WO2014087001A1 - Method and device for cracking gases - Google Patents

Abstract

The invention relates to a method for cleaving a gas, comprising the following steps: feeding the gas, wherein the gas has a specified inlet temperature T1; cooling the gas by a specified temperature difference ΔT12 to a first temperature T2; heating the gas to a second temperature T3, which preferably is at least as high as the inlet temperature T1, in such a way that a relative saturation of the gas with foreign substances is reduced; feeding the gas to at least one heat exchanger (6) after the gas has been heated.

Description

 Method and apparatus for cracking gases

description

The invention describes a method and a device for conditioning or purifying gases and aerosols, in particular such gases and aerolsols, as may be formed, for example, during the gasification of carbonaceous raw materials or residues (such as wood, coal or plastic waste). The amount of aerosols (main component tars) varies greatly with the design of the gasifier reactor and can be between 1 and 150Ό00 mg / m ³ .

In general, if one wishes to use the gas energetically (e.g., in a turbine or piston machine) or to provide a further process step, e.g. the Fischer-Tropsch, methanol, methanation or ammonia synthesis, the gas should be purified (especially from its tars). Carbon monoxide and hydrogen are particularly interesting for the syntheses, so that conversion of the methane is also an advantage. In particular, in the Fischer-Tropsch synthesis, it is important to meet high demands on the gas quality, since otherwise significantly reduce the service life of the catalysts.

Several processes are known for tar reduction and can be divided into three main categories: cracking and / or reforming, mechanical processes and physical processes. These processes have been described several times; they are found, for example, in EP 2 030 671 or US Pat. No. 5,213,587. For the synthesis processes, it is known that in addition to the tars and particles, oils, Na, K, NH ₃ , HCN, H ₂ S, COS and halogens should be removed from the gas stream.

The mechanical (e.g., cyclone) and physical (e.g., scrubber) processes suffer from the disadvantage that further energetic use of the high-energy tars is not readily possible. In the cracking and reforming process, the use of energy has a negative effect. So, for example, in a partial oxidation, a portion of the product gas is oxidized with oxygen or air or another oxygen-containing gas. The resulting heat (exothermic reaction) leads to destruction of the long-chain hydrocarbons. The aim of previous investigations was to reduce the activation energy mainly by catalysts. This results in lower heat losses due to lower temperatures.

In the patent DE 10 2004 026 646 a process for the thermal exhaust gas purification of e.g. Dioxins or furans by combustion, i. by means of oxygen excess, described with regenerative heat exchangers. A portion of the imported raw material is used as fuel and is therefore no longer available for further energy use.

In the patent DE 195 21 673 a process for regenerative exhaust air purification is described. Here, two large and one small storage mass are used to heat the exhaust air before the pollutants are burned and cooled after combustion again to use in a next step, the waste heat for heating. The present invention has for its object to provide a method and an apparatus for the utilization of hydrocarbons, which enable a high efficiency and a high efficiency. Furthermore, a method is to be created which in turn supplies the required heat to the process by means of a regenerative process.

Furthermore, the energy consumption and the heat losses for particular cracking and reforming process should be further minimized. In addition, the gas quality for subsequent processes is to be improved. These objects are achieved according to the invention by the subject matters of the independent claims. Advantageous embodiments and further developments are the subject of the dependent claims.

In a method according to the invention for processing and, in particular, cleaning or splitting a gas, the gas is first supplied, wherein the gas here has a predetermined inlet temperature. In a further method step, the gas is cooled by a predetermined temperature difference to a first temperature. Subsequently, the gas is increased (by a second temperature difference) to a second temperature which is preferably at least as high as the inlet temperature such that a relative saturation of the gas with foreign matter is reduced. Finally, the gas is supplied after its heating to at least one heat exchanger and in this case preferably cleaned.

It is thus suggested that cooling and heating of the gas take place before the actual cleaning process. As a result of this cooling and subsequent heating, the saturation of the gas with foreign substances and, in particular, tars can be reduced, and in this way also the deposition and absorption of the condensable substances at the inlet to the further heat exchanger can be prevented.

Advantageously, the said heat exchanger is a regenerative heat exchanger. Advantageously, the temperature of the gas is further increased in this heat exchanger, wherein advantageously the temperature difference by which the gas is increased in this heat exchanger, is greater than the temperature difference by which the gas is increased in the second heat exchanger, preferably at least twice as large preferably at least three times as large and preferably at least 5 times as large.

It is advantageous, as mentioned, at least with the foreign substances to tars, so that saturation is achieved with these tars.

In a further preferred method, the heat exchanger has at least one substance layer through which the gas passes. Through this passage on the one hand a heat exchange allows, on the other hand, however, also achieved a cleaning effect on the gas. Advantageously, the gas is cooled by a temperature difference which is between 10 ° and 100 °, preferably between 10 ° and 8JT, preferably between 10 ° and 70 °, preferably between 10 ° and 60 ° and particularly preferably at about 20 °.

Advantageously, the gas is further supplied at an inlet temperature which is greater than 200 °, preferably greater than 250 ° and particularly preferably greater than 300 °. Preferably, any condensate occurring at the cooling device, such as tar condensate, is removed and can preferably be made further energetically usable, for example by being returned to a gasification reactor. Advantageously, the gas is supplied from a gasification reactor (the cooling).

After cooling, the gas flows through a heating device, by means of which, as mentioned, the original or even a higher gas temperature is restored. This procedure will be explained in more detail with reference to the figures.

In a further advantageous method, the gas is supplied after its heating to the second temperature to a system of at least two heat exchangers. This system of two heat exchangers advantageously allows continuous operation. In this case, a system comprising at least two layers or two heat exchangers is advantageously provided, which particularly preferably work alternately at least temporarily.

In a further advantageous method, the gas is increased in the heat exchanger to a temperature which is greater than 500 °, preferably greater than 600 °, preferably greater than 1000 ° and particularly preferably greater than 1300 °.

In this case, the gas can flow, for example, through the mentioned regenerative heat exchanger, in particular a so-called pebble heater can be used. In order to ensure a continuous process, as mentioned, at least two such regenerative heat exchangers are made available. Advantageously, the gas flows in at least one heat exchanger in a radial direction. This is understood to mean that the flow of the gas has at least one component in this radial direction and preferably runs completely in this radial direction. Also, it would be possible for the flow of gas inside the heat exchanger once or several times is diverted. Thus, some portions of the flow path could run in a radial direction of the heat exchanger and other portions in a direction perpendicular thereto. In a further advantageous method, the gas remains in a high-temperature region of the heat exchanger for a period of at least 0.3 seconds, preferably at least 0.5 seconds. A special design of this high-temperature space ensures a residence time of more than 0.5 seconds. This could be achieved, for example, by appropriate dimensions of this high-temperature region and / or a deflection of the gas stream.

Under such conditions, the product after cleaning or cracking contains only small amounts of methane, all other hydrocarbons are destroyed. After heating and staying in the high-temperature space, the gas preferably flows through a further regenerative heat exchanger, in which it cools and preferably emits the sensible heat to a bed or a honeycomb body generally to a material of this heat exchanger. This results in a highly energy efficient process. The result is a temperature difference between the inlet and the outlet, which results on the one hand from unavoidable heat losses and on the other hand, since endothermic reactions in destroying the unwanted components require energy. Advantageously, said heat exchanger also serves as a filter. More specifically, these above-mentioned heat storage media perform a filtering function, since the high specific surface area per volume even very fine particles, such as dust can be removed from the gas stream.

In a further advantageous method, the solid minor constituents of the gas are filtered out by the at least one heat exchanger. In particular, filtering takes place through the layers of regenerative heat exchanger. In a further advantageous method, an oxidizing agent is introduced into the high-temperature space in order to raise the temperature further with a partial oxidation or at least to keep it constant. In other words, this oxidizing agent is preferably introduced in the high-temperature space in order to compensate for the heat losses and energy required for the reactions provide. In this case, partial oxidation preferably takes place. Advantageously, significantly less oxidizing agent is supplied here than would be necessary for complete combustion. Suitable oxidizing agents are, for example, oxygen or oxygen-containing gases.

In a further advantageous method, additional energy is supplied to the high-temperature space in order to raise the temperature further. For example, it would be possible to additionally increase this energy by electrical resistance heaters or by high-frequency fields such as microwaves.

In a further advantageous method, the flow directions of the gas within the heat exchanger are reversed at least at times.

In a further advantageous method, at least one heat exchanger is at least temporarily purged with an already cleaned gas for this purpose. Due to this recirculation, the risk arises that even components that have not been destroyed will be returned. Therefore, each heat exchanger is preferably purged here (at least during the switching over for a short time), in particular with already purified product gas. This results in a quasi-continuous process that preferably at least three heat exchangers and preferably at least three regenerative heat exchangers are used. Without the purge described here could be used on only two heat exchangers.

Thus, for example, it would be possible for a heat exchanger, which had been charged with the raw gas in the last phase, to be flushed with already cleaned gas during a switchover between the heat exchangers in order, as mentioned, to avoid recycling the components which have not yet been destroyed.

In a further advantageous method, an additional substance, in particular an additional gas and particularly preferably an additional amount of water vapor is added to the gas in order to further increase the hydrogen content in the synthesis gas and, preferably, to further suppress soot formation. In other words, it may be advantageous to additionally add steam to the gas upstream of the heat exchangers, in particular the regenerative heat exchangers, in order to control the cleaning process more in the direction of a steam reforming process. The fact that the fact be used that in a steam reforming process higher hydrogen content can be realized. In addition, the ratio between the water vapor to the amount of tar plays an important role. If the process is further approximated to a steam reforming process or partial oxidation, this can provide the advantage that there is no free carbon over cracking which is in the form of dust and / or soot on the heat exchanger surfaces can knock down. Honeycombs or pebbles (so-called pebbles), in particular in a fixed bed, are used as the heat store for the regenerative heat exchangers which are preferably to be used. As an alternative to the balls, other shapes may be used, such as calipers or Raschig rings. The diameter of these balls can be chosen freely, whereby the specific surface per volume increases due to smaller balls, which has a positive influence on the heat transfer. These materials, such as pebbles, honeycomb bodies and the like can be made of aluminum or of inert alumina (Al ₂ O ₃ ), for example, so that a pure thermal cracking or cleaning takes place. It may be advantageous to mix these alumina pebbles with catalytically active substances, such as, for example, cobalt, nickel, chromium or their oxides or sulfides. In addition, for example, limestone or dolomite can be used as a heat storage medium.

In a further advantageous method, a portion of the bulk material is withdrawn again and returned to the regenerator. It is possible to make this removal for the purpose of dust separation. Preferably, this bulk material is drawn down within the heat exchanger and preferably transported back up to be supplied. This transporting upwards can be done pneumatically. Thus, during this pneumatic transport, dust or soot particles can advantageously detach from the bulk material and, preferably, leave the system together with a conveying gas. Thus, in this preferred method, a cleaning of the heat exchanger material takes place.

The present invention is further directed to a device for purifying gases, which has a supply device for supplying the gas, a cooling device. to supply the cooled gas, a downstream in a flow direction of the gas of the cooling means heating means for heating the previously cooled by the cooling means gas and with a heat exchange means, which is arranged in the flow direction of the gas downstream of the heating means. In this case, this heat exchanger device is designed as a regenerative heat exchanger and has a material which can be flowed through by the gas. Thus, this material, which can be flowed through by the gas, preferably also serves as a filter or as a cleaning medium.

The material-forming heat-storing mass through which the gas can flow preferably contains catalytically active substances. It may be made of catalytically active substances or mixed with catalytically active substances.

Preferably, in a spatially delimited zone, in particular a low-temperature zone or high-temperature zone of the regenerative heat exchanger (preferably up to a temperature of about 600 °), a bed is used as the heat transfer material as a sorption layer of, for example, lime, dolomite and / or alumina with or without additives. In the hot zone (up to more than 1300 ° C), as mentioned above, alumina pebbles are used with or without additives. This has the advantage that it is possible to work at high temperatures without fear of sintering lime, dolomite or alumina. Also a burning of the lime, dolomite or alumina is avoided. The granular sorbent material is thus able to absorb, for example, HCl, H ₂ S, COS, tarry substances, carbon black or other particles and condensable salts, and to remove them from the gas stream. When flowing through the heat-storing mass of the tar-containing gas, as mentioned above, the majority of the dust contained in the gas is retained and not removed again in the return flow. In order to counteract a resulting increasing pressure loss, as mentioned above, the bulk material is preferably removed from time to time. In the case of adhering, sticky soot and / or tar deposits, in an advantageous embodiment the bulk material can be drawn from below from a relatively cold zone, for example in the vicinity of a cold grid where the deposits are most intense, and preferably from above into a hot zone, for example is formed in the vicinity of an advantageously existing hot grid, be returned again. Because of the very high temperatures that prevail there, the soot and tar deposits react with the oxygen-containing gas (H ₂ 0, C0 ₂ and free 0 ₂ ) and add as CO and H ₂ to the synthesis gas. With this in situ cleaning, no carbonaceous material will be lost. In a further advantageous embodiment, different materials are used as the heat carrier and / or catalyst in the different temperature zones of the heat storage mass. Within the bed, different temperature zones will develop, so that it may be useful in this described possibility of the design to use different materials as a heat carrier substance and / or catalyst. For example, nickel can be used at the temperatures in which it is particularly active and no impurities of the catalysts are to be feared. In this way, the service life of the catalytically active materials can be increased. In a further advantageous embodiment, the heat storage mass is made of an inert material, so that a purely thermal cleavage can take place.

The present invention is further directed to a plant for producing liquid fuels, said plant having a carburetor and a subordinate this carburetor device of the type described above.

Thus, the device described above is used here to clean or split the resulting gas in the gasification. Further advantages and embodiments will be apparent from the attached drawings:

Show:

Fig. 1 is a schematic process flow diagram; and

Fig. 2 is an illustration for illustrating a vapor pressure. 1 shows a flow chart of a method according to the invention and of a device 1 according to the invention. The latter has a supply line 12, via which a gaseous medium or the gas to be purified can be supplied. This gas to be supplied usually has secondary components such as tars.

Reference numeral 2 denotes a cooling device which cools the gas. This is a heat exchanger 2, in particular a liquid gas heat exchanger. Advantageously, however, care is taken here that the condensation temperature of tar is not reached before the cooling device 2 as well as after the cooling device 2. On the basis of atmospheric pressure, therefore, the gas in front of and behind the cooling device 2 should have a temperature which is greater than 150 °, preferably greater than 200 ° and preferably greater than 300 °. As mentioned above, the cooling device effects a temperature difference which is relatively low, for example in a range of 50 ° and advantageously in a range of 20 °. In this way, the energy losses can be kept low overall.

A possible tar condensate at the cooling device 2 can be removed and, if appropriate, further energetically utilized. Thus, it would be possible to lead this tar condensate back into a gasification reactor 14.

After the cooling device 2, the gas is then passed on to a second heat exchanger 4, in this case a heating device 4. This heater 4 heats the gas back to its original temperature in line 12 or above. In this way, the saturation of the gas with tars is relatively reduced and the deposition and adsorption of condensables at the entrance to the regenerative heat exchangers 6 is prevented. As shown by lines 22 and 24, the gas is now supplied to two heat exchangers 6. These heat exchangers 6 are operated offset in time with each other, so that it is possible to reheat or regenerate a heat exchanger, while the other is currently in operation. For this purpose, two valves 53 and 56 are provided, which supply the gas by means of appropriate wiring once the left and once the right heat exchanger 6. In the heat exchangers 6, the gas is heated to a temperature of more than 600 °, preferably of more than 1000 ° and more preferably of more than 1300 ° C.

Via a line 26, the heat exchangers each oxygen can be supplied. The valves 52 and 55 designate purge valves to purge the mass 62 of the heat exchangers 6 from time to time. For purging this heat exchanger mass 62, the purified gas can be used, which is otherwise withdrawn via discharge lines 36 and 38 and valves 54 and 57 from the heat exchangers 6. The reference numeral 48 denotes a switching device such as a switchable valve, which can control the supply of oxygen into the heat exchanger 6. Reference numeral 64 identifies the respective high-temperature region of the heat exchangers, it being provided here that the two high-temperature regions 64 of the two heat exchangers are also in fluid communication with one another via a connecting line 66.

The reference numeral 28 refers to an outlet pipe for the purified gas. The reference numeral 50 roughly indicates a further processing unit for the gas. This may for example contain other heat exchangers such as coolers to cool the gas, but also other components such as Fischer-Tropsch devices and the like. Also, a waste heat of these other heat exchangers can be used, for example, to operate the heating device 4.

In this case, as shown by the arrows P1 and P2, an oxygen input both in the high-temperature zone possible and in the connecting line, which divides the oxygen to the high-temperature regions. The reference numeral 59 shows a pump device and / or a fan which causes a pressure increase of the purified gas, so that it can be used as purge gas.

FIG. 2 shows, by way of example for tars, the vapor pressure curve K of pyrene. Here are the steps previously achieved or described by the devices 2 and 4 can be seen. From the point 1 on the X-axis or the above-mentioned inlet temperature T1 to the left (step) cooling of the gas to about 330 ° C ie to the above-mentioned first temperature T2 takes place. This means that here the gas is cooled by the temperature difference ΔΤ12 In this case, pyrene condenses along the vapor pressure curve K, as illustrated in section K1 of the vapor pressure curve.

After this condensation takes place (step 2) again instead of heating, this time to a higher temperature T3 and a temperature difference ΔΤ12, namely in the point 2 to a temperature of about 370 °. The difference a2 to the vapor pressure curve K is now greater than at 350 ° in point 1 (difference a1), so that the risk of deposits and adsorption is prevented. Advantageously, therefore, as mentioned above, the heating following the cooling by a larger temperature range as the cooling itself. In this way, the distance to the respective vapor pressure curve K can be further increased.

An upper limit of the heating in the second heating device 4 results from the course of the vapor pressure curve.

The Applicant reserves the right to claim all features disclosed in the application documents as essential to the invention, provided they are novel individually or in combination with respect to the prior art. LIST OF REFERENCE NUMBERS

1 device

 2 cooling device

 4 heating device

6 regenerative heat exchanger

 12 feed line

 14 gasification reactor

 22.24 lines

 26 line

28 outlet pipe

 36,38 discharge lines

 48 switchable valve

 50 gas processing unit

52.55 valves 53.56 valves

54.57 valves

59 pump device

62 heat exchanger mass

64 high temperature area 66 connecting line

K vapor pressure curve

K1 section of the vapor pressure curve T1, T2, T3 temperatures

 ΔΤ12, ΔΤ23 temperature differences

Claims

Method and device for cracking gases patent claims 1 . A method for splitting a gas with the steps: - Supplying the gas, the gas having a predetermined inlet temperature T1; - Cooling the gas by a predetermined temperature difference ΔΤ12 to a first temperature T2; - Heating the gas to a second temperature T3, which is preferably at least as high as the inlet temperature T1, such that a relative saturation of the gas with foreign substances is reduced; - Supplying the gas after it has been heated to at least one heat exchanger (6). 2. Method according to claim 1, characterized in that the gas is fed to a system of at least two heat exchangers (6) after it has been heated to the second temperature (T3). 3. Method according to at least one of the preceding claims, characterized in that the gas is heated by means of the heat exchanger (6) to a temperature greater than 600°C, advantageously greater than 1000°C, particularly advantageously greater than 1300°C. 4. Method according to claims 1 and 2, characterized in that the gas flows through the at least one heat exchanger (6) in a radial direction (R). Method according to at least one of the preceding claims, characterized in that the gas remains in a high-temperature area (64) of the heat exchanger (6) for a period of at least 0.5 seconds. Method according to at least one of the preceding claims, characterized in that the solid secondary components of the gas are filtered out by the at least one heat exchanger (6). Method according to at least one of the preceding claims, characterized in that at least one heat exchanger (6) is flushed at least temporarily with an already cleaned gas. Method according to at least one of the preceding claims, characterized in that part of the bulk material is removed and returned to the heat exchanger (6). Device (1) for cleaning gases with a supply device for supplying the gas, with a cooling device (2) for cooling the supplied gas, with a heating device (4) arranged downstream of the cooling device (2) in a flow direction of the gas for heating the previously through the cooling device (2) cooled gas and with a heat exchanger device (6), which is arranged downstream of the heating device (4) in the flow direction of the gas, this heat exchanger device (6) being designed as a regenerative heat exchanger (6) and a material through which the gas can flow (62). 10. Device according to claim 9, characterized in that the material that flows through the gas contains catalytically active substances. 1 1 . Device according to at least one of the preceding claims, characterized in that Different materials are used as heat transfer medium and/or catalyst in the different temperature zones of the heat storage mass. 12. Device according to at least one of the preceding claims, characterized in that In a spatially limited zone of the heat exchanger (6) a bed as a sorption layer made of lime, dolomite or clay is provided as a heat transfer material.