A steam boiler is a closed vessel, strongly constructed of steel,in which steam is generated from water by the application of heat.the generated steam is used for producing power and for industrial work and heating work.the steam boiler is also known as steam generator.
The function of steam boilers or generator is to convert chemical energy of fuel by combustion in to heat and transfer this heat to water and thus to produce steam.
The Indian boiler (amendment)act,2007,no - 49 of 2007 (12th dec. 2007) As per resolution (2) for clause (b)
"boiler" means a pressure vessel in which steam is generated for use external to itself by application of heat which is wholly or partly under pressure when steam is shut off but does not include a pressure vessel,
(i) with capacity less than 25 liters( such capacity being measured from feed check valve to the main steam stop valve)
(ii) With less than one kilogram per centimeter square (1kg/cm2)design gauge pressure (G) and working gauge pressure or
(iii) In which water is heated is below one hundred degree centigrade.
a) A small type boiler generating steam for use external to itself under pressure up to 7 kg./cm² and having a volumetric capacity exceeding 22.75 litters, but not exceeding 500 litters including the volumetric capacity of all pressure parts being heated from the same heating source and connected to the Boiler.
b) A coil type boiler or a once through boiler or a water tube boiler having the conditions specified in clause (a) above expect that -
(i) The limitation of pressure shell be 12 kg/ cm2, and
(ii) The capacity shall be not exceeding 150 litters:
Provided that in case of boilers having combined features of clauses (a) and (b), the working pressure shall be restricted to 7 kg/ cm² and the volumetric capacity of particular pressure parts shall not exceed the limits specified in the respective clauses above subject to an aggregate of 500 litters.
This is decided by application, process parameters and temperature required. If the temperature in the process required below 200° C then steam is the ultimate solution. If the temperature required above 200° C then the thermic. thermic fluid heater is the ultimate solution. However, thermic fluid can be used in close loop only. For direct heating application we need to use steam only.
One kg of steam is equivalent to 26.9 kg of thermic fluid to transfer the same heat. So the steam is more preferable than thermic fluid heater if the temperature is below 200° C.
Please refer our technical information book page no. 33 to 40. Available on the same site. To down load technical information book,contact us for password. it covers lot of information
Using the steam of low pressure for indirect heating reduces the steam required and thus the fuel consumption. This is because of steam pressure decreases the latent heat of steam increases. Most of the energy content of steam is the latent heat of evaporation & in direct heating application the latent heat of evaporation is utilized. The condensate leaves the plant equipments contains sensible heat.
Also to transfer same heat the super heated steam requires more heating surface area compare to saturated steam. Because super heated steam has lower heat transfer coefficient than the saturated steam.