Presentation on theme: "Notes on Involved Energy in Cane Sugar Processing"— Presentation transcript:
1 Notes on Involved Energy in Cane Sugar Processing Dr Carlos de ArmasDr Oscar Almazan
2 Cane Sugar Processing Extraction Separation of the sugared juice from the bagasse (fiber+water+ )Purification Separation of non desirablesubstances from juice; colloidal +Evaporation Separation of most of the waterCristallization Separation of sucrose fromdifferent classes of molassesCentrifugation Separation of sugar crystalsSteam and Power Generation
3 EXTRACTION (MILLING) bagasse purification Cane Pre- paration Mill No 1 No. NExhaust SectionCounter-currentExtraction3 to 5 MillsMixingMixed juice topurificationFirst extraction juicewaterJuiceMixed juiceBrix to15Purity 80 to 90
7 CANE SUGAR; AN ENERGY INTENSIVE INDUSTRY Cane sugar industry is an insdustry with strong involvements with energy.~The raw material, sugar cane, bring its own fuel for processing, and even more.~It shows high thermal (steam) demand for processing , while its demand of mechanical energy is low, allowing high cogeneration.
8 SUGAR AND ETHANOL PRODUCTION 9 ton of cane ton sugar2.5 ton bagasse2.0 ton cane wastes300 kg final molasses15 ton of cane m3 ethanol4.0 ton bagasse15 m3 liquid wastes
9 Energy in Processing (Main Elements) ~Steam generation efficiency~Efficient use of steam~Efficiency in the conversion ofthermal energy into mechanical
10 BagasseIt is the natural fuel in processes of production of sugar and etha-nol. Enough for fulfilling whole demands. Reaching in practice, in addition, a balance between produced and burned bagasse, through control of boilers effi-ciency. Surplus bagasse without a goal, is as bad as not enough bagasse.
11 BagasseIn Cuba, when producing in a campaign, 6 million ton of sugar, there are ground 50 mil-lion ton of cane, with a bagasse production of 15 million ton, out of which, 95 % is burned, going the difference to derivatives. This 15 million ton bagasse, are equivalent to 3 million ton fuel oil.
12 Bagasse ..and the most interesting fact ..!! While in producing cane sugar, it is spent the whole energy freed by the 2.5 kg of bagasse coming along with 1.0 kg of sugar , i.e kcal , in beet sugar proces-sing, there are spent per kg produ-ced not more than 2000, that is, potentially, there exists about 50 % surplus bagasse.Why it is not so in practice?
13 ~ Up to the seventies there were no possibilities, 1.0 bb of “fuel”costed less than US $ 400~Current policy ; to avoid surpluswithout goal. They cost money.~Seasonal fashion of sugar pro-duction~Different kinds of bussiness,laws and regulations.Bagasse
14 Generation and use of energy Sales to the grid 32-36 kW-h /tc for fulfillingwhole demand of the factory. For tc per day, 150 (ton/hour), power generation is of the order of 5000 kw (inclu-ding the mills). Energy reser-ves due to co-generation plus surplus bagasse may grow up to kw (70 kw-h/tc) as per Mauritius Island experienceGeneration and use of energy Sales to the grid
15 Generation and Use of Energy Sales to the Grid Through changes in steam generation parameters, and with efficient use of steam in process, which in general mean investments, there are reached surplus of the order of kw-h per ton of cane, i.e. for a factory grinding 150 ton per hour, it is not impossible to deliver to the grid kw with proved technologies (Mauricio Island and Hawaii).Generation and Use of Energy Sales to the Grid
16 Generation and Use of Energy Different Approaches In Operation Today 1) BackPressure TurbinesTo the Grid 10/15 kw/tc-h2) Cond.-Extr. Turbines-Mauricius Island 70 kw/tc-hIn development at present3)Combined Cycle, GT +gasifying kw/tc-h
17 Extraction- Condensing Turbines A main drawback is the sea- sonal character of cane sugarprocessing all over the worldand the scale economy of Ran-kine cycle. Possible sizes arenot enough efficient, and veryexpensive per kw to operate 60to 70 per cent time with fossilfuels. It is possible only in verysmall countries and where veryefficient cane harvest wastes useare reached or with energy canes
18 Combined Cycle Present status -Following bagasse gasification; It is almost ripe the technology.After this, semi or commercialtests. It will be ready in a fewyears.Through bagasse hydrolysis, thefuel can be fed directly to thecombustor. It is now at benchscale level, then semi or commertial tests. May be ready inten years.
19 Combined Cycle Economy Operation plus maintennance cost of a hydroelectric plant in Brazilis of the order of US $0.001/kw-h,while capital cost US$ 0.06/kw-hIn a conventional fossil fuel plantthese costs are and 0.025respectively and that of fuel 0.02for a total of US $ 0.05 per kw-h
20 Combined Cycle Economy Gasification; operation plus maintennance costs 0.005,capital cost 0.025, fuel 0.02for a total of US $ 0.05 perkw-h.
22 STEAM AND POWER GENERATION Base: 1000 kg of cane Sugar; to 140 kg Bagasse; to 320 kg and 4.0 kg/kg sugar Steam; kg to 600 kg to 7.0 kg/kg sugar Energy; to 7400 kcal/kg sugar to 31.0 MJ /kg sugar common value 4500 kcal/kg sugar MJ/kg sugar
23 MAIN ASPECTS IN THE EFFICIENT USE OF ENERGY IN CANE SUGAR PROCESSING Steam Generation ConfigurationEngineering Design of Process Steam LayoutEngineering Design in the Transformation of Thermal Energy into Mechanical Energy
24 STEAM GENERATIONCharacterizing SG Efficiency, specificationof Gross Calorific Value, or Nett Calorific Valueas a function of % moisture(W) .metric unitsNCV = *W/100 kcal/kg (Hugot)english units *(kcal/kg) = Btu/lbNCV = *W/100 Btu/lb (Hugot)1.0 kW-h = 3.6*106 watt-seg (joule) = 860 kcal;1.0 kcal = kj
25 BOILER EFFICIENCY FOR GCV AND NCV Bagasse with 50 % moistureNCV = 1825 kcal/kg GCV = 2300 kcal/kgEff. defined as the % of freed heat from the bagas-se, leaving with the steam (enthalpy of steam less enthalpy of fed water, times steam rate, divided by the Caloric Value of one mass unit of bagasse.GCV Efficiency of best bagasse boilers %NCV Efficiency of these units,(2300/1825)* = 85 %
26 GENERAL BOILER CONFIGURATION FurnaceWater wallsScreenSuperheaterWater Evaporation BundleEconomizerAir Pre-heater
27 MAIN ENERGY LOSSES IN STEAM GENERATION Sensible heat carried by gases leaving, %Non complete combustion, %Excess air over the minimum necessary,including air infiltrationConduction and convection through walls 2%Water Extractions
28 FURNACES; DIFFERENT TYPES Burning in pile; Horse shoeCellSpreader stoker (grate) oscillatingtravellingSuspension firing
29 COMBUSTION / STOICHIOMETRY Bagasse (dry) analysis, changed to ashes freeCarbon /0.975 = 48.2 %Hydrogen /0.975 = 6.7Oxygen /0.975 = 45.1AshesDividing by the MW of each element it is reached a pseudo-structural formula, with which it is easier to do the combustion calculations using the moles approach.C4.02 H 6.7 O 2.82
30 Stoichiometry Equations (/100)C4.02H6.7O2.82 ; Excess air %bagasse ; Base of Calc.+4.285(1.0 + /100)*(/100) O2oxygen in air16.12 (1.0 + /100)*(/100) N2nitrógen coming with air
31 Carbon anhydride + water from water due to COMBUSTION PRODUCTS4.02*(/100) CO2 + (3.35*( /100)+ BC*(hum/100)/18)H2OCarbon anhydride + water from water due tocombustion moisture of fuel.(/100)*(/100)O2non-used oxygen in gases(1.0 + /100)*( /100) N2nitrogen in gases
32 ……..LAST COMMENTARIES AFTER STOICHIOMETRY, IT IS POSSIBLE TO BUILD MOLAR AND ENERGY BALANCES, AND AFTR THIS , ADDING DETAILS OF CONFIGURATION, TO BUILD THE WHOLE MODEL OF STEAM GENERATION AFTER THE ADDEQUATE PROCEDURES THE REST OF THE WHOLE PROCESS ENGINEERING MAY BE MODELED, REACHING THE WHOLE PROFILE OF ENERGY TRANSFORMATIONS.
33 Liquids transportation in the factory; mixed and clarified juice to their tanks,syrup and molasses to their tanks,injection water to condensers and frombatches (barometric leg seal) to spraypond. General purpose water from sourceto tank. Imbibition and recirculation ofjuices in mill, etc.
34 Mixed juice to tank; head 15 m, flow, one ton of juice (1000 kg), 100 % mixed juice extract.1000(2.204 lb/kg))15 (3.28 ft /m) == ft-lb / ton/hour, for 300 ton / hour= *300 = ft-lb /hour= /3600 = ft-lb / secas one hp = 550 ft-lb/sec, power for pumping/550 = 16.4 hp, i e 12.3 kW
35 Another example; pumping cooling water to vacuum pans condensers Another example; pumping cooling water to vacuum pans condensers. Evaporation in pans 18% cane = 180 kg / ton cane, need of cooling water 60 times, head 20 m, taking to English system=180*60 *20 *2.204 *3.28 *300/3600/550 =237 hp or 176 kW /300 = 0.6 kW-h/tcEfficiencies has not been taken in consideration nor densities in pumping offluids other than water
36 Total Mechanical Energy Demand (different of installed power) is of the order of 32 to 36 kW-h( 115 to 130 mJ)per ton (metric) of caneIrrelevant of type of prime mover; steam or electric, it is a number slightly differentNote: metric ton may be identified also byTonne.
37 With a total, general distribution, just for giving an approximate idea as followsCutting knives, including leveling blades1.3 – 1.7 kW-h per ton cane (one machine)Shredders 1.5 – 2.5 kW-h per ton cane,depending on design
38 Milling, (only for energy demands estimations, Hugot )For three roller mills ; T= 0.134PnD / tcT; kW- h per ton cane for each millP; total hydraulic load, tons, n; speed,rpm, D; diameter of rollers, mtc; ton cane coming in per hour.
39 Change coefficient by 0.1 for crusher (two rolls) For mills with pressure feeders (Walker), multiply power demand by 1.1 For losses in gearing use 2.0 % in closed reducers with oil bath, and 8 % in open gearing. In combined gearingeff. in transmision=(1-0.02)*(0.92)=0.90Energy demand at exit prime movers == energy demand at exit of speed red./ eff.
40 Energy demand in reception-transportation and elevation of cane 0.19 kW- h per ton caneEnergy demand in intermediate carriers0.12 times number of intermediatecarriers kW- h per ton caneEnergy demand in carrier to steam boilers0.03 kW-h for each 50 m length, / ton cane