Fuel oil handling/ steam heat exchanger/ blending 2

[poseilus]

Hi to all,

I am new to this topic and I would really appreciate any advise or guidelines you could offer me.

1) Design of storage tanks with heat exchangers and thermal insulation.
2) Necessary operating conditions eg. temperature of fuel oil in order to pump in a specific flow rate.
3) Blending of fuel oil with diesel oil for bunkering at oil terminal.

Thanks in advance for your help and precious time.
Best regards

Antonis

 

[jmw]

Point three i can offer some insites; quality is the big question.
Refinery blending uses online process capillary viscometers for blend trend control. They may still use top middle and bottom samples in storage and make final adjustments by dosing in more distillate. With more modern viscometers, pipeline blending is a reality. Modern viscometers allow much tighter control over the viscosity.
However, when you get to the terminals and fuel barges, blending is usually performed with calibrated blenders e.g. a mechanically linked pair of control valves to control the flow ratio of resifual (or HFO) to distillate flow. The ratio is found using a blend calculator (you can download them from various web sites or obtain them from the oil companies such as Exxon Mobile Marine Fuels or Shell Marine Fuels; or you can ask DNV PS for a copy.)
Fule blending works on the assumption that if you know the properties of the original residual oil and cutter stock, then you can predict the qualities of the final blend. Viscosity is the most sensitive indicator of quality so if the viscosity of the blend matches the predicted value then the other parameters will also be correct. However, the theory (using Refutas, Louis or other relationships) is very vulnerable to the errors in the basic assumptions; fuel oil quality is vary variable. In storage, stratification can take place. Thus the viscosity and composition of the oil can change even as it is being blended.
New viscometry techniques can overcome these problems in the terminals and on barges, as well as contributing to improved practice in the refinery.
Estimated cost of poor fuel quality is variable but between US$3-7 a ton by various sources. Others look at the overall costs to the industry which are staggering.
Some good articles on the Black & White web site (

http://www.blackandwhitemc.com,

http://www,solartronmobrey.com,

http://www.viscoanalyser.com)

Accuracy is a big problem. 1 in 10 blends are found to be in error in at least one parameter. 1 in 120 blends has the potential to cause engine damage. This is a big issue in the marine fuel industry but less so in burner operations (or it was until environmental concerns gave it greater prominance).
Should be an article in this months Bunker News on the problems of fuel oil blending.
Visit

http://www.IBIA.com,

world bunkering and any of the marine websites.

 

[25362]

As jmw rightly says quality is the big question. I'll refer to another blending issue: incompatibility.
Incompatibility is the tendency of a residual fuel to produce a deposit on dilution, or on blending with other fuel oils.

The chief constituents of a residual fuel include asphaltenes, resins (called maltenes), and liquid hydrocarbons.
The asphaltenes cover a wide range of high molecular weight hydrocarbon structures with high carbon/hydrogen ratios and a small amount of other elements. They are believed to exist in residual fuel as "micelles" complexed with maltenes having decreasing MW and C/H ratios from their nucleus outwards suspended in the intermicellar lower MW liquid.

If the overall C/H ratio is lowered, say by the introduction of a paraffinic diluent, the resins, which are absorbed on the asphaltenes, are to a certain extent desorbed. The asphaltene particles not being completely surronded by resins, are mutually attracted, leading to precipitation which appears as sludge.

The general recommendation is that mixing and blending of fuels from different sources on board ship should be avoided so far as possible. For a realistic checking of blends, a prior laboratory analysis is always recommended.

Lab analysis would render information on other items such as density (to select the gravity disc of a purifying centrifugue), viscosity (for the handling temperature of transfer), pour point (for the danger of wax deposition at low temperatures), flash point, sulfur, water, etc., etc.
It is important to keep historical analytical data on fuels and that these be quantitative.

Regulations for marine fuel oils, concerning their use on board, refer mainly to two fields: safety and pollution; and they fall into 3 categories: national, international, and those of the organization under which the vessel is classified.

 

[jmw]

Some good information including on the points raised by 25362, can be found in "Fuel Field Manual" by Kim B Peyton, Nalco/Exxon Energy Chemicals, published by McGraw Hill.
You can also visit the site

http://www.viswalab.com

for some good advice and

http://www.dnv.com/maritime/fueltesting/fuelqualitytesting/ISO8217.asp

for fuel quality data.
Incidentlly, Lars Josephson has a fuel calculator on his site

http://www.steamesteem.com.

Another is to be found on the

http://www.cheresources.com

site. Beware, while most calculators tend to agree, some show some serious differences.
Incidentally, modern inline viscometers can measure the density at flow temperature, the density at 15degC (a quality parameter and required to convert volume flow totals to mass totals for billing purposes) and the density at 98degC, the centrifuge temperature in the fuel lines to the engines. They also give the dynamic and kinematic viscosity at flow temperature and the kinematic viscosity at the reference temperature (usually 100degC in a refinery but 50degC in terminals or on barges), and the ignition index. See

http://www.solartronmobrey.com.

 

[poseilus]

Thank you very much for your resources and sharing your knowledge on this matter.