Improve FCC Performance by Using the Best Catalyst
Changing FCC catalyst is one of the most frequently used methods chosen to improve FCC operation. The starting point to ensure the best catalyst is chosen is the thorough definition of the refiners objectives. Primary objectives are usually readily identified, for example maximization of gasoline octane or minimization of bottoms yield, but it is more difficult to identify and quantify the tradeoffs a refiner is prepared to make to achieve these goals.
This is important because there are many catalysts available that might meet a primary objective but have different or varying degrees of side effects. For instance, BASF's OCTISIV PLUS 100 and DYNASIV PLUS 800 series catalysts both would give a similar improvement in gasoline RONC relative to a gasoline catalyst such as MAGNASIV-380. However the OCTISIV PLUS would have better bottoms upgrading but slightly higher gas make than the DYNASIV PLUS. Other ways to improve octane might be to switch to a full USY catalyst such as OCTISIV PLUS 580, which would give higher RONC but result in a lower gasoline yield. It may even be economical to use an octane additive such as Z100 from BASF containing ZSM-5 to increase RONC providing the refiner can cope with the increased wet gas make. In addition, BASF has the ability to CUSTOM MAKE catalysts which effectively gives an infinite number of options in terms of catalyst selection. Clearly it is very important that both objectives and 'tradeoffs' be defined, prioritized and quantified if possible. Below is an example of how a set of objectives may be stated when setting the criteria for choosing the best catalyst for a customer.
Objectives - Example
1. Maximum gasoline yield but minimum of 92 RONC.
2. Maximum bottoms upgrading but no more than 5% increase in gas make.
3. Reduce stack particulate emissions.
4. Option to process high metals feed (1 PPM V, 0.5 PPM Nl, 0.8 Wt% con carbon) but no more than 5 tons per day of cat. addition and 40° F increase in regenerator temperature.
BASF Data Base Improves Preliminary Catalyst Selection
BASF has an extensive computerized data base consisting of the physical and chemical properties and associated Micro Activity Test (MAT) data of all BASF's standard catalysts and most major competitive catalysts. The MAT data are obtained using the same Mid-Continent feedstock, the properties of which are given in Figure 1, for all the catalysts. In addition a wide variety of customer feedstocks have been run on most of these catalysts. Consequently the results can be used to determine their relative selectivities. These selectivities combined with the catalyst physical and chemical properties, plus commercial experience, are used to select potential candidates for the catalyst changeout.
Pilot Plant Work Using Customer Feed Narrows Selection of Catalyst
BASF has a very sophisticated heat balanced projection model to estimate the commercial performance of FCC catalysts. This model is driven by relative catalyst selectivities so the performance of both the base catalyst and potential replacement catalysts must be defined. The MAT data from BASF's data base can be used directly in the FCC Projection Model but performance can be predicted more accurately if MAT data are obtained using the refinery feedstock. Usually MATs are done using fresh steamed samples of both the in unit and replacement catalysts; typically sample portions are heat treated at 1350, 1400, 1450 and 1500 deg F for 4 hours using 100% steam. Additional MATs are carried out using equilibrium samples if available. Equilibrium sample MATdata usually give a stronger indication of relative catalyst selectivity than steamed fresh catalyst MAT data. However it is much more difficult to find catalyst samples that have been exposed to the same severity of operation and similar metal contamination, both of which are required to ensure that a valid comparison is made.
In some instances, particularly when determining the effect of processing different feedstocks with various catalysts, FCC Pilot Plant data will be generated. The results are more directly comparable with commercial data. Also, sufficient product is generated thus enabling measurement of product properties such as gasoline RONC; however FCC Pilot Plant runs are more time consuming than MAT runs. A comparison of MAT and Pilot Unit operation is given in Figure 2.
BASF Projection Model Ensures Optimum Catalyst Selected
The laboratory data generated on the base and replacement catalysts together with the unit operating data obtained from the BASF FCC questionnaire (see Figure 3) completed by the refiner are then used to project the unit performance of the replacement catalysts. As mentioned previously, BASF's FCC Projection Model uses relative catalyst selectivities to predict commercial unit operation so a base case operation is essential. The Model predicts the performance of the selected catalysts, ensures the unit limitations are not exceeded and is also used to optimize unit performance by variation of reactor temperature, feed preheat, etc. The provision of product values by the refiner greatly simplifies and improves the quality of both catalyst selection and unit operation optimization since the Model can then be used to measure FCC operation profitability.
Final catalyst selection is made by comparing the predicted performance of the replacement candidates with the refiner's objectives and choosing the catalyst with the best fit. BASF's capability to custom formulate catalysts ensures that a catalyst is available to meet any requirement.
Premium Technical Service Ensures Good Unit Operation
Catalyst recommendation is only the first step in the process of optimizing unit performance. BASF has a large technical service group dedicated to ensuring refiners are satisfied with their unit performance. Data is collected on a regular basis, typically every six weeks. It is then mass balanced, corrected to constant product cutpoints, plotted, and analyzed. These data summaries are presented to the refiner, used to track unit performance and determine the reason for any unexpected changes in the operation. When necessary, recommendations are made to modify operating parameters such as preheat, catalyst addition, etc. BASF's ability to custom formulate catalysts means formulations can be 'fine tuned' to optimize performance and ensure the refiner achieves the most economical FCC unit operation.