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Combustion System Efficiency

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  1. Combustion System Efficiency Contributing Members: Kyle Bowen Brandon Todd Neal Patel DanarSampurno Ivan Victoria http://superiorboiler.com/mohawk.htm

  2. Objectives • To model efficiency estimates with numerical methods • To discuss how to optimize combustion systems. • To present future research possibilities • To understand how furnaces and boilers utilize combustion • To understand the importance of the air/fuel ratio, and how it relates to the system’s efficiency. http://www.africoal.co.za/optimal-combustion-processes-fuels-excess-air/ % Excess Air that Power Plant boilers typically operate at for various fuels http://www.sankey-diagrams.com/tag/heat-loss/

  3. Furnaces • Furnaces and Boilers operate by inputting fuel and air into the furnace and igniting it to release energy. The figure to the left shows a typical furnace • Furnaces and boilers require large amounts of fuel to operate. • Many Furnaces and Boilers take in more air than stoichiometric amounts of air to ensure complete combustion http://home.earthlink.net/~jschwytzer/gas_fired_furnace.gif

  4. Other Furnace Examples http://www.onehourairconditioningcharlotte.com/furnaces.html http://www.diychatroom.com/attachments/f17/63693d1358205795-furnace-filters-turn-black-quickly-furnace-drawing.jpg http://www.directindustry.com/prod/seco-warwick-sp-z-oo/rotary-hearth-furnaces-16223-134754.html http://koppelservices.com/furnace-repair-basics/ http://www.enggpedia.com/chemical-engineering-encyclopedia/dictionary/thermodynamics/1778-furnace-types-classification-of-furnace

  5. Boilers • Similar to furnaces, boilers operate by inputting fuel and air to release energy to boil liquid. The figure to the left shows an example of a boiler • Boilers require large amounts of fuel to operate, especially as the boiling point of the liquid increases. • These kind of systems are extremely important to Chemical Engineers because distillation columns are greatly important to chemical plants. http://www.hauserman-engineering.com/Gasification.html

  6. Other Boiler Examples http://science.howstuffworks.com/transport/engines-equipment/steam2.htm http://www.fapdec.org/boilers.htm http://www.johnstonboiler.com/ http://www.aciindustries.com/boiler.htm https://secure.sceg.com/enercom/library/furntune.asp

  7. Combustion System Efficiency • The ratio of inputted heat energy to output work is very low for combustion systems. Small increases in efficiency lead to large fuel savings. • Increasing the efficiency of the entire system allows for less fuel consumption, which leads to an increased revenue. • Gas fired furnaces are widely used, even though they are significantly less efficient than electric furnaces. http://www.rayteq.com/images/gas_vs_electric_figure1.png

  8. Air To Fuel Ratio • Combustion of hydrocarbons requires O2and are of this form: https://www.thermalfluidscentral.org/encyclopedia/index.php/Basics_(Combustion) • Air is the cheapest source of O2however, as shown in the pie chart, air is only 21% O2. When air is used, extra heat is required to heat the remaining 79% of the components of air as well • Excess Air allows more complete combustion, but it also requires more fuel in order to heat it. http://pattiisaacs.files.wordpress.com/2011/12/air-composition-pie-chart2.jpg

  9. Air To Fuel Ratio Improve Combustion System Efficiency, Bill Axon, pg. 43 Improve Combustion System Efficiency, Bill Axon, pg. 41 The graph further illustrates how fuel efficiency increases as stoichiometric Air/Fuel ratio is approached This graphic shows how the amount of fuel required greatly increases as % excess air increases

  10. Air To Fuel Methodology • In order to simulate efficiency savings, regression techniques were used with the data from the table to the left. • Polynomial Regression and Plotting techniques were used to create plots of the data to emphasize various trends from the data. Improve Combustion System Efficiency, Bill Axon, pg. 41

  11. MATLAB Program For Following Slide clear % Fuel savings by cutting back 50% excess air to 10% %x= Furnace exit gas temperature (Farenheit) %y= Fuel Savings (%) x=[2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600 400]; y=[81.1 59.5 45.3 35.3 27.7 21.8 17.1 13.2 9.98 7.25 4.91 2.88]; %Initialization N=1; i=1; P = polyfit(x,y,N); yp=polyval(P,x); erri=(yp-y).^2; err(1,i)=sqrt(sum(erri(:)))/length(y); %While loop optimizes the degree of polynomial used for the fitting. %Loop terminates whenever the sum of the squared errors increases or when %the degree is 3. while (N<3) N=N+1; i=i+1; ypold=yp; P = polyfit(x,y,N); yp=polyval(P,x); erri=(yp-y).^2; err(1,i)=sqrt(sum(erri(:)))/length(y); a=abs(err(i)/err(i-1)); if a>1, yp=ypold;N=N-1;break,end end % Plots the data figure(2) plot(x,y,'oblack',x,yp,'.blue') xlabel('Furnace Exit Temperature, x (F)') ylabel('Fuel Savings , y (%)') legend('Data',['N=',num2str(N)],2) title('Fuel Savings by cutting from 50% to 10% Excess Air')

  12. Fuel Savings • As the exit temperature of the Combustion system increases, fuel savings from decreasing excess air greatly increase. This is fitted by a cubic polynomial (N=3). • This shows that the Air/Fuel ratio is extremely important to the efficiency of high temperature combustion systems. • For low temperature furnaces, the there is still beneficial fuel savings for decreasing excess air.

  13. MATLAB Program For Following Slide clear %x=Percent of Excess Air you are operating at (%) x=[15 20 30 40 50 70]; %y= rows are percent fuel savings achieved by cutting back to 10% excess %the multiple columns are values at different Furnace Exit Gas Temperatures y=[7.44 14.9 29.8 44.6 59.5 89.3;... 4.41 8.82 17.6 26.5 35.3 52.9;... 2.73 5.45 10.9 16.4 21.8 32.7;... 1.25 2.5 4.99 7.49 9.98 15]; %Initialization n=length(y(1)); N=0; i=0; error=[]; a=0.5; yp=y; %The while loop optimizes the degree of the polynomial used to fit the data %It calculates the sum of the squared errors for a given degree and %compares it to the error of the previous degree. Will not exceed cubic while (N<3) N=N+1; i=i+1; for h=1:n ypold(h,:)=yp(h,:); P=polyfit(x,y(h,:),N); yp(h,:)=polyval(P,x); error(i)=sum((yp(h,:)-y(h,:)).^2); ifi>1 a=error(i)-error(i-1); end if a>=1,yp=ypold; break, end end end %Plot of of the X values (% excess air) vs the Y values (Fuel savings in %) %Plot displays regressions for multiple temperatures as well as data points plot(x,yp(1,:),'-black',x,yp(2,:),'--g',x,yp(3,:),'-.r',x,yp(4,:),':blue'), hold on plot(x,y(1,:),'xblack',x,y(2,:),'og',x,y(3,:),'.r',x,y(4,:),'+blue') xlabel('% Excess Air from which to cut back to 10%'), ylabel('Fuel Savings in Percent') title('Fuel Savings versus Excess Air at various temperatures') legend('2400 F','2000 F', '1600 F','1000 F',2) %display degree of polynomial N

  14. Fuel Savings • As Furnace Exit Gas Temperature increases, the effect of cutting back on excess air increases dramatically. • For lower temperature exit gases (i.e. 1000 F), the fuel savings for cutting back on excess air is less pronounced and less important to overall efficiency • For higher temperature exit gases (i.e. 2400 F), the fuel savings are dramatic for decreasing excess air

  15. MATLAB Program For Following Slide clear % Available heat is a function of fluegas temperature and 50% excess air %x= Furnace exit gas temperature (Fahrenheit) %y= available heat (%) x=[300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900]; y=[84.02 81 77.93 74.82 71.67 68.48 65.24 61.97 58.66 55.31 51.93 48.51 45.05 41.56 38.03 34.47 30.87]; %Initialization N=1; i=1; P = polyfit(x,y,N); yp=polyval(P,x); erri=(yp-y).^2; err(1,i)=sqrt(sum(erri(:)))/length(y); %While loop optimizes the degree of polynomial used for the fitting. %Loop terminates whenever the sum of the squared errors increases or when %the degree is 3. while (N<3) N=N+1; i=i+1; ypold=yp; P = polyfit(x,y,N); yp=polyval(P,x); erri=(yp-y).^2; err(1,i)=sqrt(sum(erri(:)))/length(y); a=abs(err(i)/err(i-1)); if a>1, yp=ypold;N=N-1;break,end end % Plot x vs y figure(2) subplot(1,2,1) plot(x,y,'oblack',x,yp,'-blue') xlabel('Temperature, x (F)') ylabel('Available Heat, y (%)') legend('Data',['N=',num2str(N)]) title('% Available Heat as function of Fluegas Temperature') %Plot for extrapolation subplot(1,2,2) fplot(@(x) P(1)*x^3+P(2)*x^2+P(3)*x+P(4),[200 2500]); xlabel('Temperature, x (F)') ylabel('Available Heat, y (%)') legend('50% Excess Air') title('% Available Heat as function of Fluegas Temperature')

  16. Furnace Losses • As the figure to the left shows, there are several areas of heat loss in a furnace. • The most prominent of these sources are sensible heat losses from exiting Fluegas. • The Fluegas losses can be minimized by adjusting temperature and operating excess air. Improve Combustion System Efficiency, Bill Axon, pg. 42 http://www.vesma.com/tutorial/furnaces.htm

  17. Available Heat Methodology • In order to view trends in available heat based upon excess air and fluegas temperature, regression techniques were used with the data from the table to the left. • Polynomial Regression and Plotting techniques were used to create plots of the data to emphasize various trends from the data. Improve Combustion System Efficiency, Bill Axon, pg. 41

  18. Available Heat Output The Fluegas temperature has a dramatic effect on the amount of useful heat output the system produces. Thus it is incredibly important to minimize Fluegas temp in your system. This regression plot gives is extrapolated from 0 F to 2500 F to allow estimate the amount of available heat for a system with different fluegas temperatures.

  19. MATLAB Program For Following Slide clear %x=Percent of Excess Air you are operating at (%) x=[0 5 10 25 50]; %y= Percent of Available heat as percentage of gross heat input %the multiple columns are values at different Fluegas Temperatures y=[86.14 85.93 85.72 85.08 84.02;... 79.68 79.19 78.71 77.25 74.82;... 65.91 64.85 63.79 60.61 55.31;... 58.64 57.29 55.93 51.85 45.05]; %Initialization n=length(y(:,1)); N=0; i=0; error=[]; a=0.5; yp=y; %The while loop optimizes the degree of the polynomial used to fit the data %It calculates the sum of the squared errors for a given degree and %compares it to the error of the previous degree. Will not exceed cubic while (N<3) N=N+1; i=i+1; for h=1:n ypold(h,:)=yp(h,:); P=polyfit(x,y(h,:),N); yp(h,:)=polyval(P,x); error(i)=sum((yp(h,:)-y(h,:)).^2); ifi>1 a=error(i)-error(i-1); end if a>=1,yp=ypold; break, end end end %Plot of of the X values (% excess air) vs the Y values (Fuel savings in %) %Plot displays regressions for multiple temperatures as well as data points plot(x,yp(1,:),'-black',x,yp(2,:),'--g',x,yp(3,:),'-.r',x,yp(4,:),':blue'), hold on plot(x,y(1,:),'xblack',x,y(2,:),'og',x,y(3,:),'.r',x,y(4,:),'+blue') xlabel('% Excess Air'), ylabel('Available Heat (% of gross heat input)') title('Available Heat as function of % Excess Air') legend('300 F','600 F','1200 F','1500 F') %display degree of polynomial N

  20. Effect of Temperature on Available Heat Output • For low Fluegas temperatures, the available heat is roughly constant for all % excess air • As Fluegas Temperature increases, losses in output heat are greater as % excess air increases.

  21. Improving Excess Air Control • Below figure is a pressure balanced regulator • Offers improved control over furnace environment • Can maintain constant furnace temperature • Can maintain Air/Fuel Ratio Improve Combustion System Efficiency, Bill Axon, pg. 43 • Above figure is a mechanically linked valve control • Difficult to maintain constant excess air content Improve Combustion System Efficiency, Bill Axon, pg. 44

  22. Improving Excess Air Control • The figure to the left is an Electronic Mass-flow control system • Pros: • highest level of control over composition and furnace conditions • Compensates for Ambient Temperatures and other system variances • Little human input or knowledge required • Cons: • Very expensive • May be unnecessary for qualified human valve operator Improve Combustion System Efficiency, Bill Axon, pg. 44 http://community.cengage.com/Chilton/cfs-filesystemfile.ashx/__key/CommunityServer.Blogs.Components.WeblogFiles/davids_5F00_blog/2068.gasoline.direct.fuel.injectors.jpg

  23. Furnace Pressure On Efficiency • Furnace Pressure affects heat losses. • With a lower (negative) furnace pressure than external temperature, colder external air infiltrates the furnace as portrayed by the graph. • A greater (positive) furnace pressure increases the amount of heat lost due to hot gas forced out of the furnace. http://www.nwfpa.org/nwfpa.info/component/content/article/50-process-heat/252-furnace-pressure-controllers http://www.nwfpa.org/nwfpa.info/component/content/article/50-process-heat/255-reduce-air-infiltration-in-furnaces

  24. Furnace Pressure On Efficiency • The overall effect of cold air infiltration and hot air loss is increased costs. • The figure to the left depicts how the operating costs of an experimental furnace at positive and negative furnace pressures • The graph shows that air infiltration due to negative pressure causes prices to increase much quicker than gas loss due to positive pressure. • For optimal conditions, furnace pressure should be as close to zero as possible. Valves to control the pressure inside the furnace would be beneficial to maintain an economically optimal pressure inside the furnace.

  25. Why is this important to Chemical Engineers? http://csd-new.newcastle.edu.au/simulations/distillation.html http://www.quarkology.com/12-chemistry/92-production-materials/92A-synthetic-polymers.html http://www.indiamart.com/bioenergyengineering/distillation-column.html http://www.tutorvista.com/content/physics/physics-ii/fission-and-fusion/fractional-distillation.php http://poweryoung.org/energy.cfm@page=oil_home-basics

  26. Why is this important to Chemical Engineers? • One of the most important units in any plant is the distillation column • Distillation columns require heat to boil the input mixture. This is typically done with some sort of combustion boiler • Improved efficiency with the combustion system will lead to lower energy and fuel costs and thus increase the revenue of the plant. http://www2.emersonprocess.com/en-us/news/pr/pages/1308-mol.aspx

  27. Areas for Future Research • Optimal excess air for different fuel types at different temperatures • Quantitative analysis on the effect of boiler/furnace pressure or Heat Output • Analysis of how mixing the boiler liquid can increase the heat transfer from combustion • Research in how furnace shape and design can decrease the necessity for excess air. • Economic cost analysis of improving technology for combustion systems vs. fuel savings http://www.fundamentalform.com/html/doe_report-1.html

  28. Conclusion • The air to fuel ratio is incredibly important to combustion system efficiency and any attempt to minimize excess air within a process can lead to increased revenue • Numerical Methods can be applied to better understand and predict trends and give estimates for projected savings from process improvements • For Chemical Engineers, these systems are greatly important to distillation columns in plants and refineries. An understanding of combustion efficiency improvements can be a great asset to a chemical engineer. http://www.iva-online.com/IMG/jpg/Sealed_Quench_Furnace_MKe_MKg_with_open_antechamber_zoom.jpg