US3768964A

US3768964A - Air heater

Info

Publication number: US3768964A
Application number: US00201011A
Authority: US
Inventors: I Smith
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1971-11-22
Filing date: 1971-11-22
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30

Abstract

An air heater including a pilot burner comprising an orifice therein for passing a pilot gas-air fuel mixture at a higher velocity than the pilot fuel flame propagation rate, a diffuser for reducing the fuel mixture velocity to less than the flame propagation rate, and a self-contained independent pilot gas-air fuel mixture system for providing an instantaneous pilot flame having a steady burning with no flame out, the pilot burner being mounted in a main burner diffuser of the air heater.

Description

United States Patent 1 1 Smith Oct. 30, 1973 AIR HEATER 3,265,376 8/1966 Spielman 263/19 A 3,366,373 1/1968 Reed 263/19 A [75] Invemm' Arthur 3,536,429 10 1970 Lake 431 353 [73] Assignee: Texaco Inc., New York, NY.

Primary ExaminerCarroll B. Dority, Jr. [22] Flled' 1971 Att0rney-Thomas H. Whaley et al.

[21] Appl. No.2 201,011

[57] ABSTRACT 52 us. c1. 432 222 431/285 heat" inc'uding a Pilot cmprising 51 Int. Cl. i=21l 9/04 them" Passing a Pilot fuel mixture 581 Field of Search 263/19 A; 431/285, M a higher "ebcity than Pi0t PmPaga' 431/353. 432/222 ,tion rate, a diffuser for reducing the fuel mixture velocity to less than the flame propagation rate, and a [56] References Cited self-contained independent pilot gas-air fuel mixture UNITED STATES PATENTS system for providing an instantaneous pilot flame having a steady burning with no flame out, the pilot g t burner being mounted in a main burner diffuser of the au 3,109,481 11 1963 Yahnke 263 19 A heater R25,626 7/1964 Yeo et al. 263/19 A 5 Claims, 4 Drawing Figures PATfNTEnncrso m3 3, 75 54 SHEEI 1 OF 2 l i i nmnlslm AIR HEATER BACKGROUND OF THE INVENTION A typical air heater for fluid duct cracking unit comprises a gas burner for heating a large mass of high velocity turbulent air under several psig (pounds per square inch gauge) pressure from a powerful air blower and for supplying the heated air to a regenerator of a fluid catalytic cracking unit during start up of the unit. The main burner is lighted from a gas fired pilot burner which has previously been lighted from an electrical spark ignitor. The usual and average time of hours, with a maximum of 24 hours has been required by operators in the past to successfully light the pilot burner and have it stay lighted until the main burner can be lighted. This is due to the trial and error method of adjusting the fuel to arrive at a combustible mixture with the air available at the burner in the heater and the ease in which the flame can be blown out due to the tremendous turbulence of the air in the heater.

The disclosed turbulent air heater provides a premix of compressed air and fuel gas in the combustible range for the pilot burner, with the correct combination of restrictive orifices and upstream pressure settings and particularly for air heater pressures not exceeding psig, for example.

OBJECTS OF THE INVENTION A principal object of this invention is to provide a turbulent air heater which takes much less than the average 10 hours to ignite a main air burner for heating air, as for example, for a fluid catalytic cracking unit.

Another principal object of this invention is to provide a pilot burner for a turbulent air heater that will provide an instantaneous pilot flame having steady burning with no flame out in the heater for heating turbulent high velocity air.

Another object of this invention is to provide an instantaneous lighting turbulent air heater in which flame-out is prevented.

A further object of this invention is to provide a pilot burner for an air heater having a flame arrester for preventing combustion from occurring in the air-fuel line to the burner.

Still another object of this invention is to provide a turbulent air heater and pilot burner combination that is easy to operate, is of simple configuration, and is economical to construct and assemble.

Other objects and various advantages of the disclosed turbulent air heater and pilot burner combination will be apparent from the following detailed description, together with the accompanying drawings, submitted for purposes of illustration only and not intended to define the scope of the invention, reference being had for that purpose to the subjoined claims.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings diagrammatically illustrate by way of example, not by way of limitation, one form of the invention wherein like reference numerals designate corresponding parts in the several views in which:

FIG. 1 is a schematic perspective view of the heater pilot burner system for a typical fluid catalytic cracking unit with parts deleted for clarity of disclosure;

FIG. 2 is a section taken at 2-2 on FIG. 1;

FIG. 3 is a section taken at 3-3 on FIG. 1; and

FIG. 4 is a plan view of the orifice plate of FIG. 3.

The invention disclosed herein, the scope of which being defined in the appended claims is not limited in its application to the details of construction and arrangement of parts shown and described, since the invention is capable of other embodiments and of being practiced or carried out in various other ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a schematic view of an air heater 10, with parts cut away, having a housing with a pilot burner 11 therein.

Lines

12 and 13 provide air and gas, respectively, for being mixed for the pilot burner 11. The disclosed exemplary heater is for a fluid catalytic cracking unit. Air is supplied through valve 14 to the one inch pipe 12 pasta pressure gauge 15, which air is preferably held to approximately 50 psig (pounds per square inch gauge), and passes through an orifice union 16 having an inside diameter for example, of 0.138 inches, for controlling the air flow to a T 17, another valve 18, and l l inch mixture line 19. Likewise, pilot burner fuel gas, such as natural gas, is supplied through a valve 20 to the 1 inch line 13. The fuel gas passes by a gas pressure gauge 21, which gas is at approximately 50 psig. This gas then passes through an orifice union 22 having an internal diameter, for example, of 0.098 inches, wherein from there the gas passes to the T 17 and its attendant valve 18 in which area the gas is mixed with the air. From this area the gas-air mixture exits at a pressure not exceeding 15 psig, for example, as indicated by a pressure gauge 23. This gas-air mixture passes on the pilot burner 11 of the heater 10, FIG. 1.

FIG. 2, a sectional schematic view at 22 on FIG. 1, illustrates a main burner 24, FIG. 2, having a gas line 25 for supplying raw gas to a gas tip 26. The gas escaping from the tip 26 aspirates air from therearound to provide a proper gas-air mixture in a main heater diffuser 27 mounted in the air heater 10 over the gas tip. The pilot burner 11 has an expanding section or pilot burner diffuser 35 forming the egressing end thereof. The diffuser 35 is preferably 4 inches long with ingressing and egressing openings being approximately 2 f; inches and four inches, respectively.

The pilot burner 11, FIG. 2 is mounted in juxtaposition with the main gas burner 24 having the tip 26 and extends up to the bottom of the main heater diffuser 27 to substantially the same height as the burner tip. The pilot burner 11 utilizes a self-contained independent gas-air mixture from the line 19 whereas the main gas burner 24 uses the pure or raw gas and mixes it with the air drawn in by aspiration. Therefore the pilot burner is not affected by adjustments and fluctuations of the air in the main air heater 10.

As shown in FIG. 2, a spark ignitor tube 34 is mounted in the heater l0 and extends down over and adjacent to the pilot burner 11. After being lighted by the spark ignitor tube 34, the pilot burner ll then ignites the main burner 24 of the heater l0 and its flame is held within the main diffuser mounted thereover. The feature of the self-contained independent pilot gasair mixture system accordingly provides an instantaneous pilot flame having steady burning with no flameout.

The turbulent and high velocity air to be heated may be injected into the heater at right angles through air inlet 28 from the left, as shown in FIG. 2, for example, producing very turbulent air. A typical installation which generates and heats very turbulent air and in.

which the new pilot burner has been very successful, is one in which the longitudinal axis of the main air heater diffuser 27 and pilot burner diffuser 35 are mounted at right angles to the incoming air so that the air passes directly over the heater, is heated as it passes thereover prior to turning 90, and subsequently leaves the heater through exit duct 29.

FIG. 3, a sectional schematic view at 33 on FIG. 1 illustrates the novel pilot burner l 1 with diffuser 35 deleted. This burner comprises a cylinder 30 for being se- I cured to the pilot gas-air mixture line (not shown) with a coupling 31 welded to one end of the cylinder, the

other or exit end of the cylinder being open for trans-.

mission of the gas-air mixture to a diffuser 35, FIG. 1, connected thereto. Positioned intermediate of the two ends of the burner cylinder is a quarter inch stainless steel orifice plate 32, FIG. 3, which plate of the preferred embodiment has an inside diameter of 1.939 inches for a cylinder length including the coupling of six inches. This preferred embodiment of the pilot burner has a coupling with threads one inch long made from l k inch stainless steel and spaced a quarter of an inch from the weld joint between the coupling and the cylinder. The orifice plate 32 is welded in the cylinder at a distance of one-half inches from the coupling end. The distance from the back surface of the orifice plate 32 to the exit end of the cylinder 30 is substantially four inches. The cylinder 30 is made from two inch stainless steel pipe.

The orifice plate 32 is illustrated in greater detail in FIG. 4. The exemplary orifice plate 32 comprises a round plate with nine holes 33, each hole being inch in diameter with eight holes equally spaced on a 1 7% inch diameter circle on the circularplate, with the ninth hole being in the center of the plate. These holes provide critical flow of the gas-air mixture'as it flows at psig from the ingressing upstream end of the pilot burner cylinder 30 to the egressing downstream end. These orifices must be designed to provide critical flow for the particular operating pressures, psia (pounds per square inch, absolute pressure), utilized or the pressure of the downstream fuel mix must be equal to or less than 55 percent of the pressure upstream. This ensures that the orifices pass the independently supplied pilot gas-air fuel mixture at a higher velocity than the pilot fuel propagation rate for steady burning without flame out. The diffuser 35, FIG. 1, slows the passage of the LII pilot gas-air mixture therethrough to a velocity less than that of the pilot fuel propagation rate so that with v the self-contained independent pilot gas-air fuel mixof the invention, and it is accordingly desired to comprehend within the purview of this invention such modifications as may be considered to fall within the scope of the appended claims.

I claim:

1. A turbulentair heater having a main gas-air fuel mixture supply and a pilot burner having a pilot gas-air fuel mixture supply for igniting the main fuel mixture for heating turbulent air supplied to the air heater, the pilot gas-air fuel mixture having a flame propagation rate, wherein,

a. said pilot burner has orifice means for passing said pilot gas-air fuel mixture at a higher velocity than said pilot fuel flame propagation rate,

b. said pilot burner has a diffuser means having a flared outlet for reducing said high velocity of said pilot gas-air fuel mixture to a velocity less than said pilot fuel flame propagation rate, and

c. said pilot gas-air fuel mixture supply being a selfcontained independent gas-air fuel mixture supply system for providing an instantaneous pilot flame having steady burning with no flame out when the air heater is heating the turbulent air,

d. a main burner connected to said main gas-air fuel mixture supply, a main diffuser means surrounding said main burner and said pilot burner diffuser means and having a flared outlet,

c. said air heater including means forming a passageway therethrough for air to be heated, and said main diffuser means being located in said air heater to direct combustion gases into said passageway to heat the air. 2. A turbulent air heater as defined in Claim 1 wherein,

a. said pilot burner comprises a duch secured at one I gas-air fuel mixture at a higher velocity than said pilot fuel flame propagation rate. 4. A turbulent air heater as recited in claim 1 wherein, e

a. said orifice means comprises an orifice plate with at least one orifice therein, and

b. said orifice being of the size to pass said pilot gas- 7 air fuel mixture at its critical velocity therethrough.

5. A turbulent air heater as recited in claim 1 wherein the pilot gas-air fuel mixture supply system comprises,

a. an orifice union of a predetermined critical flow size and an air valve in an air supply line connected to a gas-air fuel mixture supply line means for said pilot burner,

b. an orifice union of a predetermined critical flow size and a gas valve in a gas supply line connected to said gas-air fuel mixture supply line means, and

c. both said air valve and said gas valve being set to predetermined respective pressures for ensuring an optimum combustible mixture and resultant instantaneous pilot flame for said pilot burner.

Claims

1. A turbulent air heater having a main gas-air fuel mixture supply and a pilot burner having a pilot gas-air fuel mixture supply for igniting the main fuel mixture for heating turbulent air supplied to the air heater, the pilot gas-air fuel mixture having a flame propagation rate, wherein, a. said pilot burner has orifice means for passing said pilot gas-air fuel mixture at a higher velocity than said Pilot fuel flame propagation rate, b. said pilot burner has a diffuser means having a flared outlet for reducing said high velocity of said pilot gas-air fuel mixture to a velocity less than said pilot fuel flame propagation rate, and c. said pilot gas-air fuel mixture supply being a self-contained independent gas-air fuel mixture supply system for providing an instantaneous pilot flame having steady burning with no flame out when the air heater is heating the turbulent air, d. a main burner connected to said main gas-air fuel mixture supply, a main diffuser means surrounding said main burner and said pilot burner diffuser means and having a flared outlet, e. said air heater including means forming a passageway therethrough for air to be heated, and said main diffuser means being located in said air heater to direct combustion gases into said passageway to heat the air.

2. A turbulent air heater as defined in Claim 1 wherein, a. said pilot burner comprises a duct secured at one end of said pilot diffuser means, and b. said orifice means comprises an orifice plate in said duct having at least one orifice therein for passing said pilot gas-air fuel mixture at a higher velocity than said pilot fuel flame propagation rate.

3. A turbulent air heater as recited in Claim 2 wherein, a. said orifice means comprises an orifice plate with a plurality of orifices therein for passing said pilot gas-air fuel mixture at a higher velocity than said pilot fuel flame propagation rate.

4. A turbulent air heater as recited in claim 1 wherein, a. said orifice means comprises an orifice plate with at least one orifice therein, and b. said orifice being of the size to pass said pilot gas-air fuel mixture at its critical velocity therethrough.

5. A turbulent air heater as recited in claim 1 wherein the pilot gas-air fuel mixture supply system comprises, a. an orifice union of a predetermined critical flow size and an air valve in an air supply line connected to a gas-air fuel mixture supply line means for said pilot burner, b. an orifice union of a predetermined critical flow size and a gas valve in a gas supply line connected to said gas-air fuel mixture supply line means, and c. both said air valve and said gas valve being set to predetermined respective pressures for ensuring an optimum combustible mixture and resultant instantaneous pilot flame for said pilot burner.