Centre for Energy and Resource Technology (CERT), School of Applied - - PowerPoint PPT Presentation

Fuel Variability Effects in Pilot Scale Oxy-Combustion

(Coal and Cereal Co-Product (CCP)

Hamidreza G. Darabkhani, Nigel A. Legrave, Nigel Simms and John Oakey

Centre for Energy and Resource Technology (CERT), School of Applied Sciences, Cranfield University, UK

2nd Oxyfuel Combustion Conference

Queensland, Australia 12-16 September 2011

Outline

Introduction Experimental Set-up Experimental Conditions and Test Matrix of Fuels Gas Emissions (major and minor species) Temperature Profiles Ash Deposition Results Rig Modifications Summary and Future Works

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Introduction

 Oxy-firing of Pulverised Fuel (PF) in boilers involves the combustion of pulverised coal in a mixture of oxygen and recycled flue gas (RFG).  Cranfield University is working with five other universities to improve Britain's knowledge base for oxyfuel combustion technology.  Cranfield Contribution to the OxyCap project:

• Operation of Oxy-fired Combustor to determine process environments and impacts on

ash behaviour as conditions change.

• Modelling of the boiler environment based on rig data.
• Impact of boiler environment and ash behaviour on corrosion of boiler components.

 This study presents the results of investigations into the gaseous emissions, temperature profiles and ash deposition from combustion of El-Cerrejon coal mixed with Cereal Co-product (CCP) biomass in a 150 kWth

• xy-firing PF combustor.

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Diagram of Multi-fuel Combustion Rig

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Flue Gas Recirculation Ducting and Fan

Installation of flue gas recirculation ducting and fan Extra fan & pipe work for flue gas recycle

Recycled Flue Gas (RFG) pipe

0.65 m

3.9 m

4/20

Oxygen and CO2 Supply Systems

Installation of Oxygen and CO2 flow pipes and flow metres (varying O2 levels)

O2 supply system 5/20

Gas Analyser, Thermocouples and Deposition probes

Gas Analyser, Thermocouples and deposition probes for measurement of process environment

Protea Unit (ProtIR)

A fully assembled deposit capture probe including the ‘K’ type thermocouples connection plugs

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Trace Heating of Pipework

To prevent acid/water condensation inside the pipework

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Experimental Conditions

Fuel type Mix Ratio (wt %)

‘El-Cerrejon’ (South American coal ) + Cereal Co-product (CCP) Case 1: 100:0 Case 2: 80:20 Case 3: 60:40 Case 4: 20:80 Case 5: 0:100

Test matrix of fuels (fuels are supplied by E.ON)

Major flue gases species including CO2, H2O and O2 and the minor gaseous species (e.g. CO, SO2, NO, HCl, N2O, NOx, etc.) during 1-2 hours of stable combustion will be presented and compared in the full paper. PULVERISED FUEL RATE: 9-12 kg/h RFG: Recirculated without previous treatment (e.g. H2O or SOx removal) Percentage: 60-70% Temperature: 90-130⁰ C Addition of CO2 (35 l/min) to feed the pulverised fuel from hopper to chamber Pure O2 Injection: 175 l/min

Fuel: pulverised El-Cerrejon coal mixed with Cereal Co-product (CCP) 8/20

CO2: good concentration (~35%) H2O: 16% (almost half of CO2 concentration) O2: high oxygen concentration in the exhaust (~ 8%) CO: medium(~2040ppm) SO2: higher than air-firing mode (~660ppm) N2: ingress into the system (~40%)

5 10 15 20 25 30 35 40 45 7 14 22 29 36 43 50 58 65 72 79 86 94 101

CO2 H2O O2

Vol % Time(min)

MAIN SPECIES CONCENTRATION COAL/CCP: 80/20%

200 400 600 800 1000 1200 1400 7 14 22 29 36 43 50 58 65 72 79 86 94 101 SO2 N2O NO HCl NO2 CH4

Time(min) ppm

MINOR SPECIES CONCENTRATION COAL/CCP: 80/20% (without CO)

2000 4000 6000 8000 10000 12000 7 14 22 29 36 43 50 58 65 72 79 86 94 101 CO SO2 N2O NO HCl NO2 CH4

Time(min) ppm

MINOR SPECIES CONCENTRATION COAL/CCP: 80/20%

Gas Emissions

Case 2: COAL 80%+ CCP 20%

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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 4 7 11 15 18 22 25 29 32 36 40 43 47 CO2 100% COAL CO2 80% COAL- 20% CCP CO2 60% COAL- 40% CCP CO2 20% COAL- 80% CCP CO2 100% CCP H2O 100% COAL H2O 80% COAL- 20% CCP H2O 60% COAL- 40% CCP H2O 20% COAL- 80% CCP H2O 100% CCP Vol % Time(min)

MAIN SPECIES

64.5%RFG 70.2%RFG 64.8%RFG 59.3%RFG 65.5%RFG

Gas Emissions during the burner operation

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Trend to achieve lower temperature when increasing the content of CCP

Temperature profile in the vertical chamber

500 550 600 650 700 750 800 850 900 2 3 5 7 8 10 12 13 15 17 18 20 22 23 25 27 28 30 32 33 35 37 38 40 42 43 45 47 48 Vertical chamber 80% COAL-20% CCP Vertical chamber 60% COAL-40% CCP Vertical chamber 20% COAL-80% CCP Vertical chamber 100% CCP

Time(min)

IN FURNACE TEMPERATURE

Temperature (°C)

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Gas Emissions vs. Fuel Type

MAIN SPECIES.

• CO2 the trend of CO2 and fuel fed is the same (except in

case 1)

• O2 no much effects related to fuel feeding (due to O2

adjustments during the experiments)

• H2O concentration increases by increasing the percentage
• f CCP in the fuel composition.

So2 concentration dramatically decreases by adding more CCP into the fuel mixture.

5 10 15 20 25 30 35 40 CASE 1 100%COAL CASE 2 80%COAL-20%CCP CASE 3 60%COAL-40%CCP CASE 4 20%COAL-80%CCP CASE 5 100%CCP H2O CO2 O2

%Vol

MAIN SPECIES (Average)

2000 4000 6000 8000 10000 12000 14000 16000 18000 CASE 1 100%COAL CASE 2 80%COAL-20%CCP CASE 3 60%COAL-40%CCP CASE 4 20%COAL-80%CCP CASE 5 100%CCP CO NO NO2 N2O SO2 HCl CH4

ppm

MINOR SPECIES (Average)

100 200 300 400 500 600 700 800 CASE 1 100%COAL CASE 2 80%COAL-20%CCP CASE 3 60%COAL-40%CCP CASE 4 20%COAL-80%CCP CASE 5 100%CCP NO NO2 N2O SO2 HCl CH4

ppm

MINOR SPECIES (Average)

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Ash Deposition

Case 1: COAL 100%

0.1 1 10 100 O Na Mg Al Si Cl P S K Ca Ti Fe Cu Element (Wt %) Element Oxy-firing deposition - 100% El Cerrejon - Elemental Analysis (RFG 70.2%)

Probe 1- top Probe 1- side Probe 1 underside Probe 2 - top Probe 2- side Probe 2 - underside Probe 3- top Probe 3- side Probe 3 - underside

Deposits from the ceramic sections of the three deposition probes with surface temperatures of 700 °C (probe 1), 600 °C (probe 2) and 500 °C (probe 3) were collected after combustion runs.

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Higher K content in case 5 compared to case 1, (as expected from the ash composition analyses of the parent fuels) For several elements, their presence depend

• f the location of the deposits more than the

type of fuel used (e.g. Si, S)

Ash Deposition

(probes at 500, 600 and 700 C)

10 20 30 40 50 60 O Na Mg Al Si P S K Ca Ti Fe Cu Cl Pt CASE 1 100%COAL CASE 2 80%COAL-20%CCP CASE 3 60%COAL-40%CCP CASE 4 20%COAL-80%CCP CASE 5 100%CCP

Probe 3-Top

% (Weight) Element

Distribution of elements: Main: P, Si, K, Al, Fe Medium: S , Ca, P Minor: Na , Mg, Ti, Cu, Cl, Pt

Probe 3-Top 14/20

Ash Deposit Composition Oxy-firing vs. Air-firing

10 20 30 40 50 60 O Na Mg Al Si P S K Ca Ti Fe Cu Cl Pt Ni OXY-FIRING 100%COAL AIR-FIRING 100%COAL OXY-FIRING 80%COAL-20%CCP AIR-FIRING 80%COAL-20%CCP

% (Weight) Element

Probe 1-Top

• Comparing air and oxy-firing, the deposit S contents do not follow the levels expected from

simple mixing of the fuel ashes, indicating that complex interactions are taking place.

• The ashes generated may have more acid nature and the acid gases in the boiler also higher

than in air-firing and both are influenced by recycle rate.

• Further work is required to understand the interactions.

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New Rig Modifications:

1- Installation of an Axial Air Swirler at the Air Inlet Port

Main Flow Region Recirculation Region

*Gas Turbine Combustion- Lefebvre

• Swirler served to create a toroidal flow reversal

that entrained and recirculated a portion of the hot combustion products to mix with the incoming air and fuel.

• This will help to improve the burning efficiency and

as a result the effective flame temperature and also to drag the flame itself closer to the fuel nozzle (as it is in air firing).

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2 - Sealed RFG Fan

• Despite the efforts consumed to resolve the

problem, some air leakage still exists mainly from the recirculation fan box.

• The new gas tight fans with HT grease lubricated

and double lip seal at shaft entry is fitted in the near future.

• The Capsis system is prepared to measure the

acid dew point of the recycled flue gases.

Gas Tight RFG Fan Exhaust Fan

Capsis Probe Capsis Box

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3- Improved Fuel Feeding System

Pulverised coal feed pipe Gaseous fuel feed pipe Pilot flame input port

CO2 supply hose

Venturi A gas tight and accurate fuel feeding system is under construction which will help to prevent the blockage in the feeding pipe and also the ingress of air into the rig

4- The Primary Oxygen Line

Flow diagram of the Cranfield oxy-fuel pulverised fuel fired combustor (red: ongoing modifications)

• A primary line of oxygen is installed in order to introduce excess
• xygen to the burner to improve the burning efficiency and obtaining a

higher effective flame temperature.

• This primary O2 will be introduced through a venturi attached to the

pulverised coal feed hopper.

Oxy xy-Fu Fuel Combus bustor

• r

Recycled Flue Gas

Primary Flow

Dry Recycle Wet Recycle Water and Sox Removal CO2 Rich Flue Gas O2 Pulverised Fuel

Secondary Flow

CO2 + O2

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Summary and Future Works

• Results from pilot scale oxy-firing investigations to explore the effects of fuel

variability on the major and minor gas species emissions, temperature profiles and ash deposition have been presented. Key findings are:-  Maximum CO2 concentration of 40% has been achieved so far  H2O concentration increases and SO2 decreases by increase in the percentage

• f CCP

 Maximum vertical chamber temperature was achieved in 80%Coal+20%CCP fuel, but it generally decreases by adding more CCP to the coal  The generated ashes may have more acid nature and the acid gases in the boiler are also higher than in air-firing (more aggressive environment in oxy- firing)

• Oxy-fuel combustor modifications to improve the performance of the pilot scale

combustor are underway.

• Recycle flue gas purification methods (SOx and water removal) are under

consideration. 20/20

Acknowledgments

The authors wish to acknowledge funding and supports of:

• UK Research Councils in particular EPSRC
• EON
• UK Oxy-Cap Consortium

The data processing by Miss Nelia Jurado (PhD student at CERT) is also appreciated.

Thank you for your attention