What is a electric boiler?
Resistance furnaces work on the basis that when an electric current flows through a wire or conductor, there will be an amount of heat released according to Joule–Lenz’s law:
Q=I2RT
Q – Amount of heat in joules (J)
I – Current in Amps (A)
R – Resistance in Ohms
T – Time in seconds (s)
From the above formula, we see that the resistor R can play the role:
– Fired objects: This case is called direct firing.
– Heating wire: When the heating wire is heated, it transfers heat to the object by radiation, convection, conduction or complexation. This case is called indirect heating.
The first case is rare because it is only used to heat objects with simple shapes (rectangular, square and round sections).
The second case is often encountered in industrial practice. Therefore, when it comes to resistance furnaces, it is impossible not to mention the material used to make the heating wire, the heating part of the furnace.
Classification of electric boiler:
Electric boiler are divided into two groups: direct-acting electric boiler and indirect-acting electric boiler
- 1. Direct acting electric boiler:
This is an electric boiler in which the crucible is heated directly by an electric current flowing through it. The characteristics of this type of furnace are fast firing speed, simple furnace structure, and sometimes no need for furnace walls. To ensure even heating, the firing object must have the same cross-section along the length of the object.
- 2. Indirect electric boiler:
An indirect-acting electric boiler is an electric boiler in which heat is radiated through the resistance wire, and the resistance wire transfers heat to the object by radiation, convection or conduction.
Electric boiler typically reach temperatures up to 1200°C (when the wire is metal) 1350°C (when using a carburetor). Resistance furnaces are widely used in many industries, as well as in civil.
Structure of electric boiler:
Conventional electric boiler consists of three main parts: boiler shell, lining and heating wire.
Boiler shell:
The electric boiler shell is a sturdy frame, mainly for carrying the load during the boiler’s operation. On the other hand, the boiler shell is also used to keep the insulation loose and to ensure the complete or relative sealing of the boiler.
For boilers operating with shielding gas, it is necessary that the boiler shell be completely sealed, and for conventional electric boilers, the sealing of the boiler shell only needs to reduce the total heat loss and avoid the draft of cold air. boiler, especially according to boiler height.
In particular cases, an electric boiler can cause the boiler shell to not be sealed.
The furnace shell frame needs to be strong enough to support the load of the lining, the boiler load (the boiler) and the mechanical mechanisms mounted on the boiler shell.
– The electric boiler shell is often used in chamber boilers, continuous boilers, vibrating bottom boilers, etc..
– Round boiler shell used in well furnaces and some furnaces, etc…
– The round boiler shell bears the internal force better than the electric boiler shell when the same amount of metal is used to make the boiler shell. When the boiler shell structure is round, people often use thick steel plate.
– From 3 – 6 mm when the boiler shell diameter is 1000 – 2000 mm and 8 – 12 mm when the boiler shell diameter is 2500 – 4000 mm and 14 – 20 mm when the boiler shell diameter is about 4500 – 6500 mm.
When it is necessary to increase the rigidity of the round boiler shell, people use reinforced washers with shaped steels.
The electric boiler shell is erected using U- and L-shaped steels and sheet steel cut to the appropriate shape. The oven cover may be hermetically sealed, or not depending on the sealing requirements of the oven. The processing method of this boiler shell is mainly welding and riveting.
Lining:
Electric boiler lining is usually composed of two parts: refractory material and insulation. The refractory part can be built with standard bricks, shaped bricks and special shaped bricks depending on the given shape and size of the boiler chamber. It is also sometimes compacted with refractory powders and binders called compacting blocks. Compaction can be done inside the boiler and can also be done outside thanks to the moulds.
Refractory material must meet the following requirements:
+ Withstand the maximum working temperature of the boiler.
+ Has a large enough heat resistance when working.
+ Sufficient mechanical strength when loading the crucible and placing the transport equipment in working condition. + Ensure the ability to attach the heating wire durable and firmly.
+ Having enough chemical resistance when working, resistant to the effects of the boiler atmosphere and the influence of the burning object.
+ Ensures minimal heat accumulation. This is especially important for cyclic ovens.
The insulation is usually located between the boiler shell and the refractory material. The main purpose of this section is to reduce heat loss. Particularly for the bottom, the insulation part requires a certain mechanical strength and the other parts are generally not required.
The basic requirements of the insulation part are:
+ Minimum coefficient of thermal conductivity.
+ Minimum heat capacity.
+ Stable in physical and thermal properties under defined working conditions.
The insulation can be built with insulating bricks, can be filled with insulation powder.
Heating wire:
According to the characteristics of the materials used to make the heating wire, people divide the heating wire into two types: metal heating wire and non-metallic heating wire.
In industry, the commonly used resistance furnaces are metal heating wires.
Requirements for rheostat furnaces:
The boiler must be heat-resistant, insulated in a safe furnace chamber by insulating refractory material, in order to avoid loss of heat sources to the surrounding environment, to avoid damage to other furnace equipment and to ensure safety. for the operator.
KS – Boiler specializes in manufacturing, installing and maintaining industrial boilers:
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Website: https://ks-boiler.com
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Factory address: E2/52 B1 Da Phuoc, Hamlet 5, Binh Chanh District, HCM.
