5 replies to this topic

[nivedita]

i have 2 trv in series for a line cooing from liquifaction ino the LNG storagae tank.

The line design pressure is 150psig. Athough it is a 2 phase line which i was worried about ,on the P&ID it is split into vapor and liquid lines.

 

so the line size is 2" and the following are the conds -

for 2 phase line 

Press-  29 psia

temp-  -243.6F

Comp-95%methane

1.44 % co2

95% methane

0.03% oxygen

vapor frac 0.0530

 

the line splits to liquid and vapor lines

 

both lines have 150 psig design pressure 

I have got a this calc for liquid line as per API

 

SET PRESSURE 150 psig OVERPRESSURE 10%         HEAT SOURCE solar radiation MAXIMUM HEAT EXCHANGER DUTY 3.30E+02 Btu/hr/ft2 DIAMETER OF PIPE 2 IN LENGTH OF PIPE 20 FT (assumed) SURFACE AREA OF PIPE 20.944 FT2 φ FOR SOLAR RADIATION (330 Btu/h-ft² applied to surface area)           SPECIFIC GRAVITY, d 0.43   CUBIC EXPANSION COEFFICIENT, α_v 0.0009 1/°F MAXIMUM HEAT TRANSFER RATE, φ 1100.00 btu/hr SPECIFIC HEAT, c 1.115 Btu/lb F             RELEIF RATE 0.004168 gpm VISCOSITY 1.066 cP

 

For gas phase i have used this calc

 

Q     Length of pipe 10 assume Volume of the pipe 10.5 FT3       Pressure Max pressure of pipe 150 Psig         0.179 scfm   10.760

scfh

 

 

 

 

Q= ((V)*(MAEP/14.7)*(520/T1 - 520/T2))/60

 

Based on the following assumption 

 

T₁ = Degrees R, with 50 ^OF T₂ = Degrees R, with 100 ^OF   Based on worst case temperature rise from ambient heat gain based on 50 degree F rise in one hour

 

 

Please help me calculate the gas flow rate for the TRV i know it is 3/4"x1"

but my boss needs to know

[nivedita]

sorry it is a pipe so solar radiation is 330Btu/hr ft2 F

 

Also i sent the two phase stream through a separator hence I got my vapor and liquid conds 

[ankur2061]

Nivedita,

 

Please have a look at the link provided below:

 

http://www.cheresour...e-relief-valve/

 

Regards,

Ankur.

[Art Montemayor]

nivedita:

 

Our members' responses are all valuable information to add to your experience and knowledge bank.  However, there are some very basic and important notes I want to add to this thread because I detect a misunderstanding on your part of what, basically, constitutes the purpose and the use of a Thermal Relief Valve (TRV).

 

First, please make note that the very title, "Thermal Relief Valve", is actually a misnomer employed solely due to custom and not an accurate title.  This valve DOES NOT RELIEVE TEMPERATURE(S).  It is designed to relieve the normal hydraulic pressure exerted by a blocked-in LIQUID FLUID when subjected to unexpected external heat input(s) such as ambient or solar heating.  Normally, the fluid in question is supercooled liquid and its designed relief flow rate is very, very small - since the design basis only involves hydraulic pressure caused by liquid expansion due to temperature increase.

 

This is specifically pointed out by our member Erwin Apriandi and unfortunately is not specifically mentioned by our Ankur Srivastava in the referenced thread - although he does identify the fact that the TRV is not used in 2-phase environments.  The obvious reason for it not being applicable in 2-phase environments is that the valve is not meant to relieve vapors or gases.  Additionally, since the designed relief flow is very small (since a small hydraulic liquid expansion causes large pressure increases - due to the liquid's relative incompressibility) the corresponding TRV size is normally very small also (usually ½ to ¾ inch diameter). 

 

I make mention of the above design basis for a TRV because I believe that basic data for your application does not seem to indicate an application for such a relief valve.  You may be misunderstanding the design and application of this relief valve.  It may be that I don't understand your application.  I fail to understand the use of 2 TRVs in "series" - and certainly in 2-phase service.

 

Perhaps a detailed sketch of what you propose would better explain your proposal.

 

P.S. - Your thread title, "Thermal Expansion Of Relief Valve", doesn't make sense.  The TRV is not thermally expanding; it is the fluid.  I am changing the title to reflect what I think you mean to state.

[S.AHMAD]

Nivedita,

I believe that what you mean is TRV in parallel that is two TRVs are installed on the same pipe where blocked-in situation may occur. Normally 1 TRV is sufficient.

 

However, probably what you mean is a piggy back installation.This is what I strongly believe. A good reason for this type of installation is to save piping cost.

 

Simplified PFD may project a more clearer picture.

Edited by S.AHMAD, 22 April 2016 - 11:58 PM.

[nivedita12]

Thank you all for the valuable input got it and fixed my valve calculations