Orifice flow meter measuring natural gas error and solution

Abstract: The orifice plate flow meter measures natural gas error and solution information is provided by excellent flow meter and flow meter manufacturers and quotation manufacturers. 1. Orifice flowmeter Causes of errors in measuring natural gas The length of the upstream and downstream straight pipe sections is not enough, and the airflow is not fully developed, which will cause a large error in the measurement results. The length of the shortest straight pipe section stipulated by the measurement standard is generally difficult to meet in the field practice. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the orifice flowmeter measurement of natural gas errors and solutions. 1. The reason for the error in measuring natural gas by the orifice plate flowmeter is that the length of the upstream and downstream straight pipe sections is not enough, and the airflow is not fully developed, which will cause a large error in the measurement results. The length of the shortest straight pipe section stipulated by the measurement standard is generally difficult to meet in the field, especially because of the gas transmission process and other reasons, there are often elbows upstream of the measurement device. If it is a single elbow or a flat double elbow, the measurement result will be higher; for multiple elbows, the measurement result will be lower. 2. The solution should be to install a rectifier before the throttling device to avoid the influence of rotating current and eddy current on the measurement. Temperament and gas flow conditions of natural gas 1. Reasons for errors Remain subsonic, stable or only change slowly over time. The airflow is a homogeneous single-phase Newtonian fluid. If the gas contains no more than 2% by mass of solid or liquid particles and is uniformly dispersed, it can also be considered as a uniform single-phase Newtonian fluid. Before the airflow passes through the orifice, its beam should be parallel to the axis of the pipeline, the airflow should be fully turbulent and without vortex, and the vortex angle at all points of the pipeline cross-section should be less than 2°That is, there is no vortex. Through the measurement survey, it is found that the gas flow conditions of about 50% of the measurement points in the natural gas measurement in the oil field have the following two characteristics. (1) The gas flow is unstable, and changes greatly periodically with time, which is a pulsating fluid. The reasons for the pulsation source[2]: ①Reciprocating compressor, engine and vane turbocharger; ②The pressure regulating valve is switched violently or the valve core is loose and worn; ③A large amount of water or oil condensate moves irregularly in the pipeline . (2) The air has a large water content and entrains crude oil and trace particles of impurities, and condensate is generated when the air flows through the throttling device. If the air quality and air flow conditions do not meet the requirements specified in GB/T21446-2008 'Measurement of Natural Gas Flow Rate with Standard Orifice Flowmeter', additional errors in measurement will inevitably occur. In order to obtain accurate metering values, the pulsation of the air flow must be suppressed and the moisture and impurities in the air must be eliminated. 2. Solutions The gas entering the flowmeter must first pass through the gas-liquid separator and filter. (1) Install the measuring tube in a position that is more favorable for eliminating pulsation, such as at the inlet of the pressure regulating valve or away from the pulsation source. (2) In order to reduce the pulsation amplitude, a container can be added to the pipeline between the pulsation source and the measuring tube, or a special pulsation attenuator can be designed. Installing a throttle valve or restrictor between the pulsation source and the measuring tube is the most effective way to reduce pulsation, but this method is too much pressure drop and should not be used unless conditions permit. (3) On the premise that the differential pressure remains high, a smaller measuring tube can be used, and the opening diameter of the orifice plate is basically unchanged. (4) Install a gas-liquid separator with a certain volume at the outlet of the pressure pipe before and after the flowmeter, so that the differential and static pressure signals entering the flowmeter reach the gas-liquid separation and buffering before entering the metering device. (5) The upstream and downstream pressure-guiding valves on the pressure-guiding pipeline should use large-diameter ball valves. (6) In order to prevent the pressure-guiding pipe from freezing and blocking, the pressure-guiding pipe must be insulated, and heating compensation and heat preservation measures must be added. (7) In the case of the airflow pulsation at the metering point caused by the downstream fluctuation source, the valve position of the valve on the downstream side of the flowmeter can be adjusted (close down) to reduce the airflow pulsation amplitude at the metering point. Experiments have proved that the effect of controlling the pulsation of air flow by closing the downstream valve of the metering tube is very obvious. When this method is used in practice, it must be carried out under the condition of ensuring safe production. Experiments have proved that the above method can effectively suppress the pulsation of the air flow, eliminate the moisture and impurities in the gas, and reduce the additional measurement error of the flowmeter.

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