The current refining scenario in India is highly dynamic and appears to change on a daily basis. India currently imports approximately 80% of its crude oil while India's refining capacity is expected to grow by nearly 50% by the year 2020. Diesel demand is also projected to grow by 40% over current value. Competitive and affordable energy prices help drive strong economic growth and are an important factor in shaping the Government of India's (GoI) fiscal policies. The rise in international crude oil prices in recent years has created major challenges for the GoI, given the high reliance on imports, and has resulted in a need to maximize the utilization and conversion of crude oil processed in the country. UOP's RxCat™ technology allows the refiner to optimize the catalyst circulation rate in the riser, independent of the unit heat balance. This capability enables improved conversion, product selectivity, and emissions control while simultaneously reducing operating costs. This paper will demonstrate how RxCat technology increases the flexibility of the FCC to shift between different processing objectives while lowering costs and maximizing product values to meet the challenges faced by today's refiner.
The basic concept of UOP's RxCat technology is to recycle catalyst from the FCC reactor stripper back to the inlet of the riser. Modern catalyst systems are inherently more coke tolerant than their older counterparts and can accrue appreciable quantities of coke and still retain a substantial fraction of base activity. Hence the recycle of catalyst from the reactor stripper in modern units represents an additional activity component being added to the riser. UOP has adopted the term “carbonized” to describe this catalyst.
To date UOP has six RxCat units in operation with an additional four units in design. Figure 1 shows the layout of an FCC RxCat unit.
UOP RXCat Technology
RXCat Process and the FCC Heat Balance
In the traditional FCC process the catalyst circulation rate is fixed by the heat balance. This means that catalyst circulation only increases in response to an increased heat demand by the reactor. Therefore, in a conventional FCC system, the extent that regenerator catalyst to oil ratio (cat/oil) increases can be expressed by the following equation:
Examples of process changes that increase regenerator catalyst circulation rate and raise the amount of coke required to satisfy the altered heat balance are:
Increasing riser temperature Decreasing feed preheat
Increasing regenerator catalyst cooler duty
Injecting a heat load into the riser (steam, water, LCO)
Senior Manager –FCC, Treating and Alkylation Research & Development
Cat/OilRegen Coke Yield CpCatalyst
HRegeneration
(TRegen TReactor)
In contrast, carbonized catalyst recycle from the reactor stripper via the RxCat standpipe is not constrained by the heat balance as it does not significantly alter the total coke yield. Because catalyst is circulated from the riser outlet, down to the riser inlet, and back up to the riser outlet starting and ending at the same temperature, little enthalpy change occurs in the loop, and there is practically no impact upon the coke yield.
Thus the riser cat/oil can now be expressed as:
The RxCat process impacts the heat balance by increasing delta coke on the catalyst circulating to the regenerator. Delta coke is defined as the difference in coke content between the regenerated catalyst and spent catalyst. As the RxCat circulation rate is increased, the delta coke increases due to RxCat catalyst particles completing additional passes through the riser prior to regeneration. Because regenerator temperature is a strong function of delta coke, the increase in delta coke from RxCat increases the regenerator temperature and decreases the regenerator cat/oil ratio as shown in Table 1.
Despite the decrease in regenerated cat/oil, RxCat technology enables a refiner to increase the overall riser cat/oil to levels considerably higher than a traditional FCC unit while simultaneously increasing the regenerator temperature. Reducing feed contaminants through severe hydrotreating reduces the delta coke in the unit, which cools the regenerator and presents a significant challenge for refiners to keep the regenerator hot enough to control CO and NOx emissions below acceptable levels. RxCat technology Table 1: Reactor/Regenerator Response to Change in RxCat Cat/oil
provides an alternative solution to traditional methods of maintaining high regenerator temperatures and simultaneously enhances unit performance through increased total riser cat/oil ratio. Table 2 shows an economic comparison between utilizing the direct fired air heater (DFAH) and RxCat technology to increase regenerator temperature by an equivalent amount.
Product Pricing Source: Global Petroleum Market Outlook 2011, Purvin and Gertz
While both approaches will achieve a higher regenerator temperature, firing the DFAH will result in a lower riser cat/oil ratio and consequently a loss of conversion and margin. On the other hand, RxCat technology increases the riser cat/oil, resulting in a conversion increase and ultimately a gain in margin, all without the need to consume additional fuel gas.In addition the higher regenerator temperatures improve burn kinetics and allow the FCC operator to lower the excess oxygen in the regenerator while simultaneously reducing CO and NOx emissions.
RxCat technology can also improve product yields. The catalyst recirculating through the RxCat standpipe enters the MxR Chamber at the base of the riser at TM
temperatures several hundred degrees Fahrenheit below the regenerated catalyst temperature. When these two catalyst streams are properly blended, the resultant catalyst stream contacting the feed in the injection zone of the riser is at a significantly lower Table 2: Evaluation of DFAH vs.RxCat Technology for Regenerator Temperature Control
Fuel Gas to Air Heater (Wt-% feed) Regenerator Temp (F)
temperature, reducing thermal reactions that produce unwanted dry gas and coke. Figure 3 shows how the reactor feed injection zone temperature decreases as a function of RxCat cat/oil ratio while Figure 4 shows how dry gas decreases in response to lowering the feedinjection zone temperature, as measured in the UOP circulating riser pilot plant.
While RxCat technology increases riser cat/oil ratio, the impact of coke deposition on catalyst activity must be understood to predict the benefits of the higher catalyst circulation rate. To determine the relationship between coke deposition and catalyst activity, UOP conducted Catalyst Activity Retention as a Function of Coke
testing on several commercial equilibrium catalysts (ECATs). The physical properties of three catalysts are described in Table 3.
ACE Pilot Plant runs were then conducted for the three catalysts to determine activity retention as a function of carbon content on the catalyst surface. Results are shown in Figure 5. These data highlight a similar activity decline for catalysts A and B and a more pronounced decline for catalyst C.
Significant differences in activity retention as a function of coke are not always obvious from the catalyst physical properties. For instance, while ECAT B and C have similar MAT activities, they do not have similar activity retention properties. Therefore, it is important to conduct activity retention tests when optimizing a catalyst for RxCat technology. This testing enables the determination of the effective cat/oil response in the RxCat system which can be defined as:
Table 3: ECAT Physical Properties
Figure 5: Relative Activity vs Coke for Three ECATs Figure 3: RxCat Cat/Oil vs. Feed Contact Zone Temp
O Feed Contactzone Temp (F)
Figure 4: Pilot Plant Feed Contact Zone Temperature vs. Dry Gas Yield
Dry GasYleld (Wt.%)
Ace Micro Activity Test (MAT) UCS (A)
Total Surface Area (m2/g) Zeolite Surface Area (m2/g) Matrix Surface Area (m2/g) Micropore Volume (cc/g)
where AR is the slope of the catalyst activity retention c as a function of coke determined in the ACE unit and K is a constant.
To determine constant K, the three example catalysts were tested in the UOP circulating riser pilot plant by increasing RxCat cat/oil and maintaining a stable regenerator cat/oil. The results are shown in Figure 6.
These data illustrate that the conversion response to an increase in RxCat cat/oil is best achieved by ECATs A and B which have better AR properties relative to c ECATC.
Once the activity retention properties of the catalyst and operating severity of the unit are understood for the RxCat application, the remainder of the product yields can be estimated from the calculated increase in effective cat/oil ratio. For ECAT A the full product yield shift in response to a change in RxCat cat/oil is represented in Table 4. This table highlights the fact that while riser cat/oil increases purely as a function of the RxCat valve output and the unit heat balance, the effective cat/oil is the primary driver of yield shifts on the RxCat equippedFCC unit.
Figure 6: CRU Conversion Response to RxCat Ratio for Three ECATS
RXCat Yield Benefits
Table 4: Impact of RxCat on Product Yields for ECAT A
To confirm the theoretical pilot plant data, it is important to observe the conversion shifts in commercial RxCat units who have optimized the catalyst formulation to take advantage of RxCat technology. Figure 7 shows the conversion response for an increase in RxCat for three separate commercial units. These data were filtered for constant feed quality and riser outlet temperature in order to isolate the impact of RxCat ratio on conversion. The commercial results are consistent with the pilot plant yields, demonstrating an approximate 2.0 to 3.5 lv% yield improvement over the range of RxCat ratio.
Figure 7: Commercial Unit Conversion Response to RxCat Cat/Oil Cat/OilEffective Cat/OilRegen+Cat/OilRxCat [1-( Coke |ARc|) ]K
without major structural changes or modifying the feed injector elevations.
UOP's RxCat technology has demonstrated in both pilot plant and commercial testing a unique ability to manipulate overall riser cat/oil ratio in order to increase the effective riser catalyst activity gain outside the traditional limitations of the unit heat balance. This added flexibility enables today's FCC operator to gain a competitive advantage by offering improved yield selectivities, enhanced operational controls, and reduced operating costs. While this technology has thus far only been primarily available to new grass roots units, the development of the UOP Double Wye Mixing Riser design allows Refiners to revamp their existing units to gain the full benefits that UOP's RxCat technology has to offer.
Figure 9: Revamp Comparison of MxR Chamber vs.
Double Wye Mixing Riser Design
Summary The UOP Double Wye Mixing Riser™ Design for
Revamps
In the traditional RxCat design, regenerated catalyst from the regenerator is combined with the carbonized catalyst from the reactor stripper at the base of the riser in the MxR™ Chamber, shown in Figure 8.
For new units, the MxR Chamber can easily be incorporated into the FCC design. However, incorporating the MxR Chamber in a revamp can prove challenging due to the difficulty of physically fitting the chamber within the existing configuration without major structural modifications due to the chamber's size. To enable the RxCat technology to be widely available for revamp scenarios, UOP redesigned the MxR chamber configuration and created the Double Wye Mixing Riser design shown in Figure 9. While the MxR Chamber would extend below grade, the Double Wye Mixing Riser design fits within the existing configuration Figure 8: MxR Chamber
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Courtesy: Business India
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The Guru Gobind Singh Refinery was 'Dedicated to the Nation' by the Hon'ble Prime Minister of India, Dr. Manmohan Singh in the presence of Hon'ble Union Minister of P&NG, Shri S. Jaipal Reddy;
Hon'ble Chief Minister of Punjab, Sardar Prakash Singh Badal;
Hon'ble Union Minister of State - P&NG, Shri R. P. N. Singh; His Excellency Governor of Punjab Shri Shivraj V. Patil and other distinguished guests.
Mr. R.K. Singh, C&MD BPCL and Mr. G.C. Chaturvedi, Secretary, MoP&NG exchange documents of the MOU signed by BPCL and MoP&NG for 2012-13.