Fouling occurs in every type of refinery, including crude and natural gas. The effect of excessive fouling leads to loss of efficiency over several aspects of operations, with almost every unit, and may lead to shorter intervals between turnarounds.
Fouling of refinery process equipment may result from a variety of different mechanisms including variations in feedstock or fluid characteristics, operating practices, unit engineering and operational parameters. Regardless of the cause, determining the type of fouling will determine to the most effective chemical treatment program to employ.
Types of fouling include:
Inorganic
Inorganic fouling can manifest itself as corrosion by-products, such as iron sulfides or oxides; and contaminants, such as sand, silts, or salts. These deposits are typically found either in an aqueous environment or where the feedstock contains emulsified water.
Where inorganic fouling is noted, claimed, or otherwise found without excessive hydrocarbon contamination, acidic products should be tested for performance efficacy. However, prior to testing, the presence of iron sulfide scales should be confirmed or determined for full procedural safety. Should the fouling contain these compounds, oxidizers or other West Penetone iron sulfide remediation products require review. However, if such scaling is minimal, the use of CLEAN ADD 2 at 1-2 % v/v is viable.
Organic
Organic fouling can manifest itself either as thick and viscous or even solid precipitates. These deposits usually result from organic constituents that become either insoluble in the processing stream or system (i.e., asphaltenes or high molecular weight hydrocarbons such as paraffins) or undergo thermal degradation or dehydrogenation (i.e., in both cases leading to coke formation or carbonization by-products).
Organic fouling also occurs on the feed side of many systems that either treat or crack the feedstock or effluent. These deposits usually result from polymerization reactions that include both free radical and non-free radical mechanisms. These mechanisms lead to the formation of long chain or high molecular weight molecules. This can occur to the point where solubility is exceeded, and deposition occurs.
Organic fouling is characterized by thermographic analysis, solvent extraction, as well as with both elemental and metal analysis. Where this information is unavailable, known properties of the feedstock will also help determine the most effective chemistry for foulant removal. Once characterized and cross-checked with equipment metallurgy, the program will see the use of either an alkali, solvent, or solvent-emulsion degreaser. In all other cases where average alkanes or arenes are expected or found, ROC products should be employed while ensuring sufficient residence time for complete foulant removal.
