FIELD OF THE INVENTION

The present invention relates to system for producing construction aggregates from geopolymer materials. The production system according to the present invention makes use of fly ash from thermal power plant or incineration house as pozzolan source, thereby paying contribution to effective treatment of these wastes. Products obtained with this production system rarely exhaust C0 ₂ to the air or cost fossil fuels for heating as well as have negative impact on natural environment because of stone and sand exploitation.

BACKGROUND ART

Currently, the wastes of fly ash are usually disposed by dumping, causing severe environmental pollutions and scattering dust into the air as well as costing land space for dumping; there have been no effective solutions to fully making use of the fly ash which has been discarded from the thermal power plant.

On the other hand, current geopolymer material production systems employ wet technology with fluid mixing method, pouring the feed mixture to the mold, waiting for binding, releasing from the mold and drying in the air; this is a time-consuming process which can take at least one day to form the thin product shape, one or more days to dry the product and 7 to 28 days for the product to develop its strength. Therefore, these production systems do not yield high productivity and cause difficulties for production line automation, because of which geopolymer material production technology has been in sluggish growth.

Aggregates from geopolymer materials are expected to replace natural aggregates from stone and sand for use in construction and other areas. It has been known that an artificial sand production system employs the method of wet mixing fly ash with an alkali such as NaOH, naturally drying in 7 days to create small aggregates. This method and system is not industrially feasible.

There has been no complete equipment system for producing aggregates, such as sand and stone, from fly ash with high productivity, swift cycle, which thereby can be applied for industrial-scale production.

SUMMARY OF THE INVENTION

A basis object of the present invention is to overcome the aforementioned shortcomings, namely by proposing an aggregate production system using geopolymer materials and semi-dry and semi-plastic technologies, i.e. use of water is less than 15% with semi-dry mixing technology and less than 30% with semi-plastic mixing technology, making full use of fly ash discarded from thermal power plants.

The inventors accidentally found that creating briquettes of fly ash mixed with alkaline activator helps mixture more thorough, and helps create geopolymer material briquettes from fly ash in various sizes, which are compressively formed, which thereby increasing density and forming the aggregate briquettes. The inventors, at the same time, found that it is possible to accelerate the geopolymerization in order that the product can obtain the initial hardness which is sufficient for instant use. Based on the aforementioned discoveries, the invention was completed.

Specifically, the present invention proposes systems for producing construction aggregates from geopolymer materials, comprising:

- feed mixing component to feed the fly ash into the mixing machine via metering device; - liquid feed tank to feed predefined water amount of the alkaline activator and additives into the mixing machine;

- mixing machine to mix thoroughly the fly ash material and the alkaline activator solution to make semi-dry or semi-wet feed mixture;

- briquette forming machine to create briquettes from the feed mixture in preferred shapes and sizes; and

- dryer to dry and accelerate geoplolymerization in the feed mixing briquettes, thereby creating aggregate briquettes.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a schematic view of the aggregate production system in accordance with an embodiment of the present invention;

Fig. 2. is a schematic view of the aggregate production system in accordance with an especially preferred embodiment of the present invention;

Fig. 3. is a perspective view showing an embodiment of the built-in laminating mold horizontal axis briquette forming machine used in the present invention; and

Fig. 4. is a perspective view showing an embodiment of the external laminating mold horizontal axis briquette forming machine used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described based on preferred embodiments with reference to the accompanying drawings.

As illustrated in Fig. 1 , the system for producing construction aggregates from geopolymer materials comprises: - feed mixing component 101 to feed the fly ash into the mixing machine 103 via metering device 102;

- liquid feed tank 104 to feed predefined water amount of the alkaline activator and additives into the mixing machine 103;

- mixing machine 103 to mix thoroughly the fly ash material and the alkaline activator solution to make semi-dry or semi-wet feed mixture;

- briquette forming machine 105 to create briquettes from the feed mixture in preferred shapes and sizes; and

- dryer 108 to dry and accelerate geoplolymerization in the feed mixing briquettes, thereby creating aggregate briquettes.

The fly ash material contained in the feed mixing component 101 is fed with predefined amount via metering device 102 into the mixing machine 103. At the same time, the solution of alkaline activator, which was already mixed and contained in the liquid feed tank 104, is fed with predefined amount into the mixing machine 103.

The fly ash material in the present invention is fly ash from thermal power plant or incineration house or volcanic ash, which can be either type F or type C, which mostly contains silicon oxide, calcium oxide, aluminum oxide, iron oxide and carbon and can be considered a type of pozzolan. In the role of pozzolan, a certain amount of fly ash can be replaced by other source of pozzolan, such as volcanic ash, bottom ash, cinder, i.e. the fly ash material can be 100% fly ash or composed of fly ash and other pozzolans.

The alkaline activator in the present invention comprises alkaline activators broadly known in the geopolymer area. Specifically, the alkaline activator is selected from the group comprising: sodium hydroxide, potassium hydroxide, potassium silicate, sodium silicate, molten glass, calcium hydroxide or mixture of them. Molten glass is the aqueous solution of Na ₂ 0.nSi0 ₂ or

K ₂ 0.mSi0 ₂ , wherein n and m are silicate module available on the market, which can be used as independent alkaline activator or mixed with other alkali by any proportion. Usually the alkaline activators are used in solid form, after which they are dissolved in a predefined water amount to become a solution, which are eventually mixed with other constituents.

The mixing machine 103 is used to thoroughly mix the feed mixture comprising fly ash and the solution composed of alkaline activator and additives, the proportion of which is automatically quantified. Due to smoothness of fly ash, the mixing must be thoroughly carried out in order that the output from the mixing machine must be semi-dry (humidity of less than 15%) or semi-plastic (humidity of less than 30%). These mixing machines are available on the market and broadly known. The mixing machine 103 can be the one working constantly or by batch. If needed, it is possible to make arrangement wherein many machines do the mixing constantly to ensure thorough mixing.

The briquette forming machine 105 is used to create the feed mixture briquettes with diameter of at least I mm, and customized length of 1 to 5 times of the diameter. Thanks to the briquette forming machine, the feed mixture constituents are tightly pressed and thoroughly mixed. In order to ensure high productivity, it is best to use sawdust briquette forming machine (recommended) or cattle feed briquette forming machine available on the market.

Fig 3. and Fig. 4 represent two especially preferred embodiments of the briquette mixing machine 105.

As illustrated in Fig. 3, the briquette mixing machine 105 comprises: - briquette forming laminating mold 501 which can rotate around the center at a controllable velocity; is driven by engine (not illustrated in the drawing);

- laminating wheel 502 which is used to laminate the feed mixture into shaping holes on the briquette forming laminating mold 501 ; and

- cutter 505 which can be adjusted to cut the feed mixture briquettes into desired length.

In the embodiment illustrated in Fig. 3, briquette forming machine 105 is a vertical shaft machine. The feed mixture 503, which is output from the mixing machine 103, is dropped on the inner surface of the briquette forming laminating mold 501. The briquette forming laminating mold 501 , when rotating, works with laminating wheel 502 to press the feed mixture 503 into shaping holes on the laminating mold, the extruded cylinder-shaped feed mixture will be cut by the cutter 505 into briquettes 504 with desired length.

As illustrated in Fig. 4, the briquette forming machine 105 comprises:

- two laminating molds (603), which rotate mutually contrariwise with controllable velocity, which contains shaping holes. The feed mixture will be compressed between the laminating molds into the shaping holes on the laminating molds to go through the inner surface of the molds; the laminating molds are driven by engine (not illustrated in the drawing); and

- cutters (505), which can be adjusted to cut the feed mixture briquettes into the desired length, are located near the inner surface of the laminating molds (603). In the embodiment illustrated in Fig. 4, briquette forming machine 105 is a horizontal shaft machine. The feed mixture 503 is loaded into the briquette forming space formed by contact between two briquette forming laminating molds 603. These two briquette forming laminating molds rotate mutually contrariwise to compress the feed mixture into shaping holes on the laminating molds. The cutters are located near the inner surface of the laminating molds to cut the feed mixture briquettes into ones with desired length.

In both embodiments of the briquette forming machine 105, size and number of shaping holes are designed in correlation with feed loading velocity and rotation velocity of the laminating mold. It is best, in order to ensure productivity and quality, if the laminating mold rotates with high velocity to create high pressure and friction onto the feed mixture, thereby heating the mixture to the necessary temperature. This method is especially preferred when the feed mixture is in semi-dry state. The high temperature resulted from friction is sufficient to immediately harden small-sized feed mixture briquettes, thereby creating aggregate briquettes. The term ‘small aggregate’ is literally understood in this area.

According to another preferred embodiment, the system according to the invention thereto comprises hydrothermal autoclave machine 210 located ahead of the dryer 108 to accelerate the geopolymerization process. The hydrothermal autoclaving process helps accelerate the geopolymerization process, promote creation of crystals in the lattice, thereby increase strength of the geopolymeric material. The hydrothermal autoclave machine will supply the feed mixture briquettes with hot steam, possibly with pressure. These briquettes might stay in the machine for at least 15 minutes or several hours.

According to another preferred embodiment, the system according to the invention thereto comprises an extruder 206 located behind the briquette forming machine 105 to extrude the feed mixture briquettes from the briquette forming machine 105. Thanks to this, the briquettes are mixed more thoroughly, the degree of compression is increased which, helps increase contact among constituents. It is best if the extrusion head of the extruder 206 is equipped with the ring heater 207 to directly heat the feed mixture briquettes. Temperature of this ring heater is about 200°C, thereby the feed mixture briquettes can be quickly heated up to 1 10°C or 150°C, hardening the feed mixture briquettes, thereby creating the aggregate briquettes. These briquettes can possibly be put into hydrothermal autoclaving and/or drying processes by the dryer 108, if needed.

The dryer 108 is selected from the group comprising microwave dryer, thermistor dryer, radiation dryer or infrared dryer, it is best to use the microwave dryer. With microwave dryer, the production cycle is significantly shortened because the drying time only takes several minutes.

According to another embodiment, wherein the feed mixture is in semi dry state, water amount is less than 15% of the total weight, with the purpose of producing small aggregates, the system according to the present invention only comprises mixing machine 103, feed mixing component 101 and high-speed briquette forming machine. Rotation velocity of the briquette laminating frames is high enough to induce high friction, thereby producing temperature sufficient to initiate geopolymerization process which is also a heat-generating process that combines with temperature resulted from the friction to immediately produce aggregate briquettes without autoclaving and drying processes.

The system according to the invention, although not described in detail, obviously comprises essential components such as driving engine, conveyor belt 106, milling cutter 107, automatic control and safety devices. Thus, the system composition, depending on the size of aggregates, can be customized to balance productivity, product quality and the production cost.

The aggregate briquettes obtained from the system according to the present invention has dimension similar to sand and stone used in construction. Strength of these aggregates are similar to that of conventional ground filling materials or aggregates, thanks to which ground filling materials, concrete and other construction materials can be made from these aggregates. Compressive strength of the aggregate briquettes is adjusted in accordance with proportion of fly ash material, type of alkaline activator and proportion among them.

ACHIEVABLE BENEFITS

The present invention successfully proposed a system for producing construction aggregates from geopolymeric materials containing fly ash and alkaline activator. These systems can be easily applied in the production reality thanks to its short production cycle, the products obtained from the method can be easily customized to meet the specific demands of application, from small aggregates to coarse aggregates, with size ranging from several millimeters to several centimeters, with strength similar to that of ground filling materials or such aggregates as natural sands and stones.