Diesel Oil "Freezing" 4

[Donkin]

I am designing a diesel oil distribution system, the majority of the system is underground but at various parts there is a need to have above ground flexible pipes.

This is a gravity fed system and as such there are no pumps to circulate the diesel.

How do I calculate the time the diesel will take to "freeze" if it is static in the system.

My min design temp is 10 deg F, Hoses are 4 inch diameter.

If the diesel does freeze does it matter?
what happens when the temperature increases does the diesel revert to its initial properties?

Any help would be appreciated

 

[Latexman]

A friend of mine learned the hard way that the fuel filter on his diesel truck quickly became the "problem". In cold weather the "clouds", as in cloudpoint, of frozen hydrocarbons plugged up the filter and everything came to a screeching halt in a hurry. His solution was to add 10-20% gasoline to his tank during the coldest months.

In your case, look out for filters, strainers, and pinch points! And, a little frozen diesel will go a long way at plugging these things up, so I'm not sure how figuring a time will help. If it gets *to* the cloudpoint, it'll plug up small openings in a hurry!


Good luck,
Latexman

 

[TD2K]

The cloud point is where heavy components (essentially waxes) in the diesel solidfy and as pointed out, they will plug up filters and other sections.

I used to have a calculation for calculating cooldown lines but it's really old (like, if I do have it, it's going to be on a 360k 5 1/4" diskette for you old timers). I'll take a look for it. Freeze calculations for water lines are relatively common, I'd try google and see what you can find.

 

[MJCronin]

Donkin,

TD2K is right, diesel fuel forms solid waxes below about 20F

What many distribution facilities do is constantly circulate the diesel fuel below a certain temperature......this is one reason that these facilities incorporate a pump in the design !!

Another alternative is to purchase and use diesel fuel "additives" that are specifically for cold weather.

Adding gasoline to the diesel is an option, but this assumes that you will be doing some recirculation to keep the tank mixed.......

Facilities that store diesel fuel for long periods of time (such as CT power plants)incorporate periodic "tank turnover" (recirculation) to preserve the properties of the fuel.

I suggest that you re-think an entirely gravity fed system in a cold climate......small, cast-iron recirc pumps are fairly cheap.

My opinion only,


MJC

"There comes a time in the affairs of man when he must take the bull by the tail and face the situation." W.C. Fields

 

[Arcticdesert]

Donkin,
Are you limited to the type of diesel product in your system?

If not, you could change during the winter to a blended #2 ( I assume you are talking road Diesel) where the cloud point is -12ºF and the pour point is -15ºF. At those temperatures you would not have any problems.

Many times stations mistakenly have delivered #2 diesel into the #1 diesel tank in the winter and people have had their trucks fuel system gel up. I have heard of no problems from just warming the fuel back up.

Many people use gravity systems here for home heating oil(basically Diesel) and run #1 home heating oil with a cloud point of -58ºF for above ground tanks.

For your heat problem, a rough estimate about gel time would be to figure the volume in your above ground sections. Determine the amount of heat loss required to bring that mass of fuel to the cloud point (safety factor over pour point) from your winter ground temperature, or winter tank temperature. Figure your heat loss from the area of your above ground sections. divide. That should give you a rough ball park on time to gel.
Many tank and electric heat trace manufacures have programs which are free to calculate heat loss. Or you could pull out a thermo book and get more into it.

Keep your stick on the Ice!
ArcticDesert

 

[aviat]

There are a few other things that may be done in addition to what has been mentioned above. You could insulate the pipes, install electric strap heaters, use fuel anti-ice additives or a combination of them.

 

[pmover]

u know guys, here in AK (prudhoe bay & fairbanks - whole north slope for that matter), where it is slightly cold, diesel fuel is not a problem for vehicles. getting & keeping the engine warm is! there are additives that lower the freezing point of the fuel.

b4 u buy, tell fuel supplier temperature requirements.

mjc, while it may be done, i would not ever mix gasoline and diesel and burn it in compression ignition engine - no matter how diluted the mixture is.

my opinion only.

-pmover

 

[pierre35]

You'll have no problem with freeze up until about -30 to -40 unless you have a lot of water in the fuel.
We run diesels up here and although it is the lighter winter fuel, it is not a problem if it comes from a clean water free source.
DO NOT add gasoline to the fuel, you may however add kerosene which is how the make the fuel lighter for winter use but it will produce less power.

Hope this helps
Pierre35

 

[RogerH]

As Latexman points out it is the filter that is the main problem.
This property is reflected in the CFPP (cold filter plugging point and is specified for the diesel. For Arctic diesels this varies from -32/-36/-40 °C (-26/-33/-40 F) dependent on country. E.g (winter!) Diesel for Greenland is -40 °C in CFPP. So if the CFPP is in that order of magnitude it will work (most of the time). If it gets colder tank heating system should be applied.

The corresponding Cloud point is normally about 10 °C higher than CFPP and both these properties are important for winter diesels. CFPP properties is adjusted by using additives.
In case of plugging problems, Kerosene could be used to remove a plug but the danger using excessive amounts of Kerosene is that the Cetane gets lower.
Have seen many trucks coming from south of Europe to Scandinavia standing on the side of the road with this problem. They use (cheaper)diesel with CFPP around -2 to +5 °C.
As earlier pointed out using gasoline to dilute the diesel is dangerous, you might get away with this during (very) cold wheater but unpleasant things (at higher ambient temperature) can happen since the flashpoint will be drastically lower, i.e closer to that of gasoline.

As also pointed out water is important for "arctic" type diesels. The specification is normally max 80 ppm for these types. A typical 120 ppm spec (used frequently in Europe) is not enough to avoid free water/ice to separate in the diesel.

 

[Arcticdesert]

Donkin,
I looked in the book "Introduction to Cold Regions Engineering" by T McFadden and D Freitag and found this equation for heat loss from an above ground insulated pipe.
(One dimensional heat flow)
This equation assumes steady state heat transfer, so is it is just a way to estimate your heat loss from your above ground piping.
I have since loaned the book out, and do not have any of the coefficient values for h and k handy, or I would have added them here. You can find them in the Cold Regions book, or any good heat and mass transfer book.

The book used metric units with this equation.

Cylindrical surface heat transfer
Tin = inside temperature
Tout = outside temperature
r1 = inside radius of pipe
r2 =outside radius of pipe,inside radius of insulation
r3 =outside radius of insulation
hin = conductive film coefficient at the inside surface
hout = conductive film coefficient at the outside surface
k1 = thermal conductivity of the pipe
k2 = thermal conductivity of the insulation
L= length of pipe or height of tank
ln= natural log
pi= 3.14
q=heat loss

q=2*pi*L(Tin-Tout)/{(1/hin*r1)+((ln(r2/r1))/k1)+((ln(r3/r2))/k2)+(1/hout*r3)}


Once you have the heat loss, then find the amount of sensible heat in your mass of liquid (M*c*deltaT)

M=mass
c=Specific heat

Divide, and this an estimate of the time is when freezing will start.

For the time for freezing to complete you would have to add in the latent heat of crystallization.

Cheers!
ArcticDesert