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Description of the problem that the flow measurement range is selected unreasonably

When a meter company established a steam metering network in China's tallest building, there were 4 boilers in total, and 3 of them were opened in winter. The total evaporation was about 28t/h, but in summer, the consumption of the entire steam network was only 2t/h. . Such a wide range of variations places very high demands on flow meters. For example, there is a sub-meter, the pipeline is DN300, the data provided by the architectural design institute is 20t7h steam, so the DN200 vortex flowmeter is selected accordingly, and the minimum measurable flow rate is 2.lt/h, (the fluid is p=0. 87MPa saturated steam). After the instrument is put into operation, the maximum flow in winter is only 4t/h, which is less than 1/4 of the value of the design institute. After the arrival of summer, the flow of the road is smaller, sometimes even lower than the cut-off point of 600kg/h, causing the sum of the expressed values to be about 30% smaller than the total value. Later, the owner unit adjusted the design conditions according to the actual operating data. The DN80 vortex flowmeter is used to measure the flow of the road, so that the measurement accuracy is guaranteed, so that the flow balance data balance difference under the low load operation condition is ≤4%R, which satisfies the requirements of the client.
3 Judging the measurement data according to the mass balance relationship. Mass balance is the basic law of nature. It is no exception in the production process. From a production system to a production facility, the total amount of material produced is always equal to the total amount of input materials. For example, a single feed rectification column, the top and bottom discharges are equal to the feed amount, and the boiler steam flow rate is balanced with the boiler feed water flow rate. However, in the calculation of boiler steam-water balance, the soda sampling loss, leakage loss, steam-water loss and the loss of sewage from the steam drum should be considered. Changes in the amount of steam traps introduced by changes in drum pressure and water level should also be considered. In order to eliminate the influence of these factors on the balance calculation, it is common practice to stop the blowdown during the test. When the flow cumulative value is read, the drum pressure and water level should be within the specified range.
In the balance calculation of the flow rate measurement data according to the material balance relationship, if the data balance difference is zero, it is not certain that the error of each flow meter related to the balance calculation is zero, but there is no reason to say that the flow meter is not accurate because the measurement The data conforms to the law of material balance.
When verifying the electromagnetic flowmeters that are related to each other by the material balance method, attention should be paid to the change of the fluid working conditions, sometimes due to the difference of the fluid working conditions, causing the measurement error of the instrument, or the fluid working conditions have changed greatly. The operator still estimates the flow value according to the concept of quantity before the change. Here are two examples of this.

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