BEHAVIOR RESPONSES AND CONTROL MODELING BASED CASCADED PID CONTROLLER SCHEME FOR COMBUSTION OF A UTILITY BOILER

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1 BEHAVIOR RESPONSES AND CONTROL MODELING BASED CASCADED CONTROLLER SCHEME OR COMBUSTION O A UTILITY BOILER A.Sewin Mich Priyadharson 1 1. Asst.Prof/EIE Dept, Vetech Dr. RR & Dr. SR Technica University, Avadi, Chennai, India. emai: sewin_priyadharson@yahoo.co.in Dr.T.R.Rangaswamy 2 2. Professor/IT &Dean (Academics), B.S.Abdur Rahman University, Vandaur, Chennai, India. emai: ramy49@bsauniv.ac.in Abstract The main objective of the combustion controer in a therma power pant is to reguate fue and air in proper ratio to maintain the desired steam pressure at the turbine inet, irrespective of the changes in steam demand. To achieve a continuous suppy of steam at the desired pressure conditions is difficut to cope with inherent time deay, noninearity due to uncertainty of the combustion process and frequent oad changes. This paper deas with the design of behavior response computation based approach to get the optima controer parameters for the combustion contro of utiity boier. A separate contro mode is deveoped for ue and system. The contro mode for fue wi drive the ue controer which is cascaded with controer. controer for and ue system wi use the optimum parameter derived from response based computation method. Many steady state and dynamic behaviora responses were anayzed for different oad conditions. A ab scae experimenta setup is fabricated in the aboratory for fue and air contro and tests were carried out for severa oad conditions. Optima controer parameters were obtained when the experimenta responses have good agreement with the rea time behavior responses. The advantages of the proposed design are highighted. Key words: utiity boier, controer, combustion contro I. INTRODUCTION The utiity boiers are arge capacity steam generators used purey for the eectrica power generation. In a Therma power station, steam is produced in a boier, is expanded in the prime mover (Turbine) and condensed in a condenser before feeding it into the boier again. The turbine shaft is couped with generator, which is used to produce eectricity. Combustion contro in a utiity boier is one of the most important contro oops in a power pant. The combustion system consist of airfow and the fue fow contro oops that are driven by the firing rate demand signa through master steam pressure controer. Conventiona (Proportiona Integra Derivative) controer used for combustion contro is simpe in structure, reiabe in operation and robust to certain extent in performance. But they are not generay suitabe for non-inear, higher order, time deayed and compex systems that have no precise mathematica modes. urther it needs frequent tuning, which is not an easy task and is aso time consuming Ma Su-xia et a [1] designed software for static behaviors of circuating fuidized bed boier to provide precious technica support for optimization operation of the boier, and provide technica methods for the ISSN : Vo. 3 No. 1 eb-mar

2 deveopment of advanced circuating fuidized bed combustion technoogy. arshad et a [2] anayzed reiabiity indices for a parts of generation unit (Therma Power Pants) by using new method of modeing. Huan Zhao et a[3] in order to improve boier efficiency and to reduce the NOx emission of a coa-fired utiity boier using combustion optimization, a hybrid mode, by combining support vector regression (SVR) with simpified boier efficiency mode, was proposed to express the reation between operationa parameters of the utiity boier and both NOx emission and boier efficiency. ang et a [4] described accuratey the status of boier furnace combustion in simuation, anaysis and optimization of power generation process and to improve the accuracy of simuation. Severa researchers deveoped dynamic modes [5] for boiers. The compexity invoved in obtaining the reasonaby accurate modes is high. If assumptions were made to reduce compexity in obtaining modes, it woud yied degraded performance of controers. urther inear [6] and noninear [7] controers were designed and deveoped. Yinsong et a [8] first introduced a noninear mode combining boier-turbine-generator dynamic characteristics for a therma-power-generation unit. Based on the noninear mode, a new coordinated contro design is proposed using the backstepping method incorporating the coordinated passivation approach that considers the entire boier-turbinegenerator system as a whoe. Lee et a [9] investigated a arge-scae once-through-type utra supercritica boier power pant for the deveopment of an anayzabe mode for use in deveoping an inteigent contro system. Widd et a [1] proposed predictive controers based on inearization of the mode. urther custer [11] based performance optimization were deveoped. Horn et a [12] demonstrated an inteigent concepts superior to a standard PI controer with a setting found by cassic tuning rues through siding-mode controer. Biswa et a [13] proposed for deveopment and impementation of supervisory contro and data acquisition (SCADA) based process contro and monitoring system. Bezerra et a [14] deveoped a stochastic optimization mode for the creation of a bidding strategy for a generator in an energy ca option auction. Rajanikanth et a [15] proposed a new approach based on finite difference method for the simuation of eectrica conditions in a dc energized wire-duct eectrostatic precipitator with and without dust oading. In order to utiize the robustness and advantages of the controer, a behavior modeing approach has been proposed to get optimum parameters. The present paper is organized as foows: Section 2 deas with the design of Response behaviors approach to obtain optimum parameters for fue and air controers using fabricated hardware set up in the aboratory. Section 3 deas with Contro modeing of a Boier combustion system. Section 4 deas ab scae experimenta setup. Section 5 describes the simuation studies of conventiona & behavior responses and contro modeing based cascaded controer for combustion process. Section 6 presents the comparison of performances of & behavior responses and contro modeing schemes and Section 7 gives the summary & concusions. II. RESPONSE BEHAVIORS In the present work, many behavior responses for oad vs. pressure, fue fow and airfow with respect to steady state and dynamic states were obtained from therma power pant during rea time operation and are shown in igures (1-6). ISSN : Vo. 3 No. 1 eb-mar

3 5 4 3 Turbine Inet Pressure 2 1 ue Time in mts ig.1. Boier Start-Up curve ig.1 shows the rea time start-up response. Whie starting the boier, the drum pressure shoud be increased sowy to avoid therma stress to the boier tubes. The rate of raise of drum pressure wi be around 1kg per minute and it wi vary depending on the furnace voume of the boier. Whie increasing the drum pressure, proper air-fue ratio is maintained for combustion. Turbine Inet Pressure 9 8 ue Load Turbine irst Stage Pressure ig change in ramp oad ig.2. shows the response of 1 positive change in ramp oad from 6 to 7. Immediatey after oad increases, the turbine first stage pressure increases and turbine inet pressure decreases. In order to keep the turbine inet pressure at the desired vaue, corrective action for air and fue fow is achieved smoothy by the controer. ISSN : Vo. 3 No. 1 eb-mar

4 1 98 Drum Pressure ow ue ow ig.3.open Loop ( fue fow 1 to 95) ig. 3 shows the open oop behavior for change of fue fow in the negative direction from 1 to 95. ig.4 shows the open oop behavior for change of fue fow in the positive direction from 95 to 1. fow aso foows the fue fow to maintain required excess air for compete combustion. Drum pressure takes ong time to reach steady state vaue than fue and air fow. This effect is because of shrinking and sweing action of the water inside the drum Drum Pressure ue ow ow ig.4.open Loop ( fue fow from 95 to 1) 1 ow 8 ue fow ig. 5. Sudden oad change due to grid disturbance ISSN : Vo. 3 No. 1 eb-mar

5 ig.5. shows the behavior of air and fue fow to maintain desired turbine inet pressure and aso boier drum pressure during sudden oad change due to grid disturbance. Grid disturbance may be due to arge and sudden variation in the demand. Sudden variation in drum pressure due to change in the steam demand shoud be brought back to norma by adjusting the fue and air fow in proper ratio. 1 ow 8 4 ue fow ig. 6. Sudden run back of oad due to auxiiary faiure There are two feed water pumps to feed the water and two forced draft fans to suppy required air fow to the boier at fu oad. If anyone fais there is an automatic reduction of oad to 6 of maximum continuous rating to avoid tripping of boier due to ow drum eve and ow airfow. ig.6. shows the behavior of air and fue fow to maintain desired turbine inet pressure and aso boier drum pressure during sudden run back of oad due to faiure of any one of the auxiiaries mentioned above. After obtaining the behavior responses from power pant, rea time simuations were carried out, by mimicking a the above-mentioned cases, on the ab scae experimenta set-up for fue and airfow. In order to obtain optimum controer parameters an iustrative response for fue fow is shown in ig. 7. U E L Experimenta C L O W 4 2 A B D Behavior Point A = f ( k 1) = Experimenta ue fow sampe at k1 th Point B = f ( k 1) = Behavior ue fow sampe at 1 Point C = f ( k n) = Experimenta ue fow sampe at Point D = f ( k n) Behavior ue fow sampe at ig.7. Cosed oop behavior and experimenta responses to obtain optimum parameters. th k instant. instant. th k instant. n th k instant. n The foowing agorithm is proposed for mimicking each behavior response. ISSN : Vo. 3 No. 1 eb-mar

6 Step 1: Initiaize K p, both fue and air fow. K and K the Proportiona, Integra and Differentia gains respectivey of controer for I d Step 2: Conduct experiments and pot the response for one behavior for different oad conditions. Step 3: ind out deviations between behavior and experimenta response at different samping times. Step 4: ind average of a deviations. Step 5: Adjust k p, k I and k d of the fue and air controers. Step 6: Repeat the experiment unti deviations between behavior and experimenta response become zero. Step 7: Note down the fina vaue of k p, k I and k d of the fue and air controers, which are taken as optimum parameters for particuar behavior. Repeat the procedure for a the behaviors mentioned above. TABLE 1. Optima controer parameters for different behavior responses parameters Behavior Responses K P K I K D ue ue ue Boier Start-Up change in ramp oad from 6 to Open Loop Response (Change in ue ow to 95) Open Loop Response (Change in ue ow to 1) Sudden oad change due to grid disturbance Sudden run back of oad due to auxiiary faiure Sudden Load throw off to House Load Keeping the above optimum parameters as guidance, again severa simuations were carried out on the ab-scae experimenta set-up for a the behavior responses. inay, one set of overa optima controer parameter, which wi mimic amost same way for a the types of dynamic behaviors mentioned above was found out. The overa optimum parameters obtained for air and fue fow controers suitabe for any kind of dynamic behavior of combustion process in utiity boier is presented in Tabe2. TABLE 2. Overa Optimum Controer Parameters for ue and Contro oop Optimum parameter K P K I K D ue Controer Controer These optima parameters are used to the ue/ controer through error signa derived from contro modes. III. CONTROL MODELLING O A BOILER COMBUSTION SYSTEM Assumption1: The turbo generator is not on automatic oad dispatch contro. Assumption2: The steam demand variation is due to oad (MW) disturbance ony. Assumption3: The unit contro is under boier foow mode. ISSN : Vo. 3 No. 1 eb-mar

7 With the above assumptions a contro mode has been deveoped to get variabe fue error. P Turbine first stage steam pressure (1) P t - Throtte steam pressure (Turbine inet pressure) (2) d- Drum pressure differentia (3) P s - is the set point for the throtte pressure... (4) Contro baance error is proportiona to (Required Pressure) - (appied pressure)... (5) This is proportiona to the fue error at any oad varying condition. This wi track a desired trajectory within the boundary region. ue error = (P / P t ) P s - (appied pressure)... (6) ue error = (P / P t ) P s - (P 1 ± d )... (7) When oad increases, the steam demand increases, throtte pressure decreases. The difference between the set-point & throtte pressure wi produce the error signa to the combustion controer which wi increase the airfow first & then the fue fow to bring back the throtte pressure to the desired vaue. There wi be a time deay between the appication of the input to the combustion controer and the resuting effect on it, which wi degrade the tota performance. To improve the performance, a contro baance mode has been deveoped to give the variabe fue error to the controer for fue. beow. A contro mode for air has been deveoped which is proportiona to variabe fue error is presented or combustion contro, if ony the theoretica air required for compete combustion of fue is suppied, substantia amount of soot and Carbon Monoxide wi be observed in the fue gases. or achieving compete combustion excess air over and above the theoreticay required quantity wi have to be suppied to the boier. To maintain excess air, the set vaue for the air controer is proposed with respect to the fue error derived from equation (7). Set vaue for air controer = e f Mode + (e f Mode * Weight factor)... (8) Where Weight factor = (W/1) * e f Mode (9) W=12 for ess than 3 of oad or steam fow... (1) W = 15 for 3 to 5 of oad or steam fow... (11) W = 2 for 51 to 75 of oad or steam fow (12) W = 25 for 76 to 1 of oad or steam fow... (13) The proposed vaue of the weight factor W for air is arrived after considering severa dynamics of the boier and aso the knowedge obtained from the experts of therma power station. This wi aso satisfy the contro baance derived by practicing engineers and researchers. The above contro baance mode based air set vaue wi change the airfow immediatey after dynamic or programmed oad disturbance, which wi aways be in excess to the theoretica vaue. ISSN : Vo. 3 No. 1 eb-mar

8 Various Response Behaviors Modeing for ue e f= (P / P t) P s - (P 1 ± P d) e f ue controer- Optima k p,k I,K d ue contro vave Set point = e f + (e f * Weight factor) Damper Modeing for + e a - Actua fow controer- Optima k p,k I,K d ---- Boier Various Response Behaviors ig.8.modeing Based Cascaded Contro for ue and The cascaded controer diagram is shown in fig. 8. ue error derived from the fue mode is cascaded to air mode. When there is dynamic change due to grid disturbance the contro baance mode is proposed by considering turbine first stage pressure change, which is the first and immediate response, due to oad disturbance and considered as feed forward information. Optima k p, k I and k d vaues were obtained from behavior responses method wi be used by /ue controer. IV. LAB SCALE EXPERIMENTAL SET-UP In order to find out optimum controer parameters and aso to carry out the cosed oop studies of and behavior schemes for air and fue fow, a ab scae experimenta set-up is designed and fabricated as shown in ig. 9. Using the optima parameter agorithm, simuations on the experimenta setup for various behavior responses were carried out. The vaues of optima parameters obtained by tria and error method are presented in Tabe1. These vaues are considered as optimum for particuar behavior response because of satisfactory agreement with the rea time response obtained from 21 MW therma power pant. ig.9 Experimenta Set Up V. SIMULATION STUDIES Severa experiments were conducted on the experimenta set-up and the performances for both changes in the set point as we as in the oad perturbation were studied. The responses obtained for positive and negative step change in oad are shown in igs ISSN : Vo. 3 No. 1 eb-mar

9 u e o w t/h r ue K P =1.75, K I =1, K D =.2 ue ow Set Point 5-12 t/hr Behavior Responses and Modeing based cascaded Time in Seconds ig.1 ue fow response LOAD 21MW-42MW A I r o w t /h K P =1.5, K I =.8, K D =.2 Set Point 15-2 t / hr Behavior Responses and Modeing based cascaded Time In Seconds ig.11. ow Response Load 21MW-42MW u e o w t/hr ue K P =1.75, KI=1, KD=.2 ue ow Set Point t/hr Behavior Responses and Modeing based Cascaded Time in Seconds ig.12 ue fow response for 11 to 42 MW change in oad ISSN : Vo. 3 No. 1 eb-mar

10 A i r 5 4 K P =1.5, KI=.8, KD=.2 ow Set Point 38-2 t / hr o w t/ hr Behavior Responses and Modeing based cascaded Time in Seconds ig.13 fow response for 11 to 42 MW change in oad VI. COMPARISON O PERORMANCES O BEHAVIOR RESPONSES AND CONTROL MODELING SCHEME WITH SCHEME After impementing and Behavior Responses & Contro Modeing Based Cascaded controers, their cosed oop behaviors are compared. The comparisons of time-domain specifications and performance of the two controers for positive step change in oad are presented in Tabe 3&4. TABLE 3. Comparison of Time Domain Specifications Controer scheme Behavior Responses and Modeing based Cascaded Controer oop Rise time Peak time fow ue ow fow ue ow Setting time TABLE 4. Comparison of Performances Controer scheme Behavior Responses and Modeing based Cascaded Controer oop ISE IAE fow ue ow fow ue ow VII. CONCLUSIONS The resuts of this paper highight the robustness of the conventiona with behavior responses and contro modeing based cascaded controer scheme for step changes in oads. The response of conventiona contro system has 26 overshoot for air and 39 for fue fow. It settes down after about 83 and 74 steps of increment for air and fue respectivey. The cosed oop response of the behavior responses and contro modeing based cascaded controer scheme shows satisfactory transient response without much overshoot and settes down after about 33 and 31 steps of increment for air and fue respectivey. This shows 55 improvement over conventiona schemes in ISSN : Vo. 3 No. 1 eb-mar

11 setting time for both air and fue. The proposed controer scheme resuts in east ISE and IAE vaues for the step changes in oad showing 24 improvement for air and 3 improvement for fue contro when compared to conventiona schemes. The quaitative and quantitative comparisons of the performance of the various contro schemes revea the superiority of the behavior responses and modeing based cascaded controer scheme over the conventiona contro schemes. VII. REERENCES [1] MaSu-xia Li Hong-ge, (24Jan 211).Static Behaviors and Optimization Operation Techniques for Circuating uidized Bed Boier. Internationa Conference on Digita Manufacturing and Automation, China, Vo 2, pp [2] arshad Khosravi Naziha Ahmad Azi Ebrahim Babaei, (Dec 21). A New Modeing Method for Reiabiity Evauation of Therma Power Pants. IEEE Internationa conference on power and Energy, Kuaa Lumpur, Maaysia, pp [3] Huan Zhao Pei-hong Wang, (12 May 29). Modeing and Optimization of Efficiency and NOx Emission at a Coa-ired Utiity Boier. 29 Aciapacific Power and Energy Engineering Conference, China, pp1-4. [4] ang ang Sun Lii, (2 Sep 21). Joint modeing and simuation of furnace combustion. 29th Chinese Contro Conference, China, pp [5] Aobaida., Poster. R., Ströhe. J, Eppe. B, Hyun- Gee.K, 28. Modeing and investigation start-up procedures of a combined cyce power pant. Appied Energy, pp [6] Tan. W, ang., Tian. L, u. C, Liu. J, 28. Linear contro of a boier turbine unit: Anaysis and design. ISA Transactions, pp [7] D.Yu and Z.Xu, (25). Noninear coordinated contro of drum boier power unit based on feedback inearization. IEEE Trans. Energy Convers., vo. 2, no. 1, pp [8] Yinsong Wang., Xinghuo Yu., (Nov. 21). New Coordinated Contro Design fortherma-power-generation Units. IEEE Transactions on Industria Eectronics, Vo 57, Issue11, pp [9] Lee, K.Y., Van Sicke, J.H., Hoffman, J.A., Won-Hee Jung. Sung-Ho Kim, (Dec. 21).Controer Design for a Large-Scae Utrasupercritica Once-Through Boier Power Pant. IEEE Transactions on Energy Conversion, Vo 25, Issue 4, pp [1] Widd, A.Ekhom, K.Tunesta, Johansson, R, (15 Apr 211).Mode Predictive Contro of HCCI Combustion Phasing Using ast Therma Management and Physics-Based VVA. IEEE Transactions on Contro Systems Technoogy, Issue: 99, pp [11] Andrew Kusiak & Zhe Song, (June 28). Custering-Based Performance Optimization of the Boier Turbine System. IEEE Transactions on Energy Conversion, Vo. 23, NO. 2, pp [12] Horn, M. Reichhartinger, M. (8 eb 21). Mode-free contro of a therma pant. IEEE Internationa Conference on Contro and Automation, New Zeaand, pp: [13] Biswa, G. Maheshwari, R. Dewa, M, (Mar 211).Modeing, Contro and Monitoring of S3RS based Hydrogen Cooing System in Therma Power Pant. IEEE Transactions on Industria Eectronics, PP, Issue: 99, pp 1-4, 28. [14] Bezerra, B., Barroso, L.A., Pereira, M.V., (May 211).Bidding Strategies with ue Suppy Uncertainty in Auctions of Long-Term Energy Ca Options, IEEE Transactions on Power Systems, Vo 26, Issue: 2, pp [15] Rajanikanth, B., Jayan, M., (eb 21). Simuation of dust oaded V-I characteristics of a commercia therma power pant precipitator IEEE Transactions on Dieectrics and Eectrica Insuation, Vo 17, Issue 1, pp ISSN : Vo. 3 No. 1 eb-mar