Numerical Study of the Impact of CO2 Dilution on Emissions in Turbulent Diffusion Flame

Available online at www.sciencedirect.com

ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000

ScienceDirect ScienceDirect

www.elsevier.com/locate/procedia

Energy (2017) 000–000 273–279 EnergyProcedia Procedia139 00 (2017) www.elsevier.com/locate/procedia

International Conference On Materials And Energy 2015, ICOME 15, 19-22 May 2015, Tetouan, Morocco, and the International Conference On Materials And Energy 2016, ICOME 16, 17-20 May 2016, La Rochelle, France The 15th International Symposium on District Heating and Cooling

Numerical Study of the Impact of CO2 Dilution on Emissions in Assessing the feasibility using theFlame heat demand-outdoor Turbulentof Diffusion temperature function for a long-term district heat demand forecast 1 1 2 3 Amar Hadef *, Abdelbaki Mameri , Fouzi Tabet and Zeroual Aouachria

a a b c I. Andrića,b,c *, A. Pina , P. Ferrão , J.Université Fournier ., ElB.Bouaghi Lacarrière , O. Le Correc Département de Génie Mécanique , FSSA, d’Oum 04000 Algerie 1

a

2 DBFZ, Torgauer Straße 116, D-04347 Leipzig, Germany 3 IN+ Center for Innovation, Technology PolicyEnergétique Research - Instituto Superior Técnico, Av. 05000 RoviscoAlgerie Pais 1, 1049-001 Lisbon, Portugal Laboratoire deand Physique Appliquée, Université Batna1 b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France

Abstract The environmental and economic objectives for the reduction of fuel consumption and reduction in the polluting emissions are Abstract always of crucial news. Thus, the elucidation of new techniques of combustion using the diffusion flame (more secure) in a confined environment and the comprehension of the involved physical phenomena remains of capital challenge. The dilution of District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the the combustion air by CO2 has confirmed its technological interest; the objective of this work is to quantify numerically the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat polluting emissions in a turbulent diffusion flame. The air is diluted by CO2 and attention has been paid to its thermal and sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, chemical effects on the internal structure of the flame. It is found that CO2 addition reduces flame temperature by both thermal prolonging investment period. are also reduced by CO increasing in the air. and chemicalthe effects. Most ofreturn the emissions 2 The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 vary in both construction ©buildings 2017 Thethat Authors. Published by Elsevierperiod Ltd. and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Peer-review under responsibility of the scientific committee of ICOME 2015 and ICOME 2016. compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that whenscalar onlydissipation weather change is considered, margin of error could be acceptable for some applications Keywords: Turbulent combustion, rate, flamelet model, COthe 2 effects (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the 1.The Introduction decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the The new regulations, which protect the environment, require new technologies to reach a clean combustion and coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and high-energy efficiency. However, improve the accuracy of heat demandrenewable estimations.energies are the only ones, which can achieve this goal, therefore, it is

essential to improve the effectiveness of the conventional energy installations to reduce polluting emissions (NOx, © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: Tel.: 00213698852304; fax: 0021332697221 Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected] 1876-6102 © 2017 The Authors. Published by Elsevier Ltd.

Peer-review under responsibility of the scientific committee of ICOME 2015 and ICOME 2016. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of ICOME 2015 and ICOME 2016 10.1016/j.egypro.2017.11.208

274 2

Amar Hadef et al. / Energy Procedia 139 (2017) 273–279 A. Hadef et al. / Energy Procedia 00 (2017) 000–000

SOx, particles of soot and so on) and to reach with their outputs. In the energy installations using turbulent nonpremixed combustion, where the oxidant and the fuel are injected separately, the stabilization of the flame is difficult * Corresponding author. Tel.: 00213698852304; fax: 0021332697221. E-mail address: [email protected]

to control and the operating range of the burners is determined by the stability of the flame. The comprehension of the non-stationary phenomena of the diffusion flame is important for the development of new technologies in the industrial burners. In this directive, a new mode of operation of the furnaces with high energy which use regenerative burners is identified by Katsuki et al.[1] and Weber et al.[2]. This mode is based on the strong recirculation of the products of combustion in the combustion chamber to dilute the reactants. This mode is characterized by a weak noise which is due to weak fluctuations of temperatures and pressures with a significant reduction of the emissions of NOx and soot particles [3],[4],[5]. This new mode of combustion improves the pre-heating of fresh gases and dilutes them by the products of combustion. In the recirculation of burnt gases, the CO2 plays an important role in the internal structure of the flame and the quantities of the combustion products. Experimental works of Dally et al.[6] , Oh et al.[7], and Takahashi et al.[8] and numerical studies of Liu et al. [9], Park et al. [10], Katta et al.[11] , Briones et al. [12] and Guo et al. [13] describes the behaviour of the non-premixed hydrocarbon flames with a CO2 addition to the fuel or the oxidant. Generally, CO2 is regarded as an inert gas, however, researches in particular those developed by Liu et al. [9], Park et al. [10] and Guo et al.[13] showed numerically that there exists a modifications in the kinetics of the reactions. In this work, an inert species labelled X_CO2, which has the same physical and transport properties as CO2 but without taking part in the chemical reaction, is introduced to quantify the chemical effect of CO2. Thus, the difference between the action of species X_CO2 and that of CO2 are due only to chemical effect of CO2. This work constitutes a CFD contribution to the quantification of the polluting emissions of a turbulent diffusion flame. A volume of 0% to 24% of CO2 dilutes the air; where the last percentage represents the volume needed to extinguish the flame. Pressure is kept 1 atm and reactants injection temperature is 294 K. Chemical kinetics is modeled by the Grimech 3.0 [14] mechanism, which is composed by 53 species and 325 reactions. Chemical effects of CO2 are also elucidated by using the artificial species technique. 2. Flame configuration The burner is formed by a central jet of diameter D =7.2 mm which injects a mixture of methane-air (25% vol. CH4, 75% vol. air) with a Reynolds number of 22400. The jet is surrounded by a set of small pilot flames spread over a diameter of 18.2 mm and the burner is plunged in a flow of air. The injection velocity of the central jet is 49.6 m/s, the one of the pilot flame is 11.4 m/s and that of the air is 0.9 m/s [15].

Fig.1 Geometry of the combustion chamber.

3. Gas phase governing equation and numerical method The flow and mixture fraction fields are studied in an axisymmetric geometry. The effects of turbulence are modelled by the two transport equations ( k − ε ). It is well known that the standard model ( k − ε ) over-estimates the



Amar Hadef et al. / Energy Procedia 139 (2017) 273–279 A. Hadef et al. / Energy Procedia 00 (2017) 000–000

275 3

rate of round widening of the round jets. This over-estimation can come from the growth of the size of the swirls and the acceleration of their destruction related to the axisymmetric effects. Priest [16] takes into account this effect by adding an additional term of production of dissipation into the transport equation of ε proportional to the stretching swirl. A transport equation for the average enthalpy is solved with the radiation source term. Instead of solving the transport equations of several species, the equations of the mixture fraction and its variance are solved. Then the species are obtained from a table calculated preliminarily by the flamelet model[17]. The equations that describe the reactive turbulent flow are of convective diffusive type with a source term. These equations are converted into algebraic equations by discretization with UpWind scheme [18], the SIMPLE (Semi Implicit Algorithm for Pressure Linked Equations) algorithm is used to achieve pressure coupling, and finally the solution of the algebraic system of equations is obtained by using the Thomas algorithm. 4. Results and discussion 4.1. Validation of the calculation procedure: Figure 2 shows the profiles of the mixture fraction and the temperature along the central line. The axial decrease of the mixture fraction is well reproduced and the measured temperatures are estimated with a reasonable precision. However, the mixture fraction and the temperature are slightly underestimated between x= 100 mm and x = 350 mm which can be related to uncertainties in the velocity profile at the entry [19]. These results show that calculation by the approach of the flamelet and the model (k − ε ) correctly predicts the form of the flame, its height and the distribution of the temperature. 1.00

2000 Exp. T

k-epsilon

1500

0.50

1000

0.25

500

0.00

Mean Temperature K

Mixture Fraction Z

Exp. Z

0.75

0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 x [m]

Fig.2 Centerline mixture fraction and temperature in flame.

4.2. The effect of dilution by CO2 on the thermal field It is noted that the length of flame does not change since we did not modify the geometry and the boundary conditions (Fig.3). On the other hand, the maximum of temperature decreases from 1876 K to 1397 K. Figure 4 shows that the position of the peak of temperature XTmax, used in the determination of the length of the flame Lf (Lf = XTmax), is unchanged with the increase of dilution (Fig.4). Contrary to the length of the flame, the maximum of temperature decreases with added CO2 by about 24%.

Amar Hadef et al. / Energy Procedia 139 (2017) 273–279 A. Hadef et al. / Energy Procedia 00 (2017) 000–000

276 4

2000

45 00 % CO2 05 % CO2

1800

15 % CO2 20 % CO2

40

Mean Tmax K

Flame length ( Lf/Df)

10 % CO2

24 % CO2

35

1600

1400

1200 0 5 10 15 20 25 Dliuent in air stream (%CO2 by volume )

0

5

10

15

20

25

Dliuent in air stream ( % CO2 by volume )

Fig. 3. Effect of dilution on the length of the flame

Fig.4. Effect of dilution on the maximum temperature of the flame.

00 % addi.CO2

2000

05 % addi.CO2

Temperature (K)

10 % addi.CO2 15 % addi.CO2

1600

20 % addi.CO2 24 % addi.CO2

1200 800 400 0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

X (m)

Fig.5 Profile of the temperature on the axis of symmetry

Figure 5 represent the axial profiles of temperature for various percentages of dilution by the CO2 species. It is noticed that the axial evolution of temperature has similar behaviors for all cases. Dilution does not affect the axial profiles in the zone close to the outlet of the central methane tube, however its effect is more pronounced especially for x > 0.2m. 00% addi. CO2

8,0E-5

20% addi. CO2 24% addi. CO2

4,0E-5 2,0E-5

05% addi. CO2 10% addi. CO2

2,0x10-3 Mole fraction of OH

6,0E-5

0,0

15% addi. CO2 20% addi. CO2 24% addi. CO2

-3

1,5x10

1,0x10-3 5,0x10-4 0,0

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,0

0,1

0,2

0,3

X (m)

0,4

0,5

0,6

0,7

0,8

X(m)

(a) Mass fraction of H.

(b) Mass fraction of OH. 2,1E-4

5E-5 00% addi. CO2 10% addi. CO2

05% addi. CO2 10% addi. CO2

1,5E-4 Mole fraction of NO

15% addi. CO2 20% addi. CO2

3E-5

00% addi. CO2

1,8E-4

05% addi. CO2

4E-5 Mole fraction of HCN

Mole fraction of H

10% addi. CO2 15% addi. CO2

00% addi. CO2

2,5x10-3

05% addi. CO2

24% addi. CO2

2E-5 1E-5 0

15% addi. CO2 20% addi. CO2

1,2E-4

24% addi. CO2

9,0E-5 6,0E-5 3,0E-5 0,0

0,0

0,1

0,2

X(m)

0,3

0,4

0,0

0,1

0,2

0,3

0,4 X(m)

0,5

0,6

0,7

0,8



Amar Hadef et al. / Energy Procedia 139 (2017) 273–279 A. Hadef et al. / Energy Procedia 00 (2017) 000–000

(d) Mass fraction of HCN.

277 5

(e) Mass fraction of NO.

Fig.6 Profiles of the mass fractions of the species on the axis of symmetry.

We notice that the most important variations are around the point x = 272 mm, i.e. the maximum of the variables; it is in the zone of the flame front (T=Tmax). The none existent species in the mixture zone such as H, OH and the HCN will appear gradually and increase to reach maximum values in the zone of reaction as showed by Figs. 6 (a),(b),(c) and (e). The behavior of their mass fractions is similar. For the specie H (Fig. 6(a) ) the reduction is about 73%, and for the species OH is reduced almost with the same rate Fig. 8(b). In the rich zone of the flame, the carbonaceous radicals (CX) can easily break the nitrogen molecule following the reaction N 2 + Cɺ H → Nɺ + HCN with activation energy of 50 Kcal/mole. Due to that, the species HCN (Fig.6(d)) is formed in a very narrow zone on the axis of the flame with a considerable growth, then it is dissociated quickly with the temperature diminution. The nitric oxide will appear and increase gradually starting from the point X =150 mm to reach maximum values in the zone of reaction as show it Fig. 6(e), downstream from the flame front, the concentration of this species decreases to reach its outlet value. The concentration of nitrogen oxide decreases by 93% when CO2 with 24% in the air. 4.3. CO2 chemical effects

The chemical effect of CO2 is showed, for atmospheric pressure with different dilution percentage, by the Figs. 6, 7(a),(b),(c) and (d). The artificial inert species X_CO2, which has the properties similar (transport, radiation and thermochemical) to that of CO2 is presented to characterize the chemical effects of CO2 on the structure and the emissions. Consequently, the difference between the calculated properties of flame with the artificial species X_CO2 and CO2 is due to the chemical effects of additional CO2[10].

Thermal effects

1400 CO2 addi.

Combined effects

1600

Chemical effects

Maximum flame temperature (K)

1800

X_CO2 addi.

1200

0,00

0,05

0,10

0,15

0,20

0,25

CO2 or X_CO2 mole fraction in oxyder

5x10

-5

4x10

-5

3x10-5 2x10

-5

addi. CO2 X_addi. CO2

0,00

0,05

0,10

0,15

0,20

0,25

Mole fraction added CO2 or X_CO2

(a) Mass fraction of H.

2,0x10

-3

Thermal effets

-5

1,5x10-3 1,0x10

-3

5,0x10

-4

addi. CO2 addi. X_CO2

0,00

0,05

Combined effects

6x10

2,5x10-3

chemical effets

-5

Maximum mole fraction OH

7x10

3,0x10-3

Thermal effects

-5

Combined effects

8x10

Chemical effects

Maximum mole fraction H

Fig. 6 Chemical effects of added CO2 in the behavior of maximum flame temperature and variation of maximum flame temperature on the axis of symmetry.

0,10

0,15

0,20

Mole fraction of added CO2 or X_CO2

(b) Mass fraction of OH.

0,25

A. Hadef et al. / Energy Procedia 00 (2017) 000–000 Amar Hadef et al. / Energy Procedia 139 (2017) 273–279

addi. CO2 addi. X_CO2

5,0x10-5

thermal effects

addi. CO2 addi. X_CO2

0,0 6,0x10-7

0,00

0,05

0,10

0,15

0,20

Mole fraction added CO2 or X_CO2

0,25

0,00

0,05

Combined effects

1,0x10-4

chemical effets

8,0x10

-7

Maximum mole NO

1,0x10

1,5x10-4 Combined effects

1,2x10-6 Thermal effects

Maximum mole fraction HCO

1,4x10-6

-6

2,0x10-4

Chemical effects

6 278

0,10

0,15

0,20

0,25

Mole fraction added CO2 or X_CO2

(c) Mass fraction of HCO. (d) Mass fraction of NO. Figure 7. Chemical effects of added CO2 in the behaviour of maximum mass fractions of the species.

The temperature is very affected by CO2 ( Fig. 6), it is reduced by 79%; which represents the thermal effect of CO2. When the artificial species is introduced, the temperature is increased by 15%; which represents the chemical effect. Temperature is reduced by both thermal and chemical effects of CO2. Figures 7(a) and 7(b) represent the precursors of combustion, the species H and OH which are very affected by CO2 via the reaction CO2+H CO+OH. When adding CO2 from 0 to 24%, the radical H is reduced by 69% in which 41% is due to chemical effect and 59% is caused by thermal effect. The species OH is reduced by 70% in which 24% is attributed to chemical effect and 76% to thermal effect [20]. Figure 7(c) presents the evolution of the species HCO, which is not reduced by CO2. The most important reaction of HCO production is CO2+CHCO+HCO, it can be seen that this species is enhanced by both thermal and chemical effects. Thermal NO in Fig. 7(d) is produced according to dominant reaction N+OHNO+H, it is affected by CO2 indirectly, by the mean of OH, it takes the same way of OH, with a reduction of 85% by thermal effect and 15% of chemical one. Conclusion Carbon dioxide dilution has important chemical effects on the internal structure of the flame. The free radicals H and OH play important role on the chemical effects where the reaction CO2 + H  CO + OH is primarily responsible for the CO2 addition chemical effects. The dilution of the air stream by CO2 leads to a reduction of the concentrations of the important radical species, such as O, H, CO and the HCN which implies the reduction of NO directly. The rate of formation of NO can be reduced approximately by 93% with CO2 dilution of the air. In spite of dilution impacts on the reduction of the maximum temperature of the flame, which is about 25%, its length remains constant. References

[1] Katsuki, M.; and Hasegawa, T. The science and technology of combustion in highly preheated air. Proceedings of the Combustion Institute, 27.1998.p. 3135–3146. [2] Weber, R.; Verlan, A.D.; Orsino, S.; and Lallement, L. On emerging furnace design methodology that provides substantial energy saving and drastic reduction in CO2 and CO and NOx emissions. Journal of the Institute of Energy, 72,1999.p.77–83. [3] Wunning, J.A.; and Wunning, J.G. Flameless oxidation to reduce thermal NO-formation. Progress in Energy and Combustion Science, 23,1997.p. 81–84. [4] Milani, A.; and Saponaro, A. Diluted combustion technologies. International Flame Research Foundation Combustion Journal, 01,2001.200101. [5] Cavaliere, A.; and Joannon, M. Mild combustion. Progress in Energy and Combustion Science, 30(4),2004.p. 329–366. [6] Dally, B.B.; Karpetis, A.N.; and Barlow, R.S. Structure of turbulent non-premixed jet flames in a diluted hot coflow. Proceedings of the Combustion Institute, 29,.2002.p. 1147–1154. [7] Oh, K.C.; and Shin, H.D. The effect of oxygen and carbon dioxide concentration on soot formation in non-premixed flames. Fuel, 85, 2006.p.615–624. [8] Takahashi, F.; Linteris, G.T.; and Katta, V.T. Extinguishment mechanisms of coflow diffusion flames in a cup-burner apparatus. Proceedings of the Combustion Institute, 31, 2007.p.2721–2729.



Amar Hadef et al. / Energy Procedia 139 (2017) 273–279 A. Hadef et al. / Energy Procedia 00 (2017) 000–000

279 7

[9] Liu, F.; Guo, H.; Smallwood, G.J.; and Gulder, O.L. The chemical effects of carbon dioxide as an additive in an ethylene diffusion flame : implications for soot and NOx formation. Combustion and Flame, 125,2001.p.778–787. [10]Park, J.; Hwang, D.J.; Kim, K-T.; Lee, S-B.; and Keel, S-I. Evaluation of chemical effects of added CO2 according to flame location. International Journal of Energy Research,28,2004.p.551–565. [11] Katta, V.R.; Takahashi, F.; and Linteris, G.T. Suppression of cup-burner flames using carbon dioxide in microgravity. Combustion and Flame,137,2004.p.506–522. [12] Briones, A. M.; Aggarwal, S.K.; and Katta, V. R. A numerical investigation of flame liftoff and stabilization and blowout. Physics of Fluids, 18,2006.p 043603. [13]Guo, H.; and Smallwood, G. A numerical study on the influence of CO2 addition on soot formation in an ethylene/air diffusion flame. Combustion Science and Technology, 180, 2008.p.1695-1708. [14] Bowman, C.T.; Hanson, R.K.; Davidson, D.F.; Gardiner, W.C.; Lissianski, V.V.; and Smith, G.P., Retrieved March 24 2014,from http://www.me.berkelry.edu/gri_mech/. [15] Barlow, R.S.; Frank, J.H.; Karpetis, A.N.; and Chen, J-Y. Piloted methane/air jet flames: Transport effects and aspects of scalar structure. Combustion and Flame 143,2005.p. 433-190. [16 Smith, N.; Gore, J.P.; Kim, J.M.; and Tang, Q. Submodels Radiation. Retrieved April 25,2013,from http://www.ca.sandia.gov/tdf/Worhshop/Submodels.html. [17] Hadef, A.; Aouachria, Z.; and Rezgui, Y. Reduction of no formation by thermal effect of a turbulent diffusion flame H2/Air modeled by the concept of laminar flamelet. Journal of Engineering Science & Technology, 11(3), 2016.p.383 – 396. [18] Patankar, S.V. Numerical Heat Transfer and Fluid Flow, Chapter five: convection and diffusion. Hemisphere Publishing Corporation, 41977,1980.p.96-100. [19] Kleiveland, R.N. Modelling of soot formation and oxidation in turbulent diffusion flames. Ph.D. thesis, University of Science and Technology, Norwegian.2005. [20] Mameri.A and Tabet.,F. Numerical investigation of counter-flow diffusion flame of biogase hydrogen blends: Effects of biogas composition, hydrogen enrichment and scalar dissipation rate on flame structure and emissions, international journal of hydrogen energy , 41(3).2016.p.2011–2022