30 Air Monitoring - Biogas Focus
FTIR Solves Biogas Emissions Monitoring Challenge
Germany has created regulations and an incentive scheme to reduce the levels of formaldehyde (a carcinogen) in biogas plant emissions. However, this has created a challenge to those responsible for monitoring, and this article will explain how FTIR is being employed very successfully, to meet this challenge.
We have now supplied instruments to most of the key testing organisations as well as motor and system manufacturers in Germany. Happily, the feedback has been extremely positive because, as a portable analyser, the Gasmet FTIR systems are able to test more plants, more quickly, and this lowers costs.
One of the key issues facing the operators of biogas plants is the control of emissions whilst maintaining plant effi ciency. Emissions monitoring therefore plays an important role in plant management. However, in Germany it is necessary to monitor formaldehyde in addition to the more usual parameters such as particulates, sulphur dioxide, nitrogen oxides etc. Test and monitoring companies are therefore employing portable Gasmet FTIR analysers to measure emissions because formaldehyde monitoring is a great dealer simpler and much faster with FTIR than it would be by traditional laboratory techniques.
Germany’s large biogas industry produces emissions to air that are regulated by the Technical Instructions on Air Quality Control (TA Luft). As part of the approval process, the emissions from each plant have to be tested every three years. The TA Luft emission limit for formaldehyde is 60 mg/m³. However, the German Government’s fi nancial incentive scheme encourages process managers to lower their formaldehyde emissions to below 40 mg/m³. To be eligible for the EEG (Erneuerbare Energien Gesetz) scheme, plants must be tested every year.
Formaldehyde can be diffi cult to measure in hot, wet emissions, not least because it would dissolve in condensate if the sample gas is allowed to cool. Test engineers in Germany have therefore deployed portable (Gasmet DX 4000 and CX4000) FTIR analysers to measure formaldehyde, and a number of systems are currently in widespread use across Germany.
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The biogas industry in Germany has grown from 139 biogas plants in 1992 to almost 8,000 by the end of 2013, with an electrical capacity of about 3,400 MW – suffi cient for the energy needs of around 6.5 million households. Initially, biogas plants were built to handle the by-products of human and animal food production as well as agricultural waste, but with government incentives to generate renewable energy, farmers are now growing crops such as maize specifi cally for energy production.
Biogas is produced by anaerobic digestion or fermentation of biodegradable materials. The main constituent gases are methane and carbon dioxide, with small amounts of hydrogen sulphide and water. The products of biogas combustion are mostly carbon dioxide and water, but the combustion of biogas also produces formaldehyde.
Biogas-fuelled combined heat and power (CHP) plants are becoming a very popular source of renewable energy in many countries because they provide a reliable, consistent source of energy in comparison with wind and solar power. In addition to the renewable energy that these plants produce; the fermentation residue is a valuable product that can be used as a fertiliser and soil conditioner for agricultural, horticultural and landscaping purposes.
Exhaust Gas Tests
The exhaust emissions of each biogas plant are tested every three years for substances hazardous to air quality, such as particulates, carbon monoxide, nitrogen oxides, sulphur dioxide and formaldehyde. Most of these parameters can be measured on-site with portable equipment. However, in the early years and still to
Gasmet DX4000 portable FTIR analyzer
this day, the complexity of formaldehyde analysis has necessitated sampling and laboratory analysis – a time-consuming and costly activity.
In 2007 Wolfgang Schreier from the environmental analysis company RUK GmbH (now part of the SGS Group) started working on the use of portable FTIR gas analysers for formaldehyde analysis. The FTIR analysers are manufactured by Gasmet (Finland) and supplied in Germany by Ansyco GmbH, a Gasmet group company.
FTIR analysers are able to qualitatively and quantitatively analyse an almost endless number of gas species. However, Wolfgang Schreier says: “The Gasmet units are mainly employed for the measurement of formaldehyde, but while they are able to measure other parameters such as CO, NOx and Methane, they are not yet certifi ed for doing so in the emissions of biogas plants, unless an internal validation has been undertaken.
“The DX4000 proved to be the ideal instrument for this
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