See also:
Mini-Manual MM I. The practical determination of gas
and particle properties
Volume DRY
XI Part 1 Introduction.
Volume
DRY XI Part 2 Control and operation
of dryers.
Effective control
methods are vital for the efficient and safe operation of
dryers, and they depend in turn on the information provided
by plant instrumentation, both in its extent and accuracy.
This Part reviews the current state of control and instrumentation
of industrial dryers, in their context as a unit operation
usually integrated into a multi-operation process plant.
After a brief
introduction, Section 2 gives an overview of the operating
and control strategy for an entire plant. Next, the variables
which can be controlled are listed, and basic principles of
control are reviewed. The available measurement methods are
reviewed, with cross-references to Mini-Manual I (Determination
of Gas and Particle Properties) which covers this subject
in more detail. There are descriptions of the available types
of controllers, actuators and signal transmission methods,
and other aspects of the control system such as siting, maintenance
and hazards are briefly summarised. There is also an extensive
section detailing how control methods are applied to the major
individual dryer types.
Volume
DRY XI Part 3 Dryer troubleshooting. Dryer troubleshooting
and problem-solving is a vital area which has been almost
totally neglected in published literature. It presents a complex
problem because of the wide range of possible problems, causes
and solutions. However, the broad classes of problem and the
most common solutions can be given, and a methodology has
been defined which allows the engineer to narrow down the
possibilities. Specific examples are provided; these may be
directly relevant to the user's problem, or may suggest ideas
which lead to a solution by a parallel approach.
Part 3 begins
with an introduction and an overview of dryer troubleshooting.
The terminology and the stages of the troubleshooting process
are defined, and dryer problems are categorised. The next
section gives a methodology for troubleshooting, including
both methods for a temporary "quick fix" and for
more effective long-term solutions. The most important plant
measurements to identify the source of the problem are listed.
The various categories of problem are then described in turn;
they include commissioning, start-up and shutdown, safety
and environmental problems, underperformance, poor product
quality, material handling and blockage, transient problems
and mechanical breakdown. Some of the specific problems encountered
with individual types of dryer are then described, with the
aid of selected case studies.
It is intended to incorporate
the basic problem-solving method into a simplified expert
system, provisionally entitled DRYSOLVE, in the next couple
of years. If this approach is successful, a program using
a more detailed and rigorous methodology could be developed
later.
Volume
DRY XI Part 4 Energy Aspects.
Thermal drying is an extremely
energy intensive operation. In many instances, dryers are
operated unknowingly at efficiencies well below their potential,
adding unnecessarily to drying costs. This report aims to
give dryer users and manufacturers information on how to measure
the efficiency of an existing dryer and on how to improve
its performance. The measurement and analysis of heat and
mass balances is covered in detail. A wide variety of drying
systems is described by a series of modules which can be combined
together as required. Schemes for reducing energy consumption
are divided into two categories. First, there are those that
require negligible or minor capital expenditure, such as good
house keeping, reduction of the air supply, optimisation of
production schedules and simple improvements to instrumentation
and control. Secondly, there are those that need significant
capital expenditure such as improved mechanical dewatering,
heat recovery from exhaust gas and product, recycling of exhaust
air and advanced instrumentation and control. The report also
considers the much wider opportunities available with a new
plant at the design stage, including dry rather than wet processing,
pre-concentration by evaporation or mechanical dewatering,
replacing water by a low latent heat organic solvent, dryer
selection and the use of the Carver Greenfield process. The
final chapter describes several potential technical developments
which have yet to make a significant impact in industry, namely
high temperature closed cycle heat pumps, open cycle heat
pumps, vacuum flash evaporation and the use of "free"
heat sources.
