Your Offline boiler may be costing you money!

Author: Colin Marley | Water & Energy Manager

Most companies focus on improving efficiency while the boiler is running to lower expenses and maximize profits. What about when the boiler isn’t running!? There may be circumstances where a boiler may not be required for extended periods of time, such as seasonal boiler requirements or redundant boilers that may only be required in extenuating circumstances. These offline periods can damage the boiler, decreasing its useful life and increasing maintenance and repair costs. With proper planning and preparation, a boiler can be safely taken offline with a procedure known as a boiler layup.

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There are two main types of boiler layup to consider:

  • Wet Layup – when the boiler is idle in standby and flooded with water
  • Dry Layup – a procedure that involves removing all water and moisture from the boiler

When performed properly, both procedures are equally effective in protecting your boiler while offline and increasing its useful life.  However, there are advantages and disadvantages that should be weighed during the decision-making process.  Things to consider include:

  1. Duration of offline period
  2. Boiler type and size
  3. Manpower for maintenance and monitoring
  4. Costs associated with each layup protocol

There may not be an obvious choice when selecting the layup procedure that is best for your specific situation. Your water treatment professional can assist in this process. 

 

A wet lay-up typically requires isolating the boiler from the steam system, ensuring the burner remains offline, and chemically treating the water to protect the metal surfaces.

 

The key advantage to a wet layup is the ability to fire online within short notice as the boiler is already filled with water. Additionally, since the water in the boiler is treated water, there is sufficient protection during the start-up of the boiler as well.

 

The compromise is that this method involves some treatment costs and additional monitoring compared to a dry layup procedure.

 

Typical wet layup procedure:

  1. Isolate the boiler from the steam system.
  2. Perform aggressive column and bottom blowdowns to ensure adequate removal of suspended solids. The goal is to make sure there are no blockages that will dry and bond over the offline period.
  3. To ensure the boiler is protected from corrosion, chemical treatment is required. This can be accomplished by adding the chemical directly to the boiler or by dosing the feedtank and then pumping the treated water into the boiler.
    • For a typical steel tube boiler, it is common to target a sodium sulphite residual of 300 – 500 ppm and a pH between 9.8 – 11.8.
    • Should your specific boiler contain different types of metals, different setpoints may be required.  This should be discussed with your water treatment professional.
  4. Flood the boiler to displace any air pockets that may be within the boiler.
    • The most common method is to flood the boiler water into an overflow tank.
    • An alternate method is to displace the airspace with pressurized nitrogen and then seal the boiler to prevent losses.
  5. Recommended monitoring:
    • Periodically run the recirculation pumps to ensure adequate mixing of the layup solution.
    • While recirculating the water, test the layup solution to ensure critical parameters, typically pH and sulphite residual, and ensure the parameters remain within the procedure control limits.

A dry layup procedure involves the complete removal of the water. Since water or moisture is a required medium for corrosion to take place, boiler corrosion is prevented through the complete removal of the water and the atmospheric moisture.

 

The key advantage to dry layup is that you can set it and forget it. Compared to wet layup, there are no chemical, equipment or fuel costs. Once a dry layup is completed, the boiler only needs to be checked occasionally to ensure moisture is not getting back into the boiler.

 

The compromise is that this procedure may not be suitable should the system be required to be put back online on short notice or needs to remain in a standby state.

 

Typical dry layup procedure:

  1. Isolate the boiler from the steam system.
  2. Perform aggressive column and bottom blowdowns to ensure adequate removal of suspended solids. The goal is to make sure there are no blockages that will dry and bond over the offline period.
  3. Any recirculation pumps can now be deactivated and the boiler can be drained. Make sure to drain from the lowest point to ensure all water is completely removed.
  4. All moisture must be removed from the boiler to be effective. This can be done by opening the manholes and the water side door to allow air to circulate through the boiler to remove any moisture. It is a good idea to make sure that no water from the steam network is seeping back into the boiler.
  5. It is recommended to use a desiccant to absorb any moisture within the boiler or to run a fan to continuously remove any moisture to effectively protect from corrosion.

Conclusion

Offline periods can damage your boiler, decreasing its useful life and increasing maintenance and repair costs. With proper planning and preparation, a boiler can be safely taken offline with a procedure known as a boiler layup. When performed properly, both wet layup and dry layup are equally effective in protecting your boiler while offline and increasing its useful life. However, there are advantages and disadvantages that should be weighed during the decision-making process.

 

With your boilers now safely offline in proper layup state, you can go back to focusing on how to reduce operating costs when your boiler is brought back online by reading some of our related blogs!

Colin Marley has a degree in Mechanical Engineering from The University of Western Ontario and LEED Green Associate accreditation. As an Water & Energy Manager, he works with our clients to achieve the lowest operational costs for their heat transfer systems through well-maintained water treatment programs. Colin once came 7th in the CN Tower Climb and enjoys a large slice of pumpkin pie on most weekends.

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