The discussion on oil purifier selection often starts with the model: which one do I want, what does it cost, can there be a discount. Reversing that order is much easier. First work out how much oil this equipment has to treat in a year, divide that by the flow rate of one unit to get the minimum number of units, then decide between parallel and series operation, and only at the end compare the specific models within the same flow rate range. Once the first three steps are clear, the fourth is only detail.
First work out the volume to be treated
The flow rates of the main models in the range are: ZYD-100 at 6000 L/h, ZYD-200 at 12000 L/h, ZYD-300 at 18000 L/h; TYA-50 at 2000 L/h, TYA-100 at 4000 L/h; TYG-100 at 6000 L/h; and the plate and frame filter press LY-200 at 4800 L/h. Dividing the annual volume by the flow rate of one unit gives the minimum number of units, and if it does not divide evenly, round up. Whether the extra capacity that rounding adds is worth it is what the next step has to answer: it is worth it for a line that runs continuously without interruption, and not necessarily for intermittent operation.
Parallel buys margin, series buys a complete process
With several units in parallel each one treats a share of the oil, the total capacity is the sum of the individual flow rates, one unit can be taken out for maintenance while the others carry on, and the cost is that the floor space, the power supply and the daily operation all double. With the units run in series, the oil from the first stage goes straight into the second, the process is compact and the footprint is small, and the cost is that the load of every stage is stacked onto the same line, so a fault at one point stops the whole line, and the second stage has to be able to take the oil delivered by the first.
There is a quantity here that is easily overlooked: the flow rates have to decrease from stage to stage for the series arrangement to match. If the oil delivered by the first stage is greater than the capacity of the second, the surplus pushes back into the pipework and pulls the working vacuum of the first stage down with it. Parallel operation has no such constraint, since the units do not interfere with each other, and that is why parallel is used more often at high flow rates.
Once the number of units is fixed, the space and the power have to follow
Doubling the number of units is not just buying one more pump. The dimensions of the ZYD-100 are 1200 × 1400 × 1800 mm and the weight is approx. 720 kg; the ZYD-200 is 1800 × 1600 × 2100 mm, approx. 1050 kg; the ZYD-300 is 2200 × 1800 × 2200 mm, approx. 1400 kg. The floor space, the load capacity and the working space all have to be calculated on the basis of the heaviest machine, with room left over for pulling and changing the filter elements and for connecting the pipework. The power supply is worked out on three-phase 380V / 50Hz, and when models with a high total power are run in parallel, the circuit capacity has to be confirmed in advance together with the electrical engineer.
There is one more thing that easily gets left to the end, and that is leaving room for a standby unit. An implicit premise of a parallel scheme is that one unit may be stopped for maintenance; if the site has no spare position and no spare circuit, then once the number of units has been worked out they all have to run, and one unit down for maintenance stops the whole line, so the continuity that parallel was supposed to deliver is never realised and all that is left is the extra floor space and power capacity. In the conditions for parallel to hold, the standby position is often more critical than the number of units itself.
Conversely, if the site genuinely has room and the volume to be treated is not large, a single small-flow unit with an upstream machine in series may cost less: the flow rate of the TYA-50 is 2000 L/h and the TYA-100 is 4000 L/h, the smaller one is used first to bring the accuracy and the water content to a stable state, and large batches are then handed over to the larger one. The advantage of this combination is that the daily power consumption and the consumables follow the smaller unit instead of being configured for the largest one. Which route to take depends on whether the volume to be treated is stable or varies widely.
| Site condition | Common starting point | What must be confirmed at the same time |
|---|---|---|
| Large volume and no interruption permitted | Several units in parallel | Power capacity, floor space and load capacity |
| Oils treated in batches, tank to be emptied between batches | Few units in series | Matching of flow rates between stages, tank volume |
| Narrow site, oil tanks spread out | Several small-flow units distributed | Working space around each unit, nearby power supply |
| Steady oil volume, relaxed schedule | Single large-flow unit | Tank volume and circulation time |
Work through it in this order
- First work out the annual volume to be treated and divide by the flow rate of one unit to get the minimum number of units
- Once the number of units is fixed, check the floor space, the load capacity and the power capacity
- Whether to run in parallel or in series depends on the continuity requirement and the site layout, not on the price difference
- Only at the end compare the models and configurations within the same flow rate range
The number of units is calculated, it is not chosen; first the volume to be treated, then the number of units, and then the model, and only then does the purchasing negotiation have something to go on and the equipment any confidence of being used once it is on site.