Heating – With work cooling structure – Combustion feed air cools exiting work by contact
Patent
1996-01-24
1998-07-07
Joyce, Harold
Heating
With work cooling structure
Combustion feed air cools exiting work by contact
432 77, 432 85, F27D 1502
Patent
active
057758913
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In grate coolers for combustion material, especially for the cooling of cement clinker, the combustion material expelled from the associated kiln forms a bed on the cooler grate, which bed is flowed through by cooling air, which picks up heat and dust. Part of the cooling air is returned via a heat exchanger to the cooler. Another part is fed to the kiln as secondary air for the combustion operation. The missing volume of air is supplied as fresh air to the cooler. Ideally, a cooler of this kind can be operated free from waste air, i.e. there is no waste air passed directly into the atmosphere. This objective has so far proved unattainable in practice, since, given certain irregularities in the kiln operation, a large quantity of combustion material may briefly accumulate in the cooler, causing the temperature and volume of the secondary air and hence the pressure in the kiln hood to rise strongly. Whilst the kiln hood pressure can be regulated, under normal operating conditions, by adjusting the volume of cooling air fed to the cooler, the volume of cooling air cannot be adequately reduced when considerable quantities of combustion material suddenly accumulate, since a certain minimum volume of cooling air is necessary to prevent heat damage to the cooler. Although consideration has been given to regulating the kiln hood pressure by adjusting the drawoff from the kiln to cope with unsteady states, this is impracticable because of the long time lag. It has therefore been necessary to resort to installing an emergency stack, by means of which, in irregular states, waste air is drawn off from the cooler; this is contrary, however, to the notion of a waste-air-free system. In addition, circulating-air processes have been developed, which meet their stumbling block, however, in the additional energy which has to be expended.
In this context, it should be borne in mind that remedy is difficult, above all because the kiln and cooler constitute, in control-engineering terms, an oscillatory system. An increased accumulation of combustion material in the cooler produces an increase in secondary-air temperature. This leads to increased temperature in the kiln and hence to the formation of a higher melt-phase component in the sintering zone. This results in a temporarily reduced discharge of combustion material from the kiln, causing a renewed drop in the secondary air temperature and hence in the melt-phase component of the clinker, which again brings again a rise in material discharge and the commencement of a new cycle. In one particular example, for instance, the secondary-air temperature fluctuated between around 700.degree. C. and 850.degree. C. and the kiln drive current (as a measure of the kiln charge) fluctuated between around 180 and 250amperes in opposite directions with an oscillation period of around 2 hours. The rise in secondary-air temperature and the fall in the drive power of the kiln generally occurred abruptly within just a few minutes.
Attempts have been made to even out the energy flow by means of a variable booster-firing operation; this should be rejected however, since it adversely affects the recuperation of the cooler; for the secondary-air temperature would then need to be permanently lowered, even in the steady state.
It is also known (FR-B 2 102 623) to adjust the temperature of the secondary air to be fed to the kiln by proceeding to feed cooling air of different temperature from two different sources to the first cooler sections from which the secondary air originates as waste air. By suitably determining the relationship between the two air volumes to be fed, it is possible within certain limits to exert influence upon the secondary air. This influence materializes very slowly, however, and is too weak to produce a reasonably rapid reaction to an irregularly strong kiln discharge. The complexity of equipment which is required to provide two air-supply sources of different temperature is also very high.
The object of the invention, where there is an elevat
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Harder Joachim
Klintworth Klaus
Babcock Materials Handling Division GmbH
Joyce Harold
Lu Jiping
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