A calorifier is a heat exchanger which heats water indirectly by circulating is over a heating coil or multiple coils. The source of heat can be water or steam, heated by an external heat source, contained within a pipe immersed in the water. the two bodies of water or steam do not mix. (touch each other)
In hospitals and factories where steam is already being generated for other uses is can also be used to heat the water by the indirect method.
The calorifier may be a continuous coil of pipe or a cylinder within a cylinder with an annular space between the two vessels.
With the vertical hot water cylinder, the steam enters the coil though the top connection. the strainer or grit trap removes any solid matter suspended in the steam. The steam then passes through the inlet valve which is thermostatically controlled. the thermostat prevents overheating or boiling of the stored water.
A steam trap, fitted near the outlet of the coil, prevents the steam from leaving the coil until is condenses.
In a hot water cylinder which contains a steam coil, the coil must be able to be removed for descaling. this is more likely to occur using steam because the coil is working at a higher temperature than with the conventional hot water system.
An economiser is a mechanical device which is used as a heat exchanger by preheating a fluid to reduce energy consumption. In a steam boiler, it is a heat ex-changer device that heats up fluids or recovers residual heat from the combustion product i.e. flue gases in thermal power plant before being released through the chimney. Flue gases are the combustion exhaust gases produced at power plants consist of mostly nitrogen, carbon dioxide, water vapor, soot carbon monoxide etc. Hence, the economiser in thermal power plants, is used to economise the process of electrical power generation, as the name of the device is suggestive of. The recovered heat is in turn used to preheat the boiler feed water, that will eventually be converted to super-heated steam. Thus, saving on fuel consumption and economising the process to a large extent, as we are essentially gathering the waste heat and applying it to, where it is required. Nowadays however, in addition to that, the heat available in the exhaust flue gases can be economically recovered using air pre-heater which are essential in all pulverized coal fired boiler.