Pulsed Dehydration System (PDS)

What is Pulsed Dehydration?

 

Pulsed Dehydration or Pulse Combustion (PC) drying technologies use intermittent (pulsating) combustion of a suitable fuel and oxidant (air) to generate intensive acoustic shock waves (pulses) within a bespoke combustion chamber or combustor. These high-pressure, high-temperature pulses exit the combustor at high speed via a small diameter tailpipe designed to channel the hot oscillating gases to an “evaporation zone”, which forms the transition between the combustor and large-volume “drying chamber”.

How Does Pulsed Dehydration System Work?

 

Pulse dehydration comprise an oscillating combustion chamber, tail pipe and a thermo-acoustic atomiser.  Wet feedstock injected into the evaporation zone is exposed to a highly turbulent atmosphere of hot, oscillating gases.  This causes instantaneous atomisation and flash evaporation of the surface moisture in a process we call “Thermo acoustic Dehydration”.  The rapid dehydration process creates a concentrated region or “cloud” of super-heated steam (SHS) downstream of the atomisation zone which increases rates of heat and mass transfer without degrading product quality due to oxidation and exposure to excessive heat. In addition to retaining product taste, colour and texture, the SHS atmosphere also provides an atmosphere of reduced oxygen concentration, which is desirable when dealing with potentially ATEX sensitive powders.

Thermo acoustic Dehydration Process

 

  • High frequency acoustic shock waves shatter the bonds between moisture and solid particulate in the wet feedstock without additional mechanical equipment. These shock waves produce ultra-fine (5-50μm) droplets, thereby greatly increasing their surface area which is required for efficient evaporation.

 

 

  • The negative pressure, high temperature acoustic shock waves enhance evaporation by lowering the instantaneous boiling point and surface tension of the wet droplets.

 

 

  • Pulsating exhaust gases at temperatures between 300-800°C “flash evaporate” the surface moisture of the droplets with up to 98%.  Feedstock moisture is converted to super-heated steam within 3 to 6 milliseconds, depending on feedstock viscosity.

 

 

  • The high heat capacity and thermal conductivity properties of super-heated steam (SHS) improve evaporation above inversion temperatures and reduce oxidation reactions.  These features could, depending on the product, be beneficial to enhance porosity, re-hydration properties and retention of natural colour and texture, and simultaneously inactivate enzymes and micro-organisms.

Pulsed Dehydration System Benefits 

 

  • For dehydration of viscous slurries and pastes

 

  • No mechanical atomisation equipment required

 

  •  Low CO & NOx emissions in off gases.

 

  •  Low feedstock pump pressures- typically < 2bar

 

  • Improved product quality with little or no protein denaturing or browning

 

  • Ideal for powders produced from hydrolysed plant and animal products

 

  • Short drying time (30 - 50ms) reduces heat build-up in final product

 

  • Small plant footprint requiring no heat exchangers

 

  • Low fuel consumption. Total power ca 1.2kW/kg water evaporated

Typical PDS Dryer Diagram

 

 

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