The two-phase feed stream for the gas-liquid separator (or

Air samples from a process area are continuously drawn through a 4-in diameter tube to an analytical instrument that is located 40 m away. The tubing has an outside diameter of 6.35 mm and a wall thickness of 0.762 mm. The flow rate through the transfer line is 10 cm3/s for ambient conditions of 20C and 1 atm. The pressure drop in the transfer line is negligible. Because chlorine gas is used in the process, a leak can poison workers in the area. It takes the analyzer 5 s to respond after chlorine first reaches it. Determine the amount of time that is required to detect a chlorine leak in the processing area. State any assumptions that you make. Would this amount of time be acceptable if the hazardous gas were carbon monoxide, instead of chlorine? (Adapted from: Student Problems for Safety, Health, and Loss Prevention in Chemical Processes, AIChE Center for Chemical Process Safety, NY, 1990).

The two-phase feed stream for the gas-liquid separator (or flash drum) shown in Fig. E10.2 consists of a hydrocarbon mixture. Because the pressure in the vessel is significantly lower than the feed pressure, part of the liquid feed flashes to form a gas phase. The hydrocarbons are flammable and somewhat hazardous. Discuss the process safety issues and propose an alarm/SIS strategy.

The loss of the coolant to a process vessel can produce an unacceptably high pressure in the vessel. As a result, a pressure relief valve is used to reduce the pressure by releasing the vapor mixture to the atmosphere. But if the mixture is toxic or flammable, the release can be hazardous. For the distillation column in Fig. E10.3, which operates at above ambient temperature, propose an alarm/SIS system that will reduce the number of releases to the environment, even though the occasional loss of coolant flow to the condenser is unavoidable. (Note: The pressure relief valve at the top of the column is not shown in Fig. E10.3.)

The probability of a particular type of sensor functioning properly is 0.99. Consequently, a triply redundant sensor system has been proposed for a critical measurement. Thus, three independent sensors will be installed, and the median of the three measurements will be used for the alarms and control calculations. What is the probability that at least two of the sensors will be working at any time?

Consider the liquid storage tank with a low-level interlock, as shown in Fig. 10.4. Suppose that an independent lowlevel alarm is added, with its set-point value above the value for the low-level switch. If both the low-level alarm and the low-level interlock system fail simultaneously, the pump could be seriously damaged. What is the probability that this occurs? What is the mean time between failures?

For the reliability analysis of the flow control loop in Example 10.3, the DIP flowmeter is the least reliable component. Suppose that a second, identical flowmeter is used in a backup mode so that it could be automatically and immediately employed if the first flowmeter failed. How much would the overall system reliability improve by adding the second sensor?

Using the failure rate data in Table 10.1, evaluate thereliability and mean time between failures for the high-pressure interlock in Fig. 10.4.