Process hazards temperature deviations

Hazard and operability study (HAZOP) is a method for systematically comparing each element of a process system against its potential for critical parameters deviation from the intended design conditions that could create hazards and operability problems. An HAZOP analysis team studies the process piping and instrument diagrams and/or plant model then analyzes the effects of potential deviations from design conditions in process flow, temperature, pressme, and time. Keywords, such as more of, less... 

Materials information includes toxicity, permissible exposure limits, physical properties, reactivity, corrosivity, thermal and chemical and hazardous effects of inadvertent mixing of different materials.Process information consists of 1) process flow diagrams, 2) process chemistry descriptions, 3) maximum amounts of chemicals, 4) safe ranges for temperatures, pressures, flows oi 5) evaluation of the con.sequences of deviations. 

Control of the process. Prevention of hazardous deviations in process variables (pressure, temperature, flow), by provision of automatic control systems, interlocks, alarms, trips together with good operating practices and management. 

Process safety information is compiled and made available to ah employees to facilitate the understanding and identification of hazards. This information includes block flow diagrams or process flow diagrams, process chemistry, and process limitations, such as temperatures, pressures, flows, and compositions. Consequences of process deviations are also required. This... 

Hazard and Operability (HAZOP) Study Scenario- based Inductive/ deductive By deviation from intended operation Processing systems with parameters such as flow, pressure, and temperature Good for both procedure-based and continuous operations Can analyze complex processes with multiple safeguards Only looks at causes that could lead to identified deviations Higher... 

Chemical facilities have to be operated safely during normal operation as well as during deviations from the specified process and equipment parameters. Chemical reactions that go to completion can only become a hazard for humans and the environment when process pressures or temperatures rise beyond the equipment design parameters of a facility e.g., as result of a runaway reaction. For example unacceptable pressure increases can develop as a result of exothermic processes with inadequate heat sinks or reactions that produce gaseous products (e.g., decompositions). 

Kinetic simulation methods are used as advisory controls in potentially thermally hazardous batch amination reactions of nitroaromatic compounds. Time—temperature process data are fed as input to a kinetic simulation computer program which calculates conversions, heat release and pressure profdes. Results are compared continuously on-line with measured batch data to detect any deviations from normal operating conditions. 

At each node in a process (vessel or pipe section), possible deviations in process variables (such as temperature) from the design intent are formed by combinations of variables and guide words (such as more or high ), to determine the adequacy of existing systems to prevent hazardous deviations. 

It is quite often not realized that not only can raw materials or products be hazardous substances, but so also can by-products formed during the process. This can hapjten a result of side reactions or decomposition reactions that occur either intentionally as a result of an intrinsic property of a chemical process or unexpectedly due to deviations of the process. Examples are the possible formation of nitro-samines in nitrite-containing cooling fluids or the release of volatile monomers, e. g., styrene or formaldehyde during processing of polymers and plastics because of depolymerization at elevated temperatures. Disproportionation reactions of tri-valent organic phosphorus esters with formation of volatile toxic phosphines or decomposition reactions of unstable compounds like hydroxylamine, metal carbonyls, nitro-compounds or peroxides are further examples. 

The more complex the system or process to be evaluated, the more essential is the need for a HAZOP study. The HAZOP study is conducted in much the same way as the what-if analysis, usually by the same review team. There are minor differences, however, in terminology and approach. In the HAZOP study, certain guidewords are normally used to aid the review team and help identify specific areas where deviations from design intent can occur. Guidewords can include pressure, flow, level, temperature, and power. HAZOP also attempts to identify the severity of the outcome if such deviations from the norm occur as well as the probability or likelihood of occurrence. The hazard risk matrix established and explained in Chapter 2 (Table 2.3) can be used for this purpose since it provides both severity and probability rankings for a given hazardous situation. 

Hazard and operabdity study. This is a structured methodology to investigate each element of a system systematically for all the potential deviations that can cause hazards and operabdity issues. The effects caused by deviations from design conditions cases are examined for each key process parameter (e.g., flow, volume, pressure, temperature) using phrases such as more of, less of, none of, to describe potential deviations and causes of failure. FinaUy, an assessment is made weighing the consequences, causes, and protection requirements. 

Remember that the HAZOP guide word and the process condition (flow, pressure, temperature, pH level, etc.) is the process deviation. And the process deviations that most interest us are the ones with hazardous consequences. For example, a node with MORE PRESSURE can lead to pressure vessel rupture, killing plant operators, spilling toxic wastes to the environment, and forcing the rest of the plant to shut down due to losing a critical process. 

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