Cane has long been grown to produce sugar, a major world commodity. Sugarcane culture is dominant in many warm regions of the earth, including the Caribbean Islands. In recent years, the industry has come under increasing economic and ecological pressures, which could pose threats to traditional values in some places. A new process, AP (for Anthropogenic Peat), shows an alternative path, which may be of considerable interest to cane-growing entities.
AP was developed with the original objective of controlling the carbon dioxide (CO2) content of the atmosphere without ruinous emission restrictions. This is accomplished by growing bio mass (sugarcane preferred) to remove the gas from the air; the whole biomass is then converted by anaerobic digestion to methane (CH4) and carbon forms which can be segregated to achieve CO2 level control. Economic studies showed it was appreciably more profitable in the mid-1990's to convert cane to CH4 than to sugar; if this is done, many other world problems identified by the World Bank and the Union of Concerned Scientists are also helped along. The segregated carbon forms are expected to have a real market value. Here, a decade later, we update these conclusions.
First, the older comparison:1 Average cane yield was taken as 40 dry tons per acre-year without tops and leaves; for AP, which uses whole cane (no burning), 50 DT/AY is assumed. Sugar yield was 218#/ton of cane (USDA) with a futures price of $0.1033/#. Corresponding numbers for CH4 at 60% conversion (up to 80% is possible) were 618 mcf/AY, with $2.20/mcf futures:
| 1995: | Sugar | 8720#/AY |
$0.1033/# |
$901/AY gross |
| Methane | 618 mcf/AY |
$2.20/mcf |
$1360/AY gross |
|
Yields were solid; prices might have varied in special circumstances, but this was how the world valued these commodities on the same basis. These are gross values, of which the basic producer would realize only part. Ten years later, sugar yields and prices are changed but little, while the value of the methane option has increased substantially:
| 2005: | Sugar | 8720#/AY |
$0.112/# |
$977/AY gross |
| Methane | 618 mcf/AY |
$8-12/mcf |
$6180/AY gross |
Here an average value for methane of $10/mcf was taken, making it more valuable than sugar by a substantial amount.
Another sort of economic comparison can be extracted from the literature. Clausen and others2,3 had earlier examined the production of CH4 from "energy crops" by anaerobic digestion. Working on a different premise, they did not select sugarcane as a feedstock, but they provided a plant design and economic analysis that could be brought forward in time. Their analysis showed that digesting and sweetening the methane (taking out the CO2 which is formed with it) cost $110/acre in 1976; this grew to $203/acre in 1997. These are the costs of producing digester gas and removing CO2 from the CH4. In 2005, these operations would be expected to cost $238/acre, a rather insignificant fraction of the value of the methane produced.
It is fair to ask at this point what investment is necessary to achieve such attractive returns. One finds that investment is modest; anaerobic digesters are principally large tanks with associated pumping and piping. Clausen looked at the investment needed to produce 50 million cf/day of CH4 from his "energy crops": $50-75 million in 1976, 5-10% ROI. With sugarcane as a feedstock, investment would have fallen to $15-20 million, 40-50% ROI. If these cases are brought up to 1997, Clausen's feedstock would fail to pay off, while sugarcane would still give 40-50% ROI on investment of $30-40 million. Bringing these numbers up to 2005, ROI would increase to more then 200%, or less than one year for payoff. These figures obviously require checking for any particular case, but the overall conclusion remains that methane from sugarcane should be very attractive business.
The concept of segregatable carbon forms becoming articles of commerce is developing, mainly as opportunities arise. Two concentrated carbon sinks, pure CO2 (27.3% C) and stabilized digester residue (about 45% C) are produced when sugarcane is digested anaerobically, and there is room for much creativity in the useful disposal of both. Caribbean nations in particular may expect to play a major role here as the Kyoto Protocol develops.
World problems referred to above have been noted4 and the positive effects of AP on many of them have been shown. The basic source for this information is The World Bank5, and the importance of this topic for the present purpose lies in the fact that most of the problems are endemic to warm countries, where sugarcane is often grown as a staple. Conversion of at least some production to methane could be pivotal in turning these conditions around where they exist. Adding the economic benefits, the case for AP in warm countries becomes compelling.
1 Hartung, H.A., "Atmospheric CO2 as a Hazardous Waste: Economics of its Conversion to Methane", I&EC Special Symposium, Pittsburgh, PA, 9/15-17/97, American Chemical Society.
2 Clausen, E. C. et al., "Biological Production of Methane from Energy Crops", Biotechnology and Bioengineering, vol. 21, 1979, p. 1209-1219.
3 Price, E.C. and P.N. Cherimisinoff, "Biogas Production and Utilization", Ann Arbor Science, 1981, pages 74-75.
4 Hartung, H.A., "Industrial Development, Greenhouse Warming and Anthropogenic Peat", Proceedings IECEC 1993, Atlanta, GA, 8/8-13/93 , vol 2, American Chemical Society.
5 The World Bank, "World Development Report 1992: Development and the Environment", Oxford University Press, New York, NY, 1992.
