Format And Type Fonts CCHHEEMMIICCAALL EENNGGIINNEEEERRIINNGG TTRRAANNSSAACCTTIIOONNSS VOL. 45, 2015 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Jiří Jaromír Klemeš, Sharifah Rafidah Wan Alwi, Jun Yow Yong, Xia Liu Copyright © 2015, AIDIC Servizi S.r.l., ISBN 978-88-95608-36-5; ISSN 2283-9216 DOI: 10.3303/CET1545040 Please cite this article as: Kapustenko P.O., Ulyev L.M., Ilchenko M.V., Arsenyeva O.P., 2015, Integration processes of benzene-toluene-xylene fractionation, hydrogenation, hydrodesulphurization and hydrothermoprocessing on installation of benzene unit, Chemical Engineering Transactions, 45, 235-240 DOI:10.3303/CET1545040 235 Integration Processes of Benzene-toluene-xylene Fractionation, Hydrogenation, Hydrodesulphurization and Hydrothermoprocessing on Installation of Benzene Unit Petro O. Kapustenko a , Leonid M. Ulyev* ,b , Mariia V. Ilchenko b , Olga P. Arsenyeva a a AO SPIVDRUZHNIST-T LLC, Krasnoznamenny per. 2, off. 19, 61002, Kharkiv, Ukraine b National Technical University “Kharkiv Polytechnic Institute”, 21 Frunze Str., 61002, Kharkiv, Ukraine leonid.ulyev@gmail.com The heat exchanger network (HEN) of the unit of benzene production at petrochemical plant was inspected and the obtained data were analyzed for possible plant retrofit targeting the minimal energy consumption and increasing of plant efficiency. The benzene-toluene-xylene fractionation, hydrogenation, hydrodesulphurization and hydrothermo processing units of the plant were analysed and the data of existing HEN flowsheets were extracted. The minimum temperature difference for the retrofit was determined by analyzing the cost parameters of the proposed modifications as well as the energy cost. Using Pinch Analysis methodology the Composite Curves and Grid Diagram were obtained for the integrated processes of these plant units. The new flowsheet of the HEN of the regarded units was developed; and the possible application of heat transfer equipment was analyzed and proposed. 1. Introduction Refinery processes are one of the key components of modern industry, but at the same time they are the most power-consuming. The global rising world demand in energy for oil and petrochemical industries requires the energy efficient plant designs with the retrofitting of the existing HENs and application of effective equipment. The main part of the technological units in the countries formed after collapse of the Soviet Union was put into operation in 50ies – 70ies of the last century and more than 80 % of the equipment and flowsheets are now ineffective and consume a lot of energy as well as produce a lot of hazardous emissions. This led to the fact that the average crude oil processing yield of the oil refining plant now for some enterprises is about 70 %, when in Europe and US this parameter is usually above 90 %. The industry efficiency should be increased targeting less energy consumption and high process efficiency, what assumes its modernization and technological upgrading (Stepanov et al., 1989). The retrofit of petrochemical enterprise requires a lot of investment, high level of operating and installation costs and aimed to provide the acceptable level of crude oil processing yield by means of known techniques. The use of the methods of Pinch Analysis allows determining the rational opportunities for energy and cost minimization by improving the use of thermal energy (Kemp, 2007). The retrofit of HEN usually is performed in two steps: the first is to identify the Pinch point and to adjust properly the heat transfer loads between the heat exchangers to maximize the heat recovery between processes; the second is to propose the structural modification of the HEN focusing Pinch, which include the heat exchangers application and their installation, re-piping of the network. This approach provides various retrofit options with different degree of heat recovery, energy saving and additional capital investment (Klemeš, 2013). The petrochemical plants usually contain several process units connected to each other and to the common utility system. In the present work the enterprise OOO “Sibur-Kstovo” (Nizhny Novgorod, Russian Federation) is under consideration and its four interconnected units (benzene-toluene- xylene fractionation, hydrogenation, hydrodesulphurization and hydrothermoprocessing) involved in benzene production are analysed using the Pinch Integration. 236 2. The process description The present work observes four inter-connected units of petrochemical plant: benzene-toluene-xylene fractionation unit, hydrogenation unit, hydrodesulphurization unit and hydrothermoprocessing unit. Using Process Integration it is possible to integrate their HEN to the common network to provide the less energy consumption of these units. The unit of pyrocondensate processing consists of the following process blocks (Ulyev et al., 2014): (1) Extraction of benzene-toluene-xylene fraction from pyrocondensate in column K-301; (2) Hydrogenation, hydrodesulphurization and hydrothermoprocessing in the reactors R- 301, R-302, R-303/1 R-303/2; (3) Stabilization and separation of hydrodealkylate in columns K-305, K-306, K-307 with separation of commercial benzene; (4) Compression of hydrogen-containing gas; (5) Cleaning, drying of hydrogen-containing gas and concentration of hydrogen; (6) Compressing the low pressure methane M-303. The flowsheet of the existing processes is demonstrated in Figure 1. Figure 1: The flowchart of the existing process (COMP – compressors; R – reactors; K – distillation columns; M – mixers; HE – heat exchangers; GC – gas cooler; COL – coolers; AC – air coolers; RW - recycled water; HW – hot water; CW – cold water) The raw material for the benzene production is a benzene-toluene xylene (BTX) fraction, which is allocated from pyrocondensate in a distillation column K-301. The rectification of pyrocondensate in column K-301 is performed under vacuum in order to maintain the temperature of cube lower than 180 °C to avoid the polymerization of unsaturated hydrocarbons. Heat transfer in the extraction column of benzene-toluene- xylene fraction is carried out by circulating the bottoms liquid of column K-301. The benzene-toluene- xylene fraction is fed on the first stage of hydrogenation. The bottom product of column K-301 is fed to the column K-313. The rectification in column K-313 is performed under vacuum in order to maintain the temperature of cube lower than 170 °C to avoid polymerization of unsaturated hydrocarbons. The heat transfer in the column K-313 is provided by circulating of the column bottoms liquid. The benzene-toluene- xylene fraction after the coagulator is mixed with a hydrogen-consisted gas from the compressor M-302 and passes through the heater T-304 to the hydrogenation reactor of benzene-toluene-xylene fraction of the P-301 1 st stage. Hydrogenize from the 1 st stage of the reactor R-301 bottom comes to the separator. The hydrogenized liquid from the separator is fed to the M-301/1,2 mixer. A mixture of hydrogenize from the 1 st stage and hydrogen-consisted gas from the M-301/1,2 mixer are heated in the P-301 furnace, and enters the 2 nd stage of the R-302 hydrogenation reactor. The mixture of hydrogen-consisted gas with the aromatic recycle and hydrogenize from 2 nd stage is heated in P-302 oven and enters the R-303/1 reactor. The stream from the top of R-303/1 reactor enters the R-303/2 reactor. The hydrodealkylation from R- 303/2 reactor enters the GC-301 gas cooler and then comes to T-368. Hydrodealkylation from T-368 heat- exchanger sequentially passes through T-338 heat-exchangers, where it heats the hydrogen fraction coming to P-301; T-314, where it heats the feed stream of stabilizer column K-305; T-339, where it heats hydrogen-consisted gas from the compressor Comp-301 for the unit of hydrocracking and hydrodealkylation. Hydrodealkylate from the heat-exchanger T-339 is cooled in coolers T-308 and T-309, and enters to the separator. Hydrogen fraction from compressor Comp-302 passes the water cooler T-383 and enters to the separator; then it comes to the hydrogenation reactors R-301, R-302. 237 3. Data extraction process In the review of technological processes, the basic parameters of technological streams included in the integration process have been determined and the stream table of the process was obtained (Table 1) according to methodology described in book by Klemeš (2013). Table 1: The process streams data № Type TS, °C TT, °C G, kg/h C, kJ/(kg·°C) CP, kW/°C r, kJ/kg α, kW/m 2 ·K H, kW 1 hot 67.1 27 23,840 1.70 11.23 0.764 450.11 2 hot 126 96 2,509 6.93 4.83 0.764 144.47 3 hot 96 30 580 2.70 0.44 0.764 28.71 4 hot 90 30 1,109 2.39 0.74 0.142 44.29 5 hot 146 41 2,769 2.34 1.80 0.714 189.11 6 hot 680 163 11,024 2.30 7.04 0.467 3,641.29 7 hot 220 35 23,120 2.12 13.61 0.544 2,517.01 8 hot 65 25 21,860 11.09 67.36 0.484 2,694.60 9 hot 215 215 2,554 1,924 0.818 1,364.97 10 cold 133 145 37,419 2.56 26.56 0.173 324.00 11 cold 20 41 91,750 4.71 119.91 0.818 2,506.16 12 cold 130 278 15,388 2.14 9.16 0.818 1,355.07 13 cold 52 104 12,100 11.22 37.70 0.500 1,960.13 14 cold 32 62.2 21,860 2.73 16.55 0.375 499.30 15 cold 16 46.8 8,963 3.59 8.93 0.500 274.82 16 cold 192 211 93,781 2.80 72.99 0.818 1,364.97 17 cold 142 161.6 26,300 4.32 31.58 0.714 619.03 18 cold 270 565 15,014 2.91 12.11 0.818 3,573.45 19 cold 126 135 30,590 2.06 17.51 0.173 157.58 20 cold 146 159 90,950 2.29 57.85 0.173 752.11 The following flows were under consideration: 1 - Vapours of BTX-fraction from the K-301; 2 - Vapours of C9 fraction from the K-301; 3 - The gas phase of hydrocarbons from E-383; 4 - C9 fraction; 5 - Recycle hydrogenize; 6 - Cooling gas from the P-302; 7 – Hydrodealkylate; 8 - Hydrogen-containing gas from M- 302; 9 - Vapour from gas cooler; 10 - Bottoms liquid from K-313; 11 - Hydrogen-containing gas to Р-301; 12 – Hydrogenize; 13 - Hydrogen-containing gas from E-312; 14 - Hydrogen-containing gas from E-378; 15 - Hydrodealkylate to K-305; 16 - Bottoms liquid from K-306; 17 - Cold cooling water from the pyrolysis department; 18 - Hydrogenize of the 2 nd stage; 19 – Pyrocondensate; 20 - Bottoms liquid from K-301. Basing on the obtained data a Grid Diagram (Linnhoff and Flower, 1978) for the existing process was obtained. In Figure 2 the Grid Diagram, which demonstrates the process streams and existing heat exchangers connections between them is presented. The analyses of the obtained data showed that the heat consumption of the existing process for cold utilities (Qc) comes to 8,146 kW and 10,494 kW for hot utilities (QH), the heat recovery (QREC) equals to 2,930.90 kW if to consider all the heat exchangers involved in the flowchart of the processes for all four units. Such high power consumption needs Process Integration and more energy recuperation between the process streams. 4. The Heat Integration The Process Integration of the HEN requires proper determination of energy and capital targets. The main parameters, which influence the HEN capital cost includes number of heat exchangers, their heat exchanger area, the type of heat exchangers and pressure drop of heat carriers, the installed capital cost of heat exchanger and re-piping. The proper energy and cost targeting needs correct estimation of the minimum temperature difference (Tmin) between heat source and sink streams (Nordman, 2005). The annualized capital cost plotted together with annual utility cost for the range of minimum temperature difference, what corresponds to the different process modifications, provide the optimum energy consumption and indicate the corresponding Tmin (Smith, 2005). The capital cost of the heat exchanger is defined by Eq(1):   c T T Capital cost = Α +B S (1) 238 Figure 2: The Grid Diagram of the existing process where: AT is the cost of installing of shell-and-tube heat exchanger, AT = 10,000 USD; BT is the rate equivalent to the cost of 1 m2 heat transfer surface area, and for shell-and-tube heat exchangers, BT = 4,000 USD; S is the heat transfer surface area, m 2; C is the factor reflecting the non-linear dependence on the value of the cost of the heat exchanger to the heat transfer surface, and was taken C = 0.87. The selected prices of hot and cold utilities are not stable and affect the total cost target. In the present work the cost of hot utilities used in the process are taken equal to 316 USD/(kW·y) assuming 8,000 h/y activity, and for the cold utilities it was set to 10 USD/(kW·y). Using «PINCH 2.0» (Tovazhnyansky et al., 2003) software the Cost Curves were obtained and the optimum minimum temperature difference value was determined. For the observed process ΔTmin is equal to 16 °C. Basing on the targeted temperature difference (ΔTmin = 16 °C) the Composite Curves for source and sink streams were built (Figure 3). Figure 3: The Composite Curves of the integrated process for Tmin = 16 °C: 1 – Hot Composite Curve, 2 – Cold Composite Curve 239 The proposed retrofit project has the recuperation load of QREC = 10,250 kW, the minimum cold utilities are QCmin = 826.96 kW, and minimum hot utilities are QHmin = 3,175 kW, what comparing with the existing process shows the significant increase of the recuperation heat and decrease of the heat loads. For the flowsheet retrofit according to the achieved targeted loads the HEN structural changes were carried out for several possible solutions according to the principles of Pinch Analysis (Smith et al., 2000). Figure 4: The Grid Diagram of the integrated processes, Tmin = 16 °C Table 2: The existing and additional heat transfer area for the retrofitted process THOTin, °C ТВИХ ТВХ ТВИХ THOTout, °C ТВИХ ТВХ ТВИХ TCOLDin, °C TCOLDout, °C TLM, °C Q, kW S, m 2 Existing HE Additional surface, m 2 HE1 36 35.47 16 20 17.68 35.72 11 Т-388 32 HE2 65 36 20 43 18.84 1,953.59 432 Т-324, Т-338 - HE3 67.1 36 20 43.27 19.66 349.10 57 Т-304/1 17 HE4 50.95 36 20 30.17 18.29 203.48 44 - 44 HE5 96 36 20 31 26.09 26.10 4 - 4 HE6 90 36 20 35.79 31.31 39.96 15 - 15 HE7 137.35 41 20 63.36 42.08 173.86 18 - 18 HE8 75.91 50.95 32 52.53 21.09 339.71 92 Т-383 2 HE9 220 75.91 52 104 58.31 1,960.13 164 Т-368 55 HE10 355.25 163 130 278 52.03 1,355.07 111 Т-309 - HE11 680 355.25 270 458.79 142.59 2,286.22 69 Т-385 10 HE12 126 96 52.53 61.26 53.40 144.47 14 Т-377 - HE13 146 137.35 61,26 62.2 79.88 15.25 1 - 1 HE14 215 215 192 199 19.29 510.95 75 Т-386 35 HE15 215 215 133 145 75.84 324 37 - 37 HE16 215 215 142 158.79 64.24 530.02 26 - 26 240 The most energy and cost effective alternative was obtained and its Grid Diagram is presented in Figure 4. It demonstrated the integration of four units of benzene production plant, which are benzene-toluene- xylene fractionation unit, hydrogenation unit, hydrodesulphurization unit and hydrothermoprocessing unit, with the ΔTmin = 16 °C, Hot Pinch is 36 °C and Cold Pinch is 20 °C. The proposed retrofit needs 5 coolers and 5 heaters to provide the heat supply. For this process 15 heat exchangers are required. As all the used heat exchangers are of shell-and-tube type, it was proposed as much as possible to use the existing heat transfer capacities. The additional surface area for the existing heat exchangers is listed in Table 2. The heat transfer equipment for positions 4,5,6,7,13,15,16 requires purchasing the new units. For these positions in the present work the shell-and-tube units are considered, but also it is needed to analyze the possibility to use the compact heat exchangers, that will help to save the consuming energy, installation costs and material for production. The obtained retrofit project needs totally 1,170 m 2 of heat transfer surface area, from which 296 m 2 is needed additionally to increase the existing heat transfer surface area. For the case the shell-and-tube units were under consideration. The possibilities to use compact heat exchangers for some positions and the application of the Shifted Retrofit Thermodynamic Diagram methodology (Yong et al., 2014) and an Extended Grid Diagram (Yong et al., 2015) can be implemented further for more heat recovery and higher utilities saving, what is going to be the subject for future work. 5. Conclusions A Pinch Analysis and Pinch Integration methodologies were applied for the retrofit of four units of benzene production plant, namely benzene-toluene-xylene fractionation unit, hydrogenation unit, hydrodesulphurization unit and hydrothermoprocessing unit. The proposed retrofit allows reducing the power consumption by 7.3 MW. The hot utilities needed to the process operation are reduced by 69.94 % and cold utilities are 89.84 % less. The proposed retrofit of plant HEN applies the existing heat transfer equipment, and the additional heat transfer surface area comes to 296 m 2 . The calculated annual income from the project implementation is 1.56×10 6 USD and the expected payback period is about 6 months. Acknowledgment The authors would like to thank EC project Energy - 2011-8-1 Efficient Energy Integrated Solutions for Manufacturing Industries (EFENIS) - ENER/FP7/296003/EFENIS for the financial support. References Stepanov A.V., Sulzhik N.I., Goryunov V.S., 1989. The rational use of raw materials and energy resources in the processing of hydrocarbons, Technika, Kiev, Ukraine (in Russian). Kemp I.C., 2007. Pinch analysis and process integration. Second Edition: A User Guide on Process Integration for Efficient Use of Energy. Elsevier, Amsterdam, The Netherlands. Ulyev L., Yatsenko O., Ilchenko M., 2014. 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