FIELD OF THE INVENTION
1. The present invention relates to a process for gas based direct reduction (DR) in DRI plant
to produce high quality direct reduced iron with help of coke oven gas (COG) and/or mixture of
coke oven gas and syngas.
2. The present invention further relates to a methodology of producing DRI where the coke
oven gas (COG) can be utilized in optimum quantity.
3. COG is a by-product of coke making process and readily available at any integrated steel
plant, which reduces the Syngas consumption by using excess coke oven gas.
BACKGROUND OF THE INVENTION
4. The process reduces the Iron ore or Iron ore pellets without melting; it called the DRI
process. The feed material in this process is either Iron ore pellets or Iron ore 08-20 mm. The DRI
process can be classified according to the kind and source of reducing gas or type of reactor used.
Depending on the generation of reducing gas, two different DR processes are commercially
available: gas-based and coal/oil. The gas-based DR process is more energy-efficient (required
less than half energy) and higher metallization than the coal-based DR process.
5. The produced Syngas injected into the reduction furnace(1), which mixed with the
recycling gas, coming from the CO2 removal. The reducing gas is heated up to 920°C in the process
gas heater. Also, the oxygen gas is injected into the transfer line just before the reactor to increase
the temperature of the reducing gas to the required level for in-situ reforming and reduction inside
the reactor.
6. In this process, partial oxidation is carried out in the transfer line and hence the reducing
gas inlet temperature increases. The partial oxidation and reforming reactions are as follows:
CH4+ ½O2 → CO + 2H2 (1)
O2 + 2H2 → 2H2O (2)
CH4 + H2O → CO + 3H2 (3)
2

CO2 + H2 → CO + H2O (4)
7. In this process, the hot reducing gas is fed to the reactor reduction zone and flows upward
counter-currently to the Iron ore moving bed. The gas distribution is uniform, and there is a high
degree of direct contact between the gas and solid. The exhaust reducing gas (top gas) leaves the
reactor at about 450 °C and passes through the quenching/scrubbing system. In these units, water
produced during the reduction process is condensed and removed from the gas stream, and hence
most of the dust carried with the gas separated. Scrubbed gas is then passed through the process
gas recycle compressors, where gas pressure is increased. The compressed gas (after being sent to
the carbon dioxide removal unit) is mixed with the syngas makeup closing the reducing gas circuit.
8. The steel production through the DR route is costlier due to the higher cost of produced
syngas. This higher cost of syngas is due to the lack of availability of the superior quality of Indian
coals.
9. Therefore, a team had worked on another possible route to produce hot metal at an
economical cost. In recent past effort has been made to utilize alternative fuel in this process. This
is necessary to use lower-cost fuel to produce optimal cost of hot metal.
10. Hence, there is a long felt need to provide an economic and more improved technology for
production of DRI.
11. Based on several methodologies, the present inventors found that the coke oven gas (COG)
may efficiently use the existing DRI process with some modifications resulted comparatively
lesser cost of hot metal production.
12. The coke oven gas sometimes got wasted, which is easily utilized in the present invention
as an alternative fuel of syngas in the DRI plant. It is well known that coke oven gas has a high
calorific value as compared to syngas, and therefore it may not like to like use in the DRI plant,
but of course, it may partially replace the syngas, which will reduce the DRI cost significantly.
3

OBJECTS OF THE PRESENT INVENTION
13. It is therefore the primary object of the present invention to provide a methodology for
production of DRI with Syngas or mixture of coke oven gas and syngas.
14. Another object of the present invention for developing a methodology for injecting COG
gas in reducing gas heater(7) through COG booster compressor.
15. Yet another object of the present invention is to propose a process for utilization of coke
oven gas in reducing heater through COG booster compressor for reducing the cost.
16. Still another object of the present invention is to propose a process for reducing the
dependency of Syngas gas based DRI plant
17. Further, the object of the present invention is to propose the use of alternative fuel for
improving the process efficiency also.
18. Still another object of the present invention is to propose a process for reducing the
generation of less CO2 emission by saving the quantity of non-coking coals.
19. Another object of the present invention to provide the process, where use of COG has
reduce the use of coal in the gasification unit, and thereby it will help to decrease the DRI
production cost through the lesser cost of fuel gas.
SUMMARY OF THE INVENTION
20. One or more drawbacks of conventional systems and process for a method for assessing and
overcome, and additional advantages are provided through the method as claimed in the present
disclosure. Additional features and advantages are realized through the technicalities of the present
disclosure. Other embodiments and aspects of the disclosure are described in details herein and are
considered to be part of the claimed disclosure.
21. The present invention relates to a process for gas based direct reduction (DR) in DRI plant
4

to produce high quality direct reduced iron with help of Syngas and/or mixture of coke oven gas
and syngas.
0022. According to this, there is a developed process for replacing the syngas by utilization of
COG in reducing gas heater(7) and reduction furnace(1) comprising the steps of:
Production DRI in gas-based DRI plant;
Addition of COG in Bustle Gas in reduction furnace (1);
Addition of COG in Reheat Gas Line in reduction furnace (1);
Addition of COG in Product Cooler (2);
Maintain the same process efficiency of the DRI plant;
Reduce the fuel requirement and thereby reduce the DRI/ Sponge Iron cost.
Reduce the fuel (Syngas) requirement and thus reduce the CO2 emission.
Increase the cooling efficiency of the product cooler (2).
Reduce the production cost of DRI.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
23. The illustrated embodiments of the subject matter will be best understood by reference to
the drawings, wherein like parts are designated by like numerals throughout. The following
description is intended only by way of example, and simply illustrates certain selected
embodiments of system processes that are consistent with the subject matter as claimed herein,
wherein:
24. Figure 1 illustrates the schematic layout of Syngas based DRI plant for DRI (direct reduced
iron) production or sponge Iron.
25. Figure 2 illustrates the schematic layout of the proposed process for the addition of COG
in bustle gas line, reheat gas line (5) in reduction furnace(1) and addition of COG in product cooler
(2).
5

26. Figure 3: Schematic layout COG compressor (3).
27. Figure 4: Schematic layout COG preheater (Top view) (4).
28. Figure 5: Schematic layout COG Preheater (Side view) (4).
29. The figure depict embodiments of the disclosure for purposes of illustration only. One
skilled in the art will readily recognize from the following description that alternative embodiments
of the methods illustrated herein may be employed without departing from the principles of the
disclosure described herein.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
30. While the embodiments of the disclosure are subject to various modifications and
alternative forms, specific embodiment thereof have been shown by way the figures and will be
described below. It should be understood, however, that it is not intended to limit the disclosure to
the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications,
equivalents and alternative falling within the scope of the disclosure.
31. It is to be noted that a person skilled in the art would be motivated from the present
disclosure to arrive at a method for producing higher productivity of DRI in furnace with the
mixture of coke oven gas and syngas. Such a method for evaluating the same may vary based on
configuration of one or more workpieces. However, such modifications should be construed within
the scope of the disclosure. Accordingly, the drawings illustrate only those specific details that are
pertinent to understand the embodiments of the present disclosure, so as not to obscure the
disclosure with details that will be clear to those of ordinary skill in the art having benefit of the
description herein. The present invention relates to a process for gas based direct reduction (DR)
in DRI plant to produce high quality direct reduced iron with help of Syngas and/or mixture of
coke oven gas and syngas.
32. Table 1 provides the typical composition of Syngas

he overall process flow sheet of only syngas gas-based DRI process is mentioned in
Figure 1.
35. The process equipment used raw material (Iron ore/pellet), reduction furnace(1), gas
scrubber(5), process gas compressor, CO2 removal, reducing gas heater, turbo expander, feeding
line of syngas gas to reducing gas heater(7) and process gas feeding line to reduction furnace(1)
etc.
36. The overall process flow sheet of process i.e. with mixed gas (Syngas + COG) as claimed
is shown in Figure 2. The process equipment used raw material (Iron ore/pellet), reduction furnace
(1), gas scrubber (5), process gas compressor, CO2 removal system (6), reducing gas heater (7),
turbo expander (8), feeding line of syngas gas to reducing gas heater, COG compressors, COG
heaters, mixed process gas (Syngas + COG) feeding to bustle and reheat line in reduction
furnace(1), COG injection to product cooler (2) etc.
37. An arrangement was made to inject mixed gas (Syngas + COG), which is shown in Figure
2. A separate arrangement is made in the existing system to install compressor# 1 and
compressor#2 along with COG heater #1 and COG Heater #2. Therefore the heated COG gas @
400 - 450 Degree C is injected directly into the different part of the Reduction furnace(1). A series
of three ejectors were also installed in the proposed process for ejecting the COG in the Reheat
Gas Line (9) and Bustle Gas Line (10) in the proposed system. The injected COG goes to the
different sections of the reduction furnace(1) and helps provide the better efficiency of the
7

Reduction Furnace(1) and produce the better quality of the pellet.
38. The injected COG reduces the consumption of Syngas in the Reduction Furnace(1).
Control valves (11) are provided in the COG injection line before the Bustle gas line(10), and
another control valve is provided in the reheat gas line(9), one another control valve is provided in
the Transition Gas line. These valves regulate the flow of outgoing COG and are mixed with the
syngas based on the requirement of the Reduction Furnace(1). In the present invention additional
arrangement also has been made to inject the COG in the product cooler(2). One more control
valve has been provided in the COG Injection line to control the flow of desired COG into Product
Cooler(2). The arrangement of the COG line from the compressors, heaters, ejectors and product
cooler(2) shown in Figure 2. The flow rate of COG at the syngas line is set according to the
appropriate ratio of syngas and COG. The mixed gas is injected into the reduction furnace(1) so
that the mixed gas is uniformly distributed over the reduction furnace(1) for efficient production
and produced the desired quality of DRI.
39. The COG compressor(3) and heater are used to add COG into the bustle line, Transition
line (12) & reheat line in the reduction furnace(1). Also, COG added into the product cooler(2) in
the proposed invention. The process flow diagram is present in Figure 2. Whereas the schematic
layout of COG compressors(3) is depicts in Figure 3. Figure 4 shows the schematic configuration
of the COG preheater(4) top view. Figure 5 shows the schematic arrangement of the COG
preheater(4) side view.
40. In this invention, two COG screw compressors (3) having a capacity of 28,000 cubic meters
per hour installed. Each compressor receives 60 mbarG COG due to the low pressure of COG from
the coke oven battery, and therefore it converts to 2.5 BarG of pressure and injects. In this
invention, two separate COG preheaters (4) also installed, followed by COG compressors(2). The
preheater increases the COG temperature up to 400-450°C, which will reduce heat loss in the DRI
main Gas System. This 400-450°C preheated COG gas then injected into the reduction furnace(1)
through the RG header(12), reheat line and transition zone.
41. In this invention, a provision also made for COG injection in product cooler(2) since COG
has approximately 25% methane, which helps better cooling in DR product in product cooler(2).
8

The COG is used in the direct reduced iron plant as a supplement of reducing gas for making DRI
(Table 2). Other than the CO and H2, which are the main constituents for reduction as it contains
methane in the range of 24% to 26%, the COG consumption in the DRI process is more
challenging. Therefore, a peculiar COG addition system designed to efficiently utilise COG as a
reducing gas to overcome this challenge. For this purpose, different provision to be made to add
COG to the reduction furnace(1) in four locations:
1. RG Header(12)
2. Reheat Line
3. Transition Zone(13)
4. Product Cooler(2)
0042. The process of the present invention comprises the steps of:
Addition of iron ore lump and pellet as feed to produce DRI or sponge iron at DRI plant;
Heating of fuel gas at 920 °C in the process gas heater before charging into the reduction
furnace(1);
0043. In the original system the consumption is more and also the production of Syngas costly.
Therefore the DRI production cost is high.
Addition of COG in Bustle Gas in reduction furnace(1), addition of COG in Transition gas line
and addition of COG in Reheat Gas Line(9) in reduction furnace(1) through COG compressor(3)
and heater;
COG gas mixed in the cooling gas before charging to the Product Cooler(2) through injection.
0044. In the present invention, COG is replaced the syngas 1.18 times i.e., 56,000 Nm3/h COG
is replacing 66,080 Nm3/h syngas for the same productivity of DRI. Therefor syngas requirement
reduces significantly in the DRI and hence reduce the coal gas requirement for making 1.8 times
costlier syngas in coal gasification plant. This reduction in coal consumption in coal gasification
plant also help for reducing the CO2 emission by 300 kg/MT DRI production. Hence, by adopting
the said process, 1,72,000 INR/h i.e., 860 INR/MT of DRI production saved. By the implementing
the said process the productivity and resultant quality of DRI remain constant.
9

45. The equipment used in production of DRI comprises a COG compressor(3) and a heater to
add COG into the bustle line & reheat line in the reduction furnace(1). Also, COG added into the
product cooler (2) (as illustrated in figure 2).
46. Figure 3 depicts the schematic layout of COG compressors(3).
47. Figure 4 shows the schematic configuration of the COG preheater(4) top view.
48. Figure 5 shows the schematic arrangement of the COG preheater(4) side view.
49. In this invention, two COG screw compressors having a capacity of 28,000 cubic meters
per hour installed. Each compressor receives 60 mbarG COG due to the low pressure of COG from
the coke oven battery, and therefore it converts to 2.5 BarG of pressure and injects.
50. In this invention, two separate COG preheaters(4) also installed, followed by COG
compressors (3). The preheater increases the COG temperature up to 400-450°C, which will reduce
heat loss in the DRI main Gas System. This 400-450°C preheated COG gas then injected into the
reduction furnace(1) through the RG header (12), reheat line and transition zone.
51. In this invention, a provision also made for COG injection in product cooler(2) since COG
has approximately 25% methane, which helps better cooling in DR product in product cooler(2).
The COG is used in the direct reduced iron plant as a supplement of reducing gas for making DRI
(Table 2). Other than the CO and H2, which are the main constituents for reduction as it contains
methane in the range of 24% to 26%, the COG consumption in the DRI process is more
challenging.
52. Therefore, in accordance to another embodiment of the present invention, there is provide
a COG addition system designed to efficiently utilise COG as a reducing gas ,which comprises
different provision to be made to add COG to the reduction furnace(1) in four locations:
53. RG Header (12), where COG has added with reducing gas at a temperature of 880°C -
900°C. With the addition of COG, the methane percentage in the reducing gas has increases to 9%
from 6%. The oxygen injection is also done into the mixed feed gas with COG to ensure the
10

reduction process in the furnace. Hence, the entire gas composition changed, which is known as
bustle gas. In this bustle gas, methane gas percentage comes down due to partial oxidation of
methane to the tune of 0.8%-1.0%. Hence, gas temperature increases to 1000-1020°C, and this
temperature further helps the furnace to ensure CO, H2 reduction, and in-situ reforming of
methane. This in-situ reforming of methane generates further CO and H2. Following reactions are
taking place in the RG header (12) and reduction furnace(1).
i. Partial Oxidation of Methane
CH4+ O2 → CO + H2O (5)
CH4 + H2O → CO + 3H2 (6)
ii. In-situ Reforming of CH4
CH4 +H2O → CO + 3H2 (7)
CH4 + CO2 → 2CO + 2H2 (8)
iii. Reduction Reaction
Fe2O3 + 3CO → 2Fe + 3CO2 (9)
Fe2O3 + 3H2 → 2Fe + 3H2O (10)
0054. Reheat Line, which is located in the lower part of the reduction furnace(1) where COG is
added in the reheat line, located in the lower part of the reduction furnace(1) where hot DRI at
around 700°C - 750°C moves towards bottom of the reduction furnace(1). In this section hot DRI
temperature is utilized by reheating the COG and enhancing the carburization reaction to provide
carbon to product DRI. Other than this, hot CO and H2, and methane go up as up flow in the
reduction furnace(1), and it helps in adding additional reducing gas at the reduction zone for the
DRI production. The following Carburization reactions take place:
3Fe + CH4 → Fe3 + 2H2 (11)
3Fe + CO + H2 → Fe3C + H2O (12)
0055. The gas enters into the furnace through eight nozzles all across the furnace periphery, and
it equally distributes the COG mixed with the hot feed coming from the heater outlet RG header
11

(12).
0056. Transition Zone (13)
which is located just below the reduction zone and above the reheat zone, and in the transition
zone, Syngas/COG is added into the process mainly to ensure the product DRI carbon content by
carburization reaction.
57. In this zone, the furnace temperature (750 - 800 °C) helps to crack some methane as free
carbon to DRI and carburization reaction. Most of the carbon is from carburization. The
carburization reaction occurred in the reheat zone reaction (Equation 11 & 12). After completing
the carburization reaction, some gas goes up as up-flows to the reduction zone, enhancing the DRI
production.
58. Product Cooler(2) where the COG is mixed in a Product Cooler(2) of gas-based DRI plant
in place of the cooling medium to enhance the cooling capacity due to its nitrogen and methane
content present in the gas. This addition of COG line in the present system taken from the outlet
of the COG compressors(3) to Product cooler(2) for enhancing the cooling efficiency. By addition
of COG in the product cooler(2), percentage of methane gas increases. The methane gas has higher
specific heat as compared to CO, H2 and N2 gas. Therefore the present methane in the COG
enhances the hot DRI cooling as compared to earlier cooling media. Also, the hot cooling gas
coming out from the product cooler(2) is cooled in a cooling gas scrubber(5) and compressed in
cooling gas compressor to recycle as cooling gas to the product cooler(2), and part of it used as
process gas as makeup and to utilize the methane and CO, H2 content of the COG.
59. Table 3: Typical composition of Bustle Gas after mixing coke oven gas COG
60.
61.
0060. Table 4 discloses the typical composition of Reheat Gas after mixing coke oven gas (COG)
Table - 4
12

0065. BASIC ASSUMPTIONS FOR COMPARISON OF THE POTENTIAL OF SYNGAS
AND (SYNGAS + COG) AS FUEL
Production of DRI : 225 TPH
14

Bustle gas temperature : 1000 °C
Moisture content in pellet : 1.5 %
Feed rate of pellet : 320 MT/h
NCV of coke oven gas : 4,182 kcal/Nm3
NCV of Syngas : 3,500 kcal/ Nm3
Temperature at reducing gas at O/L of heater : 920 °C
Bed temperature of reduction furnace(1) : ~ 780 - 820 °C
Metallization : >92 %
0066. LIST OF ABBREVIATIONS
BT : Bustle gas temperature
COG : Coke oven gas
CGP : Coal gasification plant
DRI : Directly reduced iron
CDRI : Cold DRI
h : hour
kCal : kilo Calories
NCV : Net calorific value
Nm3 : Normal cubic meter
RG : Reducing gas
t : Ton
TGS : Top gas scrubber(5)
TPH : Ton per hour
TGF : Top gas fuel
O/L : Outlet
15

0067. The technical advantages of the process as claimed are given below:
i. Maintain the same process efficiency of the DRI plant;
ii. Reduce the fuel requirement and thereby reduce the DRI/ Sponge Iron cost.
iii. Reduce the fuel requirement and thus reduce the CO2 emission.
iv. Reduce the production cost of DRI.
v. The said COG is cheaper as compared to produced syngas through coal gasification
plant.
vi. The process as claimed hereinafter , when COG (56,000 Nm3/h) is used by replacing
Syngas (66,080 Nm3/h), the DRI production cost reduced by Rs. 860/MT.
vii. The requirement of production of Syngas production is ~66080 Nm3/h, i.e., 330
Nm3/MT less and thereby requirement of the non-coking coal is ~100 MT/h, i.e., 0.5
MT/ton production of DRI.
viii. The process with COG in DRI helps reducing the CO2 emission by 61 MT/h, i.e., 300
kg/MT DRI production.
ix. In the process, the DRI or Sponge iron’s productivity and resulting quality is same.
x. The process efficiency of DRI improves by utilization of COG in the reduction
furnace(1) in DRI.
xi. The utilization of COG in place of Syngas, can lead to improve the cooling efficiency
of product cooler(2) which enhance the stability of DRI operation.
16

We claim:

1. A process for gas based direct reduction (DR) in DRI plant to produce high quality
direct reduced iron comprises the steps of:
Addition of iron ore lump and pellet as feed to produce DRI or sponge iron at DRI plant;
Heating of fuel gas at 920 °C in the process gas heater before charging into the reduction
furnace(1);
Addition of COG and syngas in Bustle Gas in reduction furnace(1) and addition of COG
in Reheat Gas Line(9) in reduction furnace(1) through COG compressor(3) and heater and
through transition zone;
COG gas mixed in the cooling gas before charging to the Product Cooler(2) through
injection.
2. The process as claimed in claim 1, wherein the said COG partially replaces the existing
syngas through Coke Oven Gas Compressors and Heater with the replacement ratio of 1:1.18.
3. The process as claimed in claim 1 , wherein COG has added with reducing gas at a
temperature of 880°C - 900°C to reduce the percentage of methane.
4. The process as claimed in claim 1 , wherein COG is added in the reheat line, located in
the lower part of the reduction furnace(1) at a temperature of 700°C - 750°C.
5. The process as claimed in claim 1, wherein Syngas/COG is added into the transition
zone(13) at the furnace temperature of 750 - 800°C.
6. The process as claimed in claim 1 , wherein the COG is mixed in the Product Cooler(2)
of gas-based DRI plant in place of the cooling medium to enhance the cooling efficiency due to its
nitrogen and methane content present in the gas.
7. A COG addition system designed to efficiently utilize COG as a reducing gas comprises:
compressor 1 and compressor 2 along with COG heater 1 and COG Heater 2;
17

Series of three ejectors installed for ejecting the COG in the Reheat Gas Line(9) and Bustle
Gas Line(10) in the proposed system;
Providing Control valves(11) in the COG injection line before the Bustle gas line(10), and
another control valve is provided in the reheat gas line(9), another control valve in the
Transition Gas line regulate the flow of outgoing COG and are mixed with the syngas based
on the requirement of the Reduction Furnace(1);
Providing additional arrangement to inject the COG in the product cooler(2) through one
more control valve.
8. The COG addition system as claimed in claim 7, wherein control valve in product cooler(2)
has provided in the COG Injection line to control the flow of desired COG into Product Cooler(2.
9. The COG addition system as claimed in claim 7, wherein plurality of COG compressor(3)
and heater are placed into the bustle line, Transition line & reheat line in the reduction furnace(1).
10. The COG addition system as claimed in claim 7, wherein said COG screw compressors
having a capacity of 28,000 cubic meters per hour.
11. The COG addition system as claimed in claim 7, wherein said COG screw compressors
receives 60 mbarG COG due to the low pressure of COG from the coke oven battery, and therefore
it converts to 2.5 BarG of pressure and injects.
12. The COG addition system as claimed in claim 7, wherein plurality of COG preheaters(4)
increases the COG temperature up to 400-450°C, which eventually reduce the heat loss in the DRI
main Gas System.