Flue Gas Calculation | First Law of Thermodynamics | Energy Conservation


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Document Category Engineering
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Flue Gas Calculation

Excess air % can be calculated if O2% or CO2% in the exhaust is known (measured)
If in addition to O2% or CO2% the flue gas temperature is known, the flue gas losses can be calculated.

Charts exist to obtain % excess air and % flue gas losses if O2% or CO2% and flue gas temperature are known
Obtaining % flue gas losses, combustion efficiency ηc can be calculated as (100-% flue gas losses).

Each type or (category) of fuel would have its own chart
Charts are usually based on ambient temperature Ta of 20°C.
If Ta is different from 20°C, correction for the flue gas temperature Tfg, should be introduced, accordingly: Tfg, corrected= Tfg- [Ta-20]

First Law of Thermodynamics

It is the law for conservation of energy which means the energy cannot be created or destroyed but it can be changed from one form to another. It is the basis for energy balance.

The law states that: “The net increase in the energy content of a particular system in a given period is equal to the energy content of material leaving the system, plus the work done on the system, plus heat added to the system”. Systems are divided into closed system and open system.

A closed system where there is no mass crossing the boundary of the system (piston engines, and so on).
Open system; where mass as well as energy crossing the boundary. Such as turbine (gas or steam), boiler, pump, etc.
PV work: is known as the flow work.
H: Enthalpy which is the summation of the internal energy and the flow work.

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