Steel Plant Gases for Chemicals Manufacture and Carbon Footprint Reduction

China is the largest steel producer in the world followed by India. Indian steel industry has an emission intensity of 2.55 tonnes of carbon dioxide (CO₂) /tonne of crude steel (tCO₂/tcs) whereas the global average is 1.85‑tCO₂/tcs. The Indian steel sector contributes almost 12% to the country's CO₂ emissions, which is more than the global average. Approximately, 240‑mt of CO₂ is emitted by the steel sector each year, and given the Indian Government's infrastructure development goals, it is expected to double by 2030(1). Decarbonising the steel industry has been under active consideration for some time and various solutions have been suggested.

There are two sources of coke oven gases (COG): from integrated steel plants and independent coke producers(2).

China has been proactively working for more than one and half decades on use of steel plant off‑gases as a means of decarbonizing. With an annual production capacity of 16‑mtpa, China is the largest producer of coke in the world.

In 2014, the Wuhai Huaiqi Xilafeng LNG plant had a capacity to process 3.77‑mscm (million standard cubic metres) of COG to produce 1‑mscm of LNG each day. Per year, this plant used 1.5‑billion mscm of COG, producing about 250,000‑tonnes of LNG, which saved the use of 940,000‑tonnes of standard coal. It cut down CO₂ emissions by 1.04‑mtpa(3).

Zichen Di et al. concluded that COG‑to‑ammonia is a well‑balanced option. Promoting COG‑to‑hydrogen faces economic viability. COG‑to‑methanol is economically viable, potentially to meet 16‑34% of methanol market(4).

J. Lundgren et al.(5) have suggested various combinations of Blast Furnace Gas (BFG), COG, biogas, etc., for production of methanol. Lingyan Deng and Thomas A. Adams II(6) conducted a feasibility study for ArcelorMittal Dofasco Ontario (AMD), which demonstrated that the process of conversion of COG and BFG to methanol is efficient, and results in a net CO₂ emissions reduction of 228‑ktpa (4.6% net CO₂ emission reduction) and can fix up to 246‑ktpa of CO₂ into methanol annually.

These and other examples indicate that India's steel industry can not only be a producer of steel but can also be a producer of basic chemicals like methanol, ammonia, and downstream chemicals, using COG and BFG. The chemicals can be propylene, gasoline, LPG, acetic acid, isocyanates (TDI, MDI), ethyl carbonate, ethylene glycol, diphenyl carbonate, polycarbonate, etc. The intriguing part is that all these technologies are in commercial use.

Many publications indicate that COG and BFG can be used for methanol production and hydrogen separation (6)(7)(8). We are suggesting that COG and BFG be used to produce ammonia along with methanol.

As steel plants have very large capacities, producing vast amounts of gases, the volume of chemicals that can be produced can be quite large. Furthermore, the use of gases reduce the use of hydrocarbon resources and consequent production of CO₂.

Clean‑up of COG

COG is one of the three main process gases obtained from steel plant industries (the others being BFG and Linze‑Donnawitz gas (LDG)). It is produced during coking, wherein coal is heated in ovens to produce coke, which is used in the blast furnace for making iron. COG is a complex mixture (Table‑1), and of the listed components, hydrogen (H₂), carbon monoxide (CO), and unsaturated gases can be present in the final clean gas composition but others should be removed as much as possible through a by‑product plant(2).

Table‑1: Typical composition of COG

Chemical name	% Volume
Hydrogen	52‑59
Methane	26‑33
Nitrogen	1.9‑5.7
Carbon monoxide	4.5‑7.0
Ethylene	2.0‑2.8
Carbon dioxide	1.4‑2.1
Hydrogen sulphide	0.4‑1.2
Hydrogen cyanide	0‑1.2
Ethane	0.7‑1.1
Ammonia	0‑1.1
Benzene	0‑1.0
Carbon disulphide	0‑0.3
Toluene	0.1‑0.2

The steps followed in a COG treatment plant are:

• Tar and liquor separation;
• Primary gas cooling;
• Compression in exhausters;
• Electrostatic tar droplet removal;
• Secondary/final gas cooling;
• Ammonia removal;
• Benzol removal;
• Naphthalene removal; and
• Hydrogen sulphide removal.

These steps are carried out under 7‑kPa to 15‑kPa pressures.

A summary of the process for cleanup are given below(2)(9)(10).

Tar removal

Tar is a condensable vapour consisting mainly of aromatic hydrocarbons ranging from volatile benzene to pitches (which are solid at room temperature). Tar can be removed as a saleable material that can be further processed in a tar distillation plant. Around 70% of the tar is condensed when sprayed with liquor. Further, 20% is removed at the primary cooler and the remaining 10% in electrostatic tar precipitators.

Ammonia removal

Ammonia removal from COG is done mainly using the following three methods:

Ammonium sulphate process

There can be a few variations in this process, but it basically involves sulphuric acid and COG to be contacted to form ammonium sulphate.

Phosam process

The process uses a solution of mono‑ammonium phosphate for absorbing ammonia, forming di‑ and tri‑phosphate salt solution. The process is reversed by stripping with high pressure steam to obtain anhydrous ammonia. An alternative is the production of diammonium phosphate for fertiliser use.

Using the Phosam process, ammonia found in raw coke oven gas can be converted into commercially pure anhydrous ammonia. Compared to ammonium sulphate operations, this high value product makes the process more profitable.

Water wash process

This is the simplest and frequently used process for ammonia stripping from COG. The ammonia present in the COG is absorbed using water and the absorption liquor is then stripped of ammonia in a distillation column using steam. The stream leaving at the top of the stripper is rich in ammonia and can be converted to fertilizer or anhydrous ammonia.

Hydrogen sulphide removal

This process is used for deep desulphurization of steel plant gases. It is generally used after another desulphurization process‑ like alkalanolamine or Selexol process. In this process, the steel plant gases are passed through a bed of zinc oxide (ZnO) at high temperatures where the H₂S reacts with ZnO to produce ZnS.

Generation of gases in a steel plant

In a typical steel plant, the quantity of byproduct gases generated per tonne of hot metal (THM) are(9)(10):

• BFG – 1,200‑2,000‑m³/THM (average: 1,500‑m³/THM)
• COG – 300‑500‑m³/THM (average 400‑m³/THM)
• LDG – 80‑150‑m³/THM (100‑m³/THM).

It is also assumed that around 70‑m³/THM of COG will be used for heating and other purposes in the steel plant. So, 330‑m³/THM of COG is available for ammonia or methanol synthesis.

Based on the Ministry of Steel Annual Report (2023‑24), hot metal production in India was 87.045‑mt. Hence, the total annual gas production would on average be as follows:

• BFG – 130,567‑mscm;
• COG – 34,818‑mscm; and
• LDG – 8,704‑mscm.

The quantity of H₂ would be 20,991.7‑mscm (34,818 mscm x 60.29%) or 1.874‑mt. This is equivalent to 50 × 1.874 = 93.71‑GW of power. If electrolysers were used for hydrogen production, 93.71‑GW would be the savings in solar PV systems. This is the potential for H₂.

The utilization of these gases would require converting them to other profitable chemicals, which in most cases require H₂. The possibilities are conversion to methanol, ammonia, and certain chemicals that can be made utilizing CO or CO₂ and methanol, etc. The entire process requires that the components of steel plant gases be separated, as required by the process and then reacted to give the desired chemical.

Table‑2: Composition of gases produced per tonne of steel

Component	BFG (m³/THM)	Vol%	COG (m³/THM)	Vol%
CO	340.8	22.72	16.63	25.04
CH₄	—	—	83.52	23.86
CO₂	317.7	21.18	4.25	1.28
N₂	802.5	53.50	14.71	84.46
O₂	—	—	0.95	0.27
CₙHₘ	2.7	0.19	10.95	6.31
Total	1,500		330

For the methanol synthesis reaction with CO and CO₂, the stoichiometric number (Sn) of the syngas feed, which is defined as ((H₂ – CO₂) / (CO + CO₂)) should be: 2 ≤ Sn ≤ 2.1. Following this ratio, the CO and CO₂ requirement for the amount of H₂ present can be calculated. Methane present in the COG can be separated by adsorption using activated carbon and the separated methane can be subjected to steam reforming. Steam reforming generates CO along with H₂, which can be used for methanol production: CH₄ + H₂O → CO + 3H₂.

The production of ammonia requires N₂ and H₂ in the ratio of 1:3. N₂ is obtained using sufficient quantity of BFG, by separating N₂ from CO and CO₂. CO and CO₂ can be used for methanol production as COG alone does not have sufficient CO for methanol reaction (Figure 1).

Figure 1 [Image placeholder: Process flow diagram for methanol and ammonia production]

Mass balance

The overall mass balance for the process is shown in Table‑3. The mass balance is calculated based on the quantities of gases emitted per THM. All the data in the Table are in the basis of m³/THM.

Table‑3: Overall mass balance (m³/THM)

	COG treated	COG treated	Adsorption with AC		Methanol synthesis	Steam reforming	Adsorption with zeolite		Ammonia synthesis
			Stream 1	Stream 2			Stream 1	Stream 2
H₂	198.95	198.95	192.85	6.12	56.67	254.61	—	1.98	—
CO	16.63	16.63	12.54	4.12	120.51	120.51	—	—	—
CH₄	83.52	83.52	—	83.52	—	—	—	—	—
CO₂	4.25	4.25	—	4.25	4.25	4.25	—	—	—
N₂	14.71	14.71	—	14.71	14.71	14.71	—	—	—
O₂	0.95	0.95	—	0.95	—	—	—	—	—
CₙHₘ	10.95	10.95	—	10.95	—	—	—	—	—
CH₃OH	—	—	—	—	72.30	—	—	—	—
H₂S (1% vol)	—	—	—	—	—	—	—	—	—
NH₃ (0.5% vol)	—	—	—	—	—	—	—	82.32	—

The separation is done by selective adsorption under moderate pressure. Other methods like membrane separation are also available, however there is vast experience in adsorption methods for decades.

The COG is compressed to approx. 5 bar pressure and fed to activated carbon adsorber separating all hydrogen, and residual stream contains methane along with other components. It is of sufficient purity to be used in methanol synthesis. The residual stream is compressed and sent to steam reforming process, converting it into H₂ and CO. The output from steam reforming then goes to zeolite adsorption unit to separate H₂ from CO; the H₂ is used for ammonia synthesis.

BFG is used only to the extent to obtain sufficient nitrogen for ammonia synthesis. Thus, out of the 1,500 m³/THM only 218 m³/THM is used to provide CO, CO₂ and N₂.

Hydrogen allocation

The hydrogen use is divided as follows: hydrogen obtained from COG is used to produce methanol, and hydrogen obtained by reforming methane is used for the production of ammonia.

For convenience the available CₙHₘ were assumed as C₃H₈ and converted to CO and H₂ through steam reforming.

Production quantities

Based on the above‑mentioned data and assumptions, the ammonia and methanol production quantities per THM were calculated.

• Ammonia production: 3.675 Kmoles/THM or 82.327‑m³/THM (yield 97%)
• Methanol production: 3.228 Kmoles/THM or 72.309 m³/THM (yield 95%)

The quantity of hydrogen produced by steam reforming is around 250 m³/THM which is more than the hydrogen present in COG and BFG combined. There is a surplus of 438.51 m³ CO and 285.35 m³ CO₂ including that generated during steam reforming.

Case 2: Production of methanol only

To maximize the carbon utilisation all the hydrogen and equivalent CO is utilized. The final mass balance is given in the Table‑5.

Table 5 indicates carbon utilization of 28.6%. At 95% yield, methanol production would be 9.53‑kmol/THM or 305‑kg/THM. The capacity at 100% utilisation would be 305 × 87.045 = 26.55‑mt and at 50% utilisation it would be 13.28‑mt.

Table 4: Gas production and usage per THM (Case 1) [m³/THM]

	Feed COG	Feed BFG	Used for methanol	Used for ammonia	Surplus
CO	16.63 / 0.74	340.8 / 15.21	39.40 / 1.76	—	438.51 / 19.58
CO₂	4.26 / 0.19	317.5 / 14.18	36.71 / 1.64	—	285.25 / 12.73
H₂	198.9 / 8.88	36.3 / 1.62	192.85 / 8.61	254.68 / 11.37	—
N₂	14.72 / 0.66	802.4 / 35.83	—	84.89 / 3.79	732.33 / 32.69
CH₄	83.52 / 3.73	—	—	—	—

Table 5: Gas production and usage per THM (Case 2) [m³/THM]

	Feed COG	Feed BFG	Stream after steam reforming	Used for methanol Production	Surplus
CO	16.63 / 0.74	340.8 / 15.21	120.51 / 5.38	224.78 / 10.03	236.53 / 10.56
CO₂	4.26 / 0.19	317.7 / 14.18	4.26 / 0.19	—	321.96 / 14.37
H₂	198.96 / 8.88	36.3 / 1.62	256.67 / 11.46	449.52 / 20.07	—
N₂	14.72 / 0.66	802.5 / 35.82	14.72 / 0.66	—	817.22 / 36.48
CH₄	83.52 / 3.73	—	—	—	—

Power for gas separation

The separation processes, as mentioned, are done at low pressure of 5‑Barg, so that power consumption is low, as the volumes are large. The smaller volumes of separated gases can now be compressed to the pressure required by the process, which may be from 50‑100 atm. The compression power is calculated for the entire volume of gases generated per THM, and the calculated power requirement is tabulated in Table‑6.

Table 6: Power requirement for each gas stream [kW/THM]

Stream	Pump power (kW/THM)
Feed COG	25.98
Gases after steam reforming	32.85
Feed BFG	121.95
BFG after CO₂ removal	88.35
Total	269.15

As only 15% of BFG quantity is used for production of ammonia and methanol, the power consumption is only 31.5 kW. For ammonia production, 54% of hydrogen is consumed, and the remaining is used for methanol synthesis.

Power consumption for gas separation for Case 1 is as follows:

• Ammonia production = Power for steam reforming + part of BFG = 49.73 kW/tonne of NH₃.
• Methanol production = Power for Feed COG + part of BFG = 40.6 kW/tonne of methanol.

Potential

The hot metal production in Blast Furnace plants in India is 87.045‑mtpa. The existing plants may be utilizing the gases in many ways; if production of chemicals is planned, suitable changes have to be made, or in case of new plants these have to be incorporated at FEED stage. Table‑7 indicates the potential for methanol and ammonia production at different levels of utilization.

Even if 40‑50% of the potential is realized, the quantum of production would be substantial.

Hydrogen produced by steam reforming is 85,320‑tpa. If natural gas consumption is foregone for ammonia production, the savings is equivalent to 2.84 kg CO₂ per kg of ammonia(11). There is additional 820,000 tons CO₂ emission savings per year.

Table 7: Production potential in Indian steel plants for methanol and ammonia [mtpa]

Capacity utilization	Methanol	Ammonia	Methanol only
100%	8.99	5.43	26.55
75%	6.74	4.07	19.91
50%	4.49	2.71	13.28
25%	2.24	1.35	6.64

Estimated gas usage for production (Case 1)

• N₂ – 1.554‑mtpa or 1,243.07 mscm/year.
• CO – 1.443‑mtpa or 1,154.46 mscm/year.
• CO₂ – 2.113‑mtpa tons/year or 1,075.71 mscm/year.

Potential carbon reduction

CO used is converted to equivalent CO₂. Of the total CO and CO₂ obtained from COG and BFG, approximately, 10.5% is consumed based on the above‑mentioned process route.

Methanol alone (Case 2) appears to give almost three times higher CO₂ use over Case 1. But considering the CO₂ avoided when producing ammonia then the CO₂ equivalent is tilted towards combined production.

In Case 2 as only methanol is produced using CO, the carbon utilization increases to 28.6% which is almost three times higher than Case‑1. CO used for the production of methanol is 218.32 m³/THM or 9.746 kmol/THM.

Table 8: CO₂ savings Case 1 and 2 [mtpa]

Capacity utilisation	Methanol CO₂ savings (mtpa)	Ammonia CO₂ avoided (mtpa)	Methanol CO₂ savings (mtpa)
100%	1.30	15.47	3.84
75%	0.95	11.61	2.88
50%	0.65	7.74	1.92
25%	0.32	3.87	0.96

Further CO, CO₂ reduction

Table 5 indicates surplus CO of 236.53‑m³/THM and surplus CO₂ of 321.96‑m³/THM. Some options for using this surplus are indicated below.

Direct use of methanol and/or ammonia is well known. Conventional thinking is to use green hydrogen to convert CO/CO₂ to methanol. But green hydrogen is expensive – 2.5‑3.5x the normal cost – and requires subsidies.

Of more significance is the utilisation of surplus CO and CO₂ to produce other chemicals such as phosgene, acetic acid, and dimethylformamide. Phosgene is a very important chemical used for manufacturing isocyanates used in agrochemicals, TDI and MDI (both used in manufacture of polyurethane foams), etc. Phosgene safety is assured as it can be produced on demand without need for storage.

Methanol can also be converted to acetic acid by reaction with CO.

Asahi Kasei Corporation(12) has industrialized processes where ethylene oxide reacts with CO₂ to produce ethylene carbonate. The ethylene carbonate is reacted with methanol to produce dimethyl carbonate, along with ethylene glycol as byproduct. The dimethyl carbonate can be used to produce diphenyl carbonate, when reacted with phenol. Finally, polycarbonate can be produced by reacting bisphenol A with diphenyl carbonate. It is important to note that all the technologies are well established. Polycarbonate has various applications in automobile, electrical and electronic sectors. The ethylene carbonate and dimethyl carbonate produced by this process are extremely pure and can be used as electrolyte in lithium‑ion batteries.

Figure 2 [Image placeholder: Chemicals from methanol, CO and CO₂ – flow diagram]

CONCLUSIONS

Steel plant gases have been usually treated as source of energy based on heating value. After the internal needs of energy are satisfied the surplus can be a source of value‑added products and can contribute towards decarbonization.

Assuming 50% surplus utilisation, Case 1 indicates production of 4.495‑mtpa of methanol and 2.715‑mtpa of ammonia for steel industry producing 87.045‑mtpa. In Case 2 (where only methanol is produced), its output can be 13.28‑mtpa.

CO reduction in Case1 is 8.36‑mtpa and 1.92‑mt in Case 2.

A variety of downstream chemicals can also be manufactured. As most steel plants are in eastern India, this will aid development of chemical industry in the region.

All the technologies for processing of steel plant gases and conversion to chemicals are well established.

Dependence on imported hydrocarbon resources is reduced.

The additional advantage is the CO₂ savings that will accrue to the steel‑making process.

The potential indicated needs a more detailed technical and economic study, considering all aspects mentioned.

REFERENCES

1. IEFEA & JMK Research. (2023). Steel decarbonisation in India. (Report).
2. Razzaq, R., Li, C., & Zhang, S. (2013). Coke oven gas: Availability, properties, purification, and utilization in China. Fuel, 113, 287‑299. https://doi.org/10.1016/j.fuel.2013.05.070.
3. LNG Industry. (2014, January 23). COG LNG project completed.
4. Di, Zichen, et al. "Technical Alternatives for Coke Oven Gas Utilization in China: A Comparative Analysis of Environment‑Economic‑Strategic Perspectives." Environmental Science & Ecotechnology, vol. 21, 2024, p. 100395. https://doi.org/10.1016/j.ese.2024.100395.
5. J. Lundgren, T. Ekbom, C. Hultenberg, M. Larsson, C.‑E. Grip, L. Nilsson, P. Tuná. Methanol production from steel‑work off‑gases and biomass‑based synthesis gas. Applied Energy 112 (2013) 431‑439.
6. Deng, L., & Adams, T. A. (2020). Techno‑economic analysis of coke oven gas and blast furnace gas to methanol process with carbon dioxide capture and utilization. Energy Conversion and Management, 204, 112315. https://doi.org/10.1016/j.encan.2019.112315.
7. J.M. Bermudeza, N. Ferrera‑Lorenzo, S. Luque, A. Arenillas, J.A. Menendez (2013). New process for producing methanol from coke oven gas by means of CO₂ reforming: Comparison with conventional process. Fuel Processing Technology, 115, 215‑221. https://doi.org/10.1016/j.fuproc.2013.06.006.
8. Jun Shen and Zhi‑zhong Wang (2007). A new technology for producing hydrogen and adjustable ratio syngas from coke oven gas. Energy & Fuels, 21(6), 3588‑3592. https://doi.org/10.1021/ef700217j.
9. IspatGuru. "Coke Oven By‑Product Plant." https://www.ispatguru.com/coke‑oven‑by‑product‑plant/.
10. IspatGuru. "Coke Oven Gas Generation and usage" https://www.ispatguru.com/coke‑oven‑gas‑generation‑and‑usage/.
11. Royal Society. (2020). Ammonia: Zero‑carbon fertilizer, fuel and energy store. https://royalsociety.org/‑/media/policy/projects/green‑ammonia/green‑ammonia‑policy‑briefing.pdf.
12. Asahi Kasei. Asahi Kasei TLB – Process Licensing Business. https://www.asahi‑kasei.co.jp/tlb/en/.
13. International Energy Agency. (2021). Ammonia technology roadmap: Towards more sustainable nitrogen fertilizer production. IEA. https://www.iea.org/reports/ammonia‑technology‑roadmap.