WO2002057008A1

WO2002057008A1 - Treatment of a solid material with a fluid

Info

Publication number: WO2002057008A1
Application number: PCT/GB2002/000197
Authority: WO
Inventors: Patrick Joseph Forker
Original assignee: Forkers Limited
Priority date: 2001-01-17
Filing date: 2002-01-17
Publication date: 2002-07-25
Also published as: GB2371298A; GB2371298B; GB0101166D0

Abstract

A method and apparatus for treating a solid material with a fluid e.g. for treating waste materials with carbon dioxide in a process described in WO97/13735, wherein the material is transported through a treatment chamber (30) in which an envelope of the fluid is maintained by virtue of the chamber having an inlet (34) and an outlet at a different level from the chamber, so that the different density of the fluid from the surrounding atmosphere substantially prevents its escape. Preferably the material is transported through the chamber (30) by a feed screw (35) with formations which agitate it as it is transported to achieve maximum contact with the treatment fluid.

Description

Title: Treatment of a Solid Material with a Fluid

Description of Invention

This invention relates to treatment of a solid material with a fluid. The invention has been devised in relation to a method and apparatus for carrying out a "carbonation" process described hereafter as a step in the treatment of contaminated earth. Once treated the earth is suitable for standard methods of disposal such as landfill and for re-use as an engineered material.

Land is precious. As populations grow and global warming reduces land area we need to make the most of our natural inheritance. Unfortunately the need we have for land has not always been translated into respect for it. In the UK alone 300 000 hectares of land have been affected by industrial and natural contamination, and 30 000 of these are in need of immediate remediation.

Some of the causes of the contamination are not far to seek. The UK produces approximately 4.5 million tonnes of hazardous wastes per annum, and it is estimated that over 80% of these are sent to landfill without pre-treatment. These wastes can be stored safely, however, if they are solidified using cement based systems. Then they may even be co-disposed with domestic refuse.

Current cement based systems do not keep all heavy metals insolubilised or stabilised. In order to improve this situation and keep pace with current legislation, a new process, described in international patent application publication No. W097/13735, has been developed to treat waste materials. The waste material may be or contain one or more of many types of industrial or sewage sludges, but are essentially inorganic in nature and contain heavy metals. The process described in the above-mentioned patent application uses cement binding, with carbonation to stabilise and set the cement. Cement is added to the waste material that is to be treated. Water and / or Calcium compounds may be added at the same time if desired. Carbon dioxide is then added to the particulate, either with the cement or after the cement has been added whilst the mixture is stabilising. The cement reacts with the carbon dioxide rather than water, locking in the pollutants, chemically and physically. It forms calcium carbonate, which creates an interlocking framework that allows the waste particles to be locked in. Chemical changes also occur, raising the pH of the material, which is conducive to keeping heavy metals insoluble and therefore stable. The mixture hardens and sets with improved fixation of the contaminant species and the soils can be immediately re-used on site.

This process, which is further detailed in the above mentioned patent application, has been proven on a laboratory scale. Field trials have also established the usefulness of the system. These trials used a batch process, however, which is not practicable at the throughputs that are commercially necessary - of the order of 50 tonnes per hour.

There is therefore a need for an industrial scale . mixer and associated processing apparatus and methods to implement this process. The present invention addresses these problems. Although developed for and described with respect to the carbonation process, the apparatus and process developed has much wider application and could advantageously be used to treat many types of solid with many different types of fluid.

This invention provides, according to one aspect, a method of treating a particulate solid material with a fluid, comprising: maintaining an envelope of the fluid; feeding the solid material into the envelope of the fluid; transporting the solid material through the envelope of the fluid, to be treated in the course of such transport; and discharging the treated material.

Preferably the method includes the step of agitating the solid material during its passage through the envelope of the fluid to expose as much surface area as possible of the solid material to the fluid.

This method enables a continuous process to be operated with high tonnages of throughput. The agitation allows a thorough intermingling of the solid with the fluid, as much of the surface area of the solid as possible is exposed to the fluid. This is particularly important if a chemical reaction forms part of the treatment process.

Preferably the envelope of fluid is maintained in a treatment chamber with an inlet and an outlet, the inlet and outlet being at a higher level than the level at which the solid material travels through the envelope. If the fluid is more dense than air, such as in the case of C0₂ used in a carbonation process, this enables the fluid envelope to be maintained without substantial leakage, even if unsealed.

If the fluid were less dense than air, it would alternatively be possible for the fluid envelope to be maintained by the inlet and outlet being at lower level than that at which the particulate travels through the envelope.

Preferably the solid material is transported through the fluid envelope using feed screw means, e.g. an auger screw or screws. This effects transportation and agitation simultaneously.

Preferably prior to treatment of the solid material with the fluid, the former is prepared by one or more operations, such are crushing and/or shredding an initial material to produce a desirable particle size or range of sizes. For example a crushing operation may be followed by a shredding operation to decrease the particulate size further. The particulate form increases the ease of transportation of the material, and increases the surface area available for the treatment process. This is particularly important if a chemical reaction is involved.

Advantageously the method further comprises: adding solid or fluid materials to the particulate material before the material enters the envelope of the fluid; and mixing the solid or fluid additives with the particulate. For many treatment processes additives assist both the process and any chemical reaction that ensues.

The particulate material and the fluid may be continuously transported through a treatment chamber. This increases the tonnages that may be treated without leading to the build up of stock that occurs in batch production.

Preferably the treatment chamber comprises an upper level and a lower level, the inlet to the treatment chamber being at the upper level, and the particulate being transported from the upper level to the lower level, and to an outlet that leads from the lower level to a discharge point above the point of entry of the particulate material. If the fluid is a gas that is more dense than air, the apparatus may not need to be sealed.

In a preferred embodiment the solid is contaminated earth, and the fluid is carbon dioxide. This is the process for which the method was developed, as described in the international patent application W097/13735. In this case the additives may be one or more of cement; lime; or other substances that assist in binding and stabilising the contaminants.

The fluid may be a gas. In this case the treatment chamber may be sealed. In particular the gas may be carbon dioxide. As carbon dioxide is more dense than air there is in this embodiment no need to seal the treatment chamber. The method according to the invention, however, may be used for other processes where similar or analogous requirements arise.

According to another aspect of the invention, we provide apparatus for treating a particulate solid material with a fluid, comprising a treatment chamber having an inlet and an outlet, means for maintaining an envelope of the fluid in the treatment chamber, and means for transporting the material through the treatment chamber, to be treated by the fluid therein.

Preferably there is means for agitating the material in the course of its transportation through the treatment chamber, so that as much as possible of the surface area of the particles of material is exposed to the fluid for reaction therewith.

Preferably the inlet and the outlet of the treatment chamber are disposed at a different level from that of the treatment chamber in order to maintain the envelope of fluid in the chamber. In a preferred embodiment the inlet and the outlet are both higher than the bulk of the treatment chamber. This enables a fluid that is more dense than air, such as carbon dioxide, to be easily retained within the treatment chamber. Indeed, with liquids, or gases that are more dense than air, the treatment chamber may not even need to be sealed against the atmosphere.

In the broadest aspect of apparatus according to the invention, however, for use with a fluid that is less dense than air, the inlet and outlet could be sited below the treatment chamber. This also provides a trap for the fluid, which cannot easily escape.

Advantageously the apparatus comprises feed screw means for said transportation of the material through the treatment chamber. Preferably the feed screw means includes formations for causing or assisting said agitation of the material as it is transported thereby: such formations may extend generally lengthwise of an elongate feed screw element or auger screw, at or adjacent the outer edge thereof.

Said formations may be adapted to lift the material in the vicinity of the screw element as the latter rotates. The mode of transportation of the material then comprises, in addition to the axial displacement thereof by the feed screw element, lifting thereof to the highest part of the outer diameter of the screw element, followed by dropping of the material to the general quantity of the material being transported in the treatment chamber.

The preferred form of the treatment chamber is that of an elongate trough with a lower region which is part-circular in cross-section and within which the lower half of the feed screw element is a close fit for transporting the material therealong, and a closed upper part which provides space around the upper half of the feed screw element for establishment of the atmosphere of carbon dioxide for the treatment of the material.

In a particularly preferred embodiment, when the fluid is more dense than air, the treatment chamber comprises two portions, one above the other, the inlet leading to the upper portion and the outlet leading from the lower portion. This establishes the different levels that are optimal for the retention of the fluid. It also enables a long treatment chamber to be fitted into a compact area. Such a treatment chamber may be easily transported in, for example, a truck or trailer. The chamber can thus be transported to the particular sites where it is needed. Further portions of the treatment chamber, i.e. a third, fourth, etc. troughs arranged above and/or alongside the initial two may easily be envisaged.

The length of the treatment chamber needs to be sufficient for the material to be in contact with the fluid for a sufficient length of time for the reaction to take place. When the fluid is a gas the treatment apparatus may further comprise a storage tank and vaporisation unit for delivery of the gas at a required pressure. This enables appropriate quantities of gas to be readily supplied to the treatment chamber. This enables the envelope to be maintained therein and gas that has been consumed by reaction with the solid material or lost due to leakage to be replaced.

The apparatus may further comprise means (e.g. crushing or shredding means) for bringing a solid material into an appropriate particulate form for treatment. This enables solid earth (or other material) to be loaded into the apparatus. The treatment process can therefore operate directly on the sites that have been affected by contamination.

The apparatus may comprise a crusher followed by a shredder that is operable to receive the crushed material and further divide it into smaller particles. This enables a greater surface area of particulate material to be exposed to the fluid. It is therefore particularly important when a chemical reaction is involved in the treatment process, such as that involved in carbonation.

The treatment apparatus may further comprise a main hopper where the particulate material may be stored. It may further comprise an auger screw, leading from the main hopper to the treatment chamber. Other additives may be added at intervals along this main screw. This enables other materials, which may be essential to the treatment (such as cement in carbonation treatment), or merely advantageous to the treatment (such as lime in carbonation treatment) to be added and mixed with the solid particulate before it reaches the treatment chamber.

The invention will now be described by way of example only with reference to the accompanying drawings where:- Figure 1 shows schematically a plan view of an embodiment of the apparatus according to the invention;

Figure 2 shows schematically a side elevation of the apparatus, illustrating the carbonation chamber in further details; and

Figure 3 shows schematically an end view of the carbonation chamber.

Figure 4 shows a diagrammatic longitudinal cross section through part of a carbonation chamber in accordance with the invention.

Figure 5 is a diagrammatic transverse cross section through the carbonation chamber.

Referring firstly to Figure 1 of the drawings, this shows the overall scheme of apparatus, for carrying out the method, in accordance with the invention. A quantity of solid raw material is indicated at 1, such material typically being contaminated earth which is unsuitable for land fill disposal without treatment. The contamination may be inorganic, frequently it contains heavy metals. The material 1 is initially fed to a primary crusher 2 in which it is reduced particulate form, after which it is transported by a conveyor 3 to a shredder 4. The shredder further reduces the particle size of the material, so that the maximum surface area of particles of the material can be contacted by carbon dioxide in a carbonation process as described in International Patent Publication WO 97/13735. The material is then conveyed to a storage hopper 5.

The particulate matter is transported from the hopper 5 by an auger feed/ mixing screw 6. Silos 7 contain additives that are fed into the mixture at different points along the screw. Cement, the main binding material for the contaminant, is usually added at this point. Other binding materials such as pulverised fuel ash may be used instead, however. Other additives may include lime, which accelerates the carbonation process, and water, which further breaks down the particulate. The mixture is thoroughly mixed with these by the time it reaches a carbonation chamber 8.

A fluid, in this case carbon dioxide, is fed into the carbonation chamber 8 from a pressure regulated storage and vaporiser unit 9. This ensures that the level of gas remains constant within the carbonation chamber 8.

Further details of the arrangement of the chamber 8 may be seen in Figures 2 and 3 and the construction thereof in Figures 4 and 5. The chamber 8 is mounted on a trailer 11 and arranged as two portions: an upper portion 12 and a lower portion 13. The solid particulate and the carbon dioxide enter the upper trough 12 at the back end of the trailer 11. The material is then transported and agitated by a feed screw along the length of the upper trough 12. On reaching the end of the upper trough a gravity feed suffices to move the material to the lower chamber portion where further transportation and agitation occur. Upon reaching the end of the lower portion the material is fed into an upwardly inclined auger screw 14 to an outlet 15, above the level of inlet 16.

The speed of operation of the feed screws in the chamber portions 12, 13 is controlled to give the particulate material sufficient dwell time in contact with the carbon dioxide, bearing in mind the length of the carbonation chamber through which the particulate material travels in contact with the carbon dioxide. For example a time of several minutes may be required for effective carbonation.

The height of the outlet 15 ensures that the carbon dioxide cannot escape from the chamber. As it is more dense than air it simply sinks to the lowest level possible, forming an envelope of fluid through which the particulate material must move.

It would be possible for an envelope of carbon dioxide to be maintained in the lower trough 13 and not in the upper trough 12; in this case the auger screw feed of particulate material though the latter would ensure more effective mixing prior to carbonation. It will be appreciated that one or more further troughs could be provided as required, to enable the particulate material to be contacted with the carbon dioxide for sufficient time for satisfactory carbonation.

Referring now to Figures 4 and 5 of the drawings, these show, respectively in a longitudinal cross section and a transverse cross section, a particularly advantageous form of treatment chamber and a feed screw means therein by which the material is transported through the treatment chamber to undergo the carbonation process. These drawings show a portion indicated generally at 30 of a treatment chamber, which is in the form of an elongate trough with a lower part 31 of substantially semi-circular shape in transverse cross section and an upper part 32 which has parallel upwardly extending walls and a closed flat top 33. An inlet 34 is shown adjacent one end of the chamber. An elongate feed screw or auger element is disposed within the chamber and is indicated generally at 35. It has a central shaft 36 carrying a helical blade 37 and is rotatable about axis 38 extending length-wise of the chamber. The shaft 36 extends outwardly from an end of the chamber 30 to a drive motor 39 preferably an electric motor. The direction of rotation of the screw element is indicated by arrow 45: this causes particulate material lying in the lower part 31 of the trough forming the treatment chamber to be advanced from left to right therein having regard to the orientation of Figure 4, from the inlet 34 to an outlet at the other end of the chamber possibly leading to a further similar chamber portion disposed beneath the illustrated portion.

In carrying out the carbonation process above referred to, an atmosphere of carbon dioxide is maintained in the treatment chamber for the material being transported therethrough to react with. The space in the upper half of the chamber where walls 32 are spaced from the upper part of the periphery of the feed screw enables a substantial quantity of carbon dioxide to be maintained in the chamber for such reaction. Inherently transport of particulate material by a feed screw causes a certain amount of agitation of the material so that it is able to react effectively with the carbon dioxide but preferably such agitation is assisted by the provision of agitating formations on the feed screw.

As shown in the drawings, the radially outer most edge of the blade 37 is provided at spaced intervals with radially-extending cuts enabling small portions 40 of the material (typically steel sheet) of the material to be bent down out of the general "plane" of the blade to extend axially of the screw. The presence of these formations alone assists agitation, but in addition a number of axially extending agitation members 41 are provided, each extending between adjacent aligned formations 40 on adjacent turns of the blade 37 of the screw 35. Obviously the number provided of the members 41 and their disposition must be such that the screw 35 remains in balance, even though its rotational speed will be low e.g. less than 10 rpm.

Each of the members 41 is of L shape in transverse cross section, and fits closely within the openings left by the displacement of formations 40 from the screw blade 37. They may be secured by welding. The illustrated configuration and orientation of the members 41 is such that they will lift particulate material from the lower part 31 of the treatment chamber 30 and carry it upwardly to the uppermost part of the screw element and then drop the material down to the bottom of the treatment chamber. Clearly this causes as much as possible of the surface area of the particulate material to be exposed to the atmosphere of carbon dioxide, facilitating the carbonation process.

The carbonated material produced (17) may be replaced in the ground or used for landscaping a site. In this way it is possible to process large tonnages of contaminated land, on site, and replace the land at the end of the process. This enables contaminated sites to be reclaimed and developed, sparing greenfield sites.

In the present specification "comprise" means "includes or consists of and "comprising" means "including or consisting of.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A method of treating a particulate solid material with a fluid comprising: maintaining an envelope of the fluid; feeding the solid material into the envelope of the fluid; transporting the solid material through the envelope of the fluid to be treated in the course of such transport; and discharging the material.

2. A method according to Claim 1 further comprising the step of agitating the solid material during its passage through the envelope of the fluid, to expose as much surface area as possible to the fluid.

3. A method according to any preceding claim in which the treatment occurs in a treatment chamber with an inlet and an outlet and the fluid envelope is maintained by the inlet and outlet being at a higher level than the level at which the particulate travels through the envelope.

4. A method according to Claim 1 or Claim 2 in which the treatment occurs in a treatment chamber with an inlet and an outlet and the fluid envelope is maintained by the inlet and outlet being at lower level than that at which the particulate travels through the envelope.

5. A method according to any preceding claim in which the solid is transported and agitated using feed screw means.

6. A method according to Claim 5 wherein the feed screw means includes agitating formations for assisting in said agitation.

7. A method according to any preceding claim further comprising: crushing the solid material into particulate form; and shredding the solid material to decrease the particulate size further before the particulate is transported through the fluid envelope.

8. A method according to any preceding claim further comprising: adding solid or fluid materials to the solid particulate before it enters the envelope of solid material, or during its transport through it; and mixing the solid or fluid additives with the particulate.

9. A method according to any preceding claim in which the particulate material and the fluid are continuously transported through a treatment chamber.

10. A method according to Claim 9 in which the treatment chamber comprises an upper level and a lower level, and the inlet to the treatment chamber is at the upper level and the particulate material is transported from the upper level to the lower level, and an outlet leads from the lower level to a discharge point above the point of entry of the solid material.

11. A method according to any preceding claim in which the solid is contaminated earth, and the fluid is carbon dioxide.

12. Apparatus for treating a solid particulate material with a fluid, comprising a treatment chamber with an inlet and an outlet, means for maintaining a fluid envelope in the treatment chamber, and means for transporting the material through the treatment chamber from the inlet to the outlet, to be treated by the fluid therein.

13. Apparatus according to Claim 12 further comprising means for agitating the material in the treatment chamber, so that as much of the surface area of the material as possible is exposed to the fluid for reaction therewith.

14. Apparatus according to Claim 12 or Claim 13 in which the inlet and the outlet of the treatment chamber are disposed at a different level from that of the treatment chamber in order to maintain the envelope of fluid in the chamber.

15. Apparatus according to Claim 12 or Claim 13 in which the inlet and the outlet are both higher than the treatment chamber.

16. Apparatus according to any of Claims 11 to 15 comprising feed screw means for said transportation of the material through the treatment chamber.

17. Apparatus according to Claim 16 wherein said feed screw means includes formations for causing or assisting agitation of said material as it is transported thereby.

18. Apparatus according to Claim 17 wherein said formations extend generally lengthwise of an elongate feed screw element at or adjacent the outer edge thereof.

19. Apparatus according to Claim 18 wherein said formations are adapted to lift said material in the vicinity of the screw element as the latter rotates.

20. Apparatus according to any of Claims 11 to 19 in which the treatment chamber comprises at least two portions, alongside and/or one above the other.

21. Apparatus according to any of Claims 11 to 20 in which the fluid is a gas.

22. Apparatus according to Claim 21 in which the gas is carbon dioxide.

23. Apparatus according to Claim 19 or Claim 20 further comprising a storage tank and vaporisation unit for delivery of the gas at a required pressure.

24. Apparatus according to any of Claims 11 to 23 further comprising a crusher for dividing solid material into particulate matter.

25. Apparatus according to Claim 24 further comprising a shredder that is operable to receive crushed material and further divide it into smaller particulate.

26. Apparatus according to any of Claims 11 to 25 further comprising a main hopper where the particulate material may be stored.

27. Apparatus according to any of Claims 11 to 26 further comprising a feed screw, leading to the treatment chamber.

28. Apparatus according to Claim 25 in which other materials are added at intervals along this main screw.

29. Apparatus according to any of Claims 11 to 26 in which the solid comprises contaminated landfill.

30. A method of treating a solid particulate material with a fluid substantially as hereinbefore described with reference to the accompanying drawings.

31. Apparatus for treating a solid particulate material with a fluid substantially as hereinbefore described with reference to the accompanying drawings.

32. A method or apparatus according to any one of the preceding claims, used for the carbonation process of WO 97/13735.

33. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.