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ZHANG F, WU L W, ZHANG Q Y. Analysis of the condensate water distribution of a steam-powered system in different working conditions [J]. Chinese Journal of Ship Research, 2021, 16(2): 188–193 doi: 10.19693/j.issn.1673-3185.01686
Citation: ZHANG F, WU L W, ZHANG Q Y. Analysis of the condensate water distribution of a steam-powered system in different working conditions [J]. Chinese Journal of Ship Research, 2021, 16(2): 188–193 doi: 10.19693/j.issn.1673-3185.01686

Analysis of the condensate water distribution of a steam-powered system in different working conditions

doi: 10.19693/j.issn.1673-3185.01686
  • Received Date: 2019-07-23
  • Rev Recd Date: 2019-12-26
  • Available Online: 2020-09-12
  • Publish Date: 2021-04-01
  •   Objectives   To meet the use requirements of a steam-powered system in different working conditions, it is necessary to study the design of the condensate water distribution and pipeline optimization.  Methods  Using the Flowmaster software, a simulation model of a ship's condensate water system was created. The pressure and flow rate in the condensate water system were studied in different working conditions of the steam-powered system. Based on this, two optimal design suggestions, reducing the installation height of the water tank and adjusting the system pipeline connection, were presented.  Results  The calculation results showed that the maximum storage capacity is 0.128 (normalization result) when the openings of the throttle valve and circulation valve are 30% and 45% respectively, in reduced working conditions. Moreover, when the throttle valve opening is less than 13%, the condensate water system will not be able to store water. The maximum storage capacity was 0.404 (normalization result) when the openings of the throttle valve and the circulation valve were 90% and 18% respectively, in increased working conditions. The distribution coordination of the system was also better. Two optimization designs can effectively improve the condensate water distribution in reduced working conditions.  Conclusions  The research results can provide a reference for the optimal design of the actual ship's condensate water system.
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    YE S T, LUO X L. Coordinated control for flow regulation in branch pipes[J]. Control and Instruments in Chemical Industry, 2014, 41(6): 352–356 (in Chinese).
    [2] 周玉文, 何敏, 方琦. 基于GIS的给水管网动态水力计算模型的建立与应用[J]. 给水排水, 2006, 32(8): 96–100. doi: 10.3969/j.issn.1002-8471.2006.08.026

    ZHOU Y W, HE M, FANG Q. Establishment and implication of GIS based dynamic hydraulic calculation model for water supply network[J]. Water & Wastewater Engineering, 2006, 32(8): 96–100 (in Chinese). doi: 10.3969/j.issn.1002-8471.2006.08.026
    [3] LUO X X, YUAN M Z, WANG H, et al. On steam pipe network modeling and flow rate calculation[J]. Procedia Engineering, 2012, 29: 1897–1903. doi: 10.1016/j.proeng.2012.01.233
    [4] JIE P F, ZHU N, NA W, et al. RETRACTED: establishment and solution of the model for loop pipeline network with multiple heat sources[J]. Energy, 2011, 36(9): 5547–5555. doi: 10.1016/j.energy.2011.07.018
    [5] MILLER D S. Internal flow systems[M]. 2nd ed. London, UK: British Hydromechanics Research Association, 1990.
    [6] TVEIT T M, FOGELHOLM C J. Multi-period steam turbine network optimization, Part II: development of a multi-period MINLP model of a utility system[J]. Applied Thermal Engineering, 2006, 26(14/15): 1730–1736.
    [7] TIAN Z G, MENG X Y, ZHANG H F. Design and realization on distributed network system for on-line monitoring and fault diagnosis in the steam turbine generator sets[J]. Turbine Technology, 2005, 47(6): 401–403, 419.
    [8] JIANG S Z, YONG Q W, JIANG M, et al. Experimental research and universal hydraulic calculation of pipe flow[J]. Journal of Logistical Engineering University, 2005, 21(4): 53–56.
    [9] 刘方, 吴鹏飞. 船舶淡水冷却系统流量分配的探析[J]. 船海工程, 2012, 41(5): 87–90, 94. doi: 10.3963/j.issn.1671-7953.2012.05.024

    LIU F, WU P F. The flow distribution analysis of vessel's fresh water cooling system[J]. Ship & Ocean Engineering, 2012, 41(5): 87–90, 94 (in Chinese). doi: 10.3963/j.issn.1671-7953.2012.05.024
    [10] 张文斌, 张连山, 魏丹丹, 等. 凝水泵出口压力波动问题机理研究[J]. 船舶工程, 2017, 39(9): 20–23.

    ZHANG W B, ZHANG L S, WEI D D, et al. Mechanism investigation for outlet pressure fluctuation of condensate pump[J]. Ship Engineering, 2017, 39(9): 20–23 (in Chinese).
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Analysis of the condensate water distribution of a steam-powered system in different working conditions

doi: 10.19693/j.issn.1673-3185.01686

Abstract:   Objectives   To meet the use requirements of a steam-powered system in different working conditions, it is necessary to study the design of the condensate water distribution and pipeline optimization.  Methods  Using the Flowmaster software, a simulation model of a ship's condensate water system was created. The pressure and flow rate in the condensate water system were studied in different working conditions of the steam-powered system. Based on this, two optimal design suggestions, reducing the installation height of the water tank and adjusting the system pipeline connection, were presented.  Results  The calculation results showed that the maximum storage capacity is 0.128 (normalization result) when the openings of the throttle valve and circulation valve are 30% and 45% respectively, in reduced working conditions. Moreover, when the throttle valve opening is less than 13%, the condensate water system will not be able to store water. The maximum storage capacity was 0.404 (normalization result) when the openings of the throttle valve and the circulation valve were 90% and 18% respectively, in increased working conditions. The distribution coordination of the system was also better. Two optimization designs can effectively improve the condensate water distribution in reduced working conditions.  Conclusions  The research results can provide a reference for the optimal design of the actual ship's condensate water system.

ZHANG F, WU L W, ZHANG Q Y. Analysis of the condensate water distribution of a steam-powered system in different working conditions [J]. Chinese Journal of Ship Research, 2021, 16(2): 188–193 doi: 10.19693/j.issn.1673-3185.01686
Citation: ZHANG F, WU L W, ZHANG Q Y. Analysis of the condensate water distribution of a steam-powered system in different working conditions [J]. Chinese Journal of Ship Research, 2021, 16(2): 188–193 doi: 10.19693/j.issn.1673-3185.01686
  • 凝水系统是船用蒸汽动力系统中连接冷凝器、凝水泵、除氧器等设备的关键纽带,通过凝水节流调节阀、循环调节阀以及储水调节阀等控制元件,即可实现凝水系统的协调分配,从而满足系统在不同运行工况下的凝水流量和压力要求。如果系统的设计或布置方案不合理,则3个调节阀的组合使用将无法实现凝水系统的协调分配,进而导致凝水流量分配不均、部分设备的凝水流量过大或过小,最终影响整个凝水管网的稳定运行[1-4]

    近年来,国内外学者针对凝水管网的水力计算开展了大量研究工作。Miller[5]开展了常见元器件(例如,直管段、三通、弯头、阀门等)在不同雷诺数以及组合方式下的阻力特性分析,所得实验数据已被广泛应用于工程实践。Tveit等[6]、Tian等[7]和Jiang等[8]研究了环状及枝状等管网的水力损失情况,得出枝状管网的水力损失小于环状管网的结论。刘方等[9]针对船舶淡水冷却系统的流量分配,提出了新的流量补偿计算方法。张文斌等[10]研究了系统参数对凝水泵运行边界条件的影响。然而,现有研究大多针对的是单一稳定工况,鲜有针对系统多运行工况在不同控制方案下的凝水流量分配的研究成果。

    基于此,本文拟采用Flowmaster仿真计算软件,建立船舶凝水系统的管网仿真模型,分析凝水系统在不同运行工况下的分配协调性,用以为实船凝水系统设计和优化提供参考。

    • 搭建船用蒸汽动力凝水系统的某陆上试验台架,其组成结构如图1所示。凝水泵从冷凝器中抽取凝水,加压之后经滤器输送至除氧器。同时,系统中设有再循环管路和储水管路,分别用于冷凝器中液位偏低时的凝水再循环和除氧器中液位偏高时将部分凝水输送至水柜。选择冷凝器的安装高度为基准高度,水柜和除氧器分别位于基准高度10 m和6 m以上的位置。

      Figure 1.  The connection diagram of condensate water system

      为实现凝水的有效分配,需分别设置凝水节流阀、循环阀和储水阀这3个控制元件。其中,节流阀和循环阀配合使用,且动作方向相反,用以精确控制冷凝器的液位;储水阀通过在除氧器之前对凝水进行分流来控制除氧器的液位。

    • Flowmaster软件采用流体网络分析方法,首先将系统简化为节点和管段,然后联立求解流体的连续性方程、动量方程和能量方程。假设某管网由B条管段和N+1个节点组成,其网络模型的数学表达形式如下:

      $${{\mathit{\boldsymbol{A}}}} \cdot {{\mathit{\boldsymbol{G}}}} = \frac{{{\rm{d}}{{\mathit{\boldsymbol{M}}}}}}{{{\rm{d}}t}}$$ (1)
      $${{{\mathit{\boldsymbol{A}}}}^{\rm{T}}} \cdot p = {{\mathit{\boldsymbol{S}}}} \cdot \left| {{\mathit{\boldsymbol{G}}}} \right| \cdot {{\mathit{\boldsymbol{G}}}} + \rho g{{\mathit{\boldsymbol{Z}}}} - {{\mathit{\boldsymbol{D}}}} - L\frac{{{\rm{d}}{{\mathit{\boldsymbol{G}}}}}}{{{\rm{d}}t}}$$ (2)
      $$\overline A \cdot q - \underline A \cdot (q + r) = \frac{{{\rm{d}}H}}{{{\rm{d}}t}}$$ (3)

      式中:A为管网的N×B阶关联矩阵;G为支路的流量,其为B阶列向量;M为节点质量,其为N阶列向量;t为时间;AT为管网的B×N阶关联矩阵;p为节点处的压力;S为各支路的阻力系数,为B×B阶对角矩阵;ρ为节点处的流体密度;g为重力加速度;Z为管段高度差,其为B阶列向量;D为支路上的动力源升压,其为B阶列向量;L为各管段的流感,在数值上等于流量变化1个单位时引起的压力变化量;$\overline A \cdot q$为各支路流入节点的热流量之和,其中q为热流密度;$\underline A \cdot (q + r)$为各支路流出节点的热流量之和,其中r为热交换量;H为各节点的焓值。

      利用Flowmaster仿真计算软件建立船用蒸汽动力凝水系统的仿真模型,如图2所示,其中数字1~22为管路节点标识符。

      Figure 2.  The simulation model of condensate water system

      为便于计算,凝水系统中的滤器、弯头等器件均采用阻力元件来模拟其压力损失。由于本文将主要研究稳态运行工况下凝水系统各支路的压力和流量分布情况,而不考虑冷凝器等容器的液位动态控制,故可将冷凝器、除氧器和水柜均设定为固定压力容器(组件仅有一个接口),且水柜通大气。本文将凝水泵抽取源和循环管路回水源分开设置,其他参数均按照陆上试验系统在高/低工况下的实际性能参数进行设置。为便于对比分析,所有参数均以系统在高工况下的额定值为基准进行归一化处理,其中:冷凝器、除氧器的工作压力分别为−0.2,0.06;节流阀、循环阀和储水阀均为线性特性,节流阀的流量系数CV=1,循环阀和储水阀的流量系数CV=0.32。

    • 计算低工况下凝水系统的分配情况时,需重点监测节流阀后、循环阀后和储水阀后的压力值,以及节流阀后、循环阀后、除氧器前和储水阀后的流量值。由于该系统设有3个调节阀,为便于分析,本文将针对2种运行情况开展研究,分别为:在节流阀和循环阀定阀位下,研究储水阀的储水能力;在储水阀定阀位下,研究节流阀和循环阀在不同开度的凝水流量分配情况。

      首先,取常用状态的阀门开度值,将节流阀和循环阀的开度分别设为30%和45%,而储水阀则从0开始,以10%的步长增加阀门开度,直至全开。凝水系统压力和流量分配情况的仿真结果如图3所示。为验证仿真模型的准确性,本文将模型计算结果与试验数据(源自图1所示的陆上试验台架实测结果)进行了对比。由图3可以看出,仿真结果与试验数据基本吻合,验证了本文仿真模型的准确性;随着储水阀开度的不断增加,节流阀和循环阀后的压力有所降低,而储水阀后的压力则缓慢升高;同时,除氧器前的凝水流量逐渐降低,而储水流量则不断增加;当储水阀全开时,储水流量约为0.128。

      Figure 3.  The influence of storage valve opening on condensate water distribution under low working condition

      然后,根据低工况下的系统运行状态,按照表1设置节流阀和循环阀的开度,而储水阀的开度则固定为80%,其凝水分配情况的仿真结果如图4所示。

      组合序号节流阀开度/%循环阀开度/%储水阀开度/%
      189080
      2108580
      3138080
      4157580
      5207080
      6256080
      7304580
      8403080
      9501580
      1060580

      Table 1.  Opening combination of different regulating valves under low working condition

      Figure 4.  The influence of throttle valve and recirculation valve openings on condensate water distribution under low working condition

      图4可以看出:随着节流阀逐渐开大和循环阀逐渐关小,节流阀和储水阀后的压力随之不断增加,而循环阀后的压力则逐渐降低,直至接近冷凝器的真空值;同时,经节流阀进入除氧器和经储水阀进入水柜的凝水流量不断增加,而再循环流量则不断减小。图4还呈现了一个非常重要的问题,即当节流阀开度小于13%时,储水阀后的流量为负,这说明此时储水阀中的凝水为倒流状态,也即水柜中的凝水将倒流进入除氧器,因此此时不仅无法实现储水,反而还会导致对除氧器的反向补水。

      综上所述,在低工况下,仅当节流阀开度大于13%时,3个调节阀才可以实现对凝水分配系统的有效管理;当节流阀处于小开度时,凝水系统将无法实现储水功能;在节流阀处于30%、循环阀处于45%的常用工况下,最大储水量为0.128,储水能力较为有限。

    • 在高工况下,凝水系统的蒸发量较大,大量凝水将进入除氧器,即凝水的再循环量较小,故节流阀将处于高阀位,而循环阀则处于低阀位。

      首先,根据系统运行状态,将节流阀和循环阀的开度分别设为90%和18%,而储水阀则从0开始,以10%的步长增加阀门开度,直至全开。凝水系统压力和流量分配情况的仿真结果如图5所示。由图中可看出:随着储水阀开度的不断增加,节流阀和循环阀后的压力逐渐降低,而储水阀后的压力则有所增加,且其增加速率明显高于低工况;当储水阀的开度增加时,储水流量快速升高,而进入除氧器的流量则明显减小,这说明此时凝水分配的协调性更好;当储水阀全开时,储水流量约为0.404。

      Figure 5.  The influence of storage valve opening on condensate water distribution under high working condition

      然后,根据高工况下的系统运行状态,按照表2设置节流阀和循环阀的开度,而储水阀的开度则固定为80%,其凝水分配情况的仿真结果如图6所示。由图中可以看出:相较于低工况,高工况下节流阀后与储水阀后的压力差更大;在调节阀的各种组合控制方案下,凝水分配协调性的改善效果更为明显。

      组合序号节流阀开度/%循环阀开度/%储水阀开度/%
      1707780
      2756580
      3775580
      4804780
      5824080
      6853380
      7872580
      8901880
      9951080

      Table 2.  Opening combination of different regulating valves under high working condition

      Figure 6.  The influence of throttle valve and recirculation valve openings on condensate water distribution under high working condition

    • 为解决现有设计方案在低工况下凝水存储能力不足,甚至储水阀的凝水倒流问题,并保证系统的原组成设备性能不变,本文基于凝水系统管路布置提出了2种优化设计方案,用以为实船应用提供参考。

      第1种方案是调整设备的安装高度。为了减小储水阻力,可以适当降低水柜的安装高度。为了避免在任何运行工况下的凝水倒流问题,需保证水柜与除氧器的高度差加上水柜液面高度小于除氧器压力值所对应的水柱高度。经分析,在保证除氧器安装高度不变的前提下,水柜的安装高度应不大于8 m。因此,第1种优化方案将水柜的安装高度修改为8 m,其他均与原方案保持一致。

      第2种方案是在不调整系统设备安装位置的前提下,将储水管路连接至节流阀之前,以增加储水压头,从而保证储水阀前的足够压力。

      根据表1设置阀门的运行状态,2种优化方案与原方案的储水能力仿真对比结果如图7所示。

      Figure 7.  Comparison of water storage capacity between two optimized design schemes and the original design scheme under low working condition

      图7可以看出,2种优化设计方案均可以改善储水能力,尤其是节流阀小开度时的储水能力存在明显提升;在各种阀门组合控制下,均未出现凝水经储水阀倒流的现象,从而解决了低工况下凝水系统的储水问题。

    • 本文基于船用蒸汽动力凝水系统的仿真模型,进行了高工况和低工况下的凝水分配协调性分析。结果显示,在低工况下,不仅储水能力非常有限,而且还出现了凝水系统无法储水,甚至是水柜凝水倒流进入除氧器的问题;在高工况下,凝水分配的协调性相对较好。同时,本文还提出了降低水柜安装高度和调整系统管路连接方式这2种优化设计方案,计算验证结果表明,该优化方案可以有效改善低工况下的凝水分配协调性。

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