Troubleshooting effort solves exchanger problems in Saudi refinery

June 20, 2005
Troubleshooting efforts in the platformer unit in Saudi Aramco’s refinery identified problems related to a catalyst leak, carbon buildup on the exchanger shells, and high vibrations.

Troubleshooting efforts in the platformer unit in Saudi Aramco’s refinery (Fig. 1) identified problems related to a catalyst leak, carbon buildup on the exchanger shells, and high vibrations.

Saudi Aramco’s refinery includes a platformer unit (Fig. 1).
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A vertical heat exchanger in the platformer unit was experiencing tube failures. Based on scale, tube sample analyses, and engineering evaluations, we found that the most likely cause of the tube leaks were melted tubes due to burn out of coked catalyst that carried over into the exchanger or a buildup of hydrocarbon deposits on the shell side.

Bypassing the damaged exchanger resulted in high noise levels, which led to reduced throughput. We resolved this problem by installing a restriction orifice; this led to a revenue increase of $720,000 in a few months.

It is possible that a small amount of catalyst had been leaking for a long time or that something happened during the regeneration and a significant amount of catalyst was lost at that time. We confirmed this after inspecting the reactors and the vertical exchanger during a shutdown. We found that the third reactor’s center pipe encountered some damage.

This article highlights the root causes of the problem and presents the recommendations for preventing a repetition of this incident. This article also covers new solutions for high-pitch noise problems in chattering tubes.


Fig. 2 shows a flow diagram of a typical platformer unit.

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The feed to the platformer unit is naphtha, which is hydrotreated to lower the sulfur and nitrogen to less than 0.5 ppm. The hydrotreated naphtha combines with recycle gas and is heated in the reactor effluent exchanger.

Reactors then process the feedstock in the catalyst bed to increase the naphtha’s octane number. Product is sent to the gas concentration unit for final vapor pressure adjustments. Gas from the reactors is sent to the fuel-gas system.


After the platformer catalyst was regenerated and naphtha feed entered the unit in June 2003, a low temperature reading occurred in the tube outlet of reactor’s effluent exchangers E1C and D. In addition, the run-down product experienced a low octane number during the unit’s dry-out period.

A set of samples from the reactor’s effluent exchangers E1A-D revealed a major leak in E1C. The platformer unit was shut down and exchangers E1C and D were isolated and prepared for a shell test-E1D passed the test and E1C did not.

Two different cranes (250-ton and 360-ton) were used to remove the E1C bundle, but it was stuck in the exchanger shell. Due to safety concerns, we decided to keep the tube bundle in the shell and isolate the exchanger.

The unit started up with E1C being bypassed. Naphtha feed entered the unit at 18,000 b/d and was further increased to 30,000 b/d.

Short-term solutions

Because the damaged exchanger was bypassed, the additional flow in E1D resulted in a high noise level. The platformer unit throughput was limited to 30,000 b/d.

We conducted a detailed study to evaluate the effect of operating three exchangers instead of four. The objective was to evaluate the performance and mechanical integrity of these three exchangers and reduce the noise level in E1D.

Using a heat balance calculation around the three exchangers and a simulation program, we calculated that the reactor effluent flow to E1D was about 40% of the total flow. This resulted in the high vibration levels. Other contributing factors were the symmetrical configuration of the reactor effluent and unbalanced gas flow to the tube sides.

We unsuccessfully attempted to reduce the flow to the exchangers by varying the feed flow rate to the three exchangers.

The investigation team decided to install an orifice in the tee joint to E1C and D to force more flow to E1A and B, based on a pressure drop survey of the exchangers and other unit parameters. This dramatically reduced the noise level in E1D.

Solving the noise problem by installing the restriction orifice allowed us to raise the plant feed rate by 2,000 b/d before shutting down the plant for a turnaround and inspection in December 2003. This led to a revenue increase of $720,000.

Long-term troubleshooting

Our long-term troubleshooting efforts include a thorough review of the process data and regeneration procedures; an analysis of the catalyst, exchanger deposits, and tube metallurgy; and an inspection of the upstream reactors.

We reviewed the process data, regeneration procedures, and regeneration events to gain a better understanding of possible upset conditions and to identify the root cause of the exchanger problems.

During the carbon burn step of the catalyst regeneration, the tube outlet temperature of the two combined feed exchangers (E1C and D) decreased during the once-through waterwash step. The tube outlet’s temperature decreased from 385° C. to 100° C. then increased to 385° C. due to the presence of water.

The water was drained from both exchangers; the temperatures started increasing to normal levels (E1A, B, C, and D were 392° C., 395° C., 383° C., and 377° C., respectively). The presence of water could have caused the accumulation of scale and catalyst on the exchanger baffles.

An analysis of the catalyst samples showed no abnormalities.

Three samples of deposits collected from the refinery feed-effluent exchanger E1C were analyzed for composition. Two of the samples were analyzed with X-ray diffraction and energy dispersive X-ray fluorescence spectrometry.

Deposits from E1C bellows were 62% magnetite (Fe3O4), 28% wustite (FeO), 7% hematite (Fe2O3), 2% halite (NaCl), and 1% iron (Fe). There were no obvious Al2O3 peaks or any sulfur or sulfur-containing crystalline phase.

Deposits from E1C tube sheet were 48% magnetite, 25% wustite, 21% hematite, 3% halite, and 3% iron. There was no sulfur or sulfur-containing crystalline phase.

Damaged tubes from the platformer vertical exchanger showed localized melting and scaling (Fig. 3).
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Tube samples (Figs. 3 and 4) from the bottom section of the tube bundle were analyzed. A section of the shell was removed to get representative tube samples for analysis.

Tube and baffle samples from the damaged exchanger suggested that there might have been a fire in the platformer exchanger (Fig. 4).
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The tubes showed evidence of localized melting and extensive scaling. The remaining tube material microstructure had been modified by exposure to high temperatures, resulting in an overheated, coarse-grained, rehardened microstructure.

The scale samples from the tubes and embrittled baffle section were mainly wustite and magnetite. Wustite is an iron oxide that only forms during high temperature oxidation (scaling). The fact that the baffle had completely changed to this high temperature scale and that the remaining tube material microstructure had been degraded strongly suggests that there was a (localized) fire in the bottom area of the exchanger.

During a December 2003 shutdown, we collected more scale and dust samples from the reactors and exchangers, which confirmed our previous findings.

During a turnaround and inspection shutdown, all the three reactors and vertical exchangers were opened for inspection. We found that reactor No. 3’s center pipe was partially damaged.


From the review of the available process data, regeneration procedures, regeneration events, and inspections, we concluded that:

  • Coked catalyst and catalyst dust can melt the tubes if it burns at a high O2 content and high temperature. This scenario is supported by our findings of high Al levels in the tube sheet deposits; there is no Al in the alloy steel. This finding was also confirmed by metallurgical analysis.
  • During the regeneration, a water wash upset occurred, which caused water to flow into the vertical exchangers. Some hydrocarbons could have been in the bottom of the exchanger, which would have floated on the water and been exposed to the O2. This could then burn.
  • The visual reactor inspection revealed that the third reactor’s center pipe and some scallops were damaged. This would allow catalyst and dust to escape and accumulate at the exchanger’s low points and baffles. This finding confirmed the causes that attributed to the escaped catalyst and carbon deposit buildup inside the subject exchanger reactors.

Based on scale samples and shutdown findings, the root cause of the tubes melting was the burning of coked catalyst that carried over into the exchanger or carbon deposit buildup on the shell side of the vertical exchanger

This burn out probably occurred at the end of the catalyst oxidation step, when temperatures are elevated and the oxygen is at a maximum; these carbon deposits could catch fire, ultimately melting the tubes at the exchanger’s bottom.

In addition, the water buildup lifted the scale to the lower half of the exchanger. When the exchanger was drained, the scaling remained at the top of the baffles. This scale, when exposed to temperatures of 510° C. during the oxidation step and an oxygen level of 13%, started to burn. This caused excessive heat, which caused the tubes to melt


To prevent the melting problem from recurring, we recommended these long-term solutions:

  • Evaluate the causes of potential damage to the center pipe and scallops in the reactor.
  • Install a control valve for basic water circulation to ensure good water distribution. Evaluate the installation of two flow control valves for the recycle gas. The control valves will even the flow between E1A/B and E1C/D. This will avoid unbalanced gas flow on the exchanger’s tube side.
  • Install pressure gauges across each exchanger on the shell side only to monitor any fouling or catalyst accumulations in the exchanger.
  • Drain the exchangers every 15 min at the beginning of water wash or during a start-up of the circulation pump for 2 hr to ensure no water accumulation in the piping and at the bottom of the exchanger.

The authors

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Mohammed A. Balamesh is a process engineer in the process and control systems department of Saudi Aramco, Dhahran, Saudi Arabia. He joined Saudi Aramco in November 1990 and has about 8 years’ refining experience and 4 years’ experience in process engineering. His specialty is refining operations with a focus on catalytic reforming. Balamesh holds BS and MS degrees (1998) in chemical engineering from the University of Tulsa.

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Fahad E. Al-Shetairi is a process engineer in Saudi Aramco’s Yanbu refinery. He joined Saudi Aramco in 1991. He has worked in various areas of the Yanbu refinery including utilities, the platformer unit, kerosine Unibon unit, and gas concentration unit. He holds a BS in chemical engineering from King Abdul Aziz University, Saudi Arabia.