Enhancement of mixing efficiency in mechanical stirring reactors via chaotic stirring techniques: Application to the treatment of zinc-containing solid waste

Numerical and experimental investigations on enhancement mixing performance of multi-blade stirring system for fluids with different viscosities

The poor mixing caused by zinc powder deposition in purification process is a serious problem which can’t be avoided in treatment of zinc-containing solid waste. Here, to enhance the purification efficiency of zinc-containing solid waste treatment reactor, two kinds of multi-blade combined stirring systems are compared with single layer four straight-blade and double-layer straight-blade (DFB) stirring systems which are traditionally chosen by industry. This study simulated and explored the flow field characteristics and purification effects of these four kinds of stirred-tank reactor, further proposes the unit ion purification energy (UIPE) as a criterion for purification energy consumption and effect evaluation. The results show that multi-blade combined (MBC) stirring system enhances axial flow by 12.56% in water. Meanwhile it effectively inhibits the growth of isolated mixing region which scope has decreased by 56.25%. In high viscosity Carboxymethylcellulose sodium solution, the fluid axial speed can be increased by up to 1407 times with MBC. MBC can increase the purification rate by 24.79% while the UIPE decreases by 29.45% compared with DFB which is used in industrial purification process. MBC paddle has exhibited a wide range of fluid viscosity applicability and axial velocity improvement effect. The improvement increases collisions between the impurity particles and the zinc powder particles, which increased rate of substitution reactions. The application of MBC solves the purification problem in the process of treating zinc-containing solid waste.

Enhanced mechanical stirring by eccentric impeller stirring system in zinc hydrometallurgy process for cadmium removal

The fluid in the reactor can be poorly mixed, so an eccentric impeller is proposed to improve the fluid mixing efficiency. In this investigation, numerical simulations and cadmium removal experiments for the purification of zinc sulfate solution were conducted. The effect of eccentric impellers on the purification efficiency was discussed. The mechanism of the effect of concentric and eccentric arrangement of stirring impellers on mixing in the stirred tank was elucidated. The results showed that the average axial velocity of the eccentric impeller stirring system (EIS) was 131.52% of that of the concentric stirring system (CS) and 134.23% of that of the eccentric stirring system (ES). In the purification and removal of cadmium in the zinc hydrometallurgy experiment, unit ion purification energy was introduced to quantify the energy consumed for each 1% of Cd2+ removed. The eccentric impeller shortens the reaction time by 40% and reduces the reaction energy consumption by 31.8% compared to the non-eccentric impeller. Compared to CS and ES, EIS disrupts the periodicity of fluid flow and facilitates the destruction of isolated mixing regions. EIS can enhance mechanical stirring to improve purification efficiency.

Functional waveform pulse variable speed stirring to improve mechanistic analysis and experimental study on the purification efficiency of zinc sulfate solution

This paper builds a wireless precision control function waveform pulse variable speed stirring device with point-to-point data transmission between the host computer and the microcontroller, which uses a programmable STM32 microcontroller as the system controller, superimposed with a single closed-loop static differential-free speed control system and a pulse broadband modulation (PWM) system to control the DC brush motor driving the stirring paddle based on arbitrary waveform function variable speed stirring respectively. The effects of different pulse waveform stirring systems on the purification effect of Cadmium ions (Cd2+) from zinc sulfate solution were studied under the same pulse period and maximum speed. The experimental results show that when K P = 0.012 and T i = 100, the anti-disturbance of the motor during the variable speed stirring process can be effectively improved, and the speed adjustment time is short and robust; when the Cd2+ purification rate reaches 92%, the purification time of the variable sine function stirring system is shortened by about 40% compared with that of the uniform speed stirring system, and that of the variable trapezoidal function stirring system is shortened by about 33.3% compared with that of the uniform speed stirring system. When the reaction is finished, the Cd2+ concentration is reduced to 6 mg/L by the variable sinusoidal stirring system only, and the Cd2+ concentration is lower than 10 mg/L in a shorter time compared with the time required for cadmium removal in the actual industrial production line.