utilization of landfill gas towards high-btu methane and low-cost hydrogen fuel

Utilization of Landfill Gas towards High-BTU Methane and

Low-Cost Hydrogen Fuel

byManolis M. Tomadakis

and Howell H. Heck

Florida Institute of TechnologyMelbourne, FL 32901

Outline

Rationale Objectives Methodology Preliminary Results Anticipated Benefits

Rationale 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 adirectly supplied mixture of CO2/H2S

2.  Adsorption at the desired high pressure3.   Blowdown to the initial pressure4.   Desorption by purging with inert N2 at nearly

atmospheric pressure

Preliminary Testing

1. Molecular Sieves 13X and 4A were packed in Columns I and II, respectively

2. A mixture of CH4-CO2-H2S was supplied to Bed I to separate CH4

3. A mixture of CO2-H2S was supplied to Bed II to separate CO2 and recover H2S

4. 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

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70

time, min

Gou

t/Gin,

dim

ensio

nles

s

Bed IBed II

Ratio of Inlet to Outlet Molar Flow during Desorption

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2 4 6 8 10 12 14 16 18 20 22 24 26

time, min

Gin/

Gou

t, di

men

sionl

ess

Bed IBed II

Gas Product Composition in Bed I during Adsorption

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

time, min

Vol

ume

%

CH4

CO2

H2S

Gas Product Composition in Bed I during Desorption

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

time, min

Vol

ume

%

H2S

CO2

Gas Product Composition in Bed II during Adsorption

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

time, min

Vol

ume

%

CO2

H2S

Gas Product Composition in Bed II during Desorption

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14

time, min

Vol

ume

%

CO2

H2S

H2S/CO2 Molar Ratio in Bed II Desorption Product

0

1

2

3

4

5

6

0 2 4 6 8 10 12 14

time, min

H2S

/CO

2, di

men

sionl

ess

Current Product

Accumulated Product

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 Resultsof 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