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Experimental assessment of connection of an absorption heat pump to a multi-effect distillation unit
Desalination 250 (2010) 500–505
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Experimental assessment of connection of an absorption heat pump to a multi-effect distillation unit Diego C. Alarcón-Padilla a,⁎, Lourdes García-Rodríguez b,1, Julián Blanco-Gálvez a,2 a b
CIEMAT-Plataforma Solar de Almería, Ctra. de Senés s/n, 04200 Tabernas, Almería, Spain Dpto. Ingeniería Energética, Universidad de Sevilla. Escuela Técnica Superior de Ingenieros, Camino de los Descubrimientos, s/n. 41092 Sevilla, Spain
a r t i c l e
i n f o
Article history: Received 12 February 2008 Accepted 24 June 2009 Available online 6 November 2009 Keywords: Multi-effect distillation Absorption heat pump Solar desalination
a b s t r a c t Theoretical analysis of integrating an absorption heat pump cycle in a multi-effect distillation (MED) process has shown better performance than with other types of heat pumps conventionally used as thermocompressors. However, to date, only two pilot facilities have been implemented worldwide. Both of them have been developed and tested in the framework of two different research and demonstration projects carried out at the Plataforma Solar de Almería (Spain). Two different double-effect absorption (LiBr–H2O) heat pump (DEAHP) prototypes were coupled to an existing 14-effect MED unit. This paper reports the results of the experimental assessment of integrating the second prototype in the process. Although the initial design of the DEAHP prototype was based on fitting it to the MED unit power demand and their direct connection, the prototype was unable to achieve steady operation in this configuration. However, the indirect connection of both units by means of two auxiliary tanks was successful. An overall performance ratio of 20 was measured; therefore, integration of the DEAHP doubles the performance ratio of the MED unit alone, although the temperature of the external heat input required is increased from 70 °C to 180 °C. © 2009 Elsevier B.V. All rights reserved.
1. Introduction During the nineties, a unique experiment in solar seawater desalination at the Plataforma Solar de Almería (PSA) connected a parabolic-trough solar field to a conventional multi-effect distillation (MED) unit, optimizing the overall heat consumption of the system by integrating a double-effect absorption (LiBr–H2O) heat pump (DEAHP) [1,2]. Based on this previous background and experience, in 2001, design of a second, improved DEAHP prototype, also the only one of its kind worldwide, was begun. It was connected to the multieffect distillation (MED) plant already existing at the PSA. The stateof-the-art connection has been previously reported by the authors [3,4]. This paper describes the experimental assessment of integrating the second DEAHP prototype in a multi-effect distillation process. Two different configurations for DEAHP prototype connection to the MED unit are compared. The experimental system required for this assessment is part of the experimental facility erected under the European AQUASOL Project (Contract no. EVK1-CT2001-00102), which also includes a previously existing MED unit and its auxiliaries. The AQUASOL Project solar desalination test facility consists of a MED unit with 14 cells (SOL-14 plant), a stationary CPC (compound
⁎ Corresponding author. Tel.: +34 950 387960; fax: +34 950 365015. E-mail addresses: [email protected] (D.C. Alarcón-Padilla), [email protected] (L. García-Rodríguez), [email protected] (J. Blanco-Gálvez). 1 Tel.: +34 95 4487231; fax: +34 95 4487133. 2 Tel.: +34 950 387960; fax: +34 950 365015. 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.06.056
parabolic concentrator) solar collector field, a water thermal storage system, a double-effect (LiBr–H2O) absorption heat pump, a smoketube gas boiler, and an advanced solar dryer for final treatment of the brine connected as shown in Fig. 1. The heat transfer fluid is water, which is heated as it circulates through the solar collectors, converting the solar energy into thermal energy in the form of the sensible heat of the water, and is then stored in the tanks. Hot water from the storage system provides the MED plant with the required thermal energy. In absence of solar radiation, the gas boiler feeds the absorption heat pump, which is also fed with low-pressure steam from the last effect of the MED unit. As a result, the heat pump heats the water coming from the first effect of the MED unit from 63.5 °C to 66.5 °C. This paper evaluates connection of the new DEAHP prototype, driven by a smoke-tube gas boiler, to the MED unit. The experiments reported in this paper did not involve any energy contribution from the solar field. Two water tanks were used in one of the configurations tested for the indirect connection of the absorption pump and multieffect plant. 2. Experimental system The second DEAHP prototype was originally designed for direct connection to the PSA multi-effect distillation unit, which means that hot water circulates in a closed loop between the first MED effect and the heat pump absorber–condenser tandem. However, the PSA experimental facility allows another connection configuration (indirect) to be tested, in which the thermal power from the DEAHP is delivered
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
501
Fig. 1. Final configuration of the AQUASOL seawater desalination system.
to the MED plant by means of two water tanks. Both configurations have been tested and evaluated, and DEAHP performance in nominal and part-load operation was compared to find the best operating layout. The PSA SOL-14 desalination plant is a forward-feed MED unit manufactured and delivered by ENTROPIE in 1987 (See Table 1 for specifications) in the framework of a previous research project [5]. It has 14 effects, in a vertical arrangement. The original first cell, which worked with low-pressure saturated steam (70 °C, 0.31 bar), was replaced in the AQUASOL Project by a new one, which is able to work with hot water as the heat transfer media (See Table 2). The double-effect absorption heat pump (DEAHP) was manufactured by ENTROPIE in 2005 and was installed next to the multi-effect distillation unit (See Fig. 2). The working fluid is a water/lithium bromide solution which circulates through two solution circuits connected in series. This series flow configuration has a lower thermodynamic and heat transfer performance than parallel flow but requires less complicated control, especially in transient operation [6]. Table 1 Technical specifications of the SOL-14 desalination plant. Feedwater flow Brine reject Distillate production Seawater flow at condenser: at 10 °C: at 25 °C: Output salinity Number of cells Heat source energy consumption Performance ratio Vacuum system Top brine temperature Condenser temperature
8 m3/h 5 m3/h 3 m3/h 8 m3/h 20 m3/h 5 ppm TDS 14 190 kW >9 Hydroejectors (seawater at 3 bar) 70 °C 35 °C
3. Experimental results 3.1. Direct connection configuration The original design of the second AQUASOL DEAHP prototype was designed to be connected directly to the multi-effect distillation unit already existing at the PSA, so that water coming from the first effect of the MED (Fig. 1, Point 2) would circulate directly through the absorption heat pump absorber and condenser without passing through the water storage tanks. In nominal operating conditions, after leaving the DEAHP condenser, the water temperature rises to match the difference between the MED first effect inlet and outlet water temperatures. First, some tests were conducted with automatic regulation of the high-pressure steam valve (Fig. 1, Valve V3) in order to set nominal steady operation. Fig. 3 shows a typical cold start-up test with the MED-DEAHP direct connection configuration. The following parameters are shown: i) Inlet and outlet water flow temperatures in the MED first effect (Fig. 1, Points 1–2); water temperature at the inlet of the DEAHP absorber and the outlet of DEAHP condenser (Fig. 1, Points 3–4).
Table 2 Nominal conditions of the new PSA MED plant.
Power Inlet/outlet hot water temperature Brine temperature (on first cell) Hot water flow rate Pressure drop Nominal plant production
Desalination driven by solar collectors
Desalination driven by absorption heat pump
200 kW 75.0/71.0 °C 68 °C 12.0 kg/s 0.4 bar 3.0 m³/h
150 kW 66.5/63.5 °C 62.0 °C 12.0 kg/s 0.4 bar 2.2 m³/h
502
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
Fig. 2. The double-effect LiBr–H2O absorption heat pump in the AQUASOL plant.
Fig. 3. Start-up behaviour of the directly connected DEAHP and MED in operation. Test on 30/10/2007.
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
ii) Temperature of the steam generated in Effect 14 of the MED plant (Fig. 1, Point 7). iii) Ratio of DEAHP thermal power delivered and DEAHP power consumption from the gas boiler, QDEAHP/QBOILER (coefficient of performance, COP). iv) MED distillate production. It may be observed that the DEAHP condenser outlet temperature is unstable, and when it rises above around 71 °C, the absorption unit automatically switches off due to safety reasons. Furthermore, the mean ratio of power delivered by the DEAHP to power received from the gas boiler is 1.67, which is significantly below the design point of 2. This problem was already observed during heat pump commissioning. Then water was circulated through the MED condenser (Fig. 1, Point 10) to keep constant steam inlet temperature at the DEAHP evaporator (Fig. 1, Point 7). However, experimental data with this configuration showed that, although the temperature could be stabilized, most of the low-pressure steam was condensed inside the MED unit. For constant power to be delivered by the DEAHP, the power difference had to be supplied by the gas boiler, resulting in a very poor heat pump energy recovery ratio. Then the direct connection configuration was studied in part-load operation to stabilize the temperature. This was done by manual regulation of the steam delivered to the DEAHP high-temperature generator (Fig. 1, Valve V3). The behaviour analysis in part-load operation is also important for stand-alone solar systems. Fig. 4 shows the performance of the DEAHP-MED system with the direct connection for different DEAHP thermal loads. In this figure, the part load is represented as the ratio of the DEAHP power delivered
503
at a given high-pressure steam valve aperture and DEAHP power delivered with the valve completely open. The two plots show the COP of the absorption unit and the ratio between fresh water production at part and nominal loads. As may be observed in Fig. 4, the COP with direct connection was significantly lower than the nominal value of 2 during both part and full-load operation. Fig. 4 also shows how distillate production drops as a direct result of part-load operation. All of this significantly influences the product-water cost. Thermal performance with direct connection of the DEAHP-MED is lower than with the plant configuration tested in the AQUASOL Project [7]. It was therefore decided to perform an additional series of tests, with indirect heat pump connection through the thermal storage tanks and MED unit. 3.2. Indirect connection configuration Fig. 5 shows the results found with the indirect configuration at varying DEAHP thermal loads. As observed, at full load, the COP was very near design point. In addition, the reduction in distilled water was proportionally lower for the same DEAHP load. Finally, Fig. 6 shows an example of the dynamic behaviour of the absorption pump in response to small changes in the MED unit operating parameters. As observed, at the beginning of the time axis, there is an increase of 1.5 °C in the inlet water temperature set-point of the MED first effect (from 65 °C to 66.5 °C). The DEAHP condenser outlet temperature begins to increase at 66.5 °C and takes about half an hour to reach steady-state conditions again (68 °C). These temperatures are slightly above nominal. Once steady-state conditions were reached, the coefficient of performance (COP) was 2 and the DEAHP-MED system
Fig. 4. Performance of the DEAHP-MED system in the direct connection configuration at varied loads. Test on 14/11/2007.
504
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
Fig. 5. Performance of the DEAHP-MED system in the indirect configuration at variable loads. Tests on 13/11/2007 and 15/11/2007.
performance ratio (PR) was 20. In addition, the power delivered by the DEAHP rose from 150 kW (nominal conditions) to 200 kW. 4. Conclusions The following main conclusions may be drawn from the experimental testing of the DEAHP and MED unit connection:
The DEAHP prototype was connected directly to the MED unit, but was unable to achieve steady-state operation. The DEAHP temperature increases continuously until emergency shutdown. Other possibilities of direct connection, such as part-load DEAHP operation, or circulating water through the final condenser of the MED plant were tested. Nevertheless, neither steady operation nor good performance was achieved.
Fig. 6. Effect of a slight perturbation on working conditions and steady state reached. Test on 15/11/2007.
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
On the contrary, experimental tests with indirect connection of the DEAHP and the MED unit by means of two auxiliary water tanks were successful and this configuration is therefore recommended. DEAHP production was higher when operated at temperatures slightly above nominal with the same nominal COP and performance ratio. This suggests that the surplus thermal power production can be used instead of making the DEAHP operate at nominal temperatures by means of the control system and reducing its thermal power production to nominal. Acknowledgment The authors wish to thank the Spanish Ministry for Education and Science (OSMOSOL project ENE2005-08381-C03-01) for funding this work. References [1] E. Zarza, M. Blanco, Advanced M.E.D. solar desalination plant: seven years of experience at the Plataforma Solar de Almería, Proceedings of the Mediterranean Conference on Renewable Energy Sources for Water Production, Santorini, Greece, June 10–12, 1996, pp. 45–49.
505
[2] E. Zarza, Solar Thermal Desalination Project, Phase II Results & Final Project Report, 1st Ed, CIEMAT, Madrid, Spain, 1995. [3] D.C. Alarcón-Padilla, L. García-Rodríguez, Application of absorption heat pumps to multi-effect distillation: a case study of solar desalination, Desalination 212 (2007) 294–302. [4] D.C. Alarcón-Padilla, L. García-Rodríguez, J. Blanco-Gálvez, Assessment of an absorption heat pump coupled to a multi-effect distillation unit within AQUASOL project, Desalination 212 (2007) 303–310. [5] E. Zarza, Solar Thermal Desalination Project, First Phase Results and Second Phase Description, 1st Ed, CIEMAT, Madrid, Spain, 1991. [6] K.E. Herold, et al., Absorption Chillers and Heat Pumps, 1st Ed, CRC Press, Boca Raton, FL, USA, 1996, p. 148. [7] Alarcón-Padilla, Diego-César, Blanco-Gálvez, Julián, García-Rodríguez, Lourdes, Gernjak, Wolfgang, y Malato-Rodríguez, Sixto. First experimental results of a new hybrid solar/gas multi-effect distillation system: the AQUASOL Project. Desalination, 220, 2008, pp. 619–625.
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Experimental assessment of connection of an absorption heat pump to a multi-effect distillation unit Diego C. Alarcón-Padilla a,⁎, Lourdes García-Rodríguez b,1, Julián Blanco-Gálvez a,2 a b
CIEMAT-Plataforma Solar de Almería, Ctra. de Senés s/n, 04200 Tabernas, Almería, Spain Dpto. Ingeniería Energética, Universidad de Sevilla. Escuela Técnica Superior de Ingenieros, Camino de los Descubrimientos, s/n. 41092 Sevilla, Spain
a r t i c l e
i n f o
Article history: Received 12 February 2008 Accepted 24 June 2009 Available online 6 November 2009 Keywords: Multi-effect distillation Absorption heat pump Solar desalination
a b s t r a c t Theoretical analysis of integrating an absorption heat pump cycle in a multi-effect distillation (MED) process has shown better performance than with other types of heat pumps conventionally used as thermocompressors. However, to date, only two pilot facilities have been implemented worldwide. Both of them have been developed and tested in the framework of two different research and demonstration projects carried out at the Plataforma Solar de Almería (Spain). Two different double-effect absorption (LiBr–H2O) heat pump (DEAHP) prototypes were coupled to an existing 14-effect MED unit. This paper reports the results of the experimental assessment of integrating the second prototype in the process. Although the initial design of the DEAHP prototype was based on fitting it to the MED unit power demand and their direct connection, the prototype was unable to achieve steady operation in this configuration. However, the indirect connection of both units by means of two auxiliary tanks was successful. An overall performance ratio of 20 was measured; therefore, integration of the DEAHP doubles the performance ratio of the MED unit alone, although the temperature of the external heat input required is increased from 70 °C to 180 °C. © 2009 Elsevier B.V. All rights reserved.
1. Introduction During the nineties, a unique experiment in solar seawater desalination at the Plataforma Solar de Almería (PSA) connected a parabolic-trough solar field to a conventional multi-effect distillation (MED) unit, optimizing the overall heat consumption of the system by integrating a double-effect absorption (LiBr–H2O) heat pump (DEAHP) [1,2]. Based on this previous background and experience, in 2001, design of a second, improved DEAHP prototype, also the only one of its kind worldwide, was begun. It was connected to the multieffect distillation (MED) plant already existing at the PSA. The stateof-the-art connection has been previously reported by the authors [3,4]. This paper describes the experimental assessment of integrating the second DEAHP prototype in a multi-effect distillation process. Two different configurations for DEAHP prototype connection to the MED unit are compared. The experimental system required for this assessment is part of the experimental facility erected under the European AQUASOL Project (Contract no. EVK1-CT2001-00102), which also includes a previously existing MED unit and its auxiliaries. The AQUASOL Project solar desalination test facility consists of a MED unit with 14 cells (SOL-14 plant), a stationary CPC (compound
⁎ Corresponding author. Tel.: +34 950 387960; fax: +34 950 365015. E-mail addresses: [email protected] (D.C. Alarcón-Padilla), [email protected] (L. García-Rodríguez), [email protected] (J. Blanco-Gálvez). 1 Tel.: +34 95 4487231; fax: +34 95 4487133. 2 Tel.: +34 950 387960; fax: +34 950 365015. 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.06.056
parabolic concentrator) solar collector field, a water thermal storage system, a double-effect (LiBr–H2O) absorption heat pump, a smoketube gas boiler, and an advanced solar dryer for final treatment of the brine connected as shown in Fig. 1. The heat transfer fluid is water, which is heated as it circulates through the solar collectors, converting the solar energy into thermal energy in the form of the sensible heat of the water, and is then stored in the tanks. Hot water from the storage system provides the MED plant with the required thermal energy. In absence of solar radiation, the gas boiler feeds the absorption heat pump, which is also fed with low-pressure steam from the last effect of the MED unit. As a result, the heat pump heats the water coming from the first effect of the MED unit from 63.5 °C to 66.5 °C. This paper evaluates connection of the new DEAHP prototype, driven by a smoke-tube gas boiler, to the MED unit. The experiments reported in this paper did not involve any energy contribution from the solar field. Two water tanks were used in one of the configurations tested for the indirect connection of the absorption pump and multieffect plant. 2. Experimental system The second DEAHP prototype was originally designed for direct connection to the PSA multi-effect distillation unit, which means that hot water circulates in a closed loop between the first MED effect and the heat pump absorber–condenser tandem. However, the PSA experimental facility allows another connection configuration (indirect) to be tested, in which the thermal power from the DEAHP is delivered
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
501
Fig. 1. Final configuration of the AQUASOL seawater desalination system.
to the MED plant by means of two water tanks. Both configurations have been tested and evaluated, and DEAHP performance in nominal and part-load operation was compared to find the best operating layout. The PSA SOL-14 desalination plant is a forward-feed MED unit manufactured and delivered by ENTROPIE in 1987 (See Table 1 for specifications) in the framework of a previous research project [5]. It has 14 effects, in a vertical arrangement. The original first cell, which worked with low-pressure saturated steam (70 °C, 0.31 bar), was replaced in the AQUASOL Project by a new one, which is able to work with hot water as the heat transfer media (See Table 2). The double-effect absorption heat pump (DEAHP) was manufactured by ENTROPIE in 2005 and was installed next to the multi-effect distillation unit (See Fig. 2). The working fluid is a water/lithium bromide solution which circulates through two solution circuits connected in series. This series flow configuration has a lower thermodynamic and heat transfer performance than parallel flow but requires less complicated control, especially in transient operation [6]. Table 1 Technical specifications of the SOL-14 desalination plant. Feedwater flow Brine reject Distillate production Seawater flow at condenser: at 10 °C: at 25 °C: Output salinity Number of cells Heat source energy consumption Performance ratio Vacuum system Top brine temperature Condenser temperature
8 m3/h 5 m3/h 3 m3/h 8 m3/h 20 m3/h 5 ppm TDS 14 190 kW >9 Hydroejectors (seawater at 3 bar) 70 °C 35 °C
3. Experimental results 3.1. Direct connection configuration The original design of the second AQUASOL DEAHP prototype was designed to be connected directly to the multi-effect distillation unit already existing at the PSA, so that water coming from the first effect of the MED (Fig. 1, Point 2) would circulate directly through the absorption heat pump absorber and condenser without passing through the water storage tanks. In nominal operating conditions, after leaving the DEAHP condenser, the water temperature rises to match the difference between the MED first effect inlet and outlet water temperatures. First, some tests were conducted with automatic regulation of the high-pressure steam valve (Fig. 1, Valve V3) in order to set nominal steady operation. Fig. 3 shows a typical cold start-up test with the MED-DEAHP direct connection configuration. The following parameters are shown: i) Inlet and outlet water flow temperatures in the MED first effect (Fig. 1, Points 1–2); water temperature at the inlet of the DEAHP absorber and the outlet of DEAHP condenser (Fig. 1, Points 3–4).
Table 2 Nominal conditions of the new PSA MED plant.
Power Inlet/outlet hot water temperature Brine temperature (on first cell) Hot water flow rate Pressure drop Nominal plant production
Desalination driven by solar collectors
Desalination driven by absorption heat pump
200 kW 75.0/71.0 °C 68 °C 12.0 kg/s 0.4 bar 3.0 m³/h
150 kW 66.5/63.5 °C 62.0 °C 12.0 kg/s 0.4 bar 2.2 m³/h
502
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
Fig. 2. The double-effect LiBr–H2O absorption heat pump in the AQUASOL plant.
Fig. 3. Start-up behaviour of the directly connected DEAHP and MED in operation. Test on 30/10/2007.
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
ii) Temperature of the steam generated in Effect 14 of the MED plant (Fig. 1, Point 7). iii) Ratio of DEAHP thermal power delivered and DEAHP power consumption from the gas boiler, QDEAHP/QBOILER (coefficient of performance, COP). iv) MED distillate production. It may be observed that the DEAHP condenser outlet temperature is unstable, and when it rises above around 71 °C, the absorption unit automatically switches off due to safety reasons. Furthermore, the mean ratio of power delivered by the DEAHP to power received from the gas boiler is 1.67, which is significantly below the design point of 2. This problem was already observed during heat pump commissioning. Then water was circulated through the MED condenser (Fig. 1, Point 10) to keep constant steam inlet temperature at the DEAHP evaporator (Fig. 1, Point 7). However, experimental data with this configuration showed that, although the temperature could be stabilized, most of the low-pressure steam was condensed inside the MED unit. For constant power to be delivered by the DEAHP, the power difference had to be supplied by the gas boiler, resulting in a very poor heat pump energy recovery ratio. Then the direct connection configuration was studied in part-load operation to stabilize the temperature. This was done by manual regulation of the steam delivered to the DEAHP high-temperature generator (Fig. 1, Valve V3). The behaviour analysis in part-load operation is also important for stand-alone solar systems. Fig. 4 shows the performance of the DEAHP-MED system with the direct connection for different DEAHP thermal loads. In this figure, the part load is represented as the ratio of the DEAHP power delivered
503
at a given high-pressure steam valve aperture and DEAHP power delivered with the valve completely open. The two plots show the COP of the absorption unit and the ratio between fresh water production at part and nominal loads. As may be observed in Fig. 4, the COP with direct connection was significantly lower than the nominal value of 2 during both part and full-load operation. Fig. 4 also shows how distillate production drops as a direct result of part-load operation. All of this significantly influences the product-water cost. Thermal performance with direct connection of the DEAHP-MED is lower than with the plant configuration tested in the AQUASOL Project [7]. It was therefore decided to perform an additional series of tests, with indirect heat pump connection through the thermal storage tanks and MED unit. 3.2. Indirect connection configuration Fig. 5 shows the results found with the indirect configuration at varying DEAHP thermal loads. As observed, at full load, the COP was very near design point. In addition, the reduction in distilled water was proportionally lower for the same DEAHP load. Finally, Fig. 6 shows an example of the dynamic behaviour of the absorption pump in response to small changes in the MED unit operating parameters. As observed, at the beginning of the time axis, there is an increase of 1.5 °C in the inlet water temperature set-point of the MED first effect (from 65 °C to 66.5 °C). The DEAHP condenser outlet temperature begins to increase at 66.5 °C and takes about half an hour to reach steady-state conditions again (68 °C). These temperatures are slightly above nominal. Once steady-state conditions were reached, the coefficient of performance (COP) was 2 and the DEAHP-MED system
Fig. 4. Performance of the DEAHP-MED system in the direct connection configuration at varied loads. Test on 14/11/2007.
504
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
Fig. 5. Performance of the DEAHP-MED system in the indirect configuration at variable loads. Tests on 13/11/2007 and 15/11/2007.
performance ratio (PR) was 20. In addition, the power delivered by the DEAHP rose from 150 kW (nominal conditions) to 200 kW. 4. Conclusions The following main conclusions may be drawn from the experimental testing of the DEAHP and MED unit connection:
The DEAHP prototype was connected directly to the MED unit, but was unable to achieve steady-state operation. The DEAHP temperature increases continuously until emergency shutdown. Other possibilities of direct connection, such as part-load DEAHP operation, or circulating water through the final condenser of the MED plant were tested. Nevertheless, neither steady operation nor good performance was achieved.
Fig. 6. Effect of a slight perturbation on working conditions and steady state reached. Test on 15/11/2007.
D.C. Alarcón-Padilla et al. / Desalination 250 (2010) 500–505
On the contrary, experimental tests with indirect connection of the DEAHP and the MED unit by means of two auxiliary water tanks were successful and this configuration is therefore recommended. DEAHP production was higher when operated at temperatures slightly above nominal with the same nominal COP and performance ratio. This suggests that the surplus thermal power production can be used instead of making the DEAHP operate at nominal temperatures by means of the control system and reducing its thermal power production to nominal. Acknowledgment The authors wish to thank the Spanish Ministry for Education and Science (OSMOSOL project ENE2005-08381-C03-01) for funding this work. References [1] E. Zarza, M. Blanco, Advanced M.E.D. solar desalination plant: seven years of experience at the Plataforma Solar de Almería, Proceedings of the Mediterranean Conference on Renewable Energy Sources for Water Production, Santorini, Greece, June 10–12, 1996, pp. 45–49.
505
[2] E. Zarza, Solar Thermal Desalination Project, Phase II Results & Final Project Report, 1st Ed, CIEMAT, Madrid, Spain, 1995. [3] D.C. Alarcón-Padilla, L. García-Rodríguez, Application of absorption heat pumps to multi-effect distillation: a case study of solar desalination, Desalination 212 (2007) 294–302. [4] D.C. Alarcón-Padilla, L. García-Rodríguez, J. Blanco-Gálvez, Assessment of an absorption heat pump coupled to a multi-effect distillation unit within AQUASOL project, Desalination 212 (2007) 303–310. [5] E. Zarza, Solar Thermal Desalination Project, First Phase Results and Second Phase Description, 1st Ed, CIEMAT, Madrid, Spain, 1991. [6] K.E. Herold, et al., Absorption Chillers and Heat Pumps, 1st Ed, CRC Press, Boca Raton, FL, USA, 1996, p. 148. [7] Alarcón-Padilla, Diego-César, Blanco-Gálvez, Julián, García-Rodríguez, Lourdes, Gernjak, Wolfgang, y Malato-Rodríguez, Sixto. First experimental results of a new hybrid solar/gas multi-effect distillation system: the AQUASOL Project. Desalination, 220, 2008, pp. 619–625.