Sugar liquification system and process

An eductor-mixer has a first inlet which receives dry particulate sugar from a sugar feed system and has a second inlet which receives a pressurized working liquid adapted to mix with the dry particulate sugar to form a liquified sugar solution. The eductor-mixer also has a discharge adapted for discharging the liquified sugar solution. A tank system receives the solution discharged from the eductor-mixer. A working fluid circuit conducts pressurized working fluid to the second inlet of the eductor-mixer and includes a solution recycle line for conducting solution from the tank system to the second inlet of the eductor-mixer, and a water supply line for adding water to the solution conducted to the second inlet of the eductor-mixer. A heater adds heat to the system to increase the temperature of the solution to a temperature at or above a specified temperature. A measuring device measures the sugar content of liquified sugar solution. A control system automatically adjusts the amount of sugar supplied to the first inlet of the eductor-mixer and/or the amount of water added to the solution supplied as working fluid to the second inlet of the eductor-mixer if the sugar content of the solution, as measured by the measuring device, is different from a target sugar content. A finished solution outfeed line transfers the finished solution from the tank system to a desired location when the sugar content of the solution is substantially at the target sugar content.

BACKGROUND OF THE INVENTION
 This invention relates generally to the liquification of sugar and, more
 particularly, to a system which is capable of continuously mixing dry
 particulate sugar with a liquid, such as water, to form a liquid solution,
 and continuously pumping the solution to a location where it is stored or
 used.
 Liquified sugar is commonly used in the food industry. Heretofore,
 liquification has been carried out using a batch process in which dry
 sugar is conveyed to a tank of hot liquid (e.g., hot water) and
 mechanically mixed with the liquid to form a batch of sugar solution.
 After the batch is finished, it is pumped from the tank, usually to a
 remote location for storage or use in a food processing operation. The
 process is then repeated to complete the next batch. This type of system
 has several drawbacks, including relatively slow liquification rates, high
 equipment costs, high wear on the conveying and mixing equipment due to
 the granular nature of the sugar, clogging of the dry sugar conveying
 equipment due to steam and moisture in the area of the mixing tank, high
 equipment maintenance costs, and other disadvantages.
 SUMMARY OF THE INVENTION
 Among the several objects of this invention may be noted the provision of a
 system and process for liquifying sugar on a "continuous" rather than
 "batch" basis to achieve higher liquification rates; the provision of such
 a system and process which has lower equipment costs; the provision of
 such a system and process which is easier and less costly to maintain than
 conventional systems; the provision of such a system and process which
 operates at lower temperatures; the provision of such a system and process
 in which the sugar concentration of the solution can be selectively varied
 according to need; the provision of such a system and process which can
 automatically adjust to the rate of dry sugar feed and/or water flow rate;
 the provision of such a system and process which recirculates liquified
 sugar thereby maintaining continuous and accurate control of the sugar
 concentration of the solution; and the provision of a continuous
 steady-state mixing system having applications other than the
 liquification of sugar, such as the mixing of ingredients used for
 beverages, pharmaceuticals, paper coating and filling, food, paints, inks,
 coatings, thickeners and catalyst mixes.
 In general, a sugar liquification system of the present invention comprises
 an eductor-mixer, a tank system, a working fluid circuit, a heater, a
 measuring device, a control system and a finished solution outfeed line.
 The eductor-mixer has a first inlet for receiving dry particulate sugar
 from a sugar feed system, a second inlet for receiving a pressurized
 working liquid adapted to mix with the dry particulate sugar to form a
 liquified sugar solution, and a discharge adapted for discharging the
 solution. The tank system receives solution discharged from the
 eductor-mixer. The working fluid circuit conducts pressurized working
 fluid to the second inlet of the eductor-mixer. The working fluid circuit
 includes a solution recycle line for conducting solution from the tank
 system to the second inlet of the eductor-mixer and a water supply line
 for adding water to the solution conducted to the second inlet of the
 eductor-mixer. A heater adds heat to the system to increase the
 temperature of the solution to a temperature at or above a specified
 temperature. The measuring device measures the sugar content of the
 solution. The control system automatically adjusts the amount of sugar
 supplied to the first inlet of the eductor-mixer and/or the amount of
 water added to the solution supplied as working fluid to the second inlet
 of the eductor-mixer if the sugar content of the solution, as measured by
 the measuring device, is different from a target sugar content. The
 finished solution outfeed line conducts finished solution from the tank
 system to a desired location when the sugar content of the solution is
 substantially at the target sugar content.
 A sugar liquification process of this invention comprises the steps of:
 a) continuously feeding dry particulate sugar to a first inlet of an
 eductor-mixer,
 b) continuously pumping a pressurized working fluid including water to a
 second inlet of the eductor-mixer to enable mixing of the working fluid
 and the sugar in the eductor-mixer to form a liquified sugar solution,
 c) delivering solution from the eductor-mixer to a tank system,
 d) measuring the sugar content of solution discharged by the eductor-mixer
 and comparing the measured sugar content of the solution to a target sugar
 content,
 e) if the measured sugar content is different from the target sugar
 content, automatically adjusting the amount of sugar fed to the first
 inlet of the eductor-mixer and/or the amount of water in the working fluid
 fed to the second inlet of the eductor-mixer thereby to adjust the sugar
 content of the solution, and
 f) if the measured sugar content is substantially equal to the target sugar
 content, continuously conducting finished solution from the holding tank
 to a desired location.
 Other objects and features will be in part apparent and in part pointed out
 hereinafter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 Referring now to the drawings, and first to FIG. 1, a sugar liquification
 system incorporating the present invention is indicated in its entirety by
 the reference numeral 1. In general, the system comprises a supply of dry
 particulate sugar in a hopper 3, a sugar feed system, generally designated
 5, for feeding sugar from the supply, and an eductor-mixer 7 having a
 first inlet 9 for receiving dry particulate sugar from the sugar feed
 system 5, a second inlet 11 for receiving a pressurized working liquid
 solution 13 adapted to mix with the dry sugar to form a liquified sugar
 solution, a pressure sensor 12 for monitoring the pressure of the working
 liquid solution 13, and a discharge 15 for discharging the solution into a
 tank system generally indicated at 21. The eductor-mixer 7 also has a
 vacuum break valve 16 and a vacuum sensor 17 for sensing the vacuum at the
 inlet 9. The liquification system 1 also includes a working fluid circuit
 generally designated by an arrow 18 comprising a solution recycle line 19
 for conducting solution from the tank system 21 to the second inlet 11 of
 the eductor-mixer 7, and a water supply line 23 for adding water to the
 working fluid solution 13 conducted by circuit 18 to the second inlet 11
 of the eductor-mixer 7. A sugar content measuring circuit, or Brix
 circuit, generally designated by an arrow 25, is also provided. This
 circuit includes a Brix measuring device 27 for measuring the sugar
 content of solution 13 discharged into the tank system 21. If the sugar
 content of the solution, as measured by the Brix measuring device 27, is
 different from a target sugar content, a control system (to be described
 later) including a programmable logic controller (PLC) 29 automatically
 adjusts the amount of sugar supplied to the first inlet 9 of the
 eductor-mixer 7 and/or the amount of water added to the solution 13
 supplied as working fluid to the second inlet 11 of the eductor-mixer 7. A
 finished solution outfeed line 31 is provided for conducting finished
 solution from the tank system 21 to a desired location (e.g., storage
 tanks 33) when the sugar content of the working fluid solution 13 is
 substantially at the target sugar content. The finished solution is
 conducted from the tank system 21 at a rate controlled by PLC 29 which
 maintains the level of the solution 13 in the tank at a predetermined set
 point or within a predetermined set range.
 The various components of the overall system are described in greater
 detail below.
 The sugar feed system 5 comprises a variable-speed drive rotary feeder 35
 for feeding dry particulate sugar from the hopper 3 (or other source of
 sugar) at a selected rate controlled by PLC 29, and a delumper 37
 downstream of the feeder for delumping the sugar to insure a uniform flow.
 The feed system 5 further comprises a sugar mass flow meter 39 for
 measuring the volume of sugar flow, and a fluidizing hopper cone 41
 immediately downstream of the flow meter 39 for fluidizing the sugar with
 air for conveyance to the first inlet 9 of the eductor-mixer 7. The mass
 flow meter may be a Multicor Mass Flow Meter supplied by SCHENCK/ACCURATE
 of Whitewater, Wis. The fluidizing hopper cone 41 may be of the type
 described in co-assigned U.S. Pat. No. 4,848,975, incorporated herein by
 reference, and commercially available from Semi-Bulk Systems, Inc. of St.
 Louis, Mo. Sugar exiting the hopper cone 41 is conveyed to the
 eductor-mixer 7 via a sugar supply line 43. Other feed systems may be used
 to feed sugar to the eductor-mixer 7.
 The eductor-mixer 7 (sometimes referred to as an ejector-mixer) is
 preferably of the type described in co-assigned U.S. Pat. No. 4,186,772,
 which is also incorporated herein by reference. The device has an internal
 mixing chamber in which dry sugar and working fluid solution are mixed to
 form a liquid sugar solution of desired concentration. The discharge 15 of
 the eductor-mixer may be in the form of a long discharge tube or nozzle. A
 suitable eductor-mixer 7 is commercially available from Semi-Bulk Systems,
 Inc. of St. Louis, Mo.
 Preferably, the control system according to the invention includes a
 programmable logic controller (PLC) 29 such as a PLC Controller
 manufactured by Allen Bradley. However, it is contemplated that any type
 of control logic system may be used for controlling the system of the
 invention. For example, a microprocessor, digital logic circuitry, analog
 logic circuitry or a combination of all of these may be used to control
 the operation of the system of the invention. In FIG. 1, dashed lines are
 used to indicate input and output lines which interconnect the PLC 29 with
 various sensors, pumps, meters, valves, and other controls.
 FIG. 2 is a diagram in block form illustrating one preferred embodiment of
 decision logic by which PLC 29 may be programmed to control the sugar feed
 rate in the system of FIG. 1. The rate at which dry particulate sugar is
 fed, delumped, fluidized and provided to the eductor-mixer 7 depends upon
 the speed at which the variable speed drive rotary feeder 35 is operating.
 The PLC 29 controls the vacuum break valve 16 to open it upon start-up and
 to close it upon shut down to avoid wetting of portions of the
 eductor-mixer 7 when the system is not operating. In addition, the PLC 29
 is connected to the pressure sensor 12 to monitor the pressure of the
 working fluid. If the pressure exceeds a preset maximum, this indicates
 that the eductor-mixer 7 may be plugging up. If the pressure falls below a
 preset minimum, this indicates that pump 49 may not be operating properly.
 In addition, the PLC 29 is connected to the vacuum sensor 17 to monitor
 the vacuum. If the vacuum exceeds a preset maximum, this indicates that
 the eductor-mixer 7 may be plugging up. If the vacuum falls below a preset
 minimum, this indicates that the sugar supply may be insufficient. The PLC
 29 could shut down the system or indicate an alarm if the monitored
 pressure or vacuum exceeds the maximum or falls below the minimum.
 As shown in FIG. 2, the PLC 29 at step 202 compares the actual sugar flow
 rate (as measured by the mass flow meter 39) to a previously programmed
 set rate. If the flow rate is above the set rate, the PLC proceeds to step
 204 to reduce a drive speed control signal being provided to the feeder
 35. If the flow rate is equal to or below the set rate, the PLC proceeds
 to step 206. If the powder flow rate is less than the set rate, the PLC
 proceeds to step 208 to increase the signal to the feeder 35. If the
 powder flow rate is not less than the set rate, then it must be equal to
 the set rate so that the PLC 29 proceeds to step 210 to maintain the
 signal which is being applied to the feeder drive. The set rate may be a
 single rate or a range of rates. In either event, the set rate may be
 manually set by an operator or may be variable and controlled by a
 microprocessor or the PLC 29 or other programmable logic controller which
 sets the rate to depend on other parameters of the system. For example,
 the set rate may depend upon the sugar content of the working solution 13.
 As shown in FIG. 1, the tank system 21 comprises a single closed holding
 tank 45 having an opening in its top for receiving the discharge nozzle 15
 of the eductor-mixer 7 so that solution 13 is discharged directly into a
 closed space to reduce the emission of dust and other materials into the
 surrounding environment. As will appear later in this description (see
 FIG. 7), the tank system 21 may include more than one tank. The level of
 solution in the holding tank is sensed by a tank level sensor 47 of
 conventional design and is controlled by the PLC 29 as noted below (see
 FIG. 5).
 The working fluid circuit 18 includes a pump 49 with a variable-speed drive
 controlled by PLC 29 for pumping solution from the holding tank 45 through
 the recycle line 19 to the second inlet 11 of the eductor-mixer. A
 strainer 51 is provided downstream from the pump discharge for filtering
 the solution before it reaches the second inlet 11. The water supply line
 23 is connected to the recycle line 19 on the intake side of the pump 49
 so that water may be added to the solution as needed to vary the sugar
 concentration of the solution. Water which is added to the recycle line 19
 is drawn from a cold water source and is heated by a heater system 53 in
 line. The heater system 53 may be of any suitable type, such as a Model
 BEVB by TEMA, comprising a shell and tube exchanger 54, a hot water
 reservoir 54A, and a pump 54B for pumping heated water from the reservoir
 (see FIG. 8). A heater controller 55 is responsive to the PLC 29 as
 described below. The heater system 53 includes a temperature sensor 57
 downstream from a steam valve 59. Controller 55 opens and closes valve 59
 to heat the water supplied by line 23 to a set point temperature.
 FIG. 3 is a diagram in block form illustrating one preferred embodiment of
 the decision logic by which the PLC 29 may be programmed to control the
 water temperature in the system of FIG. 1. The controller 55 receives a
 control signal from the PLC 29 indicating the set point temperature or
 temperature range to which the cold water is heated. A temperature sensor
 61 in the Brix circuit 25 provides a signal to the PLC corresponding to
 the temperature signal of the working fluid solution 13. This signal is
 compared at step 302 to a desired temperature or a desired temperature
 range for solution 13. If the solution temperature is below the desired
 temperature, the PLC 29 proceeds to step 304 to increase the heater
 controller set point which results in an increase in the heated water
 temperature. If the solution temperature is not below the desired
 temperature, the PLC proceeds to step 306. If the solution temperature is
 above the desired temperature, the PLC proceeds to step 308 to lower the
 heater controller set point. Otherwise, the solution temperature must be
 at the desired temperature or within the desired temperature range so that
 the PLC proceeds to step 310 to hold the heater controller set point.
 As shown in FIG. 1., the flow rate through the water supply line 23 is
 controlled by a hot water flow control valve 63 and a hot water flow meter
 65. The flow meter 65 is operable to measure the rate of flow through the
 line 23. The flow valve 63 is operable by the PLC 29 to vary the flow rate
 to add the appropriate amount of water to the solution recycle line 19 to
 obtain the desired sugar concentration.
 FIG. 4 is a diagram in block form illustrating one preferred embodiment of
 decision logic by which the PLC 29 may be programmed to control the water
 flow in the system of FIG. 1. The hot water flow meter 65 provides a
 signal to the PLC 29 indicating the actual hot water flow rate. At step
 402, if the water flow rate is greater than a water flow set point, the
 PLC proceeds to step 404 to decrease the signal provided to the hot water
 flow control valve 63 thereby causing the valve to close and reduce the
 flow of hot water. The water flow rate set point needed to achieve a
 desired water/sugar ratio of the solution 13 is set in response to the
 Brix measuring device 27 and is described below with regard to FIG. 5. If
 the water flow rate is equal to or less than the flow set point, the PLC
 proceeds to step 406. If the water flow rate is less than the flow set
 point, the PLC proceeds to step 408 to increase the signal provided to the
 water valve 63 thereby opening the water valve and increasing the hot
 water flow rate. Otherwise, the water flow rate must be equal to the flow
 set point or flow set point range, in which case the PLC 29 proceeds to
 step 410 to maintain the water valve position.
 The sugar content measuring circuit 25 of FIG. 1 includes a working
 solution pump 67 with a variable-speed drive responsive to PLC 29 for
 pumping solution 13 from the holding tank 45 through the circuit 25 and
 back to the tank. As noted above, the Brix measuring device 27 measures
 the sugar content of the solution as it passes through this circuit.
 Although the measuring device has been preferably described as a Brix
 measuring device (e.g., a Process Refractometer Model 725 available from
 Liquid Solids Control, Inc. of Alpton, Mass.), it may be any device which
 indicates sugar concentration of the working solution 13. Such devices
 provide a reading indicative of the Brix number or sugar/water ratio of
 the solution. (The Brix number represents the percentage by weight of
 sugar in the solution at a specified temperature. For example, a Brix
 reading of 67 means that the solution has a sugar content of 67% by weight
 at a specified temperature.) The temperature sensor 61 is provided
 adjacent the Brix measuring device 27 to monitor the temperature of the
 solution being metered.
 FIG. 5 is a flow diagram in block form illustrating one preferred
 embodiment of decision logic by which the PLC 29 may be programmed to
 control the target sugar content (i.e., the Brix level) in the solution 13
 of the system of FIG. 1. At step 502, the PLC 29 compares the Brix level
 signal from the Brix meter 27 to a preset Brix level. If the Brix level of
 the solution is greater than the preset Brix level, the PLC proceeds to
 step 504 to determine the tank level. If the tank level sensor 47 is
 indicating that the tank level is higher than an acceptable level or
 range, the PLC proceeds to step 506 to discontinue sugar feeding by
 turning off the sugar feeder 35. In addition, finished solution (or syrup)
 transfer valve 69 transferring the finished syrup to the storage tanks 33
 is closed and a recirculate valve 71 which permits recirculation of the
 working fluid solution 13 is opened. If the system is already in a
 recirculation mode, then step 506 maintains valves 69 and 71 in this mode.
 In addition, step 506 closes the hot water flow control valve 63 to its
 lowest flow position. Alternatively, if sensor 47 indicates that the tank
 level is not higher than an acceptable level, the PLC proceeds from step
 504 to step 508 to discontinue sugar feeding by turning off feeder 35 and
 to switch or maintain the valves 69 or 71 in the recirculating position.
 The difference between steps 506 and 508 is that in step 508 the hot water
 flow control valve 63 is not closed to a minimum position since the tank
 level is not above an acceptable level.
 If the PLC 29 determines at step 502 that the Brix level is not greater
 than the preset Brix level, the PLC proceeds to step 510. If the Brix
 level of the solution is less than the preset Brix level, the PLC proceeds
 to step 512 to reduce the water flow rate set point which is used by the
 PLC 29 in accordance with the diagram of FIG. 4. In addition, step 512
 switches or maintains the valves 69 or 71 in recirculation position as
 described above with regard to step 506. If step 510 determines that the
 actual Brix level of the solution is not less than the preset Brix level,
 this means that the Brix level is within the set point or set point range
 so that the PLC 29 proceeds to step 514 to resume or hold the sugar feed
 rate of feeder 35 and to resume or hold the required water flow rate. In
 addition, step 514 continues or resumes the finished solution transfer to
 the storage tanks 33 by opening finished solution transfer valve 69 and
 closing recirculation valve 71.
 It should be pointed out that step 506 and step 508 control the Brix level
 by controlling feeder 35 and the sugar feed rate. It is also contemplated
 that the sugar concentration or Brix level can be controlled by
 controlling only the water flow rate set point and valve 63 as illustrated
 in FIG. 4. It should further be pointed out that step 512 increases the
 Brix level by reducing the water feed rate set point. It is contemplated
 that the Brix level may also be increased by increasing the powder flow
 rate set point as employed in the sugar feed rate control loop illustrated
 in FIG. 2. Alternatively, a combination of both water flow rate control
 and sugar flow rate control employing an interaction between FIGS. 2 and 4
 may be employed. In addition, both the sugar flow rate and water feed rate
 set points may be controlled in combination and in response to the logic
 of FIG. 5 in order to permit steps 506 and 508 to decrease the Brix level
 of the working fluid and to permit step 512 to increase the Brix level of
 the working fluid.
 As shown in FIG. 1, the finished solution outfeed line 31 is connected to
 the Brix measuring circuit 25 downstream from the measuring device 27.
 Flow through this line is controlled by the finished solution transfer
 valve 69. Until the sugar concentration of the solution in the holding
 tank 45, as measured by the Brix measuring device 27, reaches a selected
 target concentration, the recirculation valve 71 remains open and the
 transfer valve 69 remains closed to route solution back to the tank 45
 while blocking flow through the outfeed line 31. When the sugar
 concentration reaches (or substantially reaches) the desired target
 concentration, the transfer valve 69 opens to permit solution to flow
 through the outfeed line 31 to the storage tanks 33, and the recirculation
 valve 71 closes to block flow back to the holding tank 45. If the sugar
 concentration of the solution moves outside the target concentration, the
 transfer valve 69 closes and recirculation valve 71 opens to reroute
 solution 13 back to the tank 45 until the sugar concentration of the
 solution returns to the selected target. (The target concentration may be
 a precise concentration, e.g., Brix 67, or a range of acceptable
 concentrations, e.g., Brix 55-75.) The overall capacity of the holding
 tank 45 should be substantially greater (preferably at least about 50%
 greater) than the capacity needed when the system is operating within its
 target concentration. The additional capacity allows for any necessary
 adjustment of concentration, during which the level of solution in the
 tank will necessarily rise because the transfer valve 69 is closed.
 FIG. 6 is a diagram in block form illustrating one preferred embodiment of
 decision logic by which the PLC 29 may be programmed to control the level
 of the tank 45 in the system of FIG. 1. The tank level sensor 47 provides
 a signal to the PLC 29 indicating the level of solution 13 in the tank 45.
 At step 602, the PLC determines whether the system is in a transfer mode
 supplying finished solution or syrup to the storage tanks 33 or whether
 the system is in a recirculating mode. The mode is determined by whether
 or not the transfer valve 69 is open or closed. If the transfer valve 69
 is closed and recirculating valve 71 is open so that finished syrup is not
 being provided to the storage tanks 33, the PLC proceeds to step 604 to
 set the speed of the working solution pump 67 to a fixed recirculate speed
 previously programmed into the PLC. If the system is in the transferring
 mode, the PLC proceeds to step 606 to compare the actual tank level as
 indicated by the level sensor 47 to the tank level set point. If the tank
 level is greater than the set point level, the PLC proceeds to step 608 to
 increase the speed of the working solution pump 67. If the tank level is
 not greater than the set point level, the PLC proceeds to step 610. If the
 tank level is less than the set point level, the PLC proceeds to step 612
 to reduce the speed of pump 67. If the tank level is not less than the set
 point level, the tank level must be equal to the set point level or within
 a set point level range so that the PLC proceeds to step 614 to maintain
 the speed of pump 67.
 The storage tanks 33 illustrated in FIG. 1 may be equipped with suitable
 valving so that the tanks fill sequentially, for example. It will be
 understood that finished solution can also be routed directly to a food
 processing area for immediate use. A recirculation valve 75 and a
 recirculation line 77 are provided for recirculating solution back to the
 holding tank (if the solution needs to be warmed, for example). This line
 can also be used for cleaning the system.
 The eductor-mixer 7 and tank system 21 described above is preferably
 fabricated as a unit. To this end, the various components of this system
 may be mounted on a common frame, cart or skid for ease of transport.
 These components would include the eductor-mixer 7, the holding tank 45,
 and the working fluid and measuring circuits and associated pumps. For
 ease of use, the frame may be equipped with suitable connectors (e.g.,
 quick-connect connectors) for connecting fluid lines on the unit to fluid
 lines in the facility in which the system is installed. As shown in FIG.
 1, a connector 79 is used for connecting the water supply line 23 on the
 unit to a corresponding line from the water heater system 53, and a
 connector 81 is used for connecting the outfeed line 31 on the unit to a
 corresponding line to the storage tanks 33.
 FIG. 7 illustrates another embodiment of the system, generally designated
 701. This system is similar to the system described above and identical
 components are designated by the same reference numbers. System 701
 differs in that the tank system includes a relatively small surge tank 703
 for receiving solution discharged by the eductor-mixer 7, a holding tank
 705 at a remote location, and a transfer pump 707 for pumping solution
 from the surge tank 703 to the holding tank 705. The surge tank 703 and
 transfer pump 707 may be identical in construction and operation to that
 disclosed in co-assigned U.S. Patent No. 5,544,951 which is incorporated
 herein by reference. While FIG. 7 illustrates an arrangement wherein the
 measuring circuit 25 is connected to the remote holding tank 705, as in
 the first embodiment, it will be understood that this circuit 25 could be
 connected to the surge tank 703 instead of the holding tank 705. The
 advantage of using the FIG. 7 system is that it allows the eductor-mixer 7
 to be placed near the sugar feed system 5 and the holding tank 705 to be
 placed closer to a storage facility or food processing area.
 It is contemplated that heat could be added to the system for enhancing the
 solubility of the sugar by means other than, or in addition to, the heater
 system 53 shown in FIG. 1. For example, heat could be added to the system
 by heating the solution in the tank system 21, or in the solution recycle
 line 19, or in a separate recirculation line, as described in detail
 hereinafter.
 FIGS. 8-11 illustrate a third embodiment of the system, generally
 designated 801. This system is generally similar to the systems described
 above and identical components are designated by the same reference
 numbers. System 801 differs in that the solution recycle line 25 of system
 1 is replaced by a solution recirculation circuit, generally designated
 803, for recirculating solution from the tank system 21, and a second
 heater 805 in the recirculation circuit for heating solution passing
 through the circuit. This second heater 805 is preferably a heat exchanger
 connected to a suitable hot-water source, such as reservoir 54A. (Water
 exiting the heat exchanger 805 is routed back to the reservoir 54A via
 line 807.) In any event, the heater 805 should be capable of adding
 sufficient additional heat to the system 801 to achieve the desired
 solubility of the sugar in the desired solution in the desired amount of
 time. By way of example, the heater 805 may be sized and configured to
 heat the solution at a rate of 35 to 75 gallons per minute based on the
 requirements of the size of the system. A measuring device 813 for
 measuring the sugar content of the solution is provided in the
 recirculation circuit 803. This device 813 may be any suitable device, but
 is preferably a slurry density meter capable of accurately measuring the
 density of the sugar in the solution even in the presence of undissolved
 solids in the solution. A suitable density meter 813 is commercially
 available from Micro Motion of Boulder, Colorado. Solution is pumped
 through the recirculation circuit 803 by a pump designated 815. Suitable
 temperature gauges 817, 819 are provided upstream and downstream from the
 heater 805 and on the tank system 21 for indicating the temperature of the
 solution.
 System 801 also includes a finished solution outfeed line 823 which
 includes a transfer valve 825 (similar to valve 69) and a pump 827 for
 pumping finished solution through the outfeed line to the storage tanks 33
 (not shown). A solution holding device 829 may be provided in the outfeed
 line 823 for increasing the holding time of the solution in the line, and
 thus giving the sugar more time to fully dissolve, if this is necessary.
 This device 829 comprises a housing 831 and a length of tubing 833 bent to
 form a tortuous winding path through the housing which increases the "hold
 time" of the solution by a suitable period (e.g., 1 to 11/2 minutes) for
 achieving total solubility. Any type of suitable holding device 829 may be
 used, one such device being commercially available from Semi-Bulk Systems,
 Inc. of St. Louis, Mo. A filter 835 is provided immediately downstream of
 the holding device 829 for removing all crystal seeds and other impurities
 from the syrup. A measuring device 841 for measuring the content of the
 solution is provided downstream from the filter and upstream from a
 transfer control valve 843. If the sugar content of the solution (as
 measured by device 841) is acceptable, the control valve 843 moves to an
 open position to allow solution to be transferred to the storage tanks 33
 via line 845. If the sugar content is outside an acceptable range, the
 control valve 843 operates to divert the solution back to the tank system
 21 via line 847. The measuring device 841 may be a Brix measuring device
 or meter similar to device 27 in system 1.
 The sugar feed rate, water flow and tank level for system 801 may be
 controlled using the same logic illustrated in FIGS. 2, 4 and 6,
 respectively, for system 1. As explained in more detail below, FIGS. 9, 10
 and 11 are flow diagrams in block form illustrating preferred embodiments
 of decision logic by which the PLC 29 may be programmed to control the hot
 water temperature, sugar concentration and transfer control valve,
 respectively.
 The preferred hot water temperature flow control diagram for system 801 is
 identical to the diagram shown in FIG. 3 except for the change shown in
 FIG. 9 involving the addition of a separate branch line 851 for directing
 hot water from the heating system 53 to the plate exchanger 805.
 Referring now to FIG. 10, at step 862, the PLC 29 compares the signal from
 the density measuring device 813 to a preset (target) density level. If
 the actual density level of the solution is greater than the preset
 density level, the PLC proceeds to step 864 to determine the tank level.
 If the tank level sensor 47 is indicating that the tank level is higher
 than an acceptable level or range, the PLC proceeds to step 866 to
 discontinue sugar feeding by turning off the sugar feeder 35. In addition,
 step 866 closes the hot water flow control valve 63 to its lowest flow
 position. Alternatively, if sensor 47 indicates that the tank level is not
 higher than an acceptable level, the PLC proceeds from step 864 to step
 868 to discontinue sugar feeding by turning off feeder 35. The difference
 between steps 866 and 868 is that in step 868 the hot water flow control
 valve 63 is not closed to a minimum position since the tank level is not
 above an acceptable level.
 If the PLC 29 determines at step 862 that the density level is not greater
 than the preset density level, the PLC proceeds to step 870. If the
 density level of the solution is less than the preset density level, the
 PLC proceeds to step 872 to reduce the water flow rate set point which is
 used by the PLC 29 in accordance with the diagram of FIG. 4. If step 870
 determines that the actual density level of the solution is not less than
 the preset density level, this means that the density level is within the
 set point or set point range so that the PLC 29 proceeds to step 874 to
 resume or hold the sugar feed rate of feeder 35 and to resume or hold the
 required water flow rate.
 It should be pointed out that step 866 and step 868 control the density
 level by controlling feeder 35 and the sugar feed rate. It is also
 contemplated that the sugar concentration or density level can be
 controlled by controlling only the water flow rate set point and valve 63
 as illustrated in FIG. 4. It should further be pointed out that step 872
 increases the density level by reducing the water feed rate set point. It
 is contemplated that the density level may also be increased by increasing
 the powder flow rate set point as employed in the sugar feed rate control
 loop illustrated in FIG. 2. Alternatively, a combination of both water
 flow rate control and sugar flow rate control employing an interaction
 between FIGS. 2 and 4 may be employed. In addition, both the sugar flow
 rate and water feed rate set points may be controlled in combination and
 in response to the logic of FIG. 10 in order to permit steps 866 and 868
 to decrease the density level of the working fluid and to permit step 872
 to increase the density level of the working fluid.
 Referring to FIG. 11, at step 880, the PLC 29 compares the signal from the
 Brix measuring device to a preset (target) Brix level. If the actual Brix
 level of the solution in line is greater than the preset Brix level, the
 PLC proceeds to step 882 to switch to or maintain the transfer and control
 valves 825, 843 in a recirculation position for recirculating the solution
 through the recirculation circuit 803. If the PLC 29 determines at step
 880 that the Brix level is not greater than the preset Brix level, the PLC
 proceeds to step 884. If the Brix level of the solution is less than the
 preset Brix level, the PLC proceeds to step 886 to switch to or maintain
 the transfer and control valves 825, 843 in a recirculation position for
 recirculating the solution through the recirculation circuit. If step 884
 determines that the actual Brix level of the solution is not less than the
 preset Brix level, this means that the Brix level is within the set point
 or set point range so that the PLC 29 proceeds to step 888 to operate the
 valves 825, 843 to continue or resume syrup transfer to the storage tanks
 33.
 The sugar liquification system and process of this invention has
 significant advantages over prior systems. In the present system, after
 the system reaches a steady-state condition, sugar is continuously
 liquified to form a solution, and the solution is continuously pumped to
 storage or for immediate use in a food processing operation, which is much
 more efficient than prior "batch" systems. By using an eductor-mixer, the
 use of conventional sugar conveyors is eliminated, thereby avoiding
 cleaning and maintenance problems associated with such conveyors, and
 further reducing the emission of sugar particles into the air. Equipment
 costs are also substantially lower, and maintenance is easy since the
 entire system can be cleaned in place without disassembly simply by
 pumping a cleaning solution through the system. The system is also very
 flexible in that the sugar concentration of the solution can readily be
 varied as necessary. As noted above, the system is also easy to transport.
 It will be understood that the system and process of the present invention
 have specific applications other than the sugar industry. For example, the
 invention has applications in the beverage industry where beverage
 ingredients (e.g., citric acid powder and carbonated water; powdered
 calcium and juices) may be mixed, diluted (if necessary) and then pumped
 directly to the filling/packaging line; in the pharmaceutical industry
 where powder ingredients are mixed with liquid to form a fluid mixture
 which can be pumped to a reactor; in the paper industry where starch
 powders and filler powders (e.g., titanium dioxide, calcium carbonate,
 clay, silica) are mixed with water for use in paper coating and filling
 processes; and in the food industry where slurries can be mixed and fed
 directly to drying operations for the processing of cereal, for example.
 Other possible applications include the continuous mixing of powder
 pigments and powder fillers with water or liquid solvents to manufacture
 bases for paints, inks and coatings; the continuous mixing of dairy
 ingredients (e.g., powder protein additives or other powder ingredients
 added to water or fresh milk) to form mixes which can be pumped to
 pasteurizing and homogenization operations; the continuous mixing of
 aluminum flux powder and liquid such as water to make a flux slurry which
 can be sprayed on heat exchangers in a controlled-atmosphere brazing
 process; the continuous mixing of powders (e.g., carboxyl methyl
 cellulose, guar gum) and water or other liquid to form thickeners; and the
 continuous mixing of catalyst powders (e.g., activated carbon) and liquid
 to form catalyst mixes which can be injected into reactors/reactions at
 controlled rates using a volumetric feeder, for example.
 In view of the above, it will be seen that the several objects of the
 invention are achieved and other advantageous results attained.
 As various changes could be made in the above methods and constructions
 without departing from the scope of the invention, it is intended that all
 matter contained in the above description and shown in the accompanying
 drawings shall be interpreted as illustrative and not in a limiting sense.