Syaza Izyanni Ahmad

Inherent safety assessment technique for preliminary design stage

Safety is defined as accidents prevention through appropriate technologies to identify and eliminate hazards before an accident occurs. Safety program that prevents hazards in the first place is preferable compared to the typical approaches of controlling the hazards upon being detected. Plants should be designed so that they are user-friendlier to the workers. This can be done by preventing the presence of the hazards in the process during its design stages. The concept of preventing hazards existence early during the design stage is called inherent safety. This paper introduces an inherent safety assessment technique for preliminary design stage (ISAPEDS) of chemical process. ISAPEDS focuses on assessing inherent safety using information available from the process flow sheet diagram (PFD). ISAPEDS is a technique that is an extension of the Numerical Descriptive Inherent Safety Technique (NuDIST) and the Graphical and Numerical Descriptive (GRAND) techniques developed by the same authors for application during research and development (R&D) design stage. There are five inherent safety parameters considered in this assessment which are operating temperature, operating pressure, flammability, explosiveness and toxicity. ISAPEDS introduces four new features as an improvement to the previous NuDIST and GRAND methods. First, instead of assessing these parameters as a standalone hazard factor, the parameters are assessed in relations to each other. For example the flammability parameter is evaluated in relations to the operating pressure while explosiveness parameter is evaluated in relations to the operating temperature. The second feature is assessing the chemicals as a mixture instead of as individual substance, which is a very rare scenarios in a typical chemical processes. Thirdly, the evaluation will be done comprehensively on each of the process equipment in the process flow diagram (PFD). The last one is the score of the safety hazards assessment in the whole process will be weighted based on the chemicals composition in the mixture. In this technique, a higher score is indicated as more hazardous compared to a lower score. A simple case study is performed on the hydrodealkylation process of toluene (HDA) focusing on three equipment which are the reactor (R101), the toluene feed drum (V101) and the low pressure phase separator (V103). The overall assessment shows that R101 is the most hazardous equipment in the process with the highest ISAPEDS score of 298.6 while V101 is the least hazardous equipment in the process with the lowest ISAPEDS score of 117.1. Among the three equipment, R101 was found to be the most hazardous in all five parameters resulting it to be the most hazardous equipment in the process section.

Inherent Safety Assessment Technique for Separation Equipment in Preliminary Engineering Stage

This paper highlights the development of new numerical approach for inherent safety assessment for separation process during the preliminary engineering stage of a typical petrochemical process lifecycle. Currently, existing inherent safety assessment technique for preliminary engineering phase did not specify the type of equipment they are applicable to as most of the methods can be used for any types of equipment generally. Aside from that, their assessment parameters are not exclusive to a certain type of unit operations. This new technique offers an inherent safety assessment focusing on chemicals safety during separation process. Parameters related to chemicals involved in separation process such as volatility, toxicity, flammability as well as explosiveness will be discussed. This technique will be constructed using logistic function which offers not only hazard assessment numerically but also graphically visualizes the effect of inherent safety parameters in designing an inherently safer process. The proposed technique can be used to effectively identify the level of hazards involved in process equipment besides highlighting the potential source of hazards in the process through numerical and graphical approach.

Safety Assessment Curve (SAC) for Inherent Safety Assessment in Petrochemical Industry

This paper highlights the development of a new numerical approach for safety assessment called Safety Assessment Curve (SAC). Most of the current methods for assessing inherent safety are index based method. Among the disadvantages of such methods is it employs scaling by dividing physical or chemical properties into subjective ranges and sudden jump in the score value at the sub-range boundary. This new technique can offer more useful features because aside from assessing the routes numerically, it could also graphically visualizes the effect of temperature, pressure, heat of reaction, process inventory, flammability, explosiveness, toxicity and reactivity in designing an inherently safer design for both, grassroot and retrofit cases in petrochemical industry without including subjective scaling and sudden jump in the score value. Due to page limitations, this paper will only discuss the development of SAC for chemical safety parameters. This novel technique can be used as an effective method to find the safer route among several number of alternatives for chemical synthesis or process retrofitting, besides highlighting the potential source of hazards in the process through numerical and graphical approach. The new SAC technique illustrated in this paper has been tested on methyl methacrylate manufacturing confirming its superiority in comparison to index-based method. Tertiery butyl alcohol (TBA) route has the lowest Chemical Safety Total Score suggesting it as the safest routes among the three routes for MMA production compared to acetone cyanohydrin (ACH) and ethylene via methyl propionate (C2/MP) based routes.