WHICH REVERSE AIR FLOW DISCHARGE DIRECTION

Technical Field

Wind turbines and power generation from wind energy is the topic of this invention. The main application is in electric power generation, where these turbines are mostly utilized to drive electric generators. Desalination of water comes secondly as a side product of processes used to improve the wind turbine performance.

Background Art

Wind energy has been utilized from centuries in several human activities. It was first used by sailors to sail their boats and ships in rivers and seas. The Egyptians used the strong Nile currents to sail from Upper Egypt to the North, whereas they used the wind to sail from the North to the South against the strong water currents. Wind energy was known to several old civilizations such as the Persian civilization, which first utilized the wind energy to grind their grains. During the middle ages, wind energy was used by the Dutch and are most known for their Dutch mills. In modern eras wind energy has evolved as one of the promising renewable green energy sources that have small environmental impact. Egypt is rich in renewable energy sources. The best location suitable for extraction of energy from the wind in Egypt in view of the current economic and technological conditions is the Gulf of Suez and North of the Red Sea. This area has both high and sustainable wind speed. To efficiently extract energy from the wind, the energy conversion system (current horizontal axis machines used in industry) must be normal to the wind stream. For this reason, the horizontal axis machines are turned to face the flow or energy conversion systems are designed such that their performance is independent of the wind direction.

Other challenges in the future are those of water desalination. This challenge is related to energy challenges since the technology needed to desalinate water require high energy usage and availability of energy near the desalination sites. Generating wind energy and water desalination are both mature technologies which are not directly linked to each other. Obtaining fresh water as a byproduct from wind energy has not been used before. Disclosure of Invention

Technical Problem

Wind energy conversion systems utilize the wind energy in the airflow and convert it usually to electric energy. The objective is to extract all the energy from the flow, which is impossible because the flow cannot leave with zero velocity. The turbines efficiency is used to indicate how good it can extract energy from the wind. The available energy for extraction is equal to half the area of the energy conversion system, multiplied by the density of air and the cube of the air flowing through the system.

Increasing the area of the wind conversion system increases the energy captured. This implies the use of very long turbine blades which is very challenging. First most of the blades are manufactured as single pieces. Transportation and assembly of the blades becomes challenging to avoid fractures and bending of the blades. The towers used can be in excess of 100 meters high which further challenges the assembly process. The technical challenges do not end at the assembly of the wind turbines blades only. Heavy yaw mechanisms are needed to turn the blades into the free stream and pitching mechanisms are needed to pitch the blades appropriately for each wind speed. Another challenge is that the turbine blades must be dynamically balanced to avoid the centrifugal forces from uniting with other forces leading to the destruction of these large structures. All the previous challenges require complex technologies in the design manufacture, transport, assembly, operation and maintenance phases of the wind turbine.

As for water desalination, current methods are not directly linked with electric generation from wind. Thus, compensating water by dehumidifying flowing air to improve power generation efficiency instead of being power consumer and producing fresh water as a byproduct is a good gain. Solution to Problem

The points that discernment present invention are as follows: The first and most important point is not to assume that all the available energy associated with the mass of the flowing air passing across the energy conversion system will be obtained when the outflow speed is zero. This idea deals with the flowing air passing instantaneously through the energy conversion system as if it is a solid mass and ignores the truth that the air stream is flowing within a front. In other words we can extract energy not only from the area infront of the energy conversion system, but from the entire air front as a continuous medium train. Stopping the train infront does not mean that continuous medium train stops.

If the air flow is forced to exit from the turbine in the opposite direction from its entrance, the turbine will exchange a force with the air mass flow rate twice. In the first time it is due to exchange between the air mass and the blades (this is the implementation in the current designs) and the second time there is an exchange due to the flow leaving in the opposite direction (it is the force that can generate extra power that will be used in this invention to increase the available power). The continuous medium train of flowing air will be used to force the air flow inside the turbine to move in this path.

To ensure that the exit air flows goes in the opposite direction, several safeguards must be put in place. These safeguards add some merits to the performance. The first safeguard is to prevent the outflow from confronting the inflow and separate their paths by using large barriers. This implies that there is a physical funnel like apparatus to isolate the two flow paths. This apparatus brings in two advantages. First, the turbine portion exposed to incoming flow is only a part of the area receives the air flow in the funnel entrance which leads to decreasing the turbine size. Second the incoming airflow will accelerate as it goes through the funnel since the area decreases. This implies that even if the turbine has a smaller area than the area of the funnel entrance, it still can convert all the energy that falls upon the funnel.

Practically the funnel does not considerably increase the air velocity in current designs (there are losses inside the funnel). Current turbines - with blades designed to stop the air in order to extract the energy- act as dams, while in this invention the goal is to divert the flow direction instead of stopping it. The relative velocity between the turbine blades movement and the free stream which moves in the same direction can be seen as a factor that assists the flow instead of opposing it. This is of course taking into account the negative impact on the extracted power that must be carefully considered in the design.

From what has been discussed it is apparent that the area of the turbine is only a small portion of the front area of the wind incoming into the plant. To utilize all the turbine blades, the air is forced into a spiral path around the turbine as will be explained shortly. This leads to turning the flow entrance of the turbine around the turbine axis that will be perpendicular to the free stream. The diameter of the turbine will be much smaller than the turbine used currently. Since the second moment of inertia, which is related to dynamic forces, is proportional to the square of the radius, there is a reduction of these forces and it is simpler to deal with the dynamic problems.

To enhance the airflow inside the funnel with the turbine working to suck the flow - with proper design for not to affect the extracted power too much - there must be means to create an artificial assisting pressure gradient. One of the means is to cool the air passing through the funnel, especially along the blades that can be used as a heat exchanger since it has a large area. The cooling changes the pressure in two means; first by reducing the volume of air by the effect of cooling, and second by condensing the water vapor in the air which reduces the vapor pressure. The energy needed for cooling can be obtained from another renewable source such as solar energy, the technology which is already in use. The condensed water is fresh water which is obtained as a byproduct from the generation of energy. The humidity in the air can be increased by spraying more of the water to be desalinated in the air flow path. This procedure results in decreasing the temperature of the airflow due to the evaporation of the water into the air. The relative humidity of the incoming air must be taken into account.

The wind in Egypt mostly blows from the North directions (North West, North East and so on) with exception of severe sand storms when the air blows from the South. The most appropriate location to extract wind energy from is the Gulf of Suez, since this area creates a natural draft through the valley created by the mountains which fixes the wind direction and speed. Figure 1 shows the entrance of the funnel shaped turbine plant pointing in the northern direction to capture the winds from the different northerly sources (this is only valid in Egypt, in other countries the funnel turbine is turned in the appropriate direction, hence the setting of the funnel turbine to the north is not considered as a claim). The funnel is built from (1) a roof, (2) a western wall, (3) an eastern wall, (4) an opening facing the North, (9) the arrow represents wind direction. This shown turbine (5) can capture wind coming from the North West (6), North (7) or the North East (8). The funnel also changes the flow direction inside the funnel as the air flows inside the different cross sections. As the turbine rotates it generates electric energy from the potential wind energy using the generator attached to the turbine. It is to be noted that although the turbine is used mostly to drive electric generator, it could be used for other purposes. As shown in figure 2, the funnel also increases the air velocity. For example at section (2) the cross section area of the funnel is smaller than the cross section area at section (1). Figure 3 shows how the funnel directs the air with the appropriate angle to the turbine. After the air enters through the opening (1) the funnel surfaces (2) directs the air (3) inside the plant to the opposing turbine (6). To use all the turbine blades (7) the spiral path (4) rotates the air inside the turbine such that the air is introduced to the blades through control vanes (5).

Thus, the funnel surfaces, the spiral path, and the control vanes change the path of the air inside the plant so as to make the turbine air inflow entrance area wrapped around the axis of rotation and result in a smaller turbine dimensions compared to the capture area. The rotating elements become closer to axis of rotation and thus have less second moment of inertia compared to the large turbines used now. This results for example in lowering the dynamic forces on the blades and bearing, less accelerating and decelerating torques and less unbalance problems.

The control vanes (5) can also be used to stop the flow entering the turbine blades during maintenance, or if the wind speed is beyond the safe operation of the turbine or any other purpose. Since both the funnel and the spiral path divert the flow path to the central part of the turbine as shown in figures 1 and 2, the exit of the air is from the sides of the turbine as shown in figure 4. In figure 4 the surfaces of the funnel and the spiral path (1) as a barrier between the air inflow and outflow. The air exit from the bucket type blades (2) follows the design path (3) such that the exit air does not hit the successive blade producing negative torque. Since the opening of the funnel is much larger and wider than the turbine, it also works as a wind barrier that protects the turbine exit air from being confronted by the northerly blowing winds. The funnel also does the following:

1- Collecting amount of wind from an area larger than the turbine entrance area

2- Increasing the wind velocity inside the plant

3- Directing the wind in the appropriate direction

4- Creating a barrier between the inflowing and exiting air

5- Protecting the turbine exit air from confronting the wind and providing proper exit conditions

6- The funnel surfaces may be (but not necessarily) used as a heat exchanger as will be explained shortly It is important to avoid the exiting air from hitting the back of the blades producing a negative torque on the turbine and loss of power as shown in figure 4. To avoid this, the bucket shaped blades may be formed from tangent plates as shown in figure 5 which shows the turbine alone. Figure 5 shows a front views (1) and a cross sectional view (2) of the turbine. The bucket shaped blades are formed by side disks (3), (4) and (5) and plates (6) which are tangents to a cylinder centered at turbine center of rotation. The air enters in the tangential direction of the turbine through the central zone (7) and exits also tangential from turbine side zones (8) and (9). Since the air enters and exits tangential to a fictitious cylinder in the turbine, there is no chance for the exit air to hit backs of successive blades and cause opposing torque. The symmetry of the turbine about its middle cross plane splits the air in such a manner that the axial forces on the shaft are minimized as much as possible.

To improve the axial movement of air inside the turbine from the central entrance to the side exits, the turbine blades can be shortened as shown in figure 6. Numbering scheme in figure 6 is same as in figure 5. Shortened blades provide more free space for the air to flow axially inside the turbine. In addition to gaining larger cross section for air axial flow inside the turbine, the flow path bends are reduced and hence pressure losses are also reduced and efficiency is increased. In other words the air will not diverted 180 degrees relative to single bucket forced to flow in it from entrance to exit. The air will enter between two successive plates, flow axially inside the turbine with minimum path bends and exit between two different successive plates that exist during its exit at opposite position to air entrance. This will not affect the energy generation from the reverse flow. There will always be flow leaving in the opposite direction; the only difference here is that it will leave from two different blades other than the ones it entered from.

Since the turbine rotates in the direction of the flow, it does not stop the air, but it assists the flow till exiting in the opposite direction. This motion helps in reducing the pressure gradient inside the funnel which increases the efficiency to increase the air velocity by reducing the area. To increase the efficiency, and to reduce the negative impact on the generated power due to the reduction of the relative speed between the flow entering the turbine and its blades, the air can be cooled using the large surface areas mainly inside the turbine and secondly in the funnel (cooling in the funnel is not essential). Cooling works to improve pressure gradient by two mechanisms; first by air contraction and second by water condensation and hence subtracting vapor partial pressure from air total pressure. To utilize pressure gradient inside the turbine in guiding air flow path, the cooling rate must increase from turbine central entrance till being maximum at turbine exit sides (3) and (4) as shown in figure (5) and (6). The condensed water is fresh water and is produced as a byproduct from the electric generation by wind turbine.

To increase the amount of condensed water, it is possible to more humidifying the by atomizing saline water at the funnel entrance. Water evaporation will be promoted by pressure gradient due to the increase of the air speed through the funnel. The value of the fresh water would compensate for some of the energy loss if any. Evaporating water in this means also reduces the temperature of the air flowing through the funnel. It is relevant to note that the extra cooling inside the turbine (or through the funnel if needed) can be done using solar energy which is currently available.

As an example and clarification, figure 7 shows the different process involved. The hard water is sprayed and atomized inside the funnel (1). The water is evaporated and the solids such as the salt and impurities are segregated and collected later on. The condensed water (3) is collected in specific locations controlled by controlling the air pressure, temperature and relative humidity. In the cases of high relative humidity in the air, the water spraying will not be useful. Control of water condensation locations may differ from the cases that involve water spraying.

Another method to guide and promote air flow is by using jets inside the rotor. The jets guide the flow by their media momentum that helps the air flow to follow the desired path. The venturi effect generated in the jet path before mixing with the main flow helps also in guiding and promoting the air flow.

The injected media in the jets can also work by cooling mechanism to combine the two methods; jets and cooling, in order to guide the air flow inside the rotor. For example, if liquefied nitrogen can be produced economically in the plants, it will be one of the media suitable for being injected in the jets to work by both mechanisms. Figure 8 shows a cross- section in a rotor turbine (2) with shaft (2) designed to convey the jet media and the flow direction separator (3) where the turbine and the flow streams are symmetric. The flow enters in direction tangential to blades as described before, streams entrance are denoted as (4), jet (5) diverts the flow to axial direction then jet (6) diverts the flow to exit direction where streams exit are denoted as (7). Brief Description of Drawings

Figure 1 : Main components of the plant, including the turbine, the funnel with the different surfaces and the wind blowing direction. The opening of the funnel faces the northern side that represents most of the wind blowing in Egypt. The assembly orientation is not related to the north but to the direction with most wind blowing direction.

Figure 2: The funnel converging cross section as the air flows inside it

Figure 3: The path line of the air from the entrance of the plant to the buckets through the funnel, the spiral ducting and control vanes.

Figure 4: Flow exits from the ends in such a manner that avoids hitting the exiting air to the buckets backs and hence prevents negative torques.

Figure 5: The entry and exit of the air tangential to the turbine ensuring that the exit paths do not intersect

Figure 6: The entry and exit of the air tangential to the turbine ensuring that the exit paths do not intersect and increase of axial flow path area inside the turbine and reduce its bends to minimize the loses

Figure 7: Water condensation from the humid air and increase of the water condensation by water spraying in the entrance of the plant.

Figure 8: Jets inside the rotor turbine guides the air flow streams inside the rotor.

Industrial Applicability

1- Building a pilot plant in a location rich in wind energy potential such as the Gulf of Suez to test all the aspects of the design to reach to the optimum design

2- After reaching the optimum design, financial resources are allocated to build large plants to economically starting from the coastline and to locations close to reclaimed lands that can be cultivated.

3- After using the coastlines different locations can be used to recycle contaminated water or just build electricity generating wind farms.

The benefits and use can be summarized as follows:

1- Building wind farms to generate electricity with higher efficiency and power output than those currently available.

2- Building wind farms using the available wind energy using less technological difficulties, using smaller dimensions for the turbines than those currently used and using lower tower heights.

3- Building wind farms using the available wind energy using less technological difficulties using the funnel to direct the wind to the turbine that rotates only to generate electricity and not to turn the turbine to face the wind.

4- Building wind farms that generate electricity with less dynamic loading problems than the currently available ones.

5- Building wind farms using the available wind energy potential that can have an increased efficiency by using another source of renewable energy such as solar energy.

6- Building wind farms and producing fresh water as a byproduct for irrigation, industry and building activities and finding new communities.

7- Building wind farms on larger areas using low wind speeds that could not be used to build conventional wind farms.

8- Providing technology that could be used to connect with future power plants using several sources of renewable energy in the same power plant with the increase of experience and knowledge in design of current plants.