Comparisons and experiences in BFBCs and PC in Finland

VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD

Comparisons and experiences in BFBCs and PC in Finland Fossil Fuel Foundation workshop July 29-30Nokkala Marko, Vainikka Pasi, Kjäldman Lars, Jukola Perttu, Huttunen Marko

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Presentation contents

§ VTT’s expertise with alternative fuels§ Pulverized fuels§ CFB boilers§ The bottom line…

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Computational Fluid Dynamics (CFD) to assist pulverized fuel fired boiler retrofits§Computational Fluid Dynamics (CFD) is a powerful and

affordable tool to assist the design of boiler retrofits and the study of furnace operation and availability in varying conditions: new burners and OFA design to decrease NOx emissions, cofiring of coal with biofuels or gas, operation at partial load and in changing load conditions.

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Challenges

§The strives to meet new emission limits, the goals to replace fossil fuels by bio fuels and waste, and the increasing use of low quality fuels demand a good understanding and control of the furnace processes to ensure good operation and furnace availability. In addition, there is an increasing need to operate the boiler at partial and varying load to follow the power demand caused by the use of renewable energy sources. CFD modelling is a valuable tool for seeking and evaluating solutions to these questions.

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Solutions

§VTT has a long experience on the application of CFD toinvestigate pulverized, gas and liquid fuel fired boilerfurnaces to reduce NOx emissions and ensuringacceptable UBC and CO levels and furnace availability.The cases simulated have included:

• Burner renewals and OFA design• Cofiring coal or peat with biomass or gasified fuel• Pellet firing• Operation at partial load• Development of burners: burner near field behaviour

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Solutions continued…

§ We are continuously developing the submodels of combustion andemissions based on new challenges and customers’ needs and on thefeedback from practical applications.

§ We use ANSYS Fluent® to solve the flow equations with user definedsubmodels

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Example: Gas burner development

§CFD was utilized to support Fortum Power Solutions’ design of a new low-NOx gas burner for lean gas combustion, optimising its performance.

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Example: Reduction of NOx emissions of PC combustion with new burners and design of over fire air (OFA)

§VTT utilized CFD in cooperation with Fortum PowerSolutions to design a retrofit of Helen’s Salmisaari cornerfired 510 MW (fuel power) boiler furnace to reduce NOxemissions. The new design included new low-NOx burnersand a new OFA locations resulting in a considerabledecrease of NOx emissions

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Changes carried out

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Example: Cofiring of pulverized coal with torrefied biomass§VTT utilized CFD to study the influence of cofiring torrefied

biomass with coal in corner fired PC boiler furnace. The replacement of coal with 30 wt-% and 50wt-% torrefiedbiomass resulted in the shift of the flame and a decrease of heat transfer rate to evaporators below the nose level, and correspondingly, in a increase of furnace exit gas temperature. The influence on NOx emissions was small. Most importantly, the amount of unburnt coal increases considerably in the cofiring cases. The cause of higher UBC turned out to be poorer milling when coal and biomass were milled together.

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CDF results

CFB experience

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This much we know already…

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VTT’s CFB combustion test installationTypical R&D topics in fluidised bed combustion § Understanding in-furnace phenomena under fully

controlled conditions§ Combustion profiles§ Gas, solids, temperature

§ Heat transfer phenomena inside combustor § Emission formation and reduction (NOx, SOx)

§ Limestone utilisation, Ca/S ratio§ Ash behaviour characteristics

§ Aerosol sampling inside furnace§ Formation and analysis of deposition

§ Combustion control studies§ Test results can be connected to Apros dynamic

simulation for overall process optimisation

§ Worlds first successful oxyfuel-CFB test was carried out in 2006 at 0.1 MW unit

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Scale-up approach based on integrated experimental and modeling work

Fuel characterization tests in pilot scale

Combustion

Combustion profile (heat release), fuel

reactivity

Unburned carbon (UBC)

Emissions

Main components such as CO2, O2,

CO, H2O, SOx and NOx

Trace elements e.g. HCl, HF, N2O,

NH3, CxHy, Hg

Ash

Ash composition and split: bottom

ash vs. fly ash

Agglomeration, fouling and

corrosion tendency

Limestone

Reactivity compared to

reference one

Estimate limestone dosage to reach

the emission limits

• optimal combustion conditions (temperature, air staging)

• furnace dimensioning • type and location of heat transfer surfaces• material selections• emission control system• ash removal systems and utilization

Data to design and optimize high

performance boiler with low emissions

and high availability in terms of

Anthracite Bituminous coal Brown coal/lignite Pet coke/Coal waste Peat Oil shaleBiomass

(wood, bark etc)Agro biomass

(straw, rapeseed etc)Waste

(SRF etc) Limestone

Worldwide references of the fuels tested at VTT site

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§ Polish bit. Coal (2001)§ Estonian Oil Shale (2001)§ Hungarian brown coal (2003)§ Turkish brown coal (2004)§ Polish Bit. Coal (2004)§ Australian bit. Coal (2005)§ Polish bit. coal in oxyfuel (2006)§ Rapeseed Expeller (2007)§ Anthracite, culm, slurry (2007)§ Ligning, straw (2007)§ South-African bit. coal, Russian anthracite culm,

(2007)§ Coal, coal waste (2008)§ Polish bit. Coal, wood pellets in oxy (2008)§ Ligning (2008)§ Turkish lignite (2008) § Russian bit. Coal (2009-2010)§ Brazilian sub-bituminous coal (2010)

Some referencesDirect contract projects for customers - fuel characterisation service

§ Spanish anthracite, petcoke (2011)§ Russian anthracite, FWe (2011)§ Coal reject from Mosambique, (2012)§ Jordanian oil shale, (2012)§ Pyrolysis coke (2013)§ Turkish lignite (2013)

Companies§ FWe, Foster Wheeler Energia Oy§ Metso Power Oy (Valmet)§ ETI – ETI Aluminyum S.A., Turkey§ SAMCA - SAMCA Group, Spain§ ÅF – ÅF-Consult Ltd.§ Metso – Metso Power Oy§ Fortum – Fortum Oyj§ Promark – Promark Services Ltd. (Rio Tinto)§ Lahmeyer – Lahmeyer International GmbH

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Development steps in fluidized bed combustion

0

50

100

150

200

250

300

350

400

1976

Pilot Plant 0,05

Pihlava 5

Kauttua 20

Leykam 40

Tri-State 2 x 55

Kajaani 85

Vaski-luoto 125

Nova Scotia

180

Turow 235

MWe

1979 1981 1987 1987 1989

Year

1990 1993 1998

Alholmen240

2001

Natural circulation

First OTSC CFBLagisza

460

2009 2010 2011

CIUDEN30

EU funded R&D project ’s coordinated by VTT

*

*

*

* 550

Build up of VTT’s CFB pilot plant

Four 550 MWe blockSamcheok Green Power

Project in Korea

Demonstration ofoxyfuel combustion

CIUDEN projectIn Spain

*CFB800 Design

20xx

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On CFB and CDF in general…

§For circulating fluidized bed (CFB) furnaces, VTT hasdeveloped a novel simulation method that is based ontime-averaged models of multiphase flow. The approach isfast thus allowing the modeling of industrial scale boilerfurnaces in a reasonable time with good accuracy.

§At VTT, we are continuously developing the submodels ofcombustion and emissions based on new challenges andcustomers’ needs and on the feedback from practicalapplications

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Example

§CFD was utilized to simulate coal combustion in a 135MW CFB boiler. The simulation results gave a correct overall picture of the furnace behaviour and reasonable agreement with available measurements.

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Continued…

The bottom line…

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Why CFB is considered better than BFB?

§Quality of coal; if non-reactive, BFB cannot force efficiency in burning in its burning process due to slow response time§ High ash content§ CFB can solve these problems!

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