It is becoming a widespread norm that refineries are processing an increasing quantity of heavy and sour crudes than ever before. The depleting oil reserves of light sweet crudes have resulted in the need for deeper exploration. Considerable finds in the Orinoco belt of Venezuela, California and Canada has increased the need of refineries to cater to the heavy crude market. Heavy crudes present a host of different issues in the processing world and refiners world over are aligning their refining strategies to cater to the newer type of crude oils. During the recent economical problem, several refineries have evaluated processing such &'opportunity crudes&' to improve declining refining margins.
The significance of this has been documented in terms of crude processing within the desalter, crude column overhead corrosion concerns and high temperature fouling due to a high Total Acid Number (TAN) amongst other downstream concerns. Furthermore, the number of models used by refineries for determining crude compatibility has increased significantly. It has been found that most of the refineries that continue to foul their pre-heat exchangers in the crude unit very diligently conduct compatibility tests to determine potential incompatibility issues. If this routine is so rigid, then why does fouling still occur?
Generally as the crude density increases, the amount of sulfur and iron within the crude also increases; such crude oils have higher solids and asphaltene content. It is known that at the temperatures incurred within the crude preheat train asphaltenes foul at a rapid rate. The precipitation of these asphaltenes is accelerated by several factors although the crude blend in itself is compatible. This paper will discuss all such aspects and will share information regarding some of the work done to understand the ongoing issue of fouling in today's crude units.
The ultimate consequence of the above situation is an increase in energy required to meet the same furnace outlet temperatures - often, there can be a limitation in maintaining these temperatures without achieving adequate fouling control in the heat exchangers. The need to fire more in the furnaces also increases emission levels. This paper shall discuss in detail some of the root causes for the ongoing fouling in refineries with a mitigation plan that has been successfully commercially used.
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