| Abstract |
lnvestigation on the behavior of non-condensible gases in the cooling water circuit of Mindanao-7 power station was done using computer modeling. The power station utilizes the direct contact condenser in condensing the steam. The program used in the simulation work is CNOSR. Different scenarios were modeled to determine the effects of (7) steam compositions on the pH and the concentration of dissolved H2S on the condensate at the tuhine outlet and (2) H2S oxidation on the pH of circulating water and the amount of NaOH required to neutralize the acid generated. The predicted chemistries of the cooling water circuit were also compared with measured values. The results showed that the pH of the lquid at the turbine outlet is primarily controlled by the amount of H2S and NH3 in the steam. Both NH3 and H2S gases in the steam show a linear #/8tbnShip with the concentration of dissolved H2S in the condensate, though the change in the concentration of dissolved H2S is more sensitive to the amount of NH3 than the amount of H2S gas. Oxidation of more than lU96 of the dissolved H2S in the cooling water circuit gave unacceptable pH value of 4.50 in the hotwell fluid. In this case, remedial action like NaOH dosing or biocide treatment is necessary. The calculated dosing rates of NaOH are 14, 29 and 72 ghg steam-hour needed to neutralize the acid generated from 5, 70 and 30% oxidation of dissolved H2S in the cooling water, respectively. The concentrations of dissolved H2S in the condensates at various parts of the cooling Circuit remained the same at all levels of HS oxidation due to large supply of H2S coming from the vaporphase. The level of H2S oxidation in the acfual cooling water circuit of the power station is close to 30% based on fhe similarity of the analyzed concentrations of SO4 to the C8lcuIated values. |