In the gas recirculation arrangement, what is the purpose of introducing gas back into the furnace?

Introducing gas back into the furnace in a gas recirculation arrangement serves the primary purpose of maintaining steam temperature at lower loads. When gas is recirculated, it helps maintain a consistent temperature and improves the efficiency of the combustion process. This is especially important during periods of lower load demand, where maintaining adequate steam temperature is crucial for ensuring system performance and stability.

By recirculating the hot gases, the furnace can effectively use the residual heat, thereby creating a more efficient heat transfer process without requiring additional fuel. This not only optimizes operation but also aids in controlling emissions by promoting better combustion conditions. The technique enhances thermal efficiency, allowing for the maintenance of steam production without the need for significant increases in fuel input.

In contrast, the other options relate to negative or unrelated outcomes. Producing more pollution would not be a goal of any efficient combustion system. Reducing furnace size may be a secondary benefit in certain designs but is not the main function of gas recirculation. Lastly, increasing the gas emission rate contradicts the intent of achieving cleaner, more efficient combustion. Therefore, maintaining steam temperature at lower loads through gas recirculation is the intended and beneficial outcome of this arrangement.