| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 11.99 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 02.11.99 |
| PATENT TITLE |
Municipal solid waste processing facility and commercial ethanol production process |
| PATENT ABSTRACT |
A method of processing waste is disclosed wherein the municipal solid waste is segregated and processed to recover reusable rubber, metal, plastic, glass and the remaining organic portion of the waste stream is used to make ethanol and other chemicals. One process utilizes a pretreatment step with dilute sulfuric acid to reduce the heavy metal content of the cellulosic component of the municipal solid waste which can inhibit the fermentation of the sugars obtained from such waste. In another, the heavy metal content of the cellulosic component of municipal solid waste is removed via an ionic exchange process, after hydrolysis with sulfuric acid. A process for an economical, energy efficient production of ethanol from municipal solid waste is also disclosed. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 13.05.98 |
| PATENT REFERENCES CITED |
"Ethanol From Cellulosic Residues and Crops: Annual Report," Tennessee Valley Authority (Oct. 1987). "Integrated Fuel Alcohol Production Systems, Phase III: Experimental Facility Testing Report for the period of Jan. 15, 1984-Jan. 15, 1985," Tennessee Valley Authority, Office of Agricultural and Chemical Development. Rossiter, G., "ISEP, A Moving Bed Contractor for Chromatographic Separations: Advanced Separation Technologies Incorporated," presented at the 4th Workshop on Preparative HPLC, Mar. 28-31, 1993, Salzburg, Austria. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A method for producing ethanol and stillage useful as cattle feed from the cellulosic component of municipal solid waste comprising the following steps: (a) shredding the Cellulosic component of municipal solid waste: (b) treating the shredded cellulosic component obtained in step (a) with about 1:1 concentrated sulfuric acid to solid component, by weight, at about 30.degree. to 80.degree. C. to give a partially hydrolyzed mixture; (c) diluting the partially hydrolyzed mixture obtained in step (b) with water at a temperature of about 80.degree. to 100.degree. C. to give a solution containing about 4 to 6 parts water to about 1 parts partially hydrolyzed material, by weight; (d) agitating the diluted mixture obtained in step (c) at about 80.degree. to 100.degree. C. to give a digested material; (e) removing the solids from the digested mixture to give a filtrate; (f) separating the soluble component obtained in step (e) into an acid containing solution and a sugar containing solution; (g) concentrating( the sugar containing solution to about 12-14% sugar; (h) adjusting the pH of the concentrated sugar containing solution obtained in step (g) to about 6: (i) fermenting with yeast the solution obtained in step (h) to give a beer; (j) removing the yeast from the beer obtained in step (i); and (k) distilling the ethanol from the beer obtained in step (j) to produce a concentrated ethanol solution and a stillage solution. 2. The method of claim 1, wherein the cellulosic component in step (b) is admixed with sewage sludge or sewage sludge cake before hydrolyzing with said acid. 3. The method of claim 1, wherein in step (c), the water is waste water or sewage water containing nitrogen. 4. The method of claim 1, wherein the stillage solution produced in step (k) is concentrated to produce a stillage concentrate. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to processes and facilities for the automated treatment of municipal solid waste (MSW) (land-filled or obtained directly from the municipality), sewage sludge, and scrap tires to remove and reclaim any usable materials and for producing commercial ethanol. The present invention further relates to a method for removing the heavy metals associated with the cellulosic component of the aforementioned solid waste. 2. Related Art Generally, solid waste materials and waste sludge are disposed of by land fill and/or incineration. Environmental restrictions on both land fills and incinerators demand that an alternative solid waste solution be implemented. The public outcry concerning pollution caused by incinerators has halted construction of many new incinerator projects. The government, as a reaction to the problems associated with land fills, has mandated that recycling be employed to conserve natural resources and arrest the flow of solid waste materials into land fills. A number of technologies have been developed to recover recyclable materials from solid waste, to produce fuel, and to produce commercially useful alcohols and gas. For example: U.S. Pat. No. 5,198,074 discloses a process to produce ethanol from bamboo which involves chipping, shredding and washing of the bamboo, pressing to remove the water. The fiber is then prehydrolyzed with steam to give dissolved sugars and fermented to give ethanol. U.S. Pat. No. 5,184,780 discloses a system for treating solid waste having one or more treatment lines for processing the solid waste to recover recyclable materials such as corrugated paper, ferrous metals, plastic products, paper and glass. U.S. Pat. No. 5,135,861 discloses ethanol production from biomass which is hydrolyzed using the carbon dioxide produced from the fermentation reaction or the naturally occurring organic acids from citrus wastes as a catalyst. U.S. Pat. No. 5,104,419 discloses a method of producing methanol from solid waste, for example, municipal solid waste, by partially oxidizing and combusting solid waste material, conducting the combustion gases, oxygen and carbon dioxide through the solid waste material, separating the less volatile components of the gas from the more volatile components, and reacting the more volatile components with carbon dioxide to form methanol. U.S. Pat. No. 5,060,871 discloses methods of separating metal alloy particles by utilizing the difference in particle size, density and/or electric conductivity. U.S. Pat. No. 5,036,005 discloses a method for the continuous fermentation production of fuel grade ethanol from a sugar, where the ethanol is removed in a solvent extraction column containing a solvent which is non-toxic to the fermentation microorganisms. U.S. Pat. No. 5,009,672 discloses a process for the recycling and recovery of urban solid waste components by high pressure compression and screening as well as magnetic separation steps. The recovered putrescible organic component is then subjected to a process of anaerobic fermentation to give a biogas which can be used directly for the production of electric power. U.S. Pat. No. 4,974,781 discloses a paper and plastic separation process which subjects the materials to moisture and heat to repulp the paper. The repulped materials are then separated from the non-pulpable materials and are then recycled, combusted or used as a feedstock in a chemical process. U.S. Pat. No. 4,952,503 discloses a process for the continuous production of ethanol using a centrifugal separation step to remove the yeast. U.S. Pat. No. 4,874,134 discloses a process for treating solid waste to recover recyclable materials such as corrugated paper, ferrous metals, non-ferrous metals, plastic products, paper and glass containers, as well as biodegradable waste materials which may be processed to give a compost. The bulky valuables, non-processable materials and redeemable materials are first recovered, a first ferrous metal fraction is then separated magnetically, the waste material is then shredded, a second ferrous metal fraction is then separated magnetically, and the paper fraction is then separated pneumatically to give a biodegradable fraction which can then be composted. U.S. Pat. No. 4,692,167 discloses an apparatus for processing solid wastes for the production of a granule solid fuel by grinding, magnetically separating ferrous metals, screening, drying, gravity separation, cyclone separation, screening and press granulating. U.S. Pat. No. 4,650,689 discloses a process for the preparation of ethanol from cellulosic materials by subjecting the cellulosic materials to a highly concentrated mineral acid gas such as HCl under pressure, and treatment with hot water to give a wort containing sugars which can be fermented. U.S. Pat. No. 4,612,286 discloses a method for the acid hydrolysis of biomass having fermentable materials in a countercurrent diffusion treatment structure. Preferably, the acid is about 2 to 10% by volume sulfuric acid. U.S. Pat. No. 4,553,977 discloses a method for separating solid waste components with a first trommel screen which removes aluminum cans to give an organics-rich fraction from which recyclable fiber products may be separated. Steel cans are removed by magnetic separation. The organics are isolated for use as a fuel, with or without pulping to recover paper pulp. U.S. Pat. No. 4,541,530 discloses a method for separating metallic particles from non-metallic particles of processed solid waste by homogenizing and magnetically treating components of the waste to give a metallic concentrate, for example, an aluminum concentrate. U.S. Pat. No. 4,384,897 discloses a method for treating biomass material by a two stage hydrolysis treatment, wherein in the first stage, the more easily hydrolyzed polysaccharides are depolymerized and in the second stage, the more difficultly depolymerizable polysaccharides are depolymerized. The biomass material may be subjected to a sensitization step between the first and the second hydrolysis stages by contact with molecular oxygen. The acids are neutralized with a base such as calcium carbonate or hydroxide to give a solution which is suitable for fermentation to give ethanol. U.S. Pat. No. 4,341,353 discloses a method of recovering fuel and recyclables from refuse using disk screens and air classifiers. U.S. Pat. No. 4,288,550 discloses a method of digesting garbage by anaerobic fermentation in the presence of ethanol producing yeast to directly convert starch to ethanol without a hydrolysis pretreatment and thereafter subjecting the product to methane producing anaerobic fermentation to give methane. U.S. Pat. No. 4,069,145 discloses a method for separating particles of greater electrical conductivity from particles of lesser electrical conductivity in an electromagnetic eddy current separator apparatus. U.S. Pat. No. 4,063,903 discloses an apparatus for the disposal of solid wastes by recovering the inorganic components and converting the organic component to a fuel or a fuel supplement. The shredded material is treated with an acid which is heated and dried and ground to give a finely divided fuel product. SUMMARY OF THE INVENTION It is an object of the present invention to provide an automated, efficient process for the treatment of municipal solid waste and sewage sludge, preferably in the form of sewage sludge cake, to recover any recyclable materials and to produce usable commercial ethanol. It is the further object of the present invention to provide a method for the reclamation of existing land fills, thereby removing the future environmental impact of the old land fill. It is also the further object of the present invention to provide a processing facility that will have, in effect, no adverse environmental impact. The process for the continuous, automated treatment of municipal solid waste material and sewage sludge to remove and reclaim any usable materials and for producing commercial ethanol, comprises the following steps: (a) delivering municipal solid waste to a processing facility in bulk; (b) removing tires, bulk ferrous and non ferrous metals, plastic and glass from said waste to give a cellulosic component; (c) shredding the cellulosic component obtained in step (b); (d) treating the shredded cellulosic component and, optionally, sewage sludge with dilute (about 1 to 10%) sulfuric acid for about 0.25 to 4 hours at a temperature of about 40 to 100.degree. C. to solubilize substantially the remaining heavy metals and give a soluble component and an insoluble component; (e) removing the soluble component obtained in step (d) from the insoluble component; (f) drying the insoluble component obtained in step (e); (g) treating the dried insoluble component obtained in step (f) with about 1:1 concentrated sulfuric acid (about 70%) to insoluble component, by weight, to give a partially hydrolyzed mixture; (h) diluting the partially hydrolyzed mixture obtained in step (g) with water at a temperature of about 80.degree. C. to about 100.degree. C. to give a solution containing, e.g. about 4 to 6 parts water to about 1 parts partially hydrolyzed material, by weight; (i) agitating the diluted mixture obtained in step (h) for about 1 to 4 hours at about 80.degree. C. to about 100.degree. C. to give a digested material; (j) removing the solids from the digested mixture obtained in step (i) to give a filtrate; (k) separating the filtrate into an acid containing solution and a sugar containing solution; (l) concentrating the sugar containing solution to about 12-44% sugar; (m) adjusting the pH of the concentrated sugar containing solution obtained in step (l) to about 6; (n) fermenting with yeast the solution obtained in step (m) at about 25.degree. C. to about 36.degree. C. to give a beer; and (o) recovering the ethanol from the beer. The invention also relates to a method of removing trace heavy metals and chlorides from the cellulosic component of municipal solid waste, and/or sewage sludge comprising the following steps: (a) shredding the cellulosic component of municipal solid waste; (b) treating the shredded cellulosic component and, optionally, sewage sludge with dilute (about 1 to 10%) sulfuric acid for about 0.25 to 4 hours at a temperature of about 40 to 100.degree. C. to solubilize the trace heavy metals, and give a soluble and an insoluble component; (c) removing the soluble component obtained in step (b) from the insoluble component, to obtain an insoluble component having substantially no trace heavy metals. The invention further relates to a method of producing ethanol and removing essentially all of the heavy metals and chlorides from the cellulosic component of municipal solid waste and/or sewage sludge comprising (a) shredding the cellulosic component of municipal solid waste; (b) treating the shredded component obtained in step (a) and/or sewage sludge with about 1:1 concentrated sulfuric acid (about 70%) to solid component at about 30 to 80.degree. C. to give a partially hydrolyzed mixture; (c) diluting the partially hydrolyzed mixture obtained in step (b) with water having a temperature of about 80 to 100.degree. C. to give a suspension with a liquid:solid ratio of about 5:1 and a sulfuric acid concentration of about 12%; (d) agitating the diluted mixture obtained in step (c), e.g. for about 1 to 4 hours at about 80 to 100.degree. C. to give a digested material; (e) removing the insoluble component containing essentially all of the heavy metals from the soluble component obtained in step (d); and (f) processing the soluble component to produce ethanol. Surprisingly, the aforementioned integrated processes allow for the highly efficient and cost effective production of ethanol from sewage sludge and/or municipal solid waste. BRIEF DESCRIPTION OF THE FIGURE The method of waste recovery including features of the invention is depicted in the attached schematic drawing, which forms a portion of this disclosure, wherein FIG. 1 is a flow chart detailing the complete process for the treatment of municipal solid waste material and/or sewage sludge: Reference Equipment Description 1A/1B Raw Feedstock Storage Silo 2 Metering Vessel 3 Pre-Treatment Chamber 4 Dilute Sulfuric Acid Storage Vessel 5A Primary Screw Press 5B Secondary Screw Press 6 Dryer 7 Processed Feedstock Storage Vessel 8 Dilute Sulfuric Acid Neutralization Vessel 9 Lime Holding Vessel 10 Gypsum Belt Press 11 Neutralized Water Storage Vessel 12 Hydrolysis System 13 Cooking Vessels 14 Holding Vessel #1 15 Filter Press 16 Acid Recovery Storage Vessel 17 Acid Recovery System 18 Evaporator 19 Holding Vessel #2 20 Reverse Osmosis Filter 21 Ammonia and pH Balancing System 22 Yeast Injection System 23 Holding Vessel #3 24 Fermentation Vessel 25 Yeast Filter and Distillation Holding Vessel 26 Distillation Column 27 Chillier Coil 28 Ethanol Storage Vessel 29A/29B Water Storage Vessel 30 Concentrated Sulfuric Acid Storage Vessel 31 Waste Water Storage Vessel (Optional) 32 Water Heater A Lignin Holding Vessel B Boiler Feedstock Storage Vessel C Boiler DESCRIPTION OF THE PREFERRED EMBODIMENTS In the practice of the invention, the feed stock may be municipal solid waste material including waste obtained directly from a municipality or municipal solid waste that was previously land-filled and subsequently recovered. In addition to municipal solid waste, the feed stock can be sewage sludge, preferably in the form of sewage sludge cake which also contains substantial amounts of cellulosic material (about 35% weight:weight). The solid waste material is admitted into the facility through a fully automated receiving station. The waste material is then dumped onto a bulk conveyor. Any recyclable materials present such as valuable bulk items, ferrous metals, non-ferrous metals such as aluminum, glass, plastic, and rubber and the are then recovered. Methods for recovering such items are well known and disclosed, for example, in U.S. Pat. Nos. 5,184,780, 5,104,419, 5,060,871, 5,009,672, 4,974,781, 4,874,134, 4,692,167, 4,553,977, 4,541,530, 4,341,353, 4,069,145, and 4,063,903, the contents of each of which are fully incorporated by reference herein. Preferably, the scrap tire materials are segregated onto a separate bulk conveyor which leads to a scrap tire processing and rubber recovery system, where the scrap tires are shredded and the rubber, steel and fiber are removed. A remote controlled magnetic crane is used to remove any oversized, bulky ferrous materials from the solid waste conveyor. These oversized materials are then processed through a shredder which reduces the material to a workable size. The material is then sent to a recycling bin to await baling. The waste material remaining after the oversized material is removed is then classified by the use of a trommel or other screening mechanism which disrupts any bags and yields two separate processing streams. By appropriate classification, one stream will contain organic waste composed primarily of cellulosic material, while the other will contain metallic products of a particular size, plastic, glass and rubber. The waste materials are processed through several magnetic separations to remove any ferrous metals. The waste is then passed through an eddy current separator to remove any non-ferrous metals. The ferrous and non-ferrous metals are both conveyed to bins to await baling. The organic waste is then shredded and processed in the ethanol production system which accepts the waste material and processes it to obtain ethanol to be sold commercially. Preferably, when sewage sludge is used it should first be dried to obtain a sewage sludge cake. Methods of dewatering sewage sludge to obtain sewage sludge cakes are well known in the art. For example, the moisture content of sewage sludge can be reduced by vacuum filters to 70-75%, to obtain a sewage sludge cake. Since sewage sludge cakes will normally not contain substantial amounts of recyclable materials (aluminum, glass, plastics, etc.), they can be directly treated with concentrated sulfuric acid and processed in the ethanol production system. However, if necessary, further drying of the sewage sludge cake can be achieved by flash or spray drying, where the sewage sludge cake particles are dried in suspension in a stream of hot gases to provide almost instantaneous removal of excess moisture. Rotary dryers and indirect heating systems can also be used. These drying techniques typically comprise a pug mill, rotary kiln dryer, dry cyclone and a web-scrubber. The aforementioned drying techniques are disclosed in Sludge Digestion and Disposal, Public Works 125 (5):D47-D58 (1994), the contents of which are fully incorporated by reference herein. A portion of the byproducts from the ethanol process may be sold commercially and/or used to cogenerate electricity to aid in the operation of the facility. For example, the insoluble material obtained after hydrolysis of the cellulosic component of MSW and/or sewage sludge is primarily composed of lignin, a natural aromatic organic polymer found in all vascular plants. It has been surprisingly found that by using the lignin as a boiler fuel, the total energy costs for operating a processing facility as disclosed herein can be significantly decreased. Based upon the aforementioned energy savings, it has been unexpectedly discovered that the per gallon ethanol production cost can be reduced to about 15-20% below what it costs to produce ethanol from corn. Furthermore, the surprisingly high BTU per pound (about 4,000-13,350) rating of the obtained lignin can be increased by combining it with the clean burning, non-chlorinated plastic component of MSW. A technology capable of separating non-chlorinated plastic from chlorinated plastic (e.g. PVC), known as Vinyl Cycle.TM., is commercially available from National Recovery Technologies, Nashville, Tenn. The Vinyl Cycle.TM. technology is disclosed in U.S. Pat. No. 5,260,576, the contents of which are fully incorporated by reference herein. This composite lignin/plastic material can also be burned as a boiler fuel, thereby further decreasing the energy costs of the disclosed ethanol production process. Any non-organic materials remaining after the aforementioned screening process may be pelletized and used commercially as additives for construction materials. The present invention is entirely automated, requiring only routine maintenance at the end of each shift of operation. Fully automated screening techniques eliminate the need for unsanitary, hand sorting. The present invention allows for a completely zero discharge facility. All buildings may be fully enclosed. All air and water pollutants may be captured and summarily treated. All materials entering the facility may be treated and converted into commercially workable materials. These and other applications and advantages will become evident from the subsequent descriptions and design specifications. Table I details the composition of dry municipal solid waste (MSW) as determined by the Environmental Protection Agency. TABLE 1 ______________________________________ Composition of Municipal Solid Waste ______________________________________ Organics 74.0% Ferrous Metals 7.5% Non-Ferrous Metals 1.5% Glass 10.0% Plastics 5.0% Non-Organics 2.0% ______________________________________ The present invention is designed to receive solid waste such as detailed in Table 1, municipal solid wastes that are recovered from land fills, and sewage sludge, preferably in the form of sewage sludge cake. The last two types of feed stocks will have a different composition than that depicted in Table 1, however this will not effect their use in the disclosed invention. The rate at which the solid waste may be processed through the system is greatly dependent on the size of the community that the present invention will serve. The system may handle from 25 tons per hour up to 125 tons or more per hour. The equipment may be sized accordingly. The materials that are not treatable are hazardous waste, explosives and infectious wastes. The system is able to process refrigerators, washers, dryers, ranges, automobile scrap metal, large materials, small industrial waste and standard municipal solid waste. The present system is designed to recover plastics, glass, rubber, ferrous metals, and non-ferrous metals from the solid waste. The trucks discharge the waste onto a bulk conveyor such as may be obtained from E&H Systems which traverses the length of the initial shredder building. A remote controlled magnetic crane is then used to remove any large metallic objects. These removed objects are placed into an automated pre-shredder for size reduction. Once the size reduction is completed, the waste is reintroduced into the system, into holding bins for baling on a standard baler. A trommel screen as commonly available from such sources as MacLanahan Corporation is then used to automatically open bags, remove small impurities and crush any glass materials. The material in the ethanol stream is conveyed through a series of five magnetic separators which will remove substantially all ferrous metals. That is to say, the waste stream which consists primarily of metallic and cellulosic components is delivered from the trommel to a series of inclined conveyors, each having a magnetic separator device, such as a drum or belt, as is well known in the art. The outlet end of each conveyor is supported at a height above the inlet of each succeeding conveyor such that the material passing the magnetic screen is subjected to gravitational agitation from one conveyor to the next, thereby enhancing magnetic recovery of remaining ferrous metals by a subsequent magnetic separator. The conveyor design is such that it will allow for the fully automated extraction of ferrous metals into a centralized area. This conveyor design also allows for the mixing of the materials to ensure 98% removal of all ferrous metals. The extracted ferrous metals fall down a vertical chute and are conveyed out of the facility to a holding bin for recycling. The remaining material is then conveyed to an eddy current separator such as an Eriez Ferrous Metal Separator. The eddy current separator is utilized for the automated removal of the non-ferrous metal materials including batteries. The eddy current separator is placed after the magnetic separators to ensure that no ferrous metals will damage the eddy current separator equipment. The presence of any ferrous metal materials in or on the eddy current separator will result in serious and expensive damage to the eddy current separator. The remaining waste materials are fed by the conveyor into a hammermill shredder which reduces the material to about a minus 3" to minus 4" size. The reduction in size of the material aids in the ethanol production process. The hammermill shredder will include an explosion proof shroud to eliminate any potential dust related explosions. The material flow may be divided into two distinct paths; the ethanol production process and a humus production path. The distribution of the waste between the two systems depends on the exact volume of waste coming into the facility. As discussed previously, feed stock consisting of sewage sludge or sewage sludge cake will normally be able to bypass the above described sorting process and be directly treated with concentrated sulfuric acid for processing in the ethanol production system. The process employed in the present invention is comprehensively outlined below with reference to FIG. 1. Process Diagram Overview The level of heavy metals found in the cellulosic component of sewage sludge (and cakes composed thereof) or MSW can vary significantly depending upon the source of the waste. For instance the hydrolyzate generated from the cellulosic component of MSW obtained from urban or highly industrialized areas can be contaminated with heavy metals to an extent that the subsequent yeast fermentation process can be inhibited. Therefore, these types of MSW samples may be treated to reduce their heavy metal content prior to hydrolyzation to avoid contaminating the fermentation liquor. On the other hand, it has been discovered that the removal of heavy metals from less contaminated samples can be accomplished via an efficient ion exchange process after the hydrolysis of the cellulosic feedstock. The following discussion describes two processes which can be utilized to reduce the heavy metal content of the cellulose component of the feed stock. One which reduces the heavy metal content prior to hydrolyzation, and the other after hydrolyzation. Which process is used can be determined based upon the level of heavy metal contamination found in the feedstock. A. A Process for the Automated Treatment of MSW Stage 1: Pre-Treatment Ref. 1A/1B-11 Purpose: The purpose of the Pre-treatment Process is to separate the heavy metals that may inhibit fermentation of the hydrolyzed cellulosic component of MSW and/or sewage sludge by mixing the incoming shredded cellulosic component with dilute sulfuric acid. The solids are then pressed and the liquids are treated with lime, creating a byproduct, gypsum. The gypsum is then removed and the remaining solids are prepared to be broken down into sugars in the Hydrolysis System. Based on data from many sources, which are summarized in "the Chemistry and Biology of Yeasts," A. H. Cook, ed., Academic Press, NY, pp. 296-303 (1958), some heavy metals are necessary for fermentation but at high concentrations can inhibit the fermentation of glucose and xylose by yeast. The approximate effects are shown in Table 2: TABLE 2 ______________________________________ Effects of Heavy Metals on Fermentation by Yeast Concentration Concentration Optimum that Moderately that Severely Fermentation Inhibits Inhibits Concentration Fermentation Fermentation Heavy Metal (ppm) (ppm) (ppm) ______________________________________ Cadmium 0 0.1 2 Nickel 0 40 100 Lead 0 0.3 10 Chromium 1 50 150 Zinc 5 200 400 Copper 7-8 15 30 Iron 10-30 500 1200 ______________________________________ As previously discussed some feed stock will have levels of cadmium and iron which moderately inhibit yeast fermentation, and levels of lead, zinc and copper which severely inhibit yeast fermentation. Thus, the reduction of heavy metals found in this type of feedstock is critical to achieve the efficient fermentation of the obtained sugars. A sample treated according to the pre-treatment process which has substantially no trace metals is one which has at least about a 70% reduction of these metals. Description: Raw Feedstock Silos (Ref. 1A and 1B) receive feedstock of about 85%-90% pure organic material in a pre-shredded state of -2" (5/8".times.2") particulate size. Each Silo holds about 25 tons of material, roughly equivalent to a 21/2 days supply of feedstock. Materials having no detectable heavy metal content do not require pre-treatment so they are stored separately in Silo 1B. Material is conveyed from Silo 1A by bulk conveyor to a Metering Silo (Ref. 2). The Metering Silo dispenses the untreated feedstock to a Pre-Treatment Chamber (Ref. 3) while dilute sulfuric acid (about 1 to 10% by weight) is mixed with the feedstock at about 40 to 100.degree. C. This allows for the dissolution of heavy metals and chlorides (metal chlorides and possibly organic chlorides) from the feedstock. The material is then conveyed by a screw conveyor to Screw Presses (Ref. 5A and 5B) enabling the removal of about 60%-80% of the liquid content, thereby removing the soluble component from the insoluble component. A secondary wash is required to eliminate any trace acid (Ref. 5B). The solids from the Screw Press are then fed into a Conveyor Dryer (Ref. 6) with a feed rate of about 3.25 tons per hour. The Conveyor Dryer further reduces the moisture content of the feedstock to about 5%-10%. The dried insoluble component, having a light, fluffy consistency, is pneumatically conveyed to a Feed Process Storage Silo (Ref. 7). The liquids from the Screw Press are piped back into the Dilute Sulfuric Acid Storage Vessel (Ref. 4) for reuse. In addition, dilute acid from the Acid Recovery System (Ref. 17) is piped to the Dilute Acid Storage Vessel. Heavy metals and sediment from the Storage Vessel are evacuated to a Neutralization Tank (Ref. 8). The liquid in the Neutralization Tank is mixed with lime and pumped to a Belt Press (Ref. 10) where gypsum is removed. The remaining neutralized fluid, consisting of H.sub.2 O and particulate, is then run through a particulate filter and returned to a Water Holding Vessel (Ref. 11) for reuse in the system. As discussed below, an alternative ion exchange process for removing essentially the heavy metals involves carrying out the hydrolyzation step outlined below and recovering the aqueous-insoluble lignin. It has been discovered that essentially all of the heavy metals are bound to the lignin. Stage 2: Hydrolyzaton Ref. 12-16, 31, A, B, C Purpose: The purpose of the Hydrolyzation Process is to break down the molecular structure of the feedstock into sugars by mixing the material with concentrated (about 65 to 93%, preferably, about 70%) sulfuric acid. The sugar/acid/water solution is cooked for a determined period of time after which the solids are removed. The solution is sent to the Acid Recovery System for separation. Description: Pre-treated feedstock is metered from the Storage Silo (Ref. 7 or Ref. 1B) to the Hydrolysis System (Ref. 12) where about 70% concentrated sulfuric acid is automatically introduced at about a 1:1 ratio. Unless otherwise indicated, all ratios and % content recited herein are based upon a weight:weight ratio. Where recited, a ratio of about 1:1 includes compositions comprised of a 60:40 to 40:60 by weight mixture. Preferably, the ratio of concentrated sulfuric acid to pre-treated feed stock is about 45:55 to 55:45 by weight. Material is blended for about 2 to 15 minutes, preferably about 10 minutes, and fed into Cooking Vessels (Ref. 13) along with water raised to the temperature of about 88.degree. C. This solution consists of about a 2:1 ratio (about 2 parts water to about 1 part hydrolyzed material by weight). This material is agitated slowly, while maintaining a constant temperature of about 96.degree. C. for about 1-4 hours. Under these conditions, the cellulose and hemicellulose are converted to glucose and xylose, respectively. At the end of this period, the Cooking Vessels are evacuated into a Holding Vessel (Ref. 14) to allow the Cooking Vessel to be recharged. The Holding Vessel stabilizes the temperature of the material and regulates the flow to the Filter Press (Ref. 15). Material from the Holding Vessel is then filtered for example by pumping it into a Filter Press (Ref. 15) which removes the suspended solids to give a filtrate. The solids may be pulverized, washed and returned to the Dryer (Ref. 6) for use as boiler fuel. The filtrate is then pumped from the Filter Press to the Acid Recovery Storage Vessel (Ref. 16). Note: Municipal waste water from the Waste Water Storage Vessel (Ref. 31) may be used as a substitute for fresh water in the Hydrolysis System (Ref. 12). All pathogens inherent in the waste water are eliminated in the Hydrolysis System. The high nitrogen content of the waste water is retained, virtually eliminating the need for the addition of ammonia (a yeast nutrient useful in the fermentation process). Stage 3. Acid Recovery Ref. 16-19 Purpose: The purpose of the Acid Recovery Process is to recover the sulfuric acid from the sugar/acid/water solution to give an acid-containing solution and a sugar-containing solution. The concentrated sulfuric acid and water are then reused in the system. Once the sugars and water have been removed from the solution it is piped into the Fermentation Tanks to be fermented into ethanol. There are a number of well known methods for recovering sulfuric acid from an aqueous stream, any one of which may be used in the practice of the invention. For example, the aqueous stream may be passed through an activated charcoal filter to retain the sugars, and washed with water to rinse the remaining acid. The adsorbed sugar may then be eluted by washing with heated alcohol. See, M. R. Moore and J. W. Barrier, "Ethanol from Cellulosic Residues and Crops," Annual Report, DOE/SERI Contract No. DK-6-06103-1, Tennessee Valley Authority, Muscle Shoals, Ala., October 1987, pp. 27-49, the contents of which are incorporated by reference herein. However, this method for separating the sulfuric acid from the sugars is not preferred, as the alcohol must be evaporated from the resulting sugar solution before fermentation, which adds another step requiring energy input. Problems may also be encountered with acid carryover between the adsorption and desorption cycles which can be ameliorated by use of a nitrogen surge between the cycles. Problems may also be encountered with the effluent alcohol (ethanol) not being saturated at 70.degree. C., resulting in a lower sugar capacity. Lower ethanol flow rates and increased desorption cycle times enhance the desorption of the sugars to give effluent streams which are 95-100% saturated with sugar. More preferably, ion exchange resins may be used to separate the acid and sugar into an acid containing stream and a sugar containing stream. Such resins include the Amberlite strongly acidic cation exchanger resins of the "GEL" type, e.g. IR 120 PLUS sulfuric acid functionality, which is commercially available from the Aldrich Chemical Company. The sugar is adsorbed on the strongly acidic resin giving an acid containing stream which can be recycled. The adsorbed sugars are then recovered by eluting the resin with pure water. See, M. R. Moore and J. W. Barrier, "Ethanol from Cellulosic Residues and Crops," Annual Report, DOE/SERI Contract No. DK-6-06103-1, Tennessee Valley Authority, Muscle Shoals, Ala., October 1987, pp. 30-39, the contents of which are incorporated by reference herein. An apparatus which allows for the continuous separation of acid and sugar containing streams is commercially available from Advanced Separation Technologies Incorporated, Lakeland, Fla. (Model ISEP LC2000), which employs a strongly acidic ion-exchange resin (Finex CS16G, 310 micron mean size). Such apparatuses are disclosed, for example, in U.S. Pat. Nos. 4,522,726 and 4,764,276, the contents of which are fully incorporated by reference herein. It is also possible to separate the acid and the sugar using a solvent, which selectively extracts and removes the acid from the aqueous solution of the sugar. See, M. R. Moore and J. W. Barrier, "Ethanol from Cellulosic Residues and Crops," Annual Report, DOE/SERI Contract No. DK-6-06103-1, Tennessee Valley Authority, Muscle Shoals, Ala., October 1987, pp. 39-49, the contents of which are incorporated by reference herein. The separation may be carried out on a Karr reciprocating-plate extraction column. The column has receiving vessels at each end for solvent and hydrolyzate separation. Mixing is accomplished by teflon plates coupled to a motor. The acid-sugar solution is added to the top of the column which travels down the column where the aqueous solution is intimately admixed with the solvent. The solvent is added to the bottom of the column. An aqueous solution containing the sugar is drawn off the bottom of the column while the acid containing solvent solution is drawn off the top. The acid may then be recovered from the solvent, for example, by distillation of the solvent or by washing the solvent with distilled water. An apparatus and solvent for the continuous separation of acid from aqueous sugar solutions is available, for example, from Glitsch, Inc., Parsippany, N.J. It is expected that the sugar stream obtained from any of these separation processes will contain residual acid. Preferably, the residual acid is then neutralized with lime or ammonia to a pH of about 6. Description: Liquid containing about 10% sugar, 10% acid, and 80% water is pumped from the Acid Recovery Storage Vessel (Ref. 16) to the Acid Recovery System (Ref. 17) which separates the liquid into an acid/water solution and a sugar/water solution. The sugar/water solution is pumped to a Holding Vessel (Ref. 19); the recovered acid/water solution is pumped to an Evaporator (Ref. 18) where water is removed from the acid by evaporated and returned to the Water Storage Vessel (Ref. 29A). Removing the water brings the acid concentration to its original level of about 70%. This allows for the return of the acid from the Evaporator to the Concentrated Acid Storage Vessel (Ref. 30) for reuse into the system. Stage 4: Fermentation Ref. 19-24 Purpose: The purpose of the Fermentation Process is to concentrate the sugar solution and blend it with yeast for the production of an ethanol/water solution. The sugar solution may be concentrated to about 12-14% by evaporation (e.g., by application of heat and/or a vacuum) or with a reverse osmosis filter. After fermentation, the ethanol is recovered. The yeast may or may not be removed prior to recovery of the ethanol. As discussed below, the ethanol may be recovered by distillation or, in the alternative, may be recovered by solvent extraction with a solvent which is non-toxic to the fermentation microorganisms. See, U.S. Pat. No. 5,036,005, the contents of which are fully incorporated by reference herein. The yeast may also be removed by centrifugation. See, U.S. Pat. No. 4,952,503, the contents of which are fully incorporated by reference herein. Preferably, the remaining yeast is first removed and the fermented liquid is pumped to the Distillation Column for the extraction of ethanol. Methods for fermenting hexoses and pentoses obtained from hydrolyzed cellulosic materials and recovering the ethanol are well known and taught, for example, in U.S. Pat. Nos. 5,198,074, 5,135,861, 5,036,005, 4,952,503, 4,650,689, 4,384,897, 4,288,550, the contents of which are fully incorporated by reference herein. Description: From the Holding Vessel (Ref. 19), sugar, water and trace acid (less than about 0.1%) are pumped through the Reverse Osmosis Filter (Ref. 20) to remove some of the water in solution and bring the sugar concentration to around 12%-14%. Ammonia is added and the pH carefully monitored to ensure the required pH balance of about 6 for optimal fermentation. At this point, yeast is added (Ref. 22), blended and pumped into a Holding Vessel (Ref. 23) and subsequently into Fermentation Tanks (Ref. 24). The mixture is held for about 48 hours. A Chillier Coil (Ref. 27) helps maintain the required temperature of about 36 .degree. C. for fermentation. After 48 hours, the fermented liquid is metered to a filter and holding vessel (Ref. 25) where the yeast is removed and piped to the Yeast Storage Vessel. The remaining liquid is metered to a Holding Vessel (Ref. 25) and subsequently to the Distillation Column (Ref. 26). Stage 5. Ethanol Recovery Process Ref. 25-26 Purpose: The purpose of the ethanol recovery is to separate the ethanol from the ethanol/water solution by means of evaporation and condensation. This results in the production of pure ethanol as well as the by-product stillage. Description: Fermented stock is metered to the Distillation Column (Ref. 26). Depending on the original feedstock, the yield may range from 60 to 120 gallons of 180-190 proof ethanol per ton of input material. The ethanol from the Distillation Column is pumped to the Ethanol Storage Vessel (Ref. 28). The Ethanol Storage Vessel (Ref. 28) will have a storage capacity of 12,000 gallons of ethanol, roughly equivalent to a 12 to 14 day supply of ethanol manufactured in the process. A by-product of the distillation process is stillage. Stillage is a starchy residue that can be sold as cattle feed, or further processed to produce other valuable substances and/or chemicals. B. An Ion Exchange Process for the Removal of Heavy Metals from MSW It has been surprisingly discovered that the level of heavy metal contamination typically found in MSW or sewage sludge is low enough so the associated heavy metals essentially remain coordinated with the insoluble fraction obtained after acid hydrolysis of the cellulosic component. Therefore concentrations of soluble heavy metals remaining in the hydrolyzate are well below levels which interfere with fermentation. Based upon this discovery, the present invention further relates to an efficient process for the post-hydrolysis removal of heavy metals from the cellulosic component of MSW and/or sewage sludge. The steps for processing the feedstock are similar to the ones described herein above with the exception that the removal of the heavy metals from the pre-shredded feed stock is delayed until after the hydrolysis step. By doing so, the step involving the pretreatment of the cellulosic material with dilute sulfuric acid can be eliminated, thereby eliminating the need for a secondary wash and the time-consuming, energy-intensive, step of drying the pretreated feedstock. Therefore, rather than pretreating the preshred feedstock with dilute sulfuric acid, it is directly fed into the hydrolysis system where about 70% concentrated sulfuric acid is automatically introduced at about a 1:1 (acid/sample) ratio. This suspension is then blended at around 30-80.degree. C. for preferably about 2-20 minutes, or more preferably about 2-15 minutes, then fed into cooking vessels where the suspension is diluted with water having a temperature of about 80 to 100.degree. C. until the liquid-to-solid ratio 5:1 and the sulfuric acid concentration is about 12%. This material is agitated while maintaining a constant temperature of about 80-100.degree. C. for about 1-4 hours. Under these conditions the conversion of cellulose and hemicellulose to glucose and xylose is 87-100% complete. Once the hydrolysis is complete, the cooking vessels are evacuated into a holding vessel, thereby allowing the cooking vessel to be recharged. The holding vessels stabilize the temperature of the hydrolyzate and regulates its flow to the filter press where suspended solids are removed to give a filtrate. The filtrate is separated into an acid containing solution and a sugar containing solution and the sugar containing solution processed to produce ethanol. The insoluble component collected from the filter press is dried, optionally mixed with the nonchlorinated plastic component of MSW, and utilized as a boiler fuel to produce energy, e.g., to cogenerate electricity, which can be sold or used in the operation of the processing facility, such as in the distillation process. If required, the level of heavy metals associated with the insoluble component can be reduced prior to burning by treatment with a 1-10% salt solution followed by a rinse with water. Having now generally described this invention, the same will be understood by reference to the following examples which are provided herein for purposes of illustration only and is not intending to be limited unless otherwise specified. The entire text of all applications, patents and publications cited above and below are hereby incorporated by reference in their entirety. |
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