Electric Boilers

HV Electrode Boiler

Cochrane Engineering manufacture a wide range of 11kV HV Electrode Boilers exclusively for the EB Steam Group in South Africa, who offer a unique steam outsourcing product. To date EB Steam have over 25 sites running sucessfully in Kwa Zulu Natal, Western Cape, Eastern Cape and Gauteng, some of which have been in the field providing high quality, reliable steam for over ten years.

Contact EB Steam for more information on our Electrode Boilers.

BENEFITS:
Electrode boilers are used to produce hot water or steam by means of electric power, with the current passing directly through the water being heated.
This type of installation offers better protection for the environment than the alternative of heating with fossil-fuels which involve pollution problems.

Electrode boilers can utilise cheap surplus energy from the electricity grid, making them a profitable investment. Highly convincing results are usually obtained when calculating their profitability. The diagram shows the pay-back time for investment in electrode boilers of varying size, based on the price difference between electric power and an equivalent volume of oil.

HIGH VOLTAGE BOILERS

Our electrode boilers can be supplied for voltages up to 15 kV and outputs from 10 MW to 50 MW, and are built with a high resistance neutral point. The electrodes are fixed and output is varied by raising or lowering the water level. Very rapid regulation of steam output is achieved by using a system based on an internal water reservoir and circulation pump. This solution also provides an extremely wide control range, from about two per cent of full load up to 100 percent within 3 – 10 minutes. This allows the boiler to accurately maintain steam pressure over widely varying load conditions.

REGULATION

Control Equipment
Electrode boilers are fitted with controllers to provide automatic operation. The following control loops are fitted as standard :

Regulation of boiler pressure (boiler output – steam production)
Feed water control
Overflow control
Regulation of water conductivity (auto blowdown control)
Control of maximum boiler power.
Water Considerations
Water always contains a certain amount of substances in solution, with the volume of dissolved salts determining its conductivity. The cleaner the water, the lower the conductivity.
Boiler feed water contains salts and other substances while the departing steam takes nothing with it, so that the conductivity of the water will keep on rising. In order to keep this conductivity below a set limit, therefore, some of the boiler water must be blown down and replaced with fresh feed water. The size of this blowdown loss will depend on the conductivity of the feed water in relation to the conductivity with which the boiler can work. As a result it is important to get the feed water as clean as possible for instance by returning the maximum amount of condensate.

If little condensate is returned, it will generally be necessary to pass the water through a demineralisation or reverse osmosis plant to obtain a feed water with low conductivity. This in turn means little blowdown loss and improved efficiency.

The cost of a demineralisation plant can accordingly be recovered relatively fast. Completely demineralised water will also minimise electrode wear by eliminating destructive substances, and so reduce maintenance requirements.

Electrical characteristics
All our Electrode boilers are constructed with a high resistance neutral point. This means that the active water and electrode system are contained in a vessel supported inside the boiler on insulators, and acting as the neutral point of the three phase system.

Electrical equipment
The diagram above illustrates the way the electrical equipment for a high voltage boiler is built up in principle. The installation usually comes in two steel cabinets, one for the high voltage unit and the other with the instruments and controllers; this includes a SCADA unit which can be networked to the client’s operating control rooms.

The high voltage equipment can be installed in the boiler room, at some distant location or as an integral part of the cellular arrangement in a transformer room.
The control cabinet stands close to the boiler, however, to facilitate full supervision over all instruments during such operations as start-up.
Large boilers must be fitted with two three-electrode sets, which can either have separate circuit breakers or be linked together with a single breaker.

The current in each electrode is monitored in order to keep electrode wear under observation.

Regulations
There are no differences between electric and oil-fired boilers with regard to requirements for materials, performance and so forth, or for operating personnel.

Virtually all boilers today come equipped for unmanned operation over a period of up to 16 or more hours, which calls for a certain amount of extra automation and safety equipment. The latter is inspected and tested for functional performance on a routine basis.

Scope of supply
The scope of supply are tailored to specific user requirements, but will normally embrace  :

• electrode boiler with necessary fittings;
• circulating pump
• control cabinet with necessary instrumentation
• operating and regulation equipment
• high voltage cabinet with circuit breaker and measuring transformers.

This equipment comes either from ourselves or suppliers represented by the company, while our own personnel are responsible for installation supervision and commissioning.  A complete package of this type ensures good quality, secure service and quick delivery of spare parts.

We normally also assume responsibility for supply of piping, feed pumps, water treatment plant and ancilliaries.

Experience
We have built and supplied electrode boilers for some years in the region, giving us experience in this field.  The company is also usually responsible for installation, and the boiler comes fully tested and ready for operation.  Training is provided for boiler room staff.

A comprehensive stock of spare parts is always available to meet any service requirement.