4 replies to this topic

[kinetic123]

Hi

 

I have one query please.

 

We have a reactor with internal coil and outer jacket. Coil and jackets are used for cooling [with cooling water] and heating [using steam].

It is a batch process - and steps are:

1) add raw materials

2) Heat up to 125 deg C [use 3barg steam in coil and jacket both]

3) Exothermic reaction will bring temperature from 110 to 200 degC

4) Cool down batch from 200 to 125deg C [use cooling water in the jacket ONLY to avoid thermal sock to the coil]

5) Cool down batch from 125 to 40degC [use cooling water in a jacket + coil both]

 

 

Now if I keep coil outlet valve as air fail close, there would be two situation if my understanding is correct?

 

condition 1) Liquid expansion in the coil - batch is below 100deg C, coil is full of water and air fail close valve at coil outlet will cause trapped in water to expand.

condition 2) Vaporisation in the coil - batch is above 100deg C [let's say maximum 125deg C] , coil is full of water and air fail close valve at coil outlet will cause trapped in water to vaporise.

 

Coil is 3inch in diameter, has design pressure of 10barg and contains 400 litre water.

 

Query:

 

If I have condition 1, I have read that API 521 has guide which i can follow for sizing the relief valve

 

But if I have condition 2, am i right in saying that vapour release rate would be equal to that of heat input from batch to the coil trapped water? Also I do not know how to calculate the pressure exerted by the vapour [here water vapour] formed. 

 

Any help from members? Thanks

Edited by kinetic123, 02 April 2014 - 05:29 PM.

[AlertO]

Hi Kinetic123

 

before going to relief consideration, i still have a question about your heating/cooling system.

how many control valve do you have for your heating and cooling systems? (if possible, attach you diagram is benefit for others)

 

The problem is there are few important differences in design for heating and cooling facilities such as flowing up for cooling and flowing down for heating as well as the failure positions which fail open for cooling and fail close for heating.

 

Looking forward to hearing from you.

[kinetic123]

AlertO,

 

Thanks for your reply.

Please see attached drawing which shows major control, auto valves [along with their air fail position] and other details.

I understand all valid reasons for the fail positions of all the valves except AV04. This is because, coil does not have any relief valve at the moment and I believe AV04 should be fail OPEN?

Thanks

Attached Files

•  Drawing.PDF   208.58KB   11 downloads

[AlertO]

kinetic123

 

Your on-off valves are fail-closed positioned for isolating the steam and cooling system as well as safety except during the high temperature in the vessel. It can be probably overpressure in coil from steam expansion (step 3) and water expansion (step5). Consequently, an additional PSV is required.

 

however, i notices that the fail position of AV05 and AV06 are designed differently? are there any hidden reason?

[fallah]

Now if I keep coil outlet valve as air fail close, there would be two situation if my understanding is correct?

 

condition 1) Liquid expansion in the coil - batch is below 100deg C, coil is full of water and air fail close valve at coil outlet will cause trapped in water to expand.

condition 2) Vaporisation in the coil - batch is above 100deg C [let's say maximum 125deg C] , coil is full of water and air fail close valve at coil outlet will cause trapped in water to vaporise.

 

Coil is 3inch in diameter, has design pressure of 10barg and contains 400 litre water.

 

Query:

 

If I have condition 1, I have read that API 521 has guide which i can follow for sizing the relief valve

 

But if I have condition 2, am i right in saying that vapour release rate would be equal to that of heat input from batch to the coil trapped water? Also I do not know how to calculate the pressure exerted by the vapour [here water vapour] formed. 

 

 

Hi,

 

Generally, considering the initial pressure/temperature if the water temperature rise would be limited to liquid expansion a small TSV is adequate. But if the temperature rise would lead to steam genration then an additional PSV is needed to handle the steam relief...A PSV might handle both liquid relief due to thermal expansion and steam relief due to water vaporization...

Edited by fallah, 08 April 2014 - 03:56 AM.