1、BRITISH STANDARD BS 7420:1991 Guide for Determination of calorific values of solid, liquid and gaseous fuels (including definitions)BS7420:1991 This British Standard, having been prepared under the directionof the Refrigeration, Heating and Air Conditioning Standards Policy Committee, waspublished u
2、nder the authorityof the Standards Boardand comes into effect on 28June1991 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference RHE/-/5 Draft for comment 89/76237 DC ISBN 0 580 19482 5 Committees responsible for this British Standard The preparation of t
3、his British Standard was entrusted by the Refrigeration, Heating and Air Conditioning Standards Policy Committee (RHE/-) to Panel RHE/-/5, upon which the following bodies were represented: British Coal Corporation British Gas plc Department of Energy (Gas and Oil Measurement Branch) Institute of Pet
4、roleum Institution of Chemical Engineers Institution of Gas Engineers University College London Amendments issued since publication Amd. No. Date CommentsBS7420:1991 BSI 08-1999 i Contents Page Committees responsible Inside front cover Foreword ii 0 Introduction 1 1 Scope 1 2 General 1 3 Definitions
5、 2 4 Symbols 3 5 Determination of calorific values of solid and liquid fuels 3 6 Determination of calorific values of gaseous fuels 4 Appendix A Bibliography 6 Publication(s) referred to Inside back coverBS7420:1991 ii BSI 08-1999 Foreword This British Standard has been prepared under the direction
6、of the Refrigeration, Heating and Air Conditioning Standards Policy Committee, and represents a revision of BS526. BS 526 was first published in1933. It was revised and updated in1961, but was withdrawn in1987. However, the content of BS526 has since been found still to be needed, being referred to
7、in a number of other British Standards, and accordingly BS7420 hasbeen produced to provide up-to-date technical information, and to incorporate SI units. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their co
8、rrect application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 6, an inside back cover and a back cover. This standard has been updated (see copy
9、right date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7420:1991 BSI 08-1999 1 0 Introduction The amount of heat which would be released by complete combustion of unit quantity of a fuel under specified conditions is termed the
10、 calorific value of that fuel for those conditions. This may be determined directly by calorimetry or indirectly by inferential methods. The most useful basic expression of calorific value is often considered to be the heat released by complete combustion of a unit quantity of the fuel at a defined
11、pressure and a specified reference temperature. The products of combustion are returned to the specified reference temperature and the water formed or liberated during combustion is in the liquid phase, sulphur from the fuel is converted to sulphur dioxide, and nitrogen from the fuel either is conve
12、rted into oxides of nitrogen or remains as nitrogen gas, depending upon the type of fuel. Complete combustion is achievable with gaseous fuels at atmospheric pressure but solid and liquid fuels require higher pressures. Since the heat released at higher pressure differs from that which would be obta
13、ined with complete combustion at atmospheric pressure, the conditions for solid and liquid fuels need to be defined in such a way that this difference can be evaluated and kept small enough to be ignored in most circumstances. It should be noted that the term “calorific value” is the legal and contr
14、actual term used in common practice by the solid fuel and gas industries, whereas the oil industry uses the alternative term “heat of combustion”. 1 Scope This British Standard gives guidance on the determination of calorific values of solid, liquid and gaseous fuels. It includes definitions of diff
15、erent calorific values calculated on the basis of either constant pressure or constant volume, and with the water produced present either in the liquid or the vapour phase. The standard gives conditions for the experimental determination of calorific values and presents details of how to interconver
16、t numerical values of differently defined calorific values. It is sometimes necessary to convert a calorific value determined for a known set of specified conditions to the corresponding calorific value for a different set of conditions, and this standard gives guidance on calculations by means of w
17、hich this may be achieved. NOTE 1The titles of the standards publications referred to in this standard are listed on the inside back cover. NOTE 2Details of the other publications referred to in this standard are listed in the bibliography in Appendix A. 2 General This British Standard gives definit
18、ions of four calorific values: a) gross calorific value at constant pressure; b) net calorific value at constant pressure; c) gross calorific value at constant volume; d) net calorific value at constant volume. The word “gross” signifies that the water formed or liberated during the combustion is in
19、 the liquid phase; “net” signifies that the water formed or liberated during the combustion is in the vapour phase. For each type of fuel, a particular calorific value which can be obtained as the result of experimental determination is regarded as basic; the other three calorific values, which are
20、calculated from it, are regarded as derived quantities. For the purposes of this standard, the basic calorific value for solid and liquid fuels is the gross calorific value at constant volume, and for gaseous fuels it is the gross calorific value at constant pressure. This standard describes the con
21、ditions for the experimental determination of the basic value and the methods by which the derived values may be calculated from the basic value. Fuels cannot be compared precisely unless their calorific values are referred to the same conditions; for example calorific values of solid and liquid fue
22、ls should be converted to the corresponding values at a pressure of101.325kPa when they are to be compared with those of gaseous fuels. Methods for conversion of calorific values to a different pressure basis are given by Washburn (1933) and Rossini (1956). The definitions of calorific value given i
23、n clause 3 take into account the basis on which the quantity of fuel is measured, namely, mass for solid and liquid fuels, and volume for gaseous fuels; they also take into account the conditions under which the fuels can be burned completely.BS7420:1991 2 BSI 08-1999 3 Definitions For the purposes
24、of this British Standard the following definitions apply. 3.1 gross calorific value at constant volume of a solid or liquid fuel the amount of heat liberated per unit quantity of fuel burned in oxygen in a bomb calorimeter under standard conditions (see note 2) in such a way that the materials remai
25、ning after combustion (corrections having been made see5.2) consist of ash; the gases oxygen, carbon dioxide, sulphur dioxide and nitrogen; and liquid water in equilibrium with its vapour, and assumed to be saturated with carbon dioxide, and possibly also containing dissolved hydrogen chloride, plus
26、 oxides of nitrogen and sulphur, as acids NOTE 1Known in thermodynamics as the “specific energy of combustion”. NOTE 2The international thermochemical reference temperature is25 C. This temperature was chosen because the change in the specific heat capacity of water over the range20 C to30 C is smal
27、l. It is desirable that the reference temperature be close to the temperature at which determinations are made to ensure that corrections, which are empirical, are sufficiently accurate;25 C satisfies this requirement. Although calorific values with reference temperature 0 C are sometimes used, e.g.
28、 for heat balances, this is not to be recommended if it involves a large empirical adjustment of the observed calorific value. 3.2 gross calorific value at constant pressure of a solid or liquid fuel the amount of heat liberated per unit quantity of fuel burned in oxygen at constant pressure in such
29、 a way that the heat released is equal to the sum of the gross calorific value at constant volume and the work which would have been done by the atmosphere under isothermal conditions, had the pressure remained constant NOTEKnown in thermodynamics as the “specific enthalpy of combustion”. 3.3 net ca
30、lorific value at constant volume of a solid or liquid fuel the amount of heat liberated per unit quantity of fuel burned in oxygen in a bomb calorimeter under standard conditions (see3.1 note 2) in such a way that the materials remaining after combustion corrections having been made (see5.2) consist
31、 of ash and the gases oxygen, carbon dioxide, sulphur dioxide and nitrogen, plus water vapour 3.4 net calorific value at constant pressure of a solid or liquid fuel the amount of heat liberated per unit quantity of fuel burned in oxygen at constant pressure in such a way that the heat released is eq
32、ual to the sum of the net calorific value of the fuel at constant volume and the work which would have been done by the atmosphere under isothermal conditions, had the pressure remained constant 3.5 gross calorific value at constant pressure of a gaseous fuel the amount of heat liberated per unit vo
33、lume of fuel burned in oxygen in such a way that the materials remaining after combustion consist of the gases carbon dioxide, sulphur dioxide, oxygen and nitrogen, plus liquid water. The reactants and the materials remaining after combustion are all measured under the standard conditions, given in
34、the UK Gas Act (1986) 1) , which are15 C and101.325kPa 3.6 gross calorific value at constant volume of a gaseous fuel the amount of heat liberated per unit volume of fuel burned in oxygen in such a way that the materials remaining after combustion consist of the gases carbon dioxide, sulphur dioxide
35、, oxygen, and nitrogen, plus liquid water. The reactants are measured at 15 C and at 101.325 kPa with the materials remaining after combustion occupying the same total volume at15 C 3.7 net calorific value at constant pressure of a gaseous fuel the amount of heat liberated per unit volume of fuel bu
36、rned in oxygen in such a way that the materials remaining after combustion consist of the gases carbon dioxide, sulphur dioxide, oxygen and nitrogen, plus water vapour. The reactants and the materials remaining after combustion are all measured at15Cand101.325kPa 1) Available from HMSO, 49 High Holb
37、orn, London WC1, for personal callers, or by post from HMSO, P.O. Box 276, LondonSW85DT.BS7420:1991 BSI 08-1999 3 3.8 net calorific value at constant volume of a gaseous fuel the amount of heat liberated per unit volume of fuel burned in oxygen in such a way that the materials remaining after combus
38、tion consist of the gases carbon dioxide, sulphur dioxide, oxygen and nitrogen, plus water vapour. The reactants are measured at15 C and101.325kPa with the products of combustion occupying the same total volume at15 C 4 Symbols For the purposes of this British Standard the following symbols apply. O
39、ther symbols are defined in the text where they occur. 5 Determination of calorific values of solid and liquid fuels 5.1 General The only satisfactory method for the determination of the calorific value of solid and liquid fuels is that in which a sample of the fuel is burned in oxygen under pressur
40、e in a bomb calorimeter immersed in water, the temperature rise of which is measured; this is called the “oxygen-bomb” method. The gross calorific value of the fuel at constant volume is determined by this method. It is suitable for both solid and liquid fuels but the very high rate of combustion of
41、 some liquid fuels necessitates certain differences in procedures between solid and liquid fuels. It is essential that the particular conditions under which any calorific value has been determined be defined, where possible, by reference to the standard test method adopted for the determination (see
42、5.2). The three derived calorific values may be calculated from the gross calorific value at constant volume if the composition of the fuel is known. When the fuel is burned in the bomb calorimeter, the work which would be done by the atmosphere on the products if unit quantity of the fuel were burn
43、ed at constant pressure may be calculated and added to the gross calorific value at constant volume to obtain the gross calorific value at constant pressure. Likewise, the enthalpy of vaporization of the water formed by the combustion of unit quantity of the fuel may be calculated and subtracted fro
44、m the gross calorific value at either constant volume or constant pressure to obtain the corresponding net calorific value. 5.2 Standard test methods for the determination of gross calorific value at constant volume of a solid or liquid fuel Standard test methods for determining gross calorific valu
45、e at constant volume are given in BS1016-5 for solid fuels and BS2000-12 for liquid fuels which include procedures to correct for the formation of sulphuric and nitric acids during the test. NOTEFor a discussion of the effect of chlorine, see Barker etal.(1955). 5.3 Calculation of gross calorific va
46、lue at constant pressure of a solid or liquid fuel Let and be the percentages (m/m) of hydrogenand oxygen in the fuel (see note) on the basis (e.g. as-received, air-dried) to which the determined value, Q gr,v , refers. Then the work done by the atmosphere when unit quantity of the fuel is burned at
47、 constant pressure to give liquid water is: This expression is equal to Q gr,p Q gr,v . Thus, at a reference temperature of25 C, and with suitable rounding of the above expression, Q gr,pmay be calculated from the expression: NOTEand refer to hydrogen and oxygen in the fuel substance only, and speci
48、fically exclude the hydrogen and oxygen present in the moisture and in the mineral matter associated with the fuel. For practical purposes, values of and may be derived by multiplying the dry mineral-matter-free hydrogen and dry mineral-matter-free oxygen contents by: where Y and Z are the percentag
49、es of moisture and mineral matter, respectively, in the fuel on the basis to which Q gr,vrefers. For further explanation of calculation to different bases, seeBS1016-16. T absolute temperature R molar gas constant L molar enthalpy of vaporization of water at 25 C and constant pressure percentage by mass of hydrogen in the fuel percentage by mass of oxygen in the fuel percentage by mass of water in the fuel M H relative molecular mass of hydrogen M O relative molecular mass of oxygen M W relative molecular mass of water Q gr,p gross calorific value at constant p
