FIELD OF THE INVENTION This invention relates to internally falling film evaporators and more particularly to a liquid distributor system adapted for the internally falling film long tube evaporator.

BACKGROUND OF THE INVENTION

Internally falling film evaporators are well known for concentration of fluids in general and temperature/ heat sensitive fluids in particular. In the falling film evaporators, the fluid to be evaporated enters at the top of the evaporator and gets eventually distributed over the tubes through a liquid distributor. The liquid distributor ensures even distribution of liquid into each tube such that the liquid downwardly flows as a continuous film on the inner walls of the tubes.

The liquid distributors are normally provided as an assembly of a plurality of spray nozzles. For example, U.S. Pat. No. 4,683,025 discloses a liquid distributor chamber having a plurality of spray nozzles. Also, U.S. Pat. No. 6, 089, 312 discloses the use of a sparger having a plurality of sparger holes, wherein the sparger is positioned between the distribution plate and the upper tube sheet.

The liquid distributors known in the art are normally designed to handle clear fluids and they have substantial limitations in handling fluids with suspended solids. The suspended solids are likely to clog or block these liquid distribution systems and incur large amount of time and money in cleaning. A user may appreciate a design of the liquid distributor that is capable of distributing the slurries having significant amount of solids without clogging the liquid distribution system.

A liquid distribution system for a falling film evaporator is needed that ensures even liquid distribution of the clean liquid as well as slurries with significant amount of suspended solids without clogging the liquid distributor. Further, what is needed is a liquid distributor that efficiently prevents agglomeration of solids on the tube sheet without the need of cleaning/ removal of tube bundle from the evaporator. Further, what is needed is a liquid distributor that enables smooth liquid distribution of the liquid on the tube sheet without impact.

SUMMARY OF THE INVENTION

The present invention discloses a falling film evaporation system adapted for evaporation of a liquid/slurry that contains considerable amount of suspended solids having a particle size up to 5 mm. The system includes a falling film evaporation column, a liquid-vapor separator unit, a level control unit, and a recirculation pump. The evaporation column includes a shell and tube calendria that includes a plurality of tubes. Each of the tubes has a predefined tube length in the range of about 12 meters to 20 meters. The tubes are adapted to reduce power consumption in the calendria in the range of about 30 % to 60%.

The liquid distributor includes a nozzle body that is removably positioned with a swirler. The swirler is adapted to swirl within the nozzle body to prevent agglomeration of the solids over the tube sheet. The swirler includes a plurality of slots. The liquid distributor facilitates a wide solid spray angle of at least 120 degrees. The wide solid angle of the liquid distributor reduces bonnet extensions of the liquid distributor. The nozzle body has a non-clog big bore axial full cone spray configuration adapted to allow passage of the suspended solids The non-clog big bore axial full cone spray configuration is defined by a divergent passage, a rectangular duct, a frustoconical passage, a square duct, and a cylindrical duct. The liquid distributor is adapted to reduce impact of the slurry on the tubesheet. The liquid distributor is adapted to ensure even distribution of the liquid on the tubesheet.

The falling film evaporation system includes a recirculation pump having a non-clog design. The falling film evaporation system includes a yapor-liquid separator made of a wrap around entry pipe and a container wherein the wrap around entry pipe wraps at least half the circumference of the container.

STATEMENT OF THE INVENTION

According to present invention there is provided a falling film evaporation system adapted to handle slurry with considerable amount of suspended solids, wherein the system includes a falling film evaporation column having an extra long shell and tube type calendria and an axial full cone liquid distributor having a wide solid spray angle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram illustrating a preferred embodiment of a falling film evaporator system;

FIG. 2 is a partially expanded front view of a falling film evaporation column of the falling film evaporation system of FIG. 1 ; FIG. 3 is a front perspective exploded view of a liquid distributor of the falling film evaporation system of FIG. 1 ;

FIG. 4 is a top perspective view of the liquid distributor of the falling film evaporation system of FIG. 1;

FIG. 5 is a bottom perspective view of the liquid distributor of the falling film evaporation system of FIG. 1 ;

FIG. 6 is a front view of the liquid distributor of the falling film evaporation system of FIG. 1 ; FIG. 7 is a cross sectional side view of the liquid distributor taken along lines 7-7 of FIG. 6;

FIG. 8 is a top view of a vapor-liquid separator of the falling film evaporation system of FIG. 1 ; and

FIG. 9 is a front view of the vapor-liquid separator of the falling film evaporation system of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a schematic flow diagram of a preferred embodiment of a falling film evaporation system 10 is shown. In accordance with the present invention, falling film evaporation system 10 is specifically designed to concentrate slurry/ liquid with considerable amount of suspended solids, preferably of a particle size up to 5 mm. System 10 includes a slurry feedstock 12, a falling film evaporation column 14, a liquid- vapor separator unit 16, a level transmitter unit 18, and a recirculation pump 20. Evaporation column 14 has a shell 22, a top bonnet 24 and a bottom bonnet

26 that are bilaterally disposed along a central longitudinal axis X-X. However, it is understood here that top bonnet 24, bottom bonnet 26 may not be centrally positioned in other alternative embodiments of system 10. Top bonnet 24 and bottom bonnet 26 are preferably of hemispherical shape in this one particular embodiment. However, it is understood here that the shape of top and bottom bonnets 24, 26 may vary in other alternative embodiments of system 10. Shell 22 has a hollow interior that defines a shell and rube type calendria that has a shell side and a tube side. Slurry/ liquid feedstock 12 is adapted to be fed to bottom bonnet 26 of the evaporation column 14 through line 28 utilizing a two way control valve 30 such that feed 12 flows along the tube side of the column 14. It is understood here that feedstock 12 is preheated to a temperature that is equal or above saturation temperature before being fed to system 10. A vapor feedstock 32 is adapted to be fed to evaporation column 14 through a feed line 34. In this one particular embodiment, slurry 12 flows along the tube side of the evaporation column 14 and vapor 32 flows along the shell side of the evaporation column 14. It is understood however that vapor 32 passes heat to slurry 12 thereby forming a condensate that is removed along a condensate line 35. Top bonnet 24 has a central opening defined along the axis X-X that receives a feeder pipe 36. Feeder Pipe 36 is further connected to a liquid distributor 38. Feeder pipe 36 and liquid distributor 38 are preferably centrally positioned along the axis X-X in this one preferred embodiment. However, it is understood that feeder pipe 36 and liquid distributor 38 may have an off-centered position in other alternative embodiments of system 10.

In this one particular embodiment, recirculation pump 20 is a centrifugal pump that has a semi-open or open type impeller design. It is understood, however, that other types of recirculation pumps 20 having non-clog design may be utilized in other alternative embodiments of system 10. Pump 20 acts as a recirculation cum transfer pump in this one particular embodiment. A transfer line 40 connects bottom bonnet 26 to an inlet of pump 20. Pump 20 has an outlet that is preferably utilized for transportation of slurry 12 from bottom bonnet 26 to liquid distributor 38 via a recycle line 28. Alternatively, the outlet of pump 20 is utilized for removal of product via a transfer line 29. Pump 20 includes a sealing system (not shown) adapted to ensure constant supply of slurry 12 between bottom bonnet 26 and liquid distributor 38. In this one particular embodiment, Pump 20 is adapted to prevent entry of atmospheric gases into the system 10 under vacuum application. Pump 20 is adapted to prevent leakage of slurry 12 during the operating conditions of atmospheric pressure and above atmospheric pressure. Pump 20 has a pump shaft that is sealed by a plurality of mechanical seals that are well known in the art. The mechanical seals adapted to maintain vacuum in system 10 during operation under vacuum. The mechanical seals prevent leakage of slurry 12 during operating system 10 under above atmospheric pressure conditions.

Level transmitter unit 18 in this one preferred embodiment is a differential pressure type level transmitter. Column 14 defines a pair of diaphragm type remote seals 18A, 18B that connects to level transmitter 18 via a low pressure tapping 18C and a high pressure tapping 18D. Tappings 18C, 18D are capillary type tubings with sealed fluid in this one particular embodiment. Level transmitter unit 18 connects to a controller 19 through an electrical signal line 19A. Controller 19 is a PLC based soft or hard wired PID controller in this one particular embodiment. PID controller 19 communicates to an electro pneumatic positioner 21 through an electrical signal line 19B. Lines 19A, 19B are 4-20 mA DC lines in this one particular embodiment. Electro pneumatic positioner 21 has an input line 21 A and an output line 2 IB. Input line 21 A supplies air having pressure of about 20 psig and controlled output having pressure of about 3-15 psig via line 21B that pneumatically operates a pneumatically actuated control valve 42. Control valve 42 is adapted to dispense product via a product line 44.

Vapor- Liquid separator 16 is a tangential wrap-around vapor entry type vapor- liquid separator in this one preferred embodiment. Vapor- Liquid separator 16 is bilaterally positioned along a central vertical axis Y-Y that is substantially parallel to axis X-X. Vapor- Liquid separator 16 is adapted to entrap and separate liquid droplets from the vapors of slurry 12 formed within column 14. Vapor- Liquid separator 16 has a shape of an inverted bottom cone adapted for effective separation of liquid droplets from the vapors of slurry 12. The vapors of slurry 12 are removed at an outlet line 46. The liquid droplets of slurry 12 separated from vapors are removed via an outlet line 48. Outlet line 48 connects to line 40 to recycle the liquid droplets of slurry 12 to column 14. Referring to FIG. 2, Top bonnet 24, bottom bonnet 26 (refer FIG. 1) and shell 22 respectively include a pair of flanges 50 bilaterally disposed along the central axis X-X. Top bonnet 24 and bottom bonnet 26 are removably connected to shell 22 through a nut and bolt arrangement defined by a nut 52 A and a bolt 52B. The nut and bolt arrangement facilitates removal of top and bottom bonnets 24, 26 for removal, cleaning and replacement of tubes within calendria 54. Calendria 54 includes a plurality of tubes 56. Tubes 56 are supported on a tube sheet 58 via a plurality of support plates 60. However, it is understood here that tubes 56 are also supported on tube sheet 58 via a respective plurality of tie rods, spacer pipes and baffles that are well known in the art. Tubes 56 preferably have an extra long tube length within a range of 12 meters to about 20 meters in accordance with the present invention.

Feeder pipe 36 preferably centrally extends along axis X-X through top bonnet 24 up to a predefined distance within shell 22. Feeder pipe 36 positions liquid distributer 38 at the predefined distance over tube sheet 56. Feeder pipe 36 is supported on top bonnet 24 through an opposed pair of supporting clamps 62. Supporting clamps 62 are permanently connected on an inner surface of top bonnet 24 by a connecting means such as for example welding in this one particular embodiment. Liquid distributor 38 facilitates a wide spray angle of about A ⁰ . In this one particular embodiment angle A° is 120°, however, it is understood that angle A° may vary per intended application of liquid distributor 38. Liquid distributor 38 has an outer surface defined with a plurality of male threads (not shown) that threadably engage with a plurality of female threads (not shown) defined on an inner surface of feeder pipe 36. This removably positions liquid distributor 38 within column 14 and help assists in removal of liquid distributor 38 for maintenance. Referring to FIGS. 3-5, liquid distributor 38 includes a nozzle body 64 and a swirler 66. Nozzle body 64 and swirler 66 are annular members that are bilaterally disposed along a central vertical axis Z-Z. Nozzle body 64 defines a first annular portion 68 and a second annular portion 70 that are integrally connected along a rim 72. First annular portion 68 has a diameter relatively larger than a diameter of second annular portion 72. Swirler 66 has a sidewall 74 of substantially annular configuration that defines a plurality of slots 76. Slots 76 preferably have a rectangular configuration in this one particular embodiment. However, it is understood that configuration of slots 76 may vary per intended application of liquid distributor 38.

Swirler member 66 has a bottom surface 78 and a top surface 80. Bottom surface 78 defines an opening 82 that has a center positioned along the central axis Z-Z. Nozzle body 64 has a top surface 84 and a bottom surface 86. Bottom surface 86 defines an opening 88. Opening 88 preferably has an inner diameter that is approximately equal to an outer diameter of sidewall 74 adapted to comfortably accommodate swirler 66 within nozzle body 64. In this one preferred embodiment, swirler 66 is removably positionable within nozzle body 64 along the central axis Z- Z, preferably in a direction indicated by an arrow-B. Top surface 84 defines an opening 90. First annular portion 68 includes a plurality of slots 92 that is in the proximity to top surface 84. Slots 92 preferably have a concave configuration in this one particular embodiment. Openings 82, 88 and 90 combinedly form a wide angle big bore axial full cone spray nozzle configuration within liquid distributor 38.

Referring to FIGS. 6-7, first annular portion 68 has a height HI that is approximately twice a height H2 defined by second annular portion 70. Slots 92 define an opposed pair of divergent shoulders 94 A on first annular portion 68. Shoulders 94A are bilaterally disposed along axis Z-Z to assist in engagement of liquid distributor 38 with feeder pipe 34. First annular portion 68 and second annular portion 70 adjoin to define an opposed pair of convergent shoulders 94B. In this one preferred embodiment, axis Z-Z axially aligns along the central axis X-X to allow swirler 66 to comfortably swirl within liquid distributor 38. Swirler 66 is adapted to swirl in a clockwise direction indicated by an arrow 'C in this one preferred embodiment. However, it is understood here that swirler 66 may rotate in a counterclockwise direction indicated by an arrow 'D' in other alternative embodiments of liquid distributor 38. Opening 90 (as shown in FIG. 4) defines a divergent passage 96 within nozzle body 64 along central axis Z-Z(as shown in FIG. 3). Divergent passage 96 defines an inlet of liquid distributor 38 that is in fluid communication with feeder pipe 34. First annular portion 68 includes a rectangular duct 98 that is in fluid communication with divergent passage 96. First annular portion 68 includes a frustoconical passage 100 defined that is in fluid communication with rectangular duct 98. First annular portion 68 includes a square duct 102 that is in fluid communication with frustoconical passage 100. Square duct 102 preferably has a diameter that is approximately equal to the diameter of swirler 66. Swirler 66 includes a cylindrical duct 104 that is in fluid communication with square duct 102. Cylindrical duct 104 defines an outlet of liquid distributor 38 that is in fluid communication with slots 76 to facilitate swirling action.

Divergent passage 96, rectangular duct 98, frustoconical passage 100, square duct 102, cylindrical duct 104, and slots 76 define a configuration within liquid distributor 38 that is designed to form a wide solid angle A ⁰ , which is at least 120 degrees in this one preferred embodiment (As shown in FIG. 2).

Referring to FIGS. 8-9, vapor-liquid separator unit 16 includes a wrap around entry pipe 106 and a vapor-liquid separation container 108. Wrap around entry pipe 106 connects a bottom end portion of column 14 to vapor-liquid separation container 108. Wrap around entry pipe 106 introduces entry of two phase liquid- vapor mixture of slurry 12 from column 14 to container 108. Entry pipe 106 has a straight arm 1 10 and a wrapping arm 1 12 such that wrapping arm 1 12 preferably wraps at least half the circumference of container 108. Container 108 has a sidewall 114 that is bilaterally disposed along a vertical axis V-V. Container 108 has a top end 116, a bottom end 1 18, an inlet 120 and an outlet 122. Inlet 120 is preferably centrally located along the sidewall 1 14 that has a rectangular configuration. Outlet 122 is a circular ring that is connected to top end 116 through a plurality of connecting means 124. Outlet 122 has a diameter that is approximately half the diameter of container 108. Bottom end 118 has inverted bottom cone type of design that facilitates increased efficiency of liquid droplet removal from the vapors.

Wrap around entry pipe 106 tangentially connects to vapor-liquid separation container 108 that makes design of separator unit 16 compact. The wrap around entry pipe 106 facilitates highly permissible vapor velocities within container 108. Inlet 120 and outlet 122 have a predetermined axial distance adapted to ensure effective separation of liquid droplets from vapors.

In operation: Referring to FIGS. 1-9, system is advantageously usable for evaporation of slurry 12 having significant amount of solids that have a particle size up to 5 mm. Hence, the system 10 advantageously handles the fluids that include suspended solids and having fouling nature.

Column 14 of the present invention, in operation, includes shell and tube type calendria 54 that includes tubes 56 of extra long length, preferably in the range of about 12 meters to 20 meters. The extra long tube length design of tubes 56 enables low liquid recirculation rates of slurry 12 for same liquid film thickness that advantageously reduces power consumption per unit for same heat transfer area in said calendria 54, preferably in the range of about 30 % to 60%. The extra long tube length design of rubes 56 facilitates recirculation pump 20 to have reduced recirculation rate that makes recirculation pump 20 of a smaller design that eventually reduces capital investment costs on pump 20. The extra long tube length design of tubes 56 reduces a bundle diameter of each tube 56 that advantageously makes system 10 compact. The extra long tube length design of tubes 56 increases a vapor velocity of slurry 12 inside each tube 56 that advantageously increases overall heat transfer coefficient by increasing turbulence in the liquid film inside tubes 56 and reduces heat transfer area in said calendria 54. The extra long tube length design of tubes 56 increases residence time of slurry 12 inside tubes 56 that advantageously enhances intimacy of contact between slurry 12 and vapor 32 and subsequently the effectiveness of heat transfer. Liquid distributor 38, in operation, has the axial full cone spray nozzle that allows passage of suspended solids. This advantageously allows distributor 38 to properly distribute slurries 12 having significant amount of suspended solids, preferably up to 5 mm. In addition, the swirling action facilitated by swirler 66 is adapted to continuously swirl out or sweep out tubesheet 58 of calendria 54 to advantageously prevent agglomeration of solid material on tubesheet 58. This help facilitates proper distribution of liquid 12 by liquid distributor 38 on tubesheet 58. Liquid distributor 38 adapted to facilitate wide solid angle which is not less than 120 degrees. The wide solid angle facilitated by liquid distributor reduces impact of slurry 12 on tubesheet 58 to advantageously enable smooth distribution pattern of . liquid 12 on tubesheet 58. The wide solid angle also adapted to reduce bonnet extensions required for fitment of liquid distributor 38.

Pump 20, in operation, has a non-elog design adapted to comfortably handle slurry 12 with suspended solids without being clogged. Level control unit 18, in operation, ensures a constant level of liquid in bottom bonnet 26 of evaporation column 14 that advantageously ensures constant availability of liquid level essential for wetting of tubes 56 of shell and tube calendria 54.

Vapor-liquid separator unit 16, in operation, functions in the following manner. The vapor-liquid two phase fluid passes from the bottom end portion of column 14 to container 108 via wrap around entry pipe 106. Wrap around entry pipe 106 facilitates substantial swirling motion with enhanced centrifugal force generation. The centrifugal force causes the liquid droplets of slurry 12 to fly towards an inner surface of sidewall 12 thereby facilitating separation of liquid phase of slurry 12 from vapor phase. The separated liquid phase of slurry 12 is returned for recirculation to column 14 and vapor phase is removed from outlet 122.

The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein.