7 replies to this topic

[engineer1985]

what will happen if the stripper's top temperature (steam containing acid gases) gets too low in a MDEA based gas sweetening unit?

Higher stripper top temperature causes corrsion and solvent loses, so we control the temperature by reflux but what will happen if top temperature gets too low..

are there any adverse effect of low stripper's top temperature?

[aanita]

Low reflux will generate. If top temperature is CASCADE with steam flow to the bottom
rebooler, MDEA will not regenarate fully. Absorption capacity of acid gas components will reduce, A result in OFF spec gas from MDEA contactor outlet. I don't see any other problems.

[engineer1985]

thanx aanita,

can u please explain how low reflux will generate if top temperature reduces?

as you may know that this stream will go to reflux condenser which drops its temperature further, as a result of which steam will separate out from acid gases by condensation...

now if this top temperature is already low, then in condenser further reduction in temperature will occur which will cause more steam to condense, hence more reflux will generate...

Correct me if i am wrong...

[aanita]

Can you upload the sketch. You are talking about upstream of condenser, not downstream. If you increase top temperature, more vapor flow will come, condense in the condenser, increase the reflux flow.

[Ohm Shah]

MDEA STRIPPER OVERHEAD LOW TEMPERATURE will result in reduction of stripping of H2S and CO2 from the MDEA system, and hence lean MDEA will not have its design composition. This will result in poor efficiency of H2S/CO2 remoal from acid gas.

[engineer1985]

well i want to ask three questions here about stripper's top temp (upstream of condenser)...

1)can you explain how increase in top temperature, will cause more vapor flow...
2)how we can increase top temperature, and
3)how to reduce top temperature

[himant]

Answers:
1. It is a very basic principle of any distillation column. More the top temperature of column, more will be the losses of more volatile components
2 & 3. Top temperature depends upon reboiling duty (assuming fixed condenser duty) and composition of CO2 in your feed gas (which is to be stripped). More the CO2, lower will be your top temperature

Regards
Himant

[Shah Khan]

Let have the reply in this way.

1- The propose of the boiler is to provide the heat input into the column, with vaporizes the volatile component in the column, and the top reflux control the column temperature through providing the cooling effect in the column and therefore control vapor emission from the column. Now if the top temperature increases it means that either the boiler is providing more heat to the system or top condenser/reflux in not providing sufficient cooling effect to the column.

2-3- The controlling parameter of the top temperature are reflux flow and/heat input from boiler. Normally the reflux rate is use for this propose. The reflux rate is controlled by increasing the condenser duty. The reboiler duty are also used for propose alternatively depending Lean Amine Loading.