Since the 5th of July we know what is coming in the EU from 2018: stage V emission standards for NRMM (non-road mobile machinery). In addition to more strict limits on permissible emission of NOx, HC, and CO, particulate matter (mass and number of particles) have been focused upon
Even though this specific regulation affects engines used in non-road applications (e.g. on inland waterways vessels, construction machinery, handheld[ds_preview] machinery), it does reflect a more global trend in reducing the emission of NOx and especially particulate matter. For instance after a gradual introduction of global sulphur caps in marine fuel and special emission control areas (ECAs), focus was shifted to NOx- emissions with IMO tier III limits. Currently the tier III limits only apply to NECAs (Nitrogen ECA) which are in Northern America and the US Caribbean Sea. However, with reasonable certainty it can be assumed that the English Channel, North and Baltic Sea will also be declared as NECAs in 2021. Incentive schemes similar to a NOx fund (e.g. Norway) are also in discussion for EU coastal waters. Whereas the enforcement of IMO tier III limits depends on the built date of the vessel (keel laid), NOx funds and similar methods encourage retrofitting of NOx abatement systems (exhaust treatment systems) and punish non-compliance generally, irrespective of the built date of the vessel.
In either case of the IMO tier III emission limits or the EU stage V limits or NOx funds, compliance can no longer be achieved by adjustments of the combustion parameters alone. Essentially, either an exhaust treatment is introduced or the combustion is modified by reintroducing part of the exhaust gas. The most widely used and proven system for marine engines, as well as for on and off-road diesel engines, is the Selective Catalytic Reduction (SCR) which is often combined with a diesel particulate filter (DPF). In essence by introducing ammonia (for practical reasons introduced as a urea solution, e.g. AdBlue or diesel exhaust fluid—DEF) into the exhaust gas, the catalyst reduces NOx via a number of reactions to N2 and H2O. Correct dosing of ammonia/urea is important in order to not have any ammonia-slippage downstream of the SCR. Since the catalytic reaction requires a minimum exhaust gas temperature, careful consideration of placing the SCR within the exhaust stream has to be taken into account. If in addition to a SCR system a diesel particulate filter (DPF) is installed, feeding of additional heat may be required in order to regenerate (»burning« of collected particles) the particulate filter. In addition to temperature the exhaust differential pressure ( p) across the exhaust gas treatment system has to be carefully designed. Engine manufacturers allow only limited increases in backpressure in the exhaust system without voiding any (performance) guarantee of the engine itself.
The development team of Kontec takes all of these factors carefully into account and develops, either in cooperation with the engine manufacturer when developing a new engine or for retrofitting on installed engines, the best fitting solution in terms of exhaust gas cleaning performance and use of available space in/around the engine compartment not exceeding the allowable exhaust gas back pressure. Unfortunately, there is very little standardization of engines, load profiles, engine compartment sizing and used engine types in the maritime industry that maybe found across one specific car model for instance. Therefore, a supplier with in-depth technical expertise and equipment development/adjustment capabilities is required – off-the-shelve products will not work, latest fail at installation with positioning in exhaust stream, space requirements and performance. One project was particular tricky: A hybrid harbour tug with 700kW generators had very limited space in the engine compartment and in addition to IMO tier III NOx treatment also required a particulate filter. The solution was to develop a very compact SCR system with multiple redirection of the exhaust flow. This system had a differential pressure of <85mbar and received approval from Lloyds Register.
It is very helpful for the development of the exhaust cleaning systems, that Kontec has in-depth understanding of engine and engine systems: Kontec designs, develops and runs trials on engines for well-known car, truck and industrial engine makers world-wide.
It should be noted, that for commercial inland waterway vessels owned by German companies or individuals, a grant by the German Government for installation of exhaust treatment systems is available. For SMEs (German: KMU) up to 50% of eligible cost, 60% if based in certain development areas, are available as non-repayable grant.
NOx and PM emissions have a direct effect on health, whereas the first causes problems directly linked to the exposure, the second has a more medium to long-term effect. This is not surprising as PM, which can be smaller than 2.5 m, are recognised as a carcinogenic to humans (Group 1) [WHO, IARC]. The upcoming regulation in the EU will be applicable to a wide range of engines: from engines on inland waterways (differentiated between auxiliary and power) to construction equipment to handheld devices. Looking at a typical 210kW diesel propulsion engine for a boat on inland waterways that satisfies current emission standards (stage IIIa, 2004/26/EC), the same engine would have to perform significantly better under stage V: reducing CO by 30%, HC+NOx by 57% and PM by 66%. Whereas under stage V emissions of HC 1.0 and of NOx 2.1 shall not be exceeded. Stage IIIa is combined for both.There are no EPA (US) Tier IV limits for this engine, as it has less than 600 kW of power.
For the smaller engine in our example the EU stage V is applicable for type approvals from 1 Jan 2018 and for engines sold from 1 Jan 2019. Deadlines for the larger engine are one year later. Whereas the US tier 3 limits (EPA) apply for the smaller engine in this example from 2013 and for the larger engine from 2014, there are no tier 4 limits for the smaller engine. The larger engine needs to adhere to tier 4 from 2017. For all engines the SOx concentration in the exhaust is controlled by different maximum sulphur amount allowable in the appropriate fuel. Coastal regions already have very low sulphur contents (e.g. fuel EN590 0.001%; EU and US Emission Control Area 0.1%) whereas globally we will see 0.5% in either 2020 or 2025, down from currently 3.5%.
Origin of NOx molecules and PM
Nitric oxide (NO) is formed during the combustion process from air nitrogen (N2) as a function of temperature and residence time of nitrogen (»thermal NOx«) at high temperatures (>1,600°C), and by oxidization of hydrocarbon radicals (HCN, CN, NH, N) to NO (»prompt NOx«). Another source of NO are the nitric components in fuel (fuel nitrogen, Nf). NO is then oxidized at temperatures <800°C to NO2, whereas temperatures >1,200°C destroy NO2. Particulate matter consist of many different and very small particles, e.g. soot (carbon particles), ash and silicates. Formation of PM is very complex. For instance the formation rate of soot during the combustion of diesel is greater than with petrol following the higher content of polycyclic aromatic hydrocarbons and the higher ignition point of diesel. It is believed that the first soot particles occurring during the combustion (only 2 nanometre) act as nuclei, i.e. the starting point of forming greater particles. Formation of soot is affected inter alia by fuel injection process, combustion pressure and combustion chamber shape.
Author: Moritz Erling Fritsche
Five Oceans Maritime Asset Management
moritz.fritsche@five-oceans.de
Moritz Erling Fritsche
