3 replies to this topic

[Marcos Paulo]

Dear All,

 

I´ve been reading some archived topics related to BDVs valves in hydrocarbon service and

I’d like to hear about yours experience regarding reliability and optimization of the depressurizing system for hydroprocessing units:

 

1) Do you usually consider redundant BDVs for depressurizing hydroprocessing units?

 

2) Do you usually consider the BDV valve to be suitable for use in SIL 3 application? In positive case, which valves do you know that have this certification?

 

3) Does anyone ever seen the using of axial valve as a BDV instead of a ball valve?

 

4) As I read in the other topics, the more recommend configuration is a full bore ball valve + RO. However, as the flow is fully limited by the RO does anyone see any problem in using a ball valve with a diameter smaller than the line in order to save some money in the installation of the system?

 

Thanks.

[paulhorth]

Marcos,

 

My replies are based on my own experience, others may not agree............

 

(1) No - I have not seen redundant BDVs being used, or recommended in any company standards. Any manual isolation valves for the BDV MUST be locked open.

 

(2) Yes, I think blowdown functions are typically SIL3 and BDVs are suitable for this reliability, if they are Fail-Open using a spring actuator. (the spring has a  similar reliability to the spring in a relief valve, which is OK for SIL3). I think some BDVs can be opened by hydraulic action, then the hydraulic system would have to meet the required level of reliability.

Sorry I can't give you names of actual valves.

 

(3) No, I have not come across this.

 

(4) I would agree that a reduced bore BDV plus a suitably sized RO would be fully equivalent to a full bore BDV and smaller RO, and I have raised this point on more than one project. The problem would be to make the slightly tougher calculation to prove that this combination will give the required blowdown flow. Also, many company standards call for a full bore valve and it would be hard work to get a concession agreed on this point.

 

Paul

[fallah]

 Marcos,

 

My answers are in red color as follows:

 

 

 

1) Do you usually consider redundant BDVs for depressurizing hydroprocessing units? No, because the BDV is normally FO and also is provided with an air bottle for the case of instrument air failure...

 

2) Do you usually consider the BDV valve to be suitable for use in SIL 3 application? In positive case, which valves do you know that have this certification? Yes, it could be suitable for use in SIL 3...

 

3) Does anyone ever seen the using of axial valve as a BDV instead of a ball valve? No, i hadn't seen such using...

 

4) As I read in the other topics, the more recommend configuration is a full bore ball valve + RO. However, as the flow is fully limited by the RO does anyone see any problem in using a ball valve with a diameter smaller than the line in order to save some money in the installation of the system?  I have seen smaller size BDV than the line without any RO at downstream for depressurizing purpose. Actually by such configuration the BDV and RO have been combined to do the job...

 

 

 

Edited by fallah, 14 March 2014 - 11:33 AM.

[Himanshu Sharma]

Hi !

 

My replies though different from other forum members are marked against your questions in Blue

 

1) Do you usually consider redundant BDVs for depressurizing hydroprocessing units?

    Reply:Yes,i do typically for Emergency Depressurization of High Conversion Hydro cracker Unit         with a good enough             chance for runaway reaction( various  reasons that can trigger run away           reactions is yet another discussion topic).

     Philosophy of providing two different automated BDVs differ as per Owner and Technology Licensor. There are two prevalent methods of doing it ,

1. Provide two different BDVs for different rates of depressurization such that small venting valve open first and larger venting valves opens in case system is not effectively depressurized by small venting valve.There is simple logic of minimizing loss of inventory to flare while operating within mechanical design conditions.
2. In some designs,two BDVs of same capacity(sized for full depressurization but limited to flare system capacity) open together so as to minimize remote chance of one BDV Failure.

2) Do you usually consider the BDV valve to be suitable for use in SIL 3 application? In positive case, which valves do you know that have this certification?

Reply: Yes entire instrumentation loop SIL 3  including safety PLC shall be SIL 3 Compliant. Metal seated rotary valves by Metso are common for this dump valve application.

 

3) Does anyone ever seen the using of axial valve as a BDV instead of a ball valve?

Reply: No.

 

 

4) As I read in the other topics, the more recommend configuration is a full bore ball valve + RO. However, as the flow is fully limited by the RO does anyone see any problem in using a ball valve with a diameter smaller than the line in order to save some money in the installation of the system?

Reply: RO is installed ahead of BDV to control Peak rate of depressurization that may lead to severe damage reactor internals and may have serious concerns on flare system capacity also.

Going by the tenets of Safety,anything after RO shall not be restricting the flow towards flare.

 

Hope ,this helps

Regards

Himanshu

Edited by Himanshu Sharma, 18 March 2014 - 12:47 AM.