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School of Computing, Science and Engineering MSc petroleum and Gas Engineering MODULE 1: FUNDAMENTALS OF NATURAL GAS & PRODDUCTION SYSTEMS & DESIGN LECTURER: Dr. Martin Burby
LABORATORY REPORT ON : CALORIFIC VALUE OF NATURAL GAS, RELATIVE DENSITY, AERATION TEST BURNER NUMBER AND ANALYSIS OF NATURAL GAS COMBUSTION PRODUCTS
NAME: OPEYEMI OSHO
ROLL NUMBER: @00344819 TH
DATE OF EXPERIMENT: 19
OCTOBER, 2012
TH
DATE OF REPORT DUE: 14 DEC, 2012
GROUP 4 MEMBERS: Mr. Otunwa Gerald; Mr. Oluyide Oladipupo; Mr. Ukaeru Ukaeru Chinedu; Mr. Uyoyo – Ghene Okoro; Mr. S.Petrus; Mr. A.Raj; Miss. V.Juclcileia; Mr. P .Mattaios; Mr. M. S. Hamza; Mr. A. Mohammed; Mr. A .S .Tahir; Mr. M. Liman; Mr. Obaro Ogezo; Mr. O. Y. Samuel
TEACHING ASSISTANT: MR. Abu-Bakr Abbas and Mr. Alan Mappin
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Table of Contents LIST OF FIGURES ............................................................................................................................................ 3 LIST OF TABLES .............................................................................................................................................. 3 EXPERIMENT 1: DETERMINATION OF CALORIFIC VALUE OF NATURAL GAS .................. ........................... .................. ............. .... 4 Bibliography .................................................................................................................................................. 9 EXPERIMENT 2: DETERMINE RELATIVE DENSITY (SPECIFIC GRAVITY) ........................................................ 10 OBJECTIVE ................................................................................................................................................. 10 INTRODUCTION ........................................................................................................................................ 10 THEORY ....................................................................................................................................................... 10
EXPERIMENTAL SET-UP/ APPARATUS .................................................................................................. 11 PROCEDURE .............................................................................................................................................. 12 RESULTS....................................................................................................................................................... 13 ANALYSIS ..................................................................................................................................................... 13 DISCUSSION ................................................................................................................................................. 14 CONCLUSION ............................................................................................................................................... 14 REFERENCES ............................................................................................................................................ 15
APPENDIX 1: Relative Density Correction table. ................................................................................. 16 EXPERIMENT 3: ANALYSIS OF NATURAL GAS COMBUSTION PRODUCTS .................. ........................... .................. .................. .............. ..... 17 OBJECTIVE ............................................................................................................................................... 17 INTRODUCTION ....................................................................................................................................... 17 EXPERIMENTA SET-UP/ APPARATUS ....................................................................................................... 17 PROCEDURE OF THE EXPERIMENT .......................................................................................................... .......................................................................................................... 20 RESULT .................................................................................................................................................... 21 DISCUSSION AND CONCLUSION .............................................................................................................. 21 RFERENCES .............................................................................................................................................. 22
EXPERIMENT 4: AERATION TEST BURNER NUMBER ................................................................................... 23 OBJECTIVE ............................................................................................................................................... 23 BACKGROUND AND THEORY ................................................................................................................... ................................................................................................................... 23 EXPERIMENTAL SET-UP ........................................................................................................................... 23 EXPERIMENTAL PROCEDURE ................................................................................................................... ................................................................................................................... 24 RESULTS AND DATA ................................................................................................................................ 24
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ANALYSIS ................................................................................................................................................. 25 DISCUSSION ............................................................................................................................................. 26 CONCLUSION ........................................................................................................................................... 26 REFERENCES ............................................................................................................................................ 27
LIST OF FIGURES Figure 1 Layout of the experiment (Elevated View) ..................................................................................... 5 Figure 2 Boys Calorimeter ............................................................................................................................. 5 Figure 3 Simmance S.G bell ......................................................................................................................... 11 Figure 4 Hand Operated Aspirator analyser ............................................................................................... 17 Figure 5 Draeger Tube Analyser .................................................................................................................. 18 Figure 6 Kane May Gas Analyser ................................................................................................................. 19 Figure 7 Infra Red Analysis .......................................................................................................................... 19 Figure 8 ‘SIGMA’ AERATION TEST BURNER................................................................................................. 24
LIST OF TABLES Table 1 readings from the experiment taking both inlet and outlet temperatures ..................................... 7 Table 2 Experimental Results for Relative Density of Methane and Butane .............................................. 13 Table 3 Experimental Results for Analysis of Natural Gas Combustion Products ...................................... 21
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EXPERIMENT 1: DETERMINATION OF CALORIFIC VALUE OF NATURAL GAS OBJECTIVE This experiment is carried out and their aim is the Determination of Calorific Value of Natural Gas using a
boys’ non-recording calorimeter. Introduction Calorific value (CV), which is also known as heating value (HV) is a measure of heating power and is
dependent upon the composition of the gas. The CV refers to the amount of energy released when a known volume of gas is completely combusted under specified conditions. The CV of gas, which is dry, gross and measured at standard conditions of temperature and pressure, is usually quoted in mega joules per cubic meter ,
.
Fuel gas which contains hydrogen or hydrocarbon possess two CV the gross and the net. The heat of combustion for fuels is expressed as the HHV, LHV, or GHV, and thus is defined below as follows: Gross calorific value is the overall heat content of the gas, as defined above, when all the water which is formed in the combustion process of gas is condensed at constant te mp er at ur e, wh ile Net ca lo ri fi c v al ue is the amount of heat released by combusting a specified quantity (initially at 25°C) and returning the temperature of the combustion products to 150°C, which assumes the latent heat of vaporization of water in the reaction products is not recovered. The heating values for gaseous fuels in units of Btu/lb. are calculated based on the heating values in units of Btu/ft3 and the corresponding fuel density values. The heating values for liquid fuels in units of Btu/lb. are calculated based on heating values in units of Btu/gal and the corresponding fuel density values.
The calorific value, CV of natural gas is measured in this experiment by the calorimeter precisely (Boys Calorimeter). This was achieved by complete combustion of the natural gas at atmospheric pressure and the CV was measured by the calorimeter at constant pressure.
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DESCRIPTION OF EXPERIMENT/ APPARATUS In this experiment the major apparatus, is the calorimeter being used, but before listing the apparatuses used in this experiment, I provided below a block schematic diagram and a pictorial view of the experimental setup and position of the apparatus in this experiment.
Figure 1 Layout of the experiment (Elevated View)
Thermometers graduated glass vessel Hyde meter Boys calorimeter
Figure 2 Boys Calorimeter
Now, the following apparatuses were used in the experiment that is as followed: 5|Page
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Boys’ Calorimeter: this instrument was invented by Sir Charles Boys, and its essence is to determine the calorific values of a broad range of gas fuels currently being utilized. From the layout, it was attached to a Hyde gas meter with a capacity of 0.02 foot-cube per revolution (
), and below
is a diagram of both the
calorimeter and the Hyde type gas meter. (Naveen, 2012) Figure 2: Boys’ calorimeter and Hyde gas meter
EXPERIMENTAL ROUTINE The following, outlines the routines undertaken for the operation, and thus as followed below:
The gases from the CH4 cylinder is switched on and kindled.
Water switched on and the calorimeter placed on its base.
The flow of gas into the calorimeter is to be adjusted in a way that the time for a revolution of the meter, hands falls within the limits, being deduced from the formulae below:
T (min) =
T (max) =
Where, CV= theoretical calorific value in
; T= time in seconds (s).
The rate of water flowing through the calorimeter must be altered, so that the quantity obtained during 4 revolutions of the meter hand is around 50 ml of the value of the anticipated CV. Water must be drained, until it starts to run out of the condensate outlet pipe.
The calorimeter must then be allowed to come to rest, until temperatures from both inlet and outlet thermometers become constant, thus the following was observed during the period of experiment on the meter indicator. a) At the 3 o’ clock position, the inlet thermometer is read. At the instant when the meter hand reaches 12 o’ clock position, the change at the funnel with redirected to change the flow of water from the outlet into a container. b) When the meter hand, get to 3 o’ clock position again, the 1st reading of the outlet thermometer is made and this thermometer is also read at successive quarter of the meter, until 14 reading have been attained. The meter hand will be at the 6 o’ clock position. c) After the 1st reading of the inlet thermometer is gotten, future readings are being made when the meter hand is between 12 and 3 o’ clock giving 4 inlet thermal readings. d) When the meter hand reaches 12 o’ clock for the last reading of the outlet thermometer, the funnel is redirected away from the container.
Readings of the meter temperature, barometer, and pressure of gas at the inlet to the meter must be measured. The former reading must be added to the barometer for the total pressure, after making the necessary conversions to consistent units.
The volume of water collected during the experiment is measured and recorded in kg. (Burby & Nasr, 2012)
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DATA
Barometric pressure= 754.75 mmHg, thus pressure (gauge) =
2012
Gas pressure=20 mbar Room temperature = 23°C, thus 23+273= 296k Water obtained = 1229 ml of water=1.299 kg.s Total pressure = 1005.3 + p.t Below is the tabular readings drafted from the experiment carried out. Water temperature °C Number of cycles
1
2
3
4
Average
outlet
32.40 32.40 32.40 32.35 32.45 32.48 32.48 32.49 32.49 32.48 32.47 32.45 32.47 32.48 32.48 32.49 32.45
inlet
16.50
16.54
16.53
16.50
16.52
Table 1 readings from the experiment taking both inlet and outlet temperatures
ANALYSIS
CV=
Where, T= change in temperature °C W= weight of water obtained, Kg
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@00344819 S= specific heat of water= 1
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F= conversion factor for CV from
TO
V= volume of gas burnt during the test (corrected to MSC). Therefore, converting CV in BTU/ft³, the conversion factor, F, has the value. F=
Thus, CV in BTU/ft³=
= = 1028.85
Conversion of C.V in , first find the conversion factor, F. F=
= 37.002
C.V =
SUMMARY OF RESULTS
Calorific value in
was 1028.85 and for that of the
was 37.002.
DISCUSSION The heating value of a gas is of paramount importance in contrasting factors of gases and seriously
needs a high stability in its environment for its measurement, and determining it should be achieved
with high accuracy. In this experiment we r ecorded 37.002 as compared to the actual reading of
37.97 . Also, the error in the experiment is high minimal with a percentage error of 0.99 %, and this is due to measurement error. The derivation from the actual reading, which is to be noted as precautions are as followed:
Interaction with surrounding gases.
Parallax errors from reading measurements
Heat loss due to radiation
Laboratory condition, thus environmental state in which the experiment is performed.
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@00344819 CONCLUSION
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We obtained a heating value of 37.002 , which appears to differ slightly from the actual heating value due to the errors listed, and other conditional or experimental factor, which will affect t he commercial value of the gas, which therefore, means that using boys’ calorimeter instead of bomb calorimeter is preferable for more accurate result.
Bibliography Burby, M., & Nasr, G. (2012). Gas and Petroleum Laboratory Experiment Manual. salford: University Press. Naveen, M. (2012, November 7). CALORIMETERS. Retrieved November 18, 2012, from Deepthi Engineering: http://www.deepthiengineering.net/calorimeters.html
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EXPERIMENT 2: DETERMINE RELATIVE DENSITY (SPECIFIC GRAVITY) OBJECTIVE The objective of this experiment is to investigate and determine the Relative Density of given sample of natural gas and butane using ‘Simmance’ Specific Gravity Bell.
INTRODUCTION Relative Density (Specific Gravity) is the ratio of the density of given fluid to the density of a reference fluid under the same temperature and pressure. It is applicable to both liquid and gaseous state of existence of fluid. When used for gases as in this experiment, the relative density is the ratio of the density of a given gas to the density of air at the same temperature and pressure. Relative density has diverse application in both petroleum and other allied industries (e.g. to determine the Wobbe Number). In this experiment using ‘Simmance’ Specific Gravity Bell, the time taken for a volume of the test gas (Methane and Butane) to effuse through an orifice in the ‘Simmance’ Bell is compared with that taken by the same volume of air under identical condition.
THEORY
The determination of the Relative Density in this experiment is based on the Graham’s law of diffusion which states that, given constant temperature and pressure, the diffusion/effusion rate of two gases are inversely proportional to the square root of their respective densities as shown in the equation below:
Where:
= = = =
Also:
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B= Where:
= = = = EXPERIMENTAL SET-UP/ APPARATUS
In this experiment, the major and only apparatus used was a simmance specific gravity bell which comprises of a small water tank in which a bell is suspended from a beam carrying a pointer. The pointer moves over a scale plate on which are engraved two lines, corresponding to the upper and lower heights of the bell between which the time of effusion is measured. A balance weight is fitted to other end of the beam so that the rate of effusion can be controlled. An orifice of 0.8mm in diameter which is protected by a removable dust cap is mounted on a nipple fitted to the top of the bell. The bell is connected by a cord to the beam with the cord resting on a quadrant arm to maintain the bell in the center of the tank. Gas or air can be introduced into the bell through either of 2 cocks which are attached by a connecting tube to a standpipe located inside the bell. Below is a photograph of the apparatus.
Figure 3 Simmance S.G bell
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PROCEDURE
To carry out this experiment, the following procedure was taken into actions, which are:
We now partake by means of leveling screws, so as the bell hangs at the center inside the tank. Occupy the tank with water until the dome of the bell is just covered when the bell is static. Calibrate the scale, so the indicating punch mark is level with the pivots which is carrying the beam and also set the cord that is attaching the bell to the beam, so that the pointer is about 2cm below the lower mark on the scale , when is bell is static. Remove the cap covering the orifice from in a scheduled manner in order to examine the orifice. If dust or moisture has accumulated, try to remove it with a soft brush and clean the orifice with a splinter for soft wood. Polish, so as to avoid parallax errors. Connect one of the cocks to the gas supply leaving the other disconnected, so that air can enter as required. Lock the gas cock, and open the other cock to air. Fill the bell with air by slowly depressing the free end of the beam until the pointer is well above the upper mark on the scale and then allow the bell to immerse slowly into the water until it covers the bell crown. Repeat this scenario to purge the gases inside, except air. Observation was made for the time of effusion of Air for the three cases using stop watch. Similarly, the bell was filled with other gases (Methane and Butane) one at time as in the case by allowing the bell to rise under gas pressure. Again the gas (Methane or Butane) was allowed to effuse and the time of effusion recorded The effusion time for each of the three gases (air, methane and butane) for the three cases was recorded form which an average effusion time was obtained for each gas. The cap covering the orifice was examined time to time in order to examine the orifice.
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RESULTS
The following results were obtained from the experiment, and it is tabulated below: GASES
TIME
AIR METHANE BUTANE
56.35 48.50 82.80
average
56.18 48.70 83.73
56.68 47.90 82.86
56.40 48.37 83.13
Table 2 Experimental Results for Relative Density of Methane and Butane
CONDITIONAL DATA Barometric pressure= 754.75 mmHg
Room temperature= 22⁰C Temperature of water inside the tank= 21⁰C ANALYSIS
From Graham’s law, we then find the relative densities of methane and butane, which the equation;
( )
So for methane,
( ) And for butane,
( ) Thus, the uncorrected relative density for both methane and butane are 0.736 and 2.172 respectively. Using the uncorrected data, we correct to dry basis by applying the correction gotten from the table. And the formula used for this scenario is:
Where c = corrected value of relative density, and it is obtained from the table in appendix 1, at 22⁰C. 13 | P a g e
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For methane, this is 0.735. We find the exact error of percentage using interpolation from the table, and it is within the range of 0.7-0.8.
Thus, x = 0.00428, and C= 0.736 – 0.00428= 0.731 Similarly, for butane which is at 2.172, using extrapolation method from the table, it is within the range of 1.20-1.10.
Thus, x =0.0234, and C= 2.172 + 0.0234= 2.195
DISCUSSION
In this experiment, the relative density of methane and butane differ a little from the values commonly used by industries and academia. For instance, in Britain, relative density for methane is 0.6 and that of butane is 2.0 as to the ones gotten from the experiment which are 0.731 and 2.195 respectively. The utterance of the values might be due to the following:
Error in experiment and measurement due to parallax. Solubility of methane and butane gases in water Remains of contaminants in the equipment, which result to a much denser result, 0.735 for methane.
Despite considering all factors of errors, this experiment is slight closer to the factual values which , thus could be improve to attained to that value.
CONCLUSION
The scope of the determination of relative density of methane and butane was attained. Future considerations for the development of the specific gravity bell for better accuracy in measurement of sample gases.
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REFERENCES
1) University of Salford School of Computing, Science and Engineering 2) Determination of Relative Density of Methane and Butane Gas using (‘SIMMANCE’ SPECIFIC GRAVITY BELL) Manual.
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APPENDIX 1: Relative Density Correction table .
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EXPERIMENT 3: ANALYSIS OF NATURAL GAS COMBUSTION PRODUCTS OBJECTIVE To measure the oxygen, carbon dioxide and carbon monoxide contents of combustion products from a natural gas burner.
INTRODUCTION This experiment deals with the combustible products that are contained in combustible compound usually organic compounds. The amount or extent of these combustible products in the analysed compound characterised the combustion quality of the compound. As such, the knowledge of this amount of combustion products (carbon dioxide, carbon monoxide & oxygen) contained is important in the combustion analysis of the compound and the design of the burner that is suitable for its burning. More so, the experimental result finds its application in the determination of fuel gas air ratio which is important in the extraction of maximum energy from the fuel. EXPERIMENTA SET-UP/ APPARATUS The equipment used in this experiment is:
Fyrite analyser: This utilises the technique of chemical absorption whereby the sample of the
gas to be analysed is bubbled through a liquid that absorbs the particular constituent being analysed. Below is a schematic diagram of t his analyser. Figure 4 Hand Operated Aspirator analyser
Sample reservoir Spring loaded double seated plunger valve
Adjustable scale Absorbent fluid
Flexible diaphragm
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Drager tube: This is a simple rapid acting device that may be used to determine the presence of
a gas in air or fuel gases. The detector comprises of a hand held bellows pump into which is fitted a tube containing a solid absorbent impregnated with a reagent that reacts with the constituent being analysed. Below is the tool in a schematic diagram.
Figure 5 Draeger Tube Analyser
Paramagnetic oxygen analyser: This measures the magnetic susceptibility of the sample gas.
Only a few gases, including oxygen and nitrogen oxides are paramagnetic (exhibit a positive magnetic susceptibility), with the vast majority exhibiting a negative magnetic susceptibility. Below is a picture of this tool.
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Figure 6 Kane May Gas Analyser
Infrared analyser: This utilizes the fact that compound gases such as carbon monoxide and
carbon dioxide selectively absorbs long- wave radiation. The sample to be analysed is held in a measuring tube through which filtered radiation passes and absorption occurs at wavelengths characteristics of the gases. Below is a schematic diagram of this tool.
Figure 7 Infra Red Analysis
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PROCEDURE OF THE EXPERIMENT This experiment was carried out in 4 stages, which are:
The first stage of the experiment was when the burner was place beneath the sampling hood with the air shutter fully opened and damper closed.
The oxygen analyser was initially set at zero by nitrogen through the tool. Air was passed though the tool and the span control was calibrated.
Other measurement tools were connected and linked via the operation manual as instructed.
The burner was ignited, and exhaust gas linked to al the measurement tools were collected.
For the Bacharach fyrite, it was first adjusted with the horizontal level of fluid to a mark o f zero (rest) on the scale. 1. The exhaust gas was gotten from the sampling hood by pumping 18 times only when the Bunsen burners’ shutter was opened. 2. The suctioned gas was switched in a reciprocating positions for about 3 times, to reach proper contact with the reagent (CO₂ analysis) 3. We obtained the reading from a calibrated cylinder. 4. At the top of the cylinder, was taken out and gas escaped from the fluid. This routine is repeated during the closed session of the shutter. For the Draeger Analysis Tube, the following is being listed below: 1. The tubes carefully broken at both end and were used to obtained samples of the exhaust gas through the sampling hood. 2. Various tubes were used for oxygen and carbon dioxide analysis. 3. The sample was taken by means, a bellow type pump to suck the sample into a tube. 4. The concentration of the gases decolorized, the reagent which was obtained through reading 5. This routine was repeated when the shutter was closed. For Infra-Red Analyser, the following is being listed below: 1. The apparatus was at first adjusted by using the zero and span buttons to ensure that it produced accurate gas values. 2. Sample of the exhaust gas was obtained from the sampling hood, when the burner shutter was open. 3. Reading of the concentration of oxygen and carbon dioxide were taken after fine tuning the meter. 4. This routine was repeated for the closed session of the shutter. For the Kane May apparatus, the following is being listed:
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1. The tool was turned on and allowed to initial sequence 2. Then, the sample of the exhaust gas was collected from the sampling hood, when the shutter of the burner was open. 3. Values of the concentration of oxygen, carbon monoxide, and carbon dioxide were collected after fine tuning the meter. 4. This routine was repeated for the closed session of the shutter.
RESULT Analysis of Natural gas Combustion Products Air Shutter Open Air Shutter Closed CO
CO₂
Bacharach Fyrite Infra-Red Kane-May
0.0003% 6 PPM
0.5% 0.97% 1%
Paramagnetic Drager Tube
6 PPM
1.5%
O₂
(18 pumps) 19%
19.2%
No×
CO
CO₂
4.5% 0.062 7.07 451 6.3% PPM 500 PPM
O₂
9.8
NO×
Temperature
189°C (Open) 275°C (Closed)
5.8%
Table 3 Experimental Results for Analysis of Natural Gas Combustion Products
Infra-red reading for CO: CO₂ (Open) = 0.0005% Kane-May reading for CO: CO₂ (Open) = 0.0005 Infra-red reading for CO: CO₂ (Closed) = 0.0095 Kane-May reading for CO: CO₂ (Closed) = 0.01
DISCUSSION AND CONCLUSION In the experiment, the results obtained from the analysis of natural gas combustion products, which we used the tools and methods mentioned early in the report like the Bacharach fyrite, Draeger tubes, Infra-Red, and Kane May with a Bunsen burner which was fully opened (complete combustion), and also which was closed (incomplete combustion). My observation was the Carbon monoxide content is high when the shutter was closed, compared to when it’s opened. This explains the reasons CO is produced in the process of incomplete combustion because of minimum oxygen during combustion. Another of my observation, was that oxygen content required for combustion is very high when the shutter is open, than when it’s closed. So therefore, we conclude that the shutter closed operating conditions indicates 21 | P a g e
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incomplete combustion and vice versa. And also most of the oxygen required for the combustion is collected from air.
RFERENCES 1. Laboratory manual on Analysis of Natural Gas Combustion Products, 2009. School of Computing, Science & Engineering. University of Salford, United Kin gdom. 2. Connor, N.E and Nasr, G.G (2000) “Basic Units of Measurement, Gas Supply and Combustion”. School Of Computing, Science and Engineering, University of Salford, United Kingdom. 3. www.inspectapedia.com. Accessed December 5, 2011
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EXPERIMENT 4: AERATION TEST BURNER NUMBER OBJECTIVE The scope of this experiment is to determine the aeration test burner number (A.T.B No.) of a sample of natural gas.
BACKGROUND AND THEORY The study of the behaviour of aerated burners is complex involving the burning velocities of the constituent gases and their air inducing properties. Attention has, therefore, been concentrated on the manufacture of a standard test burner which will enable an empirical relationship to be attained which gives a signal of the relative combustion features of different gases. The A.T.B is such a burner and has been standardized as the official test burner. To determine the A.T.B number was completed alongside assistance of the Sigma’s Monogram for A.T.B Indicator (Type 600) alongside calibration chart no. 9267. The instrument reading was seized from the reading on the shutter working manipulation corresponding to the mean locale of the inner flame of the blaze at the fiducial point.
EXPERIMENTAL SET-UP The main and only apparatus in this experiment is the aeration best burner, which is defined as a burner for measuring the features of the combustion of commercial gases, (Barach). The burner comprises of a Bunsen burner with a fixed gas orifice operating at standard pressure. A primary air-shutter which is manually adjusted to provide an inner cone of specific height. The degree of the opening of the shutter is indicated as a scale calibrated in “Tens” and “units” on the shutter operating control. The whole unit is enclosed in a fire resistant cabinet with chromium fittings. It has a manometer for determining the differential/gauge pressure of the gas and a burner jacket through which the cooling water flows. A governor is fitted to the shutter operating controls which adjust the gas pressure to 20 mbar. Below is a photograph of the aeration test burner, and a schematic view
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Figure 8 ‘SIGMA’ AERATION TEST BURNER
EXPERIMENTAL PROCEDURE
The burner should be connected to a gas supply at a pressure of not less than 22 mbar, and calibrate the governor to 2o mbar.
Correct the flow of water passing through the burner jacket between 200-500 ml/minute, and maintain temperature within 10-20⁰C, and ignite the burner.
Slowly and carefully open the shutter until the tip of the inner core of the flame is brought to the reference mark, and don’t take any reading until the burner has being in combustion for 5 minutes.
As slight oscillation of the inner core of the flame, correct the air-shutter, so that the mean position of the tip corresponds with the reference line, and take the reading on the scale. And now use this reading, and read off the A.T.B number from the calibration chart.
RESULTS AND DATA The result gotten from the aeration test burner scale was 32, and from the chart the A.T.B number is 385. Thus, finding the wobbe number of natural gas, commercial propane and butane, the following data below is used to obtain it: Conditional Data Calorific value of propane= 2500 Calorific value of butane= 3200
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or 37.002 ;
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relative density= 0.715
Barometric pressure= 754.54 mmHg Temperature of water= 15-20 ⁰C
ANALYSIS CALCULATE WOBBE NUMBER OF CH4, PROPANE AND BUTANE
The formula for wobbe number of a gas =
For natural gas, using the unit of British thermal unit per cubic foot, Wobbe number =
For S.I units, Wobbe number =
For commercial propane, to find relative density Relative density=
; where Mwt= molecular weight
So Mwt (propane) = 44; and Mwt (air) =28.97 Thus R.D= 44÷28.97=1.52
,
So therefore, wobbe number=
Now for S.I units, converting to ,
Thus, wobbe number of propane= Calorific value in
And finally for commercial butane,
Thus, wobbe number = The relative density =
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. The wobbe number of butane= And for S.I unit, converting to
DISCUSSION In the experiment for A.T.B. of Natural gas, a value of 385 was obtained which falls within the acceptable range of A.T.B in Britain. This may as source of gas changes. Other calculated values of Wobbe Numbers of Methane, Propane and Butane. The accuracy of the above results obtained was limited by source/origin of the sample gas and the empirical formulae used the determination of the Wobbe Numbers. For instance, the molecular weights of the gases under study were all approximated values and not a generic representative of the three gases considered especially in Britain. In the case of Methane, there could be some amount of contaminants as the gas flows from the mains resulting in a slightly heavier relative density value of 0.67.
Error due to parallax while taking the reading from the chart .
The relative density of Butane could be affect by the structure of the butane used in the experiment e.g. Iso-butane and n-butane.
Insufficient primary air in the laboratory giving rise to more diffusion flame.
Condition of the test environment
In spite of the aforementioned challenges in carrying out this experiment and the calculations, it gave an indication of the significance of these parameters in gas quality specification and monitoring. CONCLUSION From the experiment, it was observed that the higher the Wobbe number, the greater the heating value of the quantity of gas that will flow through a hole of a given size in a given amount of time. The ATB number gives an immediate indication of the combustion characteristics of gas under test. It also helps determine gases present in a mixed gas of different characteristics In almost all gas
appliances, the flow of gas is regulated by making it to pass through a hole or orifice. Such that 26 | P a g e
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for a given orifice, all gas mixtures that have the same Wobbe number will deliver the same amount of heat. The Wobbe number is also a critical factor to minimize the impact of changeover when analyzing the use of substitute natural gas (SNG) fuels such as propane – air mixture. Wobbe number is an indicator of the interchangeability of fuel gases such as natural gas and LPG. The Calorific value of the fuel gases when related to the Wobbe number is a measure of the heating power and the amount of energy released when a known volume of gas is completely combusted under specified conditions. The higher the calorific value, the greater the Wobbe number. The objective of determination of the A.T.B. Number of Natural gas and the calculation of the Wobbe numbers of other fuel gases were achieved. These parameters (Calorific valve, Relative density, A.T.B. No. and Wobbe No.) are of great importance in the industry. However, Relative density has an inverse relation with Wobbe number, such that the higher the relative density, the lower the Wobbe number-a m easure of the interchangeability of fuel gases. REFERENCES
University of Salford School of Computing, Science and Engineering: The Aeration Test Burner section from Gas and Petroleum Engineering Laboratory Report .
http://www.cerlabs.com/experiments/1087540412X.pdf (accessed on 06/12/2012)
http://en.wikipedia.org/wiki/Wobbe_index (accessed on 06/12/2012)
http://www.sizes.com/units/wobbe_number.htm (accessed on 06/12/2012)
http://www.nationalgrid.com/uk/Gas/Data/help/opdata/index.htm (accessed on 06/12/2012) http://www.globalenergy.co.uk/gaschange.htm (accessed on 06/12/2012)
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