Table of Contents
- Why You Need to Blowdown Your Boiler
- What Does Blowingdown a Boiler Mean?
- Bottom vs. Skimmer Blowdown
- How Often Should I Blowdown My Boiler?
- What is the Proper Boiler Blowdown Procedure
- Contact Us
Why You Need To Blow Down Your Boiler
If you use a boiler for various industrial operations, you likely want to improve its reliability and longevity. Regularly blowing down your boiler is one of the most critical maintenance practices you can use to ensure your boiler performs optimally. Blowing down your boiler helps you remove impurities from it and reduce the chance your boiler fails.
As a result, it's crucial to know more about the importance of boiler blowdown and how you can properly perform it.
What Does Blowing Down a Boiler Mean?
Blowing down a boiler refers to the process of removing water from the boiler with any excess bottom sludge and dissolved solids. Companies need to blow down their boilers regularly, since the concentration of dissolved solids from makeup water increase in a boiler after removing pure water as steam. A company that periodically blows down its boiler's water can better maintain a consistent number of cycles of concentration.
What is the difference between bottom and skimmer blow down?
Water can be removed from the boiler from two main points: the bottom drain valve and a skimmer drain valve which enters the boiler somewhere just slightly below the water surface. The concentration of sludge is greatest at the bottom of the boiler and bottom blowdown is performed to remove sludge which precipitates during boiling. The concentration of dissolved solids is greatest at a point 6-8 inches below the water surface. Water removed from this depth, termed skimmer blowdown, removes the greatest amount of solids in the least amount of boiler water. Skimmer blowdown is the most efficient means of controlling cycles of concentration, but bottom blowdown is essential to prevent the build-up of sludge.
Why Do I Need to Blow Down My Boiler?
Only pure water leaves the boiler as a byproduct of steam, leaving behind any dissolved solids. Even though the condensate gets pumped back into the boiler, some of this condensate inevitably becomes lost, requiring replacement with more water. Over time, the concentration of dissolved solids from the makeup water increases in the boiler as pure water off-gases as steam.
Due to this increase in dissolved solids, your boiler can see more corrosion and scale. "Cycles of concentration" is the technical term for the relationship between the level of dissolved solids in the boiler and the dissolved solids in the feedwater. When you periodically drain water from the boiler, you can maintain a consistent number of these cycles. This process is essential to prevent scale and corrosion buildup in your boiler.
Alongside the need to remove dissolved solids to reduce scale and corrosion, boiler blowdown is critical to avoid overheating. When too much sludge or dissolved solids build up on the boiler's heating surfaces, the metal can overheat. This overheating can cause a pressure vessel to fail, resulting in expensive repairs and lost productivity. Besides overheating, high concentrations of dissolved solids can cause boiler water to carry over into the steam, leading to damaged equipment and piping.
What Is the Difference Between Bottom and Skimmer Blowdown?
Companies can remove water from their boiler from two main points — the bottom drain valve and a skimmer drain valve that enters the boiler somewhere just slightly below the water surface. Since you can drain water from these different points, you'll run into two blowdown methods — bottom blowdowns and skimmer blowdowns.While skimmer blowdown is the most efficient means of controlling cycles of concentration, bottom blowdown is essential to prevent sludge buildup.
Both boiler blowdown methods are crucial to a boiler's proper operation, so you'll likely want to know how each of them works. Find out more about these primary types of boiler blowdowns below.
The concentration of sludge is highest at the bottom of the boiler, and bottom blowdown will remove the sludge that precipitates during boiling. Since unchecked sludge can end up affecting heat transfer systems and cause tube or vessel failure, bottom blowdown is essential. When a company performs this method, they'll briefly open a valve or multiple valves to allow sludge to pass out of the boiler.
The concentration of dissolved solids is most significant at a point six to eight inches below the water surface, and a skimmer blowdown, also called surface blowdown, aims to remove water from this depth. By performing skimmer blowdowns, companies can extract the greatest amount of solids in the least amount of boiler water.
How Often Will I Need to Blow Down My Boiler?
Generally, companies that rely on boilers perform bottom blowdown once a shift or once a day. However, better-quality feedwater can extend the intervals between bottom blowdowns. Likewise, skimmer blowdown frequency and volume depend primarily on the amount of condensate returned to the boiler and the quality of your makeup water.
Since your boiler blowdown will change based on your boiler's unique needs, you'll want to develop a routine ensuring your boiler receives the proper amount of blowdown at regular intervals. As you determine the right schedule, you can speak to a water treatment professional, such as Chardon Master Service Technicians, to get the best advice possible. You'll also want to always consult your Chardon Master Service Technician before changing your blowdown routine.
What Is the Proper Boiler Blowdown Procedure?
Since boiler blowdowns are so valuable, you'll likely want to know how to complete the process. Bottom blowdowns and skimmer blowdowns have different procedures, so you must understand the distinction. Find out more about the steps you should take to perform each type of boiler blowdown below.
Bottom Blowdown Procedure
Review the following steps to complete a bottom blowdown.
- Open the valves:The bottom drain line on your boiler usually has two valves — a slow-opening gate valve and a quick-opening knife valve. The proper way to bottom blow down a boiler is to start with both valves fully closed. Next, open the knife valve first before completely opening the gate valve.
- Perform the blowdown procedure: With the valves open, you can then blow down the boiler. You can often determine how long to blow down your boiler by consulting with water treatment professionals. To thoroughly blow down the boiler, you'll close the gate valve after a specific amount of time has passed. You'll want to pay attention to your gauge glass' water level, as your boiler may need shorter blowdown cycles to ensure it has the right water level.
- Repeat blowdown procedure: After you close the gate valve, you'll want to repeat the opening and closing of the gate valve three times. By repeating the blowdown procedure, you'll rock the water in the boiler and work the sludge toward the drain line.
- Close gate and knife valves: Once you've completed the blowdown procedure, you'll close the gate valve. Next, you'll close the knife valve.
- Open gate valve: With both valves closed, you'll re-open the gate valve. By opening the gate valve, you'll drain the line located between the gate and knife opening valves.
- Close gate valve: Once the line drains, you'll close the gate valve again. After the valve cools off, check if the shutoff is tight.
Skimmer Blowdown Procedure
Skimmer blowdowns also have unique needs you should be aware of to get the best results possible. Since skimmer blowdowns often involve automated processes that a water treatment professional sets the rate for, you don't need to do as much to perform the blowdown procedure.
Though skimmer blowdowns don't require as much operator interaction, you'll still need to use a properly calibrated conductivity meter to determine the amount of skimmer blowdown needed. Based on your meter's reading, you'll want to use a needle valve or flow throttling valve to transfer boiler water through the valve into a skimmer pipe.
By transferring this water, you can maintain the conductivity of your boiler water in the range determined by your Chardon Master Service Technician. Finally, it is essential to blow down the safety valves, level switch and sight glass once every week to ensure they work when needed.
Choose Chardon Laboratories for Water Treatment Services
Since expert water treatment technicians are crucial to many steps of the boiler blowdown process, you'll likely want to turn to a team you can trust to keep your boiler running at its best. At Chardon Labs, we have achieved ISO certification, meaning you can expect our trained techs to correctly perform boiler blowdown processes. We also offer several boiler blowdown solenoids designed to fit various systems and help them deliver more consistent performance.
Matt Welsh is the Vice President and Water Consultant at Chardon Labs. He helps consult a wide range of customers utilizing various methods of water treatment, from chemical to chemical-free approaches, large and small applications, and across a wide range of geographical influences. With 20 years of water treatment experience, including a wide range of troubleshooting and service in potable water and non-potable HVAC and industrial applications, he is an expert in water treatment chemistry for cooling towers, boilers, and closed-loop systems.