Solutions to Rehabilitation of Electrostatic Precipitator (ESP) in Biomass Industry

Most of the biomass power plants in the southern part of Thailand employ palm kernel shell and empty fruit bunch (EFB) as fuel for their power boiler due to its abundancy in this tropical country and very low cost. Nevertheless, one major drawback of such kind of biomass fuel is high moisture content. High moisture content together with high frequency of rain make it difficult for biomass power plants to provide dry fuel for their power boiler. This issue causes lower heating value in the power boiler and flue gas with higher moisture entering the Electrostatic Precipitator (ESP).

Case Study: A biomass power plant located in Suratthani, Thailand

This biomass power plant in the southern part of Thailand experienced a major issue of high moisture flue gas that accelerates corrosion on ESP internal mechanical parts. Deterioration of ESP internal parts leads to decrease in dust collection efficiency and underperformance of the ESP, and thus resulting in high emission.There are 3 fields in this onechambered Indian-made ESP, but only one field was able to operate since the remaining two fields were malfunctioned because of internal mechanical problem.

The only one field operating obviously could not handle all the dust load in the flue gas from the power boiler and so the plant faced a very high emission and opacity that could easily be observed from the black smoke coming out of the stack.

Black smoke coming out of the stack indicating high emission and opacity

Natural drying process of biomass fuel

We, Tai & Chyun Associates Industries, Inc., recommended solutions to the problem by first performing a thorough inspection to determine root causes and assess current condition of the ESP. More than 10% of the total no. of Collecting Electrode (CE) and ESP casing were found severely corroded. Missing access door caused air in-leakage and contributed further to the high moisture from external surroundings aside from the flue gas entering the ESP from the power boiler.

Based on the findings, ESP internal mechanical part replacement must be carried out in order to improve its dust collection performance, which included Collecting Electrode (CE), Discharge Electrode (DE), and Rapping System for both CE and DE. Maintenance on corroded ESP casing and replacement to double-layered access door were also implemented.

ESP inspection and maintenance

Missing access door

Severely corroded CE

Severely damaged Gas Distribution (GD) screen

Corroded ESP casing

Despite the main challenge of frequent rain and strong wind, with good management, the abovementioned project work scope had been successfully completed within an extremely tight timeframe of only 10 days according to the plant’s shutdown schedule. Manpower was arranged into 2 shifts that worked 24 hours non-stop. Even with very limited timeframe, details must still be paid attention to such as making sure ESP casing was properly patched and repaired before installing new parts and lifting and installation processes of CE were done strictly in accordance with safety procedures.

During testing and commissioning, CE and DE rapping systems were tested to ensure the correctness of rotating direction and smooth operation as well as performing no-load test to confirm the normal operation of ESP system.

Lifting process of CE

Installing new CE

Newly installed CE and DE

Installing new spiral (spring) DE

After major mechanical part replacement and maintenance, ESP has resumed its performance achieving maximum secondary voltage and current of 33 kV and 149 mA during plant operation. These running values have improved from previous values of only one field operating at 19 kV and 100 mA. The plant (client) was quite satisfied with the results, in addition to no more visible black smoke coming out of the stack and stable operation at full load capacity that maximizes the plant’s benefits.

* The value implies short circuit condition and not able to operate.

About the authors

Thompson Tsai and Johnny Svenstrup, Vice President and Field Engineer of Tai & Chyun Associates Industries, Inc., a provider of optimized solutions of parts and services for Electrostatic Precipitator (ESP) to ensure emission compliance with standard regulations.