CN221071103U - Multiphase jet drying bed system for treating high-salinity wastewater - Google Patents

Abstract

The utility model relates to a multiphase jet flow drying bed system for treating high-salt wastewater, which comprises a drying bed, wherein a drying chamber is arranged in the drying bed, an air distributor is fixedly arranged in the drying chamber, a filler is arranged at the upper part of the air distributor, an air inlet of the drying bed, which is positioned at the lower part of the drying chamber, is connected with an air inlet pipe for introducing hot air which blows the filler into a fluidization state, and an air outlet of the drying bed, which is positioned at the upper part of the drying chamber, is connected with an air outlet pipe; the drying bed is provided with a heating device for heating the filling material; and a liquid-phase atomizing device is arranged in the drying chamber and is used for atomizing the high-salt wastewater and then spraying the atomized high-salt wastewater on the filler. Improves the treatment efficiency of the high-salt wastewater and avoids the blockage of the drying bed.

Description

Multiphase jet drying bed system for treating high-salinity wastewater

Technical Field

The utility model belongs to the technical field of high-salt wastewater treatment, and particularly relates to a multiphase jet drying bed system for treating high-salt wastewater.

Background

At present, industrial high-salt wastewater is generally subjected to wastewater decrement by adopting multiple-effect evaporation concentration, membrane treatment and other processes, concentrated water or filter-pressed filtrate generated after decrement is treated by a high-temperature flue gas bypass drying tower, concentrated liquid (filter liquor) is atomized by a nozzle and then sprayed into the drying tower, and meanwhile, high-temperature flue gas is led from an SCR outlet flue to enter the drying tower. In the drying tower, the high-temperature flue gas is fully mixed with atomized liquid drops, water in the wastewater is rapidly evaporated, salt in the wastewater is crystallized and combined with ash in the flue gas, and formed particles enter a dust remover along with the flue gas and are captured by the dust remover. The treatment effect of the high-temperature flue gas bypass drying tower is closely related to the spray gun atomization effect and the uniformity of a high-temperature flue gas flow field in the drying tower, and the existing high-temperature flue gas bypass drying tower system has the following problems:

1. the spray gun atomization effect is unstable, and the drying tower is easy to block.

2. The compressed air consumption is high.

3. The high-temperature flue gas flow field in the drying tower is unevenly distributed, and the drying tower is easy to be blocked.

4. The liquid flow at the outer side of the spray gun outlet is small, the internal measuring flow is large, and the high-temperature flue gas and the atomized liquid drops cannot be fully mixed and contacted.

Disclosure of utility model

The utility model aims to overcome the defects of the prior art, provides a multiphase jet drying bed system for treating high-salt wastewater, and solves the technical problems that a drying tower is easy to block and the like in the traditional high-salt wastewater treatment system.

In order to solve the problems, the technical scheme of the utility model is as follows: a multiphase jet flow drying bed system for treating high-salt wastewater comprises a drying bed, wherein a drying chamber is arranged in the drying bed, an air distributor is fixedly arranged in the drying chamber, a filler is arranged at the upper part of the air distributor, an air inlet at the lower part of the drying chamber is connected with an air inlet pipe so as to be filled with hot air which blows the filler into a fluidized state, and an air outlet at the upper part of the drying chamber is connected with an air outlet pipe; the drying bed is provided with a heating device for heating the filling material; and a liquid-phase atomizing device is arranged in the drying chamber and is used for atomizing the high-salt wastewater and then spraying the atomized high-salt wastewater on the filler.

Optionally, the heating device comprises a jacket type heat exchanger fixedly arranged on the peripheral wall of the drying bed, wherein the jacket type heat exchanger is provided with hot fluid, and the jacket type heat exchanger is opposite to the filling in the horizontal direction.

Alternatively, the hot fluid flows in a top-down direction in the jacketed heat exchanger.

Optionally, the inner wall of the jacket type heat exchanger is provided with a plurality of communication holes communicated with the drying chamber, the pore size of the communication holes is smaller than the particle size of the filler particles, the hot fluid in the jacket type heat exchanger is hot air, and the communication holes are used for allowing the hot air in the jacket type heat exchanger to enter the drying chamber to heat the filler.

Optionally, a plurality of jet holes are formed in the center of the air distributor, and a leakage-proof net for preventing filler particles from falling from the jet holes is arranged on the jet holes.

Optionally, the heating device comprises a plurality of hoods fixedly installed on the air distributor, the bottoms of the hoods are provided with openings for hot air to enter, the tops of the hoods are closed, the side walls of the hoods are provided with small holes for hot air to blow out, and the small holes are positioned in the filler at the upper part of the air distributor.

Optionally, a plurality of hoods are distributed on the air distributor at positions close to the edge, and the plurality of hoods are located at the periphery of the plurality of jet holes.

Optionally, the hood is fixedly mounted on the air distributor by welding or screwing.

Optionally, the lower part of the drying bed is a conical cylinder, the inner diameter of the conical cylinder is gradually increased from bottom to top, and the filler is positioned in the conical cylinder.

Optionally, the air inlet at the lower part of the drying bed is connected with an induced draft fan through a pipeline, the induced draft fan is connected with a hot air source through a pipeline, and hot air provided by the hot air source is hot overgrate air.

Compared with the prior art, the utility model has the beneficial effects that:

1. In the multiphase jet drying bed system, the heating device is adopted to heat the filler in the drying chamber, so that the evaporation efficiency of the high-salt wastewater attached to the filler particles is improved, and the treatment efficiency of the high-salt wastewater is improved.

2. In the multiphase jet drying bed system, the jacket type heat exchanger is adopted to heat the filler in the drying chamber in a heat conduction mode, the structure is simple, the treatment efficiency of high-salt wastewater is improved, a plurality of communication holes are formed between the jacket type heat exchanger and the drying chamber, so that hot air in the jacket type heat exchanger enters the filler to be in contact with the filler for direct heat transfer, and the heating efficiency of the filler is further improved.

3. According to the multiphase jet flow drying bed system, the plurality of jet holes are arranged at the center of the air distributor, so that hot air passing through the jet holes blows up the filler, then the filler is dispersed and falls down to form a circulating jet flow state, the uniform mixing of atomized high-salt wastewater and the filler is quickened, meanwhile, precipitated salt and particles are ground into tiny powder through friction extrusion among filler particles, and then the tiny powder is discharged from an air outlet of the drying bed along with the hot air, so that the blockage of the drying bed is avoided, and the consumption of compressed air is reduced.

4. In the multiphase jet drying bed system, the plurality of hoods are distributed at the positions, close to the periphery, of the air distributor, small holes are formed in the hoods for heating air to pass through, and after the hoods are heated by hot air in the hoods, the hoods transfer heat to the filler, so that the filler is heated.

5. In the multiphase jet drying bed system, the hot air introduced into the drying chamber and the hot air introduced into the jacketed heat exchanger come from the same heat source, so that the structure is simplified, the cost is low, the temperature difference is small, the inside and the outside of the filler are heated uniformly, and the evaporation speed of high-salt wastewater is accelerated.

Drawings

FIG. 1 is a schematic diagram of the installation of a multiphase jet dryer bed system in an embodiment;

FIG. 2 is a schematic diagram of the structure of a multiphase jet drying bed in an embodiment;

FIG. 3 is a diagram of the fluidized state inside the dryer bed of the multiphase jet dryer bed system in an embodiment;

FIG. 4 is a schematic view of the structure of the air distributor and the hood according to the embodiment;

Fig. 5 is a perspective view of an air distributor and hood in an embodiment.

Reference numerals: 1. a drying bed; 11. a drying chamber; 12. an air inlet; 13. an air outlet; 14. a conical cylinder; 15. an observation window; 16. a waste water interface; 17. a discharge port; 2. an air distributor; 21. jet holes; 22. a hood; 221. a small hole; 222. an external thread; 3. a filler; 4. a heating device; 41. a jacketed heat exchanger; 411. a heat exchange medium inlet; 412. a heat exchange medium outlet; 5. a liquid phase atomizing device; 6. a source of hot air; 61. an induced draft fan; 7. SCR; 71. an air preheater; 72. a dust remover; 73. a desulfurizing tower; 74. a chimney; 75. and (5) a waste water pump.

Detailed Description

The utility model is described in further detail below with reference to the drawings and examples.

Examples: as shown in fig. 1-5, the embodiment provides a multiphase jet drying bed system for treating high-salt wastewater, which comprises a drying bed 1, wherein a drying chamber 11 is arranged in the drying bed 1, an air distributor 2 is fixedly arranged in the drying chamber 11, a filler 3 is arranged at the upper part of the air distributor 2, an air inlet 12 of the drying bed 1 positioned at the lower part of the drying chamber 11 is connected with an air inlet pipe so as to be filled with hot air for blowing the filler 3 into a fluidized state, and an air outlet 13 of the drying bed 1 positioned at the upper part of the drying chamber is connected with an air outlet pipe; the drying bed 1 is provided with a heating device for heating the filling 3; the drying chamber 11 is internally provided with a liquid-phase atomizing device 5, and the liquid-phase atomizing device 5 is used for atomizing the high-salt wastewater and then spraying the atomized high-salt wastewater on the filler 3.

Through the arrangement, hot air enters from the air inlet 12 at the bottom of the drying bed 1, passes through the air distributor and then blows and rises the filler 3, so that the filler 3 in the drying bed 1 is in a circulating fluidization state, high-salt wastewater is atomized by the liquid-phase atomizing device 5 and then sprayed on the surface of the filler 3 in the fluidization state to form a layer of thin-layer liquid film, the high-salt wastewater is uniformly distributed in the filler 3 through fluidization of the filler 3, the filler 3 is heated by the heating device, heat of the filler 3 is absorbed by the thin-layer liquid film on one hand in a solid-liquid heat exchange mode, heat of the hot air is absorbed by the gas-liquid heat exchange mode, moisture in the high-salt wastewater is accelerated to be evaporated into water vapor, salt and particulate matters in the high-salt wastewater are deposited on the surface of the filler 3, and become tiny dust after mutual collision friction among the filler 3 is discharged from the top air outlet 13 of the drying bed 1 along with the hot air, and finally captured by the dust remover 72.

The scheme of this embodiment is different from the traditional high-salt wastewater treatment process in terms of structure and principle, the atomization effect of high-salt wastewater and the flow field distribution requirement of hot air in the drying chamber 11 are relatively low, the main purpose is to spray the high-salt wastewater onto the surface of the fluidized filler 3, then the high-salt wastewater is uniformly mixed with the filler 3 through the fluidization effect of the filler 3, so that the problems of poor atomization effect of the high-salt wastewater and uneven flow field distribution of hot air in the drying chamber 11 are replaced, the evaporation of water in the high-salt wastewater attached to the surface of the filler 3 is accelerated through various heat exchange modes, the precipitated salt and particulate matters become tiny dust through friction collision between the fillers 3, the particle size is reduced, the risk of blockage of the drying bed 1 is greatly reduced, the consumption of compressed air is also reduced, and the whole system is more stable in operation.

The hot air in this embodiment is mainly used to blow the filler 3 in a circulating fluidization state so that the filler 3 and the high-salt wastewater are uniformly mixed, and is also used to exchange heat with the high-salt wastewater, so that the requirement of fully mixing the flue gas and atomized liquid drops in the traditional equipment is reduced, and the requirement of uniform distribution of the high-temperature flue gas flow field in the drying chamber 11 is also reduced.

In the multiphase jet dry bed system of this embodiment, the filler 3 used may be aluminum silicate ceramic particles, and the height of the filler 3 may be 300mm-500mm.

Further, the SCR7 is connected to the air preheater 71, the air preheater 71 is connected to the dust remover 72, the dust remover 72 is connected to the desulfurizing tower 73, and the desulfurizing tower 73 is connected to the chimney 74. The high-salt wastewater is fed into the drying chamber 11 by the wastewater pump 75.

In the multiphase jet drying bed system of the present embodiment, the liquid-phase atomizing device 5 includes a two-fluid spray gun or a single-fluid spray gun, and the flow rate of the high-salt wastewater is controlled by the regulating valve.

In the multiphase jet drying bed system of the present embodiment, the heating means includes a jacket type heat exchanger 41 fixedly provided at the peripheral wall of the drying bed 1, the jacket type heat exchanger 41 having a thermal fluid therein, the jacket type heat exchanger 41 being opposed to the packing 3 in the horizontal direction. By arranging the jacket type heat exchanger 41, the heat of the hot fluid in the jacket type heat exchanger 41 is transferred to the filler 3 through the side wall of the drying bed 1, so that the temperature of the filler 3 is increased, the evaporation speed of high-salt wastewater in the drying chamber 11 is accelerated, the temperature in the drying chamber 11 is increased, the temperature of salt particles is further increased, the salt particles are more easily ground into powder, and the grinding efficiency is improved.

In the multiphase jet dry bed system of the present embodiment, the hot fluid flows in the jacket type heat exchanger 41 in a top-down direction. Through the arrangement, the hot fluid flows from top to bottom and is matched with the jet flow direction of the hot air in the drying chamber 11 from bottom to top to form convection, so that the heat transfer effect on the filler 3 is better.

Further, a heat exchange medium inlet 411 is provided at the upper part of the jacketed heat exchanger 41, and a heat exchange medium outlet 412 is provided at the lower part of the jacketed heat exchanger 41.

In the multiphase jet drying bed system of this embodiment, the inner wall of the jacketed heat exchanger 41 is provided with a plurality of communication holes communicated with the drying chamber 11, the pores of the communication holes are smaller than the particle size of the filler 3 particles, the hot fluid in the jacketed heat exchanger 41 is hot air, and the communication holes are used for allowing the hot air in the jacketed heat exchanger 41 to enter the drying chamber 11 to heat the filler 3.

Through the arrangement, the jacket type heat exchanger 41 is used for indirectly heating the solid filler 3 particles, the communication holes can be tiny gaps, the filler 3 particles are prevented from entering the jacket type heat exchanger 41, hot air in the jacket type heat exchanger 41 enters the drying chamber 11 through the communication holes, the solid filler 3 particles are heated in a gas-solid heat exchange mode, and the evaporation efficiency of high-salt wastewater is improved. The hot air in the jacketed heat exchanger 41 may use the same heat source as the hot air in the desiccant bed 1.

In the multiphase jet drying bed system of the embodiment, 1 or a plurality of jet holes 21 are formed in the center of the air distributor 2, and the jet holes are determined through calculation according to factors such as the height of the filler 3, the design flow rate, the property of the filler 3 and the like. The jet hole 21 is provided with a leakage preventing net for preventing particles of the filler 3 from falling from the jet hole 21. Preferably, the number of the jet holes 21 is 1 to 5, and the size of the jet holes 21 is 20mm to 50mm according to the size of the drying bed 1 and the amount of the treated water.

With the above arrangement, the jet hole 21 is located at the center of the air distributor 2, and has a large aperture, and in order to prevent the particles of the filler 3 from being lost from the jet hole 21, a leakage preventing net is installed on the jet hole 21, and the leakage preventing net may be a steel wire net. Because the aperture of the jet hole 21 is large, the hot air passing through the jet hole 21 has large blowing force on the filler 3, so that the filler 3 in the center is more easily blown upwards to a higher height, then the impact is dispersed in the drying chamber 11, after the filler 3 is scattered in the center of the bottom, the filler is blown up again by the jet hole 21 to form circulation, the filler 3 is in a jet state, and the fluidization height of the filler 3 is higher. The jet holes 21 can also heat the particles of the filler 3 along with blowing up the filler 3.

In the multiphase jet drying bed system of the embodiment, the heating device comprises a plurality of hoods 22 fixedly installed on the air distributor 2, an opening for the entry of hot air is formed in the bottom of each hood 22, the top of each hood 22 is closed, small holes 221 for blowing out the hot air are formed in the side wall of each hood 22, and the small holes 221 are located in the packing 3 at the upper part of the air distributor 2.

With the above arrangement, the hood 22 is distributed in the packing 3 above the air distributor 2, in contact with the packing 3. After the hot air enters the inside of the hood 22 from the opening at the bottom of the hood 22, the hood 22 is heated, and then the hood 22 transfers heat to the filler 3 in a heat conduction mode, so that the temperature of the filler 3 is increased.

In the multiphase jet drying bed system of this embodiment, the hood 22 is reasonably arranged around the air distributor 2, the connection mode of the hood 22 and the air distributor 2 may be threaded connection or welding, 4 small holes 221 are set on the hood 22 as 4 small holes 221, and the aperture of the small holes 221 is 2mm-5mm.

In the multiphase jet drying bed system of the embodiment, a plurality of hoods 22 are distributed on the air distributor 2 at positions close to the edges, and the plurality of hoods 22 are located at the periphery of the plurality of jet holes 21.

In the multiphase jet drying bed system of the present embodiment, the hood 22 is fixedly mounted on the air distributor 2 by welding or screwing. Through the arrangement, the hood 22 is fixedly arranged on the air distributor 2 in a welding mode, so that the installation is stable, and the manufacturing cost is low. The hood 22 is fixedly arranged on the air distributor 2 in a threaded connection mode, so that the hood 22 with different sizes and shapes can be conveniently disassembled, assembled and replaced to adapt to different working environments.

Specifically, the outer peripheral wall of the hood 22 is provided with external threads 222, and the upper edge of the air distributor 2 is provided with threaded holes corresponding to the hood 22 one by one. In addition, by controlling the screwing-in and unscrewing of the hood 22 in the screw hole, the extension length of the hood 22 at the upper portion of the air distributor 2 can be adjusted, thereby adjusting the position of the hood 22 according to the working conditions.

In the multiphase jet drying bed system of the embodiment, the lower part of the drying bed 1 is a conical cylinder 14, the inner diameter of the conical cylinder 14 is gradually increased from bottom to top, and the filling 3 is positioned in the conical cylinder 14.

Through the arrangement, after the packing 3 in the center of the air distributor 2 is blown to rise by the hot air to a certain height, the packing 3 is scattered on the inner wall of the conical cylinder 14 under the action of gravity, the packing 3 slides down to the bottom of the air distributor 2 on the inner wall of the conical cylinder 14, and the design of the conical cylinder 14 ensures that the packing 3 sliding down from the inner wall of the conical cylinder 14 flows to the center of the air distributor 2 more easily and is blown up again by the hot air, so that circulation is formed. The cone 14 has a certain height of packing 3 therein.

In the multiphase jet drying bed system of this embodiment, the lower side wall of the cone 14 is provided with a discharge opening 17 for loading and unloading the packing 3.

In the multiphase jet drying bed system of this embodiment, the air inlet 12 at the lower part of the drying bed 1 is connected with the induced draft fan 61 through a pipeline, the induced draft fan 61 is connected with the hot air source 6 through a pipeline, and the hot air provided by the hot air source 6 is hot overgrate air. The hot air source 6 of the embodiment adopts hot secondary air, so that the problem of insufficient flue gas quantity introduced into the drying tower due to small differential pressure of the air preheater 71 when the traditional equipment for treating high-salt wastewater runs under low load of a unit is solved. The hot air source 6 can adopt a power plant hot overgrate air system, hot air is hot overgrate air provided by the power plant hot overgrate air system, the temperature of the hot overgrate air is about 300 ℃, and the temperature range of the filler 3 in the working process is 250-300 ℃.

In the multiphase jet drying bed system of the embodiment, the induced draft fan 61 adopts a variable-frequency high-temperature fan, mainly provides power for jet fluidization of the filler 3, ensures that the filler 3 is fully contacted with liquid drops and hot air, enhances the heat transfer efficiency, enables moisture to be rapidly evaporated, and ensures that the filler 3 is in an optimal fluidization state by adjusting the frequency of the induced draft fan 61 in a variable-frequency mode, and ensures that high-salt wastewater is fully evaporated and dried. By adopting the variable-frequency high-temperature fan to convey the hot secondary air into the drying chamber 11 in a pressurized manner, the problem that the smoke quantity introduced into the drying tower is insufficient due to small differential pressure of the air preheater 71 when the traditional equipment for treating high-salt wastewater runs under low load of a unit is solved.

In the multiphase jet flow drying bed system of the embodiment, the side part of the drying bed 1 is provided with two observation windows 15, one observation window 15 is opposite to the wastewater interface 16 for introducing high-salt wastewater on the drying bed 1, and the other observation window 15 is positioned at the upper part of the drying bed 1.

The multiphase jet flow drying bed system of the embodiment has the working principle that: after being pressurized by the induced draft fan 61, the hot air enters the drying chamber 11 from the air inlet 12 at the bottom of the drying bed 1, and then passes through the air distributor 2 from bottom to top in the drying chamber 11 to blow the packing 3 to move upwards, so that the packing 3 is in a circulating fluidization state, and the drying bed 1 heats the packing 3 in two ways, namely by a plurality of hoods 22 arranged at the periphery of the air distributor 2, and by a jacket type heat exchanger 41 arranged outside the conical cylinder 14. The high-salt wastewater is sprayed on the surface of the filler 3 through the spray gun to form a layer of thin-layer liquid film, the thin-layer liquid film absorbs heat of the filler 3 in a solid-liquid heat exchange mode, meanwhile, the thin-layer liquid film exchanges heat with hot air introduced into the drying chamber 11 in a gas-liquid heat exchange mode, moisture in the high-salt wastewater is evaporated to become water vapor, salt and particulate matters are separated out and attached to the surface of the filler 3, and the water vapor is ground into tiny dust after mutual collision friction among the fillers 3, flows out from the top air outlet 13 of the drying bed 1 along with the hot air, and is finally trapped by the dust remover 72.

Claims (10)

1. The multiphase jet flow drying bed system for treating the high-salinity wastewater is characterized by comprising a drying bed (1), wherein a drying chamber (11) is arranged in the drying bed (1), an air distributor (2) is fixedly arranged in the drying chamber (11), a filler (3) is arranged at the upper part of the air distributor (2), an air inlet (12) at the lower part of the drying chamber (11) is connected with an air inlet pipe so as to be filled with hot air which blows the filler (3) into a fluidization state, and an air outlet (13) at the upper part of the drying chamber (11) is connected with an air outlet pipe; the drying bed (1) is provided with a heating device for heating the filling material (3); a liquid-phase atomizing device (5) is arranged in the drying chamber (11), and the liquid-phase atomizing device (5) is used for atomizing the high-salt wastewater and then spraying the atomized high-salt wastewater on the filler (3).

2. Multiphase jet drying bed system for treating high salt wastewater according to claim 1 characterized in that the heating means comprises a jacketed heat exchanger (41) fixedly arranged at the peripheral wall of the drying bed (1), the jacketed heat exchanger (41) having a hot fluid therein, the jacketed heat exchanger (41) being horizontally opposed to the packing (3).

3. A multiphase jet dry bed system for treating high salinity wastewater according to claim 2 wherein the hot fluid flows in a top down direction in a jacketed heat exchanger (41).

4. The multiphase jet drying bed system for treating high-salt wastewater according to claim 2, wherein a plurality of communication holes communicated with the drying chamber (11) are formed in the inner wall of the jacket type heat exchanger (41), the pores of the communication holes are smaller than the particle size of the particles of the filler (3), the hot fluid in the jacket type heat exchanger (41) is hot air, and the communication holes are used for allowing the hot air in the jacket type heat exchanger (41) to enter the drying chamber (11) to heat the filler (3).

5. The multiphase jet drying bed system for treating high-salt wastewater according to claim 1, wherein a plurality of jet holes (21) are formed in the center of the air distributor (2), and a leakage preventing net for preventing filler (3) particles from falling from the jet holes (21) is arranged on the jet holes (21).

6. The multiphase jet drying bed system for treating high-salinity wastewater according to claim 5, wherein the heating device comprises a plurality of hoods (22) fixedly arranged on the air distributor (2), the bottoms of the hoods (22) are provided with openings for hot air to enter, the tops of the hoods (22) are closed, the side walls of the hoods (22) are provided with small holes (221) for hot air to blow out, and the small holes (221) are positioned in the filler (3) at the upper part of the air distributor (2).

7. A multiphase jet drying bed system for treating high salinity wastewater according to claim 6, wherein a plurality of hoods (22) are distributed on the air distributor (2) at positions near the edges, and the plurality of hoods (22) are positioned at the periphery of the plurality of jet holes (21).

8. Multiphase jet drying bed system for treating high salinity wastewater according to claim 6 characterized in that the hood (22) is fixedly mounted on the air distributor (2) by means of welding or screwing.

9. Multiphase jet drying bed system for treating high salt wastewater according to claim 1 characterized in that the lower part of the drying bed (1) is a conical cylinder (14), the inner diameter of the conical cylinder (14) gradually increases from bottom to top, and the packing (3) is positioned in the conical cylinder (14).

10. The multiphase jet drying bed system for treating high-salt wastewater according to claim 1, wherein the lower air inlet (12) of the drying bed (1) is connected with an induced draft fan (61) through a pipeline, the induced draft fan (61) is connected with a hot air source (6) through a pipeline, and hot air provided by the hot air source (6) is hot overgrate air.