Vacuum-Assisted Bulk Material Treatment

The present disclosure relates to bulk material treatment and in particular to vacuum-assisted methods and systems for treating bulk material, such as soil, using thermal desorption.

Soil that has been contaminated by hydrocarbons, such as oil, must generally be processed to remove the pollutants and restore the soil's integrity and usability. In this context, thermal desorption is a method by which the soil is heated to separate the hydrocarbon contaminants from the soil matrix. When exposed to heat, the hydrocarbons vaporize, facilitating their separation from the soil.

Current methods of remediating soil using thermal desorption generally require large amounts of energy in order to remove the hydrocarbons from the soil, and as a result can be highly inefficient.

According to a first aspect of the disclosure, there is provided 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.

The bulk material may comprise soil.

The at least one substance may comprise a contaminant.

The contaminant may comprise at least one hydrocarbon.

The at least one substance may comprise water.

The heating chamber may be at a pressure of 10-20 kPa.

Introducing the bulk material into the heating chamber may comprise: 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.

Heating the bulk material may comprise heating the bulk material using electric heating.

Heating the bulk material may comprise heating the bulk material using inductive heating.

The method may further comprise condensing the at least one vaporized substance.

Condensing the at least one vaporized substance may comprise: 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.

The cooling structure may comprise 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.

The at least one vaporized substance may comprise at least one vaporized contaminant. The method may further comprise: 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.

The coolant may be water.

The method may further comprise: cooling at least some of the coolant; and recirculating the cooled coolant to the cooling plate.

According to a further aspect of the disclosure, there is provided 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; one or more vacuum pumps for generating a partial vacuum in the airlock and the heating chamber; and 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.

The method may further comprise 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.

The one or more heaters may comprise one or more inductive heaters.

The thermal desorption system may further comprise 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.

The thermal desorption system may further comprise a housing at least partially defining the heating chamber. The airlock may extend through the housing and may comprise 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.

The thermal desorption system may further comprise 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.

The cooling structure may comprise 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.

The thermal desorption system may further comprise one or more vapor ducts positioned to direct the at least one vaporized substance from the heating chamber to the condensing chamber.

The thermal desorption system may further comprise one or more duct heaters for heating the one or more vapor ducts.

The cooling structure may comprise at least one cooling plate, and the thermal desorption system may further comprise: 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.

This summary does not necessarily describe the entire scope of all aspects. Other aspects, features, and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.

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.

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.

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.

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.

Turning to, there is shown a thermal desorberaccording to an embodiment of the disclosure. Thermal desorberincludes a vesselhousing a heating chamber and a condensing chamber (not seen in). On an exterior of vesselis provided an airlock. Airlockis connected to the heating chamber and allows contaminated soil introduced into airlockto be transferred to the heating chamber, as described in further detail below.

Thermal desorberfurther includes a removal systemconnected to the heating chamber and extending away from vessel. Removal systemincludes a number of vertically-oriented conduitsand interconnected augers. As will be described in further detail below, as contaminants and water are removed from the soil, the remediated soil is passed to removal systemwhich, through the operation of augers, causes the remediated soil to be transferred away from vessel. The remediated soil may then be collected at an outletof removal system.

Turning now to, there is shown a cross-section of thermal desorber, illustrating some of its various components in more detail. In particular, heating chamberand condensing chamberof vesselcan now be seen in more detail, as well as the interconnection of airlockto heating chamber.

Within heating chamberis provided a conveyor systemcomprising an arrangement of stacked scraper conveyors. Each conveyorcomprises a fixed table plate for receiving soil that has been introduced into heating chambervia airlock. On either side of the table plate are provided barriers to prevent the soil from falling off the table plate as the conveyoris operated. Inductive heaters(described in further detail below) are provided adjacent each table plate. A number of vapor ductsextend along the sides of conveyorsand are configured to direct vaporized contaminants and water from heating chamberto condensing chamber.

Prior to introducing contaminated soil into heating chamber, the pressure within heating chamberis reduced to about 10-20 kPa, using one or more vacuum pumps (not shown). As mentioned above, by lowering the pressure within heating chamber, contaminants may be more easily vaporized and separated from the soil. In addition to reducing the pressure within heating chamber, the pressure within condensing chamberis also reduced, and may be reduced to a level that is lower than the pressure within heating chamber. This may produce a pressure differential to assist the transfer of vapors from heating chamberto condensing chamber, as described in further detail below. Generally, the pressure within condensing chambershould 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, as described in further detail below.

Within condensing chamberare provided a number of vertically-oriented cooling plates. Cooling platesare cooled by continuously flowing a coolant, such as chilled recirculated water, through coolant conduits(seen in more detail in) connected to cooling platesalong the tops of cooling plates. The chilled water is circulated through coolant conduitsand flows downwardly along cooling platesbefore flowing out of condensing chambervia an outlet.

Airlockincludes a doorproviding access to the interior of airlock. In the present embodiment, airlockcomprises a rotatable airlock drumwith a drum openingformed therein, but other forms of airlocks may be used. When airlock dooris open, and when airlock drumis rotated such that drum openingis aligned with the open airlock door, contaminated soilmay be introduced into airlock drum. When airlock dooris closed, a partial vacuum may be generated within airlock drumusing one or more vacuum pumps (not shown). The partial vacuum generated within airlock drummay be the same as the partial vacuum generated within heating chamber. Airlock drummay then be rotated to move drum openingto the position shown in, which causes soilto enter heating chamberand to be deposited onto the topmost conveyorof conveyor system.

According to some embodiments, prior to introducing soil into heating chamber, 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 chambermay facilitate the volatization of contaminants within the soil, since more heat energy may be transferred to the hydrocarbon or other contaminants.

When conveyor systemis being operated, the soil is conveyed to an end of each conveyorusing scrapers that translate relative to the surface of each table plate. The soil is advanced to an opening at the end of each conveyorat which point the soil drops to the table plate of the next underlying conveyor. As the soil is transported along each successive conveyor, inductive heatersheat 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 chambermay reach 640 degrees C.

Once the soil has reached the bottommost conveyor, it is transferred to an augerof removal system, for discharge of the remediated soil from vessel. According to some embodiments, instead of employing removal systemthat includes multiple augers, a different removal system may be used, such as an airlock similar to airlock.

The velocity of conveyorsmay be adjusted based on the water content of the soil as well as the contamination level of the soil. According to some embodiments, desorbermay 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.

As described above, a number of vapor ductsextend alongside conveyors. Vaporized water and hydrocarbons flow under pressure into vapor ductsand towards cooling plateswithin condensing chamber. Vapor ductsare heated to assist in preventing condensation of the vaporized water and hydrocarbons before their arrival at cooling plates. According to some embodiments, the vaporpositioned adjacent the lower conveyorsmay be hotter than the vaporpositioned adjacent the upper conveyors.

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

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 conduitsfor use with cooling plates.

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

Turning to, there is shown the exterior of airlockin more detail. In this drawing, there is shown a dosing drumpositioned on top of airlock. Dosing drumis configured to allow controlled volumes of soil or other bulk material being treated to enter airlock drum. A gearbox motoris also shown on the side of airlock, for controlling rotation of airlock drum.

Turning to, there is shown condensing chamberin more detail. The tops of cooling platescan be seen connected to coolant conduits.