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Stages of Drying:
Diffusion:
Final Moisture loss
Why is the Littleford so efficient?
Materials go through several physical stages during
the drying process - Paste, Granule and Powder. During the early portion of the Paste Stage, the product
is a thickening slurry which is readily put into turbulence by the action of the plows. The Dryer has been
designed to achieve the critical Froude Nr. (The Point
in which the plows force the batch into turbulence &
thus maximize the heat transfer capability of the dryer.
This attainment of the critical Froude Number enables
fast, efficient transfer of the BTU´s required to satisfy
the latent heat of vaporization, thus generating a much
shorter drying cycle.
Conventional dryers do not begin to achieve Littleford
drying rates, even in this Liquid Stage of the drying
curve where drying is most easily accomplished.
As the slurry thickens at the end of the Paste Stage ,
(end of the constant rate period), the batch thickens
to a mud-like consistency, which in conventional
dryers causes the batch to ball or cake. This makes
drying exceedingly difficult, since moisture (volatiles)
must migrate from inside thrugh capillaries to the particle surface before it can be flashed off. This point on
the drying curve is where the limited drying rate of
conventional dryers gets even worse, as internal particle drying replaces efficient external drying.
In the Granule Stage, Littleford Ploughshare Dryers,
utilizing both the action of the turbulent plows and the
high shear choppers, reduce the forming lumps to
smaller granules, thus exposing large amounts of new
surface for drying.
Constant Rate.
Surface
& Subsurface
Moisture
M
o
I
s
t
u
r
e
L
e
v
e
l
Constant
Rate
Period
Particle of
Material
Falling
Rate:
Diffusion
starts to
retard
drying
Falling Rate
Period
Diffusion
Period
Time
Paste Granule Powder
As the product moves from the Granule to the Powder Stage,
continued use of the high shear choppers will break the drying granules into fine Powder, allowing for possible elimination
of further milling of the dried product.
Heat Transfer Graphics
The Littleford Dryer exhibits superior heat transfer coefficients, often
two or three times higher than those of a ribbon or paddle dryers. As
much as ten times higher than tumble or tray dryers.
Heat Transfer Capability
Heat Transfer Coefficients
Comparative Example: Aqueous Pigment Paste, Highly Plastic
“Pasty”
Pigment Mix
49.2
U 41.0
F
a
c
t
o
r
Littleford
Ploughshare
Dryer
U
41.0
32.8
24.6
“Crumbly”
Pigment Mix
16.4
8.2
Froud Number
49.2
F
a
c
t
o
r
32.8
24.6
16.4
Paddle
Dryer
8.2
5.0
10.0
Critical Plow Speed
15.0
% Moisture
in Material
20
40
60
80
100
U Factor: BTU/Hr. - Sq.Ft. - F Degrees
Advance Drying:
The Chopper Advantages in Drying:
Fast, efficient drying without lump formation
PASTE
GRANULE
POWDER
M
O
I
S
T
U
R
E
Internal Drying
without Choppers
External Drying
with Choppers
DRYING TIME
The action of the turbulent plows and the high shear choppers reduce the forming lumps
to smaller granules, thus exposing large amounts of new surface area for drying.
Optimizing Drying in the Littleford
Main reasons for drying operations:
To facilitate handling and further processing.
To permit satisfactory utilization of the final product.
To reduce shipping costs.
To increase the capacity of other equipment in the process.
To preserve a product during storage and shipment.
To enhance the value and usefulness of waste or various products.
To make a product with physical characteristics more appealing to the customer.
Reasons for drying under vacuum:
Control temperature of temperature-sensitive products
Recover solvents for re-use.
Effective solvent removal under non-explosive conditions
and control its safe handling.
Capacity can be controlled, or varied, by processing small
or large batch sizes to meet existing process requirements.
As a general statement, all drying can be divided into distinct periods. In thecase of
Vacuum Drying, it falls into (3) categories:
Time known as the constant rate period, or that time the moisture is easily evaporated from the surface
This occurs at a time when the material is substantially at the boiling point of the evaporating liquid
under the absolute pressure conditions exixting in the dryer.
That period known as the falling rate period when the material approaches the wall temperature of the
dryer. As diffusion is taking place, the sensible heat of the material starts to approach the heating
Optimizing Drying in the Littleford
Successful Vacuum Drying Points
Numerous test results have indicated that the most successful vacuum dryings are
Achieved whenthe following conditions prevail:
THE MATERIAL IS NOT SOLUBLE IN THE SOLVENT TO BE REMOVED. THESE TYPES OF PRODUCTS
CAN BE FOUND MOSTLY IN PHARMACEUTICAL COMPANIES THAT ARE DOING MULTI-STAGE SOLVENT PURIFICATIONS. THIS TYPE OF PRODUCT IS IDEAL FOR THE LITTLEFORD DRYER. IF THE MATERIAL IS SOLUBLE IN THE SOLVENT TO BE REMOVED, WE HAVE FOUND 20% TO 30% SOLVENT
TO BE THE VERY MAXIMUM. GREATER CONCENTRATION CAUSED MASSIVE BUILD-UP AGAINST
THE HEAT TRANSFER SURFACES AND VERY HIGH POWER DEMANDS (10 HP+ IN FM-130 PILOT
UNIT).
TWO TYPES OF DRYING IN THE LITTLEFORD PROCESS VESSELS:
ATMOSPHERIC AND UNDER VACUUM
Factors that control heat transfer:
-Type of mixing tool
-Speed of agitation
-Jacket Area
-Jacket Temperature
-Boiling point of volatile component
U=
Q
.
(A) (LmTD)
Vessels that can maximize all factors for efficient drying:
FM, FKM, VT and DVT types.
Jacketing:
-Cover Max. Area of shell.
-Heat Shaft (optional)
-Heat Heads (optional)
-Circulation fluids in jacket at correct Reynolds number.
-Connect all fluid flow from bottom-up.
-Connect all steam in @ top, out at bottom through trap.
Must supply sufficient steam for process requirements.
Optimizing Drying
In the Littleford
3rd. Page.
Plow Types:
-Standard & Heat Transfer.
Explosion (overpressure) Protection:
-All sealed units must be protected.
-Units must be designed for pressure (not
necessarily stamped or coded)
Seals:
-Packing for medium vacuum or atmospheric
-Mechanical seals for high vacuum.
Discharge Valves: Std.Contour, Ball, GEMCO
Choppers:
-Used to deagglomerate lumps.
-Add small amount of heat to aid drying
-Integral shafts are recommended.
Pulse Back Filter:
-Used to contain solids in dryer.
-Use hot pulse air.
-Must be heated above “dew point of volatile”
-Sizing chart for most applications.
-Seal seams of bags.
-Use tight porosity bags with special coating.
RPM´s:
-Normal Speed is Std. – to maximize heat transfer
-Keep same Froud # during scale-up
-Some applications are at reduced speed due to
Nature of product being dried, so as to keep motor
Loads as low as possible.
Drives: Single,Two-Sp.,Varaible or Hydraulic.
Vacuum:
-Vapor pressure controls B.P. (want to maximize differential between jacket & product)
-Millimiters Hg Abs. Vs in. Hg Ref.
Vapor Port & line sizing:
-Port = less than 3 Ft/Sec
-Vapor line = less than 100 Ft/Sec.
** Expanded volume under vacuum.
Vacuum Systems (Critical Proper Design):
-Pump CFM pumping rate.
-Condenser Ft2 and tube diameter.
-Full or partial water recovery.
IMPORTANT: Draw vacuum before running.
N2 Flush: Low level moisture require it to lift
vapor out of drier.
Air drying VS Vacuum drying
Drying Heat Sensitive Low Percentage Solids
The Littleford Day drying technology offers a highly efficient & economical means of drying heat sensitive low percentage
Solids solutions. A considerable portion of the ingredients for the Food, Pharmaceutical, Nutraceutical and Biotechnical
Industries is manufactured from the extraction or reaction of plant materials using solvents (water, alcohol, hexane, etc).
This process leaves the processor with a product in the form of a liquid with a very low percent solids level (Hydrolized
Vegetable Protein, St.John´s Wort, Enchinacea, and other Nutraceutical products).
Processors have been searching for an economical way to dry these products. In the past, due to the stickiness of the
Product during drying, the processor was forced to utilize drying methods such as frezze drying, spray drying, tray
Dryers, etc., expensive methods which did not rely on mechanical agitation of the product through the high viscosity
“Power Phase”.
Typical Littleford vacuum drying process:
1.- Product is placed in the Littleford Ploughshare Vacuum Dryer. Agitation
Is initiated (plow & choppers (optional) followed by heating media (hot water,
Steam hot oil) on the vessel jacket to raise the temperature of the product in
The dryer to the predetermined drying temperature.
2.- With the vessel under vacuum, a fine spray of the low solids solution is
Atomized into the heated bed of dried material. The rate of spray is matched
To the rate of vapor evolution in order to mantain the bed of materials as a
Dry medium.
3.- After sufficient material has been dried to raise the batch size to a 70%
Fill, the product is cooled (via cooling media on the vessel jacket) to the
Required temperature for subsequent processing (other ingredients added,
Product granulated, etc.) or discharge.
Wet Product
Condenser
Dryer.
Recovery Vacuum
Tank.
Pump.
Liquid Injection
Advantages of the advanced Littleford process:
1.- Controlled drying through effective/optimum heat transfer
2.- Improved Drying rates.
3.- Increased efficiencies of drying.
4.- Efficient single unit processing of the entire process
The Littleford equipment used to accomplish this
Advanced processing is the Littleford Ploughshare
Vaccum Dryer, which combines the operational feAtures of liquid injection, vacuum operation and
Effective heat transfer (heating or cooling) to dry
in a single processing unit. It operates according
to the proven “fluidized bed” mixing principle,
Whereby the materials being processed are manTained by the plow shaped mixing elements in a
Mechanically fluidized “suspeded” state. This
Permits liquid and solid media to achieve intimate
Individualized, rapid contact with each other and
The heat transfer surfaces.
In addition, the Littleford Ploughshare Vacuum Dryer may
Be equipped with independently operated, high shear
“chopper” devices to treduce the particle size of any
Lumps or agglomerates, exposing undried materials
Thereby ensuring thoroughly dried particle interiors. This
Deagglomeration further shortens the drying time required.
It is specifically dengineered to maximize heat transfer,
Yields coefficients that are many times higher than those
Of traditional dryers. This advanced heat transfer technoLogy generates rapid drying in a single process vessel.
It can be enhanced with an optional Pulse Back Filter to
Effectively handle the vapor steam created during steam
Stripping and drying.
The Littleford process enables the processor to produce an excellent, dried product with solvent levels well below the limits set by the FDA.
The Littleford Ploughshare Vacuum Dryer is designed and constructed according to “GMP” and to meet or exceed FDA, 3A, USDA, compliance
As specified by the customer.
This proven Littleford technology has been applied to numerous complex and difficult applications in the Food, Pharmaceutical, Nutraceutical
And Biotechnical Industries. Littleford Ploughshare Vacuum Dryers can be purchased in a variety of sizes to meet most production requireMents. Littleford can interface its system controls with existing equipment or supply fully automated process control systems
Typical Applications
A-B-C
D-E-F-G
Acetoquanamine
Acetyl Salicilic Acid
Acrylic Powder
Agricultural Herbicides
Aluminum Hidroxide Slurry
Animal Byproducts
Animal Feed Products
Animal Waste for Fertilizers
Barium Stearate
Boric Acid Solution
Brewer´s Yeast
Cadmium Oxide
Calcium Stearate
Carbon Black
Carbon Fibers
Carboxi Methyl Cellulose
Carrageenan
Catalyst
Cellulose
Cetylpyridinium Chloride
Chmical Dye Intermediate
Chocolate
Citric Acid
Coal Ash Slurry
Cocoa (Dutching)
Cocoa (Processing)
Coffee (Decaffeinating)
Dental Adhesive
Dextrose
Dye Intermediates
Enzimes (Temp.Sensitive)
Ethyl Cellulose
Fillers
Fish Meal
Flammable Sludges
Flour (Toasting)
Friction Material
Graphite Filter Cake
H-I-J-K-L
Herbicides
Inks
Inorganic Filler Powders
Iron Oxide Filter Cake
Lead Phthalates/Stearates
Lecithin Oil Extract
Liquid Fungicides
Lithium Fluorite
M-N-O-P
Magnesium Stearates
Metal Binders & Reclaim
Methyl Cellulose
Modifies Protein Powdre
Molibdenum Disulfide
Paint Sludge Slurry
Para Toluene Sulfonate
Paraformaldehyde
Peat Moss (Vermiculite Mix)
Penicillin Powder
Pesticides
Pharmaceuticals (Intermediate)
Photographic Process Sludge
Pigments
Plastic Resin Beads
Polyethilens
Polymers
Polyvinil Alcohol
Potassium Boro Fluoride & Phenate
Protein Modifications
Psyllium Seed
Q-R-S-T-U-V-W-X-Y-Z
Refracting Powders
Resin Beads
Selenium Metal Filter Cakes
Sodium: Methylate, Phenate, Stearates
Specialty Chemicals
Starch Powder
Sulfonated Polystyrene
Temperature Sensitive Enzymes
Tugsten Carbide Slurry
Toxic Sludges
Vitamin Mix
Wet Friction Lining
Wheat: Bran, Farina & Germ