Two new Eskom Power Stations have a total of 12 boiler units of the same design by the same Original Equipment Manufacturer (OEM). All the commercially operating boiler units make use of a Pulse Jet Fabric Filter Plant (PJFF) for particulate emissions abatement. However, the high differential pressure issues, coupled with excessive erosion began to be experienced during the first year of operation and have not yet been corrected at these sites.

This has resulted in filter bag failures and consequently unit outages for bag replacements as well as high emissions. The installed PJFF bags were expected to remain operational for 36 000 hours before needing replacement. The effect is that the filter bags fail to reach the three to four years’ expected bag life and are currently averaging a bag life of about 12 months. Full generation load is frequently unattainable due to the PJFFs and the fabric filter bags are failing with unusual frequency. This poses insecurity in production and power supply resulting in financial loss and environmental risk.

Mechanical wear and abrasion of fabric is a kind of wear experienced by fabric filters during utilization. Abrasion is the eroding away of fabric fibers or fiber surface material through moving contact between the fiber and dust particles or adjacent fibers. There are mainly two forms of abrasion, the two body or three-body abrasion. Fiber-to-fiber rubbing or fiber-to-particle collision are two-body systems.

As a measure to investigate possible improvement of plant performance, fabric filter materials that are not traditionally used within the Eskom fabric filter fleet are being considered for trials. A project has been initiated to identify high wear resistant trial bag materials to provide interim operational relief by reducing bag failures. The objective is to establish whether alternative bag options may provide operational relief. This urgent research undertaking is required to fast track the process of obtaining a solution to the high erosion condition experienced in the PJFFs.

Eskom utilises high temperature fabric with the base fibre being Polyphenylene Sulphide (PPS) while other units utilise low temperature fabric with the base fibre being Polyacrylonitrile (PAN). The potential high wear resistant material that are being tested include Para-Aramid Needle Felt Fabric, Novates^® Fabric Treatment On Needle Felt Fabric, Resiltes^® Fabric Treatment On Needle Felt Fabric and Pyroguard^® Fabric Treatment On Needle Felt Fabric.

The intention of the test is not on filtration performance but rather proving abrasion resistance; the overall air-to-cloth ratio is expected to be influenced negatively. Each alternative trial bag type is to be tested in one compartment in the first two rows of the Cells to assess performance in the highest wear zones and to limit potential impact on the air-to-cloth ratio. Trial fabric filter bags are to be installed and experimental data collected over a period of a minimum of one year; sampled every three months or up to bag failure.

All trial bag types are to be installed in different Cells during the same period to ensure that the same operational environment is experienced by all bag types. To provide reliable trial results, the PJFF plant will need to be appropriately operated and maintained in accordance with the relevant procedures during the trial. It is anticipated that the benefit of possible longer filter bag life will outweigh the potential marginal increase in differential pressure introduced by the trial filter big materials being observed.

Although the test work is still in early stages, the first batch of results are expected by the end of July 2024 and the testing will be concluded at the end of 2025.