Revamps 2023 Issue

Optimising hydrogen consumption in a raw-diesel hydro- treater can be achieved through either catalyst selection or during the operational run.⁴ While the impact of catalyst selection on hydrogen consumption has been previously addressed, there are variables that can be managed during the run to control H₂ usage: • Feed management: One approach is to maximise the use of straight-run feed and minimise or avoid cracked feeds with high olefins and aromatic content. This strategy helps reduce hydrogen demand during the process • Pressure: Lowering the unit pressure is an effective method to decrease hydrogen partial pressure, resulting in reduced aromatic saturation and subsequently lower hydrogen consumption. However, compensatory measures, such as raising temperature, might be necessary to coun- teract the activity loss caused by lower H₂ partial pressure, and careful consideration is required to address potential increases in the deactivation rate during this period, as it could impact the unit’s overall cycle life • Hydrogen purity: Increasing the purity of make-up hydrogen provides more H₂ to the unit for a given com - Hydrogen use accounts for up to 80% of a hydrotreater’s variable operating costs, and strategies to minimise consumption will enhance refinery profitability pressor capacity while also reducing the need for purging, ultimately minimising hydrogen loss • Solution losses: A significant percentage of hydrogen loss occurs from the hot separator liquid. By reducing the separator temperature, the solubility of H₂ in the liq - uid phase decreases, thereby preserving more hydrogen in the gas phase. However, when optimising the separa- tor temperature, it is crucial to consider the downstream fractionator’s heat requirements. Furthermore, hydrogen consumption associated with dissolution losses within the process can be minimised by adjusting the operating temperature of high-pressure separator drums. This mod - ification aims to minimise hydrogen-dissolution loss and the amount of hydrogen sent to the separation unit. Minor revamps of the unit, such as modifying the scheme (hot scheme vs cold scheme), or adding a membrane to the off- gas of the medium-pressure drum (if applicable), can also help reduce hydrogen losses. Additionally, incorporating an amine absorber on the recycling loop may increase recy- cle-gas purging and eliminate the need for purging • Wash oil : Implementing a wash-oil system can help recover hydrogen that may be lost due to solution losses, contribut- ing to better hydrogen management during the process. H₂-saving catalysts and processes For low-pressure middle-distillate hydrotreaters that are hydrogen-limited, rejuvenated CoMo catalysts are said to

offer a good fit for high HDS performance with the lowest hydrogen consumption. However, in units processing more severe feeds, especially at higher pressures, the optimum catalyst design may be a combination of NiMo and CoMo catalysts to balance overall HDS and HDN activity while minimising hydrogen consumption. Processes that look to minimise H₂ consumption have also been commercialised. For example, one commercial technology saturates the feed with hydrogen before it goes to the reactor. Another process is said to be capable of removing hydrogen-consuming compounds from feeds containing LCO or CGO before hydrotreating. Adding to the attractiveness of these technologies is the fact that both may be set up as revamps of existing hydrotreating units. High-purity hydrogen Refiners can utilise high-purity hydrogen instead of 65-85%-pure catalytic-reformer hydrogen to increase the hydrogen partial pressure in their hydrotreaters. Depending on operating conditions, feedstock, set up of the plant, and bottlenecks, the following benefits can be realised from increased hydrogen partial pressure: • Higher liquid yields due to increased aromatic-ring satu- ration and increased nitrogen removal, which improve the operation of downstream units • Extended catalyst life due to the reduction of coke made from non-selective cracking • Improved sulphur removal, particularly for diesel production • Energy savings from the use of fuel, steam, and electricity. Several different parameters can impact hydrogen purity contained in the recycle gas of hydroprocessing units. These parameters may include the purity of fresh make-up H 2, the source of the recycled gas, the concentration of non-condensable gases in the make-up gas (like nitrogen and helium), the yield of light-gas components (H₂S, CO₂, C 1 -C 4), the absence of wash water at the reactor effluent air condenser inlet (which slightly reduces purity as NH₃ circu - lation increases, mainly if there is no scrubber), and so on. By adding 99%-pure hydrogen to a straight-run mid - dle-distillate hydrotreater operating at a pressure of <300 psi (2.1 MPa), a refiner increased hydrogen partial pressure and extended catalyst life by three months. The finan - cial benefit of this change would have been greater if the hydrotreater had been the factor limiting throughput to the upstream crude-distillation unit. For refiners producing hydrogen on-site, the energy required to produce hydrogen is much greater than the rest of the energy required to operate the hydrotreater combined. Hydrogen use accounts for up to 80% of a hydrotreater’s variable operating costs, and strategies to minimise consumption will enhance refinery profitability. Conclusion There are five technological pillars to reduce GHG emis - sions with future profitability and sustainability in mind⁷: u Energy management v Electrification, cogeneration/combined heat and power/ integrated gasification combined cycle, and zero-/low-car - bon fuels

Revamps 2023