Antifouling solution to improve preheat exchanger efficiency A cost-effective antifouling formulation has been developed by analysing fouling deposits from preheat exchangers and understanding what led to their formation
Eswararao Doni, Raghava Krishna Kanala, and Sairamu Madala Hindustan Petroleum Green R&D Centre (HPGRDC)
I n the petroleum refining process, crude oil is converted into various fuels and other petro-derived products. This refining process is highly energy-intensive, consuming approximately 6% of the energy from each barrel of crude oil processed in the refinery itself. 1,2 Initially, crude oil is heated and distilled into different products, which accounts for a significant portion of the energy used in the refinery. Consequently, refiners strive to conserve energy by recovering as much as possible from the hot product streams through heat exchanger networks. Crude oil contains numerous solid impurities, sediments, trace metals, and heavier hydrocarbon compounds. 3 Impurities, such as inorganic salts and sediments, are primarily removed in the desalter unit. However, the remaining impurities in crude oil tend to accumulate as fouling scales in the heat exchangers when the crude oil is further heated. 4 The deposited material can vary from gel-like material to solid-like scales. Over time, the accumulation of fouling deposits hinders energy conservation and results in poor energy recovery. Common problem areas include crude and short residue/vacuum residue preheat exchangers, furnaces, hydrotreater exchangers, reactor beds, fluid catalytic cracking (FCC) unit slurry exchangers, and thermal cracking process exchangers. Several factors influence fouling, including the type of crude, equipment design, flow rates, temperature, operational severity of the unit, and fluid characteristics. 5 All these factors contribute to energy loss, increased maintenance costs, reduced throughput, and safety issues. The total costs associated with
fouling for major industrialised nations are estimated to exceed $4.4 billion annually. Fouling has posed a significant challenge for many years, primarily due to a limited fundamental understanding of the mechanisms involved, the composition of deposits and scales, and their effects on refinery operations. Fouling deposits can be divided into two main categories: inorganic and organic. In the case of inorganic fouling, the corrosion of process equipment leads to the formation of ferrous-based corrosion products, such as iron sulphide or ferric oxide, which tend to accumulate in exchangers, particularly in regions with lower flow velocities. Additionally, solid inorganic contaminants such as sand and silt can settle in the exchanger, resulting in hydraulic or thermal blockages. Organic fouling in a crude unit arises from the precipitation of organic components, such as asphaltenes and high molecular weight hydrocarbons, which become insoluble within the system. The instability of asphaltenes can occur due to the blending of incompatible crude oils, leading to their separation and precipitation as a result of the high temperatures associated with crude heating. Moreover, organic fouling is also driven by polymerisation reactions that are triggered by fouling precursors, including dienes and alkenes. This polymerisation process “ The total costs associated with fouling for major industrialised nations are estimated to exceed $4.4 billion annually ”
Refining India
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