint is passed.
During this period of operation, carefully observe that all components function properly. Be prepared to shut the unit down should a lack of proper operation become evident. Visually observe combustion conditions for proof that gauges, meters, and other instrumentation are properly reporting operating conditions.
Maintain the normal water levels at all times. The level can be maintained by hand feeding or by blowing down as necessary. Too high a level will render the separators ineffective and cause water carryover in the steam, while too low a level will allow possible overheating of pressure parts. If the water level is not visible, firing should have been stopped automatically and the reason for the low water determined. The feedwater control valve should be cut in when the operating pressure is obtained and then the bypass valve should be closed.
If the unit is tied into a main steam line with other units and there is pressure downstream of the not-return valve, then the system must be brought up to slightly above that operating pressure. The steam stop valve can then be opened to permit flow through the non-return valve. Re-check inspection openings, fittings and piping connections for leaks, tighten as required to insure proper gasket seating. Always maintain proper water treatment as recommended by the Owner's water consultant.