Performing a "dryer audit" is a mainstay of any drying specialist, and
every reputable company that sells equipment has people specifically
trained to perform these audits. Even with vast experience and all the
necessary equipment, it takes someone skilled in the art significant
time to capture all of the pertinent field data. Thereafter, another
considerable investment is made into analyzing the data to manipulate
it into a meaningful form.
by Darren A.Traub | January 15, 2003 | Comments (0)
The levels of initial drying rates also may enhance and modify the
quality of the final product. For example, rehydration rates for
products such as instant coffee or milk tend to follow the drying rate
pattern.
by Darren A.Traub | October 1, 2002 | Comments (0)
For each and every product, there is a representative curve that
describes the drying characteristics for that product at specific
temperature, velocity and pressure conditions. This curve is referred
to as the drying curve for a specific product. Variations in the curve
will occur principally in rate relative to carrier velocity and
temperature.
by Darren A.Traub | September 1, 2002 | Comments (0)
Troubleshooting a dryer that has never operated to specification from
startup is essentially more challenging than troubleshooting a dryer
that is no longer operating to specification. Spending time with these
systems and systematically evaluating all the parameters will enable
you to draw conclusions and provide certain fixes to the problems and
other enhancements. This column, however, focuses on troubleshooting a
dryer that has previously operated to specification and is no longer.
I have never been a good fisherman. The few times that I have gone
fishing I really caught nothing worthwhile. I could not take the few
tiny fish that I did manage to hook off the hook. The sensation of them
writhing and wriggling with their slimy bodies was too much for me to
handle. I did once catch a large crab with a line and hook!
An indirect dryer that allows a high degree of temperature control, a
rotary tube furnace (RTF) dryer consists of a muffle furnace with a
steel drum passing through it. Tumbling or rolling flights rather than
the lifting flights such as those in the cascade rotary dryer are
fitted to the inside of the drum.
Direct rotary cascade dryers have internal lifters or flights to elevate
the feed and drop it in a curtain from the top to the bottom, cascading
along the length of the dryer. The carrier stream (hot gas) may be co-
or countercurrent with the primary flow being through the "bed" or
curtain, and, in this instance, multiple curtains in the longitudinal
direction. As you can imagine, the formation of each curtain is
intermittent.
Rotary dryers potentially represent the oldest continuous and
undoubtedly the most common high volume dryer used in industry, and it
has evolved more adaptations of the technology than any other dryer
classification. Rotary dryer technology includes direct rotary cascade
dryers, indirect (steam) tube rotary dryers, multipass rotary dryers,
rotary tube furnace dryers, and rotary louver dryers.
by Darren A.Traub | January 1, 2002 | Comments (1)
Conveyor dryers principally are through-the-bed dryers although
cross-flow and radiant units are used occasionally for specific
products. Units can be directly or indirectly heated by using burners
(gas, LFO or HFO) or coils (steam, electrical heater banks or thermal
oil).
by Darren A.Traub | October 25, 2001 | Comments (0)
One of the older and gentler technologies associated with drying is
conveyor drying. Conveyor dryers -- also referred to as band or apron
dryers -- are used extensively throughout a variety of industries. They
have found a particular niche in the food industry for products such as
pet food, fruits and vegetables, extruded snacks and cereals.
by Darren A.Traub | October 1, 2001 | Comments (1)
