CA2021211A1 - Fuel briquettes and process for making same - Google Patents

Abstract

ABSTRACT

A process for the manufacture of fuel briquettes, preferably used for heating purposes, includes the steps of mixing a non-caking carbon carrier of small grain size, preferably petrol coke, with a pitch containing binder to produce a starting mixture, compressing the starting mixture to briquette blanks and producing the fuel briquettes therefrom through a solidifying heat treatment. The pitch containing binder material is preferably a binder mixture of pitch and caking coal which has a temperature of 100 to 200°C. The non-caking carbon carrier is admixed with the binder mixture within the same temperature range. The briquette blanks are compressed starting at the mixing temperature. The briquette blanks are subjected to a heat treatment which has an end temperature of over 400°C. Subject of the invention are also fuel briquettes manufactured using that process.

Description

2~1211 FUEL BRIQUETTES AND PROCESS FOR MAKING SAME

The invention relates to a process for the production of fuel briquettes, especially for heating purposes, wherein a non-caking carbon carrier of small grain size, preferably petrol coke, is mixed with a pitch containing binder material to form a starting mixture, which mixture is subsequently compressed to briquette blanks and subjected to a heat treatment for solidification of the briquette blanks and production of the fuel briquettes.
Coke of sandy consistency, preferably petrol coke, is generally used for the manufacture of such fuel briquettes, whereby the coke used has a grain size range of .05 to 2 mm and is preferably selected from a narrower grain size band within that range. The carbon carrier of sandy consistency may also be or contain non-caking coal. The invention further relates to fuel briquettes manufactured by the above process. Fuel briquettes for the above identified applications must conform to certain physical requirements. The fuel briquettes m~st be of sufficient solidity for transport and combustion and should neither burn too violently nor merely smolder. These characteristics may be controlled through an adjustment of the compression force used in forming the briquette blanks.

In a prior art process known from German Published Application ~E 37 27 464, of which the present invention is an improvement, briquette blanks which are sufficiently free of caking coal are used and a binder aided briquette forming process is employed. Any admixed caking coal of fine grain is present in such a small amount that it has no influence on the binder aided briquette forming. The heat treatment is carried out in a rotary kiln, a lower part of which is filled sufficiently high with coke of sandy consistency to provide that the heat treatment takes place in a coke submersion bed. This process has proved to be advantageous. Particularly, the fuel briquettes manufactured by such a process comply with all requirements to be met during combustion. However, with respect to their longevity before combustion, fuel briquettes manufactured in accordance with 35 '~this prior art process may be much improved. The mechanical stability of such fuel briquettes decreases over time during storage, and in some cases decreases so far as to become unacceptable. This decrease may be explained by air diffusing into the fuel briquettes and water penetrating into the fuel briquettes, especially during outside storage, which leads to a reduction in the binding forces of the petrol coke structure in the fuel briquettes.

The present invention provides a process for the manufacture of fuel briquettes which do not only meet all requirements during combustion, but are also characterized by excellent long term storage properties and substantially retain their solidity especially during transport and outside storage.

This is achieved in a process in accordance with the invention, wherein a pitch containing a binder, which includes a mixture of pitch and caking coal and has a temperature between 100 and 200 C, is admixed with a non-caking carbon carrier at a mixing temperature within the same temperature range as the binder temperature, the resulting starting mixture is compressed to fuel briquette blanks starting at the mixing temperature, and the briquette blanks are subjected to a solidifing heat treatment. It is understood that the pressing of the briquette blanks is preferably carried out at a briquette forming temperature which is lower than the mixing temperature. The briquette forming temperature is, for example, about 50 C lower than the mixing temperature. The solidifying heat treatment may be carried out with a final temperature of over 400 or even over 450 C. In a process in accordance with the invention, the briquette forming process, which is used for the production of the briquette blanks, is a binder aided briquette forming process which is generally used in the manufacture of mineral coal briquettes. Therefore, the technology-of known binder aided briquette forming processes may be employed. In general, commonly known briquette presses and briquette forming pressures may be employed.

2~212~1 It is an unexpected result that, when the mentioned binder aided briquette forming process is used and the mentioned parameters are employed, the resulting fuel briquettes comply with all above-mentioned requirements even with respect to their long term properties. This is especially apparent, when a binder mixture is used which is a pitch/coal alloy. A
pitch/coal alloy in accordance with the invention occurs, if the pitch and the caking coal are, 60 to speak, dissolved in each other so that a complete integration of the two components into a new binder material has taken place. This may be readily achieved especially when coal of sufficiently fine grain is used. In the fuel briquettes, the pitch/coal alloy is substantially unaffected by air and humidity diffusing into the fuel briquettes. The alloy is very reactive. The reactivity of the alloy is comparable to the reactivity of the compressed materials in the fuel briquettes.
Several variants of the briquette manufacturing process in accordance with the invention are within the scope of the invention.
Especially good results are achieved if the non-caking carbon carrier, especially coke of sandy consistency, and the binder mixture, have the same temperature during admixture and if the admixture is carried out at a preferred temperature of about 160 C.

In contrast to the above described prior art process taught in DE 37 27 464, wherein the solidifying heat treatment must be carried out in a rotary kiln, in accordance with the present invention, the heat treatment may also be effected in a different manner, for example, on a moving grate which passes through an appropriate oven or an appropriate heat chamber and is loaded with a single layer or multiple layers of briquette blanks.
However, in a preferred embodiment of the process in accordance with the invention, the blanks are subjected to the solidifying heat treatment in a rotary kiln. A very careful heat treatment and a high final rigidity of the briquettes may be achieved, if the rotary kiln has a mineral bed of fine grain minerals. According to a preferred embodiment of the present invention, which is of special interest, briquette blanks which have a 35\~,higher specific weight than a shooting weight of the fine grain minerals, 20212~1 are produced by selecting an appropriate mixing ratio of the components in the starting mixture and an appropriate degree of compression of the starting mixture during the forming of the briquette blanks, and are fed to a heated rotary kiln for the solidifying heat treatment, which kiln is filled with fine grain minerals to such a height that the heat treatment of the blanks is effected in a mineral submersion bed. The fine grain minerals preferably have a temperature of about 500 to 530 C at least towards the exit end of the rotary kiln. In order to prevent the blanks from contacting each other in the kiln and to prevent their abrasion, the kiln is preferably filled with a volume of minerals which is larger than twice the volume of the voids within a loose briquette blank filling of the kiln. For the remainder of the process in accordance with the invention, recourse to the technology disclosed in DE 37 27 464 may be had. Accordingly, the briquette blanks may be formed in a pellet forming apparatus, which yields spherical pellets, or in a briquette forming press. The use of the latter is preferred, since the specific weight of the briquette blanks may be controlled through an adjuatment of the briquetting force of the press. The briquette blanks are fed into the kiln through an entry end thereof together with a flow of minerals for the submersion bed. Both the produced fuel briquettes and the heated minerals leave the kiln at an exit end thereof.
The length of the heat treatment of the blanks and thus their speed of passing through the kiln is adjusted to provide a sufficient solidification of the blanks. The heated minerals which exit the rotary kiln together with the heat treated fuel briquettes are separated and transported to the entry end of the rotary kiln for recycling. Thus, the heat energy stored ln the minerals may be reused for heating the briquette blanks in the kiln. The briquettes whlch exit the kiln are preferably cooled to about 50 C on a cooling conveyor. It is an advantage of the rotary kiln heat treatment, that volatile components which evaporate from the briquette blanks during the heat treatment may be combusted in the kiln. The resulting combustion heat may be used to retain the kiln at the required temperature and to make the heat treatment substantially independent of additional heat sources.
Thus, the one or more burners which are preferably provided at the entry end of the kiln may be only required ~or the start o the heat treatment process 2~21~1 and for special situations. The fine grain minerals are preferably sand, foamed perlite or vermiculite or fine grain petrol coke if the atmosphere in the oven prevents combustion of the latter. If petrol coke is used, the heated fine grain coke exiting the kiln may be recycled into the kiln or used as part of the starting mixture. In any event, it should be asserted that the temperature at the beginning of the heat treatment is sufficiently high to force highly volatile components from the briquette blanks. The gas exiting the briquette blanks generally prevents oxidation of the materials in the kiln.
To optimize the process in accordance with the invention, it is preferred to employ a binder mixture which, with respect to the starting mixture from which the blanks are pressed, contains at least 7~ per weight of pitch as crude oil or coal pitch, especially electrode pitch, and at least 12~ per weight of fine grain caking coal. The binder mixture preferably contains 7 to 12~ per weight of pitch and 12 to 14~ per weight of fine grain caking coal. Preferably, petrol coke or another non-caking carbon carrier is used, which has a grsin size below 2 mm with at least 60 below .5 mm.
It is within the scope of the invention to add small sized lime stone to the starting mixture as combustion inhibitor. Accordingly, the invention provides for a starting mixture which contains petrol coke, 3 to 6~ per weight of lime stone and the binder mixture. It is preferred to use petrol coke of a grain size below 2 mm with at least 60~ per weight below .5 mm, and lime stone with a grain size below .5 mm.

The fuel briquettes manufactured by a process in accordance with the invention, are characterized by their long term storage properties and their behavior during combustion in a furnace. The fuel briquettes manufactured bya process in accordance with the invention may also be employed as carbon carriers during the manufacture of cast iron in a cupola furnace.

Claims (11)

1. A process for the manufacture of fuel briquettes comprising the steps of:
mixing a non-caking carbon carrier of small grain size and a pitch containing binder material, compressing the resulting starting mixture to briquette blanks and producing said fuel briquettes through a solidifying heat treatment of said briquette blanks, said pitch containing binder material being a binder mixture of pitch and caking coal which has a temperature of 100 to 200°C, said non-caking carbon carrier being admixed with said binder mixture at a mixing temperature which is within the same temperature range as said binder mixture, said blanks being formed starting at said mixing temperature and said blanks being subjected to a solidifying heat treatment.

2. A process as defined in claim 1, wherein said binder mixture is a pitch/coal alloy.

3. A process as defined in claim 1, wherein said non-caking carbon carrier and said binder mixture have the same temperature during their admixture.

4. A process as defined in claim 3, wherein said mixing temperature is about 160°C.

5. A process as defined in claim 3 or 4, wherein said briquette blanks are subjected to said solidifying heat treatment in a rotary kiln and a mineral bed of fine grain minerals.

6. A process as defined in claim 5, wherein a specific weight of said briquette blanks is controlled to be higher than a shooting weight of said fine grain minerals, through adjustment of a mixing ratio of said starting mixture and a degree of compression of said starting mixture during said compressing thereof, and said briquette blanks are fed into a heated rotary kiln for said solidifying heat treatment, said kiln being filled with said fine grain minerals to such a height that said heat treatment of said briquette blanks is effected in a submersion bed of minerals.

7. A process as defined in claim 6, wherein said rotary kiln is filled to such an extent that a volume of said minerals is larger than twice a combined volume of all voids within a loose filling of said kiln with said briquette blanks.

8. A process as defined in claim 7, wherein said binder mixture contains, in relation to said starting mixture which is used for said briquette blanks, at least 7% per weight of pitch in the form of at least one of coal pitch, crude oil pitch, and electrode pitch, and at least 12% per weight of fine grain caking coal.

9. A process as defined in claim 8, wherein said starting mixture includes petrol coke, 3 to 6% per weight of lime stone and said binder mixture.

10, A process as defined in claim 9, wherein said petrol coke has a grain size below 2 mm with at least 60% per weight below .5 mm and said lime stone has a grain size of less than .5 mm.

11. Fuel briquettes manufactured by a process as defined in any one of claims 1 to 10.