ES2696674T3 - System and method for gasification of carbonaceous material - Google Patents

Abstract

Device for the gasification of carbon-containing material, especially wood, with a gas generator (1), to which the material to be gasified is fed in its upper zone and to which oxygen is fed, almost always in the form of air, in its middle zone, and in whose lower zone it is gasified in a solid bed reactor for the most part, the product gas being extracted from the lower zone of the gas generator (1) through a product gas conduit (6), and being introduced into the lower zone of a hot gas filter (2), from which solid products are separated, such as particles not yet gasified, ashes and foreign bodies, through a filter with a filter bottom (13), preferably provided with filter cartridges (7), while the pure gas passes through and is discharged through a pure gas conduit (8), an extraction (10) being provided for the discharge of solid products remaining in the bottom zone of the filter hot gas (2), characterizes Because the hot gas filter (2) is fed oxygen, preferably in the form of air, in the area below the filter bottom (13), if filter cartridges (7) are present, approximately at the lower end of the cartridges filtering, through an additional conduit (12).

Description

DESCRIPTION

System and method for gasification of carbonaceous material

The invention relates to a device and method for the gasification of wood or other carbon-containing material according to claims 1 and 3.

From WO 95/24591 a special process and an installation for the gasification of lignite are known, in which, or in which lignite is gasified in a reactor, it is then thoroughly purified in a cyclone, and finally purified finely in a hot gas filter. In this case, for the reduction of the sulfur content, an additive is added, for example lime (calcined), which nevertheless reduces the temperature of the reaction gas undesirably. To compensate for this, fine coal dust and air are added to the raw gas, by means of which reaction the temperature increases again, before the reactor, in its transport ducts before and / or after the cyclone.

Regarding the state of the art, the following can be explained: wood is chemically constituted by three main components:

- Cellulose

- Hemicellulose

- Lignin

- Rest

Cellulose

The main component of all the woody plants represents cellulose with approximately 50%. Cellulose is a structured material in the form of chains from individual glucose units. The main component of cellulose is cellobiose, a disaccharide (double sugar).

Hemicellulose

Hemicellulose is composed of polymeric carbohydrates, whose components are made up of pentoses and hexoses. Like cellulose, hemicellulose is a polysaccharide (complex sugar).

Lignin

The third component of wood is, with approximately 25-30% referred to the mass, is lignin, a polymer of phenylpropane units.

Rest

In addition to cellulose, hemicellulose and lignin, fats, resins, terpenes, dyes and tannins, as well as mineral components, are also present in wood.

Elemental composition

Molecular formula of wood:

Ca, 1HgO4.2 (1.2)

C12H22O11 (2.2)

Thermochemical transformation

By means of thermochemical refining processes (gasification), the solid bioenergetic supports are transformed into gaseous secondary energy supports, first under the influence of heat. In gasification, biomass is transformed as completely as possible into combustible gases (ie in a so-called synthesis gas) at elevated temperatures. In this case a gasification agent containing oxygen (air) in substoichiometric quantities is added to the process, through which the carbon can be transformed into carbon monoxide content, among others, in biomass. Simultaneously, by means of the partial combustion of the use material, the necessary process heat is provided so that the gasification process can take place in general (autothermal gasification). The gas of low calorific value produced can be used in burners for the provision of heat and, among others, in engines or gas turbines for the generation of current.

Gasification in fixed bed in parallel current

In this type of gasification, the particles of solid bed (wood) do not move through the gaseous current. The fuel migrates through the gasifier in the form of a charge. The gasification residue is collected in the lower zone of the gasifier. Fuel and gas follow the same route.

Heating and drying

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

Degassing and thermal decomposition (pyrolysis)

The temperature in the phase, or pyrolysis zone, ranges between 200 ° C and 400 ° C. At these temperatures oxygen (O2) and hydrogen (H2) are degassed. The wood components mentioned in the previous chapter are gasified in this phase. In the pyrolysis, carbon dioxide (CO2) and carbon monoxide (CO) are produced, as well as acetic acid (CH3COOH), acetone (C3H6O), phenols (C6H5OH) and water (H2O), from cellulose and hemicellulose. The long chain hydrocarbons produced in the pyrolysis are called pitches.

In the thermal decomposition of lignin methanol (CH3OH) and aromatic hydrocarbons (for example benzene (C6H6)) are produced.

Charcoal is produced as a solid product of the pyrolysis.

Oxidation

The energy needed for drying, pyrolysis and reduction is formed in this area. Carbon and hydrogen are burned under energy production (exothermic). In this zone, the temperatures oscillate between 650 ° C and 1100 ° C, and CO2, H2O and CH4 are produced (below without subscript).

Reduction

In the reduction zone the production of combustible gas is possible. In this the true solid carbon gasification takes place. In the reduction zone, the intermediate products produced in the previous oxidation, such as CO2 and H2O, are reduced in incandescent charcoal. In this case, CO, H2 and higher hydrocarbons are produced. This takes place at approximately 1100-650 ° C.

The reduction takes place depending on the prevailing temperature. In this case, the reaction of hydrogen and Carbon to give methane is greatly reduced between 400 ° C and 600 ° C. Methane is no longer formed at temperatures above 1000 ° C. The Boudouard reaction achieves a good performance in carbon monoxide at high temperatures. This reaction develops relatively slowly.

There is the opposite tendency dependent on the temperature between high CO production and high hydrogen production. For the rest, hydrogen production recedes in favor of methane formation. Both components have an effect of increasing the calorific value. A high hydrogen content also increases the problem of detonation of the engine. Methane, resistant to detonation, is a good combustion gas, although there are experiences that show that a generation of gas carried to a high methane content also brings with it a high charge of tar from the gas.

Development of the gasification process

First, wood is heated by heat supply, and in this case the water present in the material of the gasifier is evaporated. The amount of heat required is generated by the partial combustion of the low temperature distilled gases produced in this case and the oxidation of carbon and hydrogen.

The charcoal produced in this way serves as a reaction surface for the oxidation and reduction of carbon, carbon monoxide, carbon dioxide and hydrogen. In this case the charcoal is reduced, ie the particle surface increases, therefore the reaction rate increases.

In this case it is evident that the reaction gases must be considered as a whole, and the reduction, or oxidation, takes place simultaneously.

Since the reduction of carbon dioxide through the charcoal is endothermic, the temperature drops from the bottom upwards, with which the reactions decrease. There is no clear separation between reduction zone and oxidation zone.

A carbon combustion is supposed to give CO2 in the oxidation zone, since at the high temperatures prevailing therein, of 1000-l300 ° C, a CO2 stability is no longer given.

A part of carbon monoxide will then burn to give CO2 in the presence of oxygen. However, due to the high temperatures, it is not stable and is reduced to CO in the incandescent carbon. If the oxygen has been completely consumed, the CO no longer burns and remains stable in its concentration, despite the descending temperature. Therefore, according to the last consideration, it is also necessary to start with reduction reactions, since CO2 is present first.

As evidenced by the processes indicated above, gasification produces a mixture of combustible and non-combustible gases, which are divided as follows:

1. Combustible gases:

• Carbon monoxide CO

• Hydrogen H2

• Methane CH4

• High molecular weight hydrocarbon compounds

2. Non-combustible gases

• CO2 carbon dioxide

• N2 Nitrogen

• H2O water vapor

• Reduced amounts of oxygen O2

Process control, residence time, temperature and type of combustion, granulation and humidity influence the composition of wood gas. The typical calorific values for wood are in the order of magnitude of 3.5,5,5 Mj / m3, therefore, the wood gas is a weak gas.

Since 5-10% of the starting material remains as ash, but mainly as non-gasified wood waste, and which must be disposed of properly, there is an economic as well as an ecological interest in gasifying these components as much as possible. wood produced without burning in wood gasifications according to the state of the art. This is also the task of the invention.

The invention solves this task with a device with the characteristics indicated in the characteristic part of claim 1 and with a method with the characteristics indicated in the characteristic part of claim 3. In other words: the charcoal produced without gasifying in the The bottom area of the gas generator is transferred to the hot gas filter arranged below, at least for the most part with the gaseous stream. This can be carried out by a corresponding selection of the circulation speed in the manner of a pneumatic transport, which has been known for some time in the transport of bulk material. In the hot gas filter, charcoal, coal dust and collected ashes are precipitated on the filter surface, filtering cartridges are preferred. Depending on the pressure loss in the filter, oxygen (almost always in the form of air) is introduced as abruptly as possible in countercurrent of the filter cartridges, with which the filter cake is detached in the filter cartridges and, favored by the pressure shock and temperature, a second gasification step is carried out, with which the charcoal is gasified, or else the coal dust, partly predominantly predominant. The proportion not yet gassed is definitively gassed by the oxygen fed into the lower part of the filter - preferably also in the form of air -. Depending on the parameters of the process, which are easy to determine, if not previously known by the installation builder and the operators of the installation, it is possible to carry out the wood gasification essentially completely to mineral ash.

In the drawing, which is constituted by a single figure, an installation according to the invention is represented in a purely schematic manner. In this case, the representation of all the components not causally related to the invention was dispensed with. In particular, the numerous measuring devices, the regulating and blocking devices, the components which are pre-connected and connected to the installation, such as tanks, drying system, final product gas cleaning and transfer to the user, are well known to the specialist in the field. of wood gasification plants, and do not require a further explanation in relation to the invention.

The installation according to the invention is represented schematically in the single figure with its elements and components necessary for the invention - although without the measuring devices, etc. - 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 tank, not shown, through a supply 3, to the gas generator 1 passing through his head, and go through it the steps of drying, distillation at low temperature, oxidation and reduction, known by the state of the art and initially indicated, feeding air in the lower area, indicated by the incorporation 4, passing to through a conduit and a distributor system 5.

It is a classic wood gasifier with a fixed bed operated in parallel current. In the lower area it makes the reduction after oxidation, and the unburned parts and the ashes are extracted with the product gas through a conduit 6 in the bottom area of the gas generator, and are introduced in the middle of a hot gas filter two.

In this lower region of the hot gas filter 2 filter cartridges 7 are introduced from a filtering bottom 13 facing downwards. While a filter cartridge is sufficient under certain circumstances, for continuous operation it is convenient, although not essential, to provide at least two filter cartridges 7 of this nature. The product gas passes through the filter cartridges and the product, in this case called pure gas, reaches the upper area of the hot gas filter 2, from which it is extracted through a pure gas pipe 8 and fed to the gas. processing, or further use.

The filter cartridges 7 are adjustably connected to a pressurized air supply 9, they can be abruptly pressurized on their pure gas side by means of this air supply under pressure, in order to be able to detach and at least partially gasify the cake of accumulated filtration on the raw gas side. In the lower region of the hot gas filter 2, an extraction 10 is provided for the non-gasified components and a corresponding ash container 11.

According to the invention, as already mentioned, oxygen is supplied via a line 12, for example in the form of air, optionally heated and / or dried, in the area below the filter bottom 13 (approximately the lower end of the filter cartridges), which results in an extremely complete additional gasification of the wood components not yet gassed so far, in the raw gas zone of the hot gas filter 2.

In this way, the proportion of wood remaining, not gasified, can be reduced essentially to the mineral ash, which brings about remarkable effects both for the environment and also from the economic point of view: in the state of the art, at 10% by weight of the fuel used is not gasable and, therefore, requires an adequate elimination: through the invention, this proportion is reduced to less than 1% by weight of fuel used, so that, by the invention , there is an increase in yield from 90% to 95% up to 99%, to which is added still a reduction of waste from 10 to 20% of the waste produced so far! This is opposed by the negligible additional costs for the reinforcement of the current in the conduit 6 and the costs for the blowing of reaction air through the conduit 12 in the hot gas filter 2, which are not important.

The invention is not limited to the illustrated embodiment, but can be modified in various ways. In this way, in large installations, several gas generators and / or several hot gas filters can be suitably combined with each other, in order to achieve continuous operation even in the case of maintenance. In the gas generator for wooden components, which are also too heavy for the increased current, a discharge device can be provided for such parts, which must then be fed back to the gas generator or else eliminated, depending of the nature of the starting material and the possibility of a recirculation in the production stream.

The invention can be combined with various conditioning of the process or of the device, provided that the reaction in the hot gas filter is not interfered with, or else the other conditioning of the filtration process does not interfere.

By the implementation of the second gasification step in the hot gas filter, the condition conditions therein are not substantially modified, so that a modification or adaptation of materials would be necessary, therefore all the components can be used and materials that are taken into account by the specialist also in conventional hot gas filters.

The entrance height of the nozzles or other orifices of the supply conduit 12 in the hot gas filter 2 is adapted to its lower end in the case of the presence of filter cartridges 7. In the latter, in the case of detachment of the cake filtration is passed through the total material, also passing through the material not yet gasified, as well as during uninterrupted operation. Operating parameters, such as overpressure and volumetric current, can be easily determined by some tests. If different materials are gassed, under certain circumstances it is advantageous to provide nozzles at different heights, which can be supplied separately or in groups.

By means of an oblique arrangement of nozzles, special circulation types can be obtained, through which further gasification is favored.

List of reference signs:

01 Gasifier 08 Pure gas pipe

02 Hot gas filter 09 Pressurized air supply

03 Food 10 Extraction

Incorporation 11 Ash tank Distributor system 12 Supply duct Product duct 13 Filter background Filter cartridge (s)

Claims (3)

1.- Device for the gasification of material containing carbon, especially wood, with a gas generator (1), to which the material to be gasified is fed in its upper zone and to which oxygen is fed, almost always in the form of air, in its middle zone, and in its lower zone it is gasified in a solid-bed reactor for the most part, extracting the product gas from the lower area of the gas generator (1) through a product gas conduit ( 6), and entering in the lower area of a hot gas filter (2), from which solid products are separated, such as particles not yet gassed, ashes and foreign bodies, through a filter with a filtering bottom (13), preferably provided with filter cartridges (7), while the pure gas passes through and is discharged by means of a pure gas conduit (8), an extraction (10) being provided for the discharge of remaining solid products in the area of bottom of the hot gas filter (2), characterized by that To the hot gas filter (2) oxygen is fed, preferably in the form of air, in the area below the filter bottom (13), if filtering cartridges (7) are present, approximately at the lower end of the filter cartridges, through an additional conduit (12). Device according to claim 1, characterized in that the current in the product gas line (6) through a blower is so strong that the non-gasified particles in the gas generator are essentially drawn into the hot gas filter ( two). 3. Process for the gasification of material containing carbon, especially wood, using a device according to claims 1 or 2, with a gas generator (1) and a hot gas filter (2) connected to it in the current of product, oxygen being supplied to the product stream before the filter, preferably in the form of air, and thus carrying out an additional gasification process, characterized in that the supply is carried out in the hot gas filter (2).