Systems and methods for managing and utilizing excess corn residue

Systems and methods for managing excess above-ground corn residue are disclosed. Systems and methods for combusting corn residue to produce heat for generating steam are also disclosed. Additionally, methods and systems for harvesting and pre-processing corn residue prior to combustion of the corn residue are disclosed.

TECHNICAL FIELD

The present disclosure relates generally to systems and methods for using biomass as fuel for generating power.

BACKGROUND

Above-ground corn residue (i.e., corn stover) typically is considered to include the corn stalks, leaves, husks and cobs remaining in the field after the corn grain (i.e., the kernels of grain) has been harvested. In accordance with traditional agricultural practices, many corn growers choose to leave above-ground corn residue on their fields for the purpose of maintaining soil fertility and organic content. Corn growers that also raise cattle often use corn residue as a feed source for the cattle. For example, the corn residue can be grazed as forage, or baled and used as fodder or bedding. Corn residue has also been considered for use in the production of cellulosic ethanol and has further been considered for use as a fuel source that can be co-fired with coal in coal fired burners where coal is the primary fuel.

SUMMARY

One aspect of the present disclosure relates generally to systems and methods for assisting high yield corn growers in their effort to effectively manage excess corn residue while concurrently generating power from the excess corn residue.

Another aspect of the present disclosure relates to systems and methods for effectively harvesting and baling corn residue, and for effectively using such harvested corn residue as a primary fuel source in a steam generation facility.

Examples representative of a variety of inventive aspects are set forth in the description that follows. The inventive aspects relate to individual features as well as combinations of features. It is to be understood that both the foregoing general description and the following detailed description merely provide examples of how the inventive aspects may be put into practice, and are not intended to limit the broad spirit and scope of the inventive aspects.

DETAILED DESCRIPTION

Traditionally, corn growers have managed their corn residue by tilling the corn residue into the soil after the grain has been harvested. Traditional wisdom teaches that tilling the corn residue back into the soil is necessary to maintain the nutrient value and organic content of the soil. Thus, it has generally been believed that tilling the corn residue back into the soil helps the soil support increased yields and reduces the amount of artificial fertilizers and soil conditioners that need to be applied to the fields.

The total biomass of a corn plant includes the corn grain, the above-ground corn residue, and the underground root system. Generally, the corn grain represents about one-third of the total biomass of a corn plant, the above-ground corn residue represents another one-third of the total biomass of the corn plant and the root system represents the final one-third of the total biomass of the corn plant. A bushel of corn grain can be assumed to weigh about 56 pounds. This being the case, for each bushel of corn grain, 56 pounds of above-ground corn residue is also produced.

Advancements in farming technology have resulted in significantly increased corn grain yields per acre. With ever increasing corn grain yields, the total amount of corn residue per acre has also increased. Increased levels of corn residue have presented problems for today's farmers. For example, high levels of corn residue can jam or clog tillage equipment thereby preventing the corn residue from being effectively plowed back into the field. Moreover, the soil cannot readily accept and decompose the large amounts of corn residue that results from today's increased corn yields. As a result, corn residue is not uniformly integrated and broken down into the soil which can result in slow or uneven field warming. Also, excessive amounts of corn residue in the soil can delay germination due to slower water absorption caused by inadequate soil to seed contact. Moreover, chemicals leaching from crop residue can delay early crop growth. The above problems associated with excessive corn residue can interfere with a corn grower's ability to maximize yields. Therefore, for high-yield corn crops, it is believed that removing a significant portion of the excess corn residue from the corn grower's fields will result in higher yields without negatively impacting the long term productivity of the soil. For example, research has shown that under certain conditions, removing about half of the above-ground corn residue from the field can provide as much as a 13 bushel per acre increase in the corn grain yield which also results in approximately an additional 728 pounds per acre of extra above-ground corn residue.

The present disclosure relates to methods and systems that can help corn growers effectively solve their excess corn residue problems while concurrently being compensated for their excess corn residue. The present disclosure also provides methods and systems that benefit the community at large by providing power from a bio-renewable fuel source while simultaneously creating local jobs.

FIG. 1is a flow chart illustrating a wide-scale method for managing and utilizing excess above-ground corn residue in accordance with the principles of the present disclosure. The method starts with a first step10where a particular facility site location is identified. A number of factors should be considered when identifying an appropriate site location. For example, a suitable site location should be in close proximity to a high density of high-yield, corn-on-corn acres. As used herein, the term “high-yield” corn acres means corn acres providing a grain yield of at least 180 bushels of corn grain per acre. Corn-on-corn acres are acres where corn is repeatedly planted in successive years. It is preferred for there to be at least 880,000 acres of high-yield, corn-on-corn acres within a service area of the selected site location. Referring toFIG. 2, a site location12is shown within a service area14having a 30 mile radius in which 880,000 acres of high-yield corn-on-corn acres are located. In a most preferred embodiment, the 880,000 acres of high-yield corn within the service area14provide an average grain yield of at least 190 bushels of corn grain per acre. It is believed that utilizing 50 percent of the above-ground corn residue present on 4 percent of the 880,000 acres of high yield corn within the service area will provide a source of biomass fuel that is sufficiently large to allow the facility to operate continuously for one year. This represents about at least 174,000 tons of corn residue based bio-fuel per year. By building the site location12in close proximity to a large amount of high-yield corn, the site location12is positioned in close proximity to a large source of bio-fuel in the form of excess corn residue. The close proximity of the bio-fuel allows bio-fuel transportation costs to be minimized thereby enhancing the cost effectiveness of the overall system.

It is also significant for the site location12to be in close proximity to a market having a stable demand for electricity. This generally means that the site location is relatively close to larger population centers which provide a stable demand for electricity thereby keeping the price of electricity stable. In certain embodiments, the site location12is chosen so that electricity generated at the site location12can be sold on the PJM market or a like market for electricity.

Once a site location has been identified, the second step20of the method ofFIG. 1includes constructing a combustion and steam generation facility13(seeFIG. 3) at the site location12for pre-processing and combusting excess corn residue harvested/collected from the service area14. The facility13can include a combustion and steam generation station15. The combustion and steam generation station15can be referred to as a combustion and steam generation unit, island, arrangement, or like terms. The combustion and steam generation station15can include a furnace for combusting corn residue and a boiler that uses combustion heat from the furnace to generate steam. The facility can also include a steam turbine generator17(i.e., a steam turbine that cooperates with an electrical generator) to convert heat energy from the steam into electrical energy. Alternatively, the steam could be used for other applications. For example, the steam could be used in a cellulosic or grain ethanol production process or other processes using process steam.

It is preferred for the furnace of the combustion and steam generation station15to be configured to combust corn residue as a primary fuel. Of course, the furnace can include a source of supplemental heat such as natural gas burners that would typically be used at furnace start-up and shut-down operations. However, it is preferred for corn residue to be the primary (i.e., the main fuel) fuel burned in the furnace during normal operations between start-up and shut-down. In certain embodiments, corn stover is the only fuel burned in the furnace for certain periods of time. In other embodiments, a mixture including corn stover as a primary component and another fuel source (e.g., waste seed) as a secondary component can be burned in the furnace.

The facility13further can further include a pre-processing station19including a storage lay-out for providing storage of some of the harvested corn residue on site. In certain embodiments, the storage lay-out can include a short-term staging area21within a pre-processing building for holding the corn residue immediately before pre-processing, and an outside back-up storage area23for storing a back-up supply of corn residue (e.g., a one week supply of corn residue which typically would constitute at least 3400 bales that each weigh 1250 pounds). The back-up supply ensures that the facility13can continue to operate for a predetermined period of time in the event that weather or other factors interfere with the continuous supply of corn residue to the facility. The pre-processing station19can include processing equipment27within the pre-processing building for pre-processing (e.g., shredding) the corn residue prior to combustion.

Referring still toFIG. 3, the facility13can include a reclamation station25that provides a buffer between the pre-processing station19and the combustion and steam generation station15for staging the pre-processed corn residue in an enclosed space for a limited time prior to feeding the pre-processed corn residue into the furnace of the combustion and steam generation station15. The reclamation station25allows the pre-processing station19to be operated for set durations of time per day (e.g., 8-10 hours) while the combustion and steam generation station15is operated continuously. When the pre-processing station is operated, the rate at which the pre-processed corn residue is produced exceeds the rate at which the combustion and steam generation station15consumes the corn residue. Thus, the excess pre-processed corn residue generated by the pre-processing station19is stock-piled at the reclamation station25. The amount of corn residue stock-piled at the reclamation station25is sufficient for the combustion and steam generation station15to operate continuously over the time period in which the pre-processing station19is shut-down.

The facility13preferably further includes pollution abatement equipment. For example, the facility13can include equipment (e.g., mechanical filters, mechanical separators such as cyclonic separators, precipitators, or other structures) for removing particulate material such as fly ash from the exhaust stream generated by the facility. The facility can also include a selective non-catalytic reduction (SNCR) system to reduce the concentration of nitrogen oxides (NOx) in the exhaust emissions. Further, the facility can also include an acid gas control system for neutralizing acid gases present in the exhaust emissions.

Referring back toFIG. 1, the third step30of the depicted method involves contracting with corn growers in the service area14to harvest excess corn residue on their behalf. Typically, the facility operator will enter into multi-year contracts (e.g., three year, five year, etc.) with the corn growers with regard to harvesting of the excess above-ground corn residue. The amount of corn residue harvested may vary from corn grower to corn grower. For example, some corn growers may contract to have all of the corn residue on a given acreage harvested and removed from the field by the facility operator. However, many of the corn growers in the service area may elect to have only a portion of their corn residue harvested and removed from the field. The amount of corn residue that can be harvested is typically dependent upon the yield of the corn crop at issue. For high-yield corn acreages having a yield equal to 180 bushels per acre or more, it is preferred for the contract to specify that at least 50% of the above-ground corn residue can be harvested by the facility operator. In typical applications, 40% to 60% of the corn residue can be sustainably harvested without reducing soil productivity. This being the case, depending upon the yields of the corn crop at issue, the amount of corn residue contracted to be harvested could typically be in the range of 2.25-2.5 tons per acre.

It will be appreciated that the time period for harvesting the corn residue is rather short and limited generally to one to two months. This being the case, it is preferred for the contract to require the corn grower to notify the facility operator when the corn grower intends to harvest the grain and when the grower has actually harvested the grain. Also, the contract can require the corn grower to provide the facility operator with information relating to the corn crop (e.g., current moisture content of the corn grain, current moisture content of the corn stover). The above information allows the facility operator to efficiently plan when the above-ground corn residue can be harvested. The contract may also require the corn grower to make available a predetermined amount of the corn grower's acreage for storage of the harvested corn residue by the facility operator. The time period specified for storage of the harvested corn residue on the corn grower's property may range from 1 to 12 months.

At the fourth step40of the method ofFIG. 1, the facility operator harvests the excess corn residue on the corn grower's behalf. It is preferred for the corn residue to have a moisture content in the range of about 10-15 percent at the time the corn residue is harvested. The moisture content of the corn residue affects the efficiency at which the corn residue is combusted. If the corn residue is too moist, the British Thermal Unit (BTU) value of the corn residue drops. In contrast, energy transfer rates reduce if the corn residue is too dry. Therefore, it is often desirable for the excess corn residue to remain in the field for a predetermined amount of time after the grain has been harvested before the excess corn residue is harvested. In this way, the excess corn residue is allowed to dry to the desired level in the field due to the effects of wind, sun, and low relative humidity. Once the corn residue reaches the desired moisture content, the corn residue is harvested.

The initial moisture content data provided to the facilitator operator by the corn grower at the time the grain is harvested can provide a rough estimate as to how long the excess corn residue should remain drying in the field prior to being harvested. Moisture testing can be conducted to anticipate/predict the appropriate time at which the corn residue can be harvested. The corn residue can be tested for moisture content by inserting moisture testing probes at a plurality of locations along the lengths of a plurality of stalks, and then averaging the results. Alternatively, a number of pieces of residue (e.g., stalk, leaves, cobs) can be reduced in size (e.g., shredded) and placed in a pile, and the moisture testing probes can be used to determine the moisture content at different locations within the pile. The different moisture readings taken for the pile can be averaged to determine the overall moisture content of the corn residue.

It will be appreciated that a significant amount of harvesting will need to be completed by the facility operator in a relatively short amount of time. To accomplish this harvesting, harvesting equipment, (e.g., shredders, windrowers, balers, accumulators) can be short term leased by the facility operator. Also, third parties can be hired as independent contractors working under the supervision of the facility operator for conducting the corn residue harvesting operations.

Once the corn residue in the contracted corn grower's field dries to the desired moisture content, the corn residue can be harvested by the facility operator. At shown atFIG. 4, the harvesting process can utilize a shredder/windrower250pulled by a tractor252. The shredder/windrower250has a main housing251having a length that extends between first and second ends247,249. The shredder/windrower250defines a centerline257that bisects the housing251and is perpendicular to the length of the housing251. The centerline257extends generally along a direction of travel of the shredder/windrower250. The shredder/windrower250has a discharge chute253positioned at the first end247of the housing251. The end positioning of the chute253allows two passes across a given field to be piled into a single windrow255(i.e., a combined windrow). The shredder/windrower250can include a cutting mechanism such as cup cutters256(i.e., cup knives) mounted on a rotating carrier258such as a drum or shaft rotatable about an axis of rotation260. The cutting mechanism is mounted within the housing251. The shredder/windrower250can also include a cross-conveyor such as a cross auger262mounted within the housing251for conveying corn residue cut by the cup cutters256laterally along the length of the housing251to the end discharge chute253. One or more paddles255can be mounted on the carrier258for discharging the corn residue rearwardly out the discharge chute253. The shredding/windrowing operation preferably is undertaken when the moisture content of the corn residue is in the range 10-15 percent.

For baling purposes, it is desirable for the combined windrow to have a width w less than about 42 inches and a fairly constant/uniform height across the width of the combined windrow. To achieve such a combined windrow, it is desirable for the corn residue collected from the second pass across the field to be piled at least partially on top of the windrow from the first pass. Preferably, this is accomplished without riding over a portion of the first windrow which can cause balling and overall disruption of the windrow. To allow the second windrow to be piled over the first windrow, it is desirable for the discharge chute253to be adjustable to cause the corn residue to be discharged at least partially in a lateral direction outwardly from the first end247of the housing251. In certain embodiments, the first windrow can be deposited directly behind the shredder/windrower and the second windrow can be discharged from the chute in a direction extending at least partially laterally outwardly from one end of the shredder/windrower so that the second windrow can be piled at least partially over the first windrow.

FIGS. 4A-4Dshow various configurations for adjusting the discharge stream directed from a shredder/windrower.FIG. 4Ashows a shredder/windrower250ahaving a discharge chute253aincluding inner and outer guides264,265that can be pivoted about vertical axes266,267relative to respective inner and outer walls268,269of the chute253a. Once pivoted to a desired position, the guides264,265can be secured in place (e.g., with fasteners, clamps, etc.). The guides264,265can be oriented parallel to the centerline257or angled relative to the centerline257. When the guides264,265are angled away from the centerline257, material discharged from the chute253amoves in a direction angled laterally outwardly away from the centerline257.

FIG. 4Bshows a shredder/windrower250bhaving a discharge chute253bincluding inner and outer walls270,271. A guide272is pivotally attached to the inner wall270. The guide272can be angled relative to the centerline257so that material discharged from the chute253bmoves in a direction angled outwardly away from the centerline257. The guide272can also be oriented so that the chute253bdischarges material in a rearward direction parallel to the centerline157.

FIG. 4Cshows a shredder/windrower250chaving a discharge chute253cincluding inner and outer walls273,274. A blocking plate275is slidably attached to the inner wall273. The blocking plate275can slide along a slide orientation that is transverse relative to the centerline257to vary the discharge area of the chute253c. By moving the blocking plate275away from the centerline257along the slide orientation and securing the blocking plate275in place, the discharge area of the chute153cis made narrower. Also, because the adjustment is made at the inner wall273as compared to the outer wall274, the outside edge of the windrow formed from the chute253cis moved away from the centerline257. The smaller width of the chute253copening combined with the positioning of the outer wall274of the chute opening253cin close proximity to the outer end of the shredder/windrower250cassists in making a narrower combined windrow because two relatively narrow windrows can be deposited side-by-side with minimal gaps thereinbetween.

FIG. 4Dshows a shredder/windrower250dhaving a discharge chute253dincluding inner and outer walls280,281. One or both of the walls280,281can be moved relative to the main housing of the shredder/windrower150dto control a direction in which the corn stover is discharged form the chute250d. By moving the walls280,281about vertical pivot axes, the walls280,281can be moved to orientations angled toward the centerline257, parallel to the centerline257or away from the centerline257.

It is desirable for the shredding/windrowing operation to be controlled such that the amount of corn residue harvested from a given acreage corresponds to the contracted amount. To control the amount of residue harvested, the shredder/windrower250can be set at different cutting heights, with lower cutting heights corresponding to more tons of corn residue harvested per acre and higher cutting heights corresponding to fewer tons of corn residue harvested per acre. In certain embodiments, the cutting heights can range from 2 inches to 20 inches. In preferred embodiments, the cutting heights are in the range of 8 to 15 inches or 6-12 inches.

During the harvesting process, it is desirable to minimize the dirt and other debris present in the windrows. Corn growers prefer as much soil as possible to remain in their fields. Also, increased soil content in the harvested corn residue can dilute the value of the fertilizer that results as a by-product from processing the corn residue. Further, the weight attributable to excess dirt in the corn residue increases transportations costs. Moreover, excess dirt in the corn residue can make bales made from the corn residue more difficult to handle with equipment such as accumulators since the bales tend to slide less easily.

During windrowing, the rotation of the cup cutters256creates a vacuum effect that assists in drawing corn residue and also dirt up into the windrower250. In this regard, the amount of dirt collected is dependent upon the height the corn residue is cut during windrowing/shredding. Higher cuts result in less dirt in the windrowed corn residue while lower cuts result in more dirt in the windrowed corn residue. The amount of dirt in the windrowed corn residue can also be controlled by varying a tilt angle of a tow bar of the windrower250.

The amount of vacuum generated by the cup cutters256is directly dependent upon the speed at which the cup cutters256are rotated about the axis260. It is therefore desirable to control the rotational speed of the cup cutters so that corn residue is effectively carried to the horizontal conveyor without also carrying excessive amounts of dirt/soil. Typically, a tractor power take-off operates at a rotational speed ranging between about 900-1100 rotations-per-minute (RPM) and the power input shaft of the windrower250is driven by the power take-off at a 1-to-1 ratio. The power input shaft of the windrower drives rotation of the rotating carrier258. Under conditions where excessive dirt collection is an issue (e.g., low cuts, dry conditions), the operator can operate the tractor so as to minimize the rotational speed of the power take-off. For example, the tractor can be operated such that the power take-off speed is less than 1000 RPM or less than 950 RPM. By lowering the power take-off speed, the rotational speed of the cup cutters256is lowered thereby lowering the vacuum effect of the cup cutters256

In certain embodiments, a rotation speed adjustment mechanism (e.g., a gear box or variable speed transmission) can be used to allow the rotational speed of the rotating carrier158to be adjusted to match a given application. The rotation speed adjustment mechanism can be provided at some point between the power take-off and the rotating carrier158or can be provided at the tractor to adjust the rotation speed of the power take-off. In this way, when it is desirable to provide a low cut in dry conditions, the rotation speed adjustment mechanism can be used to lower the rotational speed of the rotating carrier158to a desired level. Also, for high cut applications, the rotation speed adjustment mechanism can be used to increase the rotational speed of the rotating carrier158to a desired level which may allow the tractor to be operated at higher ground speeds.

It is desirable for the shredder/windrower250to shred the corn residue to an average length having a target range of 3-12 inches. In certain embodiments, the corn residue output from the windrower150to the windrow255has been shredded to an average length having a target range of 6-9 inches. Shredding the corn residue to a desired length assists in subsequently producing bales having a desired size and degree of compaction.

After the shredding and windrowing operation has been completed, the corn residue in the windrows255is preferably baled (seeFIG. 5). In the baling operation, it is preferred to create rectangular bales166so as to facilitate handling and stacking. In preferred embodiments, the bales can be about 3 feet by 4 feet by 8 feet. To encourage water shedding and to minimize handling and transportation costs, it is preferred for the bales166to be relatively dense. In a preferred embodiment, the bales166have a compacted density of at least 13 pounds per cubic foot. In certain embodiments, the bales166can have a weight in the range of 1,000-1,500 pounds, or a weight in the range of 1,100-1,400 pounds, or a weight of about 1,200 to 1,300 pounds. The above weights and compaction rates are applicable for bales formed by corn residue having a moisture content of about 10 percent. In one embodiment, the bales166are held together by at least six wraps of plastic twine168having a tensile strength of at least 450 pounds. In other embodiments, other sized rectangular bales (e.g., 4×4×8 foot) or even round bales could be used.

FIG. 5shows a baler400being pulled behind a tractor402along one of the windrows255. As shown atFIG. 5, the baler400has compacted a portion of a windrow into a plurality of bales166. The baler includes a throat404that is preferably wider than the windrow255. A rotatable pick-up mechanism406is positioned in the throat404for picking up the corn residue and carrying the corn residue to a set of screw conveyors408which move the corn residue into a central compaction chamber410. In the compaction chamber410, the corn residue is compacted into a rectangular bale and then wrapped with twine. The finished bale166is discharged out a back of the baler400.

Referring toFIGS. 5 and 5A, the rotatable pick-up mechanism406includes a shaft412that is rotated about a central axis414. A plurality of radial tines416(e.g., fingers, wires, members, etc.) are carried by the shaft412about the central axis414as the shaft412is rotated. The tines416are rotated in a direction which causes the corn residue to be picked-up by the tines416and carried over the top of the shaft412to the screw conveyors408. Positioning the pick-up mechanism406too close to the ground can lead to tine breakage. However, when the pick-up mechanism406is elevated, the pick-up mechanism402is unable to pick-up a lowermost layer of the corn residue. Leaving a sizable layer of corn residue in the windrow can be problematic for corn growers practicing no-till farming since the layer can interfere with effective seed planting and germination. Also, leaving corn residue in the windrows reduces the overall corn residue harvest. To overcome this problem, the baler400can include an air assist system420for assisting the pick-up mechanism406in picking up the bottom layer of corn residue in a windrow. The air assist system420can include an air directing arrangement (e.g., one or more air knives, air nozzles, etc.) that directs a stream or streams of air under the pick-up mechanism406thereby causing the bottommost layer of corn residue in the windrow to be lifted up by the air into the path of the rotating tines416of the pick-up mechanism406. In this way, the pick-up mechanism406can be positioned elevated above the ground while still being able to pick up the bottommost layer of corn residue in the windrow255.

After the baling process has been completed, the bales are collected and stacked at a temporary storage location on the corn grower's field. The space corresponding to the temporary storage location may be leased from the corn grower for a specified time period as part of the contract with the corn grower.

The bales can be collected and stacked using an accumulator device.FIG. 6shows an example accumulator170including a vehicle172supporting an angled bed174and a front lift mechanism176. In use of the accumulator170, the accumulator170is driven across the field and the front lift mechanism176is used to lift bales over the top of a cab178of the vehicle onto the angled bed174. To pick up a given bale, it is not necessary to stop movement of the vehicle. Instead, the bale is picked up on the fly and lifted over the cab178to the angled bed174. The bale then slides down the angled bed to a stop to provide room for additional bales. Once a predetermined number of bales has been accumulated on the bed174, the accumulator170returns to the temporary storage location on the corn grower's field where the bales are slid off of the angled bed174to the storage location and stacked at the storage location.

At the fifth step50of the method ofFIG. 1, the bales are transported from the temporary storage locations on the corn grower's fields to the combustion and steam generation facility. Preferably, the bales remain stored on the corn grower's fields until the bales are needed for combustion at the facility13. Thus, the bales can be transported from the corn grower's fields and immediately/directly delivered to the pre-processing station19for pre-processing without any intermediate off-site storage of the bales. In this way, the amount of time and energy spent in handling and transporting the bales is minimized. In cases where storage on the corn grower's field is not an option, the bales can be transported to an off-site storage location where the bales are temporarily stored until the bales are needed for combustion at the facility site.

At the sixth step60of the method ofFIG. 1, the baled corn residue at the combustion and steam generation facility13is processed to produce power and useful by-products such as ash.FIG. 7is an outline that provides an overview of the sequence of operations that are conducted at the facility13. At step70, the bales are pre-processed (e.g., reduced such as by shredding) at the pre-processing station19. After being pre-processed at the pre-processing station19, the pre-processed corn residue is conveyed to the reclamation station25(see step72) where the pre-processed corn residue is piled in a stock-pile. Thereafter, the pre-processed corn residue is conveyed from the reclamation station19to the combustion and steam generation station15and is combusted (see step74). The heat from the combustion of the pre-processed corn residue is used to produce steam (see step76) which is used to generate electricity (see step78). A combustion exhaust stream resulting from combustion of the corn residue is treated by pollution abatement equipment (see step80) prior to being discharged to atmosphere. Fly ash in the exhaust stream is collected (see step82) and sold (see step84).

FIGS. 8 and 9show the pre-processing station19ofFIG. 3in more detail. The pre-processing station19includes a pre-processing building90housing one or more reducing machines92and the short-term staging area21. The short-term staging area21generally provides enough space to store 250-350 bales each weighing about 1250 pounds. The reducing machine92includes an in-feed conveyor93that feeds the bales into a reducing assembly94. The reducing assembly includes one or more rotatable reducing units96(e.g., drums, rotors, shafts) that carry a plurality reducing elements97(e.g., teeth, blades, flails, etc.) for breaking apart the bales and for reducing the average size of the corn residue components forming the bales. A screen99can be provided for controlling the size of the pieces of corn residue that exit the material reducing machine92. The screen99at least partially surrounds the rotatable reducing units96and forms a reducing chamber in which the rotatable reducing units99are positioned. In one embodiment, the reducing machine92grinds the corn residue forming the bales such that the pieces of corn residue exiting the material reducing machine92have an average length less than 3 inches. It is also preferred for the corn residue exiting the grinders to have no more than 25 percent material that is less than 0.25 inches in length. The material reducing machine92deposits the reduced corn residue on a discharge conveyor100that carries the reduced corn residue to an elevated conveyor102. The elevated conveyor102carries the reduced corn residue from the pre-processing building90to the reclamation station25.

Referring toFIG. 8, the pre-processing station19includes a truck routing path104that extends through the building90so that trucks carrying bales from the corn grower's fields can unload the bales directly onto the in-feed conveyor93or into the short-term staging area21in the event the in-feed conveyor93is full. The truck-routing path has a straight pass-through configuration through the building90. A truck scale can be provided at the pre-processing station19for determining the weight of each truck's load before the bales are unloaded. The weights can be used to determine how much each corn grower should be compensated pursuant to the contract with the facility operator.

The back-up storage area23of the pre-processing station19is divided between two dedicated areas immediately outside the building90. As described above, the corn residue is preferably continuously supplied to the pre-processing station19during operation of the pre-processing station19by delivering the baled corn residue to the pre-processing station19directly from the storage locations on the individual corn grower's fields. Therefore, it is anticipated that poor weather conditions or extremely wet fields may limit access to the corn residue on the corn grower's fields for periods of time. To address this issue, the back-up storage area23provides enough on-site storage of corn residue to allow the facility to continue to operate over the worst-case anticipated period of time (e.g., 1 week) in which the field stored corn residue can not be accessed.

As described previously, the reclamation station25provides an enclosed location for stockpiling the reduced corn residue that is ultimately fed to the combustion and steam generation station15. In one embodiment, the reclamation station25is configured to stage (e.g., stockpile, store, accumulate) at least 1000 tons of reduced corn residue.

FIGS. 10 and 11show the reclamation station25ofFIG. 3in more detail. Referring toFIG. 10, the reclamation station25includes a storage building110having a length L and a width W. An elevated in-feed conveyor112extends along the length L of the reclamation building110along the ceiling of the reclamation building110. The in-feed conveyor112receives the reduced corn residue from the elevated conveyor102that extends between the pre-processing station19and the reclamation station25. The in-feed conveyor112is used to fill the reclamation storage building110along its length. Over-the-pile reclaimers114are located at one end of the building110. The reclaimers114are used to move the reduced corn residue stored within the reclamation storage building110to an out-feed conveyor116. The out-feed conveyor116carries the reduced corn residue to a conveyor130that extends from the reclamation station25to the combustion and steam generation station15. As shown atFIG. 11, each reclaimer114includes a conveying structure118(e.g., a drag chain or belt) oriented in a continuous loop about a reclaimer boom120that pivots about a pivot axis122. Each conveying structure118is rotated in a direction of rotation124about its corresponding reclaimer boom120. The reclaimer booms120are movable about the pivot axes122between raised, upwardly angled positions126, and lowered positions128(see in dashed line).

In use, the reclaimers114are initially positioned in the raised positions126above a pile of reduced corn residue stored within the storage building110. To unload stored reduced corn residue from the storage building110, the reclaimers114are pivoted downwardly from the raised position while the conveying structures118are rotated in the direction of rotation124. As the reclaimers114are moved downwardly, the conveying structures118engage the pile of corn residue and drag the corn residue down the pile laterally along the width W of the building110to the out-feed conveyor116. Once the reclaimers114reach the lower positions128such that all of the corn residue previously stored thereinbeneath has been loaded onto the out-feed-conveyor116, the reclaimers114are raised back to the raised position126and corn residue piled at the opposite end of the building is pushed along the length L of the pre-processing building210to the area beneath the reclaimers114. In certain embodiments, equipment such as a front end loader is used to push the corn residue beneath the claim conveyors218. Thereafter, the reclaimers114can again be pivoted from the raised position126to the lowered position128to unload the corn residue pushed beneath the reclaimers114.

FIGS. 12 and 13show an alternative reclamation conveyor arrangement for the reclamation station25. The alternative reclamation conveyor arrangement includes two over-the-pile reclaimers140that cooperate to extend across the width W of a reclamation storage building142. The reclaimers140each include a continuous conveying structure144that loops about a boom146that pivots about an axis148. The conveying structures144are rotated in directions150,152about their corresponding booms146. The reclaimers140pivot about the axes148between raised orientations154where the reclaimers140are angled upwardly and lowered orientations156where the reclaimers140are generally horizontal and adjacent to the floor of the building142. An in-feed conveyor arrangement158extends along the length L of the building142and is mounted adjacent the top of the building142. The in-feed conveyor arrangement158receives the reduced corn residue from the elevated conveyor102that extends between the pre-processing station19and the reclamation station25. Out-feed conveyors160extend along the length L of the building142and are located adjacent the pivot axes148of the reclaimers140. The out-feed conveyors160carry the reduced corn residue to a conveyor130that extends from the reclamation station19to the combustion and steam generation station15. In certain embodiments, the reclaimers140can be mounted on a track162or other structure that allows the reclaimed conveyors to travel (e.g., to be indexed) along the length L of the building142.

In operation of the reclamation building142, the building142is initially filled with reduced corn residue via the elevated in-feed conveyor arrangement158. To unload corn residue piled beneath the reclaimers140, the reclaimers140are pivoted downwardly from the raised orientations154while the conveying structures144are rotated in directions150,152about their respective booms146. As the reclaimers140are lowered, the conveying structures144contact the corn residue piled beneath the reclaimers140causing corn residue to be dragged downwardly and laterally across the width of the building142toward the out-feed conveyors160. As the reclaimers140are gradually moved downwardly, the material beneath the reclaimers140is conveyed to the out-feed conveyors160at the sides of the building142. Once the reclaimers140reach the lower orientations156, the reclaimers140are raised back to the raised orientations154and then are indexed or otherwise moved by a transport drive arrangement along the tracks162to a position where the reclaimers140are oriented above reduced corn residue that had been previously loaded into the building142by the in-feed conveyor arrangement158. The reclaimers140are then lowered to move the next batch of reduced corn residue to the out-feed conveyors160. It will be appreciated that the above indexing and unload sequence can be repeated to progressively move the reclaimers140along the entire length L of the reclamation building142. In this way, the entire storage region of the building142can be unloaded without requiring movement of the stored corn residue within the building142by supplemental equipment such as a front end loader.

FIG. 14shows the combustion and steam generation station15ofFIG. 3and the steam turbine generator17ofFIG. 3in more detail. The combustion and steam generation station15includes a furnace300where corn residue is combusted to produce combustion heat used for generating steam at a boiler302. Steam from the boiler302drives a steam turbine303of the steam turbine generator17. The turbine303powers an electrical generator305which produces electricity that can be sold. A substation315is used to step-up the voltage of the electricity generated by the generator305before the electricity is sold.

The furnace300of the combustion and steam generation station15can include a stoker including a vibrating grate304on which the corn residue desired to be combusted is distributed. Combustion air can be directed into the furnace300at a location311beneath the grate304such that the combustion air flows upwardly through the grate304during combustion of the corn residue. A fan307can be used to draw warmed combustion air from a building309housing the furnace300to utilize waste heat generated by the furnace300. The combustion air can also be pre-heated by a heat exchanger310through which exhaust gas from the furnace300passes. The vibrating grate304of the stoker can be sloped and is vibrated for auto cleaning. Ash generated by the combustion of corn residue is discharged from a discharge end of the stoker grate304to an ash hopper306. A conveyor discharges the ash from the hopper to a disposal container308.

An upper combustion region/volume312is provided above the stoker grate304for combusting suspended fuel particles and combustible gases. Air/gas can be injected into the upper combustion region312at nozzles314. The air/gas can be in the form of ambient air or re-circulated exhaust from the furnace300or combinations thereof. Fans316,318can be used to move the ambient air and/or the re-circulated exhaust.

The corn residue can be delivered to the grate304by a fuel distribution system320that receives reduced corn residue from a fuel metering arrangement322. The fuel metering arrangement322receives the corn residue from the conveyor130that extends from the reclamation station25to the combustion and steam generation station15. The fuel metering arrangement feeds the corn residue down chutes to the fuel distribution system320. The fuel distribution system320can include a pneumatic system that uses a stream of gas/air to carry/blow the corn residue across the top of the grate304. The gas/air for the fuel distribution system320can be provided by a fuel distributor air fan324that delivers ambient air to the furnace300, or by a flue gas recirculation fan326that re-circulates furnace exhaust gas back to the furnace300. It will be appreciated that the air/gas sources can be used alone or in combination. The corn stover fuel fed into the furnace preferably is a mixture of corn stover pieces having a composition including an average piece length less than 3 inches with no more than 25 percent by weight being less than 0.25 inches in length. In one embodiment, the corn stover fuel fed into the furnace is a mixture of corn stover pieces having a composition including at least 75 percent by weight that is less than 3 inches in length and no more than 25 percent by weight that is less than 0.25 inches in length.

Injecting the re-circulated exhaust gas back into the furnace300, as described above, can assist in controlling NOxemissions. The system can also include a NOxremoval station354for treating the furnace exhaust. The NOxremoval station can utilize anhydrous ammonia to reduce NOxto nitrogen and water.

The boiler302of the combustion and steam generation station15receives hot exhaust gas from the furnace300and uses heat from the furnace exhaust to generate steam. The boiler302includes a plurality of steam tubes330that extend from a mud drum332to a steam drum334. Steam from the steam drum334is super heated at a superheater336. Heat of combustion from the furnace300is utilized to evaporate water in the steam tubes330such that steam is provided to the steam drum334, and is also used to superheat the steam in the superheater336. As shown atFIG. 14, hot exhaust output from the furnace300flows into the boiler300. In the boiler, the exhaust gas initially flows across the superheater336and then flows across the steam tubes330. Superheated steam from the superheater336is conveyed to the steam turbine generator17. Specifically, the superheated steam is directed to the steam turbine303which powers the electrical generator305. After passing through the steam turbine303, the steam is passed through a condenser (e.g., cooling towers) and then routed in a closed path back through a deaerator and a heat exchanger338to the mud drum332. The heat exchanger338uses heat in the furnace exhaust gas exiting the boiler302to preheat the feed water before the feed water enters the mud drum332. Make-up water can be fed into the closed system through the deaerator. The make-up water is preferably routed through a purification system prior to entry into the closed system.

In certain embodiments, the boiler is capable of continuously generating 190,000 pounds per hour to 220,000 pounds per hour of steam while operating at a pressure of 900 pounds per square inch gauge (psig) at the superheater outlet and a temperature of 900 degrees Fahrenheit steam temperature at the superheater outlet. In certain embodiments, the boiler is operated at a pressure of 800-1,000 psig, or 850-950 psig, or around 900 psig at the superheater outlet. Also, in certain embodiments, the output steam from the superheater outlet has a temperature of 800-1,000 degrees Fahrenheit, or 850-950 degrees Fahrenheit, or about 900 degrees Fahrenheit.

Corn residue has relatively high concentrations of alkali and alkaline-earth elements (e.g., potassium, phosphorous, sodium, magnesium, and calcium). Corn residue also has a high concentration of amorphous silica. This provides an increased potential for a high degree of ash deposition within the boiler (e.g., on the boiler tubes, superheater and other structures of the boiler). Deposition layers formed on the components of the boiler insulate the boiler components thereby negatively affecting the heat transfer efficiency of the boiler. Ash deposition rates are dependent upon exhaust temperature. In this regard, it has been determined that ash deposition rates resulting from the combustion of corn residue are manageable if the furnace300is operated such that the furnace300target furnace exit gas temperature (FEGT) is preferably less than 1800 degrees Fahrenheit, and more preferably less than 1700 degrees Fahrenheit. The FEGT is the temperature of furnace exhaust gas which exits the furnace300through a furnace outlet340and enters the boiler302. In certain embodiments, the FEGT is in the range of 1,400 to 1,800 degrees Fahrenheit. In a preferred embodiment, the FEGT is in the range of 1,400 to 1,700 degrees Fahrenheit. Soot blowers can also be used to help remove ash deposits.

Upon exiting the boiler302, the furnace exhaust gas can pass through the heat exchanger310to preheat the combustion air being fed into the furnace300below the stoker grate304. From the heat exchanger310, the exhaust gas passes through an ash removal component342. In a preferred embodiment, the ash removal component includes a cyclonic particulate separator that removes ash from the exhaust gas stream by centrifugal action and discharges the ash through an ash outlet343. The exhaust gas exits the particulate removal component342at an exhaust outlet and passes through the heat exchanger338where heat from the exhaust gas is used to preheat the feed water being routed from the condenser through the deaerator to the mud drum332. An acid treatment station347is provided downstream from the heat exchanger338for neutralizing acid (e.g., hydrochloric acid) in the exhaust stream by the addition of a base material (e.g., sodium bicarbonate). An induced flow fan344is positioned downstream from the acid treatment station347for pulling the exhaust flow through the system such that a slight vacuum is provided at the furnace300.

Downstream from the fan344is a re-circulated air access location346where a portion of the exhaust gas is diverted from the exhaust stream and re-circulated back to the furnace300. As shown in the depicted embodiment, the diverted exhaust gas can be directed to the pneumatic fuel distribution system320. In this way, the recirculated air is injected into the furnace300above the stoker grate as part of the fuel delivery process. The diverted exhaust gas can also be injected into the furnace300through the nozzles314provided at the upper combustion region312. A precipitator348is downstream from the re-circulated air access location346. The precipitator348functions to precipitate fly ash as well as material neutralized at the acid treatment station346. The precipitated material is collected in hoppers. A conveyor can be used to move the ash collected at the particulate removal component342and the precipitate material collected at the precipitator to an ash collection silo350. From the precipitator348, the exhaust can be directed to an outlet stack356

It has been determined that the ash has considerable nutrient value that makes it suitable for use as a fertilizer. The primary constituent of the ash includes a silica based compound (e.g., SIO2). Silica based compounds typically constitute over 30% of the ash. Additionally, potassium based compounds (e.g., K2O) can constitute at least 30% of the ash, phosphorus based compounds (e.g., PTO5) can constitute at least 5% of the ash and carbon based compounds can constitute at least 5% of the ash. Other chemicals present in the ash include Al2O3, Fe2O3, TiO2, CaO, MgO and Na2O. In certain embodiments, the collected fly ash is conveyed to a pelletizer352(e.g. pelletizing mill) where the ash is compacted into pellets. The pellets can be sold in bulk or bagged and sold as fertilizer or soil additive.

It is also possible to co-fire the above-ground corn residue in the furnace302with a secondary fuel source. For example,FIG. 14shows an optional secondary fuel source360for delivering a secondary fuel to the fuel metering arrangement322. Preferably, the above-ground corn residue remains the primary fuel source with a smaller amount of the secondary fuel being mixed with the above-ground corn residue. In certain embodiments, the secondary fuel has a higher BTU value than the above-ground corn stover. An example of a higher BTU value secondary fuel comprises excess or waste seed (e.g., corn seed, soybean seed, etc.) from a seed company. In certain embodiments, the waste seed can be chemically treated seed that has been treated with a pesticide, a fungicide or another type of chemical treatment. The blended fuel resulting from the mixture of corn stover with the secondary fuel preferably has an average piece length less than 3 inches with no more than 25 percent by weight being less than 0.25 inches in length. In certain embodiments, the blended fuel mixture has a composition including at least 75 percent by weight that is less than 3 inches in length and no more than 25 percent by weight that is less than 0.25 inches in length.

The above specification provides examples of how certain aspects may be put into practice. It will be appreciated that the aspects can be practiced in other ways than those specifically shown and described herein without departing from the spirit and scope of the present disclosure.