STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT Not applicable.

BACKGROUND TO THE INVENTION Biopulping refers generally to treating lignocellulosic starting material, such as wood chips, with a microorganism in order to bring about a desired change in the starting material. For a detailed discussion of biopulping processes, please see U. S.

Serial No. 08/824,235, which is incorporated by reference herein. Certain fungi, especially white-rot fungi, may be used in biopulping to reduce lignin content which thereby reduces the energy requirements of subsequent pulping steps or increases the strength of the paper product.

The fungal treatment of wood chips or other lignocellulosic starting materials includes the following steps and their associated material transfer operations: preinoculation preparation, inoculation, and incubation. In order for biopulping processes that employ fungi to be economically viable, large-scale commercial implementation is necessary. However, implementation of fungal treatment processes on a large scale is associated with certain technical concerns. Much research has been directed toward improving the efficacy of biopulping.

U. S. Patent No. 3,962,033 discloses that treating wood chips with at least one of several white-rot fungal species of the genus Rigidoporus, Phanerochaete (also

called Sporotrichum), Trametes, Polyporzis, Peniophora, or Coriolus may result in energy savings and increased paper strength.

A consortium ("the biopulping consortium") of the University of Wisconsin- Madison, the USDA Forest Service, Forest Products Laboratory, and several industrial partners has found that isolates of white-rot fungi genera Phlebia, Dichomitus, Phanerochaete, Poria, Hypodontia, and Ceriporiopsi are able to colonize wood chips. U. S. Patent No. 5,055,159, incorporated herein by reference, discloses that the species Ceriporiopsis subvermispora is particularly useful.

U. S. Patent No. 5,460,697 teaches a method for reducing propagation of contaminating microorganisms in biopulping by treating the wood chips with sulfite salts, on which C. subvermispora is able to grow. Other advances enhancing biopulping efficacy are known. U. S. Patent Nos. 5,750,005 and 5,620,564, incorporated by reference herein, disclose adding certain nutrient adjuvants such as corn steep liquor, molasses, or yeast extract to a fungal inoculum to reduce the fungal inoculum required to achieve efficient inoculation of wood chips. Variations in operating conditions (e. g., temperature, humidity, and air quality) that occur during the incubation phase of fungal treatment can be particularly problematic. In the absence of environmental controls, desired conditions are not maintained. Heat, moisture, and metabolic heat released during incubation results in variations in incubation conditions that may cause inconsistency in the quality of the product produced. Unless process conditions are controlled within relatively narrow limits, incubation results can be quite variable.

There is a need in the biopulping industry for a method of controlling conditions of temperature, humidity or air quality in a fungal incubation with lignocellulosic materials.

BRIEF SUMMARY OF THE INVENTION In one aspect, the present invention provides a method of ventilating material in a fungal incubation comprising introducing the material into a containment system equipped with at least two vertical air distributors; and delivering air through at least one of the vertical air distributors. In one embodiment, the air is delivered through the vertical air distributors at alternating intervals such that air delivery from each air distributor is not continuous.

In another aspect of the present invention a fungal incubation containment system comprising a substantially enclosed storage silo equipped with at least two air distributors vertically positioned within the silo is provided.

The present invention also provides a method of controlling air flow within a substantially closed biological incubation system so as to eliminate or reduce regions of relative elevated temperature or of stagnated air flow within the system comprising providing a substantially closed incubation system including multiple orifice means which are adapted to be both air inlets and air outlets, the system further including air flow generating and directing means for generating and directing air flow to and from the orifice means, the air flow generating and directing means including timing means for periodically modifying the direction and flow of air to and from the orifice means; activating the air flow generating and directing means so as to cause air to flow into the system from air inlets generally toward the air outlets; and activating the timing means to cause the air flow generating and directing means periodically to change the direction of air flow to the orifice means so that air flows within the system so as to eliminate or reduce regions of elevated temperature or air flow stagnation. Preferably, the air flow generating and directing means cause air to flow from orifice means providing air inlet and generally toward orifice means providing air outlet, with periodic alteration of the air flow direction. Alteration of the air flow may optionally include intermittent cessation of air flow.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows vertical and horizontal crosssections of linear and cylindrical or conical silo equipped with air ducts; the air ducts are shown with hatched marks.

Fig. 2 shows the alterations of air flow patterns obtained with air flow switched between air inlets.

Fig. 3 shows air flow pattern with continuous air flow from a single inlet.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to biopulping containment systems that allow biopulping under controlled conditions of temperature, humidity, and air quality.

Disclosed are biopulping containment systems and methods of biopulping that afford increased control over temperature, humidity or air quality during fungal incubation in

biopulping and which meet material handling requirements during the biopulping process.

Control of incubation conditions requires forced ventilation with air at carefully controlled conditions of temperature, humidity, and quality. The incubation period encompasses several phases of fungal behavior, with heat and moisture release rates and optimum conditions varying over time. Control of conditions during the incubation step in biopulping is further complicated by the time-dependent variations in optimal conditions.

A system that is able to accommodate changes in the requirements in optimal conditions of temperature, humidity, and air quality and variations over time of the fungi used in biopulping is desired. To achieve controlled climate conditions, it is also desirable to contain the material undergoing biopulping and thereby at least partially insulate the culture from ambient climate conditions. The design of the containment system is an important consideration in commercial applications of biopulping.

An important aspect of a containment system for biopulping processes is the volume of material being processed or held during the incubation period. For most commercial scale applications, the volume of material is preferably large. However, technical and economic constraints must be considered in designing larger volume biopulping operations.

A suitable construction for containing materials during fungal incubation is a storage silo. Storage silo economics favor internal storage heights of approximately 50-60 feet. Lower pile heights are less desirable, because a correspondingly greater base area is required to achieve the same volume as obtained with a higher pile height, and silo costs increase significantly with base area. Generally, flow of material through a silo is by gravity. The material is introduced into the top of the pile, and removed from the bottom of the pile by mechanical reclaiming equipment operating across the base area. Large base areas increase the cost per volume stored because of increased reclaimer costs, increased costs associated with silo construction, and increased plant plot area requirements. Therefore, the 50-60 ft. pile heights employed in conventional silos provide the most favorable economics for containment systems for use in biopulping.

Effective material movement equipment is needed whether the incubation step is conducted in batch, semi-continuous, or continuous mode. Wood chips are very

susceptible to"bridging", which reduces or prevents even material flow by gravity.

The geometry of the containment is important to preventing bridging, so as to ensure reliable, steady movement of the material pile. Cylindrical, conical, or linear storage silos may be used. Figure 1 shows examples of suitable silo constructions, equipped with an air manifold (shown by cross-hatching) having a plurality of air distribution ducts, in vertical and horizontal cross section. Preferred containment systems are designed such that the interior lacks horizontal surfaces, which may impede the vertical movement of materials through the silo.

Another important consideration in the design of containment systems for use in biopulping processes according to the present invention is an air flow scheme that allows for at least a portion of the pile exit air to be recovered and recycled. In conventional systems, the high cost of the power required to provide necessary pile ventilation by pumping air through a pile and properly preconditioning the air reduces the economic feasibility of commercial scale biopulping. The blower power cost increases with the square of the distance of the flow path through the pile.

Conventional ventilation geometries blowing through large pile with a 50-foot flow path will have large blower power costs. Furthermore, in most climates, preconditioning the ventilation air to the required temperature, humidity, or quality could be prohibitively expensive unless at least a portion of the pile exit air is recycled. Preferably, containment systems of the present invention are equipped with air distributors that permit at least a portion of the pile exit air to be recycled.

The present invention includes a biopulping containment system and method of use that employs a vertical gravity flow of materials. For example, if the starting material is wood chips, incoming chips are distributed on the top of the pile, while chips are removed from the pile bottom by means of a suitable reclaimer device. Chip input and output may be continuous or conducted at specific time intervals. The containment system provides contained or covered storage, which is necessary for recycling ventilation air. Conventional storage silos are a principal example of this type of storage and movement pattern.

A biopulping containment system according to the present invention includes a chip storage silo or containment means, as described above, equipped with a suitable air distribution system. The distribution system will generally include air preparation or conditioning systems and distribution ducts coupled to air inlet/outlet or air orifice means. Orifice means, according to this invention, are adapted to permit

air to flow into or out of the system. The air distribution system will also include mechanisms to generate air flow such as fans, and air flow directing means which permit the direction of air flow to be controlled. Lastly, an air distribution system of this invention will include a control structure which permits the direction of air flow within the system to be changed so that air inlet/air outlets can be periodically and alternatively used to change the direction of air flow within the pile. A timing or other control mechanism also is preferably employed so that the direction of air flow (more precisely inflow and outflow) can be periodically changed.

Generally the air inlet/outlets in accordance with the invention will be substantially vertically oriented with respect to the bulk pile. Optionally, the air inlet/return distributor is suspended from above the pile, e. g., from the ceiling or other support structure and extends vertically downward into the pile at least about 50% throughout the height of the pile. Preferably, the distributor extends at least about 75%. More preferably still, the distributor extends at least 90% or even as much as 100% the height of the pile. Any other suitable support means may be employed.

Preferably, the means by which the air distribution ducts are supported does not impede vertical flow of material within the silo.

Preferably, the containment system of the present invention is equipped with a plurality of vertical ducts arranged throughout the pile in a horizontal array pattern.

For example, the ducts could be arranged to form an array that could be a square, rectangular, triangular, or any other regular or irregular pattern.

Any suitable cross-sectional shapes can be employed for the vertical ducts.

The cross-sectional shape and dimensions may vary along the length of the pile height.

Optionally, the ducts may have internal partitions, allowing multiple segregated flows to be connected with different portions of the external surfaces of the ducts.

In one embodiment, the containment system of the present invention is equipped with an array of vertical circular ducts, suspended from the top, extending down through most or all of the pile height. The ducts could be tapered incrementally or in steps such that the diameter of a duct varies along its length. Additional air inlets/outlets could be positioned along the containment walls and in the headspace above the pile and floor space below the pile.

The containment system and biopulping method of the invention provide several advantages over conventional systems and methods. The spacing pattern and distances between the ducts may be selected to provide a much shorter average flow path length than any of the total pile dimensions. Reduced average flow path results in reduced blower power operating costs relative to simple air flow geometries not having distributors internal to the pile.

The containment system of the present invention, with its reduced blower power costs, makes it feasible to avoid shallow pile geometries and the high capital costs associated with such geometries.

It is a further advantage that conventional silo storage and material handling equipment, with top feed (stacker), downward flow by gravity, and bottom reclaimers, can be adapted to this use with modest additions and modifications. These modifications are preferably accomplished without introducing horizontal surfaces that may potentially interfere with the downward movement of the chips and cause them to"hang-up". Air distributor geometries may be selected with a mind toward minimizing the tendency for the chips to"bridge."Furthermore, the use of an array of ducts introduces only limited additional vertical surface area in contact with the bulk chip pile, minimizing any potential increase in the tendency for the chips to "bridge".

Undesired bridging of wood chips can be reduced by employing a vertical duct capable of moving vertically or rotating about its vertical axis. This may be accomplished by any suitable means, including, without limitation, a mechanism that permits vertical motion of a duct relative to its supply ducting and support. Suitable means include a sleeve/sliding mechanism. Other suitable mechanisms include hinged supply connections at one end. Vertical motion of duct may be accomplished through the force of gravity or by traction exerted on duct surfaces by surrounding solid materials. Vertical movement of duct may be achieved by forced vertical movement via hydraulic, pneumatic, or electrical mechanisms exerting vertical force on a duct sufficeint to cause vertical movement relative to surrounding solid material or relative to the containment or support structure. The forced vertical movement is preferably controlled. Optionally, the duct may be comprised of more than one vertical segment, with one or more segments being independently capable of vertical movement achieved by any suitable means.

Optionally, the vertical duct may be moveable about its vertical axis in a rotary motion. This may be achieved by any suitable mechanism that allows rotary motion of a duct relative to its supply ducting and support. For example, a sleeve/sliding mechanism is suitable for achieving rotary motion. Rotary motion of a duct may be achieved by hydraulic, pneumatic, or electrical mechanisms that exert torque on a duct sufficient to produce rotation relative to its surrounding solid material or the containment or support structure. Preferably, the mechanism permits the controlled rotary movement of the duct. The outer surface of the duct may be equipped with a helical flighting such that rotary motion of the duct causes a vertical force to be exerted on the surrounding solid material. Optionally, a duct may be comprised of more than one vertical segment, with segments being independently capable of rotary movement achieved by any suitable means.

It is specifically envisioned that the vertical ducts of the present invention may be capable of vertical motion or rotary motion, or both vertical motion and rotary motion.

Optionally, the air distribution system can be piped such that different air flow control is available at different heights within the pile. This feature will make it possible to meet the differential optimum condition requirements and release rates of heat and moisture that can occur during fungal incubation as a function of its residence time within the pile. With a downflow solid movement pattern, it may be beneficial to control different horizontal layers or zones separately.

Problems of stagnation and inlet burn that result from continuous air flow from a single inlet are represented in Fig. 3. Application of a steady air flow to the pile may result in regions of stagnation. The problem of stagnation may be reduced by periodically changing the direction of air flow. The present invention also provides more uniform average ventilation over horizontal cross-sections of the pile.

Flow switching can also reduce the incidence of inlet burn by employing a cycle phase sequence wherein no individual duct is continuously serving as an air inlet.

Periodic cycles or random time cycles of flow phases may be employed in the practice of the present invention.

An example of a suitable air duct system according to the present invention would include a rectangular array with four phases of equal duration, as represented schematically in Fig. 2. The flow of air from air inlets arranged in a rectangular array is alternated or switched between the various inlets so as to prevent stagnation and

inlet burn. In the pattern shown in Fig. 2, air flows through two adjacent air inlets designated C and D for a period of time, and then switches so that air flows from inlets C and A, such that the flow of air is at a 90 degree angle to the original flow.

Air then flows from inlets B and D for a given time interval, and then switches to inlets A and B. The proper alternation pattern would, over time, reduce stagnant regions during the individual phases. Alternation of air flow between the four ducts would also reduce inlet burn, because no one duct would continuously operate as an inlet source. As one of ordinary skill in the art will appreciate, there are several other phase sequences that may be successfully employed in the practice of the present invention. The best choice may depend on the array pattern used (e. g. rectangular or triangular pitch).

It is also envisioned that ventilation flow rate requirements may be reduced by periodically reversing the flow or switching. Reduced ventilation flow rate requirements would result in reduced operating costs.

It should be appreciated that the containment system and method of the present invention may be employed in microbial incubations of materials other than wood chips, including, but not limited to, non-woody plant material or wood waste, for example. It is envisioned that a containment system within the scope of the present invention may be optionally equipped with additional features. For example, the containment system may be equipped with a conveyor for conveying lignocellulosic material such as wood chips such that the material may be conveniently delivered to or removed from the containment system.

The system may also include a decontaminator positioned adjacent to said conveyor and capable of delivering a decontaminant onto the wood chips so as to reduce the growth of undesired contaminating organisms. By a"decontaminant"it is meant any treatment that reduces undesired growth of contaminating microorganism.

The chips may be decontaminated by any suitable method, including treatment with sulfite salts, as disclosed in U. S. Patent No 5,460,697, treating with steam at atmospheric pressure for about 10 minutes, or delivering steam onto the chips for from about 15 seconds to about 5 minutes. Preferably, the lignocellulosic materials or wood chips are treated with the decontaminant prior to inoculation with the inoculum.

In addition, an inoculator positioned adjacent to said conveyor and capable of delivering inoculum onto at least a portion of the wood chips may be used.

The present invention may employ fungal inoculum suitable for biopulping, including, but not limited to, Ceriporiopsis, Phlebia, Dichomitus, Phanerochaete, Poria, Hypodonti, a Rigidoporus, Phanerochaete (also called Sporotrichum), Trametes, Polyporus, Peniophora, or Coriolus.

The present invention is not limited to the exemplified embodiments, but is intended to encompass all such modifications and variations as come within the scope of the following claims.