RU2296187C1 - Cleaning method of briquettes of water- and oil-containing metallic cuttings - Google Patents

Abstract

FIELD: metallurgy, possibly preparation of briquettes of metallic, mainly of cast iron cuttings for further hot compaction and refining briquettes in plants of machine engineering and metallurgical industry branches.

SUBSTANCE: method comprises steps of heating briquettes of water and oil containing metallic cuttings in working chamber; feeding combustion products of fuel together with air into after-burning chambers for preliminarily and finally after-burning products; using products of preliminary after-burning for heating briquettes. Briquettes are heated in working chamber at constant presence of steam generated by continuous supply of wet briquettes. Additional air is fed to different zones of working chamber along vortex path in cross-variable direction. Final after-burning is realized at temperature 100 -1100°C.

EFFECT: possibility for producing briquettes free from oil emulsion impurities, elimination of harmful exhausts to atmosphere at thermal cleaning and melting.

1 tbl, 2 dwg

Description

The invention relates to metallurgy and can be used in factories of machine-building and metallurgical industries in the preparation of briquettes from metal (mainly cast-iron) chips for further hot compaction and subsequent melting.

The actual problem of processing metal chips requires solving a number of problems, one of which is the process of cleaning it from oil and coolant in compliance with modern environmental safety requirements.

A known method of cleaning water-oil briquettes from chips, including heating the briquettes in the working chamber, supplying fuel combustion products with air supply to the afterburning chamber with simultaneous supply of additional air, afterburning and subsequent use of afterburning products to heat the briquettes, afterburning of combustion products are carried out in two stages in the chamber afterburning, consisting of a preburning chamber and a final afterburning chamber, the combustion products are fed into the preburning chamber with a dosed they are divided from it, and when additional air is supplied, it is divided into two streams, one of which is fed into the space between the window for selecting afterburning products sent for heating briquettes and the window for supplying them to the final afterburning chamber, afterburning products used for heating briquettes, selected without excess oxygen, and their volume is regulated by the temperature of the working chamber.

The disadvantage of this method is that at a low concentration of oxygen in the air in the temperature range 400-500 ° C, the thermal decomposition of oil hydrocarbons proceeds according to an asymmetric scheme with the formation of high molecular weight hydrocarbons, soot and free carbon, for example, decomposition proceeds according to reaction (1)

since the further oxidation of C _m-1 H _n-4 by reaction (2)

impossible due to lack of oxygen, the reaction (3) prevails

There is a likelihood of the formation of polycyclic aromatic hydrocarbons, including the carcinogenic benz (a) pyrene C ₂₀ H ₁₂ , the elemental composition of which is close to the elemental composition of soot - 95% carbon and 5% hydrogen.

The temperature in the final afterburner is insufficient for the complete oxidation of the combustion products of the process fuel and oil hydrocarbons (Patent RU No. 2170882, CL F 23 G 5/00, C 22 V 1/14 dated 16/12/99).

There is also a method of cleaning water-oil-containing shavings from alloy steel, including heating the shavings in the working chamber, supplying fuel combustion products with air supply to the afterburning chamber with simultaneous supply of additional air, stage-by-stage afterburning and subsequent use of afterburning products for heating the chips.

Since the REKUMAT burner operates with a higher coefficient of excess air, a certain excess of atmospheric oxygen is formed at the entrance to the working chamber and at the very beginning of it, which in the temperature range 500-550 ° C oxidizes vaporous oil hydrocarbons. The oxidation of oil hydrocarbons is accompanied by heat and their temperature increase. The incorporation of oxygen into hydrocarbon molecules promotes their symmetrical cleavage and prevents the formation of high molecular weight compounds. The following reaction is possible for methane:

The resulting formaldehyde (CH ₂ O) already decomposes at a temperature of 300 ° C into simple combustible components

The lack of air oxygen in other parts of the working chamber does not fully suppress the splitting processes. Therefore, the formation of high molecular weight hydrocarbons, soot, and free carbon continues according to reactions (1) and (3), and the formation of carcinogens by reaction (6) is also possible

The low temperature in the afterburner of 850 ° C is insufficient to completely burn off the combustion products, ensuring compliance with modern environmental standards (see Thermal cleaning of oil spiral chips / GASWARME INTERNATIONAL / 1997 No. 7/8 - pp. 356-357 - German)

The purpose of the invention is the deep cleaning of briquettes from chips from oil and coolant, ensuring high sanitary and hygienic efficiency of the process and minimum fuel consumption. The goal is achieved in that in a method for cleaning briquettes from water-oil-containing metal shavings (mainly cast iron), which includes heating the briquettes in the working chamber, supplying fuel combustion products with the addition of air to the afterburning chambers, preliminary and final afterburning, and subsequent use of preliminary afterburning products to heat the briquettes, briquettes are heated in the working chamber with the constant presence of water vapor due to the continuous supply of raw briquettes, an additional filler is fed into the working chamber The air is perpendicular along a vortex trajectory of a transversely variable direction, and the final afterburning is carried out at a temperature of 1000-1100 ° С.

Figure 1 shows a longitudinal section in the vertical plane of the device for implementing the method.

Figure 2 is a section aa in figure 1.

The device comprises a loading window 1, an unloading window 2, a working chamber 3, lower pre-combustion chambers 4, burners 5, lower recirculation channels 6, alternating with upper recirculation channels 7, vault channels 8, vault final combustion chambers 9, refractory nozzles 10, channels removal of combustion products into the atmosphere 11, air collectors 12, air inlets 13, conveyor 14.

The working chamber 3 is in a state heated to 800 ° C. The temperature level is maintained by burning fuel in burners 5.

Water-oil briquettes are continuously fed into the working chamber 3 by conveyor 14.

Intensive heating of briquettes, evaporation of moisture and heating of water vapor, gasification and oxidation of oil hydrocarbons, their burning in the central part of the working chamber, takes place at the entrance section.

Further movement of briquettes occurs in the environment of combustion products.

The presence of water vapor both in the combustible mixture and in the combustion products has a positive effect on the combustion process and, first of all, on the flame propagation velocity, since they create a high concentration of active centers - atoms and radicals. The appearance of atomic hydrogen H and hydroxine OH in the flame zone accelerates the oxidation and combustion of oil hydrocarbons many times as a result of the development of the reaction by a chain-thermal mechanism. The accelerating effect of water vapor during the combustion of carbon monoxide is explained by the total reaction

as a result of which flammable hydrogen occurs. Subsequent homogeneous oxidation of hydrogen leads to the formation of OH radicals and H and O atoms, which determine the development of chains of the main reaction

and

and their branching

or

This explains the increase in the burning rate of CO.

The carbon remaining in the briquettes may burn out as a result of the reaction

to pass which requires the presence of water vapor near the cracking molecules of oil hydrocarbons. Since water vapor is always present in sufficient quantity, even without the combustion of H ₂ in H ₂ O, combustion of C in CO and then CO in CO ₂ will be guaranteed.

Into the working chamber 3 through the inlets 13, a zone-by-zone supply of additional air is made along a vortex trajectory of a transversely variable direction. At the boundaries of the zones between oppositely directed flows, the relative velocity is equal to the sum of the flow velocities, which creates increased turbulence, leads to equalization of pressure fields, oxygen concentration and allows to improve the supply of oxidizer to briquettes and fill their pores as much as possible. The presence of an oxidizing agent and rapid heating create favorable conditions for the thermal decomposition of oil hydrocarbons according to a symmetrical scheme with a maximum yield of volatile and a minimum yield of solid residue (carbon black and carbon).

Each zone has its own air flow coefficient α, the value of which varies between 0.85-1.4.

In the central part of the working chamber 3, due to the combustion of vaporous hydrocarbon oils, a significant amount of heat is generated, which is spent on heating the briquettes, lining the working area and the conveyor 14. Heat transfer is due to radiation of the flame and physical heat of the combustion products. This allows you to transfer the burner 5 to a partial power level, reducing fuel consumption through them. The products of oil combustion, periodically passing through the lower and upper recirculation channels 6 and 7, the lower preburning chambers 4, the vault channels 8, enter the final chambers of the final afterburning 9, where at the temperature of 1000-1100 ° С the final afterburning takes place on the refractory nozzles 10. Purified afterburning products enter the atmosphere.

In the process of burning organic compounds, redox reactions occur, as a result of which polycyclic aromatic hydrocarbons from fuel and oil hydrocarbons, which are carcinogens, can be synthesized again. In the described method, this is practically excluded, because there are no soot particles on which carcinogens are adsorbed, oxygen is in abundance and there are no conditions for pyrolysis, the final afterburning at a temperature of 1000-1100 ° C allows for high-quality afterburning of combustible components, including benz ( a) pyrene.

An example implementation of the method:

Briquettes made of cast-iron shavings with a density of 4.2 ... 4.6 g / cm ³ , ⌀ 150 mm, height 130 ± 5 mm, oil content 2.2%, water 1.8% were cleaned. The temperature in the working chamber was 800 ... 825 ° C. The temperature in the lower chambers of the preliminary afterburning was 900 ... 950 ° С, and in the vault chambers of the final afterburning was 1000-1100 ° С.

The briquettes were heated when they were continuously fed into the working chamber with a subzone supply of additional air, temperature-controlled and coinciding in direction with alternating repirling flows in the corresponding zone, which ensured the efficient combustion of both oil vapors and oil products inside porous briquettes. The resulting heat was 51% in the incoming heat balance with a corresponding decrease in the consumption of natural gas used for heating.

The table shows the results of measurements of the content of harmful substances in afterburning products.

Name The concentration of pollutants in the products of afterburning (entering the atmosphere) mg / m ³ Nitrogen (III) oxide NO 0.7 Carbon monoxide 5 Benz (a) pyrene - Sulfur dioxide SO ₂ 0.5 Suspended matter one Formaldehyde CH ₂ O - Sulfur Anhydride one

The table shows that the content of released harmful substances in afterburning products is minimized, i.e. the proposed method made it possible to obtain briquettes free of oil emulsion impurities, suitable for remelting, and to avoid harmful emissions into the atmosphere both during thermal cleaning and during melting, which made it possible to abandon expensive special treatment facilities when processing metal chips.

Claims (1)

A method of cleaning briquettes from water-oil-containing metal shavings, including heating the briquettes in the working chamber, supplying the resulting fuel combustion products with the addition of air to the afterburning chambers, preliminary and final afterburning and subsequent use of pre-burning products for preheating the briquettes, characterized in that the briquettes are heated in the working chamber lead with the constant presence of water vapor, provided by a continuous supply of raw briquettes, additional air poses into the working chamber continuously on the vortex trajectory transversely alternating directions, and the final post-combustion is carried out at a temperature of 1000-1100 ° C.

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