Exergoeconomic analysis of a combined water and power plant 4

Results and Discussion CHAPTER-5 RESULTS AND DISCUSSION In this research project, both experimental and numerical investigations were conducted to determine the performance characteristics of the system under different operating conditions. In addition, projections of the systems performance in multieffect mode and parametric studies were referred after validation of the simulation model. This chapter mainly contains the results and discussion of the important findings. The chapter has been divided in the following sections: • Validation of simulation results of the combined cycle power plant with Thermoflow® and other published literature. • Experimental parametric investigations of the MED and RO systems • Thermal and hydraulic performance comparisons of different tube profiles • Comparison of experimental and simulation results. Description of each of the sections is included in the following section. 5.1 Combined cycle power plant simulation results The major part of the research project is to utilize the waste heat from the combined cycle power plant at full load. Moreover, to analyze the effect of bleeding steam out from the power plant at part load condition was considered. In order to so, a model combined power plant (Siemens V94.2 Gas turbine series) has been taken whose operating parameters are given in Table 5.1. A series of simulation runs were carried out on the system to determine the performance characteristics under different operating conditions. Commercially available simulation software Thermoflow® was used for the verification of the simulation results. The simulation results follow the following sequence: _____________________________________________________________________ 131 Results and Discussion a. Power plant efficiency, steam cycle efficiency based on First law of thermodynamics comparison with Franco et al. (2002). b. Gross power output and other important power plant parameters verification with Thermoflow®. c. Comparison with Rensonnet et al. (2007) for power plant efficiency, exergetic efficiency and water cost comparison. Table 5.1 Different input parameters for combined cycle power plant for Siemens V94.2 Gas Turbine Work Output, WGT(full-load) 250 MW Steam Turbine Work Output WST(full-load) 115MW Compressor Inlet temperature, T1 25 oC Compressor Inlet Pressure, P1 101.3 kPa Pressure ratio, P2/P1 11.65 Gas Turbine inlet temperature Gas Turbine exit temperature, T4 1076 °C 586 °C Efficiency of gas turbine at design load , ηGT 0.89 Efficiency of compressor at design load, η C 0.89 Efficiency of steam turbine, η ST 0.9 Mass flow rate to the compressor, m1 513 kg/s Temperature of flue gas leaving HRSG II, T6 85oC HRSG I condensate inlet pressure, Pd 60 bars Temperature of water after exit of HRSG I , Td 500oC Pressure of bled steam, Pe bar Pressure at condenser, Pb 0.07 bar _____________________________________________________________________ 132 Results and Discussion 5.1.1 Power plant simulation results The developed simulation program for the power plant was executed with the data from Table 5.1 and checked with that of the Franco et al. (2002), as shown in Table 5.2. The simulation program can predict within ±8% of the published results. From the simulation results, it can be concluded that the program developed can predict the performance of the power plant fairly well under different conditions. Table 5.2. First law Power plant efficiencies and comparison with Franco et al. (2002) Load (%) 100 80 70 60 Steam cycle efficiency,, ηST Simulation Franco et al. (2002) 0.33 0.35 0.3 0.28 0.25 0.23 0.21 0.19 Combined cycle efficiency,, ηcc Simulation Franco et al. (2002) 0.49 0.5 0.45 0.45 0.4 0.4 0.35 0.35 5.1.2 Power plant simulation validation with Thermoflow® The reliability test of the developed power plant simulation program can be ensured with the checking of gross power output from gas turbine (GT), steam turbine (ST) and their efficiencies, respectively. So, several load conditions were tested with Thermoflow® taking the input parameters same as that of Table 5.1. Table 5.3 compares the gross output power of GT, ST, and total gross power output of the combined power plant. Lastly thermal efficiency of the power plant from full load / rated load to 60% of the rated load condition was checked. From Table 5.3, it shows that if the load is decreased by 20% (from 100% to 80%) the power output reduces by almost 30%. Moreover, the thermal efficiency decreases drastically if the load is reduced. _____________________________________________________________________ 133 Results and Discussion Table 5.3. Comparison of results with thermoflow for combined cycle power plant. Gas turbine relative load (%) Gross power output GT [MW] Gross power output ST [MW] Gross power output [MW] Net plant efficiency [% of LHV input] Thermoflow Simulation Thermoflow Simulation Thermoflow Simulation 100 100 80 80 60 60 285.1 287.2 196.5 198.3 147.4 148.2 144.6 146.1 119.4 121.2 102.1 104.5 429.6 433.3 316 319.5 249.4 252.7 56.3 56.78 41.3 41.76 39.1 39.62 5.2 Combined water and power plant simulation results In the previous section, the thermal efficiency of the combined cycle power plant was studied. Now, the combined cycle is coupled to the MED plant (CC+MED), and followed by the RO plant coupled to the combined cycle with the MED plant (CC+MED+RO). In case of CC+MED+RO plant, then unused electrical load is imposed onto the power plant to run the RO plant. Now, the imposed electrical load will depend on the water demand which is met by RO. This electricity consumed by RO is simulated to be 5%, 10% and 15% of the designed operating load of the combined power plant. The trend of water production with efficiency for different configurations of the combined water and power plant is also studied. _____________________________________________________________________ 134 Results and Discussion 5.2.1 Effect of Combined cycle load on Thermal Efficiency The trend of efficiency with load is shown in Figure 5.1. It shows that, the combined cycle power plant has the lowest efficiency among the modes of configurations. Thermal efficiency of the combined water and power plant increases by about 5% when the MED plant is coupled to the power plant. In addition, when the RO plant operates, there is a further increase of about 10%. Figure 5.1 Variation of thermal efficiency with Combined cycle load Therefore, the efficiencies of the combined water and power plant will increase with increasing capacity of the RO plant. The CWPP graphs show more sensitiveness across the cases rather than on the load itself. These results show tremendous prospect in terms of savings in the primary energy consumption and output of the CWPP. In short, the efficiency of the combined water and power plant increase with increasing capacity of the RO plant. Even when it is just the MED plant that is coupled to it making use of the thermal energy inherent in the flue gas that is going _____________________________________________________________________ 135 Results and Discussion out of the heat recovery steam generator of the plant, it has a higher efficiency than that of a combined cycle power plant alone. 5.2.2 Combined Water and Power Plant (CWPP) result comparison with Rensonnet et al. (2007) Water production cost relies heavily on electricity cost, steam cost and above all the exergetic efficiency of the Combined Water and Power Plant (CWPP). Rensonnet et al. (2007) studied the different combinations of desalination plants combined with power plant. In that study, when the plant runs at CC+MED mode, steam is bled from steam turbine deliberately for producing water, thereby, reducing the electricity output. It in turn increases the electricity cost. When the plant runs at CC+RO no steam is bled from the steam turbine. So, the electricity output also increses. The effect is clearly shown on the exergetic efficiecny. The maximum benefit of this type of combined water and power plant is gained when the plant runs at CC+MED+RO mode. Table 5.4. Comparison of power plant parameters with Rensonnet et al. (2007) Rensonnet et al. (2007) Simulation Result CC+MED CC+RO CC+ME D +RO CC+MED CC+RO CC+ME D +RO 70,100 70,100 70,100 70,100 70,100 70,100 29,156 42,130 29,156 29,145 42,220 29,145 Exergetic Efficiency 48.7 55.19 57.2 49.1 56.7 58.2 Cost of electricity (US¢/kWh) 12 10 13 10 11 Power of Gas Turbine (kW) Power of Steam Turbine (kW) _____________________________________________________________________ 136 Results and Discussion Cost of distillate (US$/m3) 0.95 0.80 0.60 1.02 0.83 0.63 5.2.3 Effect of Combined cycle load on Water Production The water production of 1) the combined cycle power plant with the MED plant, and 2) the combined cycle and power plant with the MED and RO (using 5% of the design capacity of the power plant) are studied. It is observed from the figure that the water production decreases with increasing electrical load. This can be explained by the changes in the amount of steam available when the load changes. When the electrical load decreases, the amount of steam available either to produce water through MED or produce electricity is increased as the amount of steam that is bled will also increase. Therefore, more steam can be sent to the MED plant for the production of distillate. Hence water production will decrease with electrical load. Figure 5.2 Variation of Water Production with Combined cycle load Naturally, with RO being added on to the combined power and water plant, the water production will increase. Through the simulation, it is found that the RO plant will _____________________________________________________________________ 137 Results and Discussion produce 4.54 MIGD of water. Hence, the curve for CC+MED+RO (5%) is shifted by 4.54 MIGD upwards relative to that of CC+MED. And for another 5% increase of load to power the RO, an additional 4.54 MIGD of water can be produced. 5.2.4 Electricity cost variation with Oil Price The electricity cost is directly proportional to the cost of oil per barrel for the power plant. From Figure 5.3, when the cost of the barrel increases, the electricity cost also increases. The cost of the fuel influences the cost of running the combined water and power plant directly. Since electricity is the product of the plant, according to the cost balancing equation, a higher fuel cost will, therefore, equate to a higher electricity Electricity Cost (US$/kWh) cost. 0.16 0.15 0.14 0.13 0.12 0.11 0.1 0.09 0.08 0.07 0.06 50 55 60 65 70 75 80 85 90 Barrel Cost (US$/bbl) Figure 5.3 Electricity cost trend with varying barrel cost _____________________________________________________________________ 138 Results and Discussion 0.47 Exergetic efficiency 0.46 0.45 0.44 0.43 0.42 0.41 0.40 0.39 60 65 70 75 80 85 90 95 100 Load (%) Figure 5.4 Exergetic efficiencyof power plants for different electrical loads From Figure 5.4, as the load increases, the exergetic efficiency of the combined cycle power plant also increases in a parabolic curve. During part load condition, the efficiency of the turbine and the compressor decreases. As a result, lesser amount of electricity is produced during the process, therefore, the lower exergetic efficiency of the power plant. Another interesting point is as the load increases the rate of improving exergetic efficiency also decreases. 5.3 Experimental Results of MED A series of experiments were carried out on the system to determine the performance characteristics under different operating conditions. The variables considered in this study are as follows: • Heating medium flow rate • Heating medium temperature • Feed flow rate • Feed temperature and flashing. • Top brine temperature. _____________________________________________________________________ 139 Results and Discussion The impacts of these operating variables have been analyzed in this section in terms of the following parameters. 1. Vapour production 2. Performance ratio. 3. Overall heat transfer coefficient. 4. Concentration factor. 5. Specific heat transfer area. 6. Flashing efficiency 7. Fraction of equilibrium. Detail results for the different tube materials are shown in tabular form in appendix E. 5.3.1 Effect of Heating Medium Flow Rate Hot water was used as the heating medium (HM) in the shell side of the evaporator. The thermal performance of the desalination system was investigated with hot water flow rate ranging from 1.5 m3/hr to 3.5 m3/hr. The feed concentration was in average 30,000 ppm. From Figure 5.5, it is clearly evident that the increase of hot water flow rate enhances the thermal performance of the desalination system with the increase in performance ratio and decrease in the specific heat transfer area for each of the tubebundle. For corrugated Cu-Ni (90-10) tube bundle, the performance ratio increases from 0.75 to 0.914 due to increased vapour production rate which is most significant compared to other tube-bundles. In MED or MSF, the increase of heating steam flow rate increase the production but it leads to decrease in performance ratio as energy input increases, El-Dessouky (1998). Specific heat transfer area found to decrease by 40%, 60%, 37% and 35% for Single-fluted Al, Smooth Cu-Ni, Corrugated Cu-Ni and PTFE-Coated tube, respectively, when the HM flow rate was changed from 1.5 to 3.5 _____________________________________________________________________ 140 Specification of SW membrane Table D2: Membrane Manufacturer data Date: Membrane: Membrane status: Feed: Feed salinity: Feed Pressure: 27.8.2005 Spiral Wound 18 hrs 33,000 ppm 44.7 mS/cm 32,845 ppm 69 bar o Temperature ( C) Feedwater 26 28 30 32 Pressure (bar) Permeator inlet Permeator outlet Booster pump outlet 10 micron outlet micron outlet Product back pressure 69 68.27 4.05 3.93 69 68.27 4.05 3.93 69 68.27 4.05 3.93 69 68.27 4.05 3.93 Flow rate Reject (gpm) Product (gpm) Reject (cm /s) Product (cm /s) Total (cm /s) PR (%) 4.00 0.77 217.16 36.60 253.76 14.42 3.93 0.81 213.73 39.15 252.88 15.48 3.86 0.85 210.30 41.71 252 16.55 3.86 0.88 210.30 44.27 254.57 17.39 Avg product Cf (ppm) Cr (ppm) Cp (ppm) SP (%) SR (%) 44.7 55.8 0.382 0.381 0.382 32845.308 37878.964 188.528 0.573 99.42 44.7 56.4 0.391 0.392 0.392 32845.308 38324.512 194.048 0.590 99.40 44.7 57.0 0.401 0.402 0.402 32845.308 38770.06 199.568 0.607 99.39 44.7 57.6 0.417 0.418 0.418 32845.308 39215.608 208.4 0.634 99.36 Solute balance Feed (mg/s) Product + reject (mg/s) Difference (%) 8335.12 8232.92382 1.22 8306.14 8198.77 1.29 8277.53 8161.78 1.39 8361.55 8256.38 1.25 Concentration Feed (mS/cm) Reject (mS/cm) Product (mS/cm) 225 Results MED Experimental Results Effect of Heating Medium flow Rate Table E1: Experimental results for the variation of heating medium flow rate (Single-fluted Aluminum Tube bundle) Operation time (hr) Heating Medium flow rate (m3/hr) 1.5 2.0 2.5 3.0 3.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 550C Feed Water Temperature 30.01 30.12 30.18 30.22 30.24 Fresh Water Production Rate (Kg/hr) Perfor mance Ratio (PR) Expermental 11.78 20.46 17.80 20.46 21.79 Expermental 0.6514 0.7233 0.7678 0.7982 0.8229 Overall Heat Transfer Co-efficient (W/m2K) (ppm) 543.08 640.45 703.54 785.98 840.33 Table E2: Experimental results for the variation of heating medium flow rate (Smooth Cu-Ni (90-10) Tube-bundle) Overall Heat Transfer Oper- Heating Heating Feed Water Fresh Water Co-efficient Medium ation Medium Feed Water Performance Flow Rate Production Rate (W/m2K) flow rate time Temperature Temperature Ratio (PR) (m3/hr) (Kg/hr) (m /hr) (hr) ( C) 1.5 2.0 2.5 0.25 550C 30.31 30.22 30.26 18.44 20.862 22.45 0.7211 0.8333 0.8427 Product Salinity 689.81 759.32 856.11 21.40 23.88 25.32 24.39 26.11 Product Salinity (ppm) 24.33 23.45 25.38 ___________________________________________________________________________________________________________________________________________ 226 Results Operation time (hr) Heating Medium flow rate (m3/hr) 3.0 3.5 Feed Water Flow Rate (m3/hr) Heating Medium Temperature (0C) Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.35 30.12 24.68 27.807 0.8612 0.8844 Overall Heat Transfer Co-efficient (W/m2K) 902.24 1042.34 Product Salinity (ppm) 26.77 28.33 Effect of Heating Medium flow Rate Table E 3: Experimental results for the variation of heating medium flow rate (Corrugated Cu-Ni (90-10) Tube-bundle) Operation time (hr) Heating Medium flow rate (m3/hr) 1.5 2.0 2.5 3.0 3.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 550C Feed Water Temperature 30.02 30.22 30.09 30.29 30.22 Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 20.48 22.98 24.76 27.87 30.49 0.75 0.83 0.87 0.90 0.914 Overall Heat Transfer Co-efficient (W/m2K) 845.11 943.28 1029.32 1156.45 1210.67 Product Salinity (ppm) 26.77 26.44 25.49 25.88 26.55 Table E4: Experimental results for the variation of heating medium flow rate (PTFE-Coated Aluminum Tube-bundle) Operation time (hr) Heating Medium flow rate (m3/hr) 1.5 Feed Water Flow Rate (m3/hr) Heating Medium Temperature (0C) Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.19 10.46 0.63 Overall Heat Transfer Co-efficient (W/m2K) 487.09 Product Salinity (ppm) 22.24 ___________________________________________________________________________________________________________________________________________ 227 Results 2.0 2.5 3.0 3.5 0.25 550C 30.25 30.32 30.41 30.52 12.34 15.53 18.24 19.21 0.68 0.71 0.74 0.78 550.13 621.34 705.22 766.41 22.55 23.78 22.89 22.98 Effect of Heating Medium Temperature Table E5: Experimental results for the variation of heating medium temperature (Single-fluted Aluminum Tube bundle) Operation time (hr) Heating Medium flow rate (m3/hr) 3.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 47 49 51 53 55 60 65 Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.21 30.29 30.46 30.32 30.38 30.14 30.08 5.39 7.26 14.30 18.24 23.89 37.72 44.46 0.6123 0.7234 0.7622 0.8215 0.8545 0.9032 0.9412 Overall Heat Transfer Co-efficient (W/m2K) 365.22 416.45 489.53 530.32 587.34 630.22 693.67 Product Salinity (ppm) 22.32 24.43 25.33 22.19 21.78 26.32 25.98 Table E6: Experimental results for the variation of heating medium temperature (Corrugated Cu-Ni (90-10) Tube-bundle) Operation time (hr) Heating Medium flow rate (m3/hr) Feed Water Flow Rate (m3/hr) Heating Medium Temperature (0C) Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) Overall Heat Transfer Co-efficient (W/m2K) Product Salinity (ppm) ___________________________________________________________________________________________________________________________________________ 228 Results 3.5 0.25 47 49 51 53 55 60 65 30.43 30.19 30.46 30.11 30.28 30.18 30.29 7.312 12.89 18.21 24.45 29.93 41.13 55.56 0.7322 0.7825 0.8312 0.8532 0.9013 0.9333 0.9718 415.22 460.44 549.23 608.22 622.88 656.88 718.32 24.35 25.21 26.77 24.32 24.59 25.85 26.22 Table E7: Experimental results for the variation of heating medium temperature (Smooth Cu-Ni (90-10) Tube-bundle) Operation time (hr) Heating Medium flow rate (m3/hr) 3.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 47 49 51 53 55 60 65 Feed Water Temperature 30.22 30.12 30.33 30.44 30.33 30.18 30.09 Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 6.54 10.78 15.89 20.78 25.43 37.42 49.37 0.7092 0.7567 0.8112 0.8294 0.8663 0.9018 0.9533 Overall Heat Transfer Co-efficient (W/m2K) 390.34 443.87 524.36 595.11 645.67 695.45 734.58 Product Salinity (ppm) 25.66 24.98 22.12 25.54 20.43 20.89 26.33 Table E8: Experimental results for the variation of heating medium temperature (PTFE Coated Al Tube-bundle) Operation time (hr) Heating Medium flow rate (m3/hr) Feed Water Flow Rate (m3/hr) Heating Medium Temperature (0C) Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) Overall Heat Transfer Co-efficient (W/m2K) Product Salinity (ppm) ___________________________________________________________________________________________________________________________________________ 229 Results 3.5 0.25 47 49 51 53 55 60 65 30.12 30.09 30.11 30.21 30.32 30.19 30.38 3.21 6.90 13.21 17.80 22.75 34.24 42.58 0.5937 0.6876 0.7434 0.7912 0.8279 0.8732 0.9132 358.43 405.89 473.21 513.88 574.87 611.66 682.88 21.34 24.89 19.76 23.78 22.89 25.43 20.77 Effect of Feed Water Flow Rate Table E9: Experimental results for the variation of feed flow rate (Single-fluted Aluminum Tube bundle) Operation time (hr) Feed Water flow rate (m3/hr) 0.21 0.25 0.3 0.4 0.5 0.75 Heating Medium Flow Rate (m3/hr) 2.5 Heating Medium Temperature (0C) 550C Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.12 30.21 30.45 30.31 30.08 30.19 15.45 13.86 11.65 10.20 9.66 8.93 0.7541 0.7123 0.6723 0.6322 0.6432 0.5621 Overall Heat Transfer Co-efficient (W/m2K) 388.86 376.45 343.28 305.87 281.32 257.41 Product Salinity (ppm) 21.32 23.66 22.32 24.39 23.82 22.98 Table E10: Experimental results for the variation of feed flow rate (Smooth Cu-Ni (90-10) Tube-bundle) Operation time (hr) Feed Water flow rate (m3/hr) Heating Medium Flow Rate (m3/hr) Heating Medium Temperature (0C) Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) Overall Heat Transfer Co-efficient (W/m2K) Product Salinity (ppm) ___________________________________________________________________________________________________________________________________________ 230 Results 0.21 0.25 0.3 0.4 0.5 0.75 2.5 550C 30.61 30.28 30.49 30.40 30.45 30.08 16.434 14.75 13.4 11.98 11.12 10.45 0.7912 0.7621 0.744 0.6656 0.6382 0.5812 453.22 421.78 393.43 370.61 335.43 302.41 24.33 23.77 21.46 20.98 21.32 20.76 Table E11: Experimental results for the variation of feed flow rate (Corrugated Cu-Ni (90-10) Tube-bundle) Operation time (hr) Feed Water flow rate (m3/hr) 0.21 0.25 0.3 0.4 0.5 0.75 Heating Medium Flow Rate (m3/hr) 2.5 Heating Medium Temperature (0C) 550C Feed Water Temperature 30.01 30.11 30.08 30.32 30.29 30.19 Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 20.31 18.95 16.89 14.56 12.22 11.98 0.8112 0.7932 0.7412 0.7145 0.6964 0.6522 Overall Heat Transfer Co-efficient (W/m2K) 565.65 534.23 497.44 451.21 412.87 388.76 Product Salinity (ppm) 20.67 23.45 25.63 22.49 21.88 20.32 Table E12: Experimental results for the variation of feed flow rate (PTFE Coated Aluminum Tube-bundle) Operation time (hr) Feed Water flow rate (m3/hr) Heating Medium Flow Rate (m3/hr) Heating Medium Temperature (0C) Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) Overall Heat Transfer Co-efficient (W/m2K) Product Salinity (ppm) ___________________________________________________________________________________________________________________________________________ 231 Results 0.21 0.25 0.3 0.4 0.5 0.75 2.5 550C 30.22 30.12 30.51 30.28 30.29 30.21 12.68 11.85 10.28 9.30 8.95 7.86 0.7212 0.6933 0.6440 0.6325 0.5722 0.5432 365.87 339.95 304.21 282.88 270.34 247.32 22.76 21.87 2454 21.50 25.43 26.12 Effect of Feed Water Temperature Table E13: Experimental results for the variation of feed water temperature (Single-fluted Aluminum Tube bundle) Operation time (hr) Heating Medium flow rate (m3/hr) Feed Water Flow Rate (m3/hr) Heating Medium Temperature (0C) 55 2.5 0.25 Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.09 35.34 40.32 42.29 45.55 47.29 50.16 14.36 16.98 19.28 22.71 25.59 28.31 31.28 0.76 0.82 0.88 0.92 1.01 1.10 1.15 Overall Heat Transfer Co-efficient (W/m2K) 648.33 690.18 725.43 740.49 753.82 774.29 786.43 Product Salinity (ppm) 26.18 25.33 26.98 27.10 27.55 29.33 30.28 Table E14: Experimental results for the variation of feed water temperature (Smooth Cu-Ni (90-10) tube-bundle) Operation time Heating Medium flow rate Feed Water Flow Rate (m3/hr) Heating Medium Temperature Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) Overall Heat Transfer Co-efficient Product Salinity ___________________________________________________________________________________________________________________________________________ 232 Results (hr) (m3/hr) 2.5 (0C) 0.25 55 30.22 35.21 40.11 42.08 45.28 47.22 50.05 22.18 23.73 25.86 28.76 29.29 31.42 33.36 0.8134 0.8722 0.9209 1.0122 1.0943 1.1640 1.2239 (W/m2K) 857.23 890.19 920.31 932.59 951.11 967.32 978.20 (ppm) 22.13 24.54 27.33 25.18 28.76 21.77 25.39 Effect of Feed Water Temperature Table E15: Experimental results for the variation of feed water temperature (Corrugated Cu-Ni (90-10) Tube bundle) Operation time (hr) Heating Medium flow rate (m3/hr) 2.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 55 Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.31 35.88 40.32 42.08 45.41 47.12 50.09 22.29 25.89 27.46 28.83 31.22 33.64 35.78 0.8512 0.9324 1.0121 1.0521 1.1453 1.2156 1.3080 Overall Heat Transfer Co-efficient (W/m2K) 970.21 996.64 1010.87 1039.87 1047.32 1068.89 1076.90 Product Salinity (ppm) 25.65 19.32 24.98 23.44 26.74 25.81 26.31 ___________________________________________________________________________________________________________________________________________ 233 Results Table E16: Experimental results for the variation of feed water temperature (PTFE-Coated Al Tube bundle) Operation time (hr) Heating Medium flow rate (m3/hr) 2.5 Feed Water Flow Rate (m3/hr) Heating Medium Temperature (0C) 0.25 Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.09 35.21 40.43 42.63 45.12 47.36 50.05 12.78 15.21 17.33 20.37 23.16 26.32 30.24 0.7135 0.7820 0.8432 0.8932 0.9624 1.0522 1.1131 55 Overall Heat Transfer Co-efficient (W/m2K) 559.10 583.18 611.76 640.33 651.27 663.88 679.89 Product Salinity (ppm) 25.44 23.87 26.31 24.38 26.16 28.50 23.98 Effect of Variable Concentration of Feed Water Table E17: Experimental results for the variation of feed water concentration (Single-flute Al Tube bundle) Operation time (hr) Feed Concent -ration (ppm) 15000 25000 30000 35000 Heating Medium flow rate (m3/hr) 3.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 55 Feed Water Temperature 30.29 30.15 30.09 30.22 Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 21.79 22.28 23.24 20.93 0.8342 0.7997 0.7825 0.7513 Product Salinity (ppm) 24.55 26.73 25.69 25.67 ___________________________________________________________________________________________________________________________________________ 234 Results Table E18: Experimental results for the variation of feed water concentration (Smooth Cu-Ni (90-10) tube-bundle) Operation time (hr) Feed Concent -ration (ppm) 15000 25000 30000 35000 Heating Medium flow rate (m3/hr) 3.5 Feed Water Flow Rate (m3/hr) Heating Medium Temperature (0C) 0.25 55 Feed Water Temperature 30.16 30.44 30.28 30.54 Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 27.807 28.982 29.337 27.034 1.0343 0.9723 0.9604 0.9622 Product Salinity (ppm) 23.22 25.87 24.39 26.77 Effect of Variable Concentration of Feed Water Table E19: Experimental results for the variation of feed water concentration (Corrugated Cu-Ni (90-10) Tube bundle) Operation time (hr) Feed Concent -ration (ppm) 15000 25000 30000 35000 Heating Medium flow rate (m3/hr) 3.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 55 Feed Water Temperature Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 30.22 30.06 30.22 30.18 29.39 28.87 28.80 30.45 0.9874 0.9753 0.9653 0.9422 Product Salinity (ppm) 22.34 27.89 22.35 26.48 ___________________________________________________________________________________________________________________________________________ 235 Results Table E20: Experimental results for the variation of feed water concentration (PTFE coated Al Tube bundle) Operation time (hr) Feed Concent -ration (ppm) 15000 25000 30000 35000 Heating Medium flow rate (m3/hr) 3.5 Feed Water Flow Rate (m3/hr) 0.25 Heating Medium Temperature (0C) 55 Feed Water Temperature 30.56 30.04 30.22 30.11 Fresh Water Production Rate (Kg/hr) Performance Ratio (PR) 24.78 24.89 23.89 25.22 0.8232 0.8121 0.7876 0.7735 Product Salinity (ppm) 24.554 23.787 26.229 27.554 ___________________________________________________________________________________________________________________________________________ 236 Property Functions ___________________________________________________________________________________ Appendix F Property Functions 1) Heat of Evaporation, (kJ/kg) (0 -120 oC) f(t) = (597.49 – 0.56624*t + (1.5082e-4)*t2 – (3.2764e-6)*t3)*4.1868 2) Specific Heat Capacity, (kJ/kg.K) (0 -160 g/kg, -180 oC) f(s,t) = (a + b*t + c*t2 + d*t3)*1e-3 where a = 4206.8 – 6.6197*s + 0.012288*s2 b = -1.1262 + 0.054178*s – (2.2719e-4)*s2 c = 0.012026 – (5.3566e-4)*s + (1.8906e-6)*s2 d = (6.8774e-7) + (1.517e-6)*s – (4.4268e-9)*s2 3) Specific Enthalpy, (kJ/kg) (0 -160 g/kg, -180 oC) f(s,t) = (h0 + a*t + (b*t2)/2 + (c*t3)/3 + (d*t4)/4)*1e-3 where h0 = ((2.3e-3)*s – (1.03e-4)*s2)*4186.8 a, b, c and d are the same as those defined in 4) Thermal Conductivity, (kJ/m.h.K) (0 -100 g/kg, 10 -150 oC) f(s,t) = (a + b*t + c*t2)*3.6e-3 where x = 28.17*s/(1000 – s) _______________________________________________________________________________ 237 Property Functions ___________________________________________________________________________________ a = 576.6 – 34.64*x + 7.286*x2 b = (1526 + 466.2*x – 226.8*x2 + 28.67*x3)*1e-3 c = -(581 + 2055*x – 991.6*x2 + 146.4*x3)*1e-5 5) Density, (kg/m3) (0 -160 g/kg, 10 -180 oC) f(s,t) = (0.5*a + b*y + c*((2*y2)-1) + d*((4*y3) - (3*y)))*1e3 where a = 2.016110 + 0.115313*z + 0.000326*x b = -0.0541 + 0.001571*z – 0.000423*x c = -0.006124 + 0.001740*z – 0.000009*x d = 0.000346 + 0.000087*z – 0.000053*x x = (2*z2) – y = (2*t – 200)/160 z = (2*s – 150)/150 6) Dynamic Viscosity, (kg/m.h) (0 -130 g/kg, 10 -150 oC) f(s,t) = 3.6*µw*µr where µw = exp(-3.79418 + 604.19/(139.18 + t)) µr = + a*s + b*s2 a = 1.474e-3 + (1.5e-5)*t – (3.927e-8)*t2 b = 1.0734e-5 – (8.5e-8)*t + (2.23e-10)*t2 _______________________________________________________________________________ 238 Property Functions ___________________________________________________________________________________ 7) Boiling Point Elevation, (K) (20 -160 g/kg, 20 -180 oC) f(s,t) = s*(b + c*s) where b = (6.71 + (6.43e-2)*t + (9.74e-5)*t2)*1e-3 c = (2.38 + (9.59e-3)*t + (9.42e-5)*t2)*1e-5 8) Demister and Condenser Tube Temperature Losses, (K) f(td) = (exp(1.885 – 0.02063*(td*1.8 + 32)))/1.8 where td is stage distillate temperature 9) Non-equilibration Loss, (K) δ = (352*((h/2.54)1.1)*((1.8*∆t)-0.25)*((0.67197e-3*w)0.5)*((1.8*td + 32)-2.5))/1.8 where h = height of brine pool in the stage, cm ∆t = stage flashing brine drop, K = tf,i-1 – tf,i w = chamber load, kg/h.m td = stage distillate temperature, oC 10) Saturated Steam Pressure, (bar) (0 -160 g/kg, -200 oC) f(t) = Pk*exp((tk/t)*Σ(b(i)*(1 – (tk/t))^((i + 1)/2))) where unit for temperature is K critical temperature, tk = 647.25 K critical pressure, Pk = 220.93 bar b(1) = -7.8889166 b(2) = 2.5514255 _______________________________________________________________________________ 239 Property Functions ___________________________________________________________________________________ b(3) = -6.7161690 b(4) = 33.239495 b(5) = -105.38479 b(6) = 174.35319 b(7) = -148.39348 b(8) = 48.631602 11) Enthalpy of Superheated Steam, (kJ/kg) (0 -200 oC) f(t,p) = 2.326*(b(8) + 0.043557*(b(5)*p + (p/t) 2*b(2)/2*(-b(6) + b(2)*(b(3) – b(4)) + 2*b(7)*(p/t) 2))) where p = pressure (atm) t = temperature (K) b(1) = 2641.61*10^(80870/t2)/t b(2) = 1.89 – b(1) b(3) = 82.546 b(4) = 162460/t b(5) = 1.89 – b(1)*(372420/(t2 + 2) b(6) = b(2)*b(4) – 2*b(5)*(b(3) – b(4)) b(7) = 2*b(5)*(0.21828*t – (126970/t)*(1 + b(2))) b(8) = 775.596 + 0.63296*t + 0.000162467*t2 + 47.3635*log10(t3) 12) Latent Heat of Vaporization of Water, (kJ/kg) Latent heat = expression (3) _______________________________________________________________________________ 240 [...]... 550C and Feed concentration: 30,000 ppm) In the study made by Khalil et al (1981), it was found that with 40 C of superheating, the flashing efficiency increases from 42 .5% to 50 % at a flow rate of 3.2 m3/hr of the feed water to a flash desalination unit In a preliminary optimization analysis on design parameters of the VTE-MED process coupled with nuclear heating reactor, Wu and Du (2003) found that... 5.10 shows the gradual decrease of the performance ratio with the increase of subcooled temperature range Alternatively, as the difference between the feed and saturation temperature decreases, the performance ratio increases gradually The reason may be because as the feed temperature rises, it takes a shorter residence time to reach near the thermal equilibrium and nucleation starts earlier in the tube... improvement of the overall heat transfer coefficient The average salt concentration in product water was 24- 32 ppm, which is fairly below the standard set by WHO (500 ppm) for potable water Average uncertainty in fresh water production was found to be about 1.9%, while that for experimental overall heat transfer coefficient was 12% 5.3.2 Effect of Heating Medium Temperature The temperatures of the hot water. .. m3/hr and 300C, respectively The saturation temperature inside the evaporator has been considered as 41 .50C at a pressure of 80 mbar As shown in Figures 5.23 and 5. 24, the temperature reaches the saturation condition at a particular distance and then remains constant, as boiling starts From Figure 5.23, the response is quicker for corrugated tube compared to the smooth profile For the case of corrugated... improvement and above all, improves the plant performance For this reason, the next section is dedicated to MED sub system parametric evaluation The variables considered are as mainly top brine temperature (TBT) and Number of effects A thorough parametric analysis is performed on the MED plant to understand the cost formation of the distillate The change in exergetic efficiency and destruction, distillate... popular However, an economic justification can also be made for the optimum performance of the desalination plant _ 162 Results and Discussion 5.5 MED parametric evaluation For any performance evaluation study, it is very important to do a parametric analysis of the system This parametric study helps to uncover the better operating region, locates major areas of improvement... material or geometry for thermal desalination process Effective design, selection of tube profile and material may increase energy efficiency of a desalination plant For this research project, four different kinds of tube profiles were selected for the design of the evaporator The aim was to select tube material and tube profile for better performance in desalination application using waste heat in... resembles with the study made by Dessouky et al (1999), where performance of plastic heat exchanger made of PTFE was evaluated An increase of 2 to 4 times more heat transfer area than metal exchanger was found there whereas in the present study it is found to be 1.2 times as only coating is applied to the metal surface instead of plastic heat exchanger So, if the coating durability proves to be efficient... Cu-Ni (90-10) and PTFE-coated Aluminum tube profiles, respectively, at a heating medium flow rate of 3.5 m3/hr The advantage of the Cu-Ni (90-10) profile over aluminum is that it can be maintained thin during the evaporator design However, for the case of Aluminum it is not possible as it affects the structural rigidity of the evaporator But Cu-Ni (90-10) is more expensive than Aluminum and that’s why it’s... form of hot water Comparisons of both experimental and simulation performance have been made in this section 5 .4. 1 Feed temperature distribution inside the tube The feed water temperature distribution inside the tube has been found from the simulation Simulation results are shown in Fig 5.23 for a heating medium flow rate of 3.5 m3/hr, temperature of 650C, and feed water flow rate and temperature of . The maximum benefit of this type of combined water and power plant is gained when the plant runs at CC+MED+RO mode. Table 5 .4. Comparison of power plant parameters with Rensonnet et al. (2007). study made by Dessouky et al. (1999), where performance of plastic heat exchanger made of PTFE was evaluated. An increase of 2 to 4 times more heat transfer area than metal exchanger was found. produce 4. 54 MIGD of water. Hence, the curve for CC+MED+RO (5%) is shifted by 4. 54 MIGD upwards relative to that of CC+MED. And for another 5% increase of load to power the RO, an additional 4. 54