电站锅炉外文翻译改进煤粉锅炉的燃烧和传热文档格式.docx

1、Clinton, NJ 08809-4000, USAStefan_LauxT. RosinTR-Tech Int. OyFIN-20100 Turku, FinlandTRAbstract The performance of pulverized coal combustion systems commonly suffers from air and fuel imbalances at the burners. Stoichiometries local to the burners must be maintained in order to achieve ultra low NO

2、x performance without significantly sacrificing combustion efficiency. In addition to the emission benefits, improvement of the air and fuel balance results in less slagging and reduced furnace wall corrosion. He paper presents results and benefits associated with operating coal fired boilers using

3、Foster Wheeler and TR-Techs Electric Charge Transfer （ECT） coal flow measurement technology. ECT systems provide boiler operators with continuous on-line indication of coal flow distribution, conduit velocity and particle fineness. The paper will show devices that control the coal flow balance. ECT

4、technology in conjunction with Foster Wheelers solutions for coal flow balancing is opening up an entire new spectrum in operational assessment and improvement as well as emission control. Ultra Low NOx Combustion New NOx regulations demand drastically reduced NOx emissions from fossil fired boilers

5、. With a few exceptions, the NOx limits for ozone control during the summer months require a post-combustion control method such as SCR on coal fired boilers, because Low NOx firing systems alone can not achieve compliance. However, investment costs and ammonia costs of an SCR DeNOx catalyst can be

6、reduced, if the output NOx from the firing system is low. Thus, more stringent emission limits and the addition of post combustion NOx control create the need for improvements of NOx emissions from the existing Low NOx coal firing systems. Regardless of the NOx reduction approach, many current low N

7、Ox systems are limited in their ability to provide significant additional reductions in NOx. New multi air zone burner designs, special coal nozzle tips, etc dont provide the reductions being sought by utilities wanting to minimize or eliminate post combustion systems.In anticipation of these requir

8、ements, Foster Wheeler has been developing new technologies to go beyond just “burner components”. Our evaluation of operating LNB systems shows that many are limited from further NOx reduction by “non burner“ barriers. By addressing and eliminating each of these, significant reductions are possible

9、. One of the most common barriers to lower NOx is related to poor coal and air distribution. These can include high unburned carbon, high CO, furnace slagging, oxygen and/or steam temperature imbalance, corrosion, etc. All low NOx firing systems depend on a defined balance of the air and coal at the

10、 burners. By monitoring and controlling the air and coal flow to the burners, existing as well as new systems greatly benefit from lower emissions and improved boiler operation. Or, if you use the following analogy for boiler emission improvement: This trend is comparable to the change from carburet

11、ors to fuel injection systems seen over time in the car industry. Foster Wheeler strongly believes that future ultra low NOx firing systems need a tight control of the air and fuel balance at each burner in the system, regardless whether it is tangential, wall or arch fired /1/. Many pulverized coal

12、 boilers experience some of the problems associated with poor air and fuel distribution:* Poor emission performance * Increased ammonia consumption of SCR and SNCR systems * Increased unburned carbon in the fly ash * Distorted oxygen profile at boiler outlet * Uneven steam temperature profiles * Fla

13、me impingement * Increased slagging * Water wall wastageAny deviation from the design air/fuel balance at individual burners result in some burners operating at a fuel lean or a fuel rich condition. The fuel rich burners are producing large amounts of CO, high LOI and longer flames while locally low

14、ering the oxygen level in the flue gas. On the other hand, the fuel lean burners produce high NOx levels at elevated O2. The outcome at the boiler exit is a flue gas with high CO and high NOx. In addition, LOI is elevated due to the burners operating at low stoichiometries. This paper shows some of

15、the successes achieved by balancing air and fuel flow in a boiler. Most Low NOx Burners and all Tangential Firing Systems allow air flow control at the burners. These are adjusted mainly during initial optimization of the Low NOx system after a retrofit. Usually, it was not necessary to address dist

16、ribution changes with load and degradation of system performance with time. In the recent past, several vendors developed control strategies and software to improve boiler and emission performance. While this is the step needed for improvement, most of the systems lack reliable flow measurement and

17、control of air and fuel.Foster Wheeler uses burner air measurement to determine the secondary airflow and uses thealready existing control devices to modulate the flow. ECT Coal Flow MeasurementFor continuous boiler optimization, an on-line measurement of the fuel flow in each conduit is required fo

18、r on-line optimization of the air and coal balance at each burner. This technology is one of the vital steps towards an Ultra-Low NOx Firing System. Foster Wheeler is partnering with TR-Tech International Oy of Finland to market the Electric Charge Transfer technology （ECT） worldwide. Foster Wheeler

19、 is the global distributor of the ECT system. The patented technology measures the electric charges present in any two-phase flow transport and uses the signals to determine the following characteristics of the flow. * ECT measures the relative coal distribution between the conduits. In addition, th

20、e system can be configured to measure the flow velocity and the absolute flow in each conduit. Coal flow balance is the key measurement for continuous Ultra Low NOx combustion. * The high data collection rate of the ECT system allows monitoring also unsteady phenomena in coal conduits that can cause

21、 problems during plant operation. The signals can be used to detect coal conduit layout due to insufficient primary airflow from the mill and coal conduit surging which results in furnace pressure and emissions fluctuations /2, 3/. * Finally, the ECT system can be applied to monitor the particle siz

22、e changes of the coal flow. The antennas and the hardware used for this system are the same as in the coal flow distribution application. Thus, the ECT system can be used to monitor mill performance on-line assuring proper coal fineness is maintained to minimize unburned carbon. The configuration of

23、 the system is described in more detail in /4/. The ECT system consists of receiving antennas in each coal conduit that are connected to a signal conditioning unit housed in a cabinet. The signals from these conditioning unit is received by personal computers that are used for data processing and an

24、alysis. TR-Techs proprietary software is used to determine the balance between the conduits of one mill, to display the results to the operator and to feed the data via a network to the plants DCS system or a continuos combustion optimization software running on a separate computer. The antennas are

25、 easily installed through the horizontal or vertical wall of the existing conduit and inserted into the coal stream. Three antennas in each conduit are needed for coal flow balance measurement and six for coal flow and velocity measurement. Their location in the pipe wall is determined so that the e

26、ffects of coal ropes on the measurement results are minimized. Antennas are made of tungsten carbide to ensure long operating life. The installation is very simple and requires only a mill taken out of service for several hours which minimizes lost generating capacity. After installation, the ECT me

27、asurement is verified by a standard ASME or Rotorprobe sampling procedures and the system is then ready to be used. The ECT system offers several distinct advantages: * All information is continuous and on-line. * The ECT measurement is not effected by coal type, moisture, ash content or coal roping

28、. * The electronics can be located up to 1200 feet from the conduits. No cabinets are needed on the burner decks. * The abrasion resistant antennas in the coal conduit are passive and need no power supply. * The installation is easy. The antennas can be installed during short mill outages. ECT syste

29、ms have been successfully installed on industrial plants and many utility steam generators. In general, the results of the ECT method compare very well with a standard ASME probe test even at extreme shifts of the coal flow between the conduits. This confirms the viability of the technology for real

30、-time coal balancing applications. Since 1998 ECT was installed at nine utility power plants and five installations are scheduled for 2001.Distributors In many tangentially fired plants riffle boxes are installed after an exhauster to distribute the fuel. These designs can be retrofitted with adjust

31、able riffle boxes to achieve improved fuel distribution. Adjustable riffle boxes （Figure 5） allow biasing the particle flow towards individual conduits. The design is similar to the fixed rifflers, but adjustable vanes are used at the riffler inlet. The change of a fuel system without distributors t

32、o this design requires additional space above the pulverizers which might be limited in retrofit applications.The Foster Wheeler Three-Way Distributor is shown in Figure 6 on top of a heart-shaped classifier. The single outlet of the mill is distributed in a vertical pipe to three outlets. Distribution fingers that can be pushed into the flow bias the flow from the central inlet pipe at