Super Crit Boilers

TECHNICAL PRESENTATION
TECHNICAL

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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

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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