In the new era of increasingly tight oil resources, ensuring the rational and effective use of oil has become the focus of attention in the industry. In the industry, in order to better ensure the accuracy of refueling quantity and correct use, it is necessary to analyze various factors that may lead to tanker errors. Among them, the error caused by flow is the most prominent, and China is mainly manifested in overshoot and so on. Here, we analyze the causes of the error caused by the flow to the tanker, and focus on the related effects.
First, the influence of liquid flow rate on the basic error of flowmeter
Flowmeter is the core of tanker and gas station, and it is also the basis of refueling measurement and marketing. However, in the past, the volumetric tank car metering technology was widely used, which limited the development of the whole flow metering work. Therefore, we must attach great importance to the measurement of the flow itself, and express its measurement content according to the past national measurement standards to ensure that the flow is within the allowable error range. It is clearly pointed out in the current verification regulations of tankers in China that the maximum error of flowmeter should not exceed 0.02% and the repeatability of measurement results should be guaranteed within 0.07%. Therefore, when measuring the flow error of the tanker, we can use the function E=f(q) to express it.
1 leakage
Leakage problem is one of the most common faults of metering device of tanker. The appearance of China is closely related to the composition of the volumetric flowmeter itself, which is caused by the unreasonable mechanical combination of the volumetric flowmeter in the metering space. Because the mechanical combination inside this device is in a state of high-speed operation for a long time, there must be motion gaps between various components. If the oil is measured at this time, the existence of these movement gaps will inevitably lead to leakage and affect the measurement work. At the same time, because the volume of metering space itself has a certain relationship with gear running-in, it will also be affected by the leakage between error and flow, which requires us to verify the volume and flow on the basis of understanding the change of leakage flow, so as to fundamentally ensure the accuracy and rationality of metering results. The analysis of this characteristic of flowmeter shows that the error of flowmeter is usually only closely related to the solvent in the container and the transmission gear, that is, the volumetric flowmeter has only a geometric relationship with the flowmeter in the measurement process, but has little to do with the fluid properties and flow value. This feature makes the error analysis in the research of volumetric flowmeter clear at a glance.
2 leakage flow error measurement
In the actual operation of tank car, due to the ubiquitous leakage flow problem, the calculation formula is fixed in the calculation composition, but the specific relationship between flow and flow error needs to be considered in the calculation. At this time we can use the formula:
q=( 1/ 12)*(a^3b/l)*(△p/μ)( 1)
In this formula, a refers to the distance between measuring elements, and b refers to the total length along the flow direction; L is the thickness of the measuring element itself; P is the front and rear pressure of the measuring element. Through formula analysis, we find that the measurement of leakage flow is directly proportional to the pressure value before and after the measuring element, but inversely proportional to the viscosity of the fluid itself. At the same time, in the work, in addition to these factors, the leakage flow is also closely related to the internal wear of machinery.
3 Basic error measurement work
In the basic error measurement of volumetric flowmeter, after considering the leakage phenomenon, the strategy of multiple volumetric flow measurement is adopted, and the error measurement curve is formed by the actual error and curve shape. In actual measurement, if the flow rate is less than the error measurement, the error value of the flowmeter will not change much, but it is a rising phenomenon with the increase of flow rate, so the error of the flowmeter will shift with the change of positive and negative directions, and the stability will also change. In the process of this change, we can identify it, as shown in the second line of the figure. In China, in order to better ensure the accuracy of the verification results, it is necessary to scientifically select the relevant design standards in the design of each flow point. For those problems that the filter screen is blocked and the leakage flow increases after a period of use, it is necessary to deal with them in time and clearly indicate the error according to the actual work. Under normal circumstances, in addition to human error, the positive and negative deviation direction of error will also drive the change of measurement error, so we should pay attention to the choice of error measurement strategy in the measurement work, otherwise the problems will inevitably increase quickly.
Secondly, the influence of flow range on the error value of tanker.
Errors caused by leakage flow are always negative errors. When the flow is greater than the leakage flow, the negative value is smaller, that is, the oil payment is relatively small. When the flow rate is less than the leakage rate, the negative value is larger, that is, the oil is relatively overpaid; When the flow is close to the leakage flow, the value of e is close to-1, that is,-100%. At this time, almost all the oil paid by the tanker is leaked oil. China, it can be seen that the inspection of tank car leakage flow is a link that cannot be ignored in the measurement of tank car metering performance. Leakage flow is one of the characteristics of all positive displacement flowmeters. According to the parallel plate theory, flow and leakage flow are interactive.
Third, the determination method of tanker verification error
In the process of tanker error verification, we should ensure the stability of tanker flow as much as possible to fundamentally prevent oil leakage accidents. At the same time, the method of one-time injection should be used to ensure the scientific and reasonable measurement time and method. When refueling with 100L measuring instrument, the oil quantity should be controlled above 95L, but because the oil quantity itself will produce bubbles and oil foam, it is often necessary to increase a certain reserved space above the container to avoid affecting the measurement results due to inaccurate injection. In order to truly reflect the maximum flow achieved at the site, we must scientifically adopt the method of determining the calibration error of the tanker in our work to fundamentally ensure the accuracy and scientificity of the measurement results.
Four. conclusion
In a word, the accuracy of liquid flow is very important in the field verification of tanker, which directly affects the verification results. The indication error of tanker and liquid flow is a nonlinear function. At the same time, the verification method of maximum flow should be further clarified. At the same time, it is suggested that the flow range, indication error and repeatability of each measuring point should be given in the verification results of the verification certificate.
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