EP3067407B1 - System and method for gasification of carbonaceous material - Google Patents

Description

The invention relates to an apparatus and a method for the gasification of wood or other carbonaceous material according to claims 1 and 3.

Out WO 95/24591 For example, a special process and a plant for the gasification of lignite are known in which the lignite or brown coal gasified in a reactor, then roughly cleaned in a cyclone and finally finely cleaned in a hot gas filter. In this case, to reduce the sulfur content, an additive, for example, (lime) lime, buried, but undesirably reduces the temperature of the reaction gas. To compensate for this, fine coal dust and air are added to the raw gas after the reactor, in its transport lines before and / or after the cyclone, by the reaction of which the temperature rises again.

• Cellulose
• Hemicellulose
• Lignin
• Rest

The state of the art can be stated as follows: Wood is chemically composed of three main components:

• cellulose
• hemicellulose
• lignin
• rest

cellulose

The main constituent of all woody plants is about 50% cellulose. Cellulose is a chain-shaped molecule of individual glucose units. The real component of cellulose is cellobiose, a disaccharide (double sugar).

hemicellulose

Hemicellulose is composed of polymeric carbohydrates whose constituents are pentoses and hexoses. Hemicellulose, like cellulose, is a polysaccharide (polyhydric sugar).

lignin

The third component of wood, approximately 25-30% by mass, is lignin, a polymer of phenylpropane units.

rest

In addition to cellulose, hemicellulose and lignin, the wood also contains fats, resins, terpenes, dyes, tannins and mineral components.

elemental composition

Molecular formula wood:

C _6.1 H ₉ O _4.2 (1.2)

Comparison of table sugar:

C ₁₂ H ₂₂ O ₁₁ (2.2)

Species C [m-%] H [m-%] O [m-%] N [m-%] Cl [m-%] Ash [% m] beech 49 6 44 0.1 0.001 0.9 Spruce 50 6 43 0.05 0.001 0.95

Thermo-chemical conversion

By thermo-chemical processing (gasification) solid bioenergy carriers are transformed primarily under the influence of heat into gaseous secondary energy sources. During gasification, biomass is converted as completely as possible into flammable gases (ie into so-called synthesis gas) at high temperatures. The process is substoichiometrically an oxygen-containing gasification agent (air) supplied by the u. a. the carbon contained in the biomass can be converted into carbon monoxide. At the same time, the partial combustion of the feed material provides the required process heat so that the gasification process can even take place (autothermal gasification). The resulting low calorific gas can in burners for heat supply and u. a. used in gas engines or turbines for power generation.

Fixed bed gasification in direct current

In this type of gasification, the solid particles (wood) are not moved by the gas flow. The fuel migrates in the form of a bed through the carburetor. The gasification residue is collected at the bottom of the carburettor. Fuel and gas go the same way.

Heating and drying

The first phase is characterized by the fact that the wood is slowly heated from the outside to the inside. Unbound water is released in the form of water vapor. This process is endothermic (energy is needed).

Degassing and thermal decomposition (pyrolysis)

The temperature in the pyrolysis phase or zone ranges between 200 ° C and 400 ° C. At these temperatures, oxygen (O2) and hydrogen (H2) are degassed.

The building blocks of wood mentioned in the previous chapter are gassed in this phase. During pyrolysis, cellulose and hemicellulose produce carbon dioxide (CO2) and carbon monoxide (CO), as well as acetic acid (CH3COOH), acetone (C3H6O), phenols (C6H5OH) and water (H2O). The resulting in the pyrolysis long-chain hydrocarbons are referred to as tars.

Thermal decomposition of lignin produces methanol (CH3OH) and aromatic hydrocarbons (e.g., benzene (C6H6)).

The pyrolysis solid is charcoal.

oxidation

The energy required for drying, pyrolysis and reduction is formed in this zone. Carbon and hydrogen burn with energy release (exothermic). In In this zone, the temperatures are between 650 ° C and 1100 ° C, resulting in CO ₂ , H ₂ O and CH ₄ (hereinafter without subscripting).

reduction

In the reduction zone, the formation of combustible gas is made possible. Here the actual gasification of the solid carbon takes place. In the reduction zone, the intermediate products such as CO2 and H2O produced by the oxidation proceeding are reduced on the glowing charcoal. This produces CO, H2 and higher hydrocarbons. This happens at approx. 1100-650 ° C.

The reduction is dependent on the prevailing temperature. The conversion of hydrogen and carbon to methane between 400 ° C and 600 ° C decreases sharply. At temperatures above 1000 ° C no methane is formed. The Boudouard reaction achieves a good yield of carbon monoxide at high temperatures. This reaction is relatively slow.

There is a temperature-dependent opposite trend between high CO production and high hydrogen production. In addition, hydrogen production recedes in favor of methane production. Both components increase the heating value. High hydrogen content also increases the knocking problem of the engine. The knock-resistant methane is a good fuel gas, however, there are experiences that lead to a high methane content gas generation also brings a high Teerbelastung the gas with it.

Expiration of the gasification process

First, wood is heated by supplying heat and thereby evaporated in the Vergasergut water. The required amount of heat is generated by the partial combustion of the resulting carbonization and the oxidation of carbon and hydrogen.

The resulting charcoal serves as a reaction surface for the oxidation and reduction of carbon, carbon monoxide, carbon dioxide and hydrogen. This reduces the charcoal, ie the surface of the particles is larger, thus increasing the reaction rate.

Here it is clear that the reaction zone must be considered as a whole and the reduction or oxidation take place simultaneously.

Since the reduction of carbon dioxide by the charcoal is endothermic, the temperature drops from bottom to top, causing the reactions to abate. There is no clear separation between the reduction zone and the oxidation zone.

It is assumed that the carbon is burned to CO ₂ in the oxidation zone, since at the prevailing high temperatures of 1000-1300 ° C there is no longer a persistence of CO ₂ .

Part of the carbon monoxide is then to be burned in the presence of oxygen to CO ₂ . However, this is not stable because of the high temperatures and is reduced to CO at the glowing carbon. When the oxygen is completely used up, CO is no longer burned and remains stable in its concentration despite the lower temperature. After the last consideration, however, reduction reactions must also be assumed here since CO _{2 is} present first.

1. 1. brennbare Gase:
   • Kohlenmonoxid CO
   • Wasserstoff H₂
   • Methan CH₄
   • Höhermolekulare Kohlenwasserstoffverbindungen
2. 2. nichtbrennbare Gase:
   • Kohlendioxid CO₂
   • Stickstoff N₂
   • Wasserdampf H₂O
   • Geringe Mengen Sauerstoff O₂

Komponenten Raum anteil Heizwert Mindestluftmasse Methanzahl [Vol.-%] [MJ/m³] [m³ _Luft/m³ _Gas] Wasserstoff H₂ 17,1-19,8 10,8 2,36 0 Sauerstoff O₂ 0,4-0,6 0 - - Stickstoff N₂ 45 0 - - Kohlenmonoxid CO 20-23,8 12,6 2,41 75-100 Kohlendioxid CO₂ 8,5-16,2 0 - - Methan CH₄ 1,5-2,9 35,9 9,57 100 Höhere KWs C_mH_n 0,2 ≈50-90 variabel - As is clear from the above-mentioned processes, the gasification produces a mixture of combustible and non-combustible gases, which are divided as follows:

1. 1. combustible gases:
   • Carbon monoxide CO
   • Hydrogen H ₂
   • Methane CH ₄
   • Higher molecular weight hydrocarbon compounds
2. 2. non-combustible gases:
   • Carbon dioxide CO ₂
   • Nitrogen N ₂
   • Water vapor H ₂ O
   • Low levels of oxygen O ₂

components Room share calorific value Minimum air mass methane number [Vol .-%] [MJ / m ³ ] [m ³ _air / m ³ _gas ] Hydrogen H ₂ 17.1 to 19.8 10.8 2.36 0 Oxygen O ₂ 0.4-0.6 0 - - Nitrogen N ₂ 45 0 - - Carbon monoxide CO 20 to 23.8 12.6 2.41 75-100 Carbon dioxide CO ₂ 8.5 to 16.2 0 - - Methane CH ₄ 1.5-2.9 35.9 9.57 100 Higher KWs C _m H _n 0.2 ≈50-90 variable -

Process control, residence time, temperature and fuel type, grain size and moisture influence the composition of the wood gas. Typical calorific values for wood are on the order of 3.5-5.5 MJ / m3, so wood gas is a lean gas.

Since 5-10 wt .-% of the starting material remain as ash, but mainly as un-gassed wood residues and disposed of properly, there is both an economic and ecological interest in this in the wood gasification according to the prior art unburned accruing wood components also as possible gas to a high degree. This is also an object of the invention.

The invention solves this problem with a device having the features specified in the characterizing part of claim 1 and with a method having the features specified in the characterizing part of claim 3. In other words, it is at least for the most part transferred to the gas stream to the subsequently arranged hot gas filter which accumulates uncharged in the bottom region of the gas generator charcoal. This can be done by appropriate choice of flow rate in the manner of a pneumatic Transportes, as he has been known for a long time as the bulk material promotion. In the hot gas filter, charcoal, as well as coal dust and entrained ash, on the surface of the filter, it is preferred filter cartridges, deposited. Depending on the pressure loss at the filter upstream of the filter cartridges, oxygen (usually in the form of air) is introduced as abruptly as possible, whereby the filter cake is blown off the filter cartridges and, favored by pressure surge and temperature, a second gasification step takes place through which the charcoal or charcoal brought along the coal dust is for the most part gasified. The still non-gasified portion is finally gasified by the oxygen supplied in the lower part of the filter - again preferably in the form of air. Depending on the process parameters, which are easy for the plant constructor and the plant operator to determine, if not already known in advance, it is possible to carry out the wood gasification essentially completely, down to the mineral ash.

In the drawing, which consists of a single figure, a system according to the invention is shown purely schematically. It was waived the representation of all the components that are not causally related to the invention. In particular, the numerous measuring devices, the control and shut-off devices, the upstream and downstream components such as bearings, drying equipment, final product gas cleaning and transfer to the user are well known to those skilled in the field of wood gasification plants and require no in connection with the invention closer explanation.

The system according to the invention is shown schematically with its elements and components necessary for the invention, albeit without the measuring devices, etc., in the single FIGURE. It essentially has: a gas generator 1 and a hot gas filter 2. wood chips, wood pellets, coal or the like are fed from a storage bin, not shown, via a feed 3 the gas generator 1 fitting at his head and go through in him from the state of Technique known and initially mentioned steps of drying, carbonization, oxidation and reduction, which is indicated in the lower part, indicated by the installation 4, via a line and a manifold system 5 air is supplied appropriately.

It is a classic wood gasifier with a co-current operated fixed bed. In the lower area, after the oxidation, the reduction and unburned parts and ash are withdrawn with the product gas via a line 6 in the bottom region of the gas generator and introduced into the central region of a hot gas filter 2.

In this lower portion of the hot gas filter 2 filter cartridges 7 project from a filter bottom 13 directed downwards into it. Even if a filter cartridge is sufficient under certain circumstances, it is advantageous for continuous operation, if not essential, to provide at least two such filter cartridges 7. Through the filter cartridges through the product gas passes and comes, here referred to as clean gas product in the upper part of the hot gas filter 2, from where it is withdrawn via a clean gas line 8 and the further processing or use is supplied.

The filter cartridges 7 are controllably connected to a compressed air supply 9, they can be set by means of this compressed air supply jerky on your clean gas side under pressure to blow off on the raw gas side accumulated filter cake and at least partially gas. In the lower part of the hot gas filter 2, a trigger 10 for the non-gasified components and a corresponding ash cone 11 is provided.

According to the invention, as already mentioned, via a line 12 oxygen, for example in the form of air, optionally heated and / or dried, fed into the region below the filter bottom 13 (approximately at the lower end of the filter cartridges), whereby it in the raw gas range of the hot gas filter 2 to another, very complete gasification of the previously not gasified wood components comes.

In this way, the remaining, non-gasified portion of the wood can be reduced substantially to the mineral ash, which has quite remarkable effects both for the environment and in economic terms: In the prior art are 5 to 10 wt .-% of the fuel used can not be gasified and therefore require proper disposal; by the invention, this proportion is pressed to less than 1 wt .-% of the fuel used, so it by the invention to an increase of the yield of 90% to 95% to 99%, to which a reduction of the waste comes to 10 to 20% of the waste so far incurred! This is the negligible additional costs for the reinforcement of the train in the line 6 and the cost of blowing the reaction air through the line 12 in the hot gas filter 2 with respect, which are not significant.

The invention is not limited to the illustrated embodiment, but may be variously modified. Thus, in large systems, several gas generators and / or several hot gas filters can be suitably combined with one another in order to achieve continuous operation even in the case of maintenance. It may be provided in the gas generator for wood components, which are too heavy for the increased train, a discharge for such parts, whether these are then returned to the gas generator or disposed of, depends on the nature of the starting material and the possibility of a return in the Product flow off.

The invention can be combined with various other embodiments of the method or the device, as long as the only reaction in the hot gas filter is not disturbed or the other embodiments of the filtering process do not interfere.

By carrying out the second gasification step in the hot gas filter, the conditions there are not changed so significantly that a change or adaptation of the materials would be necessary, it can thus all the components and materials are used, which are also envisaged in conventional hot gas filters by the expert ,

The height of the entry of the nozzles or other openings of the supply line 12 into the hot gas filter 2 is suitable in the presence of filter cartridges 7 at the lower end. There, when blowing off the filter cake, the entire material will pass, as well as during the undisturbed operation, the not yet gasified material passes as well. Operating parameters such as overpressure and volume flow can be easily determined by a few tests. If different materials are gasified, it may be advantageous to provide nozzles of different heights that can be supplied individually or in groups.

Also, by slanting arrangement of nozzles, special flow patterns can be obtained by which the further gasification is carried. LIST OF REFERENCE NUMBERS 01 carburettor 08 Clean gas line 02 Hot gas filter 09 Air Supply 03 supply 10 deduction 04 installation 11 ash container 05 distribution system 12 supply line 06 product line 13 filter bottom 07 Filter candle (s)

Claims (3)

1. Apparatus for gasifying carbon-containing material, more particularly wood, having a gas generator (1), to which the material for gasification is supplied in its upper region and to which oxygen, usually in the form of air, is supplied in its middle region, and in whose lower region it is largely gasified in a fixed bed reactor, the product gas being drawn off via a product gas line (6) from the lowermost region of the gas generator (1) and introduced into the lower region of a hot gas filter (2), where a filter, preferably provided with filter candles (7), removes solids such as particles not yet gasified, ash, and foreign bodies, while the clean gas passes through and is taken off via a clean gas line (8), an outlet (10) being provided for taking off the residual solids in the bottom region of the hot gas filter (2),
   characterized
   in that the hot gas filter (2) is supplied in its middle height region, between the filter bottom (13) and the outlet (10), in the case filter candles (7) are provided, approximately near their lower end, through a further line (12), with oxygen, preferably in the form of air.
2. Apparatus according to Claim 1, characterized in that the draft in the product gas line (6), by means of a fan, for example, is so strong that the particles not gasified in the gas generator are entrained substantially into the hot gas filter (2).
3. Method for gasifying carbon-containing material, more particularly wood, using an apparatus according to claim 1 or 2, having a gas generator (1) and downstream thereof in the product stream a hot gas filter (2), whereby, ahead of the filter in the product stream, oxygen, preferably in the form of air is supplied, and so a further gasification procedure takes place, characterized in that the supply takes place into the hot gas filter (2).

Images