EP0510341B1 - Process for controlling the operation of a gazifying reactor - Google Patents

Description

The invention relates to a method for controlling the operating sequence of a gasification reactor operating according to the entrained flow method for the gasification of finely divided carbonaceous fuels, in particular fine-grained to dusty coal, in which fuel and gasification agent are fed to the gasification reactor in a quantity ratio set as a function of the temperature in the gasification reactor.

In the gasification process of the type mentioned above, the operating conditions are normally set so that the slag can run off in the liquid state from the lower part of the gasification reactor, while the product gas produced, consisting mainly of carbon monoxide and hydrogen, is withdrawn upward from the gasification reactor. The operating temperature in the gasification reactor must therefore always be about 100 - 400 ° C above the slag melting temperature, whereby the gasification can be operated both under increased pressure and under normal pressure. Because of the short residence times of the reactants in the gasification reactor, the aim is to supply fuel and gasification agents, such as air, oxygen, water vapor and carbon dioxide, to the gasification reactor in a constant quantitative ratio throughout the process. To ensure a trouble-free operation, the quantity ratio must be set so that neither a lack of fuel nor an excess of fuel occurs. The operating temperature can only be reached if this condition is met be kept in the gasification reactor within the range specified above. On the other hand, a lack of fuel leads to the undesirable formation of carbon dioxide with increasing operating temperature and thus to a deterioration in the ratio of the calorific efficiency of the product gas produced to the calorific value of the fuel used. In contrast, excess fuel reduces the degree of gasification of the carbon due to the presence of non-gasified carbon. The temperature in the gasification reactor drops and can reach such low values that the liquid slag becomes pasty to solid, the slag removal is at risk and the operation is finally interrupted due to clogging of the slag removal.

In order to meet the conditions described above, it is therefore already known in the gasification process of the type mentioned at the outset to measure the fuel stream introduced into the gasification reactor, which in addition to the combustible substance also contains ash and water, and the gasification agent stream, both streams in one such quantity ratio are introduced into the gasification reactor that the operating temperature can be kept within the temperature range mentioned above. From EP-A-0 350 658, EP-A-0 308 027 and DE-A-33 16 368 it is known here for the determination of the fuel mass flow a radiometric density measurement of the fuel suspended in a fluidizing gas perform. Fluctuations in the nature of the fuel are only taken into account in the methods described in the references by means of a correction factor that is only determined sporadically. However, for the correct setting of the operating temperature in the gasification reactor, it is necessary that the quantitative ratio of fuel to gasifying agent is formed from the combustible substance of the fuel, that is to say without its ash and water content. In addition, the ash and water content of the fuel used must therefore be known. So far, however, it has been common for the ash and water content of the fuel to be determined only at irregular intervals by laboratory analyzes on individual samples. These analysis results are therefore only with a considerable time delay for controlling the operating sequence of the gasification reactor available. With this method of operation, the process and operating sequence of the gasification reactor can therefore only be controlled with sufficient certainty as long as the composition of the fuel does not change or changes only insignificantly and thus only very slight fluctuations in the ash and / or water content of the fuel occur.

• Der Wassergehalt ändert sich durch Störungen im Betriebsablauf der Mahltrocknung der Kohle;
• der Aschegehalt verändert sich durch den Übergang von einer Kohlensorte auf eine andere Kohlensorte;
• der Aschegehalt schwankt infolge schlechter Homogenisierung der Kohle, z.B. auf dem Mischbett.

Experience in practice has shown, however, that during the operation of a gasification reactor, for a variety of reasons, considerable and sudden changes in the ash and / or water content of the fuel can actually occur. The following reasons may exist for this:

• The water content changes due to disturbances in the operational drying of the coal;
• the ash content changes due to the transition from one type of coal to another type of coal;
• the ash content fluctuates due to poor homogenization of the coal, for example on the mixed bed.

However, these sudden changes in the ash and / or water content of the fuel cannot be compensated for with the previously customary type of regulation of the fuel to gasification agent quantity ratio, since the ash and water content values determined discontinuously in the laboratory are far too late. However, an increased ash and / or water content in the gasification reactor can lead to a lack of fuel and a reduced ash and / or water content to excess fuel with the negative consequences already described above to lead. Both operating procedures are therefore extremely undesirable, with premature wear of the wall of the gasification reactor due to excessive operating temperature in the one case and interruption of the operating procedure due to clogging of the slag discharge in the other case due to operating temperature being too low.

The invention is therefore based on the object of improving the method of the type mentioned in such a way that, even in the event of sudden changes in the ash and / or water content of the fuel used, the temperature and operating conditions in the gasification reactor can be stabilized in such a way that the negative effects described above Consequences are avoided.

The method of the type mentioned at the outset which is used to achieve this object is characterized in that the ash and water content of the fuel is determined simultaneously and continuously before it enters the gasification reactor and that the ratio of fuel to the processing of both measured values in a process computer Gasifying agent is adapted to the amount of combustible substance actually present in the fuel.

The ash content can be determined by radiometric determination. This measuring method is already used in coal processing and is described, for example, in the journal "Aufaufungs-Technik", No. 11/1988, pages 648-653. The principle of measurement is that the fuel to be examined is irradiated simultaneously or at short distance from two radioactive sources, the radiation on different Send out energy levels. They are preferably Cs 137 and Am 241 lamps. The high-energy radiation of cesium has the property of being absorbed to the same extent by all atom types present in the fuel. In contrast, the americium radiation is weakened by the atoms (Si, Al, Fe, Ca) which are characteristic of the ash substance, much more than by the atoms of the combustible substance (C, H, O, N). In this way two signals are obtained, each of which is proportional to the density of the coal dust at the measuring point. The difference between the signals of the Cs 137 and Am 241 emitters is also a measure of how much the ash content at the measuring point differs from that in the calibration state. The difference signal can therefore be defined as the ash content of the fuel and used to correct the ratio of fuel flow to gasification medium flow.

The capacitive measuring method, which takes advantage of the high dielectric constant of the water compared to the dry substance, is particularly suitable for determining the water content. This is about 2 to 5 for coal and ash and about 80 for water. The dielectric constant is determined by means of a capacitive probe for the fuel flow in the measuring cross section. However, since the pipeline in the measuring section is only partially filled with fuel, the measurement can only be achieved if the density of the fuel flow in the measuring section is additionally determined by radiometric density measurement, for example using a cesium emitter. The water content of the fuel can be determined by combining the two measured values.

However, the measurement method described above fails when the fuel used has a high electrolyte content. In this case, the determination of the water content is expediently carried out using microwaves. With regard to further details of this measurement method, reference is made to the article in the journal "Aufbereitungstechnik - Mineral Processing", Issue 1 (1987), pages 10-16.

To carry out the method according to the invention, it is advantageous if the measuring probes for determining the ash and water content in the feed line of the fuel are arranged close to the gasification reactor in close proximity to one another. Another design option is to also install the two measuring probes in the immediate vicinity of one another in the feed line close to the outlet of the supply container. If necessary, the measuring probes can finally also be installed in the allotment container itself.

The figure shows the flow diagram of a plant for carrying out the method according to the invention, in which the measuring probes for determining the ash and water content of the fuel are arranged in close proximity to one another in the feed line close to the outlet of the supply container for the fuel.

In this case, the gasification reactor 1 has two gasification burners 2. In practice, the number of gasification burners 2 can of course be arbitrary. The gasification burners 2 are supplied with fuel via the lines 3 and with gasification agent via the lines 4. The lines 3 branch off from the distributor 5, which in turn is connected to the supply container 7 for the fuel via the feed line 6. In the feed line 6, the measuring probes 8, 9 and 10 are installed in close proximity to one another. The delivery density of the fuel flow in the feed line 6 is determined radiometrically by the measuring probe 8, which contains a Cs 137 radiator. The measuring probe 9, which contains an Am 241 radiator, makes it possible to determine the ash content in the fuel stream using the reference signal of the measuring probe 8, which is carried out in the manner described above. The measuring probe 10 is finally used to determine the water content by the capacitive method or microwave method in connection with the density measurement by the measuring probe 8. The measuring results found are transferred from the measuring probes 8 to 10 to the process computer 11, where the ash and Water content of the fuel is determined. At the same time, the fuel mass flow is determined by the measuring device 12 installed in line 3. All data are therefore known which are necessary for the determination of the combustible substance actually present (ash and water-free). The result obtained is transferred from the process computer 11 to the control circuit 13, by means of which the gasification agent supply in line 4 is adapted to the target value of combustible substance and gasification agent. The measuring device 14 is used to measure the amount of gasification in the line 4, which amount can be controlled by the control valve 15. A control valve 16 is also installed in the line 3 and forms with the measuring device 12 the control circuit 17 for the fuel supply, so that the required adaptation to the target value of combustible substance and gasifying agent can optionally also be carried out by changing the fuel supply. Of course, the regulation described above only for one gasification burner 2 must also apply to the second and any further Gasification burners of the gasification reactor 1 apply.

The clear advantages of the method according to the invention are, on the one hand, a minimized risk of an interruption of operation of the gasification reactor due to an unbalanced ratio of fuel flow to gasification gas flow, and, on the other hand, the lower operating costs which are due to the optimization of this ratio at every moment of the operation.

Claims (5)

1. Method of controlling the operating cycle of a gasification reactor employing the entrained-bed process for the gasification of finely divided, carbon-containing fuels, in particular fine-grained coal to coal dust, in which method fuel and gasification medium are fed to the gasification reactor in a quantitative ratio adjusted as a function of the temperature in the gasification reactor, characterized in that the ash and water contents of the fuel are determined simultaneously and continuously before the latter enters the gasification reactor, and in that, as a result of processing both measured values in a process computer, the ratio of fuel to gasification medium is always matched to the quantity of combustible substance actually present in the fuel.
2. Method according to Claim 1, characterized in that the ash content of the fuel is found by radiometric determination.
3. Method according to Claims 1 and 2, characterized in that the water content of the fuel is determined by the capacitive measurement method or by microwave methods.
4. Method according to Claims 1 to 3, characterized in that the ash and water contents of the fuel are determined by measuring probes mounted in the immediate vicinity of one another.
5. Method according to Claims 1 to 4, characterized in that the ash and water contents of the fuel are determined either in the immediate vicinity of the gasification reactor or at the outlet of the feed container.

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