Refrigerant Handling and Safety
ASHRAE Standard 34-1992, Number Designation and Safety Classification of Refrigerants, and Standard 15-1994, Safety Code for Mechanical Refrigeration, have been recently revised to address the classification and safety requirements of alternative refrigerants. With proper installation and the incorporation of a leak detection system with proper ventilation, all alternatives can be used safely. Standard 34-1992 explains the format for refrigerant numbering and defines Safety Group...
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In Load Conditions 1, 2, and 3, generator output fluctuates with the load to maintain the import set point. Under Load Condition 4, the entire load is served by utility-derived power. Under Load Condition 5, the local on-site generators reach their full capacity and excess load must be shed at the facility to return to within the import set point. Import export I E systems are the most flexible systems for local on-site cogeneration and peak shaving appli cations. Since facility loads, the cost...
NOX Formation and Control Technologies
During combustion, NOx is formed by three fundamentally different mechanisms thermal NOX, fuel NOX, and prompt NOX formation. Thermal NOx results from the thermal fixation of molecular nitrogen and oxygen in the combustion air. Its rate of formation is extremely sensitive to local flame temperature and, to a lesser extent, to local oxygen concentrations. Virtually all thermal NOx is formed in the region of the flame where the temperature is highest. Maximum thermal NOx production occurs at a...
The Economic Value of Steam
The positive value of steam is derived from two basic features It can act as a heat transfer medium, conveying thermal energy from the heat released in a boiler from combustion of fuel to various processes and services requiring heat and It can act as a working fluid to produce useful shaft work by expanding from higher to lower pressure through a turbine or engine. Steam has negative value when it cannot be used Fig. 6-6 Mollier Diagram for Steam SI Units . Source Babcock amp Wilcox
Using Steam Tables
Using steam table nomenclature, the properties of a unit mass of a mixture of liquid and vapor saturation state properties of a quality, x, are given by the following expressions steam tables for specific volume. That can be determined by subtracting vf from vg. The energy equation applied to the vaporization process may be expressed as Vx vf xvfg hx hf xhfg Ux uf xufg sx sf fg property g value minus the f value Note that the change in property going from saturated liquid to saturated vapor...
Cooling Tower Sizing and Performance
The cooling effect of evaporation is about 1,000 Btu lbm 0.65 kWhh kg of water evaporated. Cooling towers optimize evaporation by providing the maximum transient water surface and airflow rate. Figure 36-14 shows a typical cooling tower performance curve, graphing leaving cold water temperature versus wet-bulb temperature. Figures 36-15 and 36-16 illustrate the process. In this example, the wet-bulb temperature remains unchanged across the cooling tower at 65 F 18 C , while the dry-bulb...
Steam Turbine Power Cycle Operation and Performance
The energy available per unit mass e.g., lbm or kg of steam flowing through a steam turbine is a function of the turbine pressure ratio ratio of absolute inlet pressure to absolute exhaust pressure and the inlet temperature. The maximum ideal thermal efficiency achievable with a steam turbine cycle is, therefore, the difference between the inlet and exhaust energies or enthalpies . This efficiency is based on the Fig. 11-27 Large Capacity, Central Power-Plant Type Surface Condenser. Source...
Prime Mover Cycle Terminology
There are numerous terms used to describe application of prime mover cycles. These include topping, bottoming, simple, combined, and cogeneration cycles. Definitions for these terms are flexible. Commonly, topping and bottoming are applied to cycles to indicate the stage at which an energy stream is used to produce power. Alternatively, the term base unit may be used to indicate the primary system to which a topping or bottoming cycle is applied. The topping cycle may be characterized as one...
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Fig. 17-39 Reciprocating Engine Exhaust Gas System. Source Jenbacher Energies tion. In NSCR systems, NOx is reduced in the presence of a catalyst by CO and HC or VOC in the exhaust gas, forming N2, H2O, and CO2. Currently, some engine manufacturers report NOx values as low as 0.5 g hp-h 0.7 g kWh . The remaining CO and HC in the exhaust gas can be oxidized to CO2 and H2O with oxidation catalysts. Suitable catalytic materials include platinum, palladium, and rhodium. These metals have relatively...
The Psychrometric Chart
The psychrometric chart is a plot of the properties of atmospheric air. It graphically illustrates the relationship between db temperature, wb temperature, RH, humidity ratio, and enthalpy. It is essentially a graphic representation of the condition of air air-water vapor mixture at each point in the AC process. It relates db temperature to absolute moisture content of the air and includes all of the possible combinations of temperature, moisture content, density, and heat content properties...
Centrifugal Compressor Capacity Control
Capacity can be controlled in centrifugal compressors by varying speed, bypassing hot gas, use of variable inlet guide vanes, or a combination of all of these techniques. The primary means of control for part-load operation of centrifugal compressors is variable inlet guide vane operation. Inlet guide vanes are mounted on the compressor casing just upstream of the impeller inlet and may be electrically, pneumatically, or hydraulically operated. Referring to the diagram of the impeller and...
Conventional Utility Gas Turbine Cycle Peaking Plants
The other basic thermodynamic cycle used by electric utility plants to generate electric power is the open-cycle gas turbine, which operates on the Brayton cycle. Whereas steam cycle plants are used for base and intermediate load applications, gas turbine cycle plants are used by many utilities to serve peaking power requirements. Whereas the steam cycle operates essentially on a closed loop, the gas turbine uses air in a once-through open cycle. Since air is essentially a non-condensable fluid...
Steam Turbine Drives
Known for their reliability, efficiency, and long service life, steam turbine-driven chillers have been successfully applied for most of this century. Large-capacity steam turbine-driven chillers featuring centrifugal compressors, such as the ones shown in Figures 37-51 and 37-52, remain a commonly used technology for large industrial facilities, universities, and hospitals with high-pressure steam systems, as well as for district type heating and cooling plants. Steam turbines have good speed...
Evaporator Econom
Fig. 8-36 Sectional Schematic of Unfired HRSG with Temperature Distribution Profile. Source Nooter Eriksen oxygen for combustion, the overall process becomes less thermally efficient because fresh combustion air must be introduced. Figure 8-34 shows a large capacity boiler designed for supplementary firing in conjunction with a gas-turbine combined cycle. This unit is designed and sized similar to units using outside air through forced-draft fans. The stack temperature can be dropped...
Firetube Boilers
A firetube boiler directs hot combustion gases through tubes surrounded by water within a boiler shell. The firetube design provides abundant heat transfer surface and helps distribute steam formation uniformly throughout the mass of water. During operation, firetube boilers respond fairly quickly to load swings because they contain a large reservoir of water at the saturation point. Most firetube boilers are designed to burn liquid and gaseous fuels, but some burn solid fuels. Firetube boilers...
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The four existing Cleaver-Brooks model DLD-76 watertube boilers each have a design rating of 60,000 lbm h 27,216 kg h at 150 psig 11.4 bar . The pressure vessel design rating is 260 psig 18.9 bar . Each boiler includes a dual-fuel, steam-atomized burner natural gas No. 6 oil manufactured by The Engineer Company. Partial flue gas recirculation is utilized to reduce air emissions levels using a 30 hp 22 kW blower on each boiler to return gas from the breeching to the burner. Forced-draft fans for...
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Fig. 10-13 Air Compressor with Ten Axial Stages Followed by One Centrifugal Stage. Source MAN GHH Several alternative configurations are used in applied combustor designs. Can configurations are designed with one fuel nozzle in each burner can. Annular configurations include one large combustor with multiple burners. While can combustors can be removed and replaced with limited disassembly, annular combustors require the power turbine and gas producer modules to be removed for maintenance....
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200 400 600 800 1000 1200 1400 1600 1800 2000 Output, kW Fig. 26-32 Back-Pressure Steam Turbine Performance in Output vs. Throttle Flow for Various Extraction Steam Rates. Source Cogen Designs, Inc. Maximum throttle flow of about 200,000 lbm h 90,000 kg h occurs between 8.3 and 12.0 MW The maximum exhaust flow, which is the ability of the condenser to accept steam and maintain constant condenser pressure, is about 90,000 lbm h 41,000 kg h . During conditions when no extraction steam is being...
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driver speed limitations necessitate the use of throttling in addition to speed control. In System 5 and 6, speed control results in improved performance of the driven machine under part-load operation. At two-thirds of full-load output, there is a complimentary relationship between driver and driven machine performance. At one-third of full-load output, the trend reverses for the driver. Still, system SPR improves as a result of operation at reduced speed. While System 6 includes a driver...
Conventional Utility Rankine Steam Cycle Plants
Most large utility plants rely on the conventional Rankine steam cycle, in which high-pressure steam is expanded through a set of turbine wheels to generate mechanical energy, which then drives a generator to make electric power. The high-pressure steam is produced in a steam generator, or boiler, which may be fueled by coal, oil, natural gas, wood, refuse, or nuclear fission. Figure 3-1 is a simplified schematic representation of a large utility supercritical steam power plant, featuring a...
Mollier Diagram
A convenient alternative to using the steam tables is to use a Mollier diagram. A Mollier diagram is a graphic representation of the thermodynamic properties of steam. The ordinate h is enthalpy and the abscissa s is entropy. Using the graphical representation of the relationships of various steam conditions, computations made for analysis of various cycles and processes can be performed quickly with a fairly high degree of accuracy. Figures 6-5 English units and 6-6 SI units are Mollier...
Regulatory Terminology Applied to Prime Mover Cycles
To establish federal regulations and Qualifying Facility QF cogeneration system efficiency standards, the Federal Energy Regulatory Commission FERC defined cogeneration as the combined production of electric power and useful thermal energy by sequential use of energy from one source of fuel. As defined by FERC, a topping cycle first uses thermal energy to produce electricity, and then uses the remaining energy for thermal process. In a bottoming cycle, the process is reversed. Figures 1-7...