Revista Mexicana de IQ - YSí

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   Revista Mexicana de Ingeniería Química Universidad Autónoma Metropolitana - Iztapalapa amidiq@xanum.uam.mc  ISSN (Versión impresa): 1665-2738MÉXICO   2006 R. Maya Yescas / D. Salazar Sotelo / E. Mariaca Domínguez / S. Rodríguez Salomón / L. M. García MorenoFLUIDIZED-BED CATALYTIC CRACKING UNITS EMULATION IN PILOT PLANT Revista Mexicana de Ingeniería Química, año/vol. 5, número 002 Universidad Autónoma Metropolitana - Iztapalapa Distrito Federal, México pp. 97-103 Red de Revistas Científicas de América Latina y el Caribe, España y PortugalUniversidad Autónoma del Estado de México    REVISTA MEXICANA DE INGENIERIA QUIMICA Vol. 5 (2006) 97-103 Publicado por la Academia Mexicana de Investigación y Docencia en Ingeniería Química, A. C. 97 FLUIDIZED-BED CATALYTIC CRACKING UNITS EMULATION IN PILOT PLANT EMULACION DE UNIDADES DE DESINTEGRACION CATALITICA DE LECHO FLUIDIZED EN PLANTA PILOTO R. Maya-Yescas  1* , D. Salazar-Sotelo 2 , E. Mariaca-Domínguez 3 , S. Rodríguez-Salomón 3 , and L.M. García-Moreno 3 1 Universidad Michoacana de San Nicolás de Hidalgo, Facultad de Ingeniería Química, Santiago Tapia 403, Centro, 58000, Morelia, Michoacán, México. 2  Escuela de Ingeniería Química, UNITEC, Guadalajara, Jalisco, México. 3  Instituto Mexicano del Petróleo, Programa de Tratamiento de Crudo Maya. México, D.F., México. Recibido 27 Febrero 2004; Aceptado 7 Julio 2006 Abstract Due to necessity to predict accurately the performance of fluidized-bed catalytic cracking (FCC) industrial units, after feedstock or catalyst is changed, use of pilot plant as emulation devices has been increasing. Among these pilot  plants, the Recirculation Catalyst Pilot Plant is the small-scale simulator that closer matches the behaviour of industrial units. This kind of pilot plants consists of riser, stripper, regenerator and separation column that perform duties similar to those of industrial units. Additionally, this pilot plant is able to operate using a descendant flow reactor (downer) in order to emulate several technological trends; which operation mode promises better selectivity. FCC process involves many variables interconnected in complex way, making a difficult task to predict its  performance when operating far from srcinal design conditions. Nevertheless, using the same catalyst, the same feedstock and the same main operating conditions of industrial units, it is possible to emulate the performance of industrial units in pilot plant. In this work, the characteristic relationship between pilot plant and industrial units is shown with examples of emulation, establishing its importance in research and support of technical services. Scale-up problems are addressed and solutions that mimic  operating data from an industrial plant are found. Conversion results are shown graphically to easily assess industrial potential benefits that can be drawn from pilot plant emulation. Keywords: catalytic cracking, emulation, pilot plant, reactors. Resumen Debido a la necesidad de predecir con precisión el desempeño de unidades industriales de desintegración catalítica en lecho fluidizado (FCC) después de un cambio de carga o de catalizador, el uso de plantas piloto como dispositivos  para emulación se ha incrementado. Entre estas plantas, la de recirculación de catalizador es la que logra emular más cercanamente el desempeño de unidades industriales. Este tipo de plantas consiste de riser, agotador, regenerador y columna de separación, tal que desempeña tareas similares a aquellas de las unidades industriales. Además, esta  planta es capaz de operar en flujo descendente (downer), a fin de emular diversas tendencias tecnológicas; operación que promete mejores selectividades. El proceso FCC involucra muchas variables interconectadas de manera compleja, haciendo difícil predecir su desempeño cuando operan lejos de las condiciones srcinales de diseño. Sin embargo, utilizando el mismo catalizador, la misma carga y las mismas condiciones de operación que en las unidades industriales, es posible emular la operación de estas unidades en la planta piloto. En este trabajo, se muestran las relaciones características entre la planta piloto y las unidades industriales, a través de ejemplos de emulación, estableciendo su importancia en investigación y soporte de servicios técnicos. Se tratan problemas de escalamiento y encontrando soluciones que imitan  resultados de operación industrial. Los resultados para la conversión se muestran gráficamente a fin de visualizar fácilmente beneficios potenciales industriales utilizando la emulación en planta  piloto. Palabras clave: desintegración catalítica, emulación, planta piloto, reactores.  AMIDI  *Corresponding author:  E-mail: rmayay@zeus.umich.mx  Phone: (443) 3273584 Ext. 105; Fax: (443) 3273584 Ext. 117   R. Maya-Yescas et al. /   Revista Mexicana de Ingeniería Química Vol. 5 (2006) 97-103 98 1. Introduction Fluidized Catalytic Cracking (FCC) is a very complex process combining a reaction stage (riser) with a continuous catalyst regeneration stage. Both stages strongly interact, particularly in energy balance. Catalyst regeneration severity and capacity highly influences riser behaviour. There are several factors that complicate FCC operation, among them feed composition is  probably the main one, since it is a complex mixture of hydrocarbons with different chemical reactivity (Mariaca-Domínguez et al ., 2003). The second important fact is the  big number of simultaneous reactions in the riser. Thirdly, the decaying catalytic activity coming from coke formation and catalyst deactivation produced by feed contaminants and regeneration severity. Least but not lest is the important effect from equipment design. Pilot plant studies are a support tool in research and development activities, as well as the platform for providing technical services and improvements. These plants are strategic bases for deciding about feedstock and catalyst, through evaluation of yields and quality of products. They are also important studies in feasibility. For example, in refining  petroleum industry, and particularly in FCC, it is observed a tendency to incorporate feedstock hydrotreatment because of the increasing supply of heavy oils. There is also a trend to develop better catalysts in order to look for optimal operating conditions. Due to its high impact on the  profitability of refineries, it is often unfeasible and/or impossible to try new feedstock or catalysts during FCC industrial operation. On the other hand, laboratory microactivity plants, like MAT and ACE units, give quick results that are not usable, directly, to model the industrial process  performance (Boock & Zhao, 1998; Maya-Yescas et al ., 2004). So, pilot scale equipment offers advantages and fewer risks than laboratory equipment to scale up operating conditions and process performance, quickly generating enough quantities of products for more complete and detailed analysis ( e.g . Prasad & Balaraman, 1995; Leuenberger et al ., 1988). Pilot plants are considered, in general, as reduced versions of industrial units (Boock & Zhao, 1998); however, scale reduction has implications in design and operation of these  pilot plants. Energy balance is the most important difference between industrial and  pilot plants, resulting in differences in coke yields and catalyst-to-oil ratio (C/O) when the same conditions are chosen for both  plants (Young et al ., 1988). Pilot plant size allows studying and simulating confidently the industrial unit  behaviour with no risk for production. It is also possible to develop new catalysts formulations for each feedstock in long term tests and give recommendations for better operation aiming to optimize conditions and improve profitability. Besides, pilot plant information is essential for developing, adjusting and validating FCC simulation models. As data source for simulation, pilot  plants give opportunities to explore broad ranges of process conditions, being useful to  process research and development (Dienert et al ., 1993). Taking into account the aforementioned arguments and considering the high economic impact of FCC units in refineries, it is highly advisable to use pilot scale information to provide permanent technical services, in order to optimise industrial operation and to research and development efforts. 1.1. Pilot plant description The typical arrangement of a pilot  plant scheme is shown in Fig. 1. Feedstock is taken from a couple of storage vessels, connected to the control system. This couple   R. Maya-Yescas et al. /   Revista Mexicana de Ingeniería Química Vol. 5 (2006) 97-103 99of storage vessels allows normalising operation with a reference feedstock and then introducing a new one. A dosage pump with  precision control is used to send the feed through the heater and nozzle. There is a system to control and register the flow. A nitrogen or vapour stream can be used as dispersant, feeding it through an independent heater. Feed vaporizes as soon as gets in touch with catalyst coming from regenerator and goes through the riser, as in the industrial unit. At the top of the riser, catalyst and  products are separated using cyclones. Spent catalyst falls to a vertical column within a dense phase fluidized bed, in order to strip hydrocarbons from catalyst with vapour or nitrogen flowing counter current. A slide valve controls the flow of stripped catalyst to regenerator. Stripping temperature, bed height and vapour/nitrogen flows are controlled to adjust stripper efficiency. FLOW METER    FLOW METER    CONTROL VALVE   CONTROL VALVE   FEED TANK  No 1 FEED TANK     No 2 PUMP No 1 PUMP    No 2 REGENERATORRISER HEAT EXCHANGERSTRIPPERSTABILIZING COLUMN   CONDENSER  PUMP   PREHEATER    DISPERSION GAS   STRIPPING TO PRODUCT STORAGE Fig. 1. FCC Pilot plant basic equipment.  Gaseous products go to a stabilizer column, to separate components heavier than 5 C  & 6 C ; this liquid product is fractionated to obtain gasoline, LCO and HCO. Gas  products at NTP conditions are analyzed using an online chromatograph. The spent catalyst is sent to the regenerator with a nitrogen or vapour line transfer, part of which is a double tube heat exchanger using air. Exchanger heat balance provides a reliable method for getting C/O ratios. During regeneration reactions, coke deposited on catalyst surface burns inside a fluidized bed using air, and generating flue gas. At exit of this flue gas, a control valve is used to maintain regenerator and stripper pressure. Regenerated catalyst goes through a slide valve to a return line with independent heating that fix the inlet temperature to riser. Regenerator vessel can be heated to different temperatures. Flue gas and excess air are measured and analyzed continuously ( 2 O , CO , 2 CO , X SO  and X NO ). Control system is based in flue gas composition to adjust the air quantity and keep the regeneration level required. Additionally, this  pilot plant can be operated using a descendant flow reactor (downer) in order to study other technological trends. It has been  presumed that this operation mode promises
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