3 replies to this topic

[obsidian_dust]

Dear all,

Recently some units in our refinery is struggling to produce clear and bright diesel fuel blending components. Some stream are always hazy and sometimes it leads to hazy final product albeit the water content analysis result (ASTM D-1744) is still on specification (our spec is 500 mg/kg water content maximum). My question is: when we have already analyzed the water content quantitatively and found it still within the specification, should we still worry about the hazy appearance? Is there any kind of water content whose amount cannot be determined by ASTM D-1744?

Thanks in advance

[kkala]

Unaware of the subject, I met http://www.turbotect.../product5.shtml, giving useful information as below. It is noted that "soluble" water is also measured along with insoluble water in Karl-Fischer method of ASTM D-1744 (http://www.machinery...er-oil-analysis).
1. Soluble water in diesel (not separated by gravity) is between 50 - 100 mg/kg. Beyond this limit there is insoluble water, either as free water or as emulsified water to a small extent.
2. Free water can be separated much faster in diesel than in heavy fuels.
3. A bright diesel grade can get hazy when ambient temperature falls, since solubility of water into it (that 50 - 100 mg/kg) decreases.
4. Insoluble water also causes haze.
5. A diesel grade with water content up to 500 mg/kg is expected to be hazy. To assure absence of haziness water content has to be 50 - 100 mg/kg, depending on temperature.
5. The web article (promoting a dehazer) recommends dehazing, but it concerns gas turbine diesel having stricter specifications than normal.

Mentioned diesel grade is assumed not to be automotive diesel, since max water content of the latter must be lower, 200 mg/kg (2004) (http://www.dieselnet...u/fuel_auto.php).
If reported grade is heating diesel, as expected, no problem can be anticipated. Refinery and local market has been accustomed to the grade of max water content 500 mg/kg. Specification for heating diesel here calls for max water content of about 1000 mg/kg (2003).
Water content could create a problem if it is concentrated and comes to the burner "in chunks", haze means water well distributed in the fuel.

Edited by kkala, 13 November 2011 - 03:02 PM.

[obsidian_dust]

KKala,
Thank you very much for your helpful response. And for your information, the max water content 500 mg/kg is the limit applied in our country's automotive diesel. Yet in such high water content the specification for its appearance is clear and bright.

Best regards

[kkala]

Probably automotive diesel has actual water content much lower than the 500 mg/kg posed by law. Considering conditions as here (Greece), the requirement for "clear & bright" diesel would predominate over the max water content of 500 mg/kg; that is water content should be lower than 500 mg/kg to result in clarity of liquid. On the other hand water limit of 50-100 mg/kg (supported by the supplier of dehazer) is probably exaggerated, clear diesel could be obtained even at higher water content (e.g. 200 mg/kg here, to be determined experimentally for a specific case).
Transition point between clearness and haziness might also have some tolerance.