Turbines operation

Both friction and wear measurements have been used to study boundary lubrication of fuel because sticking fuel controls and pump failures are primary field problems in gas turbine operation. An extensive research program of the Coordinating Research Council has produced a baH-on-cylinder lubricity test (BOCLE), standardized as ASTM D5001, which is used to qualify additives, to investigate fuels, and to assist pump manufacturers (21). 

Curve g is for disk flat-blade turbines operated in unbaffled vessels filled witb liquid, covered, so tbat no vortex forms. If baffles are present, tbe power characteristics at high Reynolds numbers are essentially tbe same as curve h for baffled open vessels, witb only a slight increase in power. 

FIG. 29-56 Flow diagram of a system with a power-recovery turbine operating with a makeup driver. 

FIG. 29-58 Head-horsepower-capacity characteristics of a lean pump tandem-connected with a power-recovery turbine operating as the sole driver. To convert gallons per minute to cubic meters per minute, multiply by 3.79 X 10 to convert horsepower to kilowatts, multiply by 0.746 and to convert pounds-force per square inch to megapascals, multiply by 6.89 X 10 . ... 

FIG. 29-59 Head-horsepower-capacity characteristics of a power-recovery turbine operating as the sole driver of a lean pump. If the total capacity of lean and semilean pumps exceeds the values indicated by available head limit, bypass must be used. Net recovery-pump head at 8.71 mVmin (2300 gal/min) is figured as follows ... 

In contrast to steam turbines, in which runaway overspeediug is always a problem, pump-turbines operating at design head go to zero torque at about 130 to 140 percent of design speed. Thus, overspeed protection may not be necessary if the pump-turbine can withstand 140 to 150 percent of design speed and it is the sole driver. When a steam-turbine helper is used, it should be provided with the usual overspeed trip-out mechanism. 

Off-Design Performance—This is an important eonsideration for waste heat reeovery boilers. Gas turbine performanee is affeeted by load, ambient eonditions, and gas turbine health (fouling, ete.). This ean affeet the exhaust gas temperature and the air flow rate. Adequate eonsiderations must be given to bow steam flows (low pressure and high pressure) and superheat temperatures vary with ehanges in the gas turbine operation. 

Evaporative Cooling of the Turbine. Traditional evaporative coolers that use media for evaporation of the water have been widely used in the gas turbine industry over the years, especially in hot climates with low humidity areas. The low capital cost, installation, and operating costs make it attractive for many turbine-operating scenarios. Evaporation coolers consist of water being sprayed over the media blocks, which are made of fibrous corrugated material. The airflow through these media blocks, evaporates the water, as water evaporates, it consumes about 1059 BTU (1117kJ) (latent heat of vaporization) at 60 °F (15 °C). This results in the reduction... 

Based on Gas Turbine Operating at Power=110MW iniet Temp=32 C Efficiency = 32.92 Heat Rate 10935 KJ/KW-HR ... 

Critical speeds of a turbine operating below its first critical should be at least 20% above the operating speed range. The term commonly used for units operating below their first critical is that the unit has a stiff shaft, while units operating above their first critical are said to have a flexible shaft. There are many exciting frequencies that need to be considered in a turbine. Some of the sources that provide excitation in a turbine system are ... 

A Campbell diagram is frequently used to determine the effect of multiple excitation frequencies in high-speed steam turbines. Figure 7-11 shows a Campbell diagram for a condensing steam turbine. If this partic uiar turbine operates at a speed of 8,750 rpm, the turbine blades would not be excited. But, if the turbine speed is reduced to 7,500 rpm, the turbine blades would be excited at four times running speed. If the turbine were operated at 10,000 rpm, a three-times running speed excitation would be encountered. What this means is that any vibration in the... 

For a gas turbine operating as a combined heat and power plant, the energy utilisation factor (EUF) is a better criterion of performance than the thermal efficiency. It is defined as the ratio of work output (W) plus useful heat output (Qu) to the fuel energy supplied (F),... 

The exhaust gases from a gas turbine contain substantial amounts of excess air, since the main combustion process has to be diluted to reduce the combustion temperature to well below that which could be obtained in stoichiometric combustion, because of the metallurgical limits on the gas turbine operating temperature. This excess air enables supplementary firing of the exhaust to take place and higher steam temperatures may then be obtained in the HRSG. 

By 1837 Fourneyron had water turbines operating successfully on both small falls and large ones. At St. Blasien iu Germany, a Fourneyron turbine fed by a pipe, or penstock, used a fall of354 feet (107.9 m), far more than any conventional water wheel could hope to. It developed 60 hp with a wheel only 1.5 foot (0.46 m) in diameter that weighed less than 40 pounds (18.2 kg). 

Parsons adopted this multistage design to reduce turbine operating speeds to a useful level. His initial turbine was developed to produce electricity onboard ships and had an output of about 7 kW. In 1888 he designed the first steam turbine generating unit for public utility sei-vicc. By the time of his death in 1931, his company manufactured turbines generating more than. 30,000 kW. 

Most turbines are designed to rotate at a constant speed over a specific range of wind speed conditions. The generators in these turbines produce electricity compatible with the established grid system into which electricity is fed. Operating the turbine at variable rotor speeds increases the range of wind speeds over which the turbine operates. The amount of energy produced annually is increased as well. However, sophisticated power electronics is required to convert the electricity to the gi id standard frequency. 

For example blend time as the criterion, the scale-up exponent = 0, and no change in speed is required for the larger scale equipment, requiring that the longer 48-inch diameter turbine operate at 450 rpm,... 

Most steam turbines operate in the condensing (of steam on exhaust from turbine) mode or noncondensing or backpressure mode. (Steam is exhausted or extracted from the turbine at preselected exhaust pressure for other uses.) See Figures 14-17A-C, 14-18A, 14-18B, 14-19A, 14-19B, 14-20A, and 14-20B. 

Figure 14-38B. Example of gas turbine operating cycle. (Used by permission General Electric Company.)...

The most common use of the gas turbine power system in the oil and gas industry is in combination with an electrical system (i.e., electric generators and electric motors). In 1965 such a system was used to power a rotary rig. This was a 3,000-hp rig developed by Continental-Ensco. The rig used three 1,100-hp Solar Saturn single-shaft gas turbines. These gas turbines operated at 22,300 rpm and were connected through double reduction gear transmissions to DC generators. 

Part load As the gas turbine operates with a fixed inlet air volume, its efficiency at part load deteriorates significantly. Figure 15.7 shows a typical relationship for variation in gas turbine efficiency for changes of load. 

Most turbines have relatively long bearing spans and highly flexible shafts. These factors, coupled with variations in process flow conditions, make turbine rotors highly susceptible to shaft deflection during normal operation. Typically, turbines operate in either the second or third mode and should have narrowbands at the second (2x) and third (3x) harmonics of shaft speed to monitor for mode shape. 

All turbines are variable-speed drivers and operate near or above one of the rotor s critical speeds. Narrowbands should be established that track each of the critical speeds defined for the turbine s rotor. In most applications, steam turbines operate above the first critical speed and in some cases above the second. A movable narrowband window should be established to track the fundamental (1 x), second (2x), and third (3x) harmonics of actual shaft speed. The best method is to use orders analysis and a tachometer to adjust the window location. 

These turbine units finally exhaust the steam at considerably less than atmospheric pressure to a condenser (in most circumstances a surface condenser is employed). The condenser is designed to raise turbine operating efficiency by reducing the turbine back-pressure to an absolute minimum. This is achieved by condensing the exhaust steam into a smaller volume of condensate, thus creating a substantial vacuum. 

The exhaust pressure of a steam turbine is fixed by the operating pressure of the downstream equipment. Figure 23.9a shows a back-pressure turbine operating between a high-pressure and low-pressure steam mains. The pressure of the low-pressure steam mains will be controlled elsewhere (see later). 

A steam turbine operates with inlet steam conditions of 40 barg and 420°C and can be assumed to operate with an isentropic efficiency of 80% and a mechanical efficiency of 95%. Calculate the power production for a steam flowrate of 10 kg s-1 and the heat available per kg in the exhaust steam (i.e. superheat plus latent heat) for outlet conditions of ... 

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