Furnaces – Process – Treating fuel constituent or combustion product
Patent
1994-08-15
1996-09-10
Bennett, Henry A.
Furnaces
Process
Treating fuel constituent or combustion product
110348, 110211, 110215, 110235, F23J 1100, F23J 1500
Patent
active
055535569
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for burning solid matter, particularly for incinerating garbage, in a combustion boiler, which comprises at least one combustion chamber and at least one afterburner chamber, steam being introduced into the combustion boiler.
Pollutant-containing waste gases are formed during the incineration of solid energy carriers, such as garbage or coal. For ecological and economic reasons, the combustion should be carried out with an optimum excess of air, in order to minimize the amounts of waste gases and pollutants. However, for process and equipment reasons, the ecological and economically optimum modes of operation frequently are in contradiction with one another.
Adequate combustion of the flue gases with the oxygen of the air is assured only if there is an excess of air and corresponding turbulence in or directly above the combustion chamber. To produce these turbulences, a portion of the combustion air is usually blown in as secondary air with a slight pressure and moderate velocity. The formation of carbon monoxide and nitrogen oxides is to be decreased in this way. The amount of secondary air blown in must be sufficiently large in order to ensure, at the same time, the necessary turbulence and, with that, adequate mixing. However, due to this excess air, the amount of waste gas and, with that, the loss of usable energy increase noticeably.
The adiabatic combustion temperatures fall appreciably as the excess of air increases. For example, at a high excess of air, additional formation of carbon monoxide can be caused by overcooling the combustion gases due to the addition of the secondary air. In the boundary region of the secondary air flow, however, high temperature peaks can occur which, in conjunction with the locally high oxygen concentrations, contribute to the formation of NO.sub.x.
During the incineration of garbage, the oxygen concentration in the moist flue gas after the combustion boiler usually is about 10% by volume. In this case, the excess of air is about 150%, corresponding to an air ratio of 2.5. Between 10% and 40% of the combustion air is usually blown in as secondary air. A reduction in the secondary air leads to less complete combustion of the combustion gases, while a reduction in the primary air leads to less complete combustion of the slag.
It is a further objective of the secondary air to achieve a certain flame guidance. By these means, the ascending convection current in the first flue of the combustion boiler (afterburner chamber) is to be broken and, with that, a narrow residence-time spectrum is to be produced in the first flue. At best, this objective has previously been attained incompletely. Because of the additional amount of air, the use of tertiary air for breaking the ascending convection current has also only been of limited usefulness since, for instance, additional carbon monoxide is formed and further amounts of flue gas result from the cooling.
It is a significant disadvantage of previous methods that, for reliably combusting the waste gases completely and for breaking the ascending convection current, large amounts of secondary or tertiary air are required. The addition of these large amounts of air is possible only if, at the same time, the amount of primary air is reduced, in which case, however, the completeness of the combustion on the grate is endangered. Increasing the amount of flue gas moreover leads to a shorter, average residence time in the first flue. An optimum breakdown of pollutant is therefore not ensured. Moreover, the adiabatic combustion temperature is lowered by the increased amount of air. The temperature reduction in the region of the steam generator therefore proceeds correspondingly flat. As a result, the heat utilization is decreased appreciably.
It is an object of the present invention to develop a method for incinerating solid matter, with which it is possible to decrease the amounts of pollutants in the flue gas. At the same time, either the amount of flue gas is to be decreased appreciably while t
REFERENCES:
patent: 3473331 (1969-10-01), Fernandes
patent: 4285282 (1981-08-01), Good
Bennett Henry A.
Mullkraftwerk Schwandorf Betriebsgesellschaft mbH
Tinker Susanne C.
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