Modeling and Simulation for a Fossil Power Plant

Transcription

1 Modelng and Smulaton for a Fossl Power Plant KWANG-HUN JEONG *, WOO-WON JEON, YOUNG-HOON BAE AND KI-HYUN LEE Corporate R&D Insttute Doosan Heavy Industres and Constructon Co., Ltd 555, Gwgo-dong, Changwon, Gyeongsangnam-do KOREA Abstract: - Ths paper deals wth the descrpton of the APESS (Advanced Plant Engneerng and Smulaton System), a smulaton software for a fossl power plant, and the s of computer smulaton whch were performed usng the system. The APESS was developed by Doosan several years ago for the purpose of dynamc characterstc analyss for a fossl power plant. In ths study, an exstng fossl power plant n Korea was modeled by the APESS. The smulaton model s dvded nto two parts. The frst part s the process model conssts of several systems such as ar/flue gas system, fuel system and feed water system etc. The second part s the control model ncluded control logcs and phlosophes. The verfcaton of the model wth desgn for steady state was performed. Then we predcted the behavor of the man parameters n load change. The s showed satsfyng agreement wth the real operaton. Hence, the APESS s relable to estmate the dynamc behavor of the real fossl power plant and capable to predct the operaton processes. Key-Words: - APESS, fossl power plant, dynamc behavor, process model, control model 1 Introducton In the fossl power plant ndustry, dynamc smulaton tools are becomng more mportant because of the growng needs to evaluate the dynamc behavors of a fossl power plant. The needs to predct the dynamc behavors of a fossl power plant are growng due to the change n the operaton condton of fossl power plant. Recently, many fossl power plants were operated to cover the mddle load demand as well as the base load demand. That means the operaton condton of a fossl power plant s severer than before. For example, accordng to the techncal specfcaton of Taean 5 MW fossl power plant located n Korea t should be allowable to operate the plant more than 75 cycles of start up and more than thousand cycles of load change per year [1]. To eep up wth the trend of the fossl power plant maret, our company began to develop the smulaton software for a fossl power plant n About 8 years ago, we developed the smulaton software named the APESS (Advanced Plant Engneerng and Smulaton System). After several dynamc characterstc analyses wth the use of APESS, we reported on development of the APESS [2]. Snce the APESS was developed, we have been modfyng t to mprove accuracy of predcted dynamc behavors for fossl power plant. In ths paper, we wll ntroduce the APESS and reported on the s of computer smulaton performed by the APESS. 2 Descrpton of APESS The APESS s an analyss and smulaton system for dynamc characterstc analyss of a power plant. After components comprsed power plant are modeled and proper are nput nto the smulaton model, then the APESS provdes not only the ng values but also the procedure for nferrng the s n the form of graphs and numercal values. 2.1 General Confguraton The APESS conssts of three basc elements, whch are: the component module buldng program called RMS (Resource Management System), model buldng program called GMS (Graphc Modelng System) and GMS runtme envronment called RTE (Run Tme Envronment). The RMS provdes varous facltes for a user to create a new component module or modfy any exstng modules. The GMS s used to confgure a schematc of smulaton model, nput desgn generate object orented C++ source codes and fnally create an executable mage of the model. The RTE loads, debugs and executes the runtme ISSN: ISBN:

2 Fg.1 Structural overvew of the APESS nterface related to control sgnal. The APESS was developed on the bass of the flow networ algorthm. The flow networ algorthm connects the process modules. It receves bundles of nformaton from the process modules through the flow nterface to calculate the overall characterstcs and then passes the s each process module. Fg.2 Model structural dagram mage. It also coordnates a model wth ant trends of varables and dsplayng them durng runtme. Fg.1 shows structural overvew of the APESS In the APESS, there are two types of model. The frst s the process model represented the mechancal components of a fossl power plant and a component s made of a process module. The second s the control model ncludng control logcs and phlosophes. Illustrated n Fg.2, the module created by the RMS has two types of nterface. The frst s a flow nterface related to flud stream and the second s a sgnal 2.2 Theoretcal Bacground Nomenclatures: ρ / ρ : Densty at node and branch P / P j : Pressure at node, j h : Enthalpy at node V / V j / V : Velocty at node, j and branch V : Volume at node H / H j : Heght at node, j H pump : Pump head n branch m : Mass flow rate of branch m, lea : Leaage flow rate of node u : Internal energy at node Q : Total heat rate from boundary to node INP j : Networ topology defnng a connecton mode between node and j INP = : No connecton between node and j j ISSN: ISBN:

3 dv ρl dt + ρ gh j pump 2 j 2 ρ ( V V ) = INPj( Pj P ) ρ g ( H H ) ρ gh f (2) INP j = 1: Connecton node from j INP j = -1: Connecton node to j N : Total number of node L : Length of branch Fg.3 Typcal example of process model Basc Assumptons The APESS treats the thermo-hydraulc problems wth the well-nown three fundamental conservaton equatons,.e., the mass, energy and momentum conservaton n prncple. The process s consdered as a networ composed of nodes and branches so that a process component s modeled by the networs as shown n Fg.3. The node represents a control volume and the branch denotes a flow between them. The prmary state varables of a node are pressure and enthalpy. The other parameters le, densty and vscosty, etc., may be calculated from the materal property functons. The ant problem of state varables regardng nodes and branches s fnally reduced to solvng a set of lnear algebrac equatons. The flud s assumed homogeneous and ncompressble. The mass and energy exchange between systems and boundares s assumed to tae place only n nodes. A branch, on the other hand, just plays the role of a resstance element. The mass, energy and momentum conservaton equatons are formulated at each node, and then a set of ant lnear matrx algebrac equatons s establshed. The ey factors n dervaton are summarzed below. The energy balance at node can be expressed by the followng equaton. d( V ρu ) = dt N j= 1 + h Max( INP N j= 1 j m Mn( INP,) h j j m,) + Q (3) 3 Modelng 3.1 Fossl Power Plant The plant modeled n here was a fossl power plant located n Korea. Ths plant s a once-through type boler. The overall confguraton of ths plant s shown n Fg.4. It s very complcated job to model a real fossl power plant [3, 4]. Hence, some components and systems were omtted n ths study. 3.2 Process Model As stated n 2.1, there are varous component modules provded by the RMS n the GMS. We made process model by selectng a component comprsed power plant and connectng nterfaces between components. The scope of process model n here s dvded by 7 systems. These are ar/flue gas system, pulverzer system, burner system, furnace system, boler feedwater pump/economzer system, separator/ Fundamental Conservaton Equaton Snce a flud s assumed ncompressble, the mass conservaton equaton at node may be expressed as follows. N d( ρv ) dρ = V = INPj m dt dt j= 1 + m, lea (1) For an ncompressble flow, the Bernoull s equaton n branch can be expressed as follows. Fg.4 Overall confguraton of fossl power plant ISSN: ISBN:

4 shown n Fg.6 Fg. 5 Burner system superheater system and turbne/reheater system. Fg.5 s an example of a process model, whch s a burner system. 3.3 Control Model We desgned a control model bass of the real fossl power plant to analyze dynamc behavors. In APC (Automatc Power Plant Control System), UMC (Unt Master Control) s a top control model ncludng requred control functons n boler and turbne control system to generate desred electrc power. Fuel and ar control model calculates a demanded fuel and ar condtons n complance wth load condton, then controls. The pressure of furnace s mostly controlled by IDF (Induced Draft Fan). Steam and water control model s related to steam and water system control n boler. A more detaled llustraton of control model s 4 Model Valdaton As stated above, the smulaton model was carred out usng the APESS. Before smulatng the fossl power plant, t s necessary to chec the stablty and relablty of the smulaton model we bult. The smulaton model was verfed usng open loop test and close loop test. We could chec the stablty and relablty of the process model by comparng the s of the open loop test and the desgn under the steady state condton. Smlarly, the verfcaton of the control model could be checed by comparng the s of the close loop test and the desgn. 4.1 Input It s necessary to nput desgn values nto process model n order to use the APESS for tests. Fg.7 llustrates the structure of nput schematcally. From ths fgure, the model nput are dvded nto three parts. The frst s the coal, ar and flue gas Fg.7 Schematc dagram for model nput Fg. 6 Structural dagram of control model ISSN: ISBN:

5 Table 1 Results of open loop tests 1% MGR 75% MGR 5% MGR 3% MGR Items Unt Desgn Desgn Desgn Desgn Power MW Man steam pressure Man steam flow rate Man steam Reheater steam g/cm 2 g ton/hr 2,29.8 2,29.6 1, , ,68.7 1, o C o C system. The second s the water and steam system and the last s the steam turbne system. The feed flow rate, and number of used mlls are requred n the coal, ar and flue gas system. Water and steam system requres the pressure, feed flow rate and enthalpy. Fnally, steam turbne system requres the pressure, enthalpy and output electrcal power. 4.2 Open Loop An open loop test s the test to chec the stablty of components mechancally. The control model was elmnated n ths test. We performed several open loop tests under the dfferent load condton. The test were performed under the condton of MGR, 75% MGR, 5% MGR and 3% MGR. Here, MGR stands for maxmum guaranteed ratng. The s of open loop tests are shown n Table 1. From ths table, the calculated values by the APESS converged and the dfference between the desgn and the s of open loop tests s very small. The errors are less than 1.3%. From these s, we could get the stablty and relablty n our process model. 4.3 Close Loop A close loop test s the test to chec the stablty of control logcs and phlosophes. So the control model was used n ths test n the contrast wth an open loop test. In the open loop test we manpulated the actuators to obtan desred s manually. On the other hand, we could get the desred s automatcally n close loop test by control model. On the bass of nputted n open loop test, we performed the close loop test under MGR condton Table 2 Close loop test s of MRG Item Unt Desgn Power MW Man steam pressure g/cm 2 g Man steam flow rate ton/hr 2,29.8 2, Man steam o C Reheater steam o C The s of close loop test are shown n Table 2. From ths table, there s a lttle dfference between desgn and test s. The maxmum error s equal approxmately 2.9%. Le n the case of open loop test, we can get a stablty and relablty n our control model from these s. 5 Comparson of Smulaton Results wth Operaton Data In here, the modeled plant s a fossl power plant located n Korea. The operaton condton of ths plant s the supercrtcal steam condton such as the man steam pressure of 254 g/cm 2 g, man steam and reheats steam of 569 o C. We compared the operaton and smulated n a load change. In ths study, the load decreased from 1% MGR to 75% MGR for 4 mnutes. That means the output power decreased from 8 MW to 6 MW. We obtaned the operaton per 1 mnutes from 1:3 ISSN: ISBN:

6 a.m. to 11:5 a.m. on July 5 th, 26 and smulated the model at 1 second nterval. The man parameters such as output power, man steam pressure, man steam, feed water flow rate and coal flow rate were observed durng the load change. 5.1 Output Power The output power decreased from 8 MW to 6 MW durng the load change as shown n Fg.8. The output power of the operaton was less than 8 MW but that of the smulated s was 8 MW precsely. We thought that a lmtaton of the modelng was the cause of ths dfference. The smulated was smlar to the operaton n a trend durng the load change and the output power after the load change completed was almost equal. 5.2 Man Steam Pressure The man steam pressure decreased as the load decreased. Fg.9 shows the change of the man steam pressure durng the load change. In ths fgure, the s of the smulaton showed a satsfyng agreement wth the operaton. 569 o C and ths value s closely smlar to the operaton. 5.4 Feed Water Flow Rate It s mportant to observe the feed water flow rate because the man steam pressure and depend strongly upon the feed water flow rate. The feed water flow rate must decrease durng the load decrease to eep man steam and decrease the man steam pressure accordngly wth the load change. Fg.11 shows the comparson of the operaton and the smulated s. Though there was a dfference between the operaton and smulated s, both were very smlar n trend. 5.5 Total Coal Flow Rate The coal flow rate s an mportant parameter for a fossl power plant. In Fg.12, the coal flow rate must 3 25 Smulated 5.3 Man Steam Temperature The man steam s very mportant factor for a fossl power plant because t affects the lfe of boler and turbne. So, the man steam s controlled wthn a restrctve range n a load change. In Korea, the devaton of man steam s ±8 o C. Fg.1 shows the operaton and the smulated s. Though the operaton was almost 568 o C, the s of the smulaton fluctuated snce the load change started. However, the average was Man Steasm Pressure (bar) Tme (hr:mn:sec) Fg.9 Man steam pressure Ouput Power (MW) 9 8 Smulated Tme (hr:mn:sec) Fg.8 Output power Man Steam Temperature ( C) Smulated 5 Tme (hr:mn:sec) Fg.1 Man steam ISSN: ISBN:

7 Feedwater Flowrate (ton/hr) Smulated very hgh level of accuracy and relablty accordng to the desgn. Moreover, the s of smulaton wth the APESS n condton of load change could clearly descrbe the trend of the dynamc behavor for fossl power plant. Based on these nformaton, we may conclude that APESS s relable to estmate the dynamc behavors of a real fossl power plant and capable to predct the operaton processes. 5 Tme (hr:mn:sec) Coal Flowrate (ton/hr) Fg.11 Feed water flow rate 3 Smulated References: [1] KEPCO, Techncal specfcaton of Taean Thermal Power Plant, 1999 [2] Chang-Ho Cho, K-Hyun Lee, Dong-Su Lee and Seung-Mn Km, Development of a dynamc analyss and smulaton system for power plants, POWER GEN Internatonal 23, 23 [3] Taahra Oh and Toshno Inoue, Dynamc characterstcs and control system for varable pressure operaton supercrtcal once-through steam generator, Ishawajma-Harma Engneerng Revew, Vol. 21, No. 5, 1981 [4] Taahra Oh, Toshno Inoue, Yuar Yazawa and Yuo Ohsawa, Development of dynamc smulaton system for energy plant, Ishawajma-Harma Engneerng Revew, Vol. 31, No. 5, 1981 Tme (hr:mn:sec) Fg.12 Coal flow rate decrease as the feed water decrease durng the load change. The operaton and the smulated s had very smlar trends. But there s an approxmately 1% dfference between two s. Also, n the case of the feed water flow rate, there was a dfference of about 1%. We thought that the model bult by us had affected on these dfferences. For an example, n a real fossl power plant there are many leaages but our model has no leaage pont. In spte of the dfference between the operaton and smulated s, we could predct the trends of the coal flow rate. 6 Concluson The modelng and smulaton of a fossl power plant wth the APESS have been successfully completed. In open loop test and close loop test, the s showed a ISSN: ISBN: