Why do flue gases leave the stack at high temperature?

Why do flue gases leave the stack at high temperature?

The combustion flue gases inside the flue gas stacks are much hotter than the ambient outside air and therefore less dense than the ambient air. That causes the bottom of the vertical column of hot flue gas to have a lower pressure than the pressure at the bottom of a corresponding column of outside air.

How do you calculate flue gas flow rate?

For light fuel oil the formula is: VGod = 1.76435 + 0.20060 H(N) (m3/kg) and for natural gas: VGod = 0.64972 + 0.22553 H(N) (m3/kg) or, using the volumetric net heating value at 0°C: VGod = 0.199 + 0.234 H(N) (m3/m3).

How does flue gas stack work?

Air rising through the flue gas stack is hotter and less dense than air outside the structure, so its pressure is lower. The air pressure being higher outside forces the air and gases upward and out the top of the chimney, in a process referred to as natural draft or stack effect.

What is the dew point of flue gas?

The acid dew point temperature depends on the levels of reactants present in the flue gas. It generally lies in the range 100-150°C.

Why are stacks painted red and white?

Generally, the towers must be painted intermittently in white and red/orange to make them visible during the day, with paint tones (including white) specifically and precisely mandated by the federal regulations.

How is flue gas measured?

Some of the analyzers use infrared meters for accurate reading and data, while others measure the electrochemical data of gas, but both of them are perfect to use. The probe model is most popular among people, a flue gas analyzer does not necessarily require the use of a probe to monitor the gas in the flue.

At what temp does flue gas condense?

around 135°F.
Flue gas will form and condense on a heat exchanger and in the boiler stack when it falls below its dew point, and this occurs when the return water temps of the system are around 135°F.

What is the formula for dew point?

Td = T – ((100 – RH)/5.) where Td is dew point temperature (in degrees Celsius), T is observed temperature (in degrees Celsius), and RH is relative humidity (in percent). Apparently this relationship is fairly accurate for relative humidity values above 50%.

What is stack temp?

“Stack temperature” or flue gas temperature measures the temperature of the combustion gases when they leave the boiler. If the flue gas temperature is high, it suggests the heat created by the boiler isn’t being effectively used to generate steam.

What is the difference between a stack and a chimney?

When you think of a chimney, you may picture the brick structure on top of a roof, but that is actually known as the “stack”. The chimney stack is the part that is above the roofline.

How is flue gas discharge through the chimney?

How is flue gas discharged through the chimneys? Explanation: After extracting maximum possible heat by circulating the flue gas in furnace. Induce draught fan is used to remove the left over gas via chimney. This is located near the base of the chimney.

How do you calculate pressure drop?

Pipe flow pressure drop. The pressure drop in circular pipes is calculated using Darcy-Weisbach equation: The flow is considered laminar when Re<2300. In a laminar flow the friction factor f is calculated by f=64/Re.

What is a good flue gas reading?

Generally when this level is below 0.004 the boiler is considered to be running efficiently. When between 0.004 and 0.008 this indicates a potential problem and investigation and retesting must take place. When above 0.008 the appliance must be fully investigated, cleaned and retested.

What percentage of CO is acceptable in a sample of the flue gas?

The production of carbon monoxide (CO) in the flue gases should be kept below 100-ppm air-free, even though the allowable limit in the stack is 400-ppm air-free.

Why is the pressure inside a flue gas stack low?

The combustion flue gases inside the flue gas stacks are much hotter than the ambient outside air and therefore less dense than the ambient air. That causes the bottom of the vertical column of hot flue gas to have a lower pressure than the pressure at the bottom of a corresponding column of outside air.

How does a pressure gauge work in a gas stack?

The gauge dials move clockwise with increasing pressure. The stack effect in industrial flue gas stacks is similar to that in buildings, except that it involves hot flue gases having large temperature differences with the ambient outside air.

How does the flue gas move up the chimney?

That causes the bottom of the vertical column of hot flue gas to have a lower pressure than the pressure at the bottom of a corresponding column of outside air. That higher pressure outside the chimney is the driving force that moves the required combustion air into the combustion zone and also moves the flue gas up and out of the chimney.

What are flue gases?

Flue gases are produced when coal, oil, natural gas, wood or any other fuel is combusted in an industrial furnace, a power plant’s steam-generating boiler, or other large combustion device. Flue gas is usually composed of carbon dioxide (CO 2) and water vapor as well as nitrogen and excess oxygen remaining from the intake combustion air.