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Advanced Clean Coal Technologies – What is the

future?

Dr. Ibrahim Gulyurtlu

DEECA - INETI

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1.Introduction

2.Review of clean coal technologies

3.What future could be expected? R&D needs

Sources of information used: IEA publications, Powerclean handbook, IEA Bioenergy

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1. IntroductionENERGY RESOURCES

wood

coal

oil

1870

1960’s...

1973

1979

1990

Energy and Environment

Supply Economy

Environment

ENERGY RESOURCES

wood

coal

oil

1870

1960’s...

1973

1979

1990

Energy and Environment

Supply Economy

Environment

Supply Economy

Environment

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Information from IEA

[1][1]

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Coal continues to be the fossil source with largest reserves

[1][1]

Information source: IEA

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Information source:IEA

[1][1]

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Information source: IEA

[1][1]

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It is expected that Total Primary Energy Supply will growby 1% per year

Coal share is expected to continue decreasing, from 20% in1997 to 14% by 2020Gas share is expected to increase, replacing coal, passing from 20% to 31%Share of nuclear energy is expected to decrease, from 14% to 9%Share of non-hydro renewables is expected to increase by 1%

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Information source: IEA

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The future of coal is very uncertainalthough coal has the largest reservesof fossil fuels and the reasons are:

1) It has a reputation of being dirty and leastefficient for power production,

2) It has environmental impact considered negative because of emissions of SO2, NOxand the production of ashes which need to bedisposed of,

3) It produces highest CO2/kWh,4) Coal fired power plants have become quite

costly due to gas cleaning systems and CO2abatement is still a long way from fullcommercialisation at a competitive cost.

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2.Review of clean coal technologies

PFBC

COAL

GasificationCombustion

PF AFBC IGCC

Hybrid cycles

Coal power generation options

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Combustion – Pulverised Fuel (pf) Systems

They are used to generate a large majority of the electricity produced from coal. In pf boilers, coal particles arepulverised to about 70µ and then injectedthrough burners in the flame. The particlesburn in suspension at high temperatures and release heat at large rates. The heat is then used to generate high pressure, high temperature steam. Most pf boilers work below the critical pressure of 212.2 bar.

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A typical pf power plant

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The key objective of the strategyfor pf boilers in the future is toincrease plant efficiency which canbe achieved by increasing the temperature and pressure of steam. This can be broughtabout by working under supercriticalconditions that is at pressures over 250 bars and temperatures above 600ºC. Today,supercritical technology has completely overcome the past problems and offers a more favourable cost of electricity with higher efficiency and lower emissions.

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Most of the problems were due to high thermal stresses and fatigue cracking of the heavy section components.

The current interest is ultrasupercriticial steam conditions to achieve even higher plant efficiencies. This means producingsteam at temperatures above 700ºC underpressures of about 300 bars. The main issueis the use of advanced material for construction of both boilers and for turbines.There is still some R&D needs in the area of material science.

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Best pf installations worldwide

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Other considerations

1. Fuel flexibility as mine-mouth plants arebecoming rare with the exception of lignitesand brown coal. Pf boilers have to deal withcoals of different origin and with other fuelslike biomass and some waste materials

2. Flue gas cleaning as emission limits forpollutants have steadily decreased to levelsthat are quite low due to greater concern for the environment. This increases costs and reduces plant efficiency.

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Recent trend of emission limits

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Age of coal-fired Pf for the EUcountries

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Combustion – Circulating Fluidised BedCombustion (CFBC) Systems

A technology that can be designed to burna variety of fuels, efficiently and in anenvironmentally acceptable manner and isconsidered the technology of the future forcoal-fired power plants. It burns crushedcoal with relatively large particles, thusavoiding costly milling operation.

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A typical CFBC plant

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Larger CFBC installations worldwide

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There are currently over 1200 CFBC plantsworldwide with a total installed capacity of65 GWth, more than half being in Asia.

The CFBC technology follows Pf systems inchanging to supercritical conditions thatimproves the plant efficiency due to theincrease in steam conditions. The use of about 300 bar/600ºC could give rise toabout 3% increase in efficiency.

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Technological innovations introduced byboiler companies in the new plantsinclude:

1. Cooling system for the recirculatingsolids,

2. Heat sinks integrated with the fluidisedbeds,

3. Ash cooling systems,4. Superheated steam by pass systems for

temperature control5. Cyclone retrofit for the gas/solid

separation

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The ability of CFBC systems to operate on a wide range of fuel types has been confirmed through extensive operational experience. Most major suppliers have manufactured CFBC units that have been capable of operating with the major classes of fuel types. Although many CFBC units currently in commercial operation utilise a single fuel feedstock, there are many others that regularly co-fire mixtures of fuels.

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The high degree of fuel flexibility that characterises many designs of CFBC often allows a plant operator to select fuels on the basis of what may be currently available at an economic price and where appropriate, produce a fuel blend that combines several such elements. Often, a premium fuel may be co-fired with a low grade feedstock such as paper mill or oil refinery wastes.

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Combustion – Co-firing option

A viable option for reducing emissions of greenhouse gases by 8% until 2010, as 1990 being the reference year. (Kyoto agreement obligation of EU)

This is particularly the case for the existingpower plants burning coal.

Contribute to the increase of the use ofrenewable energies from 6 to 12% by 2010.

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Activities within EU in the area of co-firing:

• EU-countries have set goals of 5 – 12% of power production utilizing biomass

• Near term goals are being accomplished through co-firing

• In The Netherlands co-firing is applied in all available Dutch coal-fired plants at about 5% of the energy input level

• 150 fluidized bed boilers in Scandinavia use secondary fuels such as sawdust, wood chips, forest residues which are co-fired with peat, wood or coal

• PC plants (Lignite and coal) in Germany:sewage sludge commercially,trials with straw and wood

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Drivers of co-firing biomass

• Reduces the emissions of greenhouse gases and other pollutants

• Co-firing in coal plants would strongly increase biomass use

• Lowest capital cost option for increasing the use of biomass to produce electricity

• Co-firing biomass and coal takes advantage of the high efficiencies obtainable in large coal-fired power plants

• Improves combustion due to the biomass higher volatile content

• Jobs creation

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Technical barriers

• Fuel flexibility (quality, quantity)• Complete combustion and well mixing in

boiler• Fouling and corrosion of the boiler (alkalis,

chlorine)• Ash utilization (unburnt carbon,

contamination)• Negative impact on flue gas cleaning

(SCR DeNOx)

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Non-technical barriers

• Economic aspects (lack of financial incentives, uncertain fuel prices, open market)

• Legislative aspects (utilization of fly ash in cement, determining green share, emission legislation)

• Public perception of co-firing of biomass/waste

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Co-firing options

• Direct co-combustion in coal fired power plants

• Indirect co-combustion with pre-gasification

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An exampleof directco-firing

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An example of indirect co-firingFoster Wheeler Project

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An example of synergy achievedduring co-firing

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Another example of synergy achievedduring co-firing

Limit value for dioxins

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Theoratical reduction of CO2 withthe addition of biomass to coalduring co-firing

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Gasification - IGCC systems

• Gasification units that can be fired with coal, coal with biomass and wastes, refinery residues. This could include gasification both for power generation and the production of chemicals and fuel gases.

• Gasification for subsequent synthesis of chemicals including refinery products, based on coal and natural gas as primary feedstocks.

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Oxygen

Nitrogen

Raw coal

Milling Drying

Pressurization

Nitrogen to gas turbine

Steam

Cool solids free gas for quenching

Syngas cooler

Boiler feed water

Stag Sulphur Nitrogen for NOx control

To air separation plant

Boiler feed water

Air

Flystag

Solids removal

Gas treatment Gas turbine Generator

Combustor

Clean Syngas

Condenser

Steam turbine Generator

Boiler feed water

Exhaust gas

Electricity

Electricity

Air separation plant

Air feed from gas turbineand/or separate air compressor

Heat recovery steam generator

Oxygen

Nitrogen

Raw coal

Milling Drying

Pressurization

Nitrogen to gas turbine

Steam

Cool solids free gas for quenching

Syngas cooler

Boiler feed water

Stag Sulphur Nitrogen for NOx control

To air separation plant

Boiler feed water

Air

Flystag

Solids removal

Gas treatment Gas turbine Generator

Combustor

Clean Syngas

Condenser

Steam turbine Generator

Boiler feed water

Exhaust gas

Electricity

Electricity

Air separation plant

Air feed from gas turbineand/or separate air compressor

Heat recovery steam generator

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Feedstock options

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There are three technology variants, as listed below: each has advantages and disadvantages together with differing commercial track records.

Entrained flow gasifiersMoving bed gasifiersFluidised bed gasifiers

With regard to suppliers, Shell and Texaco gasifiers are used in nearly 75% of the projects undertaken. Of the rest, Lurgi gasification technologies are also used to a significant extent. For the “planned” gasification projects, it is understood that approximately 75% of these will also use either the Texaco or Shell gasifiers.

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Deployment of IGCC units

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Although much attention has been focused on using coal as the primary feedstock, the large majority of gasification projects to date are based upon the use of fuels other than coal, particularly residues from refineries because of the need to gain added value.However, this has significantly contributed to thedevelopment of the IGCC market.

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New developments to achieve near-to-zero emissions technologies:

• Post-combustion capture of CO2 from combustionprocesses

• Oxy-fuel combustion to enhance CO2 capture

• Chemical looping combustion

• Pre-combustion CO2 capture

• Hybrid systems combining combustion and gasificationand gasification and fuel cells

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Principle for a Chemical Looping Combustion cycle

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Vision 21 Technology Roadmap for Combustion Systems

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What future could be expected? R&D needs

In the area of pf systems

• Materials Science to go for USC systems to improveefficiency

• Efficiency improvements in the internal process lossesof various components like water/steam cycle, steamturbine

• Fuel flexibility

• CO2 sequestration

• Ash reutilisation in markets other than just cement

• Further improvements in gas cleaning

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In the area of CFBCs

• Improved component design, such as internal recirculation systems, leading to more compact systems

• Broadened range of fuel flexibility • Introduction of supercritical and ultra-supercritical

steam cycles• Development of improved materials of construction• Re-powering applications• CFBC technology scale-up, with 600MWe the current

target • Use of CFBC technology as part of advanced cycles

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CFBC (cont.)

• Increasing solids recirculation in the combustion chamber to allow:

- improvement in abatement efficiency of SO2through hydration of ashes, reactivation and pre-treatment of the sorbent;

- efficiency improvement reducing the sorbent consumption that represents the second more important cost of production.

- prediction of comminution phenomena in order.

Cost reductions and size optimisation

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In the area of co-firing

• Corrosion mechanisms• Ash deposition mechanisms• Fuel flexibility (characterization)• Particle burn-out and gas mixing• Particle size control• Fuel mixes / use of additives• Ash reuse in building materials• Contaminated biomass• High temperature steam boilers• Effect on gas cleaning / DeNOx catalysts• Pre-treatment of biomass or waste materials

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In the area of IGCC

• Fuel flexibility• Improve plant availability• Cost reduction• Technological risks related to the following:

- Gasifier component development, including improved materials of construction for refractories and HRSGs, improved feeding and handling systems.

- Gas turbine combustor development to ensure the efficient use of hydrogen rich fuels.

- Ancillary component development, including lower cost air separation units.

- Complementary design and optimisation studies, including full integration of CO2 capture.

Multi-function IGCC systems

54Improvement of existing plantsCo-firing

Ultrasupercritical boilers

2000

2050

Combustion & Gasification/CO2 capture

Oxyfuel combustion& CO2 capture

H2economy

CFBC systems

A possible roadmap for theintroduction of new technologiesinvolving the utilisation of coalfor energy