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How To Use The Turbine Table

To utilize this table successfully, you must first choose the type of turbine required. The types are condensing, non-condensing, expander and combustion (gas). Then, there are six primary factors to consider. In order of importance, they are inlet flow or, more directly, inlet flange size, rotation, maximum inlet steam pressure, exhaust steam pressure, power output and maximum speed. Once you have narrowed your selection, you must check inlet steam temperature, exhaust size and orientation, materials of construction, overall size (if size restrictions exist), shaft centerline height, type of governor, etc.

Inlet steam flow determines the inlet flange size. A turbine may not be designed for the inlet steam pressure and temperature that you need but still be a good selection if the inlet flange is large enough. It can even be oversized and still be a good selection. Enter the table based on your power requirement but look for a unit with the necessary flange size. You can look above and below your required power when trying to locate a unit. If you find one that has the proper flange size but is low on power, it might be re-rated to your power requirement since the inlet flange is large enough to pass the required flow.

Rotation is a go, no-go. It must be the rotation you require. Rotation can be reversed but it is normally complicated and cost prohibitive.

Next check inlet steam pressure. It must have a pressure rating high enough to handle your inlet pressure. Don't just look at design inlet pressure, as most turbines are designed for a certain maximum pressure that is usually higher than the design inlet pressure. Therefore, check rated inlet pressure.

Check the rated exhaust steam pressure. Make sure it is high enough to handle your exhaust pressure. Be careful if it is too high, as that might mean that the exhaust flange is undersized for your flow requirement.

Power is difficult to check without performing a stage-by-stage calculation. Generally, if you can put the required steam flow into the inlet, you can develop the necessary power. However, the turbine may have to be re-staged to develop that power.

Required operating speed should be within the range of the selected turbine and, hopefully, close to its design speed. If it's close, it will be easier to utilize the turbine. Make sure that your required operating speed is not close to any critical speeds of the turbine.

If you gotten this far and still have a suitable turbine, you're 80% there.

Check that the inlet steam temperature is within the limit of the selected turbine. As with inlet pressure, look at rated temperature - not design temperature.

Make sure the exhaust flange is large enough to handle your exhaust flow and oriented in the proper direction. This check is an extension of your check of exhaust pressure.

Look over the materials of construction and make sure there is compatibility with your steam, and with your plant requirements. Some older turbines used cast iron for lower pressures. Your plant (and more importantly your insurance carrier) may not accept cast iron.

If you have size limitations, you should check them now. This point may not be a go, no-go as you might have some flexibility in mounting the turbine but you should identify those problems now. One size limitation that can be critical is centerline height. If you are trying to match up to an existing piece of equipment, centerline height can be important. Check it now.

The existing governor (if there is one) should match your process. For instance, some governors are not suitable for variable speed. The results of this check should not throw out your selection as the governor can be easily changed. In fact, the incorporation of a new electronic governor is highly recommended.

Induction or extraction turbines require special checks to ensure that the selected turbine is suitable. You must treat the turbine as two or more separate turbines, applying the checks outlined above to each section.

Using the above discussion points to narrow the selection of a turbine will help you choose one to focus on. There are other points that must be checked before an ultimate selection should be made but these checks will get you off to a good start.