4 replies to this topic

We have total condeser on top of methanol distillation. As there are no inerts and methanol is totally condensed in condenser. To control column pressure we have pressure control on condenser CW outlet. However this typically creates problem in low load operation and in case of clean exchanger. In these conditions, CW control valve closes to maintain pressure and CW flow reduces. This results in CW outlet temperature very high. It reaches to 60 to 65 deg C. This creates fouling and corrosion problems in CW piping and exchanger. I would like to have design solution for this problem. Any Ideas!

[mrj]

We have total condeser on top of methanol distillation. As there are no inerts and methanol is totally condensed in condenser. To control column pressure we have pressure control on condenser CW outlet. However this typically creates problem in low load operation and in case of clean exchanger. In these conditions, CW control valve closes to maintain pressure and CW flow reduces. This results in CW outlet temperature very high. It reaches to 60 to 65 deg C. This creates fouling and corrosion problems in CW piping and exchanger. I would like to have design solution for this problem. Any Ideas!

Maybe you can think of implementing a 'Heat Duty Controller'. I dont know, how viable it is.
You can have (reflux) temperature controller and a separate pressure controller on the vent of condenser with innert gas (N2) to avoid vacuum.
mrj

[djack77494]

chimu,
It's generally bad practice to try to throttle cooling water going to/from a S&T heat exchanger. You want to maintain velocity, max temperature, etc. and reducing the flow has several negative consequences. Certainly you don't want your cooling water to reach the high temperatures you indicate.

Several approaches may be possible to deal with what I presume is a wide variation in duty requirements. I think I'd try using a tempered water cooling system. Circulate tempered water in a loop around the condenser. Connect the water from the condenser to the cooling water return header. Now connect a cool water supply line from the cold cooling water header. Put a temperature control valve in this last line and size the lines and equipment so that you maintain a nearly constant water flow through the loop but you vary the amount of cold water makeup from full flow to a minimal value.

[Zauberberg]

For total condenser applications, the best solution is to consider 'hot vapor bypass' or 'flooded condenser' pressure control schemes. Throttling CW flow has always been a bad option.

Look at Andrew Sloley's document for more information: Effectively control column pressure

[DAS-PE]

How you have the condenser working is another way to consider the conditions. As an example if the methanol vapor condenses on part of the tubes and the remaining tubes are covered with nitrogen, then only the tubes cooling the methanol will be used, the rest are not participating in the heat transfer. In this way you have variable area for transfer and the pressure control will be by the nitrogen back pressure. A knock back condenser will accomplish this. Any design requires a very low pressure drop across the condenser. Condenser design is the key to this control.