Impact of Temperature and Oxygen Partial Pressure on Aluminum Phosphate in High Chrome Oxide Refractories

Abstract

Gasifiers are reaction vessels used to process carbon feedstock such as coal and/or petcoke at elevated temperature, high pressure, and in a reducing atmosphere (low oxygen partial pressure) to form CO and H2, called synthesis gas or syngas. Syngas is used as a fuel in power generation or as a feedstock material in chemical production. By-products of the gasification process include unreacted carbon, gases such as CO2 and H2S, and slag formed from mineral impurities or organic metallic compounds in the carbon feedstock that liquefy during gasification. In the gasifier, slags interact with the high chrome oxide refractory liner, causing wear and eventual failure of the refractory lining by two primary means - spalling (structural and chemical) and chemical dissolution. Failure of the refractory lining causes the gasifier to be shut down for repair, with increased service time identified by users as important for greater usage of gasification as an industrial process. Phosphate additions to high chrome oxide refractories have been found to increase service life during commercial service by reducing spalling and lowering chemical dissolution of the refractory liner. The mechanism of how they improve service life is not well understood. The microstructure and physical properties of high chrome oxide refractories with and without phosphate additions removed from a commercial gasifier after approximately eight months of exposure to a coal slag are evaluated in this report, with the emphasis on evaluating slag/refractory interaction in refractory pores. Details of the investigation are presented and possible mechanisms of how phosphate additives improve wear resistance discussed.

Spalling degradation of Cr2O3‐Al2O3‐ZrO2 refractories for coal‐water slurry gasifier linings: Role of phosphate

“…Particularly, the wear rate of bricks with phosphate during the first two‐thirds of life was only half of that comparing to the conventional bricks. This result is similar to Bennett's reports, 23,24,26 in which the running time of less than 6000 h may be only the first half of their life.…”

“…P 2 O 5 can react with CaO in infiltrating slag to form calcium phosphate and with alumina in bricks to form aluminum phosphate. According to the literature , 26 aluminum phosphates in bricks move to the cold end under the specific temperature and oxygen partial pressure during the operation of gasifier. These lead to the migration of phosphate from hot face to cold face.…”

Failure mechanisms in Pt–Rh thermocouple sensors caused by gaseous phosphorous species

“…In the earlier work by the present authors [17], the phosphorous movement inside an AlPO4containing gasifier refractory was reported to occur via vapor phase transport, following the breakdown: 4AlPO4(s) = 2Al2O3(s) + 2O2(g) + (P2O3)2(g). A similar breakdown is expected for AlP3O9 (metaphosphate): AlP3O9(s) = AlPO4(s) + P2O5(g), where P2O5 gas may be produced instead of (P2O3)2 at 700 °C (atmosphere was not reported) [18].…”

Review of Phosphorus Chemistry in the Thermal Conversion of Biomass: Progress and Perspectives

“…The decomposition of AlPO 4 was shown to be slow at temperatures of around 1500 °C; only 10% of phosphorus vaporized within the first 10 h at temperatures up to 1500 °C in N 2 , whereas no or little decomposition was observed after 8 h at 1550 °C in air . However, in similar work the decomposition rate varied with sample mass, showing that mass transfer limitations may affect the results …”

“…slagging gasifiers and coal combustion power plants, was patented . Bennet et al ,, investigated the specific mechanism(s) responsible for the improved corrosion resistance. Refractory bricks with and without phosphate was operated in a gasifier in the temperature range 1325–1575 °C, for approximately 8 months, and the composition at different locations in the refractory thereafter determined.…”