Production de la chaleur - Chaudière1 Combustion and Heat production equipment Jean-Marie SEYNHAEVE PART 1 : Theoretical background 1.1 Combustion = Chemical.

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1 Production de la chaleur - Chaudière1 Combustion and Heat production equipment Jean-Marie SEYNHAEVE PART 1 : Theoretical background 1.1 Combustion = Chemical reaction 1.2 Heating values of fuels PART 2 : Heat production : equipment 2.1 Energy balance and equipment efficiency 2.2 Combustion control 2.3 Illustration of burners 2.4 Practical problems

2 Production de la chaleur - Chaudière2 Part 1 : Theoretical background - Table of contents I - COMBUSTION : CHEMICAL REACTION 1.1 Examples of Chemical Reaction of Combustion, Fundamental Laws 1.2 Air Required for Combustion - Flue Gases contents 1.2.1 Solid or Liquid Fuel 1.2.2 Gas Fuel 1.2.3 Practical Problems II - HEATING VALUES OF FUELS 2.1 Heat of Reaction - Some Examples 2.2 Definition of the Heating Value of a Fuel 2.3 How to evaluate the Heating Value of Fuels 2.3.1 Solid or Liquid Fuel 2.3.2 Gas Fuel 2.4 Practical Examples of Evaluation

3 Production de la chaleur - Chaudière3 Combustible Elements in Fuels : C S H 2 CO CH 4 C 2 H 4 C 2 H 6 C 3 H 8...... Alcans : C n H 2n+2 Alcens : C n H 2n Aromatics... I. Combustion – Chemical reaction : Fundamental laws Combustion : C + O 2 CO 2 S + O 2 SO 2 H 2 + ½ O 2 H 2 O CO + ½ O 2 CO 2 CH 4 + 2 O 2 CO 2 + 2 H 2 O C 2 H 4 + 3 O 2 2 CO 2 + 2 H 2 O........ C n H 2n+2 + ½ ( 3n + 1 ) O 2 n CO 2 + ( n + 1 ) H 2 O Chemical Reaction of Oxidation + HEAT

4 Production de la chaleur - Chaudière4 Chemical BALANCED reactions in terms of number of MOLES C n H 2n+2 + ½ ( 3n + 1 ) O 2 n CO 2 + ( n + 1 ) H 2 O n C n C + n O 2 ( n + 1 ) H 2 ( n + 1 ) H 2 + ½ ( n + 1 ) O 2 ½ ( 3n + 1) O 2 ½ ( 3n + 1 ) O 2 Molecular weight of molecules : Example : C 2 H 6 : 2x12 kg/kmole + 3x2 kg/kmole = 30 kg/kmole

5 Production de la chaleur - Chaudière5 Some important laws : AVOGADRO At same pressure and temperature, 1 kmole of every gas occupies the same volume. For Normal Conditions ( t= 0 °C, p = 760 mm Hg) : LAVOISIER The total MASS in reaction remains constant Application to air composition (combustive) : O 2 N 2 ( Ar Ne Xe … ) - Molar Fractions = Volume Fractions for air ( Avogadro Law ) : [O 2 ] = 0.210 (kmole of O 2 / kmole of Air or m 3 of O 2 / m 3 of Air) [N 2 ] = 0.790 " N 2 " " N 2 " - For Air : 1 kmole of O 2 + 0.79/0.21 ( 3.76 ) kmole of N 2 [i] - Mass fraction for air : (i) 0.210 kmole of O 2 = 6.72 kg of O 2 0.790 kmole of N 2 = 22.12 kg of N 2 1 kmole of Air = 28.84 kg of Air

6 Production de la chaleur - Chaudière6 Air required for Combustion – Production of flue gases Pouvoir comburivore – Pouvoir fumigène Fuel composition For solid and liquid fuel : elementary mass composition Combustible Elements : C (H) (S)... Oxygen in Fuel : (O) Humidity : (H 2 O) Inert Elements : (N) (Ash) For gas fuel : molar (volume) composition Combustible components : [H 2 ] [CO ] [CH 4 ] [C 2 H 4 ] [C 2 H 6 ]... (Oxygen in Fuel : [O 2 ]) Humidity : [H 2 O ] Inert Elements : [N 2 ] [CO 2 ] … Definition : Excess of air

7 Production de la chaleur - Chaudière7 SOLID and LIQUID FUEL - Combustion accounting

8 Production de la chaleur - Chaudière8 SOLID and LIQUID FUEL – Flue gases composition The flue gases composition is usually given for a DRY SAMPLE Possible measurements … Dry sample

9 Production de la chaleur - Chaudière9 GAS FUEL - Combustion accounting

10 Production de la chaleur - Chaudière10 GAS FUEL – Flue gases composition The flue gases composition is usually given for a DRY SAMPLE Possible measurements … Dry sample !

11 Production de la chaleur - Chaudière11 Objectives of those accounting tables Practical point of viewTheoretical point of view Stack Flue Gases Analysis Device Purging Volume fraction on Dry Flue Gases Excess of air evaluation Combustion control Heat production equipment efficiency

12 Production de la chaleur - Chaudière12 II. Heating values of fuels (Pouvoir calorifique) Combustible Elements in Fuels : C S H 2 CO CH 4 C 2 H 4 C 2 H 6 C 3 H 8...... Alcans : C n H 2n+2 Alcens : C n H 2n Aromatics... Combustion :

13 Production de la chaleur - Chaudière13 Principle of Energy balance : Heating (calorific) value – Pouvoir calorifique : Definition Calorimeter of MALHER Fuel + Air P atm, t = 25 °C Adiabatic combustion Hot flue gas Cooling Cold flue gas At t = 25°C Heat which is extracted = Heating value Calorimeter of YOUNGER Experiment at constant VOLUME Experiment at constant PRESSURE

14 Production de la chaleur - Chaudière14 Type of Heating value 4 types 1 st distinction : Constant Volume or Constant Pressure ? In practice CV v never used … 2 nd distinction : Flue gas at 25 °C H 2 O Vapour Lower (Net, inférieur) CV H 2 O Liquid Higher (Gross, supérieur) CV In practice:HCV USA, UK, Natural Gas … LCV G,F,I,H,B, … Conclusion :HCV v LCV v HCV p LCV p

15 Production de la chaleur - Chaudière15 Evaluation of Heating Values of fuels Heating Values of Solid or Liquid Fuels Fuel composition : reference 1 kg of fuel Elementary composition : (C) (H) (S) … (O) (H 2 O) (N) … Heating for solid or liquid fuel :

16 Production de la chaleur - Chaudière16 Heating for gas fuel : Heating Values of Gas Fuels Composition of gas fuel : reference 1 m 3 N Combustible components Inert components

17 Production de la chaleur - Chaudière17 Combustibles solides Combustibles liquides PCI = 44000 … 42000 kJ/kg fractions légères lourdes CHARBON BOIS PCI BRUT = [1 - (cen) - (H 2 O)] PCI PUR & SEC - 2501 (H 2 O) PCI PUR & SEC = 35000 … 35500 kJ/kg PCI PUR & SEC 18500 kJ/kg si (H 2 O) = 0.20 PCI BRUT 14300 kJ/kg

18 Production de la chaleur - Chaudière18 Combustibles gazeux PCI = 802 400 kJ/kmole = 50 150 kJ/kg 1 kmole CH 4 22.414 m 3 N PCI = 35 800 kJ/m 3 N 1 kmole CH 4 2 kmole H 2 O = 36 kg H 2 O PCS - PCI = 36 x 2501 = 90 036 kJ/kg PCS = 892 436 kJ/kmole = 39 816 kJ/m 3 N CH 4

19 Production de la chaleur - Chaudière19 Examples of Evaluation 1. Liquid fuel (fuel-oil, gas-oil, gasoline, kerosene …) : Where a is the number of atoms of hydrogen per atom of carbon Calculate the HCV and the LCV

20 Production de la chaleur - Chaudière20 2. Natural gas : Calculate the HCV and the LCV

21 Production de la chaleur - Chaudière21 Part 2 : Heat Production Equipment I - ENERGY BALANCE AND EQUIPMENT EFFICIENCY 1.1 Scheme of heat production equipment 1.2 Input and output of energy 1.3 Efficiency and Description of Losses II - COMBUSTION CONTROL III - ILLUSTRATION 3.1 Gas Burners, Oil Burners, Coal-Fired Stokers 3.2 Pulverised Fuel System 3.3 Multiple Fuel Burners 2.4 Boilers (fire tubes, water tubes) IV - PRACTICAL PROBLEM

22 Production de la chaleur - Chaudière22 I. Energy balance and efficiency 1. Scheme of heat production equipment

23 Production de la chaleur - Chaudière23

24 Production de la chaleur - Chaudière24 2. Input and Output of Energy

25 Production de la chaleur - Chaudière25 3. Efficiency of heat production equipment Input of Energy Output of Energy Definition of Efficiency After calculation

26 Production de la chaleur - Chaudière26 II. Combustion control 1. Optimisation of combustion - Criteria

27 Production de la chaleur - Chaudière27 Combustion control -Diagram

28 Production de la chaleur - Chaudière28 Combustion control -Diagram

29 Production de la chaleur - Chaudière29 2. Parameters controlling the combustion

30 Production de la chaleur - Chaudière30 Corrosion acide Gasoil ; gaz naturel Fraction molaire dans gaz brûlés [H 2 O] = 0.12 ; 0.19 à = 1 [H 2 O] = 0.114 ; 0.181 à = 1.05 p sat 0.114 ; 0.181 t sat 49°C 58°C Seuil de condensation : t p = t sat t fs = 2 t sat - t a0 si t a0 = 0°C t fs = 98°C ; 116°C

31 Production de la chaleur - Chaudière31 Charge partielle Charge / Régime : Pertes fixes (parois) : Pertes proportionnelles : Puissance utile : Rendement nominal :

32 Production de la chaleur - Chaudière32 Charge partielle Rendement à charge partielle : or On obtient finalement FORMULE DE DITTRICH

33 Production de la chaleur - Chaudière33 Charge partielle

34 Production de la chaleur - Chaudière34 III. Illustrations Gas burners

35 Production de la chaleur - Chaudière35 Liquid fuel burners

36 Production de la chaleur - Chaudière36 Cas détude : Économiseur dune chaudière Brûleur Air de combustion T = 20 °C Gaz naturel Eau dalimentation Vapeur 3 bars, 135 °C Cheminée [O 2 ] = 0.03 T f = 180 °C Economiseur Chaudière Caractéristiques chaudière Puissance thermique : 10 MW Utilisation : 4000 h/an Prix du combustible : 0.25 /m 3 N Caractéristiques économiseur (AU) : 0.7 kW/K Courant croisé « fluides non mélangés » Durée de vie : 10 ans Coût de linstallation : 30000 Entretien : 2000

37 Production de la chaleur - Chaudière37 Évaluation des conditions de fonctionnement de la chaudière Combustible Pouvoir calorifique : Composition : [CH 4 ] = 0.81 [C 2 H 6 ] = 0.05 [N 2 ] = 0.11 [CO 2 ] = 0.03... PCS = 35626 kJ/m 3 N Débit nominal : Q comb = 0.287 m 3 N /s Consommation annuelle : C = 0.287 x 3600 x 4000 = 4132800 m 3 N /an Coût annuel combustible : F combustible = 1033202 /an

38 Production de la chaleur - Chaudière38 Combustion Excès d air : Pouvoir comburivore: = 1.147 Pouvoir fumigène : V a, = 9.804 m 3 N d air / m 3 N de gaz Débit dair : V f, = 10.826 m 3 N d air / m 3 N de gaz Débit de fumée : Q air = 2.814 m 3 N /s = 3.638 kg/s Q fumée = 3.107 m 3 N /s = 4.017 kg/s