Patent Application
20140034477
This invention relates to systems and methods for supplying water, in particular fresh water from sea water.
Known techniques for extracting fresh water from sea water include multi-stage flash distillation (MSF), reverse osmosis, and a system described in a PhD dissertation from Technical University of Munich by Hendrik Müller Horst entitled “Multiple Effect Humidification Dehumidification at Ambient Temperatures” (available here: http://mediatum2.ub.tum.de/node?id=601861), which involves using a solar collector to heat sea water which afterwards enters an evaporation chamber, extracting the distillate from the subsequent condensation of the generated steam. Background prior art can be found in U.S. Pat. No. 6,919,000, U.S. Pat. No. 7,225,620, U.S. Pat. No. 7,832,714, and US2010/0314238. Further background prior art can be found in: US2011/0056822; DE102008026673; FR2902666A; WO03/013682; WO2007/013099; and WO02/42221.
There is, however, a need for improved techniques.
Broadly speaking we will describe a water supply system, the system comprising: an evaporation station, the evaporation station comprising a water inlet, an air conduit, and a water evaporation system coupled to said water inlet and to said air conduit for converting water from said water inlet into water vapour and for providing said water vapour onto said air conduit to provide humidified air; a condensation station having an air inlet to receive said humidified air, a water outlet, and a water condensation system coupled to said air inlet and to said water outlet to extract water from said humidified air and provide said extracted water to said water outlet; and a pipe coupled between said air conduit of said evaporation station and air inlet of said condensation station.
In broad terms the inventor has recognised that once in vapour form water can be transported, for example upwards, without significant expenditure of energy. Furthermore the movement of air can be employed to improve the efficiency of an evaporation process, and in warm climates these observations can be combined to fabricate a water desalination system.
In embodiments the pipe has a length of at least 10 m, 100 m, 1 km, 10 km or 100 km, and in a large scale system the pipe may have a length of some 10 s of kilometres. Two alternative embodiments may be employed, one in which the pipe, evaporation station, and condensation station define a closed loop air path, and another in which the condensation station is located at a greater elevation than the evaporation station, for example at more than 10 m, 100 m or 1000 m above the evaporation station, for example on a hill or towards or at the top of a tall building. Nonetheless, some of the benefits of the invention may be obtained by locating both the evaporation station and the condensation station adjacent to a body of water, preferably substantially co-located with one another, whether or not there is a closed loop air path. This is because the body of water may be employed for efficient water condensation. Where the condensation station is above the evaporation station, energy may be extracted from the gravitational potential energy of the condensed water, for example for hydroelectric power generation.
Embodiments of the system employ a pipe with an outer surface having a solar radiant heat absorbance of at least 40%, 50%, 60%, 70%, 80% or 90% at a wavelength in the range 300 nm to 2000 nm. This may be achieved, for example, by colouring the pipe black and/texturising or otherwise configuring the surface of the pipe. In this way solar energy may be employed to assist in driving the humidified air through the system, and also to assist in maintaining the temperature of the air on its passage through the system to thus maintain the water vapour content of the air until the condensation station is reached. Optionally the system may include a solar heating system or solar concentrator to heat the pipe, for example comprising a series of mirrors along the pipe to gather and direct sunlight towards the pipe. Additionally or alternatively the pipe may be configured for heat storage and/or may be thermally insulated.
The skilled person will recognise that employing solar energy to provide heat to the humidified air in the pipe does not necessarily imply that the temperature of the air will rise or remain substantially constant—for example in a system in which the humidified air is transported to a significant height above the evaporation station the air temperature may drop even though solar energy is being supplied to the humidified air.
Additionally or alternatively the pipe may be heated using power from another renewable energy source and/or by means of waste heat from a power station employing fossil or nuclear fuel or some other source of heat.
Because the temperature of the humidified air drops, in particular in embodiments in which the condensation station is above the evaporation station, the pipe may include one or more water collection or extraction points along the length of the pipe, to remove condensed water from the pipe. However in some preferred implementations the degree of humidity of the humidified air at the evaporation station is adjusted so that at the condensation station (where the air temperature is reduced) the relative humidity is kept below a threshold of 100% (i.e. below the dew point), although in embodiments the threshold may be lower, for example 80% or 90%.
In some preferred embodiments the system is configured for large scale operation, and thus the pipe has a cross-sectional area of at least 1 m2, 5 m2 or 10 m2. In other embodiments the system may be employed at a smaller scale on a boat or other seaborne vessel.
Preferably the system also incorporates one or more fans or turbines to drive a flow of the humidified air though the pipe. In preferred embodiments one or more of these is located within the air conduit.
In preferred embodiments the water evaporation system comprises one or more spray evaporators, which can deliver substantial volumes of water into fast moving air. Thus preferably the water evaporation system comprises one or more sets or rings of nozzles within the air conduit, after the turbines or fans in a direction of the airflow, pointed to direct water droplets into a direction of the airflow. In embodiments the airflow is at least 1 m/s, 5 m/s, 10 m/s, 20 m/s or 30 m/s. Preferably an average dimension of a droplet is no more than 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm, for rapid evaporation. In embodiments, particularly those for moving fresh water, substantially all the water received by the water evaporation system may be converted into water vapour.
In some preferred embodiments the system is used to collect and evaporate salt water, which is transferred as water vapour to the condensation station where freshwater is retrieved, thus in embodiments the evaporation station and/or pipe also includes a brine collection system to collect brine resulting from the evaporation process. When used for desalination the system may be mounted on a sea-going vessel.
In some embodiments the system is configured to take account of the differential day/night heating and cooling of the ocean with respect to the desert. Thus in embodiments the system includes a controller to control day/night operation of the system, to operate the forced air flow at night when the relative temperature difference between the evaporation and condensation stations is larger. To facilitate this, in embodiments the system includes one or more water storage pools at or in fluid communication with the evaporation station, preferable thermally insulated for heat retention. Optionally these or their water inlets may be heated, for example by a solar heater such as a solar concentrator, or by other means, for example using waste heat/power from a power station. Then the controller may be configured to draw water into a pool for heating during the day, and to operate the forced air flow at night.
In embodiments the condensation station may comprise a heat exchanger thermally coupled to the air and/or ground in combination with a water collection system to collect water condensed from the humidified air. In embodiments the heat exchanger may have a tree or fan-type structure akin to a ‘lung’.
Additionally or alternatively the condensation station may include a heat engine such as a Stirling engine, or other energy harvesting system, driven by the temperature difference there (which may be >20° C., >30° C., >40° C., or >50° C.), for example thermally coupled to the heat exchanger. Energy from the heat engine may be employed to drive one or both of said water evaporation system and said airflow driving system.
These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which:
Referring to
The evaporation station comprises a water inlet to one or more spray evaporators and, preferably, one or more turbines of a similar design to those employed in wind tunnels of a similar diameter to that of pipe 130 (albeit the skilled person will appreciate that the pipe could be of smaller or larger diameter than that at a location of a turbine to adjust pressure/wind speed). Natural convection draws the warm, humidified air up to the condensation station, but for improved evaporation efficiency and greater water transport it is preferable to add a forced drive to the humidified air. In particular in a closed loop system multiple forced drives or turbines may be employed, before, after, and in between the evaporation and condensation stations.
The condensation station 130 preferably comprises one or more heat exchangers in combination with guttering or similar to collect the condensed water. Optionally a return pipe may be included from the condensation station back to the evaporation station, to encourage a greater air flow speed.
Example parameters for the system of
In embodiments the evaporation station preferably also includes a system to collect brine which is a bi-product of the evaporation process. This may be delivered via an outlet pipe back into the ocean. The brine collection may also, or alternatively, be part of the pipe with such outlets along the pipe as may be required.
Referring now to
Example parameters for the system at
Thus broadly speaking by increasing wind speed whilst actively dispersing water into the air we increase the surface/evaporation rate manifold, in embodiments by employing one or several turbines in combination with the active dispersion. In some preferred implementations we transport the vapor up, out and away from the evaporation station. Embodiments of the evaporation station merely employ a steady flow of water to be purified and as such no input reservoir (other than, for example, the ocean) is required. In some deployment scenarios (where the condensation station is at an elevated height and/or in a colder local climate) there is also the possibility of harvesting potential (or kinetic) energy through distribution of the condensed water as well as making use of natural differences in temperature. In embodiments of the system may be deployed on a very large scale (>0.1 km, >0.5 km, >1 km or >10 km), and a solar (or other renewable) heated pipe may then be advantageously employed in the system to transport the water vapour.
In some preferred implementations the degree of humidity of the humidified air in the pipe is adjusted to ensure that close to full humidity is ensured at the condensation station (where the temperature of the pipe immediately prior to the condensation temperature may be lower than in other parts of the pipe e.g. due to reduced temperatures surrounding the condensation station).
In embodiments of the above described systems the pipe may be provided along some or substantially all of its length with heat storage means for storing heat supplied to the pipe from an external source. This helps to retain the externally supplied heat during the day, and also provides a degree of thermal isolation of the pipe at night. Similarly the externally supplied heat may be provided along some or substantially all of the length of the pipe. This external heating may employ a solar concentrator partly surrounding the pipe, for example a set of mirrors at intervals along the length of the pipe, or such heat may be supplied from another renewable source, or by using fossil fuel, or by employing waste heat from another source.
No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1106403.7 | Apr 2011 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB12/50673 | 3/27/2012 | WO | 00 | 10/15/2013 |
