bias test anllares r4

Bias Testing the Coal Sample System

at Central Térmica de Anllares

Stephen Smith, M.S.

Consulting Chemical Engineer

Coalsmith Consultants, USA

Enrique Sabaté, Sales and Project Manager

Bulk Weighing & Monitoring Equipment

Process Instruments, Spain

National Weighing and Sampling Association

St. Louis, MO Feb 24, 2009

COALSMITH

CONSULTANTS

National Weighing & Sampling

Association St Louis, MO Feb 24, 2009 2

Central Térmica de Anllares

� C.T. Anllares is owned by

� UNION FENOSA generation (66.6%)

� ENDESA Generation (33.3%)

� Provides 365 MW of electric power

� Burns anthracite coal from Laciana and

Cerredo-Degaña mines delivered by truck.

� Began operations in 1982

COALSMITH

CONSULTANTS



Bias Test - Anllares

Unión Fenosa Generación and Endesa Generaciónare interested in control of quality of national coals

� Anllares burns truck coal from local mines

� Coal is weighed and sampled at delivery point

� Sample lots are 10 to 12 trucks

� Truck Auger sampler was replaced by new sweep arm sampler and bias tested

� Found no bias of commercial significance

� Sampler is now the Foundation of the coal quality control program at Anllares

COALSMITH

CONSULTANTS



C.T. ANLLARES

COALSMITH

CONSULTANTS



Central Térmica de Anllares

COALSMITH

CONSULTANTS



C.T.Anllares

The BIAS TEST was

conducted on the conveyor

belt line from the truck

hoppers to the power plant

C.T.Anllares Plant Coal Data

Fuel Storage capacity 1,200,000 tons

Reclaim capacity available 300,000 tons

Milling capacity per mill 37,809 kg/hr

Total capacity 189,046 kg/hr

Fine coal grinding 85% minus 200 US mesh

Quality 35% Ash, 7.5% Moisture

COALSMITH

CONSULTANTS



FW Boiler for 6% volatile coal

COALSMITH

CONSULTANTS



Truck coal scales and auger sample

COALSMITH

CONSULTANTS



SWAX Primary Sampler and Series 20 Scale

•Nominal Rate: 500-700 MTPH

•Belt width 1200 mm (48”)

•Belt speed 3 m/s (590 FPM)

•Material top size 50 mm (2 inches)

with 75% <25 mm (1 inch)

•Primary cutter 300 mm (11.8 “)

•Average sample 17 kg (37.5 lbs)

•Ramsey S.20 scale monitors flowrate

COALSMITH

CONSULTANTS



SCSU (Installation Phase)

COALSMITH

CONSULTANTS



Sample and reject conveyors completed

COALSMITH

CONSULTANTS



Self Contained Sampling Unit (SCSU)

COALSMITH

CONSULTANTS




Association St Louis, MO Feb 24, 2009

Secondary Sampler

Swax-7000S

Sample Feeder

Automatic

Sample

Filling

Machine

Tertiary

Splitter

CSA-3500X

Colloid Crusher

Sample Feeder

Reject Conveyor

Control Panel

SCSU Equipment

COALSMITH

CONSULTANTS



Bias Test: Scope of Work

� TASK 1 – TEST PREPARATION

� TASK 2 – GATHER OPERATING DATA

� TASK 3 – CALCULATE STATISTICS

� TASK 4 – PREPARE REPORT

COALSMITH

CONSULTANTS



TASK I: Test Preparation

1. Review contractual design data

2. Check system for conformance

3. Start, run, and evaluate system

4. Erect scaffold, modify riffle

5. Prepare table of random stop times

COALSMITH

CONSULTANTS



Design Data

Primary Sampling Stage……………Sweep arm cutter

Drive…………………………Electric

Cutter opening………………11 .8 inches (300 mm)

Main Belt Velocity……………2.5 m/s

Operating interval……………45 seconds

Primary Feeder………………………Chute and conveyor

Time to feed primary cut to crusher……530 sec.

CrusherManufacturer…………………Lightning Crusher

Type……………………………Hammer mill

Secondary Sampling Stage Drive System…….Pneumatic

Type…………………………Sweep arm cutter

Cutter opening ………………3 inches (75 mm)


Tertiary Sampling Stage Drive System……Electric

Type…………………………Rotating, fixed radial cutter

COALSMITH

CONSULTANTS



Primary Sampling Stage

Cutter opening 11 .8 inches (300 mm)

Main Belt Velocity……………2.5 m/s


COALSMITH

CONSULTANTS



Secondary Sampling Stage

Pneumatic Drive Sweep arm cutter

Cutter opening 3 inches (75 mm)

Operating interval 8 seconds

COALSMITH

CONSULTANTS



Tertiary Sampling Stage

Electric Drive System

Rotating chute, fixed radial cutter

COALSMITH

CONSULTANTS



Options Selected for Test Design

� Perform Student’s t Test for Bias� Ash and moisture

� 2% precision

� 30-minute test batch time interval

� Lot size 400 tons (10 to 12 trucks)

� Two stopped-belt reference increments

� Collect, combine, and reduce to no less than 4 kg

� Retain system sample for 30 minutes, weight 4 kg

� Sample ratio (SR) plotted continuously on control chart� SR = weight of sample / weight of lot

� Out of control conditions? Stop the test to correct problems

� 40 test pairs were planned

� 36 pairs were collected over 6 test days.

COALSMITH

CONSULTANTS



Checking System for conformance

COALSMITH

CONSULTANTS



Erect Scaffold for Stop Belt Cuts

COALSMITH

CONSULTANTS



Modify Crusher and Riffle

•Removed crusher baffle plate

•Fabricated feed chute

•Mounted riffle on table for stability

COALSMITH

CONSULTANTS



Riffle Modifications

COALSMITH

CONSULTANTS



Final Riffle Configuration

COALSMITH

CONSULTANTS



COALSMITH

CONSULTANTS



Collect Reference SB Samples

COALSMITH

CONSULTANTS



Table of random belt stop times

1830.213240

…………

2380.50797

1610.06076

29140.93715

1720.13644

26110.74463

2160.42722

2380.49151

STOPBELT 2 TIMESTOPBELT1 TIMERANDOM NUMBER

2NUMBER OF STOPBELT

SAMPLES

30 MINUTESBATCH INTERVAL

COALSMITH

CONSULTANTS



Phase 2: Gather Operating Data

1. Train test personnel to safely collect

and prepare the stopped belt sample

2. Coordinate test with yard supervisor

3. Initiate test with random stop schedule

4. Record SB and SS sample weights

5. Label paired samples for shipment

6. Monitor the sample ratio

COALSMITH

CONSULTANTS



Crush both SB Reference Samples

COALSMITH

CONSULTANTS



Riffle SB Reference Sample

COALSMITH

CONSULTANTS



SB Sample - preserve moisture

COALSMITH

CONSULTANTS



System Sample Packaging

COALSMITH

CONSULTANTS



Coordinate Test with Supervisors

COALSMITH

CONSULTANTS



Control chart of sample ratio

COALSMITH

CONSULTANTS



Continue Testing 8 sets per day

COALSMITH

CONSULTANTS



Phase 3: Calculate Statistics

1. Receive coal Ash/Moisture data

2. Check for outliers

3. Test for independence

4. Calculate Student T statistic

5. Evaluate null hypothesis (zero bias)

COALSMITH

CONSULTANTS



Lab Results

1. Subtract SB from SYS to

get difference

2. Calculate Standard

Deviation of differences

3. Plot the differences and

count runs

4. Calculate Student t statistic

COALSMITH

CONSULTANTS



Ash Differences Plot

COALSMITH

CONSULTANTS



Bias Test Ash Results

Evaluate Runs

-2.000

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

2.000

2.500

3.000

0 10 20 30 40

Sample No.

Syste

m-R

efe

ren

ce V

alu

e

System-Reference Median Difference

Etc.

Total = 16 runs

COALSMITH

CONSULTANTS



Bias Test Ash Results

The number of runs falls between the

upper and lower bias limits. The

observations within each series

appear to be independent.

TRUE

Is Independent (True if OK, False if

not independent)

24Upper Independence Limit

14Lower Independence Limit

16Number of Runs

18Number of Minuses

18Number of Plusses

0.38Median of Difference

0.34Average Difference

AshParameter

COALSMITH

CONSULTANTS



Student t Results

Bias not detected in the

sampling system.

Test Result

-2.000Lower LTB Limit

2.000Upper LTB Limit

0.020Lower Confidence Limit

0.654Upper Confidence Limit

2.156Actual Student-t

2.030Critical Student-t

36Number of Measurements

0.937Standard Deviation

0.337Mean Difference

ValuesTitle

COALSMITH

CONSULTANTS



Evaluate Null Hypothesis

The confidence interval for this

coal characteristic includes 0;

thus, the statistical analysis

for this characteristic indicates

the system is unbiased.Bias Test Result

TRUENot Biased

0.605Upper Bias Limit

-0.020Lower Bias Limit

0.295Point Estimate of Bias

COALSMITH

CONSULTANTS



Wolfware Bias Test Software

1. Easily runs calculations, tables, graphs

2. Conforms to current standards

� ISO 13909 and ASTM D6518

3. Output MS Excel for use in report prep

4. Runs ALL THREE ASTM calculations

from same data files

� Wilcoxon, Student’s t, and Hotelling’s T2

COALSMITH

CONSULTANTS



Phase 4: Prepare Report

1. Prepare Test Narrative

2. Insert Photographs and Graphs

3. Submit certified report with conclusive

bias test statement to Thermo

4. Certify report and submit to client

COALSMITH

CONSULTANTS



Ash and Moisture Conclusions

The observed mean of the difference in ash (0.337) is not significantly

different from zero. It may be concluded that, under the conditions which

prevailed during the test, the system can be accepted as unbiased.

0.020 < 0.337 < 0.654Ash LCL < Average difference< UCL

-0.011 < 0.216 < 0.443Moisture LCL < Average difference< UCL

The confidence interval for moisture includes the value zero. Since the

difference is not significant according to the Student-t statistic, the

hypothesis of no commercially significant bias in Moisture is accepted.

The observed mean of the difference in ash (0.337) is not significantly

different from zero. It may be concluded that, under the conditions which

prevailed during the test, the system can be accepted as unbiased.

-0.011 < 0.216 < 0.443Moisture LCL < Average difference< UCL

The confidence interval for moisture includes the value zero. Since the

difference is not significant according to the Student-t statistic, the

hypothesis of no commercially significant bias in Moisture is accepted.

COALSMITH

CONSULTANTS



TEST NOTES

� Series 20 belt scale is working with a tested accuracy of 1% compared with truck scales

� Sample Ratio was noted to be trending out of control in batch number 18 of August 21.� Problem was a miss alignment of rollers due probably to a very high loading rate from feeder that causes accumulation of material on scale

� When area was cleaned of coal trend stopped

� Crusher belt drives began to slip and were tightened. Wire cable was removed from crusher

COALSMITH

CONSULTANTS



Conclusion

A credible coal quality control system will withstand scrutiny and enhance business communications

� Insure compliance with ASTM and ISO standards� Perform Initial bias test and establish control ratio plots

� Produce defendable results for all lots

� Speak with data, not opinions, to defend integrity of sample results.

� Maintain and document the QC program� Conduct inspections and lab audits

� Perform maintenance and modifications

� Deliver training and managerial consulting

� Write procedures, respond to audits, and reply to board inquiries

� Certify ongoing compliance � Continue sample ratio plots

� Conduct bias tests whenever needed

� Comply with changing standards and contract provisions

� Continually monitor system integrity and promptly correct problems

COALSMITH

CONSULTANTS



Thermo Fisher Scientific

� Provides Bulk Weighing & Monitoring

Equipment and Process Instruments

� Enrique Sabaté, Sales and Project Manager

� Manuel Gonzalez, Field Service Engineer

COALSMITH

CONSULTANTS



Questions? Call Coalsmith

Stephen R. Smith, MS

Coalsmith Consultants

www.coalsmith.com

(423) 843-1815 office

(423) 280-0872 cellular

bias test anllares r4

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