Can an Lng shut-off valve be electric?

Of course. First, it must be explosion-proof; second, the cut-off time must meet the process requirements.

The explosion-proof measures for electric systems must be in place; those at our liquefying station are all pneumatic

Electric ones are acceptable; first of all, they need to have explosion-proof certification. However, electric options are much more expensive than pneumatic ones, which is why many stations do not use them.

Yes, electric valves are already being widely used in current LNG plants

ESDVs are required to be faulty; can electric valves meet this requirement for a fault state? Is it still necessary to install an additional accumulator?

For the selection of valves, reference can be made to chemical and petrochemical standards. First, understand the definition of a shut-off valve before selecting one; the following excerpt is provided for reference: What conditions must an emergency shut-off valve meet in practical use? Here, I divide these required conditions into two categories: selection criteria and operating conditions. First, I summarize the requirements regarding emergency shut-off valves in the standards as follows: According to the \"SH-T 3005-2016 Standards for the Selection and Design of Automation Instruments in Petrochemical Industries\", 10.1.6 states that when the process requires tight shutdown (TSO) of the control valve or when it is involved in emergency shut-off interlocks, the allowable leakage class for such valves should be at least grade V as specified by the GB/T 4213 or ANSI/FCI 70-2 standards. 10.3.6.7 A fusible plug should be able to be installed on the cylinder of the pneumatic actuator used for the emergency shut-off valve; the melting point of this fusible plug should be around 250°C. When the temperature of the cylinder reaches or exceeds this melting point, the fusible plug melts, allowing the pressure inside the cylinder to be released. This enables the spring on the other side of the cylinder or the compressed air in the air reservoir to push the piston and close the valve. 10.3.6.14 The pneumatic actuators and their accessories used for emergency shut-off valves shall have fire protection measures; preferably, fire protective covers should be installed. Such covers must comply with UL 1709 standards and be able to resist hydrocarbon fires for 30 minutes at 1093°C. 10.3.7.11 The electric actuators and their accessories used for emergency shut-off valves shall have fire protection measures; preferably, fire protection covers should be installed. Such covers must comply with UL 1709 standards and be able to resist hydrocarbon fires for 30 minutes at 1093°C. 10.3.7.12 The power cables and signal cables of the electric actuator used for emergency shut-off valves should be provided with fire protection measures. \"SH-T 3007-2014 Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems\" 6.4.1 Emergency shut-off valves that can be operated remotely should be installed on the inlet and outlet pipes for liquefied hydrocarbons at the bottom of liquefied hydrocarbon storage tanks. The actuator of the emergency shut-off valve shall have fail-safe measures. (Regarding fail-safe measures, the explanations of the relevant provisions take the following forms: a) Use of fail-safe single-cylinder pneumatic actuators) ； b) When using a double-acting cylinder pneumatic actuator, install an emergency air tank ； c) When selecting electric actuators, use those equipped with a UPS backup power source or built-in energy storage devices. According to SH-T 3104-2013 \"Code for Installation and Design of Instrumentation in Petrochemical Industries\", 9.4.1: Control valves and shut-off valves used in emergency shutdown interlocks do not require isolation valves or bypass valves. \"SH-T 3184-2017 Code for Design of Automation Systems in Petrochemical Tank Areas\" 5.4.1.13 Emergency shut-off valves used to interlock and cut off feed should be equipped with on-site manual valve closing buttons or switches outside the fire hazard area, so as to allow manual operation in emergency situations. Safety Supervision General Administration Document No. 3 [2013] 76, \"On Further Strengthening the Safety Design Management of Hazardous Chemicals Construction Projects\": (22) Emergency shut-off devices that can be operated automatically or manually via remote control should be installed on the pipelines for feeding and discharging materials from toxic material storage tanks, cryogenic storage tanks, and pressure spheres. GB 50160-2018 Code for Fire Protection Design of Petrochemical Enterprises, 6.4.2: When there are no buffer tanks within the station, an emergency shut-off valve that is easy to operate should be installed on the loading and unloading pipelines at a distance of 10 m from the loading/unloading cranes ； By summarizing the above provisions and standard specifications, the requirements that emergency shut-off valves must meet are as follows: (1) The actuators used for emergency shut-off valves and their accessories shall have fire protection measures; preferably, fire protection covers should be installed, and such covers must comply with UL 1709 standards, enabling them to resist hydrocarbon fires for 30 minutes at 1093°C ； (2) The power cables and signal cables of electric actuators should be provided with fire protection measures ； (3) The allowable leakage class for the isolation valve should be selected as Class V or higher as specified in the GB/T 4213 or ANSI/FCI 70-2 standards ； (4) The actuator of the emergency shut-off valve shall have a fail-safe shutdown function ； (5) On-site manual valve shut-off buttons or switches should be installed outside the fire hazard area ； (6) The emergency shut-off valves for toxic material storage tanks, cryogenic storage tanks, and pressure spheres shall have automatic or manual remote control functionality ； (7) An emergency shut-off valve may not be equipped with a isolation valve or a bypass valve ； The conditions outlined above regarding emergency shut-off valves are rather general and fragmented; they lack guidance in terms of operability and feasibility, and the details are incomplete. For example, there is no detailed discussion on aspects such as valve body selection, actuator design, the time required for closing, or specific fire prevention measures. Currently, there are two documents in China that provide guidance on the detailed selection of emergency shut-off valves. One is Document No. 518 issued by Sinopec in 2011, titled \"Regulations on the Selection and Design of Emergency Shut-Off Valves for Liquefied Hydrocarbon Spheres\", while the other is Document No. 635 issued by Sinopec in 2010, titled \"Interim Provisions on the Safety Technology Management of Liquefied Hydrocarbon Sphere Areas of Sinopec Group Corporation\". In particular, Document No. 518 details the selection criteria for emergency shut-off valves. Although the two documents issued by Sinopec are both related to liquefied hydrocarbon spheres, they can still be used as a reference for non-spherical storage devices and facilities that require the installation of emergency shut-off valves. Finally, I would like to add one more thing regarding emergency shut-off valves: compared to national standards, the foreign API (American Petroleum Institute) standards provide more detailed and specific descriptions. I’ve listed them here for those who are interested to take a look. API STD 2510-2011: Design and Construction of LPG Installations; API RP 2001-2012: Fire Protection in Refineries; API RP 553-2012: Refinery Valves and Accessories for Control and Safety Instrumented Systems; API STD 607-2016: Fire Test for Quarter-Turn Valves and Valves Equipped with Nonmetallic Seats; API STD 6FA-2018: Specifications for Fire Tests of Valves; UL 1709-2011: Rapid Rise Fire Tests of Protection Materials for Structural Steel

It’s best not to use it; advanced versions aren’t needed either. You can check the explanatory notes in the specifications for the specific reasons, as they are explained quite clearly there.