Porous Plugsa New Generation of Fluxing and Purging Technology

 in the Aluminium Industry!

透氣磚

鋁工業(yè)新一代除氣精煉技術(shù)

Dipl. Ing. Reinhard Schwaiger

Marketing Department Non Ferrous metals

RHI AG – Non Ferrous Engineering GmbH

Some years ago, due to several misconceptions as, danger of leaking metal and gas, deterioration by Cl₂ , easy irreversible blindness etc. to put a plug, which is porous into the bottom of a Aluminium furnace was nearly unthinkable. - To install more than a dozen of them in a molten metal furnace seemed to be impossible.

Necessity, however, is the mother of invention and persuasion.

When beginning to design work on the casting facilities of a Aluminium plant, some challenging fluxing and stirring goals for the furnaces had been established.

These goals were far beyond the capability of the standard handheld fluxing wands (lances) which had been used for so many years.

一直以來，人們出于對爐底漏鋁事故，氯氣腐蝕管道，管道被熔液倒灌等事故的擔(dān)心，對冶煉鋁金屬的爐底使用透氣磚這一技術(shù)產(chǎn)生過疑惑和誤解，使得在爐底安裝透氣磚這一構(gòu)想一直停留在想象階段-----要在熔煉爐、混合爐內(nèi)安裝多個(gè)透氣磚進(jìn)行吹氣攪拌聽起來更顯得不切實(shí)際。

然而，正是對生產(chǎn)工藝精益求精的需求，激勵(lì)著工程師和科學(xué)家不斷創(chuàng)新，讓構(gòu)想變成了今天的現(xiàn)實(shí)。

從著手設(shè)計(jì)生產(chǎn)線開始，一連串提高質(zhì)量和降低成本的目標(biāo)擺在了我們面前，這些標(biāo)準(zhǔn)對于多年來習(xí)慣使用的造渣棒或者噴射槍進(jìn)行熔爐除氣的傳統(tǒng)技術(shù)來說，幾乎無法達(dá)到的，隨著底吹透氣精確控制工藝的問世，使得一系列的改善標(biāo)準(zhǔn)得以實(shí)現(xiàn)。

目前，在國外鋁材熔煉以及鑄造行業(yè)已經(jīng)廣泛地在各種爐底安裝多孔透氣磚及相應(yīng)的氣體配送調(diào)節(jié)系統(tǒng)進(jìn)行有序的底吹攪拌，然而在國內(nèi)冶煉行業(yè)由于接觸國際市場比較晚，這項(xiàng)引進(jìn)工作才開始不久，這一技術(shù)為鋁鑄造行業(yè)帶來的是革命性改善：

The goals were:

目標(biāo)：

• Improve fluxing quality提高攪拌質(zhì)量
• Decrease flux time by 50%降低攪拌氣體耗時(shí)50%
• Decrease Cl₂% of flux gas減少攪拌氣體中氯氣的用量
• Improve melt rate提高排氣效率
• Decrease emissions減少氣體排放（包括有毒氣體）
• Pre-treatment of the metal實(shí)現(xiàn)金屬預(yù)處理
• Improve thermal homogenization大大改善熱循環(huán)，爐內(nèi)溫度更加均勻和諧
• Improve degassing efficiency提高熔解速率
• Reduce of thermitting dross減少鋁渣析出
• Long life and Low maintenance耐用且維護(hù)費(fèi)用極低
• Reach across the whole melter?s bottom area攪拌幅度深達(dá)爐底

Porous plug technology offered the best opportunity to achieve these design goals. - A program to develop a practice for installing and applying plugs in Aluminium furnaces had been initiated.

Basically, porous plugs have been used in the industry for bubbling flux gas through molten aluminium baths for degassing and stirring. Early successes were realised in flux boxes and smaller applications. Serious attempts to apply the technology to furnaces were not made until the late 1980’s.

多孔透氣轉(zhuǎn)攪拌技術(shù)在早期被成功的應(yīng)用在轉(zhuǎn)鋁包和在線除氣箱上，直到上世紀(jì)九十年到初才涉足嘗試應(yīng)用于真正的混合爐和熔解爐底部吹入氣體作為除氣熔劑和攪拌介質(zhì)，進(jìn)行除氣精煉。

1．Description of the APA - Porous Plug design:

APA型透氣磚設(shè)計(jì)描述

The latest Plug design is designated APA and is one of the largest porous plug designs manufactured by RHI.

The current design, shown in Figure 1, is comprised of a round reverse tapered porous refractory core (A) shrouded (shrieveld) by a metal can.(C) (Inconel or SS ) The can is continuous across the bottom of the plug and up the sides with gas tight welds. A metal (Inconel or SS) flux gas supply pipe (D) passes through and is welded to the can bottom and extends into the porous core material. Around this assembly is a refractory nest block (B) to serve as protection for the porous media and as an interface with the furnace bottom refractory.

A detached but very critical component of the plug is the external packing gland (E) which is welded at the furnace bottom. This unit provides a gas tight seal around the flux gas supply pipe when it exits the furnace bottom.

APA型透氣磚是RHI公司所生產(chǎn)的最大的透氣磚。

如圖一所示，透氣磚磚心（A）由多孔性錐型的耐火材料和（C）包裹在透氣磚周圍緊密連接的不銹鋼殼或鎳鉻合金，鋼殼從底部到側(cè)部使用氣密性焊接。透氣用的鋼管（D）通過底板從底部通入氣體到達(dá)透氣磚芯。磚芯外圍包裹一層預(yù)制成型的澆注料保護(hù)層，稱之座磚（B），主要用于保護(hù)透氣。還有一個(gè)重要的單獨(dú)的零配件是（E）密封襯套，焊接在底部鋼板用于緊密送氣管和爐殼之間的密封，防止任何氣體從爐內(nèi)逸出。

Fig. 1:  APA- AL-KIN PLUG Assembly

In operation, gas enters the plug assembly bottom via the supply pipe and disperses in the porous core.

The porous core of the plug is a pressed and fired Corundum - chrome material. The final shape is a dense, aluminium resistant unit with a texture much like that of a common high Alumina brick. The porous characteristic is derived from grain size engineering and pressing techniques.

The finished porous core is 330 mm deep which places its bottom below the freeze plane in most furnaces. The non-porous refractory liner, - the nest block is a high strength Corundum – Spinel   pre-cast and pre-fired shape.

在實(shí)際應(yīng)用中，氣體進(jìn)入通過送氣管進(jìn)入分散到多孔的磚芯里面。磚芯材質(zhì)為壓縮和燒結(jié)的剛玉氧化鋁-鉻，外形像一塊致密且?guī)Ъy理的不黏鋁的剛玉高鋁磚。其透氣特性主要來自原材料特殊的結(jié)晶顆粒篩選工藝和靜壓力成型壓磚工藝

成品多孔透氣磚高330毫米，安裝時(shí)底部將處于鋁液凍結(jié)等溫線平面以下。 - 非多孔耐火材料內(nèi)襯，是一種高強(qiáng)度剛玉 - 尖晶石預(yù)制和預(yù)焙燒的成型的。

Fig. 2:  APA Plug  .APA透氣磚實(shí)物照片

Additional, available Plug designs:

其他尺寸的透氣磚：

Application:

應(yīng)用：

APA ACA (changeable )	Aluminium Melting and Holding furnaces 鋁熔煉保溫爐用
AP; AC	Aluminium Melting and Holding furnaces 鋁熔煉保溫爐用 Dosing furnaces; Foundry furnaces, Flux boxes 鑄造爐，在線出氣箱用
AR; ARH	Ladles, Runners, Troughs; Flux boxes 轉(zhuǎn)鋁包或流槽用

2． Melter and Holder Plug Layouts:

熔煉爐保溫爐使用透氣系統(tǒng)特點(diǎn)：

2.1  Melters 熔煉爐

Customer Requirements - Melters : 客戶要求：

• Improved Melt Rate
  提高熔鋁速度
• Less Time required to achieve Alloy Chemistry
  合金調(diào)配時(shí)間短
• Pre-treatment of the metal
  金屬預(yù)處理
• Reduction of dross build up
  較少爐內(nèi)積渣
• Low Maintenance
  少維護(hù)
• Reasonable Cost
  價(jià)格合理
• Long Life
  使用壽命長

Fig. 3:  48 MT  Round Top Charge melter 48噸圓形熔煉爐	Fig. 4:  Melter - Plug Installation Detail

Figure 3/4 show a 48 ton, top charging melter. The bath level of molten Aluminium is 650 mm deep and is equipped with 10 plugs arranged around the periphery. The purpose of the plugs in the melters is primarily to reduce dross build-up on the wall at the bath line, although the melter metallurgical practice requires a brief flux at alloys.

Some of the melters are equipped with electromagnetic stirrers mounted beneath the bottom steel. Though this device is intended primarily for stirring, it does an effective job of distributing the periphery plug bubbles to the bath interior.

10塊透氣磚圍繞著邊上安裝是為了減少爐墻周圍邊上的積渣。

如果有些熔煉爐安裝了電磁攪拌，透氣磚的管路可以按照在耐材的隔熱保溫層，不影響底部電磁攪拌的安裝和正常工作。

2.2 Holders 保溫爐

Customer Requirements - Holders : 客戶要求：

• Improved Degassing Efficiency
  提高除氣效率
• Improved Thermal Homogenisation
  提高熱同步
• Less Dross
  較深燒損
• Low Maintenance
  少維護(hù)
• Low mechanical Damage of installed Refractories
  沒有任何機(jī)械磨損
• Reasonable Cost
  性價(jià)比突出
• Long Life
  使用壽命長

Fig. 5:  130 MT

Fig. 6:  Holder (Tilter) Plug Installation Detail

透氣磚整體裝示意圖

Figure 5 shows a 130 ton  CASTER. The bath level is 1220 mm  deep and is equipped with 24 plugs arranged in 3 rows.

Fig. 7:  Holding furnace: 14 porous plugs in operation

3  Conclusions on Porous Plugs Performance

透氣磚優(yōu)勢總結(jié)

TOP 10 OPERATION TRUTHS:

十大優(yōu)點(diǎn)：

1.Excellent degassing tool 一流的除氣效果	2.Operator friendly 操作簡便
3.Decreases fluxing time 減少精煉時(shí)間	4.Decreases CL2usage 減少氯氣使用
5.Eliminates bath temperature stratification	6.Decreases thermitting dross 減少熱鋁渣析出
7.Generates less dross 造渣減少	8.Decreases emissions 減少氣體排放
9.Pre-treatment of the metal 實(shí)現(xiàn)金屬預(yù)處理	10.Improve thermal homogenization 改善熱循環(huán)

From years of operating experience, can be stated with a knowledgeable certainty that the above are credible conclusions for porous plugs applied to can stock alloys 3104 and 5182 as well as rigid container alloys.

Number 1 on importance list is the metal treatment quality being realised with the plugs. Tests have indicated hydrogen levels in the bath immediately following fluxing to be reduced up to 50% compared to levels achieved by standard fluxing wand practices. Particulate counts also appear to be improved despite significant reductions in settling times which had been implemented.

根據(jù)多年的運(yùn)營經(jīng)驗(yàn)，可以確定地說，上述是透氣磚系統(tǒng)效能的結(jié)論適用于易拉罐合金3104和5182以及剛性容器合金。

最總要的一點(diǎn)是透氣磚提升了金屬處理的質(zhì)量。測試結(jié)果表明使用透氣磚比起使用傳統(tǒng)的插入式精煉噴槍將氫含量馬上降低達(dá)50％。顆粒計(jì)數(shù)也出現(xiàn)改善，但在解決已實(shí)施的時(shí)間顯著減少。操作和處理時(shí)間也相對減少， 因?yàn)椴僮魍笟獯u只需要輕按按鈕。

 

Fig. 8:  Typical pre-treatment results. Hydrogen concentration in melters

熔煉爐中合金預(yù)處理結(jié)果，氫含量比較，左邊是使用透氣磚，左邊沒有透氣磚

 

Fig. 9:  fluxing results with porous plugs, 16 MT Holding furnace,

Alloy 3003, 12 Plugs 100% Argon, 30 min fluxing

16噸保溫爐，12塊透氣磚通入100% 氬氣，冶煉3003合金

The advent of porous plugs at Alloys Plants has allowed furnace fluxing to become a pushbutton operation. The operator sets the desired flux flow rate on the control screen, starts the flux and visually checks the appearance of the bath surface. He may choose to adjust the flow to an individual plug if the bubble appears incorrect. The flux continues for a pre-set duration, after which the flux is automatically terminated and the purge cycle is begun. This closed door fluxing practice allows the furnace fluxing to proceed with minimum levels of oxygen and moisture from the atmosphere entering the furnace.

The holder flux time significantly decreases while achieving greater fluxing quality performance. The porous plugs have allowed to reduce the fluxing time significantly compared to hand-held flux wands while lowering the chlorine content of the flux gas as well. The reduced CL₂content and the more efficient fluxing bubble likewise reduce stack emissions from the holders with significantly lower amounts of free CL₂ and particles.

在合金工廠多孔透氣磚的問世，使?fàn)t精煉成為一個(gè)按鍵操作。操作員設(shè)置所需的透氣流量通過控制屏幕設(shè)定，通入氣體并檢查鋁溶液表面的流動(dòng)。如果涌起的泡沫出現(xiàn)不正確，操作員可以調(diào)節(jié)單個(gè)透氣磚的流量。通過預(yù)先設(shè)定的精煉時(shí)間，完成后系統(tǒng)自動(dòng)終止，然后周而復(fù)始的自動(dòng)運(yùn)行。全過程緊閉爐門的精煉方式，把空氣和水汽排除在爐內(nèi)環(huán)境以外，使?fàn)t內(nèi)鋁業(yè)進(jìn)行氧氣和水分吸收降低到最低水平。

保溫爐精煉的時(shí)間顯著減小，同時(shí)實(shí)現(xiàn)更高的精煉效果。多孔透氣磚，與手持式精煉噴槍相比，降低精煉氣體的氯氣含量以及，減少氯氣化合物排放和更有效的吸收精煉氣泡，使得剩余的氯氣和粒子由煙囪排放顯著降低。

Fig. 11:  Chlorine Emissions, Holding furnace (100 MT),

Total Gas Consumption per, flux : 18 litres

100噸保溫爐氯氣排放，24塊透氣磚一次精煉，使用氯氣氣體18升

One of the most significant benefits of the plugs in the holding furnaces has been their capability to eliminate temperature stratification. A relatively uniform holder bath temperature is necessary for the casting process, and the deep holder bath (1220 mm) creates a problem in this area. As the burners fire, the surface temperature begins to rise while the temperature at the bottom of the bath may continue to fall until a spread of 10°C to 40°C or more exists. Figure 12 represents a period of holder operation and plots the upper and lower thermocouple temperatures through a firing and purge cycle. During this short purge, a temperature differential of 50°C was reduced to less than 5°C in less than five minutes without opening the furnace door. These readings were taken with 100 Ton of molten metal in the furnace.

保溫爐透氣磚的最顯著的優(yōu)點(diǎn)之一，在于它消除鋁液溫度分層。對于鑄造來說，一個(gè)相對均勻統(tǒng)一熔池鋁液溫度在鑄造過程中是必需的，然而較大的熔池深度（1220mm）給均勻溫度帶來了困難。由于燃燒器火焰直接加熱到鋁液的表面，表面溫度開始上升，而在熔池底部的鋁水由于底部散熱，溫度可能會下降，導(dǎo)致上下之間10° C至40° C的溫差存在。圖12所示，使用透氣磚進(jìn)行底吹精煉，在不到五分鐘內(nèi)，上下層液面的溫差由50° C降低到小于5°，整個(gè)過程無需打開爐門。這些數(shù)據(jù)來自100噸熔化爐內(nèi)熔化的金屬。

s

Fig. 12:  Thermal homogenisation, Tilter (100 MT), 

24 Plugs / 14 l / min each, metal depth 1220 mm

100噸傾翻爐 通過24塊透氣磚，爐液面深度1220mm，熱同步處理

Possibly the most noticeable visual difference in porous plug versus wand fluxing is the amount of dross produced and the absence of thermitting dross. A study of dross generation performed by the RMC Manufacturing Technology Laboratory covering 14 cycles of 3104 alloy indicated an average dross generation of  0,7% of the molten charge weight during a complete holder cycle. Dross generation in holding furnaces with wand fluxing averaged more than twice (1,5%) and historically was a light thermitting dross which required mechanised cooling and provided poor recovery.

直觀上，透氣磚精煉與傳統(tǒng)噴槍精煉最主要的差別在于減少造灰渣和降低燒損。在RMC鋁廠測得14次出爐數(shù)據(jù)，冶煉3104合金，我們獲得的以下結(jié)論：使用透氣磚精煉比起使用噴槍精煉降低0.7%的燒損。而且這些減少的鋁渣多為輕質(zhì)灰渣，不可再生回收利用。

 

Fig. 13:  Dross Savings, 24 Plugs versus. 5 Lances

燒損

Dross from holding furnaces with plugs is generally a cold dross with an estimated recovery of 60% .The dross may be charged directly into Rotary Barrel furnaces. thermitting dross, even with high magnesium alloys, is virtually non-existent and allows discontinuation of mechanised cooling .

The singular basic difference is the existence of the porous plugs and the hourly purging practice. It follows that elimination of the thermiting dross is directly attributable to the porous plugs, the bath temperature uniformity realised with them, and the ability to flux with the furnace doors closed.

Good flow controls and purging practices are necessary to assure long-term use of porous plugs. A system which will feed either flux gas or nitrogen to a pneumatic flow control valve at a regulated pressure should be installed. Flow is measured via an orifice plate metering run with a differential pressure transmitter providing feedback to the control loop.

使用透氣磚精煉產(chǎn)生的渣多為冷渣，可以直接放到球磨機(jī)提煉后重熔，回收率一般達(dá)到60%，而熱灰渣雖然鎂含量高些，幾乎看不到金屬存在，的回收率很低。

燒損的降低主要?dú)w功于透氣磚能夠使溫度同層均勻，減少表面過度加熱造渣；全過程關(guān)閉爐門操作避免了空氣進(jìn)入。

精確的流量控制對于達(dá)到長期良好的精煉效果至關(guān)重要。系統(tǒng)必須持續(xù)提供穩(wěn)定而可控的氣流量，不管爐內(nèi)工作壓力如何因?yàn)橐好娓叩妥兓瑲饬髁渴冀K保持在設(shè)定值，不能波動(dòng)。 這需要比例調(diào)節(jié)閥和流量測量形成的回路控制。

Fig. 14:  10 line Flow Control Panel with individual mass flow meter

10 線氣體控制柜

Figure 15

帶氯氣/氬氣氮?dú)饣旌瞎竦臍怏w控制系統(tǒng)

Porous Plugs water models:

多孔透氣磚水箱模擬模型：

The improved quality may be explained by water modelling studies performed by the Reynolds metallurgical Laboratory(USA). Figure 16 depicts the currents created in a 1220 mm deep tank from the bubbling action of one plug mounted in the bottom. The model indicates the optimum flow for degassing to be approximately 12 - 14 l /min for a Model APA-20 plug. At this rate the bubble pattern is most stable and creates the least amount of surface disturbance. At higher flows, counter currents generated by the vertical column and surface disturbance can actually entrain gases and particles from the surface and draw them down into the bath.

雷諾茲冶金實(shí)驗(yàn)室（美國）的水模擬研究可以解釋透氣磚如何提高攪拌效果。圖16顯示了在1220毫米深的水箱底部安裝一個(gè)插件可以透過壓縮空氣的透氣磚。該模型表明，就一個(gè)型號APA- 20透氣磚而已，除氣精煉中最佳流量約12 - 14升/分鐘。泡沫的圖案表面，在這個(gè)流速是最穩(wěn)定和使得表面擾動(dòng)量最少的。如果繼續(xù)調(diào)整到更高的流速，氣泡變成垂直氣柱和表面擾動(dòng)所產(chǎn)生的反回流，會從表面的把鋁渣和雜質(zhì)重新帶到鋁液中。

Fig. 16:  Water Model Depiction of molten metal currents

4．Discussions of water models for porous plugs:

水箱模擬模型研究：

4.1  The process: 過程：

Inert Gas (mixed with Chlorine or pure ) is injected at the bottom of the porous  material, and enters the liquid metal in form of bubbles.

In the metal, the gas reacts with elements in the metal and induces the metal to flow.

The effectiveness of the reaction is determinated by the gas fluid interface and residence time of the bubbles in the melt. The effectiveness of the stirring action is determined by the interaction between the gas and the liquid phase. Therefore, the following parameters are of importance.

惰性氣體（混合氯氣或純氣體）通過彌散式蜂窩透氣磚，以氣泡的形式從熔池底部直接吹入鋁金屬熔體內(nèi)。

在鋁金屬熔液內(nèi)，氣泡直接接觸到金屬反應(yīng)并形成金屬液體流動(dòng)。熔體與氣體反應(yīng)的程度主要取決于氣泡跟鋁液之間接總觸面大小和氣泡在鋁液中停留時(shí)間，流體被攪拌的強(qiáng)度主要取決于氣相和液相之間的相互作用，因此以下的參數(shù)變得非常重要。

4.2  Gas flow regimes: 流譜曲線

Different regimes are observed for different gas flow rates, each with its own characteristics. For low gas flow rates, discrete bubbles form at the plug surface. At intermediate gas flow rates, the bubble frequency increases due to the fact that dormant pores in the plug get activated. Then, bubbles start to coalesce, become larger and eventually, the bubble pattern becomes completely chaotic.

不同的氣體流量產(chǎn)生不同的氣流模型，每個(gè)模型具有各自的流體力學(xué)特征。

對于低流速情況下，氣泡從透氣磚表面溢出，呈現(xiàn)不連續(xù)離散式分布；

對于中等流速情況下，氣泡數(shù)量呈現(xiàn)增加趨勢，因?yàn)楦嘣瓉聿煌獾膹浬⑹綒饪组_始冒氣工作，使得透氣磚表面氣孔使用率增加；

繼續(xù)增加流量，我們發(fā)現(xiàn)小氣泡之間開始接合成大的氣泡，繼續(xù)結(jié)合成更大的氣泡，最后氣泡圖案變成徹底的無序的紊流圖案。大氣泡與鋁熔液接觸的表面積相對于原來多個(gè)小氣泡減少了。

 

Figure 17. Variation of bubble frequency as a function of gas flow rate

at various heights above the plug.

氣泡總數(shù)量相對氣體流速的變化曲線。不同顏色代表測量點(diǎn)離透氣磚表面不同的距離（深度）

discrete bubbles 離散	Intermediate 中間過渡流譜	Chaotic 混亂無序流譜

4.3  Gas fraction distribution: 氣泡分布：

From water model experiments it is known that the gas fraction within the plume is bell shaped for all regimes. Increasing the gas flow rate widens the gas fraction profile and the gas fractions become larger. As an indication the data described in (1) where watermodel experiments on a 60 mm diameter porous element in a liquid bath of 400 mm water. For the discrete bubble pattern the fraction is found to be 0.4 close to the plug and decreases to 0.05 close to the surface. The gas fraction for different heights can be formulated as.

從水箱模型觀察可知，不管哪個(gè)流速狀態(tài)下，氣體氣泡在水中分布均呈現(xiàn)上小下大的鐘型分布，增加氣體單位時(shí)間氣流量將使得氣泡分布更寬，而且氣泡的體積也變得更加大。從以上水箱模擬模型我們發(fā)現(xiàn)，把直徑60mm的透氣磚放到400mm見方的水箱中，不連續(xù)的氣泡在靠近透氣磚表面地方是0.4，到靠近液體表面時(shí)接近0.05。

氣泡大小與氣體流速的關(guān)系可總結(jié)為以下公式：

? = 0,71 ( z/ ([Q²/ g ]^0,2))^0,9

4.4   Bubble frequency: 氣泡數(shù)量：

In characterising the interfacial area between melt and gas, the bubble frequency within the plume is an important parameter. For the discrete bubble pattern the bubble frequency lies in the order of 100 Hz close to the plug. Close to the surface, the bubble frequency decreases to 10 Hz. The development of the bubble frequency as a function of the gas flow rate is shown in Figure 1. Increasing the gas flow rate initially causes the bubble frequency to increase, activating dormant pores. But for higher frequencies, the bubble frequency reaches a maximum. A further increase of gas flow causes the bubbles to coalesce to larger bubbles, thus reducing the bubble frequency and also reducing the interfacial area.

上升過程中氣泡頻率（單位截面下的氣泡的總數(shù)量）是氣態(tài)氣泡和液態(tài)金屬之間的接觸面大小的決定性因素。

離散式不連續(xù)氣泡模型下，氣泡離開透氣磚編碼時(shí)頻率為100Hz，頻率隨著氣體流速增加的變化曲線如 圖17 所示： 增加流速一開始可以增加氣泡頻率，把原來處于休眠狀態(tài)不工作的孔激活到工作狀態(tài)，更多氣泡冒出。但如果想通過增加流速達(dá)到更高的氣泡頻率，我們發(fā)現(xiàn)氣泡頻率達(dá)到一個(gè)最大值。再繼續(xù)加大氣體流速只會使得氣泡變得無序，然后那些靠近的氣泡會融為一體成一個(gè)大氣泡。這只會降低氣泡頻率從而減少氣體和鋁業(yè)的總接觸面。

4.5  Bubble velocity: 氣泡上升速度：

A large bubble residence time in the melt can be necessary for a good reaction between gas and melt. Therefore, the bubble rise velocity is of importance.

Increasing the gas flow rate from the discrete bubble to intermediate regime causes an increase in bubble rising velocity. This indicates that the interaction between bubbles becomes important. Increasing Q = 0.72 m? /hr to Q = 2,16 m? /hr gives an increase from 1.05 m/s to 2.07 m/s. Towards the surface these velocities become 0.7 m/s and 1.2 m/s. once coalescence is established, the bubble rising velocity decreases.

氣泡在鋁液中長時(shí)間停留對增加鋁液和氣體的反應(yīng)有很大幫助。因此，很有必要有效的把握氣泡上升的速度。

當(dāng)增加通過透氣磚的氣體流速，從離散式氣泡到中等流速氣泡會使得氣泡上升的 速度加快。這表明氣泡與氣泡之間的相互結(jié)合很重要?？偭魉購腝 = 0.72 m? /小時(shí)增加到Q = 2,16 m? /小時(shí)后，相應(yīng)的，氣泡上升速度從1.05米/秒 上升至2.07米/秒。臨近鋁液表面時(shí)，以上速度分別降至0.7 米/秒 和1.2 米/秒，一旦紊流狀態(tài)形成，氣泡的上升速度又將降低。

4.6  Bubble size distribution: 氣泡體積分布：

For the discrete bubble pattern, the bubble size is constant over different liquid heights. For the intermediate and higher gas flow rates the bubble diameter decreases towards the surface. The later is mainly caused by large coalescence close to the plug and break-up towards the surface.

對于離散式下的氣泡分布，不同液面深度時(shí)氣泡的體積大小是恒定的。

對于中等流速或高流速下氣泡分布，氣泡直徑向液面方向減小。這主要是因?yàn)楹芏嗟臍馀萁Y(jié)合在靠近透氣磚附件發(fā)生，然后在靠近液面時(shí)分裂。

4.7  Liquid velocity: 液體的速率：

The liquid velocity is symmetric towards the wall. Values in (1) are 0.3 m/s for the discrete bubble pattern (where bubble rising velocities are 0.7 m/s).

液體的速率對墻體具有相稱性，如圖1中，當(dāng)氣泡呈離散式分布時(shí)為流體速度0.3米/秒，相應(yīng)的氣泡上升速率為0.7米/秒.

4.8  Surface behaviour:

The higher the gas flow rates, the higher the impact of the disengaging bubbles on the surface of the liquid. This effect is of course also caused by the size of the bubbles due to coalescence.

氣體流速越高， 有越多的氣泡在液表面分解并對鋁液表面形成更大的沖擊，同時(shí)氣體氣泡體積增大也加劇了液表面的波動(dòng)。

4.9  Optimising the process 過程優(yōu)化

In order to optimise the process, several aspects of the process must be considered and compromises might have to taken. A three step route is essential in optimising this process.

為了優(yōu)化生產(chǎn)流程，提高精煉效果，必須實(shí)施某些手段并權(quán)衡其他各個(gè)方面利益。

以下三部尤為關(guān)鍵：

1. scaling of process 定標(biāo)過程

2. measurements 觀察并測量效果

3. validation of result 確認(rèn)反饋

For the investigation on how the gas flow rate influences the different parameters, a watermodel can be used. However, this model should generate the same process or generate results that have a clear relationship with the real process. Then the proper data should be measured and finally the results should be checked with the real process.

我們可以使用水箱模擬出氣體流速是如何影響氣泡吹送效果的。我們需要按照鋁業(yè)的實(shí)際情況來模擬透氣磚底吹氣體流速與液體攪拌之間的關(guān)系。

4.10 Scaling the process: 定標(biāo)法則

The translation of the Argon-Aluminium system to the air-water system must be carried out according certain scaling rules (2). For example: the density differences and related pressure drop over the liquid layer must be scaled correctly. Also the wettability of the porous plug must be taken into account for a proper modelling of the bubble formation. Some results will be shown on how the scaling rules effect the process.

Vacuum pressure is required to account for the density differences and related pressure drop over the liquid layer. This is clarified into more detail in Appendix I .

從氣體-水箱模型到氬氣-鋁液模型的轉(zhuǎn)化我們使用了相對應(yīng)的定標(biāo)法則。比如，水和鋁液密度的差異和在不同液位高度時(shí)相對壓降必須正確地定標(biāo)。同時(shí)還必須把透氣磚的可濕性考慮進(jìn)生成氣泡的模型中。產(chǎn)生的結(jié)果將顯示出如何通過定標(biāo)調(diào)整影響精煉的過程。為了說明密度不同和壓降隨液面分層現(xiàn)象我們需要借用抽真空壓力。

4.11 Wettability: 濕潤性

Others have reported about water model experiments that have demonstrated quite different behaviour of the bubbles and flow pattern of water when the wetability was changed (3). Aluminium does not wet the porous plugs. Because water wets the porous plugs, special precautions must be taken. The plug was made non-wettable with grease

有人會說透氣磚水箱模型在可濕性變化時(shí)只能呈現(xiàn)出的氣泡活動(dòng)和液體流線譜不同于實(shí)際情況。但實(shí)際情況是透氣磚表面不會被鋁水滲透，這取決于透氣磚表面孔隙大小和鋁水的表面張力。但尤其要注意的是，水是可以滲透進(jìn)去透氣磚的，而油脂性溶劑對透氣磚是不可潤濕的。

4.12 Experimental set-up: 建立模型：

A rectangular water model (dimensions: 1m x 1m x 1m) was built. In the model a porous plug from the cast-house was mounted. Because the construction of a scaled plug is difficult, a real plug is used. In the actual furnace, multiple porous plugs are used. On average there is one porous plug on each square meter, which justifies the choice of the water model dimensions.

建立一個(gè)一立方米的安裝有透氣磚在底部的水箱模型。我們使用了實(shí)際應(yīng)用的透氣磚，在鋁熔煉保溫爐內(nèi)實(shí)際上是多個(gè)透氣磚同時(shí)使用。平均分布計(jì)算大概一平方米面積布置一塊透氣磚，與水箱模型尺寸相近。

According to the scaling laws for multiphase flow, the model should be operated under an absolute pressure of 0.2 bar and a water temperature of 60°C. Due to mechanical problems the correct scaling could not completely be implemented. The pressure is reduced to 0.5 bar absolute pressure and the water temperature is not elevated because it was expected that the high temperatures would soften the seals. However, the present results show there already is a significant difference in the results at normal pressure and proves that a different means of scaling results in a different process. From experiments on a single nozzle it is known that increasing the temperature will result in slightly smoother bubbles with a more evenly distributed bubble size. This should also be the case in the liquid aluminium.

根據(jù)定標(biāo)法則，在多種流速底吹下的，透氣磚出氣的工作壓力（絕對壓力）為0.2 Bar,

水溫度設(shè)定為60攝氏度，由于機(jī)械原因，不可能完全準(zhǔn)確地貫徹定標(biāo)法則。

把絕對壓力降低到0.5Bar，水溫保持不變，因?yàn)槲覀兿Ｍㄟ^提高溫度讓溢出的氣泡更加飽和平滑。這就好比在單孔關(guān)口出來的氣體會因?yàn)闇囟壬兊酶悠交恍?。然而，目前的結(jié)果表明，在正常壓力下的演試的定標(biāo)縮放氣體流量實(shí)驗(yàn)證明不同流速時(shí)的流譜有顯著的差異；從單一噴嘴的實(shí)驗(yàn)可知，提高液體溫度，將導(dǎo)致氣泡分布比較均勻和氣泡稍微平滑。此結(jié)論也應(yīng)該適用在實(shí)際鋁液的情況下。

In furnace operation, the gas flow rate is in between 0.3 m? /hr up to 0.6 m? /hr at a temperature of approximately 800°C. For the scaled water situation, the gas flow rate will be a factor 3,6 higher and thus vary from 1.08 m? /hr up to 2,16 m? /hr. We have taken measurements from 0.3 m? /hr up to 2,4 m? /hr.

在實(shí)際應(yīng)用中，當(dāng)爐內(nèi)溫度為800度時(shí)，氣流速度保持在0.3 m? /小時(shí) 到 0.6 m? /小時(shí)之間，對于用水做定標(biāo)縮放實(shí)驗(yàn)的條件下，氣體流量將乘以影響放大因素3.6??，因而流速范圍應(yīng)在1.08立方米/小時(shí)到2,16立方米/小時(shí)。我們測量從0.3立方米/小時(shí)至2.4立方米/小時(shí)之間的流譜。

4.13 Measurement techniques:

For the present study, visualisations are performed by using standard digital video equipment. With this method, different regimes in the flow patterns can easily be characterised. Additionally, an ultrasonic velocimeter was used for measurements of the fluid velocity thereby characterising the stirring action.

目前的研究是通過使用標(biāo)準(zhǔn)可視化的數(shù)字視頻設(shè)備。使用這種方法，可以很容易地在歸納出不同的流譜效應(yīng)。此外，超聲波測速儀也被用于測量流體的速度，從而刻畫的攪拌作用。

5 Results & Discussion

結(jié)論

Wettability: 濕潤性：

In Figure 4 the difference in the bubble formation process between a wettable and non wettable plug is shown. The close-ups of the plug in the top two photographs clearly shows the significant increase of bubble size for non wettable plugs. This can be explained by the bottom pictures. Because the liquid is not wettable to the plug, the gas phase will ‘wet’ the wall and large bubbles will form.

The resulting bubble plumes are also different. The plume narrows half way the liquid level indicating a larger liquid entrainment and thus a larger liquid displacement.

圖18所示，透氣磚的潤濕性和非可濕性對泡沫形成差異。插在上面兩張照片的特寫清楚地顯示了氣泡體積明顯隨著非可濕性透氣磚顯著增加。這可以由底部圖片看出。因?yàn)橐后w是不可滲潤進(jìn)透氣磚的，氣相將“濕”在墻上，大氣泡會形成。

由此產(chǎn)生的流譜圖線也不同。羽縮小一半的液位顯示一個(gè)較大的液體夾帶，從而較大的液體位移。

 

Figure 18