During the tire vulcanization process, it is extremely important that the stable supply and circulation of the overpressure water under the internal pressure prevails. In its complete closed loop system, the hot water circulation pump is as important as the heart of the human body and must not malfunction. However, the actual situation is inevitable accidental. Only cavitation, not only cause damage to the pump, in particular, can lead to large pressure fluctuations in the circulatory system, and even pressure loss at the moment, the tire during the initial vulcanization caused a fatal injury. Thus, it is necessary to recognize the cause of cavitation and take effective measures to prevent or properly solve the problem. 1 Cavitation Analysis 1.1 Qualitative Analysis Pump water inlet due to vaporization into bubbles, the bubbles in the pump discharge before the high pressure crushing (water particles in the impeller runner movement, is constantly increasing the energy, The location of the bubble is crushed is also unique), due to the bubble suddenly disappear, causing a strong impact of the water quality point, resulting in cavitation damage to the pump impeller, while the pump water pressure fluctuations occur in severe cases Loss of pressure. Water vaporization at the suction inlet of the pump is such that its pressure suddenly drops below the saturated vapor pressure corresponding to the water temperature there. A stable heating system, pressure, water temperature, flow and stability, in the event of one of the following conditions, it will reduce the water pressure at the pump inlet. (1) a sudden drop in the vapor pressure supplied to the deaerator; (2) a sudden drop in the temperature of the steam supplied to the deaerator; (3) a substantial replenishment of lower temperature cold water to the deaerator; (4) Water suddenly increased; (5) outside the pump outlet until the loop back to the deaerator pipe network suddenly and significantly reduce the pipeline resistance; (6) outside the pump outlet until the loop back to the deaerator pipe network suddenly a large number of leaks . Cavitation can occur if the pressure at the pump inlet falls below the saturated vapor pressure due to the above conditions. 1.2 Quantitative Analysis Figure is a schematic diagram of the oxygen heating system. Take deaerator liquid level as the reference height, defined as "1-1" interface. Pump entrance for the "2-2" interface. (1) The installation height calculation Hg = P0 / Ïg-P saturated / Ïg-Δh-Σhf (1-2) (1) Where Hg-- calculate the installation height, m; P0-- vapor pressure in the deaerator, Pa ; P saturated - hot water pump inlet, that is, "2-2" interface at the water vapor pressure, Pa; Ï - liquid density, kg / m3; g - acceleration of gravity, m / S2; Σhf (1-2) - resistance loss of hot water from deaerator to pump inlet, m; When the hot water flows from the deaerator to the inlet of the water pump, the change of water temperature can be neglected. That is to say, P full = P0 and the pump cavitation allowance Δh, which is 3.9m water column high with pump data. Input pipeline resistance loss Σhf (1-2) is estimated as 1.1m water column height. Therefore, calculated by the formula (1): Hg '= - 3.9-1.1 = -5m high water column This is calculated according to 20 ℃ water, folded at 170 ℃ water: Hg = Ï20gHg' / Ï170g = 998.2 × (-5) /897.3=-5.5m High water column means that the installation height of the hot water pump is at least 5.5m lower than the minimum operating level of the deaerator. The actual example is low 10m, the installation elevation still 4.5m margin (calculated according to 170 ℃ water). (2) Deaerator internal pressure changes can occur cavitation has been in a state of steady operation of oxygen scavenging power system, deaerator vapor pressure, water temperature, water pump inlet pressure and water temperature are relatively stable. Suppose P0 suddenly decreased at this time, the system balance will be destroyed. However, P0 decreases at the same time, the water inlet pump temperature will not immediately decline, the existing pressure of 10m170 ℃ water is: h '= 10 × 897.3 / 998.2 ≈ 9m water column height (1) calculated P0 The amount of descent is such that [(P0-ΔP) -P saturates / pg-Δh-Σhf (1-2) + h '= 0 (P0-ΔP) -P saturates [- h' + h + Σhf -2)] Ïg = [-9 + 3.9 + 1.1] × 998.2 × 9.8 = -39129.44Pa ∵P0 = ΔP -P saturated = P saturated -ΔP -P saturated = -ΔP ∴ΔP = 39129Pa That is, if the water temperature is 170 ℃, that is, the saturated vapor pressure (gauge pressure) of 0.678MPa steady state operation, when the steam pressure suddenly dropped to 0.639MPa gauge below, it is possible to cause cavitation. (3) the amount of water up to cause cavitation can occur in the pipe network in the event of a larger leak, the balance of the system damage, deaerator water level will rapidly decline, so you need to quickly fill a large number of relatively low temperature soft water. Set steady-state operation deaerator water storage capacity: 25m3 (volume) × 0.7 (duty cycle) = 17.5m3 In a relatively short period of time, due to sudden drop in water level, reducing the amount of water storage Vm3, so add low temperature water Vm3. When the low temperature water is added, P0 will also be reduced, the steam flow will increase, the entrainment heat rate will be greater than the original steady-state operation. To simplify the derivation, only the heat exchange of hot and cold water is considered here.
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