Ethanol is blended with gasoline for use as a fuel in vehicles with internal combustion engines. A blend containing 10% ethanol as an additive produces a cleaner burning gasoline. A blend containing 85% ethanol is used as a substitute for gasoline.
Ethanol can be manufactured from a number of domestically grown vegetative materials including corn, sugar cane and sugar beets. The manufacture of ethanol from domestically grown crops reduces the reliance on imported petroleum as a source for fuel for internal combustion engines. Corn is the largest domestically grown crop from which ethanol is manufactured.
Corn in a farm field is conventionally harvested by a combine, a self-propelled piece of equipment which picks the ears of corn from the corn stalks, separates the corn kernels from the corn cobs (shelling) and from the husks on the ears of corn, and returns the cobs and husks to the farm field. The shelled corn is temporarily stored in the combine and then transferred to a vehicle that transports the shelled corn to a storage facility. The cobs and husks that have been returned to the farm field, together with the stalks and leaves left on the field, are collectively known as stover, a material which beneficially helps to build soil and prevent erosion when left in the field.
Combines came into widespread use for harvesting corn in the latter half of the twentieth century. Prior to that, corn was hand picked, or it was picked by a mechanical corn picker that was mounted on or towed by a tractor and that was capable of picking, e.g., one to two rows in a single pass. After the ear corn was picked, it typically was stored on the farm and then shelled by shelling equipment typically mounted on a truck which traveled to the farm and shelled the ear corn on site. The combine replaced both the mechanical picker and the traveling sheller.
Ethanol is made from shelled corn. A multi-stage process is employed to produce ethanol from shelled corn, and some of these stages require heat supplied by the combustion of fuel, typically natural gas. Natural gas is also consumed (a) during the production of nitrogen fertilizer applied to the farm field where the corn is grown and (b) to a lesser extent, during the production of pesticides used on the corn.
Petroleum-based fuels power the vehicles used in the growing and harvesting of corn and in the transporting of corn between the farm fields and the ethanol manufacturing facility.
A drawback to conventional processes for producing ethanol from corn resides in the consumption of large quantities of energy during the ethanol manufacturing process and during the growing, harvesting and transporting of the corn. As noted above, this energy is consumed in large part by the combustion of natural gas and of petroleum-based vehicle fuel. When ethanol from corn is produced at a processing plant dedicated exclusively to the production of ethanol, the ratio of (a) the energy available from the ethanol to (b) the energy equivalent of the total fossil fuel input is 1.77. (Total fossil fuel input comprises both natural gas and petroleum-based vehicle fuel.)
The amount of energy consumed during (i) the conversion of corn to ethanol, at the ethanol manufacturing facility, is about twice the energy consumed in (ii) corn production, which includes the manufacture of fertilizer and pesticides with natural gas, as well as the operation of the farming equipment with petroleum-based fuel. Items (i) and (ii) above together constitute at least 90% of the total energy consumed. The remainder (less than 10%) is consumed in transporting the shelled corn to the ethanol manufacturing facility and in the post-production distribution of the ethanol by truck, rail and the like.
Attempts have been made to conserve the natural gas consumed during the ethanol manufacturing process by replacing the natural gas with a renewable fuel. In one such instance, the fuel was cattle manure from a massive cattle feeding lot next to which the ethanol manufacturing facility was located to eliminate the cost of transporting the manure which could otherwise be a prohibitive expense. There are, however, only a limited number of locations where this type of operation can be employed.
A residual product of the ethanol manufacturing process is a mash known as “stillage” which is dried and sold as animal feed. The dried stillage is also called “dried distiller's grain and solubles” or DDGS.
There have been proposals to use DDGS, or stover, or a combination of the two, as fuel to produce process heat for the ethanol manufacturing process. In some proposals, the material is used to fuel a cogeneration plant that produces (a) electricity to power equipment employed at the ethanol manufacturing facility and (b) steam for use as the heating medium in stages of the ethanol manufacturing process that require heat. A cogeneration plant is a substantial capital expense.
With respect to the use of stover as a fuel, there are some drawbacks. The stover has to be gathered from the field and baled for more efficient handling and transportation and then transported to the ethanol manufacturing facility, all of which entails expense and consumes fuel. Moreover, when stover is removed from the field, this deprives the field of the benefits arising when stover is left in the field (soil building and erosion prevention).
As noted above, corn intended for subsequent processing into ethanol is conventionally harvested with a combine that both picks and shells the corn. Seed corn and sweet corn are harvested by another type of self-propelled equipment known as an ear corn harvester which picks the corn but does not shell it. In the case of seed corn, the ear corn, after harvesting, is stored and dried and then shelled by a piece of equipment separate and discrete from the earn corn harvester. This protects the corn kernels that are to be used as seed, from damage that can occur when shelling is performed by a combine. Damaged corn kernels are unsuitable for use as seed.
In rural corn-growing areas, during the first half of the twentieth century and earlier, corn cobs were used as kindling for coal-burning, home heating furnaces and hot water heaters. In some rural areas, during the depression in the 1930's and during the war years in the 1940's, ear corn was used as a substitute for coal in home heating furnaces.
Stanfield U.S. Pat. No. 4,139,952 discloses a procedure in which ears of seed corn are dried by heat generated at an incinerator and then shelled to produce (a) kernels of seed corn and (b) corn cobs that are employed as fuel for the incinerator.
It is possible to produce ethanol from cellulose contained in stover. However, it is currently much more difficult to produce ethanol from stover than from shelled corn, and substantially more expensive. At the present time production of ethanol from stover is not economically attractive.