Previously published in Search, Vol. 10 No. 11, November 1979 G.A. Stewart, CSIRO Division of Chemical Technology, Canberra G. Gartside, CSIRO Division of Chemical Technology, South Melbourne
R.M. Gifford, CSIRO Division of Plant Industry, Canberra H.A. Nix, CSIRO Division of Land Use Research, Canberra W.H.M. Rawlins, CSIRO Division of Chemical Technology, Canberra J.R. Siemon, CSIRO Division of Mechanical Engineering, Clayton, Vic Fuels from crops and forests are one of the alternative options for future energy supplies. A survey of the national potential to produce ethanol and methanol from arable crops, forestry and their residues shows that more than half of present liquid fuels used in transport could be met from such sources without reducing national food and fibre production from crops. The estimated retail prices of such fuels, assuming taxes and distribution costs as for motor spirit, are more than twice the retail price of motor spirit. The cost of methanol from coal is so much lower than the cost of alcohols from biomass that there are no economic reasons for initiating production of alcohols from biomass at present, but there are several reasons why research and development on alcohols from biomass should be continued.
Oil is a non-renewable resource and limitations to its supply are likely to arise in the next ten to fifteen years (Wilson, 1977). The large increase in oil prices by O P E C countries in 1973-74 and the Iranian situation of early 1979 have emphasised both the ulimate limit of the crude petroleum resource and the uncertainty of continued supply. In 1975-76 oil made up 47 per cent of Australian primary energy use (Aust.
Dept. Nat. Dev., 1978). About 70 per cent of the oil need in that year was provided by local petroleum (Aust. Inst. Petroleum, 1977) but the proportion from local pro- duction is expected to fall markedly over the next ten years (Schirrman, 1976).
Because large reserves of coal and uranium are available in Australia for non- transport energy, it will be the supply of liquid fuels for transport, currently totally produced from oil, which will be the major energy problem in Australia.
Some countries that currently import most of their liquid fuels have already moved towards alternative fuels. Brazil has successfully initiated the production of ethanol from sugarcane and other crops for blending with motor spirit, and plans to use straight ethanol fuel in the future. South Africa has the only commercial oil- from-coal plant in the world, and is currently building a larger one. New Zealand is planning production of methanol from natural gas to blend with motor spirit and has active research programs in other alternative liquid fuels. While Australia's current oil situation is more favourable than in the above countries, the decreasing future local production of oil makes it desirable to examine alternative fuel sources.
A number of Australian workers (Gifford and Millington, 1975; McCann and Saddler, 1976; Hanks, 1976) have previously considered liquid fuel production from a single or small number of biomass sources, and concluded that the potential pro- duction was small in relation to the demand. On the other hand, Morse and Siemon (1976) concluded that 13 million hectares of forest plantations would provide a gross output of ethanol equivalent to 90 per cent of 1977-78 fuel use in transport in Aus- tralia; but the cost of the ethanol was high, the energy recovery in liquid fuel was
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very low, and the assessment of the area of land potentially suitable for the planta- tions was inadequate. We have carried out a preliminary assessment of the potential liquid fuel production over the next twenty to forty years from a wider range of crop residues, energy crops and conversion processes. The assessment, which is reported in full elsewhere (Stewart et al., 1979) and in resume in this paper, is aimed at pro- viding a basis for the identification of significant sources of liquid fuels from biomass, and of major research needs.
The assessment is restricted to reported commercial technologies or, where the re- quired technologies are not currently available, new technologies that are simple extensions of existing ones. The only liquid fuels that can be produced from crops with existing technologies are ethanol and methanol. These alcohol fuels have high octane ratings; they can replace lead additives when used as blends of up to 20 per cent with motor spirit in existing engines, or they can be used as straight fuels con- taining over 80 per cent alcohols in high-compression engines at high thermal efficiency. The conversion processes are: (a) fermentation of sugars and starches to ethanol; and (b) gasification of lignocellulose (e.g., wood, straw) with oxygen to carbon monoxide and hydrogen, followed by catalytic synthesis to methanol.
The following aspects of the assessments are summarised below: amount of exist- ing crop and forest residues; area and potential production of energy crop on 'new' land; the potential production of ethanol and methanol; the dollar costs of the ethanol and methanol; employment and decentralisation aspects; and the environ- mental impacts. Energy inputs and the relatively detailed appraisal of net liquid fuel output are explained in an Appendix.
Costs and prices are standardised in 1975-76 dollars. For cereal grains and sugarcane the home market prices were used. Other dollar and energy costs are mainly from published reports. The accuracies of estimates of potential amounts of raw materials and liquid fuels and their dollar and energy costs are probably ± 25 per cent. Numbers have not been grossly rounded to reflect that accuracy, and the final numbers of estimated amounts and cost of liquid fuels should be interpreted only very broadly.
Crop and forest residues
The major existing residues are all lignocellulosic materials — cereal field residues, sugarcane field residues and sugarmill residues, and forest and sawmill residues. The residues are now partly disposed of by burning, and the portion that is currently burned could probably be diverted to liquid fuel production without increasing the risk of deterioration of the soil.
Some cereal field residues — straw, leaf and chaff — are burnt in the field.
Limited studies indicate that the grain yield is approximately 36 per cent of the total dry matter yield above ground, and we have assumed that 40 per cent of the total dry matter could be recovered for fuel and that the remaining 24 per cent would be left for soil conservation and protection. Grain statistics were then used to arrive at an approximate recoverable residue production of 15.8 million tonnes DW (dry weight) in 1975-76 (Table 2).
Virtually all sugarcane field residues are burnt in the field. Unpublished data from the Queensland Bureau of Sugar Experiment Stations showed a linear relationship between field residue dry matter yield and fresh cane yield for specific cultivars.
These relationships were used together with data on cane production of various cultivars to arrive at an approximate estimate of total field residue production (Stewart and Kingston, 1979) of 2.67 million tonnes DW in 1975-76 (Table 2).
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Bagasse is the sugarcane fibre left after crushing out sugar juices. It is mainly used in sugarmill boilers to generate their power and steam requirements, but some sugar mills now have some surplus bagasse. The long-term maximum amount of surplus bagasse was estimated from data (Jenkins, 1966) on steam requirements for a cane sugarmill with heater-evaporator arrangements similar to those of beet sugarmills. If this had occurred in 1975-76, 1.63 million tonnes DW could have been available for liquid fuel production.
Forestry logging and sawmill residues were estimated at 7 and 2 million tonnes DW respectively. It was assumed that half the residues might be available for liquid fuel production.
Potential area and production of energy crops
Crops that appear promising and for which sufficient data could be found to make quantitative estimates of amounts and costs of product fuels include cereal grains (wheat, barley, and grain sorghum), sugarcane, plantation forests, and cassava.
Other crops that appear promising, but for which data were not sufficient for quantitative estimates, include sugar beet and fodder beet, sweet sorghum, some tree- crops, and hydrocarbon-rich plants such as Euphorbia and some algae.
In assessing the potential areas of energy crops in Australia, it was assumed that they will be restricted to 'new' land not currently developed for cropping, and that fuel forest plantations would be on marginal grazing land in the high rainfall zones.
We recognise that energy crops could be substituted into some existing crop and pasture systems, but we could not find sufficient data to estimate on a national basis the degree to which that was possible and the amounts of other crop products that would be forgone.
Estimates of the areas of arable crop land potentially available for energy crops were based on the methodology developed by Nix (1973, 1976, 1978), but in this study the estimated areas of land suitable for the selected energy crops were combined with estimates of cropping intensity and yield to arrive at potential production of the energy crops. Detailed data on soils and terrain are available for only small parts of Australia, and regional reconnaissance data were used as the main basis of area estimates, which are first approximations only. Climate, terrain and soil characteristics are the primary determinants of potential productivity and of existing and potential land use patterns. The climatic constraint was derived using a generalised crop water-balance model and weekly mean climatic data from more than 700 stations throughout Australia. Using degree-day summations for early maturing cultivars of temperate cereal grains (a threshold temperature of 3 °C) and tropical cereal grains (threshold temperature of 9 °C) to simulate the duration of the crop cycle, a threshold moisture index (Ea/E,) exceeding 0.4 for the entire crop cycle was taken as an arbitrary limit to dryland crop production. This boundary agrees closely with the present boundary of grain cropping in the south and east and corres- ponds with grain yields of 0.7-0.8 tonnes per hectare. The climatic constraint removed some 70 per cent of the continent (531 million hectares) which is too dry for rainfed cropping, leaving a total area available of 237 million hectares.
The terrain constraint was evaluated by deriving proportionality indices from de- tailed surveys of smaller regions and then applying these to the major terrain classes mapped at continental scale by Loffler and Ruxton (1969). Application of the terrain constraint reduced the possible 237 million hectares to 132 million hectares.
The Atlas of Australian Soils (Northcote, 1960-68) provided the framework for area estimates of suitable soils, again using proportionality indices derived from 163
more detailed surveys. In this case, however, only those soils judged intractable with current technology were excluded. This tends to disadvantage northern Australia, where technological solutions are not yet available for very large areas of seasonally- waterlogged and physically intractable texture-contrast soils. Application of the soil constraint further reduced the area with favourable climate and terrain from 132 million hectares to 77 million hectares. Of this 77 million hectares, some 51 million hectares are already developed, leaving 26 million hectares available for develop- ment of new energy crops (see Table 1).
Most of the land suitable for development is in the cereal zone of the eastern agro- ecological region of northern New South Wales and Queensland, which has both summer and winter rainfall, and produces both winter cereals (wheat, barley) and summer cereals (grain sorghum). The estimated area of land suitable for develop- ment is 17.0 million hectares. Present cropping factors range between 0.75 and 0.99 on a local government statistical basis, and are 1.5 to 2.0 in smaller areas near the humid fringe of the cereal belt where double cropping is possible. On new lands, concern for long-term stability dictated a more conservative cropping factor of 0.75, with the cropping factor for winter crops assumed to be 0.5 and for summer crops 0.25. Assuming, as in existing developed crop land, that 85 per cent of crops are grains suitable for ethanol manufacture, and that estimated yields of winter cereals are 1.0 tonnes per hectare and grain sorghum 1.5 tonnes per hectare, the total potential annual production of winter cereals is 7.2 million tonnes and of grain sorghum 5.4 million tonnes. Bare fallowing during the high-intensity summer rain- fall period creates a serious risk of erosion, but current performance indicates that proper management techniques, including residue management and, where appro- priate, engineering structures, can maintain stable land use systems.
Table 1. Arable land use in 1975-6 and potential areas for energy crops on new land in Australia (million hectares)
Energy crops 1. Cereal grain crops
(wheat, barley, sorghum) 2. Sugarcane
3. Cassava Associated land use
1. Other crops 2. Pastures, fallow Undeveloped arable land TOTALS
Developed lands
11.4 0.3
2.9 36.4
-
51.0
Potential areas of energy crops on new land
11.6 0.289 0.225 2.1 4.4 7.4 26.014 The southern agro-ecological regions with winter rainfall, extending from south- western Australia to southern New South Wales, are already largely developed. The estimated area of remaining land suitable for development of winter cereals is 3.85 million hectares. The cropping factor in this zone varies from 0.2 to 0.4 and averages about 0.25. Thus an arable crop is grown only one year in four, and pastures and fallow occupy the remaining three years. Assuming that 85 per cent of the crops are 164
grains suitable for ethanol, and that average grain yields are 0.85 tonnes per hectare, the annual potential production is 0.7 million tonnes of grain.
In the higher rainfall zone of Queensland there are 100 000 to 200 000 hectares of land potentially suitable for rainfed sugarcane or cassava. In the absence of criteria of land suitability for the two crops, it is assumed that half is suited to each of the crops. The remaining new lands for sugarcane are potential irrigation areas on the Burdekin and Fitzroy Rivers in Queensland, and the Ord and Fitzroy Rivers in Western Australia. The estimated yield of sugarcane of 11.2 tonnes commercial sugar per hectare for the Ord Irrigation Area (CSR, 1976) has also been used for the Fitzroy River Area, Western Australia. The estimated yield of 15.0 tonnes com- mercial sugar per hectare for the Burdekin Valley (Burdekin Project Committee, 1976) has also been used for the Fitzroy River Area, Queensland. The yield of rain- fed sugarcane on new land, which is mostly in the Northern Region of Queensland, was taken to be the same as the 1975-76 commercial yield in the Northern Region, i.e. 10.0 tonnes commercial sugar per hectare. The total potential annual production of sugar on new land is 3.56 million tonnes commercial sugar from 289 000 hectares of land harvested each year.
The other areas of land potentially usable for cassava are on Cape York Peninsula and in the northern part of the Northern Territory. From limited experimental data an average annual farm yield of 29 tonnes of fresh weight tuber per hectare is assumed. The potential annual harvest area of 225 000 hectares could thus yield 5.22 million tonnes of fresh tubers. As a row crop in a seasonally humid/arid environ- ment, cassava poses quite a serious risk of soil erosion and land degradation and very careful attention to landscape engineering and soil management will be neces- sary.
Table 2. Potential net annual production (after allowing for all liquid fuels used directly or indirectly in the production) of methanol and ethanol, expressed in petajoules (PJ = 1015J = 21 000 t motor spirit) from existing residues and from energy crops.
* Potential net liquid fuel production = million tonnes liquid fuel x calorific value (GJ per tonne) x net/gross liquid fuel ratio.
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Very limited data on availability of marginal grazing land in high rainfall zones indicate that a total area of fuel-wood plantations equal to the recently proposed 1.1 million hectares of forestry plantations (FORWOOD, 1975) designed to be in full production by the year 2010 is feasible. A much larger area of land is potentially suited to fuelwood production, but further alienation and destruction of native forests was considered to be unacceptable.
Potential amount of liquid fuels from agriculture and forestry
Table 2 shows the potential amounts of raw materials, the estimated amount of raw material per tonne of gross liquid fuel, and the potential net liquid fuel production in petajoules (10I5J). The methods of estimating energy inputs, the net liquid fuel output and the net/gross liquid fuel ratio are explained in the Appendix. The potential net liquid fuel production, explained in the footnote to Table 2, is thus the net after allowing for all liquid fuel used in the production of raw materials and their conversion to liquid fuels.
The potential net production from the thirteen components is 419 PJ per annum, which is over half of the estimated use of liquid fuels for transport (700 PJ) in Australia in 1977-78 (Aust. Dept. Nat. Dev., 1978). Thus these sources could make a significant contribution to Australian needs for transport fuels.
The potential production from existing residues, virtually all as methanol, is more than one third of the total (154 PJ), while energy crops could provide less than two thirds (265 PJ), half as methanol and half as ethanol. The largest single source is methanol from existing cereal field residues, which is about one quarter of the total (105 PJ). The potential production from cereal field residues on new land is marked- ly lower because 5.5 million tonnes DW of field residues are allocated as fuel for manufacturing ethanol from grains. The potential liquid fuel production from cereal grain residues plus energy crops is more than half of the total (230 PJ), and the potential production from sugarcane, forestry and cassava are approximately one quarter (100 PJ), one sixth (75 PJ) and one thirtieth (14 PJ) of the total respec- tively.
Estimated costs of ethanol and methanol
Table 3 shows the estimated costs (1975-1976 dollars, 20 per cent per annum return on capital) for methanol and ethanol. Methanol from residues and plantation wood ranges around 20 cents per litre, compared with about 7 cents per litre for methanol from coal. Ethanol from sugarcane and cassava is about 30 cents per litre. Ethanol from grains is about 35 cents per litre, but no credit or debit has been made for the grain and yeast residues (containing 30 per cent protein), amounting to one tonne DW per tonne of ethanol output. If a profitable outlet for a part of these residues could be found, it would make the grains more attractive as sources of ethanol.
The amount of methanol and ethanol equivalent to one litre of motor spirit has been calculated from reported thermal efficiencies of optimised engines for both blended and straight fuels (see footnotes to Table 3). For straight alcohol fuels from biomass the cost of the equivalent of one litre of motor spirit is 3 to 4 times that of motor spirit ex refinery (with little difference between ethanol and methanol). If the excise, distribution and retail costs of motor spirit of about 10 cents per litre were applied, the estimated retail cost of the equivalent of one litre of motor spirit in 1975-76 would be 37 cents to 54 cents, more than twice the comparable retail price of motor spirit.
The cost of the alcohols as blend components is slightly lower than as straight 166