Not every work station can run continuously through the year. When the maintenance windows fall into a few particular months, when the production line is scheduled batch by batch, and when the arrival of the oil is not fixed, an oil purifier spends most of its time standing idle. If the selection is based on the annual throughput alone, the throughput looks sufficient while the actual running hours cannot support it at all. The way an intermittent duty station is configured is not the same as that of a continuous production station.
Calculate the throughput over the window rather than over the year
For a station that runs continuously, equipment selection looks at how much oil has to be processed per day and whether the processing speed can keep up with the takt. The calculation for an intermittent duty station is different: concentrate the oil that genuinely has to be processed during the year into a limited working window, then look at how long that window can run and whether the machine can keep running throughout it. This calculation leads to two different conclusions.
First, if the window is short and the oil volume is large, what is needed is processing speed, and the flow rate should be selected high. Second, if the window is stretched out and only part of the oil is processed each day, what is really consumed is the maintenance cost and the standby cost of the consumables during the idle period, and the flow rate does not have to be taken to the maximum. Selecting on a throughput averaged over the whole year often satisfies neither side.
| Station characteristic | Main constraint | Configuration approach |
|---|---|---|
| Short window, large oil volume | The processing speed cannot keep up | Give priority to the flow rate and, if necessary, select a higher flow model |
| Long window, small volume each day | Maintenance and energy consumption during the shutdown | Give priority to a simple structure, low standby power consumption and the ability to stand idle for long periods |
| Support across several workshops | The machine cannot be fixed in place | Select a mobile or trailer mounted model |
The optional equipment directly affects the cost performance of intermittent duty
Two options in the ZYD series configuration are directly related to intermittent operation: a variable frequency drive, which allows the flow rate to be selected as needed, and a flow meter with a totalising function. The variable frequency drive lets the flow rate follow the actual demand, so the machine does not have to run at its rated state throughout a light window. The totalising flow meter lets the throughput of each run be recorded, so that after several operations there is a record of how much oil has actually been processed. That record is the basis of energy management and also the basis for calculating the input of consumables and labour.
The control method deserves attention as well. The TYA series offers a choice of fully automatic and semi-automatic control. An intermittent duty station does not necessarily need unattended operation throughout, and in semi-automatic mode the points at which an operator has to intervene are clearly defined, which also means a faster judgement when something is abnormal, without waiting for an alarm to find the problem.
How the machine is left during the shutdown is part of the configuration
The machine stands idle for most of the time, and the way this period is handled has to be settled before the purchase. Keeping the heating on has the advantage that the oil temperature does not have to be raised from the start when the machine is restarted; the cost is continuous power consumption, and a longer residence of the oil at a higher temperature. Switching the power off completely has the advantage that nothing is consumed and the oil stands at ambient temperature; the cost is that the oil has to be heated again at the next start, and the pipework and the pump, after standing still for a long time, also have to be checked through as items that have been out of service for a long period.
- Decide on the basis of the actual idle hours during the year; where the idle time is short, keeping the temperature is the better economy.
- Decide on the basis of the oil; an oil that is sensitive to oxidation should not stay at a high temperature for long.
- Decide on the basis of the supply arrangement; where time of use supply is available, the heating period and the working period can be offset from each other.
- Write the check items for restarting after a long shutdown into the log in advance, rather than remembering them at the next start of work.
If the work station moves between several workshops, the form of the machine matters more than the parameters. The TYG-100 uses a trailer chassis, with a processing flow rate of 6000 L/h, and can be towed straight to the door of the switchgear room to work; the JL-50 is a hand pushed trolley mounted portable filtering and oil filling unit, with an accuracy of 10 to 25 microns and a weight of approx. 210 kg, which suits tasks with low accuracy requirements where pre-filtration and oil filling are the main purpose. The complete machine can also be built as mobile, fixed, trailer mounted, fully enclosed, canopy type or open type, and which one is chosen depends on whether the working environment needs somebody on site for long periods.
The selection for an intermittent duty station is an annual balance sheet: the processing capacity over the window plus the maintenance and energy consumption during the idle period. The two have to be looked at together.
