How does an electrode boiler work

In such a way water gets heated. The boiler vessel itself is under pressure with use of inert gas system e. Water volume is regulated with a control valve. It is kept on a pretty low level, so that boiler output can be regulated almost instantly. Water conductivity is continuously monitored to ensure that the boiler gives the correct output. When the conductivity exceeds the set parameters, blowdown is initiated automatically. Steam boiler operation is based on similar principles.

Steam is collected in the upper part of the boiler, it gets out through the control valve. In case, steam pressure exceeds the setpoint, poiler power decreases automatically. It was very popular in the s, especially in countries with substantial hydropower resources such as Norway. Before the electrical grids in Europe were connected, electrode boilers provided a way of making use of cheap excess power produced from hydro plants during periods of overproduction, and using it to produce hot water or steam.

In the s, with improved grid connections between countries and increasing power prices, thermal energy storage became less attractive and electrical boilers declined in popularity, even in Norway.

Nevertheless, despite the decline in the market, the Norwegian company PARAT Halvorsen AS took a decision to continue to offer the technology and to keep it as state of the art as possible, providing it for niche applications, eg hospitals that wanted an electrical boiler as back up to complement an oil boiler.

Subsequently, in around , a new market for the electrode boiler emerged: regulation of grids coping with a growing share of intermittent wind generation. The first inquiries came from Danish municipal CHP facilities, which were required by the Danish grid regulator to install thermal storage to help ward off potential grid instabilities arising from substantial wind capacity on the grid.

In this application, the whole capacity of the boiler is bid in for negative grid regulation. This means when there is too much power in the grid, the boiler will automatically regulate up, achieving its full thermal capacity in 30 seconds, helping to stabilise the grid frequency. The electrode boiler, with its minimal pipework and no heating surfaces, is particularly suited to this kind of fast ramping.

In other countries, notably Germany, a market developed for the electrode boiler in negative secondary regulation applications, ie absorbing power from the grid, but over longer time frames.

Another market is CHP power plants that face a situation where delivering heat to district heating gives better revenues than selling power. They can use the electrode boiler to convert their power to heat instead of delivering cheap power to the grid. The electrode boiler can also be used for internal load regulation in multi-unit CHP plants when starting or stopping a unit, allowing the load on piston engines or gas turbines to be maintained at an optimal level. Some users in addition find that an electrode boiler can form a valuable part of the backup plan if gas supplies or other parts of the infrastructure should fail.

In those circumstances, the electrode boiler can deliver district heating or steam to critical clients. The electrode boiler can reach full load from cold conditions in minutes, which is advantageous for a backup boiler.

In Norway, users employ the electrode boiler because electricity is competitive with oil and gas as a source of heat. Using electricity also improves environmental credentials. The electrodes are suspended inside the inner container, which is electrically insulated from the outer shell. The water and the inner container forms an insulated zero point in the star connection between the electrodes. The compact electrode electric boiler provides warmth in the room and makes it possible to remotely regulate the temperature.

Its small size allows it to be installed in an existing heating system. When describing the advantages of electrode boilers, the main emphasis is on the absence of intermediaries in the transfer of energy from the electrical network to the coolant.

The main argument on which the marketing strategy for the promotion of electrode water heaters is bet is the direct heating of the liquid under the influence of an electric current, which occurs due to its high resistivity. When using this type of equipment, the influence on the heat transfer of the scale crust formed on the surface of traditional tubular heating elements is eliminated. The low inertia of the system is also considered an obvious advantage: the coolant begins to heat up immediately after the voltage is applied to the electrodes, while when using resistive heaters, it takes some time to heat the coil itself and its dielectric insulation.

The device of the electrode boiler: 1 - terminals for connecting to the network; 2 - sealant and insulation of electrodes; 3 - supply of cooled heat carrier; 4 - block of electrodes; 5 - coolant; 6 - boiler drum; 7 - insulating layer; 8 - outlet of the heated coolant.

However, not everything is so rosy. First of all, it is doubtful that the entire coolant is under the influence of a dangerously high potential difference.

In particular, with a zero break, all metal parts of the heating system become fatal to humans, and breakdowns are also possible if the neutral is not properly grounded. It is worth mentioning the fact that not all fluids have a resistivity high enough to convert all applied power to generate electricity.

A certain part of the current load does not meet resistance and therefore flows freely into the ground. In addition to natural losses when heating a liquid, electrode boilers have another nasty property. In the process of passing an electric current through water, the phenomenon of electrolysis is observed - the separation of the H2O molecule into gaseous components.

This, among other things, further reduces the energy efficiency of the boiler, because in this case, electricity is consumed not for heating, but for electrolysis. However, the most obvious consequence of this effect is the formation of gas locks in pipes and radiators. For these reasons, the heating medium for heating systems on electrode boilers must be selected with the greatest care.

In order to reduce the conductivity of the coolant increase the resistivity , the content of dissolved ions in the liquid used should be normalized. Distilled water is mainly used, to which electrolyte is mixed in the proportion recommended by the manufacturer, again, factory production.

The situation is more complicated if an antifreeze liquid must be used as a heat carrier. In this case, the system must be filled with a special antifreeze that cannot be diluted with water. With a significant displacement, refueling the system can cost a pretty penny, but this does not take into account the issue of the durability of the coolant. In the presence of metal parts in the system, the concentration of ions in the liquid increases over time, while effective methods for regenerating the coolant for electrode boilers have not yet been invented.

But periodically at least part of the coolant will have to be drained, because each boiler requires cleaning the electrodes from plaque, and the system itself needs to be flushed.