Process safety is a fundamental aspect of the chemical industry that must operate hand in hand with production targets. This issue became the focus of a study conducted by Nisa Eka Rahmania, a student of the Industrial Chemical Engineering Technology (TRKI) Study Program at the Vocational School of Diponegoro University, through a case study on the implementation of an Interlock System and Process Logic in the granulation recycle loop unit of the NPK Phonska plant at PT XYZ.
The study was based on a scenario in which dryer M-362 tripped due to an outlet temperature exceeding its operational limit. Under normal conditions, such an event should trigger a series of automatic shutdowns of interconnected equipment, including the furnace, blower, elevator, granulator, and finishing units. However, in the case analyzed, the granulator continued operating in bypass mode even though the dryer had stopped.
As a result, several unsafe conditions began to emerge. Pressure within the granulator increased, material accumulated in the recycle system, and several supporting units continued operating despite disruptions in product flow. These conditions ultimately triggered an Unsafe Furnace Condition alarm, indicating a deviation from safe operating conditions.
Through process logic analysis, Nisa identified several failures in the implementation of interlock and permissive logic systems. One significant finding was a situation in which the photocell could no longer detect a flame in the furnace while the gas valve remained open. This condition could potentially lead to gas accumulation inside the combustion chamber, increasing the risk of fire or explosion if an ignition source were present.
Based on the root cause analysis, the primary causes of the problem were not limited to the dryer trip itself. The uncontrolled use of bypass mode and the failure of the automatic shutdown logic to function according to the process safety design also contributed significantly. As a result, the layers of protection intended to safeguard the system were unable to operate effectively.
As corrective measures, Nisa proposed several technical recommendations. These include implementing a maximum time limit for bypass mode, ensuring that the granulator automatically shuts down if the dryer remains out of operation for a specified period. In addition, the gas valve should only be allowed to open when all safety conditions are satisfied, such as confirmed flame detection, an active combustion blower, and normal dryer operation. The use of a dedicated key switch for bypass activation by authorized personnel was also recommended to improve operational control.
This study highlights the importance of understanding control systems, interlocks, and process safety in the chemical industry. Through industry-based case study analysis, TRKI students at the Vocational School of Diponegoro University not only gain knowledge of production process engineering but also develop an understanding of how safety systems are designed to prevent potential hazards and maintain the overall reliability of plant operations.