Most of the fresh water outside the refinery for transfer measurement is a mechanical water meter. The leakage rate has always been an important indicator affecting economic benefits. The main factor for the high leakage rate is the high initial flow rate of the mechanical water meter. Users often make mechanical water meters work at critical or below the starting flow rate during actual water use, resulting in loss of water consumption and increased leakage rates. The power consumption of fresh water supply is another indicator that affects economic benefits. The large pressure loss of mechanical water meters will increase the power consumption of fresh water supply. Due to the increasing shortage of water resources and energy, water and electricity prices continue to increase. Improving the above two indicators can not only improve the economic benefits of the refinery, but also have far-reaching significance for energy saving and water saving in the refinery. It solves the problem of measurement loss and truly realizes fine management.
1 battery-powered ultrasonic water meter characteristics and measurement principles and installation requirements
1.1 Water meter characteristics
Battery-powered ultrasonic water meter medium flow rate range 0.01 ～ 32.00 m / s, accuracy ± (0.5% ～ 1%), no moving mechanical parts, no pressure loss and wear, with long-term measurement accuracy, stable and reliable The characteristics, users do not need to set parameters, can be installed at any angle. Standard single battery can work continuously for 6 years, and optional battery can work continuously for more than 10 years. The empty tube status automatically enters the power saving mode, and the full tube status automatically enters the normal measurement mode.
1.2 Water meter structure and measurement principle
The measurement principle of a battery-powered ultrasonic water meter is to use an ultrasonic transducer to generate ultrasonic waves and propagate them in the water. The sound waves travel in the water, the propagation speed increases in the forward direction, and the reverse direction decreases. When ultrasonic waves propagate in flowing water, a propagation speed difference is generated, which is proportional to the flow velocity of the water. The water meter consists of a transducer, an electronic circuit, and a flow display and accumulation system. The ultrasonic transmitting transducer converts electrical energy into ultrasonic energy and transmits it to the fluid under test. The ultrasonic signal received by the receiver passes through the electronic circuit. The signal is amplified and converted into an electric signal representing the flow rate for display and integration, thus realizing the flow rate measurement.
The measurement principle of a battery-powered ultrasonic water meter is shown in Figure 1.
Figure 1 Measuring principle of battery-powered ultrasonic water meter
，t 2 ——超声波传播时间；D——管道内径；v——管道中水的流速。 Note: t 1 , t 2 —— ultrasonic wave propagation time; D —— inner diameter of the pipeline; v —— velocity of water in the pipeline.
-t 1 )。 V∝f (t 2 -t 1 ) can be deduced from the mathematical model. >>vsinθ (其中vc为超声波在水中的传播流速), 所以时间差t 2 -t 1很短。 Since v c >> vsinθ (where vc is the velocity of ultrasonic wave propagation in water), the time difference t 2 -t 1 is very short. Therefore, the time detection resolution is less than 1ns. This index is an important factor in determining the starting flow rate of the ultrasonic water meter.
1.3 Water meter installation and application precautions
When installing an ultrasonic water meter, choose a part where the fluid flow field is evenly distributed, and ensure that there is a sufficient length of straight pipe sections to make the fluid form a stable velocity distribution. Generally, the length of the front straight pipe section is 10 times the pipe diameter and the length of the rear straight pipe section is 5 times the pipe diameter. In addition, it should be as far away from the pump and valve as possible. If the organic pump is used, the length of the front straight pipe section should generally be 50 times the diameter. , The measurement accuracy will decrease.
a) Pipeline parameters. When installing an ultrasonic water meter on an old pipeline, it is necessary to accurately obtain the parameters of the pipeline, such as the outer diameter and wall thickness of the pipeline, in order to obtain accurate measurement results.
b) Installation method. Because the bubbles and impurities in the pipeline will reflect and attenuate the ultrasonic signal, which will bring great errors to the measurement, you must choose the correct installation method when installing. When installing ultrasonic water meters on inclined and horizontal pipes, they should be installed horizontally so that bubbles can collect above the pipe and large impurities flow along the bottom of the pipe. Try to keep the ultrasonic water meter probe at an angle of 45 ° to the horizontal plane. Inside. In addition, the installation location of the ultrasonic water meter must have a certain back pressure to ensure that the pipeline is filled with fluid, and there are no air bubbles or fewer air bubbles to ensure measurement accuracy.
c) Signal strength and signal goodness check. The signal strength indicates the signal strength of the upstream and downstream probes, and the signal goodness indicates the peak value of the signal in the two transmission directions, which can help determine the superiority of the received signal.
d) Check of transmission time and time difference. The transmission time indicates the average transmission time of the ultrasonic wave, and the transmission time difference indicates the difference between the upstream and downstream transmission time of the ultrasonic wave. These two signals are the main basis for calculating the flow rate of the ultrasonic water meter, especially the difference in transmission time can best reflect whether the ultrasonic water meter is stable. If these two signals are unstable, check whether the sensor probe installation point is appropriate and the setting data is correct.
e) Application precautions. Improper installation is the main reason for the ultrasonic water meter not working properly. When installing, you need to consider the determination of the location. In addition to ensuring sufficient upstream and downstream straight pipe sections, pay particular attention to the transducer as far as possible to avoid places with contaminated power sources such as variable frequency governors and pumps.
Timely verification is the prerequisite to ensure accurate ultrasonic measurement: adhere to one installation and one school, that is, verify each newly installed ultrasonic water meter during commissioning to ensure that the position is selected, installed, and measured accurately; the ultrasonic water meter running online occurs When the flow is abrupt, a portable ultrasonic flowmeter is used for timely verification to find out the reason for the sudden change in the flow and determine whether the ultrasonic water meter is malfunctioning or the flow has changed.
Periodic maintenance is the basic work to ensure the long-term operation of ultrasound. Compared with other flow meters, the maintenance of ultrasonic water meters is relatively small. Regularly check whether the flange connection between the water meter and the pipeline is good, and consider the temperature and humidity of the site for its electronic components. Effects, etc., to ensure the long-term stable operation of ultrasonic water meters.
2 Comparison of battery-powered ultrasonic water meters and mechanical water meters
A comparison of important technical performance indicators of battery-powered ultrasonic water meters and mechanical water meters (taking DN200 as an example) is listed in Table 1.
3 Economic benefits (take DN200 water meter as an example)
3.1 Water saving effect
The starting flow rate of battery-powered ultrasonic water meters is 0.6m3 / h, and the starting flow rate of mechanical water meters is 2m3 / h. The difference is 1.4m3 / h. It is calculated with a small flow rate of 6h (less than 2m3 / h) every day. The measurement loss can be up to 3 066m3, with an average price of 3.8 yuan / m3. The fresh water supplied outside the refinery will lose 11 651 yuan each year.
3.2 Power saving effect
Mechanical water meters work at a common flow rate of 1 m / s (flow rate of 113 m3 / h), and the resulting pressure loss is about 0.07 MPa. The pressure loss of the ultrasonic water meter is almost 0; when the efficiency of the water supply pump is 80% and the annual water supply time is about 6,500 hours, calculated according to the conditions given in Table 2, the ultrasonic water meter can save 17 534 degrees of electricity per year. Calculated based on the electricity price of 0.8 yuan / kWh, it can save 14 027 yuan. The comparison of power saving effect between mechanical water meter and battery-type ultrasonic water meter is shown in Table 2 (taking DN200 water meter as an example).
Table 1 Comparison of main technical performance indicators of battery-powered ultrasonic water meters and mechanical water meters
Table 2 Comparison of power saving effect between mechanical water meter and battery-type ultrasonic water meter
It can be known from the above that after replacing the mechanical water meter with a battery-type ultrasonic water meter, the conservative economic estimate of the annual economic benefits of only two items of water saving and electricity saving should be 25,678 yuan.
4 Practical application of battery-powered ultrasonic water meters
Most of the meters currently used for fresh water outside refineries are mechanical water meters. Due to the high initial flow rate of mechanical water meters, users often make the mechanical water meters work at critical or below the initial flow rate during actual water use, resulting in loss of water consumption, leading to increased leakage rates and affecting the refinery Economic benefits. However, the large pressure loss of mechanical water meters will increase the power consumption of fresh water supply. In order to save energy and save water and improve the economic benefits of external water supply to the refinery, the plant installed a DN200 caliber battery-powered ultrasonic water meter in Longfeng Town, Heilongjiang Province. In normal water use, mechanical water meters and battery-powered ultrasonic water meters are not much different. At 22: 00 ～ 0: 00, the water flow is mostly around 2m3 / h. Mechanical water meters are intermittently measured, while battery-powered ultrasonic water meters are normally measured. The water flow rate from 0:00 to 6:30 is basically below 2m3 / h, which is lower than the starting flow rate of the mechanical water meter. The mechanical water meter has no measurement display. Since the battery-powered ultrasonic water meter is normally measured above 0.6m3 / h, the battery-powered ultrasonic water meter is still being measured normally. After 6 months of comparison and observation, the battery-powered ultrasonic water meter can restore the fresh water supply loss of nearly 6,000 yuan for the refinery. According to this figure, it can save nearly 70,000 yuan for the oil refinery every year. The application of battery-powered ultrasonic water meters not only solves the problem of loss of original mechanical water meters, improves the economic benefits of fresh water supply from refineries, but also solves the problem of power supply for fresh water supply meters in remote areas of refineries. Meter installation saves a lot of materials (meter power, cables, etc.) and maintenance costs.
In today's increasingly scarce water resources and energy, the application of battery-powered ultrasonic water meters in the measurement of fresh water transfer in Longfeng Town completely solves the problem of high starting flow, high leakage rate, large pressure loss, low accuracy, and low use of mechanical water meters. Many problems, such as short life, have improved the accuracy of fresh water supply measurement in refineries, solved the power supply problem of fresh water supply measurement instruments in remote areas of refineries, and greatly improved the economy of refineries in energy saving, water saving and energy measurement. Benefits and social benefits.
Article excerpt: Yu Qinghe, Yang Yipeng, Yu Guojun, Lin Tao. Application of battery-powered ultrasonic water meters in water metering. Petrochemical Automation, 2010, 2: 66-68