Pneumatic Ash Handling System Applications



•Environmentally friendly
Enclosed pipe work minimises dust emissions

•Minimal maintenance
Low number of moving parts

•Flexible construction
Systems can be upgraded easily at a later date

•Simple installation
To suit customer’s existing plant layout

Three basic modes of pneumatic conveying :

  1. Lean-phase
  2. Medium-phase
  3. Dense-phase

Lean-phase


•Entrains individual particles in a high velocity air flow (15 -30 m/sec) necessary to pickup the mass of the particles
•Can either be positive pressure or vacuum
•Pipe diameters must be large to achieve reasonable transfer rates
•Component and pipe wear is very high because of the high transfer velocities -specialwear-high resistant materials must be used
•Energy consumption is high as the air source runs continuously regardless of transfer rate requirements
•Silo filtration is generally large and complicated

Medium-phase

•Material travels in a moving mass in the pipe base Velocity must be high enough to avoid blocking the pipeline with material -typically 5 to
15 m/sec
•Usually positive pressure < 2>•Handles dry, homogenous fluidizable materials  over distances up to 2,000 metres
•Pipes are generally smaller than for lean-phase
•Pipe wear can be a problem if not designed & installed correctly
•Control of material flow into the pipeline is critical

Dense-phase

•A controlled use of both air pressure and volume transfers material through the pipe in discrete plugs with pockets of compressed air in between
•Positive pressure conveying using medium pressure air > 3.0 bar(g)
•Velocity is very much lower at 1.5 to 10.0 m/sec resulting in much reduced pipe wear
•Can handle a wide range of both wet and dry materials; can transfer fly ash or over distances up to 1000 metres
•Pipes are much smaller than for lean-phaseEnergy consumption is low and usually directly proportional to the actual transfer rate

Pneumatic conveying

  1. Lean-Phase -the earliest method : high volumes of low pressure air entrain material in a high velocity air stream
  2. Medium-Phase ： uses higher air pressures to convey material over longer distances at lower velocities
  3. Dense-Phase -a more modern technology high pressure air conveys material in plug form through smaller pipelines at low velocity
    and high efficiency

Selection criteria should include:

  1. Equipment/Pipe wear   (proportional to velocity3)
  2. Energy consumption at all operating conditions
  3. Lifetime operating costs