Axial displacement

S

Thread Starter

suchitra

Dear Sir/Madam

currently I am working as a Instrumentation engineer in the field of Power plant. now i need your help for to solve the issues of Axial float of Steam turbine, i.e once our turbine synchronized with grid it run with load mode. In that condition if there is any fluctuations in steam header pressure (Not much fluctuations only 1 to 2kg/cm2), it ultimately reduce the load, and governor will try to match the load at desired set point level by open the hydraulic valve so Steam flow increased. Now i come to point as follows.

1. Main steam pressure varies from 1 to 2kg/cm2 will it affect the Turbine Axial float? Now our Axial value is 0.78mm so we reduce operating header steam pressure from 86.5 kg/cm2 to 76.5 kg/cm2, but axial still raising and corresponding Thrust pad temperature also Raised and Steam flow Rate is 80.5TPH and MW is 19.5MW.

2.Instead of Load mode we put our Governor to Pressure control Mode will it control Axial float?.

Boiler Details Before Revamping

Operating Pressure: 96.5 kg/cm2
Temperature: 540 deg centigrade
Flow: 120 TPH

After Revamping

Operating Pressure: 86.5 kg/cm2
Temperature: 540 deg centigrade
Flow: 100 TPH

Turbine Details
Make: Siemens
Rpm: 3000 RPM
Capacity: 27.3MW
uncontrolled Extractions: 2
controlled Extractions:1
Type: condensing.
 
suchitra,

For a single-flow steam turbine, yes, there is a relationship between axial position and main steam pressure.

You can change the operating mode and see what effect is has on the turbine at your site, but the best person to ask this question of is the OEM who may have a graph or chart that depicts the relationship between main steam pressure and axial position.

You haven't said when this problem started, or if the axial position changed suddenly or has been changing over time. It would seem that thrust bearing/pad wear is increasing for some reason, or maybe that the wear has exceeded the manufacturer's limit and when that happens sometimes the wear rate can also increase quickly.

This is kind of an odd problem because per your information the main steam pressure has decreased since the boiler was revamped--which kind of goes against what one would think would happen. Reduced steam pressure would seemingly reduce thrust and the pressure on the thrust bearing/pads.

Some single-flow steam turbines employ a "piston" at one end of the rotor using steam pressure to help balance the thrust pressure. It's possible that by reducing the main steam pressure the thrust is no longer balanced properly.

Again, it's best to consult the manual provided with the turbine and probably the OEM to get the most concise answer that is applicable to the turbine you are operating at your site.

By the way, I wish to complement you on the information you provided about the conditions--including the information about the boiler revamping. We usually have to have several exchanges of information before we learn such details, so, thank you very much!
 
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