Coke Making

Coke is a material with high carbon content and porosity. It has high resistance to breakage and low reactivity with gases, particularly CO2. Coke production is an important part of the integrated iron and steel plants using BF-BOF route, acting as a reducing agent, as a source of thermal energy, and providing physical support for the burden in blast furnace. In modern blast furnaces 460 - 480 kg of total reductant /t-hot metal is needed, and global average is 500 kg/t-hot metal (IEA, 2007. p.117). In modern blast furnaces with supplementary fuel injection, coke consumption can be less than 300 kg/t-hot metal.

Coke is produced by heating coking coals up to 1000 to 1200 °C for several hours in coke ovens to drive off volatile compounds and moisture. For every ton of coke around 3.5 to 5.0 GJ of energy (IEA, 2007. p.110) and around 1.6 ton of coking coal is used (IEA, 2009, p.52). Coke production accounts for around 10% of the energy demand in a BF-BOF plant (IEA, 2007. p. 110). Coal characteristics play an important role on the coke consumption and thus the energy demand. A 1% increase in the ash content of coke may increase the coke demand by 2%. This is an important factor for countries like India where the coal ash content is high.

In China energy use for coking has decreased from 5.6 GJ/t-coke to 4.9 GJ/t-coke between 1995 and 2000, and further decreased to 4.2 GJ/t-coke by 2004, thanks to installation of coke dry quenching and advanced coke quenching technologies in Chinese plants (old behive coke ovens that account for one fifth of Chinese coke production are not included in these statistics) (IEA, 2007).

Coke MakingTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Coke Dry Quenching

The most efficient coke ovens use CDQ and may use up to 40% less energy.

Approximately 1.5 GJ heat/t-coke (as  ~ 400 - 500 kg high temperature steam/t-coke) and 0.55 GJ electricity/t-coke can be recovered. 

For a plant with 450 000 t/y coke capacity (~1 million t/y BF capacity), 450 GWh/y of steam and around 150 GWh/y of electricity can be produced.

Chinese flag In China energy use for coking has decreased from 5.6 GJ/t-coke to 4.9 GJ/t-coke between 1995 and 2000, and further decreased to 4.2 GJ/t-coke by 2004, thanks to installation of more than ten coke dry quenching and other advanced quenching technologies.

CO2 savings in excess of 100 000 t/y are estimated by converting two 25 t/h capacity quenching systems from wet to dry (Climatetech Wiki, 2011

Given about 300 Mt coke production without CDQ and savings of  600 g CO2/kWh, global CO2 emissions reduction potential is about 25 Mt CO2.(IEA, 2007)

Retrofit capital costs are 109.5$/ton coke. The cost of a 3-chamber plant can be estimated to be in the range of €60-70 million including equipment and installation costs.

EU Flag In Europe equipment costs for a 2 million ton-coke/year plant are estimated to be €70 million.  Depending on the electricity costs, the payback time can be 3 years - if all the steam is used for electricity generation.  (IPPC BREF, p. 276)

Japanese flag In Japan, installation of a CDQ for a 450 000 t-coke/y capacity plant required ¥ 3 billion in equipment and ¥ 500 million in construction costs.  With an electricity price of ¥17.99/kWh, approximate payback time was 3.6 years [1 ¥ = US $0.1257] (NEDO, 2008. p.67)

By converting two 25 t/h capacity quenching plants from wet to dry systems with 15 MW electricity generaton connected to each, US $9 million savings in electricity, and US $1 million in water related costs are estimated. (Climatetech Wiki, 2011

Commercial
Additional Use of Coke Oven Gas

Coke oven gas with a heating capacity of 6 to 8 GJ can be recovered for every ton of coke produced. (IEA, 2007)

Chinese flag In China, the potential of recovering COG from stand-alone coke enterprises was estimated to be around 250 PJ in 2005.

Chinese flag In China, CO2 emissions can be reduced by 25 million tons by recovering COG from stand-alone coke enterprises located near coal mines

By using COG as supplementary fuel in blast furnace, a steel mill in the US was able to save US $6 million annually.  The project required an investment of around US $6.1 million, and had a payback time of just over one year. 

Commercial
Automation and Process Control SystemThis technology can lead to fuel savings of about 10%. Estimated energy savings therefore are calculated to be 0.15 MBtu/ton (0.17 GJ/tonne) coke.The technology leads to emissions reduction of 3.8 Kg CO2/tonne coke.Retrofit capital costs are US $0.37/tonne coke.Commercial
Coal Stamp Charging Battery

This technology conserves coking coal due to use of higher proportion of high volatile & poor coal in the blend. It also increases the yield in the coke plant and may help improve the performance in heat recovery systems.  

Emissions reduction is unlikely.

Investment and operational costs are reported to be reduced, due to reduced oven compartments and ability to use lower grade coal.  

Commercial
Coal Moisture Control

Japanese flag Coal moisture control costs for a plant in Japan were $21.9/t of annual steel capacity.

Commercial
Non-Recovery Coke OvensElectrical power of about 630-700 kWh/t-coke can be produced.VOC and particulate matter emissions are mostly eliminated. SOx emissions are reduced but NOx emissions are likely to increase. Investment cost of a US coking plant producing 1.2 million tons of coke per year was $365 Million – including coke oven facilities, coke handling/blending and power plant in 1998. For the energy facility, investment costs of only USD 140 million are reported for 1998 (IPPC, 2009).Commercial
Variable Speed Drive Coke Oven Gas CompressorsVariable Speed Drive System on a compressor at a coke plant at Corus in The Netherlands saved 6 to 8 MJ/t-coke. Emissions can be reduced by 0.12 kg CO2/t-coke.Retrofitting cost is 0.47 $/tonne coke. The payback time was estimated as 21 years (US EPA, 16)Commercial
Coke Stabilization QuenchingThe technique can reduce coke consumption by 1-2% and may also reduce energy consumption in BF. Dust emissions are reduced in Coke making. CO2 emissions may be reduced if the good quality coke results in energy savings in BF. Cost data has not been provided.Commercial
Single Chamber System

SCSs offers an improvement in thermal efficiency from 38% to 70%.

The larger dimension ovens decrease the specific environmental emissions because fewer pushing operations are required per tonne coke. Emissions are directly proportional to number of pushes.

Demonstration
COURSE 50Research
SCOPE 21 - Next Generation Coke Making TechnologyCoke-making energy consumption can be reduced by 21% (NEDO, 2008. p. 70). For a plant with 1 million t/y capacity, CO2 reduction of 400,000 t-CO2/year are anticipated (NEDO, 2008. p. 70). Production costs are 82% and construction costs are 84% of conventional coke oven.Demonstration

Coke Making Publications

Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry

The U.S. Environmental Protection Agency’s (EPA) energy guide, Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry, discusses energy efficiency practices and technologies that can be implemented in iron and steel manufacturing plants. This guide provides current real world examples of iron and steel plants saving energy and reducing cost and carbon dioxide emissions.

Page Number: 

79-82

The State–of-the-Art Clean Technologies (SOACT) for Steelmaking Handbook

 

The State–of-the-Art Clean Technologies (SOACT) for Steelmaking Handbook is developed as part of the Asia-Pacific Partnership on Clean Development and Climate program and seeks to catalog the best available technologies and practices to save energy and reduce environmental impacts in the steel industry. Its purpose is to share information about commercialized or emerging technologies and practices that are currently available to increase energy efficiency and environmental performance. 

Page Number: 

29-39

Global Warming Countermeasures: Japanese Technologies for Energy Savings / GHG Emissions Reduction

This revised 2008 version of the publication from New Energy and Industrial Technology Development of Japan includes information on innovative Japanese technologies for energy efficiency and for the reduction of COemissions.  

Page Number: 

67-70