The working principle and reformation scheme of the online density meter for the differential pressure of the slurry in the desulfurization absorption tower of the power plant

The working principle of the desulfurization absorption tower slurry in the differential pressure in-line density meter power plant and the transformation plan are explained below in the form of cases. Four 300MW units are currently in service in a thermal power plant in Jiangsu Huaneng. Desulfurization transformation, the desulfurization system was put into operation in 2006; #7 and #8 units were put into operation in 2007, and the desulfurization system was put into operation simultaneously. The desulfurization system is equipped with 8 sets of Coriolis force principle density meters produced by E+H Company, except that the #6 absorption tower density meter is barely in service (the measured value only changes with the density trend, which cannot accurately reflect the actual value of the density, and depends on the operator's experience to judge ), the others have been withdrawn from operation. Among them, two mill outlet density meters have been damaged in 2008 due to serious wear and tear, #5, #7, #8 absorption tower density meters have been unable to calibrate since 2009, and finally were out of operation due to damage. The limestone slurry tank density meter was blocked too frequently due to the installation location, and it has not been put into normal operation. The density meter cannot be used, and the operation of the absorption tower is controlled by the method of manually sampling by the operator and measuring the density in the laboratory. The main problems affecting the operation of the density meter based on the principle of Coriolis force are: 1. The pipeline is blocked, and the operator needs to flush it regularly. Even so, the maintenance personnel often need to disassemble the pipeline to clear the blockage. 2. The density meter is worn, and measurement errors will occur after wear, and it needs to be calibrated frequently; after serious wear, it cannot be calibrated to pass; after further wear, the resonant coil will be burned, causing damage to the density meter. The Coriolis principle density meter has a short service life, and it is said that the trouble-free use time is only one year. 1. Working principle The above picture is the connection diagram of the equipment, the slurry sample tube (the vertical pipe with the pressure measuring point installed in the picture), the pressure measuring point 1 (PI-1), the pressure measuring point 2 (PI-2), the air control valve 1. Air control valve 2 and air control valve 3 are newly added equipment. There are two pressure measuring points on the slurry sample pipe: pressure measuring point 1 (PI-1) and pressure measuring point 2 (PI-2), which are used to measure the pressure at the installation (P1 and P2). The slurry sample pipe is connected to valve 1, Valve 2 and valve 3, valve 1 is connected to the bottom of the absorption tower, valve 2 is connected to the process water pipeline, valve 3 is installed at the bottom of the slurry sample tube, and is connected to the drain pipeline. Open valve 1 every certain time (such as 10 minutes), and judge from the signal of pressure measuring point 2 that the amount of slurry entering the slurry sample tube meets the requirements, close valve 1, delay 3S until the slurry in the slurry sample tube is stable, calculate the slurry density ( The pressure measured by pressure measuring point 1 is P1, the pressure measured by pressure measuring point 2 is P2, the slurry density is ρ, the acceleration of gravity is g, and the height difference between the two pressure measuring points is H): ρu003d(P1-P2)/Hg , the calculated value is stored until the new value is updated in the next measurement cycle. Open valve 3, drain the slurry in the slurry sample tube, confirm the emptying of the slurry by the signal of pressure measuring point 1 and a short-term delay, close valve 3, open valve 2, put industrial water into the slurry sample tube, and check the slurry sample tube and the connected equipment. Carry out cleaning, confirm that the amount of cleaning water meets the needs by the signal of pressure measuring point 2, close valve 2, open valve 3, and drain the flushing water, confirm that the flushing water is empty by the signal of pressure measuring point 1 and a short-term delay, and close valve 3. Repeat this operation for the next measurement time, complete the slurry density measurement cycle, and set the measurement cycle according to actual needs. Measurement calculation and valve control are realized by PLC. Second, the transformation implementation plan: 1. The power supply of the differential pressure online density meter adopts the original Coriolis force density meter power supply, the density signal is connected to the original Coriolis force density meter signal loop, and the original Coriolis force density meter flow signal is abolished. Differential pressure online density meter density meter is installed on site Road flushing water (desulfurization island process water). 3. The sampling tube of the differential pressure online density meter is in the form of 316L stainless steel + plastic-lined seamless steel pipe. It is difficult and expensive to install the special-shaped pipeline of the pressure transmitter to achieve plastic-lining. It is made of Ф57 (DN50) 316L stainless steel. In order to improve the measurement accuracy, the vertical pipeline used to increase the height is made of Ф57 (DN50) plastic-lined seamless steel pipe, and the distance between the two differential pressure sampling flanges is 0.5 meters. 4. Install a Rosemount flange-mounted pressure transmitter to control the liquid level entering the sample tube, and a Rosemount double-flange differential pressure transmitter to measure the differential pressure between high and low sampling points. 5. The PLC adopts Siemens S7-200, and the CPU card is CPU224, with two analog inputs, one analog output, 14 switch inputs and 10 switch outputs. 6. The calculation control box is equipped with automatic measurement, measurement operation, measurement end, and comprehensive fault indicator lights; manual test, valve test, calibration instrument, and fault reset buttons are set; automatic measurement switch is set to control the input and removal of automatic cycle measurement. 7. The DCS screen will not be changed. The density value displayed by the original Coriolis density meter is the display value of the new density meter.
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