External Fire When a storage tank is exposed to flame, the contents stored in the container are heated due to radiation, convective heat transfer, and direct contact with the flame, causing the pressure to rise. To ensure that the pressure inside the container does not exceed the maximum allowable pressure, a Gate Valve should be installed. If the Gate Valve's relief capacity is less than the amount of steam generated, the pressure in the container will rise above the maximum allowable pressure, causing a container explosion. According to APIRP520, the Gate Valve discharge amount in case of fire is calculated based on the liquid-containing surface of the container as follows:
(1) For horizontal and vertical containers, the surface area of the entire container is the wetted area.
(2) The wetted surface area of the fractionation tower can be assumed to be the sum of the surface areas of the bottom of the tower and the liquid-containing portion of the tray at a height of 715m.
(3) The compressor outlet buffer tank generally contains only half of the liquid, and the wet surface area is calculated as 50% of the total surface area of the container.
(4) The wetted surface area of the pipeline in the fire zone is 10 to 20 times the surface area of the storage tank.
The rupture of the heat exchange tube determines whether the heat exchanger is equipped with pressure protection when the heat exchange tube overpressure ruptures, and should be considered together with the overpressure situation of the entire low-pressure system. When the design pressure on the low-pressure side of the heat exchanger is less than 2/3 of the design pressure on the high-pressure side, it should be considered as an accident condition. Calculation of rupture of heat exchange tubes is based on APIRP520 regulations. Calculate the flow rate of the required pressure relief area by multiplying the medium flow rate of the ruptured heat exchange tube by 2 based on a sharp-edged orifice plate with the same fracture area as the ruptured heat exchanger tube. The size of the Gate Valve used for liquid expansion and pressure relief of liquid expansion shall not be less than DN20. The rectification system takes depropanization and rectification as an example. The Gate Valve emission considerations include equipment related to the rectification system, regulating valves and cut-off valves. The setting position and consideration of the Gate Valve See factors, emissions and calculation instructions.
The separation system of the ethylene plant mainly includes a washing tower, a distillation tower, and an absorption tower. The washing tower is mainly a primary separation tower. The decisive factor in the release amount of the
Universal Valve is the gas phase amount of the feed; the distillation tower is mainly a deethanizer tower, a deethanizer tower, and a degassing tower. For methane towers, depropanizer towers, ethylene distillation towers, propylene distillation towers, etc., the decisive factor in the release volume of the Universal Valve is the failure of condensation at the top of the tower or the maximum input volume of the reboiler at the bottom of the tower, which is closely related to the material properties and composition; absorption The determining factor of tower Universal Valve is fire and other factors. Gate Valve flow discharge coefficient The flow discharge coefficient is an important parameter that affects the Gate Valve nozzle area. It is usually taken as 01975 in the design calculation stage. It is generally difficult for domestic manufacturers to achieve this value, and it usually needs to be re-confirmed by the Gate Valve manufacturer.
Gate Valve size Due to changes in flow discharge coefficient, the structural size of the Gate Valve may change. The structural size of the Gate Valve should be re-confirmed, and the process and Gate Valve inlet and outlet piping sizes should be adjusted. Gate Valve discharge amount The calculated discharge amount of the Gate Valve is used to calculate the Gate Valve nozzle area and selection. The actual discharge amount of the Gate Valve should be back calculated based on the nozzle area determined by the selection. The discharge amount will increase to varying degrees. The inlet resistance drop of the Gate Valve and the inlet pressure drop of the spring Gate Valve must not exceed 3 times the fixed pressure value of the Gate Valve, otherwise it will affect the use of the spring Gate Valve. When calculating the pressure drop at the Gate Valve inlet, the pipeline resistance drop should include all pipelines from the protection equipment to the Gate Valve inlet. In order to reduce investment in Gate Valve, when calculating a large discharge volume, multiple Gate Valve are generally connected in parallel. When calculating, it should be noted that the discharge volumes of different pipe sections are different.
