Calculation of inventory level in the dry quenching coke pre-storage chamber and γ-ray level measurement

Thread Content

Calculation of Inventory Levels and γ-Ray Level Measurement in the Dry Quenching Chamber for Coke – Zhang Zhiqiang (MaSteel Coal Coking Company, Ma’anshan 243061). The dry quenching systems for Cokes Ovens No. 5 and No. 6 at MaSteel are among the first large-scale installations in China to be built using domestic technology; they were put into operation in 2004. After reaching full production capacity, the dry quenching rate remained stable at over 90% for a long time. The capacity of this dry quenching system is 125 t/h, with a domestic production rate of equipment reaching 90%. To ensure the smooth progress of production, it is necessary to maintain a stable level of coke in the pre-storage chamber of the dry quenching furnace. The operator adjusts the quenching speed based on the inventory level to keep it stable. 1 Calculation and adjustment of the inventory level in the storage chamber. Although the inventory level in the storage chamber cannot be measured directly, it can be determined using indirect calculation methods. The formula for calculating the inventory level is: Wn = Wn-1 + ΔWin – ΔWout ± α. In this formula, Wn represents the mass of coke in the storage chamber to be calculated, in tons; Wn-1 is the mass of coke in the storage chamber after the previous calculation, also in tons; ΔWin is the mass of coke loaded into each tank, as determined by weighing equipment, in tons ； △The mass of coke discharged by Wout is measured by an electronic belt scale, in tons ； ±α is the calculated correction value, t. In Equation (1), due to certain measurement errors in ΔWin and ΔWout, calculation corrections of the inventory level are required to eliminate cumulative errors. The correction is based on whether a signal is detected by the fixed-point monitored gamma-ray level gauge for the material level. Level correction is not performed when the radiation source of the gamma-ray level gauge is not turned on or when the mounting device is open. When the gamma-ray level gauge detects that the coke level passes through its installation level from top to bottom, the program automatically performs correction. During calibration, the program automatically sets the level calculation result to equal the calibration value (which is determined by the furnace design and the installation position of the gamma-ray level gauge; in this project, it is 87t), and the next level calculation starts with Wn-1 = 87t. Correction amount (t) = Calculation amount before correction (t) – 87t. In production, it is necessary to keep the coke level in the storage chamber constantly above the plane where the gamma-ray level gauge is installed, in order to ensure the accuracy of inventory calculations. 2 Correction of screen display: The operation instructions for correcting the inventory quantity in the pre-stored area within the HMI are shown in Figure 1. After clicking on the number displaying the inventory quantity in the pre-stored area, a window will pop up. Figure 1: Calibration screen (1). The constant term in the level calculation formula can be entered in the “Correction amount input” field. (2) In the “Correction Standard Value” field, the actual inventory value at the time of correction can be entered; for this project, it is 87t. (3) Enter the amount of coke discharged during simulation in the “Set Discharge Amount” field. (4) The “Inventory Level” data represents the result of the inventory level calculation. (5) The “correction amount applied” data represents the deviation value between the calculated inventory level and the actual inventory level at the time the correction was made. (6) Each time a can of coke is loaded, the “loading count” increases by 1; it is reset after each calibration. (7) “Number of interval charges” records the number of coke tanks charged during two calibration intervals. (8) “Correction interval time” records the interval between two corrections. (9) “Simulate Loading”: Each time it is pressed, one tank of coke is simulated to be loaded, and the “weight per tank of coke” is added to the inventory calculation result. (10) When the “Simulate Discharge” button is pressed, it is calculated based on the “set discharge volume”. Simulated discharge is effective only when the coke discharge device is stopped. (11) “HH”, “H”, and “L” are the input values for inventory level alarms and interlock settings; the setting is completed by pressing “Enter”. (12) Close the window by clicking “Exit”. In production, the coke level in the storage chamber should frequently pass through the plane where the gamma-ray level gauge is installed, so that the calculated inventory levels are continuously corrected to ensure the accuracy of these calculations. 3 Gamma-ray level measurement: Gamma-ray level gauges are important instruments for level measurement. In the production of dry quenching of coke, the correction of the inventory level in the storage chambers relies on the proper functioning of gamma-ray level gauges. 3.1 Measurement principle and structure When gamma rays pass through any material, they interact, resulting in the photoelectric effect, Compton effect, or pair production effect. Due to these effects, a portion of the gamma-ray beam is absorbed by the material, causing its intensity to decrease. The reduced strength is related to the type of substance and the thickness of the material layer. The γ-ray level gauge monitoring device consists of a source chamber and a detection unit, as shown in Figure 2. Figure 2 Block diagram of the composition of the gamma-ray level gauge. 3.2 Characteristics of the gamma-ray level gauge. Since gamma rays can penetrate steel plates, the gamma-ray level gauge can be placed outside the dry quenching furnace to perform non-contact measurement of the material level in the furnace. This device has the following features: (1) Simple structure, easy to install and debug. During installation, it is sufficient to fix the source chamber and the detector at corresponding positions on either side of the outside of the dry quenching furnace, depending on the specific requirements for level monitoring; just ensure that the aperture of the radiation source is aligned with the center of the detector’s probe. (2) High system reliability. The gamma-ray level gauge is installed on the outside of the dry quenching furnace and does not come into contact with the coke that is in motion inside the furnace. As a result, this measurement method is not affected by changes in parameters such as stress, temperature, density, or viscosity of the material, nor by impacts resulting from the movement of the material inside the dry quenching furnace. Since the detector has a sealed structure and its internal circuits are low-power digital circuits, it is highly resistant to dust contamination; as a result, this device has a long service life and is stable and reliable. (3) Maintenance-free. Gamma-ray level gauges use Co-60 as the radiation source; the nuclei of Co-60 can decay spontaneously and continuously, emitting gamma particles in all directions during this process. Since the half-life of Co-60 is 5.2 years, no maintenance or calibration of this device is required in the short term. 3.3 Protection against gamma-ray hazards: The radiation source in isotope level gauges is solid, and the container holding the source is sealed. Although this does not lead to environmental contamination, it is still necessary to pay attention to safety measures; efforts should be made to minimize unnecessary exposure levels in order to ensure the safety of the workers.