Assessment of Organic Rankine Cycle Part-Load Performance as Gas Turbine Bottoming Cycle with Variable Area Nozzle Turbine Technology

Abstract

Power cycles on offshore oil and gas installations are expected to operate more at varied load conditions, especially when rapid growth in renewable energies puts them in a load-following operation. Part-load efficiency enhancement is advantageous since heat to power cycles suffer poor efficiency at part loads. The overall purpose of this article is to improve part-load efficiency in offshore combined cycles. Here, the organic Rankine bottoming cycle with a control strategy based on variable geometry turbine technology is studied to boost part-load efficiency. The Variable Area Nozzle turbine is selected to control cycle mass flow rate and pressure ratio independently. The design and performance of the proposed working strategy are assessed by an in-house developed tool. With the suggested solution, the part-load organic Rankine cycle efficiency is kept close to design value outperforming the other control strategies with sliding pressure, partial admission turbine, and throttling valve control operation. The combined cycle efficiency showed a clear improvement compared to the other strategies, resulting in 2.5 kilotons of annual carbon dioxide emission reduction per gas turbine unit. Compactness, autonomous operation, and acceptable technology readiness level for variable area nozzle turbines facilitate their application in offshore oil and gas installations.

Development of a simulation tool for design and off-design performance assessment of offshore combined heat and power cycles

“…The simulated control strategies are sliding pressure, throttling valve control, partial addition turbine control, variable area nozzle (VAN) turbine control, and cooling water flow rate control strategies. The five implemented part-load control strategies in the tool are introduced here while a more detailed explanation of their operation principle and background can be reached in [13].…”

“…Heat exchangers performance Off-design pressure drop and heat transfer effectiveness in the heat exchangers deviates from the design values in part-load operation and are simulated based on the method presented in [13]. A 𝛽𝛽 parameter is introduced which accounts for the change in the heat transfer coefficient of a heat exchanger [17].…”

“…Partial admission turbine efficiency at off-design conditions is simulated based on the method presented in [13]. The throttle valve performance placed before the turbine is predicted according to the method presented in [13] where a constant enthalpy pressure reduction is considered in the valve.…”

“…Cyclopentene is the selected working fluid for the ORC since it has suitable pressure values in the range of operating temperatures. Design assumptions and input data to the design case are adopted from the design case in [13] except for the PPTD in the heat exchangers which is set to 15℃ for a lower footprint on the platform. A parametric study is conducted to find the optimal design point based on higher power capacity and lower footprint.…”

Thermo-Economic Performance of Organic Rankine Cycle-Based Waste Heat Recovery for Power Generation at a Wide Range of Operating Conditions

“…For instance, the ORC thermal efficiency is reported to be less than 12%, which hinders commercial adoption [12,13]. To date, the focus of many researchers is on assessing the performance of ORC configurations [14][15][16] under variations of heat source [17][18][19], working fluids [20][21][22], strategy control, and part-load [23][24][25], operational parameters [26,27]. Song et al [9] investigated the performance of a 534 kW basic ORC that used six working fluids to generate power from the gas turbine's flue gas.…”