Paddle Dryer for Chemical Wet Cake and Sludge Drying

Karan Dargode — Mon, 26 Dec 2022 06:43:48 +0000

Chemical plants end up with wet solids in many forms: filter cake from a reactor, salt from a crystalliser, sludge from the effluent plant. Each has a different problem. One is corrosive, another is sticky, a third gives off solvent. A paddle dryer can handle many of these, but only when it is built for the specific material.

Why chemical drying is different from sludge drying

Effluent sludge is mostly a disposal problem. Chemical wet cake is often a product, so purity, final moisture and what leaves the machine all matter. You also have to deal with what comes out as vapour, which may be water, solvent or both.

The questions that decide the design are:

Is the material corrosive, toxic or reactive?
How sensitive is it to heat, and at what temperature does it change?
Does the vapour contain solvent that must be recovered or scrubbed?
Must the product stay free of contamination from the machine?
How sticky is the cake in the middle of drying?

How a paddle dryer suits chemical duty

Indirect heating. The heating medium never touches the product. Steam, thermic fluid and hot water are all options, and AS Engineers states a thermic fluid range up to 400°C and steam up to 14.06 kg/cm².
Enclosed operation. The machine is closed and can be purged, which helps with solvents and with dust.
Pressure options. It can run at atmospheric pressure, under vacuum or pressurised. Vacuum lowers the drying temperature for heat-sensitive material.
Solvent recovery. Vapour can go to a condenser and solvent tank, with a scrubber for what remains.
Materials of construction. Carbon steel, SS304, SS316, duplex steel and other alloys, with surface finish options including buffing, hard facing and electropolishing.
Self-cleaning paddles. Intermeshing paddles keep heated surfaces clear and run without metal-to-metal contact.

Materials in AS Engineers’ application list

AS Engineers lists these chemical and petrochemical materials among its paddle dryer applications: aluminium hydroxide, sodium chloride, ammonium nitrate, PTBBA powder, sodium cyanide and ammonium or sodium sulphate. In mining and metals it lists gypsum, manganese dioxide, copper concentrate, coal and lithium hydroxide.

Some of these need extra care. Materials that are toxic or thermally unstable require an enclosed design, controlled temperatures and a safe vapour route, and the right design only comes from a review of the actual material and a trial.

What to prepare before asking for a quote

Material name, hazards and safety data sheet
Current moisture and required final moisture
Throughput in kg per hour
Maximum safe product temperature
Whether the vapour contains solvent and how much
Any limit on contamination or metal pickup

Beyond drying

The same machine can also heat, calcine, strip solvents, crystallise, react or cool, as AS Engineers notes in its paddle dryer FAQ. If your process needs a heating or reaction step on a wet solid, ask whether one machine can do both.

Test your material first

Chemical materials rarely behave like the textbook example. AS Engineers runs pilot trials on a 25 kg/hr paddle dryer, at its works or at your site, for a nominal fee that is waived on order. Request a pilot trial.

More from AS Engineers

See the full range on paddle dryers for the chemical industry at theasengineers.com.

For wider sludge background, read the chemical sludge treatment and reuse guide on sludgedryer.in, AS Engineers’ sludge drying resource.

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Paddle Dryer for the Chemical Industry | AS Engineers