AN APPARATUS AND METHOD FOR CONCENTRATING A FLUID

Abstract

A method of concentrating a process fluid, including a carrier fluid, including: (a) maintaining a process fluid at a predetermined temperature value/range; (b) evaporating the carrier fluid from the process fluid to produce a concentrated process fluid; (c) monitoring at least one process variable of steps (a) or (b) to detect fouling formed in either step (a) or (b); and (d) initiating a cleaning protocol if the process variable deviates from a predetermined value/range to reduce the fouling formed.

Claims

1-23. (canceled)

24. A method of concentrating a process fluid, including a carrier fluid, including: (a) maintaining a process fluid at a predetermined temperature value/range; (b) evaporating the carrier fluid from the process fluid in an evaporator to produce a concentrated process fluid and an effluent mass transfer medium; (c) monitoring at least one process variable of steps (a) or (b) to detect fouling formed in either step (a) or (b); (d) initiating a cleaning protocol if the process variable deviates from a predetermined value/range to reduce the fouling formed; and (e) directing part of the effluent mass transfer medium into a drift chamber located downstream of the evaporator having a plurality of run-off outlets to remove entrained process fluid prior to returning the mass transfer medium to the evaporator.

25. The method according to claim 24, wherein step (a) includes feeding a process fluid into a heat exchanger to maintain the process fluid at a predetermined temperature value/range.

26. The method according to claim 24, wherein step (b) includes feeding the process fluid from a heat exchanger to the evaporator.

27. The method according to claim 24, wherein step (b) includes heating the carrier fluid without using an external heating source.

28. The method according to claim 24, wherein step (b) includes direct contact of the process fluid with a mass transfer medium.

29. The method according to claim 28, including a step of humidifying the mass transfer medium prior to contacting the process fluid.

30. The method according to claim 24, wherein step (b) includes spraying the process fluid onto an evaporation fill material and directing an air stream through the evaporation fill material in the opposite direction.

31. The method according to claim 24, wherein step (c) includes monitoring pressure difference across a heat exchanger.

32. The method according to claim 24, wherein step (c) includes monitoring fluid flow rates through an evaporator.

33. The method according to claim 31, wherein step (d) includes initiating the cleaning protocol if the pressure or flow rate deviates from a predetermined value/range to reduce fouling in a heat exchanger or evaporator.

34. The method according to claim 24, including recycling part of an effluent mass transfer medium from the evaporator.

35. The method according to claim 24, wherein the cleaning protocol includes circulating an anti-fouling solution through one or more process equipment used in the method.

36. The method according to claim 24, wherein the cleaning protocol includes subjecting fluid conduits of a heat exchanger or evaporator to ultrasonication.

37. A method of producing a sugar concentrate from sugar cane, including: (a) obtaining a sugar-containing extract from sugar cane; (b) maintaining the extract at a predetermined temperature value/range; (c) clarifying the extract in the absence of added lime; (d) evaporating water from the extract in an evaporator to form a sugar concentrate and an exiting air stream; (e) monitoring a process variable of step (b) or (d) to detect fouling formed in either step (b) or (d); (f) initiating a cleaning protocol if the process variable deviates from a predetermined value/range to reduce the fouling formed; and (g) directing part of the exiting air stream into a drift chamber located downstream of the evaporator having a plurality of run-off outlets to remove entrained non-vaporised sugar cane extract droplets prior to returning the air stream to the evaporator.

38. The method according to claim 37, wherein the extract is maintained at a maximum temperature of 20-40° C.

39. An apparatus for concentrating a process fluid, including a carrier fluid, comprising: a heat exchanger to maintain the process fluid at a predetermined temperature value/range; an evaporator in fluid communication with the heat exchanger to receive the process fluid and evaporate the carrier fluid from the process fluid to produce a concentrate and an effluent carrier fluid; at least one sensor for monitoring a process variable across the heat exchanger or the evaporator to detect fouling of the heat exchanger or the evaporator; a cleaning system to reduce fouling in the apparatus; a controller configured to receive signals from the sensor or a manual user input to initiate the cleaning system if the process variable deviates from a predetermined value/range; and a drift chamber located downstream of the evaporator having a plurality of run-off outlets to receive at least part of the effluent carrier fluid from the evaporator prior to returning the carrier fluid to the evaporator.

40. The apparatus according to claim 39, including one or more pressure sensors to monitor pressure difference across the heat exchanger.

41. The apparatus according to claim 39, including a flow rate sensor to monitor a mass transfer medium or process fluid flow rate through the evaporator.

42. The apparatus according to claim 39, wherein the evaporator includes a bubble plate to facilitate humidification of a mass transfer medium prior to contacting the process fluid.

43. The apparatus according to claim 39, including an ultrasonicator to clean the heat exchanger and/or evaporator.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0121] An embodiment of the invention is hereinafter described by way of example only with reference to the accompanying drawings, wherein:

[0122] FIG. 1 is a flow diagram of the apparatus according to one form of the present invention.

[0123] FIG. 2 illustrates a spray tower of the apparatus of FIG. 1.

[0124] FIG. 3 illustrates a drift chamber of the apparatus of FIG. 1.

DETAILED DESCRIPTION

[0125] An apparatus for concentrating a process fluid as defined by the invention is marked as 10 in FIG. 1.

[0126] In this example, the apparatus is configured to process sugar cane extract (juice). However, it can be appreciated that the apparatus may be configured to process other process fluids including industrial process fluids such as wastewater.

[0127] The apparatus 10 comprises a cooler 14 including heat exchangers in the form of a condenser 24 and water-cooled evaporator coil 28, an evaporator in the form of spray tower 16, a drift chamber 18, a cleaning system comprising a first storage tank tower comprising a feed tank 12A1, concentrate storage tank 12A2, miscellaneous output interim sampling tanks 12A3 and 12A4, and a second storage tank tower comprising anti-fouling reagent tanks 20B1-B4 for storing separate anti-fouling reagents.

[0128] A control system comprising a controller, and a plurality of sensors including pressure and flowrate sensors monitoring process variables at various locations of the apparatus initiates the cleaning system if the process variables deviate from predetermined threshold limits.

[0129] Extract from crushed sugar cane is stored in feed tank 12A1 which is in fluid communication with cooler 14.

[0130] The cooler 14 includes a water-cooled evaporator coil 28 to maintain the extract at a temperature ranging from 20-40° C. before it is fed into spray tower 16. The cooler 14 also includes a condenser 24 on the cold side of the cooler to condense water out of the air stream exiting the drift chamber.

[0131] The feed tank 12A1 may be temperature controlled to maintain the extract at the same predetermined temperature range. It was determined that keeping the extract at this temperature range prevents (or at least minimizes) browning of the heat-sensitive extract (e.g. 60% sucrose solution). This avoids the need to use lime to whiten the final product which is an undesirable additive because it contributes to the fouling of the process equipment, particularly spray tower 16, the liquid side of the cooler condenser 24 and the air side of the water-cooled evaporator coil 28.

[0132] The spray tower 16 is located downstream of the cooler 14. The top of the spray tower includes a spray nozzle 26 including a process fluid inlet 30 to receive and spray the extract into the spray tower chamber. The bottom of the spray tower 16 includes a mass transfer medium inlet 32A/B to supply air upwards to meet the downward travelling extract (see FIG. 2). The counter current fluid flow arrangement optimises the mass transfer of water from the extract into the air stream to concentrate the extract.

[0133] Mass transfer medium inlet 32A is used when the evaporation step utilises evaporation fill material and mass transfer medium inlet 32B is used when the evaporation step involves bubbling mass transfer medium through water.

[0134] When evaporation fill material is used, it occupies region C of the spray tower in FIG. 2.

[0135] Water from the sugar cane extract is removed into the air stream to concentrate the extract which can be sent for further processing to produce sugar or to concentrate storage tank 12A2 for storage.

[0136] The spray tower 16 may include a bubble plate 34 to humidify the air being fed into the spray tower (see FIG. 1). In this example, the air is bubbled through water via the bubble plate to humidify the air.

[0137] A drift chamber 18 is positioned between the cooler 14 and spray tower 16 to receive at least part of the exiting air stream from the spray tower.

[0138] The drift chamber includes an eliminator 36 to capture entrained non-vaporised sugar cane extract droplets from the exiting air stream. This is done by having the eliminator 36 direct the air stream through a tortuous (e.g. zig-zag) pathway. The collected run-off is returned to the spray tower 16 via run-off outlets 38A-F. Run-off outlets 38A-E includes a horizontal fin 46 which directs run-off from the drift chamber (see FIG. 3).

[0139] The cleaned air stream is then directed to the cooler 14 to reduce the temperature of the stream before it is returned to the spray tower. The cleaned air may be used as a heat transfer medium to cool the process fluid in the cooler 14.

[0140] Having the drift chamber capture sugar cane extract droplets from the air stream minimizes fouling of the cooler condenser 24, particularly choking of the cooler air fins by sugar deposits from the entrained process fluid.

[0141] The apparatus 10 also includes a control system comprising a Programmable Logic Controller (PLC) and a plurality of sensors positioned at various locations on the apparatus to monitor process variables including pressure, humidity, temperature, fluid level and flow rate.

[0142] The controller receives signals from the sensors and initiates a cleaning protocol if the pressure or flow rate deviates from a predetermined value/range. In one example, the predetermined thresholds are a pressure difference of 10 kPa across the cooler, an air flow rate of 15 L/min through the spray tower and a process fluid flow rate of 0.25 L/min through the spray tower.

[0143] The PLC controls processing of the process fluid, monitoring of process variables, and initiating the cleaning system. The controller measures any build up of fouling by detecting increases in air or water pressure across the process equipment or decreases in process fluid, air or water flow rates.

[0144] The cleaning protocol directs the cleaning system to run humidified air or anti-fouling reagents through the apparatus to remove the fouling. This protocol can be configured to run at regular intervals independent of the signals from the sensors.

[0145] Pressure sensors PW1 and PW2, flowrate sensors VA and VB, fluid level sensors Lx (where x refers to the fluid stream being monitored), humidity sensors HA1 and HA2, and temperature sensors TW1, TW2, TA1 and TA2 monitor various parts of the system and send signals to the PLC which initiates the cleaning protocol when selected process variable measurements deviate from a predetermined threshold range.

[0146] Sensors of particular importance are pressure sensors PW1 and PW2 and flowrate sensors VA and VB.

[0147] The pressure sensors are located at the various fluid inlets and outlets of the spray tower 16 and the cooler 14 to enable differential pressure values to be calculated. The flowrate sensors are located in the process fluid, water and air lines, respectively.

[0148] Pressure sensors PW1 and PW2 are positioned to monitor the pressure difference across the cooler 14. Specifically, the pressure sensors measure the pressure difference across the conduit supplying the sugar cane extract into the cooler 14. An increase in pressure would indicate a corresponding increase in fouling, for example comprising build up of sugar deposits.

[0149] Flowrate sensors VA and VB are positioned to monitor the air and sugar cane extract flow rates of the spray tower 16, respectively. A decrease in flow rate across the spray tower would indicate an increase in fouling which reduces the area available for fluid flow.

[0150] Second storage tank tower includes anti-fouling reagent tanks 20B1-B4. Tank 20B1 stores water (preferably maintained at 35° C.), tank 20B2 stores acetic acid solution, tank 20B3 stores sodium hydroxide and tank 20B4 stores cleaning solution (e.g. non-toxic soap solution).

[0151] One or more cleaning reagents are circulated through the cooler 14 and spray tower 16 when the cleaning protocol is triggered. The anti-fouling reagent tanks may be temperature controlled to maintain the solutions at an optimal temperature. For sugar refinement, the optimal temperature range for the cleaning reagents range from 20-40° C. Higher temperature can be used if the fouling is particularly stubborn.

[0152] The cleaning protocol may involve ultrasonication of the conduits of the cooler 14 and the spray tower 16.

[0153] The cleaning system allows residual fouling caused by the process fluid or any other substances, for example lime, to be removed from the apparatus quickly and efficiently.

[0154] The cleaning system also allows the apparatus to handle process fluids containing substances that cause fouling, such as lime-containing sugar cane solutions without the fouling adversely impacting on the efficiency of the apparatus, because of its ability to monitor, mitigate and remove build up of fouling.

[0155] First storage tank tower includes interim sampling tanks 12A3-A4 to receive the sugar cane extract when the cleaning protocol is initiated or when a sample of the process fluid is required.

[0156] In operation, sugar cane is crushed and mixed with water to form a sugar-containing extract. The extract is clarified in the absence of added lime and stored in feed tank 12A1 until it is ready to be processed.

[0157] The optimal operating conditions for this example are provided in the table below. These conditions apply to the process fluid feed spray nozzle inlet conditions (and feed outlet conditions) and the air in/out of the spray tower:

TABLE-US-00001 Process variable Value Air pressure ambient Air temperature in 20° C. Relative Humidity in 95-100% Air temperature out 30° C. Relative Humidity out 95-100% Air flow rate 250 L/s Feed temperature in 34° C. Feed temperature out 30° C. Feed flow rate 15 L/min Feed water pressure 140 kPa

[0158] During processing, the extract is pumped into cooler 14 in the form of a HVAC system. The extract is cooled to a temperature about 3-5° C., preferably 4° C., when it passes through the evaporator coil 28. This temperature range is below the maximum temperature the feed can tolerate before degrading or browning the extract in the feed. Ideally, the extract is cooled to about 30° C.

[0159] Alternatively, the cooler 14 may be substituted with a heat exchanger having heating and cooling functionality. In this embodiment, if the extract entering the heat exchanger is at a lower temperature than the predetermined temperature, the heat exchanger heats the extract to the predetermined temperature.

[0160] The extract is then fed into the process fluid inlet 30 of the spray nozzle 26 located at the top of spray tower 16 and sprayed downward into a humidified air stream in the chamber of the spray tower 16. The humidified air stream is formed by bubbling a stream of air, entering the spray tower via mass transfer medium inlet 32A, through stainless steel bubble plate 34 having a plurality of 1 mm holes into a stream of water being pumped into the spray tower 16.

[0161] The extract and humidified air stream meet in counter-current fashion which causes water from the extract to be removed into the air stream to concentrate the extract. For a 250 L/day laboratory unit, about 0.17 L/min of water is evaporated from the extract. The concentrated sugar solution exits spray tower process fluid outlet 31 and is either transferred to concentrate storage tank 12A2 or directed for further processing while the humidified air exits the spray tower via mass transfer medium outlet 33.

[0162] Part of the humidified air 40 can be cleaned and recycled back to the spray tower via cooler 14. The air steam 40 is directed to drift chamber inlet 42 and into eliminator 36. In the eliminator, entrained sugar solution removed from the humidified air stream is returned to the spray tower to be reprocessed while the cleaned air exits outlet 44 into the condenser 28 of cooler 14. The cleaned air may be used to cool the process fluid in the cooler before the cleaned air is returned to the spray tower for re-use as the mass transfer medium.

[0163] The drift eliminator is employed particularly to reduce fouling in condenser 24 when the air stream circulates the cooler 14.

[0164] In one example, the PLC initiates the cleaning protocol when the pressure across the cooler 14 increases above 10 kPa, the air flow rate across the spray tower 16 falls below 15 L/min or the process fluid flow rate across the spray tower 16 falls below 0.25 L/min.

[0165] Depending on the process variable which triggers the cleaning protocol, the PLC may take a number of steps to clean the relevant sections of the apparatus.

[0166] For example, if the trigger is the water flow rate, the PLC cleans the spray tower water line by controlling the valves of the apparatus to pump process fluid from the spray tower into one or both interim sampling tanks 12A3-A4 before releasing an appropriate anti-fouling reagent from its respective storage tank to circulate the spray tower to remove the fouling.

[0167] The anti-fouling reagent is circulated in the spray tower for 10 minutes or until the water flowrate returns within the threshold range. Once this requirement is met, the PLC deactivates the cleaning system and switches back to running process fluid through the apparatus. Preferably, a rinse cycle with water is performed to purge the anti-fouling reagent from the apparatus before the PLC switches back to process fluid.

[0168] If the trigger is the air flow rate, the PLC cleans the spray tower air line by controlling the valves in the apparatus to pump process fluid from the spray tower into interim sampling tanks 12A3-A4 before circulating air through the spray tower for 10 minutes or until the air flowrate returns within the threshold range. Once this requirement is met, the PLC deactivates the cleaning system and switches back to running process fluid through the apparatus. Preferably, a rinse cycle with water is performed before the PLC switches back to process fluid.

[0169] In another example, the cleaning protocol involves performing a rinse cycle (10 minutes of 22° C. rinsing water at 30 L/min (double cycle rate)) once per day. It was shown that the rinse cycle reduces fouling pressure buildup in cooler 14 from 66 kPa to 60 kPa with minimal disruption to operation (96.5% uptime).

[0170] To demonstrate the effectiveness of the cleaning system, in one example process of concentrating thin (dilute) sugar juice based on both commercial raw sugar or industrial inedible ‘sugar cake’, water was extracted from a 145 L 12% sucrose feed stream at a rate of 120 L/day to generate a 25 L 65% sucrose concentrate without causing any irreversible clogging of the apparatus 10. Good quality sugar concentrate and a water effluent stream were produced in the process. Over 30 day cycles were run which produced a small but significant amount of scale (a few mm thick within a 25 mm tube sufficient to cause a water flow drop from 18 down to 16 L/min). The cleaning protocol using one or more of water (at varying temperatures) and food grade acetic acid reversed the build-up to restore flow rate to 18 L/min (to zero mm of scale within measurement accuracy of flow rate).

[0171] In a further example, after a 3 day continuous evaporative process run 24 hours a day, the air pressure in the cooler increased from 60 to 66 psi. The cleaning protocol reversed the pressure build-up back to 60 psi after 5-10 minutes.