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Graz, 23.01.2020

Markus Gölles, Christopher Zemann

6th Central European Biomass Conference

IEA-Workshop: TASK 32

Modern control strategies for biomass combustion systems in residential heating systems

2

automatically fed

… pellets

boilers

wood

chip

boilers

manually fed

firewood

boilers stoves

control of the

combustion process

interaction with the

heating system

stoves

control of the

combustion process

interaction with the

heating system

Overview

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Control of the

combustion process

• utilization of finite-state machines

Interaction with the

heating system

• very rare

• rule-based strategies

• manufacturer-specific

Control strategies for wood stoves

firewood

boilers

firewood

boilers

4

automatically fed

… pellets

boilers

wood

chip

boilers

manually fed

stoves

control of the

combustion process

interaction with the

heating system

control of the

combustion process

Control strategies for firewood boilers

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Goal: control strategy which simultaneously guarantees good combustion

conditions and ensures that the water temperature is kept at the desired value.

controlled variables

• feed temperature

• residual oxygen content

of the flue gas

manipulated variables

• suction fan frequency

• primary air control valve

• secondary air control valve

• boiler pump frequency

Combustion control for firewood boilers – overview

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Combustion control for firewood boilers – concept

boiler control logwood boiler

heat flow

feed

temperature

O2-content

heat

exchanger

combustion

process O2-content

controller

combustion

controller

estimated heat flow

mass flow

of water

feed temperature

controller

mass flow

controllers

mass flow of primary air suction fan

primary air control valve

secondary air control valve mass flow of secondary air

decoupling

utilization of the mass flow of

water to decouple the feed

temperature from the

combustion process

targeted combustion control

utilization of the mass flow

controllers to ensure good

combustion conditions

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Combustion control for firewood boilers – results

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The application of the new combustion control leads to:

- faster start-up

- reduced fluctuations in the residual oxygen content of the flue gas

- reduced pollutant emissions

The application of the new combustion control leads to:

- reduced settling time

- reduced overshoot

- reduced fluctuations

Combustion control for firewood boilers – results

firewood

boilers

firewood

boilers

9

automatically fed

… pellets

boilers

wood

chip

boilers

manually fed

stoves

control of the

combustion process

interaction with the

heating system

control of the

combustion process

interaction with the

heating system

Control strategies for firewood boilers

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operation of manually fed boilers

• batch combustion supply of heat depends on ignition time

• consideration refill windows defined by the user user comfort

Energy management system for firewood boilers

• utilization of forecasting methods using weather forecasts

• self-learning to adapt to the user behavior

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Conventional

operation

Superordinate

control

energy delivered to

consumers 783 kWh 782 kWh ± 0 %

number of refills

(total / within refill windows) 5 / 4 6 / 6 +1 / +2

utilized solar yield 117 kWh 126 kWh + 8 %

storage losses 122 kWh 105 kWh - 14 %

improved efficiency

Exemplary results from the application of an energy

management system for firewood boilers

improved user comfort due to no refills outside of defined refill windows

firewood

boilers

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automatically fed

… pellets

boilers

wood

chip

boilers

manually fed

stoves

control of the

combustion process

wood

chip

boilers

pellets

boilers

control of the

combustion process

control of the

combustion process

interaction with the

heating system

Control strategies for automatically fed boilers

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Combustion control for wood chip boilers - overview

Goal: control strategy which simultaneously guarantees good combustion

conditions and ensures that the water temperature is kept at the desired value.

controlled variables

• feed temperature

• residual oxygen content of the flue gas

• primary air ratio

manipulated variables

• fuel feed

• primary air fan

• secondary air fan

• boiler circuit pump

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boiler control logwood boiler

heat flow

feed

temperature

O2-content

heat

exchanger

combustion

process O2-content

controller

mass flow

of water

feed temperature

controller

mass flow

controllers

fuel feed

primary air fan

secondary air fan mass flow of secondary air

combustion

controller

estimated heat flow, primary air ratio

mass flow of fuel

mass flow of primary air

Combustion control for wood chip boilers - concept

decoupling

utilization of the mass flow of

water to decouple the feed

temperature from the

combustion process

targeted combustion control

utilization of the mass flow

controllers to ensure good

combustion conditions

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Combustion control for wood chip boilers – results (1)

The application of the new combustion control:

- leads to reduced fluctuations in the feed temperature

conventional control

0 10 20 30 40 50 60 time in minutes

fee

d te

mp

era

ture

in °

C

86

84

82

80

measured

desired

model-based control

0 10 20 30 40 50 60 time in minutes

fee

d te

mp

era

ture

in °

C

86

84

82

80

measured

desired

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O2 in

vo

l.%

15

10

5 0 10 20 30 40 50 60

0 10 20 30 40 50 60

lB

B

2

1,5

1

0,5

time in minutes

model-based control

measured

desired

measured

desired

O2 in

vo

l.%

0 10 20 30 40 50 60

15

10

5

0 10 20 30 40 50 60

2

1,5

1

0,5

lB

B

time in minutes

conventional control

measured

desired

measured

desired

Combustion control for wood chip boilers – results (2)

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O2 in

vo

l.%

15

10

5 0 10 20 30 40 50 60

0 10 20 30 40 50 60

lB

B

2

1,5

1

0,5

time in minutes

model-based control

measured

desired

measured

desired

O2 in

vo

l.%

0 10 20 30 40 50 60

15

10

5

0 10 20 30 40 50 60

2

1,5

1

0,5

lB

B

time in minutes

conventional control

measured

desired

measured

desired

Combustion control for wood chip boilers – results (2)

The application of the new combustion control:

- leads to reduced fluctuations in the residual oxygen content of the flue gas

- enables the targeted control of the primary air ratio

firewood

boilers

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automatically fed

… pellets

boilers

wood

chip

boilers

manually fed

stoves

interaction with the

heating system

control of the

combustion process

wood

chip

boilers

pellets

boilers

interaction with the

heating system

control of the

combustion process

Control strategies for automatically fed boilers

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Simple rule-based load management for wood chip boilers

Definition of a desired thermal output of the boiler depending

on the state of the buffer storage.

• ignition

– start combustion process if S1 < T1

– start combustion process if ignition request from user

• standard operation

– if S3 < T2, increase thermal output

– else: decrease thermal output

– if S1 < T1, maximum thermal output

• shut-down

– if S5 > T3, shut-down boiler

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Only desired values for the first

15 minutes are transmitted.

After 15 minutes the

optimization is repeated with

new measured variables.

Optimization-based energy management system

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Forecasting method for the load demand in residential heating systems:

- simple to implement

- self-learning (based on measurement data from weather forecasts)

no parametrization required

Simple forecasting methods

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The system is modular: it allows a quick configuration from standard components.

Variable prices and availability of systems can be taken into account.

Modular energy management system

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automatically fed

… pellets

boilers

wood

chip

boilers

manually fed

firewood

boilers stoves

control of the

combustion process

interaction with the

heating system

additional topics

Conclusion

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mass flow of flue gas

Knowledge about the mass flow of flue

gas can be used in control strategies to

ensure good the combustion conditions.

difficult to measure in biomass boilers

fuel properties

Estimation of fuel properties such as

the carbon content (wC) and lower

heating value (LHV) during the

operation of the biomass boiler.

Estimation of non-measureable quantities

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CO-l-characteristic

residual oxygen content of the flue gas

in vol.% (w.b.)

CO

-em

issio

ns in

mg

/m³

(d.b

.)

measured values

4.1 MW – 4.5 MW

2.9 MW – 3.3 MW

optimal value

typical desired

value for O2

During the long-term validation the

modular CO-l-optimization reduced the

- fuel consumption by -3,8%

- CO-emissions by -200 mg/m³

- total dust emissions by -19,5%

A long-term validation has been carried

out at a biomass boiler in a district heating

plant (nominal capacity of 2.5 MWth)

Nov. 2017 to Mar. 2019 (5 months)

CO-l-optimization

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automatically fed

… pellets

boilers

wood

chip

boilers

manually fed

firewood

boilers stoves

control of the

combustion process

interaction with the

heating system

Estimation of non-measurable quantities

and CO-l-optimization

Conclusion

BEST – Bioenergy and Sustainable Technologies GmbH

Markus Gölles

Automation and Control

E-Mail: markus.goelles@bioenergy2020.eu

Telefon: + 43 (0) 316 873-9208

Modern control strategies for biomass combustion

systems in residential heating systems