吸尘罩的空气动力性能实验研究

目的 在粉尘发生源处设置适用的局部吸尘罩，是预防尘肺病的有效措施。为了提供适宜吸尘罩的设计，使用了示踪气体法进行优选，但所得到的吸气罩对示踪气体的捕集效率并不代表它对粉尘的捕集效率，因为粉尘有质量，有惯性。因此，在优选出的吸气罩基础上，应通过空气动力学实验，找出其罩口风速分布规律，根据产尘点的控制风速求出吸风量，并提供设计吸尘罩的必需数据。方法 在空气动力学实验台上测定了吸气罩罩口前中心线垂直断面和水平断面的风速分布以及吸气罩的阻力。风速、动压、全压分别采用了热电风速仪、皮脱管和倾斜式微压计测量。结果 (1)实验得出了有延伸挡板与无延伸挡板条缝形和方形吸气罩罩口中心线在垂直断面和水平断面的风速分布状况；(2)根据风速等速线分布，经分析归纳得出了有延伸挡板、无延伸挡板的条缝形、方形旁侧吸气罩罩口相对风速Vx／V0(无因次)和距离(距罩口)Xx／(A的平方根)(无因次)的关系方程式。利用该方程式在设定的控制风速下，可计算出吸气罩的风量；(3)结合玉石雕刻吸尘罩的设计，取产尘点的控制风速Vx=0．5m／s，采用有延伸挡板的条缝形旁侧吸气罩，利用上述方程式可计算出其抽风量Q1=255m^3／h；采用无延伸挡板的条缝罩或有延伸挡板方形罩，可计算出其抽风量分别为Q2=332m^3／h和Q3=360m^／h；前的风量分别为后二的77％和71％，为通风设计手册上砂轮吸尘罩的50％。结论 提供了几种吸尘罩的罩口风速分布规律及相应的计算方法，结合玉石雕刻吸尘罩的设计，揭示了优选出有延伸挡板的条缝形旁侧吸尘罩在玉石雕刻切割轮的最大产尘点处产生同样的控制风速，其抽风量仅为其他形式吸尘罩的77％-50％。这意味着使整套通风除尘系统(包括风管、除尘器、风机等)的初投资和运行费大大节省。因此，吸尘罩的优选设计是通风除尘系统设计中必须解决的关键问题。     

上吸罩流场数值模拟及其控制效果分析

目的研究上吸罩物理参数(罩子高度、挡板宽度、排风量)与捕集效率之间的关系。方法采用计算流体力学软件 FLUENT 建立模型,获得罩子内部气流流场速度矢量图;采用气流数值模拟和物理模型复测相结合的方法,以最大限度符合生产实际的操作条件,研究上吸罩高度、挡板宽度、排风量与捕集效率之间的关系。结果在上吸罩无挡板条件下,系统风量应选择1 320m~3/h;在上吸罩有挡板条件下,系统风量应选择1 078m~3/h,可实现有害气体的快速有效排除。系统在一定风量下,降低罩子安装高度可提高呼吸带平均风速;罩子安装高度和系统风量一定时。加挡板可以提高捕集效率;系统风量一定,无挡板时,捕集效率与控制距离(无因次)呈三次多项式显示的数量关系。结论上吸罩物理参数的改变对选定的呼吸带测点捕集效率产生影响。     

吸尘罩的优选及其在玉石雕刻防尘中的应用

目的对适用吸尘罩进行优选,并在实际通风除尘系统中应用。方法用示踪气体法对吸尘罩进行优选,比较不同吸尘罩捕集效率和风量的关系;对吸尘罩前风速分布进行测定,得出罩前风速分布模型。并对吸尘罩进行空气动力性能分析,测定雕刻排气中粉尘的粒径分级组成和除尘器的粉尘粒径分级除尘效率,评估除尘器的总除尘效率。结果优选出的雕刻吸尘罩,置于切割轮正前方0.11 m处,其控制风速为0.5 m/s,能有效地控制雕刻切割轮的粉尘不向周围扩散,工作地点空气粉尘浓度由无罩时的30-297 mg/m3降低至1.1-1.7 mg/m3,吸尘罩风量为255 m3/h,为其他类型吸尘罩的50%-77%。优选出的冲击水浴除尘器,其除尘效率为97%-98%,阻力为1.5 kPa;滤袋除尘器的效率为98%-99%,阻力为2.5 kPa;除尘后尾气的粉尘浓度为20-30 mg/m3。结论提出了优选吸尘罩的设计方法及实用的除尘器,可供实际应用。     

某公司丝网印刷机局部通风排毒系统改造前后效果评价

目的对某公司丝网印刷机局部通风排毒系统改造前后效果进行比较与评价,为今后改善类似作业环境提供依据。方法对丝网印刷室设备布局、存在的污染物种类进行分析;对丝网印刷机局部排风罩的罩型选择、设计、安装情况进行现场调研与分析;按照规定的方法对局部排风罩的罩口风速及控制点风速进行现场测试;对局部排风罩改进前后丝网印刷工序操作工位污染物浓度进行现场采样及分析。结果局部排风罩正确设计、安装及使用可以有效地提高控制效果;排风罩距污染物发生源的距离较远、罩口风速及控制点风速过低都会影响局部排风罩实际控制效果;罩口围挡可提高局部排风罩的控制效果;净化系统对污染物能否达标排放起到至关重要的作用。结论改造后局部通风排毒系统能够发挥正常功效,可以及时有效地将污染物捕集,通过净化系统将达标气体排放到大气中。     

玉石雕刻作业粉尘控制的适宜技术

目的 提供玉石雕刻行业适宜的防尘技术措施。方法 车间粉尘浓度的测定按照GB／T5748－85、通风除尘系统的测定按照GB／T16157－1996的规定进行，使用WY－1型7级冲击式尘粉分级仪测定排气中粉尘的粒径分级组成和除尘器的粒径分级除尘效率。结果 采用了湿式作业，设置了适用的局部通风除尘系统：设计了专门的条缝型吸尘罩，其侧上吸罩罩口风速为2.5m/s、风量为600m^3/h；根据吸尘罩的数量及各风管的风量选定各支、干风管及总风管的直径；选择了冲击式水浴除尘器或滤袋除尘器，对玉石雕刻通风系统排出的含尘空气进行了除尘净化，除尘器的总除尘效率，前者可达97.0%，后者可达98.0%；根据通风除尘系统所需的风量、克服该系统最大阻力管线所需全压及除尘器的阻力确定了风机的机型和参数。结论 实践结果表明，所提供的玉石雕刻作业粉尘控制的适宜技术，可使作业地点粉尘浓度降低到国家卫生标准或接近卫生标准的要求；通风除尘系统排出的含尘空气可以满足排放标准的要求。     

某食品企业技术改造项目卫生工程效果分析

目的了解卫生工程在技术改造中的作用,对比技术改造前后粉尘浓度的变化,为其他相似项目的技术改造提供借鉴,同时为有关部门的管理提供可靠依据。方法依据国家有关标准、规范的要求对工作场所生产性粉尘浓度、排风罩罩口风速、风量、罩口至工作面的距离、罩口尺寸等进行检测并对检测结果进行评价及分析。结果改造前,工作场所各工位生产性粉尘时间加权平均浓度为8.67~15.10 mg/m3、超限倍数为2.31~3.26,卫生工程通风系统改造后,工作场所各工位生产性粉尘有了明显下降,时间加权平均浓度为3.35~7.07 mg/m3、超限倍数为0.57~1.44。结论卫生工程通风系统改造后,工作场所生产性粉尘浓度的检测结果前后差异明显,能有效降低工作场所生产性粉尘浓度,从而预防职业病的发生。     

某"三资"鞋业成型刷胶工序通风排毒效果评价

某“三资”鞋业是专门生产运动鞋的涉外企业,现有四条生产线,职工2200多人。1　成型生产线主要工序钉内底→刷帮面胶→结帮→刷处理剂→次刷胶→二次刷胶→合成→检验→成品包装2　通风排毒设施以刷帮面胶、刷处理剂、一次刷胶、二次刷胶、合成工序为冷源设置上吸式通风排毒系统,两条生产线共用一个通风机,使用Ｔ472Ｎ08Ｃ低压离心通风机,风量为28105ｍ3/ｈ。3　测试结果及评价经测定,在吸气罩下方(约20ｃｍ处),20个吸气罩控制风速在0.16～0.55ｍ/ｓ之间,罩口风速在0.7～3.2ｍ/ｓ之间,工人作业呼吸带空气中甲苯几何平均浓度在开启风机前为12…     

钳形排风罩应用于熔融态三硝基甲苯近距离的控制效果

目的 研究采用非标钳形排风罩近距离控制尘毒危害的新思路,为局部排风设施设计方法、罩型选取、样机制作提供参考。方法 选取某研究所化学品试制工艺TNT熔混装药工序作为研究对象,采用职业卫生调查、现场检测、气流组织模拟的方法和仿真模拟技术,对其局部排风设施进行设计、改造,对人员作业位TNT浓度、控制风速、钳形排风罩气流组织进行现场检测和发烟测试,并进行分析与评估。结果 仿真模拟结果显示,钳形排风罩罩口缝隙宽度80 mm时,罩口风速在8.0 m/s左右,风速、风压分布较为均匀,排风气流能够将有毒气体捕集至钳形罩内。气流组织模拟实验发现,模拟成料桶侧边缘和最远控制点时的发散烟雾,均能被钳形罩的侧吸气流有效捕捉,基本不受环境风的影响。TNT毒物浓度C_TWA由0.25 mg/m³降至0.03 mg/m³,C_STEL由1.3 mg/m³降至0.03 mg/m³,人员作业区域的控制风速由0.1 m/s提高至0.27 m/s。结论 仿真模拟、气流组织模拟方法与职业卫生检测技术...     

某汽车制造企业通风设施的设计及其防护效果

目的研究某汽车制造企业通风设施的设计情况及其实际防护效果。方法采用职业卫生现场调查和职业卫生检测的方法,对职业病危害因素进行识别和检测;对通风设施进行调查和研究,对风速进行检测。结果经过检测,在通风设施正常开启的情况下,大部分罩口风速、控制风速和操作位风速较大,符合相关标准的要求;冲压和焊接车间的粉尘,焊接车间电焊产生的有害因素,涂装车间油漆、固化剂、稀释剂中的有害因素,总装车间汽油及其燃烧尾气中的有害因素在空气中的浓度均符合GBZ 2.1-2007的要求。结论该汽车制造企业四大车间针对其主要的职业病危害因素,均设计通风除尘防毒设施;虽然风机风量和罩口距离设计上存在一定问题,但总体说来设计较为合理,除尘防毒设计能力有效,可以有效控制职业病危害因素的浓度,可以作为职业病危害控制关键技术的应用示范引导项目并加以推广。     

浅谈通风除尘系统在某红木家具企业中的应用

目的 系统合理地设计通风除尘系统, 有效降低工作场所空气中粉尘危害。
方法 对某红木家具企业进行现场调查分析, 针对性提出职业病防护设施设计方案, 并通过现场检测对比防护设施开启前后各作业点粉尘浓度, 评价防护效果。
结果 该企业采用1套支接局部吸尘罩的树干式集中通风除尘系统, 设计处理风量为4 230 m3/h。在通风除尘系统正常运行状态下, 各局部吸尘罩口控制风速均大于1 m/s, 粉尘浓度合格率为100%。
结论 采用支接局部吸尘罩的树干式集中通风除尘系统, 可对作业场所内空气中粉尘浓度起到有效抑制的作用。
     

Effect of cross current due to worker's arm movement on local exhaust ventilation hood

The effect of cross drafts caused by a worker's arm movements on the capture efficiency of a local exhaust ventilation hood was examined in a laboratory. The performance of the local exhaust hoods (rectangular type and slot type) and the transportation of gaseous contaminants from an emission source to the breathing zone were studied by means of the tracer gas method. Acetone vapor was used as a tracer gas. The worker's arm movement was simulated by a dummy worker and a moving forearm model. The results suggest that a worker's arm movements disturb the exhaustion efficiency and may lead to exposure or leakage from a hood according to exhaust velocity.     

Relationship between physical configuration of hood and velocity for local exhaust systems

The hood performance of a local exhaust ventilation system is determined by the capture velocity and the air flow rate. The equation proposed by Dalla Valle has been widely used to speculate this relationship. However, Dalla Valle used different formulae for slot and plain opening (rectangular) hoods, and the calculated values near the boundary between the slot and plain opening by these formulae do not always match each other. In this study, we measured capture velocity of four hoods by changing the distance from the hood face for different aspect ratios. We also tried to develop an empirical formula to express a relationship that could be applied to both types of hoods. As a result, it was found that the relationship between air velocity in front of exterior hoods and air flow rate could be expressed as the sum of two exponential functions with distance. In addition, when the hood aspect ratio was less than 9 the values of the capture velocity calculated by the proposed equation were in good agreement with the experimental ones.     

Required response time for variable air volume fume hood controllers

This paper describes results from tests made with the aim of investigating how quickly the exhaust air flow rate through fume hoods needs to be controlled in order to prevent contaminants from leaking out of the fume hood and putting the safety of the laboratory personnel at risk. The measurements were made on a laboratory fume hood in a chemical laboratory. There were no other fume hoods in the laboratory, and the measurements were made without interference from persons entering or leaving the laboratory or walking about in it. A tracer gas method was used with the concentration of dinitrogen oxide (N(2)O) being recorded by a Foxboro Miran 101 infra-red gas analyser. In parallel with the tracer gas measurements, the air velocity through the face opening was also measured, as was the control signal to the damper controlling the air flow rate. The measurements show an increased outward leakage of tracer gas from the fume hood if the air flow rate is not re-established within 1-2 s after the sash is opened. If the delay exceeds 3 s the safety function is temporarily defeated. The measurements were made under virtually ideal conditions. Under more typical conditions, the fume hood could be exposed to various other external perturbations, which means that the control system should re-establish the correct exhaust flow more quickly than indicated by the measurement results obtained under these almost ideal conditions.     

The design of local exhaust ventilation hoods for grinding wheels

The simplest method of controlling airborne contaminants produced during grinding is the free-standing local exhaust ventilation hood. However design data are sparse and not related to individual applications, for example neither extract rate nor hood size is related to the wheel size. Hoods for use with grinding wheels are usually designed as captor hoods but it is shown in this study that such hoods act as receptors and should be designed on that basis. Flow visualization, using both smoke pellets and a heated oil-impregnated wire, showed the air flow patterns which are induced by a rapidly rotating wheel. Air speeds around the wheels were measured using omnidirectional probes whilst hood capture efficiencies were measured using tracer gas techniques. These observations and measurements identified several key parameters which should lead to a more effective and efficient design of control systems for use with surface grinders.     

Tracer gas evaluations of local exhaust hood performance]

A local exhaust hood is one of the most commonly used controls for harmful contaminants in the working environment. In Japan, the performance of a hood is evaluated by hood velocity measurements, and administrative performance requirements for hoods are provided as control velocities by the Japanese Industrial Safety and Health Law. However, it is doubtful whether the control velocity would be the most suitable velocity for any industrial hood since the control velocity is not substantiated by actual measurements of the containment ability of each hood. In order to examine the suitability of the control velocity as a performance requirement, a hood performance test by the tracer gas method, using carbon dioxide (CO(2)), was conducted with an exterior type hood in a laboratory. In this study, as an index of the hood performance, capture efficiency defined as the ratio of contaminant quantity captured by the hood to the total generated contaminant quantity, was determined by measuring the CO(2) concentrations. When the assumptive capture point of the contaminant was located at a point 30 cm from the hood opening, a capture efficiency of >90% could be achieved with a suction velocity of less than the current control velocity. Without cross draft, a capture efficiency of >90% could be achieved with a suction velocity of 0.2 m/s (corresponding to 40% of the control velocity) at the capture point. Reduction of the suction velocity to 0.2 m/s caused an 80% decrease in exhaust flow rate. The effect of cross draft, set at 0.3 m/s, on the capture efficiency differed according to its direction. When the direction of the cross draft was normal to the hood centerline, the effect was not recognized and a capture efficiency of >90% could be achieved with a suction velocity of 0.2 m/s. A cross draft from a worker's back (at an angle of 45 degrees to the hood centerline) did not affect the capture efficiency, either. When the cross draft blew at an angle of 135 degrees to the hood centerline, a capture efficiency of >90% could be achieved with a suction velocity of 0.4 m/s. The reduction of suction velocity would beneficially reduce running costs of local exhaust hoods and air conditioning. Effective and economical exhaustion would be achieved if the minimum velocity obtained by the tracer gas method were to be substituted for the excessive control velocity.     

Evaluation of industrial local exhaust hood efficiency by a tracer gas technique

Efficiency of industrial local exhaust ventilation is defined as the ratio of air contaminant quantity captured by the system per unit time to the total contaminant quantity produced by the process per unit time. To date, no direct method exists for this evaluation. This paper describes a tracer gas technique, using sulfur hexafluoride (SF6), which has been developed for the evaluation of local exhaust system efficiency. SF6 was discharged at a known rate into the industrial process generation area. Then, by comparing this quantity to that captured by the exhaust system, as measured in the exhaust duct, hood efficiency is determined. Major advantages of this technique are: The tracer gas technique is able to evaluate directly the hood efficiency. The tracer gas technique is not affected by cross-contamination from nearby industrial processes. The tracer gas technique can be conducted "on site" with minimal interruption of industrial process or interference with workers' duties. The tracer gas, using SF6 is non-toxic. Since SF6 is a gas, this technique may be limited to efficiency evaluation of hoods associated with gases, fumes, vapors, or fine particles.     

Evaluation of Engineering Controls for the Mixing Of Flavorings Containing Diacetyl and other Volatile Ingredients

Exposures to diacetyl, a primary ingredient of butter flavoring, have been shown to cause respiratory disease among workers who mix flavorings. This study focused on evaluating ventilation controls designed to reduce emissions from the flavor mixing tanks, the major source of diacetyl in the plants. Five exhaust hood configurations were evaluated in the laboratory: standard hinged lid-opened, standard hinged lid-closed, hinged lid-slotted, dome with 38-mm gap, and dome with 114-mm gap. Tracer gas tests were performed to evaluate quantitative capture efficiency for each hood. A perforated copper coil was used to simulate an area source within the 1.2-meter diameter mixing tank. Capture efficiencies were measured at four hood exhaust flow rates (2.83, 5.66, 11.3, and 17.0 cubic meters per min) and three cross draft velocities (0, 30, and 60 meters per min). All hoods evaluated performed well with capture efficiencies above 90% for most combinations of exhaust volume and cross drafts. The standard hinged lid was the least expensive to manufacture and had the best average capture efficiency (over 99%) in the closed configuration for all exhaust flow rates and cross drafts. The hinged lid-slotted hood had some of the lowest capture efficiencies at the low exhaust flow rates compared to the other hood designs. The standard hinged lid performed well, even in the open position, and it provided a flexible approach to controlling emissions from mixing tanks. The dome hood gave results comparable to the standard hinged lid but it is more expensive to manufacture. The results of the study indicate that emissions from mixing tanks used in the production of flavorings can be controlled using simple inexpensive exhaust hoods.     

乡镇工业砖瓦厂适用通风除尘技术研究

为了控制乡镇砖瓦厂排放粉尘对室内外空气的污染，在改进工艺的基础上，于各产尘点设置了密闭吸尘罩，有效地控制了粉尘向周围环境扩散。根据破碎、筛分等工序排放的含尘空气及粉尘特性，采用了冲击水浴除尘器除尘，针对风选粉碎机等工序排放的含尘空气及粉尘特性，采用了冲击－喷雾联合除尘器除尘。采用上述有效控制技术后，车间工作地点粉尘浓度由原来的每立方米数百毫克降到卫生标准２ｍｇ／ｍ３以下，两套通风除尘系统排放粉尘浓度降到排放标准１５０ｍｇ／ｍ３以下。冲击水浴除尘器的除尘效率为９７．６％，阻力为１４００Ｐａ；冲击－喷雾联合除尘器的除尘效率为９７．３％，阻力为１９００Ｐａ。两种除尘器排出的污泥可返回作生产原料，无二次污染问题。该除尘器结构简单，易于管理，成本低，便于自行制作。文中还给出了两种除尘器的粒径分级除尘效率，便于其它场合下准确的选用。