WO1989001505A1

WO1989001505A1 - Process and installation for recovering reusable gas from waste through pyrolysis

Info

Publication number: WO1989001505A1
Application number: PCT/EP1988/000699
Authority: WO
Inventors: Bernd Michael Wolf
Original assignee: Pka Pyrolyse Kraftanlagen Gmbh
Priority date: 1987-08-13
Filing date: 1988-08-03
Publication date: 1989-02-23
Also published as: IN170715B; CS274679B2; FI900660A0; NO900670D0; PL154803B1; EP0376971A1; AU2326288A; NO174002B; NO174002C; DD282023A5; KR960010986B1; ATE69614T1; NO900670L; EP0376971B1; DE3727004A1; GR1000301B; DK35890A; DK35890D0; DE3866357D1; RU1836406C

Abstract

According to a process for recovering reusable gas from waste through pyrolysis, the previously comminuted waste is transformed into fluff, granulates or pellets and introduced into a degassing drum (16), in which low temperature carbonization gas is generated and separated from the residual matter. The low temperature carbonization gas is decomposed into combustion gas in a gas converter (19) and cleaned in a subsequent gas washing installation (21-24 and 47-51) with circulating washing water. Part of the water of the circulation system of washing water is withdrawn and replaced with fresh water in order to limit its concentration of toxic substances. The pyrolysis residues to be withdrawn from the low temperature carbonization drum are withdrawn through a water bath (72). At least part of the quantity of liquid withdrawn from the circulation system of washing water of the gas washing installation (21-24) is introduced in the water bath (72).

Description

Process and plant for recovering usable gas from waste by pyrolysis

The invention relates to a method for recovering usable gas from waste by pyrolysis according to the preamble of claim 1. A system for carrying out the method for this is described in the preamble of claim 11.

Methods and systems of this type are known for example from DE-OS 33 47 554 and DE-OS 35 29 445. A very low-level recovery of usable gas from waste takes place, for which purpose the water required for the various stages, in particular the amount of water required for the gas washing system of the cracked gas processed in the gas converter is circulated. In order to keep the pollutant level in the gas washing plant constant and to ensure gas purity, it was necessary to remove a certain part of the water cycle and replace it with fresh water. The withdrawn portion required post-treatment, because its residues posed a disposal problem. It had also turned out that fluctuating concentrations of cyanides, phenols and ammonium made it difficult to introduce them directly into a biogas plant that possibly worked with the pyrolysis plant. The fluctuating concentrations caused the microbes to degrade and, in extreme cases, even destroyed the culture. However, neutralization by adding chemical oxydation substances and flocculants increased the amount of residues to be disposed of as special waste.

The present invention is therefore based on the object, while maintaining a low-wastewater treatment process to achieve a further reduction in disposal-polluting environmentally harmful substances, where appropriate at the same time a further improvement in the efficiency of the system is to be achieved.

According to the invention, this object is achieved in that at least part of the water bath through which the pyrolysis residues are discharged from the degassing drum amount of liquid withdrawn from the wash water circuit of the gas washing system is introduced.

This results in wetting of the pyrolysis residue.

Surprisingly, it was found that the pyrolysis residue absorbs more than 140 percent by weight of its own weight in liquid with a sufficient residence time. This means that of the wash water, which can consist in part or in whole of the water cycle of the gas scrubbing system, can bind to a high degree. It was found that the greater the carbon content of the pyrolysis residue, the greater this liquid absorption. In addition, a sufficient dwell time for total wetting should be observed, which e.g. can be achieved by a screw conveyor system with a correspondingly slow speed.

To increase the carbon content in the pyrolysis residue, it can therefore be provided in a further improvement of the invention that the garbage entered in the degassing drum is previously removed by sorting out inert substances. This can be done using suitable sorting devices such as, for example, comb roller sorters. It has now also been shown, unexpectedly, that the pyrolysis residue treated in this way obtains an activated carbon structure with chemosorbing properties, which means that it can be used as activated carbon for any application.

In an advantageous development of the invention, it can be provided that the pyrolysis residue is introduced as an activated carbon filter into a filter device behind the drying tower of the gas washing system.

Sulfur components of the pyrolysis gas, which mainly depend on the sulfur content of the coke used in the gas converter, are known to be difficult to remove from the pyrolysis gas. If you now connect a filter device to the gas scrubber, sulfur or fluorine compounds that have not been fully washed out can be absorbed by the activated carbon filter. Because the pyrolysis residues are used for this purpose, there are no significant additional costs and the pyrolysis residues are even put to sensible use in this way. This also means that the sulfur content in the exhaust gas is economically reduced far below the prescribed air limit values, which means that coke with a slightly higher sulfur content can also be used cheaply as a further advantage in the gas converter. Due to the high absorption capacity of the pyrolysis residue, if necessary, pollutant components from other productions can advantageously be disposed of in such a way that they are mixed with the liquid portion withdrawn from the water cycle. This means that in addition to its own almost low-pollutant treatment of waste, the method according to the invention can also be used to remove pollutants from other plants.

It was found as a further advantage of the method according to the invention that the amount of wastewater from a pyrolysis gas plant which processes household waste is reduced by more than 50% and generally less than 100 liters of wastewater per ton of household waste disposal. This amount of waste water is usually so polluted that untreated discharge is ecologically undesirable. However, a significant and cost-effective reduction in pollutant pollution can be achieved if it is provided in a further development according to the invention that the amount of liquid withdrawn from the water circuit of the gas scrubbing system is pretreated in batches by ozone injection in such a way that after the treatment the concentration is treated of cyanide is ≤ 10 g / m ³ and phenols <40 g / m ³ . If the pyrolysis residue is treated in this way, it can be easily introduced into biogas plants. Such a pyrolysis residue, which has a liquid content of approx. 60 percent by weight, is a particularly nutrient-rich carrier substance for anaerobic methane gas generators, which convert the absorbed, biologically convertible groups of substances into useful gas, due to the balanced levels of phenols and cyanides due to the high carbon and ammonium content from gas scrubbing. The ozone-controlled homogenization of the pollutants minimizes the risk of overdoses and thus the destruction of culture. Experiments have shown that a short ozonization, which is generally less than a quarter of a full ozonization time, is sufficient to achieve this homogenization effect.

To further reduce pollution caused by waste water, it can be provided that the excess water not bound by the pyrolysis residue, which generally corresponds to less than 50% of the portion withdrawn from the water cycle of the gas washing system, is fed to a residual ozonization. This can be done either in parallel with a use in a biogas plant or instead. By total ozonization of the excess water, the COD can be reduced to below 400 mg oxygen per liter, the BOD to approx. 60 mg / m ³ and the proportion of cyanide and phenols to generally below 0.1 g / m ³ . Because of the elev Liche binding of the amount of liquid withdrawn from the water cycle in the pyrolysis residue but only a significantly small proportion of the wastewater needs to be treated in this way, only a minimal amount of energy is required for ozonization of the remaining amount. In contrast to the previously known methods, there is no longer any disposal problem with the method according to the invention.

It has now been further determined that, as an alternative to using the pyrolysis residue treated in accordance with the invention in biogas plants - or in parallel - this pyrolysis residue can be used for the energetic supply in lime kilns. For this purpose, it can preferably be pressed into egg briquette-like pellets. It has been surprisingly found that if a portion of the inert substances is pre-separated before degassing, its calorific value may correspond approximately to that of lignite, which is sufficient for a smelting process. If the correct mixing ratios are observed, the inert material fractions are calcined or ceramized, which in particular also includes heavy metals.

Experiments have shown that with a corresponding compression between 400 and 550 kg / cm ² to egg-briquette-like pellets in a mixture product of calcium-containing compounds such as lime, Kaikofen filter dust, lime hydrate or lime hydrate waste with a fuel component such as coal dust as well as substances containing sulfur, chlorine, fluorine and heavy metals at approx. 1200 degrees Celsius and a residence time of 45 to 120 minutes in this temperature range, a burnout residue occurs in which almost 100% of the total chlorine is present - And the sulfur content, as well as the metals are ceramized or incorporated into the ashes, almost in a non-leachable manner. This means that an environmentally friendly removal of pollutants, especially heavy metals, is achieved in this way.

The only prerequisite for the ceramization of the metals is that the molar ratio of SiO ₂ , Al ₂ O ₃ , CaO. ZnO, Fe ₂ O ₃ and / or MgO, on the one hand, is at least 6: 1 to the total molar fraction of the metals lead, chromium, manganese, cadmium, berilium, barium, selenium, arsenic, vanadium, antimony, bismuth, strontium and / or zircon.

A prerequisite for the incorporation of sulfur, chlorine and fluorine compounds is that the molar ratio of calcium, magnesium and sodium on the one hand to the total sulfur, chlorine and fluorine is at least 2: 1. The mixture product should contain a maximum of 40 percent by weight of liquid and the calorific value should be at least 100 kilocalories / kg, so that the fuel, for example in a lime kiln, with the necessary dwell time and temperature can burn up, whereby the introduced metals oxidize and are taken up in the melts of CaO and MgO, where they form relatively inert ceramic complexes. Sulfur compounds are absorbed as sulfites or sulfates, liquid chlorine and fluorine are bound to CaCl ₂ and CaF ₂ .

Experiments carried out with pyrolysis residue have shown that this can take over the function of the fuel component for temperature generation. The pollutant components absorbed in it, which can also come from other sources than the pyrolysis gas plant itself and have been integrated into the water bath of the pyrolysis residue discharge, can be disposed of in an environmentally friendly manner. The pyrolysis plant thus leaves no residual substances that require final deposition.

It was also found that after deducting the own energy requirement for the operation of the plants, the available useful energy can increase by more than 5% through a reduction in the own electricity requirement for the ozone plant for gas cleaning and through the improved energetic use of the pyrolysis residue.

If the pyrolysis residue is used in biogas plants, its economic efficiency for the thermal conversion of waste materials can be increased. The residues in the method according to the invention requiring final storage are several times smaller than the residues in a waste incineration plant, which are also highly toxic and must be disposed of as special waste.

A system according to the invention for carrying out the method is described in principle below with reference to the drawing.

Since such a system in its basic structure is already known from DE-OS 35 29 345, only the parts essential to the invention are described in more detail below. A discharge of the pyrolysis residues from the degassing drum via a screw device is described in DE-OS 33 47 554, see in particular FIGS. 7 and 8. Of course, other discharge devices are also possible instead of the screws shown. The only requirement is that there is intensive wetting of the pyrolysis residue in the water bath for a corresponding period of time.

The waste is conveyed via a conveyor belt 1 into a primary crusher 2 for coarse shredding. A conveyor trough 3 and a conveyor belt 4 with a magnetic separator 5 transport the Garbage in a sorting device 6. In the sorting device 6, the heavier, wet, vegetable fraction is separated and falls into an underlying container or onto a conveyor belt 7. Likewise, inert substances can also be separated off in order to increase the carbon content of the pyrolysis material. The remaining waste fraction is fed to a thermal screw press 14 via a further conveyor belt 8, a further shredding device 9 and a downstream hydrocyclone 10, in which heavy parts are separated again via a line 11. Via the line 11, the waste together with the separated waste from the container 7 is fed via a feed line 12 to a biogas plant 13, which can be preceded by a fluid classifier for the pre-selection of inert heavy parts, which works, for example, according to the flushing method.

In the thermal screw press 14, the formation of granules in a rapidly degassable structure and a size of approximately 3 to 50 mm is achieved in a known manner by frictional pressure at approximately 110 to 150 degrees Celsius.

Instead of in granular form, fluff, ie a loose waste form, or pellets, ie waste components compressed into briquettes, can also be produced in the specified size, which, however, generally require longer degassing times. The waste components crushed in this way pass over a rotary valve 15 or other entry devices, such as, for example, stuffing screws in a degassing drum 16, in which carbonization gas is produced in a known manner at temperatures of 450 to 600 degrees Celsius, which gas is introduced into a high-temperature gas converter 19 via a discharge line 17 and a dust separation device 18. In the gas converter 19, the carbonization gas is worked up or converted over a coal or coke bed. A gas converter of this type is described for example in DE-OS 33 17 977.

After passing through a heat exchanger 20, the gas passes into a gas scrubbing system, which essentially consists of a water spray tower 21, a blower 22 and a cleaning cylon 23 and a droplet separator 24. Via a gas line 25, the cleaned gas reaches a gasometer 26, in which excess gas can be fed to a flaring device 28 if too much gas is supplied via a secondary line 27.

Normally the gas from gasometer 26 comes to one

Gas engine 29, which is connected to a generator 30, the burned exhaust gases being introduced into a chimney 32 via an exhaust gas line 31.

The gas converter 19 receives water via a line 33 and 34 coke via a coke inlet. Ash and slag is over a discharge line 35 is discharged. Possibly. To save energy, a coke return line 36 can also be provided for the coke freed from the slag.

A branch line 37 branches off from the gas line 25 and leads to a gas burner 38 which serves to supply heat to the degassing drum 16. During the start-up phase of the system, an oil burner 39 or a separate gas burner is used to heat the smoldering drum. Subsequently, during operation, however, the heat required for the degassing drum 16 can be completely covered by the burner 38.

The scrubbing water obtained during gas cleaning passes into a scrubbing water tank 40 and then into a filter device 41 (usually a settling tank). Separated solids in the filter device are introduced into an ash container 43 via a line 42. The residues are discharged from the ash container 43 via a discharge line 44 and introduced into the carbonization drum 16 again via the insertion device, possibly a cellular wheel sluice 15.

The cleaned washing water returns from the filter device 41 via a return line 45 after passing through a cooling tower 46 back into the spray tower 21 of the gas washing system. A part of the cleaned wash water is in a Wash water neutralization system 47 is introduced into which the vapor vapor condensate from the thermal screw press 14 is also introduced via a line 58, provided that it is not fed via line 65 to the reservoir 53 of the biogas system.

From the wash water neutralization system 47, the wash water reaches the spray tower 21 via a return line 78 for circuit treatment, while a partial quantity reaches a circuit water batch treatment system 48 via a partial quantity removal line 79. In a known manner, the washing water is chemically cleaned therein by appropriate chemicals which are entered via line 49, provided that the chemical oxidation is not replaced by ozonization, as a result of which the residue-increasing additive addition can be greatly reduced. The washing water is partially removed via a circuit line 50. passed through an air filter 51 to remove foams, exhaust gases being blown off through a line 52 over the chimney 32, and partly. there is a return via a line 80 into the spray tower 21.

The chemically and mechanically cleaned water passes from the cycle water batch treatment system 48 via a line 71 into the preliminary tank 53 of the biogas system. Sewage sludge, raw compost can also be placed in the primary tank or the like. What is indicated by the arrow "54". The vapor vapor condensate, if it has not been passed through the cycle water batch treatment system 48, can be introduced directly into the preliminary container 53 via a line 65.

The substances to be worked up in the biogas plant 13 arrive in a hydrolysis stage or a hydrogenator 56 from the preliminary tank 53. A countercurrent heat exchanger 57 connects to the hydrolysis stage 56 and receives its heat through a hot water line 62, which comes from the cooling tower 46 of the wash water cleaning system branches. In a digester floor 67, a coil heating system ensures a temperature rise in the methane region of the digester of 33 to 37 degrees Celsius. In this way, the excess heat from the pyrolysis plant is used for the biogas plant 13.

The biogas plant 13 is constructed in the usual way. As a phase-separated biogas plant, it can have a normal acid phase in the upper region in the middle shaft 63, while an acetic acid phase is present in the lower region. The methane gas formed is withdrawn via a methane gas line 59 and fed to the gas line 25 or the gas washing system of the pyrolysis system for cleaning via a buffer 60 and a compressor 61. The fermentation residue is discharged through a suction line 66 and a pre-dewatering device tion 68 fed, which brings it to about 20% dry matter. The solids contained in the fermentation residue can be brought to approx. 85% dry matter via a dry press 69. The remaining fermentation water is collected in a lagoon 70 and, if necessary, fed to the treatment plant 48 or fed directly into the sewage system.

The substances separated in the cycle water batch treatment plant 48 can be fed to a sewage treatment plant via a line 64.

Pyrolysis residues are discharged in the degassing drum 16 via a water bath 72, the discharge e.g. can take place via screw conveyors. The water bath 72 is supplied with the liquid required for wetting the pyrolysis residue via a partial liquid line 73. The partial quantity line 73 branches off from the batch treatment system 48.

The pyrolysis residue wetted with liquid in this way is discharged via a line and can optionally be fed to the biogas plant 13 after treatment, for example ozonization or other cleaning. The biogas plant 13 is of course only mentioned for example. It is not necessary for the invention itself. Instead of one Introducing the pyrolysis residues into the biogas plant 13, the pyrolysis residues can, if necessary, also be transported via a line 74 A to a lime kiln 77.

Likewise, the pyrolysis residue can be introduced via a line 74 B after it has dried into a filter device 75 as an activated carbon filter. The filter device 75 is located between the gas washing system and the gasometer 26. In this case, however, the activated carbon obtained from the pyrolysis residue should be at least largely free of pollutants. This means that one operates in batches and introduces fresh water through a fresh water line 81 into the water bath instead of a water supply via the partial liquid quantity line 73 with contaminated circulating water.

If necessary, the quantity of liquid removed from the water cycle can also be treated in an ozone injection system 76. The ozone system 76 is connected to the batch treatment system 48. If the partial quantity removed from the circuit via the partial quantity extraction line 79 is appropriately cleaned before it is introduced via the liquid partial quantity line 73 into the water bath 72 in the ozone system 76, the pyrolysis residue can also be used as an activated carbon filter in the filter device 75 in this procedure, if necessary. The function and mode of operation of a lime kiln 77, into which the pyrolysis residue is introduced via line 74 A, are generally known, which is why it is not discussed in more detail here. The pyrolysis residue may be used together with other fuel components as fuel. Of course, it is not necessary that a direct line 74 A is present between the water bath 72 and the lime kiln 77. The system according to the invention is designed so that not all units have to be in one place. For example, the biogas plant 13 and the lime kiln 77 can be located at a different location, and the substances can be transported there in any way.

The partial liquid quantity which has not been completely absorbed by the pyrolysis residue in the water bath 72 can, if necessary, also be conducted via the ozone system 76, if necessary for full ozonization, before it is introduced into a sewage treatment plant.

Of course, it is not absolutely necessary for the partial liquid quantity line 73 to branch off from the wash water neutralization system 47; rather, the removal can also take place at another point in the circulating water supply if required. The same applies to the activation of the Ozone injection system 76.

Claims

Patent claims

1. Process for the recovery of usable gas from waste by pyrolysis, the pre-shredded waste being processed into fluff, granules or pellets in a size of 1 to 50 mm and brought to a dry substance content of at least 75% and then introduced into a heated degassing drum, generated in the carbonization gas and separated from the residues, such as ash and other constituents, and wherein the carbonization gas is broken down into fuel gas in a gas converter, which is cleaned in a subsequent gas scrubbing system with circulated scrubbing water, the scrubbing water circuit of the gas scrubbing system to limit it Pollutant concentration in the water of the circuit a partial amount is withdrawn and replaced by fresh water, and the pyrolysis residues to be discharged from the smoldering drum are discharged via a water bath, characterized in that at least part of the gas wash system (21-24 and 47-51) is removed from the wash water circuit in the water wash (72) Liquid subset is introduced.

2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the garbage entered in the degassing drum (16) previously removed by sorting inert substances in such an amount that the pyrolysis residues discharged from the degassing drum contain at least 25 percent by weight carbon.

3. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the treated with the subset of the washing water circuit

Pyrolysis residue is used as an activated carbon filter.

4. The method according to claim 3, characterized in that the pyrolysis residue is introduced as an activated carbon filter in a filter device (75) behind the gas washing system (21-24).

5. The method according to any one of claims 1-4, d a d u r c h g e k e n z e i c h n e t that pollutant components from other productions are added to the circuit water concentrate withdrawn from the wash water circuit for their disposal.

6. The method according to any one of claims 1-5, characterized in that the amount of liquid withdrawn from the water circuit of the gas washing system is pretreated in batches by ozone injection so that after the treatment the concentration of cyanide ≤ 10 g / m ³ and or phenols <40 g / m ³ is.

7. The method according to any one of claims 1-5, characterized in that the amount of liquid removed from the water circuit of the gas washing system, which was not absorbed during the wetting of the pyrolysis residue, is subjected to a further batchwise ozonization until its COD is <400 mg O ₂ / liter .

8. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the pyrolysis residue wetted with the amount of liquid in

Sewage or biogas plants (13) is introduced.

9. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the pyrolysis residue wetted with the liquid subset is entered in lime kilns (77).

10. Plant for carrying out the method according to one of claims 1-9 with a waste comminution device, with a drying device and a degassing drum with an inlet for the pre-comminuted waste, with an outlet for solid pyrolysis residues and with a carbonization gas discharge line, to which a gas converter for extraction of cracked gas, with a gas scrubber connected downstream of the gas converter and with a water bath adjoining the outlet for the pyrolysis residues for the discharge thereof, characterized in that a partial liquid line (73) is led to the water bath (72) from a device (48) of the gas scrubber .

11. Plant according to claim 10, characterized in that a sorting device (6) for sorting out inert substances is arranged in front of the degassing drum (16).

12. Plant according to claim 10 or 11, so that a filter device (75) is arranged behind the gas washing system (21-24 and 47-51), in which the pyrolysis residue can be used as an activated carbon filter.

13. Plant according to one of claims 10 - 12, d a d u r c h g e k e n e z e i c h n e t that an ozone injection device (76) is provided for the liquid portion withdrawn from the water circuit of the gas washing system (21-24).