Method and device for reducing harmful substances in vegetable coal

Abstract

Method and device for producing a combustible gas mixture (5, 5') from a carbon-containing starting material, in particular from lumpy wood, with a feed unit (1) for feeding the starting material to a reactor (2), wherein the reactor (2) comprises at least one discharge unit (24) for discharging a carbon-containing residue, in particular coal particles (28), wherein a post-treatment unit (7) is provided for post-treating the residue to reduce polycyclic aromatic hydrocarbons [PAH] (39) before the coal particles (28') leave the post-treatment unit (7) via a discharge opening (45), wherein in order to produce a largely uncontaminated biochar, the post-treatment unit (7) comprises a process chamber (16) into which at least the contaminated coal particles (28) are fed above, together with the PAH (39) produced during the combustion of the starting material, and below which a further gas (10,11, 12) is supplied to form a gas separation zone (17) within the process chamber (16), which largely prevents the passage of the PAH (39) in the direction of the discharge opening (45).

Description

[0001] The invention relates to a method and a device for the aftertreatment of coal from a plant for the gasification of a carbonaceous starting material according to the preambles of patent claims 1 and 9.

[0002] Pyrolysis, or biomass gasification, technology has evolved significantly in recent years. While electricity and heat generation have been considered the mainstay of many plants' economics, a previously largely untapped potential is increasingly gaining traction: biochar.

[0003] Biochar is approved for agricultural use in many countries (including Austria and Switzerland) as a soil improver and fertilizer carrier, as well as an adjuvant for composting and nutrient fixation in manure. Biochar is also used as a feed additive and food supplement. When used as a soil improver, it is considered to have great potential, among other things, as a means of offsetting carbon dioxide emissions in light of global warming.

[0004] Biochar has numerous other applications, including as insulation in building construction, in wastewater and drinking water treatment, as an exhaust gas filter, and in the textile industry. Examples of current uses include: Ground biochar is used as the food coloring E 153 without a maximum limit. In medicine, it is used as medicinal charcoal for the treatment of diarrhea. Similar to charcoal, biochar can also be used as activated charcoal.

[0005] Biochar is also used as an energy source, for example, as a substitute for barbecue charcoal, but it is considered too valuable for this purpose. The carbon dioxide balance when biochar is burned is different than when it is stored in the ground, as carbon dioxide is released during combustion.

[0006] The invention concerns a device for discharging pollutant-free, fine-grained biochar. Biochar, also known as biochar, is produced by pyrolytic carbonization of plant-based raw materials.

[0007] The conversion of biomass into biochar is possible using pyrolysis plants or gasification plants. While biomass gasification and pyrolysis should be distinguished, in most cases only the quantity ratio and quality of the resulting products, which are coal, synthesis gas / oil, and waste heat, differ.

[0008] Pure pyrolysis plants primarily serve to produce biochar. Biomass is heated without the presence of external oxygen, decomposing it into initially gaseous components and coal. Due to the lack of oxidation, coal with a relatively high carbon content of approximately 95% can be produced, with the remaining 5% consisting primarily of ash and accompanying materials.

[0009] The volatile components initially form the pyrolysis gas, which can be partially converted into pyrolysis oil through subsequent cooling. In most cases, the pyrolysis gas or pyrolysis oil is not used for any purpose other than complete oxidation or combustion in a separate combustion chamber due to qualitative deficiencies.

[0010] The waste heat is used to heat the pyrolysis process in order to maintain the process, with natural gas usually being burned during the start-up process of the plant.

[0011] The interposition of gas turbines or ORCs is rare, as these usually have only low mechanical efficiencies, but the pyrolysis plant can thus supply itself with electrical energy or even become a net electricity generator.

[0012] The heat extracted from the cooling of the system components can be used for other purposes.

[0013] In most cases, the biomass used must be subjected to technical drying, as the target moisture content is significantly lower than that achievable through dry storage. Thus, a significant portion of the waste heat is already consumed by this process.

[0014] These types of plants are optimized for coal production and produce coal with very low pollutant levels through the relatively slow pyrolysis process at a constant and uniform temperature.

[0015] The most significant pollutant in this context is polycyclic aromatic hydrocarbons (PAHs). These are produced exclusively through the pyrolysis or gasification process and can be avoided with the right plant technology.

[0016] To be certified as high-quality biochar, the internationally recognized EBC Institute guidelines, such as EBC AgroBio regarding PAHs, require that the PAH content reliably falls below the EPA limit of 6.0 mg / kg. In practice, this means that high-quality biochar should have a maximum total PAH content of 1-2 mg / kg.

[0017] This is also possible with pure pyrolysis plants, good plant technology and the quality and dryness of the biomass used.

[0018] In general, the value of coal increases with lower PAH values, regardless of whether certain limit values ​​have already been exceeded.

[0019] Compared to pure pyrolysis, biomass gasification uses an additional oxidizing agent, usually air, which is directly combined with the biomass. This produces wood gas or synthesis gas through oxidation and reduction instead of pyrolysis gas.

[0020] Adding external heat to the process is beneficial, but not a requirement.

[0021] In biomass gasification, the priority is usually on producing high-quality wood gas / synthesis gas. This gas should be of sufficient purity and quality to be suitable for further use in a heat engine with high mechanical efficiency, such as a gas-Otto combustion engine, or for gas storage for peak-energy power plants, or, after processing, for feeding into a gas / hydrogen grid or for use in the chemical industry.

[0022] Examples of biomass gasifiers are fixed bed gasifiers, fluidized bed gasifiers or entrained flow gasifiers.

[0023] The initial product of biomass gasification is fine-grained to dust-like coal, known as pyrocoal, with a carbon content of approximately 90%. This coal also has considerable potential, but has so far only been used sporadically and has never been fully exploited. The reason for the limited potential for this coal is its relatively high PAH contamination, which is higher in coal from biomass gasification than in plants designed for pyrolysis due to the nature of the process.

[0024] It is impossible to completely avoid the formation of PAHs during the gasification process. PAHs are formed as soon as temperatures in the reactor exceed 650°C and increase in quantity and toxicity with increasing temperature.

[0025] While temperatures in pyrolysis plants can be controlled and maintained at just over 650°C, they rise significantly above 1000°C during oxidation in a gasifier. However, without oxidation and reduction, high-quality wood gas or synthesis gas is not produced, making these high temperatures part of the process and unavoidable. Furthermore, a short exposure time to this temperature promotes the formation of PAHs, especially in compact gasification systems such as fixed-bed gasifiers.

[0026] In addition, to increase the efficiency of gasification, an additional increase in the peak temperatures, e.g. by preheating the combustion air or the like, may be desirable.

[0027] Although the PAH quantities produced in modern biomass gasifiers are not relevant for the operation of the plant and a downstream gas consumer, the PAH total values ​​for coal are many times higher than the limit values ​​that would qualify this coal as biochar.

[0028] In addition, there are other process-related reasons that favor the enrichment of PAHs in coal from biomass gasifiers, with condensation and sorption being relevant here.

[0029] According to the current state of the art, the coal is discharged from the reactor together with the wood gas as a particle stream, also known as a full stream. This results in a strong mixing of PAH-containing wood gas and coal particles. After the reactor's oxidation zone, the coal-gas mixture is typically not further heated, which favors the condensation of PAH as the temperature drops.

[0030] To ensure the necessary and most thorough purification of the product gas, the coal is usually separated in a gas filter consisting of a filter element to which the coal particles adhere. The PAH-containing gas stream must penetrate the coal particles, which further contaminates them. In addition, this filter element is usually cleaned or shaken off using counterpressure pulses. The pressure pulses, using a - preferably - inert gas, lead to local cooling of the filter unit and thus to increased PAH levels in the coal separated there. Simple and cost-effective filter designs are used, particularly in small plants, which increases the economic efficiency of such plants. Here, the coal-wood gas mixture is cooled before being fed into the filter, which, however, significantly increases the PAH content.

[0031] The separation of PAH-free biochar, i.e., biochar with a total EPA PAH content of <2 mg / kg, in gasification systems is currently not economically or technically feasible. The few gasification plant manufacturers that are actually capable of certifying their biochar according to the EBC criteria only achieve certifications for which only 8 of the 16 EPA PAHs are subject to a limit. However, this is biochar with severely limited potential uses.

[0032] EP 2 639 289 A1 describes previously known methods for solving the problem of PAH-contaminated coal or ash mixtures. The device disclosed here aims to reduce the amount of coal, which is no longer appropriate due to coal's potential. However, the PAH reduction also described has proven impractical in practice, and the PAH levels continue to be well above the applicable limits.

[0033] The problem with the device described here is that the coal is heated insufficiently and unevenly, which is caused by a heating unit that is only indirect.

[0034] The aim is to create a combustible gas mixture by excluding air, which should have a positive effect on the overall efficiency of the system.

[0035] The device tries to prioritize energy in the form of heat or combustible gases into the overall system by burning or converting the coal.

[0036] A heat transfer partition wall enables a material separation of the starting material or material or the reactor interior or the oxidation and reduction zones from the interior of the post-treatment or from the residual material.

[0037] EP 2 552 707 A2 describes another method for solving the problem of PAH-contaminated coal or ash mixtures. It describes the technical implementation of combustion or conversion of coal into energy such as heat or combustible gases. The device also aims to reduce the amount of coal used, which is no longer appropriate.

[0038] The invention is therefore based on the object of providing an economical process which allows PAHs arising during biomass gasification to be kept almost completely away from the end product coal or to remove coal without PAHs from the system.

[0039] The object is achieved according to the invention by the features of the independent patent claim, while advantageous embodiments and further developments of the invention can be found in the subclaims.

[0040] An advantageous feature is that the post-treatment unit comprises a process chamber into which at least the contaminated coal particles are fed above, together with the PAHs produced during the combustion of the starting material, and below which a further gas designed as a barrier gas is fed in order to form a gas separation zone within the process chamber, which largely prevents the passage of the PAHs in the direction of the discharge opening.

[0041] The additional gas forming the gas separation zone is referred to below as the barrier gas, which is capable of retaining and / or decomposing the PAH substances.

[0042] In an advantageous application, the height of the gas separation zone is the height of the process chamber x factor 0.5.

[0043] In the following, the terms wood gas and synthesis gas are used synonymously unless the composition is directly discussed.

[0044] The present invention relates to a method and a device, wherein in biomass gasification plants and pyrolysis plants, provided similar boundary conditions exist, the separation of coal particles of different sizes from a gas stream takes place, while at the same time the adhesion of PAH to the coal particles is prevented and / or PAH can be expelled and flushed out and / or cracked or burned.

[0045] This enables post-treatment and removal of the coal independent of the gasification, allowing the use of any type of biomass gasifier, depending on the requirements of the overall system.

[0046] The process chamber is designed to create a hot gas separation zone that acts as a barrier to PAHs while allowing carbon particles to pass through. This gas separation zone, created by purge air or similar, can expand within the process chamber to improve operation, thus acting as a barrier gas that forms an effective barrier against the passage of PAH-contaminated substances.

[0047] This is especially true when an oxidizing agent is used to create the gas separation zone, which is heated by a heating jacket or preheated to a defined temperature to oxidize with PAH. Thus, the heated area within the process chamber is referred to as the gas separation zone.

[0048] A constant high temperature is set in the process chamber, e.g., through oxidation, which exceeds the condensation temperature of PAHs and promotes their expulsion and flushing from the wood gas or coal particles. This is usually at least 500°C. For optimal results, temperatures up to 900°C can be set. However, increasing the temperature above 900°C in the presence of an oxidizing agent can have detrimental effects, as this leads to increased carbon reduction.

[0049] This gas separation zone is crossed by the coal particles, e.g. by gravity, with the coal particles then cooling along their further flow direction.

[0050] When passing through the gas separation zone, it is important that the coal particles have the largest possible surface area and, ideally, that each particle moves through the zone individually, without contact with other particles. This can be achieved either by gravity, with the particles falling through the zone, or by a suitable separator design that can accelerate the particles and shoot them through the separation zone. A higher relative velocity of the particles to the gas separation zone, and thus greater turbulence, can have a positive effect here.

[0051] This resulted in particularly effective heating and flushing or enclosing of the particles by the gas separation zone, particularly by the sealing gas present there. In this way, the gaseous PAHs are separated, washed away, or flushed away from the coal particles present in the wood gas.

[0052] Preferably, the gas separation zone spreads in the opposite direction to the movement of the coal particles, which can achieve an improved barrier effect.

[0053] Preferably, a largely flameless oxidation takes place within a process area of ​​the process chamber, ie there is no flame in which the coal could burn.

[0054] Such oxidation produces very uniform temperatures of 750°C, 800°C, or even 1000°C. Flame suppression is achieved by allowing the oxidizing agent and wood gas to enter the process chamber in opposite directions, and by maintaining a high proportion of already combusted wood gas, which recirculates within the process chamber.

[0055] Experiments have shown that when an oxidizing agent heated to approximately 350°C is introduced below the process chamber and encounters the wood gas at approximately 600°C in the process chamber, no mixing of these temperatures occurs, but rather an oxidation process, where much higher temperatures are to be expected.

[0056] At these high temperatures and during oxidation, the PAHs are further thermally decomposed in the gas separation zone within the process chamber. PAHs have the property of oxidizing with oxygen at temperatures above 500°C. However, when the carbon particles pass through this zone, they do not burn up, as they only remain there for a short time.

[0057] The introduced gaseous oxidant typically does not have a controllable temperature, but is introduced at a nearly constant temperature, with the amount of oxidant influencing the oxidation process. If the oxidant is air, a higher air flow rate, especially the oxygen it contains, leads to hotter oxidation and thus a rise in temperature.

[0058] In one embodiment, the gas separation zone is created in the process chamber by oxidation using bypass air as the oxidant.

[0059] In this process, an oxidizing agent preheated to at least approximately 200°C, ideally approximately 500°C, is introduced into the process chamber as a seal gas, usually ambient air, and oxidized with parts of the wood gas. The oxidizing agent can be preheated via a heat exchanger or similar device, or it can also be implemented as part of the reactor's combustion chamber and its discharge device. However, it must be ensured that the target temperature is almost reached at the moment it enters the process chamber.

[0060] The desired oxidation occurs as soon as the mixture of wood or synthesis gas and the oxidant, for example, reaches a temperature of approximately 500°C (3:1 ratio). This is not possible without preheating the oxidant.

[0061] The predominant components of wood gas, such as hydrogen, carbon monoxide and methane, require an ignition temperature of slightly above 500°C, but combustion is additionally initiated or promoted by the coal particles, which are hotter at the moment they enter the process chamber.

[0062] If the temperatures of the wood gas and thus also of the coal particles are too low at this point in the system, an initial ignition of the mixture can be initiated by a suitable device, for example by an ignition device protruding into the process chamber.

[0063] As soon as a certain temperature value is reached by heating within the thermally well-insulated process chamber, the oxidation takes place as a very stable, uniform and ideally flameless combustion.

[0064] The special advantage of such a gas separation zone using oxidation is that the PAHs are at least partially burned, thus further improving the purity of the biochar.

[0065] A further advantage has been found if the mixture of wood gas and the oxidizing agent has a lambda value of significantly less than 1.0, whereby the oxidation is directed at the wood gas and the decomposition of valuable carbon is avoided.

[0066] In addition, it is necessary that a certain degree of flow turbulence exists within the process chamber, which can ensure uniform mixing as well as the supply and removal of synthesis gas or already combusted synthesis gas and thus continuous operation.

[0067] If oxidation is used to create the gas separation zone, it must be ensured that sufficient wood gas can enter the process chamber for oxidation. Baffles, guide tubes, or similar devices are advantageous for generating and directing appropriate gas flows.

[0068] In certain cases, it may also be useful to divert a small amount of the wood gas directly and feed it into the process chamber.

[0069] Temperature control is achieved by controlling the amount of oxidizing agent supplied, for example, to increase the temperature by introducing a larger amount of oxidizing agent. A temperature-resistant ball valve, for example, can be used, which is moved by a proportional control element, e.g., an actuator, to control the amount.

[0070] The required temperature of the gas separation zone depends on many factors. Continuous operation shows that at approximately 750°C, coal or coal particles can be removed from the system with PAH concentrations below 1 mg / kg.

[0071] Temperature monitoring is usually carried out using one or more suitable sensors mounted in or on the process chamber.

[0072] In a further embodiment of the invention, a heated oxidizing agent, usually air, is introduced into the process chamber as a barrier gas.

[0073] However, due to a lower temperature (e.g. 400°C) of the wood gas and its carbon particles, which is desired at this point in the post-treatment unit and is brought about by cooling, for example, combustion does not occur and it is also not intended to achieve an initial or permanent ignition.

[0074] The temperature of the supplied air already has the target temperature for heating and flushing out the PAHs (e.g. 500°C) and thus represents the gas separation zone. The maximum temperature is limited to about 600°C, otherwise decomposition of the coal occurs.

[0075] In this case, the process chamber is designed in such a way that as little wood gas as possible can enter the chamber, since this is not needed due to the lack of oxidation.

[0076] The preheated air also has the necessary barrier effect between the interior of the biomass gasifier and the coal discharge, so that no PAHs can condense on the coal during cooling, which usually takes place during discharge.

[0077] This process is particularly suitable when the loading of the wood gas and the coal particles with PAHs is low, and only by preventing the condensation of PAHs on the coal, which usually occurs during discharge from the system, can coal be generated with acceptable PAH quantities.

[0078] Using a cold oxidizer, which is introduced as a barrier gas at an ambient temperature of, for example, 30°C, combustion as described above is made more difficult, but is possible under certain circumstances.

[0079] Even in a process chamber that is already in full operation, combustion is extinguished or at least becomes highly unstable when switching from warm to cold oxidizer.

[0080] In this case, continuous ignition is necessary to maintain combustion of the mixture. This can be achieved by a supporting firing of any kind, a local, externally heated hot surface, a piezo ignition, or something similar to ensure continuous combustion.

[0081] However, this process can lead to local flame spread and possibly even pulsations, causing coal to oxidize due to the locally higher temperatures and the locally higher proportions of unburned oxygen. Furthermore, the prevailing inhomogeneous temperature distribution would not ensure uniform and consistent PAH removal. Furthermore, the wood gas consumption required to reach the target temperature is significantly higher.

[0082] However, the process using a cold oxidizer is suitable if the wood gas and the coal particles have only a low loading of PAHs and this process thus contributes to an improvement in generating coal which has acceptable PAH amounts.

[0083] In a further embodiment, the gas separation zone is not generated by an externally supplied gas or by oxidation, but by a special design of the process chamber, whereby the gas separation zone can be created in the process chamber itself by heating.

[0084] The design of the process chamber has a significant impact on its functionality. It is generally designed to be as compact as possible to minimize the amount of wood gas or synthesis gas used for heating.

[0085] The further advantage of a compact chamber is that carbon particles from the separator must fall directly through the oxidation zone or gas separation zone.

[0086] This allows the largest possible surface area of ​​the coal particles to be used for heating and for flushing out and, if necessary, cracking and / or burning the PAHs present on the surface.

[0087] A vertical cylinder is particularly suitable, as the height significantly exceeds the diameter, since the carbon particles must travel a particularly long distance through the gas separation zone. The round cross-section of the cylinder also prevents carbon particles from descending into corners or similar areas outside the process area without adequate heating / flushing of the PAHs. A cylinder also offers the smallest surface area in relation to its area, which also reduces heat loss.

[0088] However, under certain circumstances, other geometries may also be advantageous, such as a three-sided or six-sided prism, a cuboid, or the like. The key here is that the area of ​​the vertical section significantly exceeds that of the horizontal section.

[0089] Advantageously, the geometry of the process chamber is selected such that the process chamber consists of a cylinder with a smaller diameter than the cylinder height with a ratio of, for example, 0.3.

[0090] Due to the slim design of the cylinder, there is so little gas exchange between the upper and lower ends that, under certain circumstances, the gas separation zone, which migrates or spreads in the opposite direction to the movement of the carbon particles and the barrier effect initiated thereby, can even be dispensed with.

[0091] This also prevents wood gas or synthesis gas from accumulating in the lower area of ​​the process chamber, which in turn could escape from the process chamber with the coal and cool down in the direction of movement of the coal, condensing PAH.

[0092] Furthermore, the cylinder can be surrounded by a heating jacket, which heats the interior of the cylinder and thus also the process area with the gas separation zone to a necessary or defined target temperature.

[0093] The geometry of the separator and the process chamber within the cylinder is also selected so that as little wood gas as possible can enter the process chamber, since this is no longer needed due to the lack of oxidation within the process chamber.

[0094] A suitable separator removes the coal particles from a gas stream, preferably just after the gasification reactor. Upon leaving the reactor, temperatures typically range between 600°C and 800°C, creating a so-called hot gas zone, and the wood gas is ideally processed without prior cooling.

[0095] It has been found to be advantageous if a mass force separator is used as the separator, which, due to its structural design, leads to a desired flow characteristic and turbulence of the substances flowing through.

[0096] A mass force separator also separates or prevents the particularly fine particles within the gas stream, which usually have a significantly higher ash content and make up about 5% of the mass of the substance.

[0097] These particles remaining in the wood gas stream are separated from the gas stream by a separate filter downstream of the gas flow. This allows approximately 95% of the total amount of particles to be converted into PAH-free biochar. Due to the absence of these particularly fine particles, this product is particularly high-quality, easy to process, and less prone to dust formation.

[0098] This design can be particularly advantageous in small systems if the inertia separator is followed by a gas cooling system and then the necessary additional filter unit.

[0099] This combination represents exceptional cost-effectiveness, as it eliminates the need for additional filters used to filter gases in the hot gas area. These are expensive, complex, and also pose a high risk.

[0100] Furthermore, it is advantageous if the separator is designed so that the coal particles are accelerated downwards. This ensures that they pass through the center of the gas separation zone or the oxidation area and are not deflected toward the edge or pushed into the edge area by rotation or similar forces. Furthermore, this ensures that as few particles as possible are deflected upwards again by the opposing gas flow or the expanding gas separation zone, which could potentially reduce the separation rate of the device.

[0101] An inertial separator is particularly well suited to this requirement and is shown as an example in the figures.

[0102] In another embodiment, it is advantageous if the carbon particles are mechanically removed from a particle separator and only then fall into the process chamber. This is particularly useful when a filter separator is used to ensure that no blockage occurs at the inlet to the process chamber. Typically, the filter cross-section must be significantly reduced towards the process chamber.

[0103] In addition, this allows for a uniform and controlled dosing of carbon particles.

[0104] In a further embodiment, a highly heated inert gas is introduced into the process chamber as a barrier gas instead of an oxidizing agent to form a gas separation zone. The inert gas can be taken, for example, from the exhaust stream of a combined heat and power plant. The temperature of the gas is already at the target temperature for heating and purging the PAHs, which can be, for example, 700°C.

[0105] In this case, the process chamber is designed so that as little wood gas as possible can enter the chamber, since this is not needed in this application due to the lack of oxidation.

[0106] The inert gas also provides the necessary barrier effect between the interior of the biomass gasifier and the coal discharge, so that no PAHs can condense on the coal during cooling, which usually takes place during discharge.

[0107] At the lower end of the process chamber are one or more mechanical moving elements, such as conveyor spirals, designed to transport the coal after it has left the process chamber. These elements move the coal from the lower area of ​​the process chamber to a lock, which serves to separate the process chamber from the ambient air.

[0108] This lock also serves to remove the coal from the system and ideally consists of two virtually gas-tight closure flaps or gate valves. In special designs and with low pressure conditions, a rotary valve or similar device may also be sufficient.

[0109] During the warm-up or start-up phase, it is usually unavoidable that PAH-contaminated coal accumulates in the lower area of ​​the process chamber. The mechanical conveying element is preferably still inactive at this point, but it has been shown that coal particles that have settled in the lower area only release the PAHs insufficiently, even when the operating temperature is subsequently reached.

[0110] This shows another advantage of a slim and tall process chamber as described above.

[0111] The carbon particles can now be strongly stirred towards the top of the process chamber by a larger amount of heated gas supplied or with the aid of a pressure pulse of cold sealing air and / or even brought upwards through the inlet of the process chamber back into the system.

[0112] This means that when the operating temperature is reached or reached again, the process chamber can be cleaned, emptied or re-layered once, thus ensuring that almost PAH-free coal is discharged at all times and thus consistent quality is produced.

[0113] In order to ensure that the carbon particles reach as close to ambient temperature as possible before leaving the system for better handling and to avoid glowing particles, a cold cooling gas at ambient temperature can be introduced into the system as a pressure pulse or continuously in the flow direction of the carbon particles after leaving the process chamber.

[0114] In a special design, it has been shown that a pulsating cooling gas reduces the oxidation of valuable carbon and promotes cooling.

[0115] In a further embodiment, a storage container for storing the coal particles is arranged in the opposite direction to the movement of the coal particles from the process chamber, in which container coal can be temporarily stored during the start-up phase and can be passed through the process chamber again when the operating temperature is reached.

[0116] The filling and emptying of the storage container is possible by reversing the direction of the mechanical movement element installed here, which is intended to transport the coal.

[0117] In a further embodiment, there is a separate discharge option in the opposite direction to the actual discharge direction of the coal particles, through which poor quality coal can be discharged from the system during the start-up phase or in phases with insufficient temperature in the process chamber.

[0118] It has been shown that in many known gasification systems, changes in the feedstock can result in significantly different coal qualities. The separate post-treatment unit according to the invention, which is located downstream of the reactor, eliminates small fluctuations in coal quality, significantly increasing the plant's flexibility with regard to the quality and moisture content of the biomass used.

[0119] The residence time of the coal particles in the device according to the invention can be reduced to a few seconds if functioning properly. This allows large quantities of coal to be removed from the system PAH-free, with minimal energy consumption for heating the device components.

[0120] A short residence time also prevents unwanted oxidation of carbon particles, especially when oxidizing agent is introduced into the lower area of ​​the process chamber.

[0121] In general, the low energy consumption of the process chamber to maintain the gas separation zone does not lead to a significant shift in the efficiency of the overall system.

[0122] The subject matter of the present invention results not only from the subject matter of the individual patent claims, but also from the combination of the individual patent claims with one another.

[0123] All information and features disclosed in the documents, including the abstract, in particular the spatial configuration depicted in the drawings, could be claimed as essential to the invention, insofar as they are novel, individually or in combination, compared to the prior art. The use of the terms "essential" or "according to the invention" or "essential to the invention" is subjective and does not imply that the features so named must necessarily be part of one or more patent claims.

[0124] The invention is explained in more detail below with reference to drawings illustrating only one embodiment. Further essential features and advantages of the invention will become apparent from the drawings and their description.

[0125] They show: Figure 1: Simplified representation of a hot wood gas with coal particles and PAH Figure 2: Simplified representation of a slightly cooled wood gas with coal particles and PAH Figure 3: Schematic representation of the process area Figure 4: Schematic representation of the process area with oxidizer Figure 5: Schematic of a gasifier with an inertial separator for coal particles Figure 6: Schematic of a gasifier and a process chamber with heat exchanger and cold purge air Figure 7: Schematic of a gasifier with an additional intermediate storage of coal Figure 8: Schematic of a gasifier with a centrifugal separator with an additional heating jacket and an ignition device Figure 9: Schematic of a gasifier with a post-treatment unit,where in addition a second discharge possibility for coal is available Figure 10: Scheme of a gasifier with a filter separator for coal Figure 11: Scheme of a gasifier with a filter separator for coal and a further conveying element Figure 12: Scheme of a post-treatment unit with a heat exchanger,

[0126] Figure 1 shows schematically the outlet 24 of the reactor 2, wherein the wood gas 5, the coal particles 28 and the gaseous PAH 39 flow from the reactor into the pipe 46. Within the pipe 46, when moving in the direction of arrow 47, the gas mixture cools down and the PAH 39 are deposited on or in the coal particles 28, as Figure 2 is shown.

[0127] Figure 3shows how these components then flow in the direction of arrow 31 into the process chamber 16, whereby the components are still hot. Within the process chamber 16 there is a process area 36 in which a gas separation zone 17 extends horizontally between the wall of the process chamber 16 and the cylinder 33 in which the process chamber 16 is located. The gas separation zone 17 is formed by a gas 10, 11 or 12 flowing into the process chamber 16 from below into the cylinder 33 in the opposite direction to the direction of arrow 31. The top side of the gas layer introduced here forms the gas separation zone 17 within the process area 36. Depending on the process parameters, such as the amount of gas, the gas separation zone 17 can rise and fall within the process area 36.

[0128] The components now enter the process area 36, ​​as shown in Figure 4is shown. When the coal particles 28, which were still surrounded or occupied by the PAHs 39 upon entering the process area 36, ​​impact the gas separation zone 17, the PAHs 39 dissolve and remain above the gas separation zone 17, while the coal particles 28', now freed of PAHs, fall down in the direction of arrow 31 and are conveyed towards the discharge opening 45.

[0129] The wood gas 5 is diverted upon impact with the gas separation zone 17 and flows again, opposite to the direction of the arrow 31, out of the process area 36 and can then leave the area of ​​the process chamber 16 via the pipe 49 shown.

[0130] The PAH 39 remain above the gas separation zone 17 and are removed from the process via pipeline 49.

[0131] The carbon particles 28', which have passed through the gas separation zone 17, are now located within the barrier gas, which may be, for example, an oxidizing agent 10. This example is also shown in Figure 4 shown, wherein the oxidizing agent 10, initially shown by an arrow, is introduced via the feed line 42 into the area below the process area 36, ​​the process chamber 16 rises and forms the gas separation zone 17 within the process area 36.

[0132] The coal particles 28', which have passed through the gas separation zone 17 and have been freed from the PAH 39, are now located within the oxidizing agent 10 and can be transported towards a discharge opening 45.

[0133] Regarding the Figures 1 to 4It should be added that the PAHs 39, for example, are initially present at a temperature of 480 °C and are exposed to a temperature of over 600 °C by the process within the process area 36. Initially, this is wood gas 5, which also contains gaseous PAHs, as well as coal particles 28 that are moved along with the wood gas. If this mixture now cools down, the PAHs 39 accumulate in the coarse-pored, large-surface-area coal particles 28. This, however, must be avoided. For this reason, a gas 10, 11 or 12 is introduced into the cylinder 33 against the flow direction of the wood gas 5, so that the wood gases 5 bounce off the surface (gas separation zone 17) of the barrier gas 10, 11 or 12, are deflected and discharged towards an exit.

[0134] Meanwhile, the coal particles 28' fall downward and can be removed. In another embodiment, the coal particles 28' are first collected, and only after a lock is opened can the particles 28' be removed.

[0135] Figure 5 shows a feed unit 1 for feeding a starting material into the reactor 2, in which the temperatures are typically between 600°C and 800°C. This has an oxidation zone 3 and a reduction zone 4. The produced wood gas 5, which contains carbon particles 28, then leaves the reactor 2 via the outlet 24, ideally without prior cooling.

[0136] In a manner not shown in detail, the wood gas 5 passes through a mass force separator 8, so that a wood gas 5', which now contains fewer coal particles than the original wood gas 5, can be discharged in the direction of arrow 32. By means of the separator 8, the coal particles 28 are also removed from the wood gas stream 5 and guided into a separate area, the process chamber 16. The process chamber 16 represents the area for treating the coal, whereby the coal initially has a high PAH content, which must be separated from the coal.

[0137] The process chamber 16 is designed in such a way that a hot gas separation zone 17 is formed therein, which represents a barrier to the PAH 39, but allows the passage of carbon particles 28.

[0138] For better visualization, the coal particles 28 above the gas separation zone 17 contain the PAHs 39. After passing through the gas separation zone 17 within a process area 36, ​​the coal particles 28' are then present without PAHs.

[0139] After passing through the process chamber 16, the coal particles 28' fall onto the conveying element 14, which represents a mechanical conveying element for the coal. The conveying element 14 is located within the housing 34, which is connected to the process chamber 16 in a flow-conducting and gas-tight manner. The supply of the oxidizing agent 10, usually gas, is regulated via a control valve 30. Depending on the amount of the oxidizing agent 10, the separation process within the process chamber 16 is influenced, so that the gas 5', which now contains significantly fewer coal particles, can escape in the direction of arrow 32. Depending on the amount of the introduced oxidizing agent 10, the temperature within the process chamber 16 is also influenced, with the temperature being monitored by a temperature sensor 29.

[0140] The coal particles 28', which now have a significantly reduced PAH content due to the treatment in the process chamber 16, are transported via the conveying element 14 to a coal container 19 located outside the post-treatment unit. Between the coal container 19 and the housing 34 is the lock system 15, which enables a virtually gas-tight seal against the environment 6. Downstream of the lock system, there is a discharge opening 45 through which the coal particles 28' can leave the device toward the coal container 19.

[0141] Figure 6 shows a further embodiment of the post-treatment unit, wherein the wood gas 5 with the coal particles 28 leaves the reactor 2 via the discharge unit 24 and is fed via a pipeline 46 to a vertical tube 37, which has a funnel 35 at the inlet area. Below the funnel 35, the tube 37 is surrounded by a heating jacket 38.

[0142] A pipeline 49 branches off from the pipeline 46 above the hopper 35. The wood gas 5' returning from the process area and freed of coal particles is conducted through this pipeline 49. This still warm wood gas 5' serves to heat the heating jacket 38, which is fed by the pipeline 49. The heat of the wood gas 5' is transferred to the tube 37 guided within the heating jacket 38. In this way, a process area 36 can be formed within the tube below the hopper 35, which prevents the PAH 39 from flowing through the tube 37 in the direction of arrow 31. Thus, only the cleaned coal particles 28' fall onto the conveying element 14 and are transported through the housing 34 to a coal container 19. The housing 34 is sealed from the environment 6 by means of the lock system 15.The reference symbol Delta T (ΔT) represents the temperature difference between two measuring points, in this case the process area 36 and the heating jacket 38.

[0143] The housing 34 also has a supply line 40 through which cooling gas 13 can be introduced into the housing as cold sealing air. Due to the gas-tight connection between the housing 34 and the tube 37, this cooling gas 13 is introduced into the process area 36.

[0144] Thus, the tube has a hot area in the area below the funnel 35 and a cold area in the area near the housing 34.

[0145] Figure 7 shows how, due to the treatment within the process chamber 16, the wood gas 5', with greatly reduced carbon particles, leaves the process chamber 16 in the direction of the arrow 31 and can flow out. The wood gas 5' flows in the direction of the arrow 48 into a pipe 49 branching off from the pipe 46 above the cylinder 33.

[0146] Below the process chamber 16 or the cylinder 33 is the conveying element 14, which can convey the coal particles 9' either to a storage container 20, for the intermediate storage of the coal particles 28' or to the coal container 19.

[0147] An inert gas 11 can be introduced into the housing 34, which is connected to the process chamber 16, i.e., the cylinder 33, in a virtually gas-tight manner, via the supply line 41. This gas then flows into the process area 36 and acts as a seal gas there. This inert gas can, for example, have a temperature of at least 600°C.

[0148] A cooling gas 13 can be introduced via a further supply line 40 in order to influence the process and to partially cool the system and the coal particles.

[0149] Figure 8shows a further embodiment, in which an inertia separator 8 is used. This is a cyclone separator. The carbon particles 28 enter the process chamber 16 in the direction of arrow 31. A cold oxidizing agent 12 is introduced into the housing 34 via a supply line 43 on the housing 34 and thus supplied to the process area 36 within the process chamber 16. Due to the relatively cold temperature of the oxidizing agent 12, an ignition device 25 is necessary to start the oxidation within the process area. In addition, the cold oxidizing agent 12 can be heated by a heating jacket 21 surrounding the housing as it passes through the housing 34.

[0150] Figure 9 shows a further embodiment as a further development of Figure 5Here, the conveying element 14 can convey between two coal containers 19a, 19b, providing a second discharge option for the coal. Additionally, the oxidizing agent 10 can be supplied to the process via the supply line 42, as can the cooling gas 13 via the supply line 40. The coal particle stream 9 is shown in simplified form and leaves the process chamber as coal particle stream 9' after the PAHs have been removed.

[0151] Figure 10shows a further embodiment, wherein the wood gas 5 with the coal particles 28 flows through a hot gas filter 23. Below the hot gas filter 23, the process chamber 16 is connected via the inlet area 27, in whose process area 36 the gas separation zone 17 is formed. After passing through the gas separation zone 17, the coal particle flow 9' has been freed of the PAHs, and the coal particles 28' reach the conveying element 14. In addition, the oxidizing agent 10 can be introduced into the process chamber 16. This oxidizing agent can be partially discharged through the pipeline 49 together with the wood gas 5'.

[0152] Figure 11 shows a further embodiment in which the wood gas 5, which contains the coal particles 28, is again passed through a hot gas filter 23. Compared to the Figure 10 , which also deals with a hot gas filter, is in Figure 11As an alternative to a funnel-shaped inlet area 27, a further conveying element 44 is provided. This is intended to prevent a possible accumulation of particles, as might occur with a funnel.

[0153] Figure 12 shows a further embodiment, wherein the wood gas 5' discharged via the pipe 49 is passed through a heat exchanger 18. This heat exchanger 18 also heats an inert gas 11, which at least partially absorbs the thermal energy of the wood gas 5' within the heat exchanger.

[0154] The thus heated inert gas is fed to cylinder 33 and in particular to process area 36 to separate the PAHs from the coal particle stream 9. Instead of an inert gas, an oxidizing agent can also be heated in this way. Drawing legend

[0155] 1 Feed unit 2 Reactor 3 Oxidation zone 4 Reduction zone 5, 5 Wood gas 6 Environment 7 Post-treatment unit 8 Mass force separator 9, 9 Coal particle flow 10 Oxidizer (preheated) 11 Inert gas (preheated) 12 Oxidizer (cold) 13 Cooling gas 14 Conveyor element 15 Lock system 16 Process chamber 17 Gas separation zone 18 Heat exchanger 19, 19a, 19b Coal container 20 Storage container 21 Heating jacket 22 (empty) 23 Hot gas filter 24 Output unit 25 Ignition device 26 Particle flow 27 Inlet area 28, 28 Coal particles 29 Temperature sensor 30 Control valve 31 Arrow direction 32Arrow direction 33Cylinder 34Housing (of 14) 35Funnel 36Process area 37Tube 38Heating jacket 39PAK 40Inlet (of 13) 41Inlet (of 11) 42Inlet (of 10) 43Inlet (of 12) 44Conveyor element 45Discharge opening 46Pipe 47Arrow direction 48Arrow direction 49Pipe ΔTDifference in temperature

Claims

1. A method for producing a combustible gas mixture (5, 5') from a carbon-containing starting material, in particular from lumpy wood, with a feed unit (1) for feeding the starting material to a reactor (2), wherein the reactor (2) comprises at least one discharge unit (24) for discharging a carbon-containing residue, in particular coal particles (28), wherein a post-treatment unit (7) is provided for post-treating the residue to reduce polycyclic aromatic hydrocarbons [PAH] (39) before the coal particles (28') leave the post-treatment unit (7) via a discharge opening (45), characterized in thatto produce a largely uncontaminated biochar, the post-treatment unit (7) comprises a process chamber (16) into which at least the contaminated coal particles (28) are fed above together with the PAHs (39) produced during the combustion of the starting material, and below which a further gas (10, 11, 12) designed as a sealing gas is fed in order to form a gas separation zone (17) within the process chamber (16) which largely prevents the passage of the PAHs (39) in the direction of the discharge opening (45).

2. Method according to claim 1, characterized in that the coal particles (28, 28') pass through the gas separation zone (17) essentially from top to bottom by means of gravity and / or by prior acceleration.

3. Method according to claim 1 or 2, characterized in that the gas separation zone (17) in the process chamber (16) spreads by supplying the gas (10,11,12) against the direction of movement of the coal particles (28').

4. Method according to one of claims 1 to 3, characterized in that the coal particles (28) are separated from the gas mixture (5, 5') by a separator (8) after leaving the reactor (2) and fed to the process chamber (16).

5. Method according to one of claims 1 to 4, characterized in that the gas (10, 11, 12) for forming the gas separation zone (17) is supplied to the process chamber (16) essentially at the point at which the coal particles (28) leave it.

6. Method according to one of claims 1 to 5, characterized in that an oxidizing agent (10, 12), preferably air, is introduced into the process chamber (16) as a gas, which oxidizes (17) with portions of the combustible gas mixture (5) in the process chamber.

7. Method according to one of claims 1 to 6, characterized in thatthe oxidizing agent (12) is cold and flows through the process chamber (16) at least partially against the flow direction of the coal particle flow (9) and oxidizes with portions of the combustible gas mixture (5, 5') in the process chamber (16), and that an ignition device (25) present in the process chamber (16) initiates or permanently ensures the oxidation.

8. Method according to one of claims 1 to 5, characterized in that the gas introduced into the process chamber (16) is a heated inert gas (11).

9. Device for producing a combustible gas mixture (5, 5') from a carbon-containing starting material, in particular from lumpy wood, with a feed unit (1) for feeding the starting material to a reactor (2), wherein the reactor (2) comprises at least one output unit (24) for outputting a carbon-containing residue, in particular coal particles (28), wherein a post-treatment unit (7) is provided for post-treating the residue to reduce polycyclic aromatic hydrocarbons [PAH] (39), characterized in thatIn order to produce a largely uncontaminated biochar, the post-treatment unit (7) comprises a process chamber (16) into which at least the contaminated coal particles (28) can be fed above, together with the PAHs (39) produced during the combustion of the starting material, and below which a further gas (10, 11, 12) designed as a sealing gas can be fed in order to form a gas separation zone (17) within the process chamber (16) which largely prevents the passage of the PAHs (39).

10. Device according to claim 9, characterized in that the process chamber (16) is a vertically arranged cylinder (37, 48) whose height is at least twice as large as the diameter.

11. Device according to claim 9 or 10, characterized in that at least one conveying element (14) for moving and / or discharging the coal particles (28') is present below the process chamber (16).

12. Device according to one of claims 9 to 11, characterized in thatFor removing the coal particles (28') from the overall system, a virtually gas-tight lock system (15) with at least two sealing elements connected in series but always with at least one closed sealing element such as a flap / slide valve or the like is installed.

13. Device according to one of claims 9 to 12, characterized in that the gas (10, 12, 13) is introduced into the housing (34) of the conveying element (14) via a supply line (40, 42, 43), and that the housing (34) is connected in a gas-tight manner to the underside of the process chamber (16).

14. Device according to claim 13, characterized in that For temperature control within the process chamber (16), the quantity of heated gas (10) supplied can be adjusted by means of a proportional control valve (30) in the region of the supply line (42).

15. Device according to claim 9, characterized in that the process chamber (16) is surrounded by a heating jacket (21) which forms the gas separation zone (17) by heating.

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