DE19750327C1 - Process for the production of synthesis gas from renewable cellulose-containing raw or waste materials - Google Patents

Abstract

The invention relates to a method for producing liquid hydrocarbons or synthesis gas out of renewable raw or refuse materials whose consistency makes it especially suitable for subsequent combustion in internal combustion engines. In addition, contaminated materials containing cellulose such as refuse wood should be able to be used. The materials containing cellulose are reduced in size, impregnated with an inorganic alkali salt solution, and are brought to a heated delivery device. The materials are heated to a temperature of at least 250 DEG C during delivery, and a foam-like material containing carbon is produced during heating.

Description

The invention relates to a method for manufacturing of synthesis gas from renewable, cellulose-containing Raw materials or waste materials, in particular through its Consistency for subsequent combustion in ver internal combustion engines is suitable. Thereby be especially waste wood as a raw material for the manufacturers suitable for the synthesis gas, where appropriate Contamination contained in the wood, e.g. B. Wood protection medium, no problems due to the procedure represent for the environment. Currently is in particular which is the result of demolition of buildings Waste wood is problematic and it has to be very common Special landfills, with correspondingly high costs, to be disposed of. Because of the relatively low density the waste wood is also released talking about high space requirements, so that possibilities should be found to produce waste wood dispose of with relatively little financial effort and even being able to use it.

One way of doing this has been for a long time known wood gasification, in which by pyrolysis  Gas can be obtained with its energy ge also used in internal combustion engines can be.

The countercurrent or cocurrent current used so far However, solution processes have the disadvantage that pyrolysis gas obtained in particular by tars and other substances is heavily contaminated, so that a Combustion in internal combustion engines only after a complex and costly cleaning possible becomes. Another problem with these be did not know or only unsatisfactory procedures dissolves, is the dioxin formation, which leads to a be can cause serious environmental pollution.

In addition, the Noell conversion process (DE 42 38 934 C2), in which a combustible material, which and may contain coal components, pyrolyzed and the pyrolysis gas formed with that also in this Process formed pyrolysis coke with nitrogen mobilized in an air liquefaction plant a pressure vessel with pure oxygen, which just if comes from the air separation plant, gasified becomes. This procedure can handle very large quantities waste containing organic matter at high Temperatures can be converted into synthesis gas. Here for, however, there is a very high level of system engineering and very large amounts of substances to be gasified required to be a reasonably economical Be urged to achieve such a facility. For the zu The management of the substances to be gasified is high Stik effort and correspondingly high transport costs required.

However, since cellulose-containing substances are relatively low  Having density is the required transport volume lumen accordingly high, so that operation of the No ell conversion process with cellulose alone gene raw materials is relatively ineffective.

In addition, DE 44 39 341 A1 describes a method for thermal recycling of wood with or without contact minations through pyrolysis and gasification of pyrolysis products known, in which the pyrolysis is a moveable cher heat exchanger, namely one that at a temperature that melts higher than the pyroly set temperature and lower than the gasification temperature tur is added. Such a heat transfer ger can according to the teaching described there for example, bone charcoal, a made from it sintered product, poorly water-soluble minera lical residues from thermal wood processing or carbonates of calcium or magnesium.

The object of the invention is to provide a way create from cellulose-containing renewable raw or waste a high quality syn to produce thesegas, which in its consistency Suitable for combustion in internal combustion engines is and in which also contaminated cellulose-containing Substances such as waste wood can be recycled.

The problem is solved with the features of the main claim.

According to the invention, the procedure is such that the gasifying cellulosic raw or waste materials mechanically crushed and after, but preferred at the same time when shredding with an anorga African alkali salt solution. The so before treated substances can then easily, at for example in a silo, be temporarily stored there the risk of fire by soaking with the saline solution  is eliminated and so a buffer for the after following thermal treatment can be created.

The cellulose-containing soaked in saline Substances then get into a conveyor that in a preferred form is a screw conveyor and are there up to a temperature of at least 250 ° C and preferably heated to about 300 ° C and conveyed towards a burner at the same time. The conveyor is heated via de ren outer jacket surfaces, whereby hot gases, the along the conveyor against the conveyor direction are used. For heating mung in the conveyor is convenient Waste heat used. So it is possible that with the Process produced synthesis gas in Ver internal combustion engines is burned and their Ab gases for heating the conveyor use so that the energy balance of the whole process it is improved.

During the production and warming run different processes and chemical transformations to which will be discussed below.

If temperatures above 200 ° C are reached, forms through the heating a foam-like coals fabric that is relatively porous and stiff. This can then in the conveyor, e.g. B. with the snail be finely ground, with the exception of one grit should be crushed from 10 to 100 microns. With the The carbon thus obtained is good at this grain size mobilized and in a burner in a flame un supply of preheated air is partially be burned, of course those at  Heat treatment formed in the conveyor Gases are also passed through the burner.

Following the combustion, a reduction takes place in the combustion chamber and a synthesis gas containing carbon monoxide, hydrogen and hydrocarbons is formed. This synthesis gas is withdrawn from the combustion chamber and then cooled and cleaned in a gas scrubber. At least one component of the gas scrubbing should be a Quentsche with which the residual water contained in the synthesis gas condenses, salts, such as. B. K ₂ CO ₃ , KHCO ₃ dissolved and the solid residual particles who separated the. The Quentsche should preferably be used for shock cooling of the synthesis gas in order to counteract possible formation of dioxins.

With the method according to the invention, the ver various renewable substances besides those already mentioned wood can be used. So can products and by-products of agriculture and forestry, such as Straw, brushwood, spoil, faeces, pods and barks are used. Also waste from the wood processing industry and other industries branches, like blends, residues from biological Processes (yeast, leaching), sewage sludge and greens Cases, waste paper and cardboard can be recycled the.

The cellulose-containing substances to be gasified must first classified and mechanically crushed, to once for the process and certain plant comm remove harmful components and a relatively even size distribution to back up.  

The comminution is advantageously carried out in several stages, with a first coarse shredding, that with a crusher with slow running Nip rolls is carried out and so once the Noise and dust emissions reduced and possible It is necessary to extract fine mineral ingredients ben, without unnecessarily many in the screened good organic additions are included and this Part can be deposited easily.

Before a second finer shredding can Sorting belt can be arranged to roughly remaining Impurities, e.g. B. non-ferrous metals or others Remove inorganic components manually. Before or afterwards the opposite can be done with a magnetic separator any contained proportion of ferrous metals automa be removed from the table.

The second crushing stage uses cheaper wise hammer mills. As already mentioned here at the same time soaking the inorganic alkali salt solution, reducing dust emissions and the risk of dust explosion is reduced can be. At the same time it becomes even Mixing of the substance to be gasified with the drink liquid reached.

As a liquid for soaking has turned out to be special cheap a solution of potassium carbonate and / or potash umhydrogencarbonate proven. The conc tration of the salts are at least 25 mol%. At the however, the cheapest is a cold saturated solution, which in the ratio between 300 and 500 ml per kg too gasifying substance is added.  

The cellulose-containing substance pretreated in this way is without additional heat supply is not flammable and can be off fire safety point of view harmless between be stored.

With the fine grinding, a grain size should be between between 10 and 50 mm, preferably 30 mm the, where the flowability of the different those cellulosic substances and their soakable speed, d. H. the absorption capacity for the saline solution, should be taken into account. In the soaked tent Lulose-containing fabrics start at room temperature first chemical transformations and digestions se.

The pretreated and crushed gasification material, which is also a mixture of different cellulose-containing Substances can then be heated in a conveyor given in the facility with the help of a funding snail transport in the direction of a successor combustion takes place. The conveyor check secures also that a full fill over the ge velvet free cross section in the conveyor and so a good heat transfer is achieved. The The conveyor is heated in countercurrent to the conveying direction and at temperatures up to approx. 130 ° C, which shortly after entering the Conveyor can be reached. One occurs Saponification of resin acids used in conventional thermal processes are problematic, in Resinate, a swelling by solvation of the Hydroxyl groups, especially in the intermicellar clean up. Shorter-chain polysaccharides (Hemicellulo sen) dissolve in alkaline media and condensate ren partially in the by the higher polymerisa  degree of cellulose (cleavage of Acetyl groups and some uronic acid groups from leaves Wood xylans or softwood glucomannans that are based on poly saccharide of the glucose chains can be attached nen). Delignification of the cells also occurs associations, the formation of alkililignin with increased Solubility. Polysaccharides are alkaline builds, whereby here the well-known peeling reaction, the e.g. B. in the encyclopedia of wood technology, VEB Fachbuchverlag Leipzig, 1988 is described, expires. At this Reaction takes place from the reducing end of the Polysaccharides as macromolecules. There is an En dolization of the carbonyl group; Isomerization of the terminal sugar molecule; a spin-off of the ge formed saccharic acid and the formation of a new one Carbonyl end group, which then further degraded analogously becomes. The reaction can be stopped when the Isomerization in the direction of metasacharic acid takes place and then no separation of the terminal monomer more done.

In the course of the digestion, saccharine salts acid and salts of lactic acid (lactones) and salts of formic acid (Formiade).

With inhibitors, such as. B. table salt, the last mentioned reactions are strongly suppressed.

Conterminations, such as B. wood preservatives can NEN affect such reactions, in particular especially by reducing the terminal aldehyde group pe to the alcohol group or oxidation of this group Carboxyl group is to be observed.

But since the time available for this is  If the funding is relatively short, it will run Reactions are incomplete.

In the phenolate formation and / or solution of Penta chlorphenol / -PCP-Na in the alkaline medium must be pH-dependent solubility must be taken into account. For example, at a pH of 5, only 79 mg / l dissolves in what water and at a pH of 8 but 4 g / l in water, see above that the concentration of PCP all over the substance can be evened out and also the fire behavior of the PCP with regard to the formation of poly chlorinated dibenzodioxins and furans improved can be. When investigating fire behavior under laboratory conditions it could be determined that at temperatures of approx. 300 ° C only 2.1% polychlorinated dibenzodioxyne and in the case of PCP-Na (Phenolate) only 0.03% PCDD have been formed. This is based on that in the pyrolytic dimerization of PCP regarding the prevailing reaction mechanisms Lich the dioxin precursors (Dekachloridphenylenoxid) and the associated cleavage of HCl, which leads to Formation of hexachlorobenzene, which in turn is PCP and in a parallel reaction with elimination of HCl Octa chloridbenzo-p-dioxin supplies. Of the Because of the high affinity of chloride anions for Alka is the binding as chloride, so that the described reaction is interrupted. Out of it follows that the pretreatment leads to the formation of PCDD-PCDF formation is reduced. Please note including Sandermann in the Federal Environment Agency Environment chemical pentachlorophenol, Erich Schmidt Verlag, Berlin, report 3/87 on page 186 Re action mechanisms.

With further heating above the boiling point,  that when using a potassium carbonate solution at approx. 132 ° C, the evaporator is absorbed heat the temperature in a certain range held constant longer, and the digestion processes are carried out solely without pressure increase the high salt concentration on this relatively low temperature level. At another temperature then the water evaporates completely and Due to the lack of water, it already happens described alkaline degradation is ended. By be then start pyrolytic decomposition processes lower monocarboxylic acids are formed, some of which corresponding salts react.

If temperatures above 200 ° C are reached, Potassium bicarbonate present under carbon di cleaved oxide converted into potassium carbonate and in PVC contaminants are also used in this temperature range conditions decomposed pyrolytically with elimination of HCl and react with relatively high implementation rates Potassium salt (KCl).

If temperatures above 260 ° C are then reached, coking already occurs because the coking temperature temperature by the previously expired digestion pro has been reduced. The coking is at Temperatures of around 280 ° C completed. You he follows very quickly, especially because of the filling the spaces between the fibrils in the cellulose Thermal conductivity of the medium is greatly increased and the formed by the heating in the conveyor steam and the carbon dioxide heat conduction improve.

When coking occurs, foaming occurs at the same time  of the solid to a sticky foam that however stiff immediately upon completion of this reaction becomes. The creation of this foam-like carbon fes is due to the rapid gas development, the high Heat transfer, the closure of the fibrils between spaces, through partially depolymerized polysacchar de, salts and other causes. The resulting one Carbon foam can then be easily in the conveyor device with which the snail is finely ground, so that a fine dust is obtained. The one for this force required is very small because of the foam has a relatively low strength.

The gases formed contain in addition to the coking emit a high proportion of carbon dioxide from the Ethanoic acid-potassium acetate reaction and gaseous Me ethanol from lignin decomposition (from methoxyl group pen). In contrast, the gases formed are after the coking is essentially free of higher Koh Hydrogen oils, such as the unwanted tars.

The temperatures are at the end of the conveyor at around 300 ° C and do not necessarily have to be in one be brought to a higher temperature range with would be associated with a significantly higher effort because the heat capacity of carbon with increasing Temperature also rises and preferred to Heating of the conveyor waste heat to be used then would have to be additionally heated.

The temperature treatment in the conveyor gases formed with water vapor and Carbon dioxide are enriched in the aftermath almost complete combustion leads, with an intensive mixing  render preheated air is cheap. You can do this partial preheating the gasification air under simultaneous cooling of the get in the gasification crude gas in countercurrent process (regenerative) done by heat transfer. By the scorching the flammable gas components and in some cases the finely ground carbon dust in a burner, becomes the necessary energy for the following Reduk tion processes (water gas and Boudouard processes) for Provided. Through the unburned, through the Burner of flame mobilized carbon powder that because of a maximum reaction surface of small grain sizes, the scalds Gases reduced and in the raw gas can be a flammable Share consisting of carbon monoxide, hydrogen and combustible hydrocarbons can be obtained. By the cooling of the combustion chamber in which the reduction processes can influence the gün Most temperatures are taken to e.g. B. that Boudouard balance in the desired direction influence.

The relatively high reaction surface area already mentioned of carbon causes the endothermic Reductions at temperatures down to about 600 ° C run and it can use heat very well can be achieved.

In addition, the previously formed salts (Formia te, acetates, etc.) and soaps (Resinate, etc.) can be converted into never hydrocarbons and inorganic components. Due to the aforementioned shifting of the equilibrium reactions (water gas, Boudouard reaction) and the additional provision of carbon dioxide, which has been formed in the conveyor, the energy content of the synthesis gas generated can be increased to above 5000 kJ / Nm ³ (standard cubic meter).

The raw gas thus obtained is almost tar-free. The at most known pyrolysis processes required The cost of separating tar fractions can be reduced the invention is eliminated. That after a wash of solid particles and non-flammable components white synthesis gas which has been freed from the test can then be in a Internal combustion engine, for example an Otto engine or diesel engine can be used easily and in Connection with a generator generates electrical energy become.

By different compositions of the supplied fluctuations occur due to cellulosic substances in the heat capacity and the mass flow on that when cooling the synthesis gas on the use temperature must be taken into account.

The potassium carbonate (intermediate stages K ₂ O, KOH) also contained in the raw gas serves on the one hand as a sorption agent and on the other hand leads to a reduction in the proportion of carbon dioxide in the raw gas obtained and consequently the calorific value of the gas can be increased accordingly. Due to the sorption behavior of potassium carbonate in the gas space, agglomerates form which can be washed out much better than fine particles.

The Quentsche to be used for gas cleaning and cooling of the hot raw gas, preferably leads to condensation of the residual water, to the solution of salts (K ₂ CO ₃ / KHCO ₃ ) and the solid particles can be taken up by the wall film in the Quentsche and at least partially dissolved will. The contaminated water from the Quentsche can be reused as an impregnation liquid after the separation of the soluble constituents, for example by decanting or by means of a cyclone. Since a relatively high proportion of potassium carbonate or potassium hydrogen carbonate is contained in the squeeze water, only a small additional addition of these alkali salts is required when the comminuted cellulosic substances are impregnated when the process according to the invention is operated continuously.

The remaining carbon particles come in the Wash liquid mainly in colloidal form and can follow the already described Separation of soluble minerals continued to be used or returned to the process.

The pre-cleaned raw gas can then be cleaned by centrifugal force in combination with a venturi scrubber, in which the pre-cleaned squeeze water can also be used and, if necessary, a bag filter connected downstream of this can be further cleaned. In this way, the particle content of the purified synthesis gas can be kept below 2 mg / nm ³ .

The invention is based on exemplary embodiments len are described.

Show:

Fig. 1 shows the schematic flow of the inventive method in different stages for the gasification of residual and waste wood and

Fig. 2 shows the schematic structure of a system for carrying out the procedural method according to the invention, with which the chemical energy contained in the generated synthesis gas can be converted into electrical energy with a Ge generator.

In Fig. 1, the schematic sequence for the recovery of residual and waste wood is shown as an example as a block diagram. In this example, the synthesis gas obtained is used in a gas engine that drives a generator to generate electrical energy.

The construction of a corresponding system for carrying out the method according to the invention is illustrated in FIG. 2.

After the indicated transport, the waste or residual wood to be used is reduced in two stages 1 and 2 , with a preferred edge length of approximately 30 mm to be achieved. In the fine comminution 2 , a cold saturated potassium carbonate, potassium hydrogen carbonate solution or a mixture thereof is sprayed on at the same time by means of nozzles 3 and the wood or possibly other cellulose-containing substances are soaked.

Pretreated in this way can be safely stored in a fuel silo 4 , which serves as a buffer for the subsequent thermal treatment. From the fuel silo 4 , the moist reserved goods are placed in a screw conveyor 6 driven by a motor 5 . It should be ensured that the free cross section in the screw conveyor rer 6 is filled. The screw conveyor 6 is heated from the outside. In this case, the exhaust gas of a gas engine 10 is used for heating, which is passed via the line 12 against the conveying direction of the screw conveyor 6 , so that heating takes place according to the countercurrent principle and the highest temperatures above 260 ° C. at the end of the screw conveyor 6 are sufficient .

The processes and conversions already mentioned in the general part of the description take place in the screw conveyor 6 , the corresponding local temperatures being shown in FIG. 2. However, the screw conveyor 6 must have a sufficient length to ensure sufficient dwell times.

In or on the screw conveyor 6 no susceptible locks or closures for securing the gas tightness are required, since the pressure and flow conditions of the gases forming ensure that no gas leakage from the feeder screw conveyor 6 into the fuel silo 4 can take place. This is ensured by the relatively slow gas formation in the low temperature range of the screw conveyor 6 , which has a barrier effect and the ejector effect of the burner 7.

The solid material formed at the end of the screw conveyor 6 consists for the most part of a rigid foam which is finely ground with the screw. The finely ground carbon is carried out together with the gases formed by the burner 7 , in the flame of which the combustible gases and part of the very reactive carbon dust are burned. The combustion temperature is sufficient to use the unburned carbon strongly mobilized by the flame as a reducing agent and to allow the known water gas and Boudou ard processes to take place in the burner chamber 8 , since of course water vapor and carbon dioxide are also formed during the combustion.

The combustion chamber 8 is also cooled in countercurrent from the outside with air supplied from the environment, heated in the process and fed as preheated combustion air via line 13 to the burner 7 .

The air cooling of the combustion chamber 8 should preferably be regulated in order to ensure optimal temperature conditions for the synthesis gas formation.

The extracted raw gas, which in addition to the combustible components also contains carbon dioxide and other solid impurities, is fed to a gas scrubber 9 . In a quench, shock cooling and a first rough cleaning of the raw gas take place, from which the largest proportion of solid impurities is removed in further cleaning steps, for example by means of a cyclone in combination with a Venturi scrubber and filters, and which frees and cleans as much as possible of carbon dioxide Gas can be supplied to the gas engine 10 .

The water obtained in the gas scrubber 9 can be used again after the solid components have been separated off via the line 14 through the spray device 3 for soaking the shredded wood, since it has a high content of the required potassium carbonate and potassium hydrogen carbonate.

The separated ash is heavy with approx. 25% tall, which is mainly chemically bound, charged. This high percentage offers the possibility perform recovery using known methods to lead.

The amount of ash is around 10 g per kWh of electrical energy generated, so that the small amounts could also be disposed of in special landfills. The eluate behavior can be additionally improved by sulfitation (H ₂ S).

Since the composition of the synthesis gas and consequently the calorific value can fluctuate, it makes sense to regulate the amount of combustion air supplied to the gas engine 10 in order to maintain an optimal gas / combustion air ratio.

Excess synthesis gas that cannot be used in the gas engine 10 , for example in the event of an accident or malfunction, can be discharged via line 16 for flaring with a safety torch 18.

Following the gas scrubber 9 , a compressor 17 is arranged for the transport of the synthesis gas to the gas engine 10 .

The electrical energy generated by the generator 11 can then be fed into existing networks or used as an isolated solution with the known advantages of power / heat coupling.

A plant, as shown in FIG. 2, can be designed in a relatively small version even for small capacities, so that a small feed area with a correspondingly smaller transport is sufficient.

Because a large proportion of waste heat is used an economic operation alone with the generated electrical energy achievable.

Claims (13)

1. A process for the production of synthesis gas from renewable cellulose-containing raw materials or waste materials, in which the cellulose-containing substances are crushed and soaked with an inorganic alkali salt solution, brought into a heated conveyor ( 6 ), during the conveying to a temperature of at least 250 ° C warmed and a foam-like carbon formed during the heating is finely ground, which is burned together with the gases formed and heated air and obtained by reduction a carbon monoxide, hydrogen and hydrocarbon-rich synthesis gas, which is cooled in a gas scrubber ( 9 ) and is cleaned. 2. The method according to claim 1, characterized, that the cellulose-containing substances with a Potassium carbonate and / or potassium hydrogen carbonate Solution to be soaked. 3. The method according to claim 2, characterized in that a solution with egg a salt content of at least 25% becomes. 4. The method according to claim 2, characterized in that cold saturated Lö solution in relation to the cellulose-containing substances 300 to 500 ml / kg is added.   5. The method according to any one of claims 1 to 4, characterized in that the impregnated cellulose-containing substances conveyed in a screw conveyor ( 6 ), crushed and heated in countercurrent with heat supplied from the outside. 6. The method according to any one of claims 1 to 5, characterized in that the formed foam-like carbon on grain sizes between 10 and 100 µm is crushed. 7. The method according to any one of claims 1 to 6, characterized in that the temperature after the combustion of the comminuted carbon through the along the lateral surface of the combustion chamber ( 8 ) air taken into account taking into account the water gas and Boudouard processes occurring in the aftermath for the combustion and so preheated air is used for combustion. 8. The method according to any one of claims 1 to 7, characterized in that the cooled and cleaned synthesis gas is fed to an internal combustion engine ( 10 ) and the waste heat of the internal combustion engine ( 10 ) is used to heat the cellulose-containing substances. 9. The method according to claim 8, characterized in that with the combustion engine ( 10 ), a generator ( 11 ) is driven to generate electrical energy. 10. The method according to any one of claims 1 to 9, characterized in that the cellulosic substances in at least two stages ( 1 , 2 ) are crushed to a grain size between 10 and 50 mm. 11. The method according to any one of claims 1 to 10, characterized in that metallic or other inorganic abrasive ingredients or removed after the shredding become. 12. The method according to any one of claims 1 to 11, characterized in that the washing liquid after separation of solid ingredients to the tear reduction of the shredded cellulose-containing substances is used as an inorganic alkali salt solution. 13. The method according to any one of claims 1 to 12, characterized in that the hot synthesis gas is fed to a Quentsche.