THERMOGASDYNAMICS AND ECOLOGICAL

CHARACTERISTICS OF COMBUSTION CHAMBERS

RUNNING THE NATURAL GAS

Institute for Engineering Thermophysics

National Academy of Sciences of Ukraine

Prof. A. Khalatov, Dr. S. Kobzar, Dr. G. Kovalenko,

Dr. V. Demchenko

The 11th PHOENICS Users Conference, London, UK, 2006

1. Introduction

2. Boiler «Victor» and Combustion Chamber

3. Results and Discussions:

3.1. Basic design

3.2. H2S in the natural gas

4. Conclusions.

С О N T E N T S

• Computer design is based on the flow, heat and mass transfer modeling using numerical simulation of basic transport equations.

• Commercial packages «FLUENT», «STAR-CD», «PHOENICS» and others are widely used in various applications.

• Advantages:- saving of time and money;- wide range of designs and boundary conditions;- easy changes in air and fuel regimes;- easy changes in combustion chamber design;- clear demonstration of results;- finding of information not registered in experiments.

1. Introduction

• Examples of Computer Modeling

• Flow streamlines inside the burner.

• Aerodynamics of the be-burner combustion chamber.

2. Boiler “Victor» and Combustion Chamber

• Boiler «Victor»

Boiler «Victor», 100 kWt power. Combustion chamber : D = 412mm, L = 1140 mm,

Burner: Giersсh–RG20 (gas flow rate – 12,6 m3/h; air excess – 1,2)

• Burner

Exit of gases

1. Chemical reaction: СН4 + 1,5·02 CO + 2·H20

CO + 0,5·O2 CO2

2. Average speed of the methane burning (first reaction; model of the vortex breakdown - EBU):

RCH4 = - CEBU·min {CH4; O2/3,0}··k , кg/(m3с), CEBU=2,0

4. NOx formation : Thermal and Prompt мechanizm.

3. Average speed of СО to СО2 oxidation (minimal magnitude of a speed according to EBU-model and Arrenius law) :

- RCO = - min {REBU; RAr );

- RAr= 5,4 109 ·exp {- 15000 / T}·[CO]·[O2]0,25 ·[H20]0,5 , [к·mol / (m3·с)]

3. Results and Discussions

• Kintetics of natural gas burning:

3.1. Basic design

• Flow field.

Grid : (Х, Y, Z): 90 х 19 х 46; Global convergence parameter – 0,1%

Commercial CFD Package PHOENICS v.3.6 was used in all calculations

• Temperature field: Tavr. = 1060 0C, Tмах = 1493 0C .

• NOx concentration . • Prediction: 19,56 мg/м3, Experiment: 24 мg/m3.

• CO concentration. - Prediction: 2,4 мg/m3, Experiment: 4 мg/m3

• Methane concentration.

3.2. H2S in the natural gas

• Temperature field: Toutlet = 966 0C , Tмах = 1334 0C

- Direct chemical reaction of H2S burning : H2S + 1,5·O2 SO2 + H20

- Average speed of H2S burning (EBU - model):

RH2S = - CEBU ·min {H2S; O2 / 1,41 }·(·k), [кg/(m3с)], CEBU=4,0

• Temperature field (basic design):

Toutlet = 1060 0C, Tмах = 1493 0C

The primary reason of the temperature in the combustion chamber reduction : decrease in the fuel “lowest” caloric value.

• Temperature field:

•Toutlet = 966 0C, Tмах = 1334 0C

• NOx concentration

Prediction : 20,83 мg/m3

• СО concentration

Prediction : 6 мg/m3

Temperature decrease in the combustion chamber leads to

the increased carbon monoxide (CO) generation.

4. C o n c l u s I o n s

1. The modern computer technologies are widely employed for design and modernization of boilers and combustion chambers.

2. Computer technologies enables to analyzing the number of design variants and flow regimes before the fabrication or modernization; this allows us to take more justified solutions, to save the time and funding.

3. Computer modeling enables detecting some specific features of the combustion chamber flow and temperature fields, which are actually unable to be detected in experiments.

4. The experiment keeps its important meaning; however it should be employed after basic decisions regarding combustion chamber design and flow regimes.