CHAPTER 1Introduction Since the emissions from gas turbine engine are highly polluted and harmful to the environment and to mankind especially, thus clean and stable air transportation is highly in demand nowadays. The need for clean engine with less or non-emissions has becoming great concern during the last few decades. There has been continuous development on the future design of gas turbine to diminish the rate of emission i.e. CO, UHC, NOx and SOx, yet efficient and meet required mission. All kind of emission resulted from aeroengine combustion very harmful such that they may lead to green house effect, global warming problem and depletion of ozone layer. Among the emissions, oxide of nitrogen NOx is the most dangerous and has been propulsion engineer and designer main target, due to its radical reaction with the ozone in the atmosphere. As according to Dr. John R. Richard (2000) [4] in his book Control of Nitrogen Oxides Emission, aircraft contributes five percent out of total NOx emission in the category of non-road sources. Airport when an aircraft is about to take-off is the most polluted area because at that moment, aircraft gas turbine engine is at full power with maximum NOx formation and emission. Oxides of nitrogen are produced mainly from high temperature combustion processes (Nazri, 2005) [2]. Of all nitrogen oxides, nitrogen oxide (NO) and nitrogen dioxide (NO2) are providing very adverse effect towards environment. NOx gaseous formation should happen in lean and near stoichiometric fuel and air mixture. At stoichiometric, the compound contained in the fuel and air is completely burnout. If the amount of air content is more than the stoichiometric, the combustion is said to be lean mixture, whereas the mixture of fuel and air under rich condition when the content of air is less than the stoichiometric. High oxygen concentration enhances 1 RQL Combustor the formation of NOx. Residence time needed for fuel and air to completely mix is of significance factor that cause the formation of nitrogen oxides NOx in the combustion chamber. The higher the rate of mixing residence time, the lower the potential of NOx formation should be and vice versa. One method to reduce the formation of NOx emission is through few modifications on the combustion system of the aircraft gas turbine. The modification should be focusing on the chemical reaction within the combustion chamber, followed by the combustor geometry that can sustain to the modified reaction previously. Since NOx is highly dependent to the temperature, the principles of combustion modification are aiming on minimizing the peak temperatures and residence time at the peak temperature [4]. The shorter residence time can avoid near stoichiometric combustion. John also stated that the modification techniques attempt to minimise the oxygen concentration at peak temperature. Less availability of oxygen in fuel rich condition depletes the ability of fuel bound nitrogen to react with oxygen, thus retard the formation of NOx [3]. Rich-Burn Quick-Quench Lean-Burn (RQL) combustor has been introduced as one of the way to reduce the formation of oxides of nitrogen in gas turbine combustor. The RQL concept is that to burn the fuel in the primary zone of the combustor under rich-fuel condition then quickly mix with secondary air in the lean condition [2, 3]. The RQL combustor implies quick mixing between secondary air and rich fuel from primary zone in order to minimise combustion residence time (i.e. rate of combustion). High rate of combustion avoid the near stoichiometric condition that can allow the formation of NOx. The RQL combustion has been successful in reducing the emission of NOx from fuel bound nitrogen, and in avoiding thermal NO formation [8] . The combustion takes place in two zones [7] which means the combustor will have physical separation of two chambers (i.e. primary zone and secondary zone). Where the mixing of fuel and air take place is called quickquenching section. 2 RQL Combustor The ignitability during mixing of fuel and air take place is great even though the RQL combustor providing only single fuel path in the fuel nozzle. Appropriate number of dilution holes and their patterns as well play important role since NOx formation mainly occur near the dilution zone. Particularly. By avoiding fuel droplet stagnation caused by the airflow should diminish the large smoke emission in the combustor [6] . The RQL combustor differs from conventional combustor in which it adopted double-wall liner cooling method [6] in order to sustain metallurgy limitation during high temperature combustion process in fuel rich condition. 3 RQL Combustor . Hideki. Tomoyoshi. M.M. Yoshiaki and I. large smoke emission might as well accumulate. Mitsuru (2008) in their technical report [6] stated that the RQL combustor technique features simple structure yet excellent combustion stability and performance. N. in primary zone where equivalence ratio is under fuel rich state. even during low loads. Lean-Burn Combustor First. the rich burn 4 RQL Combustor .CHAPTER 2 RQL CONCEPT Rich – Burn. Quick-Mix. Figure 2. a “rich .burn” condition in the primary zone generates the stability of the combustion reaction by producing and maintaining a high concentration of energetic hydrogen and hydrocarbon radical species. Quick – Mix. Secondly. Lean – Burn (RQL) combustor concept is predicted from a conclusion that the primary zone of a gas turbine combustor operates at the most effectively with rich mixture ratios.1: Rich-Burn. 2: Nitric Oxide Formation 5 RQL Combustor . hydrogen and carbon monoxides. This process creates a “lean – burn” condition at the exit plane of the combustor. then.conditions minimize the nitrogen oxides production due to the relative low temperature and low population of oxygen containing intermediate species. hydrogen and hydrocarbon intermediately. Figure 2. carbon monoxide (CO) and hydrocarbon (HC). is very high concentrated of partially oxidized and partially pyrolized (decomposition from high temperatures) hydrocarbons. The liquid waste form the rich primary zone. This is done by injecting a considerable amount of air through wall jets to be mixed with the primary zone effluent. and. this will result in the emission of effluent composed of the major products of combustion which is carbon dioxide (CO2). nitrogen (N2) and oxide (O2). a non-zero concentration of criteria pollutants such as nitrogen oxides (NOx). water (H2O). Thus the addition of oxygen is needed to oxidize the high concentrations of carbon monoxides. This waste cannot be exhausted without further processing. Generally. the use of air for cooling the liner wall is prevented to avoid the generation of near-stoichiometric mixture ratios and the production of nitrogen oxides in the surrounding near the wall. the combustor must be able to continuously and rapidly mix the air into the rich-burn effluent in order to rapidly produce the lean-burn conditions. A good RQL is to be able to mix the air with the waste or effluent that exits the primary zone. The mixing of the exiting air takes the reaction in which be exposed to a high production of oxides of nitrogen. Figure 2. This is near the stoichiometric conditions where the temperature and oxygen atom concentrations are elevated. create a reducing and demanding environment for the liner material.The selection of liner material is important in RQL combustor design. Thus the concentration of hydrogen and its demand require a high quality material. In the primary zone. Thus. The high temperature and composition of gases in the primary zone then.3: RQL Strategy 6 RQL Combustor . Quick-Mix. The Rich-Burn. Figure 2.Thus. the “quick-mix” label is used to describe the requirement to quickly mix the air and the primary zone effluent.4: The Process in the RQL Combustor 7 RQL Combustor . Lean-Burn combustor concept is basically the following process that takes place in the combustor in order to reduce the production of NOx. CHAPTER 3 NOx Emission in RQL Combustor Rich-burn.1 General NOx Formation in Gas Turbine Level of pollutants released by gas turbine can be related directly to pressure. Generally. temperature. In fact. lean burn or RQL combustor is introduced as a strategy to reduce the emission of nitrogen oxides (NOx). gas turbine operates at very high temperate to achieve maximum thermal efficiencies and to be said the combustion is complete. Turbine operates most effectively at primary zone with rich mixture ratio of 1. time and concentration histories of the combustion process. the level of CO and UHC is 8 RQL Combustor . Rich burn condition minimizes production of NOx due to relative low temperature and low population of oxygen containing intermediate species.8. 3. quick-mix. The high ratio enhances the stability of the combustion reaction by producing and sustaining a high concentration of energetic hydrogen and hydrocarbon radical species. 1. the flame zone temperatures are lower than high load temperature. CO and UHC levels are lower at high-power setting and vice versa and in contrast.1: CO Emissions in RQL combustor relatives to exit temperature Figure 3. NOX emission is higher at high-power setting as shown in Figure 3.decreases at this operating temperature as shown in Figure 3. Figure 3.2: NOX Emissions in RQL combustor relatives to exit temperature 9 RQL Combustor . yielding low thermal efficiencies and incomplete combustion.1. In other words. with reduced power or at frequent power fluctuation.1. However.2.1.1. 1.3 shows that NOx increases by fifteen percent when mixer holes are increased from eight to twelve holes. First. As a result. The potential utilization of RQL concept is limited by the ability of the quench process to rapidly and uniformly dilute the fuel-rich mixture and to transport in to the lean zone. The third configuration is for both jet air and main air preheat. it can be seen that as the number of holes increases. This is done via three stages. The results obtained in Figure 3. High concentration of NOx is spotted to occur in the wakes of the jets adjacent to the wall instead at the centre of the combustor. First configuration is for no preheat air wich act as a benchmark. three preheat configurations were prepared. Results obtained shown in Figure 3.1. the NOx emission also increases.4 indicates that third configuration which is main and jet air preheat increases the NOx emission while non-preheat air will only emit small percentage of NOx . RQL combustor has excellent operability range. 10 RQL Combustor . Thus. In that experiment. The second configuration is for jet air preheat which means only the jet air is heated back while main is not reheated. In recent research reported by Scott Samuelson.In RQL combustor. optimization of aerodynamic mixer may not minimize emission of nitrogen oxides. reduction in NOx is achieved by preventing stoichiometric combustion. fuel is burned in controlled fuel-rich and fuel-lean regions separated by air quenching. the number of preheat air also increases. 1.3: Composite NOx Emission Data Fig 3.Fig 3.4: Effect of Preheat on NOx 11 RQL Combustor .1. 4. This unique combustion system provides extremely low emissions without sacrificing efficiency and reliability. This steam generator has proven the superiority and ability to provide reliable.CHAPTER 4 Technology for Advanced Low NOx Advanced low NOx technology (TALON) was deployed commercially by Pratt & Whitney and this RQL is the anchor combustor technology in aeroengines.1 shows the steam generator.1 Clayton Steam Generator Clayton. Figure 4. 12 RQL Combustor . cost effective steam production around the world. one of the most respected names in the boiler industry has been a leader in the development and manufacture of innovative and highly efficient steam generators since 1930. The RQL is preferred the most over lean premixed options in aeroengine applications due to the safety considerations and overall performance throughout the duty cycle. we are going to introduce some of the products that use low NOx. In this part. The Clayton design responds rapidly to sudden or fluctuating load demands. Safe for personnel and Inherently safe. without thermal stress.1: Steam Generator Table 4.5% quality separator to minimize 13 RQL Combustor .1 below show us some advantages of the Clayton steam generators and their description. Table 4.Figure 4.1: Clayton Steam Generators Advantages Save fuel Description The unique counter flow design provides higher fuel-tosteam efficiency than traditional boilers. Star fast Provide full output from a cold start within fifteen minutes. Ensures high quality Clayton provides a 99. Compact and lightweight The Clayton design typically occupies one-third of the floor space and weighs 75% less than a traditional boiler. the Clayton design eliminates hazardous equipment Provide rapid response steam explosions. 2 show the cross section of the FIR burner and the burner mechanics respectively. Figure 4. Includes support outstanding Every steam generator is backed by Clayton factory direct sales and service plus full service feedwater treatment.1: FIR burner cross section 14 RQL Combustor .2. All of these burners are using low NOx.steam Offers advanced controls moisture in the steam. 4. variable speed drives and a linkage-less servo controlled burner management system are standard. no efficiency was lost and consumed the lowest cost premium. The FIR burner was choosen to address the Under 20 PPM to Under 9 PPM NOx requirement also used for new and retrofit applications.2. Other than FIR burner.2. A burner and S burner. In the FIR burner.1 and Figure 4. Johnston Burner products are also AR burner. Figure 4. PLC controls. J burner.2 FIR Burner This FIR burner was developed by the Johnston Burner Company. Figure 4. The FIR burner is an efficient solution for boiler low NOx applications which they are simple to be controlled and has a standard boiler packages. It will reduce NOx emission from the burner if we installed the FIR burner. 15 RQL Combustor .2.2: FIR burner mechanics We can see the difference after using the FIR burner and the uncontrolled burner in the Figure 4.2.3 below. 3. Figure 4. NOx reductions exceeding 50% from baseline levels are achieved across the load range with minimal increases in unburned carbon.2.3 Ultra NOx Coal Burner Fuel Tech’s Ultra Low NOx coal burners provide industrial and utility boiler owners with the ultimate solution to their NOx compliance needs. 16 RQL Combustor . Fuels being fired range from subbituminous through low and high sulphur eastern bituminous coals.3: NOx before and after 4.1 shows the ultra low NOx coal burner and Figure 4.2 show the performance. Each system application is specifically designed to maximized NOx reduction without sacrificing combustion performance or unit operation.Figure 4.3. 3.2: Ultra Low NOx Coal Burner Performance 17 RQL Combustor .1: Ultra Low NOx Coal Burner Figure 4.3.Figure 4. as well as the finer droplet of fuel the better. The concentration of NOx in the combustor plays important role whether the amount of emission would be much or less. RQL differ from any conventional combustor in which it implies double-liner geometry to ensure cooling ability of the combustor during fuel rich condition. Everybody is now realizing the importance of reducing the emission is due to the harmful effects the NOx providing to the environment and mankind. Few minor modifications were made on the conventional combustor in order to diminish the rate of NOx formation included the separation of the combustor into primary. Also. the technology did not only stop to gas turbine engine only but the technology on reducing NOx emission has been further adopted in other industry too such as manufacturing. power plant and boiler industry.CHAPTER 5 CONCLUSION The RQL combustor is the anchor technology proven today to reduce the amount of NOx emission from aeroengine. secondary and mixing zone. Although the contribution of aeroengine towards the emission of this oxide 18 RQL Combustor . It appears to us that everybody is giving out their effort in reducing the emission of this oxide of nitrogen. thus the design and pattern of dilution holes is an important consideration in RQL combustor. The concept of burning fuel at rich condition then quickly mix with secondary air to produce lean mixture has proven the effectiveness of the engine in reducing the emission of NOx without prior sacrificing the performance of the engine even at low load. 19 RQL Combustor . it enhances the reduction of the harmful emission by significance amount throughout many years already.of nitrogen is considered small. but by mean of RQL combustor. 4 7. 3. 2012 3.... and Samuelson G. 2000 6. Technical Review Vol.EFFECT OF AIR STAGING ON A COAXIAL SWIRLED NATURAL GAS FLAME. California.G.G. Italy. . Research and Development of a Combustor for and Environmentally Compatible Small Aero Engine. and Coghe A. Richards J. 2. 45 No. TURBULENT MIXING PROCESSES IN A SWIRLING-MULTIPLE JET CONFINED CROSSFLOW CONFIGURATION. Jenis Enjin Pesawat Udara dan Analisis Kitar. Mitsubishi Heavy Industries Ltd. Control of Nitrogen Oxide Emissions: Students Manual APTI Course 418.1. Quick-Mix. and Papailiou D. Jermakian V.3-5 Notes: Rich-Burn. Nazri M. 2008. Universiti Teknologi Malaysia. Kalogirou I. Greece.Nakae T. and Inada M. Irvine.2. Cozzi F. Moriai H. Lean-Burn (RQL) Combustor.. 5.. 2011. Combustion and Emission Issues in Gas Turbines by Wajid A.. 8.REFERENCE 1.R.D. Bakrozis A.US. Chishty and Manfred Klein 4.S.McDonell V. Scott S.D. Efficient and Low Emissions Gas Turbine Applications. Experiment Study of the Effects of Elevated Pressure and Temperature on Jet Mixing and Emission in an RQL Combustor for Stable. Miyake Y. 2005 20 RQL Combustor .