Venting rates

Required Relief Rate The required relief rate is the venting rate required to remove the volume being generated within the protected equipment when the equipment is at its highest allowed pressure ... 

The time-dependent nature of the emergency pressure relieving event is obtained by the simultaneous solution of Eqs. (26-27) and (26-28). Generally, the only unknown parameters in these two equations are the venting rate W and the vent stream quahty (Xo). The vent rate W at any instant is a func tion of the upstream conditions and the relief system geometry. 

The couphng equation is a vapor mass balance written at the vent system entrance and provides a relationship between the vent rate W and the vent system inlet quahty Xq. The relief system flow models described in the following section provide a second relationship between W and Xo to be solved simultaneously with the coupling equation. Once W andXo are known, the simultaneous solution of the material and energy balances can be accomplished. For all the preceding vessel flow models and the coupling equations, the reader is referred to the DIERS Project Manual for a more complete and detailed review. 

Use of pumps to Limit filling rate to not exceed vent rate transfer material. metering pumps to drum leading to overpressure. ACGIH 1986 CCPS G-3 CCPS G-15 CCPS G-22 CCPS G-23 CCPS G-29... 

Knox has provided the following graphs for estimating the required vent steam from boiler feedwater deaerators. Vent steam rate depends upon the type of deaerator (spray or tray type) and the percentage of makeup water (in contrast to returning condensate). Low makeup water rates require relatively lower steam vent rates, but there is a minimum rate required to remove CO2 from the returning condensate. 

Figure 1. Steam vent rate vs. deaerator rating for a spray-type deaerator.

Calculations were performed for two different venting rates, namely 3 and 5 minutes. Note that the calculation procedure predicts short-term GLC s for the single stack. This means that meteorological conditions are assumed to be... 

Tables 9 and 10 give the maximum ground level concentrations expected for worst case conditions for the 3-min. and 5-min. venting rates, respectively worst case conditions were obtained from Tables 7 and 8 (i.e., values were calculated based on the largest concentration found in Tables 7 and 8 for each distance within a stability class).

Mass vent rate per unit area is approximately eonstant (or safe value ean be used). 

Venting Rate = 513,825 SCFFI free air at 14.7 psia and 60°F Corrected venting rate for benzene in tank ... 

Ciepluch (C3) was the first to demonstrate that solid propellants could be extinguished by the rapid venting of gases from the combustion chamber. This was accomplished by suddenly opening a secondary nozzle to achieve the needed venting rate. If the depressurization rate was above a critical value, extinguishment could be achieved if below it, the pressure would seek a new steady state determined by the new chamber ballistics. 

Flammable or toxic vapors can be piped to a flare after separation of liquid is obtained. An important design problem in flare use is the very high vent rate experienced for a relatively short time, if an existing flare is used. Also back-pressure effects on the liquid separator vessel must be considered, especially if choked flow of vapor occurs downstream of the separator. 

Required Relief Rate The required relief rate is the vent rate W... 

For steady-state design scenarios, the required vent rate, once determined, provides the capacity information needed to properly size the relief device and associated piping. For situations that are transient (e.g., two-phase venting of a runaway reactor), the required vent rate would require the simultaneous solution of the applicable material and energy balances on the equipment together with the in-vessel hydrodynamic model. Special cases yielding simplified solutions are given below. For clarity, nonreactive systems and reactive systems are presented separately. 

The average dT/dt is typically an arithmetic average between the value at set pressure and the value at peak allowed pressure. The properties Cp, hfg, i, either can be evaluated at the set conditions or can be taken as the average values between the set condition and the peak allowed pressure condition. Alternatively, the term h/g/t)/g in Eq. (23-95) can be replaced by T(dP/dT)tat via the Clapeyron relation. This holds reasonably well for a multicomponent system of near constant volatility. Such an application permits direct use of the experimental pressure-temperature data obtained from a closed-system runaway VSP2 test. This form of Eq. (23-95) has been used to demonstrate the advantageous reduction in both vent rate and vent area with allowable overpressure (Leung, 1986a). 

The rate of pulp lay-down F on a paper machine is controlled by controlling both the pressure P and the height of slurry h in a feeder drum with cross-sectional area A. F is proportional to the square root of the pressure at the exit sHt. The air vent rate G is proportional to the square root of the air pressure in the box P. Feedback controllers set the inflow rates of air Gq and slurry Fq to hold P and h. The system is isothermal. 

A small amount of steam is vented from the top of the stripping tower to the atmosphere. Using a gate valve, with a hole drilled through the gate, is a simple way to control the venting rate. The dissolved air in the cold BFW is vented with this steam. 

RATED WATER INLET RATED 2 PH. Cond. Ret. RATED STEAM INLET RATED VENT RATED WATER OUTLET... 

The process is subjected to a number of disturbances, and the control structure handles all of them quite effectively. Dynamic responses to changes in the setpoint of the temperature controller in the first reactor are shown in Figure 6.109. At 0.1 h, the setpoint is increased from 245 to 255°C. At 3 h, it is decreased to 235°C. Decreasing the temperature in the first reactor results in an increase in throughput. The synthesis gas feedrate, the product rate, and the vent rate all increase. The opposite occurs when the temperature is increased. This indicates that the reaction is equilibrium-limited, not kinetically limited. Decreasing temperature increases the equilibrium constant of exothermic reactions. 

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