PTQ Q3 2022 Issue

Technology in Action

The result was that despite strong management of change policy, the refinery selected the proprietary Dynocel 680 thanks to the higher level of safety it offers. It is a spheri - cal adsorbent for the purification of vapour or liquid phase olefinic hydrocarbon streams and falls under Category 3 - a hybrid adsorbent. It is particularly useful for the removal of polar compounds such as water, alcohols, ammonia, ethers, ketones and mercaptans, and acidic compounds such as H₂S, COS, and CO₂. Dynocel 680 exhibits low reactivity, no heat release concerns, and does not require a preload step. Safety is paramount in these facilities, and Evonik is committed to the highest safety standards for its products. Therefore, Dynocel 680 has been in service in this refinery for more than five years providing safe, reliable, and predictable unit operations. Conclusion Selection of the proper adsorbent, or combination of adsor - bents, is critical to ensure the removal of all contaminants. However, on top of that, the impact of operational require - ments and adsorbent properties should be considered from a safety, reliability, and predictability standpoint to protect people, profits, and the environment.

Adsorbent choices help refiners find safer solutions

For refiners, selection of the proper adsorbent, or combina - tion of adsorbents, is critical to ensure the removal of all contaminants during olefin (such as ethylene and propyl - ene) purification. However, choosing the correct adsorbent is about more than production efficiencies and effective - ness. Reliability and safety (including heat release and reactivity) should also be key considerations. Three main adsorbent types may be used to purify olefins:  Molecular sieves: have capacity for water, light alcohols, aldehydes and ketones, nitriles, as well as for mercaptans and sulphides. They are not suitable for H₂S, CO₂ or COS in olefin streams.  Promoted alumina: has capacity for H₂S, COS and CO₂, but little to no affinity for water, light alcohols, aldehydes and ketones, and nitriles in olefin streams.  Alumina/molecular sieve hybrid (co-formed): has capac - ity for water, light alcohols, aldehydes and ketones, nitriles, R-SH, sulphides and H₂S, CO₂ or COS in olefin streams, and this combines the properties of 1 and 2 efficiently. Case study: safety matters Several years ago, a European refiner operating a propylene recovery unit (PRU) – using a 3A molecular sieve to remove water and a co-formed adsorbent to remove NH₃ – suf - fered an incident with a fresh adsorbent, and it took nearly a decade to resolve the situation satisfactorily. During start-up, a mechanical blockage occurred due to inert balls plugged in a pipe. The result was that the reactor heated up without any gas flowing out, and the tempera - ture in the vessel increased. Due to its fresh activity, the adsorbent actually catalysed the polymerisation of propyl - ene, leading to a runaway reaction. The vessel burst, and propylene ignited. Following the incident, the refiner used a complete load of 3A molecular sieve for several years, but when ammo - nia (NH₃) related issues occurred, such as corrosion and equipment blockage, it needed to find a more suitable solution. Initially, it tried reverting to a previous configuration, but with the addition of pressure release valves to the flare and multiple thermocouples. It also introduced a different type of co-formed catalyst and a preload step. However, over the next few years, this new approach turned out to be insufficient. An issue was identified in the heating process, and the gas entering the vessel was far too hot. There was a higher temperature in the bed than in the vessel inlet. Although the thermocouples and release valves meant there was no immediate safety issue, the refiner tendered for a different co-formed catalyst to ensure problems did not arise.

Todd Burkes Todd.burkes@evonik.com Evonik Catalysts

Taking thermally limited refinery functions off the critical path

Attractive benefit-to-cost ratios generated when applying temporary cooling solutions in refinery operations cannot be overlooked when operating a plant at high severity. Refineries are currently in the process of adjusting planned turnarounds to expand the project scope required to meet Tier 3 and Euro 4 specifications in the US and Europe, respectively. These stringent specifications influ - ence hydrotreaters (HDTs) and hydrocrackers (HCs) rede - signed for achieving near-zero sulphur specifications in gasoline and diesel. Impending regulations, such as MARPOL VI, could keep turnaround activity at high levels for longer than expected periods. In some cases, a ‘mini’ turnaround is all that is needed to add an additional zone of catalyst and support - ing internals (distributors, downcomers) to an existing HDT or HC reactor to increase capacity and flexibility. In other cases, a major turnaround or revamp is called for to introduce multi-functional catalysts into new reactor zones to increase the refinery’s capacity for desulphurisa - tion and other quality metrics (for example, gasoline octane enhancement, diesel cetane improvement).

PTQ Q3 2022