Universal Oil Products (UOP) in 1940 and then developed many different types of reforming ..... Down World," UOP LLC, pp. 1-32, 2011. [12]. M. I. Rahimpour, D.
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 19 (2016) pp. 9984-9989 © Research India Publications. http://www.ripublication.com
Comparison of Catalytic Reforming Processes for Process Integration Opportunities: Brief Review Badiea S. Babaqi Department of chemical and process Engineering, Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia.
Mohd S. Takriff* Department of chemical and process Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia.
Siti K. Kamarudin Department of chemical and process Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia.
Nur T. Ali Othman Department of chemical and process Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia.
Muneer M. Ba-Abbad Department of chemical and process Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia.
Abstract Catalytic reforming process is one of the most important processes in oil refineries that produce high octane number gasoline. Catalytic reforming processes are commonly classified into three types based on the regeneration systems of the catalyst, namely (i) semi-regenerative catalytic reformer process (SRCRP), (ii) cyclic regenerative catalytic reformer process (CRCRP) and (iii) continuous catalytic regeneration reformer process (CCRRP). The major difference among the three processes is the requirement to shut down for catalyst regeneration. The mechanism for the regeneration steps could be classified into fixed-bed catalyst system; fixed-bed catalyst combined a swing reactor and a move-bed catalyst with special regenerator of SRCRP, CRCRP or CCRRP type respectively. The CCRRP produces a higher octane reformates in the range 95–108 with a low feed quality compared to the other reactors types. Furthermore, the process produces hydrogen gas continuously at higher catalyst activity. High yield of hydrogen is also achieved at lower recycle ratio and lower operating pressure (50 psig). As the process requires continuous energy supply to maintain the optimum temperature of the reactor, simultaneous integration of mass and heat can be used as means to identify opportunities for design improvement. Keywords: Catalytic Reforming Process, Comparison, Process Integration Opportunities.
INTRODUCTION Catalytic reforming plays significant role in petroleum refinery and petrochemical industries that transforms lowoctane naphtha into higher octane number reformate for gasoline blending and aromatics rich reformate for petrochemicals production. It also produces high purity hydrogen gas as a by-product. Generally, the main purpose of the catalytic reforming process is to improve the octane number of the feedstock, especially of heavy naphtha. Reducing antiknock quality of naphtha as a blending stock for motor fuels is the strong reason for installing catalytic reforming. Gasoline is widely used as a transportation fuel, however, the current environmental regulations requires that the levels of benzene and total of aromatics in gasoline should be lower than 0.62 vol% due their carcinogenic properties [1-3]. Several reactions occur in catalytic reforming process in order to increase the gasoline octane number. These reactions are: (i) dehydrogenation of naphthenes compounds (ii) dehydrocyclization of paraffins compounds, (iii) isomerization of normal paraffins, (iv) hydrocracking reaction of paraffins and converted into lower molecular weight paraffins, and (v) hyrodealkylation of aromatics. The dehydrogenation, dehydrocyclization and isomerization reactions are desired reactions because it controls the octane number and hydrogen purity. In contrast, hydrocracking reaction is undesirable because it cracks paraffins into small paraffins which produce light gases (low octane, LPG). Additionally, hydrocracking reaction consumes hydrogen that decreases the reformate yield. The undesired reaction causes the coke formation and coke deposition on catalyst surface [4-6]. The best operating conditions of the reaction in
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 19 (2016) pp. 9984-9989 © Research India Publications. http://www.ripublication.com catalytic reforming process to produce high octane of aromatic compounds are high temperatures, low pressures and low hydrogen/feed ratio. However the hydrogen pressure must be high enough in order to avoid deactivation of catalyst surfaces [7, 8]. Typical catalysts that are used in catalytic reforming are mono-metallic, bi-metallic or tri-metallic catalysts supported on aluminum, such as platinum (Pt/Al2O3), Platinum-Iridium (Pt-Ir/Al2O3) or Platinum-Iridium-Tin (Pt-Ir-Sn/Al2O3) respectively. The catalysts performance in terms of its stability, selectivity and activity can be improved through modification of its properties. The best approach to achieve high yields and high quality of reformate is increasing the selectivity of desirable reactions via balance between acidic and metallic sites [9-13]. CLASSIFICATION OF CATALYTIC REFORMER PROCESSES The catalytic reforming process was first introduced by Universal Oil Products (UOP) in 1940 and then developed many different types of reforming processes to date. The performance of catalytic reforming process depended on feedstock and converts it into high octane reformate and gasoline products. In general, there are several versions of major reforming processes that have been developed by some of the major oil companies and other organizations [14-16].
i.
Semi-Regenerative Catalytic Reformer Process (SRCRP)
SRCRP is the oldest reforming process that is used for the production of gasoline and rich aromatic compounds as shown in Figure 1. It usually has three or four reactors in series with a fixed-bed catalyst system, that require shutdown approximately once every six month to two years for in-situ regeneration of the catalyst. The catalyst activity decreases gradually due to the formation of coke and affects the yield of aromatics and the hydrogen by-product. In order to keep the reaction conversion relatively constant, the reactor temperature is raised as catalyst activity drop. To maximize the time between two regenerations intervals, these early units were operated at high pressures (200 to 300 psig) that help to reduce catalyst deactivation rate by coking. This process can achieve an octane number in range of 85100, depending on the feedstock, gasoline qualities, and required additives. In SRCRP, the Pt–Re catalyst is usually used because it allows high tolerance to coke levels with simple regeneration process and allows for lower operating pressure [2, 4, 17, 18].
Figure 1. Schematic Process Diagram of SRCR
Current catalytic reforming processes are commonly classified into three types based on regeneration systems work of the catalyst. These includes: (i) semi-regenerative catalytic reformer process (SRCRP), (ii) cyclic regenerative catalytic reformer process (CRCRP) and (iii) continuous catalytic regeneration reformer process (CCRRP).
ii.
Cyclic Regenerative Catalytic Reformer Process (CRCRP) CRCRP is the least in terms of its utilization for the production of high octane number gasoline and rich aromatic compounds. Its schematic is as shown in Figure 2. It usually has four reactors in series with a fixed-bed catalyst system. The swing configuration allows for one of the reactor to undergo in-situ regeneration while the other reactors are in
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 19 (2016) pp. 9984-9989 © Research India Publications. http://www.ripublication.com operation. The interval between two regenerations for each reactor is between a few weeks to a few months. In this configuration, only one reactor is taken out of operation for regeneration at a given time, while the other reactors continue with the operation for producing high octane reformates. This configuration allows for the reforming process to be operated continuously and a high octane number in the range of 100-104 can be achieved. The CRCRP allows for more severe operation conditions such as low operational pressure (200 psig), wide boiling range feed, and low hydrogen-tofeed ratio were applied which contributes to high deactivation rate of the catalyst. The main advantages of the CRCRP are the overall catalyst activity, conversion, consistent hydrogen purity and low operational pressure. In contrast, the disadvantage of CRCRP is the complex nature of the reactor switching control and the need for higher safety precautions. The cyclic catalytic reformer units are rarely used for naphtha reforming process [18-20]
system where the catalyst regeneration occurs continuously in a special regenerator and returned to the operating reactors. This design has provided the CCRRP a step change in reforming technology compared to SRCRP and CRCRP. The main advantages of CCRRP against previous methods are the ability to produce of higher octane reformate in the range 95–108 with a low feed quality. Furthermore, the process produces hydrogen gas continuously at higher catalyst activity and yield. Finally, high yield of hydrogen with lower required recycle ratio and the lower operational pressure (50 psig) are obtained in the reforming process. In the CCRRP, the catalyst flows from top to bottom of the stacked reactors by gravity. The spent catalyst is continuously withdrawn from the last reactor and transferred to the top of the regenerator to burn off the coke then returned to the top stack-reactor. This process includes transmission of the catalyst between the regenerator and reactors that are known as the gas lift method. The CCRRP uses the platinum/tin alumina type as main catalyst. The addition of tin regeneration ability of Pt/Al2O3 enhances the selectivity of aromatics and stability.
Figure 2. Schematic Process Diagram of CRCR
iii. Continuous Catalytic Regeneration Reformer Process (CCRRP)
This catalyst regenerates continuously in CCRRP, in which the selectivity to aromatics of the catalyst is more significant compared to resistance to deactivation [21-23].
CCRRP (Figure 3) is the most modern process used in the world for producing high octane number gasoline and rich aromatic compounds. This system has four reactors in series or stacks one above the other with a move-bed catalyst
The main features, advantages and disadvantages of each type of catalytic reforming processes are presented in Table1.
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 19 (2016) pp. 9984-9989 © Research India Publications. http://www.ripublication.com
Figure 3. Schematic Process Diagram of CCRR Table 1. Some of the Main Features, Advantages and Disadvantages of each Type of Catalytic Reforming Processes Features and Conditions
Type of Process
SRCRP
Pressure
Temperature
High pressure (200 to 300 psig)
High Temperature (480-510oC)
Octane number of reformate
Catalyst system
85-100
fixed-bed catalyst system
CRCRP
Low pressure (200 psig)
High Temperature (515-520oC)
100-104
fixed-bed catalyst system
CCRRP
Low pressure (50 psig)
High Temperature (515-528oC)
95–108
move-bed catalyst system
Opportunities of process integration through the comparison of catalytic reforming processes are presented in Table1. The three types vary according to the nature of the operation, synthesis design and economic cost.
Advantages
Disadvantages
______
*Process needs to shut-down of the operation for catalyst regeneration. * Once every six month to two years for regenerating of the catalyst in situ.
*Process does not need shutdown of the operation for catalyst regeneration, but it uses a swing reactor which allows for one of the reactor to undergo in-situ regeneration while the other reactors are in operation. *Overall catalyst activity, conversion, consistent hydrogen purity. * Process does not need shutdown of the operation for catalyst regeneration, where the catalyst regeneration occurs continuously in a special regenerator. * Process produces hydrogen gas continuously at higher catalyst activity and yield. * High yield of hydrogen with lower required recycle ratio.
*The interval between two regenerations for each reactor is requested a few weeks to a few months. *Complex nature of the reactor switching control as well as needs for higher safety precautions
________
The one of SRCRP disadvantages is required to stop of operation in order to activate the catalyst. Also, the energy conservation process may be difficult because of the frequent breaks along the process operates beside the process works under high pressure. At the same time, CRCRP has a
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 19 (2016) pp. 9984-9989 © Research India Publications. http://www.ripublication.com complex design and high safety of process control. Therefore, it is more difficult to control and requiring a high cost on the part of safety when applied process integration. The third type (CCRRP) can apply process integration because the process is ongoing, it does not need to stop the operation. Therefore, the energy source will become continuously so the possibility of the application of heat integration. The production of products such as reformates and hydrogen continuously-introduce which possibility applied of mass integration. Advanced management of mass and heat in CCRRP for design enhancement provides the best opportunity via increasing efficiency which includes increase production volume, minimizing energy consumption and mass savings.
continuously under higher catalyst activity at optimum temperature of the reactor. Thus, the CCRRP showed more improvement opportunities compared to SRCRP and CRCRP. Therefore, simultaneous integration of mass and heat could be used to identify opportunities for design improvement of CCRRP in future.
CCRRP ENHANCEMENT VIA HEAT AND MASS INTEGRATION Most of the research works in catalytic reforming process have focused on model development and simulation of the reactors in order to improve the reforming process. Process integration provides a means for optimizing the CCRRP. However, a brief literature review that has been conducted shows that no study has been conducted on the combined mass and heat integration for catalytic reforming design improvement. Possible strategy that may be adopted for optimizing the CCRRP based on the heat and mass integration are as the following: • Mass integration provides the requited operation flexibility for a given feed quantity and quality, operation conditions to maximize production capacity. Therefore, the mass integration in the reaction and separation units that includes mass recovery network system could achieve high yield and profitability. Pinch analysis technique (PAT) and mathematical optimization technique (MOT) could be used to achieve of this study objectives (e.g. minimize raw materials, water-using operations, and waste reduction, etc.). • Heat integration approach: The CCRRP requires continuous energy supply to maintain the optimum temperature of the reactor and source of heat for reaction by energy stored in the reformate product that leaves from reactor. Therefore, heat recovery system and heat exchanger network could be provided for improving energy efficiency. Pinch analysis technique (PAT) and mathematical optimization technique (MOT) could be used to achieve the study objectives (e.g. improving energy efficiency, energy saving, minimize the cost of utility, decrease quantity of the gases emissions, etc.) via integrated system of interconnected processing units besides increased heat exchange area. • As the both approaches are applied as simultaneous combined heat and mass integration in the CCRRP, it could be obtained the best design improvement of future study.
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CONCLUSION The types of catalytic reforming processes were compared to identify opportunities for process integration as future study. The CCRRP produces a higher octane reformates with low feed quality compared to SRCRP and CRCRP. Furthermore, this process generates hydrogen gas as by product
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