1 reply to this topic

[Geovando]

Hello experts,

 

I am engaged in a revamp of a styrene process plant. My actual challenge is to evaluate the possibility to use a existing exchanger as reboiler of a ethybenzene recovery destillation column. To do it I've used HTRI.

 

I before shall to say: 

- the botton pressure of my column is 0,415 kgf/cm²A.

- exchenger in vertical position

- the height betwee LLL level liquid and lowest tubesheet is 3455 mm.

- the styrene flows through tube side and vapor flows through shell side.

- styrene design flow is 735 t/h

 

Primaryly I evaluated it setting the "inlet pressure" (at 0,415 kgf/cm²A) and reboiler type as "No peping specified". Until here HTRI presented me 7,34% in overdesign and all process variables (cold and hot flow, temperatures, % vapor, etc ...) converged properly.

 

The second step was to set reboiler type as "thermosiphon reboiler" and the pressure location at column botton (0,415 kgf/cm²A). As expected the styrene flow increased as a result of pressure balance. However the HTRI converges the styrene flow to a negative overdesign even in "simulation" mode. 

 

The question is: which will the styrene flow be for a null overdesign ? I already put in blank the steam and styrene flow, steam temperature, % vapor and set only outlet styrene temperature and even this the HTRI converges the results to a styrene flow higher the styrene design flow negative overdesign.

 

 

Could you help me by showing me where I'm going wrong or the best way to make the HTRI converges the results to a thermosiphon reboiler ?

 

Thanks in advance

 

[Padmakar Katre]

 

Hello experts,

 

I am engaged in a revamp of a styrene process plant. My actual challenge is to evaluate the possibility to use a existing exchanger as reboiler of a ethybenzene recovery destillation column. To do it I've used HTRI.

 

I before shall to say: 

- the botton pressure of my column is 0,415 kgf/cm²A.

- exchenger in vertical position

- the height betwee LLL level liquid and lowest tubesheet is 3455 mm.

- the styrene flows through tube side and vapor flows through shell side.

- styrene design flow is 735 t/h

 

Primaryly I evaluated it setting the "inlet pressure" (at 0,415 kgf/cm²A) and reboiler type as "No peping specified". Until here HTRI presented me 7,34% in overdesign and all process variables (cold and hot flow, temperatures, % vapor, etc ...) converged properly.

 

The second step was to set reboiler type as "thermosiphon reboiler" and the pressure location at column botton (0,415 kgf/cm²A). As expected the styrene flow increased as a result of pressure balance. However the HTRI converges the styrene flow to a negative overdesign even in "simulation" mode. 

 

The question is: which will the styrene flow be for a null overdesign ? I already put in blank the steam and styrene flow, steam temperature, % vapor and set only outlet styrene temperature and even this the HTRI converges the results to a styrene flow higher the styrene design flow negative overdesign.

 

 

Could you help me by showing me where I'm going wrong or the best way to make the HTRI converges the results to a thermosiphon reboiler ?

 

Thanks in advance

 

 

Just try understanding what happens due to change done w.r.t. location of pressure. The later case in which pressure specified is in column bottom vapor space then the boiling point elevation would be there due to static head. The major impact of this boiling point elevation will be on EMTD and leading to under-design. Possible solutions could be,

1. Reduce column operating pressure to bring down the btm temperature if increase in steam pressure is not possible

2. Issues if any with reduction in column operating pressure (column hydraulics limitations, ovhd vapor product line hydraulics etc.), increase steam pressure at same column btm pressure

3. the static head can also be altered i.e. you may like to raise the Reboiler litter up thereby lowering the static head

 

Option-2 of increase in steam pressure is best possible choice.

 

The inputs you should give in process tab would be,

1. Steam inlet pressure, temperature (in case of saturated steam specify inlet vapor fraction as 1.0) and outlet vapor fraction as 0 (total condensation).

2. Styrene side flow (thought it will be overwritten by thermosyphon loop during run), inlet temp and outlet vapor fraction (generally 0.2 to 0.3). this will fix the duty. steam flow will be estimated based on the required duty.