4 replies to this topic

[Nirmalbhatt007]

Hi

I am designing plate heat exchanger (PHE) type pasteurizer for Juice.

Problem: can easily control the pasteurization temp (fixed outlet temp of juice) by using hot water at 135 dg C in place of steam.

Generally we control the past. temp (92 dg of Juice) by steam (at 3 bar) control system that heat the water from 82 to 93-95 dg C by seperate PHE. This water will be use for heating of juice from 65 to 92 dg C by another PHE.
To control the juice temp of 92 dg C, water temp will be varying accordingly by varying steam flow through PID valve.

-If in case we want to use hot water at 135 dg C in place of steam for heating of water and hence Juice, what should be taken care for designing (Is it possible ?).

-Is system smoothly control by hot water flow control valve only?

Regards,
Nirmal

[Chris Haslego]

What you're describing is fairly common and usually done is a multi-section sanitary style plate exchanger. But, now you want to use hot water instead of steam as your heat input, and use a secondary water loop to heat the juice (as you do today)...correct? If this is the case, I would likely recommend a bypass control valve on the 135 degree C water.

If you juice is too cold, more 135 C water is pushed through the exchanger and raises the interloop water temperature. If the juice is a little too hot, some of the 135 C water is allowed to bypass the heat exchanger and lower the temperature of the interloop. I think you'll find this a better way to achieve tight temperature control versus a simple control valve on the 135 C water. Plus, if your pressure loss on this 135 C water become too great (such as at reduced juice flow), you run the risk of vaporizing it and several other potential problems.

If the reason you want to make this change is to obtain better temperature control, I would recommend researching condensate level control on the steam side.

[T.S.MURALI]

YOUR OBJECTIVE IS FLOW AND TEMP CONTROL OF JUICE .FCV in water line can control water heat input.You can achieve this by 3 element control.Water can be bypassed and relieved without affecting the other medium in any way

As you may be aware 3 element control is common where you need to control 3 variables.

[breizh]

http://www.nzifst.or...apps2.htm#pastn


You may consider this resource , it's about pasteurization.
Hope this helps

Breizh

[S.AHMAD]

Nirmal
1. Is there a specific reason that you are using secondary medium (water) instead of using primary medium (steam/135C hot water) to heat-up the juice directly? probably contamination.
2 To answer your question specifically, it is a YES that steam can be replaced with hot 135C water. However, the hot 135C/water exchanger will be bigger than the current steam/water exchanger since the heat transfer coefficient for steam condensation is high compared to hot 135C water stream coefficient.
3.