The Construction And Theoretical Analysis Of Hypothermia Multi-Stage Evaporation Concentration NaOH Solution Based On Heat Pump

The waste water of printing, dyeing and paper factory contains a small amount of NaOH. Usually, it is discarded in the environment directly, which not only pollutes the environment, but also wastes NaOH. Combining heat pump technology and concentrating NaOH solution is a excellent way to recycle factory waste liquid, which has the effect of energy-saving and environmental protection. A few scholars both at home and abroad make the research of concentrating NaOH solution based on the heat pump system, but they did not consider the impact of NaOH solution bubble point along with the concentration. According to the characteristics of the NaOH solution bubble point meeting dulin’s rule, this paper has make research of two kinds of heat pump to multi-stage evaporate concentration NaOH solution. They are multi-stage evaporation concentration NaOH solution based on mechanical vapor recompression heat pump and hypothermia multi-stage evaporation concentration NaOH solution based on refrigerant heat pump.According to the characteristics of compressing water vapor, Multi-stage evaporation concentration NaOH solution based on mechanical vapor recompression heat pump adopts roots blower as the compressor, which solves the restriction of small compressor pressure ratio and NaOH solution bubble point leading to problems, which increases along with the higher concentration. It adopts multi-stage evaporation concentration NaOH solution stlye, and evaporates of atmospheric pressure in the first level system, evaporates of low voltage in the secondary system. This paper deals with the system of material and heat balance, making sure the system can be implemented, and use an primary energy utilization factor to show system energy-saving effect. But this system evaporation temperature is too high, which may cause stress corrosion of steel equipment, namely"alkali brittleness", and this can affect the safe operation of the system. In order to avoid the harm, this paper proposes a scheme of hypothermia multi-stage evaporation concentration NaOH solution based on refrigerant heat pump. The pressure of concentrating NaOH solution (water evaporation) process is proportional to temperature, so it can realize concentrating NaOH solution at low temperature based on refrigerant heat pump cycle. In the traditional loop heat pump, refrigerant steam saturation temperature in the condenser tube is about 40℃, By adjusting the heat pump evaporation temperature, the NaOH solution concentration process pressure is reduced, so that the bubble is less than 40℃, realizing concentrating NaOH solution at low temperature. However, as the evaporation going on, the concentration is higher, and temperature difference between NaOH solution and refrigerant vapor decreases gradually, which will slow the progress of evaporation concentration, even can lead to the stop of evaporation. In order to solve the above problems, this evaporation concentration NaOH solution system can be divided into two stages, in low and high concentration of NaOH solution evaporator, respectively. The pressure of high concentration NaOH solution evaporator is lower than low concentration NaOH solution evaporator, which can guarantee that solution exporting bubble point of two NaOH solution evaporators is same, and the bubble point are lower than the refrigerant vapor in the condenser pipe. It considers the difference between refrigerant condensing temperature and NaOH solution bubble point, which guarantees the NaOH solution evaporates effectively and reliably.As NaOH solution evaporator is one of the most important parts in the system, how to evaporate to the specified concentration stably and fast is the key to the concentration system basing on heat pump, so this article analyses the process of the evaporation concentration in Aspen Plus with a combination model of exchanger (HeatX) and flash (Flash2). This simulation adopts a method of ELECNRTL in simulating the process of NaOH electrolytical aqueous solution evaporates water vapor. Basing on the simulation of evaporation concentration process,we use the Aspen Plus to simulate system, and calculate the compressor power consumption, thus the COP of heat pump system is obtained. The simulation results are compared with the thermodynamic calculation result. By comparing the thermodynamic parameters of NaOH solution obtained from the electrolytical property method in Aspen Plus and the enthalpy-concentration map of NaOH saturated solution respectively, we analyses the source of deviation in the simulation, and points measures to further improvement.