Air compressors, turbines

Turbochargers use the expansion of exhaust gas to pump combustion air to an engine. Exhaust gas is directed through a set of nozzles to drive a turbine wheel. Directly connected to the exhaust turbine is an air compressor turbine that delivers combustion air to the power cylinders. Thus, back-pressure is put on the engine exhaust, reducing power slightly, but the net effect of the increase in air mass flow available for combustion i.s to increase horsepower. 

High reactor pressure overrides steam flow to the air compressor turbine. 

One refrigeration system is electrically driven a second is operated by a condensing turbine. High pressure steam from a power house is pressure-reduced for use by the plant as it passes through one air compressor turbine, one refrigeration machine turbine, and the high pressure section of the turbogenerator. 

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. 

Alkylated aromatics are used as the base fluid ia engine oils, gear oils, hydrauHc fluids, and greases ia sub2ero appHcations. They also are used as the base fluid ia power transmission fluids and gas turbine, air compressor, and refrigeration compressor lubricants. 

The surprise was finally clarified by remembering that this was an air operated plant built in a thermodynamic cycle, (the Brayton or gas turbine cycle) with a 18,000 HP air compressor. This generated 5 MW of salable... 

Available horsepower from a gas turbine is a function of air compressor pressure ratio, combustor temperature, air compressor and turbine efficiencies, ambient temperature, and barometric pressure. High ambient temperatures and/or low barometric pressure will reduce available horsepower while low ambient temperatures and/or high barometric pressure will increase available horsepower. All industrial turbines will have high-temperature protection, but in areas subject to very low ambient temperatures horsepower limiting may be required. 

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... 

Industrial gas turbines are available as either single-shaft or multishaft engines. The turbine illustrated in Figure 16-6 has a single shaft. Both the air compressor and the power turbine section operate off the same shaft and thus rotate at the same speed. As illustrated in Figure 16-14, in a multi-shaft unit some of the power turbine wheels are on the same shaft as the air compressor, while the remainder of the power turbine wheels are on a separate shaft that provides power to the driven equipment. The speed of the wheels of the power turbine that provide the... 

Figure 16-16 shows the performance characteristic of a split-shaft turbine where the only power output limitation is the maximum allowable temperature at the inlet of the turbine section. In actual practice a torque limit, increased exhaust temperature, loss of turbine efficiency, aud/or a lubrication problem on the driven equipment usually preclude operating at very low power turbine speeds. The useful characteristic of the split-shaft engine is its ability to supply a more or less constant horsepower output over a wide range of power turbine speeds. The air compressor essentially sets a power level and the output shaft attains a speed to pnivide the required torque balance. Compressors, pumps, and various mechanical tinvc systems make very good applications for split-shaft designs. 

Hie best overall efficiency of a turbine can be ensured by maintaining tile efficiency of the air compressor section. Conversely, allowing the air compressor efficiency to deteriorate will deteriorate the overall thermal efficiency of the turbine. Air compressor efficiency can be draslically reduced in a very short time when dirt, salt water mist, or similar air con-... 

Pumps, compressors, turbines, drivers, and auxiliary machinery should be designed to provide reliable, rugged performance. Pump selection and performance depend on the capacity required and tlie nature of Uie fluids involved. Remotely controlled power switches and shutoff valves are necessary to control fluid flow during an emergency. The inlets for air compressors should be strategically located to prevent the intake of hazardous materials. 

Gas turbines can operate in open or closed cycles. In a simple cycle (also known as an open cycle), clean atmospheric air is continuously drawn into the compressor. Energy is added by the combustion of fuel with the air. Products of combustion are expanded through the turbine and exhausted to the atmosphere. In a closed cycle, the working fluid is continuously circulated through the compressor, turbine, and heat exchangers. The disadvantage of the closed cycle (also known as the indirect cycle), and the reason why there are only a few in operation, is the need for an external heating system. That is an expensive addition and lowers efficiency. 

However, information concerning thermal rise is not available for all equipment. Generally, manufacturers of critical machinery, such as centrifugal air compressors and turbines, will include information relating to thermal rise in their installation manuals in the section dealing with alignment. When not available, the only method to determine the exact amount of compensation necessary to correct for thermal rise is referred to as a hot alignment check . 

Note in practice superheated steam would probably be generated, for use in a turbine driving the air compressor. 

In an actual nitric acid plant the energy in the tail gases would normally be recovered by expansion through a turbine coupled to the air compressor. The tail gases would be preheated before expansion, by heat exchange with the process gas leaving the WHB. 

The combusted air and fuel stream (stream 12) from the high-pressure fuel cell are expanded (stream 13) in a turbine expander. The work of this turbine is used to drive the low- and high-pressure air compressors. The reduced pressure exhaust stream (stream 13) is utilized as the low-pressure fuel cell oxidant stream. Although vitiated, it still has 15% oxygen. The low-pressure TSOFC operates at 0.62 volts per cell, and fuel and air utilizations of 78 and 21.9%, respectively. The spent air and fuel effluents are combusted and sent (stream 14) to the low-pressure power turbine. The turbine generator produces approximately 1.4 MW AC. The low-pressure exhaust (stream 15) still has a temperature of 649°C (1200°F) and is utilized to... 

Turbine inlet cooling (TIC) can increase gas turbine (GT) power output on a hot day by 10 to 30 percent, while improving (reducing) the turbine heat rate (kj/ kWe) by as much as 5 percent. By increasing the air compressor inlet air density, turbine inlet air cooling is the most cost-effective method for increasing turbine gross power output, for fixed-altitude GTs. 

---