S.E. Aly

A study of a new thermal vapor compression/multi-effect stack (TVC/MES) low temperature distillation system

Abstract A novel distillation system for seawater desalination is presented. It comprises a LiBrH2O absorption machine and MES, which replaces the condenser and evaporator of the machine. The MES has 20 effects with the top one receiving the steam produced in the generator while the absorber receives the vapor produced in the bottom effect. The system is analyzed over a new record for the evaporation range of 6–63°C. Using a 3000 TR absorption machine, the system showed a yield of 1.53 mgd of fresh water at a GOR of 14.8 and PR of 14.2. In addition, the system provides a cooling effect equivalent to a 220 kW air conditioning unit. The proposed system provides the possibility of operating with a low top brine temperature down to 30°C, which would lead to low cost water and trouble-free long-life operation.

A combined RO/freezing system to reduce inland rejected brine

Abstract A combined RO/DCF system is proposed as an efficient system which would reduce the problem of the disposal of the rejected brine from inland desalination plants. Governing equations and thermodynamic relations are shown. Economical and energy comparisons between the combined system and separate RO and DCF units for 200 m 3 /h are presented. Results showed that the combined system can reduce the energy consumption by about 13 percent and 17 percent compared to separate RO and DCF plants respectively. The combined system can reduce the rejected brine by over 90 percent of that of separate RO plant at the same water production.

Vapour compression distillation using waste heat absorption systems

Abstract A novel combined vapour compression/multi-effect boiling waste heat recovery system suitable for variable temperature energy sources is presented. The multi-effect boiling system comprises 14 vertical tube evaportor effects with an extended evaporation range from 114°C to 36°C and operates in the vapour compression mode. The vapour is compressed using a LiBr—water absorption machine fired by the exhaust of a gas turbine. The absorber receives the vapour produced in the last effect of the multi-effect boiling system while the top effect receives the steam produced in the generator of the absorption machine. Analysis of the combined system shows its operational felxibility compared to other waste heat recovery systems. Using the exhaust of a GE-32670 kW gas turbine, the proposed combination would produce up to 3.44 mgd of fresh water at a performance ratio of 10 and a product rate of 4.3 gal/kWh. This is 44% higher than that of existing waste heat recovery distillation systems, with no expense for extra firing.

Combined RO/VC desalination system

Abstract An analysis of a combined reverse osmosis (RO) and a mechanical vapour compression (VC) desalination system suitable for remote areas or small communities is presented. This system consists of an RO unit with a recovery ratio of 25% and is driven by a diesel engine which is also coupled to the VC, and has a total output of 705 m2/d. Vapour discharged from the VC is superheated using a portion of the waste heat from the exhaust of the diesel engine. The degree of superheating is converted, in a desuperheater, into a 12% mass increase of saturated vapour at 112°C. This is introduced to a 3-effect VTE unit with the third effect working at atmospheric pressure and is connected to the suction side of the VC. Eleven flashing chambers are used for feed heating with a bottom temperature of 56°C. The pretreated RO brine, at high pressure, is used to cool the diesel engine. Then it is heated further, using both distillate and blowdown effluent from the bottom stage of the VTE feed heaters. Thermodynamic analysis of the combined system showed that about 46% more fresh water is produced than that for the RO alone at the expense of 29% extra diesel power. Pumping powr required to circulate the flow in various parts of the system is saved, and the whole system can be designed as a mobile one, contributing to its advantages.

Analysis of a diesel dual plant

Abstract This paper presents the thermodynamic analysis of a medium size dual purpose plant driven by 9.65 MW diesel engines. The water is produced by a 0.9 mgd RO plant to maintain a product ratio of 5 gallon/kWh. A scheme of two options is proposed to utilize the engine waste heat, from engine block and exhaust gases, to increase the RO production. One option is a Rankine Freon Cycle (RFC) while the other is a Brayton steam cycle (BSC). In RFC a Freon boiler (2 MPa, 75°C) generates the vapour required to drive a Freon turbine. Whereas in BSC, engine cooling water flashes to produce the steam required to drive a turbine. In either option the power generated is used to enhance the RO production. Layout of the scheme is presented and systems are analyzed. For 15000 inhabitants community, the water produced increases by 30 percent and 37.6 percent for the RFC and BSC respectively. The engine power increases by 6.5 and 8.2 percent with RFC and BSC respectively.

Analysis of a fuel-solar assisted central DPP

Abstract In this work, a new arrangement for central fuel fired solar assisted dual purpose plant (DPP) is presented and is thermodynamically analyzed as well. The solar energy, collected at moderate temperatures, drives an open cycle LiBr-H 2 O absorption machine with a ϕp s turbine replacing the condenser and the evaporator used in such conventional heat pumps. In a DPP, this heat pump is connected upstream of the multistage flash (MSF) distillator where the ϕp s turbine receives the pass out steam assigned to the MSF and the steam leaves the heat pump generator is fed to the MSF. Whenever it is applied to a central desert steam power plant (DSPP), the heat pump is introduced upstream of the steam condenser. The same basic steam cycle is used in analysing the combined arrangement for both the DPP and DSPP with a reheat being used to reduce the ϕp s corrosion problems. For a solar collecting temperature of 190°C for the DPP and 134°C for the DSPP the power output increased by 56 and 53 percent at an extra firing of 10.5 and 21 percent respectively. In the DPP, the combined arrangement can increase the water produced by four folds at the design power output or increasing the power output by 56 percent while maintaining the design water output.

Comparative study between conventional and vapor compression multi-effect desalination systems

Abstract In the present article, a thermodynamic analysis is given for the following systems: (i) conventional multi-effect boiling (MEB), (ii) MEB equipped with a mechanical vapor compression facility, (iii) MEB with a thermo-vapor compression device, (iv) combined conventional MEB and vapor-thermo compression systems. The analysis shows that the combination given by item (iv) is more advantageous than the other three alternatives. A case study showed that such combination could increase the productivity twice that of a conventional MEB plant utilizing the same number of effects and with almost the same performance ratio. Moreover, less number of effects work under vacuum conditions which means less leakage troubles and less evacuating motive steam.

Analysis of a fuel-solar assisted central dual purpose plant

Abstract A new arrangement for a central fuel fired solar assisted dual purpose plant (DPP) is presented and thermodynamically analyzed. The solar energy, collected at moderate temperatures, drives an open cycle LiBrH 2 O absorption machine with a lp s turbine replacing the condenser and the evaporator used in such conventional heat pumps. In a DPP, this heat pump is connected upstream of the multistage flash (MSF) distillor where the lp s turbine receives the pass out steam assigned to the MSF and the steam leaves the heat pump generator is fed to the MSF. Whenever it is applied to a central desert steam power plant (DSPP), the heat pump is introduced upstream of the steam condenser. The same basic steam cycle is used in analyzing the combined arrangement for both the DPP and DSPP with a reheat being used to reduce the lp s corrosion problems. For a solar collecting temperature of 190°C for the DPP and 134°C for the DSPP the power output increased by 56 and 53% at an extra firing of 10.5 and 21% respectively. In the DPP, the combined arrangement can increase the water produced by four fold at the design power output or increasing the power output by 56% while maintaining the design water output.

A theoretical study of enhanced condensation over horizontal fluted tubes

Abstract A numerical study of steam condensation over horizontal fluted tubes is presented. Condensate is driven by surface tension to the groove valley where it is drained by gravity. From the bottom to the top the groove domain is divided into a valley section, crest section with large variations of condensate layer curvature, and tip section with gradual change of condensate layer curvature. In the valley section the effect of indentation angle α, the minimum condensate height αo and the circumferential angle θ on the drainage flow rate ·m are studied. In the crest section ( heat transfer domain ) the effect of α, αo and θ on the heat transfer coefficient h is investigated. Results showed that, a decrease in α increases both h, and ·m per groove. The groove flooding conditions could be obtained by comparing ·m in the valley and crest sections with more flooding for small values of α. The smaller the α angle, the larger the ·m provided that no excessive flooding occurs.

Efficient energy utilization in single purpose desalination plants

Abstract Thermodynamic analyses and case studies were carried out on hybridized systems designed to improve single purpose desalination (SPD) plants. The first system considered is a conventional SPD connected to a steam generator by a pressure reducing valve (PRV). In the second system, this is replaced by a mechanical vapour compression MVC/MED unit, and in the third system by a thermovapour compression TVC/MED unit. In the fourth system, a reverse osmosis (RO) unit replaced the PRV, thus using the supplied steam to produce more fresh water. Results of the analysis emphasize the extra water produced and the overall performance ratio increase of the plant. The included case study showed that the plant performance of the SPD was significantly improved by using any of the above systems. The extra water produced amounted to 96, 84 and 46% of the initial plant production in the second, third and fourth system respectively.