Oxygen Bomb Calorimeter Experiment to find the calorific

Oxygen Bomb Calorimeter

A00201079

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A00201079 OXYGEN BOMB CALORIMETER 21/11/2013

THE OXYGEN BOMBCALORIMETER

Objectives To understand calorific values of combustible fuels To determine the calorific value of combustible fuels

Apparatus An oxygen bomb calorimeter Crucible Thongs Steel wire Combustible fuel samples Oxygen supply Balance Benzoic acid Steel bucket

Figure 1 the oxygen bomb calorimeter (Parrinstrument company)

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Figure 2: Oxygen bomb crucible (Parr instrumentcompany)

Introduction Combustion in essence is the chemical combination of a

combustible fuel with oxygen and this in turn results in the

production of heat energy. Combustion is achieved by combining

the two key elements of combustion a fuel and oxygen, at an

elevated temperature or an ignition temperature. The chemical

breakdown is simple enough with a decent understanding of the

periodic table. The air around us supplies the oxygen, which

will bond with hydrogen, carbon and other smaller elements

within a fuel to produce the by product of heat. The principle

of combustion is vital to modern day industry and engineering.

Equipment and technology is required to burn solid liquid and

gaseous fuels to a high heat recovery standard and to ensure

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the desired amount of heat is obtained from any fuel and

ensure very little waste product is left over after combustion

of the fuel. The basic functionality required from such

equipment designs is namely to provide a supply of oxygen and

mixed fuel in the desired ratio. Too much of either of these

ingredients would lead to improper and unsatisfactory

combustion of the fuel itself. The high temperature during

combustion must also be confined and retained (access

engineering).

Wood coal and simple fuels like this are the combustible

substances which in coming in contact with an air supply

produce large amounts of heat energy. The term combustion

itself refers to the exothermal oxidation of a fuel by oxygen

within the air at a rapid rate to produce a high temperature.

This is usually with a spark ignition and the appearance of a

flame. Most fuels contain carbon or carbon and hydrogen,

combustion involves the oxidation of carbon to carbon dioxide

and also hydrogen to water any sulphur which is present is

oxidised to sulphur dioxide while any mineral matter within

the fuel forms the waste product as. Coal is a complex fuel

and will undergo thermal decomposition during the stages of

combustion which then gives simpler products which are in turn

oxidised to give carbon dioxide and water.

Fuels are classified in two separate classes

1. Primary fuels – naturally occurring fuels. Fossil fuels

such as coal, oil and gas

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2. Secondary fuels – these are fuels derived from the

primary fuels due to treatment processes examples of

which would be gasoline, petroleum etc

A good fuel should have a high calorific value and in doing so

should produce large quantities of heat energy when combusted.

When a fuel contains hydrogen there are two distinguishable

calorific values the gross and the net values. The gross

calorific value refers to heat which is obtained when the

water which is a product of the combustion is then condensed

as a liquid. The net value refers to the water vapours which

are not condensed and escape along with the hot gases. This is

the lower value. It is the value of the produced heat when the

unit mass of the fuel is burned completely and the products of

combustion are allowed to escape.

a simple calculation of net calorific value can be shown in

this form

Hydrogen in a fuel reacts with oxygen to give water

H 2 + ½ O2 gives H2O

2H = ½ O2=H2O

Atomic weights then are taken for each element

2parts H=16partsO2=18partsH2O

1parts=8 parts=9 parts

So for every 1kg of hydrogen 8 kg of O2 is required for the

ideal combustion

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The calorific value of a fuel is described and defined as the

quantity of heat required which is produced by the complete

combustion (the online dictionary)of a specified mass of a

particular fuel. This quantity is generally expressed in

joules per kilogram (the online dictionary). The gross or the

higher value is heat which is available from a fuel when

complete burning has taken place , it is defined as the total

heat liberated by the complete combustion of the fuel

(department of energy and climate change). This particular

value is determined by measuring the heat removed when cooling

the products of combustion to a standard reference temperature

(department of energy and climate change). Calculations then

determine the lower value which is also referred to as the net

value. This then equals the gross calorific value minus the

latent heat of the water vapour or wet products formed from

the combustion of hydrogen and also from any moisture which

may be present in the combusted fuel (department of energy and

climate change). This net value is more representative of heat

available when a fuel is used as a heat source in industry or

home use and when the fuel is burned in boilers and furnaces.

The specific latent heat of water vapour is usually

unrecoverable from the exhaust gases. The use of gross net

calorific value tends to differ from industry to industry.

Engine and gas turbine makers will use net calorific value

where as boiler manufacturers would use the gross value when

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labelling how efficient their piece of plant is. The fuel

itself is bought on the grounds of its gross value and in turn

its energy consumption on site or in plant operation is

expressed in terms of the gross calorific value of the fuel

(department of energy and climate change).

The oxygen bomb calorimeter experiment is a very important

test in determining the specific calorific value of a

designated volume of a fuel. Its primary function is to assess

the gross calorific value which is the gross heat of

combustion of a material. The bomb calorimeter is able to

determine the potential maximum heat released by a fuel while

undergoing complete combustion (GBH International).

A test sample of fuel of a known mass is combusted under the

standard conditions the volume remains constant within the

pure oxygen atmosphere which is housed in a calibrated bomb

calorimeter. The calorific value found under these set

parameters and conditions is calculated via the observed

temperature rise in the calorimeter vessel itself while also

taking account for heat losses. The calorimeter vessel itself

is submerged in an outer water bath the heat of the water in

the water bath is constantly monitored. An embedded computer

control mechanism a keypad and an LCD enable monitoring and

usage of the test while in operation.

Procedure

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The tank fill located at the rear of the calorimeter must

be full with deionised water

The water mains must be switched on

The oxygen supply must then be switched on. The pressure

gauge on the regulator furthest from the cylinder should

read 450 PSI

The power button on the calorimeter is then switched on.

Wait 3 minutes for the system to start up

Main menu will be displayed on the touch screen

Calorimeter operation is then selected which leads to a

sub menu

The operating mode can then be selected. the operation

mode will be standardisation for initial set up and

calibration of machine and then determination for all

experiments

Then the heater are pump are turned on via the main menu

20 minutes approximately will elapse before the

calorimeter will warm up sufficiently to 30 degrees

Celsius. once it reaches this desired temperature it is

allowed to stand for another ten minutes

The test procedure is now ready to begin with the desired

set up in place

The bomb chamber is now opened via means of undoing the

screw cap on the top

2 millilitres of water is poured into the chamber

The o rings on the bomb chamber are lubricated with water

The fuse wire must then be cut and is usually a nickel

material. The wire is cut to 100mm length and the ends of

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the wire are placed through the two designated holes in

the sample holder. The adjoining clips are then pushed

down to ensure it is held in place. the exact weight of

the wire is accounted for internally in the machine

Figure 3 the wire The chamber is then placed on the spring balance and the

value is zeroed

The benzoic acid sample is then place within the chamber

and its weight of .9465 grams is accounted for and

recorded

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Figure 4 benzoic acid The chamber with the benzoic acid sample is then placed

within the chamber holder and it is ensured that the

nickel fuse wire sits just above the sample and does not

contact the sample in any way

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Figure 5 the chamber and sample The inlet valve is then opened on the chamber seal

The bomb holder seal is pushed down into the chamber and

screwed onto the male thread until sufficiently tight

Figure 6 screw down cap The valve on the chamber seal is then closed

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The oxygen pipe is then connected to the coupling on the

bomb inlet valve

Figure 7 oxygen connection The o2 fill command is then pressed on the screen and 60

seconds are allowed to pass . when this time has elapsed

the machine will automatically stop the fill

The oxygen pipe coupling is then removed

An empty bucket appropriate and designated for the test

is then placed on the spring balance for weigh in and the

weight recorded

This is approximately 790 grams

The weight is accounted for and the weight of the bucket

zeroed

2 litres of de ionised water must then be poured into the

empty bucket until the reading is exactly 2000 grams

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The bucket is then placed in position in the calorimeter

chamber within the machine the handle must be placed down

towards the back

The bomb chamber is then lifted via the provided tongs

and placed in the bucket of water

The bomb sits vertically in the bucket

The bomb tongs are then removed from the locating holes

and any residual water on the tongs is shaken off back

into the bucket to ensure no upset in mass of water

The two ignition wires are then connected to the bomb

chamber into the terminal sockets located on the top of

the chamber. When attached they must be left in such a

way that they will not become entangled in the stirrer

attached to the lid of the calorimeter chamber. the

connection of the wires to each port does not matter as

regards arrangement of the connections

Figure 8 the stirrer13


Now close down chamber door

The calorimeter process can now begin. the operating mode

is standardization when calibrating at the beginning

using the benzoic acid sample but the determination

method is used for the other tests

The bomb I.D number is 1,2,3,4 etc

Sample I.D number is 1,2,3,4 etc

The start button is pressed and the sample weight .9465

grams is entered

The calorimeter now takes over the procedure and conduct

the test. During the test period the calorimeter computer

will display PREPERIOD on the screen and will then also

display an alarm just before the bomb is fired within the

calorimeter. Once the bomb has fired the status bar on

the computer will read POSTPERIOD

The red line on the graph is the bucket temperature and

the black line is the jacket temperature

This is a temperature versus time plot as every 12

seconds the computer reads the temperature

The printer built into the calorimeter will then produce

automatically the results once the test is completed

When the operation is complete the chamber is opened and

the two connectors are disconnected

The bucket and bomb are lifted out simultaneously

Bomb holder removed from the bucket

The inlet valve is undone slightly and vents any gas left

within the bomb holder

The seal cap on top is screwed off

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The bomb seal and the chamber holder are then pulled out

The interior area of the bomb holder is examined for any

remains of the fuel like soot or ash. If such evidence

exists the test result is not true and must be discarded

The bomb holder is cleaned out

Turn off the oxygen at the tank

Turn of water at mains

Turn the heater and pump off via the computer screen

Turn off mains supply to calorimeter

The above explained procedure is the means for testing

all specimens.

Figure 9 entire apparatus

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Results

Figure 10 result one

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Above is an example of result one we believe it is for coal

but due to time constraints in the lab we were unable to

obtain our own results due to malfunctions within the

calorimeter set up. The calorimeter miss fired for each test

and we were unable to obtain any of our own results

0 100 200 300 400 500 60025.11525.12

25.12525.13

25.13525.14

25.145

f(x) = 1.94765635327555E-05 x + 25.1270556691661

f(x) = NaN x + NaNBenzoic Acid Calorimetry Data

Post-ignition Line

Time (s)

Temp

erat

ure

(C)

Figure 11 shown here is a typical example of atemperature versus time combustion of benzoicacid within the calorimeter obtained from

online (1312)Species Benzoic acid NaphthalenePellet mass (±0.0001 g) 1.03 0.4880Wire mass initial (±0.0001 g)

0.0160 0.0163

Wire mass final (±0.0001 g) 0.0034 0.0073Δmfuse wire (g) 0.0126 ±

0.000140.0090 ± 0.00014

Wire heat of combustion (cal/g)

1400 1400

Benzoic acid heat of combustion (MJ/kg)

26.454 ---

(1312)

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Above shows an online result for benzoic acid along with

naphthalene the calorific value or heat of combustion of the

benzoic acid is 26 Mj/Kg

The formula with which data from this experiment can be

applied to is

Hc= WT-e1 –e2 –e3/M

Hc= gross heat of combustion or

calorific value

T = Observed temperature

W (EE) =energy equivalent of the

calorimeter in use or the amount of

energy require to raise temp of

calorimeter by one degree

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E1 =heat produced by burning nitrogen

portion of the air in the bomb to

form nitric acid

E2 =the heat produced by the

formation of sulphuric acid from the

reaction of sulphur dioxide water and

oxygen

E3= heat produced by the heating wire

and cotton thread

M = overall mass of sample

ConclusionIt is disappointing that we as a group were unable to obtain

our own results. The calorimeter miss fired each time and due

to this we ran out of time to obtain a satisfactory result for

ourselves. We did obtain as seen above a previous result from

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a previous class session and were able to distinguish what

each reading formed on the data sheet corresponded to. The

bomb calorimeter procedure itself in essence is a simple but

perhaps time consuming procedure and is the simplest way to

obtain the calorific value of a given mass of a substance. To

draw a conclusion on results we did not obtain is rather

difficult for any experiment. But one objective can be deemed

a success from the experiment and corresponding lectures in

that my personal understanding of the importance of knowing

the calorific values of certain fuels is of great importance

in the engineering world. Fossil fuels still power the vast

majority of automation and electricity production for industry

and knowing the correct fuel to air ratio is of vital

importance in the modern day world of carbon emissions. It is

essential to know the exact amount of fuel so as not to have

too much waste or un combusted product at the end. It in turn

is also to have the correct amount of oxygen so as to burn off

the fuel sufficiently. Insufficient oxygen for the mass of

fuel also leads to leftover fuel and the full calorific value

of the fuel is not obtained. In industry these ratios become

very important as cost saving and cost effectiveness are at

the heart of any business and when you are purchasing vast

quantities of oil coal or gas you need them to be cost

effective in their operation. The right fuel also is a very

important factor when applied to industry and heat generation.

They bomb calorimeters ability to determine the exact

calorific value of a fuel is of great benefit to the consumer

as the greater the calorific value the greater the heat

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produced during combustion. So when applied to industry the

correct fuel can be chosen for different procedures. For

example a cement kiln would need a temperature of about 1500

degrees Celsius minimum where as the simple boiler at home

would not need temperatures near this level to create the heat

required. So instantly the calorific value of the fuels used

for each operation would come into play. A fuel with a very

high calorific value would be good for the cement kiln as it

would provide the massive heat required for its operation

where as the simple home boiler would be sustained with a fuel

of much lower calorific value and a slow burn.

Having completed the experimental procedure i fully understand

how to use the oxygen bomb calorimeter and this is of great

benefit because if asked to repeat such an experiment i would

feel very confident in doing so and as a budding engineer this

would be of vital importance for many tasks in the future

Bibliography(n.d.). Retrieved 12 2, 2013, from www.personal.psu.edu/users/c/p/cpf5020/.../457%20finalreport3.docx

access engineering. (n.d.). Retrieved 12 2, 2013, from http://accessengineeringlibrary.com/browse/steam-plant-operation-ninth-edition/c9780071667968ch06

department of energy and climate change. (n.d.). Retrieved 12 2, 2013,from http://chp.decc.gov.uk/cms/fuel-calorific-value/

GBH International. (n.d.). Retrieved 12 2, 2013, from http://www.gbhinternational.com/specsbomb.htm

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Parr instrument company. (n.d.). Retrieved december 2, 2013, from http://www.parrinst.com/products/oxygen-bomb-calorimeters/

the online dictionary. (n.d.). Retrieved 12 2, 2013, from http://www.thefreedictionary.com/calorific+value

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Oxygen Bomb Calorimeter Experiment to find the calorific

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