A large industrial boiler can operate successfully for 25 years or more. However, the decrease in a boiler's performance and associated gradual increase in annual maintenance and operating costs can signal a need for change. When required, the boiler-replacement process typically is not as simple as merely changing out a failing boiler. So what happens when a boiler reaches the end of its useful life? Where does the process of replacing an old boiler begin? Simply put, boiler replacement takes much more effort than pulling out an old boiler and sliding in a new one.
The replacement of a large industrial boiler easily can involve $1 million or more, so it only makes sense to put thought into boiler-related decisions, minimizing costs while maximizing benefits. This article will present several tips on how to approach industrial-boiler replacement. The tips will highlight several key factors that should be considered before an actual in-depth engineering design commences. A typical industrial boiler that produces 30,000 lb per hour of 150-psig saturated steam will be used in this article as a basis for discussion.
A large industrial boiler can take 20 to 40 weeks from order placement through drawing submittals and final approvals to arrive at a job site. It is essential to develop a preliminary project schedule at the start of a boiler-replacement project. The schedule should set a desired target for boiler operation and work backward to a drop-dead order-placement date. No project, especially one involving a boiler replacement, runs as smoothly as desired, so the schedule must include some “float time” to ensure the desired startup date is obtainable. While many scheduled tasks can occur in conjunction, some cannot. Therefore, it is important that a professional with knowledge of the overall procedures be involved in the scheduling process.
A boiler needs to be specified, priced, and purchased before emission data can be obtained for the completion of the environmental-permit process and the arrival of certified drawings, which allow for the start of a detailed design. While tending to this process, it may be possible to start other tasks, such as preparing the site before the actual design has been completed. Care must be taken not to impede the continued operation of the original boiler until the schedule allows it to be removed from service.
Plan the Space
The placement of a new boiler often is assumed to be a simple decision that continuously is postponed and finally addressed during the design stage. Unfortunately, this can cause problems later. However, only two basic placement choices are available: Situate the new boiler in the same spot as the old one, or find used space nearby. There are advantages and disadvantages with each possibility.
If a new boiler is slated to be placed in an old boiler's spot, a couple of items must be addressed. First, a facility's operating schedule must be studied to determine whether the old boiler can be removed and the new boiler installed without the facility's normal operation being disturbed. Assuming the required equipment and personnel are ready and available, an aggressive, well-coordinated schedule could demand four months for a completed change-out. Summer typically is reserved for this type of change-out, which a schedule must take into consideration.
If a new boiler must be placed in an old boiler's spot and a facility's operating schedule does not allow sufficient time to execute the change-out, a rental boiler can be moved into a temporary space and operated during the demolition and construction process. This option has the advantage of allowing the complete construction schedule to occur at any time for as long as required without operation disruptions. However, the cost of a rental boiler could add tens of thousands of dollars per month to overall project costs and many more thousands of dollars in connection costs.
The major advantage of placing a new boiler in an old boiler's spot is that most of the supporting utilities (steam and water piping, electric power, control wiring, etc.) already will be in the right area. If the schedule is unaccommodating or the cost of a rental boiler is prohibitive, a new boiler will have to be located in a space not already occupied by a piece of critical equipment. The advantages are that the work schedule allows for more flexibility of available time, probably does not require a summer time slot, and does not endanger a facility's continued operation. The major disadvantages are that the new boiler may not be adjacent to other boilers and, thus, may be considerably more difficult for an operator to see and access, and thousands of dollars will be spent connecting the new boiler to the existing water, steam, fuel, and electric systems in the boiler room.
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.
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.
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 [email protected].