As explained last month, a microwave oven will cook food with a minimum waste of energy. But it can, in principle, cook more than food. It can cook out the oil (and other fuels) from oil shale.
At present, oil shale is processed in a two-stage process. First, the shale is crushed and ground mechanically to release the kerogen contained in the rock; and the kerogen is then heated in an oxygenfree atmosphere (retorted) for conversion to synthetic crude oil. (All processes are, as yet, in the research stage. )
But there are other and more promising ways, such as using microwaves to heat the oil shale. Although the rock still has to be crushed in a preliminary stage, it need only be reduced to relatively large fragments, for the thermal stress due to the microwaves will fracture the pieces and release the kerogen, which is then heated by the same microwave field for conversion to crude oil single stage. Moreover, the electrical properties of oil shale are such that more energy is absorbed by the kerogen and less by the remaining rock, so that less energy is wasted in heating the rock. The conventional processes heat both equally.
There are yet other advantages. Oil shale also contains hydrocarbon gases and other carbonacious fuels which are released together with the kerogen. In the conventional process. the gas loses much of its heating value and is wasted. In the microwave process. both tapes ot tuel remain for use. Though the gas is not ot pipeline quality, it can be used to fuel the on-the-spot power plant energizing the microuaxe installation. as can the other fuels obtained in t he process.
All of these assertions hase been demonstrated in the laboratory The question is whether these principles can be utilized economically in a largescale facility. and this is about to be investigated by a team headed by Dr. Edward T. Wall of the Universits of Colorado in collaboration with industry. The team plans to design a vertical kiln for sequential heating of oil shale allowing eass control of both the shale flu and the microwave heat absorption. In the present process the heat of the waste rock is simply dumped into the environment when the oil has been retorted; in the sequential heating process proposed by Dr. Wall, 80% of that heat would be utilized for reheating the entering shale as it moves through the kiln in a continuous ffow.
Dr. Wall and colleagues have applied for a $500, 000 grant to NSF to build a test kiln with an input of about 30 kW of pulsed microwave power. Part of the proposed project would be devoted to study the economic feasibility of the system. At present, Dr. Wall and colleagues estimate that the entire process from mining the shale to crude oil refining, and including capital depreciation of a 50,000 b/d plant, could produce crude oil at a cost of $3.20 per barrel.