Relief liquid flow rates

W = required vapor capacity in pounds per hour, or any flow rate in pounds per hour, vapor relief rate to flare stack, Ibs/hr W(. = charge weight of explosive, lb Wj. = effective charge weight, pounds of TNT for estimating surface burst effects in free air W, = required steam capacity flow or rate in pounds per hour, or other flow rate, Ib/hr Whe = hydrocarbon to be flared, Ibs/hr Wtnt equivalent charge weight of TNT, lb Wl = liquid flow rate, gal per min (gpm)... 

The vessel nozzle diameter (inside) or net free area for relief of vapors through a rupture disk for the usual process applications is calculated in the same manner as for a safety relief valve, except that the nozzle coefficient is 0.62 for vapors and liquids. Most applications in this category are derived from predictable situations where the flow rates, pressures and temperatures can be established with a reasonable degree of certainty. 

The method used for the safe installation of pressure relief devices is illustrated in Figure 8-1. The first step in the procedure is to specify where relief devices must be installed. Definitive guidelines are available. Second, the appropriate relief device type must be selected. The type depends mostly on the nature of the material relieved and the relief characteristics required. Third, scenarios are developed that describe the various ways in which a relief can occur. The motivation is to determine the material mass flow rate through the relief and the physical state of the material (liquid, vapor, or two phases). Next, data are collected on the relief process, including physical properties of the ejected material, and the relief is sized. Finally, the worst-case scenario is selected and the final relief design is achieved. 

As mentioned previously, two-phase flow discharges for fire scenarios are possible but not likely. To size the relief for fire and a single-vapor phase, use the heat input determined from Equations 9-36 to 9-38, and determine the vapor mass flow rate through the relief by dividing the heat input by the heat of vaporization of the liquid. This assumes that all the heat input from the fire is used to vaporize the liquid. The relief area is then determined using Equations 9-3 to 9-12. 

In the catalyst preparation area where the fire occurred, aluminum alkyl and isopentane are mixed in a batch blending operation in three 8000-gallon kettles. The flow rates of components are regulated by an operator at the control room. Temperature, pressure, and liquid level within the kettles are monitored by the control room operator. The formulated catalyst is stored in four 12,000-gallon vertical storage tanks within this process unit. Aluminum alkyl is a pyrophoric material and isopentane is extremely flammable. Each vessel was insulated and equipped with a relief valve sized for external fire. 

Because of the low liquid rates in vacuum systems, downcomers will usually be oversized, and specific flow rates across the weir will be low. However, liquid rates in high-pressure columns may exceed values recommended for optimum tray performance across a single weir. The maximum specific flow is 70 gal/(min ft)[53 m3/(h m)] for a straight segmental weir and 80 gal/(min ft)[60 m3/(h m)] for a weir with relief wings. Above 80 gal/(min ft), a multiple downcomer arrangement should be considered. 

P = set pressure at which relief valve begins to open, psig Q = flow rate, in U.S. gallons per min Qr = rate of heat input due to fire, Btu/hr SGL = specific gravity of liquid at flowing temperature referred to water as 1.0 at 70°F... 

When the operation of a relief valve can release liquid chlorine or when it is necessary to limit the rate of discharge of chlorine to the receiving system, buffer tanks are useful. Those that may be subjected to liquid chlorine should have alarms that signal its presence and should be designed for low temperature. There should be provision for safe removal of the liquid after operation. Absorber design is also based on the maximum flow rate of gas at the inlet. When release rates are variable (the peak rate usually being at the start), a buffer in the system can reduce the maximum rate at the absorber. 

Positive displacement pumps are not supposed to be throttled or regulated on the discharge side. After the line has been walked and every valve has been checked, the pump can be started. Suction and pressure gauges should be carefully monitored, and flow rates tracked. Flow control loops are typically not used with PD pumps unless a series of relief valves and pressure control devices is used. A simple calculation should be made on how fast the tank will fill and how fast the suction tank will empty. Careful monitoring of liquid levels is important. Samples are frequently caught on the product lines and sent to the lab for quality checks. Some PD pumps are designed to be run liquid full at all times, whereas others can be run empty for short periods of time. 

In North America, the eductor pipe inside the vessel has an excess-flow valve at the top, immediately below the manhole cover. This valve closes the eductor pipe when the rate of liquid flow exceeds a set rate [2], [24]. North American tank cars have a spring-loaded. safety relief valve, which protects the vessel against overpressure in case of external heat. The tanks have thermal insulation. In Europe thermal insulation and safety relief valves are not used or recommended. 

The first two eases represent the smallest and largest vent sizes required for a given rate at inereased pressure. Between these eases, there is a two-phase mixture of vapor and liquid. It is assumed that the mixture is homogeneous, that is, that no slip oeeurs between the vapor and liquid. Furthermore, the ratio of vapor to liquid determines whether the venting is eloser to the all vapor or all liquid ease. As most relief situations involve a liquid fraetion of over 80%, the idea of homogeneous venting is eloser to all liquid than all vapor. Table 12-3 shows the vent area for different flow regimes. 

As the gas or vapour production rate increases, the flow regime may change from churn-turbulent to droplet flow, in which a fluidised bed of liquid droplets is present in the reactor (see Figure A3.1). This is of less practical interest for relief system sizing because if the gas or vapour rate is so high as to give droplet flow, the relief system size is likely to be impractically large. 

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