覆土式壓力儲槽之安全理論探討

Safety Assessment of the Earth-Covered Tanks

化學工業利用儲槽貯存暫時性的原料、中間原料、半成品或成品，是化工廠內極為重要的儲存設備。一般而言，儲槽可分球型、臥式圓筒型、立式圓柱型等不一而足。化學工廠內儲槽比起其它製程設備似乎脆弱許多，常因過壓、真空、附屬管線破管等等因素造成化學品外洩而引起嚴重災害。地下儲槽與地上儲槽同樣的作貯存液體及氣體之用。地下儲槽與地上儲槽有不同的應用價值，如何選擇適當的儲槽及其附屬設備作為特殊用途，則需周詳考慮許多因素。具體而言，地上儲槽較易建造及偵漏、具較低之外洩風險，且較少維修、紀錄之需求；然而，地上儲槽較易受火災的侵襲、需較大之土地面積、需設置在工廠之特別安全區、較易受無心或有意的破壞，且地上儲槽也受貯存總量的限制。相對於地上儲槽，地下儲槽具較低之火災侵襲風險、具較大之固定土地面積的使用；然而，地下儲槽需較多的維修保養、具較易外洩之風險，且地下儲槽如洩漏亦可能污染到土壤與地下水。覆土式壓力儲槽除可取代球型儲槽外，更具提高安全性、節省土地面積，並符合環保要求及降低建造成本之優點。覆土式壓力儲槽若能克服保養、腐蝕、地震、豪雨等等問題，或可成為明日之星。國內地狹人稠，一般廠區、儲槽、綠帶間之安全距離普遍不足，是故目標明顯的高壓液化氣球型儲槽，常成為社區民眾抗爭的對象，以覆土式壓力儲槽取代目前的球型槽或可成為離島工業區、內陸工業區新建高壓液化氣儲槽的參考。本文針對化學工業之覆土式儲槽提出設計與安全理論之解析。

Storage tanks are used extensively in the chemical process industries for storing raw materials, intermediate raw materials, semi-products and final products. Storage tanks are considered as very important process vessels in chemical plants. Generally, the storage tank can be categorized as spherical shape, horizontal cylindrical shape, and vertical cylindrical shape, etc. Storage tanks in the chemical process industry are usually involved in more accidents than other items of equipment, probably because they are fragile and easily damaged by fire attack, or slight overpressure, or vacuum. Underground storage tanks (USTs) and aboveground storage tanks (ASTs) are used to store a variety of liquids, fluids and gases. Many factors need to be considered before selecting the storage tank and accessories to suit a specific application. Specifically, ASTs are easier to install and to monitor for leaks. They also offer a less risk of leakage, reduced maintenance, and record-keeping requirements. However, ASTs present a greater fire risk, have increased land needs, may have special zoning requirements, are more prone to vandalism/damage, and can be limited in capacity. USTs offer a decreased fire risk, and often allow expanded land use. However, they present greater installation and maintenance challenges, as well as an increased potential for leakage, which could result in soil and/or ground water contamination. Earth-covered tanks offer both fire safety and economic land use; therefore, they can be used in substitution for spherical tanks provided that the problems such as maintenance, corrosion, earthquake and shower rains can be solved. Most often, safety distance between storage tank farms and process area are not separated enough in chemical plants of Taiwan. Earth-covered tanks have the potential in place of spherical tank spheres, both in offshore and in-land industrial area. The design and theoretical study of safety aspects of the earthcovered tanks are presented in this paper.