A blower is oxygen equipment commonly used in sewage treatment project, the sewage treatment plant selection of blower fan manufacturers, product samples were given on the performance parameters of standard flow conditions, the intake air blower standard prescribed by China: pressure P0 =101. 3 kPa, T0 = 20 DEG C temperature, relative humidity phi = 50%, P = 1.2 kg/ m3 air density. However, the fan is not in actual use standard state, when the environmental conditions such as temperature, blower air pressure and altitude and fan performance will also change, the design selection could not be used directly on the performance parameters of product samples, and according to the actual needs of the performance requirements of wind turbine using state converted to standard air intake fan parameters under the condition of the type.
Two, the blower selection should be level factors of positive displacement blower exhaust pressure on blower outlet pressure does not depend on the fan itself, but by the gas blower after discharge device, the so-called "back pressure" decision, aeration blower has the characteristics of strong gas system. Exhaust pressure blower nameplate is marked rated pressure fan. In fact, the blower can work at any pressure below the rated discharge pressure, and can be more than the rated discharge pressure, as long as the strength and exhaust temperature are allowed. For the sewage treatment plant, the absolute pressure (back pressure) of the exhaust system is the pressure loss value of the pipeline system, the depth of the aeration tank and the atmospheric pressure of the environment, as shown in figure 1. If for some reason, such as aeration head or pipe plug, the pressure loss of pipeline system increases, "back pressure" will increase, so the blower pressure also increased; and if the aeration head rupture or pipe leakage, pressure loss of pipeline system will reduce the "back pressure" will continue to reduce the air blower the pressure is reduced. In summary, when the pressure of the aeration blower is determined, the absolute pressure of the air blower in the standard state is equal to the atmospheric pressure, the water depth of the aeration tank and the loss of the pipeline.
Should pay attention to the blower air flow factor in the calculation of oxygen demand of sewage treatment three, roots blower selection, the results for the mass flow QM standard condition (kg/ min), the oxygen and then convert it to qv1 volume flow under the condition of the standard required for air (m3/ min), if the use of blower is not the standard state, such as in the plateau region, air density and humidity changes, the blower air supply volume flow and standard state is the same, but the mass flow rate of air supply will be reduced, may lead to insufficient oxygen supply. Therefore, it is necessary to calculate the volume flow that can supply the same mass flow rate. In the plateau area when in use, the ambient atmospheric pressure will change, pressure ratio increased, so the leakage flow blower will increase, which will cause the air volume flow blower supply reduction, may also be caused by insufficient oxygen. Therefore, the design must consider the influence of various factors when using the conditions change, in order to ensure that the actual air flow of the fan can meet the use requirements, and calculate the conversion flow and leakage flow.
Four, the blower selection should be concerned about the changes of gas flow blower for the same blowers in winter and summer, the volume will not change, but because of the different mass flow of air density will change, that is to say the amount of oxygen will be different. The blower in the standard state and the use state of the volume is the same, but because the air density (P), changes in moisture content, resulting in oxygen supply blower is transported to the aeration tank (FOR) decreased with increasing temperature decreasing in winter, summer temperatures rise. For example, a sewage treatment plant, the selection of Roots blower numerical examples, according to the change of environmental temperature, calculate the actual amount of oxygen blower, the annual variation in the actual operation of the process, due to changes in water quantity, water quality, water temperature, ML S S and other parameters of the system, oxygen demand (SOR) can also be changed in the summer, high temperature, aeration oxygen demand (SOR) increased, but the oxygen supply blower (FOR) decreased, which is considered the most adverse conditions, the oxygen demand of the design at the same time, the oxygen supply and oxygen demand is reduced; in winter, the water temperature, aeration oxygen demand (SOR) decreased, but the blower oxygen supply (FOR) increased, at this time, the amount of oxygen demand is much larger than. This is because the winter temperature is reduced, the air density increases, then the fan supply dry air flow than the standard state greatly increased, resulting in increased oxygen supply, from the actual measuring operation, dissolved oxygen aeration tank every winter than in summer will be higher than 1 ~ 3mg/ L. Therefore, in the process of production and operation, it is necessary to adjust the equipment timely according to the changes, so that the filling capacity of the blower and the oxygen demand in the actual operation. The roots blower, the use of inverter by changing the fan speed to adjust the air is very economical and practical. In different seasons, aeration oxygen demand (SOR), blower oxygen supply (FOR) changes of the five, in conclusion, with a blower used in different conditions, the performance change is very large, so it must be selected through rigorous calculation, otherwise it may lead to insufficient oxygen biochemical system; in addition, because changes in air density in winter and summer, the change of mass flow blower supply of oxygen, oxygen supply in winter is much more than demand, therefore, should adopt frequency control measures such as the concentration of dissolved oxygen and biochemical system remained stable.