The Study On The Technics Of NaOH Feed Continously In Equilibrium Phosphate Treatment

Equilibrium phosphate treatment(EPT) is used firstly in industry at the end of 1980'S,and then it is regard as water quality standard by EPRI. At a rough estimate, there are hundreds of boilers adopted the style of EPT at present in the world . In the past twenty years ,there happened no problems for lots of boilers about phosphate hideout.Only Na₃PO₄ is injected into boiler water in EPT, and a few free NaOH is permited to exist, so the value of pH is master of Na₃PO₄ and NaOH together. The boilers adopted the style of EPT may be permited to supply NaOH with rations.There are two ways to inject NaOH to boiler water : continuous feed and discontinuous feed . Discontinuous feed is the way which adjusts the value of pH to the stated scope by feeding NaOH when the value of pH is lower than the the stated standard and the concentration has been most; Continuous feed is the way which adjusts the value of pH to the stated scope by feeding NaOH and Na₃PO₄ together in proportion.The mathematics model which describes the relations between the concentration of Na₃PO₄ , NaOH and NH3 in boiler water and the value of pH is educed by analyzing the component chemistry balance each other. The data is calculated by the model and is used to draw the chart to show the relation .The action and interaction of the value of pH casued by the concentration of Na₃PO₄ , NaOH and NH₃ in boiler water is analyzed by analyzing reason experimentation. The interaction in low concentration is not more prominent than the action respectively .So the value of pH should be adjust by controlling the concentration of Na₃PO₄ , NaOH and NH3 respectably in the steam drum which runs EPT. By the analog experimentation of the ratio of Na₃PO₄ and NaOH in the laboratory, the conclusions as follows are drawn : Buffer action will reinforce when the value of pH of boiler feed water is controlled between 9.1 and 9.3. the concentration of Na₃PO₄ in boiler water may be 0.5mg/L¹.0mg/L and the ratio of the quality between NaOH and Na₃PO₄·12H₂O may be 1∶ 50-5∶ 50, and then the value of pH should be 9.1-9.5. The calculationalformula of the concentration of Free NaOH is educed and a new calculational methods also come into being accordingly. This methods is simple and prone to apply .It can adapt the calculation in the EPT and the result is in accord with the other reported data. Finally, the distribution of the phosphate component in boiler water is analyzing and Na2HPO4 is the main existent form when the value of pH is 9.0-10. Here the action of phosphate is equivalent to NaOH .