With the intermittent nature of renewable electricity generation technology and the ever-changing demands of the grid, IGV (Inlet Guide Vane) Optimization is a digital solution that can help to meet these challenges. It is a control modification that closes the gas turbine inlet guide vanes in a controlled way to reduce air flow at part loads and thus increase exhaust temperature while minimizing emissions. It can improve combined cycle part-load efficiency, stabilize operation at low load and improve turndown to help units stay online longer. IGV Optimization can be implemented at several levels, including adaptive and anticipatory control methodologies if needed, depending on the plant configuration and applicable grid or regulatory requirements.
From the perspective of safety and reliability, Mitsubishi Power gas turbines have two control limits on exhaust gas temperature to keep turbine inlet temperature and exhaust gas temperature within design limits. If either of these limits is breached, GT load rump rate is reduced that compromises the operational flexibility leading to insufficient margin in actual operation.
IGV optimized control
As mentioned above, there are some margins for various restrictions. However, in partial load operation, by raising the temperature of exhaust gas within the range such that the limit is not breached, the steam flow rate and temperature supplied to Steam Turbine (ST) are raised, which contributes to the improvement of ST output and plant efficiency. In addition, the control change also contributes the combustion temperature also rising, resulting in the reduction of CO emissions.
CONCEPT OF IGV OPTIMIZATION
3 menus are available as IGV Optimization in each load band.
- IGV deep close
- Exhaust gas temperature tracking
- Selectable maximum IGV opening (This feature will be introduced more detail next time.)
Since the available IGV setting depends on the customer requirement and unit specification, Mitsubishi Power can prepare the best plan in accordance with the customer’s requirements.
Exhaust Gas Temperature Tracking
- Implementing exhaust gas temperature tracking enables increasing of firing temperature and exhaust gas temperature at part-load operation by further IGV closing.
- Higher firing temperature results in reduction of CO emissions.
- Higher exhaust gas temperature improves combined cycle efficiency.
On average, combined cycle thermal efficiency has increased by +0.6%abs.
IGV Optimization (Exhaust gas temperature tracking) has been installed on 20 units worldwide.
(as of Dec. 2020)