RO119612B1 - Process for making foamed silicated melts and installation for applying the same - Google Patents

Abstract

The invention relates to a process and an installation for applying said process for making foamed silicated melts employed in manufacturing rigid heat insulating materials, masonry materials of various size, with controlled density and mechanical strength. According to the invention, the process consists in dispersing the starting material uniformly, in a hot gaseous medium having a temperature of up to 1650 C with vertical descending circulation in uniflow with the gases in a vertical kiln, both the granule melting, after crossing a maximal height of 5 m, at a gas speed of about 10 m/s, and a stirring vertical flow being ensured thereby, calcareous powder being sprayed on the free surface of the collected melt for foaming the melt. The claimed installation comprising a vertical kiln (8) is provided at its upper part with a conveyor (2) for conveying the silicated starting material on a horizontal distribution plate (3) located above a feeder hopper (1) wherein there are mounted some distribution cylinders (4) which, by means of some funnels (5), distribute the starting material uniformly into some ceramic refractory tubes (7), while, at the lower part of said installation, there is placed a collecting trough (15) having blunt angle-shaped vertical section.

Description

The invention relates to a process and to an installation in which this process is applied, for the production of foamed silicate melts, using as sterile carboniferous raw materials for washing or filter press in the coal industry, ash from power plants, metallurgical slags, earth from excavations, sands, crude flour prepared for the production of cement, pyrolysis coke with relatively high ash content, etc., the resulting foamy melts being used in: obtaining rigid insulating materials, masonry materials of various sizes, densities and mechanical strengths controlled, lightweight aggregates for medium-strength concrete and for fillers. Also, the foamed silicate melts are used for the production of the expanded clinker, in order to reduce the energy consumption necessary for grinding in the process of obtaining the cement, to make the carpets and coverings in the structure of platforms and roads, etc.

In the current technique, there are known processes and installations for the production of silicate melts, as well as their expansion-foaming.

US Pat. No. 4411679 proposes foaming by injection of gas or porous pores on the underside of the flowing melt, the gas dispersing in bubbles evenly distributed in the viscous mass, having the flow controlled by means of a butterfly flap, and the melting is carried by metal screws immersed in it. The main disadvantage is that the gas injection cannot actually cause small bubbles evenly distributed in the glass mass directed by the metal screws.

US Patent 4124365 provides for the preheating to 750 ° C of a crushed ceramic material, conveyed by means of a horizontal screw, with the amount of heat released by some burners evenly distributed around the cylinder of the screw. Next, mix the pre-heated ceramic with an agent. foam and push the mixture, through another screw, vertically, through an asbestos grate, after which it is heated to 1200 ° C, in a cylindrical tube, with the heat input of some fuel burners. of this invention is the limitation of the thermal fluxes to modest values, not industrially suitable, especially to the foam furnace, which requires a temperature field between very wide limits, having relatively cold foam in the central area, due to the thermal insulation realized by the foam already formed towards the walls of the oven. respectively.

In US patent 3348933, a non-stationary thermal regime is proposed, controlled to reduce the shrinkage upon cooling until the expanded ceramic products are rigid, under the conditions of phase expansion at various depths in the product. A disadvantage is that as long as gas is generated in the product, it must be soft. External stiffening, before foaming the entire mass, allows to increase the gas pressure from the inside to high values, until the product breaks (it is impervious to gas), which requires the establishment of a strictly controlled thermal regime, for each geometric form of the product. , composition and density.

US Patent 4,123,247 proposes to make expanded granules from silicate melts, for example metallurgical slags, by introducing water under the melting mat flowing on an inclined plane. Hot and still soft granules, expanded by the steam generated by water, are mechanically discarded and solidified during air travel, forming a quantity of hot granules. The main disadvantage is that the pores obtained are large and unevenly distributed, the structure of the granules being inhomogeneous.

Also known from the prior art is the Pilkington furnace, intended exclusively for melting glass, consisting of a cylinder of large diameter and low height, in which the milled raw materials are introduced together with the gas fuel and the combustion air through nozzles, with oriented jets, tangential to the cylinder, and in which separation is performed

EN 119612 Β1 centrifugal droplets formed, which are collected on the vertical wall. The melt is pre-leached on the vertical wall of another cylinder, with relatively small diameter and high height, in which it is degassed. This process makes the melting extremely intensive, but not the expansion of the 3 melts.

The proposed technical problem consists in the production of foamed silicate melts, having 5 controlled pores, uniformly distributed in their mass, at high temperatures.

The process for making the foamed silicate melts, from 7 fine silicate raw material, for example flour with granules below 200 µm, possibly preheated to 920 ° C, according to the invention, eliminates the mentioned disadvantages and solves the proposed technical problem, by that 9 that the raw material it is evenly distributed in a hot gas environment, with a temperature up to 1650 ° C, with a vertical flow lowering in a gas equivalent, in a vertical furnace 11, ensuring both the melting of the granules, after reaching a maximum height of 5m, in the conditions of gas velocity of about 10m / s, as well as a turbulent vertical flow, 13 and on the free surface of the collected melt, limestone flour is sprayed which, by heating, releases gases at temperatures lower or close to soil temperature. difficult to melt, and which is permanently covered by particles of molten raw material, before the particles of limestone to reach the decarbonation temperature of about 17 900 ° C, the carbon dioxide formed thus being enclosed in the melting mass and forming bubbles. The separation of the melt droplets from the combustion gases takes place by changing their direction of 19 displacement with an obtuse angle, and in order to avoid deposits on the gas exhaust channels, cold air is mixed which mixes with the melt droplets, so that the temperature of the air mixture 21 - gases to be reduced below the solidification of the melt.

The installation for the application of said process, consisting of a vertical furnace 23 provided with electrical and thermal resistances, according to the invention, eliminates the disadvantages presented and solves the proposed technical problem by the fact that, at its top, a conveyor of the silicate raw material is located, on a horizontal distribution plate, located above a feed hopper, in which are distributed distribution cylinders, 27 with peripheral grooves, which evenly distributes the raw material, through funnels, in metallic pipes, which feeds refractory ceramic pipes. , and at the bottom 29 of the installation is located a collecting trough with a vertical section, in the form of an obtuse angle, from which the foamy melt is evacuated through a slot, the supply of limestone flour 31 for foaming the melt being made of a hopper, provided with a grooved distribution cylinder, through through a connection and through some rectangular pipes. 33

The main advantages of the invention consist in:

- recovery of secondary raw materials and waste, such as: carboniferous wastes, 35 ash from all processes of combustion of fuels, soil resulting from excavations, sands, etc. 37

- obtaining materials and products for construction, with controlled densities, as a result of foam melting;

- the production of vitreous materials, practically indestructible by usual physical and chemical agents, with high physical and chemical stability;

- making very compact installations, with high efficiency for thermal processes and with minimal pollution; 43

- halving the energy consumption when grinding the clinker and increasing the quality of the cement from the molten clinker.45 below, an example of the application of the invention is given, in connection with the figure representing the vertical cross-section through a melting furnace of substances. silicate. 47

EN 119612 Β1 in the pipes through which the raw material circulates, at the same time the eventual gas fuel is introduced. In order to ensure the ignition of the fuel and to maintain the combustion from the moment of commissioning, below the lower level of the pipes, in the longitudinal vertical walls of the furnace there are provided two panels of electrical resistors, the stations initially heat, at over 1100 * C, the vertical channel of the furnace, on a height of 0,5 ... 1 m. The fuel begins to burn as soon as it enters the mentioned vertical channel, finishing drying, heating, possible chemical reactions, melting and overheating of the particles of raw material. To ensure a relatively uniform velocity flow in the vertical channel, it is necessary that Re (Reynolds number) exceeds 10 ⁴ , which conditions the value of the gas velocity, which will exceed 10 m / s. Due to the enormous intensity of the heat transfer between gases and particles with maximum diameters below 200 pm and averages below 100 pm, the burning of the particles with embedded coal is done in maximum 0.1s in the case of covering the average granule of 100 microns and the melting time requires other 0.1 s; with a gas descent velocity of more than 10 m / s, the total height of the vertical channel is 2 m, and the specific melt flow is about 7 t / m ² h; at a speed of 50 m / s, the height is 10 m and the specific flow rate of 35 t / m ² h.

The following calculation relationships are given in the technical-scientific literature:

- Preparation time of the particle: T _p = 20-10 ' ² -d ⁰ - ⁶² -T' ⁴⁰⁵ O ° - ⁵ s, with d = particle diameter in cm, T = combustion air temperature at inlet in K and 0 = oxygen concentration in the combustion air in%;

- Burning time of volatiles: T _v = 80d ² s;

- Burn time of coal residue (coke):

T _rc = 30000 d ^{1 '95} -T ⁰⁷⁸ -wr ^-0 · ³² (wr = the relative velocity of the particles relative to the gas, in m / s).

The total duration of the burn is

T _all = 20-10 ¹² -d ° ^{, 62} -T ' ^4.05 O ^0.5 + 80 d ² + 30000 d ¹ · ⁹⁵ · Τ ° · ⁷⁸ · νν r ^-0 · ³² with T = 1100 ° C = 1373 K, 0 = 21% (oxygen injection will reduce Ttot) and w _r = 0.1m / s, T _all = 0.856 d ⁰ · ⁶² + 80d ² + 338.6 d ¹ · ⁹⁵

For d = 25 microns = 0.0025 cm,

T _all = 0.0209 + 0.0005 +0.0029 = 0.0243 s;

For d = 50 microns = 0.0050 cm, T _all = 0.0451 s;

For d = 75 microns = 0.0075 cm, t, ₀ , = 0.0700 s;

For d = 100 microns = 0.0100 cm, T _all = 0.0998 s.

Heat exchange

The gas flow at 1400 ° C results from the turbulent flow condition, in order to uniformize the gas velocity throughout the section, so from the condition v

with w = average gas velocity, in m / s; d _ech = equivalent diameter of the tube which, for the experimental installation under construction, is 0,102 m and v = kinematic viscosity = 280-10 ⁶ m ² / s; deduce w> 27,5m / s (for the experimental installation).

in the case of industrial furnaces, d _eq 0.4 m, minimum gas velocity is only 7m / s at 20 ° C and atmospheric pressure. in the experienced case:

Gas flow: 27.5 - ^0.102 ^ ---- ³⁶⁰⁰ --- = 132m _n ³ / h

1+ (1400/273) which requires 132-0,347-1400 = 64125 kcal / h .-- 4

RO 119612 Β1 flour heating requires (with 80 kcal / kg = melting heat): q = 0.3-1400 + 80 = 500 1 kcal / kg.

The heat dissipation of the oven is about 2500 kcal / h. The air consumption 3 is about 1500 m _n ³ / Gcal (with excess hours of about 30%), being able to develop 132/1500 = 88000 kcal / h. The maximum flux of molten raw material results from 5

88000-2500-64125 _ 21375

500 500 = 43kg / h

Melt production: - · 10 ~ 3 = 5.26ί / ζη ² /? n n-0,102 ² with p = density of the particle substance (about 2000 kg / m ³ ), q = specific heat consumption for the evolution of silicate raw material (500 kcal / kg), the duration of heat exchange 15 for the melting of the particles results from the equality , ₂ aî nd ³ Λ * 1400-50 π-d ^ζ · α · Δ / · τ = ---- · ρ α; Δί = ----------- = 405K.

ln (1400/50). - with Nu (Nusselt) Nu = —— = 2 + 0.6Re ² Pr ³ , Nu = 2.18

Λ

Taking into account the resistance of the thermal conduction through the particle, α = ^2, θ θ.θθθ d

the previous relation becoming θι1θ · 405 · τ = —- 2000-500, where τ = - ^{d 10} - = 2572d ² hd 6 ^sc 6-0.16-405 with d in m, respectively t _sc = 9.26 d ² with d in mm and t _sc = 9.26-10 ' ⁶ · d ² with d in pm.

d (p.m) lot (S) Lc (S) ^T 9, (s) h (M) 25 243 58 301 83 50 451 232 683 188 75 700 454 1154 317 100 98 926 1925 529

The tube of the experimental furnace consists of 1.78m 01O2mm and 0.80m φ122 mm, 37 evhivalent with a total length of 2.92 m. In the oven, particles with an average diameter of max. 70 pm. 39

When preheating the air and flour, q will be max. 350 kcal / kg, and the melt output of the 102mm tube oven would reach 41

90000-20000

350____ = 200kg / h

RO 119612 Β1

An industrial furnace would produce, at a gas speed of 27.5 m / s, n-0.102 ²

The turbulence of the flow determines the possibility of the association of particles of which at least one. is melted. The increase of the diameter causes a deterioration of the convection which is counteracted by the thermal radiation of the neighboring particles, which reduces the influence of the associations on the duration of the process. The molten particles fall like a small rain on the melting surface collected below the level of the outlet of the vertical channel, the gases having a sudden change of direction and velocity, released by the suspension of molten particles, continue to move after a previous cooling to a temperature below freezing. of the melt, by mixing with cold air, in the case of molten ash, carboniferous sterile, common clay, etc., the freezing temperature of the melt exceeds 1000 ° C. The exhaust gases will preheat the combustion air of the installation to over 900 ° C and the silicate raw material to 200 ... 500'C, avoiding the loss of volatile fuels useful in the case of fuel incorporation.

for the purpose of foaming the silicate melt with a temperature above 1000 ° C, from a small height above the free level of the collected melt, it is spread evenly on the surface of the melt, the shredded limestone flour at 1% of the mass of the melt. The limestone flour being received from a system that ensures a uniform distribution, pneumatically transported by a flow of cold air, the limestone can be replaced by another similar product that, by heating, releases gas at lower temperatures and close to the freezing temperature. of the melt. The limestone particles are rapidly covered by the melting rain of particles which causes them to decarbonate, at about 900 ° C, the resulting gas (CO ₂ ) being included in the bubbles which causes the foam to melt and the porosity of the expanded final product.

In order to separate the melt droplets from the hot gases, they suddenly change their direction of travel, and in order to avoid the loss of the gas bubbles, the melt temperature will slightly exceed the freezing temperature, below which it will reach the endothermic reaction of decarbonation and possibly by limiting the limestone. with a cold air flow. The resulting product is a construction material that can have any density over 50 kg / m ³ , with closed pores and mechanical strengths at least double with respect to the autoclaved cellular concrete of the same density. The product can be cut by known means, is insensitive to the attack of atmospheric agents and retains the nail.

To protect the walls of the furnace against the physical-chemical attack of the melt, they are lined at the bottom with a thin plate of platinum or other similar refractory material, which is not watered by the melt.

The raw material, finely ground and possibly preheated with some of the hot flue gases discharged from the plant, is collected in a hopper 1, which is brought from the outside, through a conveyor 2, on a horizontal plate 3 moved horizontally, alternatively longitudinally, for the purpose of distributing the raw material, evenly, throughout the entire bunker 1 (purpose that can be achieved by other known devices as well). An assembly of cylinders 4 with longitudinal peripheral grooves, rotated slowly, simultaneously and with the same speed, extracts the raw material along the entire length of the cylinders and feeds evenly the funnel assembly 5, one for each of some metallic pipes 6, which feed another assembly of pipes. refractory ceramics 7, evenly distributed throughout the horizontal section of the parallelepipedic space 8 of the furnace; through a connection 9 the gas fuel that will enter the space 8 is introduced, through the same pipes 7 as the raw material, also distributed evenly. The raw material may also contain fuel

EN 119612 Β1 finely ground, in which case the gas fuel is only required for adjustment. By means of two 1 connections 10, the combustion air (possibly enriched in oxygen) is introduced, preheated in a exchanger, itself known, with the heat released by the hot flue gases discharged from 3 installations. The combustion air is distributed through two channels 11 (connected at the ends between them for uniform pressure in the channels), from which it enters the furnace through two longitudinal slots 12. 5

Ceramic pipes 7, about 400 mm long, ensure the uniform distribution of the combustion air at the level of their lower ends. For the purpose of ignition of the air and fuel mixture 7, two electrical resistors 13 are provided, throughout the length of the oven, which are switched on before the oven is switched on, ensuring a temperature above 9

900'C, sufficient to allow the oven to be put into operation. The rotation of the cylinders 4, so the supply of raw material to the furnace, starts as soon as a thermocouple assembly 11 indicates the operating temperature is reached. The particles of raw material in contact with the hot gases evolve thermally until their melting, during the descent on the height of the furnace up to 13 at the exit, at the bottom of it, where they are collected in a sewer 15. The entire section of the collector is scattered lime flour by two or four rows of 15 pipes 16 finished with rectangular slots, meant to spread the lime flour evenly across the entire width of the gutter 15. Through the pipes 16, the lime flour is pneumatically transported17 by a stream of compressed air. over 300 mm col. water, coming from two pipes 17, of which it is distributed through a connection 18 for each pipe 16, carrying the flour allowed through 19 another connection 19, through funnels 20. The pipes 16 receive the same flow of limestone flour, uniform by a grooved cylinder 21, which receives limestone flour from a hopper 22.21

The droplets of molten raw material, separated from the flue gases discharged from the furnace, cover the limestone granules which decarbonate after coating them, generating CO ₂ which will fill 23 all the bubbles of the molten foam formed. The separation of the droplets from the hot gases is strongly favored by the abrupt change, in the obtuse angle, of the direction of the gases at the output of 25 furnaces through two channels 23.

To avoid melt deposition on the gas exhaust channels, these are 27 mixed with cold air, injected through two pipes 24, the air-gas mixture having a temperature below that of solidifying the melt. The gases will enter a heat exchanger in which they will prevent the combustion air introduced into the furnace through the connections 10. The foam collected in the trough 15 flows through a slot 25 throughout the furnace, for various uses such as: making 31 materials molded by molding into molds (large masonry blocks, prefabricated walls, etc.), making lightweight aggregates in the form of granules of different densities and sizes, carpets for setting up various support layers for platforms, roads, highways, case in which the oven will be translated. In the case of the cement industry, the crude flour, previously decarbonated, so pre-heated to about 900 ° C, will form molten and expanded clinker, from which granules will be made which, after useful cooling, will be ground with reduced energy consumption . 37

Starting the system starts with the heating of the resistors 13, continues with the introduction of combustion air, followed immediately by the gas fuel and, after the combustion air 39 reaches the preheating temperature set using the hot flue gases, the feed is started, followed by the start of the introduction of limestone flour. 41

Claims (8)

Claims 43 1. Process for making foamed silicate melts, from finely milled silicate raw material, for example flour with granules below 200 µm, possibly preheated to 920 ° C, characterized in that the raw material is uniformly dispersed in a hot gas medium. 47 with a temperature up to 1650 ° C, with vertical descending flow in gas equilibrant RO 119612 Β1 in a vertical oven, thus ensuring both the melting of the granules, after reaching a maximum height of 5 m, under the gas velocity conditions of approx. 10m / s, as well as a turbulent vertical flow, and on the free surface of the collected melt, limestone flour is sprayed which, by heating, releases gases at lower temperatures or close to the solidification temperature of the melt, and which is permanently covered. of particles of molten raw material, before the limestone particles reach the decarbonation temperature of about 900 ° C, the carbon dioxide formed thus being enclosed in the melt mass and forming bubbles. 2. Process according to claim 1, characterized in that the separation of the melt droplets from the combustion gases takes place by changing their direction of displacement with an obtuse angle, and in order to avoid deposition on the gas outlet channels, cold air is mixed which mixes with melt droplets so that the temperature of the air-gas mixture is lowered below that of the solidification of the melt. 3. An installation for applying the process of claim 1, consisting of a vertical furnace (8) provided with electrical resistors (13) and thermocouples (14), characterized in that a conveyor (2) is located at its top. , of silicate raw material on a horizontal distribution plate (3), located above a feed hopper (1), in which are distributed distribution cylinders (4) with peripheral grooves, which evenly distributes the raw material, through funnels (5), in some metallic pipes (6), which supply refractory ceramic pipes (7), and at the lower part of the installation is placed a collecting trough (15) with a vertical section in the form of an obtuse angle, of which the foamed melt is discharged through a slot (25), the supply of limestone flour for foaming the melt being made of a hopper (22), provided with a grooved distribution cylinder (25), through a fitting (19) and and through rectangular pipes (16). 4. The installation according to claim 3, characterized in that the refractory ceramic pipes (7), evenly distributed on the horizontal section of the furnace (8), through which the raw material and the gaseous fuel circulate, have a length sufficient to allow the combustion air admitted through a furnace. fitting (10), located at the top, side of the oven (8), to be evenly distributed at the lower end of the pipes (7), each receiving the same flow of silicate raw material, possibly mixed homogeneously with ground solid fuel. 5. Installation according to claim 3, characterized in that the distribution cylinders (4), with longitudinal grooves, one for each row of pipes (6), rotate slowly, simultaneously, at the same speed, for the evacuation of the raw material, uniformly on the length of the cylinders, the raw material being collected by the funnels (5), one for each pipe (6), a device itself known ensuring the relatively uniform distribution of the flour throughout the hopper. 6. Installation according to claims 3, 4 and 5, characterized in that below the level corresponding to the lower ends of the pipes (7), in the vertical longitudinal walls of the furnace (8), there are provided two panels of electrical resistors (13), having a height 0,5 ... 1 m, located in the area where, in stationary operating mode, the wall temperature is 900 ... 1100 ° C, the resistors decoupling by the command given by the thermocouple (14), when in the oven the temperature exceeds 1100 ° C. An installation according to claims 3 ... 6, characterized in that the limestone flour is sprayed over the free surface of the melt in the gutter (15), by two or four pipes (16). 8. Installation according to claims 3 ... 7, characterized in that the walls of the oven (8) are lined at the bottom of it with a thin plate of platinum or other similar refractory material.