Abstract:
A system for introducing a homogenous mixture of natural gas and oxygen into the tuyeres of a blast furnace. Included in this system are gas conduits with flow controllers connected to a mixer that produces a homogenous mixture. Provisions are made to by-pass the mixer and to introduce inert gas into the mixer to prevent formation of explosive gas mixtures.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the field of ferrous metallurgy, specifically the blast-furnace process, and is applicable to feeding natural gas into blast furnaces. 
     In trying to reduce fuel consumption in a blast-furnace process by burning natural gas in a more efficient way, various gas regulation systems for blast furnaces have been developed. 
     One system was designed for regulation of the pressure and rate of natural gas injected into a blast furnace and for its distribution among the air tuyeres. That system consisted of: a natural gas supply pipe-line provided with a shutoff, safety, measuring and control instruments, a bypass line complete with gate valves and gas vent, and a circular manifold with connections for feeding gas to each air tuyere, the circular manifold provided with shutoff and safety devices. This gas regulation system suffers from a number of drawbacks. Among them are; lack of measuring and regulating devices in connecting pipes feeding natural gas to tuyeres, lack of devices preventing the formation of explosive mixtures in the gas regulation system, lack of a system for maintaining the prescribed ratio between the natural gas and blast air (or blast oxygen) flow rates, and lack of devices for preparation of natural gas for efficient combustion in the tuyere zone. 
     Another gas regulation system for use with a blast furnace, is the one consisting of the natural gas pipe-line with shutoff, safety, measuring and control instruments, a pipe-line, connected to the natural gas line and equipped with shutoff and control instruments, for purging and filling it with inert gas; a bypass line with shutoff and regulation instruments, and a distributing manifold with connections, equipped with shutoff, safety, measuring and regulating instruments, for feeding the gas to each air tuyere. This gas regulation system eliminates most of the drawbacks of the previous system but retains its main weakness, namely inability to prepare natural gas for efficient burning in a blast furnace which leads to excessive fuel usage in making pig iron. 
     BRIEF SUMMARY OF THE INVENTION 
     The goal of the invention is to improve the last described process above to reduce the rate of fuel usage rate in the blast-furnace process. 
     In order to achieve this goal the present invention includes a gas regulation S system for a blast furnace consisting of natural gas and inert gas pipe-lines, a distributing manifold with gas supply lines to air tuyeres and a bypass pipe-line, as well as shutoff, safety, measuring and control instruments installed in those pipe-lines and a mixer in the natural gas pipe-line and an oxygen supply pipe connected to the mixer, with a by-pass pipe connected to the natural gas pipe-line before and after the mixer, and an inert gas pipe-line connected to the oxygen supply line. 
     Thus in one aspect the present invention is a system for introducing a mixture of natural gas and oxygen into the tuyeres of a blast furnace having a source of natural gas connected to a mixer via a natural gas supply pipe or conduit, the pipe having, upstream of the mixer, a flow control valve to initiate, control and terminate flow of a natural gas to the mixer, flow control means between the flow control valve and the mixer, with a check valve between the flow control means and the mixer, a source of oxygen connected to the mixer via an oxygen supply pipe or conduit the pipe having, upstream of the mixer a flow control valve to initiate, control and terminate flow of oxygen to the mixer, flow control means followed by a check valve between the flow control valve and the mixer, means to introduce an inert gas into the mixer, and means to by-pass the mixer to deliver natural gas, without mixing with oxygen and/or inert gas, directly to the blast furnace tuyeres. 
     In a preferred embodiment of the invention the mixer is made in the form of a cylindrical chamber with a diameter to length ratio being in the range of 0.4-0.7. A perforated tube, connected to the oxygen supply pipe-line with one end closed, is inserted into the cylindrical chamber with the longitudinal axis of the tube perpendicular to the longitudinal axis of the cylinder, wherein diameter of the perforated tube is equal to 0.15-0.5× the diameter of the cylindrical chamber of the mixer. The total area of the holes in the perforated tube is in the range of 0.3-0.6× the flow area of the tube with the diameter of holes in the range of 0.03-0.07× the tube diameter. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a gas regulation system according to the present invention. 
     FIG. 2 is a schematic representation of a mixer according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1 the gas regulation system includes: a natural gas pipe line or conduit  10  connected to a source of natural gas  12 , an oxygen pipe-line or conduit  14  connected to a source of oxygen  16  and inert gas pipe-line or conduit  18  connected to a source of inert gas  20 , a bypass line or conduit  22 , a manifold  24  with delivery pipe-lines or conduits  26  for supplying the gas to blast furnace (air) tuyeres  28 , and a mixer  30 . 
     Pipe-lines  10 ,  14 , and  18  are designed to feed natural gas, oxygen and inert gas, e.g. nitrogen, respectively into the mixer  30 . The bypass pipe-line  22  serves to supply natural gas directly into the manifold  24  bypassing the mixer  30 . Manifold  24  and delivery pipe-lines  26  are intended to supply natural gas or a natural gas/oxygen mixture to the blast furnace tuyeres  28 . The mixer  30  is designed to obtain a homogeneous mixture of natural gas and oxygen. 
     Natural gas pipe-line, conduit or supply line  10  is equipped with a shut-off or control valve  32  to initiate or terminate the flow of natural gas from source  12 , a bleeder control valve  34  leading to a bleeder valve or device  36  to vent natural gas or purge the system, an orifice plate  38 , solenoid operated valve  40 , regulating valve  42 , check valve  44 , mixer  30  and mixer isolation valves  46  and  48  together with mixer bypass conduit  22  and mixer by-pass valve  50 . Pipe-line  10  supplies natural gas to a manifold  24  which supplies pipe-lines (e.g.  26 ) which in turn supply the natural gas to the blast furnace tuyere(s)  28 . Delivery pipe-line or conduit  26  includes natural gas flow control valve  52 , flow plate  54  and flow plate isolation valves  56  and  58  and a check valve  60 . Manifold  24  also includes a vent or recovery conduit  62  with a manual control valve  64  and solenoid operated control valve  66  leading to a bleeder valve or recovery or vent system  68 . 
     Oxygen pipe-line, conduit or supply line  14  is equipped with a manual control valve  70 , a dust collector or separator  72  with a clean out valve  74 . Dust collector  72  serves to remove solid particulate material from the oxygen. The pipe-line  14  is fitted with a bleeder control valve  76  leading to a bleeder valve, recovery or vent system  78 . Downstream of the system  78  is an orifice plate  80 , regulating valve  82 , solenoid operated control valve  84  and a shut-off valve  86  upstream of the location  88  where the nitrogen pipe-line  18  enters a common conduit  90  which is connected through a check valve  92  and control valve  94  to the mixer  30  as will hereinafter be more fully explained. 
     Nitrogen pipe-line, conduit or supply line  18  includes a cut-off valve  96  to initiate or terminate nitrogen flow through conduit  18 , control valve  98  and check valve  100  leading to a surge tank  102 . Inclusion of surge tank  102  is intended to enable the user to create an emergency reserve by accumulation of an excess amount of inert gas. Surge tank  102  can be bled or vented through a system including a control valve  104  leading to a recovery or vent  106 . Downstream of surge tank  102  pipe-line  18  includes an orifice plate  108  a shut-off valve  110  a branch line or conduit  112  with a control valve  114  leading to a bleeder, vent or recovery system  116 , a control valve  120  upstream of a check valve  122 , in pipe-line  18  prior to its entry into the common conduit  90  at location  88 . 
     Shut off devices, which include gate valves, solenoid-operated and manually operated valves, as well as regulating valves and cutoff valves, serve to shut off, or isolate from the gas regulation system, separate pipe-lines or sections of pipe-lines when gases supplied to the system are stopped, i.e., during repair and maintenance work and in emergency situations. 
     Safety devices which include check valves and bleeder valves are intended to a) automatically cut off oxygen supply to the mixer, b) to automatically switch on and continuously feed inert gas into the oxygen pipe-line and, c) cut off inert gas automatically with reduction of its pressure in the outer circuit in emergency situations, as well as, d) to bleed a certain amount of oxygen and inert gas from the system in case of excessive pressure. 
     Measuring instruments in addition to the orifice plates or flow meters can include pressure and temperature sensors, to measure; the flow rates of natural gas, oxygen, inert gas, natural gas/oxygen mixtures and blast air, the pressure of natural gas, oxygen, inert gas and blast air, and, the temperature of the natural gas/oxygen mixture. Instruments, not shown in FIG. 1, are intended to regulate oxygen pressure, natural gas pressure and flow rates of natural gas, oxygen and natural gas/oxygen mixtures. Such instrumentation is well known in the art. 
     Referring to FIG. 2 during the operation of the gas regulation system natural gas and oxygen are supplied into the mixer  30  through pipe-lines  10  and  14  at the pre-assigned pressure values and preset ratio of flow rates. A homogeneous natural gas/oxygen mixture formed in the mixer arrives at the manifold  24  and via connecting pipe-lines  26  is fed into tuyere(s)  28 . The mixer  30  includes a cylindrical chamber portion  130  which is disposed in pipe-line or conduit  10  between valves  46  and  48  with the axis of rotation of the cylinder coincident with or parallel to the longitudinal axis of pipe-line  10 . A tube  132  communicating with the common pipe-line  90  downstream of valve  94  is placed into the cylindrical portion  130  of mixer  30  generally perpendicular to the axis of rotation of the cylindrical chamber portion  130 . The tube  132  has a closed end  134  and a plurality of perforations  136 . The tube  132  is fixed in fluid tight relation to the cylindrical chamber portion  130  with all of the perforations  136  inside of the chamber  130 . 
     Inert gas (e.g. nitrogen) via pipe-line ( 18 ) is mixed with or injected into the oxygen from pipe-line ( 14 ) in common conduit  90  during the start-up of the gas regulation system in order to prevent the formation of explosive mixtures. 
     The maximum homogeneity of the natural gas/oxygen mixture is provided at the following ratios; 
     diameter of the mixer cylindrical chamber to its length 0.4-0.7 
     diameter of perforated tube to diameter of cylindrical chamber 0.15-0.5 
     diameter of holes in perforated tube to its diameter 0.03-0.07 
     total area of holes in the tube to its flow section 0.3-0.6 
     which ratios were determined experimentals. 
     A system according to the invention was fabricated and installed in a blast furnace shop in Cherepovets in the Russian Federation. The system had a mixer fabricated as shown in FIG. 2 with the following dimensions: 
     A. Cylindrical Chamber Portion ( 130 ) 
     Inside Diameter 410 mm (16.14 inches) 
     Length 750 mm (29.52 inches) 
     B. Tubes or Perforated Pipe ( 132 ) 
     Inside Diameter 100 mm (3.93 inches) 
     Total Cross-sectional Area of Holes or Perforations 3532 mm 2  (5.48 sq. inches) 
     Number of holes or perforation  180   
     Diameter of each hole or perforation 5 mm (0.20 inches) 
     The mixing chamber was operated to provide a homogeneous mixture of 20% oxygen, balance natural gas when the oxygen flow to the perforated pipe was 52 Nm 3  (1940.6 std ft 3 )/minute and natural gas flow was 208 Nm 3  (7762.6 std ft 3 )/minute. 
     When natural gas arrives at the tuyeres in the form of a uniform mixture with oxygen, the process of burning of natural gas accelerates which provides for its complete combustion in the tuyere zone, increases coke replacement ratio and decreases coke and total fuel consumption during blast furnace operation. 
     Having thus illustrated and described the invention herein with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Furthermore, various modifications may be made in the details within the scope of the invention that is defmed in the appended claims.