GB2371298A

GB2371298A - Treatment of a solid material with a fluid

Info

Publication number: GB2371298A
Application number: GB0101166A
Authority: GB
Inventors: Patrick Joseph Forker
Original assignee: FORKERS Ltd
Current assignee: FORKERS Ltd
Priority date: 2001-01-17
Filing date: 2001-01-17
Publication date: 2002-07-24
Anticipated expiration: 2021-01-17
Also published as: WO2002057008A1; GB0101166D0; GB2371298B

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 wherein the material is transported through a treatment chamber in which an envelope of the fluid is maintained by virtue of the chamber having an inlet 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 by a feed screw 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 WO97/13735. 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 solid material through the treatment chamber, to be treated by the fluid therein.

Preferably there is means for agitating the solid 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 need not even 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 means for transporting the material through he treatment chamber comprises screw means. In a particularly preferred embodiment the material is moved by means of an auger screw. This conveniently combines transportation and agitation of the material as it passes through the fluid envelope.

In a particularly preferred embodiment, when the fluid is more dense than air, the treatment chamber comprises two troughs, one above the other, the inlet leading to the upper trough and the outlet leading from the lower trough.

This established 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 embodiments of the treatment chamber, featuring a third, fourth, etc. troughs stacked onto 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 1 shows the various hoppers, silos and conveyers necessary for the entire process. A solid raw material 1 is fed initially into a primary crusher 2. In this case the material is contaminated earth which is unsuitable for landfill disposal without treatment. The contamination is sometimes inorganic and frequently heavy metal related. In its passage through the crusher the material is reduced to particulate form. From the crusher the particulate is transported via a conveyer 3 to a shredder 4. This further reduces the size of the particulate, exposing the maximum area of contamination for the carbonation process. It is then conveyed into a main hopper 5 for storage.

The particulate matter is transported from the hopper 5 by an auger 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 vapouriser unit 9. This ensures that the level of gas remains constant within the carbonation chamber 8.

Further details of the carbonation chamber 8 may be seen in Figures 2 and 3. The chamber 8 is mounted on a trailer 11 and arranged as two troughs: an upper trough 12 and a lower trough 13. The solid particulate and the carbon dioxide enter the upper trough 12 at the back end of the trailer 11. They are then transported and agitated by auger screws 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 trough where further transportation and agitation occur. Upon reaching the end of the lower trough 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 screw 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.

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 monoxide 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.

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, and enabling all of us to enjoy our heritage for a little while longer.

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

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 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.
7. 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.
8. A method according to any preceding claim in which the particulate material and the fluid are continuously transported through a treatment chamber.
9. A method according to Claim 8 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.
10. A method according to any preceding claim in which the solid is contaminated earth, and the fluid is carbon dioxide.
11. 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 solid material through the treatment chamber from the inlet to the outlet, to be treated by the fluid therein.
12. Apparatus according to Claim 11 further comprising means for agitating the solid material in the treatment chamber, so that as much of the surface area of the particulate material as possible is exposed to the fluid for reaction therewith.
13. Apparatus according to Claim 11 or Claim 12 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.
14. Apparatus according to any of Claim 11 or Claim 12 in which the inlet and the outlet are both higher than the treatment chamber.
15. Apparatus according to Claim 11 in which the inlet and outlet are both lower than the treatment chamber.
16. Apparatus according to any of Claims 11 to 15 in which the solid material is screw fed through the treatment chamber.
17. Apparatus according to Claim 16 in which the solid material is moved by means of an auger screw.
18. Apparatus according to any of Claims 11 to 17 in which the treatment chamber comprises two troughs, one above the other, the inlet leading to the upper trough and the outlet leading from the lower trough.
19. Apparatus according to any of Claims 11 to 18 in which the fluid is a gas.
20. Apparatus according to Claim 19 in which the gas is carbon dioxide.
21. Apparatus according to Claim 19 or Claim 20 in which the treatment apparatus further comprises a storage tank and vaporisation unit for delivery of the gas at a required pressure.
22. Apparatus according to any of Claims 11 to 21 further comprising a crusher for dividing solid material into particulate matter.
23. Apparatus according to any of Claims 11 to 22 further comprising a shredder that is operable to receive crushed material and further divide it into smaller particulate.
24. Apparatus according to any of Claims 11 to 23 further comprising a main hopper where the particulate material may be stored.
25. Apparatus according to any of Claims 11 to 24 further comprising an auger screw, leading to the treatment chamber.
26. Apparatus according to Claim 25 in which other materials are added at intervals along this main screw.
27. Apparatus according to any of Claims 11 to 26 in which the solid comprises contaminated landfill.
28. A method of treating a solid particulate material with a fluid substantially as hereinbefore described with reference to the accompanying drawings.
29. Apparatus for treating a solid particulate material with a fluid substantially as hereinbefore described with reference to the accompanying drawings.
30. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.