A systematic Hazop procedure for batch processes, and its application to pipeless plants

Abstract

Abstract Increasing technological complexity together with social and legal pressures have made it necessary to develop more effective approaches to safety. This need is particularly strong in the design and operation of chemical plants. One approach, Hazard and Operability Study (Hazop), is a method of systematically identifying every conceivable process deviation, its abnormal causes and adverse hazardous consequences in a chemical plant. The technique was developed by ICI in the 1960s, and has been standardised for use in continuous manufacturing plants. Improvised attempts have been made to modify the continuous Hazop approach for use with batch processes, such as using different guide words and deviations, without the method of application being formalised. There are different issues that need to be surmounted for the methodology to be applied to batch processing plants. The standard approach, of examining a system line by line, is ideal for continuous processes but does not lend itself to the thorough examination of batch processes. A typical batch plant can be examined by dividing the process into three operational phases: charge, reaction, and discharge. A modified Hazop methodology should then be applied to the description of each phase. Although a need for this type of approach has been recognised, there is no published information to be found on an agreed format on how this should be done. This paper presents a formalised approach to applying the Hazop methodology to batch processes. A way forward in multi-product manufacturing is the emerging technology of ‘pipeless plants’. The basic idea is to move the process vessel between fixed stations for mixing, separation and other activities. This offers great flexibility for change, and allows a company to respond quickly to market demands and technological advances. Little research has been done on the safety of pipeless plants, which are essentially batch plants with mobile vessels. Therefore the batch Hazop methodology presented in this paper has been further developed in order to improve the safe design of pipeless plants.