Heating – Work chamber having heating means – Combustion products heat work by contact
Reexamination Certificate
2000-03-17
2001-05-22
Wilson, Gregory (Department: 3748)
Heating
Work chamber having heating means
Combustion products heat work by contact
C431S215000, C126S09100A
Reexamination Certificate
active
06234789
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an alternate changeover regenerative burner system. More particularly, the present invention relates to an alternate changeover regenerative burner system suitable as a heat source for an industrial furnace and others in which re-increase in temperature is relatively often performed.
DESCRIPTION OF THE PRIOR ART
A prior art alternate changeover regenerative burner system comprises: a pair of burners each of which has a regenerator; and air supply/exhaust switching means for switching supply and exhaust of oxidizer such as air, oxygen-enriched air, pure oxygen and others (which will be simply referred to as combustion air in this specification) between this pair of burners, and the system alternately burns the pair of burners (the currently-burning burner will be referred to as a burner performing combustion) and exhausts gas in a furnace from a non-combusting burner (which will be referred to as a burner performing exhaust) to recollect heat of the exhaust gas from the regenerator so that the heat can be used for preheating the next combustion air. In this alternate changeover regenerative burner system, multiple systems are usually provided to an industrial furnace, namely, burners whose number is a multiple number of 2 are provided, and the half of the burners is alternately burned. The remaining half of the burners is used as burners performing exhaust from which the furnace gas is exhausted.
Meanwhile, in a furnace in which re-increase in temperature is often performed, for example, once a day, once a week and the like, a capacity of the burner is generally determined on the basis of a quantity of combustion in case of the rapid increase in temperature for improving the operation ratio. This is also true in the industrial furnace having the alternate changeover regenerative burners, and the operation is performed with a low quantity of combustion as compared with the capacity of the burner in the actual operation.
However, since a ratio of the number of burners performing combustion to the number of burners being stopped is always fixed and these numbers forms a rigid pair, although a non-stationary flame is formed, a flame only shifts between the pair of burners. Therefore, there is a limit in formation of the non-stationary flame, and such a formation may not be sufficient in some cases.
Further, since a total quantity of combustion of the burners becomes equal in the warm-up operation and in the subsequent operation (operation after the furnace temperature has reached a predetermined temperature), the high air velocity can not be maintained in the operation as a quantity of combustion is low as compared with the burner capacity, and agitation of the furnace gas having the low density of oxygen and entrainment of the furnace gas can not be satisfactorily active. This causes the furnace atmosphere having differences in temperatures at some places to be formed (the distribution of the furnace temperatures is not sufficiently smoothed), leading to such a tendency as that a region, in which a furnace temperature is locally high, is formed to increase an amount of generation of NOx. On the other hand, when designing the system so as to increase the air flow velocity in the high furnace atmosphere in the rated operation for reducing NOx, a low amount of generation of NOx can be maintained, but the temperature-up velocity is obliged to slow down because the capacity of combustion during the increase in the temperature can not be set high. As a countermeasure for avoiding inconsistency of the NOx reduction during the rapid increase in temperature and in the rated operation, a part of burners may be suspended, but there occur other problems such as protection of the burner suspended in the rated operation from the overheat and unevenness of the furnace temperature due to space or absence of a part of burners. As another measure for avoiding the inconsistency, changes in size or number of air nozzles can be considered, but a valve mechanism which opens and closes in a high-temperature portion is required, and hence this is practically difficult.
It is therefore an object of the present invention to provide an alternate changeover regenerative burner system capable of maintaining a high flow velocity of air belching from a burner throat even if operating with a quantity of combustion lower than a capacity of burner. It is another object of the present invention to provide an alternate changeover regenerative burner system by which a flow velocity of air belching from a burner throat is variable irrespective of changes in a quantity of combustion. It is a further object of the present invention to provide an alternate changeover regenerative burner system capable of forming a non-stationary flame in a wide range.
DISCLOSURE OF THE INVENTION
To achieve this aim, in an alternate changeover regenerative burner system according to the present invention, in a burner system which operates with a quantity of combustion during the rated operation after increasing a temperature reduced to be smaller than that during the warm-up operation, three or more units of alternate changeover regenerative burner, which is regarded as a module unit and composed of a burner having a regenerator and an air supply/exhaust switching device for switching connection to an air supply system and an exhaust system of the burner, constitute a combustion system, and the all units sequentially repeat alternate regenerative combustion without forming fixed pairs of units; a ratio of the number of burners performing combustion and the number of burners performing exhaust is variable depending on the warm-up operation for increasing a furnace temperature and the operation after increasing the temperature; and the operation after increasing the temperature is carried out with the burners performing combustion whose number is smaller than that of the burners performing combustion during the warm-up operation. Here, it is preferable that the relationship between the number of the burners performing combustion and the number of the burners performing exhaust is such that the number of the burners performing combustion is equal to or larger than the number of the burners performing exhaust during the warm-up operation and the number of the burners performing exhaust is larger than the number of the burners performing combustion during the rated operation after increasing the temperature, and it is also preferable that the number of the burner units are set to five or more units and the number of the burners performing combustion is slightly smaller than the number of the burners performing exhaust during the warm-up operation while the number of the burners performing combustion is greatly smaller than the number of the burners performing exhaust during the rated operation after increasing the temperature. Even if the burners performing combustion differ from the regenerative burners in number. The relationship between a quantity of air supply and that of exhaust does not vary even if the burners performing combustion differ from the regenerative burners in number. That is, even if a ratio of number of the burners performing combustion and that of the burners performing exhaust is 1:1 or 1:2, both a quantity of air flow and a quantity of exhaust do not change in terms of a single step. However, if the ratio of the burners performing combustion is reduced, the ratio of the air time is also reduced by just that much, and a fluid velocity flowing through the regenerator is high in case of air while the same is low in case of exhaust. Heat transfer for cooling is enhanced, and hence the efficiency of the regenerator tends to be improved. In other words, a temperature of heating air becomes high while a temperature of exhaust is lowered.
Therefore, when operating with a quantity of combustion smaller than the burner capacity, after increasing the temperature, a flow velocity of air injected from a burner throat of each burner can be maintained high by reducing the number
Nippon Furnace Kogyo Kabushiki Kaisha
Notaro & Michalos P.C.
Wilson Gregory
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