IMPROVED METHODS FOR LANDFILL VOLUME REDUCTION

Abstract

Systems and methods for reducing the volume of construction and demolition (C&D) debris waste are described. The systems include a torrefaction unit that reduces the hardness of the waste while degrading it into volatiles and particles having a range of sizes. The variation in particle size allows for a more efficient compaction due to minimal void space and the imparted softness allows for increased compressibility. This results in the processed debris having a much smaller volume than had it not undergone the presently described methods, which reduces landfill tipping fees and extends the life of the landfill.

Claims

1. A method for reducing the volume of a construction and demolition debris feedstock comprising: a) separating construction and, demolition debris into a recycle stream, a reject stream, and a construction and demolition debris feedstock, b) reducing the size of said construction and demolition debris feedstock using a size reduction unit to produce a particle size distribution diameter between about 0.1 and 10 mm; c) torrefying said construction and demolition debris feedstock in a torrefaction vessel having a temperature of 100-400° C. for at least 0.5 hours, wherein said heating evaporates moisture and volatile compounds from said construction and demolition debris feedstock; d) removing said moisture and volatile compounds from said torrefaction vessel using a heated sweep gas; e) transferring said heated construction and demolition debris feedstock to a heat exchanger to produce a cooled torrefied construction and demolition debris feedstock, wherein the heat from the construction and demolition debris feedstock is used to heat the sweep gas; f) transferring the torrefied construction and demolition debris feedstock to a landfill, wherein the volume of the torrefied construction and demolition debris feedstock is reduced by at least 40% compared to an unheated construction and demolition debris feedstock.

2. The method of claim 1, wherein the torrefaction vessel is a rotary kiln or a rotary dryer.

3. The method of claim 1, wherein said size reduction unit is a grinder, a shredder, a crusher or a mill.

4. The method of claim 1, wherein said torrefaction vessel has a temperature between about 200 and about 300° C. or between about 150 and about 300° C.

5. The method of claim 1, further comprising the step of compressing the torrefied construction and demolition debris feedstock in a compactor before transferring it to the landfill.

6. The method of claim 1, wherein said sweep gas also removes ultrafine particles from the torrefaction vessel.

7. The method of claim 1, wherein the sweep gas has a flow rate of between 5 and 70 m/s or between 30 and 46 m/s or between 15 and 25 m/s.

8. The method of claim 6, wherein said volatiles include one or more low-boiling regulated air pollutants, further comprising the steps of filtering one or more low-boiling regulated air pollutants and ultrafine particles from the sweep gas using a filter to form a clean sweep gas.

9. The method of claim 8, wherein said filtering step uses at least one of an adsorbent bed, a membrane, a candle filter, and/or a bag house.

10. The method of claim 8, further comprising the step of transferring heat from said heated construction and demolition debris feedstock to the clean sweep gas using the heat exchanger, and using the heated clean sweep gas in the removing step.

11. The method of claim 1, further comprising the step of splitting said torrefied construction and demolition debris feedstock into two streams before the transferring step, wherein a first stream comprises larger particles than a second stream and is returned to the size reduction unit to undergo steps 1b to 1e one or more times and the second stream is transferred to the landfill.

12. The method of claim 1, further comprising the step of splitting said torrefied construction and demolition debris feedstock into two streams before the transferring step, wherein a first stream comprises greater than 0 to about 60% of the cooled torrefied particles and a second stream comprising the remaining cooled torrefied particles, wherein the first stream is returned to the size reduction unit to undergo steps 1b to 1e one or more times and the second stream is transferred to the landfill.

13. A method for reducing the volume of a construction and demolition debris feedstock comprising: a) separating construction and demolition debris into a recycle stream, a reject stream, and a construction and demolition debris feedstock, b) reducing the size of said construction and demolition debris feedstock using a size reduction unit to produce a particle size distribution diameter between about 0.1 and 10 mm, wherein particles greater than 5 cm are passed through the size reduction unit again; c) torrefying said construction and demolition debris feedstock in a torrefaction unit for at least 0.5 hours, said torrefaction unit having a torrefaction vessel having a temperature between 100-400° C. a filter system and a blower; d) sweeping a sweep gas through said torrefaction vessel during said torrefying step, wherein said sweep gas removes moisture, regulated air pollutants, ultrafine particles, and volatile compounds evolved from said construction and demolition debris feedstock during the torrefying step, wherein said sweep gas exits the torrefaction vessel though a vent leading to the filter system; e) removing said regulated air pollutants and ultrafine particles from said sweep gas in said filter system, wherein said filter system has at least one filter, and separating out said moisture and volatile compounds to form a reusable sweep gas, wherein said ultrafine particles are transferred to a landfill; f) transferring said heated construction and demolition debris feedstock to a heat exchanger, wherein the heat from the debris is used to warm the reusable sweep gas before it is returned to the torrefaction vessel; g) transferring the cooled torrefied construction and demolition debris feedstock to a splitter, wherein said cooled torrefied construction and demolition debris feedstock is split into a first stream and a second stream having smaller particles than said first stream; h) transferring a first stream to a landfill; and i) returning a second stream to the size reduction unit to repeat steps b-g at least one time wherein the volume of the first stream is reduced by at least 40% compared to a similar method without a torrefaction step.

14. The method of claim 13, wherein the torrefaction vessel is a rotary kiln or a rotary dryer.

15. The method of claim 13, wherein said size reduction unit is a grinder, a shredder, a crusher or a mill.

16. The method of claim 13, wherein said sweep gas is comprised of low pressure superheated steam and oxygen lean air, a low purity carbon dioxide (about 99%), or a low purity nitrogen.

17. The method of claim 13, wherein said splitter splits the cooled torrefied construction and demolition debris feedstock based on size, with the larger sizes forming said second stream.

18. The method of claim 13, wherein said splitter splits the cooled torrefied construction and demolition debris feedstock based on volume, with greater than 0% to about 60% of said cooled torrefied construction and demolition debris feedstock forming said second stream.

19-31. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1. Schematic of a typical waste processing system at a debris collection hub.

[0077] FIG. 2. Schematic of one embodiment of the present disclosure for torrefying C&D waste.

[0078] FIG. 3. Schematic of an optional gas return on the embodiment in FIG. 2.

[0079] FIG. 4. Schematic of another embodiment of the present disclosure for a waste disposal system with a return stream for torrefied solids.

DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

[0080] The disclosure describes novel systems and methods for processing C&D waste destined for landfills. Specifically, the waste undergoes at least one size reduction step and at least one torrefaction step that reduces the hardness of the debris while releasing volatiles. The more brittle particles are now readily compacted into a much smaller volume than had they not undergone the torrefaction process, which thereby conserves landfill space.

[0081] The presently disclosed systems and methods are exemplified below with respect to a transfer site treatment center or debris collection hub for C&D wastes. However, this is exemplary only, and the invention can be broadly applied to treatment processes at landfills and the treatment of other debris. The following examples and figures are intended to be illustrative only, and not unduly limit the scope of the appended claims.

[0082] FIG. 1 displays the basic pretreatment process 100 for C&D wastes at a transfer site. Transfer sites are often an intermediate stop for debris between the construction (or demolition) site and the landfill. At the transfer site, the debris 110 is first sorted by a sorting unit 101 to separate out the recyclable materials that are to be picked up by recycle agents (individuals, businesses, and/or non-profits). This recycle stream 112 can include material that could be composted (e.g. brush) or recycled (e.g. unused drywall). The sorting unit may also have metal detectors that will activate a reject trap if metal components are present. The metal can also be reused or recycled.

[0083] The remaining debris 111 may then be loaded onto a truck or other large vehicle for transfer to a landfill or undergo additional treatment (shown with dashed arrows) to reduce their volume 113 before being sent to the landfill. By reducing the volume, more material can be loaded onto the transfer truck bed and thus lowering disposal charges. The additional treatment can be as simple as compressing the material in a compactor 104. Optionally size reduction processes, such as grinding or milling, 102 and drying processes 103 may be used before compaction 104 to further aid in volume reduction. In yet another variation, the remaining debris 111 may be separated by e.g. size, with the small items being loaded directly onto a truck destined for a landfill and the larger items undergoing optional volume reduction treatments.

[0084] Trucks or other large vehicles (trains, barges, etc.) transfer the treated and untreated C&D material to a landfill, wherein disposal fees (averages tipping fees along Gulf Coast for 2017˜$8/cubic-yard) are assessed by the size of the truck bed or other container, independent from the weight of C&D waste that is present.

[0085] During normal demand, the disposal method in FIG. 1 may be adequate to process most C&D waste. However, issues arise during periods of high demand for landfill space such as post-storm recovery. Storm related C&D waste is often bulky waste that is time consuming and costly to process. As storm related C&D waste tends to be present on a much larger scale than most landfills are able to handle efficiently, piles of C&D waste are often left behind at the original site for weeks or months after the storm. Brush and other materials that are usually separated out and composted or recycled are often present in such large amounts during post-storm recovery that they are sent to landfills instead. Further, the increase in C&D waste after a storm also utilize an unanticipated amount of landfill space. This not only limits the landfill life but also increases the cost of disposal due to the high demand for landfill reserve capacity.

[0086] The presently described systems and methods were developed to address these issues. In particular, the systems described herein handle a large variation in feed streams of both large or bulky debris, and small debris that is waterlogged. Using a torrefaction unit, moisture and volatiles are removed from the debris, while increasing the fragility/brittleness of the debris. This directly impacts the ability to break the solids up, reducing average particle size and degree to which downstream solids handling will yield further increases in tapped density. Such improvements in feed stream handling lead to fewer required truckloads to transfer the now treated debris to the landfill when compared to the original, un-torrefied debris. This results in substantial cost savings related to disposal as well as reduction in land use in the landfill.

[0087] In more detail, the present systems replace the dryer 103 and compactor 104 in FIG. 1 with a torrefaction unit, and requires the size reduction unit (it is no longer ‘optional’). Torrefaction processes have been utilized for municipal solid wastes with higher carbon content. However, it has not been considered applicable for construction and demolition debris because this type of debris has a lower carbon content with large-scale, incompressible solids. The present systems utilize a torrefaction unit that was modified to allow for moisture removal from C&D waste and increase bulk density by increasing the friability of the torrefied products. To properly treat C&D waste to obtain an increase in bulk density (i.e. moisture removal, and particle size profile optimization) needed to increase landfill space conservation, a filtration system was added to the sweep gas exit of the torrefaction vessel to collect and clean vent gases. A blower system was added after the filtration system to direct vent gases away from the sweep gas inlet of the torrefaction vessel, and to create a vacuum on the torrefaction unit to adjust the sweep gas flow rate to enable the entrainment of ultrafines in the sweep gas while avoiding excessive plugging of the filtration system.

[0088] Additional modifications to the systems include heat exchangers to enable the recycling of heat from the torrefied streams, and debris streams recycled back to the size reduction unit and/or torrefaction unit for further processing of the larger particles, and optional recycle of vent gases as sweep gases.

[0089] The torrefaction vessel can be a rotary kiln or a rotary dryer that heats the debris at an elevated temperature while it is tumbling through an oxygen lean sweep gas atmosphere along the vessel. The debris is fed at the top of the vessel, where it then tumbles down the slight incline (i.e. a decline along the vessel length from vessel entrance to exit) in a spiral type fashion towards the outlet of the torrefaction vessel. During the tumbling, the debris particles are colliding into each other and the inside walls of the torrefaction vessel, which further reduce the size of the particles as they are being torrefied. Larger particles in the debris stream act as grinding material for themselves and smaller particles for further size reduction.

[0090] Attached to the vent exit of the torrefaction vessel is a filtration system for cleaning the sweep gas exiting the torrefaction vessel. The filtration unit uses at least one adsorbent bed, a membrane, a candle filter, and/or a bag house to remove low-boiling regulated air pollutants and ultrafines from the sweep gas. These filters are replaced as needed due to saturation by the pollutants or regenerated. After filtering, the ‘clean’ gas can be released as a vent gas, reused as sweep gas in the torrefaction unit, or some combination thereof.

[0091] Attached to the filtration unit is a blower. The blower serves many purposes in the present systems. The blower directs the vent gas away from the ‘clean’ sweep gas that will be recycled to the torrefaction vessel. Further, the blower creates a vacuum on the torrefaction unit by controlling the pressure profile of the sweep gas. This allows for the use of a low flow rate to enable both the entrainment of ultrafines in the sweep gas, and the reduction or avoidance of excessive plugging of the filters in the filtration system with the fines.

[0092] This torrefaction unit removes moisture and volatiles from the debris to reduce weight of the exiting material. The torrefaction process can also reduce the hardness of the debris, resulting in friable particles. For instance, the heat removes the water that forms the paste between cement and the aggregates in concrete, leaving behind voids, which reduce the compressive strength of the material. For drywall, heat breaks down the calcium sulfate-water crystal structure, which in turn increases its density; and for wood, the increased temperature causes softening and cell wall decomposition are associated with a loss of strength. When loading the particles for transferring to a landfill, the easily broken particles can be pressed together to a much greater extent than debris that did not undergo a torrefaction process. The resulting material is much smaller in volume, allowing more C&D waste to be added to each truck destined for the landfill.

[0093] A benefit of a torrefaction unit is the flexibility of the operational conditions, which allows for treatment of a waste stream with a variable composition and physical properties. Anything that is small enough to enter the torrefaction unit can be treated, regardless of composition. If longer residence times of the solids are needed, the angle of incline in the torrefaction vessel can be modified. Alternatively, the residence time can also be increased through a reduction of feed rate or by returning or looping the torrefied solids back through the size reduction unit and/or the torrefaction unit. Similarly, the removal of moisture in the feed material can be enhanced by adjusting the ratio of solids maintained in the torrefaction vessel's bed relative to the amount of sweep gas and, if steam is used in the sweep gas, the extent of superheating of the sweep gas.

[0094] The rotary action (i.e. RPM) of the torrefaction vessel described herein also provides the action that mixes the solids (in contact with the wall and each other) through the sweep gas (flowing through the center) as the debris flows in the axial direction. The volumetric gas flow rate can also be adjusted by changing the vessel temperature and/or the pressure profile established by the blower in the torrefaction unit. Such velocity increases result in improved convective transport of heat and volatiles.

[0095] All of these features can be enhanced by the use of rotary vessel internals (e.g. “flights”), which create stagewise increases in solids temperature and provide the pauses necessary to equilibrate the water concentrations (between gas and solid phases) at each section along the axial direction. Each pass through the torrefaction unit is expected to last at least 20 minutes. Preferably, the residence time is at least thirty minutes or more. Larger particles and waterlogged materials may require addition residence time to fully remove moisture and make the particles more friable. As such, repeated passes through the torrefaction unit can be utilized to achieve the longer residence times.

[0096] As mentioned above, a sweep gas passes through the torrefaction vessel. The sweep gas is an oxygen lean gas that can be selected from a group comprising a low pressure superheated steam with oxygen lean air, a low purity carbon dioxide (about 99%), a low purity nitrogen (about 99% nitrogen), or vent gas from the torrefaction unit. The sweep gas flows co-current or countercurrent to the movement of the debris. During torrefaction, the sweep gas interacts with the treated debris to help with the desorption of volatiles and moisture. At the same time, the sweep gases can entrain ultrafine particles and carry them out the torrefaction vessel's vent exit to the filtration system.

[0097] A buildup of ultrafine particles creates a dust explosion risk anywhere they are exposed to oxygen and come in contact with an ignition source. Therefore, ultrafines are continuously filtered from the sweep gas using the filtration system. The flow rate for the sweep gas is kept below a velocity threshold to keep the solids in contact with the torrefaction vessel surface yet avoid entraining too many of the fines fraction in the filter. This velocity threshold varies with the composition of the feed stream, and can be between 5 m/s and about 70 m/s, or between 10 and 50 m/s, or between 15 and 30 m/s or between 40 and 50 m/s. For cement or concrete predominant feeds, flow rates between about 30 and about 46 m/s are expected to keep the solids in contact with the vessel and remove ultrafines. Other feed such as wood particles, flow rates can be between about 20 and about 25 m/s.

[0098] FIG. 2 displays one embodiment 200 of the presently disclosed system. This particular embodiment is a single pass torrefaction process. Additional embodiments describe optional processes for looping the torrefied solids through the size reduction and/or torrefaction unit (shown in FIG. 4) or reusing the vent gas as part of the sweep gas (shown in FIG. 3).

[0099] As before in FIG. 1, the waste 110 is first sorted at 101 to remove the recyclable material 112 and/or reject metal containing debris. The material that remains 111 will then undergo processing using a torrefaction unit in the presently described methods.

[0100] The debris will travel through a feeder 201 before undergoing a size reduction step 102 to reduce the size of the material before it is fed to a torrefaction unit. Unlike the system in FIG. 1, the size reduction step is no longer optional, even if the size of the debris is not an issue. Rather, running all debris through the size reduction unit will improve the moisture removal efficiency of the torrefaction unit saving operating cost (less torrefaction residence time). Further, processing the debris though the size reduction unit forms newly exposed surfaces on the debris, which facilitates the desorption of moisture and volatiles. The size of the debris after grinding is a function of the feed material, the mechanism used to reduce the size, and the settings of the size reduction unit. However, most particles can be reduced by a factor of 2 to 10. Preferably, the reduction factor is 5 to 6.

[0101] The size reduction unit can be any unit onsite or commercially available unit. Typically, these units incorporated grinders, shredders, mills or crushers to reduce the size of debris. In some embodiments, a grinder or shredder is preferred. The Terminator Series of Grinders from Komptech Americas, for instance, is capable of reducing the size of most debris by a factor of at least 5.

[0102] After being reduced in size, the materials are sent to a torrefaction vessel 202. In some embodiments, a screen (not shown) may be located between the size reduction unit and the torrefaction unit to prevent overly large debris from entering the torrefaction unit, while allowed smaller debris through. In this instance, the size reduction unit will process the large debris again until the debris reaches the desired size.

[0103] This torrefaction vessel 202 can have a rotary kiln or rotary dryer that heats the material at a low temperature while the materials are tumbling towards a side exit. In some embodiments, the torrefaction unit is a rotary kiln with either direct or indirect firing. Ideally, the temperature range is between about 100 and 400° C. Alternatively, the temperature can be between about 200 and 300° C. or between about 150 and about 300° C.

[0104] A sweep gas consisting of oxygen lean gas 210 flows through the torrefaction unit where it can continuously contact the moving, tumbling debris. Though shown as flowing co-current to the material in FIG. 2, either a co-current or countercurrent flow is acceptable. In some embodiments, a co-current gas flow is preferred as it is easier to maintain the temperature gradient across the fire door(s) that seals the entry points for the torrefaction vessel. The sweep gas can be heated in a heat exchanger 210 using heat derived from torrefied solids.

[0105] During the torrefaction process, moisture and volatiles are desorbed from the debris. The moisture and volatiles are entrained in the sweep gas, which sweeps them through an overhead exit out of the torrefaction unit to the filtration system 203. Ultrafines particles are also entrained in the gas. The vent gas and volatiles 211 are then filtered and separated in a filtration system 203. The filter mainly cleans the gas by adsorbing low-boiling regulated air pollutants (e.g. sulfur, chlorine or chloride, and cyanides) and the ultrafines. Filters typically included for such processes at landfill and transfers stations include adsorbent beds, membranes, candle filters, and/or bag houses, and any one or more of these are appropriate in the present system as well.

[0106] After filtering, the gas enters a blower 204 attached to the filtration system 203. In the system described by FIG. 2, the blower creates a vacuum on the torrefaction unit by controlling the pressure profile of the sweep gas. This allows for the use of a low flow rate to enable both the selective entrainment of ultrafines in the sweep gas, and the reduction or avoidance of excessive plugging of the filters in the filtration system with the larger size particles). After passing through the blower, the ‘clean’ vent gas is can be released. Alternatively, some of the vent gas can be returned to the torrefaction vessel as part of the sweep gas, as shown in FIG. 3 and described below. Recycling or looping the clean vent gas is preferred as it saves energy costs associated with the torrefaction unit, such as making fresh superheated steam from a boiler unit or supply fresh gas.

[0107] The size of the solids leaving the side exit of the torrefaction vessel is a mixture of coarse particles (particle diameter greater than 5 mm), mid-size particles (particle diameter between greater than 1 mm and 5 mm), and fine particles (particle diameter between greater than 100 microns to 1 mm). The rotary action of the torrefaction vessel combined with axial transport and torrefaction temperature provide an abrasive environment such that particles wear each other down as they tumble. The size of the solids leaving the torrefaction unit is a mixture that depends on the feed content, initial particle size distribution, and any looping through the size reduction unit. In general, however, the exiting material will be about 20% by volume of coarse particles, about 20% by volume fines (not including ultrafines removed by the sweep gas), and medium size particles making up the balance.

[0108] After the torrefaction process, the torrefied solids 212 are transferred to a heat exchanger 205 such as a double pipe, plate and frame heat exchanger, or shell and tube. This exchanger allows the torrefied solids to cool (213) before being collected in a truck destined for a landfill. The heat transferred from the solids is used to heat the sweep gas 210 being used in the torrefaction unit.

[0109] The particles being collected for transfer will be compressed by overbearing solids of the load in the truck to reduce their volume. The smaller particles, or fines, will fill the void space between coarser particles, thus allowing for more material to occupy a smaller volume. With the combined grinding/devolatilization processing of the present system, the reduction of volume is much larger than that of grinding and drying alone. This, in turn, means that more debris can be placed on the truck and/or less space is needed at the landfill. Further, as the debris is being placed on the truck, the particles can further break due to increase friability from the torrefaction process.

[0110] The reduction in volume will depend on the type of debris (e.g. cement does not reduce as much or as easily as drywall), the moisture content (waterlogged materials are not as compressible unless repeatedly recycled through the torrefaction unit), the settings on size reduction unit, the settings on the torrefaction unit (temperature, residence time, etc), and the settings on the blower. As such, the reduction in volume of debris can be anywhere from 20-90%. For construction debris such as cement or concrete, a volume reduction of about 20-40% after torrefaction is preferable.

[0111] FIG. 3 displays a variation of the embodiment in FIG. 2, wherein the vent gas exiting the blower is returned to the torrefaction unit. The first part of the process in FIG. 2 remains the same, but is not shown in detail in FIG. 3. In FIG. 3, the vent gas is separated into two streams by a valve 304: a stream that is vented or released into the environment 311a and a vent stream 311b that will be combined with fresh oxygen lean gas and reused. While 100% of the vent stream can be recycled as 311b, the purge of 311a is needed to address impurity build up in the sweep gas. For example, moisture or organic chemicals may build up in the gas exiting the filtration system, creating an unsafe environment in the torrefaction vessel if 100% of the gas was returned as sweep gas. As such, 40 to 50% of the gas may be released as 311a, with the remaining 50-60% being combined with fresh gas. Thus, 0 to about 50% of the gas can be purged as 311a, with the remaining gas being recycled as 311b. Both the vent stream 311b and fresh oxygen lean gas steam 313 are then heated in the heat exchanger 305 that cools the torrefied solids. If the sweep gas is steam based, then the preferred temperature is about 30 degrees above its dewpoint before entering the torrefaction unit. Looping the ‘clean’ sweep gas is preferred as it saves energy costs associated with using “fresh” gas and the heat needed to heat the fresh gas.

[0112] If the size of the particles exiting the torrefaction unit is too large, the solids may need to be passed through the size reduction unit again before undergoing the torrefaction process. One embodiment of the presently disclosed system having this return stream for the torrefied solids is shown in FIG. 4. The torrefied solids can be passed through the size reduction units and/or torrefaction unit one or more times to further reduce the size of the solids, increase the amount of moisture removed, and further break down the material.

[0113] In more detail, the torrefied solids are cooled in the heat exchanger 205 as before. However, they are then separated using a splitter 401, with some of the solids moving forward to the truck 411 destined for a landfill, and the remaining solids are returned to the size reduction unit (R2) or the torrefaction unit (R1).

[0114] For any of the above embodiments, the conditions of the torrefaction unit can be adjusted to address any combination of C&D waste. One with skill in the art would know how to make such adjustments based on the material exiting the torrefaction unit compared to the initial feedstock. From there, process conditions such as torrefaction residence time, torrefaction temperature profile, sweep gas flow rate, or split fraction can be adjusted to change the properties of the outgoing material.

[0115] To evaluate the presently described methods, a shelved, sealed laboratory oven was used to torrefy typical C&D debris in batches. The C&D solids were deposited in single particle layers on the shelves with nitrogen gas flowing horizontally over each shelf. This design allowed the oven to model a rotary unit whose solids layer have good contact with sweep gas. Three different C&D materials with a range of particle sizes (fine to coarse) were chosen to represent a wide variety of C&D waste, and evaluate different features of the torrefaction process (ability to remove moisture, ability to remove organics, ability to soften particles). The C&D materials were Loblolly Pine, Oriented Strand Board (OSB), and concrete.

[0116] Loblolly Pine. The first C&D material evaluated comprised Loblolly Pine (branches, leaves, bark). Loblolly Pine has a moisture content of about 55% and was selected as a feed stream to evaluate the ability to treat waterlogged wood-based material that also have naturally occurring volatile organic compounds. Such combination would be similar to wood-based C&D wastes from storm recovery efforts.

[0117] The Loblolly Pine was chipped and then ground using a hammer mill to a ‘coarse’ fraction (>4.74 mm) and a ‘fines’ fraction (<4.74 mm). Both fractions were evaluated independently to capture process performance data as a function of particle size effects (e.g. heat and mass transport limitations). Additional evaluations were performed on mixtures of both fractions.

[0118] The fractions were torrefied at 150° C. for 1 hour followed by 2 hours at 220° C., torrefied at 150° C. for 3 hours, and torrefied at 150° C. for 1 hour followed by 0.5 hours at 220° C. Table 1 displays the moisture content as well as the bulk (loose packing) and tapped (tight packing) density of both fractions before and after torrefaction.

[0119] Comparisons of bulk and tapped density represent the packing density associated with a given sample of solids and the extent to which voids in the sample can be filled with smaller particles. For a given moisture level, the tapped density is larger than the bulk density. Comparison of the densities for the coarse and fine fraction relates to solids composition differences as well as the extent to which moisture and volatiles have been removed from the particles.

TABLE-US-00002 TABLE 1 Moisture and density content of Loblolly Pine before and after torrefaction Solids Before Torrefaction Solids After Torrefaction Tapped Tapped Moisture Bulk Density Moisture Bulk Density (wt. %) Density (kg/m.sup.3) (wt. %) Density (kg/m.sup.3) Run 1A) Torrefied at 150° C. for 1 hour followed by 2 hours at 220° C. Coarse 55.5 326.5 378.7 0.0 166.0 183.0 Fine 56.2 267.2 329.3 0.8 136.7 162.4 Run 1B) Torrefied at 150° C. for 3 hours Coarse 57 326.5 378.7 1.4 179.2 213.3 Fine 53.9 267.2 329.3 0.0 155.9 169.3 Run 1C) Torrefied at 150° C. for 1 hour followed by 0.5 hours at 220° C. Coarse 56.0 326.5 378.7 −0.1 190.5 206 Fine 55.8 267.2 329.3 1.4 173.2 179.7

[0120] The density data in Table 1 shows that the process removes mass more efficiently for the fines fraction than the coarse. Fines have a smaller particle diameter and a larger surface area to volume ratio, thus heat transfer is more efficient. This is further shown by a comparison of Run 1A and 1B. Both of these runs had a three hour total residence time; however, the higher target temperature in Run 1A removed a larger amount of volatiles, resulting in lower final particle densities than Run 1B.

[0121] Table 2 displays the measured hardness of both the coarse and fine Loblolly Pine fractions before and after torrefaction. The hardness was determined by using a set ball mill procedure to grind equal-volume samples (e.g. fresh or torrefied pine) at a fixed RPM using a fixed amount of prescribed grinding media for a specified grinding time. A comparison of the relative decrease in particle size (represented here by Δd50/d50) corresponds to a decrease in hardness. The larger this value, the more brittle the material has become.

TABLE-US-00003 TABLE 2 Hardness of Loblolly Pine before and after torrefaction Solids Before Torrefaction Solids After Torrefaction d50 d50H Δd50/ d50 d50H Δd50/ (mm) (mm) d50* (mm) (mm) d50* Run 1A) Torrefied at 150° C. for 1 hour followed by 2 hours at 220° C. Coarse 14.45 6.64 0.54 12.51 2.57 0.79 Fine 2.30 1.775 0.23 1.90 0.76 0.60 Run 1B) Torrefied at 150° C. for 3 hours Coarse 14.45 6.64 0.54 12.15 3.33 0.73 Fine 2.3 1.775 0.23 2.1 1.12 0.47 Run 1C) Torrefied at 150° C. for 1 hour followed by 0.5 hours at 220° C. Coarse 14.45 6.64 0.54 12.325 3.09 0.75 Fine 2.3 1.775 0.23 1.97 0.92 0.53 *Δd50/d50 = (d50 − d50H)/d50

[0122] As shown in Table 2, both the coarse and fine fractions of the Loblolly Pine show a reduction in hardness caused by torrefaction. The torrefied coarse fractions, for example, have Δd50/d50 values of 0.79 (Run 1A), 0.73 (Run 1B), and 0.75 (Run 1C), which is much larger than the untorrefied value of 0.54. Similar results are seen for the fine fractions (0.60 (Run 1A), 0.47 (Run 1B), and 0.53 (Run 1C) are larger than 0.23). Thus, the present process was able to remove moisture and increase the friability of both coarse and fine particles of Loblolly Pine. In combination with the changes in densities shown in Table 1, the torrefaction process resulted in both removing mass (density reduction caused largely by moisture removal) and reduction in particle size (density increase by 2 mm decrease).

[0123] Table 3 shows case study calculations based on the results shown in Tables 1 and 2 to determine the overall performance of torrefaction as a function of feed particle size distribution (psd) and operating conditions. Regarding operation conditions, adjustments to the temperature or residence time only will allow a user to achieve the desired volume reduction. The results for the torrefaction at 220° C. for 30 minutes produced similar results to torrefaction at lower temperatures for 3 hours. Thus, adjusting the temperature is on par with the results longer residence times. The tradeoff is the cost of operating the system at higher temperatures. Alternatively, one could install/configure a larger torrefaction vessel or a return loop such as that shown in FIG. 4 to achieve the longer residence times. If both longer residence time and high temperatures are used, as is the case for the samples torrefied at 220° C. for 2 hours, even greater reductions in volumes can occur.

TABLE-US-00004 TABLE 3 Reduction in volume of mixed Loblolly Pine feed stream Torrefied at Torrefied at 150° C. for 1 150 C. for 1 kg kg hour followed Torrefied at hour followed Case Coarse Fines by 2 hours 150° C. by 0.5 hours Study per kg per kg at 220° C. for 3 hours at 220° C. No. Feed Feed m.sup.3 exit/m.sup.3 feed m.sup.3 exit/m.sup.3 feed m.sup.3 exit/m.sup.3 feed 1 0.8 0.2 0.57 0.50 0.56 2 0.9 0.1 0.50 0.44 0.50 3 0.7 0.3 0.42 0.38 0.42 4 0.6 0.4 0.36 0.32 0.36

[0124] Oriented Strand Board. The second C&D material evaluated comprised Oriented Strand Board (OSB), which is a type of engineered wood similar to particle board that is formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations. OSB has a relatively low moisture content of about 3%, but a high added organic chemical content (e.g. woody biomass with chemical organic additives).

[0125] The OSB was purchased from a hardware store and ground using a hammer mill to a coarse fraction (>4.74 mm) and a fines fraction (<4.74 mm). As with the Loblolly Pine, both fractions were tested independently to capture process performance data as a function of particle size effects (e.g. heat and mass transport limitations), under the same torrefaction condition. Table 4 displays the moisture content as well as the bulk (loose packing) and tapped (tight packing) density of both fractions before and after torrefaction. Despite the low level of the initial moisture content, Runs 2A and 2C were not able to remove all the moisture. It is hypothesized that some transport limitation held back the water in the solid phase since the additional residence time (RUN 2B v. Run 2C) yields a dryer solid.

TABLE-US-00005 TABLE 4 Moisture and density content of OSB before and after torrefaction Solids Before Torrefaction Solids After Torrefaction Tapped Tapped Moisture Bulk Density Moisture Bulk Density (wt. %) Density (kg/m.sup.3) (wt. %) Density (kg/m.sup.3) Run 2A) Torrefied at 150° C. for 1 hour followed by 2 hours at 220° C. Coarse 3.8 156.1 177.6 1.8 163.4 178.9 Fine 3.7 159.4 215.6 1.3 175.8 221.1 Run 2B) Torrefied at 150° C. for 3 hours Coarse 2.9 156.1 177.6 0.1 165.6 179.7 Fine 3 159.4 215.6 0.0 183.9 211.2 Run 2C) Torrefied at 150° C. for 1 hour followed by 0.5 hours at 220° C. Coarse 2.6 156.1 177.6 0.9 154 175.5 Fine 3.1 159.4 215.6 0.4 164.2 204.2

[0126] Table 5 displays the measured hardness before and after torrefaction, using the comparison of the relative decrease in particle size (Δd50/d50). As with the Loblolly Pine, the hardness was determined by using a set ball mill procedure to grind equal-volume samples (e.g. fresh or torrefied pine) at a fixed RPM using a fixed amount of prescribed grinding media for a specified grinding time. The increase in this index (Δd50/d50) shows that hardness does decrease; however, the change is less than in the Loblolly Pine.

TABLE-US-00006 TABLE 5 Hardness of OSB before and after torrefaction Solids Before Torrefaction Solids After Torrefaction d50 d50H Δd50/ d50 d50H Δd50/ (mm) (mm) d50* (mm) (mm) d50* Run 2A) Torrefied at 150° C. for 1 hour followed by 2 hours at 220° C. Coarse 9.21 5.13 0.44 9.54 3.85 0.60 Fine 1.43 1.29 0.10 1.47 0.95 0.35 Run 2B) Torrefied at 150° C. for 3 hours Coarse 9.21 5.13 0.44 8.67 4.21 0.51 Fine 1.43 1.29 0.1 1.45 1.19 0.18 Run 2C) Torrefied at 150° C. for 1 hour followed by 0.5 hours at 220° C. Coarse 9.21 5.13 0.44 8.97 3.54 0.61 Fine 1.43 1.29 0.1 1.42 1.03 0.27 *Δd50/d50 = (d50 − d50H)/d50

[0127] Table 6 shows a case study calculation based on the results shown in Tables 4 and 5 to determine the overall performance of torrefaction as a function of feed particle size distribution (psd) and operating conditions. For Case Study No. 1, the relative densities for this combination of coarse and fines resulted in a total volume exceeds 1. Thus, at least 0.2 kg fines per kg of total feed would be needed to obtain efficient packing and optimal torrefaction transport.

TABLE-US-00007 TABLE 6 Reduction in volume of mixed OSB feed stream Torrefied at Torrefied at 150° C. for 150° C. for 1 hour 1 hour followed by Torrefied at followed by kg kg 2 hours at 150° C. for 0.5 hours at Case Coarse Fines 220° C. 3 hours 220° C. Study per kg per kg m.sup.3 exit/m.sup.3 m.sup.3 exit/m.sup.3 m.sup.3 exit/m.sup.3 No. Feed Feed feed feed feed 1 0.8 0.2 1.05 1.05 1.03 2 0.9 0.1 0.95 0.95 0.93 3 0.7 0.3 0.85 0.84 0.82 4 0.6 0.4 0.74 0.73 0.71 5 0.5 0.5 0.63 0.62 0.60

[0128] As discussed above, OSB was chosen to evaluate the volatilization of organic compounds, and their removal in the vent stream. According to the MSDS for OSB, this material can contain between 1 and 14 wt % of a phenol-formaldehyde resin, a compound used to glue wood particles together. Based on this information, a Flame Ionization Detector (FID) was used to compare the Residence Time profile of vent gases dissolved in condensate generated from the oven vent gases for both the Pine Loblolly and the OSB. As shown in Table 7, the organic profiles for Pine Loblolly and OSB show peaks in common and others only associated with one material. In both materials, the torrefaction system can be designed and operated to separate the solids form the volatiles, which can then be collected by the filters in the filtration system.

TABLE-US-00008 TABLE 7 FID Results of condensate generated from the oven vent gases for both the Pine Loblolly and the OSB wt % of Organic Fractions, Residence Time 2 hr of Torrefaction at 220° C. minutes Pine OSB Coarse 5.717.sup.3 × × 7.015 × 7.022 × 9.402 × 9.775 × 10.497 × 11.510.sup.2 × 12.038.sup.1 × 13.291 × × 17.862 × 20.899 × × 22.510 × 24.554 × 26.687 × .sup.1Furfural .sup.2Formic Acid dimer .sup.3Formic Acid

[0129] Concrete. The third C&D material evaluated comprised concrete. Concrete is a large volume component of C&D waste, and represents a large fraction of storm debris that ends up in landfills even though recycling methods for concrete exist. During recycling methods, metal rebar is first removed from the concrete followed by filtering out dirt and sand. A crushing step then converts the various shapes and sizes into saleable grades of aggregate material. In this case, the “provenance” of the solids are known (e.g. roads, foundations, buildings, drainage structures) when they arrive at a concrete recycling plant. When storm/flood concrete debris is sent to DCH, there is no information about the water quality that corresponds to the moisture content and the degree to which the pH and other cement compound chemistry have changed. In contrast to Loblolly Pine and chemically treated wood products, concrete is an inorganic material with no fixed carbon to speak of and densities an order of magnitude higher. Thus, concrete undergoes often only undergoes a size reduction and optional compaction before being transferred to landfills.

[0130] For the present evaluations, 3″ and 1″ minus samples from sorted material at a Concrete Recycling Facility feed were obtained and further sieved into coarse fraction (>4.74 mm) and a fines fraction (<4.74 mm), similar to the prior feeds.

[0131] Table 8 displays the moisture content of both coarse and fine streams before and after torrefaction takes place, as well as their bulk (loose packing) and tapped (tight packing) density. According to the “Before” results, this material represents an intermediate case (6 to 10%) between the OSB and Loblolly Pine levels of moisture. With removal of moisture, the bulk density concrete changes depending on the run conditions. The final tapped densities, however, are all smaller than those corresponding to the “Before” column. In contrast to Tables 1 and 4, Run 3C yielded the lowest densities. As a result, an additional run was performed, Run 3D (150° C. for 1 hour). However, these results were even lower with not all of the moisture being removed.

TABLE-US-00009 TABLE 8 Moisture and density content of Concrete before and after torrefaction Solids Before Torrefaction Solids After Torrefaction Tapped Tapped Moisture Bulk Density Moisture Bulk Density (wt. %) Density (kg/m.sup.3) (wt. %) Density (kg/m.sup.3) Run 3A) Torrefied at 150° C. for 1 hour followed by 2 hours at 220° C. Coarse 6.4 1387.4 1606.1 0.0 1408.4 1482.0 Fine 10.3 1281.1 1554.7 0.0 1373.7 1468.1 Run 3B) Torrefied at 150° C. for 3 hours Coarse 6.8 1387.4 1606.1 0.0 1305.2 1456.0 Fine 11 1281.1 1554.7 0.0 1357.5 1513.8 Run 3C) Torrefied at 150° C. for 1 hour followed by 0.5 hours at 220° C. Coarse 7.3 1387.4 1606.1 0.0 1291.1 1438.9 Fine 11 1281.1 1554.7 0.1 1382.2 1453.7 Run 3D) Torrefied at 150° C. for 1 hour Coarse 6.6 1387.4 1606.1 0.1 1261.7 1343.3 Fine 10.0 1281.1 1554.7 0.2 1379.4 1420.4

[0132] Table 9 reports the results for volume reduction as represented by Δd50/d50. As before, the hardness was determined by using a set ball mill procedure to grind equal-volume samples (e.g. fresh or torrefied pine) at a fixed RPM using a fixed amount of prescribed grinding media for a specified grinding time. Table 9 shows that the hardness of the coarse concrete fraction was unaffected by torrefaction while the fines fraction becomes about 20% more brittle.

TABLE-US-00010 TABLE 9 Hardness of Concrete before and after torrefaction Solids Before Torrefaction Solids After Torrefaction d50 d50H *Δd50/ d50 d50H *Δd50/ (mm) (mm) d50 (mm) (mm) d50 Run 3A) Torrefied at 150° C. for 1 hour followed by 2 hours at 220° C. Coarse 17.84 1.39 0.92 16.46 1.165 0.93 Fine 3.86 1.13 0.70 3.12 0.32 0.87 Run 3B) Torrefied at 150° C. for 3 hours Coarse 17.84 1.39 0.92 15.72 0.79 0.95 Fine 3.86 1.13 0.71 3.04 0.33 0.89 Run 3C) Torrefied at 150° C. for 1 hour followed by 0.5 hours at 220° C. Coarse 17.84 1.39 0.92 16.34 1.045 0.94 Fine 3.86 1.13 0.71 3.25 0.39 0.88 Run 3D) Torrefied at 150° C. for 1 hour Coarse 17.84 1.39 0.92 17.25 1.43 0.92 Fine 3.86 1.13 0.71 3.10 0.41 0.87

[0133] Table 10 shows a case study calculation based on the results shown in Tables 8 and 9 to determine the overall performance of torrefaction as a function of feed particle size distribution (psd) and operating conditions.

TABLE-US-00011 TABLE 10 Reduction in volume of mixed Concrete feed stream Torrefied at 150° C. Torrefied for 1 at 150° C. hour Torrefied for 1 hour followed at followed Torrefied by 2 150° C. by 0.5 for 1 hrs kg kg hours at for 3 hours at at Case Coarse Fines 220° C. hours 220° C. 150° C. Study per kg per kg m.sup.3 exit/ m.sup.3 exit/ m.sup.3 exit/ m.sup.3 exit/ No. Feed Feed m.sup.3 feed m.sup.3 feed m.sup.3 feed m.sup.3 feed 1 0.8 0.2 0.96 0.95 0.95 0.88 2 0.9 0.1 0.85 0.85 0.83 0.78 3 0.7 0.3 0.75 0.74 0.73 0.69 4 0.6 0.4 0.64 0.64 0.62 0.59 5 0.5 0.5 0.53 0.53 0.52 0.5

[0134] Thus, for the concrete fed, the final density after torrefaction depended on both water removal and particle size. The hardness of the fines stream was reduced by 20% while the coarse fractions' hardness remained unchanged by the torrefaction conditions. This result is different from that obtained using Loblolly Pine and OSB. In both Loblolly Pine and OSB, the coarse particle diameter decreased by the same amount before and after torrefaction. However, additional cycles through a size reduction unit and increases in torrefaction residence time or temperature will improve the hardness for the coarse concrete.

[0135] Thus, the ability to torrefy C&D debris to reduce moisture content and hardness while collecting air regulated pollutant were exemplified with respect to a shelved oven. Though the above experiments focused on batch data using an oven, not a rotary system, the data can be extended to describe the behavior in a continuous process. For example, the length of time at the target temperature is equivalent to residence time in the rotary system; the length of the commercial torrefaction vessel is equal to the solids axial transport velocity (solids feed rate divided by the area of the vessel cross-section) multiplied by the residence time. The temperature profile for the oven as a function of time scales to length by multiplying the solids axial velocity by the residence time at different temperatures. As such, similar results are expected with commercial size equipment and torrefaction vessels with moving beds such as rotary kilns and dryers. The economically optimum setting for the torrefaction vessel will require an evaluation of the tradeoff between residence time and temperature for this process and debris under consideration.

[0136] A benefit of the currently described systems and methods is that lower volumes of treated debris at a DCH translate into fewer trips to the landfill, saving both cost and space. As exemplified by the treatment of the three materials described above, the reduction in volume after torrefaction avoids having to permit additional disposal sites in storm-prone coastal communities.

[0137] The following references are incorporated by reference in their entirety.

[0138] US20110278384

[0139] US20170190975

[0140] US20180072955