Calorific value, 3.7

Gross calorific value and ash content of waste materials can be determined by a calorimetric method. After a calorimetric analysis, the bomb washing can be used to determine of mineral content by elemental analysis. The sample is burned under controlled conditions in oxygen. The calorimeter is standardized by burning known amount of benzoic acid. The formation of acids can additionally be determined by titration. 

Impurities in benzene, toluene, xylene, naphthas, and industrial aromatic hydrocarbons are determined by a simple colorimetric analysis of an acid wash. A solvent is washed with sulfuric acid and the color of the acid layer is determined by a visual comparison with color standards prepared from solutions of cobalt chloride and ferric chloride. 

Aromatic hydrocarbons which melt below 150 C can be subjected to color analysis in the liquid (molten) state using a visual comparison with platinum-cobalt standards. Standards are prepared from a stock solution of K2PtCl2 to form a scale varying in color intensity. Similar procedure was developed to evaluate color of halogenated organic solvents and their admixtures.  

Objective color measurement is based on tristimulus colorimetryThis instrumental method measures tristimulus values of hght transmitted by a sample and compares the results to the values transmitted by distilled water. The results can be recalculated to the platinum-cobalt scale referred to in the previous standards. The results can also be interpreted by normal methods of color measurement to yellowness index, color, color depth, etc. 

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For fuels it is quite usual to employ kilocalories per kilogram as a measure of calorific value while for foods the unit used is kilocalories per gram. This, however, is often abbreviated to Calories , so that a value for carbohydrates of 4-1 Calories per gram is 4100 calories per gram. 

Gross calorific values are high, being about 100000 kJ/m ... 

All these fuel gases contain more than 50 % hydrogen and 10-30% methane, the other main components being CO, higher hydrocarbons, CO2 and Nj. In many parts of the world natural gas of calorific value of approximately 38MJ/m has become the widely-used gaseous fuel. 

Natural gas analysis has considerable economic importance. In fact, commercial contracts increasingly specify not just volume but the calorific or heating value as well. Today the calorific value of a natural gas calculated from its composition obtained by chromatography is recognized as valid. There is therefore a large research effort devoted to increasing the precision of this analysis. 

The analyst now has available the complete details of the chemical composition of a gasoline all components are identified and quantified. From these analyses, the sample s physical properties can be calculated by using linear or non-linear models density, vapor pressure, calorific value, octane numbers, carbon and hydrogen content. 

Measured in MJ/m or Btu/ft, the Wobbe Index has an advantage over the calorific value of a gas (the heating value per unit volume or weight), which varies with the density of the gas. The Wobbe Index Is commonly specified in gas contracts as a guarantee of product quality. A customer usually requires a product whose Wobbe Index lies within a narrow range, since a burner will need adjustment to a different fuel air ratio if the fuel quality varies significantly. A sudden increase in heating value of the feed can cause a flame-out. 

When a customer agrees to purchase gas, product quality is specified in terms of the calorific value of the gas, measured by the Wobbe index (calorific value divided by density), the hydrocarbon dew point and the water dew point, and the fraction of other gases such as Nj, COj, HjS. The Wobbe index specification ensures that the gas the customer receives has a predictable calorific value and hence predictable burning characteristics. If the gas becomes lean, less energy is released, and if the gas becomes too rich there is a risk that the gas burners flame out . Water and hydrocarbon dew points (the pressure and temperature at which liquids start to drop out of the gas) are specified to ensure that over the range of temperature and pressure at which the gas is handled by the customer, no liquids will drop out (these could cause possible corrosion and/or hydrate formation). 

HjS is undesirable because of its toxicity and corrosive properties. COj can cause corrosion in the presence of water, and N2 simply reduces the calorific value of the gas as it is inert. 

Table 1. International Classification of Coals having a Gross Calorific Value below 23.8 MJ/kg — ...

Moisture is lost and the chemical composition changes during coalification. Oxygen and hydrogen decrease and carbon increases. These compositional changes are accompanied by decreases in volatile matter and increases in calorific value. The volatile matter and calorific content are the main criteria used for commercial classification in the United States and for the International Classification. 

The ASTM Glassification. The ASTM classification system was adopted in 1938 as a standard means of specification. This system is used in the United States and in many other parts of the world, and is designated D388 in the ASTM Standards (18). The higher rank coals are specified by fixed carbon >69%, or for volatile matter <31%, on a dry, mineral-free basis. Lower rank coals are classified by calorific value on the moist, mineral-matter-free... 

Coals having 69% or more fixed carbon on the dry, mineral -m a tter-free basis are classified according to fixed carbon, regardless of gross calorific value. 

Ha.rd Coa.1, The amount of coal in international commerce since ca 1945 necessitated an international system of coal classification and in 1956 the Coal Committee of the European Economic Community agreed on a system designated the International Classification of Hard Coal by Type (3). Volatile matter and gross calorific value on a moist, ash-free basis are among the parameters considered. Table 4 shows the various classes of the international system and gives the corresponding national names used for these coals. 

Clas s no. Volatile matter, % Calorific value, kj/g Belgiu m Germany Erance Italy The Nethedand s Poland United Kingdom United States... 

Physical Methods of Examination. Physical methods used to examine coals can be divided into two classes which, in the one case, yield information of a stmctural nature such as the size of the aromatic nuclei, ie, methods such as x-ray diffraction, molar refraction, and calorific value as a function of composition and in the other case indicate the fraction of carbon present in aromatic form, ie, methods such as ir and nuclear magnetic resonance spectroscopies, and density as a function of composition. Some methods used and types of information obtained from them are (41) ... 

Properties Involving Utilization. Coal rank is the most important single property for appHcation of coal. Rank sets limits on many properties such as volatile matter, calorific value, and swelling and coking characteristics. Other properties of significance include grindabHity, ash content and composition, and sulfur content. 

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). 

Comprehensive reviews of energy sources are pubflshed by the World Energy Conference, formerly the World Power Conference at six-year intervals (83). The 1986 survey includes reserves and also gives total resources. In 1986 the total proven reserves of recoverable soHd fuels were given as 6 X 10 metric tons. One metric ton is defined as 29.2 x 10 MJ (27.7 x 10 Btu) to provide for the variation of calorific value in different coals. The total estimated additional reserves recoverable and total estimated additional amount in place are 2.2 x 10 and 7.7 x 10 metric tons, respectively. These figures are about double the 1913 estimates, primarily because significantly increased reserves have been indicated for Russia. 

On a uniform calorific value basis, coal constitutes 69% of the total estimated recoverable resources of fossil fuel in the United States. Petroleum and natural gas are about 7% and oil in oil shale, which is not as of this writing used as a fuel, is about 23%. The 1989 total recoverable reserves of coal are about 500 times the 1989 aimual production (2), whereas the reserves of oil and gas are smaller, the production and consumption rate of oil and gas in the United States is three times that of coal. 

The surface of the coal particles oxidizes or weathers resulting in cracks, finer particles, and reduced agglomeration all of which may destroy coking properties. If spontaneous heating takes place, the calorific value of the coal is reduced. Hot spots must be carefully dug out and used as quickly as possible. Without spontaneous heating and with good compaction, calorific value losses below 1%/yr have been recorded. 

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). 

A low calorific value gas, which includes nitrogen from air, could be produced for boiler or turbine use in electric power production, or an intermediate calorific value gas containing no nitrogen for an industrial fuel gas, or synthesis gas for chemical and methane production could be provided. This approach which has been studied in Russia, Europe, Japan, and the United States, is stiU noncommercial in part because it is not economically competitive. 

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