Aero-derivative turbines

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. 

Gas turbine size is important in the cost of the plant. The larger the gas turbine the less the initial cost per kW. The aero-derivative turbines have traditionally been higher in efficiency however, the new frame type turbines have been closing the gap in efficiency. Figure 4-3 shows typical gas... 

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 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. 

In order to verify that the RFS technique can detect, particles greater than 10 pra, the U.S. Department of Defense Joint Oil Analysis Program Technical Support Center (JOAP-TSC) prepared samples using M50 alloy particles. M50 alloy is often present in aero-derivative turbines. Some failure modes of J52 engines appear to be sudden catastrophic failures where the root cause began with the lack of lubrication of the 4 A bearing area. Initially, analysis of the samples by RDE spectroscopy did not indicate the failure mode [6]. The composition and specifications for MSO alloy are as shown below (Table 3). 

With higher shaft speed but lower airflow through the turbine, aero-derivative turbines require less complex and shorter maintenance than other ground gas turbines. They are often used in remote areas, where they are employed to drive pumps and compressors for pipelines, for example. Because of their quicker start, stop, and loading times, aero-de-rivative gas turbines are also used for flexible peak load power generation and for ground propulsion. 

Most gas-fired, heavy-duty gas turbines installed as of 1996 operate at gas pressures between 1.2 and 1.7 MPa (180—250 psig). However, aero derivative gas turbines and newer heavy-duty units can have such high air-inlet compression ratios as to require booster compressors to raise gas inlet pressures, in some cases as high as 5.2 MPa (750 psig). 

Medium-sized gas turbines between 5-50 MW are a combination of aero-derivative and frame type turbines. These gas turbines have axial flow compressors and axial flow turbines. 

The location of the plant is the principal determination of the type of plant best configured to meet its needs. Aero-derivatives are used on offshore platforms. Industrial turbines are mostly used in petrochemical applications, and the frame type units are used for large power production. 

Plant Type. The determination to have an aero-derivative type gas turbine or a frame-type gas turbine is the plant location. In most cases if the plant is located off-shore on a platform then an aero-derivative plant is required. On most on-shore applications, if the size of the plant exceeds 100 MW then the frame type is best suited for the gas turbine. In smaller plants between 2-20 MW, the industrial type small turbines best suit the application, and in plants between 20-100 MW, both aero-derivative or frame types can apply. Aero-derivatives have lower maintenance and have high heat-recovery capabilities. In many cases, the type of fuel and service facilities may be the determination. Natural gas or diesel no. 2 would be suited for aero-derivative gas turbines, but heavy fuels would require a frame type gas turbine. 

Figure 4-4. Installed cost and efficiency of aero-derIvatIve type turbines.

Aero-derivative gas turbines eannot operate on heavy fuels, thus if heavy fuels was a eriteria then the frame type turbines would have to be used. With heavy fuels, the power delivered would be redueed after about a weeks of operation by about 10%. On-line turbine wash is reeommended for turbines with high vanadium eontent in their fuel, sinee to counteract vanadium magnesium salts have to be added. These salts cause the vanadium when combusted in the turbine to be turned to ashes. This ash settles on the turbine blades and reduces the cross sectional area, thus reducing the turbine power. 

In the search for higher plant thermal efficiency, the simplicity of the two basic STIG and EGT cycles, as described by Frutschi and Plancherel, has to some extent been lost in the substantial modifications described above. But there have been other less complex proposals for water injection into the simple unrecuperated open cycle gas turbine one simply involves water injection at entry to the compressor, and is usually known as inlet fog boosting (IFB) the other involves the front part of an RWI cycle, i.e. water injection in an evaporative intercooler, usually in a high pressure ratio aero-derivative gas turbine plant. 

Gas turbines can be classified as industrial or frame machines and aero-derivative machines that are lighter weight units derived from aircraft engines. Table 23.2 compares the characteristics of the two broad classes of gas turbine machines. 

Aero-derivative gas turbines are typically used for offshore applications where weight and efficiency are a premium, to drive compressors for natural gas pipelines, and stand-alone power generation applications for peak periods of high power demand. For stand-alone applications, gas turbine efficiency becomes a critical issue. However, if heat is to be recovered from the gas turbine exhaust, the efficiency becomes less important as the waste heat is utilized. 

Distributed generation is modular generation. DG units are less than 60 MW in size and usually located near the point of use. Technologies available for DG include industrial and aero-derivative gas turbines, reciprocating engines,... 

The introduction and development of gas turbine engines led to the development of new lubricants. While the early gas turbine engines ran successfully on mineral oil lubricants, and in fact many Russian aircraft engines still operate on such lubricants, the demand for higher specific thmst, with the concomitant high operating temperatures, needed lubricants with better thermal stability. Carboxylic esters were developed which, with yet further improvements, are still used today. These lubricants are also used in aero-derived industrial and marine gas turbines, meaning that for the first time lubricants developed for aircraft were used in other applications. 

Defence Standard 91-101. Lubricating Oil, Gas Turbine Engine, Synthetic Grade 5 cSt, NATO Code 0-156, Joint Service Designation OX-27and OX-28. UK Defence Standardization. SAE AS5780A. Specification for Aero and Aero-Derived Gas Turbine Engine Lubricants. SAE International. 

Gas turbines are available in two types, namely, industrial type and aero-derivative type. In comparison, the former is cheaper, robust with single shaft and longer period of operation without overhaul but at lower efficiency. The latter is... 

Horlock, J.H. (1997), Aero-engine derivative gas turbines for power generation thermodynamic and economic perspectives, ASME Journal of Engineering for Gas Turbines and Power 119(1), 119-123,... 

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