Pressure generation rate, exothermic

A reactor system is shown in Figure 2 to which the HAZOP procedure can be appHed. This reaction is exothermic, and a cooling system is provided to remove the excess energy of reaction. If the cooling flow is intermpted, the reactor temperature increases, leading to an increase in the reaction rate and the heat generation rate. The result could be a mnaway reaction with a subsequent increase in the vessel pressure possibly leading to a mpture of the vessel. 

Aqueous sulfamic acid solutions are quite stable at room temperature. At higher temperatures, however, acidic solutions and the ammonium salt hydroly2e to sulfates. Rates increase rapidly with temperature elevation, lower pH, and increased concentrations. These hydrolysis reactions are exothermic. Concentrated solutions heated in closed containers or in vessels having adequate venting can generate sufficient internal pressure to cause container mpture. An ammonium sulfamate, 60 wt % aqueous solution exhibits mnaway hydrolysis when heated to 200°C at pH 5 or to 130°C at pH 2. The danger is minimised in a weU-vented container, however, because the 60 wt % solution boils at 107°C (8,10). Hydrolysis reactions are ... 

The evaluation of thermal stabihty requires the determination of the temperature at which an exothermic reaction occurs, the rate of such a reaction as a function of temperature, and the heat generated per unit mass of material by the reaction. In many cases, data on the increase of pressure during a reaction are also required, especially for vent sizing. The term onset temperature Toa%et is used in two contexts ... 

A runaway reaction occurs when an exothermic system becomes uncontrollable. The reaction leads to a rapid increase in the temperature and pressure, which if not relieved can rupture the containing vessel. A runaway reaction occurs because the rate of reaction, and therefore the rate of heat generation, increases exponentially with temperature. In contrast, the rate of cooling increases only linearly with temperature. Once the rate of heat generation exceeds available cooling, the rate of temperature increase becomes progressively faster. Runaway reactions nearly always result in two-phase flow reliefs. In reactor venting, reactions essentially fall into three classifications ... 

Many kinetic data can be collected from ARC experiments the exothermic onset temperature, the rate of temperature rise, the rate of pressure rise, and the apparent activation energy. The basic data obtained are, however, thermodynamic properties the adiabatic temperature rise, the maximum pressure potential, the quantity of gaseous products generated, and the heat of reaction can be obtained in one run. The heat of reaction is estimated from ... 

On further increasing the pressure, the radicals more readily destroy internally in the gas than at the walls. This results in the removal of the active species or radicals and any increase in production of radicals is again counter balanced. The reaction, therefore, proceeds smoothly. The third limit is due to thermal explosion. In exothermic reactions when the reaction is carried out in closed space, the heat generated cannot be dissipated. The reaction rate suddenly becomes very rapid and a thermal explosion occurs. These limits are shown in Fig. 3.2... 

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