Zander & Ingeström

ZETA steam boilers are used in combination with other forms of energy or as a source of standby power, operating either directly on-line or in conjunction with an accumulator.

ZETA boilers are common in the pulp and paper industries, the chemical industry and in breweries, heating systems, hospitals, etc.
A number of ZETA boilers have been installed in nuclear power plants, an application in which quality and availability are of the utmost importance.

Design

The ZETA steam boiler, type ZDKI, comprises an outer pressure vessel (boiler shell) and an inner, cylindrical vessel mounted directly on brackets or insulators inside the shell. The three-phase electrodes, each consisting of a number of bars mounted on single electrode plate, are located in the inner vessel. Each electrode is suspended in insulated bushings at the top of the boiler. The inner vessel, which also forms the neutral point of the electrical system, divides the boiler into two water chambers (inner and outer). A control valve mounted on the bottom of the inner vessel is operated by a servomotor mounted on the outside of the boiler.

The suction pipe of the circulation pump (supplied as part of the equipment) is connected to the outer vessel, while the discharge pipe is divided into three branches, each of which is connected to the inner vessel below the electrodes. A control valve is installed in the discharge pipe. The feed water inlet is located at the bottom of the shell.

The neutral point may be either the directly earthed or high-resistance insulated type. In the latter case, the inner vessel is insulated from the shell by insulators, while all pipes between the two vessels are of insulating material.

Operation

The main components of an electric steam boiler installation are the boiler and circulation pump, fittings, control and instrument panels, including the monitoring instruments and control equipment required for the automatic operation of the boiler. The feed water pump, combined feed water tank and deaerator, and dosing equipment are also included.

Electric power is converted directly into heat as the current flows through the water. The current passing through the water is a function of the active surface area of the electrodes and the water conductivity. The current is controller by regulating the water level, thus varying the active electrode area.

Technical specifications

Dimensions

The control range is (0.5-) 5-100 % of rated output. The forced circulation system ensures a very fast start-up and shut-down, as well as offering excellent control characteristics. Both the temperature and conductivity of the boiler water are important for the start-up time. If fast start-up is required, the boiler should be maintained on standby at a temperature not lower than approx. 140?C and must be filled with water of the correct conductivity. This will enable the unit to be started in 8-15 min depending on the size. Starting from 20?C will take about four times longer.