Which of the following types of fuel are generally used to fire a large steam generating unit?

Pulverized coal is commonly used to fire large steam generating units due to several operational and efficiency-related reasons. When coal is pulverized, it is ground into a fine powder, allowing it to burn more quickly and completely than larger chunks of coal. This fine particle size enhances the efficiency of combustion, presenting a larger surface area for the fuel to react with air, thus achieving higher heat release rates.

Large steam generating units typically require a high and consistent heat output to generate steam efficiently at the necessary pressures and temperatures for power generation. Pulverized coal systems can accommodate this requirement effectively. Additionally, coal-fired power plants are designed to handle the scale and infrastructure needed for pulverized coal firing, making it a practical choice for large facilities.

In contrast, while natural gas and heavy fuel oil can also be used in power generation, they are generally more suited to smaller units or specific operational contexts. Natural gas, for example, is clean-burning and suitable for combined-cycle systems but may not provide the same kind of thermal inertia required for consistency in large steam plants as pulverized coal can. Heavy fuel oil can be used in some steam generation settings but typically has higher costs and environmental considerations compared to coal fired systems. Wood pellets might be a renewable option but are