Process for reforming hydrocarbons

Abstract

The invention relates to the production of synthesis gas by means of particularly a series arrangement of heat exchange reforming and autothermal reforming stages, in which the heat required for the reforming reactions in the heat exchange reforming stage is provided by hot effluent synthesis gas from the autothermal reforming stage. More particularly, the invention relates to optimisation of the operation and control of an arrangement of heat exchange reforming and autothermal reforming stages and introduction of an additional waste heat boiler.

Claims

1. A synthesis gas production plant, comprising: first flow means for apportioning a hydrocarbon feedstock to a tube side of at least one heat exchange reformer, in which at least a portion of said hydrocarbon feedstock is reformed to produce a primary reformed gas, second flow means for conveying said primary reformed gas, an autothermal reformer (ATR), or catalytic partial oxidation apparatus (CPO) or a partial oxidation apparatus (PDX) communicating with said second flow means to produce hot effluent synthesis gas from said primary reformed gas, third flow means for conveying said hot effluent synthesis gas, said third means comprising a mean for optionally adding steam to said hot effluent synthesis gas, splitting means communicating with said third flow means for splitting said hot effluent synthesis gas into first and second synthesis gas streams, fourth flow means for conveying said first synthesis gas stream through a shell-side of said at least one heat exchange reformer, fifth flow means for conveying said second synthesis gas stream through a second heat exchanger, in which said second synthesis gas stream is cooled, first control means downstream of the shell-side of said at least one heat exchange reformer, and second control means downstream of a tube-side of said second heat exchanger for controlling the splitting of said hot effluent synthesis gas into said first and second synthesis gas streams.

2. The plant according to claim 1, further comprising an adiabatic pre-reformer upstream the heat exchange reformer.

3. The plant according to claim 1, further comprising a third heat exchanger arranged downstream the shell-side of the heat exchange reformer so as to further cool the first synthesis gas stream.

4. The plant according to claim 3, comprising means for combining the cooled second synthesis gas from the second heat exchanger with the further cooled first synthesis gas from the third heat exchanger.

5. The plant according to claim 1, wherein said first flow means for apportioning comprises a by-pass line for conveying a portion of untreated hydrocarbon feedstock directly to said second flow means, wherein said untreated hydrocarbon feedstock combines with said primary reformed gas input to said autothermal reformer (ATR), or catalytic partial oxidation apparatus (CPO) or partial oxidation apparatus (POX).

Description

EXAMPLE 1

(1) A process utilizing the bypass stream of the present invention as shown in FIG. 4 is presented in this example (as New layout). This is compared a process where the bypass stream of the present invention is not used (Reference layout).

(2) It is shown that it is possible, by implementing the present invention, to counteract the influence of fouling of the heat exchanger surface in a heat exchange reformer, by controlling the amount of hot effluent synthesis gas from an autothermal reformer sent to the shell side of the heat exchange reformer, thereby obtaining constant performance of the plant.

(3) The feed gas (not shown in FIG. 4) is mixed with hydrogen and desulphurized to form stream 11. It is mixed with steam (stream 12 in FIG. 4) and is sent to an adiabatic prereformer (15). The effluent from the prereformer (stream 10) is sent to the process side of a heat exchange reformer (25). The effluent from the heat exchange reformer (stream 30) is mixed with tail gas (stream 60) and sent to an autothermal reformer (75), where it is partly combusted and reformed to equilibrium producing a hot effluent stream (stream 90). No steam (stream 100) is mixed into the hot effluent stream.

(4) Four cases are shown:

(5) Case 1.1. Reference layout Start-Of-Run (Ref SOR). The heat exchange reformer is unfouled, and all gas from the autothermal reformer is sent to the heat exchange reformer, i.e. bypass ratio=0.

(6) Case 1.2. Reference layout End-Of-Run (Ref EOR). The heat exchange reformer is fouled, and all gas from the autothermal reformer is sent to the heat exchange reformer, i.e. bypass ratio=0.

(7) Case 1.3. New layout Start-Of-Run (New SOR). The heat exchange reformer is unfouled, and 88% of the gas from the autothermal reformer is sent to the heat exchange reformer. 12% is bypassed (bypass ratio) via stream 112.

(8) Case 1.4. New layout End-Of-Run (New EOR). The heat exchange reformer is fouled, and 99% of the gas from the autothermal reformer is sent to the heat exchange reformer. 1% is bypassed (bypass ratio) via stream 112.

(9) The performance of the heat exchange reformer in the 4 cases is summarized in Table 1.1

(10) It is seen that it is possible to have the same performance of the heat exchange reformer at Start-Of-Run and End-Of-Run using the New layout as per the present invention. The outlet temperature and the transferred duty are the same at SOR and EOR conditions. Transferred duty is the amount of energy that is transferred per unit time from the shell side gas stream to the tube side gas stream in the heat exchange reformer. By gradually adjusting the amount of gas from the autothermal reformer throughout the operating period from unfouled to fouled conditions, it is possible to maintain the same performance at any time.

(11) This is not the case in the Reference layout (without bypass stream). The performance is inferior at EOR conditions compared to the SOR. The outlet temperature at EOR conditions is 15 C. less and the transferred duty is 8.1 Gcal/h less corresponding to 7%.

(12) TABLE-US-00001 TABLE 1.1 Performance of heat exchange reformer. 1.1. Ref 1.2. Ref 1.3. New 1.4. New Case SOR EOR SOR EOR Bypass % 0 0 12 1 Fouling No Yes No Yes Tout (STM 10) C. 730 715 730 730 Tout (STM 121) C. 649 678 591 639 Transferred duty Gcal/h 115.6 107.5 116.2 116.3

(13) Table 1.2 show the overall performance of the syngas plant for the 4 cases. It is seen that in the New layout, utilizing the present invention, the same amount of syngas and CO is produced at EOR conditions compared to SOR. The amount of CO produced per unit natural gas and per unit oxygen is also constant throughout the operating period from unfouled to fouled conditions.

(14) In the Reference layout, the amount of syngas and CO produced at EOR condition is less at EOR conditions compared to SOR. The amount of CO produced is 1213 Nm3/h less corresponding to 0.7%. The amount of CO produced per unit natural gas and per unit oxygen is also less, per unit oxygen the amount is 2.3% less.

(15) TABLE-US-00002 TABLE 1.2. Overall process performance 1.1. Ref 1.2. Ref 1.3. New 1.4. New Case SOR EOR SOR EOR Bypass ratio % 0 0 12 2 Fouling No Yes No Yes NG feed Nm3/h 150000 150000 150000 150000 Ox flow Nm3/h 88614 90031 88556 88512 Syngas flow Nm3/h 611403 607726 611438 611579 (Dry) CO prod Nm3/h 175258 174045 175280 175324 CO prod/NG 1.168 1.160 1.169 1.169 feed flow CO prod/ 1.978 1.933 1.979 1.981 Oxygen flow

(16) In summary, this example shows that the performance of the heat exchange reformer and a syngas plant can sustain constant performance by using a layout including a bypass stream according to the present invention. If the bypass stream of the invention is not used, and all the gas from the autothermal reformer is sent to the heat exchange reformer, the result will be a gradual decrease in performance.

EXAMPLE 2

(17) A process utilizing the present invention as shown in FIG. 3 (no tail gas addition) is presented in this example (as New layout). This is compared to the Reference layout which is a process where the present invention is not used, i.e. all gas (stream 111 in FIG. 3) is send through the shell side of the heat exchange reformer.

(18) It is shown that it is possible, by implementing the present invention, to counteract the influence of fouling of the heat exchanger surface in a heat exchange reformer, by controlling the amount of hot effluent synthesis gas from an autothermal reformer sent to the shell side of the heat exchange reformer.

(19) Referring to FIG. 3. The feed gas (not shown in FIG. 3) is mixed with hydrogen and desulphurized to form stream 11. It is mixed with steam (stream 12) and is sent to an adiabatic prereformer (15). The effluent from the prereformer (stream 10) is sent to the process side of a heat exchange reformer (25). The effluent from the heat exchange reformer (stream 30) is sent to an autothermal reformer (75), where it is partly combusted and reformed to equilibrium producing a hot effluent stream (stream 90). No steam (stream 100) is mixed into the hot effluent stream. No tail gas is mixed into the heat exchange reformer effluent (stream 30).

(20) Four cases are shown:

(21) 2.1. Reference layout Start-Of-Run (Ref SOR). The heat exchange reformer is unfouled, and all gas from the autothermal reformer is sent to the heat exchange reformer via stream 111, i.e. bypass ratio=0.

(22) 2.2. Reference layout End-Of-Run (Ref EOR). The heat exchange reformer is fouled and all gas from the autothermal reformer is sent to the heat exchange reformer via stream 111, i.e. bypass ratio=0.

(23) 2.3. New layout Start-Of-Run (New SOR). The heat exchange reformer is unfouled, and 84% of the gas from the autothermal reformer is sent to the heat exchange reformer (stream 111). 16% is bypassed via stream 112, ie. bypass ratio=16%.

(24) 2.4. New layout End-Of-Run (New EOR). The heat exchange reformer is fouled and 96% of the gas from the autothermal reformer is sent to the heat exchange reformer (stream 111 ). 4% is bypassed via stream 112, ie. bypass ratio=4%.

(25) The performance of the heat exchange reformer in the 4 cases is summarized in Table 2.1.

(26) It is seen that it is possible to have the same performance of the heat exchange reformer at Start-Of-Run and End-Of-Run using the New layout with the present invention. The outlet temperature and the transferred duty are the same at SOR and EOR conditions. Transferred duty is the amount of energy that is transferred per unit time from the shell side gas stream to the tube side gas stream in the heat exchange reformer. By gradually adjusting the amount of gas from the autothermal reformer throughout the operating period from unfouled to fouled conditions, it is possible to maintain the same performance at any time.

(27) This is not the case in the Reference layout. The performance is inferior at EOR conditions compared to the SOR. The outlet temperature at EOR conditions is 19 C. less and the transferred duty is 8.5 Gcal/h less corresponding to 10%.

(28) TABLE-US-00003 TABLE 2.1. Performance of heat exchange reformer 2.1 Ref 2.2 Ref 2.3 New 2.4 New Case SOR EOR SOR EOR Shell bypass % 0 0 16 4 Fouling No Yes No Yes Tout (STM 30) C. 685 666 685 685 Tout (STM 121) C. 646 687 566 627 Transferred duty Gcal/h 85.88 77.30 85.78 86.15

(29) Table 2.2 shows the overall performance of the syngas unit for the 4 cases. It is seen that in the New layout, utilizing the present invention, the synthesis gas module from SOR is maintained at EOR operation. Also, the same amount of syngas and CO is produced at EOR conditions compared to SOR.

(30) The amount of CO produced per unit natural gas and per unit oxygen is also constant throughout the operating period from unfouled to fouled conditions.

(31) In the Reference layout, the synthesis gas module has decreased by 1.5% at EOR compared to SOR. The amount of syngas and CO produced at EOR condition is less than at SOR conditions. The amount of produced CO is 342 Nm3/h less corresponding to 0.3%. The amount of CO produced per unit natural gas and per unit oxygen is also less; the latter by 2.7%.

(32) TABLE-US-00004 TABLE 2.2. Overall process performance Case 2.1 Ref SOR 2.2 Ref EOR 2.3 New SOR 2.4 New EOR Shell bypass % 0 0 16 4 Fouling No Yes No Yes NG feed Nm3h/ 150000 150000 150000 150000 Ox flow Nm3h/ 71477 73264 71470 71466 Syngas flow (STM 90) Nm3h/ 566063 566632 566061 566060 Module (H.sub.2CO.sub.2)/ Nm3/Nm3 2.00 1.97 2.00 2.00 (CO + CO.sub.2) CO prod Nm3h/ 117771 117429 117772 117773 CO prod/NG feed flow 0.785 0.783 0.785 0.785 CO prod/O.sub.2 flow 1.648 1.603 1.648 1.648

(33) In summary, this example shows that the performance of the heat exchange reformer in a syngas plant can sustain constant performance by using a layout of the present invention. If this invention is not used, and all the gas from the autothermal reformer is sent to the heat exchange reformer a gradual decrease in performance will be the consequence.

EXAMPLE 3

Start-up

(34) A process utilizing the present invention as shown in FIG. 3 is presented in this example (as New layout). This is compared to the Reference layout which is a process where the present invention is not used, i.e. all gas leaving the autothermal reformer is sent through the shell side of the heat exchange reformer (bypass ratio=0).

(35) In this example it is shown that it is possible, by implementing the present invention, to counteract an excessive temperature increase in the stream leaving the process side of the heat exchange reformer (stream 30) during an operating configuration, in which part of the synthesis gas (stm 130) is recycled to the Autothermal Reformer (75) in order to reach an H.sub.2/CO-ratio low enough for starting (or operating) an FT-synthesis unit in case no tail gas is available. In the present example the target H.sub.2/CO-ratio has been set to 2.3 but various FT synthesis will have various requirements in may cases different from H.sub.2/CO=2.3. Note that the recycle of part of the synthesis gas (stm 130) to the Autothermal Reformer (75) is not shown in FIG. 3.

(36) In this case the heat exchange reformers have been designed for normal operation with a feed flow of 150,000 Nm3/hr of natural gas (see Example 1). The heat exchange reformers have been designed to have an exit temperature from the catalyst side of 730 C. during normal operation at unfouled conditions. The unit in this example 3 operates with a natural gas feed rate of 75,000 Nm3/hr corresponding to 50% of the design flow rate.

(37) Referring to FIG. 3; the feed gas (not shown in FIG. 3) is mixed with hydrogen and desulphurized to form stream 11. It is mixed with steam (stream 12) and is sent to an adiabatic prereformer (15). The effluent from the prereformer (stream 10) is sent to the process side of a heat exchange reformer (25). The effluent from the heat exchange reformer (stream 30) and a portion of the synthesis gas (stream 130) are combined and sent to the autothermal reformer (75), in which it is partially combusted using oxygen (stream 80) and reformed to equilibrium producing a hot effluent stream (stream 90). No steam (stream 100) is mixed into the hot effluent stream. No tail gas is mixed into the heat exchange reformer effluent (stream 30) at this operating point.

(38) In all three cases the flow, feed gas composition, temperature, pressure, and steam-to-carbon ratio have the same values in the stream just upstream the heat exchange reformer (stream 10 in FIG. 3).

(39) Three cases are shown:

(40) 3.1. Reference layout (unfouled). All gas from the autothermal reformer is sent to the heat exchange reformer via stream 111. No flow in the bypass steam 112, ie. bypass ratio=0.

(41) 3.2. New layout (unfouled). 70.1% of the gas from the autothermal reformer is sent to the heat exchange reformer (stream 111). 29.9% is bypassed via stream 112, ie. bypass ratio=30%.

(42) 3.3. New layout (unfouled). 64.6 % of the gas from the autothermal reformer is sent to the heat exchange reformer (stream 111). 35.4% is bypassed via stream 112, i.e. bypass ratio=35%.

(43) The performances of the heat exchange reformers in the 3 cases are summarized in Table 3.1.

(44) It is seen that it is possible to considerably reduce the transferred duty and process side outlet temperature of the heat exchange reformer using the New layout with the present invention. Transferred duty is the amount of energy which is transferred per unit time from the shell side gas stream to the tube side gas stream in the heat exchange reformer. By adjusting the amount of gas from the autothermal reformer to the heat exchange reformer shell side, it is possible to maintain conditions without excessive temperatures at the catalyst outlet of the heat exchange reformer also at reduced load and with recycle of part of the synthesis gas for example for start-up of the downstream Fischer-Tropsch synthesis unit.

(45) This is not the case in the Reference layout. The large transferred duty in case 3.1 results in a large temperature increase of the process side gas (stream 30) from 730 C. at normal operation to 781 C., both at un-fouled condition.

(46) TABLE-US-00005 TABLE 3.1. Performance of heat exchange reformer 3.1 3.2 New 3.3 New Reference layout layout Case un-fouled un-fouled un-fouled Shell bypass % 0 29.9 35.4 Fouling No No No Tout (STM 30) C. 781 743 730 Tout (STM 121) C. 632 529 513 Transferred duty* Gcal/h 68.39 57.03 53.28

(47) Table 3.2 shows the overall performance of the syngas unit for the 3 cases. It is seen that in the New layout, utilizing the present invention, the required synthesis gas recycle flow for obtaining H.sub.2/CO=2.3 in the synthesis gas decreases considerably (by 11.3% with a shell bypass of 29.9%) compared to the reference layout. This has a positive impact on the recycle equipment which becomes smaller and cheaper and requiring less power. Also, due to the lower temperature the New layout utilizing the present invention, results in operation with a larger margin to the carbon formation limit (reaction according to eq. 1) compared to the reference layout. As indicated previously, for otherwise identical conditions, the margin to carbon formation increases with decreasing temperature. The catalyst temperature is substantially lower in the new layout compared to the reference layout.

(48) TABLE-US-00006 TABLE 3.2. Overall process performance 3.1 3.2 New 3.3 New Case Reference layout layout Shell % 0 29.9 35.4 bypass Fouling No No No NG feed Nm3/h 75000 75000 75000 Ox flow Nm3/h 39244 40633 41093 Syngas Nm3/h 439698 422686 416030 flow (STM 90) H.sub.2/CO Nm3/Nm3 2.30 2.30 2.30 ratio Syngas Nm3/h 160,000 142,000 135,000 recycle flow CO prod Nm3/h 60167 59938 59835 (STM 130)

(49) In summary, this example shows that by using a layout with the present invention excessive temperatures outlet the process side of the heat exchange reformer during low load and process configurations for start-up of a downstream Fischer-Tropsch unit can be avoided. Further, the required synthesis gas recycle flow for reaching the desired H.sub.2/CO ratio is smaller, and the distance to the carbon limit for CH.sub.4 decomposition is larger than in the reference case.