looping system: Design of a heat and mass flow control

Transcription

1 Prof. Dr. Ing. V. Sh Scherer CFD odel of a fluidized bed cheical looping syste: Design of a heat and ass flow control H. Kruggel Eden; S. Wirtz; V. Scherer

2 Cheical looping cobustion - A solid oxygen carrier (etal oxide) is circulated in the syste and is alternately oxidized/reduced - Air reactor: Oxidation of the oxygen carrier - Fuel reactor: Bonded oxygen of the carrier reacts with the gaseous, liquid or solid fuel Air Reactor O 2, N 2 oxidized carrier Fuel Reactor CO 2, H 2 O Gaseous products are CO 2 + H 2 O Air reduced carrier Fuel => No additional separation of N 2 necessary: good efficiencies => Low foration of theral NO x due to low teperatures

3 Scale up of cheical looping processes Existing CFB power plants: e.g. Lagisza III 46MW? Hereby necessary: Siulation ethods 1kW.1kW 1kW 1kW 1kW 1MW????

4 Applicable siulation ethods for fluidized systes - Macroscopic odels - Multi-phase CFD - Fuel reactor - gaseous fuel [Jung/Gawo 28, Deng et al. 28, Jin et al. 29, ] - Solid fuel conversion [Mahalatkar et al. 29] - Fuel reactor odel validation [Mahalatkar et al. 211] - Interconnected odeling [Shuai et al. 211, Mahalatkar et al. 21, Kruggel- Eden et al. 21] - Particle based odels & CFD

5 Interconnected ulti-phase CFD cheical looping odel air exhaust Airreactor Fuelreactor General paraeters Tie step Δ.2 Mean particle diaeter d p [].1525 Angle of internal friction ξ [ ] 3 Maxial packing liit ε s,ax [-].6 Restitution coefficient e [-].9 Kinetic odel Spherical shrinking core Theral power P [MW].5 (.4,.3) Buffer fuel air s, buf s, feed

6 Interconnected ulti-phase CFD cheical looping odel air exhaust Airreactor Fuelreactor General paraeters Tie step Δ.2 Mean particle diaeter d p [].1525 Angle of internal friction ξ [ ] 3 Maxial packing liit ε s,ax [-].6 Restitution coefficient e [-].9 Kinetic odel Spherical shrinking core Theral power P [MW].5 (.4,.3) Buffer fuel Buffer specifications Initial ass [kg] Initial state of reduction [-].65 Initial teperature [K] 12 Initial ass flow d/dt s,feed [kg/s] 3.5 Initial ass flow d/dt s,red [kg/s] Feed teperature [K] 12 Feed state of reduction [-].65 air s, buf s, feed

7 Interconnected ulti-phase CFD cheical looping odel air exhaust Airreactor Fuelreactor General paraeters Tie step Δ.2 Mean particle diaeter d p [].1525 Angle of internal friction ξ [ ] 3 Maxial packing liit ε s,ax [-].6 Restitution coefficient e [-].9 Kinetic odel Spherical shrinking core Theral power P [MW].5 (.4,.3) air s, buf Buffer s, feed fuel Air reactor specifications Width of vessel [].225 Height of vessel [] 8. Gid Grid nuber [-] 15 Inlet gas teperature [K] 3 Inlet gas velocity [/s] 1.45 Inlet gas coposition [kg/kg] N 2 :.77; O 2 :.23 Initial bed height [] Inlet solid velocity [/s]

8 Interconnected ulti-phase CFD cheical looping odel air exhaust Airreactor Fuelreactor General paraeters Tie step Δ.2 Mean particle diaeter d p [].1525 Angle of internal friction ξ [ ] 3 Maxial packing liit ε s,ax [-].6 Restitution coefficient e [-].9 Kinetic odel Spherical shrinking core Theral power P [MW].5 (.4,.3) air s, buf Buffer s, feed fuel Fuel reactor specifications Width of vessel [].25 Height of vessel [].8 Wi Weir hiht[ height [].4 Initial bed height [].21 Initial solids packing [-].42 Initial teperature [K] 1223 Initial state of reduction [-].5 Grid nuber [-] 25 Inlet gas teperature [K] 3 Inlet gas velocity [/s].61 Inlet gas coposition [kg/kg] CH 4: 1 (.594,.354); CO 2 : (.46,.646)

9 Governing gas/solid reactions Oxygen Carrier Materials: Mn 3 O 4 -Mg-ZrO 2, NiO/MgAl 2 O 4, Fe 2 O 3 /MgAl 2 O 4 Mn3O4 CH4 12MnO CO2 2H2O 12MnO 2O 4Mn 2 3O4 4NiO CH CO2 2H2O 4Ni 2O 4NiO 4 2 4Ni Unreacted zone 12Fe 2 O 3 CH 4 8Fe 3 O 4 CO 2 2H 2 O 8Fe O 2O 12Fe O3 Reacted zone Reaction odel and kinetic data d/dt 3b k exp E C R T n ~ 2 / 3 gas ( 1-) n, k, E, b - Derived according to experiental data fro: Q Zafar, A Abad, T Mattisson, B Gevert, M Strand, Che. Eng. Sci. 27, 62, Q Zafar, A Abad, T Mattisson, B Gevert, En. & Fu. 27, 21(2), 61. A Abad, et al., Che. Eng. Sci. 27, 62(1-2), 533.

10 Operation of the interconnected odel T Fuel- reactor air exhaust q Air- reactor Buffer fuel air s, buf s, feed d/dt s,buf =fixed=3.5kg/s Carrier: Mn 3 O 4 -Mg-ZrO 2 => Heat and ass flow control essential

11 Teperature control design Excess heat flux and excess heat flux density air exhaust set act set act Q c T p s ox s, T s ox Ts ox c p g ox g ox g ox ox s ox,,, g T T,, ox,,, fuel exhaust Airreactor Fuelreactor q t Kp / Asurf Q 1/ Tn Q d where set set T g, ox Ts, ox q Kp and Tn fro an open loop step response Bff Buffer fuel, s bub Kp=.35 Tg/Ks/Tu Tn=1.2 Tg air s, buf s, feed KL Chien, JA Hrones, JB Reswick, in: Transact. of the A. Soc. of Mech. Eng. 74, Cabridge 1952

12 Teperature control design Open loop step response for Mn 3 O 4 -Mg-ZrO 2 2 T air exhaust 1.6 d/dt s,buf Kp Tn x(t) 2 kg/s s q set Airreactor x(t).8.4 q (A) d/dt s,buf=2kg/s d/dt s,buf=4kg/s d/dt s,buf=6kg/s kg/s s 6 kg/s s Closed loop progression of T s,ox (left), solid ass flow rate d/dt s,ox (right) d/dt s,buf=2kg/s d/dt s,buf=4kg/s d/dt s,buf=6kg/s air 4 T s,ox (d/dt=2kg/s) 11 T s,ox (d/dt=4kg/s) s, buf s, buf, set T s,ox (d/dt=6kg/s) 2 T(t) [K] d/dt s,ox (t) [kg/s] T s,ox,set, (C) (D)

13 Teperature control design T x(t) q set air exhaust Airreactor x(t) q (A) Open loop step response for NiO/MgAl 2 O 4 d/dt=.5kg/s d/dt=1kg/s d/dt=1.5kg/s Open loop step response for Fe 2 O 3 /MgAl 2 O 4 d/dt s,buf Kp Tn.5 kg/s s 1. kg/s.88 3.s 1.5 kg/s s 2.4 air s, buf s, buf, set x(t) d/dt=2kg/s.4 d/dt=4kg/s d/dt=6kg/s (B) d/dt s,buf Kp Tn 2 kg/s s 4 kg/s s 6 kg/s s

14 Mass flow control design Mass flow rate according to a PI-controller air exhaust fuel exhaust t set act set act s, buf Kp ( s, red s, red ) 1/ Tn ( s, red s, red ) d Airreactor Fuelreactor Kp and Tn derived fro a siplified odel V fuel exhaust Bff Buffer fuel, s bub set s, buf act air s, buf s, feed fuel

15 Mass flow control design Optiization of: f Kp, Tn t t ( act,, ) dt set s red s red V fuel exhaust through a genetic algorith set s, buf act Paraeters of a PI-controller with t del =[3s, 4s, 5s] ox [-] s,buf [kg] Kp [-] Tn [s] Kp [-] Tn [s] Kp [-] Tn [s] fuel Mn 3 O 4 /MnO NiO/Ni Fe 2 O 3 /Fe 3 O

16 Cheical looping syste: Load change P=(.5;.4;.3)MW Solid ass flow (left) and teperatures (right) for Mn 3 O 4 -Mg-ZrO 2 as carrier /s] d/dt [kg/ (A) d/dt s,red d/dt s,feed d/dt s,buf d/dt s,ox Heat flux density (left) and degrees of reduction (right) for Mn 3 O 4 -Mg-ZrO 2 as carrier T [K] (B) T s,buf 8 Tsox s,ox T s,ox,set q [W/ 2 ] (C) (D) s,red.1 s,ox s,red,set

17 Cheical looping syste: Teperature setpoint change Solid ass flow (left) and teperatures (right) for Mn 3 O 4 -Mg-ZrO 2 as carrier /s] d/dt [kg/ d/dt s,red d/dt s,feed d/dt s,buf d/dt s,ox T [K] (A) (B) 8 T s,buf 7 Tsox s,ox T s,ox,set Heat flux density (left) and degrees of reduction (right) for Mn 3 O 4 -Mg-ZrO 2 as carrier q [W/ 2 ] (C) (D).2 s,red.1 s,ox s,red,set

18 Cheical looping syste: Reduction rate setpoint change Solid ass flow (left) and teperatures (right) for Mn 3 O 4 -Mg-ZrO 2 as carrier /s] d/dt [kg/ (A) d/dt s,red d/dt s,feed d/dt s,buf d/dt s,ox T [K] (B) T s,buf Tsox s,ox T s,ox,set Heat flux density (left) and degrees of reduction (right) for Mn 3 O 4 -Mg-ZrO 2 as carrier ] q [W/ (C) (D) s,red.1 s,ox s,red,set

19 Cheical looping syste: Other carrier aterials Solid ass flow NiO/MgAl 2 O 4 (left) and Fe 2 O 3 /MgAl 2 O 4 (right) d/dt [kg/s] d/dt s,red d/dt s,feed d/dt s,buf d/dt s,ox d/dt [kg/s] d/dt s,red d/dt s,feed d/dt s,buf d/dt s,ox 5 5 (A) (A)

20 Conclusions An interconnected ultiphase CFD-odel was derived Teperature and ass flow controls were ipleented and necessary paraeters derived Various setpoint changes for a selection of carrier aterials were considered The applied controllers allow steady operation of the cheical looping odel Detailed investigations of the dynaics in further refined odel fraeworks becoe possible