微孔扩散器形状对曝气增氧性能影响的试验

为了探究不同形状(直线型、C型、S型和圆盘型)的微孔曝气扩散器对增氧性能的影响,在3个水深和5个曝气流量下进行了一系列的室内曝气增氧试验.结果表明:相同水深和流量下,直线型的氧体积传质系数、充氧能力、动力效率和氧利用率均最大,例如在0.7 rn水深时4个技术指标的范围值分别为0.853～1.762 h-1、8.701～17.432 g/h、4.146～6.869 kg/(kW·h)、3.257％～4.912％;而S型是最低的,其范围值分别为0.798～1.504 h-1、6.850～12.627 g/h、2.630～4.444 kg/(kW·h)、3.823％～2.339％;其次是C型和圆盘型微孔曝气扩散器,其他水深试验条件下也得到了类似的规律.由此说明直线型的增氧效果最好.为了仅探究扩散器形状对增氧性能的影响,在试验水池表面铺设薄膜阻隔了空气-自由水表面氧传质后,4种扩散器的氧体积传质系数均下降,最大的下降率分别为12.29％、8.73％、12.26％和6.74％,空气-自由水表面氧传质对不同形状的扩散器的影响程度不同.但下降后的氧体积传质系数值最高的仍是直线型,其次是C型和圆盘型,S型仍然最低;直线型、C型、圆盘型、S型在0.7 m水深下分别为1.693、1.470、1.438和1.227 h-1,在其他工况下也得到了类似的规律.因此,增氧性能最好的是直线型微孔曝气扩散器.此研究结果可为微孔曝气技术的绿色环保应用以及实际工程中对微孔扩散器形状的选取提供一定的参考价值.

Experiment on effects of microporous diffuser types on aeration oxygenation performance

Abstract: In lakes, reservoirs, rivers, estuaries, aquaculture ponds and sewage treatment plants where the dissolved oxygen concentration needs to be increased, aerator is the most important oxygen equipment to maintain the dynamic balance of dissolved oxygen. Among different kinds of aeration facilities, the microporous aeration aerator has been more widely used, because of its large ventilation capacity, strong oxygenation capacity, energy saving and environmental protection, easy installation and strong adaptability. There are many factors that affect the aeration performance of microporous aeration aerator, mainly including external factors and self factors. The microporous aeration aerator uses a microporous aeration tube as its diffuser, but the current study of the effect of the type of the diffuser on the aeration performance of the microporous aeration aerator is almost blank. And conventionally, the microporous diffuser always uses disc-type, but this way is empirically and even blindly adopted. Therefore, in order to explore the effect of the microporous diffuser with different shapes on the oxygenation performance, a series of oxygenation experiments were carried out under different types of air diffuser rolled up by a same length (1.1 m) of aeration tube in laboratory. The type of the microporous diffuser was the main influence factor. The types were linear-type, C-type, S-type and disc-type. The experimental apparatus mainly included glass tank, microporous aeration system, dissolved oxygen meter and computer. The size of the glass tank was 2 m × 0.8 m × 0.8 m (length × width × height). The test was based on the standard test method for oxygen from American Society of Civil Engineers (ASCE) in different water depth and air flow. The air flow rate was set as 0.6, 0.9, 1.2, 1.5, and 1.8 m3/h and the water depth was set as 0.4, 0.55, and 0.7 m. The results show that, under the same water depth and air flow rate, the oxygen volumetric mass transfer coefficient, standard oxygen transfer rate, standard aeration efficiency and standard oxygen transfer efficiency of the linear-type microporous aeration diffuser are the highest. In the 0.7 m water depth, the ranges of the 4 technical indices are 0.853-1.762 h-1, 8.701-17.432 g/h, 6.869-4.146 kg/(kW·h), and 4.912%-3.257%, respectively, while the S-type is the lowest, and the range values are 0.798-1.504 h-1, 6.850-12.627 g/h, 4.444-2.630 kg/(kW·h), and 3.823%-2.339%, respectively. Between the linear-type and S-type microporous aeration diffuser are the C-type and disc-type. The same law is also obtained at another depth of water. It meant that the oxygenation performance of linear-type was the best, while the lowest one was the S-type microporous aeration diffuser. It could be known that it is not the best for the oxygenation effect of the disc-type microporous diffuser, which we have chosen empirically. After the film was covered on the top of tank to cut off the air-free water surface oxygen mass transfer, the values of oxygen volumetric mass transfer coefficients of these 4 types of diffusers were decreased and the degree of descent was different, and the largest decline rates were 12.29%, 8.73%, 12.26% and 6.75%, respectively. So, the influence degree of air-free water surface oxygen transfer on different diffuser types is different. But the best oxygenation effect occurred still under linear-type microporous aeration diffuser, followed by the C-type and disc-type, and the S-type is still the lowest one. And the values of oxygen volumetric mass transfer coefficients in 0.7 m water depth of linear-type microporous aeration diffuser, C-type and disc-type and S-type are 1.693, 1.470, 1.438 and 1.227 h-1, respectively. Therefore, oxygen performance of linear-type microporous aeration diffuser is the best. Based on these conclusions, for the shallow water to oxygenate, the linear-type microporous aeration diffuser is the first to use as aeration equipment, which provides a certain reference value for us in the practical selection of microporous diffuser shape.