PTQ Q3 2024 Issue

0.0004

0.00 30.00 20.00 10.00 50.00 40.00 80.00 70.00 60.00 90.00

50 40 80 70 60 90

Solid NHCl

0.0003

0.0002

0.00 30 20 10

0.0001

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Temperature (˚C)

Figure 2 Solid NH4Cl formation with respect to temperature

Figure 3 Relative humidity across the feed/effluent exchangers

• Metallurgical upgrades and adding new equipment when operating solutions are impractical. • Robust analysis program to monitor and control process conditions. The wash water’s flow rate and quality are critical to prevent increased corrosion and deposition of NH₄HS and NH₄Cl. The following case studies aim to analyse how these two variables affect corrosion prevention in refineries. Case study: Renewable diesel plant With the growing tendency to produce fuels with a low carbon footprint, co-processing vegetable oil with crude oil fractions is attracting attention to study corrosion in refin- eries. Vegetable oil contains oxygen, which is part of the carboxyl group of the fatty acid molecule. Co-processing is typically done in hydrotreating units, and the oxygen in fatty acids will produce H₂O, CO, and CO2. These three compo- nents will now be part of the reactor effluent composition. Originally, the hydrotreater’s design and material spec- ifications may not have considered these components. For example, in a diesel hydrotreater with 15 vol% co-process- ing of vegetable and animal oils (11 wt% palmitic acid, 23.4 wt% oleic acid, 53.2 wt% linoleic acid, 7.8 wt% linolenic acid, 4 wt% stearic acid, and others), the reactor effluent may have approximately 2.2 mass% of CO, 2.0 mass% of CO₂, and 1.2 mass% of H₂O. The vegetable oil is assumed to be pretreated for this case study, as it is a typical practice to eliminate chlorides and phosphorous. The reactor effluent cooling train and separation plant are shown in Figure 1 . When the reactor effluent stream contains approximately 30 ppm-wt% of HCl, it is important to determine whether solid NH 4 Cl can form in this stream when it leaves the reac - tor precooling system at 250ºC (482ºF). This can be achieved by using the Petro-SIM modelling software and the OLI thermodynamic engine. Figure 2 shows that solid NH₄Cl is imminent inside the REAC, and corrective action is necessary based on these results. The corrective action normally involves injecting wash water, generally sour water.⁴ As a result of the computer model, the optimum amount of wash water to use is approx- imately 0.09 kg of reactor effluent when stripped sour water

estimates the formation of corrosive chemicals. With the presence of CO₂ in the reactor effluent, the composition of carbonates ( CO 2₃ – ) and pH needs consideration. A leading process provider has estimated that corrosion accounts for 37% of major issues in hydroprocessing units.3 For example, corrosion in the REAC alone contributes up to 24% of major corrosion issues. Their study identified the following key contributing factors responsible for corrosion:  Compositional dependant • Metallurgy • Nitrogen and sulphur content in the feed • H₂S and NH₃ partial pressure • Chloride presence • Wash water quality and rate • Vapourise wash water injection points. v Operational dependant • Fluid velocity • Balanced and unbalanced headers, the latter causing more corrosion than the former • Single vs multiple wash water injection points. Proactively managing corrosion In operating plants, OLI Systems has developed simulation technology that rigorously calculates corrosion-causing electrolyte species. To cater to the industry’s specific needs, KBC’s proprietary Petro-SIM simulation software now inte- grates into the powerful OLI thermodynamic engine. This strategic integration enables process, materials, corrosion, and plant integrity engineers to: • Enhance the electrolyte chemistry simulation capabilities • Predict general corrosion • Estimate localised corrosion • Simulate corrosive environments • Identify and debottleneck corrosion issues • Manage corrosion. Simulation results support and validate recommendations to mitigate corrosion, such as: • Detailed assessment to determine corrosion issues sitewide • Enhanced use of neutralisers, inhibitors, anti-fouling addi- tives, chloride control, and wash water facilities

PTQ Q3 2024