Drying Equipment

RVPD – Rotary Vacuum Paddle Dryer

Mechotech engineers and manufactures the RVPD Rotary Vacuum Paddle Dryer as turnkey process equipment for pharmaceutical, nutraceutical, food, and botanical processing lines that need to dry pastes, wet cakes and sludges that would cake or bake onto a static heated surface. A horizontal, jacketed shell houses a shaft fitted with intermeshing paddles that continuously lift, fold and shear the product against the heated wall, breaking up lumps as they form so drying stays uniform from a wet, sticky feed through to a free-flowing dry powder.

The RVPD Rotary Vacuum Paddle Dryer is built in SS 316L (or a process-appropriate grade) as a horizontal cylindrical vessel with a fully jacketed shell and, on many designs, hollow jacketed paddles on the internal shaft so heat is delivered from both the vessel wall and the agitator itself. The paddles rotate at low speed, continuously lifting and turning the wet mass, breaking up the lumps and agglomerates that form as a sticky paste dries, and constantly presenting fresh product surface to the heated metal. With the shell under vacuum, moisture or solvent evaporates at a reduced temperature and is drawn off to a condenser, allowing pastes, filter cakes, sludges and slurries to be dried in a single vessel from wet feed through to a dry, free-flowing powder without a separate size-reduction step. Electropolished product-contact surfaces, a fully enclosed shell, and PLC-based control of paddle speed, jacket temperature and vacuum support batch or semi-continuous operation, and capacity is configured to the customer's requirement from pilot-scale vessels to larger commercial dryers.

Process Flow

Technical Specifications

Equipment Type	Rotary Vacuum Paddle Dryer (RVPD) — horizontal paddle-agitated vacuum dryer
Vessel Shape	Horizontal cylindrical shell, fully jacketed
Construction	SS 316L (or process-appropriate alloy), electropolished product-contact surfaces
Agitator	Intermeshing paddle shaft, low-speed rotation; hollow jacketed paddles (design-dependent)
Heating	Jacketed shell and paddles, heated by hot water / steam / thermic fluid
Vacuum System	Vacuum pump with rotary joint (paddle-heated designs) and external condenser
Feed Type	Wet cake, paste, slurry or sludge
Operating Mode	Batch or semi-continuous (configurable)
Lump Handling	Continuous mechanical lump-breaking via intermeshing paddle action
Discharge	Bottom discharge valve, manual or pneumatically actuated
Automation	PLC-based control of paddle speed, jacket temperature and vacuum level
Cleaning	CIP-capable, fully enclosed shell
Capacity	Configured to requirement — pilot-scale vessels to larger commercial dryers
Utilities	Hot water / steam / thermic fluid for shell and paddle heating, vacuum system utilities, electric power
Compliance	GMP / WHO-GMP / Schedule M hygienic design

Plant Capacities

Vessel Scale	Typical Use	Paddle Heating	Operating Mode
Pilot-scale	Process trials, paste-drying validation	Jacket-heated shell (paddles optional)	Batch
Production-scale	Commercial paste/cake drying	Jacket-heated shell and paddles	Batch or semi-continuous
Large production-scale	High-throughput sludge/cake drying	Jacket-heated shell and paddles	Semi-continuous

Shell length, paddle configuration and heat-transfer area are sized to the feed's stickiness, solids content and target drying time; exact capacity is configured to your process.

Manufacturing Process

Charging

The wet cake, paste, slurry or sludge is charged into the horizontal vessel through a top port, typically fed directly from an upstream filter, centrifuge or reactor.

Vessel Sealing & Vacuum Draw

The shell is sealed and evacuated to the target vacuum level, lowering the boiling point of moisture or solvent to allow drying at a controlled, reduced temperature.

Paddle Agitation

The internal shaft, fitted with intermeshing paddles, rotates at low speed, continuously lifting, folding and shearing the product against the heated shell wall and paddle surfaces.

Jacket Heating

Hot water, steam or thermic fluid circulates through the shell jacket and, on hollow-paddle designs, through the paddles themselves, conducting heat directly into the agitated product mass.

Lump Breaking & Uniform Drying

As the product dries and passes through its sticky, paste-like phase, the paddles continuously break up lumps and agglomerates, preventing caking or bake-on and keeping the drying bed uniform.

Vapour Removal & Condensation

Evaporated moisture or solvent vapour is drawn from the vessel headspace to an external condenser under vacuum, recovering solvent where applicable and sustaining the vacuum level.

Endpoint Sampling

The product can be sampled during the cycle, or endpoint inferred from torque/power draw and vapour generation trends, to confirm the target residual moisture before the cycle ends.

Discharge & Cleaning

The dried, free-flowing powder is discharged through a bottom valve, and the fully enclosed vessel is cleaned in place between batches for fast, validated product changeover.

Major Plant Equipment

Horizontal jacketed drying vessel (SS 316L, electropolished)
Intermeshing paddle agitator shaft
Hollow jacketed paddles (design-dependent)
Paddle drive motor, gearbox and mechanical seal
Rotary joint for paddle-heating circuit
Jacket heating system (hot water / steam / thermic fluid)
Vacuum pump and vacuum receiver
Solvent/vapour recovery condenser
Top charge port
Bottom discharge valve
Instrumentation (vacuum, jacket temperature, paddle torque/speed)
PLC-based control panel

Plant Output

Dried free-flowing powderDried granular solidRecovered process solvent (via condenser)

Applications

Drying of pharmaceutical and API wet cakes and pastes
Drying of pigment, dye and chemical filter cakes
Nutraceutical and botanical extract paste drying
Effluent sludge and process-residue drying
Drying of gums, resins and sticky intermediates
Food-grade paste and concentrate drying
Catalyst and specialty-chemical cake drying
Solvent-wet solids requiring in-process solvent recovery

Key Features

Handles Sticky Pastes Without Caking
Intermeshing paddles continuously break up lumps and agglomerates as the product dries, preventing the bake-on and caking that would foul a static heated surface.
Dual Heat Transfer via Shell and Paddles
On hollow-paddle designs, heat is delivered from both the jacketed shell wall and the rotating paddles themselves, increasing heat-transfer area and shortening drying time.
Single-Vessel Wet-to-Dry Conversion
Wet cake or paste is converted to a dry, free-flowing powder in one vessel, without a separate size-reduction or granulation step to break up dried lumps.
Vacuum Operation with Solvent Recovery
Drying under vacuum lowers process temperature for heat-sensitive products and allows evaporated solvent to be condensed and recovered rather than vented.
Batch or Semi-Continuous Operation
The vessel can be run as a discrete batch dryer or configured for semi-continuous feed-and-discharge operation to match upstream and downstream throughput.
GMP-Compliant, CIP-Capable Construction
Electropolished SS 316L surfaces and a fully enclosed, CIP-capable shell meet WHO-GMP and Schedule M hygienic-design expectations for regulated manufacturing.

Frequently Asked Questions

What is a Rotary Vacuum Paddle Dryer (RVPD) used for?

An RVPD dries wet cakes, pastes, slurries and sludges under vacuum using an internal rotating paddle shaft that continuously lifts and turns the product against a heated shell wall. It is chosen specifically for feeds that would cake, bake-on or form hard lumps if dried on a static heated surface.

How do the paddles prevent the product from caking?

As the wet paste dries it naturally wants to stick and agglomerate. The intermeshing paddles continuously lift, fold and shear the mass, breaking up lumps as they form so the product passes through its sticky phase and emerges as a free-flowing dry powder rather than a hardened cake.

Are the paddles themselves heated?

On many RVPD designs, yes — the paddles are hollow and heated by the same circuit as the jacketed shell, so heat is delivered from both the vessel wall and the rotating paddle surfaces, which increases the effective heat-transfer area and speeds drying compared with a shell-only heated design.

Can the RVPD recover solvent from the drying process?

Yes. The vessel operates under vacuum with the vapour outlet connected to an external condenser, so solvent or moisture evaporated from the product is captured and recovered rather than released, which is valuable for solvent-wet pharmaceutical or chemical cakes.

Is the RVPD a batch or continuous dryer?

The RVPD is typically run as a batch dryer but can be configured for semi-continuous operation with staged feed and discharge, depending on how it needs to integrate with upstream filtration and downstream packaging or milling.

What capacity range is available?

Shell length, paddle configuration and heat-transfer area are configured to your feed's stickiness, solids content and target drying time, from pilot-scale vessels used to validate drying behaviour up to larger production-scale dryers for commercial manufacturing.

How does an RVPD differ from an ANFD or RCVD?

An ANFD filters the slurry and dries the resulting cake in the same vessel, while the RVPD dries a feed that has typically already been separated upstream. Compared with the RCVD, which rotates the whole vessel for a gentler tumbling action, the RVPD's fixed shell and internal paddle shaft give more aggressive mixing better suited to sticky pastes that would otherwise cake against the wall.

How does an RVPD differ from a Vacuum Paddle Dryer?

Both use a paddle-agitated, jacketed shell under vacuum, but the RVPD steps up the duty: its twin intermeshing paddle shafts are typically hollow and independently heated alongside the shell, giving more heat-transfer area and more aggressive mixing for heavier, stickier pastes and higher throughput. The Vacuum Paddle Dryer uses a single rotating paddle shaft for gentler, lower-shear agitation, and suits lighter-duty or smaller-batch drying where the extra heat-transfer area and mixing intensity of the RVPD aren't required.

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RVPD – Rotary Vacuum Paddle Dryer