GB2425537A

GB2425537A - Manufacture of coke from a blend of coal and polymers

Info

Publication number: GB2425537A
Application number: GB0608068A
Authority: GB
Inventors: Peter William Herbert Bennett
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-25
Filing date: 2006-04-25
Publication date: 2006-11-01
Anticipated expiration: 2026-04-25
Also published as: WO2006114650A3; WO2006114650A2; GB2425537B; GB0608068D0

Abstract

In the manufacture of coke, it is conventional to use blends of coals so that they are compatible with each other. For compatibility, the range of temperatures for which one coal is fluid (the fluidity range) needs to overlap the fluidity range for another coal in the blend by at least 30{C, preferably 50{C. Coke may be made from a mixture of at least two incompatible coal types in combination with a polymer (eg an elastomer such as rubber obtained from granulating discarded motor vehicle tyres). The polymer extends the fluidity ranges of the incompatible coals so that they become compatible and make a good commercial quality coke. Coke may also be made from a mixture of at least one coal and a polymer wherein the volatile content of that coal is sufficiently high that the mixture has a maximum fluidity at least as great as that of the mixture without the polymer. The polymer, in increasing the maximum fluidity, thus makes it possible to use a greater proportion of additives that would tend to have the opposite effect and also makes it possible to use a higher proportion of other coals having low maximum fluidity values.

Description

MANUFACTURE OF COKE FROM A BLEND OF COAL AND

POLYMERS

This invention relates to a method of making coke from a blend of coal and a polymer or elastomer such as rubber.

Coals are ranked according to the proportion of volatile material in them and this can be measured by observing the reflectance of the coal particles which is generally recognized as being inversely proportional to volatile content.

Fig 1 shows the coal classification system used by the United Kingdom National Coal Board. From this it can be seen that coals are viewed as belonging to one of three categories: (1) low-volatile steam coals and anthracites, having a volatile content of less than 19.6%; (2) medium volatile coals, having a volatile matter content of between 19.6% and 32%; and (3) high volatile coals having a volatile content of over 32%.

For the purpose of this specification the terms "low volatile," "medium volatile", and "high volatile" are defined as referring to coals having respective volatile content ranges as specified in the aforementioned classification system.

The medium volatile coals, namely those having a rank code of between 300 and 400 (equating to a volatile content of between 19.6 and 32) are the best for coke manufacture.

Coke made from high volatile coals having a rank code of 400 and above (equating to a volatile content of 32 and above) as shown on Fig 1, will be too weak for certain purposes, e.g. for steel production.

Low volatile coals produce high pressures in the coking ovens and therefore risk causing damage to the coking ovens. Low volatile coals also tend to have a low maximum fluidity which may make coking impossible for the reasons explained above.

Another characteristic of coal, known to be an important influence on coke quality, is its maximum fluidity. During the formation of coke, the coal first becomes fluid and then solidifies to form a single solid mass which is broken up into individual lumps as the coke is finally pushed from the oven. Coals whose maximum fluidity is too low will not make good coke because this process does not occur properly. As a general rule, high volatile coals have a high maximum fluidity whilst low volatile coals have a low maximum fluidity.

Fluidity can be measured using an instrument called a Gieseler Plastometer. This instrument measures the plastic properties of coal by applying a constant torque to a stirrer placed in a crucible containing the coal sample under test. The coal sample is heated at a rate of 3 degrees Centigrade per minute (the same rate of temperature rise as is experienced in a coking oven) over a temperature range of 300 to 550 degrees Centigrade. At first, the coal softens and develops plasticity and the stirrer begins to move in the sample because of the applied torque. The speed of movement is a measure of plasticity and is measured in dial divisions per minute (ddpms). The plasticity increases to a maximum value and then, as temperature increases further, the plasticity decreases and the stirrer finally stops moving as the coal solidifies into coke.

In the manufacture of coke in situations where a number of different coals are available, it is known to assess the maximum fluidity of each available coal and to create a blend of them in proportions such that the average of the maximum fluidity values is within a range known to give a coke of the required quality.

When selecting coals to be blended, it is important also to consider a coal property known as "fluidity range." When any coal is heated in a coking oven it becomes fluid at a particular temperature and time and becomes solid at a later time and a higher temperature. There exists, therefore, a range of temperatures at which the coal is fluid. This temperature range is called the "fluidity range." If one attempts to make coke from a blend of two coals having fluidity ranges that do not overlap by a sufficient amount the coals are "incompatible" and do not make coke of a quality that is acceptable for most purposes. The overlap needs to be at least 30 C and preferably at least 50 C for the coals to be compatible, the exact value depending on circumstances such as the intended use for the coke.

Where three or more coals are blended, it is preferable that each coal be compatible with each other coal in the blend. However it may be acceptable in some situations for the blend to contain two coals that on their own would be incompatible but each of which is compatible with an intermediate coal or an intermediate group of coals that are themselves compatible. Any coal having a fluidity range which does not overlap others by a sufficient amount has to be rejected as incompatible.

Thus, the term "compatible" when used in this specification is defined as the relationship between two coals such that their fluidity ranges overlap sufficiently to allow them to interact so as to form an acceptable coke. This overlap is preferably at least 30 C and more preferably at least 50 C.

The assessment of fluidity range overlap can be made by conducting fluidity tests on the actual coals to be processed, or can be made using an assumption that coal from a particular seam has properties similar to those measured earlier from samples from the same seam.

It is common practice to mix additives with coal to achieve the desired characteristics in the resulting coke. Traditional materials include coke breeze, petroleum coke and anthracite. There have also been proposals to use rubber crumb as an additive. One such proposal is described in a paper "Qualified Utilization of Technogenic Wastes in by-product Coke Plants" by A. V. Saltanov published in "Coke and Chemistry" No 1, pp. 40- 47, 2002. Proposals involving the use of rubber crumb have principally been aimed at providing a convenient method for disposing of waste rubber and it is believed that none has been employed commercially because the effect of the rubber on the coking process has not hitherto been thoroughly understood and there has therefore been a risk of damage to the coking ovens, uncertainty about the quality of the resulting coke and a likelihood of unacceptable atmospheric pollution.

When an additive is included it would normally be expected to degrade the fluidity of the coal and therefore additives need to be included with caution since the reduced fluidity may have a detrimental effect on the coke quality. However, Saltanov suggests that rubber crumb can, like some conventional inert additives, be added to a conventional coking coal with a positive effect on quality.

It has now been discovered that, when a polymer such as rubber is used as an additive, it appears to behave more like a coal than an inert additive, and has the remarkable effect of increasing the fluidity range of the coal with which it is mixed. The inventor has realized that this makes it possible to use, in a coking process, a blend of coals which, hitherto, would have been considered incompatible.

Thus, according to the invention there is provided a method of making coke from a mixture of coal and a polymer characterized in that the coal includes particles of at least two coal types having different fluidity ranges such that, in the absence of the polymer, they would be incompatible, the polymer being present in a proportion such that, if mixed with coal of each individual type in the same proportion, would cause the ranges to overlap or would increase an existing overlap to an extent making the coals compatible.

By employing the invention, because the fluidity range of each coal type is known to be extended by the presence of the rubber or other polymer, coals which might previously have been rejected as incompatible can now be included in the blend.

As previously mentioned, satisfactory coke can be made from a blend of coals whose fluidity ranges overlap by at least 30 C or, more preferably, 50 C.

Therefore, in order to benefit from the above discovery, the fluidity ranges of the individual coals without the addition of rubber or other polymer (but possibly with the addition of an inert additive) need to overlap by less than a critical figure within the range of about 30 C to 50 C inclusive. Expressed another way, the constituents of the blend need to be such that they are incompatible without the addition of the polymer.

The blend of coals preferably includes a high volatile coal. It has been discovered, as will be explained later, that that the addition of polymer, especially an elastomer such as rubber, to high volatile coals can increase the maximum fluidity values. This improves the variety of choices available for other components of the blend. For example, more inert additive could be used, or another component of the blend could be a coal of relatively low maximum fluidity. This feature is considered to have independent inventive merit and thus, according to a second aspect of this invention there is provided a method of making coke from a mixture containing at least one coal and a polymer characterised in that the volatile content of the said coal is sufficiently high that the mixture has a maximum fluidity at least as great as that of the mixture without the polymer.

One way of utilizing the invention will now be described by way of example with reference to the accompanying figures in which:- Fig I shows the coal classification system used by the UK National Coal Board; Fig 2 is a record of the results of an experiment in which tests were carried out on high, medium and low volatile coal samples a) on their own, b) with the addition of 7% breeze, c) with the addition of 7% by weight tyre crumb and d) with the addition of 10% tyre crumb; and Fig 3 is a diagrammatic illustration showing how the fluidity range overlap is increased by the presence in the blend of 7% by weight of tyre crumb A coking plant has three ranks of coal available: high volatile, medium volatile and low volatile. Conventional practice would predict that the medium volatile coal would be the most suitable for making high quality coke e.g. for steel making. The high volatile coal would result in a coke having insufficient strength, whilst the low volatile coal can produce dangerously high pressure within the oven; and therefore these coals would only be used when blended with medium/high volatile coal.

In the coking process to be described it is assumed that a high strength coke needs to be prepared, requiring the components of a coal blend to be compatible to the extent that their fluid range overlap is at least 50 C Also located at the coking plant is a supply of scrap used motor vehicle tyres and a machine, known per se, for reducing the tyres to small particles of rubber (rubber crumb) and for removing the steel reinforcing material. The rubber particles are between 2 and 1 Omms in diameter.

Using a Gieseler Plastometer, fluidity measurements have been performed on samples of each of a high, medium and low volatile coal having respective volatile contents of 34.4%, 28.5% and 19.2% respectively. For each coal type, measurements were made: a) without any additive; b) with the addition of 7% breeze; c) with the addition of 7% tyre crumb; and d) with the addition of 10% by weight tyre crumb. The results are shown in Fig 2.

Fig 3 uses the measurements taken from Fig 2 to illustrate, diagrammatically, the ranges at which the high and low volatile coals are fluid for the addition of the 7% by weight of tyre crumb. It can be seen that there is an overlap of only 47 C without the addition of tyre crumb, this being insufficient for compatibility.

However, the overlap is massively increased to 56 C when the tyre crumb is added, making the coals clearly compatible.

Referring to the final column of Fig 2, it can be seen that the addition of tyre crumb to the low volatile coal very significantly decreases its maximum fluidity; and a similar effect is obtained for the medium volatile coal, though not so dramatic if the quantity of rubber is limited to 7% by weight. For the high volatile coal, however, the results show, surprisingly, that an addition of 7% by weight of rubber crumb increases the maximum fluidity, this effect being diminished when the amount of tyre crumb is increased to 10%.

Therefore, making use of the results of the above experiments, a quantity of high volatile coal (volatile content 34.4) was blended with an equal quantity by weight of low volatile coal (volatile content 19.2) and 7% by weight tyre crumb, having a range of diameters from 2 to l0mms. The blend was loaded into a conventional coking oven and heated in a conventional maimer in the absence of oxygen. The result was: a high quality lump coke; a higher yield of by-products per given volume of coal as compared with conventional processes in which no rubber is added; and no increase in air pollution. Furthermore, this was achieved using relatively low-cost coals which would, without the rubber, be considered incompatible or where their limited compatibility would have been expected to result in a lower quality of coke. Also, this process has been found to produce a remarkably low level of air pollution and it therefore offers a highly acceptable method of disposing of unwanted used tyres as well as providing the desired quality of coke.

It is emphasized that the example that has been described is just one of many different ways in which the invention can be performed. For example, it is anticipated that the results obtained using rubber are likely to be representative of other polymer materials such as waste plastics. The particular ranks of coal used in the example were not highly incompatible. It would be possible to use coals having a much smaller or non-existent fluidity overlap, the effect of the rubber being to create an overlap which is sufficient to give a strong coke. It would also be possible to vary the quantity of rubber included in the blend, which can be varied between about 3% and 10% by weight and possibly more.

The particular ranks of coal used in the example were not highly incompatible.

Using the principle of the invention it would be possible to use coals having a much smaller or non-existent fluidity overlap, the effect of the rubber being to create an overlap which is sufficient to give a strong coke. Also, although experiments have so far been conducted only with rubber, it is predicted that a similar beneficial result can be achieved using other scrap polymer or elastomer products.

Claims

1. A method of making coke from a mixture of coal and a polymer characterized in that the coal includes particles of at least two coal types having different fluidity ranges such that, in the absence of the polymer, they would be incompatible, the polymer being present in a proportion such that, if mixed with coal of each individual type in the same proportion, would cause the ranges to overlap or would increase an existing overlap to an extent making the coals compatible.

2. A method according to claim 1 characterized in that one of the coal types has a volatile content sufficiently high that when the coal is mixed with the polymer in the said proportion, the maximum fluidity does not become less.

3. A method according to Claim 1 or 2 characterized by the step of mixing an inert additive to the mixture.

4. A method according to Claim 1, 2 or 3 including the step of assessing properties of the different coal types and adding polymer to the mixture in a proportion which is a function of the individual results of such assessment.

5. A method according to any preceding Claim characterized in that the fluidity ranges overlap by less than 50 C without addition of the polymer and by greater than 50 C with the addition of the polymer.

6. A method according to Claim 5 characterized in that the fluidity ranges overlap by less than 30 C without addition of the polymer and by greater than 30 C with the addition of the polymer.

7. A method according to any preceding Claim characterized in that the polymer is present in the mixture in a proportion which, if mixed with the individual coal types in the same proportion, would cause an overlap to exceed a critical value in the range from 30 C to 50 C.

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8. A method according to any preceding claim for manufacturing coke of a particular type comprising assessing fluidity characteristics of available coal sources; predicting the proportions of coal from those different sources which when mixed with a polymer will produce a coke having the required characteristics; mixing the coal and polymer in the predicted proportions; and coking the mixture.

9. A method according to Claim 8 characterized by the step of granulating scrap motor vehicle tyres to form rubber crumb.

10. A method of making coke from a mixture containing at least one coal and a polymer characterised in that the volatile content of the said coal is sufficiently high that the mixture has a maximum fluidity at least as great as that of the mixture without the polymer.

11. A method according to Claim 10 characterised in that the mixture also contains an inactive or inert additive.

12. A method according to Claim 10 or 11 characterised in that the volatility of the coal is in excess of 32%.

13. A method according to any preceding Claim characterised in that the polymer is an elastomer.

14. A method according to any Claim 13 characterised in that the elastomer is rubber.

15. A method according to any one preceding Claim characterised in that the polymer is present in a proportion of the mixture which is less than 10% by weight.

16. A method according to Claim 15 characterised in that the polymer is present in a proportion of the mixture which is less than 9% by weight.

17. A method according to any Claim 16 characterised in that the polymer is present in a proportion of the mixture which is less than 8% by weight.

18. A method according to Claim 17 charactensed in that the polymer is present in a proportion of the mixture which is about 7% 1% by weight.

19. Coke manufactured by a process as defined in any preceding Claim.