Abstract:
A process is provided for converting waste fibers to solid fuel. The process includes providing a supply of animal waste including the waste fibers in a predetermined quantity, subjecting the supply of animal waste to anaerobic digestion, producing a waste byproduct, dewatering the waste byproduct, and compressing the dewatered waste byproduct to form briquettes.

Description:
CROSS REFERENCE 
       [0001]    The present invention claims priority to a U.S. provisional patent application Ser. No. 61/905,397 filed on Nov. 18, 2013 under 35 U.S.C. §119(e), which is incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is broadly concerned with processes designed to obtain fuel formed from dairy livestock waste and more particularly, a process for creating fuel from anaerobic digester waste products. 
       BACKGROUND 
       [0003]    There is a tremendous amount of dairy manure waste generated by dairy farms each year that must be managed, estimated to be in the range of 694,950 tons per day generated in the US. However, there are limited options for disposing of this material, specifically manure coming from dairy Concentrated Animal Feeding Operations (CAFOs). Due to the high density of cows in such facilities, an extremely large quantity of manure is produced daily, resulting in often strong smells and continual odors that are objectionable to many people living near the facilities. Currently, the waste is usually stored in lagoons due to the relatively high percentage of water in the waste. However, lagoons and other current methods do not eliminate odor problems from dairy farming operations. Additionally, current disposal/storage methods, along with land farming, in many cases, run the risk of contaminating the air, land, and water in and around these CAFOs. Among other thing, excessive application of manure upon fields results in unwanted runoff into water supplies. Farmers often have to pay to have the excess manure hauled to landfills. 
         [0004]    At the same time, in the global economy, increasing quantities of fossil fuels are utilized each year for electricity production, heating, steam generation, transportation and other needs. There are continual efforts by various environmentally-minded groups to encourage the decreased consumption of fossil fuels to preserve the limited quantity of the fuels, as well as to decrease the quantity of pollutants produced by burning fossil fuels. While these efforts have had some success, there is always the need for additional processes and products which utilize energy sources other than fossil fuels. 
         [0005]    Anaerobic digestion has been used as an initiative to manage dairy manure waste and to produce a methane biogas. The methane biogas can be converted into electricity. One aspect of the use of methane for this purpose is that since the source of supply of the gas is often remote from the electricity distribution infrastructure, much of the gas is wasted. However, despite the generation of methane through anaerobic digestion, there is still a need to dispose of the solid waste resulting from anaerobic digestion. 
         [0006]    Additionally, many dairy farms have used dried manure waste solids as bedding for dairy cows. However, when the dried manure bedding is soiled with urine or additional fecal matter, the bedding facilitates bacteria growth. The use of dried manure waste solids as dairy cow bedding leads to poor animal health, and farmers have reacted by giving the dairy cows more antibiotics to combat ailments contracted from the bedding. As a result of dried manure waste solids bedding contamination, dairy and beef food supplies are exposed to bacteria and antibiotics through the cows. Alternatively, many dairy farms have explored the use of inorganic materials, such as sand, for bedding to minimize bacterial growth and to readily drain moisture. However, sand is more costly to use, and there is a need to optimize the use of sand as bedding at a lower cost. Also, the grade of sand used previously for animal bedding has been found to be overly coarse, which irritates the animals. 
         [0007]    At the same time, there is always a need to improve the complete water footprint of the agricultural supply chain and community. Wastewater recovered from dairy waste manure processing can be recycled for use in irrigation or on farms. To do so, however, the wastewater needs to be disinfected to cure airborne microbial issues. Alternatively, if not recycled, the wastewater also is treated before it can be discharged safely, to reduce CAFO contribution to lake and river pollution. Nitrogen and phosphorous are two nutrients present in animal waste and in excessive amounts cause an explosion of toxic algae in lakes and rivers. Activated carbon can be used as a filter for the process wastewater. However, there is a shortage of activated carbon. Thus, activated carbon can also be very costly, and there is a need for production of activated carbon from within the agricultural supply chain. 
         [0008]    There is a need for products and processes which can utilize the dairy waste byproduct from anaerobic digestion for producing energy in a sustainable, renewable, and efficient manner, while reducing the depletion of natural resources. 
       SUMMARY 
       [0009]    The above-listed needs are met by the present process, which features the use of dairy cow manure to form a fuel product. In the present process, dairy cow manure is fed into an anaerobic digestion process, producing a methane biogas and a solid/liquid waste byproduct. The solid/liquid waste byproduct is delivered to a thermal torrefaction process to further convert dairy manure waste fibers to solid fuel. This thermal torrefaction process is described in U.S. patent application Ser. No. 14/195,313 which is herein incorporated by reference. The solid fuel can additionally be converted by further thermal torrefaction into activated carbon, which can be used to filter water from the present process to be recycled for irrigation or other farm purposes. In a related embodiment, sand used for animal bedding is recycled to remove animal waste products, which are in turn passed through the above-identified torrefaction process for utilizing the waste as fuel. The sand is separated from the waste and recycled for use as dairy cow bedding. 
         [0010]    More specifically, a process is provided for converting waste fibers to solid fuel. The process includes providing a supply of animal waste including the waste fibers in a predetermined quantity, subjecting the supply of animal waste to anaerobic digestion, producing a waste byproduct, dewatering the waste byproduct, and compressing the dewatered waste byproduct to form briquettes. 
         [0011]    In another embodiment, a process is provided for converting waste fibers to solid fuel. The process includes providing a supply of animal waste including a supply of sand with particle size according to ASTM C-44 or ASTM C-33 standards, with a sieve size ranging from #4 to #8 and waste fiber in a predetermined quantity, separating the supply of sand from the supply of animal waste, dewatering the supply of animal waste, compressing the dewatered supply of animal waste to form a plurality of briquettes, and torrefying the briquettes in a torrefaction reactor using a heat source at a predetermined torrefying temperature for a predetermined torrefying period. 
         [0012]    In yet another embodiment, a process for converting waste fibers to solid fuel is provided. The process includes providing a supply of animal waste including the waste fibers in a predetermined quantity, dewatering the supply of animal waste, compressing the dewatered supply of animal waste to form briquettes, torrefying the briquettes in a torrefaction reactor using a heat source at a predetermined torrefying temperature for a predetermined torrefying period to produce solid fuel, and heating the torrefied briquettes to increase adsorbency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]      FIG. 1  is a schematic flow chart depicting the present process. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , the present dairy manure waste fiber to energy process system is generally designated  10 , and is designed for converting a byproduct of anaerobic digestion to solid fuel. A reception trough or pit  12  is supplied with a slurry  14  of dairy manure and bedding sand that was flushed from at least one dairy cow&#39;s stall. The sand will preferably have a particle size according to ASTM C-44 or ASTM C-33 standards, with a sieve size within those standards ranging from #4 to #8 to measure the sand. Because the sand is used for dairy cow bedding, the preferred range of particle sizes is comfortable for the cows, because the sand conforms to their bodies when they lie down upon it, and is non-abrasive to their hooves and udders. It is contemplated that finer sand can be used depending on environmental conditions, such as wind and rain. 
         [0015]    The flushed manure slurry  14  in the trough or pit  12  is delivered via an inclined manure auger  20  or the like having sufficient capacity for carrying the weight and amount of the manure slurry  14  to a sand separation device  22 , which is a typical solids dewatering device known in many industries, such as paper making. The sand separation device  22  separates the sand from the manure slurry  14 . A tank  24  underneath the inclined manure auger  20  catches the manure liquids and solids  26 . Those familiar with the art should understand the operational use of these devices, as they are commercially available from various manufacturers. In a preferred embodiment, sand is separated from the manure slurry  14  prior to anaerobic digestion and the thermal torrefaction process. Sand-laden dairy manure can be processed through anaerobic digestion, however the sand will settle at the bottom of the anaerobic digester and damage the anaerobic digester equipment over time. 
         [0016]    Before leaving the sand separation device  22 , the recovered sand is rinsed with a stream of water, sifted, then discharged into a recovered sand storage area  30 , and allowed to drain. The storage are  30  is contemplated to vary in size to suit the application and also to accommodate as many 72 hours of operation of the present system. Further, as needed, partitions (not shown) may be provided in the storage area  30  to separate portions of the sand to enhance drainage of batches of sand. In a preferred embodiment, the rinsed sand  32  will drain in the recovered sand storage area  30  for up to 72 hours before it is used. Preferably, the recovered sand  32  contains between 10-12% moisture content by weight, and less than 2% organic material content (dried manure solids) by weight. The sand  32  is ready to be collected and re-deposited in the parlors for the cows&#39; bedding. In a preferred embodiment, the sand/manure separation process recovers approximately 80-98% of the sand from the manure slurry  14 . 
         [0017]    The manure liquids and solids  26  collected in the tank  24  are then delivered via piping  34  sufficient to carry the weight and amounts of the manure liquids and solids  26  to a solid/liquid separation device  36 . Also supplied to the separation device  36  is manure collected from the feedlot or other sources at  37 , which represents a distinct liquids/solids separator from the separator  36 , such as, but not limited to a centrifuge or other mechanical separator as described below. It is contemplated that the solid/liquid separation devices  36  and  37  can separate the manure solids and liquids  26  by using gravity, such as with a settling basin or pond, or by using a mechanical separator. Mechanical solid/liquid separation devices include, but are not limited to dewatering screens, presses, and the like. Those familiar with the art should understand the operational use of these devices as they are commercially available from various manufacturers. 
         [0018]    The liquid  38  separated from the manure is collected in a storage tank  40 . The liquid stored in the storage tank  40  is then delivered to a filtration column  42  via piping sufficient to carry the weight and amounts of the separated liquid stream  38 . The liquid  38  enters the filtration column  42  through inlet  44  and exits through outlet  46 . In a preferred embodiment, the separated liquid stream  38  is filtered by ultra-fine filtration, reverse osmosis or similar technology. It is also contemplated that other suitable liquid filtration methods are employed at this point in the process. The filtration column  42  separates out nitrogen, phosphorous, potassium, and other nutrients present in animal waste from the separated liquid stream  38 . The nutrients are delivered via piping  48  to a storage tank  50  until they can be sold or used. Those familiar with the art are aware that nitrogen, phosphorous, and potassium are three nutrients that are in many commercially available fertilizers. To enhance the separation of solids, a recirculation conduit  51  connects the storage tank  40 , preferably at the bottom with the separator  37 . 
         [0019]    The filtered water  52  exiting from outlet  46  is delivered to a storage tank  54  until further processing, and can be used to irrigate fields, be put back into use on farms or otherwise discharged safely, and in some cases is potentially potable upon completion of required further treatment steps. The filtered water  52  in storage tank  50  would need to be further disinfected to cure microbial and airborne issues. It is also contemplated that a new or existing lagoon can be used as storage for the water  52  that comes from the wastewater treatment system instead of storing the water  52  in above ground tank  54 . The lagoon can be covered or open, but the manure solids must not be put into the lagoon or the usefulness of the wastewater treatment system would be obviated. In a preferred embodiment, if a reverse osmosis filtration method is used on the liquid  38 , the filtered water  52  would be stored in tank  54  as it would be much cleaner and would have a higher value for use with heifers or other young developing cows. 
         [0020]    The solids  56  separated from the manure liquids and solids  26  are delivered to an anaerobic digester  58  via substrate inflow piping  60  sufficient to carry the weight and amounts of the manure solids  56 . As is known in the art, the anaerobic digester  58  produces an effluent gas  62 , typically methane, and an effluent substrate  64 . As is well known in the art, the effluent gas  62  from anaerobic digestion can be converted into electricity. The effluent substrate  64 , which is a solid/liquid byproduct of the anaerobic digestion process, contains dairy waste fibers. These fibers are the undigested elements of the cow&#39;s diet. Optionally, the effluent substrate  64 , or the digestate, can be delivered to a solids separation device (not shown) to separate solids from the digestate  64 . The separated digestate solids can then be used for soil amendments, dried manure bedding for cows, fertilizer, or any additional products that are known in the art. 
         [0021]    In a preferred embodiment, the effluent substrate (the anaerobic digestion solid/liquid byproduct)  64  is delivered to a thermal torrefaction process, generally designated  66 , to further convert dairy manure waste fibers in the byproduct  64  to solid fuel through piping  68  sufficient to carry the weight and amounts of the byproduct effluent substrate  64 . This thermal torrefaction process  66  is described in U.S. patent application Ser. No. 14/195,313, which is incorporated by reference. Generally, this process  66  first dewaters the waste fibers and compresses the waste fibers to form briquettes. The dewatering step produces a wastewater stream  70 , which contains contaminants from the manure, such as nitrogen, phosphorous, and other nutrients present in animal waste. The compressed, dewatered briquettes are then torrefied. In a preferred embodiment, the torrefaction step lasts up to 30 minutes and is carried out in the approximate range of 600 to 700 degrees Fahrenheit. The briquettes  72  formed by the torrefaction step can be used as a solid fuel product to provide the necessary energy for the process  66 . 
         [0022]    After the torrefaction reaction, the briquettes  72  can be further heated in a reactor  74  to convert the briquettes to activated carbon, increasing the adsorbency. It is contemplated that the reactor  74  used for the activated carbon conversion step can be the same machinery used in the thermal torrefaction step  66 , but different reactors can also be used. The reactor  74  is preferably a furnace constructed and arranged to be capable of producing activated carbon using thermal processes, in the general range of 2,000° F., and depending on how it is heated, should have a thermometer  76  for measuring the internal temperature, as well as an external temperature gauge  78 . A sealed lid  80  at the opening of the reactor  74  is necessary for reducing the entry of outside oxygen into the reactor  74 . It is contemplated that the seal is pressurized, but optionally may be non-pressurized. 
         [0023]    The external heat source, generally designated  82 , is configured for generating heat applied to the reactor  74  for the activated carbon conversion step, and can be from any commercially available apparatus, such as a propane gas burner  84 . The reactor  74  is preferably disposed above the gas burner  84 , which is supplied with fuel by a propane tank  84  by a propane tank feed line  86 . 
         [0024]    Activated carbon has a high surface area available for adsorption, and is, therefore, useful in removing contaminants from the wastewater stream. The activated carbon conversion step within the reactor  74 , in a preferred embodiment, lasts up to 20 minutes depending on the amount of briquettes  72  in the reactor  74 . Also in a preferred embodiment, the activated carbon conversion step within the reactor  74  is carried out in the approximate range of 600-900 degrees Fahrenheit. The briquettes undergoing the activated carbon conversion step within the reactor  74  are tested at various time intervals with iodine to measure the iodine number. The iodine number indicates the micropore volume content of the briquettes undergoing conversion by measuring adsorption of iodine by carbon from a testing solution. Once the briquettes have the iodine number of activated carbon, the activated carbon conversion step is complete. As is known to those skilled in the art, the iodine number of activated carbons used for water treatments typically ranges from 600-1100 mg/g. 
         [0025]    Next, the reactor  74  is removed from the external heat source  82 , and allowed to cool down. While the reactor  74  is cooling down, the lid  80  should remain closed to prevent the exposure of the briquettes  72  to fresh oxygen through the ambient air. 
         [0026]    After the activated carbon  88  is removed from the reactor  74 , the activated carbon  88  can be formed as pulverized activated carbon (PAC) or granular activated carbon (GAC) in an activated carbon processor  90  to provide processed activated carbon. A filtration column  94  is prepared with the processed activated carbon. The activated carbon can be sold in bulk for flue gas remediation or without activation as carbon for agricultural soil amendments. The size and operational use of the filtration column  94  should be sufficient to handle the volumetric and mass flow rates of the wastewater stream  70 . In a preferred embodiment, the filtration column  94  is a packed bed filtration column. It is also contemplated that other suitable filtration column applications are employed at this point in the process. 
         [0027]    The wastewater stream  70  is delivered to the filtration column  94 , and enters the filtration column  94  at an inlet  96 . In the column  94 , the wastewater stream  70  passes through the column  94  as a gravity fed system, similar to a settling tank application. The filtration column  94  reduces the amounts of salts and nutrients from the animal waste, such as nitrogen, phosphorous, and potassium present in the wastewater stream  70 . The filtered wastewater stream  98  exits the filtration column  94  via outlet  100 . With reduced contamination, the filtered water  98  can be used for irrigation, a water supply for dairy cows, or other useful farm purposes. The filtered water  98  is delivered to a storage tank  102  until it is used. As discussed above, it is also contemplated that a new or existing lagoon can be used as storage for the water  98  that comes from the wastewater treatment system instead of storing the water  98  in above ground tank  102 . The lagoon can be covered or open, but the manure solids must not be put into the lagoon or the usefulness of the wastewater treatment system would be obviated. 
         [0028]    While particular embodiments of the present manure treatment process with anaerobic digester have been described herein, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the present disclosure in its broader aspects.