Combustion – Process of combustion or burner operation – Flame shaping – or distributing components in combustion zone
Reexamination Certificate
1998-05-01
2001-03-27
Lazarus, Ira S. (Department: 3743)
Combustion
Process of combustion or burner operation
Flame shaping, or distributing components in combustion zone
C431S010000, C431S187000
Reexamination Certificate
active
06206686
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to the field of burners, particularly industrial burners of the type used in various high-temperature process applications. It is well established that, in burner systems used in industrial furnaces where two reactants are combusted, (i.e., where a hydrocarbon fuel is combusted with an oxidant) various nitrogen oxide compounds are generated (known collectively as NOx) which has been identified as an environmental pollutant. The reduction of NOx production has become the policy in recent years of various state and federal regulatory agencies. Typical mandates require NOx levels of about 30 ppmv for ambient temperature air. Thus, methods of NOx reduction are of great value.
The factors contributing to NOx production are understood, qualitatively if not quantitatively. In general, it is believed that NOx production is a path-dependent phenomenon resulting from uneven mixing of the fuel and oxidant, which results in sharp temperature gradients, localized peak flame temperatures and elevated oxygen concentrations in the hottest parts of the flame. Various techniques are typically used to reduce these factors. However, such schemes offer various tradeoffs in installed cost and operating efficiency.
A frequently used technique for reducing NOx emissions is external flue gas recirculation (FGR) in which inert combustion products are mixed with the oxidant and/or fuel streams upstream of the burner. This adds a thermal ballast to the system and reduces flame temperatures, thus inhibiting NOx formation. However, FGR systems require additional installation due to larger fans and motors and increased pipe requirements. FGR systems require more energy to operate and are less efficient in the yield of useful heat. Also, FGR components tend to have a short useful life, requiring increased maintenance and/or replacement expenses. During operation, FGR systems tend to be unstable and difficult to control, resulting in increased production expenses due to down time of the system. These difficulties are aggravated as lower NOx levels are attempted, and such systems may become economically unfeasible if further NOx reductions are mandated by the regulatory agencies.
Other burner system designs have been contemplated for complying with NOx production mandates that avoid the problems associated with external FGR. Such systems include air or fuel staged burners in which mixing of fuel and air takes place in multiple stages, allowing heat loss and dilution of reactants with products of combustion between the physically defined stages, thus reducing peak temperatures. However, staged burners are physically large and have complex oxidant and/or fuel passages, increasing installed costs and maintenance requirements.
Another method involves dilute reactant injection in which a furnace is heated to auto-ignition temperature, and fuel and oxidant are injected into the furnace in such a way that each entrain combustion products prior to mixing and combustion. While these systems provide very low NOx levels, additional penetrations to the furnace walls are required compared to conventional burners. This adds to the cost of a new furnace, and makes retrofitting an existing furnace difficult and expensive.
BRIEF DESCRIPTION OF THE INVENTION
In view of the difficulties and drawbacks associated with previous systems, there is therefore a need for a low NOx burner that is simplified in construction.
There is also a need for a low NOx burner with improved efficiency.
There is also a need for a low NOx burner that can be installed to existing furnace penetrations.
There is also a need for a low NOx modification which can be easily installed as an insert to existing burners.
There is also a need for a low NOx burner that permits easy and inexpensive retrofitting to existing furnaces.
These needs and others are satisfied by the low NOx burner and method of the present invention, including the steps of supplying a first reactant stream and introducing a second reactant stream into the first reactant stream at a first point so as to produce co-flowing streams. This resulting fuel/oxidant stream is discharged into a furnace environment having inert combustion products substantially equilibrated to furnace temperature, so as to entrain the combustion products and mix them together with the co-flowing stream. The temperature of the co-flowing stream is increased by the entrained products until it ignites in a combustion region displaced from the first point. Thus ignition cannot occur until the reactant stream has been diluted by inert products of combustion, reducing both oxygen concentration and peak flame temperature, so as to suppress NOx production.
As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modification in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive.
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Cain Bruce E.
Newby John N.
Nieszczur Keith J.
Robertson Thomas F.
Sutton Richard D.
Jones Day Reavis & Pogue
Lazarus Ira S.
Lee David
North American Manufacturing Company
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