Particle- and Gaseous Emissions from an LNG Powered Ship

Sep 30, 2015 - Today there is a large interest in LNG as a marine fuel, as a means to comply with sulfur and NOX regulations. Particles were studied i...
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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)