Boilers - Mechanical Operations - Chemo Concept

In the chemical industry and in the petroleum industry, polymer industry, food industry, pharmaceutical industry, and textile industry, Steam plays an important role in the proper functioning of the plant. 

And the equipment which generates steam from the water is called boiler which we will discuss today. 

In today's articles, we will not only understand what is Boiler but also We will understand how the boiler works, the importance of boiler, types of boiler, some widely used boilers, boiler water treatment process and we will end this post by understanding boiler accessories which is essential for the proper functioning of the boiler.

What is Boiler

The boiler is a closed vessel designed to create steam from water. Steam generated in the boiler is generally are saturated steam. 

Some boiler also has an arrangement of superheating of steam which results in the production of superheated steam.

Superheating is offer carried out on steam to increase its temperature above saturation temperature and to reduce chances of water condensation in steam lines. 

In the Boiler indirect heating of water by flue gas generated by a fuel, burning takes place to generate steam. 

How Boiler Works

Let's learn about how a boiler works. 

First of the fuel is burned in the furnace to generate flue gases. Flue gases travel through the boiler and contact with cold or preheated water. Heat Transfer between water and flue gases takes place and steam generation takes place. 

Due to the high temperature of flue gases steam generation takes place from water. 

Steam is collected into the steam drum and transported out of the boiler. 

Flue gases are sent to the recovery section to recover heart energy from it or sent to profit to remove Contaminants and pollutants from flue gases. 

Importance of Boiler in Industry

The boiler is one of the most important utilities because steam has many applications in chemical plants. 

Let's list down some applications of steam

1. As a heating medium

Steam can be used as direct heating or indirect heating medium. 

Indirect heating, Steam is directly injected into the product to be heated. Proper mixing of substances is also provided for proper and uniform heating of substances. Sparger tubes are provided to mix steam with the substance. 

In indirect cooling, Steam is indirectly contacted with the substance in a heat exchanger. The heat transfer between steam and the product takes place due to the temperature difference between them. 

2. As reactant in reactions such as steam reforming

In a steam reforming reaction, steam is injected into a reformer and mixed with a hydrocarbon such as methane, ethane, propane, etc which on reaction yields water gas ( Carbon Monoxide and Hydrogen gas). Which is further purified to get pure hydrogen. 

3. To generate electric power

As the steam contains energy which can be utilised to rotate the turbine and extract electricity from the energy of the steam. 

In every power plant, there is a similar process in which fuel is burned to generate steam which is further used to generate electricity. 

4. Steam as Humidifier

Humidification treatment is often required for equipment where a static charge may generate where steam can be used as a humidifier. Humidification helps to nullify that static charge. 

5. Steam as Drying Agent

Due to Its heating property of steam, It can be used to dry some substances. There is more indirect contact Drying while using Drying a heating medium. 

Types of Boiler (Classification of Boiler)

There are many types of boilers based on different parameters. 

Let's list out and understand the types of boiler

A boiler can be classified according to the pressure of the steam Boiler can create

1. High-pressure steam Boiler - which creates high-pressure steam. The pressure of steam these Types of Boiler generates are greater than 100 bar. 
2. Medium pressure steam boiler: This type of boiler creates steam of pressure less than 100 but greater than 10. 

For low-pressure steam, generally, the boiler is not used but medium pressure steam is often stepped down at lower pressure or it's directly get generated when steam pressures lower in any equipment. 

According to fuel used in firing boilers can be classified as 

1. Solid fuel-fired boiler: Solid fuel such as coal, wood, coke, etc is used as a fuel to generate flue gases which further heats the water. 
2. Liquid fuel-fired boiler: Liquid fuel such as fuel oil, furnace oil etc is used to generate steam by heating water with flue gases. 
3. Gaseous fuel-fired boiler: These types of boiler uses gaseous fuel such as CNG, Petroleum Gas, etc as the heating medium for steam generation. 

A boiler can be also be classified according to furnace count

1. Single furnace boiler: Single fired boiler contains only one heater to generate flue gas. 
2. Double furnace boiler: A pair of furnaces in a double furnace boiler generates flow gases. 

The boiler can also be classified according to air circulation technique

1. Natural circulating boiler: Natural circulating boiler exhibits natural circulation of air inside the boiler without the use of any fan. Hot gases are light in density so goes to the top and creates suction for atmospheric air. 
2. Forced circulation boiler: Boilers in which there are a set of fans or only one fan depending on air circulation rate to exhibit the flow of air. The induced draft fan is used to suck air from the furnace which crafts suction for atmospheric air. Forces draft fan forces atmospheric air into the furnace. 

A boiler can also be classified according to the Arrangement of water and flue gas in tubes or in the shell.

1. Fire-tube boiler: In a fire tube boiler there is the flow of flue gases inside the tube of the boiler. The fuel burned in the furnace generates flue gases that pass through tubes and breasts the water which is in the shell. 
2. Water-tube boiler: In a water tube boiler water flows in tubes and the flue gases generated on the furnace flows in the shell. 

Most Popular Boiler (Commonly Used)

Cochran boiler

A Cochran boiler is a fire tube boiler that contains tubes held in a horizontal direction in which flue gases flows and heats the water outside tubes. 

Cochran boiler is a vertical type of Boiler. 

In Cochran, boiler flue gases get generated at the bottom tank of the boiler and flow to the middle of the tank which is connected with the number of horizontal tubes. Flue gas passes through the tube and heats water outside. Then flue gases leave from the end of the tube to stack. 

Babcock-Wilcox Boiler

Babcock-Wilcox Boiler is a water tube boiler in which fuel is burned at bottom of the boiler and the flue gases generated travels vertical to the top.
Some tubes are connected with a water tank and water circulates into it. Water gets heated from flue gases, generates steam and steam flows over water in the water drum, and recovers from the top.

Lancashire Boiler

Lancashire Boiler is a horizontal fire tube boiler. Flue gases generated from fuels travel horizontally in tune and heats the water in the shell. Steam generated in the shell is taken out from the top of the boiler. 

Flue gas path can be straight or maybe u shape style.

Boiler Water Treatments

The boiler is a critical piece of equipment that needs special care. The feed water which is used to generate steam in the boiler should be pure. 

The water taken from any source such as River, lake, underground water etc can not be directly used as boiler feedwater. 

Water is first screened to remove floating or suspended macro impurity. Then coagulation (flocculation) is done on water in the coagulation tank to remove all suspended impurities.

Then water is filtered by a sand filter and then by the charcoal filter to remove micro impurities from water. The ion exchange process is also used to remove dissolved salts from water and to remove their hardness. Salts responsible for hardness causes scaling and sludge problems in the boiler. 

Finally, gases dissolved in water such as oxygen, carbon dioxide which causes corrosion inside the boiler are removed in the deaerator. 

Finally water free from and dissolved gases or salts are sent to the boiler for steam generation. 

Condensate generated is a condensation of steam from many types of equipment that is recycled back to the boiler after treatment. 

Boiler Accessories

Accessories are incorporated into the boiler to get specific use of it. 

Some common boiler Accessories are 

1. Pressure gauge: A pressure gauge is fitted in the boiler to measure the pressure of steam inside the Boiler. 
2. Water level indicator: The water level indicator indicates the level of water in the tank which is used to know the amount of water present inside the boiler. 
3. Pressure relief valve: A pressure relief valve is used to control excessive pressure of steam. If the pressure of steam increase to a certain level pressure relief valve opens and release steam into the atmosphere to lower pressure inside Boiler. 
4. Safety valve: In case pressure relief valve fails and pressure inside Boiler increase to an alarming value. The safety valve opens and releases all the excessive pressure into the atmosphere. 
5. Feed check valve: The feed check valve is fitted where feed water enters the water drum. Check valve only allows one side of the flow of water which confirms water from boiler doesn't go out. 
6. Drain valve: When there is the requirement of removing complete water from the boiler for reasons such as shut down or maintenance drain valve is open to remove all the water from the boiler.
7. Manhole: Manhole is provided for a human to enter into the boiler for cleaning and maintenance works.