Maintenance/cleaning cycles

An active flux maintenance procedure was initiated at this point (about 330 h TOS), beginning with a 2 s back-flush of clean permeate through the filter membrane. This active flux maintenance cycle was continued every 30 min for just over 24 h. The flux initially recovered to 0.90 lpm/m2 (32.0 GPD/ft2), but declined again within 24 h to a baseline value of 0.76 lpm/m2 (26.7 GPD/ft2) without clean permeate back-flush. The flux maintenance method was then returned to passive (no back-flush with clean permeate) mode, only increasing the flux off-time to 60 s every 30 min. Thereafter, the flux steadily declined over the next 120 h TOS from 0.77 to 0.58 lpm/m2 (27.3 to 20.4 GPD/ft2). At 480 h TOS, a 1 h flux off-cycle was attempted, resulting in an increase of the flux back to 0.82 lpm/m2 (29.1 GPD/ ft2), a 42.6% increase. When the flux off-cycle was returned to the 60 s off-cycle for the next 48 h, it was found that the permeate flux decreased to 0.62 lpm/m2 (21.9 GPD/ft2). Applying another 1 h flux off-cycle returned the flux to 0.721pm/... 

Anode maintenance used to take 3 days for 36 cells, but it is now possible to clean 40 cells in 2 days. This practice helped to minimize any significant extension of the overall maintenance cycle. The history of the changes in the anode maintenance procedure is listed below. 

In the campaign context of a batch plant, it is important to note that throughput and cycle time should include time required for cleaning, transportation and maintenance as these can dramatically affect the overall times and the utilization of any part of a plant. For example, a simple model developed from the AstraZeneca survey calculates the time for a... 

The dampproofmg admixtures will, therefore, improve the aesthetic qualities of concrete in terms of maintenance of a clean appearance over a prolonged period of time without adverse effects on other properties, and in the areas of freeze-thaw resistance, shrinkage under wet-dry cycling and reinforcement protection, may contribute beneficially. 

Where possible, components such as valves or joints should be permanently fixed in place, e.g. by fusion- or solvent-welding. When this is not possible - e.g. when removability is required for maintenance - the type of joint must be chosen to be hygienic, that is free draining and easily cleaned, and resistant to leaks. Temperature cycling stresses pipework and can cause leaks from plant previously shown to be leak-free. 

---