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CEMENT INDUSTRY APPLICATION
Isothermal calorimeters have been known to test the reaction of cement on hydration. Determining the heat of hydration of cement is important and traditionally, the heat of hydration has been determined by measuring the heat of solution. Typically, samples are mixed with water, where the cement hydration process can continuously be monitored over time. The heat flow is used recorded and will reflect the cement hydration process and different phases of the complex process can be determined. The addition of mixtures will change the shape of the heat flow curve and the mixture affect can be quantified. The integrated heat flow over time will give the extent of hydration. Using isothermal calorimetry, the heat of hydration is measured by monitoring the heat flow from the specimen while both the specimen and the surrounding environment are maintained at the same temperature.
The DDS Calorimeters range can be used to study the reaction of cement pastes as well as the temperature during the reaction. It can be used for quality control in cement plants, for optimization of additives to give cement a certain property, as well as a general research tool for the cement laboratory.
Cement is made by heating limestone( calcium carbonate), with small quantities of other materials in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate for form calcium oxide, or quicklime, which is then blended with other materials that have been included in the mix. The resulting hard substance is then ground into a powder to make cement. The manufacture of cement includes mining and crushing of the raw material( limestone, clay, and sand), drying and grinding in a mill, burning in a rotary tube furnace, and finally pulverization of the cement. The oxygen bomb calorimeter is used in the analysis of the raw materials and the burning process of fossil fuels and waste materials.
FOSSIL FUEL REQUIREMENTS
A cement plant can consume 3-6 GJ of fuel per ton of cement produced, depending on the raw materials and the process used. Most cement kilns use coal and petroleum coke as primary fuels, and to a lesser extent natural gas and fuel oil. Selected waste and by-products with recoverable calorific value can be used as secondary fuels, replacing a portion of conventional fossil fuels, like coal, if they meet strict specifications. Secondary fuel can contain all types of polymers, paper, wood and low fractions of metal. Also recycled wood or parts of automobile tyres might be used as secondary fuel. Before using it as a fuel in the production of cement, several chemical analyses are necessary as quality control. One of this is the determination of the calorific value. When accepting waste materials as substitutes for raw materials and / or fuels in the cement production process, it is important to evaluate the contribution of the waste products to the process.
To determine the fuel requirement during production, the gross and net calorific values of the fuels utilized must be identified. The gross calorific value is determined in a bomb calorimeter according to DIN 51900 in an oxygen atmosphere and at a pressure of 30 bar; a bomb vessel is inserted into the combustion chamber that can assumed isothermal or adiabatic. The fuel to be examined is put into the bomb vessel, ignited, and combusted. The gross calorific value can be determined by measuring the heat released during this combustion process.
To minimize the cost of the production of cement and to reduce the use of fossil energy more and more cement plants utilize secondary fuels. Several chemical analyses for quality control, like the calorific value, must be carried out.
DDS Calorimeters | Feb / March 2017 Issue www. ddscalorimeters. com