Coal burning indicators that boiler operators should know

Coal burning indicators that boiler operators should know
The first indicator: moisture
Water in coal is divided into internal water, external water, Water of crystallization and decomposition water. Excessive moisture in coal is not conducive to processing, transportation, etc. During combustion, it can affect thermal stability and heat conduction. During coking, it can reduce coke yield and prolong coking cycle. The water content indicators we often report now include: 1. Total water content (Mt), which is the sum of all internal and external water content in coal, also commonly represented by Mar. It is usually stipulated to be below 8%. 2. Air drying based moisture (Mad) refers to the moisture content of coal in the air drying state. It can also be considered as intrinsic moisture, which is referred to as "analytical basis moisture" in old national standards.
Second indicator: ash content
Refers to the residue left by coal after combustion. It is not the total amount of minerals in coal, but the residue of these minerals after chemical and decomposition. A high ash content indicates a low combustible content in coal. Calorific value is low. At the same time, in clean coal coking, the ash content determines the ash content of the coke. Common ash content indicators include air dry ash content (Aad), dry ash content (Ad), and so on. It is also useful to receive the base ash content (Aar).
Third indicator: volatile matter
It refers to the products of organic matter and some minerals in coal after heating and decomposition, which are not all inherent components in coal, but also some pyrolysis products, so it is called volatile yield. The size of volatile matter is related to the degree of coal metamorphism, and the higher the degree of coal metamorphism, the lower the yield of volatile matter. In combustion, used to determine the model of the boiler; In coking, it is used to determine the proportion of coal blending; It is also an important indicator of vaporization and liquefaction. Commonly used are air dried volatile matter (Vad), dry volatile matter (Vd), dry ash free volatile matter (Vdaf), and received volatile matter (Var). Vdaf is one of the important indicators for coal classification.
Fourth indicator: fixed carbon
Unlike elemental analysis, carbon is calculated based on moisture, ash, and volatile matter. The relevant formula for FC+A+V+M=100 is as follows: FCad=100 Mad Aad Vad FCd=100 Ad Vd FCdaf=100 Vdaf
Fifth indicator: total sulfur
It is a harmful element in coal, including organic sulfur and inorganic sulfur. Less than 1% can be used for fuel. In some regions, the requirements are below 0.6 and 0.8, and now commonly referred to as environmentally friendly coal and green energy refer to coal with lower sulfur content. Commonly used indicators include: total sulfur on air drying basis (St, ad), total sulfur on dry basis (St. d), and total sulfur on received basis (St, ar).
Sixth indicator: calorific value
The calorific value of coal, also known as the calorific value of coal, is the amount of heat emitted by the complete combustion of a unit mass of coal. The calorific value of coal is the basic indicator for coal pricing based on its calorific value. As a power fuel, coal mainly utilizes its calorific value. The higher the calorific value, the greater its economic value. At the same time, the calorific value is also the basis for calculating the Thermal equilibrium, thermal efficiency and coal consumption, as well as the parameters for boiler design. The calorific value of coal represents the degree of metamorphism (coalification degree) of coal. The calorific value of coal here refers to the calorific value of floating coal after separation with 1.4 specific gravity solution (or the calorific value of raw coal with ash content not exceeding 10%). The peat with the lowest degree of coal formation during the latest coal formation period has the lowest heat value, generally ranging from 20.9 to 25.1 MJ/kg. The brown coal that formed coal earlier than peat has an increase in heat value of 25 to 31 MJ/kg, and the bituminous coal continues to increase in heat value. When it comes to coking coal and lean coal, although the carbon content increases, due to the reduction of volatile matter, especially the hydrogen content is much lower than bituminous coal, some of which are less than 1%, equivalent to 1/6 of bituminous coal, So the coal with the highest calorific value is still some types of coal in bituminous coal. Given that the calorific value of low coalification coal varies greatly with the degree of coalification, some countries commonly use the high calorific value of coal on a constant humidity and ash free basis as an indicator to distinguish the types of low coalification coal. China uses the high calorific value of coal on a constant humidity and ash free basis to classify brown coal and long flame coal.