WO2017019449A1

WO2017019449A1 - Continuous solids dryer

Info

Publication number: WO2017019449A1
Application number: PCT/US2016/043336
Authority: WO
Inventors: James Russell Steeves; Raymond Thomas FRASER
Original assignee: Artisan Industries, Inc.
Priority date: 2015-07-24
Filing date: 2016-07-21
Publication date: 2017-02-02

Abstract

A continuous solids dryer includes a jacketed cylindrical body and a rotor shaft disposed within the cylindrical body. The dryer has input and output ports at respective ends of the cylindrical body. The rotor shaft has baffles attached thereto for rotation with the shaft. The baffles limit longitudinal translation speed of material to be dried, to control residence time of the material. Each baffle includes an agitating bar/scraper, which agitates drying material and prevents material sticking to an inside wall of the dryer. Material may be continuously fed into the dryer while the dryer operates under vacuum. The dryer approximates plug-flow processing, thereby yielding relatively narrow residence time distributions (RTD).

Description

Continuous Solids Dryer

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No.

62/196,369, filed July 24, 2015, titled "Continuous Solids Dryer," the entire contents of which are hereby incorporated by reference herein, for all purposes.

TECHNICAL FIELD

[0002] The present invention relates to chemical process equipment and, more particularly, to continuous rotary solids dryers.

BACKGROUND ART

[0003] With few exceptions, most products of chemical processes must be dried for further processing or sale. Such products include food ingredients, such as herbs and spices, pharmaceutical formulations, copolymers and instant coffee. Drying involves removing liquids, such as water or other solvents, that may be naturally present in a product or that may have been added in an earlier processing stage. Market research suggests the global market for drying equipment is about $1.9 billion. Available drying technologies may be distinguished by heat transfer methods used to affect drying. The most common methods include convection, conduction, and radiation.

[0004] It is known in the prior art to use a vertical or horizontal thin-film evaporator

("TFE") to remove a solvent from a resin, dehydrate a food product, purify an antioxidant or perform a chemical reaction in relation to processing thermally unstable, viscous, solids- containing and foaming materials. See, for example US Pat. Nos. 4, 160, 692, 5,582,692 and 6, 160, 143, the entire contents of each of which are hereby incorporated by reference herein. Using a thin-film evaporator entails placing a thin film of the material being processed on an inner wall of an externally heated (typically cylindrical) chamber to provide a surface for evaporation.

[0005] However, TFEs are inappropriate for drying when the feed materials are non- pumpable free-flowing solids, such as powders, granules, peanuts or coffee beans (collectively referred to herein as "solids" or "particles"), because thin films cannot be formed from free- flowing solids and steady, continuous metering of free-flowing solid materials into TFEs (often operated under vacuum) is impractical. To dry particles to low moisture concentrations, free and bound moisture must be removed. Free moisture refers to liquid that is either on surfaces of particles or between particles. Bound moisture is liquid held within particles that must first diffuse from the interior of the particles to the particle surfaces. Although TFEs may adequately remove free moisture from appropriate input materials, free-flowing solids produced by TFEs often require further drying, with a longer residence time than a TFE can readily provide, to remove or reduce bound moisture.

[0006] Some materials should or must be processed under low oxygen conditions to avoid spoiling. Such materials are often processed under partial vacuum (referred to herein simply as "vacuum"). Drying particles under vacuum also provides other advantages, such as reducing temperature requirements for drying. Lower temperatures are advantageous or necessary when drying certain temperature-sensitive materials or to reduce energy consumption. Indirect vacuum dryers have been used to dry heat- sensitive biopharmaceutical or active pharmaceutical ingredient materials. In the polymer industry, they have been recommended for drying high-density polyethylene (HDPE), nylon and polyester. In the food industry, they have been used to dry fruit pulps, cheeses, instant potatoes and infant formula.

[0007] Most conventional solids dryers operate in batch mode, in which a fixed quantity of material to be dried is placed into process equipment, a vacuum is drawn, the material is dried and then the entire quantity of dried material is removed from the equipment. The process may be repeated with subsequent batches of material. However, the equipment processes only one batch at a time. The vacuum is released each time the equipment is opened to remove dried material or to introduce a new batch of material to be dried. Consequently, a vacuum must be drawn for each batch, with energy and air consumed each time.

[0008] Batch processing may be disfavored for several reasons. For example, batch processing does not produce products with properties, such as residual moisture, color, flavor or chemical composition, as consistent as products of steady-state continuous processes, because inherent variations can occur from batch to batch. Batch processing does not lend itself to statistical process controls. Batch processing is less efficient than continuous processing. While continuous processing of liquids under vacuum is possible in TFEs, continuous processing of solids under vacuum poses significant problems. For example, free-flowing solids cannot be continuously fed into conventional TFE-type driers. Also, the high rotational speeds of TFE-type dryers can impart shear energy into the solids with potential negative consequences, such as product degradation due to over-heating.

SUMMARY OF EMBODIMENTS

[0009] An embodiment of the present invention provides a continuous solids dryer. The continuous solids dryer includes a cylindrical body, a first air lock valve assembly, a jacket surrounding at least a portion of the cylindrical body, a single rotor, at least eight baffles attached to the rotor, for each baffle, a distinct agitating bar/scraper, an adjustment rod, an adjustable weir and a second valve.

[0010] The cylindrical body has a longitudinal axis. The cylindrical body defines an inner surface and an inner volume within the inner surface. The cylindrical body has a first inlet port in fluid communication with the inner volume proximate one end of the cylindrical body. The cylindrical body has a first outlet port in fluid communication with the inner volume proximate a second end, opposite the first end, of the cylindrical body. The first outlet port defines a circular cross-section lumen. The lumen has a longitudinal axis.

[0011] The first air lock valve assembly is in fluid communication with the first inlet port.

[0012] The jacket surrounds at least a portion of the cylindrical body. The jacket defines a volume between the jacket and the at least a portion of the cylindrical body. The jacket includes a second inlet port and a second outlet port. Each second port is in fluid communication with the volume defined by the jacket.

[0013] The single rotor is disposed within the inner volume of the cylindrical body. The rotor has an axis of rotation. The axis of rotation is coaxial with the longitudinal axis of the cylindrical body. The rotor has a rotation direction.

[0014] The at least eight baffles are attached to the rotor. The at least eight baffles rotate with the rotor. Each baffle includes an annular sector having an angle of about 90-170 degrees.

Each baffle is attached at its minor radius to the rotor. Each baffle extends substantially perpendicularly from the rotor. Adjacent baffles are offset from each other about 20-80 degrees about the longitudinal axis of the cylindrical body. [0015] For each baffle, a distinct agitating bar/scraper is attached to a trailing side, given the rotation direction of the rotor, of the baffle. Each distinct agitating bar/scraper is not attached to any other baffle. Each agitating bar/scraper extends a length parallel to the longitudinal axis of the cylindrical body. Each agitating bar/scraper is disposed about 1/16-3/8 inch from the inner surface of the cylindrical body. Each agitating bar/scraper has a thickness, as measured along a line radially inward from the inner surface, of at least about 1/2 inch. Each baffle is spaced apart, longitudinally along the rotor, from an adjacent baffle a distance. The spacing distance is no greater than about the length of the mixer bar/scraper attached to the baffle.

[0016] The adjustment rod is coaxial with the longitudinal axis of the lumen. The adjustment rod is rotatable about the longitudinal axis of the lumen.

[0017] The adjustable weir is disposed in the lumen. The weir includes a plate perpendicular to the longitudinal axis of the lumen. The weir is shaped as a portion, less than all, of a circle. The portion of the circle is defined by a chord of the circle. The weir is attached at the center of the circle to the adjustment rod. The weir rotates with the adjustment rod.

[0018] The second valve is in fluid communication with the first outlet port, downstream of the weir.

[0019] A leading side, given the rotation direction of the rotor, of each baffle may be chamfered.

[0020] Each mixer bar/scraper may have a triangular cross-sectional shape. One side of the triangle may form an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

[0021] Each baffle may be sized to extend to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

[0022] The inner surface of the cylindrical body may be formed without machining.

[0023] Thickness of each baffle, measured along a line parallel to the longitudinal axis of the cylindrical body, may be tapered toward a leading edge, given the rotation direction of the rotor, of the baffle. The taper may extend along at least a portion of the annular sector of the baffle, such that the leading edge is thinner than other portions of the baffle. [0024] For each baffle, the leading edge may extend along an intersection of a first surface and a second surface of the baffle. The first surface may be flat. At least a portion of the second surfaces may be not parallel to the first surface.

[0025] At least a portion of the second surface may be parallel to the first surface.

[0026] The first surface may be perpendicular to the axis of rotation of the rotor.

[0027] Each mixer bar/scraper may have a triangular cross-sectional shape. One side of the triangle may form an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

[0028] Each baffle may be sized to extend to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

[0029] The second valve may include a second air lock valve assembly.

[0030] The continuous solids dryer may also include a detachable air-tight vessel having an interior in fluid communication with the first outlet port, downstream of the second valve.

[0031] The continuous solids dryer may also include a sparge gas inlet port. The rotor may define a hollow in fluid communication with the sparge gas inlet port. The rotor may further define a plurality of apertures extending between the hollow and an outside surface of the rotor.

[0032] The continuous solids dryer may also include a sparge gas inlet port. The rotor may define a hollow in fluid communication with the sparge gas inlet port. Each baffle may define a plurality of apertures on an outside surface thereof and in fluid communication with the hollow of the rotor.

[0033] The solids dryer may be capable of sustaining a vacuum of at least about 50 Torr

(6,666 Pa) within the inner volume of the cylindrical body.

[0034] Another embodiment of the present invention provides a reconfigurable continuous solids dryer. The reconfigurable continuous solids dryer includes a cylindrical body, a first air lock valve assembly, a jacket surrounding at least a portion of the cylindrical body, a single rotor, for each baffle, a distinct agitating bar/scraper, at least sixteen attachment points, at least eight baffles, an adjustment rod, an adjustable weir and a second valve.

[0035] The cylindrical body has a longitudinal axis. The cylindrical body defines an inner surface and an inner volume within the inner surface. The cylindrical body has a first inlet port in fluid communication with the inner volume proximate one end of the cylindrical body. The cylindrical body has a first outlet port in fluid communication with the inner volume proximate a second end, opposite the first end, of the cylindrical body. The first outlet port defines a circular cross-section lumen. The lumen has a longitudinal axis

[0036] The first air lock valve assembly is in fluid communication with the first inlet port.

[0037] The jacket surrounds at least a portion of the cylindrical body. The jacket defines a volume between the jacket and the at least a portion of the cylindrical body. The jacket includes a second inlet port and a second outlet port. Each second port is in fluid communication with the volume defined by the jacket.

[0038] The single rotor is disposed within the inner volume of the cylindrical body. The rotor has an axis of rotation. The axis of rotation is coaxial with the longitudinal axis of the cylindrical body. The single rotor has a rotation direction.

[0039] Each attachment point is permanently attached to the rotor. Each attachment point defines at least one hole suitable for receiving a bolt.

[0040] Each baffle is removably attached to the rotor via a respective one of the attachment points and a respective at least one bolt. Each baffle rotates with the rotor. Each baffle includes an annular sector having an angle of about 90-170 degrees. Each baffle extends from the rotor. The attachment points are distributed about the rotor to accept adjacent baffles at various offsets from each other in a range of about 20-80 degrees about the longitudinal axis of the cylindrical body. The attachment points are distributed about the rotor to accept adjacent baffles at various inter-baffle distances along the longitudinal axis of the cylindrical body.

[0041] For each baffle, a distinct agitating bar/scraper is attached to a trailing side, given the rotation direction of the rotor, of the baffle. The agitating bar/scraper is not attached to any other baffle. The agitating bar/scraper extends a length parallel to the longitudinal axis of the cylindrical body. Each baffle is spaced apart, longitudinally along the rotor, from an adjacent baffle. The spacing distance is no greater than about the length of the mixer bar/scraper attached to the baffle.

[0042] The adjustment rod is coaxial with the longitudinal axis of the lumen. The adjustment rod is rotatable about the longitudinal axis of the lumen.

[0043] The adjustable weir is disposed in the lumen. The weir includes a plate perpendicular to the longitudinal axis of the lumen. The weir is shaped as a portion, less than all, of a circle. The portion of the circle is defined by a chord of the circle. The weir is attached at the center of the circle to the adjustment rod for rotation therewith.

[0044] The second valve is in fluid communication with the first outlet port, downstream of the weir.

[0045] The leading side, given the rotation direction of the rotor, of each baffle may be chamfered.

[0046] Each mixer bar/scraper may have a triangular cross-sectional shape. One side of the triangle may form an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

[0047] Each baffle may be sized to extend to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

[0048] The inner surface of the cylindrical body may be formed without machining.

[0049] Thickness of each baffle, measured along a line parallel to the longitudinal axis of the cylindrical body, may taper toward a leading edge, given the rotation direction of the rotor, of the baffle. The taper may extend along at least a portion of the annular sector of the baffle. The leading edge may be thinner than other portions of the baffle.

[0050] The leading edge may extend along an intersection of a first surface and a second surface of the baffle. The first surface may be flat. At least a portion of the second surface may be not parallel to the first surface.

[0051] At least a portion of the second surface may be parallel to the first surface.

[0052] The first surface may be perpendicular to the axis of rotation of the rotor.

[0053] Each mixer bar/scraper may have a triangular cross-sectional shape. One side of the triangle may form an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

[0054] Each baffle may be sized to extend to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

[0055] The second valve may include a second air lock valve assembly. [0056] The reconfigurable continuous solids dryer may also include a detachable air-tight vessel. The vessel may have an interior in fluid communication with the first outlet port, downstream of the second valve.

[0057] The reconfigurable continuous solids dryer may also include a sparge gas inlet port. The rotor may define a hollow in fluid communication with the sparge gas inlet port. The rotor may further define a plurality of apertures extending between the hollow and an outside surface of the rotor.

[0058] The reconfigurable continuous solids dryer may also include a sparge gas inlet port. The rotor may define a hollow in fluid communication with the sparge gas inlet port. Each baffle may define a plurality of apertures on an outside surface thereof and in fluid communication with the hollow of the rotor.

[0059] The solids dryer may be capable of sustaining a vacuum of at least about 50 Torr

(6,666 Pa) within the inner volume of the cylindrical body.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0060] The invention will be more fully understood by referring to the following Detailed

Description of Specific Embodiments in conjunction with the Drawings, of which:

[0061] Fig. 1 is a plot showing an exemplary hypothetical drying rate, as known in the prior art.

[0062] Fig. 2 is a plot showing vapor pressures of selected components at various temperatures and pressures, as known in the prior art.

[0063] Fig. 3 is a perspective schematic illustration of a continuous solids dryer, according to an embodiment of the present invention.

[0064] Fig. 3 a is a line drawing of the continuous solids dryer of Fig. 3.

[0065] Fig. 4 is a cross sectional view (Section A-A) of a cylindrical body of the continuous solids dryer of Fig. 3.

[0066] Fig. 5 is another perspective schematic illustration of the continuous solids dryer of Fig. 3, in which an outlet port from the cylindrical body is more clearly visible.

[0067] Fig. 6 is a perspective schematic illustration of a rotor of the continuous solids dryer of Figs. 3-5, according to an embodiment of the present invention. [0068] Fig. 7 is a side view of a representative baffle of the continuous solids dryer of

Figs. 3-6, according to an embodiment of the present invention.

[0069] Fig. 8 is an enlarged view of a portion of the baffle of Fig. 7.

[0070] Fig. 9 is a top view of the baffle of Figs. 7 and 8.

[0071] Fig. 10 is a top view of a plate of a weir of the continuous solids dryer of Figs. 3-

6, according to an embodiment of the present invention.

[0072] Fig. 11 is a perspective illustration of a baffle, according to another embodiment of the present invention.

[0073] Fig. 12 is a perspective schematic illustration of a portion of a rotor shaft with several baffles of Fig. 11 attached thereto and disposed within a cylindrical body of a dryer, according to an embodiment of the present invention.

[0074] Fig. 12a is a line drawing of the portion of a rotor shaft of Fig. 12.

[0075] Fig. 13 is a perspective schematic illustration of the continuous solids dryer of

Fig. 3, without any inlet or outlet valves and without vapor outlet piping, but illustrating modules that may be used to construct the dryer, according to an embodiment of the present invention.

[0076] Fig. 14 is a perspective schematic illustration of a batch solids dryer made from some of the modules of Fig. 13, according to an embodiment of the present invention.

[0077] Fig. 15 is a perspective view of a baffle attachment point for a reconfigurable continuous solids dryer, according to an embodiment of the present invention.

[0078] Fig. 16 is a perspective view of a number of the attachment points of Fig. 15 attached to a rotor shaft of the reconfigurable continuous solids dryer, according to an embodiment of the present invention.

[0079] Fig. 17 is a perspective schematic illustration of the continuous solids dryer of

Fig. 5, with some external components removed to reveal internal components.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0080] In accordance with embodiments of the present invention, methods and apparatus are disclosed for continuous drying of solids under vacuum. These embodiments approximate plug-flow processing, thereby yielding narrow residence time distributions (RTD). "Plug flow" refers to processing in which material flows through a system, ideally with no back mixing. As a result, ideally, all particles have identical residence times. [0081] An extent to which a wet material dries is typically proportional to an amount of time the material is exposed to heat, assuming the material is exposed to a constant drying temperature. Ideally, all particles in a free-flowing solid should be dried equally, but at a minimum, none should be under-dried. Batch drying attempts to produce even drying by exposing an entire batch of material to heat for given amount of time. In some cases, the material is agitated while it dries, to promote even and more efficient drying. However, batch-to-batch variations in charge time, drying time, discharge time, and temperature and pressure can lead to variations in the final product.

[0082] In a continuous dryer, ensuring all particles are exposed to heat for approximately equal amounts of time is challenging. An amount of time a particle is exposed to heat in a dryer is referred to as residence time. Some particles may be exposed to heat longer than other particles, yielding a range of residence times. A distribution plot of residence times versus number or fraction of particles exposed to heat at the residence times is referred to as a residence time distribution (RTD) plot. In a continuous dryer, when operated under "steady- state" (non- changing) conditions (feed rate, temperature, pressure, agitator speed), one can expect a continuous, consistent mix of dried particles in the product stream, of varying individual residence times, dictated per the RTD. However, it is generally important to ensure the product stream does not contain any under-dried particles. Thus, for approximately equally dried particles, a relatively narrow RTD is desired, and for a product stream containing a minimum amount of under-dried products, an RTD with a non-gradual onset or "front end" is desired.

[0083] Embodiments of the present invention convey material through an elongated heated chamber in ways that ensure RTDs are narrow and do not have a gradual onset (which would be indicative of wet or under-dried feed material leaving the drier). A central rotor shaft extends longitudinally through the chamber and rotates relatively slowly. Sector-shaped baffles attached to the rotor shaft rotate along with the rotor shaft. The baffles are oriented at least approximately perpendicular to the longitudinal axis of the chamber. Thus, the baffles impede, but do not prevent, longitudinal movement of the material. The baffles are sized and positioned to counterbalance forces that drive the material longitudinally toward an output port and thus control speed of the longitudinal movement of the material, so as to achieve a relatively narrow RTD for the material and prevent short-circuiting of wet material through the unit. [0084] To maintain a vacuum in the drying chamber, embodiments of the present invention utilize air locks at their input ports. In some embodiments, each air lock includes two spaced-apart on/off valves (butterfly, gate, ball, ball segment, sliding disc or other suitable type). The air lock enables material to be admitted into the heated chamber, without losing vacuum. The air lock operates periodically. Each time the air lock operates, a predetermined quantity of material is admitted into the chamber. The amount admitted is small, compared to the capacity of the chamber. Less than about 25% of the chamber capacity is admitted each time the air lock operates.

[0085] To maintain the vacuum in the drying chamber, embodiments of the present invention also utilize valves at their output ports. In some embodiments, each output port valve includes a second air lock. Such an arrangement enables dried material that exits the chamber to dump into a bin, onto a conveyor or into some other equipment or container open to atmospheric pressure.

[0086] In other embodiments, a single output port valve is used, and a removable airtight material collection vessel is coupled to an output of the valve. In these cases, the valve may remain open, so dried material exits the chamber and enters the collection vessel. When the collection vessel is full, the valve may be temporarily closed, so the vessel may be uncoupled from the valve and taken away or emptied. An empty collection vessel is coupled to the valve and evacuated, and then the output port valve is reopened.

[0087] Assuming the time taken to replace the full collection vessel is relatively short, such as less than about the period of the input air lock, and less than about 25% of the mean residence time in the dryer, the drying process is effectively continuous and steady-state. In principle, the drying process can continue for an arbitrary amount of time, not limited to the amount of time required to dry material admitted by one cycle of the input air lock, and not limited to the amount of time required to dry the amount of material that fits simultaneously within the drying chamber. As used herein, continuous means more than the volume of a drying vessel may be dried, without opening the vessel and without breaking vacuum in the vessel. Continuous means material to be dried is fed into the drying vessel (including intermittently), transported through the length of the drying vessel and exited (even intermittently) from the vessel at an end opposite the feed end of the vessel. Batch versus Continuous Dryers

[0088] A primary difference between a batch dryer and a continuous dryer is movement of material. In a batch dryer, wet solid material is placed into a dryer, the batch of material is dried and then all the material is removed once the required residence time, and thus dryness, has been met. Some conventional batch dryers stir the material while it dries. However, stirring does not involve transporting the material along a length of the drier, such as from an inlet port to an outlet port. Batch dryers do not include elements for transporting material longitudinally within the dryers.

[0089] In contrast, in a continuous dryer, material must be continuously conveyed from one end of the dryer, proximate an inlet port, to the other end of the dryer, proximate an outlet port. Embodiments of the present invention simultaneously convey and stir material, while minimizing longitudinal dispersion. That is, these embodiments at least approximate plug-flow processing and, therefore, provide relatively narrow RTDs.

[0090] Another important difference between a batch dryer and a continuous dryer is the mechanics of the two operations. With a batch dryer, wet material is charged (placed) into the machine under atmospheric pressure. The vessel is then sealed so that vacuum can be applied. Once at the desired sub-atmospheric operating pressure, the material is held for a required residence time to achieve a target moisture specification. After this time has elapsed, the vessel is vented and brought back to atmospheric pressure, at which time the material can be removed from the machine, and the dried material can proceed to further processing.

[0091] In contrast, for a vacuum dryer to operate continuously, the material must be both fed and discharged while the drying vessel is under vacuum. With liquid feeds, a back-pressure valve, or a similar orifice device, placed directly at the inlet of the dryer vessel can be used as a barrier between a high-pressure condition (pump discharge pressure) and a low pressure condition (dryer vessel operating at a lower pressure). Naturally, due to voids between particles in a free-flowing solid, back-pressure valves or the like cannot maintain a vacuum-to-atmosphere seal in a feed or discharge line, as they can with liquids. Quantitative Principles involved in Drying

[0092] Drying of solids may be simplified into two well-understood operations, i.e., constant-rate drying and diffusion-rate drying. Constant-rate drying refers to removal of "free" moisture. Free moisture is liquid mainly on the surface of particles or held between particles. Constant-rate drying may be modeled by a familiar equation for heat transfer, q(BTU/hr), according to equation (1).

q = UA(T_m - T_s) (1) [0093] In equation (1), U is the overall heat transfer coefficient (BTU/hr-ft²-°F). A is the heat transfer surface area available (ft²). For a rotary dryer, this may be the internal surface area of the heated cylinder. T_m is the temperature of the heat transfer medium, and T_s is the temperature of the solid particle (°F). Equation (1) may be varied if heat is transferred by conduction to affect evaporation.

[0094] Diffusion-rate drying refers to mass transfer of "bound" moisture within particle pores to the particle's surface and its subsequent evaporation to a surrounding atmosphere. In this case the drying rate can be approximated by equation (2).

= K(X - X_e) (2)

[0095] Here, X is the concentration of volatiles in the solid, X_e is the equilibrium volatiles concentration in the surrounding atmosphere, K is the mass-transfer coefficient (ft./min.) and t is time (min). As shown in Fig. 1, the drying rate slows considerably as moisture removal proceeds. In Fig. 1, "constant rate" drying (the horizontal portion of the plot) is governed by heat transfer, as described by equation (1). "Falling rate" drying refers to drying as a result of diffusion mass transfer and is governed by equation (2).

[0096] The overall residence time required may be found by solving both equations (1) and (2) separately, and then determining the interaction between the two equations. For constant- rate drying, the equipment-dependent £/-value can be found by summing individual resistances to heat transfer, as shown in equation (3).

= + + + + (3)

U h_h h_w h_f h_m h_v

[0097] Here, — is resistance to heat transfer between the heating medium and the

hh

conducting wall of a dryer. For a jacketed rotary dryer, this resistance, for example, could be related to steam condensing on the cylinder wall, or dryer process shell, that separates the steam heat source from material being dried.— is the resistance to heat transfer across the cylinder

h_w

wall. For a jacketed rotary dryer, this is conduction across the material of construction for the dryer process shell.— is the resistance to heat transfer between the inner dryer process shell wall hf

and the surface of the bed of drying material touching the wall.— is the resistance to heat transfer across the bed of drying material and — is the resistance to heat transfer at the evaporating surface. While h_h and h_w can be calculated based on known properties of the heating medium and the conducting wall, h h_m, and h_v are specific to a particular material and may be determined empirically.

[0098] Operating a process under vacuum enables residual moisture to evaporate at reduced temperatures. This is important for solids that are sensitive to heat. In the case of solids drying, the propensity of residual moisture to evaporate is related to its vapor pressure at a corresponding temperature. Equation (4), known as Antoine's Equation, can approximate the relationship between vapor pressure and temperature of a pure substance.

log₁₀P = A - _c- (4)

[0099] Here, P is the vapor pressure of a substance in Torr (or mm Hg absolute), J is the temperature of the substance and A, B, and C are coefficients that are specific to the same. Table 1 includes examples of Antoine's parameters for water, where pressure is in Torr and temperature is in °C.

Table 1 : Antoine's Parameters for Water

No. A B C Tempmin CC) Temp_max(°C)

1 8.07131 1730.63 233.426 1 100

2 8.14019 1810.94 244.465 99 374

[0100] Fig. 2 is a graph illustrating vapor pressures of selected components at various temperatures and pressures. The graph may be used to ascertain preliminary drying conditions for removing particular volatile components.

[0101] As an example, at standard atmospheric pressure (760 Torr), water is at its saturation vapor pressure at a temperature of 212°F (100°C). This is generally referred to as its normal boiling point. If the pressure in the dryer were reduced to 100 Torr, the same tendency for evaporation would be realized at a temperature of approximately 125°F (52°C). This example illustrates a solution for a drying challenge where water is desired to be removed from a product that is sensitive to temperatures greater than 150°F (66°C), for example. Drying under vacuum applies to both the constant and falling-rate regimes.

[0102] Modeling the falling-rate (diffusion-rate) period of drying may involve experimentally determining correlations for a particular material. Values of the mass-transfer coefficient K are dependent on solubility parameters, particle temperature, porosity, size, surface texture and equilibrium concentration constants. Table 2 lists empirically determined drying constants for several exemplary products.

Table 2: Empirically determined mass transfer coefficients for selected materials Product Equation

Ξ

Barley K = b_Qe ^TA

Rice K= b₀ + b_±T_A— b₂a_w

Carrots _{K= e} (-b_{1 +}b₂ in u_A)

[0103] Here, K is a drying constant; ¾ is temperature; UA is air velocity; a_w is water activity; and bo, bj, and b₂ are constants.

A Continuous Solids Dryer According to one Embodiment

[0104] Fig. 3 is a perspective schematic illustration of a continuous solids dryer 300, according to an embodiment of the present invention. Some portions of the dryer 300 are shown as being transparent for illustration purposes. The dryer 300 includes a cylindrical body 302 that has a longitudinal axis 304. Fig. 4 is a cross sectional view (Section A-A) of the cylindrical body 302 of Fig. 3. The cylindrical body 302 is circular in cross-section, as taken perpendicular to the longitudinal axis 304. At least a portion of the cylindrical body 302 includes two coaxial cylindrical members 400 and 402. The inner member 402 of the cylindrical body 302 defines an inner surface 404 and an inner volume 406 within the inner surface 404.

[0105] The outer member 400 forms a jacket that surrounds at least a portion of the inner member 402 of the cylindrical body 302. The jacket 400 defines a volume 408 between the jacket 400 and at least a portion of the cylindrical body inner member 402. The jacket 400 includes an inlet port 306 and an outlet port 308. Both the inlet port 306 and the outlet port 308 are in fluid communication with the volume 408 defined by the jacket 400.

[0106] Steam, heated oil or another fluid may be circulated through the volume 408, via the inlet and outlet ports 306 and 308. The fluid heats the inner member 402 and, therefore, the inner surface 404 of the cylindrical body 302. Wet solids, represented by solids 410, are dried by heat from the inner surface 404 of the cylindrical body 302. In some embodiments, chilled, rather than heated, fluid is circulated through the volume 408 defined by the jacket 400, in which case the solids 410 are cooled, rather than heated.

[0107] Some embodiments include multiple jackets, each of which may have a different temperature fluid flow through it. For example, as shown in Fig. 3, a second set of inlet and outlet ports 344 and 346 may be included. These inlet and outlet ports 344 and 346 maybe in fluid communication with a second jacket that is fluid-isolated from the above-described jacket 400.

[0108] The cylindrical body 302 includes an inlet port 309 in fluid communication with the inner volume 406 of the cylindrical body 302. As can be seen in Fig. 3, the inlet port 309 is proximate one end 310 of the cylindrical body 302. A vapor outlet port 312 is also in fluid communication with the inner volume 406 of the cylindrical body 302. Vapors released by the solids 410 within the dryer 300 may be drawn off via the vapor outlet port 312. The vapor outlet port 312 may also be used to draw a vacuum within the inner volume 406 of the cylindrical body 302. A sight glass 313 may also be provided, so the inner volume 406, and in the particular material 410 being dried therein, may be observed.

[0109] The cylindrical body 302 also includes an outlet port 314 in fluid communication with the inner volume 406 of the cylindrical body 302. The outlet port 314 is proximate the other end 316 of the cylindrical body 302, opposite the first end 310 of the cylindrical body 302.

[0110] Fig. 5 is another perspective schematic illustration of the continuous solids dryer

300, in which the outlet port 314 from the cylindrical body 302 is more clearly visible. The outlet port 314 from the cylindrical body 302 defines a circular cross-section lumen 500 in fluid communication with the inner volume 406 of the cylindrical body 302. The lumen 500 has a longitudinal axis 502.

[0111] Returning to Fig. 3, an air lock valve assembly 318 includes a chamber 319 and is coupled in fluid communication with the inlet port 309 of the cylindrical body 302. A feed hopper, conveyor, or other source (not shown) of free-flowing solids to be dried may be coupled to an inlet 320 of the air lock valve assembly 318. The air lock valve assembly 318 may include two butterfly valves, two gate valves or any other arrangement of members, represented by valves 322 and 324, on opposite sides of the air lock chamber 319 that enable the air lock valve assembly 318 to admit a quantity of the wet free-flowing solids via its inlet 320, into the chamber 319, without breaking the vacuum in the cylindrical body 302.

[0112] Closing the bottom valve 324 maintains the vacuum in the cylindrical body 302 while the air lock chamber 319 accepts the quantity of wet solids. Opening the top valve 322 admits the quantity of wet free-flowing solids into the air lock chamber 319. Once the quantity of wet solids has been admitted, the top valve 322 is closed, and the air lock chamber 319 may be evacuated via an evacuation port (not visible), such that its internal pressure becomes approximately equal to the pressure inside the cylindrical body 302. Once the air lock chamber 319 has been evacuated, the bottom valve 324 is opened to transfer the quantity of feed solids from the air lock chamber 319 to the inner volume 406 of the cylindrical body 302. As noted, each time the air lock valve assembly 318 operates, a predetermined quantity of solids, typically determined by the volume of the chamber 319, is admitted into the cylindrical body 302. The amount admitted is small, compared to the capacity of the cylindrical body 302, and the air lock cycle time is small, compared to the average residence time of the solid materials within cylindrical body 302.

[0113] A single rotor 326 is disposed within the inner volume 406 of the cylindrical body. A motor 328 and drive 330 rotate the rotor 326 about an axis of rotation, which is coaxial with the longitudinal axis 304 of the cylindrical body 302. The rotor 326 is rotated in a rotation direction, for example as indicated by an arrow 332. The rotor 326 is rotated at a rotation speed that depends on the material being dried, temperature of the inner surface 404 of the cylindrical body 302 and other process parameters. In some embodiments, the rotor 326 may be rotated at about 5-200 RPM, although other rotation speeds may be used.

[0114] Fig. 6 is a perspective schematic illustration of the rotor 326, according to an embodiment of the present invention. The rotor 326 includes a shaft 600 and at least six baffles, represented by baffles 602, 604 and 606, attached to the shaft 600. Each baffle 602-606 extends substantially perpendicularly from the axis 607 of the shaft 600. The baffles 602-606 rotate with the shaft 600, for example as indicated by an arrow 608. [0115] An agitating bar/scraper, represented by agitating bars/scrapers 610, 612 and 614, is attached to each baffle 602-606. Each agitating bar/scraper 610-614 is attached to a trailing side of its respective baffle 602-606, given the rotation direction 608 of the rotor 326. The agitating bars/scrapers 610-614 are distinct. That is, each baffle 602-606 has its own agitating bar/scraper 610-614. No agitating bar/scraper 610-614 is attached to more than one of the baffles 602-606.

[0116] Each agitating bar/scraper 610-614 has a length 616 parallel to the longitudinal axis 304 of the cylindrical body 302. Adjacent baffles, such as baffles 602 and 604, are spaced apart longitudinally along the shaft 600 a distance 618 no greater than the length 616 of the agitating bar/scraper 610-614. Consequently, as the shaft 600 turns, collectively the agitating bars/scrapers 610-614 sweep over a longitudinally contiguous area of the inner surface 404 of the cylindrical body 302. Prior art thermal processing equipment, such as a Model 8W twin- shaft paddle dryer/cooler from Komline-Sanderson, does not sweep the entire area of the inner surface, leaving ridges of material stuck to the inner surface.

[0117] Fig. 17 is a perspective schematic illustration of the continuous solids dryer 300, from the same perspective as in Fig. 5, with some external components removed to reveal internal components.

[0118] In some embodiments of the present invention, the agitating bars/scrapers 610-

614 are longer 616 than the inter-baffle spacing 618. In such embodiments, the agitating bars/scrapers 610-614 sweep out overlapping areas on the inner surface 404 of the cylindrical body 302.

[0119] Adjacent baffles 602-606 are offset from each other about 20-80° about the longitudinal axis 304 of the cylindrical body 302, as indicated at 620.

[0120] Fig. 7 is a side view of a representative baffle 700 of the baffles 602-606, and Fig.

8 is an enlarged view of a portion of the baffle 700. Fig. 8 includes a portion of the inner surface 404 of the cylindrical body 302. As can be seen in Fig. 7, the baffle 700 includes an annular sector 702 of about 90-170°. In some embodiments, the annular sector is about 135°. The baffle 700 is attached to the shaft 600 (Fig. 6) at a minor radius 704 of the annular sector. The direction of rotation is indicated by an arrow 608. As a result of this rotation, the baffle 700 has a leading side 708 and a trailing side 710. [0121] An agitating bar/scraper 610-614 can be seen at 712. The agitating bar/scraper

712 is attached to the trailing side 710 of the baffle 700, given the direction of rotation 608. The agitating bar/scraper 712 has a thickness 714, as measured along a line radially inward from the inner surface 404 of the cylindrical body 302, of about 1/2 to about 1 inch (15-25mm), although other sizes may be used. In general, the thickness 714 should be sufficient to impart mechanical strength sufficient to withstand expected forces agitating expected materials.

[0122] In some embodiments, as shown in Fig. 7, the agitating bar/scraper 712 has a triangular cross section, as indicated by section marks in Fig. 8. One side 800 of the triangle forms an acute angle 802 with a tangent to the inner surface 404 of the cylindrical body 302. In other embodiments, the agitating bar/scraper 712 may have other cross-sectional shapes. Although Figs. 7 and 8 show a right isosceles triangular agitating bar/scraper 712, in other embodiments other triangular or non-triangular shapes may be used. For example, as shown in an insert in Fig. 7, an agitating bar/scraper 713 with a relatively thin rectangular cross section may be used.

[0123] The agitating bar/scraper 712 is disposed a distance 804 of about 1/16-3/8 inch

(1.6-9.5 mm) from the inner surface 404 of the cylindrical body 302. This distance may be selected to be small enough to prevent individual items, such as coffee beans, in the free-flowing solid to fit between the agitating bar/scraper 712 and the inner surface 404 of the cylindrical body 302. Due to manufacturing imperfections in the inner member 404 (Fig. 4), the spacing 804 between the agitating bar/scraper 712 and the inner surface 404 of the cylindrical body 302 may vary, within a tolerance, about the inner circumference of the cylindrical body 302, i.e., as the rotor 326 rotates. Particularly with large granule sizes, such as coffee beans, the inside diameter defined by the inner surface 404 of the cylindrical body 302 need not necessarily be precisely machined, or machined at all. Consequently, commercial off-the-shelf pipe or tubing may be used for the cylindrical body 302, without machining, thereby saving cost and manufacturing time.

[0124] The agitating bars/scrapers 610-614 perform several functions. As the rotor 326 turns, the agitating bars/scrapers 610-614 agitate solids 410 (Fig. 4) in the dryer 300, so particles in the solids are approximately equally exposed to heat from the inner surface 404 of the cylindrical body 302. The acute angle 802 (Fig. 8) of the agitating bars/scrapers 610-614 prevents solids sticking to the inner surface 404 of the cylindrical body 302. The acute angle 802 also aids in agitating the solids. As can be seen in Fig. 6, in some embodiments, each agitating bar/scraper 610-614 forms a "T" shape, as enclosed by dashed line 621, with its corresponding baffle 602-606. This "T" shape reduces the number of baffles required along the length of the shaft 600, while fully covering the inner surface 404 of the cylindrical body 302.

[0125] Returning to Fig. 8, an outer edge 806 of the baffle 700 may be spaced 808 from the inner surface 404 of the cylindrical body 302 the same as the agitating bar/scraper 712 is spaced 804 from the inner surface 404. That is, the baffle 700 may be sized to extend to within about 1/16-3/8 inch (1.6-9.5 mm) of the inner surface 404 of the cylindrical body 302. In other embodiments, baffle 700 may be sized differently, so the edge 806 of the baffle 700 is closer or further from the inner surface 404 of the cylindrical body 302 than the agitating bar/scraper 712, as desired.

[0126] Fig. 9 is a top view of the baffle 700. The leading side 708 of the baffle 700 may be chamfered. This chamfer can also be seen in Fig. 6, for example at 622. Returning to Fig. 9, given the direction of rotation 608, as the baffle 700 rotates, the chamfer drives material in the cylindrical body 302 in a direction indicated by an arrow 900, longitudinally along the cylindrical body 302. This longitudinal translation of material being dried is indicated by an arrow 334 in Fig. 3. Although a straight chamfer is shown in Fig. 9, other shapes, such as convex or concave curves, including compound curved surfaces, may be used.

[0127] Achieving a desired residence time and plug flow (narrow residence time distribution) requires balancing two opposing forces on material to be dried. One force urges the material to translate longitudinally inside the cylindrical body 302, as indicated by an arrow 334 in Fig. 3. This force is provided in part by material being added to the cylindrical body 302 via the inlet port 309 and in part by chamfers on leading sides of the baffles 602-606 as the baffles rotate. Agitating the material with the agitating bars/scrapers 610-614 keeps the material free flowing by preventing the material packing down and, therefore, promotes the longitudinal translation of the material.

[0128] Unlike the prior art, for example a model DISCOTHERM 50 000 CONTI from

List AG, embodiments of the present invention include segmented agitating bars/scrapers 610-

614. That is, no agitating bar/scraper extends, and is attached, to several baffles 602-606. An agitating bar/scraper that extends across all baffles, as in the above-referenced prior art dryer, acts as a flight of a screw feed, which translates material too quickly and preferentially translates material located near the outside diameter of the baffles, over material located closer to the rotor shaft, leading to a wide RTD.

[0129] The other force inhibits the longitudinal translation of the material. The inhibiting force is provided by sides of the baffles 602-606. The sides of the baffles 602-606 act as partial dams. However, inasmuch as each baffle 602-606 occupies only about 90-170° (angle 702) of the cross-sectional area of the inside of the cylindrical body 302, and adjacent baffles 602-606 are offset from each other about 20-80° (angle 620), material can bypass each baffle 602-606 at a controlled rate. Thus, the combination of the offset 620 between adjacent baffles 602-606, the segmented agitating bars/scrapers 610-614, and the annular sector angle 702 provides a good balance between inhibiting longitudinal translation of material to be dried and longitudinal propulsion of the material, thereby providing narrow RTDs.

[0130] As best seen in Fig. 5, an adjustable weir 504 is disposed within the lumen 500 defined within the outlet port 314 from the cylindrical body 302. The weir 504 controls the fill level of dried material in the outfeed end of the cylindrical body 302. The weir 504 includes a plate disposed perpendicular to the longitudinal axis 502 of the lumen 500. Fig. 10 is a top view of the plate 1000 of the weir 504. The plate 1000 is shaped as a portion, less than all, of a circle.

[0131] The outer edge 1002 of the circular portion of the plate is sized to fit within the circular cross-section of the lumen 500 with enough clearance to permit rotation of the plate 1000 about its center 1004, preferably without the outer edge 1002 touching the inside wall of the outlet port 314. The clearance should, however, be sufficiently small to prevent any or an appreciable amount of dried material passing between the outer edge 1002 of the weir 504 and the inside wall of the outlet port 314.

[0132] The portion of the circle may be defined by cutting a circular plate along a straight or curved line. In the embodiment shown in Fig. 10, the plate is cut along a straight line 1006. In the embodiment shown in Fig. 10, the plate is cut along a chord of the circle. As best seen in Fig. 5, the plate 1000 is attached at the center 1004 of the circle to an adjustment rod 506. The adjustment rod is coaxial with, and rotatable about, the longitudinal axis 502 of the lumen 500. The adjustment rod 506 may be mechanically coupled to an adjustment knob 336, shown in Figs. 3 and 5. Rotating the adjustment knob 336 rotates the adjustment rod 506 and, consequently, the plate 1000 of the weir 504. An optional second sight glass 337 enables observation of the weir 504. Optionally or alternatively, the adjustment rod 506 may be rotated by a motor (not shown) coupled to an automatic control system (not shown)

[0133] The angle of the line 1006 of the plate 1000 determines an allowable fill level of material in the outfeed end 316 of the cylindrical body 302 (Fig. 5). In general, enough dried material must build up behind the plate 1000 to overflow the lowest portion of the line 1006. If the line 1006 is horizontal and at the top of the rotation of the weir 504, the weir 504 provides a maximum fill level of the dried material within the dryer, and if the line 1006 is horizontal and at the bottom of the rotation of the weir 504, the weir 504 provides a minimum fill level. Intermediate rotations of the weir 504 provide intermediate fill levels. Thus, rotating the weir 504 through 180° can adjust the weir 504 from its maximum fill level to its minimum fill level. The weir 504 may be rotated to any desired angle. The weir 504 may be adjusted by turning the knob 336 to adjust residence time of material being dried by the dryer 300.

[0134] A typical prior art weir includes a fully circular plate with a circular hole cut therethrough. Such a weir is subject to clogging due to the limited flow-through area provided by the circular hole. In contrast, the weir 504 is much less likely to clog, because it provides a much larger flow-over area than a comparably- sized prior art weir. In addition, cutting a circular disk along a straight line, as in the embodiment of Fig. 10, is easier and less expensive than cutting a circular hole in the disk, such as with a milling machine or hole saw, as in the prior art.

[0135] As best seen in Fig. 5, downstream of the weir 504, the outlet port 314 includes a nozzle 508. As shown in Fig. 3, a second valve 338 is coupled in fluid communication with outlet port 314, via the nozzle 508. A collection vessel (not shown) capable of holding a vacuum may be coupled to an output 340 of the second valve 338. Alternatively, a second air lock (not shown) may be used as the second valve 338.

[0136] Some embodiments of the solids dryer 300 are capable of sustaining a vacuum of at least about 1 Torr (133 Pa) within the inner volume 406 of the cylindrical body 302. Some embodiments are capable of sustaining a vacuum of at least about 5 Torr (666 Pa). Other embodiments are capable of sustaining a vacuum of at least about 50 Torr (6,666 Pa). In part, the circular cross-sectional shape of the cylindrical body 302 facilitates sustaining such a vacuum.

For example, some prior art dryers, such as the Model 8W twin-shaft paddle dryer/cooler from

Komline-Sanderson, have large removable rectangular flat top plates. Sealing such a removable flat plate sufficiently to maintain a required vacuum is difficult, in part because a gasket must extend along the entire perimeter of the plate. Furthermore, the large plate and a large body to which it is removably attached can deflect under atmospheric pressure, thereby distorting the body and/or plate over regimes that should remain in intimate contact with the gasket.

[0137] Having a single rotor and the consequential circular cross-sectional shaped body

302, as in embodiments of the present invention, therefore provides advantages over prior art dryers. For example, main sections 1300, 1302 and 1304 (described below, with respect to Fig. 13) may be connected using much smaller O-rings than the gaskets required for the above- described Komline-Sanderson device. Furthermore, a single rotor dryer is less expensive to manufacture than a twin rotor dryer.

[0138] Experiments performed with a prototype solids dryer similar to the one described with respect to Figs. 3-10 yielded actual residence time distributions in line with calculated mean theoretical residence times (MTRT) and values that would be commercially desirable. It was found that annular sector angles and adjacent baffle offsets, as described herein, yielded desirable RTD better than prior art devices yielded. These are not, therefore, mere design choices.

[0139] In some embodiments, to increase the heat transfer area-to-volume ratio of the dryer, the rotor shaft 600 (Fig. 6) and, optionally, the baffles 602-606 are hollow, and heated fluid flows through the shaft 600 and, optionally, the baffles 602-606.

Alternative Baffles

[0140] Fig. 11 is a perspective illustration of a baffle 1100, according to another embodiment of the present invention. The baffle 1100 is similar to the baffle 700 of Fig. 7, in that the baffle 1100 includes an annular sector 1102 and an agitating bar/scraper 1104. The baffle

1100 also attaches to the rotor shaft 600 (Fig. 6) at a minor radius 1106 of the annular sector

1102, and the baffle rotates in a direction indicated by an arrow 1108. The baffle 1100 has a first face (surface) 1110 and an opposite second face (surface) 1112. The second face 1112 is not visible in Fig. 11. The two faces 1110 and 1112 intersect at a leading edge 1113 of the baffle

1100, given the direction of rotation 1108 of the baffle 1100. A distance between the two faces

1110 and 1112, at any point such along the annular sector 1102 and measured along a line parallel to the longitudinal axis 304 (Fig. 3) of the cylindrical body 302, defines a thickness of the baffle 1100 at that point. An exemplary thickness is indicated at 1114. [0141] However, rather than a chamfer, the baffle 1100 is tapered toward the leading edge 1113. That is, the thickness of the baffle 1100 is tapered toward the leading edge 1113. This taper extends along at least a portion 1116 of the annular sector 1102. The leading edge 1113 is thinner than other portions of the baffle 1100. In the embodiment shown in Fig. 11, the thickness of the baffle 1100 at 1118 is equal to the thickness at 1114. However, continuing along the annular sector 1102, beginning at a location indicated by dashed line 1120, the thickness of the baffle 1100 progressively decreases toward the leading edge 1113. Thus, the thickness at 1122 is less than at 1118, and the thickness at 1124 is less than at 1122.

[0142] In the embodiment shown in Fig. 11, the first face 1110 is flat and perpendicular to the longitudinal axis 304 (Fig. 3) of the cylindrical body 302 and perpendicular to the axis of rotation of the rotor 326. The second face 1112 is not flat. A portion 1117 of the second face 1112 is parallel to the first face 1110, but the portion 1116 of the second face 1112 is not parallel to the first face 1110. In some embodiments, the second face 1112 defines a dihedral angle, although the transition between the two planes of the dihedral angle need not be a ridge line. That is, the transition may be rounded over.

[0143] Fig. 12 is a perspective schematic illustration of a portion of rotor shaft 1200 with several baffles 1100, exemplified by baffles 1202, 1204 and 1206, attached thereto and disposed within a cylindrical body 1208 of a dryer, according to an embodiment of the present invention. The body 1208 is shown as being transparent for illustration purposes.

[0144] Returning to Fig. 11, in other embodiments, the portion 1116 of the second face

1112 need not be flat. In some embodiments, the portion 1116 of the second face 1124 is curved. The curve may be simple or compound. The curve may form a convex or a concave face portion. In yet other embodiments, both faces 1110 and 1112 are tapered, and may be flat or include curves, as described with respect to the second face 1112. In some embodiments, the first face 1110 is not perpendicular to the longitudinal axis 304 (Fig. 3) of the cylindrical body 302 and not perpendicular to the axis of rotation of the rotor 326. In such embodiments, the entire baffle 1100 may contribute to translating material longitudinally along the length of the dryer 300.

Sparge Gas Option

[0145] Optionally, dry gas, such as air or nitrogen, may be sparged directly into the inner volume 406 (Fig. 4) of the cylindrical body 302 via a sparging inlet (not shown) that is in fluid communication with the inner volume 406. In some embodiments, the rotor shaft 326 (Fig. 6) is hollow and the sparging inlet is in fluid communication with the rotor shaft hollow. The rotor shaft 326 and/or the baffles 602-606 may define apertures, represented by apertures 624-628, through which the sparge gas may be introduced into the inner volume 406 of the cylindrical body 302. Sparging effectively maintains a dry surrounding atmosphere within the inter volume 406, as the rotor 326 agitates the material and brings moisture-containing particles to the bed's surface. For explosive or combustible solids, the sparge gas can be an inert gas, such as nitrogen. Sparging promotes diffusion by reducing Xe in equation (2), thus decreasing residence time required for diffusional mass transfer. Sparge gas velocity also has an effect on the mass transfer coefficient in some materials, as presented in Table 2.

[0146] Table 3 lists some operational parameters that may be adjusted to meet requisite dryer residence times.

Table 3 : Exemplary Adjustable Operational Parameters

Feed rate

Bed volume/height (by manipulation of the discharge weir)

Heating medium type (hot water, hot oil, saturated steam)

Heating medium temperature and flow rate

Rotor speed

Dry gas/sparge rate/velocity

Operating pressure/vacuum

Batch Configuration

[0147] Although a solids dryer 300 (Fig. 3) that operates continuously has been described, in an alternative embodiment, some components of the dryer 300 may be reconfigured to operate in batch mode. As can be seen in Fig. 13, the solids dryer 300 can be constructed with three main sections 1300, 1302 and 1304. An air lock valve assembly 318 (as in Fig. 3), vapor outlet port 312 and second valve 338 are omitted from Fig. 13, for clarity. The first section 1300 may be termed an infeed/process section. The second section 1302 may be termed a process section. The second section 1302 may be identical to the first section 1300. The third section 1304 may be termed an outfeed section. [0148] Removing the second and third sections 1302 and 1304, replacing the rotor 326 with a shorter rotor, possible with fewer baffles, and attaching a detachable end cap 1400, optionally with a sight glass 1402, to the first section 1300 yields a batch dryer 1404, as shown in Fig. 14. The batch dryer 1404 may be loaded through the top port 313 and emptied by removing the end cap 1400. What served as the inlet port 309 when the first section 1300 is used in a continuous dryer 300 may be used to withdraw vapors and draw a vacuum in the batch dryer 1404. Thus, the components 1300, 1302 and 1304 may be used in a modular fashion to construct either a continuous dryer 300 or a batch dryer 1404 or to reconfigure either dryer 300 or 1404.

[0149] The batch dryer 1400 may be used to perform experiments on solids to be dried, such as to empirically determine parameters, such as drying temperature, rotor rotation speed and drying time. Once a material's required dryer residence time has been determined using the batch configuration, the volumetric flow rate range for a given dryer size can be estimated using equations (5), (6) and (7).

Vw.max = °-⁵ * V_F)and min = 0.2 * (y_F (6)

V_W ,max

vR,range °^ R _DT_T \ ' )

[0150] Here, V_F is the total volume of the dryer, d_{S ID} is the inside diameter of the dryer process shell (ft.), d_{r 0D} is the outside diameter of the rotor shaft (ft), L is dryer inside length (ft.), V_w is the steady state working volume (ft³), calculated as a percentage of the total volume and assumed to be about 20-50%, RT is the residence time required (min.) and V_{R range} is the ft³

range of volumetric flow rates (——) for a particular dryer size.

min

Reconfigurable Continuous Solids Dryer

[0151] In some embodiments, the baffles 602-606 (Fig. 6) are permanently attached to the rotor shaft 600, such as by welding. In other embodiments, interchangeable baffles may be removably attached to the rotor shaft to provide a reconfigurable continuous solids dryer. In particular, the rotor shaft may have plural attachment points, and baffles may be selectively attached to some, but not necessarily all, of the attachment points. Furthermore, in some embodiments, the baffles may be attached to the attachment points at selectable angles, relative to the longitudinal axis of the rotor shaft, not necessarily perpendicular to the longitudinal axis of the rotor shaft. Such embodiments facilitate experimenting with various baffle shapes, various numbers of baffles attached to the rotor shaft and/or various baffle angles, not all necessarily the same, and other variations.

[0152] Fig. 15 is a perspective view of a baffle attachment point 1500, according to an embodiment of the present invention. The baffle attachment point 1500 defines an inner radius 1502, along which the attachment point 1500 may be permanently attached, such as by welding, to the rotor shaft. The inner radius 1502 should match the outside radius of the rotor shaft. Fig. 16 is a perspective view of a number of attachment points, represented by attachment points 1600, 1602 and 1604, attached to a rotor shaft 1606.

[0153] The number and placement of the attachment points 1600-1604 should be sufficient to permit attachment of baffles according to various arrangements, such as at various offset angles between adjacent baffles and/or at various longitudinal spacings between adjacent baffles. In some embodiments, at least sixteen baffle attachment points 1600-1604 are attached to the rotor shaft 1606. In other embodiments, more or fewer attachment points 1600-1604 may be used. Groups of the attachment points 1600-1604 may be distributed about the circumference of the rotor shaft 1606, for example at about 20° offsets (about a longitudinal axis 1608 of the rotor shaft 1606). As noted, not all the attachment points 1600-1604 may necessarily be used in a given experiment or use.

[0154] Returning to Fig. 15, each baffle attachment point 1500 defines a suitable number, such as two, of holes 1504 and 1506 therethrough. The holes 1504 and 1506 may, but need not, be internally threaded. A baffle, such as the baffle described with reference to Figs. 7-9 or the baffle describe with reference to Figs. 11 and 12 or any other baffle, may be removably attached to the attachment point 1500 with bolts and nuts or other suitable fasteners. "Removably attached" here means the baffle may be detached from the baffle attachment point 1500 without damaging either the baffle or the baffle attachment point 1500. After removal, the baffle may be removably reattached to the same or a different baffle attachment point. If the baffle is not reattached to the same baffle attachment point, another baffle may, but need not, be attached to the baffle attachment point. Such a reconfigurable continuous solids dryer may, for example, find utility in a pilot plant, such as for experimentally determining a desired baffle size, shape, number, orientation, angular offset, annular sector angle, longitudinal distribution along the rotor shaft, chamfer angle and the like, given a particular material to be dried.

[0155] While the invention is described through the above-described exemplary embodiments, modifications to, and variations of, the illustrated embodiments may be made without departing from the inventive concepts disclosed herein. For example, although specific parameter values, such as dimensions and materials, may be recited in relation to disclosed embodiments, within the scope of the invention, the values of all parameters may vary over wide ranges to suit different applications. Unless otherwise indicated in context, or would be understood by one of ordinary skill in the art, terms such as "about" mean within +20%.

[0156] As used herein, including in the claims, the term "and/or," used in connection with a list of items, means one or more of the items in the list, i.e., at least one of the items in the list, but not necessarily all the items in the list. As used herein, including in the claims, the term "or," used in connection with a list of items, means one or more of the items in the list, i.e., at least one of the items in the list, but not necessarily all the items in the list. "Or" does not mean "exclusive or."

[0157] Disclosed aspects, or portions thereof, may be combined in ways not listed above and/or not explicitly claimed. In addition, embodiments disclosed herein may be suitably practiced, absent any element that is not specifically disclosed herein. Accordingly, the invention should not be viewed as being limited to the disclosed embodiments.

Claims

CLAIMS What is claimed is:

1. A continuous solids dryer, comprising:

a cylindrical body having a longitudinal axis, defining an inner surface and an inner volume within the inner surface and having a first inlet port in fluid communication with the inner volume proximate one end of the cylindrical body and a first outlet port in fluid communication with the inner volume proximate a second end, opposite the first end, of the cylindrical body, the first outlet port defining a circular cross-section lumen having a longitudinal axis;

a first air lock valve assembly in fluid communication with the first inlet port;

a jacket surrounding at least a portion of the cylindrical body, the jacket defining a volume between the jacket and the at least a portion of the cylindrical body, the jacket including a second inlet port and a second outlet port, each second port being in fluid communication with the volume defined by the jacket;

a single rotor disposed within the inner volume of the cylindrical body, the rotor having an axis of rotation coaxial with the longitudinal axis of the cylindrical body and a rotation direction;

at least eight baffles attached to the rotor for rotation therewith, each baffle comprising an annular sector having an angle of about 90-170 degrees, attached at its minor radius to the rotor and extending substantially perpendicularly from the rotor, adjacent baffles being offset from each other about 20-80 degrees about the longitudinal axis of the cylindrical body;

for each baffle, a distinct agitating bar/scraper attached to a trailing side, given the rotation direction of the rotor, of the baffle and not attached to any other baffle, the agitating bar/scraper extending a length parallel to the longitudinal axis of the cylindrical body, being disposed about 1/16-3/8 inch from the inner surface of the cylindrical body and having a thickness, as measured along a line radially inward from the inner surface, of at least about 1/2 inch, each baffle being spaced apart, longitudinally along the rotor, from an adjacent baffle a distance no greater than about the length of the mixer bar/scraper attached to the baffle;

an adjustment rod coaxial with, and rotatable about, the longitudinal axis of the lumen; an adjustable weir disposed in the lumen, the weir comprising a plate perpendicular to the longitudinal axis of the lumen, shaped as a portion, less than all, of a circle, the portion being defined by a chord of the circle, the weir being attached at the center of the circle to the adjustment rod for rotation therewith; and

a second valve in fluid communication with the first outlet port, downstream of the weir.

2. A continuous solids dryer according to claim 1, wherein a leading side, given the rotation direction of the rotor, of each baffle is chamfered.

3. A continuous solids dryer according to claim 1, wherein each mixer bar/scraper has a triangular cross-sectional shape, one side of the triangle forming an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

4. A continuous solids dryer according to claim 1, wherein each baffle is sized to extend to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

5. A continuous solids dryer according to claim 1, wherein the inner surface of the cylindrical body is formed without machining.

6. A continuous solids dryer according to claim 1, wherein thickness of each baffle, measured along a line parallel to the longitudinal axis of the cylindrical body, is tapered toward a leading edge, given the rotation direction of the rotor, of the baffle, along at least a portion of the annular sector of the baffle, such that the leading edge is thinner than other portions of the baffle.

7. A continuous solids dryer according to claim 6, wherein, for each baffle, the leading edge extends along an intersection of a first surface and a second surface of the baffle, wherein the first surface is flat and at least a portion of the second surfaces is not parallel to the first surface.

8. A continuous solids dryer according to claim 7, wherein at least a portion of the second surface is parallel to the first surface.

9. A continuous solids dryer according to claim 8, wherein the first surface is perpendicular to the axis of rotation of the rotor.

10. A continuous solids dryer according to claim 9, wherein each mixer bar/scraper has a triangular cross-sectional shape, one side of the triangle forming an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

11. A continuous solids dryer according to claim 10, wherein each baffle is sized to extends to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

12. A continuous solids dryer according to claim 1, wherein the second valve comprises a second air lock valve assembly.

13. A continuous solids dryer according to claim 1, further comprising a detachable air-tight vessel having an interior in fluid communication with the first outlet port, downstream of the second valve.

14. A continuous solids dryer according to claim 1, further comprising:

a sparge gas inlet port; wherein:

the rotor defines a hollow in fluid communication with the sparge gas inlet port and further defines a plurality of apertures extending between the hollow and an outside surface of the rotor.

15. A continuous solids dryer according to claim 1, further comprising:

a sparge gas inlet port; wherein:

the rotor defines a hollow in fluid communication with the sparge gas inlet port; and each baffle defines a plurality of apertures on an outside surface thereof and in fluid communication with the hollow of the rotor.

16. A continuous solids dryer according to claim 1, wherein the solids dryer is capable of sustaining a vacuum of at least about 50 Torr (6,666 Pa) within the inner volume of the cylindrical body.

17. A reconfigurable continuous solids dryer, comprising:

at least sixteen attachment points, each attachment point being permanently attached to the rotor, each attachment point defining at least one hole suitable for receiving a bolt;

at least eight baffles, each baffle being removably attached to the rotor, for rotation therewith, via a respective one of the attachment points and a respective at least one bolt, each baffle comprising an annular sector having an angle of about 90-170 degrees and extending from the rotor, the attachment points being distributed about the rotor to accept adjacent baffles at various offsets from each other in a range of about 20-80 degrees about the longitudinal axis of the cylindrical body and at various inter-baffle distances along the longitudinal axis of the cylindrical body;

for each baffle, a distinct agitating bar/scraper attached to a trailing side, given the rotation direction of the rotor, of the baffle and not attached to any other baffle, the agitating bar/scraper extending a length parallel to the longitudinal axis of the cylindrical body, each baffle being spaced apart, longitudinally along the rotor, from an adjacent baffle a distance no greater than about the length of the mixer bar/scraper attached to the baffle;

18. A reconfigurable continuous solids dryer according to claim 17, wherein a leading side, given the rotation direction of the rotor, of each baffle is chamfered.

19. A reconfigurable continuous solids dryer according to claim 17, wherein each mixer bar/scraper has a triangular cross-sectional shape, one side of the triangle forming an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

20. A reconfigurable continuous solids dryer according to claim 17, wherein each baffle is sized to extend to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

21. A reconfigurable continuous solids dryer according to claim 17, wherein the inner surface of the cylindrical body is formed without machining.

22. A reconfigurable continuous solids dryer according to claim 17, wherein thickness of each baffle, measured along a line parallel to the longitudinal axis of the cylindrical body, is tapered toward a leading edge, given the rotation direction of the rotor, of the baffle, along at least a portion of the annular sector of the baffle, such that the leading edge is thinner than other portions of the baffle.

23. A continuous solids dryer according to claim 22, wherein, for each baffle, the leading edge extends along an intersection of a first surface and a second surface of the baffle, wherein the first surface is flat and at least a portion of the second surfaces is not parallel to the first surface.

24. A continuous solids dryer according to claim 23, wherein at least a portion of the second surface is parallel to the first surface.

25. A continuous solids dryer according to claim 24, wherein the first surface is perpendicular to the axis of rotation of the rotor.

26. A continuous solids dryer according to claim 25, wherein each mixer bar/scraper has a triangular cross-sectional shape, one side of the triangle forming an acute angle with a tangent to the inner surface of the cylindrical body at a point proximate a leading portion of the mixer bar/scraper, given the rotation direction of the rotor.

27. A continuous solids dryer according to claim 26, wherein each baffle is sized to extends to within about 1/16-3/8 inch of the inner surface of the cylindrical body.

28. A reconfigurable continuous solids dryer according to claim 17, wherein the second valve comprises a second air lock valve assembly.

29. A reconfigurable continuous solids dryer according to claim 17, further comprising a detachable air-tight vessel having an interior in fluid communication with the first outlet port, downstream of the second valve.

30. A reconfigurable continuous solids dryer according to claim 17, further comprising: a sparge gas inlet port; wherein:

31. A reconfigurable continuous solids dryer according to claim 17, further comprising: a sparge gas inlet port; wherein:

32. A reconfigurable continuous solids dryer according to claim 17, wherein the solids dryer is capable of sustaining a vacuum of at least about 50 Torr (6,666 Pa) within the inner volume of the cylindrical body.