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PETROMAKS2-Stort program petroleum

Compact Offshore Steam Bottoming Cycles

Alternative title: Kompakte Damp Sykluser for Offshore Bruk

Awarded: NOK 12.0 mill.

COMPACTS aimed to develop the next generation design methodology and recommendations for materials standards to allow design of more compact, lightweight and robust steam-based bottoming cycles. This can promote their broad implementation in offshore oil and gas production for both stationary and movable rigs and ships. Implementation will increase energy efficiency of offshore power production by reducing fuel consumption up to 21% and equally reduce CO2 emissions. Offshore gas turbines now have efficiencies of 38%. The remaining energy is expelled as waste heat in the exhaust leading to unnecessarily high CO2 emissions. By hooking up a steam turbine that can produce power from the excess heat, the "combi plant" can produce power from the combustion heat twice. A widespread implementation of bottoming cycles offshore has not happened due to their large weight and volume, lack of available space on existing platforms, and challenges with lifetime and reliability. The key deliverable from COMPACTS was design recommendations for novel offshore bottoming cycles with up to 50% weight reduction compared to current weight and enhanced operational reliability. It was achieved by new modelling that optimizes compactness and reduces weight by replacing steel components with lighter metals like Al in the framework. A robust geometry- based model of the main heat exchanger extracting heat from the gas turbine exhaust was developed. This model was integrated into the system model enabling optimization of the heat exchanger geometry to minimize the weight given requirement or desire for power output. Through PhD work, it set up a detailed numerical model based on CFD (Computational Fluid Dynamics) for different types of fins and tubes and efforts to verify the model against measurements is underway. The CFD-model has recently been applied to quantify the accuracy of the main heat exchanger model. A qualitative CFD study with focus on stability of the gas flow entering the heat exchanger was undertaken. Here, an existing design was compared qualitatively with a new design developed in the COMPACTS project. Steady state and transient simulations were conducted to evaluate transient effects and the applicability of various turbulence models. The conclusion was that the flow pattern was more stable in the new design than in the existing design. COMPACTS has helped set the stage for significant reductions of CO2 emissions on the NCS by reducing the weight and volume of bottoming cycles making them easier to implement. The overall weight reduction of the bottoming cycle is now at 38 % for a 16 MW system and 58% for a 12 MW system while there is still potential for further optimization of the framework for the 16 MW system. This is when comparing to an existing reference facility. The bottoming cycle has been designed to utilize heat from the exhaust of two LM2500 + gas turbines running at 90% load at a certain permissible pressure drop across the system. Recommendations have been made for improvements to condensate treatment equipment and routines. The expected potential for reducing CO2 emission from offshore gas turbines is 17% when implementing a 12 MW bottoming cycle and 21% when implementing a 16 MW bottoming cycle. This can be achieved by reducing the number of gas turbines and replacing them with bottoming cycles on the remaining turbines. The uncertainty in this estimate is ±2%. This will result in lower fuel cost and CO2 tax, helping make the investment economically viable. The emission reduction on a particular platform will be case-specific and depend on the platform's power requirement and the equipment efficiency under part-load The optimization of bottoming cycles in COMPACTS was performed with a main emphasis on reducing weight in a given configuration; there are still opportunities for further weight reductions, possibly in combination with a higher emissions reduction. The results from the project are published in several Scientific journal and news articles.

COMPACTS aims to develop next generation design methodology and recommendations for materials standards that will allow design of more compact, light-weight and robust steam-based bottoming cycles. This can promote their broad implementation in offshore o il and gas production for both stationary and movable rigs and ships. Implementation will reduce fuel consumption and thereby CO2 emissionsfrom offshore power production by up to 30%. The gas turbines now have efficiencies of 38%. The remaining energy is expelled as waste heat in the exhaust which leads to unnecessarily high CO2 emissions. Applying bottoming cycles will increase their efficiency to 50%. A widespread implementation of bottoming cycles offshore has not happened due to the large weight and volume of the systems, lack of available space on existing platforms, and challenges with lifetime and reliability. The key deliverable is a technology knowledge platform that allows for design of novel concepts for steam bottoming cycles that convert e xhaust heat from offshore gas turbines to electricity. Compactness can be obtained through existing FE-optimization software. Light weight by replacing steel components with lighter metals like Al in the framework, or Ti or inconel in the heat exchanger. Particularly large weight reduction will come from novel framework concepts which currently contribute 50% of total weight. Implementing bottoming cycles will reduce fuel consumption, lowering CO2 emissions by 70 000 tonnes/yr for a 30MW turbine resulting in lower fuel cost and CO2 tax. It will contribute significantly to meeting the goals of OG21 where "Energy Efficient and Environmentally sustainable technologies" is one of four focus areas. Their vision to "Support the Norwegian industry to become the most energy efficient oil and gas industry in the world". It is essential for the industry in order to attain society's acceptance for continued growth, particularly in the environmentally sensitive Arctic areas

Publications from Cristin

Funding scheme:

PETROMAKS2-Stort program petroleum