Neutralization of asbestos waste

ASBESTOS

 

Asbestos is naturally occurring mineral fibres with specific physical and chemical  qualities. There are two groups of asbestos in mineralogical regard: serpentines and amphiboles. First group is only one type: chrysotile asbestos. The amphiboles are: amosite, anthophyllite,  krokidolite, thermolite and actinolite. Fibres from chrysolite and krokidolite groups have the most common meaning for industry because of their qualities. Chrysolite asbestos makes 85-90% of all usage. These are hydrated magnesium silicate, with characteristic yellowish colouration. Krokidolite asbestos, called “blue” is soda-iron silicate. Volumetric density is the essential parameter that determines area of application and procedures of removing impurities. “Class I” encloses “soft” products with volumetric density below 1000kg/m3. They are used in protective textiles production (like fire blankets, spraying fire insulations). Above this value starts “class II” – “hard” products. Asbestos-cement cardboards are the most widespread in this group. It is used as roofing and facade covering.

 

Among all asbestos fibres exists small group of fibres with strictly specified dimensions (diameter above 3µm and length 5µm), that is a serious menace to health and life of all living beings – respirabile fibres.

 

TECHNOLOGY

The ATON-HT company has worked out and introduced a technical solution – thermic destruction of dangerous asbestos fibres by heating them with microwave energy. In this method (which is protected by home and foreign patents) eternit or others wastes containing asbestos, are  preliminarily crushed (in crusher with a special air-tight sealed construction). Then they are mixed with small amounts of assistant substances and put to the microwave reactor chamber. As a result of heating this mixture to a temperature of 900 - 1100 ° C, crystalline structure of asbestos fibres changes into amorphous form.

Characteristic for this method is “no contact” heating of dangerous wastes, by properly concentrated microwave energy beam, to required temperatures, in gas atmosphere optimum for the process. Known conventional methods don’t cause such possibilities. Crushed wastes (aside from their constitution) absorbs microwaves. This process is being rationalized thanks to proper assistant substances. The temperature of dangerous asbestos fibres total destruction  is reduced. It has essential meaning for full effectiveness of changing all asbestos fibres into safe material and for energetic efficiency of process. Microwave radiators located on reactor’s walls are connected with microwave oscillators and they emit concentrated microwave beams to material (that is being displaced in reactor). Process of heating wastes by microwaves is controlled by system of high temperature sensors and thermocouples. Cone crusher located at the bottom of reactor has changeable rotational speed, that allows to regulate speed of displacing material inside reactor. All this process is automatically controlled by properly programmed controller.

 

MICROWAVES IN ASBESTOS NEUTRALISATION TECHNOLOGY

 

 Fig. 1 Block diagram of ATON 200 HR reactor.

 

 

 

ATON 200 HR – Reactor to rendering asbestos wastes.

 

During the heat treatment of eternit cardboards, or other asbestos wastes, water vapour and small quantities of other volatile substances from impurities (paint coatings, oils, organic impurities – moss and lichens) are released. Despite minute quantities of potentially dangerous substances emission, reactors are equipped with conventional systems of catalytic after-burning (ceramic catalyst) or with innovative system of after-burning impurities in tail gases.

 

 

Fig 2 

 

Technical parameters:

 

SUPPLY	3 x 400V (50Hz)
MAX. POWER INPUT	80kW
MICROWAVES INSTALL POWER	40kW (f=2450MHz)
PRODUCTIVITY	200-250kg/h
WORK TEMPERATURE	1000-1100°C

 Fig 3

 

 

Taking into consideration specific of asbestos wastes spacing and transport of large quantities of dangerous wastes, it has been worked out a construction of devices installed on two containers. In one of them are installed devices that are crushing eternit cardboards, mixer and system that transports dangerous material to reactor’s chamber (reactor, microwave and controlling installations is located on second container). Containers should be situated in the vicinity of place where eternit cardboards are disassembled – it’s important to minimize threats connected with displacing this dangerous waste.

 

 

Fig. 4 Material with asbestos fibres – eternit.

 

 

Fig. 5 Product of microwaves rendering
without fibres structure - ATONIT

This is “no waste” process – as a result of this process obtains a useful product. It could be used most of all in building industry. As a result of this process forms pumice-structure material, porous, with large surface of particles, easy to crush. Trade name of this product is ATONIT. It isn’t toxic, it doesn’t have dangerous fibres, it can be used as an addition to concrete, in concrete blocks production, in road-making technologies, etc. It’s worth to admit that it is permitted to commercial traffic and has required approvals  of Institute of Architectural Engineering, Institute of Occupational Hygiene and National Hygiene Department.

 

Fig. 6  Asbestos wastes during microwaves heating.

This device allows to process about 200 kg of eternit and render it harmless during an hour! It’s electric power supplied. Supply from local power network 3 x 400V or current generator is also possible.