Parts of Steam Boilers and their Functions
The main components of the boiler consist of furnaces, membrane walls, shell boilers, economizers, cyclones, water storage tanks, deaerators, coal bunkers, hoppers, conveyors and chimneys.
The following will be discussed one by one:
Furnace or also commonly called a furnace is a device used for heating. The name comes from the Latin Fornax which means oven. Sometimes people also refer to the kiln. The process of transferring heat to the furnace occurs in three ways:
Radiation heat transfer, where there will be a radiant heat from the fire and will be absorbed by the fluid flowing in it.
Conduction heat transfer, heat flows through the conduit from the side of the pipe that receives heat into the side of the pipe which gives heat to the water.
Convection heat transfer, heat that occurs with the contact of water molecules so that heat will spread to each stream of water.
The wall consists of tubes / pipes which are joined by a membrane, therefore it is called the membrane wall. Inside the membrane wall flows water to be boiled. The construction of tubes / pipes is from the bottom up where the bottom of the pipe contains water that is heavier in mass and it is expected that the upper part has become steam through the combustion process where the mass vapor is lighter and will rise naturally
Membrabe wall has two headers at the bottom which serve to channel water from downcomers. Downcomers are pipes that connect the steam drum with the bottom of the low header. To prevent the spread of heat and to minimize touch contact with humans, the outer side of the membrane wall is installed with insulation walls made of rockwool wire blankets.
3. Shell Boiler
The boiler shell in the picture above is a fire tube type. In a fire tube boiler, hot gas passes through the pipes and boiler feed water is inside the shell to be converted into steam.
The function of the boiler is:
· Accommodating water to be heated in the membrane walls and storing steam from the membrane wall and tube bundle before flowing to the factory or production room.
· Separating steam and water that results from heating in the furnace.
· Regulates water quality, by removing impurities dissolved in the boiler through continuous blowdown.
· Adjust the water level so that there is no shortage of water when the boiler is operating, because if there is a lack of water it can cause overheating of the pipe.
The water level of the drum must always be kept at a fixed height so that the amount of fill water entering the boiler is proportional to the amount of steam leaving the boiler so that the water level can be constant.
The economizer absorbs heat from the combustion gases after passing through the boiler, to heat the fill water before entering the boiler. The heat given to water is sensible heat (heat that causes an increase in temperature but the phase / form does not change). The heating of this water is done so that the temperature difference between the filler water and the water in the boiler is not too far away, so there is no thermal stress (tension that occurs due to heating) in the boiler. In addition, by utilizing combustion gas, it will increase the efficiency of the boiler and the process of forming steam faster. The Economizer is in the form of water pipes installed in the place where the combustion gases are passed.
The heat transfer that occurs in the economizer occurs in the direction of the flow of the two counter flows. The boiler boiler fill water flows upward towards the boiler, while the heating air flows downward.
Cyclone is one of the dust collectors that uses the principle of centifugal force to separate dust particles from the air based on differences in density from air and particulates.
The components of cyclone consist of:
Vertical cylindrical cone (cone) with the bottom forming a funnel.
Dirty air inlet at the top.
Inner cylinder and clean air outlet.
Dust bin at the bottom to hold dust particles.
The working principle of Cyclone is as follows:
· Particles from the gas flue are separated by making a centrifugal force.
· Flue gas which contains a lot of dust particles enters the inlet cyclone and is rotated in the cyclone cone in order to separate the dust and air particles using the principle of weight difference. Dust particles that are heavier than air will drop and fall into the dust bin.
Performance cyclone is strongly influenced by:
· The particle size, because according to the stroke law states that the particle diameter is directly proportional to the terminal velocity setting so that the larger the particle size, the cyclone efficiency will increase.
· The smaller the diameter of the cyclone cone, the higher the efficiency.
· The greater the viscosity, the smaller the cyclone efficiency.
6. Water Storage Tank and Deaerator
Water storage tank is a tool used to hold water from the water softener to the boiler. In addition to accommodating water, the preheater also occurs here before being heated again at the economizer. The heat source is taken through the steam injection line and the temperature in the water storage tank can reach more than 1000C. Water storage tanks are also equipped with a level gauge to see the water level inside and also equipped with sensors.
Deaerator is a tank that functions to separate oxygen from water because O2 levels that are too high in the water softener can cause corrosion of pipes in boilers and other supporting pipes. Deaerator works based on the nature of oxygen, the solubility in water will decrease with the increase in temperature.
7. Coal Bunkers
Coal bunkers are the final storage place for coal which is stored in a bunker (silo) before being used as fuel. The coal bunker is given a height detection device or an indicator level, so that if the coal bunker is full, then the coal entering the coal bunker will automatically stop.
Hopper is a fuel storage device such as silos but has a diameter that is generally larger than silos. This storage device is usually made of carbon steel where the bottom is cone shaped to minimize the coal discharge point right below which there is a conveyor to move from hopper to coal bunker.
Conveyor is a device that is used to move goods from one place to another. Conveyors are usually used to move goods that are continuous and continuous, in this case move the coal from the hopper to the coal bunker.