含能物質銷毀爐之模擬與設計

Abstract

含能物質從早期多使用於武器中的槍砲彈藥，演進至近期擴展應用於工程方面的建築物拆除，科技方面的複合材料製作等，其用途愈來越廣。由於用途的改變，或儲存過久，部分含能材料不再使用，因此須將其安全地銷毀。本文設計一可利用一般貨櫃車之貨櫃大小運送的含能物質銷毀爐，其銷毀量可達每小時40公斤之含能物質。為驗證焚燒過程不致對爐壁產生過高的爆轟壓力衝擊與高溫度熾燒，本文利用數值模擬軟體Fluent進行數值計算模擬，分析不同邊界條件對於整個銷毀爐腔體內氣體流場的影響，以及爆炸後高溫高壓氣體的排放效果。藉由分析結果，探討不同條件下銷毀爐排熱效果的優劣。 本文的數值模擬分為兩步驟，首先比照Kuhl等人[1]所做的TNT密閉空間爆炸實驗裝置建立數值模型，模擬密閉空間內的爆炸過程，並驗證計算結果與實驗數據是否吻合。在密閉空間爆炸模擬結果顯示，在空氣或氮氣中爆炸所產生的壓力波傳遞至壁面之峰值皆為7.64 bar，與Kuhl等人[1]所做實驗數據結果相近，而後燃燒所造成之影響在模擬果中，腔體內的平衡壓力為2.5 bar，經校正有效體積後，與實驗結果的2.8 bar誤差為4.5%。經比對實驗數據後，確定密閉空間爆炸數值模擬算則與計算結果可以準確地預測爆炸過程。 本文接著將爆炸過程的數值模擬算則應用於本研究所設計之銷毀爐數值模型，以數值實驗的方式觀察炸藥在銷毀爐中爆炸的情況。此銷毀爐以一直徑1.5 m、長2 m之圓柱為主要腔體，其一側設有軸向與徑向進氣口，右側則為漸縮道以及抽氣口，此銷毀爐的總長度約3.5 m、寬約1.75 m、高約1.5 m，總體積約為4.15 m3。接著改變進氣口及出口的壓力值，比較不同邊界條件下之降溫效果，找出可達到每小時40公斤含能物質銷毀量之設計。在含能物質銷毀爐模擬結果中，銷毀200克TNT在爆炸後，所產生的壓力波傳遞至壁面約3 bar ，爆炸後約0.05秒內腔體內即達壓力平衡，壓力約為1.9 bar，而腔體內溫度最高約1,000K；由於兩進口不斷導入冷空氣以及出口排氣，能有效地將然氣排出使溫度持續下降；在爆炸後4秒，爐內的溫度即降至室溫左右，爐內壓力場則回復至爆炸前之壓力場，可進行第二次投入含能物質作業，達到銷毀容量的設計要求。

From military pyrotechnics to destruction of buildings and production of composites, energetic materials have a large variety of applications. Some energetic materials may no longer in service due to changes of their usages or being stored over a long period of time, and therefore should be incinerated safely. This thesis intents to design a movable incinerator for energetic materials that can be transported by a regular-size container and can handle up to 40 kilograms of energetic materials per hour. In order to validate that the incinerator will not be damaged by detonation pressure waves or burning out by extremely high temperature flames, Fluent, a computational fluid dynamics (CFD) software, was used to simulate the detonation and combustion processes in this thesis. The computational results of several boundary conditions were analyzed to explore the thermal and flow fields in the incinerator, focusing on the emission of high-temperature and high-pressure gas after combustion. The numerical simulation in this thesis can be divided into two phases. First, a numerical model was constructed based on the experimental chamber built by Kuhl et al. [1]. The TNT detonations in the confined chamber were simulated via the designed numerical scheme as the chamber was filled with air or nitrogen. The simulation results of the confined detonation in the chamber show that the peaks of shock pressures at the wall are both 7.64 bar when detonated respectively in air and in nitrogen, which are highly consistent with the data acquired in Kuhl’s experiments. In addition, the computed equilibrium pressure in the chamber with after-burning in air is 2.5 bar, which is only 4.5% lower than the Kuhl’s result of 2.8 bar, as corrected to the net volume in the experimental chamber. The high consistency of the simulation results and the experimental data validates that the designed numerical scheme can accurately predict detonation processes of energetic materials in the chamber. Secondly, the validated numerical scheme was applied to explore thermal and flow fields in a newly designed incinerator for energetic materials. The main chamber of the incinerator is circular cylinder of 1.5 m in diameter and 2 m in length. There is an end plate installed with an axial and a radial air inlets on the one side of the cylinder, and a gradually contracted duct connected to an air outlet on the opposite side. This incinerator measures 3.5 m in length, 1.75 m in width, 1.5 m in height and 4.15 m3 in total volume. This research aims at searching a better design of incinerator which has a capacity of incinerating 40 kilograms energetic materials per hour among several inlet and outlet pressure conditions in terms of lower pressure and temperature on the interior walls. The simulation results of burning 200 g of TNT at a time in the incinerator showed that the peak pressure at the wall was about 3 bar, and pressure maintained shortly at 1.9 bar when it reached an equilibrium. The highest temperature of the chamber is about 1,000 K. Due to continuously importing cool air from the two inlets and exhausting waste gas through the outlet, the temperature in the chamber continuously dropped to the ambient temperature in 4 seconds after combustion. The pressure field in the chamber also reduced to the previous condition before the incineration. By that time, the incinerator is ready for a second incineration, which meets the mission of incineration rate as designed.