English - Kühne Intertech GmbH

kuehneintertech

English - Kühne Intertech GmbH

Why measure torque?

Kühne Intertech GmbH

Torquetronic

Continuous Duty Torque Measurement

During the commissioning, testing and operation of critical turbo-machinery, it is often vital that the precise power

transmitted between drive and driven machinery is known.

This power level can be calculated from various measurements of pressure, temperature and flow using the typical

instrumentation fitted to the machinery train.

The power absorbed by the compressor can be expressed = m Cp ∆T (+ Losses)

(Where ‘m’ is mass flow, ‘Cp’ specific heat and ∆T is temperature rise across the compressor)

However, there are several factors which influence the degree of accuracy to which mechanical power can be derived

by thermodynamic calculation.

Firstly, irrespective of quality of instrument, each sensor system is subject to error and these errors are compounded in

the power calculation. Also the accuracy of this site instrumentation is lower than shop test equipment resulting in

even lower precision.

Secondly, ambient conditions such as temperature and gas composition are not as predicted and this can significantly

affect the validity of the calculation process.

Continuous Duty torque measurement provides a single direct measure of power which is not reliant on other

parameters or affected by variation in site conditions. Accuracy and reliability of power data is therefore substantially

higher than power derived by calculation.

A simple comparison of power measurement methods is shown below;

Comparison of methods Thermodynamic Torque Measurement

# of measurements 10 1

Frequency of

measurement

Infrequent Continuous

Accuracy

Typical

4 – 8 %

1%

Test cost High Low

Benefit of Torque measurement over the complete machine life cycle

o Works string test – base-line performance definition

o Commissioning & Acceptance testing

o Define compressor operating envelope

o Machinery performance monitoring

o Process control

o Condition monitoring strategy

o Re-vamp proving ~ eg re-wheel testing

o Mechanical protection

Kühne Intertech GmbH

Witternstrasse 20, 21107, Hamburg - Germany

Telephone: +49 (0)315001 Fax: +49 (0)40 315060

email: info@kuehne-intertech.de - www.kuehne-intertech.de


Typical application examples:

Uncertainties in Mol weight may result in

inaccurate field data.

Precise power data from Torquetronic

defines operating point on power / flow

chart.

Accurate operating point applied to

compressor map.

Facilitates optimum operational envelope

below surge condition.

Works site test:

Turbine test; Accurate load measured by torquemeter.

Compressor test; Thermodynamic power measurement data confirmed by

torquemeter.

Gas transmission applications typically have low Δt across compressor (eg; 25ºK)

0.1º C temperature measurement error = 80kW power measurement error at

12.5MW

Direct power measurement alleviates problems caused by uncertain gas properties:

Optimised condition and performance monitoring with high accuracy base-line power data:

Torquemeter

power value used

as high accuracy

base line data to

performance

monitoring

package.

Torquemeter power data for performance monitoring system provides base-line value, independent of changes in

ambient conditions, gas composition and time related drift.

Torquetronic Continuous Duty Torquemeter

o Better than 1% accuracy for the life of a machine

o Simple mechanical design

o Unrivalled reliability

o Recognised and accepted by all major end users

o Over 1,000 units installed and operational

o Operates with any brand high performance coupling

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