Centrifugal Blowers and Paddle Dryers for the Chemical Industry
Chemical plants ask more of their air-handling and drying equipment than almost any other industry. The media being moved or dried can be corrosive, abrasive, flammable, or laden with volatile organic compounds. A standard blower or dryer — designed for clean air or benign dust — fails quickly in these conditions. The casing corrodes, shaft seals leak, and impeller surfaces erode, often within the first year of operation.
AS Engineers has been designing and fabricating blowers and dryers specifically for chemical processing environments since 1997. Our equipment is selected on the basis of the actual media: the chemical composition, temperature, moisture content, and pressure requirement your process demands. ISO 9001:2015 certified across the full manufacturing cycle.
Centrifugal Blowers for Chemical Plants
Centrifugal blowers in chemical plant service fall into two categories depending on what they handle: gas-phase applications where the blower moves corrosive or reactive vapour, and solid-phase applications where it conveys dust-laden or abrasive air streams. Both categories require a different impeller geometry, a different MOC, and different seal arrangements.
Applications in the chemical industry
- Reactor and vessel ventilation — exhausting corrosive gases, acid vapours, and solvent-laden air from reactors, storage tanks, and processing vessels
- Selective catalytic reduction (SCR) systems — supplying combustion or process air to SCR units in chemical boilers and incinerators for NOx reduction
- Spray dryer and fluid bed dryer air supply — providing large volumes of air at consistent pressure to dryer systems; typical duty points range from 30,000 to 90,000+ CMH at pressures of 300 to 600 mmWC
- Pneumatic conveying — moving powdered or granular chemical intermediates through pneumatic conveying systems where high static pressure and dust resistance are required
- Fume extraction and stack emission control — working in combination with wet scrubbers and bag filters to meet CPCB stack emission norms
- ETP aeration — providing aeration air for effluent treatment plants, where sub-corrosive duty and continuous operation reliability are the two most important criteria
MOC selection for chemical-grade blowers
Material selection is not a standard offering decision in chemical plant blowers — it is an engineering decision made on the basis of the process gas. This table summarises typical selections:
| Application / Media | Recommended MOC | Notes |
|---|---|---|
| Acid fumes (HCl, H2SO4, HNO3 vapour) | SS316L casing and impeller | Higher molybdenum content resists chloride pitting |
| Chlorine and chlorinated gas streams | FRP casing with SS316 impeller [VERIFY with Kartik — FRP casing availability] | |
| Mild corrosive vapour, solvent fumes | SS304 casing and impeller | Standard choice for moderately corrosive environments |
| Abrasive dust (catalyst, calcined powder) | MS casing with hard-faced or SS410 impeller | Hard-facing applied to impeller wear surfaces |
| General corrosive exhaust | Rubber-lined MS casing | Cost-effective where contact is intermittent |
| High-temperature corrosive gas (>250°C) | SS321 or SS316 with thermal expansion provision | Design must account for casing distortion at elevated temperatures |
All blowers are tested to IS 4894 before dispatch. Dynamic balancing is carried out to G6.3 as standard, G2.5 available on request.
Verified case study — chemical plant application
One backward curved centrifugal fan supplied for a chemical processing application:
- Capacity: 91,500 CMH
- Static pressure: 458 mmWC
- Motor: 270 HP / 4P
- Drive: belt drive with split-type casing
- MOC: SS410 casing, SS316 impeller, MS structural frame
Split casing configuration allows in-place impeller access without dismantling the ductwork — a practical requirement in process plants where scheduled downtime is limited.
Paddle Dryers for Chemical Industry Applications
The paddle dryer for chemical industry works on indirect contact heat transfer. The product never contacts the heating medium. Heat is transferred through the hollow wedge-shaped paddles and the jacketed trough wall, using steam, thermic fluid, or hot water as the heating medium. Operating temperatures up to 400°C (with thermic fluid) are achievable.
This makes the paddle dryer suitable for chemical applications where direct-contact hot-air drying would cause oxidation, ignition risk, contamination, or loss of volatile value.
Key chemical industry applications
Drying of inorganic compounds — metal hydroxides, metal oxides, and metal salts where consistent outlet moisture below 5% is required and the product cannot tolerate direct flame or hot-air contact.
Solvent stripping under vapour-tight conditions — the paddle dryer can be supplied with a vapour-tight casing and a closed-circuit vapour recovery connection. The solvent vapour driven off during drying is collected at the outlet rather than released to atmosphere, which matters both for process economics and for compliance with HW Rules 2016 (Hazardous Waste Management and Handling) requirements for volatile organic compound containment.
Controlled thermal reactions and calcination — at higher thermic fluid temperatures (up to 400°C), the paddle dryer can carry out controlled calcination of materials such as metal carbonates and hydroxides. The indirect contact ensures uniform heating without localised overheating or hot spots.
ETP sludge drying — chemical plant effluent treatment plants generate sludge with inlet moisture content of 70 to 85%. The paddle dryer reduces this to below 15% outlet moisture, reducing disposal weight and enabling the dried sludge to be processed as per HW Rules 2016. Volume reduction of 80 to 90% is typically achieved.
Cooling of exothermic process materials — by circulating cold water through the paddles and jacket instead of a heating medium, the same equipment reverses function and cools powders and granules that exit exothermic processes.
Construction for chemical-grade service
| Parameter | Standard option | Chemical-grade option |
|---|---|---|
| Casing material | Carbon steel | SS304L or SS316L |
| Paddle and shaft material | Carbon steel | SS304L or SS316L |
| Shaft seals | Standard gland | Mechanical seal or purged stuffing box |
| Casing design | Atmospheric | Vapour-tight with flanged outlet |
| Surface treatment (abrasive sludge) | Standard | Abrasion-resistant lining on paddle faces |
| Heating medium | Steam or thermic fluid | Steam, thermic fluid, or hot water up to 400°C |
Inlet moisture: 40 to 85% handled. Outlet moisture: 5 to 15% typically achieved. Operating cost in the range of Rs 5.45 to 7.50 per kg of dried output (at Rs 10 per kWh) based on thermal modelling; exact figure depends on inlet moisture and throughput.
What Chemical Plant Buyers Typically Ask Before Specifying
Can the blower handle intermittent acid vapour without casing corrosion failure?
Yes, provided the MOC is selected correctly for the specific acid and concentration. For HCl or H2SO4 vapour duty, SS316L is the standard choice because the molybdenum content resists chloride-initiated pitting corrosion that SS304 does not. For very high acid concentration, rubber-lined MS or special alloy liners may be needed — contact our team with your process gas composition for a specific MOC recommendation.
What is the lead time for a corrosion-resistant blower in SS316?
Typically 6 to 10 weeks from confirmed order, depending on impeller size and drive configuration. For urgent replacements, our centrifugal blower services team can assess whether an existing frame can be relined or re-impellered in a shorter cycle.
Does the paddle dryer handle sticky or paste-like chemical intermediates?
Yes. The wedge-shaped paddle geometry is specifically suited to sticky and cohesive materials. The paddles provide a self-wiping action during rotation. Back-mixing with dry product is available to reduce inlet stickiness where required.
Is the paddle dryer enclosed enough for solvent recovery compliance?
A vapour-tight casing design is available with a flanged vapour outlet port that connects to your solvent condenser or scrubber system. This configuration supports compliance with HW Rules 2016 requirements for closed-loop VOC handling.
Can AS Engineers supply both the blower and the paddle dryer for an integrated ETP + drying system?
Yes. We supply centrifugal blowers for ETP aeration and the paddle dryer for sludge drying as separate or integrated orders. The blower and dryer can be specified together with matched air volumes and thermal loads for the same ETP capacity.
Discuss Your Chemical Plant Requirement
If you have a specific duty point, process gas composition, or sludge moisture profile, our engineering team will review it and recommend the right equipment configuration. We supply across India and export to Southeast Asia, the Middle East, and Africa.