Main factors affect the Normal operation of EDI system

I. The Conductivity of Feed water

Under the premise that other conditions remain unchanged, if the conductivity of feed water increase to exceed the certain range, the working area of EDI module will move downward, even the regeneration will disappear to penetrate the working area, most of the filled resin in the module will be in the saturated state to lose effectiveness. Meantime the ion concentration in the water increase, when the voltage is constant, the current increase so the process of ionizing water is weakened.

II. The Flow rate of Feed water

Under the condition of constant product water capacity of the EDI system, the worse the feed water quality, feed water capacity should be adjusted to be smaller. When turn on the system, should note that the instantaneous flow if too large will cause perforation of the module.

Because the electron flow in the module mainly transfer by the filling resin, so the current of concentrated water has become a key to affect the electric current in module. Thus decrease the concentrated water capacity and help to improve the current of the system to improve product water quality. However, the flow of concentrated water should not be as small as possible. When the flow of concentrated water is too small, the concentration difference between the two sides of the module will be greater to affect the product water quality and affect the normal operation of the system.

III. The pH value, temperature and pressure of Feed water

1) The pH value of feed water indicate the H+ concentration of feed water,it should be control as 5-9.5. Normally low pH value cased by the dissolution of CO2. CO2 is also one factor which cause the water quality become worse, so before the water entering EDI module can consider to install the device to remove CO2 and control its content to lower than 5mg/L. There is a certain dissolution relationship between pH value and CO2 in water. Theoretically, when pH value of feed water > 10, the removal efficiency of CO2 is the best. High pH value can help to remove weakly charged ions, but should remove Ca2+ and Mg2+ ions before the water entering the EDI module.

2) The temperature of feed water has a direct impact on the system pressure and product water current. Normally the feed water temperature should be controlled between 5-35℃, the optimal temperature should be about 25℃. The decrease of temperature will reduce the activity of water so the viscosity of water will increase to cause the system pressure increase.

3) Normally when product water pressure> concentrated water pressure> electrode water pressure, can effectively prevent the phenomenon of concentrated water to contaminate the product water. The change of pressure is also effective method to judge whether the module has been contaminated. When the inlet and outlet of concentrated water pressure increase, the concentrated water pipes might be blocked, so will need to clean pipes to lower the pressure difference. Thus in the inlet part of the EDI module, should ensure that the pollution index of inlet water is in the qualified range.

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