In industries where steam is not used for direct process needs, energy recovery through steam turbines offers a viable solution for power generation. Waste heat recovery boilers are utilized to generate process steam from the exhaust of engines, which is then used to power steam turbines and produce electricity. This approach is particularly advantageous in industries with high exhaust heat, allowing for the efficient conversion of waste energy into electrical power.
System Overview:
Superheated Steam Generation: Waste heat recovery boilers are used to generate superheated steam, which is passed through a steam turbine to power an alternator. This system is feasible when the number and size of gas engines allow for the generation of 8-10 tons of superheated steam per hour, capable of delivering 1.0-1.6 MW of power.
Saturated Steam Utilization: In cases where steam quantity ranges from 4 to 8 tons per hour, a more cost-effective and simple system involves the use of an expander coupled with an electric generator. This system requires saturated steam, preferably at 12.5 bar(g), which can generate up to 340 kW/hr.
DDFC’s Experience and Projects:
DDFC has successfully engineered, manufactured, and delivered several combined cycle projects and expander units for energy recovery through steam turbines:
Combined Cycle Projects:
- International Steels Ltd., Karachi: The first combined cycle project executed by DDFC produced 1200 kW of power. This system utilized waste heat recovery to generate steam and power a steam turbine.
- Fazal Textile Mills Ltd., Muzzafargarh (2018): DDFC’s most recent combined cycle project involved seven engines and superheated boilers delivering 10 TPH of steam at 17 bar(g) and 370°C. This steam powered a MAN brand steam turbine, generating 1600 kW of power.
Expander Units:
- AA Spinning Mills, Faisalabad: DDFC commissioned its first expander unit at this facility, where a waste heat recovery boiler connected to five engines produces 5 TPH of saturated steam at 12.5 bar(g). This steam is used by the expander to generate 340 kW of power.
Benefits and Feasibility:
- Cost-Effective: Using steam turbines for energy recovery is a cost-effective solution, especially when the system can utilize saturated steam to generate significant power, like the 340 kW output from the expander unit.
- Simplicity of Operation: The expander system is simple to operate and does not require complex controls, making it an attractive option for industries looking to recover energy from exhaust gases.
- Efficiency: The systems provide a high level of energy efficiency by converting waste heat into useful electrical power, reducing the dependency on external power sources and enhancing operational cost savings.
