Abstract:
A system and method of anaerobically digesting ethanol stillage and reintegrating substantially all by-products thereof back into the system is disclosed. The system includes an ethanol producing facility for producing ethanol and an anaerobic digestion facility for anaerobically digesting stillage from the ethanol producing facility to produce a plurality of by-products. A plurality of sub-systems utilize the plurality of by-products from anaerobic digestion to produce a plurality of end-products. At least one of the plurality of end-products from the various sub-systems is integrated back into the ethanol producing facility and into at least one of the sub-systems such that the system of anaerobically digesting stillage is a continuous and self-sustaining operation.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the field of anaerobic digestion, and more particularly, it relates to a system of anaerobically digesting distillery stillage and using the by-products thereof within an integrated process.  
       BACKGROUND OF THE INVENTION  
       [0002]     Ethanol is an alcohol made by fermenting and distilling simple sugars. Typically, ethanol is produced from crops such as corn, grain, wheat, sugar, and other agricultural feedstocks. Zymase, or other enzymes from yeast, changes the crops into simple sugars after they have been ground and slurried with water. The fermentation reaction converts the simple sugars into ethanol and carbon dioxide. The ethanol is then concentrated by distillation such that the composition of the vapor from aqueous ethanol is 96 percent ethanol and 4 percent water. Dehydrating agents may be used to remove the remaining water to produce absolute ethanol. Because ethanol is produced from crops or plants that harness the power of the sun, it is considered a renewable fuel.  
         [0003]     Ethanol is miscible and therefore useful as a solvent for many substances and in making perfumes, paints, lacquers, and explosives. Ethanol may also be added to gasoline to form cleaner burning fuel. Gasoline comprises many toxic chemicals such as benzene. By adding ethanol, which contains 35% oxygen, the potency of the toxic chemicals in gasoline is diluted. Because ethanol molecules contain oxygen, ethanol added gasoline burns more completely, which results in fewer emissions and helps reduce air pollution.  
         [0004]     Whole stillage is the residual by-product from the distillation of ethanol. Up to 20 litres of whole stillage may be generated for each litre of ethanol produced. Whole stillage is typically separated by centrifugation into a coarse grain fraction called wet cake and an aqueous fraction called thin stillage. Conventionally, the wet cake and thin stillage are dried by evaporation and natural gas dryers and the remaining solids are sold as animal feed. Whole stillage may have a considerable pollution potential that exceeds a chemical oxygen demand (COD) of 100 g/L, depending on the production process and the feedstock used. For example, the use of molasses as feedstock is associated with high levels of sulphates in the stillage and barley fermentation produces stillage having high nitrogen content. Furthermore, heavy metals such as copper, chromium, nickel and zinc may also be found in the effluent due to corrosion ofpiping, tanks, and heat exchangers.  
         [0005]     The problem with processing whole stillage in the above described manner is the high capital and operation costs and energy demand associated with separating, evaporating, and treating the whole stillage. Up to 50% of the cost of operating an ethanol facility is devoted to drying whole stillage constituents by separation and evaporation and processing the effluent in a manner such that environmental standards are met. To reduce such costs, anaerobic treatment of whole or thin stillage has been developed as an effective and economic treatment option.  
         [0006]     Anaerobic digestion is a biological process that produces biogases such as methane and carbon dioxide from organic wastes. The advantage of anaerobic digestion is that it reduces odor and water pollution caused by unprocessed wastes and produces a biogas fuel that can be used for process heating and/or electricity generation.  
         [0007]     Anaerobic digestion typically occurs in an airtight container called a digester. The process of anaerobic digestion consists of three steps. First, the organic matter is decomposed to break down the organic material to usable-sized molecules such as sugar. The second step converts the decomposed matter to organic acids. Finally, the acids are converted to methane gas and carbon dioxide. Depending on the waste feedstock and the system design, biogas is typically 55 to 75 percent pure methane. The collected methane may fuel an engine-generator to generate electricity.  
         [0008]     The problem with current systems of anaerobically treating ethanol stillage is that various other by-products of anaerobic digestion are wasted or are not fully utilized. Furthermore, conventionally, the lack of synergies, that is efficient cooperation, between the anaerobic digestion facility and other systems discourage commercial usage because the cost of the overall system cannot be economically justified. U.S. Pat. No. 6,355,456 to Hallberg et al. discloses a system wherein a feed yard, an anaerobic digestion system, and an ethanol plant are integrated in a continuous operation to create what is disclosed as a cost-effective system and environmentally friendly livestock feeding operation. Hallberg describes the use of ethanol stillage as feed for livestock in the feed yard, anaerobically digesting the manure from the livestock to produce methane, and converting the methane into electricity to operate the ethanol plant. Although Hallberg discloses a synergistic system, it fails to provide a fully self-contained and self-sustaining system whereby all by-products of the anaerobically treated organic material are fully re-integrated into the system. In addition the cattle eat the byproduct therefore making more waste product and CO 2 .  
         [0009]     Therefore, there is a need for a synergistic system of anaerobically treating ethanol stillage wherein all or substantially all of the by-products thereof are used and re-integrated back into the system such that the system is a continuous and autonomous operation.  
       SUMMARY OF THE INVENTION  
       [0010]     An object of the present invention is to provide a synergistic system whereby whole or thin stillage from an ethanol facility is anaerobically digested and the by-products thereof may be used by various other sub-systems.  
         [0011]     Another object of the invention is to provide an integrated, self-sufficient system such that the synergistic interactions between each sub-system taken together create an economically viable operation of each of the various sub-systems.  
         [0012]     Another object of the invention is to provide an ethanol facility, an anaerobic digestion facility for digesting ethanol stillage, a greenhouse, a generator, and an ethanol user such that each of the subsystems is integrated with one another to form a self-sustaining and independent unit.  
         [0013]     Another object of the invention is to provide an integrated system that is environmentally friendly by recycling and/or using virtually all by-products of each system, therefore making the ethanol production an environmentally neutral or positive net process.  
         [0014]     The present invention provides a synergistic system of anaerobically digesting ethanol stillage and reintegrating substantially all by-products thereof back into the system. The system includes an ethanol producing facility for producing ethanol and an anaerobic digestion facility for anaerobically digesting stillage from the ethanol producing facility to produce a plurality of by-products. A plurality of sub-systems utilize the plurality of by-products from anaerobic digestion to produce a plurality of end-products. At least one of the plurality of end-products from the various sub-systems is integrated back into the ethanol producing facility and into at least one of the sub-systems such that the system of anaerobically digesting stillage is a continuous and self-sustaining operation.  
         [0015]     The plurality of sub-systems include a generator sub-system for producing electricity, a greenhouse sub-system for producing greenhouse end-products, and an ethanol user sub-system for producing ethanol end-products and an organic fertilizer subsystem. Each of the sub-systems, the ethanol producing facility, and the anaerobic digestion facility are locatable within close proximity to one another such that the plurality of sub-systems, the ethanol producing facility, and the anaerobic digestion facility, taken together, form a self-contained tightly integrated unit. The ethanol end-products produced by ethanol users include herbal remedies and tinctures, fuel oxygenate, fuel additive, and industrial solvents.  
         [0016]     The ethanol producing facility further produces carbon dioxide which may be transported to the greenhouse sub-system such that the carbon dioxide may facilitate photosynthesis of the biomass and other greenhouse end-products. The greenhouse end-products also include a plurality of herbs and plants that may be supplied to the natural products manufacturer for producing herbal remedies and tinctures with the ethanol. Waste from the greenhouse sub-system may be added to the whole stillage for anaerobic digestion at the anaerobic digestion facility.  
         [0017]     Stillage from the ethanol producing facility is transported to the anaerobic digestion facility which is substantially adjacent to the ethanol producing facility. In addition to the stillage, any organic waste and any organic discard from the plurality of sub-systems may be added to the stillage to be anaerobically digested at the anaerobic digestion facility. The anaerobic digestion facility comprises at least one air tight digester for receiving the stillage, the organic waste, and the organic discard for anaerobic digestion. The plurality of by-products produced from the anaerobic digestion facility include methane gas, carbon dioxide, hot water, and effluent. The digester is a continuous digester wherein the stillage, the organic waste, and the organic discard are continually fed into the digester such that methane gas and carbon dioxide are continually produced, and the effluent and the hot water are continually removed from the digester.  
         [0018]     The methane gas may be collected from the digester and scrubbed and compressed to be supplied as natural gas to various consumers. Alternatively, the methane gas may be compressed and provided as a natural gas supply. Alternatively, the methane gas may be transported from the digester to the generator sub-system to produce electricity. The generator sub-system comprises a boiler wherein the methane gas is burned to heat the boiler. Steam produced by the boiler drives a turbine which turns electric generators to produce electricity. The electricity may be sold to a utilities company via a substation or the electricity may be integrated back into at least one of the plurality of sub-systems to operate the sub-system. Preferably, the electricity is integrated back into the ethanol producing facility to operate the ethanol producing facility. Heat and steam produced from converting the methane gas to electricity may be collected and transported to the ethanol producing facility and used to aid in the fermentation and distillation process.  
         [0019]     Carbon dioxide produced in the digester may be collected and transported to said greenhouse sub-system to facilitate photosynthesis of the greenhouse end products. Hot water from the digester may be collected and used for heating the greenhouse facility of the greenhouse sub-system. Effluent from the digester may be collected and used as an organic and pathogen free soil conditioner to facilitate growth of the greenhouse end-products. Alternatively, the effluent may be separated into a solid and a liquid wherein the solid may be used as compost and the liquid used as a fertilizer to facilitate growth of the greenhouse end-products. The remaining liquid may be subjected to reverse osmosis to create purified water. The purified water may be reintroduced into the ethanol producing facility to produce ethanol. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a flow chart depicting a system of anaerobically digesting ethanol stillage and using by-products thereof according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]      FIG. 1  depicts a synergistic system of anaerobically digesting ethanol stillage and using by-products thereof, the system  10  comprising an ethanol producing facility  15 , an anaerobic digestion facility  20 , a generator  25 , a greenhouse  30 , and an ethanol user  35 .  
         [0022]     To synthesize ethanol, biomass  12  such as sugar crops (i.e. sugar cane, sugar beets), starch crops (i.e. corn, grain, wheat), or cellulosic materials (i.e. crop residues, municipal solid waste, wood) are transported via railcar  40  or any other form of transportation from various sources and milled or otherwise broken-down and prepared for fermentation and distillation in ethanol producing facility  15 . Greenhouse  30  may also produce and supply the necessary biomass, in part or in whole, for the production of ethanol at ethanol producing facility  15 . Generally, the process of producing ethanol typically involves converting biomass  12  into sugars by hydrolysis and then fermenting the sugars to produce ethanol. Because cellulosic materials are more difficult to convert to sugar than are carbohydrates, grain is the preferred biomass used to produce ethanol.  
         [0023]     However, ethanol facility  15  may be designed to convert virtually any biomass  12  into ethanol using techniques known in the art.  
         [0024]     Ethanol made from a biomass  12  such as grain may be produced by a dry mill process or a wet mill process. In an embodiment of the present invention, grain biomass  12  is dry milled, although the wet mill process may be used as well. Typically in the dry mill process, after grain biomass  12  has been ground into a firm powder called meal, the meal is mixed with water and a first enzyme. The biomass mixture is then passed through cookers where it is liquefied into a mash. Heat is applied at this stage to enable liquefaction and to reduce bacteria levels in the mash. The mash is then cooled and a secondary enzyme is added to convert the mash to fermentable sugars. The biomass may also be treated with ammonia to assist in the breaking down of the biomass. The ammonia may be recovered in a process described below so as to enable the re-introduction of the ammonia to the ethanol producing process. Yeast is added to the mash to ferment the sugars to produce ethanol and carbon dioxide. The fermentation process generally takes between 40 to 50 hours. The fermented mash is then pumped to the distillation system where the ethanol is removed from the solids and the water. The solids and water are typically referred to as stillage. The ethanol is extracted from the top of a distillation column and the residual stillage is transferred from the base of the column to the anaerobic digestion facility  20 .  
         [0025]     The ethanol from the top of the column passes through a dehydration system where the remaining water may be removed. The ethanol is then denatured or made unfit for human consumption if ethanol user  35  is the fuel additive industry or industrial solvent industry. If ethanol user  35  is the natural products industry which uses ethanol for producing, as for example, extracts of various natural products such as propolis and black cohosh, the ethanol produced would not be denatured.  
         [0026]     Ethanol producing facility  15  is similar to a conventional ethanol plant except for the absence of the drying equipment typically used to dry the whole stillage and the thin stillage to produce dried distillers grain. By eliminating such drying, handling, and storage equipment, the energy usage of ethanol producing facility  15  may be significantly reduced compared to other ethanol plants. Furthermore, there may also be a significant reduction in capital costs associated with the construction of an ethanol facility without such drying equipment. By providing anaerobic digestion facility  20  adjacent to ethanol producing facility  15 , the whole and thin stillage may be transported directly to the digesters of anaerobic digestion facility  20  without drying first.  
         [0027]     The major products of fermentation and distillation of biomass  12  include ethanol  16 , carbon dioxide  17 , and stillage  18 . Ethanol  16  is supplied to various ethanol users  35 . In one  15  embodiment of system  10 , ethanol user  35  is a manufacturer of health products wherein ethanol  16  is used to prepare various herbal remedies and tinctures, vitamins, minerals and specialty supplements. In another embodiment, ethanol  16  may be sold to the fuel industry and used as a renewable fuel, primarily as a gasoline volume extender and also as an oxygenate for high-octane fuels.  
         [0028]     Carbon dioxide  17  may be collected in storage vessels and supplied to various industries, such as manufacturers of carbonated drinks and suppliers of industrial grade carbon dioxide. In an embodiment of system  10 , carbon dioxide  17  may be supplied to greenhouse  30  to facilitate photosynthesis. Carbon dioxide  17  contributes to plant growth by enabling plants to combine carbon dioxide  17  and water with the aid of light energy to form sugars which are then converted into complex compounds for continued plant growth. When the supply of carbon dioxide  17  is insufficient, plants cannot utilize the sun&#39;s energy fully and growth is inhibited.  
         [0029]     Applicant believes that in most cases rate of plant growth under otherwise identical growing conditions is directly related to carbon dioxide concentration. Commercial growers have long used carbon dioxide to increase plant health and crop yields because increasing carbon dioxide levels accelerates photosynthesis. Plants grown in carbon dioxide enriched environments exhibit thicker, lush foliage, increased branching, and more plentifull blooms.  
         [0030]     Stillage  18 , which comprises whole stillage and thin stillage, is transported to anaerobic digestion facility  20  for anaerobic treatment. Additional organic waste  22  generated by ethanol user  35  such as residual organics from manufacturer of health products may be added to stillage  18  for anaerobic digestion. Furthermore, other organics  24  such as city waste or sewage may be provided for anaerobic digestion. Organic waste from greenhouse  30  may also be added to stillage  18  for anaerobic treatment.  
         [0031]     Depending on the incoming waste stream (feedstock) a thermal hydrolysis (TDH) process may be used to pre-treat the organic waste before anaerobic digestion. TDH increases pressure and temperature applied to the organic part of the waste. The waste is thereby split-up in a first step into short-chain fragments that are biologically well suited for microorganisms. The following fermentation runs much faster and more complete than in conventional digestion processes and the biogas yield is increased. Left is just a small amount of a solid residue that can be easily dewatered and utilized as surrogate fuel for incineration or as compost additive. The thermal hydrolysis process allows a substantially complete energy recovery from organic waste. During the total procedure more energy sources are produced than are needed for running the plant. The procedure is especially suited for wet organic waste and biosolids that are difficult to compost, such as food scraps, biological waste from compact residential areas and sewage sludge. As a complete disinfection is granted due to the process temperatures the procedure is also suited for carcasses.  
         [0032]     Anaerobic digestion facility  20  comprises a plurality of digesters. Digesters are large air-tight tanks which are typically made out of concrete, steel, brick, or plastic. They may be shaped like silos, troughs, basins or ponds, and may be placed underground or on the surface of the ground. A digester comprises a pre-mixing area or tank, a digester vessel, a system for collecting biogas, and a system for distributing the effluent or the remaining digested material. There are two basic types of digesters: batch and continuous. Batch-type digesters are operated by loading the digester with organic materials, allowing it to completely digest, removing the effluent, and repeating the process again. In a continuous digester, organic material is constantly fed into the digester such that biogas is continually produced without the interruption of loading organic material and unloading effluent. In an embodiment of the present invention, anaerobic digestion facility  20  comprises a plurality of continuous vertical tank digesters which are typically better suited for larger operations and produce a steady and predictable supply of usable biogas, such as methane gas  45 .  
         [0033]     Stillage  18  is transported into digesters where microorganisms convert stillage  18  into organic acids. Methane-producing (methanogenic) anaerobic bacteria utilize these acids and complete the decomposition process. The rate of digestion and biogas production depends on the temperature that the anaerobic bacteria can endure. Typically, they thrive best at temperatures of about 98° F. (36.7° C.) (mesophilic) and 130° F. (54.4° C.) (thermophilic).  
         [0034]     Methane gas  45  and carbon dioxide  50  produced by anaerobic treatment of stillage  18  may be collected by a gas collection system and stored separately in a plurality of vessels, such as collapsible collection domes. A series of valves and tubes control the flow of gases to their respective storage locations or use locations. Methane gas  45  may be scrubbed and compressed and supplied as natural gas  47  and transported to various consumers. In an embodiment of the present invention, methane gas  45  may be transported to generator  25  where methane gas  45  is converted into electricity  48 . In one embodiment, methane gas  45  is burned to heat a boiler  55 . Boiler  55  produces steam to drive a turbine  60  which turns electric generators  25  to produce electricity  48  and steam. In another embodiment, methane gas  45  may be burned in turbine  60  to produce electricity  48 . Electricity  48  may then be supplied to operate ethanol producing facility  15 . Alternatively, electricity  48  may be sold to a local utilities company via a substation  65  to supply electricity to the city. Electricity generated from methane gas  45  is renewable and cleaner as there are no net emissions of carbon dioxide. Although the process of extracting energy from methane gas  45  is not 100% efficient, the energy lost as heat or steam  67  is collected and transported to ethanol facility  15  and used to heat the process water required to aid in the fermentation process. In embodiment an integrated recovery unit is provided which reclaims exhaust gas heat through a heat exchanger and consequently generates steam for use in the process plant.  
         [0035]     Like carbon dioxide  17 , carbon dioxide  50  produced from anaerobically digesting stillage  18  may also be supplied to greenhouse  30  to provide plants with the necessary greenhouse gas to photosynthesize. In an embodiment of the invention, greenhouse  30  may be used to grow herbs, plants and other organic products  32  to supply ethanol user  35  with the natural products to manufacture herbal remedies, tinctures, and other health products. In another embodiment of the invention, greenhouse  30  may be used to produce and supply at least some of the biomass  12  to ethanol producing facility  15 .  
         [0036]     Because anaerobic digestion is an exothermic process, hot water generated by the anaerobic digestion of stillage  18  may be used for heating greenhouse  30  to keep the plants warm enough to live in the winter. Hot water pipes may be laid near to the plants. Alternatively, hot water  70  may be supplied to heat exchangers to heat the air in greenhouse  30 .  
         [0037]     Another by-product of anaerobically treating stillage  18  is called organic slurry, or effluent. Organic slurry is rich in nutrients (ammonia, phosphorus, potassium, and more than a dozen trace elements) and is an excellent organic and pathogen free soil conditioner. In an embodiment of the present invention, the organic slurry may be provided to the plants in greenhouse  30  to facilitate their growth. Alternatively, the organic slurry may be centrifuged to  25  separate the solid from the nutrient rich water. The solid may be used as compost  75  for greenhouse  30  or dried and sold as a livestock feed additive. The remaining nutrient rich water  80  may be used as a liquid bio-fertilizer for greenhouse  30 .  
         [0038]     Alternatively, nutrient rich water  80  may be subjected to reverse osmosis to create purified water  85  to be transported to ethanol producing facility  15  and used in the production of ethanol  16 . Reverse osmosis, also known as hyperfiltration, allows the removal of particles as small as ions from a solution. Reverse osmosis may be used to purify water and remove salts and other impurities in order to improve the color, taste or properties of the fluid. Reverse osmosis uses a membrane that is semi-permeable, allowing water to pass through it, while rejecting other ions that remain. As nutrient rich water  80  passes through the membrane and continues to purify nutrient rich water  80  to produce purified water  85 , what remains is a liquid having an increasingly high concentration of nutrients as the membrane continually rejects the nutrients in nutrient rich water  80 , thereby producing a concentrated liquid bio-fertilizer. In an embodiment of the present invention, the concentrated liquid bio-fertilizer may be provided to the plants in greenhouse  30  to facilitate their growth. In an alternative embodiment, the ammonia in the concentrated liquid bio-fertilizer may be separated out such that the ammonia may be re-introduced back into the ethanol producing process to assist in breaking down the biomass.  
         [0039]     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.