PRECIP 
NEWSLETTER 

December 2009
No. 407

Often the performance of existing ESPs can be improved by utilizing appropriate upgrading technologies. At ICESP XI, Tuomas Timonen, Alstom Power Service, Environmental Product Group, Vaxjo, Sweden, with others, stated that for existing ESP upgrade applications, some technologies may be better suited than others. This can be for reasons of layout and cost, process integration, age and design of the plant and the emission levels required. The most appropriate solution can be selected after detailed inspection and assessment of the present electrical, mechanical and gas distribution status as well as process conditions.

There is no doubt that there is a large ESP retrofit/rehabilitation market for a variety of reasons. First, the number of power plants approaching 40 years of age (a nominal life time) in the next decade will be large. Second, the imposition of tougher emission requirements will force change. It is estimated, based on experience, that roughly 20 percent of plants in the 40-year-age bracket will be rehabilitated and this represents approximately 20 GW/year. In the last two years, the trend toward plant upgrades has increased significantly. Alstom has globally executed more than one hundred ESP upgrades in coal, oil and bio-fired power plants as well as iron and steel, cement, pulp and paper industry and waste-to-energy plants.

The basis of operation and maintenance is an awareness of the operating situation of the air pollution control equipment. Regular mechanical and electrical inspections are recommended to determine the actual condition of the equipment, in order to maintain optimum efficiency. Analysis is necessary to determine the best type and the best time to repair or replace parts to minimize service interruption. A process of continual inspections in numerous locations allows performance comparisons, detection of trends and possibly advance notice of a failure.

For an ESP with good flow, mechanical and electrical conditions, there are several ways to improve particulate collection efficiency. There are a series of upgrade techniques ranging from transformer/rectifier (T/R) control, high voltage power supply Switched Integrated Rectifiers (SIR), flue gas conditioning, more efficient ESP design and field extensions. The most suitable technique is chosen based on the actual conditions, outage opportunity and economical aspects. The cost for different upgrading techniques differs significantly.

Alstom has developed a new generation of high voltage power supplies, called SIRs. The upgrade of conventional T/Rs to SIRs will usually result in a significant ESP performance improvement. This is due to a higher power input possible at operations that were limited by voltage or sparks. For example, a South African coal-fired boiler (2 x 315 MW electrical) ESP 4 T/R was upgraded with four SIR sets. The main challenges were high space charge combined with high resistivity flyash. Before the upgrade, dust emission levels were around 35 mg/Nm³. After the upgrade and extensive tuning the dust emission level dropped to 25 mg/Nm³.

Increasingly, operators are interested in advanced control system and optimization software solutions. Optimization software as part of an overall air pollution control plan has been shown to not only improve environmental compliance, but to also provide a number of financial benefits for users, such as a decrease in overall operating costs, an increase in equipment life time and even the ability to manage valuable air pollution trading credits. Based on process experience in particulate control, Alstom developed the Electrostatic Precipitator Optimizing of Charges (EPOQ) control algorithm. The control algorithm is a self-adapting expert software, with the main aim of minimizing emissions.

Another upgrade possibility is a control and monitoring system that offers opportunity for continuous process supervision. Regular monitoring and fine-tuning of the air pollution control equipment can guarantee the lowest possible emissions and energy consumption. Analysis of operating data allows maintenance measures to be implemented in a planned and optimal manner and also produces a rapid advance warning if the operating conditions should deviate from the norm.

To further innovate in the service area, Alstom offers a new, long-term service option that may solve many operating problems. This long-term agreement is backed by a complete performance guarantee for operating economy and emission levels. The agreement is based on a longer period of time (for example, 10 years) to give the customer complete control over the cost of their air pollution control equipment, without any surprises caused by extended downtime or faults in the design.

Today’s power generators and industrial producers need to operate their plants more cost-effectively while complying with more stringent environmental regulations. Challenges such as emissions compliance have caused operators to look for ways to help existing plants do what once seemed impossible — to simultaneously produce more power and products, increase profitability and yet become more environmentally friendly.

Back to PRECIP Newsletter No. 407 Table of Contents