This kind of set-up is also available as an explosion proof version – in all cases the maintenance for these process gauges is minimal with the measuring cell being easily accessible, the light source of the long life variety (being one of the few consumerables) and the operating procedures optimized towards ease of usage. These photo-transmission gauges can also be used to measure water in Ammonia, Butane, Ethyl chloride, Propane, Propylene oxide, Vinyl acetate, to name a few.
Online water measurement in bio-ethanol
With the implementation of the EU Bio-fuel directive in 2003 it is required of member countries of the EU to add 5.75% Bio-fuel by 2010 to their fossil fuel consumption to lower carbon emissions by 8% below their 1990 emissions. South Africa has ratified the UNFCCC in 1997 and the Kyoto protocols in 2005, and although not bound by the same directives as the EU member states, has a large interest in reducing its emissions, being the largest single emitter in Africa. To this effect the government has granted an incentive in the form of a reduction in the fuel levy.
Bio-ethanol is produced from the starch component in renewable plant materials such as sugar cane, maize, sorghum, etc – the advantage of bio-ethanol therefore is that it is an endless energy source and by virtue of its oxygen component allows for better combustion of the fuel used, thereby allowing the burning process to have less residue.
The production processes, however, cannot achieve 100% pure ethanol (alcohol) as it forms an azeotropic mixture with water – the best azeotropic ratio achievable is 95.4% ethanol / 4.5% water.
To achieve a higher purity, pressure swing distillation or drying agents have to be employed, for example. A further problem for motor vehicle owners using this new fuel blend, is that atmospheric water and ethanol can mix very easily which then causes other problems such as a lowering of the boiling point of the resultant mixture to about 78.1°C or a change of the evaporation pressure – this could, for example, lead to a situation where the recommended pressure value of 60 kPa cannot be maintained on a hot summers day.
Another problem of the mixture is higher corrosion in the fuel tanks of older vehicles – for instance, in New Zealand it is recommended that ethanol blended bio-fuel is stored for less than 2 months so as to not absorb too much atmospheric moisture.
It follows that it is very important to monitor the water content in the bio-ethanol production as a first step to maintaining quality control in order to reduce the above mentioned problems. To this effect photo-transmission meters lend themselves perfectly – the bio-ethanol can be piped directly through a measuring cell with transparent glass walls which prevents contamination of the fluid and allows containment of dangerous vapours inside the production piping. A near IR light source in the correct wave spectrum is then transmitted through the sample cell, on the other side of which is a receiver which compares the received wavelength to a comparative wavelength to calculate the amount of water present in the fluid sample as it flows through the measuring cell.