Coal homogenization refers to the process of mixing coal to reduce the variance of the product supplied. This homogenization process is performed during the coal stockpiling operation. Although the terms blending and homogenization are often used interchangeably, there are differences, as the definitions show. The most notable difference is that blending refers to stacking coal from different sources together on one stockpile. [1] The reclaimed heap would then typically have a weighted average output quality of the input sources. In contrast, homogenization focuses on reducing the variance of only one source. A blending operation will cause some homogenization.
Mixing is defined as a random rearrangement of particles by means of mechanical energy, e.g. rotary devices, in a fixed volume. Traces of individual components can still be located within a small quantity of the mixed material of two or more material types. Application: small-scale storage. [2]
Blending is defined as the integration of a number of raw materials with different physical or chemical properties in time in order to create a required specification or blend. The aim is to achieve a final product from, for example, two or more coal types, that has a well-defined chemical composition in which the elements are very evenly distributed and no large pockets of one type can be identified. When sampled, the average content and the standard deviation from the average are the same. Application: e.g. using different types of coal for specific recipes.
Homogenizing is defined as the systematic regrouping of the input flow in order to provide a more homogeneous output flow of one type of material so that inherent fluctuations of chemical or physical properties in time are evened out compared to the input flow. Application: e.g. one batch of limestone or coal, i.e. to homogenize the material in itself. [3]
Worldwide, industry uses bulk material, like coal, as a source of energy or as a raw material for production processes. Intermediate storage facilities (for example stockpiles) are required to decouple the (discontinuous) supply of raw materials from the (continuous) production process. Large quality fluctuations of the material properties can occur due to the geographical origin of the raw materials. This means that processes using these raw materials have to deal with these fluctuations in order to produce products with a constant quality. The fluctuations can be dealt with in two ways:
Upgrading is defined as achieving a more constant quality throughout the material flow, where the mean quality cannot be influenced, but the frequency and amplitude of fluctuations around the mean value can.
Homogenization aims to upgrade the raw material to a uniform composition of the product being homogenized. In coal homogenization, the primary aim is to reduce the variance [4] of the quality of the product supplied (in comparison to the variance in quality of the different sources of supply). This is necessary to ensure consistent (or homogeneous) quality, as well as a constant calorific value of the coal. [5] Homogenization can be used at coal mines in order to get a better overall quality product from a stockpile. It can thus form an integral part of the quality management system in coal mines. [5] When processing coal by more than one supplier like power stations and heat plants, coal homogenization can serve well as a strategy of processing the coal in order to get to the best acceptable quality. Coal homogenization could be applied whenever a consistent quality is needed and multiple sources of different qualities are supplied or mined.
Typically, a large number of thin layers are thrown by the stacker on a stockpile. Stacking the layers on each other ensures that the variance in input quality is reduced once the coal is reclaimed in a vertical cross-section. After the coal is stacked in horizontal layers, it is reclaimed in vertical slices. When the standard deviation of each slice’s quality is determined, the resulting standard deviation is much smaller than that of the non-homogenized stockpile.
In a simplified form, the effectiveness of the homogenization process is represented by E, the homogenization effect:
In practice, varying stockpile layer thickness, type of stacking and different reclaiming methods makes the above formulae of little use. Thus, in practice the homogenization effect E is calculated as follows:
The different types of stacking will influence k. [6]
In statistics, the standard deviation is a measure of the amount of variation of a random variable expected about its mean. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range. The standard deviation is commonly used in the determination of what constitutes an outlier and what does not.
The Allan variance (AVAR), also known as two-sample variance, is a measure of frequency stability in clocks, oscillators and amplifiers. It is named after David W. Allan and expressed mathematically as . The Allan deviation (ADEV), also known as sigma-tau, is the square root of the Allan variance, .
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in decibels. A ratio higher than 1:1 indicates more signal than noise.
Filter design is the process of designing a signal processing filter that satisfies a set of requirements, some of which may be conflicting. The purpose is to find a realization of the filter that meets each of the requirements to an acceptable degree.
Quantitative genetics is the study of quantitative traits, which are phenotypes that vary continuously—such as height or mass—as opposed to phenotypes and gene-products that are discretely identifiable—such as eye-colour, or the presence of a particular biochemical.
In industrial process engineering, mixing is a unit operation that involves manipulation of a heterogeneous physical system with the intent to make it more homogeneous. Familiar examples include pumping of the water in a swimming pool to homogenize the water temperature, and the stirring of pancake batter to eliminate lumps (deagglomeration).
In probability theory and statistics, the coefficient of variation (CV), also known as normalized root-mean-square deviation (NRMSD), percent RMS, and relative standard deviation (RSD), is a standardized measure of dispersion of a probability distribution or frequency distribution. It is defined as the ratio of the standard deviation to the mean , and often expressed as a percentage ("%RSD"). The CV or RSD is widely used in analytical chemistry to express the precision and repeatability of an assay. It is also commonly used in fields such as engineering or physics when doing quality assurance studies and ANOVA gauge R&R, by economists and investors in economic models, and in psychology/neuroscience.
A reclaimer is a large machine used in bulk material handling applications. A reclaimer's function is to recover bulk material such as ores and cereals from a stockpile. A stacker is used to stack the material.
A stacker is a large machine used in bulk material handling. Its function is to pile bulk material such as limestone, ores, coal and cereals onto a stockpile. A reclaimer can be used to recover the material.
Bulk material handling is an engineering field that is centered on the design of equipment used for the handling of dry materials. Bulk materials are those dry materials which are powdery, granular or lumpy in nature, and are stored in heaps. Examples of bulk materials are minerals, ores, coal, cereals, woodchips, sand, gravel, clay, cement, ash, salt, chemicals, grain, sugar, flour and stone in loose bulk form. It can also relate to the handling of mixed wastes. Bulk material handling is an essential part of all industries that process bulk ingredients, including: food, beverage, confectionery, pet food, animal feed, tobacco, chemical, agricultural, polymer, plastic, rubber, ceramic, electronics, metals, minerals, paint, paper, textiles and more.
A stockpile is a pile or storage location for bulk materials, forming part of the bulk material handling process.
Safety stock is a term used by logisticians to describe a level of extra stock that is maintained to mitigate risk of stockouts caused by uncertainties in supply and demand. Adequate safety stock levels permit business operations to proceed according to their plans. Safety stock is held when uncertainty exists in demand, supply, or manufacturing yield, and serves as an insurance against stockouts.
In electronics, noise is an unwanted disturbance in an electrical signal.
A coal preparation plant is a facility that washes coal of soil and rock, crushes it into graded sized chunks (sorting), stockpiles grades preparing it for transport to market, and more often than not, also loads coal into rail cars, barges, or ships.
Pelletizing is the process of compressing or molding a material into the shape of a pellet. A wide range of different materials are pelletized including chemicals, iron ore, animal compound feed, plastics, waste materials, and more. The process is considered an excellent option for the storage and transport of said materials. The technology is widely used in the powder metallurgy engineering and medicine industries.
Pharmaceutical manufacturing is the process of industrial-scale synthesis of pharmaceutical drugs as part of the pharmaceutical industry. The process of drug manufacturing can be broken down into a series of unit operations, such as milling, granulation, coating, tablet pressing, and others.
The term bulk material analyzer is the generic noun for that device which fits around a conveyor belt and conducts real-time elemental analysis of the material on the belt. Other names often found for such a device include belt analyzer, crossbelt analyzer and elemental analyzer. This product first found popularity in the cement industry during the 1990s, and today most new cement plants include at least one analyzer, if not two.
Sensor-based sorting, is an umbrella term for all applications in which particles are detected using a sensor technique and rejected by an amplified mechanical, hydraulic or pneumatic process.
Coal blending is the process of mixing coals after coal has been mined to achieve quality attributes that are desirable for the coal’s intended application. The quality attributes that are most important in blending will differ from one mine site to another and also depend on how the coal seams vary in quality and their final intended use. In thermal coals, quality attributes of interest often include ash, volatile matter, total Sulfur, and gross calorific value. For coking coals, additional attributes are sometimes considered including crucible swelling number, fluidity, and RoMax.
NIAflow is simulation software for mineral processing plants. Based on a flowsheet interface, it calculates the material flow through a variety of processing machinery.