An SCR system reduces hazardous nitrogen oxides (NOx) by using ammonia (NH3) and a catalytic converter. The term SCR stands for Selective Catalytic Reduction, which means that the ammonia only reacts with the nitrogen oxides under the influence of the catalytic converter material and not with other substances in the exhaust gases. Xeamos SCR systems operate with standard aqueous urea solutions (AdBlue, AUS32/40 or DEF) that decompose at temperatures above 200°C and supply the required ammonia to the process.
The type of catalyst applied depends on the required NOx reduction, available space in the engine room, fuel type and engine exhaust characteristics. During the design process an optimum match is made between engine and catalyst type and required volume. This enables our engineer to design a compact as possible solution while taking into account the design constraints regarding available back pressure, fuel type and design life time.
Xeamos urea injection systems use pressurised air atomization that is very reliable and allows a high urea injection rate per injector. The urea droplet size is very small which enables SCR operation at temperatures down to 230C with ultra low sulphur fuels. Depending on the geometry of the reactor housing one or multiple injectors can be applied. All system parts such as injectors, urea pumps and dosing units have been developed in-house.
Airless injection can also be applied for the next-generation modular SCR systems for engines below approx. 800 kW.
An SCR system is complex to control in all circumstances. The right amount of urea has to be injected to guarantee the correct emission reduction while preventing any ammonia slip from urea over-dosing. Dosing parameters are therefore adjusted for each specific engine. The system control and monitoring are performed by a state-of-the-art PLC-based closed-loop control system with advanced NOx Control Diagnostics (NCD). This means that the system is tamper-proof, meeting the requirements of the applicable legislation. Xeamos control systems are class-approved and ensure a reliable and safe operation. The controller allows for easy communication or integration with the ship’s AMS through a MOD bus protocol or analogue I/O. Xeamos systems offer remote monitoring to provide support to chief engineers when required. All system values and signals as well as events, warnings and alarms are recorded and stored in a non-erasable log file. All logged data can be easily uploaded through a remote connection for further analysis and reporting by Xeamos engineers.
Reactor housing design
The reactor housing for our SCR and/or DPF systems is designed for the specified operating conditions. The pressure drop, flow uniformity and temperature distribution are accurately simulated using advanced CFD software. Mechanical stress calculations are made with our FEM software tools using worst-case scenarios of maximum exhaust temperatures and pressures. The effect of low-cycle fatigue on the steel has to be taken into account to prevent premature failure of the system, especially with wet underwater exhausts. Different (stainless) steel types can be applied depending on the application and customer requirements.
The engine rooms in most ships have limited space for an exhaust system, making the need to integrate emission reduction and silencers inevitable. Using our knowledge of acoustics, we offer solutions to integrate DPF, SCR and silencers according to your requirements. The sound attenuation is tuned to the engine characteristics to give an optimum reduction of the ignition frequencies and its harmonics, suppressing that annoying exhaust hum.
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