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Also in Coal explained Coal Mining and transportation Where our coal comes from Imports and exports How much coal is left Use of coal Prices and outlook Coal and the environment. In , three industry sectors made up approximately two-thirds of total U. The first two of these sectors have been subject to emissions standards for years and as a result have reduced their mercury emissions by more than 95 percent.
In addition, mercury standards for industries such as cement production, steel manufacturing and many others have reduced mercury emissions from these sources. The final rule establishes power plant emission standards for mercury, acid gases, and non-mercury metallic toxic pollutants which will result in:.
Controls to Meet Limits are Widely Available. The Mercury and Air Toxics Standards provide regulatory certainty for power plants. Additionally, these standards level the playing field so that all plants will have to limit their emissions of mercury as newer plants already do. Use of widely-available controls will reduce harmful air toxics and help modernize the aging fleet of power plants, many of which are over 50 years old. The regulated transition to a low-carbon electricity grid could secure the co-benefits of reduced emissions and water use.
In this case, the power grid could sustainably support population growth and changes in demand while freeing-up droves of water for other sectors, like agriculture. Switching the power industry over to natural gas and renewables is just one of many low-carbon options. Rubin points out that carbon capture and storage CCS can be fitted to coal and gas power plants to reduce the tonnage of CO2 released into the atmosphere.
CCS removes an impressive 90 percent of CO2 from emissions, although it adds significantly to cooling water requirements. Several process variants have been investigated which would use this property of coal as part of an overall methods for producing oil from coal.
By a suitable choice of the severity fo the processing conditions, a low-sulfur and low-ash solid fuel can be produced from coal without converting the coal to a liquid product. The fuel produced is a satisfactory clean fuel for use under boilers for one coal tested 0. It was designed to make a product containing about 0. The pilot plant will be. Although the pilot plant has been in operation for some time, no data have yet been released about its operation.
Sohio has announced that it is attempting to arrange for private financing of a ton per day prototype plant using this type of process. It would be constructed near Toledo, Ohio adjacent to an existing power plant. The project is designed to demonstrate production of lcean fuel from coal on a scale sufficiently large so there would be little or no risk in scaling up to a full size plant and to demonstrate that the fuel produced can be used in a full size boiler.
Even if the Sohio project is consummated, it will probably be late before testing can begin. With a one year test period, the first commercial plants could not be operational before or and it is unlikely that many plants would be built simultaneously until at least one plant has actually been used on a commercial scale.
A combustion test on 30 tons of SRC is planned for February Costs of producing a low-sulfur, low-ash coal are still difficult to estimate even roughly. A large number of different estimates have been published but the rapidly increasing costs of both the coal and heavy construction make most of the earlier estimates low.
A number of other coal liquefaction processes are under study but they are either being tested on a smaller scale, so that commercialization will be at an even later date,. Gasification of coal was a commerically used process both in the U. The water gas was enriched with light gaseous hydrocarbons made by thermally cracking petroleum to make a gas with a BTU per cubic foot heating value. The process was cyclic, inefficient and expensive. When a clean dust-free gaseous fuel was needed by industry e.
The hot gas produced producer gas had a low BTU content BTU per cubic foot because of the dilution with the nitrogen in the air from which it was made.
As a result it could not be transported economically very far. Since air pollution from sulfur oxides was not considered a problem at the time, the hot gas was burned with the hydrogen sulfide still in it.
In a few installations the hydrogen sulfide was removed. When interest in coal gasification was revived in this country it was because the pipeline transmission companies and the gas distribution companies became concerned that they would be unable to continue their growth as natural gas supplies were depleted. Thus, all the early research was directed at making a high BTU gas as a substitute for natural gas.
A large number of new processes to make town gas had been tried in Europe after World War II since at that time coal was still their main. Almost all the processes were designed to be continuous in order to avoid the high costs of cyclic operation and the air that was used in making producer gas was replaced by oxigen. The large scale use of oxygen became possible as the result of development of such plants for use in other types of commercial industrial processes.
In addition, if the process was able to operate under pressure, there were economic advantages over the older atmospheric pressure operations. With the continuous processes made possible by the use of oxygen in place of air, the new processes were also designed to operate at pressure. Three processes for making town gas from coal had been used in a significant number of installations so that they can be considered commercial.
There are the fixed bed, high pressure Lurgi process, the atmospheric pressure entrained Kippers Totzek process and teh Winkler fluid bed atmospheric process of Davey Power Gas, Inc. Commercial scale plants using any of these processes could be built with a high degree of confidence that satisfactory operation would be achieved.
However each of these processes has disadvantages so that more advanced processes are being studied in an effort to overcome these shortcomings. A large number of new processes are under study and two have been operated intermittently on a large pilot plant scale for several years IGT-Hygas and CO 2 Acceptor. A third large pilot plant, the Synthane process, is due to start operation in late or early Construction on a fourth plant using the Bigas process was started recently. Unless there are unexpected breakthroughs the first commerical plant using any of these technologies will not be operational until about to In the last several years, interest has turned to making a low-BTU low-sulfur content gas for use under industrial and utility boilers.
This type of gas should be able to be produced at lower costs than high BTU gas since oxygen is replaced with air and a number of downstream process steps are eliminated. Moreover, the overall efficiency of conversion. Although it is believed that most of the processes that were under investigation for making high BTU could also be used for making low BTU gas there has been no testing of any of the commercial processes Lurgi, Kioppers Totzek or Davey Power Gas, Incorporated in the U.
A Lurgi generator, using air instead of oxygen, has been under test in Germany for several years. The Lurgi generator is operated under pressure, then to a pressurized steam boiler to produce steam to generate electricity and to a gas turbine to produce additional electricity. The exist gases from the turbine are used to preheat steam. Total output of the power plant is MW of which 74 MW is produced by the gas turbine. The test results on this plant have not been reported in detail so that it is not known how successful it has been, but no new installations using the process have been announced.
Plans are being made to test a Lurgi unit in the U. As of January no announcements have been made that contracts have been awarded for this plant. Full scale, long term tests are required before even the Lurgi gasifier for making low-BTU low-sulfur gas can be considered to be available for commercial use. Illinois coals that are used extensively by Commonwealth Edison possess some mild coking properties.
Tests in a specially designed Lurgi gasifier were conducted in the U. The gas cleaning system that has been developed creates potential environmental problems and improved and lower cost methods for gas clean-up would be desirable. As with solvent refined coal it is difficult to estimate the costs accurately in the absence of any large scale plants. In order to operate the Kippers Totzek process with air instead of oxygen, changes in design would be required.
No experimental data have been reported although Koppers is said to be planning to run a test with air on one of the commerical gasifiers that is already in operation abroad. The timetable for commerical operation of the advanced processes to make a low-BTU low-sulfur gas that are still in the prototype or pilot plant stage to make a high-BTU gas is even less favorable.
Liquid fuel from coal was produced during World War II in Germany using two different processes and the product was used as a refinery feedstock. Because of the existence of these processes and the expectation that when oil resources were depleted, coal liquefaction to a refinery feedstock would again be needed; most of the research on coal liquefaction was directed toward making this type of product.
Unfortunately, coal liquefaction research was not pursued as intensively as coal gasification during the s and s. The oil industry expected that our limited domestic oil resources would be first supplemented by imported oil since oil.
One of the two German processes The Fischer Tropsch would not be a useful method to pursue if a low-cost low-sulfur boiler fuel is all htat is needed. The Fischer Tropsch process first completely gasifies the coal and then recombines the carbon monoxide and hydrogen over a catalyst in a fluidized bed to produce relatively low molecular wight products.
If a fixed catalyst bed is used, higher molecular weight products are formed. The other German process used Bergius dissolved the coal in a suitable hydrogen donor solvent. However, the process would not have to be modified extensively to take advantage of the development of new types of hydrogeneration catalysts and of advances in chemical engineering.
As a result, if a low sulfur oil is now the desired commercial product, one of the several coal hydrogenation processes that have been tested only on a bench scale would have to be used. In addition to operating the low-sulfur low-ash process at more severe pressures and temperatures to make a liquid product, see the discussion above of low-sulfur, low-ash coal the Synthoil process of teh Bureau of Mines and the H-coal process of Hydrocarbon Research Incorporated could be considered as likely process candidates.
If a successful modification of any of these processes can be accomplished, it might be possible to have a first commercial plant in operation in the priod — If any of the processes still at an early state of investigation must be developed for producing a low-sulfur oil for boiler fuel, commercial plants will probably not be in operation until to Because of the shift in interest away from producing synthetic high BTU pipeline gas and refinery feedstock from coal to producing a clean boiler fuel, methods for using coal directly have also been receiving increasing.
Pulverized coal combustion used almost universally in large power plants has reached a high degree of perfection although there remain areas in which improvements are possible. These include optimization of the configuration of the heat transfer surfaces, the use of alloys capable of handling higher steam temperatures and pressures and the development of methods to reduce the fouling and corrosive effects of the ash of certain coals.
Other important drawbacks to using pulverized coal boilers include the fact that nearly all of the sulfur in the coal is converted into sulfur oxides which appear in the flue gases and that emissions of nitrogen oxides are high.
Fluidized bed combustion, another method of burning coal directly in boilers, offers the potential for overcoming most of the difficulties that arise when pulverized coal is used. With fluidized bed combustion sulfur oxide and nitrogen emissions can be reduced, the efficiency and reliability of the units are expected to be increased and the size, weight and cost of the boiler may be reduced. In some pilot scale tests, it was possible to operate so that only about 1 to 4 percent of the sulfur in the coal appeared in the flue gas with pressurized fluidized bed combustion and about 10 percent with atmospheric combustion.
The heat transfer tubes are embedded in the fluid bed so that combustion tempertures are much lower than in pulverized fuel furnace while still giving much greater heat release rates per unit of boiler volume.
Fluidized bed combustion studies have been supported by several government agencies for a number of years.
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