WO2002101361A1

WO2002101361A1 - Long-term sampling system

Info

Publication number: WO2002101361A1
Application number: PCT/EP2002/006240
Authority: WO
Inventors: Albert Merz; Bernhard Oser; Helmut Seifert; Reinhold Siegel; Günther ZIMMERMANN; Hubert Vogg
Original assignee: Forschungszentrum Karlsruhe Gmbh
Priority date: 2001-06-13
Filing date: 2002-06-07
Publication date: 2002-12-19
Also published as: EP1399725A1; DE10128632A1; JP2004530140A

Abstract

The invention relates to a long-term sampling system used to continuously monitor dust and pollutant emission and to determine dust emission in flowing media by taking isokinetic samples of a partial gas flow from the main gas flow of a source of pollutants by means of a partial flow sampling probe (2) and by removing the dusts by cake filtration on an ultra-fine filter (18, 19) and of volatile, that is filter-passing chemical substances dissolved in the partial gas flow on an adsorber stage (23, 24). The aim of the invention is to modify the long-term sampling system so that in addition to continuously carry out quantitative long-term sampling of dusts in flowing systems the system is also adapted to quantitatively determine volatile and thus filter-passing substances with an optimized, that is more sensitive detection limit and a simultaneously reduced costs and time required for measuring. To this aim, during the continuous monitoring, the entire partial gas flow flows through the adsorber stage (23, 24) which is mounted downstream of the ultra-fine filter (18, 19).

Description

Long-term sampling system

The present invention relates to a long-term sampling system for the continuous monitoring of dust and pollutant emissions and for determining the dust emission in flowing media with isokinetic removal of a partial gas stream from the main gas stream of a pollutant emitter, preferably an industrial incinerator, by means of a partial flow sampling probe with separation of the dust in the exhaust gas by cake filtration a filter and tapping the pressure loss caused by the flow through the same.

The required scope of emission duration monitoring is determined by the relevant national legal regulations. For example, the 17th BlmSchV (Federal Immission Protection Ordinance), which is binding in Germany, also stipulates repeated individual measurements for the continuous monitoring of flue gas emitting systems in order to detect and assign relevant dust constituents and filter-compatible pollutants such as heavy metals or organic compounds prove with knowledge of the exhaust gas moisture to be determined as well.

Known methods for monitoring the duration of emissions are absorption methods of light waves or other radiation sources. It is also known to monitor dust filters for their pressure loss by assuming a threshold value that the filter is loaded and must be replaced. Only then can the integral quantity of the particles deposited on the filter be determined gravimetrically. A continuous monitoring of the separated quantity in given time steps cannot be achieved with this method.

DE 41 15 212 C2 describes a method and an associated long-term sampling system for the continuous determination of dust contents in flowing media under isokinetic partial Current extraction of samples from the main gas stream of a pollutant emitter by means of a probe and with separation of the dusts by cake filtration on a filter are known. An isokinetic partial flow withdrawal from a main gas flow exists if the partial flow to be extracted and measured has exactly the same composition with regard to the flue gas composition and the chemical components as the main gas flow (cf. [1]). The following flow parameters are measured in order to constantly maintain the isokinetic partial flow withdrawal conditions on the partial flow withdrawal probe: the total pressure p _G , the static pressure pst. _{H of} the main gas _stream , the static pressure p _{stιT of} the partial gas stream, the system temperature T, the gas humidity, and via an analysis unit downstream of the filter which taps into a partial stream, the gas composition. The density, the viscosity η, the volume flow and the Reynolds number Re of the partial gas flow can be calculated from these flow parameters. These flow data serve to regulate the isokinetic partial flow draw in the event of changing flow conditions in the main exhaust gas flow. To determine the dust emission, the pressure loss in the unoccupied filter is measured at the start of a separation process. During the separation process, the instantaneous pressure drop Δp _F in the filter is continuously measured while the isokinetic partial flow removal conditions are maintained, the filter assignment h = ΔP _F / (η »v _F ), v _F being the filtration speed, being continuously calculated , The change in the filter occupancy Δh _{x over time} is then represented by the relationship Δh _x = h _{1 + 1} -, where h _{x is} the filter occupancy at a time t and _{1 + 1 is} the filter occupancy at a further time t _{1 + 1} . Using the relationship E _r = / (h _end -ho) (m = amount of dust separated), the emission constant E _{r is} empirically determined within an entire sampling cycle between h ₀ and h _end . With the same relationship, a filter-specific, ie practically table-unchangeable E _r at known Δh _x the amount of dust Δrri deposited in a time interval between t and t _{1 + 1} _! determine which can then be assigned for documentation to a partial gas volume determined in the same time interval in the normal state. Please refer to the relevant literature and textbooks (e.g. [2]) for heat and heat transfer for the formal relationships in this procedure.

In the method and the long-term sampling system disclosed with this, however, a substream is branched off from the substream of the exhaust gas cleaned of dust for an analysis of the volatile, ie. H. filterable chemical ingredients after the filter and before the pump not according to isokinetic conditions.

Based on the prior art mentioned, the object of the invention is to modify a long-term sampling system in such a way that in addition to the continuous quantitative long-term sampling of dusts in flowing media, the possibility is also created of volatile and thus filterable ingredients with optimized, i.e. H. Sensitive detection limit with simultaneous reduced measurement effort continuously quantitatively.

To achieve the object, the invention proposes the features set out in claim 1. The further claims indicate preferred design options of the invention.

Details of the invention are explained in more detail below with reference to figures of an embodiment of the long-term sampling system according to the invention. Show it

Fig. 1 shows the long-term sampling system in principle, and Fig. 2 shows the partial flow extraction probe in the area of the probe mouth.

Fig. 1 shows the schematic of the illustrated embodiment of the long-term sampling system for the continuous determination of dust levels, gas composition, gas moisture and the volatile, ie. H. filterable chemical ingredients in flowing media under isokinetic partial flow removal conditions.

1 shows the section of an exhaust gas duct 1 which is connected downstream of the flue gas cleaning stage as part of a previously described emission duration monitoring and in which the main gas stream 3 of the exhaust gas is directed in the direction indicated by the arrow. Ideally, the section shown is straight and vertical, the cross section of the exhaust duct 1 is round and the main gas stream flows upwards. In this section, the isokinetic partial flow withdrawal takes place by means of a partial flow withdrawal probe 2, the probe mouth 6 of which is oriented against the flow in the flow profile of the main gas flow in the exhaust duct 1 in accordance with VDI guideline 2066. The vacuum in the suction line 4 required for the suction of the partial flow is generated by a suction fan 5. The flow data of the partial flow withdrawal probe 2, in particular the flow resistance coefficients of the probe mouth 6 in the main gas flow, are included as parameters in the regulation of the isokinetic partial flow withdrawal. They are determined in advance as part of separate wind tunnel measurements, changing depending on the temperature, pressure conditions and viscosity of the flow medium and taking into account when controlling the suction fan 5.

FIG. 2 shows a possible design of the partial flow sampling probe 2 in the area of the probe opening 6. To determine the control parameters for the isokinetic partial flow withdrawal, the static pressure p _St , _{H of} the main gas flow is at the outside via at least one radial outer opening 7, behind the probe opening the partial flow extraction probe, the static pressure p _s _ _, τ of the partial gas flow via at least one radial inner opening 8 in the partial flow extraction probe and the total pressure p _G via three pitot tubes 9, which tap the pressure values clearly in front of the opening of the probe opening, tapped in the main gas flow and in each case via one Pipeline not shown in the figures parallel to the suction line 4 to a pressure measuring device, which are located in a housing 10 at the end of the suction line 4 outside the exhaust duct, pneumatically forwarded and converted by this into electrical signals. Furthermore, the system temperature T of the main gas flow is measured via a thermal sensor 11, which also taps the measured values clearly before the probe mouth.

The system temperature T and the three system pressures Ps _t , H Pst, τ and p _G mentioned above are fed as four electrical signals 12 in parallel and simultaneously to a measuring and control unit 13 for controlling the suction fan 5 via an operating unit 14.

In continuous operation, the partial gas flow sucked off via the partial flow extraction probe 2 and by means of the suction fan 5 can be switched over alternately via a feed line 15, a discharge line 22 and two multi-way valves 20 and 21 alternatively by one of the two filter housings 16 and 17, in which the dusts contained in the partial gas flow and others Solid particles are continuously separated on the fine filters 18 and 19, passed. Teflon filters, for example, are suitable as fine filters.

New to the long-term sampling system are the adsorber stages 23 and 24 arranged in the two filter housings 16 and 17 and directly downstream of the ultra-fine filters 18 and 19. The volatile, i.e. filterable chemical ingredients, for example heavy metals or organic pollutants, dissolved in the partial gas stream accumulate on these Absorber material so that they can be quantified by a suitable analysis method after completion of the sampling. When the entire partial gas flow is passed through the adsorber stages 23 or 24, the entire proportion of the volatile constituents dissolved in the entire partial gas flow is also advantageously available for analysis. In this way, the detection limit for individual ingredients is lowered, so that the substances to be detected are much easier to detect even at very low concentrations. It is therefore no longer necessary to branch off a partial gas flow from the partial gas flow of the exhaust gas cleaned of dust at the level of the discharge line 22 for a pollutant analysis of the volatile constituents dissolved in the exhaust gas, which according to the prior art cited does not take place according to isokinetic conditions. These are intercepted in the adsorber stages 23 or 24 or can also be used for the detection of e.g. B. HC1, S0 ₂ , NO _x , HF or other pollutants are supplied.

Furthermore, in contrast to the prior art mentioned, the adsorber stages 23 and 24 connected downstream of the fine filters 18 and 19 do not require their own drive or control units, which considerably reduces the measurement effort previously required. The long-term sampling system is therefore also suitable for continuous, long-term sampling of volatile substances without additional measuring technology.

The following substances can usually be detected on the adsorbent (e.g. polypropylene, activated carbon, etc.) of adsorber stages 23 and 24: polybrominated or polychlorinated dibenz-p-dioxins polybrominated or polychlorinated dibenzofurans polychlorinated biphenyls polychlorinated benzenes polychlorinated phenols polychlorinated naphthalene polycyclic aromatic hydrocarbons volatile heavy metals, such as B. Hg and their compounds

After the ultra-fine filters 18 and 19 and the adsorber stages 23 and 24, a bypass line 25 is connected in the discharge line 22, via which a minimal amount of lower current is constantly sucked in and fed directly to an analysis unit 26 and from there to the outside. The gas composition is determined in the analysis unit, in particular with regard to C0 ₂ , 0 ₂ and the gas moisture. The measured values determined in the process are supplied to the measuring and control unit 13 as electrical measured values 27. With these and the system temperature T determined at the probe mouth 6 of the partial flow extraction probe 2 and the three system pressures p _stιH , Ps _t , τ and p _G as well as the pressure reductions Δp (measured by the ultra-fine filters 18 and 19 and measured at these), the differential pressure before and behind the ultrafine filter 18 or 19, which is supplied to the measuring and control unit 13 as electrical measurement signals 28), the density, the viscosity η, the volume flow and the Reynolds number Re of the partial gas flow are further processed and in a further step to regulate the isokinetic Partial current draw is used in changing flow conditions in the main guest flow. A corresponding control variable 29 for the fan motor is fed to the suction fan 5.

Compared to the prior art mentioned, the partial gas flow from the partial gas flow is reduced at the level of the discharge line 22, since the partial gas flow now only has to be branched off for the analysis unit 26.

Following the discharge line 22, the partial gas flow flows through the suction fan 5, from where it is fed back to the main gas flow via a further line, specifically at one point after the partial gas flow has been taken in the direction of flow. To avoid unwanted condensation, in particular of gaseous pollutant compounds in the fine filters 18 and 19 or in the suction fan 5, these can optionally be provided with a heater, not shown in the figures. With the aid of such a shift in the dew point, in particular the volatile constituents dissolved in the partial gas stream can also be safely transported through the ultra-fine filters 18 and 19 into the adsorber stages 23 and 24.

In order to carry out a continuous long-term sampling, the differential pressure upstream and downstream of the fine filter 18 and 19, respectively, which is switched through the multi-way valves 20 and 21, ie the pressure reduction Δp, is measured in the unoccupied state. This begins the sampling process, which takes place without interruption and without switching over to the other, inactive fine filter 18 or 19 until it is completely occupied, i. h until a pressure difference specified as a limit is exceeded by the active fine filter. If Δpcrit is exceeded, the partial gas flow is switched over to multi-way taps 20 and 21 to the previously inactive fine filter 18 or 19 and the now occupied fine filter is removed from the filter housing for further analysis and / or archiving. Furthermore, the real emission constant E _{r can be determined} as the quotient of the separated dust quantity m to the total filter assignment Δh = h _end - hO and can be used for the subsequent correction of the cyclically determined dust quantities per time interval. Since the emission constant E _r, as the specific size of the dust particles, practically never changes, such a correction is only necessary if the emission constant E _a is unknown, ie used as an estimate during the first measurement.

Reference is made to the previously cited prior art for the individual process steps and for the algorithms for determining the emission data to be documented from the measurement data obtained. To check the functionality of the long-term sampling system, six one-week measuring cycles were carried out on a waste incineration plant. The tests were carried out with two different partial flow sampling probes with an effective diameter d _w of 16 or 25 mm. To check the effectiveness of the adsorber stages, the bed in these was divided into three adsorber layers, the partial gas stream passing through the fine filter first flowing through the upper, then the middle and finally the lower adsorbent layer. The dioxin and furan concentrations in pg TEQ / Nm ³ (TEQ = toxicity equivalent) of the dioxins and furans accumulated in the adsorbent layers after long-term sampling were evaluated quantitatively and given for the three adsorbent layers in the following table.

Table: Example of the adsorption of dioxin / furan on the adsorbent layers of an adsorber stage

The table clearly shows the enormous decrease in the concentration of furans and dioxins between the upper and middle adsorbent layer, which already has a value of 0.01 pg TEQ / Nm ³ in the second adsorbent layer and is therefore already in the range of the detection limit. For this reason, an analysis of the lower and possibly also the middle segment can be dispensed with for routine measurements.

Instead of the adsorber stages, depending on the intended use and the type of volatile constituents to be detected, absorption stages or combined ad and absorber layers are also included the same or different adsorbents which can be selected in each case with regard to the adsorption capacity for a specific pollutant.

Furthermore, a plurality of ad and / or absorber stages arranged one behind the other and / or in parallel can also be used, which can be analyzed separately and coordinated with one another.

In addition to the continuous long-term sampling of dusts described above using the ultra-fine filters and the volatile constituents via the adsorber stages, the long-term sampling system according to the invention offers the possibility of connecting additional analysis devices. For example, a branching of a lower part flow between the ultrafine filter and the adsorber stage or within the adsorber stage is suitable for additional, further gas analysis. In particular, it makes sense to have the leads 31 and 32 also open out between two ad or absorption stages. Certain pollutants, which should not be measured in an independent gas analysis, can be trapped in the ad or absorber stages, for example, to avoid cross-sensitivity in gas analysis. In addition, portions of the pollutants absorbed or adsorbed before the derivation 31 or 32 are not lost for balancing the amounts of pollutants in the absorption or adsorption stages.

In principle, the long-term sampling system is also suitable for the assessment and optimization of a combustion process. The essential information with regard to the assessment of a combustion process, in particular the efficiency of combustion or the formation and release of pollutants from the process, is namely in the raw gas, i.e. between the waste heat boiler and the first flue gas cleaning stage. As part of a measurement, the partial crude gas flow must also be removed isokinetically from the main crude gas flow directly after the waste heat boiler. Generally is the prevailing flow state is characterized by considerable fluctuations in the raw gas velocity and by particle segregation in the raw gas, so that isokinetic partial flow extraction and extensive network measurements are prerequisites for the concept of sampling and the representativeness of the sample material. Quartz fiber filters, for example, are suitable as fine filters 18 and 19 for this application.

[1] Röthele, S .: Process for suction at the same speed with differential pressure probes; Clean dust. Luft 42 (1982) pp. 6-10

Reference numerals:

1 exhaust duct

2 partial flow sampling probe

3 main gas flow

4 suction line

5 suction fans

6 probe mouth

7 outside opening

8 inside opening

9 pitot tube

10 housing

11 thermocouples

12 Electrical signals

13 measuring and control unit

14 control unit

15 supply line

16 filter housing

17 filter housing

18 ultra-fine filter

19 ultra-fine filter

20 multi-way valve

21 multi-way valve

22 derivative

23 adsorber stage

24 adsorber stage

25 bypass line

26 analysis unit

27 Electrical measurements

28 Electrical measurement signals

29 Control variable blower motor

30 line

31 derivative

32 derivative

Claims

Claims:

1. Long-term sampling system for the continuous monitoring of dust and pollutant emissions and for the determination of the dust emission in flowing media with isokinetic removal of a partial gas stream from the main gas stream of a pollutant emitter, preferably an industrial combustion plant, by means of a partial flow sampling probe (2) and with separation of the dusts by cake filtration on one Ultra-fine filter (18, 19) as well as volatile, ie filterable chemical constituents dissolved in the partial gas flow in an adsorber stage (23, 24), whereby a) the following flow parameters are measured on the partial flow extraction probe (2) in order to constantly maintain the isokinetic partial flow extraction conditions: the _Total pressure p _G , the static pressure p _{SCjH of} the main gas _flow , the static pressure Ps _t , τ of the partial gas flow, the system temperature T, and additionally at an analysis unit (26) which is connected to the fine filter (18, 19) and which taps the partial gas flow, di e Gas composition and the gas moisture are measured, and the density, the viscosity η, the volume flow and the Reynolds number of the partial gas flow are calculated from these measured variables, b) to determine the dust emission, the pressure loss in the unoccupied fine filter (18, 19) is measured at the start of the separation process , the instantaneous pressure drop Δp in the ultra-fine filter (18, 19) is constantly measured while maintaining the isokinetic partial flow removal conditions, the filter assignment h = Δp _F / (η «v _F ), v _F is the filtration speed, the change in the filter assignment over time is calculated Δh _{L is represented} by the relationship Δh _x = h _{1 + ι} -hi, where _{λ is} the Filter assignment at a time tj _. and h _{1 + 1 is} the filter occupancy at a point in time t _{1 + 1} , the real emission constant E _r as the quotient of the amount of dust m deposited on the ultrafine filter (18, 19) during the sampling time to the total filter occupancy Δh = h _end - h ₀ between The beginning and the end of sampling is determined, the change over time in the amount of dust Δm _x deposited on the ultra-fine filter (18, 19) is calculated from the product of the change over time in the filter assignment Δh _x and the actual emission constant E _r , and that in each case The period of time separated dust quantity is assigned to the current partial gas volume in the normal state, characterized in that c) the adsorber stage (23, 24) is connected downstream of the fine filter (18, 19) while the entire partial gas flow flows through it during continuous monitoring.

2. Long-term sampling system according to claim 1, characterized in that the adsorber stage (23, 24) consists of several cascaded adsorbent layers with the same or different, each with regard to the adsorptivity selectable for a certain pollutant absorbents.

3. Long-term sampling system according to claim 1 or 2, characterized in that the adsorber stage (23, 24) can be replaced by a plurality of adsorber stages connected in parallel or in series.

4. Long-term sampling system according to claim 1, characterized in that between the fine filter (18, 19) and the downstream adsorber stage (23, 24) an additional derivative (31, 32) for the removal of a lower part gas flow from the partial gas flow is provided.

5. Long-term sampling system according to claim 2 or 3, characterized in that at one or more selected locations between two adsorbent layers of an adsorber stage (23, 24) or between two successive adsorber stages, an additional derivation is provided for the removal of a partial gas stream from the partial gas stream.

6. Long-term sampling system according to one of claims 1 to 5, characterized in that instead of the adsorber stages, depending on the intended use and the type of volatile constituents to be detected, also absorption stages or combined ad- and absorber stages with the same or different, in each case with regard to the absorption or adsorption capacity selectable adsorbents are used for a certain pollutant.