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United States Patent (19) 11 Patent Number: 5,364,476 Poor Et Al

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United States Patent (19) 11 Patent Number: 5,364,476 Poor Et Al USOO5364476A United States Patent (19) 11 Patent Number: 5,364,476 Poor et al. (45) Date of Patent: Nov. 15, 1994 (54) INDUSTRIAL VARIABLE CARBON Surface Combustion, Inc. brochure "RX Endothermic POTENTIAL GAS GENERATOR Gas Atmosphere Generator'. Pp. 125-131 of Dec. 1965 issue of "Iron and Steel Engi (75. Inventors: Ralph P. Poor; Michael J. Huber, neer” by E. Spielberger both of Toledo, Ohio Primary Examiner-Peter D. Rosenberg (73) Assignee: Surface Combustion, Inc., Maumee, Attorney, Agent, or Firm-Frank J. Nawalanic Ohio 57 ABSTRACT (21) Appl. No.: 148,871 A variable gas generator is disclosed which is capable of 22 Filed: Nov. 8, 1993 producing a wide variety of product gas compositions heretofore produced only by either exothermic gas 51 Int. Cl. .............................................. B23K 35/24 generators or endothermic gas generators or a combina 52 U.S. C. .................. .............. 148/27; 148/235 tion of gas generators. The variable gas generator in (58) Field of Search .................................. 148/235, 27 cludes a nitrogen membrane module producing a nitro gen-oxygen feed gas which is combined with a hydro 56 References Cited carbon fuel and fed into a conventional endothermic gas U.S. PATENT DOCUMENTS generator. By controlling the nitrogen membrane mod 2,897,158 7/1959 Sanzenbacher ..................... 252/372 ule to produce a desired oxygen-nitrogen feed gas and 4,236,941 12/1980 Main .................................... 148/235 by controlling the addition of methane and the catalyst 4,249,965 2/1981 Schultz.................................. 148/27 bed temperature of the gas within the endothermic 4,805,881 2/1989 Schultz................................ 266/257 generator, a wide variety of product gas composition with carbon potential varying anywhere from one to OTHER PUBLICATIONS 80% combustibles can be produced. Generon brochure "The Gold Line Membrane Mod ules for Nitrogen Production'. 32 Claims, 3 Drawing Sheets 75 GAS SUPPLY ck C 63 28 M 29 MEMBRA NE MODULE He 27 25 4. U.S. Patent Nov. 15, 1994 Sheet 1 of 3 5,364,476 NATURAL. GAS FLUE PRODUCTS WET COMPOST ON EXOTHERMC GENERATOR OPERATIVE RANGE 2227 - 2 U.S. Patent Nov. 15, 1994 Sheet 2 of 3 5,364,476 NTRO GEN FLOW VS. PURITY S pa O- 3OO o g Ol - 25O 35 s RS 2OO 2O 2 SSs 50 OO gg loo s:2 5O an O.5 ... O 1.5 2.O 2.5 3.O PRODUCT OXYGEN CONCENTRATION (%) a .2 PRODUCT FLOW VS. TEMPERATURE 4. O 6O 8O IOO 12O 4O 5O s7O 90 O 3O 5O TEMPERATURE (°F) Ezz7 . 2, U.S. Patent Nov. 15, 1994 Sheet 3 of 3 5,364,476 WBWBNV893TºnQOW 5,364,476 1. 2 ities and does have a tendency to produce trace ele INDUSTRIAL VARABLE CARBON POTENTIAL ments of the liquid as a gas in its original form, i.e., NH3. GAS GENERATOR The last commercially-acceptable method for pro ducing furnace atmospheres, and the one to which this This invention relates generally to method and appa invention relates, is the use of gas generators to develop ratus for generating a variety of gas compositions for a variety of furnace gas compositions by reacting a use in various industrial processes and more particularly hydrocarbon fuel, such as natural gas (methane) with to industrial processes which use or employ heat or are a. heat driven. Traditionally gas generators are defined as either The method and apparatus is particularly applicable O exothermic or endothermic. An exothermic gas genera to and will be described with specific reference to gas tor means a generator where the air is mixed with natu generators for use or in combination with industrial heat ral gas at ratios of anywhere between 6 to 9 parts air to treat processes and/or furnaces in which the carbon 1 part natural gas (stoichiometric combustion occurring potential of the gases used in the process must be con at about or slightly less than 9). At these ratios the air trolled. However, it will be appreciated that the inven 15 and gas burn with the products of combustion giving off tion has broader applications and can also be used in heat and thus the designation of such generators as applications where the presence of oxygen cannot be exothermic. Exothermic generators typically produce tolerated such as food service, grain storage etc. lean or inert atmospheres without (or with very little) combustibles and their applications typically involve INCORPORATION BY REFERENCE annealing, furnace purging, brazing etc. Endothermic Schultz U.S. Pat. No. 4,805,881 and Sanzenbacher generators typically involve generators where the air to U.S. Pat. No. 2,897,158 were developed by the present gas ratio is typically less than 6 to 1 and more specifi assignee, Surface Combustion, Inc., and are incorpo cally is generally set at 2.5 to 1. When air and CH4 are rated by reference herein so that details and concepts Supplied in such ratios, heat must be inputted to the 25 mixture to dissociate the gases to their elemental form. known in the art need not be restated herein. The pa As explained in the prior art patents, the gas reactions tents do not form part of the present invention. resulting during the dissociation of the gases are not BACKGROUND entirely endothermic (just as certain gas reactions in the As a general concept, industrial heat treat processes exothermic generator are not entirely exothermic). (such as annealing, carburizing, clean hardening, etc), 30 However, the term, endothermic, is used to describe and various heat driven process (such as sintering, braz Such generators since heat is initially supplied to the ing, purging, blanketing) require a furnace atmosphere air/natural gas mixture to raise the temperature of the or furnace gas having certain characteristics, or gener mixture prior to entering the catalyst bed within the ally speaking, a certain potential for producing carbon. generator. Endothermic generators are typically used 35 to produce Class 300 gas and any gas which is reducing The gas composition is well defined, as for example by or has combustibles such as H2 or CO. Within the heat Class designation specified by the American Society for treating art generators which lack combustibles are Metals. Thus, the carrier gas used in carburizing is an viewed as non-reducing. Generated gases which con endothermic base carrier gas specified by ASM as a tain less than 4% combustibles or 1% oxygen are class 300 gas typically having a gas composition of 40 viewed as inert. approximately 40% N2, 40% H2 and 20% CO. A typical Because a number of heat treat processes require gas composition would be: certain percentages of gases it is not unusual to couple exothermic generators such as Surface Combustion's Gas Element Percentage DX generators with endothermic generators such as H2 40.4% 45 Surface Combustion's RX generators. Nor is it unusual CO 19.8% for specific process applications to use molecular sieves N2 39.0% or desiccants to remove or reduce certain elements, CH4 0.5% H2O 0.2% Such as CO2 from the gas, in installations where HNX CO2 0.1% generators are employed such as in tin lines and other 50 coating lines. In general summary of the natural gas generator art Conceptually, there are three ways to supply at least as it now exists, two fundamentally different kinds of some of the furnace atmospheres. First the furnace at generators must be used depending on whether the gas mosphere can simply be supplied as a gas and stored on composition is to be non-reducing or reducing (rich in site for use in the process, i.e., liquid nitrogen. How 55 combustibles). Further, depending on process require ever, certain heat treat processes require tighter and ments, a wide variety of additional equipment items are tighter control of gas compositions so that even in the used to produce a wide range of gas compositions re inert applications, such as nitrogen, oxygen presence of Sulting from the product gas compositions produced by low PPM levels cannot be tolerated. It is possible, that the endothermic and exothermic gas generators blend even with commercial grade nitrogen stock, oxygen 60 ing "RX” and "DX' gases. Thus, the existing generator concentrations of 20 PPM can occur which exceeds the art lacks flexibility to produce a wide variety of gas low oxygen concentrations now being specified. compositions. This results then in the user purchasing a A second way to form the furnace gas, is to react or relatively large number of expensive equipment items or dissociate a liquid, usually in the presence of heat, to adopting alternative gas producing approaches which produce its gaseous components. A typical example is 65 have their own problems. Further, process control re ammonia which is dissociated to produce nitrogen and quirements are becoming increasingly tighter for gas hydrogen. This is a commercially acceptable process compositions. As already noted, the presence of oxygen but is somewhat costly, requires liquid gas storage facil in certain inert type annealing atmospheres which can 5,364,476 3 4 adversely affect the metal as an oxidizer, now require 500 to 10,000 CFH at turndown ratios at anywhere oxygen content to have no more than 1 PPM. from about 3-1 to about 2-1. Apart from any considerations relating to gas genera It is still yet another feature of the invention to utilize tors, membrane nitrogen generators remove nitrogen the oxygen enriched permeate gas stream produced by from air by passing the air through a membrane which 5 the air separation module to increase the oxygen con separates certain elements from the air. Specifically, a tent of the first prime outlet stream fed to the gas gener gas stream comprised substantially of nitrogen with ator to be greater than the oxygen content present in air, varying amounts of oxygen can be produced.
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