Hard coal, which is mined in mines underground, needs an additional processing process. Coal enrichment is necessary because raw materials mined underground have many unnecessary impurities.
Why is enrichment so important? All due to the fact that the impurities present in this material will give a low combustion temperature if you start using them. Thus, it turns out that you will have to burn a large amount of coal, which will give a low combustion temperature. Enrichment of coal is the purification of raw materials from all unnecessary substances that interfere with its combustion.
During this procedure, several goals are achieved. Firstly, minerals and impurities are removed, and secondly, the mined coal is divided into fractions according to the size and grade of grains. Only after passing through these procedures and checking the quality of the final product, coal is delivered to the consumer.
Screens and wet separation
The process of coal enrichment includes several stages. The first of these is screening, or the separation of raw materials intofractions by size and grade. In order to carry out the primary processing, equipment such as a vibrating screen is used. This is a huge sieve. Most often, there are several of them at the enrichment plant, and their main difference lies in the size of the cells. Getting on screens with different cells, coal is divided into several groups. If we talk about the classification of coal by size, then there is a generally accepted standard scheme that includes several types - seed, nut, etc.
One of the most common types of coal preparation is wet. This procedure is based on the principle of density separation. Since impurities have a lower indicator of this parameter, and coal has a larger one, their separation will occur in the aquatic environment. The machines in which this process is carried out are called jigging machines. This equipment belongs to gravity enrichment devices.
The raw material used to carry out these works is called food. During the processing of stone raw materials, you can get such coal enrichment products as:
- Concentrate. This is the name of those processed products that have retained the maximum amount of combustible substances in their composition, and the content of rock components has decreased to a minimum.
- Product. This raw material is an intermediate product. The content of combustible substances in it did not reach its maximum value, but the amount of rock components did not increase too much. Such productsprocessing is considered unfinished and needs additional processing.
- Mixed, or waste. With this raw material, everything becomes clear from its name - the content of combustible components is minimal, and rock components are maximal.
Coal washing technology
Concentrators have several different processes, which are divided into groups depending on their technological purpose.
The first category is preparatory procedures. The main task at this stage is to reveal the components of the rock mass, divide into machine classes, etc. This stage includes such types of operations as screening and crushing. If we talk about the crushing process, then it is quite simple. The task of this stage is to break the existing pieces of rock to the required size. For this, external forces are used, that is, special equipment. Screening, as mentioned earlier, is the procedure for separating pieces of rock into classes by size.
After completing the preparatory stage, you can proceed to the main one, the task of which is to separate the available pieces of coal into concentrate, middling or mixed.
Currently, rock beneficiation plants use such types of gravity beneficiation as jigging, screw and countercurrent separation, heavy slurry beneficiation.
Some facilities use coal washing plants that perform a flotation procedure. The essence of technologyenrichment in this way lies in the fact that the difference in the physical and chemical properties of coal and impurities is used.
In addition to the main processes, several auxiliary ones are used at the enrichment plants. These include operations for dehydration or dedusting.
Naturally, the dehydration procedure is applicable only to those enrichment products that have passed through gravity treatment. Several different methods are used to accomplish this task. Large pieces, more than 13 mm, are dewatered on screens, elevators or in drainage bins. Crayons of the same breed classes go through the process of centrifugation, and in winter also thermal drying of the material.
Dedusting is a procedure for separating dust particles smaller than 0.5 mm from coal. To accomplish this task, two methods are used. Wet method - screens or hydrocyclones are used. The dry method uses air classifiers with different designs.
Coal washing schemes
It is important to note here that there is no single scheme for enrichment. In each case, you have to choose from several available options. The decisive factors that affect the outcome are the properties of the ore itself, as well as its purpose.
For example, if we talk about the depth of enrichment, then there are several following technological schemes:
- The first method involves the enrichment of only the largest parts,the size of which exceeds 25 (13) mm. The subsequent shipment of rock is carried out either jointly, that is, both concentrate and waste are shipped together, or separately.
- The second method is the enrichment of only the middle class of rocks with a size of more than 6 (3) mm. The separation of the resulting products can also occur jointly or separately.
There is also a division into several schemes, depending on the quality of the concentrate obtained during enrichment. One of the most common technological schemes of this type is the release of one marketable product. It is used only for the enrichment of thermal coal of such grades, which during the processing process were not allocated several classes by size. A striking example of such a scheme was coal marked P.
Actually, there are few rules for coal enrichment. To be precise, it is only one, but quite important, and lies in the fact that it is necessary to observe all production processes during the processing of the rock. Such mandatory processes include sorting into fractions and directly enriching the product. Since the breed initially cannot be of the same size, it is conditionally divided into large, medium and small, after which it is sent to the screening stage.