Process safety lessons from Chinese PX projects

Control Engineering International: Heavy chemical engineering enterprises are often involved in lengthy and complicated production processes. An accident can occur if an error occurs in any process. Advanced diagnosis and safety management systems can help enterprises predict and prevent accidents before and during occurrence, according to Control Engineering China.


Image courtesy: Control Engineering ChinaWith the explosion in Gulei Town, Zhangzhou, Fujian Province on the night of April 6, the term p-Xylene (PX) became a target of public criticism of safety accidents of chemical enterprises in the eyes of Chinese people. People who were unaware of the truth expressed their fury directly against site selection of the PX project and the supervision of government. For a moment, "keeping PX away from our home" became the appeal of the masses and environmental protection groups.

The explosion from the PX project in Gulei Town, Zhangzhou, was the second explosion at this factory within two years. Fires also occurred in PX devices in China National Offshore Oil Corporation's (CNOOC) Huizhou Refinery, Dalian Fujia Dahua, PetroChina Liaoyang Petrochemical, and Sinopec Shanghai Jinshan Petrochemical. As a combustible and low-toxicity chemical substance, PX has a very small influence on the surrounding environment during normal PX production and operations. Currently, no safety accidents have had a significant impact on the environment from PX facilities worldwide. So, why did accidents like fire and explosions occur in China's PX projects?

Process technology and devices?

Sinopec already mastered a whole set of aromatic hydrocarbon protection technologies including complete technology design, engineering construction, and production of high-efficiency absorbent as early as 2011. As a result, it became the third company owning complete aromatic hydrocarbon technology with proprietary intellectual property rights in the world (the other two companies were from the U.S. and France, respectively). Li Junfa, chief engineer of China National Petroleum & Chemical Planning Institute said, "Due to relatively late development, China has late-mover advantage instead, for the latest devices are available in the beginning. They are leading in the world in terms of energy conservation, environmental protection, and energy consumption. PX project construction of China is often settled at one go. The operation model and equipment level are better than what they reconstructed."

Technology-based safety guarantee?

Experts guessed that this accident resulted from the explosion and fire of the heating furnace and oil tank about 329 feet away from a burst heating furnace pipeline in the production operation area. Engineering, procurement, and construction (EPC) and site installation were handled by three Sinopec companies for the aromatic hydrocarbon heating furnace in question. Many engineers from Dragon Aromatics (Zhangzhou) Co., Ltd. disclosed that certain problems occurred with the material of the heating furnace tube. The person in charge of construction contracting unit of Dragon Aromatics also indicated that material problems existed in the equipment provided by Dragon Aromatics, stating, "Cracks can be seen during grinding. Although the product passed various detections, I can judge that it was not a brand-new product based on my industry experience."

We know that enterprises like Sinopec usually install a safety interlocking system in the production operation area. If the temperature of the heating furnace is too high, the automatic control devices of the safety interlocking system will control the supply of oil and catalyst, according to process operations set up in the project.

An engineer from Dragon Aromatics present at the explosion scene disclosed that the production operation area of this enterprise was also installed with a safety interlocking system. Unfortunately, it failed to prevent the expansion of the accident. A technical expert from Sinopec also thought that the explosion was related to operations: "If the heating furnace catches fire, the valve of the pipeline shall be shut down immediately to cut off connection. It can be at least manually shut down. If it is not shut down, it is because of wrong operation. As a result, the fire was spread to the tank area to trigger [the] explosion." 

Safety management is the last defense line of enterprise

Heavy chemical engineering enterprises often are involved in lengthy and complicated production processes. A safety accident is likely to occur if errors occur in any process. Effective safety management is the last defense line of enterprise. It is not difficult to sense the lack of safety management awareness from the explosion accident of the PX project in Zhangzhou.

Foreign PX companies attach great importance to employees' safety education and training: Chevron Phillips Chemical Company LLC, the largest PX producer in the U.S., requires regular check of various kinds of equipment, and its employees have to receive emergency operation training on a regular basis; Samsung Total, a famous PX producer of South Korea, requests new employees to receive safety training eight times a year. Additionally, each plant area is allocated with an independent firefighting teamand plans against natural disasters like lightning and tsunamis.

Aileen Jin, editor-in-chief, Control Engineering China, explains that the new environmental protection law in China may translate into large investments in controls, automation, and instrumentation. Courtesy: Control Engineering ChinaAs a large, technologically mature refining project, PX project shall be highly automated during the production process. Its advanced diagnosis and safety management system helps the enterprise predict and prevent accidents before occurrence and helps mitigate the effects during an occurrence. Safe operation and effective preventive measures are also a reason why many foreign PX projects dare to construct plants several hundred feet away from residential areas.

With the gradual enhancing of people's awareness of environmental pollution and protection, the past model of "governance after occurrence of problems" has been increasingly denounced. People can become willing neighbors to PX projects only if the safety management issues of the heavy chemical engineering industry are resolved first.

- Aileen Jin, editor-in-chief, Control Engineering China; edited by Joy Chang, digital project manager, Control Engineering,

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This was translated and edited for Control Engineering from Control Engineering China. 

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