Multi-Modular Coordination Control of HTR-PM600 Plant

Transcription

1 Mult-Modular Coordnaton Control of HTR-PM600 Plant Maoxuan Song, Zhe Dong, Xaojn Huang, Zuoy Zhang, Zongxn Wu Insttute of Nuclear and New Energy Technology (INET), Collaboratve Innovaton Center of Advanced Nuclear Energy Technology of Chna, Key Laboratory of Advanced Reactor Engneerng and Safety of Mnstry of Educaton, Tsnghua Unversty, Bejng, Chna ABSTRACT HTR-PM600 s a hgh temperature gas-cooled reactor plant based on the mult-modular scheme,.e. sx modular hgh temperature gas-cooled reactor (MHTGR) drvng a common secondary loop system. Sx MHTGR-based nuclear steam supplyng system (NSSS) modules are tghtly coupled by the secondary flud flow network (FFN) whch contans the secondary sde of steam generators, feedwater system, man steam system, turbne generator system. The secondary FFN control, whch focuses on the feedwater flowrates and man steam pressure, plays a central role n mult-modular coordnaton of HTR-PM600 plant. In ths paper, a dfferental algebrac model of ths secondary FFN s frst proposed. Then, the correspondng flowrate-pressure control strategy s proposed, whch takes the smple form of proportonal-ntegral feedback laws. Numercal smulaton results show both the feasblty and satsfactory transent performance of ths controller. Key Words: HTR-PM600, Flud Flow Network, Flowrate-pressure control 1 INTRODUCTION Due to ts nherent safety and good economc performance, modular hgh temperature gas-cooled reactor (MHTGR) has been vewed as one of the most nnovatve and challengng technologes. Because of ts low power densty, slm shape and strong negatve temperature feedback effect, MHTGR owns nherent safety features. By mult-modular scheme, mult-mhtgrs provdng steam for one steam turbne set, the nherent safety feature can be applcable to large power plants of any desred power ratngs [1-2]. In Chna, the study of MHTGR technology began n the mddle of 1970s.The constructon of a 10MW th pebble-bed hgh temperature gas-cooled test reactor HTR-10 was accomplshed by Tsnghua Unversty n the 1990s [3]. Based upon HTR-10 test reactor, a hgh temperature gas-cooled reactor pebble-bed module(htr-pm) demonstraton project was then proposed. The HTR-PM takes the HTR-10 as a prototype, and uses the German HTR-module and the US MHTGR as references. The HTR-PM conssts of two pebble-bed reactor based nuclear steam supplyng system (NSSS) modules of about 250MW th coupled wth a common steam turbne/generator set of 210MW e [4]. Based on HTR-PM, a concept desgn of a 660MW e sx modular hgh temperature gas-cooled nuclear plant HTR-PM600 has been fnshed by Tsnghua Unversty, whose schematc vew s shown n Fg. 1 [5]. Fg. 2 gves a smplfed process dagram of HTR-PM600 plant, where the NSSS module of s the same as that of the two-modular HTR-PM plant, and the combned superheated steam flow from the sx modules drves the steam turbne for electrcty. It can also be seen from Fg. 2 that one pump and sx regulatng valves govern feedwater functon, where the pump generates the header, and the valves realze flow dstrbuton. Therefore, the secondary loop of HTR- PM600 plant can be regarded as a flud flow network (FFN) shown n Fg. 3, where branches b 1-b 6 denote the secondary sde of the OTSGs wth feedwater valves, branch b 7 contans the equpment of the plant secondary loop such as the steam turbne, condenser, low/hgh pressure heaters, gland heater and deaerator, and branch b f s the pump branch. NPIC&HMIT 2017, San Francsco, CA, June 11-15,

2 Fgure 1. Scheme vew of the HTR-PM600 plant Fgure 2. Smplfed flow for the HTR-PM600 plant NPIC&HMIT 2017, San Francsco, CA, June 11-15,

3 b 7 2 b 1 b 2 b 3 b 4 b 5 b b f The sold lnes n Fg.3 are called the tree branches whch form a tree wthout a crcle, and the other dashed lnes are called the co-tree branches. The control of ths FFN focuses on the regulaton of man steam pressure and feedwater flowrates, whch s key n realzng mult-modular coordnated control of HTR-PM600. In ths paper, a dfferental algebrac dynamc model for the FFN wth topologcal structure shown n Fg. 3 s frst gven. Then, the flowrate-pressure control of ths FFN s realzed based on the smple proportonal-ntegral (PI) feedback laws. Numercal smulaton results show that the control strategy can provde satsfactory closed-loop stablty and transent performance. 2 DYNAMIN MODEL OF THE FFN In ths secton, a dfferental algebrac model of the FFN shown n Fg. 3 s proposed. 2.1 Branch Dynamc Fgure 3. FFN of the HTR-PM600 plant Dong [6-7] has made a detaled analyss of branch dynamc. Refer to hs results, a dfferental equaton s wrtten as dq K R Q Q K H, 1,...,7 (1) dt where Q, R, H and K s the flowrate, resstance, pressure drop and nerta coeffcent of branch b (=1,,7) shown n Fg. 3 respectvely. 2.2 Graph Propertes From Fg. 3, the water/steam FFN s dvded nto a tree contanng the pump branch and ts complement. Branches denoted sold lne,.e. branches b 7 and b f, form the tree of ths FFN, and branches denoted dashed lne,.e. branches b 1, b 2, b 3, b 4, b 5 and b 6, consttute the co-tree. From Krchhoff s current law(kcl) [8], we have Q -η I2 O Qf (2) where NPIC&HMIT 2017, San Francsco, CA, June 11-15,

4 η = (3) where Q= [Q 1,, Q 7] T, Q f= [Q f], Q s the flowrate of branch b (=1,, 7), Q f s the flowrate of branch b f. From Krchhoff s voltage law(kvl) [8], we have T H I 6 η O H f (4) where H= [H 1,, H 7] T, H f =[H f], H s the pressure drop of branch b (=1,, 7), H f s the pressure drop of branch b f. Here, H f can be further expressed as Hf Hd RQ (5) f f where H d s the pressure head provded by pump, R f s the resstance coeffcent of branch b f. Moreover, H d s proportonal to the square of the rotaton speed of the pump. From algebrac equatons (2) and (4), the pressure-drops and the flowrates of the tree branches are NOT ndependent. The flowrates of tree branches Q 7 and Q f can be represented by the flowrates of the cotree branches as Q 7 6 Q (6) 1 Q f 6 Q (7) 1 Moreover, t s clear from equaton (4) that the pressure-drops of co-tree branches H (=1,,6) can be determned by the pressure-drops of tree branches,.e. 2.3 Dfferental Algebrac Model H, 1,...,6 Hd H7 RQ f f (8) From equatons (1) -(8), we have obtaned the dfferental algebrac model of the FFN as Q K ( H RQ RQ H ), 1,...,6 (9) 2 d f f ( d f f) (10) H K K H RQ RQ K R Q The equatons (9) and (10) consttute the dfferental algebrac model, whch s just the nonlnear statespace model for FFN flowrate-pressure control desgn whose object s to realze the mult-modular coordnaton. And t s packaged n Mat Lab/Smulnk software envronment and used as the dgtal smulaton platform. NPIC&HMIT 2017, San Francsco, CA, June 11-15,

5 - Q k Qp Q r 1/s k Q Fgure 4. Feedback Control Loop of the flowrate controllers: Qr : the setpont of the flowrate Q of the cotree branches, R0, : the ntal value of the resstance coeffcent of the co-tree branches, kqp: proportonal coeffcent, kq: ntegral coeffcent R 0, dfferental-algebrac model of the FFN - H 7 k Hp H 7r 1/s k H R 0,7 dfferental-algebrac model of the FFN Fgure 5. Feedback Control Loop of the pressure-drop controller:h7r : the setpont of the pressure-drop H7 of the tree branch b7, R0, 7: the ntal value of the resstance coeffcent of the tree branch b7, khp: proportonal coeffcent, kh: ntegral coeffcent 3 FLOWRATE-PRESSURE CONTROL LAWS The flowrate-pressure control of the water/steam FFN shown n Fg. 3 can be vewed as a water dstrbuton problem coupled wth pressure-drop mantenance essentally. The control objectve s to regulate the flowrate n both co-tree branches b (=1,, 6) by adjustng the openng of the feedwater valves and to mantan the pressure-drop n tree branch b 7 through adjustng the openng of the valve mountng at the nlet of the steam turbne. Usng the proportonal-ntegral(pi) control algorthm, the feedback control loops of flowrate controllers of co-tree branches b (=1,, 6) can take the form as Fg. 4. In the same way, the feedback control loop of the pressure-drop controller of tree branch b 7 can take the form as Fg SIMULATION AND DISCUSSIONS In ths secton, the FFN flowrate-pressure control laws are appled to realze the coordnated control between the sx NSSS modules of the HTR-PM600 plant. Numercal smulaton results under the condtons that flowrate step or ramp are gven as followed wth dscussons. 4.1 Smulaton Descrpton Numercal smulaton here s dvded nto two cases, one s used to verfy the PI parameters on the control performance, the other s used to analyze the stablty. 4.2 Smulaton Results Case A (Flowrate Step) Intally, the HTR-PM600 plant remans at full power,.e. all the sx NSSS modules operate at 100% reactor full power-level (RFP) wth all feedwater flowrates at 96kg/s and the man steam pressure at 13.24Mpa. At 10000s, the flowrate of 1#NSSS module steps from 100% to 90% RFP, whch means that the setpont of Q (=1,,6) steps from 96 to 86.4 kg/s, and the pressure-drop n branch b 7 should be NPIC&HMIT 2017, San Francsco, CA, June 11-15,

6 Fgure 6. Dynamc Responses of Case A: 3 ntegral parameters of the flowrate controller Fgure 7. Dynamc Responses of Case A: 3 proportonal parameters of the flowrate controller mantaned at 13.24Mpa constantly. Dynamc responses of the flowrates Q and resstance coeffcents R of co-tree branches b (=1,,6), and the pressure-drop H 7 and resstance coeffcent R f are shown n Fgs NPIC&HMIT 2017, San Francsco, CA, June 11-15,

7 Fgure 8. Dynamc Responses of Case A: 3 ntegral parameters of the pressure-drop controller Fgure 9. Dynamc Responses of Case A: 3 proportonal parameters of the pressure-drop controller Case B (Flowrate Ramp) The HTR-PM600 plant remans at the steady state that the sx modules are runnng at 100% RFP ntally. The flowrates of 1#-6# modules maneuver lnearly from 100% to 50% RFP wth the speed of 5% NPIC&HMIT 2017, San Francsco, CA, June 11-15,

8 RFP/mn at 10000s, 15000s, 20000s, 25000s, 30000s and 35000s respectvely, whch s the process of HTR- PM600 total thermal power decreases from 100% to 50% PFP (Plant Full Power-level). In the above process, the setpont of Q (=1,, 6) n 100% and 50% RFP are 96 and 48 kg/s respectvely and the referenced pressure drop n branch b 7 should be mantaned at 13.24Mpa constantly. The flowrate Q 7, proportonal to HTR-PM600 total thermal power, s equal to the sum of the flowrates Q (=1,, 6). Dynamc responses of the flowrate Q 7 and the pressure-drop H 7 are shown n Fg Dscussons Fgure 10. Dynamc Responses of Case B From Fgs. 6-10, t s clear that the closed-loop stablty s well guaranteed, and the responses of feedwater flowrates Q (=1,, 7) as well pressure-drop H 7 are satsfactory. In case of flowrate step, the need of decreasng of Q 1r leads to the ncrease n R 1 determned by the regulatng valves openng, whch further causes the decrease n flowrate Q 1. Due to the decrease of Q 7, pressure drop H 7 s smaller, whch s n turn results n the ncrease of Q 2-Q 6. Thanks to the feedback effect of the FFN flowrate-pressure controller gven n Fgs. 4-5, R 7 s then enlarged for mantanng the pressure drop n branch b 7 and R 2-R 6 s enlarged for keepng Q 2-Q 6, the closed system enters to a steady state when Q 1 meets ts referenced value. Smlarly, n the case of flowrate ramp. Due to the decrease of Q 7, H 7 becomes smaller. Due to the feedback effect of the FFN control, R 7 s then enlarged for keepng H 7. When Q 7(Q 1-Q 6) meets ts referenced value, the closed system enters to a steady state. Moreover, n case of flowrate step, there are four sets of experments based on the PI parameters, whose results are shown n Fgs Here, choosng the flowrate controller s ntegral parameter as an example, From Fg. 6, t s very ntutve to see that as the larger the ntegral parameter k Q, the greater the overshoot and the faster the response tme. The dfferental equaton (9) combned wth the flowrate control law can dervate nto a second-order system, the ncrease of k Q causes the decrease of the dampng coeffcent, whch determnes the overshoot and the response tme. The ncrease of the dampng causes the decrease of the overshoot and the ncrease of the response tme. Smlarly, the ncrease of the proportonal k Qp causes the ncrease of the dampng coeffcent as results shown n Fg. 7, and the algebrac equaton (10) NPIC&HMIT 2017, San Francsco, CA, June 11-15,

9 combned wth the pressure-drop control law can dervate nto a frst-order system, the ncrease of k H (Fg. 8) or the ncrease of k Hp (Fg. 9) causes the ncrease of the tme constant, whch determnes response tme. The response tme s smaller as the tme constant becomes larger. Based on four sets of smulaton results above, a set of better PI parameters (k Q =0.0002, k Qp =0.01, k H =0.001, k Hp =0.01) s chosen for case of flowrate ramp. As the set of better PI parameters above was set under the full plant power, t caused H 7 had dfferent gans under other plant power, whch s shown n Fg. 10. It s meanngful to make further research of PI parameters tunng under dfferent plant power. From the smulaton results shown n Fgs. 6-10, the module coordnaton of the HTR-PM600 plant s well realzed by the FFN flowrate-pressure control laws. By adjustng the openng of the feedwater valves and the valve mountng at the nlet of the steam turbne, the control laws guarantee satsfactory stablty and transent performance of flowrates Q 1-Q 6 and pressure-drop H 7. Due to PI form, the controller laws are easly to apply to the dgtal control system platforms. 5 CONCLUSIONS Sx MHTGR-based NSSS modules provde steam for one steam turbne set by mult-scheme, each module has the same degn wth ndependent safety system and shared auxlary, the nherent safety features of sngle MHTGR can apply to HTR-PM600 plant of any desred power ratngs. However, the sx NSSS modules are tghtly coupled wth each other through the secondary FFN. Due to dfferent values of the thermal power of a NSSS module needs dfferent feedwater flowrates, and snce the outlet steam pressure should be well mantaned, the coordnated control of the sx modules s just the flowrate-pressure regulaton of the water/steam FFN. In ths paper, the dfferental algebrac model s frst gven by analyzng the branch dynamc and topologcal propertes of the secondary FFN. Then, the correspondng flowratepressure control strategy s proposed, whch takes the smple form of PI feedback laws. Numercal smulaton results show the feasblty and satsfactory transent performance of ths modular coordnated control. 6 REFERENCES 1. D. D. Lannng, Modularzed hgh-temperature gas-cooled reactor systems, Nuclear technology, 88(2), pp (1989). 2. G. H. Lohnert, Techncal desgn features and essental safety-related propertes of the HTR- MODULE, Nuclear Engneerng and Desgn, 121(2), pp (1990). 3. Z. Wu, D. Ln, D. Zhong, The desgn features of the HTR-10, Nuclear Engneerng and Desgn, 218(1), pp (2002). 4. Z. Zhang, Z. Wu, et al., Current status and techncal descrpton of Chnese 2 250MW th HTR-PM demonstraton plant, Nuclear Engneerng and Desgn, 239(7), pp (2009). 5. Z. Zhang, et al., The Shandong Shdao Bay 200 MW e Hgh-Temperature Gas-Cooled Reactor Pebble- Bed Module (HTR-PM) Demonstraton Power Plant: An Engneerng and Technologcal Innovaton, Engneerng, 2(1), pp (2016). 6. Z. Dong, et al., Module coordnaton control of MHTGR-based mult-modular nuclear plants, IEEE Transactons on Nuclear Scence, 63(3), pp (2016). 7. Z. Dong, Dsspaton analyss and adaptve control of flud networks, Proceedngs of the 2015 Amercan Control Conference, Chcago, USA, July 1 3, pp (2015). 8. C. A. Desoer, E. S. Kuh, Basc Crcut Theory, McGraw-Hll, New York (1969). NPIC&HMIT 2017, San Francsco, CA, June 11-15,