Intermittent reaction kettle, issues with the Safety Instrumented System (SIS) setup
Thread Content
Regarding the installation of a SIS in the batch reactor, the main reaction temperature is around 45°C; the temperature interlock value for the SIS is currently set at 50℃； However, before the reaction begins, there is a step of drying the tank, with the temperature at around 60°C. If the SIS remains active, it will be triggered during the can drying process. Currently, SIS is manually activated at the start of a reaction, but safety checks generally do not allow this. Do the experts have any solutions? Production is carried out in two batches per day, requiring repeated bypassing of the SIS before it can be put back into use.
Regarding your question, the following possible solutions can be considered: 1. **Use a two-stage temperature alarm system:** The first alarm level is set at 50°C; when this temperature is reached, the operator receives a notification to take action； The second level is SIS, which sets a higher cut-off temperature value such as 65°C or 70°C. In this way, the temperature can reach 60°C during tank drying without triggering the SIS ； During the actual reaction process, if the temperature exceeds 50°C, the operator still has time to take action; cutting off occurs only when the temperature rises further to the second alarm level. 2. **Secondary equipment design:** Consult equipment suppliers or design firms to see if it is possible to install secondary equipment for proper can drying; such equipment allows for a higher cutting temperature to be set. 3. **Set up a dedicated can drying mode:** Define a can drying mode in the control system; it is only in this mode that the SIS cut-off temperature increases. Once the can drying is complete, this mode is exited and the cut-off temperature returns to its original setting. All of the above solutions require a detailed evaluation in light of the actual operating environment and relevant safety regulations, and it is essential to consult with the relevant safety inspection departments and obtain their approval before making any adjustments. .
I would like to share my personal opinion for discussion: Could we add a step for judging the reaction status? For example, by using the liquid level in the reactor as a criterion – if there is no liquid or the level is low during drying, the program should determine that it is in the drying phase, and at that point the temperature control parameters specified for that step should be applied； The reaction process, on the other hand, uses control parameters determined based on the liquid level to carry out the reaction. Of course, the parameters or meter readings used for determining this sequence must be reliable; for example, a three-to-two voting mechanism can be employed. The above are my personal thoughts; please discuss and offer suggestions on their feasibility.
We also operate in a semi-batch mode; the SIS system is used to determine the production conditions. For example, it takes into account the opening degree of the feed control valves for the main reactants, as well as other parameters such as temperature and pressure. In other words, interlock actions are triggered only when these parameters exceed the set values, and this occurs during the process of adding the main reactants to the reactor – assuming a semi-batch mode, where reactants are added gradually rather than all at once in a pure batch process.
The SIS interlock value is not designed properly; it should be higher than 60 degrees Celsius, as 50 is considered a value suitable for process-related interlocks.
The interlocks (SIS) and process interlocks (DCS) are not clear; the interlock at 50°C should be implemented within the DCS. Step-based checks can be added to ensure that interlocking occurs only when all conditions are met； The 60℃ interlock should be implemented via SIS (condition-based checks are not recommended, although they can be added; generally experts reject this approach due to safety concerns regarding the possibility of those conditions failing).
It should have been taken into consideration during the design phase, when determining this SIL rating
This is the most feasible approach; additional conditions can be added to trigger the SIS interlock – for example, the interlock activates when the temperature reaches 50 degrees while the mixer is running, but no interlock occurs even if the temperature reaches 100 degrees when the mixer is not running
A BOOL variable is set on the DCS side, with two states: oven operation and normal reaction. These two states have different SIS temperature values, and logical interlocks are implemented by using the status value from the DCS. As for the 2 states on the DCS side, they can be switched manually by the operator or determined through DCS logic. It is not recommended to disable the SIS interlocks in order to dry the equipment; with the SIS interlocks still in place, the interlock value for the drying temperature will simply be a bit higher.
This post was last edited by sun_fm on 2023-11-1 09:55. In such cases, an OOS setting should be used (please note the difference between OOS and MOS, as well as the requirements for management). The procedures for implementing OOS – such as the regulations regarding bypass operations and automatic mechanisms – can be found in standards such as HGT20511, GBT50770, GBT50892, and GBT50823. For example, according to 5.3.6 of GB50823, input signals that affect the start-up of a process should be equipped with operation override (bypass) switches; the delay time for these overrides should be set based on the process requirements, and the operation override should be automatically disabled once the process is operating normally or after the specified delay has elapsed.
Is it possible to implement sequential control, such that after a process starts, a certain defined period of time is considered the first step? . .