SUGAR AND ETHANOL INDUSTRIES Energy view. 24/02/2006 Energy Technology, Stockholm, Sweden 1

Transcription

1 SUGAR AND ETANOL INDUSTRIES Energy view 24/02/2006 Energy Technology, Stockholm, Sweden 1

2 SUGAR CANE Sugar cane is a 1 year crop, and when harvested it is about 3m tall. The sugar content is about 10% on the total mass, 70-75% is moisture 24/02/2006 Energy Technology, Stockholm, Sweden 2

3 Where does the cane grow? 24/02/2006 Energy Technology, Stockholm, Sweden 3

4 Sugar cane producers (2003) -Brazil 386 Million tons -India 290 Million tons -China 94 Million tons -Thailand 74 Million tons -Mexico 45 Million tons -Australia 36 Million tons -Cuba 35 Million tons 24/02/2006 Energy Technology, Stockholm, Sweden 4

5 SUGAR CANE Products 8.5 tons millable sugar cane 1 ton of sugar or 12.5 tons millable sugar cane 1000 L alcohol and Byproduct: Bagasse 8.5 tons sugar cane 2.5 ton bagasse (50% hum) 24/02/2006 Energy Technology, Stockholm, Sweden 5

6 BAGASSE Bagasse is the fibrous residue left over from the cane after having pressed out the sugar juice. 24/02/2006 Energy Technology, Stockholm, Sweden 6

7 SUGAR CANE OTER 40% Total Biomass moisture) GREEN TOP 80-88% MOISTURE Tops Attached Leaves Ground Trash GENERALLY WASTED COMPONENTS ATTACED TRAS 18-30% MOISTURE EXPANDING CROWN MILLABLE STEM 70-75% MOISTURE MILLABLE CANE 60% Total Biomass 70-75% Moisture 15-20% Fiber 10-15% Sucrose NOW ARVESTED PORTION 24/02/2006 Energy Technology, Stockholm, Sweden 7

8 ARVESTING Traditional arvest - Makes the canes easy to handle - Pollutes the nearby environment - Loss of biomass potential Green arvest -Machines separates the tops and leaves (cane trash) from the cane. 140kg dry cane trash can be recovered per ton of cane. 24/02/2006 Energy Technology, Stockholm, Sweden 8

9 Overview of Sugar processing SUGAR CANE Washing Juice Extraction Juice Treatment Juice Treatment Sugar Production SUGAR Fermentation Distillation ALCOOL 24/02/2006 Energy Technology, Stockholm, Sweden 9

10 JUICE EXTRACTION The sugar rich juice is pressed out from the cane in a series of mills 24/02/2006 Energy Technology, Stockholm, Sweden 10

11 CLARIFIER The sugar juice contains dirt (mud and soil) By adding Lime (Ca-compound) to the juice, the dirt is settled out and can be separated by gravitational force in a settling tank (Clarifier) 24/02/2006 Energy Technology, Stockholm, Sweden 11

12 EVAPORATORS Steam is heat exchanged with the sugar juice to evaporate the water in the juice and hereby concentrating the liquid to a viscous syrup. 24/02/2006 Energy Technology, Stockholm, Sweden 12

13 BOILER (CRYSTALLISATION) With aid of heat in a vacuum pan, sugar crystals are formed in the mother liqour. The crystals are clean sugar; impurities stay in the mother-liquor. A receiving tank, the crystalliser cools the liquid containg the growing crystals. 24/02/2006 Energy Technology, Stockholm, Sweden 13

14 CENTRIFUGES The last step in the raw (brown) sugar production is to separate the crystals from the liquor (molasses). This is done with steps of centrifuges.thereafter the brown sugar crystals are dried in a hot-air dryer. Photo from 24/02/2006 Energy Technology, Stockholm, Sweden 14

15 SUGAR REFINING The aim with sugar refining is to remove the last impurities, turning the sugar into white color. The refining steps are: -Affination -Carbonatation -Decolourisation -Boiling 24/02/2006 Energy Technology, Stockholm, Sweden 15

16 AFFINATION The sugar crystals formed in the earlier process have a outer layer of molasses. The sugar is mixed with a syrup with slightly higher purity. The surrounding molasses attach to the syrup and the molasses-free crystals are separated through centrifugation. The washed crystals are now dissolved in water 24/02/2006 Energy Technology, Stockholm, Sweden 16

17 CARBONATATION The liquor with the dissolved sugar, still contain non-sugar particles. Chalk or lime is added, and CO2 is bubbling through the liquid, reacting with the lime forming Ca-carbonate, to which the solid impurities attach. The liquor is thereafter filtered, and also becoming whiter. 24/02/2006 Energy Technology, Stockholm, Sweden 17

18 DECOLOURISATION Columns with Granular Activated Carbon (GAC) adsorbs colour from the liquor, turning the sugar to white. As the liquor is too dilute for new crystals to grow, the liquor passes through EVAPORATION steps again. 24/02/2006 Energy Technology, Stockholm, Sweden 18

19 BOILER (CRYSTALLISATION) The liquor is now containing white sugar, which has to form new sugar crystals. Crystal is planted and let grow in the crystalliser, and a centrifuge separates the white sugar from the liquor. 24/02/2006 Energy Technology, Stockholm, Sweden 19

20 DRYING and PACKING The refined sugar is dried in hot air and packed into sacks. 24/02/2006 Energy Technology, Stockholm, Sweden 20

21 EAT AND POWER eat demand in the sugar process -Evaporation -Crystallisation -Drying Power demand in the sugar process -Mills (Juice extraction) -Conveyor belt -Centrifuges -Auxiliary equipment 24/02/2006 Energy Technology, Stockholm, Sweden 21

22 FUEL The main fuel in the raw sugar process industry is bagasse, which is burnt in a steam boiler. Properties: Coming out from the mills, it has 50% humidity It is a very fibrous material It is very inhomogenous and non-uniform As for the high humidity content it cannot be stored Burning it directly gives a low combustion efficiency 24/02/2006 Energy Technology, Stockholm, Sweden 22

23 TE STEAM PLANT The need of heat in the sugar process controls the steam generation. A typical steam power plant has following data: Steam pressure and temp: bars, ~ 300ºC Steam flow: kg per ton of millible cane Electricity: kwh per ton of millible cane The steam turbine is a backpressure turbine, delivering process steam at typically 4 bars These numbers meet the onsite sugar mill need 24/02/2006 Energy Technology, Stockholm, Sweden 23

24 Why do not sugar mills deliver electricity to the grid year-round? The sugar process is SEASONAL, which means that it only operates parts of the year. The process heat demand controls the steam plant and steam parameters. In order to be able to deliver electricity to the grid, an year-round operating power plant is needed, and in all probability also other fuels than bagasse. 24/02/2006 Energy Technology, Stockholm, Sweden 24

25 POWER PLANT IMPROVEMENTS Drying of BAGASSE Increases the comb. eff. and overall eff. as the waste heat in flue gases can be recovered. May require a new boiler to deal with the higher temperatures. Introduce a condensing turbine with steam extractions instead of a backpressure type. This enables pure electricity generation off-season. Increase steam pressure to 80 bars gives in a condensing turbine ~100 kwh electricity surplus/ ton of cane (the steam for process has been extracted). 24/02/2006 Energy Technology, Stockholm, Sweden 25

26 FURTER IMPROVEMENTS Drying of BAGASSE, thereafter PELLETISE the bagasse. Pellets allow use of new types of combustion /gasification devices and STORAGE to off-season REPOWER the whole steam plant to a BIGCC Net export of electricity up to 170 kwh/ ton of cane if the sugar process is improved using less steam flow BIGCC = Biomass Integrated Gasification Combined Cycle 24/02/2006 Energy Technology, Stockholm, Sweden 26

27 WAT IS GASIFICATION? GASIFICATION is a thermal process converting a solid fuel into a combustible gas to be used in an IC-engine or gas turbine. Was widely used during World War II to power vehicles 24/02/2006 Energy Technology, Stockholm, Sweden 27

28 TE GASIFICATION PROCESS With understoichometric combustion conditions, a gas containing combustibles such as CO and 2 is created 24/02/2006 Energy Technology, Stockholm, Sweden 28

29 TYPES OF GASIFIERS 24/02/2006 Energy Technology, Stockholm, Sweden 29

30 UPDRAFT AND DOWNDRAFT Gas Biomass Biomass Fixed bed of biomass Oxidant Fixed bed of biomass Oxidant Grate Throat Oxidant Ash Gas+ Ash a) Updraft b) Downdraft 24/02/2006 Energy Technology, Stockholm, Sweden 30

31 FLUIDISED BEDS Product gas Gas, ash and bed material Product gas Freeboard Cyclone Ash Fluid bed Biomass Fluid bed Biomass Ash Oxidant Ash Oxidant Ash Bubbling Fluid Bed Circulating Fluid Bed 24/02/2006 Energy Technology, Stockholm, Sweden 31

32 FUEL GAS COMPOSITIONS 2 CO CO 2 C 4 N 2 Tars Dust Downdraft Air Good Fair Downdraft Good Good Oxygen Updraft Air Poor Good Fluid bed Air Fair Poor 24/02/2006 Energy Technology, Stockholm, Sweden 32

33 TE BIGCC PLANT The electricity efficiency is >40% 24/02/2006 Energy Technology, Stockholm, Sweden 33

34 ALCOOL FROM SUGAR CANE Ethanol can be made from: -Sugar Juice (in a pure ethanol process) -Molasses -Bagasse (cellulose needs to be split into sugars-ydrolysis) Picture from 24/02/2006 Energy Technology, Stockholm, Sweden 34

35 ETANOL PROCESS SUGAR LIQUOR FERMENTATION DISTILLATION ETANOL 24/02/2006 Energy Technology, Stockholm, Sweden 35

36 YDROLYSIS OF CELLULOSE O C 2 O O O O O C 2 O O O O O C 2 O O O O O C 2 O O O O O CELLULOSE YDROLYSIS O C 2 O O O O O O C 2 O O O O O GLUCOSE GLUCOSE 24/02/2006 Energy Technology, Stockholm, Sweden 36

37 ETANOL AS A FUEL Gasoline Ethanol Lower eating Value (MJ/L) 32,3 21,3 Octane Number Latent eat of Vapourisation (kj/kg) Ignition temperature (deg C) Stoichiometric air to fuel ratio 14,5 9 The higher octane number allows higher compression ratios and hereby a larger engine efficiency. Up to around 20% ethanol can be mixed into gasoline without changing the engine. 24/02/2006 Energy Technology, Stockholm, Sweden 37

38 ETANOL AS A FUEL/Disadvantages Compared to gasoline, the ethanol has following disadvantages: - Lower heating value - Water dissolves in ethanol - Is corrosive - Shortens the engine wear OWEVER, ethanol is a RENEWABLE 24/02/2006 Energy Technology, Stockholm, Sweden 38

39 The Brazilian Ethanol Program/1 Was launched in 1975 due to the oil-crisis and increased economical burden on the Brazilian government of the oil import Ethanol produced from sugar cane replaced fully or partly gasoline for vehicle drive Still it is the world s biggest commercial renewable project 24/02/2006 Energy Technology, Stockholm, Sweden 39

40 The Brazilian Ethanol Program/2 In 1998 about 5.2 million cars are powered with ethanol only (20% of the cars). Their consumption was in 1998 about 7.6 billion liters of ethanol GASOOL is a blend between gasoline and ethanol (78% gasoline, 22% ethanol). About 5.3 billion liters of ethanol was used to produce this blend for the remaining cars 24/02/2006 Energy Technology, Stockholm, Sweden 40

41 The Brazilian Ethanol Program/3 Economical impact: 1.8 billion USD/ year is saved from reduced need of oil import. owever, the production cost of ethanol is still somewhat higher than for gasoline Social impact: jobs were created directly and about jobs indirectly. Environmental impact: Compared to if only gasoline was used, a reduction of CO2 to the atmosphere is estimated to about 10 Million tons per year. 24/02/2006 Energy Technology, Stockholm, Sweden 41

42 The Brazilian Ethanol Program/4 Periods of insufficient ethanol production, and still cheaper gasoline has led to a decrease in amount of pure ethanol cars during the 90 s Latest development: The release of flex-fuel cars in Brands like VW, Fiat and GM manufacture. These can run on 100% gasoline, 100% ethonal or any blend between the two fuels. Today, around 20% of all new cars sold in Brazil are flex-fuel (around cars were sold in 2004). 24/02/2006 Energy Technology, Stockholm, Sweden 42

43 More about ethanol as a fuel For more info on ethanol, please visit: 24/02/2006 Energy Technology, Stockholm, Sweden 43