Notes on Involved Energy in Cane Sugar Processing Dr Carlos de Armas Dr Oscar Almazan

Cane Sugar Processing Extraction Separation of the sugared juice from the bagasse (fiber+water+ ) Purification Separation of non desirable substances from juice; colloidal + Evaporation Separation of most of the water Cristallization Separation of sucrose from different classes of molasses Centrifugation Separation of sugar crystals Steam and Power Generation

EXTRACTION (MILLING) bagasse purification Cane Pre- paration Mill No 1 No. N Exhaust Section Counter-current Extraction 3 to 5 Mills Mixing Mixed juice to purification First extraction juice water Juice Mixed juice Brix 13 to15 Purity 80 to 90

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.

SUGAR AND ETHANOL PRODUCTION 9 ton of cane 1.0 ton sugar 2.5 ton bagasse 2.0 ton cane wastes 300 kg final molasses 15 ton of cane 1.0 m3 ethanol 4.0 ton bagasse 15 m3 liquid wastes

Energy in Processing (Main Elements) ~Steam generation efficiency ~Efficient use of steam ~Efficiency in the conversion of thermal energy into mechanical

Bagasse It 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.

Bagasse In 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.

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. 4500 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?

~ Up to the seventies there were no possibilities, 1.0 bb of “fuel” costed less than US $ 400 ~Current policy ; to avoid surplus without goal. They cost money. ~Seasonal fashion of sugar pro- duction ~Different kinds of bussiness, laws and regulations. Bagasse

Generation and use of energy Sales to the grid 32-36 kW-h /tc for fulfilling whole demand of the factory. For 3000-3500 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 10000 kw (70 kw-h/tc) as per Mauritius Island experience Generation and use of energy Sales to the grid

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 70-80 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 12000 kw with proved technologies (Mauricio Island and Hawaii). Generation and Use of Energy Sales to the Grid

Generation and Use of Energy Different Approaches In Operation Today 1) BackPressure Turbines To the Grid 10/15 kw/tc-h 2) Cond.-Extr. Turbines - Mauricius Island 70 kw/tc-h In development at present 3) Combined Cycle, GT + gasifying 240 kw/tc-h

Extraction- Condensing Turbines A main drawback is the sea- sonal character of cane sugar processing all over the world and the scale economy of Ran- kine cycle. Possible sizes are not enough efficient, and very expensive per kw to operate 60 to 70 per cent time with fossil fuels. It is possible only in very small countries and where very efficient cane harvest wastes use are reached or with energy canes

Combined Cycle Present status -Following bagasse gasification; It is almost ripe the technology. After this, semi or commercial tests. It will be ready in a few years. Through bagasse hydrolysis, the fuel can be fed directly to the combustor. It is now at bench scale level, then semi or com mertial tests. May be ready in ten years.

Combined Cycle Economy Operation plus maintennance cost of a hydroelectric plant in Brazil is of the order of US $0.001/kw-h, while capital cost US$ 0.06/kw-h In a conventional fossil fuel plant these costs are 0.005 and 0.025 respectively and that of fuel 0.02 for a total of US $ 0.05 per kw-h

Combined Cycle Economy Gasification; operation plus maintennance costs 0.005, capital cost 0.025, fuel 0.02 for a total of US $ 0.05 per kw-h.

SUMMARISING

STEAM AND POWER GENERATION Base: 1000 kg of cane Sugar; 80 to 140 kg Bagasse; 260 to 320 kg 2.0 and 4.0 kg/kg sugar Steam; 380 kg to 600 kg 2.7 to 7.0 kg/kg sugar Energy; 3700 to 7400 kcal/kg sugar 15.5 to 31.0 MJ /kg sugar common value 4500 kcal/kg sugar 18.8 MJ/kg sugar

MAIN ASPECTS IN THE EFFICIENT USE OF ENERGY IN CANE SUGAR PROCESSING Steam Generation Configuration Engineering Design of Process Steam Layout Engineering Design in the Transformation of Thermal Energy into Mechanical Energy

STEAM GENERATION Characterizing SG Efficiency, specification of Gross Calorific Value, or Nett Calorific Value as a function of % moisture(W) . metric units NCV = 4250-4850*W/100 kcal/kg (Hugot) english units 1.8*(kcal/kg) = Btu/lb NCV = 7650-8730*W/100 Btu/lb (Hugot) 1.0 kW-h = 3.6*106 watt-seg (joule) = 860 kcal; 1.0 kcal = 4.186 kj

BOILER EFFICIENCY FOR GCV AND NCV Bagasse with 50 % moisture NCV = 1825 kcal/kg GCV = 2300 kcal/kg Eff. 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 67.5 % NCV Efficiency of these units, (2300/1825)*67.5 = 85 %

GENERAL BOILER CONFIGURATION Furnace Water walls Screen Superheater Water Evaporation Bundle Economizer Air Pre-heater

MAIN ENERGY LOSSES IN STEAM GENERATION Sensible heat carried by gases leaving, 12-30 % Non complete combustion, 2-12% Excess air over the minimum necessary, including air infiltration Conduction and convection through walls 2% Water Extractions

FURNACES; DIFFERENT TYPES Burning in pile; Horse shoe Cell Spreader stoker (grate) oscillating travelling Suspension firing

COMBUSTION / STOICHIOMETRY Bagasse (dry) analysis, changed to ashes free Carbon 47.0/0.975 = 48.2 % Hydrogen 6.5/0.975 = 6.7 Oxygen 44.0/0.975 = 45.1 Ashes 2.5 ----- Dividing 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

Stoichiometry Equations (/100)C4.02H6.7O2.82 ; Excess air % bagasse ; Base of Calc. + 4.285(1.0 + /100)*(/100) O2 oxygen in air 16.12 (1.0 + /100)*(/100)  N2 nitrógen coming with air

Carbon anhydride + water from water due to COMBUSTION PRODUCTS 4.02*(/100) CO2  + (3.35*( /100)+ BC*(hum/100)/18)H2O Carbon anhydride + water from water due to combustion moisture of fuel. + 4.285(/100)*(/100)O2 non-used oxygen in gases + 16.12 (1.0 +  /100)*( /100)  N2 nitrogen in gases

……..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.

Liquids transportation in the factory; mixed and clarified juice to their tanks, syrup and molasses to their tanks, injection water to condensers and from batches (barometric leg seal) to spray pond. General purpose water from source to tank. Imbibition and recirculation of juices in mill, etc.

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) = =108437 ft-lb / ton/hour, for 300 ton / hour = 108437*300 = 32531040 ft-lb /hour = 32531040/3600 = 9036.4 ft-lb / sec as one hp = 550 ft-lb/sec, power for pumping 9036.4 /550 = 16.4 hp, i e 12.3 kW

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. 176/300 = 0.6 kW-h/tc Efficiencies has not been taken in consideration nor densities in pumping of fluids other than water

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 cane Irrelevant of type of prime mover; steam or electric, it is a number slightly different Note: metric ton may be identified also by Tonne.

With a total, general distribution, just for giving an approximate idea as follows Cutting knives, including leveling blades 1.3 – 1.7 kW-h per ton cane (one machine) Shredders 1.5 – 2.5 kW-h per ton cane, depending on design

Milling, (only for energy demands estimations, Hugot ) For three roller mills ; T= 0.134PnD / tc T; kW- h per ton cane for each mill P; total hydraulic load, tons, n; speed, rpm, D; diameter of rollers, m tc; ton cane coming in per hour.

Change coefficient 0.134 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 gearing eff. in transmision=(1-0.02)*(0.92)=0.90 Energy demand at exit prime movers = = energy demand at exit of speed red./ eff.

Energy demand in reception-transportation and elevation of cane 0.19 kW- h per ton cane Energy demand in intermediate carriers 0.12 times number of intermediate carriers kW- h per ton cane Energy demand in carrier to steam boilers 0.03 kW-h for each 50 m length, / ton cane