WASTE INCINERATION METHOD

Description

[0001] The invention relates to a method for burning waste on a combustion grate of a combustion plant.

[0002] Waste incineration plants have the unique characteristic of producing only low CO₂ concentrations in their exhaust gases. This is advantageous in some respects. However, the removal of the remaining CO₂ is complex and costly, as relatively large volumes of gas must be processed. These large flue gas volumes necessitate elaborate flue gas cleaning systems, for which carbon dioxide removal components are generally not economically viable.

[0003] The oxygen enrichment of the primary combustion air described in the prior art does indeed lead to a reduction in the amount of flue gas. However, the enrichment of the combustion air is limited because the substitution of atmospheric oxygen with pure oxygen, due to the increased adiabatic combustion temperature, places a high thermal load on the system. Furthermore, the control system is complex, as the time-delayed response of the entire system to a change in the oxygen supply must be taken into account.

[0004] A generic process is known from WO 2007 / 011141 A1. Further combustion plants are known from WO 96-04507 A1 and from US 2002 / 009399 A1.

[0005] The invention is therefore based on the objective of further developing a process for the combustion of waste in such a way that the separation of CO2 in the flue gas is facilitated.

[0006] This problem is solved by a method having the features of claim 1.

[0007] The inventive method provides that, during the combustion of waste on a combustion grate of a combustion plant, oxygen is added to the combustion process as an oxygen-carrier gas mixture, wherein the carrier gas is recirculated gas from the combustion plant with a CO₂ concentration of 10 to 99%. Thus, an oxygen-carrier gas mixture is added to the combustion process, and the carrier gas in this oxygen-carrier gas mixture is itself a carrier gas mixture containing 10 to 95% CO₂. This results in oxygen being added to the combustion process along with CO₂ and, optionally, other gases. Consequently, the CO₂ concentration in the exhaust gas of the combustion plant increases, and the controllability of the plant via the supplied gases is facilitated.

[0008] This results in easier CO2 separation from the exhaust gas due to the higher CO2 concentration in the exhaust. Furthermore, the volume of flue gas is reduced because the carrier gas is extracted from the flue gas. Combustion temperatures can also remain within permissible limits for the components.

[0009] DE 102 13 788 B4 and DE 102 13 790 already describe waste incineration plants with a combustion control system that enriches the primary combustion air with oxygen to 25 vol.% to 40 vol.%.

[0010] In this process, the oxygen enrichment of the primary air is used to improve the slag quality. The higher oxygen content increases the temperatures in the combustion bed, causing the slag to sinter. This results in better incorporation of pollutants.

[0011] However, such processes are complex in terms of control and procedural engineering, and the improved slag quality often does not justify the effort.

[0012] In the process according to the invention, it is advantageous if the oxygen-carrier gas mixture is added with an oxygen concentration of 5 to 40% and preferably of 16 to 40%. That is, more than half of the oxygen-carrier gas mixture is carrier gas.

[0013] The oxygen, and in particular the oxygen-carrier gas mixture, is added to the secondary combustion.

[0014] Since the CO₂ concentration of the gas recirculated from the combustion system ranges from 10 to 99%, the carrier gas also contains a further gas component, primarily air, and especially ambient air. The recirculated gas can have an extremely high CO₂ content, and the CO₂ gas from the capture process can have a purity level of 80 to 99%. Before the recirculated gas is added to the combustion system, it can be adjusted to the operational requirements and, for example, mixed with air. This allows the CO₂ content to be individually adjusted. In practice, the gas added to the combustion system can have a CO₂ content between 30 and 84%. This makes it possible to maintain a minimum O₂ content of 16% to sustain combustion.

[0015] One particularly preferred embodiment provides that the recirculated gas is extracted after the exhaust gas from the combustion plant has been treated.

[0016] The inventive method makes it possible to feed at least a part of the exhaust gas from the combustion plant to a post-processing stage in which CO2 is separated.

[0017] An unclaimed device provides that the combustion system has at least one secondary air supply above the combustion grate, which has a connection for air and / or recirculation gas, a valve and a secondary air nozzle in the direction of flow, wherein an oxygen supply line is arranged between the valve and the secondary air nozzle, which has a connection for oxygen.

[0018] In the long term, this makes it possible to supply oxygen from hydrogen production to the combustion plant and to facilitate CO2 separation in the flue gas by increasing the CO2 content in the flue gas and reducing the nitrogen content.

[0019] An exemplary embodiment is shown in the drawing and is explained in more detail below. It shows Fig. 1 schematically shows a section through an incineration plant and Fig. 2 a diagram of the plant and the material flows.

[0020] The one in Figure 1 The combustion system 1 shown has a combustion grate 2 to which primary air supply lines 3 to 6 lead. These primary air supply lines 3 to 6 lead to individual zones 7 to 10 of the combustion grate 2. In addition to the primary air supply lines 3 to 6, recirculation gas supply lines 11 to 14 are located under the combustion grate 2. The primary air supply lines 3 to 6 have a connection 15 for primary air, the recirculation gas supply lines 11 to 14 have a connection 16 for recirculation gas, and the oxygen supply lines 17 to 20 have a connection 21 for oxygen.

[0021] Valves 22 to 24 (numbered only as examples) in the primary air supply lines 3 to 6, the recirculation gas supply lines 11 to 14 and the oxygen supply lines 17 to 20 make it possible to supply different gases to the combustion grate 2 in a very targeted manner, tailored to the individual zones 7 to 10.

[0022] Above the combustion grate 2 is the flue gas passage 25 with secondary air supply lines 26 to 29, each or jointly having a connection 30, 31 for air and / or recirculation gas. Each secondary air supply line has a valve 32 to 35 to adjust or regulate the supply of air and / or recirculation gas. The air and / or recirculation gas is supplied via valves 32 to 35 to secondary air nozzles 36 to 39, through which the secondary air enters the flue gas passage 25. Between the valves 32 to 35 and the secondary air nozzles 36 to 39, an oxygen supply line 40 to 43 is arranged, each having a connection 44, 45 for oxygen.

[0023] This also allows secondary air to be supplied as air and / or recirculation gas via nozzles 36 to 39 in the flue gas passage 25.

[0024] When using combustion plant 1, waste 46 is burned on the combustion grate 2, and during combustion, oxygen is supplied to the combustion grate 2 via lines 17 to 20 and to the flue gas passage 25 via lines 40 to 43. This oxygen is added together with recirculation gas, which can be added via connections 16, 30 and 31.

[0025] The Figure 2Figure 1 schematically illustrates the process according to the invention. Fuel 50 is added to the combustion plant 1, and the flue gases 51 pass to a heat recovery unit 52 and from there to an exhaust gas cleaning unit 53. From the exhaust gas cleaning unit 53, the exhaust gas 51 passes to a post-treatment unit 54, where CO₂ can be separated. After the post-treatment unit 54, at least a portion of the exhaust gas returns to the combustion plant 1. Exhaust gas streams 55 and 56 from the exhaust gas cleaning unit 53 or the heat recovery unit 52 can be added to this exhaust gas stream from the post-treatment unit 54 to the combustion plant 51. Furthermore, a supply line 57 for air and a supply line 58 for oxygen are provided.

Claims

1. Method for incinerating waste (46) on a combustion grate (2) of a furnace (1), in which oxygen having a carrier gas is fed to the combustion as an oxygen-carrier gas mixture, wherein the carrier gas is recirculated gas from the furnace (1) with a CO2 concentration of 10 to 99%, and the oxygen is mixed with the carrier gas prior to being supplied into the furnace (1), wherein the oxygen-carrier gas mixture is added to the secondary combustion, characterized in that, before the oxygen-carrier gas mixture is fed to the furnace, it is set to the needs of the operation by adding oxygen in order to individually adjust the CO2 content in the oxygen-carrier gas mixture.

2. Method according to claim 1, characterized in that the oxygen-carrier gas mixture is added at an oxygen concentration of 5 to 40% and preferably of 16 to 40%.

3. Method according to one of the preceding claims, characterized in that the carrier gas contains air, in particular ambient air.

4. Method according to one of the preceding claims, characterized in that the recirculated gas is extracted after a processing of the exhaust gas (51) from the furnace (1).

5. Method according to one of the preceding claims, characterized in that at least a part of the exhaust gas (51) from the furnace (1) is supplied to a post-processing (54), in which the CO2 is separated out.