Although the initial investigators, such as Lodge (1886), employed an electrostatic generator such as a Wimshurst Machine successfully to demonstrate the precipitation phenomenon, once the development was applied in the field, it became apparent that more electrical power, in terms of current, was necessary to ensure satisfactory particle charging such that the particles could be continuously precipitated. More correctly the process should be referred to as electrical precipitation, because with modern installations one can find rectifier equipment having outputs up to 200 kW and for large power station applications a power consumption up to 2 MW.

This chapter presents the design and operation of an electrostatic precipitator. It discusses the production of ions, discharge electrode and its spacing, collector electrodes, precipitator sectionalism, high tension insulators, electrical clearances, deposit removal from the collector and discharge systems, hopper dust removal, and the reentrainment from hoppers.

Most modern precipitator installations are invariably energised from mains fre quency rectified equipment utilising the latest electrical and electronic components as described in Chapter 5. Generally the transformer input conditions are controlled by anti-parallel connected thyristors/silicon controlled rectifiers, which in turn are controlled by some form of microprocessor based automatic voltage control (AVC) system. Although the supply is generally a fully rectified voltage, many modern equipment designs have the facility of intermittent ener gisation to cater for specific fly ash conditions, or for power saving while meeting a target emission. The basic operating characteristics of a mains frequency rec tified power supply and the types of control will be examined in the following sections.

There have been few departures in the past from the use of traditional mains frequency rectified supplies for precipitator energisation, owing, in part, to the lack of availability of suitable high frequency high voltage transformers and high speed switching power thyristors; consequently the conventional 50/60 Hz design has dominated the precipitation market. The circuit architecture of the conventional design, whilst being robust and simple has, however, a number of technical drawbacks.

In terms of performance, the modern electrostatic precipitator can be designed to operate and produce particulate collection efficiencies in excess of 99.8 per cent. To meet this level of performance, however, it is essential that all elements comprising the precipitator installation operate satisfactorily. As the unit is composed of a large number of mechanical and electrical items, the perform ance can suffer from various limitations, either because of component failure or changes in the inlet conditions presented to the precipitator. These limitations can be often identified by careful examination and interpretation of the output of installed monitoring equipment and the electrical operating conditions.