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Cimac Congress | Shanghai 2013
Thursday May 16th / 08:30 – 10:00
Aftertreatment – SCR Experience
Testing SCR in high-sulphur application
Kati Lehtoranta, VTT Technical Research Centre of Finland, Finland
Raimo Turunen, VTT Technical Research Centre of Finland, Finland
Hannu Vesala, VTT Technical Research Centre of Finland, Finland
Sami Nyyssoenen, VTT Technical Research Centre of Finland, Finland
Niko Soikkeli, Wärtsilä Finland Oy, Finland
Lucas Esselstroem, Wärtsilä Finland Oy, Finland
Room C
NOx and SOx emissions from ship exhausts are limited by IMO
ship pollution rules. NOx emission limits are set for diesel engines
depending on the engine maximum operating speed. Limits are set
globally (Tier I and Tier II) and in addition for emission control
areas (Tier III). Tier III standard is dated to 2016 and is expected to
require the use of emission control technologies. SCR is an available
technology capable of meeting this requirement. This technology
uses a catalyst and ammonia for the reduction of NOx to
elemental nitrogen. On the other hand, SOx limits require the use
of lower sulphur level fuels or aftertreatment systems, like scrubbers,
to decrease SOx emissions. Scrubbers might become popular
as they allow the use of inexpensive heavy fuel oil. The sulphur is
usually considered as poison to catalysts. In SCRs, a V2O5 catalyst
has been widely employed due to its high activity and sulphur tolerance.
Even so, sulphur-related challenges do occur. At high temperatures,
the SO3 can result in an unwanted visible plume, while
at low temperatures, the SO3 can react with the ammonia to form
ammonium sulphates, which deposit on and foul the catalyst. This
brings certain requirements for the SCR optimisation in high sulphur
applications. Ships utilise large engines, which require large
catalyst volumes to deal with the emissions. Installations to large
engine applications can be difficult and testing rather complex.
Only minor (or none) tuning of the parameters is possible in real
applications. In this study, a slipstream emission control test bench
is utilised to test smaller SCR units with a proper exhaust gas from
a medium-speed diesel engine. The test bench has an advantage
of easily tuned and controlled parameters (like temperature and
exhaust flow). A heavy fuel oil with a sulphur content of 2.5% is
utilised as test fuel. Two different SCR catalysts with a volume of
40dm3 are tested using engine loads of 100%, 75% and 50%. In addition,
different exhaust gas flow rates and temperatures, adjusted
by the test bench, are utilised in testing. The test bench utilises NOx
sensors placed upstream and downstream of the test SCR reactor.
In addition, the standard analyser to measure the NOx (chemiluminescence)
was in use. FTIR was used to measure the NH3. Hydrocarbons,
carbon monoxide and carbon dioxide were measured
as well. The effect of SCR on particle emissions was studied by collecting
particles on filters both before and after the catalyst. The
particle filters were further analysed for sulphates and organic and
elemental carbon. The results for both test catalysts show NOx conversions
of nearly 80% at 100% load and even 95% at 75% load.
The HC and PM emissions were also found to be reduced by both
catalysts. The organic carbon fraction of PM was reduced by the
catalyst as well as the sulphates. While the organic carbon reduction
can be explained by the oxidation in the catalyst ,the sulphates
are believed to be stored in the catalyst. Overall, the two catalysts
showed nearly the same results except in the case of a lower exhaust
flow (i.e. lower space velocity) were the behaviours differed.
Field experience of marine SCR
Johnny Briggs, IACCSEA, UK
Joseph McCarney, IACCSEA, UK
SCR is an established technology and has been used to remove
acidic NOx from the exhaust gases of engines, boilers and other
combustion processes for over 50 years. The first SCR demonstration
on a ship engine was conducted more than 30 years ago and
since then over 500 vessels have installed SCR technology. Today,
SCR is considered a proven, commercially available technology capable
of removing 95% or more of NOx in an exhaust gas. As such,
it is expected to be one of the major technical options capable of
meeting IMO Tier III standards. Whilst there has been considerable
success in the application of marine SCR, the experience in
the field is mixed and contrary messages have emerged. As part of
the IMO NOx review, the International Association for the Catalytic
Control of Ship Emissions to Air (IACCSEA) committed to
sponsoring an independent review of field experience of marine
SCR. A database comprising most of the shipping SCR installations
was compiled and a representative sample was surveyed. In
this paper we propose to explore the following findings from the
dataset and survey:
• The extent to which SCR has been applied to a wide range of
marine engine types, utilising different fuels (of differing sulphur
content) and operating over a range of engine conditions
over the past 30 years;
• The major problems that operators have had with SCR and a
description of how these issues were managed, resolved or mitigated;
• An outline of the most important lessons learnt that may be
applicable during and after the transition to IMO Tier III.
First operational experiences with a combined dry
desulphurisation plant and SCR unit downstream of
a HFO-fuelled marine engine
Ralf Juergens, Couple Systems GTmbH, Germany
In December 2011, Couple System successfully managed the commissioning
of a dry scrubber (DryEGCS) in combination with a
SCR catalyst. The application consists of an engine test bed on
which marine diesel engines up to an output of 24 MW are running.
The exhaust gases of the HFO-fueled engine are fed into the
dry scrubber, named DryEGCS, where the exhaust gas is cleaned
off of SOx in a magnitude of more than 99%. Particles are removed
in excess of 90%. The temperature of the exhaust gas is
maintained and represents the optimum temperature for the reduction
of NOx by the SCR catalyst. The SCR process requires the
injection of ammonia, which in this case is done in the form of an
aqueous ammonia solution. The installed SCR system is one of the
largest systems operated downstream of a marine diesel engine.
The combined DeSOx and DeNOx system meets all present and
future IMO regulations including a potential PM regulation. The
entire system is monitored by a continuous monitoring system
according to scheme B (MEPC.1849). The paper includes a full
technical description as well as operational data.
Urea SCR system for pollution control in marine
diesel engines
Yoshinori Izumi, IHI Corporation, Japan
Hiroaki Ohara, IHI Corporation, Japan
Hiroyuki Kamata, IHI Corporation, Japan
Hayato Nakajima, IHI Corporation, Japan
Takeshi Yamada, IHI Corporation, Japan
Mamoru Irie, Diesel United, Ltd, Japan
Kouji Moriyama, Diesel United, Ltd, Japan
Kenji Goto, Japan Marine United Corporation, Japan
70 SPECIAL
Schiff&Hafen | Ship&Offshore | May 2013