MICRO-GASIFICATION

Cooking applications for developing Countries Davide Caregnato

The 4 stages of combustion •

Drying: (endothermic T150°C) thermal degradation in absence of an externally supplied oxidizing agent

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Gasification: (exothermic T>250°C) thermal degradation in the presence of an externally supplied oxidizing agent

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Combustion: (highly exothermic T>700°C) complete oxidation of the products given by the previous phases

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In order to have a complete and efficient combustion the 3 T's are fundamental: –

TEMPERATURE must be high enough to ignite the fuel

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TURBULENCE must be vigorous enough for the fuel constituents to be exposed to the oxygen of the air

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TIME must be long enough to assure complete combustion

Traditional fuel consumption •

2.5 billions of people rely on woodfuels for most of their energy needs, most of them using highly inefficient ang dangerous cooking methods

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Drying, Pyrolysis, Gasification and Combustion occur simultaneously in an uncontrolled manner

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3T's are too low and uneven in many reaction zones

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High production of dangerous air pollutants like CO, Particulate, and smoke in general (due to incomplete combustion of many particles)

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Accumulation of smoke and air pollutants inside the habitation

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Very Low combustion efficiency

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Low cooking efficiency given by huge heat dispersion

3-stone fire

Wood-gas stoves Energy •

A WGS consists of a micro-gasifier combustion unit and a heat-transfer unit

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WGS allow a separation in space of the gasburning zone from the gas-production zone

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WGS can produce biochar as solid remaining after combustion

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The technology needed to build an efficient WGS is very simple

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WGS are very cheap and available even for very poor people

Biochar

Biomass

Carbon sequestration

Versatility and usable biomass

Combustion vs Micro-gasification Traditional combustion

Micro-gasification

Micro-gasifier combustion unit •

Micro-gasifier is the most important part of a WGS

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It is a batch reactor, which gasifies a fixed fuel bed, and burns the produced gas apart

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It can reach temperatures of 900-1000°C so it should be made of metal or a refractory material

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There are many kinds of Micro-gasifier but the TLUD type is the most common and suitable for cooking applications

Top-Lit Up-Draft gasifier (TLUD)

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Top-Lit: Fuel is ignited from the top

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Up-Draft: Air and other gases draft proceed upward

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Biomass fuel fixed bed (porousness needed)

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Often biomass requires preaparation

Single pipe vs 2 coaxial pipes FLAME AND BURNT GASES OUTLET

SECONDARY AIR INLET REACTION CHAMBER

PRIMARY AIR INLET

FLAME AND BURNT GASES OUTLET

HOLLOW SPACE

SECONDARY AIR

REACTION CHAMBER

PRIMARY AIR INLET

SECONDARY AIR INLET

Operating principle •

Biomass gasifies progressively from the top to the bottom of the fixed bed thanks to a Flaming-Pyrolysis (F-P) front moving downward

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Primary inlet supplies the strictly necessary oxygen amount to sustain F-P front thanks to a primary combustion

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Wood-gas produced moves upward and after mixing with secondary air burns over the top of the reactor

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The entire process is auto-thermal and it doesn't need any external energy supply

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Separation in the space between the gas generation zone and the burning zone

TLUD's combustion phases separation FLAME COMBUSTION BIOCHAR

FLAMING-PYROLYSIS FRONT

UNBURNT BIOMASS

PYROLYSIS

PYROLYSIS + PRIMARY COMB.

DRYING

Flaming-Pyrolysis front •

Is the reaction zone where simultaneously occur a controlled primary Combustion and the Pyrolysis of biomass

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The wood-gas is produced in this zone

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Thanks to the controlled primary combustion it provides the heat needed by Pyrolysis and Drying reactions in the entire chamber

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In this zone fuel assume a bright red colour typical of oxidative reactions

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It has the shape of a thin disk extended along the entire horizontal section of the chamber (its thickness depends on primary air amount, fuel calorific value and fuel bed porousness)

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F-P front moves downward from the top to the bottom of the fuel packed column

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F-P front velocity varies from 3 to 20 mm per minute depending on primary air amount, fuel calorific value and fuel bed porousness

Gas flow

Legend: Fresh air

WOOD-GAS + SECONDARY AIR MIXING ZONE

Pre-heated air Hot wood-gases

WOOD-GAS PRODUCTION ZONE

Temperature gradient T [°C] USABLE HEAT GENERATION

700-1100

350-600

AUTOTHERMAL HEAT GENERATION

600-850 20-150

Emissions comparison

Advantages given by micro-gasification •

Simple technology and low costs of production

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High combustion efficiency with low fuel consumption

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Very low emissions

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Possibility to use poor biomass or agricultural residues as fuel

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Possibility to save biochar for many purposes

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Stable combustion process during a long time (even 2-3 hours with no human needed intervention)

Woodgas Campstove Area

United States

Designed by

Tom Reed

Price

55 US dollars

Numbers sold

Not Avaiable

Features

Projected in 1995 it was the fist wood-gas stove Fan assisted draft Created for camping purposes

Peko Pe Area

Uganda

Designed by

Paal Wendelbo

Price

Not Avaiable

Numbers sold

Not Avaiable

Features

Parallel independent Projected to the Tom Reed stove (1996) One of the simplest and cheapest gasifier stoves Created to reduce smoke desease in the Uganda refugee camps

Elsa

Elsa features •

Scalabiliy

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Durability

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Great versatility

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Obtainable from flat metal sheets

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Large amounts of stoves can be shipped at a low cost

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Free projects available for free

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User manual and Assembly manual provided

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Training workshops and survey

Cooking with Elsa

Elsa research

Thank you..

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Website: E-mail:

www.blucomb.com [email protected]

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Davide Caregnato: – Phone: +39 328 2297197 – E-mail: [email protected]