3 replies to this topic

[deltaChe]

Dear Sir/Madam

I have a project given poor S&T thermosiphon & VLE data and to be required to find optimum size exchanger through HTRI.

The TEMA type : NEM ( vertical), shell per unit : 1, in series : 1
Tube dimension: OD 19.05 mm, length:3048 mm, pitch: 23.81, flow angle:30 degree

The Shell side
Fluid name : steam
Inlet Temp : 270.5C
Inlet Pressure: 40kg/cm2g
Fouling Factor: 0.0001 m2-hr-C/kcal

The tube side
Fluid Name : phenol
Fluid quantity : 336610kg/hr
Lquid in : 336610 kg/hr (density:889.8kg/m3)
Liquid out : 249176kg/hr (density:890.9kg/m3, viscosity : 0.217CP, MW=94.12, specific heat=0.633kcal/kg-C,thermal conductivity=0.1081kcal/hr-M-C)
Vapor out : 87435kg/hr (density:5.49kg/m3, 0.012CP, MW=94.12, specific heat=0.406kcal/kg-C, thermal conductivity=0.0223kcal/hr-M-C)
Inlet Temp: 214C
Inlet Pressure :1.29kg/cm2g
Pressure drop allowable:0.265kg/cm2
Fouling Facotr :0.0002 m2-hr-C/kcal

Heat duty : 9.615 MMKcal/hr

Here is my question :
1. The VLE data seems not cover the tube side out pressure so the HTRI has to be extrapolated to get the data.

The running message is following:

The pressure profiles given for the cold fluid do not cover the operating pressure range of the heat exchanger. The vaporization profile inside of the exchanger for this run may not be accurate since heat release and fluid properties have been extrapolated. It is recommended that the maximum and minimum system pressures be used as reference pressures.

2. The steam velocity =0.99 m/s in shell seems to slow, beside that I can’t see any problem of this thermosiphon case. Is any special input requirement for thermsiphon design in HTRI, such as recirculation ratio or pressure drop ?

I would look forward your any comments and really appreciated for your time and effort.Thank you so much.

Attached Files

•  poor VLE.doc   290.5KB   30 downloads

[Jiten_process]

@deltache

The warning message that you have mentioned is appearing because the outlet pressure on phenol side is beyond the range of the curve that is provided. I have also encountered such instances. In such cases normally designer keeps some overdesign margin for the scope of error. OR the other way is you generate curve through HTRI to cover the pressure ranges. You need to draw attention of licensor or PMC in this case if the curve is provided by them. If you are the generator try and generate the curve from simulator.

To my view,Theoratically you can go ahead with your design if this is the only warning you are getting and all other parameters (e.g. B stream, velocities, Pre Drops etc) are inline.

[knapee]

I notice the reboiler type has to be inputted, either thermosiphon reboiler, or force reboiler.( In this case, it is thermosiphon type). Also, the required liquid static head, and inlet pressure location (either at inlet nozzle or at column bottom) have to be inputted.

But, I don't quite know how to clarify the physical meaning between the pressure location at inlet nozzle and column bottom. Besides that, the main inlet/outlet pipe length has to be inputted.
Can anyone suggest typical choose for this?

if the total driving force of the reboiler less than the total resistance, it will seriously impact the operation of the reboiler and distillation column. And, the low recirculation will make the hold time of reboiler increasing so that the unwanted heavies will be overheated to increase the vaporization rate.

Also, to increase the inlet/outlet spacing to avoiding the acoustic vibration. But, any good reference could be suggested so that we can choose proper spacing quickly and physical intuitively.

Thanks.

[Robert Montoya]

My friend due the inlet conditions of phenol is saturated liquid (as well I understand according to the data) and the outlet conditions is a mixed liquid-vapor therefore is very important specify the properties to outlet conditions due that steam quality should vary nd should does not correspond to those which the process requires and therefore the design could not be the that is required.
I suggest you request a property data more in line with the conditions or you can load the properties to HTRI through the HYSYS