文章编号:1006-7043(2001)06-0012-04
庞凤阁，明申金，贾 辉，闫素英
(哈尔滨工程大学动力与核能工程学院，黑龙江哈尔滨150001)
摘 要：对热力除氧器和给水加热器进行了对比火用分析，从除氧器与低压给水加热器的火用分析经济指标比 较来看，低压给水加热器火用效率较除氧器排汽回收情况及除氧器排汽不回收都要低(63.6>61.0%>53.9%)，而火用损系数较除氧器排汽回收和排汽不回收两种情况都要高(0.201%<0.215%<0.260%).所以，除氧器的火用经济指标较给水加热器要好些.得出结论是：在动力装置中除氧器和给水加热器的火用损失系数都不大，除氧器的火用效率略高于给水加热器.从能量利用经济性的观点来看，除氧器可以取代给水加热器.这样不仅可以提高循环的热效率，而且可以增加设备和系统的使用寿命.①关 键 词：火用分析；除氧器；给水加热器中图分类号:T K223 文献标识码:A
目前在某些船用蒸汽动力装置中，未设除氧器而设有给水加热器，除氧功能是由冷凝器来兼任的.由于冷凝器运行时参数的波动，除氧效果得不到保障，这造成了整个动力装置的腐蚀严重，从而带来安全性
和可靠性上的隐患.若在这些动力装置中采用除氧器而不设给水加热器，则可以很好地解决氧腐蚀带来的问题.本文正是从火用分析的角度来论证用除氧器取代给水加热器的可行性.
1 物流火用
对于一个物流而言，设其热力学参数分别为压力p (Pa )，温度T (K )，比熵s (J Πkg ・K )、比焓h (J Πkg )，流量为G (kg Πs )，流速为u (m Πs )，单位质量位势gz (J Πkg )，则由火用的定义得出此物流火用的计算式
[1～4]
为
E x =G 〔(h -h e )-T e (s -s e )+
u
2
2
+gz 〕
(1)
物流的比火用为
e x =E x ΠG
(2)
式中:h e ,s e 分别为物流与环境处于力平衡和热平衡时所具有的比焓与比熵.
许多情况下，动能和势能项很小，可以忽略.此时物流火用的计算式为
E x =G [(h -h e )-T e (s -s e )](1a ) 比火用为
e x =E x ΠG =(h -h c )-T e (s -s e )(2a
)
pdsc
图1 除氧器和给水加热器火用分析模型
Fig.1 Exergy analyses model of the deatertor
and the feed water heater
式中T e 为环境温度,K.
2 除氧器和给水加热器对比火用分析
模型
热力除氧器和管壳式给水加热器火用分析模型
如图1所示[5]
.假设除氧器和给水加热器的进水温度和进汽的热力学参数分别一致.不妨设进水温度为T w ；进汽温度为T s ，比火用为e xs .且设环境温度为T e ；而除氧器的进水比火用为e xw ，出水温度为T o ，比火用为e o ，排汽温度为T c ，比火用为e xc ；给水加热器的进水比火用为e ′xw ，出水温度为T ′o ，比火用为e ′xo ，冷凝水温度为T ′sat ，比火用为e ′xsat .又设除氧器的进水流量为G w ，进汽流量为G s ，出水流量
①收稿日期:2001-05-28；修订日期:2001-11-19. 作者简介：庞凤阁(1945-)，男，吉林公主岭人，教授，主要研究方向为核动力装置性能.
第22卷第6期 哈 尔 滨 工 程 大 学 学 报 Vol.22,№.62001年12月 Journal of Harbin Engineering University Dec.,2001
为G
o
ldo，排汽流量为G c，除氧器本体压力为p，除
氧器内的火用损失为ΔE；设给水加热器的进水流量
同样为G
w
，而进汽流量为G′s，且进汽完全凝结
成饱和水，汽侧压力为p′
s
，水侧压力为p′w，给水加热器内的火用损失为ΔE′.
将式(2)应用于除氧器和给水加热器有
进汽比火用为
e xs=(h s-h e)-T e(s s-s e)+u2s
2
+gz s
除氧器进水比火用为
e xw=(h w-h e)-T e(s w-s e)+u2w
2
+gz w
除氧器出水比火用为
e xo=(h o-h e)-T e(s o-s e)+u2o
2
+gz o
除氧器的排汽比火用为
e xc=(h c-h e)-T e(s c-s e)+u2c
2
+gz c
给水加热器进水比火用为
e′xw=(h′w-h e)-T e(s′w-s e)+u′2w
2
+gz′w
给水加热器出水比火用为
e′xo=(h′o-h e)-T e(s′o-s e)+u′2o
2
+gz′o
给水加热器凝结水的比火用为
e′xsat=(h′sat-h e)-T e(s′sat-
s e)+u′2sat
2
+gz′sat
从而，对于除氧器:
进水带入的火用为
E w=G w e xw 进汽带入的火用为
E s=G s e xs 出水带出的火用为
E o=G o e xo 排汽带出的火用为
E c=G c e xc 同理，对于给水加热器：进水带入的火用为
E′w=G w e′xw 进汽带入的火用为
E′s=G′s e xs 出水带出的火用为
E′o=G w e′xo 凝结水带出的火用为
eisE′c=G′s e′xsat
广西劳动力市场 对于除氧器，若有排汽回收装置，则E
c并未在除氧这一过程中损失掉.在此种条件下，除氧器的火用效率为
η
ex
=
E c+E o
E w+E s
×100%
设除氧器所在的动力装置的总供给火用为E
t
，则除氧器的火用损系数为
Δη
ex
=
(E w+E s)-(E c+E o)
E t
×100%
又若除氧器的排汽直接排入环境而浪费掉，则除氧器的火用效率为
η
ex
=
E o
E w+E s
×100%
相应地，火用损失系数为
Δη
ex
=
E w+E s-E o
E t
×100%
对船用给水加热器而言，由于凝水直接排入冷凝器，所以凝水火用损失掉，故其火用效率为
η′
ex
=
E′o
E′w+E′s
×100%
假设动力装置的总供给火用也为E
t
，则火用损失系数为
Δη′
ex
=
E′w+E′s-E′o
E t
×100%
3 除氧器与给水加热器对比火用分析实例
已知条件如表1所示.
对于除氧器，由质量守恒
G w+G s=G o+G c
能量守恒
G w h w+G s h s=G o h o+G c h c
以及排汽率定义
χ=G
cΠG s
解出
G s=
G w(h o-h w)
h s-(1-χ)h o-χh c
=30.87tΠh
从而有
G c=0.926tΠh,G o=279.944tΠh
对于低压给水加热器，能量守恒为
G w h′w+G′s h s=G w h′o+G′s h′sat
・
3
1
・
第6期 庞凤阁，等：除氧器和给水加热器的对比火用分析
表1 热力除氧器及低压给水加热器已知参数表
T able 1 G iven d ata for the deaerator and the feed w ater heater
流量(t ・h
-1
)绝对压力ΠMpa
温度Π℃
除
氧器本 体
0.12
进 水2500.440进 汽待定0.2饱和出 水待定 0.12饱和排 汽排汽率3%
0.12饱和
低压给水加热器
汽侧压力0.2水侧压力 2.4进 水250 2.440进 汽待定0.2饱和出 水250 2.4105冷凝水
同进汽0.2
饱和
表2 除氧器及低压给水加热器热力系统各物流参数表
T able 2 Data of w orking fluid for the deaerator and the feed w ater heater
压力MPa
温度℃
比焓kJ Πkg
小马拉多纳
比熵kJ Π(kg ・K )
进 汽0.2 120.21 2706.31 7.1269 除氧器进水0.4 40 167.86 0.5722 除氧器出水0.12 104.79 439.36 1.3609 除氧器排汽0.12 104.79 2683.46 7.2984 加热器进水 2.4 40 169.63 0.5719 加热器出水 2.4 105 440.45 1.3631 加热器凝水0.2 120.21 504.69 1.5301 环 境
0.1
20
84.01
0.2965
解得
G ′s =
G w (h ′o -h ′w )
h s -h ′sat
=30.75t Πh
2)确定各物流的比火用
由1)中查得物流及环境参数，由式(2a )确定各物流的比火用为
e xw =(h w -h e )-T e (s w -s e )=
2.9092kJ Πkg
e xs =(h s -h e )-T e (s s -s e )=619.9682kJ Πkg
e xo =(h o -h e )-T e (s o -s e )=43.3211kJ Πkg
e xc
=(h c -h e )-T e (s c -s e )=
546.8430kJ Πkg e ′xw =(h ′w -h e )-T e (s ′w -s e )=4.8865kJ Πkg e ′xo =(h ′o -h e )-T e (s ′o -s e )=
43.7662kJ Πkg e ′x sat
=(h ′sat -h e )-T e (s ′sat -s e )=59.0502kJ Πkg
3)确定火用分析指标
(a )除氧器的火用分析指标
在排汽有回收装置的情况下: 火用效率
ηex =G o e xo +G c e xc
G w e xw +G s e xs ×100%=63.6% 火用损失
ΔE x =(G w e xw +G s e xs )-(G o e xo +
G c e xc )=2008.85kW 火用损失系数
Δηex =
ΔE x
E t
×100%=0.201% 在认为排汽火用损失掉的情况下:
火用效率ηex =
G o e xo
G w e xw +G s e xs
×100%=61.0%
火用损失
ΔE x =(G w e xw +G s e xs )-G o e xo =2149.51kW 火用损失系数
Δηex
=ΔE x
E t
×100%=0.215%・
41・ 哈 尔 滨 工 程 大 学 学 报 第22卷
(b )低压给水加热器的火用分析指标火用效率
η′ex =G w e ′xo
G w e ′xw +G ′s e xs ×100%=53.9% 火用损失ΔE ′x =(G w e ′xw +G ′s e xs )-G w e ′xo =
2595.58kW
火用损失系数
Δη′ex =
ΔE ′x
E t
×100%=0.260%4 结 论
1)除氧器及低压给水加热器的火用效率是不
低的(>50%)，且在整个动力装置中它的火用损失
系数又是相当低的(<0.5%)，几乎可以忽略.所
以除氧器和低压给水加热器不是动力装置火用损失的主要环节.
2)从除氧器与低压给水加热器的火用分析指
标比较来看，低压给水加热器火用效率较除氧器排汽回收的情况及除氧器排汽不回收的情况都要低(63.6%>61.0%>53.9%)；而火用损系数较除氧器排汽回收和排汽不回收两种情况都要高
(0.201%<0.215%<0.260%).所以，除氧器的火用经济指标较给水加热器要好些.
3)除氧器与低压给水加热相比，除氧器具有改善动力装置安全性、可靠性及提高装置的运行寿命的功能是低压给水加热器所没有的.因此，用它取代低压给水加热器，既可以保证除氧又可以达到给水加热的要求.
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尔滨工程大学,2000.
[责任编辑：李玲珠]
(上接第3页)
图5 非定常时K F s -J 曲线图及对比
Fig.5 K F s to J curves of unsteady condition
在实际情况中，横向力系数K F z 和垂向力系数K F y 的数量应是相同的，本文的计算结果正表明了这一点.计算结果中的K T 、K Q 随进速系数J 的变化规律符合实际情况.
计算结果表明，本文所提供的全方向推进器运动水动力性能预报的升力面方法可以作为工程设计应用的基础.
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[责任编辑：刘玉明]
・
51・第6期 庞凤阁，等：除氧器和给水加热器的对比火用分析
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