WO2008096213A1

WO2008096213A1 - Solids handling equipment

Info

Publication number: WO2008096213A1
Application number: PCT/IB2007/054538
Authority: WO
Inventors: Marthinus Jacobus Schutte; Paul Smit Baumann
Original assignee: Sasol-Lurgi Technology Company (Proprietary) Limited
Priority date: 2007-02-07
Filing date: 2007-11-08
Publication date: 2008-08-14

Abstract

A closure component (10) for solids-handling equipment includes a metallic substrate or carrier body (12), and a cemented carbide sealing element (14) metallurgically bonded to the substrate body (12).

Description

SOLIDS HANDLING EQUIPMENT

THIS INVENTION relates to solids-handling equipment. In particular, the invention relates to a closure component for solids-handling equipment, and to a solids- handling closure mechanism.

For some solids-handling equipment, such as a Sasol-Lurgi (trade name) fixed bed dry bottom gasifier, it is necessary intermittently or continuously to load and unload particulate material. In the case of a fixed bed dry bottom gasifier, particulate carbonaceous feedstock is thus loaded, and ash is discharged, respectively through a feedstock closure mechanism and an ash closure mechanism on a batch basis.

Typically, each closure mechanism consists of separate and distinct cone and seat assemblies. The seat and cone assemblies in turn each include or consist of a substrate or carrier body, usually a carbon steel forging, and a separate tungsten carbide sealing element (ring element), fixed to the substrate body. A sealing interface is then in use established by pressing the sealing elements of the seat and cone assemblies against one another under hydraulic action. The closure mechanism has the dual purpose of allowing or denying solids flow as well as providing a differential pressure seal when denying solids flow.

One way of fixing the sealing element to the substrate body involves the use of a clamping ring, bolts and nuts. This approach however provides a leak path between the substrate body and the sealing element, which can lead to premature functional failure of the closure components.

The inventors believe that improved closure components and an improved solids-handling closure mechanism or assembly will be an advantage.

According to the invention, there is provided a closure component for solids-handling equipment, the closure component including: a metallic substrate or carrier body; and a cemented carbide sealing element metallurgically bonded to the substrate body.

The substrate body, or at least a part of the substrate body metallurgically bonded to the sealing element, may be of a graphite cast iron or ductile iron. Ductile iron is also known as spheroidal graphite or nodular cast iron, which is iron containing carbon in excess of its solubility in solid iron. The excess carbon is precipitated during solidification in the form of pure, crystalline graphite spheroids or nodules which are dispersed throughout the casting. Typically, the graphite content of the ductile iron is 8% - 12% by volume.

The substrate body is typically cast onto the cemented carbide sealing element. In order to reduce or totally eliminate differential shrinkage between the substrate body and the sealing element, heat treatment subsequent to the casting is typically employed partly or totally to transform residual austenite in the cast iron substrate body under a volume increase to bainite. The substrate body consequently has a microstructure which typically includes bainite.

A cemented carbide sealing element includes a carbide phase which preferably includes tungsten carbide. Advantageously, tungsten carbide is hard enough to provide extended resistance to wear induced by the flow of paniculate material over the sealing element, to provide erosion resistance in the face of high velocity steam flow, and to cut through a solid particle caught between two sealing elements, during use of closure components in accordance with the invention in a closure mechanism, e.g. a valve, lock or the like for solid particulate material.

The cemented carbide sealing element may also include a binder phase.

The binder phase may include one or more of the metals selected from the group consisting of cobalt, nickel and chromium.

In one embodiment of the invention, the closure component is in the form of or forms part of a displaceable cone assembly for a gasifier feedstock closure mechanism or a gasifier ash closure mechanism.

In another embodiment of the invention, the closure component is in the form of or forms part of a stationery seat assembly of a gasifier feedstock closure mechanism or a gasifier ash closure mechanism. The invention extends to a solids-handling closure mechanism or assembly which is operable to allow or deny flow of solid particulate material, the closure mechanism including a displaceable closure member or cone assembly movable between a closed condition and an open condition to open or close a solids flow path; and a seat for seating the closure member when in the closed condition, wherein at least one of the closure member and the seat is, or includes, a closure component as hereinbefore described.

The solids-handling closure mechanism may form part of a gasifier. Thus, the closure member may thus be a feedstock closure mechanism of a gasifier. Alternatively the closure member may be an ash closure mechanism of a gasifier. The gasifier may be a fixed bed dry bottom gasifier.

Similar closure mechanisms may be applied in carbonaceous feedstock

(e.g. coal) beneficiation or upgrading plants, in which event the ash closure mechanism is more aptly named a product closure mechanism.

Preferably, both the closure member and the seat are in the form of or include a closure element as hereinbefore described.

Further features of the invention will become apparent from the following description presented by way of example with reference to the accompanying drawings.

In the drawings: Figure 1 shows a three-dimensional view of a closure component according to the invention in the form of part of a displaceable cone assembly of a solids-handling closure mechanism;

Figure 2 shows a partial sectional elevation of the closure component of Figure 1 ;

Figure 3 shows a sectional elevation of a portion of a solids-handling closure mechanism which includes the closure component of Figure 1 , in an open position, and a seat assembly in accordance with the invention;

Figure 4 shows the solids-handling closure mechanism of Figure 3 in a closed position; and

Figure 5 shows a sectional elevation of another embodiment of a closure component in accordance with the invention.

With reference now to Figures 1 and 2 of the drawings, reference numeral 10 generally indicates a closure component according to the invention. The component 10 includes a metallic substrate or carrier body 12 and a cemented carbide sealing element 14, metallurgically bonded to the substrate body 12.

A carbide phase of the sealing element 14 is predominantly tungsten carbide, while a binder phase of the sealing element 14 includes cobalt, nickel and chromium.

The substrate body 12 is of a graphite cast iron, typically with a graphite content between 8 % and 12 % by volume. The substrate body 12 was cast on to the sealing element 14. During the casting process, metallurgical bonding is achieved by allowing the molten iron to melt a small surface layer of the sealing element 14. Metallurgical bonding may occur to a depth of up to 3 mm. In heat treatments subsequent to the casting, at least some residual austenite in the substrate body 12 is transformed to bainite under a volume increase. In this manner, differential shrinkage between the substrate body 12 and the sealing element 14 is largely reduced. The microstructure of the substrate body 12 thus includes bainite.

Referring now to Figure 3 and Figure 4, reference numeral 100 generally indicates a solids-handling closure mechanism, in particular an ash closure mechanism of a gasifier, in accordance with the invention. The closure mechanism 100 includes a displaceable cone assembly or closure member 102 and a stationery seat assembly 104. The closure member 102 includes the closure component 10, a cone-shaped end- piece 106 welded to the closure component 10, and a collar 108 securing a hydraulically actuated arm 1 10 to the closure member 102.

The seat assembly 104 includes a cast iron substrate body 1 12 and a cemented carbide sealing element 1 14 metallurgically bonded to the substrate body 12, and is a closure component in accordance with the invention.

The closure member 102 is displaceable with the arm 1 10 in the direction indicated by arrow 1 16 between an open position (shown in Figure 3) and a closed position (shown in Figure 4). In the open position, a solids flow path 1 18 is defined between the closure member 102 and the seat assembly 104. In the closed position, a sealing interface is established by pressing the sealing element 14 on to the sealing element 1 14.

The conical shape of the cone-shaped end-piece 106 prevents the collection of material on top of the closure component 10, when the closure mechanism 100 is in the closed position as shown in Figure 4, and thus prevents the ingress of any material in between the sealing elements 14 and 1 14 when the closure member 102 moves from the open position to the closed position. The cone-shaped end-piece 106 is therefore important to the correct functioning of the closure mechanism 100.

It must be appreciated that the closure mechanism 100 may find application in carbonaceous feedstock (e.g. coal) beneficiation or upgrading plants, in which event the closure mechanism 100 is more aptly named a product closure mechanism.

For use as a feedstock closure mechanism, the closure mechanism 100 is inverted so that the closure mechanism is in a closed position when the closure member 102 is at an upper end of its stroke.

Referring now to Figure 5, another embodiment of a closure member in accordance with the invention is indicated by reference numeral 200. The closure member 200 is similar to the closure member 102 and, unless otherwise indicated, the same reference numerals are used to indicate the same or similar parts or features of the closure members 102, 200. The closure member 200 is fabricated such that the cone-shaped end- piece 106 forms an integral part of the substrate body 12.

Advantageously, the metallurgical bond between the sealing element 14, 1 14 and the substrate body 12, 1 12 eliminates a leak path that is provided between the substrate body and the sealing element when conventional technology involving a clamping ring is used. With the closure mechanism 100, differential pressures of the order of 80 bar can be handled. Also, the sealing interface is established between hard cemented carbide materials that are effective to cut through residual solids on the sealing element 14, 1 14 when changing the closure mechanism 100 to the closed position. In addition, the hard cemented carbide materials provide extended resistance to wear induced by the flow of particulate material over the sealing element, and also provides erosion resistance in the face of high velocity steam flows. The closure mechanism 100, as illustrated, can also be fabricated and assembled using fewer fabrication steps and less time than the conventional closure mechanisms of which the inventors are aware.

Claims

CLAIMS:

1 . A closure component for solids-handling equipment, the closure component including: a metallic substrate or carrier body; and a cemented carbide sealing element metallurgically bonded to the substrate body.

2. The closure component according to claim 1 , wherein the substrate body, or at least a part of the substrate body metallurgically bonded to the sealing element, is of a graphite cast iron or ductile iron.

3. The closure component according to claim 2, wherein the ductile iron contains 8% - 12% graphite by volume.

4. The closure component according to any one of the preceding claims, wherein the substrate body has a microstructure which includes bainite.

5. The closure component according to any one of the preceding claims, wherein the sealing element has a carbide phase which includes tungsten carbide.

6. The closure component according to any one of the preceding claims, wherein the sealing element includes a binder phase.

7. The closure component according to claim 6, wherein the binder phase includes a metal selected from the group consisting of cobalt, nickel and chromium.

8. The closure component according to any one of the preceding claims, which is in the form of, or forms part of, a displaceable cone assembly of a gasifier feedstock closure mechanism or a gasifier ash closure mechanism.

9. The closure component according to any one of claims 1 to 7 inclusive, which is in the form of, or forms part of, a stationery seat assembly of a gasifier feedstock closure mechanism or a gasifier ash closure mechanism.

10. A solids-handling closure mechanism which is operable to allow or deny flow of solid paniculate material, the closure mechanism including: a displaceable closure member or cone assembly movable between a closed condition and an open condition to open or close a solids flow path; and a seat for seating the closure member when in the closed condition, wherein at least one of the closure member and the seat is, or includes, a closure component in accordance with any of claims 1 to 7 inclusive.

1 1 . The closure mechanism according to claim 10, which is a feedstock closure mechanism of a gasifier.

12. The closure mechanism according to claim 10, which is an ash closure mechanism of a gasifier.

13. The closure mechanism according to claim 1 1 or claim 12, wherein the gasifier is a fixed bed dry bottom gasifier.

14. The closure mechanism according to any of claims 10 to 13 inclusive, wherein both the closure member and the seat are, or include, a closure component in accordance with any of claims 1 to 7 inclusive.