What is Steam Boiler?
A steam boiler or steam generator is a device used to create steam by applying heat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure (7–2,000 kPa or 1–290 psi) but, at pressures above this, it is more usual to speak of a steam generator.
A steam boiler or steam generator is used wherever a source of steam is required. The form and size depend on the application: mobile steam engines such as steam locomotives, portable engines, and steam-powered road vehicles typically use a smaller boiler that forms an integral part of the vehicle; stationary steam engines, industrial installations, and power stations will usually have a larger separate steam-generating facility connected to the point-of-use by piping.
A notable exception is the steam-powered fireless locomotive, where separately generated steam is transferred to a receiver (tank) on the locomotive.
The Function of Steam Boiler
The main function of a steam boiler is to producing, storing and troubling the vapor. The liquid contained boiler is nothing but a shell and the heat energy produced while burning of fuel will be moved to water, and then it converts into steam at the required pressure as well as temperature.
The main conditions of this boiler mainly include the water container should lock very carefully. The vapor of water should be supplied in the preferred conditions namely, quality, rate, pressure, and temperature.
Component of Steam Boiler
The steam generator or steam boiler is an integral component of a steam engine when considered as a prime mover. However, it needs to be treated separately, as to some extent a variety of generator types can be combined with a variety of engine units.
A boiler incorporates a firebox or furnace in order to burn the fuel and generate heat. The generated heat is transferred to water to make steam, the process of boiling. This produces saturated steam at a rate that can vary according to the pressure above the boiling water. The higher the furnace temperature, the faster the steam production.
The saturated steam thus produced can then either be used immediately to produce power via a turbine and alternator or else may be further superheated to a higher temperature; this notably reduces suspended water content making a given volume of steam produce more work and creates a greater temperature gradient, which helps reduce the potential to form condensation.
Any remaining heat in the combustion gases can then either be evacuated or made to pass through an economizer, the role of which is to warm the feed water before it reaches the boiler.
Working Principle of Boiler
The basic working principle of the boiler is very simple and easy to understand. The boiler is essentially a closed vessel inside which water is stored. Fuel (generally coal) is burnt in a furnace and hot gasses are produced.
These hot gasses come in contact with water vessels where the heat of these hot gases transfer to the water and consequently steam is produced in the boiler.
Then this steam is piped to the turbine of the thermal power plant. There are many different types of boilers utilized for different purposes like running a production unit, sanitizing some areas, sterilizing equipment, warming up the surroundings, etc.
Steam Boiler Efficiency
The percentage of total heat exported by outlet steam in the total heat supplied by the fuel (coal) is called steam boiler efficiency.
Steam Boiler Efficiency= (Heat exported by outlet steam/ Heat supply by fuel) * 100
It includes thermal efficiency, combustion efficiency, and fuel to steam efficiency. Steam boiler efficiency depends upon the size of the boiler used. The typical efficiency of a steam boiler is 80% to 88%.
Actually, there are some losses that occur like incomplete combustion, radiating loss occurs from steam boiler surrounding wall, defective combustion gas, etc. Hence, the efficiency of the steam boiler gives this result.
Types of Steam Boiler
1. Fire Tube Boiler
One of the most basic types of boilers, the fire tube boiler is also one of the oldest designs.
The burner shoots the flame into a tube that is immersed in water contained in the main vessel of the boiler itself. There may be multiple fire tubes. The heat of the flame transfers into the water, heating it to its boiling point.
The resultant steam is captured in the space above the water and escapes through a steam outlet to whatever purpose it is intended for, whether heating a radiator or driving a locomotive. But because both steam and water are contained within this shared vessel, steam pressure is somewhat limited.
In the event that the main vessel should succumb to increased pressure beyond its capacity, there could be catastrophic consequences.
Within the realm of fire tube boilers are two main types. These types are dependent on the physical location of the furnace (flame production). These are described as external and internal furnaces.
Each of the two main types includes subsets. For example, there are three types of external furnaces:
- horizontal-return tubular fire tube boiler;
- short firebox fire tube boiler; and
- compact fire tube boiler.
For internal furnaces, there are two subsets:
- horizontal tubular; and
- vertical tubular fire tube boiler.
Let’s examine the workings of a horizontal return tubular fire tube boiler. In this configuration, a large steam drum is installed horizontally within the housing and supporting structures. Multiple fire tubes emanate from the furnace and are also aligned in a horizontal fashion within the drum. This makes sense, as the drum is horizontal. As the drum is filled with water, the tubes become submerged.
Fuel is combusted within the furnace, heating gases that pass through the tubes, transferring heat to the water, which, in turn, heats the water to its boiling point. Spent gases pass through the fire tubes and into a smoke box that is connected to an exhaust stack.
However, as steam is produced in the drum, so is pressure. A pressurized system results in water boiling at a higher temperature. Hence, the more that steam pressure builds inside the drum, the boiling temperature of the water increases, resulting in a reduction in steam production overall. In essence, the boiler is self-controlled via the steam pressure it produces through its operation.
Types of Internal Furnace Fire Tube Boilers
Internal fire tube boilers are characterized as having their firebox within the unit. They include the following.
Cornish Fire Tube Boiler
This style of boiler includes a plain cylindrical shell, and a single heat pipe through its center. It has a single exhaust flue connected to its single heat pipe.
Lancashire Fire Tube Boiler
The construction of the Lancashire boiler is similar to the Cornish, except it has two internal fire tubes and two exhaust flues.
Locomotive Fire Tube Boiler
The locomotive boiler is an obsolete design. Originally found in steam locomotives, wood or coal was burned in the combustion chamber (furnace). A unit with a horizontal tube design, it was a rugged piece of equipment, with a high steam capacity.
Vertical Fire Tube Boiler
A vertical tube boiler is a simple boiler with a vertical cylinder design. It includes cross tubes, and the furnace is located at the bottom of the boiler. Combustion cases escape through the top of the unit via the flue.
Cochran Fire Tube Boiler
The Cochran boiler is also a vertical-type boiler of multi-tubular design. It includes multiple horizontal fire tubes.
Immersion Fire Tube Boiler
This style of boiler incorporates a horizontal single-pass design. Flames are pushed into corresponding small-diameter tubes. The multiple small-diameter tubes are individually immersed in water. There is one tube for each flame nozzle.
2. Water Tube Boilers
Water-tube boilers offer advances in steam-producing technology. It is different than fire-tube technology in that the flame from the furnace is shot into a large containment area, where it literally bounces off the rear wall and distributes heat more evenly and efficiently, thus reducing fuel costs.
Fire tubes send flames into tubes immersed in water, as opposed to a chamber. As there is less water to produce a steam explosion in the event of a failure, operations are much safer, and the unit is easier to inspect and maintain.
Within the chamber is a series of tubes containing water. The tubes run the length of the boiler. Tubes are sealed and can withstand pressure individually, not affecting the adjacent tubes. Heat is transferred through the metallic tubes to the water flowing through them.
This is a notable difference from fire tube boilers, in which the water that’s being used to create steam will surround the heat source. With water tube boilers, the heat surrounds the water tubes. This results in less stress on the boiler as a unit, as compared to fire tube designs.
The water that has been heated inside the tubes rises to the top of the boiler and into the steam drum. The process typically takes only a few minutes. Steam is produced at a high rate. The effects of heating and cooling create a condition known as thermal siphoning, which allows for the circulation of water in the boiler.
The efficiency of the operation of the boiler allows it to occupy a smaller footprint than fire tube units. Water-tube boilers are mainly used for generating steam at higher pressures and at higher volumes.
Advantages of Steam Boiler
The advantages of this boiler include the following.
- The construction cost of these boilers is low.
- This boiler uses any kind of chimney
- It occupies less floor area.
- It is portable.
- It has a self-enclosed boiler
Disadvantages of Steam Boiler
The disadvantages of this boiler include the following.
- The design of the steam boiler is vertical so the capacity of steam rising is low.
- It has limited pressure and capacity.
- The cleaning and examination of these are difficult.
- It requires high headspace
Applications of Steam Boiler
The applications of this boiler include the following.
- These are used to generate power in steam turbines or engines.
- These are used for various processes in process industries
- These are used in houses or buildings in cool weather for generating a hot water supply
Characteristics of Steam Boiler
The characteristics of a steam boiler include the following.
- Steam boiler generates the highest amount of steam with low fuel utilization.
- It must be less weight as well as needs small space
- It must be immediate starting.
- These boilers must be cheap as well as needless concentration.
- These boilers handle any kind of fluctuating load.