Vent gas scrubber

VS = vent gas scrubber EC = ethylbenzene recovery column DC = diethylbenzene recovery column. 

Methyl isocyanate (MIC) is a colorless liquid that must be stored in a cooled enclosure before it is subsequently used in the manufacture of carbamate, a common insecticide. MIC liquid is highly reactive in the presence of water and iron oxide, and it generates heat. In sufficient quantities, this heat may generate vapor, which, as explained previously, is highly toxic. Three adjacent bunkers were used for MIC storage. These were mounted in a berm and a refrigeration coil was used to ensure that the temperature did not exceed 5°C. A vent gas scrubber was used to prevent vapor escape, and despite a low operating pressure, a closed relief... 

For several months before the accident, conditions at the plant had been deteriorating. Procedures were not carefully followed and several mechanical features were either shutdown or compromised. Examples include the refrigeration circuit that was depleted of coolant and the vent gas scrubber that was out of service. The temperature indicator on one tank was defective. The temperature in one of the tanks had been allowed to exceed the maximum limit by as much as 15°C with no corrective action. 

The agent holding and surge tanks are located in an enclosed toxic cubicle. Each neutralization processing line is located in a separate enclosed cubicle. No vent gas scrubber or carbon filter is located in either of the neutralization cubicles to treat vent gases. 

The most intriguing question is why the plant s safety equipment and controls, which should liave been designed to cope with a chemical tliat is known to be subject to violent reactions, did not work. Tlie MIC tank liad tliree safety devices. A pipe leading from tlie tank contained a valve tliat was set to rupture if the pressure in the tank e.xceeded 40 psi. Beyond the valve there were two other safety devices. One was a flare (tower) to bum escaping gas. The other was a vent gas scrubber, a tower packed with loose niaterial tlirough wliich a solution of caustic soda could be poured onto rising MIC to decompose it. On December 3, 1984, tlie operator of the factory s control room noticed tliat the pressure in tlie MIC tank (see Figure 1.3.2) luid risen from 2 to 30 psi, and in a... 

In 1984, one of the most notable process incidents occurred in Bhopal, India, at a plant owned by Union Carbide. On December 3, 1984, methyl isocyanate (MIC) was vented to the atmosphere from a vent gas scrubber after a run away reaction overwhelmed the scrubber. It is reported that more than 2500 people died and 20,000 people were injured as a result of exposure to MIC. The subsequent investigation showed that the run away reaction occurred in the MIC tanks after water was reportedly intentionally added to the tank. The safety systems, a pressure relief valve, a vent gas scrubber, and a flare were reportedly poorly maintained. The relief valve worked to vent the pressure, but the scrubber was overwhelmed, and the flare was down for maintenance. This incident highlighted several loss prevention areas that needed improvement. The first was mechanical integrity. No strong preventive maintenance effort appeared to be in place. The second was emergency preparedness and response. It appears that while the plant was built 1.5 miles away from the community, zoning problems allowed the community to expand to the plant limits. It does not appear that much effort was made to work with the community on commimication/notification or evacuation needs. ... 

Vent gas scrubber with continuous caustic circulation Active... 

We may note in Table 1.4 that the vent gas scrubber was an active safeguard, while a passive type (as well as a change from active to passive of the other safeguards) would probably have avoided the accident, as discussed later. 

When water started to react with MIC, no control of the temperature/pressure started, because it was late at night and the operational staff was reduced to a minimum, and the MIC tank s alarms had not worked for 4 years. The gas leakage followed, for the first 30 min, approximately the inverse route of water entrance (Figure 1.6), except that which reached the atmosphere through the vent collection system (VCS). However, the flare tower and the vent gas scrubber (Figure 1.7) had been out of service for 5 months before the disaster. After the first 30 min, the rupture disk bursts and this increased the rate of release of MIC. 

MIC Reactor Side Relief Valve Vent Header Process Valve Vent Header Vent Gas Scrubber Flare Vent Header R( t ( rjngr ... 

Principles of Green Chemistry, Sustainable Chemistry and Risk 19 Vent gas scrubber system... 

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