PROCESS India1-2012 34PHARMA/BIOTECHOIL/GASWATER/WASTEWATERCHEMICALDESIGN OPERATIONFOOD/BEVERAGESAFETYProcess and/or safety engineers and managers need to clearly understand, plan and execute future emergency relief system design work for plant projects, such as Process Hazard Analyses (PHA), unit expansions, debottlenecking studies etc. This article focuses on the usefulness of Design of Emergency Relief Systems (DERS), Hazard and Operability (HAZOP) and Safety Integrity Level (SIL) tools.ASHISH PARIKHThe author is the Delivery Head at Shiva Engineering Services, Vadodara. Contact Tel.: 912652321418.Chemical industry in general, deals with varieties of flammables and toxic materials on day-to-day basis wherein the risk of exposure of people to such chemicals is always present. Handling of such chemicals from safety point of view is a major chal-lenge for key decision makers. On one hand the industry has pressure to deliver increased production and on the other hand it needs to ensure the process safety. Any accidental event, which arises out of failure of safety measures, causes loss of production and affects plant personnels health. There are various ways to mitigate such incidents, for example, properly designed pressure relief systems can save operating equipment in the event of an emergency, avoiding both capital spending to replace damaged equipment and costly downtime.Classification of hazardous chemicalsChemicals are broadly defined into three categories as per Schedule I (Part I & Part II ) guidelines of Ministry of Environment and Forests (http://envfor.nic.in/legis/hsm/hsm2sch1.html):Part Ia) Toxic chemicalsb) Flammable chemicalsc) Explosives Part IIThere are about 429 chemicals defined as hazardous and toxic chemicals in Part II clas-sifications. Some of them that are widely used are acetone, acrylonitrile, ammonia, ammonium nitrate, aniline, benzene, butane, carbon monoxide, chlorine, liquefied petro-leum gas, nitrobenzene and sulphuric acid.Operational risk mitigation is possible through right designDesigning the emergency relief systemThere are various ways to mitigate risk in chemical plants where plant personnel regularly need to handle flammable and toxic materials.Source: depositphotos.com Sergey Solomakhin2357319PROCESS India1-2012 35Process hazard analysisThe key to implementation of effective process safety and risk management systems lies in developing a common framework, which includes all local regulatory require-ments and all corporate standards.A proactive approach, coupled with prop-erly planned and implemented process safety management system can help minimise loss of life, environmental impact, equipment damage, citations and litigation.Effective process safety and risk manage-ment starts with understanding the hazards that are present in the process. Process Haz-ard Analysis (PHA) should be conducted throughout the life of a process from initial laboratory trials, through operation, until the process is decommissioned.At different stages of a process life cycle, different PHA techniques may need to be used. Various current techniques used for conducting PHAs are: Preliminary or Inherent Hazard Analysis, HAZOP studies, Failure Modes and Effects Analysis and Emergency Relief System (ERS) Design.ERS designEmergency Relief System (ERS) design is an essential part of process safety management and keystone in achieving process safety. Effective ERS design helps companies meet risk-management goals, compliance require-ments and sound business practices. DIERS (Design Institute for Emergency Relief Sys-tems) Technology is an example of good engineering practice for process safety man-agement of highly hazardous chemicals.There are several software like Su-perChems, ioXpress, which are used for con-ducting risk screening, documenting PHAs and Source: Shiva Engineering ServicesTemperature ( oC )Time (min)Onset ofRunawayInduction400300200100100 125 150 175 200 2250+ Academic distance learning study program Pump Engineer+ Certified Energy Consultant for Pumps and Pump Systems+ Open to all engineers and professionals working with pumps+ Developed by professors from leading European technical universities and internationally renowned experts+ Practical on the spot training by highly qualified pump specialists Englsh lnguage iacourse to star in tMach 2012rIn cooperation with institutes from:SAFETYPROCESS India1-2012 36Safety integrity levelWhile the Hazard and Operability (HAZOP) study identifies and risk-ranks hazards, Safety Integrity Level (SIL) determination focuses on the adequacy of safeguards to mitigate haz-ards. The chemical industry relies on Basic Process Control System (BPCS) and Safety Instrumented System (SIS). In a process plant, the operator supervises the operation and takes necessary action through BPCS. The BPCS is the lowest layer of protection and is responsible for normal operation of the plant.There are four different SIL levels: SIL 1 - Probability of failure on demand between 10-1 and 10-2, SIL 2 - Probability of failure on demand between 10-2 and 10-3, SIL 3 - Prob-ability of failure on demand between 10-3 and 10-4, SIL 4 - Probability of failure on demand between 10-4 and 10-5.Each level represents an order of magni-tude of risk reduction. Higher SIL level indi-cates higher is the safety level and lower probability that the system will fail to per-form. The ideal time for SIL determination is during the Front-End Engineering Design (FEED) and project definition stages, and typically as a supplement to the HAZOP. But SIL determination may also be used effec-tively during the plants life to determine if improvements are needed, and to provide guidance as to the form of the improvements.SIL level can be identified based on the plant owner risk tolerance. Plant owner should determine the acceptable level of risk based on corporate strategy, legal require-ment, capital and other factors. Selection of appropriate SIL level calls for a careful analy-sis. Costs increase with higher SIL levels. It has been observed that typically the chemi-cal industry has opted to go up to SIL level 2 based on the requirement.conducting hazard assessments. These tools are essential for any plant manager with safety or risk management responsibility. Legal compliance requires process expan-sions or modifications of relief system design documentation up to date, and non-conformi-ty of the same results in costly fines. Relief and flare systems are affected by processing modification, expansion, debottlenecking and other changes, and documentation must be updated accordingly. Using software tools such asSuperChems, one can perform sizing calculations, account for header and flare stack hydraulics, and calculate the radiation effects due to flaring.HAZOP studyA Hazard and Operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation, in order to identify and evaluate problems that may represent risks to personnel or equipment. Hazard means any operation that could possibly cause a catastrophic release of toxic, flammable or explosive chemicals or any action that could result in injury to personnel.Operability means any operation inside the design envelope that would cause a shutdown that could possibly lead to a viola-tion of environmental, health or safety regu-lations or negatively impact profitability.The HAZOP process is based on the prin-ciple a team-approach to hazard analysis identifies more problems than done by an individual. The HAZOP team consists of indi-viduals with varying backgrounds and skill. The expertise is assembled during HAZOP sessions and through a collective brainstorm- effort that stimulates creativity and new ideas, a complete review of the process under consideration is made.ERS case studyShiva Engineering Services (SES) recently carried out ERS study for one of its polymer clients. As per the present status, the AO-Butyl Stearate Tank is currently protected by a rupture disk of 8, set at 4-7psig @ 50C.The purpose of this Emergency Relief Sys-tem (ERS) design package was to examine the adequacy of the existing installation with regards to overpressure protection. Also it included, if found inadequate, SES would design a relief system to protect the AO-Butyl Stearate Tank from unallowable overpressure. Pressure rating of equipment: 70 psig @122FTwo-phase Vessel Dynamics was carried out in order to establish the relief rate. The relief rate was 159 lb/sec. Piping was anal-ysed to find out maximum flow it could take. Then it was found that the piping was able to take flow rate more than 159 lb/sec. Maximum flow possible through piping was 180.5 lb/sec. Afterwards the complete study report was submitted to the client regarding the existing relief device and adequacy of piping to pre-vent the vessel from overpressure during external fire case.Risk assessmentThis can be done both qualitatively and quantitatively and at varying levels of detail. To carry out qualitative risk assessments, ioMosaics ioFIRST software supports risk screening activities, while risk survey approach guides more detailed assessments.Fault-tree and event-tree analyses may be done to determine the frequency of potential incidents and evaluate risk for quantitative review. SuperChems hazard assessment modelling software includes source term and vapour dispersion models. STEPS INCLUDED IN THE HAZOP METHODOLOGY1. Collect data2. Understand the subject3. Prepare nodes and activities4. Mark-up the drawings5. Devise a list of appropriate keywords6. Prepare table headings and an agenda7. Select the team8. Prepare a timetableDATA TO BE COLLECTED BEFORE STARTING THE HAZOP STUDY IN GENERAL1. Process description2. P&I diagram3. Process parameters4. Material safety data sheet ofchemicals involved in the process5. Interlock and logics6. Start up and shutdown procedure7. Emergency shutdown procedure8. Prepare a timetableSIL STUDY REQUIRES VARIOUS DATATHESE WILL BE INCLUDED,BUT WILL NOT BE LIMITED TO1. All relevant studies (HAZOPs, QRAs, etc)2. P&IDs3. Cause and effect charts4. Current maintenance andshutdown details5. Relevant operational information