EP2609388B1 - High-temperature furnace, use of a spinel ceramic and method for carrying out t(o)c measurements of samples - Google Patents

Description

The present invention relates to a high-temperature furnace, with the aid of which T (O) C measurements of samples can be carried out in order to be able to determine, in particular according to DIN EN 1484, the fraction of oxidizable carbon of a wastewater. The present invention further relates to a suitable use of a spinel ceramic and a method for carrying out T (O) C measurements of samples.

In particular, in water and wastewater analysis according to DIN EN 1484, the proportion of oxidizable carbon of a wastewater is determined by determining the TOC value (English: total organic carbon), whereby the measured carbon content does not necessarily have to be organically bound depending on the sample ( "T (O) C-value"). This is done in a high temperature oven, such as in DE 102 008 025 877 A1 described, dripped a particular liquid sample into a vaporizing space and substantially completely oxidized, so that the entire carbon is present as CO ₂ . The concentration of the resulting CO ₂ can be determined over time using an NDIR (Non-Dispersive Infrared Detector). The resulting integral of the CO ₂ concentration over time is proportional to the carbon released from the sample. For the oxidation of the sample, the high-temperature reactor is heated to temperatures of about 700 ° C to 1000 ° C. For this purpose, the evaporation space of the high-temperature reactor with a correspondingly temperature-resistant oxide ceramic, z. B. Al ₂ O ₃ , lined. However, it has been found that after some time salts deposit, which impairs the T (O) C measurement, so that the high-temperature furnace aged by the salt deposits has to be slowly cooled and manually cleaned at certain maintenance intervals before the high-temperature reactor is again slow can be heated to the operating temperature.

It is the object of the invention to provide measures that allow a reduction in the extent of aging effects of a high-temperature furnace for T (O) C measurement.

The object is achieved according to the invention by a high-temperature furnace with the features of claim 1, a use with the features of claim 10 and a method for performing T (O) C measurements of samples having the features of claim 11. Preferred embodiments of the invention are given in the subclaims.

The high-temperature furnace according to the invention for T (O) C measurement of a sample has a furnace housing delimiting a evaporation chamber, which has a sample opening for dripping in the sample. According to the invention, the furnace housing is lined with a spinel ceramic on an inner side facing the evaporation space. The evaporation space is the entire volume, which is limited by the oven housing.

Due to the spinel ceramic, the evaporation space is lined by a material that allows particularly high temperatures within the evaporation space and thus the most complete combustion and at the same time is very resistant to thermal shock. This makes it possible to substantially clean the evaporation space at operating temperature with a rinsing liquid and dissolved salts, in particular recrystallized inorganic salts from the evaporation space dissolved in the rinsing liquid or to remove undissolved. Aging of the high-temperature furnace by deposited salts can thereby be avoided or at least significantly delayed, whereby the operating costs over the life of the high-temperature furnace are reduced. Cleaning by hand is not required. In particular, a cleaning of the remaining at operating temperature high temperature furnace between two measurements can be provided without the particular continuous T (O) C measurement of samples is significantly delayed. Damage to the spinel ceramic by the impinging rinse liquid can be avoided due to the high thermal shock resistance, so that microcracks and material fatigue of the spinel ceramic during rinsing are substantially avoided. Furthermore, increased corrosion resistance, especially in the case of alkali-containing slags, is achieved, so that the range of application of the high-temperature furnace can be extended to a large number of different, for example particularly alkaline, samples. Furthermore, the spinel ceramic does not react acid with water, whereas, for example, an Al ₂ O ₃ -SiO ₂ ceramic reacts acidically with water as a conventional ceramic. According to the invention, therefore, the occurrence of additional acid can be avoided, which relieves in particular the analysis. At the same time, the measurement accuracy can be improved because subsequent measurements are not affected by deposited salts. This allows fast and accurate online T (O) C measurement, in particular of wastewater, such as those that occur during the operation of chemical plants. Depending on the application, the properties of spinel ceramics can be adapted by using different powders with different additives during production. Furthermore, different particle sizes and / or particle size distributions can be set for the spinel ceramic. In addition, depending on the mixing ratio of the starting materials and / or temperature profiles during the firing process, different activated and / or non-activated phases can be provided in each case with corresponding components provided.

A spinel ceramic is understood in particular to mean a ceramic material which has the structure of a spinel. A ceramic is a material which has been sintered in particular by annealing or firing fine-grained, inorganic material at elevated temperatures, for example in a range of ≥ 900 ° C to ≤ 1500 ° C. Ceramics often have preferred properties with respect to temperature resistance, hardness, electrical insulation, chemical resistance, et cetera. A spinel structure is a cubic structure which can be formed by a compound of the general type AB ₂ X ₄ , where A and B are in particular metallic elements. In this case, A may be a divalent metal cation, B may be a trivalent metal cation and X may be an oxide. Examples of the divalent cations are Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Mn ²⁺ , Cu ²⁺ , Ne ⁺ , Co ²⁺ , whereas the trivalent cations may in particular be formed by Al ³⁺ , Fe ³⁺ , Mn ³⁺ , Cr ³⁺ , Fe ³⁺ , Ga ³⁺ . There is an interchangeability between the cations within wide limits. Special spinels which may be suitable according to the invention include in particular the usual spinel (MgAl ₂ O ₄ ), zinc spinel (ZnAl ₂ O ₄ ), iron spinel (Fe, Mg) (Al, Fe) O ₄ , chromium spinel (Fe, Mg) ( Al, Cr, Fe) ₂ O ₄ or nickel spinel (NiAl ₂ O ₄ ). The spinel ceramic according to the invention comprises materials as described above, as well as materials which have mixed mixed crystals as substitution mixed crystals, as well as crystals with defect sites. In addition, the composition can vary within wide limits. For example, with respect to the ordinary spinel, stoichiometric MgAl ₂ O ₄ spinels are also included in the invention, such as MgO-rich and Al ₂ O ₃ -rich spinels, respectively.

The furnace housing has at least one flushing opening for introducing a flushing liquid. The flushing opening may in particular be different from the sample opening, so that the flushing liquid does not contaminate the path of the sample and may possibly falsify a subsequent measurement. For example, the flushing opening is oriented substantially vertically, so that the flushing liquid can trickle down in the direction of gravity over the surface of the spinel ceramic facing the evaporation space in order to clean the high-temperature furnace. The at least one flushing opening is preferably aligned substantially horizontally, so that the flushing liquid can run along the boundary of the evaporation space via the side of the spinel ceramic facing the evaporation chamber. The rinsing liquid can be discharged together with the washed out salts, which may be dissolved in the rinsing liquid or undissolved, in particular via a lower outlet in the direction of gravity. Rinsing liquid remaining in the evaporation space can be vaporized and discharged from the evaporation space, comparable to a sample measurement. As rinsing liquid, water can be used. However, it is also possible to use an organic, in particular carbonaceous, solvent as rinsing liquid. By anyway provided CO ₂ measurement can be determined when the rinse liquid is completely evaporated and removed from the vaporizing space.

The flushing opening is preferably connected to at least one injection nozzle for introducing an aerosol mist from flushing liquid, wherein the at least one injection nozzle has a substantially horizontally oriented introduction direction. The rinsing liquid can thereby be introduced as mist or vapor and sprayed at a corresponding pressure against the respective rinsing opening opposite region of the spinel ceramic. The rinsing liquid can more easily detach from the baked salts by the impact pressure which can be achieved thereby on the spinel ceramic. Particularly preferably, a multiplicity of flushing openings is preferably uniformly distributed in the circumferential direction at a substantially common vertical height.

Particularly preferably, the spinel ceramic comprises at least one additive which is selected from liquefiers, ceramic fibers or further inorganic fillers. It is particularly preferred if at least one additive in the ceramic is finely dispersed or distributed. In this way, an adaptation to special requirements of the spinel ceramic can be realized.

The addition of a condenser, also known as water reducer, superplasticizer or dispersant, significantly reduces the need for mixing water. Due to the dispersion, all grains can be wetted homogeneously from all sides despite a lower water content. Through the targeted use of ceramic fibers, the ceramic can be optimized, for example, with respect to thermal shock resistance or surface finish and adapted to the desired requirements.

It is further preferred if the spinel ceramic has a discontinuous particle size distribution. As a result, the thermal shock resistance or the thermal shock behavior is further improved. The thermal shock resistance is particularly important for flushing the furnace. A discontinuous particle size distribution in the context of the invention means that the particle size distribution has a gap in a certain particle size range. For example, the spinel ceramic may have 60-65 mass% coarse grain and 35-40 mass% fine grain, the fine grain may comprise grain sizes in a range of ≥ 1μm to ≤ 74μm and the coarse grain grain sizes in a range of ≥ 74μm to ≤ 700μm ( ≥ means greater than or equal to, ≤ means less than or equal to).

In particular, the spinel ceramic has pores having a size in a range of ≤ 10 μm. Such small pores further improve the thermal shock resistance and, if crack formation nevertheless occurs, result in a rounding of the crack tip, which leads to lower stress at the corresponding point. The pores may in particular have a size of ≥ 0.1 μm to ≤ 10 μm. With respect to the pores, it is further advantageous if the open porosity has a value in a range of ≥ 10% by volume to ≤ 30% by volume. Here, the open porosity of the material is the sum of the cavities that communicate with each other and with the environment, and is also referred to as Nutzporosität. As a result, a high thermal shock resistance is achieved at the same time sufficient stability.

In particular, the spinel ceramic is produced as a substantially isostatically pressed molding or produced by a plasma coating process. It is possible to apply the spinel ceramic to the substrate by means of the plasma coating process, comparable to a rapid prototyping process in several layers. This allows the spinel ceramic to be applied to a substrate that is easier to install to line the evaporation space. If necessary, a plurality of spinel ceramic layers can be provided one above the other, so that during a revision, one or more of the upper layers can be separated from an underlying layer in order to provide a uniform unused surface.

In particular, the different layers have a different composition and / or particle size distribution. As a result, sufficient stability can be ensured, for example, in lower layers, whereas the upper layers are adapted to the measuring task. Overall, an even better adaptation of the spinel ceramic to the measurement tasks is possible.

The vapor / CO ₂ mixture obtained from the liquid sample to be measured by evaporation and oxidation is typically sent directly to the NDIR (Non-Dispersive) via an outlet port located on the furnace housing defining the evaporation space Infrared detector), via which the concentration of the resulting carbon dioxide is determined. The spontaneous evaporation of the sample to be measured produces pulsed measuring signals at the detector. This correlates with the dripping frequency of the sample at the furnace inlet. The amount of CO2 resulting from the sample thus flows frequently, pulsing past the NDIR detector. Accordingly, the detector determines not constant but highly fluctuating measured values, under which the measuring accuracy of the measuring system can suffer. In order to obtain more constant measurement signals, the high-temperature furnace according to the invention for T (O) C measurement may be modified such that the steam / CO ₂ mixture is deflected by structural elements on the way within the evaporation space to the outlet opening. The structural elements may be unattached in the evaporation space by touching each other. Alternatively, the structural elements may be variably mounted by horizontal and / or vertical elevations in the evaporation space of the high-temperature furnace. The constructive elements may be attached to the inner wall of the evaporation space. Alternatively, the constructive elements can also be fastened to one another. In this case, different structural elements can be combined. It is also possible to combine fastened and unpaved constructional elements, both when they are of the same or different shape. The interconnected cavities created by the structural elements act as buffer volumes. As a result, the pressure fluctuations on the way within the evaporation space via the outlet opening to the NDIR are compensated. The constructive elements may be, for example, three-dimensional bodies, such as spheres, cuboids, rings, cones or cylinders or any other shaped three-dimensional body. Other structural elements such as straight or curved plates, struts or other flat elements may also be used. The constructive elements may consist of different materials. The structural elements are preferably made of or coated with spinel ceramic. The structural elements are particularly preferably made of or coated with the same spinel ceramic as used to line the evaporation space of the high-temperature furnace for T (O) C measurement. Another effect of this constructive change is that by diverting the vapor / CO ₂ mixture non-vaporizable components, usually inorganic salts, which are formed during the oxidation of the sample or contained in the sample, are preferably retained in the evaporation chamber and not go to the outlet and continue to the NDIR. As a result, maintenance intervals of the entire analysis device are additionally increased and thus reduced operating costs.

The invention further relates to a use of a spinel ceramic for lining an evaporation space of a high-temperature furnace for T (O) C measurement of a sample, the high-temperature furnace in particular as described above and further educated. The spinel ceramic is preferably formed and refined as described above with reference to the high temperature furnace. Due to the spinel ceramic, the evaporation space is lined by a material that allows particularly high temperatures within the evaporation space and thus the most complete combustion and at the same time is very resistant to thermal shock. This makes it possible to substantially clean the evaporation space at room temperature with a rinsing liquid and deposited salts, in particular recrystallized inorganic salts dissolved in the rinsing liquid from the evaporation space or to remove undissolved. An aging of the high-temperature furnace by deposited salts can be avoided or at least significantly delayed. Here, the knowledge is exploited that a spinel ceramic is not only good for handling liquid metal melts or metal slags, for example as a casting mold, but also in analytical equipment, such as in the T (O) C measurement, which is not so much depends on the otherwise in the foreground standing temperature stability but on the thermal shock resistance.

The invention further relates to a method for carrying out T (O) C measurements of samples, in which provision is made of a high-temperature furnace, wherein the high-temperature furnace has an evaporation chamber lined with a spinel ceramic. The high-temperature furnace is in particular as described above and further developed. Furthermore, the evaporation space is heated to operating temperature and a sample is introduced into the evaporation space. In addition, evaporation and / or oxidation of the sample in the evaporation space and measurement of the amount of CO _{2 produced} . According to the invention, a flushing liquid is introduced into the evaporation space substantially at the operating temperature for the removal of inorganic salts which have been recrystallized within the evaporation space from the sample. The method can in particular be designed and developed further as described above with reference to the high-temperature furnace. Due to the spinel ceramic, the evaporation space is lined by a material that allows particularly high temperatures within the evaporation space and thus the most complete combustion and at the same time is very resistant to thermal shock. This makes it possible to substantially clean the evaporation space at operating temperature with a rinsing liquid and dissolved salts, in particular recrystallized inorganic salts from the evaporation space dissolved in the rinsing liquid or to remove undissolved. An aging of the high-temperature furnace by deposited salts can be avoided or at least significantly delayed.

Thus, it is possible according to the invention to carry out a method for TOC measurement of samples, comprising the steps of providing a high-temperature furnace, wherein the high-temperature furnace has a spinel-lined evaporation chamber, heating the evaporation space to operating temperature, introducing a sample into the evaporation space, evaporating and / or oxidizing the sample in the vaporizing space, measuring the amount of CO _{2 produced,} and introducing a rinsing liquid into the vaporizing space substantially at the operating temperature to remove inorganic salts recrystallized within the vaporizing space from the sample.

In particular, the rinsing liquid is injected into the evaporation space as an aerosol mist. The rinsing liquid can thereby be introduced as mist or vapor and sprayed at a corresponding pressure against the respective rinsing opening opposite region of the spinel ceramic. The rinsing liquid can more easily detach from the baked salts by the impact pressure that can be achieved thereby on the spinel ceramic. Particularly preferably, a multiplicity of flushing openings is preferably uniformly distributed in the circumferential direction at a substantially common vertical height.

Preferably, after the removal of the inorganic salts, the evaporation space is dried essentially at operating temperature and subsequently another sample for T (O) C measurement is introduced into the evaporation space. As rinsing liquid, water can be used. However, it is also possible to use an organic, in particular carbonaceous, solvent as rinsing liquid. By anyway provided CO ₂ measurement can be determined when the rinse liquid is completely evaporated and removed from the evaporation chamber. Contamination of the T (O) C measurement by residues of the rinsing liquid remaining in the evaporation space is thereby avoided.

An operating temperature T _O of 500 ° C. ≦ T _O ≦ 2000 ° C., in particular 800 ° C. ≦ T _O ≦ 1700 ° C., preferably 1000 ° C. ≦ T _O ≦ 1500 ° C. and particularly preferably 1200 ° C. ≦ T is particularly preferred _O ≤ 1300 ° C set. At such high temperatures, substantially complete oxidation of the carbon can be achieved without risking material damage in the spinel ceramic due to temperature effects. In particular, it is possible to achieve significantly higher temperatures compared to known high-temperature furnaces for T (O) C measurement, so that the use of (spherical) catalysts can be reduced or even eliminated. The operating costs can be further reduced. Additionally or alternatively, the use of catalyst balls can be reduced by means of an internal predetermined, constructive gas path.

In particular, the same operating temperature is regulated immediately after the introduction of the sample and immediately after the introduction of the rinsing liquid as the target variable. The temperature control of the high-temperature furnace does not have to differentiate between a normal operation and a flushing operation, so that the control is simplified. At the same time, unsteady temperature effects, for example by heat conduction, can be avoided or at least significantly reduced, since interim cooling and heating as well as waiting until reaching a stationary operating state are avoided.

The stability and thermal shock resistance of the spinel ceramic is also caused by their chemical constitution. The formulation of the spinel ceramic used can combine the properties of an oxide and a non-oxide ceramic by a suitable choice of the ceramic components. For example, oxide ceramics are harder, more wear-resistant and heat-resistant, but also more brittle than hard metals. Non-oxide ceramics, such as nitrides, carbides or borides, for example, are characterized by high chemical and thermal stability, hardness and strength compared to oxide ceramics, however, accompanied by low ductility and quite high brittleness, caused by higher covalent and lower ionic bond fractions and thus by the strong binding energies. Therefore, the selection of modified spinel ceramics is possible. For example, in the case of a MgAl ₂ O ₄ ceramic, additional alumina or magnesium oxide may be added to obtain, for example, an Al ₂ O ₃ -rich or MgO-rich spinel ceramic.

Claims (15)

1. High-temperature furnace for T(O)C measurement on a sample, having
   a furnace housing which bounds a vaporization space and has a sample opening for introducing the sample dropwise,
   characterized in that
   the furnace housing is lined with a spinel ceramic on an inner side facing the vaporization space and has at least one flushing opening for introduction of a flushing liquid.
2. High-temperature furnace according to Claim 1, characterized in that the flushing opening is connected to at least one spraying-in nozzle for introducing an aerosol mist as flushing liquid, where the at least one spraying-in nozzle has an essentially horizontally oriented input direction.
3. High-temperature furnace according to either Claim 1 or 2, characterized in that the spinel ceramic comprises at least one additive selected from among plasticizers, ceramic fibers and further inorganic fillers.
4. High-temperature furnace according to any of Claims 1 to 3, characterized in that the spinel ceramic has a discontinuous grain size distribution.
5. High-temperature furnace according to any of Claims 1 to 4, characterized in that the spinel ceramic has pores having a size in the range ≤ 10 µm.
6. High-temperature furnace according to any of Claims 1 to 5, characterized in that the spinel ceramic has an open porosity in the range from ≥ 10% by volume to ≤ 30% by volume.
7. High-temperature furnace according to any of Claims 1 to 6, characterized in that the spinel ceramic has been produced as an essentially isostatically pressed shaped part or has been produced by a plasma coating process.
8. High-temperature furnace according to Claim 7, characterized in that the spinel ceramic has various layers having a different composition and/or grain size distribution.
9. High-temperature furnace according to any of Claims 1 to 8, characterized in that structural elements which deflect the vapor/Co₂ mixture produced in the high-temperature furnace on the path within the vaporization space to the outlet opening and are selected from the group consisting of three-dimensional bodies are installed in the interior of the furnace housing.
10. Use of a spinel ceramic for lining a vaporization space of a high-temperature furnace according to any of Claims 1 to 9, for T(O)C measurement of a sample.
11. Method for carrying out T(O)C measurements on samples, which comprises the steps of
    provision of a high-temperature furnace according to any of Claims 1 to 9, which has a vaporization space lined with a spinel ceramic,
    heating of the vaporization space to operating temperature,
    introduction of a sample into the vaporization space,
    vaporization and/or oxidation of the sample in the vaporization space,
    measurement of the amount of CO₂ formed,
    introduction of a flushing liquid into the vaporization space at essentially the operating temperature in order to remove inorganic salts from the sample which have recrystallized within the vaporization space.
12. Method according to Claim 11, wherein the flushing liquid is sprayed as an aerosol mist into the vaporization space.
13. Method according to Claim 11 or 12, wherein the vaporization space is dried essentially at operating temperature after removal of the inorganic salts and a further sample for T(O)C measurement is subsequently introduced into the vaporization space.
14. Method according to any of Claims 11 to 13, wherein an operating temperature T_O of 500°C ≤ T_O ≤ 2000°C, in particular 800°C ≤ T_O ≤ 1700°C, preferably 1000°C ≤ T_O ≤ 1500°C and particularly preferably 1200°C ≤ T_O ≤ 1300°C, is set.
15. Method according to any of Claims 11 to 14, wherein the same operating temperature is set as target parameter immediately after introduction of the sample and immediately after introduction of the flushing liquid.