Gas Turbines for Heat Generation

Abstract

Firing industrial installations, like boilers, with a cogeneration gas turbine instead of a classic burner have several beneficial aspects. A cogeneration system allows for a more efficient utilization of energy and lowered emissions. What makes such a system especially interesting is that the revenue of the generated electrical power can outweigh the extra costs required to operate a gas turbine for producing a specific amount of thermal energy. The technical challenge, covered in this thesis, consists of improving a gas turbine for cogeneration applications relative to a classic burner. The solution can be found in reduction of the high stack losses, as these comprise the main disadvantage of firing a boiler with a gas turbine. This research focuses specifically on cogeneration with the PowerBurner, a gas turbine developed and manufactured by Innecs Power Systems, located in Ter Aar, the Netherlands.

The goal of this study was to identify, analyze and conceptualize methods that reduce the stack losses of a PowerBurner used for the production of steam. Implementation of such methods should allow the PowerBurner to become a more attractive alternative for steam production compared to a conventional burner. Four concepts were identified which could improve operation of a cogeneration gas turbine: Steam injection, flue gas recirculation, supplementary firing and implementation of a boiler in the combustion chamber, the Velox boiler.

A thermodynamic model of a gas turbine was created in Thermoflex. The model was based on the design point specification of the PowerBurner, from which it deviates less than 1% at any point in the process. Implementation of steam injection was able to induce the largest increase the electrical efficiency, from 10.5% to 20%, whereas flue gas recirculation resulted in the highest increase in total efficiency, from 85% to 95%. With supplementary firing and the Velox-type boiler, the thermal capacity and -efficiency could be increased the most, from 2 MW to 6.8 MW and from 74% to 90%, respectively.

The profitability of each setup compared to making use of a conventional burner for an equal thermal output was determined. Supplementary firing allows for the most profitable operation. A qualitative cost analysis showed that supplementary-fired setup required the least capital expenditures. From a combination of the thermodynamic and economic characteristics, the supplementary-fired PowerBurner was chosen to be the best alternative for replacing a conventional burner for the production of steam.

A conceptual design of a burner for such an application was created in ANSYS Fluent. The design was able to operate with fuel inputs of at least 0.485 MW up to 4.85 MW. 100% Combustion efficiency was achieved over the full range. Pressure losses over the burner are low at 1.6 mbar. Whether the current burner design results in a stable flame cannot be determined from the model. A NOX analysis in Fluent indicated that the emissions of NOx are over the Dutch regulation standards for gas turbines, but the accuracy of this result is not known. Therefore, future research is required to determine flame stability and pollutant emissions.