As one of the basic industries of China's paper industry, with the improvement of people's living standards and the increasing demand of the society, it is a challenge to the production technology and product quality. Paper industry is a water consumed huge industry, to the needs of the production of a variety of raw materials need through water solution to operation and participation. In recent years, along with the increasing of science and technology, the domestic paper enterprises, especially the special paper enterprises have gradually begun to replace the traditional differential pressure flow meter with electromagnetic flowmeter. At the same time, the requirements of the manufacturers are higher, which also promote the technological progress of electromagnetic flowmeter.
Working principle and superior performance of electromagnetic flowmeter
Sensors, transducers and displays are the basic components of the electromagnetic flowmeter, which is based on the principle of Faraday electromagnetic induction law is made of a measurement of the flow of the instrument. The electromagnetic flowmeter has the unique advantage of other flowmeter can not be compared, especially used for the measurement of dirt and corrosion fluid fluid. Electromagnetic flowmeter in the 70's to the 80's due to a major breakthrough in technology, making it a wide range of applications in the field of modern industrial monitoring instrument.
Main advantages: (1) because of the measurement channel is a smooth straight pipe, not blocked, especially for solid particles of liquid solid two-phase fluid, such as pulp, sewage, mud, etc., without pressure loss, energy saving effect is good. (2) stable and reliable performance, high measurement accuracy, long service life. (3) the influence of humidity, density, viscosity and pressure of the fluid is not affected by the fluid. (4) the traffic is large and wide in diameter. (5) measurement of a corrosive fluid.
Major shortcomings. (1) does not apply to the measurement of fluid in petroleum products. (2) not suitable for gas, steam and liquid containing large bubbles. (3) is not suitable for high temperature applications. (4) a certain requirement for the installation of the site.
Two. Application of electromagnetic flow meter in paper industry
Papermaking is a continuous production process, so the production line of continuous and orderly control has become a bottleneck restricting the quality and output of finished paper. How to effectively stabilize the quality of paper products, electromagnetic flow meter in this area plays an important role.
(1) application of electromagnetic flow meter for slurry system.
For the pulp system including the following steps: 1) the process of crushing. 2) pulping process. 3) with the slurry process.
In repulping process, using electromagnetic flowmeter precise metering of the broken solution of slurry flow to ensure pulp slurry stability, ensure that subsequent refining process of slurry is stable; in the refining process, the electromagnetic flowmeter and the control valve is composed of PID control circuit to ensure disc refiner pulp inlet flow stability, in order to improve the disc grinding efficiency, stable slurry buckle solution of, and improve refining quality; in pulp process must meet the following conditions: the ratio and concentration of slurry to a constant, fluctuation cannot be more than plus or minus 2% (fluctuation according to the specific paper request). The slurry to be stable and the normal supply of paper machine. Reserve a certain amount of slurry to suit the change of speed and variety of paper machine. Therefore, the most important is the control of the flow of the pulp in the pulp. In each of the pulp slurry pump outlet installed electromagnetic flowmeter, through the valve to regulate the flow of slurry, to ensure that each kind of slurry according to process requirements of the proportion of the pulp flow regulation, finally realize the slurry ratio is stable and uniform.
(2) the application of paper making flow system of electromagnetic flowmeter.
The whole paper system, pulping, pulp mixing section is an important link, but if the subsequent section is not ideal, that of the paper machine, is not qualified. Therefore, paper of the flow system to assume the more important role, its stability and not directly related to paper basis weight, moisture content, ash content, and other physical indicators of whether or not qualified, it is paper is qualified or not is an important part of. Therefore, in this system, we have carried out the flow detection and control of pulp and filler, and the pulp flow is regulated by pulp quantitative valve to stabilize the paper's quantitative analysis. Adjust the filler flow through the filler regulating valve to stabilize the ash content of the paper. Electromagnetic flowmeter plays a very important role in this system. It plays an important role in the improvement of the quality of paper.
(3) the application of electromagnetic flowmeter in water system.
Paper industry enterprises are high energy consumption enterprises, water, electricity, steam consumption accounted for a large proportion of the country in the "five eleven" period, the energy consumption of the paper industry has been examined, and eliminated most of the high energy consumption, low capacity of small enterprises. Therefore, water-saving has become the focus of the paper industry transformation.
Electromagnetic flowmeter has a large diameter measurement range and does not interrupt the work can replace the electronic unit, low power consumption, wet part is made of stainless steel or ceramic structure, no moving parts, maintenance free, it has a series of characteristics make it become the paper industry for industrial water is measured, making paper white water and sewage flowmeter of choice. Through the flow monitoring and assessment of the water main, the waste water, and the workshop of the workshop, the water consumption of the paper is reduced, and the waste of water resources is reduced, and the utilization rate of circulating water is improved.
After many years of practice, the electromagnetic flowmeter in the field of paper is generally used in the PTFE (for pulp, white water, industrial water) or other fluorine plastic liner (for chemicals), the electrode is selected according to the different liquid properties, the actual effect is satisfactory.
(4) preparation and application of electromagnetic flow meter in the system.
Because in deinking, pulping, streamed, coating, sizing and so on site to use a large number of chemicals, in the preparation of chemicals, to ensure stable chemical performance of each batch of, concentration is stable; in use, the amount of the added also has strict requirements, so as to guarantee paper product quality and stability. Therefore, in the process of preparation of chemicals, the use of anti corrosive electromagnetic flow meter for the measurement of chemical composition, coupled with the regulation valve for flow regulation, and ultimately the stability of chemical properties. In the chemical adding system, the use of anti corrosive electromagnetic flow meter for measurement of chemicals, coupled with the regulation valve to adjust the flow, to ensure that the paper machine system in the chemical is quantitative, but also stable. The quality of the paper is very important.
Three, electromagnetic flowmeter installation of some of the attention
(1) installation environment.
Install the site to avoid direct sunlight, to avoid rain water leaching; avoid the nearby large motors, large transformers, so as not to cause electromagnetic interference; can not be too large, the pipeline system has a strong vibration, can be added on both sides of the sensor tube.
(2) horizontal or vertical installation can be.
In measuring the size of the slurry, the best vertical installation, fluid flow from the bottom up. This not only ensures that the measurement medium is filled with the medium, but also avoids the shortcomings of the electromagnetic flow meter at the lower part of the lower part of the electromagnetic flow meter and low flow velocity.
(3) straight pipe section requirements.
In order to ensure the accuracy of the electromagnetic flowmeter, the general electromagnetic flow meter requires the upstream 5D, downstream side 3D. The high accuracy of the instrument requires the upstream side of 10D, the downstream side of the 3D. When the flow velocity in the tube is not required, the flow velocity in the tube is non axial symmetric distribution, and the error will be caused.
(4) the installation and connection of the converter.
The distance between the transducer and the transducer of the fission type electromagnetic flowmeter is controlled by the electrical conductivity and the signal cable type. The conductivity of the fluid is within a certain range, which determines the maximum length of the cable between the sensor and the converter. Cable type of cable used in manufacturing plant. Single shielded cable is generally used for industrial water or acid and alkali solution, typically 100 m. When the electrical conductivity of the medium is less than 100 s/cm, the two core dual shielding cable is required. Low conductivity, long transmission distance, there are provisions for the use of a 3 layer shielded cable.
(5) to avoid negative pressure in the pipe, especially PTFE PTFE liner.
(6) ground.
Electromagnetic flow meter requires a separate ground. The grounding resistance is less than 10. If the pipe is coated with an insulating layer or a non metal pipe, the sensor should be installed on both sides of the ground. Electromagnetic flow meter is easily influenced by external electromagnetic interference, therefore, a good grounding to a great extent determines the accuracy of the measurement.
Four, the above summary
At present, there are new measurement technology, the traditional type of flowmeter has a certain share of the market, all kinds of flow meter in the paper industry are in use, according to the results of scientific research and marketing personnel survey show that electromagnetic flowmeter products have accounted for the dominant position in the paper industry. Because of its stable performance, convenient maintenance and high cost performance ratio, it will be more widely used in the paper industry.
