Vapor emergency venting

The data required for the emergency vent design includes [191] (1) the thermokinetic and pressure history monitored under near adiabatic conditions, (2) the character of the type of vented system (vapor, gassy, or hybrid), (3) the phase of the vented material (vapor, liquid, or two-phase), and (4) the degree of two-phase disengagement (turbulent, bubbly, or homogeneous). To determine these characteristics, the VSP defines the system as viscous (100 cp) or nonviscous, and also whether or not it has a foaming tendency. 

Operating pressure There are three modes of operation of a quench tank atmospheric pressure operation, nonvented operation, and controlled venting operation. Atmospheric operation is usually feasible when the effluent Being emitted has a bubble point well above the maximum ambient temperature. A very small quantity of vapor escapes with the air that is displaced as the tank fills with the emergency discharge (typically about 0.2 percent of the reactor contents). Depending on the toxic or flammable properties of the vapor, the vent from the quench tank can be routed to the atmosphere or must be sent to a scrubber or flare. 

Prevention of hot spots and efficient removal of the heat of reaction are very important because of the thermal instability of hypochlorites. The continuing reaction of hypochlorite to form unwanted byproducts is part of the discussion of emergency vent scrubbers (Section 9.1.10.3A), where it is more of an issue. Here, we note that the production of high-quality bleach depends on a consistent supply of chlorine in the tail gas and on adequate temperature control. The absorbing solution is therefore circulated by titanium centrifugal pumps around the reactor(s) through titanium coolers, usually of the plate-and-frame type. The recirculation of liquor in itself provides turbulence in the reaction zone, and the volume of circulation determines the maximum temperature possible in the reactor. A gas feed or the vaporization of a liquid chlorine supply may also be used to promote turbulence. 

The contractors did not seem to be aware that the wastewater tank had flammable contents and the tank was not adequately protected from welding activities. There were several openings in the vessel, which allowed ignition of the flammable vapors within the tank. The tank was not equipped with a frangible roof or other emergency venting so the tank barrel separated from the floor plate as in the previous incident [10],... 

The second emergency system is an automatic depressurization system. In the event of an uncontrolled reaction, the reaction can be safely limited by depressurizing the reactor to the vent system. The heat of vaporization of the boiling reaction mass safely removes heat from the reactor. The emergency vent system will be sized to handle the peak venting needs of the reactor system. 

Install flame arresters on atmospheric vents to prevent fire on the outside of the tank from propagating back into the vapor space inside the tank. Provide fire resistant insulation for critical vessels, piping, outlet valves on tanks, valve actuators, instruments lines, and key electrical facilities. Provide remote controlled, automatic, and fire-actuated valves to stop loss of tank contents during an emergency provide fire protection to these valves. Valves should be close-coupled to the tank, and must be resistant to corrosion or other deleterious effects of spilled fluids. Vessels should be provided with overpressure relief protection. 

Vapor Pressure The pressure exerted by a vapor above its own liquid. The higher the vapor pressure, the easier it is for a liquid to evaporate and fill the work area with vapors which can cause health or fire hazards. Venting Emergency flow of vessel contents out of a vessel. The pressure is controlled or reduced by venting, thus avoiding a failure of the vessel by overpressurization. The emergency flow can be one-phase or multi-phase, each of which results in different flow characteristics. 

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