Volume
DRY VI Part 1 Introduction.
This describes the
basic features of pneumatic conveying dryers and their advantages
and disadvantages relative to other types of dryer.
Volume
DRY VI Part 2 State of the technology.
This covers the currently available
equipment options and operational considerations. A pneumatic
conveying or flash dryer entrains the wet feed by hot gas
at the bottom of a tube which is frequently straight and vertical.
At the top of the tube the dried particles are separated from
the conveying gas, usually in a cyclone. Although residence
times are very short, these dryers can be extremely effective
for drying fine particles at high throughputs. A large number
of more elaborate designs have been developed to broaden the
range of possible applications, and these are reviewed in
detail. Variants such as centrifugal flow units, swept mills
and ring dryers are described and illustrated. There are separate
chapters on the feed system, particle classification and product
recovery from the gas stream. The short residence time of
pneumatic conveying dryers makes it most important to consider
aspects such as feeding and instrumentation and control. Finally,
safety and environmental considerations are discussed.
Volume
DRY VI Part 3
State
of the science.
This
covers the underlying science of the processes occurring in
pneumatic conveying dryers in depth. It is divided into the
following sections:
- Particle motion: acceleration
and steady-state zones, isolated particle and suspension
models, choking, feedpoint effects, horizontal flow, attrition,
erosion and agglomeration, and particle movement in cyclones.
- Heat transfer: gas-to-particle
heat transfer, heat losses to walls.
- Drying kinetics: mass transfer
in solids, overall drying rates, heat and mass balances.
- Design procedures: the theoretical
basis of published tube sizing procedures and the SPS methods
for scoping design, detailed design and scale-up.
Volume
DRY VI Part 4 Design
guide.
This
part covers the design procedure for a new pneumatic conveying
dryer, scale-up methods from pilot plant data and the performance
assessment of an existing unit. The layout is designed to
be compatible with the PC program DRYCON and the spreadsheet
program PNEUCONV, which can be used to perform the calculations.
Extensive worked examples are provided.
The design procedure
begins with calculations of particle terminal velocity and
selection of the ideal conveying velocity. Heat and mass balances
give the gas flowrate and the dryer diameter. Conditions along
the dryer are found using an "incremental model"
where the following calculations are performed on a small
section of dryer: heat and mass balances (giving gas and solids
temperatures), heat transfer rate, drying rate, and particle
motion. This calculation is repeated in steps along the dryer,
and yields the dryer length (for a new design) or the outlet
moisture content (for an existing dryer). Because the stepwise
procedure is complex and requires a computer program, a simplified
scoping procedure has also been devised. There are important
effects such as agglomeration which are difficult to predict
theoretically. Hence it is highly desirable to obtain pilot
plant results which can be compared with the predictions and
used to refine the model. The text describes how to perform
these fitting mode calculations and shows how they can be
used for rigorous scale-up.
The contents
of the Part are as follows:
- Formulation of the design
problem, collection and collation of data
- Heat and mass balance, terminal
velocity calculation and duct diameter
- Scoping design procedure for
dryer length
- Fitting mode calculations
and scale-up techniques
- Detailed design procedure
- Ancillary design calculations:
feedpoint configuration, cyclone, heater duty (indirect
or direct-fired), gas recycle systems, fan and condenser.
Volume
DRY VI Part 5 DRYCON User Guide.
This is the printed User Guide
to the DRYCON calculation software which implements the design
algorithm in DRY VI.4.
