Exhaust combustor

The hot gases from the combustor, temperature controlled to 980°C by excess air, are expanded through the gas turbine, driving the air compressor and generating electricity. Sensible heat in the gas turbine exhaust is recovered in a waste heat boiler by generating steam for additional electrical power production. 

Fig. 9. Brayton cycle, where A = compressor inlet, B = combustor inlet, C = power turbine inlet, and D = exhaust (a) thermodynamic relationships and...

Control of nitrogen oxides ia aircraft exhaust is of increa sing concern because nitrogen oxides react with ozone ia the protective layer of atmosphere which exists ia the altitude region where supersonic aircraft operate. Research is under way to produce a new type of combustor which minimizes NO formation. It is an essential component of the advanced propulsion unit needed for a successflil supersonic transport fleet. 

Once an undesirable material is created, the most widely used approach to exhaust emission control is the appHcation of add-on control devices (6). Eor organic vapors, these devices can be one of two types, combustion or capture. AppHcable combustion devices include thermal iaciaerators (qv), ie, rotary kilns, Hquid injection combusters, fixed hearths, and uidi2ed-bed combustors catalytic oxidi2ation devices flares or boilers/process heaters. Primary appHcable capture devices include condensers, adsorbers, and absorbers, although such techniques as precipitation and membrane filtration ate finding increased appHcation. A comparison of the primary control alternatives is shown in Table 1 (see also Absorption Adsorption Membrane technology). 

Combustion Many organic compounds released from manufacturing operations can be converted to innocuous carbon dioxide and water by rapid oxidation (chemical reaction) combustion. However, combustion of gases containing halides may require the addition of acid gas treatment to the combustor exhaust. 

The steam used in this process is generated by the turbine exhaust gas. Typically, water at 14.7 psia (1 Bar) and 80 °F (26.7 °C) enters the pump and regenerator, where it is brought up to 60 psia (4 Bar) above the compressor discharge and the same temperature as the compressor discharged air. The steam is injected after the compressor but far upstream of the burner to create a proper mixture which helps to reduce the primary zone temperature in the combustor and the NO output. The enthalpy of State 3 hi,) is the mixture enthalpy of air and steam. The following relationship describes the flow at that point ... 

The power train consists of an HP and LP expander arranged in series that drives the motor/generator, which in this mode is declutched from the compressor train and is connected by clutch to the HP and LP expander train. The HP expander receives air from the cavern that is regeneratively heated in a recuperator utilizing exhaust gas from the LP expander, and then further combusted in combustors before entering the HP expander. The... 

The starting system can be manual, semiautomatic, or automatic, but in all cases should provide controlled acceleration to minimum governor speed and then, although not called for in the standards, to full speed. Units that do not have controlled acceleration to full speed have burned out first- and second-stage nozzles when combustion occurred in those areas instead of in the combustor. Purging the system of the fuel after a failed start is mandatory, even in the manual operation mode. Sufficient time for the purging of the system should be provided so that the volume of the entire exhaust system has been displaced at least five times. 

The startup speed and temperature acceleration curves as shown in Figure 19-2 are one such safety measure. If the temperature or speed are not reached in a certain time span from ignition, the turbine will be shutdown. In the early days when these acceleration and temperature curves were not used, the fuel, which was not ignited, was carried from the combustor and then deposited at the first or second turbine nozzle, where the fuel combusted which resulted in the burnout of the turbine nozzles. After an aborted start the turbine must be fully purged of any fuel before the next start is attempted. To achieve the purge of any fuel residual from the turbine, there must be about seven times the turbine volume of air that must be exhausted before combustion is once again attempted. 

Retrieval by turbine exhaust temperature. The exhaust temperature can be an important parameter in failure investigations. An analysis of this parameter in failure investigations. An analysis of this parameter can verify the existence of a problem with either the combustor or turbine. 

Improvements also have been made to the gas turbine for naval applications. An intercooled recuperative (ICR) gas turbine has been designed to improve the fuel consumption of naval power plants. The engine has a recuperator to take the heat that would otherwise be wasted m the exhaust and transfers it to the air entering the combustor. The new engine is expected to save about 30 percent ot the fuel consumed, compared to the simple gas turbine. The ICR engine is, however, larger and more expensive than the simple gas turbine. 

In second-generation PFBC, a topping combustor is used to raise the turbine rotor inlet temperature to state-of-the-art levels. Pulverized coal is fed to a partial-gasifier unit that operates about 870° to 925°C (1,600° to 1,700°F) to produce a low heating value fuel gas and combustible char. The char is burned in the PFBC. The fuel gas, after filtration, is piped back to the gas turbine, along with the PFBC exhaust. 

Previous data have concerned rmconfined flame configurations driven by velocity perturbations. These cases are less dependent on the geometry because sound generation is not modified by reflection from boundaries. It is also easier to examine rmconfined flames with optical techniques. However, in many applications, combustion takes place in confined environments and sound radiation takes place from the combustor inlet or exhaust sections. The presence of bormdaries has two main effects ... 

The combination of the fuel cell and turbine operates by using the rejected thermal energy and residual fuel from a fuel cell to drive the gas turbine. The fuel cell exhaust gases are mixed and burned, raising the turbine inlet temperature while replacing the conventional combustor of the gas turbine. Use of a recuperator, a metallic gas-to-gas heat exchanger, transfers heat from the gas turbine exhaust to the fuel and air used in the fuel cell. 

There can be many different cycle configurations for the hybrid fuel cell/turbine plant. In the topping mode described above, the fuel cell serves as the combustor for the gas turbine, while the gas turbine is the balance of plant for the fuel cell, with some generation. In the bottoming mode, the fuel cell uses the gas turbine exhaust as air supply, while the gas turbine is the balance of plant. In indirect systems, high-temperature heat exchangers are used. 

Combined Brayton-Rankine Cycle The combined Brayton-Rankine cycle. Figure 9-14, again shows the gas turbine compressor for the air flow to the cell. This flow passes through a heat exchanger in direct contact with the cell it removes the heat produced in cell operation and maintains cell operation at constant temperature. The air and fuel streams then pass into the cathode and anode compartments of the fuel cell. The separate streams leaving the cell enter the combustor and then the gas turbine. The turbine exhaust flows to the heat recovery steam generator and then to the stack. The steam produced drives the steam turbine. It is then condensed and pumped back to the steam generator. 

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