Diesel hydrogenation reaction temperature
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The operating procedures state that when the surface temperature at any point of the reactor is below 50°C (after the first start-up, the allowable temperature for subsequent start-ups is 93°C), the inlet pressure of the reforming reactor must not exceed 3.0 MPa in order to prevent the equipment from becoming brittle due to backfire. How should this sentence be understood?
When chromium-molybdenum steel is operated under high-temperature conditions for an extended period, it develops varying degrees of temper embrittlement, that is, a decrease in toughness and an increase in the temperature at which toughness transitions to brittleness. When the operating temperature of chromium-molybdenum steel pressure vessels is below or near the ductile-brittle transition temperature, and the stress reaches a certain level, brittle failure may occur in such vessels. For chromium-molybdenum steel pressure vessels, such as those used in hydrogenation refining and hydrocracking reactors, it is necessary to first increase the temperature before raising the pressure during startup, and to first reduce the pressure before lowering the temperature during shutdown, in order to prevent brittle failure.