Corrosion Of Brick Research Articles

Corrosion behavior of CaO–Al2O3–SiO2–MgO-Cr2O3 slag on MgO refractory brick for smelting of chromite

The MgO bricks were generally used as the refractory linings in electric furnace smelting of chromite ore. The reaction mechanisms between the MgO refractory and CaO-Al2O3-SiO2-MgO-Cr2O3 slags were experimentally investigated. The elemental distribution and phase compositions at the contact surface between slags and refractory bricks were studied using thermodynamic calculations and SEM-EDS techniques analysis. The main phase of the refractory brick was MgO, while the main phases of slag were pyroxene ((Ca, Mg) AlSi2O6), chromium spinel (Mg (Al, Cr)2O4), and magnesium olivine (2MgO·SiO2). The EDS analysis showed that the main phases at the contact surface of slag and refractory brick were calcium magnesium olivine and magnesium olivine, and the proportion of calcium magnesium olivine phase increased with the increase of slag basicity. Furthermore, the thermodynamic calculation indicated that the melting temperature and the slag viscosity decreased with the increase of slag basicity, and then the molten slag more easily penetrated the pores of refractory brick and caused brick corrosion.

The study of the effect of gas-phase fluctuation on slag flow and refractory brick corrosion in the slag tapping hole of an entrained-flow gasifier

The effects of gas-phase fluctuation on the brick corrosion process were studied in this work in order to investigate the corrosion mechanism of refractory brick in the slag tapping hole. The results explained the reason for the low service life of the refractory brick of the slag tapping hole in the commercial gasifiers. It was found that when the low-frequency fluctuation changed to the high-frequency fluctuation, the brick corrosion rate decreased gradually. Compared with the gas-phase velocity fluctuation, the gas-phase temperature fluctuation had a more significant influence on the brick corrosion rate. • The effect of gas temperature and velocity fluctuation on slag flow was studied. • Low-frequency fluctuation had a significant effect on the brick corrosion rate. • The brick corrosion rate increased with the increase of temperature fluctuation. The service life of refractory brick in the slag tapping hole of the entrained flow gasifier was significantly lower than that in other locations. It was critically important to study the corrosion mechanism of refractory brick in the slag tapping hole for guiding industrial production. Considering the complex flow field in the slag tapping hole, the influence of gas velocity and temperature fluctuation on the service life of refractory brick was investigated in this study. The results showed that the slag flow characteristics periodically changed with the gas temperature and velocity fluctuations. The brick corrosion rate increased with the decrease of fluctuation frequency. Compared with the gas-phase velocity fluctuation, the gas-phase temperature fluctuation had a more significant influence on the brick corrosion rate. When the fluctuation frequency was 0.01 Hz and the gas temperature fluctuation amplitude was 200 K, the corrosion rate of refractory bricks increased by 25%. It could be concluded that the fluctuation of gas-phase temperature was the main cause for the low service life of refractory bricks in the tapping hole.

Interactions of Cr2O3–Al2O3–ZrO2 refractory with slags in an entrained-flow coal-water slurry gasifier

The corroded microstructures of the Cr 2 O 3 –Al 2 O 3 –ZrO 2 refractory brick in an industrial opposed multi-burner (OMB) coal water slurry gasifier were investigated. It was found that the chromite spinel isolation layer rich in iron and magnesium was formed on the surface of the corroded brick body. By comparing and analyzing the corrosion of different zones in the gasifier, the results indicated that the molten slag entered the brick through the gaps and generated the spinel layer along the edge of the gaps, causing the dense structures of the refractory surface destroyed. In addition, in the high chrome brick corrosion experiment conducted by HTSM, 3 μm sized spinel were observed covering on the surface. The FactSage calculation results showed that the amount of spinel produced would drop significantly as the slag penetrated.

The effect of the shear force applied by gas-flow in furnace on slag flow characteristics and gasifier performance

The gas-flow in the furnace had a significant influence on the slag flow characteristics in the entrained-flow gasifier. However, the gas-flow was generally neglected to simplify the calculation process in the limited studies. In this work, the model of gas shear force on slag was derived in detail. And the evolutions of slag thickness, and slag flow velocity, and heat flux with gas-flow were investigated. Besides, the effects of gas-flow on the gasifier performance were studied. The results showed that when the gas concurrent flowed with the slag, the slag thickness and slag velocity decreased and increased with the increase of gas velocity, respectively. Compared with the concurrent flow, the slag flow characteristics were more sensitive to the evolution of gas velocity when gas countercurrent flowed with slag. When the gas velocity changed from 15 m/s to 15 m/s, the heat loss in the membrane wall gasifier increased by approximately 100%. The refractory brick corrosion rate increased rapidly as the gas-flow velocity increased. The profile of the brick corrosion rate was consistent with the industrial experience. The results explained the reason for the low service life of the refractory brick of the slag tapping hole in the commercial gasifiers.

Modelling of slag flow and prediction of corrosion state of refractory bricks in an entrained-flow gasifier

The corrosion rate of refractory brick is a key factor for long-term and stable operation of a gasifier. In situ measurement of refractory brick corrosion was always a challenging topic due to the extreme temperature and pressure in the gasifier. In this paper, numerical simulations were adopted to accurately predict the corrosion depth of the refractory brick. Models for slag flow and refractory brick heat transfer were built, and various models of refractory brick corrosion rate were derived in detail. Heat transfer and brick corrosion models were validated with available industry data and the prediction accuracies of the different models were compared and discussed. Results showed that the external diffusion model could accurately predict the corrosion state, and the correlation coefficient with industry data was 0.998. The slag shear rate on the surface of the refractory brick was a key control parameter for corrosion, especially for a top single-burner down-flow gasifier.

Corrosion mechanism of MgO‐C bricks used as linings in a vanadium extraction converter

AbstractTo extend the service life of MgO‐C bricks used as linings in vanadium extraction converters, their corrosion mechanism was investigated using stationary immersion and rotary crucible methods at 1673 K. The effects of oxides in vanadium slag were studied using the slag invasion method. The results showed that a decarburization layer was formed but was not effectively sintered under vanadium extraction conditions, resulting in it having a loose structure and poor binding strength. When slag‐splashing technology was applied to protect the converter, the decarburization layer and slag‐splashing layer easily fell off due to scouring by the molten pool. Consequently, the poor strength of the decarburization layer was the main reason for the poor anti‐erosion performance of the MgO‐C bricks and the weak effect of slag‐splashing technology. In addition, higher contents of SiO2 and TiO2 in vanadium slag could form low melting point compounds and increase the thickness of the decarburization layer, thereby accelerating the MgO‐C brick corrosion rate. Higher contents of FeO in the vanadium slag not only formed low melting point compounds but also caused a decarburization reaction with the MgO‐C bricks. However, with increases of V2O3 in the slag, the formation of high melting point compounds decreased the corrosion rate and corrosion depths.

Influence of TiO2 on the Viscosity of a High Alumina Slag and on Carbon Brick Corrosion

The influence of TiO2 on viscosities of CaO–SiO2–MgO–Al2O3–Cr2O3‐based slags and the corrosion mechanism of carbon brick used in blast furnace hearth by slags was investigated in this work. From the viscosity experimental results, it was found that the viscosity decreased with the addition of TiO2. Furthermore, the critical temperature and activation energy for the viscous flow of slags also decreased with increasing content of TiO2. The corrosion of carbon brick depended on the component of the brick surface in contact to the molten slags. In the region consisting mainly of carbon, the corrosion of carbon brick may be caused by the oxidation of carbon and in lower carbon content area, the corrosion of brick was mainly caused by the dissolution and slag penetration. The corrosion of carbon brick by slags could be a consequence of carbon oxidation, brick dissolution and slag infiltration, and the degradation of carbon brick was accelerated with the addition of TiO2.

Modeling of multiphase reaction and slag flow in single-burner coal water slurry gasifier

The slag flow properties and temperature distribution have a critical influence on the lifetime of refractory bricks. A comprehensive model has been developed to simulate a multiphase flow and reaction process within the spatial region and refractory wall, and is applied to a study on the multiphase flow characteristics of a single-burner entrained-flow gasifier. The gasifier performance, gas temperature distribution, and outer surface temperature distribution of the wall are compared with industry measurement data. The simulation results are in good agreement with the industrial data. The capture efficiency of the refractory wall is approximately 91%, and 82% of the particles are trapped by the wall. The distribution of the gas temperature near the refractory wall, the slag surface temperature, and the refractory wall surface temperature aresimilar. The slag surface temperature first decreases from top to bottom, and then increases to the highest temperature at 2.2D. The slag attack rate coincides with the refractory brick corrosion rate. The refractory surface temperature, molten slag fluidity, and molten slag flow rate have a significant impact on the refractory brick corrosion rate. No solid slag layer is present on the refractory bricks, and the molten slag layer thickness increases from 0 to 5mm along the flow direction. In the molten slag layer, the non-dimensional slag velocity profile shows a self-similarity and follows a parabolic equation.

Corrosion of Al2O3–Cr2O3 refractory lining for high-temperature solid waste incinerator

Al2O3–Cr2O3 refractories containing a minor amount of ZrO2 usually have excellent heat stability and corrosion resistance. However, a short service life is observed in high-temperature solid waste incinerators. Therefore, the phase compositions and microstructure of the Al2O3–Cr2O3 refractory linings, both with and without corrosion, were analyzed. The results show that Al2O3–Cr2O3 bricks were corroded by both molten slag and gas in the solid waste incinerator. Regarding the corrosion by molten slag, SiO2 and CaO contained in the slag entered into the bricks along pores, which caused densification of the matrix and reaction of SiO2, CaO, and Al2O3 to form CAS2; FeO entered into the refractory and reacted with Al2O3 and Cr2O3, forming the composite spinel FeO·Cr(Al)2O3. Moreover, the gas mixture of CO and Cl2 also infiltrated into the Al2O3–Cr2O3 brick and accelerated brick corrosion by reacting with ZrO2, Al2O3, and Cr2O3 one after another.

A CASE STUDY OF TYPES OF FAILURE IN REFRACTORY BRICKS LINING CEMENT KILNS

The failure of refractory bricks lining cement kilns is a costly process not only due to the cost of replacing bricks but also due to the lost in production time during the replacement period. The present work aims to investigate types and causes of failure of refractory bricks in one of Kufa cement factory kilns using chemical analysis and X-Ray diffraction technique. The results showed that there are detrimental components in raw meal and cement clinker like alkalis (K2O, Na2O) and SO3 which tend to react with lining bricks at high temperatures. Cement clinker infiltrated into the hot faces of magnesia bricks resulting in a formation of a coat layer which protect the brick from spalling. When the kiln operates under equilibrium conditions, the coating maintain itself, otherwise coating will start to come off causing brick corrosion. For all Alumina samples, significant ratios of alkalis are infiltrated into bricks during period of service, the amount of infiltration increased with the ratio of alumina content. X-ray diffraction showed formation of detrimental compounds by reaction between alkalis, sulfur and Alumina bricks. Formation of these toxic compounds was associated with increased volume making the brick more brittle and easy to be damaged by thermo-mechanical stresses.