Batch process HAZOP

Here are three examples of hazards uncovered during hazops of batch processes ... 

HAZOP studies may be made on batch as well as continuous processes. For a continuous process, the working document is usually a set of flow sheets or piping and instrument diagrams (P IDs). Batch processes have another dimension time. Time is usually not significant with a continuous process that is operating smoothly, although start-up and shutdown must also be considered, when the continuous process will resemble a batch process. For batch processes, the working documents consist not only of the flow sheets or P IDs but also... 

In the process industry, a HAZOP study is most commonly applied to process line diagrams. A standard P ID (Process and Instrumentation Diagram) is a description of the future intent, typically the steady state of a continuous process. Batch systems can also be studied but in those cases a description of the batch process steps is required in addition to the P ID. In systems of mechanical process technology (powder and bulk solids), at various points, the characteristics of the solids and, if applicable, their interactions with each other and with process fluids and their possible deviations must be included in the study. 

A What-If analysis can be organized in one of two ways. The first is to divide the facility into nodes, rather like a HAZOP, except that the nodes are typically bigger and more loosely defined. The second approach is to organize the analysis by major items of equipment rather like an FMEA, and then to discuss the different types of failure mode for each. These two approaches are discussed below. Guidance to do with utilities, batch processes, operating procedures, and equipment layout is also provided. 

As defined in the CCPS Book "Guidelines for Hazard Evaluation Procedures (CCPS, 2008), the nodes can be the operating steps in a batch process analyzed by a HAZOP study. Following this approach, the nodes were based on the coke drums steps hsted on Table 1. Therefore, for each step of the coke drum cycle, a node was defined considering the drum and aU the ahgmnents needed to perform that phase. Preferably, the nodes boimdaries included the valves that should be opened to allow the operating step to occur. 

The batch process reactor system adds more flexibility but is probably the biggest contributor to waste generation. A detailed breakdown of the unit operations will give clear indications to the areas of manipulation which give most impact on waste minimisation. A step by step breakdown, as used in a Hazard and Operability (HAZOP) study, is applicable to optimising batch processes with respect to waste minimisation. 

Out of sequence and missing are additional guide words found in batch processing. This checklist of guided words will be helpful in HAZOP analysis. In most cases, parameters and associated guided words are quite obvious With these general ideas and HAZOP study philosophy in mind, it is better to concentrate on the actual procedure. 

Batch process relies highly on procedures to be followed, and in batch process, state changes are much more in normal operation than a continuous plant. In batch process, deviations can develop both from process variable deviation as well as from procedure deviation. In its simpler term, a (chemical) batch process can be conceived of three major operations, viz. charge, reaction, and discharge operations. Therefore, a HAZOP can be carried out thrice in terms of charging operation and discharging, as shown in Fig. Vl/3.4 1. 

A mle-based system for automated batch HAZOP is another approach for batch process. In this system, state-based simulation units and CHECKOP rule-based system can be used. In order to limit tbe size of this book, this is not detailed out here, but an interested reader may refer to Ref. [7]. 

Another option is modeling approach, where a qualitative model is developed to include batch process. One of the objectives of such models is to concentrate on the understanding of how hazardous scenarios develop in batch processing plants. For this, different types of information can be integrated within a model to allow reliable prediction of tbe behavior of a system. Software tools are used for modeling of batch plant systems viz. HAZOP expert—LDGHAZOP. Based on the... 

HAZOP in a batch process, Internet document http //www.processoperations.com/HazIDRA/ HZ Chp04b.htm. 

Online HAZOP Analysis for Abnormal Event Management of Batch Process... 

In this work, we describe an approach to integrate multivariate statistical process monitoring and online HAZOP analysis for abnormal event management of batch processes. The framework consists of three main parts process monitoring and fault detection, automated online HAZOP analysis module and a coordinator. Multiway PCA is used for batch process monitoring and fault detection. When abnormal event is detected, signal-to-symbol transformation technique based on variable contribution is used to transfer quantitative sensor readings to qualitative states. Online HAZOP analysis is based on PHASuite, an automated HAZOP analysis tool, to identify the potential causes, adverse consequences and potential operator options for the identified abnormal event. 

A HAZOP is used to question every part of a process to discover what deviations from the intention of the design can occur and what their causes and consequences may be. This is done systematically by applying suitable guidewords. This is a systematic detailed review technique, for both batch and continuous plants, which can be applied to new or existing processes to identify hazards. 

In critical and complex batch operations it is sometimes helpful to mark up the study drawing to show the condition of the plant appropriate to a particular step in the process, and hazop this as a quasi-steady state. However, this is lengthy and tedious to apply as a general approach. 

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