Combustion apparatus and method for radiating wall heating system

A burner and combustion method for a radiant wall heating system wherein each burner fuel ejector is positioned such that at least a substantial portion of the burner combustion air is discharged from an area beyond the ejector located the greatest distance from the radiant wall.

FIELD OF THE INVENTION

The present invention relates to burners and combustion methods for use in heating systems having upwardly extending radiating walls for radiating combustion energy.

BACKGROUND OF THE INVENTION

Radiant wall heating systems are commonly employed in chemical, petroleum, and other industrial processes. A typical prior art radiant wall heating system2is illustrated inFIGS. 1 and 2. The prior art radiant wall system2comprises: a furnace, boiler, or other fired heater4having a housing5, an outer wall6, and a floor8; a plurality of process tubes10which carry the process fluid through the housing5; an upwardly extending radiating wall12within housing5; and at least one radiant wall burner14. The radiant wall12within heater5is typically comprised of a radiating ceramic tile material or other material which will radiate the combustion energy generated by burner14toward and onto the process tubes10.

The prior art burner14shown inFIGS. 1 and 2comprises: a burner housing16positioned primarily outside of the heater wall6; a burner wall18which extends horizontally from burner housing16through the heater wall6and into the interior of the furnace housing5; a combustion air flow passage20extending through burner housing16and burner wall18; a damper or other regulating device22in burner housing16for regulating the flow of combustion air26through the burner14; an upwardly facing flow passage opening24provided through the upper end of the burner wall18for delivering the combustion air26upwardly as illustrated inFIG. 1; a plurality of primary fuel ejectors28for ejecting some (typically most) of the burner fuel into a primary combustion stage30; and a plurality of secondary fuel ejectors32for ejecting the remainder of the burner fuel into a secondary combustion stage34. The combustion air26will typically be delivered to the burner14by forced circulation, natural draft, or a combination thereof. Although the prior art burner assembly14shown inFIG. 1extends horizontally through the heater wall8, it is also known in the art to extend the burner assembly vertically through the floor8of the heater.

Each of the fuel ejectors28and32will typically comprise a fuel ejection tip36or38secured on a vertical end portion of a fuel pipe40or42. Each ejector tip36and38has one or more orifices or other flow ports provided therein for ejecting fuel in a desired direction and pattern. The ejection tips38provided on the secondary fuel ejectors32will typically be effective for ejecting fuel upwardly into a flat flame combustion stage34against the radiating wall12.

As shown inFIG. 2, the upper end of the burner wall18provides a periphery44which surrounds and establishes the boundaries of the upwardly facing combustion air opening24. A first (near) side46of the periphery44is positioned closest to the radiating wall12and establishes a near boundary48of the combustion air opening24. A second (outer) side50of the periphery44is positioned furthest from the radiating wall12and establishes an outer boundary52of the combustion air opening24. The near boundary48of opening24will include or consist of one or more “closest” point(s)49which is/are closer than any other portion of the upper opening24to the radiating wall12. In like manner, the outer boundary52includes or consists of one or more “furthest” point(s)53which is/are further than any other portion of the upper opening24from the radiating wall12.

As shown inFIG. 2, the upper discharge end of burner14has a rectangular shape so that the near boundary48of the upper opening24is a straight line segment which is adjacent to and runs parallel to the radiating wall12. Because all portions of the near boundary line48are equidistant from the radiating wall12, each point on line48is therefore a near boundary point “closest” to the radiating wall12. Similarly, the outer boundary52of the upper opening24is also a straight line segment running parallel to the radiating wall12. Thus, each point on line52is an outer boundary point which is “furthest” from the radiating wall12. The linear outer boundary52and near boundary48of combustion air opening24are spaced apart a maximum width54, as shown inFIG. 2, perpendicular to the radiating wall12.

As illustrated inFIGS. 1 and 2, at least some of the ejectors28and32employed in the radiant wall burners heretofore known in the art are commonly positioned either in or beyond the outer peripheral wall50of the combustion air opening24. Thus, the ejectors28will typically be spaced outwardly from the near boundary line48of the upper opening24by a distance58which exceeds the maximum width54of the opening24.

As indicated above, the prior art radiant wall burner14is a staged fuel burner having a primary stage combustion zone30and a secondary stage combustion zone34. An intended objective of the staged fuel burner is to lower the amount of NOXemissions produced in the combustion process. In the staged fuel design, excess air is typically present in the primary combustion stage28so that the overall temperature of the burner flame is lowered and the production of NOXcompounds is thereby reduced.

Unfortunately, in the radiant wall burners heretofore used in the art, flue gas currents60within the heater4commonly act to pull the combustion flame30produced by ejectors28outwardly away from the radiating wall12. This reduces the efficiency, effectiveness, and stability of the burner14and also reduces the overall efficiency and heating capacity of the radiant wall system2. In addition, it is not uncommon that the flue gas currents60will pull the flame30outward to such a degree that it is very close to and/or impinges upon the process tubes10. The impingement or near impingement of the burner flame30on the process tubes further diminishes the performance and reduces the efficiency of the heating system, can damage the process tubes10or other internal components, and can result in accelerated coke production and lay down within the tubes10.

Thus, a need exists for an improved radiant wall burner and a better method for operating radiant wall systems which will provide greater flame stability and will prevent or at least significantly reduce the flame drift and impingement problems experienced with the prior art burners. The improved radiant wall burner and method will preferably also be effective for maintaining low NOXproduction rates and will most preferably be effective for further reducing NOXemissions.

SUMMARY OF THE INVENTION

The present invention provides an improved radiant wall burner and an improved method of producing combustion energy in radiant wall systems. The inventive burner and method satisfy the needs and alleviate the problems discussed above. The inventive burner and method are effective for both eliminating or at least substantially reducing flame drift and impingement problems while also reducing the production of harmful NOXemissions. In addition, the inventive burner and method provide improved operating stability and higher available turn-down ratios.

In one aspect, there is provided an improvement in a burner for use in a heating system having an upwardly extending radiating wall for radiating combustion energy. The burner includes a burner wall having an upper opening for delivering combustion air upwardly into the heating system. The upper opening has at least one near boundary point which will be closest to the radiating wall and at least one outer boundary point which will be furthest from the radiating wall. The upper opening has a maximum width perpendicular to the radiating wall and the burner includes one or more ejectors for ejecting a fuel. The improvement comprises each of the one or more ejectors of the burner being positioned such that it will be located between the radiating wall and a plane parallel to the radiating wall. The plane is located between the near boundary point and the outer boundary point at a distance from the near boundary point which is 75% of the maximum width.

In another aspect, there is provided an improvement in a burner for use in a heating system having an upwardly extending radiating wall for radiating combustion energy, wherein the burner includes a burner wall having a substantially rectangular upper opening for delivering combustion air. The substantially rectangular opening has a first side which will be positioned closest to the radiating wall and a second side, opposite the first side, that will be positioned furthest from the radiating wall. The substantially rectangular upper opening has a width between the first side and the second side and the burner includes one or more ejectors for ejecting a fuel. The improvement comprises each of the one of more ejectors of the burner being positioned such that it will be located between the radiating wall and a plane parallel to the radiating wall. The plane is located between the first side and the second side at a distance from the first side which is 75% of the width.

In another aspect, there is provided a method of producing combustion energy in a heating system having an upwardly extending radiating wall for radiating the combustion energy. The method uses a burner having one or more ejectors for ejecting a fuel and an opening for delivering combustion air. The method comprises the steps of: (a) ejecting the fuel from the one or more ejectors in a manner effective for producing an upwardly projecting flame pattern and (b) delivering the combustion air from the opening upwardly into the heating system such that less than half of the combustion air from the opening is delivered between the radiating wall and a horizontal line parallel to the radiating wall. The horizontal line is a line extending through an upper end centerpoint of at least one of the one or more ejectors located furthest from the radiating wall such that the burner does not have any ejector positioned outwardly from the radiating wall beyond the horizontal line.

Further aspects, features, and advantages of the present invention will be apparent to those skilled in the art upon examining the accompanying drawings and upon reading the following detailed description of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment100of the inventive heating system is depicted inFIGS. 3 and 4. The inventive heating system100includes at least one inventive improved burner110. As with the prior art burner14, the inventive burner110includes: a housing116; a burner wall118which extends horizontally from housing116through the outer wall106and through the radiating internal wall112of the heater102; an air flow passage120extending through burner housing116and burner wall118; an air flow damper or other regulator122within the burner housing116; and an upper opening124for discharging the combustion air126upwardly into heater102.

In the inventive burner, the upper combustion air opening124and peripheral wall144surrounding the upper opening124can be circular, oval, rectangular (including square), or any other desired shape. As with prior art burner14, the combustion air opening124of inventive burner110is rectangular. Consequently, the near boundary148of upper opening126is a straight line segment which runs parallel to the radiating wall112. All points on the near boundary line148are therefore equidistant from the radiating wall112so that each point on line148will constitute a near point of the upper opening124which is closest to the radiating wall112. Similarly, the outer boundary152of upper opening124is also a straight line segment running parallel to the radiating wall112so that each point on the outer boundary line152will constitute an outer boundary point which is furthest from the radiating wall112.

It will be understood however, that if, by way of example, the upper opening190of the burner wall were to have an oval or circular shape as illustrated inFIG. 7, then the upper opening would have only a single near boundary point191which is closest to radiating wall192and only a single outer boundary193point which is furthest from radiating wall192. As another example, if a D-shaped opening195of the type illustrated inFIG. 8were used with the flat side196thereof being positioned adjacent and parallel to the radiating wall197, then each point on the flat side196would be a near boundary point closest to the radiating wall197. However, the D-shaped opening195would have only a single outer boundary point199located furthest from the radiating wall197.

The inventive improved burner110shown inFIGS. 3 and 4includes one or more (preferably a plurality of) fuel ejectors162. In contrast to the prior art burner14, none of the ejectors162of the inventive burner110are located in or beyond the outer periphery150of the burner wall118. Each fuel ejector162is positioned such that it will be located between the radiating wall112and a plane164. The plane164is parallel to radiating wall112and is located between the nearest and furthest boundary points148and152at a distance166which is no more than 75% of the maximum width154of the upper opening124. The distance166of plane164from the near boundary point148closest to radiating wall112will preferably be not more than 50% of the maximum width154of the air discharge opening124and will more preferably be not more than 30% of the width154. The distance166of plane164from the near boundary point148will more preferably be not more than 15%, most preferably not more than 5%, of the maximum width154of the combustion air opening124.

In accordance with these placements of the one or more fuel ejectors162, less than 75%, preferably less than 50%, more preferably less than 30% or less than 15%, and most preferably less than 5% of the combustion air126discharged upwardly from the combustion air opening124will be delivered into the heater102from the area168between the radiating wall112and a horizontal line172which is parallel to the radiating wall112. The horizontal line172extends through the upper centerpoint170of whichever one or more of the fuel ejectors162is/are located furthest from the radiating wall112. By saying that the horizontal line172runs through the one or more ejectors162which are located furthest from the radiating wall112, it will be understood that the burner110will not have any ejectors positioned outwardly beyond line172.

By locating the fuel ejectors162in the manner described above, the inventive burner ensures that a substantial portion of, and preferably at least most, of the combustion air126is discharged upwardly from an area174beyond line172such that this outer combustion air will operate to both urge the fuel from ejectors162toward the radiating wall112and shield the ejected fuel from the effects of the internal flue gas currents160. Thus, the air discharged from the outer area174acts to assist in preventing the combustion flame176from being pulled outwardly toward or onto the process tubes178.

Each of the fuel ejectors162includes one or more flow ports or orifices180which is/are positioned and directed for ejecting the fuel upwardly to produce an upwardly projecting flame pattern182. As will be understood by those in the art, the upwardly projecting flame pattern will preferably be a flat flame pattern directed against the radiating wall112. Further, the inventive burner110will preferably be a single stage burner having only a single combustion stage zone182. Because a substantial portion, preferably at least most, of the combustion air126is delivered from the outer area174beyond line172, an excess fuel condition will exist in the single stage combustion zone182. In other words, a sub-stoichiometric amount of oxygen will be present in zone182for the complete immediate combustion of the fuel. This slows the combustion rate in zone182and thereby lowers the overall flame temperature and reduces the amount of NOXproduced.

Although each of the fuel ejectors162of the inventive burner110are shown inFIGS. 3 and 4as being located within the upper combustion air opening124, it will be understood that the burner ejectors162can be located anywhere between the radiating wall112and plane164. For example, one or more or all of the one or more ejectors of the inventive burner can alternatively be located: (a) outside of a burner side wall184, (b) within or partially within the near burner wall146as illustrated inFIGS. 5 and 6, and/or (c) between the radiating wall197and the near burner wall196as illustrated inFIG. 8.

An alternative embodiment200of the inventive burner is illustrated inFIGS. 5 and 6. The inventive burner200is substantially the same as inventive burner110except that: (a) the burner200extends vertically through the floor202of the furnace rather than through the side wall204; (b) two of the fuel ejectors206of inventive burner200are positioned in the near wall208such that they are not located within the air discharge opening210; and (c) the near wall208of the inventive burner200includes an upwardly inclined guide wall212which assists in guiding the burner flame upwardly against the radiant wall214.