5. GEOTHERMAL ENERGY

- This is the thermal energy from

earth crust

- It is a non-conventional source of

energy

- It is naturally occurring and

capable of direct exploitation and

application

About the Earth

- The earth is described as a giant

furnace

- The earth core is at very high

temperature of about 4,200oC

- The heat transport through cracks

and faults to the surface

Sources of Geothermal

Resources

1. Dry Steam: Produced from dry

geothermal fields at very high pressure

2. Wet steam: Produced from wet

geothermal fields. The hot water is

pressured and range from 175 to 315oC

in Temp.

3. Hot brines: They are very hot salt

solutions that occur in deep

sedimentary basins containing

moderately high temp. of about 160oC

4. Hot rock: hot dry rocks occurring at

moderate depths.

Advantages of GE

- It is cheaper than fossil based

fuels

- It delivers more energy than other

energy modules

- It has vast applications

- It is the least polluting compared

to other conventional sources

- It is consistent and available

throughout the year

Disadvantages of GE

- Overall production efficiency is

low

- The steam and hot water coming

out from the ground may contain

impurities and some gases that

pollute the atmosphere

- Noise from drilling

INFORMATION

- Class test (s): 1) Next class

should be a day of test (2) There

may be one or two tests

- Assignment: Should be submitted

both in soft and hard copy

- Next class: Probably July 9th

2012

but will be communicated

6. Biomass

Definition: Biomass is organic

matter produced by plants, both

terrestrial and aquatic. It includes

forest crops and residue, crops

grown especially for their energy

content on energy farms and

animal manure.

- Biomass energy is indirectly solar

energy that comes from

photosynthetic action of the sun

on plants.

- It contains stored energy from the

sun

- It is the organic matter in trees,

agricultural crops and living

plants

Biomass energy conversion

processes

Biomass conversion processes are

divided into two broad headings:

- Wet processes and

- Dry processes

Wet processes

These are processes that are used

to harvest energy through non

solid means.

The processes include: anaerobic

digestion, fermentation and

chemical reduction

Anaerobic digestion

It is the production of biogas from the

bacterial decomposition of wet

sewage sludge, animal dung or

green plants in the absence of

oxygen

The decay process can be sped up by

heating to a temperature of about

35oC, stirring to have even

distribution of bacterial action and

heat, and thermally insulating the

digester

Fermentation

- This is the breakdown of

carbohydrates by microorganisms

- Ethanol (used as bio-fuel) is

produced by fermentation of

sugar solution via natural yeasts

Chemical Reduction

- This is the least developed of the

wet process

- It involves pressure-cooking

animal wastes or plant cellulosic

slurry with an alkaline catalyst in

the presence of CO at temp. of

btw 250oC and 400

oC

Dry Processes

- These are processes that are

used to harvest biomass energy

from solid state biomasses via

non wet procedures

- A major dry process is called

Pyrolysis.

- Pyrolysis is act of heating dry

wood for example in the absence

of oxygen.

- However, when pyrolysis is

carried out in the presence of

small oxygen, it is called

gasification

- When it is small water, it is steam

gasification

- When it is small hydrogen, it is

hydrogenation

Biogas Plants

Biogas plants are reactors in which

biomass is converted to useful

gaseous form called biogas

Types of Biogas Plants

1. Biogas plant with the floating gas

holder

2. Biogas plant with a fixed dome

digester

Classification of Biogas

Plants

1. Continuous and batch type

2. The dome and the drum type

3. Different variations in the drum

type

Materials used for biogas

generation

1. Animal wastes

2. Human wastes

3. Agricultural wastes

4. Wastes of aquatic origin: this can

be water hyacinth, algae, sea

weed (or ocean kelp)

5. Industrial wastes

7. Tidal Wave Energy

Definition: This is energy from

ocean tides.

- Tides are the cyclic rising and

falling of ocean surface caused by

the tidal forces of the moon and

sun acting on the ocean.

- They are caused by the gravitational

attraction of the moon and the sun

acting upon the ocean waters of the

rotating earth.

- Tides cause changes in the depth of

the marine and estuarine water

bodies and produce oscillating

currents known as tidal streams.

- The generation of electricity using

the mechanical force created by the

rise and fall of ocean surge is called

tidal power.

- It is a renewable, largely

abundant non-depleting and clean

source of energy

- Tidal stream generators mounted

on ocean floors are used to

convert the mechanical energy of

moving stream of water to

electrical energy at low velocity

compared to wind turbines

8. Nuclear Reactors:

Operation and Safety issues

Basic Atomic Theory:

- All matter is composed of small

particles called atom

- An atom is described as the

smallest particle of an element

- The atom is made up of proton,

neutron and electron

- The neutron and proton are

contained in the nucleus

- The total number of nucleons in

an atomic nucleus is called the

atomic mass number in atomic

mass unit (amu)

- 1 amu = 1.66 x 10-27

kg

- Some elements occur in isotopes

- Molecules are formed when two

or more atoms combine together

Nuclear theory

Nuclear fission:

- This is the disintegration of atoms

of a chemical elements into two or

more fragments, releasing huge

amount of energy. This occurs when

the nucleus is bombarded by

neutrons

- The energy as a result of atomic

disintegration is given by Eistein as:

E = mc2

Where c = 3 x 108

m/s, E = energy in

Joules and m = mass of the atom

in kg

Thus, 1 amu = 1.66 x 10-27

x (3 x

108)2

= 14.94 x 10-11

J = 4.147 x 10-

17kWh

For instance:

235U +

1n

92Kr +

141Ba + 3n +

With the mass defect for each

fission given as 0.215 amu, the

amount of energy lost in form of

heat is given by Eistein as:

E = mc2 = (0.215)(1.66 x 10-27

) x (3 x

108)2

= 3.2 x 10-11

J/fission

Class exercise

1. If 1 kg of U235 containing 2.5 x

1024

is completely fissioned,

determine the amount of energy

dissipated. ANS: 8 x 1013

J

2. What mass of U235 has the

energy equivalent of 1 ton (1000

kg) of coal? (Given 1 ton of coal is

equivalent to 3 x 1010

J). ANS:

2670 tons of coal

Radioactivity

- The nucleus of unstable isotopes

undergo continuous disintegration

to achieve stability.

- The substances that undergo this

form of disintegration to achieve

a more stable energy from is

known as radioactive substances.

- The process of disintegration is

called radioactive decay

Decay rate

The rate of decay is given as:

dN/dt = - N = decay rate = activity

The negative sign denotes that the

number of atoms decreases with

increasing time

The half life (T1/2

) of disintegration

is given as:

T1/2

= 0.693/

The time of decay, t is given as:

t = (ln (No/N))/

Example

1. How long does it take a

radioactive source to decay to

1/10 of its original size? ANS: t =

3.32 T1/2

.

2. What is the value for U235 which

has a half life of 7.1 x 108

years?

ANS: 2357 million years

Forms of radiation from

radioactive sources

a) Alpha particles

b) Beta particles

c) X radiation

d) Gamma radiation

e) Cosmic radiation

f) Neutrons (n)

NB: d, e and f are classified as

ionising radiation

Environmental issues of

nuclear reactors

Class discussion