CONVERSION OF OXGENATES IN PURGE FROM RAW METHANOL EVAPORATOR

Abstract

The invention relates to a processes comprising the steps of: in an evaporator forming a gas phase methanol rich stream from a feed stream; withdrawing a liquid purge stream from the evaporator, said liquid purge stream comprising oxygenates and water; providing the gas phase methanol rich stream to a conversion step; and adding at least part of said liquid purge stream upstream the conversion step.

Claims

1. A processes comprising the steps of: in an evaporator forming a gas phase methanol rich stream from a feed stream, withdrawing a liquid purge stream from the evaporator, said liquid purge stream comprising oxygenates and water, providing the gas phase methanol rich stream to a conversion step, and adding at least part of said liquid purge stream upstream the conversion step.

2. A process according to claim 1, wherein the conversion step is a gasoline conversion step.

3. A process according to claim 1, wherein the feed stream comprises raw methanol.

4. A process according to claim 1, wherein the oxygenates comprises ketones, aldehydes and/or higher alcohols.

5. A process according to claim 1, wherein the liquid purge stream is added to a recycle stream from the conversion step.

6. A process according to claim 1, wherein the liquid purge stream is added to the recycle stream from the conversion step up- and/or downstream a point where the gas phase methanol rich stream is added to the recycle stream from the conversion step.

7. A process according to claim 1, wherein the liquid purge stream is added to the recycle stream from the conversion step by quenching.

8. A plant comprising an evaporator or boiler, a conversion loop, at least one methanol mixing point and at least one purge mixing point.

9. A plant according to claim 8 wherein the conversion loop comprises a conversion step, a separator and means for returning a recycle stream to the conversion step.

10. Plant according to claim 8 wherein the conversion loop further comprises one or more heaters for heating the recycle stream, one or more coolers and condensers for condensing the converter effluent.

11. Plant according to claim 8, wherein one or more purge mixing points are arranged up-steam and/or downstream the methanol mixing point.

12. A plant comprising an evaporator or boiler, a conversion loop, at least one methanol mixing point and at least one purge mixing point, arranged to carry out the process according to claim 1.

13. Gasoline product produced according to the process of claim 1.

14. Gasoline product produced by the plant of claim 8.

Description

DRAWINGS

[0046] In the following the process and plant is further describe by reference to the figures. The embodiments in the figures are exemplary and are not to be construed as limiting to the invention.

[0047] FIG. 1 shows a simplified diagram of the process and plant.

[0048] FIG. 2 shows a diagram of the process and plant indicating some options for the process and plant.

[0049] FIG. 1 shows a principle diagram of the present process and plant. The diagram shows an evaporator 1 receiving a feed 2 in form of raw methanol. From the evaporator a gas phase methanol rich stream 3 and a liquid purge 4 are withdrawn. The methanol rich stream and the liquid purge is mixed into a gasoline conversion loop comprising a conversion step 5 in which at least the methanol rich stream is converted into at converted mixture (converter effluent) comprising raw gasoline. The converted mixture is separated into at least a recycle stream 6 and a raw gasoline stream 7. At least part of the recycle is returned to the conversion step and the raw gasoline may be send to further treatment, use and/or storage.

[0050] FIG. 2 shows options for various embodiments of the present process and plant. The base process is the same as described in FIG. 1 and for like parts like numbers are used. The mixing point 8 where the methanol rich stream is mixed with the recycle is here arranged up-steam a heater 9 which helps ensure a desired temperature of the stream to the converter 5. As indicated by dotted lines several converters may be arranged in parallel. The number of converters may e.g. depend on the flow in the system. The parallel converts may be worked one or more at a time while one or more converters are being regenerated.

[0051] The purge mixing point 10 is here arranged downstream a heat exchanger 11 heating the recycle stream and upstream the methanol mixing point 8, thus vaporizing the totality of the liquid purge. Alternative positions 10a, 10b 10c for the purge mixing point are indicated by dotted lines. If point 10a is used, insufficient vaporization may under disadvantageous parameters lead to a second phase. If point 10b is used, a similar result to that in alternative 10 is obtained, being the difference that a higher gas/liquid ratio goes through the nozzle. If point 10c is used, several nozzles are required (one per converter) which may increase the operation complexity due to parallel flow but may still be a functional and relevant alternative.

[0052] Processes and plants comprising more than one methanol mixing point and/or more than purge mixing point are also possible setups where e.g. temperature or flow conditions renders it advantageous.

[0053] In FIG. 2 is also indicated how the effluent 12 from the converter 5 is preferably cooled by at least a cooler 13 before being separated in a separator 14 into the recycle stream 6, the raw gasoline stream 7 and process water 15. A purge 16 can be taken e.g. from the recycle stream in order to reduce the amount of inerts etc. in the system.

[0054] A pump 17 for the liquid purge from the evaporator 1 and a compressor 18 for the recycle stream is also indicated in the figure.

[0055] In several embodiments one or more of the heat exchangers 9 and 11 utilize the heat in the converter effluent 12 whereby the (mixed) feed to the converter is heated while the effluent from the converter is cooled before condensing and separation.