Pressure Relief valve on a chiller

[jojack]

Hi ,

I am new here..My question is about a chiller with relief valve set 100 kPa above the desgin pressure.The vessel is design verified to AS1210.

Manufacturer says the the pressure relief valve is for fire protection only so it can be set higher than design pressure as per AS1210. The High Pressure Switches are the safety instruments that make the refrigerant circuits are systems of limited pressure.HPS (High Pressure Switches) considered as an “electrical pressure control instrument” as per paragraph 2 of 8.2.5.

But in AS1210 sec 8.2.7.1

"Where it is not practical to use conventional pressure relief valves and fittings, or where such equipment is demonstrated to be unable to provide adequate protection against overpressure,then a safety instrumented system (SIS) may be used to control and manage overpressure. Such a system shall comply with AS 61508 and AS IEC 61511.

NOTE: A SIS is a designated system that both—
(A) implements the required safety functions necessary to achieve or maintain a safe state for the equipment under control; and
(B) is intended to achieve, on its own or with other electrical/electronic programmable electronic safety-related systems, other technology safety-related systems or external"

I believe these two statements contradict each other.. Can anybody advise the purpose of fire safety valves in chiller or manufacturer trying to get away by saying these are for fire protection if there is a fire in the plant room.

Cheers
Jo

 

[georgeverghese]

Though I'm not familiar with all of what is in AS1210, a code constructed vessel must have a code approved overpressure protection device to account for all credible overpressure scenarios, including external fire.

Believe the EU standards have provisions for not having a firecase only RV on the condition that fluids handled are not flammable, loosely speaking. But I dont think this is the case with AS.

A high integrity instrumented protection system (HIPS) is usually permitted on the grounds that a PSV poses some threat to the containment / disposal system or has some HSE concerns; or the PSV poses a severe economic penalty on the project. None of which are applicable in this case. An RV should be fitted and the design pressure of the chiller should ideally enable sufficient headroom for the complementary PSHH also (if applicable).

If the refrigerant is an non flammable CFC, the manufacturer is applying EU like rules here? Check with the latest AS1210 edition.

 

[EmmanuelTop]

I don't know the AS1210 Code, but it does sound a bit strange that the PSV set point can at 110% of design pressure. However, if the Code really allows for such provision, I don't see any issues there.

I fail to understand what is the real problem with the design. Is it that only a fire case PSV has been provided (whereas you believe that there are other credible scenarios), or there are other scenarios but the vendor is telling you that these are supposed to be covered by Safety Instrumented System response and not by a PSV?

SIS can replace relief devices, in cases when it is not technically feasible or economically justifiable to provide a relief/flare system.



Dejan IVANOVIC
Process Engineer, MSChE

 

[georgeverghese]

Even if EU like rules were to be in the AS1210 now, it would be valid only if BOTH sides of the chiller are handling non flammable streams.

 

[nightmareyan]

In my opinion,I don't think the PRV(Pressure relief valve) is only for fire protection. HSP/LSP is for refrigerant circuit and pressure relief valve is for water circuit. The purpose of the PRV is to discharge the pressure(by discharge water) if some instrument in chiller system system is false. For Example,If Expansion tank/Mark up water isolation valve have problem and still continue supplying to system, the system will be pressure rise and spoiled to chiller.
For me, it should not be more than Max allowable pressure of chiller.
LET ME KNOW ANYTHING THAT I STILL DON'T KNOW ABOUT THIS PROBLEM.

 

[MintJulep]

SIS likely applies to prevention of self-generated pressure within the system while the ambient environment is "non-extraordinary".

I think AS1210 allows for fire protection over-pressure devices to be 121% of design pressure.

I don't see anything wrong with the manufacturer's approach.