Operation of a cement plant with a retrofitted oxyfuel calcinator for optimal CO2 separation

Abstract

The present invention relates to a method for operating a cement plant, wherein a cement plant is selected comprising a primary cooler 41, a primary kiln 31 and a primary preheater 11, as well as a secondary calciner 22 and a secondary preheater 12, wherein a solids stream is fed into the primary preheater 11 and from the primary preheater 11 into the secondary calciner 22 and from the secondary calciner 22 into the primary kiln 31 and from the primary kiln 31 into the primary cooler 41, wherein a primary gas stream is fed from the primary cooler 41 into the primary kiln 31 and from the primary kiln 31 into the primary preheater 11, wherein the primary gas stream supplied to the primary preheater 11 has a first temperature, characterized in that a cold air stream is supplied to the primary preheater 11, wherein the cold air stream has a second temperature, the second temperature being lower than the first temperature.

Description

2 / 10 leads to the conclusion that its adaptation must be carried out in order to maintain the guidance in entrained flow operation. The object of the invention is to optimize the operation of a cement plant with a retrofitted oxyfuel calcinator with regard to CO2 separation.5 This object is solved by the method with the features specified in claim 1. Advantageous further developments result from the dependent claims, the following description and the drawings. 10 The inventive process serves to operate a cement plant. Preferably, the cement plant is a conventional cement plant which has been retrofitted with a secondary calciner operated according to the oxyfuel process in order to obtain a large proportion of the CO2 produced in highly enriched form and thus be able to separate it more easily. A cement plant with a primary cooler, a primary kiln and a primary preheater is selected. Usually, this is the existing old plant which was designed without CO2 separation.Furthermore, the selected cement plant has a secondary calciner and a secondary preheater, which are preferably retrofitted and operated according to the oxyfuel process. In the oxyfuel process, (ideally) pure oxygen is used, so that only a mixture of mainly CO2 and water vapor is obtained at the end. An attempt is made to keep the nitrogen content as low as possible in order to minimize the costs of CO2 separation. Nitrogen is introduced partly with the oxygen and partly enters the system via false air. A solids stream is fed into the primary preheater and from the primary preheater into the secondary calciner, and from the secondary calciner into the primary kiln and from the primary kiln into the primary cooler. A secondary solids stream is fed to the secondary preheater. The solids stream is fed from the secondary preheater to the secondary calcinator. Here, the solids stream and the secondary solids stream are usually combined before entering the secondary calcinator.By dividing the feedstock into the solids stream in the primary preheater and the secondary solids stream, waste heat from both the primary furnace and the secondary calciner can be recovered and fed back into the process. In the overall scheme, a primary gas stream is fed counter-currently to the solids stream from the primary cooler into the primary furnace and from the primary furnace into the primary preheater. This then passes through the secondary calciner. A primary calciner can be arranged in the primary gas stream between the primary furnace and the primary preheater, which is a possibility in the case of subsequent retrofitting with a secondary calciner. However, the primary calciner is no longer used as a calciner but serves in this case to guide the primary gas stream. The primary gas stream, as is customary for cement plants, preferably has a typical nitrogen content resulting from the use of air as an oxygen source. The primary gas stream fed to the primary preheater reaches an initial temperature.10 According to the invention, a cold air stream is supplied to the primary preheater. The cold air stream generates a second temperature, which is lower than the first temperature. This has two effects. Firstly, the supply of the cold air stream reduces the maximum temperature in the primary preheater, which results in the mineral material being heated less intensely and therefore being less deacidified, i.e., releasing less CO2. Thus, the deacidification, the release of CO2, from the primary preheater to the secondary calciner is shifted, which means that this CO2 also ends up in the highly enriched CO2 gas stream of the secondary calciner and can therefore be separated more easily. In addition, this allows the amount of gas supplied from the primary furnace to the primary preheater to be reduced. to reduce, which can reduce the amount of heat supplied, which in turn can reduce the proportion of material that can be supplied to the primary preheater and thereby increase the proportion of material supplied to the secondary preheater.This has two further positive effects. Firstly, it increases the volume of the highly concentrated CO2 exhaust gas stream from the secondary calciner, and secondly, it lowers the temperature of the CO2-containing gas stream leaving the secondary preheater, which is advantageous for further CO2 processing. The introduction of the cold air stream thus significantly increases the overall efficiency of the CO2 separation. 30 In a further embodiment of the invention, the cold air stream is taken from the primary gas stream leaving the primary preheater. A portion of the gas that has been cooled by the primary preheater is thus recirculated. To further improve this effect, in a further development, the cold air stream taken from the primary gas stream leaving the primary preheater can be passed through a heat exchanger and cooled in the heat exchanger. This further development is particularly advantageous if the heat dissipated in the heat exchanger is used, for example, for the CO2 separation process, thereby creating a further synergy effect.5In a further embodiment of the invention, the cold air stream is alternatively or additionally directed from the primary cooler to the primary preheater. Typically, the primary cooler has several zones, in particular three, at different temperatures. The warmest zone is used for the most intensive preheating, and the gas from it is usually fed to the primary furnace. The coldest zone can be used either for heat recovery, drying, or power generation, or it is simply cooled with air, which is then released to the environment if the temperature level is too low for practical use. For the cold air stream, the middle zone with a moderate temperature but still suitable for practical heat recovery is therefore preferably selected. In a further embodiment of the invention, the proportion of the solids flow supplied to the secondary preheater is increased by the supply of the cold air flow compared to the solids flow supplied to the primary preheater.As already explained, this is made possible by the supply of the cold air stream and thereby increases the shift of CO2 release to the secondary calciner. In a further embodiment of the invention, the primary gas stream supplied to the primary cooler has a nitrogen content of at least 50 vol.%. In contrast, the gas stream supplied to the secondary calciner preferably has less than 50 vol.%, further preferably less than 20 vol.%, and particularly preferably less than 5 vol.% nitrogen. The secondary calciner is therefore preferably operated according to the oxyfuel principle, the primary furnace according to the conventional method. The method according to the invention is explained in more detail below with reference to exemplary embodiments shown in the drawings. BE2025 / 5017 5 / 10 Fig. 1 first example Fig. 2 second example Fig. 3 third example 5 In Fig. 1 a first example of a cement plant for carrying out the process according to the invention is shown.The cement plant typically has a primary preheater 11, optionally a primary calciner (not shown and preferably no longer in use), a primary kiln 31, and a primary cooler. These originate, for example, from a conventional existing plant. For example, as a retrofit solution 10, the cement plant has a secondary preheater 12 and a secondary calciner 22. These are operated according to the oxyfuel principle with enriched oxygen, for example, with at least 95 vol% oxygen as gas from the oxygen source 50, so that the gas reaching the CO2 purification 60 has a very high proportion of CO2, which makes separation particularly economical. 15 In particular, in a retrofit solution, the secondary calciner 22 replaces an existing primary calciner, whereby the calcination removes the largest part of the mineral bound CO2 is released, and thus, in a relatively simple retrofit solution, a large part of the existing system can continue to be used while still capturing the majority of the CO2. Such a retrofit is known in principle.According to the invention, a portion of the primary gas stream leaving the primary preheater 11 is recirculated and combined with the primary gas stream coming from the primary furnace 31. This lowers the inlet temperature in the primary preheater 11, which in turn lowers the maximum temperature of the mineral material, thus minimizing the degree of calcination and consequently the CO2 emissions occurring in the primary preheater. At the same time, the primary gas stream through the primary furnace 31 can be reduced, which allows for the separate optimization of the processes in the primary furnace 31 and also results in less oxygen input through the primary furnace 31 into the primary preheater 11, which is advantageous in the case of CO2 removal downstream of the primary preheater, for example, cryogenic removal. BE2025 / 5017 6 / 10 Fig. 2 showed a second example in which, in addition to the first example, a filter 70 for dust separation and a heat exchanger 80 are also arranged in the return flow. The filter 70 prevents clogging of the heat exchanger 80.The heat recovered in the heat exchanger 80 is particularly suitable for use in CO2 purification and separation due to the temperature level 5. I.