FI83290B - Treatment of chlorine-containing material - Google Patents

Description

83290

HANDLING OF CHLORINE-BASED SUBSTANCES BEHANDLING AV KLORHALTIGA MATERIAL

The present invention relates to a process for treating various chlorine-containing substances, such as waste, bio-sludges and even metal concentrates, at high temperatures and for cooling the formed process gases in order to minimize the amount of polyhalo aromatic compounds in the generated process gases.

In connection with the incineration of municipal waste, but also in the incineration of industrial sludges and smelting processes, chlorine-containing environmental toxins formed in 10 incineration have been identified as a problem. Polychlorinated aromatic compounds, such as coplanar PCBs, polychlorinated dioxins and polychlorinated furans, which are classified as super toxins, have been found to be abundant in both municipal waste-15 incinerators and industrial biomass incinerators. Dioxins have also been found in the flue gases of metal smelters. These chlorine compounds are super toxic to animals and humans, cause genetic damage and are also likely to be carcinogenic. Compounds that are toxic to the environment are spread mainly when bound to airborne dust.

It has been found that the lower the temperature and the shorter the residence time, the more super toxins are formed. Incineration at 500-700 ° C has been found to be particularly favorable for the formation of polychlorinated dioxins and furans. From this it has been concluded that incineration should take place at a higher temperature and with a long residence time in order to decompose the super toxins. On the other hand, it has also been shown that waste can be safely disposed of by incineration at relatively low temperatures if the flue gases are afterburned at a temperature so high as 283290 that, for example, dioxins and furans are decomposed.

Recently, heavy metals have been found to play a significant role in the formation of dioxins in combustion 5. Heavy metals have been found to catalyze e.g. dioxins. Dioxins are formed by the synthesis of chlorine compounds in the presence of carbon, water and oxygen at favorable temperatures, e.g. in flue gases. It has therefore been found that a large proportion of the 10 fly ash dioxins are formed by so-called "de Novo synthesis" only after combustion in heat exchangers and chimneys because the "de Novo synthesis" of dioxins is highly temperature dependent and the temperature at 250-400 ° C is particularly favorable for synthesis. With as complete combustion as possible, high combustion temperature and long residence time1a, the aim has been to avoid ash-free fly ash as much as possible, which would prevent synthesis. Separation of metals from waste has also been used to reduce the amount of polychlorinated aromatics in the flue gases.

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U.S. Patent No. 4,762,074 proposes the incineration of wastes containing toxic dioxins and furan precursors with oxygen-enriched air at a high temperature of at least 1200 ° C to eliminate toxins. At the same time, a large excess of oxygen is used to keep the increasing amount of nitrogen oxides at high temperatures to an acceptable level.

Swedish patent publication SE 453 777 discloses a method for incinerating solid waste in a fluidized bed in a reactor at a temperature below 900 ° C. The temperature of the flue gases in the reactor is raised above the actual fluidized bed to at least 950 ° C by adding secondary air and insulating the reactor walls. The flue gas temperature is maintained above 950 ° C for the time required for the decomposition of hydrocarbons and dioxins by passing the flue gases through an uncooled gas duct. The gases are cooled before the heat exchangers by introducing air or flue gas into the gases.

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U.S. Pat. No. 4,794,871 discloses a two- or three-step process in which the waste is first treated at a maximum of 500 ° C in a rotating drum and the solid waste thus formed is treated at a minimum of 500 ° C, preferably 500-1000 ° C, to remove toxic substances. The flue gases from both treatment steps are combined and combusted at such a high temperature that the toxic compounds in the gases; disappear 10 completely.

It is an object of the present invention to provide a simple method for minimizing emissions of polyhalo aromatics in the treatment or incineration of waste and other solids.

The object of the invention is in particular to provide a method by which even the lowest possible emissions of dioxins and furans can be achieved even without separate final combustion.

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The process according to the invention is characterized in that the substances to be treated are first treated at least at 830 ° C with an oxygen-containing gas, whereby the polyhaloaromatic compounds which may be present in the substances are decomposed. The resulting process gases are rapidly cooled to below 250 ° C, thus preventing the synthesis of polyhaloaromatic compounds from the chlorine compounds contained in the gases. The cooling rate is preferably above 1000 ° C per second.

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According to the invention, municipal waste or industrial bio-sludges can advantageously be incinerated in a circulating mass-type fluidized-bed reactor at 830-1000 eC, whereby the above-mentioned super-toxins 35 contained in the waste or sludge are mainly decomposed. Flue gases are quickly cooled cheap! below 200 ° C. Cooling also takes place in a circulating fluidized bed reactor, where very fast cooling can be achieved, even above 7000eC

4 83290 per second. The flue gases can thus be cooled practically immediately below 200 ° C. Rapid cooling below, for example, the favorable temperature range for dioxin synthesis at 250-600 ° C minimizes the formation of polyhaloaromatic compounds. At the same time, a significant proportion of the low-melting and evaporating heavy metals in the flue gases, such as Hg, As, Zn, Cd, Pb and Sn, and their compounds are removed by condensation in the circulating mass.

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The invention can also be applied to other flue gases containing chlorine compounds and possibly small amounts of carbon and oxygen, in which polychlorinated aromatic compounds are formed at higher temperatures. For example, the flue gases of copper smelters are preferably rapidly cooled below the critical temperature zone in which polychlorinated and aromatic compounds are synthesized.

The invention will now be described in more detail with reference to the accompanying schematic drawings, in which Fig. 1 schematically shows an apparatus 25 for carrying out the process according to the invention. The first fluidized bed reactor comprises a furnace 30 3, in the lower part of which a base plate 4 is arranged to conduct fluidizing air to the reactor. The waste is fed into the furnace by means 5 arranged on the wall of the furnace. The walls of the upper part of the furnace can be so-called membrane walls to recover the heat of the furnace. In addition to the heat sink, heat transfer members 6 can be arranged in the heat sink 35.

The flue gases are led through an opening 7 to a cyclone separator 8, where solid particles are separated from the flue gases.

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The particles are returned via pipe 9 to the bottom of the furnace. A large upward flow of fluidized air is maintained in the furnace, which carries with it a part of the fluidized bed bed material, the so-called circulating mass to the upper part 5 of the furnace and through the opening 7 out of the furnace to the particle separator. From the particle separator, most of the solids are returned to the bottom of the furnace. With circulating mass, the temperature in the entire circulating system equalizes and remains almost the same.

10 In a circulating reactor, the waste fed to it is instantly mixed with a large amount of bed material and the waste reaches the temperature in the reactor very quickly without having a substantially degrading effect on the temperature in the reactor. In the circulating mass reactor, the combustion process 15 also continues in the entire circulating system, whereby a long residence time for combustion is obtained. The reactor can therefore be used to burn waste safely at lower temperatures than, for example, in grate incineration, where complete incineration must be ensured at high temperatures.

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The hot flue gases are led from a cyclone separator to a second circulating mass reactor comprising a mixing chamber 10 and a particle separator 11. A gas inlet 12 is arranged in the lower part of the mixing chamber, from which the hot gas flows into the mixing chamber 25 as a fluidizing gas in the reactor. A mixing pipe 13 is further arranged in the mixing chamber, from which cooled solid particles are fed into the mixing chamber. The amount of cold particles fed to the mixing chamber is such that they rapidly cool the flue gases in large quantities below the critical temperature zone for the synthesis of chlorine compounds.

The upper part of the mixing chamber continues as a cooling section 14, where the gases and solid particles are cooled together 35 before the particles are separated from the gases. The particles can advantageously also be cooled after the particle separator in a separate particle cooler 15. The flue gases leave the reactor via a pipe 16.

83290 The cooling reactor 2 can also be adapted after a normal rotary kiln or a grate kiln or other type of kiln, when rapid cooling to prevent the synthesis of super-toxins is desired.

Claims (8)

A process for the treatment of chlorine-containing substances, such as waste or bio-sludge (or metal concentrate), at high temperature and cooling of formed process gases to minimize the amount of aromatic polyhalogen compounds in the process gas, characterized in that - the substances are first treated at least 830 ° C in the presence of oxygen-containing gas, to decompose aromatic polyhalogen compounds present in them and process process gases cooled to below 250 ° C, the formation of aromatic polychlorinated compounds, such as polychlorobiphenol, polychlorinated dioxins and furans, contained in the gas the chlorine compounds in the presence of koi and oxygen have essentially ceased and that - the cooling rate is at least 1000 ° C per second. 2. A process according to claim 1, characterized in that - municipal waste or industrial bio-sludge is incinerated in a circulating bed fluidized bed reactor at 830 - 1000 ° C, whereby the polychlorinated biphenyls, the polychlorinated dioxins and the furans are decomposed. combustion. 25 3. A method according to claim 1, characterized in that - the cooling of the formed process gases is carried out in a fluidized bed fluidized bed reactor, wherein - a large amount of circulating particles cooled in a heat exchanger are involved in the process gas for rapid cooling of the process gas. that - the circulating particles are separated in a particle separator from the cooled process gas and returned to the reactor. 35 4. A method according to claim 3, characterized in that the circulating particles are cooled in a heat exchanger before being separated from the process gas. 10 83290 Process according to claim 3, characterized in that circulating particles are cooled in a heat exchanger after they have been separated from the process gas. 5 Process according to claim 1, characterized in that - metal oxides are reduced in the presence of carbonaceous material and oxygen-containing gas at a temperature of more than 830 ° C and the chlorine-containing process gases formed are rapidly cooled to prevent the formation of aromatic polychlorinated compounds. Process according to Claim 1, characterized in that - municipal waste or industrial chlorine-containing waste or sludge is incinerated at above 1000 ° C for decomposition of aromatic polychlorinated compounds and the flue gases are quickly cooled below 200 ° C. 8. A process according to claim 1, characterized in that the flue gases are cooled above 2000 ° C / second.