Reactor vent systems

JACOBS AND KRUPA Safe Reactor Vent Systems... 

Develop sketches of reactor vent systems for the following four cases ... 

The basic process usually consists of a large reaction vessel in which air is bubbled through pressuri2ed hot Hquid toluene containing a soluble cobalt catalyst as well as the reaction products, a system to recover hydrocarbons from the reactor vent gases, and a purification system for the ben2oic acid product. 

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 ... 

To reduce the risk of container failure, the pressure vessels are equipped with several safety features. These can include an effective self-venting system where unforeseen overpressure is released by a quick open-resealing step, or the use of safety disks which rupture when their pressure limit is reached. The small vials (0.2-20 mL) of some monomode reactors are protected by the pressure limit (20 bar) of the caps used, which is significantly lower than the operating limit of the vials themselves (40-50 bar). 

Advanced Reactive System Screening Tool (ARSST ) The ARSST measures sample temperature and pressure within a sample containment vessel. The ARSST determines the potential for runaway reactions and measures the rate of temperature and pressure rise (for gassy reactions) to allow determinations of the energy and gas release rates. This information can be combined with simplified methods to assess reactor safety system relief vent requirements. 

In a reactor which cannot be isolated from its venting system and which is equipped with a jacket for heating and cooling via an open water circuit the following exothermic reactions of the type... 

Fauske s method14,51 (given below) is based on emptying the reactor (or achieving vapour/ liquid disengagement) before the pressure has risen from the relief pressure to the maximum accumulated pressure in a vented system. The method incorporates the simplified equilibrium rate model, ERM, for saturated liquid inlet (see 9.4.2) together with the Clausius-Clapeyron relationship (discussed in 6.3.3). The method makes use of adiabatic experimental rate data for the runaway, whose measurement is described in Annex 2. 

Loss prevention of polyethylene plants is outlined in Chapter 7.2. The major hazard that can occur is the runaway of the high-pressure reactor and decomposition of ethylene besides fire and disintegration of high-pressure separators, pipes, and compressors. The critical conditions for runaway and ethylene decomposition during homo- and copolymerization are revealed together with the influence of decomposition sensitizers. Relief devices and venting systems are described. 

If a Safety Interlock System exists, describe what is to happen when shutdown is triggered for example, reactor feed MV closes, reactor vent MV opens, etc.)... 

The simpler and most reliable approach to the use of the DIERS methodology is the use of FAUSKY s reactive system screening tool (RSST). It is an experimental autoclave which simulates actual situations that may arise in industrial systems. The RSST runs as a differential scanning calorimeter that may operate as a vent-sizing unit where data can readily be obtained and can be applied to full-scale process conditions. The unit is computerized and records plots of pressure vs. temperature, temperature vs. time, pressure vs. time, and the rates of temperature rise and pressure rise vs. the inverse of temperature. From these data it determines the potential for runaway reactions and measures the rates of temperature and pressure increases to allow reliable determinations of the energy and gas release rates. This information can be combined with simplified analytical tools to assess reactor vent size requirements. The cost of setting up a unit of this kind is close to 15,000. 

The heating and cooling system consists of an inert hydrocarbon mixture. The height of the system is around 2.5 meters (to the top of the stirrer) and 5-6 meters in total. The metal-clad pipes on the right of the reactor are the condensers. The box is equipped with a direct venting system and a flame-retarding valve for safe removal of the hydrogen. 

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