Process for co-production of ammonia, urea and methanol

Abstract

A process for co-production of ammonia, urea and methanol from natural gas, comprising the steps of (a) producing a synthesis gas by simultaneous feeding natural gas to an autothermal reformer (ATR) and to a steam methane reformer (SMR), the two reformers running in parallel, (b) feeding air to an air separation unit (ASU), where the air is split into oxygen, which is fed to the ATR, and nitrogen, (c) subjecting the synthesis gas from the SMR to a water gas shift, (d) removing the carbon dioxide from the synthesis gas from step (c) and leading it to urea synthesis in a urea synthesis unit, (e) combining the hydrogen-rich gas from step (d) with the nitrogen from step (b), removing catalyst poisons from the gases and leading the gas mixture to ammonia synthesis in an ammonia synthesis unit, (f) optionally removing part of the carbon dioxide from the syngas from the ATR in step (a) and leading it to urea synthesis in a urea synthesis unit and (g) leading the syngas from step (f) to the methanol synthesis unit, wherein synthesis gas from step (a) may be led either from the ATR outlet to the SMR outlet upstream from the shift stage or the other way.

Claims

1. A process for co-production of ammonia, urea and methanol from natural gas, comprising the steps of: (a) producing a synthesis gas by simultaneous feeding natural gas to an autothermal reformer (ATR) and to a steam methane reformer (SMR), the two reformers running in parallel; (b) feeding air to an air separation unit (ASU), where the air is split into oxygen, which is fed to the ATR, and nitrogen; (c) subjecting the synthesis gas from the SMR to a water gas shift stage to form a CO.sub.2 rich gas; (d) removing carbon dioxide from the synthesis gas from step (c) and producing a hydrogen-rich gas and removed CO.sub.2, and leading the removed CO.sub.2 to urea synthesis in a urea synthesis unit; (e) combining the hydrogen-rich gas from step (d) with the nitrogen from step (b) to form a mixed gas, and removing catalyst poisons and part of inerts from the mixed gas to form an ammonia feed, and leading the ammonia feed to an ammonia synthesis in an ammonia synthesis unit; (f) removing part of carbon dioxide from the syngas from the ATR in step (a) and leading the CO.sub.2 removed from the ATR to the urea synthesis unit; and (g) leading CO.sub.2 reduced syngas from step (f) to a methanol synthesis unit, wherein a part of the synthesis gas from the ATR of step (a) is led to the SMR outlet upstream from the shift stage or part of the synthesis gas from the SMR from step (a) is combined with the syngas from the ATR.

2. The process according to claim 1, wherein the syngas from the ATR has a steam-to-carbon ratio (S/C ratio) of between 0.4 and 1.8.

3. The process according to claim 1, wherein the syngas from the SMR has an S/C ratio of between 1.4 and 3.3.

4. The process according to claim 1, wherein syngas from the SMR is sent to the methanol synthesis unit to increase methanol production.

5. The process according to claim 1, wherein CO.sub.2 present in the syngas from the ATR is optionally removed upstream of the methanol synthesis unit and fed to the urea synthesis stage.

6. The process according to claim 1, wherein SMR syngas is directed to the methanol synthesis, to obtain higher proportions of methanol.

7. The process according to claim 1, wherein ATR syngas is directed to the shift downstream the ATR, and CO.sub.2 is removed from the synthesis gas fed to the methanol synthesis unit and used for urea production to provide a higher proportion of urea.

Description

EXAMPLE

(1) The conditions for an ATR reforming section and an SMR reforming section are listed in Table 1. Pure methane is used as feed in the example, but it can be any typical hydrocarbon feed. The result for a natural gas containing higher hydrocarbons and/or CO.sub.2 will result in a relatively larger SMR section compared to the ATR section than used in the example.

(2) Table 1 below lists the dry gas composition of the synthesis gases, the oxygen consumption and the available nitrogen.

(3) The dry gas compositions show the difference in hydrogen and carbon composition making it possible to optimise the CO.sub.2 management such that the overall process can be made without excess CO.sub.2.

(4) TABLE-US-00001 TABLE 1 Reforming step ATR SMR flow, Nm.sup.3/h 160000 21000 steam/carbon, S/C 0.6 2.5 CH.sub.4, mole % 100 100 syngas, Nm.sup.3/h 470000 80850 H.sub.2, mole % 66 74 CO, mole % 27.5 16.5 CO.sub.2, mole % 5 6 CH.sub.4, mole % 1.5 3.5 oxygen, Nm.sup.3/h 78000 nitrogen, Nm.sup.3/h 300000

(5) It is clear that even if all the synthesis gas is used to make urea, there will be an excess of nitrogen.

(6) In Table 2 below, the results of various product scenarios are calculated. A common feature for all cases is that all process CO.sub.2 is used for producing urea and/or methanol. The table illustrates that the concept allows any product split between urea and methanol without excess CO.sub.2 from the process.

(7) TABLE-US-00002 TABLE 2 ATR, CH.sub.4flow 160 160 160 160 160 100 100 1000 Nm.sup.3/h SMR, CH.sub.4flow 23 22 21 21 21 20 40 1000 Nm.sup.3/h % SMR syngas 100 100 100 100 100 0 50 to urea % ATR syngas 100 75 50 25 0 0 0 to urea MeOH, MTPD* 0 1200 2400 3600 4800 3700 3700 Urea, MTPD* 11100 8700 6300 3900 1500 0 1100 *MTPD = metric tons per day