Municipal DREWAG utility has teamed up with Siemens Energy on an ambitious project to modernize a 25-year old combined heat and power (CHP) plant in Dresden powered by three 60MW V64.3 gas turbines. Scope and goals:
- Engineering. Replace first-stage vane with Additive Manufacturing redesign that reduces cooling air con-sumption by 25%.
- Performance. Increase gas turbine power output and efficiency with ability to operate at higher turbine inlet temperature.
- Environment. Reduce gas turbine NOx emissions thereby improving air quality and facilitating regulatory compliance.
In cooperation with Siemens Energy, DREWAG formed a dedicated project engineering team charged with the job of replacing the gas turbine’s original first-stage vanes with a new, greatly simplified design that improves operating efficiency and reduces cost.
A key objective of the DREWAG Siemens project was to use Additive Manufacturing (AM) technology to produce a set of replacement vanes with optimized internal cooling geometries that would reduce cooling air consumption by 25 percent.
The project team also achieved an upgrade of the gas turbine’s combustion chambers to lower emissions and expand operating range. “This will help increase peak load capacity while also improving part-load capability,” says Jan Münzer, an AM Principal Key Expert for Siemens Energy.
“As a result, DREWAG will be able to reduce exhaust emissions and increase the flexibility of their gas turbine operations in the face of strongly fluctuating demand.”
The change-out of turbine first-stage vanes will be accomplished as part of the machinery’s standard hot section maintenance scope in summer 2021, scheduled after 33,000 equivalent operating hours (EOHs) between inspections.
Because highly-efficient gas turbine plants are an important bridging technology in Germany’s “Energiewende” (Energy Transition) effort to eliminate use of fossil fuels, this project is enabling the utility to extend its operating permit and state subsidy.
Axel Pechstein, DREWAG’s Head of Gas and Steam Turbine Plants, notes that renewable energy sources are a complementary addition to the traditional fuel mix for power generation in Germany, so the plant’s production infrastructure must be flexible in that regard. It also must accommodate ever-tightening emissions regulations.
“That’s why it is particularly important for us to be able to economically operate our plants with high availability and flexibility in this increasingly challenging environment.
Use of Additive Manufacturing technology instead of the more complex and costly casting methods to manufacture our turbine’s first-stage vanes is expected to simplify operations and contribute.”
Reverse engineered stator vane
Applying AM technology to redesign and replace the first-stage vanes required some creative reverse engineering. Siemens’ Münzer points out that the existing design is about 30 years old, predating the DREWAG turbines.
“Since the existing 2D drawings had not fully captured all the changes made to the original design during manufacturing qualification so long ago, we had to create a 3D model from those drawings.”
This was supplemented by scanning the current vanes using advanced computer tomography to determine actual internal details.
“Next, we imported the tomography data into sophisticated 3D modeling and simulation software to create a digital twin that we could then manipulate. This allowed us to evaluate performance of various designs under the range of operating conditions to which the gas turbines would be subjected.”
This reverse engineering was the first phase of the DREWAG project. “From the stator vane’s digital twin, we used a selective laser melting (SLM) process to manufacture the first test vanes as full-scale replicas of their legacy counterparts, using IN939 metal powder,” Münzer says.
Those vanes have operated for AM material validation for more than 11,000 EOHs in Dresden to date, without any issues. He notes that the 3D modeling combined with AM/SLM production techniques enable precise component outputs that can be reproduced serially, or in parallel, with little-to-no deviations in their physical specifications. He also points out that IN939 is a nickel-based super alloy containing precise amounts of chromium, cobalt, titanium, tungsten, aluminum, tantalum, and niobium.
Owing to its superior high-temperature mechanical properties, IN939 powders are widely used by Siemens Energy in the AM/SLM fabrication of turbine components.
Complex component geometries
With AM/SLM, it’s possible to produce complex component geometries that cannot be achieved economically or by any other manufacturing processes, including the vacuum investment casting process, which is the industry standard.
The vanes were produced at Materials Solutions, a Siemens Energy subsidiary specializing in AM/SLM solutions for high performance industries. “Not only are we using Additive Manufacturing to fabricate a completely new stator vane for DREWAG’s turbine retrofit project but, in the second phase, also designing a highly efficient cooling system and to generally simplify the entire manufacturing chain through maximum functional integration,” says Münzer.
“What’s more, AM/SLM is considerably faster than casting because it’s tool-less production and supports a continuous digital process chain from design and construction to production.
“This enables us to get new components and products to market much earlier and provide customers with much shorter ordering times for spare parts,” he says.
“In turn, this can provide them with greater operating and inventory flexibility, while significantly lowering capital and logistics costs.”
By simplifying manufacturing and shortening lead times from several months to a few weeks’ time, Additive Manfacturing can support an on-demand spare parts model that can reduce turbine lifecycle costs and generally lower total cost of ownership.
Additional operating benefits
Ultimately, AM, supported by 3D digital modeling, enabled the DREWAG-Siemens Energy project team to simplify the turbine vane design so it could be manufactured as a single piece rather than as an assembly of five components.
Also, besides cutting cooling air consumption by 25 percent, the improved cooling design has reduced hotspot temperatures by 50-100°C.
Because the project schedule allowed just 14 months for the design, manufacturing, deployment and commissioning, using Additive Manufacturing to cut lead time by as much as two-thirds was a critical success factor.
Another key element in the project’s success was the close collaboration of the DREWAG and Siemens engineers working as a dedicated project team. “The cooperation with Siemens was constructive from the very beginning,” says Pechstein. “We were able to incorporate our concerns and requirements into the project every step of the way.”
Münzer concurs: “DREWAG is a longstanding development partner of Siemens Energy with a lot of experience in operating our turbines.
Based on the experience we gained in this project, we will be able to digitally develop similar solutions for them and other customers very quickly in the future, using modern design methods, and then use AM to manufacture them economically and on-demand.”