Burners for OxyBurners for Oxy--coalcoalA review of OxyA review of Oxy--coal Burner Researchcoal Burner Research

G.CoraggioG.Coraggio and T. and T. KlajnyKlajnyIFRF Livorno, ItalyIFRF Livorno, Italy

The content

1. Past oxy-combustion projects in IFRF

2. Critical aspects in oxy-coal combustion

3. Burner examples• AE&E oxy-coal burner (Austrian Energy)

• TEA-C burner (ENEL)

2

Oxy-com. projects in IFRF in the past

• First document related to combustion with air enriched with oxygen:

Michaud M, Suggestions on the use of oxygen in the experimental furnace in IJmuiden,

C85/bc/1, 1955.

• IFRF document G24/y/1, 2006 - List of all the IFRF documents related to combustion

with oxygen-enrichment (88 documents, about 50 F and K document)

Main IFRF Projects on Oxy-combustion:

1. OXYFLAM project (1994-1998)Oxygen and natural gas combustionOxygen and natural gas combustion

2. Advanced Power Generation (APG) project (1993-1995)Oxygen and coal combustion

3. TEA-C burner (ENEL) (2009-2012)

4. AE&E burner (Austrian Energy) (2009-2012)

5. RELCOM project (2011-2015)

3

Oxy-fuel combustion

Oxy-fuel combustion regimes

oxygen mole fraction and the preheat temperature of the reactant stream

4

Oxy-fuel combustion

Oxy-fuel combustion regimes

oxygen mole fraction and the preheat temperature of the reactant stream

5

Relcom

Conventional combustion system:

Fosper ENEL facilities

6

Conventional combustion system

We want to modify it to oxy-coal combustion

7

1. Oxygen feeding line

2. Flue Gas Recycle line

Combustion system with FGR

Blue lines: oxygen injection

Pink lines: recycled flue gas

8

Combustion system with FGR

Blue lines: oxygen injection

Pink lines: recycled flue gas

N2 → CO2

9

Stabilisation of the flame

Matching mass ratio, momentum or velocities we face ignition delay problem

10

Stabilisation of the flame

11

Stabilisation of the flame

• …

12

• Increase oxygen concentration • Decrease primary stream velocity

Oxygen concentration for oxy-coal burners

Hjartstam et al. using German lignite at Chalmers 100kW unit

• The stable combustion could not be established with O2 mole fractions lower than 25% in the feed gas streams

• improved combustion stabilisation was achieved when maintaining a stoichiometric fuel-oxygen ratiowhen maintaining a stoichiometric fuel-oxygen ratioand increasing the oxygen concentrationin the staging streams from 25% to 29%

13

Air combustion Oxy-coal combustion Oxy-coal combustion

No stable combustion Stable combustion

21% O2 < 25% O2 25% to 29% O2

Oxygen concentration for oxy-coal burners

Liu at al:

• the O2 mole fraction in the mixture of O2/CO2 has to be raised to 30% or higher to match the gas temperature profile of oxy-coal combustion to that of air-coal combustion

Kimura at al:

• During their trials an unstable, dark combustion • During their trials an unstable, dark combustion zone with high unburned carbon (UBC) was reportedwhen the O2 concentration in the secondary streamwas lower than 30%

• However, when a central oxygen nozzle was usedto directly inject O2 in the centreline axial directionof the burner, the flame was stable

14

Injection of pure oxygen

Nozaki et al.:

• the direct O2 injection improved combustion stability and coal ignition comparing to the conditions with the same O2 content in the combustion gas but without O2 injection

15

Oxygen injection nozzles

Praxair reviewed various oxygen nozzle prototypes for flame stabilisation

16

Oxygen injection nozzles

Praxair reviewed various oxygen nozzle prototypes for flame stabilisation

Oxygen injection into primary air

on temperature profile of the flame

17

Tests at 1.2 MWth industrial scale burner facility of Alstom Power

O2 injection in various streams

Standoff distances of co-axial turbulent diffusion oxy-coal flames:

• attached stable flame for > 52% O2 in the secondary stream

• or shifting O2 injection from secondary stream to the primary stream(maintaining the overall oxygen concentration at 40%, a constant λ=1.15)

18Zhang et al.- Tests at 40 kW non-swirl burner at the University of Utah

O2 injection in various streams

Standoff distances of co-axial turbulent diffusion oxy-coal flames:

• attached stable flame for > 52% O2 in the secondary stream

• or shifting O2 injection from secondary stream to the primary stream(maintaining the overall oxygen concentration at 40%, a constant λ=1.15)

19Zhang et al.- Tests at 40 kW non-swirl burner at the University of Utah

However, preheating the secondary stream from 216°C to 271°C makes the flame more stable.

Burnout in oxy-coal combustion

Volatiles combustion Char particles

20

Summary

Retrofitting units to oxy-coal combustion we have to solve:

1. Increasing complexity of the system

2. stabilisation of the flame - Oxy-coal ignition delay problem

3. Overall oxygen concentration to match heat transfer

4. Which stream to inject pure oxygen to4. Which stream to inject pure oxygen to

5. Methods of injecting pure oxygen

6. Preheating the RFG streams

7. Different combustion characteristic of the fuels

21

Other areas in oxy-coal combustion

• Flame temperature to avoid high NOx emissions

• Scaling criteria for Oxy-coal burners

• Oxy-coal combustion and gas-side corrosion

(higher concentration of CO2, H2O, SO2/SO3, HCI)

• Ash deposition and slagging• Ash deposition and slagging

• Exhaust gas cleaning

• Safety issues with oxygen lines

• Flame monitoring and control system

22

Oxy-coal burners review

1. TEA-C burner (ENEL)

2. AE&E oxy-coal burner (Austrian Energy)

23

The furnace – FOSPER

• …

24

Test fuel – Sebuku coal

• Indonesian Sebuku coal was used during all tests

composition of the coal cumulative particle size distribution

25

TEA – C burner (Triflusso ENEL Ansaldo)

ENEL Oxy-coal burner tests

2.5MW conventional low NOx burner for coal, oil and gas combustion

Tested in oxy-coal condition

26

TEA-C burner in oxy-coal comb.

• …

27

Optimisation of recycle ratio (oxy comb.)

1. The higher recycle ratio the higher NOx emission

2. The higher O2 in flue gas the higher NOx emission

28

Temperature profiles

Recycle ration = 0,61 (oxy comb.)

Port 1 – 170 mm from the burner

Port 2 – 460 mm from the burner

29

NOx profiles (oxy comb.)

30

The emissions in oxy combustion are lower

than conventional combustion for R<0,64

AE&E burner

This burner was designed by AE&E and tested for Austrian Energy

2.5MW coal burner designed for oxy-fuel combustion

31

• Conventional air-NG firing

• Conventional air-coal firing

• Coal combustion with pure oxygen and recycled flue gas

Tests parameters

Flame was always stable during the tests both for:

• Air-coal combustion (baseline)

• Oxy-coal combustion

NOx emission was measured for operative parameters:

• Air-coal combustion:

• Swirler setting

• Thermal load

• Oxy-coal combustion:

• Swirler setting

• Thermal load

• Pure oxygen injection

32

NOx emission vs. swirler position

air combustion oxy-coal combustion

33

NOx emission vs. thermal load

air combustion oxy-coal combustion

34

Temperature profiles

A higher temperature in the centre of the flame in the air-combustion case

35

NOx profiles (oxy comb.)

the NO production via

thermal mechanism is

favoured

36

A peak of NO

concentration can be

spotted close to the high

temperature peak

The burner after tests

the burner throat and the gas lance after the trial

Despite the fact that the burner underwent very hard conditions because of the pulses in the coal feeding, no particular sign of damage were reported

37

Concluding remarks on tests

• AE&E and TEA C burners: good stable performances in oxy-RFG conditions, both with NG and coal

• AE&E burner was stable for all tested conditions

• Both burner show lower NOx emission with oxy-coal combustion

• Modified FOSPER plant is suitable for oxy-combustion studies

• Important air in-leakage is present at high R (Ljungstrom/dry mode-evaluated on the basis of mass balances)

• Air in-leakage is resulted the major cause of the level of the CO2 in the flue gases lower than expected.

38

• The in-flame data are to be used to develop a better understandingof the changes in the chemical and physical processes involved in oxy-coal combustion.

• Overall and In-flame measurements provide good sets of data for more fundamental analysis (flame structure, NOx, carbon in ash, etc.)

Concluding remarks on tests (2)

• They can also provide modelers with a starting hint for the development of oxy-combustion flame mathematical simulation.

39

Thank youThank you