HAZOP ANALYSIS ON ETHYLENE OXIDE REACTOR (R100) The Ethylene Oxide reactor converts ethylene to ethylene oxide using oxygen and a sliver catalyst. The operating temperature of the reactor is 280 o C and operating pressure is 8 atm. Ethylene oxide is very dangerous, carcinogenic, flammable and explosive. When it reaches its decomposition temperature of approximately 400 o C, a very deadly explosion may occur. Figure 1: Simple Diagram Showing Ethylene Oxide Reactor Streams BFP -Back-flow Prevention (Non-Return Valve) Oxygen and ethylene is combined and forms the feed stream. Oxygen inlet concentration and ethylene inlet concentration is dependent on the oxygen and ethylene supply respectively as shown in the diagram. The combined feed rate, feed compositions and coolant streams will be analysed. The reactor products stream only needs a non-return valve to prevent backflow of reactor products to the reactor. Deviations Property Possible Causes Possible Consequences (Guide Words) No Oxygen Inlet COMBINED FEED TO THE REACTOR (R-100) Control valve Technological Problem. Concentration failure. Ethylene Oxide Conversion (EO) is 0. More Oxygen Inlet Concentration Control valve failed to close Thermal runaway effect (Reactor Temperature Increase) and possible explosion due to Ethylene Oxide decomposition. Less Oxygen Inlet Other Than Concentration Oxygen Inlet Control valve failed to open Wrong reagent Concentration As Well As Oxygen Inlet No Concentration Ethylene Inlet or raw material. Impurities in raw material Ethylene Concentration Technological Problem and Conversion is too low. Vessel Rupture Formation of undesirable Products. Decreased conversion Technological Problem in Reactor Technological Problem and pipeline may be conversion is zero. clogged. Control valve failure. More Ethylene Inlet Concentration Control valve failed to close A very high wt. % of ethylene may form explosive mixtures of hydrocarbon and oxygen. Low selectivity. R Less Ethylene Inlet Control valve Technological Problem and Other Than Concentration Ethylene Inlet failed to open Wrong reagent or raw material. Conversion is too low Vessel Rupture Formation of undesirable Impurities in Products. Decreased conversion Technological Problem in raw material Flow Controller Reactor Loss of feed to reaction section failure. Line fracture. Line blockage. Flow Controller failed to close Low flow Concentration As Well As Ethylene Inlet No Concentration Flow More Flow and no output Increased EO Conversion. High concentrations of ethylene oxide and oxygen controller valve leading to explosive mixtures. bypass failed to Less As Well As Other Than close. Flow Controller Less EO Conversion Flow failed to open Water Out of spec. supply Flow Contamination Impurities Wrong Feed Decreased conversion. Increased formation of undesirable products This may form explosive Flow Delivered Reverse Flow Pump failure, non-return valve mixtures since ethylene is failure, flammable and explosive in the More Temperature Over- presence of high levels of pressurisation of oxygen. reactor. Temperature O2 concentrations increases Controller and forms potential explosive Failure. External Fire. mixture of hydrocarbons and oxygen. Decreased conversion and selectivity. Increased Reaction Temperature leading to runaway effect. Less Temperature Temperature Controller Decreased Selectivity. Low Pressure. Failure Higher COOLING (COOLANT) STREAM PASSING THROUGH REACTOR (R Inlet and Outlet Cooling water Thermal runaway effect and Temperature valve possible explosion malfunction or Lower Inlet and Outlet Temperature failure. Control valve failure, operator The temperature of the reactor may become very cool fails to take action on alarm No Flow Cooling water valve or flow controller malfunction. Cooling water service failure. Runaway effect and possible explosion More Less Flow Flow Control valve The reactor becomes very cool failure, operator and reactant concentration fails to take builds up and potential action on alarm. runaway effect on heating. Pipe Leakage. Temporary Temperature of process fluid Water Source remains constant or increases Thermal runaway effect Less Cooling, Potential Failure. Partially clogged cooling line. Part of Flow Partially clogged cooling As Well As Flow line. Contamination runaway effect. Decreased Conversion. Less cooling, runaway effect (Presence of Reactor product) in Reverse Flow cooling tubes Failure of water source or high backpressure resulting in backward flow and explosion More Temperature REACTOR PRODUCTS LEAVING THE REACTOR (R-100) Temperature O2 concentrations increases Controller and forms potential explosive Failure. External Fire. High Reaction mixture of hydrocarbons and Temperature. oxygen. Increased Ethylene Oxide Temperature leading to runaway effect. Less Temperature Temperature Low Reactor Pressure. No production of ethylene Controller No Flow Failure Flow Controller failure. Line fracture. Full Line blockage. Wrong Catalyst oxide. or Catalyst is fully consumed. More Flow Feed Flow More production of ethylene oxide. High concentrations of Controller failed to close. Low feed flow ethylene oxide and oxygen controller valve leading to explosive mixtures. bypass failed to Less Flow close. Feed Flow Controller failed As Well As Other Than Flow Flow to open Water Contamination Impurities Wrong Feed Delivered to the Reactor Less production of Ethylene oxide. Out of spec. supply to the reactor. Decreased Ethylene oxide production. Stream may contain a large amount of undesirable Reverse Flow Pump failure, products. This may form explosive non-return valve mixtures since ethylene is failure, Over- flammable and explosive in the pressurisation of oxygen. presence of high levels of reactor. More Reactor Pressure OPERATING CONDITIONS OF REACTOR (R-100) Increased steam Reduced Yield. Formation of undesirable flow rate. Relief valve fails closed. products. Development of Temperature Gradients with localized hot spots leading to impairment of the catalyst to produce Less Reactor Pressure Release valve fails open. Filling hose ethylene oxide. Vessel overpressure or rupture. Decreased Conversion. O2 concentrations increases ruptures. More Temperature Temperature Controller and forms potential explosive Failure. External Fire. mixture of hydrocarbons and oxygen. Decreased conversion and selectivity. Increased Reaction Temperature leading to Less Temperature Temperature Controller Failure runaway effect. Decreased Selectivity. Low Pressure. Thermal runaway An exothermic reaction can lead to thermal runaway, which begins when the heat produced by the reaction exceeds the heat removed. The surplus heat raises the temperature of the reaction mass, which causes the rate of reaction to increase. This in turn accelerates the rate of heat production. Thermal runaway can occur because, as the temperature increases, the rate at which heat is removed increases linearly but the rate at which heat is produced increases exponentially. Once control of the reaction is lost, temperature can rise rapidly leaving little time for correction. The reaction vessel may be at risk from over-pressurisation due to violent boiling or rapid gas generation. Executive temperatures may initiate secondary, more hazardous runaways or decompositions. An over-pressure may result in the plant failing catastrophically resulting in blast or missile damage. A release of flammable materials from the process could result in a fire or an explosion in the workroom. Hot liquors and toxic materials may contaminate the workplace or generate a toxic cloud that may spread off-site. There can be serious risk of injuries, even death, to plant operators, and the general public and the local environment may be harmed. At best, a runaway cause loss and disruption of production, at worst it has the potential for a major accident.