The plant performance analysis should consider comparisons to the original equipment design limitations, including maximum
allowable equipment working pressures and temperatures, the maximum continuous operating speeds for rotating equipment,
the maximum safe operating metallurgy temperatures, and all such similar limitations as specified in the original equipment
designs. Operating deviations beyond maximum allowable equipment operating conditions should be carefully noted, and
immediately ceased to prevent equipment damages, outages, or injury to plant personnel, plant visitors, and neighboring
facilities, property and people.
A critical process issue for all chemical plant production capacity improvement goals is overcoming process fluid pressure
losses which occur in piping, valves and fittings, and process vessels or equipment that is undersized. Engineering personnel
evaluating the Base Case plant performance should concentrate on those key areas in the plant where substantial or
excessive fluid pressure losses have been measured. High equipment pressure losses may exist because of the equipment
being overloaded, or undersized, or because of abnormalities, such as mechanical blockage, fouling, broken or degraded
catalyst or other internal vessel media, partially open valves, restriction orifices, abnormally low operating pressure, or high
temperature, or equipment damage. Engineering personnel need to verify that extremely high pressure losses are real, and
not errors in measurement, and establish from rating calculations what should be normal fluid pressure losses for the specific
equipment having excessive measured pressure loss. If the high fluid pressure losses are determined to be the result of
excessive load, hence equipment undersize, then such items of equipment would be candidates for upgrade by replacement,
or in some circumstances, by modification.
Chemical plant reactors have a design rating basis. When the plant is operated at increased production capacity, reactants
conversion is affected. At substantially higher plant rate than original design, reactant conversion may deteriorate sufficiently
to suggest to plant engineering personnel and management that modifications are required to achieve higher future plant
production rates. This may be accomplished by revising the reactor catalyst type, shape, size, or composition, or by
replacement of the existing reactor vessel and the catalyst. This choice may best be determined by closely working with the
established catalyst suppliers, as well as verifying equipment performance comparisons of related plants within the specific
sector of the Chemical Industry where the particular reactor type is commonly used.
Heat exchanger capacity limitations for chemical plants depend heavily on their purpose. As plant capacity increases for
existing heat exchange equipment, stream temperature approaches widen, and fluid pressure drop also increases, as noted in
the earlier discussion. For certain heat exchangers, such as process cooling, increased fouling may take place with higher
heat transfer and heat flux, deteriorating the thermal performance of the heat exchanger. Higher process fluid outlet
temperatures as the result of increased fouling may directly affect plant rate, or indirectly, through the influence on capacity of
downstream process equipment, such as compressors, fans, blowers, and pumps.
High shell side fluid flow rate can cause mechanical damage of heat exchanger equipment, from tube vibration induced wear at
baffles and also directly from tube surfaces rubbing, or vibrating. Resultant tube leakage generally causes eventual plant
periodic or sudden plant shut-downs for tube plugging or replacement, reducing plant on-stream time and overall production
capacity. When heat exchangers cause excessive frequency of plant outages for repair, then higher capacity replacement
equipment becomes a necessity for both reliable continuing operations, as well as achieving greater plant production capacity.