NO174002B - PROCEDURE AND PLANT FOR RECOVERY OF RECOVERABLE GASFLE SOAPLE BY PYROLYSE - Google Patents

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 Part of the water of the circulation system of washing water is withdrawn and replaced with fresh water in order to limit its concentration of toxic substances. The pyrolysis residues to be withdrawn from the low temperature carbonization drum are withdrawn through a water bath (72). At least part of the quantity of liquid withdrawn from the circulation system of washing water of the gas washing installation (21-24) is introduced in the water bath (72).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

The present invention relates to a method for extracting usable gas from rubbish by pyrolysis according to the preamble in claim 1. A facility for carrying out this method is described in the preamble to claim 10.

Methods and facilities of this type are known, for example, from DE-OS 33 47 554 and 35 29 445. Thereby, a very low-water recovery of usable gas from garbage takes place whereby the necessary water from the various stages, especially that for the gas washing plant to that in the gas furnace generator processed fission gas required amount of water is fed into the circuit. However, in order to keep the level of harmful substances in the gas washing plant constant, and to ensure a certain gas purity, it was necessary to withdraw a certain sub-quantity from the water circuit and replace this with refreshing water. However, the withdrawn sub-quantity needed a post-treatment because the residues from this water raised a disposal problem. Thereby it turned out that, due to fluctuating concentrations of cyanides, phenols and ammonium, it was difficult to directly use a biogas plant cooperating with a pyrolysis plant. The fluctuating concentrations caused performance reductions for the microbes and, in extreme cases, even cultural extinction. However, neutralization due to the addition of chemical oxidizing agents or flocculating agents increased the residual amount of special waste that had to be taken care of.

The present invention therefore has the task, while maintaining a waste water-poor processing method, to achieve a further reduction of substances required for disposal and environmentally harmful, thereby possibly simultaneously achieving a further improvement of the plant's efficiency.

According to the invention, this task is solved by a method of the type described in the introductory part of claim 1 and which is characterized by the features that appear in the characterizing part of claim 1.

In this way, a moist pyrolysis residue is obtained.

In a surprising way, it has been established that the pyrolysis residue absorbs more than 140 wt-# of liquid, calculated on its own weight, with sufficient residence time. This means that of the washing water, which can be wholly or partly made up of the amount secreted from the water circuit in the gas washing system, can be bound to it to a high degree. Thereby, it was established that this liquid uptake is greater the greater the carbon content in the pyrolysis residue. In addition, a sufficient residence time for a total moist should be observed, which can, for example, be achieved by a screw transport system with a correspondingly low rotational speed.

In order to increase the carbon content in the pyrolysis residue, a further embodiment of the invention can therefore work so that inert substances are extracted in advance from the rubbish which is brought to the degassing drum during sorting. This can happen, for example, with suitable sorting devices such as cam rollers.

In an unexpected way, it has also been shown that the pyrolysis residue treated in this way achieves an activated carbon structure with chemisorbing properties, whereby this can be used as activated carbon for any areas of application.

In an advantageous further development of the invention, one can further aim for the pyrolysis residue to be used as an activated carbon filter in a filter device downstream of the drying tower in the gas washing plant.

Sulfur content from the pyrolysis clean gas, mainly depending on the sulfur content of the coke used in the gas furnace generator, can, as is known, only be removed with difficulty from the pyrolysis clean gas. If you now connect a filter device after the gas washing system, for example sulfur or fluorine compounds that were not completely washed out can be absorbed on the activated carbon filter. The fact that pyrolysis residue can be used for this means that no significant additional costs arise and the pyrolysis residue was also used sensibly in this way. This in turn means that the proportion of sulfur in the exhaust gas is cost-effectively reduced to far below the prescribed air limit value, whereby as an additional advantage in the gas converter, coke with a somewhat higher sulfur content can also be advantageously used.

Due to the high absorption potential of the pyrolysis residue, in a given case, it is advantageous to also treat hazardous substance components from other productions in such a way that these are mixed with liquid sub-quantities that have been withdrawn from the water cycle. This means that, in addition to the suitable, so to speak, harmful substance-free processing of garbage according to the invention, you can also work to remove harmful substances from other facilities.

As a further advantage of the method of the invention, it has been determined that the amount of waste water in a pyrolysis gas plant that processes household waste is reduced by more than $50 and generally does not amount to more than 100 liters of waste water per tons of household waste. This amount of waste water is usually so loaded with risk substances that an untreated disposal is undesirable from an ecological point of view. However, a significant and cost-effective reduction of the harmful substance load can be achieved if, in a further embodiment of the invention, it is aimed that the amount of liquid withdrawn from the water circuit in the gas washing plant is treated in batches by ozone injection so that the concentrations of cyanide are < 10 g/m<5> or of phenol is < 40 g/m5, after the treatment.

If the pyrolysis residue is treated in this way, it can be introduced into the biogas plant without any problems. Such a pyrolysis residue which has a liquid content of approx. 60%, due to the equalized load value of phenols and cyanides due to its high carbon and ammonium content from gas washing, is a particularly nutritious carrier for anaerobic methane gas generators which convert the absorbed biologically convertible substance groups into useful gas. The ozone-controlled homogenization of the harmful substances thereby minimizes the danger of overdose and thereby a cultural destruction. Experiments have shown that to achieve this homogenization effect, a short ozonization is sufficient, which is usually shorter than a quarter of a full ozonization time.

For a further reduction of the harmful substance load due to waste water, it can be aimed that the unbound excess water from the pyrolysis residue, which usually corresponds to less than 50$ of the partial amount that is deducted from the water cycle in the gas washing plant, is supplied to a restozonization. This can be carried out both in parallel with an application in a biogas plant or instead of it. Due to total ozonization of the surplus water, the C0D value (chemical oxygen demand) can usually be lowered to below 400 mg of oxygen per litres, the BOD value (biological oxygen demand) to approx. 60 mg/m<5> (values for 5 days) and the proportion of cyanide and phenols to generally below 0.1 g/m<5>. Since, due to the significant binding of the partial liquid amount withdrawn from the water cycle in the pyrolysis residue, only a significantly lower proportion of waste water must be treated in this way, no more than a minimal supply of liquid is necessary for ozonization of the residual amount. In contrast to the currently known methods, no deposition problems arise with the method of the invention.

It has now been further established that, as an alternative to using the pyrolysis residue treated according to the invention in a biogas plant, or in parallel with it, this pyrolysis residue can also be used for energy supply to lime kilns. In this way, the material can preferably be pressed into egg briquette-like pellets. It has surprisingly been found that when pre-separating part of the inert substances before degassing, you work with a calorific value that corresponds to that of lignite, which is sufficient for a smelting process. By having the correct mixing conditions for the eye, a calcination or a ceramization of the inert substance portion thereby takes place, whereby this in particular also includes heavy metals.

Experiments have thereby shown that with a corresponding pressing between 400 and 550 kg/cm<2> into egg briquette-like pellets, with a mixed product of calcium-containing compounds such as lime, lime kiln filter dust, lime hydrate or lime hydrate waste with a fuel component such as carbon dust waste as well as sulphur, chlorine, fluorine - and substances containing heavy metals at approx. 1200°C and a residence time of 45 to 120 minutes in this temperature range, a combustion residue is obtained where, so to speak, 100$ of the present total chlorine and the proportion of sulfur as well as the metals are bound in a ceramized, or so to speak, unleachable form in the ash. This means that in this way an environmentally friendly removal of harmful substances and especially of heavy metals is achieved.

The only prerequisite for ceramizing the metals is that the molar ratios for SiO^, AI2O3, CaO, ZnO, Fe203 and/or MgO on the one hand to the total molar ratio for the metals lead, chromium, manganese, cadmium, beryllium, barium, selenium, arsenic, vanadium , antimony, bismuth, strontium and/or zirconium make up at least 6:1.

The prerequisite for the incorporation of sulphur, chlorine and fluorine compounds is that the molar ratio of calcium, magnesium and sodium and the total content of sulphur, chlorine or fluorine is at least 2:1. The mixture product should therefore contain a maximum of 40% by weight liquid and the calorific value should be at least 100 kcal/kg so that the fuel, i.e. introduced into a lime kiln, at the required residence time and temperature, can glow, whereby the introduced metals oxidize and are taken up in the smelting of CaO and MgO so that they form relatively inert ceramic complexes. Sulfur compounds are absorbed as sulphites or sulphates, liquid chlorine and fluorine are bound to CaCl2 and CaF2-

Experiments carried out with pyrolysis residues have shown that this can thereby take over the function of the fuel component for temperature attainment. The harmful components absorbed therein which, as mentioned, may originate from sources other than the pyrolysis gas plant and which can be integrated by mixing into the water bath of the pyrolysis residue outlet, can thereby be deposited in an environmentally friendly manner. The pyrolysis plant thereby leaves no residue that needs final disposal.

It has thereby also been established that the available useful energy after deducting the energy requirement for operation of the plant can be increased by a reduction of the own power requirement for the ozone plant for gas purification and by the improved energetic utilization of the pyrolysis residue, by more than $5.

When the pyrolysis residue is used in biogas plants, the economics of thermal conversion of waste materials can be increased.

The residue that requires final storage and that is obtained according to the invention is several factors smaller than the residue that occurs at a waste incineration plant, these are also very toxic and must be treated as special waste.

As mentioned at the outset, the invention also relates to a plant for carrying out the method described above, and this plant is characterized by the features that appear in the characterizing part of claim 10.

As such a plant in its basic structure is already known from DE-OS 35 29 345, only the parts essential to the invention will be described in more detail below. An extraction of the pyrolysis residue from the degassing drum via a screw device is described in DE-OS 33 47 554, see especially figures 7 and 8. Of course, in addition to the screws shown there, other devices are also possible. The prerequisite, however, is an intensive wetting of the pyrolysis residue in the water bath for a corresponding period of time.

The garbage enters via a conveyor 1 to a pre-crusher 2. A conveyor chute 3 and a conveyor belt 4 with a magnetic separator 5 transport the garbage to a sorting device 6. In this, the heavy vegetable wet fractions are separated and fall into a container below or onto a conveyor belt 7. Likewise, inert substances can thereby also be separated to increase the proportion of carbon in the pyrolysis material. The other waste fractions are fed via a further transporter 8, a further crushing device 9 and a downstream hydrocyclone 10 where once again heavy components are separated via a line 11 to a thermos screw press 14. Via the line 11 the rubbish together with separated rubbish from the container 7 via a supply 12 led to a biogas plant 13, possibly first through a fluid classifier for the pre-separation of inert heavier particles, as this classifier can for example work by flotation.

In the thermal screw press 14, a granule in a rapidly degassable structure and with a size of 3 to 50 mm is formed in a manner known per se by friction pressing at 110 to 150° C.

Instead of granules, for example, fluff, i.e. a loose form of rubbish, or pellets, i.e. rubbish components pressed into briquettes of a specified size, can be produced, which, however, usually requires longer degassing times. The finely divided waste components in this way are then fed via a cell wheel sluice 15 or another introduction device such as a stuffing auger to a degassing drum 16 where at temperatures of 450 to 600°C in a manner known per se smoldering gas is obtained which then via an exhaust line 17 and a dust separator 18 is fed to a high-temperature gas converter 19. In the converter 19, the processing or conversion of the furnace gas takes place over a layer of coal or coke. A converter of this type is, for example, described in DE-OS 33 17 977.

After passing through a heat exchanger 20, the gas comes to a gas washing plant which essentially consists of a water-sprayed tower 21, a fan 22 and a cleaning cyclone 23 as well as a droplet separator 24. Via a gas line 25, the purified gas comes to a gasometer 26 in which via delivery of too much gas via a side line 27 excess gas can be supplied via a flare 28.

Usually, the gas from the gasometer 26 comes to a gas engine 29 which is connected to a generator 30 whereby via the exhaust line 31 the burnt exhaust gases can be led to a stove 32.

The gas converter 19 receives via a line 33 water and via a suitable feed line 34, coke. Ash and slag are removed via an output line 35. Optionally, for energy savings, a coke return line 36 can also be arranged for the coke freed of slag.

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

The amount of wash water obtained by gas cleaning goes to the wash water tank 40 and then to a filter device 41 (usually a settling basin). Separated solids in the filter device are led via a line 42 to the ash container 43. Via an output line 34, the residual substances are led from the ash container 43 and via a push-in device or a cell wheel sluice 15 brought back to the smoldering drum 16.

The cleaned washing water comes from the filtering device 41 via a return line 45 after passing through a cooling tower 46 again back to the spray tower 21 in the gas washing plant. Part of the purified wash water is led into a wash water neutralization plant 47, into which also steam condensate from the thermos shell press 14 is introduced via a line 48 if this steam is not led via a line 65 to the reservoir 53 in the biogas plant.

From the wash water neutralization plant 47, the wash water comes via a return line 78 to the circuit treatment in the spray tower 21, while a partial quantity via a partial quantity removal line 79 comes to a circuit batch treatment plant 48. There, a chemical purification of the wash water takes place in a known manner using corresponding chemicals which comes in via line 49, as long as the chemical oxidation is not replaced by ozonation, through which the residual-increasing additive addition can be greatly reduced. Via a circuit line 50, the washing water is partly led to an air filter 51 for removing foam, whereby the exhaust gases are blown off through a line 52 and the chimney 32, and partly a return via a line 50 to the spray tower 21 takes place.

The chemically and mechanically purified water comes from the circuit water batch treatment plant 48 via a line 71 to the reservoir 53 in the biogas plant. If necessary, clarification sludge, raw compost or the like can also be fed to this, which is indicated by the arrow 54. Via a line 65, as long as this is not fed through the circuit water batch treatment plant, steam condensate can be fed directly to the reservoir 53.

From the storage tank 53, the substances to be processed in the biogas plant 13 go to a hydrolysis stage or a hydration stage 56. To the hydrolysis stage 56, a counter-current heat exchanger stage 57 is added, which receives its heat from a hot water line 62 which branches off from the cooling tower 46 for the washing water treatment plant. On a fermentation rhombus 67, a tube heater ensures a temperature rise in the methane area in the fermentation room from 33 to 37°C. In this way, the excess heat from the pyrolysis plant is used for the biogas plant 13.

The biogas plant 13 is built in the usual way. As a phase-separated biogas plant, the middle shaft 63 in the upper area can exhibit a normal acid phase, while in the lower area there is an acetic acid phase. The formed methane gas is drawn off via a methane gas line 59 and fed via a buffer 60 and a compressor 61 into the gas line 25 or the gas washing plant for the pyrolysis plant, for purification. The fermentation residue is led out via a suction line 66 and led to a pre-dewatering device 68, whereby a content of approx. 20$ dry matter. The solids contained in the fermentation residue can be brought to a content of approx. 85% dry matter using a dry press 69. Remaining fermentation water is collected in a lagoon 70 and, if necessary, this is taken to the treatment plant 48 or directly to the drain.

The substances separated out in the circuit water batch treatment plant 48 can be taken via a line 64 to a clarification plant.

Pyrolysis residues are carried out into the degassing drum 16 via a water bath 72, whereby the removal can take place, for example, via screw transport devices. The water bath 72 is fed via a partial liquid line 73 with the necessary liquid for wetting the pyrolysis residue. The partial quantity line 73 is thereby branched off from the batch processing facility 48.

The pyrolysis residues moistened in this way with liquid are led away via a line and can possibly, after a treatment, for example ozonization or another purification, be led to the biogas plant 13. The biogas plant 13 is of course only mentioned as an example. For the invention itself, this is not necessary. Instead of introducing the pyrolysis residues to the biogas plant 13, the pyrolysis residues can, if necessary, also be transported to a lime kiln 77 via a line 74a. Likewise, the pyrolysis residue can be fed via a line 74b, after drying, to a filter device 75 as an activated charcoal filter. The filter device 75 is thereby located between the gas washing plant and the gasometer 26. In this case, however, the activated carbon recovered from the pyrolysis residue should at least be largely free of harmful substances. This means that in this case one works in batches and instead of supplying water via the liquid partial quantity line 73 with contaminated circuit flow water, fresh water is introduced via a fresh flow line 81 to the water bath.

If necessary, the partial amount of liquid removed from the water circuit 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 amount that is withdrawn from the circuit via the partial volume line 79 before being introduced via the liquid partial volume line 73 to the water bath 72 can be correspondingly cleaned in the ozone system 76 in this method, the pyrolysis residue is used as an activated carbon filter in the filter device 75.

The function and operation of a lime kiln 77 to which the pyrolysis residue is introduced via line 74a is generally known and is therefore not to be discussed further here. The pyrolysis residue is thereby used, where appropriate, together with other fuel components as fuel. Of course, it is not necessary that there is a direct line 74a between the water bath 72 and the lime kiln 77. The plant of the invention is designed so that not all aggregates have to be in a common place. Thus, for example, the biogas plant 13 and the lime kiln 77 can be located in another location, whereby the transport of the substances can also take place in any way.

The liquid portion, which is not completely taken up in the water bath 72 of the pyrolysis residue, can, if necessary, before introduction to a clarification plant, optionally also be fed via the ozone plant, optionally for full ozonization.

Of course, it is not absolutely necessary that the liquid portion line 73 from the wash water neutralization system 47 be branched off, on the contrary, the extraction can also take place at another place in the water circuit if necessary. The same applies to the connection of the ozone injection system 76.

Claims (13)

1. Process for recovering usable gas from garbage by pyrolysis, whereby the previously divided garbage is processed into fluff, granules or pellets with a size of 1 to 50 mm and brought to a dry matter content of at least 75$ and then introduced into a heated degassing drum where smoldering gas is produced and then separated from residual substances such as ash and other components, and whereby the flue gas is split in a gas converter into fuel gas which is cleaned in a subsequent gas washing plant with circulating washing water, whereby from the washing water circuit in the gas washing plant and to limit the concentration of harmful substances in the water in the circuit, it is withdrawn of a partial quantity that is replaced by fresh water, and whereby the pyrolysis residue removed from the smoldering drum is passed over a water bath, characterized in that at least part of the liquid partial quantity withdrawn from the washing water circuit for the gas washing plant (21-24 and 47-51) is passed to the water bath (72), whereby the pollutants contained in the wash water from the flue gases bind es of the pyrolysis residues. 2. Method according to claim 1, characterized in that the rubbish introduced to the degassing drum (16) is freed beforehand of inert substances by sorting to such an extent that the pyrolysis residues removed from the degassing drum contain at least 25% carbon by weight. 3. Method according to claim 1, characterized in that the pyrolysis residue treated with the partial amount of the washing water circuit is used as an activated carbon filter. 4. Method according to claim 3, characterized in that the pyrolysis residue is added to a filter device (75) downstream of the gas washing plant (21-24) as an activated carbon filter. 5 . Method according to any one of claims 1 to 4, characterized in that to the circuit water concentrate removed from the washing water circuit, harmful substance components from other production lines are added to ensure their treatment. 6. Method according to any one of claims 1 to 5, characterized in that the liquid quantity withdrawn from the water circuit to the gas washing plant is treated by ozone injection in such a way that the concentration of cyanide < 10 g/m<5> and/or phenols < 40 g/ m<5>by ozone injection. 7. Method according to any one of claims 1 to 5, characterized in that the portion of liquid withdrawn from the water cycle to the gas washing plant and which has not been absorbed by wetting the pyrolysis residue, is subjected to a further batch ozonization until COD < 400 mg Og/litre. 8. Method according to claim 1, characterized in that the pyrolysis residue moistened with the amount of liquid is added to the clarification or biogas plant (13). 9. Method according to claim 1, characterized in that the pyrolysis residue moistened with the liquid sub-quantity is added to lime kilns (77). 10. Installation for carrying out the method according to any one of claims 1 to 9 with a waste separation device, with a drying device and a degassing drum with an inlet for reduced waste, an outlet for solid pyrolysis residues and with a flue gas extraction line which is connected to a gas converter for the extraction of split gas, with a gas washing plant downstream of the gas converter and with, after the outlet for pyrolysis residues, finally a water bath, characterized in that a liquid partial volume line (73) leads from the device (48) in the gas washing plant to the water bath (72). 11. Plant according to claim 10, characterized in that a sorting device (6) for sorting out inert substances is arranged upstream of the degassing drum (16). 12. Plant according to claim 10 or 11, characterized in that the downstream gas washing plant (21-24 and 47-51) is equipped with a filter device (75) in which the pyrolysis residue can be used as an activated carbon filter. 13. Installation according to any one of claims 10 to 12, characterized in that an ozone injection device (76) is arranged for the liquid sub-quantity which is drawn off from the washing circuit of the gas washing installation (21-24).