Combustion Control of Small Scale Wood Chip and Pellet Fired...

Department of Automation Science and Engineering

Combustion Control of Small Scale Wood Chip and Pellet Fired Systems

IV Liekkipäivä23.1.2008 Tampere

Timo [email protected]

mailto:[email protected]

TAMPERE UNIVERSITY OF TECHNOLOGYInstitute of Automation and Control

Combustion control

• Process control is a tool to manageEmission levels now and in the future

gaseous emissions and fine particlesLarge load, fuel and power fluctuationsFouling, drifting, wearing

• GoalsContinuous monitoring and minimization of losses and emissions

advanced sensors and signal processingmonitoring and optimization of combustionadaptable control methods

Reduction of maintenance and service costsmethods for monitoring and managing process deviationscondition monitoring


Automated control of small-scale combustion

• MethodsMathematical modelling and simulation

- advanced methods and strategies for controlling air and fuel feed (MPC, optimal control, fuzzy/neural,…)

Embedded systems, advanced sensors, signal processing

• Challenges Price of small production unitsSolutions must be reliable- behaviour of combustion process depends on time, disturbances and combustion conditions- number of combustion units dissimilarity of combustion environments adaptation neededSmall scale CHP


Automated control of small-scale combustion

• Benefits and influences

– Improved management of non-steady statesstabilisation of combustion processfaster recovery after disturbances

– Optimization of combustion temperatures and air stagingmaximisation of annual efficiencyminimisation of emissions

– Modernisation of combustion systemscost effectivenessenergy savingsease of use


Projects

• Control of wood chip combustion 1 & 2

– Tekes– HT Enerco Oy– Säätötuli Oy

• Control potential of different operating methods in small-scale wood pellet combustion (COPECOM)

– Tekes (ERANET Bioenergy)

– University of Oulu

– Växjö University, Sweden

– HT Enerco Oy

– MBIO Energieteknik Ab, Sweden


Mathematical modelling and simulation of combustion

• Dynamical modelling for control purposes

• Case – Wood pellet combustion simulator – 5 % step change to fuel feed– Temperature response– Power responses at different combustion

zones

1T Tc r C r T ht r rr

ρ λ ρΓ ΓΓ

∂ ∂ ∂⎛ ⎞′′= − + Δ⎜ ⎟∂ ∂ ∂⎝ ⎠∑& &


Stabilisation of combustion temperature (1/2)

• Project: Control of wood chip combustion

• The goal is to compensate for variations in filling factor of fuel feeding screw

• Indirect measurement– Interesting quantities O2 and CO– Temperature measurement at the

upper part of combustion chamber is used

• Set point control

• Fuzzy reasoning based on temperature measurement


Stabilisation of combustion temperature (2/2)80 kW wood chip combustion , moisture content c. 30 %

Normalized temperature distribution

0

0.05

0.1

0.15

0.2

0.25

500 550 600 650 700 750

Temperature (oC)

Dist

ribu

tions

Control OFF Control ON

Normalized oxygen distributions

0

0.05

0.1

0.15

0.2

0.25

0.3

5 6 7 8 9 10 11 12 13

O2 (%)

Dis

trib

utio

ns


Normalized CO distributions

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 100 200 300 400 500 600 700 800 900 1000

CO (ppm)

Dist

ribut

ions


• Problem: How to get proper set point value for temperature control?


Control strategy: Cascade control

• High level control is based on lambda measurement

• Lambda-sensor is used only when needed

• O2-controller have to be tuned about a decade slower than T-controller

• Controllers need to be switched off during grate sweeping


Cascade control200 kW wood chip combustion

• Controller finds a balance after a start-up• Moisture content of whole tree chips was 33,5 %

19:50 20:00 20:10 20:20 20:30 20:40 20:50 21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:204

6

8

10

12

Time

0 2, %

Scaled O2 measurement and its set point

19:50 20:00 20:10 20:20 20:30 20:40 20:50 21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:20500

550

600

650

700

Time

T, °C

Temperature measurement from upper part of surface and its set point

19:50 20:00 20:10 20:20 20:30 20:40 20:50 21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:20

10

15

20

Time

Freq

uenc

y, H

z

Control frequency of fuel feeding screw

19:50 20:00 20:10 20:20 20:30 20:40 20:50 21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:2050

100

150

200

250

Time

Q (m

3 /h) /

P (k

W)

Primary and secondary air flow measurements and power generated to water circulation

19:50 20:00 20:10 20:20 20:30 20:40 20:50 21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:200

500

1000

Time

CO

,ppm

CO measurement. Additionally, time when grate sweeping happens is indicated by pulses

O2 lambda *

O2 set point *

T meas.T set point

Prim, m3/h

Sec, m3/hPower, kW


Extended control strategy

O2 controller Combustion process

Integral controller

Fuzzy controller

T measurement

O2measurement

Actuator(feeding screw)

+ +

- -

Disturbance(grate

sweeper)

O2T

+

+

O2 set point fTset point

Actuator(prim air blower)

Actuator(sec air blower)

Compen-sation

Power controller

kW measurement

Moisture

Power set point

+

-

Vprim

Vsec

kW

Air flow controller

Air flow controller

Air flow measurement

Air flow measurement

+

+

-

-

Qprim air

Qsec air

Qprim set point

Qsek set point

Qfuel


COPECOMResearch focus and targets

• Control potential of pellet burners – research on gasified and direct combustion, experimental

• Physical + data-based modelling and control development, experimental/theoretical

• An analysis of integrated small-scale power production and storage, theoretical


Velmax-burner tests, Measurements


Conclusion

• By modelling and sophisticated control methods– Cost-effectiveness – Reduction of emissions– User-friendliness – Understanding of combustion process for control purposes

• Tools for small scale combustion– Indirect measurements– Adaptive control– Anticipatory condition monitoring


Appendix

• Korpela Timo, Björkqvist, T. and Lautala, P. 2006. Modelling of Wood Pellet Combustion for Control Purposes. Pellets 2006, 2nd World Pellet Conference, Jönköping, Sweden, 30 May-1 June 2006, Proceedings, p. 97-104.

• Korpela Timo, Hakepolton hallinta –projektin loppuraportti. Tampereen teknillinenyliopisto, Automaatio- ja säätötekniikan laitos. Raportti 2006: 1. Tampere 2006. 31 s. ISBN 952-15-1694-1.

• Korpela Timo, 2005. Puupellettipolton mallintaminen säädön ja kunnonvalvonnannäkökulmasta. Diplomityö. Tampere. Tampereen teknillinen yliopisto, Automaatio- jasäätötekniikan laitos. 98 s.

• Combustion Control of Small Scale Wood Fired Appliances - International Workshop 17 June 2005 VTT Processes, Jyväskylä, Finland.

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