Technology
Fuel processes must consider energy costs Energy crunch may force fuel production systems designers to base crucial decisions on energy rather than monetary balance All of the proposed methods of supplementing our dwindling auto fuel reserves are agreed generally to be more costly than the present production systems. N o t generally recognized, however, is the fact that the increase in cost may be due to an increase in energy value as well as an increase in monetary value of the energy produced. The idea is that, in addition to costing money, it also costs energy to produce energy. In the age of new energy production systems the crucial decisions may wind up being based on the ener-
gy balance of a proposed process more than on the monetary balance. One of the principal advocates of giving due consideration to the energy costs of any new system is Dr. Donald L. Klass, assistant director of the Institute of Gas Technology. For some time Klass has been pointing out that very few studies have been made concerning the energy budgets in any of the proposed energy systems. Part of the reason may be that it is exceedingly difficult because of the often obscure energy inputs of any given system. Klass mentions that one of the in-depth studies that has been made concerns the production of corn in the U.S., and includes all of the nonsolar inputs such as electric power, equipment fuels, and the energy needed to produce fertilizer ammonia from natural gas. Some of the information in this study has been converted to thermal efficiency (energy in/energy out), and the nonsolar energy input required to
produce a pound of corn has been computed. The result reveals that less energy was expended to produce a pound of corn in 1940 than is expended today, meaning that the U . S . is using energy less efficiently in corn production in 1975. Professionally concerned with the production of synthetic natural gas (SNG), Klass notes that this type of analysis is related directly to SNG because one of the important factors that has been ignored in the development of new energy systems concerns the energetics of those systems. Valid comparisons of different systems cannot result solely from synthetic fuel cost estimates, capital required, and operating cost projections. These factors, says Klass, do not necessarily correlate with net energy production. Nor can valid comparisons be made simply by calculating the thermal efficiency or the energy in and out of a process. All of the energy inputs involved in planting,
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C&EN June 2, 1975
Processing of giant kelp may be promising way to make LN< Biomass
Rice (U.S.) Corn (U.S.) Giant kelp, floating Land based Land based Land or water based
Conversion process
Fuel efficiency yield
End product
End product cost ($ per million Btu)
Net energy production ratio
None None Digestion None Air dry, pyrolysis Digestion
— — 70% — 69% 35%
Rice Corn LNG Biomass SNG SNG
$26.70 9.70 2.48 0.65 2.09 0.73tol.77
-0.67 to-0.80 1.82 5.07 17.40 2.34 3.79
Source: Institute of Gas Technology
harvesting, transportation, fuel production, and recycling of product streams also must be considered. Two of the measures of effective fuel production Klass uses to evaluate proposed systems are fuel efficiency yield and net energy production ratio. Fuel efficiency yield is defined as 100 times the ratio of the net energy content of the salable product to the energy content of the dried biomass or fossil fuel source material. Net energy production ratio is the difference between the energy content of the salable product and the sum of all the external nonsolar inputs, all divided by the external inputs. The latter ratio, if greater than zero, indicates that more energy is produced than is consumed in running the
process, with the added assumption that the net energy content of the converted biomass is zero. This is reasonable, Klass maintains, because the energy value of the biomass is derived essentially from solar radiation. Klass has computed the data for several proposed schemes for converting biomass to fuels and other products. Comparing the energy costs with the monetary costs presents some interesting dilemmas for the engineer who must decide which system to pursue. Since the various measures of effectiveness do not always exhibit the same trends, some new rules for optimizing effectiveness in the new processes may be required from the planners. This is the point that Klass continually
drives home. Namely, although economics does dominate the thinking of the systems designers, due attention also must be given the energetics of any proposed system. Klass has developed his ideas in the context of the conversion of biomass to useful fuels, particularly to SNG. The obvious advantage of such a scheme is that, by using biomass, the U.S. can have a perpetually renewable source of fuel. Biomass includes organic wastes as well as harvested land-based and marine plants, and the technology for conversion already is available. But just how soon the technology will be considered seriously remains to be seen. •
Pollutant recovery, water re-use mulled With the Federal Water Pollution Control Act of 1972 aiming at eventual zero discharge of pollutants into the watershed, alternatives to zero discharge may seem academic. But this was not the case in Chicago last month at the Second National Conference on Complete Water Reuse, when methods to reduce— but not eliminate—pollutants and to make better use of even polluted waters were debated. The conference, sponsored jointly by
economically. Anywhere in your plant. Lab. Analysis Reporting Process Control Points
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June 2, 1975 C&EN
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