WO1999015255A1

WO1999015255A1 - Method and apparatus for monitoring, controlling and operating rotary drum filters

Info

Publication number: WO1999015255A1
Application number: PCT/US1998/019280
Authority: WO
Inventors: Wallace Leung
Original assignee: Baker Hughes Incorporated
Priority date: 1997-09-19
Filing date: 1998-09-16
Publication date: 1999-04-01
Also published as: WO1999015255B1; AU9487998A

Abstract

A method and apparatus for monitoring, diagnosing, operating, and controlling various parameters and processes of rotary filters are presented. Particularly important parameters are the solid mass throughput, the percent of cake solids, and the cake purity. Preferably, a computer control system actuates at least one of a plurality of control devices based on input from one or more monitoring sensors so as to provide real time, continuous, operational control of the rotary filter parameters. As a result of the analysis, at least one output may be generated to activate a control device that effects changes in the operation and input stream of the rotary filter.

Description

METHOD AND APPARATUS FOR MONITORING, CONTROLLING, AND OPERATING ROTARY DRUM FILTERS

Background of the nvention

1. Field of the Invention

This invention relates generally to rotary drum filters. More particularly, this invention relates to methods and apparatus for automatically monitoring, controlling, and operating rotary drum filters using intelligent computer control systems and remote sensing devices. This invention is particularly useful for the control of parameters such as throughput, cake moisture, and cake purity.

2. Description of the Related Art

A rotary drum filter is a machine designed for the separation of solids from liquids by filtration, using pressure or partial vacuum. Such filters are referred to as rotary drum filters, rotary vacuum filters, rotary pressure filters, or simply rotary filters. Rotary filters can be single-chamber, or multi-chamber filters having a rotary drum upon which a filter medium or cloth is disposed. The rotary drum is axially connected to a center pipe. A source slurry is filtered by immersing the lower part of the rotating drum in a source slurry bath. The fraction of the drum submerged in the slurry ranges between 5% to 20% for single-chamber rotary filters and 25% to 35% for multiple- chamber filters. After dewatering a cake of solids is formed on the filter medium or cloth.

Under a differential pressure (higher at the drum outer diameter) across the drum both solid and liquid in the slurry move toward the drum surface. The outer periphery of the drum is lined with a filter medium. The liquid filters through the medium and is collected in the interior of the drum while the solids form a cake deposited on the filter medium. The cake is further washed and dewatered. The differential pressure can be a vacuum drawn inside the drum, or a positive pressure applied across the drum. The process steps of slurry feeding, initial dewatering, cake washing, final dewatering and cake discharge all take place in one revolution of the drum. After initial dewatering, the formed filter cake may be washed, followed by a final dewatering. The cake formed on the outer surface of the filter cloth is discharged by a doctor blade or scraper, strings, discharge rollers, or back-blown with air delivered from a slit of a valve shoe fixed to the center pipe via a small pressure differential. Without proper discharge, remains of cake (cake heel) left on the filter medium reduces the effectiveness of subsequent filtration effectiveness. In some applications, filter aids such as diatomaceous earth, celite and rice hulls are added to the feed slurry so as to reduce the cake resistance to filtration. The optimal amount/dosage of the filter aid depends on the nature of the feed solids contained in the feed slurry. Monitoring, controlling, and optimizing the operation of rotary filters is a difficult task considering that the surface area of the drum (360° circumference) is used to carry out the multiple tasks of feeding, preliminary dewatering, washing, final dewatering, and cake discharge. If time required for one or more of these processes needs to be lengthened, the time for performing the other processes will necessarily be shortened. For example, if washing is important and the wash takes place along an arc of 90° instead of 60°, then the final dewatering will need to be reduced from, for example, 120° down to 90° or less. In addition, the changing characteristics of the input or feed stream (slurry) and the filtrate and cake outputs contributes to the difficulties encountered in monitoring, controlling and optimizing the operation of rotary drum filters. A number of patents disclose various non-computerized, mechanical methods and apparatus directed to control rotary filters. The majority of these are addressed to controlling removal of the filter cake from the drum, for example U.S. Patent No. 3,616,908 to Rokitansky (manual adjustment of a device holding the scraper); U.S. Patent No. 3,814,260 to Daubman et al. (adjustment of the table on which the scraper sits in relation to the rotary filter); U.S. Patent No. 4,618,424 to Lundin (attachment of the doctor knife to a rotatable trough); and U.S. Patent No. 4,735,730 to Bratten (clutch mechanism for engaging the scraper in response to the build-up of solids).

U.S. Patent No. 3,979,289 to Bykowski et al. discloses use of an electronic timer to control the spray of liquid used to dislodge the filter cake collected internally on a rotary filter. Another non-computerized arrangement for automatically cleaning the filter medium is disclosed in U.S. Patent No. 5,423,977 to Aoki et al., comprising a series of high pressure nozzles and a guide plate. U.S. Patent No. 5,190,673 also discloses a non-computerized arrangement of nozzles for cleaning a rotary filter used for dewaxing. Mechanical control of the reservoir depth is disclosed in U.S. Patent No.

3,869,389 to Rokitansky, using a fluid- actuated motor for raising or lowering the reservoir. JP 8-112509 discloses an adjustable weir for changing the height of the feed slurry. Non-computerized methods for adjusting or changing the filter medium are disclosed in U.S. Patent Nos. 5,112,485 and 4,826,596 to Hirs. In contrast, a computerized control system for addition of flocculent during operation of a rotary filter apparatus is disclosed in U.S. Patent No. 4,824,581 to Cooper. Flocculent control is based on continuous or intermittent ultrasonic measurement of pool depth at the upper end of an inclined filter belt, or on the measurement of torque required to rotate the filter drum. A method for controlling cleaning of the filter medium is disclosed in U.S.

Patent No. 5,362,401 to Whetsel. The pressure in a suction nozzle used during backwashing is monitored by a bubbler-type differential pressure sensor, and a high- pressure wash is initiated after the pressure in the suction device reaches a preselected sub-atmospheric pressure. A microprocessor controls operation of the filter apparatus, as well as the cleaning sequences. Cleaning sequences may also be initiated based on signals from multi-probe liquid level sensors.

Another controller-operated cleaning system for a rotary filter is disclosed in U.S. Patent No. 5,213,696 to Patrone et al. A "control network means" communicates with a status apparatus, a drain apparatus, and a cleaning apparatus. The "control network means" is undefined, while the remaining apparatus is a system of valves and drains. No sensors per se are disclosed. Another undefined "control unit" is disclosed in connection with an ultrasonic system for cleaning ceramic filter plates in U.S. Patent No. 4,946,602 to Ekberg et al. Ultrasonic "detectors" are used to generate ultrasound to clean the plates. The ultrasonic "detectors" are apparently not used as sensors, but rather as sources of ultrasound to aid in cleaning.

The various computerized control methods and apparatus described above are directed to specific systems and parameters of the rotary filters. However, none of the prior art is directed to a comprehensive, computerized control system for operating, controlling, and monitoring rotary filters. The ability to provide precise, real-time control and monitoring of such rotary filters constitutes an on-going and critical industrial need.

Summary of the Invention:

The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the several methods and apparatus of the present invention for providing computerized systems for operating, controlling, monitoring, and diagnosing various process parameters of rotary filters. Preferably, the computerized system is an "intelligent" system comprising computerized control methods. These include, but are not limited to, neural networks, genetic algorithms, fuzzy logic, expert systems, statistical analysis, signal processing, pattern recognition, categorical analysis, or a combination thereof, which are used to analyze input variables in terms of one or more self-generated, continuously updated, internal models, and to make changes in operating variables as suggested by those models. An intelligent rotary filter of the type disclosed herein has the capability of providing information about itself, predicting its own future state, adapting and changing over time as feed and machine conditions change, knowing about its own performance and changing its mode of operation to improve its performance. Specifically, the control system of the present invention regularly receives instrument readings, digitized video images, or other data indicating the state of the rotary filter analyzes these readings in terms of one or more self- generated, continuously updated, internal models and makes changes in operating variables as suggested by the internal models.

In one embodiment, the present invention comprises a rotary filter, at least one sensor, at least one control device, and a computer-based control system which actuates the at least one control device based on input from the at least one sensor, whereby at least one operating parameter of the rotary filter is sensed and controlled by the computer-based control system. The sensing and control feedback allows the rotary filter to operate continuously at or near optimal performance.

At least one sensor may sense process and other parameters, including machine operation parameters and parameters related to the input and output streams of the rotary filters. Examples of parameters sensed in real time include the mass throughput, the drum rotation speed, the percent submergence of the drum in the feed trough, the temperature of the feed slurry, the percent of solids in the feed slurry, the fraction of cycle time for filtration and cake formation, the cake height, the cake resistance, the percent cake moisture, the pressure drop across the cake and filter, the wash ratio, the temperature of the wash fluids, cake purity, the fraction of cycle time for washing the cake, the fraction of cycle time for drying and dewatering the cake, the viscosity of the filtrate, and the air flow rate across the filter media and cake.

These variables may either be controlled by the at least one control device, or determined as a fixed property of the material to be filtered. Monitoring and control of these parameters enables the operator to adjust the operating variables to achieve the optimal mass throughput, percent of cake solids, and cake purity to their optimal levels. In a preferred embodiment, the sensor or sensors comprise load cells, proximity sensors, ultrasonic transducers, conductivity sensors, infra-red absorbance sensors, photonic sensors of any type, sonar sensors, pressure transducers, ultrasonics, speed pickup sensors, tachometers, temperature sensors, probes sensitive to percent contaminants present in the cake, air flow meters, and rotameters for wash rate.

The response of the control system is preferably based on a series of expert rules, determined initially in advance and continually updated based upon the control system's own analysis of its performance. The control system generates and continually updates its own "process model", using the data input described above and one or more of several advanced analysis techniques, including but not limited to neural networks, genetic algorithms, fuzzy logic, expert systems, signal processing, pattern recognition, categorical analysis, statistical analysis, or a combination thereof. Preferably, the control system has the ability to independently select the best analysis technique for the current data set. Thus, the computer controller may actuate one or more control devices to control any number of process and operational control variables based not only on one or more of the sensor inputs but also on the currently selected process model. Based on one or more of these analyses, the controller may activate one or more control devices to control at least one process control variable including, but not limited to, a variable speed drive vacuum pump or compressor, bleed-off valve openings, heaters, heat exchange apparatus for heat exchange with cooling water through the vacuum pump, volumetric flow valves, density flow valves, motor drive speed controls for turning the filter drum.

In another preferred embodiment, the present invention comprises a rotary drum filter comprising modules in communication with each other in terms of fluid flow and having at least one node located between each module. The modules include a filter module, a suction pipe module, a bleed valve module, and a vacuum pump module. It is within the scope of the present invention that the vacuum pump module is replaced by a compressor module located upstream of the rotary filter to pressurize the slurry for filtration. The operating characteristics for each module are described in terms of pressure differentials across the module as measured at the node locations and flow rate of fluid (gas and liquid) through the module. Sensors are located at each of the nodes to monitor the level of pressure on a continuous basis. Flow meters are also installed to monitor the flow rate through each module. The operating characteristics of each module is entered into the computer controller as the process model (preferably as a series of expert rules). The sensors communicate the pressure levels at each node and flow rate of fluid through the module to the computer controller on a continuous basis. The computer controller uses the sensor input to determine the relative level of operation of each of the modules against the process model. The computer controller sends output commands to control devices to change certain operating parameters to bring the relative level of the filter system toward an optimal level. Output control devices may change a number of components comprising a module such as a variable speed vacuum pump or compressor, a bleed valve opening, submersion levels, etc.

Because the sensors continuously monitor the pressure at the nodes as well as the flow through the modules, the control system of the present invention is constantly adjusting and maintaining the entire filter system toward an optimal level of operation. The computer controller used in the system of the present invention is preferably a personal computer or workstation, with an associated display device (CRT screen) and input/output device (keyboard or touch-sensitive screen). The controller may be located at the rotary filter, or at a remote location such as a central control room in a plant. Importantly, the controller may control one or a plurality of rotary filters at a single or plurality of sites. The above-described computerized control and monitoring system for rotary filters provides a comprehensive scheme for monitoring and controlling a variety of input and output parameters as well as a plurality of operational parameters resulting in greater efficiency, optimization of operation and increased safety.

The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.

Brief Description of the Drawings

Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: FIGURE 1 is a simplified cross-sectional schematic of a generic, single- chamber prior art rotary filter having a bottom feed;

FIGURE 2 is a simplified perspective view partially in section of single- chamber prior art rotary filter; FIGURE 3 is a cross-sectional schematic taken about the rotational axis of a prior art rotary filter of the type shown in FIGURE 2;

FIGURE 4 is a simplified perspective view partially in section of a multi- chamber prior art rotary filter having individual filter segments and a filter valve;

FIGURE 5 is a simplified cross-section schematic view taken in cross-section of the rotary filter shown in FIGURE 4;

FIGURE 6 is an exploded perspective view of the individual filter segments of the rotary filter shown in FIGURE 4;

FIGURE 7 is a schematic view of the filter valve arrangement of the rotary filter shown in FIGURE 4; FIGURE 8 is a schematic diagram showing a sensing and control system for rotary filters in accordance with the present invention;

FIGURE 9 is a simplified cross sectional schematic of a slurry level control system for rotary filters in accordance with the present invention;

FIGURE 10 is a graphical representation showing the effect of the control system in FIGURE 9 on slurry height;

FIGURE 11 is a schematic diagram showing the four modules or components typical of rotary filter systems, the interfacing nodes, and associated air and liquid flow streams in accordance with the analytical method of the present invention;

FIGURE 12 is a graphical representation showing the cumulative volume of collected liquid (V_f), for a fixed vacuum or pressure differential (Δp), as a function of time (t);

FIGURE 13 is a graphical representation showing the effect of vacuum (Δp or P_G) on the rate of filtration for a fixed time for incompactible, moderately compactible, and highly compactible cakes; FIGURE 14 is a graphical representation showing the effect of other factors on the pressure drop filtration rate characteristics;

FIGURE 15 is a schematic diagram illustrating the parameters of a pickup tube module for flow of a two-phase air and liquid mixture in accordance with the present invention;

FIGURE 16 is a graphical representation showing the effect of girt pressure (P_G) and different tube diameters on a two-phase fluid, air and liquid, flow rate;

FIGURES 17 is a graphical representation showing the condition of equilibrium wherein the filtrate rate established from filtration is equal to the fluid rate in the pick up tube wherein the equilibrium girt pressure can be determined;

FIGURE 18 is a graphical representation showing the effect of vacuum on the filtration rate for two different filter areas when the vacuum level at the separator p_s is held constant;

FIGURE 19 is a graphical representation showing the effect of pickup tube diameter on the equilibrium girt pressure P_G;

FIGURE 20 is a graphical representation showing the effect of separator vacuum pressure P_s on the total air flow rate (Q_ajr) and liquid filtrate rate (Q_f);

FIGURE 21 is a graphical representation of the air flow rate versus the vacuum pressure P_s generated for different vacuum pump speeds; FIGURE 22 is a graphical representation showing the effect of separator vacuum pressure (P_s) on the air flow rate (Q_air) for bleed valve module opened to atmosphere and having orifices of different diameters;

FIGURE 23 is a graphical representation showing the effect of separator vacuum pressure on total air flow from both the bleed valve and the filter; FIGURE 24 is a graphical representation of equilibrium wherein the total air flow from both the bleed valve and the filter is maintained by the vacuum pump. This equilibrium can be controlled by the amount of bleeding to atmosphere and the vacuum pump RPM;

FIGURE 25 is a graphical representation showing the effect of vacuum pressure of the separator on the filtrate flow (Q_f); and FIGURES 26-A-C are schematic cross-sectional diagrams of rotary filters illustrating differential pressure drops across the filter for (A) feed and filtrate at one bar (Δp = about 1 bar); (B) feed at 4-5 bar and filtrate at 4-5 bar (Δp = about 1 bar); and (C) feed at 4-5 bar and filtrate at about one bar (Δp = about 4-5 bar).

Detailed Description of the Invention

This invention relates to methods and apparatus for automatically controlling, operating, and monitoring rotary filters using computer control systems. In a first embodiment, this invention comprises a rotary filter, at least one sensor, at least one control device, and a computer-based control system which actuates the at least one control device based on input from the at least one sensor, whereby at least one parameter of the rotary filter is sensed and at least one parameter is controlled by the computer-based control system. The computer-based control system may be either a computer or a computer-type, central processing unit (CPU) in conjunction with a programmable logic controller (PLC). The sensing and control feedback allows the rotary filter to operate at or near optimal performance.

FIGURE 1 is a schematic diagram illustrating the essential components of a generic rotary filter 10 using a bottom feed. Rotary filter 10 generally comprises a filter drum 12 lowered into trough 14 containing a suspension, or slurry, 16 to be filtered. Filter drum 12 is of cylindrical configuration, the outer cylinder wall having a plurality of perforations or drainage openings (42 in FIGURES 2 & 3). Filter drum 12 provides a means of supporting the filter medium 17. Filter drum 12 is rotatable about a conduit or center girt 18, also referred to as a "pickup tube", in the direction indicated by arrow 19. A partial vacuum may be produced within filter drum 12 by a vacuum source (indicated by arrows 21 in FIGURES 2 and 3) via conduit 18. As the filter drum rotates over suspension 16, also referred to as feed segment indicated by 5, both the liquid and solid in the slurry are drawn to the drum by means of the vacuum. The liquid filters through the medium while the solids are retained to form a filter cake 20. As the drum continues to rotate, through predry segment 6, the cake is pre-dried with additional liquid removed from the cake through filter drum 12 by virtue of the partial vacuum inside the drum. Filter cake 20 is washed during rotation through wash segment 20 using wash liquid 22 from spray nozzles 24. Alternatively, overflow from a wash box is used during rotation through wash segment 7 to obtain displacement wash by laying wash liquid 22 uniformly on the cake 20 to displace the residual mother liquor.

Filter cake 20 is dewatered, if necessary, by means of the applied vacuum through segment 8, and then is discharged pneumatically via air nozzles 26, via doctor blade 28, or a combination of the two devices. Pneumatic means are particularly advantageous, as the conventional rotary filter using doctor blade 28 alone typically requires the filter to be backwashed after a set number of cycles to avoid glazing of the cake heel left on the cloth. This is because the doctor blade stands at a small distance from the cloth to avoid ripping of the cloth, yet this leaves a cake heel behind. A dead segment 9 exists between the time the drum rotates past doctor blade 28 and reenters suspension 16. As shown in FIGURE 1 in phantom, a pressurized rotary filter further comprises housing 30, allowing isolation of the filter from the atmosphere, or to allow the application of pressure above atmospheric to aid in filtration.

As used herein, "rotary filter" refers to all configurations of rotary drum filters unless specifically indicated otherwise. Rotary drum filters have many different configurations, including top and bottom feeds and various discharge mechanisms. One of the more important differences between typical configurations is in the method of applying vacuum or pressure to the system in order to effect filtration. In one type of configuration, vacuum or pressure is applied to the entire drum interior or exterior, with perforations through the drum for passage of filtrate. FIGURES 2 and 3 show a vacuum driven single-chamber rotary filter 40 of this type. Referring now to FIGURES 2 and 3, rotary filter 40 comprises filter drum 12 having a plurality of perforations 42 or drainage openings. Filter drum 12 is rotatable about the pickup tube 18 in the direction indicated by arrow 19 in Figure 2 and a vacuum is produced within filter drum 12 by a vacuum source indicated by arrow 21 via conduit 18. Liquid filtrate and gases, indicated by arrow 43, is removed from the cake through filter drum 12 by virtue of the partial vacuum inside the drum. Internal wash collection pan 46 is used to ensure discrete separation between washes, minimizing dilution of filtrate and contamination of wash liquid. As shown in FIGURE 2, the rotary filter may further comprise housing 50, allowing isolation of the filter from the atmosphere. Shoes" 48 located at the discharge zone on the inside of drum 12 block the flow of vacuum and permit cake discharge through a differential pressure of between 0.2-0.5 psig between the shore and the housing 50. This type of rotary filter effects thin cake filtration, washing, and drying by using a high drum rotation speed (typically 10 to 40 rpm) under vacuum or differential pressure. As a result, certain prior art rotary filters achieves high solids capacity with low cake moisture, and high product purity.

FIGURE 4 shows a conventional multi-chamber rotary filter 60 in which operational control of filter is provided by a filter valve 62 such as is shown in detail in greater detail in FIGURES 5, 6, and 7. This particular rotary filter results in thicker cake filtration, washing, and drying than those described herein above by using lower drum rotation speeds in the range from 1/3 to 10 rpm. Referring to FIGURES 4, 5, 6, and 7, vacuum is applied to drum 12 via individual filter segments 64 connected through internal pipes 66. Ports 68 of internal pipes 66 at the manifold disk 68a, are either open or closed to vacuum source indicated by arrow 21 via bridge blocks 70. The filter segments 64 with the internal pipes 66 and the manifold disk 68a all rotate in the direction 66a shown in Figures 5 and 6. The bridge blocks 70 are shown disposed in the stationary vacuum distribution ring 72 in FIGURES 6 and 7. The bridge blocks can be adjusted to cover or expose the ports connected to the separate sections of the filters. Vacuum is supplied to valve 62 from the vacuum source through the stationary suction housing 76. Filter valve 62, which consists of the rotating manifold disk 68a and the mating stationary vacuum distribution ring 72, is thus used to regulate, for each filter segment 64, the relative duration of each phase of the filtration cycle, as well as to isolate the active portions of the cycle from the "dead" portions of the cycle as indicated by segment 9 in Figure 1.

In accordance with the present invention, rotary filters are provided with one or more sensors for the sensing of one or more parameters related to the operation of the rotary filter, and one or more control devices for controlling one or more parameters related to the operation of the rotary filter. A computerized control system is further provided, which may be located at the rotary filter, near the rotary filter, or at a remote location from the rotary filter. The computerized control system may be a computer or a computer-type, central processing unit (CPU) in conjunction with a programmable logic control (PLC). The sensing and control feedback allows the rotary filter to operate at or near optimal performance.

FIGURE 8 shows a schematic diagram of a rotary filter generally illustrating examples of the monitoring sensors, control devices and computerized control system in accordance with the present invention. FIGURE 8 more particularly shows rotary filter 10 associated with one or more process sensors 82 and/or operational sensors 84 and with one or more process control devices and/or operational control devices 88. Both the sensors 82, 84 and the control devices 86, 88 communicate through a suitable communications system with computer controller 90. Controller 90 has associated therewith a display 92 for displaying data and other parameters, and a keyboard 94 for inputting control signals, data and the like. Optionally, controller 90 has an electrical memory 96 and a modem 98 for inputting and outputting data to the controller 90 from a remote location. One or more power sources (not shown) provide power to controller 90 display 92, keyboard 94, electronic memory 96 as well as the sensors 82, 84 and control devices 86, 88.

Still referring to FIGURE 8, the microprocessor controller 90 receives a variety of inputs which have been categorized generally in terms of (1) information which is stored in memory 96 when the rotary filter is produced or in operation; (2) information programmed at the site where the rotary filter is to be used; (3) operating parameters sensed by sensors 82; and (4) process parameters monitored by sensors 84.

Examples of information stored in memory when the rotary filter is produced or in operation include information relating to the operation and maintenance of the rotary filter, and training information, all of which will be readily available to an operator on display 92 associated with controller 90. Examples of information programmed at the site where the rotary filter is to be used include the filter operating ranges, output parameters, desired feed properties, and other site-specific data such as relative humidity, ambient temperature, and other environmental factors.

Still referring to FIGURE 8, the outputs from the microprocessor controller may be generally categorized as (1) data for storage in memory 96 associated with the controller 90; (2) data or signals communicated to process control devices 86 or operational control device 88 for operational control of the rotary filter and (3) realtime information provided to the operator at the display monitor 92 associated with the microprocessor 90. Referring more particularly to the data stored in electronic memory 96, it will be appreciated that the computerized monitoring and control system of this invention may utilize the aforementioned sensors to monitor various parameters with respect to time and thereby provide a detailed historical record of the rotary filter operation. This record may be used by the microprocessor to model rotary filter operation, adjust models for rotary filter operation, or generally learn how the rotary filter behaves in response to changes in various inputs. This record may also be used to provide a data log 100, provide preventative maintenance information 102, utilized to, among other things, predict failure, and predict machine wear. Operational control of the rotary filter will be described in more detail below.

In an important feature of the present invention, a number of sensors 82, 84 are disclosed which sense a variety of aspects related to the rotary filter, its operations and its input (slurry) and output (filtrate and cake) streams and other process parameters.

Examples of the operating parameters include vacuum level, speed of rotation of the drum, percent submergence of the drum, feed and wash liquid temperatures, percent feed solids, wash ratio, and the fraction of time the cake spends in each stage (feed, predry wash, dewater, and discharge stage). Examples of parameters relating to the input and output streams and other process parameters include mass throughput, flow rates, temperature of the feed suspension, percent solids in the feed suspension, percent impurities in the feed suspension, cake height, cake moisture, percent impurities in the cake, cake resistance, viscosity of the filtrate, wash ratio, temperature of the wash, air flow rate, percent solids in the filtrate, percent solids in the wash liquid, and percent contaminants in the filtrate and the spent wash liquid. It will be appreciated that the aforementioned rotary filter parameters sensed using the control system of the present invention will be more fully explained in detail hereinafter with regard to the several examples.

An important feature of this invention is that in response to the many parameters sensed by the sensors 82, 84 associated with the rotary filter 10, the operation of the rotary filter and thereby its ultimate efficiency and functioning can be adjusted, changed and preferably optimized. Based on the sensor input to the microprocessor controller 90, the microprocessor may actuate control devices 86, 88 to control any one or more of the parameters discussed above. In some cases, control devices 86, 88 will be actuated if certain sensed parameters are outside the normal or preselected rotary filter operating range. This operating range may be programmed into the control system either prior to or during operation. The foregoing operational controls and examples of actual control devices which will provide such operational controls will be described in more detail hereinafter. Other outputs from the microprocessor controller include the real-time status of various parameters at the rotary filter for use by the operator. Thus, the operator may use the computerized control and monitoring system of the present invention to diagnose the present condition of equipment, order spare parts including using the modem 98 for spare parts ordering, and obtain a read-out of operating parameters, and also as part of an overall Supervisory Control and Data Acquisition (SCAD A) system.

Suitable techniques for communicating among the sensors, microprocessor, and other components include hard-wired electrical systems, optical systems, RF systems, acoustic systems, video systems, and ultrasonic systems.

The three process parameters which are particularly important for optimal operation of rotary filters include mass throughput, percent solids in the cake

(conversely, percent moisture in the cake), and cake purity ( the concentration of contaminants in the cake). For example, in the dewatering of gypsum using rotary drum filters, the dissolved chloride contaminants in the cake needs to be below 50 ppm for the gypsum to be usable as wall-board grade material. Ideally, the specific mass throughput (dry solid rate per filter area) is in the range from about 50-1,100 lb/hr/ft². The percent of solids in the cake is ideally in the range from about 70% - 95% (5% - 30% cake moisture), and the purity of the cake is dictated by the particular application. Table 1 below illustrates the effect of an increase (<*) of the various control and fixed slurry properties on each of these three important process parameters.

Table 1.

As can be seen in Table 1, the various operational and process parameters have a complex and multi-variate effect on mass throughput, percent of cake solids, and cake purity. In addition, each parameter may itself be affected by controlling the other parameters, as shown in Table 2 below:

Table 2.

Pertinent data for use in the program as well as other computer programs may be obtained from the various sensors 82, 84 associated with the rotary filter. Sensors which are useful for a typical vacuum rotary filter are summarized in Table 3 below.

Table 3.

Notably, the majority of sensors for a pressurized filter will be required to be internal to the pressure housing. Accordingly, such sensors must be capable of communication with the microprocessor control 90 and control devices 86, 88 external to the housing 30. Pressure sensors, for example, may be located adjacent conduit 18. It is particularly important in a pressurized filter to measure both the pressure drop across the filter and the volumetric filtrate flow rate. This allows one to establish the filtration characteristics of a given slurry. Sensors types which are particularly useful for a pressurized type of rotary filter are similar to Table 3 above but the cake would have to be discharged through a series of depressurizing chambers and the load cell method of measuring cake discharge to a hopper under atmospheric is not applicable.

As just mentioned, control of vacuum (or pressure) in a single-chamber type of rotary filter is particularly important for optimization of filtration. Referring now to FIGURES 26 A-C, in a single-chamber type of rotary filter, the drum interior is usually under vacuum, whereas the drum exterior is either at atmospheric pressure or only slightly elevated pressure, for example 1-3 psig above atmospheric pressure. The pressure drop across the filter (Δp) is accordingly less than or equal to about 1 bar (atmospheric pressure is about 14.7 psi and 1 bar = 1 atmosphere). The cake discharges at atmospheric pressure. However, in some applications, the process stream is maintained at 4-5 atmospheres (4-5 bars), which necessitates an intermediate step before rotary filtration in order to take the pressure down to about 1 atmosphere and to apply the vacuum required for filtration. In such cases it is therefore advantageous to carry out the filtration at the higher pressures. This results in two advantages: first, a vacuum pump is not required (even though a constant lower pressure is maintained downstream of the filter); and second, the high pressure can be accompanied by an elevated temperature, thereby lowering the viscosity of the slurry and thus enabling more effective filtration. In such cases, the drum exterior may be maintained at 5 bars and the drum interior at 4 bars, so that the pressure drop across the filter is still about 1 bar. The pressure on the cake, however, is about 4 bars. In order to discharge this highly pressurized cake, a two-stage chamber depressurizing mechanism is used to bring the cake from about 4 bars to an intermediate pressure and then to about atmospheric pressure before discharge. Compressed inert gas or steam is used to maintain the pressure of the filtrate collection downstream at about 4 to 5 bars. In another preferred embodiment of the present invention, the higher pressure is used for filtration and dewatering, i.e., the drum internal pressure is maintained at 1 bar such that the pressure drop across filter is about 4 to 5 bars. These high differential pressures are especially useful for difficult-to-filter and dewater materials. Preferably, the cake also goes through a two-stage depressurizing sequence before discharge. Compressed inert gas or steam is used to maintain the pressure of the filtrate downstream of the filtration at about 1 bar.

Sensors which are useful for a multi-chamber type of rotary filter using a filter valve mechanism are similarly to the ones shown in Table 3 except that any pressure drop in individual lines 66 to the individual filter 64 are monitored, see FIGURE 6. Notably, filter valve-type rotary filters provide an additional means for control of the filter by adjustment of one or more bridge blocks 70 (FIGURE 5, 6, and 7). Ordinarily, the placement of the bridge blocks is set prior to the filtration cycle. However, in a particularly preferred embodiment of the present invention, bridge blocks 70 are adjusted during the cycle based on real-time measurements and computer analysis during the course of the cycle , in order to optimize the cycle. As with the single-chamber rotary filter, counter-current washing may be used to optimize the wash cycle. Counter-current wash requires addition of a bridge block.

In another preferred embodiment, pressure sensors 72 are placed at least two locations within pipes 66, in order to determine pressure drop in the pipe, indicating a clogged pipe.

In another preferred embodiment, sensors 82, 84 may comprise a load cell associated with a hopper for cake discharge, for determination of mass throughput. Mass throughput may also be calculated indirectly from the measured cake height, filter rotation speed, and the percent solids in the cake. Cake height may be determined by proximity gauge or by ultrasonic distance probe. Filter speed may be determined using a speed pickup detector or a tachometer. The percent of cake solids may be determined by conductivity measurements on the cake, or infrared beam absorbance method, microwave absorption, or spectroscopic analysis.

In response to these data, one or more control units 86, 88 may be activated to change the various parameters which affect the filtration process (see Table 2). For example, filter speed may be changed using a variable-speed drive or the percent of time spent washing may be varied by changing the positions of spray nozzles 24.

Other data, which may be communicated to the microprocessor controller and used to control the rotary filter system, include conductivity measurements (if the impurities are ionic) or laser spectroscopy to determine cake impurities. Temperature sensors can be used to measure the temperature of the slurry or the wash liquid. In a particularly preferred embodiment shown in FIGURE 9, the percent submergence of a filter drum 12 in a feed tank 14 may be measured ultrasonically or by a pressure transducer 76. The level of slurry 16 in the tank may then be lowered using valve 77, which controls the flow of slurry from feed tank 14 through gravity feed from conduit 78 to storage tank 79. Conversely, the level of slurry in the tank may be raised by pumping slurry from storage tank 79 through conduit 80 using pump 81. The relationship between the liquid head of the slurry pool represented by the double arrow 103 (h_p00l) and the total flow of liquid through valve 77 is shown in FIGURE 10 for an open valve depicted by line 104 and a more closed valve depicted by line 105, where Q_d represents the drain rate controlled by valve 77, Q_p represents the rate at which slurry is pumped into tank 14, and Q_f represents the rate of feed into the drum 12 of the rotary filter.

One method for providing control of the various parameters which affect rotary filter operation in accordance with the present invention is to view the rotary filter system as comprising multiple dynamic components, or modules, each module comprised of elements described herein above for a rotary drum filter system, and each module having its own set of dynamic characteristics. As shown schematically in FIGURE 11, the key four modules of system 200 comprise the rotary filter module 210, the pickup tube module 212, the bleed valve module 214, and the vacuum pump module 216. These modules are physically interfaced by flow through the modules and the input and output of each module overlap each other. The dynamic behavior of each module may characterized by the pressure drop (Δp) across the module for a given mass flow rate, from entrance of the module to the exit of the module. There are two nodes for each module, one upstream and one downstream of the module in the direction of the fluid (liquid and gas) flow. The pressure drop across each pair of nodes depends on the flow rate and the dynamic characteristics of the module. For example, the pressure drop across module 210 is the difference between the pressure at node 203 and node 202. Similarly the pressure drop across module 212 is the difference between the pressure at node 204 and node 203. Note that module 210 and module 212 share node 203. Since the downstream node of one module becomes the upstream node for the next module, the pressure for the common nodes for the modules is identical. This provides a relative connection between the various modules. In particular, as shown in FIGURE 11, the rotary filter module 210 and the pickup tube module 212 form two modules linked in series. Three nodes 202, 203, 204 are associated with these two modules. Node 202 is open to the atmosphere, represented by P_atm, and located upstream relative to the rotary filter module 210. Node 203 is located between the rotary filter module 210 and the pickup tube module 212 at a point referred to as the "girt pressure" represented by P_G. Node 204 is located downstream of the pickup tube module 212 at a point referred to as the separator pressure represented by P_s which actually represents the pressure at the separator tank. Air indicated by arrow 206 and/or liquid indicated by arrow 207 flows through all three of these nodes. The liquid 207 is either the filtrate, or the wash liquid used to displace the filtrate or a mixture of the two liquids. In a particularly preferred embodiment of the invention, the rate of filtration Q_f, as well as other important parameters, can be controlled and optimized by monitoring and controlling the pressure drop across modules once the module characteristics have been captured. For example, the cumulative volume of filtrate liquid collected (V_f) over a period of time (t) for most material, non-compactible cake for example, abides by the parabolic law of filtration where

from which the rate of filtration (Q_f) may be derived:

dV f, _ ΔpA²

Q ^f dt \| 2μαCf

This relationship demonstrates that as the thickness of a cake increases over time and thereby the resistance to filtration increases, the overall filtration rate decreases. This relationship also demonstrates the ability to control a rotary drum filter by exploiting operating relationships between modules and their respective pressure differentials in accordance with the present invention. Curve 217 in FIGURE 12 represents the cumulative volume of collected liquid (V_f) through rotary filter 210 and pick-up tube 212 over time (t) for a fixed level of vacuum provided by vacuum pump

216. FIGURE 13 shows the effect of increasing pressure differentials caused by vacuum pump 216 (ΔP) on the rate of filtration (Q_f) for a fixed time period for incompactible cakes represented by the quadratic curve 218, moderately compactible cakes represented by curve 219, and highly compactible cakes represented by curve 220. The single chamber vacuum filter typically operates at a small filtration time and small cake heights. This results in a high filtration rate (Q _f). A conventional filter, on the other hand, operates at a higher filtration time, thick cake height and lower filtration rate. Both modes of operation still follows the filtration laws as discussed. Depending on the application, a filter can be adaptable to operate at either mode and the sensing and control of the present invention allows the filter to tune to either operating mode without difficulty. . As demonstrated by FIGURE 6 the rate of filtration (Q_f) is further related to the applied pressure wherein Q_f may vary as a quadratic function with respect to changing pressure (Δp) as depicted by line 218 for an in compactible cake, or increasing at a much reduced rate as compared to the increase in pressure as depicted by line 219, depending on the compactibility behavior of the cake. The more compactible the cake is, the less increase in Q_f. In addition, for a given cake compactibility, the filtration rate may be decreased by changing other operating parameters and conditions, such as: (1) increasing cake thickness; (2) low cake permeability due to the presence of fine solids; (3) longer filtration times due to increased submergence of the tank or lower filter rpm; (4) higher feed solids concentration; and (5) smaller filtration areas.

FIGURE 14 shows the effect of pressure drop on filtration rate (Q_f), where the pressure drop (Δp) is the difference between the pressure measured at node 202, typically at atmospheric pressure (zero) or at some elevated casing pressure above atmospheric and the suction pressure at the pickup tube as measure at node 203 in accordance with the present invention. The relationships depicted by curves 221, 222, 223 represent enhancements of the parameters and conditions on the rate of filtration (Q_f) such as increased filter area, reduced filtrate viscosity through higher process temperature, reduced cake resistance through addition of filter aid, reduced feed solids concentration, or reduced filtration time. Another operating relationship which is particularly important to the present invention is the relationship of the pressure differentials between nodes 203 and 204 with respect to the flow of air 206 and liquid 207 in the pickup tube 212, as illustrated in FIGURES 11, 15 and 16. Figure 15 shows the introduction of air represented by arrow 206, and liquid (filtrate) 207, into pickup tube 212 having a diameter represented by 224 and FIGURE 15 further shows the locations of node 203 and node 204. In accordance with the present invention the suction pressure P_G is monitored at node 203 and the separator pressure P_s is monitored at node 204. The relationship between pressure differentials at nodes 203 and 204 and rate of liquid filtrate co-exist with air flow in the pickup tube. (Q_f) is graphically represented in FIGURE 16 for increasing pickup tube diameters 224 represented by curves 225, 226, and 227 respectively. The respective pressures upstream and downstream of the tube are, respectively, P_G and P_s as measured at nodes 203, 204. For a fixed pressure P_s at node 204, represented by curves 225, 226 and 227, as the flow rate of the two-phase mixture increases, the pressure drop, (P_G - P_s) also increases. The minimum pressure drop corresponds to the condition with infinitely large diameter (no flow resistance) where the pressure at the nodes is equal and the vacuum level at the separator P _s is equal to that at the entrance of the pickup tube P_G , or interior of the filter drum. This provides the maximum drainage force for filtration. The flow resistance, and therefore pressure drop, is sensitive to pipe diameter as well as to any bend in the pickup tube. As the diameter of the pickup tube increases, the pressure drop decreases, as represented by arrow 229 in

FIGURE 16.

Referring now to FIGURE 17, performance curve 230 represents the flow rate versus pressure drop relationship for the pick-up tube module 212 having a fixed diameter. Curve 231 represents the filtration characteristics (or pressure drop versus filtrate rate) of a given slurry using a rotary filter module 210. Node 202 is shown at zero pressure corresponding to atmospheric pressure conditions at the entrance of the rotary filter module (i.e. periphery of the actual filter in a housing). Node 204 is shown at a pressure less than zero corresponding to partial vacuum pressure existing at the exit of the pick-up tube module (i.e. where the pickup tube connected to the separator). As discussed herein above, rotary filter module 210 and pick-up tube module 212 share node 203. Equilibrium exists only when the flow rate through both modules are equal and the pressure at node 203 is identical. Perturbation about this equilibrium condition occurs when there is variation in the operating variables. This corresponds to the intersection of the two curves 230, 231, in FIGURE 17, each of which represents the dynamic characteristics of one of the pick-up tube module 210 and the rotary filter module 210, respectively. It is shown in FIGURE 17 for the modules operating in series, in a steady state condition, the pressure at node 203, as represented in FIGURE 17, is the equilibrium, and more particularly the optimum, operating pressure.

Another factor of particular importance in accordance with the present invention is the size of the filter area of the rotary filter module and its relationship with respect to pressure differential across the module. Referring to FIGURE 18 there is shown a graphical representation showing the effect of filtration rate (Q_f) on the vacuum measured at node 203 (P_G) for two different filter areas represented by performance curves 232 and 234. Curve 232 for example represents a rotary filter module 210 having a filter area measuring 4 feet in diameter by 4 feet in length and curve 234 represents by way of example a rotary filter module having a filter area measuring 4 feet by 8 feet. Curve 230 represents a pick-up tube module having a fixed tube diameter. As shown in FIGURE 18 changing from a 4 x 4 foot filter to a 4 x 8 foot filter reduces the magnitude of the vacuum at node 203 from P_G) to P_G2, with a corresponding increase in filtration rate from Q_π to Q_β. The effect of pick-up tube diameter 224 on the rate of filtration for a given rotary filter module is illustrated ,in FIGURE 19. As shown in FIGURE 19, an increase in pick-up tube diameter from that represented by curve 236 to that represented by curve 238 when plotted against line 240 representing a rotary filter of fixed size results in an increase in magnitude of the vacuum measured at node 203 from P_G1 to P_G2, with a corresponding increase in filtration rate from Q_n to Q_β. Accordingly, filter area and pickup tube diameter are the two particularly important variables in achieving optimal operating conditions.

In another embodiment of the present invention vacuum pump module 216 is replaced with a compressor module 216 to pressurize the slurry and direct it through the filtration system.

Of similar importance to the present invention is the relationship between pickup tube module 212, the bleed valve module 214, and vacuum pump module 216 and is shown schematically in FIGURE 11. These modules share common node 204 located downstream of the pickup tube and the bleed valve, and upstream of the vacuum pump.

Referring to FIGURE 20 a series of pick-up tube modules having differing characteristics is represented by curves 245-251 and is plotted against curve 231 which represents a rotary filter module having a specific pressure/filtration rate characteristic. The intersection of the series of curves 245-251 and curve 231 represent the pressure at node 203 for the equilibrium rate of filtration indicated on the horizontal axis of FIGURE 20 in the same manner as described in FIGURE 17 herein above. The vacuum at node 204 (the separator) for each of the curves 245-251 is plotted on the vertical axis as points 252-258 corresponding to different levels of vacuum. The relationship between the magnitude of vacuum at node 204 (or separator) and the filtration rate for the change in the separator pressure shown for the particular rotary filter is established by curve 259. Increasing the suction pressure measured at the separator increases the filtrate rate of the rotary filter as evident by curve 259. In addition, the air flow rate (Q_aιr) as measured at node 204 is shown in FIGURE 20 across the top horizontal scale. It is perceivable that the air flow rate to node 204 from the filter follows the trend of curves 259 for the liquid filtrate.

The suction pressure as measured at node 204 can be varied as described herein above by changing the characteristics of the vacuum pump module 216. Referring to FIGURE 21, lines 242 and 244 represent air rate (Q_aιr) at node 205 in FIGURE 11 measured in cubic feet per minute (CFM) for two different vacuum pump speeds as a function of the magnitude of vacuum as measured at node 204 (P_s). This relationship shows that in order to achieve a high vacuum, only a small air flow rate can be drawn. Conversely, at lower vacuum, a higher flow of air can be accommodated. This is because the pump is delivering air against a back pressure at atmospheric. This is especially true at high vacuum levels, which show precipitous drops in air flow. Furthermore, for a given air flow rate, as the speed of the pump increases from curve

242 to curve 244, either a lower vacuum or a higher flow rate can be maintained. It is also important to note that for a given increase in the magnitude of vacuum and the air flow rate there is a corresponding increase in the power consumption which is equal to ΔP x Q of the vacuum pump module where ΔP, the differential pressure, is the vacuum level below atmospheric and Q is the gas flow rate. For any given vacuum pump module 216, therefore, the pump speed represents another important control parameter for optimization of the pump module in accordance with the present invention.

The relationship between the bleed valve module 214 and the vacuum pump module 216 is also of particular importance in controlling and optimizing a rotary filter system in accordance with the present invention. The bleed valve module 214 includes an orifice to allow the introduction of air at atmospheric pressure into the rotary filter system 200 at node 204 to influence the air flow rate and vacuum at node 204. The characteristics of the bleed valve module can be altered by changing the size of the diameter of an orifice plate contained within the module or using a unit that has a central stem connected to a series of nozzles of different diameters each of which are feeding directly to the central stem. The bleeding rate depends on the nozzle selected. Referring to FIGURE 22, lines 260, 262, and 264 represent the effect of an increasing orifice plate diameter on the air flow rate Q_air at node 205 and the vacuum (P_s) at node 204. Curves 260, 262, and 264 represent increasing diameter of the nozzles and signify the increase in air flow rate at a corresponding increase in pressure drop and the air flow rate increases for the same pressure drop for the increasing diameters.

For the three-module system comprising pickup tube module 212, bleed valve module 214 and vacuum pump module 216 illustrated schematically in FIGURE 11, the total air flow rate measured at node 205 (Q_air) is equal to the air intake 206 through the rotary filter module during drying of the cake as measured at node 203 and the air intake 207 from the bleed valve module 214. Referring to FIGURE 16, the total air flow as measured at node 205 is represented by curve 266 and is made up of the air intake 207 from bleed valve 214 as represented by curve 268 and the air intake 206 from rotary filter module 210 as represented by line 270 . The relationship between total air rate represented by line 266, bleed air rate represented by line 268 and vacuum pump speed 242 is shown in FIGURE 24. Given that the total air flow rate must match that of the pump curve for any given speed, the intersection of the total air flow 266 and pump speed 242 define the equilibrium operating pressure at node 204 represented by P_S1. The operating pressure (vacuum) at node 204 can be altered by changing the amount of bleed air introduced by bleed valve module 214 as discussed herein above and shown in FIGURE 24 wherein curve 270 represents the total air flow rate at node 205 when there is no bleed air intake. The corresponding pressure at node 204 is represented by P_so. Likewise the amount of bleed air can be increased by increasing the diameter of the orifice plate diameter in bleed valve module 214 represented by curve 272 resulting in an increased total air rate represented by curve 274. With increased bleed air intake and increased pump speed to line 244, the operating pressure is reduce to the level represented by P_S2. It is a particularly important aspect of the present invention to understand that by selectively adjusting the aperture of the bleed valve, and the vacuum pump speed, that the suction pressure (P_s) at the separator, as measured at node 204, can be adjusted from P_so (without bleeding) to, P_sl and P_S2 for example, to further affect the filter performance upstream. The effect of the increased air intake 207 from bleed valve module 214 results in a lowering of the magnitude of vacuum at node 204 and therefor a reduction in the pressure differential between nodes 204 and 202. FIGURE 25 shows the effect of increasing the bleed air on the rate of filtration for a specific rotary filter represented by curve 231. Curves 276, 277 and 278 represent different filtration rate relationships for pick-up tube modules operating with pressures at node 204 of P_so, P_S1, and P_S2 respectively and the corresponding decrease in filtration rates are represented by Q_ro, Q_π, and Q_G.

Preferably, the methodology described above is programmed in software for use with microprocessor controller 90, to utilize the information provided by the analyses and relationships shown in FIGURES 11-25. Such methodology provides solutions to optimization of the rotary filter system. Most preferably, the software provides the conditions necessary to arrive at a given end result, to improve filter performance by diagnosing the inefficiency of a given module or physical part in the system of modules and to compensate by either operating variables or design change, to size a new filter or other ancillary equipment, or to provide guidelines as to the limitations of an existing rotary filter system.

The same methodology as discussed herein can be applied to a pressure filter where the compressor would replace the vacuum pump. In this particular embodiment the compressor is located upstream of the rotary filter.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation. What is claimed is:

Claims

CLAIM 1. A method for controlling a rotary filter comprising: monitoring the values of at least one parameter of the rotary filter; comparing the monitored values with other values; and adjusting the parameters of the rotary filter to optimize the monitored values.

CLAIM 2. The method of claim 1 wherein the parameter includes at least one of mass throughput, percent of cake moisture and cake purity values.

CLAIM 3. The method in accordance with claim 1, wherein: the monitored values are measured or calculated in real time.

CLAIM 4. The method in accordance with claim 2, wherein: the cake height is measured by proximity sensor, ultrasonic sensor, or laser or photonic ranging devices.

CLAIM 5. The method in accordance with claim 2, wherein: the percent of cake solids is monitored by conductivity sensor, infra-red absorbance sensor, infra-red reflectance sensor, laser spectrometer, moisture meter, or a combination thereof.

CLAIM 6. The method in accordance with claim 2, wherein: the cake purity is monitored by conductivity sensor, laser spectrometer, X-ray diffractometer, gas chromatograph, gas-liquid chromatograph, pH sensor, or a combination thereof.

CLAIM 7. The method in accordance with claim 2, wherein: the adjusted parameter is at least one of vacuum level, pressure of filtrate collection, speed of rotation of the drum, percent submergence of the drum, feed temperature, wash heater temperature, wash ratio, fraction of time for feeding, fraction of time for preliminary dewatering, fraction of time for washing, fraction of time for dewatering, and fraction of time for discharging and dead time, feed pool depth, pressure drop across the filter, gap between the shoe and the inside of the drum, position of wash fluid baffle, mass throughput, flow rates, temperature of the feed suspension, percent solids in the feed suspension, percent impurities in the feed suspension, cake height, cake moisture, percent impurities in the cake, cake resistance, viscosity of the filtrate, wash ratio, temperature of the wash, air flow rate, percent solids in the filtrate, percent solids in the wash liquid, and percent contaminants in the filtrate and the spent wash liquid.

CLAIM 8. The method in accordance with claim 2, wherein the parameter is adjusted by at least one control device, wherein the control device comprises a vacuum pump variable speed drive, compressed air control valves, drum variable speed drive, bleed-off valves, heaters, volumetric flow valves, density flow valves, flow rate in heat exchanger, and pump rate for feed trough.

CLAIM 9. The method in accordance with claim 1, wherein the comparing is by computer controller, which actuates at least one control device for adjusting the parameters of the rotary filter.

CLAIM 10. The method of claim 9 wherein: the controller actuates the at least one control device based on an internal process model and the process model is at least partially generated and updated by means of at least one of analytical models, neural networks, genetic algorithms, fuzzy logic, expert systems, statistical analysis, signal processing, pattern recognition, categorical analysis, or a combination thereof.

CLAIM 11. The method of claim 1 wherein the rotary filter has a drum, a slurry source, and a discharge mechanism with a discharge hopper, wherein: said monitored parameter comprises solid mass throughput.

CLAIM 12. The method in accordance with claim 11, wherein: the solid mass throughput is monitored by measuring the mass of the discharged filter cake using a load cell in the discharge hopper, or by calculating mass throughput from the measured cake height, filter rotation speed, and the percent solids in the cake.

CLAIM 13. The method of claim 1 wherein the rotary filter has a drum, a slurry source, and a discharge mechanism with a discharge hopper, wherein: said monitored parameter comprises cake solids.

CLAIM 14. The method of claim 13, wherein: the percent of cake solids is measured by at least one of conductivity sensor, infrared absorbance sensor, infra-red reflectance sensor, or laser spectrometer.

CLAIM 15. The method of claim 1 wherein the rotary filter has a drum, a slurry source, and a discharge mechanism with a discharge hopper, wherein: said monitored parameter comprises the purity of the cake.

CLAIM 16. The method of claim 15, wherein: cake purity is monitored by at least one of a conductivity sensor, or an on-line analytical device such as spectrometer.

CLAIM 17. The method of claim 1 wherein the rotary filter has a drum, a bottom-feed slurry source, and a discharge mechanism, wherein: said monitored parameter comprises the percent submergence of the tank; and the adjusted parameter comprises adjusting the level of the slurry in the tank.

CLAIM 18. The method of claim 17, wherein: the level of slurry in the tank is measured by an ultrasound sensor or by a pressure transducer and the level of the slurry is adjusted by controlling the feed into the tank or out of the tank.

CLAIM 19. The method of claim 1 wherein the rotary filter has a drum, a slurry source, and a discharge mechanism, wherein: said monitored parameter comprises at least one of the trajectory of the cake discharge or the spit-back or blow-back moisture; said comparison comprising comparing the trajectory of the cake discharge, spit- back or blow-back moisture with said predetermined value; and said adjustment comprises adjusting the trajectory of the cake discharge, spit-back or blow-back moisture.

CLAIM 20. The method of claim 19, wherein: the cake discharge trajectory, spit-back or blowback is monitored by at least one optical sensor and the cake discharge trajectory, spit-back, or blow-back is adjusted by blow-back pressure in a valve or a knife location associated with the drum surface and filter cake.

CLAIM 21. The method of claim 1 wherein the rotary filter comprises a single-chamber rotary filter having a drum, a slurry source, and a discharge mechanism, wherein the monitored parameter comprises the pressure internal to the drum and including: communicating the monitored pressure to an external computer controller.

CLAIM 22. The method of claim 1 wherein the rotary filter comprises a single-chamber rotary filter having a drum, a slurry source, an intake tube, and a discharge mechanism, wherein: said monitored parameter comprises the input slurry level relative to the intake tube; said comparison comprises comparing the input slurry level with a predetermined value; and said adjustment comprises adjusting the fluid level of the input slurry, thereby preventing the intake slurry from rising above the intake of the intake tube.

CLAIM 23. The method of claim 1 wherein the rotary filer comprises a single-chamber rotary filter having a drum, a slurry source, an intake tube, and at least one fluid activated shoe for discharge of the filter cake, wherein: said monitored parameter comprises the gap between the shoe and the inside of the drum; said comparison comprises comparing the gap with a predetermined value; and said adjustment comprises adjusting the size of the gap, thereby optimizing operation of the rotary filter.

CLAIM 24. The method of claim 1 wherein the rotary filter comprises a single-chamber rotary filter having a drum, a slurry source, and a discharge mechanism, wherein: said monitored parameter comprises the pressure drop across the filter; said comparison comprises comparing the pressure drop with a predetermined value; and said adjustment comprises adjusting the vacuum level of the centrifuge to so as to maintain a pressure drop of about 1 bar.

CLAIM 25. The method of claim 1 wherein the rotary filter comprises a single-chamber rotary filter having a drum, a slurry source under a pressure greater than about 1 bar, collected filtrate under pressure, and a discharge mechanism, wherein: said monitored parameter comprises the pressure drop across the filter; and said adjustment comprise adjusting pressure on the collected filtrate so as to maintain the pressure drop at about 1 bar.

CLAIM 26. The method of claim 25, wherein the rotary filter further comprises a two-stage chamber depressurizing mechanism to bring the dewatered cake from a first pressure above about 1 bar to an intermediate pressure between the first pressure and about 1 bar, and then to about 1 bar before cake discharge.

CLAIM 27. The method of claim 1 wherein the rotary filter comprises a single-chamber rotary filter having a drum, a slurry source under a pressure greater than about 1 bar, collected filtrate under pressure, and a discharge mechanism, wherein: said monitored parameter comprises the pressure drop across the filter; and said adjustment comprises adjusting pressure on the collected filtrate so as to maintain the pressure drop at a pressure greater than about 1 bar, thereby optimizing operation of the rotary filter.

CLAIM 28. The method of claim 27, wherein the rotary filter further comprises: a two-stage chamber depressurizing mechanism to bring the dewatered cake from the pressure above about 1 bar to an intermediate pressure between the first pressure and about 1 bar, and then to about 1 bar before cake discharge.

CLAIM 29. The method of claim 1 wherein the rotary filter comprises a multiple- chamber rotary filter having a drum, a feed slurry, a filter valve with at least one bridge block, and a discharge mechanism, wherein: said monitored parameter comprises at least one of solid mass throughput, percent of cake solids, and cake purity during the filtration cycle; and said adjustment comprises adjusting the position of at least one bridge block during the filtration cycle, thereby optimizing operation of the rotary filter.

CLAIM 30. A method of optimizing operation of a rotary filter having a drum, a slurry source, and a discharge mechanism, comprising washing a first portion of the filter cake, and collecting the filtrate by a baffle; washing a second, subsequent portion of the filter cake and collecting a second filtrate by the same baffle; and recirculating the second filtrate for use in washing the first portion of the filter cake.

CLAIM 31. The method of claim 30 wherein the rotary filter comprises a multiple- chamber rotary filter having a drum, a slurry source, a filter valve assembly having at least one bridge block, and a discharge mechanism, wherein: the first and second washing phases are separated by the bridge block in the filter valve assembly.

CLAIM 32. A rotary filter apparatus having a rotatable drum, a source of slurry and a discharge mechanism and further comprising at least one sensor.

CLAIM 33. The rotary filter of claim 32 wherein said at least one sensor comprises at least one load cell associated with a hopper for cake collection, a proximity gauge, an infrared absorbance sensor, an infrared reflectance sensor, a microwave absorption sensor, a conductivity sensor, a laser spectroscopy sensor, an ultrasonic sensor or pressure transducer for measurement of the submergence of the tank, a valve for controlling the flow of slurry into the tank and an optical sensor for determining the trajectory of the cake discharge.

CLAIM 34. The apparatus of claim 33 wherein the rotary filter comprises a single- chamber rotary filter apparatus and wherein said at least one sensor comprises: a pressure transducer and ultrasonic probe for the measurement of filtrate level inside the drum in order to ensure that the opening remains open to air, at least one internal baffle for collection of wash liquid for counter-current washing, and at least one proximity sensor adjacent at least one shoe for monitoring the gap between a pneumatic shoe discharge mechanism and the internal surface of the drum.

CLAIM 35. The apparatus of claim 32 wherein the rotary filter comprises a single- chamber rotary filter apparatus and further comprising: a slurry source maintained at a first pressure above 1 bar; a source of inert gas or steam for maintaining a downstream filtrate collection at a second pressure above about one bar, thereby maintaining pressure across the filter at about 1 bar, and a two-stage chamber depressurizing mechanism for bringing the cake from the first pressure above one bar to an intermediate pressure below the first pressure but above about one bar, and then to about one bar before cake discharge.

CLAIM 36. The apparatus of claim 32 wherein the rotary filter comprises a single- chamber rotary filter apparatus and further comprising: a slurry source maintained at a first pressure above 1 bar; a source of inert gas or steam for maintaining pressure at downstream filtrate collection at about 1 bar, thereby resulting in a pressure across the filter about equal to the first pressure above about 1 bar, and a two-stage chamber depressurizing mechanism for bringing the cake from the first pressure above one bar to an intermediate pressure below the first pressure but above about one bar, and then to about one bar before cake discharge.

CLAIM 37. The apparatus of claim 32 wherein the rotary filter comprises a multi- chamber rotary filter and further comprising: at least one of an adjustable bridge block mechanism for control of each fraction of the filtration cycle during the filtration, a bridge block for collection of filtrate for counter-current washing, and at least two pressure sensors placed at at least two locations within pipes connecting the slurry source to individual filtration units in order to determine pressure drop in the pipe.

CLAIM 38. An apparatus for monitoring and controlling a filter system having fluid flow there through comprising a plurality of modules arranged in fluid communication with each other, each of the modules having a node positioned at an upstream side and a downstream side in accordance with the direction of fluid flow through the module.

CLAIM 39. The apparatus as set forth in claim 38 further comprising: a controller for storing a knowledge base for each of the modules, the knowledge base comprising an operational relationship between operational parameters at the nodes; at least one sensor located at least one of the nodes measuring an operational parameter at the node and communicating the said measured parameter to the computerized controller; and at least one of the modules having a control device disposed therein for varying the operation of the at least one module.

CLAIM 40. The apparatus as set forth in claim 39 wherein the controller compares the operational parameter to the knowledge bases and the control device varies at least one module in response to the comparison.

CLAIM 41. The apparatus of claim 38 further comprising: a controller for storing a knowledge base for each of the modules, the knowledge base comprising an operational relationship between operational parameters at the nodes; at least one sensor located at at least one of the nodes measuring an operational parameter at the node and communicating the parameter to the computerized controller at least one of the modules having a control device disposed therein for varying the operation of the at least one module; and the computerized controller comparing the measured pressures and flow rates to the knowledge bases and the control device varying the at least one module in response to the comparison.

CLAIM 42. The apparatus as set forth in claim 41 wherein the plurality of modules includes a rotary drum module, a pick-up tube module, a bleed valve module, and a vacuum pump module.

CLAIM 43. The apparatus as set forth in claim 41 wherein the plurality of modules includes a compressor, a rotary drum module, a pick-up tube module, and a bleed valve module.

CLAIM 44. The apparatus as set forth in claim 41 wherein the at least one module is varied to optimize an operational parameter of the filter system wherein the operational parameters include fluid flow rate, pressure, mass throughput, wash liquid amount, time spent on each segment of the filter cycle, percent of cake solids, cake purity, cake height, percent of drum submergence, filter speed, and air flow rate.

CLAIM 45. The apparatus as set forth in claim 41 wherein the plurality of modules comprises: a rotary drum module having a first node disposed at its upstream stream side and a second node disposed at its down stream side and the control device disposed within the rotary drum module varying at least one operational parameter of the rotary drum module in response to the operation parameters measured at the first and second nodes; a pick-up tube module disposed down stream of the second node and having a third node disposed at its down stream side the control device disposed within the pick-up tube module varying at least one operational parameter of the pick-up tube module in response to the operation parameters measured at the second and third nodes; a vacuum pump disposed downstream of the third node and having a fourth node disposed at its downstream side, the control device disposed within the vacuum pump module varying at least one operational parameter of the vacuum pump module in response to the operation parameters measured at the third and fourth nodes; and a bleed valve module having a fifth node disposed at its upstream side and the third node disposed at its downstream side, the control device disposed within the bleed valve module varying at least one operational parameter of the vacuum pump module in response to the operation parameters measured at the fourth and fifth nodes.

CLAIM 46. The apparatus as set forth in claim 41 wherein the plurality of modules comprises: a compressor having a first node disposed at its upstream side and having a second node disposed at its downstream side, the control device disposed within the compressor module varying at least one operational parameter of the compressor module in response to the operation parameters measured at the first and second nodes; a rotary drum module having the second node disposed at its upstream stream side and a third node disposed at its down stream side and the control device disposed within the rotary drum module varying at least one operational parameter of the rotary drum module in response to the operation parameters measured at the second and third nodes; a pick-up tube module disposed down stream of the third node and having a fourth node disposed at its down stream side, the control device disposed within the pick-up tube module varying at least one operational parameter of the pick-up tube module in response to the operation parameters measured at the third and fourth nodes; and a bleed valve module having a fifth node disposed at its upstream side and the first, second or third node disposed at its downstream side, the control device disposed within the bleed valve module varying at least one operational parameter of the vacuum pump module in response to the operation parameters measured at the fifth node and either the first, second, third or fourth nodes.

CLAIM 47. A method of controlling the filtration process of a filter system as in claim 38 with the aid of a controller, comprising: providing the controller with a knowledge base for each of the modules, the knowledge base comprising an operational relationship between operational parameters at the nodes; measuring an operational parameter at each of the nodes; providing the controller with at least one operational parameter corresponding to each node; and comparing the measured operational parameters to the knowledge bases.