外文翻译.docx

1、外文翻译Fly-ash removal efficiency in a modified multi-stagebubble column scrubberB.C. Meikap a, M.N. Biswas b,Department of Chemical Engineering, National Institute of Technology (formerly Regional Engineering College),Deemed University, Rourkela 769008, India Department of Chemical Engineering, Indian

2、 Institute of Technology, Kharagpur 721302, India Received 7 January 2002; received in revised form 15 July 2003; accepted 15 July 2003AbstractBubble columns are being widely used in chemical process industries for its various advantages and simplicity. A pilot plan tnovel multi-stage bubble column

3、wet scrubber has been conceived, designed and fabricated. This novel scrubber has been used as dust collecting wet scrubber in presence of other gaseous and vapor pollutants. This paper reports on the detailed experimental investigations carried out on the scrubbing of fly-ash in this novel wet scru

4、bber using water as the scrubbing medium. It has been found that the present system yielded very high efficiency for the scrubbing of fly-ash. In most cases, the fly-ash removal efficiency is more than 95% and many cases approaches 99.5%. A correlation has been developed for prediction of particulat

5、e (fly-ash) removal efficiency. The scale-up of this pilot plant in Indian thermal power plant shows excellent performance and meets the stringent pollution control standards. Attempt has also been made to install the above wet scrubber in Indian Thermal Power Plants and Ceramic Industries to combat

6、 particulate pollution control and found excellent performance. 2003 Elsevier B.V. All rights reserved.Keywords: Air pollution; Wet scrubber; Fly-ash; Modified multi-stage bubble column scrubber; Percentage removal of fly-ash1. IntroductionThe emission of particulate matter (fly-ash) from various in

7、dustrial sources always occurs in association with sulfur dioxide, in varying composition and quantities. The effects of particulate and sulfur dioxide individually are very severe. However, several tox-icological/epidemiological investigations have shown that in the presence of particulate matters

8、synergistically modify the effects of other gases and the combined synergistic effects are much more severe than the simple additive effects of the individual pollutants. This synergism modified effects have motivated the public and private sector industries, government agencies to work out a reliab

9、le background information, enforceable regulations and viable control options for the particulate laden sulfur dioxide emission. The increasingly stringent compliance requirements based on the synergism modified standard has put tremendous constraints on the industries to control particulate laden s

10、ulfur dioxide to a very high degree and the existing pollution control devices like gravity settling chambers, cyclones, bag filters, electrostatic precipitators and wet scrubbers, either alone or in combination, are not fully satisfactory and/or cost effective to meet the demands of the pollution c

11、ontrol regulations.The various wet scrubbers used in practice offer a choice between the liquid dispersed and gas dispersed system. Because of their intrinsic pressure drop and flow rate characteristics, the bubble column may be more convenient than packed column in air pollution control application

12、s involving particulate laden gaseous pollutants. Furthermore, EPA, US 1 has restricted the maximum discharge limits from coal based thermal power plants to 0.1634 g/Nm3 for an Indian thermal power plant. Calculations show that at least 76% removal of particulate less than 2 _m in size isessential t

13、o meet the stringent standards prescribed by EPA. The existing emission standards for particulate matter in India are higher (0.150 g/Nm3) than the proposed World Bank standards of 0.050 g/Nm3. Furthermore, the World Bank guidelines propose that the particulate removal efficiency should be at least

14、99.9% if 50 mg/Nm3 are not achievable and operated at least at 99.5% efficiency. Development of highefficiency systems, which can operate under flexible operating conditions, is thus very much demanded under the above context.Mashelkar 2 reported that, bubble column scrubber (BCR) offers many advant

15、ages like, little maintenance requirement due to simple construction and no problems with sealing due to the absence of moving parts, high liquid phase content for the reaction to take place, excellent heat transfer properties and hence easy temperature control and low initial costs. Survey of the l

16、iterature revealed that various wet scrubbing systems have been used for collecting particulate from waste gas streams. Literature survey also reveals that most of the work reported on the scrubbing of fly-ash, SO2 and fly-ash laden SO2 were used venture scrubbers 3, spray columns 48 and various oth

17、er columns 913.Literature survey further reveals that very little work has been reported on the scrubbing of fly-ash in a bubble column. Ranz and Wong 14 undertook fundamental studies on the mechanisms of collection of dust and smoke particles, in several elementary collectors. The systems reported

18、were rectangular and round aerosol jets impinging on flat plates, cylindrical and spherical collectors placed in aerosol streams (fibrous filters and wet scrubbers). They proposed a correlation for determining the efficiency of impaction, even under the most complicated situations.Calvert et al. 15

19、reported particle collection efficiency and pressure drop for venturi and other atomizing scrubbers. Dullien and Spink 16 used a different hypothesis for the particle capture. They reported removal efficiencies of both mist and dust were in the range of 90100% under conditions where existing theorie

20、s predicted much lower efficiencies.Bandopadhyay and Biswas 7,8 reported experimental investigation on the scrubbing of fly-ash in aspray-cum-bubble column. They reported that, experimental removal efficiency were a strong function of inlet fly-ash loading in both spray and bubble sections.In the bu

21、bble column very limited studies on scrubbing of fly-ash have been reported. Many of the processes reported have been covered by patent protections 1721. In the present investigation a bubble column, operating in three stages have been designedthe staging effect being achieved through hydrodynamical

22、ly induced continuous bubble generation and breakup through bubble rupture and regeneration. The system has been designed to operate with relatively large sized bubbles, so that internal circulation can be induced in the bubbles and faster transfer of gas and fly-ash can take place by turbulent diff

23、usion through the interface of the bubbles and also due to the direct rupture of the relatively large diameter bubbles.Detailed experimental investigations on pressure drop have been carried out on the multi-stage bubble column and reported else where 22. In addition, the performance of the scrubber

24、 is also dependent on disperse phase hold-up, interfacial area of contact and liquid side mass transfer coefficient which have been reported by Meikap et al. 2325. A comparison for energy dissipation (pressure drop), interfacial area of contact and gas hold-up of various types of wet scrubber report

25、ed by Scott 26 like venturi scrubber, spray column with the present system is presented in Table 1. In the present investigation the modified multi-stage bubble column, has been used to investigate the removal of particulate (fly-ash). In the studies the effect of gas flow rate, liquid flow rate, co

26、lumn height and inlet fly-ash loading on percentage removal of fly-ash has been investigated from the airfly-ash mixture with a composition similar to that of existing exhaust of an Indian coal fired thermal power plant.2. Experimental setup and techniquesThe experimental bubble column consisted of

27、a vertical cylindrical Perspex column, 0.1905m in diameter and 2.0m long, fitted onto a fructo-conical bottom of mild steel with a divergence angle of 7 and a height of 0.87 m. The minimum diameter of the fructo-conical section was 0.10 m. The vertical cylindrical column was fitted with a total of f

28、ive hollow disks termed as stages (three contraction disks and two expansion disks). The expansion and contraction disks had central axial openings of 0.095 and 0.0476 m, respectively.At the bottom most section of the cylindrical column, just above the fructo-conical cone, was fitted an antenna type

29、 of sparger 24 of 1.6mm diameter and 144 holes for generating bubbles uniformly throughout the entire cross section of the column. The first contraction disk (known as first stage) of 0.0476m central opening was placed at a height of 0.26m above the sparger. The second disk (second stage) of 0.095m

30、central opening was fitted at a height of 0.52m above the sparger and the third disk (third stage) was fitted at a distance of 0.78m above the sparger. The column is divided into three distinct sections. Section 1 consists of sparger and first contraction disk of 0.26m height, Section 2 consists of

31、first contraction disk, first expansion disk and second contraction disk of 0.78m height and Section 3 a height of 1.30 m. A 0.50m clear space was provided above Section 3, for allowing time for gasliquid separation and also to accommodate bed expansion due to bubbly flow.Experiments were conducted

32、both with a constant liquid batch and continuous liquid down-flow. For conducting experiments with liquid down-flow, a water inlet was provided at a height of 1.80m as shown (L) in Fig. 1. At the bottom of the column a water outlet was provided as shown (WO). Four solenoid valves, at positions V1V4

33、were provided at the liquid and gas inlet and outlet, respectively, for quickly trapping the flow when necessary. The liquid and gas flows into the column were controlled by valves V6V8 and pressure was measured by pressure gauge PG1PG8.The airfly-ash mixture, in composition similar to that existing in th