Abstract:
A solar-powered device for converting sludge into one or more products is disclosed. The device includes a pyrolysis reactor selectively operable by solar energy, for carrying our thermal decomposition, into one or more products, of sludge introduced into the reactor via a dedicated sludge inlet. The reactor includes at least one outlet for discharging from the reactor one or more products obtained from the sludge decomposition. The device also includes a sensor for sensing sunlight radiation and providing an output data indicative of the amount of solar energy corresponding to the sensed sunlight, and a control unit for receiving the output data and operating or shutting down the pyrolysis reactor based on the amount of solar energy generated from the sunlight.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a system and method for sludge treatment. 
       BACKGROUND OF THE INVENTION 
       [0002]    The spread of increasing amounts of waste biomass, such as wastewater sludge or sewage sludge, pose a worldwide problem associated with their disposal. Composting, direct land-filling, compression/concentration, liquid extraction and thermal treatment (incineration, gasification or pyrolysis) are some of the available for biomass treatment. 
         [0003]    Pyrolysis is widely used for biomass conversion, utilizing heat to chemically decompose the organic materials in the biomass. 
         [0004]    U.S. Pat. No. 3,993,458 describes a method for producing gases such as H 2 , CO, CH 4  and CO 2  by pyrolysis organic solid waste, the method comprising subjecting, in a reactor, the organic solid waste to steam at elevated temperatures allowing the chemical decomposition (pyrolysis) to take place. The elevated temperatures are obtained by the use of solar heating by means of a solar top furnace providing temperatures of 600°-700° C. 
         [0005]    U.S. Pat. No. 4,415,339 describes solar biomass gasification reactor with pyrolysis gas recycling. Specifically, biomass (e.g. coal) is converted into gases (e.g. H 2 , CH 4  and CO 2 ) by feeding the biomass into a solar reactor and directing solar energy into the reactor, wherein chemical decomposition of the biomass takes place. 
         [0006]    International patent application publication WO2008/027980 also describes method for carrying out biomass pyrolysis or gasification using solar energy. The solar thermal reactor is comprised of a an outer protection shell and an inner reaction shell having an inlet and an outlet, the outlet protection shell being at least partially transparent or having an opening to the atmosphere for transmission of the solar energy. The biomass is carried by a gas stream, via the inlet, into the reactor, wherein it is heated to a temperature of at least 950° C., at least in part by exposing the reactor to a source of concentrated sunlight. 
         [0007]    U.S. Pat. No. 5,980,605 describes a solar energy installation for the production of an alkali metal (metallic sodium and potassium) by reaction of their hydroxides or carbonates with carbon that is produced in situ by pyrolysis of a pyrolyzable carbonaceous material. 
         [0008]    The use of solar energy for biomass processing is also described in Solar-Powered Biomass Gasification; Biomass Magazine (www.biomassmagazine.com/article.jsp?article_id=1674). 
       SUMMARY OF THE INVENTION 
       [0009]    The inventors of the present invention have surprisingly found that by employing a system combining a thermo-regulated sensor, a solar tower and a pyrolysis reactor connected to a high throughput sludge dewatering device they can produce green energy from sludge using solar power. This system is emission free due to high temperatures of up to 1200 C.° in pyrolytic conditions and is self sustainable since sludge treatment does not require around the clock, continuous work (sludge may be accumulated and used when necessary). Thus, the system provides a reliable and comprehensive solution relying on solar power alone to convert sludge into energy. 
         [0010]    The system can treat various types of sludge originating in the following urban waste treatment plants, industrial waste treatment plants, agricultural wastewater treatment plants, petrochemical industry, chemical industry, pharmaceutical industry, food industry among other biomass sludge sources. In a preferred embodiment, the term “sludge” denotes wastewater sludge, sewage sludge and any by-product of [wastewater (i.e. liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture which can encompass a wide range of potential contaminants and concentrations) treatment and production. The system described therein will provide an ecological solution to sludge treatment in factories and purification plants. 
         [0011]    Thus, in one aspect the present invention provides a solar-powered device for converting sludge into one or more products comprising: 
         [0012]    (a) a pyrolysis reactor selectively operable by solar energy, for carrying out thermal decomposition, into one of more products, of sludge introduced into said reactor via a dedicated sludge inlet; the reactor comprising at least one outlet for discharging from said reactor one or more products obtained from said sludge decomposition; 
         [0013]    (b) a sensor for sensing sunlight radiation and providing an output data indicative of the amount of solar energy corresponding to the sensed sunlight sensed by said sensor; 
         [0014]    (c) a control unit for receiving said output data and operating or shutting down at least said pyrolysis reactor based on the amount of solar energy generated from said sunlight. 
         [0015]    In another aspect, there is provided a solar-powered system for converting sludge into one or more products comprising: 
         [0016]    (i) solar-powered device for converting sludge into one or more products comprising:
       (a) a pyrolysis reactor selectively operable by solar energy, for carrying out thermal decomposition, into one of more products, of sludge introduced into said reactor via a dedicated sludge inlet; the reactor comprising at least one outlet for discharging from said reactor one or more products obtained from said sludge decomposition;   (b) a sensor for sensing sunlight radiation and providing an output data indicative of the amount of solar energy corresponding to the sensed sunlight sensed by said sensor;   (c) a control unit for receiving said output data and operating or shutting down at least said pyrolysis reactor based on the amount of solar energy generated from said sunlight.       
 
         [0020]    (ii) a solar power sub-system configured to concentrate sunlight and to direct at least a portion of solar energy generated from said concentrated sunlight to said solar powered device; 
         [0021]    (iii) a conveyor for conveying sludge into said pyrolysis reactor via said dedicated inlet; 
         [0022]    (iv) one or more collection units, each connected to a discharge outlet for collecting a product discharged from said pyrolysis reactor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
           [0024]      FIG. 1  is a schematic illustration of a sludge treatment system in accordance with one embodiment of the invention. 
           [0025]      FIG. 2  is a schematic illustration of a sludge treatment plant in accordance with one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0026]    Reference is now made to  FIG. 1  providing a schematic illustration of a sludge treatment system  100  in accordance with one embodiment of the invention. The sludge treatment system comprises a dumping funnel  102  for introducing sludge into the system. The dumping funnel has a top opening  104  for receiving the sludge and a bottom opening  106  for discharging the sludge onto a conveyor  110 . While not illustrated in  FIG. 1 , the conveyor  110  may be adapted to remove an amount of liquid, typically water, from the sludge, to obtain a partially dewatered sludge comprising between 40-60% of initial weight. Typically, dewatering is carried out at temperatures of up to 400° C. yielding dewatered sludge ready for pyrolysis. Dewatering can be achieved, for example, by the use of a hot air blower or a spiral press conveyor. Liquid (typically water) removed from the sludge may be collected and directed for re-use (not illustrated). Conveyor  110  is connected dewatering unit  120  and is configured to convey the partially dewatered sludge into the dewatering unit  120 . Typically, the conveyor is a screw conveyor that can receive pressurized air, as well as sludge, in its interior and thus act to heat the transferred sludge to a temperature effective to dewater the sludge, thereby resulting in dewatering of sludge while being transported to the pyrolysis reactor  130 . The screw conveyor is based on a helical screw including a shaft along an axis allowing the feeding of sludge material therein. The conveyor, in turn, can also recieve residual heat from the pyrolytic reactor. 
         [0027]    Dewatering unit  120  may be any apparatus capable of removing liquid from the sludge, such as a vacuum or vacuum less evaporation unit. In the context of the present disclosure it is noted that sludge which enters the system will typically contain between about 40%-90%, more typically between 75% to about 85% liquid. For the purpose of pyrolysis it is required that the matter introduced into the reactor contain no more than about weight 40 to about 60% liquid. Thus, dewatering unit  120  is adapted to remove the majority of liquid from the sludge, so as to obtain dewatered sludge with no more than 60%, at times and preferably no more than 40% liquid. To ensure sufficient liquid removal, the dewatering unit may be equipped with a sensor (not illustrated) for sensing the amount of liquid in the sludge contained therein and providing an output data indicative of the same. Once the amount of humidity is below a desired threshold of between about 40 to about 60%, the dewatered sludge is conveyed by conveyor  110  into pyrolysis reactor  130 . For illustration purposes, the direction of movement of sludge onto said conveyor  110  is illustrated by arrow  112 . In one embodiment, the conveyer is adapted to collect from about 20% to about 60% of liquid from the sludge. 
         [0028]    Liquid removed from said sludge within dewatering unit  120  is collected into a condensing unit  122  and the condensed liquid is discharged from the condensing unit by dedicated pipe  124 . It is noted that water vapor, being a byproduct of the dewatering process can be used as steam energy production. The water vapor can also be condensed and return as liquid to the sewage purifying system which receives the sewage/sludge to be treated by the sludge treatment system. For example, char produced by pyrolysis can be gasified and converted into H 2  and CO 2  by low pressure steam. This will allow the system to be self sustainable. In addition, low pressure steam can be used to preheat the system using liquid filled pipes, which carry liquid through the system, that are preheated by said steam. 
         [0029]    Pyrolysis reactor  130  may be of any type used for thermal decomposition of biomass including, without being limited thereto fixed bed reactors, fluidized bed reactors, vacuum pyrolysis reactor and super critical water reactors. Pyrolysis reactor  130  is at temperatures of between 400° C.-1200° C. The desired heat is produced by solar energy  140  generated by dedicated sun tracking mirrors or by a solar power tower (not illustrated) directing concentrated sunlight towards the reactor. The concentrated solar energy  132  enters the reactor  130  through a light transmitting window or an opening  134 . The window may be a quartz window. The energy entered into the reactor acts on the dewatered sludge fed into the reactor, producing one or more products, including gas and charcoal. Technology is currently available for building solar energy operated pyrolysis reactors in which sunlight is focused (e.g. onto a tower) from concentrating mirrors (heliostats). It is noted that the concentrated solar energy may also be utilized for operating other components of the sludge treatment system, such as the dewatering unit, the conveyor, etc. The pyrolysis reactor  130  may also be connected to a catalyst feeder (not shown) for feeding catalysts typically used for pyrolysis of biomass. 
         [0030]    The various products, such as gas, char, tar and ash, are withdrawn from the reactor  130  via respective products outlets, illustrated in  FIG. 1  as outlets  136 A,  136 B and  136 C. While  FIG. 1  illustrates only three products outlets, it should be appreciated that only one as well as more than three products outlets can be included in the system. 
         [0031]    The sludge treatment system also comprises a sensor  140 , namely, a solar measuring unit for sensing sunlight radiation around pyrolysis reactor  130  and providing an output data indicative of the amount of solar energy corresponding to the sensed sunlight sensed by said sensor  140 . The solar sensor  140  may be a temperature sensor in the pyrolytic reactor which will facilitate in determining the rate of sludge entry into the system at a function of the amount of solar energy, said sensor being adapted to continuously measure the amount of sunlight at the area proximal to said reactor  130 . The sensor  140  provides output data indicative of the amount of solar energy generated by the sun tracking mirrors. To this end, the sensor  140  is connected to a control unit  150  (wire or wireless communication) that receives the output data from the sensor  140  and processes the data so as to operate the sludge treatment system in accordance with the amount of solar energy produced in real time. To this end, the control unit  140  comprises a processor  152  for processing the output data received by a receiver (not shown) within the control unit  150 . The sensor  140  may also be used to determine the system&#39;s internal heat (e.g. residual heat) and to provide output data indicative of same such that the control unit that received the output will process the amount of solar energy in combination with the amount of residual heat and operate the system based on the total heat available. At times, sensor  140  may comprise more than one sensing units (not illustrated), one for sensing the internal heat and the other for sensing the sunlight energy, the different sensing unit independently connected to the control unit and the control unit being adapted to receive output data from a plurality of sensing units. 
         [0032]    The control unit  150  is configured to operate, based on the real time amount of solar energy generated and internal heat, the sludge conveyer (e.g. sludge feed rate, rate of initial dewatering), the dewatering unit, the pyrolysis reactor (rate of pyrolysis, rate of product discharge) etc. Thus, for example, on a sunny day, the system will operate at its maximum capacity, while on a cloudy day, the rate of pyrolysis will be relatively lower. Further, as an example, during nighttime, when there is no sun, the control unit will deactivate the system until sunrise. Thus, the control unit is operable to receive at least data indicative of the solar energy and data indicative of the internal heat. Accordingly, in order for pyrolysis to take place to conditions need to be met: (i) the amount of sludge accumulated in dumping funnel  102  is sufficient for processing and (ii) there is sufficient solar energy and internal heat in the reactor for allowing pyrolysis to take place. 
         [0033]    The control unit  150  also comprises a display unit for real time display of parameters associated with the operation of the entire system  100 , including the amount of sunlight sensed by the solar sensor, the amount of solar energy produced by the concentrating mirrors, and the amount of solar energy used by the reactor, the rate of sludge feed into the dewatering unit or into the reactor, the rate and amount of product discharge from the reactor, the rate and amount of steam removed from the sludge, etc. 
         [0034]    Reference is now made to  FIG. 2  which schematically illustrates a sludge treatment plant  200  in accordance with an embodiment of the invention. For simplicity, like reference numerals to those used in  FIG. 1 , shifted by  100  are used to identify components having a similar function. For example, component  230  in  FIG. 1  is a pyrolysis reactor having the same function as pyrolysis reactor  130  in  FIG. 1 . 
         [0035]      FIG. 2  shows the delivery to the sludge treatment plant of sludge by a truck  260 , dumping the sludge into dumping pit  262  from which it is carried by a conveyor belt  264  into dumping funnel  202 . In  FIG. 2 , drying is performed using a multistage drying conveyor and the produced steam is collected by cooling system  222 . The dewatered sludge is introduced into pyrolytic reactor  230  and syngas and other products are withdrawn and collected.  FIG. 2  also illustrates a collector  268  for collecting of inert material, such as char, a storage unit  250  and a solar energy detecting and concentrating arrangement  270 . 
         [0036]    The solar energy detecting and concentrating arrangement  270  comprises the sensor  240 , a sunlight concentrating mirror  272 , and a focused mirror  274  directing the concentrated sunlight to the pyrolytic reactor. 
         [0037]    Further illustrated in  FIG. 2  is a generator  280  and a steam boiler  282  which in some exemplary systems may employ the thus obtained syngas for producing energy. 
         [0038]    In operation, sludge is introduced into the dumping funnel and is directed towards the dewatering unit (which may be a single, two or multistage dewatering unit). Preferably, although being optionally, the sludge is at least partially dried while being on the conveyor, or the sludge can be dried only when on the conveyor, without the use of a dedicated dewatering unit. This can be achieved, for example, by pressurized air which is introduced into the screw conveyor to dry sludge while being transported. 
         [0039]    Liquid removed from the sludge while directed toward the dewatering unit is then withdrawn from the conveyor. The withdrawn water can be returned to the system. At this stage, typically about 15-25% of the liquid is removed from the sludge. The sludge (or partially dewatered sludge, if some part of the liquid was already removed) is then introduced into the dewatering unit  120  where it is concentrated. The dewatered sludge is then withdrawn from the dewatering unit into the pyrolysis reactor  130  where pyrolysis takes place. 
         [0040]    As indicated above, the conditions of operation of the system are dictated by the amount of sunlight sensed by the sensor (translated into data indicative of the amount of solar energy that is produced by sunlight) at the site and the amount of internal heat of the system. While typically the system will continuously operate during daytime, it is to be understood that, at times, the output data provided by the sensor can indicate that the amount of solar energy generated is too low for the system&#39;s proper operation and as a result some or all the system&#39;s components will be shut down. Thus, the sludge feeding rate into the system can be determined by the heat created during pyrolysis 
         [0041]    The temperature sensor of the invention may be an external sensor for sensing solar energy (e.g. sun rays) or an internal sensor forming an integral part of the reactor for sensing solar energy in conjugation with internal heat within the reactor. When using an external sensor for sensing solar energy, the system typically contains at least one additional sensor for sensing internal heat, within the reactor. When an internal temperature sensor is employed said sensor can sense the temperature of at least one part of the pyrolysis reactor. For example said sensor may receive as input temperature data from different parts of the reactor such as the reactor chamber and the dewatering unit. 
         [0042]    The temperature sensor may be any type of temperature sensor know in the art such as a thermocouples, a Resistance Temperature Detectors (RTD), a thermistor (solid temperature sensor). The sensor may work on batteries but may also be battery independent. Typically, the temperature sensor can measure temperatures over very wide temperature ranges. The temperature sensor may be a contact temperature sensors measuring its own temperature or a non-contact temperature sensor as commonly known in the art.