2006:141 CIV MASTER’S THESIS Flue Gas Condenser for Biomass Boilers MARC CORTINA M.Sc PROGRAMME IN MECHANICAL ENGINEERING Luleå University of Technology Department of Applied Physics and Mechanical Engineering Division of Energy Engineering 2006:141 CIV • ISSN: 1402 - 1617 • ISRN: LTU - EX - - 06/141 - - SE II III Acknowledgements Firstly I would like to express my gratitude to the international offices of Luleå University of Technology and Enginyeria Tècnica Superior Industrial de Barcelona. They have made it possible to me to spend this great period in Sweden, and this project. To Sweden in general, this country that has always helped me, and especially to this University in Luleå, thanks to it I have had at my disposal all the information to make the thesis. Secondly, I am grateful to my supervisor Roger Hermansson, who suggested this project to me and has helped me whenever it has been necessary. And to Joakim Lundgren, who has also been interested in listening to me and giving his point of view and help in some difficult steps. I have also received some help from Catalunya, my country. From Bonals and Velo, two teachers from the University of Barcelona who suggested a basic book to handle the condensation topic when it seemed impossible to find the information. Also my friends Josep Cots, Josep Cortina and Dani appeared to improve the final result with the excel, word and power point programs. And Andi, the student who has spent more time with me in this Erasmus, also to discuss about heat transfer, iterations, and others. And finally I would also express my gratitude to my family for their unconditional support in my studies and my whole life in general, whatever I do. Luleå, March 2006 Marc Cortina i Grau IV INDEX 1 INTRODUCTION .................................................................................................. 1 1.1 BACKGROUND ....................................................................................................... 1 1.2 GENERAL DESCRIPTION ....................................................................................... 1 1.3 METHOD ................................................................................................................ 2 2 THEORY .................................................................................................................... 3 2.1 GAS ....................................................................................................................... 3 2.1.1 Gas composition ..................................................................................... 3 2.1.2 Fuel Flow ................................................................................................... 4 2.1.3 Enthalpy of the Gases .......................................................................... 5 2.2 WATER .................................................................................................................. 6 2.3 HEAT EXCHANGER ................................................................................................ 7 2.3.1 FLUE GAS CONDENSER (WITHOUT SPRAYING WATER) ........ 7 2.3.2 FLUE GAS CONDENSER (SprayING water) ................................ 21 3 RESULTS AND ANALYSIS ............................................................................. 23 3.1 INTRODUCTION .................................................................................................. 23 3.2 GAS COMPOSITION ............................................................................................ 23 3.2.1 Fuel mass flow, total gas mass flow, and dry gas mass flow depending on the moisture content ............................................................. 23 3.2.2 Gas composition depending on the moisture content ........... 24 3.2.3 Amount of steam in the stack gases ............................................ 24 3.2.4 Dew point ................................................................................................ 25 3.3 HEAT RECOVERED .............................................................................................. 27 3.4 WATER AND GAS FLOWS AND HEAT TRANSFER COEFFICIENTS ....................... 28 3.4.1 Total water flow .................................................................................... 28 3.4.2 Water flow inside tubes, gas flow outside, and heat transfer coefficients .............................................................................................................. 28 3.5 AREA NEEDED ..................................................................................................... 33 3.5.1 FLUE GAS CONDENSER (WITHOUT SPRAYING WATER) ...... 34 3.5.2 FLUE GAS CONDENSER (SprayING water) ................................ 39 3.6 PROTOTYPE STUDY ............................................................................................. 41 3.6.1 CONDENSER WITHOUT SPRAYING WATER ............................... 42 3.6.2 CONDENSER SprayING Water ........................................................ 44 3.7 COMPARISON AND FINAL PROTOTYPE ............................................................... 46 4 CONCLUSIONS AND FURTHER IMPROVEMENTS ............................ 49 4.1 CONCLUSIONS .................................................................................................... 49 4.2 IMPROVEMENTS .................................................................................................. 49 4.2.1 improvements in the boiler .............................................................. 49 4.2.2 Improvements in the software ....................................................... 50 5 REFERENCES ....................................................................................................... 51 6 APPENDIX A ........................................................................................................ 52 V 7 APPENIX B (EXCEL EXPLAMATION) ......................................................... 55 VI TABLE OF SYMBOLS Symbol Meaning Units m& w Mass flow rate of water Kg / s m& wt Mass flow rate of water in each tube Kg / s m& g Mass flow rate of gas Kg / s m & d g Mass flow rate of dry gas Kg / s λ Air Factor ------------ Hi Heating values J/kg fuel h1,h2 Specific enthalpy at entrance and exit from the exchanger J/kg Q& Rate of heat recovered W F, MC Moisture content Kg water / kg fuel Pout Power output W η Boiler Efficiency ------------ Cp g Specific heat of the gas J/kgK Cp dg Specific heat of the dry gas J/kgK Cw Specific heat of the water J/kgK hwe Latent heat of Vaporization kJ/kg Tr 1,Tr 2 Temperature entrance and Temperature exit of the radiator ºC Temperature entrance and Temperature exit of the heat T1,T 2 exchanger ºC Temperature entrance and Temperature exit of the heat t1,t 2 exchanger ºC T Temperature K t Temperature ºC pa Atmospheric pressure Pa Re Reynolds Number ------------ ρ Density Kg / m 3 uw Average Speed Water m / s u∞g Average Speed Gas m / s umax g Maximum Speed Gas m / s Di Diameter inside m Do Diameter outside m µ Dynamic Viscosity Kg / m·s µw Dynamic Viscosity at the wall Kg / m·s Nu Nusselt Number ------------ Pr Prandt Number ------------ 2 St Cross section area inside tub m Ф Viscosity Correction ------------ k Thermal conductivity W / m·K Nt Number of tubes ------------ Ry Rows of tubes in the y direction ------------ VII Rz Rows of tubes in the z direction ------------ Sy Separation between rows y direction m Sz Separation between rows z direction m 2 Ait Area inside tube m 2 Aot Area outside tube m 2 Ai Total area inside tubes m 2 Ao Area outside total tubes m L, L x Length of the heat exchanger m Ly Witdth of the heat exchanger m Lz Height of heat exchanger m E Exchanger heat transfer effectiveness Q& max Maximum heat transfer rate between the two flows W Cmin Minumum heat capacity rate, Cp gas ·m gas W Cmax Maximum heat capacity rate, Cp water ·m water W 2 Ui Overall inside heat transfer coefficient W/m ·K 2 Uo Overall outside heat transfer coefficient W/m ·K Tdew Dew point K pws Saturation pressure of water Pa pg Partial pressure of the gas Pa pc Pressure of condensate film Pa pv Partial pressure of the steam Pa pt Pressure total Pa pgf Log mean of p g and p’ g Pa p’ g pt - p c Pa madw Mass flow of water added (Sprayed) Kg/s xad Water added (Sprayed) per kg dry air Kg w / kg dry air m’ w Total mass rate water flow (After spray) Kg/s x’ Total water flow (After spray) per kg dry air Kg w / kg dry air m’ g Total gas flow rate (After spray) Kg/s tb Bulk Temperature ºC Tb Bulk Temperature K hw Heat transfer coefficient of the water W/m2·K hg Heat transfer coefficient of the gas W/m2·K taspray Temperature of the gas after spray water ºC tbspray Temperature of the gas before spray water ºC Q& lat Transfer rate of latent heat W Q& sens Transfer rate of sensible heat W Vg Specific volume of the gas mol/kg Vsteam Specific volume of the steam mol/kg Mg Molecular weight of the gas ------------ Msteam Molecular weight of the steam ------------ Marc Cortina Flue Gas Condenser page 1 1 INTRODUCTION 1.1 BACKGROUND In Sweden district heating is widely used in cities and more dense populated areas. However there are communities where houses are heated by oil or electricity and the population is dense enough to motivate the building of a district heating netwok. These combustibles are not renewable and collaborate with the greenhouse effect. In addiction, in general each building has its own boiler for heating, what makes the boiler very inefficient since the consumtion of heat in a house is very irregular, and consequently very often the optimum