Air leakage is a common problem cement mill system. The system air leakage not only causes the specifications of auxiliary equipment to increase, increases the investment and operating costs, and will affect the system operating conditions, reducing system output and increasing energy consumption. Leakage caused by the reasons in addition to the system process needs (such as air volume control devices, etc.) is unavoidable, mainly due to the device close (lock) sealing device performance and installation improper use caused. In the mill to participate in the grinding system, grinding tailgate good or not, directly affect the grinding air ventilation and grinding performance. Therefore, the choice of a good wind lock device is the key to solve the problem of air leakage. Nanjing Cement Industrial Design and Research Institute developed the mill discharge overflow lock air valve, with the principle of advanced, simple structure, is one of the more ideal lock device, has been used in many cement plants, in general Good effect, but there are some manufacturers can not achieve the desired effect. In this regard, we after investigation and analysis that, mainly the user of the device principle, the lack of understanding of the structure, coupled with the installation, use improper due. The following on the device structure, principles, the main parameters and applications should be noted to determine the matters such as an introduction for readers reference. 1 The main structure and its role Locking valve is mainly composed of the valve body, maintenance door, adjusting plate and inflatable box. The valve body is divided into â… , â…¡ chambers by a fixed partition in the middle, which makes the fluidized bed form a U-shaped structure to achieve the purpose of locking the wind. Access door is mainly used to adjust the adjustment plate and lock the effect of wind detection. Adjustment plate is mainly used for the control of the flow rate and iron slag cleaning. The inflatable box is composed of a breathable layer, a perforated plate and the like. The gas from the Roots blower is evenly distributed to inflate the bottom of the fluidized bed and make the material in the upper part form a fluidized bed. In order to make the slag, iron slag and other coarse particles timely discharge, the inflatable box should be horizontal and not less than 30 ° angle arrangement. 2 Working principle Overflow lock air valve is designed using fluidized technology. According to the process of forming fixed fluidization, it is generally divided into fixed bed, fluidized bed and continuous fluidized bed three states. Figure 2 shows the void fraction ε of the particle layer, the flow velocity u'f as the fluid passes through the particle layer, and the change in the fluid loss resistance ΔP under three conditions. In the fluidized bed state, the bed height of the fluidized bed increases with the increase of the void fraction ε, but the actual flow rate of the fluid passing through the bed u'f and the fluid resistance of the fluidized bed The effect of the effect) remains unchanged. According to the characteristics of the fluidized bed, the conditions for the stable flow of the material stream should satisfy the following formula: F + (L1-L2) · Ï Â· g + (P1-P2) -V2 · ξ · Ï / 2 = 0 Medium: F - Impact force of material on unit area, N / m2; L1, L2 - Effective material height of chamber â… , m; Ï - Bulk density of material after gasification, kg / m3; , â…¡ chamber material surface static pressure, N / m2; V - flow velocity, m / s; ξ - flow resistance coefficient, depending on â… , â…¡ channel cross-sectional area between rooms, g - Gravitational acceleration, g = 9.8m / s2 Similarly, at equilibrium, the pressure drop ΔP of the fluid passing through the fluidized bed can be obtained from the stress analysis of the bed: â–³ P = L · (1-ε ) · ΡP · g = L · Ï Â· g (2) where: â–³ P - fluidized bed pressure drop, Pa; L - fluidized bed height, m; ε - fluidized bed The porosity. From equation (2), we can see that the pressure drop is approximately equal to the weight per unit area of ​​the bed, that is, the static pressure drop of the bed has nothing to do with its air velocity. Overflow lock air valve is the use of this fluidized bed column resistance to achieve the purpose of locking the wind. Therefore, the conditions for wind-lock: (L1-L2) · Ï Â· g≥P2-P1 3 to determine the main operating parameters The main operating parameters of the overflow lock air valve, including air pressure, air volume and discharge capacity, are described below . (1) Wind pressure. The wind from the Roots blower and into the overflow lock air valve to overcome the three resistance, one is the effective fluidized bed layer resistance, the value of the equivalent per unit area of ​​the weight of the powder; the second is â… , â…¡ room Barrier below the material layer resistance (including iron slag, etc.) ?; Third, the resistance of the breathable layer and the intake pipe. Practice has proved that the effective use of wind blocking material layer resistance for the entire proportion of wind pressure is very small, therefore, whether the lock pressure is required to change, the wind turbine for the wind supply pressure has little effect. According to the information provided by the Danish company FLS, the pressure required to enter the inlet of the inflatable box is 20 kPa, while the experimental data of the relevant institutes in our country is? (10-25) kPa. Therefore, the actual selection of fans, the required wind pressure (20 ~ 30) kPa can be. (2) air volume. From the fluidized bed formation conditions know, the appropriate section of the rising wind speed is necessary. In a certain range of wind speed, wind speed and the size of the discharge capacity. Therefore, the amount of air flow and the size of the unit area. Table 1 for some units of the design parameters. Combined with the actual use of the situation, I believe that the overflow air lock valve air volume selection per ton of flour (0.35 ~ 0.40) m3 range is more appropriate. (3) discharge capacity. Discharge capacity depends on the flow rate and flow through the cross-sectional area. The cross-sectional area through which the material flow passes is easy to determine. From equation (1), the velocity of the material flow is related to the flow resistance coefficient ξ, which in turn is related to the geometry of the air-lock valve, material properties, Click here to calculate more complicated. According to the experimental study conducted by the institute concerned, the discharge capacity can be estimated according to the amount of material passing through the inflatable area per unit area. That is, the discharge capacity can be selected as (400 ~ 800) t · h-1 · m2. 4 should pay attention to the use of several issues In addition to the use of relief lock valve should be aware of the structure and principles, but also pay attention to the following questions: (1) before installation should check the breathable layer for damage or soaked in rain And so on. If present, it should be eliminated to avoid stringing or blocking. Roots blower fan valve from the overflow far, the connecting pipe must be added support to prevent vibration. (2) At the beginning of use, pay attention to observe the flow of material, through the adjustment plate to adjust the size of the cross-section of the flow through to achieve the control of the flow rate. (3) When the L1 and L2 values ​​are too small, the material bed may be penetrated or blown by the air flow, failing to achieve the purpose of air lock. Therefore, at the beginning of the mill operation or system is not normal, this phenomenon may occur, pay attention. (4) Check the effect of lock wind through the overhanging door on the top of the overflow lock air damper. If it is slightly under-pressured here, the lock air is good; on the contrary, it needs to be adjusted. (5) When the adjusting plate on the exit side of the overflow lock air damper is adjusted, neither the lower passage can be sealed completely, so as to prevent the iron slag from blocking the flow passage after long-term operation. But not too big, in order to prevent short-circuit flow, affect the lock wind.