In the first part this file, I noted that it is necessary by desire and, in many
instances, by law, to separate and recover final product, dust and other
potential solid emission products from the exhaust airstream. Various
technologies are available to perform this separation, each having its
own intended application, benefits and limitations. In this column,
I’ll look at the most common systems available to separate solid
particulate from main gas or exhaust streams.
An inherent result of thermal drying is a relatively hot, humid exhaust
gas stream. Depending on the type of dryer employed, this stream may
contain final product, dust or myriad other potential solid emissions
products. It is necessary by desire and, in many instances, by law to
separate and recover these products from the exhaust airstream. Various
technologies are available to perform this separation, each having its
own intended application, benefits and limitations.
by Darren A.Traub | January 2, 2004 | Comments (0)
Developments in drying have been largely refinements of existing
technology. These refinements are multidirectional and include
refinements in design, control, materials and application. Other
developments have been due to the emergence of new requirements such as
those of the wood plastic composite (WPC) market, which needs very dry
wood flour at relatively high rates.
by Darren A.Traub | January 1, 2004 | Comments (0)
Continuing my discussion of the psychrometric chart and how to use it, in my last column,
I showed a psychrometric chart, plotting four points. Allow me to
proceed with the topic by picking up our ongoing example and taking it
further, by putting that air inside a piece of process equipment such
as a dryer or oven.
by Darren A.Traub | November 1, 2003 | Comments (0)
In this column, I will continue to will deal with the interpretation
and manipulation of this data so that a better understanding of the
operation can be gleaned. Let's get back to the terms I was
reviewing so that you can understand the "parts" before we take a look
at the whole psychrometric chart.
My "Tools of the Trade" series dealt with various instruments used in the acquisition of system
parameters. For the data collected to have some value requires
understanding and manipulation of the data, ultimately resulting in a
model of your system. The next few "Drying Files" will deal with the
interpretation and manipulation of this data so that a better
understanding of the operation can be gleaned.
When comparing bids, we all know (or need to stop fooling ourselves if
we deny it) that initial capital cost is the primary consideration
before placing a purchase order. Certainly, there are other factors,
like brand loyalty. But, when comparing two systems that are identical
in every aspect except that one has insulated exhaust ducting as well
as recuperating systems for preheating the combustion air and
recirculating a percentage of the air, how many of you would spend an
extra $10,000 -- or even $10 -- if these additions have no effect on
the quality of the final product?
In my last two columns, I've been looking at some of the methods of
obtaining the required field data to enable an effective dryer audit.
I left off with the discussing simple mercury bulb thermometers, which
are suitable for performing both dry and wet bulb temperature
measurements, and the infrared (IR) thermometer, which measures surface
temperature and can be targeted and focused. I'll pick it up there.
Pressure in drying systems is fundamental. Note that vacuum is negative
pressure, so when I refer to pressure, I am talking about an absolute
value. Because gas is being moved around the dryer, there is a
requirement for the primary and secondary movers to be able to produce
sufficient pressure to overcome all of the losses as the gas moves
across the system. A manometer is used to establish the static pressure
across the system, and a static pressure profile can be developed to
illustrate the losses across the system.
