Combined power plant

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. 

The term "cogeneration is sometimes used to describe a combined power plant, but it is better used for a combined heat and power (CHP) plant such as the one shown in Fig. 1.6 (see Ref. [2] for a detailed discussion on CHP plants). Now the fuel energy is converted partly into (electrical) work (W) and partly into useful heat (Qu) at a low temperature, but higher than ambient. The non-useful heat rejected is (2nu-... 

Horlock, J.H. (2002), Combined Power Plants, 2nd edn, Krieger, Melbourne USA. 

Consider a combined power plant made up of two cyclic plants (H, L) in series (Fig. 7.1). In this ideal plant, heat that is rejected from the higher (topping) plant, of thermal efficiency tjh, is used to supply the lower (bottoming) plant, of thermal efficiency tjl, with no intermediate heat loss and supplementary heating. 

The most developed and commonly used combined power plant involves a combination of open circuit gas turbine and a closed cycle (steam turbine), the so-called CCGT. Many different combinations of gas turbine and steam turbine plant have been proposed. Seippel and Bereuter [3] provided a wide-ranging review of possible propo.sed plants, but essentially there are two main types of CCGT. 

Horlock, J. H. (1994). Combined Power Plants—Past, Present and Future. Tr3iis3ctioiis of the ASME, Jourii3l of Engineering for Gas Turbines 3iid Power 1 17 608-616. 

Wu, C., Maximum obtainable power of a Carnot combined power plant. Heat Recovery Systems and CHP, 15(4), 351-355, 1995. 

More efficient coal utilization can be realized with combined power plant cycles. For instance, the post combustion gases of a conventional combustor or an advanced MHD system can be further utilized to drive a gas or steam turbine. However, the sustained durability of downstream turbine or heat exchanger components requires minimal transport of corrosive fuel impurities. Control of mineral-derived impurities is also required for environmental protection. For the special case of open cycle-coal fired MHD systems, the thermodynamic activity of potassium is much higher in the seeded combustion gas (plasma) than in common coal minerals and slags. This results in the loss of plasma seed by slag absorption and is of critical concern to the economic feasibility of MHD. 

A further promising field for application of pyrolysis (not a topic of this chapter) seems to be the coupling of the pyrolysis units with a thermal plant. The pyrolysis fractions can be used as precleaned feed support for the combined power plant as shown in Table 20.1 for ConTherm at Hamm-Uentrop with a capacity of 100000 l/yr high caloric feed [15, 17]. 

Recent years have seen large efforts to build hybrid plants combining high-temperature fuel cells and gas turbines. The basic idea is that of highly efficient coordination of gas and heat flows entering and leaving the two components of these combined power plants. This coordination serves to lower the energy losses and raises the overall plant efficiency dramatically. 

Niksa S, Fujiwara N. Predicting complete Hg speciation along coal-fired utility exhaust systems. Presented at the Combined Power Plant Air Pollutant Control Mega Symposium, Washington, DC, Aug 30-Sept 2, 2004 www.awma.org/onlinelibrary Lee SJ, Seo Y-C, Jang H-N, Park K-S, Back J-I, An H-S, Song K-C. Speciation and mass distribution of mercury in bituminous coal-fired power plant. Atmos Environ 2006,40,2215-24. 

Milobowski MG, Amihein GT, Kudlac GA, Yurchison DM. Wet FGD Enhanced Mercury Control for Coal-fired Utility Boilers. The U.S. EPA/DOE/EPRI Combined Power Plant Air. Pollutant Conti ol Symposium The Mega Symposium Chicago, Illinois, USA, 2001. 

Pearce, R. and J. Grusha. 2001. Tangential Low NOx System at Reliant Energy s Limestone Unit 2 Cuts Lignite, PRB, and Pet Coke NOx. Proc. EPRI-DOE-EPA Combined Power Plant/Air Pollution Control Symposium. Clearwater, FL. August 20-24. 

Chemical-Process Vessels. Explosion-bonded products are used in the manufacture of process equipment for the chemical, petrochemical, and petroleum industries where the corrosion resistance of an expensive metal is combined with the strength and economy of another metal. AppHcations include explosion cladding of titanium tubesheet to Monel, hot fabrication of an explosion clad to form an elbow for pipes in nuclear power plants, and explosion cladding titanium and steel for use in a vessel intended for terephthaHc acid manufacture. 

Demand. The demand for uranium in the commercial sector is primarily determined by the requirements of power reactors. At the beginning of 1993, there were 424 nuclear power plants operating worldwide, having a combined capabity of about 330 GWe. Moderate but steady growth is projected for nuclear capacity to the year 2010. The capacity in 2010 is expected to be about 446 GWe (29). 

Code of Federal Regulations, Tide 10, Part 52, "Eady Site Permits, Standard Design Certifications, and Combined Licenses for Nuclear Power Plants," Washington, D.C. 

Conventional fossil fuel-fired power plants, nuclear power faciUties, cogeneration systems, and combined-cycle faciUties all have one key feature in common some type of steam generator is employed to produce steam. Except for simple-cycle cogeneration faciUties, the steam is used to drive one or... 

Because of the simplicity and reUabiUty of the Rankine cycle, faciUties employing this method have dominated the power industry in the twentieth century and typically play an important role in most modem combined-cycle faciUties. Water is the working fluid of choice in nearly all Rankine cycle power plants because water is nontoxic, abundant, and low cost. 

Gas turbine-based power plants, particularly natural gas-fired cogeneration and combined-cycle faciUties, have proven to be highly rehable, efficient, and environmentally attractive. Advances in machine design, more efficient plant integration, and optimistic forecasts for the availabiUty of affordable natural gas worldwide have boosted the appeal of these systems for both base-load and peaking service. 

The next generation of gas turbine-based, combined-cycle power plants, under constmction in many parts of the world, is to feature net plant efficiencies in the 60% range based on LHV of fuel input. These faciUties, scheduled for start-up in the latter 1990s, are anchored by large gas turbines capable of simple-cycle efficiencies >40% LHV in some cases. To develop these machines, manufacturers have scaled up and improved upon designs that have already proved to be highly rehable. 

As of the mid-1990s, many older conventional steam plants have been converted to combined cycle. The old boiler is removed and replaced by a combustion turbine and heat recovery steam generator. Although the cycle efficiency is not as high as completely new plants, substantial capital cost is avoided by the modification and reuse of existing steam turbine and auxiHary equipment. In many combined cycle power plants, steam is injected into the combustors of the combustion turbine to lower peak flame temperatures and consequendy lower NO. ... 

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