破坏水库水温分层系统的能量效率估算:以金盆水库为例

为指导高效节能的破坏水库水温分层技术及系统的选择,需建立统一的能量效率基准.根据质量守恒和热量守恒定律,求出分层水库水体完全混合后的水温,计算水库水体混合前后的重心;采用库容以及与水温相关的密度等数据,对水深方向各微小水层的势能进行积分得到水体总势能,混合后水体总势能的增加量即为破坏分层所需的最小理论能量,应用耗电量估算法得到破坏分层所产生的最小碳排量;破坏分层系统的能量效率为破坏分层的最小理论能量与实际输入能量之比.以西安金盆水库为例,采用数值模拟方法计算不同水位下的水库库容,应用该方法估算了水库不同季节破坏分层所需最小能量和扬水曝气破坏分层系统的能量效率.采用数值模拟方法计算不同水位下的水库库容,计算破坏分层所需最小能量.结果表明随水体垂向温度梯度的增加而增大,在6~10月期间相对较高,7月达到最大值2432.08kW?h;该水库扬水曝气破坏分层系统的能量效率约为4%;在水温分层开始阶段运行破坏分层系统可有效降低破坏分层所需的能耗,减少碳排放量.

Estimation of energy efficiency of a destratification system for reservoirs:a case study of Jinpen Reservoir

In order guide the selection of effective and energy-saving destratification technologies for reservoirs, an uniform criteria of energy efficiency should be developed. The average water temperature after complete mixing can be calculated based on the conservation laws of mass and heat, the reservoir’s gravity centres before and after mixing were calculated.The total potential energy (PE) was determined by integrating the PE in each thin sub-layer over the water depth with data of water volume and density depending on the water temperature. The difference of total potential energy before and after mixing is the minimum energy input required for destratification. The minimum carbon emission from destratification was then calculated based on conversion ratio of the energy consumption to carbon emission. The energy efficiency of a destratification system was the ratio of the minimum required energy input to the actual energy input for destratification. Taking Jinpen Reservoir in Xi’an as a study case, water volumes under different water levels of the reservoir were numerically calculated using the geometry data, this new method was applied to estimate the energy input required for destratification and energy efficiency of destratification system. Minimum energy required for destratification of different months were both calculated using the geometry data. The results showed that minimum energy increase with the temperature gradient, was relatively high during the period from June to October, and reached a peak of 2432.08kW?h in July. The energy efficiency of the water-lifting aeration system was about 4%. It would be efficient at reducing the energy required for destratification and saving carbon emission by running the destratification system at the initial stratification period.