Ex-situ hydroprocessing catalyst regeneration and pool management
Hydroprocessing catalysts deactivate over time. The cycle length may be as short as a few months or up to several years, but eventually the temperature required to achieve sufficient conversion reaches EOR (End-Of-Run) condition due to hardware constraints. The deactivation can be reversible due to carbon deposition, or irreversible due to permanent catalyst poisons such as for instance arsenic, silica, nickel or vanadium. When deciding on the option of ex-situ catalyst regeneration it is good to know the reason for the deactivation and the expected activity after commercial regeneration. The ex-situ regeneration will remove the carbon by means of a controlled burn, minimizing damage to the pore structure and surface area of the catalyst. The activity of the regenerated catalyst must meet certain performance criteria to justify re-use. Different regeneration companies can provide a laboratory analysis of the spent catalyst, conduct a laboratory regeneration, and perform a laboratory activity test comparing the performance of the regenerated catalyst to that of a fresh reference catalyst. This information allows a refinery, who owns the spent catalyst, to decide upon its regeneration or disposal. Optimal catalyst performance is of high importance.
Catalyst regeneration economicsEx-situ regeneration, if technically possible, is usually more attractive than buying fresh catalyst. Re-use of the (regenerated) catalyst conserves resources such as the carefully produced carrier with its controlled pore structure, and the metals deposited on the carrier to give the catalyst its activity. To benefit from these advantages, one needs to overcome a few hurdles that have to do with quality constraints, legal constraints and process control.
Quality constraintsThe quality constraints have to do with the fact that the quality of the spent catalyst (particle length distribution, contaminants) is unknown until it is unloaded, sampled and analysed. When the spent catalyst is unloaded from the reactor it is almost impossible to do a regeneration and to re-load the same batch during the turnaround. While this was practiced in the past it is physically impossible these days due to much larger reactor inventories and the need for more elaborate analysis including activity testing prior to regeneration. This being said turnaround regeneration can still be practised for specialty catalysts such catalyst used for ethylbenzene, or cumene production, or reformers, where the cost of a spare-batch are prohibitive, and the risk of contamination is almost non-existent. However to minimize downtime and eliminate the risk of a poor quality spent catalyst, most hydrotreating units will have a good quality re-placement batch (fresh or regenerated) on-site before the start of the turnaround, so that the unit can be reloaded and started up as per the refinery production schedule. Although there are some costs involved in having a spare-batch, having a spare batch also allows for detailed characterization of the spent catalyst before making a decision on its re-use. Regeneration companies (like for instance Eurecat and Porocel) can analyse the spent catalyst and advise on its condition and performance after a laboratory regeneration. This information allows an informed decision by the refiner whether to regenerate the spent catalyst or to send it for disposal and metal reclaim. It is important to create this degree of freedom (time) to do a proper evaluation of the spent catalyst quality before deciding on regeneration and re-use.
Legal constraintsThe spent catalyst is a hazardous material and a spent hydrotreating catalysts are considered self-heating solids and classified as UN 3190 for packaging and ADR Class 4.2 for transportation. A refinery can load the spent catalyst into UN approved steel drums on pallets or in catalyst flo-bins. The use of drums may require the handling of hundreds and possibly thousands of drums and that slows-down the unloading of the reactor and creates extra handling with forklift trucks and associated safety concerns. The catalyst flo-bins are much larger (each bin holds about ten drums), and they allow for efficient and safe unloading of the reactors. Such flo-bins can be rented from several companies for instance HooverFerguson. Whichever, packaging is used, it is important to note on each container the reactor and bed number as well as a sequential number, so that the regeneration company can sample and analyse each reactor / bed individually and if necessary separate the irreversibly contaminated catalyst from the catalyst that can be regenerated. The drums need to be secured on the pallets and the pallets need to be secured on the truck. The same is true for the catalyst flo-bins. The regeneration companies can advise on the latest transport requirements. It is important that there is no catalyst outside the drums or flo-bins on the truck, as random road-side inspections can result in hefty fines and costly delays.
Process controlThe laboratory regeneration of the spent catalyst prior to industrial regeneration gives an indication of the yield and activity of the regenerated catalyst. For this indication to be fulfilled during the industrial regeneration it is important that the sampling and analysis of the spent catalyst was representative. As representative sampling of large quantities of granular material is difficult, it is good practise to divide the spent catalyst bed in smaller sub-lots and to analyse each lot individually. Furthermore, contaminants coming into the reactor with the feedstock tend to deposit on the catalyst from the top down, creating a gradient along the axis of the reactor. During gravity unloading or vacuum unloading the catalyst from different locations inside the reactor will end up in different containers, and therefore it is important to number the containers so that contaminated catalyst can be separated from material that is suitable for regeneration. This pre-analysis and selection of catalyst for regeneration per sub-lot will also avoid contamination of the entire batch. After a decision by the refiner to regenerate all or part of the batch, the regeneration company will schedule the regeneration. During the regeneration, the spent catalyst is screened to remove spent catalyst dust and fines, and subsequently exposed to air at elevated temperatures to burn off the carbon deposits. It is important to control the burn and avoid local high temperatures. Complete monitoring of all temperatures is impossible, so that the regenerator needs to control the process and verify good surface area retention, and retention of a good pore structure by means of analysis of the regenerated catalyst. A good regeneration is characterized by a low carbon loading of the spent catalyst (typically less than 0.5wt% for hydrotreating catalysts) and a good surface area retention. With the introduction of type II hydrotreating catalysts additional requirements apply to the metals dispersion, not directly evident from the BET surface area. For type II catalysts it is recommended to test the activity of the regenerated catalyst (after an additional rejuvenation as needed). Regeneration vendors need to guarantee the activity of regenerated / rejuvenated type II catalysts. Irreparable loss of surface area or metals dispersion due to high temperatures during regeneration are for the vendors account. In addition to low carbon level and retained micro-structure, the other important characteristic of the regenerated catalyst is its particle length distribution and associated compacted bulk density in view of reactor pressure drop requirements. The regeneration vendor will screen the regenerated catalyst before sampling and packaging. It is important to get detailed analyses including activity tests on composite samples of sub-lots not exceeding 50 Mt each.
Conclusion: ex-situ catalyst regeneration can be an interesting business option to refineriesAfter more than 40 years ex-situ catalyst regeneration is proven technology, it is economically attractive, and it saves resources. The quality of the spent catalyst needs to be investigated after unloading and prior to the decision to regenerate or dispose of the catalyst. During the regeneration, the process temperature needs to be controlled to remove the carbon under mild conditions to avoid damage to the catalyst micro-structure. After the regeneration the catalyst needs to be screened and or length graded to remove dust and fines/ shorts to produce a catalyst with sufficient void fraction after dense loading. The regenerated catalyst can be activity tested by the regeneration vendor to confirm suitability for re-use. Refineries can choose to maintain their own pool of regenerated catalysts for re-use, or to buy and sell into a re-sale pool managed by a regeneration vendor or catalyst trading company.
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