African Fusion July 2022

Babcock to upgrade ESPs

Babcock to upgrade boiler units to meet emission regulations

Babcock has come full circle at a major power station where it will be upgrading electrostatic precipita tors (ESPs) on six boiler units that the company designed and built in the 1980s.

U sing technology not available at the time they were first built in the 1980s, Babcock will be bring ing some of South Africa’s boiler units into the 2020s, enabling the power station to comply with latest emission regulations of below 50 mg of particulate per normal cubic metre (Nm 3 ) of flue gas and essentially halv ing the impurities. This power station has provided reliable power to the utility formore than four de cades, ranking as the best-perform ing and lowest-cost generating station in the utility’s fleet. The boiler was designed to burn coal with a low calo rific value and an ash content of above 40%. Producing fly-ash with a low carbon content proved beneficial to the cement industry, which relies on these properties to improve water resistance in cement. Tomeet the latest emission regulations, a three-part programme is required to enhance the total precipitator capability in order to achieve levels of below 50 mg: • Upgrade and refurbish the SO 3 condi tioning plant. • Change the technology on the ESPs’ transformers to convert them into high frequency sets. • Upgrade and refurbish the ESPs to maximise dust collection efficiency to comply with new legislation. Babcock has been awarded the third portion of the programme and will refur bish four precipitator cases in each boiler, beginning in 2023. Dave Brook, Technical Director at Bab cock, explains that ESPs use an electric charge to remove impurities from air or gases through a series of collector and discharge electrodes. “Fly ash is a very fine dust found in hot flue gases from coal combustion. It travels through the heat transfer surfaces of the boiler and the air heater, and even tually emerges through the ducting and

A 3D model of the modern Babcock & Wilcox-owned electrostatic precipitator (ESP) technology that will be used on six boiler units designed and built by the Babcock in the 1980s.

wire-type discharge electrodes with modern and more reliable rigid discharge electrodes. After time, the 12-metre long weighted discharge electrode wires have started to perish, diminishing the electric or corona field, causing the collector elec trodes to lose efficiency and collect less dust. The new rigid discharge electrodes, which will be manufactured in South Af rica, cannot break and will create a more stable corona field, thereby maximising efficiency of the ESPs. Babcock is the lead contractor responsi ble for all projectmanagement, integration, delivery and construction for the project, and will be working in partnership with USA-based Babcock & Wilcox (B&W). B&W owns the technology of the original design of the precipitators andwill be undertaking the process and detailed engineering. As one of the most established and experienced steam generator and indus trial plant suppliers in Africa, Babcock has delivered solutions to many of the power stations in this country. The company is present at several sites undertaking proj ects that include high-pressure piping, coal burner overhauls and mill maintenance. www.babcock.co.za

through electrostatic precipitators. After it is removed and deposited in the hoppers below, the fly ash is either removed or sold to the cement industry,” Brook says. “The fine dust in the gas travels a tortur ous route in the boiler, resulting in areas where there is more dust, and others with less dust. In order for the ESPs to function optimally, the gas distribution should be as homogenous as possible,” adds Brook. He explains that an ESP is a box with a series of electrodes or plates strung verti cally inside of it. The dust particles are charged creating a flow to the collector electrodes upon which the dust is depos ited and collected. When these plates get full, they are rapped (struck), and all the dust slides down into the hopper. Babcock will use computational fluid dynamics modelling, which was not avail able in the 1980s, to model the gases from the outlet of the boiler into the precipitator cases, to better understand and manage what is happening with the gases under different load conditions and improve dust distribution, thereby improvingdust collec tion and removal. Also included in Babcock’s scope of work is the replacement of the current

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July 2022

AFRICAN FUSION