Page 104 - Impiantistica industriale

NEW TECHNOLOGIES

red for sCO application, but the rising technology Barg (sCO )
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trend and lack of specific study/papers about sCO • Max. Shaft Diameter: ~ 100 mm
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behavior through sealing gap, brought Flowserve • Motor power (VFD): 200 kW
to plan a DGS test program with sCO to mirror the • Dynamic Torque measurement
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turbomachine’s operating conditions. The test allo- • Multi-Channel Data Acquisition System
wed to achieve the necessary industrial knowledge
to support this technological step change. This ar- For testing with CO , a dedicated system was im-
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ticle summarizes the DGS design, test rig arrange- plemented, and some challenges needed to be
ment and test results. overcome, like maintaining CO in liquid phase
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A thermal calculation performed on the compres- during compression by the pump or the selection
sor, showed temperature distribution around the of the pressure regulating valve. Additional expe-
seal ranging from 200 to 220°C. riences were gained by controlling the CO phases
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The high-density gas like sCO at high pressure, is in the low-pressure venting lines, to avoid ice for-
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generating heat by windage and the expected ther- mation.
mal equilibrium @ DGS operating condition show- Starting from the medium pressure (75 barg) CO
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ed a resulting temperature at seal close to 300°C. tank, the liquid CO is cooled down prior entering
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The DGS testing should simulate the compressor the piston pump. The pump compresses the liquid
environment as close as possible. A new sCO te- CO up to 270 barg into a heated bottle rack to
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sting loop at Flowserve facility in Dortmund, Ger- keep the CO in supercritical state. Afterwards, the
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many was built in Q3/2020. The initial tests perfor- CO is controlled by a PCV to supply the seal with
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med allowed to validate the thermal model used the correct pressure.
for DGS and to develop a dedicated algorithm for The DGS test set-up simulates the compressor
windage losses at high pressure with sCO fluid. cavity, but contains further features, like tester se-
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Parallel to the structural analysis, the available als or cooling chambers, which are necessary for
test results from those high-end references were the testing. The tester main housing and seal fluid
integrated in the seal analytical model using sCO injection lines are insulated. The tester adapter-
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project operating condition, with focus on: housing (reflecting the housing of the compressor)
• heat generation @ dynamic condition; is equipped with 18 heating rods.
• temperature profile within the seal cartridge; The seal and the tester adapter-housings are
• leakage trend. equipped, with 28 thermocouples. In picture 1 the
cabling of the thermocouples and the heating rods,
The knowledge of the seal face temperature de- show the complexity of the test set-up to monitor
velopment @ the various operating conditions, in- and control the test conditions (Fig. 1).
cluding standstill, is essential to design a reliable During the complete test campaign, the tester it-
DGS. The gas film stability allows to keep sepa- self, the CO2 System and the seal were monito-
rated the sealing faces and the temperature has a red, to perform accurate system control and data
great impact on that as it may cause instability, flow acquisition.
fluctuation or extremely rapid increasing/ decrea-
sing leakage trend. The CO properties depending
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on pressure & temperature is relatively unknown for ®
narrow gap (3÷5 µm) analysis. FLOWSERVE Gaspac
Flowserve is using MSTI as standard tool for DGS DGS test procedure
performance analysis. Test results are used to de-
velop the software continuously, to improve accu- The sCO seal test plan simulates the compressor’s
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racy, but when the application is beyond the expe- operational scenarios, as well as design parameter,
rience, it´s still a prediction. to validate the seal’s capability with sCO fluid (See
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Tab. 1). In general, the Matrix Test distributes into
three main parts, with different temperatures of the
DGS test description tester housing, reflecting the compressor cavity
Based on the seal cavity temperature profile and The Cold Matrix Test consists of two scenarios:
the need to mirror those conditions during the DGS 1. Ambient temperature: to simulate a pro-
testing, a detailed thermal analysis of the tester longed, pressurized stop of the compressor,
was conducted. To achieve stable conditions du- the inboard seal cavity was flooded with liquid
ring steady state test steps and to adjust to the CO . After static testing a startup was perfor-
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speed and pressure condition an external heat med until the liquid turned into gaseous CO
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source was necessary directly into tester housing. phase.
This allows also to mirror compressor housing tem- 2. Hot seal gas: the seal gas was heated up to
perature. 130 °C and the seal was started-up to normal
For the CO test campaign, the ultra-highspeed- speed and pressure, to see the temperature
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tester, located at Flowserve, Dortmund Germany development of the seal up to steady state
was used. Here the tester features: conditions.
• Max. Speed 70.000 rpm
• Max. Pressure 500 Barg (Air) / 270 To reflect compressor conditions, two Warm Ma-

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