Industrial Steam Boilers – Plant Selection Guide
There are several different types of industrial steam boiler system commercially available in the UK, and selecting the best one for your company or process requires careful consideration. In this plant selection guide the specialists at Water Treatment Services review the most popular types of steam boiler system looking at their design, how they work, where they are commonly used, and any additional operational and maintenance issues that need to be considered.
What is a steam boiler?
In simple terms, a boiler is defined as any closed vessel in which fluid is heated, usually to its boiling point.
Most often, when we talk about boilers we mean heating water which then forms in to a vapour, usually steam.
The steam is then used for heating, power generation or other processes.
The boilers we have at home to provide heating and hot water operate on the same basic principles as the large industrial boilers which are used for providing greater volumes of steam for production processes.
Types of industrial steam boiler
Just as there are different types of boilers for domestic use, boilers used in industrial settings come in a range of designs, styles and outputs.
The type of boiler you select for your process or application will be determined by a number of factors, and what the steam is going to be used for.
Here we consider some of the most popular industrial steam boilers:
Fire tube and shell boilers
Industrial fire tube and shell boilers are one of the most common designs of steam generator used in commercial and industrial applications throughout the UK and elsewhere.
They are typically most suitable for installations in small and medium sized enterprises.
As these boilers are so widely used, it’s usually possible to buy an “off the shelf” package of boiler, complete with all the controls and pumps which you need to get it up and running quickly.
Simply put, all you need to do is get it plumbed in, hooked up to the right fuel supply, and then switch it on.
How do fire tube boilers work?
Fire tube boilers work by confining both the flames and the heated gases in tubes within a water-filled drum.
The water moves around the outside of the tubes, and takes on heat.
As the water’s temperature rises it converts to steam.
The steam rises up through the top of the drum, and leaves through the steam header.
Fire tube boilers are a good choice when your requirements for steam pressure are less than 15 bar.
Some of the larger, higher capacity fire tube boilers can produce steam at up to 30 bar, and total output rates of as much as 70,000 kilos per hour.
However, running at a higher rate means that the boiler needs to have much thicker plates to contain the steam generated and this can make this style of boiler less economic when running at a higher capacity.
Generating steam using water tube boilers
The differences between a fire tube boiler and a water tube boiler are fairly straightforward.
In a water tube boiler, the water is contained within the tubes, and the air heats the water from outside.
Usually, some of the water tubes also form the walls of the furnace.
The water tube is a very old design of boiler, the best known of which is called a “Lancashire Boiler”.
The Lancashire Boiler was invented in 1844, and initially had no way of recovering heat from the boilers exhaust gases.
This made them fairly inefficient, and over time the design was refined to improve performance and reduce running costs.
How do water tube boilers work?
In water tube boilers, bubbles of steam start to collect on the heated side of the boiler’s tube as temperatures increase.
The water on the unheated side of the tube is cooler, and this forces the heated water to rise.
The circulation continues until the steam reaches the steam drum… from there, the steam is then released into the vapour space.
Depending on the design of the water tube boiler, there may also be natural circulation.
This occurs when differences in density causes circulation between the mud drum at the bottom of the boiler and the steam drum at the top.
In most cases however, a pump is used to keep the water circulating around the steam boiler system.
The addition of a pump allows the boiler operator a greater degree of control than simply relying on natural circulation.
This concept is more important when boilers are needed to produce a range of different steam outputs.
Water tube boilers are a very poplar choice in large factories or power generation plants where the key requirement is for either high pressure, large capacity, or both.
Given the size of the system, most boilers of this type are custom designed for each client’s needs, and assembled on site by the supplier.
However, smaller water tube boilers designed along the same lines are gradually becoming available to buy for an off-the-shelf installation.
Industrial coil boilers
Water and fire tube boilers represent a high percentage of the industrial boilers you will come across in plants and factories up and down the UK.
However, they are not the only types of industrial boiler on the market.
In situations where high steam capacity is needed, there are some other options which might be an equally good, or even better choice… and one of these alternatives is the coil boiler.
How do coil boilers work?
Coil boilers come in many shapes and sizes, but all designs follow the same basic layout.
A coil boiler works by pumping the boiler feedwater into one or several coils, which are arranged around the boiler.
The steam which exits the coil after being heated has a wetness level of between 10% and 20%.
Depending on the way in which the steam is going to be used, the steam might also be passed through a superheater and separator.
Coil boilers can heat up either raw feedwater, or use condensate return around the coil system and be heated another time.
Water which drains into the separator can also be used to flow around the coils again and be re-heated, or can be drained away depending on system requirements.
One of the main advantages of this type of industrial steam boiler is that there can be very high levels of dissolved solids in the steam without any adverse effects on steam purity.
It is also important to keep the inside of the coils free from corrosion and deposits of solids material.
This type of steam boiler is more prone to corrosion than other types of boilers.
This is because there is no way for oxygen or carbon dioxide dissolved in the steam to escape from the boiler system.
If your company uses a coil boiler, then having a robust programme of boiler water treatment should be a priority.
Electrode boilers for steam generation
This style of boiler is a good choice in smaller applications as they can generate small amounts of steam quickly.
There are two main types of electrode boilers.
Immersion electric boilers
Immersion electric boilers have a lot in common with fire tube boilers.
The main difference is that the water is heated by electricity, not combustion.
Electronic resistance
Electronic resistance boilers operating on this principle use internal resistance to generate heat.
The level of conductivity in the feedwater is the essential component in ensuring these boilers are effective.
Electronic resistance boilers are more prone to scale and corrosion, so care needs to be taken over providing high quality feedwater and maintaining a good water treatment programme.
Boiler water treatment training
The industrial and process water treatment specialists at Water Treatment Services have developed an extensive series of professional water and wastewater treatment training courses that includes WTS 0040 “Boiler Water Treatment & Steam Generation”.
This specialist boiler treatment training course comprises an intensive one day session designed for boiler plant operators, plant managers, maintenance and engineering contractors, water treatment specialists and those with responsibility for the operation and on-going maintenance of commercial and industrial boilers and steam generating plant.
Industrial steam boiler treatment specialists
Water Treatment Services offer a comprehensive range of water treatment solutions for the management of industrial boilers and steam generating systems.
Our experts can help you optimise costs and operational efficiencies, reduce downtime, achieve water and energy savings, and increase plant reliability and safety.
With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained technicians and consultants we can offer professional, cost effective boiler water treatment and engineering services throughout the UK and Internationally.
Contact us today to learn how our steam boiler management solutions can help you.
Further reading…
More information about our steam boiler management solutions.
