燃烧学的理论方法及应用(船舶排放).ppt

1、REGULATIONS：,There are a number of national and international regulatory organizations that propose limitationson NOx as well as other harmful emissions. The International Maritime Organization (IMO) , through the International Convention for the Prevention of Pollution from Ships (MARPOL, Annex VI)

2、 regulates this on a global level. They have developed an approach to reducing green house gas (GHG) emissions, including NOx. Member countries of the IMO must therefore adhere to the regulations that they have put forth. However, some organizations have committed to adopting regulations that are mo

3、re stringent. The Environmental Protection Agency (EPA) of the United States and the European Union (EU) are two such examples. These regulatory bodies have used the IMO criteria as a starting point for GHG emissions reduction but are developing certain aspects of the policy that are stricter than t

4、hat of the IMO.,International Maritime Organization (IMO) is an agency of the United Nations which has been formed to promote maritime safety.IMO ship pollution rules are contained in the “International Convention on the Prevention of Pollution from Ships”, known as MARPOL 73/78. On 27 September 199

5、7, the MARPOL Convention has been amended by the “1997 Protocol”. Annex I Regulations for the Prevention of Pollution by Oil Annex II Regulations for the Control of Pollution by Noxious Liquid Substances in Bulk Annex III Prevention of Pollution by Harmful Substances Carried by Sea in Packaged Form

6、Annex IV Prevention of Pollution by Sewage from Ships Annex V Prevention of Pollution by Garbage from Ships Annex VI Prevention of Air Pollution from Ships MARPOL Annex VI sets limits on NOx and SOx emissions from ship exhausts, and prohibits deliberate emissions of ozone depleting substances. was a

7、dopted September 1997 andentered into force on 19 May 2005.,国际海事组织IMO 批准了修订的船舶废气排放规则:,IMO第57届海洋环境保护委员会于2008年3月31日4月4日在伦敦召开。会上批准了对MARPOL 附则VI修正案，以减少船舶有害气体的排放。 硫氧化物（SOx） 主要的变化是逐步减少船舶硫氧化物(SOx)的排放, 燃油含硫量从当前4.50%减少到3.50% 从2012年1月1日生效，然后减少至0.50 %从2020年1月1日起生效，并最晚不迟于2018年完成可行性评估计。 硫排放控制区（Sulphur Emission C

8、ontrol Area-SECA）的适用标准将减少到1.00%（当前为1.50 %），从2010年1月1日起生效，并进一步减少的0.10 %，于2015年1月1日起生效。 目前的附则VI，指定了两个硫排放控制（SECA），也就是波罗地海（the Baltic Sea）和北海（the North Sea），也包括英吉利海峡（the English Channel）。,逐步减少发动机氮氧化物(NOx)排放的建议获得通过。Tier I 适用于2000年1月1日后2011年1月1日前安装在船上的发动机，即氮氧化物的排放量为17 g/kWh，已在现在的附则VI中有规定。 Tier II将氮氧化物的排放量

9、减少到14.4 g/kWh，适用于2011年1月1日后建造或装船的发动机。 Tier III将氮氧化物的排放量减少到3.4 g/kWh，适用于2016年1月1日安装在船上的发动机，但仅在排放控制区（Emission control Area）适用，在非排放控制区，等级II仍然适用。 对1990年1月1日后2000年1月1日前安装的输出功率为5000 kW，单缸排量为90L或超过90L的柴油发动机，海洋保护环境委员会（MEPC）同意用17.0 g/kWh的氮氧化物排放标准。 海洋环境保护委员会（MEPC）批准了氮氧化物技术规则修订草案，并在2008年出台修订的氮氧化物技术规则。新的技术规则包括新

10、的第7章，对2000年前发动机氮氧化物排放进行了规定，此外还包括对现有发动机的直接测量和进行监测的方法以及发证程序，以及对适用等级II和等级III的发动机的测试。,氮氧化物(NOx),废气清洗系统(Exhaust Gas Cleaning Systems) 本次会议同意将对废气清洗系统中间冲洗水的排放标准纳入到修订的废气清洗系统的导则中。 挥发性有机物（VOCs） 本次会议批准了（Volatile Organic Compounds）挥发性有机物管理计划导则的草案。 挥发性有机物管理计划的目的是为了确保适用于附则VI第15条的液货船，能防止或者将挥发性有机物的排放减少到可能的程度。 附则VI第

11、15条要求缔约国向IMO递交一个通报，该通报应包括所控制的液货舱尺寸、液货所需蒸汽控制系统及所采取得控制措施生效的日期等信息。 海洋环境保护委员会通知IMO秘书处邀请国际化标准组织(ISO)考虑燃油标准的制订，重在强调空气质量、船舶安全，发动机性能以及船员健康并推荐给IMO考虑。,温室气体(GHG) 本次会议批准了秘书长关于加快温室气体排放工作的建议，特别是二氧化碳CO2排放指数方案的制订以及二氧化碳CO2排放基线调查的开展。温室气体排放工作组编写了下一步实际工作计划包括控制CO2排放的短期及长期措施，该计划获得了海环会批准。 短期措施包括建议建立全球航运燃油税征收方案（global levy

12、 scheme）以减少温室气体排放。根据该计划，所有从事国际航运的船舶将需缴纳基于每吨定值的燃油税。 GHG工作组确认的长期的措施获得了海环会的批准并需进一步研究，这些措施包括：船舶设计的技术措施；使用替代燃料； 新船的CO2-设计指数； CO2运行指数的外部查验；统一的CO2运行指数限制以及对不符合的惩罚；排放交易机制（Emissions Trading Scheme-ETS）和/或清洁发展机制(CDM),以及港口基建费征收中的CO2排放因素。,NOx Emission Standards,NOx emission limits are set for diesel engines depe

13、nding on the engine maximum operating speed (n, rpm), as shown in Table 1 and presented graphically in Figure 1. Tier I and Tier II limits are global, while the Tier III standards apply only in NOx Emission Control Areas.,Figure 1. MARPOL Annex VI NOx Emission Limits,Emission Control Areas. Two sets

14、 of emission and fuel quality requirements are defined by Annex VI: (1) global requirements, and (2) more stringent requirements applicable to ships in Emission Control Areas (ECA). An Emission Control Area can be designated for SOx and PM, or NOx, or all three types of emissions from ships, subject

15、 to a proposal from a Party to Annex VI.Existing SOx Emission Control Areas include the Baltic Sea (adopted: 1997 / entered into force: 2005) and the North Sea (2005/2006). Future Emission Control Areas could also include zones around pollution sensitive ports.,Tier II standards are expected to be m

16、et by combustion process optimization. The parameters examined by engine manufacturers include fuel injection timing, pressure, and rate (rate shaping), fuel nozzle flow area, exhaust valve timing, and cylinder compression volume. Tier III standards are expected to require dedicated NOx emission con

17、trol technologies such as various forms of water induction into the combustion process (with fuel, scavenging air, or in-cylinder), exhaust gas recirculation, or selective catalytic reduction. Pre-2000 Engines. Under the 2008 Annex VI amendments, Tier I standards become applicable to existing engine

18、s installed on ships built between 1st January 1990 to 31st December 1999, with a displacement 90 liters per cylinder and rated output 5000 kW, subject to availability of approved engine upgrade kit.,Testing. Engine emissions are tested on various ISO 8178 cycles (E2, E3 cycles for various types of

19、propulsion engines, D2 for constant speed auxiliary engines, C1 for variable speed and load auxiliary engines). Addition of not-to-exceed (NTE) testing requirements to the Tier III standards is being debated. NTE limits with a multiplier of 1.5 would be applicable to NOx emissions at any individual

20、load point in the E2/E3 cycle. Engines are tested using distillate diesel fuels, even though residual fuels are usually used in real life operation. Further technical details pertaining to NOx emissions, such as emission control methods, are included in the mandatory “NOx Technical Code”, which has

21、been adopted under the cover of “Resolution 2”.,Sulfur Content of Fuel Annex VI regulations include caps on sulfur content of fuel oil as a measure to control SOx emissions and, indirectly, PM emissions (there are no explicit PM emission limits). Special fuel quality provisions exist for SOx Emissio

22、n Control Areas (SOx ECA or SECA). The sulfur limits and implementation dates are listed in Table 2 and illustrated in Figure 2. Heavy fuel oil (HFO) is allowed provided it meets the applicable sulfur limit (i.e., there is no mandate to use distillate fuels). Alternative measures are also allowed (i

23、n the SOx ECAs and globally) to reduce sulfur emissions, such as through the use of scrubbers. For example, in lieu of using the 1.5% S fuel in SOx ECAs, ships can fit an exhaust gas cleaning system or use any other technological method to limit SOx emissions to 6 g/kWh (as SO2).,Figure 2. MARPOL An

24、nex VI Fuel Sulfur Limits,EU Standards for Non-Road Engines（April 2004）,Stage III/IV limits are harmonized with the EPA Tier 3/4 standards.,The Environmental Protection Agency of the United States has been protecting human health and the environment since 1970. Like the EU, the EPA has adopted the r

25、egulations issued by the IMO but has used it as a foundation for a more stringent policy for marine emissions (for non-road engines).The EPA regulation system is divided into three tiers that are meant to progressively lower emissions. Tier 1 standards are equivalent to the MARPOL Annex VI NOx limit

26、s and were voluntary when first implemented but mandatory by 2004. The Tier 2 standards for all engine sizes, which are more restrictive than Tier 1, are to be in place by 2007. Tier 3 standards for engines rated over 37 kW (50 hp) will phase-in from 2006 to 2008. The Tier 4 standards that currently

27、 exist do not apply to marine diesel engines. However, Tier 4 criteria were issued along with an Advance Notice of Proposed Rulemaking, which outlined the intended future emission standards for marine diesel engines.,Environmental Protection Agency (EPA),EPA Tier 2 Marine Emission Standard,Overall t

28、he EPA regulations, like those of the EU, are more restrictive than IMO MARPOL Annex VI.The EPA policy for marine engines requires better engine cooling, electronic controls and other design modifications. Also, as with the Stages of the EU system, the standards outlined in the Tier system list spec

29、ific restrictions for a number of air pollutants (e.g. PM, HC, CO and NOx), while IMO does not .,Combustion in High Speed Diesel Engines,ASI- After the Start of Injection,Conceptual diesel Spray Combustion Model,From SAE paper 1997 -970873, Society of Automotive Engineers, Inc.),1、柴油(约350K)喷入气缸内后，热空

30、气 (约950K) 卷入并加热燃油，油束破裂。当燃油被热空气加热至约650K时，在浓混合气区(燃空当量比约4.0，当地温度约825K)出现预混合火焰，生成大量富油燃烧产物 (CO、未燃 HC、 PM)当地温度升高到约1600K，此时的放热量约为总放热量的10%-15% 。 2、在油束外围出现扩散火焰层，富油燃烧产物不断进入扩散火焰层进行扩散燃烧，产生约2700K的高温，使 PM氧化，并生成CO2和水蒸汽。同时，扩散火焰层的高温使空气中的N2和O2反应，生成大量NOX。扩散燃烧放热量占总放热量的85%-90%。,There are a number of different formation

31、mechanisms responsible for NOx in combustion processes. The relative importance of these different mechanisms is strongly affected by the temperature, pressure, flame conditions, residence time and concentrations of key reacting species.The reacting species can potentially proceed through a number o

32、f different chemical mechanisms resulting in the formation of NOx. At the temperatures greater than 2000K oxygen combines with nitrogen to form oxides of nitrogen. Initially, NO is formed, then during the gas expansion process in the cylinder a portion of the NO converts to form nitrous oxide (N2O)

33、and nitrogen dioxide (NO2).The combination of NO, NO2 and N2O is known as NOx.,NOx Formation,生成NO主要化学反应链见下图，该反应链已得到大多数研究人员的认可。,在燃烧过程中生成的氮氧化物主要源于燃烧空气中的氮气(N2)和燃料中的有机氮。在燃料中如有机氮的重量含量大于1，NO的最终排放通常会增加1030。在燃油的雾化过程中，这些有机氮会从燃料中释放出来， 并快速生成氢氰化物(HCN)和氨气(NH3 )。,Thermal NO,The thermal mechanism, also known is th

34、e extended Zeldovich mechanism, is responsible for the majority of NOx emissions from diesel engines when peak combustion temperatures exceed 2000K.Since temperatures of this magnitude are desirable to maximize engine efficiency, this mechanism has been studied extensively and is fairly well underst

35、ood. The three chemical reactions that are important in this mechanism are: O + N2 = NO + N 1 N + O2 = NO + O 2 N + OH = NO + H 3 The overall reaction rate for this mechanism is slow and it is very temperature sensitive. As a consequence, thermal NO only appears in significant quantities in the post

36、 combustion. Also, the actual NO concentration from this mechanism deviates significantly from equilibrium concentrations.This gives this mechanism a very strong time dependence that is important for low speed engines.,Thermal NO,The forward rate of reaction 1 and the reverse rates of reactions 2 an

37、d 3 have strong temperature dependencies. Therefore, this mechanism is very important at higher temperature and at air/fuel mixtures that are close to stoichiometric. Its contribution to NOx emissions is almost insignificant at temperatures below 1700K, but is strongly accelerated as temperature inc

38、reases above 2000K. The temperature sensitivity of this mechanism also means that as the temperature in the combustion chamber drops during the expansion stroke, the NO concentration freezes shortly after top dead centre. Post combustion equilibrium concentrations of O and OH are very important for

39、this mechanism.Factors that increase or decrease the concentrations of these radicals can have a significant impacton NO from this mechanism.,Prompt NO,The prompt NO mechanism, also known as the Fenimore mechanism, is very rapid and results in NO formation in the combustion zone. The most important

40、pathway for prompt NO is initiated by the rapid reaction of hydrocarbon radicals from the fuel with molecular nitrogen, leading to the formation of amines or cyano compounds that subsequently react to form NO. The most important initiation reaction for prompt NO is: CH + N2 = HCN + N 4 Subsequent ra

41、pid conversion to NO is strongly affected by O and OH. Prompt NO is most significant when combustion occurs at fuel concentrations higher than stoichiometry where there is a high concentration of hydrocarbon radicals to form HCN and the concentrations of O and OH are still high enough to cause the H

42、CN to proceed to NO through the following reaction sequence:,HCN + O = NCO + H 5 NCO + H = NH + CO 6 NH + H = N + H2 7 N + OH = NO + H 8 The rates of these reactions are not very sensitive to temperature. Reactions are rapid and the sequence results in NO formation in the flame zone. High temperatur

43、es do not affected prompt NO to the same extent as thermal NO.,Prompt NO,Zeldovich mechanism反应链 Thermal NO 对于反应温度是非常敏感的。通过计算流体动力学的仿真模拟计算和燃烧实验发现：当温度低于1700K时，NO的生成速率比较缓慢；温度上升，特别当温度大于2000K，NO的生成度， 并在高温时尽可能地减少供氧量，可以有效地降低NO的生成和排放。 然而Fenimore mechanism反应链Prompt NO对于反应温度是非常不敏感。燃料中如有机氮在燃油雾化过程中将从燃料中释放出来， 会快速

44、生成氢氰化物(HCN)并在较低的温度下(小于1100K )反映生成NO 。,N2O Pathway Another NO formation mechanism important in combustion is the N2O pathway. The initial reaction for this pathway is the three body reaction: O + N2 + M = N2O + M 9 While N2O generally reverts back to N2, this is not always the case. Under conditions

45、where the airfuel ratio is lean, NO can form through either of the following two reactions: N2O + O = NO + NO 10 H + N2O = NO + NH 11 This NO formation route is fuel and pressure dependent. At higher pressures and lower temperature, the three-body initiation becomes competitive with the O + N2 react

46、ion in the thermal mechanism.,Fuel Nitrogen Many heavy fuel oils contain organic nitrogen bound to the fuel molecule. This nitrogen can react to form additional NO. The extent of the conversion of fuel nitrogen to NO is nearly independent of the identity of the model compound, but is strongly depend

47、ent on the local temperature and stoichiometry and on the initial level of nitrogen compound in the fuel-air mixture. The pathway that fuel nitrogen follows to form NO depends on whether the nitrogen is bound to an aromatic ring or an amine. If the fuel nitrogen is bound to an aromatic ring, the nit

48、rogen in the fuel forms hydrogen cyanide (HCN). In the flame, equilibrium exists for the reaction HCN + H = CN + H2 and the nitrogen would form NO through a mechanism that is essentially that of prompt NO.,If however the fuel nitrogen is bound to an amine, ammonia (NH3) would form quickly in the fla

49、me zone. In large radical pools, the NH compounds are in equilibrium: NH3 = NH2 = NH = N 12 The important reactions for forming NO from this radical pool are : NH2 + O - NHO + H 13 NH2 + O2 - NHO + OH 14 HNO + X - NO + XH 15 HNO + M - NO + H + M 16,NOx in Diesel Flames The critical flame zone in Die

50、sel combustion for NO formation is the diffusion flame that surrounds the jet. In normal Diesel combustion, the fuel hydrocarbon radicals are broken down into fuel fragments, H2 and CO in the partially premixed zone the core of the fuel jet. While NO can form in partially premixed flames, the temper

51、ature of this zone in Diesel engines is generally too low to result in significant NO formation. The fuel fragments, H2 and CO from the core of the jet are the fuel that feeds the outer diffusion flame.,NOx in Diesel Flames Under diffusion flame conditions fed with hydrocarbon fragments, H2 and CO,

52、the NO formation mechanisms mentioned can all play an important role. Thermal NO is especially important when peak temperatures in conditions exceed 2000K. Prompt NO will almost certainly be produced from hydrocarbon fuel fragments and its relative role would tend to increase as measures such as cha

53、nges in combustion phasing are taken to lower combustion temperatures to reduce thermal NO.The importance of the N2O mechanism under Diesel engine conditions has also been recognized. Its relative importance is increased under conditions of increased turbulence . It is especially important to consid

54、er the NO formed from organic fuel nitrogen in engines burning heavy fuels. Most of these fuels contain significant amounts of nitrogen. The relative importance of fuel nitrogen would increase as other measures are taken to reduce NOx formed by other mechanisms.,NOx REDUCTION GENERAL OVERVIEW,Method

55、s to reduce NOx emissions may be categorized as either Primary or Secondary. Primary methods reduce NOx formation at the source in the engine and include methods such as engine tuning/modifications and water based technologies. Secondary methods reduce NOx in the exhaust gas by downstream treatment

56、(reduction of NOx after formation in the exhaust). Although some secondary methods are very effective, for example, Selective Catalytic Reduction (SCR) has a reduction capability of up to 95%, overall costs are typically higher. Primary methods typically have higher initial costs, usually associated

57、 with the modifications to the engine, but the overall expense is considerably less. The effectiveness of different NOx reduction methods varies considerably. Data is oftenmanufacturer claimed and effectiveness can be dependent on the specific engine, installation and load conditions.,NOx Reduction

58、Methods,1. Intake air humidification / water injection 2. Stratified fuel water injection 3. Direct water injection (DWI) with a “two-needle type” fuel and water injection nozzle 4. DWI with a “separate water injection nozzle” 5. Fuel-water emulsion,Water-Based Emission Control Technologies,The effe

59、cts of this DWI at both an earlier timing ( EDWI) and a later timing (LDWI) on combustion were clarified mainly by high speed visual studies of burning sprays.,Humid Air Motor (HAM) (4-Stroke),Diagram of HAM principle,1.Sea water injection into the charge air by an add. 2.HAM vessel between TC and charge air manifold 3.HT-cooling water and/or exhaust gas heat used for water preheating 3.CAC bypassed 4.NOx reduction: 65% (with additional heat),NOx Humidity T