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Low Viscosity Fuel Oil


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#1 enkim

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Posted 27 February 2015 - 03:03 AM

Hello.

Our refinery steam boiler use no.6 fuel oil. Our oil burner's viscosity requirement(specification) is under 30cst.

Sometimes we feed in lower viscosity fuel oil produced in our refinery, whose viscosity is about 6cst just before burner.

We experienced flame instability and carbon deposit in nozzle tip.

Our burner is external mixing type using steam for atomizing.

We think the finer droplet due to lower viscosity make flame closed to tip and it may cause overheat the tip and coking.

To solve this problem, we plan to change the atomizing medium from steam to air.

But we are not sure that our plan will solve our problem.

 

How do you think about our trouble and our plan?



#2 Napo

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Posted 28 February 2015 - 07:45 AM

Hello Enkim,

 

I think you need review the boiler´s manual, troubleshooting section.

 

After, you need verify the secondary air and primary air.

 

Also you need verify differential pressure between vapor and fuel.

 

The combustion is a reaction, if you put excesive air it is possible that your burner shut-down.

 

If you think to do this change, please consult with boiler vendor. Please evaluate the risk.

 

Can you change the temperatura of light fuel oil?

 

Regards,

 

Napo.



#3 enkim

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Posted 01 March 2015 - 06:25 AM

Thank you for your comment.

We also think installation of the water cooling jacket for light oil fuel line.

However, the viscosity of the light fuel at ambient temperate is about 10cSt. It is still low. 

Why do you think the excessiv air shut-down the burner?

And could you explain why you mentioned the differential pressure between vapor and fuel?



#4 Napo

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Posted 01 March 2015 - 01:38 PM

Dear Enkim,

If you put excessive air, then the flame turns off.

You need a differential pressure '(dp) between vapor and fuel oil for atomizer the fuel, this value is 0.5-5 psi (please verify the dp in your boiler manual).

If you change the fuel (and now you work with light), you need less dp.

Regards,


NAPO.
,

#5 Arsal

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Posted 02 March 2015 - 06:01 AM

NAPO is right i want to add more...

I think change from steam to air is not a right decision without permission of a vendor.

First you should monitor the Differential pressure of steam and fuel oil.This is very important factor to control the atomizing of a fuel.

what is your DP?



#6 enkim

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Posted 12 March 2015 - 02:01 AM

Thank you, NAPO and Rao Arsalan

This week, i visited the boiler site that are firing the low viscos oil.

According to your comments, i tried to find out the guidelines for DP. But, there was no manual or guidelines about it.

The local burner vendor has been trying to solve the problems, but they didn't make it.

Our boiler operating engineers thinks that the vendor doesn't have any solution and doesn't even know the right causes of the problems.  And there are no good burner maker here. 

 

The fuel is the blended fuel of light heavy fuel oil(like No.4 or No.5)and No.1(like gasoline).

The viscosity of them are 80cSt and 1.3 at 50 celcius degree(122 Fahrenheit), respectively.

The blending ratio of them is 4:6 or 5:5 or 6:4.

The viscosity of the blended fuel ranges from 3.5 to 8 cSt at 50 celcius degree.

The manual of burner vendor said the burner could cover those viscosity range. But, they don't suggest the operation condition like DP.

The flame envelop the nozzle tip. So, I couldn't see the end of the nozzle tip through the peeping hole.

The angle of the flame is over 150 dgree. The flame color is yellowish but a little hazy.

There are severe carbon deposits around burner tile.  The swirler got damaged quickly.

To reduce the flame angle, the operators increased the primary air. But it caused higher NOx emission.

 

Some handbooks recommend to use air atomizing for light oil.

So the operators are thinking of chaing the atomizing media.

As you mentioned, they don't know how the change will effect on the boiler operation.

 

 

Thanks again for your comments.

And i hope you will give more comments how to solve my problems.



#7 Napo

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Posted 12 March 2015 - 06:49 AM

Dear Enkim,

 

How many burners do you have in this boiler?

What is the capacity of boiler?, How many kg/h produce?

Can you decrease the amount (flow) the vapor to burner?. Maybe manually. Steam can be a deterrent to atomization of light fuels because the steam temperature can cause carbonization of distillates within the burner (Perry, Chemical Engineers´Handbook, 4th. edition).

 

At this moment, if vendors can´t you give assistance, you need gradually change the operation mode. Can you modified the temperature of light fuel?.

 

Maybe an you give me a picture of this burner?, primary air is for combustion, and the secondary air is for to regulate the lenght of flame. Normally is more easy to burn light fuels.

 

Regards,

 

Napo.



#8 Napo

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Posted 14 March 2015 - 05:42 PM

Dear Enkim,
 
I found the following information:
 
Where don´t have vapor, it can substitute with compressed air without moisture (Rosaler R, Standard Handbook of Plant Engineering, 2nd. edition, vol. 1, section 4, p. 57, in spanish).
 
In Belakhowsky, "Introduxction aux combustubles et a la Combustion", we have an explanation of air in burners to low, medium and high pressure (p. 234, in french)..
 
Attached I send you an information of Cremer and Watkins, Chemical Engineering Practice, Vol. 10, Academic Press-Butterworths Scientific Publications).
 
At this moment, if you review the previous information I think you can change the steam for air, gradually.
 
Regards,
 
Napo.
 
 

 

 

Attached Files



#9 enkim

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Posted 16 March 2015 - 01:37 AM

Dear Napo

 

Thank you for your advices and attached file.

We have two boilers for the fuel.  One is 80 ton of steam/hr, the other is 150 ton of steam/hr of capacity.

In 80T/H boiler, we have two burners at lower and upper side of the furnace wall.

In 150T/H boiler, we have four burners which can produce tangential firing.

 

I'm sorry, but i can give you the picture of the burner because of company's security policy. But, it is old-fashioned one that was installed in 1990's.  Typical Y-Zet atomizer.  6 Spray(Atomizing) Holes. Spray angle of spray holes: 85 degree.

Our nozzle tip's configuration is almost same as the figure 1 of the reference (http://www.ilasseuro.../papers/014.pdf). 

 

Regarding light fuel oil temperature, we can lower the temperature only by additional method like water cooling jacket or something.

Because of the chemical plant operation condition, the oil's temperature is maintained around 50 to 60 celcius degree.

 

Thank you.






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