The first generation of MS3002 gas turbines (a.k.a. Frame 3) delivered approximately 7,000 horsepower to the load compressor operating at approximately 6,000 rpm. Later models were rated at 11,000 hp at approximately the same speed. As the demand grew, designs improved to include a model series MS5002 (a.k.a. Frame 5) gas turbine. Most two-shaft turbines burn natural gas, because it was readily available at the plant.
Fig. 8-1 shows a factory isometric view of a frame 3 gas turbine. The accessory base is in the lower right-side foreground. A tilted compressor inlet is shown in the center. Also, three of the six turbine combustors are shown on the far left, partially assembled. This configuration allowed for shipment on rail cars or trucks.
Hundreds of GE Frame 3s are still used to deliver natural gas from the Gulf Coast of the USA to consumers in Northeastern and Central regions. Others are used in process industries in chemical plants, many of which are also along the coast from Texas to Louisiana. These turbines are also popular in oil refineries, most of which are located in the southern states.
Many MS3002 gas turbines were regenerative (R) cycle units. This type takes on the abbreviation MS3002R. Regenerative-cycle units became popular because of their improved thermal efficiency (i.e. reduced heat rate). A heat exchanger, like the one shown in Fig. 8-5, transfers exhaust heat to the compressor discharge air reducing fuel consumption.
Fuel consumption (that is, the BTU burned in each hour of operation) is divided by the horsepower (hp) developed in the load compressor to calculate heat rate: HR = BTU/HP-hour.
Variable-speed load devices (that is, compressors not generators) are best suited for using 2-shaft gas turbines. The two compressors, by design, typically operate at two different speeds. The variable-area, second-stage turbine nozzles (abbreviated: VASN), located between the HP and LP turbines, allow for the division of thermal energy between stages, so that each can operate at their respective optimal speed.
Fig. 8-4 shows a side view of a MS3002 gas turbine. The turbine shell (see item #3 in the photo) shows the outer linkages and control ring of the VASN. These nozzles act as the energy divider between the two turbine stages. The hot gases from the combustion system pass through the HP section (Stage 1) before it continues through the LP section (Stage 2). The nozzles between the stages are controlled to optimize the division in energy per the speed setpoints for each shaft. The speed setpoints for the HP and LP turbines are determined by the horsepower requirements and the turbine exhaust temperature limit for the operating conditions of the particular time of day.
The schematic shown below in Fig. 8-5 shows a typical regenerative cycle gas turbine (plan and elevation views). Arrows depict the air flow to/from the regenerator and turbine exhaust. Study this diagram to better understand the gas flow and heat exchanged from the exhaust to and the compressor discharge air.
The petro-chemical industries of the world have successfully used 2-shaft gas turbines to drive load compressors for over 60 years. Most are regenerative-cycle turbines that allow exhaust heat recovery to minimize fuel consumption. Base load operation, where these turbines run continuously during the plant manufacturing processes, or along the gas pipelines northward from the Gulf Coast, is the best application for efficient use. The General Electric designs described herein have been very successful. In recent years, GE purchased Nouvo Pignone of Italy to offer both the 2-shaft gas turbines and the load compressors in a “packaged” arrangement.