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Laboratory Notes

Gas Turbine Combustor Lab Exercise (approx. 3-4 hours laboratory exercise)

By Jeevan Jayasuriya / Arturo Manrique

Division of Heat and Power Technology The original text was written by Antonio Pons

STOCKHOLM 31-jan-05

Laboratory Notes Avdelningen för Kraft- och Värmeteknologi Kungliga Tekniska Högskolan 100 44 STOCKHOLM

Laboratory guide 05-01-31

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NOMENCLATURE

P [kW] Power T [K or °C] Temperature Tid [K] Initial reactant temperature Tad [K] Adiabatic flame temperature u [m/s] Air velocity ∆P [kPa] Difference of pressure (A/F) [ − ] Air – fuel ratio (A/F)stoic [ − ] Stoichiometric air – fuel ratio φ [ − ] Equivalent ratio ρ [kg/m3] Fluid density

[ ] flow Mass kg/s m&


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1. INTRODUCTION The study and design of a gas turbine combustor is a complex process, which is much less amenable to theoretical treatment than other components of the gas turbine. The problem is basically reaching one of the best compromises between a number of conflicting requirements, which will vary widely with different applications. Thus, to optimize the running conditions and design of a combustion chamber the lab work acquires a great importance. The gas turbine combustion is often considered a steady flow process in which a hydrocarbon fuel is burned with a large amount of excess air to keep the turbine inlet temperature at an appropriate value. This is essentially a clean and efficient process and for many years there was no concern about emissions, with the exception of the need to eliminate smoke from the exhaust. Recently, however, control of emissions has become probably the most important factor in the design of industrial gas turbines, as the causes and effects of industrial pollution become better understood and the population of gas turbines increases. These two subjects make the laboratory exercise a very interesting training to achieve a large comprehension of the problems behind these current topics.

2. EDUCATIONAL OBJETIVES

The main objective with this lab exercise is to make the students understand and give the opportunity to work with the factors and concepts involved in the combustion inside a combustor. At the same time it will be a great training to introduce the study and comprehension of the pollutant emission levels in a gas turbine combustor. Other objectives with the execution of this lab exercise are: • To get a better knowledge about combustors and its operation. • To apply the acquired theoretical knowledge to a real situation and to

solve actual problems during the analysis process. • To get familiar with different measurement equipment related to

combustion. • To understand some of the difficulties and problems that a research

projects can introduce. • To learn to critically evaluate different results, both experimental and

theoretical.


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3. METHOD OF ATTACK The laboratory exercise will be performed as teamwork during the experiments. The calculations before and after them will be made individually, as well as the graphs, conclusions and answers to present in the report. There will be two distinct groups; each of them will make one of the two different experiments that form the lab. After making the experiments each team will provide the data extracted to the other team, and the most relevant aspects and impressions of each experiment will be explained. The steps to carry out the lab are the following: • Make a deep and detail reading of the lab guide. • Perform preliminary calculations. Make the theoretical calculations

necessary to run the combustor and to guide the execution of the experiment and after it, compare these theoretical results with the data measured.

• Run the experiments. • Extraction of data: This part is dedicated to the experiments. The two ways

to execute them and how to obtain the different data will be explained. • Final Calculations: In this point some calculations to complete different

tables, obtain flame temperatures from the gas emissions and sketch different graphs will be made.

• Write down the report.


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4. COMBUSTORS GENERAL THEORY 4.1 Introduction A conventional “pressure-volume” diagram, illustrated in figure 4.1, for a gas turbine, shows that between the compressor and the turbine there is a stage in which the air expands at constant pressure. This expansion is achieved through heating the air by injection and the following combustion of a hydrocarbon fuel in a device that is commonly described as a combustor or combustion chamber. The work output of the gas turbine is directly related to the area enclosed within the pressure-volume diagram. Thus a large degree of expansion, that is, a large horizontal separation of points 2 and 3, will give a large amount of work. However, since the gas is being expanded by raising its temperature, a practical limit is set by the maximum temperature the material of the engine components located at the outlet of the combustor, notably the turbine blades can accept. The full line 2-3 in figure 4.1 is drawn horizontally to represent expansion at constant pressure. In practice, a pressure loss is always incurred, so the real combustion process is represented by the dashed line shown in figure 4.1. An important design objective is to keep this pressure loss as low as possible, since any reduction in the area of the pressure-volume diagram constitutes a loss in engine power output. Other important combustor design requirements are high combustion efficiency, reliable and smooth ignition, wide stability limits, low pollutant emissions and outlet temperature distribution.

Figure 4.1: Pressure-Volume diagram for a simple gas turbine


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4.2 Gas turbine combustor types There are two basic types of gas turbine combustors, tubular and annular. A compromise between these two different types gives another kind of combustor, the tuboannular: • A tubular combustor is composed of a cylindrical liner mounted

concentrically inside a cylindrical casing. Most of the early jet engines featured tubular chambers, usually in numbers varying from seven to sixteen per engine. Nowadays the tubular combustor is used mainly for small gas turbine of low power out.

Figure 4.2: tubular combustor

• The annular combustors comprise an annular liner mounted concentrically

inside an annular casing. It represents an ideal configuration in terms of compact dimensions. Unfortunately, annular combustors presents serious difficulties, firstly, although a large number of fuel jets can be employed, it is more difficult to obtain an even fuel/air distribution and an even outlet temperature distribution. Secondly, the annular chamber is inevitably weaker structurally and it is difficult to avoid buckling of the hot flame tube walls. Thirdly, most of the development work must be carried out on the complete combustion chamber, requiring a test facility capable of supplying the full engine air mass flow.

Figure 4.3: Annular combustor

• In the tuboannular combustor, a group of cylindrical liners is arranged

inside a single annular casing, as illustrated in figure 4.4. This type represents an attempt to combine the compactness of the annular combustor with the test features of the tubular system. Compared with the annular design, the tuboannular combustor has an important advantage in that much useful chamber development can be carried out with modest air


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supplies. Tuboannular chambers are still in widespread use, although the great majority of modern combustors for large engines are of annular form.

Figure 4.4: Tuboannular combustor

4.3 Main parts of a gas turbine combustor The following figure shows the different parts of a gas turbine combustor:

Figure 4.5: Main components of a gas turbine combustor

4.3.1 Diffuser The function of the diffuser is to reduce the velocity of the combustor air inlet to a value at which the combustor pressure loss is acceptable but also to recover as much of the dynamic pressure as possible, as well as present the liner with a smooth and stable flow.


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4.3.2 Primary zone The purpose of the primary zone is to anchor the flame and, at the same time, provide sufficient time, temperature, and turbulence to achieve essentially complete combustion of the fuel. An essential feature is the toroidal flow reversal that is created and maintained by air entering trough swirl vanes located around the fuel injector and through a single row of holes in the wall of the liner. This flow reversal ensures that some of the hot gases produced in combustion are recirculated back into the primary zone to mix with the incoming air and fuel. 4.3.3 Secondary or intermediate zone The secondary zone is the region that lies between the primary and dilution zones. At low combustion pressures the rate of chemical reaction is slow, and the combustion is far from complete at exit from the primary zone. Under these conditions the intermediate zone serves principally as an extension to the primary zone, providing increased residence time for combustion to proceed to completion. At high combustion pressures the intermediate zone serves a different purpose. Although high pressures ensure complete combustion, at the high temperatures prevailing in the primary zone, dissociation of carbon dioxide to carbon monoxide and oxygen occurs and, to a lesser extent, dissociation of water vapor to hydrogen and oxygen. Lowering the flame temperature, by injecting prudent amounts of air into the secondary zone, inhibits dissociation and allows the combustion of carbon monoxide and hydrogen to proceed to completion upstream of the dilution zone. 4.3.4 Dilution zone The role of the dilution zone is to admit the air remaining after the combustion and wall-cooling requirements have been met, and to provide an outlet stream with a mean temperature and a temperature distribution that are acceptable to the turbine. The dilution air is introduced through one or more rows of holes in the airs liner walls. 4.4 Combustion performance The most important aspects of combustion performance are combustion efficiency, flame stabilization and pollutant emissions. 4.4.1 Combustion efficiency Combustion efficiencies below 100% represent a waste of fuel and also give rise to the presence of undesirable or harmful pollutant emissions in the engine exhaust gases. In practice, high levels of combustion efficiency are achieved over most of the engine operating range by ensuring that the primary combustion zone provides sufficient time and temperature to fully


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evaporate the fuel, mix the fuel vapor with air and recirculating combustion products, and allow combustion to proceed to completion. 4.4.2 Flame stabilization For any particular combustion chamber there is both a rich and a weak limit to the air/fuel ratio beyond which the flame is unstable. Usually the limit is taken as the air/fuel ratio at which the flame blows out, although instability often occurs before this limit is reached. Such instability takes the form of rough running, which not only indicates poor combustion, but sets up aerodynamic vibration which reduces the life of the combustor and causes blade vibration problems. The range of air/fuel ratio between the rich and weak limits is reduced with increase of air velocity, and if the air mass flow is increased beyond a certain value it is impossible to initiate combustion at all.

Figure 4.6: Stability loop

4.4.3 Pollutant emissions For many years the attention of combustion engines was focused on the design and development of high efficiency combustors that were rugged and durable, followed by relatively simple solutions to the problem of smoke. When the requirements for emission control emerged, much basic research was necessary to establish the fundamentals of pollutant formation. Smoke is the most obvious pollutant from gas turbine engines because it can be seen with the naked eye. Other pollutants of importance are carbon monoxide (CO), unburned hydrocarbons (UHC) and oxides of nitrogen (NOx).


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The single most important factor affecting the formation of NOx is the flame temperature, this is theoretically a maximum at stoichiometric conditions and will fall off at both rich and lean mixtures. Unfortunately, while NOx could be reduced by operating well away from stoichiometric, this results in increasing formation of both CO and UHC. The formation of NOx is slightly dependent on the residence time of the fluid in the combustor, decreasing in a linear fashion as residence time is reduced; an increase in residence time has a favorable effect on reducing both CO and UHC emissions.

Figure 4.7: Emission characteristics of gas turbine engines


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Fuel Flow

5. LAB EQUIPMENT The exercise will be done with the test facility given in the laboratory of the Division of Heat and Power Technology at KTH. The figure 5.1 shows the set up scheme of the lab exercise and the disposition of all the equipment. 1 Fan valve 6 Manometer

2 Thermocouples 7 Fuel valve 3 Pressure outlet 8 Flame arrest 4 Emissions outlet 9 Pressure regulator

5 Opening fuel mass valve 10 Main valve

2 3 5 6

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Figure 5.1: Lab equipment scheme

Air Mass Flow

Air Mass Flow

PRESSURE SYSTEM

FAN

COMPUTER

CONTROL PANEL

7

8

9

10 A/D CONVERTER

CO, CO2 ANALYZER

O2 ANALYZER

Gas cooler

1

C3H8

Propane


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5.1 Rover combustor The Rover combustion chamber is a tubular combustor used in the IS/60 and IS/90 gas turbines for fire pumps in navy boats. The figure 5.2 shows the combustor working at the highest equivalent ratio it can be run. The primary and the secondary zone are clearly identified.

Figure 5.2: Rover Combustor

Technical data for the IS60 and IS90 gas turbines:

IS/60 IS/90

Shaft Power (continuous) 60hp / 44.1kW 107hp / 78.6kW Jet Pipe Temperature

( Max. Power) 600°C 670°C

Fuel Diesel; Kerosene Diesel; Kerosene

Specific Fuel Consumption 1.45 lb/bhp./hr 0.658 kg/hp/hr

1.38 lb/hp./hr 0.626 kg/hp/hr

Compressor Speed 46000 r.p.m. 46000 r.p.m. Compressor Performance

( Air Mass Flow) 1.35 lb/s

0.612 kg/s 1.95 lb/s

0.884 kg/s

Weight 140lb 63.52 kg

140lb 63.52 kg


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5.2 Control panel The control panel (Figure 5.3) will allow the setting of the fuel flow and the air mass flow at the corresponding values. A fan placed at the outlet of the combustor provides the air mass flow through the combustor, as shows the lab equipment scheme in figure 5.1. To modify this mass flow there is a valve before the fan that is manipulated from the control panel, when the valve opens the air speed is increased, therefore the mass flow rises, and vice versa. The amount of air mass flow through the combustor will be calculated by the calibration curve in appendix A1 and the difference of pressure given by the measurement equipment between the atmospheric and the static pressure inside the combustor. The fuel flow can be also modified by a valve, which is controlled from the panel. The maximum fuel flow that the system can provide is 0.01276 Kg/s or 0.39 m3/min when the valve is completely opened. The fuel window shows a fuel percentage relative to the limits mentioned above.

Figure 5.3: Control Panel


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The control panel also informs about the temperature at the outlet of the combustor, which can not be over 1000oC, and the temperature at the valve that control the mass flow, which can not be over 250oC. If one of these temperatures is reached the fuel valve will close automatically and the fuel supply will be switch off. 5.3 Measurement equipment 5.3.1 Pressure measurement equipment The pressure acquisition system employed is a PSI 8400 (Figure 5.4). It is an electronic pressure scanning system in which semiconductor transducers, microprocessor based data acquisition and on-line calibrations are integrated.

Figure 5.4: PSI 8400

The concept of this pressure measurement technique consist of one high accuracy pressure transducer with traceable calibration against national and international standards and long-term stability, and a large set of lower quality transducers with good short-term accuracy specifications. These two types of transducers are combined in such a way that the high-quality transducer is used as a reference during the calibration of the cheaper ones. The calibration is performed by applying control air to one side of the movable calibration valve given by a pump. Known pressures are then applied while transducer voltages are scanned and stored in memory [Fransson, 1995].


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The PSI 8400 system consists of pressure scanner units in the range of ±7Kpa, ±35Kpa and ±100Kpa relative atmosphere. Advantageous of the system is the feature of scanning several pressures at the same time. The maximum possible frequency for pressure measurements only is 50000 channels per second [Svensdotter, 1995]. Accuracy of the pressure calibration unit is stated by the manufacturer to be ±0.02% full scale; for the pressure scanning, the accuracy of the ±7Kpa pressure scanner is given as ±0.1% full scale and ±0.05% full scale for the ±35Kpa and ±100Kpa pressure scanners. 5.3.2 Temperature measurement equipment The flame temperature is measured with thermocouples. They are essentially formed of two metal conductors, brazed together on each side as it is shown in figure 5.5. The connection of these two metals will give an electromotive force, which depends on the temperature in each junction, and the materials used. This electronic signal goes to the A/D converter that will convert it into the temperature, given in °C, at the end of one junction of the thermocouple (T2), while the other one keeps constant as a known reference (T1). A T1 T2 B U

Figure 5.5: Schematic view of the Thermocouple The design of this temperature measurement technique is based in three simple thermoelectric lows: - Law of homogenous metals - Law of intermediate metals - Law of intermediate temperatures The first of these laws indicates that there is no electric current in a homogenous metal, independent of the variation of the section, if a variation temperature is applied. Therefore, if it is connected the two wires with different temperatures, the electromotive force is independent of the temperature distribution along the wires.


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The second law gives that is possible to put in, at any position in the circuit, a third metal without any change in the resulting voltage, under the condition that the connections are at the same temperature. This gives the possibility to use expensive (pure) metals at the connections at T1 and T2, while using cheap metals for the rest of the wires. The usual reference value in the “cold junction” (T1), at which the thermocouples are calibrated, is 0oC, but for many industrial applications it is not practical to keep the reference connection at a constant temperature. The law of intermediate temperatures allows to have the reference temperature at any value. This law indicates that the sum of two electromotive forces, generated by two thermocouples (one thermocouple with the junctions at 0oC and a new reference temperature, and the other thermocouple with the junctions at the same reference temperature and the unknown to be measured) is equivalent to the electromotive force generated by one thermocouple with its two junctions at 0oC and the unknown temperature to be measured [Fransson, 1995]. The thermocouples used in the lab will be according to the norm “DIN IEC 584-1” type “N” made of Nicrosil/Nisil alloys. They will be placed at different ratios in the outlet of the combustor. The maximum temperature range given by the manufacturer for this kind of thermocouples is –270 to 1300 °C, and the limits of error are: ±2.2 °C or 0.75% above 0°C and ±2.2°C or 2% below 0°C.

Figure 5.6: Temperature measurement equipment

(The A/D converter and one thermocouple) 5.3.3 O2 analyzer The equipment used to measure the O2 is the Mannesman&Braun Paramagnetic Oxygen-analyzer Magnos 6G (Figure 5.7). The concept of this technique is based in the paramagnetic properties of the oxygen when it is exposed to a magnetic field. The test gas is mixed with a reference gas. When the oxygen concentration changes, the electrical balance of a Wheatstone bridge inside the analyzer is disturbed due to attraction of paramagnetic oxygen molecules into a magnetic field provoked


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by a magnet. The bridge signal is proportional to the oxygen concentration in the test gas, which will be converted in the percentage of O2 showed in the monitor [Váña, 1993]. The measurement range is 0 – 30% and its uncertainty is ±2% of the full scale. Taking in account the gas calibration effect, the measurement uncertainty is ±3% of the full scale.

Figure 5.7: O2 Analyzer

5.3.4 CO, CO2 analyzer The equipment used is the Mannesman&Braun NDIR (Non Dispersive Infra Red) Industrial Photometer Uras 10P (Figure 5.8). It measures the heating that a reference gas has when an infrared beam falls upon it. This beam goes through a tube that contains the emission gas, the CO absorbs part of the radiation in a concise band of the spectrum. Therefore, the larger the CO concentration in the emissions, the more radiation is absorbed and the heating of the reference gas will be lower. The same concept is applied to measure the CO2 [Váña,1993]. Measurement ranges are 0 – 25% for CO2 and 0 – 1000 or 5000 ppm for the CO. The accuracy of the instrument is given by the manufacturer to be ±2% of the full scale taking in account the calibration gas uncertainty. The CO2, CO and O2 analyzers will show the percentages of each component by volume of dry air since before it analysis the air will go trough a gas cooler that will extract the water of it.

Figure 5.8: CO+CO2 Analyzer


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5.4 Safety requirements This laboratory exercise contains dangerous experiments if not run absolutely correctly so the following safety requirements have to be clearly understood and completely followed while the combustor is running: • The gas sensor has to be placed just below the fuel supply connection to

the combustor. The density of the propane is higher than the density of the air, therefore if there is any leak the propane will move down and the gas sensor will be able to detect it inmediatly. See figure 5.9.

Figure 5.9: Safety requirements

• One of the thermocouples placed at the outlet of the combustor has to be

connected to the control panel to check the temperature at this point is not over 1000 °C. If the thermocouple is not connected the fuel system will shut down and it will not be possible to run the combustor. If the temperature goes over 1000 °C the fuel valve will close automatically and the fuel supply will be switch off. See figure 5.10.

• To cool down the air at the outlet of the combustor a hose plugged to the

water supply has to be connected to the combustor cooler tube. The water has to be turned on while the combustor is running and during five minutes after the experiment is finished. See figure 5.10.

• Ear and face protection equipment will be distributed to the students and it

has to be worn all the time during the lab experiment. • To safeguard the ignition system, placed at the top of the combustor, from

the high temperatures a radiation board protection has to be situated below it. See figure 5.10.


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• The students have to be informed before starting the experiments where the emergency stop buttons are located. Ask where are the emergency buttons in case the supervisor of the experiments forgets it.

Figure 5.10: Safety requirements

Other safety regulations that are not shown in the picture will be: • A mesh on both sides of the combustor to avoid the students could touch

or fall on the combustion chamber by accident. • A “box” placed at the beginning of the combustor right below the fuel

supply to retain the propane on it in case of leakage. • Finally a support system to give a better attachment to the combustor.


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6. PRELIMINARY CALCULATIONS Before running the combustor several calculations has to be done to guide the performance of the experiments, and to compare them with the actual data that the measurement equipment will provide. 6.1 Adiabatic flame temperature The first calculation to carry out is the constant-pressure adiabatic flame temperature for the combustion at different equivalence ratios of propane-air mixture. The pressure will be 1 atm and the initial reactant temperature is 298K. The equivalent ratios will be φ = 0.15, 0.2, 0.25 and 0.3 Use the following assumptions: 1. Complete combustion. 2. The product mixture enthalpy is estimated using constant specific heats

evaluated at ≈ 0.5(Ti + Tad), where Tad is guessed in the beginning and checked at the end of the calculations (Iterate).

6.2 O2 and CO2 emissions The next step is to obtain the O2 and CO2 percentages by volume of dry air (the water will be extracted from the test emissions by the gas cooler) at the same equivalent ratios of the previous calculations. Consider complete combustion. The results of both calculations should be written down in the appendix A2 table. 6.3 Air mass flow and fuel flow To set the desired equivalent ratios in the combustor during the experiments it is necessary to develop a table with values of the data that can be read with the measurement equipment. These will be the ∆P given by the pressure system and the percentage of fuel showed in the control panel. To translate the equivalent ratios 0.15, 0.2, 0.25 and 0.3 into the parameters that can be modified operate as follows: The air mass flow will be set up at different values 0.1, 0.15, 0.2 and 0.25 kg/s. With these values and the calibration curve showed in appendix A1 it is obtained the ∆P at the outlet of the combustor.


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To obtain the values of the percentage of fuel at each operating condition calculate the stoichiometric air-propane ratio, and with the corresponding equivalent ratio obtain the air-fuel ratio:

Once the air-fuel ratio is obtained and with the air mass flow (A) set with the same previous values, the fuel flow is calculated immediately. The total propane flow that the fuel system can provide is 0.01276 kg/s, which means the control panel will show 100% in the fuel window. Therefore, the amount of fuel flow previously calculated could be translated easily into the corresponding percentage of fuel that will be written down in the control panel. It is necessary as well to determine the ∆P for the different air mass flow rates in the table 2 shown in the appendix A3. The results of these calculations will be written down in the tables shown in appendix A3. The mass flow and fuel flow calculations are indispensable to run the combustor at the desired running conditions. Anyhow, the student must understand that these values calculated can not be set exactly in the experiments due to the turbulence reached inside the combustor when is in operation. Therefore, the ∆P and percentage of fuel obtained in the experiments will be very close to the values calculated but not strictly the same. Thus, the values of the ∆P and percentage of fuel have to be written down again in the corresponding tables, as it will be explained later, this way, the student will have the exact numbers of ∆P and percentage of fuel reached in the experiment for the different running conditions.

( ) ( )φ

==φ ⇒ stoicstoic A/FA/F

A/FA/F

)()(


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7. INSTRUCTIONS FOR LABORATORY EXPERIMENTS 1. Check that all the safety requirements are fulfilled. 2. Make sure all the lab equipment is connected: Measurement systems,

control panel, the fan and the computer with the corresponding programs open to show and save the temperatures and difference of pressure.

3. Light the combustor from the control panel. 4. Set the desired running conditions from the control panel (opening or

closing the fan valve to set the mass flow and operate in the same way with the fuel valve to set the fuel flow).

5. Wait until the combustor reach the desired running condition (all the measured values will remain constant when the running condition is achieved).

6. Write down the starting time shown in the computer when the running condition is reached.

7. Wait two minutes before write down the CO, CO2 and O2 levels in the corresponding tables in appendices A4 and A5. The temperatures from the thermocouples and the ∆P will be saved in a computer file. Write down as well the percentage of fuel shown in the fuel window of the control panel.

8. Write down the finish time before change to other running condition. 9. Set the new values for a new running condition and operate in the same

way than the last operating point. 10. When all the operating points have been tested, switch off the fuel supply

and let the fan valve open to absorb all the propane that could remain without burning.

11. Close the main valve of the fuel supply system. 12. After five minutes close the fan valve and the water for cooling down the

combustor. 13. Get the two files where the temperatures and difference of pressure were

saved. The programs will save the year, month, time (hour, minute, second) and the temperature or ∆P. The program will save these values once every second.

14. Turn off the measurement equipment, the computer and the fan.


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8. EXTRACTION OF DATA The preliminary calculations are indispensable to run the combustor at the desired operating points. The experiments will be executed in two different and specific ways, thus it will be extracted the suitable data (temperatures, CO, CO2 and O2 levels) to analyse them much easier: • The first way to perform the experiments is to maintain the air mass flow

constant and change the percentage of fuel. Every time an operating point is set it is necessary to let the combustor running a couple minutes at the same conditions to let the gas analyzers extract the right emission levels. The calculations made to fill up the table 1 in appendix A3 will be the ones used in this part of the exercise.

• The other way to perform the experiments is to maintain the fuel flow

constant and the air mass flow at different rates; the table 2 in appendix A3 will be needed in this other part of the lab exercise.

The temperature and ∆P values will be saved in a computer file. The emission levels will be written down in the tables shown in the Appendices A4 and A5, for the first and the second ways to perform, respectively. Note that when the temperature increases the ∆P decreases. This happens due to the density of the air. When the temperature rises the density descends, so the mass flow goes down and therefore the ∆P decreases:

This way, to keep the mass flow constant it will be necessary to open or close the fan valve controlled from the panel, so the velocity (u) will change to offset the variation of the density.

( ) ( ) ↓∆∆=⇒↓=⇒↓⎟⎟⎠

⎞⎜⎜⎝

⎛=⇒↑ PP0.2263m m Au m TP T &&& ρρ

ρR


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9. FINAL CALCULATIONS After the experiments some calculations and graphs have to be done to analyze and understand the behaviour of the combustor and to extract the suitable conclusions of the obtained data. 9.1 Complete the tables Once the experiments are finished the first step is to calculate the average of all temperatures and ∆P for each operating condition saved in the corresponding computer file and complete the tables of appendices A4 and A5. The power that has to be calculated is the nominal power. The higher heating value of propane used is 50368 kJ/kg, therefore:

9.2 Flame temperature from the gas emissions With the emission levels extracted from the experiments calculate the flame temperature and compare these with the ones obtained from the thermocouples and from the preliminary calculations. To avoid heavy calculations, which will give just slight more accurate results, it is possible to perform an approximate computation. Calculate the equivalent ratio from the O2 levels and assume there is complete combustion, do not forget the analyzers show the percentage by volume of dry air. With the equivalent ratio obtained just keep the same steps made to get the adiabatic temperature flame. 9.3 Graphs For a better study and comprehension of the combustor behaviour and the extraction of conclusions of the experiments the sketch of the following graphs will be very helpful: From the table of appendix A4 draw the graphs: 1. CO – Power (mair=const) 2. CO – Power (φ = const) From the table of appendix A5 draw the graphs 1. CO – φ (Power = const) 2. Temperature – φ

(kg/s)m50368 P(kW) fuel&×=


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10. REPORT REQUIREMENTS • Present the graphs requested in the previous point. • Discuss the CO levels variations with the power and the equivalent ratio. • Analyse the relationship between temperature and equivalent ratio. • According to the pollutant emissions try to predict the best working

conditions for the combustor. • Discuss the differences between the temperatures for each point obtained

in different ways. Find the explanations for these differences. • Write down a brief essay with impressions and suggestions of the lab

exercise: Are the handout and experiments good, or what should be improved? Do you think is information missing? Which information is not necessary? …


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11. REFERENCES Cohen, H.; Rogers, G.F.C.; Saravanamuttoo, H.I.H.; 1996 “Gas Turbine Theory”, Fourth edition. Fransson, T.H.; 1995 “Measuring Techniques in Thermal Engineering: an Introduction in the Form of Lecture Notes”, Chair of Heat and Power Technology, KTH,Stockholm, Sweden. Svensdotter, S.; 1995 “Investigation of the Flow trough an Axial Turbine Stage”, Licentiate Thesis, Division of Heat and Power Technology, KTH, Stockholm, Sweden. Turns, S.R.; 1996 “An Introduction to Combustion: Concepts and Applications” Mc Graw-Hill,Inc. Váña, J.; 1993 “Comprehensive analytical chemistry, Vol 17: Gas and Liquid Analyzers”, ed. by Cecil L. Wilson and David W. Wilson.

Mass flow through the Rover combustor

0.000

0.050

0.100

0.150

0.200

0.250

0 0.2 0.4 0.6 0.8 1

∆P [kPa]

mas

s flo

w [k

g/s]

P 0.2263 mA1 APPENDIX∆=&

26

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APPENDIX A2 CONSTANT-PRESSURE ADIABATIC FLAME TEMPERATURES Assumptions: complete combustion initial reactant temp is 298 K

pressure 1 atm

φ Tad (K) 0.15 0.2 0.25 0.3

CO2 and O2 EMISSIONS

Assumptions: complete combustion

φ CO2 (% by volume) 02 (% by volume) 0.15 0.2 0.25 0.3

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APPENDIX A3 TABLE 1 (mass flow constant performance)

mair (kg/s) φ ∆P(kpa) mfuel (kg/s) %mfuel

0.1 0.15 0.2 0.25 0.3

0.15 0.15

0.2 0.25 0.3

0.2 0.15

0.2 0.25 0.3

0.25 0.15

0.2 0.25 0.3

TABLE 2 (fuel flow constant performance)

%mfuel mfuel (kg/s) Mair (kg/s) ∆P(kpa) 15 0.1

0.15 0.175

0.2 20 0.15

0.175 0.2

0.25 25 0.15

0.175 0.2

0.25 30 0.175

0.2 0.25

0.3

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Appendix A4 (mass flow constant performance)

∆P(kpa) %mfuel Mair (kg/s) mfuel (kg/s) φ P(KW) CO(ppm) CO2 O2 Time Temperature (C) Temperature (K) / / / / / / / /

/ / / /

/ / / /

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APPENDIX A5 (fuel flow constant performance)

%mfuel ∆P(kpa) mfuel (kg/s) mair (kg/s) φ P(KW) CO(ppm) CO2 O2 Time Temperature (C) Temperature (K) /

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lab instruction-combustor lab - energiteknik | kth combustor la… · · 2005-01-31gas turbine...

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