Live plant startup

This procedure is similar to cold plant startup:

1. Ensure that the boiler vent and the drain between the main stop and the non-return valve are open.

2. Open the equalizing valve around the main stop valve.

3. Open the main stop valve.

4. Close the boiler vent when the steam pressure reaches 2 to 3 lb.

5. Perform an evaporation test on the low-water cutoff.

6. When the boiler pressure reaches approximately 80 percent of the line pressure, open the non-return valve.

7. Raise the boiler pressure slowly, allowing the non-return valve to cut in the boiler online.

8. Close the drain between the non-return and stop valves.

Once a boiler is safely online, the burner can be tuned for optimum operation. This requires skill and understanding and is not for amateurs. It also requires proper tools. One such tool is the combustion analyzer, which is used to check products of combustion as a burner modulates between low and high fire. Properly adjusted burners maintain a given fuel/air ratio from low to high fire, limiting the amount of excess air and maximizing combustion efficiency. With gas, excess air normally is in the 10-to-20-percent range; with oil, it normally is in the 20-to-25-percent range. Another benefit of a well-tuned combustor is that it burns cleanly, eliminating excessive soot formation on fire-side surfaces while keeping carbon-monoxide levels as close to zero as possible and below 50 ppm.

After adjusting a burner, a technician makes sure the operating, modulating, and high-limit controls are set properly, ensuring adequate system response and continuity between boiler cycles. He or she also checks the operating pressure and firing rate against the boiler's stack temperature. Depending on the operating pressure and firing rate, a well-tuned, efficient boiler should have a stack temperature 50 to 150°F above the saturated-steam temperature. A 40°F elevation will result in a 1-percent loss in efficiency.

BOILER STORAGE

At times, after being cleaned and inspected, a boiler will be stored.

Dry layup

If a boiler is to be stored for an extended period of time (more than three months), the recommendation is to lay it up “dry” to avoid corrosion. For this to be accomplished, a boiler must be dried out completely, with the steam and water lines secured. A desiccant should be placed on the water and fire sides to keep moisture from forming. Once the desiccant is in place, the unit should be sealed with new gasketing material. (The American Society of Mechanical Engineers suggests quick lime or silica gel.) Also, the passageway to the vent stack should be interrupted to prevent warm, moist air from coming into contact with boiler tubes.

Wet layup

If a boiler is to be stored for a short period of time (one to three months), wet layup is recommended. Secure the boiler, and allow it to cool, introducing the amount of scavenging/neutralizing chemical prescribed by a water-treatment consultant. Next, flood the boiler, allowing water to escape through the vent(s), and fire the unit to the steaming temperature with the vent(s) open. This allows the greatest amount of oxygen to be eliminated from the vessel. Lastly, close all of the valves, disconnect all electrical power, and ensure that the passageway to the vent stack is interrupted.

Savings Beyond a Boiler

Once a boiler has been opened, cleaned, inspected, and closed, and the burner has been tuned or retrofitted, a full audit of the steam system should be considered.

A steam-system audit includes the assessment of load profiles and pressures to determine if economizers and other ancillary equipment would accelerate payback. Also, it takes into consideration piping and steam-user systems, evaluating if they can be upgraded for energy and process-improvement reasons.

A full steam-system audit goes beyond a boiler, identifying ways to save up to an additional 30 percent in annual fuel costs, “cash on the floor” that can come back to a business a hundredfold year after year.

SUMMARY

Following the foregoing suggestions is an excellent way to get on the path of proper asset protection, utilization, and fuel conservation, conservation that puts considerable cash back into your business while playing a key role in protecting the finite resources we so often take for granted, the fuel we burn, and the air we breathe. It starts with awareness, followed by the will to make it happen.

For past HPAC Engineering feature articles, visit www.hpac.com.

The director of marketing/communications for Cleaver-Brooks Inc., Steve Connor has more than 40 years of experience in the steam-generation field, including engineering, service training, and field application sales. He has spoken and written articles on boiler design, efficiency, and safety. He can be contacted at sconnor@cleaver-brooks.com.