Turbine exhaust steam

Figure 14-16F. Cutaway of large steam turbine, multistaged, multivalve, for driving mechanical rotating equipment. Connection to mechanical driven equipment shaft shown as a flange joint on right end of turbine shaft. Exhaust steam is at lower right, inlet steam is at bottom center near smaller wheels. (Used by permission Bui. 8908-E0MD. Dresser-Rand Company.)...

A safety valve is usually needed on the steam exhaust side of the turbine to protect against high pressure on shut down. Most turbine case designs will not safely handle inlet steam pressure on the exhaust side, as the case is not designed to withstand intake pressure throughout. These valves are normally rated for 110% of the design steam rate. 

Most boiler plants with electrical power generating facilities employ surface condensers. These are shell-and-tube heat exchangers in either one-, two-, or four-pass configurations. Surface condensers typically receive cooling water on the tube-side and steam on the shell-side of the heat exchanger. The LP turbine steam generally is received at the top of the condenser and proceeds through the condenser in a downward flow, while the FW turbine exhaust steam enters at the side. 

With high fuel costs, the search is on for processes with higher thermal efficiency and ways to improve efficiencies of existing processes. One process being discussed lately for its high efficiency is the gas turbine combined cycle. The gas turbine exhaust heat makes steam in a waste heater boiler. The steam drives turbines, perhaps even a gas turbine steam helper. References 10, 11, and 12 treat this subject and mention alternate equipment hookups, some in conjunction with coal gasification plants. 

The simplest of the geothermal cycles is the direct-intake non-condensing type. Steam from the geothermal well is directly passed through a turbine and exhausted to the atmosphere without condensation. Such cycles require 15-20 kg steam per generated kWh. Condensing plants (with condensers at the turbine outlet) need only... 

Discounting the presence of air leaks, the temperature inside the surface condenser determines the pressure of the steam exhausting from the turbine. This pressure is the vapor pressure of water at the surface condenser outlet temperature. 

Computation of the thermodynamic efficiency in a steam cycle (1) inlet, (2) pre-combustion, (3) post-combustion, pre-compressor, (4) post-turbine to exhaust, (5) gas inlet. 

The cost rate balance for the turbine, Eq. (5.5), yields the specific cost of steam exhausted by the turbine ... 

If the steam is expanded to atmospheric pressure or above, the turbine is called noncondensing. Noncondensing turbines are used when the exhaust steam is needed for process heating. On the other hand, if the steam is expanded to below atmospheric pressure, the turbine is called condensing. Usually, the exhaust pressure is between 0.0040 to 0.0053 bar (3 to 4 mm Hg, 0.058 to 0.0769 psia), but can be anywhere from 0.0013 to 0.020 bar (1 to 15 mm Hg, 0.0189 to 0.29 psia). In condensing turbines, the exhaust steam may contain as much as 15 % moisture by mass, but 10 % is common practice [32]. 

The figure illustrates a simple system having medium-pressure (MP) and low-pressure (LP) steam. MP steam is consumed in a turbine having two LP-steam exhausts, and E.>. E is held at constant pressure. E may fluctuate and is always lower than that of E. Various steam consumers (boilers, heat exchangers, etc.) are connected to E -So is the first stage of feedwater deara-tion, Si, a stripper open to the atmosphere via a throttling valve. 

Exhaust gas at 673.15 K (400°C) and 1 bar from intemal-combustionengines flows at tile rate of 125 mol into a waste-heat boiler where saturated steam is generated at a pressure of 1200 kPa. Water enters tlie boiler at 293.15 K (20°C) (Ta), and tlie exhaust gases are cooled to within 10 K (10°C) of the steam temperature. The heat capacity of tile exliaust gases is Cp/R = 3.34 "I" 1.12 x IQr T/K. The steam flows into an adiabatic turbine and exhausts at a pressure of 25 kPa. If the turbine efficiency rj is 72%,... 

Low-presstire Turbines.—The capacity of an existing reciprocating engine plant (even though operated condensing) may be increased from 60 to 100 per cent by the appropriate installation of a turbine receiving steam exhausted by... 

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