System runaway

The average dT/dt is typically an arithmetic average between the value at set pressure and the value at peak allowed pressure. The properties Cp, hfg, i, either can be evaluated at the set conditions or can be taken as the average values between the set condition and the peak allowed pressure condition. Alternatively, the term h/g/t)/g in Eq. (23-95) can be replaced by T(dP/dT)tat via the Clapeyron relation. This holds reasonably well for a multicomponent system of near constant volatility. Such an application permits direct use of the experimental pressure-temperature data obtained from a closed-system runaway VSP2 test. This form of Eq. (23-95) has been used to demonstrate the advantageous reduction in both vent rate and vent area with allowable overpressure (Leung, 1986a). 

Understanding how sudden pressure releases can occur is important. They can happen, for example, from ruptured high-pressure tanks, runaway reactions, flammable vapor clouds, or pressure developed from external fire. The proper design of pressure rehef systems can reduce the possibility of losses from unintended overpressure. 

The second context is the process reac tor. There is a potential for a runaway if the net heat gain of the system exceeds its total heat loss capabihty. A self-heating rate of 3°C/day is not unusual for a monomer storage tank in the early stages of a runaway. This corresponds to 0.00208°C/min, 10 percent of the ARC s detection limit. ARC data for the stored chemical would not show an exotherm until the self-heating rate was 0.02°C/min. Therefore, onset temperature information from ARC testing must be used with considerable caution. 

Vent Sizing Package (VSP) The VSP is an extension of ARC technology. The VSP is a bench-scale apparatus for characterizing runaway chemical reactions. It makes possible the sizing of pressure relief systems with less engineering expertise than is required with the ARC or other methods. 

Reactive System Screening Tool (RSST) The RSST is a calorimeter that quickly and safely determines reactive chemical hazards. It approaches the ease of use of the DSC with the accuracy of the VSP. The apparatus measures sample temperature and pressure within a sample containment vessel. Tne RSST 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 reac tor safety system relief vent reqiiire-ments. It is especially useful when there is a need to screen a large number of different chemicals and processes. 

Develop and install emergency system and procedures to shortstop runaway reaction. 

Reactive Systems Screening Tool (RSST ) Temperature history of runaway reaction, rates of temperature and pressure rise (for gas producing reactions)... 

External fire exposure resulting in runaway reaction and/or system overpressure. 

Unwanted reaction Clean and inspect equipment after each use Design with compatible materials contaminants. Maintain integrity of the system Design emergency relief system (ERS) for runaway scenario CCPS G-13 CCPS G-22 CCPS G-23 CCPS G-29... 

Runaway reaction Interlock manway with vessel pressure with manway, Design system for closed manual operation open—foam out (can be acid based), operator contacted by process materials. CCPS G-22 CCPS G-23 CCPS G-29 Fisher 1990 ISAS84.01... 

A polymerization process involving a monomer, an organic peroxide initiator and an organic solvent underwent an energetic runaway reaction. All the contents in the polymerization reactor were lost. The emergency relief system prevented major damage to the equipment. 

After the incident, an investigation team determined that the first operator had not added the initiator when required earlier in the process. When the relief operator added the initiator, the entire monomer mass was in the reactor and the reaction was too energetic for the cooling system to handle. Errors by both operators contributed to the runaway. Both operators were performing many tasks. The initiator should have been added much earlier in the process when much smaller quantities of monomer were present. There was also no procedure to require supervision review if residual monomers were detected. The lesson learned was that operators need thorough training and need to be made aware of significant hazardous scenarios that could develop. 

Runaway A thermally unstable reaction system which exhibits an uncontrolled accelerating rate of reaction leading to rapid increases in temperature and pressure. 

Once a decision to use QRA has been made, you must decide whether frequency and/or consequence information is required (Steps 6 and 7). In some cases you may simply need frequency information to make your decision. For example, suppose you wish to evaluate the adequacy of operating procedures and safety systems associated with a chemical reactor. The main hazard of concern is that the reactor could experience a violent runaway exothermic reaction. You believe that you know enough about the severe consequences of a runaway and nothing more will be gained by quantifying the consequences of potential run-... 

Some systems may show stiff properties, especially those for oxidations. Here the system of differential equations to be integrated are not stiff . Even at calculated runaway temperature, ordinary integration methods can be used. The reason is that equilibrium seems to moderate the extent of the runaway temperature for the reversible reaction. 

As can be seen most of the tubes were still in a non-sensitive state while about ten were in runaway conditions. This wiU give an operational feel for how uniform the catalyst charge should be and how closely the system may approach incipient runaway, for a single tube in a multi-tube production unit. 

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 ... 

In some hybrid systems, the generated vapor in a vented reaetion is high enough to remove suffieient latent heat to moderate or temper the runaway (i.e., to maintain eonstant temperature). This subsequently gives a smaller vent size. 

Vent sizing for two-phase (runaway reactions) flow vent sizing for a tempered system... 

Runaway A thermally unstable reaction system, which shows an accelerating increase of temperature and reaction rate. The runaway can finally result in an explosion. 

Temperature of no-return Temperature of a system at which the rate of heat generation of a reactant or decomposition slightly exceeds the rate of heat loss and possibly results in a runaway reaction or thermal explosion. 

Vapor pressure system A vapor pressure system is one in whieh the pressure generated by the runaway reaetion is solely due to the inereasing vapor pressure of the reaetants, produets, and/or solvents as the temperature rises. 

Fauske, El. K., Clare, G. El., and Creed, M. J., Lahoratory Tool for Charaeterizing Chemieal Systems, Proeeeding of tlie Int. Symp. on Runaway Reaetions, AIChE/CCPS, Boston, MA, Mareh 7-9, 1989. 

Eauske, El. K., The Reaetive System Sereen Tool (RSST) An Easy, Inexpensive Approaeh to the DIERS Proeedure, Int. Symp. on Runaway Reaetion, Pressure Relief Design, and Effluent Handling, AIChE, pp. 51-63, Mareh 11-13, 1998. 

Fauske, H. K., Emergeney Relief System Design for Runaway Chemieal Reaetion Extension of the DIERs Methodology, Chem. Eng. Res. Des., Vol. 67, pp. 199-202, 1989. 

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