11 replies to this topic

[fahrudin]

Dear Engineer.

We have not insulate tank for storing high pour point Oil. (36 deg C).
This tank is located in shore for unload Oil from Vessel (initial temp Oil around 60 degC)

Inside Tank we install heating coil (steam) with lenght: 470 m (2'')
this coil is design for operating pressure 3.5 barg.
But unfortunately due to the limitation of steam supply, steam inlet to tank just 1 barg.

So, gradually temperature is decrease until about 50 deg C.
This mean Heat loss from tank shell is higher than heat release from steam coil.
due to no flow meter So, we can't exactly know how much steam supplied to this tank.

Could you help me to give overall guidance how to estimate l steam flow to tank
refer above case (Temperature continuosly decrease).

Thank you

Fahrudin

[AlertO]

hi fahrudin

As you know the steam consumption is required accordingly to the heat loss from the tank to atm. There are many ways to find out this heat loss from very simply like the grapical method to the complex math calculation (if you want this, i can give you).
However, for your case, it seem the steam flow rate is limited by the insufficient inlet pressure (is there an temperature CV at steam or condesnate line?).

i'll give you few solutions as follows:
1. Coil pressure drop reduction: this aim to get more flow through the steam coil. the method is to modify the coil configuration from one long route coil to double parallel coil. however, this cause a lot of site works.
2. Provide the Hot insulation to the tank, unfortunately the temp is not so high (what is the ambient temperature there?) this will help to reduce the steam requirement and the maintained temperature will be higher.

Hope my post can help you

[breizh]

Hi ,
How big is the tank ?
Will it make sense to install an electrical tracing + Hot insulation ?
Can you collect the condensate to estimate the flow rate , it will tell you your steam usage ?
This resource could help you
http://www.thermon.c...us/default.aspx

Breizh

[fahrudin]

Dear Mr. Devilchicken

I already have they heat loss calculation from tank shell. but it would be better if you share to me for reference.
Ambient temp is around 25 ~ 32 deg C.
We will not conduct any modification to this tank (insulation or coil), cause this is just temporary utilization for high pour point (1 year) after finish is tank utilization will be back to original.

Dear Breizh,
Tank Capacity is 60,000 Barrel.
yes, we can do by conventional way by collect condensate to estimate steam flowrate.

in my mind i consider below method.

Q1= Heat loss from tank shell
Q2= Heat release from Steam to Oil

in ideal condition expected Q1=U A DT= Q2= M L
Steam flow will get from M.


initial temperature 60 deg C
after 2 week temperature become 50 deg C.
So, Q1> Q2
Q2=???

Q2= Q1 - (M Cp DT)
DT= (60-50) deg C
M= Quantity Oil inside tank.


after we get Q2
calculate M from
Q2= M L
L= spesific heat steam @ pressure 1 barg.

is there my method correct???

Please help me

Regards,
Fahrudin

Edited by fahrudin, 27 September 2011 - 08:57 PM.

[AlertO]

fahrudin

i have attached a simplified chart for quick heat loss prediction. You can see the trend when any parameters are deviated.

From your calculation part, i have a comment that Q2 should be equal to tank heat loss at 50 degC storaged liquid.

Any more discussion as welcome.

 Tank heat loss.pdf   231.01KB   185 downloads

[breizh]

Devilchicken,

thanks for the link www.ogdenmfg.com ,
Breizh

Edited by breizh, 27 September 2011 - 11:26 PM.

[breizh]

thanks for the link and the resource.
Breizh

[S.AHMAD]

Salam Fahrudin

Since you are interested to know the steam flowrate, my suggestion is as below:

1. Collect the condensate over specific period and measure the volume, as proposed by Breizh. This is the practical method.

2. Q1 the heat loss is depending on the fluid temperature (e.g 60 C or 50 C). Heat loss at 60 C is higher than at 50 C. Once you have computed Q1 then check with equation Q1 = UA(delta T) to determine whether the A is sufficient for the heat transfer to take place. Since A depends on the steam temperature. The design steam pressure s higher than actual, your required A will be bigger. This calculation will tell you whether A is adequate or not.
If the fluid temperature of 50 C is the final temperature (no more temperature drop) this indicates that you have reached the equilibrium or steady state conditions. Thus, calculate Q1 based on 50 C temperature, and hence calculate mass of steam (M) using heat of condensation at the actual pressure.

Compare mass of steam (calculated) with the one collected (practical). It should be close to each other.

The dropping in fluid temperature is due to either one or both:
1. Inadequate A the surface area
2. Insufficient Mass flow rate of steam due to system hydraulic limitation (piping + steam trap + condensate discharge line).

Changing the steam pressure will effect both A and maximum M

If you need further guidance, please ask. Good luck.

Edited by S.AHMAD, 28 September 2011 - 10:25 PM.

[tarafdar]

Hi Fahrudin,

If your requirement is only theoritical,by this time you have got sufficient information from Mr.Breizh,S.Ahmad & devilchicken.They have given you some practical tips also.

The informations given by you are :
1.Oil is of high pour point.
2.Tank is not insulated.
3.Oil is received at 60⁰C.
4.Steam coil dia 2".
5.Design operating pr. for steam 3.5barg.
6.Available steam pr. 1barg(Saturation temp. 120⁰C).
7.Temp. dropped to 50⁰C within a span of 2 weeks.
8.No flow meter for steam.
9.Ambient temp. 25-32⁰C.
10.Tank capacity 9500,000 lit.

You also mentioned that :
a)You don't want to insulate the tank.You don't want any modification with the steam coil.
b)The arrangement is temporary & it is for 1 year only.

My comments are:
1.The tank is large & the coil is not designed for the relevant purpose.
2.Temp. drop is 10⁰C in 336 hrs.
3.Ambient temp. variation is 7⁰C.
So when the oil temp is 60⁰C the deltaT with ambient is 28-35⁰C(At the beginning).
when the oil temp is 50⁰C the deltaT with ambient is 18-25⁰C(At the end of 14 days)
The saturation temp of 1barg steam is 120⁰C.Since the coils are of 2" dia,there should not be any flow limitation.The heat transfer area may not be sufficient.
Since the radiation loss differs(18-35⁰C deltaT with ambient),so is your heating requirement.

What you can do is:
a)The steam trap may not be sufficient to discharge the condensate.You can make a by-pass of steam trap & keep it opened after trial & error.
b)You can make steam sparger & spray steam at very slow rate to keep the surface temp. of tank at say 40⁰C to reduce radiation loss.But the area arround the tank must permit it.

[fahrudin]

Dear Ahmad & Tarafdar.

Thank you for attention.
we will not modified steam coil due to this is temporary tank for high pour point Oil.
We are lease this tank from another party (mother company) include steam supply.
after our new tank project is finish we will not utilize this tank again.

regarding steam qty, I have try to collect steam condensate outlet from tank.
it has found that steam flow rate per hour is: around 450 kg/hr.

now we are on going for take comparison data for another checking by do below item:
1) Closing steam coil
2) Open steam coil

1. Checking Heat loss without steam supply (close steam coil valve)
we will calculate heat loss
Q1= heat loss from tank
Q2 = Heat release from steam to Oil
Q3 = Total heat loss or release (in t1 to t2)

Q3= Q1 - Q2
Since no steam supply --> Q2=0
So, Q1 = Q3 = m cp DT = x

2. Open steam supply to tank
Find Q2: ???
Q1 = x
Q3 = Q1 - Q2
Q3 = x - Q2 -----> x is minus since heat loss
Q2 = x - Q3 ------> Calculate Q3 = M Cp. DT (delta T)
Find Q2

Q2 = M . L
get M = Steam quantity

expected M will be close to 400 Kg/hr

[tarafdar]

Hi Fahrudin,

You should take care of the following points :

1.DT will very (most likely) during the two tests (DT in test 1 & DT in test 2 will be different).Because oil temp. & ambient temp. are changing.
2.If you like to do the test for same DT then your test time for two cases will very.
3.Before starting the test without steam, be sure that all hot condensate is drained.
4.The longer the test time, the better will be the result.

Thanks

[S.AHMAD]

Salam Fahrudin

In addition to Tarafdar comments please note that the heat loss to surrounding is a function of fluid temperature, ambient temperature and the surface area. When fluid temperature drop, the heat loss is also reduced. Thus, the heat loss in the two cases is not the same. However, you can use the heat loss in the 1st test to calculate the overall U, heat transfer coefficient and assume that this U is constant, Keep in mind also that the surface area is the total area in contact with the fluid, not the total area of the storage tank.