WO2012126122A1

WO2012126122A1 - Apparatus and method for slurry dewatering by evaporation

Info

Publication number: WO2012126122A1
Application number: PCT/CA2012/050179
Authority: WO
Inventors: Joaquim FRAZAO; Maurice LABBÉ; Arnaud CHEYROU-LAGREZE
Original assignee: Environnement Mechtronix Inc.; Bergeron, Jean
Priority date: 2011-03-22
Filing date: 2012-03-22
Publication date: 2012-09-27

Abstract

Applicants have discovered a new method of manufacturing a plenum for slurry dewatering by evaporation. The method comprises using high energy beam welding to provide a more even plenum surface and another surface that can be welded from an outer side of the surface. Applicants have also discovered a new slurry handling device having a rear portion comprising a rotating brush for spreading non-dewatered slurry on a plenum surface and a forward portion comprising a rotating brush for removing dried slurry from the plenum surface. The dewatering device comprises a motion system for creating relative motion between the plenum surface and the slurry handling device. A plurality of slurry handling devices and plenums can be used in an enclosed area where a motion system is adapted to move essentially in a forward and backward longitudinal direction; simultaneously over a plurality of plenum surfaces to dewater the slurry.

Description

APPARATUS AND METHOD FOR SLURRY DEWATERING BY EVAPORATION Technical Field

This present invention relates generally to dewatering slurries, more specifically, the invention relates to apparatuses and methods for removing water from slurries by evaporation.

Background of the Invention

Urbanisation and increased population density has lead to increased generation of wastewater sludge slurry and to a greater need for wastewater treatment plants. Transportation of sludge for land application, incineration, digestion/gasification are some of the methods known in the art for the disposal of the substance. Dewatering sludge prior to disposal is one way to increase efficiency of most methods by reducing the quantity of sludge to be disposed, thus saving money. Wastewater sludge (also known as biosolids) is a complex mixture of sewage and the bacteria produced during the treatment of the sewage. Sludge is unpredictable in composition and complex to dewater. Girovich (US Pat. No. 5,069,801 ) teaches an apparatus where municipal sludge is dried in an indirect heating dryer to simultaneously dry and pelletize the sludge while preventing the escape of malodorous gases. Evaporated water from the dryer is used to preheat the sludge prior to mechanical dewatering. The multi-stage vertical dryer of Girovich is composed of many immobile heated trays having arms that spread and scrape the sludge pellets off the drying surface. The air that is used to cool the pellets and that is used as sweep air in the dryer contains malodorous gases. In order to prevent the escape of these malodorous gases, the pellet cooling air and sweep air, which also includes the water vapor generated during the drying of the sludge, is deodorized by thermal treatment, preferably in a high temperature combustion zone. Bourdel (US Pat. No. 5,810,975) teaches an apparatus for extracting solid residues from aqueous slurry using an ingenious method of evaporation, compression and condensation. Slurry is applied to the upper surfaces of rotating disks in a hollow cylindrical vessel for evaporation. Oscillating slurry dispensing arms are oriented radially relative to the axis of a hollow shaft that supports the disks. Slurry flattening rollers press the slurry on to these disk upper surfaces and separate slurry scraping means remove the residue from the rotating disk upper surfaces. Finally, a condensation enclosure is provided for removing liquid condensate from the vapor produced in the evaporation enclosure. Means are also provided for eliminating non-condensable gases periodically from the condensation enclosure. Some drawbacks of the Bourdel apparatus are its large number of moving parts. Indeed, the apparatus of Bourdel is designed in such a way that many mechanical pieces interact with one another as in a clock mechanism. In such a construction, when one disk or oscillating arm breaks down or must be maintained or serviced, the whole apparatus, and therefore treatment time, must be stopped. For example, if the scraper elements responsible for removing dried, stuck-on slurry from the plenum chip or break, the apparatus must be shut down until the whole scraper can be replaced.

Another drawback of the Bourdel apparatus is its absence of efficient modularity. Indeed, the phyisco-structural limits to the surface area of each disk is such that increasing treatment surface can only be achieved by increasing the number vertically stacked disks, and again, the number of moving parts.

Due to the drawbacks of the prior art methods and apparatuses described above, it was desirable to provide new and more efficient methods and apparatuses for dewatering slurries using evaporation-condensation.

Summary of the Invention

The apparatus of some embodiments of the present invention should be cost effective and easy to manufacture, operate and maintain. Furthermore, it should be designed with the objective of minimizing the number of moving/mechanical parts, it should be modular such that treatment surface area can be easily adjusted and maintenance of one part of the apparatus should not necessarily require shutting down the whole apparatus. It is an object of some embodiments to use components that wear down instead of suddenly failing, so as to extend the mean time between failures (MTBF) of a wastewater sludge treatment system. The use of a brush instead of a scraper to remove dried slurry from a heated plenum surface avoids the use of a fragile breakable scraper element, and potential damage to the plenum surface by using a brush that gradually wears down during a predictable service life after which it can be replaced during scheduled maintenance.

It is an object of some embodiments of the present invention to provide a plenum for evaporating a slurry comprising a top rectangular sheet having an outer surface for receiving a slurry and an inner surface for receiving the hot gas; a bottom rectangular sheet adapted to evacuate a fluid, wherein the top and bottom sheets are joined together defining therebetween a inner plenum chamber; a plurality of ribs disposed between the top sheet and the bottom sheet for providing structural support to the outer surface; a hot gas inlet in fluid communication with the inner plenum chamber for receiving hot gases; and a fluid outlet in fluid communication with the inner chamber for evacuating a fluid.

It is another object of some embodiments of the present invention to provide a method of manufacturing a plenum for dewatering slurries by evaporation using high energy beam welding (such as laser welding) to join a plurality of ribs to one or more sheets forming a top plenum surface and a bottom plenum surface. The high energy beam welding provides a more even top surface of a plenum without welding induced grooves or dimples.

In some aspects, the outermost ribs form a frame around the top and the bottom surface, wherein the frame and the top and bottom plenum surfaces define an inner plenum chamber. In other embodiments, one of the top plenum surface or the bottom plenum surface is welded from an outer side of the plenum surface. In yet other embodiments, the bottom surface and the ribs are an integral piece and need not be welded.

It is an object of some embodiments of the present invention to provide an apparatus for dewatering slurries by evaporation comprising one or more surface for receiving a slurry; the surface having a longitudinal length and a lateral length and adapted to be heated to a temperature that allows for slurry evaporation; at least one slurry handling device having a rear portion comprising a slurry spreading device for spreading a non dewatered slurry on the surface and a forward portion comprising a slurry removing device for removing dried slurry from the surface; and a motion system for creating relative motion between the surface and the slurry handling device.

In yet other embodiments, the motion system causes the slurry handling device to move from a starting point in a forward longitudinal direction along the surface to add a new batch of non-dewatered slurry and to remove an old batch of dried slurry; and then move in a backward longitudinal direction to return to the starting point.

In some embodiments, the slurry handling devices are located on both sides of a central support housing, and the inside of the central support housing is isolated from the inside of the evaporation chamber and further comprises a motion system for moving a robot. In some embodiments of the present invention there is provided an apparatus for dewatering slurries by evaporation comprising a heat exchange surface for receiving and heating non-dewatered slurry; a slurry spreading device for spreading the slurry on the surface; a brush for removing dried slurry from the surface, the brush comprising a bristle support member for supporting a plurality of bristles, the bristle support member having an axis of rotation passing through its center and extending horizontally, a rotation actuator for allowing the bristle support member to rotate about its axis of rotation and bristles extending outward from the bristle support member for removing dried slurry by contacting the surface while rotating about its axis; and a motion system for creating relative motion between the surface and the brush to remove the dried slurry from the surface. In some embodiments, the brush further comprises a height adjustment device for adjusting a distance between the horizontal axis and the surface. In other embodiments, the brush further comprises a bristle length adjustment device for adjusting the length of bristles.

In other embodiments, the direction of rotation of the brush is clockwise when a relative horizontal motion of the brush is from right to left or when a relative horizontal motion of the surface is from left to right.

In yet other embodiments, there is provided an apparatus for dewatering slurries by evaporation comprising a heat exchange surface for receiving and heating non-dewatered slurry; a brush for spreading the slurry on the surface, the brush comprising a bristle support member for supporting a plurality of bristles, the bristle support member having an axis of rotation passing through its center and extending horizontally, bristles extending outward from the bristle support member for contacting and evenly spreading the non- dewatered slurry over the surface, a rotation actuator for allowing the bristle support member to rotate about the axis of rotation; a slurry removal device for removing dried slurry from the surface; and a motion system for creating relative motion between the surface and the brush to efficiently spread the slurry on the surface. In some aspects of the present invention, the method comprises selecting a brush of appropriate diameter and rotating the brush in a predetermined direction, wherein the brush comprises bristles of adjustable length.

In yet other aspects of the present invention, there is provided a feeding system for feeding liquid slurry onto an evaporation plenum comprising a slurry line for transporting the slurry wherein at least part of the slurry line is located above the plenum; one or more isolating valves for isolating a predetermined volume of slurry from the slurry line by closing the isolating valves; and one or more batch dumping valves for dumping the predetermined volume of slurry onto the plenum.

In still other aspects of the present invention, there is provided a method of feeding slurry to a slurry evaporation plenum comprising filling a slurry line with liquid slurry; wherein at least part of the slurry line is located above the slurry evaporation plenum; closing isolating valves to define a predetermined volume of slurry; wherein the isolating valves, wherein the predetermined volume is located in part of the slurry line located above the evaporation plenum; and opening batch dumping valves to release the predetermined amount of slurry onto the slurry evaporation plenum, wherein the slurry.

In yet other aspects of the present invention, there is provided a modular evaporator having an inlet for receiving non-dewatered slurry and outlets for evacuating dried slurry (solids) and a liquid, the modular evaporator comprising: an evaporation chamber having a longitudinal direction and a lateral direction; a robot inside the chamber having a plurality of slurry handling devices for spreading non-dewatered slurry and removing dried slurry, the robot adapted to move essentially in a forward and backward longitudinal direction; a plurality of rectangular plenum surfaces inside the chamber for receiving the non-dewatered slurry and evaporating slurries inside the evaporation chamber, the plenum surfaces immobile with respect to the evaporation chamber. In some aspects, the chamber further comprises doors for allowing the robot to move in and out of the chamber and be replaced by another robot to minimize Mean Time to Repair (MTTR). It is yet another object of the present invention to provide a method of dewatering a slurry by evaporation comprising providing a plenum with a hot outer surface and a slurry handling device; wherein the slurry handling device and the plenum move essentially linearly with respect to each other as a non-dewatered slurry is spread along the outer surface of the plenum and dried slurry is removed.

Brief Description of the Drawings

The invention will be better understood by way of the following detailed description of embodiments of the invention with reference to the appended drawings, in which:

Figure 1 is a schematic view of the laser welding process used to manufacture a plenum according to the present invention.

Figure 2 is a schematic isolated view of the plenum showing the top surface and location of ribs underneath top surface.

Figure 3A is a schematic side isolated view of the plenum and 3B is a schematic back isolated view of the plenum and Figure 3C is a cutaway schematic front isolated view of the plenum to highlight possible rib structure.

Figure 4 is a highly schematic side view of one module of a slurry evaporation apparatus showing the plenum and the slurry handling device, including the slurry spreading device and the slurry removing device.

Figure 5 is a schematic representation of a brush with bristles used as a slurry removal device.

Figure 6 is a schematic representation of a brush with bristles used as a slurry spreading device.

Figure 7 is a schematic front view of a modular slurry evaporation apparatus showing 6 plenum modules and the flow of liquids and gases in the enclosed area comprising the inner plenum chamber in the pressurized evaporation chamber.

Figure 8 is a schematic representation of a system for implementing a batch dumping approach.

Figure 9 is a schematic partial view of one embodiment of the modular apparatus.

Figure 10 is a schematic side view of a pin-rack and sprocket motorization system. Detailed Description of the Invention

Figure 1 is a schematic view of the laser welding process used to manufacture a plenum according to the present invention. Because at least some slurries evaporated with the apparatus/plenum of the present invention are highly liquid, they will take the shape of the plenum surface upon which they are being dumped/spread. If there are significant grooves/troughs (such as those caused by traditional welding), the slurry in the groove/trough will be thicker than the surrounding slurry and the time required to evaporate the slurry will vary according to its thickness. In order to optimize processing time, slurry must be at constant thickness such that the minimal predetermined treatment time will suffice to evaporate the slurry. Applicants have discovered that laser welding (or any high energy beam welding type) using a laser 18 is advantageous for manufacturing a plenum according to the present invention because it allows welding a thin top surface to ribs 16 without creating grooves or dimples in the top surface. Traditional welding would cause grooves that decrease the efficiency of the evaporation process due to areas of varying slurry thickness.

There are many types of welding methods available for joining two metal pieces. Among the "thermal" welding methods, arc welding, electric resistance welding, chemical welding, braze welding, and high energy beam welding approaches such as electron beam welding, laser beam welding and plasma arc welding are the most common. It will be appreciated that any method of high precision automated welding providing a small, focused "heated" area will be useful for manufacturing a plenum according to the present invention. In addition, non thermal welding methods such as "ultrasound" welding could also be used.

Applicants used laser welding to manufacture the plenum because it allowed to achieve predetermined planarity/tolerance, precision, and versatility requirements. In laser welding, the materials to be welded melt under the heat obtained from a narrow beam of coherent, monochromatic light. Typically, laser welding does not require filler metal to be used and is advantageous for thin workpieces, such as plenum surface sheets. Other advantages of laser welding for manufacturing a plenum include welding areas that are not readily accessible (such as the bottom plenum surface to the ribs), providing excellent welding precision (to limit the welding groove), permitting assembly of different metals (to optimize costs and functionality of the plenum by using less expensive materials/metals), not using electrodes, and importantly, laser welding does not cause significant thermal damage to the pieces being welded due to the small area being heated. The focused heat source provided by laser welding allows to the welded area to be rapidly heated and rapidly cooled, which is advantageous in manufacturing a plenum. It will be appreciated that the lower overall welding temperatures in turn cause less deformation of the metals at the welded areas and provides more uniform, planar surfaces. Another advantage of laser welding, in the present invention, is its ability to weld through a material by adjusting the focal point of a laser. In this case, laser welding is performed through the bottom outer surface in order to weld the bottom surface and ribs. This is possible, in part, due to the thinness of the bottom surface and is necessary because the top sheet(s) has already been welded to the top surface of the ribs. Because welding a metal surface to metal ribs through that metal surface can cause some detrimental effect on the planarity of the surface, it is therefore advantageous to weld the bottom sheet from the outside and the top sheet from the inside.

As shown in Figure 1 , the steps for manufacturing the plenum comprise placing a plenum top sheet 12 with inner surface facing up; placing ribs 14 and frame 16 on top sheet 12 and laser welding ribs and frame to top sheet using a laser 18; placing bottom sheet 3 on ribs16 and frame 14 ; welding the bottom sheet 13 to the ribs 16 and frame from the outer surface of bottom sheet 13. It will be appreciated that reversing the top and bottom sheets could also allow to manufacture the plenum.

In some embodiments, due to the large surface area of the plenum, it is necessary to weld more than one sheet of material that makes the top or bottom surface. Planarity of the plenum is important for two reasons. The first reason is that optimal evaporation requires homogenous slurry thickness across the whole plenum surface. The second reason is has to do with removing dried slurry with the slurry removal device. If the removal device comprises scrapers or pushing elements, planarity is very important. However, if the slurry removal device is based on a flexible bristle-based brush, planarity is not as important because the brush has an improved ability to adapt to the shape of the plenum. Notwithstanding the previous and as mentioned above, planarity of the outer (top) plenum surface also ensures proper slurry spreading and uniform slurry thickness, which have an impact on overall evaporation efficiency. According to the present invention, a laser welding approach can be used to assemble two or more sheets forming the top and bottom surfaces. Assembling the top and bottom surface, along with a frame 14 between the two surfaces, defines an inner closed chamber of the plenum. The top sheet 12 is one or more metal sheets and defines an outer surface for receiving the slurry and an inner surface for receiving hot gases to conductively heat the outer surface. The bottom sheet 13 of the plenum (not to be confused with the inner surface of the top sheet), is used to close off the inner chamber of the plenum and to collect water condensing at the inner surface. Welding large sheets of thin metal does not allow achieving the desired level of planarity without the use of reinforcing ribs 16.

Figure 2 is a schematic isolated elevation view of the plenum 10 showing the top surface of the top sheet 12. The location of ribs 16 underneath the top sheet 12 is shown in dashed lines. Applicants have discovered a new plenum design that optimizes overall apparatus efficiency as compared to the rotating disc plenum evaporator of Bourdel (US Pat. No. 5,810,975). The plenum design allows for a simpler method of achieving modularity. Indeed, such a plenum can be adapted to fit a particular space (footprint) by modifying its longitudinal length 22 or lateral length 26, as long as the slurry handling device (see figure 4) is also adapted accordingly. In the discoid plenum model of Bourdel, only the diameter of the disc can be adjusted and, because there is a "structural" limitation of about 2 m with respect to disc diameter, modularity could only be achieved by stacking additional discs on top of existing discs. As seen in Figure 2, the ribs 16 occupy a substantial longitudinal length 22 of the plenum 10. The first function of the ribs 16 is to offer structural support to the top sheet 12 (top surface) of the plenum which is made of thin heat conducting material and must support above ambient pressures. The second function of the ribs 16 is to help segregate the various longitudinal sections of the plenum 10 in order to guide the gases and liquids along the longitudinal length 22 of the plenum 10 from the compressed gas inlets 20 end to the fluid outlet 24 end of the plenum 10. Applicants have found that ribs 16 prevent the accumulation of non-condensable fluids in certain areas of the plenum 10. The compressed gas inlets 20, due to the design of the ribs, feed hot gas in separate lanes formed by the ribs. It will be appreciated that the plenum's frame structure surrounding the rectangular top and bottom surfaces offers structural support and allows to seal off and thus create an inner plenum chamber having one or more compressed gas inlets 20 and one or more fluid outlets 24. The top surface of the plenum can also have a longitudinal siding 28 that prevents very liquid slurries from flowing off the top surface of the plenum.

The inner plenum chamber receives gases at pressures greater than atmospheric pressure. On the one hand, the top surface of the plenum needs to be a certain thickness to ensure meeting structural requirements in the presence of above ambient inner chamber pressures while on the other hand, the plenum needs to be thin enough to offer good heat exchange capabilities between the inner and outer chambers. Figure 3 provides schematic isolated views of the plenum showing a side view (Fig. 3A), a back view (Fig. 3B) and front cutaway view (Fig. 3C). The side view (Fig. 3A) shows the top surface 32 and bottom surface 36 and allows to see the longitudinal siding 28 which goes from the gas inlet end 30 to the fluid outlet end 34 and is designed to prevent the overflow of slurry in cases where the slurry is very runny (i.e. not viscous). The back view (Fig. 3B) shows the top surface 32 and bottom surface 36 of the plenum 10 where the fluid outlet 24 tube is located and the end of a sloping bottom surface wherein the slope is from a side without the fluid outlet to a side with a fluid outlet 24. Once liquids have reached the fluid outlet end 34 of the plenum (also called the plenum reservoir 38, an end section adjacent the bottom surface is also sloped to allow liquid to evacuate to the fluid outlet 24 by gravity. The front cutaway view (Fig. 3C) shows possible rib structures which can, for example be a C-shaped rib 35 or a Z-shaped rib 37 for the first and third rib, respectively. The C-shaped rib 35 and Z-shaped rib 37 can also be flipped about a vertical axis, as shown for the second and fourth ribs, respectively. It will be understood that any rib structure or shape that satisfies the structural requirements can be used.

In another embodiment, the plenum structure could be entirely made of elongated rectangles or opposable C-shaped ribs 35 (thus forming rectangles) where the top of multiple elongated rectangles form the top surface 32 of the plenum and where the sides of some rectangles form the outer perimeter (frame) of the plenum 10. It will be appreciated that many designs/configurations of the plenum that allow for liquid condensate to evacuate are possible. In one embodiment, a "directional" pressure developed inside the plenum chamber is sufficient to force the liquid condensate to reach the plenum reservoir 38 for receiving condensate formed in the inner plenum chamber and evacuate the condensate through the fluid outlet end 34 of the plenum 10. In figures 2 and 3 and best seen in figure 3B, only the bottom surface of the plenum reservoir portion is angled to allow fluid to evacuate by gravity to the fluid outlet. The bottom surface 36 of the plenum separates near the end of the longitudinal length 22 to provide a slope in the direction of the lateral length 26 which facilitates fluid evacuation by gravity to a predetermined side of the plenum 10. In an alternate embodiment, it would also be possible to provide a sloped bottom surface essentially along the entire longitudinal direction. The slope would go downward from the compressed gas inlets 20 end to the fluid outlet 24 end and be designed to allow liquids to flow to the fluid outlet end by gravity. Alternatively, and in addition to the plenum reservoir 38, condensate can be collected from all plenums into a larger reservoir near the bottom of the enclosed area using pumps. A pump could transfer fluid from the larger reservoir to the boiler where the amount of fluid evacuated by the system is determined by a level of fluid in the boiler or in the larger reservoir, the objective being to maintain a constant level of liquid in the system.

Figure 4 is schematic side view of one unit (or module) of a slurry evaporation apparatus showing the plenum and the slurry handling device. The slurry handling device 40 has a motor to move it along the plenum 10 for spreading wet or non-dewatered slurry 41 and removing dry "slurry" 42. As slurry evaporation gas 43 is generated on the top surface 32 of the plenum 10, slurry evaporation gas 43 can be captured, compressed and redirected to the inner surface of the plenum to heat the plenum 10 while condensing the slurry evaporation gas 43 back into liquid form for easy removal through a condensed fluid outlet 24 (not shown on this drawing). It will be appreciated that this is one plenum only and that the shape, size and footprint of the whole apparatus, which critically depends on the plenum, can vary according to the treatment plant in which it is installed. Due its modularity, the apparatus can comprise a large number of plenums 10, where the number of plenums or total plenum surface area depends on the total amount of slurry to be treated/dewatered/evaporated. Plenums are developed with the objective of optimising manufacturing cost by using the minimal amount of material. The materials must be able to support above ambient temperature and pressure.

In some embodiments, the plenum surface has low planar tolerance due to, among others, the liquid nature of slurries and the interaction between slurry removal device and the plenum surface. The plenum material, as well as all other materials in contact with the slurry and/or the vapours must be able to withstand high temperatures, pressures and importantly, it must be corrosion resistant as some slurries are highly corrosive when evaporated. One such material is Stainless Steel.

The system can be adapted to treat non-condensable vapours using scrubbers such as those described by Bourdel (US Pat. No. 6,623,546). The plenum material must also have good heat transfer (conductive) properties such that providing a hot compressed gas to the inner chamber of the plenum allows to provide a predetermined temperature to the outer surface that receives the slurry. Heat transfer depends on characteristics such as heat conductivity and thickness of the plenum surface material. The apparatus of the current invention can also comprise, prior to slurry being directed to the plenum outer surface for evaporation, a slurry heating means. Pre-heating the slurry can be accomplished at least partially, using a heat exchanger according to Bourdel (US Pat No. 6,513,580). Using this heat exchanger, heat from a hot fluid (such as the evacuated fluid) is transferred to the non-heated slurry through a heat exchanger. Figure 4 shows an embodiment of the present invention having a slurry thickness adjuster 44 for indirectly adjusting the thickness of the slurry by adjusting the height of the slurry spreading device 45 with respect to the plenum 10.

The slurry handling device 40 comprises, in a preferred embodiment, the slurry containment chamber 46 for containing non-dewatered slurry 41 , the slurry spreading device 45 and the slurry removal device 47. The slurry handling device 40 can comprise the above three elements or they can all be separate entities. When joined, the slurry handling device 40 must be able to move the 3 elements essentially along the whole length of the plenum 10, from a starting point 48 to an end point 49. The slurry handling device 40 must be easily interchangeable and serviceable for maintenance and cleaning purposes.

When more than one slurry handling device 40 is required, such as in a modular apparatus having many plenum surfaces, the plurality of slurry handling devices (and the motion system) are referred to as the robot. The slurry handling device should, for example, be able to lift the 3 elements for returning them from the end point 49 of the plenum 10 back to the starting point 48. Alternatively, the plenum can be lowered while the slurry handling device 40 moves along an essentially horizontal track. In either case, slurry 41 is received through a slurry inlet conduit which can be a slurry feeding device 54 and directed to a slurry containment chamber 46 designed to receive and store the slurry until it is ready to be spread. It also "holds" the slurry while the slurry handling device 40 spreads it along the plenum 10. The slurry handling device 40 has several important characteristics. For example, the volume of the containment chamber 46 can be designed to allow for storage of the total volume of slurry 41 required for spreading along the whole surface of the plenum 10. Alternatively, the slurry can be delivered through a flexible conduit that moves with the slurry handling device 40 (or robot). In some embodiments, the slurry handling device 40 should be at least slightly liftable in order to allow for the "return" run to the starting point 48 of the plenum 10. The slurry handling device 40 should also be made of corrosion and heat resistant materials as well as being as simple and trustworthy as possible in addition to having easy maintenance and accessibility inside an enclosed area.

Due to the varying nature and composition some slurries such as wastewater sludge, it is important to adjust thickness of the slurry being spread using a slurry thickness adjuster 44. In some embodiments, the adjuster can consist of a threaded screw with a rotating crank and handle system which allows to adjust the height of the slurry spreading device 45 with respect to the plenum surface 32 as this is what determines the thickness of the slurry being spread on the plenum. In some embodiments, the slurry thickness adjuster is an automated adjustment system controlled by a controller or any other mechanical means such as a wedge. Sludge thickness after spreading onto the plenum according to present embodiment can vary from 0.5 mm to 4 mm.

The slurry removal device 47 should allow to thoroughly clear the surface of the plenum thereby removing the evacuated dry slurry 51 ), in order to allow for optimal heat transfer upon the following round/batch of treatment. The thorough clearing should not, however, damage the plenum surface which can also be made of stainless steel. The slurry removal device allows to remove evacuated dry slurry 51 from the plenum by pushing it over the edge of the plenum into a solids capture device shown as a conveyor in figure 7. There are other methods for capturing and removing evacuated dry slurry 51 from the apparatus such as an Archimedes screw. Rotating orbital scrapers can evacuate slurry over the sides of the plenum or a rotating brush can remove dried slurry and evacuate it over the "lengthwise" end of the plenum (i.e. the end point). Accompanying this approach can be a slurry transport device that pushes the dried removed slurry forward toward the end of the plenum, in a similar motion as that of the slurry handling device 40. However, the slurry removal device 47 described above must limit wear and damage to the plenum outer surface 32. The plenum should be as thin as possible and the rotating brush described above should be as gentle as possible to avoid damaging the plenum surface, yet the brush must remove as much dry slurry as possible to favour heat exchange of the next batch slurry spread on the plenum.

Laterally extending horizontal cylinders rotate on an axis that is perpendicular to the longitudinal direction of motion. It will be appreciated that the slurry removing device 47 is in front of the slurry spreading device 45. Both devices rotate clockwise (as shown by the arrows in Figure 4) when the slurry removing device 47 moves in the forward direction 52 from right to left. Clockwise rotation helps remove the dried slurry 42 by having bristles contact the surface and lift the slurry off the surface. Clockwise rotation helps spread the non-dewatered slurry 41 more efficiently on the plenum 10, as long as a slurry projection stopping device 53 prevents the non-dewatered slurry from being projected in a forward direction. The forward longitudinal direction of movement of the slurry handling device 40 is from right to left. It is understood that all drawings, including Figure 4, are not to scale.

Figure 5 is a schematic representation of a slurry removal device 47, showing a central cylinder 55, bristles 56 and the rotation axle 57 which defines the axis of rotation of the slurry removal device 47, which, in this embodiment, is a brush. For some slurry types, a brush rotation speed between 40 and 80 (preferentially 60) rpm, allows for proper slurry removal. Rotation of the slurry removal device 47 is variable and can be adjusted as a function of dried slurry 42 characteristics by a controller. For example, for certain "hard to remove" dried slurries, it may be more efficient to increase rotation speed or the type of bristles 56.

Figure 5 shows a brush with bristles 56 extending diagonally around and along the cylinder like threads of a screw. Depending on the circular arrangement of the bristles 56 along the length of the cylinder 55, the slurry could be propelled preferentially to one side of the plenum, if so desired. It will be appreciated that many bristle arrangements/configurations are possible that will allow the bristles to perform their function. For example, the bristle arrangement may comprise two sets of inwardly directed bristles meeting at the center such that dried slurry 42 is preferentially directed toward the center. It will also be appreciated that, without appropriate cleaning, such a slurry removal device 47 would likely become "encumbered" with contaminants which could decrease its efficiency. For this reason, it is advantageous to provide a cleaning device (not shown) that is able to properly remove "contaminants" from the slurry removal device 47. This cleaning device can be a high pressure water or fluid jet that is located at one end of the plenum 10. Such a jet can move laterally from one end of the brush to another end while the brush is rotating. Alternatively, the cleaning device can be a specific material upon which the brush is rotated in order to remove the contaminants by "rubbing action".

Applicants have discovered that a brush made with stainless steel bristles 56 allows to achieve such objectives (see Figure 5). Due to the similar nature of the material between the plenum 10 and the bristles 56, dried slurry 42 can be efficiently removed without causing significant damage to the plenum surface or to the brush itself. It will be understood by those skilled in the art that the brush bristles need not be made of stainless steel as any material could be used if it has the desired mechanical properties and corrosion resistance. For example, bristles 56 could be made from carbon-based sources such as carbon fibre and/or heat-resistant plastics or polymers. Figure 6 is a schematic representation of a slurry spreading device 45, showing a central cylinder 65, bristles 66 and the rotation axle 67 which defines the axis of rotation of the slurry spreading device 45. For some slurry types, a slurry spreading device 45 rotation speed between 40 and 80 (preferentially 60) rpm, allows for proper slurry spreading. Rotation of the slurry spreading device 45 is variable and can be adjusted as a function of sludge characteristics by a controller. The drawing shows a brush with bristles extending diagonally around and along the cylinder like threads of a screw. Arrangement of the bristles should allow for homogenous spreading along the length of the cylinder (i.e. the lateral length of the plenum). It will be appreciated that many bristle arrangements/configurations are possible that will allow the bristles to perform their spreading function. It will also be appreciated that, without appropriate cleaning, such a slurry spreading device 45 would likely become "encumbered" with contaminants which could decrease its efficiency. For this reason, it is advantageous to provide a cleaning device (not shown) that is able to properly remove "contaminants" from the slurry spreading device 45. This cleaning device can be a high pressure water or fluid jet that is located at one end of the plenum. Such a jet can move laterally from one end of the slurry spreading device 45 to another end while it is rotating. Alternatively, the cleaning device can be a specific material upon which the slurry spreading device 45 is rotated in order to remove the contaminants by "rubbing action". As shown in figure 4, the slurry spreading device has a slurry thickness adjuster for adjusting the thickness of the resulting layer of slurry on the plenum surface.

Other methods have previously been used to spread a layer of slurry on a surface. Applicants have discovered that using a rotating brush allows for more efficient spreading of slurry using a mechanical process of rotation. Additional advantages are that, in addition to sharing the same mechanical process, the slurry removal brush and the slurry spreading brush are interchangeable. For example, when the slurry removal brush has worn out significantly and is no longer useful for removing slurry, it can nevertheless be used in the slurry spreading device as bristle length can be shorter for this brush.

Figure 7 is a schematic side view of a multi-module slurry evaporation apparatus showing 6 plenum modules. A modular linear evaporator according to the present invention is proposed where plenums are immobile to facilitate distribution of hot vapour and the slurry handling device(s) 40 moves to spread and remove the slurry. In some embodiments, it can be important to minimize the horizontal distance between plenums in order to maximise the surface area of treatment for a given three dimensional footprint. Having plenums 10 and slurry handling devices 40 on two sides of a central support housing 72 is advantageous because the common central support housing 72 and corridor can be used for moving the slurry handling device(s) 40 using a motorization system 71. The motorization system 71 , the central support housing 72 and the slurry handling devices 40, together, form what is referred to throughout this document as the robot. Figure 7 shows a slurry inlet 73 where slurry is fed into the system and distributed to each slurry handling device 40 in a slurry conduit 83 in order to be spread over plenums 10 as a thin-layer of slurry (shown as a black circle). Slurry 41 is spread over the plenum 10 and evaporation gas 43 is generated due to the high temperature of the plenum in the evaporation chamber 74. Evaporation gas 43 from all plenums found inside the enclosed area 75 are collected through an evaporated fluid capture device (not shown) and sent to a compression chamber 76 to be compressed using a compressor, for example. The compressed gas 80 can be delivered through a compressed gas conduit 86 to the inside of the plenum (i.e. the inner plenum chamber 77) at a higher temperature (and pressure) than that of the outside of the plenum, thus causing condensation at the inner surface of the plenum and flow of liquid, by gravity for example, through a fluid conduit 85 to a condensate liquid outlet 78, in addition to concomitant heat transfer across the plenum surface. Figure 7 shows one outlet for dried slurry 42 (solids) and one liquid outlet 78 for evacuating liquid 81 (condensate). The liquid outlet 78 can be directed to a heat exchange device (not shown) for "heat" energy recovery. It will be appreciated that the hot liquid being evacuated from the enclosed area can be used in various energy recovery processes such as heat exchangers.

In an alternate embodiment of the dry solids conveyor 82 for exiting dried slurry 42 from the enclosed area 75 (bottom of Figure 7), it will be appreciated that one or more endless screw devices (Archimedes screw) can be provided to remove dried slurry 42 that reaches the bottom of the enclosed area 75 (in the evaporation chamber). Because in some embodiments, a slight positive pressure can be provided in the evaporation chamber 74, a sealing mechanism must also be provided in the endless screw or conveyor mechanisms for exiting dried slurry 42 from the enclosed area 75 without a significant drop in pressure. According to the present invention, the non-dewatered slurry 41 , in this case wastewater sludge (primary or secondary sludge), is spread and levelled (using a rotating brush 45) as a thin layer along the length of the plenum 10, which has been previously heated up to a temperature above 100°C. The plenum is heated from the inner side using a two-step process. In the first step, upon system startup, a boiler or any other appropriate heating method, heats vapours to above 100°C. Once the boiler has heated the system to a predetermined temperature, the boiler stops and the compressor(s) take over. It will be appreciated that once this transition occurs, the temperature can be maintained by only using energy to run compressors (rather than the boiler). In this second step, evaporation gas is evacuated from the evaporation chamber 74, compressed in the compression chamber 76 and returned to the inner plenum chamber 77. Compression of the gas allows to increase its temperature and pressure such that contact with the inner side of the plenum will, on the one hand, conductively heat the outer surface of the plenum and on the other hand condense on the inner surface. The liquid 81 thereby generated can be evacuated by appropriate conduits, pumps, and gravity as necessary. The robot 84 spreads slurry 41 along the length of the plenum 10 as it moves from a starting point 48 to an end point 49 on the plenum 10. As a new (wet) batch of slurry 41 is spread from a rear portion of the robot 84, an old (dry) batch of slurry 42 which had been spread in the previous "run" is removed from the plenum surface. When the robot 84 reaches the end point 49 on the plenum, it is lifted slightly and returned to the starting point 48, and then lowered back to the appropriate level. The slurry containment device 46 is filled with another batch of slurry 41 and the process is repeated for as long as slurry needs to be treated (i.e. dewatered by evaporation). It is critical that the slurry 41 be spread in an even manner to favour heat exchange between the plenum and the slurry.

The apparatus typically comprise a plurality of plenums 10, one or more slurry handling devices 40 which itself comprises a slurry spreading 45 and slurry removing devices 47, and an enclosed area 74 in order to capture the evaporated gas 43 from the slurry 41. The slurry handling device 40 must be adapted to spread and remove slurry on each plenum module. The multi-module system shown in Figures 7 and 8 must therefore be designed to support, in a preferred embodiment, the weight of the slurry spreading and removing devices in addition to the motion system for moving these devices along the length of the plenum. The robot 84 must be able to move the slurry spreading device 45 and removing device 47 whilst having at least some mechanical parts "outside" or isolated from the evaporation chamber 74. This is to protect the mechanical parts of the robot 84 from the corrosive vapours and fluids evacuated from the slurry and is afforded by the central support housing 72 which will contain a relative motion or motorization system 71. In addition to or instead of proper "sealing", a slightly positive pressure can also be provided inside the central support housing 72 to prevent the entry of corrosive vapors from the evaporation chamber 74. Furthermore, thermal protection of the sensitive system components can be provided by insulating the central support housing 72 to decrease heat transfer from the evaporation chamber 74. Other cooling mechanisms can also be provided to the central support housing 72 such as cooling fans, cooling systems etc.

Furthermore, individual slurry spreading devices 45 and removing devices 47 must be easily accessible for maintenance purposes and easily changed without the need for disassembling other modules in a multi-modular system. This ensures the highest "run- time" for the whole dewatering apparatus. The sludge handling devices (or robot 84) must be designed to allow an adjustable thickness of slurry to be spread along the plenum. In addition to the height of the slurry, the sludge handling devices (or robot 84) needs to be lifted with respect to the plenum in order to return to a starting point 48 after moving along the length of the plenum 10. In some embodiments, the plenum may be configured to be lowered (rather than lifting the robot) in order to facilitate returning the robot to its starting point. In some embodiments, temperature sensitive, non-corrosion resistant and/or complex mechanical pieces can be advantageously located inside the central support housing, and in addition to being isolated from the corrosive vapours of the evaporation chamber, can ventilated to prevent overheating. Movement of the slurry handling device 40 with respect to the plenum 10 can be achieved in many ways. For example, in one approach, a track system allows the slurry handling device to be suspended. Alternatively, the sludge handling device can be free standing and move around a large plenum similar to an ice resurfacing machine moving on an ice rink. Such a device could use a platform "elevator" to move up and down to the various plenum levels or at least one device per level can be provided. Finally, the plenum can move with respect to a stationary slurry handling device if the plenum is designed as an endless belt conveyor, for example, with a slurry spreading device on a first end and a slurry removal device on a second end of the belt.

The enclosed area 75, which comprises the evaporation chamber 74 and at least part of the inner plenum chamber 77, can be designed according to several characteristics. In some embodiments, the enclosed area 75 should be designed to support pressures above atmospheric pressure. The enclosed area 75 should support the plenum structures and have easy access "doors" to allow access to the mobile parts and plenum surfaces. The enclosed area 75 should be designed such as to prevent fluid leaks with reasonable construction costs. The enclosed area 75 can be a thin tubular structure made of steel outside and stainless steel inside. The plenums 10 can also be made of stainless steel and be attached to the inside of the tubular structure. The inside of the enclosed area 75 and the central support housing 72 can be isolated using pulverised polyurethane to ensure leak protection (fluid proof) and to prevent the formation of thermal bridges. Alternatively, and due to the above atmospheric pressures found in the evaporation chamber 74, the enclosed area 75 can be made from a dome-shaped flexible material that inflates when the apparatus is in use. The material can be heat- and corrosion-resistant and provide an apparatus with a slightly smaller footprint when not in use or simply an apparatus that is easier or more cost effective to manufacture. In a preferred embodiment, one single robot 84 is used to move all slurry handling devices 40 simultaneously as shown in figure 7. In figure 7, a modular apparatus having 3 levels of plenums on two sides of a central support housing 72 is shown. Several elements of this drawing are omitted for simplification. A robot 84 can comprise a robot cart to move the robot along the plenums 10 in the enclosed area 75. In some embodiments, it may be advantageous to have a second robot (and cart) such that, while a first robot 84 is being used in the apparatus, a second robot can be cleaned, repaired or cooled down.

It will be appreciated that, in order to stabilize a mechanical and/or electrical load on the robot 84 and pumps during operation, the system can be designed such that, for example, in a 6 level plenum as shown in figure 9, three levels (A, C and E) move in a forward direction (from right to left) spreading and removing slurry while three other levels (B, D and F) are slightly lifted and moved in a rearward direction, thus returning the slurry handling devices 40 to a starting point 48. In such as system, although the robot 84 moves integrally, only half of the slurry handling devices 40 are treating slurry 41 at one time. This configuration also has the added advantage of stabilizing the slurry feeding operation such that it can work in continuous mode, rather than batch mode if all levels work simultaneously. As seen in figure 9, the slurry handling devices of levels B, D and F are reversed in direction and slightly lifted in order to avoid contact with the plenum during the return path. In yet another alternate embodiment of the apparatus, there can be provided one easily interchangeable and separate robot 84 for each plenum level. Although this approach is more expensive to manufacturer and has more moving parts, its run-time is optimized because non-operational robots (maintenance, reparations, etc) can be easily removed and/or replaced while other robots (at other levels) continue to do perform work. Furthermore, due to the fact that some parts of the robot are located in the central support housing 72 and therefore physically separated from the evaporation chamber 74, certain maintenance procedures can be provided without pressuring down the apparatus, if the apparatus is configured appropriately. For example, a first door would open up to allow insertion of a first robot into the first end of an enclosed area 75 and, upon closing the door (not shown) to create a "sealed" enclosed area 75, a predetermined pressure could be built up inside the enclosed area for evaporating slurries. If one robot inside the central support housing needed maintenance during operation, a second door either inside the first door at the first end of the apparatus or at the second end of the apparatus could allow access to the inside of the central support housing without pressuring down the enclosed area, thus saving valuable time and energy. A motorization system 71 (Fig.7) is provided for moving the central support housing 72 along the plenum surface (the central support housing is understood to have an interior part which "houses" the sensitive material and an exterior part which comprises the slurry handling device(s) 40). One embodiment of the motorization system 71 is shown in more detail in figure 10 as a pin-rack and sprocket system.

According to some aspects of the present invention, the plenum surface area can be increased by making longer or wider plenums or by adding adjacent plenums at the same level while using the same robot for spreading and removing slurry. In such apparatuses, more surface area is achieved without increasing the number of robots or adding another plenum level on top of the existing plenums.

In the embodiment described previously in Figure 4, slurry was added in known amounts, using dosing pumps, to the slurry containment chamber 46 and then spread as the slurry handling device 40 moves along the plenum 10. In an alternative embodiment, and notwithstanding the need to have relatively liquid slurry, a batch dumping approach can be used where liquid slurry spreads at least partially over a flat delimited surface of the plenum and wherein a full batch of liquid slurry can be dumped onto the plenum substantially all at once. Such a substance can at least partially spread along the surface of the plenum due to slurry rheology characteristics and gravitational forces. It will be appreciated that, whether or not the batch dumping approach is used, the slurry spreading device is necessary due to the critical requirement of having an evenly spread thin-layer of substance on the plenum.

In the batch dumping approach, the slurry containment chamber can be the slurry conduit 83 itself. In operation, a slurry conduit 83 forms a loop that passes from a holding tank 90, above the plurality of plenums 10, in series, and returns to the holding tank 90. The holding tank 90 receives slurry from a slurry inlet 73. The slurry conduit 83 is filled with non-dewatered slurry 41 that can flow in the loop with the help of a pump 91. The holding tank 90 is filled with slurry from a slurry inlet 73. The slurry conduit 83 should pass over all individual plenums 10. When a new "batch" of slurry is to be treated, the slurry conduit 83 is filled and isolating valves 92 close to define a predetermined volume of slurry. At this point, batch dumping valves 93 configured for uniform spreading of slurry over the plenum surface can open up to "dump" the predetermined volume onto the plenum 10.

As shown in Figure 8, isolating valves 92 close to affect/influence the horizontal movement of the slurry in the non-dewatered slurry 41 conduit 83 and the batch dumping valves 93 open to affect/influence the vertical movement of the slurry from the slurry conduit 83 onto the plenum 10. Furthermore, this embodiment is shown with only one isolating valve 92 per plenum 10 because it is understood that the isolating valve of the subsequent plenum will serve to define the predetermined volume. It will be appreciated that two isolating valves per plenum can achieve the objective of defining a predetermined volume of slurry.

The batch dumping approach is useful because it allows to provide a good measure or volume of sludge without significantly increasing the cost of manufacturing the apparatus. Indeed a few valves are added to existing conduits that serve the double purpose of isolating a predetermined volume of slurry and allowing that volume to spread quickly across the surface of a plenum. By spreading quickly across the plenum due to its liquid nature, the slurry has more contact time with the hot plenum surface. A holding tank 90 is provided for receiving non-dewatered slurry 41 from a source of slurry (e.g. waste water treatment plant). The holding tank 90 allows to accumulate slurry when the source of slurry is greater than the treatment capacity of the apparatus. It also allows to mix in certain substances that are beneficial for slurry treatment, such as lime, polymers, flocculants, etc. A slurry bypass tank 94 can also be provided to receive non-dewatered slurry during the "batch isolation" and "batch dumping" operations. This allows to maintain a constant flow of slurry and thus constant pump activity as the slurry conduits 83 are being used for feeding purposes.

It will be appreciated by those skilled in the art that the "batch dumping system" can, in some embodiments, be the slurry spreading device because it can function to spread the slurry over the surface of the plenum. However, in other cases, because some slurry areas are less liquid, it is useful to use the substance spreading in conjunction with the batch dumping system, to further even out the slurry thickness across the surface of the plenum.

When this "batch dumping" approach is used and possibly in other cases as well, the plenum can be adapted to have elevated sides at its distal and proximal extremities, in addition to the longitudinal sidings 28, to prevent liquid slurry 41 from falling off the plenum. These elevated sides (lateral and longitudinal sidings) could be moveable such as not to negatively affect the slurry removal step. In an alternate embodiment, a dosing chamber can be affixed to the slurry handling device to define a predetermined amount of slurry but they can also be fixed, on the inside or outside surface of the enclosed area 75. Dosing can alternatively be performed by gravity or compressed air rather than using pumps.

Figure 10 shows a schematic side view of a pin-rack and sprocket motorization system. This system has many advantages for providing motorization to the robot 84 which comprises the slurry handling devices 40 and central support housing 72. In the embodiment shown, the system comprises a pin rack 103 made from two L-shaped pieces with pin holes 104 disposed longitudinally along the desired direction of motion. The pin-rack 103 and sprocket 105 system is designed to prevent clogging from falling dried solids due to round pins 102 and high pitch in the rack system. It is simple, easy and quick to construct from metallic (or other) material. The pin-rack 103 provides a solid guide for the robot and allows sensitive elements (e.g. electrical) to be located inside the central support housing 72. Other advantages of this system are that are that it does not comprise a flexible chain and allows for the immobilized rack to be easily disassembled and removed from the enclosed area. Finally, the high inter-pin pitch and big sprocket teeth allow for easy cleaning.

Due to the high temperatures and slurry dryness levels reached by apparatus and methods of the present invention, they are known to decontaminate slurries such as wastewater sludge. For example, such processes are known to kill bacteria, viruses, and other pathogens such as helminth ova to levels that are required for achieving class A designation according to the US Environmental Protection Agency (EPA). In some cases, lime can be added to the non-dewatered slurry prior to evaporation in order to impart particular characteristics to the wet (or dry) slurry.

A slurry is any substance containing solids and liquids which can be evaporated to yield a dryer slurry. Throughout this document, dried slurry is used interchangeably with dewatered slurry, treated slurry and dried solids while wet slurry is used interchangeably with non-dewatered and non-treated slurry. If all liquid present in a slurry is evaporated (100% dryness), it is nevertheless considered a dried slurry, even though the slurry no longer contains liquids.

It will also be appreciated that in an embodiment with a fixed plenum where the robot 84 provides a reciprocal back and forth motion, the spreading and removing can be joined or at least close together. In this type of setup, a first forward pass allows to spread a new layer of slurry while removing a previous layer of slurry. Alternatively, in a setup were an endless belt conveyor acts as a moving plenum (a continuous rather than reciprocal motion), the fixed slurry handling device must provide a greater distance between slurry spreading device and slurry removal device. Ideally, this distance determines the longitudinal length of the plenum.

It will be appreciated that planarity of the outer plenum surface is important for sludge dewatering efficiency using an apparatus of the present invention. Planarity is also important for the interaction between the slurry removal device and the plenum surface because an uneven plenum can lead to higher friction as well as premature degradation of the brush bristles. Planarity is also important for overall efficiency because one of the most critical slurry characteristics is its thickness which needs to be homogenous and constant. If the plenum surface has grooves or indentations, sludge will be thicker at some locations and evaporation will not be efficient. Furthermore, if evaporation is not complete upon passing the slurry removal device (due to a thicker initial layer of slurry), wet slurry will contaminate the bristles to a greater extent than dried slurry. Although not shown in the drawings for simplicity, it will be appreciated that the apparatus of the present invention is more efficient with the use of a controller. The controller receives input from sensors disposed at various locations in the apparatus such as temperature sensors, pressure sensors, humidity (slurry dryness) sensors, conductivity sensors, volume sensors, location sensors, etc. Based on the information received from the various sensors and/or pre-programmed sequences, the controller controls various aspects of the apparatus such as rotation speed of the brushes, speed of the robot along the plenum, height of the slurry spreading and removing devices above the plenum surface, pump activity, compressor activity, boiler activity (when required), inner plenum pressure, evaporation chamber pressure, central support housing pressure, valve activity, etc.

Further examples of sensors for determining the efficiency of solids removal from the plenum surface are electric roller contacts. Such roller contacts are attached to the slurry handling device and send electric signals to the controller when the presence of solids is detected on the surface of the plenum. For example, the presence of solids detected behind the slurry removal device would indicate that slurry removal is not optimal. Brush rotation speed or brush height can thus be adjusted in real time. It will be understood by those skilled in the art that the longitudinal length of the plenum need not be longer than the lateral length of plenum because in some embodiments, the lateral length of the plenum will be longer than the longitudinal length. While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosures as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features herein before set forth, and as follows in the scope of the appended claims.

Claims

What is claimed is:

1. A method of manufacturing a plenum for dewatering slurries by evaporation

comprising using high energy beam welding to join a plurality of ribs to one or more sheets forming a top plenum surface without welding induced grooves or dimples.

2. The method of claim 1 , wherein said manufacturing steps comprise placing said top plenum surface with inner side facing up; placing said ribs on said top plenum surface; welding said ribs to said top plenum surface; placing a bottom plenum surface on said ribs with outer side facing up; welding said bottom plenum surface to said ribs.

3. The method of claim 1 or 2, wherein outermost ribs form a frame around said top and said bottom plenum surface, and wherein said frame and said top and said bottom plenum surfaces define an inner plenum chamber.

4. The method of any one of claims 1 to 3, further comprising welding at least one of said top plenum surface and said bottom plenum surface from an outer side of said plenum surface.

5. The method of any one of claim 2 to 4, wherein said bottom surface and said ribs are an integral piece.

6. The method of any one of claims 1 to 5, wherein said high energy beam welding is laser welding.

7. An apparatus for dewatering slurry by evaporation comprising: a plenum surface for receiving and heating a non-dewatered slurry; a slurry spreading device for spreading said non-dewatered slurry on said plenum surface; a brush for removing a dried slurry from said plenum surface, said brush comprising: a bristle support member for supporting a plurality of bristles, said bristle support member having an axis of rotation passing through its center and extending horizontally; a rotation actuator for allowing said bristle support member to rotate about said axis of rotation; and bristles extending outward from said bristle support member for removing dried slurry by contacting said surface while rotating about its axis; a motion system for creating a horizontal motion between said plenum surface and said brush to remove said dried slurry from said plenum surface.

8. The apparatus of claim 7, wherein said bristle support member is an elongated

cylinder.

9. The apparatus of claim 7 or 8, further comprising a height adjustment device for adjusting a distance between said horizontal axis and said plenum surface.

10. The apparatus of any one of claims 7 to 9, further comprising a bristle length

adjustment device for adjusting the length of bristles.

11. The apparatus of any one of claims 8 to 10, wherein said bristles are arranged

circumferentially around said cylinder.

12. The apparatus of any one of claims 7 to 11, wherein said rotation actuator rotates said brush between 40 and 80 rotations per minute.

13. The apparatus of any one of claims 7 to 11 , wherein said rotation actuator rotates said brush at approximately 60 rotations per minute.

14. The apparatus of any one of claims 7 to 13, wherein said bristles are made of a

material that adapts to said plenum surface.

15. The apparatus of claim 13, wherein said material has a hardness that is less than the hardness of said plenum surface and more than the hardness of said dried slurry.

16. The apparatus of any one of claims 7 to 15, wherein said plenum surface is a heat exchange surface comprising stainless steel.

17. The apparatus of any one of claims 7 to 16, wherein said bristles comprise stainless steel.

18. The apparatus of any one of claims 7 to 17, wherein slurry is one of industrial and wastewater sludge.

19. The apparatus of any one of claims 7 to 18, wherein said rotation actuator comprises bearings.

20. The apparatus of any one of claims 7 to 19, wherein said bristles are oriented in a direction that allows said dried slurry to be evacuated from said plenum surface to a predetermined side.

21. The apparatus of any one claims 7 to 20, wherein said direction of rotation of said brush is clockwise when a horizontal motion of said brush is from right to left or when a horizontal motion of said surface is from left to right.

22. An apparatus for dewatering slurry by evaporation comprising: a plenum surface for receiving and heating non-dewatered slurry; a brush for spreading said non-dewatered slurry on said plenum surface, said brush comprising: a bristle support member for supporting a plurality of bristles, said bristle support member having an axis of rotation passing through its center and extending horizontally; bristles extending outward from said bristle support member for contacting and evenly spreading said wet slurry over said plenum surface; a rotation actuator for allowing said bristle support member to rotate about said axis of rotation; and a slurry removal device for removing dried slurry from said plenum surface; and a motion system for creating relative motion between said plenum surface and said brush to efficiently spread said slurry on said plenum surface.

23. The apparatus of claim 22, wherein said bristle support member is an elongated cylinder.

24. The apparatus of claim 22 or 23, further comprising a height adjustment device for adjusting a distance between said horizontal axis and said plenum surface.

25. The apparatus of any one of claims 22 to 24, further comprising a bristle length

adjustment device for adjusting the length of bristles.

26. The apparatus of any one of claims 23 to 25, wherein said bristles are arranged

circumferentially around said cylinder.

27. The apparatus of any one of claims 22 to 26, wherein said rotation actuator rotates said brush at a speed between 40 and 80 rotations per minute.

28. The apparatus of any one of claims 22 to 26, wherein said rotation actuator rotates said brush at a speed of approximately 60 rotations per minute.

29. The apparatus of any one of claims 22 to 26, wherein said plenum surface is a heat exchange surface comprising stainless steel.

30. The apparatus of any one of claims 22 to 29, wherein said bristles comprise stainless steel.

31. The apparatus of any one of claims 22 to 30, wherein slurry is one of industrial and wastewater sludge.

32. The apparatus of any one of claims 22 to 31 , wherein said rotational means comprise bearings.

33. The apparatus of any one of claims 22 to 32, wherein said bristles are oriented in a direction that allows dry slurry to be evacuated from said plenum to a predetermined side.

34. The apparatus of any one of claims 22 to 33, wherein said direction of rotation of said brush is clockwise when a horizontal motion of said brush is from right to left or when a horizontal motion of said surface is from left to right.

35. An apparatus for dewatering a slurry by evaporation comprising: one or more surface for receiving a slurry; said surface having a longitudinal length and a lateral length and adapted to be heated to a temperature that allows for slurry evaporation; at least one slurry handling device having a rear portion comprising a slurry spreading device for spreading a non-dewatered slurry on said surface and a forward portion comprising a slurry removing device for removing dried slurry from said surface; and a motion system for creating relative motion between said surface and said slurry handling device.

36. The apparatus of claim 35, wherein said slurry removing device is a rotating brush for removing slurry from said surface by contacting said surface, wherein said brush extends horizontally along said lateral length of said surface and rotates about an axis defined by said lateral length.

37. The apparatus of claim 35 or 36, wherein said slurry spreading device is a rotating brush for spreading slurry on said surface, wherein said brush extends horizontally along said lateral length of said surface and rotates about an axis defined by said lateral length; and wherein a vertical distance between said brush and said surface determines the thickness of the slurry being spread.

38. The apparatus of any one of claims 35 to 37 wherein said motion system causes said slurry handling device to move from a starting point in a forward longitudinal direction along said surface to add a new batch of wet slurry and to remove an old batch of dry slurry; and then move in a backward longitudinal direction to return to said starting point.

39. The apparatus of any one of claims 35 to 38, further comprising a controller for

controlling operation of said apparatus.

40. The apparatus of claim 39, wherein said controller receives input from one or more of pressure, temperature, humidity, location and height of slurry handling device with respect to said plenum, and sends output to one or more of a boiler, compressor, valve, pump, motion activator and motor.

41. The apparatus of any one of claims 35 to 40, further comprising a compressor for compressing evaporation gas from said slurry and directing compressed gas to an inner chamber of said plenum to condensate said gas.

42. The apparatus of claims 35 to 41 , wherein said motion system causes surface to

move, and wherein said slurry handling device is immobile.

43. The apparatus of claim 35, wherein said slurry spreading device is on a first end of said surface and said slurry removing device on said second end of said surface.

44. The apparatus of claim 35, wherein said surface is an endless belt conveyor.

45. The apparatus of any one of claims 35 to 44, wherein said surface is a plenum.

46. The apparatus of any one of claims 35 to 45, wherein said slurry is wastewater sludge.

47. A method of dewatering a slurry by evaporation comprising providing a plenum with a hot outer surface and a slurry handling device; wherein said slurry handling device and said plenum move linearly with respect to each other as a non-dewatered slurry is spread along said outer surface of said plenum and a dried slurry is removed.

48. The method of claim 47, further comprising moving said slurry handling device from a starting point with respect to said plenum in a forward linear direction until an end point with respect to said plenum and then moving in the reverse direction back to said starting point.

49. The method of claim 47 or 48, further comprising spreading said non-dewatered slurry with a rotating brush.

50. The method of any one of claims 47 to 49, further comprising removing said dried slurry with a rotating brush.

51. The method of claim 49 or 50, further comprising selecting a brush of appropriate diameter.

52. The method of any one of claim 47 to 51 , further comprising compressing an

evaporation gas evacuated from said slurry and returning it to an inner side of said plenum to condense, thereby heating said outer side of said plenum by conduction.

53. A feeding system for feeding non-dewatered slurry onto an evaporation plenum

comprising: a slurry conduit for transporting said slurry, wherein at least part of said slurry conduit is located above said plenum; one or more isolating valves for isolating a predetermined volume of slurry from said slurry conduit by closing said isolating valves; and one or more batch dumping valves that open for dumping said predetermined volume of said slurry onto said plenum.

54. A method of feeding non-dewatered slurry to an evaporation plenum comprising: filling a slurry conduit with said non-dewatered slurry, wherein at least part of said slurry conduit is located above said evaporation plenum; closing isolating valves to define a predetermined volume of the non-dewatered slurry, wherein said predetermined volume is located in part of said slurry conduit located above said evaporation plenum; and opening batch dumping valves to release said predetermined amount of non- dewatered slurry onto said evaporation plenum.

55. The method of claim 54, further comprising spreading said non-dewatered slurry with a slurry spreading device according to claims 22 to 34.

56. A modular evaporator having an inlet for receiving non-dewatered slurry and outlets for evacuating dry solids and liquid, said evaporator comprising: an enclosed area having an evaporation chamber and an inner plenum chamber, said enclosed area having a plurality of plenums that separate said evaporation chamber from said inner plenum chamber, said plenums being immobile with respect to said enclosed area; a robot having a plurality of slurry handling devices for spreading wet slurry on a plenum outer surface and removing dry slurry from said plenum outer surface, said robot adapted to move essentially linearly inside said enclosed area.

57. The evaporator of claim 56, wherein said robot further comprises a central support housing that houses a motion system for moving said robot, wherein said housing is isolated from said evaporation chamber and said plenum chamber; and wherein said slurry handling devices extend from both sides of said central support housing.

58. The evaporator of claim 57, wherein said plenums are located on either side of said central support housing.

59. The evaporator of any one of claims 56 to 58, wherein said robot is configured to have a portion of said slurry handling devices spread and remove slurry as said robot moves in a forward direction and another portion of said slurry handling devices spread and remove slurry as said robot moves in a rearward direction, wherein said orientation of the two portions of said slurry handling devices are reversed with respect to each other.

60. The evaporator of any one of claims 59, wherein said portion is approximately 50%.

61. The evaporator of any one of claims 56 to 60 wherein said enclosed area further comprises a door for allowing said robot to move in and out of said enclosed area.

62. The evaporator of any one of claims 56 to 61 , further comprising a counter-current heat exchange device for transferring heat from a first section containing hot evacuated fluids to a second section containing said non-dewatered slurry, wherein the first section and the second section are separated by heat conducting material.

63. The evaporator of any one of claims 56 to 62, further comprising a boiler for heating said inner plenum chamber to a predetermined temperature.

64. The evaporator of any one of claims 56 to 63, further comprising a compressor for compressing said gas from the evaporation chamber before directing it to the inner plenum chamber.

65. The evaporator of any one of claims 56 to 64, further comprising a plenum, said

plenum comprising: a top rectangular sheet having an outer surface for receiving said non-dewatered slurry and an inner surface for receiving a hot gas; a bottom rectangular sheet, wherein said top rectangular sheet and said bottom rectangular sheet are joined together defining therebetween said inner plenum chamber; a plurality of ribs disposed between said top rectangular sheet and said bottom rectangular sheet for providing structural support to said outer surface; a hot gas inlet in fluid communication with said inner plenum chamber for receiving hot gases; and a fluid outlet in fluid communication with said inner plenum chamber for evacuating a fluid.

66. The evaporator of claim 65, wherein said plenum further comprises conduits

connected to said fluid outlet for collecting an evacuated fluid.

67. The evaporator of claim 65 of 66, wherein said plenum further comprises a bottom surface configured to drain said fluid to said fluid outlet by gravity.

68. The evaporator of any one of claims 65 to 67, wherein said plenum further comprises a top surface made of one or more sheets of stainless steel.

69. The evaporator of claim 68, wherein said stainless steel has a thickness in a range of 1 mm to 3 mm.

70. The evaporator of claim 68, wherein said stainless steel has a thickness in a range of 1.2 mm to 2 mm.

71. The evaporator of claim 68, wherein said stainless steel has a thickness in a range of 1.5 mm to 1.7 mm.

72. The evaporator of claim 68, wherein said stainless steel has a thickness of

approximately 1.59 mm.

73. The evaporator of claim 57, wherein said motion system further comprises a pin-rack and sprocket design.