Pressure vessels surge volume

In very extreme cases, total containment can be provided to prevent any atmospheric emission or to provide a surge volume for controlled flaring, absorption, or other disposal methods. This approach, however, requires use of a very large pressure vessel to provide the required volume, and is usually only a last choice alternative. 

Operating pressure and temperature constrain practical size of vessel. Design codes for pressure vessels vary slightly with the country. In general, for operating pressures >10 MPa, vessel volume usually <1 m Pressure decreases as temperatures exceed 250°C. For temperatures above 350°C, consider carbon/molybdenum, and for temperatures >500°C, consider austenitic steels. Corrosion allowance 1.5 mm for corrosion rates 0.08 mm/a 3 mm for rates 0.09 to 0.3 nun/a 4.5 nun for 0.31 to 0.4 mm/a 6 mm for >0.4 mm/a. If pressure <400 kPa, use L/D of 2 to 3 1. For pressures >400 kPa, use L/D of 4 to 5 1. For surge, allow 2-min liquid residence time for draw-off, use 15 min for reflux, use 5 min, provided this allows sufficient time for controllers to function. Total volume = 1.3 X holdup if the holdup volume is >3 m ... 

The stability of the pressure of the primary system is assured by the pressurizer (8). This is a vertical vessel whose volume is normally 60 per cent filled with water and 40 per cent by steam. The lower part of it (filled with water) is connected by a surge line with one of the two primary cooling circuits electrical heaters are immersed in the water. The upper part (filled with steam) can be sprayed by cold water. 

In addition to discussing phase separators, it is also appropriate to eonsider the apphcation of accumulators in processes. Accumulators or surge vessels are necessary to reduce fluctuations in flow rate, pressure and composition and thereby improve process control. Although accumulators are not phase separators, they are discussed here because they are sometimes contained in the same vessel as a phase separator. For example, in a gas-liquid separator, the volume of liquid at the bottom of the separator is determined by the need to dampen fluctuations in flow rate. 

It is always desirable to have an immediate and convenient indication how a reaction is progressing. In this way, unproductive experiments can be aborted before much time is lost, and equipment failures etc. become immediately apparent. In a reaction that consumes a gas, this can be done by monitoring the gas consumption. In a gas reaction in a constant-volume batch reactor, the pressure drop is a direct measure of the reaction rate and can be followed at a glance on the pressure gauge or the strip chart of a pressure recorder. For a reaction at constant pressure, a set-up as shown in Figure 3.8 can be used A surge vessel at... 

Surge vessel for N2 gas (volume shall be sufficient to take care of pressure fluctuations during pressurisation and de-pressurisation),... 

Primary coolant pressure is maintained sufficiently to prevent hoiling at any point In the system hy means of a pressurlzer vessel. This vessel Is maintained about 6o par cent full of water with a steam blanket. Pressure Is regulated by a combination of electric heaters in the water fill l and spray cooling In the steam filled portions of the vessel. Ihe pressurlzer also serves as a surge tank to accommodate part of the water volume fluctuations resulting from density variatior due to temperature transients This is augmented by a wstar injection system and a spill cooler for the more extreme tran sients. 

---