6.2.1 SETUP AND DESCRIPTION OF THE TESTED EQUIPMENT ALONG WITH MEASURING TECHNIQUES

A test bench has been developed (as shown in the Figure 1) in order to ex­amine the emissions from a prototype downdraft stove. The test bench is designed in such a way that it can facilitate the analysis of dust composition.

For the determination of flue gas and combustion chamber tempera­ture profiles, the thermocouples of Type K (manufactured by the company “Newport Electronics GmbH”) have been used. For this purpose, a set of various thermocouples has been inserted into the grate, in the middle of upper and lower combustion chambers as well as in the walls of the lower combustion chamber. Moreover, the pressure conditions were recorded with the help of pressure sensors, inserted into the combustion chambers (upper and lower) as well as into the exhaust pipe. The measurement of static and dynamic pressures in the flue gas has been done with the aid of Prandtl tube produced by the company “Testo AG”. The continuous transmission and data recording of Prandtl tube and pressure nozzles in the combustion chamber is carried out through data logging module provid­ed by the company “Ahlborn”. The data of the thermocouples have been recorded through a data logger of the company “National Instruments” along with the help of the software “Labview”.

The emissions coming out of the stove are measured by means of a gas analyzer which consists of a Fourier Transform Infrared Spectrometer (FTIR, Manufacturer: Calcmet), a Flame Ionization Detector (FID, Manu­facturer: Mess- & Analysentechnik GmbH, Typ: thermo-FID ES) and a paramagnetic oxygen analyzer (Manufacturer: M&C, Type: PMA 100). The infrared spectrum of FTIR can measure simultaneously organic as well as inorganic components. At the moment, about 44 different compo­nents can be recorded through FTIR.

The Volatile Organic Compounds (VOC) can be recorded by means of both FID and FTIR measuring devices. In case of VOC, the concentrations ranging under 50 mg/m3 (at standard conditions i. e. =0°C, 1 atm) can be considered from the FID measuring device. On the other hand, the values above 50 mg/m3 (at standard conditions i. e. =0°C, 1 atm) can be assumed from the FTIR measuring device. Following parameters can be measured simultaneously:

1. Oxygen O2 (paramagnetic analyzer)

2. Carbon dioxide (FTIR)

3. Moisture in the flue gas i. e. H2O (FTIR)

4. Carbon monoxide CO (FTIR)

5. Volatile organic compounds (VOC) as organic carbon (Org.-C) (FTIR and FID)

6. Nitrogen oxide as nitrogen dioxide equivalent (NO2equi) (FTIR)

7. Sulphur dioxide SO2 (FTIR)

8. Methane CH4 (FTIR)

9. Organic compounds like, alkanes, alkenes, aromatics, aldehydes as well as ketones (FTIR)

10. Flue gas temperature, gas velocity and draft conditions.

The recording of the above mentioned parameters took place on con­tinuous time basis except for the dust measurement. During the evaluation of the data, the average values of the pollutants were calculated for each dust sampling cycle whereas each cycle lasts for 30 minutes. With the aid of a chimney fan, a constant negative pressure of 12 Pa has been main­tained in the chimney stack in order to achieve a fuel thermal output from 8 to 9 kW.

The gravimetric analysis of total amount of dust was done in accor­dance with VDI guidelines 2066-1, according to which a partial volume flow must be taken in isokinetic manner out of the main flue gas stream. In this process, the accompanied particles can be deposited on the already weighed plane filter. Since the filter housing is located outside the flue gas pipe, this sampling procedure is termed as “outstack process”. The filter system was heated up with a heating jacket in order to prevent the falling down of temperature under saturation temperature of the flue gas. The temperature of the filter was maintained at 70°C so that the semi-volatile hydrocarbons could also be deposited on the filter. After the experiment, the deposited dust amount was determined gravimetrically and then can be specified by taking into consideration the measured partial volume and oxygen concentration. The plane filter was made of micro-glass fibers hav­ing a diameter of 45 mm.