Rotary coke drum un-heading valve

Abstract

A rotary coke drum un-heading valve adapted for engagement to an extremity of a coke drum having an orifice therein. The rotary coke drum un-heading valve includes a valve body, having a passage which extends therethrough along a mass flow axis and at least two valve seats that circumscribe the passage. The passage is aligned for mass flow communication with the orifice. A rotatable flow obstructing member defines a bore therein and is rotatable within the valve body between an open position, wherein the bore is in communication with the passage permitting mass flow through the un-heading valve, and a closed position, wherein mass flow through the un-heading valve is prevented by the flow obstructing member. In one embodiment, the flow obstructing member is a gate pivotable in a plane perpendicular to the mass flow axis by a valve stem rotatable about its central axis which intersects the plane.

Description

TECHNICAL FIELD

The present invention relates generally to a device for opening and closing a vessel containing hazardous materials, and more particularly an un-heading system for a coke drum and an un-heading valve for such a system.

BACKGROUND OF THE INVENTION

Delayed coking is a process employed in petroleum refineries to recover the heavy residual oil by-products left over after regular refining operations have been completed. Such recovered distillates and coke are typically emptied into large, vertical pressure vessels called coke drums or coking drums. Coke drums accordingly serve as waste disposal systems for high residual, tarry oils. Volatile fumes from the coke drums are recycled to make useful products such as gasoline and the solid material deposited in the coke drum is resold as coke for a variety of purposes. Delayed coking thus contributes significantly to the gross margin of the refineries and therefore to their overall financial performance. As such, the efficient operation of the delayed coking operations is vital.

Delayed coking is typically performed using pairs of coke drums, which are alternately filled and emptied in a continuous batch operation. Filled coke drums must be emptied such that the desirable hydrocarbon by-products can be saved. This process of emptying a coke drum is often called de-coking. Generally, one coke drum is filled with the refining by-products while the other is being emptied, or de-coked. Once fully emptied and resealed, the by-products can then be redirected to the empty drum, so that the filled drum can in turn be de-coked.

De-coking typically involves cooling the entire drum by quenching with steam followed by water, and purging the drum of all coke built up therein. Coke which is not loose within the drum must be forcibly removed, usually by cutting the coke from the walls of the drum using high pressure water. Often, a drilling rig on top of the drum is used which directs water under high pressure into the drum to fracture the solid coke bed so the coke can be removed for sale. In order to permit this, the top and/or bottom heads of the drum are typically removed to provide access to the inside of the drum and to permit the dislodged coke to fall from the drum into a waiting receptacle below. The removal or displacement of the top and/or bottom heads of the coke drum such that the built up coke therein can be removed is called un-heading or de-heading the coke drum.

The heads of such huge coke drums have, in the past, been completely removed with each de-coking cycle. As coke drums are typically in the range of 20-30 feet in diameter and 100 feet in height, the sheer size of the heads of such drums caused their removal to be a process which was fraught with danger, both to the operators and the surrounding equipment. Many other risks have been assumed in the past by workers who carry out the removal of such coke drum heads during the de-coking process. For example, during the loosening and removal of the bottom head, un-drained water (which has become heated during the quenching process) and chunks of loose coke can fall onto workers below. Workers also run the risk of being exposed to hazardous materials and fumes from the drum when the heads are opened.

As such, attempts have been made to devise automated un-heading systems which can be remotely operated to remove at least the bottom head of a coke drum, thereby limiting the risks assumed by workers during the de-coking operation. For example, U.S. Pat. No. 4,960,358 issued to DiGiacomo et al. on Oct. 2, 1990 discloses a bottom un-heading device for coke drums which includes a heat unit removably connected to a lower end of the coke drum by swing bolts which can be disconnected by remotely operated de-tensioning equipment. Thus, the fastening mechanism between the bottom head and the drum can be remotely disconnected such that the cover unit can be completely removed from the drum by a displaceable platform device. U.S. Pat. No. 5,785,843 issued to Antalffy et al. on Jul. 28, 1998 also discloses a coke drum de-heading device, wherein the coke drum head is hinged from the drum body by a compound joint which reduces the amount of headroom required to swing the disengaged head away from the drum. An actuator is used to remotely move the hinging head between open and closed positions.

However, while systems such as those described above are remotely operable to minimize the risks to human operators, any procedure which requires the coke drum head to be disengaged from the drum, whether by hinged operation or otherwise, remains dangerous. The complex nature of such mechanisms and the size and weight of the coke drum heads they displace, nevertheless leave open the possibility of catastrophic consequences should the mechanism or a part thereof fail. As such, more recent attempts to simplify the de-heading process and make it more efficient and safe have been made

U.S. Pat. No. 6,565,714 issued to Lah on May 20, 2003 addresses exactly this problem, by providing a coke drum de-heading system which comprises a rising stem, horizontally positioned de-header gate valve. The de-header valve comprises a linear sliding blind, displaceable in a by-directional manner within the de-header valve between opposed static and live loaded valve seats. Thus the linear sliding blind acts to open and close the bottom of the coke drum, thereby obviating the need to remove the entire bottom head. The de-header valve is coupled to the coke drum, preferably the bottom thereof. Thus, actuation of the linearly sliding blind of the valve from a closed position to an open position de-heads the coke drum.

However, deficiencies exist with the linear gate de-header valve design disclosed by Lah. Particularly, the linear motion of the stem increases the risk of causing leaks in the valve packing as a result of the dirty service encountered when positioned at the bottom of a coke drum, and the linearly displaceable blind requires guiding during its closing stroke by guide plates and stem bushings which can also become clogged and galled by the coke particles to which they are exposed. Another major problem with the de-header valve taught by Lah is the relatively large amount of space which it requires around the coke drum. As the long valve stem is horizontally displaced together with the linearly travelling sliding blind, the overall length of the entire de-header valve assembly could actually be greater than the diameter of the drum itself, as seen in FIG. 2 depicted by Lah, and can therefore transversely protrude well beyond the drum support structure which can prevent access to the protruding portions of the valve Thus, although only limited bottom headroom (the space available below the bottom head and the base or support substrate of the coke drum) is required, the overall length of the sliding blind de-header valve disclosed may be a long as 30 feet. This can be problematic for a number of reasons. The protruding end of the actuator in the de-header valve taught by Lah can overhang the entire coke drum structure, limiting the access to parts of the valve. Further, while new coke drum installations could be designed to accommodate such a long and protruding bottom head valve, existing older coke drums already in service would be difficult to retrofit with such large de-header valves due to relatively limited clearances around the equipment.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved system for un-heading a coke drum.

It is another object of the present invention to provide an improved coke drum de-header valve which is compact and reliable.

Therefore, in accordance with the present invention, there is provided a rotary coke drum un-heading valve adapted for engagement to an extremity of a coke drum having an orifice therein, the coke drum un-heading valve comprising: a valve body having a passage extending therethrough along a mass flow axis and at least two valve seats circumscribing said passage, said passage being aligned for mass flow communication with said orifice; and a rotatable flow obstructing member defining a bore therein, said flow obstructing member being rotatable within said valve body in contact with said valve seats between an open position, wherein said bore is in communication with said passage permitting mass flow through said un-heading valve, and a closed position, wherein mass flow through said un-heading valve is prevented by said flow obstructing member.

There is also provided, in accordance with the present invention, a coke drum un-heading system comprising: a coke drum having an orifice in at least one extremity thereof; a rotary un-heading valve fastened to said extremity in mass flow communication with said orifice and being selectively operable to seal and open said orifice such that one of mass flow into and out of said coke drum is possible; and said rotary un-heading valve comprising a valve body having a passage extending therethrough along a mass flow axis and valve seats circumscribing said passage, said passage being in mass flow communication with said orifice; a rotatable flow obstructing member defining a bore therein, said flow obstructing member being rotatable within said valve body in contact with said valve seats between an open position, wherein said bore is in communication with said passage permitting mass flow through said rotary un-heading valve, and a closed position, wherein mass flow through said rotary un-heading valve is prevented.

There is further provided, in accordance with the present invention, a method of un-heading a coke drum having an orifice in at least one extremity thereof, the method comprising: providing a rotary un-heading valve fastened to said extremity in mass flow communication with said orifice; and rotating a flow obstructing member within said rotary un-heading valve about a pivot axis between a closed position, wherein mass flow through said rotary un-heading valve is prevented by said flow obstructing member, and an open position, wherein mass flow through said rotary un-heading valve is permitted.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

FIG. 1 is a schematic side elevation view of a coke drum having a bottom un-heading valve in accordance with the present invention;

FIG. 2 is a schematic perspective view of the coke drum bottom head and the un-heading valve in accordance with the present invention;

FIG. 3 is a perspective view of the coke drum un-heading valve of the present invention;

FIG. 4 is a top plan view of the coke drum un-heading valve of FIG. 3;

FIG. 5 is a cross-sectional view taken through line 5-5 of FIG. 4;

FIG. 6 is a side elevation view of an un-heading valve of FIG. 3;

FIG. 7 is a cross-sectional view taken through line B-B of FIG. 6, showing the valve fully open;

FIG. 8 is a cross-sectional view taken through line B-B of FIG. 6, showing the valve fully closed;

FIG. 9 is a cross-sectional view taken through line B-B of FIG. 6, showing the gate partially open;

FIG. 10 is a detailed cross-sectional view of the biased valve seat, taken from detail C of FIG. 5;

FIG. 11 is a top perspective view of a coke drum un-heading valve in accordance with an alternate embodiment of the present invention, showing the valve fully open; and

FIG. 12 is a top perspective view of a coke drum un-heading valve in accordance with another alternate embodiment of the present invention, showing the valve fully closed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As schematically shown in FIG. 1, a vertically oriented pressure vessel, such as a coke drum 12 as employed in the delayed coking process of a petroleum refinery, is supported by an adjacent support structure 11 mounted on a lower platform 13 below the coke drum 12. Such delayed coking drums typically have a diameter between about 20 and 30 feet and stand about 75 to 100 feet tall. The lower portion 14 of the coke drum 12 may have a conical shape and terminates in a lower flange 16 which may be in the range of 5 to 10 feet in diameter and which defines a bottom orifice of the coke drum 12 through which the contents of the drum may be evacuated during the decoking cycle. A coke drum un-heading valve 20 is fastened to said lower flange 16 in fluid flow communication with the orifice defined in the base of the coke drum. The un-heading valve 20 is selectively operable to seal the orifice while the coke drum is being filled and open the drum orifice such that mass flow out of the coke drum and through the exit chute 18 is permitted during the decoking cycle of the coke drum. The un-heading valve 20 is opened and closed by an actuating system 22.

Referring now to FIG. 2, the coke drum de-heading system is shown in greater detail, wherein the lower flange 16 at the base of the conical lower portion 14 of the coke drum 12 is matingly fastened to the un-heading valve 20 disposed in line between the lower flange 16 of the coke drum and the mass flow exit chute 18 which extends through the lower platform 13 to expel contents of the drum into a receptacle (not shown) positioned beneath the chute. The un-heading valve 20, which will be described in greater detail below, is positioned in line and in mass flow communication with the orifice defined within the lower drum flange 16 such that opening and closing of the un-heading valve, respectively opens and seals the bottom head of the coke drum. Thus, with the valve in an open position, mass flow through the valve from the inside of the coke drum 12 to the exit chute 18 is permitted such that decoking of the coke drum is possible. With the valve in a closed position, the bottom head of the coke drum is sealed such that refilling of the coke dram by the delayed coking by-products of the refining process is enabled. Although described here with reference to the bottom of the coke drum, it is understood that the un-heading valve 20 may also be disposed at the top of the coke drum in communication with a top orifice defined therein.

The un-heading valve 20 is a rotary valve which provides dead end isolation for the bottom and/or top orifices in a coke drum. The rotary un-heading valve of the present invention can be any type of rotary valve in which the flow obstructing member travels in a rotary or pivoting motion between the open and closed positions. For instance, the rotary un-heading valve of the present invention may be a rotary gate valve, a ball valve or a butterfly valve for example, which is adaptable to the severe service conditions of the delayed coking environment. In a preferred embodiment described below, the rotary un-heading valve is a rotary gate valve, pivotable in a plane substantially perpendicular to the direction of mass flow by a valve stem which is preferably parallel to the direction of mass flow. However, it is to be understood that the rotary un-heading valve can also be another type of rotary valve as defined above.

In the preferred embodiment of the rotary un-heading valve 20, rotation of the valve stem 50 about a central axis 30 thereof enables pivoting of the flow obstructing member, in this case a rotatable gate 44, within a plane which is substantially transverse to a direction of mass flow 32 through the valve body, between open and closed positions. Although the central axis 30 at least intersects the plane, it is preferably perpendicular thereto. The actuating system 22 employed to rotate the valve stem 50 preferably comprises an elongated torque arm 26 to which the valve stem 50 is engaged at a center thereof such that a portion of the torque arm protrudes outwardly from the valve stem, preferably substantially perpendicular thereto. Thus, rotation of the torque arm 26 about the axis 30 causes the necessary rotation of the valve stem in direction 34. Preferably, both opposed ends of the torque arm 26 are pivotably linked to a translating end of a linear actuator 24 used to push and pull in opposite direction from each other to rotate the torque arm about the central axis 30. Although only a single linear actuator 24 is necessary to rotate the torque arm, and therefore the valve stem, to open and close the gate of the un-heading valve, two such actuators 24 may be provided to ensure a redundancy such that failsafe operation of the actuating system 22 to open and close the un-heading valve 20 is ensured. Further, the actuating system comprises a computerized control system having at least a microprocessor programmed with logic which ensure a safe operation of the valve.

Referring to FIGS. 3 and 4, the rotary un-heading valve 20 comprises generally an outer valve body 36, which in the embodiment shown includes first and second portions 36 and 39 joined together at a bolted flange 41. The first portion 38 of the outer valve body 36 comprises upper and lower spaced apart walls 40 and 42 between which a substantially flat gate 44 is received for displacement within the outer valve body. The upper and lower walls 40 and 42 define corresponding and concentric apertures 45 therein to create a passage 46 extending through the valve body 36. Flanges 48 circumscribe the apertures 45 on each of the upper and lower walls 40 and 42, and are respectively fastenable to the lower flange 16 of the coke drum 12 and the coke chute 18. The gate 44 defines a bore 48 therein which may be selectively aligned with the apertures 45 of the upper and lower walls of the valve body to permit mass flow through the valve passage 46 along a mass flow axis 49, as will be described in greater detail below. Particularly, the gate is rotatable between open and closed positions in a plane substantially perpendicular to the mass flow axis 49 by a valve stem 50, itself rotatable about its own longitudinal axis 52 which is substantially parallel to the mass flow axis 49, and therefore also substantially perpendicular to the plane within which the gate 44 is rotated.

As seen in FIG. 5, the gate 44 is rotated by the valve stem 50, within the substantially horizontal plane 56, between open and closed positions of the valve. The valve stem 50 is rotatable about its longitudinal axis 52 which is substantially parallel to the mass flow axis 49 and perpendicular to the plane 56. Thus the bore 48 defined within the gate 44 can be selectively aligned with the apertures 45 in the upper and lower walls 40 and 42 of the outer valve body 36 to open or close the passage through the valve. Upper and lower valve seats 58 and 60 are positioned within the valve outer body circumscribing the apertures 45 therein, and respectively mate with the upper surface 62 and lower surface 64 of the gate 44. The valve seats 58 and 60 accordingly provide a sealing contact with the gate which pivots and is guided therebetween on at least guiding surfaces of the valve seats. Particularly, the gate is self-aligned between the opposed valve seats at all times and throughout the opening and closing strokes of the gate. This becomes especially useful under differential thermal expansion, for example when the hot contents of the coke drum first hits the relatively cooler valve. As the valve seats 58,60 maintain contact with the pivoting gate 44 throughout its rotary stroke and the gate is self-aligning relative to the valve stem, the valve seats alone guide the gate as it is pivoted between open and closed positions. Accordingly, no additional guiding structure is required. In contrast, the gates of a rising stem linear gate valves of the prior art require additional guide plates and stem bushings to guide the gate during at least the closing stroke thereof. These additional components increase the risk of becoming caked with coke, which can cause damage to the valve seats and the additional guide components, eventually leading to leaking during service. Particularly, the significant linear movement through the packing of the rising stem of prior art linear gate valves, greatly increases the risk of leaking during the severe and dirty service to which they are exposed when employed in a coke drum un-heading valve. If coke particles get into the guide components of the linear gate valves, the gate position can change resulting in unloading of a valve seat and accordingly leakage through the valve. Additionally, the rotary motion of the gate 44 minimizes movement in the packing box of the valve body, thus enabling a superior stem seal and reducing the possibility of packing leaks.

At least the upper valve seat 58 is biased against the upper surface 62 of the gate 44 by a biasing device, such as bellows, Belleville washers, a graphite stack and/or wave springs. In the depicted embodiment, the biasing device comprises bellows 66 which make the upper valve seat 58 a live-loaded seat which exerts a constant load force on the upper surface 62 of the gate 44. Thus, extremely minimal tolerances can be maintained between the surfaces of the gate and the upper and lower valve seats throughout the entire stroke of the rotatable gate 44 within the plane 56. Preferably, the biasing device does not require any external adjustments once installed in place between the upper valve seat and the upper wall 40 of the first portion 38 of the valve outer body. Accordingly, no additional seat force adjustments, such as external seat force adjusting screws, exist which can increase potential leak paths through the valve. Additionally, the biasing device preferably provides a fixed predetermined load force on the upper valve seat about its entire circumference, thus eliminating the possibility of improper adjustment causing non-uniform seat loading, which is possible with live-loaded valve seat systems of the prior art that employ external adjusting means about the entire circumference of the live-loaded seat. The lower valve seat 60 may be either a fixed seat, as shown in FIG. 5, or may alternately be loaded against the lower surface 64 of the gate 44 by a similar biasing device. In this case, both the upper valve seat 58 and the lower valve seat 60 are live-loaded to exert a constant predetermined load on the opposed surfaces 62,64 of the gate 44.

In order to ensure pressure boundary integrity within the un-heading valve 20, as in all gate valves, an effective working seal must exist between the moving valve stem and the valve body. Thus, the stem seal is a very important element to ensure complete pressure containment and is also often the most common site for fluid leakage through a valve because this a dynamic seal. The rotary motion of the valve stem 50 permits a greatly improved packing integrity which reduces the possibility of leaks through the valve stem packing in comparison to rising stems of linear gate valves of the prior art, where packing leaking about the stem is common for valves in dirty service. Particularly, such rising valve stems of the prior art typically employ a single packing box wherein the stem must be retained from blowing out.

The packing of the valve stem 50 which extends completely through the un-heading valve 20 comprises a double packing box 70, having upper and lower valve stem packing 72 and 74 which seal the valve stem 50 on either side of the gate 44. This permits the pressure acting on the stem to be equalized at both upper and lower sealing points, ensuring that, together with the fact that the valve stem 50 is substantially perpendicular to the gate 44, the valve stem is blowout proof. Thus, no additional need for anti-blowout shoulders on the stem and/or thrust washers, which are typically employed in prior art rising stem un-heading gate valves. The design of the double packing box 70 also ensures that the stem is axially self aligned, allowing the gate to be itself axially self aligned between the opposed valve seats. Outer stem gasket seals 76 are provided about the valve stem, and are preferably spiral wound gasket inserts which provide improved sealing over traditional packing ring-style seals. In addition to a standard packing arrangement, the packing chamber relies on a steam purge sealing arrangement which allows for steam block to ensure a superior seal in the upper packing chamber. The upper packing chamber is of modular design which simplifies maintenance.

The gate 44 is engaged to the valve stem 50 by valve stem keys 68, which fit within corresponding keyway slots in both the valve stem and the gate. The gate 44 is therefore rotatable within the plane 56 by a corresponding rotation of the valve stem 50. The keyed engagement between the gate 44 and the stem 50 permits a limited amount of play in an axial direction (ie: in a direction parallel to the mass flow direction 49). As such, the gate is axially self-aligning between the opposed valve seats at all times. This ability to self-align permits the gate to be maintained in constant contact with the valve seats, even when thermal growth differentials between the two parts occur.

As seen in FIGS. 6-9, the outer valve body 36 of the un-heading valve 20 is substantially half-moon shaped, and the pivotable gate valve 44 has a partially oval-shape with a curved outer edge 53 having a radius of curvature which substantially corresponds to that of an outer wall 55 of the valve body. The gate 44 accordingly has a total rotary stroke of approximately 70° between the fully open position, shown in FIG. 7, and the fully closed position, shown in FIG. 8. FIG. 9 shows the gate 44 partially open, particularly about 15° from the fully open position, in which a relatively large unsupported area of the lower valve seat 60 occurs as the gate is pivoted within the valve outer body by the rotatable valve stem 50. When moving between the open and closed positions, the leading edges of the gate 44, which are in tight tolerance abutment with the valve seats, provide a scraping action which tends to remove any coke build-up on the valve seats. Similarly, the valve seats remove any coke build up on the flat surfaces of the gate. To improve the service life and valve effectiveness, the gate 44 may also be hardness treated using an air-cooled spray, such as for example, HVOF2, hard chrome plating and/or nitriding.

Referring now to FIG. 10 showing the live-loaded upper valve seat 58 in greater detail, the biasing device 66 is permanently loaded at one end to a portion of the valve body 36 and at an opposed end to the upper valve seat 58. Thus the valve seat 58 is constantly biased in fixed load contact with the upper surface 62 of the pivotable gate 44 throughout its entire stroke within plane 56. The constant dynamic load provides a seal through a range of fluctuating temperatures and ensures that the scraper edged valve seat maintains the blind/gate free of coke build-up.

Referring to FIG. 11, the rotary coke drum un-heading valve 120 is operated by an actuating system 122 mounted directly on the outer valve body 36. The actuating system 122 includes actuators 24, each having one end thereof fixed to the outer valve body by mounting brackets 137. The actuators 24 are disposed in a common plane and orientated at an angle relative to each other, generally defining a V-shaped configuration. Each actuator has a longitudinal axis, which intersect one another at a point remote from the valve. The movable ends 35 of the actuators are accordingly linearly displaceable along their respective longitudinal axes, in opposed movement to each other. Thus, as one actuator retracts, the other extends a corresponding distance and at a corresponding rate. The moveable ends 35 of the actuators are pivotably engaged at opposed ends of the torque arm linkage 126, which is fixed to the valve stem 50 at a point between the opposed ends of the torque arm linkage. Thus, the actuators act to rotate the torque arm linkage 126 about the valve stem 128, causing the gate 44 of the valve to open and close. Although both actuators can be driven simultaneously to exert the most torque on the torque arm linkage 26, as noted above one of the two actuators alone is capable of operating the valve.

In FIG. 12, another configuration of the actuating system is provided. Particularly, the rotary un-heading valve 220 includes an actuating system 222, also having two actuators 24 which are mounted to the outer valve body 36 by mounting brackets 237. However, the actuators 24 of the actuating system 222 are substantially linearly aligned, such that their longitudinal axes are near co-linear. In this configuration, the actuators 24 act to push and pull in opposed relation to each other in order to pivot the torque arm linkage 226 between open and closed positions thereof, thereby opening and closing the gate. The torque arm linkage 226 therefore has a first end fixed to the valve stem 50 and an opposed second end pivotably connected to the movable ends 35 of the actuators 24.

The rotary un-heading valves 20,120,220 provide a generally compact overall footprint in comparison with the significantly larger rising stem linear gate valves of the prior art. Particularly, the un-heading valves of the present invention preferably fit within a perimeter defined by the outer wall of the coke drum. This allows for an easier retrofit of existing delayed coke drums, wherein space surrounding the drum is at a premium. In many such existing delayed coke drums, the limited space available proves often too small to permit a relatively large and cumbersome un-heading gate valve to be installed onto the coke drum as a retrofit operation. In addition to its more compact nature, the rotary un-heading valves 20,120,220 provide, due generally to the rotary movement of the flow obstructing member, improved sealing and reliability. These become vital factors for severe service uses such as delayed coking or nuclear applications, for example.

The embodiments of the invention described above are intended to be exemplary. Those skilled in the art will therefore appreciate that the forgoing description is illustrative only, and that various alternatives and modifications can be devised without departing from the spirit of the present invention. Accordingly, the present is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.

Claims

1. A rotary coke drum un-heading valve adapted for engagement to an extremity of a coke drum having an orifice therein, the coke drum un-heading valve comprising:

a valve body having a passage extending therethrough along a mass flow axis and at least two valve seats circumscribing said passage, said passage being aligned for mass flow communication with said orifice; and

a rotatable flow obstructing member defining a bore therein, said flow obstructing member being rotatable within said valve body in contact with said valve seats between an open position, wherein said bore is in communication with said passage permitting mass flow through said un-heading valve, and a closed position, wherein mass flow through said un-heading valve is prevented by said flow obstructing member.

2. The rotary coke drum un-heading valve as defined in claim 1, wherein said flow obstructing member is a gate.

3. The rotary coke drum un-heading valve as defined in claim 2, wherein said gate is rotatable within said valve body in a plane.

4. The rotary coke drum un-heading valve as defined in claim 3, wherein said plane is substantially perpendicular to said mass flow axis.

5. The rotary coke drum un-heading valve as defined in claim 4, wherein a valve stem is engaged to said gate, said valve stem being rotatable about a central axis thereof which intersects said plane.

6. The rotary coke drum un-heading valve as defined in claim 1, wherein said valve seats provide guiding surfaces thereon for guiding said flow obstructing member during opening and closing strokes thereof.

7. The rotary coke drum un-heading valve as defined in claim 5, wherein said central axis is substantially parallel to said mass flow axis and substantially perpendicular to said plane.

8. The rotary coke drum un-heading valve as defined in claim 1, wherein at least one of said valve seats is biased against said flow obstructing member by a biasing device.

9. The rotary coke drum un-heading valve as defined in claim 8, wherein said biasing device provides a load force which is constant about said at least one valve seat.

10. The rotary coke drum un-heading valve as defined in claim 9, wherein said biasing device has fixed spring properties which define said load force.

11. The rotary coke drum un-heading valve as defined in claim 9, wherein said biasing device includes at least one of bellows, springs, Belleville washers and graphite stacks.

12. The rotary coke drum un-heading valve as defined in claim 5, wherein a double packing box seals said valve stem with said valve body, said double packing box having packing seals about said valve stem on opposed sides of said gate.

13. The rotary coke drum un-heading valve as defined in claim 12, wherein said double packing box includes bearings disposed about said valve stem on opposed sides of said gate.

14. The rotary coke drum un-heading valve as defined in claim 1, wherein said valve body includes a lower wall surface fastenable to a coke chute.

15. The rotary coke drum un-heading valve as defined in claim 1, wherein said flow obstructing member is hardness treated.

16. The rotary coke drum un-heading valve as defined in claim 1, further comprising an actuating system operable to rotate said flow obstructing member between said open and closed positions.

17. The rotary coke drum un-heading valve as defined in claim 16, wherein said actuating system is remotely actuable.

18. The rotary coke drum un-heading valve as defined in claim 16, wherein said actuating system includes at least one linear actuator operable to rotate said flow obstructing member about a pivot axis and thereby to open and close said rotary un-heading valve.

19. The rotary coke drum un-heading valve as defined in claim 18, wherein said actuating system comprises two linear actuators.

20. The rotary coke drum un-heading valve as defined in claim 19, wherein a torque arm is engaged with said flow obstructing member, said linear actuators being pivotably linked to said torque arm for pivoting said torque arm about said pivot axis.

21. The rotary coke drum un-heading valve as defined in claim 2, wherein a total rotary stroke of said gate between said open position and said closed position is about 70 degrees.

22. A coke drum un-heading system comprising:

a coke drum having an orifice in at least one extremity thereof;

a rotary un-heading valve fastened to said extremity in mass flow communication with said orifice and being selectively operable to seal and open said orifice such that one of mass flow into and out of said coke drum is possible; and

said rotary un-heading valve comprising: a valve body having a passage extending therethrough along a mass flow axis and valve seats circumscribing said passage, said passage being in mass flow communication with said orifice; a rotatable flow obstructing member defining a bore therein, said flow obstructing member being rotatable within said valve body in contact with said valve seats between an open position, wherein said bore is in communication with said passage permitting mass flow through said rotary un-heading valve, and a closed position, wherein mass flow through said rotary un-heading valve is prevented.

23. The coke drum un-heading system as defined in claim 22, wherein said rotary un-heading valve is fastened to a bottom end of said coke drum.

24. The coke drum un-heading system as defined in claim 22, wherein a coke chute is fastened to said rotary un-heading valve in fluid flow communication with an exit aperture of said passage.

25. The coke drum un-heading system as defined in claim 22, wherein said flow obstructing member is a gate.

26. The coke drum un-heading system as defined in claim 25, wherein said gate is rotatable within said valve body in a plane.

27. The coke drum un-heading system as defined in claim 26, wherein said plane is substantially perpendicular to said mass flow axis.

28. The coke drum un-heading system as defined in claim 27, wherein a valve stem is engaged to said gate, said valve stem being rotatable about a central axis thereof which intersects said plane.

29. The coke drum un-heading system as defined in claim 22, wherein said valve seats have guiding surfaces thereon for guiding said flow obstructing member during opening and closing strokes of said gate.

30. The coke drum un-heading system as defined in claim 29, wherein said central axis is substantially parallel to said mass flow axis and substantially perpendicular to said plane.

31. The coke drum un-heading system as defined in claim 22, wherein at least one of said valve seats is biased against said flow obstructing member by a biasing device.

32. The coke drum un-heading system as defined in claim 31, wherein said biasing device provides a load force which is constant about said at least one valve seat.

33. The coke drum un-heading system as defined in claim 31, wherein said biasing device has fixed spring properties which define said load force.

34. The coke drum un-heading system as defined in claim 33, wherein said biasing device includes at least one of bellows, springs, Belleville washers and graphite stacks.

35. The coke drum un-heading system as defined in claim 28, wherein a double packing box seals said valve stem with said valve body, said double packing box having packing seals about said valve stem on opposed sides of said gate.

36. The coke drum un-heading system as defined in claim 35, wherein said double packing box includes bearings disposed about said valve stem on opposed sides of said gate.

37. The coke drum un-heading system as defined in claim 22, wherein said rotary un-heading valve is sized to fit at least within a perimeter defined by an outer wall of said coke drum.

38. The coke drum un-heading system as defined in claim 22, further comprising an actuating system operable to rotate said flow obstructing member between said open and closed positions.

39. The coke drum un-heading system as defined in claim 38, wherein said actuating system is remotely actuable.

40. The coke drum un-heading system as defined in claim 38, wherein said actuating system includes at least one linear actuator operable to rotate said flow obstructing member about a pivot axis and thereby top open and close said rotary un-heading valve.

41. The coke drum un-heading system as defined in claim 40, wherein said actuating system comprises two linear actuators.

42. The coke drum un-heading system as defined in claim 40, wherein a torque arm is engaged with said flow obstructing member, said linear actuators being pivotably linked to said torque arm for pivoting said torque arm about said pivot axis.

43. The coke drum un-heading system as defined in claim 25, wherein a total rotary stroke of said gate between said open position and said closed position is about 70 degrees.

44. A method of un-heading a coke drum having an orifice in at least one extremity thereof, the method comprising:

providing a rotary un-heading valve fastened to said extremity in mass flow communication with said orifice; and

rotating a flow obstructing member within said rotary un-heading valve about a pivot axis between a closed position, wherein mass flow through said rotary un-heading valve is prevented by said flow obstructing member, and an open position, wherein mass flow through said rotary un-heading valve is permitted.

45. The method as defined in claim 44, further comprising rotating said flow obstructing member by rotating a valve stem engaged thereto, said valve stem having a central longitudinal axis coaxial with said pivot axis.

46. The method as defined in claim 45, further comprising remotely actuating rotation of said flow obstructing member using an actuating system.