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5.11 Boiler Design5.11–Pressure boiler ,there is no steam drum ,but rather an arrangement of tubes in which steam is generated and superheated .the boiler is a drun-or once- through type ,whether it is an individual unit or a small part of a large complex ,it is necessary in design to give proper consideration to the为确定锅炉和其它传热设备所吸收的热量，使用最佳效率值，燃料的类型或者设计的设备所需燃料。
确定所需的炉膛的尺寸和形状，考虑炉膛的位置，燃料床的燃烧器的空间要求，并结合完成完全燃烧所需要的充足的炉膛容积。
对流换热表面的大体布置必须是这样计划，就是过热器和再热器，在设置时，必须放置在最佳温度区域内，这个最佳温度区域内的烟气温度是足够高的，可以较好的把烟气温度传然而在饱和位置或锅炉表面有一定的灵活性，在过热器前后必须有足够的对流换热表面用来传热使给水达到饱和温度以及产生炉膛内不能产生的多余的蒸汽。
20％的需要蒸汽。
．锅炉设备或附件必须把炉膛、锅炉、过热器、再热器及空气加热器紧密联系在一起，密封的气体燃料或输送管道必须用来传送烟气到烟囱。
After the steam requirements-steam flow ,steam pressure and temperature-and boiler feedwater temperature are determined ,the required rate of heat absorption ,q, is q=w’(h’2- h’1)+ w”(h”2- h”1) (5.1)q，由方程确定： q=w’(h’2- h’1)+ w”(h”2- h”1)（5.1）其中：q=热吸收率，英热/小时w’=primary steam or feedwater flow ,lb/hw’ =主蒸汽或给水流量，磅/小时w”=reheat steam flow , lb/hrw” =再热蒸汽流量，磅/小时h’1=enthalpy of feedwater entering , Btu/lbh’1=给水入口焓，英热/磅h’2=enthalpy of primary steam leaving superheater , Btu/lbh’2=主蒸汽离开过热器的焓，英热/磅h”1=enthalpy of steam entering reheater , Btu/lbh”1=蒸汽进入再热器的焓，英热/磅h”2=enthalpy of steam leaving reheater , Btu/lb”蒸汽离开再热器的焓，英热/磅100减去热损失的总和的百分比表示。
第一章热科学基础1.1工程热力学基础热力学是一门研究能量储存、转换及传递的科学。
能量以内能（与温度有关）、动能（由物体运动引起）、势能（由高度引起）和化学能（与化学组成相关）的形式储存。
不同形式的能量可以相互转化，而且能量在边界上可以以热和功的形式进行传递。
在热力学中，我们将推导有关能量转化和传递与物性参数，如温度、压强及密度等关系间的方程。
因此，在热力学中，物质及其性质变得非常重要。
许多热力学方程都是建立在实验观察的基础之上，而且这些实验观察的结果已被整理成数学表达式或定律的形式。
其中，热力学第一定律和第二定律应用最为广泛。
1.1.1热力系统和控制体热力系统是一包围在某一封闭边界内的具有固定质量的物质。
系统边界通常是比较明显的（如气缸内气体的固定边界）。
然而，系统边界也可以是假想的（如一定质量的流体流经泵时不断变形的边界）。
系统之外的所有物质和空间统称外界或环境。
热力学主要研究系统与外界或系统与系统之间的相互作用。
系统通过在边界上进行能量传递，从而与外界进行相互作用，但在边界上没有质量交换。
当系统与外界间没有能量交换时，这样的系统称为孤立系统。
在许多情况下，当我们只关心空间中有物质流进或流出的某个特定体积时，分析可以得到简化。
这样的特定体积称为控制体。
例如泵、透平、充气或放气的气球都是控制体的例子。
包含控制体的表面称为控制表面。
因此，对于具体的问题，我们必须确定是选取系统作为研究对象有利还是选取控制体作为研究对象有利。
如果边界上有质量交换，则选取控制体有利；反之，则应选取系统作为研究对象。
1.1.2平衡、过程和循环对于某一参考系统，假设系统内各点温度完全相同。
当物质内部各点的特性参数均相同且不随时间变化时，则称系统处于热力学平衡状态。
当系统边界某部分的温度突然上升时，则系统内的温度将自发地重新分布，直至处处相同。
当系统从一个平衡状态转变为另一个平衡状态时，系统所经历的一系列由中间状态组成的变化历程称为过程。
4.2 Refriger ant evaporators11Several ty pes of evapor ators c an be used in multistage systems.2A tubular, dir ect expansion evapor ator oil easily and requires the smallest refrigerant charge.3Where dir ect expansion is impr actical, a flooded system or a recirculated system may be used, but these methods c ompound oil r eturn pr oblems.24Some problems that can bec ome mor e acute in low-temper ature systems than in high-temperatur e sy stems include oil transport pr operties, loss off c apacity caused by static head from the depth of the pool of liquid r efrigerant in the evaporator, deterioration of refriger ant boiling heat tr ansfer c oeff icients, and higher specif ic volumes for the vapor.35The effect of pressure losses in the evapor ator and suc tion piping is mor e acute in lowtemperatur e sy stems because of the lar ge change in satur ation temperatures and specif ic volume in relation to pr essur e changes at these c onditions.6Sy stems that oper ate near zero absolute pressure are particularly affected by pressur e loss.7F or example, with R-12 and R-22 at 140 kPa suction and 27℃liquid feed temper ature, a 7 kPa loss incr eases the volume flow r ate by about 5﹪.8A t 35 kPa suction and -7℃ liquid feed temperature, a 7 kPa loss increases the volume flow rate by about 25﹪.49The depth of the pool of boiling r efrigerant in a flooded evaporator causes a liquid head or static pressur e that is exerted on the lower part of the heat transfer surfac e.10Therefore, the saturation temperatur e at this sur face is hi gher than the pr essure in the suction line, which is not affected by the static head.11A lthough tubular dr y expanded evaporators do not have appreciable static liquid head, gas pressur e dr ops from the inlet to the outlet of the evaporator create a velocity head that c auses a similar condition.512The liquid depth penalty for the evaporator can be eliminated if the pool of liquid is below the heat transfer surface and a r efrigerant pump spr ays the liquid over the surface.13Of course, the pump energy is an additional heat load to the system, and more refrigerant must be used to prov ide the Net Positive Suction Head (NPSH) requir ed by the pump.14The pump is also an additional item to be maintained.615Another type of low-temperatur e evaporator is the flash cooler in w hic h liquid refrigerant is cooled by boiling off some vapor.16The r emaining cold liquid c an then be pumped from the flash c ooler to the evaporator.17There it is either top or bottom fed at a r ate greater than the evapor ation rate to ensure wetting of the entire evaporator surface for maximum heat tr ansfer without an appreciable static head penalty.18This liquid over feed system is fr equently used in large refrigerated war ehouses with many evapor ators. 719Another less frequently used system pumps the liquid r efrigerant as a secondar y cooler, or coil, heat transfers to it from the material being cooled.20The liquid temperature rises to develop a temper ature r ange, but bec ause pr essur e is maintained suff iciently above satur ation by the liquid pump, the coolant does not evapor ate until it returns via a restriction to the flash cooler.21Suff icient refriger ant must be circ ulated to acc ommodate the temperatur e range.22The flash c ooler in this sy stem is an acc umulator r eceiver similar to that used in a liquid overfeed system, except that no excess r efrigerant is fed to the remote heat transfer surfac e.823In both types of liquid r ecirculation systems, the cold liquid can be moved by mec hanic al pumps or by pressure from the compr essor dischar ge. 4.2制冷剂的蒸发器11有几种类型的蒸发器，可用于在多级系统。
毕业设计外文翻译原文标题：Proposal for a high efficiency LNGpower-generation System utilizing wasteheat from the combined cycle中文标题:一个高效的利用液化天然气联合循环余热的发电系统学院名称：能源与动力工程学院专业名称：热能与动力工程Proposal for a high efficiency LNG power-generation system utilizing waste heat from the combined cycleY. Hisazumi*, Y. Yamasaki, S. SugiyamaEngineering Department, Osaka Gas Co., 1-2 Hiranomachi 4-chome Chuo-ku, Osaka 541, Japan Accepted 9 September 1998AbstractHigh-efficiency power-generation with an LNG vaporizing system isproposed: it utilizesthe LNG's cold energy to the best potential limit. This system can be applied to LNG vaporizers in gas companies or electric power companies and recovers the LNG's cold energy as electric power. The system consists of a Rankine cycle using a Freon mixture, natural-gas. Rankine cycle and a combined cycle with gas and steam turbines. The heat sources for this system are the latent heat from the steam-turbine's condenser and the sensible heat of exhaust gas from the waste-heat recovery boiler. In order to find out the optimal condition of the system, several factors, such as gas turbine combustion pressure, steam pressure, condensing temperature in combined cycle, composition of mixture Freon, and natural gas vaporizing pressure are evaluated by simulation. The results of these studies show that in the total system, about 400 kWh can be generated by vaporizing 1 ton of LNG, including about 60 kWh/LNG ton recovered from the LNG cold energy when supplying NG in 3.6 MPa.. About 8.2MWh can be produced by using 1 ton of LNG as fuel, compared with about 7 MWh by the conventional combined system. A net efficiency of over 53%HHV could be achieved by the proposed system. In the case of the LNG terminal receiving 5 million tons of LNG per year, this system can generate 240 MW and reduce the power of the sea water pump by more than 2MW. 1998 Elsevier Science Ltd. All rights reserved.1. IntroductionIn the fiscal year 1994, the amount of LNG imported to Japan reached about 43 million tons; of this 31 million tons were used as fuel for power generation. As shown in Fig. 1, about 20% of the LNG imported was used for power generation [2]. Fig. 2 shows the major LNG power generation systems now in operation and their outputs. Several commercial LNG power generation plants have been constructed since 1979, and their total output has reached approximately 73 MW. Among the new power-generation plants without CO2 emission, this value of 73 MW is second to the 450 MW input of geo-thermal power generation plants in Japan, with the exception of power generation by refuse incinerators, and is much larger compared with the 35 MW output of solar-power plants and the 14 MW output of wind-power stations.Table 1 shows the LNG power generation plants constructed in Japan. The economics of LNG power generation became worse as the appreciation of the yen madethe cost of energy kept constant but while raising the construction cost; the adoption of the combined cycle utilizing gas-turbine and steam turbine (hereafter called combined cycle) increased the gas send-out pressure and lowered the power output per ton of LNG. Therefore, no LNG powergeneration plants were constructed in the 1990s due to lower cost effectiveness of the systems.As for the thermal power plant using natural gas as fuel, the steam turbine produced only about 6 MWh of power output per ton of LNG. But recently, improvement in blade-cooling technology and materials of the gas turbine enabled a 1400℃class turbine to be designed and increased the combustion pressure up to 3 MPa. Therefore, as shown in Fig. 3, the heat efficiency of the combined cycle has been improved and the electrical output from 1 ton of LNG has reached about 7MWh.In this paper, a proposal is made for the high-efficiency LNG power generation system based on a new concept which fully utilizes the cold energy without discarding it into the sea. The system is composed of the combined cycle and the LNG power-generation plant.2. High-efficiency LNG power-generation system2.1. Basic componentsFig.4 shows the process flow diagram of the high-efficiency LNG power-generation system. This complex system consists of the combined cycle and the LNG power generation cycle. The combined cycle is composed of a gas turbine (GAS-T) and a steam turbine (ST-T) using natural gas (NG) as fuel, while the LNG power generation cycle is composed of a Freon (uorocarbon) mixture turbine (FR-T) and a natural-gas turbine (NG-HT, NG-LT) using the latent heat of condensation from the exhaust steam and the sensible heat of the exhaust gas as heat sources. The plate fin type heat exchanger can be used for the LNG/natural gas (LNG-CON) and LNG/ Freon mixture (FR-CON). The shell-and-tube type can be selected as exchangers for exhaust steam/natural gas (LNG-VAP),exhaust steam/Freon mixture(FR-VAP), and exhaust gas/natural gas (NG-SH) applications according to the operating conditions.Ice thickness on the surface of the heat-exchanger tubes becomes a problem as heat is exchanged between exhaust gas and cold natural gas or Freon mixture. The ice thickness can be estimated by the technology of heat transfer between LNG and sea water, thus enabling one to avoid blockages due to ice inside the tubes.In addition, stable and continuous send-out of gas is made possible by using a bypass system, even if turbines and pumps for the Freon mixture and natural gas circulating systems (FR-RP, LNG-RP) stop.2.2. Features of the systemThe practical use of the following existing technologies in combination shows the high feasibility of the proposed system:. Power generation using Freon or hydrocarbon type Rankine cycle,. Power generation by natural-gas direct expansion],. TRI-EX type vaporizer which vaporizes LNG by using an intermediate medium or vacuum type LNG vaporizer.The Freon mixture is made up of the HFC type, which is a fluorocarbon consisting of H, F, and C and has no adverse influence on the ozone layer; it enables reduction in exergy loss at the heat exchanger and increases itscirculating flow rate to be achieved.The effective recovery of cold exergy and pressure exergy is made possible by the combined system using natural gas and Freon mixture Rankine cycle.Fig. 5 shows the temperature-heat duty relation when vaporizing 1 kg of LNG in the system shown in Fig. 4. Separation of the condensed natural-gas in two sections enables an increase in the heat duty between Freon (FR) and LNG, and a reduction of difference in temperature of LNG and natural gas between the inlet and outlet of the heat exchanger.3. Evaluation of the characteristics of the proposed system3.1. Process simulationThe characteristics of this system were evaluated by using process simulator. The followings are the conditions used for the calculation:Effciencies of rotating machines LNG compositionGas turbine (GAS-T) 88% CH4 89.39%Steam turbine (ST-T) 85% C2H6 8.65%Natural-gas turbine (NG-HT, LT) 88% C3H8 1.55%Freon turbine (FR-T) 88% iC4H10 0.20%Air compressor (AIR-C) 85% nC4H10 0.15%LNG pump (LNG-MP, RP) 70% iC5H12 0.01%Freon pump (FR-RP) 70% N2 0.05%Natural gas gross heat-value: 10,510 kcal/Nm3AIR/NG flow ratio of gas turbine: 323.2. Effects of send-out pressure of the natural gasWhen natural-gas is sent out at 3.5 or 1.8 MPa, evaluations were made of the effects of send-out pressure of the LNG and change in superheating temperature of the natural gas on the total output of the high pressure (NG-HT) and the low pressure (NG-LT) natural-gas expansion-turbines. Fig. 6 shows the results of this calculation, where self consumption of power is calculated from the power, raising the pressure of the LNG up to the inlet pressure of the turbine minus the power required for the original send-out pressure. In both cases, the inlet pressure rise for the turbine causes an increase of self consumption power, but brings about a greater out-put. About 7 MPa of the inlet pressure of the turbine is appropriate considering the pressure tolerance of the heat exchangers.When the superheating temperature of the natural gas at the inlet to the turbine becomes high, the recovery of power increases, but the temperature of the exhaust gas from the outlet of the natural-gas super heater (NG-SH) declines, thus indicating that there is a limitation to superheating gas.3.3. Effects of combustion pressure of the gas turbineThe outputs of the gas turbine and the steam turbine, and the efficiency per gross heating value were evaluated by changing the combustion pressure of the gas turbine operating at 1300℃turbine-inlet temperature - see Fig. 7.If the combustion pressure of the gas turbine becomes high, the output of the gas turbine increases, but the output of the steam turbine decreases because the rise in combustion pressure causes a lowering of the exhaust-gas temperature at the outlet of the gas turbine and consequently a decline in the steam temperature at the inlet of the steam turbine. However, the overall efficiency of the turbines increases upon increasing the combustion pressure because the increment of gas-turbine output exceeds the decrement of steam turbine output. As a result, taking the pressure loss into account, it is appropriate to set the send-out pressure of the natural gas at the LNG terminal at 3.5 MPa.（FR-vap），3.4. Effects of Inlet pressure of the steam turbineFig. 8 shows the relations between the steam-turbines output and exhaust gas temperatures by changing the steam pressure in the range of 3-7 MPa. As the steam pressure increases, the output of the steam turbine rises and the temperature of the exhaust gases also increase. Besides, the power required for the water-supply pump increases with a rise in the steam pressure. Therefore, the current combined cycles operate at steam pressure of 7 MPa or more because the increment of the output of steam turbine exceeds the additional power required for the water-supply pump.3.5. Rankine cycle using a Freon-mixture refrigerant.The Freon refrigerant was selected from the HFC refrigerants on the basis of marketability, boiling point and freezing-point. Table 2 shows the physical properties of HFC Freon.When only HFC-23 is used as the medium, because of its low freezing-point it never freezes even if heat is exchanged between the LNG and HFC-23. But if HFC-23 is heated by the exhaust steam of the steam turbine, the pressure rises approximately up to the critical pressure. Therefore, the use of HFC-23 is not cost effective, because it is then necessary to set a high design pressure. To cope with this problem, we evaluated the compound refrigerant composed of HFC-134a (with high boiling point) and HFC-23.Fig. 9 shows saturated vapor pressure at various temperatures, the boiling point and the dew point at atmospheric pressure for mixtures of HFC-23 andHFC-134a of various compositions. The saturated pressure at each temperature rises with the increasing mole ratio of HFC-23: Hence, 40-45% of the mole ratio of HFC-23 is the optimal value considering the design pressure of the equipment.Fig. 10 shows the plots of the output of the Freon turbine versus the condensing temperature of the steam turbine when changing the composition of the HFC-23. In this figure, the turbine outlet pressure is determined in such a way that thedifference in temperature between the LNG and Freon mixture is not less than 5℃in the Freon condenser (FR-CON). The Freon turbine's inlet-pressure is set to the saturatedtemperature of the Freon mixture, i.e. less than 2℃from the steam-condensing temperature.This figure indicates that the output of the turbine scarcely correlates with the mole ratio of HFC-23. The higher the steam-condensing temperature becomes, the greater the output per ton of LNG the turbine produces, but in such a case, it is necessary to evaluate the system as a whole because more fuel is required, as described below. The result indicates that the optimal mole composition of HFC-23 and HFC-134a is 40%/60% considering both design pressure and the output of the turbine.3.6. Comprehensive evaluation from the viewpoint of the steam-condensing Temperature.As the dew point of the exhaust gas is 42℃, it is wise to set the exit temperature of the exhaust gas from the natural-gas super heater (NG-SH) to 80℃or more in order to prevent white smoke from the smoke stack. Table 3 shows the effect of the steam-condensing temperature on the generated output of the total system. The lower steam-condensing temperature brings about a higher efficiency of the total system, but also causes a lowering in the inlet temperature of natural-gas turbine. Therefore, it is appropriate to set the steam-condensing temperature at approximately 30℃.When the condensing temperature is 30C, the generated outputs per ton of LNG of the combined cycle and LNG power generation plant are 342.83 and67.55 kWh, respectively, resulting in 402.64 kWh of total generated output aftersubtracting the self-use power. As 48.94 kg of fuel is used for operating the system, the generated outputs of the combined cycle and the total system reach about 7 and 8.2 MWh, per ton of fuel respectively.3.7. Evaluation of exergyNatural-gas is liquefied at an LNG liquefaction terminal, with the consumption of about 380 kWh/LNG-ton: 1 ton of LNG having about 250 kWh of physical exergy as cold exergy and 13.5 MWh of chemical exergy. Fig. 11 shows the result of evaluating the exergy of the system shown in Fig. 4 under the optimal condition. The total output of Freon and natural gas turbines is 67.5 kWh, and the effective recovery percentage of cold exergy is 56%. As 90 kWh out of the pressure exergy can be recovered as output, about 157 kWh of net recovery can be obtained, which indicates the recovery percentage reaches about 63% for 250 kWh of LNG cold exergy. This conversion efficiency is higher than that achieved from chemical exergy to electric power.Most of the exergy loss occurs in the heat exchanger and the turbine, and in mixing with re-condensed LNG. As for the turbines, the loss of energy may be improved by using high-efficiency turbines. On the other hand, modification of the heat exchanger to reduce the energy loss may cause increased complexity of the system and is difficult to be done from the economic viewpoint. Though the recovery.percentage of cold energy in this system is low compared with the 80% in air-separation equipment, this system has the advantage of recovering a large amount of the available cold energy.4. ConclusionThe paper has proposed a high-efficiency LNG power generation system in combination with a combined-cycle power generation system fueled by natural-gas. The system utilizes LNG cold energy and it requires no sea water as a heat source.This system can be applied to LNG vaporization and send-out processes of gas companies or electric-power companies. The system recovers LNG coldenergy as an electric-power output without wasting it into sea water. The system consists of Rankine cycle with Freon mixture and a natural-gas Rankine cycle using the latent heat of exhaust steam from the steam turbine and the sensible heat of exhaust gas from the waste-heat recovery boiler. To improve the total efficiency of the system, a simulation was conducted to evaluate several factors, such as the composition of the Freon mixture, natural gas send-out pressure, as well as the combustion pressure steam inlet pressure, and steam-condensing temperature of the combined cycle. As a result, not less than 60 kWh/LNG-ton of output was generated even at a high natural-gas send-out pressure of 3.5 MPa. This value is considerably higher than the output generated at a LNG send-out pressure of 3 or 4 MPa, as given in Table 2.The system can produce about 400 kWh of net output when vaporizing 1 ton of LNG. While the conventional combined-cycle system in operation generates about 7 MWh when 1 ton of LNG is used as fuel, the system using the same amount of fuel generates about 8.2 MWh with a high degree of efficiency: a not-less-than 53% conversion efficiency was achieved per gross heat value.In the case of an LNG terminal receiving 5 million tons of LNG per year, this system can generate a power of about 240 MW when 600 t of LNG is used in an hour. With the elimination of about 24,000 tons per hour of sea water, which has been used for vaporizing 600 t/h of LNG in the conventional system, no less than 2 MW of electric power for operating sea water pumps can be saved.The proposed system emits no CO2, and can generate a large amount of electricity with high cost efficiency when incorporated into a combined cycle, with no use of sea water. Therefore, we consider that installation of this system is the one of the most favorable means of investment to put a new energy source or energy-saving equipment to practical use.To realize the full potential of this system, it is necessary to understand the heat characteristics of the Freon mixture, the icing and heat transfer characteristics of exhaust steam, the controllability of total system and the characteristics against partial load.References[1] The Center for Promotion of Natural gas Foundation. Research and development report of cold energy utilizing system, 1994[2] Japan's Energy and Economy Research Center. Energy and economy statistical data in 1995[3] Abe. Operating results and future prospect of a recent combined-cycle power generation plant. Thermal and Nuclear Power 1995;46(6):33-41[4] Maertens J. Design of Rankine cycles for power generation. Int. Refrig. 1986;9:137-43[5] Terada, Nakamoto. Power generation utilizing LNG cold. Thermal and Nuclear Power Generation 1986;37(10):66-71[6] Ooka, Ueda, Akasaka. Advanced LNG vaporizer and power generation utilizing LNG cold. Chemical Engineering 1981;45(3):187-90[7] Miura. The development of LNG vaporizer using vacuum steam heat (VSV). Journal of Japan Gas Society 1992;45:34-6[8] Nagai. Software-package and the usage. Chemical Equipment1994;August:31-7[9] Daikin Co. Ltd. Freon Data Sheet of HFC23一个高效的利用液化天然气联合循环余热的发电系统日本大阪541燃气有限公司工程部1-2平野町4肖梅中央谷，1998年9月概述本文提出了一个高效液化天然气气化发电系统，它是利用液化天然气冷能的最佳潜能极限。
Every free surface emits energy in the form of electromagnetic waves;the amount of energy is a function of the surface temperature. This emitted energy is known as radiant thermal energy. The nature of this radiant energy is not completely understood, but laws have been formulated that describe its behavior. It is recognized that, as with other forms of radiant energy ,radiant heat energy is transmitted in the form of electromagnetic waves. The complete formulation of the laws governing radiant heat energy must consider that this energy is quantized,that is, the energy is transferred in quanta. In contrast with other modes of heat transfer, no medium is required to transmit radiant energy. In fact some gases, for instance, carbon dioxide and water vapor, absorb some of the radiant energy passing through them.每一个自由表面都会以电磁波的形式发射能量，能量的量是表面温度的函数。
6.1‟s most efficient speed is usually much higher than that of the machine it is driving ,so a speed reduction gear usually has to be used .600 000马力的汽轮机。
转子——叶轮上装有动叶，转子两端装有轴颈。
轴承箱——安装在气缸上，用来支承转子的轴。
调速器和阀门系统——通过控制蒸汽流量来调节涡轮的速度和出力，同时还有轴承润滑系统以及一套安全装置。
某种类型的联轴器——用来连接从动机械…catch ‟the steam from the nozzle smoothly ,and they are curved so that they change the direction of the jet and in so doing receive an impulse which pushes6.1（见原文）所示为一种简单的冲动式汽轮机。
…reaction ‟ turbine .moving blades are also nozzles ,similar to the stationary nozzles but facing the other way ,and in addition to catching and deflecting the steam issuing from the stationary（见原文中图6.2）它综合了冲力和反作用力的原理。
6.2中的涡轮壳带有一整圈喷嘴，这些喷嘴和反冲式涡轮机里的一样，也是弯曲的，并以最有效的角度引导蒸汽喷向转动的叶片。
,under these conditions the exhaust volume flow becomes large ,and it is necessary to have more than one exhaust stage ;for example ,a large turbine may have three are“axial flow ”turbine .“double flow ”.drops can damage the blades and reduce the turbine efficiency ,and this is one reason why the steam ,after passing through the high-pressure turbine ,idea sometimes。
2.5 Natural Convection自然对流Heat transfer involving motion in a fluid caused by the difference in density and the action of gravity is called natural or free convection. Heat transfer coefficients for natural convection are generally much lower than for forced convection, and it is therefore important not to ignore radiation in calculating the total heat loss or gain. Radiant transfer may be of the same order of magnitude as natural convection, even at room temperatures, since wall temperatures in a room can affect human comfort.传热流体中涉及运动所引起的密度和不同的重力作用称为自然或自由对流。
对自然对流传热系数通常远远低于强迫对流,因此,重要的不是忽略辐射总散热量的计算或利益。
辐射传递可能是同一个数量级的自然对流,即使在室温下,因为壁温度在一个房间里会让人安慰。
Natural convection is important in a variety of heating and refrigeration equipment:（1）gravity coils used in high humidity cold storage rooms and in roof-mounted refrigerant condensers,(2)the evaporator and condenser of household refrigerators, (3) baseboard radiators and convectors for space heating and(4)cooling panels for air conditioning. Natural convection is also involved in heat loss or gain to equipment casings and interconnecting ducts and pipes.自然对流是重要的多种加热和制冷设备:(1)应用于高湿度下重力线圈在车顶安置房、冷藏冷冻冷凝器、(2)家用电冰箱蒸发器和冷凝器,(3)脚板散热器和提出对于空间供热;(4)冷却板,空调。
Unit2：An atom’s nucleus can be……原子核可以分裂，当这种分裂发生时，巨大的能量就会释放出来。
这是一股发热发光的能量。
爱因斯坦曾说过微小质量的物体包含巨大的能量。
当这种能量缓慢释放时，就可以利用它产生动力发电。
当这种能量瞬间释放时，就如原子弹一样产生巨大的爆炸。
A nuclear power plant……核电站用铀作为燃料。
铀是一种能从世界上的许多地方挖出的元素。
它被加工成小丸装入伸进核反应堆的长棒中。
The word fission means to……裂变一词意思就是分裂。
在核电站的反应堆内部，铀原子以可拉链式反应进行分裂。
In a chain reaction……在链式反应中，原子分裂释放的粒子离开并且撞击正在分裂的其它铀原子。
在核电站的链式反应中，那些分裂产生的粒子继续分裂其它的原子，控制棒用来使这种分裂受控因此这种分裂就不会进行得太快。
Unit3Continued research has made renewable……不断的研究使现在可再生能源的利用比25年前更能支付得起。
但是对于可再生能源的利用仍有一些缺点。
For example, solar thermal energy……例如，通过收集器收集太阳光来得到太阳能需要大量的占地面积来安装收集器。
这会影响生态环境，也就是会影响当地的动植物。
当建筑物、道路、输电线和变压器建造时，环境也会受到影响。
通常太阳能电站所用的流体大多数是有毒的而且泄露可能会发生。
Solar or PV cells……太阳能或光伏电池使用相同的技术生产电脑硅芯片。
生产过程使用了有毒的化学药品。
有毒的化学药品用来制造电池储存太阳电能来渡过黑夜和阴天。
制造这种装置也会有环境影响。
Also,even if we……即使我们想马上转换太阳能，仍然存在很大的问题。
世界上所有的太阳能生产设备使太阳能电池满载也只能产生大约350MW，大约够一个300000人口的城市使用，相对我们的需求而言那是微不足道的。
第九章火力发电厂的环境污染控制9.1 概述保护环境和合理利用自然资源是现阶段社会发展的最迫切的问题。
电力工程作为工业、运输、农业发展的基础，发展速度快，生产规模大。
在火力发电厂中燃烧的有机燃料含有许多有害杂质，这些有害杂质作为燃烧产物以气态或固态成分排放到环境中，对大气和水环境造成了负面影响。
火力发电厂的大气污染控制主要是减少有毒物质向大气中的排放。
在这方面成效最显著的是降低固体颗粒物的排放（目前火力发电厂的灰捕集率已高达99.5%）。
硫氧化合物对大气的污染可以通过从燃料中除硫和烟气脱硫的方式加以控制。
现今，电站锅炉使用的减少NO x排放的技术主要是改善燃烧过程，即利用低NO x燃烧器，并通常结合运用燃尽风（OFA）。
那些面临更加严格的环保要求的电厂可能不得不使用燃烧后处理技术，比如选择性催化还原法（SCR），或选择性非催化还原法(SNCR)等，这些技术可以单独使用或结合低NO x燃烧器使用。
保护大气及流域水的洁净既是本国的又是全球各国的义务，因为在大气和海洋中人为污染物的扩散是没有国界的。
有效解决上述问题的基本先决条件是对电力工程专家的培训，专家应该明确火电厂排放物可能对环境产生的影响，并且在热电站的设计、建设和运行维护方面，能采用有效的手段保护大自然。
本章将重点讲述火力发电厂中灰分捕集以及硫氧化合物和氮氧化合物的排放控制。
9.2灰分捕集9.2.1静电除尘器静电除尘器的应用日益广泛，特别是在大型火电厂中更是如此。
该方法能够在阻力不超过150Pa，无需降低温度和加湿烟气的条件下，确保达到很高的烟气净化率（η=0.99-0.995）。
在静电除尘器中，含有大量飞灰的烟气通过由集尘电极形成的烟气通道，在集尘电极之间每隔一定间隔布置电晕电极（如图9-1（a））。
通过高压直流电形成电场（集尘电极为正极，电晕电极为负极）。
在足够高的电场作用下，烟气被电离，灰尘颗粒获得电荷（通常是负电荷）。
在电场力的作用下，荷电灰尘粒子被集尘电极捕集。
4.4 Absorption Heat Pump吸收式热泵（4·4）Functions Of Absorption Heat Pump 1.吸收式热泵的功能An absorption heat pump extracts heat from a low- temperature heat source ，such as waste heat or surface water ，and delivers its heat output at a higher temperatur for winter heating or Other applications at a coefficient of performance greater than 1 ．吸收式热泵从低温热源（如废热或地表水）取热，在较高的温度下输出热量用于冬天或其他场合供热，其效能系数大于1。
In Japan and Sweden ，absorption heat pumps have been installed in dustrial and district heating plants using industrial waste heat to pmvide hot water ，typically at 165 。
F ，for winter heating or other purposes at a COP between 1 ·4 and l. 7 ·在日本和瑞典，吸收式热泵已经安装于利用工业废热来提供热水的供热工厂（代表性的温度是165F），用于冬天供热或其他用途，其COP（效能系数）在1·4~1·7之间。
Absorption heat pumps can be used either for winter heating or for cooling in summer and heating in winter ·吸收式热泵单向用于冬天供热或双向用于夏天制冷、冬天供热。
