Chapter 3: CONVERSION OF AGRICULTURAL WASTE TO ENERGY BY DIRECT COMBUSTION

3.50%

Presently, the domestic consumption of agricultural waste is about ___.

increase

The continued ____ in the cost of fuel energy both for heat and power necessitate to convert agricultural waste into fuel.

agricultural waste

is a potential materials to replace the conventional energy sources especially the fossil fuel.

Rice Straw

This can be obtained from paddy field after harvesting mature rice.

Rice Husk

This can be obtained from milling of rice.

20%

About ___ of the paddy constitute of rice husk.

Sugar Cane Bagasse

This can be obtained from sugar mills. It is the by-product of sugar cane after crushing and squizzing action of the roller mills.

Corn Cobs

This can be obtained after the shelled corn is removed from the corn cobs.

Coconut Husk

This is the by-product from copra production after the meat from coconut is removed.

4.1668 KJ

1 Kcal

252 Cal

1 BTU

Combustion

It is a chemical process to which one of the reactants is oxygen from the air and the other is a fuel.

Complete Combustion

This is when all the combustible components are gasified and all the carbon is burned to carbon dioxide, all the hydrogen is converted to water, and sulfur to sulfur dioxide.

*note

The primary aim of a combustion system is to convert carbon (C) and hydrogen (H) contained in a fuel to carbon dioxide (CO2) andwater vapor (H2O), respectively.

Stoichiometric Air

It is the theoretical amount of air required to burn a fuel completely to product with no dissociation.

Percent Excess Air

It is the additional amount of air needed to achieve complete combustion of fuel.

Percent Excess Air

It can be determined by the actual amount of air used minus the stoichiometricair.

65-75%

In general, excess air of about ____ of the theoretical air is needed for complete combustion.

maximum

For biomass fuel, ____ excess is required.

Percent Theoretical Air

It is the amount of air actually used divided by stoichiometricair.

Efficient combustion

can be achieved by providing the stove or furnacewith sufficient supply of air.

*note

Efficient burning of fuel can maximize its utilization.

*note

Inefficient combustion of fuel is wasteful and contributes to pollution of the atmosphere.

Incomplete combustion

will produce significant amount of carbon in the fuel and will produce high percentage of CO instead of CO2.

carbon

Production of ___ during combustion reduces the amount of heat produced and may cause emission of toxic gases which is hazardous to health and in the environment.

Primary Air

It is the air admitted to or with the fuel.

fuel bed

In the case of solid fuel, air is pass through the ____.

admitted and mixed

For gas or liquid, air is ___ the fuel prior to combustion.

Secondary Air

It is the air fed into the furnace system which does not pass through the fuel bed.

Secondary Air

it is use to further or completely burn volatile combustible gases.

Excessive amount of secondary air

_____ may dilutes air necessary for combustion and reduces heat transfer efficiency.

1:1 to 1.5: 1

Primary to secondary air ratio for biomass fuel ranged from ______

additional air

Combustion of volatile gases can be further improved by introducing ____

volatile gases

During burning of fuel ____ is produced

Bulk Density

It is the mass of loosely packed specified volume of agricultural waste material.

Bulk Density

This is important in the cost of transport and storage, and design of handling and conveying of furnace systems.

Bulk Density

It is also a factor to take account in the design of combustion chamber.

Moisture Content

This is the amount of water contained in the fuel.

Free moisture

____ in the fuel influences performance of the furnace.

Moisture Content

It must be taken into account in the design of the combustion equipment to ensure that combustion chamber temperature are maintain within limits at which combustion can take place without causing ash fusion and fouling

Proximate Analysis

It is used to determine the percentages of volatile matter, fixed carbon, and ash in the fuel.

Proximate Analysis

It gives the indication of the flaming and glowing combustion.

ash

provides a measure of the incombustible mineral matter in the fuel.

Ultimate analysis

It determines chemical composition of fuels in terms of carbon, hydrogen, oxygen, nitrogen, and sulphur as mass percentages of dry and ash free biomass material.

Ultimate analysis

This is essential in estimating air requirements, flue losses, and emission of pollutants.

Calorific Value

It is important since it determines the quantity of fuel which must be burnt to meet a given duty.

bomb calorimeter

Calorific value can be determined in the laboratory using _______ of can be computed using an equation.

Ash Properties

This plays a very important in role in the fouling, slagging, clinker formation and erosion properties.

fusion temperature

Knowledge of the ____ of biomass ashes can help in the choice of the optimum temperature to suitably operate a furnace.

size reduction

Some biomass fuel requires ___ and/or other properties which is dependent upon the type and scale of the combustion equipment.

uniformly sized

Feeding biomass fuel and controlling its operation using automatic feeders, conveyors, spreaderswill require fuel that is _________.

Agri-Waste Stoves

It denotes a burning device for supply heat energy for domestic and institutional uses that utilizes solidagricultural waste as fuel

Boiling

It is the process of raising the temperature of the mixture of food in water at 100 C and then allowed to simmer until the exothermic reaction in the food is completed.

Frying

It is a short duration high power input process generally between 200-300 C using cooking oil.

Baking

It is the process which is accomplished in an oven or in an open pan at a relatively high temperature of about 130 C through convection and radiation from the oven wall or by conduction in an open pan.

Grilling

It is the mode of cooking where heat is transferred to the food primarily though radiation from the charcoal fuel or heated metal plate and to some extent through convection.

Steaming

It is a process where the operating temperature during cooking process is nearly to boiling temperature.

Pressure cooking

It is similar to boiling except that the temperature is considerably above the boiling point of water.

agricultural waste fuelled furnace

is a heating device where fuel is burned to supply heat to various processing operation or generate steam to produce power.

complete combustion

Burning of fuel in the furnace must be accomplished in such a way that there is ______ of fuel.

source of heat for thermal systems, source of heat for boilers to generate steam

Uses of Agri-Waste Furnace

flat grate, step-grate, center-tube, cyclone, spouted bed, fluidized bed

Classifications of Biomass Furnaces

fuel storage, feeding mechanism, combustion system, heat exchanger, flue gas outlet

Component Parts of a Furnace System

combustion chamber, fuel stoker, ash removal

Parts of combustion system

Fluidized Bed

This system are suited for burning both large and small particulates wood waste and agricultural residue and can operate with these fuel at relatively high moisture content.

Fluidized Bed

The system comprise a combustion chamber containing a sand bed acting as the heat transfer medium.

hot bed

Under fluidized bed, particulate biomass is introduced into the ____ where it undergoes combustion.

Cyclonic

These are suitable to burn particulate waste wood and agricultural residues typically of regular size and shape and relatively at low moisture content.

Cyclonic

The system comprises a cylindrical chamber where the combustion air is introduce tangentially.

intimate mixing

The cyclonic regime of the combustion promotes _____ of suspended particulate residue allowing efficient combustion.

Grate

This is the most commonly used method [of combustor].

Grate

They are suitable for burning a wide range of biomass material.

Grate

is designed to support the biomass fuel and allows air to circulate freely through it.

firebox, narrow

The ____ must be large enough to accommodate the size and type of fuel to be used. However, it must be ____ enough to confine the fire beneath the pot.

pot, radiant heat

The ___ should be as close to the heat source as possible to take full advantage of the ____ but not too close to smoother the fire.

firebox entrance, cris-cross

The ____ should be wide enough to permit easy access to fire and _____ placement of fuel pieces.

dampers, tightly closed

The ____ which controls the flow of air should be _____ as much as possible.

front damper, back damper, draft

The ___ should be designed to focus air on the base of the fire while the ____ should be provided to control the air flow by reducing the ____ from the chimney.

baffles, bottom

There should be ____ under all pots not over the firebox to allow heat to concentrate at the ____ of the pot.

35-70 mm

The space between the bottom of the pot and the baffles should be the minimum required to maintain adequate draft. Recommended gap for baffles ranged from _____.

chimney

A ____ should be provided to carry smoke out of the kitchen.

draft of the chimney

The _____ should be strong enough to aid combustion and draw the smoke out of the stove but not too strong to draw excess air that dilutes the heat of exhaust gases.

0.4 to 1 liter per sec.

Average suggested velocity for chimney ranged from _____

75 cm

The chimney should extend ___ above the highest point of the roof for safety and to prevent down draft.

non-flammable spacer, cap, screen

The chimney should be provided with ____ around it and a ___ to prevent rain from coming in and ____ to prevent spark from flying out.

Physical Properties of Fuel

This includes the bulk density, porosity, angle of repose, and coefficient of friction of the fuel.

Fuel-Bed Temperature

Continuous burning of fuel in the furnace can be sustained when the temperature at the bed approximates the kindling temperature of about 300 to 400 C.

Volume Change-Temperature-Time Relationship

It determines how long does the firing chamber can hold the fuel for burning at a specified temperature.

rate of burning

The ______ should not be too short to cause consolidation of fuel or arching of material or too long to cause an obstruction for airflow.

60%

Rice husk burn with about ____ of its volume remain in the form of char or ash.

25 to 28%

Coconut husk and sawdust can be reduced to ____ of the original volume.

Air Requirement for Combustion

The chemical composition of the fuel directly related to the amount of air required for combustion and the amount of product of combustion.

space, leakage

The furnace should be sufficient to permit ____ for combustion of air but not be too large to permit ____.

dimension, combustion equipment

The ___ of the furnace should have sufficient space for _______ such as burners and smokers.

Impingement

____ of flame should be avoided on any part of the furnace.

slag deposit

Combustion and temperature condition in the furnace should be free from ___ unless required in the design.

Wall construction, circulation of water

______ of the furnace should be resistant to expansion, prevent heat loss, minimum maintenance, and strong enough to resist failure. There should be adequate ______ when water wall are used for the furnace.

*note

Furnace imension should be adequate to complete combustion of fuel.

Passages

___ must be provided for proper transportation of combustion product from the furnace before temperature is reduced to a point where flow is inhibited.

Fly ash or slag

____ formed deposit to the furnace must be eliminated.