Agitator failures

Runaway Reactions Runaway temperature and pressure in process vessels can occur as a resiilt of many fac tors, including loss of cooling, feed or quench failure, excessive feed rates or temperatures, contaminants, catalyst problems, and agitation failure. Of major concern is the high rate of energy release and/or formation of gaseous produc ts, whiai may cause a rapid pressure rise in the equipment. In order to properly assess these effec ts, the reaction kinetics must either be known or obtained experimentally. 

Implement procedure and/or back-up equipment for dealing with imminent danger relating to agitator failures... 

Additionally, consequences of possible process maloperations, such as incorrect charging sequence, contamination of reactants, agitation failure and poor temperature control, adding reactants too quickly. 

GAGBYP Glycol tanks bypass agitator failure... 

Agitator failure either due to electrical or mechanical failure could result in loss of system control and "hot spots" in the reactor. In suspension systems loss of agitation could negate much of the "heat sink" effect as the immiscible phases separate and stratify. 

Agitation failure during a reaction can affect the following system parameters ... 

The start-up procedure after an agitation failure can be studied in detail in bench-scale testing as well. 

Agitator failure or restart of agitator after failure Contamination of reactants Additions too quickly Delayed addition... 

In some cases the worst case for relief sizing may be agitator failure, particularly if a more reactive, more volatile layer could form on top and then run away without the diluting effect of the more dense layer. 

In our facility, this system is performing satisfactorily, and agitator failures and the resulting production outages have been avoided. Operations are now running smoothly, production is higher, and product quality has improved. 

At least one accident is known where liquid NC13 could separate in a waste-water treatment where bleach was used to oxidize cyanide ions. After an agitation failure, the actuation of a bottom valve triggered the detonation. Direct chlorination would lead to the same dangerous situation. 

The effect of any maloperations — agitation failure, rapid charging, loss of cooling, extended reaction times and so on — which have not been considered previously should be evaluated. The integration of the process with other manufactures may also need to be considered. 

This process definition covers faults which, though not common, are known to occur in chemical processing. Examples are agitator failure, loss of plant cooling, leaks of cooling liquid into the batch, and process maloperation. Malopera-tion covers over- and under-charging of reactants, solvents or catalysts. Non-specific faults are so called because they are not specific to individual processes and the effect of them can be included in the hazard assessment without additional process description. 

Whilst this technique does not directly provide data on the course of a reaction, the shape of the trace does give an indication. For example, the time for the temperature rise to occur will seem to increase on subsequent additions if the reaction rate is falling off. The technique can also be used to investigate typical maloperations. Examples are the effect of a double charge — does reactant accumulation occur — and the effect of agitator failure — is there any build-up of reactants or does the reaction continue ... 

In the event of agitator failure additions should be stopped. In two-phase systems the reactants will separate, and if the agitator is restarted the resulting rapid mixing can cause dangerously high temperature excursions. 

These instructions must define the limits of authority of the plant operators. Many plants suffer problems such as agitator failure or blocked pipes, and restarting the agitator or clearing the blockage can be hazardous. The operators instructions should make clear which methods are permissible and when advice from technical supervision is necessary. 

The process could be operated safely, without emission, provided the temperature does not exceed 130°C and accumulation of unreacted A, which could cause a subsequent uncontrolled temperature rise, is prevented. To achieve this, addition of A should be stopped if the reactor temperature falls below 50°C or in the event of agitator failure. 

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