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PETROMAKS2-Stort program petroleum

Compact Offshore Steam Bottoming Cycles Phase 2: COMPACTS2

Alternative title: Kompakte offshore bunnsykler fase 2: COMPACTS2

Awarded: NOK 11.1 mill.

COMPACTS2 has supported work in COMPACTS and developed novel technology allowing a significant reduction of CO2 emissions on the NCS by reducing weight and volume of bottoming cycles and increase operational reliability so that they become implementable. The estimated potential for reduction in CO2 emissions from offshore gas turbines is 17% when implementing 12 MW bottoming cycles and 21% if implementing 16 MW bottoming cycle. Offshore power production is mainly conducted by burning natural gas in gas turbines. The gas turbines produce power and release hot exhaust gas. By installing a bottoming cycle extracting heat from the exhaust gas to drive a steam turbine, the combined cycle (gas turbine and steam turbine) can produce more power than a single gas turbine. This means that the offshore power demand can be covered with a lower consumption of natural gas than today, and the CO2 reduction potential is 25%. Combined cycles (gas turbine and steam turbine) have large weight and volume and the lack of space on existing platforms is the main reason that widespread implementation of offshore bottoming cycles has not yet taken place. In a previous project, COMPACTS, it was demonstrated that the total weight of a bottoming cycle can be reduced by 40% without reduction in the power production. Hence, the main focus in COMPACTS2 is to analyze the robustness of the new light-weight power production system and possibly modify the design to ensure reliability. The project work focused on the robustness of the heat recovery steam generator (HRSG), which is the largest and heaviest component of a bottoming cycle. Models for flow-induced vibrations are being implemented in a thermal simulation software, enabling weight minimization while maintaining thermal performance and a vibration free design. Other activities in the project support this task by supplying additional insight: The bending stiffness of tubes with and without fins are investigated numerically to elicit whether fin geometry may influence vibration patterns. The flow in the diffuser between the gas turbine and the HRSG is modelled using CFD. Flow induced vibrations of a single tube with different fins and tube arrays have been investigated in a wind tunnel. Models for the analysis of transient conditions of the HRSG have been developed with the aim to simulate load changes and start/stop events for the bottoming cycle, since these can be sources of potential thermal stresses. This is important in order to gain insight in and evaluate the mechanical integrity of the HRSG under realistic operating conditions. An analysis of user experiences with EDI water treatment systems has been performed. A new sensor scheme has been developed for water treatment of steam cycles and progress has been made in design of water treatment systems that are very operationally reliable. The results from all these studies will be of use to both offshore as well as land-based industry in order to reduce CO2 emissions. Several of the findings coming out of the COMPACTS and COMPACTS2 project are currently in the process of being implemented in two industry projects. One is the green platform project LINCCS where the concrete task is developing an offshore power hub with a combined cycle power plant with CO2 capture. The other is a direct industry project on water treatment for a steam cycle. A potential technology demonstration project for performing a DEMO of the compact OTSG developed in the KPNs COMPACTS and COMPACTS2 is being prepared with two Energy companies.

The results from all these studies will be of use to both offshore as well as land-based industry in order to reduce CO2 emissions. Several of the findings coming out of the COMPACTS and COMPACTS2 project are currently in the process of being implemented in two industry projects. One is the green platform project LINCCS where the concrete task is developing an offshore power hub with a combined cycle power plant with CO2 capture. The other is a direct industry project on water treatment for a steam cycle. A potential technology demonstration project for performing a DEMO of the compact OTSG developed in COMPACTS is being prepared with two Energy companies. COMPACTS2 has enabled a significant reduction of CO2 emissions on the NCS by reducing weight and volume of bottoming cycles and increase operational reliability so that they become implementable. COMPACTS and COMPACTS2 has achieved 49 and 37% reduction in weight of the bottoming cycle for a 12MW and 16 MW steam cycle respectively when compared to a reference project. The bottoming cycle has been designed to recover heat from two LM2500+ gas turbines that are running at 90% load with an allowed The estimated potential for reduction in CO2 emissions from offshore gas turbines is 17% when implementing 12 MW bottoming cycles and 21% if implementing 16 MW bottoming cycles. This could be done by reducing the number of gas turbines and replacing them with bottoming cycles on the remaining turbines. The uncertainty in this estimate is ±2%. The exact emission reduction on a platform will be case specific and will depend on the platform’s power need and efficiency of the gas turbine and bottoming cycle on part load. The optimization in COMPACTS2 was performed to reduce weight in a certain design. It could be possible to reduce weight of the bottoming cycle further and optimize with respect to achieving higher emission reduction.

COMPACTS2 aims to validate methodology for design of more compact, lightweight and robust steam bottoming cycles that will promote their implementation in offshore oil and gas production. This will increase platform energy efficiency and reduce fuel consumption and CO2 emissions by up to 25%. Improved energy efficiency is one of the most effective means of protecting the global environment. The EU has set a goal of 40 % reduction in CO2 emissions from 1990 to 2030, which Norway also supports. Since the Paris agreement improved energy efficiency is one of the main priorities of oil and gas industry. Availability of space and weight for installing new equipment is limited offshore. The prior COMPACTS project showed how weight and volume of offshore steam bottoming cycles could be reduced by at least 40 % which means they can be more widely implemented than the current technology. In COMPACTS2 the aim is even further weight reduction and to validate that the novel design of the compact steam cycle has sufficient mechanical strength. This will be performed by a combination of thermo-hydraulic modeling, materials strength analysis and Computational Fluid Dynamics (CFD). Operational routines for bottoming cycles will be improved to increase reliability. Methods will be suggested to design around the challenges found in the current bottoming cycles. In COMPACTS operational data from two of the existing offshore steam bottoming cycles helped bring forward novel designs. In COMPACTS2 operational experience from the only other offshore combined cycle on the NCS will be used to validate and improve the design further. Case studies will be conducted on an operating offshore platform and a FPSO to validate that the technology meets its goals. A successful outcome of COMPACTS2 can help far along the way towards the 2030 emissions reduction goal. This is essential for the industry in order to attain society's acceptance for continued growth in a future carbon constrained world.

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Funding scheme:

PETROMAKS2-Stort program petroleum