DE19608093C2 - Process for recycling residual and waste materials as well as low calorific fuels in a cement kiln - Google Patents

Description

The invention relates to a method according to the preamble of the first Claim.

The invention is applicable wherever residues and waste materials as well Low calorific or high-ballast fuels, regardless of their nature and their content of toxic heavy metals, Chlorine compounds and salts, energetically and materially used and one or more cement rotary kilns are available.

Residual and waste materials are household waste, commercial waste, municipal and industrial sewage sludge, residues from treatment used industrial goods with organic components such as cables, old cars, Electronic waste, remnants from collections such as DSD and production residues from various technological Processes especially in the recycling industry. Low-calorific fuels are for example biofuels such as straw, wood, grass, leaves, special cultivated plants intended for energy use, but also polluted weak gases, e.g. landfill and sewage gases as well Solid / oil or water / solid slurries of various origins.

It is generally known to have high calorific wastes, e.g. B. old tires as Use additional fuel for cement kilns.

The direct energetic and material recycling of these materials will often complicated by their heterogeneous composition and  possibly high concentrations of inorganic and organic toxic substances such as heavy metals, dioxins and furans, organochlorine Compounds, salts and cyclic hydrocarbons. So be for example at the high firing temperatures in the cement rotary tube volatile heavy metals from residual and waste materials that are used directly be carried away with the exhaust gas, resulting in extensive exhaust gas purification plants to prevent their release into the atmosphere. Furthermore, the salts introduced with the residual and waste materials, such as alkali chlorides, to reduce the quality of the Cement.

On the other hand, it is known that residues and waste materials are also low in calorific values Fuels for the generation of combustible gases by gasification with air or technical oxygen. The gasification can as is known in the fluidized bed, see "Thermal Residual waste treatment by means of fluidized bed gasification ", 67. Waste technology colloquium of the University of Stuttgart, in a fixed bed, e.g. B. according to DE 41 25 521 C1, or in the entrained flow, such as u. a. DE 41 39 512 or EP 0 523 815 A1 teaches to take place.

DE 42 08 977 C1 describes a method for producing cement known, where high-quality fuels through low-quality fuels to be replaced, with the inferior fuels in a fluidized bed be gasified and the gas is divided into three partial flows.

In fluidized bed gasification as proposed in this document the mineral components of the input materials fall as powdery fine-grained ash, the toxic heavy metal compounds contains and a post-treatment process, for example one subsequent gasification, with separate registration of volatile, toxic Heavy metals must be subjected. To the required  To secure carbon turnover during the gasification and that for the To be able to comply with the maximum permitted carbon content in future are special technological measures such as internal or external Circulation of the gasification material required.

The gasification temperatures must be below the ash melting or Ash softening point are to caking the Exclude ash particles. Low gasification temperatures in turn affect carbon turnover. Bring also higher alkali levels in the feed, this is especially true for biofuels, Household waste, but also with sewage sludge, the risk of eutectic Melting from ashes and fluidized bed with it, which in addition to forces lower gasification temperatures.

To heterogeneously composed feedstocks, such as Household waste, commercial waste, waste wood or some biofuels from To develop entrained-current gasification, entrained-current gasification becomes a Pyrolysis upstream, as shown in DE 41 39 512 and DE 42 38 934 A1.

The last-mentioned document describes a process for the gasification of raw materials and waste materials containing organic or organic materials on the basis of an entrained-flow gasification process known per se. The end product from this process is a gas rich in CO and H ₂ . A fuel gas, which can also contain N ₂ , is not mentioned in this document. It is proposed to use the gas generated to operate gas turbines, gas engines or as synthesis gas. The use of slag granules in the cement industry is also not suggested in this document.

With pyrolysis, the feed material becomes a brittle, easily grindable solid residue, the pyrolysis coke, and that from gaseous and vaporous  Decomposition products converted pyrolysis gas converted. To Appropriate processing will be both pyrolysis coke and Pyrolysis gas and the eventual cooling of the pyrolysis gas condensates are fed to the entrained-flow gasification stage.

A key advantage of entrained-flow gasification is that Gasification temperature well above the melting temperature of the mineral components of the input material. The mineral Components are thus converted into a molten slag, which after cooling as glass-like granules and no after-treatment requirement. It is also advantageous that a hydrocarbon-free Raw synthesis gas is created.

DE-AS 11 41 575 describes a method for producing a sulfate-resistant cement using glassy slags described. The slags added to the cement in this document do not result from a high temperature entrained flow gasification process. They also do not come from a process in which residual and Waste materials were thermally recycled.

The use of melt granules in entrained-flow gasification there is an opinion in the professional world that for the environmental compatibility of Cement primarily the entry of difficultly volatile heavy metals is decisive; Sprung S., "Environmental pollution from recycling Secondary raw materials "cement-lime-gypsum 1992, pp. 213-221 / chapter 6. It is therefore recommended substances with higher heavy metal concentrates only in use small amounts.

Those skilled in the art are aware that waste materials are heavy metal concentrates contain the elements chrome, nickel and zinc. Since these elements in Melting granules of entrained-flow gasification are still present  it is not obvious to a person skilled in the art, this melt granulate for Use cement manufacturing.

The invention has for its object to a method combination create that allows residual and waste materials and low calorific value or ballast fuels regardless of their nature and their Content of toxic heavy metals, chlorine compounds and salts for to use cement production.

This object is achieved by the features of the first claim solved. The subclaims give advantageous refinements of Invention again.

The solution according to the invention is based on the residues and waste materials or the low calorific value or high ballast fuels, which because of their Pollutant content or its nature so far a cement kiln, in usually a rotary kiln, not fed as fuel and raw material could first be subjected to a gasification at which a Raw gas containing volatile heavy metals, volatile salts and optionally hydrogen chloride is formed. Under the conditions of Gasification these volatile heavy metals lie like mercury, Cadmium, thallium, lead or zinc mainly in the form of sulfides. It it was found that the heavy metals practically quantitatively by a Water washing can be separated from the raw gas and used as a filterable sulfidic sludge is present in the washing water running off. Corresponding According to the invention, the washing water running off to separate the Heavy metal sludge subjected to filtration.

With the water wash, volatile salts contained in the raw gas, especially alkali chlorides, and possibly hydrogen chloride are washed out of the gas at the same time. They remain dissolved in the wash water. The gas cleaned in this way from the components which are harmful to the quality of the cement is then fed as fuel to the heating device of the cement kiln. The gas is not desulfurized before being used in the cement kiln, but instead contains sulfur in the form of hydrogen sulfide from the feed for the gasification reactor. When burning in a cement kiln, usually a rotary kiln, hydrogen sulfide is converted to sulfur dioxide, which is then bound in contact with the cement components to such an extent that the environmental protection limits for the SO ₂ content in the exhaust gas of the cement kiln are far be undercut. When the sulfur binds to the cement components, the quality of the cement produced is not impaired.

It has proven to be advantageous to carry out the gasification in the form of entrained-flow gasification with a gasification agent containing free oxygen at temperatures above the melting temperature range of the mineral constituents of the feed material. In general, as a gasifying agent technical oxygen with z. B. 96% O ₂ used, but mixtures of technical oxygen with nitrogen, carbon dioxide or water vapor are also possible. The gasification takes place in a free reaction space in the form of a flame reaction. The organic components and the carbon content are completely converted into a CO and H ₂ -rich, hydrocarbon-free fuel gas. The mineral components are at the reaction temperatures of z. B. melted 1500 ° C. After the cooling of the melting granulate with a glass-like structure, they are present together with the raw gas.

As an advantage of entrained-flow gasification in the connection according to the invention with the operation of a cement kiln it turns out that the resultant Slag granulate is free from soluble alkali chlorides and also soluble  Alkali and alkaline earth salts, of combustible carbon and of particularly critical volatile, toxic heavy metals, especially mercury, cadmium and thallium. Volatile Heavy metals such as nickel and chrome are resistant to elution in the glassy structure of the melt granules is integrated. It corresponds therefore the invention, the resulting melt granules as a raw material for the To use cement production. In particular, the granules Feeding the rotary kiln added or as a lean Cement clinker supplied after the fire and with it to the finished Cement be ground.

In many cases, waste materials of very heterogeneous nature, such as domestic waste, municipal residual waste, commercial waste similar to household waste or shredder, are not readily available for use in cement rotary kilns. Waste of this type cannot be subjected to entrained-flow gasification immediately or after simple drying and comminution. In such a known manner, the entrained-flow gasification stage is therefore preceded by a homogenization and pretreatment stage consisting of

• - Pre-shredding to piece sizes of less than about 200 mm
• - thermal treatment at temperatures between 250 and 800 ° C by pyrolysis with exclusion of air or largely Exclusion of air and conversion into a pyrolysis coke and a gas and vaporous decomposition products of existing pyrolysis gas,
• - Separation of the pyrolysis gas from pyrolysis coke and supply of the Pyrolysis gas for entrained-flow gasification and
• - Grinding at least part of the pyrolysis coke and feeding of the ground coke to the entrained flow gasification reactor.

It can be advantageous if the pyrolysis coke is initially used with conventional Processing methods such as magnetic or eddy current separators, ferrous metals  and separated non-ferrous metals and a separate recycling are fed in before the remaining pyrolysis coke is ground up and entrained flow gasification is abandoned.

Depending on the nature of the waste to be used and the Overall design of the cement plant, it can be advantageous Pyrolysis coke or part of the pyrolysis coke, optionally after Separation of metal fractions, bypassing entrained-flow gasification can be used directly to heat the cement kiln. Such a solution lends itself particularly well if the cement rotary kiln for the Operation with coal dust is set up, the amount of pyrolysis coke compared to the gases and vapors volatile during pyrolysis or - due to the given composition of the used Waste - the pyrolysis coke only low with alkali salts, chlorine and undesirable heavy metals.

It is also possible to feed the cement furnace directly Pyrolysis coke e.g. B. by water washing beforehand of soluble salts, especially to rid unwanted alkali salts. It is cheap at this embodiment of the invention when the wet by the laundry Pyrolysis coke if necessary together with hard coal or brown coal Is subjected to grinding drying before it is the dust burner of the Cement kiln is fed. That when washing out salts from the Coke-producing, salt-laden washing water can, for example be prepared together with the gas washing stage.

The pyrolysis can be carried out in a manner known per se externally heated rotary tube reactor can be used. The heating this reactor can e.g. B. with natural gas. However, it is also possible a partial stream of volatile by water washing Heavy metals, volatile salts and possibly hydrogen chloride  liberated but sulfur-containing gas for heating the pyrolysis reactor to use. In this case, the combustion gases of the Pyrolysis reactor combined with the exhaust gas from the cement kiln and with this together the exhaust gas cleaning in the form of a high-quality dedusting subject. By binding to the exhaust gas from the cement kiln sufficient dust desulphurization is achieved.

The advantages that can be achieved with the invention are that with the Combination of entrained-flow gasification according to the invention with or without Upstream pyrolysis and cement kiln so far not for this purpose pullable, polluted homogeneous, but also heterogeneous composite residues and waste materials energetically and materially for the Production of cement can be used without the burden of Environment or degradation in cement quality may occur high thermal efficiencies can be achieved with low investment costs.

The process according to the invention is illustrated by two examples below are explained.

Example 1 describes the utilization of a heterogeneously composed waste material such as household waste according to FIG. 1.

The garbage delivered in silo vehicles is first emptied in a bunker 1 in order to be able to compensate for daily and weekly fluctuations in the accumulation. After pre-shredding using shredder shears 2 to piece sizes of approximately 100 mm, the domestic waste from a pyrolysis 3 is fed in, heating to 400 to 600 ° C. being carried out. Natural gas or recycled partially cleaned gas from our own generation can be used as heating gas. In the case of very damp domestic waste, there is the possibility, not shown in the diagram, of arranging a drying stage before pyrolysis 3 , which is heated with steam from the waste heat boiler connected downstream of the entrained-flow gasification reactor. In a separation chamber 4 downstream of the pyrolysis, the volatile gaseous and vaporous pyrolysis products, the pyrolysis gas, are separated from the solid pyrolysis coke.

In the simplified cooling and condensation 5 , the pyrolysis gas is cooled to approx. 60 ° C. An oil-water mixture condenses out, which also carries the residual dust carried by the pyrolysis gas from the separation chamber 4 . The cooled pyrolysis gas and the oil / water / dust mixture are fed with a compressor 6 or a pump 7 to the entrained-flow gasification reactor 8 operated under a pressure of 5 bar. Alternatively, the uncooled pyrolysis gas, including its oil and water vapor content, can be fed to the entrained-flow gasifier. However, because of the difficulty in compressing hot gases loaded with oil vapors, the pressure of the gasification reactor is reduced.

The pyrolysis coke separated from the pyrolysis gas in the separator 4 first passes through a magnetic separator 9 and an eddy current separator 10 for separating ferrous and non-ferrous metal fractions. The remaining pyrolysis coke is brought to a fineness of less than 1 mm in the mill 11 , here a ball mill, and is added to the entrained-flow gasification reactor 8 by pneumatic means.

In the reaction chamber of the gasification reactor 8 , the pyrolysis products supplied are reacted with oxygen in a flame reaction. This creates a hydrocarbon-free, flammable raw gas with H ₂ and CO as the main components. By adjusting the ratio of oxygen to combustible components of the pyrolysis products, the gasification temperature which arises in the reaction space can be influenced. It is chosen so that the mineral components of the feed are melted. Usually temperatures above 1300 ° C are necessary.

Under the conditions of gasification become volatile, with the Heavy metals such as mercury, cadmium, Thallium, lead or zinc evaporates and is absorbed by the hot raw gas. The same applies to alkali salts. Organic chlorine compounds will fully implemented. The resulting hydrogen chloride remains hot Raw gas, possibly also after binding to excess alkalis in Form of evaporated salts. It is also characteristic that Sulfur compounds in the feed converted to hydrogen sulfide become.

The raw gas formed during the gasification and loaded with heavy metal and salt vapors and the molten slag pass together into a quench chamber 12 downstream of the reaction chamber, in which spontaneous cooling takes place by injecting water down to the dew point of the raw gas which is dependent on the pressure in the gasification reactor.

Contact with water causes the slag to solidify, which breaks down into fine-grained melt granules. It is discharged via a lock 13 and a water-filled discharge trough 22 .

Starting in the quench room and continuing in the downstream venturi scrubber 14 , the raw gas is intensively water-washed. Alkali salts or still free hydrogen chloride are dissolved from the wash water, while the heavy metals are absorbed virtually quantitatively as sulfidic sludge from the wash water under the action of the sulfur content.

At a gasification pressure of approx. 5 bar, the raw gas saturated with water vapor and freed of alkali salts and heavy metals leaves the venturi scrubber 14 at a temperature of approx. 135 ° C. It passes through a heat exchanger designed as a waste heat boiler 15 , in which the now partially cleaned raw gas is further cooled with the formation of low-pressure steam and the majority of the saturated water vapor is condensed.

The partially cleaned but still hydrogen sulfide gas is now fed to the burner of the cement kiln, a rotary kiln 16 . With combustion in a rotary kiln with excess air, the hydrogen sulfide content is converted to sulfur dioxide, but is practically quantitatively absorbed by the fuel. The exhaust gas treatment 17 following the rotary kiln 16 according to the technology customary in the cement industry is limited in addition to the heat recovery for the preheating of the combustion material to a dedusting of the exhaust gases before the cleaned gas is expelled via the chimney 18 .

The melt granulate obtained during gasification becomes the raw material batch added for the cement kiln.

The scrubbing water, which is expelled from the quench chamber 12 and the sump of the venturi scrubber 14 and is loaded with salts and sulfidic heavy metals, passes through a filter stage 19 in which the heavy metal sludge is separated off. A partial flow of the filtered water is returned to the quenching and washing circuit together with the condensate obtained in the waste heat boiler 15 . The rest goes to the evaporation stage 20 , in which a mixed salt is obtained. The resulting clean condensate is available for technological purposes.

The heavy metal sludge can in principle be fed to a non-ferrous metal smelter for recycling, since e.g. B. zinc levels up to 8%, lead levels up to about 2% can occur. Alternatively, an underground landfill is possible for the relatively very small amount. The same applies to the mixed salt from the evaporation stage 20 .

The pyrolysis reactor 3 is heated with a partial flow of the gas generated and partially cleaned by entrained flow gasification.

With regard to the sulfur content of this gas, the flue gas generated during heating is added to the exhaust gas stream of the cement rotary kiln 16 , specifically before the exhaust gas treatment 17 . In this way it is ensured that the SO ₂ content from the fly dust of the cement kiln exhaust gas is almost completely bound.

Example 2

The second exemplary embodiment, see also FIG. 2, relates to the recycling of a heterogeneously composed commercial waste. The design of the method largely corresponds to the first embodiment. However, after the metal fractions have been separated off, the pyrolysis coke is subjected to a water wash 21 in order to remove salts, essentially sodium, potassium and calcium chloride, contained in the coke. The washed pyrolysis coke is used directly as a fuel component for heating the rotary kiln 16 after appropriate processing 22 , for example after mill drying.

The embodiment of the method shown in this example is particularly advantageous when the amount of pyrolysis coke is small in relation to the amount under the pyrolysis conditions volatile gases and vapors.  

The commercial waste used in the example contained larger proportions Plastic waste, including polyvinyl chloride waste, from the Scrapping of household appliances. This was the condition.

In this example, use is also made of the fact that in the pyrolysis of waste of the type described, a considerable part of harmful, volatile heavy metals, in particular cadmium and mercury, becomes volatile and with the pyrolysis gas or with the mixture of condensates and fly dust separated from the pyrolysis gas subjected to gasification and, as explained in more detail in the first exemplary embodiment, is separated from the raw gas generated in the gasification reactor 8 . This ensures that the cement kiln in particular is not contaminated with cadmium and mercury from the waste.

It was also found that pyrolysis decomposes organic chlorine compounds in the feedstocks, especially chlorine-containing plastics, to the extent that chlorine compounds remain in the pyrolysis coke only in the form of soluble salts, especially as sodium and potassium chloride. These salts are separated from the pyrolysis coke by the water wash 21 before it is fed to the rotary kiln 16 as fuel.

Contained in the feed or arising in the course of pyrolysis volatile organic chlorine compounds, including toxic compounds such as polychlorinated biphenyls, dioxins and furans, go the way Gasification and are completely destroyed there. The resulting ones Salts or hydrogen chloride are as described above from the Gasification gas separated and so before entering the cement kiln held back.

Claims (5)

1. Process for recycling residual and waste materials as well as low calorific fuels in cement kilns, whereby the energetic components of the combustion and the material components of the clinker grinding are supplied, characterized in that the combination of pyrolysis, entrained flow gasifier and cement kiln process the residual and Waste materials after pyrolysis as coke and gas in entrained flow gasification with technical oxygen as a gasifying agent are gasified at temperatures above the boiling point range of the mineral residues, whereby after cooling, a melting granulate and a raw gas with contents of volatile heavy metals, volatile salts, especially alkali chlorides and other alkali salts , Hydrogen sulfide and possibly hydrogen chloride are formed and the entire raw gas is subjected to a water wash, the volatile heavy metals being obtained as heavy metal sulfides in the form of a precipitated sludge and the volatile salts and possibly the hydrogen chloride are dissolved in the wash water before it is fed to the heating device of the cement kiln, the melt granules being fed to the clinker grinding. 2. The method according to claim 1, characterized in that the technical oxygen used as a gasifying agent Nitrogen, carbon dioxide or water vapor is added. 3. The method according to claims 1 and 2, characterized in that the pollutant-free, elution-resistant melt granulate before Clinker grinding is fed to the cement kiln process.   4. The method according to claims 1 and 3, characterized in that that of volatile heavy metals, volatile salts and possibly Part of the hydrogen chloride liberated gas for heating the Pyrolysis and the resulting combustion gas combined with the exhaust gas from the cement kiln and together with this is subjected to exhaust gas cleaning. 5. The method according to one or more of claims 1 to 4, characterized in that Residual and waste materials with a sufficient proportion of flowable Components bypassing the pyrolysis of high temperature Entrained-flow gasification can be fed directly.