Why upgrade from hydraulic cylinders to pneumatic cylinders?
The ram cylinders in a vertical grinding mill / pulverizer ensure the correct grinding pressure is exerted on the material being ground. Older, hydraulic cylinders use a sophisticated hydro-pneumatic control system, which provides lubrication to the ram bearing, as well as providing a balanced pressure characteristic to the oil/gas interface.
The fact is, that a hydraulic ram, no matter how good the sealing, and/or wiping thereof, will always be wet. This means that any ingress of dust to the extended, exposed portion of the ram, can adhere to the ram, allowing the possibility of grit being transported back into the front oil seal, resulting in premature wear, and subsequent oil leakage.
This becomes an environmental as well as a fire hazard.
Records obtained from various clients, show that repair frequencies on the older hydraulic type cylinders can vary between 9 and 18 months.
Comparative results, show an average life expectancy of 4 years between repairs for bag cylinders.
Large coal grinding mills have been identified as one of the main systems responsible for lost steam generation capacity of large coal fired utility boilers1.
Upgrading older hydraulic cylinders to pneumatic cylinders reduces down time due to maintenance and therefore improves uptime and plant performance.
Another benefit of the bag cylinder installation, is the fact that the larger effective operating area, achieved by the configuration of the bag cylinder itself, allows for lower operating pressures in the system, thus reducing the stresses in the pipe work, panel and other components.
Note: We have had instances of cylinders working for 8 and even as many as 10 years without maintenance, although we admit that this is not the expected norm.
Upgrading is easy!
The operation of the pneumatic cylinders is, to all intents and purposes, similar to that of the older hydraulic cylinders. It is simply a case of removing the old cylinders, the old pipe work and control cabinet, and replacing the bag cylinders, new pipe work and new control cabinet.
All the Babcock & Wilcox mills in the UK have been converted from hydraulic cylinders to pneumatic cylinders.
1 EPRI study on large coal fired utility boilers (greater than 600MW) using grinding mills with capacities greater than 50 tons per hour.