SUPER CRITICAL TECHNOLOGY

Presented By:Amit Joshi

UPES Dehradun,India

Introduction"Supercritical" is a thermodynamic

expression describing the state of a substance where there is no clear distinction between the liquid and the gaseous phase.

Supercritical Power plants operate at higher temperatures & higher pressure resulting in higher efficiencies i.e., up to 46 percent for supercritical plants and lower emissions than traditional (subcritical) coal-fired plants.

WHAT IS A SUPERCRITICAL BOILER?Supercritical steam generators (also known as Benson

boilers) are frequently used for the production of electric power.

In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3,200 psi/22.06 MPa 3,200 psi/220.6 bar that actual boiling ceases to occur, and the boiler has no water - steam separation.

There is no generation of steam bubbles within the water, because the pressure is above the "critical pressure" at which steam bubbles can form.

It passes below the critical point as it does work in the high pressure turbine and enters the generator's condenser.

This is more efficient, resulting in slightly less fuel use. The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" actually occurs in this device.

WHAT IS SUPERCRITICAL TECHNOLOGY?Above 221 bars, two phase mixtures of water and steam

cease to existThey are replaced by a single supercritical fluid. This eliminates the need for water/steam separation in

drums during operationThus allowing a simpler separator to be employed during

start-up conditions.The transition to steam temperatures of 600°C and higher

is now a further major development step, which decisively affects many aspects of the design of the power plant, especially of the boiler

Critical Point

22.1MPa-373ºC

Special feature of supercritical boilersCapacity to operate under low load. Suitability for continuous variable loads. Suitability for cyclic operations. Suitability for two shift operations. Quicker start up and shut down capability. Larger unit size.

Advantages of Supercritical technology Today supercritical units can achieve thermal

efficiency of more than 45 percent, compared with a typical subcritical plants 30-38 percent.

Higher firing temperatures and pressures translate into better efficiency, defined as more electricity generated per BTU of coal consumed. 

super critical technology will result in saving of about 4% of fuel and correspondingly less emission.

The Benson design offers a number of advantages, including simplified start up and the ability to operate in sliding pressure mode.

“LIMITATIONS” Economy of scale.

Problem with the metallurgical limit .

An increase in steam temperature (>700 C) is possible but without NICKEL based materials it is not possible to obtain more than 10K to 20K.

Double reheating is required to prevent Inlet pressure turbine exhaust wetness

Extremely high initial build cost. More complicated to operate. Much higher O&M costs. Not very flexible, generation changes are

slow and minimal, usually only for "base-load" generation.

Environmental considerations.

1960s 1970s 1980s 1990s 2000s 2010s

MatureTechnology

R&D- Advance USC

Subcritical 170/540oC/540o

Super critical 245/540/540

245/540/565

245-580/600

285-600-620

285-630/650

382-700/720

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USCA-USC

Super Critical

Capacity addition based on Supercritical technology

11 number supercritical units totaling to 7,540 MW under construction during 11th Plan.

20 number supercritical units totaling to 14,000 MW ordered so far for 12th Plan

13 number UMPP, each of about 4,000 MW capacity, based on supercritical technology planned. Four UMPP already awarded

About 62 number supercritical units totaling to 44,000 MW likely to be added during 12th Plan.

Super Critical Technology in NTPC UPCOMING PLANTS

North Karanpura, Jharkhand – 3x660 MW Darlipali, Orissa – 4x800 MW Lara, Chattisgarh – 5x800 MW Marakanam, Tamilnadu – 4x800 MW Tanda-II, Uttar Pradesh - 2x660 MW Meja, Uttar Pradesh - 2x660 MW Sholapur – 2x660 MW New Nabinagar-3x660 MW Many more projects including 800 MW ultra super critical

units under consideration