Batch and continuous drying solve different problems. Compare the batch vacuum rake dryer and the continuous plate dryer on feed form, area and changeover.
Feed consistency decides, not equipment size
Move from batch to continuous only when the feed stops changing. A continuous plate dryer assumes one material arriving at a steady rate for hours, while a batch vacuum rake dryer absorbs variation because every charge is a separate closed cycle. That difference, not throughput, decides which machine suits a plant.
Feed consistency has three parts: a moisture band the upstream process can hold, a physical form the feeder can meter, and a recipe that stays fixed long enough to justify a campaign. If any of the three drifts between shifts, the continuous unit produces a drifting product, because wetter or coarser material reaches the next plate before the previous plate has finished with it. Batch equipment turns the same drift into a longer cycle instead of a different product.
What the batch vacuum rake dryer is built for
The ZPG is a horizontal batch vacuum dryer with nine standard models, working volumes from 300 to 3600 L, heat-transfer areas from 3.2 to 16.5 m², a jacket design pressure of 0.3 MPa and a vessel rated -0.096 to 0.15 MPa.
Its scraper rake clears material off the heated wall and folds it back into the bed, which is how a paste or a filter cake keeps receiving heat instead of insulating itself with a dry crust. The same body carries the options that decide whether a batch line is workable: models above 5 m³ use a half-pipe jacket, the shaft can be sealed mechanically or by packing, and the vapour outlet takes configurable filter media to keep fines out of the vacuum system.
- Paste, paste-like and powdery feeds, including solvent-wet filter cake.
- Heat-sensitive, easily oxidised, explosive, strongly irritating or toxic materials, which the closed vessel keeps away from air and operators.
- Organic solvent recovery, where the vapour is condensed rather than vented.
- Batch sizes that change between campaigns, because the charge, not the machine, sets the output.
What the continuous plate dryer is built for
The PLG is a conduction-type continuous dryer offered in 32 standard configurations across four base sizes, with drying areas from 3.3 to 180 m², drive power from 1.1 to 15 kW and plates rated 0.4 MPa generally and 1.6 MPa maximum.
Wet material is fed onto the top plate and raked in an exponential spiral; large and small plates alternate so the material drops through the centre opening and continues downward in one direction, without back-mixing. Dried material leaves from the last plate and is discharged at the shell bottom by the rake blades. Because the flow is single-pass, the residence time is set by the feed rate rather than by a timer.
The series is available in atmospheric, closed and vacuum types. The closed and vacuum versions support solvent recovery and inert-gas closed-loop operation, so the same frame covers duties that a batch vessel would handle under vacuum.
The two ranges side by side
Read this as a boundary rather than a scorecard: every row states what the product data fixes for that series, and the row that changes an answer is usually the feed form, the vapour path or the temperature profile.
What the Ruibo product data states for each series
| What the data states | ZPG batch vacuum rake dryer | PLG continuous plate dryer |
|---|---|---|
| Operating mode | Horizontal batch, intermittent | Continuous, single pass from top plate to bottom discharge |
| Feed forms named in the data | Paste, paste-like and powdery materials | Chemical powders and granules, pesticide formulations, pharmaceutical intermediates, food and feed materials |
| Heat-transfer area | 3.2 to 16.5 m² across nine models | 3.3 to 180 m² across the standard configurations |
| Working volume | 300 to 3600 L | Not stated; the plate stack is sized by drying area |
| Drive power | 4 to 22 kW | 1.1 to 15 kW |
| Heating-surface rating | Jacket design pressure 0.3 MPa | Plate 0.4 MPa generally, 1.6 MPa maximum |
| Temperature along the path | One jacket set point per batch | Each plate can take hot or cold medium independently |
| Vapour path | Vacuum port to the vacuum system, condenser for solvent recovery | Top vent, or a vacuum port on vacuum-type models |
Source: Ruibo spec tables and product notes for the ZPG vacuum rake dryer and the PLG continuous plate dryer.
Area per litre is the number that moves with scale
A batch vessel gains volume faster than it gains heated wall, so the area available per litre falls as the model grows: 10.7 m² per m³ on the smallest ZPG and 4.6 on the largest. That ratio is arithmetic from the spec table, and it is the reason a large batch needs a longer cycle at the same jacket temperature.
Heat-transfer area per cubic metre of working volume, ZPG series
| Model | Working volume (L) | Heat-transfer area (m²) | Area per m³ (m²/m³) |
|---|---|---|---|
| ZPG-500 | 300 | 3.2 | 10.7 |
| ZPG-2000 | 1200 | 8.1 | 6.8 |
| ZPG-4000 | 2400 | 12.3 | 5.1 |
| ZPG-6000 | 3600 | 16.5 | 4.6 |
Derived by dividing the heat-transfer area column by the working volume column of the ZPG spec table. It is a geometric ratio, not an evaporation rate.
Continuous drying escapes that ratio by adding plates instead of volume. PLG drying area rises from 3.3 m² on a 1200/4 to 180 m² on a 3000/30 while drive power stays between 1.1 and 15 kW, and the area is bought in the vertical direction: the 3000/30 stands 10,650 mm tall. A plant that needs more than the 16.5 m² of the largest batch model has to change the mode of operation, not just the model number.
Zoned temperature is what a batch jacket cannot do
On a continuous plate stack each plate receives its own heating medium, so the first plates can run on hot water below 100 °C and the last on steam at 100 to 150 °C. A batch jacket holds one set point for the whole charge.
Zoning matters whenever wet material skins, foams or discolours on contact with a hot surface. The first plate can be kept cool enough that the surface does not case-harden, and later plates can run hotter because the material is already partly dry. Thermal oil from 150 to 320 °C is available for the final plates when the product tolerates it: the data states hot water below 100 °C, steam from 100 to 150 °C and oil from 150 to 320 °C as the three media bands for plate heating.
The trade is control complexity. A zoned stack needs a medium circuit per zone and a temperature profile that has been tested on the material; a batch jacket needs one set point and one validation.
Putting the decision into one table
Find the observation that matches the plant, then read what the choice rules out before it reaches a specification.
From observation to series to what it rules out
| What you observe | What it points to | What it rules out |
|---|---|---|
| One product, steady feed, campaigns of several days | Continuous plate dryer with zoned plates | Batch equipment and its changeover time between campaigns |
| Several products or recipes sharing one line | Batch vacuum rake dryer | A continuous unit that would have to be emptied and re-stabilised between products |
| Feed arrives as filter cake or paste that will not meter | Batch vacuum rake dryer with scraper rake | Any continuous unit that needs a free-flowing, meterable feed |
| The material tolerates only a surface below 100 °C | Hot-water plates, or a batch vessel with a low jacket set point | Atmospheric steam, which cannot run below 100 °C |
| Required area exceeds the 16.5 m² of the largest batch model | Continuous plate stack, sized by drying area | A larger batch vessel, which loses area per litre as it grows |
Source: selection rules used in Ruibo dryer engineering, with figures taken from the ZPG and PLG spec tables.
Questions engineers ask before the switch
These come up whenever a batch line is being considered for continuous operation. Each answer stays inside what the product data states.
- Can a continuous plate dryer handle a paste?
- The data names chemical powders and granules, pesticide formulations, pharmaceutical intermediates and food or feed materials as PLG duties, and feed is metered onto the top plate. A paste that will not meter belongs on the ZPG, whose scraper rake is designed around paste, paste-like and powdery feeds.
- Does a larger batch model dry faster?
- Not per litre. Area per m³ falls from 10.7 on the ZPG-500 to 4.6 on the ZPG-6000, so a bigger charge has less heating surface per unit of material and the cycle lengthens unless the jacket temperature or the vacuum changes.
- Can the plate dryer run under vacuum?
- Yes. The PLG is offered in atmospheric, closed and vacuum types, and the closed and vacuum configurations support solvent recovery and inert-gas closed-loop operation.
- What decides how many plates a continuous dryer needs?
- Drying area, which runs from 3.3 m² on a 1200/4 to 180 m² on a 3000/30 in the standard configurations. Base size and plate count both follow the area, so area is the figure to put in an enquiry.
- Is continuous drying better for heat-sensitive material?
- Only if the temperature profile is actually used. Zoning lets the first plates run cooler than the last, which follows a drying curve; a batch jacket applies one set point to the whole charge, which is simpler to validate but cannot follow that curve.
Where this leaves the selection
Choose batch when the feed or the product changes, and continuous when it does not. The dryer follows that decision; it does not make it.