Extraction and air/water cooling system for large quantities of heavy ashes

Abstract

The present invention relates to an extraction and air / water cooling system and energy recovery for large flows of heavy ashes, produced by solid fuel boilers (100), able to reduce final temperature of the extracted ash, without increasing the air flow entering the throat of the boiler. When the air flow needed for cooling process exceeds the maximum flow admissible in the boiler, the system allows to the exceeding air and to the possible steam to be sent to the fume duct in the most appropriate point, thanks to a separation of the cooling environment 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 at the system exhaust. If the cooling air is not sufficient to cool the ash, the cooling efficiency can be increased by adding atomized water. The added water flow usually is dosed based upon the ash flow and temperature so as to guarantee the full evaporation of the injected water in order to obtain at the exhaust, if necessary, dry ash suitable to be ground and transported pneumatically so as to be mixed to lighter ashes.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a system and a method for extracting, cooling and recovering energy for large quantities of heavy ashes produced by solid fuel boilers.BACKGROUND OF THE INVENTION[0002]The constant growth in the request for solid fossil fuels for the production of electric energy makes more frequent the combustion also of coals and lignites with high ash content. The combustion of the latter in high-power boilers involves a considerable production of heavy ashes, even up to 100 tons / hour, often containing high percentages of unburnt matters. The dry cooling or mainly dry cooling of such quantities requires large quantities of cooling air, even twice or thee times greater than the fossil fuels with high calorific value.[0003]As illustrated in EP 0 471 055 B1, in some known ash extraction and dry cooling systems, cooling air, once heated due to the thermal exchange with the latter, is introduced into the boiler from the bottom thereof. There...

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Benefits of technology

[0010]The main advantage consists in that the present invention allows to carry out an adequate, effective and efficient dry cooling or mainly dry cooling of the ashes without exceeding the above-mentioned limit of 1.0-1.5% for the cooling air introduced into the combustion chamber from the bottom. Such advantage is particularly important in the above-mentioned case of coals with high content of heavy ashes. This is mainly obtained by separating the whole extraction and transport system into two environments with different atmospheric pressure, the first one connected to the combustion chamber and the second one to the economizers' area. Such separation, among other things, allows sending to the latter area some air exceeding the above-mentioned 1.5% and the possible steam contained therein.

[0011]Based upon a preferred and particularly advantageous embodiment, said environment separation is implemented by means of a head of the same transported ash and therefore substantially without the need of additional devices for the system. This allows obtaining the above-mentioned effective cooling also of large flows of ashes with high temperature by keeping, however, an extreme construction and operation simplicity of the system itself, to the advantage of the implementation, handling and maintenance costs. Based upon such preferred embodiment, the invention substantially allows to optimize the system described in EP 0 471 055 B1 by widening the potentiality of applications thereof to large flows of heavy ashes coming from coals or lignites with high ash content.

[0013]The separation of the environments of the cooling system is automatically handled by the system upon ash and / or flow measurement performed at the exhast. If the cooling air is not sufficient to cool the ash, the cooling effectiveness can be increased by adding atomized water. The added water amount usually is dosed based upon the ash flow and temperature so as to guarantee the full evaporation of the injected water to obtain if necessary, at the exhaust, dry ash, suitable to be ground and transported pneumatically. The water has the great advantage, with respect to air, to allow an effective cooling of the ash itself with considerable lower weight quantities (in a ratio around 1:100 under the working conditions which are considered in this case) and it allows then a drastic reduction of the air quantity to be sent to the fume duct. This allows reducing the negative impact, until making it practically negligible, that an increase in the quantity of the fumes involves for the possible oversize of the apparatuses and the increase in the energy necessary for treating the fumes themselves until the ejection from the chimney.

[0021]7. a final discharge apparatus, able to allow the discharge of the ash by preventing at the same time the entrance of uncontrolled air into the system (for example a valve or a vibrating extractor or simply a closed connection with other transport or storage closed apparatus);

[0024]a final discharge apparatus equivalent to the one described in item 7., able to allow the ash discharge from the system by preventing at the same time the re-entering of the outer air;

Problems solved by technology

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

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

In particular, even when such cooling, recovery of the thermal energy and disposal are succeeded to be obtained, they are achieved with considerable plant complications and with consequent very high implementation and handling costs.

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