2. 2
U/G UNLOADING PIT – Grade Level Unloading
FEATURES :
1. UNLOADING FROM GRADE LEVEL
2. PITS UNDERGROUND
PROS :
1. UNLOADING FROM GRADE
LEVEL: RAMP COST
ELIMINATED
CONS :
1. EXCAVATION COST TO MAKE PITS
UNDERGROUND
2. VIBRATORY SCREEN TO CAPTURE DEBRIS – NOT
POSSIBLE
3. HELICAL SHAFT AGITATOR – NOT POSSIBLE
4. VERTICAL PUMP INSTALLATION- NOT POSSIBLE
5. SUBMERSIBLE PUMPS IN DIRTY THIXOTROPIC
SLURRY- NOT RECOMMENDED
6. PUMP PITS WILL BE NECESSARY; INCREASING
THE EXCAVATION COST
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3. 3
A/G UNLOADING PITS – Bucket Elevators
RECOMMENDED SOLUTION
FEATURES :
1. UNLOADING FROM GRADE LEVEL
2. PITS ABOVE GROUND
3. TRANSFER THROUGH BUCKET-ELEVATORS
PROS :
1. UNLOADING FROM GRADE
LEVEL: RAMP COST ELIMINATED
2. EXCAVATION COST TO MAKE PITS
UNDERGROUND – ELIMINATED
3. HORIZONTAL PD PUMPS CAN BE
LOCATED AT GRADE LEVEL
CONS :
1. NOMINAL INCREASE IN
COST FOR INSTALLING
BUCKET ELEVATOR
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4. 4
1. CAPACITY UPTO
30TONS/HR AVAILABLE
EXTENSIVELY USED IN
PAPER AND PULP
INDUSTRY
EASY MAINTENANCE & V-
BELT DRIVE
BUCKET ELEVATORS
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7. 8
DIGESTION PROCESSES
The digestion process consists of two main phases: -
a) Acidification (Acid formation),
b) Methanation (Methane formation).
The better the two phases merge into each other, the shorter & effective is the digestion
process
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8. 9
DIGESTION PROCESSES
The following types of digestion are distinguished according to the temperature in
the digester : -
- Psychrophilic digestion (10-20 °C, retention time over 100 days),
- Mesophilic digestion (20-35 °C, retention time over 20 days ),
- Thermophilic digestion (50-60 °C, retention time over 8 days).
We intend to go for enhanced rate of the production and fermentation at elevated
temperatures maintained by water heating.
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10. 11
MAJOR CONTAMINANTS
Moisture , CO2 – To enrich the BIOGAS, these need to be eliminated.
Hydrogen Sulfide – combustion of biogas produces corrosive acids, detrimental to
the equipment and wetted surfaces of the storage vessels.
Sulfur Compounds – combustion produces sulfur dioxide and sulfuric acid which are
corrosive and environmentally hazardous.
Ammonia – combustion produces nitrogen oxides, which are environmentally
hazardous and toxic in nature.
Siloxanes – Siloxanes are compounds of silicon present in the biogas, produces silicon
oxides upon combustion and are hazardous.
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11. 12
PURIFICATION PROCESSES
1. Pressure Swing Adsorption (PSA) system
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SALIENT PROS/CONS :
1. METHANE LOSS HIGHER THAN
OTHER PROCESSES
2. PRE-REMOVAL OF H2S REQUIRED
3. COMPLEXITY / AUTOMATION
REQUIREMENT IS HIGHER
4. POWER CONSUMPTION IS
LESSER THAN OTHER PROCESSES
12. 13
PURIFICATION PROCESSES
2. Water Scrubber system
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SALIENT PROS/CONS :
1. METHANE LOSS LESSER THAN
PSA.
2. PRE-REMOVAL OF H2S IS NOT
REQUIRED.
3. WATER REQUIREMENT IS
HIGHER.
13. 14
PURIFICATION PROCESSES
3. Membrane Separation system
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SALIENT PROS/CONS :
1. EASIER TO OPERATE.
2. METHANE LOSS HIGHER
THAN OTHER PROCESSES.
3. RELATIVELY LESSER CH4
PURITY.
14. 15
PURIFICATION PROCESSES
4. Cryogenic Separation system
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SALIENT PROS/CONS :
1. HIGHER OPERATING PRESSURE
/ MORE PRESSURE DROP.
2. METHANE LOSS LOWER THAN
OTHER PROCESSES
3. PRE-REMOVAL OF H2S
REQUIRED
17. METHANE PURITY
3/16/2023 18
Table 2. Biogas cleaning methods, number of plants and averaged purities of output CH₄.
Adapted from [2].
Method Number of plants Ave. CH₄ purity, %
Water scrubbing 107 96.1
Pressure swing adsorption 55 95.8
Chemical absorption 53 94.6
Membrane permeation 22 90.3
Cryogenic process 1 88.0
18. 19
RECOMMENDED SYSTEM
We propose : Aqueous Chemical Scrubbing in the following manner: -
1) Ferric Chloride scrubbing of Biogas for H2S removal.
2) Caustic Soda or Lime washing for CO2 removal.
3) Activated Silica Gel adsorbent on regenerative lead-lag flushing system
for Moisture Separation/ REFRIGERANT BASED DESCICANT SYSTEM (RELATIVELY
HIGHER CAPEX WITH ZERO METHANE LOSS)
4) Nitric Acid solution scrubbing for Ammonia removal.
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19. 20
ADVANTAGES OF THE
RECOMMENDED SYSTEM
1) Using Nitric acid solution for neutralisation of Ammonia results in a highly soluble Ammonium
nitrate solution which is also a fertilizer and can be added to the generated after-product
fertilizer.
2) Ferric chloride is a fantastic pH buffer and aids to boost up gas production in the anaerobic
digester, being immune to catalyst poisoning.
3) Caustic Soda and/or Lime solution reacts with the CO2 effectively and removes CO2 without the
cost of MEA which is an expensive industrial product.
4) Scrubbing results in minimum gas losses which is only evident in final stage for silica gel.
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![METHANE PURITY
3/16/2023 18
Table 2. Biogas cleaning methods, number of plants and averaged purities of output CH₄.
Adapted from [2].
Method Number of plants Ave. CH₄ purity, %
Water scrubbing 107 96.1
Pressure swing adsorption 55 95.8
Chemical absorption 53 94.6
Membrane permeation 22 90.3
Cryogenic process 1 88.0](https://image.slidesharecdn.com/techpresentation-16-03-23final-250715094636-edb0a496/85/TECH-PRESENTATION-on-Unloading-Arrangements-17-320.jpg)
