PRODUCTS INTENDED FOR COMBUSTION

Technical field

This invention concerns a procedure for the manufacture of pellets and briquettes and other products intended to be combusted, particularly such as are made from wood mass, making use of a disintegrator and utilising the waste heat.

Background Art

The current procedure to manufacture pellets, briquettes and other products consisting mainly of wood mass is as described below - this is an example of the design, modifications are possible:

1. Pellets and briquettes and other products intended to be combusted are mainly made from sawdust obtained by sawing timber. Prior to pelleting it, the raw material (sawdust) must be modified to the required parameters for feeding to the pelleting/briquetting press in which the core of the manufacture of the pellets, briquettes or other products intended to serve as feedstock for combustion proceeds.

2. The sawdust must be freed from unwanted admixtures, such as pieces of wood, stones and sand; pieces of metal from the saw mill, ferromagnetic and/or non-ferrous, may also be present.

3. The moisture content must then be reduced roughly to 12% and the material crushed to the required size.

4. The raw material, largely sawdust, dried solely by using external heat, produced by firing fossil fuels or biomass. The dry raw material is fed to the pelleting or briquetting press for pressing into the required shape.

The drawbacks of this process include high energy use, particularly for drying the incoming material.

Disclosure of the invention

The drawbacks outlined above are largely eliminated by the procedure based on this invention, where the technological procedure - production line - includes a branch with a disintegrator, with one disintegrator as a minimum serving to crush a fraction of the material into tiny, dust particles - the crushed component, which is dried directly in the disintegrator to the required moisture content by using the waste heat generated during the crushing process, the water vapour generated being exhausted off the facility. The crushed fraction coming from the disintegrator possesses a moisture content and particle size different from those of the sawdust coming from the conventional line branch. The two fractions are mixed at a specific ratio to form a mixture whose properties are appropriate for subsequent pressing on a pelleting/briquetting press. The moisture contents of the sawdust and of the crushed component as well as the particle size of the constituents are monitored continuously and the proportions of the components are modified to achieve correct mixing. The precise proportioning and input parameter monitoring enable a high-quality product to be obtained. This sawdust/crushed component mixture not only exhibits better bonding properties: it also ensures a lower moisture content of the final product owing to the presence of the crushed component, prior subjected to the drying procedure. In other respects the procedure is no different from the established procedures.

The share of the crushed component (coming from the disintegrator) in the final mix lies within the range from 25 vol.% to 98 vol.%. The ratio of the fractions is controlled based on the water content of the incoming material (sawdust), which may be different depending on the season of the year and on the starting type of timber.

The main benefit of and reason for using the disintegrator is major energy savings during the manufacture of the pellets, briquettes or other products serving as feedstock for combustion. Owing to the drying of the crushed fraction in the disintegrator by using the heat generated in the system, the dependence of the drying heat is lowered appreciably, so that the amount of heat required to dry the sawdust can be reduced to 20% compared to the background status.

1. The conventional drum dryer or belt dryer for drying the sawdust, which requires heat from an external source, is completed with a system enabling the wood mass to be dried by mechanical energy of the disintegrator.

2. Drying of the crushed fraction in the disintegrator is considerably more efficient than moisture removal with a warm air stream on a conventional dryer.

3. The system breaks down the solid particles, thereby generating a certain amount of heat.

In addition, the fraction being crushed in the disintegrator chamber collides / impacts on the rotating parts of the system. The heat generated together with the energy of the motion is able to heat the material very efficiently, whereby water is released as vapour and exhausted off the system. 4. The drying process in the disintegrator is very fast and efficient.

5. The drying process and the crushed fraction properties are controlled through the disintegrator setting.

6. The drying process in the disintegrator can be monitored very precisely by using appropriately selected sensors.

7. It has been demonstrated during the research that appropriate control of the crushed fraction can improve the physical properties of the product, in particular, reduce the crumbliness of the pellets/briquettes/other fuel material. The fine fraction, added in an appropriate proportion, improves appreciably the pellet's abrasion resistance, one of the principal quality indicators.

8. The crushed fraction-to-sawdust ratio can be varied to control the raw material moisture content throughout the manufacturing process, thereby improving the material passability through the press. So refined, the manufacturing process reduces the energy used by the press and improves the pressing efficiency. The pellets, briquettes or other feedstock for combustion leaving the press possess a precisely defined moisture content.

9. The proposed technical solution is used for the manufacture of pellets and briquettes and is applicable to the manufacture of other feedstock for combustion as well. The pellet quality can be improved by adding a fraction of the dried uncrushed sawdust to the crushed component.

10. Compared to the conventional processes, the solution proposed is considerably less energy demanding while enabling higher-quality pellets, briquettes ad other feedstock for combustion to be manufactured.

11. Addition of a disintegrator to the drying section of the line enables the line throughput to be increased also in settings where heat input cannot be increased any more.

Brief Description of the Drawings

The manufacturing chain will be better illustrated on a drawing, Fig. 1 showing the layout of the production line for the manufacture of pellets and briquettes and, as the case may be, other feedstock for combustion.

Modes for carrying out the invention The transporting and proportioning conveyor 1_ conveys the sawdust to a belt dryer 2 and a fraction of the semi-finished product to a disintegrator 3. The semi-finished product is crushed in the disintegrator 3 to tiny wood dust particles - the crushed component, and heat is generated by the crushing process and is transferred to the crushed material directly in the disintegrator. Owing to this the crushed material is heated and dried. The moisture released, i.e. water vapour, is exhausted off the disintegrator 3. Subsequently, the semi-finished product from the belt dryer and from the disintegrator is fed into a mixing bin 4, where the dry sawdust and the crushed fraction are mixed in a predetermined ratio into the feedstock for the press to obtain pellets, briquettes or other fuel products. The proportioning conveyor sends then the mix to the pelleting press 5 and the pellet conveyor conveys the product for packaging.

Industrial applicability

The procedure is applicable to the production of pellets, briquettes and other wood products primarily intended for combustion.