Summer is the perfect time to inspect a boiler, sizing up its energy use, carbon footprint, and overall ability to support a process reliably and safely. Once inspected, a boiler must be restarted and tuned properly to ensure maximum performance.

This article discusses key considerations governing the annual inspection of firetube boilers ranging in size from 100 to 1,000 hp and 3,450 to 34,500 lb of steam per hour.

FIRE SIDE

Once a boiler is opened for inspection, the first order of business is assessing the condition of the fire side of the unit:

• Are the refractory and insulation in good condition? If the refractory shows evidence of serious cracking (¼ in. or more) or deterioration, which can lead to overheating and metal fatigue/failure, patch it with cement or plastic and lightly wash-coat it.

• Do the pressure-vessel and heat-transfer surfaces show signs of poor combustion (sooting) and possible metal fatigue and weldment cracking? Sometimes, these are evidenced by rust formation, the result of water leakage when the boiler cooled (metal contraction) and still was under pressure. A hydrostatic dye test under pressure will manifest such leakage.

When soot is found on fire-side surfaces, it is time to retune the burner, making sure the fuel/air ratio properly tracks the turndown of the burner from low to high fire. Often, that is all that is required to eliminate the problem and substantially improve combustion efficiency. However, you also might want to consider installing independent motorized actuators, removing much of the linkage assembly, to prevent slippage and hysteresis. Additionally, an oxygen-trim system may be considered to continuously compensate for variances in ambient-air temperature, barometric pressure, etc. Both of these retrofits are relatively inexpensive and can, under the right operating conditions, reduce fuel usage by 5 to 10 percent over the course of a year.

WATER SIDE

Once a boiler is drained, it is time to inspect the water side of the vessel, looking for signs of excessive scale (⅛ in. or more), corrosion, and pitting of metal.

When problems related to the water side of a boiler are discovered, it is imperative that a water-treatment consultant be engaged. Failure to remedy a problem quickly can result in major repair costs and downtime or complete loss of a boiler's pressure vessel.

SAVING ENERGY

If a boiler's pressure vessel is in good shape, with only minor scaling (magnetite) and no evidence of weldment deficiencies and pitting, it likely has many years of life left in it. As such, it is an excellent candidate for upgrading, especially if its capacity meets current and anticipated process and heating needs.

The upgrading of an old but serviceable boiler with the latest advances in burner and control technology may be just what the doctor ordered when it comes to saving energy and improving reliability. This might be a good time to add other fuel-saving enhancements, such as a feedwater economizer or blowdown heat-recovery system. The options are considerable, leading to thousands, if not hundreds of thousands, of dollars in fuel savings annually.

SYSTEM CUT-IN AND RECOMMISSIONING

Once a boiler has been cleaned, inspected, and closed, it should be restarted and tuned by a qualified technician, one with the experience to properly set the controls and adjust the burner to maximize fuel-to-steam efficiency.

The tuning of a burner requires a load allowing the boiler to fire throughout its operating range while the burner-management system controls the various operating and safety sequences and checks. For this to occur, the boiler needs to be reintroduced to the system in a precise manner, one ensuring safety and system integrity.

Cold plant startup

A cold plant startup typically is conducted when a boiler has been offline for two to three days, with the system piping and components reaching near-ambient conditions. The procedure is as follows:

1. Ensure all boiler valves are returned to their operating position.

2. Fill the boiler to the proper operating level, as seen in the water-column gauge glass.

3. Open the non-return and boiler stop valves.

4. Open all drains in the header and mains to allow for air purging.

5. Ensure the boiler feed line and pumps are in the ready position.

6. Open any vents on the boiler.

7. Start the burner in the manual low-fire mode, raising the temperature/pressure gradually to temper the metal, avoiding thermal stresses.

8. Once the boiler reaches 2 to 3 psig on the steam gauge, close the vents and drains.

9. Perform an evaporation test on the low-water cutoff and pump control. This is done by securing the feedwater supply, allowing the boiler to steam off naturally until the low-water trip point.

10. When the boiler reaches approximately 60 percent of its operating set point, switch the operation from manual to automatic, allowing the unit to modulate the firing rate to match the load.

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