emission reduction of wood log buring

8/14/2019 emission reduction of wood log buring

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EMISSION REDUCTION OF WOOD LOG

BURNIN IN HEAT RETAININ T VE

P.O Box 1603 40101 Jyvskyl


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VTT TECHNICAL RESEARCH CENTRE OF FINLAND

Small wood fired appliances in Finland

2.2 million fireplaces vs 5.3 million inhabitants

1.2 million in small houses

0.8 million in holiday houses (summer cottages)

0.2 million in row houses and blocks

1.5 million saunastoves or sauna water heaters

Firewood is used about 6 million m3 annually

Firewood use is ex ected to rise

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IEA Biomass combustion and cofiring workshop:Next generation small scale biomass combustion technologies20 October 2008 in Amsterdam


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Fireplaces in small houses

Heat retaining stoves

Wood stoves

Pellet stoves

Sauna stoves Baking ovens

oo ers

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Heat storing stoves

Very typical in Finland

Typical features:

Ver massive 1000 3000 k

Fuel is burned only about 2 hours per day while energy isstored into the mass. Burning rate is 20 30 kW

( ~ 2 4 kW)

New CEN-standard EN 15250 in force 2008

erm: ow ea e ease pp ance

Can be pre-fabricated or one-off appliances (built on site)

Soap stone is one of the most popular materials

High heat storing capacity because of high weight

Easiness to process

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General requirements for low emission combustion

3 T's (Temperature, Time and Turbulence)

Temperature is quite tricky.

In higher temperature chemical reactions are quicker but

Also pyrolysis of wood is quicker, which may lead to lack of oxygenin the pyrolysis phase for few minutes

temperature of SHRA appliance is higher

===> later addings lead to higher emissions

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Temperature requirement to burn COCase: ideal mixing

0,10 700 C

0,08

[vol-%]

800 C

0,04

,

oncentratio

900 C

0,02CO-c

1000 C

1100 C

0

0 0,2 0,4 0,6 0,8 1,0

Time [s]

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y r. a p nen n esearc rogramme


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How to keep high temperature

New type of after-burning chamber has been studied at VTT

The aim was to keep flue gases in as high as possible temperatureafter the combustion chamber

We were able to rise the temperature about 200 K by electricheatin but it was difficult

However, reduction in CO/OGC-concentration was not good One reason might be that due to higher temperature,

= ,

Due to lack of money we could do only preliminary experiments

However, our conclusion was that one should do all tricks in there ox.

Most important is precise combustion air instroduction and goodmixing

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10/17


How wood logs burn in a conventional SHRAFuel added 3 kg at a time.

9000

3)

3

6000

7500

s(mg/

2

2.5

(%)

4500carbo

1.5onten

t

3000

lh

ydr

1CO-

0

Tot

0

.CO

10


Time


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New strategy

Ignition with 100% primary air through the grate. Small amount of

secondary air in this phase Pyrolysis phase with 100% secondary and hardly any primary air to

prevent fast pyrolysis

During char burnout phase only primary air

In ideal case the ratio of primary/secondary air should be controlled

continuously e a a pro ec o s resu ng n some ower ng o em ss ons

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Example of this strategy

After fuel ignition, primary air

through the grate is closed.

A small amount of primary air isintroduced through the holes

as secondary air into the flames.

Picture: NunnaUuni O

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The whirl chamber is a new inventionpatented by Tulikivi.

eng ens e me com us ongases remain in the fire chamber,allowing combustion to be not onlyefficient, but also exceptionally clean.

Emissions from the fireplace remain ata fraction of the worlds strictestnorms. And the new ash box solutionremains nicel out of si ht.

Source: Tulikivi Oyj

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30000

CO

20000

25000

old: 4092 mg/MJ, 85%

New: 664 mg/MJ, 83,1%

Wood logs 3x9 kg

15000

CO[mg/M

J]

CO (TTU2700 Old)

5000

10000

00 20 40 60 80 100 120 140 160 180 200

t[min]

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State of the art now

CO-concentration is < 0.1 % (at 13% O2), which is enough today to

fulfil the requirements Also OGC and NOx are low enough

As well as TSP

In near future requirements will be more strict

It may result in necessity to use secondary measures

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emission reduction of wood log buring

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