PROCESS AND APPARATUS FOR THE RECOVERY OF METHANOL

Abstract

There is proposed an efficient recovery of methanol from waste gases loaded with methanol in an integrated flow chart for the production and processing of methanol. The methanol fractions separated from the waste gases are recovered within the already existing, distillative processing of the crude methanol to pure methanol, so that no separate apparatuses are required for the recovery of the methanol from the loaded scrubber waste waters. The valuable substance methanol is recovered and the impact on the environment is reduced. By means of particular aspects of the invention the need for water as washing agent can be reduced further.

Claims

1-18. (canceled)

19. A process for the recovery of methanol from process waste gases of the methanol synthesis, comprising the following process steps: a) converting a synthesis gas stream under methanol synthesis conditions in at least one methanol synthesis reactor which is arranged in a synthesis gas circuit for non-converted synthesis gas; b) discharging a liquid crude methanol stream from the synthesis gas circuit and discharging a purge gas stream from the synthesis gas circuit, wherein the purge gas stream is loaded with methanol vapor; c) introducing the purge gas stream into a purge gas washing apparatus, contacting the purge gas stream in the purge gas washing apparatus with a water stream as washing agent which is guided through the purge gas washing apparatus in counterflow to the purge gas stream, wherein the water stream absorbs at least a part of the methanol from the purge gas stream; d) discharging a water stream loaded with methanol and a purge gas stream depleted of methanol from the purge gas washing apparatus; e) introducing the liquid crude methanol stream into an expansion tank in which the pressure of the liquid crude methanol stream is reduced, wherein an expansion gas stream loaded with methanol and a depressurized crude methanol stream are obtained; f) introducing the expansion gas stream into an expansion gas washing apparatus, contacting the expansion gas stream in the expansion gas washing apparatus with a water stream as washing agent which is guided through the expansion gas washing apparatus in counterflow to the expansion gas stream, wherein the water stream absorbs at least a part of the methanol from the expansion gas stream; g) discharging a water stream loaded with methanol and an expansion gas stream depleted of methanol from the expansion gas washing apparatus, wherein the water stream loaded with methanol is added to the depressurized crude methanol stream; h) introducing the depressurized crude methanol stream into a storage tank in which it is stored until its further processing or further use and in the process is covered by an inertizing gas which thereby is loaded with methanol; i) discharging an inertizing gas stream loaded with methanol from the storage tank and introducing the same into an inertizing gas washing apparatus, contacting the inertizing gas stream in the inertizing gas washing apparatus with a water stream as washing agent which is guided through the inertizing gas washing apparatus in counterflow to the inertizing gas stream, wherein the water stream absorbs at least a part of the methanol from the inertizing gas stream; and j) discharging a water stream loaded with methanol and an inertizing gas stream depleted of methanol from the inertizing gas washing apparatus.

20. The process according to claim 19, wherein the purge gas stream depleted of methanol, which is obtained in step (d), is supplied to a hydrogen recovery apparatus.

21. The process according to claim 19, wherein the water stream loaded with methanol, which is obtained in step (d), is at least partly supplied to the expansion tank.

22. The process according to claim 19, wherein the water stream loaded with methanol, which is obtained in step (d), is at least partly used as washing agent in the expansion gas washing apparatus.

23. The process according to claim 19, wherein at least a part of the depressurized crude methanol stream obtained in process step (e) is supplied to a distillation apparatus without intermediate storage in the storage tank.

24. The process according to claim 19, wherein at least a part of the expansion gas stream depleted of methanol, which is obtained in step (g), is introduced into the storage tank as inertizing gas.

25. The process according to claim 19, wherein at least a part of the water stream loaded with methanol, which is obtained in step (j), is used as washing agent in the expansion gas washing apparatus.

26. The process according to claim 19, wherein at least a part of the water stream loaded with methanol, which is obtained in step (j), is supplied to the expansion tank.

27. An apparatus for the recovery of methanol from process waste gases of the methanol synthesis, the apparatus comprising: a) a methanol synthesis reactor which is arranged in a synthesis gas circuit for non-converted synthesis gas; b) a conduit for discharging a liquid crude methanol stream from the synthesis gas circuit and a conduit for discharging a purge gas stream from the synthesis gas circuit, wherein the purge gas stream is loaded with methanol vapor; c) a purge gas washing apparatus designed as countercurrent washer, a conduit for introducing the purge gas stream into a purge gas washing apparatus, a conduit for supplying a water stream as washing agent, a conduit for discharging a water stream loaded with methanol, and a conduit for discharging a purge gas stream depleted of methanol from the purge gas washing apparatus; d) an expansion tank in which the pressure of the liquid crude methanol stream is reduced, a conduit for introducing the liquid crude methanol stream into the expansion tank, an expansion gas washing apparatus designed as countercurrent scrubber which is connected with the expansion tank, a conduit for introducing a water stream as washing agent into the expansion gas washing apparatus, a conduit for discharging a depressurized crude methanol stream, and a conduit for discharging an expansion gas stream depleted of methanol; e) a storage tank, a conduit for introducing the depressurized crude methanol stream into the storage tank, a conduit for introducing an inertizing gas and a conduit for discharging an inertizing gas stream loaded with methanol from the storage tank, a conduit for discharging the crude methanol; and f) an inertizing gas washing apparatus designed as countercurrent scrubber, a conduit for introducing an inertizing gas stream loaded with methanol into the inertizing gas washing apparatus, a conduit for introducing a water stream as washing agent into the inertizing gas washing apparatus, a conduit for discharging an inertizing gas stream depleted of methanol, and a conduit for discharging a water stream loaded with methanol from the inertizing gas washing apparatus.

28. The apparatus according to claim 27, furthermore comprising a hydrogen recovery apparatus and a conduit for introducing a purge gas stream depleted of methanol into the hydrogen recovery apparatus.

29. The apparatus according to claim 27, furthermore comprising a conduit for supplying the water stream loaded with methanol, which is obtained in process step (d), to the expansion tank.

30. The apparatus according to claim 27, furthermore comprising a conduit for supplying the water stream loaded with methanol, which is obtained in process step (d), to the expansion gas washing apparatus as washing agent.

31. The apparatus according to claim 27, furthermore comprising a distillation apparatus and a conduit for supplying the depressurized crude methanol stream obtained in process step (e) to the distillation apparatus.

32. The apparatus according to claim 27, furthermore comprising a conduit for supplying at least a part of the expansion gas stream depleted of methanol, which is obtained in process step (g), into the storage tank as inertizing gas.

33. The apparatus according to claim 27, furthermore comprising a conduit for supplying at least a part of the water stream loaded with methanol, which is obtained in process step (j), to the expansion gas washing apparatus as washing agent.

34. The apparatus according to claim 27, furthermore comprising a conduit for supplying at least a part of the water stream loaded with methanol, which is obtained in process step (j), to the expansion tank.

35. A plant configured for the production of methanol by conversion of coal=based synthesis gas comprising the apparatus as claimed in claim 27.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Further features, advantages and possible applications of the invention can also be taken from the following description of exemplary embodiments and numerical examples as well as the drawings. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

[0057] In the drawings:

[0058] FIG. 1 shows the schematic representation of the process according to the invention and the apparatus according to the invention in a first aspect,

[0059] FIG. 2 shows the schematic representation of the process according to the invention and the apparatus according to the invention in a second aspect,

[0060] FIG. 3 shows the schematic representation of the process according to the invention and the apparatus according to the invention in a third aspect,

[0061] FIG. 4 shows the schematic representation of the process according to the invention and the apparatus according to the invention in a fourth aspect.

DETAILED DESCRIPTION OF THE INVENTION

[0062] The process of the invention and the apparatus of the invention according to a first aspect are explained in FIG. 1. Via conduit 1 synthesis gas consisting of hydrogen and carbon oxides is introduced into the methanol synthesis reactor 2 arranged in a synthesis gas circuit, which here is shown only schematically and is not explained in detail, in which the synthesis gas is partly converted to methanol under the conditions of methanol synthesis. The crude methanol produced in the process is discharged from the methanol synthesis reactor via conduit 10.

[0063] The largest part of the synthesis gas not converted during the methanol synthesis is recirculated to the inlet of the methanol synthesis reactor via the non-illustrated synthesis gas circuit. Via conduit 3, the remaining fraction of the non-converted synthesis gas is discharged from the methanol synthesis reactor as purge gas or flushing gas and guided to the purge gas washing apparatus 4. This is a washing column known per se, which can be equipped with trays, packed beds or structured packings, in order to intensify the mass transfer between gas and liquid. The purge gas stream is charged to the purge gas washing apparatus at its bottom side and is countercurrently brought in contact with a water stream supplied as washing agent via conduit 5, whereby its content of methanol vapor is reduced. In the present exemplary embodiment and in those described below, demineralized water is used as washing agentunless otherwise noted.

[0064] The purge gas depleted of methanol leaves the purge gas washing apparatus via conduit 6. It can then optionally be heated in the heat exchanger 7 by indirect heat exchange against low-pressure steam as heating medium and via conduit 8 be discharged from the process and be guided to a non-illustrated hydrogen recovery system.

[0065] The water loaded with methanol in the purge gas washing apparatus is discharged from the same via conduit 9 and together with the crude methanol supplied via conduit 10 guided to the expansion tank 12 via conduit 11. The mixture of crude methanol and water is depressurized in said expansion tank from 7.0 MPa,g to a pressure of 0.5 MPa,g (,g designates the corresponding pressure unit at overpressure). In the expansion gas washing apparatus 13 constructionally connected with the expansion tank and in fluid connection with the same the gases or vapors released during the depressurization are brought in contact with a water stream supplied as washing agent via conduit 14, whereby its content of methanol vapor is reduced. The expansion gas washing apparatus also is a washing column known per se, which can be equipped with trays, packed beds or structured packings, in order to intensify the mass transfer between gas and liquid. The expansion gas stream depleted of methanol leaves the expansion gas washing apparatus via conduit 15.

[0066] The depressurized mixture of crude methanol and water is discharged from the expansion tank 12 via conduit 16. Via conduit 17 it can completely or partly be guided to a non-illustrated distillation apparatus in which the crude methanol is processed further to pure methanol by distillative separation of water.

[0067] Via conduit 18, the fraction of the mixture of crude methanol and water not guided to the distillation apparatus is guided to the tank 19 and introduced into the same. At a later time, crude methanol can be withdrawn from the tank and be supplied to the distillative processing. Supply and discharge conduits for crude methanol are not shown in the drawing. The tank 19 is a fixed-roof tank in which the free inner volume of the tank is filled by nitrogen, which is supplied via a non-illustrated conduit, and thus is inertized. The nitrogen atmosphere thereby is saturated with methanol. When loading the tanks or due to tank breathing, for example due to solar radiation, nitrogen loaded with methanol is discharged from the tank via conduit 20, in order to avoid an overpressure in the tank. This inertizing gas stream loaded with methanol vapor is guided to the inertizing gas washing apparatus 21, charged to the same on its bottom side, and is countercurrently brought in contact with a water stream supplied as washing agent via conduit 22, whereby its content of methanol vapor is reduced.

[0068] The inertizing gas washing apparatus also is designed as washing column and equipped with trays, packed beds or structured packings, in order to intensify the mass transfer between gas and liquid. It is, however, separated into an upper and a lower part by a separation tray arranged approximately in the middle of the column, which is designed as chimney tray. The washing agent partly loaded with methanol accumulates on the same, as due to the design as chimney tray it cannot get into the lower column part within the column, whereas the inertizing gas stream to be purified freely can flow from the lower into the upper column part. The washing agent partly loaded with methanol, on the other hand, is guided out of the column via a conduit, cooled in an intermediate cooler and again charged to the column at the upper end of the lower column part. Due to cooling of the partly loaded washing agent, its absorption capacity for further methanol is increased.

[0069] Via conduit 24, the washing agent loaded with methanol is discharged from the inertizing gas washing apparatus and via conduits 25 and 11 guided to the expansion tank 12. If distinctly different pressures exist in the conduits 25 and 11, the washing agent loaded with methanol also can be guided to the expansion tank separate from conduit 11 and/or an expansion valve is provided in the junction of conduit 25 and conduit 11.

[0070] FIG. 2 schematically illustrates the procedure of the process according to the invention and the construction of an apparatus according to the invention in a second aspect. The process according to the invention and the apparatus according to the invention correspond to the aspect shown in FIG. 1 up to the plant component 25. Now, however, a conduit 30 is added, with which the water stream loaded with methanol, which is discharged from the purge gas washing apparatus, is at least partly supplied to the expansion gas washing apparatus and finally to the expansion tank. In this way, the water stream loaded with methanol can be supplied to the further processing together with other water streams containing methanol, so that no separate processing apparatuses are required for the water stream loaded with methanol, which is obtained in the purge gas washing apparatus. In addition, the water stream loaded with methanol can replace at least a part of the demineralized water used as washing agent.

[0071] FIG. 3 schematically illustrates the procedure of the process according to the invention and the construction of an apparatus according to the invention in a third aspect. The process according to the invention and the apparatus according to the invention correspond to the aspect shown in FIG. 1 up to the plant component 25. Now, however, a conduit 31 is added, with which the water stream loaded with methanol, which is discharged from the inertizing gas washing apparatus, is at least partly supplied to the expansion gas washing apparatus and finally to the expansion tank. In this way, the water stream loaded with methanol can be supplied to the further processing together with other water streams containing methanol, so that no separate processing apparatuses are required for the water stream loaded with methanol, which is obtained in the inertizing gas washing apparatus. In addition, the water stream loaded with methanol can replace at least a part of the demineralized water used as washing agent.

[0072] FIG. 4 schematically illustrates the procedure of the process according to the invention and the construction of an apparatus according to the invention in a fourth aspect. The process according to the invention and the apparatus according to the invention correspond to the aspect shown in FIG. 1 up to the plant component 25. Now, however, both conduit 30 and conduit 31 are added, whose function has been shown in the aspects illustrated in FIG. 2 and FIG. 3 and discussed above in connection with the same. Due to the design as shown in FIG. 4, a particularly large fraction of the demineralized water used as washing agent can be replaced by water streams loaded with methanol from the purge gas washing apparatus and the inertizing gas washing apparatus.

Numerical Examples

[0073] In the following Tables numerical examples are listed for the inventive purification of purge gas (Table 1), of expansion gas (Table 2) and of tank waste gas (inertizing gas) (Table 3). Furthermore, Tables 4 and 5 show the purification of expansion gas according to particular aspects of the invention, in which partly loaded waste water from the purge gas washing apparatus (Table 4, conduit 30) or from the inertizing gas washing apparatus (Table 5, conduit 31) is recirculated to the expansion gas washing apparatus and used there as washing agent.

TABLE-US-00001 TABLE 1 Purge gas purification Purge Demin. Purge gas Waste gas water purified water Mole fraction CH3OH 0.0057 0.0000 0.0000 0.0461 H2O 0.0001 1.0000 0.0015 0.9515 CO2 0.0424 0.0000 0.0424 0.0013 CO 0.0643 0.0000 0.0646 0.0001 H2 0.7990 0.0000 0.8026 0.0009 AR 0.0000 0.0000 0.0000 0.0000 N2 0.0883 0.0000 0.0887 0.0001 CH4 0.0002 0.0000 0.0002 0.0000 Total stream 1288.1 152.9 1282.1 158.9 kmol/h Total stream 10223.7 2754.9 10010.3 2968.3 kg/h Temperature 40.0 42.2 43.9 44.7 C. Pressure 7.0 8.1 7.0 7.0 MPag

TABLE-US-00002 TABLE 2 Expansion gas purification Expansion Expansion Demin. gas gas water purified Mole fraction CH3OH 0.0579 0.0000 0.0000 H.sub.2O 0.0018 1.0000 0.0132 CO2 0.2285 0.0000 0.2392 CO 0.0397 0.0000 0.0417 H2 0.3607 0.0000 0.3789 AR 0.0379 0.0000 0.0398 N2 0.2676 0.0000 0.2812 CH4 0.0058 0.0000 0.0061 Total stream 177.9 277.5 169.3 kmol/h Total stream 4072.5 5000.0 3769.8 kg/h Temperature 40.6 40.0 40.4 C. Pressure 0.5 0.5 0.5 MPag

TABLE-US-00003 TABLE 3 Inertizing gas purification Inertizing Inertizing Demin. gas Waste gas water purified water Mole fraction CH3OH 0.3338 0.0000 0.0043 0.2671 H.sub.2O 0.0000 1.0000 0.1425 0.7328 CO2 0.0000 0.0000 0.0000 0.0000 CO 0.0000 0.0000 0.0000 0.0000 H2 0.0000 0.0000 0.0000 0.0000 AR 0.0000 0.0000 0.0000 0.0000 N2 0.6662 0.0000 0.8532 0.0000 CH4 0.0000 0.0000 0.0000 0.0000 Total stream 180.0 183.2 140.5 222.6 kmol/h Total stream 5284.5 3300.0 3739.2 4845.3 kg/h Temperature 40.3 40.0 53.1 50.2 C. Pressure 0.0 0.4 0.0 0.5 MPag

TABLE-US-00004 TABLE 4 Expansion gas purification with conduit (30) Expansion Expansion Waste gas gas water purified Mole fraction CH3OH 0.0575 0.0461 0.0082 H.sub.2O 0.0012 0.9515 0.0202 CO2 0.2264 0.0013 0.2339 CO 0.0399 0.0001 0.0412 H2 0.3625 0.0009 0.3745 AR 0.0380 0.0000 0.0392 N2 0.2686 0.0001 0.2769 CH4 0.0058 0.0000 0.0060 Total stream 176.9 158.9 171.7 kmol/h Total stream 4036.8 2968.3 3819.4 kg/h Temperature 39.9 44.6 49.6 C. Pressure 0.5 0.5 0.5 MPag

TABLE-US-00005 TABLE 5 Expansion gas purification with conduit (31) Expansion Expansion gas gas Waste water purified Mole fraction CH3OH 0.0571 0.2671 0.0344 H.sub.2O 0.0012 0.7328 0.0165 CO2 0.2259 0.0000 0.2263 CO 0.0399 0.0000 0.0403 H2 0.3630 0.0000 0.3666 AR 0.0380 0.0000 0.0384 N2 0.2690 0.0000 0.2716 CH4 0.0058 0.0000 0.0058 Total stream 176.7 222.6 174.9 kmol/h Total stream 4027.1 4845.3 3929.7 kg/h Temperature 39.7 50.0 49.7 C. Pressure 0.5 0.5 0.5 MPag

INDUSTRIAL APPLICABILITY

[0074] With the invention, an efficient recovery of methanol from waste gases loaded with methanol is proposed in an integrated flow chart for the production and processing of methanol. The methanol fractions separated from the waste gases are recovered within the already existing, distillative processing of the crude methanol to pure methanol, so that no separate apparatuses for the recovery of the methanol from the loaded scrubber waste waters are required. The valuable substance methanol is recovered and the impact on the environment is reduced. By means of particular aspects of the invention the need for water as washing agent can be reduced further.

[0075] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0076] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0077] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0078] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0079] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0080] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0081] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

LIST OF REFERENCE NUMERALS

[0082] 1 conduit [0083] 2 methanol synthesis reactor [0084] 3 conduit [0085] 4 purge gas washing apparatus [0086] 5 conduit [0087] 6 conduit [0088] 7 heat exchanger [0089] 8 conduit [0090] 9 conduit [0091] 10 conduit [0092] 11 conduit [0093] 12 expansion tank [0094] 13 expansion gas washing apparatus [0095] 14 conduit [0096] 15 conduit [0097] 16 conduit [0098] 17 conduit [0099] 18 conduit [0100] 19 tank [0101] 20 conduit [0102] 21 inertizing gas washing apparatus [0103] 22 conduit [0104] 23 conduit [0105] 24 conduit [0106] 25 conduit [0107] 30 conduit [0108] 31 conduit