(51b) Risk Assessment of Hydrogen for Use in Hazardous Process

Background:

CO2 emissions in BF-BOF based steel industry is mainly attributed to usage of coal as a fuel & reducing agent for smelting of iron ore. This results in emission of approximately 1.80 tons of CO2 per tonne of hot metal. In line with fuel rate reduction in iron making through blast furnace route, alternate fuel injection, alternate reductants are being practiced in different parts of the world. Most of these also are hydrogen rich. These injectants also lead to reduction of CO2 footprint, thereby participating in carbon direct avoidance (CDA). Different such possible injectants, that are being in use are oils, tar, natural gas, hydrogen, coke oven gas etc.

Our company recently concluded its one of its kind, month-long trial with Coal Bed Methane (CBM) injection in one of its blast furnaces with encouraging results in terms of lowering of coke rates. Considering the same, effort was made to inject pure hydrogen in one of its blast furnaces.

News publication link:

Tata Steel initiates trial for record-high hydrogen gas injection in Blast Furnace at its Jamshedpur Works

Scope of the project:

Hydrogen injection trial was done in 4 tuyeres via hydrogen tanker. This helped in gaining important answers related to technology required for safe handling and injection of hydrogen in blast furnace.

Project Description:

Trial was carried out with hydrogen injection via 4 tuyeres in one of the blast furnaces. Main objectives of this revolves around learning usage of hydrogen and are listed as follows:

• Hydrogen handling and safety concerns
• Basic engineering
• Plant technology requirements
• Suitability and compatibility of injection hardware

Hydrogen supply for these trials was sourced using truck mounted cascades from potential suppliers along with necessary skid for regulating pressure for injection. Pressure reduction skid and transportation pipelines was laid from tanker position till designated tuyere for injection with all safety features and interlocks.

Injection Scheme:

In the existing tar injection system at one of the blast furnaces, there is a compressed air system present for cooling of the lance. In the concentric lance, tar travels from the center and compressed air flows through the annulus. In this system, compressed air system was used for hydrogen injection with no-tar.

The proposed system was itself a unique design and was modified considering the hazards of blast furnace and peripheral area

Challenges in Hydrogen Handling:

• Very Low Ignition energy - 0.017 mJ as compared to other gases.
• Wide range of explosive mixture 4 – 72% as compared to other gases.
• Leakage probability due to low molecular weight of H2 & High pressure handling
• Colourless and odourless and can embrittle some metals

Uniqueness:-

• HMI developed with PSM critical real time parameters with more than 100 safety interlock was built in the logic.
• Automatic stoppage of H2 in case of trip activation interlock and immediate switchover to N2 Inertising/ purging sequence in each tripping.
• Real time simulations & testing of all safety interlocks was done before injection start up.
• Total no of H2 Tankers used –25 Nos with Hydrogen Tanker Pressure - 200 bar and Furnace Injection pressure – 4.5 Bar
• Two stage Pressure reduction from 200 bar to 8 bar and from 8 bar to 4.5 bar with pipeline distance from tanker to furnace ~ 300 mtr
• Excess flow check valve and three way valve with changeover facility and start of purging and venting
• Elimination of entire electrical system from high pressure PRS where multi fold pressure reduction (15 times) is done
• The 1st stage PRS is an inherently safer and reliable design as it consists of mechanical system only, even the flow control valves etc are free from electronic and electrics.
• Safe logistic management of tankers to support the peak hydrogen injection rate @ above 1500 nm3/hr
• The entire injection process of 38000Nm3 is completed safely without a single leak
• Unique system followed to detect leak during injection trial of duration 60 hrs with the help of portable electrochemical H2 PPM detector and Thermography camera as hydrogen leak phenomenon follows opposite to Joule Thomson effect
• There was no unintended leakage of hydrogen.
• Hazop, Consequence modelling through PHAST software, Bow Tie, PSSR conducted before the trial.

Achievements:

• Our company became 1^st to inject such large volume of hydrogen in any Blast Furnace
• During Hazop, 52 number of high risk scenarios were identified and mitigated at the design phase itself
• Hydrogen Injection is one of the key strategy of our company in the decarbonisation journey . The endeavour is aligned with the Company’s vision of becoming Net Zero by 2045 kick started with this project
• The trial has the potential to reduce the coke rate by 10%, translating into around 7-10% reduction in CO2 emissions per ton of crude steel produced saving millions of money.
• Very encouraging process results were observed during the trial and team learnt Safe handling/managing hydrogen injection in Blast Furnace.
• The process sees hydrogen substituted in for carbon as the reducing agent in the extraction process at 40% of the furnace’s injection systems.