脱硫塔从工作原理上可分为开式与闭式两类。
Desulfurization tower can be divided into open type and closed type from the working principle.
其中，开式脱硫塔的基本原理是利用表层海水天然的弱碱性中和发动机燃烧废气中的硫氧化物，从而达到脱硫的最终目的，其优势是设备工作原理简单，改造方便，且改造成本低。运行过程中不会产生额外的污染物，也无需额外的消耗品，总体经济性较好。
Among them, the basic principle of the open desulfurizer is to neutralize the sulfur oxide in the combustion exhaust gas of the engine by using the natural weak alkali of the surface seawater, so as to achieve the ultimate goal of desulfurizing. The advantages of the open desulfurizer are simple working principle of the equipment, convenient transformation, and low transformation cost. In the operation process, there will be no additional pollutants and consumables, so the overall economy is good.
但从本质上来说，开式脱硫塔相当于将原本排放到空气中的污染物直接排放到海水中，这种做法对于不少港口国，特别是海洋环境相对封闭的港口国而言都是难以接受的。
But in essence, the open desulfurization tower is equivalent to directly discharging the pollutants originally discharged into the air into the sea water, which is unacceptable for many port countries, especially those with relatively closed marine environment.
特定港口国对于开式脱硫塔的禁令在影响上只是局部性的，而由于巴拿马运河是连接太平洋与大西洋的重要水道，因此运河当局对开式脱硫塔的禁令则是全局性的。
As the Panama Canal is an important waterway connecting the Pacific Ocean and the Atlantic Ocean, the ban on open desulfurizer by canal authorities is overall.
从目前巴拿马运河的通航能力来看，这相当于是禁止所有13500TEU以下集装箱船、苏伊士型以下油轮、大型矿砂船(VLOC)以下散货船等国际航运市场上的绝大部分船型，安装开式脱硫塔。
From the perspective of the navigation capacity of the Panama Canal at present, this is equivalent to banning the installation of open desulfurizer towers on most ship types in the international shipping market, such as container ships under 13500teu, tankers under Suez, bulk carriers under VLOC, etc.