0 前言
潮州發電廠1、2號機組為600MW火力發電機組,配1、2、3、4號4臺循環水泵,1號機組用1、2號2臺循泵,2號機組用3、4號2臺循泵,每臺機組的兩臺循泵互為聯鎖備用,2臺機組循泵出口母管通過聯絡門可以互為備用。循泵出口蝶閥為長沙閥門廠生產的重錘式液控止回閥,控制裝置為PLC控制。在實際應用中發現液控蝶閥控(kong)制存在不足,為提高循環水控(kong)制的可靠性,將液控(kong)蝶閥的控(kong)制引入到DCS系統(tong),并在DCS邏輯(ji)中對原有控(kong)制思想進(jin)行優化。
1 改造前的液控蝶閥控制方式和存在的問題
1.1 改造前的控制方式
該廠循環水泵與出口液控(kong)(kong)(kong)蝶(die)閥(fa)之間的(de)聯鎖(suo)邏(luo)輯做在DCS中(zhong),液控(kong)(kong)(kong)蝶(die)閥(fa)自身的(de)控(kong)(kong)(kong)制邏(luo)輯都通過(guo)(guo)(guo)PLC控(kong)(kong)(kong)制,就地(di)開(kai)、關液控(kong)(kong)(kong)蝶(die)閥(fa)指令也送至PLC。開(kai)啟液控(kong)(kong)(kong)蝶(die)閥(fa)和運行過(guo)(guo)(guo)程中(zhong)補壓通過(guo)(guo)(guo)啟動油泵實(shi)現;關閉液控(kong)(kong)(kong)蝶(die)閥(fa)時由電磁鐵帶電打(da)開(kai)泄油通道,利用重錘自身重力關閉蝶(die)閥(fa)。液控(kong)(kong)(kong)蝶(die)閥(fa)油路圖和控(kong)(kong)(kong)制原理圖如圖1、2所示。
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圖1 油路圖
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圖2 液控蝶閥控制原理圖
1.2 液控蝶閥控制系統存在的問題
液控蝶(die)(die)閥與循環水泵存在(zai)著密切的聯系。從保護循環水泵和系統可靠性方(fang)面分析,該廠液控蝶(die)(die)閥控制存在(zai)如下(xia)問題:
(1)液控蝶閥掉錘判斷條件單一(yi),只用關向15°(即(ji)蝶閥已經關閉了(le)75°)信(xin)號(hao)作為條件。若循環水(shui)泵在運(yun)行,關向15°信(xin)號(hao)誤發,將導致循環水(shui)泵跳閘,真空下降,嚴重(zhong)影響(xiang)機組安全運(yun)行;
(2)油(you)(you)(you)壓(ya)低聯啟油(you)(you)(you)泵(beng)補油(you)(you)(you)條件(jian)不合理(li)。從圖(tu)2的PLC原(yuan)理(li)圖(tu)中可知,補油(you)(you)(you)邏輯可簡化如圖(tu)3所示,在(zai)關蝶(die)閥時,關指(zhi)令存在(zai),液壓(ya)油(you)(you)(you)泵(beng)不會聯啟。但(dan)是(shi)當蝶(die)閥關到(dao)位后,關閥指(zhi)令消失(shi),若此時全開(kai)限位未脫(tuo)開(kai),油(you)(you)(you)壓(ya)低信號就會將油(you)(you)(you)泵(beng)聯啟,把蝶(die)閥開(kai)啟,導致母管中循環水倒流,容易損壞循環水泵(beng)且(qie)嚴重影(ying)響機組安全;
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圖3 油壓(ya)低聯鎖啟油泵條件(jian)
(3)控(kong)(kong)制電(dian)源(yuan)取自(zi)電(dian)源(yuan)轉換模塊,且無(wu)冗余配置,一旦電(dian)源(yuan)轉換模塊發生故障,液(ye)控(kong)(kong)蝶閥將失(shi)去(qu)控(kong)(kong)制電(dian)源(yuan),導(dao)致液(ye)控(kong)(kong)蝶閥在(zai)循(xun)環水(shui)泵事(shi)故跳(tiao)閘時不能(neng)聯鎖關閉,同時也導(dao)致液(ye)控(kong)(kong)蝶閥在(zai)液(ye)壓油(you)壓力不足時不能(neng)及時補油(you);
(4)就地控制也(ye)是通(tong)過PLC實(shi)現(xian)(xian),沒(mei)有實(shi)現(xian)(xian)真正意義上的就地控制,如果PLC裝置故障,液(ye)控蝶閥(fa)只(zhi)能通(tong)過圖1中的手搖泵和(he)并(bing)聯手動門(men)開啟和(he)關(guan)閉(bi)蝶閥(fa);
(5)液控(kong)蝶閥(fa)采(cai)用PLC控(kong)制(zhi),液控(kong)蝶閥(fa)的(de)PLC接收(shou)DCS或(huo)就地控(kong)制(zhi)柜的(de)開閥(fa)和(he)關(guan)閥(fa)指(zhi)令,其(qi)開閥(fa)、關(guan)閥(fa)、油(you)壓(ya)低聯(lian)啟油(you)泵(beng)、油(you)壓(ya)高聯(lian)停油(you)泵(beng)邏輯(ji)均在(zai)PLC中實(shi)現(xian)。無(wu)法(fa)在(zai)線監(jian)視和(he)強制(zhi)邏輯(ji),且不(bu)便于事(shi)故分析(xi);
(6)就(jiu)地液(ye)控蝶閥無(wu)(wu)液(ye)壓油壓力變送(song)器,DCS無(wu)(wu)法(fa)監視油壓,不(bu)利于運行人(ren)員提(ti)前判斷(duan)液(ye)控蝶閥是(shi)否(fou)工作(zuo)正常。
2 改造方案內容和實施
2.1 邏輯優化
(1)掉(diao)錘(chui)判斷(duan)條(tiao)件優化。若液控蝶閥掉(diao)錘(chui),會(hui)引起循環(huan)(huan)水(shui)泵(beng)出(chu)(chu)口壓(ya)力(測點在(zai)循環(huan)(huan)水(shui)泵(beng)與蝶閥之間)急劇上升(sheng)。故可將(jiang)循環(huan)(huan)水(shui)泵(beng)出(chu)(chu)口壓(ya)力的高限(xian)值(暫取0.15MPa)作為(wei)一個掉(diao)錘(chui)判斷(duan)條(tiao)件。更改(gai)后邏輯如(ru)下圖4所(suo)示。
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圖4 優化后掉錘判斷條件(jian)
(2)油(you)壓(ya)低(di)聯鎖(suo)啟油(you)泵(beng)條件(jian)優化。油(you)壓(ya)低(di)聯鎖(suo)啟油(you)泵(beng)條件(jian)中加入(ru)開(kai)閥指(zhi)令,開(kai)閥指(zhi)令發(fa)出后由RS觸發(fa)器保持住,不(bu)妨礙油(you)泵(beng)的(de)正常聯鎖(suo)啟。關閥時,關閥指(zhi)令將開(kai)指(zhi)令復位,無論全(quan)開(kai)反饋(kui)是否存(cun)在(zai)都不(bu)會聯啟油(you)泵(beng)。更改后邏輯如圖5所示(shi)。
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圖5 油壓低聯鎖(suo)啟油泵(beng)條件
2.2 液控蝶閥控制進入DCS
該廠采(cai)用(yong)的DCS為日立的H5000M系(xi)統(tong)(tong)(tong),H5000M系(xi)統(tong)(tong)(tong)采(cai)用(yong)雙冗余配置的控(kong)制(zhi)(zhi)器、二重化環(huan)狀冗余網絡和全冗余的電源系(xi)統(tong)(tong)(tong),具有較高的可(ke)靠性。液控(kong)蝶閥控(kong)制(zhi)(zhi)思(si)想改(gai)為DCS邏輯(ji)后更直觀,且可(ke)以在線監視邏輯(ji)和修改(gai)相關參數。在液控(kong)蝶閥控(kong)制(zhi)(zhi)中,主要涉及:
(1)循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵與液(ye)控(kong)蝶(die)(die)閥(fa)的(de)聯鎖(suo)。啟(qi)循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵時,若單臺機組兩臺循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵均未運行(xing)時,蝶(die)(die)閥(fa)開15°后才聯鎖(suo)啟(qi)動(dong)(dong)循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵;若單臺機組任一循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵已(yi)運行(xing),蝶(die)(die)閥(fa)與循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵同步啟(qi)動(dong)(dong)。停循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵時,蝶(die)(die)閥(fa)關閉75°后聯鎖(suo)停止循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵。如此設計可有(you)效防止循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)倒流和(he)循(xun)(xun)(xun)(xun)環(huan)(huan)(huan)(huan)水(shui)(shui)(shui)(shui)泵倒轉現象發生;
(2)將原來送(song)(song)至PLC的(de)油(you)壓(ya)高(gao)、油(you)壓(ya)低、油(you)溫高(gao)、循環水泵急停、控制(zhi)電源消失等信號(hao)送(song)(song)至DCS系統(tong);
(3)增加液控蝶(die)閥液壓(ya)油(you)壓(ya)力(li)變送器,將油(you)壓(ya)模(mo)擬量信號上傳(chuan)DCS系(xi)統并(bing)在DCS畫面(mian)上做壓(ya)力(li)顯示(shi)點;
(4)液控蝶閥(fa)(fa)液壓(ya)油泵以及(ji)泄油電磁閥(fa)(fa)的控制,DCS邏輯如圖6。DCS邏輯包含了(le)原PLC邏輯的控制思想并進行了(le)優(you)化,增加了(le)油壓(ya)模擬量高于14MPa停油泵的保(bao)護。
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圖(tu)6 液壓(ya)油泵和泄(xie)油電磁閥(fa)控制
2.3 就地電氣控制回路設計
改造前,蝶閥(fa)(fa)控(kong)制(zhi)電(dian)(dian)(dian)(dian)源(yuan)取自電(dian)(dian)(dian)(dian)源(yuan)模塊(220VAC/24VDC),電(dian)(dian)(dian)(dian)源(yuan)模塊損壞,液控(kong)蝶閥(fa)(fa)就(jiu)(jiu)失(shi)去(qu)控(kong)制(zhi)。取消PLC后(hou),就(jiu)(jiu)地控(kong)制(zhi)電(dian)(dian)(dian)(dian)源(yuan)改為220VAC直(zhi)接控(kong)制(zhi),消除(chu)了危險集中在電(dian)(dian)(dian)(dian)源(yuan)模塊上的(de)(de)問題,提高了控(kong)制(zhi)系統的(de)(de)可靠性。因無可匹配的(de)(de)由220VAC供電(dian)(dian)(dian)(dian)的(de)(de)泄油電(dian)(dian)(dian)(dian)磁閥(fa)(fa)型號(hao),且24VDC供電(dian)(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)(dian)磁閥(fa)(fa)使(shi)用(yong)壽命較長,故保留原(yuan)有的(de)(de)電(dian)(dian)(dian)(dian)源(yuan)模塊和(he)泄油電(dian)(dian)(dian)(dian)磁閥(fa)(fa),電(dian)(dian)(dian)(dian)源(yuan)模塊只為泄油電(dian)(dian)(dian)(dian)磁閥(fa)(fa)供電(dian)(dian)(dian)(dian),電(dian)(dian)(dian)(dian)氣(qi)原(yuan)理圖設計如圖7。
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圖(tu)7 液控蝶閥就地(di)控制(zhi)電氣原理圖(tu)
3 結論
2011年1、2號機組(zu)小修期間,對液(ye)控(kong)蝶閥控(kong)制系統(tong)(tong)進行(xing)改造,4臺(tai)液(ye)控(kong)蝶閥的控(kong)制進入DCS系統(tong)(tong),液(ye)控(kong)蝶閥控(kong)制系統(tong)(tong)試(shi)運(yun)成功。經(jing)過邏輯(ji)優化后(hou),消除(chu)了液(ye)控(kong)蝶閥運(yun)行(xing)不(bu)可靠(kao)而(er)造成設備(bei)損壞和危及機組(zu)安全運(yun)行(xing)的隱患。