Ethylene oxide storage tanks typically operate at a temperature of 0 5 and are designed to slow down the ethylene oxide polymerization reaction and reduce vaporization losses, which means that cooling facilities are necessary. 40% ethylene glycol-aqueous solution was used for coolingThe operating pressure is the saturation pressure at the corresponding temperature;The design pressure must be greater than the saturated vapor pressure corresponding to the ambient temperature (about 40) after the cooling outbreak, and 08mpa；The single tank charging factor is 085. If the double tank is set, the charging coefficient can be 05. It is convenient to pour the can when needed.
Gas. 
1) Key points of material selection and design.
Correct material selection is the most basic guarantee for project safety.
1. The material of the storage tank and pipeline is 304 or 316L, and cast iron, magnesium alloy, amalgam and other materials cannot be used
2. Double-end mechanical seal pump, preferably canned pump, magnetic pump or nitrogen pressure feeding, no packing seal or single-end mechanical seal machine pump Shielded pump: The cavitation allowance (NPSHA) of the device is not less than the required cavitation allowance (NPSHR) Magnetic pump: the inlet should be equipped with a strong magnetic filter;
3. Thermal insulation materials should prevent moisture absorption, do not use asbestos, porous mineral wool, magnesium silicate, calcium silicate, etc., and recommend the use of closed-cell insulation materials, such as foam glass wool
4. The material of the thermal insulation protective layer is preferably stainless steel, and the melting point of the aluminum protective layer is too low, so the iron protective layer cannot be used, and it is not recommended to use polyvinyl chloride (PVC).
5. The gasket is made of stainless steel winding high-purity (98%) flexible compressed graphite, with inner and outer rings, and gaskets with asbestos and asbestos filled materials and rubber materials cannot be used
6. The valve packing is made of corrugated high-purity (98%) flexible compressed graphite and pure polytetrafluoroethylene (PTFE) ring, and asbestos and asbestos filled materials cannot be used, and PTFE filled with glass fiber or ceramic is easy to absorb ethylene oxide
7. Gate valves, globe valves, high-performance butterfly valves, plug valves, and ball valves are relatively easy to polymerize, and it is necessary to consider whether the valve cavity structure is easy to accumulate ethylene oxide.
2) Key points of system design.
In the ethylene oxide process, it is important to prevent the mixing of dangerous impurities (e.g. water, air, rust, etc.), as well as to prevent leakage, gasification and polymerization. Ethylene Oxide Process System Design Essentials:
1. Conveying pipeline.
1) Avoid air bags and flexitanks, and take measures to prevent the backflow of materials
2) Use welding instead of flange connection to reduce the possibility of leakage;
3) The ethylene oxide pipeline should be cooled and insulated
4) The pipeline is equipped with a nitrogen purge line, and there are backstop measures
5) Avoid the situation of closed pipe section, such as a section of pipe between the two shut-off valves, if unavoidable, a safety valve should be set.
2. Nitrogen purge system.
1) It should be clear in the design description or operation instructions: before the storage tank is put into operation, it must be replaced with nitrogen to ensure that the nitrogen purity is 99More than 9%, and after the analysis and laboratory test qualified, the feeding;
2) The material is stainless steel;
3) Set the backstop and shut-off valves.
3. Blanketing system.
1) The blanketing pressure is not less than 05mpa；
2) Set the backcheck and shut-off valves.
4. Pump system.
1) The pump and the storage tank are arranged separately, and there is sufficient safety distance
2) Interlocking measures to prevent idling, no material conveying, and low-flow conveying;
3) High outlet temperature, high inlet and outlet temperature difference interlock pump stop measures.
5. Unloading system.
1) Design temperature: -10 20;
2) The filling coefficient is not more than 079kg/l；
3) The design pressure is 08MPa, and at the same time should be -01MPa check tank stiffness, design wall thickness to take the greater of the two;
4) The loading and unloading method of materials shall be adopted, and the loading and unloading pipeline shall be stainless steel metal corrugated hose, and the quick-connect joint with rubber sealing ring shall not be used
5) The automobile tanker containing ethylene oxide should be equipped with high-purity nitrogen cylinders, and should be equipped with an interface connected to the tank;
6) The purity of nitrogen for replacement should not be less than 999%, the oxygen content in the blanketing shall not be greater than 05%；
7) Car tanker should be equipped with flame arrester device.
6. Safety venting system.
1) Double safety valves, and used at the same time as the rupture disc;
2) The nitrogen purge measures set up in the vent pipeline can not only dilute the vent gas, but also prevent clogging
3) Separate discharge, prohibit mixed discharge into the flare system, device venting system;
4) There should be collection and treatment measures, and direct emptying is prohibited.
7. Safety Instrumented System (SIS).
1) The volume of the storage tank is greater than 11m?, you must set sis;
2) The SIS should be independent of the DCS operating system.
3) Safety instrumented system for ethylene oxide storage tanks.
1. The criterion of whether to set up a safety instrumented system.
If the volume of ethylene oxide storage tank is greater than 11m?In accordance with the regulations, an independent safety instrumented system must be installed. According to the requirements of the No. 116 document of 2014 of the General Administration of Work Safety: from January 1, 2016, chemical enterprises should design safety instrumented systems that meet the requirements of relevant standards for new chemical installations and hazardous chemical storage facilities involving "two key and one major" (i.e., key supervision of hazardous chemicals, key supervision of hazardous chemical processes and major hazard sources of hazardous chemicals).From January 1, 2018, all new chemical plants and hazardous chemical storage facilities involving "two key points and one major" must be designed with safety instrumented systems that meet the requirements.
2. List of safety instrument functions.
Due to the low critical level of major hazard sources of ethylene oxide, safety instrumented systems are generally required.
1) Ethylene oxide storage tank:
Trigger the liquid level gauge high-level alarm interlocking high-level interlock to cut off the ethylene oxide feed valve;
Trigger the combustible gas alarm instrument high-concentration alarm chain high-concentration open fire sprinkler on/off valve, and close the ethylene oxide feed valve at the same time
Trigger the combustible gas alarm (loading and unloading point) high limit alarm chain high high limit to open the fire sprinkler valve, and close the ethylene oxide feed valve at the same time
2) Emergency stop: trigger the manual confirmation interlock, close the discharge valve, open the fire sprinkler valve, close the circulating pump after 5min, and emergency venting, and the above actions are executed at the same time.
The design principles, key points, safety facility settings, and safety management points of ethylene oxide storage facilities are all based on the physical and chemical characteristics of ethylene oxide, which have the generality of engineering design and the particularity of the object, and the two are unified with each other. Designers and managers should firmly grasp the physical and chemical characteristics of ethylene oxide, and flexibly judge and apply it in combination with actual work, and implement safety principles and measures in place. Only in this way can we effectively improve the design quality, reduce the possibility of accidents from the source, and ensure the safe and stable operation of production equipment.