Abstract:
An apparatus for raising and lowering a cutting tool within a decoking drum, a decoking system and a method of raising and lowering a decoking system cutting tool. Instead of using metallic ropes, chains, or a self-propelled gear-based approach, non-metallic belts are secured at respective ends to a crosshead and one or more counterweights to enable vertical movement of the crosshead that in turn permits vertical movement of the cutting tool throughout the height of the drum. A motorized pulley system controls the movement of the belt, and preferably avoids having the motor be carried by the crosshead. The belts on each pulley are preferably arranged as cooperative sets so that within each set, both primary load belts and secondary load belts are present. Enhanced engagement between at least the primary load belts and the pulleys promotes greater load-bearing capability, while the secondary load belts are sufficiently strong to ensure positional stability of the crosshead and decoking tool upon damage to or failure of one or more of the primary load belts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 62/059,406 (DUR 1093 MA) filed Oct. 3, 2014. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to devices for carrying a cutting and drilling tool and other components for use in delayed coking reactor operation, and more particularly to the use of non-metallic belts that provide a fail-safe lifting design for raising and lowering such components. 
         [0003]    In conventional petroleum refining operations, crude oil is processed into gasoline, diesel fuel, kerosene, lubricants or other useful materials through distillation or related means. In such an operation, the crude oil (which is typically subjected to various upstream processing or production steps at or near the well from which the oil is extracted) is heated to elevated temperatures in a fractional distillation unit in order to selectively release—depending on differing boiling points—the valuable volatile hydrocarbon components contained therein. The heavy remaining oils are drained from the fractionation unit, heated, and transferred into vessels (known as coke drums) at a temperature (specifically, a thermal cracking temperature) sufficient to drive off the remaining volatile materials to leave the drums full of solid coke. Because large-scale refineries can produce as much as 2,000 to 3,000 tons per day of solidified coke, the drums—which are as large as 30 feet in diameter and 140 feet in height—must be frequently cleared to make room for the next incoming batch. 
         [0004]    One method of breaking up the coke residue is by using a decoking (or coke cutting) tool in conjunction with a decoking fluid, such as high pressure water. The tool (which is typically secured to a tower that is in turn mounted onto a support structure that surrounds the coke drum) is lowered into the coke drum through an opening in its top, and the high pressure water supply is introduced into the tool so that it can be selectively routed through—depending on the mode of operation—either the drilling or cutting nozzles of the tool to impinge on the coke in the drum and act as a coke-breaking fluid jet. Such tools require high flow rates and pressures (for example, flows of 1000 gallons per minute (gpm) at 3000 to 4000 pounds per square inch (psi) or more). Moreover, the tower, tool and its ancillary equipment (including among others drill stems, drive mechanisms, water-filled hoses or related conduit, collectively referred to as a cutting train that can be supported by a crosshead) can be extremely heavy, weighing (depending on the size and configuration) up to 15,000 pounds or more. A steel cable operated by a winch is used to raise or lower the cutting train. In addition, separate fall arresting gear is required in numerous decoking tool crosshead designs to prevent a freefall in the event of a cable break or a winch failure within the tower; such redundancy adds significantly to the maintenance and operation complexity, as well as the weight and cost of the decoking system without contributing to the efficiency of the actual decoking process. 
         [0005]    To avoid having complex support structures for movement of the water jet cutting head and related equipment through the vertical entirety of the coke drums, a self-climbing crosshead-based lifting configuration may be employed, an example of which is depicted in U.S. Pat. No. 6,050,277 (the &#39;277 patent) that is owned by the Assignee of the present invention and incorporated herein by reference in its entirety; such a configuration forms a crosshead drive system. An additional way that redundancy and complexity is avoided in the &#39;277 patent is through the use of rollable carriages (such as those depicted in  FIG. 3B  thereof) on a track or rail so that a single tower (rather than multiple towers) that is used to support the cutting train can be transported between adjacent drums. 
         [0006]    Despite the improvements made by such a configuration, difficulties remain. For example, the long lengths of the rack-and-pinion configuration must still rely upon rigid support by a vertical member that—while not as cumbersome as a complete tower—must be robust enough to ensure that precise engagement of their meshing gear teeth of the self-propelled drive system is maintained, as misregistration between them can lead to faulty (or no) crosshead movement; such rigidity can exact significant weight, cost and complexity tolls. Moreover, if a metallic wire cable (also called rope) is used to couple the cutting train to a set of counterweights over a corresponding set of pulleys in an attempt to permit the use of a smaller motor, significant additional weight (often 5000 to 8000 pounds or more) may be present. 
       SUMMARY OF THE INVENTION 
       [0007]    According to one aspect of the present invention, an apparatus for moving a cutting tool within a decoking drum is disclosed. The apparatus includes one or more rigid members extending above the decoking drum a sufficient height to permit a range of vertical movement of the cutting tool throughout a substantial majority of the drum. A crosshead drive system is made to facilitate vertical movement of the crosshead may take place relative to the rigid member or members. The crosshead may be made to carry the tool (such as through a fixed or rotatable drill stem or the like), and itself may be raised or lowered within the rigid member by a motorized set of pulleys and belts where the motor and the pulleys are not mounted on the crosshead; in this way, the weight of the vertically-movable components is significantly reduced. Substantially opposing ends of the belts define connection or securing points; thus, one end of each of the belts is secured to the crosshead, while the opposing end is secured to counterweight that can be made to move vertically within or adjacent the rigid member along a travel path that is substantially parallel to the travel direction of the crosshead. In a preferred form the belts and pulleys cooperate such that one or more primary load belts and one or more secondary load belts can be made to travel within corresponding side-by-side channels that are formed in the pulleys; the secondary load belts may be used in the event one or more of the primary load belts suffers a cut or related damage that impairs its ability to raise and lower the crosshead. 
         [0008]    According to another aspect of the invention, a decoking assembly is disclosed. The assembly includes a decoking tool configured to receive a cutting fluid from a high pressure fluid source; and an apparatus coupled to the decoking tool for moving it within a decoking drum. The apparatus includes one or more rigid members and crosshead drive system similar to that of the previous aspect. 
         [0009]    According to yet another aspect of the invention, a method of operating components within a decoking system is disclosed. The method includes arranging an assembly to be adjacent a decoking drum and using a motorized pulley system that is part of the assembly to selectively raise and lower at least a crosshead and coke cutting tool that may receive a cutting fluid from a high pressure fluid source. As with the previous aspects, numerous non-metallic belts engage each pulley so that rotating the pulley causes movement of the crosshead and a counterweight affixed to opposite ends of each set of belts. As before, at least the motor is statically mounted so that it doesn&#39;t have to raise and lower along the crosshead and the coke cutting tool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The following detailed description of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
           [0011]      FIG. 1  shows a view of two-drum decoking system which can be retrofitted to use the crosshead drive system of the present invention; 
           [0012]      FIG. 2  shows a detailed representation of a crosshead drive system according to the prior art; 
           [0013]      FIGS. 3A through 3D  show various detailed views of the crosshead drive system according to one aspect of the present invention; 
           [0014]      FIGS. 4A through 4C  show a simplified view of the cooperation of a belt and pulley according to one aspect of the present invention; and 
           [0015]      FIG. 5  shows a notional configuration of a toothed pulley and a complementary-shaped belt according to another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring first to  FIG. 1 , a decoking system  1  includes a pair of coke drums  5 , a cutting and boring (also called a decoking) tool  10 , a drill stem  15 , a pair of towers  20 , a flexible water supply hose  25  and a rotary joint  30 . The drum  5  on the left shows a partial cutaway that is full of coke  7  that needs to be removed, while the drum  5  on the right shows the decoking tool  10  being lowered through the coke  7  during boring of a pilot hole  9 . The decoking tool  10  is mounted at the lower end of the drill stem  15  such that both can move translationally (specifically, vertically) along the length of drum  5 . The upper end of drill stem  15  is coupled to the rotary joint in such a way that the decoking tool  10  and drill stem  15  can rotate about a longitudinal axis formed by both. The flexible water supply hose  25  is also coupled to the rotary joint  30  and is used to supply high pressure water to the decoking tool  10 . While the decoking tool  10  is mentioned as a single device, it will be appreciated by those skilled in the art that such functions may be separated, as a separate tool that provides boring and a separate tool for cutting may be employed. The construction of the rotary joint  30  is such that it acts as the intermediary between the flexible, yet non-rotational water supply coming from the flexible water supply hose  25  and the rigid, yet rotational drill stem  15  and the decoking tool  10 . Each tower  20  acts as a hoist to lift and lower a respective one of the decoking tools  10 , drill stems  15 , flexible water supply hoses  25  and rotary joints  30 . 
         [0017]    Drill stem  15  and towers  20  extend vertically above a cage-like support structure  40  that surrounds the drums  5 , where in one form the towers  20  may be mounted onto a floor-like upper deck (also referred to as a cutting deck)  45  of the support structure  40  Likewise, the top of the towers  20  and a framework  35  may form a derrick that provides support for the decoking tool  10 , drill stem  15 , water supply hose  25  and rotary joint  30 . As can be seen, the height of each drill stem  15  and its tower  20  is at least as much as the length of the drums  5  to permit drill stem traversal along a substantial entirety of the volume of coke  7  contained therein. As will be discussed in more detail below, the crosshead drive system according to one or more embodiments of the present invention may be placed at or near the top of the tower  20 . As mentioned above, the two-tower  20  system of  FIG. 1  may also be retrofitted (not presently shown) to use only one horizontally moving tower  20  that can be shuttled back-and-forth between the two drums  5 . In such configuration, a single tower  20  may be mounted to a mobile transport in the form of a wheeled carriage that is situated on upper deck  45  of the support structure  40  above the coking drums  5 . In one form, the transport may be self-propelled (such as by a motor (not shown)), while in another, it can be guided by a winch or related towing mechanism (not shown) with cables. In a more particular version, the transport may be mounted on rails or tracks that in one form may resemble those used to carry trains. In this way, a single movable decoking tower  20  may be used to operate on multiples drums  5 . The crosshead drive system  200  of the present invention can be retrofitted onto existing decoking tool system  1  in order to reduce overall system  1  complexity and redundancy. 
         [0018]    Referring next to  FIG. 2 , a decoking tool carrier with a crosshead drive system  100  according to the prior art is shown. The system  100  includes a self-propelled rigid crosshead  110  rigid with a motor  120  mounted thereon and a reduction gearbox (not shown) having a worm gear (not shown) drivably engaged with the output shaft of the motor  120 . The worm gear has output shafts  130 , each defining a pinion  135  at its respective end. The output shafts  130  are rotatably supported in bearing blocks  140  to promote secure connection between the pinions  135  and the crosshead  110 . The rotary joint  30  is mounted below the crosshead  110  between a pair of vertically-upstanding members  145  that can be used in place of or as part of the tower  20  of  FIG. 1 . Two vertical toothed racks  150 , one secured to each respective vertically-upstanding member  145 , cooperate with the pinions  135  such that rotation of the pinions  135  under the influence of motor  120  causes the crosshead  110  to climb or to descend on the toothed racks  150 . The pinions  135  are kept in engagement with the racks  150  by means of wheels (not shown) that are mounted on axles (not shown) to bear against the rear surfaces of the racks  150  in a clamping-like relationship. Two cables  155  are attached to the top surface of the crosshead  110  and extend upward over pulleys  160  and thence downward to counterweights  165  which are preferably made to travel within a generally vertical path defined by the construction of the vertically-upstanding members  145  (which in one form may be made from pipes or the like). 
         [0019]    Referring next to  FIGS. 3A through 3D and 4A through 4C , the crosshead drive system  200  according to one or more embodiments of the present invention is shown. System  200  includes (among other components, as discussed below) a crosshead  210  and motor  220 . In one form, the rotational speed of the motor  220 —which may be electrically-powered—may be controlled by a conventional device, such as a variable frequency drive (VFD—not shown). Preferably, the motor  220  and gearbox  224  combination limits the linear raising and lowering speeds of the crosshead  210  to no more than about 41 feet per minute. In addition, the motor  220  can be operated remotely to minimize exposure of an operator to the decoking operation, while in another form, the entire system may be automated. Unlike the self-climbing system  100  of the prior art, motor  220  is statically mounted onto a rigid member deck (such as framework  235  (only the bottom portion of which is shown) that is similar to framework  35  of the towers  20  shown in  FIG. 1  that permits a secure mount for the motor  220  (as well as the pulleys that will be discussed in more detail below); this decoupling of the motor  220  from the crosshead  210  means that the crosshead  210  carries less weight, which in turn can permit a less robust rigid member to act as a crosshead  210  support structure. Instead, the crosshead  210  is responsive to movement of belts  255  that are cooperative with the rotation of the output shaft  222  of the motor  220 . Referring with particularity to  FIG. 3B , in one form, the rotational movement of the output shaft may be imparted through a dual output gearbox  224  to promote equal (but opposite) rotational movement to the belts  255  through pulleys  260  that are mounted onto the framework  235  in a manner generally similar to that of motor  220 . The pulleys  260 , by virtue of their rotational coupling to the motor  220 , impart movement to the belts  255 . As before, the rotary joint  30  is mounted below the crosshead  210 . Instead of vertical toothed racks  150 , pinions  135  and cables  155  of the prior art, the belts  255  driven by pulleys  260  raise or lower the cutting train. The pulleys  260  can be driven by motor  220  and gearbox  224  combination, synchronized motors, or similar apparatus. The belts  255  are secured at one end to the crosshead  210  and to the other end to counterweights  265  that in one form can be made to travel within a generally vertical path defined by the upstanding member  245  portions of the support structure in a manner generally similar to that depicted in  FIG. 2 . In the present context, the secured nature of the connection may be through any conventional means so long as slippage or inadvertent release is avoided. As such, the belts  255  do not replace the toothed rack  150  of the prior art of  FIG. 1 , but rather replace the cables  155 . Instead, it is the toothed features of the pulley  260  and belt  255  arrangement of the present invention working together that replaces the rack and pinion arrangement of  FIG. 1 . In  FIG. 3B , the pulley  260  is shown in notional form in a single channel width configuration; as will be discussed below in more detail in conjunction with  FIGS. 3C, 3D and 4C , the pulley  260  may in fact comprise multiple channels across its width, and may or may not include teeth to help engage complementary-shaped teeth in the belts  255 . As such, the motor  220 , gearbox  224 , belts  255 , pulleys  260 , counterweights  265  cooperate to define a motorized system that can selectively raise and lower the crosshead  210 . 
         [0020]    In one form, the motor  220 , belts  255 , pulleys  260  and counterweights  265  (as well as other components as discussed herein) may define a motorized pulley system that is part of the crosshead drive system  200 . Details of augmented forms of engagement between the belts  255  and pulleys  260  is shown with particularity in  FIG. 4A , where complementary-shaped teeth  256  and  261  are formed on the belts  255  and pulleys  260 , respectively in order to facilitate a meshed cooperation between them upon pulley  260  rotation. Furthermore, although the crosshead  210  and its ancillary equipment are shown in  FIG. 3A  as being situated between two upstanding member  245  portions of the support structure that acts as the towers  20  of  FIG. 1 , it will be appreciated by those skilled in the art that it may also be supported by a single tower or derrick in order to facilitate an even more lightweight (and moveable) structure that can be shuttled back-and-forth between adjacent decoking drums. In one such form, such a single-tower structure may be moved by rollers, wheels or the like across a planar surface (such as upper deck  45  of the decoking system  1  of  FIG. 1 ); either embodiment is deemed to be within the scope of the present invention. 
         [0021]    Referring with particularity to  FIGS. 3C and 3D  (both of which show a cutaway view along Section A-A of  FIG. 3A  of one of the pulleys  260  to highlight how multiple channels may define the engagement region of the pulley  260  and belt  255 ) as well as  FIG. 4C , in one embodiment, the use of pulley  260  may be configured to include teeth  261  in one or more of the channels  260 A through  260 D (as shown with particularity channels  260 B and  260 C). As will be appreciated by those skilled in the art, the number of such teeth  261  may be varied according to the needs of system  200 , taking into appropriate consideration overall system  200  weight, cost, fail-safe needs or the like, and that all such variants (i.e., with or without teeth  261  formed in some or all of the channels  260 A through  260 D) are deemed to be within the scope of the present invention. Likewise, even though four channels  260 A through  260 D are shown in  FIGS. 3C, 3D and 4C , the number of such channels may be greater or fewer, depending on the need; as with the use of teeth  261 , all such variants in the number of channels are deemed to be within the scope of the present invention. 
         [0022]    In the embodiment depicted in  FIGS. 3C and 3D , two central channels  260 B,  260 C are sized and shaped to cooperate with drive belts  255 A that function as primary load belts, while two outer channels  260 A,  260 D accept fail-safe (also referred to as secondary load) belts  255 B that do not carry a load during normal operation, but can do so upon failure of one of the primary load belts  255 A. As discussed above, the pulley  260  embodiment of  FIG. 4C  has two of the channels  260 B and  260 C configured to accept the drive belts  255 A (and are also shown possessing teeth  261 ), while channels  260 A and  260 D (presently shown without teeth) are configured to engage the fail-safe belt  255 B; it will be appreciated that any combination of drive belts  255 A and fail-safe belts  255 B—as well as a corresponding number of channels to engage them, and whether such channels are outfitted with teeth  261 —is also deemed to be within the scope of the present invention. The combination of at least one primary load belt  255 A and at least one secondary load belt  255 B that together engages one of the pulleys  260  is referred to herein as a belt set (or more simply, set). As shown with particularity, the size and number of pulley channels  260 A through  260 D, as well as the number and size of both drive belts  255 A and fail-safe belts  255 B that as a set cooperate with such channels, may be varied according to the needs of the particular crosshead drive system  200 . 
         [0023]    Both the drive belts  255 A and the fail-safe belts  255 B can be made from the same materials, while in another configuration, they can be made from different materials, depending on the end-use application and related design requirements. For example, the drive belts  255 A may include continuous fiber reinforcement to provide additional load-carrying capability. Referring with particularity to  FIG. 4B , details of one embodiment of the drive (i.e., primary load) belt  255 A construction is shown. In particular, drive belt  255 A includes elongated, axially extending structural fibers  257  embedded in a flexible matrix or support  258 . In one form, the material making up the fibers  257  imparts a high tensile strength and low stretching/elongation to the drive belt  255 A; such material may be a carbon fiber-based material such as that found in U.S. Pat. No. 5,807,194 entitled TOOTHED BELT the entirety of which is incorporated by reference herein. Likewise, the material making up the flexible support  258  can be a rubber- or synthetic-based material, such as polyurethane or the like. Additional materials (not shown) may be used to improve environmental resistance, handling, frictional resistance or the like. In a preferred form, the fibers  257  are continuous and extend for a substantial entirety of the length of the drive belt  255 A as it extends from the counterweight  265  to the crosshead  210 . In a likewise preferred form, the cross-sectional profile of the drive belts  255 A is generally rectangular with the longer of its two lateral dimensions sized to fit within a comparable channel  260 B,  260 C or the like of pulley  260 . Although the fibers  257  are presently shown as only being present in the base (i.e., flat) portion of the support  258  of drive belt  255 A, they may also be present in the portion that corresponds to the teeth  256 , and in such case may be made of discontinuous (i.e., chopped) fiber reinforcements. In another variant (not shown), the fibers  257  are present throughout a partial depth of the base portion of the support  258  of drive belt  255 A, while the teeth may or may not include additional reinforcement. 
         [0024]    In one non-limiting form, the profile of teeth  256  of the belt  255  (whether in the form of the primary load belt  255 A or the secondary load belt  255 B) can be generally trapezoidal in shape (including curvilinear variants) with a belt thickness, tooth height and tooth-to-tooth spacing suitable for the belt operational environment. In one non-limiting configuration suitable for use with the pulleys  260  that may be used with decoking system  1 , the primary load belt  255 A may include a roughly 0.55 inch spacing between adjacent teeth that are about 0.25 inch tall as part of a belt maximum thickness of about 0.40 inch. The teeth  261  of the companion pulley  260  may be similarly shaped and sized to promote secure engagement between them during belt-to-pulley meshing. The speed of the drive system is such that it imparts a relatively low rotational speed to the pulley  260 ; in one form, such speed is no more than about 10 revolutions per minute (rpm) for a pulley  260  with a diameter of between about 24 and about 36 inches. Likewise, the width of each channel  260 A,  260 B,  260 C or  260 D may be between about 1.5 and 2 inches. By using the non-metallic belts  255  of the present invention, the inventor believes that between about 2,000 and 4,000 pounds may be reduced from a 15,000 pound cutting train of the decoking system  1 . Furthermore, this permits removal of winches and secondary safety equipment (the latter of which often requires extensive periodic maintenance) to further simplify the system  1 . 
         [0025]    By way of the four-channel variants shown in  FIGS. 3C, 3D and 4C , two of the belts  255  may be of the primary load belt  255 A variety; each would include substantially continuous carbon fiber reinforcement along the belt longitudinal axis; as discussed above, these belts  255 A will include teeth  256 . Thus, each four-channel pulley  260  would include two of these primary load belts  255 A to engage the corresponding teeth  261  to transfer the forces due to the cutting train load. The remaining two of belts  255  would be the secondary load belt  255 B that could define a flat or rectangular cross-sectional profile with no teeth. This belt  255 B, as well as the corresponding channel  260 D, will remain as part of the fail-safe operation in the event one of the primary load belts  255 A fail. Various material choices, dictated by cost, ease of manufacture, load-bearing abilities or the like, may be used; such materials may include engineered plastics (such as with Dyneema® or related ultra high molecular weight polyethylene fibers). 
         [0026]    The system fail-safe characteristic may be achieved in different ways. For example, a sensor-based device (not shown) as part of a condition monitoring system may be included to continually monitor belt  255  tension to look for evidence of wear; such a device may be coupled to a processor-based controller (not shown) that includes a comparitor, algorithm or other means for determining when belt  255  replacement is necessary. In a related way, the condition of the driving belts  255 A can potentially be monitored using optical methods coupled with image processing algorithms that are cooperative with such a controller. In a more particular form, once one of the belts  255  is determined to be in need of replacement, it can be done while leaving the others in place. In another form, the fail-safe operation may be achieved by having one or more secondary belts  255 B configured to engage the pulley  260  in such a way that the corresponding one or more of the channels  260 A- 260 D of the pulley  260  are devoid of teeth or other belt-engaging enhancements, thereby making the cooperation between them based solely on frictional contact between their contacting surfaces. In other words, because the weight of the system  200  is always counterbalanced, the secondary load belts  255 B only need to overcome inertia loads, making manipulation of the system  200  into a more favorable belt-replacement location simpler. In this configuration, the secondary load belt  255 B remains substantially unloaded, over a flat pulley without carrying any load during normal raising and lowering operations of the system  200 , decoking tool  10  and rotary joint  30 , but capable of holding the full load in its present position if the primary load belt part of system  200  breaks. In such circumstance, a new primary load belt  255 A may replace the one that failed, while the secondary belt  255 B is robust enough to permit some movement of the system  200  to a more convenient position to change the effected belts. 
         [0027]    The secondary load belt  255 B (which is shown in cross-sectional profile in  FIG. 3D ) is preferably made from an engineered plastic material (such as Dyneema® as mentioned above) in order to impart to it enhanced mechanical (for example, strength) properties. Such engineered plastic may include a blend of various materials, including continuous or discontinuous fiber reinforcement; in the former configuration, secondary load belt  255 B may generally resemble the primary load belt  255 A with its toothed features, although perhaps with a lighter fiber loading. In yet another form, such engineered materials may include those with very small (i.e., nanotechnology-sized, for example, below about 10 nanometers in diameter) particles or related reinforcement materials. Likewise, in another form, these fail-safe secondary belts  255 B may be of similar construction as that of primary load belts  255 A, or may be made of a simpler construction, such as by not including any fiber reinforcement, maintaining a strictly flat (i.e., rectangular cross-sectional profile) shape, or the like. 
         [0028]    Referring again with particularity to  FIG. 4C  in conjunction with  FIG. 4B , in one form, pulley  260  includes two side-by-side channels  260 B and  260 C. Each belt  255  is about 1.75 inches wide; with teeth, each two-channel pulley  260  may carry up to about 15,000 pounds of load (making the total rating for a two-pulley system about 30,000 pounds for a safety factor of about two for a notional 15,000 pound cutting train). Thus, if two of the four belts  255  are operational, an ongoing cutting operation may be completed before changing the belts. Even in situations where the two belts  255  that fail are on the same pulley  260 , the secondary load belt  255 B will still keep the crosshead  210  leveled to move it into a position where the broken belt can be replaced, as the actual load across the system  200  remains substantially weight-balanced. In another form, pulley  260  includes four side-by-side channels  260 A,  260 B,  260 C and  260 D. Thus, if the six of the belts  255  (of a total of eight belts for a two-pulley system) fail, the previously-dormant flat secondary belt  255 B will engage and hold the load. In such case, it may be necessary to use a separate portable winch to slowly bring the crosshead  210  up to where repair personnel can access it to connect one new belt  255  in each pulley  260 . The gearbox  224  may be equipped with a worm gear to avoid rotation with the force coming from the weight-driven side. Using the exemplary form of  FIG. 4C , if all three of the primary load belts  255 A in one side of the crosshead  210  are cut, the fail-safe secondary load belt  255 B is strong enough to hold the load and consequently keep the crosshead  210  leveled; this in turn allows the other three still-functioning primary load belts  255 A on the opposite side of the crosshead  210  to continue to move the crosshead  210  up and down Likewise, if subsequently these other three drive belts in the other side collapse, the fail-safe secondary load belt  255 B on that side will also hold the load in place. At this point, a service technician has a few repair options. First, some of the primary load belts  255 A may be replaced; as mentioned above, the load-bearing capacity of the secondary load belts  255 B along with the counterweight-based design of the system  200  permits the system  200  to be move to a position at which the broken primary load belts  255 A may be replaced. Another option is to lift or lower the (still balanced) cutting train with temporary ropes until the crosshead  210  gets to a point in which the broken primary load belts  255 A can be changed easily. 
         [0029]    An additional cover  275  may be placed over the top of the pulleys  260  in order to keep debris from collecting on them or belts  255 . Such cover  275  may also include an optically-transparent inspection window to allow quick visual assessment of the belts  255 . Cover  275  may also include cutouts defined in its lower surface that are shaped to complement that of the radially-outward edge of pulley  260  in order to keep the belts  255  from jumping out of the channels  260 A through  260 D; this can be seen with particularity in  FIG. 3D . Even though the cover  275  is particularly well-suited for configurations where the pulley  260  is toothed, it also works with the other versions discussed herein as well. 
         [0030]    Referring next to  FIG. 5 , an alternate configuration for a toothed version of the pulley  260  and belt  255  of  FIG. 4A  is shown in an inverted form for clarity of view. In actual use, the drive belt  355  would be situated above the pulley  360  such that instead of teeth (such as teeth  256  of the belts  255 ,  255 A of  FIGS. 4A and 4B ), it includes cutouts  356  formed therein that would engage the teeth  361  of the pulley  360  near the top in order to permit the belt  355  to fulfill its weight-bearing function for the crosshead  210  and ancillary equipment. In a manner similar to pulley  260  with teeth  261 , belt  355 —which while continuing to define a generally rectangular cross-sectional profile—now includes numerous apertures or cutouts  356  that are of a generally oval or rectangular shape with the prolate axis oriented widthwise (i.e., across the width W) on belt  355 . The size of the cutouts  356  formed along the length L is such that their dimensions could be generally similar to that of the teeth  361  that are formed on pulley  360 , depending of the nature of the engineered material (an example of which is Dyneema®, carbon fiber or the like) that is used for the belt  355 . In one form, these cutouts  356  may be lined with an additional wear resistant fabric-reinforcement, to achieve better edge distribution of the load. As such, of the two types of belts discussed herein (i.e., the load-bearing primary or drive belts and the secondary fail-safe belts), the first preferably include teeth or cutouts such that they can be used with toothed pulleys, while the second preferably defines a rectangular cross section without teeth or holes such that these latter belts act as a sling. 
         [0031]    It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention Likewise, for the purposes of describing and defining the present invention it is noted that the term “substantial” (and its variants) is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
         [0032]    Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.