New LOI Monitor for Maximizing Accuracy andReliability Using Calcination Techniques

Francisco Rodriguez1, Enrique Tova1, Miguel Morales1, Miguel A.Delgado1 and Mariano Reyes1

1INERCO Ingeniería, Tecnología y Consultoría S.A. Industrial Processes Division.Parque Tecnológico de la Cartuja, c/ Tomás Alba Edison, 2, 41092, Seville, Spain

KEYWORDS: LOI, carbon-in-ash, unburnt coal, efficiency, heat rate, CO2, monitoring,on-line, Loss On Ignition, reference technique

INTRODUCTION

The adequate measurement of Loss On Ignition (LOI) in pulverized coal boilers is anissue of the utmost importance for optimizing all-round boiler operation, as thisparameter has direct influence on efficiency and marks the limit to establish targetedboiler tunings for NOx minimization. Additional benefits are those related to thesurveillance of ash quality for its sale to the cement industry, the proper calculation ofCO2 emissions or the continuous monitoring and control of downstream facilities for coalash separation or postcombustion.

The benefits associated with the measurement of this parameter also becomes evidentby the possibility of providing appropriate monitoring of ash characteristics to assure therevenues coming from its sale, in addition to defining applicable limits for NOx controloperative strategies or other combustion optimization tunings.

Despite its importance, the process of monitoring this parameter is reduced to dailymanual ash sampling, generally from the electrofilter hoppers, for laboratory analysisafterwards. It takes a long time to generate measurements from this procedure (in somecases up to a day) making impossible to effectively adjust the combustion conditions ona continuous base.

In addition, the usual on-line equipment currently used to measure unburnt matter inash generally demonstrates significant sensitivity to variations in fuel and ash nature, aswell as on boiler dynamics. Typical indirect methods (microwaves, infra-red, etc) arenormally applied which in some cases cast considerable doubt on the values theyprovide, resulting in requirements of periodic calibrations when any of theaforementioned parameters is modified.

This boiler operator demand has been satisfied through the application of the new LOImonitor developed by INERCO (commercialized as ABACO-Loi, patent pending),thanks to years of expertise in designing custom-built equipment for pulverized solidshandling and analysis.

The ABACO-Loi monitor, specifically designed to withstand industrial working conditionsand minimize maintenance actions, provides accurate measurements by automaticallyand precisely reproducing the laboratory standard procedure, that is to say, combiningappropriate weight and calcination stages. The result is an innovative calibration-freetechnology producing reliable LOI measurements without affection of typical variationsin the physical-chemical properties of coal or fly-ash.

REFERENCE METHODOLOGY

The principle behind the ABACO-Loi monitor is the determination of the LOI (Loss OnIgnition or loss of mass for a sample of particles when it is heated to a constant weightin a kiln at temperatures assuring its total combustion, normally over 750 ºC, althoughcalcination temperature is fully configurable).

Drawing on their vast experience in handling and sampling powdered solids, INERCOhas developed the automatic ABACO-Loi system which, when connected directly withthe particle pneumatic transport pipe or even with the ash hoppers, reproduces thelaboratory measuring process on an industrial scale. In this way, the ABACO-Loi is anon-line monitor, specifically designed to withstand industrial working conditions,providing reliable unburnt matter measurements for the coal ash and whose accuracy interms of laboratory measurement has been verified by INERCO, obtaining standarderrors as low as 0.15%.

In addition to assuring accurate analysis of unburnt matter, ABACO-Loi pays particularattention to the sampling procedure, in order to guarantee that the ash being analyzedis representative of the ash generated by the power station. This aspect is generally nottaken into account by other systems and, as a result, usually affects their results to agreater extent than the accuracy of the analysis process itself.

It should be also considered that in the LOI test method for some kind of ashes theweight loss could not be only related to the presence of unburnt carbon in fly ash, butalso to carbonates, and combined water, present in hydrated lime or residual claymineral. Moreover, the presence of sulphides, sulphur, and some iron minerals willdecrease the LOI value due to gain in weight because of oxidation (however, it isaccepted that carbon is the substance most responsible for ignition loss).

In case of managing ashes containing such components that interfere with the LOIdetermination, INERCO has developed a specific procedure, implemented in theABACO-Loi system (as an option) based in thermogravimetric analysis of the massloss. This method is based in calcination under inert/oxidizing atmospheres permittingone to differentiate between the contribution of hydrated lime and calcium carbonate tothe LOI and the contribution of unburnt carbon contents in fly ashes.

In this case, N2 is needed to be supplied to ABACO-Loi to produce the heating of theashes to be analyzed in an inert atmosphere. During this process, oxidation of carbonby gaseous O2 would be hindered and carbonate content is determined; subsequently,the sample is heated in an oxidizing atmosphere and carbon oxidation takes place.

Thus, this advanced online monitor is found to be applicable not only for the accuratedetermination of LOI in conventional coal ashes but in those problematic coal asheshaving big interferences when applying the standard method.

OPTIMIZED CONFIGURATION

The ABACO-Loi has been engineered and designed to respond to the main constrainsand challenges demanded by plant operators: maximum accuracy, representativeness,repeatability and flexibility, compatible with minimum capital expenditure, operatingcosts and maintenance needs (that includes no preventive maintenance and no needfor calibration, based on the measuring principle used).

To this end, the LOI monitor is conceived as modular equipment, in order to assureflexible application and easy assembly in small spaces. The system is made up of 3independent modules (Figure 1), connected together:

• Sampling Module

This module has the equipment required to extract and collect particle samples ofenough size to assure total representativeness.

In the process of application of this LOI monitor, the most appropriate points forextracting the ash are assessed, as well as the proper configuration of the SamplingModule in accordance with installation characteristics, process dynamics and customerrequirements.

In the particular case of power plants, the Sampling Module is normally connected toone or several pneumatic transport ducts conveying the ash to the silo. This is the ideallocation according to INERCO’s experience, as these small ducts convey all the powerplant’s ash, minimizing representativeness errors generated when ash is extracted fromthe boiler’s gas outlet ducts. In this case, the sampler offers the option of beingsynchronized with the electrofilter hopper emptying sequence, for which a dischargingdigital signal system must be provided.

As an optional scope, it may include a manual sample collection system to contrastequipment measurements or to analyze other parameters in the laboratory.

• Analysis Module

This module provides the equipment to transport the aliquot to be analyzed from theSampling Module. This aliquot is weighed on sensitive scales before and aftercalcination in a kiln at temperatures over 750 ºC (fully configurable to attend specificdemands), after which it is returned to the coal ash transport system.

The Analysis Module can be connected to multiple Sampling Modules, from which itpneumatically receives samples in a sequential manner. This way, it can producevalues of LOI from different points that can be further processed for optimizing theprocess or for obtaining the average LOI. Total distance for the ash transport from thedifferent sampling unit should be taken into account so as to avoid ash depositphenomena, among other problems. This drawback can be easily solved by applyingdifferent Analysis Modules, which presents also additional advantages as reducing evenmore the total response time for several sampling demands.

SAMPLINGMODULE

ANALYSISMODULE CONTROL

MODULE

Figure 1. ABACO-Loi sampling, analysis and control modules

• Control Module

This module is equipped with a PLC and all the electrical apparatus to control theoperation of the Sampling and Analysis Modules, as well as, managing thecommunications with the Control Room.

ADVANTAGES OF APPLYING THIS ADVANCED ONLINE LOI MONITOR BASED ONREFERENCE METHOD

Among others, it should be underlined the following items:

Maximum accuracy within the entire range of measurement, ranging from 0% to100% LOI in fly ash (see Figure 3). Typical standard errors are below 0.2%.

Unaffected by variations in physical-chemical properties of coal ash. This is ofgreat interest in the case of Power Stations, or Coal Ash treatment units(separators, post combustors, etc.), managing coal ashes of different nature(i.e. resulting from the combustion of various fuel types as coal blends,biomass, biomass + coal blends, etc.).

Based on reference techniques (weighing and calcination, equivalent to thelaboratory procedure), avoiding frequent calibrations or adjustments required byother systems applying indirect measuring principles (microwaves, IR, etc.).

Maximum reliability of results, making possible the avoidance of parallellaboratory test dedications.

Robust, simple and service-free monitor. Bends and other components that areprone to wear are made of special anti-wearing steel and designed to guaranteelong life service. The layout of valves has been optimized in order to facilitatemaintenance and substitution, if necessary, in very short-time operations.

Time saver, accounting both the avoidance of laboratory dedication and plantoperators’ duties for maintenance purposes.

Modular design for providing versatile application in order to fulfill clientdemands (customized solutions).

Optimized control software. Optional remote diagnosis and adjustment of themonitor via internet.

Response time: as low as 5 minutes per sample.

Possible extension to other solid sample analyses (i.e. ash content in pulverizedcoal, including isokinetic sampling in accordance to US or EuropeanStandards).

CASE STUDY. APPLICATION TO SEPARATION TECHNOLOGIES’ PLANT ATBALTIMORE, MD

Despite its relatively recent development, the advantages of this new LOI monitortriggered its applications at both European and US Power Plants, counting on up to 10operative units (9 of them in Europe and 1 at ST Baltimore’s plant).

Other ABACO-Loi applications are currently under evaluation in different US PowerPlants, as well as, coal ash separators and postcombustors.

This chapter discusses the results being produced at the ST Baltimore’s plant. For thisapplication, one single unit of ABACO-Loi is being used to monitor the product ashcoming from two different coal ash separators. This way, using two Sampling Modules,product ash samples are directly forwarded to the Analysis Module of the LOI monitor(Figure 2) to sequentially determine the quality of the resulting product ash.

Figure 2. ABACO-Loi Analysis and Control Modules at ST Baltimore’s plant

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ST Baltimore'splant results

Other resultsat EuropeanPower Plants

STANDARD ERRORBELOW 0.2%

Coal ashessampled from ESPhoppers or ducts

to ash silos

Product ash fromSeparators'

discharge chute(low LOI values)

Figure 3 shows the comparison established between LOI results produced by ABACO-Loi and the results of the laboratory determinations over samples of product ashmanually extracted at the same moment at ST Baltimore’s plant.

To show the real potential of the ABACO-Loi monitor when analyzing coal ashes withhigher LOI values, Figure 3 also represents the results of similar comparison processmade for other round tests carried out at European power plants, to complement thedata obtained at ST Baltimore’s plant with other having higher LOI results.

It can be observed a very good agreement between ABACO-Loi and laboratorymeasurements. The standard error of ABACO-Loi results has been assessed to besimilar to the one of the reference procedure used by plant operators, which isestimated to be in 0.15%, this highlighting the significant accuracy and reliability of theresults produced by the ABACO-Loi monitor.

Moreover, Figure 4 shows the LOI signal produced by ABACO-Loi (purple circles) andthe representation of periodic laboratory determinations (black diamond) producedaccording to the preexisting procedure for controlling the quality of the product ash.Although samples are taking in different moments, and even in different sections, theoverall results show a very tight correspondence of the determinations made by

Figure 3. Comparison between ABACO-Loi and reference laboratory results

ABACO-Loi monitor. The results also corroborate an ideal adjustment to the dynamicsof the separation plant, processing different coal ashes coming from different units.

Both analyses exhibit the following overall results:

Maximum accuracy or ABACO-Loi for this application, with a perfect adjustmentto the dynamics of the separation plant.

Precise correlation with the results obtained from the reference procedure usedfor controlling the quality of the product ash.

Maximum reliability on LOI monitor performance and results.

No need for calibration. The measuring principle and conceptual design of thismonitor makes it no necessary.

No drift on results, even when more than 8,000 samples are processedmonthly.

CONCLUSIONS

The new online LOI monitor developed by INERCO fully satisfies the demands andexpectations of plant operators for an accurate and reliable measurement of such a

Figure 4. ABACO-Loi results vs Laboratory checks for Separator B

ABACO-Loi monitor. The results also corroborate an ideal adjustment to the dynamicsof the separation plant, processing different coal ashes coming from different units.

Both analyses exhibit the following overall results:

Maximum accuracy or ABACO-Loi for this application, with a perfect adjustmentto the dynamics of the separation plant.

Precise correlation with the results obtained from the reference procedure usedfor controlling the quality of the product ash.

Maximum reliability on LOI monitor performance and results.

No need for calibration. The measuring principle and conceptual design of thismonitor makes it no necessary.

No drift on results, even when more than 8,000 samples are processedmonthly.

CONCLUSIONS

The new online LOI monitor developed by INERCO fully satisfies the demands andexpectations of plant operators for an accurate and reliable measurement of such a

Figure 4. ABACO-Loi results vs Laboratory checks for Separator B

ABACO-Loi monitor. The results also corroborate an ideal adjustment to the dynamicsof the separation plant, processing different coal ashes coming from different units.

Both analyses exhibit the following overall results:

Maximum accuracy or ABACO-Loi for this application, with a perfect adjustmentto the dynamics of the separation plant.

Precise correlation with the results obtained from the reference procedure usedfor controlling the quality of the product ash.

Maximum reliability on LOI monitor performance and results.

No need for calibration. The measuring principle and conceptual design of thismonitor makes it no necessary.

No drift on results, even when more than 8,000 samples are processedmonthly.

CONCLUSIONS

The new online LOI monitor developed by INERCO fully satisfies the demands andexpectations of plant operators for an accurate and reliable measurement of such a

Figure 4. ABACO-Loi results vs Laboratory checks for Separator B

crucial parameter for combustion optimization, solving the main problems affecting toother LOI monitors based on indirect measuring principles.

This LOI monitor is designed to withstand aggressive industrial environments whileproducing optimized performance with no need for calibration or preventivemaintenance. As a consequence, man labor is avoided as regards the typicaldedications to adjust or calibrate the LOI monitor to produce consistent results for coalashes of different nature or properties, and even avoiding the necessity of laboratorydeterminations for contrasting the accuracy of the LOI monitor based on indirectmeasuring principles.

Moreover, once results uncertainty is removed, thanks to the high reliability standardsoffered by ABACO-Loi monitor, the resulting signal produced by this advanced monitorcould be perfectly integrated into the control algorithms of the unit to achieve a real andcontinuous optimization of both the combustion process and the post treatment of coalash byproduct, which is a big challenge that industry could easily solved by applying thisfront-line LOI monitor.

The effectiveness of this state-of-the-art technology has been proved at US andEuropean industrial plants resulting in accurate LOI results and improved control of theprocess.

This LOI monitor is, on the one hand, a must-have tool for plant operators so as tomanage a proper combustion performance, and additionally a perfect complement toother combustion optimization technologies offered by INERCO, focusing on heat rateimprovement and/or NOx control.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the collaboration of other personnel involved inactivities resulting in this paper. Special thanks are given to the management andtechnical staff of Separation Technologies, and to the INERCO Industrial ProcessesDivision.

REFERENCES

[1] Doe, P.O., Smith, Z., and Noel, Q. Fuel, 1992, 9, p.161.

[2] Parekh, B.K. and Groppo, J.G. (Eds.) Processing and Utilization ofHigh-Sulfur Coals, Elsevier, Amsterdam, 1993, pp. 183-195.

[3] Roe, Z.P. and Doe, A. In: Processing and Utilization of High SulfurCoals, (Eds Y.P. Chugh and R.D. Caudle), Elsevier, New York, 1987, pp. 366-7.

[4] J. Payá, J. Mozó et al. Thermogravimetric methods for determining carbon content infly ashes, Cement and Concrete Research, Vol. 28, Nº 5, pp 675-686, Elsevier ScienceLtd., USA, 1998.

[5] Robert C. Brown, Jeff Dykstra. Systematic errors in the use of LOI to measureunburned carbon in fly ash. Fuel, Vol. 74, Nº 4, pp 570-574. Elsevier, UK, 1995.

[6] Francisco Rodríguez, Enrique Tova, Sixto López, Miguel A. Delgado, MiguelMorales. Parallel Heat Rate and NOx Optimization by Innovative Control of PulverizedCoal and Combustion Air Supplies. EPRI Megasymposium, Baltimore, MD, 2010.