Energy in Agriculture最新文献

The energy required to operate linear-move irrigation machines fed by flexible hoses is analyzed in this paper. The total energy requirement was divided into five components: three related to distributing the water, and two related to moving the machine and dragging the hose. The energy components are represented by mathematical equations and a numerical example is presented using available data for a typical short (72 m) and long (360 m) lateral move irrigation machine. The major findings are: (a) 60–70% of the energy is required to distribute the water; (b) the energy required to move the machine and to drag the flexible hose is less than 3%; and (c) the short machine consumes 30% less energy than the long machine, mainly due to the low-pressure control system for water distribution on the soil surface.

The model detailed in the first part of this paper is used to analyse the influence of varying certain parameters on the performance and the behaviour of two heat-storage greenhouse systems. Influence of soil thermohydraulic properties and pipe geometry is discussed for both systems. Short- and long-term simulation runs are performed and show that different space scales are involved in the energy exchange phenomenon.

Among many farm crops, bright leaf tobacco is the most energy- and labor-intensive crop. The greenhouse solar system (solar bulk-curing/greenhouse system, or solar barn) was developed to provide multiple-use facilities for year-round solar energy utilization to save fossil fuels in tobacco curing and plant production and to facilitate the total mechanization of tobacco culture. Two types of full-size greenhouse solar systems, the load-supporting wall design and the shell design, both utilizing the thermal envelope concept, were designed and constructed for solar bulk-curing of tobacco, growing transplants and horticultural crops under controlled environment, and aiding automation of transplanting operations.

Full-scale field tests of solar bulk curing showed that the fuel savingswere consistantly improved from 37% in 1975 to 51% in 1978 for this solar bulk-curing system as compared with a conventional bulk-curing barn as a control. The feasibility of the system to save energy by using solar energy as a first priority source was significantly demonsrated. Three-year greenhouse and field tests showed that high germination rate of 95–97% with excellent emergence frequency was obtained for tobacco seeds under the controlled environment provided by the greenhouse solar system. In general, the containerized transplants from greenhouse solar system significantly exceeded the conventional bare-root transplant in growth, leaf-quality and yield.

A linear programming model is used to assess the impacts of large-scale ethanol production from corn and grain sorghum on U.S. agriculture. Annual ethanol production of 22.7 and 45.4sx10⁹ L, corresponding to approximately 6 and 12%, respectively, of U.S. gasoline consumption is examined. Current conversion technology allows 387 L of ethanol to be obtained from a metric tonne of corn or grain sorghum, and more advanced conversion technology would allow up to 447 L. U.S. agriculture has the capacity to produce both food and large quantities of ethanol. If large-scale ethanol production occurs, the major change in production is the substitution of corn for soybeans in the north central states. With current ethanol production technology, per unit production cost increases for individual crops range from 3 to 12% and from 6 to 30% for annual ethanol production of 22.7 and 45.4×10⁹ L, respectively. Advanced ethanol production technology allows crop production costs to be reduced significantly, about 100o million dollars if 45.4×10⁹ L of ethanol are produced.

Energy-efficient dewatering of fermentation ethyl alcohol is essential whether the alcohol is for fuel or chemical use. Adsorption of water on dried grain such as corn is one method that can meet this objective. Adsorption of water from liquid solutions containing 88–95 wt% ethyl alcohol onto fixed beds of unrefined corn is described here. Water adsorption capacity was 40–50% of the theoretical value for perfectly selective adsorption of water, but still adequate so that the water-saturated grain used in adsorption could also be feedstock to the fermentation, Cincurrent with the dewatering of the ethyl-alcohol by the corn grain, curde corn oil was extracted by the ethyl alcohol. When the capacity of the grain for producing anhydrous alcohol was reached, up to 80% of the oil had been extracted. Benefits include improved energy efficiency for the complete conversion of grain to anhydrous ethyl-alcohols as compared to existing methods, a 7% gain in the fuel value of products relative to conversions where no oil is recovered, and a potential for increased product diversity in small-scale operations where only ethyl alcohol is usually produced.

A simple methodology was developed to evaluate the real energy contribution of biomass to replacing conventional sources of energy and their specific technologies.

To this effect, energy content, replacement energy value, energy cost and energy return of biomass (kJ per kg dry matter) were considered. Thus some figures valid under Italian conditions were calculated by this methodology and are reported here.

6.4 × 10⁶ t (dry matter) of wood and cellulosic residues are available yearly in Italy and could replace 73 PJ/year (1.8 × 10⁶ toe/year) if they were used exclusively for heat generation by direct combustion, or 47 PJ/year (1.15 × 10⁶ toe/year) if used in gasification processes to generate electricity and replace the energy currently supplied by the national grid.