'' United States Environmental Protection Agency Industrial Environmental Research Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-84-139 Sept. 1984 Project Summary Process Design Manual for Stripping of Organics Harish M. Shukla and R. Edwin Hicks Procedures and correlations for de- signing and costing stripping towers for the removal of organics from aqueous streams are presented. The emphasis is on practical methods suitable for engi- neering estimates. The designs cover steam strippers with and without con- densers and reflux, as well as air stripping. Steam stripping is treated as an isothermal process and simplified equations for determining tower height may be used. Determination of the height adiabatic air strippers involves a tedious, iterative solution of heat and material balances. A BASIC computer program for carrying out these calcula- tions is provided. Capital costs are determined, essenti- ally, by estimating the quantity of materials required in conjunction with material costs. Cost factors for a range of materials and installation factors are suggested. Methods for costing ancil- lary equipment such as heat exchangers, pumps, compressors, and storage ves- sels are included. It is recommended that vendor quotes be obtained wher- ever possible. Typical operating costs for energy and maintenance are also given. This Project Summary was developed by EPA's Industrial Environmental He- search Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Stripping is one of several processes used commercially for separating organ- ics from water and wastewater. The selection of the optimum process for any given application is dependent on the characteristics of the organics as well as on other factors including cost and the need to recover the separated organics. In the case of a mixture of organics having different properties, two or more treatments in series may have to be provided. The use of two different pro- cesses, for example, one with cost de- pendent on throughput, followed by a polishing step having cost dependent on feed concentration, can result in a lower overall treatment cost. In a wastewater treatment train, stripping is typically the first process that separates dissolved substances. It follows clarification or filtration steps that are used for removal of suspended solids and may precede polishing steps such as carbon or resin adsorption. The essential characteristic that deter- mines the effectiveness of stripping in separating dissolved organics is the rela- tive volatility or vapor pressure of the organic above the aqueous phase. It has been shown that at least half of the 186 organics on the USEPA's toxic pollutant list are sufficiently volatile to be effectively removed from aqueous waste streams by stripping. Sixty-eight of these can be very easily stripped by air at ambient tempera- tures. Others can be stripped by air at ambient temperatures with steam. The remaining substances on the list have relatively low vapor pressures and are not easily stripped. Stripping is emerging as a cost-effective alternative for treating a wide range of aqueous streams containing organics. It may be used both as an in-plant process for the recovery of organics from relatively concentrated aqueous streams and as an end-of-pipe treatment for removal of dilute and even trace quantities of organ- ics from wastewaters prior to discharge ------- or recycle. Steam stripping is typically used for in-plant separation, whereas air or steam may be used for end-of-pipe treatment, depending on the volatility of the organics and post-treatments pro- vided. In addition, air stripping is being increasingly used for the removal of trihalomethanes (THMs) and trichloro- ethylene (TCE) from drinking water supplies. Purpose The purpose of this manual is to provide, within a single document, both data and procedures for designing and costing stripping systemsfor organics separation. A major objective was to develop and summarize simplified and practical engi- neering procedures of study grade ac- curacy. The designs and costs obtained are suitable for evaluating the feasibility and viability of stripping relative to other control technologies and for checking commercial designs. They are not in- tended for detailed or definitive designs. Scope The design procedures cover: 1. Tray and packed towers 2. Air and steam stripping 3. Live and reboil steam 4. Refluxed and non-refluxed steam stripping 5. Isothermal and adiabatic operation 6. Continuous operation 7. Ancillary equipment including heat exchangers The design and cost procedures are summarized in a stepwise fashion to facilitate their routine use. Procedures for using the simplified analytical equations appropriate to most stripping applications are demonstrated by means of a worked example. A BASIC program suitable for desk-top computers is provided for the case of adiabatic air stripping where the usual simplified equations are less reli- able. A comprehensive review of the theory of stripping and the development of the design equations is also included. Although the manual is not intended as a text, the reader may find the background material useful as a refresher course in stripping. We recommend that all users scan the background sections, particularly with reference to the limitations on the procedures and data. The process design is oriented towards single-component relatively dilute sys- tems. Other systems can nevertheless be handled as well. For example, multicom- ponent systems can be sized by designing for the least volatile organic, and then determining the distribution of the other components separately. Use of the simpli- fied design correlations for concentrated streams may result in errors due to thermal effects and deviations from vapor-liquid equilibrium correlations. The more rigorous design equations may, however, be used without difficulty pro- vided the necessary enthalpy and equi- librium constant data are available. The design of ancillary systems such as decanters and other vapor handling equipment is specifically not handled. Multiple towers and batch stripping are also not treated. Maintenance and opera- tional problems are not discussed, and controls, instrumentation, and civil design are not covered. The cost of these items is nevertheless included in the budget estimates. Harish M. Shukla andR. Edwin Hicks are with Water General Corp., Waltham, MA 02154. Kenneth A. Dostal is the EPA Project Officer (see below). The complete report, entitled "Process Design Manual for Stripping of Organics," (Order No. PB 84-232 628; Cost: $14.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Industrial Environmental Research Laboratory U.S. Environmental Protection Agency Cincinnati. OH 45268 -Cf\JS GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7811 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 ------- |