Industrial boilers do a lot of heavy lifting when it comes to keeping production processes or even facilities operating as effectively as possible. Yet, maintenance personnel may forget how important regular service and cleaning are to boiler performance. Process heating equipment, including boilers, should not be neglected; instead, a preventive maintenance plan should include tuning, regular cleaning and descaling. This is especially true for equipment that has experienced a shutdown for an extended period.
In many plants and facilities, maintenance personnel are dealing with increased workloads and, in some cases, reduced workforces and budgets. This makes finding the time and resources to conduct proper maintenance more challenging. It does not take much soot or scale buildup on a boiler, however, to affect overall operations — and a company’s bottom line. Foregoing routine boiler maintenance may seem like the easier choice, but that decision could lead to expensive and disastrous failures.
The amount of fuel burned is tied directly to the heat transfer of the vessel. Buildup on the inside and outside of the tubes creates a layer of insulation and affects the rate of heat transfer. As the buildup increases, more fuel is needed to get the desired results. In addition, boiler performance will continue to deteriorate gradually. This wastes thousands of dollars in extra fuel as the boiler runs longer than needed to produce the heat. For example, if a 200-hp boiler operates 8,000 hours per year with a medium level of calcium scale, the boiler could lose 5 percent of its efficiency.
When a boiler needs to work harder to keep up, it can increase the chances of repairs or even necessitate boiler replacement. Neglecting buildup also can lead to corrosion in the boiler tubes. By contrast, eliminating buildup has a positive impact on efficiency, energy savings, overall cost savings and equipment life span.
Soot or scale buildup on a boiler can affect overall boiler operations. Photos credit: Goodway Technologies
Preventive Maintenance for Industrial Boilers
Boilers generally have two sides that need to be cleaned: the waterside and the fireside. In either case, the insulating effect of scale and soot means more fuel must be burned to produce the same amount of heat transfer. This increases costs and reduces system longevity.
The waterside is where water is heated or turned to steam. During the heating process, minerals in the water accumulate on the water-contacted surfaces, reducing heat transfer just as soot does on the fireside.
Mineral water scale is removed through either mechanical or chemical cleaning methods. Mechanical cleaning removes scale with the use of tools like scrapers, brushes or sandblasters. Chemical scale removal uses acids or other liquid descalers to dissolve the minerals through a chemical reaction between the scale and the liquid.
Improvements in the equipment used to clean boiler tubes and remove scale can reduce the amount of time needed to effectively clean the tubes. Photos credit: Goodway Technologies
When fuel like oil or coal is burned, the soot and combustion products collect on the internal components of the fireside. This creates an insulating layer of ash, preventing heat from getting to the water.
The severity of firetube corrosion and fouling is related to the fuel being burned. Natural gas, propane and petroleum fuels like gasoline or No. 2 diesel fuel produce a light fouling that can be removed by brushes, without the need for heavy scrapers. Boilers burning heavy petroleum fuels like No. 6 fuel oil, or wood, medical or municipal waste often suffer from thick fouling. In such cases, the buildup typically must be removed using a cleaning system with strong brushes and scraping tools.
Soot and corrosion from combustion can foul the fireside of boilers, causing the tube-wall temperature to get so hot that the tube itself weakens and can rupture. Fireside fouling can be removed mechanically with rods and brushes, compressed air, bead blasting or motor-driven rotary-brush cleaners.
The method used for cleaning — mechanical or chemical — differs depending on the thickness and type of deposits being removed. Not all scale is the same. Every facility needs to look at the type of scale occurring in their boiler to determine the most effective approach.
Some descaling chemicals dissolve scale on contact, eliminating the need for boiler tube scraping. Photos credit: Goodway Technologies
Include Cleaning in the Maintenance Plan
For boilers to operate efficiently and avoid frequent breakdowns, a regular schedule for maintenance and cleaning — as well as monitoring during operation — is important. When process heating is required year-round, however, scheduling maintenance and cleaning are essential to minimize the effects of an offline system. (For HVAC applications, routine maintenance is recommended at least once a year.)
Monitoring stack temperature is a proactive method for identifying the presence of heavy boiler fouling. When the inside of the boiler is coated with scale and soot, heat from combustion cannot transfer through the tube wall and into the water. The unused combustion heat is pushed out of the flue and dispersed to the atmosphere.
By tracking the flue-gas temperature, maintenance personnel can monitor for fouling increases that would indicate it is time to clean the boiler. A consistent flue temperature is evidence of a clean boiler. The cost of annual descaling and tube cleaning is small compared to the price of a major boiler repair or unplanned process downtime.
Eliminating boiler tube buildup will have a positive impact on process heating equipment efficiency. Photos credit: Goodway Technologies
Boiler Cleaning Equipment
From boiler tube-cleaning systems to scale-removal systems, various solutions can reduce the amount of time and effort needed to clean the tubes effectively.
For instance, firetube boiler cleaning systems require little physical effort from maintenance personnel, and their designs help keep debris from escaping into the boiler room. Firetube boilers can be cleaned using rotating brushes or scrapers that loosen soot, and a vacuum can pick up the dust. Tools that combine these functions help avoid environments where soot dust can combust or be breathed in.
Likewise, the waterside of tubes can accumulate sediment, biological contaminants or scale. For lighter deposits, these tubes can be cleaned using rotary cleaners with soft brushes. If mineral scale has formed, it may require heavier-duty scraping tools or the use of descaling chemicals.
Specific to mineral scale, in the past, hand scrapers were used to break away these deposits. Chemical engineering advances have produced descaling chemicals that dissolve scale on contact, eliminating the need for scraping. Also, recirculation cleaning systems can continuously pump descaling chemicals through the boiler or heat exchanger, dissolving solids as the chemical passes over the scale.
During many boiler cleaning operations, the role of maintenance staff is limited to monitoring the pH of the descaling solution as it returns to the cleaning system. (When descaling is complete, the pH of the descaling solution will be neutral, indicating that there is no more chemical reaction taking place between the scale and the chemicals.) The removal of scale deposits means clean tubes are behind to effect heat transfer.
In conclusion, developments in cleaning tools, descaling chemicals and flue-temperature monitoring mean boilers are easier to maintain and can remain efficient throughout their operational lives.