POROUS MASS ASBESTOS FREE FOR ACETYLENE VESSELS

Abstract: The new porous mass without asbestos contents is intended for the filling of the vessels for storaging, transportation and consumption of acetylene, based on calcium silicates, obtained from lime, quartz and boric acid, containing up to 10 mass per cent, counted towards dry matter, of a fine dispersed mixture of the synthetic fibres based on carbon and alkali resistant glass fibres, with the addition, if necessary, up to 0,5 mass per cent carboxymethylcellulose, containing fine, uniformly distributed pores, mainly without the cavities within the mass, whose porosity at least equals to 88 %.

Description: POROUS MASS ASBESTOS FREE FOR ACETYLENE VESSELS Technical Held This invention falls into the technology of materials production scope based on calcium hydrosilicates having the intention to serve as a filler material in the steel vessels, thus enabling a safe storaging, transportation and the consumption of solved acetylene. Technical problem which is solved by means of this invention is the procedure for the production of a new high porous material intended for acetylene vessels, based on the calcium silicates, reinforced by means of a mixture of synthetic fibres on the basis of carbon and glass fibres resistant to alkali with addition of boric acid and carboxymethylcellulose. The mentioned product, the porous mass having porosity of 88 % up to 93 % in volume, hardened to a monolithic structure in a steel vessel, soaked by means of solvents, having the gap between the mass and the steel vessel being below 3 mm, thus enabling a safe filling, storaging and discharging the acetylene in gaseous state. Background Art Technical gasses, depending on their nature and aggregate state, are kept and storaged in different ways. Acetylene is usually kept in gaseous state solved in some of the solvents such as acetone soaked by a porous mass, in this particular situation the calcium silicate. Asbestos used to be taken for reinforcement of calcium silicates, which was added into the mixture of various materials whose basis is calcium oxide, silica and water. Such mixed suspension was introduced into the vessels equipped with special regulation valves, where, under the influence of a raised temperature and pressure in the autoclaves conditions, there came to stiffening of the suspension into a crystalline calcium silicate structure. The stiff mass, together with the steel vessel without a pressure gauge, was then exposed to a raised temperature with the aim of releasing of nearly whole amount of free water quantity, aside from the bound water in crystal structure of calcium silicate. The role of asbestos was, beside reinforcing calcium silicate, to enable a uniform fill-up of the vessel with raw mass, without an increased slackening of the input components in the raw mass. This is of special importance , knowing that acetylene is an unstable gas and the empty spaces can be the source of danger leading to explosion and a spontaneous disintegration of acetylene into its constituent elements. The role of porous mass as a filler material is to uniformly fill the vessel's volume intended for storaging, thus enabling the inlet of the acetylene solvent ( mostly acetone or dimethylformamide), as well as the inlet of the gas which is solved in it. This is enabled by exceptionally high porosity of the material provided - the calcium silicate which is characterised by very fine and uniformly distributed pores whose dimensions are up to about 25 μm, which make an effective contact possible of the gas and solvent as well as a proper filling and discharging of the acetylene vessels. The stiffening and drying processes of the mass is performed in such a way that the distance between the steel vessel's shell and monolithic mass should not exceed 3 mm. The porosity of calcium silicate mass reinforced by means of asbestos fibres amounts to 85 % up to about 92 % in vol. Beside prevention of the settling of the raw mass before autoclaving, the role of asbestos was to prevent the forming of cracks in the mass as well as of free cavities under the influence of outer mechanical impacts, to which the vessels are exposed in the conditions of exploiting or transportation. In addition to aforesaid, calcium silicate mass has the task of preventing a progressive disintegration of acetylene in the vessel, and when it comes to sparkling inside it, caused by the possible dragging in of the back fire from the burner, in the conditions of regular consumption of acetylene in practice. The crystal phase of the porous mass and the mutual ratio of the obtained crystals structures Tobermorite and Xonotlite in it during the phase of autoclaving, plays an important role in obtaining the favourable characteristics of strength and shrinkage of the product. All mentioned positive characteristics of the calcium silicate filler material intended for the vessels for storaging and keeping of solved acetylene, can be obtained by using asbestos fibres as the means for reinforcement and prevention of settling inside the vessels, as defined in USA patent No. 2.883.040. However, it is generally known that asbestos has been proclaimed a material causing health problems with people coming into contact with it. It was the reason for some national and international institutions to forbid the use of asbestos for these purposes. For this reason, it has been worked on the invention of the new filler materials intended for the storaging and keeping the acetylene without asbestos contents. Adequately, for example, the new procedures for production of monolithic fillings of acetylene vessels without asbestos contents EP 264550, EP 625963, US 4,970,246. have been patented. Disclosure of the Invention The new product, whose basis is the monolithic calcium silicate without asbestos contents, reinforced by uniformly distributed mixture of synthetic fibres on the basis of carbon and glass fibres resistant to alkali, with the addition of boric acid and carboxymethylcellulose, representing a good variant of the filler for the vessels in which the gaseous acetylene solved in the solvent, for example acetone, is safely storaged, kept and transported. Calcium silicate monolithic filler obtained by the new procedure, contains a mixture of crystal phase Tobermorite and Xonotlite, having the porosity 86 - 93 % and the equally distributed fine pores. Calcium silicate monolithic filling without asbestos contains an equally dispersed mixture of glass fibres resistant to alkali and synthetic fibres based on carbon, to which boric acid is added, secure a satisfactory mechanical strength of material, at the same time retaining a high porosity, which obtains optimum characteristics bound to the gas quantity which is possible to be storaged in the vessels, providing a high degree safeness, when used. The biggest importance for the monolithic crystal filling is to be formed in such a way so that the initial components should be homogeneously mixed according to the following mass ratios. 1. The contents of carboxymethylcellulose does not exceed 0.5 %. It is added with the aim of preventing of settling of components in the raw mass, before the stiffening phase in autoclave. During baking procedure there occurs to its disintegration - pyrohsys, so favourably affecting the final porosity of the silicate mass. 2. Up to 3 % of boric acid which favourably affects onto the ratio of obtained crystals phases during autoclaving procedure, which has a positive influence on the shrinkage during baking process. 3. Mixture of glass fibres resistant to alkali, containing approximately 17 to 20 % of ZrO 2 and synthetic fibres based on carbon, whose total mass contents does not exceed 10 % counted for dry material. The contents of the synthetic fibres based on carbon in this invention amounts to 0.5 to 5 % of dry material, the rest represents the glass fibres resistant to alkali. The length of both fibres is from 5 to 20 mm, and the thickness being within 5 to 20 μm. 4. The high reactive quick lime - calcium oxide (CaO) and ground silica (SiO 2 ) in this procedure are mixed within the components mass ratio CaO : SiO 2 = 0,80 - 1,00. Production of the new calcium silicate filler material together with the raw materials within the said mass ratios is performed the following way. The soft water, whose total contents depends on the aimed porosity, approximately in the range of 3 : 1 up to 4 : 1 related to dry substance, is added the CaO in order to obtain, by means of agitating, the Ca(OH) 2 , the lime suspension. The so obtained suspension, during its continuous agitation, is added the synthetic fibres based on carbon, boric acid , carboxymethylcellulose if necessary as well as the necessary quantity of silica within the mass ratios as previously explained. Such homogeneous, well agitated suspension of all components, is poured into the vessels for keeping the acetylene which are vacuumised at the same time. The suspension must be previously cooled to 20 - 35°C, having in mind it was, in the exothermic process of "slaking" the quick lime, heated up to about 50°C. The suspension is equally distributed in the whole volume of the vessel so as to avoid the possible cavities and bubbles of air in the mass. In this stage of filling along with provision of a good fluency of the mass and maintaing a complete fulfilness of the vessel preventing the settling, the decisive part is on the dispersed components of the carboxymethylcellulose solution and the mixture of glass and synthetic fibres based on carbon. The so filled vessel is equipped with a special shutting device having a pressure regulating unit which is screwed onto the vessel opening provided with a valve. The so prepared vessel is exposed to autoclaving process in the furnace with residing temperature from 180 to 220°C. The autoclaving process lasts about 20 to 50 hours, depending on the vessel volume, during which time it comes to the stiffening of suspension into a monolithic mass in the vessel itself On elapsing the necessary time, the vessel is taken out of the furnace and is left to be completely cooled. The shutting device together with pressure regulator is dismantled from the vessel and the opened vessel with calcium silicate filler material is taken into the furnace where the drying process takes place. The drying process takes as long as nearly the whole quantity of free water is removed out from the calcium silicate mass. The regime of drying process is adjusted so as not to cause an abrupt water evaporation out of the mass itself, which could imply to building up of major cavities and canals within the mass. For that reason, the increase of temperature up to 180°C lasts for 4 hours, and then it is gradually raised to 230 and up to 350°C at which it is maintained to the end of the drying process. Total time of drying process amounts to about 80 hours. During drying process there occurs the shrinkage of the porous mass within its whole volume and building up of interspace between the mass and metal shell of the vessel which, as aforesaid, must not exceed 3 mm. By adding boric acid, with this invention, in the process of autoclaving there comes to the aimed effect i.e. shrinkage of mass at raised temperatures, which provides satisfactory characteristics of accepting the solvent and gas and release of gas out from the vessel during the exploitation stage. Figure 1/1 shows the example of vessel outlook intended for storaging, keeping and transportation of solved acetylene gas, which contains the metal shell with accompanying valve (2), metal support (3), calcium silicate monolithic filling without asbestos contents (4), a bored hole in monoUthic mass filled with quartz sand (5), felt (6), steel net (7), and a free space up to 3 mm (8) between the steel cylinder body and the filling. The following is the text giving the examples of obtaining the calcium silicate filler material which are characteristic of this invention. Example I 42,1 kg of quicklime is slaked in 200 htres of soft water which is previously heated to 25°C, applying an intensive agitating. In another mixer 2 kg of boric acid is solved in 166,4 htres of water. After 1,5 hours of agitating the lime the solution of boric acid is added, then 2,5 kg of synthetic fibres based on carbon having the length of 7mm and thickness of 8 μm are added, then 4,1 kg of glass fibres resistant to alkali having the length of 12 mm and thickness of 20μm and 50,8 kg of quartz powder which is well homogenised by agitating it. The so prepared mass is poured into the acetylene vessels which are at the same time vacuumized with the purpose of removal of the remained air. The vessels are taken into the furnace where the process of autoclaving is performed at the temperature of 190°C. On finishing the autoclaving process the drying takes place at the temperature of 350°C. The obtained calcium silicate filling has the volumetric mass of 255 g/1. Porosity is 91,9 %, and the compression strength is around 240 N/cm . Example II 57,5 kg of quicklime is slaked in 250 htres of water. In another mixer 1,4 kg of boric acid and 0,28 kg of carboxymethylcellulose are solved agitating it by means of propeller mixer at a speed of 150 revolutions per minute until the total solution of carboxymethylcellulose and boric acid. This solution is added into mixer containing lime, and then gradually 4,2 kg of synthetic fibres based on carbon, then 7 kg of glass fibres resistant to alkali and 69,3 kg of quartz powder and then the mixing procedure is continued at a speed of 55 revolutions per minute, until a homogeneous mixture is obtained. After autoclaving and drying a homogeneous porous filler of the acetylene vessel is obtained, of the volumetric mass 250 g/1, porosity 92,81 % and compression strength of about 250 N/cm 2 . Example III The procedure of mass preparation is the same as described in Example I, where 49,3 kg of quicklime is slaked in 200 htres of water, and in the rest of 130 htres of water 1,2 kg of boric acid is solved. Other components which are added into the lime suspension after mixing with solved boric acid with 3,6 kg of synthetic fibres based on carbon, 6 kg of glass fibres resistant to alkali and 59,3 kg of quartz powder. The mass obtained after autoclaving and drying has the porosity 91,2 % and compression strength of 270 N/cm 2 . Volumetric mass is 253 g/1. The vessels with calcium silicate filler intended for filling of the interior of the vessel for storaging, transportation and exploitation of acetylene, obtained in accordance with this invention as shown in Examples I, II and in, completely meet the requirements of safety precautions tests according to ISO 3807.

Claims: CLAIMS 1. Porous mass without asbestos based on calcium silicates intended for filling up the vessel interior for storaging of acetylene, characterized by, its being obtained of lime, quartz and boric acid, containing up to 10 mass per cent, counted towards dry matter, of a fine dispersed mixture of the synthetic fibres based on carbon and alkali resistant glass fibres, with the addition, if necessary, up to 0,5 mass per cent carboxymethylcellulose, containing fine, uniformly distributed pores, mainly without the cavities within the mass, whose porosity at least equals to 88 %. 2. Porous mass without asbestos according to claim 1, characterized by, the contents up to 10 mass per cent of mixture of synthetic fibres based on carbon and glass fibres resistant to alkali, with the fact that the contents of synthetic fibres based on carbon equals from 0,5 to 5 mass per cent of the dry matter, while the rest represents glass fibres resistant to alkali. 3. Porous mass without asbestos according to claim 1, characterized by, the contents up to 3 mass per cent of boric acid. 4. Porous mass without asbestos according to claim 1, characterized by, the contents fine, uniformly distributed pores, whose contents equals to 88 - 93 volumetric per cent. 5. The procedure for the preparation of the vessel for storaging of acetylene, according to claims 1, 2, 3 and 4, characterized by, comprising the preparation of water suspension CaO and SiO 2 in the ratio CaO : SiO 2 = 0,8 - 1, then up to about 3 mass per cent of boric acid, counted towards dry mass, mixture up to 10 mass per cent of synthetic fibres based on carbon and glass fibres resistant to alkali, counted towards dry mass, carboxymethylcellulose, if necessary, up to 0,5 mass per cent counted towards dry mass, inletting the obtained suspension into metal vessel, autoclaving of it with the aim of stiffening at about 190°C, and drying at about 350°C, so that a monolithic calcium silicate filler is obtained, capable to safely accept the solvent and acetylene, and in exploitation it easily frees the gas from the solution.

Inventors: GOJKOVIC JOVAN, RADICEVIC RADOS, GOJKOVIC, JOVAN, RADICEVIC, RADOS
Applicants: TEHNOGAS D D, "TEHNOGAS" D.D.
Application year: 1997
Main classification: F17C11
IPC codes: C10L3, F17C11