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.
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. [2]
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 [3] 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. [4] 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. [4] 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:
E = k √n, k usually varies between 0.5 and 0.7. (where n is the number of layers and k is a constant determined for each stockpiling operation)
The different types of stacking will influence k. [5]
A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials that are feedstock for future finished products. As feedstock, the term connotes these materials are bottleneck assets and are required to produce other products.
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).
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 on to 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.
In electronics, noise is an unwanted disturbance in an electrical signal.
In engineering, a process is a series of interrelated tasks that, together, transform inputs into a given output. These tasks may be carried out by people, nature or machines using various resources; an engineering process must be considered in the context of the agents carrying out the tasks and the resource attributes involved. Systems engineering normative documents and those related to Maturity Models are typically based on processes, for example, systems engineering processes of the EIA-632 and processes involved in the Capability Maturity Model Integration (CMMI) institutionalization and improvement approach. Constraints imposed on the tasks and resources required to implement them are essential for executing the tasks mentioned.
Plastics extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weatherstripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation.
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.
Material flow accounting (MFA) is the study of material flows on a national or regional scale. It is therefore sometimes also referred to as regional, national or economy-wide material flow analysis.
Freshwater environmental quality parameters are those chemical, physical or biological parameters that can be used to characterise a freshwater body. Because almost all water bodies are dynamic in their composition, the relevant quality parameters are typically expressed as a range of expected concentrations.
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.
A die in polymer processing is a metal restrictor or channel capable of providing a constant cross sectional profile to a stream of liquid polymer. This allows for continuous processing of shapes such as sheets, films, pipes, rods, and other more complex profiles. This is a continuous process, allowing for constant production, as opposed to a sequential (non-constant) process such as injection molding.
Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled. A wide range of applications include scientific and industrial processes, food production and storage and breathing gases.
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.
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