Storage tank level measurement configuration 1

[Jack Nicholson]

Hi. I have a question. would you please help me?
We have a C5+ (pentane) storage tank with T=40C, P=0.5 barg with one radar level transmitter. The tank height is 14 meter. I want to add another level measurement device in order to get more assurance. What is your proposal? Which type we should use? How about using level gauge instead of level transmitter?

Thanks in advance.

 

[pierreick]

Hi,

If I was in your shoes I would select the same technology (radar) with level displayed on field and DCS and probably the same brand if the equipment is working well !
My preferable brand is Vega.

My view
Pierre

 

[thebard3]

I have used ultrasonic, GWR, DP, and radar for sensing levels in all kinds of vessels and would probably say that neither is really any better than the other, provided that they are used inside of their intended design envelope.

Brad Waybright

The more you know, the more you know you don't know.

 

[TiCl4]

Why do you need more "assurance"? Do you need to not overfill the tank? A high level switch is a normal backup to a level instrument for high level protection. Need an in-line spare in case one device fails? Install a direct copy of the currently installed device to avoid any complications of setup or measurement type.

 

[Jack Nicholson]

Dear Ticl4, thanks foe your precious reply.
For the first one you mentioned, overfill prevention, we have PSV on drum, and I think we don't need any other device.

My reason is the secons one (in-line spare). Because based on our experience, radar level transmitter has been failed occasionally.

But I think that the same radar transmitter is not suitable, because based on our experience, usually the same dual radar transmitter can fail on the same time!. So I prefer to use another type of level trans., like vibrated level trans. . What do you think?

 

[LittleInch]

The issue you get with two analogue instruments is then which one do you believe?

Sure if one is totally U/S and gives you 0 or no reading you have the other, but if not?

Hence why the switches or float based devices would seem to make more sense as LL or HH switches.

Or maybe a sight glass or a magnetic sight glass?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hacksaw]

Level gauges work fine and don't require calibration.

 

[TiCl4]

Jack,

If you have had simultaneous failure of radar level devices, you need to figure out why they both failed at the same time.

Electrical failure? That'll hit both systems anyways. Multiple devices not needed.
Process conditions (foam, condensation?) cause occasional blips? You may need to replace the radar with something else entirely - multiple devices not needed, just a more robust measuring system.

Typically, I only see dual measurement on SIL-rated systems that require independent measuring devices where level control is critical. I guess the other usage would be if the process conditions tend to foul the instrument. There, an in-line spare and staggered cleaning PM can be employed so as to avoid any downtime.

I mean, you can install multiple devices if you want. It's just costly and has its own issues the LI alluded to (which instrument do you believe when, not if, their readings diverge?). When the radar device failed in the past, what did it cost you? Downtime? Hazardous release through the PSV?

Others more knowledgable can comment on the process conditions particular to pentane, and what factors come in to play with device selection.

 

[Jack Nicholson]

Dear Ticl4, yes, it's cost Hazardous release through the PSV.
Why did it fail at the same time? it's because of an instrumental failure.
Installing local guage? hmmmmm, the drum altitude is about 12m, so I guess we have to install 3 or 4 series local guage, and because of not having nozzle connection on drum, we have to fabricate it!, So it's costly.

 

[TiCl4]

Jack, I’m not following. You already said it’s an instrument failure. You said you have seen parallel radars fail simultaneously. What was the failure mechanism?

 

[georgeverghese]

For modern applications, in the wake of Buncefield, a 2oo3 voting system for HH sensing and shutdown (2 SDV in parallel) is a must to enable approach to a SIL-3 trip loop. For HH trip, you only need to look at the top range of the tank. Keep the monitoring and control LT separate.

Choices are radar, ultrasonic, GWR - you choose. Call in the vendors for each and see what they can do for you.

 

[Jack Nicholson]

TiCl4
I talked with instrument engineer and I found out that it was just coming out of calibration! (both LT showed 50% level but actually it was 100%). and I thought it was due to failing.

 

[Sesquipedalianist]

Jack, I would concur with others before me that provision of independent high and low switches for level detection would give you that assurance you want. However as you have indicated help was given by the instrument engineer nonetheless take it into consideration that the use of sight glasses and the likes with the proposed switches may help you avoid the scenario you were in.

cheers,
Sesq