5 replies to this topic

[chessboss]

I need a topping column to remove incondensables from methanol. From my HYSYS simulation, I am getting negative temperature. But an article I am reading has the temperature at 70C. I have a product stream consisting of 92% methanol, 3% water and 5% incondensables coming out of the methanol reactor.

Edited by chessboss, 26 November 2017 - 11:30 AM.

[Saml]

First: there is no negative temperature.  There is below zero in the centigrade scale  (below 273K) or below zero in the Fahrenheit scale (255K).

 

I don't know fo a methanol plant that feeds fom the reactor outlet. Usually there is a condenser and only the liquid is fed to the topping column. Regarding non-condensibles, please clarify that you are not referring to ligth ends.

 

Also, pleas post the spec for you column. If you specified too little methanol loss from the top, probably that is the reason your temperature is low.

 

There is no much we can help with the information you provided.

[Nikolay_]

Hello,

 

It's interesting for me to know how will you workaround it. I faced with such problem, when I had to reduce traces of gases in methanol product (0,93 % wt). There was to options to resolve it: 1st Instalation of low pressure vessel for degassing and then to send product in atmoshperic reservoir;

2nd Do nothing and send product to spheric reservoir under pressure. Second option was chosen.

Edited by Nikolai T, 27 November 2017 - 09:32 PM.

[DB Shah]

Hi,

You need to purge out non condensibles from the Topping top, this will be a continuous vent stream.

Your reactor outlet Methanol is 92%, that is very high for conventional reactors, which reaction process do you have?

[chessboss]

Hello, I am using a Lurgi methanol reactor with a flash drum to recycle unreacted syngas. The feed to the topping column is the bottom stream of this flash drum.

 

I'm referring to carbon dioxide and a bit of unreacted syngas, which the flash drum cannot fully separate from methanol. I specified a 99.9% recovery for methanol at the condenser as a liquid, while the non-condensibles leave through an offgas line at the top.

Edited by chessboss, 02 December 2017 - 02:13 AM.

[DB Shah]

Hi,

Dissolved gases (CO2 and lighter components Ketones, Methyl formate etc) will be purged out from top of Topping Column. Do not specify column as "total condensing" column in simulator. Specify vapour draw as product. Give a higher value of this draw initially and then optimize. Practically this gases can be used in Reformer fuel (if your source of C & H is reformer)

 

Bottom of Topping column will be fed to Refining column. From top all the vapour is condensed and fed as reflux. Normally product is drawn from 3rd tray from top tray of Refining column. 

 

You can opt for two column or three column configuration.

 

Normally Methanol in crude is in the range of 65wt% to 80wt% based on feed stock. It will be interesting to know your feed stock resulting into such a high Methanol concentration of 92% in crude.