AISTech 2011 Conference Proceedings

Enhancing Coke Production Energy Efficiency While Reducing Emissions

Robert A. Kramer, Ph.D.

Director, Energy Efficiency and Reliability Center

NiSource Charitable Foundation Professor of Energy and the Environment

Purdue University Calumet

Hammond, Indiana

219-989-2147

Liberty Pelter, Ph.D.

Associate Professor, Chemistry and Physics Department

Purdue University Calumet

Hammond, Indiana

Hardarshan S. Valia, Ph.D., Alan Ellis

Coal Science Lab.

Gary, IN

Keywords: Reduced Coke Emissions, Multipurpose Coke Facility, Coal Blending, Lower Rank Coals

Introduction

A viable supply of iron is one mainstay of economies throughout the world. Issues associated with the supply and

price of iron, which is used to produce steel, play either a direct or indirect role in all modern business operations.

There is currently enormous incentive to assure the supply, quality, and price of raw materials used in iron

production and that these raw materials are produced in an environmentally friendly manner. One of the major

components used in the iron making process is coke. Coke is a solid carbon fuel and carbon source produced from

coal that is used to melt and reduce iron ore. Although coke is an absolutely essential part of iron making and

foundry processes, currently there is a shortfall of 5.5 million tons of coke per year in the United States. This

shortfall has resulted in increased imports and drastic increases in coke prices and market volatility. In addition,

historically there have been concerns with emissions from traditional coke production facilities.

A new approach to coke production is being developed involving the continual optimization of the process in

concert with the production of other value streams based upon market price and availability. The developed process

leverages non recovery/heat recovery coke production methods by using pyrolysis gas extracted at specific operating

temperatures and conditions. This optimizes high value product production and minimizes by-product emissions in

comparison with more conventional techniques. Using the developed technology, it is estimated that such a Multi-

Purpose Coke Facility would use up to 40% low rank coal and thereby significantly reduce coal costs and at the

same time environmental emissions. By producing multiple value streams as part of the coke production process, it

will be possible to increase economic value of the process and simultaneously reduce the impact of price

fluctuations in the coke market.

The market price of coke has varied from $130 to $800/ton since 2009. Such fluctuations have caused considerable

production planning issues. The current research, through the use of optimized multiple value streams, can reduce

the effects of this market volatility by providing alternative revenue streams from multiple products including coke,

fertilizer, electricity, Fischer-Tropsch transportation fuels, and hydrogen. It also helps to produce jobs and a new

market for lower rank coal. By utilizing pyrolysis gas to produce multiple high value products in conjunction with

coke production it is possible to leverage value of the coke oven investment. Recent circumstances in the coke

market have placed enormous strain on the steel industries. The developed process can provide at least a partial

resolution and/or mitigation of this formidable problem through the use of a blend of low rank and conventional coal

in a mine mouth or local, environmentally friendly, high efficiency coking/coal gasification facility which would

increase coke supply and production, while, at the same time, reducing the cost for the steel and foundry industry.

Background

A significant aspect of the current research is utilization of multiple value streams from the coke production process

that are optimized in real time to produce maximum value. In the proposed process, pyrolysis gas is extracted over a

temperature range in which there is a desired gas composition. This reduces the post process chemical treatment of

the gas and further reduces the capital and operating costs in comparison to a conventional coal gasification plant.

Lower rank coals produce additional pyrolysis gas and consequently they are often not used since they can exceed

gas handling capabilities at a particular facility. By extracting high value streams of this gas it is possible to reduce

the net flow during high gas production periods and thereby reduce operating issues including hot spots in sole

plates or down comers. The use of a blend of low rank and conventional coal in a Multipurpose Coke Facility can

reduce the effects of this price volatility while maintaining coke physical parameters (especially CSR and Coke

Stability) and chemical parameters. The multiple value streams for the proposed process optimize value based upon

market pricing for the various value streams. When there is a sudden decrease in one product value it is possible to

at least partially shift production to optimize the production of a different and more valuable product. Within the

constraints of the physical production process the output from each of the value streams is optimized to produce the

maximum net value in essentially real time. Efforts to extend coal blending techniques to also consider optimizing

the composition of the produced pyrolysis gas are ongoing. By optimizing both aspects simultaneously it is possible

to obtain coke of acceptable quality for use in large blast furnaces and other applications and at the same time obtain

a supply of pyrolysis gas that can be used for the production of liquid transportation fuels through the use of the

Fischer-Tropsch process, fertilizer, electricity, and low grade bulk hydrogen. Net facility environmental emissions

will be reduced by using a non-recovery approach with selective extraction of pyrolysis gas and the coproduction of

other high value energy products. One essential requirement is, however, to assure that the coke produced in this

process meets the physical and chemical requirements for use in modern large blast furnaces.

Before the coke property called CSR (coke strength after reaction with CO2) was implemented in the USA during

the 1970s, Illinois Basin coal was used extensively at Midwestern steel companies in blends. These blends produced

coke with high cold strength properties (stability, hardness, impact resistance, and abrasion resistance). But, CSR

was poor. For small blast furnaces, poor CSR values did not cause operating issues, but as furnace sizes increased

dramatically in the late 1970s, issues arose with blast furnace component and wall integrity. With increased

emphasis on CSR as an operating parameter, the use of Illinois coal was discontinued for production of coke.

At present there are two main methods of producing coke. First, a recovery (Slot Oven) process in which the coal is

heated in a completely reducing atmosphere and the volatile products are recovered in an associated chemical

processing plant. The tar, ammonium sulfate, light oils, coke oven gas are generally the type of products recovered

from slot oven coke making. As the ovens get older, emission becomes a problem. Air, water, and VOC emissions

from coke production can be reduced by using a non-recovery (Heat Recovery) coke battery.

In the non-recovery process air is introduced above the top of the coke bed in the oven and the volatiles are

combusted. The Environmental Protection Agency has stated that new ovens must meet non recovery emission

standards. The hot gases from the oven can then be used in a heat recovery boiler to produce steam and subsequently

generate electricity; hence, the process is then called Heat Recovery Coke Making. Relatively small amounts of

hydrogen are produced in this process and this along with other gases is recirculated to the sole section of the oven

providing heat to the process. Recently, a new design non recovery coke oven has been introduced in China. This is

essentially a vertical non recovery coke oven. Initial indications are that it provides the emission reduction benefits

of a non recovery (Heat Recovery) design and additional operational benefits including reduced space. This design

has the potential to further extend the economic and environmental efficiency and process benefits made possible by

this research effort.

A Multi-Purpose Coke Facility could be located either near or at a coal mine or at an existing production facility

depending on business issues and available transportation capabilities. Transportation of both coal and coke is

necessary in this process since the coal used for coke production would be a blend of Indiana and other metallurgical

coals. Production of coke at mine mouth would afford a transportation savings because a large portion of coal used

by the coking facility would not have to be transported over a long distance.

In the proposed process, existing or planned non recovery (Heat Recovery) coke production facilities would be used

as part of the developmental process at reduced risk in comparison to construction of a dedicated test facility. The

value of products, including liquid fuels, would be evaluated in comparison with conventional coke production

operation. The process would be designed to adapt to changing market conditions. The amount of each product

produced would be determined by optimizing the value of the various product streams. This would reduce the risk of

developing new coal based liquid fuel production capability since the major capital expenditure, the gasifier, is

already justified for conventional coke production. A general overview of the major process considerations is shown

in Figure 1.

Figure 1. Multi Purpose Coke Facility Process Overview

Process Description

During the coke production process pyrolysis gas evolves as the coal is heated. Producing combustible gases from

solid fuels has been done since ancient times. Pyrolysis is a process in which feed material is heated with a restricted

air supply. Towards the end of the eighteenth century gas was produced from coal by pyrolysis on a larger scale. In

1812 the London Gas, Light, and Coke Company commercialized gas production. The most important gas produced

at this time was Town Gas. Town Gas can be produced by pyrolysis (producing gas with a heating value of 20,000-

23,000 kJ/m3) or by the water gas process (coke is converted into a mixture of equal parts of hydrogen and carbon

monoxide with a heating value of approximately 12,000 kJ/m3).

i The coke oven was developed for the metals

industry in order to provide a substitute for charcoal during the second half of the eighteenth century. One metric ton

of coal typically produces 600-800 kg of blast-furnace coke and 296-358 m3 of coke oven gas.

ii Preliminary

estimates show that from .1 - .25 barrels of liquid transportation fuel could be produced from each ton of coal used

in the coking process.

Much of the pyrolysis gas from coal arises from the contained aliphatic material. This gas consists of various

amounts of hydrogen, methane, carbon monoxide, nitrogen, acetylene, and carbon dioxide. The composition of the

pyrolysis gas changes as the coal is heated. For example, hydrogen concentration increases with increasing

temperature. Depending on its composition, Pyrolysis gas can be used in Fischer-Tropsch processes for the synthesis

of liquid transportation fuels. Producing gas from coal or coke is common in the steel industry and hence new

methods to maximize the value of this important material can be most beneficial. There is much discussion today

about methods to produce gas from coal. It should be noted that the steel industry has been actively involved in

gasifying coal and coke for over 100 years. In this context, blast furnaces can be considered large gasifiers.iii

The

current effort is attempting to leverage the extensive pool of steel industry coke production knowledge to reduce the

technical and financial risk associated with new approaches to coal gasification.

A device has been developed to facilitate the testing of pyrolysis gas from various coal samples. This device is

constructed of 316L stainless steel with the exception of the vapor traps which are copper. A schematic of the device

is depicted in Figure 2.

Figure 2. Pyrolysis Gas Apparatus

Coal samples are placed in the test vessel. The vessel is then evacuated (.1 mm) and backfilled with dry nitrogen.

This process is repeated three times to establish an inert atmosphere. The vessel is then heated in the furnace. At

various temperatures a partial vacuum is momentarily drawn on the system and pyrolysis gas from the coal at that

temperature refills the apparatus. Gas is then extracted from the apparatus at the particular temperature through a

small diameter peek tubing line and is analyzed using a Varian micro Gas Chromatograph equipped with a mol.

Sieve column.

Samples of washed coal were obtained from mines in Southern Indiana and from a coke plant in North West

Indiana. These coal samples are stored under an Argon atmosphere to minimize the influence of oxygen. The

samples were blended with washed metallurgical coal and the blends were evaluated for use in the coke production

process. The samples were split 3 ways and replicate tests were conducted on different days.

Efforts to extend the blending to also consider optimizing the composition of the pyrolysis gas produced in the

coking process are also underway. By optimizing both aspects simultaneously it will be possible to obtain coke of

acceptable quality for use in blast furnaces and other applications and at the same time obtain a supply of pyrolysis

gas that can be used for the production of liquid transportation fuels through the use of the Fischer-Tropsch process,

fertilizer, and possibly low grade bulk hydrogen.

Laboratory tests of several Indiana coals were conducted. As the temperature of the coal is increased in the coke

production process pyrolysis gas of varying composition is released. In the proposed concept it is anticipated that

portions of this gas will be gathered from the coke process at specific temperature ranges with the proper

composition for the production of liquid transportation fuels, fertilizer, and hydrogen. Figures 3-5 depict typical test

results for the pyrolysis gas composition from various tested coal samples at different temperatures. Figure 6 shows

the apparatus used to collect the produced pyrolysis gas. This apparatus is connected to a gas chromatograph for

analysis of the produced gas and has the capability of testing 10 samples simultaneously.

Figure 3. Pyrolysis Gas Analysis, Sample 1

Figure 4. Pyrolysis Gas Analysis, Sample 2

Figure 5. Pyrolysis Gas Analysis, Sample 3

Figure 6. Pyrolysis Test Equipment

Testing of additional washed coal samples and blends are currently underway. Methods to evaluate optimal coal

blends that maximize Indiana coal usage are being developed. Efforts to characterize coal blends and related

chemical and physical characteristics are ongoing since this directly influences the potential use in the Steel

Industry. Initial coal sample analysis results are shown in Table 1.

Table I. Initial Coal Analysis Results for Individual and Blended Coals

1 Blend A contains 35% HV and 65% LV

2 Blend B contains 50% HV and 50% LV

Individual Coals

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Blend A1 Blend B

2

Total Moisture 14.67 14.34 7.95 5.57 7.75 7.18 8.44

Ash (%) 4.08 5.81 9.68 9.93 6.61 8.70 7.76

Volatile 39.27 38.09 20.26 29.28 15.87 21.89 24.67

Sulfur 1.58 1.32 0.35 1.11 0.77 0.75 0.87

HV(BTU/lb) 14129 13873 14040 13980 14635 14195 14245

Carbon 78.32 77.70 80.57 78.86 86.05 81.43 81.44

Hydrogen 5.40 5.42 4.21 4.90 4.12 4.46 4.64

Nitrogen 1.59 1.67 1.16 1.61 1.31 1.41 1.45

Oxygen by difference 9.03 8.08 4.03 3.59 1.14 3.25 3.84

Initial Ash Deformation

Temperature (°F) 2176 2388 >2700 2259 >2700 2572 2633

FSI 5 3 6.5 6.5 5.5 7.5 6.5

Reflectance (%) .53 .58 1.31 1.03 1.69 1.26 1.25

Total Inerts (%) 12.4 16.6 43.0 20.1 22.2 24.4 20.8

Total Reactives (%) 87.6 83.4 57.0 79.9 77.8 75.6 79.2

Liptinite (%) 11.8 10.8 .2 8.0 2.6 3.6

Fluidity Softening Temp

(°C) 426 378 450 412 410

Solidification Temp(°C) 499 489 510 505 500

Temp. Range (°C) 73 111 60 93 90

Temp. at Max. Fluidity

(C) 471 444 484 467 465

Max Fluidity ddpm 26 60,111 7 507 259

The multiple value streams for the proposed process optimize value based upon market pricing for the various value

streams. When there is a sudden decrease in one product value it is possible to at least partially shift production to

optimize the production of a different and more valuable product. The interaction between these various value

streams is depicted in Figure 7. Within the constraints of the physical production process the output from each of the

value streams is optimized to produce the maximum net value in essentially real time. This provides the ability to

quickly respond to market price changes and reduce the influence of market volatility. The general product value

flow is depicted in Figure 8. The process flow is depicted in Figure 9. Process values are shown in Figure 10.

Figure 7: Economic Interactions

Blended Coal

Electricity

Fischer Tropsch

Coke Cost

Reduction

Fertilizer

Liquid

Transportation

Fuel

(military and other

applications)

Figure 8. Value Streams

Coke Oven

Coke to Blast

Furnace

Coke Oven

Gas

Gas Cleanup

(See Detail)

Fischer

Tropsch

Fischer

Tropsch

Fuels

Methane and

HydrogenFertilizer

Waste Gas

and Heat

Steam Boiler

Turbine –

Electricity

(internal and

to grid)

Gas Cleanup

Ammonia, H2S

Scrubber

ESP

(tar removal)

Primary Cooler

(Tar removal)

Separator Device

(need to develop)

Fischer TropschTar

Ammonium

Sulfate for

Fertilizer Market

Liquid

Transportation

Fuels

HCO

CO2

Conversion Plant Heating

CH4

Figure 9. Process Flow

Fischer Tropsch

Heating

Tar

12,000 ft3

Gas (STP)

700 lbs Coke

($150-$800/ton)

1 Ton Coal

Fertilizer

(ammonium

sulfate)

Liquid

Transportation

Fuel

(.25 -.5 bbl)

30% min

20%

Electricity

Figure 10 . Process Values

Indiana/Illinois Basin coals are highly suitable for gasification and can also produce good quality coke if blended

with other coals or lower quality coke if carbonized alone. Some of these coals when analyzed petrographically

under white light and fluorescence light show higher amounts of exudatinite, sporinite, and cutinite macerals, all

grouped as Liptinite in Table I. Liptinite is reported to give higher liquefaction yield than associated vitrinite

maceral.iv Liptinite contributes to higher hydrogen and higher liquid fuel yield. Additional hydrogen contributes to

higher fluidity resulting in enhancement of coking properties. Hence, some Indiana/Illinois Basin coals are good

candidates for both coke making and production of pyrolysis gas.

Table II. Liptinite Content in White Light and Fluorescence Lightv

Concerns with the relative strength of the coke produced from Indiana coal can be reduced by carefully blending

various types of coal. Through blending many potential issues with coke characteristics can be reduced or

eliminated. Methods are under development to customize the blending process maximizing the use of

Indiana/Illinois Basin coal. Two examples of coke quality produced via pilot oven carbonization using Indiana and

Illinois coals (as a single component and as blended components) are given in Table III and IVvi:

Table III. Carbonization Pilot Oven Test Results of 100% Indiana and Illinois Coalsvii

In Table IV it can be observed that a blend of 45% of Indiana Coal can be used in a slot oven to produce acceptable

coke quality (see TC1941 containing 45%Indy-15%EHV-40%WCM). TC 1995 (50% of Indiana Brazil Block coal

when blended with 50% of LVM Alabama coal) also produces acceptable coke quality in a slot oven. If such a

blend is carbonized in a Heat Recovery/Non Recovery Coke Oven, it is anticipated that there will be similar or

better performance in coke quality. One example is depicted in Table V where a blend containing 12% of Indiana

coal was carbonized in six ovens of a Non Recovery Battery producing excellent quality cokeviii

.

% Liptinite (White Light) % Liptinite (Fluorescence Light)

Indiana Coal (c) 7.40 14.40

Indiana Coal (R) 7.20 10.80

Indiana Coal (a) 8.0 9.40

Indiana Coal (LFC) 23.6 No Data

5-ILL 7-Ind I 6-Ind II

Coking Parameters:

Moisture (%) 7.42 8.0 11.2

Grind(%, -3.55mm) 89.2 80.8 85.0

D.O.B.D.(kg/m3) 776 737 739

M.O.W.Pressure(kpa) 5.44 2.20 2.96

C. Time(h) 18.62 17.9 20.15

Coke Properties & Charge Contraction:

Stability 31 25 33

CSR 27 46 30

Hardness 71 65 69

C.Size(mm) 48.5 57.8 55.1

C.Yield(%) 67.9 60.1 67.0

SHO Contraction(@52.2%) -2.1 -10.10 -3.67

Table IV. Carbonization Pilot Oven Test Results of Indiana and Illinois Coals in Blendsix

TC1931 TC1933 TC1935 TC1940 TC1941 TC1951 TC1952 TC1953 TC1954 TC1995

30% Ill 30%EHV

40%

EMV

30% Ind

30%

EHV

40% EMV

80% Ind

20% PC

45% Ind

15%

EHV

40% EM

45% Ind

15% EHV

40%WCM

30% Ind

30% EHV

40%WCM

30% Ill 30% EHV

40%WCM

20% Ind

10% PC

30% EHV

40%WCM

20% III 10% PC

30% EHV

40%WCM

50% Ind

50%LVM

Moisture

(%) 2.94 2.5 4.98 5.15 4.48 4.03 3.29 3.24 3.4

Grind (%, -

3.35mm)

97.1 93.3 87.6 90.7 91.1 91.9 92.7 94.6 96.9 91.0

Dry oven bulk

density

(kg/m3)

792 816 754 801 788 801 804 804 805 794

Max oven wall

pressure

(kPa)

5.65 6.27 2.55 4.62 3.45 4.07 4.07 3.58 7.23

Coking time (h)

16.87 16.37 16.05 17.13 17.03 17.05 17 16.6 16.1 17.02

Stability 61 60 42 58 63 57 61.1 60.5 60.7 62

CSR 61 68 24 57 65 65 70 72 71 66

CRI 30 22 44 32 24 21 20 28

Hardness 70 70 51.3 70 68 70 70 69 68 72

Coke size

(mm) 61.73 65.53 70.9 70.74 69.3 62.8 59 61.3 64.2 62.6

Coke yield

(%) 73.58 70.15 69.6 73.39 74.6 74.9 76.3 78 76.9 74.9

SHO contraction

%

-7.99 -9.57 -11.94 -11.13 -10.14 -12.82 -7.93 -10.59 -12.93

Coke sulfur

(%) 0.66 0.93

Coke ash (%)

11.1 8.9

Note: Ill=Illinois Coal; Ind=Indiana Brazil Formation coal; WCM=Western Canadian medium volatile coal,

EHV=Eastern high volatile; EMV=Eastern medium volatile coal; LVM=Alabama low volatile coal; PC=petroleum

coke

Table V. Non Recovery Six Oven Carbonization Test Resultsx

65%HVM, 35%MVM/LVM

(with 12% Indiana coal)

64%HVM, 35%MVM/LVM

CSR 70 71

CRI 21 20

Stability 64 64

Hardness 70 72

This research effort has also considered how it could be possible to modify the mass balance in the coking process in

a way that would allow for a usable level of gas production that could be used to power a combustion turbine for

electric production. In discussions with various operational, research, and engineering personnel it has been found

that there is a possibility that a portion of the pyrolysis gas could be extracted from the gas stream as it is leaving the

crown section and going in to the sole section of the oven. The degree of gasification and influence on operations

would need to be considered in a subsequent detailed study. Preliminary process modeling was done with the

Metsim computer model.xi

Metsim is a computer program that can model industrial processes, unit operations, and

chemical and metallurgical processes.

The location of the proposed coke production process would take place either near or at an Indiana coal mine or at

an existing production facility. The choice of location would be made based on business issues and also on the

availability of transportation capabilities. Transportation of both coal and coke is necessary in this process since the

coal used for coke production would be a blend of Indiana and other metallurgical coals. Production of coke at mine

mouth would afford a transportation savings because a large portion of coal used by the coking facility would not

have to be transported over a long distance. But, coal for blending as well as the finished coke would need to be

transported. If sufficient transportation capability exists total transportation cost would be reduced since the mass of

the product coke is less than the coal needed to produce it. Thus, a significant cost savings from the reduced weight

per mile of material being transported would result if transportation capability was available. A concept for a

process for the capture of the carbon dioxide produced by the process was also identified. Investigations into the use

of transition metal catalysis for the production of chemical products from carbon dioxide are ongoing.

Summary

The research described in this paper is developing a new approach to the production of coke that involves reduced

environmental emissions and enhanced economics. In this process multiple optimized value streams are produced

from a coke facility located at mine mouth or locally at an existing plant. As part of the process, less costly lower

rank coals will be blended with conventional metallurgical coals. The blending process will be optimized to meet

coke quality requirements and simultaneously to obtain a pyrolysis gas composition suitable for production of

ancillary products including liquid transportation fuels, fertilizer, hydrogen, and electricity. By using lower rank

coal it will be possible to reduce net coal costs. This process can provide a new direction and approach for the

production of coke in the future that optimizes value over multiple product streams while reducing both business and

technological risk by leveraging existing coke production technology and reducing environmental emissions.

Methods to reduce the carbon foot print of the plant are also being considered.

Acknowledgement

The authors would like to thank the Center for Coal Technology Research located at Purdue University and the

Illinois Clean Coal Institute for their support of this effort. Without their assistance this research would not have

been possible.

References

i Gumz, W., Gas Producers and Blast Furnaces, New York, John Wiley & Sons, 1950.

ii The Making Shaping and Treating of Steel, Association of Iron and Steel Engineers, Herbick & Held, Pittsburgh,

1985. iii

Gumz, W., Gas Producers and Blast Furnaces, New York, John Wiley & Sons, 1950. iv Elliott, M.A., Chemistry of Coal Utilization, 2

nd Supplementary Volume, Wiley, NY, pg. 155, 1981.

v Valia, H. S., “Coal Cost Reduction Using Low Rank Coals”, AIST, pg. 170-175, March 2006.

vi Ibid.

vii Ibid.

viii Ibid.

ix Ibid.

x Ibid.

xi Metsim computer model, John Bartlett