Thread Content
Current Status and Development Trends of Wastewater Treatment in U.S. Refineries – Information on the Petroleum and Petrochemical Industry http://mmbiz.qpic.cn/mmbiz_jpg/V30nKrJZmDTgKnMbaS9SCCBibic8ll39jfNS2soodXv5GiaqFibMBO4j86IqE1DhPIoTorm2e0Xw9buFynTtls6V6A/0?wx_fmt=jpeg 1. Introduction: The wastewater generated during oil refining processes has a complex composition; it contains high levels of organic substances, particularly hydrocarbons and their derivatives, and has poor biodegradability； Affected by emulsification, oil pollution is severe ； Affected by alkaline slag wastewater and pickling water, the pH of the wastewater changes significantly; it is necessary to adjust the water usage procedures frequently based on the conditions of the raw materials, which results in frequent and substantial fluctuations in water quality and quantity. This makes it a type of wastewater that is difficult to treat. In recent years, the refining capacity of many refineries in our country has increased to the tens of millions of tons per year. Under the circumstances of increasingly stringent environmental policies, how to handle large amounts of refinery wastewater has become a major issue in the development of the refining industry. Globally, the United States has the strongest oil refining capacity; 5 of the 22 large-scale refineries in the world with an annual processing capacity of over 20 million tons are located in the United States. According to statistics from the U.S. Energy Information Administration, as of 2014, there were 139 refineries in operation in the United States, with a total processing capacity of 17.73 million barrels per day, accounting for about 20% of the world’s total crude oil processing capacity. Currently, the U.S. petroleum refining industry discharges 0.48 to 0.95 cubic meters of wastewater per ton of crude oil processed. In 2011, the amount of toxic pollutants released by this industry was third highest, only behind the organic chemical and papermaking industries, making it a major source of water pollution in the United States. In recent years, influenced by the overall conditions in the global refining industry such as declining crude oil quality and stricter requirements for deep processing, many additional catalytic reforming and desulfurization units have been installed. As a result, sulfur compound emissions in wastewater have decreased by 54% compared to 2009. However, the total amount of toxic pollutants emitted has doubled; emissions of dioxins and mercury have increased by 38% and 4 times respectively, making wastewater treatment increasingly difficult. This situation is similar to that in China’s refining industry. Therefore, understanding the current status and development trends of wastewater treatment at this American oil refining giant holds significant reference value for the sustainable development of China’s refining industry. 2. Current status of wastewater treatment in U.S. refineries 2.1 Sources and water quality analysis of wastewater from U.S. refineries Refinery wastewater originates from various stages of the refining process, and depending on its source, the degree of pollution and the types of pollutants present vary. In U.S. refineries, wastewater primarily originates from the production processes, circulating cooling systems, and the preparation of chemical water. The wastewater generated across the plant includes process wastewater, cooling water waste, wastewater from water treatment processes, steam condensate, laboratory wastewater, as well as wastewater resulting from various other activities such as daily operations, maintenance, etc. The types of pollutants and their emission levels in the wastewater generated by typical U.S. refineries are shown in the table below: Waste water discharge from major units and types of pollutants; Unit name, type of waste water and main pollutants, Waste water discharge volume (cubic meters per ton), Proportion of total waste water (%). Crude oil desalination: Desalination wastewater (salts, metals, phenols, floating oils, ammonia nitrogen, sulfides, and suspended solids) – 0.03–0.14. Crude oil distillation: Acidic water (ammonia nitrogen, sulfides, phenols, chlorides, thiols) – 1.0844. Thermal cracking: Acidic water (hydrogen sulfide, ammonia nitrogen, phenols, suspended solids) – 0.053. Catalytic cracking: Acidic water (ammonia nitrogen, sulfides, phenols, oils, cyanides, suspended solids) – 0.3626. Hydrocracking: Acidic water (high concentrations of sulfides, ammonia nitrogen, suspended solids) – 0.053. Coking: Acidic water (hydrogen sulfide, ammonia nitrogen, suspended solids) – 0.022. Alkylation: Alkali sludge wastewater (alkali sludge, hydrofluoric acid) – 0.064. Isomerization: Acidic water (sulfides, ammonia nitrogen) and alkali washing wastewater (small amounts of phenols and chlorides) – 0.022. Catalytic reforming: Acidic water (sulfides, ammonia nitrogen, suspended solids, thiols, oils) – 0.1410. Hydroprocessing: Acidic water (hydrogen sulfide, ammonia nitrogen, phenols) – 0.022. Etherification pretreatment wash water (nitrogen pollutants)