Turbines, steam topping

Figure 14-16B. View of Elliott YR Single Stage Steam Turbine, with top cover removed. (Used by permission Elliott Co.)...

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. 

In order to control the compressor, its purpose in terms of a process variable needs to be known. The purpose of the compressor in this application example is to control the pressure at the top of the column. A suitable measuring instrument would be a pressure transmitter located at the knock out (KO) drum. The compressor throughput is controlled by speed control on the steam turbine. Steam turbines generally have... 

In this accident, the steam was isolated from the reactor containing the unfinished batch and the agitator was switched ofiF. The steam used to heat the reactor was the exhaust from a steam turbine at 190 C but which rose to about 300°C when the plant was shutdown. The reactor walls below the liquid level fell to the same temperature as the liquid, around 160°C. The reactor walls above the liquid level remained hotter because of the high-temperature steam at shutdown (but now isolated). Heat then passed by conduction and radiation from the walls to the top layer of the stagnant liquid, which became hot enough for a runaway reaction to start (see Fig. 9.3). Once started in the upper layer, the reaction then propagated throughout the reactor. If the steam had been cooler, say, 180 C, the runaway could not have occurred. ... 

In apphcation to electric utihty power generation, MHD is combined with steam (qv) power generation, as shown in Figure 2. The MHD generator is used as a topping unit to the steam bottoming plant. From a thermodynamic point of view, the system is a combined cycle. The MHD generator operates in a Brayton cycle, similar to a gas turbine the steam plant operates in a conventional Rankine cycle (11). 

Eig. 8. Cost of electricity (COE) comparison where represents capital charges, Hoperation and maintenance charges, and D fuel charges for the reference cycles. A, steam, light water reactor (LWR), uranium B, steam, conventional furnace, scmbber coal C, gas turbine combined cycle, semiclean hquid D, gas turbine, semiclean Hquid, and advanced cycles E, steam atmospheric fluidized bed, coal E, gas turbine (water-cooled) combined low heating value (LHV) gas G, open cycle MHD coal H, steam, pressurized fluidized bed, coal I, closed cycle helium gas turbine, atmospheric fluidized bed (AEB), coal J, metal vapor topping cycle, pressurized fluidized bed (PEB), coal K, gas turbine (water-cooled) combined, semiclean Hquid L, gas turbine... 

Figure 4-29. 360-t/d packaged unit—top foundation plate 13 m long, 3.6 m wide, 0.93 m high. The oil system is situated at the front end, followed by the steam turbine, compressor, and expander. The oil coolers are located separately. 

Figure 6.2-2 shows its operation. A mixture of 14% steam and 86% water from the pressure tubes went to steam drums, used to separate steam from liquid water with steam on top and liquid on the bottom. Steam drives the turbine, leaving at reduced temperature and pressure, condensing in the condenser and combining with liquid from the steam drier as feedwater for recycle to the reactor. 

An important field of study for power plants is that of the combinedplant [ 1 ]. A broad definition of the combined power plant (Fig. 1.5) is one in which a higher (upper or topping) thermodynamic cycle produces power, but part or all of its heat rejection is used in supplying heat to a lower or bottoming cycle. The upper plant is frequently an open circuit gas turbine while the lower plant is a closed circuit steam turbine together they form a combined cycle gas turbine (CCGT) plant. 

Lloyd argues that for a plant with fixed pressure ratio and top temperature, the turbine work output (and hence the net work output) is increased linearly with the. steam quantity 5 that is injected, but the (2n and Qa terms increase more slowly. Thus, the efficiency similarly increases with S. but also more slowly. 

With the gas temperature at turbine exit known (T ), the top temperature in the steam cycle (T ) is then obtained from (a). It is assumed that this is less than the prescribed maximum steam temperature. 

Heat recovery tor steam generation, pre-heating combustion air, and high efficiency burners Adjustable speed drives, heat recovery coke oven gases, and dry coke quenching Efficient hot blast stove operation, waste heat recovery for hot blast stove, top gas power recovery turbines, direct coal injection... 

First, for Figure 14-22, enter at the top at rpm and move to the first estimating turbine wheel diameter then read down to the TSR (calculated or from tables) at Ib/kw-hr read across to base steam rate in Ib/hp-hr. Note that the base steam rate is per hp-hr, and the TSR is per kwh (or kw-hr). Now correct the base steam rate for the horsepower loss (i.e., the portion of blades of turbine spinning outside the nozzle arc, creating friction and windage). From Figure 14-23, at the top read rpm at the exhaust pressure on curved lines noted cond, read down to the estimated wheel diameter, and read the horsepower loss on the left vertical axis. 

The electrical and heat analysis, as discussed in Section 15.3, will show the relationship between power and heat and how this varies over time. It may be necessary to use steam bypass and stations or dump condenser, as discussed in Section 15.2. The uses of dump condensers for meeting part-load requirement is inefficient and should be avoided. It is more acceptable to reduce turbine power output accordingly and import or top-up from an alternative supply. 

The boiler steam-water circulation system is designed to promote the delivery of steam from the various generating tubes to the boiler steam drum (top drum). From here the steam is separated from the BW and transferred to the steam delivery system for possible superheating and subsequent use in a turbine generator or other downstream process application. 

In this design, the secondary circuit FW is again on the shell side, but recirculation takes place within the steam generator, resulting in the formation of a steam-water mixture that covers the top of the inverted U-tube bundle. Saturated (but not superheated) steam passes through high-efficiency moisture separators and from here is again distributed to the turbine. 

Another advantage is that the IGCC system generates electricity by both combustion (Brayton cycle) and steam (Rankine cycle) turbines. The inclusion of the Brayton topping cycle improves efficiency compared to a conventional power plant s Rankine cycle-only generating wstem. Typically about two-thirds of the power generated comes from the Brayton cycle and one-third from the Rankine cycle. 

A Rankine/Rankine combined cycle is shown in Fig. 5.16. The exhaust from the top steam turbine (TURl) is hot enough to generate freon vapor in a waste-heat boiler. The freon vapor generated can power a freon turbine, thus increasing the total work produced. The Rankine/Rankine combined cycle has a thermal efficiency greater than either a steam or freon cycle may have by itself. The power plant occupies less area, and the fuel requirements are less. 

Thus, the net reaction is just Eq. 15.77. Methane-fueled MCFCs are leading candidates for local power plants in the range 1-3 MW, as their cost and efficiency are more attractive than those of PAFCs. The relatively high temperature of the exhaust gases means that they can be used effectively to drive conventional gas or steam turbines to generate additional ( topping ) electricity for increased overall efficiency. Less CO2 per kilowatt-hour is produced than by other fossil fuel-fired power generation methods, and emissions of NO , SO , and unburned hydrocarbons are minor. 

As the oxidation equation shown at the top of Figure 11.12 demonstrates, the hydrogen and hydroxide ions react to produce energetic water molecules that arise in the form of steam. This steam may be used for heating or to generate electricity in a steam turbine. Furthermore, the water that condenses from the steam is pure water, suitable for drinking ... 

Figure 17.1 is a conceptual drawing of a simple topping steam turbine. An actual turbine does not look anything like this sketch. The 400-psig... 

Most of the turbines you will encounter in your work are called topping, or extraction, turbines. The idea of such a turbine is to extract much of the potential work from the motive steam, and then use the exhaust steam to reboil towers. Typically, the energy content of the exhaust steam is only 10 to 20 percent less than that of the motive steam. That is the calculation we just did with the Mollier diagram. The rest of the energy of the steam may then be used as the steam condensers, to reboil towers. This sounds pretty efficient. It is the basis for the new cogeneration projects you may have heard about. Of course, this system was used by the British Navy in the nineteenth century. 

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