Abstract:
A lime stabilization system for treatment of sewage sludge, and method is provided in which dewatered sludge and lime are provided to a mixer. Lime and sludge are mixed to raise the pH during which volatiles are driven off with or without supplemental heat. A forced air draft prevents steam from backing up into the lime supply. The sludge goes to a discharge station via a transfer apparatus, and air containing any dust, odors, steam or ammonia is cleaned via a scrubber. The system is computer-controlled via gravimetric load cells and/or volumetric means. The system includes computer controlled means for dissolving scale resulting from exposure of surfaces to lime, using acid, water or combinations thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part of U.S. patent application Ser. No. 13/302,312 filed Nov. 22, 2011, the complete disclosure of which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to apparatus and process for treatment of sewage sludge (also known as biosolids), and a process thereof. 
       BACKGROUND OF THE INVENTION 
       [0003]    The need for treating sewage sludge for disposal, and particularly municipal sewage sludge, has increased substantially in recent years. One way of dosing so, is by mixing or blending alkaline materials with the sludge. There is also developing an increasing demand, particularly with respect to municipal sewage sludge, that the treatment of the sludge be sufficiently thorough that is will allow beneficial re-use of sludge, such as enabling the sludge to be applied to land on which agricultural and ornamental corps may be grown. One way of doing so is to mix alkaline products with sludge in a manner that blends the alkaline and sludge. 
         [0004]    When sewage sludge is only treated with an alkaline material such as lime, without a sufficient increase in sludge temperature, the resulting mix may be only partially stabilized, such that higher pathogenic organisms are not destroyed. 
         [0005]    In the treatment of sewage sludge, such can produce dust as a result of the treatment process and odors, and steam can result from the temperature reached during the treatment process. Additionally, ammonia can be produced during the treatment process. 
         [0006]    Additionally, the use of lime during the treatment process can results in build-up of scale resultant from the lime treatment on surfaces that are exposed to the lime treatment. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to a precision lime stabilization system and method for the treatment of sewage sludge, which can be automatically controlled via a computer, which results in a clean system that substantially reduces the discharge to atmosphere of dust, odors, steam and ammonia, whereby clean air is delivered to the atmosphere from the system. The system is essentially an enclosed system in which the lime and sludge are mixed to raise the pH thereof to a range of about 10 to about 12.5. The system is also controlled preferably by controlling the weight of sludge and lime that are delivered to a mixer, via weight measurement from load cells, which weights are transmitted to a computer, which controls various other functions of the system. Alternatively, the control of sewage sludge delivered into the system can be the result of volumetric control. 
         [0008]    The system also allows for various means of providing heat to the mix of sewage sludge and lime, for example, to volatize compounds. 
         [0009]    A control hood for capturing odors, steam, dust and ammonia as a result of the treatment is provided, for delivering the same to a wet scrubber and stack, for discharge to atmosphere. 
         [0010]    The thus treated sewage sludge/lime mix is discharged from the system via a substantially enclosed conveyor after withdrawal of the dust, odors, steam and any ammonia as a result of the treatment process. 
         [0011]    The resultant treated mix can then be discharged to be applied to land, as may be desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0012]      FIG. 1  is a schematic illustration of a treatment system of this invention, from a dewatering device, through a sewage sludge delivery system to a sludge/lime mixer, and a lime supply to the sludge/lime mixer, to a substantially enclosed transfer conveyor. 
           [0013]      FIG. 1A  is a schematic alternative delivery system for delivering lime from the lime addition screw conveyor to the centrifuge cake screw conveyor. 
           [0014]      FIG. 2  is a continuation of the schematic of  FIG. 1 , from the transfer conveyor, to the hood for removal of odors, steam, dust and any ammonia and delivery of the same through a wet scrubber and out the discharge stack of a control tower, to the environment, with the sludge being delivered from the substantially enclosed transfer conveyor to discharge. 
           [0015]      FIG. 3  is a horizontal sectional view taken generally along the line III-III of  FIG. 2 , wherein a curtain type enclosure is illustrated, for receiving air at the lower end through the curtained enclosure, for delivery to a wet scrubber. 
           [0016]      FIG. 4  is a sectional view taken along the line IV-IV of  FIG. 1 , illustrating volumetric control of sewage sludge being delivered to the sludge/lime mixer. 
           [0017]      FIG. 5  is a sectional view taken along line V-V of  FIG. 2 , through the purified air discharge stack, wherein a means for withdrawing air through the stack is illustrated. 
           [0018]      FIG. 6  is an alternative to the substantially enclosed transfer conveyor of  FIGS. 1 and 2 , whereby the sludge/lime mix is delivered from the sludge/lime mixer to a pasteurization chamber prior to discharge to a discharge conveyor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring now in detail to the drawings, wherein like reference numeral indicate like elements throughout the several views, there is shown in  FIG. 1  a dewatering device  10  in the form of a centrifuge. It will be understood that any suitable dewatering device or solids concentration device may be used in place of the centrifuge. The device  10  delivers sewage sludge via the line  11 , in the direction of the arrow  12  to a centrifuge cake screw conveyor  13 . A discharge line  14  is provided from the centrifuge or other dewatering device, for delivery of water that is removed from the sewage sludge, to discharge. 
         [0020]    The screw conveyor  13  is provided with an auger  15  therein, schematically shown as illustrated. It will be understood that where an auger such as that  15  is illustrated in the drawings, only partially occupying the conveyor device, such is only a schematic illustration, and that the auger (or other belt or other conveyor mechanisms within the conveyor) will, in fact, exist from one end of the conveyor to the other, such as from end  16  to opposite end  17 . 
         [0021]    The auger  15  is controlled via a motor  18  that provides for auger rotation, via a control line  20 , that is controlled from the computer C. 
         [0022]    The discharge from the screw conveyor  13 , is via line  21 , delivering sludge in the direction of arrow  22 , to a sludge transverse screw conveyor  23 , entering the same at location  24 , such that the sludge is delivered through the conveyor  23  via a rotatably driven auger  25 , driven from a motor  26  that, in turn is controlled by the computer C, via control line  27 . 
         [0023]    The sludge transverse screw conveyor  23  is disposed at an upward angle from end  28  to end  30  by means of supports  31  and  32 , as shown. The supports  31  and  32 , in turn, are mounted on respective load cells  33  and  34  that measure the weight of sewage sludge being delivered on a time basis, such as per minute, based upon increase of weight over time, for control of the amount of sewage sludge being delivered to the sludge/lime mixer from the conveyor  23  over any given time basis. This can be done by temporarily discontinuing the rotation of the auger  25  of the screw conveyor  23  to accumulate solids over time in the sludge/lime mixer  41  to establish a sludge/lime mixing rate. 
         [0024]    The load cells  33  and  34  are connected to the computer C via electrical information communication lines  35  and  36 , respectively. 
         [0025]    The load cells  33  and  34 , and any of the load cells used in connection with the system of this invention and/or its method of operation may be made in accordance with any of U.S. Pat. Nos. 5,770,823; 4,064,744; 4,166,997; 4,454,770 and 5,313,022, the complete disclosures of which are herein incorporated by reference. 
         [0026]    Near the upper end  30  of the sludge transfer screw conveyor, there is a discharge opening  37 , communicating with a duct  38 , for delivering sewage sludge from the conveyor  23  via line  38 , in the direction of the arrow  40 , into the sludge/lime mixer  41 , near the left end thereof as shown in  FIG. 1 . The sludge/lime mixer is essentially enclosed. 
         [0027]    Lime is provided from a source such as a truck  45  delivered via a delivery line  46  to a lime silo  47 , in which it resides until the programmable logic computer C calls for delivery of lime to the sludge/lime mixer  41 . At that point, an openable discharge gate within the bottom  48  of the lime silo  47  is activated, to be opened via activation of a motor  50  via control line  51  from the computer C for delivery of lime via discharge line  52 , as allowed by valve  53  controlled from the computer C via control line  54 , to allow lime to flow into the lime feeder  55 . An auger  56  within the lime feeder  55 , delivers lime to lime feeder discharge line  57  upon controlled rotation of the auger  56  via motor  58 , that, in turn, is controlled from the computer C via control line  60 . 
         [0028]    Lime thus passes downward from the delivery line  57  to the lime supply hopper  61 , in the direction of the arrow  62 . 
         [0029]    The lime supply hopper  61 , as shown, is essentially of tapered configuration, but it will be understood that the same can be of any configuration that will result in a satisfactory feed of lime to the lime feed screw conveyor  63 . 
         [0030]    The lime supply hopper is supported on supports  64 ,  65 , that, in turn, are disposed on load cells  66 ,  67 , respectively, which load cells  66 ,  67  transmit delivery weight over time information to the commuter C, via electrical information delivery lines  68 ,  70 . Lime is thus delivered from the lower end  71  of the lime hopper, via delivery line  72 , in the direction of the arrow  73 , to the right-most end of the lime feed screw conveyor  63 . An auger  74  running from end-to-end of the conveyor  63  therefore delivers lime leftward as shown in  FIG. 1 , due to rotational control of the auger  74  via motor  75  as controlled via control line  76  from the Computer C. 
         [0031]    At the left-most end of the screw conveyor  63 , there is shown an air intake line  77 , for receipt of incoming air via an air impeller  78  disposed at the upper end thereof, which impeller  78  is driven via line  80  from a motor  81 , which motor  81  is, in turn, controlled via electrical control line  82  from the computer C, for delivery of air through duct  77  in the direction of arrow  83 , entering the lime feed screw conveyor at inlet  84 . 
         [0032]    Thus, lime and air enter a discharge duct  85  from the left-most end of the conveyor  74 , in the direction of the arrow  86 , to be delivered to the lime addition screw conveyor  87  at the left end thereof as shown in  FIG. 1 . The lime addition screw conveyor  87  likewise has an auger disposed therein from end-to-end (although only a portion thereof is illustrated schematically). The auger  88  is motor driven by motor  89 , controlled via control line  91 , from the computer C. The screw conveyor  87  is illustrated as having a plurality, such as five, potential lime discharge locations  90 , at various locations along the screw conveyor  87 . The left-most discharge location  90 , is shown with a phantom connection to the lime/sludge mixer, which phantom connection appears as  93 . The center two of the discharge locations  92  are not illustrated as having any connection to the sludge/lime mixer  41 , and the right-most connections from the lime addition screw conveyor  87  to the sludge/lime mixer  41  are shown at  93 . It will be understood that any of the discharge locations  92  from the lime addition screw conveyor may have suitable connections to the sludge/lime mixer  41  located as may be desired. 
         [0033]    Sometimes a greater amount of mixing within the mixer  41  is desired, in which case, one of the left-most connections  93  will be installed. Other times a lesser amount of mixing of lime is needed, at which point one or more of the more rightward located connections  93  will be employed. 
         [0034]    Thus, lime is supplied to the sludge/lime mixer  41  under controlled supplying conditions. As an alternative to the delivery of lime from the lime addition screw conveyor  87  to the sludge/lime mixer  41 , lime can be supplied to the centrifuge cake screw conveyor  213 , prior to increasing the solids concentration of the sludge. Thus, as shown schematically in  FIG. 1A , lime is delivered from a lime addition screw conveyor  287  to a centrifuge cake screw conveyor  213 , prior to increasing the solids concentration of the sludge. 
         [0035]    Within the sludge/lime mixer  41 , there is an augers  95 , schematically illustrated, but running from the left end to the right end of the mixer  41 , such that delivery of sludge into the mixer  41  via delivery line  38 , and delivery of lime and air from the lime addition screw conveyor  87  enters the sludge/lime mixer  41  via any or all of inlet lines  93 , depending upon which lines  93  have been chosen to be the sources of air and lime delivery into the mixer  41 , depending upon the amount of mixing of lime with the sludge is desired. 
         [0036]    The rotation of the augers  95  is controlled from motor  96  via control line  97 , that, in turn, is controlled from the computer C. 
         [0037]    The sludge/lime mixer  41  sits on load cells  100 ,  101  that are responsive to the weight of sludge and lime being mixed in the mixer  41 , and deliver that information via respective electrical information delivery lines  102 ,  103  to the programmable logic computer C. 
         [0038]    A heating device, preferably comprising an electrical heater  104 , is located inside the sludge/lime mixer, for supplying heat thereto, to heat the sludge and lime in the mixer  41 , especially at the location of inlet  38  of sludge thereto, with the heating element  104  being controlled from the programmable computer C, via electrical lines  105 ,  106 . The computer C is provided with electric power via power supply  79 . Alternatively, instead of electrical heater  104 , heat can be provided to either the conveyor  41  or the auger  95  by the use of a hot oil or hot gas heating means, as may be desired. 
         [0039]    Alternatively, or in addition thereto, the heat may be provided via a methane heater  107 , for example, or any other type of heater that would heat a thermal fluid such as hot oil or hot gas delivered thereto from a thermal fluid supply  108 , via delivery line  110 , for recirculation of the thermal fluid to and from the inside of the sludge/lime mixer, such as, but not limited to, through the augers  95  via thermal fluid lines  111  and  112 . 
         [0040]    The delivery and use of heated thermal fluid from the fluid heater  107  may be as is disclosed in any of U.S. Pat. Nos. 7,669,348 and 8,065,815, the complete disclosures of which are herein incorporated by reference.           complete disclosure of which is herein incorporated by reference, or in any other manner such as will satisfactorily convey and mix the sludge and lime in the mixer  41 . 
         [0041]    The sludge/lime mix is thus delivered to the right end of the sludge/lime mixer  41 , for discharge therefrom via discharge line  113 , in the direction of the arrow  114  to a transfer conveyor  115 . The transfer conveyor may be a belt conveyor, suitably motor driven from a motor  116  thereof (see  FIG. 2 ) that in turn in controlled via a motor control  117  that, in turn, is controlled from the computer C via electrical control line  118 . 
         [0042]    The transfer conveyor  115  is contained within a substantially completely enclosed enclosure  120 , with the exception of the inlet for the sludge/lime mix at inlet  113 , in order to maintain control of odors, steam, dust or any ammonia resultant from the treatment process from entering the atmosphere prior to cleaning the same through a control hood, scrubber and discharge stack, as will be discussed hereinafter with respect to  FIG. 2 . 
         [0043]    It will be apparent that the transfer conveyor  115  is shown in two parts, one part in  FIG. 1  and the remainder in  FIG. 2 , via a drafting expedient breaking the same in parts, due to the length of the system which appears in part in  FIG. 1  and in part in  FIG. 2 . 
         [0044]    After the sewage sludge has been stabilized with lime in the sludge/lime mixer and deposited onto the transfer conveyor  115 , it is delivered into the lower end of a control hood  121  as shown in  FIG. 2 , by which the sludge/lime mix enters the hood  121  through an opening  119  on the left side thereof. 
         [0045]    The hood  121 , as illustrated in  FIGS. 2 and 3 , it is comprised of four corner supports  122  and a curtain  123 , which curtain  123  is preferably comprised of a generally flexible material. The curtain  123  may preferably be comprised of a plurality of vertical strips  124  of plastic sheeting, on each of the four sides of the hood  121 , which, in the aggregate, form an enclosure at the periphery of the hood  121  around the interior  125  of the hood  121 . The vertical strips  124  may be of transparent plastic, and, in the aggregate, will allow ingress of air through the curtain  123 . 
         [0046]    Air will also be drawn upwardly through the interior  125  of the hood  121  in the direction of the arrows  126 , by creating a low pressure zone from above the hood  121 , as will be described hereinafter. 
         [0047]    Air is drawn through the hood  121  by means of an exhaust connection  128  in the top  127  of the hood  121  of a duct  130  connected to an air scrubber  131 . The scrubber  131  is provided with one or more spray nozzles  132  therein, for spraying water into the upper end of the scrubber  131  to create liquid droplets that will absorb dust, odor, steam, ammonia, and any combinations thereof that are entrained within or carried by the air drawn through the scrubber  131 . A mist eliminator  133  is disposed at the upper end of the scrubber  131  to prevent such droplets or spray from being drawn upwardly out of the scrubber  131  through the scrubber outlet duct  134 . The scrubber may be made in accordance with any of U.S. Pat. Nos. 3,969,094; 4,539,024 and 5,292,353 or in any other manner. Water is delivered to the one or more spray nozzles  132  in the scrubber  131  via a delivery line  135 , preferably under pressure provided, as by a pump  136 , controlled by a motor  137  that, in turn, is controlled via an electrical control line  138  from the programmable logic computer C. Droplets that dissolve or absorb the dust, odor particles, steam, ammonia or other impurities are collected at the bottom of the scrubber  131  and may be discharged therefrom via the liquid discharge line  140 . It will thus be seen that pollutants are removed from the air entering the scrubber  131 . 
         [0048]    The thus purified air passes through the scrubber discharge duct  134  to enter the bottom of a stack  141  that is supported on a stack support tower  142 . 
         [0049]    A fan, impeller or other air movement device  143  is located in the stack  141 , as shown in the cross-section of  FIG. 5 , for creating air flow up through the stack  141 , and drawing a partial vacuum through the scrubber  131 , the duct  130 , and hood  121  in the direction of the arrow  144 . The impeller or other such partial vacuum drawing device  143  is driven by a motor  144  having an electrical control line  145 , controlled by the programmable logic computer C. 
         [0050]    The stabilized sludge/lime mix is deposited from the transfer conveyor  115  onto a discharge conveyor  150 , dropping from the right end of the transfer conveyor  115  as illustrated in  FIG. 2 , down onto the discharge conveyor  150  in the direction of the arrow  151 , to pass in the direction of the arrow  152 , up the discharge conveyor, to be delivered to a truck  153 , dropping into the truck  153  as shown by the arrow  154 . The truck  153  can then deliver the thus treated sludge to another location, such as for distribution onto land or the like. 
         [0051]    As an alternative to delivery of the sludge/lime mix from the sludge/lime mixer  41  to the transfer conveyor  115 , the sludge/lime mix can be delivered via line  113  to a pasteurization vessel  215  prior to discharge to the discharge conveyor  150 , with air being drawn off via the hood  121  as described above. The pasteurization vessel can be as described in U.S. Pat. No. 5,783,073, the complete disclosure of which is herein incorporated by reference, or via any other suitable pasteurization vessel. 
         [0052]    The discharge conveyor is driven by a motor  155  that, in turn, is controlled from the programmable logic computer C, via an electrical control line  156 . 
         [0053]    While the transfer of untreated sludge from the sludge transfer conveyor  23  to the sludge/lime mixer  41  will preferably be controlled by controlling the weight of sludge delivered from the sludge transfer screw conveyor by means of the load cells  33 ,  34 , there is provided an alternative or additional volumetric control of sludge passing from the sludge transfer screw conveyor  23  to the sludge/lime mixer  41 . With reference to  FIG. 4 , there is shown, in the discharge  37  of the sludge transfer screw conveyor  23 , a means for controlling the volume of sludge passing through the discharge  37 , by means of a volumetric feeder  160 , shaft-driven at  161 , with the volumetric feeder being comprised of three pockets  162 ,  163  and  164 , substantially equidistantly spaced apart, so that, upon rotation of the shaft  161  in the direction of the arrow  165 , as shown, untreated sewage sludge from the transfer screw conveyor  23  will enter the pockets  162 - 164  to be rotatingly moved downward so that the sewage sludge falls through the duct or conduit  38  into the sludge/lime mixer  41 . 
         [0054]    It will be understood that other forms of volumetric feeder other than that  160  may be used, within the scope of this invention, and that the sludge delivery apparatus could comprise a structure other than the auger  35 , such as a moving belt, a paddle conveyor, or any other sludge delivery apparatus. 
         [0055]    The motor  165  that drives the shaft  161  is controlled via an electrical control line  166 , controlled by the programmable logic computer C. 
         [0056]    A system is provided for dissolving scale that accrues to surfaces in the system as a result of exposure of those surfaces to lime. In accordance therewith, at the right side of the schematic of  FIG. 1 , there is shown a vessel  170  containing an acid  171 . A source  172  of water is also provided for the vessel  171 , so that either acid  171  or water via supply line  172  is provided to the vessel  170 , or combinations thereof A pump  173  with a suction line  174  is provided into the vessel  170 , for delivering acid or water, or both via line  175  to spray devices (unnumbered) in any of the discharges  92  from the lime addition screw conveyor  87 , to pass through any of the desired appropriate delivery ducts  93 , into the sludge/lime mixer  41 . The pump  173  is controlled from a motor  176  that, in turn, is controlled from an electrical control line  177  from the computer C. Similarly, a pump  180  has a suction line  181  in the vessel  170 , for drawing acid, water, or combinations thereof via line  182  to the hood  121  via suitable spray nozzles  183 , and optionally to the spray nozzles  132  in the scrubber  131 , via line  135  and pump  136 . The programmable logic computer C can likewise control the operation of the motor  183  for delivery of acid and/or water and/or other scale dissolving chemcials. from the vessel  170 , via the electrical control line  184 , connected thereto. 
         [0057]    The delivery of acid and/or water can be provided from the vessel  170  to the scrubber  131 , via the optional connection line  186  shown in dotted, connecting delivering line  182  with delivery line  135 , as shown in  FIG. 2 . 
         [0058]    It will be apparent from the foregoing that various modifications may be made in the apparatus and method of this invention all within the spirit and scope of the invention as defined in the appended claims. Where structure is recited in means plus function language or steps plus function language, it will be understood that the same is to be of the broadest possible scope, embodying not only the particular apparatus or steps set forth in the claims hereof, but also all equivalents thereof that would be within the scope and understanding of those skilled in this art, whether or not such are specifically disclosed in this application.