Chapter 4: CONVERSION OF AGRICULTURAL WASTE BY GASIFICATION

Agricultural waste

is one of the potential source of materials that can be converted into energy.

gasification, gasifiers

The knowledge of the basic principle of ___ can be a tool in designing and developing ____ for various applications in agriculture.

Gasification

is the process of converting a solid carbon into combustible carbon monoxide by thermo-chemical reaction of a fuel.

excess air, excess carbon

In complete combustion, the process takes place with ____ while in gasification the process takes place with _____.

Gasification of solid fuel containing carbon

____ is accomplished in an air sealed, close chamber under slight suction or pressure relative to ambient pressure.

15 - 30 %

Carbon monoxide (CO) Composition of Producers Gas

12 - 20 %

Hydrogen (H2) Composition of Producers Gas

0.5 - 7 %

Methane (CH4) Composition of Producers Gas

3 - 15 %

Carbon dioxide (CO2) Composition of Producers Gas

50 - 58 %

Nitrogen (N2) Composition of Producers Gas

fuel column

Limited amount of air is introduced to the reactor of the gasifier and it passes through the _____.

thermo-chemical reaction

As the air passes through the column of fuel, _____ takes place to produce combustible gases.

oxygen and the carbonized solid fuel

The ______ reacts to produce carbon dioxide and heat.

carbon monoxide,

When complete gasification takes place, all the carbon will be reduce to _____.

Drying zone, Pyrolysis or distillation zone, Reduction or gasification zone, Oxidation or combustion zone

The different zones in fixed bed gasifiers are:

heat transfer

The process taking place in the drying, pyrolysis, and reduction zones are driven by ____ from the combustion zone.

Equivalence Ratio

it is the ratio of the amount of stoichiometric air needed to gasify fuel.

0.2 to 0.4

The equivalence ratio for gasification process ranged from ____.

Heat Application

Agri-waste is converted to combustible gas and is consequently used as source of heat for drying, kiln firing, etc.

Mechanical Power Generation for Steady Load

Agri-waste is converted to combustible gas, clean, and fed to internal combustion engine to run stationary pumps, rice mill, generator, etc.

Mechanical Power Generation for Unsteady Load

Similarly, this convert agri-waste fuel in to gas to fuel internal combustion engine to run vehicles such as trucks and tractors.

bubbling, circulating

Types of Gasifier under fluidized bed

updraft, downdraft, crossdraft

Types of Gasifier under fixed bed

Fixed Bed Gasifiers

It is a very old technology, usually used for small-scale application

Fixed Bed Gasifiers

Design and operation is relatively simple, 􀀃 Require large dense and uniformly size fuels

densification

"Agri-residues as fuel requires ____ which will add cost"

*note

Special complex gasifier design are required for quality operation.

Updraft

Fixed Bed Gasifier wherein the gas stream flows in parallel direction with the fire zone.

Updraft

It has the higher efficiency because the hot gas passes through the entire fuel bed and leaves the gas producer at a low temperature.

Downdraft

Fixed Bed Gasifier wherein the gas flow in opposite direction with the fire zone causing the burning of tars before it leaves the reactor.

Cross-draft

Fixed Bed Gasifier wherein the flow of the gas stream crosses the fuel bed and the direction of the fire zone.

Fluidized Bed Gasifiers

It is a new technology in which fuel particles, together with an inert bed material such as sand can be fluidized by air movement

Fluidized Bed Gasifiers

Gas stream passes vertically upward through a bed of inert particulate material to form a turbulent mixture of gas and solid

Fluidized Bed Gasifiers

Fuel is continuously added at a such a rate that it is only a few percent by weight of the bed material.

Fluidized Bed Gasifiers

The fuel particle undergo rapid heating up to bed temperature on entering the bed and reacts with the incoming stream.

Fluidized Bed Gasifiers

The violent stirring action makes the bed uniform in temperature and composition with the result that gasification occurs simultaneously at all locations in the bed.

Bubbling Fluidized Bed

The solid particles behave like a boiling fluid but not transported by the air stream.

Circulating Fluidized Bed

The gas velocity is higher and therefore part of the bed material leaves the reactor vessel and transported back to the reactor vessel via a cyclone and return pipe.

combustible and non-combustible gases

The gas leaving the producer gas consists of ____.

corrosive and produces pollutants

Gases including tar from the reactor are ______ which may seriously interfere the operation of a burner or an internal combustion engine.

*note

Gases and other pollutants from the gasifier includes: (a) Sulphur compounds, (b) Nitrogen Compounds, (c) Dusts, (d) moisture, and (e) tars or hydro carbons.

Cyclone Separator

It is a dust collector without moving parts wherein the velocity of the inlet stream is transformed into a confined vortex and separates the dust from the gas.

Scrubber

It cools and separates pollutants and the solid particles while it passes through a spray liquid droplets.

Water or Oil Bath Filter

It removes dust and particulates by allowing it to pass through the bed of water or oil.

pressure drop

The degree of dust removal of water or oil bath filter is usually limited by the _______ through the system.

Fabric Filter

It removes dust and particulates through mechanical screening using a cloth of fabric material.

gasifier

All three types of engine (gas, gasoline, and diesel) can be fueled with ___.

diesel oil

All diesel engine cannot operate on gasifier alone but must be mixed with ____.

50 to 70%

Due to the part behavior of a diesel engine, only ____ of the diesel oil can only be replaced by gasifier.

gas

The efficiency of ICE will not be changed much when fueled with ___.

10 to 20%, 30 to 50%

The power output of the engine fueled with gasifier at an arbitrary rpm will decrease by ____ for dual fed diesel engine, and ____ for gasoline engine.

*note

High speed engines are not as suitable with low speed engines.

15 to 30#

In some cases such as charcoal gasifier engine system, it is advisable to advance the ignition of the engine to ____ before top dead center.

*note

The choice of the proper engine oil is important but no close opinion exist which oil is most suitable. One can expect to have engine oil changed as twice as often for an engine fueled with gasifer.

slow, high

In case of gasifier, it is advantageous to use ____ speed engines with a ___ internal inertia.

cast iron

Engine with ___ sleeves are more suitable since the sleeve when scratched ca be replaced easily.