Device 1. Electric Motor =2. Home Oil Furnace = 3. Home Coal Furnace =4. Steam Boiler (power plant) =5. Power Plant (thermal) =6. Automobile Engine =
Efficiency(%)
90
65
55
8936
25
A coal-fired thermal power station.
1. Cooling tower. 6. Boiler drum2. Electric generator (3-phase). 7. Superheater3. Condensor. 8. Economiser 4. High pressure turbine. 9. Air preheater 5. Feed heater 10. Chimney Stack.
CRITICAL CONDITION IS THERMODYNAMIC
EXPRESSION DESCRIBING THE STATE OF A
SUBSTANCE BEYOND WHICH THERE IS NO
CLEAR DISTINCTION BETWEEN THE LIQUID
AND GASEOUS PHASE
DEFINITION OF CRITICAL CONDITION
WHAT IS SUPERCRITICAL PLANT
The power plant which operates above the critical condition is a ”SUPER CRITICAL POWER PLANT
Water reaches to this state at a critical pressure above 22.1 MPa and 374 oC.
Rankine Cycle Supercritical Unit
8
1 - 2 > CEP work
2 – 2s > Regeneration
2s - 3 > Boiler Superheating
3 – 4 > HPT expansion
4 – 5 > Reheating
5 – 6 > IPT & LPT Expansion
6 – 1 > Condenser Heat
rejection
This advanced technology for power generation
Higher Efficiency, Clean, Safe Overall Environment
The development of coal fired supercritical power plant technology can be described as an evolutionary advancement towards greater power output per unit and higher efficiency.
Sub-Critical vs Super CriticalSub-Critical vs Super Critical
Description Sub Critical Super Critical
Full Load Pressure <190 atm >240 atm
Flow in Water wall 2-Phase 1-Phase
Cycle efficiency Base + 2 - 3 % Approx
Fuel saving Base +8 - 10 % Approx
Boiler weight Base + 10 %
Stages of reheat 1 2 Preferred
Supercritical power plants are highly efficient plants with best available pollution control technology, Reduces existing pollution levels by burning less coal per megawatt-hour produced, capturing the vast majority of the pollutants. Increases the kWh produced per kg of coal burned, with fewer emissions.
WHY ADVANCED SUPERCRITICAL
• Efficiency of the Rankine Cycleincreases with increasing Turbine inletTemperature and Pressure
• Cycle efficiency of typical sub-criticalplant is 38% whereas today’ssupercritical technology increases thisto around 45-47%
Coal-fired Supercritical Power plants operate at very high temperature [580°C temp.] & with a pressure of 23 MPa)
Resulting much higher heat efficiencies (46%), as compare to Sub-Critical coal-fired plants.
Sub-Critical coal-fired plant operates at 455°C temp., and efficiency of within 40%.
Supercritical & Ultra-Supercritical Power Plants
BENIFITS: High Thermal Efficiency Environment Friendly Lower fuel cost per unit of power Run-of-Mine Coal can be directly used
Weaknesses: Materials Limitation High levels of corrosion Increased supervision and maintenance
costs Limited scope for retrofitting
opportunities
Supercritical & Ultra-Supercritical Power Plants
CONCLUSION The current state-of-the-art for coal-fired supercritical
steam cycles is –600C/300 bar maximum steam conditions, with a net thermal efficiency of about 45% (LHV, based on UK inland conditions). 620C plant are expected within five years while, in the longer term (10-20 years). 650-700C is expected, with resulting cycle efficiencies in the range 50-55%.
Materials limitations are the major factors limiting further development, with key constraints at the furnace wall, superheater and reheater outlets, and the first stages of the HP and IP turbines. Considerable materials R&D is under way in Europe, Japan and the USA.
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