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Product Certification Using Tank Quality Integration (TQI)

Product Certification Using Tank Quality Integration (TQI). Nigel Fleming, Esso Petroleum and Jonathan Love, Newcastle University APACT 03, April 2003. Contents. Definitions What is TQI? What is Give-away? The Problem Systematic Give-away. The Solution TQI Certification.

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Product Certification Using Tank Quality Integration (TQI)

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  1. Product Certification Using Tank Quality Integration (TQI) Nigel Fleming, Esso Petroleum and Jonathan Love, Newcastle University APACT 03, April 2003

  2. Contents • Definitions • What is TQI? • What is Give-away? • The Problem • Systematic Give-away. • The Solution • TQI Certification. • Justification for Change • Statistical Precision comparison between TQI and existing method.

  3. Every 6 minutes q q v Online analyser Product • Applied recursively: What is TQI? • TQI calculates product tank qualities as the tanks fill, e.g. density, sulphur, cetane, octane ....

  4. What is Give-away? • A laboratory test method is used to certify the tank quality. (ISO test methods.) • Give-away is the difference between the quality you release product at to the customer and the legitimate manufacturing limit. • It reduces profit because it debits yield and/or adds to the cost of manufacture. • The purpose of this talk is to explain a way of using TQI to reduce give-away.

  5. Systematic Give-away • Realized that there was a limit to how small give-away could be reduced. • Right First Time (RFT). Due to the rate of product demanded and the no. of tanks per product grade a target of RFT  95% is set. • Even if the TQI result is an unbiased estimate of the quality it is still subject to random errors. • Error distribution characterized by a variance 2TQI. • The Laboratory methods used to test and certify the product quality are subject to random errors. • Error distribution characterized by a variance 2ISO. • Since TQI is used to manufacture and the Lab. to certify, the delta is important. • QD = QT - QL • Since the TQI and Lab. results are independent their variances add. • 2 = 2TQI + 2ISO

  6. ISO Giveaway ISO ISO  5% Max. 52 51 50 49 48 Lab Cetane 52 51 50 49 48 Lab Cetane

  7. Systematic Give-away • To ensure RFT 95%, • Give-away  = 1.645  • This acts as a manufacturing margin which adds a significant additional cost. • TQI quality target = min. specification + 1.645 

  8. TQI Certification • Alternatively, why not certify TQI for release and remove the manufacturing margin? • The risk of litigation if a customer questions a fuel quality. • TQI is a complex system relative to, taking a sample in a pint bottle to the lab. • Two enabling conditions were set, as follows. • Is a TQI result an accurate estimate of the true quality; i.e. an unbiased estimate of the mean? • Does a TQI result have a smaller error than a single result using the reference ISO lab. method, i.e. TQI < ISO?

  9. ISO Test Method Precision? • Test methods quote Repeatability and Reproducibility values. • Repeatability applies to a sample multi-tested in the same lab. (2r) • Reproducibility applies to a sample multi-tested in different labs. (2R) • 2R > 2r • For the method, 2ISO = 2r + 2R

  10. What is TQI Precision? • The online analyser accuracy and precision provide the basis for assessing the accuracy and precision of TQI results. • Analyser accuracy is set using a validation sample which has been multi-tested in different laboratories. • Analyser precision is defined by how much error is introduced by the online analyser. • The error in the validation sample and the analyser itself are independent of each other. •  2TQI = 2val +

  11. 2r / M + 2R Variance (q) = = 2val N Validation Sample Precision (2val)? • Multi-testing M times in N different labs. using the ISO method generates a sample with a mean qualityq. • E(q) = q the true value of the validation sample • The validation sample mean is a true estimate of the quality and its precision improves with multi-testing.

  12. Analyser Precision? • Another way to look at TQI is as a time series.

  13. Analyser Precision? • Each analyser reading is made up of a deterministic and a stochastic part. Where at is the true quality t is a random measurement error • Given that variance(t) = 2anl, it can be shown: • n is typically between 100 - 200, which significantly reduces the effect of analyser error on the TQI result.

  14. TQI Precision Defined • Then TQI Precision can be determined from equation (1). • For example, for sulphur2TQI = 5.4, 2ISO = 10.5 • TQI < Ref

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