Another factor affecting boiler placement is size, which can be impacted greatly by boiler type (firetube or watertube). While both types of boilers can meet the 30,000-lb-per-hour-of-150-psig-saturated-steam requirement, firetube boilers are longer and heavier than watertube boilers and may not fit in the same space or be supported by the same foundation. Although firetube boilers are considerably less expensive than watertube boilers, if access to or space within a boiler room is limited and the only location available is an old watertube boiler's spot, a firetube boiler probably will not fit.

Choose a Fuel

When a facility's original boiler was placed in service, the natural-gas rate may have been $3 per million British thermal units, with annual fuel costs of $500,000. With fuel costs having risen so much in recent years, a replacement boiler in the same size range easily could consume $2 million of fuel annually in today's dollars. Because of the volatility of fuel costs, boiler-fuel choices should be deliberate. While natural gas probably will remain the fuel of choice because it is the easiest and cleanest fuel to burn, other fuels, such as waste products, that can be burned to turn into steam are available.

The major concern with any waste or alternative fuel is whether it can be used in a cost-effective manner. Waste-fuel-fired boilers typically are larger and have higher associated capital and operating labor costs and far more stringent environmental regulations. Assuming waste fuel is virtually free, the potential for saving millions of dollars a year is very tempting.

Fuel choice should be recognized as a deliberate decision and its pros and cons considered carefully, but it is too broad a topic to be covered in this article. The potential of burning any waste fuel is site-dependant because one plant may have wood or paper available while another has waste-processed oils. The costs of preparing waste for burning (e.g., chipping wood or filtering oil) must be considered, as must environmental impacts (e.g., cleaning particulate matter from flue gas for wood burning). The capital costs of installing a boiler to burn waste fuel could be two to five times higher than the costs of a simple gas-burning boiler and all of its required associated equipment, so the energy-cost savings must be able to justify the additional expense.

Maximize Energy Efficiency

Because of the volatility of boiler fuel costs, getting every bit of energy out of fuel is paramount. It is only common sense to do everything possible to convert all of the heat value in any fuel to useful steam energy, which also can help reduce the emission of greenhouse gases. For example, a new boiler installation should include a feedwater economizer to preheat water going into the boiler, which potentially can increase overall thermal efficiency by up to 3 percent, and new combustion controls to reduce excess air within the burner, which can increase thermal efficiency by another 3 to 5 percent. Assuming fuel costs $2 million annually, these efficiency improvements could result in annual fuel savings of $50,000 or more. However, there are more unconventional efficiency enhancements.

Condensing flue-gas economizers can produce a steady flow of cheap hot water, increasing overall thermal efficiency by 5 to 10 percent. However, this increased thermal efficiency may or may not be applicable. A condensing economizer involves the capture of low-grade heat energy that normally does not have a beneficial use in a boiler room, so an external energy user (such as laundry equipment, parts washer, etc.) is required to make this type of heat recovery practical.

Ensure Safety

Steam-producing technology has changed little over the years, whereas boiler control has advanced by leaps and bounds. The two major aspects of boiler control involve burner-management safety and combustion control. It can be assumed that any new boiler should take advantage of the latest technology in these areas.

First, burner-management control has moved from old relay-logic controls to new solid-state controllers that monitor and supervise all of the parameters of a boiler's operation to ensure a burner system's safe operation. These new controllers can be equipped with “first-out” annunciation, which helps clearly identify the specific variable that caused a trip of the boiler. This is a great advantage in troubleshooting boiler operation. Also, careful and deliberate design of a new boiler's complete burner-management system can provide for its periodic testing and calibration, which is important to long-term, safe boiler operation and required by some national safety standards.

Second, combustion-control systems have changed from simple single-loop controllers to more complex distributive control systems that resemble computer monitoring and control. Some programmable logic controllers successfully have been adapted to this type of control system and can monitor boiler operation remotely from great distances. Steam pressure can be monitored and fuel added as needed to maintain set points, and a steam drum's water level can be maintained with combustion-control systems. Additionally, combustion-control functions can be monitored from distant control centers to help supervise a control room's daily operation.

Obtain an Environmental Permit

The environmental-permit process for a new boiler begins with a permit to install (PTI) and ends with a permit to operate. In many states, a PTI is required before ground can be broken for a new boiler. Because a PTI application requires information on a new boiler that is known only after it has been selected, it is essential for selection to take place as soon as possible. The PTI process varies by state and locality, but easily could require three to six months for final approval. Therefore, it should be a major factor in the scheduling process. The actual time needed for an agency to review and approve a PTI depends on multiple factors, such as location, fuel choice, and boiler size and, therefore, is unpredictable. This is another example of the importance of a flexible, yet structured, schedule and why the schedule should have float time to allow for unknown and uncontrollable events, such as agency approvals. A professional knowledgeable of the environmental-permit process should be involved in the preparation and submittal of a PTI.

Conclusion

The process of replacing an industrial boiler involves as much planning as technical know-how. The best-designed new-boiler installation with the greatest equipment and best of intentions can run late and over budget, especially if it does not begin with the necessary, careful kind of planning required to identify and avoid various pitfalls.

Glenn Showers, PE, is director of mechanical engineering for GAI Consultants Inc., a full-service, multidisciplined engineering and environmental consulting firm serving clients worldwide in the energy, transportation, real-estate, industrial, and governmental markets. With degrees in mechanical and environmental engineering, he has more than 37 years of experience as a design, construction, and startup engineer for boilers and other combustion systems. He can be reached at g.showers@gaiconsultants.com.