Furnaces, pellet-burning

Steel mills Blast furnaces charging, pouring CO, fumes, smoke, particulates (dust) Good maintenance, seal leaks use of higher ratio of pelletized or sintered ore CO burned in waste-heat boilers, stoves, or coke ovens cyclone, scrubber, and baghouse... 

The silicothermic, or ferrosilicon, process involves mixing ground burned dolomite with ground ferrosilicon and fluorspar (eutectic) and pelletizing after which the pellets are charged into the furnace. High vacuum and heat (1170°C) are applied and the calcium oxide present in the burnt dolomite forms infusible calcium silicate that is removed from the retort. 

The pellets are then delivered in bulk by lorry, train or boat and also in large or small sacks to consumers. Pellets are burned in pellet furnaces to produce heat in small-, medium- and large-scale facilities. Since the quality of pellets may vary during production there are some parameters that can be used to evaluate this. The most important physical parameters are bulk density, pellet density, durability, which can be measured by determining the amount of fines, and particle size distribution of the raw material. Chemical parameters include pellet moisture content, calorific heat value as a determinant of energy content, element content (such as K, Mg, Ca, N, S, Cl), ash content and ash melting behaviour in order to prevent the agglomeration of the ash in the furnace. The net calorific heat value of pellets is about 19 MJ kg-1, which is less than 50% of the oil equivalent. Pellets consist... 

Shaft furnaces had been used for several centuries for the smelting of ores and the burning of lime. Because of their high thermal efficiency and ease of operation they were the first, both in Sweden and the USA, to be adapted for iron ore pelletizing. In North America the first pilot plants were installed in Aurora and Babbitt, which started-up between 1948 and 1952. The first commercial plant was built for Erie Mining Co., Hoyt Lake, Mirmesota, beginning in 1954 and began operation in 1955. 

In addition to wood burning stoves, a range of wood-fueled boilers are also now available tbat are as efficient as modern furnaces—converting over 90 percent of tbe fuel into heat. Compared to a conventional furnace, it does take effort to keep wood burners fed, and log stoves need to be refueled every day, but wood chip or corn or wood pellet stoves can be automated to control temperature settings and only need refilling every few days. 

The pellets are then fed onto the sinter strand and are heated by burning blast furnace gas. This ignites the coke and raises the temperature of the solids to about 1280 °C. The limestone is calcined and reacts with silica and alumina in the ore to produce a molten calcium silicate-aluminate-ferrite system, which bonds the iron ore particles and produces strong pellets. 

Heating of the pellet with burning charcoal was sufficient to remove moisture and organic lubricant. Then the pellet was raised to white heat in a Staffordshire coke furnace. This caused the pellet to contract as the particles sinteed together. Pounding the hot pellet with a hammer produced a mataial which was 99% dense and which produced platinum wire of the highest tenacity. ... 

The compound is placed in the sample dish and is heated by the furnace. Vapor of the compound burns in O2 in the presence of CuO pellets, giving CO2 and H20.The water vapor is collected by a drying agent, and CO2 combines with the sodium hydroxide. Amounts of CO2 and H2O are obtained by weighing the U-tubes before and after combustion. 

Distribution of the particle size was studied in order to examine the uniformity or disparity in the dimensions of the solid powder obtained by different processes. The results are presented in figure 5 where the curves for pyrolysis process at 450"C and 750"C are compared to the curve acquired for thermal shock process. It is possible to observe the similarity in the three evnves even when the two procedures are different especially in the burning time inside the furnace. Curves initiate with an exponential increment for small sizes fi om 0 to about 180 qm then a maximum appears at about 210 and 250 qm. Finally the curves go down towards stabilization at about 600 jtm and continue to low levels of bigger particles. Invariably the particle sizes in any process are identical this could be attributed to the manual pulverization with a pestle and mortar by using the same conditions such as pressure force and time for powdering the solids obtained. This is the result of irregular thickness as no special technique was followed in the preparation of the sample other than mere pulverisation of the pellets. 

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