why cndensation takes place in boiler combustion?

Answer 1

Where I live it is mandatory that new domestic boilers have to be of the condensing type. This means that heat is recovered from the hot exhaust gases to preheat incoming combustion air. The temperature of the exhaust gases is lowered below its dew point and condensation of water (a product of combustion) occurs. There is steam in the exhaust gas. The boiler is considerably more efficient.

Answer 2

Water is a combustion product. As the combustion gases go up the stack you could have condensation inside the stack but that would be pretty rare. Generally the stack temperature is high enough that water vapor in the exhaust does not condense till the exhaust gases hit the cooler aire outside the stack.

Pure water is very corrosive if you have condensation the the exhaust stack you will have corrosion problem. The only thing I can think of is if you have a stack economizer which recovers heat from the exhaust stack you could have some condensation at that point.

Answer 3

If the boiler combustion process burns a hydrocarbon (coal, oil or gas, etc.) oxygen combines with the hydrogen to make water vapor and oxygen also combines with the carbon to make carbon dioxide (or carbon monoxide). If the water vapor reaches a surface cooler than 212F, some water may condense. For example, it is said that burning a gallon of gasoline (a hydrocarbon) in an automobile will produce about a gallon of water (and this appears as water vapor clearly visible on a very cold day!).

Answer 4

Steam Information
Steam is an invisible gas that's generated by heating water to a temperature that brings it to the boiling point. When this happens, water changes its physical state and vaporizes, turning from a liquid into a gas.

Conversely, when heat energy is removed from steam, it loses its ability to retain a gaseous state and condenses back into a liquid. The resulting liquid is called condensate. The temperature at which condensation takes place is known as the dew point.

When water is heated at atmospheric pressure, its temperature rises until it reaches 212°F (100°C), the highest temperature at which water can exist at this pressure. Additional heat does not raise the temperature, but converts the water to steam.

One pound of water takes 1 BTU per Degree of Temperature rise up to 212°F; to form steam, an additional 970 BTUs is required for the "Latent Heat of Vaporization". Therefore, steam has (970 + (212 - Condensate Temperature)) BTUs per pound.

EXAMPLE: If the condensate temperature is 160°F, (970 + (212 - 160)) = 1,022 BTUs per pound. This clearly shows why steam has more energy content than hot water.

Answer 5

It doesn't normally take place there. You'd normally see some condensation in the gasses after combustion, as these cool going out the stack.

Answer 6

At higher pressures steam will condense to water at higher temperatures than 100C. For example using the steam tables water at approx 600psi does not boil until about 240C, therefore it would also condense at 240C as well.

Answer 7

Possibly there is an expansion system that causes rapid evaporation and cooling allowing for condensation.