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Particle- and gaseous emissions from a LNG powered ship Maria Anderson, Kent Salo, and Erik Fridell Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 30 Sep 2015 Downloaded from http://pubs.acs.org on October 6, 2015
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Environmental Science & Technology
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Particle- and gaseous emissions from a LNG powered ship
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Maria Anderson* a, Kent Salo a & Erik Fridell a, b
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a
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96 Gothenburg, Sweden
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b
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*Corresponding author: Maria Anderson, Department of Shipping and Marine Technology,
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Chalmers University of Technology, 412 96 Gothenburg, Sweden; Tel: +46-31 772 2640; e-
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mail:
[email protected] (M. Anderson)
Department of Shipping and Marine Technology, Chalmers University of Technology, 412
IVL Swedish Environmental Research Institute, PO Box 5302, 400 14 Gothenburg, Sweden
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Abstract
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Measurements of particle number and mass concentrations and number size distribution of
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particles from a ship running on liquefied natural gas (LNG) were made on-board a ship with
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dual-fuel engines installed. Today there is a large interest in LNG as a marine fuel, as means
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to comply with sulphur and NOX regulations. Particles where studied in a wide size range
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together with measurements of other exhaust gases at different engine loads and different
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mixtures of LNG and marine gas oil. Results from these measurements show that emissions
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of particles, NOX and CO2 are considerably lower for LNG compared to present marine fuel
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oils. Emitted particles were mainly of volatile character and mainly had a diameter below 50
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nm. Number size distribution for LNG showed a distinct peak at 9-10 nm and a part of a peak
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at diameter 6 nm and below. Emissions of total hydrocarbons and carbon monoxide are
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higher for LNG compared to present marine fuel oils, which point at the importance of
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considering the methane slip from combustion of LNG.
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Keywords: LNG, ship emission, particle emission, gas emission, emission factor
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TOC/Abstract graphic
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PN
LNG
PM CO 2 NOX SO
PN PM CO2 NOX SO
CO THC
CO THC
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Present marine fuel oils
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1. Introduction
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An increased awareness regarding the emissions to air from ship operations has made the
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International Maritime Organization (IMO) implement regulations to reduce these emissions.
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The regulations consider emissions of nitrogen oxides (NOX) and sulphur oxides (SOX), of
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which the latter is regulated through the sulphur content in marine fuel oils. Since January
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2015, in sulphur emission control areas (SECAs), the allowed sulphur content in marine fuel
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oils is limited to 0.1 wt%. The global limit is 3.5 wt% S, with stricter regulations (0.5 wt% S)
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coming in 2020, or latest in 2025. The limits for NOX emissions are divided into three Tiers
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and depend on the engine speed (rpm) with stricter limits for high speed engines than for low
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speed. The strictest Tier III-limit enters into force in 2016, for new build ships and only in
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NOX emission control areas (NECAs). Tier I and II apply to a global level and Tier I for ships
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constructed after 1st of January 2000 and Tier II for ships constructed after 1st of January
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2011. Designated SECAs are the Baltic Sea together with the North Sea and the English
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Channel and coastal waters around North America and United States Caribbean Sea. The
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latter areas are also the only designated NECA.1
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The regulations in SECAs force the maritime sector to either use other fuel types than heavy
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fuel oil (HFO) or abatement technologies, like scrubbers, to comply with the regulations. One
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available fuel is natural gas. Natural gas has been used in stationary engines for a long time
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and the interest for natural gas as energy source for internal combustion engines has increased
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during the last decade.2 Natural gas can be used as compressed natural gas (CNG) or cooled 2 ACS Paragon Plus Environment
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Environmental Science & Technology
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to -162°C and liquefied to liquefied natural gas (LNG). This causes a huge reduction in
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volume and makes transportation on ships and trucks more feasible. Use of LNG, which
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mainly consists of methane (CH4, 87-99 mole%), reduce the emissions of NOX, SO2, particles
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and carbon dioxide (CO2) in comparison to present marine fuels.3 Reduced emissions of NOX
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are a result of reduced peak temperatures in the engine chamber during combustion.4 Today,
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most ships using LNG is operating in Norway. Globally, there are 34 ships using LNG, and
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more are under construction.5 The main challenge with designing LNG-powered ships is the
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fuel system. The tanks for storage of LNG needs special arrangements and take up more
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space than tanks for diesel fuel and the cargo space may therefore be reduced. Safety and
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regulations for handling LNG are also major issues. Further, the higher costs for LNG engines
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compared with regular engines and the low availability of LNG in ports have been important
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factors for the slow development.6
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To our knowledge, there are no existing studies that have reported measurements of particle
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emissions on-board ships running on LNG. A literature study found a number of studies that
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focus on particle emissions from engines running on CNG or LNG, primarily installed on
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buses.7-15 This study is a first attempt to assess the particle emissions from a ship running on
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LNG, with the aim to characterize the particle and gaseous emissions. The measurements
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were made on a cruise ferry running on LNG in the Baltic Sea. In order to have data for
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comparison, measurements were also made at a natural gas power plant running on CNG.
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2. Experimental
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The measurements were conducted in December 2013 on-board a cruise ferry, operating in
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the Baltic Sea, on one of the four lean-burn dual-fuel engines4 (DF-engine) installed (Wärtsilä
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8L 50 DF). The installed power was 7600 kW per engine. Both LNG and marine gas oil
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(MGO) were used for propulsion (properties presented in Tables 1 and 2, respectively). MGO
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was used as a pilot fuel and injected in small amounts for ignition of LNG. Around 1-5%,
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normally 1-2%, of the total energy to the engine came from MGO when running on LNG,
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with higher proportion of MGO at lower loads.
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Table 1: Properties and chemical content of the LNG used during the on-board
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measurements Day 1
Day 2
Methane (mole%)
92.54
92.34
Ethane (mole%)
6.27
6.3
Propane (mole%)
0.73
0.73
Nitrogen (mole%)
0.43
0.43
Ibutane (mole%)
0.05
0.05
Carbon dioxide (mole%)
0.002
0.002
Sulphur (ppm-mole)
