RU2168463C2 - Method of preparing calcium carbide - Google Patents

Abstract

FIELD: chemical industry, more particularly preparation of acetylene. SUBSTANCE: blend is prepared from limestone having coarse crystalline marbleized structure (calcium grain size varies from 0.1 to 3 mm) and coke. Blend is charged into ore thermal furnace wit round bath having three electrodes of 350 mm in diameter. Blend is melted at peripheral electrode resistance of 1.17-1.67 ohm.cm. Prior to being poured out, melt is kept for 3 to 15 minutes at peripheral resistance of 0.83-1.2. Ohm.cm. Yield of high-volume (in liters) calcium carbide varies from 280 to 300 l/kg. Electrodes with diameter of 400-500 mm are used. EFFECT: more efficient preparation method. 1 ex, 2 tbl

Description

 The invention relates to the chemical industry, in particular, to a technology for producing calcium carbide.

A known method of producing calcium carbide in an ore-thermal furnace by melting a mixture consisting of lime obtained by preliminary calcining of limestone in a kiln, and carbon material (coke), comprising the following stages:
- compilation of a mixture of lime and coke with a ratio of fineness in the range of 1.9-2.0;
- loading the resulting mixture into the furnace;
- power supply through the electrode;
- fusion of the charge;
- draining the melt and processing it into commercial products (L.A. Kuznetsov Production of calcium carbide, M.: Goskhimizdat, 1954, p. 26, 41, 104) (I).

 The disadvantages of the method are the complexity of the technological scheme, the instability of quality indicators due to fluctuations in the degree of calcination of limestone (the displacement of the resulting calcium carbide is 240-295 l / kg).

The closest in technical essence and the achieved result is a method of producing calcium carbide according to Russian patent N 1806991, class. C 01 to 31/32, declared 06/14/90, publ. 04/07/93, B.I. N 13 (III), comprising the following stages:
- preparation of a mixture of fine crystalline limestone with a grain size of calcite in its particles of 0.001-0.015 mm and coke with a mass ratio of limestone to coke of 2.8-3.2 and with a particle size ratio of 4.5-5.0;
- loading the mixture into the furnace;
- power supply through the electrode;
- fusion of the charge while maintaining a given electrode current and operating power of the furnace by moving the electrode and / or switching the steps of the transformer;
draining the melt and processing it to marketable products.

 The displacement volume of the resulting calcium carbide is 265-275 l / kg.

 According to this method, pelitomorphic (finely crystalline) limestones are used as a calcium-containing rock, which, when rapidly heated to form lime, do not decompose into small pieces. Similar limestones by their firing behavior belong to classification I or II. Limestones of group III — coarse-grained marbled ones with calcite grains of 0.1–3 mm in size — are not thermally stable and break up into small pieces when heated. As a result, the size ratio of the pieces of lime and coke (which does not collapse when heated) decreases to 0.5-1. This is reflected in the melting results.

 The displacement displacement of calcium carbide is reduced to values that are unacceptable for commercial calcium carbide (less than 240 l / kg according to GOST 1460-81 with additions). The product yield in terms of conventional carbide - 250 l / kg is 96%. As a result of the foregoing, the processing of thermally unstable limestones is not economically viable.

Thus, the disadvantages of the prototype are:
- limitation of the raw material base for the production of calcium carbide;
- obtaining a second-class product with unstable quality indicators.

 The technical task of the invention is the expansion of the raw material base for the production of calcium carbide and an increase in the yield of standard calcium carbide (250 l / kg) by producing high-calcium calcium carbide.

The solution of the technical problem is achieved by the fact that in the known method of producing calcium carbide in an ore-thermal furnace, including the preparation of a mixture of limestone and coke with a mass ratio of limestone to coke of 2.8-3.2 and with respect to the size of the furnace, the mixture is melted while maintaining a given the current of the electrode and the operating power of the furnace by moving and / or switching the voltage levels of the transformer and periodically draining the melt,
the melting of the charge is carried out at a peripheral resistance of the electrode of 1.17-1.67 Ohm • cm, and before draining the melt is held for 5-15 minutes at a peripheral resistance of 0.83-1.2 Ohm • cm.

 Distinctive features of the proposed method are the value of the peripheral resistance of the electrode at the melting stage of 1.17-1.67 Ohm • cm, the exposure time of the melt before discharge and the value of the peripheral resistance of the electrode at the stage of exposure of the melt is 0.83-1.2 Ohm • cm.

 These differences allow us to expand the raw material base of carbide production due to the possibility of processing thermally unstable limestones and increase the yield of calcium carbide in terms of conventional carbide by 12-24% due to the production of high-calcium calcium carbide in comparison with the processing of thermally unstable limestones under the conditions of the prototype.

Peripheral resistance is a factor characterizing the technology of smelting calcium carbide, and is
K = UPD / I Ohm • cm,
where U is the voltage at the electrode, V;
I is the current strength at the electrode, A;
D is the diameter of the electrode, cm (S.A. Miller, Acetylene, its properties, preparation and use, vol. 1, Chemistry Publishing House, 1969, p. 210) (III).

The values of the peripheral resistances of the electrodes of the carbide furnace determined experimentally optimal from the point of view of improving the quality of calcium carbide allow:
- choose the optimal current electric mode to obtain a high-capacity product:
- determine, if necessary, the optimal dimensions of the electrodes, and therefore, the furnace bath.

 The essence of the proposed method is as follows.

When limestone is fused with coke, reactions of the T type occur: F dissolution of lime and carbon material in the primary carbide melt
CaO _TB + (Ca ₂ • CaO • C) _W ---> (CaC ₂ • 2 CaO • C) _W ; (1)
Since _coke + (CaC ₂ • CaO • C) _x ---> (CaC ₂ 2 • CaO • C _{f disp} (2)
with the accumulation in the bath of the furnace of a small product. This process is especially active when there is a violation of the sizes of pieces of raw materials (a lot of dust and fines), deviations during dosing. For these reasons, it is practically impossible to stably obtain high-calcium calcium carbide using thermally unstable limestone rocks.

At the same time, melt saturation reactions take place in the melt with calcium carbide:
CaC _2g + CaO _x ---> 2Ca + CO + C; (3)
2Ca + 2C _DISP ---> 2 (CaC ₂ ) _w (4)
To accelerate reactions (3) and (4) in the melt, it is necessary to increase the temperature in the reaction crucible by reducing the fraction of energy spent on the formation of a low-melt melt.

This can be achieved:
1) moving the electrode to the melt zone with or without changing the electric mode on the electrode;
2) by changing the diameter of the electrode.

 The process of producing calcium carbide at the declared values of the peripheral resistance of the electrodes at the melting stage and the stage of exposure of the melt, as well as the time of exposure of the melt allows to obtain high-density calcium carbide from thermally unstable limestones.

Example 1. For the smelting of calcium carbide at JSC "Cherepovets Nitrogen" used limestones from the Smychka deposit (Nizhny Tagil) of the following composition, wt. %: CaO 55.7; MgO 0.43; SiO ₂ 0.46; Al ₂ O ₃ 0.17; Fe ₂ O ₃ 0.26; P 0.015; S 0.02.

 These chemically pure limestones have a coarse-grained partially marbled structure with a calcite grain size of 0.1-3 mm and are not heat resistant.

 Limestones with a particle size of 20-60 mm were mixed with coke of a class of 10-25 mm (ash content - 12 wt.%, Moisture - not more than 5 wt.%, The rest of the carbon in a mass ratio of 2.8-3.2 and with a ratio of fineness of 4, 5-5.0.

 The smelting was carried out on a carbide furnace with a round bath having three electrodes with a diameter of 350 mm, the installed electric power of the furnace is 2.5 mVA, the maximum operating current is 14000 A, the voltage regulation limit is 48-107 V.

 The resulting mixture was loaded into the furnace between the electrodes to the level of the furnace bath. The melting process was carried out continuously with periodic discharge of the melt after 1.6 hours into steel molds.

 The smelting process between drains included the following stages.

 1. The precipitation of the calcined charge after draining the melt with the electrodes lowered.

2. Download adjustments if necessary;
3. Loading the raw charge to the top level.

 4. An exit to an operating mode and melting at a current strength of up to 10000 A, voltage of 65-107 W and active power of 1.1-2 MW. At this stage, the melt accumulated, accompanied by the rise of the electrodes by 25-30 cm. The resulting melt contains <55% carbide (204 l / kg). The peripheral resistance of the electrodes at this stage was 1.17-1.67 Ohm • cm.

 5. Before draining the melt, the electrodes were lowered, increasing the current load to 14000 A, and the melt was held for 5-15 minutes. The peripheral resistance of the electrodes at the melt holding stage was 0.83-1.2 Ohm • cm.

 The experimental results are presented in table. 1.

 Reducing the current load at the melting stage to 4136 A leads to a high position of the electrodes, the development of an arc mode and, accordingly, to sintering of the charge in the upper part of the bath due to the release of power between the electrodes, which does not allow the process to proceed normally through a coal bottom.

 Reducing the current load at the stage of heating the melt to 5495 A (increasing the peripheral resistance to 1.4 Ohm • cm) reduces the amount of heat released in the melt during the passage of current through the circuit "electrode - bottom - electrode", increasing the proportion of the charge released between the electrodes. In this mode, the melt under the electrode can partially crystallize due to the lack of temperature, making it difficult to drain from under all three phases.

 An increase in current loads (at the melting stage to 7540 A and at the stage of melt holding up to 9497 A) and a decrease in peripheral resistance values to 1.02 Ohm • cm and 0.81 Ohm • cm at low power (70 V), respectively, are accompanied by a decrease in the charge volume smelted in the reaction space under the electrode. Due to excess power, overheating and decomposition of part of calcium carbide occurs, i.e. reduced productivity and quality of calcium carbide.

 With a decrease in the melt holding time of less than 5 min, stability of product quality indicators is not achieved.

 An increase in the melt holding time of more than 15 min can lead to a decrease in carbide quality due to dissociation.

 The experimentally determined range of values of the peripheral resistance of carbide furnaces, regardless of the furnace power, allows you to choose the optimal electric mode to obtain a high-capacity product with various electrode diameters, as illustrated in Table. 2.

 Thus, the inventive method for producing calcium carbide allows you to expand the raw material base for the production of calcium carbide due to the possibility of processing thermally unstable limestones, to increase the yield of the product by obtaining a high-capacity product (up to 280-300 l / kg), and also makes it possible to determine, if necessary, the optimal dimensions of the electrodes and, consequently, the bathtubs of the furnace.

Claims (1)

 A method of producing calcium carbide in an ore-thermal furnace, including the preparation of a mixture of limestone and coke, loading the mixture into the furnace, melting the mixture while maintaining the specified current and operating power of the furnace by moving the electrode and / or switching the steps of the transformer and periodically draining the formed melt, characterized in that the melting of the charge is carried out at a peripheral resistance of the electrode of 1.17 - 1.67 Ohm • cm, and before draining the melt is held for 5 to 15 minutes at a peripheral resistance of 0.83 - 1.2 Ohm • cm.

Images