CINAR NOx Assessment and Reduction

Dr Tom Lowes

NOx Assessement NOx is normally measured quite well at the stack for legislation

purposes and varies from < 500 to > 1500 mg/Nm3 at 10% O2 without SNCR

This range of NOx emissions are a function of:- The fuel used Operation of the kiln Design of the calciner

To get to < 500 mg/Nm3 without AFR or SNCR requires either luck or a CINAR hot reburn design either in the plant build or retrofit afterwards

The concept of reburn is not new, however as developed by Hupa and applied by CINAR is, as detailed in its 2011 IEEE paper above, namely:- 1200 C reburn and staging for @1sec at a SR for vols at < 0.9 (locally) 1300 C for 0.15 sec followed by @ 0.5 sec with meal addition for a

customised retrofit for calciners (including AT) at a SR < 0.9 The reason for the RT before, the TA is to allow the CHi reburn of

NO to NHi compounds to further react to form N2 and not with O2 to reform NO

IEEE NOx and CO

NOx Assessment

The next 2 slides show the reactions/kinetics, This is followed by a slide that shows NOx from 2 new FLS

kilns, one that needed a hot reburn 3 at 10% O2 and another that did not as by a miracle the TA was delayed mixing with the coal volatile

N.B for a complete pass through of kiln NOx the slope is @ 0.4 and zero for 100% reburn

Fundamentals of NOx

Fuel N HCN/NH3

+ O 2

+ NO

NO Products

N2

Thermal NOx

NHi - this is SNCR Opt. T very CO dependent

+CHi / HCCO

Reburn – 1 sec plus 1200C, 1300C and higher < 0.2 secs

AFRs with high volatiles a benefit, need to aim for 30% sub stoichiometric conditions

Staged combustion of Fuel NOx,

Need to combust the vols sub stoichiometric by @ 30 %.

N.B. In actual practise the measured vols are an underestimate of the practical situation by up to a factor of 2.

It should be noted that this is the SNCR reaction and is very temperature sensitive to drop the NO via the NH3 route

To paraphrase Cardinal Newman “Optimum Reburning/Staging is easy just like walking on a tight rope at 100m”

Needs TIME

Optimum Air Ratio for Reburn and Staged Combustion

Target initial operation for vols in riser

Normal Plant operation based on volatiles, if NHi mixed fast with TA then no good reburn or staging

Key Reactions in Hot Reburn

y = 0.0365x + 192.32

y = 0.1143x + 294.16

y = 0.3172x + 569.05

y = 0.2868x + 644.92

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0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0 1800.0 2000.0

Stack

mg/Nm3

at

10%

O2

KBE NO ppm

St Gen /Pueblo before TAD mods/Burners Down Stack NOx vs Kiln NOx

St Gen Burners Down Before TAD After TAD

Linear (St Gen) Linear (Burners Down) Linear (Before TAD) Linear (After TAD)

Burners Down rebutn 73%, staging - 50%

ST Gen reburn 92% staging 70%

Plant G and SG

NOx Reduction The next 2 slides shows a comparison of volatile residence time and

temperatures for Plant G and SG If SG had had temperatures as low as G then the NOx emission levels

would have been higher than current It should be noted that further reduction could have been achieved at G via

more burner optimisation, however the Plant were happy to get below 2.3 lbs/st and there is room for further improvement at SG via MI-CFD driven calciner burner optimisation

While reburn will drop the NOx emission, it is a also important to stage the N in the calciner fuel – the constant on the previous slide

Normally the maximum value of this constant seen is @ the NOx level associated with the fuel volatile * % N, however the 3rd slide shows an evaluation of the base case data from Alesd shows that in high local O2 conditions – as in an RSP – on devolatilisation then the calciner fuel NOx contribution can be higher

When there are more volatiles available than in a bituminous coal then the reburn becomes easier. The 4th slide shows a horizontal line with brown coal.(FLS info) The 5th slide shows the hot reburn plus MI-CFD breakthrough in NOx reduction compared to the classic information

0.0500.0450.0400.0350.0300.0250.0200.0150.0100.0050.000

C-vol. (fr)

17m

.85s(20m/s)

Plant G needed retrofit Plant SG No retrofit needed

0.0500.0450.0400.0350.0300.0250.0200.0150.0100.0050.000

C-v.i(fr)

0.2300.2070.1840.1610.1380.1150.0920.0690.0460.0230.000

O2 (fr)

12m

0.15 sec- 3.5 m Hot reburn Then 0.5 sec with meal

0.2300.2070.1840.1610.1380.1150.0920.0690.0460.0230.000

O2 (fr)

20m

.65s(30m/s)

Total RT:1.5

10

1400128011601040920800680560440320200

1400128011601040920800680560440320200

Temperature SimulationsPlant SG

1200 C maintainedPlant G before reburn mods

That moved the burners

down 3.5 m -1100C maximum

It should be noted for Plants with an excess of SO3 over alkalis in the hot meal that hot reburn will produce build up issuesThis is well covered in the 3.5 m hot reburn zone at Pueblo by a non coating refractory plus blastersIt is believed that St Gen has some build up issues

Stack NOx = 0.63KBENO+ 629.R² = 0.7763

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NOx

Kiln NO

Alesd Calciner Stack NOx vs Kiln NOx

Dilution and conversion to NO2 would mean the stack NOx was 0.82 KBENOThe 0.63 factor indicates 25% reburn with tyres and sludgeFor the average KBENO of 986 from the data set , this means @ 50% stack NOx is from the kiln and 50% from the calcinerThe calciner contribution to the stack is very high considering the fuel (25% calciner) splitThe 629 mg/NM3 at 10% O2 represents almost a 50% conversion of the fuel N (3.5%)which is an exceptionally high %age for a < 30% Vols coalRecommend lower N coal , more kiln fuel and higher KBEO2

RSP

Brown Coal a good Natural Reburn for SR < 0.9Note the emissions levels are @ 250 mg/Nm3 at 10% O2

It appears as if with a high volatile Brown Coal/Lignite or an AFR that a hot reburn may not be needed and a SR < 0.9 plus @ 0.6 sec RT before O2 from the TA may be all that is required to get a good reburn

Reburn Guidelines Before Hupa and CINAR

80% reburn at 6 N/MWAt Pueblo

MI-CFDRules

Typical Hot Reburn Installation

NO [ppm]

Normal FLS configuration.Coal and meal inlet @ 10 m below the TA inlet giving a stack NOx of 800 to 1000 mg/Nm3 at 10% O2Note local NOx in red

Hot Reburn for coal moved the coal injectors 0.15 secs RT below the meal inlet and optimised their angle and velocity via MI-CFD at to get stack NOx of < 500 mg/Nm3Note red zone has gone

Conclusions on ReburnFor reburn to work as effectively as possible one needs:- Local micro substoichiometric combustion for at least 0.5 secs before the gases

mix with the TA to complete the combustion The temperature of the reburn as well as the RT at the temperature will depend

on the fuel used. For a normal bituminous coal 0.15 sec is required at 1300C followed by @ 0.5 secs at @ 1000C (meal quench) before the TA .

For lignite and AFR the RT appears to be more important than the reburn temperature

For a hot reburn section, non coating refractories and blasters/cardox are recommended

This is normally manageable for ILC, RSP calciner are more difficult but manageable by taking some of the fuel out of the calciner and reburning in the riser.

AT calciners need a detailed knowledge of the KBE O2, CO and NOx distribution and detailed design of the reburn burners to exploit this. CINAR have had some success in the US with a AT calciner on low volatile coal at 30% in the AT calciner, as a shown on the next slide, which involves a JAMS to produce better local sub stoichiometric conditions. With a lignite aor volatile AFR the burner system and even the use of JAMS may not be needed and can be developed via MI-CFD

Kiln Inlet KBE O2 : 5 %Kiln Gases: 152327 Nm3/hTemperature: 1200 oCNOx: 1200 ppm

1.1%1.3%

Exit, NOx = 450 mg/m3> 50 % Reduction

Oxygen Coal Volatiles NOx

Higher JAMS27973 Nm3/h

4 Burners (1/4 in each)Total Transport Air: 2210 Nm3/hTotal Fuel Flow Rate: 6.76 t/h

Temperature: 77 oC

Case 10: 5% KBEO2, 4 Burners(2Original,2Lower) Upper JAMS

State of the ARTProcess Knowledge on SNCR

Tom Lowes

NOx Reduction with SNCR

While CINAR would always advocate looking at a hot reburn optimisation in preference to SNCR, customers also need to be able to drop NOx via SNCR to go even lower on some occasions while minimising NH3 slip and using SNCR as effectively as possible

The forthcoming regulations in the EU where 200 mg/Nm3 at 10% O2 may have to be met for all cement Plant using AFR means that even hot reburn and even customised calciner designs will struggle to meet these numbers.

Hence in the future CINAR will need to help its customers optimise the use of SNCR as well as hot reburn to meet its permit limits

This note gives info on what controls the effectiveness of SNCR

19

Course on Environment 2006

SNCR for NOx Reduction in Cement Production

Temperature is most critical for successful SNCR Urea, photochemical residues need higher temperatures than

ammonia (impact of local temperatures)

For calciners Urea is not as effective as aqua NH3

Typical molar ratios applied (1 -2 )NH3\NOx ratio Efficiencies 40 to 80%

Generally recognised to be the optimum range for NOx reduction and Minimum NH3 slip, but is it?

What about the impact of CO?

How many injectors?

Micro mixing?

Impact of CO on optimum SNCR Temperature

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CO impct on SNCR optimisation

Optimum temperature with 1000 ppm CO – 850C

Calculated Impact of CO in SNCR Optimum Temperature

22

Hence for optimum SNCR operation it is needed to:-

• Identify CO and hence the optimum temperature range

• Get good coverage of the process gases with the injected NH3 (multiple lances)

• Ensure a good local micro mixing – JAMS if needed

• CFD provides an optimal solution

The next slide shows some SNCR optimisation work based on the CO level

SNCR utilization

Calciner Temperature Profile & Lance Placement

830 o C

880 o C

950 oC

900 oC

880 o C

830 o C

900 oC

950 oC Lance placement 1

Recommended temperature range of 950 to 1000 oC

8 nozzles flowing 10 gpm of ammonia

80% reduction

Calciner DIA ~ 6100 mm

Lance placement 2

Lower than recommended temperature range

8 nozzles flowing 8 gpm of ammonia

80% reduction

Calciner DIA ~ 6100 mm

Lance placement 3

Lower than recommended temperature range

6 nozzles flowing 6 gpm of ammonia

88% reduction , with 25% less NH3

Stage 5 inlet DIA ~4300 mm

NH3/NOx = 1

Solution 20% aqueous NH3

CO ex calciner 1000 ppm

In position 3, 200 mg/Nm3 could be achieved on a regular basis with an 88% efficiency and no NH3 slip

Aqueous NH3 of < 30% used in US for Homeland security reasons and safety regulationsThere is not much use of Urea as it is much less effective than NH3

Conclusions on SNCR Significant improvement can be made in the cost NOx reduction via

SNCR by:-

Knowing what is the best temperature location as a function of CO

Where best to located the NH3 injectors as a function of the impact of the NH3 solution on local temperatures

How much NH3 to put through each injector – and its design - as a function of the predicted NOx profiles in the calciner

The key Questions to lower NH3 costs are:-

What

Where

How

These questions can only adequately be answered with MI CFD experts who are very conversant with Cement Production.