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The steel industry's energy-intensive nature has long made waste heat recovery a strategic priority for hot rolling operations, where billet reheat furnaces release substantial thermal energy through flue gas at exhaust temperatures of 250 to 350 degrees Celsius. NatSteel Singapore originally installed an Organic Rankine Cycle (ORC) system in 2014 at the exhaust of its billet reheat furnace to convert this otherwise lost energy into electrical power. Following changes in operational mode and rolling mill scheduling, the ORC was deemed uneconomical to operate and was mothballed shortly after commissioning. Approximately a decade later, NatSteel engaged Gas Cleaning Technologies (GCT) to restore the system and resume green power generation under a new commercial arrangement.
The 600 kW ORC system operates on hexamethyl-disiloxane, a silicone-based working fluid selected for its 100 degrees Celsius boiling point and 340 degrees Celsius ignition temperature, characteristics well suited to the low-temperature waste heat profile of reheat furnace exhaust gases. Process heat from the furnace flue gases evaporates the organic fluid in a heat recovery unit, driving a turbine generator before the working fluid is condensed and recirculated through a closed-loop system. Effective integration depends on adequate condenser cooling capacity and resilient water-side circuitry capable of handling all operating conditions, with selection of the working fluid playing a decisive role in plant safety, performance, and long-term reliability.
Under the refurbishment program, GCT assumed ownership and operational responsibility for the asset and contracted to supply power back to NatSteel at a discounted tariff, creating a mutually beneficial commercial structure that lowers NatSteel's electricity costs while monetizing recovered waste heat. Following commissioning, the plant has consistently produced approximately 350 kW of electrical power, with stable turbine performance and reliable heat recovery confirmed through SCADA-based real-time monitoring. The restoration effort surfaced several engineering lessons, including an undersized cooling tower, undulating water piping that introduced unnecessary head losses, and pipe corrosion accumulated during the 13-year shutdown, each addressed through targeted modifications during recommissioning. Remote performance monitoring and optimization by GCT now allow the system to operate with minimal supervision from steel production crews.
This case study demonstrates the durability and economic viability of ORC technology for industrial waste heat recovery, even after extended periods of disuse, and offers a practical framework for steel producers and other heavy industry operators seeking to defray rising electricity costs through on-site green power generation. Gas Cleaning Technologies' integrated capability across feasibility assessment, system refurbishment, commissioning, and long-term remote monitoring enables clients to capture waste heat opportunities without dedicating internal resources to ORC operations. For mill operators evaluating decarbonization roadmaps, the NatSteel project provides a relevant reference point illustrating how legacy assets can be restored and optimized to deliver reliable low-carbon power while supporting broader corporate sustainability and energy efficiency objectives.
