NO20161364A1

NO20161364A1 - Aeration vessel

Info

Publication number: NO20161364A1
Application number: NO20161364A
Authority: NO
Inventors: Agnar Hellenes
Original assignee: Hellenes Holding As
Priority date: 2016-08-26
Filing date: 2016-08-26
Publication date: 2018-02-27

Abstract

The present invention relates to a system for cleaning and final treatment of bulk solids of contaminated solid waste originating from thermal desorption plants processing oily wastes or storage places for solids of contaminated solid waste, suen as drilling mud or drilling wastes, to levels acceptable for safe disposal and reuse. The system comprises an aeration vessel provided with a first inlet for the contaminated solids and a first outlet for cleaned solids, a second inlet for a processed gas received from a thermal separator for oils/liquids and a second outlet for contaminated gas, the aeration vessel further being in fluid communication with the thermal separator for oils/liquids through a first cireulation loop, the thermal separator for oils/Liquids further being connectedto a cooler through a second cireulation loop, a gas being circulated through the first circulation loop and a liquid being circulated through the second circulation loop. The present invention also relates to a method for use with the system, according to the present invention.The present invention relates to a system for cleaning and final treatment of bulk solids of contaminated solid waste originating from thermal desorption plants processing oily wastes or storage places for solids of contaminated solid waste, suen as drilling mud or drilling wastes, to levels acceptable for safe disposal and reuse. The system comprises an aeration vessel provided with a first inlet for the contaminated solids and a first outlet for cleaned solids, a second inlet for a processed gas received from a thermal separator for oils / liquids and a second outlet for contaminated gas, the aeration vessel further being in fluid communication with the thermal separator for oils / liquids through a first circulation loop, the thermal separator for oils / liquids further being connected to a cooler through a second circulation loop, a gas being circulated through the first circulation loop and a liquid being circulated through the second circulation loop. The present invention also relates to a method for use with the system, according to the present invention.

Description

Present invention relates to drilling operations such as oil and gas well drilling or geothermal drilling and more particularly to thermal treatment of solids originating from the separation of hydrocarbons from cuttings, by separation processes, thermal adsorption processes, or drying processes offshore and onshore.

Even more particularly, the present invention relates to a system and a method for cleaning of solids or cuttings as a final-/end treatment to achieve hydrocarbon (HC) contents below legislation requirements for disposal, and/ or below legislation limits for reuse in applications not limited by the fact that the cuttings/rock cuttings/drilled solids have been generated from drilling activity.

Such a system and method may, for instance, be used during drilling operations such as oil and/ or gas well drilling operations, or even after such drilling operations have been completed, for instance in connection with needs for disposal or reuse of the dry material from the processed cuttings/rock cuttings/drilled solids arising subsequently after such drilling operations.

This after treatment of solids may be actual on several locations, such as onshore, offshore, subsea, on a vessel or installation, internally on an oil rig, between an oil rig and a vessel, onboard a vessel, inside a pipe or on and a shore facility.

The vessel may be a ship, a drillship, a FPSO, a barge, a supply ship or the like, and the oil rig may be offshore or onshore. Furthermore, the after treatment of the cuttings/rock cuttings/drilled solids may be done offshore, onshore or subsea.

In the drilling of oil and gas wells, a drill bit is used to drill many thousands of meters into the earth’s crust. Oilrigs typically employ a drilling rig or derrick that extends above the well drilling platform and which can support joint after joint of drill pipe connected end to end during the drilling operation.

As the drill bit is pushed further and further into the earth, additional pipe joints are added to the ever-lengthening string or drill string. The drill pipe or drill string thus comprises a plurality of joints of pipe, each of which has an internal, longitudinally extending bore for carrying fluid drilling mud from the well drilling platform through the drill string and to a drill bit supported at the lower or distant end of the drill string.

Drilling mud lubricates the drill bit and carries away well cutting generated by the drill bit as it digs deeper. The cuttings are carried in a return flow stream of drilling mud through the well annulus and back to the well drilling platform at the earth’s surface. When the drilling mud reaches the surface, it is contaminated with small pieces of shale and rock, which are known in the industry as well cutting or drill cuttings.

In the past, cuttings have been separated from the reusable drilling mud with commercially available separators, known as shale shakers. Other solids separators include mud cleaners and centrifuges. Some shale shakers are designed to filter coarse material from the drilling mud while other shale shakers are designed to remove finer particles from the well drilling mud. After separating well cuttings therefrom, the drilling mud is returned to a mud pit where it can be supplemented and/ or treated prior to transmission back into the well bore via the drill string and to the drill bit to repeat the process.

The disposal of separated shale and cutting is a complex environmental problem. Drill cuttings contain not only the mud product that would contaminate the surrounding environment, but also can contain oil that is particularly hazardous in the environment, especially when drilling in a marine environment.

Oil and gas drilling operations produce drill cutting or tailings that consist of material removed from a well with mixtures of other fluids and materials that are used to facilitate drilling. This other material is typically called drilling mud.

Several factors motivate cleaning of drill cuttings or drilling methods. From a drilling operations perspective, the drilling mud requires constant surveillance and adjustments in order to retain or adapt its properties in order to facilitate drilling. The surplus mud, or mud that falls outside of the aimed drilling parameters at the time, is either stored, or processed in order to reuse, separate its constituents or clean them for other reuse or disposal in light of environmental concerns. Drill cuttings keep being excavated from the drilling hole, usually adding up in intermediate storage skips, most often in order to be processed further, for final disposal. Thermal desorption units are the most frequent used technology, all with a shared limited ability to clean the solids so that the material can be considered environmentally safe for disposal without specific restrictions.

State of the art methods of thermal desorption technologies typically share capabilities in cleaning with variable success down to approximately 0,5% (500 ppm) OOC (Oil On Cuttings). Achieving further levels of cleaning the solids have proven difficult with existing technologies, where the balancing economic throughput capability often may be found as much as an order of magnitude above the levels found acceptable by environmental legislation and, legal authorities and acceptance levels set by society in general and Public Network Operators (PNOs). As late experience demonstrate, authorities now demonstrate required OOC levels as low as 0,05% (wt.), for operators to consider offshore disposal of cleaned drilling waste.

EP 224.353 A1 discloses a method and apparatus for treating sludge streams, where heavy hydrocarbon containing sludges such as waste streams, oil storage tank sludges and marine oil tanker ballast are treated by passing the sludges in a flow stream through an indirect dryer to vaporize liquids having a boiling point at atmospheric pressure of less than about 700<0>F and to provide substantially dried solid particles discharged from the dryer. The dried particles, containing heavy hydrocarbons as a coating or as a part of the solids, are conducted to a combustor/oxidizer and exposed to high velocity flow stream of oxygen containing gas, typically low pressure forced air, to burn the residual hydrocarbons in the solids and to reduce heavy metals and the like to oxides thereof. A sludge handling system includes a rotary disk type indirect dryer connected to a lift pipe type combustor/oxidizer for thorough exposure of the dried solids to an oxygen containing atmosphere. A centrifugal or cyclone type gas-solids separator receives the flow stream discharged from the lift pipe and a portion of the dried solids may be diverted after discharge from the dryer back to the dryer inlet to reduce the moisture content of the sludge flow stream introduced to the dryer to minimize caking and clogging of the dryer itself.

WO 2015/065201 A2 regards a method for reducing the amount of oil in an oil containing mixture, where the method comprises to heat the mixture and to inject oxygen or a mixture of gases into said heated oil containing mixture.

US 5.370.801 A regards a method for treating polluted material such as industrial waste or polluted water from other sources, sewage or sewage sludge, to degrade oxidizable substances therein. The polluted material is subjected to a wet oxidation process in a tubular reactor so as to decompose and/or modify oxidizable substances therein and improve the filterability of any solids present in the material.

Search for prior art demonstrates that the challenge of cleaning the treated solids from thermal adsorption methods to sufficiently low levels for safe environmentally sustainable disposal, remains unsolved, and require further efforts to require satisfactory levels of OOC (Oil on Cuttings).

The prior art systems for separating solids from thermally processed cuttings/rock cuttings/drilled solids are typically not satisfactory, in that they all struggle in achieving sufficiently low hydrocarbon content on the final treated solids.

In addition, the equipment is bulky, require a large footprint and are voluminous, thus take up much often expensive or scarce place, as for instance would be the case offshore or onboard a vessel. The sheer space and volume required for such equipment, implies equipment and installations that weigh a great deal.

Consequently, such equipment and their installation tend to become more expensive with increasing efforts made to mitigate the problem.

Some methods also require very large storage capacities, which also is a costdriving factor that limits practical achievements due to the limited space available on particular locations.

Further to this, in various efforts made to further reduce the hydrocarbon content in the drill cutting solids, applying more power could be a strategy that has its natural limitations for profitable feasibility, as often has been seen with proposed and existing solutions.

The solids originating from oil containing substances, resources or waste, such as for instance spent drilling mud or cuttings, processed by thermal desorption methods in general, this currently being the most widespread and leading technology, are produced in large amounts of solids from the cuttings, due to the fines produced by mechanical crushing and dividing into finer particles.

One significant issue connected with any thermal desorption process taking place in a confined vessel, is leakage. Every vessel has its individual minimum amount of leakage, due to the fact the equipment is handling hot solids, in connection with gases and steam at elevated temperatures, to some extent even pressures significantly above atmospheric, a combination that inevitably must be seen with some acceptable degree of leakage, considering any level of sound engineering practice. These minor leakages are often happening in equipment connected to an environment colder than the processing temperature, consequently leading to some degree of unavoidable condensation on the equipment surfaces that is in contact with the solids, sometimes also within the bulk solids their self. Accumulation of this condensate over time will also increase the risk of sometimes contaminating already “cleaned” solids.

Another problem with these fines is that as they appear in bulk form, a significant portion of their volume is constituted by voids, and not only the fines’ geological mass, reducing the original geological density, taking up more volume per mass of solids.

The voids present in the bulk solids, consequently constitute free space for gases, containing volatile hydrocarbons in gas form, besides steam, inert gases and other chemical compounds that were present prior to processing, as well as products of reactions due to processing.

These constituents typically remain within the solids as they are transported out from whatever cleaning process they have been subjected to.

When the heated solids are cooled, a significant portion of these constituent gases may typically condense, and may form liquid or solid forms of hydrocarbons or other chemicals that will remain bound to the solids, thus remaining inside the bulk volume of the solids.

As this volume is quite significant, even “normal” amounts of hydrocarbon gases may produce significant remaining hydrocarbons on cuttings (OOC).

The object of the present invention is to provide a system and a method to clean the solids received from thermal desorption units and processes that are used to clean polluted materials or oily wastes or from an intermediate storage place for the solids, such as drilling mud or drilling wastes, to levels acceptable for safe disposal and reuse of the solids from an environmentally sound perspective, where the system and method minimize and possibly alleviate one or more of the disadvantages of the prior art, or to provide a useful alternative.

This object is obtained according to the invention by the features disclosed in the following independent claims, with additional features of the invention set forth in the dependent claims and the description below.

According to the present invention it is provided a system for an after treatment/a final cleaning of hydrocarbon contaminated solids originating from thermal desorption plants and/or (intermediate) storage places for the hydrocarbon contaminated solids, to levels acceptable for safe disposal and reuse of the solids, where the system comprises an aeration vessel provided with a first inlet for hydrocarbon contaminated solids and a first outlet for cleaned solid oil waste, a second inlet for a processed gas retrieved from a thermal separator for oils and liquids and a second outlet for contaminated gas. The aeration vessel is further connected to the thermal separator for oils and liquids through a first circulation loop, such that the aeration vessel is in fluid communication with the thermal separator. Furthermore, the thermal separator for oils and liquids is connected to a cooler through a second circulation loop, where a gas is circulated through the first circulation loop and a liquid is circulated through the second circulation loop.

The system will provide a solution where the voids present in the bulk solids are aerated with an inert gas, in order to “transport” the “contaminated” gas separated from the solids, for further treatment elsewhere, away from the voids inside the solids. One important aspect of this “aeration,” is that the temperature of the replacing gas is kept at a temperature level that avoid condensation, around or above the processing temperature of the processed solids, so that no portion of the processed solids is allowed to cool down and subsequently cool the void between each individual solid particle in the solid bulk volume. Any such cooling would lead to the immediate condensation of any condensable gases inside the voids made up by the volume between the particles in the bulk volume.

Leading this contaminated gas separated from the solids, away from the solids for separate treatment, would simplify the further treatment of both treatment of the gas bound contaminants, and the processed bulk solids. Further treatment of the latter, could thereby even be entirely avoided.

Another significant advantage over prior art/existing technologies according to the present invention, is that the present invention represent a treatment method that by nature is explosion safe, simplifying the safeguarding and level of ATEX (ATmosphère EXplosible) compliant measures required for this type of processing equipment.

In one embodiment of the present invention the first and second circulation loops are arranged to be closed circulation loops. However, it could also be envisaged that each of, or both of the first and second circulation loops could be arranged to be partly closed circulation loops. A closed circulation loop, as used herein, should be understood to be a loop in which a gas or a liquid is passed around the loop without the possibility to escape from the loop, while a partly closed circulation loop should be understood to be a loop where a gas or liquid can escape and/or be added to the loop.

According to the present invention, the aeration vessel receives the hydrocarbon contaminated solids from a thermal desorption unit, whereby the aeration vessel and the thermal desorption unit can be connected with each other through a conduit, or alternatively through a conveyor, where the aeration vessel, the thermal desorption unit and the conveyor then will be connected through appropriate conduits extending between the thermal desorption unit and the conveyor and the conveyor and the aeration vessel. However, it should be understood that the aeration vessel may also receive the hydrocarbon contaminated solids from elsewhere than the thermal desorption unit, for instance from a storage place for the contaminated solids or the like.

In a first aspect of the present invention, the first circulation loop may comprise one fan and one heater, but a person skilled in the art would understand that additional fan(s) and/or heater(s) could be provided in the first circulation loop, for instance could one fan and one heater be arranged upstream the aeration vessel and one fan and one heater downstream the aeration vessel.

The first circulation loop could also comprise one or more exhaust outlets for superfluous gas, where such exhaust outlet(s) may be arranged in the thermal separator.

The gas circulation through the first circulation loop may be an inert gas, but other gases could also be used. Examples of such other gases, could be different mixtures of gases, where reactive gas components might be present, for instance air, where oxygen is present. This could probably cause an exothermal reaction to take place, completely or only to some extent. Partly reaction of the hydrocarbons with oxygen would not interfere with the main objectives of the invention, namely flushing and transport of hydrocarbon gases away from the aeration vessel, in order to separate and later process the gas elsewhere, typically in a condenser system.

The second circulation loop may comprise one pump and one cooler, but it should be understood that additional pump(s) and/or cooler(s) could be arranged in the second circulation loop. In addition, or as an alternative, the second circulation loop could also be provided with an outlet for sludge.

The thermal separator may be arranged to be a condenser. By cooling the gas in the first circulation loop below the condensation temperature of hydrocarbons entrained with the gas entering the thermal separator, these hydrocarbons, completely or part thereof, will change phase from gas to liquid, making them easier to concentrate and thereby concentrate, extract and separate from the gas. Even hydrocarbon aerosols entrained in the same gas will benefit from temperature being lowered from the gas phase to below the gas components’ condensation temperature, as condensation will be facilitated by the cooling of the entrained aerosols, creating colder surfaces for the present hydrocarbon gases to condense onto.

To facilitate condensation in the thermal separator, the fan should preferably be located immediately after the thermal separator, which is the coldest location in the circuit.

In a second embodiment of the invention, the thermal separator may be arranged as a cooler. Presuming that the pressure of the gas in the first circulation loop is kept constant, or relatively constant, in order to facilitate condensation, a local lowering of the temperature in the cooler (thermal separator) is required, and may be considered a precondition for the function of the thermal separator. Given constant or relatively constant pressure in the gas throughout the first circulation loop, allowing for the pressure difference that occurs due to that produced by the fan to overcome the conduit and component resistance of the first circulation loop required to ensure circulation of gas in the first circulation loop, the only way for condensation to occur, is by lowering of the temperature, locally inside the cooler. The cooler may physically be placed either inside the thermal separator, or outside the thermal separator. The preferred execution of the cooler would be an indirect cooler. The cooler would in both cases be in fluid communication with the second circulation loop.

If the cooler is placed inside the thermal separator, the preferred execution of the cooler, would be that it is in thermal connection with the gas flow through a given heat exchanger surface area. If placed outside the thermal separator, the cooler would be in thermal communication with the secondary cooling circuit, however not in direct fluid communication with the gas.

In a third embodiment of the invention, the thermal separator may be described as a scrubber. One primary function of a scrubber is that it has ability to wash and clean a gas from particles and aerosols entrained with the gas. This means that the circulating cooling fluid from the second circulation loop is in direct fluid communication with the cooled gas from the first circulation loop. The cooling circuit in turn, would be cooled by a cooler, as described above. One advantage with direct contact condensing and heat exchange, is that the heat exchange is facilitated with very little loss of temperature difference, due to the fact that there is no material in between the hot and cold media that would mean a temperature fall that needs to be compensated for. From an efficiency perspective, this is usually a preferred solution. This system also have the advantage of allowing for continuous cleaning of particles, avoiding fouling build-up onto heat exchanging surfaces, thus having certain advantages with regards to system maintenance, system uptime, continuity of operation and system longevity.

In one aspect of the present invention a gas device may be connected to the thermal separator, such as to supply the gas to the first circulation loop. The gas device may then be a gas supply unit, a gas vessel or a gas generator.

The system for an after treatment/a final cleaning of hydrocarbon contaminated solids originating from thermal desorption plants, to levels acceptable for safe disposal and reuse of the solids may comprise one or more additional aeration vessels and/or one or more thermal separators.

In one aspect of the present invention the system for an after treatment/a final cleaning of hydrocarbon contaminated solids originating from thermal desorption plants, to levels acceptable for safe disposal and reuse of the solids may include a control system to control the flow of fluids in the first and/or second circulation loops, where such a control system may comprise valve(s), temperature and/or pressure sensors etc.

The system for an after treatment/a final cleaning of hydrocarbon contaminated solids originating from thermal desorption plants, to levels acceptable for safe disposal and reuse of the solids may also be insulated. A person skilled in the art would know how the system should be insulated and it is therefore not described any further herein.

The present invention also relates to a method for an after treatment/a final treatment of hydrocarbon contaminated solids originating from thermal desorption plants, to levels acceptable for safe disposal and reuse of the solids, where the method comprises the following steps: feeding an amount of hydrocarbon contaminated solids from a thermal desorption unit to an aeration vessel, supplying continuously a gas from a first circulation loop to the aeration vessel in order to aerate the hydrocarbon contaminated solids within the aeration vessel, returning the contaminated gas through the first circulation loop to a thermal separator, cleaning and cooling the contaminated gas in the thermal separator through a second circulation loop comprising a cooling fluid and returning the gas to the aeration vessel, and discharging the cleaned solids from the aeration vessel.

Further objects, structural embodiments and advantages of the present invention will be seen clearly from the following detailed description, the attached drawings and the claims below.

The invention will now be described with reference to the attached figures, wherein:

Figure 1 shows a first embodiment of a system for an after treatment or a final cleaning of contaminated solid waste from thermal desorption plants according to the present invention, and

Figure 2 shows a second embodiment of a system for an after treatment or a final cleaning of contaminated solid waste from thermal desorption plants according to the present invention.

The present invention relates to a system S for an after treatment/a final cleaning of hydrocarbon contaminated solids originating from thermal desorption plants, to levels acceptable for safe disposal and reuse of the solids.

Figure 1 show in a schematic way a first embodiment of the system S for an after treatment/a final treatment of hydrocarbon contaminated solids, where the system S, for instance, is arranged on an oil rig (not shown).

The system S comprises an aeration vessel 3 which is connected to a thermal desorption unit 1, such that hydrocarbon contaminated solids can be supplied from the thermal desorption unit 1 to the aeration vessel 3. The aeration vessel 3 is provided with a first inlet 4A for the contaminated solids, to which first inlet 4A a conduit 2 is connected, and a first outlet 4B for cleaned solids, to which first outlet 4B a conduit 4 is connected. The first outlet 4B for cleaned solids is used to discharge the cleaned solids from the aeration vessel 3. The cleaned solids may then be transported away from the aeration vessel 3 through the conduit 4 to be stored in another place or to be transported to a vessel etc. for further transport.

Furthermore, the aeration vessel 3 is also provided with a second inlet 4C for a processed gas, to which second inlet 4C a conduit 16 is connected, and a second outlet 4D for contaminated gas, to which second outlet 4D a conduit 8 is connected.

The conduits 8, 16 is part of a first circulation loop 8, where the first circulation loop 8 is used to circulate a gas in the system S according to the present invention. The first circulation loop 8 will then also comprise a fan 14 and a heater 15.

Furthermore, the aeration vessel 3 is in fluid communication with a thermal separator 9 through the first circulation loop 8.

The thermal separator 9 is also connected to a second circulation loop 10, where this second circulation loop 10 comprises a conduit 10, a pump 11 and a cooler 12. The second circulation loop 10 is used to circulate a liquid in the system S according to the present invention.

Through the above described arrangement, the aeration vessel 3 is aerated by the gas, for instance an inert gas, which is circulated through the first circulation loop 8, where the first circulation loop 8 can be a closed or partly closed loop. The purpose of this first circulation loop is primarily to replace gas present inside the bulk solids within the aeration vessel in order to separate contaminant bound to the gas elsewhere in the system, with cleaned processed (inert) gas. Another, secondary purpose of the first circulation loop 8 is to maintain a stable temperature in the aeration vessel 3.

The primary purpose of the thermal separator 9 is to act as a separator for oils and liquids in gas form that may condense at lower temperatures. A secondary purpose of the thermal separator 9 is to clean the circulating gas from contamination by any solids and matter in small particulate form that entrained by the transported gas being circulated through the bulk solids in the aeration vessel 3 and through the first circulation loop 8.

The main purpose of the second circulation loop 10 is to cool the gas in the first circulation loop 8.

The cleaning process is divided in two separate processes taking place in the aeration vessel 3 and in the condenser unit 9 respectively.

In the aeration vessel 3, a heated, inert gas is being flushed through the fines and particles present in the aeration vessel 3. Trapped in the bulk of dry solids, there is gas containing hydrocarbons. By ensuring sufficient flow of inert gas flushing through the bulk of solids and fine particles, the entrapped hydrocarbon containing gas may be transported out of the aeration vessel 3 for separation elsewhere in a vessel designed for the separation of the hydrocarbon containing gas. The gas flow is adjusted, so that there is a sound balance between the gas flow and entrained solids with the gas flow, which should be kept to an acceptable minimum.

The gas circulates in a the first circulation loop 8 through the aeration vessel 3 by a fan 14, forcing hydrocarbon containing gas within the solids present in the aeration vessel 3 to be flushed and transported into the condenser unit 9. The temperature in the aeration vessel 3 is kept above the saturation point of hydrocarbons in the gas mixture. This is ensured by heating the gas flow in the heater 15, mounted in the gas first circulation loop 8. In the condenser unit 9, the gas mixture is cooled, in order to allow the hydrocarbons present in the gas to condense. The temperature in the condenser unit 9 is kept below the saturation point of hydrocarbons. The temperature in the condenser unit 9 is controlled by a second, separate cooling circuit 10, containing a cooler 12 and a pump 11, which ensures sufficient circulation of the cooling medium in the second cooling circuit 10. Excess sludge, that will be allowed to accumulate due to direct contact cooling of the circulated gas containing some degree of entrained solids, is allowed to escape through a specifically designed outlet 13. This outlet 13 may be operated by overflow, level control, viscosity control, density control or by mechanical conveying of the surplus sludge, to achieve a steady state balance that avoids any permanent accumulation of sludge.

Figure 2 show in a schematic way a second embodiment of the system for an after treatment/a final treatment of hydrocarbon contaminated solids.

The system S comprises an aeration vessel 3 which is connected to a thermal desorption unit 1, such that hydrocarbon contaminated solids can be supplied from the thermal desorption unit 1 to the aeration vessel 3. The aeration vessel 3 is provided with a first inlet 4A for the contaminated solids, to which first inlet 4A a conveyor 6 through a conduit 7 is connected, and a first outlet 4B for cleaned solids, to which first outlet 4B a conduit 4 is connected. The first outlet 4B for cleaned solids is used to discharge the cleaned solids from the aeration vessel 3. The cleaned solids may then be transported away from the aeration vessel 3 through the conduit 4 to be stored in another place or to be transported to a vessel etc. for further transport.

The conveyor 6 is connected to the thermal desorption unit 1 through a conduit 5. The conveyor may well be a screw conveyor, or any other conveying equipment ensuring stirring or agitation by mechanical means such as wings, paddles, arms mounted onto an axle or even a rotating drum, that being either a rotor placed inside the vessel, or a drum constituting the walls of the vessel/ confinement or walls of the vessel.

Through the above described arrangement, the aeration vessel 3 is aerated by the gas, for instance an inert gas, which is circulated through the first circulation loop 8, where the first circulation loop 8 can be a closed or partly closed loop. The purpose of this first circulation loop is primarily to replace gas present inside the bulk solids within the aeration vessel in order to separate contaminant bound to the gas elsewhere in the system, with cleaned processed (inert) gas. Another, secondary purpose of the first circulation loop is to maintain a stable temperature in the aeration vessel 3.

The primary purpose of the thermal separator 9, is to act as a separator for oils and liquids in gas form that may condense at lower temperatures. A secondary purpose of the thermal separator is to clean the circulating gas from contamination by any solids and matter in small particulate form that entrained by the transported gas being circulated through the bulk solids in the aeration vessel 3 and through the first circulation loop 8.

In this embodiment the conduit 2 in figure 1 may be completely replaced by a conveyor, or also assisted by a conveyor, either in series with a conduit, or in parallel with one or more conduits or conveyors. The above described ways of transporting solids into the aeration vessel, will have that in common, regardless of execution, that they will penetrate the aeration vessel 3 through one or more openings (4A) in the vessel wall, sides, top or bottom.

The other feature described in figure 2 that is not shown in figure 1, is the supply of an inert gas from a vessel, a generator or other form of supply. In the simplest form, the circulating gas could be air, that when circulated on a continuous basis would be considered practically inert. Air could be supplied from said sources, or be supplied from the atmosphere through a vent. Air could also be forced into the system, implying that the air would also contain some oxygen, and thus could not be completely inert. This however, would not change the effect of flushing, transport of hydrocarbons, separation and condensation of entrained hydrocarbons in the gas.

As condensation, or for that matter evaporation, is depending on the simultaneous available pressure and temperature in a gas mixture at any given point and moment, this phase transition can be controlled by either temperature, or pressure, or both.

In one aspect according to the present invention, it is desired to maintain the system in a relatively steady state, i.e. having a more or less same temperature and pressure for a given location in the first circulation loop. To achieve this, a control system is used to control the temperature and pressure, at the points in the first circulation loop where the efficiency of the means of regulation is considered to be best, i.e. is most efficient.

Temperature control (given practically constant pressure):

For the aeration vessel, it is desirable to maintain a temperature above the flash point of hydrocarbons present in the vessel. To achieve this, heat loss must be prevented, achieved typically by sufficient insulation of the aeration vessel 3. Some heat loss is always unavoidable, thus this needs to be compensated for. Heating is achieved by the heater (15), preferably located close to the aeration vessel 3.

Heating may also be arranged around or within the aeration vessel 3, as the primary objective is to keep the contents of the aeration vessel 3 at its prescribed temperature.

Much of the same control philosophy applies for the condenser unit, with the main objective being different in that the temperature should always be kept below the flash point of hydrocarbons in the gas mixture. To control the temperature in the condenser, a cooler (12), located in the second circulation circuit (10) is used to transport excess heat away from the second circulation circuit (10), thus providing effective temperature control inside the condenser (9).

Pressure control (given practically constant temperature):

For the aeration vessel 3, it is desirable to maintain more or less constant pressure inside the aeration vessel 3. Lower pressure may result in evaporation, and does no harm inside the aeration vessel 3, as transport of present hydrocarbons away from the aeration vessel 3 is desirable. However, the pressure should be maintained practically constant, and the efficient means of keeping the pressure would be to regulate the pressure with the machine producing pressure, namely the fan 14. Preferably the fan 14 should be located immediately after the condenser vessel 9, although any location in the first circulation circuit 8 is feasible. The fan 14 may be controlled by speed, for instance by variable frequency (VFD). Another option is controlling the pressure by a control valve placed in the first circulation circuit 8. Such a control valve may be placed anywhere in the first circulation circuit 8.

For the condenser vessel, it is desirable to maintain more or less constant pressure inside the vessel. An efficient means of keeping the pressure would be to regulate the pressure with the machine producing pressure, namely the fan 14. The fan 14 may be controlled by speed, for instance by variable frequency VF. Another option is controlling the pressure by a control valve placed in the first circulation circuit 8.

The present invention has now been explained with reference to exemplary embodiments, but a person of skill in the art will understand that changes and modifications could be made to these embodiments which are within the scope of the invention as defined in the following claims.

Claims

1. A system (S) for an after treatment/a final cleaning of contaminated solids, the system (S) comprising an aeration vessel (3) provided with a first inlet (4a) for the contaminated solids and a first outlet (4b) for cleaned solids, a second inlet (4c) for a processed gas received from a thermal separator (9) for oils/liquids and a second outlet (4d) for contaminated gas, the aeration vessel (3) further being in fluid communication with the thermal separator (9) for oils/liquids through a first circulation loop (8), the thermal separator (9) for oils/liquids further being connected to a cooler (12) through a second circulation loop (10), a gas being circulated through the first circulation loop (8) and a liquid being circulated through the second circulation loop (10).

2. A system according to claim 1, characterized in that the system (S) further comprises a thermal desorption unit (1).

3. A system (S) according to claim 1, characterized in that each of the first and second circulation loops (8, 19) is/are a closed or partly closed circulation loop.

4. A system (S) according to claim 1, characterized in that the aeration vessel (3) is connected to the thermal desorption unit (1) through a conduit (2) or through a conveyor (6) and conduits (5, 7).

5. A system (S) according to any one of the proceeding claims 1-3, characterized in that the first circulation loop (8) comprises at least one fan (14) and at least one heater (15).

6. A system (S) according to claim 5, characterized in that the first circulation loop (8) comprises an outlet (17) for exhaust of (noncondensible) gas.

7. A system (S) according to any one of the proceeding claims 1-5, characterized in that the second circulation loop (10) comprises at least one pump (11), at least one cooler (12) and an outlet (13) for sludge.

8. A system (S) according to any one of the proceeding claims 1-6, characterized in that the thermal separator (9) is a cooler/scrubber/condenser.

9. A system (S) according to any one of the proceeding claims 1-7, characterized in that a gas supply/vessel/generator (18) is connected to the thermal separator (9).

10. A system according to any one of the proceeding claims 1-8, characterized in that the system (S) comprises at least one additional aeration vessel (3).

11. A system according to any one of the proceeding claims 1-9, characterized in that the system (S) comprises at least one additional thermal separator (9).

12. A system according to claim any one of the proceeding claims 1-10, characterized in that the system (S) comprises a control system (not shown) for controlling the flow of fluids in the first and second circulation loops (8, 10).

13. A system (S) according to claim 1, characterized in that the system (S) is insulated.

14. A system (S) comprising external heating to avoid condensation for all components in circulation loop (8).

15. A system (S) comprising external heating to avoid condensation for all components in circulation loop (8), except for system (9).

16. A method for an after treatment/a final treatment of contaminated solids, the method comprising the following steps: feeding an amount of hydrocarbon contaminated solids to an aeration vessel (3), supplying continuously a gas from a first circulation loop (8) to the aeration vessel in order to aerate the hydrocarbon contaminated solids within the aeration vessel (3), returning the contaminated gas through the first circulation loop (8) to a thermal separator (9), cleaning and cooling the contaminated gas in the thermal separator (9) through a second circulation loop (10) comprising a cooling fluid and returning the gas to the aeration vessel (3), and discharging the cleaned solids from the aeration vessel (3).

17. Method according to claim 14, characterized in that an inert gas is used in the first circulation loop (8).

18. Method according to claim 14 or 15, characterized in that the gas is heated before it is supplied to the aeration vessel (3).

19. Method according to any of the proceeding claims 14-16, characterized in that the cleaning of the drilling waste solids is done in one or several steps.