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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

4

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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Boilers Ship Fast-Track for Emergency Need

Sometimes boilers are rented in advance for planned maintenance or additional capacity, and other times they are needed immediately in an emergency outage. No matter the situation, Nationwide Boiler has the capacity to provide equipment to support our customers at their best and at their worst.

We received a call on Sunday afternoon from a customer in an emergency situation, with an immediate need for rental equipment. Our Rental Sales Manager, Tim McBride, quickly sent information on two (2) 70,000 lb/hr trailer-mounted boilers that were available from our heaquarters in Fremont, CA. The order was received Monday morning, and we began working diligently to process paperwork, perform outbound equipment inspections, and coordinate shipment. The two units shipped this afternoon, just three days after the initial call, and are on their way to the South. With the help of our partner, ADCO Companies, the equipment will be up and running in no time!

We plan ahead for situations just like this, so we can support our customers through any unexpected outage and provide them with reliable equipment and un-matched service.

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New 110,000 lb/hr Superheat Boiler Provides Increased Steam Capacity

With short summers and weather as unpredictable as it is charming, much of Newfoundland and Labrador relies on NARL Refining’s ability to provide warmth and clean fuel. We were able to assist with the refinery’s needs by providing them with one of our new in-stock 110,000 lb/hr trailer-mounted superheat boilers. The 750 psig design watertube boiler was manufactured by Babcock & Wilcox, who recommended Nationwide Boiler for the job per our stock boiler program.

To learn more about the boiler sale and how we were able to accommodate the customer’s need for an immediately available unit, read our latest case study. (PDF will download in a new window.)
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