Desiccant

Hi-performance desiccant tower

Desiccant Abstract
The invention resides in a process air dryer system for plastics processing machines and method for drying process air comprising two desiccant towers repeatedly alternating between process and regeneration cycles. In addition to conventional bottom heaters, each tower has an additional generally central heater so as to reduce the time required to regenerate saturated desiccant. When a tower is undergoing regeneration of its desiccant, generally centrally heaters aid conventional bottom heaters in drying saturated desiccant so as to reduce conventional regeneration cycle time by as much as 25% to 30%.

Desiccant Claims
I claim:

1. A system of drying and heating process air to be circulated for drying hygroscopic thermoplastic material contained in a drying hopper before the material is introduced into a plastic processing machine, the system including:

a drying hopper for containing hygroscopic thermoplastic material before the thermoplastic material is introduced into a plastics processing machine;

process air for drying said hygroscopic thermoplastic material contained in said drying hopper;

first and second desiccant towers, each of said towers alternating between a process cycle and a regeneration cycle while the other tower is in an opposite cycle;

desiccant contained in said first and second desiccant towers for adsorbing moisture from the process air;

regeneration air for driving moisture off saturated desiccant in one of said towers in a regeneration cycle;

air conduit means providing a path for circulating the process air between the drying hopper and the first and second desiccant towers;

air circulating means for circulating the process air through the air conduit means;

air flow directing means for directing the process air to the top end of one of said desiccant towers thereby placing said one of the towers in a process cycle while the other of the towers is placed in a regeneration cycle, said air flow directing means also directing the regeneration air exiting from a top end of said other of the towers in a regeneration cycle to a vent;

means for regulating the time period and temperature of the process and regeneration cycles;

first and second bottom heater means respectively housed adjacent to a bottom end of the first and second desiccant heating towers and extending in a plane traverse to the longitudinal direction of the respective desiccant heating towers to heat the desiccant so as to adsorb moisture from said process air circulating downwardly through one of said towers in a process cycle, and for simultaneously super-heating and driving moisture off the desiccant by means of said regeneration air circulating upwardly through the other of said towers in a regeneration cycle, said regeneration air carrying by means of convection a generally bottom-originating hot convection wave front propagating upwardly through the desiccant in said tower in a regeneration cycle; and

first and second generally central heater means respectively housed between top and bottom ends of said first and second desiccant towers and extending in a plane transverse to the longitudinal direction of the respective desiccant heating towers for super-heating and driving moisture off the desiccant by means of said regeneration air carrying a generally centrally-originating hot convection wave front propagating upwardly through the desiccant of one of said towers in a regeneration cycle, the generally centrally-originating hot convection wave front coupled with the bottom-originating hot convection wave front considerably reducing the time to completely regenerate the saturated desiccant in said one of said towers in a regeneration cycle.

2. A system of drying and heating process air according to claim 1, wherein said first generally central heater means is closer to the top end than that of the bottom end of said first desiccant tower, and said second generally central heater means is closer to the top end than that of the bottom end of said second desiccant tower.

3. A system of drying and heating process air according to claim 2, wherein the distance between said first generally central heater means and the top end of said first desiccant tower is approximately between sixty percent and seventy percent of the distance between said first generally central heater means and the bottom end of said first desiccant tower; and wherein

the distance between said second generally central heater means and the top end of said second desiccant tower is approximately between sixty percent and seventy percent of the distance between said second generally central heater means and the bottom end of said second desiccant tower.

4. A system of drying and heating process air according to claim 1, wherein a small portion of the process air exiting one of the desiccant towers in a process cycle becomes regeneration air to circulate upwardly through the other desiccant tower in a regeneration cycle.

5. A system of drying and heating process air according to claim 1, wherein the adsorbent is a molecular sieve.

6. A system of drying and heating process air according to claim 1, wherein the first and second bottom heater means and the first and second generally central heater means are heater coils.

7. A system of drying and heating process air according to claim 1, wherein the means for regulating the period and temperature of the process and regeneration cycles is a microprocessor controller.

8. A system of drying and heating process air according to claim 1, wherein the air conduit means takes the form of hollow cylindrical tubes.

9. A system of drying and heating process air to be circulated for drying hygroscopic thermoplastic material contained in a drying hopper before the material is introduced into a plastic processing machine, the system including:

a drying hopper for containing hygroscopic thermoplastic material before the thermoplastic material is introduced into a plastics processing machine;

process air for drying said hygroscopic thermoplastic material contained in said drying hopper;

first and second desiccant towers, each of said towers alternating between a process cycle and a regeneration cycle while the other tower is in an opposite cycle;

desiccant contained in said first and second desiccant towers for adsorbing moisture from the process air;

regeneration air taken from a small portion of the process air that is newly dried, the regeneration air driving moisture off saturated desiccant in one of said towers in a regeneration cycle;

air tubes providing a path for circulating the process air between the drying hopper and the first and second desiccant towers in a virtual closed-loop path;

blower for circulating the process air through the air tubes;

valve means directing the process air to the top end of one of said desiccant towers thereby placing said one of the towers in a process cycle while the other of the towers is placed in a regeneration cycle, said valve means also directing the regeneration air exiting from a top end of said other of the towers in a regeneration cycle to a vent;

control means for automatically regulating the time period and temperature of the process and regeneration cycles;

first and second bottom heater coils respectively housed adjacent to a bottom end of the first anti second desiccant heating towers and extending in a plane transverse to the longitudinal direction of the respective desiccant heating towers to heat the desiccant so as to adsorb moisture from said process air circulating downwardly through one of said towers in a process cycle, and for simultaneously super-heating and driving moisture off the desiccant by means of said regeneration air circulating upwardly through the other of said towers in a regeneration cycle, said regeneration air carrying by means of convection a generally bottom-originating hot convection wave from propagating upwardly through the desiccant in said tower in a regeneration cycle; and

first and second generally central heater coils respectively housed generally centrally of top and bottom ends of said first and second desiccant towers and extending in a plane transverse to the longitudinal direction of the respective desiccant heating towers for super-heating and driving moisture off the desiccant by means of said regeneration air carrying a generally centrally-originating hot convection wave front propagating upwardly through the adsorbent of one of said towers in a regeneration cycle, the generally centrally-originating hot convection wave front coupled with the bottom-originating hot convection wave front considerably reducing the time to completely regenerate the saturated desiccant in said one of said towers in a regeneration cycle.

10. A system of drying and heating process air according to claim 9, wherein said first generally central heater coil is closer to the top end than that of the bottom end of said first desiccant tower, and said second generally central heater coil is closer to the top end than that of the bottom end of said second desiccant tower.

11. A system of drying and heating process air according to claim 10, wherein the distance between said first generally central heater coil and the top end of said first desiccant tower is approximately between sixty percent to seventy percent of the distance between said first generally central heater coil and the bottom end of said first desiccant tower; and wherein

the distance between said second generally central heater coil and the top end of said second desiccant tower is approximately between sixty percent to seventy percent of the distance between said second generally central heater coil and the bottom end of said second desiccant tower.

12. A system of drying and heating process air according to claim 9, wherein a small portion of the process air exiting one of the desiccant towers in a process cycle becomes regeneration air to circulate upwardly through the other desiccant tower in a regeneration cycle.

13. A system of drying and heating process air according to claim 9, wherein the adsorbent is a molecular sieve.

14. A system of drying and heating process air according to claim 9, wherein the means for regulating the period and temperature of the process and regeneration cycles is a microprocessor controller.

15. A system of drying and heating process air according to claim 9, wherein the air conduit means takes the form of hollow cylindrical tubes.

16. A method of drying and heating process air to be circulated for drying hygroscopic thermoplastic material contained in a drying hopper before the material is introduced into a plastic processing machine comprising the steps of:

upwardly circulating hot, dry process air so as to dry thermoplastic material contained in a drying hopper;

providing two desiccant towers each containing desiccant for adsorbing moisture from the process air;

directing moist process air leaving the drying hopper to one of the towers thereby placing said one of the towers in a process cycle while the other of the towers is simultaneously placed in a regeneration cycle;

downwardly circulating the moist process air through said one of the desiccant towers in a process cycle to adsorb moisture from the moist process air and to heat the moist process air to a predetermined process temperature;

returning the dried process air back to the drying hopper to further dry the thermoplastic material contained therein;

simultaneously circulating hot, regeneration air upwardly through said other of the desiccant towers in a regeneration cycle whereby moisture is driven off saturated desiccant by means of upwardly propagating hot convection wave fronts originating within said other of the desiccant towers from the bottom and from a generally central portion thereof;

redirecting the moist process air leaving the drying hopper to said other of the desiccant towers after completion of the regeneration cycle thereby placing said one of the desiccant towers in a regeneration cycle and said other of the desiccant towers in a process cycle; and

continuing to alternate the process and regeneration cycles between said one and said other of the desiccant towers so as to form a repeating sequence.

17. A method of drying and heating process air according to claim 16 wherein a small portion of the process air exiting one of said desiccant towers in a process cycle is directed to become the regeneration air to circulate upwardly through the other of said desiccant towers in a regeneration cycle.

18. A method of drying and heating process air according to claim 16 wherein said upwardly propagating hot convection wave front of said generally central portion of one of said desiccant towers in a regeneration cycle originates from a location which is closer to a top end of said desiccant tower than is a bottom end of said desiccant tower.

19. A method of drying and heating process air according to claim 18 wherein said upwardly propagating hot convection wave front of said generally central portion of one of said desiccant towers in a regeneration cycle originates from a location whose distance to a top end of said desiccant tower is approximately seventy percent of the distance between said generally central portion and a bottom end of said desiccant tower.

Description
I claim:

1. A system of drying and heating process air to be circulated for drying hygroscopic thermoplastic material contained in a drying hopper before the material is introduced into a plastic processing machine, the system including:

a drying hopper for containing hygroscopic thermoplastic material before the thermoplastic material is introduced into a plastics processing machine;

process air for drying said hygroscopic thermoplastic material contained in said drying hopper;

first and second desiccant towers, each of said towers alternating between a process cycle and a regeneration cycle while the other tower is in an opposite cycle;

desiccant contained in said first and second desiccant towers for adsorbing moisture from the process air;

regeneration air for driving moisture off saturated desiccant in one of said towers in a regeneration cycle;

air conduit means providing a path for circulating the process air between the drying hopper and the first and second desiccant towers;

air circulating means for circulating the process air through the air conduit means;

air flow directing means for directing the process air to the top end of one of said desiccant towers thereby placing said one of the towers in a process cycle while the other of the towers is placed in a regeneration cycle, said air flow directing means also directing the regeneration air exiting from a top end of said other of the towers in a regeneration cycle to a vent;

means for regulating the time period and temperature of the process and regeneration cycles;

first and second bottom heater means respectively housed adjacent to a bottom end of the first and second desiccant heating towers and extending in a plane traverse to the longitudinal direction of the respective desiccant heating towers to heat the desiccant so as to adsorb moisture from said process air circulating downwardly through one of said towers in a process cycle, and for simultaneously super-heating and driving moisture off the desiccant by means of said regeneration air circulating upwardly through the other of said towers in a regeneration cycle, said regeneration air carrying by means of convection a generally bottom-originating hot convection wave front propagating upwardly through the desiccant in said tower in a regeneration cycle; and

first and second generally central heater means respectively housed between top and bottom ends of said first and second desiccant towers and extending in a plane transverse to the longitudinal direction of the respective desiccant heating towers for super-heating and driving moisture off the desiccant by means of said regeneration air carrying a generally centrally-originating hot convection wave front propagating upwardly through the desiccant of one of said towers in a regeneration cycle, the generally centrally-originating hot convection wave front coupled with the bottom-originating hot convection wave front considerably reducing the time to completely regenerate the saturated desiccant in said one of said towers in a regeneration cycle.

2. A system of drying and heating process air according to claim 1, wherein said first generally central heater means is closer to the top end than that of the bottom end of said first desiccant tower, and said second generally central heater means is closer to the top end than that of the bottom end of said second desiccant tower.

3. A system of drying and heating process air according to claim 2, wherein the distance between said first generally central heater means and the top end of said first desiccant tower is approximately between sixty percent and seventy percent of the distance between said first generally central heater means and the bottom end of said first desiccant tower; and wherein

the distance between said second generally central heater means and the top end of said second desiccant tower is approximately between sixty percent and seventy percent of the distance between said second generally central heater means and the bottom end of said second desiccant tower.

4. A system of drying and heating process air according to claim 1, wherein a small portion of the process air exiting one of the desiccant towers in a process cycle becomes regeneration air to circulate upwardly through the other desiccant tower in a regeneration cycle.

5. A system of drying and heating process air according to claim 1, wherein the adsorbent is a molecular sieve.

6. A system of drying and heating process air according to claim 1, wherein the first and second bottom heater means and the first and second generally central heater means are heater coils.

7. A system of drying and heating process air according to claim 1, wherein the means for regulating the period and temperature of the process and regeneration cycles is a microprocessor controller.

8. A system of drying and heating process air according to claim 1, wherein the air conduit means takes the form of hollow cylindrical tubes.

9. A system of drying and heating process air to be circulated for drying hygroscopic thermoplastic material contained in a drying hopper before the material is introduced into a plastic processing machine, the system including:

a drying hopper for containing hygroscopic thermoplastic material before the thermoplastic material is introduced into a plastics processing machine;

process air for drying said hygroscopic thermoplastic material contained in said drying hopper;

first and second desiccant towers, each of said towers alternating between a process cycle and a regeneration cycle while the other tower is in an opposite cycle;

desiccant contained in said first and second desiccant towers for adsorbing moisture from the process air;

regeneration air taken from a small portion of the process air that is newly dried, the regeneration air driving moisture off saturated desiccant in one of said towers in a regeneration cycle;

air tubes providing a path for circulating the process air between the drying hopper and the first and second desiccant towers in a virtual closed-loop path;

blower for circulating the process air through the air tubes;

valve means directing the process air to the top end of one of said desiccant towers thereby placing said one of the towers in a process cycle while the other of the towers is placed in a regeneration cycle, said valve means also directing the regeneration air exiting from a top end of said other of the towers in a regeneration cycle to a vent;

control means for automatically regulating the time period and temperature of the process and regeneration cycles;

first and second bottom heater coils respectively housed adjacent to a bottom end of the first anti second desiccant heating towers and extending in a plane transverse to the longitudinal direction of the respective desiccant heating towers to heat the desiccant so as to adsorb moisture from said process air circulating downwardly through one of said towers in a process cycle, and for simultaneously super-heating and driving moisture off the desiccant by means of said regeneration air circulating upwardly through the other of said towers in a regeneration cycle, said regeneration air carrying by means of convection a generally bottom-originating hot convection wave from propagating upwardly through the desiccant in said tower in a regeneration cycle; and

first and second generally central heater coils respectively housed generally centrally of top and bottom ends of said first and second desiccant towers and extending in a plane transverse to the longitudinal direction of the respective desiccant heating towers for super-heating and driving moisture off the desiccant by means of said regeneration air carrying a generally centrally-originating hot convection wave front propagating upwardly through the adsorbent of one of said towers in a regeneration cycle, the generally centrally-originating hot convection wave front coupled with the bottom-originating hot convection wave front considerably reducing the time to completely regenerate the saturated desiccant in said one of said towers in a regeneration cycle.

10. A system of drying and heating process air according to claim 9, wherein said first generally central heater coil is closer to the top end than that of the bottom end of said first desiccant tower, and said second generally central heater coil is closer to the top end than that of the bottom end of said second desiccant tower.

11. A system of drying and heating process air according to claim 10, wherein the distance between said first generally central heater coil and the top end of said first desiccant tower is approximately between sixty percent to seventy percent of the distance between said first generally central heater coil and the bottom end of said first desiccant tower; and wherein

the distance between said second generally central heater coil and the top end of said second desiccant tower is approximately between sixty percent to seventy percent of the distance between said second generally central heater coil and the bottom end of said second desiccant tower.

12. A system of drying and heating process air according to claim 9, wherein a small portion of the process air exiting one of the desiccant towers in a process cycle becomes regeneration air to circulate upwardly through the other desiccant tower in a regeneration cycle.

13. A system of drying and heating process air according to claim 9, wherein the adsorbent is a molecular sieve.

14. A system of drying and heating process air according to claim 9, wherein the means for regulating the period and temperature of the process and regeneration cycles is a microprocessor controller.

15. A system of drying and heating process air according to claim 9, wherein the air conduit means takes the form of hollow cylindrical tubes.

16. A method of drying and heating process air to be circulated for drying hygroscopic thermoplastic material contained in a drying hopper before the material is introduced into a plastic processing machine comprising the steps of:

upwardly circulating hot, dry process air so as to dry thermoplastic material contained in a drying hopper;

providing two desiccant towers each containing desiccant for adsorbing moisture from the process air;

directing moist process air leaving the drying hopper to one of the towers thereby placing said one of the towers in a process cycle while the other of the towers is simultaneously placed in a regeneration cycle;

downwardly circulating the moist process air through said one of the desiccant towers in a process cycle to adsorb moisture from the moist process air and to heat the moist process air to a predetermined process temperature;

returning the dried process air back to the drying hopper to further dry the thermoplastic material contained therein;

simultaneously circulating hot, regeneration air upwardly through said other of the desiccant towers in a regeneration cycle whereby moisture is driven off saturated desiccant by means of upwardly propagating hot convection wave fronts originating within said other of the desiccant towers from the bottom and from a generally central portion thereof;

redirecting the moist process air leaving the drying hopper to said other of the desiccant towers after completion of the regeneration cycle thereby placing said one of the desiccant towers in a regeneration cycle and said other of the desiccant towers in a process cycle; and

continuing to alternate the process and regeneration cycles between said one and said other of the desiccant towers so as to form a repeating sequence.

17. A method of drying and heating process air according to claim 16 wherein a small portion of the process air exiting one of said desiccant towers in a process cycle is directed to become the regeneration air to circulate upwardly through the other of said desiccant towers in a regeneration cycle.

18. A method of drying and heating process air according to claim 16 wherein said upwardly propagating hot convection wave front of said generally central portion of one of said desiccant towers in a regeneration cycle originates from a location which is closer to a top end of said desiccant tower than is a bottom end of said desiccant tower.

19. A method of drying and heating process air according to claim 18 wherein said upwardly propagating hot convection wave front of said generally central portion of one of said desiccant towers in a regeneration cycle originates from a location whose distance to a top end of said desiccant tower is approximately seventy percent of the distance between said generally central portion and a bottom end of said desiccant tower.