Mist cooling tower

Abstract

The present invention relates to a device called as Mist Cooling Tower. The device reduces the temperature of the inlet hot water effectively ensuring an approach of 2 to 3°C to design WBT with a temperature drop up to 10°C with an increased efficiency of around 80% by integration of two technologies that is mist creation and induced draft air flow. The device does not use the fills / fins.

Description

[0001] TITLE OF INVENTION: MIST COOLING TOWER

[0002] FIELD OF INVENTION:

[0003] The present invention relates to a device called as Mist Cooling Tower. The device reduces the temperature of hot water effectively by integration of two technologies that is mist cooling and induced draft air flow. It does not use the fills / fins as used in conventional Induced Draft Cooling Towers. The present application is based on, and claims priority from an Indian Application Number 202321058445 filed on 31stAugust, 2023, the disclosure of which is hereby incorporated by reference herein.

[0004] BACKGROUND OF THE INVENTION:

[0005] Water Cooling has played an important role in all types of Process Industries & Power Plants. The vapors generated in the process are condensed in a heat exchanger and retrieved back in the liquid state. The condensation of steam or vapor requires a cooling medium.

[0006] In early days this was achieved by using water from a river, a pond or sea water. The cold water was pumped through a heat exchanger and the warm water was discharged back to the water source. This is called “once through” cooling system. A once through system is an open loop system. However, this cooling system required huge amount of water which was not readily available at all times. In order to provide cooling system which requires less water, closed loop system was introduced. Thus, the wet cooling system which is a closed loop system came into effect where hot water generated in the process will be cooled in a cooling tower.

[0007] In a wet cooling system, water is circulated within the system to condense the steam in the same type of heat exchanger that is used in the once through cooling system. The warm water instead of being returned to the water source, is cooled in a device called as a cooling tower which uses air as the cooling medium. Only the water carried away due to evaporation, drift and blow-down needs to be replenished by make-up water. Thus, the quantity of water required for this process is less.

[0008] There are several types of cooling towers available in the industry such as natural draft, jet cooling towers and induced draft cooling towers.

[0009] In natural or jet cooling tower as shown in Fig. 7, the hot water is sprayed from the hot water inlet (22) at top with high pressure and cooling is achieved by natural draft phenomenon where the air is sucked-in from the top (23) and humid air goes out from bottom louvers (24). Due to ineffective design of water jet-nozzles (25) and the unavailability of sufficient amount of air as fans are not used, these towers work with very low efficiency of around 50% with an approach to wet bulb temperature (WBT) of 6°C. Efficiency of a cooling tower is determined by how much lower the cooling water temperature can be achieved by a cooling tower with respect to wet bulb temperature of air represented by approach to wet bulb temperature. Approach to wet bulb temperature (WBT) means difference between cooled cold-water temperature and wet bulb temperature of air.

[0010] The second type of cooling tower which is normally used in the industry is an induced draft cooling tower (IDCT) as shown in Fig. 8 in which a fan (28) is used at the top which sucks air through bottom louvers (29). At the same time, nozzles (32) spray water on the fills / trays (30) for giving required surface area for air water contact. These fills, depending on their types, are arranged in layers called film fills or water splashes as it hits vertical bars called V bar fills to get the required cooling efficiency up to 70% at which these induced cooling towers run.

[0011] A conventional induced draft cooling tower ensures an approach of 4°C to wet bulb temperature with a temperature drop of 8°C. Temperature drop (AT) is the difference between sprayed hot water and cooled cold water temperature in a cooling tower. Typically, in an industry, the quality of water which is used for the cooling water circuit is not very good due to dusty environment and mainly high total dissolved solids (TDS) level in water. These salts / dust / dirt start depositing on the fill surfaces as the cooling tower is operated which get choked or clogged frequently. Due to this, cooling tower efficiency starts dropping. Hence, these fills need to be cleaned periodically and also replaced within 1 or 2 years of operation. However, plant operation needs to shut down in order to facilitate such replacement and this causes direct loss in production.

[0012] EP0081664A1 discloses a device called Induced Draft Cooling Tower which cools water by providing a counterflow of downward water spray and upward air flow where in a block of cellular packing which is called as Fills is placed at the center of Induced draft cooling tower to make contact between water and air for it to cool down.

[0013] The device includes a structural body made of steel or plastic material having generally a cylindrical upward and lower portion. The lower portion has bottom louvers for air entry. An axial fan is placed at the top below which there are drift eliminators and then there is water distribution piping with nozzles for spraying the water downwards. This sprayed water falls on Fills placed at the center of Induced Draft Cooling Tower which are arranged in layers to give sufficient time for air and water contact for water to cool down. These Fills are generally block of cellular packing or vertical V-Bars which have a common purpose of increasing the surface area and contact time between water and air either by distribution in layers or breaking the water particles to smaller diameter for better evaporation. These Fills often get choked or clogged thereby requiring continuous maintenance of the towers. However, maintenance / replacement requires shutdown which is direct loss in production.

[0014] Indian Patent No. 330946 is a device called Jet water cooling tower with zero drift which is a type of natural draft cooling tower which uses jet / spray nozzles placed at the top of the cooling tower which spray water downwards under pressure which creates a downward draft of air by natural draft phenomenon and humid air goes out from the bottom louvers. This device consists of a structural body generally in rectangular shape made of steel / plastic material. Jet or spray nozzles are placed at the top which is open to atmosphere. The said spray consists of horizontal pipes interconnected to each other having spray nozzles facing downwards. The bottom portion consists of air openings which are called as louvers. Drift eliminators are placed at bottom air openings for arresting the spray particles from going outside the tower. These towers operate with very low efficiency due to insufficient availability of air flow (due to limitation of natural draft) and insufficient or no mist formation of sprayed water. Also, the nozzles are made in plastic material of low quality to make tower cost effective. It is often observed that these nozzles tend to fall down as they cannot handle higher return water pressure and hence need often replacement.

[0015] There is therefore a need for a mist cooling tower having no fills or trays, using minimum fan power.

[0016] There is also a need for a mist cooling tower wherein the spray mist will be effectively operated in upward or downward direction placing it at such adequate position inside the tower as per availability of return line water pressure from the plant.

[0017] OBJECT OF THE INVENTION:

[0018] It is an object of the present invention to provide a device for efficient mist formation for cooling the water more effectively.

[0019] It is an object of the present invention to provide a device that operates at a low pressure of around 0.3 to 0.4 kg / cm2 (g). It is another object of the present invention to provide a device with very low pressure drop across its cross-section in order to operate with lowest energy consumption, so that it will save 50% of fan power in comparison to conventional design.

[0020] It is yet another object of the present invention to provide a device to cool hot water with an approach of 2 to 3 °C to design Wet Bulb Temperature with temperature drop of 8 to 10°C.

[0021] It is yet another object of the present invention to provide a device which does not use fills or trays and thus is totally maintenance free.

[0022] It is yet another object of the present invention to provide a device where mist could be effectively formed either in upward or downward direction by placing the nozzles at such adequate position inside the tower as per availability of return line water pressure from the plant.

[0023] SUMMARY OF THE INVENTION:

[0024] A mist cooling tower having a body (1), comprising combination of an axial exhaust fan assembly (6) at the top, drift eliminators (10) below the axial exhaust fan assembly (6), water inlet (17) providing having inlet water pressure of at least 0.3 kg / cm2, said water inlet connected to a water distribution header (2) having a grid of branch piping (3) with nozzles (4) having outlet of 8 to 16 mm diameter, water collection tank (12) at the bottom of the body (1) and air intake louvers (11) above the water collection tank (12).

[0025] Typically, a mist cooling tower wherein the axial exhaust fan assembly (6) comprises of an axial flow fan (6A), a fan guard (7), a fan deck panel (8) and a fan stack (5). Typically, a mist cooling tower wherein water distribution header (2), branch piping (3) and nozzles (4) are located above the air intake louvers (11) at a distance of about 300 to 500 mm from the top of the air intake louvers (11) and the nozzles (4) point upwards.

[0026] Typically, a mist cooling tower wherein water distribution header (2), branch piping (3) and nozzles (4) are located below the drift eliminators (10-10) at a distance of about 300 to 500mm and the nozzles (4) point downwards.

[0027] Typically, a mist cooling tower wherein spray height is 3 to 9 meters.

[0028] BRIEF DESCRIPTION OF DRAWINGS:

[0029] Fig. 1 shows the top view of the Mist Cooling Tower (the device)

[0030] Fig. 2 shows the General Arrangement (GA) Drawing of the device for co-current (upward) spray pattern

[0031] Fig. 3 shows the cross-sectional front view of the device for co-current (upward) spray pattern

[0032] Fig. 4 shows the General Arrangement (GA) Drawing of the device for countercurrent (downward) spray pattern.

[0033] Fig. 5 shows the cross-sectional front view of the device for counter-current (downward) spray pattern

[0034] Fig. 6 shows pictorial inside view of Mist Cooling Tower

[0035] Fig. 7 shows Jet Type Cooling Tower.

[0036] Fig. 8 shows Induced Draft Cooling Tower (IDCT).

[0037] The following are the details of the main components of the device called as Mist Cooling tower which is used for cooling of hot water effectively by combination of technology of Mist & Induced draft air flow but without using any FILLS / FINS with the present invention which are used with reference to Figs. 1, 2, 3, 4, 5 and 6. 1 = Structure / Body

[0038] 2 = Water Distribution header

[0039] 3 = Branch piping

[0040] 4 = Nozzles

[0041] 5 = Fan stack

[0042] 6 = Axial Exhaust Fan Assembly

[0043] 6A = Axial Flow fan

[0044] 7 = Fan guard

[0045] 8 = Fan deck panel

[0046] 9 = Drive Motor and shaft

[0047] 10 = Drift Eliminators

[0048] 11 = Air Intake Louvers

[0049] 12 = Water Collection Tank

[0050] 13 = Gear Box

[0051] 14 = Plenum area

[0052] 15 = Ladder

[0053] 16 = boundary protection Railing

[0054] 17 = Main header from process or heat exchanger

[0055] 18 = Isolation Valve

[0056] 19 = Riser Pipe

[0057] 20 = Circulation water pump-set

[0058] 21 = Fine Mist

[0059] The following are the details of jet type cooling tower with reference to Fig 7.

[0060] 22 = Hot Water Inlet

[0061] 23 = Fresh air Induced (Sucked) from top of tower

[0062] 24 = Bottom louvers

[0063] 25 = Water Jet Nozzles

[0064] 26 = Distribution Header

[0065] 27 = Circulation water pump-set The following are the details of Induced Draft Cooling Tower (IDCT) with reference to Fig 8.

[0066] 28 = CT Fan

[0067] 29 = Bottom Louvers

[0068] 30 = Fills

[0069] 31 = Hot Water Inlet

[0070] 32 = Nozzles

[0071] 33 = Circulation water pump-set

[0072] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

[0073] DETAILED DESCRIPTION OF THE INVENTION:

[0074] The invention will now be described with reference to the accompanying drawings wherein same reference numerals are used to denote the same parts. However, it is made clear that the description only illustrates the invention and in no way limits the same.

[0075] The terms and words used in the following description are not limited to the bibliographical meanings but are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined in the description.

[0076] In the accompanying drawing: Fig. 1 shows the top view of Mist Cooling Tower (the device). The device comprises of a body (1) made of pultruded fiber-reinforced plastic or Hot Dip Galvanized Iron material with Fiber-reinforced plastic casing as shown more clearly in Fig. 3 and Fig. 5.

[0077] Referring to figs. 2, 3, 4 and 5, an axial exhaust fan assembly (6) comprises of an axial flow fan (6A) located at the top of the cooling tower with drive motor (9) which is directly mounted or has a gear box (13), a fan guard (7), a fan deck panel (8) and a fan stack (5). The axial flow fan (6A) creates induced draft of air. The fan deck panel (8) is located below the axial flow fan (6A). A boundary protection railing (16) is also provided above the fan deck panel (8). Both the fan deck panel (8) and the boundary protection railing (16) are made of Fiber-reinforced plastic panels and used as a platform. The fan deck panel (8) has a cut out equal to the diameter of the fan stack (5). At center of the fan deck panel (8), the fan stack (5) is placed in such a fashion that it covers the fan totally with a blade clearance margin of 10 mm to 30 mm which varies as per diameter of the fan. The fan stack (5) is either cylindrical or parabolic in design as per requirement criticality and design. The Fan Guard (7) which is made of mild steel hot dip galvanized iron material of construction and is placed at top of the axial flow fan (6A) which is a physical barrier that protects and prevents any person or bird from injuries due to any accidental contact with running axial flow fan (6A).

[0078] Below the fan deck panel (8) drift eliminators (10) are placed at a distance equivalent to one third the diameter of the axial flow fan (6A). A cavity is formed below the fan deck panel (8) and the drift eliminators (10). This cavity is called as plenum area (14) which is kept for the purpose of proper distribution of air. Drift eliminators (10) are available in many types such as C Type (Single pass), S Type (double pass), W Type (four pass) and also in multiple profiles such as single wall, double wall, etc. The drift eliminators (10) are usually made of Rigid PVC with PVC or PP Multi spacers. Air intake louvers (11) made of fiber-reinforced plastic are present at the bottom side of the device (1). The air intake louvers (11) are located at an angle of 35 to 50 degrees, preferably at 45 degrees for sucking the air in.

[0079] Water Distribution header (2) and branch piping (3) is either located just above the air intake louvers (11) at the bottom side at a distance of about 300 to 500 mm from top of the air intake louvers (11) which is shown in Fig. 2 and 3 when operation is co-current i.e. water spraying upward or located just below the drift eliminators (10) at the top side at a distance of about 300 to 500 mm just below the drift eliminators (10) which is shown in Fig. 4 and 5 when operation is counter-current i.e. water spraying downward. Nozzles (4) are fitted to the distribution header (2) and branch piping (3). The nozzles (4) have special venturi type design which breaks the particle of water to average size of 50 microns which creates Fine Mist (21), thus exposing huge surface area for cooling. The minimum bore opening of the outlet of the nozzles (4) is in between 8 mm to 16 mm & inlet bore size of 25.4 mm to 50.8 mm (1 Inch to 2 Inch) in diameter. They are fitted in such a fashion that they have thread type connection for adjusting nozzle angle & avoiding pockets or gap into Mist Creation zone. Nozzles (4) have special whirling type choke less design which ensures a maintenance free operation for lifetime. Co-current or counter current spray pattern is selected in design as per availability of water pressure in the hot water return line.

[0080] Water collection tank (12) is made of reinforced cement concrete or fiber- reinforced plastic coated mild steel material is used as collection tray. Circulation water pump-sets (20) are connected to the water collection tank to circulate water to the process or heat exchanger (not in figures) and back.

[0081] For the maintenance purpose ladder (15) is provided at one side of tower wall from which person can reach fan deck at the top. WORKING OF THE INVENTION:

[0082] Hot water from process or heat exchanger (not in figures) enters main header (17) located at ground level near cooling tower and then to the Water Distribution header (2) via riser pipe (19). Isolation valve (18) is provided at the start of riser pipe (19). Hot water is further distributed via branch piping (3) and then to the nozzles (4). These nozzles (4) enable creation of fine mist (21) of hot water in upward direction i.e., in co-current direction to air flow which forms a mist zone with average water particle size of 50 microns which provides the required surface area for cooling having a spray height of 3 to 9 meters as shown in Fig. 2 and 3. Alternatively the nozzles (4) enable creation of fine mist (21) of hot water in downward direction i.e. in counter current direction to air flow having a spray height of 3 to 9 meters as shown in Fig. 4 and 5. Due to sudden release of pressure from the nozzles (4) and sub-division of water particles, a low-pressure zone gets created inside the cooling tower. Axial flow fan (6A) located on the fan deck (8) draws air through the air intake louvers (11). This combined air then comes in contact with the fine mist particles of hot water. Water gets exposed to maximum amount of air thus ensuring huge surface area to atmospheric air ensuring best possible evaporative cooling. When the air and water come in close contact, a small volume of water evaporates, creating an action of cooling. With both the flow patterns the fine mist created enables huge surface area of exposure thus cooling water more effectively than prior art.

[0083] The cooled water gets collected into water collection tank (12) and pumped to the process or heat exchanger (not in figures) and back. Also, the moist air escapes from top from the Fan stack (5).

[0084] Although the above description explains the working of the device for cooling hot water effectively, however, the scope of application or use of the device as per the present invention is not limited to clean water. The device as per the present invention is suitable for any quality of water used in any industry RESULTS OF TRIAL FOR MIST COOLING TOWER IN COMPARISON

[0085] TO CONVENTIONAL COOLING TOWERS

[0086] Average of 3 Days Trial at different time of the year:

[0087] It is seen from above table the device ensures approach of 2 to 3°C to design WBT (higher CT efficiency) as against higher approach to WBT from the Induced Draft Cooling tower or the Jet water cooling tower. Further, since the device does not have any Fills, the energy consumption is low due to low pressure drop across the device. In Jet Water Cooling Tower, although Fills are not used, due to inefficient spray and no fan used, it gives very high Cold Water Temperature resulting in higher approach to WBT which means lower efficiency of cooling towers & process capacity is reduced. Also, additional circulation pump has to be employed for more flow as Temperature difference (AT) is less, thus, consuming high pumping power. ADVANTAGES:

[0088] 1. The present invention allows cooling in the most ideal manner as the water can be sprayed either in upward or downward direction as per inlet water pressure availability for efficient cooling.

[0089] 2. The present invention produces and uses mist for better evaporative cooling.

[0090] 3. The present invention eliminates the use of any fills or trays as fine mist formation provides better surface area for air water contact required for cooling. Also, choke less design of nozzles ensure a maintenance free operation for lifetime.

[0091] 4. This present invention ensures an approach of 2 to 3°C to design WBT with a temperature drop up to 10°C with an increased efficiency of around 80%.

[0092] 5. The present invention saves up to 50% of fan power due to combination of two technologies a) mist creation providing better surface area for cooling which is higher than that provided by fills and b) induced draft fans operating with lower pressure drop.

[0093] This allows the Mist Cooling Tower to operate with minimum pressure drop across the system, as fills are not used which saves huge energy on cooling.

[0094] 6. The present invention ensures steady / constant designed performance up to end of its life time and its performance does not deteriorate with time as may happen in prior art conventional induced cooling towers having Fills as salts get deposited over Fills.

[0095] 7. The present invention has Rugged structure with Pultruded Fiber-reinforced plastic / Hot-Dip Galvanized Iron Material of construction and Fiber-reinforced plastic casing with special nozzles in SS 304 or Glass filled Polypropylene material of construction having choke-less design ensuring a life of 15 years plus. Many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appendant claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention

Claims

I Claim:

1. A mist cooling tower having a body (1) comprising combination of an axial exhaust fan assembly (6) at the top, drift eliminators (10) below the axial exhaust fan assembly (6), water inlet (17) having inlet water pressure of at least 0.3 kg / cm2, said water inlet connected to a water distribution header (2) having a grid of branch piping (3) with nozzles (4) having outlet of 8 to 16 mm diameter, water collection tank (12) at the bottom of the body (1) and air intake louvers (11) above the water collection tank (12).

2. The mist cooling tower as claimed in claim 1, wherein the axial exhaust fan assembly (6) comprises of an axial flow fan (6A), a fan guard (7), a fan deck panel (8) and a fan stack (5).

3. The mist cooling tower as claimed in claim 1 , wherein water distribution header (2), branch piping (3) and nozzles (4) are located above the air intake louvers (11) at a distance of about 300 to 500 mm from the top of the air intake louvers (11) and the nozzles (4) point upwards.

4. The mist cooling tower as claimed in claim 1, wherein water distribution header (2), branch piping (3) and nozzles (4) are located below the drift eliminators (10-10) at a distance of about 300 to 500 mm and the nozzles (4) point downwards.

5. The mist cooling tower as claimed in claim 1, wherein spray height is 3 to 9 meters.Dated 6thday of August, 2024

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