Effect of economizer in boiler operation:
The job of the economizer is to heat the feed water to a boiling or near boiling point before the water enters the boiler.
According to the task, it can be divided into two types of economizer: boiling type and non-boiling type:
– Boiling type economizer, the water coming out of the heater reaches the boiling state, the boiling point can reach up to 30%. Boiler type water heaters can be made of plain steel or finned steel tubes.
– The economizer is not boiling, the water coming out of the economizer has not reached the boiling temperature. Non-boiling type economizer can be made of steel or cast iron depending on the sulfur content of the material.
As the steam pressure increases, the amount of heat needed to bring the water to a boil increases, so the heat absorbed in the water heater must increase. At that time, a boiling economizer must be built (for medium-pressure furnaces, the heat to generate steam accounts for about 60% of the total heat supplied to the furnace).
What types of economizers are included?
Plain steel pipe economizer
The plain steel pipe economizer has a similar structure to the superheater, consisting of steel pipes with a diameter of 28 to 38mm that are bent many times and the two ends are connected to the two manifolds of the heater. The economizer is made in clusters about 1m high and the clusters are spaced 0.6m apart to create space for easy cleaning. Normally, the coils of the economizer are arranged on a sole, creating a large smoke flow rate and a lot of vortex to enhance heat transfer.
Steel pipe economizer with wings
In terms of structure, the steel pipe economizer has wings like the plain steel water heater, except that on the outside of the tube, people make additional wings to increase the heat exchange surface area to enhance heat transfer.
The winged economizer has disadvantages: the ability to collect dust is very large, it is difficult to clean, so it is rarely used.
Cast iron economizer
Cast iron has the advantage of being resistant to acid corrosion and ash abrasion, so in sulfur fueled boilers, cast iron economizer are used. Of course, cast iron has the disadvantage of poor bearing and beating. Therefore, to avoid the phenomenon of water hammer causing impact force in the tubes of the heater in the economizer must not boil, i.e. cast iron economizer are only fitted to those ovens that require a non-boiling type economizer.
Cast iron has a lower coefficient of thermal conductivity than steel, so the outside of the pipe is cast with wings to enhance heat exchange.
The cast iron economizer set consists of cast iron pipes with an inner diameter of 76-120mm, 1.5 to 3m long, connected by flanges and bolts, so installation is very easy.
The disadvantage of the cast iron economizer is its large size and heavy weight.
Cast iron pipes are often used for furnaces with small or medium capacity. Usually these furnaces do not have a water treatment system or have but are not completed, so there are many substances in the water that can cause corrosion. , but cast iron has good corrosion and abrasion resistance, so the service life will be longer than that of a steel economizer.
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