Understanding Boiler Blowdown and Selecting the Right Vessel

Blowdowns are an important part of industrial boilers and commercial boilers; a blowdown is the process of flushing water from the tank to mitigate and control the build-up of impurities. There are many things to consider when choosing a new boiler, but guaranteeing you have the correct blowdown vessel is key to ensuring a safe and unhindered steam boiler operation.

The basics of a blowdown

A blowdown is the intentional flushing of water from a steam boiler to remove any contaminants that may have built up over the course of its operation and control the level of totally dissolved solids (TDS). Contaminants include particles from any treatment chemicals, that, over time can form solid sludge at the bottom of the tank or remain suspended and will continue to grow if not “blown down”.

Blowdowns can be initiated automatically or manually (depending on the type of valve installed); their frequency depends on several factors including the size and type of boiler. Our boiler sales team know boilers inside out and will help to establish a manual blowdown schedule for you based on your specific boiler. As a rule of thumb, blowdown rates should be between 4% – 8% of the boiler’s feedwater flow rate.

Why do contaminants need to be blown down?

If allowed to remain in the boiler tank, the contaminants will affect the quality of the steam leading to reduced performance and pipe damage/corrosion. Steam boiler blowdown must be performed regularly to avoid corrosion; high contaminant levels will accelerate pipe corrosion which can become costly and require avoidable boiler maintenance services.

The blowdown vessel

When a blowdown occurs, it must be performed in a carefully controlled manner — this is what the blowdown vessel is for, a tank that shares physical similarities with a vertical compressed-air receiver. The blowdown process pipes down the expunged water into the vessel for depressurisation; it then vents off any flash steam and collects the condensed water and solids for cooling and disposal via the premises’ wastewater collection system.

Choosing the right blowdown vessel 

When working with our boiler sales team to select an industrial or commercial boiler they will be able to recommend an appropriate vessel for your unit. There are still some general aspects that should be considered, though.

  • The blowdown vessel should be at least three times larger than the water blowdown volume; our sales team will advise on the largest blowdown your boiler will experience and choose the right vessel for you accordingly.
  • The tank pressure and the pressure of the blowdown water as it leaves the tank should not exceed 35 kPa.
  • Blowdown vessels should not be insulated as they’re meant to cool the water down; because of this, other safety protocols and measures should be considered such as guard rails and placing the vessel in an area where contact is less likely to be made.

Temperature control

As the boiler is in operation when blowdown is performed, the temperature of the water can be quite high. As a rule of thumb, the blowdown water should not exceed 71° C. This can become quite tricky in situations where the boiler water is evidently above this temperature. In these situations, our boiler sales team will recommend installing a cold-water injection system to cool the water as it leaves the tank and enters the vessel.

This is typically done by installing a direct-acting temperature control valve system, or a digital control system coupled to a solenoid valve. When a predetermined temperature is reached within the water mass, the control valve or solenoid valve will open, injecting cold water into the tank and ensuring it’s suitable enough to enter the blowdown vessel. Please note that a certified backflow prevention device will need to be installed should the cold water be sourced from a potable supply.

Are you looking for new industrial boilers in Australia?

Tomlinson Energy Service has been providing premium, first-class industrial and commercial boilers to Australia for over 100 years and is the country’s largest packaged boiler supplier. Our boiler sales team can provide you with optimal product recommendations including blowdown vessel fittings and operation requirements.

If you would like to get in touch with our team today, then please call us on +61 3 8560 0419 or fill out the contact form below.

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