Add a flow-limiting orifice plate to the feed pipeline;

Regarding your process, since the pressure upstream is higher than that downstream, if the downstream valve is closed and gas flow stops, pressure buildup will occur; that is, the downstream pressure will become equal to the upstream pressure (whether it is a pressure regulator or a flow control orifice, when the fluid is at rest, the pressure drop is zero). Or, if the pressure relief valve fails and stays fully open, losing its pressure-reducing function, the pressure downstream may also become excessive. Therefore, if the design pressure of the downstream pipeline is lower than the operating pressure upstream, a safety valve must be installed to prevent damage to the downstream pipeline or system due to overpressure. Therefore, whether it is a pressure relief valve or a flow control orifice plate, if the design pressure downstream is lower than the highest operating pressure upstream, a safety valve must be installed. The difference lies in the discharge capacity of the safety valve, which may vary. If the gas flow rate is not constant, it is best not to install a flow control orifice plate, as the pressure drop changes with the flow rate.

As a supplementary note, this pipeline leads into the reactor, and the pressure rating of all pipelines is 5.0 MPa. The pipeline is connected to the reactor vessel, which is equipped with a safety valve in its gas phase area at the top. Since this is a renovation project, it is not possible to connect the medium discharge system to the flare system at present; therefore, efforts are being made to install additional safety valves

It seems that the purpose of the owner in installing a safety valve is mainly to ensure the safety of the reaction vessel, so that the reaction pressure inside it does not exceed 1.8 MPa. To this end, a safety valve can be installed on the pipeline before it enters the reaction vessel for overpressure relief. As the name implies, a flow control orifice plate serves to reduce the flow rate entering the next system, and the pressure level is then determined based on the conditions of the pipes downstream. For this reason, it is safer to install a safety valve; unless the amount of raw material fed in is quite large, flow control measures can be considered. This post was last edited by tiger771 on 2008-2-15 13:22.]

What is the design pressure of the reactor? It seems that the pipeline pressure rating is high enough, so there is no need to install a safety valve for this purpose. If the design pressure of the reactor is also higher than the highest operating pressure upstream, then overpressure is not possible in the event that the downstream valve closes or the control valve fails. In the case of overpressure, it turns into a fire; or if it is an exothermic reaction, the effect of the heat released by the reaction must also be taken into account. Check the design operating conditions and size of the safety valve on top of the reactor, as well as the set pressure. But we need to look further downstream as well – is the design pressure of the pipelines and equipment downstream of the reactor lower than the pressure upstream? As for controlling the reaction pressure, it falls under the scope of process control rather than safety protection; pressure control using control valves, along with high-pressure alarms and shutdown mechanisms, is fully sufficient. If necessary, a control valve for high-pressure venting can be added to allow for venting in case of overpressure. Safety valves are generally rarely used to control process conditions, as their operation for discharge is considered an accident.

A vent must be installed, as well as a safety valve.

There is already another safety valve on your equipment; if the material goes directly into the reactor, I don’t think it’s necessary to add another one, right?

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I think what you need to ensure is that the pressure behind the control valve reaches 1.8 MPa. If feed is introduced without adding a safety valve, and reliance is placed on the reactor’s own safety valve, then excessive pressure will affect the entire reactor. Add a flow control orifice plate; if the feed is unstable, it may affect subsequent reactions.

To reduce the pressure from 3 Mpa to 1.8 MPa, a diaphragm-type flow control valve can be used, which allows for more precise control of the flow rate of the medium in the tank. If a regular pressure control valve is used, a flow restriction orifice plate is necessary

For equipment and pipelines of the same pressure rating, if the equipment is equipped with a safety valve, there is no need to add one on the pipeline as well