Notes on Involved Energy in Cane Sugar Processing

1
Notes on Involved Energy in Cane Sugar Processing

• Dr Carlos de Armas
• Dr Oscar Almazan

2
Cane Sugar Processing

• Extraction Separation of the sugared
  juice
• from the bagasse
  (fiberwater )
• 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

3
(No Transcript)
4
(No Transcript)
5
(No Transcript)
6
(No Transcript)
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 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

9
Energy in Processing (Main Elements)

• Steam generation efficiency
• Efficient use of steam
• Efficiency in the conversion of
• thermal energy into mechanical

10
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.

11
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.
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. 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?
13
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
14
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

15
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 EnergySales to
the Grid
16
(No Transcript)
17
(No Transcript)
18
-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.
19
(No Transcript)
20
(No Transcript)
21
SUMMARISING
22
STEAM AND POWER GENERATIONBase 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
23
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

24
STEAM GENERATION

• Characterizing SG Efficiency, specification
• of Gross Calorific Value, or Nett Calorific Value
• as a function of moisture(W) .
• metric units
• NCV 4250-4850W/100 kcal/kg (Hugot)
• english units 1.8(kcal/kg) Btu/lb
• NCV 7650-8730W/100 Btu/lb (Hugot)
• 1.0 kW-h 3.6106 watt-seg (joule) 860
  kcal
• 1.0 kcal 4.186 kj

25
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

26
GENERAL BOILER CONFIGURATION

• Furnace
• Water walls
• Screen
• Superheater
• Water Evaporation Bundle
• Economizer
• Air Pre-heater

27
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

28
FURNACES DIFFERENT TYPES

• Burning in pile Horse shoe
• Cell
• Spreader stoker (grate) oscillating
• travelling
• Suspension firing

29
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

30
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
• 
  

31
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

32
..LAST COMMENTARIES AFTER STOICHIOMETRY, IT
IS POSSIBLE TO BUILD MOLAR AND ENERGY
BALANCES, ANDAFTR THIS , ADDING DETAILS OF
CONFIGURATION, TO BUILD THE WHOLE MODEL OF
STEAM GENERATIONAFTER THE ADDEQUATE
PROCEDURESTHE REST OF THE WHOLE PROCESS
ENGINEERING MAY BE MODELED, REACHINGTHE 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 from batches (barometric leg
seal) to spray pond. General purpose water
from source to tank. Imbibition and
recirculation of juices 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)
108437 ft-lb / ton/hour, for 300 ton / hour
108437300 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
35
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
18060 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

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
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.
37
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
38
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.
39
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.
40
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