Transcript Design of a Pressure Swing Adsorption Process for the

Utilization of Landfill Gas
towards High-BTU Methane and
Low-Cost Hydrogen Fuel
by
Manolis M. Tomadakis
and Howell H. Heck
Florida Institute of Technology
Melbourne, FL 32901
Outline
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Rationale
Objectives
Methodology
Preliminary Results
Anticipated Benefits
Rationale
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H2S is among the components of landfill
gas, which contains primarily CO2 and CH4
Photolytic decomposition of H2S provides
an alternative source of hydrogen fuel
Removal of H2S from landfill gas would
help prevent odors, hazards and corrosion
Removal of CO2 would increase the BTU
value of the remaining methane gas
Objectives
1. Test the efficiency of molecular sieves 4A, 5A, 13X
in separating landfill gas towards high-BTU methane
and FSEC- quality H2S (>50% H2S and <1% CO2)
by Pressure Swing Adsorption (PSA)
2. Investigate the effect of the landfill gas H2S content
on the PSA process efficiency, by varying the H2S
feed volume fraction in the range 0-1 %
Objectives (cont’d)
3. Determine the effect of pressure on CH4 and H2S
product recovery and purity, by varying the
system high pressure in the range 40-100 psig.
4. Examine the effect of near-equilibrium operation
of the PSA process on the percent utilized sieve
capacity and overall process efficiency, by
varying the gas feed flowrate.
Pressure Swing Adsorption System Layout
Pressure Swing Adsorption Apparatus
Experimental Methodology
Column I
1. Pressurization to the desired adsorption
pressure by pure CH4
2. Adsorption - supplying a mixture of CH4,
CO2 and H2S
3. Blowdown to the initial pressure (~1 atm)
4. Desorption - purging with inert N2 at nearly
atmospheric pressure
Experimental Methodology
Column II
1. Pressurization to the selected adsorption pressure
by the adsorption product of column I or a
directly supplied mixture of CO2/H2S
2. Adsorption at the desired high pressure
3. Blowdown to the initial pressure
4. Desorption by purging with inert N2 at nearly
atmospheric pressure
Preliminary Testing
1.
2.
3.
4.
Molecular Sieves 13X and 4A were packed in
Columns I and II, respectively
A mixture of CH4-CO2-H2S was supplied to
Bed I to separate CH4
A mixture of CO2-H2S was supplied to
Bed II to separate CO2 and recover H2S
Adsorption and desorption in Beds I & II
were carried out at 100 psig & 0 psig,
respectively
Preliminary Experiments
Ratio of Outlet to Inlet Molar Flow
during Adsorption
1
Gout/Gin, dimensionless
0.9
0.8
Bed I
Bed II
0.7
0.6
0.5
0.4
0
10
20
30
40
time, min
50
60
70
Ratio of Inlet to Outlet Molar Flow
during Desorption
1.0
Gin/Gout, dimensionless
0.9
0.8
Bed I
0.7
Bed II
0.6
0.5
0.4
0
2
4
6
8
10
12
14
time, min
16
18
20
22
24
26
Gas Product Composition in Bed I
during Adsorption
100
90
80
Volume %
70
60
CH4
50
40
CO2
30
H2S
20
10
0
0
10
20
30
time, min
40
50
60
Gas Product Composition in Bed I
during Desorption
45
40
35
Volume %
30
25
20
H2S
15
10
CO2
5
0
0
5
10
15
time, min
20
25
Gas Product Composition in Bed II
during Adsorption
100
90
80
CO2
Volume %
70
60
50
40
30
H2 S
20
10
0
0
10
20
30
40
time, min
50
60
70
Gas Product Composition in Bed II
during Desorption
60
50
Volume %
40
30
H2 S
20
10
CO2
0
0
2
4
6
8
time, min
10
12
14
H2S/CO2 Molar Ratio in Bed II
Desorption Product
6
Current Product
H2S/CO2, dimensionless
5
Accumulated Product
4
3
2
1
0
0
2
4
6
8
time, min
10
12
14
Sieve Capacity & Utilization
1.
Column I adsorption loads:
0.9 kg CH4, 2.4 kg CO2, & 2 kg H2S/100 kg 13X
Column I sieve equilibrium capacities:
23 kg CO2 or 19 kg H2S per 100 kg 13X
2.
Column II adsorption loads:
2.8 kg CO2 and 1.9 kg H2S per 100 kg 4A
Column II sieve equilibrium capacities:
18 kg CO2 or 14 kg H2S per 100 kg 4A
Summary of Preliminary Results
1. A 50% CH4 feed over 13X ZMS resulted to
98%-99% product CH4 during adsorption
2. A 68% CO2 - 32 % H2S feed over 4A ZMS
resulted to 71% H2S and 29% CO2 product
during desorption
3. A 20-30% utilization of equilibrium sieve
capacity was encountered
Expected Technical Results
of Proposed Study
Variation of the PSA product purity and recovery
(CH4%, H2S%, CO2%) and utilized % sieve
capacity with:
a) Type of utilized molecular sieve (4A, 5A, 13X)
b) H2S content of landfill gas (0-1%)
c) Maximum applied pressure (40-100 psig)
d) Landfill gas feed flowrate
Anticipated Benefits
Development of environmentally acceptable
& financially sound end use for landfill gas,
providing both a high-BTU CH4 stream and
a low-cost H2S feed stream supply for the
FSEC renewable hydrogen fuel program