Oil shale (part II)September 5, 2008
In the previous post on oil shale, something about the geology and nature of oil share in Jordan was given. In this post, more on the options of how to utilize this material will be presented. Essentially, these options are either direct combustion for electrical generation or retorting to extract the oil from the rock.
From a technical point of view, the simplest approach is to burn the shale to produce heat, and then electricity. A number of experiments have been made on this, and have been discussed in the Bseiso report I referred to in the first post. All of the tests indicated economic feasibility of direct burning. Essentially, the idea is to crush the oil shale to sand-sized fragments and to ignite the kerogen in the rock. One concern about this is the high level of sulfur in the oil shale, potentially causing air pollution problems. Fortunately, the limestone in which the kerogen is present decomposes in heat to lime, which can react with the sulfur dioxide produced by burning the shale to produce calcium sulfate. The sulfur issue needs to be considered during any designing of a shale burning plant.
Another issue is what to do with all of the residue (fly ash) that will result from burning oil shale. Depending on the scale of use, large volumes of lime-rich ash have the potential of polluting aquifers (by reaching extremely high pH values, possibly leaching heavy metals into the ground water) as well as being sources of dust that may impact air quality and ecosystem stability in the areas where it is kept.
Some studies have suggested that the fly ash would be suitable raw material for cement production. Preliminary tests have suggested that cement produced with this material does not shrink in a predictable pattern, which may be a problem. However, other properties such as strength and thermal conductivity show more promising results. Further experimentation may lead to a better product.
Other potential uses that have been investigated include the use of the ash is soil stabilization, the production of zeolites for water treatment (we have natural zeolites that can be used in a similar way) and improving asphalt mixtures (which is something to be welcomed).
In conclusion, the use of oil shale for direct combustion is economically feasible, although it may no be the optimal way to use the resource. Comparative studies of oil extraction versus direct combustion show that the former is a more lucrative option (see the table on page 37 here. The numbers are outdated but the variations are still similar). Environmental problems of direct burning include the large amount of waste produced (fly ash) and the potential problem of sulfur, which can be managed provided there is good engineering and monitoring.
I will discuss retorting in a future post (In Sha’ Allah).