Proceedings of the International Symposium on Marine Engineering (ISME) October 17-21, 2011, Kobe, Japan Summary or Paper-ISME586Tier III EGR FOR LARGE 2-STROKE MAN B&W DIESEL ENGINES Johan Kaltoft MAN Diesel & Turbo, Teglholmsgade 41, 2450 Copenhagen SV, Denmark Abstract The IMO Tier III NOx regulations that will come into force in 2016 means that NOx emissions from large two-stroke diesel engines must not exceed a cycle value of 3.4 g/kWh, and NOx emission must not exceed 5.1 g/kWh at individual load points of the load cycle. To comply with the Tier III requirements, MAN Diesel & Turbo (MDT) is involved in targeting development of Exhaust Gas Recirculation (EGR). This paper describes the EGR principle, the investigation of EGR on two-stroke diesel engines as well as service test experience and test results. Test on MAN Diesel & Turbo´s two-stroke diesel engine in Copenhagen has proved that EGR is a compliant IMO Tier III NOx technology and service tests are currently ongoing in order to investigate long term influence on engine components and the EGR system. Keywords: IMO Tier III, Exhaust Gas Recirculation (EGR), MAN B&W engines. 1. INTRODUCTION The worlds marine engine manufacturers have since the ratification of the IMO Tier III criteria for NOx emission in Emission Controlled Areas (ECA´s) from large marine diesel engines, been challenged to develop new measures in order to reduce NOx. The extend of the necessary measures for NOx reduction up to 80% for meeting the IMO NOx criteria from January the 1st 2016, is beyond well known adjustments of the combustion process in two-stroke diesel engines. NOx reduction in his magnitude on two-stroke diesel engines, requires “add-on” technologies like Exhaust Gas Recirculation (EGR) or Selective Catalytic Reduction (SCR) as described in the ISME paper number 587 (2011). Back in 2004, MAN Diesel & Turbo started the first test program with EGR on the large 4T50ME-X two-stroke diesel test engine in Copenhagen, in order to verify the effect of EGR. The effect of EGR on smaller four-stroke diesel engines used in the automotive sector has been known since the 1970’ies as a very efficient means to reduce NOx in combustion engines. The HFO burned in large marine engines is a challenge when using EGR, due to the presence of high sulphur content and high content of solids thus a wet scrubber was introduced in the EGR system. In parallel with the EGR investigation on the 4T50MEX test engine, MAN Diesel & Turbo planned to make a service test on a ship in order to investigate long term effects on the engine components. In March 2010, a retrofit EGR system was installed on a 10MW 7S50MC Mk-6 engine onboard A.P. Moeller Maersk 1100 TEU container vessel Alexander Maersk. The recent EGR investigation and service test is a part of the large European development project named HERCULES-B with focus on high engine efficiency and low emissions. This paper describes the investigation and testing which MAN Diesel and Turbo have completed with EGR on large two-stroke diesel engines. 2. EXHAUST GAS RECIRCULATION The principle of EGR is based on exchange of the incylinder oxygen (O2) with carbon dioxide (CO2) from the exhaust gas which is re-circulated into the scavenge air. The exchange of O2 with CO2 leads to a decrease of combustion speed, resulting in lower peak temperatures during combustion. Besides the exchange of O2 with CO2 results in a higher in-cylinder heat capacity of the gas, which also lowers the combustion temperature. Lower combustion temperatures and especially lower peak temperatures result in lower formation of thermal NOx during the combustion process. There are different ways to utilise EGR on a two-stroke diesel engine: A) Internal EGR (primary methods) - Poor scavenging of the combustion chamber. - Internal trapping of combustion gas in the combustion chamber. B) External EGR (secondary methods) - Low pressure EGR on the exhaust side of the turbocharger, downstream the turbine. - High pressure EGR on the engine side of the turbocharger, upstream the turbine. 3. THE EGR SYSTEM FOR A MAN B&W ENGINE The reasons why the high pressure EGR in MAN Diesel & Turbo´s large two-stroke diesel engines is chosen as the preferred EGR solution are: The system is compact compared to the low pressure EGR system and is an “on engine” system. Copyright: 2011 ISME The Sludge tank size is depending on engine size. The quality (pH. The system controls the water supply to the scrubber (quality and amount) dependant on engine load. while the EGR system is not operated. C/O valve. The temperature of the exhaust gas entering the Pre scrubber can vary from 200-500ºC over the engine load range. is not exposed to additional sulphur. The water evaporated in the pre scrubber is condensed in the EGR cooler. particles and water droplets than conventional engines. particles and water droplets than in conventional engines. Scrubber for removal of particles and residual SO2 in the exhaust gas before it is introduced into the scavenge air receiver and further into the combustion chamber. 2. The EGR cooler cools the scrubbed gas down to approx. which varies from 16-21 % v/v. which is approx. for discharge to the sea. The EGR blower speed is controlled by a frequency converter control of the blower motor. The size of the NaOH tank is depending on the engine size. EGR cooler for cooling of the EGR gas and conversion of the enthalpy in the EGR gas to the cooling water. sailing patterns.e.5 m3/MW (installed engine power). turbidity and poly aromatic hydrocarbons) of the scrubber water. is also controlled by the WTS. The quality of the discharge water to the sea is hereby ensured to be within the IMO criteria’s for scrubber water discharge criteria’s. A guiding size for a container vessel is approx.. The drainer’s ensure that only scrubber water is discharged from the scrubber to the buffer tank without leakage of EGR gas. the EGR system comprises the following main components: EGR blower for creating a flow from the exhaust receiver to the scavenge air receiver of up to around 40% of the total exhaust gas amount. The gas is washed with re-circulated scrubber water supplied from the same pipe that feeds the Pre scrubber. The valve is operated as a throttle valve with variable positioning. pipes etc. i. 100°C over the load range. Change over valve (C/O Valve) for control of the EGR gas amount in cooperation with the EGR blower speed.2-0. Alfa Laval and MAN Diesel & Turbo are via continuous cooperation developing a WTS solution on a unit base. The valve is gas tight and ensures no flow of scavenge air into the exhaust system. NaOH neutralizes the sulphuric acid that is formed in the scrubber water. EGR As seen from Figure 1. depended on engine load and engine mode. The components from air intake to the scavenge air receiver.3 bar at 100% engine load and the EGR blower has to overcome this pressure difference as well as the pressure loss through the scrubber. Buffer tank is a part of the WTS.0 m3/MW (installed engine power).- The turbo compressor is not exposed to additional sulphur. The EGR gas amount is controlled by the oxygen content in the scavenge air receiver. The pressure difference between the receivers is around 0. The temperature of the EGR gas entering the EGR Scrubber varies from 50- . 0. Pre scrubber for removal of SO2 and for energy conversion by humidification. sailing patterns and disposal facilities. Water cleaning loop. NaOH tank for bunkering and storage of the NaOH.3 bar. A guiding size for a container vessel is approx. in order to precondition the exhaust gas before the gas enters the EGR scrubber. Sludge tank for collection of sludge from the WTS system. Water Treatment System (WTS) for handling of the scrubber water in the system. the main engine cooler. for installation in an adjacent room close to the engine. bunkering facilities and NaOH concentration. Around 95% of the scrubber is continuously re-circulated. The exhaust gas is washed with re-circulated fresh water with addition of sodium hydroxide (NaOH). cooler. Scrubber water loop. 1. Shut Down valve (S/D valve) for switching on and off the EGR system. scavenge air temperature between 35-40ºC. The valve is “on/off” controlled. Only the rugged engine components from the scavenge air receiver to the exhaust gas funnel is affected. Input is O2 concentration in the scavenge air and controlled components are the S/D valve. Figure 1: Basic EGR system layout diagram The MAN Diesel & Turbo EGR system basically consists of three flow loops: EGR gas loop. The safety of the EGR system is covered by the EGR control system via appropriate alarms and an EGR shut down sequence if necessary. Drainers for separation of the scrubber water and the EGR gas before collecting the scrubber water in a buffer tank. Oxygen sensor for measurement of the oxygen content in the scavenge air receiver. EGR control system for starting and stopping the EGR system and for controlling of the amount of EGR gas reintroduced to the scavenge air receiver. compression pressure (Pcomp). when operating the EGR system. Pcomp/ Pscav Incr. Increased hydraulic injection pressure can compensate for reduced heat release in the early part of the .1 Objective of the EGR test programme During 2009 and 2010 EGR was thoroughly investigated on MAN Diesel & Turbo’s 7MW 4T50ME-X test engine in Copenhagen.8 16.2 3. the heat release is only slightly affected by EGR.4 0 +4. Figure 3 shows the two very different operating areas for the compressor running with and without EGR.6 0.6 16.6 16. see Figure 2 below.82 1. The effect on NOx. both IMO Tier III (ECA) operation and Tier II (Non ECA) operation and the switch between the two modes were tested as well as different control strategies.83 2.2 Figure 2: Design of 6S80ME-C9 engine with EGR and two turbochargers.8 16. other system layouts will be relevant utilizing turbocharger cut valves for compensating the reduced exhaust gas during EGR operation. separator and pumps is not included in dSFOC). Increased Pscav has a positive impact on the SFOC penalty. For engines with more than one turbo charger.Blower and the WTS system.9 +3. Pscav Incr. Moreover. hydraulic injection pressure (Phyd) etc. This highlights the need for compensating means.18 1. Specific Fuel Oil Consumption (SFOC). Increased Phyd has a positive impact on CO and hereby also visible smoke. scavenge air temperature (Tscav). The system components described above is the current system design for engines with only one turbo charger. Incr. %) 17. Phyd Incr. The design of the EGR system is currently being matured and the target for MAN Diesel and Turbo is to integrate the engine related EGR components on the engine to an extent that is viable in order to keep the engine installation as simple as possible and with a minimum need for additional space around the engine. The reduced energy to the turbine side of the turbo charger.2 Test results from EGR test on 4T50ME-X engine The study of engine parameter variations during EGR operation revealed the following effects on SFOC and emissions as also seen from Table 1: Increased Pcomp/Pscav ratio has a positive impact on the SFOC penalty.17 2.0 4. Increased Tscav has a negative impact on the SFOC penalty. The investigation covered influence of variations on different engine parameters.6 3.9 3.12 2. NOx (g/kWh) No EGR Max. scavenge air pressure (Pscav).8 16.3 3. corresponding to utilisation of a turbocharger cut out solution.8 +1. maximum pressure (Pmax). Also the EGR scrubber was tested during the test programme in order to verify the performance with regard to particle trapping and SO2 removal.9 +3. carbon monoxide (CO) and hydro-carbons (HC) were studied. Both variable turbine geometry and cylinder bypass has been tested and seems to be able to compensate the decrease in scavenge air pressure. EGR EGR ref.5 +2.65 4. Increased Phyd has a positive impact on the SFOC penalty. Particulate Mass (PM).34 152 151 151 156 151 156 156 157 0 39 36 36 37 37 34 41 16. Figure 3: Turbocharger compressor maps running the engine with and without EGR. The objective of the test programme was to examine how IMO Tier III NOx compliance could be achieved by using high pressure EGR on a large two-stroke diesel engine. Tscav Tier III setup dSFOC (g/kWh) CO (g/kWh) Pmax (bara) EGR rate (%) O2 (vol. results in reduced scavenge air pressure and hereby negative effects on the SFOC.8 2.7 4. up to around 40%.0 16.0 +2. 4. Table 1: Test results from engine parameter variations at 75% engine load (auxiliary power for EGR blower.6 +0. As seen from Figure 4. 4.57 2. INVESTIGATION OF EGR ON 4T50ME-X TEST ENGINE 4. the EGR gas is introduced before the main engine coolers in order to ensure good mixing of the EGR gas and the compressed air from the turbo compressor. . P.5 17.0 6.0 4. - burning HFO with high content of sulphur and solids.5 18. cylinder cover. Alexander Maersk is installed with a 10. 50. Besides. is mainly to investigate the long term impact on the engine during EGR operation. Moeller Maersk and MAN Diesel and Turbo agreed on testing a High Pressure EGR system on one of A. reliable and safe operation. A retrofit EGR system was designed by MAN Diesel and Turbo from August 2008 to March 2009.0 22.5 19. piston rod.0 Figure 6: Arrangement of the EGR system on Alexander Maersk.0 18. EGR service test 5. The SO2 removal efficiency could more or less be controlled by the amount of added NaOH in the scrubber water.1 g/kWh of NOx at each engine load point 25. The scrubber performance was also measured during the EGR test programme and showed a particle trapping efficiency of around 70% according to ISO 8178 standard for PM measurements. 75 and 100% were proved during the test.0 IMO Tier 3 cycle value 20. The investigation on the 4T50ME-X test engine has showed that IMO Tier III NOx compliance is achievable by use of High Pressure EGR solely. piston. when It was necessary to exchange the two existing turbo chargers on the 7S50MC engine with one new larger turbocharger with variable turbine geometry in order to compensate for the reduced exhaust gas amount in EGR running mode.0 16.0 16.0 17.0 15. 5.Rec (wet. 100% load 75% load 50% load 25% load Specific NOx (g/kWh) 18.5 16. which still is ongoing. Components were manufactured and the main EGR components were installed in August 2009 at Lisnave shipyard in Lissabon in Portugal. A cycle value below 3. exhaust valve etc. The more detailed objectives is outlined below: Investigate impact of EGR operation on engine components: cylinder liner. Moeller Maersk’s smaller container vessels. An ABB A175L VTG turbocharger was chosen for this purpose. Investigate impact on the EGR components. 24. piston rings.0 5.126 kW.1 Objectives of the EGR service test The main objective of the service test. in order to adjust the system for easy.5 22.combustion.4g/kWh of NOx was obtained and also the Not To Exceed (NTE) level of 5.0 15. vol %) Figure 5: NOx emission at different engine loads as a function of oxygen content in the scavenging air.2 Preparation for EGR service test During the summer 2008.0 21.0 20. Hand over operation of the EGR system to the ship crew in order to get feedback on operation of the system.0 0.5 20.0 12.0 14. The EGR scrubber.5 21. EGR blower and the EGR cooler is integrated in one unit mounted on the fore end of the engine as seen from Figure 6 and 7. Figure 4: Heat release running with and without EGR. A. P.0 10. it was of interest to investigate how the main engine coolers were affected by the sulphur and particles in the EGR gas. On Alexander Maersk. NTE NOx 2. 127 rpm 7S50MC Mk 6 engine produced by Hitachi Zosen Cooperation. Reduce NOx with 50% during the test. The vessel pointed out was Alexander Maersk a 1092 TEU container feeder operating in the Mediterranean. in Scav. see Figure 5 below.0 Oxygen conc.0 8.0 19. the capacities and material of some selected specified EGR components for Alexander Maersk are listed: Table 2: List of capacities and materials for selected components specified for Alexander Maersk. e. Corrosion of non stainless components.6 bar Housing: coated mild Power: 240 steel. Scrubber 4. due to insufficient coatings.3 EGR service test results Currently the EGR system onboard Alexander Maersk has been in operation close to 500 hours with the engine running on HFO with 3% sulphur. Figure 9: Measurements of NOx reduction on board Alexander Maersk during a performance test. The challenges have mainly been related to the following issues: Figure 8: Left . Commissioning of the EGR system in automatic mode was also successfully completed. The EGR system is a push bottom system controlled from the engine control room. 20 m3 Coated mild steel WTS 30 m3/h Rotating parts is stainless separator steel and housing is coated mild steel. Figure 10: Piston rings before and after approx. Right – scrubber water samples before and after test of discharge scrubber water. Housing: coated mild steel. Figure 7: EGR unit on board Alexander Maersk Below in Table 2. 300 running hours in EGR operation on HFO. has been quite challenging due to HFO operation with high sulphur and solids content. except for the separator in the WTS system. Figure 10 shows the piston rings before and after approx. drainers. 316L Sludge tank Approx. EGR cooler element. EGR pipe and separator in the WTS system. Heavy corrosion has been experienced on the EGR cooler housing. which still is ongoing.5. The service test. . 300 running hours in EGR operation. Component Capacity Material s EGR Blower Flow: 4. The EGR system is currently operated by the ship crew. dp: 0.5 kg/s EGR Cooler Heat transfer: Copper tubes and nano 2300 kW coated copper fins. Until now. The thermo dynamical performance of the EGR components was successfully tested and the EGR components fulfilled the expected performance. EGR blower wheel.Alfa Laval testing a separator at 4T50ME-X test engine. different separators from Alfa Laval have been tested at the 4T50ME-X test engine. kW EGR Gas flow: Stainless steel 316L. which has to be started up on-site by the crew. NaOH tank 4 m3 Stainless steel 316L NaOH pump Flow: 60 l/min Teflon. In order to ensure an efficient WTS solution for the EGR system. the combustion chamber components and the exhaust gas path are not negatively affected by EGR operation.5 kg/s Wheel: Corten steel.g. Until this state of the service test the engine components is not affected by high pressure EGR operation. the overall conclusion is that High Pressure EGR on large two-stroke marine diesel engines burning HFO is a very promising measure for IMO Tier III NOx compliance. The challenges have so far been related to corrosion of EGR components. 50. have successfully shown that the discharge criteria’s can be met. NOMENCLATURE EGR : Exhaust Gas Recirculation ECA : Emission Controlled Area SCR : Selective Catalytic Reduction IMO : International Maritime Organisation HFO : Heavy Fuel Oil NTE : Not To Exceed SFOC : Specific fuel oil consumption [g/kWh] TEU : Twenty-foot equivalent units WTS : Water Treatment System S/D : Shut Down C/O : Change Over WMC : Water Mist Catcher Pscav : Scavenge air pressure [bara] Pmax : Maximum pressure [bara] Pcomp : Compression pressure [bara] Phyd : Hydraulic Injection Pressure [bara] Tscav : Scavenge Air Temperature [°C] PM : Particulate Mass ISO : International Organization for Standardization NOx : Nitrogen Oxides CO : Carbon Monoxide CO2 : Carbon Dioxide SO2 : Sulphur Dioxide HC : Hydro Carbon DISCLAIMER All data provided in this document is non-binding. This data serves informational purposes only and is especially not guaranteed in any way. In addition. components. In order to deal with corrosion challenges. The EGR system is operated in fully automated mode by the ship crew. and will be in the future. NaOH dosing and scrubber water quality control are equally important parameters to control. Right – almost no deposits when water carry over from EGR scrubber system is avoided.- Difficulties with controlling the dosing of the correct amount of NaOH. A cycle value below 3. Figure 10: Left – deposits of sodium sulphate. The EGR cooler element will be exchanged with a stainless steel element.4g/kWh of NOx was obtained and also the NTE level of 5. 8. The tests have also revealed which parameters to adjust in order to obtain the optimal trade off between SFOC. Furthermore. Depending on the subsequent specific individual projects. This will depend on the particular characteristics of each individual project. drainers and some valves in the WTS system. Regarding compliance on the scrubber water discharge. an important test platform for knowledge on how the engine and the EGR components are affected by EGR and for identifying by which means reliable and safe operation can be ensured. water carry over from the EGR scrubber system. deposits in the EGR system and deposits on the main engine coolers. especially specific site and operational conditions. The EGR service test on Alexander Maersk has until now. 75 and 100%. The service test has gained a lot of important learning and information on what the challenges are when running EGR on a HFO burning two-stroke marine diesel engine. a comprehensive repair of the EGR cooler housing and the EGR pipe from the blower to the connection on the charge air pipe have been completed due to insufficient coatings. 500 running hours with EGR on HFO with 3% sulphur showed no negative impact on vital engine . Water carry over from the scrubber system. were proved during tests. the following components have been exchanged with stainless steel: EGR blower wheel. Corrosion of EGR components and deposits in the EGR system is important to target. resulting in heavy deposits in the EGR system. the development in separator designs for this purpose.1 g/kWh of NOx at each engine load point 25. although there still is a need for further investigation and testing of the technology. caused by water carry over from the scrubber system. the relevant data may be subject to changes and will be assessed and determined individually for each project. NOx CO and HC. At current state. The test has after approx. iron sulphate and soot on main engine cooler top. CONCLUSIONS The comprehensive investigation in High Pressure EGR on large two-stroke marine diesel engines carried out at MAN Diesel & Turbo’s test centre in Copenhagen have proven that the IMO Tier III NOx emission limits coming in to force by January 1st 2016 are possible to meet with EGR.
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