SIST EN 14918:2010
(Main)Solid Biofuels - Method for the determination of calorific value
Solid Biofuels - Method for the determination of calorific value
This European Standard specifies a method for the determination of the gross calorific value of a solid biofuel at constant volume and at the reference temperature 25 °C in a bomb calorimeter calibrated by combustion of certified benzoic acid. The result obtained is the gross calorific value of the analysis sample at constant volume with all the water of the combustion products as liquid water. In practice, biofuels are burned at constant (atmospheric) pressure and the water is either not condensed (removed as vapour with the flue gases) or condensed. Under both conditions, the operative heat of combustion to be used is the net calorific value of the fuel at constant pressure. The net calorific value at constant volume may also be used; formulae are given for calculating both values. General principles and procedures for the calibrations and the biofuel experiments are presented in the main text, whereas those pertaining to the use of a particular type of calorimetric instrument are described in Annexes A to C. Annex D contains checklists for performing calibration and fuel experiments using specified types of calorimeters. Annex E gives examples to illustrate some of the calculations.
Feste Biobrennstoffe - Bestimmung des Heizwertes
Diese Europäische Norm legt für feste Biobrennstoffe ein Verfahren zur Bestimmung des Brennwertes bei konstantem Volumen und bei einer Referenztemperatur von 25 °C fest, wozu ein Bombenkalorimeter verwendet wird, das durch die Verbrennung zertifizierter Benzoesäure kalibriert wurde.
Bei der Verbrennung des zu untersuchenden Biobrennstoffes wird als Prüfergebnis der Brennwert einer Analysenprobe bei konstantem Volumen ermittelt, der dadurch gekennzeichnet ist, dass das gesamte Wasser in den Verbrennungsprodukten in flüssigem Zustand vorliegt. In der Praxis werden Biobrennstoffe bei konstantem (atmosphärischem) Druck verbrannt, wobei eine Kondensation des Wassers entweder stattfindet oder nicht stattfindet (d. h. Wasser wird als Wasserdampf zusammen mit den Abgasen abgeführt). In beiden Fällen ist anzuwendende wirksame Verbrennungswärme der Heizwert des Brennstoffes bei konstantem Druck. Der Heizwert bei konstantem Volumen darf ebenfalls angewendet werden; im vorliegenden Dokument sind Gleichungen zur Berechnung beider Werte angegeben.
Die bei den Kalibrierungen und Biobrennstoffprüfungen allgemein anzuwendenden Prinzipien und Verfahren sind im Hauptteil dieser Norm dargelegt, während Prinzipien und Verfahren im Zusammenhang mit der Anwendung spezieller Kalorimeter-Typen in den Anhängen A bis C beschrieben sind. Anhang D enthält eine Checkliste zur Durchführung der Kalibrierungen und Brennstoffprüfungen unter Anwendung bestimmter Kalorimeter-Typen. Im Anhang E sind Berechnungsbeispiele angegeben.
Biocombustibles solides - Détermination du pouvoir calorifique
La présente Norme européenne spécifie une méthode de détermination du pouvoir calorifique supérieur à volume constant d'un biocombustible solide et à une température de référence de 25 °C dans une bombe calorimétrique étalonnée par combustion d'acide benzoïque certifié.
Le résultat obtenu est le pouvoir calorifique supérieur de l'échantillon pour analyse à volume constant, la totalité de l'eau des produits de combustion étant à l'état liquide. En pratique, les biocombustibles sont soumis à combustion à pression (atmosphérique) constante et l'eau est condensée ou non (s’évapore avec les gaz de combustion). Dans les deux cas, la chaleur effective de la combustion à utiliser est le pouvoir calorifique inférieur du combustible à pression constante. Le pouvoir calorifique inférieur à volume constant peut également être utilisé, des formules sont indiquées pour le calcul des deux données.
Les principes et les modes opératoires généraux relatifs aux essais d’étalonnage et aux essais sur les biocombustibles sont présentés dans le corps du texte du présent document alors que ceux relevant de l'utilisation d'un type particulier d'instrument calorimétrique sont décrits aux Annexes A à C. L'Annexe D spécifie des listes de contrôle pour réaliser l'étalonnage et les essais sur les combustibles à l'aide de modèles de calorimètres spécifiés. L’Annexe E fournit une série d'exemples illustrant certains des calculs.
Trdna biogoriva - Metoda za ugotavljanje kalorične vrednosti
Ta evropski standard opredeljuje metodo za določevanje bruto kalorične vrednosti trdnega biogoriva pri konstantni prostornini in pri referenčni temperaturi 25°C v komori-kalorimetru, kalibriranem s sežiganjem certificire benzojeve kisline. Dobljeni rezultat je bruto kalorična vrednost vzorca analize pri konstantni prostornini, pri čemer je vsa voda, ki nastane pri zgorevanju, v tekočem stanju. V praksi se biogoriva sežigajo pri konstantnem (atmosferskem) tlaku in voda je bodisi kondenzirana ali ne (odstranjena kot para z izpušnimi plini). V obojih pogojih je delovna temperatura zgorevanja, ki se uporablja, neto kalorična vrednost goriva pri konstantnem tlaku. Lahko se uporablja tudi neto kalorična vrednost pri konstantni prostornini; podane so formule za izračun obeh vrednosti. Splošna načela in postopki za kalibracijo in poskuse z biogorivi so predstavljeni v glavnem besedilu, tisti, ki se nanašajo na uporabo določenega tipa kalorimetričnega instrumenta, pa so opisani v Dodatkih A do C. Dodatek D vsebuje kontrolne sezname za opravljanje kalibracije in poskusov z gorivom ob uporabi opredeljenih tipov kalorimetrov. Dodatek E podaja primere za ponazoritev nekaterih izračunov.
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Feste Biobrennstoffe - Bestimmung des HeizwertesBiocombustibles solides - Détermination du pouvoir calorifiqueSolid Biofuels - Method for the determination of calorific value75.160.10Trda gorivaSolid fuelsICS:Ta slovenski standard je istoveten z:EN 14918:2009SIST EN 14918:2010en,fr,de01-marec-2010SIST EN 14918:2010SLOVENSKI
STANDARDSIST-TS CEN/TS 14918:20051DGRPHãþD
SIST EN 14918:2010
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 14918
December 2009 ICS 75.160.10 Supersedes CEN/TS 14918:2005English Version
Solid biofuels - Determination of calorific value
Biocombustibles solides - Détermination du pouvoir calorifique
Feste Biobrennstoffe - Bestimmung des Heizwertes This European Standard was approved by CEN on 10 October 2009.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2009 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 14918:2009: ESIST EN 14918:2010
EN 14918:2009 (E) 2 Contents Page Foreword .41Scope .52Normative references .53Terms and definitions .54Principle .65Reagents .76Apparatus .87Preparation of test sample . 118Calorimetric procedure . 129Calibration . 1810Gross calorific value . 2311Precision . 2712Calculation of net calorific value at constant pressure . 2713Test report . 28Annex A (normative)
Adiabatic bomb calorimeters . 30A.1Principle . 30A.2Sources of error for the real calorimeter . 30A.3Adiabatic conditions . 30A.4Initial steady state and length of the main period . 31A.5Correction for drift at the final temperature . 32A.6Strategy for checking on bias . 32Annex B (normative)
Isoperibol and static-jacket bomb calorimeters . 34B.1Principle . 34B.2Sources of error for the real calorimeter . 35B.3Choice of jacket temperature . 36B.4Rating periods . 36B.5Calculation of the corrected temperature rise
............................................................................ 37Annex C (normative)
Automated bomb calorimeters . 40C.1The instrument . 40C.2Calibration . 40C.3Precision requirements for calibrations . 41C.4Comparability of calibration and fuel experiments . 41C.5Documentation and print-out . 42C.6Precision requirements for fuel experiments . 42Annex D (informative)
Checklists for the design and procedures of combustion experiments . 43D.1Introduction . 43D.2Choice of general parameters . 43D.3Adiabatic calorimeters . 44D.4Isoperibol calorimeters . 46D.5Automated bomb calorimeters . 47Annex E (informative)
Examples to illustrate the main calculations used in this document when an automated bomb calorimeter is used for determinations . 48SIST EN 14918:2010
EN 14918:2009 (E) 3 E.1Gross calorific value at constant volume . 48E.2Gross calorific value at constant pressure. 49E.3Net calorific value . 50E.4Use of typical or default values to calculate calorific values . 51Annex F (informative)
List of symbols used in this document . 52Annex G (informative)
Key-word index . 55Annex H (informative)
Default values of most used biofuels for the calculations of calorific values
............................................................................................................................................................... 59Annex I (informative)
Flow chart for a routine calorific value determination . 60Bibliography . 61 SIST EN 14918:2010
EN 14918:2009 (E) 4 Foreword This document (EN 14918:2009) has been prepared by Technical Committee CEN/TC 335 “Solid biofuels”, the secretariat of which is held by SIS. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by June 2010, and conflicting national standards shall be withdrawn at the latest by June 2010. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document supersedes CEN/TS 14918:2005. WARNING – Strict adherence to all of the provisions prescribed in this document should ensure against explosive rupture of the bomb, or a blow-out, provided that the bomb is of proper design and construction and in good mechanical condition. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.
SIST EN 14918:2010
EN 14918:2009 (E) 5 1 Scope This European Standard specifies a method for the determination of the gross calorific value of a solid biofuel at constant volume and at the reference temperature 25 °C in a bomb calorimeter calibrated by combustion of certified benzoic acid. The result obtained is the gross calorific value of the analysis sample at constant volume with all the water of the combustion products as liquid water. In practice, biofuels are burned at constant (atmospheric) pressure and the water is either not condensed (removed as vapour with the flue gases) or condensed. Under both conditions, the operative heat of combustion to be used is the net calorific value of the fuel at constant pressure. The net calorific value at constant volume may also be used; formulae are given for calculating both values. General principles and procedures for the calibrations and the biofuel experiments are presented in the main text, whereas those pertaining to the use of a particular type of calorimetric instrument are described in Annexes A to C. Annex D contains checklists for performing calibration and fuel experiments using specified types of calorimeters. Annex E gives examples to illustrate some of the calculations. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 14774-3, Solid biofuels
Determination of moisture content
Oven dry method
Part 3: Moisture in general analysis sample prEN 14778-1, Solid biofuels
Methods for sampling prEN 14780, Solid biofuels
Methods for sample preparation prEN 15296, Solid biofuels
Calculation of analyses to different bases EN ISO 10304-1, Water quality
Determination of dissolved anions by liquid chromatography of ions
Part 1: Determination of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate (ISO 10304-1:2007) ISO 651, Solid-stem calorimeter thermometers ISO 652, Enclosed-scale calorimeter thermometers ISO 1770, Solid-stem general purpose thermometers ISO 1771, Enclosed-scale general purpose thermometers 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 gross calorific value at constant volume absolute value of the specific energy of combustion, in joules, for unit mass of a solid biofuel burned in oxygen in a calorimetric bomb under the conditions specified SIST EN 14918:2010
EN 14918:2009 (E) 6 NOTE The products of combustion are assumed to consist of gaseous oxygen, nitrogen, carbon dioxide and sulfur dioxide, of liquid water (in equilibrium with its vapour) saturated with carbon dioxide under the conditions of the bomb reaction, and of solid ash, all at the reference temperature. 3.2 net calorific value at constant volume absolute value of the specific energy of combustion, in joules, for unit mass of the biofuel burned in oxygen under conditions of constant volume and such that all the water of the reaction products remains as water vapour (in a hypothetical state at 0,1 MPa), the other products being as for the gross calorific value, all at the reference temperature 3.3 net calorific value at constant pressure absolute value of the specific heat (enthalpy) of combustion, in joules, for unit mass of the biofuel burned in oxygen at constant pressure under such conditions that all the water of the reaction products remains as water vapour (at 0,1 MPa), the other products being as for the gross calorific value, all at the reference temperature 3.4 reference temperature international reference temperature for thermochemistry of 25 °C is adopted as the reference temperature for calorific values NOTE 1 See 8.7. NOTE 2 The temperature dependence of the calorific value of biofuels is small (less than 1 J/(g x K)). 3.5 effective heat capacity of the calorimeter amount of energy required to cause unit change in temperature of the calorimeter 3.6 corrected temperature rise change in calorimeter temperature caused solely by the processes taking place within the combustion bomb.
NOTE 1 The corrected temperature rise is the total observed temperature rise corrected for heat exchange, stirring power, etc. (8.6). NOTE 2 The change in temperature may be expressed in terms of other units: resistance of a platinum or thermistor thermometer, frequency of a quartz crystal resonator, etc., provided that a functional relationship is established between this quantity and a change in temperature. The effective heat capacity of the calorimeter may be expressed in units of energy per such an arbitrary unit. Criteria for the required linearity and closeness in conditions between calibrations and fuel experiments are given in 9.3. A list of the symbols used and their definitions is given in Annex F 4 Principle 4.1 Gross calorific value A weighed portion of the analysis sample of the solid biofuel is burned in high-pressure oxygen in a bomb calorimeter under specified conditions. The effective heat capacity of the calorimeter is determined in calibration experiments by combustion of certified benzoic acid under similar conditions, accounted for in the certificate. The corrected temperature rise is established from observations of temperature before, during and after the combustion reaction takes place. The duration and frequency of the temperature observations depend on the type of calorimeter used. Water is added to the bomb initially to give a saturated vapour phase prior to combustion (see 8.2.1 and 9.2.2), thereby allowing all the water formed, from the hydrogen and moisture in the sample, to be regarded as liquid water. SIST EN 14918:2010
EN 14918:2009 (E) 7 The gross calorific value is calculated from the corrected temperature rise and the effective heat capacity of the calorimeter, with allowances made for contributions from ignition energy, combustion of the fuse(s) and for thermal effects from side reactions such as the formation of nitric acid. Furthermore, a correction is applied to account for the difference in energy between the aqueous sulfuric acid formed in the bomb reaction and gaseous sulfur dioxide, i.e. the required reaction product of sulfur in the biofuel. The corresponding energy effect between aqueous and gaseous hydrochloric acid can be neglected due to the usually low chlorine content of most biofuels (induced correction value low). NOTE The typical chlorine content of wood based solid biofuels is below 0,05 % (m/m), of herbaceous 0,1 % to 1 % (m/m) and of fruit based < 0,2 % (m/m) in dry matter. 4.2 Net calorific value The net calorific value at constant volume and the net calorific value at constant pressure of the biofuel are obtained by calculation from the gross calorific value at constant volume determined on the analysis sample. The calculation of the net calorific value at constant volume requires information about the moisture and hydrogen contents of the analysis sample. In principle, the calculation of the net calorific value at constant pressure also requires information about the oxygen and nitrogen contents of the analysis sample. 5 Reagents 5.1 Oxygen, at a pressure high enough to fill the bomb to 3 MPa, pure with an assay of at least 99,5 % (V/V), and free from combustible matter. NOTE Oxygen made by the electrolytic process may contain up to 4 % (V/V) of hydrogen. 5.2 Fuse 5.2.1 Ignition wire, of nickel-chromium 0,16 mm to 0,20 mm in diameter, platinum 0,05 mm to 0,10 mm in diameter, or another suitable conducting wire with well-characterized thermal behaviour during combustion. 5.2.2 Cotton fuse, of white cellulose cotton, or equivalent, if required (see 8.2.1). 5.3 Combustion aids of known gross calorific value, composition and purity, like benzoic acid, n-dodecane, paraffin oil, combustion bags or capsules may be used. 5.4 Standard volumetric solutions and indicators, only for use when analysis of final bomb solutions is required. 5.4.1 Barium hydroxide solution, c[Ba(OH)2] = 0,05 mol/l. 5.4.2 Sodium carbonate solution, c(Na2C03) = 0,05 mol/I. 5.4.3 Sodium hydroxide solution, c(NaOH) = 0,1 mol/I. 5.4.4 Hydrochloric acid solution, c(HCI) = 0,1 mol/I. 5.4.5 Screened methyl orange indicator, 1 g/I solution. Dissolve 0,25 g of methyl orange and 0,15 g of xylene cyanole FF in 50 ml of 95 % (V/V) ethanol and dilute to 250 ml with water. 5.4.6 Phenolphthalein, 10 g/I solution. Dissolve 2,5 g of phenolphthalein in 250 ml of 95 % (V/V) ethanol. SIST EN 14918:2010
EN 14918:2009 (E) 8 5.5 Benzoic acid, of calorimetric-standard quality, certified by (or with certification unambiguously traceable to) a recognized standardizing authority. NOTE Benzoic acid is the sole substance recommended for calibration of an oxygen-bomb calorimeter. For the purpose of checking the overall reliability of the calorimetric measurements, test substances, e.g. n-dodecane, are used. Test substances are mainly used to prove that certain characteristics of a sample, e.g. burning rate or chemical composition, do not introduce bias in the results. A test substance shall have a certified purity and a well-established energy of combustion. The benzoic acid is burned in the form of pellets. It is normally used without drying or any treatment other than pelletizing; consult the sample certificate. It does not absorb moisture from the atmosphere at relative humidities below 90 %. The benzoic acid shall be used as close to certification conditions as is feasible; significant departures from these conditions shall be accounted for in accordance with the directions in the certificate. The energy of combustion of the benzoic acid, as defined by the certificate for the conditions utilized, shall be adopted in calculating the effective heat capacity of the calorimeter (see 9.2). 6 Apparatus 6.1 General The calorimeter (see Figure 1), consists of the assembled combustion bomb, the calorimeter can (with or without a lid), the calorimeter stirrer, water, temperature sensor, and leads with connectors inside the calorimeter can required for ignition of the sample or as part of temperature measurement or control circuits. During measurements the calorimeter is enclosed in a thermostat. The manner in which the thermostat temperature is controlled defines the working principle of the instrument and hence the strategy for evaluation of the corrected temperature rise. In aneroid systems (systems without a fluid) the calorimeter can, stirrer and water are replaced by a metal block. The combustion bomb itself constitutes the calorimeter in some aneroid systems. In combustion calorimetric instruments with a high degree of automation, especially in the evaluation of the results, the calorimeter is in a few cases not as well-defined as the traditional, classical-type calorimeter. Using such an automated calorimeter is, however, within the scope of this document as long as the basic requirements are met with respect to calibration conditions, comparability between calibration and fuel experiments, ratio of sample mass to bomb volume, oxygen pressure, bomb liquid, reference temperature of the measurements and repeatability of the results. A print-out of some specified parameters from the individual measurements is essential. Details are given in Annex C. As the room conditions (temperature fluctuation, ventilation, etc.) may have an influence on the precision of the determination, the manufacturers instructions for the placing of the instrument shall always be followed. Equipment, adequate for determinations of calorific value in accordance with this document, is specified in 6.2 to 6.8. 6.2 Calorimeter with thermostat 6.2.1 Combustion bomb, capable of withstanding safely the pressures developed during combustion. The design shall permit complete recovery of all liquid products. The material of construction shall resist corrosion by the acids produced in the combustion of biofuels. A suitable internal volume of the bomb would be from 250 ml to 350 ml. WARNING – Bomb parts shall be inspected regularly for wear and corrosion; particular attention shall be paid to the condition of the threads of the main closure. Manufacturers' instructions and any local regulations regarding the safe handling and use of the bomb shall be observed. When more than one bomb of the same design is used, it is imperative to use each bomb as a complete unit. Swapping of parts may lead to a serious accident. SIST EN 14918:2010
EN 14918:2009 (E) 9 Key 1 Stirrer 4 Thermometer 2 Thermostat lid 5 Calorimeter can 3 Ignition leads 6 Thermostat
Figure 1 – Classical-type bomb combustion calorimeter with thermostat 6.2.2 Calorimeter can, made of metal, highly polished on the outside and capable of holding an amount of water sufficient to completely cover the flat upper surface of the bomb while the water is being stirred. A lid generally helps reduce evaporation of calorimeter water, but unless it is in good thermal contact with the can it lags behind in temperature during combustion, giving rise to undefined heat exchange with the thermostat and a prolonged main period. 6.2.3 Stirrer, working at constant speed. The stirrer shaft should have a low-heat-conduction and/or a low-mass section below the cover of the surrounding thermostat to minimize transmission of heat to or from the system; this is of particular importance when the stirrer shaft is in direct contact with the stirrer motor. When a lid is used for the calorimeter can, this section of the shaft should be above the lid. NOTE The rate of stirring for a stirred-water type calorimeter should be large enough to make sure that hot spots do not develop during the rapid part of the change in temperature of the calorimeter. A rate of stirring such that the length of the main period can be limited to 10 min or less is usually adequate (see Annexes A and B). SIST EN 14918:2010
EN 14918:2009 (E) 10 6.2.4 Thermostat (water jacket), completely surrounding the calorimeter, with an air gap of approximately 10 mm separating calorimeter and thermostat. The mass of water of a thermostat intended for isothermal operation shall be sufficiently large to outbalance thermal disturbances from the outside. The temperature should be controlled to within ± 0,1 K or better throughout the experiment. A passive constant temperature ("static") thermostat shall have a heat capacity large enough to restrict the change in temperature of its water. Criteria for satisfactory behaviour of this type of water jacket are given in Annex B. NOTE 1 For an insulated metal static jacket, satisfactory properties are usually ensured by making a wide annular jacket with a capacity for water of at least 12,5 I. NOTE 2 Calorimeters surrounded by insulating material, creating a thermal barrier, are regarded as static-jacket calorimeters. When the thermostat (water jacket) is required to follow closely the temperature of the calorimeter, it should be of low mass and preferably have immersion heaters. Energy shall be supplied at a rate sufficient to maintain the temperature of the water in the thermostat to within 0,1 K of that of the calorimeter water after the charge has been fired. When in a steady state at 25 °C, the calculated mean drift in temperature of the calorimeter shall not exceed 0,000 5 K/min (see A.3.2). 6.2.5 Temperature measuring instrument, capable of indicating temperature with a resolution of at least 0,001 K so that temperature intervals of 2 K to 3 K can be determined with a resolution of 0,002 K or better. The absolute temperature shall be known to the nearest 0,1 K at the reference temperature of the calorimetric measurements. The temperature measuring device should be linear, or linearized, in its response to changes in temperature over the interval it is used. As alternatives to the traditional mercury-in-glass thermometers, suitable temperature sensors are platinum resistance thermometers, thermistors, quartz crystal resonators, etc. which together with a suitable resistance bridge, null detector, frequency counter or other electronic equipment provide the required resolution. The short-term repeatability of this type of device shall be 0,001 K or better. Long-term drift shall not exceed the equivalent of 0,05 K for a period of six months. For sensors with linear response (in terms of temperature), drift is less likely to cause bias in the calorimetric measurements than are non-linear sensors. Mercury-in-glass thermometers shall conform to ISO 651, ISO 652, ISO 1770 or ISO 1771. A viewer with magnification about 5× is needed for reading the temperature with the resolution required. A mechanical vibrator to tap the thermometer is suitable for preventing the mercury column from sticking (see 8.4). If this is not available, the thermometer shall be tapped manually before reading the temperature. 6.2.6 Ignition circuit The electrical supply shall be 6 V to 12 V alternating current from a step-down transformer or direct current from batteries. It is desirable to include a pilot light in the circuit to indicate when current is flowing. Where the firing is done manually, the firing switch shall be of the spring-loaded, normally open type, located in such a manner that any undue risk to the operator is avoided (see warning in 8.4). 6.3 Crucible, of silica, nickel-chromium, platinum or similar unreactive material. The crucible should be 15 mm to 25 mm in diameter, flat based and about 20 mm deep. Silica crucibles should be about 1,5 mm thick and metal crucibles about 0,5 mm thick. If smears of unburned carbon occur, a small low-mass platinum or nickel-chromium crucible, for example
0,25 mm thick, 15 mm in diameter and 7 mm deep, may be used. SIST EN 14918:2010
EN 14918:2009 (E) 11 6.4 Ancillary pressure equipment 6.4.1 Pressure regulator, to control the filling of the bomb with oxygen. 6.4.2 Pressure gauge (e.g. 0 MPa to 5 MPa), to indicate the pressure in the bomb with a resolution of 0,05 MPa. 6.4.3 Relief valve or bursting disk, operating at 3,5 MPa, and installed in the filling line, to prevent overfilling the bomb. CAUTION – Equipment for high-pressure oxygen shall be kept free from oil and grease (high vacuum grease recommended by the manufacturer can be used according to the operating manual of the instrument). Do not test or calibrate the pressure gauge with hydrocarbon fluid. 6.5 Timer, indicating minutes and seconds. 6.6 Balances 6.6.1 Balance for weighing the sample, fuse, etc., with a resolution of at least 0,1 mg; 0,01 mg is preferable and is recommended when the sample mass is of the order of 0,5 g or less (see 8.2.1). 6.6.2 Balance for weighing the calorimeter water, with a resolution of 0,5 g (unless water can be dispensed into the calorimeter by volume with the required accuracy, see 8.3). 6.7 Thermostat (optional), for equilibrating the calorimeter water before each experiment t
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