Ethanol Custody Transfer, flow vs tank gauging 4

[HiLevel]

I'm designing a barg loading facility where we will be refurbishing an old abandoned 180' petroleum storage tank and installing a 12" line to an off-shore barg loading berth. I'm evaluating the relative merits of using turbine meters or a tank gauging system for custody transfer of this ethanol. From what I've learned the tank will require the development of strapping tables and probably a third party to perform and certify the calibration. The gauging equipment isn't cheap either. Another obstacle is that you can't pump into the tank while your pumping out without somehow capturing the outflow - inflow. Installation of a pair of turbine meters in the transfer line seems more straight forward. Any deviation indicates either a meter problem or a leak. I'm wondering the best way to certify these meters. The plant's down part of the year; so, we could send them off annually. Or, if services are available, we could hire someone to calibrate on-site. I'm wondering if there are special calibration barges designed for this purpose. Any advice would be appreciated. By the way, the site is Trinidad.
Thanks!

 

[JLSeagull]

The API Manual of Petroleum Measurement Standards (MPMS) covers just about all aspects of the tank gauging and flow measurement that you need. Several chapters apply to the tank gauging and metering.

 

[jmw]

I would suggest that for 12" turbines you have a couple of options; to have a contract with a calibration service to come to site with a mobile prover and periodically prove the meters or have your own prover and prove a single meter as often as necessary.

I don't know how common a requirement this would be in Tinidad but if there are others with similar needs then a local service might be available already or you may get together with others to share the costs... either of acquiring a mobile prover for all to use or of scheduling mobile provers to be brought to Trinidad when necessary.... if several such calibrations are require dit might help to share the overheads such as time to site transportation etc.

A good place to place your query might be with the meter supplier. For example, SMith Meters not only produce custody transfer PD and Turbine meters, they also produce tank loading systems and meter provers. They may be able to provide the service or the equipment. Probably any supplier of large custody transfer meters will offer similar capability and good advice.

JMW

http://www.ViscoAnalyser.com

 

[HiLevel]

There are several barg loading platforms in this bay that are used for petrochem. I'll see if I can get any info. on what the other folks do for meter calibration. You're right, we could probably use the same contractor to prove them during the same visit.

 

[Ashereng]

There are many meters with custody transfer certifications. In addition to turbine, there are the positive displacement (PD) meters, coriolis, orifice plate (DP) and a whole host of others. You should take a look and ask around.


For my last client, they decided to outsouce the meter proving to a meter proving company. These guys come to your site, hook up, prove the meters, and leave. I guess it is a annual contract (or per visit). Anyway, it is a good arrangement since if you have your own meter prover, it would most likely site idle most of the time - not a good use of capital.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[jmw]

Sorry, yes Ashereng you are right, and at 12" we should also include Ultra-sonic.

Faure Herman has them OIML approved and so has Khrone.

However, at 12" (turbine flow equivalents), price, size and headloss are all issues generally.

For ethanol, I would suspect turbines have the balance of advantage in all areas, except for entrained air or air blowing. The installation would need to ensure the lines are purged from a point downstream of the meters.


JMW

http://www.ViscoAnalyser.com

 

[HiLevel]

I've gotten a lot of good input and gathered a lot of additional information over the internet and from various gauging and flow meter vendors. I believe I'll propose a "belt and suspenders" approach. I'll put a gauge well and a basic float level transmitter on this floating roof tank. Intent will be that they can have the tank strapped and characterized if they need to, and they could then manually check level change before and after a transfer to compare to flow meter totals. They may want to do this periodically for inventories anyway. Otherwise; I'll install two turbine flow meters, one at each end of the 5000' undersea transfer line to function both as a custody transfer master/prover pair, and a spill detection system alarming on flow reading differential. They can either ship the meters off every year to have them calibrated/certified or have it performed on site.
Thanks for all the input and let me know if anyone sees any holes in this approach.
WCL

 

[BigInch]

In my experience you can't move in and out of a tank in a custody transfer situation if you have gauging or meters, until the product is settled and tested and released.

A resident prover decision should be made based on the volume moved and the loss potential in consistant mismeasurements. It also seems to me that two turbines, for example would experience the same ware rates and hence have the same average error at any given time, thus making discovery of the error rather difficult. It brings to mind this old quotation, "A man with one watch always knows what time it is. A man with two watches is never sure".

It is unusual to find a high volume pipeline without a prover on hand.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[JimCasey]

Turbines are good in that they are very very repeatable.
Emerson/Daniel "Birotor" is a good choice for positive displacement, particularly if you get the pulse output feature and feed it to an electronic totalizer.

Watch the sizing of the flowmeters. They get the best accuracy when they are running on the high end of their capacity range. If you try running them at 5% of capacity you may not get a reading at all. Orifice plates are notoriously hideous this way and if you get 3:1 out of a plate you are doing exceptionally well.

Emerson also makes a "compact" prover that fits in the bed of a pickup truck.

 

[BigInch]

Jim, not so much the sizing of the turbine as keeping within the operating range of the size installed.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[HiLevel]

BigInch,
I've learned more about the custody transfer, and in Trinidad, they apparently use manual readings via tape on the storage tank before and after transfers for custody transfer purposes. They use flow meters for loading trucks; however for tankers, they use manual tank measurements. They apparently even have a 3rd party witness the transfer and verify the readings and calculations. Kind of shoots my highly automated automatic proven certified flow meter idea in the seat. The manual method seems a little dated to me; especially when you consider that whether the tape reader rounds up or down 1/16" could put a couple grand in someone's pocket. However, it's apparently very common.

I agree on the turbine meter wear. It makes sense. I believe you'd still need to send them off annually to get them calibrated and recertified. I would expect the K factors to drift, probably uniformly, as the meters wear at the same rate.

I know that this violates one of the fundamental tennants of instrument engineering. NEVER put two flow meters in series. I liked your watch analogy.

Thanks for your insight!

WCL

 

[BigInch]

I've been in a lot of places with 2 of all the latest tech gadgets online + prover and they still use the strap reading. Go figure. I really don't know why we bother with the gadgets.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[jmw]

HiLevel,
what you are describing is the system commonly used with bunker fuels which, despite being very much less value than ethanol, are prone to a great variety of quantity and quality errors.
There have been prosecutions not just of corrupt operators but also of corrupt "independent" third party surveyors.
In one port the surveyors were earning upto 5 x annual salary in bribes.
One study showed that for tank gauging (on fuel barges) there were nerly a dozen different frauds commonly used.
Now I'm not saying anything about what happens in Trinidad and with ethanol, but the point is that tank gauging/dipping systems are very open to frauds. Of course, metering is also vulnerable if they blow air through the meters (another problem) but the way around that is with air detection interlocks with the counters, though if you are using turbines, you may also need to replace the turbines on a frequent basis, hence you need a good installation and metering.
Of course, in heavy fuel oils they have a few other scams such as adulterating it with water both to replace a proportion of fuel sold off separately and to boost the measured density (sold by weight, measured by volume).
I just wonder, if these scams are operating with fuel oils, what kind of small scams can be performed with ethanol, more value so a smaller less noticable scam will generate just as much profit.
By the way, do you cross check the density? do you load by weight?
You might include a good density meter in the meter system and use it for quality checking and meter correction...

JMW

http://www.ViscoAnalyser.com

 

[HiLevel]

JMW,
This is very interesting. I'm mostly specialty chemical background; so, this is all new to me.
Our product is 99+% dry ethanol. So, the density is constant and the thermal expansion is well established at .00063/F. I expect that the buyer of the ethanol will have a dryness spec that the product has to meet. Ethanol and water are extremely miscible. I know this being from Kentucky. So, you couldn't hide a slug of water. I suppose that if you wanted to play games, you could locate the gauge well on the opposite side of the tank from the inlet. Assuming that the material will come in warm and gradually cool, the temperature sample from the gauge well would be lower than the overall tank average. Thus the computed volume would be higher. These tanks are existing; so, thankfully, I won't have to get into this.
WCL

 

[BigInch]

HiLevel, got a question for you. Just something I'm interested in. What's the corrosion situation on these ethanol facilities? Good, Bad or Ugly? Any gasket problems around, anything unusual?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[HiLevel]

I'm not a very good source of detailed info on corrosion I'm afraid. I know we're using just carbon steel piping and storage tanks. I did talk to some turbine flow meter guys about some things I'd heard about corrosion or build up on the turbines. Looks like the Daniels folks recommend teflon coated blades while the Smith folks say that this is not required. There are apparently differences based upon whether you're dealing with sugar cane ethanol vs corn ethanol as far as contaminants. But all in all, compared to the chemical industry stuff I'm used to dealing with, this is very tame. It hasn't corroded any of my pipes yet, at least that I know about.
WCL

 

[BigInch]

Thanks for the comment. There seems to be some pipeline companies that don't want to pump ethanol because of possible corrosion problems, but there exists quite a wide difference of opinion and I think its an excuse they use just because they don't want to pump it.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[JLSeagull]

Several API studies are available.

Tanks
Water may condense in a gasoline or other product tank. With ethonol, the water and alcohol may combine - and that phase may separate from the gasoline. The potential for increased conductivity may affect the corrosion rate in the alcohol rich water bottoms. For a cited publication search for -

Geyer, Wayne B., Compatibility of Steel with Oxygenated Fuels, Presented at 16th Annual ILTA Conference, 6/10-11/1996, Steel Tank Institute.

Check API TR 939-D, Stress corrosion cracking of carbon steel in fuel grade ethanol Review and survey. This review reflects concerns regarding stress corrosion cracking of steel tanks, vessels, piping and equipment in fuel ethanol service.

On the other hand, I have worked projects with ethanol storage tanks - not associated with ethanol fuel. These tanks have been in operation for sixty years.