What material is used in modern furnaces to form the furnace walls?

The correct answer is that modern furnaces utilize watertubes to form the furnace walls. Watertubes are designed to absorb heat from the combustion process efficiently while simultaneously circulating water through them to produce steam or hot water. This material is particularly effective in handling the high temperatures within the furnace, maintaining the structural integrity of the furnace walls while also serving a functional purpose in heat recovery and steam generation.

Using watertubes allows for better thermal efficiency and safety, as they help manage the high heat loads typically found in furnace operations. Their design facilitates not only heat transfer but also ensures that the system operates effectively and within the required safety standards. This is crucial for the overall performance and longevity of the furnace systems used in various industrial applications.