Safe operating conditions

Eail-Safe Design features which provide for the maintenance of safe operating conditions in the event of a malfunction of control devices or an interruption of an energy source (e.g., direction of failure of a control valve on loss of signal). A system is fail-safe if failure of a component, signal, or utility that would create a hazard initiates an action that maintains the system in a safe condition. 

The client generally supplies processing technology and specific operating parameters related to safe operating condition. The Technical Package may include, but not be limited to, the following ... 

Corrosion protection not only maintains the value of industrial plants and structures but also ensures safe operational conditions and the reliability of these structures it prevents damage that can endanger people and the environment. For this reason corrosion protection of such installations forms the most important means of protecting the environment. 

There are few chemical plants that are so forgiving that a control system or a safety interlock system is not required. Process engineers provide controls to assure product yield and quality and maintain safe operating conditions. This type of control system is a BPCS. The BPCS acts to alarm and moderate a high or low operating condition specified by the normal operating limits within the never exceed critical limits. The SIS is provided to shut down or otherwise place the process in a safe state if the BPCS fails to maintain safe operating conditions. A BPCS should not be used as the sole source of a process safety shutdown. 

Fig. 2.21 Safe operating conditions for various steels in nitric acid solutions. Isocorrosion lines at 0-1 g irT h" ...

Sodium azide remains the source of nitrogen, however a thorough evaluation of the safety issues was conducted and safe operating conditions defined. 

The scope of this book includes several aspects of safe process design and operation, such as the choice of reactor type, safe operating conditions, and the selection of protective systems, primarily related to chemical reactivity. However, even in a process plant where these aspects have been carefully considered and thoroughly applied, there are still numerous events that can occur and can lead to hazardous incidents. Examples of such events are ... 

GR-5.23.2 Procedures for Maintaining Pipe-Type and Bottle-Type Holders in Safe Operating Condition... 

The pressure-control and pressure-limiting equipment shall be examined and tested periodically to see if it is in a safe operating condition and has adequate capacity. 

Where control of corrosion is dependent on the concentration of contaminants or moisture, the operator should demonstrate that procedures and the necessary controls are in place to maintain a safe operating condition. Similarly, where inhibitors are added or systems such as cathodic protection are used, the operator should demonstrate that these systems are inspected and adequately maintained to ensure continued protection of the process. 

Figure 5.3 Inherently safe operating conditions for a slow reaction in the continuous phase showing the boundary line for runaway conditions.

Tr(C) reported in Fig. 4.8, and corresponding to safe operative conditions according to the Adler and Enig criterion, are obtained with the Semenov number Se = 0.47, which is well above the maximum critical value provided by the Semenov criterion, Sec = 0.377, as given by (4.28). This difference mainly arises from the inclusion into the mathematical model of the terms accounting for consumption of reactant A. 

The advantage of pressurization - compared with other protection techniques, e.g. restricted breathing enclosure - is given by a positive pressure differential permanently maintained in the apparatus interior. Load cycles of the p-apparatus do not affect this pressure differential, and by this way, a cooling-down period caused by reduced or no-load conditions cannot cause an inverted pressure differential (the pressure of the surrounding atmosphere is somewhat higher compared with that in the apparatus interior) which may force the backstream of environmental flammable atmosphere into the interior of an apparatus. Pressurization guarantees safe operational conditions completely independent of load cycles. 

Step 1. For this process we must be able to set the production rate of vinyl acetate while minimizing yield losses to carbon dioxide. During the lifetime of the catalyst charge, catalyst activity decreases and the control system must operate under these different conditions. To maintain safe operating conditions, the oxygen concentration in the gas loop must remain outside the explosivity region for ethylene. The azeotropic distillation column must produce an overhead product with essentially no acetic acid and a bottoms product with no vinyl acetate. The absorber must recover essentially all of the vinyl acetate, water, and acetic acid from the gas recycle loop to prevent yield losses in the CCf removal system and purge,... 

Whether a pressurized structure will leak or burst when suddenly cracked depends on the material s resistance to rapid crack propagation and its ability to arrest a crack. Thus, the governing material property, namely the stress intensity-crack velocity relationship, is necessary input for designing pressurized pipes and vessels and establishing safe operating conditions. Unfortunately, this material property is not easily measured, and reliable data do not generally exist. 

In addition, various inequality constraints, which define acceptable (safe) operating conditions, can be specified. These set limits on ... 

Safe operating conditions include safe equipment, chemicals, process operations, and personnel safety. Details for safe laboratory operations have been published [4,5]. 

Two separate models based on Dow Advanced Continuous Simulation Language (DACSL) were used in these studies. The first model used laboratory data and parameter estimation to determine the Arrhenius constants for two desired and eight undesired reactions in a process. The second model used the Arrhenius constants, heats of reaction, different physical properties, and reactor parameters (volume, heat transfer properties, jacket control parameters, jacket inlet temperature) to simulate the effect of reaction conditions (concentration, set temperature, addition rate) on the temperature of the reaction mixture, pressure and gas flow rates in the reactor, yield, and assay of the product. The program has been successfully used in two scale-ups where the optimum safe operating conditions, effect of various possible failures, and control of possible abnormal conditions were evaluated. 

---