Power turbine

Long-chain esters of pentaerythritol have been used as pour-point depressants for lubricant products, ranging from fuel oils or diesel fuels to the high performance lubricating oils requited for demanding outiets such as aviation, power turbines, and automobiles. These materials requite superior temperature, viscosity, and aging resistance, and must be compatible with the wide variety of metallic surfaces commonly used in the outiets (79—81). 

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

The power turbine is free (i.e., the power turbine is not physically coupled to the gas generator but is closely coupled to the gas generator by a transition duct that transports the gas From the gas generator to the power turbine). The power turbine is an industrial-type turbine in design characterized by heavy wall casings, hydrodynamic (tilting... 

The Reheat Cycle The regenerative cycle improves the efficiency of a gas turbine but does not provide any added work per pound of air flow. To achieve this latter goal, the concept of the reheat cycle must be utilized. The reheat cycle utihzed in the 1990s has pressure ratios of as high as 30 1 with turbine inlet temperatures of out 2100° F (1150° C). The reheat is done between the power turbine and the compressor trains. The reheat cycle, as shown in Fig. 29-35, con-... 

Cathodic protection of water power turbines is characterized by wide variations in protection current requirements. This is due to the operating conditions (flow velocity, water level) and in the case of the Werra River, the salt content. For this reason potential-controlled rectifiers must be used. This is also necessary to avoid overprotection and thereby damage to the coating (see Sections 5.2.1.4 and 5.2.1.5 as well as Refs. 4 and 5). Safety measures must be addressed for the reasons stated in Section 20.1.5. Notices were fixed to the turbine and the external access to the box headers which warned of the danger of explosion from hydrogen and included the regulations for the avoidance of accidents (see Ref. 4). 

Flexibility of service and fuels are criteria, which enhance a turbine system, but they are not necessary for every application. The energy shortage requires turbines to be operated at their maximum efficiency. This flexibility may entail a two-shaft design incorporating a power turbine, which is separate and not connected to the Gasifier unit. Multiple fuel applications are now in greater demand, especially where various fuels may be in shortage at different times of the year. 

Aeroderivative gas turbines eonsist of two basie eomponents an aireraft-derivative gas generator, and a free-power turbine. The gas generator serves as a produeer of gas energy or gas horsepower. The gas generator is derived... 

The use of pyrometers in control of the advanced gas turbines is being investigated. Presently, all turbines are controlled based on gassifier turbine exit temperatures, or power turbine exit temperatures. By using the blade metal temperatures of the first section of the turbine the gas turbine is being controlled at its most important parameter, the temperature of the first stage nozzles and blades. In this manner, the turbine is being operated at its real maximum capability. 

The turboprop engine has a power turbine instead of the nozzle as seen in Figure 4-2. The power turbine drives the propeller. The unit shown schematically is a two-shaft unit, this enables the speed of the propeller to be better controlled, as the gasifier turbine can then operate at a nearly constant speed. Similar engines are used in helicopter drive applications and many have axial flow compressors with a last stage as a centrifugal compressor as shown in Figure 1-14. 

Mechanical Drives. Mechanical drive gas turbines are widely used to drive pumps and compressors. Their application is widely used by offshore and petrochemical industrial complexes. These turbines must be operated at various speeds and thus usually have a gasifier section and a power section. These units in most cases are aero-derivative turbines, turbines, which were originally designed for aircraft application. There are some smaller frame type units, which have been converted to mechanical drive units with a gasifier and power turbine. 

Small standby power turbines less than 2-MW. The smaller size of these turbines in many cases have centrifugal compressors driven by radial inflow turbines, the larger units in this range are usually axial... 

Large power turbines over 50 80 MW, these are frame-type turbines, the new large turbines are operating at very high firing temperatures about 2400°F (1315°C) with cooling provided by steam, at pressure ratios approaching 35 1. 

The gas turbine during the start-up is on an auxiliary drive, initially it is brought to a speed of about 1200-1500 RPM when ignition takes place and the turbine speed and temperature rise very rapidly. The bleed valves are open to prevent the compressor from surging. As the speed reaches about 2300-2500 rpm, the turbine is declutched from its start-up motor, the first set of bleed valves are closed, and then as the turbine has reached near full speed, the second set of bleed valves are closed. If the turbine is a two or three shaft turbine as is the case with aero-derivative turbines, the power turbine shaft will break loose at a speed of about 60% of the rated speed of the turbine. 

The use of pyrometers in eontrol of the advaneed gas turbines is being investigated. Presently all turbines are eontrolled based on gasifier turbine exit temperatures or power turbine exit temperatures. By measuring the... 

The calculation of the turbine expander module depends whether or not this is a single shaft gas turbine or a multiple shaft gas turbine. In aero-derivative turbines, there are usually two or more shafts. In the latest aero-derivative turbines, there are usually two compressor sections, the LP compressor section, and the HP compressor section. This means that the turbine has three shafts the third shaft is the power shaft. The turbines that drive the compressor section are known as the gasifier turbines, and the turbine, which drives the generator, is the power turbine. The gasifier turbine produces the work to drive the compressor. 

The corrected speed for both the gasifier and power turbine defines the corrected engine performance. 

A variation of the two-shaft gas turbine is the aircraft derivative machine. The gas generator is an aircraft jet engine or an adaptation thereof. The power turbine may be of a custom design. Alternately, aircraft based designs may be used. They are covered in API Standard 616 [12]. 

Rice [15] made a comprehensive study of the reheated gas turbine eombined plant. He first analysed the higher (gas turbine) plant with reheat, obtaining (t o)h> turbine exit temperature, and power turbine expansion ratio, all as funetions of plant overall pressure ratio and firing temperatures in the main and reheat burners. (The optimum power turbine expansion ratio is little different from the square root of the overall pressure ratio.) He then pre-seleeted the steam eyele eonditions rather than undertaking a full optimisation. 

Regeneration or recouperation uses a heat exchanger in which exhaust heat is recovered to preheat the compressed inlet air prior to the combustion chamber as shown in Figure 16-9. The increased combustion air temperature reduces the fuel requirement to maintain power turbine inlet temperatures. 

Figure 16-12 shows the effect of ambient temperature on the horsepower output of a typical two-shaft gas turbine engine. At high temperatures the horsepower is limited by the maximum allowable power turbine inlet temperature. At low ambient temperatures, the available horsepower is limited by the maximum allowable air compressor speed. 

The horsepower output of a gas turbine is a direct function of flow rate across the power turbine, which is a function of air compressor speed and combustion temperature. Figure 16-13 shows the relationship between... 

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