The emergency block valve is also known as an emergency shutdown valve (ESDV) or an emergency isolation valve (EIV). API RP 553, specification of Refinery Valves and Accessories for Control and Safety Instrumented Systems, defined emergency block valve as follows: “Emergency block valves are designed to control a hazardous incident. These are valves for emergency isolation and are designed to stop the uncontrolled release of flammable or toxic materials. Any valve in the fire zone handling flammable liquid should be fire-safe.
Generally, a metal-seated ball valve, gate valve, butterfly valve can be used as an EBV to cutting off or isolation. It is generally installed between the inlet pressure source and the regulator. When the pressure of the protected system reaches a specified value, the valve will be quickly closed, cut off or isolated to avoid the occurrence of fire, leakage and other accidents. It is suitable for gas, natural gas and liquefied petroleum gas and other combustible gas storage, transportation, etc.
The emergency block valve is installed on the inlet and outlet pipeline of the liquefied hydrocarbon spherical tank. API 2510 “design and construction of liquefied petroleum gas (LPG) facilities” provides that the block valve on the liquefied hydrocarbon pipeline shall be as close as possible to the tank body, preferably close to the tank wall pipe outlet flange for easy operation and maintenance. When a 38 m³ (10,000 gals) liquefied hydrocarbon tank is on fire for 15 min, all block valves located in the pipeline below the highest liquid level of the tank shall be able to close automatically or operate remotely. The block valve control system shall be fire-safe and manually operated. API RP2001 “oil refinery fire prevention” explicitly requires that “emergency block valves should be installed at the nozzles below the liquid level of containers containing a large amount of flammable liquid.
API RP553 specifies the basic principles of setting emergency block valves for compressors, pumps, heating furnaces, containers, etc. It is closely related to the size of the equipment volume, medium, temperature, as well as the pump power and capacity. According to the requirements and design cases, emergency cut-off valve EBV shall be installed on the exit (or inlet) line adjacent to the high fire hazard equipment and fully isolated to stop the release of flammable or toxic materials. The emergency block valve is generally required for high – fire equipment and fire zone.
High fire equipment includes:
A container larger than 7.571m (2,000 gallons);
LPG storage tanks larger than 15.5 m (4 000 gallons);
A container or heat exchanger whose internal temperature of combustible liquid exceeds 315℃ or whose temperature has exceeded spontaneous combustion;
The capacity of transporting combustible liquid such as hydrocarbon exceeds 45 m/h;
The power of the combustible gas compressor is greater than 150 kW;
A heating furnace in which combustible liquid is heated through a furnace tube;
The internal pressure is greater than 3.45mpa, and the mode is an exothermic hydrocarbon reactor.
An area within 9 m horizontal or 12 m vertical from high fire hazard equipment;
The area within 9 m from the spherical tank containing combustible medium, etc.