Explain me the construction & working of Smoke tube oil Fired Package Boiler?

A boiler is a simple Heat Exchanger, the most common design is a large cylinder with tubes running thru the 'shell' and ends which form tanks common to the tube ends...ther are two ways to heat the water in this design- water can be piped through the tubes, with a heat source inside the shell, or, the shell can be filled with water, and a heat source ( flame) can be pulled through the tubes, with the same end result- high pressure steam...Your design is the latter, for cleaning the 'smoke' tubes, most likely. Package Boiler means that it is either fully embled, or may need some simple embly but for the most part, ready to hook up to electricity, and water, and away it goes...KJH