The steam boiler is a closed tank in which the water in the boiler tank is converted into water vapor by the heat produced by burning the fuel. This water vapor has high pressure. According to the type of steam boilers, they are divided into two categories:
cast iron and steel
cast iron boilers are used to produce low pressure steam. Most boilers are made of steel. In general, two types of boilers are made in the world: firetube and watertube boilers. Watertube boilers are made in two types of cast iron and steel. Firetube boilers are of steel type.
Firetube boiler
consists of a number of tubes containing hot gas, around which water flows. which, as a result of the heat of the gas, turns water into steam with high pressure.
These boilers are made and used in various industries as portable and fixed boilers. Since firetube boilers are made They are pressurized from a large water tank and are limited in terms of pressure and capacity.
Water tube boiler
Watertube boilers contain containers called drums that are connected by pipes. These tubes contain water, and hot gas flows around them. As a result of the heat of the gas, water turns into steam with high pressure. Watertube boilers have more water pipes, so they have a wide heat level. Due to the thermal flow of water, it is faster than firetube boilers. which results in higher heat transfer and more efficiency.
The capacity of these boilers can be upgraded, which is an advantage over watertube boilers.
Classification of types of steam boilers based on the direction of movement of gases
Boilers are divided into several categories based on the number of paths they take to enter the chimney:
Single pass: These boilers are no longer manufactured. In this type of boiler, the combustion gases go through the boiler once to enter the chimney. Two passes: In this type of boiler, the combustion gases go through the boiler twice to enter the chimney.
Three passes: In this type of boiler, the combustion gases pass through the boiler three times to enter the piston.
Four Pass: These pots are only for Steam is produced in large quantities in this type of boiler. The combustion gases pass through the boiler four times to enter the piston.
Uses of steam boilers
Chemical industries, refineries, petrochemical industries, power plants, food industries (production of tomato paste, production of dairy products), washing industry (car washes, roads, etc.) and...
types of boilers especially Firetube types are widely used in the food industry. which are used for fermentation, cooking, heat generation, washing, sterilization, drying, humidification.
Advantages of using a steam boiler instead of a hot oil boiler in the food industry:
Steam boiler, hot water and hot oil are usually used to produce steam and hot water in food industry systems. Of course, due to the other advantages of steam, which are mentioned below, this method is usually used to carry out the process. The advantages of a steam boiler over a hot oil boiler include the following:
Working in low pressure conditions, no clogging and increased efficiency, no need for boilers, no corrosion in the boiler, no need for a deaerator and tank. Condensation
Principles of boiler water treatment:
It is necessary to always check the quality of water used in all types of steam boilers in terms of the amount of dissolved gases in water and sediments. Because these gases can combine with metal and produce precipitation. which causes corrosion and device failure.
There are two ways to remove these gases: deaerator or physical deaeration, chemical injection
Application of deaerator in boilers
Oxygen is the main cause of corrosion in tanks, pipes and body of boilers and liquefied steam return lines. In the presence of carbon dioxide, the pH of the water decreases, the water becomes acidic and the corrosion rate increases. And as a result, it causes irreparable losses from an economic point of view. In order to remove corrosive gases (oxygen and carbon dioxide) from the feed water of the boiler, a deaerator is used.
External treatment in boilers
In external purification, removal of suspended particles, removal of undissolved gases such as oxygen and water hardness are done. At the end of this part, the hardness, alkalinity, amount of sulfates and suspended particles in the water should be the lowest. Internal purification is done by injecting suitable chemicals into the boiler feed water.