Preliminary Study on the Inclusion of Inherent Safety Principles Using Property Design Framework

Fadwa T. Eljack, Department of Chemical Engineering, Qatar University, P.O. Box 2713, Doha, Qatar and Mario Richard Eden, Department of Chemical Engineering, Auburn University, 222 Ross Hall, Auburn, AL 36849-5127.

The word safety in design signals accident prevention and protective measures. On a larger scale, safety in processes involves the risk of operating process units and operating conditions, supplied and generated substances as well as a number of other parameters that would affect the safety of people, the environment or the surrounding property (Suardin et al., 2006).

Traditionally there are safety preventive/protective measures, generally applied after implementation of process plant design; and it has been reported to account for 15-30% of capital cost in the petroleum and gas industry (Palaniappan, 2004). Such methods are not all encompassing and hence, failure to identify risks, and according the inability to address or "control" these risks, can result in massive costs, both human and economic. To minimize the risk of hazardous conditions, Kletz (1991) introduced four inherent safer design concepts: minimize, substitute, moderate and simplify. Inherent safer design looks at involving safer concepts at the pre-design stage in order to identify a truly optimal design. Incorporating Kletz's safety design issues into a design algorithm changes the dynamic of what is truly an optimal design. Typically in process design the objective is to identify most favorable operating conditions that maximize productivity. However, considering the safety of those operating conditions (Kletz's second design concept) might alter the optimality of the proposed design.

The objective of the work here is to use the property platform as means of incorporating process safety in the preliminary stages of design. Current application of inherent methods exists, however according to Hendershot (2006), there is still a need to develop specific tools and techniques for the application of inherently safer design. The literature clearly shows that the lack of information in the preliminary phases of design complicates the inclusion of safety in traditional design approaches. Recently, the Property Integration design framework was introduced as a targeting methodology that identifies optimum process performance ahead of design. The clustering method defines and solves the design problem within a property framework. The key feature of this method is that it transforms all of the constraints placed on the design problem into properties, and it uses it as way to identify the feasible solution region. At the same time, principles of inherent safety such as minimization and limiting effects refer to changing the initial conditions/constraints of the design problem. So it would make sense to include such safety principles into the property design methodology.

The work will outline a robust property-based process design methodology using recently developed property clustering technique that will consider the needs of operating process units and the safety risk within the formulation and solution steps. Moreover, the methodology will develop a systematic scheme to transform safety hazards associated with the various process units and streams in terms of properties or functionalities. Safety risks or process hazards will be utilized as another constraint on the design problem. The translated constraints placed on the design allow for the identification of process unit property targets ahead of design. This is a systematic method for placing bounds on the search space without loosing accuracy; hence the approach will be able to enumerate all design alternatives. Thus the presented paper will propose a framework for the incorporation of safety in the preliminary stages of design by infusing Inherent Safety Principles into the Property Clustering Platform.

Keywords: process design, inherent safety, property design