Method of controlling combustion in fluidized bed incinerator

Details Method of controlling combustion in fluidized bed incinerator Method of controlling combustion in fluidized bed incinerator

1989-07-28

1991-01-22

Favors, Edward G.

Furnaces

Process

Incinerating refuse

110188, 110189, 110190, 110245, 122 4D, F23G 300

Patent

active

049861980

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a method of controlling combustion in a fluidized bed incinerator which is suited to inhibit the discharge of gas not yet burnt without causing fluctuations in the amount of air available for combustion and the amount of gas discharged by controlling the combustion rate of matters to be incinerated which is charged into a furnace, i.e., the combustion rate per unit time in a fluidized bed incinerator for burning matter to be incinerated by causing fluidization of a fluidizing medium such as sand or the like with the aid of air fed from the lower portion of a furnace bed. The fluidized bed incinerator used herein includes a fluidized bed boiler designed for heat recovery.


BACKGROUND OF THE INVENTION

Fluidized bed incinerators have heretofore been used for incinerating municipal refuse. Where municipal refuse is burnt in a fluidized bed incinerator, refuse is consecutively charged into it. In the great majority of cases, a tremendous amount of trash is charged in one mass with different articles entangled with each other and forced into an agglomerated mass. Fluidized bed incinerators have a rather higher rate of combustion than other types of incinerators, and also exhibit the advantage of providing in some cases a condition in which matter is well burnt. Paradoxically, this causes the drawback that, once the matter to be incinerated has been charged into the fluidized bed, it may be burnt within a few seconds because of the high combustion performance. For this reason, if the feeder used to feed the matter to be incinerated into the furnace is inferior in terms of maintaining a constant feed rate, there will be a problem in that any variation in the amount of matter to be incinerated which is charged into the furnace will directly lead to fluctuations in the concentration of oxygen contained in the combustion gas.
If the concentration of oxygen contained in the discharged combustion gas is approximately 5% or less, the critical amount depending on the type of fluidized bed incinerator, carbon monoxide and carbon hydrides such as methane, ethylene, propylene, acetylene and benzene will be discharged without being completely burnt. Thus, materials such as ammonium chloride and ammonium hydroxide will be generated, which lead to the emission of white smoke from the stack. Because fluidized bed incinerators exhibit high combustion performance, combustion can be effected so long as the superficial velocity of the fluidizing air is adequate for fluidization even if the theoretical air ratio of the fluidizing air blown into the fluidizing medium is smaller than 1. In order to inhibit the generation of unburnt gases such as carbon monoxide, however, the air ratio is increased. In some cases, extra air is fed beforehand so as not to reduce the concentration of oxygen even if the supply of the matter to be incinerated is increased to cope with the risk that the ability of the feeder to provide a constant feed rate will deteriorate.
The amount of air blown into the furnace is, at the maximum, twice as much as the theoretical quantity of air, depending on the ability of the feeder to ensure a constant feed rate. Even in this case, however, the various items of refuse are entangled with each other to form large agglomerated lumps, particularly when dealing with the municipal trash. Finally, a so-called massive drop takes place, leading momentarily to a lack of oxygen, and thus unburnt gas (not yet burnt) like carbon monoxide is sometimes discharged from the stack.
In prior art methods of inhibiting the discharge of unburnt gas, it has been necessary to improve the capability of the feeder to provide a constant feed rate. In addition, as disclosed in, e.g., Japanese patent application No. 223198/1984 (Japanese Patent Laid-Open No. 100612/1986), a measuring means may be provided for the purpose of measuring the amount of matter for incineration actually charged, allowing that amount to be reduced by lowering the rotational speed of the feeder when it is sensed t

REFERENCES:
patent: 4499857 (1985-02-01), Wormser
patent: 4742783 (1988-05-01), LaSpisa et al.

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