PM2.5連續排放監測採樣系統研發

Abstract

空氣污染是對人體健康最大的環境威脅之一，改善空氣品質是全球各國政府的首要任務。對於粒狀污染物（PM），特別是氣動粒徑小於2.5 μm的PM2.5所帶來的健康風險，已引起各個領域的廣泛關注。先前的研究發現PM2.5能夠輕易進入人體肺部甚至血液循環，進而影響呼吸和心血管系統，長期接觸粒狀污染物可能會增加死亡率並降低平均預期壽命。在世界衛生組織（WHO）在2021年9月發布的最新空氣品質指南中，將PM2.5的年平均濃度從之前的10 μg/m3降低至5 μg/m3。這一調整將推動全球各國實施更積極和嚴格的污染控制策略以持續實現減排目標。 固定污染源是PM2.5排放的重要來源之一，為了加強對這些來源的監測和控制，並促進操作變更許可制度的實施，有關部門積極推動對排放管道中PM的檢測。定期檢測的目的不僅在於檢查和控制污染防製措施，還在於逐步建立台灣不同空氣品質區域固定污染源的總PM排放數據，這些數據可作為未來制定空氣品質標準和實施減少空氣污染措施的重要基礎。然而傳統的人工採樣技術面臨一些挑戰，它們需要熟練的操作，這會耗費大量的資源和時間。此外，它們還容易受到天氣條件的影響，限制了行政效率的提高。 隨著科技的進步，粒狀物連續排放監測系統（PM CEMS）已成為一種解決方案。PM CEMS可以在無人干預的情況下監測排放管道，並且不受天氣條件的影響，提供粒狀物排放濃度的即時數據。因此，PM CEMS有望成為公平、公正地實施粒狀物控制政策的重要工具，同時也能提高行政效率。然而，確保PM CEMS的資料品質對於決定政策實施的成功與否至關重要。準確性、可靠性以及遵守標準化的測量協議是維護數據完整性的關鍵考量。必須實施強大的品質保證和品質控制程序，以驗證和確認PM CEMS數據的準確性，確保其對於決策過程和政策制定的可信度。 市售的PM CEMS通常可分為兩種主要類型：現址式和抽取式。現址式PM CEMS直接在排氣管的內壁上安裝監測設備。但是現址式PM CEMS的讀數易受粒狀物本身特性和水分凝結等因素的干擾。除此之外，隨著粒狀物處理方法的改善，排放濃度已逐步降至低於光學傳感器偵測下限的濃度，這使得獲取有效監測數據變得具有挑戰性。這些因素導致現址式PM CEMS逐漸被抽取型PM CEMS取代。抽取式PM CEMS使用安裝在排氣管外壁上的採樣管從排放管道中進行採樣，並將其引入分析儀器中進行濃度測量。以往對抽取式PM CEMS的研究主要集中在其檢測原理，例如比較β粒子衰減傳感器（β-gauge）或錐形元件振動微天平（TEOM），採樣管道中粒狀物的沉積損失尚未受到足夠的關注。實際上，不適當的採樣管道設計和操作設置可能導致採樣結果出現顯著偏差。因此，下一代的PM CEMS除了需要更敏感和快速的檢測器外，還應該致力於避免或減少粒狀物在採樣管道中的沉積損失。解決這個問題對於確保工業上粒狀物排放的準確可靠測量以及支持有效的空氣污染控制策略至關重要。 較高的吸入效率（aspiration efficiency）與傳輸效率（transport efficiency），是具有代表性氣膠微粒採樣的理想要件。吸入效率的確保是透過等動力採樣（isokinetic sampling）的實施，其中「同軸」與「等速」是等動力採樣的兩大執行要點。當採樣的微粒粒徑越大時，需嚴格遵守上述的原則。由於排放管道大多以垂直地面的方式設立，因此抽取式PM CEMS的採樣導管通常需要透過直管與彎管的組合以調整吸氣嘴方向，以符合同軸採樣的要求。而當氣膠微粒進入採樣導管之後，便開始受到重力沉降、慣性衝擊及擴散等機制的作用，使得微粒有機會與導管內壁接觸，造成沉積損失。而上述作用機制的效率都是微粒粒徑的函數。目前雖然已經有許多的理論模式，可以分別計算直管或彎管的微粒沉積損失，但在組合管道的採樣過程中，需要加裝溫、濕度調理裝置時，就只能夠透過實際實驗的方式，以評估不同粒徑微粒在整個採樣導管中的輸送效率。 因此，本研究旨在於實驗室中建立一套可調控微粒粒徑分布、溫度、含水率、氣體流速的實驗系統，並搭配直讀式氣膠量測技術，實際測試不同管徑與管長的金屬直管，以及不同彎曲角度與曲率的彎管，分別在不同擺放角度與不同抽氣流率下的微粒穿透率曲線。進一步利用這些結果，計算不同大小顆粒因重力沉降、慣性沖擊和紊流擴散等機制引起的損失。通過比較結果，尋找適合的數值模型，以促進並加速未來採樣管道的設計。另一方面，提出了粒徑選擇式PM CEMS的概念，旨在將監測範圍從總懸浮微粒縮小到僅監測對人類健康和環境造成更大風險的小微粒。這是因為微粒的運輸效率是其粒徑大小的函數，較小的微粒具有較高的運輸效率，通過適當的設計即可以將小微粒的損失降低到足夠低的水平。本研究選擇了2.5 μm作為截取粒徑，這是因PM2.5被的危害被廣泛認可。通過實際測試，設計並驗證了具有最小顆粒損失特性的通用PM2.5採樣系統。 在第一章中，我們在實驗室中建立了一套通用的氣膠微粒產生及量測系統，並討論了使用APS測量液態顆粒的校準方法。通過此系統，我們驗證了現存的用於預測微粒在直采樣管中微粒傳輸效率的預測模式，並提出直採樣管道的設計原則。 在第二章中，對於彎管中微粒傳輸效率的預測模式進行了實驗驗證，並討論了影響彎管微粒傳輸效率的因素。在本研究中，我們通過大量的實驗獲取了一個新的經驗公式，彎管采樣管的佳化設計也進行了討論和驗證。 在第三章中，我們開發了一個低微粒損失的氣膠調理器用以預處理高溫和高含水量的煙道氣體。然後通過過模式計算設計了調理器前端的采樣管用以組成PM2.5 CEMS的採樣系統。本章介紹並討論了PM2.5 CEMS的概念，並探討了其潛在需要達到的性能規格。 在第四章中，開發了一種向下出口的PM2.5旋風分徑器，與VSCC和180°彎管的組合進行了比較。此外，我們還探討了分徑器的結構設計及負載效應對分徑器效能的影響，並在綜合評估後進行了PM2.5 CEMS分徑器的構型選擇。

Air pollution is one of the greatest environmental threats to human health, and improving air quality is a top priority for governments worldwide. Health risks associated with particulate matter (PM), particularly particles smaller than 2.5 μm (PM2.5), have drawn significant attention from various sectors. Previous research has shown that PM2.5 can easily enter the lungs and even the bloodstream through respiration, thereby affecting the respiratory and cardiovascular systems. Long-term exposure to PM can increase mortality rates and reduce average life expectancy. In September 2021, the World Health Organization (WHO) published the newest Air Quality Guidelines, lowering the annual average concentration of PM2.5 from the previous 10 μg/m3 to 5 μg/m3. This revision is expected to drive countries worldwide to implement more proactive and stringent pollution control strategies to continue achieving emission reduction targets. Stationary pollution sources remain a significant contributor to PM2.5 emissions. To enhance the inspection and control of these sources and facilitate the implementation of a permit system for operational changes, authorities have actively promoted the detection of PM in emission stacks. Regular monitoring serves the purpose of not only inspecting and controlling pollution prevention measures but also gradually establishing crucial data on the total emissions of PM from stationary pollution sources in different air quality regions of Taiwan. This data can serve as a primary foundation for formulating future air quality standards and implementing measures to reduce air pollution. However, manual sampling techniques present several challenges. They require high technical expertise and consume significant resources and time. Moreover, they are susceptible to weather conditions, which limit administrative efficiency improvement. With technological advancements, particulate matter continuous emission monitoring systems (PM CEMS) have emerged as a solution for monitoring PM emissions without human interference and being unaffected by weather conditions. These systems can provide real-time data on PM emission concentrations. As a result, PM CEMS are poised to become essential tools for implementing policies on PM control fairly and equitably while also improving administrative efficiency. However, ensuring the quality of data generated by PM CEMS is critical in determining policy implementation's success or failure. Accuracy, reliability, and adherence to standardized measurement protocols are key considerations in maintaining data integrity. Robust quality assurance and quality control procedures must be implemented to validate and verify the accuracy of PM CEMS data, ensuring its credibility for decision-making processes and policy formulation. Commercially available PM CEMS can generally be categorized into two main types: in-situ and extractive. In-situ PM CEMS involves directly installing monitoring equipment on the inner wall of the exhaust duct. However, readings from in-situ PM CEMS are susceptible to influences and disturbances caused by the physical characteristics of particles and moisture condensation. Additionally, as particulate matter treatment methods improve, emission concentrations have decreased to levels below the detection limit of optical sensors, making it challenging to obtain effective monitoring data. These factors have led to the gradual replacement of in-situ PM CEMS by extractive PM CEMS. Extractive PM CEMS, as the name suggests, uses sampling pipes installed on the outer wall of the emission duct. These pipes extract gas samples containing particulate matter from the emission duct using a power source and introduce them into the analytical instrument for measurement. Previous research on extractive PM CEMS has primarily focused on detection principles, such as comparing beta particle attenuation sensors (β-gauge) or tapered element oscillating microbalance (TEOM). However, the deposition loss of particles in the sampling pipes has not received sufficient attention. In reality, inadequate sampling pipe design and incorrect operational settings can lead to significant deviations in the sampling results. Therefore, the next generation of PM CEMS, in addition to requiring more sensitive and rapid detectors, should also aim to avoid or minimize the deposition loss of particles in the sampling conduits. Addressing this issue is crucial to ensure accurate and reliable measurement of particulate matter emissions in industrial processes and support effective air pollution control strategies. Achieving higher aspiration and transport efficiency is essential for representative aerosol particle sampling. To ensure aspiration efficiency, isokinetic sampling is implemented, with "coaxial" and "isokinetic" being the fundamental principles of stack sampling. These principles should be strictly followed when sampling particles with larger diameters. As emission stacks are typically oriented vertically, the sampling tube of extractive PM CEMS often requires a combination of straight tubes and elbows to adjust the nozzle's direction for intake, ensuring compliance with coaxial sampling requirements. Once aerosol particles enter the sampling conduit, they are subjected to mechanisms such as gravitational settling, inertial impaction, and diffusion. These mechanisms can cause particle contact with the inner wall of the conduit, leading to deposition loss. The efficiency of these mechanisms depends on the particle size. While various theoretical models exist to calculate particle deposition losses in straight tubes or elbows individually, when dealing with sampling processes involving combined tubes and the installation of temperature and humidity conditioning devices, it becomes necessary to evaluate the transport efficiency of particles of different sizes throughout the entire sampling assembly through experimental methods. By conducting experiments, the transport efficiency of particles in different size ranges can be determined, taking into account the effects of combined tubes and the presence of temperature and humidity conditioning devices. This comprehensive evaluation is crucial for optimizing the sampling assembly design, minimizing particle deposition losses, and ensuring accurate measurement of aerosol particles in industrial emissions. Therefore, this study aims to establish an experimental system in the laboratory that can control the particle size distribution, temperature, humidity, and gas flow rate. It will be combined with direct-reading aerosol measurement technology to conduct practical tests on straight metal tubes of different diameters and lengths, as well as bent tubes with different bending angles and curvatures. The particle penetration curves will be examined under different orientations and extraction flow rates. The results will be further used to calculate the losses caused by mechanisms such as gravity settling, inertial impaction, and turbulent diffusion for particles of different sizes. By comparing the results, suitable numerical models will be sought to facilitate and expedite the design of sampling conduits in the future. On the other hand, the concept of size-selective PM CEMS has been proposed, which aims to narrow down the monitoring range from Total Particulate Matter to only monitoring the smaller particles that pose greater risks to human health and the environment. This is because the particle transport efficiency is a function of particle size, and smaller particles have higher transport efficiency. With proper design, the loss of small particles can be reduced to a sufficiently low level. This study selected a cutoff size of 2.5 μm as the cut point, as PM2.5 is widely recognized as a severe particulate pollutant. A universal PM2.5 sampling system with minimal particle loss characteristics was designed and validated through actual testing. In Chapter 1, a general aerosol particle generation and measurement system was established in the laboratory, and the calibration method for measuring liquid particles using APS was discussed. The predictive models for particle transport efficiency in straight tubes was validated. In Chapter 2, the predictive models for particle transport in bent tubes were experimentally validated, and factors influencing particle transport efficiency in bend was discussed. A new empirical model was developed. Besides, an optimal design for improving the bend tube was discussed. In Chapter 3, a novel low particle loss aerosol conditioner was developed for pre-treating high-temperature and high water content flue gas, and a set of sampling pipelines was designed. In this chapter, the concept of PM2.5 CEMS was introduced and discussed, and the performance specifications of PM2.5 CEMS was explored. In Chapter 4, a downward outlet PM2.5 cyclone separator was developed to compare with the combination of a VSCC and a 180° bend. The factors affecting the separation curve sharpness and cutoff particle size was investigated. The particle loading effect was also tested. The final selection was made after a comprehensive evaluation.