(d) FIGURE 1 shows an external intermediate vessel which receives a continuous m
ID: 703803 • Letter: #
Question
(d) FIGURE 1 shows an external intermediate vessel which receives a continuous mixture of hydrocarbon liquid and small variable amounts of water. The water must be separated by settlement into the sump to prevent contamination of a later hydrocarbon processing stage. The sump should be drained every 4 hours by an operator. The operation is facilitated by a sight glass and high level alarm. Under normal conditions the sump would fill in approximately 10 hours Carry out a hazard and operability study (HAZOP) on the sump and drain line for deviation of No Flow' and More Flow' of water, listing possible causes, consequences and recommendations to avoid future deviations. Feed Senling tank Product Water sump Level gauge Isolation valve an high level alarm To drain FIG. 1Explanation / Answer
Case 1: No flow:
Possible causes:
1.Failure of water addition in inlet line. Please note that water is added in the hydrocarbon industry to neutralize atomic hydrogen which if left loose might cause "hydrogen blistering"
2. Drain valve is inoperable due to choking or solid deposition.
3. Clouding of level gauge glass due to which operator assumes no water in sump.
Consequences:
1. If there is no water being added, as explained above, hydrogen blistering will result and thus, the pipelines will get damaged and might result in leaks.
2. If the drain valve is choked or if the gauge glass gets cloudy, there will be a build up of water level in the accumulator and carryover to the products. Thus, the quality of the product will be compromised.
Recommendations:
1. Perform routine maintenance of water addition pump and ensure appropriate quantity of addition.
2. Ensure operability of outlet valve through regular maintenance.
3. Routinely clean the gauge glass and check high level alarm.
Case 1: No flow:
Possible causes:
1.Too much water added in inlet line and gauge glass reading becomes very high.
2. Drain valve flow is higher than expected when opened due to damage.
Consequences:
1. If the water accumulation becomes very high, there is chance of potential carryover to products and quality compromise.
2. If the flow is high due to operation of valve, there could be carryover of hydrocarbon into the drain line. This would cause an explosion when the sour water is being treated for sulphur removal.
Recommendations:
1. Perform routine maintenance of water addition pump and ensure appropriate quantity of addition.
2. Ensure operability of outlet valve through regular maintenance.
3. Routinely clean the gauge glass and check high level alarm.
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