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Chapter 10: BiomassHandling System
Mech 4840 Jake Young
Steam Plant B00451186
Engineering October 2, 2009
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Why is the Handling System so
important?
Metering the fuel feed system is animportant aspect of the biomassgasification plant because it is used to
control the entire process. The handling system controls the flow rate
of fuel into the gasifier. If the flow isvariable then the gasifier will not maintainthe desired temperatures and will not beas efficient.
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The problem
Unlike liquids, the biomass solids do notdeform under shear stresses (causesjamming) and this is why the storage and
handling of biomass is so important. Reasons for many shutdown incidents of
biomass gasifier plants can be traced tothe failure of the biomass handling system.
Some biomass contains rocks and otherdebris when it arrives at the plant.
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Biomass Handling System
The Biomass Handling System can bebroken down into 5 stages:
Biomass receiving
First Stage Screening (Optional)
Storage
Feed preparation
Conveying
Feeding
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Biomass Receiving
The Biomass is first transported via truckor rail-car and unloaded at the receivingstation.
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First Stage Screening (optional)
Sometimes depending on the type ofbiomass there is a first stage screening toremove foreign materials.
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Storage
Once received (or screened) the biomassis transported by conveyor belt to one ofthe 2 types of storage types:
Above ground storage for large biomass
Silo or bunker for enclosed storage of smallerbiomass.
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Above Ground Storage
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Silo or Bunker Storage
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Retrieval from Storage
The following are some methods of biomassretrieval from storage
Simple gravity feed or chute
Screw type auger feed Conveyor belt
Pneumatic blower
Pumped flow
Bucket conveyor
Front loader
Bucket grab
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Feed Peparation
Once retrieved the biomass is transported to theFeed Preparation System because biomass cannot be fed directly into the gasifier for thefollowing reasons Presence of foreign materials like rocks and metals
Unacceptable level of moisture in biomass
Too large (or uneven) in size
The feed preparation process consists of Screening
Drying
Sizing
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Screening
The most common foreign materials that mustbe removed are:
Stones
Ferrous metals like iron Non-ferrous metals like aluminum
This is why there is a screening (possiblysecond) process that consists of
De-stoner
Non-ferrous metal separators
Magnetic metal separation
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De-stoner
The purpose of a de-stoner is to separateheavier-than-biomass materials like glass,stones and metals.
Typically use vibratory actions in serieswith airflow to separate materialsaccording to specific gravity.
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Magnetic Metal Separation
Use powerful magnets for separation ofiron and other magnetic materials.
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Drying
Freshly cut biomass can contain up to 40-60%surface moisture and a gasification processtypically requires moisture to be less than 10-
15%. Use heat in the flue gas or external sources of
heat to reduce moisture levels.
If moisture is not removed then the gasifier cannot reach high enough temperatures and theefficiency of the plant is decreased.
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Sizing
Typical equipment that are used for cuttingbiomass into different sizes.
Chunker: 250 to 50 mm
Chipper: 50 to 5 mm
Grinder:
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Conveying
Once the biomass prepared, it is thentransported to the hopper which gravityfeeds the feeder.
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Hopper
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6 Main Types of Feeders
Gravity Chute
Screw Conveyor
Pneumatic Injection Rotary Spreader
Moving Hole Feeder
Belt Feeder
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Gravity Chute
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Screw Conveyor
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Pneumatic Injection
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Rotary Spreader
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Moving Hole Feeder
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Belt Feeder
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Mode of Fuel Injection in Fluidized Beds
Over-Bed System handles coarser particles
Under-Bed System handles fine particles
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References
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Chapter 10: Biomass Handling System byDr. Basu