chapter 10 - biomass handling system

8/7/2019 Chapter 10 - Biomass Handling System

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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

chapter 10 - biomass handling system

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