Introduction to Boilers
What is a boiler?
A Boiler is simply an enclosed system or vessel in which a fluid is heated. For example, by combustion and transferring heat to water, it is possible to turn the water into steam or simply making it hot. The hot water or steam is then used in order to transfer heat to any subsequent process. Boilers are used for a variety of reasons and applications such as water heating, power generating, central heating, cooking, sanitation, etc. Therefore, making efficient boilers extremely important for daily life activities whether that be industrial applications or domestic activities. Now let us see how a boiler works:
How do Boilers Work?
While there are many types of boilers, they generally follow the same principles (with a few differences of course). A boiler system is made out of the following stages:
- Feedwater System: The feedwater system is responsible for providing water to the boiler and automatically regulating it in order to meet the demands of the steam. The water that is provided to the boiler is then converted into steam. There are mainly two sources of feedwater:
- Condensed steam which is returned from a prior stage
- Raw water which comes from outside of the boiler.
- Steam System: The steam system is responsible for controlling and collecting the steam that is produced in the boiler. The steam is then directed towards the point of use through a system of piping. The steam pressure is also controlled, checked and regulated via various items such as valves and gauges.
- Fuel System: the fuel system is responsible for providing fuel to the boiler in order to generate the necessary heat. Usually, the fuel will be coal, oil or natural gas.
- The vessel itself is made out of steel or alloy steel in some cases. Stainless steel is also sometimes used for superheater sections that will not be exposed to boiling water in order to avoid stress corrosion cracking.
Types of Boilers
Below describe some types of boilers:
Water Tube Boilers
A water tube boiler is a boiler in which the water is inside the tubes and the combustion gas passes outside of the tubes. Water tube boilers are available for various great sizes and are able to handle pressures up to 5000 psig. In addition, they are able to reach very high temperatures. However, a water tube boiler has its own shares of disadvantages such as
- The considerably high initial capital cost
- The complexity of the boiler’s design that makes its cleaning process very difficult
- The physical size which could be a problem
Despite the above disadvantages, the use of such boilers depends on where they would be used.
Fire-tube boilers are sometimes regarded as the opposite of water tube boilers. In the design of the fire-tube boilers, instead of water, it is the combustion gas that flows in the tubes and the water surrounds outside of the tubes. Fire-tube boilers are sometimes preferred over their cousin, the water tube boiler. Due to the fact that they are usually inexpensive, easier to clean and maintain, relatively small in physical size, they are often used for industrial process applications or simply space heating. However, fire-tube boilers also do have their own drawbacks. For example, they can’t be used for high-pressure applications not to mention their inability to reach high steam generation levels.
Combi boilers are smaller than water tube boilers or even fire-tube boilers. They provide heating and hot water directly from the boiler. The pros of Combi boilers are:
- High efficiency when it comes to energy
- Significantly cheaper than water tube boilers
- Small in physical size due to their compact design.
- Easy to install and maintain.
The cons of Combi Boilers are:
- They Dependent on mains water pressure
- If the boiler breaks, then the central heating will not be working.
Gas boilers are very similar to Combi Boilers, however, they have their differences especially when it comes to pros and cons
- Very Cheap
- Almost 90% efficiency rate
- Extremely fast water heating
- Gas leaks can be extremely dangerous and even fatal.
- A gas supply is needed.
The Efficiency of Boilers
A key factor in choosing the right boiler is the right efficiency. Efficiency can be simply explained as the ability to avoid wasting energy, or materials or even money while doing something or producing the desired result. There mainly two ways of knowing the efficiency of a boiler, the direct method, and the indirect method.
- Direct method: the heat output is divided by the heat input then multiplied by a 100.
- Indirect Method: which is the measuring of such factors as the temperature at the outlet, ambient temperature, the percentage of O2 and CO2, the percentage of ash in the combustion fuel among other parameters.
How to Choose the Right Boiler?
In reality, there is no boiler which is the best for all requested aspects and each type of boiler is perfect only for the right application. Therefore, if a boiler is needed for industrial purposes, then a water tube boiler would be the best option and of course, since there are many brands of water tube boilers, one must choose the right one depending on the budget, the size, and the efficiency.
In conclusion, due to the variety of boiler types, depending on the needed task, users have a lot of opportunities to choose the right one. Therefore, before buying a boiler, one must first take into consideration its application, and based on that decide on the physical size, the price, its maintenance, lifetime, and of course its energy efficiency.