Thermodynamic Design of a Fire-Tube Steam Boiler

1. Thermodynamic Design of a Fire-Tube Steam Boiler Prepared for: Professor Kamran Shavezipur Prepared by: (Team 16) John Walter Austen Kennedy Muhammad Shuhaimi December 11th, 2014 2. 2 Table of Contents Introduction.......................................................................................................................................3 DesignAnalysisandCalculations……………………………………………………………………………………………………………..4 DesignOutcome……………………………………………………………………………………………………………………………………...6 References…………………………………………………………………………………………………………………………………………… .8 3. 3 Introduction: The body of the boiler is usually the pressure vessel and contains the fluid. The fluid is normally the water which will circulate for heating purposes and sometimes is converted to steam for process use. The horizontal fire tube boiler has three passes. The first pass consists of furnace while both of the second and third passes consist of tubes. While the fire tube boiler operates, only the second and third passes are considered for the heat transfer process. The advantages of the fire tube boiler are the cost is inexpensive, easy to clean, compact in size, easy to replace tubes, and well suited for space heating and industrial process applications. The disadvantages of the fire tube boiler are not suitable for high pressure applications and it has limitation for high capacity steam generation. This is the list of the main components in the fire tube boiler: o Boiler shell is the outer component in a cylindrical shape that covers the pressure vessel. o Burner is located in the vertical walls of the furnace and it brings fuel and air into the furnace at the desired velocities, turbulence and concentration. o Furnace is the enclosed space where the combustion takes place. o Drain is the valve connection that removes all the water from the pressure parts. o Feed Pump supplies water to the boiler o Safety valve is a spring loaded valve that automatically opens when pressure attains the valve setting. It is used to prevent excessive pressure from building up in the boiler. o Steam separator removes the entrained water from steam o Firebox absorbs radiant heat from the fire. o Accumulator stores the heat of steam to be used during late period and at lower pressure. o Insulation is made from a material of low thermal conductivity and is sued to reduce heat losses. o Safety shut-off valve is electrically operated to automatically shut off fuel when de- energized. o Circulator is used to pass steam or water between upper boiler drum which is usually located where the heat absorption is low. o Strainer is a filter that is used to retain solid particles allowing a liquid to get pass. o Breeching transports the product for the production between parts of the generating unit. 4. 4 DesignAnalysis and Calculations: Temperature Distribution Tw=180 degC(Givenvalue forwater) 𝑇1 = 𝟏𝟏𝟎𝟎 𝒅𝒆𝒈𝑪 (𝑜𝑛𝑙𝑖𝑛𝑒 𝑠𝑜𝑢𝑟𝑐𝑒 𝑓𝑜𝑟 𝑜𝑖𝑙 𝑓𝑢𝑒𝑙) 𝑇3 = 𝑇𝑤 + 50 𝑇2 = 𝑇1 + 𝑇3 2 𝑇3 = 180 + 50 = 𝟐𝟑𝟎 𝒅𝒆𝒈𝑪 𝑇2 = 1100 + 230 2 = 𝟔𝟔𝟓 𝒅𝒆𝒈𝑪 𝑇2 𝑎𝑖𝑟 = 𝑇1 + 𝑇2 2 = 1100 + 665 2 = 𝟖𝟖𝟐. 𝟓 𝒅𝒆𝒈𝑪 𝑇2 𝑎𝑖𝑟 = 𝑇2 + 𝑇3 2 = 665 + 230 2 = 𝟒𝟒𝟕. 𝟔 𝒅𝒆𝒈𝑪 Heat Transfer within the Steam Boiler 𝐴𝑠𝑠𝑢𝑚𝑒𝑑 𝐸𝑛𝑡ℎ𝑎𝑙𝑝𝑦 𝑉𝑎𝑙𝑢𝑒𝑠: ℎ 𝑎𝑖 𝑟 = 𝟕𝟓 𝑾 𝒎 𝟐 𝑲 , ℎ 𝑤 = 𝟕𝟎𝟎 𝑾 𝒎 𝟐 𝑲 𝐺𝑖𝑣𝑒𝑛 𝑣𝑎𝑙𝑢𝑒𝑠 𝑓𝑜𝑟 𝑡ℎ𝑒 𝑡𝑢𝑏𝑒: 𝑘 𝑡𝑢𝑏𝑒 = 𝟓𝟏 𝑾 𝒎𝑲 , 𝑡 𝑡𝑢𝑏𝑒 = 𝟎. 𝟎𝟎𝟑𝒎(𝑡𝑢𝑏𝑒 𝑒𝑥𝑡𝑒𝑟𝑛𝑎𝑙 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠) 𝐻𝑒𝑎𝑡 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑜𝑣𝑒𝑟 𝑎𝑟𝑒𝑎(𝑈𝑠𝑒𝑑 𝑓𝑜𝑟 𝑝𝑎𝑠𝑠𝑒𝑠 3 𝑎𝑛𝑑 2 𝑜𝑛𝑙𝑦): 𝑄 𝐴 = (𝑇𝑎𝑖𝑟 − 𝑇 𝑤) 1 ℎ 𝑎𝑖𝑟 + 𝑡 𝑡𝑢𝑏𝑒 𝑘 𝑡𝑢𝑏𝑒 + 1 ℎ 𝑤 𝑄2 𝐴2 = 882.5 − 180 1 75 + 0.003 51 + 1 700 = 702.5 0.0148 = 47466.2 𝑊 𝑚2 = 𝟒𝟕. 𝟒𝟔𝟔𝟐 𝑲𝑾 𝒎 𝟐 𝑄3 𝐴3 = 447.5 − 180 1 75 + 0.003 51 + 1 700 = 267.5 0.0148 = 18074.3 𝑊 𝑚2 = 𝟏𝟖. 𝟎𝟕𝟒𝟑 𝑲𝑾 𝒎 𝟐 To findbothQ values,the equationforQinisused.Afterthe Qinissolved,differentamountsthateach Q2 andQ3 contribute tothe Qin are testedinthe excel file.The Q2 andQ3 valuesthatare usedare the onesthat allowthe areasA2 and A3 to be relativelyclosetoeachother. 𝐺𝑖𝑣𝑒𝑛 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒: 𝑚̇ = 5000𝑘𝑔 ℎ𝑟 = 𝟏. 𝟑𝟗𝒌𝒈/𝒔 hg at 10 bar isusedbecause the givenpressure was10bar forwithinthe tube.hf at 21 degCisused because thisisaroundwhat the temperature of waterwouldbe outsideof the tube before itenters. 𝑄2 + 𝑄3 = 𝑄𝑖𝑛 = 𝑚̇ (ℎ10𝑏𝑎𝑟 − ℎ21 𝑑𝑒𝑔𝐶) = (1.39)(2778.1 − 88.14) = 𝟑𝟕𝟐𝟗.𝟎𝟒 𝑲𝑾 Aftertestingdifferentpercentagesinthe excel document,the bestonestouse were 72% forQ2 and 28% forQ3: 𝑄2 = (0.72) 𝑄𝑖𝑛 = 𝟐𝟔𝟗𝟐. 𝟏𝟏𝟐 𝑲𝑾, 𝑄3 = (0.28) 𝑄𝑖𝑛 = 𝟏𝟎𝟒𝟔.𝟗𝟑𝟐 𝑲𝑾 5. 5 Areafor A2 and A3 are solvedforusingQ2 and Q3 valuesandQ/A values: 𝑄2 𝐴2 = 47.4662 𝐾𝑊 𝑚2 = 2692.112 𝐴2 → 𝐴2 = 𝟓𝟔. 𝟕𝟏𝟔𝟑 𝒎 𝟐 𝑄3 𝐴3 = 18.0743 𝐾𝑊 𝑚2 = 1046.932 𝐴3 → 𝐴3 = 𝟓𝟕. 𝟗𝟐𝟑𝟖𝟐 𝒎 𝟐 Volume Ratio Volume valueswere determinedusingthe designthatwascompletedonthe solidworksprogramaswell as the values thatare displayedinthe designoutcome. 𝑇𝑜𝑡𝑎𝑙 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑏𝑜𝑖𝑙𝑒𝑟: 𝜋(1.95)2(5) = 59.7 𝑚3 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐹𝑢𝑟𝑛𝑎𝑐𝑒 𝑜𝑢𝑡𝑒𝑟: 𝜋(0.475)2(5) = 3.54 𝑚3 𝑉𝑜𝑙𝑢𝑚𝑒 𝑤ℎ𝑒𝑟𝑒 𝑤𝑎𝑡𝑒𝑟 𝑜𝑟 𝑣𝑎𝑝𝑜𝑟 𝑖𝑠 𝑝𝑟𝑒𝑠𝑒𝑛𝑡: 59.7 − 3.54 = 56.16 𝑚3 The volume of vapor was determined by seeing that roughly 10 percent of the total front area was empty at the top. This is where the vapor would be present above the water. 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑉𝑎𝑝𝑜𝑟 ≈ (0.1)56.16 = 5.616 𝑚3 Tube area and number of tubes The surface area of the tubeswere calculatedusingthe assumed tube diameter. 𝐴 𝑡𝑢𝑏𝑒 = 2𝜋(.025)(5) + 2𝜋(0.025)2 = 0.789 𝑚2 The numberof tubesforeachpass were foundbydividingA2andA3 by the tube A_tube. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑢𝑏𝑒𝑠, 𝑃𝑎𝑠𝑠 2 = 𝐴2 𝐴𝑡𝑢𝑏𝑒 = 56.79581 0.789 = 72 𝑡𝑢𝑏𝑒𝑠 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑢𝑏𝑒𝑠, 𝑃𝑎𝑠𝑠 3 = 𝐴3 𝐴𝑡𝑢𝑏𝑒 = 58.00486 0.789 = 74 𝑡𝑢𝑏𝑒𝑠 6. 6 DesignOutcome: There were many assumed and given values used for the design of the steam boiler system. Given Values: - The tube external diameter is 50mm, and its thickness is 3 mm. -The thickness of furnace plate is 16mm -The thickness of main shell is 12 mm. -Tube diameter is 50mm Values determined by team: - Boiler length: 5m - Boiler Diameter: 2m - Furnace Diameter: 0.8m 7. 7 Excel Data (Also sent in a separate Excel File) Assumed/Given mass flowrate (kg/s) 1.39 pressure (Pa) 1000000 boilerlength(m) 5 boilerdiameter(m) 2 tubesdiameter(m) 0.8 h-w 700 h-air 75 k-tube 51 t-tube (m) 0.003 T1 (celsius) 1100 T3 (celsius) 230 T-w(celcius) 180 Calculated/Determined T2 665 h2 2778.1 T2-air 882.5 h1 88.14 T3-air 447.5 Q-in 3739.044 Q2/A2 47.39983 Q3/A3 18.04905 Q2 2692.112 Q3 1046.932 A2 56.79581 A3 58.00486 Areaof tube 0.789 Numberof tubes:Pass2 72 Numberof tubes:Pass3 74 Total Numberof Tubes 146 8. 8 References Godil. Junaid. Boiler. Web. 10 Dec 2014. Firetube or Watertube? What is the difference? P.C.Mc.Kenzie Company. Web. 10 Dec 2014. http://www.mckenziecorp.com/boiler_tip_8.htm http://www.energy.kth.se/compedu/webcompedu/ManualCopy/Steam_Boiler_Technology/Heat_ exchangers/thermal_design_of_heat_exchangers.pdf