THE RAW MATERIAL The principal raw material of interest is cellulose and hemi-cellulose, which are a part of a broad spectrum of wastes available, many of which include a market value for their ultimate disposition. These negative cost materials include, but are not limited to, wood and paper products of all types as singular separated feed streams or as mixed and blended scraps such as newsprint, magazine clay papers, office papers, cardboard, pulp and paper wastes, cotton cloth, fiberboard, demolition wood, new construction wood waste, garden waste, landscaping wastes, palm fronds and Municipal Solid Waste from which grit, glass, metal and plastics have been removed. Collected materials of agricultural origin of interest include citrus wastes, spent grain liquor from brewing, grain ethanol production residuals, bagasse, sugar beet wastes, restaurant wastes, and expired food and drink shelf products.

Supplement wastes, in lesser percentages, having merit for their enhanced negative costs and for their nutrient value in the process include domestic wastewater treatment plant sludge, septic tank wastes. While not a premium value for disposal (low negative processing cost), animal manure has some process nutrient and feed stock advantages. Other available community waste candidates include sewage bar screenings, storm sewer screenings and road sweepings.

Given an established return on investment from the basic operations, to some degree materials may be purchased for the costs of collection and transportation (moderate and limited positive processing costs) as appropriate for the use of periodic unused processing plant capacity which may include off specification crops, chaff, corn stover, or crops grown specifically dedicated for saccharides processing.

The available feed stock of raw materials will vary from city to city and vary from season to season depending on the nature of the production and collection of the raw material stream. He strongest economic incentive involves broad spectrum unsorted wastes. Historically, even special purpose wastes are not delivered fully separated or a "pure" raw material for the process. Accordingly, the challenge is to receive wastes in the form most convenient to the client, with appropriate service fees, and train employees to produce specified products from the available raw materials load duration.

THE PREPARATION For MSW associated and similar raw material sources, the first step in preparation includes opening the loads of raw materials and accomplish visual inspection. At this stage the objective is to isolate and exclude large listed toxic or hazardous materials such as florescent tubes, fuel containers, lead acid batteries and the like as may be present in certain waste streams. Small toxic items such as mercury switches will have to depend on water detritus separation in step two. Other sources of cleaner raw materials may be able to avoid this first step, but experience has shown that avoidance of this step to be unlikely.

Step two of preparation will be rough chopping using either a tub hammer mill or a rotational rough cutter as appropriate for the feed materials to reduce the incoming stock to a uniform size of about 3 inch (7.6 cm) size. A scale conveyor will advance and control feed rate to produce a density of suspended solids in water of roughly 5%, to the first detritus tank used to separate over-dense and under-dense materials. The med range density materials suspended in water then advance through a grinder pump reducing particle size to about 0.25 inch (0.64 cm) size bits and the detritus separation operation is repeated. Both detritus tanks are monitored and fed with calcium hydroxide for a pH condition of 8.0, to preclude premature cellulose de-polymerization, and a water temperature of 140ºF (60ºC) to assist in density separation. Liquid suspension incoming raw materials such as pulp and paper wastes are proportioned into the process stream after the second detritus operation. The target removals for the covered detritus operations include grit -- sand – gravel, glass bits, penlight batteries, metal bits, sharps, floatable, debris and to waterlog paper and wood bits.

Step three is a polishing step utilizing wastewater treatment plant clarifiers operating at warm water conditions to further refine the separation of polyethylene bits or chlorinated plastic bits. The clarifier subnatent is thickened to roughly 10% to 12 % suspended solids and the supernatant is returned to plant water for processing incoming solids.

THE GRAVITY PRESSURE VESSEL A day tank maintains a supply of slurry to be processed providing a twenty minute equalization for the gravity pressure vessel operation. As the materials descend in the outer annulus of the gravity pressure vessel, the mix is preheated by processed materials coming up from the bottom of the vessel. Anticipated problems of abrasion or plugging from particles in suspension have not materialized at either the much deeper the Longmont or Appledorn gravity pressure vessels. The design flow rate for a typical gravity pressure vessel is a little over 1 foot (0.305 meter) per second, the governing parameter being thermal efficiency or heat recovery from processed fluids and to engineer about a 15 degree terminal temperature difference between the inlet and the outlet of the gravity pressure vessel.

For very weak acid hydrolysis operations a peak temperature of 450ºF (232ºC) is approximated, but the actual peak is determined empirically for each recipe to enhance yield as selected by the gravity pressure vessel operator. The depth of a hydrolysis gravity pressure vessel is typically 2000 feet (610 meters). The peak pressure is determined by the net mean density of the expanding water with the pressure being higher than the pressure associated with heat saturated water at the peak operating temperature. Losses of pressure due to water friction are usually less than 100 pounds per square inch (6.8 atmospheres). In this example the accumulated peak bottom water pressure (correcting for expansion and friction) will be about 750 pounds per square inch (51 atmospheres). During the descent it should be anticipated that organic debris will undergo pyrolysis creating organic acids that cause the pH condition to go down somewhat.

The initial alkalization is intended to insure that the mixture remains in a slightly alkaline condition before starved wet oxidation or the initiation of the hydrolysis reaction. The first stage of the reaction chamber at the bottom of the gravity pressure vessel is wet oxidation providing only sufficient oxygen to react with organic debris dissolved in water which will use some of the lignin and other dissolved materials to provide exothermic heat to help sustain the process. It has been observed that slightly alkaline conditions also aid in dissolving portions of the lignin from the cell walls. Cellulose fibers are known to be refractory to short duration wet oxidation at these temperatures. (cite the Longmont gravity pressure vessel and the Zimpro results at Lansing Michigan). Note also the refractory fibers from each wet oxidation process had been oxygen bleached.

The second stage of the reaction zone reduces the pH condition to initiate de-polymerization of the cellulose using carbonic acid derived from later process fermentation steps, and supplemented using sulfuric acid or malaec acid in proportions at the operator's discretion.

The gravity pressure vessel is a continuous plug flow chemical reactor with an aspect ratio of cross section to flow path which is the antithesis of the batch reactor. The reaction time is determined by the flow rate and distance between the point of acid injection and alkali quench, which is nominally engineered to be between one and ten seconds. Complete mix to complete quench. The quench is designed to be a mixture of calcium hydroxide with a seeding of calcium salts anticipated to be produced by the quenching reaction to mitigate calcium salts deposits. Secondary means of continuous cleaning deposits in the gravity pressure vessel reaction zone are provided. The de-polymerized cellulosic materials are then cooled and depressurized by returning the fluids to the surface.

GRAVITY PRESSURE VESSEL SIZING The pilot stage gravity pressure vessel is 9.625 inch (24.45 cm) diameter vessel housed within a 12.5 inch (31.75 cm) containment casing with an overall depth of 2,000 feet (609.6 meters). The annulus between the containment casing and the gravity pressure vessel is evacuated to at least 1/1000 of an atmosphere. Concentrically spaced within the gravity pressure vessel is a 7.5 inch (19.05 cm) heat exchange tubular open at the bottom within the gravity pressure vessel. The annulus between the gravity pressure vessel wall and the heat exchange tubular is defined as the downdraft. Concentrically spaced within the heat exchange tubular is a 4 inch diameter (10.16 cm) jacketed tubular bundle delivering selected fluids to the reaction zone within the bottom of the sealed gravity pressure vessel. The nominal capacity would be 25 to 100 tons of suspended solids per twenty four hour period.

Design details have been worked out for individual vessels of as much as 1000 tons per day, as well as gravity pressure vessels as large as one meter in diameter. Given the commercial considerations in the central states of the USA, the minimum size commercial facility should have a capacity of not less than 400 tons per day (ignoring the weight of water in the raw material). In the event ethanol as the primary base load product does not enjoy legislative use requirement which impacts the sale value, a privately funded viable commercial facility marketing ethanol at commercial gasoline wholesale prices would have to be between 800 and 1200 tons organic raw materials per day. Commercial facilities would involve at least two gravity pressure vessels or more depending on the client needs and the annual peak average twenty four hour -- two day loading. The depth of the gravity pressure vessel is determined by a minimum pressure requirement and a minimum heat transfer area between the downdraft and the updraft.

POST TREATMENT After the gravity pressure vessel fluids pass through a clarifier sized to settle out oxidized metals (2 to 20 microns), dust particles and calcium salts. If the raw material feed has significant hemi-cellulosic materials, furfural may be stripped from the solution. The cleaned saccharides solution then advances to temperature controls and fermentation. Considerable interest of late has focused on the technique of "cascade fermentation" to take maximum advantage of the anticipated mix of saccharides produced from broad spectrum raw materials. Refractory cellulosic fibers may be recycled through the gravity pressure vessel, or separated for enzyme treatment.

Multiple byproducts are anticipated for cost effective removal including yeasts, urea, acetic acid xylose, glycol, and others to be removed from the pre-distillation stream and from plant water directed to wastewater treatment and/or plant recycle. Any materials that can be extracted will reduce the cost and degree of difficulty of wastewater treatment, even if the value of the extracted material in unit value and amount, is not fully self supported.

The entire process (including wastewater treatment) is closed without intentional loss of water or product vapors.

Graphical Overview