Jigging machine coal selection is a process in which coal and other materials are separated based on particle density differences in a variable medium flow that pulsates up and down. The jigging machine is a crucial piece of equipment in coal selection plants, with its performance directly impacting product quality and yield. Since the coal selection process through the jigging machine is influenced by multiple factors, it is necessary to analyze these influencing factors and promptly address any issues that arise.
Influencing factors during the operation of a jigging machine can be categorized into three aspects: the machine's own structure, the properties of the raw coal, and the working system of the jigging machine.
Key structural factors affecting the gravity separation efficiency include the shape of the jigging machine body, the height of the overflow weir, and the size of the screen holes. For screen-side air chamber jigging machines, additional influencing factors are the ratio of the air chamber width to the jigging chamber width and the guide plate. The structure of the jigging machine is determined during the design phase and cannot be adjusted during the production process.
The selectivity of coal has a decisive impact on the gravity separation effect. Coal with good selectivity undergoes the process of particle stratification by density more quickly and distinctly during separation, resulting in better separation indices. However, for difficult-to-separate or moderately difficult-to-separate coal with poor selectivity, even with extended separation time, particles cannot be well stratified by density, leading to poor separation indices.
The composition of the coal's particle size determines the hydraulic resistance of the bed on the jigging screen. During the sorting process, the raw coal does not completely layer by density. The movement speed of the material is not only related to density but also to the particle size of the grains.
During the rising water flow phase, finer particles move faster while larger particles move slower. Additionally, the rising water flow may also wash fine gangue particles to the upper bed layer, where they are discharged along with floating coal through the overflow. In the descending water flow phase, larger particles move faster, and finer particles move slower; fine particles may also fall through the spaces between larger particles to the bottom of the sieve. Consequently, this may result in some mismatched materials present in each layer.
Flat-shaped particles can affect the gravity separation efficiency. When flat-shaped gangue or gangue coal fall horizontally, they are lifted to the upper bed layer by the upward water flow, and are discharged together with the concentrate, contaminating the concentrate and affecting the separation efficiency.
When sorting hard coal containing tough, non-swelling minerals, the sorting effect is better. In contrast, when sorting coal containing friable minerals that easily mudify when wet, there is a tendency to produce more fine particles and coal sludge, which affects the sorting efficiency. The operating regime of the jigging machine should be determined based on the properties of the raw coal to be cleaned and the required quality of the concentrate. The various parameters of the operating regime are interrelated, so it is necessary to analyze the specific situation when establishing the jigging machine's operating regime. The main adjustable factors in the operation of the jigging machine include the jigging frequency and amplitude, bed thickness, valve characteristics, feed rate, air and water flow, and discharge rate.
During operation, the jigger frequency and amplitude, bed thickness, and valve characteristics must not be altered arbitrarily by the coal selection operator. The frequently adjusted parameters are the coal feeding rate, water injection rate, and discharge rate.
The combination of jigging frequency and amplitude directly affects the bed looseness. Under constant conditions, a higher jigging frequency results in a significantly reduced bed looseness. For coarse coal sorting, a low-frequency (40-52 Hz) and high-amplitude working regime is generally used, which leads to greater bed looseness and faster stratification. For fine coal sorting, a high-frequency (50-68 Hz) and low-amplitude working regime is typically employed, making operation easier and ensuring better product quality, though with reduced production capacity.
The thickness of the bed is related to the properties of the raw coal being processed (density and particle size). If the raw coal has a significant density difference between light and heavy products, a thinner bed can be used to accelerate the separation of materials. If the density difference between light and heavy products is small or if a higher quality of clean coal is required, a thicker bed should be employed. If the bed is too thick and there is insufficient wind pressure and airflow, the bed cannot achieve the required looseness, resulting in poor separation effects. Thinning the bed not only speeds up the separation process but also enhances the aspiration effect, which is beneficial for the separation of unsorted raw coal. However, if the bed is too thin, it can cause an overly strong aspiration effect, leading to losses of fine coal through the sieve.
