At many sites, procurement asks one question: whether to buy the mobile type or the fixed type, or whether to have one of each. There is no standard answer to this, because it depends on four specific conditions: the number of stations, the maintenance window, the type of oil and the site conditions. The criteria are set out below along those four dimensions, so that the person doing the selection can compare them against their own situation.
Start with the number of stations and the maintenance pattern
Where the stations are concentrated in an oil treatment room and the oil can be supplied centrally, fixed equipment is easier to make full use of: the pipework can be fixed, the oil inlet and outlet can be connected to the storage tank, and the unit does not have to be moved around during operation. Where the stations are spread out and the bays or plant rooms are far apart, the mobile type is more suitable; the TYG-100 is a mobile vacuum oil purifier with a flow rate of 6000 L/h and can be used in turn at several stations. The flow rate of the TYA-50 is 2000 L/h and of the TYA-100 is 4000 L/h; these are models for a fixed arrangement and cover different throughputs in flow rate steps.
If the maintenance is arranged centrally, for instance several bays handled in one outage window, both the number of machines and the number of moves are reduced; if the maintenance is arranged one job at a time, the scheduling of the mobile equipment between two jobs becomes the main cost. This point is often overlooked, but it affects the total expenditure more than the unit price of the machine.
Select the stage by the type of oil and the accuracy required
Different models solve different problems, and selecting the stage by the conditions is clearer than selecting by model. Vacuum degassing deals with gas and water, which corresponds to the ZYD series: working vacuum -0.08 ~ -0.0999 MPa, filtration accuracy ≤1 μm, cleanliness NAS 1638 class 5. The plate and frame filter press covers the high-flow, high-contamination case: the flow rate of the LY-200 is 4800 L/h, with 40 sets of 300×300 filter frames and an 11 kW motor. The centrifugal type corresponds to the separation problem; the LX-100 and the LX-200 are centrifugal oil purifiers. The lightweight oil filter trolley belongs to the end stage and the pre-treatment stage; the filtration accuracy of the JL series is 10–25 μm.
So the question of fixed or mobile in practice becomes which section of the equipment is put in a fixed position and which travels with the crew. The pre-treatment and coarse filtration stage generally depends more on the layout of the site, while the final fine treatment stage depends more on the stable conditions of a fixed position; but for each individual site it still comes down to the oil and the accuracy required.
| Site condition | The combination that fits more closely | The main basis |
|---|---|---|
| Stations concentrated, continuous oil supply | Fixed equipment as the main part | With the pipework fixed, the throughput and the degassing performance are easier to keep stable |
| Stations dispersed, maintenance windows not fixed | Mobile equipment as the main part | The TYG-100 has a flow rate of 6000 L/h and can be scheduled between stations |
| High contamination, high throughput required | Plate and frame pressing followed by fine treatment | The LY-200 has a flow rate of 4800 L/h and 40 sets of 300×300 filter frames |
| Only the particles need to be brought down to the ten-plus micron range | Lightweight oil filter trolley | The filtration accuracy of the JL series is 10–25 μm |
| The oil needs decolouring | A decolouring and purification unit as a separate item | The TL-50 and the TL-100 belong to this class |
Two machines or one
There are usually two reasons for taking two machines: one is to cover different states of the oil, the other is to avoid the scheduling risk of the maintenance window. But two machines also mean two sets of fixed costs, including floor space, the power supply and maintenance. When making the judgement, compare taking two machines with one large machine plus one small one: the flow rate of the ZYD-100 is 6000 L/h, of the ZYD-200 is 12000 L/h and of the ZYD-300 is 18000 L/h; if one large machine can cover the peak load, then the case for the second machine has to rest on factors other than the peak, and not on the flow rate figures.
There is one practical condition that is often left out: what the standby machine is worth. A machine held as standby and two machines each carrying half the workload do not have the same operating cost. The standby machine does not work in normal running, but it has to be maintained, energised and test-run at intervals, and that cost has to go into the overall account.
- Rank first by the number of stations and the maintenance pattern, and only then decide which equipment is fixed and which is mobile.
- On a site where the oil types differ widely, break the treatment process into stages first, and then match each stage to a model.
- Write down clearly whether the reason for two machines is to cover the peak load, to cover the oil types or to secure the maintenance window.
- Energise and test-run the standby equipment at intervals according to its actual condition; a standby that is not energised is not necessarily usable when it is needed.
- For mobile equipment consider the route it has to travel and the ground conditions on site, since that decides whether it can actually reach every station.
The order of selection is: first the working conditions, then the stage, and only then fixed or mobile. Done the other way round, the usual result is a machine that turns out not to be needed.
