A FEASIBILITY STUDY OF THE PRODUCTION OF ETHANOL FROM SUGAR CANE
Department of Chemical Engineering University of Queensland
Report by: F.H.C. Kelly, A.M.T.C. M.Sc.(Melb). D.Sc.(Tas) F.R.A.C.I.,F.S.N.I.e.,M.I.E.(Aust) Chartered Chemist (Australia), Chartered Engineer (Australia) Head of Department: D.J. Nicklin
Supporting Body: Queensland Department of Commercial and Industrial Development
ACKNOWLEDGMENT
We gratefully acknowledge the continuing support of the Queensland Department of Commercial and Industrial Development for this work.
November , 1977
G a r d e n s P o i n t A 2 2 3 3 5 0 4 0 B
A f e a s i b i l i t y s t u d y of the p r o d u c t i o n of e t h a n o l from sugar cane
i PREFACE
For a period now spanning more than ten years, the Queensland Department of Commercial and Industrial Development has sponsored research and feasibility studies within the Department of Chemical Engineering of the University of Queensland. A series of reports has been produced, each concerned with some aspect of Queensland's Development.
The work has been carried under my broad supervision, generally by research officers. Earlier workers who have produced reports in this series include Mr. J.G. Job, Dr. P.J. McKeough and Dr. F.K. Mak.
When we accepted the present assignment to write a report on the feasibility of producing ethanol from sugar cane, we had expected to follow much the same procedure used in the past. However, at about this time, Dr. F.H.C. Kelly visited the Department, and the possibility of a somewhat different approach became clear.
Dr. Kelly is a man with very broad experience in the sugar industry - experience in Queensland and overseas and in many aspects of the sugar industry, which would be difficult to match. I invited him to work on the project for the Department, and the report is attached.
I believe this will be a very useful starting point for consideration of a massive expansion of the Queensland sugar industry to produce ethanol.
Others may prefer to fit alternative numbers to the various relationships outlined or even to modify some of the relationships. If we have provided a useful base from which to consider the alternatives, and if we have caused others to think about better alternatives, I believe we will have achieved our goal.
D.J. Nicklin 9.11.77
ii SUMMARY
1. A comprehensive study has been made of factors related to the production of ethanol from sugar cane and problems related to its use in internal combustion engines. All ethanol costs are "ex-distillery" estimates.
2. Cost estimates calculated for 25 sets of conditions range from 27 to 8c/l, summarised in Table A and illustrated graphically in figure 4 with 12 relevant parameters.
3. Preliminary experiments with juice are deemed necessary at estimated R.6D.
cost of $100,000.
4. Highest costs are for distilleries associated with the present Queensland sugar industry.
5. It is considered unwise to tamper in any way with the structure of the present sugar industry for the purpose of obtaining low cost ethanol.
6. Full advantage should be taken of experience in growing sugar cane, control of pests and diseases and of extracting juice.
7. If the sugar industry should wish to divert cane to ethanol production in the event of failure of the export market this should be considered only as a short term palliative.
8. Sugar cane grown in new areas specifically for ethanol would appear to have good prospects for lower cost development if_ a new social and economic structure suited to its own needs can be developed.
9. The social changes would include 7 days/week of operation for 39 weeks/year for which 12 month employment conditions could be negotiated to cover agricultural as well as processing areas. A suitable agreement with unions would be a necessary preliminary determination.
10. An Industrial Alcohol Energy Authority should be established to oversee the development and operation of the new industry with representation from government and unions as well as producer and consumer groups.
11. Economic changes would include full mechanization of all agricultural activities with programmed maintenance and 24 hr/day - 7 day/week operation.
This is not compatible with small farm units and the cost advantages of 1600 ha properties or 35,000 ha estates have been examined.
iii 12. Absolute costs are very difficult to estimate but the relativity of costs
is believed to be satisfactorily indicative. Cost evaluations have been broken down to 12 main units and numerous sub-units providing a stability to the cost structure. Thus for the lowest costing route at 8C/1 the capital cost of the processing plant represents the highest cost component at 26%. A 50% error in this figure would alter the overall cost by 1c/1.
13. Association with the present sugar industry could enable about 400 Ml/annum to be produced at around 25.5C/1 with one distillery in each of the four districts and using also all of the molasses produced from all of the mills.
Any increase beyond this could only result in a higher price for ethanol produced within the structure of the present sugar industry.
14. Recent experiments in Brazil have indicated that ethanol can develop 18%
more power per litre than petrol but 15 to 20% more volume is used. A compression ratio of 10:1 is needed to achieve these results. The Fiat motor company in Brazil is prepared to make appropriate engine changes.
15. Logistic constrictions on the rate of development of a new industry in Australia would mean initially blends with petrol in areas close to production progressively extending through Australia. A 7 to 10% limit is advised in high humidity areas (e.g. Queensland tropical wet season) but up to 15% would probably be safe in low humidity areas.
16. Australia's present consumption of petrol of around 14Gl/year would require seven Queensland sugar industry (QSI) units to supply the whole amount as ethanol if only juice from stalk cane is processed.
17. If cellulose from fibre is hydrolyzed and fermented with 50% recovery and whole cane (including tops and leaves) is processed only 4QSI units would be needed.
18. A great deal of information is known about cellulose hydrolysis but not with respect to sugar cane fibre. A research and development
investment of $2m specifically directed towards this objective is commended.
19. District area units of 35,000 ha or 0.1 QSI units are commended for new area development, subject to qualifications relevant to item 15 table A.
iv 20. Capital costs for each new area are estimated to total approximately
$350m or $3,500m/QSI unit.
Carrying present knowledge of cellulose hydrolysis to a viable stage for
$2m could make the difference between a capital investment of $23,500m or $13,500 m i.e. $10,000m. A R. & D. investment of $20m could well be justified.
21. The average productivity in Te sugar/ha - season of the present QSI is the best in the world, but Te cane/ha - season are only about 40% of local well demonstrated achievable figures. Evolutionary improvement is at the rate of 1.1 to 1.6% per year.
22. If actual average productivity could be increased to 80% of achievable limit by wider application of already well known agricultural practices this would double unit area ethanol production and reduce the number of QSI units required to 2 or 3.5 depending on whether cellulose is processed or not.
23. An establishment R.S D. investment of $llm is considered necessary for such an achievement to be realised.
2*+. Since larger water supplies for irrigation would be required as well as larger or more numerous processing plants the total capital investment per QSI unit would be nearer $4,500m. The outcome of the $llm. R.£D.
investment would determine the real need or otherwise of capital expenditure of $13,500m or $8,700m - again an investment that would be well justified if it cost 10 times as much.
25. An establishment R.SD. investment of $3m is commended for developing the requirements for optimum agricultural operations other than those specifically relating to area productivity. This would have only marginal influence on capital expenditure but would relate to a difference in the price of ethanol of 5-8C/1 or $7-11,200m per year.
The initial gross benefit would be very much less but the manner in which a new area development may be initiated will have long term price influences.
V
26. The possibility of growing cassava as a fallow rotation crop has been examined. It would seem to have little influence on the estimated cost of ethanol but would increase area productivity by about 10(±3)%.
27. If cellulose hydrolysis is practised it may be done either with or without using coal as fuel. The estimated productivity and cost differences are marginal but more capital is required for the ethanol plant if coal is not burned. The pro-rate capital investment for the coal plant and transport is probably about half of that required at the ethanol plant.
28. If coal is used total consumption would be up to 4.3MTe per 14G1 of ethanol or 3256 litres of ethanol per tonne of coal. On the other hand the use of this tonne of coal has enabled only 1333 1 of extra ethanol to be produced which is still favourable when compared to 300 1 of petrol possible from the same tonne of coal by hydrogenation.
Producing ethanol from sugar cane by the routes described may represent a net gain of energy varying between 10% and 64% according to the constrictions applied.
29. The energy input for full mechanization of farming procedures is estimated at about 1% of ethanol output.
30. Up to 90% of fertilizer requirements are expected to come from recycled evaporated distillery slops. When coal is burned about 74% of the heat from this source is needed for slops evaporation if looked on as a marginal effort. A very costly fertilizer - but convenient. On the other hand when processing from stalk cane juice the fuel required is readily available from surplus bagasse and two disposals are satisfactorily handled.
31. A R. & D. investment to study the thermal balance of the distillery could conceivably reduce coal consumption by up to 50% and make the non-coal route more attractive. The possibility of recycling slops to the hydrolysis heap needs investigation. An investment of $lm could ultimately be worth $100m/year but much less initially and not critically important until perhaps 1990.
vi 32. A levy of at least 1% and preferably 2% of the value of the product
is commended for R. & D. as a continuing investment.
33. A system of indexed amortization has been suggested to enable development capital to be serviced at currently realistic rates of interest.
34. Employment prospects are envisaged at 10,000 to 20,000 persons/14Gl - year directly concerned in field and factory, generating supporting employment 3 times this number. A similar number is envisaged as being employed during development stages. Each district would have a community of 6000 located in 3 sub-communities - one of 3000 and two of 1500. These numbers relate to 1600ha property or 35,000ha estate development. For 50ha farms an overall community of a million people is indicated and believed to be too large a proportion of the nation's manpower resources for a single product investment.
35. The possibility of applying space-age technology through remote control has been examined and seems feasible with known technology. Complete control could be effected from the Brisbane area reducing the need for remote living to 1500 persons per district for maintenance and operator-assisted duties.
TABLE A - SUMMARY
ITEM
1.
1 2'
[ 3.
4.
5.
6.
Dual production with raw sugar, from stalk cane plus molasses from surrounding district mills. Restricted to one unit per district. Table VI
Sole product from stalk cane at an existing mill plus molasses from district. Restricted to one unit per district. Table IX
Mew area developed, Stalk juice.
Social change to 7 day-week, 39 week season3 annual employment on farm as well as factory. 50ha farms.
Table XVIII.
As for 3 - 1600 ha properties.
Table XVIII
As for 3 - 35,000 ha estates Table XVIII
As for 3 - whole cane processing including cellulose - 50 ha farms Table XIX
LAND1
AREA QSI UNITS no extra
no extra
6.7
7.2
7.6
3.6
ESTIM.
COST EtOH
2 7 ± 24
28 ± 25
24
15.5
14.5
15.6
GROSS CAPITAL INVEST.
A$m.
23,500
25,250
26,500
1 13,000 R. S D.
o.i2
As
2.5
3.0
3,5
0.22
3.0
R.&D. BENEFIT
(a) to process juice (b) thermal balance
for 1.
concept dev.3 save 3C/1. =
$420m/year..
extra capital $1750m. cf.3, save 8.5cyi = $1200m/year extra capital $3000m. cf.3, save 9.5c/l = $1330m/year
cellulose hydrolysis. concept dev. save capital $10,500m. cf.3 !
& 8.4c/1 = $1176m/year
t
7.
8.
9.
10.
11
12
13.
As for 6 - 1600 ha properties.
Table XIX
As for 6 - 35,000 ha estates Table XIX
As for 3 - plus cassava fallow crop.
50 ha farms. Table XXI
As for 9 - 1600 ha properties Table XXI
As for 9 - 35,000 ha estates Table XXI
As for 6 - plus cassava fallow crop, 50ha farms. Table XXII
As for 12 - 1600 ha properties Table XXII
3.9
4.1
5.4
5.8
6.0
3.2
3.4 11.1
10.6
22
15.2
14.1
15.8
11.6
13,500
14,250
19,000
203300
21,000
12,000
13,000 0,2 3.5
0.2 4.0
3.0
4.0
4.5
0.2 3.5
0.2 4.0
cellulose hydrolysis. concept dev. extra capital $500m cf.6.
save 4.54/1 = $630m/year
cellulose hydrolysis, concept dev. extra capital
$1250m.cf.6. save 54/1 -
$700m/year
concept dev. save capital
$4500m cf. 3. and 24/1 = $280m/
year
concept dev. extra capital
$1300m,cf.9. save 6.84/1 =
$950m/year
concept dev, extra capital
$2000m.cf.9. save 7.9c/1 =
$1100m/year
cellulose hydrolysis concept dev. save capital
$1000m.of.6.extra 0.2c/1 =
$28m/year
cellulose hydrolysis concept dev. extra capital
$500m.cf.7.extra 0.54/1 =
$70m/year
14.
15.
16.
17.
18.
19.
As for 12 - 35,000 ha estates Table XXII
As for 6 - but with agricultural productivity doubled. 50 ha farms Table XXIII
As for 15 - 1600 ha properties Social advantages over 17.
Save capital of $15,400m, cf. 3, Save 15.6*/1 = $2180m/year cf.3.
Table XXIII
As for 15 - 35,000 ha estates Table XXIII
As for 12 - but with portion of bagasse as fuel and no coal. 50 ha farms.
Table XXIV,
As for 18 - 1600 ha properties Table XXIV
3.6
1.8
1.9
2.0
3.7
3.9 11.1
11.5
8.4
8.0
12.4
9.6
13500
8100
8700
9000
14000
14700 0.2 4.5
! 0.2 11.0
! 0.2
[ 11.0
0.2 12.0
0.3 5.0
0.3 5.5
cellulose hydrolysis, concept development.
save capital $750m. cf.8.extra .5c/l - $70m/year
cellulose hydrolysis, concept development, save capital
$4900 m. of.6. save 4.1c/1 =
$570m/year
cellulose hydrolysis, concept development, save capital
$4800 in. cf.7. save 2.7£/l = : $378m/year
cellulose hydrolysis- concept development, save capital $5250m, o f . 8 , save 2.6C/1 = $360m/year
cellulose hydrolysis.
concept development.
extra capital $2000m, cf.12.
save 3.4C/1 = $476m/year I
cellulose hydrolysis, concept development, extra capital $1700m. cf. 13.
save 2.0C/1 = $280m/year
*
20.
21.
As for 17 but with space-age technology with remote control.
Table XXV.
ESTIMATED MINIMUM PRICE ACHIEVABLE FOR ethanol FROM SUGARCANE
2.0 7.5
7
9200 As for 17 plus
5.0 space-age technology development - extra capital = $200m,cf.17.
save 0.5C/1 = $70m/year. save remote location of 90,000 persons
1. To produce 14Gl/year of ethanol.
2. Essential for development of entire concept. Initial investment only.
3. 30% of all concept development costs to process studies, 60% to agricultural studies.
4. Total production achievable at this price range = 200Ml/year 5. Total production achievable at this price range = 400Ml/year,
xi FLOW SHEETS AND GRAPHS
FIGURE
1 Simplified flow sheet for dual production of sugar and ethanol
2 Simplified flow sheet for producing ethanol from juice of sugar cane
3 Simplified flow sheet for whole cane processing with cellulose hydrolysis
4 Relationship between estimated price of ethanol as related to the size of the farm unit.
Total steam 603
Figure Is Simplified flow sheet for dual production of sugar and ethanol.
CONTENTS Page i
ii Preface
Summary
Flow Sheets and Graph xi
Introduction 1 Alternative fuels and their sources 6
The fermentation process 15 Agricultural considerations 19 Sugar cane for ethanol production 23
Technology studies 32 Basic fundamental information 38
Dual purpose factory 39 Effect of varying proportion of products 55
Locality for dual product operation 55 Dual product plant with molasses supplement 59 Single purpose ethanol-sugar cane plant 64 The precision of pricing procedures 76 The price of sugar and the price of oil 78 Ethanol from sugar cane in a new growing area 88 Location of a new sugar cane/ethanol complex 90
Seasonal considerations 92 Sunshine requirements for growing sugar cane 95
Water requirements for growing sugar cane 99 Fertilizer needs in sugar cane culture 105 Unit operations in sugar cane agriculture 110
Size of a sugar cane farm 112 New land development 117 Capital repayment alternatives 119
Methods of calculation for Table XIV 122 Estimated cost of mechanical component of farm unit operations 125
Irrigation application 128 Harvesting of sugar cane 129
Fuel Costs 134 Transportation of sugar cane 135
Factory equipment 138 Computer control factors 142 Farm equipment maintenance 143 Management of agricultural operations 144
Agricultural extension services 147 Productivity development on existing farm areas 150
The cellulose component of sugar cane 154
Cassava as a fallow crop 162 Effect of farm productivity on cost of ethanol 169
Coal as energy supplement 173 Carbon dioxide production 175 Fusel oil production 177 Denaturing of ethanol 178 Ethanol storage 181 The environmental impact of a large scale sugar cane/
ethanol industry 182 Ethanol and the internal combustion engine 185
Application of ethanol as a motor fuel 188
Development options 196 Predicting the future 198 Overall employment and income prospects 204
Application of space-age technology 208
Energy balance 213 Estimates of future Queensland and Australian requirements 216
Related relevant literature 218
TABLES Page
A Summary of estimated costs of ethanol production vii I Net Thermal Values of Selected Fuels 11 II Dual product plant without additional molasses - raw 53
material costs
III Dual product plant without additional molasses - total 54 costs
IV Queensland mill size and land productivity criteria 60 V Dual product plant with additional molasses. Raw
material costs 62 VI Dual product plant with total estimated costs of ethanol 63
VII Single product plant to produce ethanol without additional
molasses 67 VIII Single product plant to produce ethanol plus additional
molasses (raw material costs) 68 IX Single Product Plant with total estimated costs of ethanol
production 69 X Summary of estimated costs of ethanol production -
primary options 70 XI Total ethanol potential for an 817,000 Te cane complex 71
XII Effect of doubling the size of a sugar mill on ethanol cost 75 XIII Estimate of photosynthetic efficiency of sugar cane in
Queensland 97 XIV Tabulated indexed capital repayment rates 123-:
XV Effect of size of field on cost of tractor usage 126 XVI Cost estimates for cane grown on large properties or
estates 129 XVII Estimated costs of road transport for sugar cane 137
XVIII Estimated cost of processing sugar cane stalk juice
for ethanol 14-1 XIX Estimated cost of ethanol from whole cane including
cellulose hydrolysis 161 XX Cost estimates for growing cassava for ethanol 166
XXI Estimated cost of producing ethanol from sugar cane stalk
juice and cassava 167 XXII Estimated cost of producing ethanol from whole sugar cane
plus cassava 168 XXIII Estimated costs of producing ethanol from whole cane
but with 80% achievable productivity. Coal as fuel. 171
XXIV As for XXIII but no coal as fuel 176
1 INTRODUCTION
Producing alcohol by the fermentation of plant sugars is probably one of man's oldest technologies but until the development of distillation as a means of concentration its use was restricted to such applications as were suited to the relatively low concentrations it was possible to achieve in this way.
Although) a distillation technique was described as early as Aristotle in the 4th century B.C. it was not until the beginning of the 19th century that its application to alcohol concentration became significant.
By the end of that century it had been developed to such a degree that the fermentation and distillation of potatoes in Germany supplied substantial quantities of alcohol for industrial purposes.
The word alcohol is of generic significance when used in organic chemistry but in the current context the only alcohol with which we will be closely concerned is ethanol (C.H OH) although some reference to other alcohols will be made at appropriate stages.
Ethanol is the major product of alcoholic fermentations but small quantities of amyl alcohols (d- and/or iso-) as well as some butyl and propyl may also be produced and are generally referred to as fusel oil.
The amount varies between about 0.1 and 0.7% and may also include trace amounts of fatty acids, esters, furfural and other substances.
Ethanol is the most important of the many products which can be produced by fermentation for industrial purposes. The basic raw material for this is the sugar glucose but this in turn is usually derived from the breakdown of a higher molecular weight entity such as sucrose, starch or cellulose. The relative importance of these as raw material will be
2
considered. There are a number of reasons for giving primary consideration to sugar cane which will be given later. Suffice it for the time being to say that there is already a well established sugar cane growing community in Australia and the agro-technology is well understood. Sugar cane is known to be one of the best plants for efficiently utilizing sunshine in the synthesis of carbohydrate and it grows well under a wide range of soil and climatic conditions with appropriate cultural techniques. In fact Australia leads the world in the annual rate of production of sugar in cane per unit of area under cultivation.
Ever since the internal combustion engine was invented, the
possibility of using ethanol as a fuel or partial fuel has been considered and very detailed study went into the subject during the latter part of the 19th and earlier part of the 20th century. The net conclusions have been that it can be used successfully under a wide range of conditions without significant modification being required for the engine as marketed during the 1970's. There have been periods when certain countries have made quite significant use of ethanol for internal combustion engines and this includes Australia during the 1930's and 1940's. Special circumstances have had their influence and these will be discussed later. Brazil currently is an important user and is developing this capability rapidly.
Ethanol is a fuel which can be continuously regenerated as long as there is sufficient land available for cultivation.
For some years the Halthusian predictions of population growth
outstripping available food supplies and apparently abundant mineral supplies of liquid fuels militated against serious consideration being given to wide scale growth of plant materials for industrial energy. These are no
3
longer the spectre painted in the 1950's. Population growth now appears to be most closely related to the economic advantages or disadvantages of a large family. As long as there are economic advantages, as in a labour intensive agricultural economy, population growth is for all practical purposes, uncontrollable. With the development of machine intensive cultivation techniques, the disadvantages of a large family unit become apparent and slowly the rate of population growth slows to controllable figures. The supply of food is also related very strongly to the efficiency of harvesting and storage techniques as well as to distribution facilities. The net result is that with the exception of local conditions of drought or flood the world in fact does have a surplus of food and there are good reasons for believing that the situation will continue for the forseeable future.
Ho person likes radical changes in their way of life, and a sudden change from a petrol based liquid fuel economy to an entirely ethanol based economy would be fraught with many problems. Fortunately this should not be necessary in Australia and it could be introduced progressively to replace imported petroleum fuel as it blends very well with petrol in proportions which would be adequate to effect this change with minimum of frustration and provide an extensive and well needed development of employment in Australia involving a wide range of skills.
Ehhanol is a lesser fire hazard than petrol in storage and transport situations. On the other hand it does have its own specific problems such as unsocial results in human consumption and its miscibility with water. There are ways and means of dealing . with these problems and they will be discussed.
The environmental impact of large scale development would be expected to be most prominent in two areas. Firstly the substantial extension of
cultivated land and new housing development, possibly but not necessarily at the expense of forest land. Secondly there would be the problems of waste disposal from the fermentation process. The installations would need to incorporate equipment and procedures to cope with this. On the other hand ethanol can effectively displace alkyl-lead additives commonly employed for increasing the anti-knock rating of petrol and which pollute the atmosphere by their presence in exhaust gases. Internal combustion engines operate at lower temperatures and run more quietly when ethanol is used as a petrol additive. As a complete replacement for petrol there are more problems including a significantly lower thermal value, but when used in minor additive proportions there is no noticeable increase in volumetric consumption, nor are changes required in the tuning of the engine of significance.
These matters will each be considered in detail at an appropriate stage.
When considering alternative energy sources it is thought to be impracticable to attempt to displace all currently used types of mineral based energy with a single type of energy derived in one way from a solar source. This study will confine itself to problems involved in the progressive development of liquid fuel derived from nature's solar cell- chlorophyll through the intermediate natural synthesis and storage of carbohydrate in sugar cane.
Reasons for the selection will be elaborated during the course of this study.
Two questions of major concern become significant - (1) can ethanol be produced at a satisfactory price and in substantial volume and (2) can ethanol be used effectively as a major liquid fuel? The two
5
questions revolve around each other and both must be answered effectively, but it is largely a matter of choice as to which is discussed in detail first. In this study the choice has been made firstly to study production and secondly consumption, but always being cognisant of interactions and side effects.
6
ALTERNATIVE FUELS AND THEIR SOURCES
The internal combustion (I.C.) engine has become such a widely used device in present day living that it is almost inconceivable to imagine alternatives achieving more than marginal significance. These engines have been developed to employ fuels in either the gas or liquid phase, endeavours to employ powdered solid phase fuels or mixtures of solid and liquid phases have not been successful due mainly to problems concerned with the exhausting of ash constituents of solid fuels.
Only a very small proportion of I.C. engines employ gaseous fuels.
Whilst they do enjoy many advantages including a continuing supply of fuel in the event of a development of a hydrogen based energy economy, the major disadvantage is the difficulty experienced in developing satisfactory storage techniques especially for small mobile units such as the motor car. From time to time there have been developments in the use of producer gas units including their attachment to mobile vehicles. It is not proposed to consider these more than marginally in the present study.
For our purposes we will consider the development of the I.C. engine along two main lines to which we will apply simply the terms ::diesel::
and "petrol1 engines and in this context, the terms will be used essentially to define the method of ignition - the diesel engine relying on pressure ignition and the petrol engine relying on spark ignition.
There is an interaction of these two mechanisms as the compression ratio of internal combustion engines is increased and the implications of this will be shown to be important. The development of the diesel engine was dependent very largely upon the successful development of fuel injection to specific cylinders under pressure. On the other hand, the carburettor system of the petrol engine has become progressively more complex and there has been a marginal but growing encroachment of direct
6
ALTERNATIVE FUELS AND THEIR SOURCES
The internal combustion (I.C.) engine has become such a widely used device in present day living that it is almost inconceivable to imagine alternatives achieving more than marginal significance. These engines have been developed to employ fuels in either the gas or liquid phase, endeavours to employ powdered solid phase fuels or mixtures of solid and liquid phases have not been successful due mainly to problems concerned with the exhausting of ash constituents of solid fuels.
Only a very small proportion of I.C. engines employ gaseous fuels.
Whilst they do enjoy many advantages including a continuing supply of fuel in the event of a development of a hydrogen based energy economy, the major disadvantage is the difficulty experienced in developing satisfactory storage techniques especially for small mobile units such as the motor car. From time to time there have been developments in the use of producer gas units including their attachment to mobile vehicles. It is not proposed to consider these more than marginally in the present study.
For our purposes we will consider the development of the I.C. engine along two main lines to which we will apply simply the terms T;diesel::
and !ipetrol: engines and in this context, the terms will be used essentially to define the method of ignition - the diesel engine relying on pressure ignition and the petrol engine relying on spark ignition.
There is an interaction of these two mechanisms as the compression ratio of internal combustion engines is increased and the implications of this will be shown to be important. The development of the diesel engine was dependent very largely upon the successful development of fuel injection to specific cylinders under pressure. On the other hand, the carburettor system of the petrol engine has become progressively more complex and there has been a marginal but growing encroachment of direct
7
fuel injection into the petrol engine field.
The diesel engine is designed essentially to operate on low volatility liquid fuels whereas the petrol engine and high volatility fuels are largely designed for each other. In the competitive area of society as distinct from controlled economics there is usually a substantial cost advantage in using low volatility liquid fuel. This has been largely accentuated by the tax structure which has been developed with progressively increasing intensity on volatile liquid fuels.
For the present considerations it is necessary to eliminate as far as possible the incidence of tax on fuels for a true comparison of their relative usefulness as energy sources, but at the same time, recognise that taxation in some form or another is inevitable.
Ethanol can effectively displace either diesel or petrol type fuels, but initially it will be considered as a partial substitute for petrol type fuels with cognisance being taken of the likely results of progressively increasing the proportion in petrol type fuels as well as of progressive displacement of diesel fuels as well as petrol.
For ethanol to become a commodity generally available to the public it becomes of major importance for its use to be restricted to that of a motor fuel or related industrial applications and not be readily converted to human consumption. There are two reasons for the latter requirement, one involves the unsocial side effects, the other relates to the loss of revenue imposed more heavily on alcoholic drinks of all types than on motor fuels. The measures taken to effect desired control in this area are known as denaturing of alcohol. While this will be discussed in some detail later, it is well to point out at this stage that the selection of a suitable denaturant is one of the most important and at
8
the same time one of the most difficult of the problems which relate to the production and widespread use of ethanol as a liquid fuel.
Whilst primary consideration is given to ethanol as a liquid fuel it is recognised that numerous other alternatives have been proposed from time to time, as either a partial or complete substitute for use in either petrol or diesel engines.
Hydrogen is the simplest possible substitute when considered from the point of view of chemical structure. It is a gas at atmospheric conditions of temperature and pressure and is difficult to liquify requiring high pressures for appropriate compression. Some attention has been given in global planning to the prospect of developing a fuel economy entirely based on hydrogen, which in turn can be a product of solar energy. The most commonly studied route being the generation of
electricity with solar cells and the employment of this electricity to decompose water into its elements - hydrogen and oxygen.
There are still so many problems related to the economic development of electricity in this sequence that a fuel economy based entirely on solar-hydrogen is believed to be still many years ahead. Also hydrogen is of very low specific gravity and this reduces it to the status of a second grade gaseous fuel.
Vlhen considering relative thermal values of fuels employed in internal combustion engines the net value is of more significance than the gross value since the latter includes the latent heat of condensation contained in the water vapour of the products of combustion and condensation does not take place in these fuel cycles.
9
Hydrogen gas is rated at 10.8 MJ/m3 at S.T.P. compared with 35.7 for methane. On a weight basis however, this would represent 120 kJ/g as compared with 43.7 for petrol.
Methane (CR4) as the most important constituent of natural gas or produced by anaerobic fermentation is also difficult to liquefy and currently of no real practical significance as a possible alternative to petrol.
Methanol (CH3OH) is one of the most important products of high- pressure organic syntheses used today, reacting carbon monoxide with hydrogen produced as synthesis gas by the reforming of natural gas.
As natural gas is currently available in relative abundance in Australia, the possibility of converting it to methanol as a liquid fuel supply must be given significant credence.
Methanol can be used as a fuel for I.C. engines but it is not a particularly good fuel having a nett thermal value (N.T.V.) of 20kJ/g or 48% of that of petrol with ethanol at 27 or 63% of the value of petrol on a V/V basis. Methanol is more volatile than ethanol which should favour easier starting but the lower latent heat of vapourization is less advantageous from the point of view of thermal efficiency.
Methanol has been important in the marketing of non-potable ethanol by virtue of its usefulness as a denaturant. The classical denaturing fluid has been "wood spirit" or "wood naptha" which used to be a product of the distillation of wood. It is not a chemically pure material but is considered to be about the nearest approach to a perfect denaturant for ordinary purposes.
There may well be merit in blending up to 10% of methanol with ethanol to be used for motor spirit but this will be discussed in more detail later.
Diethyl ether [(C2H5)20] can be produced in a relatively straight- forward manner from ethanol by dehydration with sulphuric acid. It is not a particularly strong competitor for ethanol as a straight motor spirit although it does have a thermal value about 14% higher on V/V basis.
It is too volatile - boiling point 34.6 - to be useful alone, but when blended with ethanol it is beneficial in improving starting characteristics.
Up to 40% has been used in Natal (S.A.) blended with 60% ethanol and known as "Natalite". When converting ethanol to ether there is a loss of 37.5% on a volume basis offset by an associated gain of 20% in thermal value.
Acetone (CH3.C0.CH3) is intermediate between ether and ethanol in terms of volatility (B.P.56.5°) and with a N.T.V. of 28.5 kJ/g or 23 MJ/litre is 69% of petrol (V/V).
Ethanol by way of comparison has a B.P. of 78.5 and a N.T.V. of 26.8 kJ/g or 21 MJ/litre.
Although acetone can be produced by chemical synthesis it is also a product of fermentation using Clostridium genus bacteria.
Unfortunately, acetone is normally produced in association with butanol by this process, a typical product being 60% butanol, 30% acetone and 10% ethanol. The butanol is of little value as a motor spirit because of its low volatility (B.P. 117.7).
The net thermal values for a range of gaseous and liquid fuels are listed in Table I. Whilst the N.T.V. of a fuel is by no means the only criterion for selection it is an important one in -the screening
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procedure. Three gases are included in the table - hydrogen, methane and acetylene. A major problem in each case is that of liquefaction for the purpose of compressing it into a reasonable volume. It can be seen that hydrogen even when liquified by compression has a very low volumetric thermal value and combining this with the heavy weight of cylinders required for storage it becomes a quite uneconomical fuel for most I.C. engines.
Acetylene cannot be used in the simple compressed form owing to its unfavourable explosive characteristics but may be compressed into a solution of acetone. However, this is not an important possibility in the current context and will receive no further consideration.
TABLE I - NET THERMAL VALUE OF SELECTED FUELS
Whilst the N.T.V. is a useful primary criterion for evaluating a fuel for an I.C. engine it is by no means the only one and this will be discussed in more detail with respect to ethanol at a later stage in this report.
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The history of ethanol production has seen several important changes related to developments which have taken place in technology.
It was in the latter part of the 19th century that ethanol first became available on a large enough scale to justify classifying it as an important industrial chemical. This industry was based on carbohydrate fermentation but the product invariably contained 5% of water because of the ethanol - water binary constant boiling point mixture which could not be economically separated by then known techniques of distillation.
For special purposes anhydrous ethanol could be made by preferential reaction with a dehydrating agent such as lime or anhydrous calcium sulphate but was very expensive.
During the first two decades of the twentieth century various modifications of this technique were developed (although the first patent for the use of CaO goes back to 1842) and incorporated in the distillation technique to be removed with the water either at the bottom or at the top of the column depending upon the relative volatility of the additive as compared with ethanol.
Initially dehydration was very costly and only carried out for special laboratory requirements. It was economically unthinkable even to contemplate the possibility of anhydrous ethanol becoming an important industrial commodity.
A radical change developed with the ultimate development of the technique of introducing a third component to the distillation column which would form a ternary C.B.M. (ethanol-water-benzene) and which would separate into two liquid phases on condensation allowing a continuous recirculation of the additive. This was perfected to the stage at which the cost of anhydrous ethanol was very little higher than the 95% aqueous azeotrope.
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Another development in the production of anhydrous ethanol has been for a process to handle directly a fermentation mash at 6% ethanol making use of an extractive distillation technique.
The development of these techniques had, however, only a marginal influence on the employment of ethanol as a motor fuel since 95% aqueous ethanol can be used quite readily as a mild blend with petrol with no significant influence from the water. It can also be used directly or as a methanol-denatured spirit, in fact as much as 50% of water can be tolerated in a spark ignition I.C. engine provided a more volatile fuel is employed for starting. The water does of course reduce the thermal value of the fuel pro rata.
During the 1940's the production of ethanol as a petrochemical began to become important with a progressive phasing out of the fermentation product and synthetic ethanol dominated the ethanol market until the recent substantial use in the price of crude oil.
Synthetic ethanol may be produced either from acetylene originating from calcium carbide or from ethylene available from processing crude oil. The acetylene route only enjoyed a relatively short period of serious interest once the price of natural gas and crude oil fell with the extensive discovery and development of resources since the second world war. The conversion of ethylene into ethanol is a relatively straightforward chemical procedure involving for example firstly sulphonation with strong sulphuric acid
followed by hydrolysis and reconcentration of the liberated sulphuric acid. Alternatively, a more straightforward vapour phase hydration may be effected in the presence of phosphoric acid at a temperature of 300 and pressure of 70 kilopascals.
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Certain countries have continued to provide incentives for the production of fermentation ethanol to encourage home industry and reduce dependence on overseas energy supplies although generally the latter effect has been largely marginal.
Since the rapid rise of the international price of crude oil there has been a resurgence of interest in raw materials suited to fermentation procedures. Future market situations will be influenced by relative costs of raw materials, costs involved in processing techniques and the development of technology related to the use of ethanol or its competitors. The combination of these factors makes forecasting hazardous. Venturing into forecasting will be deferred until later until a more detailed study has been made of factors involved in the production and use of fermentation ethanol.
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THE FERMENTATION PROCESS
Ethanol produced by fermentation originates mainly from the monosaccharide glucose (or dextrose) although its close relative fructose (or levulose) ferments with equal facility. Mannose is also a natural sugar which is fermentable but is not of industrial significance. Galactose which is met with among the hydrolysis products of many plant tissues is only fermented with difficulty.
Neither glucose nor fructose are sufficiently prominent in nature to be important in themselves as raw materials but are produced from the hydrolysis of more abundant carbohydrates.
On the other hand nature builds up complex carbohydrates from carbon dioxide and water with the aid of sunlight with glucose and fructose appearing fairly early in the synthesis chain. Whilst much attention has been given to the development of plants of elementary or single cell structure the stage has not been reached where these might be given serious consideration as viable sources of raw material in competition with more complex plant products.
There are three materials made by nature and which are currently of significant importance as raw materials for fermentation industries.
These are cellulose, starch and sucrose. Both cellulose and starch are hydrolyzable to glucose whereas the hydrolysis product of sucrose is a 50-50 mixture of glucose and fructose. None of these three materials is directly fermentable itself and nature has not developed a useful storage system for glucose or fructose.
Cellulose functions essentially as part of the fibrous structure of plants as a polymer of glucose units and similar in chemical composition -
(C6H10O5)n.
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Associated with cellulose in the fibres of plants are significant amounts of pentosans which are polymers of pentose sugars (C5H10O5)n and of lignin which is of slightly variable composition and of very complex and variable chemical structure. There are also smaller quantities of specialised substances such as resins which are developed in specific types of plants.
The only material in this complex group of cellular substances which is reasonably amenable to fermentation is the cellulose which must first be hydrolysed to glucose. This seldom constitutes more than 50%
of the fibrous components of plants and not unusually as low as 40%.
Pentosans can be hydrolysed to pentose sugars and these are amenable to a small amount of fermentation but except under special circumstances they are more of an impediment than a benefit to the use of cellulosic plant materials for the production of ethenol by fermentation.
The lignin component is even more untractable from the fermentation point of view and a waste product difficult to handle from the point of view of a polluting effluent.
Starch is a food for both plant and animal and is stored in the plant in a seed or tuber and to a lesser extent it often occurs in stalks and leaves but usually en route to the storehouse. Hydrolysis of starch is much more easily effected than of cellulose producing a readily fermentable glocose solution. Whereas cellulose is usually hydrolysed with the aid of mineral acid and high temperature - commonly with high pressure steam, starch may be hydrolysed with very much milder conditions and at higher reaction rates.
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The plant enzyme - diastase is preferred when the fermentation product is to be a potable alcohol. Diastase is an amylase enzyme which hydrolyses starch to a mixture of glucose and maltose, the latter being a disaccharide having the same empirical formula as sucrose - C12H22O11 and like sucrose is non fermentable itself. It must therefore be further hydrolysed to two molecules of glucose which is then fermented.
The diastase is usually prepared from a grain of which barley is reported to be the best although sorghum grain is also a useful source in tropical countries. The diastase is developed during germination of the grain in a process known as malting.
Alternatively, amylase may be produced by using certain moulds of the Aspergillus or Mucor genera.
Starch as it exists in nature is in the form of small grains which usually need rupturing before they can be attacked by amylase. This is done thermally to produce a gelatinised material.
Many different methods have been developed for the ultimate preparation of the carbohydrate to a form fermentable by yeast, which is the organic catalyst employed for the conversion of the glucose to ethanol.
If we start with sucrose as the raw material the hydrolysis step is rather less complex than is the case with either cellulose or starch since we start with a disaccharide. Yeast of the variety Saccharomyces cerevisiae is commonly preferred for the fermentation step. Since this contains the enzyme Invertase which is capable of catalysing the
hydrolysis of sucrose the yeast is sufficient to effect the double function.
However it is often an economic advantage to employ some acid and heat to accelerate the hydrolysis.
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Whilst sucrose occurs in many plant juices it is most strongly concentrated in the sugar cane or sugar beet.
Alcohol has for many years been produced either in potable form or for industrial purposes from the molasses resulting from production of cane or beet sugar. In the case of beet molasses there may be a significant amount of the trisaccharide-raffinose. Upon hydrolysis this yields glucose and the disaccharide melebiose which further hydrolyses to glucose and galactose.
Normally galactose is a difficult sugar to ferment but it may be effected with a bottom fermenting yeast whereas glucose and fructose are satisfactorily fermented with either a top or bottom yeast.
Molasses is commonly a relatively low-priced commodity as there is only limited scope for alternative uses such as fertilizer or animal food. However the amount available is limited by the amount of associated crystal sugar which is produced and local fermentation for industrial purposes is seldom economically viable from the point of view of actual size of equipment. Transport of molasses adds to the cost if a central distillery is operated and the time came during the 1950's when even molasses could not compete with crude oil as a raw material for industrial ethanol.
Since the steepening of the price of crude oil in the 1970's there has been a re-awakening of interest in supplies of molasses, especially by the Japanese.
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AGRICULTURAL CONSIDERATIONS
Many agricultural materials have been used at one time or another as a raw material for industrial ethanol production by fermentation and others have been studied.
In the latter half of the 19th century and the early part of the 20th century, Germany encouraged the production of industrial ethanol from potatoes (4/5ths) and grain (l/5th). The industry was not originally established to find a cheap substitute for petrol, but was one of the consequences of a policy primarily directed towards the extension and improvement of agriculture. Progressively the quantity of production increased until an overproduction situation developed around the turn of the century. However, the industry suffered heavily as a result of the 1914-18 war and never recovered in the face of developing competition from sulphite pulp, wood and carbide in spite of substantial preliminary subsidies.
Although conditions are very different today there are many lessons which could well be learned from a detailed study of Germany's experience.
The growth of the industry was undoubtedly closely related to the agricultural methods and dietetic habits of the people. In 1913 there were some 6000 distilleries producing 300 Ml of ethanol which represented 80% of Germany's total ethanol production at the time. However, it is apparent that such success as was achieved was due not so much to an economically costed product as to the effect of State subsidies. The differential nature of some of these subsidies and taxes also had a significant influence on technology including the development of strong mash fermentation. With an average yield of 16 tonnes per hectare a yield of 1.4 kl was considered a good figure for potato culture.
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Of other tuberous crops Jerusalem artichoke, sweet potato and yam could be expected to provide yields of the same order of magnitude.
Cassava however could probably more than double this yield to something of the order of 3.5 kl/ha. The starch content of cassava tubers is much higher than potato and are the source of the tapioca of commerce. Its cultivation is more restricted to tropical locations as it is sensitive to cold. The soil soon becomes exhausted after successive cropping and rotation. Crops of maize, sorghum or legumes are not uncommonly grown.
Unfortunately cassava cultivation has not responded particularly well to mechanisation. The tubers are long and spreading and can only be ploughed out with difficulty, it being necessary to dig them out or pull them by hand. Modern developments have been to breed better rooted varieties able to be harvested mechanically and these together with improved cultivation techniques have been able to double potential yields of the above-mentioned value to figures over 7 kl/ha.
The yam (Dioscorea) and the sweet potato (Ipomona batotus) are two other tuberous crops which store starch and can be heavy yielding in tropical climatic conditions. They grow best in sandy soils and also present problems for mechanisation.
Many statistics have been recorded for the yield of agricultural products and many of these can be misleading unless there is appropriate qualification. For example, we may compare average yields on a world basis but find that the best country yields are at least twice as much as the average and the best area within the best country may yield twice as much as the average for that particular country or more than four times the world average.
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Another qualification required is the time taken to grow the crop. In most countries sugar cane is an annual crop with a growth cycle averaging about 9 months. Hawaii which records by far the best yield may harvest annually, but the growing cycle extends to 2 years.
Some other areas have a similarly long growing cycle with suitable local reasons for maintaining production.
Similarly in the sugar beet situation although it is an annual crop, the related sugar mangold can crop more heavily in weight/hectare but with a lower concentration of sugar and is commonly a biennial crop.
Trees which are frequently considered as a source of cellulose for fermentation take a number of years to grow. Alfalfa on the other hand can be harvested every few weeks for a useful portion of the year.
Certain species of palm trees are sources for the production of a low quality sugar in village communities throughout areas from India to Indo-China. When calculated in terms of sugar yield per hectare per annum they compare quite favourably with sugar cane grown in those countries. However, sugar cane in those countries is relatively low yielding and there are substantial harvesting problems with the palms.
In sugar palms, sap must be extracted from the florescent zone which is 6 to 15 metres above the ground. On the cultivation side the palm goes on yielding suitable juice for perhaps 50 years with little cultivation, fertilizing or irrigation and ground level cropping or grazing may be carried on over the same area. The palm does, however, take about 7 years before it reaches maturity levels of production.
The cultivation of alfalfa to yield both protein and carbohydrate has been suggested with annual yields of up to 63 tonnes of carbohydrate per hectare suggested as achievable, but the value of an associated 25 tonnes of vegetable Drotein would in itself be a quite significant factor in costing.
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It is of some importance to know the nature of the carbohydrate in the plant. If we assume an ethanol recovery in production of 88% of that theoretically obtainable from the carbohydrate, then a yield could be expected of 600 1/tonne for sucrose whereas starch or cellulose would yield 634 and glucose or fructose 570.
Whilst the hydrolysis of sucrose can be expected to be stoichiometric, the efficiency of cellulose hydrolysis is usually very low and often as low as 50% or even 35% with recalcitrant types. A high degree of saccharification can be achieved with starch and a yield of 634 1/tonne is not unusual. This represents a 5.6% benefit over sucrose and 11%
over glucose or fructose.
Cellulose hydrolysis and fermentation processes of a commercially viable character have been particularly difficult to achieve and there is still a great deal of investigation going on in this field both in Australia and overseas.
SUGAR CAME FOR ETHANOL PRODUCTION
After reviewing a wide range of possible plant sources of carbohydrate suitable for ethanol production it is evident that the sugar cane is high on the list. Poor sugar cane may not compare particularly well with very good alfalfa, cassava or sugar beets, however, Australia stands well to the top of the list in world sugar cane productivity with Hawaii ahead and Ethiopia also reporting very good yields. The latter are no doubt related more to climatic benefits than cultural expertise.
Furthermore, the sugar cane is recognised as being one of the most efficient users of sunshine in the plant kingdom. Not only does the sugar cane produce substantial quantities of sugar which it conveniently stores in the stalk, but the fibre in the stalk is additional
carbohydrate of a similar magnitude to the sucrose. The fibre could be a source of cellulose for fermentation, but it has significant value as a fuel and this will also be examined in detail in this analysis. Sugar beet, cassava and cereal grains provide nothing in the way of
associated fuel and the cost of this commodity required in the ethanol production must be added.
Sugar cane juice also contains the hexoses glucose and fructose (known collectively in the trade as "reducing sugars") which are useful sources of ethanol but not of crystal sugar. The relative amount of the hexoses varies according to the season and the quality of the cane.
Sugar cane which is poor in terms of sucrose for any reason may contain twice as much hexose as better quality cane. This serves as a beneficial balancing influence if the sugar cane is thought of in terms of a source of ethanol.
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Sugar beet juices do not have any significant residual
unsynthesized hexose sugars, all soluble carbohydrate being in the form of sucrose unless some deterioration has taken place.
Perhaps the next question to consider is the useful yield which might be expected from an Australian crop of sugar. The pricing system in the Australian sugar industry has been designed to give financial encouragement to those farmers whose cane is able to produce the highest proportion of crystal sugar. The farmer also recognises the economic advantages of heavy yields of the cane itself per unit area. These two desiderata are not necessarily compatible, in fact increases in tonnage of cane often results in lower yields per tonne.
The net result of these two influences is that in Australia over the long term the tonnage of cane per hectare has shown an average annual increase of 1.1% and tonnes of sugar per hectare a corresponding growth rate of 1.58% on a compound interest basis. Throughout the 75 years over which these figures have been taken, the question has continually been asked as to whether continued improvement could be expected.
There have always been fluctuations from year to year and it would be invidious to select any particular year as being representative, and if a ten year period were taken and averaged, the average for the next ten year period would be more predictable and could be expected to be higher by 11 1/2% for tonnage of cane and by 17% on tonnage of sugar.
Furthermore, there is substantial variation from district to district throughout the cane growing areas of Queensland. There is sugar cane grown in northern N.S.W. but as the sugar produced in those areas represents less than 4% of the total Australian production consideration of ethanol production prospects will be restricted to Queensland although some reference will be made at a later stage to possible areas for development in other parts of Australia.
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There are further difficulties with statistics. Sugar production is referred to in terms of 94 Net Titre (N.T.) in Australia. This is a quality criterion of local concern, designed to estimate the actual amount of refined sugar crystal which can be produced from raw sugar of a certain quality and involves corrections for the ash and hexose content of the raw sugar.
Furthermore sugar contents are referred to in terms of "pol"
which is an abbreviation for polarization and refers to the technique universally employed for analysis. It is well known that this does not reflect the true sucrose content but is a sufficiently close approximation for most purposes to allow full advantage to be taken of the rapidity of the method. We can get an indication of the order of precision of the pol value if we have an analysis of the final molasses from the same factory at the same time in terms of both pol and sucrose. If we take as an example a sample of 100 tons of crystal sugar having the following analysis which is typical of Australian conditions:
Pol = 98.37 per cent Reducing sugar = 0.37 Ash = 0.38 Moisture = 0.43
The N.T. value then equals Pol - R.S. - (5xAsh) = 96.10
Tonnes of 94 N.T. sugar = tonnes actual sugar x actual N.T. = 102.23.
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Experience indicates that the actual sucrose content would probably be closer to 98.52 than to the pol value of 90.37. Thus if the figure for tonnes of 94 N.T. sugar be reduced by 3.8% a better representation of the weight sucrose in crystal raw sugar would be obtained. Actually a discount of 4% is commonly applied which very closely represents the weight of pol.
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In actual fact there is no such substance as polr. The term is an abbreviation for the word "polarization which refers to the technique commonly employed for analysing sugar house products. It is obtained by observing the sugar solution with a beam of light which has been optically polarised. The sugar in the solution proportionately affects the degree of polarization and the instrument is appropriately calibrated.
Unfortunately sucrose is not the only substance in a cane sugar juice or raw sugar solution which affects the polarised light in this way.
The two main non-sucrose substances in sugar cane products which act in this way are the hexose sugars glucose and fructose. The fact that they have an influence opposing each other and which largely compensates has enabled the convenience of the method to be extensively applied in the sugar industry. Under conditions of poor technology, it does not matter very much but the better the standard of technology the more significant is the difference between the sucrose and pol values. To perform a true sucrose analysis is difficult, complex and tedious with the consequence that experimental analytical error can be of the same magnitude or even greater than the real difference.
However, it is considered to be valid to take into account the differences between pol and sucrose for the purpose of the current exercise and to apply the correction in accordance with the best experience.
Statistics recorded in Queensland literature for yields of sugar per hectare are in terms of 94 N.T. quality and require appropriate correction.
This however represents only the sugar recovered as crystal. From the point of view of ethanol production, we are more concerned with the total sugar content of the juices in the cane since both glucose and fructose can be fermented to ethanol. Unfortunately these are even more difficult
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to estimate because sugar cane in Australia is evaluated in terms of C.C.S. which letters stand for "Commercial Cane Sugar". The C C S . is calculated from a formula designed to estimate the actual amount of
"94 N.T." sugar which can be produced from a particular tonne of cane.
The C C S . is calculated as follows:
C.C.S. = Pol in Cane - 1/2 Impurities in Cane
Since Impurities in Cane = Brix in Cane - Pol in Cane then C.C.S. = 3/2 Pol in Cane - 1/2 Brix in Cane
Like Pol the term Brix does not refer to any substance in particular.
It also refers to the result of a convenient analytical technique and approximates the total solids dissolved in the juice or syrup. The measurement involves a determination of the density of the liquid usually using a type of hydrometer especially calibrated for sugar solutions.
In high purity juices and syrups the readings are usually sufficiently accurate for most purposes but in low purity juices and molasses there is a progressive deviation from the true figure as the proportion of non- sucrose increases. Brix may also be measured by means of a refractometer the values for which are intermediate between the true total dissolved solids and the hydrometric value. The measurement of Brix is not particularly critical at this stage as far as the ethanol proposal is concerned.
The C.C.S. formula was designed also to evaluate the Pol and Brix content of the cane itself from the analysis of the juice expressed by the first roller of the milling tandem. Whilst the technique has distinct advantages from the point of view of speed and simplicity it does have limitations from the point of view of precision. Present day techniques prefer to sample the cane rather than the juice and to perform a direct analysis on the sample of cane. The added complexities have very largely been minimised by the development of better technology for sampling, sample preparation and sample analysis.
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In the example which has been quoted the C.C.S. for the corresponding cane was 13.11 and the density of cane growth was 84.6 tonnes of cane per hectare. The pol in cane was recorded as 14.41%. If this be corrected to a sucrose value it would probably have been 14.83 or 2.9% higher than pol.
It is estimated from the analysis of juice resulting from the cane that the hexose concentration would have been about 3% of the pol or 0.43% on cane. For the purpose of estimating ethanol production it is convenient to convert this to "equivalent sucrose" or 0.41%. Some other workers in this field prefer to convert to "equivalent glucose".
Thus the fermentable sugars "as sucrose" in the cane would be 15.24%
and the production per hectare 12.9 tonnes.
If productivity and quality of cane continue to improve at the rate of 1.58% per annum then for the 11 year period 1980/90 a mean value of 15.2 tons per hectare would be indicated as compared with the mean of the 11 year period 1963/73. Predictions for specific years have a lower precision (St.D. ~ 7.5%) than predictions for a decade (St.D. - 2.5%) owing to variable seasonal influences. There is some levelling out of these influences by virtue of the north/south relationship of the Queensland sugar belt in that a bad season in one area seldom extends through all the other sugar growing areas and vice versa.
There is a substantial difference between the highest and the lowest yielding areas with the Burdekin as high as 18.7 tons of 94 N.T. per hectare in 1973 as compared with 8.84 for the Mackay and Proserpine areas in the same year.
Traditionally ethanol production in the cane sugar industry has been very largely restricted to the use of molasses as a raw material. There is no technical reason however, restricting production from the juice itself.
