HEATING CHAMBER FOR MEASURING CARBONACEOUS AEROSOL AND A DEVICE COMPRISING THE SAID CHAMBER

Abstract

The present invention belongs to the field of systems adapted for detection and quantification of carbonaceous aerosol. It relates to an improved heating chamber for a device for measuring carbonaceous aerosol, the chamber comprising at least: an upper part and a lower part with a ring for closing and holes for pins through which heaters receive the voltage needed for heating; an inlet for leading the sampled air to a filter and a system of valves, which regulates the sampled air flow and air flow during the analysis; two heaters encasing the filter, each heater comprising at least a housing and a heating wire, wherein the first heater is installed in the upper part and the second heater is installed in the lower part, wherein the distance of the heaters from the filter is from 1 to 10 mm, and wherein the heaters are controlled with electronics; and an outlet for leading the created CO.sub.2 towards a CO.sub.2 detector.

Claims

1. A heating chamber for a device for measuring carbonaceous aerosol, characterized in that the chamber comprises: housing of the heating chamber with two heaters (15) encasing a filter (16), the heaters (15) being arranged to be controlled with suitable electronics from the exterior of the chamber, wherein the housing of the heating chamber and the heaters (15) are made of stainless steel, one of the said heaters (15) is placed above the filter (16), while the other heater (15) is placed below the filter (16), and the distance of the heaters (15) from the filter (16) is from 1 to 10 mm.

2. The heating chamber according to claim 1, characterized in that it comprises at least the following: an upper part (11) and a lower part (12) with a ring (13) for closing and holes (14) for pins through which the heaters (15) receive the voltage needed for heating, wherein all holes (14) are provided with airtight seals, which withstand heating up to 300° C.; a filter (16) located between the upper (11) and lower part (12); an inlet (1a) for leading the sampled air to the filter and a system of valves, which regulates the sampled air flow and air flow during the analysis; two heaters (15a,15b) comprising at least a housing of the heater, pins for connection with electronics for controlling heating, these pins being welded to a heating wire (153), wherein the first heater is installed in the upper part (11) and the second heater is installed in the lower part (12) of the chamber housing, wherein the distance of the heaters from the filter is from 1 to 10 mm, and wherein the heaters (15) are controlled from the exterior with electronics comprising at least a voltage driver and voltage clamps; and an outlet (1b) for leading the created CO.sub.2 out of the chamber towards a CO.sub.2 detector.

3. The heating chamber according to claim 1, characterized in that each heater (15) comprises a steel housing also serving as the holder of the filter, wherein the following components are housed within the said housing: the heating wire (153) shaped as winding line to cover as much surface of the filter (16) as possible; suitably shaped ceramic pins (155) for protecting the heating wire from short circuits due to the metal (steel) housing; and at least one pin (154) welded to the heating wire (153) for connection to the electronics in order to allow heating of the heating wire (153) by applying suitable voltage.

4. The heating chamber according to claim 2, characterized in that the heating wire (153) is made of material that does not release carbon upon heating, the preferred option being ferritic iron-chromium-aluminium alloy.

5. The heating chamber according to claim 1, characterized in that said heaters (15) are controlled by electronics, the main component of the latter being a voltage driver, one for each of the heaters, wherein the voltage driver through contact pins (154) of the heaters regulates the voltage on the heating wire (153) with 0.1 V precision, wherein the power of the heaters is measured with a voltage clamp.

6. The heating chamber according to claim 1, characterized in that said electronics turn on the first heater (15) below the filter (16) before the second heater (15) above the filter (16).

7. The heating chamber according to claim 1, characterized in that said electronics are arranged to control the heaters (15) by performing the following steps in the following order: i. heating of the first heater (15a) below the filter (16) with a high voltage to achieve fast heating; ii. heating of the second heater (15b) above the filter (16); iii. adjusting the voltage on the first heater (15a) to achieve a temperature around 940° C., which prevents overheating and unwanted degradation of the heating wire (153); iv. turning of the second heater (15b) above the filter (16); v. turning of the first heater (15a) below the filter (16); and vi. cooling both heaters (15) to a temperature below 50° C., wherein step iii) may also be performed immediately after step i) or at the same time as step ii).

8. The heating chamber according to claim 7, characterized in that the electronics repeat the sequence of steps i) to vi).

9. The heating chamber according to claim 1, characterized in that said filter (16) is any filter stable at temperatures up to 1100° C., preferably a quartz fibre filter.

10. The heating chamber according to claim 1, characterized in that the chamber is equipped with a temperature sensor for measuring temperature below the filter (16), wherein the said sensor is usually placed in the lower part (12) of the chamber.

11. A device for quantification of carbonaceous aerosols comprising at least one, preferably two parallel flow channels, each provided with one chamber according to claim 1, wherein one channel is intended for collecting samples and the other channel is intended for analysing the sample collected during a previous sampling period; and further comprising a CO.sub.2 detector located downstream of the chambers to measure the amount of CO.sub.2 formed during combustion of sampled air.

12. A method of operation of the device according to claim 11, the method comprising the following steps: a) collecting a sample of atmospheric aerosols on the quartz fibre filter enclosed in the stainless-steel chamber, preferably at a controlled sampling flow rate of 16.7 LPM, wherein the sampling time is from 20 minutes to 24 hours, b) combusting the sample from step a) with two flash-heating elements to convert all carbonaceous compounds into CO.sub.2, wherein the first heater below the filter is turned on first and the second heater above the filter is turned on after the first heater, followed by a preferred step of adjusting the voltage on the first heater; c) detecting in step b) created CO.sub.2 by the NDIR CO.sub.2 detector, wherein the background level of CO.sub.2 in ambient air during the heating cycle is determined before and after the heating cycle to provide the baselines against which the combustion pulse is measured, and d) cooling the chamber and combustion elements after analysis, wherein cooling is enabled with at least one fan located outside of the chamber in the device, where the chamber is installed.

13. The method according to claim 12, characterized in that step b) is performed as follows: i. heating of the first heater (15a) below the filter (16) with a high voltage to achieve fast heating; ii. heating of the second heater (15b) above the filter (16); iii. adjusting the voltage on the first heater to achieve a temperature around 940° C., which prevents overheating and unwanted degradation of the heating wire; iv. turning of the second heater (15b) above the filter (16); v. turning of the first heater (15a) below the filter (16); and vi. cooling both heaters (15) to a temperature below 50° C.; wherein step iii) may also be performed immediately after step i) or at the same time as step ii).

14. The method according to claim 13, characterized in that after step vi) the sequence of steps i) to vi) is repeated one more time.

15. Use of the heating chamber according to claim 1 in environmental monitoring, especially in measuring carbonaceous aerosols.

16. The device according to claim 11 in environmental monitoring, especially in measuring carbonaceous aerosols.

17. The method according to claim 12 in environment monitoring, especially in measure carbonaceous aerosols.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 The upper part of the chamber according to the invention

[0036] FIG. 2 The bottom part of the chamber according to the invention

[0037] FIG. 3 An explosion view of the preferred embodiment of the heater

[0038] FIG. 4a Operation of the device for measuring carbonaceous aerosol wherein the first chamber is performing analysis and the second chamber is sampling

[0039] FIG. 4b Operation of the device for measuring carbonaceous aerosol wherein the first chamber is sampling and the second chamber is performing analysis

[0040] FIG. 5 Activity of both heaters, the temperature and CO.sub.2 amount depending on the cycle stage

[0041] FIG. 6 Temperature of the filter in a regular heating cycle in the chamber

[0042] FIG. 7 The chamber according to the invention with the temperature sensor

DETAILED DESCRIPTION OF THE INVENTION

[0043] FIGS. 1 and 2 show the chamber 1 according to the invention, the chamber comprising: [0044] an upper part 11 and a lower part 12 with a ring 13 for closing and holes 14 for pins through which the heaters 15a, 15b receive the voltage needed for heating, wherein all holes 14 are provided with airtight seals, which withstand heating up to 300° C.; [0045] a filter 16 located between the upper 11 and lower part 12; [0046] an inlet 1a for leading the sampled air to the filter and a system of valves, which regulates the sampled air flow and air flow during the analysis; [0047] two heaters 15a, 15b comprising at least a housing and a heating wire, wherein the first heater is installed in the upper part and the second heater is installed in the lower part, wherein the distance of the heaters from the filter is from 1 to 10 mm, and wherein the heaters are controlled with electronics comprising at least voltage driver, pins and voltage clamps; [0048] preferably a temperature sensor installed in the lower part 12; and [0049] an outlet 1b for leading the created CO.sub.2 out of the chamber 1 towards a CO.sub.2 detector.

[0050] FIG. 3 shows construction of each heater 15, wherein each heater 15 comprises: [0051] a housing comprising a first heater cover 151a and a second heater cover 151b; [0052] a heating wire 153 in the shape of a winding line installed between the first 152a and second heater cover 152b, wherein one heater isolator is placed between the cover and the heating wire on each side; [0053] two contact pins 154 welded to the heating wire 153; and [0054] a multitude of ceramic pins 155 mounted through the isolator 152 and installed in both heater covers 151.

[0055] FIG. 4 is a schematic view of operation of the device for measuring carbonaceous aerosol with the chamber according to the invention, wherein the first chamber is performing analysis and the second chamber is sampling (FIG. 4a) and vice versa (FIG. 4b). FIG. 4a shows the flow diagram of the device, controlled by a system of valves which alternate the two channels to the common elements of pump, CO.sub.2 analyzer, etc. The device collects the sample of atmospheric aerosols on a central spot area of a 47-mm diameter quartz fiber filter enclosed in the chamber according to the invention, at a preferred controlled sampling flow rate of 16.7 LPM, i.e. 1 m.sup.3 per hour, provided by a closed-loop-stabilized internal pump. The second chamber Ch2 is performing sampling, therefore the first ball valve BV12 is open and also the second ball valve BV22 is open. The first chamber Ch1 is performing analysis, wherein the ball valves BV11 and BV21 are closed and solenoid valves SV11, SV21 and SV31 are off. The analytic air is let into the first chamber Ch1, where the first heater H11 is turned on first, followed by the second heater H12. Heating is controlled with the electronics as described above, while the CH1Fan provides cooling after the analysis. When the combustion of carbonaceous aerosols collected on the filter between both heaters H11 and H12 is concluded, the resulting CO.sub.2 is led to the CO.sub.2 sensor downstream of the first chamber Ch1. FIG. 4b is essentially a mirror image of FIG. 4a.

[0056] FIG. 5 shows the heating of the heaters during analysis and the level of temperature and released CO.sub.2. This figure is based on the preferred embodiment of the method of operation of the device with the chamber according to the invention, wherein heating is performed as follows: [0057] i. heating of the first heater below the filter with a high voltage to achieve fast heating (C1); [0058] ii. heating of the second heater above the filter (C2); [0059] iii. adjusting the voltage on the first heater to achieve a temperature around 940° C., which prevents overheating and unwanted degradation of the heating wire (end of C2 and beginning of C3); [0060] iv. turning of the second heater above the filter (end of C3); [0061] v. turning of the first heater below the filter (C4); [0062] vi. cooling both heaters to a temperature below 50° C. (C5); and repeating the above sequence of steps i) to vi) (C6 to C10).

[0063] In the sequence of steps the CO.sub.2 signal increases in the first heating cycle, wherein CO.sub.2 signal could also be present in the second cycle. C5 and C10 cycle stages are longer as the heaters take longer to cool than to heat to the required temperature.

[0064] The filter reaches its final temperature around 940° C. in approximately 10 seconds, wherein the temperature rise is shown in FIG. 6. The chamber is preferably equipped with a temperature sensor 17 for measuring temperature below the filter 16, wherein the said sensor 17 is usually placed in the lower part 12 of the chamber as shown in FIG. 7. Both heaters 15a and 15b are also visible in this figure.

[0065] The newly developed chamber and the device for measuring carbonaceous aerosols according to the invention enables measurement of the concentrations of total aerosol carbon continuously with high time resolution as rapid as 20 min. Two parallel flow channels provided with the improved chamber allow continuous operation: while one channel analyzes, the other collects the next sample. Thermal analysis by flash-heating of the sample collected on a quartz fiber filter inside the chamber efficiently converts all the particulate carbon to CO.sub.2. The increase in CO.sub.2 concentration above baseline in a flow of analytic air is measured by an integrated NDIR detector. When the device according to the invention is combined with an AE33 Aethalometer, the TC-BC method yields OC-EC data with much greater time resolution than that offered by the analysis of offline filter-based samples.