Measuring and testing – Gas analysis
Reexamination Certificate
2000-06-02
2002-09-10
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Reexamination Certificate
active
06446487
ABSTRACT:
The invention relates to a method for measuring and/or regulating the quantity of heat which is present in a fuel gas and is supplied to a gas-consuming device, in particular a natural-gas-consuming device, the calorific value of the fuel gas being used as an input variable.
In known measurement methods of this nature, the amount of gas supplied and the heat properties of the fuel gas are often determined. The conditions, in particular the temperature and pressure, under which these values are determined generally differ for each measurement variable.
For example, the amount of gas supplied is often measured under operating conditions, while the heat properties are often determined under standardised conditions, such as for example the normal conditions 0° C. and 1.01325 bar(a). To determine the quantity of heat, it is important for uniform temperature and pressure conditions to be observed both for the amount of gas supplied and the thermal properties. In practice, the amount of gas supplied is to this end generally converted to standardised conditions, for example the normal conditions 0° C. and 1.01325 bar(a). This conversion is known as ‘volume conversion’.
The quantity of heat supplied to the gas-consuming devices can be determined by means of direct and indirect methods. In indirect methods, the composition of a natural gas is determined by means of gas chromatography, for example. Then, on the basis of this gas composition, the parameters for the volume conversion are calculated and the calorific value of the fuel gas is determined using the calorific values of the pure substances. Although these methods provide very accurate results, they have the drawback of being technically complex and therefore expensive. As a result, it is impossible to use these methods in private households, for example. In contrast to indirect methods, in direct methods the calorific value is determined directly. Commercially available calorific-value meters indicate the calorific value, generally under standardised conditions, such as for example normal conditions (0° C. and 1.01325 bar(a)). Usually, the volume conversion which is required to determine the flow of energy is derived from density measurements under standardised conditions, such as for example normal conditions (0° C. and 1.01325 bar(a)), and the conditions of the volumetric flow measurement. However, volume conversion based on density measurements are technically complex. Moreover, density cells of this nature have to be calibrated at regular intervals.
The object of the invention is to reduce the effort involved in the direct measurement and/or regulation of the quantity of heat supplied to consumption devices and, in particular, to provide a reliable and accurate measurement method.
According to the invention, this object is achieved by the fact that, in the method referred to in the introduction, the fuel gas or a part-stream of the fuel gas is guided through a volumetric meter or a mass flow meter, and the volumetric flow rate or the mass flow rate is measured, the speed of sound of the gas is determined under first reference conditions, one of the measurement variables dielectric constant, speed of sound under second reference conditions, carbon dioxide content of the fuel gas, nitrogen content of the fuel gas or density under standardised conditions, for example normal conditions (0° C. and 1.01325 bar(a))is measured; and the quantity of heat supplied is derived from these parameters, together with the calorific value of the fuel gas, as a measurement variable or control variable.
The advantage of this method lies in the fact that there is no need to carry out any density measurements under any conditions apart from standardised conditions. In most embodiments, there is no need to carry out any density measurement at all.
Particularly accurate results can be achieved for fuel gases whose calorific value at normal conditions is from 20 to 48 Mj/m3, whose relative density compared with dry air is from 0.55 to 0.9, whose proportion of carbon dioxide is less than or equal to 0.3 and whose proportion of hydrogen and carbon monoxide is less than 0.1 and 0.03 respectively. Particularly suitable measurement conditions are temperatures in the range from 225 to 350 K and pressures of less than or equal to 6 MPa.
Operating conditions are the actual conditions in the installation, for example a gas conduit, containing the gas of which the quantity of heat is measured or controlled. Reference conditions can be chosen freely within the specified ranges, preferably corresponding to conditions at which the relevant parameters are known from one or more reference gases. By standardised conditions are denoted conditions that are more generally used in the relevant technical field like normal conditions (0° C. and 1,01325 bar(a)) and standard conditions (15° C. and 1,01325 bar(a)).
The first reference conditions set are preferably normal conditions or a pressure in the range from 1 to 10 bar, more preferably from 3 to 7 bar. Although the temperature is not very critical and can be selected within a wide range, for technical reasons the temperature is above 225 K, for example from 270 K to 295 K. For the second reference conditions, a pressure of above 30 bar is preferably set. Although the temperature is not very critical and can be selected within a wide range, for technical reasons the temperature is from 225 K to 350 K.
The operating conditions are most preferable for this parameter.
The speed of sound at the reference conditions mentioned, including operating conditions, can be determined in a separate measuring unit, for example via the resonant frequency of vortex pipes or of hollow bodies or a distance travelled-time measurement, e.g. in ultrasonic flow meters.
In practice, there are various proven measurement methods available for measuring the volumetric flow rate, for example turbine flow meters or ultrasonic flow meters.
The dielectric constant can be measured inexpensively and with high accuracy even under operating conditions. The proportion of carbon dioxide is simple to determine under all conditions mentioned using known measuring instruments, e.g. by measurement of the light absorption in the infrared region.
The use of the density under normal conditions is advantageous in particular when, in the arrangement, a volume conversion is at the same time being carried out on the basis of density measurements. The use of a speed of sound measurement instead of the density measurement under operating conditions offers the advantage that the most critical component is exchanged, while there is no need to spend money on measuring other variables.
Consequently, the three measurements which are required can each be carried out reliably, accurately and without a high level of technical effort, so that linking the measured values provides suitable results for measuring and/or regulating the quantity of heat supplied to gas-consuming devices.
To establish the reference conditions, the parameters temperature and pressure are required. These can be additionally measured in step b). If a lower measurement accuracy is permissible, the values estimated from practice can also be used for these parameters.
If the calorific value does not change, or changes only slightly, such as for example in the case of a gas emanating from the same source, it is sufficient to introduce a fixed value for the calorific value into the calculation of the quantity of heat. In the event of substantial fluctuations in the calorific value of a gas flow, as may occur, for example, in collection networks, it is recommended that the calorific value be determined at regular intervals or continuously. To this end, the calorific value can be recorded inexpensively and with a high level of accuracy using various proven measurement methods, such as for example controlled catalytic oxidation of the gas to be tested.
In total, there are five variations on the method according to the invention for measuring the quantity of heat supplied of fuel gas.
In all the variants, the sp
Jaeschke Manfred
Schouten Johannes A.
Van Wesenbeeck Petrus J. M. M.
N.V. Nederlandse Gasunie
Pillsbury & Winthrop LLP
Politzer Jay L.
Williams Hezron
LandOfFree
Method for measuring the quantity of heat present in fuel gas does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for measuring the quantity of heat present in fuel gas, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for measuring the quantity of heat present in fuel gas will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2863381