GB2318115A

GB2318115A - Lightweight aggregate from fly ash and coal tailings

Info

Publication number: GB2318115A
Application number: GB9716064A
Authority: GB
Inventors: Allen Grievson; Stephen Newcomb
Original assignee: CINTAG Ltd
Current assignee: CINTAG Ltd
Priority date: 1996-08-01
Filing date: 1997-07-31
Publication date: 1998-04-15
Also published as: GB9716064D0

Abstract

A lightweight aggregate material is formed by sintering a pelletised mixture which includes coal tailings and fly ash. Applications of the material include use in the building and construction industry and in agriculture and horticulture.

Description

LIGHTWEIGHT AGGREGATE This invention relates to lightweight aggregate and a process for the production thereof.

Lightweight aggregates of various kinds are well known. They are used mainly in the building industry, but they can be used elsewhere. There are a number of different known processes for making lightweight aggregates. They all have one disadvantage in common, however, which is that they are expensive, because of the cost of the starting materials or because of the processing costs or a combination of both. The present invention has been made in order to overcome this problem.

According to the invention there is provided a lightweight aggregate material comprising a sintered mixture said mixture comprising coal tailings and fly ash.

The invention also provides a process for producing the lightweight aggregate just defined comprising the steps of mixing coal tailings with fly ash to form pellets and sintering the pelletised mixture.

The proportion of coal tailings to fly ash may be in the range of from 1:99% to 50:50%, preferably 10:90% to 50:50%, more preferably 20:80% to 40:60% and particularly from 25:75% to 35:65% all by volume. The particular proportions chosen may depend upon the nature of the starting materials, that is to say for example the proportion of coal in the coal tailings, the moisture content of both tailings and fly ash and the like. In that connection it is preferred that the moisture content of the mixture does not exceed about 35.0% by volume nor be below about 5.0% by volume. Outside these limits it may prove difficult to form pellets which retain their form while being transferred to, and during, the sintering step.

During sintering the pellets will normally coagulate. It may be advantageous, therefore, to break up the sintered product as by crushing or other appropriate procedure followed if desired by classification according to particle size.

In contrast with some known processes for making lightweight aggregates, particularly those using pep coke, the use of coal tailings can lead to undesirable emissions being produced during the sintering stage due to the tar content of the coal tailings. It is desirable therefore that any gases produced during the sintering stage are subjected to scrubbing before discharge into the atmosphere.

A particular advantage of the invention is that is uses as the starting materials, what are effectively waste products, that is to say coal tailings and fly ash. Present day concern about the environment has created problems about the disposal of both coal tailings and fly ash. The coal mixing industry which produces coal tailings is looking for a way of getting rid of this byproduct which does not just consist of dumping it. Similarly power stations which produce fly ash have a disposal problem for that by-product. Utilising these waste products in the present invention is not only economically beneficial, but it also provides an environmental benefit in that is solves the problem of an environmentally acceptable way of disposal of the waste products.

The lightweight aggregate of the present invention can be used for all the purposes for which presently known lightweight aggregates are used. Thus they can be used in the building and construction industry, they can be used for making surfaces, in particular specialised surfaces for sports. They can also be used for agriculture and horticulture.

The following example further illustrates the invention.

Fly ash and coal tailings in the form of a slurry containing between 10 to 20% coal are provided in the ratio 80% fly ash to 20% coal tailings, by volume.

The fly ash and coal tailings are fed into a crusher where they are crushed and mixed to form a powdered mixture of the ingredients. Additional water may be added to the mixture at this stage to bind the mixture.

The resulting mixture is formed into pellets, either by extrusion or by using a rotating barrel type pelletiser. The pellets are then fed onto a moving sinter strand and into a high temperature furnace at a temperature of approximately 900-1200 C. The proportion of coal in the pellets is ignited by the furnace.

The pellets leave the furnace in a sintered state. Gases emitted during sintering are fed to a scrubber.

The final stage in the process is the classification of the sintered pellets.

The pellets are passed over a screen where they are classified according to size.

Any pellets which have become baked together are separated in a crusher and returned to the screen for reclassification.

The above example is not to be taken as limiting in any way, many variations are possible without departing from the invention.

Claims

1. A lightweight aggregate material comprising a sintered mixture, said mixture comprising coal tailings and fly ash.

2. A lightweight aggregate material according to claim 1, wherein the proportion of coal tailings to fly ash is in the range 1:99% to 50:50% by volume.

3. A lightweight aggregate material according to claim 1, wherein the proportion of coal tailings to fly ash is in the range 10:90% to 50:50% by volume.

4. A lightweight aggregate material according to claim 1, wherein the proportion of coal tailings to fly ash is in the range 20:80% to 40:60% by volume.

5. A lightweight aggregate material according to claim 1, wherein the proportion of coal tailings to fly ash is in the range 25:75% to 35:65% by volume.

6. A lightweight aggregate as claimed in any preceding claim, wherein the moisture content of the mixture lies in the range 5% to 35% by volume.

7. A lightweight aggregate substantially as herein described.

8. A process for producing a lightweight aggregate comprising the steps of providing coal tailings, providing fly ash, mixing the coal tailings with the fly ash to form pellets and sintering the pelletised mixture.

9. A process according to claim 8, wherein the proportion in which the coal tailings and fly ash are provided is in the range of 1:99% to 50:50% by volume.

10. A process according to claim 8, wherein the proportion in which the coal tailings and fly ash are provided is in the range of 10:90% to 50:50% by volume.

11. A process according to claim 8, wherein the proportion in which the coal tailings and fly ash are provided is in the range of 20:80% to 40:60% by volume.

12. A process according to claim 8, wherein the proportion in which the coal tailings and fly ash are provided is in the range of 25:75% to 35:65% by volume.

13. A process according to any of claims 8 to 12, wherein the coal tailings and fly ash are mixed to form a mixture with a moisture content in the range 5% to 35% by volume.

14. A process according to any of claims 8 to 13, wherein the mixture is crushed after sintering.

15. A process according to any of claims 8 to 14, wherein any gases emitted during the sintering of the pellets are subjected to scrubbing before release to the atmosphere.

16. A process for producing a lightweight aggregate substantially as herein described.