Apparatus and method for optimizing the use of oxygen in the direct reduction of iron

Abstract

An apparatus and method for adjusting the parameters of a reducing gas stream prior to introduction into a direct reduction furnace, such parameters including temperature of the gas stream, and amount of hydrocarbon, carbon monoxide, and hydrogen contained in the reducing gas. The apparatus is placed in-line with the reducing gas recycle loop of a direct reduction furnace, which has an enrichment section which introduces hydrocarbon components to the main stream, and an oxygen/fuel injection system, located downstream from the enrichment section, which injects a shrouded stream of oxygen and hydrocarbon gas into the reducing gas stream. Temperature, carbon monoxide content, and hydrogen content of the reducing gas are adjusted by controlling the flow of oxygen and the ratio of hydrocarbon to oxygen injected in the oxygen/fuel injection system. Hydrocarbon content of the reducing gas is adjusted primarily by controlling the flow rate of the enrichment section.

Description

FIELD OF THE INVENTION

[0002] The present invention relates an apparatus and method for the direct reduction of iron oxide, and more particularly to an apparatus and method for the reformation or modification of reducing gas for use with a direct reduction furnace.

BACKGROUND OF THE INVENTION

[0003] The production of direct reduced iron in a vertical shaft reactor involves reduction of the ore in a reduction zone through which is passed a suitable hot reducing gas, known as bustle gas, largely composed of carbon monoxide and hydrogen at temperatures in the range of 700° C. to 1000° C. and cooling of the directly reduced iron in a cooling zone through which is passed a gaseous coolant at a temperature below about 200° C. The ore to be treated is charged to the top of the reactor and caused to flow downwardly through the reduction zone wherein it is reduced by heated reducing gas which flows upwardly through the reactor, after which the reduced ore flows into and downwardly through the cooling zone to be cooled and carburized by contact with a stream of suitable cooling gas. The cooled iron is then discharged through the bottom of the reactor. Typically, both the reducing gas and cooling gas are recirculated, optionally in closed loops, to which streams of fresh (i.e. “make-up”) reducing gas are added and from which streams of spent gas are removed.

[0004] In various known direct reduction processes, the reducing gas required for reduction of the iron ore is generated in a catalytic reforming unit by conversion of natural gas in accordance with the following reactions:

(1) CH4+H2O=>CO+3H2

(2) CH4+CO2=>2CO+2H2

[0005] In the reforming reactions the natural gas, comprised mainly of methane, is converted to hydrogen and carbon monoxide in the presence of an oxidizing agent. As a result, the reformed gas is substantially composed of hydrogen and carbon monoxide. In recent times, due to the ever decreasing availability and increasing cost of natural gas it has become extremely important and therefore desirable to develop a direct reduction process in which the required quantity of natural gas is minimized.

[0006] The reducing gas being fed to the reduction zone of the reactor is typically at an elevated temperature and is caused to contact the downwardly moving iron ore to reduce the iron oxides therein according to the following basic reduction reactions:

(3) 3Fe2O3+H2/CO−>2Fe3O4+H2O/CO2

(4) Fe3O4+H2/CO=>3FeO+H2O/CO2

(5) 3FeO+H2/CO=>3Fe+H2O/CO2

[0007] The spent reducing gas leaving the reactor is cooled to remove water produced by the reduction of the iron ore with hydrogen after which the cooled and de-watered effluent gas is recycled and then reintroduced to the reduction zone of the reactor. The recirculation, or recycling, of the effluent gas can be accomplished in various ways. For example, the gas may be recycled directly back into the reactor, the gas may be recycled through a reformer and a heater, or the gas may simply be recycled through the heater. In each case, however, fresh reducing gas must be added to the recycled effluent gas prior to injection into the reactor. Since the amount of carbon dioxide generated in the process by the reduction reactions occurring in the reactor is considerable, a portion of the spent gas must be vented or purged from the system in order to reduce the amount of carbon dioxide and to maintain a proper overall carbon balance within the reduction system.

[0008] Efficiency in the direct reduction process is determined, in large part, by the quality and temperature of the reducing gas. “Quality” of a reducing gas is defined by the ratio of carbon monoxide and hydrogen (the reductants) to carbon dioxide and water (the oxidants), i.e., [CO and H2]/[CO2 and H2O]. Hydrogen and carbon monoxide are the preferred components of the reducing gas. Carbon dioxide is not desired because of its inability to reduce iron oxides. Excessive amounts of hydrocarbons are not desired because they react endothermically upon entering the reactor, which reduces the kinetics of the desired iron reduction reactions. And, of course, free oxygen is not desired in the reducing gas because of its tendency to re-oxidize reduced iron. The temperature of the reducing gas affects the reaction kinetics between the various components of the reducing gas with each other and with the iron and iron oxide.

[0009] Reducing gas generators of the prior art, that use oxygen and/or fuel to generate reducing gas, can be classified in two categories; oxygen injection systems and oxy-fuel burners. Oxygen injection systems combust mostly reductant and minor amounts of hydrocarbons. This elevates the temperature of the reducing gas entering the reduction reactor. Excessive reducing gas temperatures will cause sintering of the metal and plugging of the reducing reactor.

[0010] Oxy-fuel burners are designed specifically to maximize the amount of reductant formed by precisely adjusting the flows of oxygen and fuel to a burner. However, the use of oxy-fuel burners does not allow independent control of reducing gas temperature and reduction reactor temperature, because oxy-fuel burners must be operated within certain limits of oxygen and fuel throughput to obtain good conversion of fuel to reductant, to prevent soot formation, to prevent overheating of the burner, and to maintain flame stability. Also, the use of oxy-fuel burners is often prohibitively expensive.

[0011] What is needed is an apparatus and method which generates reducing gas, adding to the recycled/reformed reducing gas, therefore increasing the quantity of hydrogen and carbon monoxide within the reducing gas, while effectively controlling the temperature of the resulting gas stream, and while controlling the amount of CH4 in the resulting gas stream, so that the reduction reactor temperature may be controlled effectively. Such an invention would greatly enhance the economics of the direct reduction process by: 1) controlling reduction reactor temperature for optimum utilization of hydrogen and carbon monoxide in the reduction reactor, thereby minimizing the amount of natural gas required for the direct reduction process; and 2) by minimizing the cost of the apparatus which generates the fresh reducing gas.

OBJECTS OF THE INVENTION

[0012] The principal object of this invention is to provide means for generating reducing gas, particularly H2 and CO, from the combustion of oxygen and fuel, particularly natural gas.

[0013] Another object of the invention is to provide means for increasing the amount of reducing gas generated, particularly H2 and CO, from the combustion of oxygen and fuel, and to produce a high quality reducing gas by combustion of oxygen and fuel, particularly natural gas.

[0014] Another object of the invention is to provide means for increasing the amount of reducing gas generated, particularly H2 and CO, from the combustion of oxygen and fuel, and to produce a high quality reducing gas by combustion of oxygen and fuel, particularly natural gas, while accurately controlling the temperature of the reducing gas stream.

[0015] Another object of the invention is to generate reducing gas, particularly H2 and CO, from the combustion of oxygen and fuel, particularly natural gas, while accurately controlling the concentration of methane/hydrocarbons in the reducing gas stream.

[0016] Another object of the invention is to provide means for increasing the amount of reducing gas generated, particularly H2 and CO, from the combustion of oxygen and fuel, and to produce a high quality reducing gas by combustion of oxygen and fuel, particularly natural gas, while accurately controlling the temperature of the reducing gas stream and simultaneously controlling the level of methane/hydrocarbons in the gas stream.

[0017] Another object of the invention is to provide means for generating reducing gas, particularly H2 and CO, from the combustion of oxygen and fuel, particularly natural gas, while simultaneously minimizing the temperature of the reducing gas stream, for a given oxygen to fuel ratio, and minimizing the cost of the apparatus that generates the reducing gas.

SUMMARY OF THE INVENTION

[0018] The present invention is an apparatus and method for increasing the amount of reducing gas within the reducing gas stream of a direct reduction furnace, while also simultaneously controlling the temperature of the reducing gas stream, and the temperature of the reduction reactor. The method improves the efficiency of direct reduction, by removing and reforming spent reducing gas from a direct reduction furnace to form a high percentage of H2 and CO therein for use as bustle gas, injecting hydrocarbon-containing enrichment gas into the bustle gas, injecting an oxygen-hydrocarbon gas mixture into the bustle gas and combusting the mixture, and introducing the hydrocarbon-enriched bustle gas into the direct reduction furnace. The apparatus is a refractory lined shaft through which reducing gas, also called bustle gas, passes before entering the direct reduction furnace. The improved apparatus has two main sections, an enrichment section and an oxygen/fuel injection section which communicate with the bustle of the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows a block diagram of how the method proceeds.

[0020] FIG. 2 shows a side cutaway view of the invented apparatus.

[0021] FIG. 3 shows a front cutaway view of the invented apparatus.

DETAILED DESCRIPTION

[0022] The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein; rather, this embodiment is provided so that this disclosure will be, thorough and complete, and will convey the scope of the invention fully to those skilled in the art. Like numbers refer to like elements throughout.

[0023] Referring now to the drawings, the present invention is a method and an apparatus for increasing the amount of reducing gas within the reducing gas stream, also referred to as “bustle gas stream” of a direct reduction furnace while simultaneously controlling the temperature and hydrocarbon content of the reducing gas stream. The apparatus is a refractory lined shaft 10 through which reducing gas, also called bustle gas, passes before entering the direct reduction furnace. The apparatus has two main sections, an enrichment section 12 and an oxygen/fuel injection section 14.

[0024] The invented apparatus is located between the reducing gas output of the direct reduction furnace and the reducing gas input of the direct reduction furnace. Upon entering the apparatus, concentration of simple hydrocarbons, typically CH4, is increased by the enrichment section 12 of the apparatus. As the reducing gas continues through the apparatus, the temperature of the gas is adjusted by combustion of an oxygen and fuel mixture injected by the oxygen/fuel injection system 14.

[0025] The invented apparatus is preferably operated in conjunction with a reducing gas reformer unit. In operation, the apparatus is placed between the output of the reformer and the reducing gas input of the direct reduction furnace. Spent reducing gas exits the furnace and enters the reforming unit, completing the recycling circuit of the reducing gas. The reformer, preferably a catalytic reformer, reacts the methane in the reducing gas stream to improve the quality of the reducing gas according to the equations:

(1) CH4+H2O=>CO+3H2

(2) CH4+CO2=>2CO+2H2

[0026] The enrichment section 12 is positioned in the upstream region of shaft 10. The enrichment section 12 introduces natural gas or other hydrocarbon fuels into the shaft 10 so that the main reducing gas stream is enriched with hydrocarbons as the gas stream passes through the shaft 10. The controlled injection of natural gas or other hydrocarbon increases the methane (and other hydrocarbon) content of the reducing gas. Preferably, the natural gas injected by the enrichment section 12 is preheated, up to about 450° C., though the natural gas need not be preheated for effective use of the invention.

[0027] The enrichment section 12 comprises a header 16, external to the shaft 10, which is connected to several separate nozzles 18 which protrude into the shaft 10 from the header 16. In the preferred embodiment, there are 12 such nozzles 18 equally spaced about and protruding through the shaft 10. The nozzles 18 may be constructed from any suitable material but are preferably constructed from stainless steel.

[0028] The nozzles 18 project the natural gas in such manner that the gas enters the shaft 10 perpendicular to the main reducing gas stream. The flow of natural gas into the enrichment section 12 is measured by a methane sensor 20 located far downstream from the enrichment section 12 but located at a location upstream from the reducing gas input to the furnace. Through control means commonly known in the art, the flow rate of hydrocarbons introduced by the enriching section 12 is adjusted by control valve 22 based upon the measurements of methane sensor 20 so that the methane concentration of the reducing gas entering the furnace remains in the range of from about 1% to about 10%.

[0029] The oxygen/fuel injection section 14 is positioned in the shaft 10 downstream from the enrichment section 12. The oxygen/fuel injection section 14 has two sets of components, each set composed of a header and a series of injection ports. The first set of components, the oxygen injection components 24, carry oxygen or an oxygen containing gas into the shaft 10. The second set of components, the fuel injection components 26 for fuel injection, carry a hydrocarbon fuel which is preferably natural gas into the shaft 10. Preferably, the natural gas injected by the oxygen/fuel injection section 14 is preheated, up to 450° C., though the natural gas need not be preheated for effective use of the invention.

[0030] In the preferred embodiment, oxygen injection components 24 of the oxygen/fuel injection section 14 are shrouded by fuel injection components 26 of the oxygen/fuel injection section 14. The key to the preferred embodiment is that the oxygen injection components 24 are coaxially disposed within the fuel injection components 26. This arrangement of injection components in the oxygen/fuel injection section 14 promotes the immediate mixing of oxygen supplied by components 24 with the hydrocarbons supplied by components 26 upon entry into the main shaft. The mixing promotes the combustion of the natural gas injected in the oxygen/fuel injection section 14, rather than allowing the injected oxygen to combust with the hydrogen and carbon monoxide already present in the reducing gas.

[0031] Controlling the manner and extent to which the injected oxygen combusts the natural gas injected by components 26 increases the quantity of the reductant in the resulting reducing gas while, at the same time, regulating the temperature of the reducing gas. By properly controlling the ratio of hydrocarbons and O2 injected by the oxygen/fuel injection system 26, the mixture may be maintained as a rich mixture, resulting in the desired incomplete combustion which results in CO and H2 as products of the combustion. At this stage, excess O2 is undesirable for two reasons. First, any O2 which is not combusted with the hydrocarbons provided by the fuel injection components 26 is free to further combust the CO and H2 already present in the main reducing gas stream into the undesirable products of CO2 and H2O. Second, limited O2 combusted with the hydrocarbons provided by oxy-fuel injection system 26 results in incomplete combustion of the hydrocarbon stream, producing CO and H2 as products rather than the CO2 and H2O which would theoretically result from complete combustion.

[0032] The unique arrangement of shrouding the oxygen with the hydrocarbons supplied by the oxy/fuel injection system 26 results in combustion of the injected oxygen with the shrouding hydrocarbon fuel which reduces the flame temperature within the main shaft. The partial combustion of the inputted oxygen with natural gas or other hydrocarbon, CH4 for example, results in a low temperature flame, and also results in the production of CO and H2, both desired reductants. If the injected oxygen were not shrouded by the natural gas and allowed to combust with the H2 or CO already present in the main reducing gas stream, higher temperatures would result and H2O and CO2, both undesired oxidants, would be generated.

[0033] In operation, the temperature of the reducing gas is measured downstream 20 from the oxygen injection section 14. The flow of oxygen to the oxygen injection section 14 is increased or decreased to maintain the desired reducing gas temperature. The flow of hydrocarbon fuel to the oxy/fuel injection section 26 is increased or decreased by valve 27 in order to remain in constant ratio with the oxygen flow. Adjustment of hydrocarbon fuel to the oxy/fuel injection section 26 is preferably made by measuring the flow of oxygen to the oxygen injection section 24 and using an electronic control device 36 to adjust a flow valve 38 in-line with the hydrocarbon supply of the oxy/fuel injection system 26 such that the hydrocarbon is supplied in a ratio or other predetermined relationship to the amount of oxygen supplied.

[0034] Preferably, proper mixing of the oxygen and the injected hydrocarbons in the oxygen/fuel injection system 14 is accomplished by using dual external headers 42, 44 feeding twelve separate stainless steel nozzles, each having a plurality of oxygen injection ports 46 coaxially aligned with and disposed within a hydrocarbon injection port 48. This arrangement allows the injected hydrocarbon to shroud the injected oxygen as the two gases are projected into the shaft 10. The tips of the hydrocarbon injection ports 48 converge upon the tips of the oxygen injection ports 46 to promote better mixing between the oxygen and the injected hydrocarbons. The injection ports 46,48 are housed in nozzles 28, which are angled downstream into the main bustle gas shaft 10, unlike the perpendicular alignment of the nozzles 18 in the enrichment section 12, to allow for longer flame lengths, avoiding damage to the refractory on the opposite side of the shaft 10. Of course, more than or less than twelve injection ports 46, 48 may be used in the oxygen/fuel injection system 14 with favorable results. Also, a port (46,48) arrangement other than the disclosed shrouding arrangement may be utilized. For instance, a side by side or other port arrangement may be utilized as long as the oxygen and fuel of the oxygen/fuel injection system remain in intimate contact with one another as they are projected into the shaft 10.

[0035] The refractory inside the bustle gas shaft 10 is designed to allow the oxygen/hydrocarbon fuel mixture to burn outside of the turbulence of the main stream of reducing gas. A section of the refractory 50 protrudes slightly from the inner wall of the shaft 10, beginning downstream of the enrichment section 12 and sloping gently inwards to a point just upstream of the oxygen/fuel injection system 14. The oxygen/fuel injection ports 46,48 are positioned just downstream of the protruding refractory section 50, and are angled downstream such that the flow of reducing gas and enriched gas flowing through the shaft 10 are directed to the center region of the shaft 10, and such that the oxygen and hydrocarbons introduced in the oxygen/fuel injection system 14 enter the shaft 10 and are momentarily maintained outside of the turbulence of the main gas stream, thereby allowing the oxygen and fuel of the oxygen/fuel injection system 14 to mix well and bum with one another before entering the main gas stream.

[0036] The oxygen header 42, hydrocarbon fuel header 44, and nozzles 28 have been designed so the oxygen nozzle can be easily removed for inspection, maintenance, etc. The oxygen injection nozzles 46 preferably are made of stainless steel and designed to promote mixing with the shrouding hydrocarbon fuel.

[0037] The enrichment section 12 is located upstream from the oxygen/fuel injection section 14 so that the hydrocarbons injected in the enrichment section 12 can potentially bum with any unconsumed oxygen from the oxygen/fuel injection section 14 before the oxygen combusts with H2 or CO in the main reducing gas stream.

EXAMPLE

[0038] The following are examples of the calculated flow rates of oxygen and hydrocarbon fuel expected given the component properties and measured variables below:

[0039] Reducing Gas from Reformer

[0040] Temperature: 940° C.

[0041] H2/CO is 1.55

[0042] Composition is 1.6% CH4, 2.8% CO2, 6.0% H2O, 54.2% H2, 34.9% CO, 0.5% N2

[0043] Flow is 300,00 Nm3/h

[0044] Enrichment Gas (same as fuel for oxygen/fuel injector)

[0045] Temperature: 400° C.

[0046] Composition is 87.55% CH4, 8.86% C2H6, 2.45% CO, 0.5% CO2, 0.6% C3+

[0047] Oxygen

[0048] Temperature: 20° C.

[0049] Composition: 99.5% O2

	Case 1	Case 2
Measured Bustle Gas Temp	1050° C.	1050° C.
Measured Reduction Shaft Temp	850° C.	900° C.
Measured Bustle Gas CH4	4.72% wet	3.30% wet
Oxygen/Fuel Injection Flow (O2)	3766 Nm3/h	3141 Nm3/h
Oxygen/Fuel Injection Flow (Hydrocarbon)	6277 Nm3/h	5235 Nm3/h
Enrichment Flow (Hydrocarbon)	5923 Nm3/h	1490 Nm3/h

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION

[0050] From the foregoing, it is readily apparent that we have invented an improved method and apparatus for optimizing the use of oxygen in the direct reduction of iron which may be utilized to increase the amount of reductant generated from the combustion of oxygen and fuel relative to the current oxygen injection systems; which is capable of producing a higher quality reducing gas than present oxygen injection systems; and which can accurately control the temperature of the gas stream and control the level of methane/hydrocarbons in the reducing gas stream.

[0051] It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention, which is therefore understood to be limited only by the scope of the appended claims.

Claims

1. A method of controlling the properties of a stream of bustle gas for use in the direct reduction of iron, comprising: supplying a hydrocarbon-containing enrichment gas at a controlled flow rate; supplying a hydrocarbon-containing fuel gas at a controlled flow rate; supplying an oxygen containing gas at a controlled flow rate; injecting the enrichment gas into the bustle gas stream; and simultaneously mixing the fuel gas with the oxygen containing gas to form a fuel/oxygen gas mixture, and injecting the fuel/oxygen gas mixture into the bustle gas stream and causing the injected fuel/oxygen gas mixture to be substantially combusted prior to becoming dispersed within the bustle gas stream.

2. A bustle gas control method according to claim 1, further comprising: receiving reformed bustle gas from a bustle gas reforming unit prior to injecting enrichment gas into the bustle gas stream.

3. A bustle gas control method according to claim 2, further comprising: introducing the stream of bustle gas into a direct reduction furnace after injecting the enrichment gas and the fuel/oxygen gas mixture into the bustle gas.

4. A bustle gas control method according to claim 1, wherein the enrichment gas is injected into the bustle gas stream by projecting the enrichment gas stream substantially perpendicular to the flow of the bustle gas stream.

5. A bustle gas control method according to claim 1, further comprising: analyzing the hydrocarbon content of the bustle gas stream at a point downstream from the point of injection of the fuel/oxygen gas mixture; and, adjusting said controlled flow rate of enrichment gas such that the resulting analyzed hydrocarbon content is within a predetermined range.

6. A bustle gas control method according to claim 5, wherein said hydrocarbon is methane.

7. A bustle gas control method according to claim 6, wherein said methane content is from about 1% to about 10%.

8. A bustle gas control method according to claim 1, further comprising: measuring the temperature of the bustle gas stream at a point downstream from the point of injecting the fuel/oxygen gas mixture; and adjusting the controlled oxygen flow rate so that the resulting bustle gas temperature is within a predetermined range.

9. A bustle gas control method according to claim 8, wherein the resulting bustle gas temperature range is from about 950° C. to about 1250° C.

10. A bustle gas control method according to claim 8, further comprising: adjusting the controlled fuel gas flow rate in relationship to the adjusted oxygen flow rate such that said resulting fuel/oxygen gas mixture contains an excess of fuel.

11. A bustle gas control method according to claim 1, further comprising lowering the temperature of the bustle gas stream prior to the injection of enrichment gas.

12. A bustle gas control method according to claim 1, further comprising preheating the enrichmnent gas.

13. A bustle gas control method according to claim 1, further comprising preheating the fuel gas.

14. An apparatus for installation between the spent bustle gas output and the reformed bustle gas input of a direct reduction furnace for improving the efficiency of the direct reduction furnace, such apparatus comprising: a shaft means for containing a stream of said bustle gas; means for injecting a hydrocarbon-containing enrichment gas into said shaft; and, means for injecting an oxygen-hydrocarbon gas mixture into said shaft downstream of said enrichment gas injecting means.

15. An apparatus according to claim 14, wherein said enrichment gas injection means comprises a header, positioned exterior to the shaft, in communication with several separate nozzles which protrude into the interior of the shaft.

16. An apparatus according to claim 15, wherein the internal surface of the portion of the shaft through which the nozzles protrude is generally cylindrical; and the protruding nozzles are flush with the internal surface of the shaft.

17. An apparatus according to claim 14, wherein the gas mixture injection means comprises an oxygen injection component and a fuel injection component.

18. An apparatus according to claim 17, wherein said oxygen injection means comprises a header, positioned exterior to the shaft, in communication with several separate nozzles which protrude into the interior of the shaft; and, wherein said fuel gas injection means comprises a header, positioned exterior to the shaft, in communication with several separate nozzles which protrude into the interior of the shaft.

19. An apparatus according to claim 18, wherein said oxygen injection component is disposed within said fuel injection component.

20. An apparatus according to claim 19, wherein said oxygen injection component is coaxially disposed within said fuel injection component.

21. An apparatus according to claim 18, wherein the nozzles of the gas mixture injection means are angled with respect to the internal surface of the shaft such that a mixture of oxygen and fuel injected into the shaft is injected at an angle of between 15° and 75° with respect to the direction of flow of the bustle gas.

22. An apparatus according to claim 21, wherein a portion of the inner surface of the shaft forms a protrusion between the enrichment gas injection means and the mixture gas injection means of the shaft; whereby bustle gas flowing through the shaft is directed towards the center of the shaft by said protrusions.

23. An apparatus according to claim 17, further comprising a temperature measurement means in communication with said bustle gas stream downstream of said gas mixture injection means; and, an oxygen flow control valve operatively connected to said temperature measurement means, said oxygen valve situated in-line with said oxygen injection component.

24. An apparatus according to claim 15, further comprising: a hydrocarbon measurement means in communication with said bustle gas stream downstream of said enrichment gas injection means; an enrichment gas supply line in communication with said enrichment gas injection means; and an enrichment flow control valve operatively connected to said hydrocarbon measurement means, said enrichment valve situated in-line with said enrichment gas supply line.