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technical article
Application of flow meter in gas plant
2011-9-7 15:23:00

煤气流量 测量一直是仪表检测的难点, 但是 锥型流量计 为煤气流量测量提供了新的测量方法, 以下是 锥型流量计在 测量 现场的使用情况和特点。 In daily instrument testing, the measurement of gas flow has always been a difficult point for instrument testing, but the cone flowmeter provides a new measurement method for gas flow measurement. The following are the use conditions and characteristics of the cone flowmeter at the measurement site.
焦炉煤气 一般 一直使用标准孔板 均速管进行计量。 In the past, coke oven gas has always been measured using standard orifice plates and averaging tubes. 使用过程中存在以下几方面的 主要 问题: (1) 由于 焦炉煤气脏, 因此 孔板容易污染, 但是 由于连续生产不能拆除孔板进行清洗, 所以 影响系统测量 精度; (2) 由于 焦炉煤气脏, 因此 仪表导压管 堵塞 所以 必须定期用蒸汽吹扫仪表导压管,否则就会影响测量精度, 严重时 甚至系统不能正常运行; (3) 由于 煤气中所夹带的蒸汽或 水雾,当温度降低时 凝结成水, 因此 在管道中很难排除 影响系统测量精度 (4) 由于 直管段要求长,煤气管道口径通常比较大, 因此 要保证流量测量准确的20~40D 直管段很难满足。 However , there are the following main problems in the use process : (1) The orifice plate is easy to be polluted because the coke oven gas is dirty , but because continuous production cannot remove the orifice plate for cleaning, it affects the accuracy of the system measurement ; (2) Because Coke oven gas is dirty, so the instrument pressure pipe is easy to be blocked , so the instrument pressure pipe must be blown regularly with steam, otherwise the measurement accuracy will be affected , and the system may not operate normally in severe cases ; (3) Steam or water mist will condense into water when the temperature decreases , so it is difficult to exclude it in the pipeline , which will affect the measurement accuracy of the system ; (4) Due to the long requirements of straight pipe sections, the diameter of gas pipelines is usually large, so the flow rate must be guaranteed Accurate measurement of 20 ~ 40D straight pipe is difficult to meet. 低谷时要求输送煤气量的不同,出厂煤气计量的输送量在一天内的变动超过10 1 因此 孔板 流量计 因量程比小就达不到使用要求。 (5) The range ratio is small, only 3 : 1. For example, due to the difference in the amount of gas that is required to be transported at the peak or low of city gas usage , the delivery volume of the factory gas metering fluctuates more than 10 : 1 in one day , so the orifice flow rate Due to the small range ratio, the meter cannot meet the requirements for use.
Measurement principle
管壁摩擦力减小了流过管壁的流体速度, 因此 在管道中流速分布为:在管壁处 流速接近 零, 靠近管线中心流速愈大,在管线中心处 流速 达到 最大。 Because the friction of the pipe wall reduces the velocity of the fluid flowing through the pipe wall , the flow velocity distribution in the pipeline is as follows: the velocity at the pipe wall is close to zero , the closer to the center of the pipeline, the greater the velocity, and the maximum velocity is reached at the center of the pipeline . 锥形流量计是通过在管线中心悬挂一个锥形体来节流 所以 锥体直接与流体高速中心部分相互作用,迫使管线中心的高速流体与接近管壁的低速流体均匀化, 也就是 两者的流速趋于一致。 When the fluid flows through the cone flowmeter, because the cone flowmeter is throttled by hanging a cone in the center of the pipeline , the cone directly interacts with the high-speed center portion of the fluid, forcing the high-speed fluid in the center of the pipeline to approach The low-velocity fluid of the tube wall is homogenized, that is , the flow velocity of the two tends to be the same.
     其它 各种节流装置的结构 比较 :( 1 标准孔板是流体在管道中心 突然收缩,不 阻力损失大,而且 加剧了流体流速分布的不均匀性,管道边缘阻断,脏污介质 容易 聚集在标准孔板前后; 2 文丘里管 和标准孔板 是标准节流装置的一种 ,也 是在管道中心逐渐收缩,虽然流体流速分布的不均匀性仍然存在,但 阻力损失稍有降低, 同时 脏污介质聚集的情况 有所改善, 是制作 比较 困难; 3 环形孔板是在管道中心 的放 置一 圆盘,而管道边缘可 流通, 也就是 从标准孔板的管道中心突然收缩转变为管道边缘突然收缩, 所以 使管道内流速均匀化, 同时也 使脏污介质不 容易 聚集在环形孔板 前后; 4 )而 锥形流量计是在管道中心 的放 置一圆锥,它的结构是管道边缘逐渐收缩,阻力损失小, 且可使管道内流速均匀化, 同时 Compared with the structure of other various throttling devices : ( 1 ) Standard orifice plate is the sudden contraction of fluid in the center of the pipeline , which not only has a large loss of resistance, but also exacerbates the unevenness of the fluid velocity distribution, and the edges of the pipeline are blocked. Dirty media easily accumulate before and after the standard orifice plate; ( 2 ) Venturi tube and standard orifice plate are both a type of standard throttling device , and they gradually shrink in the center of the pipe, although the unevenness of fluid velocity distribution still exists, However, the resistance loss is slightly reduced, and the accumulation of dirty media is also improved, but it is more difficult to make; ( 3 ) a circular orifice plate is a disk placed in the center of the pipe, and the edge of the pipe can be circulated That is , the sudden shrinkage of the center of the pipe from the standard orifice plate to the sudden shrinkage of the pipe edge, so that the flow velocity in the pipe can be uniformized, and at the same time, the dirty media can not be easily gathered around the annular orifice plate ; ( 4 ) cone meter in the center of the pipe is placed opposite a cone, its structure is a pipe edge tapers, resistance loss is small, the flow rate can be made uniform and the pipe, while 使脏污介质不 容易 聚集在环形孔板前后。 Dirty media is not so easy to gather around the annular orifice. 可以 得出结论: 锥形流量计是节流装置发展过程中一系列革新的必然结果。 It can be concluded from this that the conical flowmeter is the inevitable result of a series of innovations in the development of throttling devices.
2. Features
     (1) Low straight pipe requirements. 差压式流量计都是依据伯努利定理 进行测量,但 伯努利定理有一个基本要求, 也就是 被测量的流体必须为理想流体。 Although all differential pressure flowmeters measure according to Bernoulli's theorem , Bernoulli's theorem has a basic requirement, that is , the fluid to be measured must be an ideal fluid. 采用孔板、喷嘴等传统的差压流量计的节流装置时,为了尽量满足伯努利定理的 基本 要求, 因此 必须 有非常长的前、后直管段,以 便将不规则流动的流体尽可能 整形成为理想流体。 When using a traditional differential pressure flow meter throttling device such as orifice plate and nozzle, in order to meet the basic requirements of Bernoulli's theorem as much as possible , it is necessary to have very long front and rear straight pipe sections to facilitate the irregular flow. The fluid should be as perfect as possible . 它们不同的是, 锥形流量计 流量采用独特的置于管道中心的流线型节流结构设计, 因此 在检测流量之前,对不规则流动的流体进行整流, 同时 在不增加流体整流器的情况 妙地解决 流体整流的问题。 Unlike them, the flow of the cone flowmeter uses a unique streamlined throttling structure design placed in the center of the pipe, so before the flow is detected, the irregular flow of fluid is rectified, and without the addition of a fluid rectifier , Cleverly solved the problem of fluid rectification. 中心悬挂的流线型锥体能重塑流速曲线,在紧靠锥体上游和下游较窄的区域内,将流速不规则的液体直接整流成理想液体, 这样 充分满足伯努利定理的要求,获得很高的测量精度和重复性。 Because the center-suspended streamlined cone can reshape the velocity curve, in a narrow area immediately upstream and downstream of the cone, the liquid with irregular velocity can be directly rectified into an ideal liquid, which can fully meet the requirements of Bernoulli's theorem. Obtain high measurement accuracy and repeatability. 不需要非常长的直管段整流,这在流量计的安装过程中有很重要的意义。 And it does not require very long straight pipe rectification, which is of great significance in the flowmeter installation process.

   易堵 (2) Pollution resistance, not easy to block . 孔板流量计和均速管流量计, 但是 由于煤气中含有焦油、萘、硫、氨水等多种杂质,孔板或 均速管必须 定期清洗或 用蒸汽吹扫,否则孔板上下游端面、上游侧直角入口边缘 将受到污染,仪表导压管会 由于 不畅通或 堵塞 导致 系统测量精度 不准 ;孔板前、后直管段 积水会 导致 管道流通面积减小,流速提高,差压增加,流量显示值偏高,严重时 会因为 导压管堵塞,变送器无法正常运行。 For gas flow measurement, the orifice plate flow meter and averaging tube flow meter were originally used , but because gas contains various impurities such as tar, naphthalene, sulfur, ammonia, etc., the orifice plate or averaging tube must be cleaned regularly or Purge with steam, otherwise the downstream end face of the orifice plate and the right-angled inlet edge of the upstream side will be contaminated, and the meter pressure tube will be inaccurate due to the obstruction or blockage of the system ; It will lead to a decrease in the flow area of the pipeline, an increase in the flow rate, an increase in the differential pressure, and a high flow display value. In severe cases, the pressure transmitter tube will be blocked and the transmitter will not operate normally. 能够 正常稳定 运行, 所以 仪表工维护工作量很大。 In order to ensure the normal and stable operation of the meter, the maintenance work of the meter worker is very heavy. 锥形流量计有自吹扫式的结构设计特点, 没有 滞留死区。 However, the conical flowmeter has a self-purging structure design feature, and there is no dead zone. 介质流过锥体时会加速,不断冲刷正压取压孔、锥体外壁及锥体附近管壁, 而负压取压孔则被一小段不流动介质所隔离,脏污杂质进不去,因此锥形流量计可用于各种含杂质、易结晶的脏污介质,如焦炉煤气、发生炉煤气等介质。 Therefore, when the medium flows through the cone, it will accelerate and continuously wash the positive pressure tapping hole, the outer wall of the cone and the pipe wall near the cone. However, the negative pressure tapping hole is isolated by a small section of non-flowing medium, and dirty impurities enter No, so the conical flowmeter can be used for a variety of dirty media containing impurities and easy to crystallize, such as coke oven gas, generator gas and other media.
     (3) Wide range ratio and large differential pressure value, suitable for flow measurement of low pressure and low flow medium. 基本 特点是管道直径大、压力低,流速慢 In the process of gas flow measurement in a coking plant, the basic characteristics of the measurement object are a large pipe diameter, low pressure, and slow flow rate . 孔板流量计一般选配微差压变送 煤气压力为3500Pa 时,正常的差压在 100~1000Pa 之间变化, 因此 流量计的差压信号较小。 Therefore, the orifice plate flowmeter is generally equipped with a micro differential pressure transmitter . When the gas pressure is 3500Pa , the normal differential pressure changes between 100 ~ 1000Pa , so the differential pressure signal of the flowmeter is small. 因为 管道煤气流速低, 所以 差压信号非常小对系统精度影响很大。 In the case of averaging tube flowmeters, because the pipeline gas flow rate is low, the differential pressure signal is very small and has a great impact on system accuracy. 校验、使用的精度;孔板有污染、仪表导压管不畅、管道有积水对系统精度影响也很大。 A small differential pressure signal will affect the accuracy of the calibration and use of the transmitter ; contamination of the orifice plate, the poor impulse of the instrument pressure pipe, and the accumulation of water in the pipeline will greatly affect the accuracy of the system. 锥形流量计的 管道边缘逐渐收缩,阻力损失小,因而可在阻力损失相同的情况下,设计时可选用差压值较大的锥形流量计 The conical flowmeter is a throttling member similar to an orifice plate, and the differential pressure value is much larger than that of an average speed tube. Compared with an orifice plate, the pipe edge of the cone flowmeter gradually shrinks and the resistance loss is small. In the case of the same resistance loss, a cone flowmeter with a large differential pressure value can be selected during design .