PRELIMINARY STUDY OF GASIFICATION WITH
STEAM / ENRICHED AIR MIXTURES OF SEWAGE
SLUDGE AND OF THE CHAR OBTAINED IN ITS
PYROLYSIS PROCESS
N. Gil; J.L. Sánchez; M.B. Murillo
Thermochemical Processes Group (GPT), Aragon Institute for Engineering Research (I3A), Zaragoza (Spain)
e-mail: [email protected]
Bioenergy III: Present and New Perspectives on Biorefineries
May 22-27, 2011; Lanzarote, Spain
OUTLINE
1. INTRODUCTION AND OBJECTIVES
2. MATERIALS AND METHODS
Materials
Experimental plant
3. RESULTS
Effect of H2O/O2 molar ratio used as gasifying agent
Effect of temperature
4. CONCLUSIONS AND FUTURE WORKS
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
OUTLINE
1. INTRODUCTION AND OBJECTIVES
2. MATERIALS AND METHODS
Materials
Experimental plant
3. RESULTS
Effect of H2O/O2 molar ratio used as gasifying agent
Effect of temperature
4. CONCLUSIONS AND FUTURE WORKS
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
1. Introduction and objectives
Sewage sludge is the waste produced during the
purification of the wastewater in the wastewater treatment
plants.
Sewage sludge: heterogeneous material
Organic matter
Proteins
Fibers
Fats
Inorganic matter
Pathogenic
agents:
salmonella,
viruses, etc.
Moisture
Heavy
metals
sand,
calcite,
Persistent
organic
contaminants:
PAHs, PCBs,
PCDFs. etc.
etc
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
1. Introduction and objectives
Strict legislation (Directive 91/271/ECC)
sewage sludge generation
Thousands of tonnes of dry matter
Millions of tonnes of dry matter
European Union
15
9
10
5.5
10
6.5
5
0
1987
1991
2000
2005
Year
Spain
1200
1000
800
686 716
853 892
600
400
200
0
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Year
Source: Eurostat
Source: PNIR 2008-2015
12%
Sewage sludge
management
ways in European
Union (2008)
785
1055
987 1012 1005 986
37%
Agriculture
Incineration
Landfill
40%
11%
Other areas
(forestry…)
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
1. Introduction and objectives
Thermochemical processes as a way of sewage sludge management
Gasification is the thermal process during which carbonaceous content of sewage sludge is
converted to a gaseous fuel by heating in a gasification medium such as air, oxygen or
steam.
Gas: CO, CO2, H2, light hydrocarbons (CH4, C2H6,
C2H4, C2H2), N2 (gasification with air), impurities (H2S, NH3)
• Electrical / heat energy
• Chemical feedstock
Char
Tar +
water
Tar is undesirable problems associated with condensation,
formation of tar aerosols and polymerization.
Pyrolysis is the thermal decomposition of a material in an inert atmosphere.
Char is the main byproduct in flash pyrolysis it still has carbonaceous content raw material for
gasification process.
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
1. Introduction and Objectives
OBJECTIVE OF THE WORK
Study the influence of some OPERATIONAL CONDITIONS:
Raw material: sewage sludge and char obtained in sewage sludge pyrolysis.
Gasification medium: mixtures of enriched air / steam (H2O/O2 molar ratio = 1 and
3).
Temperature: 820ºC and 850 - 860ºC
on some RESPONSE VARIABLES of the gasification process:
Distribution of products (mass yields of gasification products: gas, solid, tar, water)
Gas composition and LHVgas
Carbon conversion efficiency
Apparent thermal efficiency
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
OUTLINE
1. INTRODUCTION AND OBJECTIVES
2. MATERIALS AND METHODS
Materials
Experimental plant
3. RESULTS
Effect of H2O/O2 molar ratio used as gasifying agent
Effect of temperature
4. CONCLUSIONS AND FUTURE WORKS
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
2. Materials and methods. Materials
Materials
Anaerobically digested and dried sewage sludge, suplied by a Spanish urban waste water
treatment plant (it is ground and sieved to 250-500 µm).
Char obtained from sewage sludge pyrolysis (530ºC) in fluid bed.
Sewage sludge
Char from sewage sludge
pyrolysis
Ultimate analysis (wt. % as received)
Moisture
Ash
Volatiles
Fixed carbon
6.6
41.3
46.1
6.0
1.7
74.2
15.0
9.1
Elemental analysis (wt. % as received)
C
H
N
S
LHV (MJ/kg)
27.7
4.4
3.9
0.8
Lower Heating Value
10.80
15.5
1.0
1.9
0.4
4.96
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
2. Materials and methods. Experimental plant
Experimental plant
Fluidized bed reactor
(atmospheric pressure)
uf /umf ≈ 6
Continuous feed of solids
and continuous removal of
ash
Operational conditions
Gasifying agent mixtures of steam and enriched air with different H2O/O2 molar ratios: 1 or 3.
Gasifying agent (H2O + O2) to biomass ratio: 1.1 kg H2O+O2/kg biomass daf (dry and ash free).
Bed temperature: 820 or 860oC
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
OUTLINE
1. INTRODUCTION AND OBJECTIVES
2. MATERIALS AND METHODS
Materials
Experimental plant
3. RESULTS
Effect of H2O/O2 molar ratio used as gasifying agent
Effect of temperature
4. CONCLUSIONS AND FUTURE WORKS
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
3. Results. Effect of H2O/O2 molar ratio used as gasifying agent
Effect of H2O/O2 molar ratio used as gasifying agent (I)
Sewage sludge gasification
Char gasification
. H2O/O2 molar ratio = 1
Solid
Gas
Water
Tar
70.6
78.1
Solid
Gas
Water
0.6
0.9
9.5
14.2
80
70
60
50
40
30
20
10
0
38.8
34.1
Yield (wt.. %)
6.8
7.5
31.8
37.0
70.3
61.4
. H2O/O2 molar ratio = 3
43.6
36.6
Yield (wt
wt. %)
. H2O/O2 molar ratio = 1
. H2O/O2 molar ratio = 3
80
70
60
50
40
30
20
10
0
Temperature = 820oC
Tar
steam proportion gas yield; solid, water and tar yields.
The main product obtained in sewage sludge gasification was the gaseous product, while solid was the main
product in char gasification.
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
3. Results. Effect of H2O/O2 molar ratio used as gasifying agent
Effect of H2O/O2 molar ratio used as gasifying agent (II)
Sewage sludge gasification
Char gasification
. H2O/O2 molar ratio = 1
. H2O/O2 molar ratio = 3
. H2O/O2 molar ratio = 1
. H2O/O2 molar ratio = 3
49.6
46.4
H2 S
N2
0
H2
22.2
20.3
11.1
10.1
0.1
0.2
C2
0.0
0.0
0.4
0.1
CO
0.4
0.6
1.5
1.9
CO2 CH4
10
0
H2
30
20
2.7
3.6
10
40
15.6
22.8
23.1
17.7
7.9
8.0
20
50
vol. %
vol
40
14.8
22.3
vol. %
50
50.6
46.1
60
60
30
Temperature = 820oC
CO CO2 CH4 C2 H2S
N2
steam proportion H2 and light hydrocarbons; CO2.
vol. % of CH4 and C2 were lower in the gas obtained in char gasification than in those obtained in sewage
sludge gasification.
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
3. Results. Effect of H2O/O2 molar ratio used as gasifying agent
Effect of H2O/O2 molar ratio used as gasifying agent (III)
Gas LHV
(MJ/Nm3)
Carbon conversion
efficiency (%)
Temperature = 820oC
Apparent thermal
efficiency (%)
Sewage sludge gasification
H2O/O2 molar ratio = 1
4.55
83.83
49.72
H2O/O2 molar ratio = 3
5.87
75.67
64.30
Char gasification
H2O/O2 molar ratio = 1
3.25
76.18
42.85
H2O/O2 molar ratio = 3
3.97
66.12
49.40
steam proportion LHVgas ( vol. % of H2, CH4 and C2); carbon conversion efficiency; apparent thermal efficiency.
LHVgas, carbon conversion efficiency and apparent thermal efficiency are lower in char gasification
than in sewage sludge gasification.
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
3. Results. Effect of temperature
Effect of temperature (I)
H2O/O2 molar ratio = 3
Sewage sludge gasification
Char gasification
Solid
Gas
Water
Tar
Solid
Gas
Water
0.9
0.9
14.2
36.0
34.1
77.4
80
70
60
50
40
30
20
10
0
13.4
7.5
3.2
37.0
39.5
Yield (wt. %)
61.4
65.0
43.6
39.9
Yield (wt. %)
80
70
60
50
40
30
20
10
0
78.1
. Ta = 820oC
. Ta = 850oC
Ta = 820oC
Ta = 860oC
Tar
temperature gas yield; solid yield; tar yield in sewage sludge gasification, but this difference was not
significant in char gasification.
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
3. Results. Effect of temperature
Effect of temperature (II)
H2O/O2 molar ratio = 3
Sewage sludge gasification
Char gasification
. Ta = 820oC
. Ta = 860oC
30
30
H2 S
0.6
0.6
N2
H2
CO
CO2 CH4
0.2
0.1
CO2 CH4 C2
0.0
0.0
CO
10.1
11.3
0
0
H2
20
10
0.1
0.3
1.9
2.0
3.6
3.3
10
vol. %
17.7
17.6
8.0
8.6
20
20.3
19.5
40
22.8
24.7
50
40
22.3
22.4
vol. %
50
46.1
44.0
46.4
46.0
.Ta = 820oC
.Ta = 850oC
C2
H2 S
N2
Gas composition was hardly influenced when temperature was increased in both sewage sludge and char
gasification.
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
3. Results. Effect of temperature
Effect of temperature (III)
H2O/O2 molar ratio = 3
Gas LHV
(MJ/Nm3)
Carbon conversion
efficiency (%)
Apparent thermal
efficiency (%)
Sewage sludge gasification
T = 820oC
5.87
75.67
64.30
T = 860oC
5.88
79.96
67.50
Char gasification
T = 820oC
3.97
66.12
49.40
T = 850oC
4.32
70.90
56.98
temperature LHVgas was hardly influenced; carbon conversion efficiency; apparent
thermal efficiency.
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
OUTLINE
1. INTRODUCTION AND OBJECTIVES
2. MATERIALS AND METHODS
Materials
Experimental plant
3. RESULTS
Effect of H2O/O2 molar ratio used as gasifying agent
Effect of temperature
4. CONCLUSIONS AND FUTURE WORKS
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
4. Conclusions and Future works
CONCLUSIONS
The H2O/O2 molar ratio used as gasifying agent had a significant effect on gasification
process of both, sewage sludge and sludge derived char.
H2O/O2 molar ratio gas yield but LHVgas and apparent thermal efficiency; H2
formation.
H2O/O2 molar ratio H2/CO molar ratio in gas product (above 2).
temperature gas yield; gas composition and LHVgas were hardly influenced.
Char gasification yielded a gas with a very low LHV, being the advantage the low tar
content.
FUTURE WORKS
To analyze the influence on tar composition
To deepen into the gas cleaning process
Bioenergy III: Present and New Perspectives on Biorefineries – Lanzarote, May 2011
PRELIMINARY STUDY OF GASIFICATION WITH
STEAM / ENRICHED AIR MIXTURES OF SEWAGE
SLUDGE AND OF THE CHAR OBTAINED IN ITS
PYROLYSIS PROCESS
N. Gil; J.L. Sánchez; M.B. Murillo
Thermochemical Processes Group (GPT), Aragon Institute for Engineering Research (I3A), Zaragoza (Spain)
e-mail: [email protected]
Bioenergy III: Present and New Perspectives on Biorefineries
May 22-27, 2011; Lanzarote, Spain