‘Supercritical coal-fired p

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Coal continues to be a major energy source for power producers worldwide. However,

as carbon consciousness becomes more prominent, technologies for gaining efficiency

and reducing emissions from coal-fired plants become more important. That is one

reason why supercritical and ultra- supercritical boiler technologies are reemerging as

new materials and designs help drive higher efficiency levels and ease of operation.

Contents

Introduction

Supercritical technology and its advantages Conclusion

Supercritical coal-fired power plant - This advanced technology for power generation is for achieving

higher efficiency, clean and safe overall environment:

Energy, in general, and electricity in particular, plays a vital role in improving the standard of life everywhere.

World has abundant proven reserves of coal and thus coal-based thermal power plants dominate almost

everywhere. The development of coal fired supercritical power plant technology can be described as anevolutionary advancement towards greater power output per unit and higher efficiency. Energy conversion

efficiency of steam turbine cycle can be improved by increasing the main steam pressure and temperature.

ercritical coal-fired power plant - a knol by Partha Das Sharma http://knol.google.com/k/supercritical-coal-fired-po

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As name suggests, coal-fired supercritical power plants operate at very high temperature and pressure (580

degree centigrade temp. with a pressure of 23 MPa) resulting much higher heat efficiencies (46%), as

compare to sub-critical coal-fired plants which operates at 455 degree centigrade temp., and efficiency of

within 40%. Some of the benefits of advanced supercritical power plants include:

(a) Reduced fuel costs due to improved plant efficiency;

(b) Significant improvement of environment by reduction in CO2 emissions;

(c) Plant costs comparable with sub-critical technology and less than other clean coal technologies;

(d) Much reduced NOx, SOx and particulate emissions;

(e) Can be fully integrated with appropriate CO2 capture technology.

In other words, 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. This increases the kWh produced per kg of coal burned, with fewer emissions.

Because of the above techno-economic benefits along with its environment-friendly cleaner technology; moreand new power plants are coming-up with this state-of-the-art technology. As environment legislations are

becoming more stringent, adopting this cleaner technology have benefited immensely in all respect. As LHV

(lower heating value) is improved (from 40% to more than 45%); a one percent increase in efficiency reduces

by two percent, specific emissions such as CO2, NOx, SOx and particulate matters.

"Supercritical" is a thermodynamic expression describing the state of a substance where there is no clear

distinction between the liquid and the gaseous phase (i.e. they are a homogenous fluid). Water reaches this

state at a pressure above 22.1 MPa. The efficiency of the thermodynamic process of a coal-fired power

describes how much of the energy that is fed into the cycle is converted into electrical energy. The greater the

output of electrical energy for a given amount of energy input, the higher the efficiency. If the energy input to


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the cycle is kept constant, the output can be increased by selecting elevated pressures and temperatures for

the water-steam cycle.

Increased thermal efficiency observed when the temperature and pressure of the steam is increased. By

raising the temperature from 580 C to 760 C and the pressure out of the high pressure feed-water pump

from 33 MPa to 42 MPa, the thermal efficiency improves by about 4% (Ultra-supercritical steam condition).

Moreover, there are various operational advantages in case of supercritical power plant. There are several

turbine designs available for use in supercritical power plants. These designs need not fundamentally differfrom designs used in sub-critical power plants. However, due to the fact that the steam pressure and

temperature are more elevated in supercritical plants, the wall-thickness and the materials selected for the

high-pressure turbine section need reconsideration. The supercritical plant needs once-through boiler,

where as drum type boiler is required by sub-critical power plant. In fact, once-through boilers are better

suited to frequent load variations than drum type boilers, since the drum is a component with a high wall

thickness, requiring controlled heating.

The performance of supercritical plant depends on steam condition. Steam conditions up to 30 MPa/600C

/620C are achieved using steels with 12 % chromium content. Up to 31.5 MPa/620C/620C is achieved

using Austenite, which is a proven, but expensive, material. Nickel-based alloys, would permit 35 MPa/700C

/720C, yielding efficiencies up to 48%. Thus, higher firing temperatures and pressures translate into better

efficiency, defined as more electricity generated per BTU of coal consumed. Naturally, this is attractive topower producers, as these increased efficiencies translate into reduced fuel costs and emissions. Lot of R&D

inputs and allying with suppliers are required to achieve higher performance.

Apart, fuel flexibility is not compromised in Once-Through Boilers. A wide variety of fuels have already been

implemented for once-through boilers. All types of coal as well as oil and gas have been used.

Because of its abundance and affordability, coal continues to be a major energy source for power producers


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worldwide. However, as carbon consciousness becomes more prominent, technologies for gaining efficiency

and reducing emissions from coal-fired plants become more important. That is one reason why supercritical

and ultra- supercritical boiler technologies are reemerging as new materials and designs help drive higher

efficiency levels and ease of operation. Todays supercritical units can achieve thermal efficiency of more

than 45 percent, compared with a typical sub-critical plants 30-38 percent.

Thus, new pulverised coal combustion systems utilising supercritical and ultra-supercritical technology

operate at increasingly higher temperatures and pressures and therefore achieve higher efficiencies than

conventional sub-critical units with significant CO2 reductions. The objective of power plants within toadys

market boundaries is more than ever to ensure high efficiency (to reduce the environmental impact as much

as possible) while at the same time to increase their economics in competition to existing alternatives. The

development of an economical and efficient concept needs to look at the steam turbine all other main

components like boiler, flue gas cleaning equipment and the optimization of the water-steam-cycle as main

parts for the optimization.

Current designs of supercritical plants have installation costs that are only 2% higher than those of sub-critical

plants. Fuel costs are considerably lower due to the increased efficiency and operating costs are at the same

level as sub-critical plants. Specific installation cost i.e. the cost per megawatt (MW) decreases with increased

plant size. This plant concept fulfils the requirement to balance reliable power supply, sustainable use of

existing resources and economic operation.

Today, supercritical steam turbine cycle is the leading clean coal technology in widespread application.

Supercritical steam cycle technology has been used for decades and is becoming the system of choice for new

commercial coal-fired plants in many countries. Because of the high performance, efficiency and preservation

of much cleaner environments than sub-critical coal-fired power plants, more than 500 supercritical coal-firedpower plants are operating in the developed countries like US, Europe, Russia and in Japan. Most of the new

power plants coming up now-a-days are of supercritical coal-fired technology. Recent plant built in Europe

and Asia use supercritical boiler-turbine technology and China has made this standard on all new plant

600MW and upwards.

In fact, Supercritical steam cycles are not just applicable to coal-fired plant; oil- and gas-fired plants are also

well proven. Research and development is under way for ultra-supercritical units operating at even higher

efficiencies, potentially up to around 50%. The introduction of ultra-supercritical technology has been driven

over recent years in countries such as Denmark, Germany and Japan, in order to achieve improved plant

efficiencies and reduce fuel costs.


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Research is focusing on the development of new steels for boiler tubes and on high alloy steels that minimise

corrosion. Since the first supercritical plants were commissioned high temperature steel has improved

remarkably. However, steel cannot continue to improve forever and crossing the "steel barrier" will need

nickel-based "Super Alloys" for the hottest areas of the water steam cycle. Commissioning of the advanced

plant is foreseen for 2010 and maximum steam temperatures will be in the range of 700-720C and net

efficiencies 52-55%, depending on site and fuel conditions. An important part of the project is also to

demonstrate ways of lowering investment costs.

References:

http://environmentengineering.blogspot.com/2008/02/cleaner-coal-fired-supercritical-power.html1.

http://environmentengineering.blogspot.com/2008/02/fludised-bed-combustion-fbc-technology.html2.

http://www.powergeneration.siemens.com/NR/rdonlyres/025ABC46-9AA8-451B-

88D1-FFE1B42B8966/0/2_Balancing_economics.pdf

3.

Y. Oka and S. Koshizuka, Supercritical-pressure, once-through cycle light water cooled reactor

concept, Journal of Nuclear Science and Technology, vol. 38, no. 12, pp. 10811089, 2001.

4.

http://saferenvironment.wordpress.com/2008/12/29/%E2%80%98supercritical-coal-fired-power-

plant%E2%80%99-necessary-to-promote-advanced-technology-in-power-generation-for-achieving-

better-efficiency-cleaner-and-safer-environment/

5.

http://www.science.nd.edu/research/profiles/holvey.htm6.http://www.elsamprojekt.com.pl/usc.html7.

Comments

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shi indians

A few suggestion

Thanks Mr. Sharma for the nice article. Shall be obliged in case if you kindly look in to sub critical plant

efficiencies and temperature . Most of the sub critical utility stations operate at temp ~ 540degC as comparedto 455degC mentioned. Also with this temperature it is hardly possible to achieve 40% efficiencies. In India

overal generation efficiencies very low. In fact with supercritical to the best of my knowledge 45%

afficiencies have been achieved only with USC ( double Re heating) it is ~ 46%

Will you kindly throw some light on this!

Last edited Dec 2, 2009 11:13 PM

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shi indians

A few suggestion

Thanks Mr. Sharma for the nice article. Shall be obliged in case if you kindly look in to sub critical plant

efficiencies and temperature . Most of the sub critical utility stations operate at temp ~ 540degC as compared

to 455degC mentioned. Also with this temperature it is hardly possible to achieve 40% efficiencies. In India

overal generation efficiencies very low. In fact with supercritical to the best of my knowledge 45%

afficiencies have been achieved only with USC ( double Re heating) it is ~ 46%

Will you kindly throw some light on this!

Last edited Dec 2, 2009 11:15 PM


0 View/post replies (1) to this comment

Robin

Devlopment of cleaner Coal Technologies for High Sulfur Coal Power Plants

I hope my comments are not to late. In 2006 my partner and i were finally granted a patent to reduced So2

emissions as well as treat heavy metals at the same time. our tests showed capture of 98 to 99 percent. Itseems that many of the power utility companies really do not want to change, it works lets not fix it. Ours is a

very simple technology and most plants could convert very easily. how do you get the attention of thr right

people, that the power players seem to be able to do

RBS

Last edited Mar 11, 2009 12:42 PM


0 Post reply to this comment

jackie cox

coal fired power plant toxic emission scrubbers

Having studied these plants seriously for years, the answer is simple, circulate the high temperature emissions

through commercial heat exchangers to reach ambient temperature, then send the emissions through

commercial waterwash equipment, lastly serarate the particles via a host of technologies( temporary solution )


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Long term solution, liquify coal and began distillation process engineering to actually use the elemental

components in the petrochemical, coal, similar to oil, instead of burning it up. We are controlled by an

oloigarchy as utilities providers, who must be stopped, lest they destroy all of nature

Last edited Jan 24, 2009 4:09 PM


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