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Implications of inverting the rotation of a Steam Turbine 1

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josesb

josesb

Mechanical
Jun 17, 2019
2
Hi, I´m a senior year Mechanical Engineering Student, I´m writing this post because I need some advice from engineers with experience in tribology and lubrication for my internship project. Summarizing, the subject of the project is about studying the impact of inverting rotation of an axial Steam Turbine model 503T (two stages, non-condensing) manufactured by Dresser-Rand and how this change will impact the performance and life of the mechanical components of the turbine.

At this moment the turbine is at the workshop and repair duties are being made to allow the turbine to rotate counter wise. However I´m doubtful about whether the hydrodynamic bearings of the turbine ( sleeve bearings, tilting pad type) will be lubricated properly during operation if they were not replaced, lubrication of bearings is by oil rings by the way.

I´ve read a technical paper about oil ring lubrication for sleeves bearings which mentions that lubrication is not independent of rotational direction and therefore bearings should be engineered for a specific direction, say clockwise or counterclockwise (there are exceptions).

I will really appreciate your comments to know whether lubrication of sleeve bearings is independent of rotation of direction, thanks in advance.

bearing_direction_of_rotation_ch1x2p.jpg

turbine_diagram2_m1hnci.jpg

turbine_diagram_hme2js.jpg

 
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That is a single stage turbine. It has two wheels, but only one set of nozzles. We have reversed a little single stage turbine like this before. It can be done. The bearings only need to be changed if they are rotationally specific. A tilt pad radial bearing with center pivots is probably not directionally specific. If it has embedded temperature probes, they will need to be moved to the trailing edge of the pads. Does it use the same bearing (same part number) on both ends? If so, the bearings are suitable for reverse rotation since they are installed for opposite rotation on each end of the turbine now.

I suspect you have already identified the other changes needed:

New rotor to reverse the blading.
New reversing ring.
New nozzle ring.
New hydraulic governor (if equipped) or reverse the rotation of the existing governor if it is a type that can be reversed (Woodward TG).

Johnny Pellin
 
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We have several turbines of that model. I have never seen one with tilt-pad radial bearings. And, if I had one with tilt-pad radial bearings, I would expect it to be lubricated with a pressurized, circulating lube oil system, not oil rings. Are you sure those are tilt-pad bearings lubricated only with oil rings?

Johnny Pellin
 
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Thanks fo your quick answer, yes I already figured out most the changes that you pointed out, the governor is a Woodward TG 611-17 so it can work in reverse direction (the proceure can be found in the manual). Regarding the sleeve bearings the same model number is mounted on both ends.

I have never worked with turbomachinery before (I´m an undergrad) so I want to ask you about that "reversing ring" since I don´t know it´s function and where to find it.

About the bearings, I was told that those bearings were tilt pad type but after checking the technical documentation again I can´t confirm this to be true (it´s not specified). I have a picture (see below) which shows the radial bearings, it might help:

bearings_p1vyey.jpg
 
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Those bearings appear to be plain cylindrical sleeve bearings. They are not tilt-pad since they have no moving parts. If both bearings use the same part number, but are installed facing opposite directions, then they are suitable for either rotation. The picture makes it look like the bearings are the same (oil feed groove, anti-rotation pin, etc.) I would recommend contacting Dresser-Rand and asking them to confirm that those bearings are suitable for reverse rotation.

The reversing ring is a segment of stationary blades that is positioned between the two sets of rotating blades. The steam strikes the first row of blades and is deflected off at an angle. The stationary reversing ring, redirects the flow of steam back in the original direction so it strikes the second wheel at the ideal angle. Because this flow of steam is only occurring in an area in line with the steam nozzles, it is only in an arc near the bottom of the turbine. I tried to find a good picture of a set of reversing buckets, but couldn't.

Capture_kzvkbi.jpg


Johnny Pellin
 
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The reversing ring is in the bottom of the turbine case in line with the nozzle ring.

Capture_z5vaao.jpg


Johnny Pellin
 
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