Jorivaldo Medeiros

A study about the contribution of the α-β phase transition of quartz to thermal cycle damage of a refractory used in fluidized catalytic cracking units

The deterioration of refractories used in fluidized catalytic cracking units (FCC-units) is responsible for high costs of maintenance for the petrochemical industry. This is commonly associated with coke deposition during the production of light hydrocarbons. However, other mechanisms responsible for causing damage may also occur, such as the generation of cracks by expansive phase transition. The aim of the work herein was to study the contribution of the a-b phase transition of quartz particles to the deterioration of a commercial aluminosilicate refractory used in a riser by the means of slow thermal cycles. Such damage may occur if the working temperature of the equipment fluctuates around the a-b transition temperature (573 °C). The current study considered the material with and without coke impregnation to evaluate the combined effect of coke presence and phase transition. To evaluate the damage, it was used the Youngs modulus as a function of temperature by applying the Impulse Excitation Technique under controlled atmosphere. An equipment recently developed by the authors research group was applied. Specimens were prepared and submitted to slow thermal cycles of temperatures up to 500 °C and up to 700 °C, with a heating rate of 2 °C/min. Part of the specimens was previously impregnated with coke by a reactor using propen. To complete the evaluation, characterization by X-ray diffraction, as well as by dilatometry and scanning electron microscopy were performed. The findings of this study showed that the presence of quartz particles determine the thermo-mechanical behaviour of the material, as well as the thermocycling damage resistance. In spite of the fact that the a-b phase transition stiffens the material during the heating stage, it increases the damage by slow thermal cycling. The coke impregnation increases the resistance to slow thermal cycles, however it decreases the resistance to the damage evolution.

Efeito do tempo de exposição a uma atmosfera coqueificante na microestrutura e nas propriedades de um concreto refratário usado na indústria petroquímica

Refractory castables used in Fluidized Catalytic Cracking Units (FCCU) are said to deteriorate due coke formation during the production of light hydrocarbons, causing a shortening in the operating time of the reactor. Consequently, a significant financial loss for the petrochemical will occur. Several studies have been carried out, but none of them showed clearly how much is the contribution of the coke for the concrete final deterioration. It still remains the doubt if the coke is the responsible for the damage observed macroscopically in a FCCUs riser. In this way, this work aimed to study the effect of the time in a cokemaking atmosphere on an anti-erosive class-C refractory castable, seeking for microstructural changes or on physical properties that indicate degradation mechanisms and give support to the understanding of the phenomenon. Samples of an industrial refractory castable used in petrochemical units were prepared and subjected to a forced cokemaking process in a simulation reactor. The temperature and the heating rate were kept constant at 540 oC and 50 oC/h, respectively. The values of 10, 60, 120, 240 and 480 h were used for the time of exposition to the propene gas. The microstructure of the samples was characterized through optical and scanning electron microscopy and its mineralogical phases through X-ray diffraction. Complementary analyses were necessary to a better understanding of the phenomenon. The results show that the surface and the microstructure are gradually impregnated by coke, which fills up pores, microcracks and cracks. Evidences of microcracking around the coke filled pores were not found. However, many aggregates present some type of deterioration related to the time of exposition to propene. Those damages are not necessarily caused by coke directly.

Analysis of Expansion Joints Movement Test in FCC Unit

The turboexpander is an equipment that works under very critical conditions requiring very low allowable nozzle forces and moments. A solution to minimize the piping loads transmitted to the equipment is the use of expansion joints (EJ). A usual piping stress analysis normally is not enough to guarantee the turboexpander reliability. This paper shows the results obtained in a movement test realized on metallic bellows EJ used in a turboexpander piping system. The EJ were designed according to the expansion joints manufacturer association code (EJMA), the diameters range from 0.457 to 2,898 m, the material of the bellows is Inconel 625 LCF and the shell materials are “killed” carbon steel, for refractory lined EJ or stainless steel 304H. A special test device was developed to apply the design movements on the EJ at the factory. A digital dynamometer was used for data acquisition and the tests were performed on 16 EJ of two distinct types: hinged and gimbal. The EJ were pressurized with water during the test. The reactions and corresponding displacements for each step of the test were recorded during loading and unloading.

Seleção de concretos refratários densos antierosivos para unidades de craqueamento catalítico fluidizado de petróleo

In the petrochemical industry the fluidized catalytic cracking unit is an important vessel for refractory castables application due the necessity of obtaining specialized products. Usually, the selection of these materials is based on the chemical analysis, apparent density, cold crushing strength and cold erosion test. For the evaluation of the present selection requirements, five high-alumina castables, being three of low cement and two conventional of commercial use, were characterized under cold crushing strength and cold erosion tests. Additional tests that are actually not used in the selection were also performed, such as: thermal shock cycling, hot modulus of rupture and carbon deposition by CO atmosphere exposure. The analysis showed that the present specifications are mainly based in the experience with the use of products not designed for this application and that the development of more suitable castables is inhibited due to the close restrictions of the present specifications. It is also verified that the materials selection is limited by the absence of tests for the performance evaluation next to in-service conditions. In this sense, the carbon deposition test by CO atmosphere exposure was interesting in order to provide the better selection of dense antierosive refractory castables.

ANALYSIS OF FCC EXPANSION JOINTS MOVEMENT TEST

The Turboexpander is an equipment that works under very critical conditions requiring very low allowable nozzle forces and moments. A solution to minimize the piping loads transmitted to the equipment is the use of expansion joints. A usual piping stress analysis normally is not enough to guarantee the turboexpander reliability. This paper shows the results obtained in a movement test realized on metallic bellows expansion joints (EJ) used in a turboexpander piping system. The EJ were designed according to the expansion joints manufacturer association code (EJMA), the diameters range from 457 to 2,898 mm, the material of the bellows is Inconel 625 LCF and the shell materials are “killed” carbon steel, for refractory lined EJ or stainless steel 304H. A special test device was developed to apply the design movements on the EJ at the factory. A digital dynamometer was used for data acquisition and the tests were performed on 16 expansion joints of two distinct types: hinged and gimbal. The EJ were pressurized with water during the test. The reactions and corresponding displacements for each step of the test were recorded during loading and unloading.Copyright