Process Intensification Vs. Reliability

Over the centuries the equipment used by the process industry went through little changes: it have been perfected but it have never been substantially changed. Indeed the type of chemical reactor currently used is the stirred tank, that works in the same way of a similar one built in 1800; logically, materials, control systems or safety systems changed, but the basic engineering remained the same. In recent years, a new equipment was proposed: it performs the same functions as the existing one, occupying less space, requiring less power and operating in a safer way. The changes required in a plant to achieve the above mentioned objectives are called Process Intensification; it can be described as the following: “Any chemical engineering development that leads to a substantially smaller, cleaner, safer and more energy efficient technology is process intensification”. From the Process Identification point of view, it is possible to mention the development of new equipment, such as the Spinning Disk Reactors and Heat Exchange (HEX) Reactors, characterized by a remarkable technological jump with respect to the existing equipment: designers began to use physical phenomena previously neglected, such as the centrifugal force in the spinning disk reactor, or to combine into one equipment more unit operations, such as Reverse-Flow Reactors, Reactive Distillation ... These recent developments certainly provide more compact and cleaner plants, but there are more uncertainties about their capability to produce an actual increase of the safety. The use of more complex equipment, in example with moving parts or with more intense sources of energy, can even bring to safety problems not detected in traditional plants, also modifying the reliability of the system. Under the definition of Process Intensification it is possible to indicate different kinds of improvements to the plants: in order to analyze the effects of these improvements on safety and reliability, we made an assessment of the reliability in a traditional plant, and in an intensified plant, comparing their results. The process analyzed is related to a plant for the VOC (Volatile Organic Compound) abatement in a stream of inert gas. The traditional system is based on a fixed bed reactor; the intensified plant uses a Reverse-Flow Reactors. The selected plants were firstly subjected to a traditional safety analysis, using an operability analysis and then operating the extraction and quantification of the fault trees. During the analysis, we realized that the traditional methods (HAZOP and FT) worked well if applied to conventional systems, which arrive to a steady-state, but they were less suitable for modern plants, that work in a transitional regime. After the traditional safety analysis, we proceeded with a Integrated Dynamic Decision Analysis, that allows to evaluate more in detail the behavior for not stationary plants, in case of failure. From the application of the methodology to the specific case some general conclusions have been drawn.