VACUUM-ASSISTED BULK MATERIAL TREATMENT

Abstract

A bulk material comprising at least one substance to be removed from the bulk material is treated. The method includes introducing the bulk material into a heating chamber. The heating chamber is in a partial vacuum. The method further includes heating the bulk material in the heating chamber and in the presence of the partial vacuum to cause the at least one substance to vaporize. The method further includes extracting the bulk material, with the at least one vaporized substance separated therefrom, from the heating chamber.

Claims

1. A method of treating a bulk material comprising at least one substance to be removed from the bulk material, comprising: introducing the bulk material into a heating chamber, wherein the heating chamber is in a partial vacuum; heating the bulk material in the heating chamber and in the presence of the partial vacuum to cause the at least one substance to vaporize; and extracting the bulk material, with the at least one vaporized substance separated therefrom, from the heating chamber.

2. The method of claim 1, wherein the bulk material comprises soil.

3. The method of claim 1, wherein the at least one substance comprises a contaminant.

4. The method of claim 2, wherein the contaminant comprises at least one hydrocarbon.

5. The method of claim 1, wherein the at least one substance comprises water.

6. The method of claim 1, wherein the heating chamber at a pressure of 10-20 kPa.

7. The method of claim 1, wherein introducing the bulk material into the heating chamber comprises: loading the bulk material into an airlock; with the bulk material in the airlock, generating a partial vacuum in the airlock; and transferring the bulk material from the airlock to the heating chamber.

8. The method of claim 1, wherein heating the bulk material comprises heating the bulk material using electric heating.

9. The method of claim 8, wherein heating the bulk material comprises heating the bulk material using inductive heating.

10. The method of claim 1, further comprising condensing the at least one vaporized substance.

11. The method of claim 10, wherein condensing the at least one vaporized substance comprises: transferring the at least one vaporized substance from the heating chamber to a cooling structure; and condensing the at least one vaporized substance on the cooling structure.

12. The method of claim 11, wherein the cooling structure comprises at least one cooling plate over which a coolant is flowed, or a heat exchanger comprising one or more conduits through which a coolant is flowed.

13. The method of claim 1, wherein: the at least one vaporized substance comprises at least one vaporized contaminant; the method further comprises: condensing the at least one vaporized contaminant into a condensate on a cooling plate on which is flowing a coolant; and separating the condensate into: the condensed contaminant; the coolant; and particulate matter entrained in the condensate.

14. The method of claim 12, wherein the coolant is water.

15. The method of claim 12, wherein the method further comprises: cooling at least some of the coolant; and recirculating the cooled coolant to the cooling plate.

16. A thermal desorption system for treating a bulk material comprising at least one substance to be removed, comprising: an airlock for receiving the bulk material; a heating chamber connected to the airlock; a condensing chamber; one or more vacuum pumps for generating a partial vacuum in the airlock and the heating chamber; one or more heaters in the heating chamber for heating the bulk material when the bulk material has entered the heating chamber from the airlock to cause the at least one substance to vaporize; and one or more vapor ducts positioned to direct the at least one vaporized substance from the heating chamber to the condensing chamber, wherein, by causing the at least one substance to vaporize, the one or more heaters are configured to cause a pressure in the heating chamber to be higher than a pressure in the condensing chamber and thereby produce a pressure differential to passively transfer the at least one vaporized substance from the heating chamber to the condensing chamber via the one or more vapor ducts.

17. The thermal desorption system of claim 16, further comprising one or more controllers comprising circuitry and configured to: activate the one or more vacuum pumps to generate the partial vacuum in the airlock and the heating chamber; operate the airlock to transfer the bulk material from the airlock to the heating chamber; activate the one or more heaters to heat the bulk material when the bulk material has entered the heating chamber from the airlock, and cause the at least one substance to vaporize; and extract the bulk material, with the at least one vaporized substance separated therefrom, from the heating chamber.

18. The thermal desorption system of claim 16, wherein the one or more heaters comprise one or more inductive heaters.

19. The thermal desorption system of claim 16, further comprising: one or more conveyors in the heating chamber positioned to receive the bulk material from the airlock and to transport the bulk material to an outlet of the heating chamber.

20. The thermal desorption system of claim 16, wherein: the thermal desorption system further comprises a housing at least partially defining the heating chamber; and the airlock extends through the housing and comprises a drum that is rotatable between: an open position in which an opening in the drum is open to an exterior of the thermal desorption system such that the bulk material may be loaded into the drum; and a closed position in which the opening is positioned to permit the loaded bulk material to enter the heating chamber.

21. The thermal desorption system of claim 16, further comprising: a condensing chamber comprising a cooling structure for condensing, into a condensate, the at least one vaporized substance that has flowed from the heating chamber to the condensing chamber.

22. The thermal desorption system of claim 21, wherein the cooling structure comprises at least one cooling plate over which a coolant is to be flowed, or a heat exchanger comprising one or more conduits through which a coolant is to be flowed.

23. (canceled)

24. The thermal desorption system of claim 21, further comprising one or more duct heaters for heating the one or more vapor ducts.

25. The thermal desorption system of claim 20, wherein the cooling structure comprises at least one cooling plate, and wherein the thermal desorption system further comprises: a coolant recirculation system for flowing a coolant over the at least one cooling plate; and a decanter for separating the condensate into the at least one condensed substance and coolant that has flowed over the at least one cooling plate, wherein the coolant recirculation system is configured to recirculate the separated coolant to the at least one cooling plate.

26. The thermal desorption system of claim 16, wherein the one or more conveyors comprise at least one scraper conveyor.

27. The thermal desorption system of claim 16, wherein the pressure differential mediates the passive transfer of the at least one vaporized substance from the heating chamber to the condensing chamber without the at least one vaporized substance being routed through a pump.

Description

DRAWINGS

[0030] Embodiments of the disclosure will now be described in detail in conjunction with the accompanying drawings of which:

[0031] FIG. 1 shows a thermal desorber according to an embodiment of the disclosure;

[0032] FIG. 2 shows a cross-section of the thermal desorber of FIG. 1, according to an embodiment of the disclosure;

[0033] FIG. 3 shows an airlock of the thermal desorber of FIG. 1, according to an embodiment of the disclosure;

[0034] FIG. 4 shows cooling plates of the thermal desorber of FIG. 1, according to an embodiment of the disclosure;

[0035] FIG. 5 shows a cross-section taken through a conveyor system of the thermal desorber of FIG. 1, according to an embodiment of the disclosure;

[0036] FIG. 6 shows a first cross-section of an inductive heater of the thermal desorber of FIG. 1, according to an embodiment of the disclosure;

[0037] FIG. 7 shows a second cross-section of the inductive heater, according to an embodiment of the disclosure; and

[0038] FIG. 8 is a flow diagram of a method of performing vacuum-assisted thermal desorption using the thermal desorber of FIG. 1, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0039] The present disclosure seeks to provide novel methods and systems for performing vacuum-assisted bulk material treatment. While various embodiments of the disclosure are described below, the disclosure is not limited to these embodiments, and variations of these embodiments may well fall within the scope of the disclosure which is to be limited only by the appended claims.

[0040] According to some embodiments of the disclosure, there is described a method of remediating a bulk material, such as soil, using thermal desorption. Soil contaminated by at least one hydrocarbon is introduced into a heating chamber. The heating chamber is in a partial vacuum. For example, the heating chamber may be at a pressure of 10-20 kPa. The soil is then heated in the heating chamber and in the presence of the partial vacuum to cause the hydrocarbon to vaporize. In addition to the hydrocarbon, the soil may also comprise a certain amount of water content or moisture, in which case such water is also vaporized. The soil, with the vaporized hydrocarbon and any vaporized water separated therefrom, is then extracted from the heating chamber. Advantageously, the partial vacuum environment may reduce the amount of energy required to evaporate the moisture and hydrocarbons from the contaminated soil.

[0041] According to some embodiments, the soil may be heated using electric heaters, such as inductive heaters. Current thermal desorption systems are typically powered by burning natural gas or other hydrocarbon fuels. Therefore, embodiments of the thermal desorption processes described herein may remove hydrocarbons from soil without the need to burn hydrocarbons, and may therefore emit no or little carbon dioxide. This may avoid the need for additional equipment that would otherwise be required to treat the desorber's exhaust gases.

[0042] In the case of induction heating, in order to increase the efficiency of the heat transfer from the heaters to the soil, the heaters' induction coils may be assisted by one or more soft magnetic composites.

[0043] Turning to FIG. 1, there is shown a thermal desorber 100 according to an embodiment of the disclosure. Thermal desorber 100 includes a vessel 10 housing a heating chamber and a condensing chamber (not seen in FIG. 1). On an exterior of vessel 10 is provided an airlock 20. Airlock 20 is connected to the heating chamber and allows contaminated soil introduced into airlock 20 to be transferred to the heating chamber, as described in further detail below.

[0044] Thermal desorber 100 further includes a removal system 30 connected to the heating chamber and extending away from vessel 10. Removal system 30 includes a number of vertically-oriented conduits 32 and interconnected augers 34. As will be described in further detail below, as contaminants and water are removed from the soil, the remediated soil is passed to removal system 30 which, through the operation of augers 34, causes the remediated soil to be transferred away from vessel 10. The remediated soil may then be collected at an outlet 36 of removal system 30.

[0045] Turning now to FIG. 2, there is shown a cross-section of thermal desorber 100, illustrating some of its various components in more detail. In particular, heating chamber 12 and condensing chamber 14 of vessel 12 can now be seen in more detail, as well as the interconnection of airlock 20 to heating chamber 12.

[0046] Within heating chamber 12 is provided a conveyor system 16 comprising an arrangement of stacked scraper conveyors 17. Each conveyor 17 comprises a fixed table plate for receiving soil that has been introduced into heating chamber 12 via airlock 20. On either side of the table plate are provided barriers to prevent the soil from falling off the table plate as the conveyor 17 is operated. Inductive heaters 40 (described in further detail below) are provided adjacent each table plate. A number of vapor ducts 13 extend along the sides of conveyors 17 and are configured to direct vaporized contaminants and water from heating chamber 12 to condensing chamber 14.

[0047] Prior to introducing contaminated soil into heating chamber 12, the pressure within heating chamber 12 is reduced to about 10-20 kPa, using one or more vacuum pumps (not shown). As mentioned above, by lowering the pressure within heating chamber 12, contaminants may be more easily vaporized and separated from the soil. In addition to reducing the pressure within heating chamber 12, the pressure within condensing chamber 14 is also reduced, and may be reduced to a level that is lower than the pressure within heating chamber 12. This may produce a pressure differential to assist the transfer of vapors from heating chamber 12 to condensing chamber 14, as described in further detail below. Generally, the pressure within condensing chamber 14 should be kept above a minimum level (e.g., at or above 10 kPa) to avoid evaporation of the cooling water that is used in condensing chamber 14, as described in further detail below.

[0048] Within condensing chamber 14 are provided a number of vertically-oriented cooling plates 11. Cooling plates 11 are cooled by continuously flowing a coolant, such as chilled recirculated water, through coolant conduits 18 (seen in more detail in FIG. 4) connected to cooling plates 11 along the tops of cooling plates 11. The chilled water is circulated through coolant conduits 18 and flows downwardly along cooling plates 11 before flowing out of condensing chamber 14 via an outlet 15.

[0049] Airlock 20 includes a door 22 providing access to the interior of airlock 20. In the present embodiment, airlock 20 comprises a rotatable airlock drum 26 with a drum opening 27 formed therein, but other forms of airlocks may be used. When airlock door 22 is open, and when airlock drum 26 is rotated such that drum opening 27 is aligned with the open airlock door 22, contaminated soil 24 may be introduced into airlock drum 26. When airlock door 22 is closed, a partial vacuum may be generated within airlock drum 26 using one or more vacuum pumps (not shown). The partial vacuum generated within airlock drum 26 may be the same as the partial vacuum generated within heating chamber 12. Airlock drum 26 may then be rotated to move drum opening 27 to the position shown in FIG. 2, which causes soil 24 to enter heating chamber 12 and to be deposited onto the topmost conveyor 17 of conveyor system 16.

[0050] According to some embodiments, prior to introducing soil into heating chamber 12, the soil may be pre-processed to remove as much water content from the soil as possible. Reducing the water content of the soil prior to introducing the soil into heating chamber 12 may facilitate the volatization of contaminants within the soil, since more heat energy may be transferred to the hydrocarbon or other contaminants.

[0051] When conveyor system 16 is being operated, the soil is conveyed to an end of each conveyor 17 using scrapers that translate relative to the surface of each table plate. The soil is advanced to an opening at the end of each conveyor 17 at which point the soil drops to the table plate of the next underlying conveyor 17. As the soil is transported along each successive conveyor 17, inductive heaters 40 heat the table plates on which sit the soil, and thereby heat the soil. Heating of the soil causes any water contained in the soil, as well as the contaminants such as hydrocarbons, to vaporize and separate from the soil. According to some embodiments, the temperature within heating chamber 12 may reach 640 degrees C.

[0052] Once the soil has reached the bottommost conveyor 17, it is transferred to an auger 34 of removal system 30, for discharge of the remediated soil from vessel 10. According to some embodiments, instead of employing removal system 30 that includes multiple augers 34, a different removal system may be used, such as an airlock similar to airlock 20.

[0053] The velocity of conveyors 17 may be adjusted based on the water content of the soil as well as the contamination level of the soil. According to some embodiments, desorber 100 may be configured to treat 10-20 tonnes of soil/hour, assuming about a 10% water content and 10% contamination. According to some embodiments, this may result in about 2,500 litres of removed oil, 2,000 litres of removed water, and 15,000 litres of clean soil.

[0054] As described above, a number of vapor ducts 13 extend alongside conveyors 17. Vaporized water and hydrocarbons flow under pressure into vapor ducts 13 and towards cooling plates 11 within condensing chamber 14. Vapor ducts 13 are heated to assist in preventing condensation of the vaporized water and hydrocarbons before their arrival at cooling plates 11. According to some embodiments, the vapor 13 positioned adjacent the lower conveyors 17 may be hotter than the vapor 13 positioned adjacent the upper conveyors 17.

[0055] Upon entering condensing chamber 14, the vaporized water and hydrocarbons condense on top of the chilled water flowing downwardly along cooling plates 11, and the condensate that is formed flows downwardly towards the bottom of cooling plates 11. The liquid is collected and discharged from condensing chamber 14 via outlet 15.

[0056] The liquid may then be directed to a tri-phase decanter (not shown) configured to separate the condensate into water, the hydrocarbons, and any solid particulate matter (e.g., fines) that has been entrained in the condensate. The water may then be recirculated to a chiller (not shown) configured to lower the temperature of the water. This chilled water may then be recirculated to coolant conduits 18 for use with cooling plates 11.

[0057] According to some embodiments, the temperature of the chilled recirculation water is about 4 degrees C. at the inlet of coolant conduits 18, about 25 degrees C. at outlet 15, and about 13-14 degrees C. on cooling plates 11.

[0058] Turning to FIG. 3, there is shown the exterior of airlock 12 in more detail. In this drawing, there is shown a dosing drum 25 positioned on top of airlock 20. Dosing drum 25 is configured to allow controlled volumes of soil or other bulk material being treated to enter airlock drum 26. A gearbox motor 28 is also shown on the side of airlock 20, for controlling rotation of airlock drum 26.

[0059] Turning to FIG. 4, there is shown condensing chamber 14 in more detail. The tops of cooling plates 11 can be seen connected to coolant conduits 18.

[0060] FIG. 5 shows a cross-section taken through conveyor system 16, illustrating vapor ducts 13 in more detail.

[0061] Turning to FIG. 6, there is shown a cross-section of an inductive heater 40. Heater 40 is provided beneath table plate 41 of conveyor 17. A flame-sprayed iron layer 42 is provided on the underside of table plate 41. Heater 40 comprises a housing 45 and an electrical and thermal isolating layer 43 positioned beneath iron layer 42. Within housing 45 are provided induction coils 44 beneath isolating layer 43, and a magnetic flux conductor 46. To improve the electromagnetic coupling between induction coils 44 and table plate 41, it was found that a flame-sprayed iron layer 42 with a thickness of 0.6 mm gave an efficiency of about 92%.

[0062] Turning to FIG. 7, there is shown a horizontal cross-section of heater 40. A pair of induction coils 44 are connected together forming a butterfly coil. The coil turns are encapsulated in magnetic flux conductor 46 and contribute to the heating of table plate 41.

[0063] Although heating of the soil has been described in the context of inductive heating, other forms of electrical heating may be used. For example, resistor heating and/or microwave heating may be used. According to some embodiments, non-electrical forms of heating may be used, at the expense of increased CO.sub.2 emissions.

[0064] Turning to FIG. 8, there is shown a flow diagram of a method of remediating soil using vacuum-assisted thermal desorber 100. It shall be understood that the order of the operations shown in FIG. 8 is exemplary in nature and is not fixed, and one or more of the operations may be performed simultaneously, or in a different order to what is shown.

[0065] Prior to loading airlock 20 with contaminated soil, vessel 10 is sealed, and the vacuum pumps are activated to lower the pressure within vessel 10, for example to within 10-20 kPa. The water recirculation system and tri-phase decanter are also activated, as are conveyor system 16 and inductive heaters 40.

[0066] At block 705, airlock 20 is loaded with contaminated soil. In particular, with drum opening 27 aligned with airlock door 22, soil is fed into airlock drum 26. Airlock door 22 is then closed.

[0067] At block 710, air within airlock drum 26 is evacuated and the pressure is lowered, for example to within 10-20 kPa.

[0068] At block 715, the contaminated soil is transferred to heating chamber 12. In particular, airlock drum 26 is rotated until drum opening 27 is in the position shown in FIG. 2, and the contaminated soil falls under gravity onto the table plate 41 of the topmost conveyor 17.

[0069] At block 720, the soil is heated as it is moved over the inductive heaters 40 of conveyor system 16. Heating of the soil gradually causes the contaminants and any water contained in the soil to vaporize.

[0070] At block 740, the soil has been transferred from the topmost conveyor to the bottommost conveyor, and has been largely separated from its water content and contaminants. The remediated soil is then extracted from vessel 10 by being discharged using removal system 30.

[0071] Meanwhile, the vaporized hydrocarbons and water flow to condensing chamber 14 via vapor ducts 13, and condense on top of the chilled water flowing down cooling plates 11. At block 725, the water-oil condensate is collected at the bottom of condensing chamber 14 and flows out via outlet 15.

[0072] At block 730, the condensate is transferred to a tri-phase decanter where it is separated into the water, the hydrocarbons, and any solid particulate matter that has been entrained in the condensate.

[0073] At block 735, the water is recirculated to a chiller and then to coolant conduits 18 to continue cooling of cooling plates 11.

[0074] Thermal desorber 100 described herein may provide a number of benefits over existing methods and systems of remediating soil. For example, by using electrical heaters, desorber 100 may be powered using only electricity that can be drawn, for example, from the grid, one or more fuel cells, or a generator. Furthermore, the relative proximity of inductive heaters 40 to table plates 41 may provide improved heating of the soil. Desorber 100 may additionally be mobile, and can be operated relatively shortly after arrival at a contamination site.

[0075] Furthermore, while the disclosure has been presented in the context of remediating soil, the methods and systems described herein may be used to remediate any bulk material having a size up to about .

[0076] Further still, while the disclosure has been presented in the context of remediating soil contaminated by hydrocarbons, the methods and systems described herein may be used to separate other contaminants from other bulk materials. This may be achieved, for example, by controlling the degree of exposure of the bulk material to the heat in the heating chamber. According to some embodiments, other contaminants that may be removed may include pesticides (e.g., chlorine or fertilizers). Other examples of bulk material that may be treated include drill cuttings from drilling operations.

[0077] According to some embodiments, the methods and systems described herein may be used purely to heat a bulk material, without the need to remove any contaminants therefrom. For example, according to some embodiments, frack sand or similar bulk material may be heated within heating chamber 12 to lower its water content. The treated frack sand may then be extracted from heating chamber 12 as described above.

[0078] According to some embodiments, instead of cooling plates, another cooling structure may be used, such as a heat exchanger comprising conduits through which cooling water or some other coolant flows. In such a case, vaporized oil will condense on the pipes without mixing with the coolant. After condensing, the oil may flow downward under gravity to a dedicated oil outlet.

[0079] The word a or an when used in conjunction with the term comprising or including in the claims and/or the specification may mean one, but it is also consistent with the meaning of one or more, at least one, and one or more than one unless the content clearly dictates otherwise. Similarly, the word another may mean at least a second or more unless the content clearly dictates otherwise.

[0080] The terms coupled, coupling or connected as used herein can have several different meanings depending on the context in which these terms are used. For example, as used herein, the terms coupled, coupling, or connected can indicate that two elements or devices are directly connected to one another or connected to one another through one or more intermediate elements or devices via a mechanical element depending on the particular context. The term and/or herein when used in association with a list of items means any one or more of the items comprising that list.

[0081] As used herein, a reference to about or approximately a number or to being substantially equal to a number means being within +/10% of that number.

[0082] Use of language such as at least one of X, Y, and Z, at least one of X, Y, or Z, at least one or more of X, Y, and Z, at least one or more of X, Y, and/or Z, or at least one of X, Y, and/or Z, is intended to be inclusive of both a single item (e.g., just X, or just Y, or just Z) and multiple items (e.g., {X and Y}, {X and Z}, {Y and Z}, or {X, Y, and Z}). The phrase at least one of and similar phrases are not intended to convey a requirement that each possible item must be present, although each possible item may be present.

[0083] While the disclosure has been described in connection with specific embodiments, it is to be understood that the disclosure is not limited to these embodiments, and that alterations, modifications, and variations of these embodiments may be carried out by the skilled person without departing from the scope of the disclosure.

[0084] It is furthermore contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification.