Determination of Calorific Value

The common method of determining the gross calorific value of coal is with either an adiabatic calorimeter (ASTM D-2015 this test method was discontinued without replacement in 2000 but is still in use in many laboratories) or an isothermal bomb calorimeter (ASTM D-3286). In these methods, a weighed sample is burned in an oxygen bomb covered with water in a container surrounded by a jacket. 

An adiabatic calorimeter is a calorimeter that has a jacket temperature adjusted to follow the calorimeter temperature so as to maintain zero thermal head, and the test method (ASTM D-2015, ISO 1928) consists of burning the coal sample in the calorimeter, and the jacket temperature is adjusted during the burning so that it is essentially the same as the calorimeter water temperature. The calorific value is calculated from observations made before and after the combustion. In the isothermal method (ASTM D-3286 ISO 1928), the calorific value is determined by burning a weighed sample of coal in oxygen under controlled conditions, and the calorific value is computed from temperature observations made before, during, and after combustion with appropriate allowances made for the heat contributed by other processes. The value computed for the calorific value of coal 

After firing, the contents of the bomb are washed into a beaker and titrated with standard sodium carbonate solution to determine the amount of acid (nitric acid, HN03 and sulfuric acid, H2S04) produced in the combustion. Corrections for the amount of acid, the amount of fuse wire used in firing, and the sulfur content of the sample are then made to the total heat produced in the calorimeter (energy equivalent times corrected temperature rise) to determine the gross calorific value of the solid fuel. 

One source of error in this method (ASTM D-3286) is in temperature measurement. If a mercury-in-glass thermometer is used, it must be calibrated accurately and consistent readings must be made. Many calorimeters are equipped with digital thermometers with thermistor probes and microprocessors to control the firing and record the temperatures at prescribed intervals. This alleviates most of the human error in recording the temperature changes. 

After firing, restoring the bomb pressure to atmospheric pressure too rapidly may result in the loss of oxides of sulfur and nitrogen. A correction must be made to the gross calorific value for the amounts of these acid-forming oxides produced in the bomb. Their loss results in a high calorific value. The pressure of the bomb must be restored very slowly to prevent this. 

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Satisfactory combustion of hydrocarbon gases depends on the matching of burner and appliance design with certain gas characteristics. Various types of test methods are available for the direct determination of calorific value (ASTM D900,... 

If the determination of calorific value is carried out with a bomb calorimeter, the figure reported is usually corrected for the heat of formation of sulfuric acid and its dilution by water, but if the calorific value has to be reported on a dry, mineral-matter-free basis, the air-dried figure must be adjusted further to allow for the heat of formation of ferric oxide from the pyrites originally in the coal. The heat developed in the combustion of pyrite (FeSi) is approximately 3000 calories per gram of pyrite sulfur, so the correction to be applied is dependent on whether the calorific value is expressed as the heating power per gram or per pound. 

Total sulfur is determined by combustion in a bomb calorimeter (ASTM D-129, IP 61) and is often carried out with the determination of calorific value. The contents of the bomb are washed with distilled water into a beaker after which hydrochloric acid is added and the solution is raised to boiling point. Barium chloride is added drop by drop to the boiling solution to precipitate the sulfuric acid as granular barium sulfate. After cooling, and standing for 24 h, the precipitate is filtered off on an ashless paper, washed, ignited, and weighed as barium sulfate. 

Methods of testing cement. Physical tests. Test for heat of hydration Specification for calorimeter bombs Guide for determination of calorific values of solid, liquid and gaseous fuels (including definitions)... 

Equilibrium is characterized by constancy of some properties but it is not the only requirement. When some of the properties of a system are constant but equilibrium does not exist, the system is said to be in a steady state. In the experimental determination of calorific value of a gaseous fuel by Boy s Gas Calorimeter, the following conditions characterise the steady state ... 

Calorific Value. To determine calorific value, a sample is placed in a bomb, pressurized with oxygen, and ignited. The temperature rise in the water bath of the calorimeter surrounding the bomb is used to determine the calorific value (D2015, D3286, or D1989) (18). 

In an experiment to determine the calorific value of the fuel at temperature 1, . and for the same fuel flow the steady flow energy equation would yield... 

There are relatively few modern determinations of the heats of combustion of organic compounds containing carbon, hydrogen, and oxygen only which have not been carried out to high precision standards. The advent of fairly accurate commercially available combustion calorimeters for determining the calorific value of fuels such as the Griffin-Sutton bomb calorimeter 89 has meant that very many laboratories are now equipped to do combustions of... 

For most residual fuel oils, the range of calorific value is relatively narrow and limits are not usually included in the specifications. When precise determinations are not essential, values of sufficient accuracy may be derived... 

Density or specific gravity (relative density) is used whenever conversions must be made between mass (weight) and volume measurements. This property is often used in combination with other test results to predict oil quality, and several methods are available for measurement of density (or specific gravity). However, the density (specific gravity) (ASTM D-1298, IP 160) is probably of least importance in determining fuel oil performance but it is used in product control, in weight-volume relationships, and in the calculation of calorific value (heating value). 

The basis for the assignment of an enthalpy of formation to a natural material consists of the chemical composition, the structure information, and the calorific value. To determine the calorific value the prepared sample is completely oxidized (burned) in a calorimeter in an excess of oxygen. The heat liberated in this exothermic process is determined as the calorific value Qp>0. In the case of endothermic processes, such as calcination, Qp would be negative. 

The quantity of solid fuels used is generally controlled by some form of batch weighing which gives a high consistency. Variations in calorific value are, however, more problematic. They are generally resolved by a combination of blending deliveries and determining the calorific value daily on a representative sample. 

Before distribution of town gas to users, LNG must be vaporized by raising its temperature using seawater and LPG must be added to maintain its calorific value at a determined level. Calorific value control is carried out using a computerized cascade. When a discrepancy occurs between the determined level and the value obtained by continuous calorimetry, a corrective operation is performed on the ratio between LNG and LPG. 

A diagram of a flame calorimeter for combustion is shown in Figure 4. This type of calorimeter is used in several ASTM methods to determine the calorific value of gases or other fuels, for example D 1826 (1994). 

Floor coverings are tested by the radiant panel method, which is already in use in most European countries. The test methods for determining the calorific value and to confirm the nature of noncombustible materials (currently Class A building materials in Germany) are also well established and have been modified only slightly for the European classification system. 

Combustion. Most of the mined coal is burned to produce steam for electric power generation (qv). The calorific value determines the amount of steam that can be generated. However, the design and operation of a boiler requires consideration of a number of other properties (see Furnaces, FUEL-FIRED). 

The analyses of gases in the oil industry comprises the determination of the inert gases (He, Hj, O2, Ar and N2), low-boiling compounds (CO, CO2, H2S, COS) and the lower hydrocarbons, saturated and unsaturated, up to hexane. Some special samples. Such as natural gas, have to be analysed for low concentrations of higher-boiling compounds (up to CiqS) since such compounds have an important influence on the calorific value and dew point. 

The economic value of natural gas is primarily determined by the thermal energy it contains, which is expressed in British thermal units (Btu) or calorific value (CV). Other important physical properties comprise the liquid content, the burning characteristics, the dew point and the compressibility. In order to enable the calculation of these properties from its composition, a natural gas analysis should contain a detailed determination of all of the individual components, even in the low-concentration range. 

Heizwert, m. heating value, calorific value, -bestimmung, /. determination of heating... 

With regard to pro pints, brisance, power and detonation velocity are not tested. It is, however, necessary to determine the burning rate, press developed on burning, vol of gas evolved, calorific value, thermal stability, etc. If one is... 

Other factors which, together with the calorific value, will determine the economic value of an off-gas as a fuel are the quantity available and the continuity of supply. Waste gases are best used for steam raising, rather than for direct process heating, as this decouples the source from the use and gives greater flexibility. 

The results of the tests to determine the calorific power show satisfactory values for coprocessing, be it for mixed materials, otherwise unusable material from separation or plastics in general. As observed by [6], the level of chlorides is closely related to the quantity of plastics in the mixture, and also depends on the type of plastic. 

Coal is a rich source of carbon and has been a valuable source of fuel for centuries. It is classified by both coal type and coal rank. Coal type is determined by the nature of the original biomass that led to the formation of the coal. Coal rank signifies the degree of maturation or chemical change in coal and usually determines coal quality. The calorific value, moisture content, elemental analysis, volatile matter, ash, and fixed carbon content are important qualities of coal. 

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