Case Study: An Indian Plants all turbines’ low Vacuum & Saudi Plant turbo-compressor only
|Root Cause Analysis (RCA)
|High Speed, Hi KW Major Rotating Machines
|S. Raghava Chari
Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of one or two decades ago. These articles will help you to improve your troubleshooting skills and knowledge.
An Indian fertilizers plants’ two years in service all large turbines 700 mm Hg condenser vacuum dropped to 600 mm Hg.
Similar vacuum drop problem surfaced with Saudi K‑601 T turbine only also few months after commissioning.
Surprisingly, both plants’ tech service engineers (TSE) attributed the poor vacuum to ejectors’ poor performance.
On maintenance crew opening and showing fine ejectors, the Indian plant TSE attributed the problem to insufficient cooling water flow through the surface condensers and recommended adding an 1800 kW 10000 m3/H CW pump in parallel with the existing two.
Since the Saudi plant only one of the 21 surface condensers posed the problem, the perplexed tech service engineers offered no immediate solution.
Since, the Indian plant tech service engineers’ proposal was very expensive, the author himself troubleshot the problem.
Authors RCA Queries and Answers
Q- Why poor vacuum?
A-The vacuum corresponds to hot well condensate temperature. Hence, one should check the hot well temperature first. He noted the below given data from log sheets:
The data clearly points out that the actual vacuum is close to the steam table shown vacuum, hence the ejectors are fine, and the to address root cause is excessive hot-well temp two years later.
The author asked crew opened a shutdown machine lube oil cooler. It’s tube bores so much fouling by water borne algae and other products made all wonder, how water ever flowed!
The author arranged hydro-jet contractor cleaned the entire plant water using heat exchangers metal shine during a 1-day SD. All surface condensers hot well temp reverted back to 40O C and the vacuums close to former 58 mm Hg abs values on starting back.
The Saudi turbine K-601 T extracts 330 T of 40-bars steam for other turbines use out of the 360 T 100 bars steam admitted. The condenser condensing only 30 T/H steam is very small. It’s hot well temp too was excessive.
Hence, he took a 2 hr shutdown, opened a small hand-hole to check tube bore fouling though unlikely. He found a 400×300-tramp rubber sheet covering around 40% of the tubes – the too low seawater flow, consequent high hot well temperature and hence, the poor vacuum Root cause. He fished out the rubber piece using a hook-end rod.
On starting the hot well temp reverted to 35o C and vacuum to 45 mm Hg abs against steam table 41mm Hg abs.
In both cases the turbines consumed around 5% less steam than before.
Author: S. Raghava Chari
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