Operational Range Extension to Lower Loads by Fuel Processing

Motivation

The gradual shutting down of the nuclear power plants and the increasing implementation of renewable energy sources, which are both enforced by energy policy, lead to technical challenges for combined cycle power plants running on natural gas. Amongst other the extension of the operational range towards reduced loads is one important topic that needs to be dealt with. Conventional methods for this purpose e.g. staged fuel use and reduced air intake are more or less exhausted.

A rather new approach is the partial conversion of natural gas to syngas, which exhibits lower lean blow out limits. The addition of even a small amount of syngas thus enhances combustion stability and holds the potential for a leaner combustion, which is crucial for extending the operational range to lower loads.

A process as shown below gives the possibility to control the ratio of syngas to natural gas in the Combustion Chamber (CC) by handling the fuel massflows to the CC and the fuel processor. For higher syngas ratios a leaner combustion is possible and thus a gradual decrease of the power output.

In-Situ Production of Syngas

The fuel processor is in the scope of the research. This converts natural gas, mainly consisting of methane to syngas, which should exhibit a share of hydrogen as high as 30 vol-%. The fuel processor will be processed in an auto-thermal reforming (ATR) stage. The ATR couples the benefits of fast oxidative with the lower temperatures and the high hydrogen yield of a steam reformeing process. The hydrogen share in the thermodynamic equilibria for different methane/air/water-vapour are shown in the figure below.