Customized waste heat recovery
The environmental aspect is a crucial factor of sustainability, performance and competitiveness for the industry. Fives’ expertise in energy-intensive industries (aluminum, cement, steel, glass, etc.) minimizes heat losses by recapturing residual energy losses through external energy recovery systems.
The steelmaking process is complex and involves many waste heat recovery opportunities both for the upstream and downstream processes. Steel makers use waste heat recovery (WHR) to optimize plant performance and decrease the costs of fuel and energy consumption. However, waste heat recovery in the downstream process (reheat furnaces, strip processing lines) is more challenging as the parameters of reheating and heat treatment are finely tuned to achieve specific mechanical properties of steel.
Additional heat exchanges for waste heat recovery purposes may have an effect on steel quality and must be designed by qualified experts. Depending on the plant needs, waste heat can be used to produce steam at different quality levels for internal use in the plant, e.g. for degreasing steel strips, or to produce mechanical power for direct drive of rotating equipment or for conversion into electricity.
Fives offers effective WHR solutions customized for each industrial issue that are able to manage the variability of waste energy supply and ensure production continuity – a key success factor.
The reheating furnace is critical equipment of the hot rolling section. Its function is to continuously heat billets, slabs or blooms of different sizes and grades up to around 1,250°C. A key performance criterion for reheating furnaces is heating homogeneity.
20% to 30% of the energy input is typically wasted, and divided between several thermal losses, such as furnace exhaust gas, water loops, walls and doors.
Fives proposes combining several heat sources to ensure better profitability: heat from a skid cooling system and exhaust gases. The two heat sources are recovered separately thanks to organic heat fluid loops and then combined to form a common heat source. As a reheating furnace does not function at full capacity all year long, the WHR system should be sized according to the actual production mix. The following case assumes a furnace operating 90% of the time at 70% load, and 10% at full capacity.
An existing furnace can be equipped with an ORC (Organic Ranking Cycle) sized at 70% of the furnace capacity instead of 100%, thanks to combined recovery of both waste heat sources. In this configuration, extra losses generated over 70% of maximum capacity are dispatched to the backup feed water cooling of the skid system. With this configuration, the ORC system operates at its maximum efficiency all the time.
Fives' configuration for a 450 t/h waling beam furnace with mixed gas:
- Reduce heat losses from the skid system by 2 MWth due to the new skid installation at 21 bars and water cooled skid pipes used at higher temperature
- Produce 2 MWe (11% net efficiency including auxiliaries) - typical for an ORC at this temperature
- Avoid energy consumption of the conventional skid cooling system 90% of the time