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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.

06 29

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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10 Tips to Improve Boiler Efficiency

The need to operate a boiler efficiently in today's environment and competitive landscape is at the top of many plant owners and operators list. Unfortunately operating a boiler efficiently while meeting local emission regulations do not always go hand in hand. However, advances in boiler system design and low NOx technology solutions have made this a much more achievable task.

The list below includes 10 tips which can instantly improve overall boiler performance and sustainability, helping to achieve more cost-effective maintenance and operations of your steam system.

This list, along with general guidelines for each, will be published in an upcoming issue of Process Heating magazine. Please email Nationwide if you are interested in obtaining a copy.

1.    Reduce Excess Air

2.    Install an Economizer

3.    Install a Condensing Economizer

4.    Upgrade to VFD Fan Controls

5.    Install a Selective Catalytic Reduction System (SCR) with a Standard Low Excess Air/No FGR Burner

6.    Perform Proper Water Treatment

7.    Reduce Boiler Pressure

8.    Consider Boiler Blowdown Heat Recovery

9.    Upgrade to a High Turndown Burner & Controls

10. Implement an Energy Efficiency Program
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Boiler Scale & How to Avoid It

All boilers are subject to damage if proper chemical treatment, water analysis and blowdown procedures are not followed. If these items are ignored, both during operation and idle periods, serious damage to the boiler will result.

When Nationwide Boiler delivers a rental unit, it is the boiler operator's responsibility to maintain and supervise the water treatment conditions of their rental boiler in order to avoid any additional charges that may result from improper operation or maintenance. It is recommended that the services of a reputable boiler chemical consultant are retained in-order to supervise the water treatment conditions on a regular basis. At least once each week, daily boiler logs, chemical treatment tests, a chemical treatment consultant's report and maintenance records should be implemented and sent to Nationwide Boiler. This ensures that the proper maintenance is being done on the equipment and provides accurate maintenance reports for Nationwide's equipment files.

As a boiler operator it is important to inspect the waterside condition of watertube boilers that may result in heavy scale or oxygen pitting or corrosion. Waterside scale can be cause for concern on the reliability of a boiler by the following:

  • If the boiler tubes contain heavy scale, tubes can overheat and/or fail leading to tube leaks

  • If the boiler has some scale but it is not heavily deposited, certain types of water treatment plans can cause the scale to quickly be removed in large flakes, plugging tubes and eventually leading to overheating and tube failures

  • Certain types of scale can be easily removed such as a conventional soft phosphate scale, while others are very difficult to remove such as silica


If scale is present, any scale greater than 1/8 inch or 0.125 inch should be removed from the boiler prior to placing it back in operation.

Oxygen corrosion is not as easily detected as scale. O2 pitting can occur under deposits and in very small areas that can escape detection by the naked eye. If O2 pitting is suspected, a tube needs to be removed from the boiler for more close examination.

Therefore, it is extremely important to assess the waterside condition of a boiler and then to determine the type of scale and the method for removing it. There are several methods for removing boiler scale including high pressure water blasting and other proprietary methods offered by water treatment representatives. Overall, with proper boiler maintenance and water treatment plans, such procedures can be avoided.

Examples of (1) Heavy Scale, (2) Medium Scale and (3) No Scale

1.
scale2.jpg
2.
scale1.jpg
3.
noscale.jpg
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Recent comment in this post
Guest — Edward
I want to make a small monotube boiler ( 1/3 TPH at over 50 bar ) what would you suggest for scale?
Sunday, 26 April 2020 06:20
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