Method of extracting heat from manure sewage mud and other wet w

Details Method of extracting heat from manure sewage mud and other wet w Method of extracting heat from manure sewage mud and other wet w

1980-11-17

1982-11-16

Favors, Edward G.

Furnaces

Process

Incinerating refuse

110224, 110238, F23G 504

Patent

active

043590063

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method of extracting heat from manure, sewage mud, and other wet waste by combustion, the method comprising using a combined drying-, combustion-, and steam-condensing-process.
2. Description of the Prior Art
Organic waste such as for instance manure and sewage mud occurs in large quantities and often causes problems as a consequence of the content of vira, unpleasant smelling substances or dangerous toxicants. This implies that spreading of the organic waste in fields has been prohibited or connected with the risk of infection and inconveniences for the surroundings.
The wet waste contains a considerable amount of energy, which as for the manure alone corresponds to about a quarter of the energy annually consumed for heating in Denmark.
The extraction of heat from this waste is, however, difficult due to the high content of water, which implies that a direct combustion is impossible. Instead of combustion, biological methods for converting the substances may be employed, anaerobic conditions permitting generation of gas and aerobic conditions permitting generation of heat. These methods, however, require rather expensive plants, and in practice maximum about 30% of the total energy of the waste can be extracted.
By mixing sewage mud and household waste in an appropriate ratio, it is possible to combust the mud. However, the major part of the energy of the dry matter is used for evaporating the water and is thereby lost through the chimney.


SUMMARY OF THE INVENTION

The method according to the invention for extracting heat from manure and other wet waste by combustion is characterised in that the waste is dried prior to the combustion and the drying is performed by means of heat from the combustion of already dried waste, the entire amount of flue gas from the combustion, which is mixed with auxiliary air to obtain an appropriately low temperature of the drying air, being blown through the wet waste in the drier in such a manner that the water content is reduced. Furthermore, the method is characterised in that the flue gas mixed with auxiliary air after having passed through the drier is carried through a scrubber, i.e. an apparatus in principle constructed as a cooling tower. In this tower the air is cooled during the condensation of steam at the same time as the wash water is heated. Moreover, the method may have the special feature that the wash water releases the heat in a heat exchanger connected to a heat consumer. Having passed the heat exchanger, the wash water is carried to a clearing tank, in which impurities are precipitated before the wash water is recirculated to the scrubber by means of a pump.
By this method, waste having a water content of up to about 80% may be combusted at the same time as 50 to 70% of the energy contained in said waste is extracted as heat at a temperature sufficiently high for direct use for space heating. The method furthermore ensures that dust and fumes are intercepted by the water in the scrubber. Furthermore, the wash water intercepts part of the nitrogen and sulphur compounds as well as smelling substances deriving from the combustion and the drying. As a result the discharge air is cooled and cleaned in such a manner that a chimney in most cases is unnecessary.
The most simple method according to the invention is preferably a continuous drying-, combustion-, and steam-condensing-process, which can utilize the energy in waste containing up to about 80% of water, and which operates with a moderate efficiency.
The efficiency may, however, be essentially improved by recirculating part of the discharge air and use it as auxiliary air, whereby the loss of energy in the discharge air is reduced.
In preparation of combustion of still wetter waste containing up to about 85% of water, energy may furthermore be recirculated to the drier by preheating the auxiliary air and optionally also the combustion air by passing said air through an air heater receiving hot water from the heat e

REFERENCES:
patent: 2032402 (1936-03-01), Colby et al.
patent: 2066418 (1937-01-01), O'Mara
patent: 3734036 (1973-05-01), Abos
patent: 4213407 (1980-07-01), Headley
patent: 4245570 (1981-01-01), Williams

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