HEAT-RATE AND NO X OPTIMIZATION IN COAL BOILERS USING AN ADVANCED IN-FURNACE MONITORING SYSTEM

Transcription

1 HEAT-RATE AND NO X OPTIMIZATION IN COAL BOILERS USING AN ADVANCED IN-FURNACE MONITORING SYSTEM PAPER PRESENTED AT THE US EPA/DOE/EPRI COMBINED POWER PLANT AIR POLLUTANT CONTROL SYMPOSIUM THE MEGA SYMPOSIUM AUGUST 2001, CHICAGO (USA)

2 Heat-rate and NO x optimization in coal boilers using an advanced in-furnace monitoring system Luis Cañadas, Vicente Cortés AICIA, University of Seville. Dept. of Chemical and Environmental Engineering Parque Tecnológico de la Cartuja. Camino de los Descubrimientos, s/n 41092, Seville, Spain canadas@esi.us.es Francisco Rodríguez, Enrique Tova INERCO, Process Engineering Group Parque Tecnológico de la Cartuja, c/ Tomás Alba Edison, s/n, Seville, Spain frodriguez@inerco.es Pedro Otero, Pedro Gómez-Yagüe ENDESA, Compostilla Power Station Ctra. Cubillos del Sil, s/n, Ponferrada León, Spain potero@endesa.es ABSTRACT This paper will present the OPTICOM monitoring technology, which has been extensively applied in several Spanish and Portuguese coal-fired power stations. This novel monitoring system allows to measure local gas concentration levels (O 2, CO, NO x, SO 2, CO 2 ) in any interior point of the furnace. OPTICOM provides significant and direct information about the real development of the combustion process, guiding the operator to obtain the most adequate tuning of any individual burner and, therefore, bringing about the overall optimization of the boiler. This new tool has been demonstrated as a critical step forward respecting the demands of power plant operators, for which up to now combustion was almost a black box process. Application of this new in-furnace monitoring system to pulverized coal boilers has enabled heat rate improvements over 1%, coupled with NO x emission reductions up to a 30%. This significant performance upgrading has been achieved through targeted boiler tuning, aimed to correct combustion malfunctions detected by the OPTICOM monitoring approach.

3 OPTICOM uses custom-made water-cooled probes for extractive analysis of gas samples and other sensors positioning. These probes are specially designed for insertion into the furnace through the fins joining the water-wall tubes. Therefore, this new concept of extremely narrow probes allows to obtain local and direct combustion information at any furnace location (for example, at the level of each burner), without any significant boiler structural modification. OPTICOM data have been demonstrated as critical input parameters for testing programs or on-line advisory systems aiming at optimizing heat rate and NO x emissions. INTRODUCTION Application of primary measures based on optimized combustion adjustments is one of the most cost-effective means for heat rate improvement and NO x emissions control in thermal power plants 1. Nevertheless, this optimization approach is normally limited by the ignorance of power plant operators of real combustion conditions. These uncertainties about the actual combustion process lead to situations in which operators keep constant most of boiler settings, although significant variations occur respecting fuel properties, fuel flowrate imbalances, load range or air flow disturbances. As it has been stated in previous works 2,3, the inadequate monitoring means that, in general, the operation of the boilers is based on the use of certain combinations of global or indirect variables, derived either from the recommendations of the boiler supplier or from the accumulated experience of the operators of each particular facility. These combinations frequently have more to do with operational stability and historical inertia, i.e. following customary practices, than with true optimum operating conditions. A clear example of this situation is the adjustment of combustion air. The minimization of excess air is, in fact, one of the most direct and effective primary measures (combustion regulation adjustments) for optimizing performance and NO x emissions in any type of boiler. However, boiler operators are extremely loath to use this type of adjustment, due to the possible creation of sub-stoichiometric areas in the furnace which may cause high levels of unburnt fuel or even a plant shutdown. Therefore, relatively high base levels of excess air are habitually used, in spite of its negative effect on heat rate and on the generation of NO x, with priority being given to considerations of operational safety. However, this critical parameter is usually calculated as the average of

4 measurements taken at only 4 or 6 points in the boiler outlet, whose representativeness, with regard to the combustion conditions near each burner, is very limited. Similar situations occur respecting the adjustment of individual burner settings affecting flame geometry, the control of local fuel and air supplies, or the definition of adequate fuel properties and firing configurations. In order to solve the mentioned monitoring limitations, AICIA (a research centre linked to the University of Seville, Spain), INERCO (a Spanish engineering and consultancy firm), and ENDESA (Spain s major utility) have developed the OPTICOM technology, with the aid of partial financing from the European Coal and Steel Community (ECSC). This development has constituted one of the main stages within the extensive optimization program undertaken at Compostilla Power Station 1,4. Apart from activities at the 3 main units of this power station, this novel approach has been industrially validated at the pulverized coal power stations of Puente Nuevo, Teruel and Cercs (ENDESA, Spain) and Pego (PEGOP, Portugal). This paper will be focused on the developments and results obtained at these power stations with boilers of very diverse design (arch-fired and front-wall). Results for tangential units will be included in a following publication. DEVELOPMENT AND APPLICATION OF OPTICOM TECHNOLOGY Description of OPTICOM Technology The OPTICOM technology offers one of the most powerful diagnosis tools currently available for performance optimization in industrial boilers. The use of OPTICOM allows identifying and resolving different hidden boiler malfunctions, like significant fuel and air imbalances between furnace zones. These imbalances might give rise to high carbon in ash levels, in spite of operation being under correct average combustion conditions. In this sense, OPTICOM presents clear advantages over other technologies for combustion optimization aimed at characterizing air and coal flowrates, or conditions in the postcombustion area. The OPTICOM technology consists essentially of a system which allows measurements to be taken in any area of the interior of the furnace of industrial boilers, especially near the burners. An example of this type of measurement is the evaluation of local levels of gas concentrations,

5 in these areas of high temperature and very limited access in boilers of traditional design. The objective of these measurements is to identify the combustion conditions at any particular point inside the boilers, in order to be able to optimize heat rate, auxiliaries consumption, generation of pollutants and slagging. This local information makes it possible to consider the unit as a collection of small virtual units, each made up of a single burner. The targeted adjustment of each of these smaller units results in overall optimization of the boiler. In order to meet these goals, OPTICOM allows these measurements to be made through small openings made in the fins which join the tubes making up the water walls of membrane tube boilers (this approach would not be directly applicable to boilers of tangent tube construction). These fins are typically between 14 and 22 mm for most boiler designs. Therefore, the width of these openings is limited by the width of the fins themselves, while the height is unlimited, due to the geometry of the fins 3. This new concept for measurement inside the furnace of industrial boilers, currently being patented, makes it possible to place the openings in any location required, without being limited to those inspection ports included in the original design of the boiler, and permits the direct measurement of combustion conditions inside the furnace. In this way, it is possible to take measurements at the level of each burner in the boiler, without any significant structural modifications to the unit. In order to access the inside of the furnace, a extremely narrow water-cooled probe has been specially designed for insertion through the openings described above. This probe (10-12 mm width) is able to withstand, in addition, the high temperatures ( ºC) in these areas of the furnace. A first version of the application of OPTICOM technology is that consisting in its utilization by plant operators in order to characterize and adjust the combustion process. This approach has been extensively applied in several Spanish and Portuguese power units. Additionally, and due to the proven interest of these monitoring capabilities, a totally automated version has also been developed 3. At this moment, this totally automated system has been installed at Compostilla and Puente Nuevo Power Stations, and it is planned to be extended to other power stations within the next few months. The Automated OPTICOM System is able to perform a continuous monitoring of combustion conditions through extractive analyses of gas samples taken in the near burner regions. The system allows automatic operation by means of the following: I) Automatic movement of the probes (insertion extraction, lateral movement), in accordance to monitoring sequences selected by the user.

6 II) III) IV) Continuous treatment and analysis of gas samples collected and data processing. Probe cleaning system which guarantees the system autonomy. Advanced monitoring software that, in addition to controlling system full operation and results processing, provides operational recommendations based on INERCO s wide expertise in combustion optimization. Pictures and a sketch of the automation of the OPTICOM system are given in Figures 1 and 2. These figures show the narrow water-cooled probe coupled to a pneumatic cylinder, which is controlled by a multi-way valve, to insert or retract the probe in or out of the boiler furnace. The sample collected by the probe passes through a heated filter to retain fly ash and then goes to a set of valves which either send the sample to the conditioning system, or send pressurised air towards the heated filter and the probe, giving rise to a reverse flow which cleans both of these items. Figure 1: Pictures of the automated OPTICOM system installed at Compostilla P. S. Figure 2: Sketch of the automated OPTICOM system

7 A programmable logic controller (PLC) is used to collect the analysis results, monitor the entire process and report on possible incidents. This information is sent to the Control System, responsible for storing and transferring data, or to a control room computer with the necessary user interfaces. The OPTICOM measurements can be used as additional information for the plant operators and as inputs to the SIRE advisory system 3,5. Figure 3 shows a typical OPTICOM monitoring screen, presenting the profiles of gases from each burner. Figure 3: OPTICOM measurement of existing combustion profiles in an arch-fired boiler Using this automated OPTICOM system, it is possible to obtain a complete measurement set of gas composition in a boiler with 24 burners in around 30 minutes. The advantage of automation is not only that no human resources are needed to take the measurements, but also that the periodically obtained results can be processed by the plant Supervision System, in order to provide for correct optimization of the unit. Advantages of OPTICOM as Diagnosis Tool Conventional Monitoring Systems At present there is a wide variety of monitoring systems aimed at obtaining a correct characterization of the combustion process in industrial boilers. These systems, applied fundamentally to power plant boilers and very unevenly implemented, can be divided into the following four categories:

8 I) Postcombustion systems for the analysis of combustion gases (O 2, CO) or carbon in ash, located at the boiler outlet 6. These systems are generally used for adjusting and controlling the overall combustion process, although they present significant limitations related to the distance of their location from the actual combustion area. II) III) IV) Conventional intrusive probes, including different commercially available equipment (water-cooled probes, suction pyrometers, high speed thermocouples, etc.) 7, that allow for direct determinations inside the furnace. These systems are used through the boiler inspection ports, which are several centimetres in size and are located only at certain points on the furnace. Therefore, this type of measurement inside the furnace has limited representativeness, since it is restricted to the areas where direct access is available through the inspection ports originally installed. This restriction exists because making more openings of this type would require important structural modifications to the boiler tube layout. Wall or contour sensors, such as flame detectors, infrared and acoustic pyrometers, corrosion monitors, cameras or heat flow sensors located in the tubes 8. These sensors are, in any case, indirect measurements of the real combustion process, since they are based on determinations taken at the edge of the furnace. Besides this, their usefulness is heavily restricted by the high complexity of the reality they attempt to characterize. Precombustion systems, based on the determination of individual inputs of air and fuel. The information supplied by these characterizations is very important for the purpose of identifying the origin of combustion malfunctions. Various types of commercial equipment are available, such as the EMIR II semiautomatic reference system 9, which allows precise periodic measurements of fuel inputs to each burner of a pulverized coal fired power plant. In this context, in addition to systems for the continuous measurement of air flows (orifice plates, venturis, etc.) 10, there is other equipment available for totally continuous measurement of coal input flows 11. Most of these sensors, based on microwave, electrostatic, acoustic or extractive techniques, are currently in the final stages of development or industrial testing. The reliability of these systems varies substantially, giving important, although partial and indirect, information on the combustion process. A novel development in this subject is the INERCO s EMIR III automatic coal flow measurement system. 9

9 The Operators Point of View Tuning of an industrial combustion process is quite a difficult task, especially if the information about how the process really evolves is very limited. In this sense, and apart from combustion malfunctions derived from improper manufacturer design or preliminary tuning, there are certain phenomena motivating that in-furnace conditions might be substantially different from time to time, although external boiler registers are kept nearly constant. These phenomena are related to burner elements wear or to slagging deposits in the areas through which air or coal is to be supplied to the furnace. In order to be able to cope with this difficult situation, boiler operators typically demand procedures for properly adjusting each individual burner. This was limited up to now because the existing monitoring approaches, described above, present limitations respecting measuring representativeness, specificity or reliability. In particular, straightforward methodologies for controlling air and coal supply imbalances and optimizing flame geometry are extensively demanded. Summary of OPTICOM Technology Capabilities The OPTICOM technology presents the main advantage of conventional intrusive probes, i.e. direct assessment of the combustion process, but with the additional capability of accessing any interior point of the furnace. This is due to the specific design of the OPTICOM probes, as a small size intrusive system, capable of being inserted in openings between the membranes of the boiler tubes. This permits the individual optimization of each burner with the aim of achieving a true overall optimization of the boiler, and without the need for substantial boiler structural modifications. This approach allows the following complementary capabilities: I) Measurement of imbalances in the air and coal supplies, either due to incorrect design, regulation or maintenance of burner elements, or to slagging deposits in the combustion air or coal outlets. For the case of correcting significant coal flow imbalances, OPTICOM presents significant advantages respecting other methodologies, being in any case complementary:

10 a) OPTICOM allows an adequate on-line optimization, as it has a faster response than manual characterizations of coal supplies, and a more accurate response than most on-line coal flowrate monitors. b) OPTICOM gives the overall result of the combustion process, and therefore also takes into account the additional effects of air maldistributions. II) III) IV) Adequate characterization of flame geometry (length, turbulence), by measuring the evolution of each flame at different points. In this sense, controlling parameters have been demonstrated to be the O 2, CO, CO 2 and NO x profiles within the flame and the correlations CO/O 2, CO 2 /CO and NO x /O 2 at certain measurement points. The interpretation of these profiles and correlations is specific of each boiler design. Characterization of flame stability, by assessing CO and O 2 fluctuations at constant measuring points. Correct determination of the real levels of excess air for the adjustment of combustion, allowing optimization of this parameter, which is critical regarding operation safety aspects. In this context, OPTICOM will not only provide information on imbalances between the different levels and areas of the furnace, but also on possible infiltration of air to the boiler, which could render meaningless the excess oxygen control values taken at the boiler outlet. V) Possibility of optimization in scenarios with high variability of fuels, by associating SO 2 results to coal S content for each burner. These capabilities have been demonstrated and adapted to each specific boiler design through the extensive industrial validation program that has been undertaken for the OPTICOM technology. Examples of results obtained are detailed below. Examples of OPTICOM Application in Pulverized Coal Power Plants Overall Approach Once the difficulties affecting a reliable and precise measurement with OPTICOM probes were completely overcome, a critical aspect of the OPTICOM technology was to determine those sampling locations, parameters and data processing criteria that provide the most useful information for combustion optimization.

11 Therefore, a significant amount of testing campaigns has been undertaken in order to define the capabilities and specific conditions of OPTICOM application for different types of boiler. Measurement reliability, simplicity and representativeness have been taken into account with the objective of establishing the optimum approach for each case. This paper includes some of the results that have been obtained for arch-fired and front-wall boilers. Application in Arch-fired boilers Figure 4 shows the arrangement of the measurement area for the OPTICOM probes, close to the burners, for an arch-fired boiler. Probes of 1.5 m length located around 5 m above the burners arch have been finally chosen as the best option for this case. This figure also indicates the location of other complementary monitoring systems. The general procedure for balancing combustion in the near burner area for arch-fired units has been described in previous papers 1,3. It was demonstrated the critical importance of proper stoichiometry and flame geometry adjustment for each specific burner, in order to improve unit performance. Application of this methodology within an extensive optimization program based on primary measures allowed to achieve improvements of 1.2% in heat rate, with parallel reductions in NO x emissions of around a 30%. After-tuning boiler regulation also provided more stable combustion conditions, lower slagging tendency and improved flyash quality. Figure 4: OPTICOM location for an arch-fired boiler 5. Carbon in-ash and gas distribution at boiler exit 3. EMIR: Coal flow measurement 1. Temperature of gases (infrared pyrometers): Detection of height of flame 2. OPTICOM: monitoring of imbalance levels inside the boiler 4. Wind-box monitoring system: Prediction of air flow supplies into the furnace

12 This optimization program also showed the dynamic characteristics of combustion conditions due to changing coal properties, burner elements wear or localized slagging deposits. In this sense, Figure 5 shows how slagging in particular areas of the boiler, identified in a following maintenance shutdown, is related to unbalanced profiles detected by the automated OPTICOM system. In this particular case, the localized slagging occurred in the extreme areas of the lower secondary air sections. Adjustments in coal flowrates and air damper positioning were applied to equalize combustion conditions within the furnace. Therefore, on-line in-furnace monitoring was proven as absolutely necessary for achieving optimized operation at any time. As it has been said, OPTICOM measurements were also demonstrated to characterize variations in flame geometry for arch-fired units. Figure 6 shows how the correlations CO/O 2 obtained for a single burner vary, for this specific boiler, when the ratio Tertiary/Secondary Air is modified. Similar correlations were obtained for NO x /O 2 measurements, that also provided significant information about the degree of mixing and residence times related to each flame regulation. OPTICOM also allowed to identify unstable flames. This was attained by looking at the fluctuations of CO and O 2 for each burner, that were characterized by calculating the measurement standard deviations for integration periods of 3 minutes. In this context, unstable burner performance was associated to local oxygen standard deviations above 1%. Figure 5: Measurements of the automated OPTICOM system in an arch fired boiler, as a function of slagging blockage percentage % Blockage due to slagging at Lower Secondary Air Section O 2 (%) CO(ppm) NO(ppm)

13 Figure 6: Detection of variations in flame geometry through OPTICOM measurements CO (ppm, 6% O 2, d.b.) TERTIARY AIR REFERENCE CONDITION + SECONDARY AIR O 2 (%, d.b.) Other tests have been conducted in order to confirm the capabilities of OPTICOM measurements for identifying those furnace areas where different fuels were supplied. This was accomplished by means of SO 2 measurements using sulfur content as a tracer. This is of special interest in situations where different fuels are fed into diverse boiler areas simultaneously and in variable amounts. This variability, difficult to characterize in a time frame with the usual methodologies, significantly affect boiler performance. This problem is resolved with the type of measurements made possible by OPTICOM, since these are direct measurements of what is actually happening at a particular time in the boiler furnace; quite the opposite of other types of measurement, such as those based on measurements at a particular point in time (flow or chemical composition) of the individual coal inputs to each burner. Application in Front-Wall Boilers OPTICOM has also been successfully applied in several front-wall units, with the aim of tuning the combustion process in this type of boilers. Capabilities of OPTICOM technology for this furnace design are as important as for the arch-fired units. In this sense, some representative examples are included below.

14 For this specific case, OPTICOM probes were located at the rear wall of the boiler, one in front of each burner. In order to characterize flame evolution, measuring points were placed for each burner at different distances from the rear wall. Due to the importance of the information provided, the OPTICOM on-line application for front-wall boilers considers the measurement at 3 points for each burner, located at different distances from the opposite rear wall. Figure 7 presents the results obtained at a front-wall unit, using the OPTICOM approach, respecting oxygen contents near the rear wall (corresponding to each flame tail). This figure also shows the results of coal flowrate supplied to each burner (using EMIR II 9 ), oxygen levels at different areas of the furnace exit, and average CO and temperature levels in the upper and lower parts of the furnace.in this example for front wall boilers, significant differences between the oxygen levels corresponding to the tail of each flame (measured at 1 m from the rear wall) have been registered. These differences between the upper and lower levels of burners, also confirmed by CO measurements, are related to coal supply imbalances identified for this boiler. Figure 7: OPTICOM and coal measurements for a front-wall boiler OXYGEN CONCENTRATION AT FURNACE EXIT T2 (T ºC) 28 % (62 t/h) LEVEL 6 (D) CO < ppm LEVEL 5 (C) COAL SUPPLY PER BURNER (FRONT WALL) 30 % (68 t/h) LEVEL 4 (E) LEVEL 3 (B) OXYGEN CONCENTRATION PER BURNER (REAR WALL) 42 % (90 t/h) LEVEL 2 (F) LEVEL 1 (A) CO > ppm T1 < >9 <1,5 1,5-2,5 2,5-3,5 3,5-4,5 >4,5 COAL SUPPLY (t/h, w.b.) OXYGEN CONCENTRATION (% v/v, d.b.) Measurements at the furnace exit also showed additional imbalances between the oxygen levels near the front and rear walls, that might be associated with differences in flame type. This has also been confirmed through oxygen measurement at different distances (1, 2 and 3 m) from the rear wall.

15 Another example of the information that OPTICOM might provide in front-wall furnaces is presented in Figure 8. This figure shows the preliminary situation at the 4 burners corresponding to a bottom level of a front-wall boiler, that had been preliminary tuned according to manufacturer s recommendations. Coal flowrates to each burner, determined through EMIR technology 9, varied from 6 to 11 t/h, resulting in an overall coal feed rate of 19.0 t/h at the 2 left side burners of this boiler level, whilst 12.3 t/h of coal were supplied to the right side couple of burners. Similar situations were reported for the other burner levels, resulting in a higher total coal supply to the left side of the boiler (48.4 vs t/h). Total air supplies to the left and right side burners were approximately equal. This situation of coal maldistribution was easily identified through the OPTICOM measurements (at 1.5 m from the rear wall), that showed oxygen levels below 1% and CO contents reaching 2%, for the left side burners, whereas O 2 was near 3% and CO content was below 0.5% for the right side burners (as it can be observed for the lower level in Figure 8). Figure 8: OPTICOM s O 2 and CO and coal flowrates for the lower level in a front wall boiler COAL (t/h, d.b.) O 2 (% d.b.) CO (%, 6% O 2, d.b.) BURNERS Coal O 2 CO 0.0 Improvement of this situation was attempted through the adjustment of the coal flow regulation devices of this boiler, and a subsequent tuning of burner air registers. This adjustment was guided on the basis of the OPTICOM measurements. After this tuning, maximum CO levels were below 1%, causing an improvement of 1.1% in heat rate, and increasing the combustion stability of this boiler. NO x emissions were also reported to decrease a 15%. Later

16 measurements of coal flowrates showed that the initial imbalances of 5 t/h were reduced to less than 1 t/h. It is very interesting to study for this same case the different flame typologies existing in both sides before tuning. In this sense, Figure 9 presents the results obtained for two different columns of burners at the top of each of them. As it can be seen in this figure, the commented higher total coal supply to the left side of the boiler determined the formation of longer flames at this furnace area. This was characterized by the evolution of O 2, NO x and CO levels from the burners to the flame tail. In this context, left side flames showed a decreasing curve for O 2 and a rising for CO, indicating that a significant part of the combustion process took place near the rear wall. This was also confirmed by temperature measurements and the lower NO x average levels, typical of a less turbulent and longer flame. Alternatively, turbulent right side flames presented increases in O 2 and significant reductions in CO at the regions near the rear wall. Figure 9: OPTICOM s characterization of coal imbalances for front-wall burners 7.0 m 5.0 FLAME EVOLUTION BURNERS NOx 823 REAR WALL CO NOx (mg/nm 3 ) v/v, 3.0 NOx 727 CO 1574 and CO ( ppm), 6% O 2, d.b. 2.0 NOx 866 CO 642 Left side (48.4 t/h coal, d.b.) NOx 593 CO 4460 Right side (38.9 t/h coal, d.b.) DISTANCES FROM THE REAR WALL (m) A final example about OPTICOM application, corresponding to another front-wall boiler, is given in Figure 10, where typical results obtained through burner regulation are presented. In this figure, it can be observed how the O 2 and NO x profiles evolved in the flame tails, when the outer register was closed in order to obtain a less turbulent flame.

17 Figure 10: OPTICOM s characterization of burner regulation aimed at producing a longer flame 11.4 m BURNER FLAME EVOLUTION REAR WALL Overall NO x emissions: 803 mg/nm 3, 6% O 2 NO x (mg/ Nm 3, 6% O 2) OUTER 20% O 2 (%) , NO x (mg/ Nm 3, 6% O 2) Overall NO x emissions: 716 mg/nm 3, 6% O 2 OUTER 10% O 2 (%) ,5 DISTANCE FROM THE REAR WALL ( m ) O 2 NO x

18 This modification aiming at bringing about a longer flame is characterized by average lower NO x levels and significantly higher O 2 levels at the area near the rear wall. These characterizations were used to adjust flame typologies for the different burners, as identical boiler control settings for each burner could correspond to very different real in-furnace situations, due to problems associated to slagging deposits at certain areas or wear at specific burner elements. As a consequence of this flame tuning, overall NO x emissions were reduced from 803 to 716 mg/nm 3 (11% reduction), for a similar unit heat rate. Burner regulation, targeted at optimizing heat rate, achieved decreases of a 1.1% for this performance parameter, by means of improving air distribution between the lower and upper parts of the furnace, reducing 0.3% excess oxygen, and decreasing the Primary Air-Coal ratio. For this new boiler adjustment, NO x emissions were reported to increase around a 10%. CONCLUSIONS Unlike other industrial processes, combustion monitoring in large boilers is, in general, markedly deficient. The application of OPTICOM technology for local monitoring inside the furnace is a new approach, of proven effectiveness, for the performance optimization of these processes. OPTICOM technology has a number of advantages with respect to other traditional combustion monitoring systems. The most straightforward of these advantages, common to any type of boiler, is the capability of providing a direct combustion characterization in any part of the boiler furnace, that allows the assessment of imbalances in the air and coal supplies (based on O 2 and CO mapping) and the correct determination of the real levels of excess air for the adjustment of combustion. This in-furnace direct measurement might be also used for identifying the geometry (through gas composition profile and correlations assessment) and stability (by signal variability evaluations) of the flames. Finally, OPTICOM is capable of characterizing the distribution of fuels of different properties within the furnace (by associating SO 2 results to coal S content for each burner). The application of OPTICOM technology in several arch-fired and front-wall p.c. units, in the scope of optimization programs based on the use of primary measures, has brought about substantial improvements in the overall performance of these plants, with decreases over 1% in heat rate, coupled with NO x emission reductions up to a 30%. All of this without having to modify boiler parts or use scrubbing equipment, and increasing boiler operation stability and reliability.

19 In this sense, OPTICOM measurements have enabled to develop an optimization approach based on the controlled adjustment of overall excess oxygen, maintaining an adequate stoichiometry for each burner, the adjustment of the flame type (based on appropriate control of air inputs and the operation of the mills), the identification of the optimum number of active burners for each operating load, or the introduction in specific zones of limited quantities of cocombustion fuels. All of these adjustments to be made under the premise of appropriate control of the individual operational conditions of each burner, based on the OPTICOM measurements. Extensive testing campaigns have also allowed to identify those OPTICOM s sampling locations, parameters and data processing criteria that provide, for each boiler design, the most useful information for combustion optimization. Application of OPTICOM to tangentially fired units is currently being assessed, with preliminary results also showing promising prospects for this technology. In order to improve even further the capabilities of OPTICOM, several projects are at present being developed. These works are focused on three specific areas: I) Integration of OPTICOM with other complementary monitoring technologies, such as those aimed at measuring windbox pressures, furnace temperatures, and air and coal flowrates. II) III) Development of improved regulation systems for coal and air, managed from the Control Room. Monitoring software for the local control of combustion in a closed loop (with limited range), based on OPTICOM measurements, and integration in the SIRE 5 overall boiler monitoring system. ACKNOWLEDGEMENTS The authors gratefully acknowledge the collaboration of other personnel involved in activities resulting in this paper. Special thanks are given to the technical staff of Compostilla, Puente Nuevo, Teruel, Cercs and Pego Power Stations, and to the ENDESA s R&D Group. This work

20 has been carried out with a partial financial grant from the European Coal and Steel Community. REFERENCES 1. Cañadas, L.; Cortés, V.; Rodríguez, F.; Otero, P.; González, J. F. (1997) "NO x Reduction in Arch-Fired Boilers by Parametric Tuning of Operating Conditions". EPRI- EPA Megasymposium, Washington (USA). 2. Rodríguez, F. (1998). Aumento de la Competitividad Energética y Medioambiental de Grandes Instalaciones de Combustión. Química Hoy. 3. Rodríguez, F.; Tova, E.; Cortés, V.; Cañadas, L. (2000). OPTICOM: Advanced Automatic Monitoring System of Local Combustion Conditions for Improving Boiler Performance in PC Power Plants. 3 rd U.K. Meeting on Coal Reserch and its Applications, Sept. 2000, Proceedings, FUEL. 4. Otero, P.; Gómez, P.; Albadalejo, J.L.; Rodríguez, F.; Cañadas, L. (1999). Efficiency and Environmental Improvement Programme in Compostilla P.S.. PowerGen 99- Europe Conference. Pennwell. 5. Copado, A.; Rodríguez, F.; Cañadas, L.; Cortés, V.; Gómez, P.; Pérez-Santos, E. (2001). Boiler Efficiency and NO x Optimisation through Advanced Monitoring and Control of Local Combustion Conditions. Clean Air Conference, Technologies and Combustion for a Clean Environment, Oporto (Portugal). 6. Lamar Larrimore, C.; Sorge, J. Evaluation of On-line Carbon-in-Ash Measurement Technologies. Third Annual Conference on Unburned Carbon on Utility Fly Ash, Energy and Environmental Research Corporation. Guidelines for Fireside Testing in Coal-Fired Power Plants. EPRI CS-5552, Schmidt, D. Modern Tools and Concepts to Optimise Flames and Combustions, e.g. in Power Plants and Industrial Furnaces, by Using Optical Flame Information (Radiation). PowerGen 99- Europe Conference. Pennwell.

21 9. Salvador-Camacho, L.; Rodríguez, F.; Cortés, V.; Cañadas, L.; Albaladejo, J.L.; Otero, P. (2001). Cost Reduction in Coal Fired Power Stations through Optimisation of Milling Systems. Clean Air Conference, Technologies and Combustion for a Clean Environment, Oporto (Portugal). 10. Vierstra, S.A.; Earley, D. (1998). Balancing Low NO x Burner Air Flows through the Use of Individual Burners Airflow Monitors. Power-Gen International 1998 Conference, Orlando, Florida (USA). 11. Yan, Y.; Reed, A. R. (1998). On-Line Flow Measurement of Particulate Solids. A State of the Art Review. Proceedings of 1 st International Symposium on On-Line Flow Measurement of Particulate Solids, Greenwich (U.K.). Key Words Combustion, monitoring, in-furnace, optimization, heat rate, NO x emissions, flame adjustment, pulverized coal, advisor