CONDUCTING A HAZOP STUDY OF THE PYROLYSIS PROCESS FOR PROCESS SAFETY IMPROVEMENT

ПРОВЕДЕНИЕ HAZOP-АНАЛИЗА ПРОЦЕССА ПИРОЛИЗА ДЛЯ ПОВЫШЕНИЯ БЕЗОПАСНОСТИ ТЕХНОЛОГИЧЕСКОГО ПРОЦЕССА

Тегиспай Дильназ Алибековна

магистрант, школа химической инженерии, Казахстанско-Британский технический университет,

РК, г. Алматы

Негим Аттиа Эльсайд

научный руководитель, проф., Казахстанско-Британский технический университет,

РК, г. Алматы

ABSTRACT

Ensuring the safety of technological processes in the oil, gas, and petrochemical industries requires the application of systematic hazard identification methods at early stages of design and operation. One of the most effective tools for such analysis is the HAZOP methodology, which enables the identification of potential process parameter deviations and the assessment of their impact on operational risks. Pyrolysis is among the most hazardous industrial processes due to high temperatures, pressure fluctuations, flammable product formation, and the risk of thermal runaway. This study examines the key stages of conducting a HAZOP analysis for a typical pyrolysis unit, including node selection, deviation identification, modeling of potential causes and consequences, and evaluation of existing protective barriers. The results demonstrate that systematic hazard analysis allows for the early identification of critical failure scenarios, reduction of accident probability, and development of recommendations aimed at improving the technological and industrial safety of the facility.

АННОТАЦИЯ

Повышение безопасности технологических процессов на предприятиях нефтегазовой и нефтехимической отрасли требует применения системных методов анализа опасностей на ранних стадиях проектирования и эксплуатации. Одним из наиболее эффективных инструментов такого анализа является метод HAZOP, позволяющий выявлять потенциальные отклонения параметров процесса и оценивать их влияние на риски. Процесс пиролиза относится к категории наиболее опасных технологических операций из-за высокой температуры, давления, образования легковоспламеняющихся продуктов и возможного теплового разгона. В данной работе рассматриваются ключевые этапы проведения HAZOP-анализа для типовой установки пиролиза, включая выбор узлов анализа, идентификацию отклонений, моделирование возможных причин и последствий, а также оценку эффективности существующих защитных барьеров. Результаты исследования демонстрируют, что систематический анализ опасностей позволяет своевременно выявлять критические сценарии отказов, снижать вероятность аварийных ситуаций и формировать рекомендации для повышения технологической и промышленной безопасности объекта.

Keywords: HAZOP; hazard identification; pyrolysis; process safety; technological risks; deviations; safety barriers.

Ключевые слова: HAZOP; анализ опасностей; пиролиз; промышленная безопасность; технологические риски; отклонения параметров; защитные барьеры.

Pyrolysis is an energy-intensive and highly dynamic thermochemical process used for the conversion of hydrocarbon feedstocks into valuable petrochemical products such as ethylene, propylene, butadiene, and aromatics. The operation typically involves extremely high temperatures (450–900 °C), rapid heating rates, complex reaction mechanisms, and a high degree of sensitivity to variations in operating parameters. These characteristics place pyrolysis units among the most hazardous installations in petrochemical facilities. Conducting a HAZOP study for such a process provides a structured framework for identifying potential deviations, understanding their causes and consequences, and evaluating the adequacy of existing engineering and administrative safeguards. [1-2]

A classical pyrolysis system consists of several major components, including feed preparation units, furnaces or reactors, transfer-line exchangers, quench systems, separation columns, compression trains, and product recovery sections. Each of these nodes exhibits distinct risk profiles due to the interplay of temperature, pressure, feed composition, and catalyst or heat-transfer medium behavior. The HAZOP methodology allows for a systematic examination of each node, using guidewords such as No, More, Less, As well as, Reverse, and Other than to uncover hidden failure scenarios that may not be evident during routine design or operation.

The feed system is typically one of the critical nodes analyzed first. Deviations such as “No flow,” “Low flow,” or “Wrong composition” can originate from pump malfunction, blockage, incorrect blending, or contamination with oxygenated compounds. Such deviations may lead to incomplete vaporization, cold spots in the reactor, increased coking rates, or dangerous interactions with hot process streams. The presence of oxygen in particular poses an immediate risk of explosive mixtures when introduced into a high-temperature reactor environment.

In the reactor or furnace zone, the key hazards relate to excessive temperatures, loss of heat transfer control, and thermal runaway. A deviation such as “High temperature” may be caused by burner malfunction, fouling of heat-transfer surfaces, poor circulation of feed, or unexpected exothermic side reactions. The consequences include accelerated coking, tube metal overheating, structural deformation, breaches of containment, and fire hazards. Conversely, a “Low temperature” deviation results in incomplete cracking, reduced product yield, increased tar formation, and the buildup of unstable intermediates. The dynamic characteristics of pyrolysis can amplify minor disturbances, meaning that the lack of effective and well-tuned control loops significantly increases operational risk.

Further downstream, the quenching and separation systems also present significant hazards. Because pyrolysis products must be rapidly cooled to inhibit secondary reactions, deviations such as “Low quench flow” or “Delayed quench” may allow undesirable polymerization reactions or runaway exothermic behavior, leading to plugging or overpressure events in the downstream equipment. Separation columns, especially those involving light hydrocarbons, introduce additional risks related to reflux failures, tray flooding, excessive pressures, and reboiler malfunction. The physical properties of cracked gas mixtures, which often include hydrogen, methane, ethylene, acetylene, and aromatics, mean that even small deviations can create flammable or explosive atmospheres. [3]

One of the strengths of the HAZOP methodology is its ability to evaluate the sufficiency of existing safety barriers. For pyrolysis units, typical safeguards include high-integrity pressure protection systems (HIPPS), emergency shutdown valves, relief and flare systems, inerting and purging arrangements, interlocks, dual instrumentation, predictive temperature control, and advanced diagnostic monitoring. The HAZOP assessment identifies gaps in these safeguards, such as insufficient reaction-rate monitoring, inadequate trip setpoints, poor alarm management, and slow operator response times.[1] For example, if a “High pressure” deviation occurs in the cracking furnace transfer line, the analysis evaluates whether existing relief devices are adequately sized, whether isolation valves respond quickly enough, and whether the flare system can handle the surge capacity without excessive backpressure.[4]

The findings of this study reveal that conducting a comprehensive HAZOP analysis for pyrolysis units significantly enhances process safety. The technique enables the identification of domino-type failure sequences, where minor deviations evolve into major accidents through a chain of interdependent events. Additionally, the study highlights the importance of integrating HAZOP results into broader risk-management frameworks, such as layers of protection analysis (LOPA), safety instrumented systems (SIS) design, reliability calculations, and management-of-change (MOC) procedures. Implementing recommendations derived from the HAZOP, such as installing additional temperature sensors, improving quench reliability, upgrading burner management systems, or strengthening operator training, contributes to substantial reductions in operational risk. [5]

Overall, the application of the HAZOP methodology to the pyrolysis process demonstrates its value as a systematic, rigorous, and highly informative tool for enhancing industrial safety. By identifying critical deviations, understanding the mechanisms of hazard escalation, and evaluating protective layers, the method supports safer process design, more reliable operation, and improved emergency preparedness. The detailed results of the HAZOP study form a solid basis for engineering decisions aimed at reducing accident probability, optimizing process stability, and ensuring compliance with increasingly stringent industrial safety standards.

References:

1. DeSantis, E. A. Non-proprietary summary: process hazard assessment of autothermal pyrolysis system // LLNL-TR-819118. — 2021. — P. 1–27.
2. Marhavilas, P. K., Filippidis, M., Koulinas, G. K., Koulouriotis, D. E. A HAZOP with MCDM-based risk-assessment approach: focusing on deviations with economic / health / environmental impacts in a process industry // Sustainability. — 2020. — Vol. 12, № 3 — Article 993.
3. Elsdon, R.; Pal, D. Waste-to-energy plant process safety challenges (including pyrolysis) // Hazards XXII Symposium, IChemE. — 2011. — P. 1–12.
4. Choi, J. Y. HSE-HAZOP: application of HAZOP for health, safety and environmental engineering in process industry // International Journal of Environmental Research and Public Health. — 2020. — Vol. 17, № 10 — Article 3665.
5. Almousa, A. A., … Incorporating resilience into HAZOP to enhance process safety // Journal of Loss Prevention in the Process Industries / process safety journal. — 2025.