Heat Exchanger Network Synthesis with Complex Phase Changes under the Consideration of Carbon Emissions based on Pinch Point Method
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摘要: 以某乙烯裂解工艺中6股用公用工程换热的物流为对象,存在混合物的复杂相变的物流,根据其热负荷和物料特性把相变段折算成一股或多股恒定热容流率的物流,确定温度区间,再用问题表确定夹点。传统夹点法确定最小传热温差△Tmin为11℃,加入碳排放目标函数后确定△Tmin为9℃,夹点热物流温度为88.3℃,冷物流温度为79.3℃,此时该换热网络所需的最小热公用工程为12727.27 kW,最小冷公用工程为38719.59 kW。根据夹点技术的设计原则和物流匹配准则,可得到能量最优的换热网络结构。Abstract: Heat exchanger network, HEN, is one of the most important parts in chemical production process. HEN optimization become an effective tool to save energy and keep sustainable development. There are many methods to optimize HEN. In principle, mathematical programming seems a comprehensive solution, while the pinch point method is still a handy tool, due to its simplicity and clear physical meaning. Special arrangement is required when phase change is considered in the system. The aim of this paper is to investigate six streams distributed in adjacent sections in an ethylene cracking process from systematic perspective, as no heat recovery is involved, and only utility is matched to meet their temperature requirement in process. Problem table is used to determine the pinch point for the design of HEN. Due to the complex phase change of the mixture in the heat exchange system, the phase change section is converted into one or more streams with constant heat capacity flow rate according to its thermal load and material characteristics, so as to determine the temperature interval. In traditional pinch point method, △Tmin is found as 11℃, and it is determined to be 9℃ with the consideration of carbon emission. The pinch point is determined by problem table at 88.3℃ for the hot stream and 79.3℃ for the cold stream. Under this condition, the minimum thermal utility required by the heat exchanger network is 12727.27 kW, and the required minimum cold utility is 38719.59kW. The total annual cost is reduced by 2620585.49 USD/a, and the carbon emission is reduced by 61453.50t/a. According to the design principles of pinch technology and stream matching criteria, the energy-efficient heat exchanger network structure has been obtained.
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Key words:
- heat exchanger network /
- pinch technology /
- phase change /
- carbon emission /
- optimization
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表 1 H1流股信息表
Table 1. Information Sheet for stream H1
Stream label Tin/℃ Tout/℃ Heat capacity flow rate/(kW·℃−1) H1 88.2 50.9 293.82 50.9 38.0 639.28 表 2 其余物流信息表
Table 2. Information table for other streams
Stream label Tin/℃ Tout/℃ Heat capacity flow rate/(kW·℃−1) H2 88.4 53.0 292.57 53.0 38.0 503.88 H3 88.3 57.4 294.80 57.4 38.0 456.11 C1 42.8 120.1 312.66 C2 37.9 50.0 276.57 C3 37.5 51.4 115.20 表 3 问题表
Table 3. Problem table
SN DK The outside hot source input the quantity of heat No Yes /kW IK/kW OK/kW IK/kW OK/kW SN1 12756.53 0 −12756.53 12756.53 0 SN2 −15776.81 −12756.53 3020.28 0 15776.81 SN3 −719.94 3020.28 3740.22 15776.81 16496.75 SN4 −316.62 3740.22 4056.84 16496.75 16813.37 SN5 −1301.57 4056.84 5358.41 16813.37 18114.94 SN6 −1199.31 5358.41 6557.72 18114.94 19314.25 SN7 −5491.69 6557.72 12049.41 19314.25 24805.94 SN8 −13916.65 12049.41 25963.06 24805.94 38719.59 表 4 不同△Tmin下结果信息表
Table 4. Cost saving achieved by heat integration under different
$\varDelta T_{\rm{{min}}}$ △Tmin/℃ Pinch/℃ Hot Utility/kW Cold Utility/kW Energy saving potential Hot utility Cold utility 5 85.8 11476.63 37439.47 60.58% 32.03% 6 85.3 11818.50 37642.23 59.41% 31.66% 7 84.8 12131.20 37943.37 58.33% 31.11% 8 84.3 12414.61 38377.82 57.37% 30.33% 9 83.8 12727.27 38719.59 56.29% 29.71% 10 83.3 13039.93 39002.77 55.22% 29.19% 11 82.8 13381.85 39312.03 54.05% 28.63% 12 82.3 13694.51 39506.67 52.98% 28.28% 13 81.8 14007.17 39750.24 51.81% 27.84% 14 81.3 14319.83 40558.70 50.83% 26.38% 表 5 费用相关参数表
Table 5. Cost-related parameters
Parameters Heat exchanger unit area cost CA/USD·a−1 Unit hot utility cost CHU/USD·kW−1·a−1 Unit cold utility cost CCU/USD·kW−1·a−1 Heat transfer coefficient between process steams KHC/W·m−2·K−1 Heat transfer coefficient between hot utilities and
streams KHU/W·m−2·K−1Heat transfer coefficient between cold utilities and streams KCU/W*m-2·K−1 Value 60 100 15 250 540 400 表 6 费用表
Table 6. Cost details
△Tmin/℃ Investment costs/(USD·a−1) Utilities costs/(USD·a−1) Total annual cost/(USD·a−1) 5 1196046.86 1709255.09 2905301.95 6 1046183.21 1746483.48 2792666.694 7 939406.52 1782270.58 2721677.099 8 859665.82 1817128.39 2676794.21 9 798614.79 1853520.89 2652135.68 10 750618.90 1889034.59 2639653.49 11 711523.79 1927865.59 2639389.27 12 679833.45 1962051.08 2641884.53 13 653313.02 1996970.60 2650283.62 14 631144.59 2040363.56 2671508.15 表 7 碳排放费用参数表
Table 7. Parameters in cost calculation for carbon emission
Parameters NHV/kJ·kg−1 C% ηBoiler/% Carbon tax/USD·t−1 Value 30000 74.5 70 20 表 8 含碳排放费用表
Table 8. Cost with the consideration of carbon Emission
△Tmin/℃ Carbon emission/(t·a−1) Carbon tax cost/(USD·a−1) Cost with the consideration of carbon Emission/(USD·a−1) 5 43033.82 860676.50 3765978.45 6 44315.73 886314.56 3678981.26 7 45488.26 909765.13 3631442.23 8 46550.96 931019.21 3607813.42 9 47723.34 954466.78 3606602.46 10 48895.72 977914.35 3617567.84 11 50177.81 1003556.16 3642945.43 12 51350.19 1027003.74 3668888.26 13 52522.57 1050451.31 3700734.93 14 53694.94 1073898.88 3745407.02 -
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