Upset conditions

The wisest fan choice is frequently not the cheapest fan. A small fan operates well on its curve but may not have adequate capacity for maximum flow control, future needs, or process upset conditions. It may be so lightly constmcted that it is operating near its peak speed with no provision for speed increases in the future, if needed. As fan size is increased, efficiency generally improves and wheel speed is lower. These factors decrease operating cost and provide reserve capacity for the future. However, it is also possible to oversize a fan and impair its performance. 

Consider upset conditions that could exceed the test conditions at which the arrester was certified. These include the gas composition with regard to concentration of sensitive constituents such as ethylene or hydrogen, maximum system pressure during an emergency shutdown, and maximum temperature. Under certain upset conditions such as a high-pressure excursion, there may be no flame arrester available for the task. 

Consider Inherently Safer Design alternatives (e.g., to withstand maximum upset conditions—temperature, pressure, flow)... 

The thrust capacity of a magnetic bearing is limited when compared to a conventional oil bearing. Simulation of potential upset conditions... 

Consideration must be given to the pressure and temperature that the seal will see during normal operation, startup, shutdown, and upset conditions. 

Have there been any upset conditions A quick review of the strip eharts and alarm logs together... 

Upset An upset digester does not decompose organic matter properly. The digester is characterized by low gas production, high volatile acid/alkalinity relationship, and poor liquid-solids separation. A digester in an upset condition is sometimes called a "sour" or "stuck" digester. 

The desirable operating characteristics of equipment include simplicity, convenience and low cost of maintenance simplicity, convenience and low cost of assembly and disassembly convenience in replacing worn or damaged components ability to control during operation and test before permanent installation continuous operation and steady-state processing of materials without excessive noise, vibration or upset conditions a minimum of personnel for its operation and, finally, safe operation. Low maintenance often... 

Overpressme which may occur at normal or below normal pressures, as a result of reduced allowable stresses at higher than design temperatures, are also evaluated and appropriate protective features applied in the design. For example, such conditions may result from chemical reactions, startup or upset conditions. Likewise, low metal temperature must be considered, such as from autorefrigeration, to make sure that brittle fracture conditions do not develop. 

Process technology information will be a part of the process safety information package and should include employer-established criteria for maximum inventory levels for process chemicals limits beyond which would be considered upset conditions and a qualitative estimate of the consequences or results of deviation that could occur if operating beyond the established process limits. Employers are encouraged to use diagrams that will help users understand the process. 

Hands-on training, where employees actually apply lessons learned in simulated or real situations, will enhance learning. For example, operating personnel, who will work in a control room or at control panels, would benefit by being trained at a simulated control panel. Upset conditions of various types could be displayed on the simulator, and... 

Key features of the 1,300 MWe System 80+ (Bagnal, 1992) are 15% improvement in thermal margin, slower response to upset conditions, no fuel damage up to a 6-in. break, and the ability to withstand an 8-hour station blackout. System 80+ integrates the nuclear island, turbine island, and balance of plant. 

For historical and regulatory reasons, a PSA of a nuclear power plant begins with the system analysis to determine the ways that an upset condition could occur, its probability... 

Safety analysis concepts are discussed in this chapter by first describing a generalized hazard tree for a production facility. From this analysis, decisions can be made regarding devices that could be installed to monitor process upset conditions and to keep them from creating hazards. 

Testing should address the maximum operating temperature and pressure normally seen at the arrester location. This does not include certain pressure upsets (such as emergency shutdown) that produce unusually high system pressures. In many cases it may not be possible to design an arrester that will function effectively during upset conditions, and other protective measures should be considered (e.g., venting, suppression). 

Process definition and design criteria Process and equipment design Company memory (management information) Documentation of risk management decisions Protective systems Normal and upset conditions Chemical and occupational health hazards... 

The equipment and systems of the processing phuit are designed to contain tlie chemicals mider processing conditions and to provide tlie controlled environment required for production. This equipment is designed to function under both specific process conditions and upset conditions. Upset conditions tliat are considered in design include fire, explosions, and accidental chemical releases. 

Absorb thrust loads during upset conditions and provide back-up to hydraulic thrust balancing. 

For a flare stack to function properly and to handle the capacity that may be required, the flows under emergency conditions from each of the potential sources must be carefully evaluated. These include, but may not be limited to, pressure relief valves and rupture disks, process blowdown for startup, shutdown, upset conditions, and plant... 

Type and horsepower (Type often signifies motor design. Horsepower should equal the maximum anticipated requirement of the driven machine, or under upset conditions if the service is vital. Also give horsepower requirements of driven device. (If in doubt, give application details.)... 

Air distributors. Improvements in the metallurgy, refractory lining of the outside branches, and better air nozzle design, combined with reducing L/D of the branch piping, have reduced thermal stresses, particularly during start-ups and upset conditions. 

Mechanically withstands a wide range of operating conditions, including start-up, shutdown, normal operation, and upset conditions... 

The FCC process is very complex and many scenarios can upset operations. If the upset condition is not corrected or controlled, each scenario could lead to a reversal. Table 8-1 contains a cause/effect shutdown matrix indicating scenarios in which a shutdown (reversal) could take place. In most cases, a unit shutdown is not necessary if adequate warning (low alarms before low/low shutdowns) is provided. The operating staff must be trained to respond to these warnings. 

Developing new chemical engineering design tools to deal with the multiple objectives of minimum cost process resilience to changes in inputs minimization of toxic intermediates and products and safe response to upset conditions, start-up, and shutdown. 

Some data from corrosion-monitoring probes do not measure corrosion rate, but rather give other useful information about the system. For example, suppose conditions change dramatically during a process upset. An ejq)erienced corrosion engineer can examine the data and correlate it with the upset conditions. Such analysis can provide insight into the process and help to improve performance and extend equipment lifetime. Changes in simple parameters such as pH, ion content, and temperature may lead to detection of a process upset. Without careful analysis, process upsets can reduce the corrosion lifetime of equipment and even cause a system failure. 

The material handled in Process Unit 1, propane vapor, has the potential for VCE and fire, as discussed in Chapter 3. Since the propane is not handled in a liquefied state, even under upset conditions, no potential exists for a boiling liquid expanding vapor explosion (BLEVE). 

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