Final answer:
The amount of limestone injected into the furnace does not affect carbon monoxide emissions from a boiler since it's involved in sulfur dioxide removal and not the combustion process.
Step-by-step explanation:
The aspect that does not affect carbon monoxide emissions from a boiler is (a) the amount of limestone injected into the furnace. This is because limestone is typically used in the process of removing sulfur dioxide from flue gases and does not directly influence the formation of carbon monoxide during fuel combustion. On the other hand,
- the amount of combustion air provided greatly affects the amount of carbon monoxide because insufficient air results in incomplete combustion, leading to higher CO levels,
- the time the fuel spends in the furnace can affect how completely the fuel burns, thus influencing CO emissions, and
- the percentage of Carbon in the fuel being used is crucial since more carbon content could potentially lead to more CO generation if not burned completely.
Therefore, it is the limestone that does not have an effect on carbon monoxide production during combustion processes in a boiler.