Environmental assessment of woody

biomass ash valorization in cement mortars

Évaluation environnementale de la valorisation des cendres de

la biomasse ligneuse dans les mortiers

Tamíris da Costa, Paula Quinteiro, Luís Tarelho, Luís Arroja, Ana Cláudia Dias

University of Aveiro - Centre for Environmental and Marine Studies (CESAM),

Department of Environment and Planning

Introduction

Policies promoting bioenergy production from forest residues

200 THOUSAND TONS OF ASH ARE PRODUCED ANNUALY IN PORTUGAL FROM POWER PLANTS FUELLED BY FOREST BIOMASS

•Climate change mitigation

•Forest fire prevention

This amount of ashes is projected to increase

Introduction

In Portugal, less than 10 % of the ashes are recycled

adsorbents

End-of-life alternatives for woody biomass ashes

agriculture

ceramics

construction materials

glass

Concrete

Asphalt

Cement mortar

Objective

HOWEVER, environmental aspects should be assessed

Entire life cycle

Several impacts

Environmentalsustainability

The objective of this work is to evaluate the environmental benefits and impacts of

ash incorporation in cement mortar.

Methodology

Eucalyptus globulusand Pinus pinaster

Residues left in the forest floor

Logging residues for bioenergy

Fluidized bed

Fly ash (FA)

Bottom ash (BA)

Electricity

Asphalt

Landfill

Avoided burdens

Energy

conversion

Ash

processing

1 t - 1 t

T

Sand

extraction

Cement

production

T

System boundary

FU = 1 t

Ashes(FA or BA)

Cement

mortar

production T

Base scenario (Landfilling)- The landfilling scenarios for woody biomass ash under study are, as follows:

• FA landfilling.

• BA landfilling.

- The landfill gas is partially captured and used to produce electricity.

- A short-term leachate treatment for leached ash was included.

- The life cycle inventory was built upon the existing models available for waste disposal in Ecoinvent

(Doka, 2003; Ecoinvent, 2017), according to the ash composition.

Landfill gas

Leached

Valorisation scenarios

Scenario 1: cement mortar with FA (substituting cement in 10 %).

Scenario 2: cement mortar with FA (adding 20 % to the mortar).

Scenario 3: cement mortar with BA (substituting the sand in 50 %).

Scenario 4: cement mortar with BA (substituting the sand in 100 %)

with ash pre-treatment (washing and drying).

Cement mortar

• The production of sand and cement and all upstream activities were taken from Ecoinvent database.

• Both ashes are grinded and sieved to achieve the desired size.

• In scenario 4, the ash was previously washed with deionised water (liquid/solid ratio of 2 L/kg) with a running

capacity equal to 10 ton/h (Modolo et al., 2013). The average weight loss of fly ash on washing is equal to 12 %

(Berra et al., 2015). The ash is dried to remove excess moisture with an average energy consumption of 0.2 MJ/kg

(Kasser and Pöll, 1998).

Transportation

Table 1 presents the transport profiles in the different systems and the distances considered for woody biomass ash and the

avoided materials.

aThis distance corresponds to an outward journey, based on distances of existing facilities in Portugal.

Inventory data for diesel consumption and air emissions were taken from the Ecoinvent database (Ecoinvent, 2017).

Material transport Distance (km)a Type of transport Load (t) Return journey

Power plant to landfill

FA and BA 15 Freight lorry, EURO 3 7.5-16 Empty

Power plant to mortar facility

FA and BA 35 Freight lorry, EURO 3 7.5-16 Empty

Avoided materials to concrete and mortar facility

Cement 0 Freight lorry, EURO 3 16–32 Empty

Sand 30 Freight lorry, EURO 3 16–32 Empty

Results (ILCD methodology)

Figure 1 presents the environmental impact and the relative contribution of each stage, obtained for the base.

0

5

10

15

20

25

30

35

40

FA BA

Clim

ate

chan

ge (

kg C

O2

eq

)

0,000

0,002

0,004

0,006

0,008

0,010

0,012

0,014

FA BA

Par

ticu

late

mat

ter

(kg

PM

2.5

eq

)

0,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

0,16

FA BA

Ph

oto

chem

ical

ozo

ne

form

atio

n (

kg

NM

VO

C e

q)

0,00

0,05

0,10

0,15

0,20

0,25

FA BA

Aci

dif

icat

ion

(m

olc

H+

eq)

0

1

2

3

4

5

6

FA BA

Min

eral

an

d f

oss

il d

eple

tio

n (

mg

Sb e

q)

Landfill gas

Leachate

Processing during landfill

Transport to landfill

0

1

2

3

4

5

6

7

8

9

10

FA BA

Fres

hw

ater

eu

tro

ph

icat

ion

(g

P e

q)

Results (ILCD methodology)

Figure 2. Impact assessment results for valorization scenarios.

-10000

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

1 2 3 4

Clim

ate

chan

ge (

kg C

O2

eq

)

-2,5

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

1 2 3 4

Par

ticu

late

mat

ter

(kg

PM

2.5

eq

)

-20

-15

-10

-5

0

5

10

15

20

1 2 3 4

Ph

oto

chem

ical

ozo

ne

form

atio

n

(kg

NM

VO

C e

q)

-30

-20

-10

0

10

20

30

1 2 3 4

Aci

dif

icat

ion

(m

olc

H+

eq)

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

1 2 3 4

Fres

hw

ater

eu

tro

ph

icat

ion

(kg

P e

q)

-0,012

-0,010

-0,008

-0,006

-0,004

-0,002

0,000

0,002

0,004

0,006

0,008

0,010

1 2 3 4

Min

eral

an

d f

oss

il d

eple

tio

n (

kg S

b e

q)

Portland cement

Aggregates

Ash processing

Electricity

Avoided product

Results (ILCD methodology)

Figure 3. Net impact results in each scenario (1 to 4) per functional unit.

-800

-700

-600

-500

-400

-300

-200

-100

0

100

1 2 3 4

Clim

ate

chan

ge (

kg C

O2

eq

)

-0,05

-0,04

-0,03

-0,02

-0,01

0,00

0,01

0,02

1 2 3 4

Par

ticu

late

mat

ter

(kg

PM

2.5

eq

)

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

0,2

1 2 3 4

Ph

oto

chem

ical

ozo

ne

form

atio

n (

kg

NM

VO

C e

q)

-1,4

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

1 2 3 4

Aci

dif

icat

ion

(m

olc

H+

eq)

-0,07

-0,06

-0,05

-0,04

-0,03

-0,02

-0,01

0,00

0,01

0,02

1 2 3 4

Fres

hw

ater

eu

tro

ph

icat

ion

(kg

P e

q)

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0,0

0,1

1 2 3 4

Min

eral

an

d f

oss

il d

eple

tio

n (

g Sb

eq

)

Net impact

Landfilling

Conclusion

The production of cement mortar with bottom ashes avoids the extraction of sand and the production with fly ashes

avoids the emissions during cement production.

The best end-of-life scenario is:

• Fly ashes

• Bottom ashes

The environmental impact of ash valorisation in cement mortars are lower than the impacts of ash landfill.

Therefore, the production of cement mortar appears to be an end-of-life destination environmentally adequate for the

woody biomass ashes.

Scenario 1: cement mortar with FA (substituting cement in 10 %).

Scenario 2: cement mortar with FA (adding 20 % to the mortar).

Scenario 3: cement mortar with BA (substituting the sand in 50 %).

Scenario 4: cement mortar with BA (substituting the sand in 100 %) with ash pre-

treatment (washing and drying).

Acknowledgments:

The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ - Brazil) for

the scholarship granted to Tamíris Pacheco da Costa (203483/2014-6). Thanks are also due to the FCT and POHP/FSE

funding program for the scholarship granted to Paula Quinteiro (SFRH/BPD/114992/2016). Ana Cláudia Dias

acknowledges the financial support from FCT (IF/00587/2013). The authors recognise FCT (Science and Technology

Foundation - Portugal) and FEDER (European Regional Development Fund) for the financial support to CESAM

(UID/AMB/50017) as well as the project SABIOS (PTDC/AAG-MAA/6234/2014) and SustainFor (PTDC/AGR-

FOR/1510/2014), both funded under the project 3599-PPCDT.