Brayton power generation cycle

Figure 5.2-9 The closed Brayton power generation cycle.

A comprehensive analysis of much of the data for dilute gas-solid suspension was reported by Pfeffer et al. [248]. Correlations for both heat transfer coefficient and friction factor were developed. These investigators presented a feasibility study of using suspensions as the working fluid in a Brayton space power generation cycle [249]. A subsequent presentation of design information and guide to the literature is given by Depew and Kramer [250]. 

R. Pfeffer, S. Rossetti, and S. Lieblein, The Use of a Dilute Gas-Solid Suspension as the Working Fluid in a Single Loop Brayton Space Power Generation Cycle, AIChE Paper 49c, AIChE, New York, presented at 1967 national meeting. 

In apphcation to electric utihty power generation, MHD is combined with steam (qv) power generation, as shown in Figure 2. The MHD generator is used as a topping unit to the steam bottoming plant. From a thermodynamic point of view, the system is a combined cycle. The MHD generator operates in a Brayton cycle, similar to a gas turbine the steam plant operates in a conventional Rankine cycle (11). 

Figure 9-14. Combined Brayton-Rankine Cycle Fuel Cell Power Generation System... 

Another advantage is that the IGCC system generates electricity by both combustion (Brayton cycle) and steam (Rankine cycle) turbines. The inclusion of the Brayton topping cycle improves efficiency compared to a conventional power plant s Rankine cycle-only generating wstem. Typically about two-thirds of the power generated comes from the Brayton cycle and one-third from the Rankine cycle. 

Microturbines, pumps, and compressors are key components used to implement thermodynamic cycles for power generation, propulsion, or cooling. Thermodynamic power cycles use a working fluid that changes state (pressure and temperature) in order to convert heat into mechanical work. To achieve high power density, the pressures and temperatures of the fluid in the cycle should be kept to the high levels common at large scale. Common cycles are the Brayton gas power cycle and the Rankine vapor power cycle, described next. 

The Gas Turbine - Modular Helium Reactor (GT-MHR) is a power unit for the production of electricity or the co-generation of electricity and process heat. The GT-MHR power unit couples the passively safe Modular Helium Reactor (MHR) with a highly efficient energy conversion system. The energy conversion system is based on an intercooled and recuperated closed Brayton (gas turbine) cycle that has a projected efficiency of approximately 48%. The GT-MHR produces electricity directly with the reactor primary helium coolant driving a gas turbine generator derived from technologies developed in the gas turbine and aerospace industries. 

The GT-MHR design directly couples the reactor with a turbogenerator in a closed helium Brayton cycle to produce electricity with 48% net plant efficiency. This high efficiency and the expansion of the power output to 600 MW(t) within the existing GT-MHR physical envelope results in a substantial reduction in the busbar power costs compared to the steam cycle modular helium reactors. The power generation costs are forther reduced by the simplified operation and maintenance required of the gas turbine plant, as compared to the steam cycle plant with its much more complicated balance of plant. 

The Brayton and Rankine power cycles, which are most commonly used in power generation, are identical except that the Rankine cycle employs a vapor with a phase change and the Brayton cycle operates on a single phase gas. In both cases, there is a pressure increase process (using a pump or compressor), a heat addition process, expansion in a turbine, and a heat removal process. Nuclear power generation currently uses the Rankine cycle almost... 

Regarding the potential to share design and technology development with reactors of other types, a remarkable example is provided by the AHTR, a pre-conceptual system that is part of the U S. Department of Energy Generation IV reactor programme. About 70% of the R D required for the AHTR is shared with that for helium cooled high temperature reactors. This includes fuel development, materials development, and Brayton power cycles. Annex XXVI. 

The latest evolution made for the purpose of economics has been replacement of the Rankine steam cycle power conversion system with a high efficiency Brayton (gas turbine) cycle power conversion system to boost the thermal conversion efficiency to -48%. The coupling of the MHR with the gas turbine cycle forms the GT-MHR. The GT-MHR retains all of the MHR passive safety characteristics but is projected to have more attractive economics than any other generation alternative. 

Figure 2.4 GFR Helium gas-cooled, fast neutron spectrum reactor with closed fuel cycle and outlet temperature of about 850°C (shown with direct gas turbine Brayton power cycle). Courtesy of Generation IV International Forum.

In addition, supercritical carbon dioxide (Pioro and Duffey, 2007) was considered as a modeling fluid instead of water due to significantly lower critical parameters. Also, in the 2000s, supercritical carbon dioxide Brayton gas turbine cycle became quite attractive in some coimtries, including the US as an alternative power conversion cycle compared to subcritical and supercritical pressure Rankine steam turbine cycle for a number of Generation IV nuclear reactor concepts. 

The Combined (Brayton-Rankine) Cycle The 1990s has seen the rebirth of the combined cycle, the combination of gas turbine technologies with the steam turbine. This has been a major shift for the utility industry, which was heavily steam-tnrbine-oriented with the use of the gas turbine for peaking power. In this combined cycle, the hot gases from the turbine exhaust are used in a heat recoveiy steam generator or in some cases in a snpplementaiy fired boiler to produce superheated steam. 

The Joule-Brayton (JB) constant pressure closed cycle is the basis of the cyclic gas turbine power plant, with steady flow of air (or gas) through a compressor, heater, turbine, cooler within a closed circuit (Fig. 1.4). The turbine drives the compressor and a generator delivering the electrical power, heat is supplied at a constant pressure and is also rejected at constant pressure. The temperature-entropy diagram for this cycle is also... 

Figure 5.5a depicts a combined plant in which a closed Brayton helium nuclear plant releases heat to a recovery steam generator, which supplies heat to a Rankine steam plant. The generator is provided with a gas burner for supplementary additional heat when the demand of steam power is high. The Rankine plant is a regenerative cycle. 

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