Combustion – Process of combustion or burner operation – Flame shaping – or distributing components in combustion zone
Reexamination Certificate
2001-03-09
2003-02-25
Ferko, Kathryn (Department: 3743)
Combustion
Process of combustion or burner operation
Flame shaping, or distributing components in combustion zone
C431S354000, C431S181000, C431S190000, C239S400000
Reexamination Certificate
active
06524097
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable
BACKGROUND OF THE INVENTION
The present invention pertains to oxy-fuel methods and devices for producing elevated temperatures in industrial melting furnaces for such diverse products as metals, glass, ceramic materials and the like. In particular, the present invention pertains to combustion and methods and apparatus for continuation of combustion in the event of curtailed or terminated availability of oxygen for the oxy-fuel process.
Use of oxy-fuel burners in industrial processes such as glass melting, permits the furnace designer to achieve varying flame momentum, glass melt coverage, and flame radiation characteristics. Examples of such burners and combustion processes are described in U.S. Pat. Nos. 5,256,058, 5,346,390, 5,547,368, and 5,575,637 the disclosures of which are incorporated herein by reference.
One particularly effective process and apparatus for utilizing oxy-fuel combustion in the manufacture of glass concerns staged combustion, which is disclosed in U.S. Pat. No. 5,611,682, the specification of which is incorporated herein by reference.
In the beginning of the 1990s, glass manufacturers began converting furnaces from air-fuel combustion to oxy-fuel combustion. Oxygen enrichment of some air-fuel systems has been accomplished where the oxygen concentration is increased up to about 30%. Higher oxygen concentrations in the range of 40-80% are not used because of the increased potential for forming NO
x
pollutants. It has also been found that using oxy-fuel combustion where oxygen is present in a concentration of between 90-100% results in more favorable economics for the user.
Many of the larger oxy-fuel glass furnaces are supplied by oxygen generated on site using well-known cryogenic or vacuum swing adsorption techniques. It is customary and, to date, the only method for backing up the supply of on-site generated oxygen is to keep an inventory of liquid oxygen at the same site. Thus, when the on-site generation facility is taken off-line either due to a process problem or for routine maintenance, the inventory of liquid oxygen is utilized to supply the oxygen for the oxy-fuel combustion. This method of backing up the on-site generated oxygen requires large insulated tanks for storage of the oxygen in liquid form and vaporizers to enable the liquid oxygen to be converted into gaseous oxygen for use in the oxy-fuel process. It is conventional to utilize trucks to haul liquid oxygen to the site from a larger air separation facility. Utilizing liquid oxygen back-up with an on-site generated oxygen system permits the user to continue using an oxy-fuel process without interruption. Any oxy-fuel combustion system, e.g. one of those disclosed in the above-referenced patents, would benefit from on-site production having a back-up system.
Until now, backing up oxy-fuel glass furnaces with an inventory of liquid oxygen has not been considered to be a problem. However, with the conversion of more and more furnaces at multi-furnace sites and the use of oxy-fuel combustion in flat or float glass furnaces which are much larger and use more oxygen, liquid oxygen backup becomes a significant concern to the user because of the high capital cost of storage tanks and vaporizers. In addition to the cost issue, a logistics problem arises relating to the transportation of the liquid oxygen to the site and having enough liquid oxygen available on short notice from a nearby air separation facility used to produce the liquid oxygen. Transportation of liquid oxygen to user sites in remote locations becomes even a greater problem fraught with greater difficulties.
Normally, when a glass furnace is converted from air-fuel to oxy-fuel, heat recovery devices such as regenerators and air supply systems are removed. For the user, one of the incentives to convert to oxy-fuel is reduced capital costs due to elimination of the heat recovery devices. Due to the design of oxy-fuel burners, the furnace cannot be operated by simply substituting air for oxygen in conventional combustion systems in use today. The pressure requirement to provide an equivalent amount of contained oxygen using air in an oxy-fuel burner would be extremely high, requiring an expensive air supply system. Further, some oxy-fuel burners would be sonic flow limited if fired at an equivalent firing rate.
When using oxy-fuel combustion where the oxygen supply is curtailed or disrupted, the conventional technique is to maintain the furnaces in a condition called “hot hold”. Hot hold is a condition where production is stopped and the furnace is kept hot so that the glass does not solidify. Allowing the glass to solidify would severely damage the furnace. Several companies specialize in furnace heat-ups following cold furnace repairs. They use specially designed air-fuel burners to provide the initial increase in temperature in the furnace. In case of oxygen supply disruption, the same burners could be used to provide enough heating for hot hold. In this procedure, no special temperature profile for production would be attempted and the maximum temperature achieved by these devices could be about 2200° F. This temperature is not sufficient for production of glass and is the least preferred option to be used by glass manufacturers. The cost of not producing glass is very high to the glass manufacturer, in terms of lost product sales as well as disruption of downstream glass forming lines.
Therefore, there is a definite need to provide a method and apparatus for maintaining production in a furnace used for glass manufacturing in the event of a curtailment or disruption in the availability of oxygen.
BRIEF SUMMARY OF THE INVENTION
The present invention pertains to a method and apparatus to backup an oxy-fuel combustion system with an air-fuel combustion system that can be used with or oxygen enrichment to maintain production in an industrial furnace such as glass melting furnace. According to the present invention, a system has been devised which permits oxy-fuel, air-fuel, or an oxygen enriched air-fuel operation. The burner and burner block assembly according to the present invention permits the user to operate in different modes without replacing the burner block. Thus, the same burner block can be used for all modes of operation for providing combustion close to the glass for better heat transfer by introducing fuel underneath the oxidant in the air-fuel and oxygen enriched air-fuel operating modes. A burner according to the present invention can utilize oxygen enrichment to effect the process.
According to the present invention, a burner block, i.e. conventional burner block such as described in U.S. Pat. No. 5,611,682 can be used for either oxy-fuel or air-fuel combustion, allowing the combustion system to be rapidly converted between the two modes. According to the present invention, when a problem with oxygen supply occurs, the oxy-fuel burners would be turned off, disconnected, and replaced by air-fuel backup burners that have the same configuration for a connection to the burner block. With the air-fuel backup system, the user would retain the air supply systems from previous air-fuel systems used in the melting operation or, air blowers would be supplied as part of the back up system. Air-fuel burners according to the present invention should be capable of firing at rates substantially higher than the oxy-fuel burners.
In its' broadest aspect the present invention pertains to using air or oxygen enriched air and fuel as a substitute for oxy-fuel combustion, in the event oxygen supply is diminished or interrupted in order to maintain heating in an industrial environment, the air or oxygen enriched air being introduced into the environment in sufficient volume with a fuel to effect the required level of heating. The substitution of air or oxygen enriched air-fuel combustion for oxy-fuel combustion can be made in any manner to achieve equivalent heating to that obtained using oxy-fuel combustion. In this aspect water cooling of the exhaust
D'Agostini Mark Daniel
Hoke, Jr. Bryan Clair
Lievre Kevin Alan
Pietrantonio Joseph Michael
Slavejkov Aleksandar Georgi
Air Products and Chemicals Inc.
Ferko Kathryn
Wolff Robert J.
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