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In this study, a cycle designed for capturing the greenhouse gas CO 2 in a natural gas combined cycle power plant has been analyzed. The process is a pre-combustion CO 2 capture cycle utilizing reforming of natural gas and removal of the carbon in the fuel prior to combustion in the gas turbine. The power cycle consists of a H 2 -fired gas turbine and a triple pressure steam cycle. Nitrogen is used as fuel diluent and steam is injected into the flame for additional NO x control. The heat recovery steam generator includes pre-heating for the various process streams. The pre-combustion cycle consists of an air-blown auto thermal reformer, water-gas shift reactors, an amine absorption system to separate out the CO 2 , as well as a CO 2 compression block. Included in the thermodynamic analysis are design calculations, as well as steady-state off-design calculations. Even though the aim is to operate a plant, as the one in this study, at full load there is also a need to be able to operate at part load, meaning off-design analysis is important. A reference case which excludes the pre-combustion cycle and only consists of the power cycle without CO 2 capture was analyzed at both design and off-design conditions for comparison. A high degree of Preprint submitted to Elsevier 10 February 2009 * Manuscript Click here to view linked Referencesprocess integration is present in the cycle studied. This can be advantageous from an efficiency stand-point but the complexity of the plant increases. The part load calculations is one way of investigating how flexible the plant is to off-design conditions. In the analysis performed, part load behavior is rather good with efficiency reductions from base load operation comparable to the reference combined cycle plant.

Effective heat and power supply to offshore installations leads to environmental benefits, but the efficiency is often limited by requirements and constraints connected to the offshore environment. An exergetic analysis of gas turbines exhaust heat recovery on offshore platforms is performed to identify optimal approaches to produce heat and power. Two different configurations are presented, with heat delivery at two temperature levels and power production by an organic Rankine cycle (ORC). In one system (cascade), the high temperature heat is taken from the exhaust after the ORC, while low temperature heat is taken from the ORC condenser.Alternatively, high and low temperature heat is taken from the exhaust gas before the ORC feeds on the remaining exhaust thermal energy (series system). Four different working fluids (three siloxanes, one refrigerant) are considered. In addition, the exergetic effects of the heat loads and heat source temperatures are investigated. The results revealed that MM and R124 are the best working fluids for the cascade and series system, respectively. A recuperated ORC in the series

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Combined cycles applied on offshore oil and gas installations could be an attractive technology on the Norwegian continental shelf to decrease costs related to CO 2 emissions. Current power plant technology prevailing on offshore oil-and gas installations is based on simple cycle gas turbines for both electrical and mechanical drive applications. Results based on process simulations showed that net plant efficiency improvements of 26-33% (10-13%-points) compared to simple cycle gas turbines can be achieved when the steam bottoming cycles are designed for compactness and flexibility. The emitted CO 2 could be decreased by 20-25% by opting for a combined cycle rather than a simple cycle gas turbine. A clear disadvantage for offshore applications is that the weight-to-power ratio was 60-70% higher for a compact combined cycle than for a simple cycle gas turbine based on results in this study. Once-through heat recovery steam generator technology can be an attractive option when designing a steam bottoming cycle for offshore applications. Its flexibility, the avoidance of steam drums, and, with the right material selection, the possibility to avoid the bypass stack while allowing for dry heat recovery steam generator operation are all advantages for offshore applications. All process models, that were developed for offshore installations in the study presented, included once-through technology. A combined cycle plant layout for an offshore installation with both mechanical drive and generator drive gas turbines was included in the study. This setup allows for flexibility related to changes in demand for both mechanical drive and electricity. With the selected setup, designed for 60 MW shaft power, demand swings of approximately ±10 MW could be handled for either mechanical drive or electrical power while keeping the other drive-mode load constant.Keywords: once-through, Rankine cycle, steam bottoming cycle, process simulation, steady-state