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Boiler Basics 101: Blowdown

Routine maintenance on your boiler is a critical component for proper and efficient boiler operation. One of the main factors to improper maintenance that can also lead to boiler failure is not understanding the concept of blowdown. In this month’s Boiler Basics 101, we will be going over what blowdown is and how it will help improve your boiler’s health.

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When boiler water turns to steam, solids from the water are left behind. The blowdown process involves partially draining the boiler to remove the sludge those solids create. If these are not removed, boiler performance will be reduced and ultimately, it can lead to boiler failure.

Industrial boilers have three types of blowdown procedures:

  • Low Water Cutoff
    This blowdown procedure should take place after every shift. The water column must be kept clean to ensure the water level in the gauge glass accurately represents the water level in the boiler. Regular checks on the boiler verifies that the low water cutoff is operating correctly and cleans it out.
  • Bottom Blowdown
    Bottom blowdown is done by manually opening a set of two valves that drains water out of the bottom of the boiler. The purpose of the bottom blowdown activity is to clean out solids that accumulate at the bottom of a firetube boiler or in the mud drum of a watertube boiler. Solids are pushed through a blowdown separator designed to take water from the boiler during blowdown and reduce it to atmospheric pressure for disposal. During this process, steam is rapidly separated from blowdown water and vented out the top of the blowdown separator. From there, the cooled blowdown solids can be safely removed from the boiler.
  • Continuous Blowdown
    The purpose of the continuous blowdown is to help control the water quality in the boiler; the more impurities and the more chemical treatment required, the greater the amount of blowdown required. It is a procedure facilitated by a pipe entering the upper section of the boiler, typically located in the steam drum of a watertube boiler or the upper steaming portion of a firetube boiler.

The continuous blowdown process is generally automated and does not require much manual interaction, like with bottom blowdown. When operating continuous blowdown, adjust the valve to maintain the recommended boiler water dissolved solids level. This helps control the dissolved solids in boilers that are operated at a steady load.

It is important to consider proper blowdown procedures to keep the water piping clean and the boiler in working condition. If you would like to learn more about the different blowdown procedures, check out ABMA’s article outlining the steps for each type.

Be sure to check out our previous Boiler Basics 101 blogs and stay tuned for the next edition!

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Temporary Facility Closures Call For Proper Boiler Shut Down Procedures

When offline, boilers can still be at risk of accumulating corrosion and deterioration that decreases the useful life of a boiler and increases maintenance and repair costs. With proper planning and preparation, a boiler can be taken offline safely with a procedure known as boiler lay up. There are two specific ways to properly shut down your boiler: dry lay up or wet lay up.

Dry lay up is a procedure that involves removing all water and moisture from the boiler. The main advantage of a dry lay up is that you can basically “set it and forget it”. There are no chemical, equipment, or fuel costs. Once completed, the boiler will just need to be checked occasionally to ensure moisture is not getting back into the boiler. A dry lay up is best for extended periods of shutdown. If the system will need to be put back online on short notice or remain in standby, this procedure would not be suitable.

A typical dry lay up procedure involves the following steps:

1 Perform a lock-out and tag-out and isolate the boiler from the steam system
2 Perform column and bottom blowdowns and drain the boiler completely
3 Open the fireside and remove any soot from the tubes. Look for rust or scale on the pressure boundary wall, and further evaluate any leakage. Inspect refractory and insulation

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Open the waterside and look for signs of gasket leakage and corrosion of the gasket seating surface. Inspect the entire waterside and evaluate any scale and corrosion.
      - Any scale left on the waterside can trap moisture and oxygen and corrode the boiler further, 
        so remove as much scale as possible.
5 Dry all surfaces with a fan or electric air heater.
6 Have a certified boiler inspector perform a thorough examination of all surfaces, internal and external.
7 Determine if any repairs are required – this may be the ideal time to perform repairs without incurring downtime, since you are already preparing for an extended offline period.
8 Coat the fireside with mineral oil, let dry, and close all openings including the stack. A moisture-absorbing material like silica gel or lime should be placed inside the system and replaced every 2 months during the shutdown.

 
A wet lay up is performed when the boiler is idle in standby; it is still full of water but isolated from the steam system while the burner remains offline. The procedure involves chemically treating the water to protect the metal surfaces of the boiler and is  the ideal lay up method when a boiler might need to be fired on short notice. It does, however, require additional monitoring and treatment costs that aren’t required for a dry lay up.

A typical wet lay up procedure is very similar to a dry lay up, however, the fireside should not be swabbed with mineral oil.

1 Follow steps 1-7 above.
2 Fill the boiler with the chemically treated hot water (greater than 180F) to its normal operating level. Allow air to continue to vent until the boiler is full or until the steam boiler is at its normal operating level and warm.
3 Once complete, boiler water should be circulated periodically to prevent stratification of chemicals. Chemical concentrations should also be monitored routinely.

 
Before starting a steam boiler in wet lay-up, blow down the boiler to reduce alkalinity, ensure that all tags and locks are removed, and be sure to witness a minimum of three steam cycles before allowing the boiler to run in automatic. This will help ensure proper operation after bringing a system back online from a wet lay up.

If your facility falls under a temporary business closure mandate due to the current state of the COVID-19 pandemic, it is imperative that you follow one of the procedures outlined above to properly shut down your boiler system. View this technical article provided by the National Board for more detailed information on these two types of boiler lay up procedures.

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Protect Your Rental Equipment This Winter

As we enter the heart of the winter season, it’s important to remember that cold weather conditions have the potential to cause freeze damage to any boiler installed outdoors. In particular, the protection of non-enclosed rental boilers and equipment installed outdoors is imperative to avoid damage. Rental boilers and equipment come in various designs and configurations, and each unique type will require different forms of freeze damage protection. Knowing the type of equipment will help determine the right steps on how to prevent damage.  

 Here are the most common types of rental boilers: 

  - Mobile Boiler Rooms
  - Mobile Steam Plants
  - Trailer-Mounted Boilers
  - Skid-Mounted Boilers
  - Mobile Feedwater Systems
  - Skid-Mounted Deaerators and Other Auxiliary Equipment

Just remember that any lines without a constant flow of water will freeze and must be properly protected from the cold. Always make sound engineering judgment calls to avoid the repercussions of freeze damage. If you have a temporary boiler and want to learn more about the proper ways to avoid freeze damage, read the recent issue of Process HeatingNationwide Boiler was featured and our Marketing Manager, Chelsey Ryker goes over the specifics of boiler protection for each model.

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14 Steps for Winter Boiler Maintenance

Winter is officially here! When cold weather settles in, it is important to make sure that your boiler is well-maintained. Like any other mechanical system, boilers will tend to wear down over time. Boilers can be dangerous if not properly inspected and not working properly. Full boiler efficiency will help avoid boiler downtime and unnecessary expenses. Here are 14 steps to follow to help you get on track with your winter maintenance:

1. Inspect the fuel source.

The fuel used needs to have the proper viscosity for atomization. Test and gauge the fuel viscosity to ensure full efficiency. 

2. Inspect the fireside.

Inspect the fireside and look for any indication of corrosion.  If no corrosion is found, continue to clean the fireside and the furnace area as necessary. 

3. Check the refractory.

Due to the cooler weather, be aware of thermal expansion. Boiler refractors are designed to expand and contract with temperature changes. But all boilers will incur some cracking due to those constant changes. If excessive cracks are found, repair as needed.

4. Inspect the waterside.

Inspect the waterside of the boiler for scale and remove as necessary. Scale prevents heat transfer inside the boiler and can significantly lower efficiency. All water-level controls need to be properly inspected, opened, and cleaned.

5. Inspect the burner.

While the boiler is open, inspect the burner components.  Visually check the boiler’s flames. If there are inconsistencies in the flame patterns or color, there may be an underlying issue. Make sure everything is in order before proceeding. Failure to maintain the fuel system in good working order could result in excessive fuel costs, loss of heat transfer or even a boiler explosion.

6. Inspect the controls.

Any controls used to monitor the water level of the boiler should be checked after reinstalling onto the boiler. Before starting the boiler, inspect all the operating controls and look out for any signs that show of overheating.

7. Close all openings.

Make sure all of the boiler’s openings which include all doors, manholes and handholes are properly closed.

8. Open the boiler’s valves.

This is inclusive of the boiler’s header valves, piping drains and vent valve. Make sure all are operating as required and that the vent is not clogged. All ventilation requirements for the boiler need to be checked and met. 

9. Test the pumps and valves.

You will need to test all of the boiler’s pumps and valves before fully operating to make sure everything is working properly. Once everything has been tested and approved for operation you can start warming up your boiler.

10. Warm up your boiler.

To account for the colder weather it is important to increase the boiler pressure slowly. This allows the joints and metals to heat up evenly and reduce expansion stress. 

11. Switch to automatic operation.

Once your boiler is up to operating pressure, switch to automatic operation.   

12. Analyze combustion.

When you perform a combustion analysis this helps increase performance, verify component operation, decreases maintenance and fuel requirements. This will save some potential expenses made in operation. 

13. Water treatment.

Water treatment is needed before feedwater can be pumped into a boiler. Test the boiler water and treat accordingly. Follow the guidelines provided in the Installation and Operations Manual.

14. Monitor your boiler. 

Within the first few days after start-up, monitor the boiler for any leaks or any additional maintenance items. If you discover water or steam leaks at this point, shut the boiler down and have the leaks repaired.

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