The calculation of carbon dioxide concentration in steam condensate |

Steam condensate is corrosive due to the presence of carbon dioxide in it. As a rule, the concentration of carbon dioxide in the condensate is required to be less than 20 mg/l.

The concentration of carbon dioxide in the condensate can be easily determined by knowing the concentration of bicarbonate ion in the feed water and the share of decomposition of bicarbonate in the thermal deaerator and then in the steam boiler.

Carbon dioxide in the condensate appears due to the fact that in a steam boiler, bicarbonates decompose to form hydrate and carbon dioxide. Carbon dioxide is carried away with steam and then passes into condensate.

Thus, if we assume that all bicarbonate is decomposed in the boiler, the concentration of carbon dioxide in the steam will be equal to the concentration of bicarbonate in the feed water in mg-EQ/l.

However, the bicarbonate in the boiler does not decompose completely. It is assumed that the percentage of bicarbonate decomposition in the boiler depends on the pressure in the boiler. Indeed, it can be assumed that the greater the pressure is in the boiler, the more intense the removal of carbon dioxide with steam is and the more complete the decomposition of bicarbonates is.

In fact, to a much greater extent, the complete decomposition of bicarbonates in the boiler is affected by the coefficient of evaporation of boiler water and the value of the alkalinity (hydrate) for phenolphthalein of boiler water.

The fact is that the higher the coefficient of evaporation of boiler water, the longer the temperature effect on 1 liter of feed water of the initial ionic composition is. That is, if the water volume of the steam boiler is 10 m3, the steam capacity is 5.0 t/h and the salt content of the boiler water is 3000 mg/l, then the ionic composition (equal to 200 mg/l) entering the boiler with 1 liter of feed water will be subjected to thermal effect for 30 hours!

That is   (3000/200)*(10/5)=30 hours

During this time, bicarbonate can almost completely decompose.

full version -