Civil Engineering Reference
In-Depth Information
Availability of electric power must also be taken into account because of
the relatively high power needed, in comparison with that required by
the whole site (roughly 1 t of steam per hour corresponds to 0.8 MW of
electric power).
6.5.5 Oil Boilers
Oil and other organic fluids can be used as the heating medium to transfer thermal
energy to end users for particular process demands (presses, dryers, ovens, etc.).
Steam can also be generated outside the boiler by means of a hot oil/water vapor
exchanger.
Forced circulation of oil is implemented by electrically driven pumps inside the
tubes while flue gas is outside. The pumps' electric power and related energy
consumption are relevant, although they are not included in the calculation of boiler
efficiency (see Sect.
6.7
).
Care must be taken to limit temperature peaks throughout the circuits, particu-
larly if there is a power outage and pumps are switched off. Maximum temperatures
of heating medium fluids are roughly 573-623 K (300-350
C; 572-662
F).
Steam, usually at low pressure, is produced by heat exchangers outside the boiler
itself.
Local regulations may accept for this system a lower control level, in both
personnel and instrumentation, because there is no direct contact between flame
and pressurized equipment.
6.6
Technical Parameters of Industrial Steam Boilers
The main parameters used to qualify any industrial boiler are as follows:
• Fuel type and rated consumption per hour;
• Temperature of cold feedwater and condensate;
• Temperature of combustion air;
• Flow of steam expressed in kg/h or t/h;
• Output steam pressure;
• Temperature of saturated or superheated steam;
• Temperature of flue gases from the stack;
• Design pressure which all parts of the boiler must resist. This value is generally
10 % higher than the steam pressure;
• Useful output (generally in the form of steam or hot water) expressed in kW
(or practically t/h of steam).
It follows that:
useful output k
ðÞ¼
m
ð
h
h
0
Þ
where
m
¼
steam flow-rate in kg/s,
h
¼
enthalpy of the output steam in kJ/kg,
h
0
¼
enthalpy of the input water or condensate in kJ/kg.
