To prevent flue gas leakage from the furnace of a packaged watertube boiler, what is used?

The correct answer involves the use of a steel casing to form a seal for the furnace in a packaged watertube boiler. This steel casing plays a critical role in containing the flue gases produced during combustion. By providing a robust barrier around the furnace, it prevents any leakage of flue gases into the surrounding environment, ensuring both safety and efficiency in the operation of the boiler.

Sealing the furnace is essential for maintaining the proper pressure and temperature balance within the system, which contributes to optimal combustion processes and energy recovery. Additionally, by minimizing flue gas leakage, the boiler can achieve better fuel efficiency and reduced emissions, aligning with environmental regulations and safety standards.

Other options, while related to boiler operation, do not specifically address the prevention of flue gas leakage. Induced draft fans, for instance, are primarily designed to enhance airflow and ensure proper combustion but do not directly seal the furnace. Similarly, taller smoke stacks are meant to disperse emissions effectively but do not prevent leakage within the boiler itself. An economizer is used to recover waste heat from flue gases to improve efficiency but does not serve as a sealing mechanism. Thus, the use of a steel casing is the most direct and effective method for preventing flue gas leakage from the