Thermal processing of bulk solids

An apparatus for drying or conditioning bulk solids, includes a housing including an inlet for receiving the bulk solids, and an outlet for discharging the bulk solids, a plurality of spaced apart heat transfer plates assemblies disposed in the housing between the inlet and the outlet for passage of the bulk solids that flow from the inlet, through spaces between the heat transfer plates, and a sweep gas delivery system for the flow of sweep gas in a first direction across the direction of flow of the bulk solids. The sweep gas delivery system includes at least one valve for reversing the flow of the sweep gas from the first direction to a second direction, opposite to the first direction.

FIELD OF THE INVENTION

The present disclosure relates to the thermal processing for drying or conditioning bulk solids such as soybeans, canola, or sunflower seeds.

BACKGROUND

Drying or conditioning materials such as soybeans, canola, sunflower seeds, and other bulk solids is desirable. Dryers that utilize hot air to pick up moisture, which is then vented, may be utilized but such dryers are inefficient.

Higher air temperatures improve drying efficiency but the air temperature is limited by the material being dried. In particular, materials such as soybeans, canola, and sunflower seeds degrade with temperatures that are too high. In the example of soybeans, low drying temperatures are desirable to reduce moisture content without causing cracking of the soybeans. In addition, significant heat is lost when the hot air is vented after picking up moisture.

Dryers utilizing steam-filled tubes or heated plates may be utilized but such dryers require a purge or sweep air to absorb water vapor and carry the water vapor out of the dryer. Large quantities of air are therefore required to remove the moisture.

Efficiency of heating and control of drying temperatures and residence time in the dryer are desirable. Further improvements in bulk solids dryers or conditioners are therefore desirable.

SUMMARY

According to an aspect of an embodiment, an apparatus for drying or conditioning bulk solids is provided. The apparatus includes a housing including an inlet for receiving the bulk solids, and an outlet for discharging the bulk solids. A plurality of spaced apart heat transfer plates assemblies are disposed in the housing between the inlet and the outlet for passage of the bulk solids that flow from the inlet, through spaces between the heat transfer plates. The apparatus also includes a sweep gas delivery system for the flow of sweep gas in a first direction across the direction of flow of the bulk solids, the sweep gas delivery system including at least one valve for reversing the flow of the sweep gas from the first direction to a second direction, opposite to the first direction.

According to another aspect of an embodiment, a method of drying or conditioning bulk solids is provided. The method includes introducing the bulk solids into an inlet of a housing through which the bulk solids flow through spaces between spaced apart heat transfer plates, subjecting the bulk solids to heating utilizing the heat transfer plates as the bulk solids flow, by the force of gravity, through the spaces between the heat transfer plates, toward an outlet of the housing, directing a sweep gas through the bulk solids as the bulk solids flow toward the outlet of the housing, the sweep gas being directed to flow in a first direction across the direction of flow of the bulk solids, and reversing direction of flow of the sweep gas by directing the flow of the sweep gas through the bulk solids, in a second direction opposite to the first direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For simplicity and clarity of illustration, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Numerous details are set forth to provide an understanding of the embodiments described herein. The embodiments may be practiced without these details. In other instances, known methods, procedures, and components have not been described in detail to avoid obscuring the embodiments described. The description is not to be considered as limited to the scope of the embodiments described herein.

As stated hereinabove, dryers utilizing steam-filled tubes or heated plates require a purge or sweep air to absorb water vapor and carry the water vapor out of the dryer. Large quantities of air are therefore required to remove the moisture. A significant pressure drop occurs as large quantities of air is pumped through a dryer, for example, from bottom toward the top of the dryer as the air must pass through the bulk solids being dried. As a result, high pressures are required to continue to move air through the dryer.

Rather than passing air upwardly through the dryer, the air may be passed across the dryer, generally transverse to the direction of flow of the bulk solids. The air pumped through the dryer, however, introduces significant differences in mass flow from one side to the other.FIG. 1is a simplified representation of an interior of an example of a dryer, illustrating the mass flow profile102in the dryer. The airflow is illustrated by the arrow104. As illustrated, drag effects106,108along the side walls110,112reduce the flow rate of bulk solids immediately adjacent the walls. The bulk solids, however, flow at a faster rate near the side wall110at which the air enters the dryer compared to the rate at which the bulk solids flow near the side wall112at which the air exits the dryer. This effect is a result of the generally horizontal air movement across the bulk solids. The mass flow profile illustrated affects residence time in the dryer, with a significant difference in residence time across the dryer. Control and consistency of residence time in the dryer, however, is desirable.

Referring toFIG. 2throughFIG. 4, the disclosure generally relates to a method and an apparatus for drying or conditioning bulk solids. The apparatus200includes a housing202including an inlet204for receiving the bulk solids, and an outlet206for discharging the bulk solids. A plurality of spaced apart heat transfer plates208are disposed in the housing202between the inlet204and the outlet206for passage of the bulk solids that flow from the inlet204, through spaces between the heat transfer plates208. The apparatus200also includes a sweep gas delivery system210(shown inFIG. 5andFIG. 6) for the flow of sweep gas in a first direction across the direction of flow of the bulk solids. The sweep gas delivery system includes at least one valve for reversing the flow of the sweep gas from the first direction to a second direction, opposite to the first direction.

A perspective view of an apparatus, which in the present embodiment is a dryer, and partially cut away views of the dryer are shown inFIG. 2throughFIG. 4. The apparatus200includes the housing202, which has a generally rectangular cross-section. The housing202has a top214and a bottom216. The top214of the housing202includes the inlet204for introducing bulk solids into the housing202. The bottom216of the housing202provides a discharge hopper218, which includes the outlet206for discharging the bulk solids from the housing202. A generally vertical axis extends from a center of the inlet204to a center of the outlet206. A plurality of heat transfer plates208are disposed within the housing202, between the inlet204and the outlet206. The plurality of heat transfer plates208are horizontally spaced apart along axes that extend transverse to the vertical axis and the heat transfer plates208are arranged generally parallel to each other in rows, referred to herein as banks.

In the example shown inFIG. 2throughFIG. 4, the apparatus200includes four banks of heat transfer plates208. The four banks are arranged in a stack. The stack includes a top bank220, a bottom bank226, and two intermediary banks, referred to as the second bank222and the third bank224, located between the bottom bank226and the top bank220. For the purpose of the present example, each heat transfer plate bank includes a plurality of the heat transfer plates208. Although the apparatus200ofFIG. 2throughFIG. 4includes four banks, other suitable numbers of banks may be utilized. For example, the apparatus may include a single bank of heat transfer plates208. Other numbers of banks of heat transfer plates may be successfully implemented. Also, other suitable numbers of heat transfer plates208in each heat transfer plate bank may be utilized.

The banks220,222,224,226of heat transfer plates208are spaced apart. The heat transfer plates208of the top bank220are spaced apart by spacers228and by the spacers230, which also support the top bank220of heat transfer plates208. The heat transfer plates208of the second bank222are spaced apart by the spacers230and by the spacers232, which also support the second bank222. The third bank224of heat transfer plates208are spaced apart by the spacers233and by the spacers234, which also support the third bank224. The bottom bank226of heat transfer plates208are spaced apart by the spacers234and by the spacers236, which also support the bottom bank226of heat transfer plates208. The spacers236support the bottom bank226of heat transfer plates208and the weight of the bulk solids introduced into the apparatus200as the weight of the bulk solids is transferred to the heat transfer plates208via friction.

The top bank220of heat transfer plates208, which is the bank that is located closest to the inlet204, is sufficiently spaced from the inlet204to provide a hopper238in the housing202, between the inlet204and the top bank220. The hopper238facilitates distribution of bulk solids that flow from the inlet204, as a result of the force of gravity, over the heat transfer plates208of the top bank220and into spaces between adjacent heat transfer plates208of the top bank220. The bottom bank226of the stack, which is the bank that is located closest to the outlet206, is sufficiently spaced from the outlet to facilitate the flow of bulk solids through the outlet206. The discharge hopper218is utilized to create a mass flow or “choked flow” of bulk solids and to regulate the flow rate of the bulk solids through the apparatus200. An example of a discharge hopper is described in U.S. Pat. No. 5,167,274, the entire content of which is incorporated herein by reference. The term “choked flow” is utilized herein to refer to a flow other than a free fall of the bulk solids as a result of the force of gravity.

The apparatus200also includes fluid inlet manifolds240that provide heating fluid to the heat transfer plates208, and fluid discharge manifolds242that receive the heating fluid from the heat transfer plates. In the present example, each of the banks220,222,224,226of heat transfer plates208is coupled to a respective fluid inlet manifold240and a respective fluid discharge manifold242. The fluid inlet manifold240coupled to the top bank220of heat transfer plates208is coupled to the housing202and is in fluid communication with each heat transfer plate208of the top bank220. A respective fluid line extends from each heat transfer plate208of the top bank220to the respective fluid inlet manifold240. The fluid discharge manifold242coupled to the top bank220of heat transfer plates208, is coupled to the housing202, and is in fluid communication with each heat transfer plate208of the top bank220. A respective fluid line extends from each heat transfer plate208of the top bank220to the fluid discharge manifold242. Similarly, each of the second bank222, the third bank224, and the bottom bank226are coupled to a respective fluid inlet manifold240and a respective fluid discharge manifold242.

In this example, each of the banks220,222,224,226of heat transfer plates208is coupled to a respective fluid inlet manifold240and a respective fluid discharge manifold242. Alternatively, banks of heat transfer plates may share a fluid inlet manifold and a fluid discharge manifold. For example, a respective fluid line may extend from each heat transfer plate of two or more banks of plates to a fluid inlet manifold and a respective fluid line may extend from each heat transfer plate of the two or more banks of plates to a fluid discharge manifold. Alternatively, heat transfer plates may be interconnected such that, for example, a respective fluid line extends from the fluid inlet manifold to each heat transfer plate of one bank, and each heat transfer plate of the one bank is coupled by a fluid line to respective heat transfer plates of an adjacent bank. Each heat transfer plate of the adjacent bank may then be coupled by a respective fluid line to the fluid discharge manifold.

Each heat transfer plate208of each bank220,222,224,226generally extends the width of the housing202, between a first sidewall244of the housing202and an opposing second sidewall246of the housing202. The heat transfer plates208are horizontally spaced apart and arranged generally parallel to each other such that spaces are provided between adjacent heat transfer plates208.

Optionally, the heat transfer plates208of any one of the banks220,222,224,226may be horizontally offset, i.e., not vertically aligned, with the heat transfer plates208of any of the other banks220,222,224,226. Thus, the heat transfer plates208of the top bank220may be horizontally offset from the heat transfer plates208of the second bank222. Similarly, the heat transfer plates208of the second bank222may be horizontally offset from the heat transfer plates208of the third bank224. The heat transfer plates208may of the third bank224may be horizontally offset from the heat transfer plates208of the bottom bank226.

Each bank220,222,224,226of heat transfer plates208is provided with a pair of sweep gas plenums located on opposing sides of the housing202for the flow of sweep gas across the direction of flow of the bulk solids as the bulk solids pass through the spaces between the heat transfer plates208. The sweep gas plenums include first sweep gas plenums250,251,252,253on the first sidewall244of the housing202and second sweep gas plenums254,255,256,257on the second sidewall246of the housing202, which is opposite to the first sidewall244.

Each first sweep gas plenum250,251,252,253has an air pervious side adjacent to end edges260of the heat transfer plates208of the associated bank of heat transfer plates208. The air pervious side of the first sweep gas plenum250,251,252,253facilitates the flow of sweep gas from the first sweep gas plenum250,251,252,253into the spaces between the heat transfer plates208and from the spaces between the heat transfer plates208into the first sweep gas plenum250,251,252,253. The air pervious side of the first sweep gas plenum250,251,252,253may be made of any suitable material that allows the passage of sweep gas through the air pervious side while inhibiting passage of bulk solids into the first sweep gas plenum250,251,252,253.

The second sweep gas plenums254,255,256,257have an air pervious side adjacent to opposite end edges of the heat transfer plates208of the associated bank of heat transfer plates208. The air pervious side of the second sweep gas plenum254,255,256,257facilitates the flow of sweep gas from the spaces between the heat transfer plates208into the second sweep gas plenum254,255,256,257and from the second sweep gas plenum254,255,256,257into the spaces between the heat transfer plates208. The air pervious side of the second sweep gas plenum254,255,256,257may be made of any suitable material that allows the passage of sweep gas through the air pervious side while inhibiting passage of bulk solids into the second sweep gas plenum254,255,256,257.

In the present example, the first sweep gas plenum250and the second sweep gas plenum254associated with the top bank220of heat transfer plates208are coupled to respective ports of a four-port valve262by ducting. Thus, first ducting264extends from the first sweep gas plenum250to the four-port valve262and second ducting266extends from the second sweep gas plenum254to the four-port valve262. The four-port valve262is coupled, via a third port, to a sweep gas source, such as a fan or blower for blowing sweep gas in a direction generally across the direction of flow of the bulk solids. The four-port valve262is also coupled, via a fourth port, to a sweep gas draw, such as a fan or blower for drawing sweep gas out of the housing202.

The four-port valve262is operable to be switched between a first flow configuration and a second flow configuration. The four-port valve262controls the flow of the sweep gas to cause the sweep gas to flow in a first direction, through the first sweep gas plenum250, through the spaces between the heat transfer plates208, and out of the second sweep gas plenum254when the four-port valve is in the first flow configuration. The four-port valve262also controls the flow of the sweep gas to cause the sweep gas to flow in a second direction, opposite to the first direction when the four-port valve262is in the second flow configuration. Thus, the sweep gas flows through the second sweep gas plenum254, through the spaces between the heat transfer plates208, and out of the first sweep gas plenum250when the four-port valve262is in the second flow configuration.

FIG. 5andFIG. 6are schematic representations of a portion of an apparatus, which in this example may be a dryer, including a sweep gas delivery system210and a bank of heat transfer plates. For the purpose of the present example, the portion of the dryer includes the top bank220of heat transfer plates208. It will be understood, however, that the bank of heat transfer plates illustrated inFIG. 5andFIG. 6may be any bank of heat transfer plates.

In the schematic representation, the first sweep gas plenum250is coupled to the first port502of the four-port valve262by the ducting264and the second sweep gas plenum254is coupled to the second port506of the four-port valve262by the ducting266. The four-port valve262is coupled, via a third port510, to the sweep gas source512for blowing sweep gas in a direction generally across the direction of flow of the bulk solids. The four-port valve262is also coupled, via the fourth port514, to a sweep gas draw516to provide suction for drawing sweep gas out of the housing.

The four-port valve262is shown inFIG. 5in the first flow configuration in which the sweep gas source512is coupled to the first sweep gas plenum250for blowing sweep gas into the housing through the first sweep gas plenum250. In the first flow configuration, the sweep gas draw516is coupled to the second sweep gas plenum254to draw sweep gas out of the housing via the second sweep gas plenum254.

The fourth port514that is coupled to the sweep gas draw516is located physically lower or below the third port510that is coupled to the sweep gas source512. The location of the fourth port514relatively lower or below the third port510facilitates the flow of condensate toward the fourth port514via gravity, for the reduction of condensate, for example, utilizing a condensate collector.

In the schematic ofFIG. 6, the four-port valve262is shown in the second flow configuration in which the sweep gas source512is coupled to the second sweep gas plenum254for blowing sweep gas into the housing through the second sweep gas plenum254. In the second flow configuration, the sweep gas draw516is coupled to the first sweep gas plenum250to draw sweep gas out of the housing via the first sweep gas plenum250.

Although a four-port valve is shown inFIG. 5andFIG. 6and is described herein in relation to each bank of heat transfer plates, more than one valve may be utilized. Thus, any suitable number of valves may be utilized to facilitate switching between the first configuration and the second configuration.

Referring again toFIG. 2throughFIG. 4, the first sweep gas plenum251and the second sweep gas plenum255associated with the second bank222of heat transfer plates208are coupled to respective ports of a four-port valve268by ducting. Thus, first ducting270extends from the first sweep gas plenum251to the four-port valve268and second ducting272extends from the second sweep gas plenum255to the four-port valve268. The four-port valve268is coupled, via a third port, to a sweep gas source, such as a pump or blower for blowing sweep gas in a direction generally across the direction of flow of the bulk solids. The four-port valve268is also coupled, via a fourth port, to a sweep gas draw, such as a pump for drawing sweep gas out of the housing202.

The four-port valve268is operable to be switched between a first flow configuration and a second flow configuration. The four-port valve268controls the flow of the sweep gas to cause the sweep gas to flow in a first direction, in through the first sweep gas plenum251, through the spaces between the heat transfer plates208, and out of the second sweep gas plenum255when the four-port valve is in the first flow configuration. The four-port valve268also controls the flow of the sweep gas to cause the sweep gas to flow in a second direction, opposite to the first direction when the four-port valve268is in the second flow configuration.

Similarly, the first sweep gas plenum252and the second sweep gas plenum256associated with the third bank224of heat transfer plates208are coupled to respective ports of a four-port valve274by ducting. The four-port valve274is also coupled, via a third port, to a sweep gas source and, via a fourth port, to a sweep gas draw for drawing sweep gas out of the housing202. The four-port valve274is operable to be switched between a first flow configuration and a second flow configuration. In the first flow configuration, sweep gas flows in the first direction, from the first sweep gas plenum252, and out the second sweep gas plenum256. In the second flow configuration, sweep gas flows in the second direction, opposite to the first direction.

The first sweep gas plenum253and the second sweep gas plenum257associated with the bottom bank226of heat transfer plates208are coupled to respective ports of a four-port valve276by ducting. The four-port valve276is also coupled, via a third port, to a sweep gas source and, via a fourth port, to a sweep gas draw for drawing sweep gas out of the housing202. The four-port valve276is operable to be switched between a first flow configuration and a second flow configuration. In the first flow configuration, sweep gas flows in the first direction, from the first sweep gas plenum253, and out the second sweep gas plenum257. In the second flow configuration, sweep gas flows in the second direction, opposite to the first direction.

In the examples shown and described herein, each four-port valve is coupled to a sweep gas source for blowing sweep gas in a direction generally across the direction of flow of the bulk solids and to a sweep gas draw to provide suction for drawing sweep gas out of the housing. Alternatively, both the sweep gas source and sweep gas draw may be provided by a single fan or blower. In addition, a single valve may be utilized to control the flow of sweep gas across all of the banks of heat transfer plates208such that the valve controls the flow configuration for all of the banks. Thus, a single valve is operable to be switched between a first flow configuration and a second flow configuration for all of the banks. In this example, all of the sweep gas plenums are coupled to a single valve.

FIG. 7is a side view of a heat transfer plate208utilized, for example, in the apparatus200shown inFIG. 2throughFIG. 4. The heat transfer plate208includes a pair of metal sheets702. The sheets702may be made from stainless steel, such as 316L stainless steel. The sheets702are arranged generally parallel to each other. The sheets702are welded together at locations that are spaced from the edges of the sheets702and are seam welded along the edges of the sheets702. After the two sheets702are welded together, slots are cut for insertion of nozzles that are welded to the sheets702and are utilized as a fluid inlet706and a fluid outlet708. The sheets702are inflated utilizing the nozzles such that generally circular depressions704are formed on each sheet at the welded locations. The generally circular depressions704are distributed throughout each sheet702and may be located at complementary locations on each sheet702such that the generally circular depressions704on one of the sheets702are aligned with the generally circular depressions704on the other of the sheets702. When the sheets702are inflated, spaces are formed between the sheets702, in areas where the sheets702are not welded together.

The fluid inlet706extends from a front edge714, near a bottom710of the heat transfer plate208. The fluid outlet708extends from the front edge714, near a top712of the heat transfer plate208. The fluid inlet706and the fluid outlet708both extend substantially perpendicular to and away from the front edge714of the heat transfer plate208.

The flow of heating fluid through a heat transfer plate208is illustrated by the arrows inFIG. 7. In operation, heating fluid flows from the fluid inlet manifold240through the respective fluid lines, through the fluid inlet706and into the respective heat transfer plates208. For the purposes of explanation, the flow of heating fluid through one of the heat transfer plates208is described with reference toFIG. 4.

The heating fluid flows through the fluid inlet706and into the heat transfer plate208. The generally circular depressions704distributed throughout the heat transfer plate208facilitate the flow of the heating fluid throughout the heat transfer plate208. The heating fluid then flows from the heat transfer plate208into the fluid outlet708and into the fluid discharge manifold242associated with that bank of heat transfer plates208.

In the above-described example, each of the banks220,222,224,226of heat transfer plates208is coupled to a respective fluid inlet manifold240and a respective fluid discharge manifold242. Alternatively, banks of heat transfer plates may share a fluid inlet manifold and a fluid discharge manifold. For example, the heating fluid may flow from the fluid outlet708of each heat transfer plate208of the bottom bank226, through the respective fluid lines, into the respective fluid inlets706of the heat transfer plates208of the third bank224. Similarly, the fluid outlets708of heat transfer plates208of the third bank224may be fluidly coupled to the fluid inlets706of heat transfer plates208of the second bank222. The fluid outlets708of heat transfer plates208of the second bank222may be fluidly coupled to the fluid inlets706of heat transfer plates208of the top bank220. In this alternative, the heating fluid then flows from the fluid outlet708of each heat transfer plate208of the top bank220and into a fluid discharge manifold.

Optionally, the heating fluid may flow in the opposite direction to that illustrated inFIG. 7. For example, the fluid inlet706and the fluid outlet708may be reversed such that the fluid flows in near a top edge of the heat transfer plate208and flows out closer to a bottom edge of the heat transfer plate208. The heating fluid may also flow downwardly from bank to bank in the apparatus.

As indicated above, the air pervious side of each second sweep gas plenum254,255,256,257may be of any suitable material that allows the passage of sweep gas through the air pervious side while inhibiting passage of bulk solids into the second sweep gas plenum254,255,256,257. For example, the air pervious side may be formed of wedge-wire screens800as illustrated inFIG. 8. The screens800include elongate members802that have generally triangular or V-shaped cross sections. The elongate members802are spaced apart a suitable distance and together inhibit bulk solids from passing through the spaces between the elongate members802while facilitating flow of sweep gas therethrough. The elongate members802are located such that a generally smooth surface is formed by faces of the members802and the generally smooth surface faces the bulk solids.

Alternatively, the air pervious side may be formed of louvers902as shown inFIG. 9. The louvers902are spaced apart to provide passages904between adjacent louvers to facilitate the flow of sweep gas between the louvers902. The louvers902are inclined such that bulk solids abut the face of the louvers902and slide down the steeply inclined faces. The bulk solids are thus inhibited from passing through.

A bottom906of each of the first sweep gas plenums250,251,252,253may be sloped downwardly toward a center of the housing. The sloped bottom906facilitates the flow of bulk solids out of the first sweep gas plenums250,251,252,253. Similarly, a bottom908of each of the second gas plenums254,255,256,257may be sloped downwardly toward a center of the housing. The sloped bottom908facilitates the flow of bulk solids out of the second gas plenums254,255,256,257. A respective bottom one910of the louvers902on the side of each first sweep gas plenum250,251,252,253is spaced from the respective bottom906of the first sweep gas plenum250,251,252,253to facilitate the flow of bulk solids past the louvers902and out of the first sweep gas plenum250,251,252,253when the air flow is reversed. Similarly, a respective bottom one912of the louvers902on the side of each second sweep gas plenum254,255,256,257is spaced from the respective bottom908of the second sweep gas plenum254,255,256,257to facilitate the flow of bulk solids out past the louvers902and out of the second sweep gas plenum254,255,256,257when the air flow is reversed.

Referring toFIG. 10with continued reference toFIG. 2throughFIG. 9.FIG. 10shows a flow chart illustrating a method of drying or conditioning bulk solids. The method is indicated generally by the numeral1000. The method may contain additional or fewer processes than shown and described, and parts of the method may be performed in a different order. Bulk solids are fed into the housing202through the inlet204at1002and the bulk solids flow downwardly, as a result of the force of gravity, from the inlet204into the hopper238. The hopper238facilitates distribution of the bulk solids to the top bank220of the heat transfer plates208. The bulk solids flow through the spaces between the heat transfer plates208, toward the outlet206. Bulk solids that contact the heat transfer plates208are deflected into the spaces adjacent the heat transfer plates208.

As bulk solids flow through the spaces between adjacent heat transfer plates208of the banks220,222,224,226, heating fluid is circulated through the heat transfer plates208at1004and the bulk solids are indirectly heated as the heat from the heating fluid in the heat transfer plates208is transferred to the bulk solids.

Sweep gas enters the sweep gas plenums and is directed across the direction of flow of the bulk solids at1006to remove moisture or volatiles from the solids as the solids are heated by indirect heating from the heat transfer plates208. In the present example, the four-port valves262,268,274,276are each in the first flow control configuration in which the sweep gas flows in a first direction. Thus, the sweep gas enters each first sweep gas plenum250, travels across the housing202via the spaces between the heat transfer plates208out the second sweep gas plenums252. After a period of time, the direction of flow of the sweep gas is reversed at1008by switching the four-port valves262,268,274,276to the second flow control configuration in which the sweep gas flows in the second direction, opposite to the first direction.

The direction of flow of the sweep gas is switched at1008. As the bulk solids feed continues and thus the drying or conditioning of bulk solids continues at1010, the direction of flow of the sweep gas is repeatedly switched. Thus, the sweep gas direction is repeatedly changed at1006and1008at regular intervals in time. Thus, the flow of sweep gas is directed in the first direction and then reversed by directing the flow in the second direction at regular intervals in time. The valves that are utilized to control the direction of flow of the sweep gas are therefore regularly switched between the first flow control configuration and the second flow control configuration.

Alternatively, the four-port valves262,268,274,276may be in different configurations. For example, the sweep gas may flow in the first direction, into the housing202, between the heat transfer plates208of the top bank220, and out of the housing202while the sweep gas flows in the second direction, opposite the first direction into the housing202, between the heat transfer plates208of the second bank222. Similarly, the sweep gas may flow in the first direction into the housing202, between the heat transfer plates208of the third bank224, and out of the housing202while the sweep gas flows in the second direction, opposite the first direction, into the housing202, between the heat transfer plates208of the bottom bank226. In this example, the banks of plates are spaced apart vertically by a sufficient distance to reduce the chance of sweep gas short-circuiting the travel across the housing by travelling generally vertically.

The bulk solids then flow into the discharge hopper218, where the bulk solids are discharged under a “choked” flow.

The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. All changes that come with meaning and range of equivalency of the claims are to be embraced within their scope.