Exhaust gas measurement using analysis hoses
Towards less air pollution in the shipping industry
To minimise air pollution in the shipping industry, exhaust gas cleaning systems – known as scrubbers – are used, amongst other measures. Scrubbers clean ship exhaust gases using water or dry granules. In the process, pollutants – in particular sulphur oxides, soot and fine dust particles – are filtered out. The filtered pollutants are then temporarily stored in tanks and disposed of onshore.
In addition, the pollutant levels in the exhaust gases are continuously monitored on board. To do this, a small amount of exhaust gas is channelled from the funnel to a gas analyser in the control room located directly adjacent to it. Sensors measure the pollutant levels and trigger an alarm if the readings exceed the normal range.
Accurate measurement results thanks to intelligent temperature control
eltherm’s electric trace heating systems are used on ships to maintain the temperature of exhaust gases from the sampling point to the analytical measuring instrument. If the temperature of the medium drops, there is a risk of condensation, which can lead to blocked pipes and inaccurate measurement results. It is therefore essential to prevent the temperature from falling below the dew point.
Depending on the type of exhaust gas to be monitored – such as sulphur dioxide (SO₂), nitrogen oxides (NOₓ), carbon monoxide (CO) or carbon dioxide (CO₂) – the required temperature range and the dew point vary. For typical marine exhaust gases, the dew point lies between approximately 150°C and 180°C. Heated analysis tubes must therefore reliably maintain temperatures of typically 180°C to 220°C throughout the entire transport path. The components used must withstand the specific challenges of the marine environment: constant vibrations and mechanical shocks from ship engines, high humidity and salty air with an increased risk of corrosion, significant temperature fluctuations between the engine room, deck routing and the analysis cabinet, as well as stringent explosion protection requirements in potentially hazardous areas on board.
Analyser hoses are the preferred solution for trace heating in emissions measurement. A heated analysis hose consists of one or more media-carrying inner cores (made of PTFE, PFA or stainless steel), a temperature sensor, heating cable, insulation, an outer sheath and an end cap. In accordance with customer-specific requirements and specifications, each heated hose is designed by our experienced application engineers and subsequently manufactured at our own production facility. For subsequent use, heated analysis hoses are usually integrated into the permanent structure of the system.
Key facts
- Temperature control from the sampling point to the measuring instrument
- Prevention of condensation
- Prevention of inaccurate measurement results
- Reduction of air pollution
In addition to the heating element, a complete trace heating system for marine exhaust gas measurement comprises temperature sensors (typically thermocouples or PT100 resistance sensors) for continuous monitoring along the sampling line, controllers to regulate the heating output in order to maintain the temperature safely above the dew point, alarm and monitoring systems that detect faults such as line breaks, short circuits or temperature deviations and report them to the control room, as well as connection and termination kits for safe, reliable and watertight electrical connections – particularly important in potentially explosive atmospheres on board.
FAQ
‘Condensation’ refers to the transition of a substance from a gaseous to a liquid state.
During the combustion of exhaust gases, the dew point is approximately 150–180°C, depending on the gas being measured. If the temperature of the components is lower than this, condensation of the exhaust gases begins. This can lead to blocked pipes, inaccurate measurement results and even damage to the analysis system.