TechnicalHome >> Technical

Abstract Mixing is an important process in municipal, industrial and other various wastewater treatment processes, which directly affects the final treatment effect.This paper introduces a new type of efficient hyperboloid stirring impeller stirring scheme compared with the commonly used stirring method in the current water treatment process.Its unique hyperbolic impeller structure and working process are more in line with the characteristics of water flow, can achieve excellent mixing effects, and have the characteristics of energy saving and high efficiency.

1 Development background

In urban sewage treatment and other various processes, water agitation is one of the key processes.The stirring impellers currently used are mostly propeller stirring schemes such as double-blade or multi-blade paddles, multi-blades or special-shaped curved surfaces.The structural form of these blades determines that the stirring effect is relatively concentrated on the two-dimensional level, and can only form unidirectional laminar flow. Due to the shape of the structure, it is difficult to stir uniformly, and it is easy to form a dead angle of stirring.In order to change the current situation of large energy consumption and low efficiency of the traditional underwater mixing machinery, we must first break through the structural form of the impeller; we use the working principle of the washing machine pulsator and absorb the technology of foreign counterparts. , Successfully developed a hyperboloid mixer with independent intellectual property rights, and has applied for a national patent, filling the gap in the domestic production of this product, becoming the preferred product to replace imports.The first batch of products has been put into operation in Beijing Gaobeidian Sewage Plant and Shanghai Wusong Sewage Plant.Through practice, we have a rough understanding of the working principle of the hyperboloid impeller. Now we have summarized the following points, and are willing to share with colleagues, and use this to try to improve the technical level of special equipment for water treatment in China.

2 Working principle

The unique impeller design perfectly combines the fluid features and mechanical movement to the maximum degree.The curved surface of hyperboloid impeller is shaped by the curve of formula xy=b rotating around y axis; in order to cater to the water flowing, the impeller is designed to feed water from the center, on one hand, the turbulent flow is reduced, on the other hand, the pressure of the liquid on the impeller surface is equal and even, therefore the machine will be balanceable in the move ment status.

Eight guide vanes are equally distributed on the involute dual cambered surface. The kinetic energy is created with help of the potential energy from the supplementary water fed by the deadweight pressure of the fluid and the centrifugal force by the impeller rotating; the fluid will move along the tangent of the impeller circumference under the condition of acceleration of gravity, with reflection of the pond wall, a circulating water flow is formed from bottom to top, therefore the cross-water flow is fonned in the direction of axial Y and radial X. The structure features and special installation mode (in the bottom of the pond) of the hyperboloid mixer impeller decided the ideal mixing effectiveness, and effectively avoids mixing dead spots. 

3 Structure type

The hyperboloid impeller is composed of two parts, the upper part is the flow guide part, and the lower part is the stirring and mixing part (Figure 1).Multiple agitating wing ribs (wave wheels) are evenly distributed along the circumferential direction near the edges of the hyperbola,The protrusion can be a small blade shape or other special-shaped boss shape that is straight or involute in the radial direction, and its main function is to agitate the water body, so that the water flow is thrown from the center to the surroundings along the bottom surface, causing the entire water body to flow around the stirring axis. 

The hyperboloid impeller mixer consists of a power part, a hyperboloid impeller and installation accessories. In order to meet the requirements of different working conditions, we divide the hyperboloid mixer into dry (vertical shaft) and submersible type according to the installation method Species .

Figure 1 is a dry installation. The reduction motor is positioned above the pool through a bridge, and the transmission shaft transmits power to the underwater hyperboloid impeller. The length of the transmission shaft depends on the depth of the pond. Generally, the impeller is about 300 mm from the bottom of the pond.

1.jpg

Figure 1

Figure 2 is a submersible installation, which consists of a submersible motor, a hyperboloid impeller and a lifting attachment. The use of a submersible motor relies on the device's own weight to position it without additional fixtures.

2.jpg

Figure2

4  Working characteristics

This type of hyperboloid impeller is not only suitable for round pools and square pools, but it is also more commonly used in the arrangement of cells in rectangular pools.

In China's existing sewage treatment process, the stirring process mainly uses an underwater mixer to horizontally stir, the impeller is three or two blades, and the flow is pushed in one direction, which is prone to mixing dead angles;The aeration process mainly uses an underwater propeller and an underwater aeration pipe, and the water-air mixing effect is not good.The hyperboloid stirring impeller can overcome its shortcomings and make use of its advantages of uniform stirring. The main characteristics are shown in the following aspects:

a)It can be used in the occasion where various liquids are mixed with solids and gases. It can  replace the existing stirring equipment to achieve three-dimensional, spiral mixing and even mixing, and improve the stirring efficiency.

b)Large specific area impeller has small power equipment, large circulating water flow and  low energy consumption.

c)The whole machine has a compact structure, reliable operation and convenient installation and maintenance.

d)The impeller is made of reinforced fiber or steel material, which can adapt to different working conditions and has a long service life.

e)Application prospects.