Method for making briquettes from comminuted straw and a device to produce briquettes

The subject of the invention is a method for the manufacture of briquettes from comminuted straw, as well as a device to manufacture briquettes from comminuted straw. The method consists in that comminuted straw is compressed in a continuous process using a screw-type extruder until the material reaches a temperature at which the material after pressing solidifies to a density exceeding 1.3 g/cm 3. The device has a screw (3) composed of three segments of decreasing helix pitches toward the outlet. The forming die (8) is housed in a tank (11) connected through a water system (12) to a cooler (13). The cooling system has a temperature sensor (17) installed, said sensor being part of the pump supply circuit (15).

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Section 371 National Stage Application of International Application No. PCT/PL2010/000049, filed Jun. 18, 2010 and published as WO 2010/147493 A1 on Dec. 23, 2010, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The subject of the present invention is a method for making briquettes from comminuted straw and a device for producing briquettes from comminuted plant waste.

PRIOR ART

Known methods for making briquettes from comminuted plant feedstock rely on compressing the raw material in a screw-type extruder while heating the extruder barrel and the forming die using electric heaters. During the compression the material solidifies, with the outer layer of a briquette formed having the most compact structure. In order to reduce cross-sectional heterogeneity of the resulting end product, the product is made in the form of a cylinder with a central hollow.

Polish patent No 198907 discloses a screw-type briquetting machine having a screw consisting of two segments, the first of which, counting from the inlet has a greater diameter and helix pitch than the other one which serves as a densitying segment of the screw. The barrel working chamber and the die are heated. Fitted at the face of the forming die is an annular die with a guide with pressure control. The screw is supported on bearings and actuated through an electric motor and a gearbox. The extruder barrel is equipped with a chute to supply the feedstock from a hopper. Solution to the problem

SUMMARY

According to the present invention, comminuted straw, pre-dried to a moisture content between 15 to 25%, is fed to a screw extruder and then gradually compressed until it reaches a temperature above 290° C. and a density above 1.3 g/cm3, and the resulting mass is extruded in a continuous process in the form of a cylinder with a uniform structure. During the extrusion a constant temperature span is maintained at the die, not exceeding 340° C. Preferably, the mass resulting from such compression has a density in the range from 1.3 to 1.5 g/cm3.

The subject of the present invention is also a device for the manufacture of briquettes from comminuted straw, said device having disposed in the barrel a three-segment screw with different helix pitches, said segment pitches decreasing toward the outlet. The forming die, disposed downstream the screw, is housed in a tank connected via a water system to a pump and a fanned cooler.

Preferably, a temperature indicator and a temperature sensor are installed inside the tank, integrated into the supply system of the pump.

The barrel chute is connected to a hopper equipped with a screw feeder driven by a separate motor. The motor of the screw feeder is equipped with a rotation speed controller. Screw feeder helix mates the arms of a rotating scraper installed on an inclined wall of the hopper.

ADVANTAGEOUS EFFECTS OF INVENTION

The method according to the present invention allows obtaining briquettes with a uniform structure throughout the transverse cross section. The feedstock, heated uniformly throughout its mass has a stable form that does not change during long storage. In steam environment, the raw material is converted into compact briquettes. This process of briquette manufacture results in obtaining a 100% natural and ecological fuel. Since the final product is characterized by a compact structure, its combustion is a process of long duration.

The briquetting device according to the present invention is energy-efficient, because attaining the right temperature does not require any heaters. The hopper ensures continuous and uniform feeding of the raw material in the form of comminuted straw. The device is also able to operate at negative temperatures.

DESCRIPTION OF EMBODIMENTS

First, comminuted rye straw was prepared in a comminutor, then the straw was pre-dried to 20% moisture and fed to the briquetting machine's hopper. After the hopper had been filled with the comminuted straw, the screw feeder and the extruder screw were started simultaneously. The straw was gradually compressed. Screw rotation speed was initially set at 5 rpm and the machine operated at that speed until steam appeared at the outlet of guide10, then the speed was increased to 25 rpm. During the operation of the extruder screw, the temperature of the raw materials was rising. Initially, the stabilizing sleeve produced incompletely solidified briquettes. After 5 minutes, as a result of temperature rise, the outgoing product in cylindrical form had reached the required density of 1.3 g/cm3. The temperature sensor of the cooling system was set at 50° C. After that value had been exceeded, the cooling system pump was started. Further, the process ran in a continuous mode, provided that the material in the hopper was made-up when necessary. In case that excessive accumulation of raw material is found at the hopper outlet, the rotation speed of the screw feeder driving motor is reduced.

Comminuted straw, pre-dried to 15% moisture, was fed to the briquetting machine's hopper and processed like in Example 1. The product obtained in the form of a cylinder had a density of 1.4 g/cm3.

A device for the manufacture of briquettes is reproduced, as an example, in the enclosed drawing in whichFIG. 1shows the device in partial cross section along the axis of the barrel, andFIG. 2is a side view with a section of the hopper.

Inside the barrel1which is seated on a foundation2there is disposed a screw3whose shaft4, supported on bearings5, is driven by an electric motor6through a belt transmission7. The screw3has three helix segments of decreasing pitch toward the outlet. Bolted at the face of the barrel1is a forming die8having a conical bore, which is connected to a stabilizing sleeve9. The stabilizing sleeve9has a guide10attached to it. The forming die8is housed in a cooling liquid tank11which is connected through the water system12to a fanned cooler13equipped with a fan14. The water system12is equipped with a pump15and a temperature indicator16, while at the tank11a temperature sensor17is installed which is part of the supply system of the pump15. The barrel1has a chute18connected to a hopper19, at the bottom of which there is a screw feeder20driven by an electric motor21while on an inclined wall of tank19a rotary scraper22is installed whose ends mate the helix of the screw feeder20.