Coal, O&M

Magnetic Filtration improves efficiency and reduces maintenance requirements

22 December 2004 – Most electric generating companies are responsible for the operation and maintenance of a diverse range of power stations. Utility engineers must review operating practices with a goal of improving efficiency and extending asset life. A 2040 MW coal-fired power station with coal crushing gearbox systems first commissioned in 1972, is a prime example of how such policies can be effectively implemented in practice.

Gearbox systems within utility operations are susceptible to ferrous (steel, iron, rust, etc.) particle contamination by the resulting “chain reaction of wear.” This means that as ferrous particles circulate within a system, they generate additional particles at an exponential rate. Arresting this wear process and efficiently removing harmful contaminants that cause increased maintenance costs, lost productivity and, more importantly, lost revenue is a primary goal.

To meet some of these demands, a joint project between ExxonMobil and the utility was initiated to improve the reliability of the coal mill gearboxes. This led to the search for a much less restrictive lube oil circuit to maintain oil pressure at elevated temperatures.

Having reviewed numerous options, the utility turned to the Magnom magnetic field effect conditioning system to address the problem. Magnom, developed, patented and supplied by UK-based Fluid Conditioning Systems (FCS), is a revolutionary product comprised of a series of annular magnets and innovatively designed formed steel plates. Through its patented design, the Magnom removes ferrous (and other) contaminant of less than one micron, including the smallest and most abrasive of particles that are responsible for the destructive chain reaction of wear, from a wide variety of fluids, thus lending the technology to the enhanced transmission protection that has been demonstrated at the station.

The Magnom’s design ensures a negligible pressure drop across the unit. As the fluid flows through the highly focussed magnetic field, contaminants are drawn out of the fluid flow and into special collection zones. These zones hold significantly more contaminant than a conventional filter without obstructing fluid flow or risking “wash-off” commonly associated with other magnetic separation devices.

The key features that attracted the project team to the Magnom were the low pressure drop, its efficient removal of ferrous (and other) particles to submicron levels, its large contaminant holding capacity and the ease with which it can be cleaned and reused.

Having identified this potential solution, the project team decided to install a single process unit as a replacement to the existing edge filtration system on the external oil circuit of one of the station’s coal mill gearboxes. This application was considered to be particularly stringent due to the high viscosity of the synthetic lube oil in use (ISO VG320 and VG460).

The team’s primary objective, maintaining oil pressure at elevated temperatures, was quickly realized with no discernible pressure drop being recorded across the unit, which has subsequently been maintained. More significantly, the resulting improvements in oil cleanliness have been a real bonus with a dramatic reduction in ferrous contaminant and additional reductions in aluminium, silicon, copper and soot levels.

As the oil analysis data furnished in the ExxonMobil Oil Analysis Service report shown here indicates, the ferrous levels, previously running at a dangerously high level of 350 to 450 parts per million (ppm) dropped to a consistent 40 to 50 ppm. The report also shows the positive influence of the unit on the other nonmagnetic contaminants of concern.

Following the dramatic success of the Magnom trial, the utility is now working to integrate the technology on all 32 coal mill gearboxes. The benefits of extended oil life and reduced consumption, coupled with exceptional dirt holding capacity, mean that routine maintenance can be reduced to a minimum, with the units requiring cleaning every three to four years only, well within the schedule for routine outages.