REGATEC 2015 | Barcelona, Spain
Process for cost-effective Removal of Sulfur and Oxygen from Biomethane on Iron Oxide Sorbents
Toni Raabe (a), Sven Kureti (b), Ronny Erler (a), Hartmut Krause (c)
(a)
DBI - Gastechnologisches Institut gGmbH Freiberg; (b) Technische Universität Bergakademie Freiberg;
Background: Increasing injection of biomethane in natural gas grid
(c)
DBI Gas- und Umwelttechnik GmbH
Methodology
Requirements with respect to oxygen:
Screening of different commercially available iron-based adsorbents
DVGW-worksheets G 260 and G 262 (3 vol-% in dry areas of the low pressure gas grid, 10 vppm in
high pressure gas grid) [1,2]
Physio-chemical characterization (average grain size,
specific surface, porosity, gross and pure density,
average porediameter, chemical analysis, thermogravimetric analysis)
EASEE-gas CBP 2005-011-02 (10 vppm O2 daily average) for medium und high pressure gas grid
[3]
Investigation of break-through behaviour in laboratory scale (Fig. 4)
Optimization of process parameters
Resulting problems:
Mathematical modeling of the process
Corrosion respectively geo-chemical reactions in moist
areas of gas infrastructure, especially pore and aquifer
underground gas storage [4-6]
Blocking of pores and channels in underground gas
storage (formation of elemental sulfur due to oxidation
of hydrogen sulfide, Fig. 1)
Figure 4: Adsorption lab equipment
Experimental results
Investigation of break-through behaviour (O2 on sulfidized iron oxide) with following parameters:
- Superficial gas velocity, inlet concentration of oxygen, moisture and temperature (Fig. 5)
- Paramters for desulfurization were held constant (comparability of results)
Figure 1: Rhomboidal sulfur crystals on stainless steel [7]
How does oxygen get into biogas?
Substrate input
Biogas purification
- Desulfurization (e.g. in-situ desulfurization with air, drip-body systems, iron-based adsorbents)
- Separation of carbon dioxide (e.g. pressure water scrubbing (Fig. 2), Genosorb® process)
vol-%
CH4
0.109
0.233
CO2
46.328
99.755
N2
0.0043
0.009
O2
0.0014
0.000
m³/h
vol-%
CH4
0.109
0.073
CO2
46.328
31.726
N2
78.737
53.921
O2
20.85
14.278
m³/h
vol-%
N2
0.2631
63.751
O2
0.1496
36.249
drying
absorber
biogas plant
m³/h
stripper
O2-content of biomethane: 300…8.000 vppm
Figure 5: Break-through loading of oxygen XDB,O2 on sulfidized iron oxide over superficial gas velocity u,
inlet concentration of oxygen cO2,0, moisture φ and temperature T in different combination [8]
Significant loading of the adsorbent with hydrogen sulfide is required for efficient oxygen removal
m³/h
vol-%
CH4
52.42
52.42
CO2
46.37
N2
O2
m³/h
vol-%
CH4
52.311
96.922
46.37
CO2
0.0331
1.01
1.01
N2
0.20
0.20
O2
m³/h
vol-%
CH4
52.311
96.922
0.061
CO2
0.0331
0.061
Residence time in fixed bed should be high (chemical reaction rate-determining step, eq. (3), (4))
1.2731
2.367
N2
1.2731
2.367
0.3496
0.650
O2
0.3496
0.650
Relative gas humidity of about 15 % is necessary (consumption during regeneration, eq. (4))
Temperature is the most important influential parameter on break-through curve (activation energy)
Figure 2: Sankey diagram of O2 contamination during pressure water scrubbing (ChemCad model) [8]
Fieldtest
Simultaneous removal of H2S and O2 from biogas was successfully tested in a pilot plant [14]
(Fig. 6)
How can oxygen be removed?
Chemisorption on copper with H2
Catalytic removal with LPG
cH2S / vppm
Chemisorption on sulfidized iron oxides
Technology description: oxygen-chemisorption on sulfidized iron oxides
Desulfurization on iron-based sorbents, such as α-Fe2O3 or α-FeOOH, state of the art since 1950s
[9-12]:
0
(1)
(2)
24
48
72
96 120 144 168 192
t/h
0
6
12
18
24
30
t/h
36
42
48
54
Figure 6: Break-though curves of sorbents in pilot plant [14]
─ raw biogas – sorbent A
─ raw biogas – sorbent B
-- pure biogas – sorbent A
-- pure biogas – sorbent B
Regeneration by addition of air (1…2 vol-%) into raw gas
• Fe2S3 + 3/2 O2 → Fe2O3 + 3/8 S8
• 4 FeS + 3 O2 + 2 H2O → 4 FeOOH + ½ S8
cO2 / vppm
Methane oxidation on Rh, Pt-catalyst
• Fe2O3 + 3 H2S → Fe2S3 + 3 H2O
• 2 FeOOH + 3 H2S → 2 FeS + ⅛ S8 + 4 H2O
1000
900
800
700
600
500
400
300
200
100
0
1000
900
800
700
600
500
400
300
200
100
0
(3)
(4)
Summary and outlook
New process: separation of these two process steps in different columns and removal of residual
oxygen from biomethane (Fig. 3)
Verification of basic suitability of the procedure for oxygen removal below 10 vppm (EASEE-gas [3])
Identification of optimum process parameters
Problem: usually higher O2-concentration in biomethane than with H2S-content in raw gas
removable
biomethane
O2-free
Current useful application: pressure swing adsorption or amine scrubber
Further optimization of sorbents for O2 conversion as well as process and reactor design necessary
H2Sremoval
O2removal
Biogas plant
Literature
CO2 - removal
CO2-free gas /
laden with O2
raw biogas
Figure 3: Simultaneous removal of H2S and O2 during biogas purification process [8]
Contact
DBI - Gastechnologisches Institut gGmbH Freiberg
Halsbrücker Straße 34 | D-09599 Freiberg | Germany
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
DVGW, Gasbeschaffenheit 2013 (G 260).
DVGW, Nutzung von Gasen aus regenerativen Quellen in der öffentlichen Gasversorgung 2011 (G 262).
EASEE-gas, Harmonisation of Natural Gas Quality 2005 (2005-001/02).
U. Gronemann, R. Forster, J. Wallbrecht, H. Schlerkmann, gwf Gas|Erdgas 2010, 151 (4), 244.
T. Raabe, R. Erler, H. Krause, gwf Gas|Erdgas 2013, 154 (11), 854.
T. Muschalle, M. Amro, Influence of oxygen impurities on underground gas storage and surface equipment, DGMK research report, Vol. 753, DGMK,
Hamburg 2013.
T. Raabe, A. Fiedler, R. Erler, H. Krause, energie | wasser-praxis 2014 (September), 56.
T. Raabe, Untersuchungen eisenhaltiger Gasreinigungsmasse in Bezug auf Sauerstoff- und Schwefelwasserstoffentfernung, Masterarbeit, Technische
Universität Bergakademie Freiberg 2012.
A. L. Kohl, F. C. Riesenfeld, Gas Purification, 2nd ed., Gulf Publishing Company, Houston, Texas 1974.
Verfahren der Gasaufbereitung: Erdgas Brenngas Synthesegas (Eds: J. Schmidt), VEB Deutscher Verlag für Grundstoffindustrie, Leipzig 1970.
G. Drautzburg, gwf Gas|Erdgas 1985, 126 (1), 36.
A. A. Davydov, K. T. Chuang, A. R. Sanger, J. Phys. Chem. B 1998, 102 (24), 4745.
A. A. Davydov, Molecular spectroscopy of oxide catalyst surfaces, Wiley-VCH, Chichester [u.a.] 2003.
T. Raabe et al., gwf Gas|Erdgas 2014, 155 (11), 828.
phone: +49 (0) 3731-4195-310
fax:
+49 (0) 3731-4195-319
web:
www.dbi-gti.de
e-mail: [email protected]

Download - EU COST

Robert Stork-Beimfohr

Modification report

785 - DGMK