DETERMINING CONCENTRATIONS OF POLYHALOGENATED COMPOUNDS

Abstract

Method for determining a concentration of one or more polyhalogenated compounds in a gas. The method comprises the steps of exposing at least one sampler (10) containing or constituted by a material (14) comprising a polymer matrix that is suitable for absorbing one or more polyhalogenated compounds, and a filler that is suitable for absorbing and adsorbing one or more polyhalogenated compounds which is distributed through said polymer matrix, to gas (12) containing one or more polyhalogenated compounds during a sampling period, whereby said gas (12) constitutes at least part of said gas whose concentration of one or more polyhalogenated compounds is to be determined, determining an amount of one or more polyhalogenated compounds adsorbed or absorbed by said material, (14), and calculating a concentration of one or more polyhalogenated compounds in said gas (12) to which said material (14) was exposed, either upstream or downstream of said at least one sampler (10).

Claims

1. A method for determining a concentration of one or more polyhalogenated compounds in a gas, wherein the method comprises the steps of exposing at least one sampler containing or constituted by a material comprising a polymer matrix that is suitable for absorbing one or more polyhalogenated compounds, and a filler that is suitable for adsorbing one or more polyhalogenated compounds which is distributed through said polymer matrix, to gas containing one or more polyhalogenated compounds during a sampling period, whereby said gas constitutes at least part of said gas whose concentration of one or more polyhalogenated compounds is to be determined, determining an amount of one or more polyhalogenated compounds adsorbed or absorbed by said material, and calculating a concentration of one or more polyhalogenated compounds in said gas to which said material was exposed, either upstream or downstream of said at least one sampler.

2. The method according to claim 1, wherein it comprises the steps of measuring or calculating said material's-polyhalogenated compound absorption and adsorption efficiency, and calculating a concentration of one or more polyhalogenated compound in the gas whose concentration of one or more polyhalogenated compounds is to be determined.

3. The method according to claim 1, wherein said at least one sampler is a passive sampler.

4. The method according to claim 1, wherein said polymer matrix is a polyolefin matrix, such as a polypropylene matrix, and/or said filler comprises carbon, preferably activated carbon, soot or ground hearth-furnace coke.

5. The method according to claim 1, wherein said filler is in particle, granulate or powder form.

6. The method according to claim 1, wherein comprises the step of sampling all, or a substantial amount of the gas whose concentration of one or more polyhalogenated compounds is to be determined by exposing said material of the at least one sampler to all of the gas whose concentration of one or more polyhalogenated compounds is to be determined.

7. The method according to claim 1, wherein it comprises the step of passing said gas containing one or more polyhalogenated compounds through a plurality of samplers, and then mixing said plurality of samplers together for analysis as a single sample.

8. The method according to claim 1, wherein said one or more polyhalogenated compounds is/are at least one of the following: polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs).

9. The method according to claim 1, wherein comprises the step of extracting a sample of said material and analysing its surface to determine whether surface scaling is present.

10. A non-transitory computer readable medium storing a computer program containing computer program code that causes a computer or a processor to execute all of said calculation steps of a method according to claim 1.

11. A material comprising a polymer matrix that is suitable for absorbing one or more polyhalogenated compounds and a filler that is suitable for adsorbing one or more polyhalogenated compounds which is distributed through said polymer matrix for determining a concentration of one or more polyhalogenated compounds in a gas to which said material is exposed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended figures where;

[0037] FIG. 1 shows how polyhalogenated compounds accumulate with time in a sampler material used in a method according to the present invention,

[0038] FIG. 2 shows the PCDD/F concentration in samples extracted after different exposure times, up to 2000 days (i.e. up to 5.5 years),

[0039] FIG. 3 schematically shows a plurality of samplers being used in a method according to an embodiment of the invention,

[0040] FIG. 4 shows PCDD/F concentrations according to Example 1 versus PCDD/F concentrations measured by extractive long-term isokinetic sampling, and

[0041] FIG. 5 shows PCDD/F concentrations according to Example 2 versus PCDD/F concentrations measured by extractive short-term isokinetic sampling.

[0042] It should be noted that the drawings have not necessarily been drawn to scale and that the dimensions of certain features may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION OF EMBODIMENTS

[0043] FIG. 1 shows how the concentration of polyhalogenated compounds in a sampler material changes with time. The accumulation of one or more polyhalogenated compounds in the sampler is limited by kinetics in a first regime. After a sufficient amount of time, the concentration of the one or more polyhalogenated compounds reaches equilibrium.

[0044] Since the material (as described in U.S. Pat. No. 7,022,162 B2) has been used in more than 120 incineration lines worldwide in order to remove PCDD/Fs from gas flows, a large number of time-concentrations have been recorded.

[0045] FIG. 2 shows the PCDD/F concentration in samples extracted after different exposure times up to 2000 days (i.e. up to 5.5 years) and shows that the absorption rate was fairly constant over a period of 2000 days. There is a linear dependence of concentration with sampling time and FIG. 2 shows that a sampler can operate in the kinetic regime for several years. The at least one sampler used in a method according to the present invention is preferably arranged so that it/they operate(s) in the kinetic regime.

[0046] FIG. 3 shows a plurality of samplers 10 being used in a method for determining a concentration of one or more polyhalogenated compounds in a gas according to an embodiment according to the present invention. The samplers 10, which are preferably passive samplers operating in the kinetic regime, are arranged in a gas channel 18 to sample a gas 12 containing one or more polyhalogenated compounds. The samplers 10 comprise a polymer matrix that is suitable for absorbing one or more polyhalogenated compounds and a filler that is suitable for adsorbing one or more polyhalogenated compounds which is distributed through the polymer matrix. The sampler material 14 is exposed to a gas 12 containing one or more polyhalogenated compounds which flows through the gas channel, whereby the gas 12 is the gas whose concentration of one or more polyhalogenated compounds is to be determined.

[0047] The polymer matrix of the material 14 may comprise a polyolefin matrix, such as a polypropylene (PP) matrix, and/or the filler of the material 14 may comprise carbon, preferably activated carbon, soot or ground hearth-furnace coke or any combination thereof. The filler content in the polymer matrix may be in the range of 0.1 to 30 weight-%.

[0048] The filler may be in particle, granulate or powder form or any combination thereof. The material 14 may be formed in any suitable shape and size retained or contained in one or more containers of any suitable shape and size. In the illustrated embodiment the samplers are in the form of spherical filler bodies located in a gas channel 18 in order to maximise the surface area of material 14 exposed to the gas flow and to permit a flow-through of gas 12. Conventional scrubber tower packings have a shape that is suitable for such an embodiment. Injection-molding may for example be used for producing the material 14. A dual screw-type extruder is for example is suitable for mixing the filler with the polymer matrix. If a plurality of samplers 10 are used, not all of the sampler material 14 which has been exposed to a gas 12 needs to be sent for chemical analysis in order to determine an amount of one or more polyhalogenated compounds adsorbed or absorbed by the sampler material 14. It is sufficient to send at least one part of the material 14 of at least one sampler 10, or the entire material from one or many samplers 10, such as from all samplers 10, for analysis. According to an embodiment of the invention, just one sampler 10 is used in the claimed method.

[0049] By determining the amount of one or more gaseous polyhalogenated compounds absorbed and adsorbed by the material 14, and measuring or calculating the material's polyhalogenated compound-absorption and adsorption efficiency, the concentration of one or more gaseous polyhalogenated compounds in the gas 12 to which the material 14 has been exposed, the concentration of one or more polyhalogenated compounds in the gas to which the material was exposed may be calculated.

[0050] The concentration of polyhalogenated compounds in gas upstream and downstream of the material 14 may be calculated as outlined below:

C.sub.in=C.sub.removed/η

C.sub.out=(1−η)*C.sub.in

wherein:
η=the material's polyhalogenated compound removal efficiency;
C.sub.in=concentration in gas upstream of the material;
C.sub.removed=polyhalogenated compound concentration removed from the gas; and
C.sub.out=concentration in gas downstream of the material.

[0051] The method according to the present invention may comprise the step of sampling all of the gas 12 whose concentration of one or more polyhalogenated compounds is to be determined by exposing the material 14 of at least one sampler 10 to all of the gas 12.

[0052] Alternatively, the method may comprise the step of exposing the material 14 of at least one sampler 10 to only a fraction of a gas 12, whose concentration of one or more polyhalogenated compounds is to be determined.

[0053] According to an embodiment of the invention the method comprises the step of passing a gas 12 containing one or more polyhalogenated compounds through a plurality of samplers 10, and then mixing the outcoming gas 16 that has passed though the plurality of samplers 10 together for analysis as a single sample. The plurality of samplers 10 may be arranged at different positions across a gas flow cross-section, such as at different positions along the diameter of a flue gas channel.

[0054] According to an embodiment of the invention the method comprises the step of extracting a sample of the material 14 from the at least one sampler and analysing its surface to determine whether any surface scaling is present. If a sampler is partly or intermittently exposed to an aqueous solution supersaturated with an inorganic compound, then a scaling of the inorganic component may be formed on the surface on the sampler material 14, which may adversely affect the absorption and adsorption rate.

[0055] In order to monitor and optimize the lifetime and performance of the material 14 and ensure that accurate determinations or estimations of the concentration of polyhalogenated compounds in a gas are being made, samples of material 14 may be extracted from a sampler 10 and the polyhalogenated compound concentration, surface scaling and mechanical properties of the sample of material 14 may be checked. It has been found that the mean service life of the material 14 is six years.

[0056] The calculations required to determine a concentration of one or more polyhalogenated compounds in a gas may be executed by a computer or a processor using a computer program product according to the present invention.

Example 1

[0057] A random tower packing produced from sampler material 14 was secured by a polytetrafluoroethylene (PTFE) wire and inserted into the gas duct downstream of a wet scrubber of a flue gas treatment system where it was exposed to a gas flow. After a sampling period of one month, the tower packing was extracted from its exposed position and analyzed for PCDD/Fs. Thereby, the PCDD/F concentration in the flue gas could be calculated.

[0058] FIG. 4 shows PCDD/F concentrations in ng I-TEQ/Nm.sup.3 d.g. (act. O.sub.2) determined for two different plants, marked with squares and circles, respectively. The graph shows good agreement between in-situ sampled PCDD/F concentrations as measured according to the inventive Example 1 on the y-axis, versus PCDD/F concentrations as measured using extractive long-term isokinetic sampling for the same two plants on the x-axis. The error bars show the estimated measurement uncertainties. In some cases, the long-term sampler had not been operating during the entire sampling period of the sampler according to Example 1, due to maintenance or automated idle mode.

Example 2

[0059] Random tower packings produced from sampler material 14 were installed in one or more wet scrubber stages of a flue gas treatment system in such a manner, that a significant fraction, such as 20-99%, of PCDD/Fs was separated from the entire flue gas. After a certain time, for example one year of operation, a number of packing elements were extracted from each stage and analyzed for PCDD/Fs. By applying a mass balance to the total amount of sampler material 14 and the total volume of gas that had passed through the material during the sampling period, the concentration of polyhalogenated compounds absorbed and adsorbed by the material was calculated. The PCDD/F removal efficiency was measured or calculated and the input and output concentrations were calculated. For comparison, the material's polyhalogenated compound-absorption and adsorption efficiency can also be measured using extractive short-term isokinetic gas sampling methods. The material's polyhalogenated compound-absorption and adsorption efficiency can furthermore also be measured by placing sampler material 14 in the inlet and outlet gas, i.e. the gas 12 upstream and the gas 16 downstream of the samplers 10.

[0060] FIG. 5 shows that the PCDD/F concentrations sampled for 5 years according to Example 2, marked by a dashed line (---), and the PCDD/F concentrations measured by comparative extractive short-term isokinetic sampling, marked (∘), are in good agreement. The concentrations are given in ng I-TEQ/Nm.sup.3 d.g. (11% O.sub.2).

[0061] In Example 1, the material of the single random tower packings was exposed to only a part of the gas whose concentration of one or more polyhalogenated compounds was to be determined.

[0062] In Example 2, the material of the plurality of random tower packings was exposed to a substantial amount of the gas whose concentration of one or more polyhalogenated compounds was to be determined.

[0063] There are very large economic incitements for large plants to run near 100% of their capacity for most of the time, typically 8000 hours per year. The variations of the gas flow over time are typically relatively small, typically in the order of ±10-20% for the majority of the time. Moreover, the temperature of the gas flow is usually quite constant (typically plus or minus a few degrees Centigrade). These circumstances are ideal for determining a concentration of one or more polyhalogenated compounds in a gas flow using a method according to the present invention accurately, since the absorption and adsorption rate of one or more polyhalogenated compounds into/onto the material may be temperature and gas velocity dependent.

[0064] Further modifications of the invention within the scope of the claims would be apparent to a skilled person. For example, any feature disclosed with reference to one embodiment of the invention may be combined with one or more features of another embodiment of the invention unless such a combination is explicitly excluded.