Abstract
South Africa’s Eskom is the African continent’s   largest electricity Utility, generating 98% of South Africa’s electricity needs and 60% of Africa’s needs.   It currently burns in excess of 100 million tons of coal annually and this is more than any other single Utility.   Electrostatic precipitators (ESP’s) remain the primary device used for gas cleaning to clean 75% of this coal.

Eskom has now more widely applied the research lessons in the practical use of loadcells as a means of enhancing  electrostatic  performance  by  continuous  real-time  mass  measurement  of  the  collecting  electrodes (CE’s).   A previous paper presented at ICESP VIII detailed this work at Eskom’s Lethabo power station and its effectiveness in optimising plant operation.   This paper will describe the continuation of this work at another Power Plant and focus on real-time, in-situ measurements.

The technology has been implemented on a single casing at Eskom’s 3 000 MW Kriel Power Plant as part of its upgrade and refurbishment program.   This paper will detail this work and present measured results from both before and after the refurbishment.   Other ESP operational CE patterns, will be also be presented with the aim to providing further insight into ESP operational behaviour.

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Abstract
An integrated approach must be taken to achieve the best possible precipitator performance, rather than addressing each aspect in isolation. This requires the collection of a significant amount of data before the implementation of an emission management strategy to coordinate all areas of influence.

To allow an integrated approach it is necessary to install a Precipitator Process Management Systems (PMS) also referred to as Air Emission Management Systems (AEMS).

Assuming that the precipitator itself is in sound mechanical condition with acceptable gas distribution and rapping, the integrated approach can only take place after the collection and detailed analysis of process and electrical data. Trending of process and energisation parameters is used as the base data for the management strategy.

An acceptable decrease in emissions has already been achieved at Eskom Matimba Power Station as a  result  of  improved  mechanical  integrity  and  better  electrical  energisation (see  the  previous presentation “Trials and tribulations of an ESP Systems Engineer - Back to basics at Matimba”).

This presentation describes the operation of a PMS subsequently installed at Matimba during 1999-2000 and the further improvement in emissions achieved as a result.

Abstract
The increasing concern for the environment and consequent stringent norms for air quality from thermal power plant emissions, have resulted in a greater demand on the performance of ESP. ESP being a down stream equipment is affected by various boiler parameters, requires close control and monitoring. This has resulted in the development and deployment of microprocessor based controllers for high voltage energisation and for rapping functions. For total control of ESP in a co-ordinated manner, often PC based or similar integrated control systems are used.

Such a PC based system is designed for single point operation of ESP of a boiler. It integrates control and monitoring function of all sub-controllers like ESP energisation controller & rapper controller.   As a co-ordinated controller, it is able to manage the total ESP operation like adjustment of rapper timings depending on field availability or boiler load.   It also optimises the energisation of all fields in an ESP and improves the rapping performance by bringing down the current in the rapped field.

In a power plant complex, there may be a number of boiler units, spread out over a larger area.   This often calls for viewing or controlling the ESPs of all boiler units from a single location for analysis. Towards achieving this, a centralized controller for multiple PC based control systems was developed.

The centralized controller is a PC based system developed on Windows platform. All the PC based integrated control systems of all boiler units in a plant are connected to centralized controller through RS-485 over MODBUS protocol. Any parameter from any ESP can be monitored and controlled from the centralized controller.

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Abstract
For over 40 years the most commonly used device to power electrostatic precipitators were standard 50/60 Hz SCR Controller and Transformer/Rectifier sets. However, in the last 4 years a new Power Supply has been introduced to the ESP industry. This Power supply is based on High Frequency Switchmode technology. The new Switchmode Power Supplies are capable of dramatically different performance than the older, 50/60-hertz linear transformer/rectifier sets.

Recent comparative tests of the two technologies were performed in the USA at Southern Company’s Savanna electric Plant Kraft 163 MW unit number 3. During a rebuild of the ESP on this unit, in the spring of 2002, standard 50/60 Hz transformer were installed on the east ESP casing and Switchmode Power Supplies were installed on the west casing. This modification also resulted in plate spacing change from 9” to 11.25” with ridged electrodes and a SCA of 322 ft²/1000 acfm. This paper will discuss the performance enhancements seen with the Switchmode Power Supply during testing conducted between the two sides using US EPA Method 17 particulate testing

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Abstract
Within the ESP industry, power supply synchronous pulsing is a well known method of dealing with Back Corona resulting from the precipitation of high resistivity particles. Often, especially in the case of moderate Back Corona, or on a stable process, a set-up once and forget method of adjusting the  controllers  is  satisfactory.  In  these  circumstances,  the  time  taken  and  skill  level  required  to establish the initial settings is not an important factor.

Under extreme conditions of Back Corona, or with an unstable process, this approach is not viable. Automated optimization algorithms were developed and run at regular intervals in order to establish and update the controller settings.

The paper describes the development of a dynamic algorithm which having established the optimum pulse repetition frequency, attempts to further optimize on-the-fly in order to compensate for short term changes in the operating conditions.

It is understood that this type of control algorithm is often required to be retro-fitted in older plants  where  these  types  of  problems  are  already  known  to  exist.  The  paper  takes  a  practical approach to this in considering how to deal with less than perfect voltage divider signals when utilizing existing T/R sets for example.

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