Electrode boiler

An electrode boiler (jet type) is a type of boiler that uses electricity flowing through streams of water to create steam. The conductive and resistive properties of water are employed to carry electric current.

Technical principle

The most common type of electrode boiler pumps water from the lower part of the vessel to an internal header that has nozzles that allow the water to flow to electrodes. Generally the working pressure is maintained at 10 bar. If more pressure is needed (more steam) the controls speed up the pump to increase flow through additional nozzles. As the needed pressure is reached the pump controls the flow of water to obtain the desired steam output (in kg per hour) at the desired pressure. On larger systems the pump can be controlled by a variable frequency drive so energy is not wasted. This control system can also control de-aerator pumps and controls.

The electrodes are connected to a medium voltage (1-35 kV) AC source. Electrode boilers can work on both single phase and three phase supplies. If DC voltage is used, electrolysis of water occurs, decomposing water into its elements H2 at the cathode (negative electrode) and O2 at the anode (positive electrode). The electrode boiler is 99.9% efficient with almost all the energy consumed producing steam.[1] Losses are radiant heat from the vessel only.

During the operation of the boiler, it is fed with water which contains conductive substances like salts. Because the departing steam is free of these substances, conductivity of water increases. With cleaner water in the boiler, the conductivity decreases. When conductivity rises beyond a set limit, some of the water must be removed and replaced with fresh water. The conductivity of the water and the voltage applied determine how much steam is generated in each stream of water.

Advantages

  • All electrical energy is converted to heat.
  • An electrode boiler has a very quick response time.
  • As it doesn't directly generate pollution, no pollution control system is needed.[2]
  • Unlike fossil fuel or conventional electric boilers, no boiler component is at high temperature except the water itself.
  • As compared to other boilers, electrode boilers experience little thermal stress.[3]
  • The compact size of electrode boiler makes it easier to work with than other boiler types.
  • Low voltage transformers are not required due to which a medium voltage (1-35 kV) grid connection can be established.
  • Electric boilers have few components making it easier to control and maintain.
  • Dropping water levels inhibits current flow and allows the boiler to self-regulate.

Drawbacks

  • Due to the water serving as a conductor, the water becomes live at a significant portion of the input voltage. This creates a serious shock hazard when used, for example, to heat water for a bath or for tea making.
  • Use of DC sources leads to electrolysis of water as a result, water gets broken down into its components hydrogen and oxygen, thus stops the working of boiler.[4]
  • Scale formation will insulate the electrodes which results in reduction of current and boiler output.

Safety measures

  • Water level should be maintained up to certain level and it should not be allowed to lower than that limit.

If water level falls below the limit level, current stops flowing as the circuit is not complete. This stops heating the water and producing steam.

When evaporated into steam, deionized or distilled water leaves little or no ions in the boiler respectively. Thus, scale formation is reduced.

References

  1. "Archived copy". Archived from the original on 2010-09-17. Retrieved 2010-03-01.CS1 maint: archived copy as title (link)
  2. "Archived copy". Archived from the original on 2012-01-14. Retrieved 2011-10-03.CS1 maint: archived copy as title (link)
  3. "emt-india.net". www.emt-india.net.
  4. "TLC Electrical Supplies". www.tlc-direct.co.uk.
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