RU2798113C1 - Air and water cooling method - Google Patents

Abstract

FIELD: heat engineering.

SUBSTANCE: used for cooling air and water for recycling water supply. In the method of cooling air and water by indirectly cooling the outside air in an air-to-air surface heat exchanger, and then directly cooling the air and water under adiabatic conditions in a cooling tower, the outside air is first dried under isothermal conditions, passing through a layer of granular adsorbent in the tube space of a shell-and-tube heat exchanger-adsorber, in the annular space of which tap water circulates to provide isothermal conditions for air drying.

EFFECT: organization of a three-stage processing of outdoor air for a stable decrease in air and water temperature by cooling water to a temperature below the dew point temperature of the outdoor air.

1 cl, 4 dwg

Description

The invention relates to the technology of recycling water supply.

The purpose of the invention is to intensify the method of cooling water with direct evaporative cooling of water in a stream of dried cooled outside air.

Known contact device for cooling water in the circulating water supply system of energy-consuming equipment (condensers of refrigerators, injection molding machines, etc.), in particular, fan cooling tower [1, p. 286].

Structurally, the cooling tower is a column unit of rectangular or round section with a packing. Ceramic rings (Raschig rings), saddles, nets, gravel, etc. can be used as packing.

The nozzle is located in the form of a continuous layer on the support grid. It serves to create an interfacial surface between liquid (water) and air. Water is supplied by a pump to the top of the nozzle and sprayed over its cross section with the help of a nozzle. Air is supplied from below the support grid by means of a fan. With the countercurrent movement of the water and air phases, a direct evaporative process of cooling air and water occurs.

The air, giving off heat to the water, lowers its temperature, the water uses the heat received for partial evaporation, and its vapor humidifies the air. Air and water temperatures drop to about wet bulb temperature. Humidified air from the upper part of the cooling tower is discharged into the atmosphere, and water with a reduced temperature from the lower part of the cooling tower is collected in a tank and used as a cooling medium, for example, it is supplied to the condenser of a refrigeration compressor machine (or other consumer) by means of a pump to condense the refrigerant vapor . The heated water from the consumer is again directed to the cooling tower for spraying, where it is cooled in the air flow and reused in a closed cycle: cooling tower - consumer - cooling tower, i.e. in recycling water supply. This allows to reduce the consumption of water consumed by the organization (enterprise) for cooling energy-consuming equipment. The consumption of fresh water from the water supply here is associated with the replacement of a small part (~ up to 3%) of the evaporated water in the air flow emitted from the cooling tower to the atmosphere.

The disadvantage of this design is the relatively low cooling capacity of the cooling tower. Thus, the temperature of the chilled water leaving the cooling tower is almost always several degrees higher than the wet bulb temperature. In modern compact fan cooling towers, the lowest achievable chilled water temperature - t _w exceeds the outdoor air wet bulb temperature t _pl by 3°С, i.е.

Also known is a device in which increasing the cooling capacity of the cooling tower and lowering the water temperature below the wet bulb temperature of the air is achieved by using the principle of two-stage air cooling [2].

The scheme of the device is shown in Fig. 1, the processes of two-stage air cooling on the I-d-diagram of moist air - in FIG. 2.

The positions in FIG. 1 stand for:

1 - cooling tower body; 2 - nozzle; 3 - spraying device (mechanical nozzle); 4 - drop catcher; 5 - air-to-air surface heat exchanger; 6 - water tank; 7 - pump; 8 - fan; a, b - gate valves; c, d - valves.

The lines (rays) in Fig. 2 designate: NK - indirect air cooling (cooling in a surface heat exchanger) - I stage of cooling; KO - direct air cooling with water under adiabatic conditions (direct evaporative cooling mode) - II stage of cooling.

The water cooling device comprises a cooling tower body 1 of rectangular or circular cross section, inside which a nozzle 2 is located in the form of a vertical layer. A sprinkler device is installed on top of the nozzle - a mechanical nozzle 3 for spraying water. Above the nozzle in the upper part of the body there is a drop catcher 4, which prevents the removal of water drops. An air-to-air surface heat exchanger 5 is installed on top behind the droplet eliminator.

At the bottom of this device is a water tank 6, a pump 7 for water supply and a fan 8 for air supply. The fan is connected by means of air ducts to the heat exchanger 5 and to the lower part of the cooling tower casing 1.

The device works as follows.

The outside air, due to the vacuum created by the fan 8, passes through the air-to-air surface heat exchanger 5, then it is directed to the cooling tower under the packing layer 2.

Passing the nozzle, the air is subjected to direct evaporative cooling and humidification due to contact with a film of water flowing down the nozzle. After the nozzle, humidified air passes through the drop eliminator 4, the air-to-air surface heat exchanger 5 and is released into the atmosphere.

Due to the temperature difference, the air leaving the cooling tower (flow Y) receives heat from the outside air (flow H) and heats up, while the outside air cools down (the process corresponds to the NK beam in Fig. 2).

The surface heat exchanger 5 operates on the principle of a recuperative air-to-air heat exchanger. Structurally, it can be made in the form of a plate heat exchanger.

Thus, air pre-cooled in the surface heat exchanger 5 passes through the packing layer 2. This air medium forms a direct evaporative cooling mode upon contact with a film of water flowing down the packing. As mentioned above, as the temperature of the air flow decreases, the temperature of the water decreases accordingly. If the water circulation is carried out in a closed circuit (recirculating water is used): tank 6 - pump 7 - nozzle 3 - nozzle 2 - tank 6, the air cooling process in the nozzle will be adiabatic and correspond to the KO beam (Fig. 2). The water temperature will correspond to t _MK (Fig. 2). In this case, the air temperature as a result of adiabatic cooling will drop to ~ t ₀ . At a given time (let's conditionally call this period stage II) the driving force of indirect cooling of the outside air in the air-to-air surface heat exchanger 5 Δt=(t _n -t ₀ ) increases, i.e. the cooling power of the air flow coming from the nozzle will increase. Outside air will be cooled in the heat exchanger 5 to a temperature even lower than t _to , i.e. t<t _to (Fig. 2), which, accordingly, will cause a further decrease in the temperature of the recirculating water in the system.

Thus, when organizing a two-stage cooling of outside air in a known device (indirect and direct cooling), conditions are created for a steady decrease in water temperature to values below the temperature of the wet air bulb.

The present invention proposes a technical solution on the basis of the described devices - a method for cooling air and water, which makes it possible to lower the water temperature with air below the dew point temperature of the outside air. Three-stage air treatment is offered: isothermal dehumidification, indirect cooling, direct cooling. The implementation of the method for cooling water with air below the dew point temperature is schematically shown in Fig. 3. For comparative analysis, FIG. 3 saved base points (H, K, O), characterizing the state of the air in two-stage air treatment in accordance with FIG. 2.

The points in Fig. 3 stand for:

t. H - the state of the outside air;

m. K - the state of the air after indirect cooling;

v. O - the state of the air after direct evaporative cooling of the air;

v. O ^I - the limiting (theoretical) state of the outside air during adiabatic cooling (humidification);

t. H* - the state of the outside air after dehumidification;

m. K* - the state of the dried air after indirect cooling;

t. O* - the state of dried air after direct evaporative cooling.

The lines (rays) in Fig. 3 stand for:

НН* - isothermal dehumidification of air - I stage;

Н*К* - indirect air cooling (cooling in an air-to-air surface heat exchanger) - II stage of cooling;

К*О* - direct air cooling with water under adiabatic conditions (direct evaporative cooling mode) - III stage of cooling;

(NK - indirect air cooling; KO - direct air cooling under adiabatic conditions with two-stage air cooling).

Isothermal dehumidification is proposed to be carried out using a shell-and-tube heat exchanger-adsorber with granular silica gel, a description of its design and operation is given in [3], the subsequent processes - indirect cooling of air and its direct cooling with water under adiabatic conditions, should be carried out according to the scheme of two-stage cooling of dried outside air using the known devices (Fig. 1). From the construction of the three-stage air treatment processes shown in FIG. 3 it can be seen that the numerical value of the water temperature t _w with direct air cooling under adiabatic conditions is less than the dew point temperature of the outside air t _r :

The implementation of the technical solution - the method of cooling air and water below the dew point temperature is shown in Fig. 4.

The positions in FIG. 4 stand for:

1 - housing (cooling tower); 2 - nozzle; 3 - spraying device (nozzle); 4 - drop catcher; 5 - air-to-air surface heat exchanger; 6 - water tank; 7 - pump; 8, 9 - fans; a, b, c, d, e, f, g, h, - gate valves; 10a, 10b - shell-and-tube heat exchanger-adsorber.

The device works as follows.

Outside air with the help of operating fans 8, 9 passes through the shell-and-tube heat exchanger-adsorber 10a or 10b, where it is dried from the state H to the state H*, it also passes through the air-to-air surface heat exchanger 5, for indirect cooling from the state H* to the state K* , then goes to the cooling tower 1 under the packing layer 2.

Passing the nozzle, the air is subjected to direct evaporative cooling and humidification due to contact with a film of water flowing down the nozzle. After the nozzle, humidified air passes through the drop eliminator 4, the air-to-air surface heat exchanger 5 and is released into the atmosphere.

Due to the temperature difference, the air leaving the cooling tower (flow U) receives heat from the dried outside air (flow H*) and heats up, while the outside dried air cools (the process corresponds to the H*K* beam (Fig. 2).

The surface heat exchanger 5 operates on the principle of a recuperative air-to-air heat exchanger, as mentioned above; structurally, it can be made in the form of a plate heat exchanger.

Thus, dried air passes through the packing layer 2, pre-cooled in the air-to-air surface heat exchanger 5. This air medium, as mentioned earlier, forms a direct evaporative cooling mode upon contact with a water film flowing down the packing. As the temperature of the air flow decreases, the temperature of the water decreases accordingly. If the water circulation is carried out in a closed circuit (recirculating water is used): tank 6 - pump 7 - nozzle 3 - nozzle 2 - tank 6, the air cooling process in the nozzle will be adiabatic and correspond to the K * O * beam (Fig. 3). The water temperature will correspond to t _micro *. In this case, the air temperature as a result of adiabatic cooling will drop to ~ t ₀ *. At a given time (let's call this period stage III), the driving force of indirect cooling of the outside air in the air-to-air surface heat exchanger 5 Δt=(t _n *-t ₀ *) increases, i.e. the cooling power of the air flow coming from the nozzle will increase. Outside air will be cooled in the heat exchanger 5 to a temperature even lower than t _to *, i.e. t<t _to * (Fig. 3), which, accordingly, will cause a further decrease in the temperature of the recirculating water in the system.

Let us consider in more detail the stage (system) of air dehumidification using heat exchangers-adsorbers 10a, 10b (Fig. 4). Structurally, they are made in the form of shell-and-tube heat exchangers-adsorbers [4]. Their pipe space is filled with KSM granular silica gel and is intended for the passage of outside air. The annulus serves for the circulation of tap water in order to extract the heat released as a result of capillary condensation of water vapor by silica gel during air drying and to stabilize the isothermal adsorption mode [1, 3]. There are two shell-and-tube heat exchangers-adsorbers with alternating operating modes: one is in the mode of adsorption of water vapor from the air, the other in a given period of time - in the mode of desorption of water vapor from the adsorbent. Desorption of water vapor from the adsorbent is carried out by passing part of the dried air through a layer of granular silica gel in the opposite direction than in the adsorption mode (the principle of displacement desorption is used). Synchronously, these processes are carried out as follows. Outside air H (Fig. 4) in the amount of G _n fan 9 is fed into the dehumidification system. At the same time, gate valves c, d, e, e are open, gate valves g, h are closed. Passing the pipe space through a layer of granular adsorbent in the shell-and-tube heat exchanger-adsorber 10a, the outside air is isothermally dried, 0.5 _Gn enters the air-to-air surface heat exchanger 5 for indirect cooling by the flow of exhaust air from the cooling tower, the other part of the external dried air flow 0.5 G _n enters the heat exchanger-adsorber 10b for desorption of water vapor from the pore space of the granular adsorbent with subsequent release into the atmosphere. After the adsorbent is saturated with water vapor in the heat exchanger-adsorber 10a, the sliding gate valves are switched as follows: valves c, e - close, valves g, e, d, h - open. At the same time, the air flow of outside air, passing through the shell-and-tube heat exchanger-adsorber 10b, is dried, 0.5 G _n enters the air-to-air heat exchanger 5, another 0.5 G _n enters the shell-and-tube heat exchanger-adsorber 10a for desorption of water vapor from the pore space of the granular adsorbent with subsequent release into the atmosphere, etc.

Thus, when organizing a three-stage processing of outdoor air in the developed device (drying, indirect and direct cooling), conditions are created for a steady decrease in air and water temperature, the water is cooled to a temperature below the dew point temperature of the outdoor air.

Information sources

1. Bogoslovsky B.N., O.Ya. Kokorin O.Ya., Petrov L.V. Air conditioning and refrigeration. - M.: Stroyizdat, 1985. - 368 p.

2. Water cooling device. Pat. No. 2274813 Ros. Federation: IPC F28C 1/00 / Averkin A.G., Eremkin A.I., Mironov K.V., Rodionov O.V.; applicant and patent holder Penzen. state un-t architect. and builds. - No. 2004115007; dec. 05/17/04; publ. 20.04.06, Bull. No. 11.

3. Averkin, A.G. I-d-diagram of humid air and its application in the design of technical devices. - St. Petersburg: Lan, 2022. - 192 p.

4. The method of utilization of the heat of the gas (air) flow. Pat. 2300056 Ros. Federation: IPC F24F 3/14 / Averkin A.G.; applicant and patent holder Penzen. state un-t architect. and builds. - No. 2005104727; dec. 02/21/05; publ. May 10, 2007, Bull. No. 15.

Claims (1)

A method for cooling air and water by indirectly cooling the outside air in an air-to-air surface heat exchanger, then directly cooling the air and water under adiabatic conditions in a cooling tower, characterized in that, first, the outside air is dried under isothermal conditions, passing through a layer of granular adsorbent in the tube space of a shell-and-tube heat exchanger-adsorber, in the annular space of which tap water circulates to provide isothermal conditions for air drying.

Images