Presentation on theme: "COMPARISON BETWEEN MSF AND RO"— Presentation transcript:
1 COMPARISON BETWEEN MSF AND RO Multi-Stage FlashReverse OsmosisADVANTAGESreliable, robust processmore than 30 years of experiencenot sensitive to feed water qualitylong service life timesignificant cost savings due to the possible manufacturing in the client countryDISADVANTAGEShigher specific investment costhigher specific exergy consumptionlimited to high capacitiesADVANTAGESlower specific investment costlower specific exergy consumptionany capacity possibleDISADVANTAGESsensitive to feed water quality, danger of biofoulingstrong dependence on membrane/module manufacturerhighly qualified manpower needed for operation and maintenancehigh consumption of chemicals
2 KEY ISSUES FOR MEE PROCESS approximately the same performance ratio with fewer than half of number of effectshigher thermal efficiency using a lower temperature heating steamlower power consumption for pumpingpossibility of simple modification in the process configurationhigher operating flexibility with a shorter start-up periodstable operation over a load range of 30 120% versus 70 110%reliable capability of combination with both thermal and mechanical vapour compressionlower specific capital costlower maintenance and operating expensesMultiple Effect Evaporation process has many attractive characteristics in comparison with Multi-Stage FlashMain reasons of the enormous diffusion of MSF in MENA countries are:reliabilitylong-time experiencehigh capacityscarce importance of energy saving
3 SOLAR DESALINATIONcountries with fresh water shortage can generally rely on high values of solar irradiancesolar energy availability is maximum in the hot season when fresh water demand increases and resources are reducedwater constitutes a medium which allows to store for a long time possible energy surplus, economically and without significant losseslack of water usually takes place in isolated areas, like rural regions or small islands, where the soil occupation is not critical and the cost of traditional means of supply may dramatically risePOSSIBLE BENEFITSADDITIONAL REMARKS FOR SMALL SCALE APPLICATIONSCapacity up to 1,000 m³/d [domestic water needs of a community of more than 5,000 people]low capital costreduced construction timeutilisation of local manpower and materialssimple management
4 In general solar energy can feed any desalination process COUPLING OPTIONSDESALINATION PROCESSSOLAR TECHNOLOGYMSFMEEMVCROConcentrating Parabolic Collectors (Solar thermoelectric station producing both electricity and eventually heat through a cogeneration arrangement)Flat Plate/Evacuated Tubular CollectorsSalt Gradient Solar PondPhotovoltaicIn general solar energy can feed any desalination processSystems for the generation of high temperature heat (linear parabolic collectors, solar towers)MEE driven by low temperature solar thermal collectors, both flat plate and evacuated tubularOptionsRO coupled with photovoltaic panelsMEE coupled with salt gradient solar pondlarger capacities are requesteda combined demand of power must be presenteconomic feasibility is still too farAlternative systems
5 Accurately estimate the production cost of desalted water; 1. ECONOMIC ANALYSIS OF THE TWO OPTIONSSpecial attention was paid to two different options for possible coupling between solar system and a desalination unit (PV/RO and ST/MEE), in order to:Accurately estimate the production cost of desalted water;Single out the possible factors to fill the gap between theproduction cost by solar and conventional technologies;Address other basic aspects of a solar system such as theinitial investement and required area.Overall water production cost is influenced by several local factors, like the market status of solar systems, financing conditions, labor and pre-treatment cost, fuel and electricity price.
6 The values of the technical parameters and solar irradiance assumed to estimate the water production cost, are reported below.Utilization factor0.9Annual solar energy (kWh/m²)2,000Peak radiation(W/m²)1,000PV modules efficiency0.1Motive steam temperature for MEE (°C)70Solar collector average efficiency0.5Electric energy need in RO (kWh/m³)5Electric energy need in MEE (kWh/m³)2Thermal energy need in MEE (kWh/m³)60
7 Maintenance (% of plant cost) Values of the common economic parameters are listed in the table given below.PV/ROST/MEEConventionalSystem life (years)2530Interest rate (%)85Maintenance (% of plant cost)2Manpower ($/m³)0.10.05Pre-treatment ($/m³)0.0350.025Electricity ($/kWh)0.04
8 PV modules cost for a 10 MW size ($/Wp )3PV modules cost for a 100 kW size ($/Wp6Battery supply(h)12Battery cost (% of modules cost)15Annual rate of batteries replacement (%)Electronic device cost (% of PV plant cost)5RO plant cost for a 10,000 m³/d size ($/(m³/d))1,000Scale factor0.9Membranes cost (% of RO plant cost)60Annual rate of membranes replacement (%)10Values assigned to estimate the water cost by the PV/RO system.
9 Values assigned to estimate the water cost by the ST/MEE system Collector cost for a 100,000 m² area ($/m²)150Collector cost for a 10,000 m² area ($/m²)250Storage cost (% of collector cost)20MEE plant cost for a 10,000 m³/d size ($/m³/d)1,200Scale factor0.7Values assigned to estimate the water cost by the ST/MEE system
10 For each analyzed option the trend of the production cost, when the capacity varies between 500 and 5,000 m³/d, is shown in theFig.
11 Specific plant cost as a function of plant capacity by means of two solar systems (PV/RO and ST/MEE) and a conventional one.
12 Operation and maintenance specific cost as a function of plant capacity by means of two solar systems (PV/RO and ST/MEE) and a conventional one.
13 ALTERNATIVE OPTIONS CONVENTIONAL RO/PV SOLAR MEE/SGSP reference value for the water production cost can be assumed equal to 1 $/m³ in case of medium to small size desalination processes connected to the electric gridCONVENTIONALdesalination system typically used in stand-alone configuration is a reverse osmosis process coupled with a diesel powered generator; due to the additional charges for transporting and fuel storage, water production cost can rise up to 1.5 $/m³Specific capital cost 4,200 $/(m³/d)Water production cost 2 $/m³Specific area 10 m²/(m³/d)RO/PVSOLARSpecific area 70 m²/(m³/d)Specific capital cost 3,700 $/(m³/d)Water production cost 1.5 $/m³MEE/SGSP
14 COMPARISON BETWEEN SOLAR OPTIONS RO COUPLED WITH PHOTOVOLTAICADVANTAGESDRAWBACKSlowest specific soil occupationideal for stand-alone configurationany capacity possible with no dramatic rise in costbest potential towards further cost reductionsensitive to feed water qualityadvanced materials requiredcomplexity of design and managementmost costly operation due to membrane and battery replacementMEE COUPLED WITH SALT GRADIENT SOLAR PONDADVANTAGESDRAWBACKScompetitive water production costlowest investmentsimplified operation due to limited piping and absence of coveringsuse of discharged brine for salt gradient preservationavailability of a huge areaadequate mechanical and thermal characteristics of the groundlong time for design, simulation, construction and fully operatingdifficulty in reliable predictions
15 SOLAR DESALINATION (CONCLUSION) Compared to conventional processes, water cost using solar desalination for plants of capacity 1000– 5000 m3/day, is still quite expensive.For remote areas with no access to electricity, conventional systems water cost rises up to 1.5 $/m³Cost is 0.6 $ lower for the PV/RO system in comparison with ST/MEE systemAlso, solar field area in case of PV/RO system is small (nearly 8 m2 compared to little less than 20 m2 per m3/day of installed capacity).ST/MEE is more sensitive to scale effect: doubling capacity MEE and RO cost falls down over 20% and less than 10% respectivelyHybrid system i.e. ST/MEE with auxiliary fossil fuel boiler allows quite a large cost reduction, because solar source exploitation can be optimised and consequently solar field cut down
16 CONCLUSIONS (IN GENERAL) Seawater desalination has already confirmed its potentiality to resolve the fresh water problems in numerous countries. It is, however, to be noted that in spite of the good reliability and favourable economic aspects of desalination processes, the problem of high energy consumption till remains to be resolved.In particular, advantages of photovoltaic become decisive for stand-alone configurations and smaller sized systems (approx m3/day). In addition, ground requirements are less than half with better expectations of cost reduction.On the other hand photovoltaic coupled with reverse osmosis is not suitable for severe operational conditions regarding the feed water. Also, the technology may become too onerous under specific circumstances, for example if know how and materials are not locally availableFor large scale plants coupling of desalination processes with high temperature solar technologies needs to be investigated thoroughly.In case of extraordinarily costly traditional means of water supply and availability of possible financing at low interest rates for renewable sources, solar desalination can be a viable option.
17 PERSPECTIVESCompetitiveness of low temperature solar thermal collectors driven desalination systemsSolar collectorsMultiple effect evaporation processIncrease in collectors efficiency to specific cost ratioDevelopment of relatively low priced concentrating collector to feed more efficient desalination systems, as TVC-MEEMarket growth due to innovative applications of the productImprovement of the efficiency of low top brine temperature systemsReduction of electric energy requirementsDevelopment of reasonably priced small size devicesBy far the most critical system component
18 Solar Laboratory activities R&D activities on desalination have been undertaken during the recent years with the main purpose of extending the field of solar energy applicationIn the past, a solar still was designed, installed and experimentedPhotovoltaic driven desalination plant has been designedNew Generation of Solar Thermal SystemsNEGSTMain targets of ENEA:pre-normative work collaborating with Demokritosidentification and characterization of the most suitable technologies in collaboration with main South European Institutionsdevelopment of simplified tools for designing and performance assessment with support from Polytechnic of Milan.18 organisations out of 14 different European countries
19 Acknowledgements Ing. Domenico MARANO Dr. Vincenzo SABATELLI Dr Vincenzina SARNODr. Isabella DE BARILast but not the least my thanks are due to all the participants.