Extracting and cooling system for large flows of heavy ashes with efficiency increase

Abstract

The present invention relates to a system for extracting and recovering energy for large for large flows of heavy ashes produced by solid fuel boilers, able to decrease the final temperature of the extracted ash without increasing the air flow entering the boiler flue, usually fixed by the boiler designers at a value around 1.5% of the total combustion air. When the air flow needed to the cooling exceeds the maximum quantity allowable in the boiler, the system allows the air and the possible vapour to be sent to the air inletting duct entering the air / fume exchanger on the air side, thanks to a separation of the cooling environments made by the ash itself. The separation of the environments of the cooling system is handled automatically based upon a temperature signal of the ash to the discharge from the system. If the cooling air is not sufficient to cool down the ash, the cooling efficiency can be increased by the addition of nebulised water.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a plant and to a method for extracting, cooling and recovering thermal energy for large flows of heavy ashes produced by solid fuel boilers.BACKGROUND OF THE INVENTION[0002]The continuous increasing demand for solid fossil fuels for the production of electric energy makes more and more frequent the combustion of coals or lignites with high ash content, too. The combustion of the latter in high power boilers involves a huge production of heavy ashes, even up to 100 tons / hour, often containing high percentages of unburnt materials. The dry or mainly dry cooling of such quantities requests huge cooling air flows, even two or three times higher than the fossil fuels with high heat-producing power.[0003]As illustrated in EP 0 471 055 B1, in some known extraction and dry cooling of ashes the cooling air, once heated under the effect of the thermal exchange with the latter, is introduced into the boiler from the bottom thereof. T...

AI Technical Summary

Benefits of technology

[0015]The main advantage lies in the fact that the invention allows to maximize the recovery of the sensible heat contained in the exceeding cooling air used in the second plant portion downstream of the pressure insulation.

[0035]a discharge end apparatus equivalent to the one described at step 8, able to allow the ash discharge from the system by preventing at the same time the outer air return;

Problems solved by technology

The combustion of the latter in high power boilers involves a huge production of heavy ashes, even up to 100 tons / hour, often containing high percentages of unburnt materials.

As to what just illustrated, the known cooling systems do not succeed in implementing in an effective and efficient way the dry or mainly dry cooling of the heavy ashes and the disposal of the related cooling air, above all if said ashes are in large flows, with high content of unburnt materials and therefore at high temperature.

In particular, even if one succeeds in obtaining said cooling, thermal energy recovery and disposal, they are reached with huge plant complications and consequent very high implementation and handling costs.

In fact, in case of inletting hot air downstream of the air / fume exchanger the thermal content of the cooling air is wholly lost and it translates in an overall temperature increase in the flue fumes, apart from increasing the power absorbed by the apparatuses necessary for the fume process.

In case of inletting the hot air into the fume duct upstream the exchanger, as the cooling air is at a lower temperature than the combustion fume flow, a whole increase in the flow of hot air flow+fumes inletting the exchangeresults, which worsens the efficiency of environment air / fume thermal exchange of the device.

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