SYSTEM AND METHOD FOR COOLING A METHANOL REACTOR EFFLUENT VAPOR STREAM IN METHANOL PRODUCTION PLANT

Abstract

Provided is a method for cooling a methanol r synthesis reactor effluent vapor stream in a methanol production plant, wherein the method comprises the steps of: receiving, using an inlet of a cooler, the methanol synthesis reactor effluent vapor stream from an interchanger or a methanol synthesis reactor of the methanol production plant; and spraying, using a recirculation pump connected to a spraying device, a liquid condensate received from a methanol synthesis loop onto a tube sheet of the cooler which enables direct contact of the liquid condensate with the methanol synthesis reactor effluent vapor stream and cools the methanol synthesis reactor effluent vapor stream.

Claims

1. A cooling system for cooling a methanol synthesis reactor effluent vapor stream in a methanol production plant, wherein the cooling system is integrated with the methanol production plant, wherein the cooling system comprises: a cooler, preferably a tube and shell heat exchanger, comprising cooling tubes for cooling the methanol synthesis reactor effluent vapor stream, a shell side for passing of a fluid cooling medium, a tube sheet for separating the cooling tubes from the shell side, and an inlet that receives the methanol synthesis reactor effluent vapor stream from an interchanger or from a methanol synthesis reactor of the methanol production plant; and a recirculation pump connected to a spraying device that is configured to spray a liquid condensate received from a methanol synthesis loop onto the tube sheet of the cooler which enables direct contact of the liquid condensate with the methanol synthesis reactor effluent vapor stream and cools the methanol synthesis reactor effluent vapor stream.

2. The cooling system according to claim 1, wherein the liquid condensate spray is configured to cool metal surfaces of the cooler.

3. The cooling system according to claim 1, wherein the liquid condensate comprises a stabilized crude methanol, a product methanol, or a wastewater obtained from the methanol synthesis loop.

4. The cooling system according to claim 1, wherein the liquid condensate is cooled to a temperature below about 50 degrees Celsius, more preferably below about 40 degrees Celsius.

5. The cooling system according to claim 1, wherein the spraying device is arranged at the inlet of the cooler.

6. The cooling system according to claim 1, wherein a mixture temperature of the sprayed liquid condensate and methanol synthesis reactor effluent vapor is below about 100 degrees Celsius, preferably below about 90 degrees Celsius.

7. The cooling system according to claim 1, wherein the cooling system further comprises a vapor-liquid separator for separating a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream.

8. The cooling system according to claim 1, wherein the cooler comprises an integrated vapor-liquid separator for separating a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream.

9. The cooling system according to claim 1, wherein the cooling system does not comprise an air cooler.

10. A method for cooling a methanol synthesis reactor effluent vapor stream in a methanol production plant, wherein the method comprises the steps of: a. receiving, using an inlet of a cooler, the methanol synthesis reactor effluent vapor stream from an interchanger or from a methanol synthesis reactor of the methanol production plant; and b. spraying, using a recirculation pump connected to a spraying device, a liquid condensate received from a methanol synthesis loop onto the tube sheet of the cooler which enables direct contact of the liquid condensate with the methanol synthesis reactor effluent vapor stream and cools the methanol synthesis reactor effluent vapor stream.

11. The method according to claim 10, wherein the liquid condensate spray cools metal surfaces of the cooler.

12. The method according to claim 10, wherein the liquid condensate comprises a stabilized crude methanol, a product methanol, or a wastewater obtained from the methanol synthesis loop.

13. The method according to claim 10, wherein the liquid condensate is cooled to a temperature below about 50 degrees Celsius, more preferably below about 40 degrees Celsius.

14. The method according to claim 10, wherein the spraying device is arranged at the inlet of the cooler.

15. The method according to claim 10, wherein a mixture temperature of the sprayed liquid condensate and methanol synthesis reactor effluent vapor is below about 100 degrees Celsius, preferably below about 90 degrees Celsius.

16. The method according to claim 10, wherein the method comprises separating, using a vapor-liquid separator, a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream.

17. The method according to claim 16, wherein the method comprises recycling a part of the liquid condensate stream to the spraying device and discharging at least a part of the residual gas stream as purge stream.

18. The method according to claim 10, wherein the method comprises integrating a vapor-liquid separator in the cooler for separating a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream.

19. The method according to claim 18, wherein the method comprises recycling a part of the liquid condensate stream to the spraying device and discharging at least a part of the residual gas stream as purge stream.

20. The method according to claim 10, wherein the cooler is a tube and shell heat exchanger and comprises cooling tubes for cooling the methanol reactor effluent vapor stream, a shell side for passing of a fluid cooling medium, a tube sheet for separating the cooling tubes from the shell side

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. To illustrate the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, the same elements have been indicated by identical numbers. Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:

[0021] FIG. 1 is a schematic illustration of a single-stage methanol synthesis system according to the prior art with a water cooled reactor (WCR) without an air cooler for methanol production;

[0022] FIG. 2 is a schematic illustration of an embodiment of the invention, comprising a cooling system integrated with a methanol production plant for cooling a methanol synthesis reactor effluent vapor stream according to an embodiment of the present disclosure;

[0023] FIG. 3 is a schematic illustration of an embodiment of the invention, comprising a cooling system integrated with a methanol production plant cooler comprising an integrated vapor-liquid separator in the cooler according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

[0025] According to a first aspect, the present disclosure provides a cooling system for cooling a methanol synthesis reactor effluent vapor stream in a methanol production plant, wherein the cooling system is integrated with the methanol production plant, wherein the cooling system comprises: a cooler, preferably a tube and shell heat exchanger, comprising cooling tubes for cooling the methanol synthesis reactor effluent vapor stream, a shell side for passing of a fluid cooling medium, a tube sheet for separating the cooling tubes from the shell side, and an inlet that receives the methanol synthesis reactor effluent vapor stream from an interchanger or from a methanol synthesis reactor of the methanol production plant; and a recirculation pump connected to a spraying device that is configured to spray a liquid condensate received from a methanol synthesis loop onto a tube sheet of the cooler which enables direct contact of the liquid condensate with the methanol synthesis reactor effluent vapor stream and cools the methanol synthesis reactor effluent vapor stream.

[0026] The cooling system according to an aspect of the invention for cooling the methanol synthesis reactor effluent vapor stream in the methanol production plant according to the present disclosure enables cost-effective production of methanol in small capacity plants, either from conventional syngas, comprising CO and little or no CO.sub.2, or from the combination of carbon dioxide (CO.sub.2) and hydrogen. The cooling system enables a single cooler to be used for cooling the methanol synthesis reactor effluent vapor stream instead of multiple cooling systems used in typical methanol processes, thus providing an economic advantage for small-scale methanol production facilities. The cooling system provides direct cooling of the methanol synthesis reactor effluent vapor stream with a simple liquid spray using the recirculation pump with low head requirements at the cooler inlet. The cooling system also cools tube sheet, and other metal surfaces, thereby allowing the use of conventional materials without issue and avoiding the problem of high inlet temperatures. The recirculation pump is a small pump with low head requirements which further reduces the cost of the cooling system.

[0027] Optionally, according to an aspect of the invention, the liquid condensate spray cools metal surfaces of the cooler. The cooling of the metal surfaces relaxes the constraint of the material and improves the efficiency of the cooler.

[0028] Optionally, according to an aspect of the invention, the liquid condensate comprises a stabilized crude methanol, a product methanol, or a wastewater obtained from the methanol synthesis loop. The liquid condensate comprising the stabilized crude methanol, the product methanol, or the wastewater obtained from the methanol synthesis loop is cooled and used directly to cool the methanol reactor effluent vapor stream with no additional cooling equipment, e. g. a separate air cooler.

[0029] Optionally, according to an aspect of the invention, the liquid condensate is cooled to a temperature below about 50 degrees Celsius, more preferably below about 40 degrees Celsius. Experiments and/or calculation data have shown this temperatures to allow a safe and reliable condensation of the major part of the crude or raw methanol produced in the methanol synthesis reactor, while keeping the energy requirements at a tolerable level.

[0030] Optionally, according to an aspect of the invention, the spraying device is arranged at the inlet of the cooler. This allows a direct contact of the liquid condensate with the methanol synthesis reactor effluent vapor stream and thus cools the methanol synthesis reactor effluent vapor stream very effectively.

[0031] Optionally, according to an aspect of the invention, a mixture temperature of the sprayed liquid condensate and methanol synthesis reactor effluent vapor is below about 100 degrees Celsius, preferably below about 90 degrees Celsius. By lowering the mixture temperature to below these upper values, corrosion of the cooler internals and the downstream equipment is effectively prevented, especially when chlorides are present.

[0032] Optionally, the cooling system according to an aspect of the invention, further comprises a vapor-liquid separator for separating for separating a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream. The crude methanol comprised in the liquid condensate stream is a raw methanol product in a mix with water and impurities. The residual gas is unreacted syngas that may comprise carbon monoxide (CO), methane, ethane, and dimethyl ether.

[0033] Optionally, according to an aspect of the invention, the cooler comprises an integrated vapor-liquid separator for separating a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream. Such configuration has advantages for small capacity plants because the vapor-liquid separator is also eliminated as a separate equipment position.

[0034] Optionally, according to an aspect of the invention, the cooling system does not comprise an air cooler. Since the cooling of the methanol synthesis reactor effluent vapor stream is effected by the cooling system according to the invention, comprising the spraying of the liquid condensate onto the tube sheet of the cooler, the expensive air cooler can be omitted.

[0035] According to a second aspect, the present disclosure provides a method for cooling a methanol synthesis reactor effluent vapor stream in a methanol production plant, wherein the method comprises the steps of: receiving, using an inlet of a cooler, the methanol synthesis reactor effluent vapor stream from an interchanger or from a methanol synthesis reactor of the methanol production plant, wherein the cooler is preferably a tube and shell heat exchanger and comprises cooling tubes for cooling the methanol synthesis reactor effluent vapor stream, a shell side for passing of a fluid cooling medium, a tube sheet for separating the cooling tubes from the shell side; and spraying, using a recirculation pump connected to a spraying device, a liquid condensate received from a methanol synthesis loop onto the tube sheet of the cooler which enables direct contact of the liquid condensate with the methanol synthesis reactor effluent vapor stream and cools the methanol synthesis reactor effluent vapor stream.

[0036] Optionally, according to an aspect of the invention, the liquid condensate spray cools metal surfaces of the cooler. The cooling of the metal surfaces relaxes the constraint of the material and improves the efficiency of the cooler.

[0037] Optionally, according to an aspect of the invention, the liquid condensate comprises a stabilized crude methanol, a product methanol, or a wastewater obtained from the methanol synthesis loop. The liquid condensate comprising the stabilized crude methanol, the product methanol, or the wastewater obtained from the methanol synthesis loop is cooled and used directly with no additional cooling equipment, for example an air cooler.

[0038] Optionally, according to an aspect of the invention, the liquid condensate is cooled to a temperature below about 50 degrees Celsius, more preferably below about 40 degrees Celsius. Experiments and/or calculation data have shown this temperatures to allow a safe and reliable condensation of the major part of the crude or raw methanol produced in the methanol synthesis reactor, while keeping the energy requirements at a tolerable level.

[0039] Optionally, according to an aspect of the invention, the spraying device is arranged at the inlet of the cooler. This allows a direct contact of the liquid condensate with the methanol synthesis reactor effluent vapor stream and thus cools the methanol synthesis reactor effluent vapor stream very effectively.

[0040] Optionally, according to an aspect of the invention, a mixture temperature of the liquid condensate and methanol synthesis reactor effluent vapor is below about 100 degrees Celsius, preferably below about 90 degrees Celsius. By lowering the mixture temperature to below these upper values, corrosion of the cooler internals and the downstream equipment is effectively prevented, especially when chlorides are present.

[0041] Optionally, according to an aspect of the invention, the method comprises separating a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream. Such configuration has advantages for small capacity plants because the vapor-liquid separator is also eliminated as a separate equipment position. The liquid condensate stream comprises a raw methanol product in a mix with water and impurities. The residual gas is unreacted syngas that may comprise hydrogen, carbon monoxide, carbon dioxide, methane, ethane, and dimethyl ether.

[0042] Optionally, according to an aspect of the invention, the method comprises separating a liquid condensate stream and a residual gas stream from the cooled methanol synthesis reactor effluent vapor stream. Such integration of vapor-liquid separator in the cooler has advantages for small capacity plants because the vapor-liquid separator is also eliminated as a separate equipment position.

[0043] An example embodiment illustrates the principle for a 250 tons/day capacity methanol plant. The synthesis gas is produced using an autothermal reformer (ATR). The Stoichiometric Number SN equals 2.65, the Recycle Ratio RR equals 2.1. The amount of crude methanol produced at this scale is 14.6 tons/hours (t/h). The base case has an exit of the interchanger at approximately 117 degrees Celsius (° C.) with a total volumetric flow rate of 1830 cubic meter per hour (m3/h). High temperature would lead to difficulties on the cooling water side of the cooler. Implementing the recirculation flow using the recirculation pump connected to a nozzle as spraying device that sprays into the cooler inlet, in the amount of 40 t/h, lowers the stream inlet temperature to below 100° C., relaxing the constraint of the material. A consequence is to also lower the volumetric flow rate of the cooler inlet stream.

TABLE-US-00001 Cooler Inlet Cooler Inlet Recirculation Temperature Flow Spray @ 40 C. ° C. m3/h t/h 117.2 1830 0 98.9 1750 40 81.9 1724 100

[0044] A 40 t/h pump with low head requirements is a small piece of equipment compared to the deletion of an air cooler. The cooler has the same duty as the previous. With lower inlet temperature, the area required will increase because of lower logarithmic mean temperature difference (LMTD). However, the lower pressure drop of the exchanger leads to savings in compression costs. The 100 t/h pump is a more significant equipment item but still compares favorably to the deletion of an air cooler.

[0045] Embodiments of the present disclosure substantially eliminate or at least partially address the aforementioned technical drawbacks in existing technologies in providing a system and method for cooling a methanol reactor effluent vapor stream in a small-scale methanol production plant where the capital costs are dominant in determining the overall economics.

[0046] FIG. 1 is a schematic illustration of a single-stage methanol synthesis system 100 according to the prior art, but without an air cooler, for methanol production. The single-stage methanol synthesis system 100 includes a steam drum 102, a water-cooled methanol synthesis reactor 104, a methanol interchanger (heat exchanger) 108, a final cooler 110, a methanol separator 112, a recycle gas compressor 116, and a synthesis gas compressor 118. Liquid water flows down from the steam drum 102 to a cooling jacket of the water-cooled methanol reactor 104. The heat from the reaction boils part of the water. A vapor-liquid mixture from the water-cooled methanol reactor is returned to the steam drum 102 for separating the vapor and liquid. Steam leaves the steam drum 102 and liquid is retained in the steam drum 102 for additional cooling. Methanol reaction products from the water-cooled methanol synthesis reactor 104 are passed into the final cooler 110 for cooling after passing through the methanol interchanger 108. The final cooler 110 includes a cooling water supply (CWS) and cooling water return (CWR) for cooling the reaction products from the water-cooled methanol synthesis reactor 104. The cooled methanol reaction products from the final cooler 110 are passed into the methanol separator 112 where crude methanol is separated as liquid from uncondensed vapor (residual vapor or gas). A first portion of uncondensed vapor from the methanol separator 112 after separating crude methanol becomes purge gas and is used directly as fuel, e. g. in the synthesis gas production plant. The remaining portion of uncondensed vapor is compressed for recycle using the recycle gas compressor 116. The purge and recycle gases comprise unreacted gases and gaseous products such as hydrogen, carbon monoxide (CO), carbon dioxide (CO.sub.2), methane, ethane, and dimethyl ether. A make-up gas composed of CO.sub.2 and/or CO and also hydrogen is compressed with the synthesis gas compressor 118 and mixed with the recycle gas and supplied into the water-cooled methanol synthesis reactor 104 through the methanol interchanger 108.

[0047] The omission of the air cooler in the flowsheet of FIG. 1 may result in a temperature of 120° C. or more for an inlet gas to the cooler 108. Such a temperature is higher than typically allowed for process-compatible steel metallurgies in cooling water service where chlorides are present. Further, high metal surface temperatures can result in a breakdown of the cooling water treatment chemicals and give rise to corrosion on a process side and/or fouling on a cooling waterside. For example, when chlorides are present, such temperatures can cause corrosion and fouling on the cooling water side of the cooler. Chloride content when using stainless steel can cause stress corrosion cracking. Using higher-grade metallurgy or a lower chloride content can avoid the corrosion problem, but then the equipment or the cooling water supply becomes more expensive. Even in this case, the cooling water chemistry may still cause fouling in an exchanger even without corrosion.

[0048] FIG. 2 is a schematic illustration of a cooling system 200 integrated with a methanol production plant for cooling a methanol synthesis reactor effluent vapor stream according to an embodiment of the present disclosure. The cooling system 200 includes a cooler 202, a vapor-liquid separator 204, a recirculation pump 206. The cooler 202 receives the methanol reactor effluent vapor stream from a methanol interchanger or a methanol synthesis reactor of the methanol production plant. The cooler 202 includes a cooling water supply (CWS) and a cooling water return (CWR) for cooling the methanol reactor effluent vapor stream from the methanol interchanger or the methanol reactor. The cooled methanol synthesis reactor effluent vapor stream from the cooler 202 is directed into the liquid-vapor separator 204 where crude methanol and uncondensed vapors (residual vapor or gas) are separated. A first portion of uncondensed vapor from the vapor-liquid separator 204 after separating crude methanol becomes purge gas and is used directly as fuel, e. g. in the synthesis gas production plant, and the remaining portion of uncondensed vapor is compressed using a recycle gas compressor and used as a recycle gas. The purge gas comprises unreacted gases and gaseous products such as hydrogen, carbon monoxide (CO), carbon dioxide (CO.sub.2), methane, ethane, and dimethyl ether. A portion of crude methanol from the liquid-vapor separator 204 is recirculated through the recirculation pump 206 and sprayed back, by means of a spraying device, e. g. a nozzle, onto a cooling inlet and a tube sheet of the cooler 202. The recirculated crude methanol has an effect of direct-contact cooling of the incoming methanol reactor effluent vapor stream.

[0049] FIG. 3 is a schematic illustration of a cooling system 300 integrated with a methanol production plant cooler comprising an integrated vapor-liquid separator 304 in the cooler 302 according to an embodiment of the present disclosure. The cooling system 300 includes an integrated vapor-liquid separator 304 in the cooler 302 and a recirculation pump 306. The cooler 302 receives the methanol reactor effluent vapor stream from a methanol interchanger or a methanol synthesis reactor of the methanol production plant. The cooler 302 includes a cooling water supply (CWS) and a cooling water return (CWR) for cooling the methanol reactor effluent vapor stream. The integrated vapor-liquid separator 304 in the cooler 302 is configured to separate crude methanol and uncondensed vapor (residual vapor or gas) from the cooled methanol synthesis reactor effluent vapor stream. A first portion of the uncondensed vapor from the integrated vapor-liquid separator 304 becomes purge gas and is used directly as fuel, e. g. in the synthesis gas production plant, and the remaining portion is compressed using a recycle gas compressor and used as a recycle gas. The uncondensed vapor comprises unreacted gases and gaseous products such as hydrogen, carbon monoxide (CO), carbon dioxide (CO.sub.2), methane, ethane, and dimethyl ether. A portion of crude methanol from the integrated vapor-liquid separator 304 is recirculated through the recirculation pump 306 and sprayed back, by means of a spraying device, e. g. a nozzle, onto a cooling inlet and a tube sheet of the cooler 302. The recirculated crude methanol has an effect of direct-contact cooling of the incoming methanol reactor effluent vapor stream.

[0050] Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as “including”, “comprising”, “incorporating”, “have”, “is” used to describe, and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural.

[0051] 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.

[0052] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0053] “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.

[0054] “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.

[0055] 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.

[0056] 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.

LIST OF REFERENCE NUMERALS

[0057] 100—Single-stage methanol synthesis system [0058] 102— Steam drum [0059] 104—Water-cooled methanol synthesis reactor [0060] 108—Methanol interchanger [0061] 110—Final cooler [0062] 112—Methanol separator [0063] 116—Recycle gas compressor [0064] 118—Synthesis gas compressor [0065] 200— Cooling system [0066] 202— Cooler [0067] 204—Vapor-liquid separator [0068] 206—Recirculation pump [0069] 300—Cooling system [0070] 302—Cooler [0071] 304—Integrated vapor-liquid separator [0072] 306—Recirculation pump