Computers and Chemical Engineering 24 (2000) 2093 – 2113 A review of recent design procedures for water networks in refineries and process plants  Miguel Bagajewicz * School of Chemical Engineering and Materials Science, Uniersity of Oklahoma, 100 E. Boyd St, T-335, Norman, OK 73019, USA Abstract This paper presents a review of the procedures to design and retrofit water networks. Although the emphasis is in showing results for refineries, the methods are valid for any process plants. It is first shown that the problem has been decomposed into the design of two interacting subsystems. One problem is the freshwater and wastewater reuse allocation and the other is the wastewater treatment problem. It is also shown how the wastewater treatment problem was modeled as a distributed and decentralized treatment. The roadmap towards zero liquid discharge and energy integrated solutions is then discussed. Several solution approaches are briefly outlined emphasizing the main trend leaning towards the use of mathematical programming. The major claim made is that mathematical programming can produce globally optimal solutions and practically important sub-optimal solutions when conceptual insights are employed to build the models. Although the paper intends to be comprehen- sive, it emphasizes the author’s recent work. Finally, a few of the existing challenges of the area are outlined. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Water systems; Wastewater minimization; Wastewater reuse; Wastewater recycle; Wastewater regeneration; Wastewater treatment www.elsevier.com/locate/compchemeng 1. Introduction Water is a key element for the normal functioning of the chemical and petrochemical industry. Steam strip- ping, liquid – liquid extraction and washing operations are among the many processes present in refineries and chemical plants where water is intensively utilized. In refineries, steam is used in atmospheric and vac- uum crude fractionation, as well as in coking, hydroc- racking, FCC, visbreaking, sweetening, hydrotreating, alkylation, ether synthesis, etc. In addition, water is used in desalters to remove primarily the salted water droplets that the crude contains. However, several other contaminants are also removed (H 2 S, suspended solids, ammonia, etc). In caustic treating water is used and the principal contaminants are H 2 S, ammonia, phenol, mercaptans, etc. Water is also intensively used in hy- drometallurgy where many suspended solids as well as a large variety of ionic metals can be found. In addi- tion, since liquid – liquid extraction is often used, or- ganic solids are also present. In the iron and steel industry vast amounts of water are used in cooling of blast furnaces and casting machinery, quenching of slag, scrubbing of gases with waste waters containing sulfides, cyanides, sulfur dioxide, calcium oxide and chromates. The food and agricultural industries (sugar factories, dairy industries, breweries) make use of water for a variety of washing operations and steam in evapo- rators. Other industries with intense use of water are the textile industry, the pharmaceutical and electronic component industry. Several measures exist to assess the quality of water for discharge. For example, the total organic carbon (TOC), the biochemical oxygen demand (BOD) and the chemical oxygen demands (COD) indicate the organic matter content. Oil and grease (O&G) and total petroleum hydrocarbons (TPH) give a measure of the presence of oil, grease and other hydrocarbons. The physical characteristics of the wastewater are also ad- justed before disposal. These characteristics include the total suspended solids (TSS), pH, temperature, color and odor. In compliance with the United States EPA Clean Water Act of 1977, wastewater must be treated  II Pan American Workshop in Catalysis and Process Systems Engineering, September 2 – 3, 1999, Santa Fe, Argentina * Tel.: +1-405-3255811; fax: +1-405-3255813. E-mail address: bagajewicz@mailhost.ecn.uoknor.edu (M. Baga- jewicz). 0098-1354/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0098-1354(00)00579-2