DE102014016407A1 - Process for the production of synthesis gas - Google Patents

Abstract

The invention relates to a process for the production of synthesis gas, wherein as a first process step in a reactor, a high-temperature gasification is performed in which heat energy is released by the released heat energy is used for the additional production of synthesis gas in a second process step, inside or outside the reactor is carried out.

Description

The invention relates to a process for the production of synthesis gas, wherein as a first process step in a reactor, a high-temperature gasification is performed, is released in the heat energy.

Processes for the production of synthesis gas from various solid and gaseous raw materials are already known. Solid raw materials are advantageously converted into H ₂ and CO in so-called gasification processes. Particularly suitable for this purpose are biological raw materials, such as used and residual wood, energy wood or agricultural residues such as straw or peat.

Processes and plants for the at least partial gasification of solid, organic feedstock are for example out EP 0 745 114 B1 . DE 41 39 512 A1 and DE 42 09 549 A1 known. The present application relates in particular to methods or systems which have a low-temperature gasifier and a high-temperature gasifier, as explained below. Compared with other methods, these allow, inter alia, a lower consumption of feedstock and have a higher cold gas efficiency.

In a low-temperature gasifier, the feedstock, such as biomass, by partial gasification with a gasification agent at temperatures between about 300 ° C and 600 ° C to coke (in the case of biomass so-called biococ) and carbonization reacted. The carbonization gas is then transferred into a combustion chamber of the high-temperature gasifier and there with an oxygen-containing gas, for example with more or less pure oxygen, but also with air and / or oxygen-containing exhaust gases, eg. B. from gas turbines or internal combustion engines, partially oxidized. By this oxidation released heat causes a temperature increase to 1200 ° C to 2000 ° C, for example 1400 ° C. Under such conditions, aromatics, tars and oxo compounds contained in the carbonization gas are completely decomposed. This forms a synthesis gas which consists essentially of carbon monoxide, hydrogen, carbon dioxide and water vapor. In a further stage, the synthesis gas thus produced is brought into contact with coke from the low-temperature gasifier, for example in a quench unit integrated in the high-temperature gasifier or in a quench unit connected downstream of it. The coke can be previously treated separately (eg by grinding and sifting) and then introduced into the quench unit. By endothermic reactions between coke and syngas, the latter is cooled to about 900 ° C. This causes partial conversion of the carbon dioxide to carbon monoxide. The CO and CO ₂ rich synthesis gas thus produced can then be further conditioned. The conditioning includes, for example, a further cooling, a dedusting, a desulfurization, CO to CO2 conversion, a compression and / or the separation of residual carbon dioxide. Synthesis gas resulting from such gasification typically has a relatively low 0.8 / 1 H ₂ / CO ratio.

The heat produced by the cooling of the synthesis gas stream to about 200 ° C, is converted in most cases by the generation of steam and stored. The steam can be heated only to a maximum of 400 ° C in order to keep the cost of materials, especially for the heat exchangers and storage facilities in an economically meaningful context. However, higher energy is converted into less valuable (with a lower exergy content, that is, it can do less work). The steam produced in this way is usually not completely needed for the biomass gasification itself, so that for the excess generated steam more customers must be found or this even has to be discarded. The heat transfer to other intermediate media, such as heat transfer oils, has similar disadvantages.

Synthesis gas can also be produced via the reforming of gaseous and solid substances. For this purpose, in particular a steam reforming of methane-rich gases is customary. In this case, biogas or natural gas with steam is usually reacted on a heterogeneous catalyst to synthesis gas. This usually produces a H ₂ / CO ratio of about 3: 1.

For many production processes starting from synthesis gas, in particular for methanol synthesis, Fischer-Tropsch synthesis or dimethyl ether synthesis, a very specific H ₂ to CO ratio is necessary in order to achieve the highest possible conversion and high selectivity with respect to the desired products. The necessary H ₂ to CO ratio is achieved by various methods. On the one hand, the CO and CO ₂ rich synthesis gas from the gasification device, for example H ₂ can be mixed from an electrolysis (for example, known from EP2166064 A1 ). Disadvantages arise, however, from the fact that the electrolysis can be carried out economically only at very low electricity prices, for example in surplus electricity from renewable sources. On the other hand, the H ₂ rich synthesis gas stream a reformer and the CO and CO ₂ rich synthesis gas stream from a parallel gasifier are mixed in the required ratio. In another process variant, a part of the CO can be reacted with H ₂ O in a water gas shift reaction to CO ₂ and H ₂ until, for example, an H ₂ / CO ratio of about 2: 1 is reached. It is considered to be disadvantageous that CO ₂ which is produced here too can not be used for many subsequent processes, for example for the provision of liquid hydrocarbon hydrocarbons, and thus is lost for such processes. In particular, in the synthesis of methanol, the CO ₂ , when not separated, leads to the formation of water, which must be separated from the methanol consuming.

Object of the present invention is to provide a method of the type mentioned in such a way that an improved heat utilization is achieved.

This object is achieved in that the released heat energy is used for the additional production of synthesis gas in a second process step, which is carried out inside or outside the reactor. The previously used method for using the released heat energy for the production of water vapor or a transfer of energy to other heat transfer media always requires a further use of heat for other processes. Furthermore, the previously practiced production of steam at a temperature of 200-400 ° C does not lead to energy losses, but the proportion of usable high-temperature energy decreases, while the entropy increases, whereby the available energy is not optimally utilized. Temperatures of 1000 ° C usually do not fall as waste heat, but must usually be generated by combustion of chemical energy sources such as hydrocarbons. It is therefore important to use this high temperature of waste heat as beneficial as possible.

In the heat transfer shown here has the advantage that the yield of the desired product, in this case the synthesis gas, can be directly increased and the heat is used directly at a high level.

A particular advantage also results if the production of the additional synthesis gas in a second process step is carried out internally, within the same reactor via a conversion of natural gas or biogas, which is added to the hot synthesis gas of the first process step. So can be fed in particular at the upper end of the high-temperature gasifier natural gas or biogas. The temperature is still so high that it is sufficient for the direct conversion of the gas to synthesis gas. Optionally, the reactor length can be extended to achieve a sufficient residence time. In order to improve the reaction rate and the yield, it is additionally possible to incorporate a preferably monolithic catalyst. In addition to the better use of heat, there are two more advantages. On the one hand, by adding the colder gas and the endothermic reaction, the necessary cooling takes place for further processing of the synthesis gas. On the other hand, the H ₂ content in the synthesis gas is increased because more H _{2 is produced} as CO in the conversion of natural gas or biogas.

Another preferred embodiment results if the production of the additional synthesis gas in a second process step is carried out externally, in a second reactor, in particular by means of steam reforming. The released thermal energy can be used directly for a further reaction by not being first transferred to steam, but being used directly. In addition, the resulting synthesis gas from the first step can be mixed in whole or in part with the synthesis gas from the second step. This also allows the stoichiometric ratio of H ₂ and CO to be varied.

Conveniently, the resulting synthesis gas can be additionally enriched with H ₂ , which is produced in particular by electrolysis. This results in an even better flexibility with respect to the stoichiometric ratio of H ₂ and CO.

The process is particularly preferred when the resulting synthesis gas is further processed, in particular in a process for the synthesis of methanol and / or dimethyl ether or for Fischer-Tropsch synthesis. In particular, for these processes, a H ₂ / CO ratio of 0.8: 1, resulting from a gasification usually not high enough, so that additional H _{2 is} necessary.

A further preferred embodiment is when in the second process step, in addition to the waste heat of the hot synthesis gas, further energy is fed in, in particular regenerative electrical energy. By using a favorable excess flow, more natural gas or biogas can be converted in this reactor in order to achieve an optimum H ₂ / CO ratio of 2: 1. This is an energetically meaningful combination of waste heat and surplus electricity, especially with favorable electrical energy from regenerative sources. The energy can be introduced via at least one electrode become. In the case of using a metallic monolithic catalyst for steam reforming, this metal structure itself may be used as an electrode. By using a plurality of electrodes, which may also have different lengths, or by the subdivision of the monolithic catalyst, certain zones can be heated differently and thus specifically the temperatures can be set in certain reactor zones. The use of electric current also ensures a short claim time for changing the temperatures.

The advantages of the invention result in particular from the possibility of optimally utilizing the heat produced during the cooling of the synthesis gas streams, since no intermediate medium is used any longer. Even with the external arrangement of the second reaction step, the hot synthesis gas of the first reaction step is used directly for the transfer. By cooling the second synthesis gas stream, steam can continue to be used for heat transfer. In addition, the H ₂ / CO ratio can be optimally adjusted for subsequent production processes. If the reforming of the methane-rich gas is integrated into the upper part of the carburetor, an external steam reformer can be saved. The additional use of surplus electricity from regenerative energies, in particular from wind turbines and photovoltaic systems, can also contribute to the stabilization of the power grids and the excess energy can be stored chemically.

The invention is suitable for all processes of synthesis gas production via gasification processes, regardless of which raw materials are used. Both biological and fossil raw materials or waste can be used. Likewise, not only natural gas and biogas can be used for the reforming, but also other hydrocarbon-rich gases, in particular exhaust gases (overhead gases) from further processing processes. Depending on the H ₂ / CO ratio of the synthesis gas stream, numerous further processing steps for the synthesis gas are also possible. These include, in particular, the synthesis of methanol, of dimethyl ether, of ammonia, fermentations or the Fischer-Tropsch synthesis. In the following, the invention shall be explained in greater detail on the basis of exemplary embodiments shown schematically in the figures:

Show it

1 a schematic view of a high-temperature gasifier with internal second reaction stage

2 a schematic view of a plant for the production of synthesis gas with external second reaction stage

3 a schematic view of a plant for the production of synthesis gas with external second reaction stage with additional heating electrodes

In 1 is shown schematically the section of a plant, which combines two different syngas production methods and thus effectively uses the resulting heat. The product stream 101 from a high temperature carburetor becomes a Quenchteil the carburetor 104 fed at 1400 ° C. In the lower part of the reactor 104 is usually coke 102 added, which is also converted to CO and at the same time ensures a certain cooling. In the upper part of the reactor 104 will now also methane-rich gas 103 added, which is also reacted at the correspondingly high temperatures of about 1000 ° C to synthesis gas. Due to the additional metered addition of methane-rich gas 103 the heat is used effectively in the upper part of the reactor. In addition, the H ₂ portion of the total synthesis gas 105 elevated. Following is the entire synthesis gas 105 in particular, it is further cooled down, desulfurized, dedusted and cleaned. To improve the reaction rate and the yield, in addition, a monolithic catalyst in the upper part of the reactor 104 to be built in.

In 2 schematically a plant is shown, which produces synthesis gas in two separate stages, wherein the heat for the operation of the second stage is taken directly from the product flow of the first stage. That from the gasification 201 derived CO and CO ₂ rich synthesis gas 203 usually has a temperature of> 900 ° C. This is used directly as a heat medium for a steam reformer 204 used, which is usually operated at about 500 to 850 ° C. The cooled synthesis gas 208 can then be prepared in which it is further cooled in particular, desulfurized, dedusted and cleaned. The steam reformer 204 is usually with a mixture of methane-rich gas and water vapor 202 operated, which in the case described here via a preheating in the steam reformer 204 is supplied. However, the steam can also be added only after the preheating stage. The resulting H ₂ rich synthesis gas 205 is first used to preheat the mixture 202 used and then can also similar to the syngas stream 208 be prepared. The work-up of the synthesis gas streams can be carried out separately or together. Further processing of the conditioned synthesis gas stream takes place in particular in a methanol synthesis, dimethyl ether synthesis or Fischer-Tropsch synthesis.

3 shows the already in 2 illustrated attachment. In addition to heating by the hot syngas stream 203 becomes the steam reformer 204 with electrical electrodes 301 heated. As a result, favorable surplus stream can be used for heating and the sales can be increased. The electrodes can be inserted in different numbers and lengths in the catalyst bed. When using a metallic monolithic catalyst, this metal structure can be used directly as an electrode.

Table 1 shows a comparison of a method from the prior art with the two embodiments, in the event that methanol is to be produced from the synthesis gas obtained. Table 1: Comparison of the previously used method and the two embodiments. State of the art Example 1 (Fig. 1) Example 2 (Fig. 2) Synthesis gas from step 1 - Nm ³ / h 12,500 12,500 12,500 Methane-rich gas - Nm ³ / h 0 1,085.4 1,085.4 Methanol yield - t / day 102.8 114.5 140.4

It can be clearly seen in Table 1 that more methanol could be obtained by the two-stage embodiment, in particular the external example with constant energy input. The reason for this is the energy-neutral improvement of the H ₂ / CO ratio in the direction of the optimal synthesis gas composition of 2: 1 instead of 0.8: 1, as it arises in a conventional gasification process.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0745114 B1 [0003]
• DE 4139512 A1 [0003]
• DE 4209549 A1 [0003]
• EP 2166064 A1 [0007]

Claims (6)

Process for the production of synthesis gas, wherein as a first process step in a reactor a high temperature gasification ( 201 ), in which heat energy is released, characterized in that the released heat energy is used for the additional production of synthesis gas in a second process step, which within ( 104 ) or outside ( 204 ) of the reactor. A method according to claim 1, characterized in that the production of the additional synthesis gas in a second process step internally, within the same reactor ( 104 ) on the conversion of natural gas or biogas ( 103 ), which is added to the hot synthesis gas of the first process step. Process according to Claim 1, characterized in that the preparation of the additional synthesis gas ( 207 ) in a second process step externally, in a second reactor, in particular by means of steam reforming ( 204 ), is carried out. A method according to claim 3, characterized in that in the second process step, in addition to the waste heat of the hot synthesis gas ( 203 ), another energy ( 301 ), in particular by means of regenerative electrical energy. Method according to one of claims 1 to 4, characterized in that the resulting synthesis gas is additionally enriched with H ₂ , which is produced in particular by electrolysis. Method according to one of claims 1 to 5, characterized in that the resulting synthesis gas is further processed, in particular in a process for the synthesis of methanol and / or dimethyl ether or for Fischer-Tropsch synthesis.

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