CORE ENGINE FOR TB5000

Published on: January 1, 2016

There are over 850 Siemens TB5000 gas turbines sold which have accumulated more than 88 million fleet operating hours. First introduced in 1970 and retired in 2002, the TB5000 product line offered high reliability and long life. Many of the units are operating in challenging climate conditions, such as in the the Middle East and in the Alaskan North Slope.

Based on the size and age of the operating fleet, Siemens recently determined the majority of these units could benefit from newly designed core engines and has set out to build and assemble the first 20 new core engines for the TB4900 and TB5400 at the Siemens Service Product Centre of Competence in Scotland. These core upgrades will lower costs by reducing the need to replace parts. Siemens has introduced a new blade and disc design for the compressor turbine section.

Faster supplemental firing

Siemens has also introduced a way to make supplemental firing faster. In combined cycle power plants with supplemental firing, load changes after the gas turbines have reached full load are typically achieved by increasing or decreasing the amount of fuel supplied to the duct burners. The fuel change alters the heat input to the heat recovery steam generator (HRSG), resulting in a change in the amount of water heated and steam created, thus raising or lowering the power output of the steam turbine.

Due to the physics behind the boiling process, the water heating process is not instantaneous. This slows down the reaction time when changing load with a duct burner. As typical ramp rates for duct firing are in the range of 3 MW/min in a traditional duct fired plant, the GT is dispatched first and then the duct burners are fired for additional power. A reduction in output is achieved by doing the reverse. Duct burners are ramped off before the GT is ramped down. The result is that the ramp rate for load changes is limited to the slower reaction time of the duct firing.

Siemens Dash enables a Siemens Flex- Plant with supplemental firing to move quickly by taking the ramp rate limitation of the duct burners out of the equation. With Dash, the GT and duct burners work together to keep the plant ramp rate fast.

By dispatching the duct burners earlier, the GT can react to load demand changes at maximum ramp rate. This requires operating the duct burners while the GT is part loaded. Working in partnership with NEM, Siemens developed the system so that all temperatures and pressures are maintained within the normal operation regime of the boiler during Dash operation.

Benefits include rapid response to changing load demands through elimination of duct burner ramp limitation, ability to light off duct burners at lower gas turbine loads, no 100% gas turbine load hold to light off duct burners, elimination of the plant load dead band between 100% GT load with and without duct burners, and base load power with full duct burners in operation from minimum plant load in less than 15 minutes.

Finally, Siemens released the Simatic S7-1500 software controller, which can now be operated from industrial PCs. This software-based controller includes integrated system diagnostics, motion and security functions. It operates independently of the Windows system ensuring continued operation during restart or Windows failure.