Abstract:
A powered in-line blender for mixing additives to sludges or other flowable liquid/solid mixtures. The blender is particularly useful in a method of blending polymer to municipal sewage sludges to improve the dewatering characteristics, and thus improving total costs for dewatering, handling, and disposal.

Description:
TECHNICAL FIELD  
         [0001]    This invention is directed to the field of blenders, and more particular, to blenders adapted for mixing polymers with sludge.  
         BACKGROUND  
         [0002]    Various mixing devices have long been utilized for mixing polymeric flocculants to improve their contact with a low solids mixture. A water based slurry containing solids from which the water is to be removed is a common situation which presents itself in many industries. Many techniques have been utilized in handling such slurries (whether sludges or whether having other physical properties) for enhancing water removal, such as improved centrifugation or filtration, including vacuum filtration. In many of such water removal process techniques, the dewatering can be even further enhanced via the addition of a suitable polymeric substance. Suitable polymeric substances vary widely, depending upon the substance to be dewatered and its chemical, physical, and electrostatic properties. In many sludge handling applications a suitable polymer might be a high molecular weight and high charge density cationic polymer. However, in many commonly encountered applications, such as in the treatment of sewage sludge, achieving enhanced water removal even with addition of a suitably selected polymer is often difficult to achieve. One approach often used, which is rather expensive, is simply to increase the polymer dosage. However, in some cases, even that technique does not provide much improvement. In such cases, the ultimate solids dryness remains sufficiently low that significant savings in further handling costs (particularly with respect to charges for drying, transportation, and disposal) could be achieved if only the polymer addition achieved the performance results in full scale that were (and sometimes still are) seen in comparable bench scale trials.  
           [0003]    A common problem encountered in the methods heretofore tried which are of interest to us is that polymer addition is often done only in conjunction with pumps designed to move the material. In such cases, the amount of work done on both the sludge and to the polymer being added has been primarily (if not totally) dependent on the work that the pump device, such as a progressive cavity pump impeller, did in the process of moving the sludge or slurry from one location to another. Thus, those methods inevitably leave the results in the hands of the selection of a few variables, namely polymer selection and dosage rate, since the pump itself is usually provided for a fixed service (i.e., flow, impeller rpm, and pressure differential). It is often rather difficult (if not impossible) to accomplish a quick adjustment of the pump, so, plant workmen are often found to be simply too lazy or too pressed for time to properly make use of the available adjustments, if any. So, a commonly encountered situation is that vendors of polymers are called in to test their various products, at different dosages, until an optimum product and dosage selection are attained to most cost effectively achieve the desired dewatering results.  
           [0004]    Thus, there remains a continuing and as yet unmet need for a device that would provide immediate and precise control over polymer mixing, and which separates the work of sludge/polymer mixing from sludge pumping, and which can withstand the hazards inherent in sludges from sources such as municipal wastewater treatment plant operations. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0005]    In order to enable the reader to attain a more complete appreciation of the invention, and of the novel features and the advantages thereof, attention is directed to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0006]    [0006]FIG. 1 is a perspective view of a novel in-line sludge blender, showing the blender housing with inlet, outlet, cleanout port, and internal baffles, a non-ragging impeller, and support mounts for supporting the blender at a desired location, as well as the mixer drive including the pipe housing for housing a mechanical seal (not shown), a bearing spool, and a motor and motor remote control unit.  
         [0007]    [0007]FIG. 2 provides a close up of one embodiment for a motor control unit, indicating the push button control for starting, stopping, and running the mixer forward and backward at various speeds, and the speed controls for increasing or decreasing the speed of the blender impeller.  
         [0008]    [0008]FIG. 3 is a vertical end view, taken as if looking back through section  3 - 3  of FIG. 4, showing the blender housing, outlet flange, inlet flange, cleanout flange and cover, a non-ragging impeller, and support mounts for supporting the blender.  
         [0009]    [0009]FIG. 4 is a vertical and longitudinal partial cross-sectional view of a blender, looking from the side into the internals of the blender housing, showing the non-ragging impeller, cleanout port, and the seal housing located within the pipe housing, a bearing spool, and motor.  
         [0010]    [0010]FIG. 5 is a horizontal and longitudinal partial cross-sectional view of a blender, looking from the top down into the internals of the blender, showing the blender housing, internal baffles, the non-ragging impeller, and the inlet and outlet nozzles and flanges, and a primary polymer addition fitting on a first nozzle (here the inlet), with block flow diagram indicating one possible flow configuration.  
         [0011]    [0011]FIG. 6 is a horizontal and longitudinal partial cross-sectional view of a blender, similar to FIG. 5, looking from the top down into the internals of the blender, showing the blender housing, internal baffles, the non-ragging impeller, and the inlet and outlet nozzles and flanges, but now showing the blender in a secondary flow configuration, wherein the primary polymer addition fitting is capped on the first nozzle (which here serves as the outlet nozzle), but with a secondary polymer addition fitting in use on a second nozzle (which here serves as the inlet nozzle).  
         [0012]    [0012]FIG. 7 is an exploded perspective of the various components of the blender, showing the various components thereof, including blender housing with a first nozzle, a second nozzle, a cleanout port, and internal baffles, a non-ragging impeller, and support mounts for supporting the blender at a desired location, along with a mixer drive including pipe housing for housing the seal housing and internal seal components, a bearing spool, and a motor, as well as an externally mounted motor remote control unit.  
         [0013]    [0013]FIG. 8 is an exploded perspective of the various components of the seal, (including those components contained within the seal housing), as well as a mounting ring for securing the seal housing to the pipe housing, as well as a bearing which is located in the bearing spool (not shown here, see FIG. 7) located adjacent to the pipe housing.  
         [0014]    [0014]FIG. 9 is side view of one embodiment for a non-ragging impeller of exemplary design for construction of an in-line blender, and for the practice of the method of operation taught herein, showing along the shaft, from proximal end to distal end, the drive region, the sealing region, and mixer drive clearance region of the shaft which has an extremely short wetted shaft prior to impeller attachment, and one embodiment for a backward curved impeller blade design, both of which contribute to the success of the impeller for this service.  
         [0015]    [0015]FIG. 10 is side view of another embodiment for a non-ragging impeller of exemplary design for construction of an in-line blender, and for the practice of the method of operation taught herein, showing along the shaft, from proximal end to distal end, the drive region, the sealing region, and mixer drive clearance region of the shaft which has an extremely short wetted shaft prior to impeller attachment, and one embodiment for an auger or screw type impeller blade.  
         [0016]    [0016]FIG. 11 is a vertical and longitudinal cross-sectional view of a blender, looking from the side into the internals of the blender housing, showing a non-ragging, screw type impeller, a cleanout port, a primary and a secondary polymer addition fittings, and mixer drive components, as well as mounting feet for supporting the blender on a desired substrate.  
         [0017]    [0017]FIG. 12 is a flow diagram illustrating one embodiment for employing the blender depicted herein to add polymer to a sludge in a method for mixing polymer with sludge, followed by the further dewatering of the sludge/polymer mixture in a centrifuge to produce dewatered sludge cake and a clear centrate stream which is primarily water. 
     
    
       [0018]    The foregoing figures, being exemplary, contain various elements that may be present or omitted from actual implementations depending upon the circumstances. An attempt has been made to draw the figures in a way that illustrates at least those elements that are significant for an understanding of the various embodiments and aspects of the invention. However, various other elements of an in-line blender and of a method of mixing polymer with sludge are also shown and briefly described to enable the reader to understand how various optional features, methods, or structures may be utilized in order to provide a useful in-line blender application that easily accommodates adjustment of polymer application rates and of the mixing work accomplished on a sludge/polymer mixture, in order to achieve optimization of sludge dewatering and drying processes.  
       DETAILED DESCRIPTION  
       [0019]    Attention is directed to FIG. 1, where a novel in-line blender  20  is shown. The blender  20  includes a blender housing  22  with a first nozzle  24  which in one configuration serves as an inlet, a second nozzle  26  which in that same configuration serves as an outlet, a cleanout port  28 , and a mixer mounting nozzle  30  to which is affixed the mixer drive components  32 . In the embodiment illustrated in FIGS. 1 and 7, the mixer drive components include (a) a pipe housing  34  having a bushing  36  to which a seal housing  38  is affixed within by the attachment ring  40 , (b) a bearing spool  42  with bearing  44  (see FIGS. 4 and 8), and a drive motor  46 . An access cover  50  may be provided for convenient access and seal housing  38 . Within the blender housing  22 , a non-ragging impeller  60  is provided. Such an impeller  60  design is especially of value in applications of the in-line blender  20  to the mixing of polymer with municipal sewage sludge, where items such as hair and feminine napkins or tampon residuals tend to catch on improperly designed mixer impellers and quickly build up on a shaft which is then found less than totally effective, or even completely inoperative, having been wound up with balls of hair, string, and fiber. Such a phenomenon also tends to be hard on mixer components, mechanically, especially on bearings and seals.  
         [0020]    An attachment system such as flange  62 , attachment ring  63 , gasket  64 , and bolt  66  with matching nut  68  is used to sealingly affix the first component of the mixer drive  32 , namely the nozzle side  70  of pipe housing  36 , to the mixer mounting nozzle  30 . As illustrated, the pipe housing  34  is provided in the shape of a tubular cylindrical component having nozzle side  70  with sealing face  72  (see FIG. 7), a partial tubular sidewall  74  of a length L 34  sufficient to accommodate the length L 38  of seal housing  38  and also to provide access to nuts  68 , and a rear or bearing spool side  76  in the shape of an annulus with central hole defined by edge wall  78  sized and shaped to accommodate shaft  80  of impeller  60 , as well as to provide space for bearing  44  affixed to bearing spool  42 . Bearing spool  42  is attached to the rear side  76  of the pipe housing  34  by suitable fasteners such as bolts  80  sized and shaped to fit threads in apertures  82  through rear side  76  of the pipe housing, or by alternate bolt and nut fastener system. The motor  46  is operable affixed to bearing spool  42  via suitable fastener system, details of which may vary to suit a particular design and which may be easily configured by those of ordinary skill in the art and to which this disclosure is directed. Bearing spool  42  may be provided in a unique design, where first  90  and second  92  attachment flanges are spaced apart by a plurality of radially inward partitions  94 , and wherein adjacent partitions have an inward root, and wherein the inward roots of adjacent partitions  94  are connected by an access plate  96  having therein an access aperture defined by edge wall  98  which provides visibility of and access to the coupling  100  (also see FIG. 11) which mechanically links and affixes the drive end  102  of shaft  90  to the shaft  104  of motor  46 . In one embodiment the impeller  60  is configured for direct drive via motor  46 . The bearing spool  42  is affixed to the bearing spool side  76  of pipe housing  34 , and is centered along the shaft axis  122  of impeller  60 , and includes a bearing  44  secured within the bearing spool  42 .  
         [0021]    [0021]FIG. 2 provides a close up of one embodiment for a motor control unit  110 , indicating the push button control for starting  112 , stopping or resetting  114 , and running the mixer forward or reversel  16  at various speeds, which can be increased  118  or decreased  120 , which speed controls enable adjustably increasing or decreasing the rotating speed of the blender impeller  60  to a selected or experimentally determined optimum speed. Appropriate indicator lights and readouts provide the RPM of the impeller  60 , the percent of maximum load, and an indication of whether the blender is running in forward or reverse mode.  
         [0022]    As easily seen in FIG. 9, and also clearly indicated in FIG. 7, the impeller  60  has a rotating shaft  120  extending along a longitudinal axis indicated by centerline  122 . The shaft  120  has a distal end  124 . The impeller  60  has a plurality of blades  130  attached to the rotating shaft  120 . One or more of blades  130  is in an outermost, or most distal position, and one or more of blades  130  is in an axially innermost, or most proximal position. In FIG. 9, blades  130   1  and  130   2  are paired and are located in an axially outermost position, and blades  130   3  and  130   4  are paired and located in an innermost position. As shown an axially innermost blade, here blades  130   3  and  130   4  have proximal ends  130   3 -P and  130   4 -P (see FIG. 5) which are located spaced apart from but closely adjacent the mixer drive  32 . As shown in FIG. 7, this just mentioned spacing is with respect to the wetted side  136  of bushing  36 . Also, to achieve non-ragging performance, the plurality of blades  130  are configured to assure that, along the shaft axis, at least some of the blades  130  overlap lengthwise, (as shown, pairs of blades  130  overlap lengthwise) so that from said proximal end  130   3 -P and  130   4 -P of the innermost blade  130   3  or  130   4  to the distal end  124  of shaft  120 , a bare rotating shaft  90  (i.e., devoid of impeller blades) is substantially avoided.  
         [0023]    In the embodiment illustrated in the figures herein, the blender housing  22  is provided with a main housing portion  140  having a cylindrical tubular configuration along a longitudinal axis having an interior housing wall  144 . As illustrated, the blender housing  22  is provided with a plurality of baffles  146  that are mounted to the interior housing wall  144 , In the configuration illustrated, the baffles  146  are provided as narrow, elongated structures extending from the interior housing wall  144  inward toward, but spaced apart from, the impeller  60 . In one embodiment, baffles  146  are provided a baffle pairs  146   1  and  146   2 , mounted in opposing fashion on the interior housing wall  144 , as indicated in FIG. 5.  
         [0024]    Turning now to FIGS. 7 and 8, the seal housing  38  is provided to confine mechanical seal components  150 , as indicated in FIG. 8, and to provide a pressurizable compartment into which seal water is provided via fitting  152 . A lip seal  154  and bushing  156  in pipe housing  34  seal against rotating shaft  90  of impeller  60 . The seal housing  38  has a bushing flange face  160  which seals against seal face  162  of bushing  156 . Within seal housing  38  are provided a throttle or flow restrictor  164  which restricts the flow of water out from seal housing  38 , a collar  170  which is affixed to shaft  90  via threaded pin  171  to compress spring  172  against a ceramic seal seat  176  and bearing  180 , which is located at the motor side of seal housing  38 , as is more evident in FIGS. 4 and 11. Although one exemplary design for a mechanical seal and seal housing  38  has been provided, it will be understood by those of ordinary skill in the art that various seal and bearing designs may be utilized without departing from the fundamental developments in the art provided by an in-line blender  20  as described and claimed herein.  
         [0025]    In order to receive an additive stream such as a liquid polymer, a first nozzle such as inlet nozzle  24  shown in FIG. 5 further includes an additive inlet fitting  200 , which is adapted to receive a liquid stream containing an additive such as polymer  202  for mixing with a sludge stream  204 , to create a sludge/polymer mixture  206  for feed to a dewatering device such as centrifuge  208 , which further dewaters the sludge/polymer mix  206  to create a relatively dry cake  210  and a relatively clear centrate or water stream  212 .  
         [0026]    In some applications, it is advantageous to use a “reverse flow” configuration as shown in FIG. 6, wherein a second nozzle such as tapered portion, here diverging nozzle  214  provided as part of nozzle  26 ′ further includes the additive inlet fitting  216  which is adapted to receive a liquid stream containing an additive such as polymer  202 . In such a case, the “forward flow” inlet  24  becomes an outlet  24 ′. In other words, an in-line blender  20  is provided in an arrangement, and with capped additive fittings as necessary, so that flow within the blender housing  22  can be (a) directed from mixer drive  32  toward the distal end  124  of the impeller  60 , or (b) directed from the distal end  124  of the impeller  60  toward said mixer drive  32 . When the blender  20  is configured for a “forward flow” mode, the blender housing  22  is of larger diameter than the outlet  26 , and in such case, a converging nozzle  214 ′ is provided as shown in FIGS. 4 and 5.  
         [0027]    As shown in FIG. 10, an impeller  60  can in one embodiment be provided with two pairs of paddle blades, specifically blades  130   1  and  130   2 , and blades  130   3  and  130   4 . Each one of these blades, as better seen in FIG. 3, have a root portion  230  extending radially from the shaft  90 , and an outer portion  232  extending outward from the root portion  230  and ending in a tip  234 . The outer portion  232  is radiused with respect to the root portion  230  to provide a convex leading surface  240  of each blade,  130   1 , etc. As noted in FIG. 3, in one configuration, the tip  234  ends at a location angularly rearward of the root portion  230  by a preselected angle alpha (a) of about twenty five degrees. Also note that the successive blades  130   3  and  130   4  are mounted along the shaft  90  at uniform longitudinal spacing. As shown, successive blade pairs  130   1 / 130   2 , and  130   3 / 130   4  are mounted at a radial displacement of 90°. In this manner, the when said blades are provided in mirror image pairs, the root portion of each one of the companion blade pairs is mounted at a radial displacement angle of sigma (Σ), here configured for 180°.  
         [0028]    Alternately, as indicated in FIGS. 10 and 11, an impeller  60 ′ can be provided in the form a screw type auger, having flytes  250 .  
         [0029]    For ease of inspecting, cleaning, and servicing the impellers  60  or  60 ′, a cleanout access nozzle  260  has been provided. The nozzle  260  has a flanged outlet  262  sealed by a blind cover plate  264  removeably and sealingly secured to the flanged outlet  262  by seal  266 , mounting ring  268 , and appropriate fasteners such as bolts  270  and nuts  272 . To support the in-line blender  20 , a pair of support feet  290  and  292  are provided. In one embodiment, apertures  294  in support feet  290  and  292  are adapted for compatibility with the nut and bolt system used for affixing (1) the pipe housing  34  to the mixer mounting nozzle, and (2) for affixing outlet flange  296  to the outlet nozzle  26 . Also, such support feet  290  and  292  can be provided in the form of L-shaped brackets, including foot apertures defined by edge walls  297  suitable for mounting anchor bolts  298  to a selected substrate  299 , as seen in FIG. 4.  
         [0030]    As briefly mentioned above, a motor controller  110  is provided to adjustably set the speed of the motor  46  to drive impeller  60  or  60 ′ at a predetermined rotational velocity. Normally, the motor  46  is, but need not necessarily be, an electric motor. The motor controller  110  is usually configured for continuous drive of the motor  46 . However, the motor controller  110  is of the type suitable for adjustably controlling the speed at which the motor  46  drives the impeller  60  or  60 ′.  
         [0031]    By use of the in-line blender described herein an improved method of dewatering of sludge can be practiced. This method includes providing an in-line blender downstream of a sludge pump  300  (see FIG. 12) and upstream of a sludge dewatering device  302 . In the method, the speed of the impeller  60  or  60 ′ is adjustably fixed. An additive such as polymer  202  to enhance the dewatering properties of the sludge  204  is combined with the sludge  204  at the in-line bender. The step of adjustably fixing the rate of addition of such additive is also important, since polymer or other additive savings can be enhanced. By controlling the amount of work done on the sludge/polymer mixture, sufficient, but not excessive amounts of work can be applied. This is important in some applications where excessive work might result in degradation of polymer molecular weight or other properties. The amount of work performed can be done via use of a load sensor for measuring the load on the in-line blender. Also, a controller  110  can be provided responsive to torque developed by the blender impeller  60  or  60 ′, for operating the mixer drive  32  in response to the torque encountered in a particular application or at a particular time. The step of adjustably fixing the speed of the impeller includes providing a controller for manually or automatically varying the rotational speed of the impeller  60  or  60 ′ of the in-line blender  20 . Also, an additive controller may be provided suitable to vary and control the rate at which an additive such as polymer  202  is provided via pump  310 .  
         [0032]    Subsequent to the mixing step, the sludge/polymer mixture is subjected to the step of dewatering in a dewatering apparatus  302 , such as a centrifuge  208 . Alternately, the dewatering unit  302  can be practiced in the form of filtration, such as via a belt filter. The method is particularly applicable and useful for the treatment of a municipal wastewater treatment sludge.  
         [0033]    Thus, the in-line blender described herein provides the necessary apparatus for carrying out a method for optimizing the application of polymer as used for solid/liquid separation in dewatering a particular wastewater sludge, to minimize the overall life cycle costs for dewatering, handling, hauling, and disposing of sludges or other dewatered solids. The method includes providing an in-line blender located between a sludge or solids feed pump and a dewatering apparatus and in fluid communication with each. A reagent is provided for addition to the solids or sludge for improving the dewatering characteristics thereof. First, it is important to measure the input variables, including (1) the rate of flow of a sludge to be dewatered, (2) the water content of said sludge, (3) the flow rate of a dilute reagent be mixed with the sludge, and (4) the water content of the dilute reagent stream (5) a mixing rate, as measured by rotational speed of said blender. Then, it is important to measure the output variables, including (1) sludge cake flow rate, (2) sludge cake dryness, (3) output water flow rate, and (4) solids content of output water, which variables are measured as achieved after a dewatering step subsequent to the step of blending polymer with the sludge or other solids. After such measurements, an operating point is located during operation to determine a characteristic operational range. Then, the reagent flow rate is adjustably fixed and reagent application rate is adjustably fixed, and the mixing rate is adjustably fixed, so as to bring the in-line blender and reagent application operating point into a range considered to be a stable and optimal operating range for mixing the sludge/polymer blend. Depending on the results of the treatment from the inputs on the sludge flow rate, the polymer flow rate, and mixing rate, the input variable are optimized to achieve a desirable throughput and sludge dryness result, in order to attain preselected economic and product specification goals.  
         [0034]    In summary, the in-line sludge mixing apparatus and the method of employing such a blender in a method of dewatering materials such as sewage sludge is unique in that it separates the mixing work from the pumping work, and in that the impeller design is non-ragging and thus suitable for use in sewage sludge applications.  
         [0035]    It is to be appreciated that the in-line blender system provided herein is an appreciable improvement in the art of the dewatering of sewage sludge. Although only a few exemplary embodiments have been described in detail, various details are sufficiently set forth in the drawings and in the specification provided herein to enable one of ordinary skill in the art to make and use the invention(s), which need not be further described by additional writing in this detailed description. It will be readily apparent to those skilled in the art that the in-line blender system may be modified from those embodiments provided herein without materially departing from the novel teachings and advantages provided. Thus, the aspects and embodiments described and claimed herein may be modified from those shown, and may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, the embodiments presented herein are to be considered in all respects as illustrative and not restrictive. As such, this disclosure is intended to cover the structures described herein and not only structural equivalents thereof, but also equivalent structures. Numerous modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention(s) may be practiced otherwise than as specifically described herein. Thus, the scope of the invention(s), as set forth in the appended claims, and as indicated by the drawing and by the foregoing description, is intended to include variations from the embodiments provided which are nevertheless described by the broad interpretation and range properly afforded to the plain meaning of the claims set forth below.