AF泡沫泵離心壓縮機的工況調(diào)節(jié)

合理地選擇離心壓縮機,應(yīng)該使壓縮機在設(shè)計工況附近運行，因為此時壓縮機效率高。但由于生產(chǎn)上工藝參數(shù)不可避免地會發(fā)生變化，所以經(jīng)常需要對壓縮機進行手動或自動調(diào)節(jié)，使壓縮機能適應(yīng)生產(chǎn)要求。
    離心壓縮機的調(diào)節(jié)一般有兩種:一是等壓調(diào)節(jié)，即在壓縮機排氣壓力不變的前提下調(diào)節(jié)流量;另一種是等流量調(diào)節(jié),即在保證流量不變的情況下調(diào)節(jié)壓縮機排氣壓力，前者用得更為普遍。壓縮機調(diào)節(jié)的實質(zhì)就是改變壓縮機的工況點，所用的方法從原理上講就是設(shè)法改變壓縮機的特性曲線或者改變管網(wǎng)特性曲線，主要有以下幾種調(diào)節(jié)方法。
1.出口節(jié)流調(diào)節(jié)
    在機器出口安裝調(diào)節(jié)閥(圖3- 28)，如果管網(wǎng)中容器壓力不變，要求把流量從Gs減到Gs，這時只要把出口調(diào)節(jié)閥關(guān)小，使管網(wǎng)特性曲線變陡，由曲線2變?yōu)榍€3，壓縮機工況點就由S點移到S”點，S”點的流量為Gs,達到調(diào)節(jié)目的。此法無論是調(diào)節(jié)機構(gòu)還是操作方法都極簡單，缺點是浪費功率較大，壓差(ps:- ps)完全消耗于閥門的節(jié)流損失上。如果容器中壓力改變,但要求流量不變，也可用出口節(jié)流方法調(diào)節(jié)壓力。
    由此可見，出口節(jié)流調(diào)節(jié)是不經(jīng)濟的，尤其當壓縮機性能曲線較陡而調(diào)節(jié)流量的范圍又較大時,它的缺點更為突出。因此，目前除在風(fēng)機及小型鼓風(fēng)機使用這種方法外,壓縮機很少采用。
2.進口節(jié)流調(diào)節(jié)
    如圖3- 29所示,在壓縮機進氣管路上安裝調(diào)節(jié)閥。當調(diào)節(jié)閥全開時，閥后的氣體壓力P等于閥前的氣體壓力ps.此時壓縮機特性曲線為圖3- 29(b)曲線1。關(guān)小調(diào)節(jié)閥，壓縮機進氣壓力就降為Ps <ps如圖3- 290)曲線2所示。進氣壓力降低直接影響到壓流機指介壓力pa,使壓縮機朱特性曲線由曲線1下移至曲線3.如果繼續(xù)關(guān)小進氣調(diào)節(jié)閥，進氣壓力與進

氣流量的關(guān)系由曲線2變至曲線4，此時壓縮機特性由曲線3變?yōu)榍€5。

假若壓縮機原在S點工作，容器壓力pr不變，現(xiàn)在要求流量從Gs到Gs。當采用進口節(jié)流方法調(diào)節(jié)時，只要關(guān)小進口調(diào)節(jié)閥,使壓縮機特性曲線下移至曲線3,此時壓縮機工況點就是S",流量為Gs",達到調(diào)節(jié)目的。同樣，如果要求減小壓縮機排氣壓力而希望流量保持不變,也可以用進口節(jié)流調(diào)節(jié)來實現(xiàn)壓縮機在S"位置。和出口節(jié)流法相比,進口節(jié)流法的經(jīng)濟性較好，所以這是種比較簡便而常用的調(diào)節(jié)方法。
3.改變轉(zhuǎn)速調(diào)節(jié)
    對于由汽輪機、燃氣輪機以及變頻電動機等驅(qū)動的壓縮機采用轉(zhuǎn)速調(diào)節(jié)做方便。當壓縮機改變轉(zhuǎn)速時，其特性曲線也會相應(yīng)改變，所以可用這個方法來改變工況點，滿足生產(chǎn)的要求。

如圖3-30所示，如有一臺壓縮機向壓力為pr的容器中輸氣，設(shè)計流量為Gs，設(shè)計轉(zhuǎn)速為n，此時工況點為S。現(xiàn)若要求pr不變，而流量減小到Gs(或增大至Gs)，此時只要將壓縮機的轉(zhuǎn)速降為1n15 (或升至ns),就可使壓縮機特性曲線改變到新的工況點S" (或S),使流量達到Gs(或Gs)。同樣，當容器壓力降到p，;而要求流量保持不變時.則只要把轉(zhuǎn)速降至ns ,使工作

點由S點移至S"即可。

由于離心壓縮機的能頭Ht正比于n2,所以用變轉(zhuǎn)速調(diào)節(jié)法可以得到相當大的調(diào)節(jié)范圍。圖3-31為轉(zhuǎn)速調(diào)節(jié)時的特性曲線，即壓縮機壓比和效率隨流量的變化曲線。由圖中可知,改變轉(zhuǎn)速調(diào)節(jié)法并不引起其他附加損失,所以它是目前大型壓縮機經(jīng)常采用的調(diào)節(jié)方法。
4.轉(zhuǎn)動進口導(dǎo)葉調(diào)節(jié)

在壓縮機葉輪入口前設(shè)置可轉(zhuǎn)動的進口導(dǎo)向葉片，并由專門機構(gòu)使各導(dǎo)向葉片能繞自身軸旋轉(zhuǎn)，從而可改變導(dǎo)向葉片的安裝角，使進入葉輪的氣流產(chǎn)生預(yù)旋繞，以改變壓縮機特性曲線而實現(xiàn)壓縮機的工況調(diào)節(jié)。進口導(dǎo)葉轉(zhuǎn)動后若葉輪進口氣流得到一個與葉輪轉(zhuǎn)向一致的旋繞，稱為正旋繞;若產(chǎn)生與葉輪轉(zhuǎn)向相反的旋繞，稱為負旋繞，,因此又將這種方法稱為進氣預(yù)旋調(diào)節(jié)。根據(jù)歐拉方程Hr=u2C2u- unCu,可知壓縮機能頭Hτ隨Cu改變而改變。正旋繞時C1o>0,Hr將減小，壓縮機性能曲線下移;負旋繞時cu<0,Hr將增大,性能曲線上移。圖3- 32為不同正旋繞時的曲線，預(yù)旋角越大，性能曲線越陡，喘振流量則有所減小。同時.轉(zhuǎn)動進口導(dǎo)葉后，葉輪入口處存在沖角，增大了沖擊損失，故效率有所下降,但與進口節(jié)流相比能量損失要小些。

可轉(zhuǎn)動導(dǎo)葉本身的調(diào)節(jié)機構(gòu)比較復(fù)雜，特別對多級壓縮機，如果每一級前都采用可轉(zhuǎn)動導(dǎo)葉，整臺機器就非常復(fù)雜.甚至無法實現(xiàn)。一般在通風(fēng)機或鼓風(fēng)機上采用，因為它們的D1/D2比壓縮機大，由可知，此時的調(diào)節(jié)效果比較明顯。

圖3-33所示為進口節(jié)流、轉(zhuǎn)動進口導(dǎo)葉調(diào)節(jié)和改變轉(zhuǎn)速三種調(diào)節(jié)方法的經(jīng)濟性對比。AP是以進口節(jié)流為比較基礎(chǔ)所節(jié)省的功率，曲線1表示轉(zhuǎn)動進口導(dǎo)葉比進口節(jié)流所節(jié)省的功率曲線;曲線2表示改變轉(zhuǎn)速比進口節(jié)流所節(jié)省的功率曲線，顯然改變轉(zhuǎn)速的經(jīng)濟性最佳。
四、離心壓縮機的串聯(lián)和并聯(lián)
    壓縮機可以在串聯(lián)或并聯(lián)情況下工作。如果一臺壓縮機工作時,壓力不能達到所需要求，就可以考慮將兩臺壓縮機串聯(lián)工作。同樣，如果一臺壓縮機工作時，流量不能滿足所需要求，也可以將兩臺或多臺壓縮機并聯(lián)工作。
    以下以兩臺壓縮機聯(lián)合工作為例，分別介紹其并聯(lián)和串聯(lián)時的工作特性。
1.并聯(lián)特性
    壓縮機的并聯(lián)常用于以下情況，一是必須增加輸氣量.而又不需要對現(xiàn)有的壓縮機作重新改造;二是氣體用量很大,用一臺壓縮機可能尺寸過大或制造上有困難,這時應(yīng)考慮兩臺小的壓縮機并聯(lián)供氣;三是用戶的用氣量經(jīng)常變動，當所需的輸氣量大時,兩臺壓縮機同時運行，當輸氣量少時則只開一臺壓縮機。例如,天然氣長輸管線輸氣量在冬天和夏天波動量大.這時利用兩臺壓縮機并聯(lián)可實現(xiàn)輸氣量的調(diào)峰。圖3 - 34為天然氣長輸管道壓氣站采用兩臺壓編機并聯(lián)時的流程圖。
    離心壓縮機并聯(lián)工作的主要目的是增加流量,其性能曲線如圖3-35所示，兩臺壓縮機的性能曲線分別為I、II，按照并聯(lián)時壓比相等和流量相加的原則，得到兩臺壓縮機并聯(lián)后的性能曲線(I+lI)。

The reasonable selection of centrifugal compressor should make the compressor run near the design working condition, because the compressor efficiency is high at this time. However, due to the inevitable change of process parameters in production, it is often necessary to manually or automatically adjust the compressor to meet the production requirements.

There are generally two kinds of adjustment of centrifugal compressor: one is equal pressure adjustment, that is, the flow is adjusted on the premise that the compressor discharge pressure is unchanged; The other is equal flow regulation, that is, to regulate the discharge pressure of the compressor under the condition of ensuring constant flow. The former is more commonly used. The essence of compressor regulation is to change the operating point of the compressor. In principle, the method used is to try to change the characteristic curve of the compressor or the characteristic curve of the pipe network. There are mainly the following adjustment methods.

1. Outlet throttling regulation

Install a regulating valve at the outlet of the machine (Fig. 3 - 28). If the pressure of the vessel in the pipe network remains unchanged, the flow is required to be reduced from Gs to Gs. At this time, just turn down the outlet regulating valve to make the pipe network characteristic curve steeper, from Curve 2 to Curve 3, the compressor operating point moves from S point to S "point, and the flow at S" point is Gs, so as to achieve the purpose of regulation. Both the regulating mechanism and the operation method of this method are very simple. The disadvantage of this method is that it wastes a lot of power, and the differential pressure (ps: - ps) is completely consumed on the throttling loss of the valve. If the pressure in the vessel changes, but the flow is required to remain unchanged, the outlet throttling method can also be used to adjust the pressure.

It can be seen that the outlet throttling regulation is not economical, especially when the compressor performance curve is steep and the range of regulated flow is large, its shortcomings are more prominent. Therefore, except for fans and small blowers, compressors are rarely used.

2. Inlet throttling regulation

As shown in Fig. 3-29, install the regulating valve on the air inlet pipe of the compressor. When the control valve is fully open, the gas pressure P behind the valve is equal to the gas pressure ps in front of the valve. At this time, the compressor characteristic curve is shown in Figure 3-29 (b) Curve 1. Turn down the regulating valve, and the compressor inlet pressure will drop to Ps<ps, as shown in Fig. 3 - 290) Curve 2. The reduction of inlet pressure will directly affect the medium pressure pa of the compressor, moving the compressor characteristic curve from curve 1 to curve 3. If you continue to close the inlet regulating valve, the inlet pressure will

The relationship of air flow changes from curve 2 to curve 4, and the compressor characteristics change from curve 3 to curve 5.

If the compressor used to work at point S, the vessel pressure pr would not change, and now the flow would be required from Gs to Gs. When the inlet throttling method is used for regulation, just turn down the inlet regulating valve to make the compressor characteristic curve move down to curve 3. At this time, the operating point of the compressor is S ", and the flow is Gs", so as to achieve the purpose of regulation. Similarly, if the discharge pressure of the compressor is required to be reduced and the flow rate is expected to remain unchanged, the inlet throttling regulation can also be used to achieve that the compressor is in the S "position. Compared with the outlet throttling method, the inlet throttling method is more economical, so it is a relatively simple and commonly used regulation method.

3. Change the speed regulation

For compressors driven by steam turbine, gas turbine and variable frequency motor, speed regulation is adopted for convenience. When the compressor changes its speed, its characteristic curve will also change accordingly, so this method can be used to change the operating point to meet the production requirements.

As shown in Fig. 3-30, if a compressor delivers gas to a vessel with pressure of pr, the design flow is Gs, the design speed is n, and the operating point is S. Now, if pr is required to remain unchanged while the flow is reduced to Gs (or increased to Gs), as long as the speed of the compressor is reduced to 1n15 (or increased to ns), the compressor characteristic curve can be changed to a new operating point S "(or S), so that the flow can reach Gs (or Gs). Similarly, when the pressure of the container is reduced to p, while the flow is required to remain unchanged, as long as the speed is reduced to ns to work

Move the point from S to S ".

Since the energy head Ht of the centrifugal compressor is proportional to n2, a considerable adjustment range can be obtained by using the variable speed adjustment method. Figure 3-31 shows the characteristic curve of speed regulation, that is, the curve of compressor pressure ratio and efficiency changing with flow. It can be seen from the figure that changing the speed regulation method does not cause other additional losses, so it is the regulation method often used by large compressors at present.

4. Adjust the inlet guide vane

A rotatable inlet guide vane is set in front of the inlet of the compressor impeller, and each guide vane can rotate around its own axis by a special organization, so as to change the installation angle of the guide vane, so that the air flow entering the impeller can generate pre rotation, so as to change the compressor characteristic curve and realize the compressor condition adjustment. After the inlet guide vane rotates, if the air flow at the inlet of the impeller gets a rotation that is consistent with the rotation direction of the impeller, it is called positive rotation; If the rotation direction of the impeller is opposite to that of the impeller, it is called negative rotation, so this method is also called intake pre rotation adjustment. According to Euler equation Hr=u2C2u - unCu, the compressor head H τ Change with Cu. When C1o>0, Hr will decrease and the compressor performance curve will move downward; When cu<0, Hr will increase and the performance curve will move up. Figure 3-32 shows the curves for different positive turns. The larger the pre turn angle, the steeper the performance curve, and the smaller the surge flow. At the same time, after rotating the inlet guide vane, there is an attack angle at the inlet of the impeller, which increases the impact loss, so the efficiency decreases, but the energy loss is smaller than that of the inlet throttling.

The regulating mechanism of the rotatable guide vane itself is relatively complex, especially for multi-stage compressors, if the rotatable guide vane is used in front of each stage, the whole machine will be very complex, or even impossible to achieve. Generally, they are used on ventilators or blowers because their D1/D2 is larger than that of compressors. It can be seen that the regulation effect is obvious at this time.

Figure 3-33 shows the economic comparison of three adjustment methods: inlet throttling, rotating inlet guide vane adjustment and changing speed. AP is the power saved based on inlet throttling. Curve 1 shows the power saved by rotating inlet guide vane compared with inlet throttling; Curve 2 shows the power curve saved by changing the speed compared with the inlet throttling, obviously, the economy of changing the speed is the best.

4、 Series and Parallel Connection of Centrifugal Compressors

Compressors can operate in series or parallel. If the pressure of one compressor fails to meet the required requirements when it is working, the two compressors can be considered to work in series. Similarly, if the flow of one compressor cannot meet the required requirements when it is working, two or more compressors can also be operated in parallel.

Taking the joint operation of two compressors as an example, the working characteristics of parallel and series compressors are introduced respectively.

1. Parallel connection characteristics

The parallel connection of compressors is often used in the following situations: first, the gas transmission capacity must be increased without the need to rebuild the existing compressor; Second, the gas consumption is large, and one compressor may be too large or difficult to manufacture. In this case, two small compressors should be considered to supply gas in parallel; Third, the user's gas consumption often changes. When the required gas transmission capacity is large, two compressors operate at the same time. When the gas transmission capacity is small, only one compressor is opened. For example, the gas transmission capacity of long distance natural gas pipeline fluctuates greatly in winter and summer. At this time, the peak shaving of gas transmission capacity can be achieved by using two compressors in parallel. Figure 3-34 shows the flow chart when two crimping machines are used in parallel in the compressor station of the long-distance natural gas pipeline.

The main purpose of parallel operation of centrifugal compressors is to increase the flow. Its performance curve is shown in Figure 3-35. The performance curves of the two compressors are I and II respectively. According to the principle of equal pressure ratio and flow addition in parallel, the performance curve (I+lI) of the two compressors after parallel operation is obtained.