新莊煤礦0.6Mt新井設(shè)計(jì)-60萬(wàn)ta含5張CAD圖-采礦工程.zip
新莊煤礦0.6Mt新井設(shè)計(jì)-60萬(wàn)ta含5張CAD圖-采礦工程.zip,新莊,煤礦,0.6,Mt,設(shè)計(jì),60,ta,CAD,采礦工程
英文原文Introduction of Longwall MiningExecutive SummaryLongwall mining is one of the principal underground mining methods in the United States. Its importance as a coal production technique has grown steadily since the introduction of modern longwall technology into this country in the 1950s and 1960s. In the past decade longwall production and productivity grew rapidly, as a result of significant improvements in longwall equipment and operating practices. By 1993, longwall mining accounted for 40 percent of the Nations underground coal productionup from 27 percent in 1983. Labor productivity at longwall mines more than doubled between 1983 and 1993. Productivity is now higher for longwall mining than for other underground production methods, and productivity is expected to keep g rowing as new technological advances are introduced.Longwall mining is one of two basic methods of under ground coal mining. The other method is room-and-pillar mining, historically the traditional method used in the United States. In room-and-pillar mining, “rooms” are excavated, and pillars of coal are left in place between the rooms to support the mine roof. In contrast, longwall mining involves the essentially complete extraction of the coal contained in a large rectangular block or “panel” of coal, and the roof in the mined-out area is allowed to collapse.The sequence of operations in longwall mining is basi- cally simple. The rectangular longwall panel, averaging nearly 800 feet wide, 7,000 feet long, and 7 feet high, is “blocked out” by excavating passageways around its perimeter. Room-and-pillar mining is used to block out the panel. Excavation of the coal in the panel is an almost continuous operation. Working under the steel canopies of hydraulic, movable roof supports, a coal cutting machine runs back and forth along the 800-foot face, taking a cut ranging anywhere from a few inches to 3-1/2 feet deep during each pass. The cut coal spills into an armored chain conveyor running along the entire length of the face. This face conveyor dumps the coal onto belt conveyors for transport out of the mine. As the cutting machine passes each roof support, the support is moved closer to the newly cut face to prop up the exposed roof. The roof is allowed to collapse behind the supports as they are advanced towards the face. Mining continues in this manner until the entire panel of coal is removed.Because longwall mining is essentially a continuous, highly mechanized operation, longwall productivity is potentially higher than room-and-pillar productivity. Longwall mining also offers improved safety through better roof control, more predictable surface subsidence, and better opportunity for full automation. On the other hand, capital costs for longwall equipment are much higher than for room-and-pillar equipment, productivity during development (“blocking out”) of the longwall panels is typically low, and large amounts of dust and methane are generated during the mining process.IntroductionLongwall mining is one of the principal underground mining methods in the United States. In 1993,longwall mines accounted for 40 percent of the Nations under-ground coal outputcompared with 27 percent in 1983. Although basic longwall mining techniques were de- veloped in England in the 17th century, there was little interest in longwall mining in the United States until the 1950s, when new German technology was introduced. As the technology was developed further in the United States, longwall production grew steadily. By 1993, 85 longwall units were operating in 12 States. Labor productivity at longwall mines more than doubled between 1983 and 1993. Productivity is now higher for longwall mining than for other underground production methods, and productivity is expected to keep growing as new technological improvements are introduced. The purposes of this report are to describe the longwall mining process, analyze the most important changes in longwall mining over the past decade, and discuss factors that will shape the future of longwall mining.The History of Longwall MiningLongwall mining is not a new approach to coal mining.In fact, the basic principles of longwall mining have beentraced back to the latter part of the 17th century to Shropshire and other counties in England, where it was described as a “totally different method of mining” called the “Shropshire method.” Many modifications in the original methods have occurred, but all longwall mining has involved extracting coal from a long wall or face. The area from which the coal was extracted, the “gob” (from a Celtic word for cave or hollow), was partly or wholly filled with stone and refuse, upon which the overlying strata settled.Until the early 1900s, coal mining in England was mostly by the “bord and pillar” method (equivalent to “room-and-pillar”). The “bords,” or passages, were areas 12 to 20 feet wide from which the coal was extracted; the pillars were made of coal, some 50 feet wide and as many as 100 feet long, that was left unmined to support the overlying strata. Efforts to extract some or all of the coal left in the pillars at a later stage of mining either were not attempted or were not always successfulAs the demand for coal increased, bord and pillar mining soon was regarded as wasteful, and the advantages of the longwall technique were noted: “It enables a colliery to be opened with less capital expenditures . . . and to become remunerative in the smallest possible time . . . The yield per acre is greater . . . Ventilation is easier, the workmen are concentrated, and the expense of supervision is reduced . . . in seams giving off large quantities of explosive gas . . . shot firing can almost entirely be dispensed with because the weight on the face is in itself sufficient to bring down the coal”The overall layout of early longwall mines was generally circular, with mining radiating out from a central shaf. The main roadways ran diagonally from the shaft pillar like the spokes of a wheel, while the intervening areas were subdivided into smaller and smaller sectors by subsidiary roadways. The roadway were kept open by “pack walls” of waste rock constructed on either side of them. The roof in the working area, or face, was supported by a line of timbers, which were moved forward as mining advanced, and by “packs” or “cribs” of waste rock, while the roof in the mined out area was allowed to collapse.Longwall mining was practiced on a very small scale in the United States in the late 1800s and early 1900s. The pioneering longwall attempts were generally in thin coalbeds that could not be mined effectively by room-and-pillar techniques, and that required a minimum of packwall construction and backfilling for roof support. Where successful, those early longwall operations resulted in complete removal of the coal at minimal expense, with less timbering, more controlled subsidence, and better ventilation in the working area than room-and-pillar methods.Until undercutting machines became available in the early 1900s, longwall miners undercut the coal by hand with picks. The early working faces generally were in the form of an arc about 40 feet across, but as mines became deeper and mechanized, straight faces were found to be more efficient.The undercut coalbed was temporarily supported by short wooden props or “sprags” set every 4 to 6 feet. When the props were knocked out, the undercut coal fell because of its own weight and roof pressure, but if necessary, it was knocked down; explosives were seldom used. The broken coal was then loaded by hand into cars (tubs) for transport out of the mine. By 1924, productivity was improved when conveyors were installed along the longwall face in some mines.Overall, the experience of early longwall mining in the United States showed that it was not competitive with the room-and-pillar method. Although steel jacks replaced wooden props for roof control around 1912, and mines were becoming mechanized, the large number of workers required to move the jacks and to construct other types of roof supports made longwall mining a labor-intensive effort. With longwall productivity averaging only about 3 tons or less per worker per shift, U.S. underground mining technology focused on improving room-and-pillar mining, a better method for extracting coal from relatively thick beds. In contrast, longwall mining remained predominant in Europe, where conditions were more suitable for the technique because the coalbeds were deeper and overlain by thinly layered strata that caved more easily than those in the typical U.S. coal mine.1950-1960After World War II, U.S. interest in longwall mining was renewed by the possibilities of using the German developed plow (or planer) and “panzer,” or armored face conveyor. The plow is pulled across the coalface while riding on a base that slides under the conveyor. It shaves off 2 to 4 inches of coal that spills onto the conveyor. In 1952, Eastern Gas and Fuel Associates, with support from the U.S. Bureau of Mines, tested longwall mining with a plow and face conveyor at the Statesbury mine, near Beckley, West Virginia, to learn if this type of equipment could be used to extract some U.S. coal. Roof support was provided by mechanical props with I-beam caps and wood cribs. The test was successful and the equipment was used in three other longwall operations between 1952 and 1958.During the 1950-1960 period, there were an average of six longwall operations per year, mostly in West Virginia and Pennsylvania, but also in Arkansas. The plow was he principal coal-cutting machine, replacing the early labor-intensive mechanical undercutting method. However, about three-fourths of the longwall operations were not successful because the coalbeds were not friable enough for extraction with a plow, or because roof control presented problems.Although the hydraulic props introduced in the late 1950s were an improvement over the earlier mechanical friction props, a large amount of manual labor was still needed to recover and reset the props. Moreover, as the face advanced, wood cribs had to be constructed for additional roof support, requiring additional manual labor. As a consequence, by 1960 longwall mining was generally considered a last resort, used only for extracting thin beds of premium coal when room-and-pillar methods failed. Other factors also constrained the use of longwall mining in the United States. These included the lack of familiarity with the method on the part of the U.S. coal industry, and the high capital investment required for the equipment. Furthermore, by this time, continuous mining machines were improving the efficiency of room-and-pillar mining.1960-1970Interest in longwall mining in the United States revived in the 1960s, and the number of installations rose to about 20 before 1970, due mainly to the introduction of self-advancing hydraulic roof supports. These powered supports replaced jacks and wood cribs, eliminating the need for substantial labor. They also had the advantage of being able to push the conveyor forward automatically as the face advanced. Self-advancing hydraulic roof supports were first used, together with a plow, in 1960 to excavate a 52-inch coalbed in Eastern Associates Keystone mine near Welch, West Virginia.The first self-advancing roof supports were frames. A frame consisted of two single hydraulic jacks connected to a beam, and two frames were linked together to operate as a pair. They advanced in two steps. While one frame remained set between the roof and floor, the other was lowered and then pushed forward by a ram; the procedure was reversed to move the other frame. Frames with a two-leg design could support as much as 88 tons before yielding; those with four-leg designs were about twice as strong.Frames successfully supported the roof when the overlying strata caved easily, but they were often inadequate if the strata “hung up.” A number of longwall installations in the Illinois Basin were discontinued because frames could not control the mine roof.In the mid 1960s, better designed, high-capacity, self- advancing roof supports, capable of holding about 700 tons, became available in the form of the chock. Described as a mobile crib, the chock consists of two frame supports tied together with a rigid canopy and semi-rigid base. More stable than frame supports, the chock is also safer because it has a canopy that provides protection against material falling from the mine roof. The chock can also be advanced as a single unit by a hydraulic ram attached to the face conveyor. Although the chock represents a great improvement in roof control technology, it can become unstable when the roof caves in large pieces and creates rotational or horizontal stresses. The instability can occur because the chocks canopy is connected to its base only by the hydraulic leg cylinders. Several longwall operations in southern Illinois were abandoned because chocks failed as the result of serious roof control problems.The 1960s also saw the introduction of the shearing machine in the United States, first at Kaiser Steel Corporations Sunnyside mine in Utah in 1961, and later in mines in the East. The shearing machine is an electrically powered rotating drum that not only excavates harder coal, but also cuts a wider strip (24 to 28 inches) from the coalbed than the plow.However, the early shearers were not free of problems. A shearers performance could be reduced if the supports were not advanced uniformly, resulting in poor alignment of the shearer with the coal face. Furthermore, the shearers heavier weight required the use of stronger armored face conveyors to support it. Shearers also produced finer sized coal than plows, and this tended to jam face conveyors, reducing productive mining time. Health problems became a concern because the shearer also generated more respirable dust. Nevertheless, by 1966, after improvements were made, shearers produced 42 percent of the coal at U.S. longwall operations. By 1970, shearers outnumbered plows, and the first double drum ranging shearer was in service in the northern Appalachians.1970 to 1980In this period, the last major impediment to the acceptance of longwall mining in the United States was overcome through the introduction of shield supports, a major step in the evolution of roof control. Although new to the U.S. coal mining scene, shields had been used successfully since the 1960s in the Soviet Union and ther Eastern European countries.Safety and productivity factors favored the shield over the chock. The average support capability of a shield and chock are about the same, but the shield is more stable. The shield provides additional roof support because its canopy and base are connected by structural members other than the hydraulic leg cylinders. As a result, the leg cylinders of the shield, unlike those of the chock, are not subjected to damaging bending movements.The first shields in the United States were installed in 1975 in the Shoemaker mine of Consolidation Coal Company, near West Virginia. Shortly afterwards, shields were applied to other U.S. longwall operations, proving successful in areas where other roof supports failed. The basic shield design was improved, and by the late 1970s, shields were the leading roof supports in longwall installations.Advances made to the double-drum and ranging arm shearers developed in the 1960s made them more adaptable. Their cutting height could be quickly adjusted when coalbed thickness changed or when it was necessary to leave a layer of coal at the top of the bed to strengthen the mine roof. Improvements were also made in the method of hauling the shearer across the coal face. The early shearers were pulled by chains stretched along the length of the face. If the chain broke, it could cause serious injuries. By the early 1970s, shearers moved by safer “chainless” methods using self-contained traction units. Although development concentrated on the shearer, the plow was also improved. A plow designed to be stronger and more rugged was placed in service in 1974 at Clinchfield Coal Companys No. 2 mine, near Dante, Virginia. It operated successfully in a thin coalbed that had been too hard for earlier plows.1980-1994Since 1980, an average of more than 100 longwall installations have been in operation annually in the United States. In recent years, however, the number has declined slightly, reflecting partly economic and market conditions for coal and partly the ability of the current longwall operations to meet demand without the need for additional installations.Shields have become the predominant type of roof supports in U.S. longwall mines, and shearers the principal cutting machines. The reliability of armored face conveyors, like that of roof supports, has been improved to the extent that they are no longer responsible for major interruptions in longwall mining.The list of wide-ranging advances in longwall technology includes shearers that are designed to mine relatively thin coalbeds (less than 42 inches). Better dust control has been achieved with water sprays and improved design of cutting drums and cutting bits. Power supply problems for large multiple shearer motors and longer face conveyors have been overcome.Because longwall mining is a repetitive process, it has the potential to be automated. Among the health and safety benefits from an automated longwall installation are the removal of personnel from hazards such as dust exposure, roof falls, and noise. The economic benefits include improved coal quality, higher productivity, reduced maintenance costs (for example, reduced wear on the shearers cutting bits), increased speed of operation, and better use of personnel.Automation is being incorporated in all phases of longwall mining. Push-button control to begin a sequence of predetermined patterns is now becoming the norm. Shield advance can be automatically controlled by a signal from the shearer. Sensors and control systems have been developed to detect the coal-rock interface and provide automatic vertical ranging of the shearer drums.An example of the mature state that longwall mining has reached is the 15-million dollar system installed by the CONSOL Coal Group in 1994 at its Robinson Run mine, near Shinnston, West Virginia. Reportedly the worlds most advanced longwall system, it integrates sophisticated computer technology, instrumentation, and robotic controls to automate most of the routine tasks of longwall mining, using a 42-inch coal shearer and 172 hydraulic roof support shields.Longwall Mining Compared with Other Underground Coal Mining TechniquesLongwall mining is one of two basic methods of mining coal underground. The other is room-and-pillar mining, historically the standard method in the United States. Both of these methods are well suited to extracting the relatively flat coalbeds (or coal seams) typical of the United States. Although widely used in other countries, longwall mining has only recently become important in the United States, its share of total underground coal production having grown from less than 5 percent before 1980 to 40 percent in 1993. 1 Currently, 85 longwalls operate in the United States, most of them in the Appalachian region.The basic principle of longwall mining is simple. A coalbed is selected and blocked out into a panel averag- ing nearly 800 feet in width, 7,000 feet in length, and 7 feet in height, by excavating passageways around its perimeter. A panel of this size contains more than 1 million short tons of coal, most of which is recovered. In the extraction process, numerous pillars of coal are left untouched in certain parts of the mine in order to support the overlying strata. The mined-out area is allowed to collapse, gene
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