Brayton cycle power plants

Staudt, J. E., Design Study of an MGR Direct Brayton-Cycle Power Plant PHD Thesis, Massachusetts Institute of Technology, May 1987. 

In a combined-cycle power plant, electricity is produced by two turbines, a gas and a steam turbine. The term combined cycle comes from the fact that the combustion gas turbine operates according to the Brayton cycle and the steam system operates according to the Rankine cycle. As shown in Figure 2.115, the dual-shaft combined-cycle plant consists of a gas turbine (GT)... 

The GT-MHR is projected to have economic advantages over other plants for the addition of new base load generation capacity. The economic competitiveness of the GT-MHR is a consequence of the use of the direct Brayton cycle power conversion system and the broad implementation of inherent safety features and passive safety systems. The direct Brayton... 

Combined-cycle power plant (combination of Brayton gas-turbine cycle [fuel = natural gas or liquefied natural gas combustion product parameters at the gas-turbine inlet Tin 1650°C] and Rankine steam turbine cycle [steam parameters at the turbine inlet = 620°C (r = 374°C ]). Up to 62... 

Natural gas is considered as a clean fossil fuel compared to coal and oil, but still, due to the combustion process, emits a lot of carbon dioxide when it used for electrical generation. The most efficient modem thermal power plants with thermal efficiencies within a range of 50—60% (up to 62%) are, so-called combined cycle power plants (combination of Brayton gas turbine and Rankine steam turbine power cycles) (see Figs. Al.l—A1.4, and Tables Al.l and A1.2), which use mainly natural gas as a fuel. 

Figure Al.l Simplified schematics of combined cycle power plant (courtesy and copyright of Mitsubishi Heavy Industries MHI). Thermal efficiencies are the highest in power industry, up to 62% (Brayton cycle 30% and Rankine cycle 40%). Current level of inlet temperatures to gas turbine is about 1600—1650°C and to steam turbine, 620°C.

Helium and xenon pure component and mixture viscosity and thermal conductivity were required for Project Prometheus calculations of a direct cycle Brayton nuclear power plant concept. The purpose of tWs evaluation was to recommend the best methods to calculate the transport properties with the current available information. 

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). 

A comparison of the effect of the various cycles on the overall thermal efficiency is shown in Fig. 29-40. The most effective cycle is the Brayton-Ranidne (combined) cycle. This cycle has tremendous potential in power plants and in the process industries where steam turbines are in use in many areas. The initial cost of the combined cycle is between 800- 1200 per kW while that of a simple cycle is about 300- 600 per kW. Repowering of existing steam plants by adding gas turbines can improve tne over plant efficiency of an existing steam turbine plant by as much as 3 to 4 percentage points. 

The most effective cycle is the Brayton-Rankine cycle. This cycle has tremendous potential in power plants and in the process industries where steam turbines are in use in many areas. The initial cost of this system is high however, in most cases where steam turbines are being used this initial cost can be greatly reduced. 

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... 

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. 

The maximum and minimum temperatures and pressures of a 40 MW turbine shaft output power ideal air Brayton power plant are 1200 K (Ta), 0.38 MPa (P3), 290 K (TO, and 0.095 MPa (Pi), respectively. Determine the temperature at the exit of the compressor Tj), the temperature at the exit of the turbine (P4), the compressor work, the turbine work, the heat added, the mass rate of flow of air, the back-work ratio (the ratio of compressor work to the turbine work), and the thermal efficiency of the cycle. 

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. 

Determine the power required by the compressor, power required by pumps 1 and 2, power produced by turbines 1, 2, and 3, rate of heat added by the nuclear reactor, net power produced by the Brayton gas turbine plant, net power produced by the Rankine plant, rate of heat removed by coolers 1 and 2, rate of heat exchanged in the heat exchanger, rate of heat added in the gas burner, mass rate flow of helium in the Brayton cycle, mass rate flow of steam extracted to the feed-water heater (mixing chamber), cycle efficiency of the Brayton plant, cycle efficiency of the Rankine plant, and cycle efficiency of the combined Brayton-Rankine plant. 

Determine the mass rate flow of air through the Brayton cycle, and the thermodynamic efficiency and net power output of the Brayton/ Rankine combined plant. Plot the sensitivity diagram of r] (cycle efficiency) versus pn (pressure at state 11). 

The connection scheme developed by the European Projects HYTHEC and RAPHAEL (Le Duigou, 2007) represents a self-sustainable plant concept in which, in addition to the heat supply to the S-I cycle, the electrical demand of the internal consumers is provided by the nuclear reactor. The high temperature flow exiting the nuclear reactor transfers its heat via an IHX to a secondary loop which interacts with the components of the S-I cycle components. The high temperature heat flow is split and partially directed to the chemical part of the cycle and another part to a Brayton cycle for electricity production needed to power pumps, compressors, heat pumps and other auxiliaries. 

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