Final answer:
The presence of 7 to 9 percent CO2 in flue gas reflects a heating unit's efficiency and combustion completeness, with higher CO2 percentages indicating more complete combustion. It also highlights the environmental impact of the heat released to the surroundings and the need for efficient use of the produced energy.
Step-by-step explanation:
The presence of 7 to 9 percent CO2 in flue gas signifies certain aspects of a heating unit's performance. A furnace converts the chemical energy stored in fuel into heat, and subsequently, into electricity or other forms of useful power. However, during combustion, not all carbon in the fuel is completely oxidized to CO2; a portion is only partially oxidized to CO. The ratio of CO2 to CO in the flue gas can indicate how complete the combustion process is, impacting the furnace's efficiency.
For coal-burning power stations, typical efficiency is around 42 percent. This number implies that a substantial 59.2 percent of the energy from the fuel is not converted to electricity but is rather transferred as heat to the environment. This heat transfer can have negative environmental impacts, such as warming nearby bodies of water and contributing to global warming. The performance of a heating unit, therefore, not only relies on its ability to produce energy but also on its emission standards and impact on the environment.
Efficiency can also relate to how energy is utilized after production. For instance, direct usage of energy for heating in homes is more efficient than using electricity generated from power plants due to energy losses in conversion and transmission. Flue gas composition serves as a diagnostic tool to evaluate the combustion efficiency and by extension, the overall performance of power generation systems.