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Improving FCC unit profitability

Upgrading the FCC catalyst and additive system enabled a refiner to increase olefins production with lower bottoms to coke and no increase in dry gas.

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Article Summary
This article presents the results of the common efforts between Grace and the FCC team of Hellenic Petroleum1 S.A.’s (HELPE) Aspropyrgos refinery to further enhance FCC unit profitability. In this context, Grace proposed adding Midas catalyst to the base Grace catalyst which had been used until then in combination with OlefinsUltra MZ additive, the latest ZSM-5 based technology launched in the EMEA.2 The clear improvement in profitability was based on lower bottoms to coke and higher product olefinicity at no higher dry gas, while at the same time reducing catalyst addition.

The reformulation and subsequent evaluation was based on clear target setting from the HELPE FCC team as well as the reliability of the data provided. Grace worked with the FCC team to manage the change and ensure a smooth transition to the new catalyst system. This was achieved by performing a series of lab studies to predict the new catalyst system’s performance and by discussing with the FCC team ways to optimise the process to achieve maximum benefit. The estimated further improvement in the HELPE FCC unit’s profitability via the new technology amounts to at least 
0.6 $/bbl.

Following the successful introduction of Midas as an efficient matrix component to further improve bottoms upgrading, Grace continues to work with HELPE to further enhance the FCC unit’s profitability by tailoring its latest catalyst and additives technology according to operating targets.

Aspropyrgos refinery’s FCC unit is an Exxon FlexiCrackeR design, aiming primarily at propylene production at minimum bottoms yield. The FCC team is focused on continuous improvement in operations, supported by Grace since 2004. Aiming at further enhancing profitability, HELPE made a series of improvements to debottleneck certain downstream units. This resulted in higher capacity for propylene and LPG processing.

Grace’s catalyst and propylene additive technology
The benefits of Grace’s base catalyst were enhanced by the addition of Midas catalyst as a blending component.

Midas is a high matrix input, high porosity FCC catalyst, maximising conversion of bottoms. Midas catalyst has been successfully applied in over 130 applications worldwide and its success is driven by the fact that it effectively cracks all feed types: heavy resids, severely hydrotreated light feeds, and shale oil derived feed streams. The catalyst design minimises the thermal and catalytic factors that result in coke formation. Optimal porosity is required for effective kinetic conversion of bottoms. The result is deep bottoms conversion, regardless of the starting feedstock.

It should be stressed that the introduction of the matrix component in the case of the HELPE FCC unit was very carefully tailored to the targets of the unit, by exploiting the ‘best of both worlds’: the highly selective base catalyst component on the one hand, and the highly active Midas matrix part on the other. This ensured further improved activity and stability, while achieving higher product olefinicity and lower bottoms to coke, without compromising dry gas make or attrition resistance.

As a leading supplier in the LPG olefins maximisation segment, Grace is serving the majority of the high propylene FCC units worldwide. To support the demands of this market segment, the company continuously invests in R&D innovation. The latest development in LPG olefins maximisation technology is OlefinsUltra MZ, launched in 2015. This was supplied for the HELPE FCC unit to be added to the catalyst system on an as-need basis to boost LPG make further.

Performance of the catalyst blend and additive
The addition of Midas as a blend component and the upgrade to the OlefinsUltra MZ additive were decided after a screening study which took place in Grace’s laboratory facilities in Worms, Germany. The selected formulation showed:
• Lower bottoms to coke
• Substantially higher propylene and isobutylene selectivity
• No debits in dry gas make
• Excellent attrition resistance
• Higher activity retention and metals tolerance, resulting in lower delta coke and catalyst additions.

An extract of the performance benefits is depicted in the following graphs, based exclusively on the raw data provided by the HELPE FCC unit team. More specifically, Figure 1 shows the clear improvement in bottoms to coke, which is particularly important when planning to process worse feedstocks under coke limitations.

This feature is based on the lower delta coke make of new formulation, as can be seen in Figure 2. This graph shows the difference between the temperatures of the regenerator dense bed and reactor outlet temperature (a direct measure of delta coke) against the Concarbon processed in the unit (a measure of the delta coke contribution from the feed). For the same coke make tendency level, the base catalyst/Midas blend results in lower delta coke and therefore lower regenerator temperatures.

It is important to stress that this could not have been achieved without a well tuned and balanced zeolite to matrix ratio. Excess matrix would have had the opposite effect.

The significant operational flexibility gained is complemented by increased LPG olefins selectivity (see Figures 3 and 4). Propylene and isobutylene selectivities are plotted against the P2O5 content of the inventory in order to account for the other two major factors contributing to LPG olefins selectivity: conversion and ZSM-5 additive content.

The increase in propylene selectivity is to be attributed mainly to the OlefinsUltra MZ additive which brings higher activity for the same content in the inventory. The C4 olefinicity is the combined effect of the Midas component as well as OlefinsUltra MZ which started to be used at the same time.

As mentioned previously, these performance benefits came at no increase in dry gas make (see 
Figure 5).

In addition to the performance benefits, Figure 6 shows the specific catalyst additions needed to maintain activity versus the vanadium equivalent in the feed. The 
average difference was at 0.3 kg per ton of feed processed and, apart from the offset, the trend lines have a different slope, indicating less deactivation of the base catalyst/Midas blend under the effect of metals. Although the improvements in unit operations and performance prevail by far in unit economics, a reduction in catalyst additions also assists in catalyst handling and opex minimisation.
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