TECHNICAL FIELD

The present invention relates to water and energy use, and particularly to a self- sustaining, closed-circuit cooling and desalination system. BACKGROUND ART

District cooling plants can be used to reduce energy consumption, as well as carbon dioxide emissions. However, district cooling plants typically rely on wet cooling towers for disposing excess heat to the environment. This heat disposal results in a significant loss of fresh water. As such, heat disposal can present a major problem in hot, arid countries, such as Qatar and other GCC countries, which place a high demand on air cooling and rely on costly and energy intensive desalination processes for securing fresh water supply.

One proposed solution is the use of treated sewage effluent (TSE) for wet cooling towers, instead of fresh water (e.g. potable water). As TSE water quality is not suitable for cooling towers, TSE requires treatment prior to its use in district cooling towers. Effective treatment of TSE can be done through membrane processes, ideally with low pressure reverse osmosis desalination technology. Conventional systems for desalinating TSE, however, can be costly. In addition, the disposal of brine resulting from reverse osmosis is a major health and environmental concern.

Thus, a hybrid cooling and desalination system solving the aforementioned problems is desired.

DISCLOSURE OF INVENTION

The hybrid cooling and desalination system includes a first subsystem having a first circulation assembly, a second subsystem having a second circulation assembly, and a heat pump templifier in fluid communication with the first subsystem and the second subsystem. The first subsystem is configured for desalinating feed water from a feedwater source to provide purified water. The first subsystem includes a filtration unit for desalination of the feed water to produce a first amount of purified water and a brine solution and a zero liquid-discharge system for providing an additional amount of purified water from the brine solution released from the filtration unit. The filtration unit can include a nano- filtration unit and/or a reverse osmosis unit. The second subsystem can include a district cooling plant (DCP) and a cooling tower. The purified water from the first subsystem can be supplied to the cooling tower in the second subsystem as make-up water. The heat pump templifier can extract waste heat from water discharged from the district cooling plant (DCP) to preheat the feed water FW supplied to the filtration unit, while cooling part of the outlet hot water from the district cooling plant condenser to a lower temperature level, such as a considerably lower temperature level, than the water leaving the cooling tower. The transfer of heat from the second circulation assembly to the first circulation assembly also reduces the thermal duty and evaporation loss in the cooling tower. Furthermore, the temperature of the cooling water supplied to the condenser of the district cooling plant is lowered by mixing with the cooled part of the outlet hot water from the district cooling plant condenser.

The hybrid cooling and desalination system can maximize energy and water use efficiency in district cooling plants by integrating desalination processes with district cooling plants. The desalination processes can include Reverse Osmosis (RO) and/or thermal desalination technologies. The hybrid cooling and desalination system can polish and reuse treated sewage effluent (TSE) water as well as desalinate seawater and brackish water with 100% water recovery and zero liquid discharge (ZLD). The hybrid cooling and desalination system can close the water and energy circuits in the district cooling plants and recycle waste heat and waste water in the system.

These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a diagram of a hybrid cooling and desalination system, according to the present invention.

Fig. 2 is a diagram of a zero liquid discharge system for use in a hybrid cooling and desalination system, according to the present invention.

Unless otherwise indicated, similar reference characters denote corresponding features consistently throughout the attached drawings. BEST MODES FOR CARRYING OUT THE INVENTION

Referring to Figs. 1 and 2, a hybrid cooling and desalination system 10 is generally illustrated. The hybrid cooling and desalination system 10 includes a first subsystem 100 having a first circulation assembly 103, a second subsystem 200 having a second circulation assembly 205, and a heat pump templifier 50 in fluid communication with the first subsystem 100 and the second subsystem 200. The first subsystem 100 is configured for desalinating feed water FW, such as feedwater from a feedwater source FWS to provide purified feed water PFW. The first subsystem 100 can include a filtration unit 120 and a zero liquid-discharge system 121. The filtration unit 120 desalinates feed water FW to produce a first amount of purified water PW and a brine solution BS. The zero liquid-discharge system 121 provides an additional amount of purified water PW from the brine solution BS released from the filtration unit 120. The filtration unit 120 can include a nano-filtration unit and/or a reverse osmosis unit. The second subsystem 200 can include a district cooling plant (DCP) and a cooling tower 250. The purified water PW from the first subsystem can be supplied to the cooling tower 250 in the second subsystem 200 as make-up water. The heat pump templifier 50 can extract waste heat from water discharged from the district cooling plant (DCP) to preheat the feed water FW supplied to the filtration unit 120. It is to be noted that the blow down from the cooling tower 250 can be recycled, such as completely recycled, in the zero liquid-discharge system 121.

As described in detail below, the heat pump templifier 50 is configured for transferring heat from the second circulation assembly 205 to the first circulation assembly 103 as well as lowering the temperature of water traveling to the cooling tower 250 from the district cooling plant DCP. As such, thermal duty and evaporation loss in the cooling tower 250 can be reduced. It is to be noted that the hybrid cooling and desalination system 10 can be a closed circuit system.

The feed water (FW) can be seawater (SW), brackish water (BW), or tertiary treated sewage effluents (TSE). For example, the hybrid cooling and desalination system 10 can treat TSE to provide water having a quality acceptable for use in cooling towers (CTs). Heat from the waste water produced in the district cooling plant (DCP) can be conveyed to the first subsystem 200 by the heat pump templifier 50 to preheat a first amount of TSE in the first subsystem 200 before it is treated by the filtration unit 120. For example, the filtration unit 120 desalinates the TSE by reverse osmosis, e.g., low pressure reverse osmosis, to provide a first amount of purified water PW. The resulting brine solution BS in the filtration unit 120 is further processed by the zero liquid discharge (ZLD) system 121 to provide a second amount of purified water PW and achieve 100% water recovery. The zero liquid discharge system (ZLD) 121 obviates the need for reverse osmosis brine disposal. The system efficiently enhances permeate flux rate of reverse osmosis through preheating reverse osmosis feed water.

The first circulation assembly 103 can include a feedwater pretreatment module 105 positioned in fluid communication with a feedwater source FWS, a condenser unit 110 positioned in fluid communication with the feedwater pretreatment module 105 and in fluid communication with the heat pump templifier 50, and a first heat exchanger 115 positioned in fluid communication with the condenser unit 110. Pretreating the feedwater in the feedwater pretreatment module 105 can include coagulation, passing the feed water FW through an auto strainer and/or a disc filter to remove dirt and other particles suspended in the water, and/or ultrafiltration.

The filtration unit 120 is in communication with the feedwater pretreatment module 105 and a first heat exchanger 115. As described previously, after the feedwater FW is pretreated in the pretreatment module 105, the first portion of the pretreated feedwater PFW is preheated in the condenser unit 110 of the first circulation assembly 103 by heat conveyed by the heat pump templifier 50, and introduced to the filtration unit 120. The first portion of the pretreated feedwater PFW can be preheated to a temperature of about 38-40°C. The filtration unit 120 can have a semi-permeable membrane 125 configured for filtering the pretreated feed water PFW received from the feedwater pretreatment module 105. For example, the filtration unit 120 can be a reverse osmosis unit. Preferably, low pressure (10- 15 bar) reverse osmosis is used to form a brine solution BS and purified water PW (e.g. potable water) in the filtration unit 120. A second portion of the pretreated feedwater PFW is preheated by the heat conveyed by the heat pump templifier 50 and conveyed to the first heat exchanger 115. The brine solution (BS) emitted from the filtration unit 120 can have a temperature of about 38-40°C. The first heat exchanger 115 heats the brine solution BS emitted from the filtration unit 120. The brine solution leaving the heat exchanger 115 can have a temperature of about 62-69°C. A second heat exchanger 130 is positioned in communication with the first heat exchanger 115. The second heat exchanger 130 is configured for receiving superheated steam S, such as steam from a natural gas boiler or a liquefied petroleum gas (LPG) boiler to further heat the brine solution BS heated by the first heat exchanger 115 and for discharging a condensate into a boiler B. It is to be noted that the filtration unit 120 can be positioned in fluid communication with a feedwater holding tank 310 (Fig. 2) instead of a pretreatment module 105

The zero liquid discharge (ZLD) system 121 is positioned in fluid communication with the second heat exchanger 130. The ZLD system 121 includes an evaporation module 140 for thermal desalination of the brine solution (BS) and a condensation module 150 in which water vapor from the evaporator module 140 is condensed and returned to the second subsystem 200. The brine solution (BS) entering the zero liquid discharge (ZLD) system 121 can have a temperature of about 65-90°C. The ZLD system 121 can further include a dryer/crystalizer 330 (Fig. 2) for dewatering and removing crystals precipitated from the brine solution (BS). The condensation module 150 is positioned in communication with the feedwater pretreatment module 105. The condensation module 150 includes a recooler 340 configured for receiving a third amount of the pre treated feed water PFW to dissipate heat of condensation in the condensation module 150. As such, the thermal brine concentrator or condensation module 150 of the ZLD system 121 can be efficiently cooled.

The first circulation assembly 103 can include a plurality of valves. A first valve

107, such as a three-way valve, can be coupled to the feedwater pretreatment module 105 to regulate the flow of pretreated feed water PFW throughout the first circulation assembly 103. The pretreated feed water PFW can flow from the feedwater pretreatment module 105 to the condenser unit 110, as illustrated by a first arrow Al, to the filtration unit 120, as illustrated by a second arrow A2, and to the condensation module 150, as illustrated by a third arrow

A3. A second valve 109, such as a three-way valve, can be coupled to the condenser unit 110 to regulate the flow of heated pretreated feed water PFW from the condenser unit 110 to the first heat exchanger 115, as illustrated by a fourth arrow A4, and to the filtration unit 120, as illustrated by a fifth arrow A5.

The second circulation assembly 205 of the second subsystem 200 includes a first evaporator unit 210 positioned in fluid communication with a district cooling plant DCP, a compressor unit 220, and a condenser unit 230. The first evaporator unit 210 is configured to extract waste heat from return water RW used by the district cooling plant DCP for cooling. The compressor unit 220, positioned in fluid communication with the first evaporator unit 210 and the condenser unit 230, is configured for receiving heat, such as in the form of vapor, from the first evaporator unit 210 and supplying the compressed heat to the condenser unit 230 of the second circulation assembly 205. The condenser unit 230 of the second circulation assembly 205 condenses the vapor and discharges water W, which is distributed from between the first evaporator unit 210 and the cooling tower 250 at ratios that can be determined by thermodynamic analysis. It is to be noted that the second subsystem 200 can include a third valve 235, such as a two-way valve, positioned between the condenser unit 230 and the first evaporator unit 210 so as to regulate the flow of liquid throughout the second circulation system 205, such as from the condenser unit 230 to the first evaporator unit 210 and to the cooling tower 250. The condenser unit 230 of the second circulation assembly 205 uses water supplied from the cooling tower 250 to condense the steam from the compressor 220.

The chilled water CH passing through the first evaporator unit 210 is mixed with cooled water at the outlet of the cooling tower 250, thereby reducing the inlet cooling water temperature to the condenser unit 230 from about 33°C to 34°C to about 28°C to 29°C. This reduction in temperature can reduce pumping power and the pump size of the condenser unit 230 by up to 60% due to an increase in the temperature difference through the condenser unit 230, e.g., about 7°C in conventional district cooling plant technology compared to about 10°C -12°C in the present system. Further, reducing the cooling water temperature upstream of the condenser unit 230 of the second circulation assembly 205 can improve the coefficient of performance of the district cooling plant and can reduce the energy consumption of the chillers, which can represent a major part of the total energy consumption in district cooling plants. As such, a total energy reduction, such as a reduction of between 25% and 30%, can be achieved in the district cooling plant (DCP) energy consumption. Chilled water returning to the DCP can have a temperature of about 4°C.

The second circulation assembly 205 also includes a second evaporator unit 240 positioned in fluid communication with the condenser unit 230 of the second circulation assembly 205 and in fluid communication with the heat pump templifier 50. The second evaporator unit 240 is configured to transfer heat from the water supplied by the condenser 230 of the second circulation assembly 205 to the heat pump templifier 50. As such, the amount of water to be cooled through the cooling tower 250, (e.g. the thermal load on the cooling tower 250) can be considerably reduced. The water leaving the second evaporator unit 240 can have a temperature of about 10-12°C. A blow down valve 255 is coupled to the cooling tower 250 to remove a portion of the circulating water flow in order to maintain the amount of dissolved solids and other impurities at an acceptable level. The blow down B from the cooling tower 250 is channeled into the first circulation assembly to be combined with the brine solution BS before the brine solution BS enters the first heat exchanger 115. A collection basin 253 is positioned beneath the cooling tower 250 to collect the cooled water. The second circulation assembly 205 can include a permeate tank buffer 260 positioned in fluid communication with the filtration unit 120 and the ZLD system 150. The permeate tank buffer 260 is configured for receiving product water PW from the filtration unit 120 and from the ZLD system of the first subsystem 100 and channeling the product water PW back to the cooling tower 250 as make-up water to replace all losses due to evaporation, leaks, or discharge.

It is to be noted that for reverse osmosis, the pretreated feed water FW is pumped into the filtration unit 120 with sufficient pressure so as to overcome natural osmotic pressure in the filtration unit 120. For example, when the pretreated feed water PFW enters the filtration unit 120 from the feedwater pretreatment module 105, the semi-permeable membrane 125 allows the solvent (i.e. water) to permeate and retains the solute (i.e. dissolved salts), thereby separating desalinated product water PW (e.g. potable water) and the brine solution BS. Additionally, the pretreated feed water PFW enters the filtering unit 120 with sufficient pressure so as to prevent product water PW from flowing back into the brine solution BS by osmosis.

The feedwater pretreatment module 105 can be formed from any type of material suitable to receive the feed water FW, such as seawater, brackish water, or treated sewage effluents, from a feed water source FWS, such as from sewage treatment plants or the sea. The feedwater pretreatment module 105 can be configured for pretreating the feed water FW, such as by coagulation and/or ultrafiltration. The filtration unit 120 can be formed from any type of material suitable to receive pretreated feed water PFW from the feedwater pretreatment module 105. The first semi-permeable membrane 125 can be any type of semipermeable membrane that allows the solvent (i.e. water) to permeate and retains the solute (i.e. dissolved salts).

The ZLD system 121 can be formed from any type of material suitable to receive pretreated feed water PFW from the feedwater pretreatment module 105 and heated brine solution from the second heat exchanger 130, respectively. Further, the permeate tank buffer 260 can be formed from any type of material suitable to receive product water PW from the first subsystem 100.

The waste heat recovery heat pump templifier 50 can be any suitable type of heat pump capable of transferring heat, such as in the form of vapor, from the second evaporation unit 240 of the second circulation assembly 205 to the condenser unit 110 of the of the first circulation assembly 103. The hybrid cooling and desalination system 10 can be used for recycling water in district cooling plants or other facilities where waste heat and

contaminated water is available.

By way of operation, feed water FW can be drawn into the feedwater pretreatment module 105 from a feed water source FWS, such as by any type of suitable pump (not shown), where it can be pretreated to produce the pretreated feed water PFW. The pretreated feed water PFW can subsequently be pumped through the first valve 107 into the condenser unit 110 of the first circulation assembly 103 as illustrated by the first arrow Al, the filtration unit 120 as illustrated by the second arrow A2, and into the ZLD condenser subsystem 150 as illustrated by the third arrow A3.

The pretreated feed water PFW that is pumped through the first valve 107 into the condenser unit 110 mixes with heat, in the form of vapor, discharged by the heat pump templifier 50 to increase the temperature of the pretreated feed water PFW, e.g., from between 25°C and 35°C to a temperature greater than about 65°C. A first portion of the pretreated feed water PFW that is heated, e.g., to a temperature greater than 65 °C, can then be pumped to the filtration unit 120, while a second portion of the heated pretreated feed water PFW is pumped to the first heat exchanger 115 to heat the brine solution BS created by the filtration unit 120 via reverse osmosis, as discussed herein. It is to be noted that the brine solution BS can have a temperature in the range of between 38°C and 40°C upon exiting the filtration unit 120. As the brine solution BS is heated by the pretreated feed water PFW, the pretreated feedwater PFW is cooled. For example, after heating the brine solution BS in the first heat exchanger 115 to a temperature of between 62°C and 69°C, the pretreated feed water PFW can then be further cooled down to meet the allowable threshold temperature level by mixing with feed water FW from the feed water source FWS, such as TSE from the network, and then can be discharged back into the feed water source FWS, whereas the brine solution BS having a temperature of between 62°C and 69°C can be injected into the second heat exchanger 130, i.e., brine heater, so that the brine solution BS can be heated up to the required temperature, such as between 65°C and 90°C, for the ZLD system.

The heat transfer in the condenser unit 110 of the first circulation assembly 103 between the pretreated feed water PFW entering the condenser unit 110 and the vapor discharged by the heat pump templifier 50 can condense the vapor discharged by the heat pump templifier 50 to form condensate (water) in the condenser unit 110 that can

subsequently be pumped through a fourth valve 112 through the second evaporation unit 240 to the cooling tower 250. Once in the cooling tower 250, the water can be further cooled as is conventionally known. The pretreated feed water PFW can be pumped through the first valve 107 into the filtration unit 120 to form product water PW and brine solution BS through reverse osmosis, as discussed above. Once formed, the brine solution BS can be discharged by the filtration unit 120 into the first heat exchanger 115 where, as discussed above, the temperature of the brine solution BS can be increased, such as from between 38°C and 40°C to between 62°C and 69°C.

Referring to Fig. 2, after the brine solution BS is discharged from the first heat exchanger 115, the temperature of the brine solution BS can be increased further by superheated steam S in the second heat exchanger 130 to temperatures between 70°C and 90°C, for example, prior to entering the ZLD system 121. Once inside the ZLD system 121, the brine solution BS can undergo flash vaporization to produce a condensate, such as dry salt DS. The dry salt DS can then enter the dryer/crystalizer 330 and, once crystalized, be discharged. The heat H created by flash vaporization in the evaporator system 140 can be transferred to the recooler 340 in the ZLD condenser system 150 to be dissipated by the pretreated feed water PFW from the feedwater pretreatment module 105. The pretreated feed water PFW can then be recirculated through the filtration unit 120. Condensate from the condenser system 150 can be mixed with product water PW discharged from the filtration unit 120 and channeled into the permeate tank buffer 260, as shown in Fig. 1. The product water PW then flows into the cooling tower 250 for circulation through the second subsystem 200.

It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.