Coal analyzers are bulk material analyzers used by coal producers, coal preparation plants, and coal-fired power plants to determine coal quality in real time.
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.
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.
It is primarily in USA analyzers were the most used, in particular to reduce pollution from coal combustion
Coal quality parameters of greatest interest include ash, moisture, sulfur, and energy density (also known as heat content). Although most coal operations can obtain this information about coal quality by taking physical samples, preparing the samples, and analyzing them with laboratory equipment, these processes often involve a time lag of up to 24 hours from gathering the sample to final analysis results. In contrast, coal analyzers provide analysis information each minute on material being transported by conveyor either at the mine or the power plant. This timely coal quality information in turn allows the operator to improve his process by taking timely process control actions, such as sorting, blending, coal homogenization, or prep plant control.
Energy density is the amount of energy stored in a given system or region of space per unit volume. Colloquially it may also be used for energy per unit mass, though the accurate term for this is specific energy. Often only the useful or extractable energy is measured, which is to say that inaccessible energy is ignored. In cosmological and other general relativistic contexts, however, the energy densities considered are those that correspond to the elements of the stress–energy tensor and therefore do include mass energy as well as energy densities associated with the pressures described in the next paragraph.
Enthalpy, a property of a thermodynamic system, is equal to the system's internal energy plus the product of its pressure and volume. In a system enclosed so as to prevent matter transfer, for processes at constant pressure, the heat absorbed or released equals the change in enthalpy.
Automatic process control in continuous production processes is a combination of control engineering and chemical engineering disciplines that uses industrial control systems to achieve a production level of consistency, economy and safety which could not be achieved purely by human manual control. It is implemented widely in industries such as oil refining, pulp and paper manufacturing, chemical processing and power generating plants.
There are several different types of coal analyzers. Some of the more sophisticated analyzers use prompt gamma neutron activation analysis (PGNAA) or pulsed fast thermal neutron activation (PFTNA) to determine the elemental content of the coal. Another emerging technology for elemental analysis is laser-induced breakdown spectroscopy (LIBS). PGNAA and LIBS enable analysis of sulfur and ash (the latter, by summing the ash constituents). When combined with a second type of analyzer, the moisture meter, they provide moisture and energy value as well. Moisture meters are often found in conjunction with the elemental analyzers, but sometimes are used alone, or in conjunction with ash gauges. Most moisture meters use microwave technology. The emerging technology of magnetic resonance (MR) offers a more direct measurement. Most ash gauges employ gamma attenuation principles.
Prompt-gamma neutron activation analysis (PGAA) is a very widely applicable technique for determining the presence and amount of many elements simultaneously in samples ranging in size from micrograms to many grams. It is a non-destructive method, and the chemical form and shape of the sample are relatively unimportant. Typical measurements take from a few minutes to several hours per sample.
Laser-induced breakdown spectroscopy (LIBS) is a type of atomic emission spectroscopy which uses a highly energetic laser pulse as the excitation source. The laser is focused to form a plasma, which atomizes and excites samples. The formation of the plasma only begins when the focused laser achieves a certain threshold for optical breakdown, which generally depends on the environment and the target material. In principle, LIBS can analyze any matter regardless of its physical state, be it solid, liquid or gas. Because all elements emit light of characteristic frequencies when excited to sufficiently high temperatures, LIBS can detect all elements, limited only by the power of the laser as well as the sensitivity and wavelength range of the spectrograph & detector. If the constituents of a material to be analyzed are known, LIBS may be used to evaluate the relative abundance of each constituent element, or to monitor the presence of impurities. In practice, detection limits are a function of a) the plasma excitation temperature, b) the light collection window, and c) the line strength of the viewed transition. LIBS makes use of optical emission spectrometry and is to this extent very similar to arc/spark emission spectroscopy.
Moisture meters are used to measure the percentage of water in a given substance. This information can be used to determine if the material is ready for use, unexpectedly wet or dry, or otherwise in need of further inspection. Wood and paper products are very sensitive to their moisture content. Physical properties are strongly affected by moisture content and high moisture content for a period of time may progressively degrade a material.
Coal analyzers were first introduced in the early 1980s with the US and Australia leading the way. The demand for coal analyzers has been highest in the US, due to the need to control sulfur as mandated by the Clean Air Act Amendments of 1977. By 2005, more than 600 coal analyzers were in use throughout the world. Most of these analyzers are mounted around an existing conveyor belt, although a significant minority analyze sample streams taken from the main process stream.
