LATVIA UNIVERSITY OF AGRICULTURE - Latvijas ...

Toms KomassSOLID FUEL BOILER AUTOMATION FOR BRIQUETTE USETransfer function of the PI (Proportion-Integral)controller:WPI( s)( s)1= KP+( s) T sUR= , (1)∆Uwhere T i– integral time constant, min;K p– transfer coefficient (gain) of theproportional link;U R(s) – Laplace transform of PI output variable, V;ΔU(s) – Laplace transform of PI input variable, V;s – Laplace variable, min -1 .Transfer functions of motor-valves:Wink kskv2k,out=sv1i1( s) = W ( s)ii2, (2)where k v1– transfer coefficient of inlet valve, l s -1 ;k i1– coefficient of inlet valve angular speed, V -1 s -1 ;k v2– transfer coefficient of inlet valve, l s -1 ;k i2– coefficient of inlet valve angular speed, V -1 s -1 .Transfer function of the boiler for transient processsimulation:Wh( s)( s)Kb=( s) T s + 1θS=, (3)QBbwhere Ө S(s) – Laplace transform of boiler outputvariable, °C;Q B(s) – Laplace transform of boiler input variable,kW;T b– time constant of the boiler, min;K b– transfer coefficient of the boiler, °C kW -1 .Transfer function of the temperature transmitter fortransient process simulation:Wfb( s)U=θF( s)Kfb= , (4)( s) T s + 1fbfbwhere U fb(s) – Laplace transform of temperaturetransmitter output voltage , V;Ө F(s) – Laplace transform of furnace output airtemperature, °C;T fb– time constant of temperature transmitter,min;K fb– transfer coefficient of temperaturetransmitter, V °C -1 .The transfer coefficient of the furnace:QBkf= , (5)qinwhere Q B– boiler input heat power, kW;q in– furnace input air flow, l s -1 .Results and DiscussionThe humidity of the wood briquette is 10.6%. Theoptimal briquette humidity for burning is 10 – 18%(Križan et al., 2009).First experimentIn the first experiment, the main target was todetermine the burning process time in the stationaryposition where the position of both motor valves were100% – they were fully opened. Burning process timestarts from the briquette load in the furnace till theend condition achieved. Period end conditions werethe same process data values as they were in the startconditions. In the process graph, temperatures Ө SandӨ F(Fig. 3) were obtained as an average values of threeretries of one experiment. The whole process time was1 hour 8 minutes (01:08:46).The Ө F1temperature rose up to 169.0 °C and within30 minutes reached the process end temperature85.0 °C. The supply water temperature Ө S1remainedin values of 72.2 ± 3.0 °C. Motor valve positionsduring the whole process time were opened for 100%.The furnace flue gasses temperature was high andlosses from the flue gasses were considerable. Theflue gasses average temperature Ө F1= 128.2 ± 35.0 °C(Fig. 3).Second experimentIn the second experiment, the main target wasto determine the time of the burning process at thestationary position where the position of both motorvalves were 50%. The whole process time wasmeasured 1 hour 18 minutes (01:18:04). The fluegasses temperature Ө F2rose up to 196.0 °C in 21minutes, remained the temperature for 18 minutes,and within 40 minutes reached end temperature of theprocess - 85.0 °C. The supply water temperature Ө S2remained of the value of 72.6 ± 4.0 °C. The motorvalve during the whole process time was openedfor 50%. The average temperature of flue gassesӨ F= 152.7 ± 44.0 °C.Third experimentThe third experiment showed the burning processwith motor valve stationary position where inletmotor-valve was closed (5%) and outlet motorvalvewas opened for 50%. The whole process timewas 1 hour 16 minutes (01:16:51). The flue gassestemperature Ө F3rose up to 183.0 °C in 41 minute,within 35 minutes reached end temperature of theprocess - 85.0 °C. The supply water temperature Ө S3varied within71.3 ± 4.0 °C. The average temperatureof flue gasses Ө F3= 139.87 ± 37.0 °C.Fourth experimentIn the fourth experiment, the main target was toobserve the burning process time in the automaticResearch for Rural Development 2012225