PROCESS FOR PREPARING A SYNGAS AND SYNGAS COOLING DEVICE

Abstract

The invention relates to a process for the preparation of a syngas comprising hydrogen and carbon monoxide comprising the steps of:

(a) reacting a preheated methane comprising gas with an oxidising gas to obtain a hot raw syngas comprising carbon monoxide and hydrogen;

(b) cooling the hot raw syngas resulting from step (a) to obtain the syngas by indirect heat exchange against water to produce saturated steam;

(c) further cooling the raw syngas obtained in step (b) by indirect heat exchange against a methane comprising gas to obtain a cooled raw syngas and the preheated methane comprising gas for use in step (a),

wherein:

(i) steps (b) and (c) take place in a single cooling device for combined indirect heat exchange against water and against the methane comprising gas; and

(ii) the preheated methane comprising gas obtained in step (c) has a temperature between 400 and 650 C.

Claims

1. A process for the preparation of a syngas comprising hydrogen and carbon monoxide comprising the steps of: (a) reacting a preheated methane comprising gas with an oxidizing gas to obtain a hot raw syngas comprising carbon monoxide and hydrogen; (b) cooling the hot raw syngas resulting from step (a) to obtain the syngas by indirect heat exchange against water to produce saturated steam; (c) further cooling the raw syngas obtained in step (b) by indirect heat exchange against a methane comprising gas to obtain a cooled raw syngas and the preheated methane comprising gas for use in step (a), wherein: (i) steps (b) and (c) take place in a single cooling device for combined indirect heat exchange against water and against the methane comprising gas; and (ii) the preheated methane comprising gas obtained in step (c) has a temperature between 400 and 650 C.

2. The process according to claim 1, wherein the methane comprising gas used in step (c) is first preheated to a temperature of up to 400 C. by indirect heat exchange against the cooled raw syngas leaving the single cooling device to obtain a further cooled raw syngas.

3. The process according to claim 2, wherein the water used in step (b) is first preheated by indirect heat exchange against the further cooled raw syngas.

4. The process according to claim 1, wherein the process comprises the further step of: (d) further cooling the cooled raw syngas obtained in step (c) by indirect heat exchange against water in the single cooling device to obtain further saturated steam and further cooled raw syngas.

5. The process according to claim 1, wherein the process comprises the further step of: (d) further cooling the cooled raw syngas obtained in step (c) by indirect heat exchange against the saturated steam obtained in step (a) in the single cooling device to obtain superheated steam and further cooled syngas.

6. A cooling device for cooling a hot raw syngas by indirect heat exchange against water in an evaporation section I and against a cooling gas in gas heat exchange section II, which device comprises a vertically oriented vessel 1 comprising at least one spirally ascending conduit an inlet for the hot gas fluidly connected to the upstream end of each conduit for upward passage of the hot raw syngas through each spirally ascending conduit, an outlet for cooled raw syngas fluidly connected to the downstream end of each conduit, an inlet for fresh water and an outlet for dry steam, a water bath space in the lower part of the vessel 1, a saturated steam collection space above said water bath space and a dry steam collection space above said saturated steam collection space in the upper part of vessel 1, wherein (i) the evaporation section I is located in the lower part of vessel 1 and the gas heat exchange section II is located immediately above the evaporation section I in vessel 1, (ii) each spirally ascending conduit comprises an evaporating section located in the water bath space in evaporation section I and a preheating section located in gas heat exchange section II, (iii) each conduit of the preheating section is surrounded by a second conduit forming an annular space between said conduit and said second conduit, (iv) the annular space is provided with an inlet for cooling gas fluidly connected to an inlet for cooling gas and an outlet for heated cooling gas located at the opposite end of said annular space which outlet is fluidly connected to outlet for the heated cooling gas, (v) the inlet or outlet is located in water bath space below the water level, (vi) a separation means is arranged inside vessel between steam collection space and dry steam collection space.

7. The cooling device according to claim 6, wherein (vii) separation means comprises a support tube centrally positioned inside the spirally ascending conduit of the preheating section and connected at its lower end to a ring-shaped separation plate and at its upper end to a demister, (viii) the separation plate is located between steam collection space and gas heat exchange section II and is fixed at its outer end to the inner wall of vessel 1, (ix) the demister is fluidly connected with dry steam collection space and is positioned above gas heat exchange section II.

8. The cooling device according to claim 7, wherein the evaporation section I comprises a centrally positioned downcomer in water bath space.

9. The cooling device according to claim 6 further comprising a superheater section III positioned between gas heat exchange section II and dry steam collection space in vessel 1, wherein each spirally ascending conduit further comprises a superheating section located in the superheater section III and ascending around the central axis and is surrounded by a second conduit forming an annular space between said conduit and said second conduit, said annular space being provided with an inlet for saturated steam fluidly connected to the saturated steam collection space and an outlet for superheated steam located at the opposite end of said annular space and fluidly connected to an outlet for superheated steam in the wall of vessel 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 shows a schematic drawing of a cooling device according to the present invention suitable for operation of the indirect heat exchange of raw syngas against the methane comprising gas in co-current mode.

[0044] FIG. 2 shows a schematic drawing of a cooling device according to the present invention suitable for operation of the indirect heat exchange of raw syngas against the methane comprising gas in counter-current mode.

[0045] FIG. 3 shows a schematic drawing of the upper part of a cooling device according to the present invention with a superheater section positioned above gas heat exchange section II.

DETAILED DESCRIPTION OF THE DRAWINGS

[0046] In FIG. 1 vertically oriented pressure vessel 1 is divided into an evaporation section I, a gas heat exchange section II located immediately above evaporation section I and a dry steam collection space 23 in the top part of vessel 1. This vessel should be capable of withstanding high pressures of up to 14 MPa and is therefore also referred to as pressure vessel. The pressure vessel 1 comprises conduits 2 which spirally ascend around the vertical axis 3 and are fluidly connected to inlet 4 for the hot raw syngas and outlet 5 for the cooled raw syngas. The outlet 5 as shown in FIG. 1 is positioned in evaporation section I, but may obviously also be positioned in the gas heat exchange section II. The conduits 2 comprise an evaporating section 10 located in the water bath space 8 in evaporation section I and a feed preheating section 11 located in gas heat exchange section II. FIG. 1 only shows two conduits 2. The cooling device may have one single conduit 2, but it is preferred to use two or more conduits 2 which suitably run in parallel. Generally between 2 and 24 conduits 2 may run in parallel. The conduits 2 are suitably positioned around the vertical axis 3 of vessel 1 in parallel paths as ascending spirally shaped coils. Such spiral configuration could consist of one ascending cylinder of 1 to 10, preferably 2 to 8, spirally wound parallel conduits 2. A configuration with two ascending cylindersan outer cylinder and an inner cylinder, each consisting of 1 to 10, preferably 2 to 8, spirally wound heat conduits 2is also a suitable configuration. Likewise, the same configuration of one or two ascending cylinders of multiple, spirally ascending conduits 2 can be used in gas heat exchange section II. FIG. 1 shows dotted lines in evaporation section I and gas heat exchange section II to illustrate how each conduit 2 runs spirally through vessel 1.

[0047] Also shown is an inlet 6 for fresh water. This inlet is preferably positioned such that the direction of the flow as it enters the vessel 1 enhances the circulation of water in a downward direction through a preferred downcomer 18. Alternative entry points for fresh water are, however, possible. For example, fresh water could also be added at an water inlet point in hot raw syngas inlet 4 (not shown). Downcomer 18 is preferably an open ended tubular part centrally positioned in water bath space 8 as shown. An upward direction of the water through an annular space 24 between downcomer 18 and inner wall of the vessel 1 will then result and circulation of water is created as shown by arrows in FIG. 1. This circulation is beneficial for an effective heat transfer from the hot raw syngas in conduits 2 to the water. The conduits 2 are positioned in the water bath space 8 around such downcomer 18 in parallel paths as ascending spirally shaped coils as described above. In an alternative embodiment two or more, suitably between four and eight, downcomers 18 may be positioned in water bath space 8 around central axis 3. In this embodiment each downcomer may be surrounded by one or more spirally ascending conduits 2. The water in water bath space 8 has a water level 21 and the wet saturated steam resulting from the evaporation of the water by absorbing the heat from the hot raw syngas is collected in the steam collection space 9 above water level 21. This steam collection space 9 is separated from dry steam collection space 23 by separation means 25. It was found advantageous to arrange the spirally ascending conduits 2 of the preheating section 11 in the dry steam collection space 23, thereby eliminating cooling (and hence heat loss) of the outside of second conduit 12 surrounding such conduits 2 through evaporation of water droplets, which are normally present in a wet steam space. Such cooling would go at the expense of the effectiveness of the preheating of the methane comprising gas in preheating section 11.

[0048] The separation means 25 as shown in FIG. 1 comprises a support tube 19 which is centrally positioned inside the spirally ascending conduit 2 in gas heat exchange section II and through which the wet saturated steam flows upwardly. At its lower end the support tube 19 is connected to a ring-shaped gas-tight separation plate 20 which is located between steam collection space 9 and gas heat exchange section II and is fixed at its outer end to the inner wall of vessel 1. At its upper end the support tube 19 is fluidly connected with demister 22. In FIG. 1 the demister 22 is arranged in the centre part of ring-shaped support plate 26, but this support plate 26 may also be replaced by other support means to fixate the demister 22 on top of support tube 19. The demister 22, in return, is fluidly connected with dry steam collection space 23 and is positioned above gas heat exchange section II. The dry steam is, accordingly, collected in dry steam collection space 23 and leaves vessel 1 via outlet 7.

[0049] Demister 22 can be any demister means suitable to remove liquid water droplets from the saturated steam collected in saturated steam collection space 9 and moving upward through support tube 19. For example, the demister 22 may be a demister mesh, a vane pack or a swirl tube cyclone deck.

[0050] The conduits 2 of the preheating section 11 are each surrounded by a second conduit 12 forming an annular space 13 between the conduit 2 and the second conduit 12. This annular space 13 is provided with an inlet 14 for cooling gas, which inlet 14 is fluidly connected to a vessel inlet 15 for the cooling gas. At its downstream end the annular space 13 is fluidly connected with an outlet 16 for the heated cooling gas. This outlet 16 is fluidly connected to vessel outlet 17 for the preheated cooling gas. When used in the process of the present invention, the cooling gas is a methane comprising gas. FIG. 1 shows the cooling device for co-current flow of cooling gas and hot raw syngas in gas heat exchange section II.

[0051] In such configuration it is important that the inlet 14 is located in water bath space 8 below the water level 21 to provide cooling to the hot raw syngas carrying conduit 2. In this way overheating of the walls of this conduit 2 can be avoided where the methane comprising cooling gas enters the annular space 13. For the counter-current flow embodiment shown in FIG. 2 the outlet 16 of annular space 13 should be below water level 21 to provide cooling to the hot raw syngas carrying conduit 2 where the preheated methane comprising gas leaves the annular space 13.

[0052] In the transition from the evaporation section I to the gas heat exchange section II the multiple spirally ascending conduits 2 suitably run in a vertical direction through a common header or may individually run into gas heat exchange section II. If a common header is used, this common header is in fluid communication with annular space 13 surrounding the conduits 2 via inlet openings 14 (in co-current mode as shown in FIG. 1) or outlet openings 16 (in counter-current mode as shown in FIG. 2). In turn the common header is fluidly connected to either vessel inlet 15 (co-current mode) or vessel outlet 17 (counter-current mode). Such common header is preferably circular in a horizontal plane to accommodate efficiently the numerous conduits 2 which may run parallel in vessel 1. An example of a suitable configuration with a common header is described in WO-A-2007/131975.

[0053] The conduits 2 can be made of materials being resistant to metal dusting. Because of the corrosive nature of the syngas such metal dusting resistance is important. Suitable materials include chromium-molybdenum steel andthe more preferrednickel based metal alloys. Example of a suitable nickel based metal alloys are Inconel alloy 693 as obtainable from Special Metals Corporation, USA.

[0054] FIG. 2 shows a cooling device where the methane comprising gas is preheated against the hot raw syngas in gas heat exchange section II in a counter-current mode. The difference with the cooling device as depicted in FIG. 1 is that vessel inlet 15 and gas inlet 14 are positioned in the upper part of gas heat exchange section II, while gas outlet 16 and vessel outlet 17 are positioned in evaporation section I below water level 21. When in operation the methane comprising gas now enters the annular space 13 via vessel inlet 15 and inlet 14 in the upper part of gas heat exchange section II and flows downwardly through annular space 13, counter-currently to the flow of upwardly flowing hot raw syngas through conduits 2.

[0055] The cooling device of the present invention may be combined with a superheater section positioned above gas heat exchange II for further heating the saturated steam produced in evaporation section I to superheated steam. This embodiment is further illustrated in FIG. 3.

[0056] FIG. 3 shows the upper part of a cooling device according to FIG. 1 (co-current flow of methane comprising gas and raw syngas in gas heat exchange section II) with a superheater section II positioned between gas heat exchange section II and dry steam collection space 23. Each spirally ascending conduit 2 leaving gas heat exchange section II further comprises a superheating section 30 located in the superheater section III and ascending around the central axis 3. Each such conduit 2 is surrounded in its superheating section 30 by a second conduit 31 forming an annular space 32 between said conduit 2 and said second conduit 31, said annular space 32 being provided with an inlet 34 for saturated steam fluidly connected to the saturated steam collection space 9 and an outlet 35 for superheated steam located at the opposite end of said annular space 32 and fluidly connected to a vessel outlet 36 for superheated steam in the wall of vessel 1. The outlet 5 for the cooled raw syngas is now positioned in superheater section III in the top part of vessel 1.

[0057] In order to ensure continuous cooling of the raw syngas flowing through conduit 2, the second conduit 12 surrounding the conduit 2 of the preheating section 11 is connected with second conduit 31 surrounding conduit 2 of superheating section 30. They are, however not fluidly connected: annular space 13 is separated from annular space 32 by gas-tight separation plate 37. By ensuring such continuous cooling of the hot raw syngas the wall temperature of the conduit 2 can be kept low enough to avoid metal dusting.

[0058] The device shown in FIG. 3 shows a counter-current flow of saturated steam through annular space 32 and raw syngas through conduit 2 in superheating section 30. The superheater section II can also be designed such that saturated steam and raw syngas flow co-currently. Further details of how a superheater section can suitably be designed are described in WO-A-2007/131975.

[0059] The superheating section III may also be integrated with gas heat exchange section II. For example, spirally descending conduits 2 with second conduits 31 which form the superheating section III could be arranged inside the bundles(s) of spirally ascending conduits 2 surrounded by a second conduits 12 which form gas heat exchange section II. When in operation the syngas flows ascending in the gas heat exchange section II and descending in the superheating section III.

[0060] The cooling device may also be combined with a further evaporation section in which the raw syngas leaving gas heat exchange section II is passed back to a further evaporation section positioned in water bath space 8 to produce further saturated steam. Such second evaporation section is suitably located inside evaporating section 10 of spirally ascending conduit 2 in water bath space 8, wherein such second evaporation section comprises at least one spirally descending conduit fluidly connected at its upstream end to the spirally ascending conduit 2 leaving the gas heat exchange section II and at its downstream end with vessel outlet 5 for cooled gas. Alternatively, the second evaporation section comprises one or more straight heat exchange tubes fluidly connected at their upstream end to the spirally ascending conduit 2 leaving the gas heat exchange section II and at their downstream end with vessel outlet 5 for cooled gas, wherein at least one of these straight tubes is surrounded by a sheath tube comprising closing means at its upper end and being open at its lower end as further described in co-pending European patent application No. 14174590.1. By using such sheath tubes the heat exchange capacity of the heat exchange tube can be varied.

[0061] The heat exchange tubes in the second evaporation section may also comprise a combination of spirally descending conduits and straight conduits with sheath tubes around it or may comprise heat exchange tubes consisting of a spirally descending section fluidly connected with a straight section surrounded by a sheath tube as described above.

EXAMPLES

[0062] The invention is further illustrated by the following examples. The examples are calculated examples using an integrated calculation model which includes detailed heat transfer algorithms and gas properties.

Example 1

[0063] Hot raw syngas having a temperature of 1350 C. and a pressure of 6 MPa is fed into a cooling device comprising an evaporation section and a gas heat exchange section with counter-current flow of syngas and methane comprising gas.

[0064] The temperature of the cooled raw syngas leaving the cooling device is 400 C. at a pressure of 5.4 MPa, whilst the preheated methane-comprising gas has a temperature of 525 C. with the methane-comprising gas entering the cooling device at a temperature of 273 C. In the evaporation section saturated steam is produced having a temperature of 293 C.

Example 2

[0065] Example 1 was repeated except that the cooling device now also contains a superheater section downstream of the gas heat exchange section and that the gas heat exchange section has a co-current flow of syngas and methane comprising gas. Saturated steam produced in the evaporation section is passed through the superheater section to produce superheated steam of 410 C. The temperature of the cooled raw syngas leaving the cooling device is 400 C. at a pressure of 5.2 MPa, whilst the preheated methane-comprising gas has a temperature of 525 C. with the methane-comprising gas entering the cooling device at a temperature of 385 C.

Example 3

[0066] Example 1 was repeated except that the cooling device now also contains a second evaporation section downstream of the gas heat exchange section and that the gas heat exchange section has a co-current flow of syngas and methane comprising gas.

[0067] The temperature of the cooled raw syngas leaving the cooling device is 400 C. at a pressure of 5.8 MPa, whilst the preheated methane-comprising gas has a temperature of 480 C. with the methane-comprising gas entering the cooling device at a temperature of 385 C. The combined saturated steam from the first and second evaporation section has a temperature of 293 C.