GB2112805A - Reaction furnace for the indirect heating of crackable fluids - Google Patents

Abstract

A reaction furnace capable of functioning efficiently in off-shore process installations which comprises a plurality of vertical reaction tubes arranged in a firing chamber having one or more burners, and a plurality of horizontal beams, suitably hollow, having external insulation which extend through the central region of the furnace without impeding the fuel gas flow and to which one or more reaction tubes are attached, either being mounted externally or being mounted internally. The beams may be air cooled and can be adapted, e.g. by strengthening, to form inspection platforms within the furnace. <IMAGE>

Description

SPECIFICATION Reaction furnace for the indirect heating of crack" able fluids The invention relates to a reaction furnace for the indirect heating of crackable fluids, particularly for cracking hydrocarbons to obtain gases rich in CO and H2, said furnace consisting of a plurality of vertical reaction tubes arranged in a firing chamber having internal fuel-gas burners. The invention is primarily concerned with furnaces in which cracking takes place at high pressures and termperatures and which can be used on floating carriers such as ships or marine installations.

Many tubular cracking furnaces have been proposed in which the reaction tubes are arranged in the firing chamber in the form of registers or bundles.

These tubes may be filled with a catalyst or packing to control the chemical reaction. Normally, the tubes are arranged vertically in the firing chamber such that they can be filled with a catalyst in a uniform and complete manner. In such an arrangement, the tubes may be mounted or supported at their upper and lower ends. In other designs, only the upper or lower end is supported, while the free ends of the tubes project into the firing chamber. Both types of designs prevent thermal stress. The reaction fluid is usually piped to the reaction tubes via a header system and withdrawn from the tube ends via a product gas header.

In the conventional design, the reaction tubes are generally fixed at one end to compensate for tube elongation caused by thermal expansion. In order to maintain the position of the reaction tubes in the furnace, the upper and lower ends of the tubes are arranged such that the tubes cannot move horizontally.

Tubular cracking furnaces have, so far, only been installed ashore. In such cases, horizontal dynamic forces do not act on the tube registers during operation. If conventional tubular cracking furnaces are to be installed on floating carriers such as floating process plant platforms, the structure must withstand static as well as horizontal dynamic loads caused by, for example, the sea or storms. The normal tube length of 10 to 14 m and the weight of a catalyst additional to that of the tubes, cause bending stresses which also act on the reaction tubes during operation. If the conventionally-mounted reaction tubes are designed to accommodate such loads, the resulting wall thickness and tube length give rise to insufficient operating times.

There is a need for means by which reaction tubes of tubular cracking furnaces used in such a furnace in floating or marine plant installations are supported such that dynamic loads caused by the movements of the floating platform etc., are reduced to an acceptable minimum, still enabling efficient operation of the furnace.

We have found that the need can be met by arranging a plurality of parallel horizontal, suitably duct-type, beams in the centre section of the firing chamber. The beams should have external insulation and be of wall-to-wall length. The rows of vertical reaction tubes may penetrate the gastight beams and be fixed horizontally therein. The space between the beams should be sufficient to ensure passage of the fuel gas.

We have further found that the need can also be met by attaching the plurality of parallel horizontal, suitably duct-type, beams, which may be positioned on the vertical axis of the central region of the firing chamber and be of at least wall-to-wall length, to the external side of the vertical tube rows and arranged such that passage of the fuel gas is not impeded.

The present invention accordingly provides a reaction furnace for the indirect heating of crackable fluids which comprises a plurality of substantially vertical reaction tubes arranged in a firing chamber having one or more fuel-gas burners, and one or more substantially horizontal, insulated beams extending through the central region of the firing chamber, each beam being of at least wall-to-wall length and being arranged such that fuel gas can flow freely around the beam, and each reaction tube being attached externally to a beam or mounted in gastight manner within a beam.

Preferably, the beams are of the lattice type and are equipped with a gastight sheet lining, suitably made of metal, for example a steel lining. Preferably the beams are designed such that they project beyond the front and rear walls. Suitably, the beams are hollow and can be air-cooled. In order to protect the suitably duct-type beams against heat, it is further preferred to insulate any reaction tube section sited within a beam, using insulation packages and elements.

Several reaction tubes maybe mounted on or in a single beam or a single beam may only support one reaction tube. Arrangements of beams and tubes within a furnace of the invention maybe such that both tubes mounted within and tubes mounted on a beam maybe present. Normally, the beams are arranged parallel to one another and, usually, there is more than one beam present in a furnace of the invention.

The intermediate tube supports of the invention can reduce the necessary length of the free tube ends arranged in the firing chamber and improve the service life of the reaction tubes when used in furnaces based on land or water. The beams maybe designed such that they have to resist a minimum load and be fully protected against the hot gas in the firing chamber. Moreover, it is possible to walk on the structure, even when the furnace has not completely cooled down, for inspection purposes.

Two furnaces of the invention will now be described by way of example only, with reference to, and as illustrated by, the accompanying drawings in which Figure lisa longitudinal section of a tubular reaction furnace of the invention; Figure2 is a cross section of a hollow beam in the furnace which beam has a reaction tube penetrating the beam centre; Figure 3 is a cross section of a hollow beam penetrated centrally by a two-part reaction tube; and Figure 4 is a cross section of a hollow beam on which two reaction tubes are mounted.

Referring to Figure 1, the tubular cracking furnace is a structure, suitably made of steel, consisting of heat-insulated walls 2, ceiling 3 and floor 4. A plurality of reaction tubes 5, which maybe filled with a catalyst, are arranged in vertical rows. The upper end of each tube penetrates the ceiling 3 and is connected to and supported, if necessary, by an inlet header 6, while the lower end of each tube penetrates the floor 4 and is connected to and, if necessary, supported by a product gas header 7. The tubes are fixed in a straight and substantially vertical manner and are attached to spring assemblies 8 which compensate for thermal expansion. The tube rows are heated by means of burners 9 arranged in the ceiling 3. A plurality of flue gas ducts 10 are arranged, in parallel, on the floor 4 in order to ensure a uniform feed of fuel gas and a uniform withdrawal of flue gas.

The reaction tubes 5 are fixed in the central region of the furnace by means of horizontal duct-type beams 11 having external insulation; the presence of the beams enables the free-end length of the reaction tubes to be reduced to e.g. from 10 to 14 m.

Said beams 11 are arranged substantially parallel to the tube rows and extend from one wall to the opposite wall. The space between the beams is sufficient to ensure the free flow of fuel gas.

Referring to Figure 2, the beam 11 consists of two or more sectional beams 12 and is reinforced by a gastight sheet lining, suitably a metal lining. External insulation 14 protects the supporting members of the beam against heat. The upper surface of beam 11 incorporates a layer of refractory concrete 15 making the surface suitable for foot traffic.

An undivided reaction tube is fixed horizontally in the beam by means of two support plates 16 which also interconnect the two parts of the beam. Insulation packages 17 and insulation elements 18 substantially protect the beam from heat from the reaction tube. Seals 19 are placed between the reaction tube and insulation packages 17 and substantially prevent the penetration of fuel gas from the firing chamber into the beam. The beam maybe of a suitable dimension such that it can be equipped with grids or decking suitable for foot trafic.

Referring to Figure 3, the external insulation elements 18 are not required if the reaction tube consists of two parts connected by a flange in the beam 11. In this arrangement, the reaction tube section penetrating the beam can be thermally insulated by means of a liner 21, allowing both tube parts to be filled with a catalyst and substantially preventing the product gas in the tubes from heating the other tubes in the beam to an inadmissible degree.

Referring to Figure 4, the reaction tubes may also be attached to an external side of a horizontal beam, i.e. with one, two or more rows to one beam. Tube support plates 22 may penetrate only a minimum section of the external insulation in order to reduce the heat transfer to a minimum. Said support plates are thermally insulated by means of insulating articles, suitably prefabricated insulation rings 23, which substantially protect the plates against the hot gas.

It has been found advantageous to allow the beams, when hollow, to protrude from the front and rear walls of the furnace and be connected to a duct for withdrawing the combustion air from the tubular reaction furnace. The through-flow suction caused enables the beams to be cooled internally.

Claims (13)

1. A reaction furnace for the indirect heating of crackable fluids which comprises a plurality of substantially vertical reaction tubes arranged in a firing chamber having one or more fuel-gas burners, and one or more substantially horizontal, insulated beams extending through the central region of the firing chamber, each beam being of at leastwall-to wall length and being arranged such that fuel gas can flow freely around the beam, and each reaction tube being attached externally to a beam or mounted in gastight manner within a beam.

2. Afurnace as claimed in claim 1, wherein at least one beam is hollow.

3. A furnace as claimed in claim 2, wherein at least one beam is cooled by an internal through-flow of air.

4. Afurnace as claimed in any one of claims 1 to 3, wherein at least one beam is a lattice girder reinforced by an internal sheet lining.

5. A furnace as claimed in anyone of claims 1 to 4, wherein at least one beam extends beyond the walls of the furnace.

6. Afurnace as claimed in anyone of claims 1 to 5, wherein, for a tube mounted in a beam, each reaction tube section contained within a beam is insulated.

7. A furnace as claimed in claim 6, wherein the insulation of each tube section comprises insulation packages and insulation elements.

8. A furnace as claimed in anyone of claims 1 to 7, wherein one or more tubes consist of two tube sections which are joined to each other in the area of attachment to the beams.

9. Afurnace as claimed in anyone of claims 1 to 8, wherein at least one beam is adapted to form an inspection plafform.

10. Afurnace as claimed in anyone of claims 1 to.

8, wherein at least one of the beams present is adapted to form an inspection platform.

11. Afurnace as claimed in claim 1, which is substantially as described herein with reference to, and as illustrated by, the accompanying drawings.

12. A process plant which comprises a reaction furnace as claimed in anyone of claims 1 to 11.

13. A marine installation which contains a reaction furnace as claimed in anyone of claims 1 to 11.