TEMPERATURE FIELD INSIDE THE DIAPHRAGM GAS METER

Transcription

1 TEMPERATURE FIELD INSIDE THE DIAPHRAGM GAS METER Tomáš Hlinčík, Václav Koza Deartment of Gas, Coke and Air Protection, University of Chemistry and Technology Prague, Technická 5, Praha 6, A large roortion of natural gas consumtion is metered by diahragm gas meters with no temerature comensation. For billing uroses, an estimate of the gas temerature inside the meter is used. The estimate is currently based on ambient temerature (atmosheric temerature). Whenever a converter has been installed, the gas temerature used for the comensation of the gas volume is measured at the outlet of the meter, i.e. at the sot where the temerature sensor of the converter resides. In this article, we focus on determining the oerating temerature of the gas, i.e. the mean temerature inside the diahragm chambers of the meter where the volume of the assing gas is actually measured. The results also describe the temerature field inside the diahragm gas meter at different volumetric gas flow rates. The measured data were used to describe the relationshi between the oerating temerature and the temerature at the outlet of the meter. The results of this article may hel clarify the relationshi between the ambient temerature and the oerating temerature of the gas inside the diahragm gas meter, and so refine the formula for the conversion of the gas volume measured into the volume billed to the customer. Keywords: Temerature; Diahragm Gas Meter; Natural Gas Received , acceted Introduction Consumtion of natural gas in almost all residential and other low-demand installations is measured by diahragm gas meters. In some countries diahragm gas meters are gradually being relaced by ultrasonic gas meters that enable remote shutdown, remote reading of gas consumtion, etc. [1, 2]. Nevertheless, the diahragm gas meter still retains great advantages, including its durability, long-term stability, low ressure dro, heat fire resistance (u to 650 C), low cost, etc. [3, 4]. Measurement of gas consumtion is carried out by measuring the volume of the gas that had assed through the meter at the oerating ressure and the oerating temerature inside the measuring chambers with diahragms. When invoicing, the actual measured volume must be recalculated into the volume at reference conditions (15 C, Pa) [5]. The amount of energy delivered during the given billing eriod is calculated as: Q V. k. H, (1) 0 where Q is the amount of energy sulied, V is the oerating volume of the gas [m 3 ], H 0 is the average calorific value of the gas delivered during the billing eriod at reference conditions of 15 C and Pa [kwh/m 3 ], k is the volumetric conversion factor [-] comrising the conversion of the oerating volume V (measured at the oerating temerature and oerating ressure) to the billable volume V u valid for the same amount of gas at the reference conditions. The volumetric conversion factor is therefore the ratio between the volume of the gas at reference conditions V v and the oerating volume V. For zero gas humidity: V T z k.. V T z v v b v. (2) v Where V v is the volume of gas at reference conditions ( Pa, 15 C) [m 3 ], V is the oerating volume of the gas [m 3 ], T v is the reference temerature ( K) [K], T is the oerating temerature of the gas [K], is the oerating ressure [Pa], b is the atmosheric ressure at the gas samling oint [Pa], v is the reference ressure ( Pa) [Pa], z v is the comressibility factor at reference conditions [-], z is the comressibility factor at oerating conditions [-] [6]. When billing the consumed volume of natural gas, it is exected that the meter indicates the oeration volume of gas V measured at the oerating temerature t and the absolute ressure abs = + b. (3) Both the oerating temerature t, and the absolute ressure abs exress average values in the gas meter, which change over the billing eriod. A secified single value of the oerating temerature for the entire billing eriod for a gas meter without any temerature comensation therefore always reresents only an estimate [7]. To find the difference between the measured and the actual amount of gas consumed, which results from metering the amount of natural gas with the hel of a diahragm gas meter with no temerature comensation, it is necessary to know the effect of ambient air temerature on the temerature inside the gas meter. In other words, it is necessary to determine the temerature distribution inside the gas meter. The ultimate goal is to a) Determine the oerating temerature t, i.e., the mean temerature in the diahragm chambers of the meter at which the meter actually measures the volume of the assing gas. 39

2 b) Comare the determined oerating temerature t, with the temerature at the exit of the meter. The comarison is done in consideration of meters containing a conversion device where the temerature sensor of the converter is always laced at the exit of the meter. 2. Exerimental The laboratory aaratus consisted of two diahragm gas meters without temerature comensation connected in series. One meter was tye Actaris Gallus 2000 size G4 (maximum volumetric flow rate of 6 m 3 /h) and the second meter was tye MKM size G2.5 manufactured by Premagas (maximum volumetric flow rate of 4 m 3 /h). The meters were connected in a closed circuit with a fan, a heat exchanger and a silica gel column. Both gas meters and other arts of the aaratus were connected via coer ies and socket joints with rubber seals. The total length of the iing was 501 cm. A section of the iing was exosed to temeratures in the laboratory and a section resided in an air conditioning box. The first meter was laced inside the air conditioning box in which the temeratures were alternately set at 0 C, -5 C and - 10 C. This meter (tye MKM size G2,5) simulated a gas meter located outside a home and exosed to atmosheric temeratures. The second meter was laced in the laboratory. Gas circulation through the iing and the gas meters was carried out with the hel of a fan (Tye 401 Standard). The gas flow rate was adjusted using triac seed control of the fan. An adsorber containing silica gel resided behind the fan in order to remove any moisture before it could condense inside the gas meter in the conditioning box. The dry gas rogressed from the adsorber to the meter inside the air conditioning box and then to the meter in the laboratory. Behind the gas meter in the laboratory, in the direction of gas flow, there was a manometer and a ball valve whose artial closure maintained a slight ositive ressure in the aaratus (with the excetion of immediate intake of the fan). To comensate for the heating of the gas occurring during its assing through the fan, a cooler was laced between the fan and the adsorber. Platinum resistance temerature detectors Pt100 were used to measure the temerature of the gas. The detectors were laced at the inuts and oututs of the two gas meters, the inut and outut of the air conditioning box and the cooler. Identical detectors were also laced nearby the two gas meters to measure the ambient temerature in the laboratory and the temerature within the air conditioning box. The gas flow rates through both diahragm gas meters were measured using imulse sensors. The measured data were recorded and collected in a datalogger MS3 made by Comet Systems. The recorded data were then transferred to a comuter and evaluated. The measuring aaratus with the air conditioning box is shown in figure 1. The gas meter in the laboratory was laced under a metal cover from which only the counter of the meter was visible. The urose of the cover was to shield the gas meter from raid fluctuations in temerature and air movement caused by traffic in the laboratory (oening doors, windows, movement of ersons etc.). With regard to safety, exeriments were erformed using air instead of natural gas. Fig. 1 Layout of the aaratus Descrition: (1) cooler; (2) adsortion column with silicagel ; (3) diahragm gas meter laced in the air conditioning box; (5) datalogger; (6) comuter; (7) diahragm gas meter; (8) manometer; (9) ball valve. 40

3 The following figures 2 and 3 show a dismantled gas meter with temerature sensors. changes of the temerature along the flow of the gas through the gas meter. The gas enters through the inlet line to the to art of the meter 1. Here the gas is slightly delayed. Then it roceeds through the front oening 2 or the rear oening 3 (movable stoer) into the sace with diahragms. From there the gas flows into the bottom art of the meter in both directions 4 and 7. There a ortion of the gas moves towards the bottom art 5 on the left. At the same time the gas is exhausted through the narrow oening towards the outlet 8. From there, the gas is directed to the outlet of the meter t e. Fig. 2 The uer art of the meter G2.5 MKM with mounted temerature sensors Fig. 3 The lower art of the meter G2.5 MKM with mounted temerature sensors The temerature in the conditioning chamber was consecutively adjusted at 0 C, -5 C and -10 C. At each temerature, three volumetric gas flow rates were used so as to cover the entire working range of the volumetric flow rate in G2.5 MKM diahragm gas meter ( m 3 /h). Before each measurement, the aaratus was temered, i.e., at the set temerature in the air conditioning box, the volumetric flow rate of the gas was maintained at zero. After temering, which lasted aroximately three hours, the desired flow rate of the gas was set u with the hel a triac controller of the fan s seed. During the measurements, the temerature changes were monitored and after the temerature had stabilized, the measurement was stoed. Temeratures measured by the temerature sensors and the volumetric flow rates measured with the hel of transmitter imulses were recorded in the data logger MS3 and then exorted to the comuter where the results were evaluated. Figure 4 shows the temerature sensors located inside the diahragm gas meter. Temerature sensors were laced so that they had best chance of detecting the Fig. 4 Location of the temerature sensors inside the diahragm gas meter Position of temerature sensors: t i inlet of the gas meter; 1 behind the entrance into the meter; 2 inlet to the front diahragm; 3 inlet to the rear diahragm; 4 lower art on the left, outside the diahragm; 5 down in the lower art on the left, outside the diahragm; 6 down in the lower art on the right, outside the diahragm; 7 bottom art on the right; 8 exhaust of the gas in the gas meter; t e outlet from the gas meter. 3. Results and discussion Figures 5, 6 and 7 dislay the results of measurements for three different values of the temerature around the gas meter inside the air conditioning box. Labeling of the measurements corresonds with the indications of temerature sensors in figure 4. The grahs dislay the measured temeratures lotted against the locations of the temerature sensors in the diahragm gas meter. It shows that the lowest temerature is indicated by the sensor 6. 41

4 Fig. 5 Temeratures measured within the diahragm gas meter. Temerature in the air conditioning box 0 C Fig. 6 Temeratures measured inside the diahragm gas meter. Temerature in the air conditioning box -5 C This sensor is located down on the right, in the bottom art of the meter. Behind this oint, in the direction of the gas flow, the assing gas undergoes slight heating. This can be exlained by the heating of the assing gas by the gas from the to of the meter, which has a higher temerature. These two arts of the meter are searated by a thin wall, and thus there may be heat transfer from warmer to the cooler gas. Prior to entering the meter, during its assage through the inlet iing that is exosed to the ambient temerature t a, the gas is cooled to the temerature t i. From the inlet the gas roceeds to sensor 1 in the uer sace of the gas meter and then it is divided into the two diahragm chambers. Temerature sensor 2 detects the temerature of the gas in the front chamber and sensor 3 detects the temerature in the rear chamber. 42

5 Fig. 7 Temeratures measured within the diahragm gas meter. Temerature in the air conditioning box -10 C These sensors should be equivalent and should show the same temerature. Systematically higher temerature t 2 detected by sensor 2 can be attributed to the fact that a ortion of the sace in the front art of the gas meter is occuied by the counter. The gas assing over sensor 2 therefore has a higher velocity then the gas assing over sensor 3. The temerature at the inlet of the diahragm chambers was consequently exressed as the average of t 2 a t 3. The temerature at the outlet of the membrane chambers is best exressed by t 4 because the sensor 4 is directly and only exosed to the gas exiting from the diahragm chambers. In a similar osition towards the oututs of the diahragm chambers as sensor 4 is sensor 7. However, due to the roximity of the outlet from the gas meter, sensor 7 is exosed to a mixture of the gas leaving the chambers and the gas that has assed through the entire volume of the bottom art of the gas meter and was there cooled by the meter s wall. This situation is reflected by the temerature t 5 that is lower than t 4, and subsequent temerature t 6 that is again lower than the temerature of the oosite gas stream t 5. The desired oerating temerature, i.e. the temerature inside the diahragm chambers t, could not be found by sensors directly laced inside the diahragm chambers as the sensors would interfere with diahragm movement. Therefore t, was exressed as the average of the temeratures measured immediately ustream and downstream of the chambers, i.e. t 2 t 3 2t t 4. (4) 4 In the above formula, temerature t 4 is weighted by a factor of 2 because t 4 alone reresents the temerature behind the chambers, while for the temerature in front of the chambers we have data from sensor 2 and sensor 3. Next, we will examine the deendence of the oerating temerature t on the ambient temerature in the vicinity of the gas meter t a, the temerature at the inlet to the gas meter t i, and the flow rate of the gas through the meter. The measured values of the gas temerature at the outlet of the meter t e and the calculated oerating temerature t are listed in table 1. Tab. 1 The measured values of the gas temerature at the outlet of the gas meter and the calculated oerating temeratures t a box [ C] Temerature Low flowrate Medium flowrate High flowrate t e [ C] t [ C] t e [ C] t [ C] t e [ C] t [ C] The correlation between the outut and the oerating temerature of the gas is shown in the grah (Fig. 8). 4. Conclusion When calibrating a gas meter without temerature comensation it is assumed that the oerating temerature t is identical to the temerature of the gas exiting the meter t e. This assumtion is valid for calibrations erformed at a constant gas temerature that is equal to the temerature of the surroundings of the meter. 43

6 Gas oerating temerature t [ C] PALIVA 8 (2016), 1, S t = 1,02t e + 1,18 R² = 0, Gas exit temerature t e [ C] Fig. 8 The relationshi between the outut temerature and the oerating temerature of the gas Such a calibration rocedure is described for examle by international and domestic standards [8]. Under the oerating conditions, the temeratures of the measured gas t i, t e, and the temerature of the gas meter s surroundings t a differ. Although the oerating temerature t must lie in the interval <t i; t e>, the calibration formula t = t e stated by the standards does not have to be valid. Measurements described in this article rovided values of t needed for the correct billing of the amount of consumed gas shown by a gas meter with no built-in temerature comensation. The measurements show that for a diahragm gas meter G 2.5, over its working range of flow rates and outside temeratures from 0 to -10 C, there is a close relationshi between the oerating temerature t and the temerature of the gas at the outlet of the meter t e. It is still necessary to aly the same methodology to study the effects of the size of the gas meter and the effects of resective volumetric flow rates on the oerating temerature in the examined meters. Literature 1. Jena, A.; Mágori, V.; Russwurm, W. Ultrasound gas-flow meter for household alication. Sensor and Actuators A 1993, 37-38, Buonnano, G. On field characterization of static domestic gas flowmeter. Measurement 2000, 27, Ficco, G. Metrological erformance of diahragm gas meters in distribution networks. Flow Measurement and Instrumentation 2014, (37), Treloar, R. D. Gas installation technology, 2nd ed.; Wiley-Blackwell: Oxford, Nath, B. Temeraturverhalten von Balgengaszählern. Gas-Erdgas 1995, 136, International Recommendation OIML R 137-1&2. Gas Meter. Paris: Organisation Internationale de Métrologie Légale, Jandačka, J.; Malcho, M. Simulácia stavových zmien zemného lynu v membránovom lynomere. Acta Metalurgica Slovaca 2005, (11), Cascetta, F.; Comayyi, M.; Musto, M.; Rotondo, G. An exerimental intercomarison of gas meter calibrations. Measurement 2012, (37),