Presented by Ashis Kumar Chakraborty, Climate Change Future Guidelines for Environmental Benefits. from Super Critical Power Generation Units

This advanced technology for power generation is for achieving: 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.

CO 2 emissions can be lowered by improving the efficiency of coal fired power plants. Increasing the temperature & pressure in a steam turbine increases the efficiency of the Rankine steam cycle used in power generation, It decreases the amount of fossil fuel consumed and the emissions generated. Large amount of carbon-di-oxide (CO 2 ) emissions produced by them which contribute in a large measure to greenhouse effect and global warming.

PREAMBLE 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. Energy conversion efficiency of steam turbine cycle can be improved by increasing the main steam pressure & temperature.

Environmental Issues Primary sources of energy consisted of :  Petroleum 36.0%,  Coal 27.4%,  Natural gas 23.0%,  Amounting to an 86.4% share for fossil fuels in primary energy consumption in the world.  World energy consumption was growing about 2.3% per year  The burning of fossil fuels produces around 21.3 billion tonnes (21.3 gigatonnes) of Carbon dioxide (CO 2 ) per year,

Environmental Issues

Source: 'Coal Information 2006’

Environmental Issues * Source: 'Assessment of Generation Technology through Lifecycle CO2 Emissions' by Power Systems Central Research Laboratory (2000) * Source: 'Assessment of Generation Technology through Lifecycle CO2 Emissions' by Power Systems Central Research Laboratory (2000)

Environmental Advantages  At supercritical pressures (above 3200 psi;22.1 MPa),  steam turbine efficiency improves significantly compared to the typical subcritical cycle. This efficiency improvement leads to reductions in  fuel input  emissions output.

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A simple word equation for this chemical reaction is: A simple word equation for this chemical reaction is : where stoichiometric coefficients x and y depend on the fuel type. A simple example is the combustion of coal (taken here as consisting of pure carbon):stoichiometric coefficients C + O 2 CO 2. In words: carbon + oxygen carbon dioxide.

A coal-fired thermal power station. 1. Cooling tower. 2. Cooling water pump. 3. Transmission line (3-phase). 4. Unit transformer (3-phase). 5. Electric generator (3-phase). 6. Low pressure turbine. 7. Condensate extraction pump. 8. Condensor. 9. Intermediate pressure turbine. 10. Steam governor valve. 11. High pressure turbine. 12. Deaerator. 13. Feed heater. 14. Coal conveyor. 15. Coal hopper. 16. Pulverised fuel mill. 17. Boiler drum. 18. Ash hopper. 19. Superheater. 20. Forced draught fan. 21. Reheater. 22. Air intake. 23. Economiser. 24. Air preheater. 25. Precipitator. 26. Induced draught fan. 27. Chimney Stack.

PREAMBLE 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.

Coal-fired Supercritical Power plants operate at very high temperature [580°C temp.] & with a pressure of 23 MPa)* * megapascals (MPa = N/mm2) or gigapascals (GPa = kN/mm2) 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%.

Benefits of advanced supercritical power plants include a)Reduced fuel costs due to improved plant efficiency; b)Significant improvement of environment by reduction in CO 2 emissions; c)Plant costs comparable with sub-critical technology & less than other clean coal technologies. d)Much reduced NOx, SOx and particulate emissions; e)Can be fully integrated with appropriate CO 2 capture technology.

Supercritical technology and its advantages Techno-economic benefits along with its environment-friendly cleaner technology; more and 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.

LHV (lower heating value) is improved (from 40% to more than 45%); One percent increase in efficiency reduces by two percent, specific emissions such as CO 2, 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 greater the output of electrical energy for a given amount of energy input, the higher the efficiency. If the energy input to 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 to760°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 ).

Super Critical means no distinction between water & steam Critical point of water-steam: MPa,

Definition of SC and USC Units Sub-critical units: Main steam pressure < MPa Super-critical units: Main steam pressure > MPa Ultral-supercritical units: Commercial concept means higher steam pressure and temperature than supercritical units Japan: Main steam pressure >24.2MPa, or Steam temperature reaches 593 ℃ Denmark: Main steam pressure >27.5MPa China: Main steam pressure >27MPa

Supercritical and USC Coal-fired Units Over 600 super-critical coal-fired units (SC) have been under commercial operation worldwide, of which over 60 units are ultra-supercritical units (USC). Net plant efficiency achieved: Sub-critical units:(16.6MPa/538/538): 38%~ 40% Supercritical units: ( 24MPa/566/566): 40%~42% ％ Ultrasupercritical units: ( 25~30MPa/600/600):43%~46% To improve the steam parameters and develop large capacity units are the main measures for the improvement of overall plant efficiency.

Effects of Supercritical Steam Parameters to Turbine Heat Rate For every 1 MPa improvement of main steam pressure, turbine heat rate could be reduced by 0.13%~0.15% For every 10 % improvement of main steam temperature, turbine heat rate could be reduced by 0.25%~0.30% For every 10 % improvement of reheat steam temperature, turbine heat rate could be reduced by 0.15%~0.20%

Supercritical coal-fired power plant Advanced technology for power generation is for achieving higher efficiency, clean and safe overall environment Coal continues to be a major energy source for power producers worldwide. 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.

What is global warming? Global warming is the rise in temperature of the earth's atmosphere..

If Earth gets hotter, some of the important changes could happen: Water expands when it's heated and oceans absorb more heat than land,  Sea levels would also rise due to the melting of the glaciers and sea ice.  Cities on coasts would flood.  Places that usually get lots of rain and snowfall might get hotter and drier.  Lakes and rivers could dry up.

Is global warming bad? The earth is naturally warmed by rays (or radiation) from the sun which pass through the earth's atmosphere and are reflected back out to space again. The atmosphere's made up of layers of gases, some of which are called 'greenhouse gases'. They're mostly natural and make up a kind of thermal blanket over the earth.

Some of the rays back out of the atmosphere, keeping the earth at the right temperature for animals, plants and humans to survive (60°F/16°C). So some global warming is good. But if extra greenhouse gases are made, the thermal blanket gets thicker and too much heat is kept in the earth's atmosphere. That's when global warming's bad. Is global warming bad?

What are the greenhouse gases? Greenhouse gases are made out of: water vapour carbon dioxide methane nitrous oxide ozone chlorofluorocarbons (CFCs) They are all natural gases, but extra greenhouses gases can be made by humans from pollution.

How are extra greenhouse gases produced? Extra greenhouse gases are produced through activities which release carbon dioxide, methane, nitrous oxide and ozone CFCs (chlorofluorocarbons). These activities include: Burning coal and petrol, known as 'fossil fuels' Cutting down of rainforests and other forests Animal waste which lets off meth ane

PARTICULATES :  Higher suspended particulate matter affects Respiratory organ. HYDROCARBONS (HC):Main contribution from Transportation Industrial Process CARBON MONOXIDE (CO) EFFECT of SULPHURDIOXIDE (SO 2 )  SO 2 is colourless gas with suffocating odours.  SO 2 remains airborne for 2 to 4 days during which it can be transported to 1000 km.  SO 2 irritates mucous membranes of Respiratory tract & cause bronchitis.  It can damage plants. Vegetables etc.  Fossil fuel are more responsible for SO 2 emission.  Sulfur dioxide is one of the elements forming ACID RAIN

EFFECT of NITROGEN OXIDES (NO X )  Nitric Oxide (NO)  Nitrogen Oxide (NO 2 )  Nitrous Oxide (N 2 O )  Nitrogen sesquioxide (N 2 O 2 )  Like sulphur dioxde, it is acidic & can affect oxygen carrying capacity of blood.  NO 2 affects lungs and respiratory system.

Environmental Control Dry Electrostatic Precipitator (Dry ESP) Electrically charges ash particles in the flue gas &collects the particles on collector plates Mechanically removed through the ash hoppers Flue gas passes horizontally through a series of parallel vertical collector plates Arrangement of charging electrodes are centered between the plates Electric field to charge the particles & attract them to the grounded collecting plates. Nitrogen Oxides Control Selective Catalytic Reduction (SCR) Systems are the technology of choice as the most effective method of post-combustion NO x reduction. NO x reduction can be achieved by integrating low NO x burners and staged combustion (overfire air) into the overall system.

Environmental Control Sulfur Dioxide Control FGD [Flue-gas desulfurization] technologies offer the highest SO 2 reduction levels in the industry. Wet FGD systems: Spray tower scrubber design used for SO 2 control, with proven tray design for more uniform flue gas distribution and improved absorption. Reagents include limestone, lime, magnesium-enhanced lime, sodium carbonate and ammonia.Wet FGD systems Spray Dry Absorber (SDA) systems: A rotary atomizer delivers a slurry of an alkaline reagent into the hot flue gas to absorb the SO 2 and other acid gases control on utility boilers burning low sulfur coals.Spray Dry Absorber (SDA) systems Circulating Dry Scrubber (CDS) systems: Creates a dry waste product and does not require wastewater treatment facility.Circulating Dry Scrubber (CDS) systems

Emissions standards for Power Plant & projected emissions from 660 MW Unit Parameters Projected Emissions per Unit (660 MW Unit) Indian LimitWorld Bank Norm SO mg/Nm TPD (141.6 g/s) 700 TPD2,000 mg/Nm3 NO X 650 mg/Nm 3 (460.2 g/s) Low NOx burner prescribed 650 mg/Nm3 PM50 mg/Nm 3 (35.5 g/s) 100 mg/Nm350 mg/Nm3 mg/Nm 3 = milligram per normal cubic meter, NOX = nitrogen oxide, PM = particulate matter, SO 2 = sulfur dioxide, TPD= tons per day. The expected emissions are based on assumption of 0.5% of Sulfur in Coal, SO 2 emissions are without FGD in place, PM emissions with a limit of 100 mg/Nm 3 and Nox limit of 650 mg/Nm3.

Development  Japan worked on Waste Management or eliminating wastage & saving through Gemba Kaizen. Coal / fossil Fuel Heat Energy  Ferritic & austenitic materials for high temperature developed that are 1.5 times higher strength at high temperature.  Example: A21TP310HCbN [HR3C- Japan] A213UNS S30432 [Super304-Japan] [ C, Si, Mn,Cu, Cr, Ni, Co, Mo ]

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