Steam injection cycle

The Steam Injection Cycle Steam injection has been used in reciprocating engines and gas turbines for a number of years. This cycle may be an answer to the present concern with pollution and higher efficiency. Corrosion problems are the major hurdle in such a system. The concept is simple and straightforward Steam is injected into the compressor discharge air and increases the mass flow rate... 

The prevacuum technique, as its name implies, eliminates air by creating a vacuum. This procedure faciUtates steam penetration and permits more rapid steam penetration. Consequendy this results in shorter cycle times. Prevacuum cycles employ either a vacuum pump/steam (or air) ejector combination to reduce air residuals in the chamber or rely on the pulse-vacuum technique of alternating steam injection and evacuation until the air residuals have been removed. Pulse-vacuum techniques are generally more economical vacuum pumps or vacuum-pump—condenser combinations may be employed. The vacuum pumps used in these systems are water-seal or water-ring types, because of the problems created by mixing oil and steam. Prevacuum cycles are used for fabric loads and wrapped or unwrapped instmments (see Vacuum technology). 

For NO control only, steam is injected into the combustor directly to help reduce the primary zone temperature in the combustor. The amount of steam injected is in a ratio of 1 1 with the fuel. In this cycle, the steam is injected upstream of the combustor and can be as much as 5-8 percent by weight of the air flow. This cycle leads to an increase in output work and a shght increase in over l efficiency. Corrosion problems due to steam injection have been for the most part over-... 

FIO. 29-37 Performance map showing the effect of pressure ratio and steam flow rate on a steam injection cycle. 

In the case of the steam-injected cycle, steam must be injected after the turbine has been brought up to full speed otherwise, compressor... 

Steam injection has been used in reciprocating engines and gas turbines for a number of years. This cycle may be an answer to the present concern... 

Figure 2-20. The steam injection cycle, with the amount of fuel needed to be added to this cycle as...

Figure 2-21 show the effect of 5% by weight of steam injection at a turbine inlet temperature of 2400 °F (1316 °C) on the system. With about 5% injection at 2400°F (1316 °C) and a pressure ratio of 17 1, an 8.3% increase in work output is noted with an increase of about 19% in cycle efficiency over that experienced in the simple cycle. The assumption here is that steam is injected at a pressure of about 60 psi (4 Bar) above the air from the compressor discharge and that all the steam is created by heat from the turbine exhaust. Calculations indicate that there is more than enough waste heat to achieve these goals. 

This cycle, as shown in Figure 2-23, is a regenerative cycle with water injection. Theoretically, it has the advantages of both the steam injection and regenerative systems reduction of NO emissions and higher efficiency. The work output of this system is about the same as that achieved in the steam injection cycle, but the thermal efficiency of the system is much higher. 

This system, as can be seen from Figure 2-27, indicates that the net work is about the same as one would expect in a steam injection cycle, but the efficiencies are much higher. The disadvantages of this system are its high initial cost. However, just as in the steam injection cycle, the NO content of its exhaust remains the same and is dependent on the gas turbine used. This system is being used widely because of its high efficiency. 

Water injection, or steam injection systems, are being used extensively to augment power. Corrosion problems in the compressor diffuser and combustor have not been found to be major problems. The increase in work and efficiency with a reduction in NO makes the process very attractive. Split-shaft cycles are attractive for use in variable-speed mechanical drives. The off-design characteristics of such an engine are high efficiency and high torque at low speeds. 

The code provides for the testing of gas turbines supplied with gaseous or liquid fuels (or solid fuels converted to liquid or gas prior to entrance to the gas turbine). Test of gas turbines with water or steam injection for emission control and/or power augmentation are included. The tests can be applied to gas turbines in combined-cycle power plants or with other heat recovery systems. 

Fig. 6.2 shows a simplified diagram of the basic STIG plant with steam injection S per unit air flow into the combustion chamber the state points are numbered. Lloyd 2 presented a simple analysis for such a STIG plant based on heat input, work output and heat rejected (as though it were a closed cycle air and water/steam plant, with external heat supplied instead of combustion and the exhaust steam and air restored to their entry conditions by heat rejection). His analysis is adapted here to deal with an open cycle plant with a fuel input/to the combustion chamber per unit air flow, at ambient temperature To, i.e. a fuel enthalpy flux of/7i,o. For the combustion chamber, we may write... 

Fraize, W.E. and Kinney. C. (1979), Effects of steam injection on the performance of gas turbines and combined cycles, ASME J. Engng Power Gas Turbines 101.217-227. 

Cerri, G. and Arsuffi, G. (1986), Calculation procedures for steam injected gas turbine cycle with autonomous distilled water production, ASME Paper 86-GT-297. 

Also, corrosion may result in contamination at some downstream point in the steam-water cycle. For example, iron and copper ions often may be present as corrosion products in steam and condensate and consequently will reduce the purity of the steam. This may render the steam unsuitable for certain industrial processes or applications where live steam injection is required. 

The injection of water or steam in gas turbines has been known (Nicolin, C., A gas turbine with steam injection. Swedish Patent application No.8112/51, Stockholm, Sweden, 1951) as an efficient method for NO abatement and power boosting. Several cycle configurations are possible with respect to water/steam injection. Figure 4.36 is the schematic diagram of the Steam-injection gas turbine cycle. Air is compressed from state 1 to state 2. Water is pumped from state 7 to state 8. Steam at state 9 is generated in a recovery boiler (heat exchanger) from state 8 by the hot exhaust gas. Steam at state 8... 

The beneficial influences of the steam-injection gas turbine cycle include ... 

CyclePad is not able to perform the steam-injection gas turbine cycle, because there is no binary working fluid in the substance menu of the software. 

Review Problems 4.10 Steam-Injection Gas Turbine Cycle... 

Draw the schematic diagram of the steam-injection gas turbine cycle by placing the mixing chamber between the combustion chamber (heater) and the turbine. 

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