SEDIMENTOLOGYSTRATIGRPHY GEOL 103A
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Date Created: 10/05/15
Geology 103 Lecture 17 Coal carbonaceous rocks oil shale Reading Boggs 4th edition pp 229 239 Today will talk about fossil fuels a nonrenewable energy resource 2 main topics coal oil shale 1 Coal A Introduction The most abundant fossil fuel Coal may be our energy supply for the next century as oil and natural gas run out But this is a goodnewsbadnews situation Much of the coal isn39t located where we can use it Much of the coal is high sulfur coal which creates atmospheric pollution when it burns B Coal terms Maceral N mineral Coal contains many types of macerals 10039s Describes the different vegetative fragments in coal 3 main groups of macerals See Crelling and Dutcher SEPM short course 8 Principles and Applications of Coal Petrography table 1 p 25 1 Vitrinite Origin cell wall material or woody tissues of plants Abundance the most common maceral 5090 of most North American coals Chemistry intermediate carbon hydrogen contents Re ectance is related to degree ofheating Is used in petroleum studies Vitrinite also occurs in shales 2 Liptinite Origin waxy and resinous cuticles spores and wound resins Abundance 510 of North American coals Chemistry high hydrogen low carbon content Re ectance is low lower than Vitrinite 3 Inertinite Origin plant material that has been strongly altered or degraded in the peat stage of coal formation EX fossil charcoal Have high carbon low hydrogen content Each of these maceral groups is subdivided into smaller groups C Formation and geochemical identi cation of coal Coal forms when plant material is compressed buried Coal name is assigned based on geochemical properties See Crelling and Dutcher SEPM short course 8 Principles and Applications of Coal Petrography p 41 With time continued burial and pressure volatile components are driven off coal forms Composition Is dominantly carbon Small amounts of nitrogen sulfur Identi cation is based on C H content BTU value per pound Re ectivity of vitrinite D Macroscopic identi cation of coal See Crelling and Dutcher table from above 1 Peat Abundant original plant material still visible Low density low caloric value low no vitrinite re ectance High moisture content high volatile content Slightly compressed slightly strati ed 2 Lignite Woody stems and roots still visible Compacted into layers Slight increase in density caloric value vitrinite re ectance Lower moisture volatile content Breaks into blocky chunks 3 Bituminous Dull or re ective varies Horizontal laminae still represent original bedding No visible plant parts Jump in vitrinite re ectance caloric value Much lower moisture volatile content Dense coali ed rocklike 4 Anthracite Shiny glassy vitreous luster Conchoidal fracture Brittle May still have remanant layering OR may be relatively homogeneous Highest caloric and vitrinite re ectance values Lowest volatile moisture content E Occurrence 1 World coal reserves 3 countries contain 6080 ofthe world s coal resources US USSR China North America has 26 of world s coal reserves World coal reserves are projected to last 220 years at current use rates With 2 increase per year coal will last at least 149 years With projected discoveries resources coal could last 900 years Remember reserve is a proven deposit resource isn39t economic at the present time 2 Domestic U S coal reserves Most of North America39s coal 96 is in the United States See Figure 1315 from Castillon Conservation of Natural Resources p 288 Although this looks promising there are 3 problems here a Most coal in the US is Bituminous not the hottest burning anthracite coal See Table 131 From Castillon Conservation of Natural Resources p 288 shows BTU content of coal b Bituminous coal often has a high sulfur content Creates environmental problems High sulfur coal causes acid rain Ask class has anyone been to the Adirondack Mtns lately c Location of reserves is not favorable Most low sulfur coal reserves are in the west Most industries are located in the east F Summary of coal as a resource Coal will help bridge the energy gap when we run out of oil The cost of this energy will be very expensive Must include the cost of transporting coal from west to east Must include the cost of adding scrubbers environmental cleanup when we burn high sulfur bituminous coal 11 Oil ShaleTar Sands A Intro What are oil shale and tar sand Comes from negrained rock shale or sandstone that have a high organic carbon content Organic carbon is thick sticky kerogen or bitumen instead of lighter weight oil B Oil shale and tar sand reserves 1 Oil shale Another potential energy source when we run out of oil The US also has vast reserves of oil shale In Colorado Wyoming Utah Worldwide reserves in Canada China Soviet Union US reserves could supply our present oil demand for 50 100 years Other countries with no oil reserves are already using oil shale as a source for oil eX South Africa gets N 60 of it s oil from oil shale 2 Tar sand The largest reserves are in Canada Canada supplies 12 of it s oil needs from tar sand All of Canada39s tar sand deposits would supply the world oil demand for 2 years US tar sand reserves would supply M needs for 3 months C Producing oil shale Note tar sand is so negligible that we won t discuss it Oil shale is processed extracted from the rock See overhead Figure 18 5 from Miller p 479 Rock is heated Heating boils the kerogen or bitumen out of the rock Leaves a tarry sticky residue Residue is processed to remove sulfur nitrogen Hydrogen is added to make it ow easier At this point it is N equal to crude oil quotoilquot is re ned Process is expensive Costs 5060barrel to produce D Environmental limitations Converting shale oil or tar sand to oil and burning the oil Releases more C02 than burning conventional oil Processing requires large amounts of water But most oil shale and tar sands are in arid areas These areas don39t have the necessary water for processing Chemicals released during processing aren t quotearth friendlyquot Include carcinogens heavy metals C0 C02 802 N02 are also emitted So oil shale is only marginally acceptable as an energy alternative 111 Summary US and Canada have vast reserves Could potentially supply our oil demand for 10039s of years But requires high energy water inputs and may be dirty energy