FF in Sulphur Recovery unit

[binkaFF]

Hi

We are a leading consulting organisation in Instrumentation. One of our clients is now planning to go FF with a new Sulphur Recovery unit. This unit is a highly corrosive atmosphere and the field instruments get severe pitting.

The customer initially thought of going with a High Power trunk concept with Field Barrier installations. now due to the critical nature of pitting they are in a fix. Can the field barriers and its electronics withstand this type of corrosive atmosphere?

Alternate is the FISCo power supply. But Redundancy of the FISCO power supply is a weak link. Can any manufacturer provide FISCO Redundancy. We prefer MTL because of the no. of installatins they have. Please let us know if there is any mechanism by which FISCO redundancy can be achieved and any of the standards which can support the same.

The slient might drop the whole idea of FF if these things are not addressed by us. Please help on SOS.

[rezabejd]

DDG,

Will the field barrier be in a junction box? Can you cite a specific model number?

I am not trying to conform to I.S. here (we are classified according to API-500 and use Class 1 - Division 2 Group BCD for 99% of installations, typically current limited spurs (via Relcom / MTL) and non-incendive devices.

I have several "megablocks" in my possession, and appear to be pretty well potted. I spoke with Mike Strausser, an engineer at Relcom; he says the potting encapsulates most of the board, the only leakage path is possibly around the terminals themselves.

"Conformal coating" of circuit boards is also very common and an option for this device. This would give the circuit board resistance to corrosion on par with your electronic field devices.

In my mind, fieldbus can go anywhere a conventional device can, and more than likely do better. The concern about corrosion is a reason to use fieldbus; you will want your devices to alert the operator to impending failures before your client's plant experiences an upset. Fieldbus physical layer diagnostics are the only offering I'm aware of that can also deliver 24/7 assessment of the health of the network. You can also get immediate notification of conditions like plugged impulse lines or a failed sensor.

I would use the high power trunk with redundant conditioners and, if necessary, choose a field barrier with conformal coating on par with what the instruments themselves use.

There are other people on this forum using field barriers in corrosive environments. Some have been completely submerged; I'd have to think an IP66 device will keep the Sulfur and Ammonia acid gases out as well.

John Rezabek, ISP Lima

[binkaFF]

we were considering to use P+F Field Barrier with the redundant power supplies.

Can this Field Barrier withstand the corrosive gases for a long time without getting corroded.

Rgds

B

[chriss]

B
most of our Fieldbarrier is potted- so only the terminals have direct contact to the surrounding corrosive atmosphere. The rest of the Fieldbarrier is coated conformally. The fieldbarrier is G3 conformant.

We offer standard housings up to IP66 in stainless steel which restrict the gas exchange and therefore help to prevent corroding on the inside.

With the Power Hub you have the possibility to mount the advanced diagnostic module (ADM) to monitor the segments 24/7.

Best regards

[spragujl]

Blinka,

We don't build SRU's any different that the rest of our plants, and we haven't had excessive corrosion problems. We're building SRUs now with FF, using the non-incendive / current limited spur design John R mentioned above. This for Zone 2 installations (+95% of everything) and we get live disconnect capability with no hot work permit. For instruments in Zone 1, we use the exact same design, only with epoxy potted glands to make it explosion proof. We're using predominantly Relcom Megablocks - mounted in SS weatherproof JBs. Runs from JBs to instruments are armored cable and JB to Marshalling as multipair PLTC in tray.

Regards - Jim Sprague - Aramco

[Mike ONeill]

Hi Binka,

Here's a link to an article in Chemical Processing magazine:
http://www.chemicalprocessing.com/articles/2007/022.html
that relates to your question.

[Bilal]

This is addressed to Christian and Jim.

Christian
As for the G3 Conformance, using non G3 conformant terminals is probably as bad as not having a G3 confromed field barrier. Also for proper grounding connection the din rail in the JB needs to be equivallently G3 coated.

Jim,
Are your SS JBs equipped with the breathers. There must be an issue of using breather in SRUs/G3 enviornment.