The number of heat exchangers in a firetube boiler does not directly correlate with its tonnage rating. The tonnage rating of a boiler refers to its cooling capacity, specifically the amount of heat it can remove in one hour. It is not directly related to the number of heat exchangers.
Firetube boilers typically have a single heat exchanger, which is the shell and tube configuration inside the boiler. In a firetube boiler, the heat exchanger consists of a large cylindrical shell with multiple tubes running through it. Hot gases produced by the combustion process flow through these tubes, transferring heat to the water surrounding them. This heat transfer process occurs within a single heat exchanger unit.
While firetube boilers generally have a single heat exchanger, there may be variations depending on the specific design or modifications made to the boiler. However, without further information on the specific model or design of the 2-ton firetube boiler in question, it is challenging to provide a more precise answer.