<p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US"><font face="Times New Roman">5)</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">当被加热物料的温度过低时</span><span lang="EN-US"><font face="Times New Roman">(</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">例如</span><chmetcnv wst="on" tcsc="0" numbertype="1" negative="False" hasspace="False" sourcevalue="50" unitname="℃"><span lang="EN-US"><font face="Times New Roman">50</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">℃</span></chmetcnv><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">一</span><chmetcnv wst="on" tcsc="0" numbertype="1" negative="False" hasspace="False" sourcevalue="80" unitname="℃"><span lang="EN-US"><font face="Times New Roman">80</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">℃</span></chmetcnv><span lang="EN-US"><font face="Times New Roman">)</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">,因为当在蒸汽工况失常</span><span lang="EN-US"><font face="Times New Roman">(</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">蒸汽总管压力低于设计压力或流量低于设计值</span><span lang="EN-US"><font face="Times New Roman">)</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">时,由于调节阀装在蒸气管线上,蒸汽冷凝液温度可能接近工艺流体</span><span lang="EN-US"><font face="Times New Roman">(</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">即被加热物料</span><span lang="EN-US"><font face="Times New Roman">)</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">的温度,在这个温度下,相应的蒸汽冷凝液压力可能低于大气压,使冷凝液不能正常排除</span><span lang="EN-US"><font face="Times New Roman">(</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">指蒸汽冷凝液疏水阀的背压为大气压的情况</span><span lang="EN-US"><font face="Times New Roman">)</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">。其冷凝液不能正常排除的情况是这样的</span><span lang="EN-US"><font face="Times New Roman">:</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">在出现冷凝液压力低于大气压时,冷凝液在加热器内积聚‘使传热面积减小”,使传热量减小,使被加热物料的温度</span><span lang="EN-US"><font face="Times New Roman">t2</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">下降,这时由于温度调节的作用使调节阀打开</span><span lang="EN-US"><font face="Times New Roman">~</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">使蒸汽流量增加</span><span lang="EN-US"><font face="Times New Roman">~</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">因为这时传热面积还不大,也就是传热量较小</span><span lang="EN-US"><font face="Times New Roman">~</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">所以蒸汽压力</span><span lang="EN-US"><font face="Times New Roman">p2:</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">会增加,当</span><span lang="EN-US"><font face="Times New Roman">p2</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">增加到大于大气压时,冷凝液被疏水阀排除</span><span lang="EN-US"><font face="Times New Roman">~</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">这时传热面又增加“传热量也显著增加”由于汽源供应不足,又会使</span><span lang="EN-US"><font face="Times New Roman">2:</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">显著下降,使冷凝液压力又低于大气压一冷凝液又在加热器内积聚……。可见,加热器内的冷凝液排除是呈脉冲式的,使</span><span lang="EN-US"><font face="Times New Roman">t2</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">将产生很大的波动,这是不允许的。特别应该指出的是,当此种温控方案用于精馏塔的再沸器,而</span><span lang="EN-US"><font face="Times New Roman">t2</font></span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman";">又是敏感塔板的物料温度时,对塔顶产品的产量和纯度将产生很大的影响,后果不可低估</span><span lang="EN-US"><font face="Times New Roman">:</font></span></p>