Control of Biomass Fired CHP Generation TUT Energy Seminar: Bioenergy Yrjö Majanne, AUT
Outline What is control engineering? Biomass as a fuel control perspective Control issues in CHP generation Unit control (boiler & turbine) District heating power plants Industrial power plants 11.4.2018 2
What is CHP Generation? It is Combined Heat and Power generation in a same generation unit with high total efficiency. Fuel input: 100 Losses: 17 (17%) Fuel input: 148 Losses: 65 (44%) 11.4.2018 3
Control Engineering Analysis: Control system design is based on dynamic properties of the controlled process Synthesis: Design of the control system to fulfill performance requirements set for the controlled system 11.4.2018 4
Control Engineering Analysis => System modelling; data based, first principal, hybrid Gain, Phase shift, Time constants, τ i, i = 1:n Delays, τ d Linear or nonlinear Time invariant or time variant 11.4.2018 5
Control Engineering Synthesis: Controller design how to generate an optimal control signal (magnitude, timing) Set point 11.4.2018 6
Biomass as a fuel Control perspective Properties affecting combustion dynamics Reactivity Volatiles Moisture Particle size Properties affecting combustion control Homogeneity of bulk properties Bulk properties, e.g. density Heat value 11.4.2018 7
Biomass as a fuel Control perspective Combustion dynamics Typical mass loss from small fuel samples during pyrolysis in inert atmosphere (share of volatile components) Source: Saastamoinen J. Modelling of Dynamics of Combustion of Biomass in Fluidized Beds. Thermal Science: Vol. 8 (2004), No. 2, pp. 107-126 8
Biomass combustion Grate firing Bubbling fluidized bed Circulating fluidized bed 11.4.2018 9
Generation Unit Control Control goals Supply power demand steady state => disturbance attenuation transient operation => load tracking Efficient operation Combustion control => fuel / air ratio Follow emission limits Air distribution in the furnace Attain the expected process life time Avoiding thermal stresses 11.4.2018 10
Generation Unit Control Load control Problem: Power variations caused by uneven fuel mass flow in the furnace and fluctuations of heat value Solution: Combustion power estimation and control Kalman filter based estimation of oxygen consumption in the furnace Flue gas O 2 Combustion air Fuel properties Combustion power estimation, fast dynamics Pressure control, slow dynamics + Fuel & air PC Superheated steam XC QI Power control Flue gases O2 G 11.4.2018 11
Generation Unit Control Load control, Control Hierarchy Coordinating control Cooperation with dynamically fast steam turbine and slow boiler Transient operation Limitation of thermal stressing Stress estimation Stabilizing control Control of unit processes New features for improved tracking performance Coordination of boiler turbine feed water preheating system with MPC Stabilization of unit processes Boiler turbine process 11.4.2018 12
Generation Unit Control Load control, Coordinated control Detailed process models 11.4.2018 13
Generation Unit Control Load control, Coordinated control criteria calculations boiler load margin Pressure setpoint S p steam pressure reduction control fuel feed control unit coordinator turbine control power setpoint S droop gain S ΔP Δf turbine load margin criteria calculations G Power & frequency P f 11.4.2018 14
Generation Unit Control Load control, boiler storage capacity Boiler s steam storage capacity C e C e = t t 1 2 [ () () ( ) ( )] h t q t h t q t dt m ( ) p( t ) p t 1 2 1 m 1 Characterizes how much extra steam a boiler can temporary produce as a function of unit pressure drop in the boiler drum with constant combustion power 11.4.2018 15
Producing extra steam by discharging the thermal storage by steam pressure drop Reducing steam flow by charging of the thermal storage by steam pressure increase Tube wall Tube wall Steam mass flow Temperature and pressure Stored energy Steam mass flow Temperature and pressure Stored energy
Generation Unit Control Thermal stressing of boiler structures Maximum change rate 3 C/min 11.4.2018 17
Control of CHP generation Conventionally boiler s load is defined by heat load and electricity is generated as a side product. Boiler & turbine unit control analog with normal power plant control Boiler pressure control PC Superheated steam PC Flue gases Heat load control G Heat load Fuel & air 11.4.2018 18
Control of CHP generation Optimization of district heating networks Minimizing heat losses by minimizing supply water temperature Dynamic modeling of district heating network by delay distribution model Neural network model for load prediction Source: Laakkonen et al. Predictive supply temperature optimization of district heating networks using delay distributions. The 15th International Symposium on District Heating and Cooling September 4-7, 2016, Seoul, Republic of Korea. 11.4.2018 19
Control of CHP generation Flexible generation Enabling CHP unit to participate power system frequency containment reserve and balancing energy markets Utilization of DH network storage capacity and possible supporting hot water boilers for temporary decoupling of CHP generation from heat load Source: Korpela et al. Utilization of district heating network to provide flexibility in CHP production. The 15th International Symposium on District Heating and Cooling September 4-7, 2016, Seoul, Republic of Korea. 11.4.2018 20
Control of CHP generation Industrial power plant case Dynamic model library for modelliing of industrial steam networks Dynamic simulation assisted Process design Capacity of steam accumulators Requirements for actuator dynamics Control design Development and testing of control strategies Steam flow and pressure during a paper machine web break Scheduling of load levelling controllers as a function of pressure control error Control error B7 Pressure B6 B5 B1 B2 B3 B4 Blow out Aux. condenser Accum. charge Turbine Accum. discharge Reduction valve Overriding control SP Flow Pressure B4 B3 B2 B1 B5 B6 B7 11.4.2018 21 t t
[e_c001] 0 1 C001 From4 [e_c004] fuel1 fuel2 1/0 [%] [%] PB2 C004 0 1 [kg/s] SH 140 [bar] RB123 fuel1 fuel2 1/0 [%] [%] PB1 Out1 [bar] [%] C008&009 [kg/s] [kg/s] R138->82 [kg/s] Valve coordinator In1 C002 [e_c002] SH 82 [e_c003] Out1 C003 C007&014 [bar] [%] [%] [e_c005] [e_c006] TG1 [bar] [%] TG1 C005 Out1 C012&013&019 [bar] [%] R82->4,7 Out1 C010&011 [bar] [%] R82->12,8 [bar] [%] [%] TG2346 HP IP C006 TG5BP Cond Extraction outlet [kg/s] MW Gen.pow. P_gen GEN Freq P_con [kg/s] IPL [kg/s] Attempered outlets [kg/s] [kg/s] EL 0 Out1 C016&017&018 IP_load [bar] [%] SH 12 R138->4,7 [kg/s] Out1 Out1 C020&023 [%] [bar] [%] C021&022 ACCUMULATOR PM6 [bar] [kg/s] LP_load 0 M [%] SH 4 [bar] [e_c015] C015 11.4.2018 22
145 140 bar header [bar] 90 82 bar header [bar] 13 12 bar header [bar] 4 4 bar header [bar] 140 135 85 80 75 12 11 10 3.8 3.6 130 PB2 [kg/s] 110 70 PB1 [kg/s] 60 9 TG2346 extr. [kg/s] 120 TG2346 out [kg/s] 350 100 50 110 300 90 40 100 80 TG5 inlet [kg/s] 105 30 RB123 [kg/s] 400 90 R82/12 [kg/s] 20 250 TG5 extr [kg/s] 50 100 95 350 15 10 5 45 90 Accumulator pressure [Bar] 12 300 Accumulator charge and discharge [kg/s] 20 0 Blow out [kg/s] 20 40 G1+G5 and G2346 [MW] 250 10 8 6 4 15 10 5 15 10 5 200 2 Frequency [Hz] 50.5 0 TG2346 inlet [kg/s] 0 Load [kg/s] 350 150 R82/4 R140/4 [kg/s] 15 50 49.5 Time [min] 400 380 360 Time [min] 340 330 320 310 300 Time [min] 10 5 0 Time [min] 11.4.2018 23
Control of CHP generation Industrial power plant case Definition of required steam accumulator capacity for stabilizing a steam network by utilizing simulation and Model Predictive Control (MPC) with and without constraints MPa 11 10.5 MPa 10 9.5 10 MPa header 9 35 40 45 2 MPa header 3 2 1 CONSTRAINED EXCESS UNCONSTRAINED DIFICIT 0 35 40 45 0.5 MPa header 0.52 MPa 0.51 0.5 EXCESS DIFICIT 0.49 35 40 45 Time [min] 11.4.2018