OTR Tanker Offload Rate?

[blackwed]

What does experience say is a good rate to expect to get when offloading jet fuel from a tank truck? Most everyone I've talked to agrees on about a 325+/- gpm max rate for a gravity drop. Can the rate be improved appreciably with a pump or will that just vaporize the product (RVP <0.1 psia)?

DB

 

[blackwed]

jte, complex, man, not imaginary

Mr. Montemeyer, I'm afraid I've not written in the same tone as I have thought. I wrote amiss if I wrote in a way that is read so as to imply I am am weary of the board here and of the advice and comments. That has been the product of other influences most assuredly.

All the necessary calculations will ultimately be done and whatever system changes made will be engineered.

I agree my technical abilities in the area of fluid dynamics is not central in the successful completion of this effort. It is important for me to have enough of a rudimentary understanding of the field to be able to get the effort headed in the right direction to begin with and not down a path that won't work or at best will have to be altered. The project is at the point where I am trying to help the facility's owner (USA), not the operator, come up with what it is he should direct to happen.

My original post was simply to solicit the experiences of others who are, well, more experienced than I in a specific area and if there is any typical performance in this area that one should not reasonably expect to exceed.

Again, I do thank you all for your time and inputs.

Dan

 

[CRG]

Dan, for a rudimentary understanding of truck off loading at bulk fuel facilities, you may want to look at the Petroleum Fuel Facility Handbook used by one of the world’s largest owner/operator of these types of facilities. MIL-HNBK-1022-A Look at section 3.3.2 through 3.3.2.3 for a rudimentary discussion of tank truck offloading. See the attached link:

http://www.hnd.usace.army.mil/techinfo/misc/HD1022.pdf

 

[jmw]

OK, temperature correction/compensation

There are several different effects of temperature to be looked at:
[ul][li]meter swept volume[/li]
[li] density change in the fluid[/li]
[li]slip flow due to change in tolerances[/li]
[li] slip flow change due to viscosity change[/li][/ul]

Volume flow meters e.g. PD and Turbine, suffer an increase in geometry with increase in temperature; thus for each rotor rotation a larger volume passes through the meter. Since I imagine that you are operating at ambient temperature and that this is the temperature for which the meter is designed, these changes may be negligeable but note that custody transfer operations do often account for these changes, however small, if they are quantifiable, and is more usual with turbine meters because of the facility to make corrections electronically, but less common with PD meters due to the mechanical hear train and fixed meter factor.

Fluid density changes are more significant. For those applications wher the fluid is metered by volume but invoiced/accounted for by mass, some form of density compensation is required that is based on the known density at 15degc (or 60degF) and the operating temperature. This is what most "temperature correction" addresses.

Most usually the temperature compensator on PD meters is a varaiable ratio device in the calibration gear train controlled by a temperature element.
While this used to be used for truck meters for LPG where the base density values were usually consistent, I see that they are also available for all LC meters including fuel oil (domestic fuel oil used to be sold by volume so wasn't necessary) and for aviation fuel.
Because the density variation with temperature of fuel oils is predictable, once you know the reference density these can work fine but I don't know how different the temperature compensator on an LC meter is for Aviation fuels. I imagine it would require a dial for the operator to enter the base density as this can vary significantly from one batch of fuel to another.

Slip flow is the amount of fluid that "slips" through the working tolerances of the meter unrecorded.
It will vary with the flow rate, with temperature and viscosity.
Usually this is a small percentage (especially for a meter of the LC type) and, in the linear flow range of the meter, is constant within the accuracy limits. For Piston type meters the value is typically 3% maximum. The meter tolerances are often adjusted for both temperature and viscosity so it is important to use PD meters only for the duty and conditions for which they were designed.

While the tolerances may be selected for the viscosity of operation (a higher clearance for high viscosity in some meters such as gear or vane) this isn't to say that the slip is a constant throughout the flow range. It is notable that viscosity change can affect the amount of slip both for temperature and flow rate.
For a given tolerance and low viscosity we might find the slip is 3% of flow but as viscosity increases the slip flow reduces. In a psiton meter it can actually become positive as the boundary layer of bitumen, say, not only closes the tolerances but also reduces the swept volume.

I would suggest that for meters where the total chamber volume is high compared to the swept volume e.g. gear meters, slip flow is more critical. Designs such as the LC meter or piston meters ensure that the swept volume (fluid per rotation)is as close to the total volume (fluid plus rotating elements) as possible and slip flow is minimised but still significant.

In calibrating positive displacement meters these effects can cumulatively add up to quite a significant proportion of the flow but a particular meter for a specified duty will be far less sensitive as most of the effects are calibrated out.

It is increasingly common, now that PD meters enjoy electronic registers and high resolution pulse transmitters, for the meter performance to be enhanced by more extensive calibration that enables full compensation for all effects including meter linearisation, density correction, temperature, pressure and viscosity comepensation.

In the case of aviation fuels I would not expect to see a pressure compensation as, even for a single case meter, the operating pressures are quite low. It is encountered with turbine meters at high pressures because of (a) the effect on the volume (b) effect on hydrocarbon density.
Nor, though the viscosity can also vary significantly relative to the mean viscosity, the range of actual viscosity for aviation fuels is quite small compared to the overall viscosity capability and overall slip effect of the meter (unlike turbines which are far more viscosity sensitive and where viscosity compensation is increasingly common, and PD meters used over a wide viscosity range).

Basically, a mechanical temperature compensator is limited to the accuracy of the base density value entered (which is presumably obtained from the fuel analysis) and to the limitations of the mechanical gear train in having only a single average/mean meter factor.
An electronic register will allow the meter to be linearised for a variety of fluid conditions, including density and viscosity, to give an accurate volume measurement at the operating temperature. It also allows a live density measurement to be used for mass flow correction or standard volume determination.

Note:
slip flow will also vary with wear and if this meter has continuously suffered uncontrolled air both as a mjor inclusion due to empty startup lines, air purging of the lines on completion or vapour releas/cavitation etc then the chances are that even if it has not been damaged, it will require re-calibration and/or repair. This may be an opportunity to consider having a pulse transmitter fitted and a more extensive calibration that will allow you the option of density measurement for mass flow.

I note that LC also have electronic registers and it is worth investigating if these will accept a live density signal. If not once you have a pulse output you can choose from a variety of proprietary electronics to perform this function, including from manufacturers of density meters. i.e. you are not limited to the LC sollutions by retaining the meter and there may be cost/benefit advantage to using density meters rather than a mechanical temperature compensator.

One other effect of a live density signal is that they are affected by entrained air in a characteristic manner. The best of them include algoithms that will ignore the effects of trace air but will alarm if there is any significant air entrainment and this feature can be used to prevent false registration in electronic totalisers or batch counters.

This will, I hope, enable you to approach LC with some pertinent questions about their specific options and if necessary, to eplore a combination of the LC meter with other electronics and sensors.

I will be pleased to advise on density meters if you require. There are a number of good suppliers out there, increasing all the time.

JMW

http://www.ViscoAnalyser.com