FIELD OF THE INVENTION

The present invention relates to a system for drying bulk material and a process thereof.
Particularly, the present invention relates to a system for dehumidifying and heating air and a process thereof.

BACKGROUND

In industries, drying of bulk material is done by passing a dry heated gaseous medium through a drying chamber/silo containing the bulk material. The dry gaseous medium, typically dry hot process air, is made to pass through the material, where, the dry hot air absorbs the moisture from the material thereby giving dried material and moist air having elevated temperature. This moist air is generally regenerated and subsequently recirculated to the drying chamber. The regeneration process involves dehumidifying the air and subsequent reheating to a desired temperature. The dehumidification is generally accomplished by passing the moisture laden air through an adsorbent material such as a membrane, molecular sieve, zeolite, silica, and alumina. The adsorbent material adsorbs the moisture thereby dehumidifying and drying the process air. The dehumidified air is then heated and the dry hot air is recirculated to drying chamber.

The adsorbent materials, used for the dehumidification of process air, are effective only within a certain temperature range, and when subjected to a higher temperature get damaged. Due to this constraint, the moist air is typically cooled in air or water coolers prior to drying through the adsorbent material. The use of air or water coolers accounts for higher energy consumption and therefore increased operational costs.
Some of the known methods and apparatus for drying bulk material are listed in the prior art below:

US 4,870,760 discloses a method and an apparatus for drying bulk material, using dry air, wherein, the exhaust gas escaping a drying hopper is cooled in a heat absorbing portion of a heat pump and subsequently dried by means of humidity adsorbing means in a drier, the dried air is then recycled to the drying hopper.

US 4,974,337 discloses an apparatus and a method for drying and dehumidifying plastic in a container with a current of warm dry air. The apparatus as disclosed in US4974337 comprises a desiccant means for removing moisture, a cooling means for cooling the current downstream of the desiccant means, a heat exchanger means for heating the current downstream from the desiccant means, sensing means for measuring temperature, and control means for varying the cooling and heating.

Referring to FIGURE 1, the graph represents the energy consumption by a conventional system for drying bulk material, using an air cooler or a water cooler. It is observed that a constant energy consumption under all operating conditions leads to low energy efficiency. Even during partial load condition or during production stop, i.e. when very little or no air is made to flow through the bulk material in the drying chamber, the energy consumption remains constant.

Therefore, there is felt a need for a system for drying bulk material using dry hot air and simultaneously regenerating the air, which conserves energy by selectively cooling, dehumidifying, and heating the moist air to be regenerated based on the working condition, minimizes wastage of heat, requires optimum cooling, and provides a continuous process operation.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a system for continuously dehumidifying bulk material.

Another object of the present invention is to provide a system for dehumidifying bulk material using dry hot air and regenerating the used air, which, depending upon the temperature of the moist air to be regenerated, selectively cools, dehumidifies, and heats the air, thereby giving substantial energy-saving and minimum air wastage.

SUMMARY OF THE INVENTION

In accordance with the present invention, is disclosed a system for dehumidifying bulk material using dry hot air, said system comprising:

■ a silo for containing bulk material to be dried, said silo being adapted for conveying a current of dry hot air in an upflow direction, wherein, the dry hot air absorbs moisture from the bulk material to become moisture-laden air;

■ a regeneration unit provided in operative communication with said silo for receiving the moisture-laden air, said regeneration unit comprising:

• filtering means for removing particulate matter from the moisture-laden air to obtain filtered moisture laden-air;

• a first blower provided downstream from said filtering means for controlling the flow of the filtered moisture laden-air;

• a first desiccating means provided downstream from said first blower for removing moisture from at least a portion of the filtered moisture-laden air to obtain a first portion of dehumidified air, wherein, a first three-way valve is provided upstream from said first desiccating means for regulating the quantity of moisture-laden air through said first desiccating means, and a second three-way valve is provided downstream from said first desiccating means for regulating the quantity of the first portion of dehumidified air to at least one means selected from said silo and a second desiccating means;

• a cooling means provided downstream from said first blower for cooling at least a portion of the filtered moisture-laden air to obtain cooled moisture-laden air, wherein, a third three-way valve is provided upstream from said cooling means for regulating the quantity of moisture-laden air through said cooling means;

• a second blower provided downstream from said cooling means for controlling the flow of at least one stream selected from the cooled moisture-laden air and at least a portion of the first portion of dehumidified air; and

• a second desiccating means provided downstream from said second blower for removing moisture from at least one stream selected from at least a portion of the cooled moisture-laden air and at least a portion of the first portion of dehumidified air, to obtain a second portion of dehumidified air, wherein, a fourth three-way valve is provided upstream from said second desiccating means for regulating at least one quantity selected from at least a portion of the cooled moisture-laden air and at least a portion of the first portion of dehumidified air through said second desiccating means and the second portion of dehumidified air to said silo, and the third three-way valve is provided downstream from said second desiccating means for regulating the quantity of the second portion of dehumidified air through said cooling means;

• a plurality of temperature sensors for measuring temperature of the moisture-laden air and the dehumidified air at a plurality of locations including upstream and downstream of said silo and upstream and downstream of said first desiccating means and said second desiccating means;

• a heat exchanger means for heating the dehumidified air downstream from said first desiccating means and said second desiccating means providing the dry hot air; and

■ a control means cooperating with said regeneration unit provided in operative communication with said plurality of temperature sensors, said first blower, said second blower, and said first, second, third, and fourth three-way valves, for varying at least one parameter selected from cooling supplied by said cooling means, heating supplied by said heat exchanger means, and dehumidification by said first and second desiccating means, in response to the temperature sensed by said plurality of temperature sensors, by controlling at least one means selected from said first blower, said second blower and said first, second, third, and fourth three-way valves.

Typically, in accordance with the present invention, a first heating means is provided downstream from said first desiccating means for selectively heating the first portion of dehumidified air.

Preferably, in accordance with the present invention, a second heating means is provided upstream from said second desiccating means for selectively heating the stream entering said second desiccating means.

In accordance with the present invention, said first desiccating means and said second desiccating means are positioned in at least one arrangement selected from parallel and series.

Typically, in accordance with the present invention, said control means is adapted for varying the cooling and the dehumidification of the moisture-laden air by controlling the operation of said first blower, said second blower, and said first, second, third, and fourth three-way valves, in response to the moisture-laden air temperature measured by said temperature sensors.

Preferably, in accordance with the present invention, said control means is adapted for varying the heating of the dehumidified air by controlling the operation of said second and fourth three-way valves, in response to the dehumidified air temperature measured by said temperature sensors.

In accordance with the present invention, is disclosed a method for dehumidifying bulk material using dry hot air, said method comprising the steps of:

■ dehumidifying bulk material in a silo by using a current of dry hot air traversing in an upflow direction so as to absorb moisture from the bulk material and form a current of moisture-laden air; and

■ receiving the current of moisture-laden air in a regeneration unit to regenerate the dry hot air.

Typically, in accordance with the present invention, the method for
dehumidifying bulk material includes the steps of:

■ measuring the temperature of the current of moisture-laden air and depending upon the temperature controlling the flow of the current of moisture-laden air in said regeneration unit to select at least one path for regenerating air from the group of paths consisting of,

a) dehumidifying at least a portion of the current of moisture-laden air in a first desiccating means to generate a first portion of dehumidified air which is fed to at least one means selected from a second desiccating means and a heat exchanger means, wherein, optionally, said first portion of dehumidified air is heated downstream of said first desiccating means; and

b) dehumidifying at least a portion of the current of moisture-laden air by passing through a series of steps including: cooling the portion of the current of moisture-laden air in a cooling means to generate a current of cooled moisture-laden air, feeding the current of cooled moisture-laden air to at least one means selected from said second desiccating means and said heat exchanger means, adjusting the temperature of the portion of the current of cooled moisture-laden air entering said second desiccating means, dehumidifying the portion of the current of cooled moisture-laden air in said second desiccating means to obtain a second portion of dehumidified air, receiving the second portion of dehumidified air, via said cooling means, in at least one means selected from said second desiccating means, said first desiccating means, and said heat exchanger means.

■ combining the first portion and the second portion of dehumidified air;

■ measuring the temperature of the current of dehumidified air; and

■ heating the current of dehumidified air, depending upon the temperature, in said heat exchanger means, to regenerate the dry hot air.
Preferably, in accordance with the present invention, the method for dehumidifying bulk material includes the step of filtering the current of moisture-laden air to remove particulate matter.

In accordance with the present invention, the method for dehumidifying bulk material includes the step of controlling the operation of said regeneration unit, based upon the temperature measured by a plurality of temperature sensors, by means of a first blower, a second blower, and first, second, third, and fourth three-way valves.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 shows a graphical representation of the energy consumption by a conventional system for drying bulk material;

FIGURE 2 illustrates a schematic of the system for dehumidifying bulk material, in
accordance with the present invention; and

FIGURE 3 shows a graphical representation of the energy consumption by the system for dehumidifying bulk material, in accordance with the present invention.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The invention will now be described with reference to the accompanying drawings which do not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.

The present invention envisages a system for dehumidifying bulk material, typically plastic material, using dry hot air. The system of the present invention provides simultaneous regeneration of the used air, thereby providing a continuous operation. Further, the system of the present invention is adapted to measure the temperature of the air to be regenerated at various locations along the flow path so as to selectively cool, dehumidify, and heat the air to be regenerated depending upon the requirement, thus providing high process efficiency, 30-60 % energy saving, minimal air wastage, and a smooth process operation. The system of the present invention is automatically controlled to make-use of the heat in the moist air to be regenerated, thereby conserving energy.

The system of the present invention is typically useful for drying plastic granules, particularly polyethylene terephthalate (PET). These plastic granules are dried by means of dry hot air flowing through a silo (the drying chamber), wherein the temperature of the dry hot air is generally greater than 150 °C. The hot air flows through the silo and dries the bulk material therein by absorbing moisture from the material, thereby becoming moisture-laden air having temperature in the range of 120 - 140 °C. This moisture-laden air is regenerated and recirculated to the silo for further drying. The moisture-laden air must be cooled, dehumidified, and subsequently reheated to temperature greater than 150 °C before it can be recirculated.

Since the temperature of the moisture-laden air is significantly high to cause damage to the moisture adsorbing/desiccating material, such as zeolite, silica gel, alumina, molecular sieve, and the like; therefore, the moisture-laden air must be either cooled to a temperature range most preferred by the moisture adsorbing material or the flow rate of the moisture-laden air through the moisture adsorbing material must be such that no damage occurs. The present invention aims at providing a system that selectively controls the flow rate and cools the moisture-laden air by continuously measuring the air temperature at various locations along its flow path.

Referring to FIGURE 2, therein is illustrated the system for industrial dehumidification of bulk material using dry hot air in accordance with the present invention. The bulk material to be dried is contained in a silo 12 adapted to receive dry hot air at the operative bottom. The dry hot air traverses in an upflow direction in the silo 12 thereby drying the bulk material and absorbing the moisture therein to form moisture-laden air. The moisture-laden air is discharged from the operative top of the silo 12. The moisture-laden air is then received in a regeneration unit 20 adapted to regenerate the dry hot air, wherein, the regeneration unit 20 is provided in operative communication with a control means 14 adapted to control the regeneration unit 20 to provide optimum operation.
A first temperature sensor Tl is provided downstream of the silo 12 to measure the temperature of the moisture-laden air exiting the silo 12. The temperature data is received by the control means 14 which depending upon the temperature controls the operation of a first blower 26 adapted to manipulate the flow of the moisture-laden air. The moisture-laden air is primarily passed through a filtering means 27 for removing any particulate matter trapped therein. The flow of the filtered moisture-laden air is then manipulated by means of the first blower 26 which is controlled by the control means 14. The current of the filtered moisture-laden air is selectively bifurcated after the first blower 26 such that at least a portion of the current passes through a first desiccating means 24b via a first three-way valve 22b and at least a portion of the current enters a cooling means 28 via a third three-way valve 22a. The first three-way valve 22b is controlled by the control means 14 to regulate the quantity of filtered moisture-laden air through the first desiccating means 24b. A second temperature sensor T5 is provided downstream of the first three-way valve 22b for measuring the temperature of the moisture-laden air just prior to entering the first desiccating means 24b. The flow rate of the filtered moisture-laden air through the first desiccating means 24b is a very crucial factor and in the system of the present invention this factor is completely controlled by means of the first blower 26 and the first three-way valve 22b which prevent any damage to the first desiccating means 24b. The filtered moisture-laden air loses moisture to the adsorbent material in the first desiccating means 24b to become a first portion of dehumidified air. A third temperature sensor T3 is provided downstream of the first desiccating means 24b to measure the temperature of the first portion of dehumidified air. The temperature data is received in the control means 14 which accordingly controls the operation of a first heating means 25b provided downstream of the third temperature sensor T3 for heating the first portion of dehumidified air. Therefrom, the first portion of dehumidified air is communicated via a second three-way valve 23b; the second three-way valve 23b directs the first portion of dehumidified air to at least one means from a second desiccating means 24a and the silo 12, wherein, the second three-way valve is controlled by the control means 14 depending upon the temperature sensed by the third temperature sensor T3.

At least a portion of the current of the filtered moisture-laden air is received in the cooling means 28 via the third three-way valve 22a. The operation of the cooling means 28 is varied by means of the first blower 26 and the third three-way valve 22a, which are controlled by the control means 14. In the cooling means 28, the current of the filtered moisture-laden air is cooled to a suitable temperature range. The heat from the moisture-laden gases can be utilized in heating fluids. The cooled stream of moisture-laden gases is then received in the second desiccating means 24a via a second blower 21. The second blower 21 is adapted to manipulate the flow of the cooled moisture-laden air, wherein the second blower 21 is also controlled by the control means 14. The cooled moisture-laden air is received in the second desiccating means 24a via a fourth three-way valve 23a which is adapted to selectively regulate the flow to at least one means from the second desiccating means 24a and the silo 12 based on signal received from the control means 14. A second heating means 25a is provided downstream from the fourth three-way valve 23a for adjusting the temperature of the cooled moisture-laden air to be in a temperature range most preferred for adsorption. A fourth temperature sensor T4 is located downstream of the second heating means 25a for measuring the temperature of the moisture-laden air stream just prior to entering the second desiccating means 24a. The temperature data is sent to the control means 14.

In the second desiccating means 24a the cooled moisture-laden air loses moisture to the adsorbent material to become a second portion of dehumidified air. A fifth temperature sensor T6 is provided downstream of the second desiccating means 24a for measuring the temperature of the second portion of dehumidified air. The temperature data is received at the control means 14, which thereby control the third three-way valve 22a provided downstream of the second desiccating means 24a, to regulate the current of the second portion of dehumidified air through at least one means from the cooling means 28 and first desiccating means 24b. At least a portion of the dehumidified air from the second desiccating means 24a is ecirculated through the cooling means 28. A fresh stream of filtered noisture-laden air is continuously received in the regeneration unit 20, a >ortion of the fresh stream is received in the first desiccating means 24b and i second portion is combined with the dehumidified air from the second lesiccating means 24a and the current is passed through the cooling means !8 and the circuit is repeated. A portion of the second portion of the lehumidified air selectively by-passes the second desiccating means 24a via he fourth three-way valve 23a.

The first portion and the portion of the second portion of the dehumidified dr are combined and carried through a return duct connecting the silo 12. A iixth temperature sensor T2 provided upstream from the silo 12 measures he temperature of the current of dehumidified air. The temperature data is eceived at the control means 14 which control the operation of heat exchanger means 11 provided upstream from the silo 12. The current of the lehumidified air is heated to a desired temperature to obtain the dry hot air vhich is conveyed to the silo 12 for drying the next batch of bulk material, deferring to FIGURE 3, therein is shown a graph representing the energy consumption by the system of the present invention, which is in contrast to FIGURE 1 which illustrates energy consumed by a conventional system for Irying bulk material, it is observed that the system of the present invention consumes significantly lesser energy.

TECHNICAL ADVANTAGES

A system for dehumidifying bulk material using dry hot air and a method thereof; as disclosed in the present invention has several technical advantages including but not limited to the realization of:

• the system provides continuous dehumidification of bulk material using dry hot air;

• the system provides dehumidification of bulk material using dry hot air and simultaneous regeneration of the used air, wherein, depending upon the temperature of the moist air to be regenerated and the desired dry hot air temperature, the system selectively cools, dehumidifies, and heats the moisture-laden air, thereby giving 30-60 % energy-saving as compared to a conventional system, a minimum air wastage, and no discontinuity in the process operation.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We Claim:

1. A system for dehumidifying bulk material using dry hot air, said system comprising:

■ a silo for containing bulk material to be dried, said silo being adapted for conveying a current of dry hot air in an upflow direction, wherein, the dry hot air absorbs moisture from the bulk material to become moisture-laden air;

■ a regeneration unit provided in operative communication with said silo for receiving the moisture-laden air, said regeneration unit comprising:

• filtering means for removing particulate matter from the moisture-laden air to obtain filtered moisture laden-air;

• a first blower provided downstream from said filtering means for controlling the flow of the filtered moisture laden-air;

• a first desiccating means provided downstream from said first blower for removing moisture from at least a portion of the filtered moisture-laden air to obtain a first portion of dehumidified air, wherein, a first three-way valve is provided upstream from said first desiccating means for regulating the quantity of moisture-laden air through said first desiccating means, and a second three-way valve is provided downstream from said first desiccating means for regulating the quantity of the first portion of dehumidified air to at least one means selected from said silo and a second desiccating means;

• a cooling means provided downstream from said first blower for cooling at least a portion of the filtered moisture-laden air to obtain cooled moisture-laden air, wherein, a third three-way valve is provided upstream from said cooling means for regulating the quantity of moisture-laden air through said cooling means;

• a second blower provided downstream from said cooling means for controlling the flow of at least one stream selected from the cooled moisture-laden air and at least a portion of the first portion of dehumidified air;

• a second desiccating means provided downstream from said second blower for removing moisture from at least one stream selected from at least a portion of the cooled moisture-laden air and at least a portion of the first portion of dehumidified air, to obtain a second portion of dehumidified air, wherein, a fourth three-way valve is provided upstream from said second desiccating means for regulating at least one quantity selected from at least a portion of the cooled moisture-laden air and at least a portion of the first portion of dehumidified air through said second desiccating means and the second portion of dehumidified air to said silo, and the third three-way valve is provided downstream from said second desiccating means for regulating the quantity of the second portion of dehumidified air through said cooling means;

• a plurality of temperature sensors for measuring temperature of the moisture-laden air and the dehumidified air at a plurality of locations including upstream and downstream of said silo and upstream and downstream of said first desiccating means and said second desiccating means; and

• a heat exchanger means for heating the dehumidified air downstream from said first desiccating means and said second desiccating means providing the dry hot air; and

■ a control means cooperating with said regeneration unit provided in operative communication with said plurality of temperature sensors, said first blower, said second blower, and said first, second, third, and fourth three-way valves, for varying at least one parameter selected from cooling supplied by said cooling means, heating supplied by said heat exchanger means, and dehumidification by said first and second desiccating means, in response to the temperature sensed by said plurality of temperature sensors, by controlling at least one means selected from said first blower, said second blower and said first, second, third, and fourth three-way valves.

2. The system as claimed in claim 1, wherein a first heating means is provided downstream from said first desiccating means for selectively heating the first portion of dehumidified air.

3. The system as claimed in claim 1, wherein a second heating means is provided upstream from said second desiccating means for selectively heating the stream entering said second desiccating means.

4. The system as claimed in claim 1, wherein said first desiccating means and said second desiccating means are positioned in at least one arrangement selected from parallel and series.

5. The system as claimed in claim 1, wherein said control means is adapted for varying the cooling and the dehumidification of the moisture-laden air by controlling the operation of said first blower, said second blower, and said first, second, third, and fourth three-way valves, in response to the moisture-laden air temperature measured by said temperature sensors.

6. The system as claimed in claim 1, wherein said control means is adapted for varying the heating of the dehumidified air by controlling the operation of said second and fourth three-way valves, in response to the dehumidified air temperature measured by said temperature sensors.

7. A method for dehumidifying bulk material using dry hot air, said
method comprising the steps of:

■ dehumidifying bulk material in a silo by using a current of dry hot air traversing in an upflow direction so as to absorb moisture from the bulk material and form a current of moisture-laden air; and

■ receiving the current of moisture-laden air in a regeneration unit to regenerate the dry hot air.

8. The method for dehumidifying bulk material as claimed in claim 7,
which includes the steps of:

■ measuring the temperature of the current of moisture-laden air and depending upon the temperature controlling the flow of the current of moisture-laden air in said regeneration unit to select at least one path for regenerating air from the group of paths consisting of,

a) dehumidifying at least a portion of the current of moisture-laden air in a first desiccating means to generate a first portion of dehumidified air which is fed to at least one means selected from a second desiccating means and a heat exchanger means, wherein, optionally, said first portion of dehumidified air is heated downstream of said first desiccating means;

b) dehumidifying at least a portion of the current of moisture-laden air by passing through a series of steps including: cooling the portion of the current of moisture-

laden air in a cooling means to generate a current of cooled moisture-laden air, feeding the current of cooled moisture-laden air to at least one means selected from said second desiccating means and said heat exchanger means, adjusting the temperature of the portion of the current of cooled moisture-laden air entering said second desiccating means, dehumidifying the portion of the current of cooled moisture-laden air in said second desiccating means to obtain a second portion of dehumidified air, receiving the second portion of dehumidified air, via said cooling means, in at least one means selected from said second desiccating means, said first desiccating means, and said heat exchanger means.

■ combining the first portion and the second portion of dehumidified air;
■ measuring the temperature of the current of dehumidified air;
■ heating the current of dehumidified air, depending upon the temperature, in said heat exchanger means, to regenerate the dry hot air.

9. The method for dehumidifying bulk material as claimed in claim 8, which includes the step of filtering the current of moisture-laden air to remove particulate matter.

10.The method for dehumidifying bulk material as claimed in claim 8, which includes the step of controlling the operation of said regeneration unit, based upon the temperature measured by a plurality of temperature sensors, by means of a first blower, a second blower, and first, second, third, and fourth three-way valves.