The measurement of industrial sludge water has been one of the problems that metrology workers have yet to overcome. The main reasons are twofold. First, the fluid characteristics: the medium is dirty, solid-liquid two-phase, complex composition, easy adhesion, deposition and so on. Second, the measurement characteristics: the field working conditions are bad, the detection device is easy to damage, difficult to repair, and the reliability of the measuring instrument is high.
In recent years, with the continuous deepening of the low-cost strategy of Jigang, the implementation of measures such as solid waste recycling and zero discharge of sewage, the process will recycle iron-making dust-removing water, steel-making dust-removing water and dephosphorization water (collectively referred to as industrial sludge water). After being filtered by the sedimentation tank, it is pumped and sent to the sinter plant for reuse. The accurate measurement of the industrial sludge water is directly related to the quality of the sinter. To this end, we conducted a series of measurement techniques on the accurate measurement of industrial sludge water. Such as ultrasonic flowmeters, mass flowmeters, electromagnetic flowmeters, etc., through years of practice, the electromagnetic flowmeters of Huaheng Instrument are popularized and applied for their low price, reliable performance and maintenance-free.
1.1 Measurement principle
The electromagnetic flowmeter is a meter that measures the volumetric flow rate of a conductive liquid by using Faraday's law of electromagnetic induction.
As shown in Fig. 1, the conductive liquid flows in a non-magnetic measuring pipe perpendicular to the magnetic field, and an induced electromotive force proportional to the flow rate of the liquid is generated in a direction perpendicular to the direction of the fluid, and the direction of the electromotive force is determined according to the right-hand rule. The induced electromotive force is detected by two electrodes in direct contact with the fluid and transmitted to the amplifier through the cable and then converted into a uniform output signal.
Its value is as follows:
Where E is the induced potential, ie the flow signal, V;
B is the magnetic induction, T;
D is the inner diameter of the measuring pipe, m;
is the average flow rate, m/s;
K is the meter factor.
1.2 Sensor structure
The excitation tube is provided on the upper and lower sides of the measuring tube, and the excitation current is supplied by the converter. The excitation current generates a magnetic field to pass through the measuring tube, and a pair of electrodes are buried in the inner wall of the measuring tube to contact the liquid, thereby extracting the induced electromotive force and feeding the converter. It actually becomes an electromagnetic flow transmitter.
(1) The industrial sludge water of Jinan Iron and Steel Co., Ltd. generally contains 38% to 50% iron fine powder and other oxides, and belongs to the pulp measuring medium. The electromagnetic flowmeter sensor uses SCLDG series, built-in stainless steel electrode, neoprene lining, standard pressure is 1.6MPa, and the supporting flange is installed on the sludge water pipeline.
(2) The converter selects split type, standard output, spoof characters, realizes instantaneous flow, cumulative total liquid crystal display, etc., and is installed on the production side console. A special electric slow connection is used between the sensor and the converter for easy installation.
(3) Main performance characteristics
a. Non-blocking flow detecting component: It is not easy to block, and can be used for measuring the measurement of industrial sludge water of solid-liquid two-phase dirty medium containing hidden particles.
b. No pressure loss: the resistance of the instrument is only the resistance of the pipeline of the same length, and the energy saving effect is remarkable.
c. The measured volume flow rate is not affected by the change of liquid density viscosity, temperature, pressure and conductivity. The measured degree is high, and the flow in both forward and reverse directions can be measured.
d. The sensor has no moving parts. The low-frequency rectangular wave excitation is not affected by the power frequency and various stray electromagnetic field interferences on the site. The working draft is reliable.
e. The range ratio is large, it is 1500: 1, the flow can be fully tracked, the small flow rate can be accurately measured, and the full-scale flow rate setting range is wide.
f. The requirements for the front straight pipe section are lower: upstream ≥ 5D, downstream ≥ 2D, D is pipe diameter.
g. Sensor installation is flexible: it can be installed horizontally, vertically and obliquely as long as the acute angle between the electrode axis and the horizontal plane is ≤45°C.
h. The sensor has a simple structure, convenient installation and low maintenance cost. 3 application
The system has been running normally since installation. The flow measurement range is wide and the performance is stable. It can be seen from the daily check data of Table 1.
At the production site, the duty scheduler and production personnel can operate and control the sludge valve according to the instantaneous flow value of the electromagnetic flowmeter to adjust the amount of sludge water to ensure reasonable mixing of water, so as to maximize the use of industrial sludge water. cut costs. Accurate metering of sludge water is of great practical significance for production.
(1) Industrial sludge water generally contains a large amount of wear medium, and the sensor is preferably installed vertically.
(2) The sensor cannot be mounted on a free-vibrating pipe.
(3) System grounding should be reliable.
(4) The measuring tube must be completely filled with the medium.
(5) Selection of electromagnetic flowmeter: The composition of the measured medium should be understood in order to reasonably select the sensor lining material, electrode material and so on.
(6) The conductivity of the measuring medium should be ≥ 5 μs/cm.
We all know that flow meters are one of the few instruments that are much more difficult to manufacture than in manufacturing. Therefore, in the process of measuring industrial sludge water (fluid flow meter), we focus on two properties: the reliability and accuracy of the instrument. The reliability of the instrument includes reliable quality and maintainability or maintenance-free operation.
In recent years, the practice has proved that the electromagnetic flowmeter has become the instrument of choice and popularization in the measurement of industrial sludge water at its inherent performance price. We believe that with the development of fluid flow measurement technology, especially the continuous development and application of various electromagnetic flowmeters, it will provide a more solid foundation for the accurate measurement of industrial sludge water, and the prospects will be broader.