DE102011107621B4 - Fine purification of product gases - Google Patents

Abstract

Process for cleaning a product gas, which is generated by processing biomass, comprising the following process steps: - generating a product gas by thermochemical conversion of biomass in a reactor (20), - deriving the product gas generated from the generation and feeding it into a wet-working main gas purification stage (22), the product gas being cooled in the main gas cleaning stage (22) to at least its cooling limit temperature of less than 90°C,- the product gas, now cleaned to a maximum contamination load of 10%, is fed into a wet-operated filter (24), the essential Part of a depth filter material (26 or 26a) of the filter (24) is preceded by radially symmetrically arranged preseparator layers (26d) in relation to the main part of the depth filter, which are arranged vertically opposite the filter (24), and making the product gas cleaned in this way available for a Consumer.

Description

The present invention relates to a method and an at least one-stage filter device for the filtering and blockage-free fine cleaning of product gases. The invention relates to a method for producing and purifying a product gas with a high calorific value, which is produced from biomass by thermochemical conversion (gasification or pyrolysis). In particular, it relates to a purification process for a product gas produced in this way.

Product gases with a high calorific value can be generated by the processes of thermochemical gasification or pyrolysis under conditions of air deficiency from biomass such as wood, fermentation residues from biogas plants, green waste, roadside greenery, biomasses that typically occur in composting plants or animal manure, e.g. dried chicken manure. Irrespective of this, these biomasses can be fed directly to the thermochemical conversion or can be pretreated beforehand by hydrothermal carbonization. Such methods and devices for hydrothermal carbonization of biomass are in particular from WO 2008/095589 A1 known.

Process for wet high-performance gas cleaning of such product gas are, inter alia, in DE 10 2007 002 895 A1 described.

the U.S. 2007/0094929 A1 discloses a gasification technique for converting difficult-to-treat biomass into a clean gaseous fuel that can be burned in a cogeneration plant, comprising a first stage of fluidized bed catalytic gasification and a second stage of tar gasification and catalytic reforming.

the DE 26 15 180 A1 discloses a method for cleaning off-gases containing mist droplets of non-evaporating adhesive substances under processing conditions, wherein the off-gases are treated with water and filtered, the water being introduced into the off-gas stream in a finely divided manner in the manner of a mist, the subsequent filtering of the off-gas stream takes place with the filter being soaked through, and the filtering is carried out with low flow resistance and a large filter depth.

The problem with the known methods for producing and in particular for cleaning such a product gas obtained from biomass lies in the impurities that are contained in the product gas and which can only be removed inadequately or complex and prone to failure by gas cleaning according to the prior art . It is known, for example, that wood gasification produces product gases heavily laden with tar and dust, which leads to blockages, impairments and malfunctions in downstream machines that use the product gas. Similar problems also arise with product gases generated from other biomasses. Tar is a collective term for higher hydrocarbons, which occur mainly at ambient temperature through condensation as tar aerosols. Dust is the term used to describe solid contaminants, such as unburned carbon and ash, which appear as solid dust particles regardless of temperature. For the exact definition of tar, reference is made to the so-called tar protocol.

Gas cleaning has therefore been the most critical point in the use of the product gases in question for many years. The aim is a gas quality that is such that a turbo engine can be operated with the product gas. Turbochargers are used in turbo engines. These tend to clog, deposits build up in them, etc. All of this should be prevented. However, mechanical impairment of the engine should also be prevented, the dirt load in the product gas should not lead to mechanical impairment of the turbo engine. In the case of turbo engines, for example, Otto engines are meant here.

The process according to the invention for the production and purification of the product gas should take place in such a way that the maintenance intervals are within a reasonable range. This means maintenance between one and three months as an example. The corresponding system should therefore run trouble-free for at least a month before the fine cleaning according to the invention has to be serviced again. The cleaning interval of the downstream components, especially the turbocharger, can be extended to up to once a year. These maintenance cycles have not yet been achieved with current systems based on the general state of the art.

The subject matter of the invention is also a filter device which can be used for the fine cleaning of a high-calorific product gas produced in a reactor (20) by direct thermochemical conversion of biomass and/or biomass pretreated by other methods, which gas is produced in a wet-operating main gas purification stage before entry into the filter device according to the invention (22), which contains at least one electrostatic precipitator with prequench or a high-performance gas scrubber, which reduces the dirt load from at least 100% to 10% (related to dust particles and tar aerosols with a diameter of 1 µm when the raw gas exits the reactor (20) and exit of the pre-cleaned product gas from the gas main cleaning stage (22) at gas temperatures of 10 to 50 °C) and during this pre-cleaning it is cooled down to at least its cooling limit temperature of less than 90 °C, preferably below 50 °C, in order to Product gas occurring unwanted tars condensable as aerosols and in the filter device according to the invention a fibrous depth filter with great depth, ie at least 1.5 kg of fibers per square meter inflow area can be used, which can be operated wet and with an inflow velocity of the product gas in the operating state of 0.2 up to 20 meters per minute, preferably from 2 to 8 meters per minute, and which can be post-moisturized during operation under differential pressure control by means of an additional external liquid and/or steam feed and which delivers the product gas with a high calorific value to a subsequent consumer so cleaned that it can be used with long maintenance int expected is operable, is usable.

Accordingly, the invention has set itself the task of further developing the known processes for the production and purification, in particular for the purification of product gases, which are obtained from biomass by thermochemical conversion, in such a way that the purification only has to take place at longer intervals and the quality of the product gas in is a range that is suitable for the continuous operation of turbocharged engines. Large intervals within the meaning of the invention are in particular maintenance intervals of at least one month. A permanent operation within the meaning of the invention is in particular the possibility of an uninterrupted operation until the next maintenance or the next maintenance interval.

This object is achieved by a method with features according to claim 1 and a filter device according to claim 10.

Advantageous configurations of the invention are characterized by the features of the dependent claims.

Advantageously, the dirt load still remaining in the clean gas after the fine cleaning process according to the invention, in particular comprising dust particles and tar aerosols, is less than 1 mg/m ³ _N.

The invention consists of a filtering and blockage-resistant gas cleaning process which has two stages, namely a main stage and a fine or final separator which is installed downstream of the main stage for the gas pre-cleaning.

The fine cleaning stage is based on wet depth filtration and is also simply referred to as a filter. The main stage is based on the principle of wet gas cleaning. The gas cleaning method according to the invention can significantly reduce the emissions of dust, aerosols and condensing gas components, and the maintenance effort on subsequent components can be reduced.

The process according to the invention relates to the fine purification of product gases with a calorific value of 3 to 20 MJ/m ³ _N , in particular 4 to 7 MJ/m ³ _N , and a volume flow of 10 to 40,000 m ³ _N /h, preferably 20 to 2000 m ³ _N /h and more preferably from 50 to 1500 m ³ _N /h. The invention expressly excludes applications other than the purification of product gases with a high calorific value, in particular medical applications. In addition, the invention excludes applications for gas cleaning in the field of thermochemical conversion of household and comparable municipal waste and hazardous waste that is subject to monitoring.

In the process engineering area of gas cleaning, dry filtering, electrostatic, thermal, catalytic and wet separation processes are used, among others. The best separation performance for dust is achieved with filtering separators. The operation of conventional filters, e.g. designed as dry-operated bag, cartridge or bag filters, is often problematic when there is moisture or condensing components in the gas, such as tar, since the filter media can become clogged with wet sticky dust adhesions when the dew point is undershot. As a result of this clogging, a filter can completely lose its functionality after a short period of operation.

Even an increase in the gas temperature, in particular after it has fallen below the dew point, does not completely eliminate the condensed droplets, so that it can be used to adjust the droplet loading of the gas before it enters the filter.

Especially for the operation of rather small power generation systems, it is therefore assumed that after the water and/or tar has fallen below the dew point once, conventional filters, e.g. bag filter systems, can no longer be operated with sufficient safety.

Wet separators can be considered for the process. They are rather insensitive to moisture and condensing gas components. Generally speaking, the wet separators can be divided into normal ones and high-performance scrubbers. The group of high-performance scrubbers includes rotary and venturi scrubbers. However, even high-performance scrubbers have a lower separation efficiency for small particles than filters.

For a more detailed description of the known gas cleaning processes, reference is made to the specialist literature, such as Löffler: dust separation, Vauck-Müller: basic operations of chemical process engineering, and the homepages of manufacturing companies, such as MikroPul (www.mikropul.de), Lufttechnik Bayreuth (www.ltb. de) and DSD-ChemTech (www.dsd-chemtech.de for brink filters).

Electrostatic precipitators and/or wet precipitators can be considered for the main stage. In terms of cleaning performance, electrostatic precipitators are classified between scrubbers and filters. With regard to the robustness of the operation, which is particularly important for the cleaning of product gas with a high calorific value, they cannot compete with the scrubbers by far. Electrostatic separators are therefore suitable for use according to the invention in the main purification of product gases, but not for the subsequent stage. In addition, the 100% exclusion of explosion hazards from electrostatic precipitators is hardly possible, especially in small systems, so that the use of scrubbers for the main cleaning represents a further process-related advantage.

One way of combining the robust operating characteristics of the scrubber with the high separation efficiency of the filter is to place the filter downstream of the scrubber. The scrubbers serve as a coarse, pre- or main separator and the filter as a fine or final separator for dust, aerosols and condensing gas components.

In this case, the present invention relates to the downstream connection of the clogging-resistant and wet-operated deep-bed filter behind a wet-operating main stage that once falls below the water dew point. The main stage has at least one wet cleaning component, such as a pre-quench, scrubber or wet-cleaned electrostatic precipitator collecting electrodes, or a wet precipitator, preferably a scrubber, which enables a predetermined minimum degree of pre-cleaning. The service life of the fine cleaning stage is increased thanks to the good pre-cleaning of the main stage. Also, the present invention includes placing the clog-resistant filter downstream of any form of wet gas cleaning process having a main stage. The main stage uses either a scrubber, in particular a high-performance gas scrubber and/or electrostatic gas cleaning with an upstream wet stage, e.g. prequench. Spraying the gas with water, such as that done by spray towers or steel washers, is considered a pre-quench.

The described invention also relates to a filtering and clog-resistant gas cleaning process downstream of an at least partially wet main gas cleaning stage. This improves the separation performance and reduces emissions and the maintenance effort, especially on downstream components. At least 90% of the total dirt load, preferably at least 95% and in particular at least 98% and even more preferably at least 99% is retained in the main stage. A separation of at least 98% of the dirt load is a typical value for high-performance washers. This specification relates to a diameter of the dirt particles, in particular dust, tar and/or aerosols, of around 1 μm in diameter.

The subsequent filter retains the remainder, that is to say no more than 10%, preferably no more than 5% and in particular no more than 2%, with a value of 0% being reached behind the filter in each case. The dirt load before entering the main cleaning stage is referred to as 100%. A dirt load is described as 0%, which is permissible for the operation of an Otto engine, in particular an engine working with a turbocharger. Ideally, the residual loading of the clean gas with dust and tar at a gas temperature of about 10 to 50°C is less than 1 mg/m ³ _N.

Due to the upstream at least partially wet gas cleaning in the main stage before the filter, the water dew point in the product gas is always undercut. If a conventional filter were used here, it could be operated poorly or not at all under these operating conditions, since moisture (e.g. water or tar) is deposited on the filter surface and a sticky layer forms with the dust also present in the gas, which can hardly be cleaned off and thus renders the filter unusable.

It is to the credit of the present invention to have recognized a fortunate combination between the wet-working main stage and the downstream filter. This combination achieves both long service lives and very good fine cleaning of the product gas.

For the first time in the process of cleaning a product gas generated from biomass, which has long been considered extremely difficult, a simple ches, reliable and robust method specified in which the cleaning stages, i.e. the main stage and the filter, can be operated for a month or more without the need for maintenance, in particular without the material of the filter having to be replaced or the subsequent components need to be cleaned.

With this historic wood gas application, which was primarily designed for retrofitting in existing vehicle concepts and for weight reduction for mobile use, the maintenance intervals were typically in the range of five to 50 operating hours.

Concepts such as the concept of very good pre-separation upstream of the gas cleaning process according to the invention were not yet considered due to the state of the art at the time and the specification of the weight reduction required for operation in the mobile sector. Cork or wood shavings were used as depth filter material, which could be burned after use or returned to the gasification process or disposed of.

The long maintenance intervals that can be achieved by the gas cleaning process according to the invention are achieved in particular by retaining at least 90%, preferably at least 95% or 98% of the dirt load from the main cleaning stage. Dirt load means particles and aerosols, in particular dust and tar as sum parameters, with a size of about 1 micron. The dirt load is given in mg/m ³ _N and relates to a gas temperature of 10 to 50°C. The loading of the gas with water droplets is not understood as a pollution load, as this water does not lead to any contamination of the subsequent components, such as a turbocharger.

An essential feature of the invention is the blockage resistance, especially under difficult operating conditions for conventional filters, in particular exposure to dust while water or hydrocarbon-containing condensate (tar) falls below the dew point due to moisture or condensate.

To implement the filtering and blockage-resistant gas cleaning method according to the invention, a highly fibrous depth filter material, such as glass wool, can be used for the filter, for example. Instead of glass wool, other fibrous depth filter materials such as rock wool and aluminum silicate fibers, sheep's wool, felt, hemp, flax or coconut fibers and with appropriate parameters with regard to the filter properties according to the invention and other biogenic or artificial fiber materials with comparable filter properties can be used.

Due to the large inner surface of the material, the filter material is able to absorb the dust, aerosols and condensing gas components that have already been greatly reduced by the pre-cleaning over a long period of operation without the pressure loss of the filter medium increasing significantly. In particular, the service life of the filter medium used can be increased by the fact that the gas impingement takes place at low inflow speeds, for example in the range of a few meters per minute, i.e. a sufficiently large filter surface is available. Typical values for the inflow speed in the operating state are 0.2 to 20 meters per minute, preferably 2 to 8 meters per minute.

There is the possibility of wetting the filter medium in addition to loading the gas flow with residual droplets by applying an additional external liquid. In any case, the operation of liquid-impacted filter media is associated with a higher pressure loss compared to dry operation, which requires an increased fan output. The advantage, on the other hand, is a significant improvement in cleaning performance, service life of the gas cleaning process according to the invention and the subsequent components.

Descriptions of externally wetted filters can be found, for example, in EP 0 134 297 . In contrast to the gas cleaning process according to the invention, this is a description of an independent filter apparatus which generally provides for wetting of technically formed filter elements, eg filter bags, via nozzles and compressed gas cleaning of the filter elements through which flow occurs from the outside to the inside.

In EP 0 876 190 B1 a variant of the aforementioned filter apparatus is described in which two-substance nozzles are used to wet the filter elements.

In DE 196 29 500 C1 describes a multi-stage multi-scrubber equipped with diagonally arranged wetted mass exchangers, e.g.

In EP 0 249 400 B1 describes a gas-liquid contact apparatus in which at least two inclined disk-shaped contact planes formed of rods and flushed with liquid.

In U.S. 3,925,040 a gas scrubbing process is presented with detailed description of droplet separation and less specific description of the gas-liquid contact zone.

The aforementioned methods mainly relate to individual devices for gas cleaning.

The fine cleaning process on which the invention is based for product gases with a high calorific value from the thermochemical conversion of solid fuels relates to the downstream installation of the gas cleaning process (fine filter) according to the invention after an at least partially wet main cleaning of the product gas. An application of the fine filter described for cleaning product gases from waste pyrolysis or use in the field of medical technology are not the subject of the invention described here.

The aim of the invention is to significantly improve gas cleaning processes, such as those currently implemented in many biomass gasification plants, both through retrofitting and in new planning, in particular with regard to cleaning performance and maintenance costs.

According to the invention, as described in claim 1 and 1 shown, a filter downstream of an at least partially wet gas pretreatment taking place in the main stage.

The gas cleaning systems to be improved by the invention, which include (high-performance) gas scrubbers, electrostatic precipitators with pre-quench and dry or wet collecting electrode and other gas scrubbers that meet the required minimum pre-cleaning, are all based at least in part on wet gas cleaning.

The separating principle of the filter or fine filter can consist of surface filtration (preferably) depth filtration or a combination of both principles. In its simplest form, the gas cleaning process according to the invention is implemented as a thick layer of fibrous depth filter material without additional external wetting, in which wetting is effected by the residual droplets from the wet main cleaning stage. In addition, this depth filter can also be wetted continuously or discontinuously with a washing liquid.

If a depth filter material is covered with a large amount of scrubbing liquid, large parts of the gas components to be separated can already be separated in the scrubbing liquid layer that is forming. In this case, from a physical point of view, there is a combination of depth and surface filtration.

Dust and/or tar is advantageously deposited primarily in the upstream layer, in particular with a layer thickness of approximately 1 to 2 cm. When the fine filter according to the invention is operated, it is noticeable that the contamination builds up predominantly in the border area to the raw gas side. This means that a change in the filter material caused by an increase in pressure loss becomes necessary, mainly through the layer of contaminated filter material that is a few centimeters thick on the side facing the raw gas. For example, in a filter layer made of three glass wool mats with flow from bottom to top, which when new have a height of 100 mm and a density of 16 to 25 kg/m ³ , more than 50% of the dust and tar deposits are in the bottom one to two centimeters.

The pressure loss when flowing through the filter medium is highly dependent on the degree of contamination and wetting of the fine filter material. In general, the pressure loss increases with increasing inflow speed and wetting and strongly in combination with increasing contamination. There is a complex relationship between these influencing factors.

Detailed descriptions of the filter material used and its regeneration are described in the claims.

• 1: eine prinzipielle Darstellung des Verfahrens zur Herstellung und Reinigung eines heizwertreichen Produktgases, bei der das Filter (24) einer nassen Hauptreinigungsstufe (22) nachgeschaltet ist;
• 2: eine prinzipielle Darstellung eines Filters in einer ersten Ausführung, mit senkrecht zum Gasstrom angeordnetem Filtermaterial;
• 3: eine Darstellung wie 2 des Filters in einer zweiten Ausführung, mit schräg zum Gasstrom angeordnetem Filtermaterial;
• 4: eine Darstellung des Filters gemäß 2 in einer dritten Ausführung, mit topfförmig ausgebildetem Filtermaterial;
• 5: eine Darstellung des Filters gemäß 2 in einer vierten Ausführung, mit U-förmig ausgebildetem Filtermaterial;
• 6: eine Darstellung des Filters gemäß 2 in einer fünften Ausführung, analog zu 2 jedoch mit zusätzlicher externer Flüssigkeitsaufgabe;
• 7: eine Darstellung des Filters ähnlich 2 in einer sechsten Ausführung, analog zu 4 jedoch mit zusätzlicher externer Flüssigkeitsaufgabe;
• 8: eine Darstellung des Filters in einer siebten Ausführung, analog zu 5 jedoch mit zusätzlicher externer Flüssigkeitsaufgabe;
• 9: ein Schnitt entlang der Schnittlinie VIII-VIII in 8, der die für die externe Flüssigkeitsaufgabe einsetzbare fallfilmerzeugende Ringleitung darstellt;
• 10: eine prinzipielle Darstellung des Filters in einer neunten Ausbildung, bei der das Filtermaterial in kleinen Stücken während des Betriebs zur Zuführung und Austrag über Fördereinrichtungen erneuert werden kann;
• 11: eine prinzipielle Darstellung des Filters in einer zehnten Ausführung, bei der das Filtermaterial während des Betriebs in Bahnen erneuert werden kann;
• 12: eine Darstellung des Filters in einer elften und detaillierteren Ausführung, die für die Ausführung des Filters für senkrecht zum Gasstrom angebrachtes den Gehäusequerschnitt ausfüllendes Filtermaterial, das in Richtung des Gasstromes an Packungsdichte zunimmt, mit externer Flüssigkeitsaufgabe und weiteren Peripheriekomponenten (Tropfenabscheider, Überlaufsiphon, Deckelschwenkvorrichtung, Differenzdrucküberwachung, Wasserkreislauf) zeigt;
• 13: eine prinzipielle Darstellung des Filters in einer zwölften Ausführung, analog zu 12, bei der das Filtermaterial jedoch in einzelnen Patronen eingesetzt wird;
• 14: eine prinzipielle Darstellung einer mit Filtermaterial bestückten Patrone;
• 15: eine prinzipielle Darstellung des Montagedetails einer Filterpatrone an der Kopfplatte des Filtergehäuses;
• 16: eine prinzipielle Darstellung einer Filterpatrone mit Haltegriffen und Auspressvorrichtung des Filtermaterials zur Erleichterung der Montage und Demontage der Patronen;
• 17: eine prinzipielle Darstellung von Ausführungsvarianten von Filterpatronen, hier dargestellt zum Einbau in runde Apparatequerschnitte;
• 18: eine prinzipielle Darstellung des Filters ähnlich 13, bei der jedoch zur Erhöhung der Standzeiten der Filterpatrone dünne Vorabscheiderschichten vorgeschaltet sind, die sowohl in fester als auch flexibler Form ausgebildet sein können und zumindest teilweise aus dem Hauptgasstrom genommen werden können;
• 19: eine prinzipielle Darstellung des Filters ähnlich 18, jedoch mit mehreren radialsymmetrisch angeordneten dünnen Vorabscheiderschichten, die in Richtung des Gasstromes und senkrecht zum in der Filterpatrone eingesetzten Tiefenfiltermaterial angebracht sind und im Gegensatz zu 18 über eine deutlich größere Anströmfläche als die Filterpatrone verfügen und daher nicht aus dem Gasstrom genommen werden brauchen;
• 20: ein Schnitt entlang der Schnittlinie B-B in 19, der den radialsymmetrischen Aufbau der Vorabscheiderschichten mit Ein- und Ausströmkammern parallel zum Filtermaterial der Vorabscheider darstellt; und
• 21: eine prinzipielle Darstellung des Filters bei der das Filtermaterial in Kassettenform eingebracht ist und durch die eine einfache und gezielte Demontage einzelner Ebenen des Filtermaterials erfolgen kann.

Further features and advantages of the invention are exemplified in the other claims and in the following description with reference to the drawings. These example illustrations are not to be construed as limiting further variations of the invention. It show in the drawing:

• 1 : a basic representation of the process for the production and purification of a product gas with a high calorific value, in which the filter (24) is connected downstream of a wet main purification stage (22);
• 2 : a basic representation of a filter in a first embodiment, with filter material arranged perpendicularly to the gas flow;
• 3 : a representation like 2 of the filter in a second embodiment, with the filter material arranged at an angle to the gas flow;
• 4 : a representation of the filter according to 2 in a third embodiment, with a pot-shaped filter material;
• 5 : a representation of the filter according to 2 in a fourth embodiment, with a U-shaped filter material;
• 6 : a representation of the filter according to 2 in a fifth embodiment, analogous to 2 but with additional external liquid feed;
• 7 : a representation of the filter similar 2 in a sixth embodiment, analogous to 4 but with additional external liquid feed;
• 8th : an illustration of the filter in a seventh embodiment, analogous to 5 but with additional external liquid feed;
• 9 : a section along line VIII-VIII in 8th , which represents the falling film-generating ring main that can be used for the external liquid task;
• 10 : a basic representation of the filter in a ninth embodiment, in which the filter material can be replaced in small pieces during operation for feeding and discharge via conveyors;
• 11 : a basic representation of the filter in a tenth embodiment, in which the filter material can be renewed during operation in strips;
• 12 : A depiction of the filter in an eleventh and more detailed version, which is used for the design of the filter for filter material that fills the housing cross section and is attached perpendicularly to the gas flow and that increases in packing density in the direction of the gas flow, with external liquid feed and other peripheral components (drop separator, overflow siphon, lid swivel device, differential pressure monitoring, water circuit);
• 13 : a basic representation of the filter in a twelfth embodiment, analogous to 12 , but in which the filter material is used in individual cartridges;
• 14 : a basic representation of a cartridge equipped with filter material;
• 15 : a basic representation of the mounting details of a filter cartridge on the top plate of the filter housing;
• 16 : a basic representation of a filter cartridge with handles and squeezing device for the filter material to facilitate assembly and disassembly of the cartridges;
• 17 : a basic representation of design variants of filter cartridges, shown here for installation in round apparatus cross-sections;
• 18 : a basic representation of the filter similar 13 , in which, however, to increase the service life of the filter cartridge, thin pre-separator layers are connected upstream, which can be designed both in solid and flexible form and can be taken at least partially from the main gas flow;
• 19 : a basic representation of the filter similar 18 , but with several radially symmetrically arranged thin pre-separator layers, which are attached in the direction of the gas flow and perpendicular to the depth filter material used in the filter cartridge and in contrast to 18 have a significantly larger inflow area than the filter cartridge and therefore do not need to be taken out of the gas flow;
• 20 : a section along section line BB in 19 , which shows the radially symmetrical structure of the pre-separator layers with inflow and outflow chambers parallel to the filter material of the pre-separator; and
• 21 : A basic representation of the filter in which the filter material is inserted in the form of a cassette and through which individual levels of the filter material can be dismantled easily and in a targeted manner.

1 shows a general representation of the individual parts of the procedure. According to the prior art, product gas is produced in a reactor 20, for example a wood gasifier according to Imbert, by thermochemical conversion from a biomass. It leaves the reactor with a temperature T1 and a dirt load of 100%. The product gas is now fed into a wet-working main stage 22, also called the main cleaning stage, which has a high-performance gas scrubber, for example a rotary scrubber, a Venturi scrubber, or another corresponding gas scrubber that removes at least 90% of the dirt particles (dust, tar, aerosols) with a diameter of 1 µm can be used.

There are two alternatives for this. The first alternative, which is preferred, uses a high-efficiency scrubber, such as a rotary scrubber, a venturi scrubber, or other equivalent high-efficiency scrubber capable of separating at least 90% of dirt particles with a diameter of 1 µm. The second alternative uses an electrostatic precipitator that is preceded by a quench.

At the outlet of the reactor for thermochemical biomass conversion (20), the product gas has a temperature T1 that is well above 100° C. and a low gas humidity f1. In the main cleaning stage (22), which is at least partly operated wet, the product gas is simultaneously cooled considerably. When the product gas is first wetted with water, part of this water evaporates. The heat required for vaporization (enthalpy of vaporization) is extracted from the product gas. At the same time, the humidity of the product gas increases due to the evaporation. This cooling process continues until the humidity of the product gas is 100%. This moisture-saturated gas (f2) can no longer absorb any more water vapor, so that no more water is evaporated and therefore no further cooling takes place. This point is commonly called the cooling limit temperature and is often in the range of 60 to 70°C.

The product gas can be further cooled by a further cooling stage, which is operated with chilled water, for example. This is advantageous since more tar components condense out at cooler gas temperatures and thus better cleaning of the product gas can be achieved.

At the outlet of the main stage 22, the product gas has been cleaned to such an extent that the dirt load is in any case less than 10%, preferably less than 5%, in particular less than 2%. The product gas now has a temperature T2, which is at most in the range of the cooling limit temperature, in any case below 100°C, preferably below 65°C. Typically it is in the range 40 to 70°C. Preferred values are 20 to 50°C. At the outlet of the main stage 22, the product gas is still laden with residual water droplets.

These water droplets come from both the wet main stage and from condensed water vapor. These water droplets are the part that was not separated in the droplet separator downstream of the gas scrubber or by the electrostatic precipitator. This entry of residual water droplets is advantageous for the downstream filter 24, since this results in wetting of the downstream deep-bed filter, which improves further gas cleaning.

In the simplest embodiment, the thick layer of fibrous depth filter material (26 or 26a) according to the invention can be used without additional external application of liquid (cf. 2 until 5 ). This mode of operation is referred to as wet due to the impact of droplets originating from the upstream, at least partially wet gas cleaning and/or due to condensate formed when the water vapor falls below the dew point. An additional external application of liquid is possible.

In the 2 until 5 differently designed layers of depth filter material 26 are shown. 2 Figure 12 shows a cylindrical disc of depth filter material 26 in a round housing 28. Also shown are the entry, arrow 30, and exit, arrow 32, of the product gas. At the outlet, ie at arrow 32, the product gas can be removed in purified form and is available, for example, for an Otto engine, generally referred to as consumer V. In 3 if the depth filter material 26 is arranged at an angle, this has the advantage that water and other liquids can drain off better.

In 4 the depth filter material 26 is pot-shaped, which results in an even larger surface area than in 3 and even bigger than in 2 reached. In execution after 5 the depth filter material is arranged in a U-shape. It can be seen that the depth filter material is 26 in 2 until 5 flow is always from bottom to top. Other arrangements and flow directions are also part of the invention, even without an explicit graphic representation.

In order to increase the cleaning performance and service life of the gas cleaning process according to the invention at the same time, the filter can advantageously be additionally exposed to liquid from the outside (cf. 6 until 8th ). This additional application of liquid can take place, for example, on the raw gas side via nozzles 34 and/or a (falling film-generating) ring line 40 . In addition, a liquid feed on the clean gas side is also possible, see nozzle 38 (cf. 6 , 7 and 8th ) and/or a (falling film-generating) ring line 40, in which the washing liquid is applied to the filter medium 26 via outlet openings 41 (cf. section VIII-VIII in 8th , shown in 9 ).

The depth filter material 26 is preferably carried by a support grate 42, which can be arranged on the clean gas side and/or on the raw gas side. 8th shows that two nozzles 34 and 35 are provided on the raw gas side.

With sufficiently high exposure to liquid, a layer of liquid forms on the filter medium 26, which runs down the filter medium 26 as a falling film and in which a large part of dust, aerosols and condensing gas components is retained. This can cause storage in the depth of the Filtermate rials only take place very slowly, and the service life is thus significantly increased.

In addition, improved separation also occurs inside the filter medium 26, even when there is little exposure to liquid, since the wetting causes the filter fibers to have higher adhesive forces and the free pore space between the filter fibers is reduced by the liquid.

In the descriptions relating to the filter 24, the gas at the entrance to the filter is referred to as raw gas (dark arrow 30) and at its outlet as clean gas (light arrow 32).

The filter materials 26 generally rest on a gas permeable grid-like support 42 by which they are held against, for example, gravity. In addition, a second, gas-permeable, rust-like support, the so-called hold-down device 43, ensures that the filter material 26 is not deformed by the operational pressure loss. The hold-down device 43 can be designed so that it can be easily removed, for example to change the filter material 26 .

The assembly of filter materials 26 between support 42 and hold-down devices 43 is a standard method, so it does not have to be shown explicitly, i.e. in 2 until 9 and 11 has been omitted for clarity. The depiction of support 42 and hold-down device 43 in 10 differs from this, since a fixed support 42 and an optional movable hold-down device 43 are used here.

According to 2 , which shows a basic, sectional side view of a housing 28 of the filter 24, the filter medium 26 (shaded area shown) is essentially flat, introduced perpendicularly to the gas flow and designed without external wetting.

In 3 the filter medium 26 is installed at an angle, with a substantially flat filter medium 26 and without external wetting.

In 4 the filter medium 26 is spatially profiled, otherwise flat, for example in the form of a pocket or tube, without external wetting.

In 5 the filter medium 26 has a large spatial depth, it has bulges, without external wetting.

6 12 shows an essentially flat filter medium 26 with external wetting installed perpendicularly to the gas flow. A slanted, substantially flat filter medium 26, analogous to 3 , is part of the invention even without an explicit pictorial representation.

In 7 the filter medium 26 is shown in the form of a bag or tube, analogously to FIG 4 , but with external wetting of the profiled filter medium.

In 8th the filter medium 26 is shown in the form of a bag or tube, analogously to FIG 7 , but in reverse installation direction and with additional external wetting of the filter medium 26. A variant of the filter medium 26 analogous to 5 with wetting variants is the subject of the invention even without an explicit graphic representation.

The additional external wetting can take place both on the raw gas side and on the clean gas side by spraying or dripping. A further possibility is wetting by liquid distributors 37 lying on top, such as, for example, hoses or pipelines with holes. In addition, external wetting of the filter medium with a falling film-generating device is also possible, as exemplified in 7 and 8th shown.

In 9 is the falling film generating device with ring line 40 with outlet openings 41 in plan view (in the direction of in 8th illustrated Section VIII-VIII) shown. This in 7 and 8th The filter medium 26 , which is shown as tubular by way of example, is acted upon by liquid via a ring line 36 and its outlet openings.

With filter media that are bulged on the raw gas side, e.g 8th , the wetting can also take place via at least one internal nozzle 35. Analogously, this type of wetting can also be used for 5 take place without this being explicitly shown graphically.

This variant of the falling film generation is exemplary and not to be understood exclusively. In addition, the wetting can also take place through a combination of the variants shown.

In 10 a further basic side view of the filter, designed as a sectional view, is shown, in which during operation a quasi-continuous or discontinuous renewal of the filter medium 26 can take place. Fresh, small-scale filter material 26 (eg wood shavings) can be introduced via an entry device 46, which is shown here as a screw conveyor, where it forms a layer of filter medium on a support grate 42. This filter layer can be optional be fixed or compressed via a movable hold-down device 43 . The loaded filter medium 26 can be discharged via a discharge device 52, which is shown here as a screw conveyor. The additional external wetting of the filter medium 26 is part of the invention even without an explicit graphic representation. In particular, but not exclusively, for the in 10 shown variant, the wetting on the raw or clean gas side in question.

In 11 a further basic side view, executed as a sectional view, of the filter 24 used for the method according to the invention is shown, in which a (quasi-)continuous renewal of the filter medium 26 can take place during operation. The filter medium 26 can, for example, as in 11 1, unwound from a supply roll 54 for fresh media 26 and wound onto another roll 56 for used media.

In addition, other options for supplying fresh filter material are conceivable. A) There may be a roll of fresh material and the spent material placed in a waste bin in loose, disordered form. B) Fresh filter material is in folded form from C) The filter material is in the form of a “larger plate” from which only a small part is exposed to the product gas to be cleaned. The filter is regenerated by pushing or turning the entire filter plate.

The additional external wetting of the filter medium 26 is part of the invention even without an explicit graphic representation. This wetting can be accomplished with water, steam, rapeseed methyl ester, or other washing liquid, with water being preferred.

In particular, but not exclusively, for the in 10 until 13 , 18 until 21 shown variant a wetting on the raw or clean gas side in question.

Further variants of the filter (not illustrated here) are shown 2 until 21 result from possible changes in the direction of flow of the raw and clean gas. For example, this can be done by reversing the gas flow from top to bottom, or a horizontal or sloping flow, as well as a combination of vertical, horizontal or sloping flow in or out. In addition, the housing 28 of the filter can also be designed horizontally or at an angle. The housing can be round, square or have another shape (e.g. oval). These variants also belong to the described scope of the invention without a pictorial representation.

Further variants according to the invention, which are not explicitly shown graphically, consist in the combination of several levels of the fine filter. These levels can be operated partially dry and with external wetting, whereby the use of different washing liquids is also possible.

The invention includes the downstream connection of droplet separators after the fine filter, even without this being explicitly represented graphically, since droplet separation after wet gas cleaning processes is part of the prior art and therefore does not have to be mentioned separately.

The invention implements a filtering and blockage-resistant fine gas cleaning process for product gases with a high calorific value, which were generated for energy production by substoichiometric thermochemical conversion of solid fuels, have a calorific value of 3 to 20, in particular 4 to 7 MJ/m ³ _N and as a volume flow of 10 to 40,000, preferably 20 to 2,000 m ³ _N / h and in particular from 50 to 1,500 m ³ _N / h, characterized in that it is a gas pretreatment downstream, which is at least partially based on the principle of wet gas cleaning.

The filter 24 according to FIG 12 consists of a gas-tight cylindrical housing 28 with a housing partition 29, which is designed as a housing flange and which ensures accessibility for maintenance work.

The raw gas 30 flows through the raw gas connection 31 into the cylindrical housing 28 and leaves it as cleaned clean gas 32 through the clean gas connection 33. In the cylindrical housing 28 there is a layer of non-compacted mineral wool as filter material 26, e.g Glass wool, density when new, unsoiled and dry from 12 to 75 kg/m ³ , preferably 16 to 25 kg/m ³ , average fiber diameter from about 2 to 30 µm, preferably 3 to 6 µm, from about 10 to 50 cm, preferably 20 up to 40 cm thickness when new.

Above the non-compacted mineral wool layer 26 is a layer of compacted mineral wool 26a, for example glass wool, also with a fiber thickness of 3 to 6 μm. Compared to the uncompacted state, the compacted mineral wool has a density that is 2 to 4 times higher when new, ie about 50 to 100 kg/m ³ . The layer thickness of the compacted mineral wool 26a is also about 10 to 50 cm, preferably 20 to 40 cm thick when new.

A hold-down device 43 is located on the layers of mineral wool, which keeps the layers of wool in their position, even with the differential pressure that occurs during operation. The gas to be cleaned flows through the layers of wool from below. The gas flows into the layers of wool from below and is cleaned at the top. The wool is intermittently wetted with a washing liquid, eg water, from above in countercurrent to the flow direction of the gas. For this purpose, a pump 58 is installed, which brings the washing liquid via a water feed device 38 to the upper, compacted wool layer 26a. The water feed device 38 can, as an alternative to the 6 until 8th variants shown, can also be designed as a pipe, channel or spout distributor and has 20 drip points per square meter of surface of the wool packs 26 and 26a. The differential pressure across the wool layers is monitored by a sensor 62.

In the upper part of the cylindrical housing 28, another mineral wool layer 26b can optionally be provided as a droplet separator. This non-compacted mineral wool layer 26b has a layer thickness of 50 to 100 mm and a density when new, unsoiled and dry of 12 to 75 kg/m ³ , preferably 16 to 25 kg/m ³ , with an average fiber diameter of about 2 to 30 μm 3 to 6 µm. Mineral wool with a fiber diameter greater than 3 to 6 µm can optionally be used in this layer.

It must be ensured, even with heavily soiled wool layers 26 and 26a, that the water applied to the wool via the water feed device 38 cannot rise so much that it can enter the clean gas 32 via the upper gas outlet. This water could damage the engine downstream of the fine cleaning.

This safety is ensured by an overflow pipe 60 that protrudes a few centimeters, e.g. 2 cm, above the upper wool layer 26a and is open at the top and bottom, so that the water level on the upper wool layer 26a cannot be too high. So that no raw gas can reach the clean gas side via the overflow pipe during operation, the overflow pipe is closed with a siphon 61 at its lower open end.

• Wenn nach längerer Betriebszeit so viel Staub und Teer im Filtermaterial eingelagert sind, dass der Druckverlust des Gasstromes über das Filtermaterial seinen Maximalwert von beispielsweise 25 mbar erreicht, wird ein zumindest teilweiser Wechsel des Filtermaterials notwendig.

The maintenance of the fine filter according to the invention is advantageously carried out as follows:

• If, after a long period of operation, so much dust and tar has accumulated in the filter material that the pressure drop in the gas flow across the filter material reaches its maximum value of 25 mbar, for example, at least a partial change of the filter material becomes necessary.

This in 12 Cylindrical housing 28 shown can be opened for maintenance work on the housing partition 29. For this purpose, the connection from the clean gas connector 33 to the downstream pipeline, not shown here, is first released. The upper part of the housing can be lifted and swiveled to the side. The pivoting device consists of a gallows-shaped rectangular tubular structure 70 which is stabilized by a stiffener 71. The upper housing part can be raised via a threaded rod 72 by manual operation of the handle 73. For better force distribution, the threaded rod 72 is attached to a lining plate 77 on the upper housing part. To facilitate manual lifting, there is at least one disk below the handle 73, for example made of metal or hard PTFE.

In order to prevent twisting of the raised upper housing part, a retaining plate 75 is attached to the vertical part of the tube structure 70, which is connected to a retaining bracket 76 provided with a slot on the upper housing part by a screw connection.

Optionally and/or additionally, the fine filter can consist of several layers of mineral wool. In 12 shows the structure of a fine filter with cross-section-filling filter mats. Each of the filter layers 26 and 26a can consist of several layers of mineral wool. The lower filter layer 26 consists, for example, of 4 layers of non-compacted glass wool with a density when new, unpolluted and dry of 12 to 75 kg/m ³ , preferably 16 to 25 kg/m ³ , with an average fiber diameter of about 2 to 30 μm, preferably 3 to 6 µm and an installation height of 100 mm each. Each of these 4 layers can consist of one or more glass wool mats, but during installation care must be taken to ensure that the individual mats are a few centimeters oversized so that no gaps form either to the housing wall 28 or between the mats.

To exchange primarily the lower filter layers of 26 and 26a - to use filter material sparingly - it is optionally and/or additionally also possible to remove the bottom filter layer that is the most heavily soiled and to replace it with the second-bottom filter layer. A clean layer of filter material is inserted as the top layer. This exchange of filter material layers can take place separately both in the looser layer 26 and in the more heavily compressed layer 26a.

13 shows a similar filter structure as 12 However, the filter material layer is in one or more filter elements 78, which are designed as filter cartridges, attached to a head plate 79, which is provided with openings for the filter elements and otherwise gas-tight with the wall of the cylindrical housing 28 closes. The filter elements are attached to the top plate with a screw connection, for example, so that the raw gas can only get through the filter elements to the clean gas side.

Beneficial at the in 13 The configuration shown is that the filter elements can be mounted from above, ie from the clean gas side. As a result, the maintenance personnel are not exposed to dirt, in contrast to the manual change of loose filter mats 12 , largely excluded.

To further increase the ease of maintenance, the weight of the filter elements is limited by the fact that the individual elements are only so large that the cross-sectional area for the gas flow through the support grate 42, filter material 26 or 26a and hold-down device 43 is not greater than 0.15 m ² . Due to this size restriction, the filter elements can still be dismantled by hand even when they are wet and dirty.

In 14 the assembly of such a filter segment is shown. The side of the filter element consists of gas-tight walls 44, so that the raw gas can only flow through the support grate 42, the two filter layers 26 and 26a and the hold-down device 43 onto the clean gas side. Attached to the side of the gas-tight wall 44 is a peripheral fastening collar 80 with which the filter element can be connected to the head plate 79 via a screw connection 84 .

The overflow pipe 60 can be mounted both in a filter element and on the top plate. In any case, it protrudes beyond the hold-down device 43 by a few centimeters, so that a bubbling layer of water can also form above the filter material.

15 shows a detailed representation of the fastening situation 81. The filter element is pressed with the fastening collar 80 via a screw connection 84 to the head plate 79 and is sealed against the passage of gas by means of a seal 85 located between the head plate and fastening collar. The screw connection that can be reached from above from the clean gas side can be held, for example, by nuts or sleeves 86 fastened on the underside of the head plate. These nuts or sleeves must be welded gas-tight on all sides on the raw gas side so that no leakage flows can form.

In 16 further aids for assembly and disassembly are shown. The filter elements can be lifted in and out of the top plate openings using a carrying handle 87. To reduce the weight during disassembly, it makes sense to press out the water in the filter material. For this purpose, the filter material can be lifted via a grid or perforated plate 89 fastened to handles 88 and pressed upwards against the hold-down device 43 . A large part of the water is squeezed out of the filter material, so that the filter element can be lifted out of the top plate more easily.

In 17 different geometries for the filter elements are shown. This representation is exemplary and not to be understood as exclusive. The filter element 78a is designed in the shape of a part circle, so that in the type shown here, four such filter elements could be mounted in the cylindrical housing cross section. The filter element 78b is circular and would also allow four elements to be mounted as shown. The two filter elements 78c are rectangular and would also allow the assembly of four elements in the housing cross section. To increase clarity, the carrying handle 87 and handles 88 for squeezing out the filter material prior to dismantling are only shown for some of the filter elements.

To increase the service life of the fine filter, additional thin layers, e.g. of non-compacted filter material with a density in new, unpolluted and dry condition of 12 to 75 kg/m ³ , preferably 16 to 25 kg/m ³ , with an average fiber diameter of about 2 to 30 μm , Preferably 3 to 6 microns (26c or 26d) are used, which are only a few centimeters, such as 1 to 2 cm deep in the direction of flow.

18 shows two assembly variants of the pre-separator layers 26c, which can be embedded in both a fixed (95a) and a flexible (95b) delimitation structure similar to the support grids 42 and hold-down devices 43. In both cases, all preseparator layers are initially fixed by a holding mechanism 90 in such a way that the raw gas must flow through them. On the side opposite the holding mechanism, the preseparator layer is permanently attached. This fixed holding point can be provided as a pivot point 91 in the case of the fixed delimitation structure 95a and by simply fastening the material in the case of the flexible delimitation structure.

In the 18 The illustrated embodiment of the attachment of the pre-separator with a lateral fixed point is to be understood as an example. The invention also includes other types of attachment, such as central, off-center or other attachment points of the pre-separator, even without explicit pictorial and textual representation.

When one of the holding mechanisms 90 is triggered via a Bowden cable 92, it releases the corresponding pre-separator layer, which then moves downwards because it is equipped with a weight 93. As an alternative to weight loading, the triggering could also take place via a spring mechanism or via rods etc. or by directly pulling off the pre-separator via the Bowden cable 92 without a holding mechanism 90 at an angle downwards. These variations are not shown for the sake of clarity, although they are also part of the invention.

The Bowden cables 92 are guided upwards along the filter element, where they are guided through the cylindrical housing of the fine filter through gas-tight bushings 96, which can be designed, for example, as bellows, so that they can be triggered from the outside, for example using handles 98. The Bowden cables can be provided with couplings 94 to facilitate the assembly of the filter elements.

In 18 two filter elements are each shown with a fixed (95a) and flexible (95b) limitation of the pre-separator material, with two pre-separator layers being fitted in front of each filter element, one of which has already been removed from the gas flow and the other is still used as a pre-separator. This representation, each with two pre-separator layers, serves to illustrate and increase clarity. Other numbers of preseparator layers are possible and also part of this invention. In the representation in 18 the two lower handles 98 are pulled outside of the housing 28 and the lower layer of the pre-separator is thereby taken out of the flow.

Since, despite the pre-separator layers in the gas flow, the filter material layers above are also contaminated with dust and tar, there is no linear relationship between the number of pre-separator layers and the increase in service life. In addition, the service life also depends on the ratio of dust to tar.

19 shows a similar configuration of the filter as 18 , but where the thin pre-separator layers 26d are vertical and radially symmetrical in this graph. With this radially symmetrical arrangement of the pre-separator layers, with the appropriate number and height, an inflow area can be achieved which is significantly larger than that of the subsequent filter cartridge 78. To increase the service life, it is therefore not absolutely necessary to remove these pre-separator layers and, for reasons of clarity, they have not been shown separately in the graphic . However, it is also part of the invention without a graphic representation, just like other nested (eg angular or oval) arrangements of the pre-separator material 26d. To simplify maintenance of the filter cartridge 78 and the radially symmetrical pre-separator stage, both parts are connected to one another via a fastening 29c, shown here as a flange connection by way of example, so that the filter materials 26, 26a and 26c can be easily exchanged.

The raw gas 30 passes through the vertical, radially symmetrical inflow chambers 51 into the pre-separator stage, passes through the radially symmetrical pre-separator 26d and flows through the likewise radially symmetrical outflow chambers to the filter cartridges 78.

In 20 is the plan view along section BB in 19 are shown by way of example for two vertical concentric pre-separator layers 26d per filter element 78. Other numbers and designs of the vertical arrangement (for example angular or oval) of the pre-separator layers are possible and also part of the invention.

The raw gas 30 flows from the outside inwards into the inflow chambers 51, through the pre-separator 26d into the outflow chambers 53 and from there upwards, out of the plane of the drawing to the filter cartridges.

Another arrangement, in which the gas would be routed from the inside to the outside through inflow chambers, pre-separators and outflow chambers, is also part of the invention without an explicit graphic representation. Since the pre-separator material is very thin, the differences in area between the inflow and outflow sides are comparatively small.

21 12 shows a variation of the filter according to the invention, in which the filter material is delimited by fixed cassette-like structures which allow the cassettes to be changed sideways. In this variant, the filter housing 28 has a preferably angular cross-section (in the flow direction of the gas); however, round or other shaped cross-sections can also be used. Changing the filter cassettes from the side has a different effect than the vertical one shown above Change the advantage that the housing cover does not have to be dismantled for this purpose. Changing the filter from the side is a widespread state of the art, for example in ventilation technology. Another advantage of changing from the side is that the lower, more heavily soiled filter layers can be changed in a targeted manner.

The filter material 26 or 26a is placed in fixed cassettes 55 or 55a, which are placed laterally in the housing 26 and are fastened with the aid of a screw connection 84 analogously to the illustration in 15 be connected to the housing in such a way that no gas can enter or exit through the mounting opening in the housing.

Seals 85 are attached to the inside of the housing opposite the assembly opening, which seals prevent the raw gas 30 from being able to flow past the cassettes onto the clean gas side 32 . Analogously to the previously mentioned variants, the cassettes have support grids 42 and hold-down devices 43. Redistributors 99 for the washing liquid dripping down can be mounted below the cassettes. These redistributors seal tightly with the housing wall, so that they lead water running down the housing wall away from the wall and continue to distribute it centrally through openings to the lower level. This redistribution means that the accumulation of washing liquid on the housing wall can be limited, so that uniform moistening over the entire cross-section of the filter material is ensured.

In the upper part of 20 a cassette 55 is shown in which a thick layer of filter material 26 and optionally also 26a is embedded. In the lower part of 20 several flat cassettes 55a are shown. All types of cassettes are connected to the housing 28 in a gas-tight manner with a screw connection 84 in the area around the assembly opening. Gas slippage from the pipe gas side to the clean gas side past the filter elements is prevented by seals 85 between the cassettes and the inner wall of the housing.

Function and mode of operation: The filter 24 is a wet depth filter for separating particles from a thermochemical gasification of biomass. The filter 24 is a gas cleaning system for the pre-cleaning, namely downstream of a wet high-performance gas scrubber as a fine filter. At the filter inlet, the pre-cleaned gas has a temperature of around 40°C and a relative humidity of 100%. It is loaded with water droplets (from scrubbers or quench) that were not completely separated in the pre-cleaning. In addition, the gas is loaded with dust particles and aerosols (tar and water) condensed from the gas phase. By pre-cleaning the gas, long service lives of the fine filter material can be achieved. The pre-cleaning should achieve degrees of separation of more than 90%, in particular more than 95%, for particles and aerosols with a size of 1 μm.

Due to the fiber density of the wool, the particles are separated to a large extent. During operation, the washing liquid creates a foam within the wool, which multiplies the separation and also has a cleaning function. The depth of the wool package causes a strong distribution, so that the operational dirt entry only leads to a very slow increase in pressure loss.

The gas-side flow-related differential pressure increases both with increasing liquid content and with increasing soiling of the wool, since in both cases the free space between the wool fibers is reduced.

The countercurrent flow of the liquid to the gas direction means that the wool is effectively cleaned. The gas flows from bottom to top through the wool pack and partly “carries” the washing liquid, a part flows off and is applied again by the pump 58 depending on the differential pressure or time. The washing medium is cleaned in the circuit via a settling tank 64 and an optional water filter or hydrocyclone 66.

The size of the inflow area of the wool pack is selected so that 0.2 to 20, in particular 2 to 8 (e.g. 3.7) cubic meters of gas per square meter of inflow area flow through the wool pack per minute. When it is put into operation, the wool pack is moistened with around 35 liters of washing liquid per square meter of flow area. The rewetting during operation is 0.5 to 10, in particular 2 to 5, liters per square meter of inflow area and hour. The pressure loss during operation is in the range of 10 to 25 millibar and increases with increasing loading of the depth filter material during the operating time.

The filter 24 was developed and added because it is not possible with conventional methods to bring the gas purity to a level that meets the requirements of today's internal combustion engines, in particular turbo engines, economically, safely and permanently. In particular, this avoids contamination and deposits in the intake tract of the engines and wear is reduced.

The filter is suitable for continuous operation, since the maintenance intervals can be extended to one to several months by washing out particles.

To change the wool, the filter can be removed from the gas flow through a bypass line without having to shut down the entire gasification plant. Due to the installed pre-cleaning, fast filter maintenance leads to negligible contamination of the downstream combustion engine. Maintenance can also be carried out during operation if several filters are connected in parallel. To do this, the filter to be serviced is removed from the gas flow. During this time, the other filters are operated with a higher gas flow to be cleaned.

In contrast to electrostatic precipitators, effective explosion ignition sources can be avoided in particular by means of wet gas scrubbing for pre-cleaning of the gas. Wet scrubbers also block the spread of flame fronts in the event of a deflagration in the gasifier.

In the thermochemical gasification of wood, the gas must be cleaned of dust and tar before it can be used in engines. When using other biomass for thermochemical gasification, the gas can also be contaminated with other substances such as ammonia or urea. The entry of ammonia can lead to severe corrosion in the engine.

Nitrous oxide can also be formed in the combustion engine through de novo synthesis through the entry of ammonia and urea. Nitrous oxide is a greenhouse gas about three hundred times stronger than carbon dioxide. In addition, it is included in the nitrogen oxide balance when measuring the emissions of the engine exhaust.

Ammonia can be removed using an acidic scrubbing liquid (e.g. scrubbing water acidified with sulfuric acid). This forms readily water-soluble ammonium sulfate. Urea is also readily soluble in water.

The washing liquid circuit can be regenerated by discharging a partial flow and feeding in fresh washing liquid. Since both ammonium sulphate and urea are used as nitrogen fertilizers in agriculture, there are sensible uses for the discharged partial flow of the washing liquid.

The main stage 22 preferably has at least one gas scrubber, in particular a high-performance gas scrubber, with the group of gas scrubbers including all high-performance gas scrubbers and also dynamic scrubbers, wetted fans, packed columns (e.g. also with wood wool or wood chips as packing), spray scrubbers and quenchers. The group of high-performance gas scrubbers includes single-stage or multi-stage rotary scrubbers, venturi scrubbers (in particular with a fixed or adjustable venturi throat or adjustable throat cross-section), multi-venturi scrubbers, disintegration scrubbers and Bayer-Reither scrubbers.

The additional external liquid impingement can take place in co-current, counter-current or cross-current direction to the gas flow. The additional external liquid impact can take place with water, fuel oil, vegetable oil, biodiesel or another liquid. Several filter levels are optionally available, in which at least some different wetting liquids are used. Optionally, at least one stage, eg the filter 24, is followed by a droplet separator. Optionally, the filter material consists at least predominantly of small-scale material, such as (activated) carbon, expanded clay, foam, small-scale filter material. The filter material 26 is preferably exchangeable, in particular renewable during operation. Preference is given to using filter material with an average layer thickness of at least 2 millimeters, in particular more than 50 millimeters, and in particular with a layer thickness of 20 to 40 cm. Glass wool data (www.isover.de): Density, uncompacted: when new, unpolluted and dry from 12 to 75 kg/m ³ , preferably 16 to 25 kg/m ³ with an average fiber diameter of about 2 to 30 µm, preferably 3 to 6 µm. Density of compressed glass wool: up to 80 kg/m3 (including for applications that require increased compressive strength, such as roof insulation). Rock wool data (www.rockwool.de): Density, uncompacted: 30 to 40 kg/m3. Mean fiber diameter: 2 to 9 µm. Densities of compacted rockwool: 80 to 170 kg/m3 (use for fire protection and soundproofing), as used in filter 24. The pressure loss as detected by sensor 62 is: Dry mode: clean condition: 1 mbar, dirty condition just before changeover: 7 mbar. Wet mode: pressure drop of 25 mbar (range: 15 to 50 mbar).

• Zur Bestimmung des Verschmutzungsvorganges wurden drei Glaswollmatten, die im Neuzustand eine Höhe von 100 mm und ein Raumgewicht von 16 bis 25 kg/m³ haben, zur Feinreinigung von Holzgas eingesetzt. Aus den drei Matten wurden gleichgroße Probestücke geschnitten und getrocknet. Die Trocknung erfolgte bei Raumtemperatur mit einem Trocknungsmittel, da bei thermischer Trocknung mit einem hohen Verlust an leichter flüchtigen Teerbestandteilen zu rechnen wäre. Durch Bestimmung der Materialdichten der verschmutzten im Vergleich zu einer sauberen Glaswollmatten wurde die Einlagerung von Staub und Teer in den einzelnen Materialtiefen bestimmt. Von der Rohgasseite aus betrachtet wurden in den ersten 10 bis 20 mm etwa 55%, in den ersten 100 mm etwa 30%, zwischen 100 und 200 mm gut 10% und zwischen 200 und 300 mm etwa 5% der insgesamt abgeschiedenen Mengen an Staub und Teer nachgewiesen (die Höhenangaben beziehen sich auf den sauberen Einbauzustand, das Zusammensinken des Filtermaterials wird für diese Betrachtung bewusst vernachlässigt).

The distribution of contamination within the filter material is as follows:

• To determine the contamination process, three glass wool mats, which when new had a height of 100 mm and a density of 16 to 25 kg/m ³ , were used for fine cleaning of wood gas. Sample pieces of the same size were cut from the three mats and dried. The drying took place at room temperature with a desiccant, since thermal drying involves a high loss of more volatile tar components would be expected. By determining the material densities of the soiled in comparison to a clean glass wool mat, the storage of dust and tar in the individual material depths was determined. Viewed from the raw gas side, about 55% of the total separated dust and Tar detected (the height information relates to the clean installation condition, the collapse of the filter material is deliberately neglected for this consideration).

• Bei sauberer Glaswolle (drei Schichten à 100 mm, 16 bis 25 kg/m³) steigt der Druckverlust bei Durchströmung des trockenen sauberen Materials nur geringfügig an. Bei einer Gasflussrate von 3 m/Min. Beträgt der Druckverlust knapp 0,5 mbar (Prüfen O-Daten) und steigt bei einer Verdoppelung der Anströmgeschwindigkeit nur auf gut 1 mbar (Prüfen, O-Daten) an. Bei einmaliger Benetzung der sauberen Glaswolle mit 25 Litern Wasser pro Quadratmetern Anströmfläche erhöht sich der Druckverlust nur geringfügig gegenüber dem trockenen Zustand. Selbst bei Verdoppelung der Benetzung erhöht sich der Druckverlust für die beiden Anströmgeschwindigkeiten gegenüber dem trockenen Zustand nur um etwa 1 mbar.

The pressure loss across the filter layers is given as follows:

• With clean glass wool (three layers of 100 mm each, 16 to 25 kg/m ³ ), the pressure drop when flowing through the dry, clean material increases only slightly. At a gas flow rate of 3 m/min. The pressure loss is just under 0.5 mbar (test O data) and only rises to a good 1 mbar when the inflow speed doubles (test, O data). If the clean glass wool is wetted once with 25 liters of water per square meter of inflow area, the pressure loss increases only slightly compared to the dry state. Even if the wetting is doubled, the pressure loss for the two inflow velocities increases by only about 1 mbar compared to the dry state.

With a moderately heavily soiled gas wool layer (original: three layers of 100 mm each, 16 to 25 kg/m ³ , a total of approx. 80 kg/m ³ of dust and tar, dried, but with residual moisture), the pressure loss after mats dried through storage is zero additional wetting at an inflow speed of 3 m/min with 4.5 mbar is already significantly higher than with the clean mats. Additional wetting with 50 liters of water per square meter of inflow area increases the pressure drop to over 6 mbar at this inflow speed.

• Zur Bestimmung der Abscheideleistung der erfindungsgemäßen Feinreinigung wurden Messungen eines externen Dienstleisters an einer Holzgasanlage durchgeführt.

The clean gas measurement is given as follows:

• To determine the separation efficiency of the fine cleaning according to the invention, measurements were carried out by an external service provider on a wood gas plant.

The wood gas system essentially consists of a 70 kW _el wood gasifier based on the Imbert principle and a wet pre-cleaning of the gas with water-loaded rotary washers. During these measurements, the content of dust and tar in the clean gas was determined as a cumulative parameter. For this purpose, isokinetic gas samples were taken from the clean gas in accordance with the provisions of the VDI guideline 2066/1. The extraction filters were dried at room temperature with a desiccant to minimize the loss of volatile organic tar components. Clean gas values of less than 0.5 mg/m ³ _N were detected. Even shortly after the plant was restarted, the clean gas values were still below 1 mg/m ³ _N .

Due to the construction, the extraction of the raw gas from the wood gasifier could not be done isokinetically. Therefore, the gas samples were taken here outside of the rules of the VDI guideline 2066/1. The mean value of the gas samples taken showed a dust and tar load of a good 2 g/m ³ _N. The cleaning performance based on the mean values of the raw and clean gas measurements is 99.97%.

The applicant reserves the right to combine any features and sub-features from the above description and/or from the claims with one another in any way.

Claims (16)

Method for cleaning a product gas, which is generated by processing biomass, having the following method steps: - Generation of a product gas by thermochemical conversion of biomass in a reactor (20), - Deriving the generated product gas from the generation and feeding it into a wet main gas purification stage (22), the product gas being cooled in the main gas purification stage (22) to at least its cooling limit temperature of less than 90°C, - Feeding the product gas, which has now been cleaned to a maximum dirt load of 10%, into a wet-operated filter (24), with the major part of a depth filter material (26 or 26a) of the filter (24) being arranged radially symmetrically in relation to the major part of the deep-bed filter pre-separator layers ( 26d) are connected upstream, which are arranged vertically opposite the filter (24), and - Making the product gas cleaned in this way available to a consumer. procedure after claim 1 , characterized in that the product gas is cooled in the main gas purification stage (22) to at least below 50°C. procedure after claim 1 or claim 2 , characterized in that in the wet gas main cleaning stage (22) at least 95% of the dirt load with a diameter of 1 µm is separated. Procedure according to one of Claims 1 until 3 , characterized by a reheating of the product gas above the cooling limit temperature of the product gas between the main gas purification stage (22) and the wet-operated filter (24). Procedure according to one of Claims 1 until 4 , characterized in that this is operated with additional external humidification with washing liquid, raw gas and / or clean gas side. procedure after claim 5 , characterized in that the additional external moistening with washing liquid is carried out continuously or discontinuously. procedure after claim 5 or claim 6 , characterized in that the external humidification is carried out with steam. Method according to one or more of the Claims 1 until 7 , characterized in that the filter material of the wet-operated filter (24) at an inflow speed of the product gas in the operating state of 0.2 to 20 meters per minute, is flown. Method according to one or more of the Claims 5 until 8th , characterized in that the additional external moistening of the deep-bed filter material (26 or 26a) takes place via an additional external liquid and/or steam task when the operational pressure loss has fallen below a minimum value. Filter device (24), which is set up to be operated wet, for use with a method according to one or more of Claims 1 until 9 , wherein a fibrous depth filter that has at least 1.5 kg of fibers per square meter of inflow area, which is designed to - be operated wet, - be inflowed with a product gas in the operating state at an inflow velocity of 0.2 to 20 meters per minute, and - to be post-humidified during operation under differential pressure control by means of an additional external liquid and/or steam feed, characterized in that the main part of a depth filter material (26 or 26a) of the filter device (24) is arranged radially symmetrically in relation to the main part of the filter device (24). Preseparator layers (26c or 26d) are connected upstream, which are arranged vertically opposite the filter device (24). Filter device (24) after claim 10 , characterized in that it predominantly has glass wool as the fibrous depth filter material (26 or 26a). Filter device (24) after claim 11 , characterized in that the glass wool has an average fiber diameter of 2 to 30 µm, with a density when used, unpolluted and dry with 12 to 75 kg/m ³ , and with a layer thickness of 20 to 100 cm when new and dry as a depth filter. Filter device (24) after claim 10 , characterized in that this has predominantly rock wool and also aluminum silicate fibers, sheep's wool, felt, hemp, flax or coconut fibers as the fibrous depth filter material (26 or 26a). Filter device (24) according to one of Claims 10 until 13 , characterized in that the compression of the depth filter material increases in the installed state in the clean and dry new state in the direction of the gas flow. Filter device (24) according to one of Claims 10 until 14 , characterized in that the filter material (26 or 26a) is packed at least partially in the form of cassettes (55 or 55a) or cartridges (78). Filter device (24) one of Claims 10 until 15 , characterized by squeezing devices at least for washing liquid from the essential parts of the depth filter material (26 or 26a) to facilitate disassembly.

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