TECHNICAL
CETHAR LIMITED
Types of boilers
Sub critical boilers
Drum type natural circulation boilers
Drum type controlled circulation boilers
Once through boilers
Super critical boilers
Once through boilers
CETHAR LIMITED
Evaporator systems
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Design Criteria
Description
OT Super critical
Sub-Critical
Furnace sizing
Decided by Fuel and Gas side parameters Same
Evaporator
Supercritical fluid;
Variable evaporation end point; Superheated steam at evaporator outlet;
Water and Steam mixture;
Fixed evaporation end point;
Saturated steam at evaporator outlet (Supported by BENSON
Technology)
Natural / controlled circulation
Drum
Replaced by smaller
Separators and collecting vessel. Required only during low loads (about 35-40%)
Required for water and steam separation at all loads
Start up and low load circulation system Required.
(Supported by BENSON
Technology)
Not applicable
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Design Criteria
Description
OT Supercritical
SH and RH sizing
Same for both sub critical and supercritical
Economiser
Same for both sub critical and supercritical
Pulveriser sizing
Same for both sub critical and supercritical
Fans. RAPH & ESP and ducts and Same for both sub critical and supercritical
Controls
Feed water flow is controlled based on load
SH steam temperature is controlled by spray followed by firing rate.
Feed water flow is controlled by drum level.
SH outlet temperature is maintained by spray.
Water treatment and water chemistry AVT and Oxygenated water treatment (mandatory)
Generally AVT
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Sub-Critical
Furnace Design
FEGT = IDT - 50 K
FEGT = Furnace exit gas temperature
IDT = Initial deformation temperature of ash
Furnace design and size are decided by coal and ash quality
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Evaporator wall design
Key Issues
Heat absorption