脈衝噴氣式濾袋屋洗袋性能之研究

Abstract

在脈衝噴氣式濾袋屋洗袋過程的數值模擬研究中，數值洗袋模式用來模擬不穩態的脈衝洗 袋過程，此研究的目的在提供一個最佳的設計及操作條件以獲得較高的洗袋作用力，數值 模擬的結果顯示，預測的洗袋壓力值與實驗結果非常符合。研究結果顯示，壓力儲槽的初 始壓力、噴嘴大小、噴嘴與濾袋口的距離與脈片閥開畢時間間隔為影響濾袋內洗袋壓力衝 量 (pressure impulse) 最重要的參數，其最佳值分別為，噴嘴大小：30 mm；脈片閥開 畢時間間隔：300至600 msec；噴嘴與濾袋口的距離：60 cm，在其他的操作條件固定之下 ，增加壓力儲槽的壓力為提高洗袋效率最方便的方法。對於不同於此系統的脈衝噴氣式濾 袋屋而言,此數值模式亦可適用於模擬最佳化洗袋參數.在噴射泵的性能對洗袋效果影響的 研究中，使用乾淨濾袋進行洗袋實驗，濾袋的加減速度及濾袋內的壓力脈衝可用來當成洗 袋作用力的指標，在濾袋屋中，文氏管與噴嘴的組合可視為一個噴射泵，噴射泵的流量與 壓力的特性曲線與濾袋的操作曲線的交點為濾袋洗袋時的操作點，由此點可預測洗袋時， 作用在濾袋內的洗袋壓力。此外本研究亦針對影響噴射泵的參數進行因次分析 (dimensio nal analysis)。此研究的結果顯示，在未加裝文氏管的情形下，低阻力係數的乾淨濾袋 具有較高洗袋壓力值；在加裝文氏管時，高阻力係數的乾淨濾袋具有較高的洗袋壓力值， 且利用噴射泵特性曲線與濾袋操作曲線交點所得的預測壓力值與實驗結果非常吻合。此外 ，因次分析與實驗結果皆顯示，在不同操作條件下的噴射泵特性曲線，經無因次化後可重 合在一條無因次的特性曲線上，此無因次化的噴射泵特性曲線對濾袋屋的設計與操作上有 很大的幫助。在模型廠脈衝噴氣式濾袋屋的研究中，針對不同操作條件下濾袋屋的的過濾 曲線及洗袋性能進行研究。結果顯示，洗袋系統的儲槽壓力與噴嘴大小對過濾曲線有很大 的影響，過濾週期隨洗袋系統的儲槽壓力與噴嘴大小增加而增加，但當儲槽壓力超出某一 定值後，過濾週期會到達一定值。本研究中，有效殘餘壓差 (effective residual press ure loss) 用來當成洗袋效率的指標，而作用在濾袋內的過壓力(overpressure)則用來當 為洗袋作用力的指標，實驗結果顯示，在洗袋系統中存在一個臨界的洗袋作用力，太高的 儲槽壓力與噴嘴大小會造成洗袋能量的損失。在本實驗中，加裝文氏管時會增加作用在濾 袋內的平均過壓力，因此增加洗袋效果。因此由此結果建議加裝文氏管以獲得較高的洗袋 作用力與洗袋效果。但在濾袋屋洗袋系統中,是否加裝文式管端視粉塵餅性質與濾袋的過 濾面積而定. In the study for simulating pulse-jet cleaning process, a numerical model was developed to simulate the unsteady, compressible pulse-jet cleaning process fo r a fabric filtration system. The objective is to find best design and operat ing conditions that provide more cleaning force for bag cleaning. The simulat ed results of air pressure and flow distributions in the system agree reasonab ly well with the experimental data. The study shows that initial tank pressur e, nozzle diameter, distance between nozzle and bag top and pulse duration are the four major parameters influencing the pressure impulse in the fabric bag . The optimized nozzle diameter is 30 mm, pulse duration is from 300 to 600 m s, distance between nozzle and bag top is 60 cm. Given all other conditions f ixed, increasing the tank pressure seems to be the most convenient way to achi eve a higher bag cleaning efficiency. For optimizing a pulse-jet cleaning sys tem other than the current system, the same model can also be used.In the stud y for investigating the performance of the jet pump curve, a filter test syste m with a clean bag was used to measure the pulse pressure and acceleration/dec eleration of filter bag. Fabric acceleration and pulse pressure were used as an index of bag cleaning intensity. The jet pump curves which relate the flow rate through the venturi to the average developed pressure by the venturi wer e measured by the similar system. The bag operating lines which relate the pr essure drop to flow rate across the bag during pulse-jet cleaning were also de termined. The intersection of the jet pump curve and the bag operating line i s the system operating point which was used to predict the average pulse press ure of the bag during the pulse-jet cleaning. Dimensional analysis for jet pu mp performance was also developed in order to reduce the experimental works. Experimental results of this study show that a higher pulse pressure can be a chieved without the venturi at the bag top for bag materials with low resistan ce coefficient. For bags with higher resistance coefficients, higher pulse pr essure are obtained with venturi installed at the bag top. The predicted pres sure values are in good agreement with experimental data. The analyzing resul ts for the experimental data of jet pump curves show that the jet pump curves obtained under different operating conditions can be shifted to the same nondi mensional curve. The nondimensional curve can be used to facilitate the desig n and operation of a pulse-jet cleaning system. In the pilot-scale baghouse st udy, filtration curves and pulse-jet cleaning effect for different operating c ondition is investigated. It is found that filtration curves vary with the in itial tank pressure and nozzle diameter of the bag cleaning system. The filtr ation time increases with the increasing initial tank pressure or nozzle diame ter. However, a critical value of the tank pressure exists for effective bag cleaning. In this study, effective residual pressure loss is used as an index of bag cleaning effect. Average pulse overpressure inside the bag is used as an index of bag cleaning intensity. It is found that an critical effective r esidual pressure loss value exists for this pulse-jet cleaning system. Too la rge initial tank pressure and nozzle diameter result in a waste of cleaning en ergyThe addition of the venturi appreciably increases the average pulse overpr essure, hence increasing the cleaning effect. In this study, a venturi is sug gested to be installed to increase the bag cleaning effect and to maximize cle aning energy. However, the necessity of venturi dependson the property of dust and the filtration area of fabric filter.