Implementation of the safety production technical specifications for nitration processes

1. In accordance with regulatory requirements, a dual thermometer should be installed for the nitration reaction, and it must be calibrated regularly. DCS thermometers and SIS thermometers are not considered dual thermometers; two separate thermometers should be installed, with the monitoring points located on different cards. 2. The basic process control system should be equipped with an automatic (emergency) shutdown function, which should be implemented in the DCS. However, a “soft” button should be provided on the operator interface, a physical button should be installed at the control room, and another physical button should be placed in a suitable location in the workshop, along with clear markings. This allows operators and on-site personnel to stop the machine quickly in emergency situations. SIS is also an independent protection system that can serve as a supplement in emergency situations. 3. In accordance with regulatory requirements, the automation control system shall be equipped with an independent dual-channel online uninterruptible power supply UPS on top of the normal grid power supply, with a continuous power supply duration of more than 60 minutes. DCS and SIS systems are each equipped with separate UPS units; these do not constitute independent dual-line online uninterruptible power supplies, and adjustments should be made in accordance with the requirements of relevant standards. .

Here is my understanding: 1. Redundant thermometers refer to two thermometers that serve the same purpose; for example, if there is one thermometer installed in the middle of a tubular reactor and another at the outlet, then these are not redundant thermometers. However, if there are two thermometers at the outlet, then those are redundant thermometers. 2. As long as you have temperature sensor redundancy and control valve redundancy, assign them to different cards to keep the instruments isolated; be careful that the interlock logic and instrument tag addresses change. The CPU, communication, power supply, and other modules of a basic process control system should be designed with redundancy – this is unnecessary to mention, as they are all redundant by design. 3. For the DCS soft buttons, hard stop buttons, and on-site stop buttons: run a cable from the site to the DCS control panel, connect it to a DI card, and program some logic such that when operators click on the screen buttons or press the hard buttons, the feed control valve is closed. 4. On top of the normal power supply, automated control systems should be equipped with independent dual-line online uninterruptible power supplies UPS – is this meant to be the mains power plus 2 UPS units? If the DCS and SIS use UPS power supplies, it can become 2 circuits.

There are already DCS and SIS in place; requiring a second thermometer for the DCS isn’t too much to ask… And since there’s an SIS shutdown system, does it really make sense to require another shutdown system as well? This high requirement is acceptable; the key point is that DCS and SIS are separate systems, each equipped with mains power and a UPS. Does DCS also need its own separate dual-UPS system? The cabinet is powered by two power sources: one from the mains and the other from a UPS. Is it necessary to set up a switching mechanism between the two UPS power sources? Do two UPS units supply power to the cabinet via one circuit?

Wasn’t this standard not officially released yet?

Yes, it’s a draft for gathering opinions, but experts use these standards to conduct their reviews……

My understanding is as follows: 1. For the nitration reaction, two thermometers should be used, and they need to be calibrated regularly. According to 5.4.5 a) 1), two thermometers should be installed for the nitration reaction, and these two thermometers must be located on different holders in order to ensure the safety and accuracy of the nitration process. Both DCS thermometers and SIS thermometers can be used as temperature sensor modules, but it is necessary to ensure that they are installed on different cards. Therefore, if the DCS thermometer and the SIS thermometer are located on different cards, the company is already in compliance and no changes are required. Of course, it is necessary to regularly check whether these thermometers are working properly. 2. Basic process control systems should be equipped with an automatic (emergency) shutdown function. In accordance with clause 5.4.6, the DCS shall be equipped with an automatic shutdown function; a \"soft\" button shall be provided via the operator interface, physical buttons shall be installed in the control room and on-site, and prominent signs shall be placed at the workshop site. In addition, the SIS system should also be equipped with an automatic emergency shutdown function to prevent accidents such as operational errors. Therefore, both DCS and SIS systems should be equipped with appropriate shutdown functions to ensure safety. 3. The automated control system shall be equipped with independent dual-channel online uninterruptible power supplies (UPS), with a continuous power supply time of over 60 minutes. In accordance with the provisions of 5.4.9, automated control systems shall be equipped with dual-line online uninterruptible power supplies (UPS), and the continuous power supply time of such UPS should be greater than 60 minutes to ensure that the system can continue to operate in emergency situations such as power outages. DCS and SIS systems should be equipped with separate UPS units, and these UPS units must meet the required standards to ensure the continuous operation of the systems. Therefore, both DCS and SIS systems should be equipped with UPS units that meet the required standards to ensure system reliability in emergency situations.

5.4.2 DCS systems should be the preferred choice for basic process control systems. The CPU, communication, power supply, and other modules of the basic process control system should be provided redundantly. Key monitoring points that require redundant setup, such as dual thermometers and dual shut-off valves, must be configured on different IO cards. There’s another sentence earlier saying that for DCS, two thermometers are required, while SIS needs one; three thermometers per reactor... What exactly is a shutdown system? The DCS emergency shutdown feature seems a bit, how should I put it, an extra layer of safety measure – and it’s certainly good to have that – but I still think it’s excessive, a bit overkill. It's certain that both DCS and SIS need to have independent UPS. But the expert I met this time said that the original text states that an automated control system should be equipped with independent dual-Path UPS, which means the same thing: two DCS systems and one SIS system, along with one UPS

A parking system refers to a mechanism by which, in abnormal situations, the control system automatically shuts down the equipment and takes appropriate safety measures to ensure the safe operation of the factory, such as overload protection, power failure protection, leakage protection, etc. In the design of control systems, the application of parking systems is crucial, as they can ensure safety in emergency situations. The independent dual-UPS systems for DCS and SIS systems are designed to ensure that the control systems can continue to function properly in the event of sudden power outages or other power supply failures, thereby maintaining the safety of the factory. Furthermore, an independent dual-path UPS can also ensure the reliability and redundancy of the system, as there is another path available to use if one of the paths fails. In general, both the parking system and the independent dual-path UPS are designed to ensure the safety and reliability of automated control systems. In the design and operation of control systems, it is necessary to pay attention to the settings and applications in these areas in order to further improve the production efficiency and safety of factories.

It’s pretty absurd. 1. The so-called dual thermometers as specified mean one for DCS and one for SIS – that’s what constitutes dual thermometers. Furthermore, from the perspective of process hazards, whether a DCS is equipped with dual thermometers has no effect on reducing the likelihood of potential hazards. 2. Installing emergency shutdown systems separately for DCS and SIS is of no practical value; it does not improve availability nor safety. Before the SIS system was introduced in China, emergency shutdown operations were ultimately carried out through DCS; the same is true for some companies that still do not have a SIS system today. If a company has an SIS system in place, emergency shutdown operations are generally carried out through that system. Whether it is DCS or SIS, an emergency stop can only be triggered by the operator pressing the emergency stop button; even if multiple systems are installed, this does not help reduce the potential for harm.

5.4.2 DCS systems should be the preferred choice for basic process control systems. The CPU, communication, power supply, and other modules of the basic process control system should be equipped with redundancy. Key monitoring points that require redundant setup, such as dual thermometers and dual shut-off valves, must be configured on different IO cards. 5.4.5 The safety control and interlock requirements for the nitration reaction are as follows: 1) The nitration reactor shall be equipped with dual thermometers, which must be calibrated regularly ； The experts conducted their checks based on these two requirements; in their view, the DCS system used in the nitration process should be equipped with two thermometers. I completely agree with what you say – that’s also my understanding. But the experts… well, they do it in order to maximize safety and reduce their own liability