36,000 hours of operation for P84+PPS bags at Eskom

Eskom owns and operates more than 40 GW of installed capacity and is the largest utility in Africa. The Arnot Power Station consists of six nominally rated 350-MW coal-fired units originally installed between 1968 and 1975. The station burns a relatively poor South African bituminous coal composed of 25% ash with a heating value of 26 to 27 megajoules per kilogram (MJ/kg). The plant has posted 92.07% average availability over the past three years.

Arnot Power Station was upgraded from ESPs to baghouses in the 1990s as part of a project to increase plant capacity. Phase 1 added baghouses to Boilers 4, 5, and 6 (each containing 11,000 bags) with a maximum gas-to-cloth ratio of 3.5 cfm/ft 2. Phase 2 added baghouses (each with 14,000 bags) to the remaining three boilers with a maximum gas-to-cloth ration of 2.8 cfm/ft 2.

Once Eskom understood that blinding was the predominant bag failure mechanism across the various plants, it embarked on research aimed at retarding the blinding rate, hence extending bag life and performance. After a number of trials, and in collaborative effort with fiber and fabric suppliers (including the full-scale evaluation at Arnot), the solution chosen was to install composite bags with a P84 cap applied to a PPS substrate, which ensured the formation of a porous and stable dust cake that promoted complete acid neutralization and surface filtration. The service life of the latest sets of P84+PPS bags is more than 36,000 hours, with less than 10% failure of the 27,000 bags installed per unit.

The switch to P84+PPS bags has resulted in significant savings for Eskom, about $500,000 annually. That figure does not include reduced costs for labor, or production losses, which can be significant. In one instance, prior to the switch to P84+PPS bags, two boilers were shuttered for four months waiting for replacement bags.

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