Powder Recovery of Fertilizers

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The recovery of fertilizers typically after drying tunnels or drum dryers is associated with a high load of particulates and very humid gas streams. To recover these products, cyclone collectors are very convenient equipments for allowing a direct powder capture and avoiding filter clogging due to condensation. Arrangements with cyclones or with bag filters are usual in the industry.

Client's needs include a low maintenance high efficiency cyclone system that is efficient enough to comply with regulatory PM limits avoiding the use of a bag filter as the primary or final stage deduster.

The recovery of fertilizers after a dryer is commonly performed by dryer cyclones to capture most of the powder and an end stage dedusting system (either Bag Filter, a Hurricane or Mechanical ReCyclone) before the stack.

Numerically optimized cyclones, considering particle agglomeration
Hurricane geometries maximize powder collection for each different application, while minimizing reentrainment and keeping pressure drop at reasonable levels.

These high efficiency cyclones are the output of nonconvex nonlinear problems formulated and solved after years of work in partnership with the Faculty of Engineering of Porto.

A single Hurricane is more efficient than any other known cyclone available in the market for the same pressure drop, usually resulting in less than half of the emissions of other high efficiency cyclones available.

  1. Air and Dust from Dryer or Boiler
  2. Hurricane Cyclone
  3. Valve
  4. Collected Particles
  5. Clean Air

In order to obtain very high efficiencies and compliance with emission limits, an improve recirculation system has been designed to take advantage of the Hurricane cyclones. A mechanical ReCyclone

(ReCyclone MH) is made up of a Hurricane with a particle separator (straight-through cyclone), placed downstream of the cyclone - called the 'recirculator'.

The main purpose of the recirculator is to reintroduce the fine non captured particles into the cyclone after those have been driven to the outer walls of the recirculator by centrifugal forces. While this tangential gas stream is enriched in particles, the axial gas stream exhaust to the stack is clean of particles. Recirculation is achieved through an additional fan.
Since the recirculation system only serves the purpose of dust separation (and not collection), the particles are exclusively collected in the cyclone and the need of rapping mechanisms is thus avoided.

Efficiency increases due to recirculation and agglomeration of very small particles with larger ones coming directly from the process. A ReCyclone MH decreases emissions of Hurricane cyclones alone by 40 to 60 %. As with cyclone systems, ReCyclone MH systems are very robust, do not have temperature limitations and do not have moving parts to be frequently changed. Finally, recirculation control provides the benefit of handling variable process flow rates.
 
The next figure exemplifies a ReCyclone MH in stainless steel AISI 304L for particle recovery in drying process. Recirculators can be disposed vertically, as shown, or horizontally.

  1. Air and dust from boiler or dryer
  2. Hurricane cyclone ( Batteries of 2, 4, 6 or 8 units )
  3. Discharge valve
  4. Collected Particles
  5. Clean air
  6. Recirculator
  7. Fan

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