Industrial operating experiences and burner design optimisation using low NOx ROTAFLAM burners in cement kiln coal
combustion
Dr J-C. GAUTHIER Pillard 13 Rue R. Teissere 13272 Marseille Cedex 8 - France jean-claude.gauthier@pillard.com Dr R. RIZZI Technologies Central Management - Combustion Department via G. Camozzi, 124 24121 Bergamo, Italy r.rizzi@itcgr.net
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS
PILLARD AKTUELL 19th MARCH 2003
WIESBADEN (GERMANY)
LOW NOx BURNER CONCEPT
The operating principle of a low NOx burner is based on a stepwise combustion which delays the mixing and input of fuel and air at appropriate stages to achieve a controlled combustion process. The flame is ignited and stabilised as close as possible to the burner tip entraining a minimum of secondary air and mixing between primary air jets, which are properly designed to allowing the formation of the hot internal re-circulation zone. This results in a fuel rich flame and lower peak temperature. The first generation of low NOx burners used the air staging principle. Nowadays, the new generations of low NOx burners use air staging technology but also specific fuel injection points which help to reduce NOx emissions.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND
To date it can be considered that there are three burner generations for rotary kilns:
single circuit burners using a long soft flame which was
originally suitable for the long kilns as well in the wet as in the dry process;
multi-circuit burners developed in order to reduce the
primary air supply and to obtain a short, divergent with strong swirl flame suitable for firing pulverised coal; they were introduced in the 1970s when the kilns became shorter with the use of PRS and PRC and the solid fuels were reused
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND Low NOx condition by partition of the primary air
Until some years ago this type of burner represented the state of the art. The primary air was divided into a swirl and an axial component whose relative flow rates allow to modify the flame shape. They can be adjusted via damper. The coal stream was designed for low velocity and high coal concentration. concentration
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND
The interior radial air flow was designed to expand the coal and stabilise the flame by generating an internal re-circulation zone. In this manner, it was possible to control the flame shape in conjunction with the constricting effect of the exterior axial air component.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND
To reply to the increasing environmental needs, at the end of
the 80s a new burner generation was introduced characterised by a slightly longer but less divergent flames. From a combustion point of view the advantages concern: - the formation of high temperature flames with reduced primary air using high velocities at the burner outlet - the environmental pollution control by the reduction of NOx concentration. The experience gained from low NOx burner technology permitted PILLARD to develop ROTAFLAM burner in which a complete revision of the burner tip geometry was realised.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND Axial-swirl-core air adjustment during burner operation
The burner includes axial, swirl, core primary air circuits and coal or pet coke circuit. The relative position of each pipe is adjustable so as to be able to modify the flow rate of each stream and hence enable flame shaping to suit the kiln needs.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND
The revisions were : for flame stabilisation a perforated buffer plate was installed in the central part of the burner outlet cross section to induce inflame flue gas re-circulation in order to guarantee flame stability at its root the pulverised fuel channel was relocated to the central part of the burner with respect to the radial and axial channels the radial and axial air channels were designed to convert the available pressure of the primary air supply to a maximum tip outlet velocity so as to maximise the momentum necessary for flame control while minimising the primary air flow
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND
the previously designed annular gap for the axial air channel was replaced by a number of slots. The purpose was to maintain perfect concentricity of the axial air channel and to promote the introduction of re-circulated combustion gases into the flame root, thus reducing the local free oxygen content an extended outer tube was added to handle the axial air component and thus to prevent premature mixing of the fuel and primary air mixture with hot secondary air.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
BURNER GUIDELINES
just an example:
Burners without hot tube extension permit the secondary air swallowing into the flame which reduces the low NOx performance
by the way:
Snowman formations enhance hurtful bowl effects on the outside burner part reducing at the same time the combustion efficiency along the flame axis.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
HISTORIC BACKGROUND
CEMFLAME, an European consortium of cement producers and CEMFLAME associated research organisations, was formed with the purpose of funding research on a scale simulation of an industrial cement kiln. To this aim the effects of fuel type and burner design on NOx emissions have been studied. It turned out the main parameters affecting NOx formation are: location of the pulverised coal circuit with respect to the primary air ones air distribution and intensity of the related momentums, that is local mixing location of the ignition point and flame temperature which are directly connected to the local oxygen concentration
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES
In order to qualify the low NOx burner design concept, tests have been carried out in two Italcementi Group s cement plants (700 and 800 tpd) equipped with Lepol grid and housing two different ROTAFLAM burner prototypes. In the first set of experiments the original burner (an indirect fired mono channel type firing 100 % petroleum coke) was replaced by a multi-channels low NOx ROTAFLAM burner. In the second set of experiments a specific burner had been realised to test the effect of the pulverised fuel channel location on NOx emissions at the kiln back end. This ROTAFLAM burner, 100 % pet-coke burning, is characterised by three different ways of coal injection: standard, splitted and staged channels
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (1st application)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (1st application)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (1st application)
Experimental campaign
kiln back end total P.A. flow rate delta-NOx (% vs. tube b.) (% stoich.air) 28 45 54 35 17.5 12.5 11.4 13.6
remarks
commissioning 1st optimisation 2nd campaign final set up
slight higher heat consumption no problem for some weeks few kiln operating problems burner designed as a compromise
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (1st application)
Each point shows the average burner performance obtained with different burner geometry and set-up. Concept of the NOx dependence on heat input and burner design SARCHE is evident. ROTAFLAM burner
4000
tip #6 different ax / sw
3500
different tips
NOx kiln back end (mg/Nm @ 0% O2)
3000
2 6 5 1 comm 3
2500
2000
tip #6 4
tip #7
tip #5
1500
tip #1
tip #3
tip #4 tip #2
1000
500
0 1700
1800
1900
2000
2100
2200
2300
PET-COKE FLOW RATE at main burner (kg/h)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (2nd application)
35 MWth 30 Gcal/h 3.65 t/h pet coke 10 % total P. Air
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (2nd application)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (2nd application)
During the first experimental campaign using the standard channel, the burner settings were adjusted to improve the clinker channel production whilst maintaining clinker quality. NOx reductions in the order of 30 % were obtained. In the second experimental campaign the pulverised fuel was released by the splitted channel. NOx emissions, flame channel temperature and clinker quality were similar to those obtained using the standard channel. The lack of NOx reduction could be explained. In the third experimental campaign the combustion was staged (coal in the centre of the burner and in the standard channel). It seems possible to obtain lower NOx emissions if burner will be operated at a higher coal concentration.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (2nd application)
BRONI pet-coke: 25 - 26 MWth + 0.5 - 0.6 t/h in Lepol raw meal: 50 - 51 t/h
4000
previous burner
5600
3500
Rotaflam burner standard coal channel
4900
NOx kiln back end (mg/Nm @ 3% O2)
3000
4200
2500
3500
NOx
2000 2800
1500
2100
1000
1400
500
CO
700
0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
OXYGEN kiln back end (% )
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
CO kiln back end (mg/Nm @ 3% O2)
IN FIELD EXPERIENCES (2nd application)
Splitted and staged tests have not given significant NOx reduction with respect to the use of the standard channel also because during the tests two parameters have been changed: the coal concentration in the transport air and the burner position inside the kiln. The latter aspect is connected to the flame surrounding. surrounding In this condition it was evident that the well known phenomenon of flue gas back-circulation affected the NOx emissions. The effect of the re-circulation was proportionally higher with increasing the burner penetration even if a progressively larger kiln diameter affected with synergy the NOx reduction.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (2nd application)
BRONI - ROTAFLAM burner pet-coke: 25 - 26 MWth + 0.5 - 0.6 t/h in Lepol raw meal: 50 - 51 t/h
4000
before the tests 2002 132 cm
standard coal
standard coal
5600
170 cm
85 cm
3500
standard coal 32 - 192 cm
splitted coal 228 cm
4900
NOx kiln back end (mg/Nm @ 3 % O2)
3000
4200
splitted coal
staged coal
131 cm
199 cm
147 cm
85 cm
staged coal
2000
STAGED COAL
2800
1500
2100
1000
1400
500
CO
700
0 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
RATIO "coal / equivalent transport air" (kgpet/kgair )
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
2500
STANDARD and SPLITTED COAL
staged coal
3500
CO kiln back end (mg/Nm @ 3% O2)
NOx
splitted coal
214 cm
IN FIELD EXPERIENCES (2nd application)
BRONI - ROTAFLAM burner pet-coke: 25 - 26 MWth + 0.5 - 0.6 t/h in Lepol raw meal: 50 - 51 t/h
3000
burner at 23-85 cm
burner at 110 cm
170 cm
6000 5500 5000 4500
2500
burner at
NOx kiln back end (mg/Nm @ 3% O2)
2000
4000 3500
1500
3000 2500
1000
2000 1500
500
1000 500
0 1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
2.05
2.10
2.15
2.20
2.25
2.30
2.35
0 2.40
RATIO "coal / equivalent transport air" (kgpet / kgair )
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
CO kiln back end (mg/Nm @ 3% O2)
IN FIELD EXPERIENCES (1st application)
SARCHE - ROTAFLAM burner (20-21 MWth) pet-coke: 2.1-2.2 t/h + 0.6-0.7 t/h in Lepol Lepol grid velocity: 50-52 %
4000 5600
3500
4900
3000
NOx kiln back end (mg/Nm 3 @ 3% O2)
4200
CO kiln back end (mg/Nm3 @ 3% O2)
2500
3500
NOx
2000 2800
1500
main burner: 2 m travelled back
2100
main burner: 1 m travelled back
1000
main burner:
totally inserted
1400
500
700
CO
0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
OXYGEN kiln back end (%, wet)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (1st application)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
BURNER PERFORMANCES
NOx concentration is not the only pollutant to be taken into account. CO and SO2 are likewise important from an emission control standpoint, but also in particular for guaranteeing high combustion efficiencies which in turn mean low heat consumption. NOx, CO and SO2 are each other dependent.
1000 900 800 PORTO EMPEDOCLE - Kiln #2 ITC three-circuit burner
NOx
500 450
SO2
400
NOx (ppm as measured)
600 500 400 300 200 100 0 0 1000 2000 3000 4000 5000 6000 CO (ppm as measured)
300 250 200 150 100 50 0 7000
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
SO2 (ppm as measured)
700
350
BURNER PERFORMANCES
In the previous figures the CO concentrations are better correlated with the excess air than the coal / transport air ratio. It can be noted that the smoking point (i.e. the oxygen concentration at which the CO concentration begins to increase progressively) is very low. low This is due to an high combustion efficiency permitted by the ROTAFLAM burner as a consequence of its particular flexibility in guaranteeing the correct and optimum burner set-up suitable for satisfying different kiln operating conditions.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
LESSON LEARNED
NOx concentration depends mainly on the coal / transport air ratio for a certain specific heat input and burner position
B R O N I - N ew P illard kiln b u rn er stan d ard co al tests
2,500 N O x kiln b.e. (m g/N m 3 @ 3% O 2 ) 2,300 2,100 1,900 1,700
170 cm 110 cm
2,500 N O x kiln b.e. (m g/N m 3 @ 3% O 2 ) 2,300 2,100 1,900 1,700
23-85 cm
1,500 0.6
1,500
0.8
1.6
1 1.2 1.4 1.6 1.8 2
2.4 2.2 2
1.8
N O x con cen tration 2,500+ 2,400 to 2,500 2,300 to 2,400 2,200 to 2,300 2,100 to 2,200 2,000 to 2,100 1,900 to 2,000 1,800 to 1,900 1,700 to 1,800 1,600 to 1,700 1,500 to 1,600
O xygen kiln back end (% )
coal / transport air ratio (kg/kg)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
LESSON LEARNED
CO and SO2 concentrations are consistent with the available excess air and they can be controlled, to a certain extent, by an ad-hoc set-up of the outer air flows (axial and radial)
NAZARETH #1 - ROTAFLAM burner (axial air 6,750 Nm /h)
3
4000 3500
meal 300-310 st/h; 150 MWth
5000 4500 4000 3500
NOx
radial air 2,650 Nm3/h
meal 315-325 st/h;
155 MWth
NOx kiln back end (mg/Nm @ 6% O2)
2500 2000 1500 1000 500 0
CO
radial air 2,000 Nm3/h
3000 2500 2000 1500 1000 500 0
-500 -1000 0 1 2 3 4 5 6 7 8 9 10 11 12 OXYGEN kiln back end (% )
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
CO kiln back end (mg/Nm @ 6% O2)
3000
radial air 3,150 Nm3/h
meal 320-330 st/h;
156 MWth
BURNER GUIDELINES
Swirl level is a parameter deeply affecting the flame and the combustion. The great combustion difference between a mono tube and a multi-circuit burner is evident so as for the swirler intensity. It is a good tool for flame control and coating protection but it is often misused. misused Operators have opposing view on appropriate flame shapes and they make too many and frequent hurtful adjustments. adjustments
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
No swirl
Regular swirl
High swirl
LESSON LEARNED
NAZARETH #1 - 100% coal at main burner commissioning ROTAFLAM burner
4000 3500
coal 15.8 t/h; meal 220 - 225 st/h
coal 17.3 t/h; meal 240 - 280 st/h coal 15.7 t/h; meal 230 - 260 st/h
coal 16.5 t/h; meal 240 - 255 st/h
axial air 6,700 Nm3/h radial air 2,400 Nm3/h
5000 4500
NOx kiln b.e. (mg/Nm3 @ 6% O2)
2500 2000
3500 3000
NOx
1500 1000 500 0 -500 -1000 0 1 2 3 4 5 6 7 8 9 10 11 12 OXYGEN kiln back end (%)
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
2500
axial air 5,600 Nm3/h radial air 3,300 Nm3/h
2000 1500 1000
CO
500 0
CO kiln b.e. (mg/Nm3 @ 6% O2)
3000
4000
BURNER GUIDELINES
Mathematical modelling helps to study the aerodynamic of the near field of the burner and to solve the relative problems. Figures show how the bowl effect (and consequently the expected wear problem) can be modified by shortening the hot outer tube and changing the axial air flow rate.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
LESSONS LEARNED
The flame surrounding, due to the burner penetration in the surrounding kiln, could produce an in-flame flue gas back-circulation which in turn gives an efficient NOx reduction because the oxygen concentration at the flame root is reduced, practically where the volatile matters are released and NOx are formed.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
IN FIELD EXPERIENCES (2nd application)
3,100
NO x kiln b.e. 2,900 (mg/Nm 3 @ 3% O 2 )
3,100
2,700 2,500 2,300 2,100 1,900 1,700 0.6 0.8
1 1.2 Oxygen 1.4 kiln back end (%) 1.6 1.8 2
214 - 228 cm
NO x kiln b.e. 2,900 (mg/Nm 3 @ 3% O 2
2,700 2,500 2,300
131 - 132 cm
2,100 1,900 1,700
2 2.2 2.4
1.8
1.6
coal / transport air ratio (kg/kg)
NOx kiln back end 2,500+ 2,400 to 2,500 2,300 to 2,400 2,200 to 2,300 2,100 to 2,200 2,000 to 2,100 1,900 to 2,000 1,800 to 1,900 1,700 to 1,800 1,600 to 1,700 1,500 to 1,600
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
CONCLUSIONS
The above mentioned scheme confirms what has been found in other recent applications and it shows the common way for reading the kiln emissions
K IL N B U R N E R S C o m p a ris o n a m o n g d iffe re n t a p p lic a tio n s
4000
P IC T O N
N A Z A R ET H #1
4800
1 2 5 M W th
1 1 5 M W th
1 1 0 M W th
1 6 0 M W th
1 5 5 M W th
1 1 3 M W th
25
25
m e a l 2 2 0 - 2 3 5 t/h
m e a l 2 1 5 - 2 2 5 t/h
m e a l 1 9 0 - 2 0 0 t/h
m e a l 3 2 0 - 3 2 5 t/h
m e a l 3 2 5 - 3 3 0 t/h
m e a l 3 2 5 - 3 3 5 t/h
m eal 48 - 50
m eal 49 - 50
3500
N A Z A R ET H #1
N A Z A R ET H #1
4200
NOx kiln back end (mg/Nm @ 6 % O2)
BRONI
M W th
M W th
t/h
t/h
32 - 200 cm
85 cm
2500
NOx
BRONI
3000
2000
2400
1500
1800
1000
1200
500
CO
600
0 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
R A T IO " c o a l / e q u iva le n t tra n s p o rt a ir" (k g c o a l / k g a ir )
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
CO kiln back end (mg/Nm @ 6% O2)
3000
N A Z A R ET H #1
G A U R IN # 4
3600
CONCLUSIONS
NOx formation depends on different parameters, a few parameters among them are typical of the clinker process. Consequently manipulation of combustion process does not always produce the expected results on NOx control. Therefore each kiln-burner arrangement has to be apart considered and optimised.
5 TH INTERNATIONAL CONFERENCE on FIRING SYSTEMS PILLARD AKTUELL 19th MARCH 2003 WIESBADEN (GERMANY)
