Cement grinding system of air leakage is a common problem. System of air leakage not only increase the specifications of auxiliary equipment to increase the investment and operating costs, and will affect the system operating conditions, the system to increase production to reduce energy consumption. In addition to leakage caused by the reasons for the need for system processes (such as wind volume adjustment device, etc.) is inevitable, the equipment was mainly due to close (lock) closure device performance and caused by improper installation.
Participation in the mill grinding system, lock the end of the wind mill is good or not, with a direct impact on ventilation and grinding mill performance. Therefore, the choice of a good wind-lock device is the key to solve the problem of air leakage. Nanjing Cement Industry Design and Research Institute to develop the design of the mill discharge valve lock overflow with the principle of advanced features such as simple structure, it is more desirable to lock one of the wind plant, a cement plant in use more than the whole result is good, but some manufacturers of less than desired results. In this regard, our investigation and analysis, the main user of the device, the structure of a lack of understanding, together with the installation, improper use. Following on the device structure, principle, main parameters and applications and other matters they should pay attention for an introduction for readers to reference.
1 the main structure and its role
Lock valve by valve, repair the door, adjusting the composition of boards and inflatable box. Body from the middle of a fixed partition will be divided into Ⅰ, Ⅱ room, so that the formation of U-bed structure, to achieve the purpose of locking the wind. Maintenance is mainly used to the adjustment of the door panels to adjust and lock the detection of the effect of the wind. Adjustment plate is mainly used for material flow control and clean-up of iron. Inflatable box by the air layer, porous plates, etc., will the gas from the Roots blower evenly distributed at the bottom of the inflatable bed and the upper part of the material to form a fluidized bed state. In order to feed slag, iron and other coarse particles discharged in a timely manner, the level of inflation as me should be not less than 30 ° angle layout.
2 Working Principle
Lock overflow valve is designed Fluidization. The formation of a fixed fluidized bed process, in general be divided into fixed bed, fluidized bed and fluidized bed for three states. Figure 2 in the three states, the granular layer of the void fraction ε, when the fluid through the granular layer of the flow resistance and fluid u'f loss △ P changes. State in the fluidized bed, fluidized bed voidage with bed height increased with increasing ε, but the fluid bed through the actual velocity and fluidized bed u'f fluid resistance (neglected wall effect) has remained unchanged.
From the characteristics of fluidized bed, we can see that the stability of the flow of material flow conditions should meet the following formula:
F + (L1-L2) ρ g + (P1-P2)-V2 ξ ρ / 2 = 0? (1)
Where: F - per unit area on the momentum material, N/m2;
L1, L2 - Ⅰ, Ⅱ room high-effective material, m;
Ρ - material density after gasification, kg/m3;
P1, P2 - Ⅰ, Ⅱ expected upper chamber static pressure, N/m2;
V - the speed of material flow, m / s;
ξ - flow resistance coefficient, depending on the Ⅰ, Ⅱ Room of the channel between the cross-sectional area, factors such as inflation situation;
G - acceleration due to gravity, g = 9.8m/s2
Similarly, in the balance, the fluid through the fluidized bed pressure drop of △ P, can be obtained in accordance with the bed stress analysis:
△ P = L (1-ε) ρP g = L ρ g (2)
Where: △ P - fluidized bed pressure drop, Pa;
L - height of fluidized bed, m;
Ε - porosity of the fluidized bed.
By (2)-type, we can see that in the approximate pressure drop per unit area equal to the weight of the bed, that is, the static bed pressure drop has nothing to do with the air flow velocity. Lock overflow valve is to use the fluidized bed column resistance of materials to achieve the purpose of locking the wind. So, lock the wind conditions are as follows:
(L1-L2) ρ g ≥ P2-P1
3 Determination of the main operating parameters
Overflow valve lock the main operating parameters, including air pressure, wind and nesting capabilities, is as follows.
(1) air pressure. From the Roots blower and drums lock into the overflow valve to overcome the wind resistance of three, first, the expected effective fluidized bed resistance, and its value per unit area equivalent to the weight of the powder material; Second, Ⅰ, Ⅱ Room partitions resistance following material (including the effects of iron, etc.); Third, breathable layer and into the airway resistance. Practice has proved that the real effective lock wind resistance material used in total for the small proportion of wind pressure, so, regardless of whether the requested lock changes in wind pressure on the blower of choice for small wind pressure. FLS from Denmark provided information, we can see that requests me to the entrance of inflatable pressure 20kPa, and the relevant institutions for the experimental data? (10 ~ 25) kPa. Is therefore recommended that the actual choice of fan, the requirements for wind pressure (20 ~ 30) kPa can.
(2) air flow. From the formation of fluidized bed conditions, we can see that the appropriate cross-section increase in wind speed is essential. In the framework of a certain wind speed, wind speed and the size and the ability of nesting. Therefore, the air volume and air units of the size of the area. Table 1 shows the design parameters of some units. Combination of actual usage, I believe that the overflow valve of the air lock selected powder material per ton (0.35 ~ 0.40) m3 more appropriate range.
(3) discharge capacity. Capacity depends on the nesting material flow velocity and flow through the material, such as cross-sectional area. Expected to flow through the cross-sectional area is easy to determine, from the type (1), we can see that material flow velocity and flow resistance coefficient ξ, and the valve lock ξ with the geometric dimensions, material nature of the situation factors such as inflation, so , this calculation more complicated. Test in accordance with the relevant research institutions believe that the ability to discharge per unit area through the inflatable material to estimate the amount that may be nesting capacity (400 ~ 800) t h-1 m2 selected.
4 in use should be noted that several issues
In addition to understanding the use of overflow when the lock valve structure and principle, we must also pay attention to the following questions:
(1) should be checked prior to installation damage permeability layer, or by rain water and so on. If it exists, should be eliminated, so as to avoid wind or blockage of string. Roots blower away from the overflow valve lock, the connection pipe must be added support to prevent vibration generated.
(2) the beginning of use, to observe the material flow through the adjustment plate to adjust material flow through the cross-section size, to achieve the speed of material flow control.
(3) When the value of L1 and L2 is too small, the bed may be expected to penetrate the air or wind run, wind not the purpose of locking. Therefore, at the beginning or in the mill system is not functioning normally, it is possible that this phenomenon of attention.
(4) through the overflow valve at the top of lock repair lock the door to detect the wind effects, if negative pressure here at the micro-state, indicates that the wind a good lock; the other hand, should be adjusted.
(5) of the overflow valve lock plate to adjust the export side of adjustment, can not access all the lower part sealed to avoid long-term operation, the iron will be expected to plug the flow of Road. But they can not be too large in order to prevent short-circuit feed stream, the impact of air lock.
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