Seal for sealing a penetration point of a support strap supporting a pyrolysis tube in a pyrolysis chamber

Abstract

A seal for a mid-span support passing through a pyrolysis chamber roof, comprising a seal housing 16, a seal puck 18 retained in the seal housing by a seal retaining plate 17, a seal shaft 15 passing

Description

Description Introduction and background to the invention 5 This invention relates to an improved sealing system for the penetration point of the support strap used in Mid-Span Support systems for Pyrolysis Tubes. Mid-Span Supports have been previously developed to minimize static stresses on Pyrolysis Tubes. While the Mid-Span Support itself represents existing technology, this application focuses specifically on the design for the Seal where the Mid-Span Support strap penetrates the Pyrolysis Chamber roof. 10 Pyrolysis Tubes operate in high temperature environments and are subjected to significant thermal stresses. They must be supported in a way that allows axial and hogging movements while minimizing bending stresses. The Mid-Span Support system, consisting of an exterior lifting device and interior support strap wrapping around the tube, provides an upward force to counteract the tube's self-weight. 15 However, an effective seal design is critical for the penetration point of the support strap through the Pyrolysis Chamber roof, to prevent leaks of hot exhaust gases and ingress of air. The novelty of this invention lies in the seal design that can accommodate the dynamic movements of the support strap while maintaining sealing integrity. The following sections describe this inventive Seal in more detail. 20 Summary of the Invention (Also known as a ‘statement of invention’) While the Mid-Span Support system represents previously developed technology, the focus of this application is the novel Seal design for the penetration point of the support strap through the Pyrolysis Chamber roof. This Seal accommodates multi-axis dynamic movements of the support strap while maintaining sealing integrity, overcoming limitations of seals used 25 previously with the Mid-Span Support system that were prone to degradation fouling and catastrophic leakage in the harsh Pyrolysis Chamber environment. Definitions: Auger - a spiral shaped screw used to transfer material. Creep - a failure mode in which a material deforms or thins over time when subjected to a 30 continued stress. Fatigue - a failure mechanism that involves the cracking of materials and structural components due to cyclic stress. Hogging - is the upward bending deflection of a beam. For the purposes of this document hogging is the bending deflection of the tube due to different temperatures on the sides of the 35 tube. It is not limited to the vertical plan. 21 05 25 Mid-Span Support System - A structural system designed to provide support and reduce stresses on a structure, typically implemented at the midpoint of a span or member. Seal - A device or mechanism designed to prevent the passage of fluid or gas between two adjoining surfaces, typically by forming a tight barrier or closure. 5 Static Stress - A stress that results from a slowly applied load and which does not involve any acceleration forces. Stress corrosion cracking - is the growth of crack formation in a corrosive environment. Thermal expansion - is the tendency of matter to change in shape, volume, and area in response to a change in temperature. 10 List of Figures The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows a schematic diagram of the Pyrolysis Tube support system as detailed in prior art. 15 Figure 2 shows schematically the movement that the Seal must accommodate to allow the axial expansion of the Pyrolysis Tube. Figure 3 shows schematically the movement that the Seal must accommodate to allow the vertical movement of the Pyrolysis Tube due to hogging. Figure 4 shows schematically the movement that the Seal must accommodate to allow the 20 horizontal movement of the Pyrolysis Tube due to horizontal hogging. Figure 5 shows a schematic diagram of the Mid-Span Support with a gravitational lever system Lifting Device. Figure 6 shows a sectional elevation of how the Seal, the Lifting Device Hinge and the Support Strap forms part of the Mid-Span Support System detailed in prior art. 25 Figure 7 shows a sectional elevation of the Seal identifying the parts of the Seal assembly. Figure 8 shows a sectional elevation of the Seal illustrating how the Seal Puck is free to move within the Seal Housing on a horizontal plane. Figure 9 shows a sectional elevation of the Seal illustrating how the Seal Shaft can move vertically and tilt. 30 Detailed Description of the Invention The Mid-Span Support configuration previously developed primarily addresses unrestricted thermal expansion to reduce thermally induced stresses on the Pyrolysis Tube. However, the present invention introduces a novel Mid-Span Support Seal designed to specifically address the challenges associated with sealing the Supporting Strap of the Mid-Span Support System in 35 pyrolysis applications. This inventive seal design represents a significant advance compared to existing elastomeric or bellows seals that fail rapidly in pyrolysis environments. By employing heat resistant metals and tailored clearances, the dynamic multi-axis seal withstands harsh temperatures up to 550°C as well as axial, vertical and lateral movements simultaneously without leakage or degradation. Figure 1 shows the previously developed Mid-Span Support system as background. The remaining figures illustrate the novel Seal, which is the focus of this application. 5 In Figure 1, a Pyrolysis Tube (1) penetrates through a Pyrolysis Chamber (2) that provides heat to the Pyrolysis Tube. In some implementations, heat is provided by hot gases such as exhaust gases at temperatures upto 1000C and the Pyrolysis Tube reaches temperatures ranging from 500 to 900C. Due to the high operating temperature of the Pyrolysis Tube, the Pyrolysis Tube will experience significant thermal expansion. Furthermore, to prolong the life in this arduous 10 environment, of the it is important to minimise the stresses within the Pyrolysis Tube. The pinned support configuration primarily addresses unrestricted thermal expansion to reduce thermally induced stresses on the Pyrolysis Tube. This prior art recommends that the Pyrolysis Tube is simply supported with a Fixed Pinned Support (3) and Sliding Pinned Support (4) as shown in Figure 1. 15 Additionally, a Mid-Span Support System comprising an external Lifting Device (5) and Supporting Strap (6) is detailed in the prior art. This Mid-Span Support System minimises the bending moment stresses caused by the self-weight of the Pyrolysis Tube. This prior art for the Mid-Span Support System identifies that a Seal (7) is required where the Mid-Span Support System penetrates the Pyrolysis Chamber (2), but it does not detail how this Seal is to be LO 20 achieved. CXI The present invention introduces a new design of Seal (7) specifically designed to address the LO challenges associated with sealing the Supporting Strap (6) of the Mid-Span Support System in pyrolysis applications. While the Mid-Span Support System itself represents prior art, the innovation lies in the design and functionality of the Seal, which offers advantageous . 25 capabilities in accommodating the dynamic movements of the Supporting Strap while ensuring effective sealing and operational integrity. The purpose of the Seal (7) is to minimise the ingress of air into the Pyrolysis Chamber (2) if the Pyrolysis Chamber is above atmospheric pressure since leakage of air into the Pyrolysis Chamber is detrimental to the pyrolysis process. Additionally, the Seal must minimise the 30 egress of the hot gases from the Pyrolysis Chamber (2) if the Pyrolysis Chamber is above atmospheric pressure since this is a danger to operatives in the locality and detrimental to the pyrolysis process and the environment. Other requirements of the Seal (7) are listed as follows: • The Seal must accommodate all the movements of the Supporting Strap (6) without 35 limiting the movement in anyway. This includes axial movement, vertical movement and lateral movement. These movements can occur at the same time in varying proportions. • The Seal must withstand the high operating temperature of the working environment. • The Seal must allow the Supporting Strap (6) to be lowered for Pyrolysis Tube (1) removal. 40 • The Seal should be simple and robust to provide a low operating cost. • The Seal should have a reasonably low capital cost. Figure 2 Illustrates schematically the movement that the Seal must accommodate to allow the axial expansion of the Pyrolysis Tube as the Supporting Strap (6) pivots about the Lifting Device Hinge (8). The dotted line shows the pivoted position of the Supporting Strap when the Pyrolysis Tube is hot and has expanded axially. Figure 3 Illustrates schematically the movement that the Seal must accommodate to allow the vertical movement of the Pyrolysis Tube due to hogging. The dotted line (10) illustrates the 5 hogged position of the Pyrolysis Tube due to differential movement in the vertical direction. The Supporting Strap (6) will move upwards through the Seal (7). For clarity, this is additionally shown as an end elevation schematic in Figure 4. Figure 5 Illustrates schematically the movement that the Seal must accommodate to allow the horizontal movement of the Pyrolysis Tube due to horizontal hogging. The dotted line (11) 10 illustrates the hogged position of the Pyrolysis Tube due to differential movement in the horizontal direction. The Supporting Strap (6) will move horizontally through the Seal (7). The distances that the Seal must traverse to accommodate movement in each of the primary directions can be determined by someone skilled in the art. This determination involves considering temperature differentials and the relative positions between the Fixed Pinned 15 Support (3), Sliding Pinned Support (4), and Lifting Device Hinge (8). Additionally, experimentation and measurement can aid in establishing the precise dimensions necessary. Typically, the axial movement will be the most significant, followed by vertical movement, with lateral movement being the least pronounced. / 20 CXI In summary, as the Pyrolysis Tube (1) undergoes axial, vertical, and horizontal movements due to thermal expansion, the Supporting Strap (6) must similarly adjust within the Seal (7) as it pivots about the Lifting Device Hinge (8). Traditional seals are usually designed to function effectively in a single degree of freedom, such as rotary or axial seals. However, there are few conventional seals capable of accommodating multiple degrees of freedom aside from rotation. Metallic expansion joints, sometimes referred to as bellows seals, are one such type that can manage the movements required by the Seal (7). In contrast, elastomeric expansion joint seals are unsuitable due to the high operating temperatures involved. While metallic expansion joints could theoretically work in this application, they come with several drawbacks. These joints would need to be lengthy to accommodate the relatively large 30 movements of the Supporting Strap, increasing the overall height of the Lifting Device Hinge (8) and exacerbating horizontal movements. Moreover, parts of the metallic expansion joint might operate below the acid gas dew point within the Pyrolysis Chamber, leading to dew point corrosion and potentially shorter lifespans and higher replacement costs. The innovation of this invention lies in its capacity to accommodate the multiple degrees of 35 movement required by the Seal while maintaining a low profile and robust design, thus requiring minimal maintenance expenditure. Figure 6 shows how the Seal (7), the Lifting Device Hinge (8) and the Support Strap (6) forms part of the Mid-Span Support System. This sectional elevation shows a pneumatic cylinder as the Lifting Device (5). The Pyrolysis Chamber (2) is a thick structure lined with refractory insulating 40 material. A hole (14) is cut into his refractory insulating material. This hole is shaped to accommodate all possible movements of the Supporting Strap. Figure 7 shows a sectional elevation of the Seal (7) identifying the parts of the Seal assembly. The Supporting Strap (6) is welded to the Seal Shaft (15). Although the Supporting Strap is fabricated from a special alloy such as Inconel Alloy 617 (RTM), the Seal Shaft is fabricated from a lower specification heat resistant alloy such as 304SS since it operates at significantly lower temperature than the Supporting Strap. The Seal Shaft passes through the Seal Puck (18). The Seal Puck is retained within the Seal Housing (16) with a Seal Retaining Plate (17). The Seal Puck is machined from a heat resistant alloy such as 304SS.The materials for the Seal Puck and the Seal Shaft are selected for their heat resistant and corrosion resistant properties. The Seal Housing, Seal Retaining Plate and Seal Puck are circular in shape. Figure 8 shows a sectional elevation of the Seal (7) illustrating how the Seal Puck (18) is free to move within the Seal Housing (16) on a horizontal plane to accommodate the horizontal movement of the Seal Shaft (15) due to the lateral and axial movement of the Pyrolysis Tube. The interface (19) between the Seal Puck and the Pyrolysis Chamber casing is machined and fabricated so that it is sufficiently smooth and flat to allow the Seal Puck to slide freely. The Pyrolysis Chamber is normally under a slight negative pressure. This negative pressure and the weight of the Seal Puck provides a downward pressure on the interface (19). This downward pressure combined with a smooth interface surface provides a sufficiently effective seal for the purposes of this application. The clearance gap (b) between the Seal Puck and the Seal Housing is the same as the clearance gap (c) between the Seal Shaft and the Seal Retaining Plate (17). The clearance gaps (b &c) are approximately 15-20mm and designed to provide sufficient horizontal movement for the Seal. The clearance gap (a) between the Seal Puck and the Seal Retaining Plate is approximately 1 mm and ensures that the Seal Puck is securely retained by free to move even if it expands due to differential temperatures. Figure 9 shows a sectional elevation of the Seal (7) illustrating how the Seal Shaft (15) can move vertically and can also tilt to accommodate the vertical movement of the Supporting Strap (6) and any tilting movement of the Supporting Strap caused by movement of the Pyrolysis tube. The dotted line (19) illustrates and example tilt angle for the Seal Shaft. The Seal Shaft and Seal Puck interface (d) have a free running clearance fit such as D9 / h9 or H9 / d9. The Seal Puck (18) has a bull-nose shape (20) and opens out internally with a clearance gap (e) of approximately 5mm. This shape, dimensions and tolerances allows the Seal Shaft to move vertically freely while also tilting to accommodate the horizontal movements of the Pyrolysis Tube. The clearance fit allows for differential thermal expansion between the Seal Shaft and the Seal Puck and allows for tilting of the Seal Shaft within the Seal Puck. The clearance fit is not so loose that it causes excessive leakage. Although a free running clearance fit between the Seal Shaft (15) and the Seal Puck (18) will allow leakage through the gap, the typical pressure drop between the Pyrolysis Chamber and the atmosphere is slight at 10-30mbar, and the perimeter of the Seal Shaft is small, typically 40mm. This means that the leakage rate through the gap is small and has negligible effect on the pyrolysis process and acceptable safety and environmental implications. The air leakage into the process will have a small advantage in purging the Seal system with fresh air, reducing internal dust deposition, and providing a small cooling affect. 21 05 25

Claims

1. Asealforsealinga penetration pointof a support strap supporting a pyrolysis tube in a pyrolysis chamber, the seal comprising:a seal housing;a seal retaining plate;a seal puck retained within the seal housing by the seal retaining plate; anda seal shaft passing through the seal puck;wherein the seal puck is free to move within the seal housing on a plane; andwherein the seal shaft is free to move within the seal puck along an axis and tilt, wherein the axis is perpendicular to the plane.

2. The seal of claim 1, wherein the seal puck has a bull-nose shape; and wherein a clearance gap is provided between the seal puck and the seal shaft to allow the seal shaft to tilt within the seal puck.

3. The seal of claim 1 .wherein a clearance fit is provided between the seal shaft and the seal puck to allow the seal shaft to move within the seal puck along the axis.

4. The seal design of claim 3, wherein the clearance fit provided between the seal shaft and the seal puck is a H9 / d9 clearance fit.

5. The Seal design of claim 1, wherein the seal housing, the seal retaining plate and the seal puck are fabricated from 304 stainless steel.

6. The seal of claim 1, wherein a clearance gap is provided between the seal puck and the seal retaining plate.

7. A mid-span support system of a pyrolysis tube in a pyrolysis chamber comprising:a seal according to any of claims 1 to 6;a support strap welded to the seal shaft of the seal; anda lifting device attached to the seal shaft of the seal.

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