Session: 33-03 Modeling deposition and erosion

Paper Number: 123617

123617 - Comparison of Ash Deposition Models in Gas Turbine Blade Rows for Alternative Solid Fuels With Low Ash Melting Temperatures 

Gas turbines can help stabilise the volatile electricity grid from conventional renewable energies. In addition, they offer the possibility of providing thermal energy, which can be used in district heating networks or adjacent industrial processes. Traditionally, fuel from fossil sources is used to operate gas turbines. However, in order to obtain a fully sustainable energy supply, gas turbines will also have to be converted to a substitute fuel in the future. One possibility is to use fuel of biogenic origin, which is primarily in solid form.

In order to use solid fuels in gas turbines, the IGCC (Integrated Gasification Combined Cycle) process was developed in the past. This process focused mainly on the gasification of coal with subsequent gas purification to fire the product gas in the gas turbine. Due to the primary gasification in a fluidised bed, the product gas was loaded with a high degree of impurities, which made fuel gas purification necessary. One of the main reasons why this process has not become widely accepted is the trade-off between costly fuel cleaning and allowing deposits to build up in the turbine, as gas turbines generally have high maintenance costs. The same deposition issue is expected when using biogenic residues, as can be seen with boilers in waste incineration plants, for example. In the long term, however, the use of residual materials in combination with gas turbines is a promising way to make a major contribution to a stable energy supply. This can be achieved by reducing the maintenance effort, the use in smaller decentralised plants and the reduction of fly ash deposits during operation.

Therefore, it is first necessary to make gas turbines ready for using solid biogenic fuels by solving the problem associated with pollution. In order to prepare gas turbines for this application, the deposition behaviour in relation to the utilisation of biogenic residues must first be understood in order to take countermeasures in the next step.

First, a representative example fuel was selected, with sewage sludge being chosen. In addition, the mean value from the investigations of several sewage sludge compositions was set for the ash content. With the selected composition, a combustion calculation was then performed in FactSage to determine the complete gas composition at the turbine inlet. The resulting composition was then applied to different adhesion models, which include both the viscosity and velocity approaches. Additionally, the condensation of components in the gas phase at decreasing pressure and temperature was considered. The adhesion models were then applied to a CFD simulated blade to investigate the actual deposition on a blade.

The calculation of the combustion gas composition not only shows the appearance of oxides and salts, also acids occur as a gas. When using the adhesion models, especially salts and oxides containing potassium seem to show a great tendency to deposit. The condensation of acids from the gas phase is also a non-negligible deposition phenomenon. Overall, the deposit phenomena show a high potential for problems, which nevertheless appear to be technically solvable. The next step, based on the findings, is to take appropriate countermeasures against pollution in order to receive a sustainable energy supply in the future.

Presenting Author: Luis Wunder Institute of Process Engineering and Environmental Technology

Presenting Author Biography: Luis Wunder studied mechanical engineering at Coburg University of Applied Sciences, Bavaria, with a bachelor's and master's degree in thermodynamics and turbomachinery. After graduating, he began his doctorate at the Technical University of Dresden, where he now works as a research associate.

Authors:

Luis Wunder Institute of Process Engineering and Environmental Technology
Daniel Bernhardt Institute of Process Engineering and Environmental Technology
Michael Beckmann Institute of Process Engineering and Environmental Technology