RU2130152C1 - Air preheater - Google Patents

Abstract

FIELD: boilers working on natural gas or oils. SUBSTANCE: air preheater is made in form of U-shaped unit with evaporating stage 3 mounted in its left-hand leg in way of motion of waste gases: mounted above evaporating stage 3 are upper nozzle 5 and pipe lines 6 and 7 for continuous and periodic blow; water-to-air heat exchanger 1 located in lower portion is placed in volume of condensate receiver 14 provided with cleaning pipe line 16. It connects evaporating stage 3 with lower nozzle 13 mounted in right-hand leg and condensation stage 11. Fan 4 with water evaporation and sprinkling pipe lines 12 and 2 is mounted at inlet of condensation stage 11 in air end. It is also connected to water-to-air heat exchanger 1 and evaporating stage 3. EFFECT: intensification of heat exchanger process; avoidance of low-temperature corrosion effect. 1 dwg

Description

 The invention relates to boiler equipment in which natural gas and liquid fuel are used as fuel.

 A known installation of heat recovery of combustion products [1], containing a flue with sequentially installed in it along the gas evaporator, combined with a sprinkler, condenser and aftercooler, additionally connected to the chimney.

 Known air heater [2], the heat exchange tubes of which are provided with slotted holes located in longitudinal staggered rows in the pointed zone, and the fan is placed after the tube bundle along the air.

 Known utilization plant [3], adopted as a prototype, including a condensation stage with a condensate collector located below it and an overflow pipe connected through an overheating heat exchanger with a smoke exhaust and a chimney.

In known installations, combustion products with a temperature of approximately 250 ^° C. are used to heat the exhaust gases in the superheat exchanger after the disposal unit. This overheating eliminates moisture condensation on the surfaces of the duct and chimney.

 After the heat exchanger overheats, the combustion products enter the evaporator, in which they are saturated and cooled by condensate falling from the condensation part of the heat exchanger. Condensation of water vapor from a gas-vapor mixture is accompanied by the release of latent heat of vaporization due to being used as heated among cold water. Then, the cooled flue gas passes through the separator and enters the overheating heat exchanger.

The process of condensation of water vapor from the combustion products during the combustion of natural gas and liquid fuel occurs when the temperature of the flue gases reaches 50-70 ^o C. Their increased temperature level automatically leads to convective heat transfer, which dramatically reduces the efficiency of heat transfer of the combustion products to heat exchange surfaces.

The presence of SO ₂ and SO ₃ in the flue gases leads to the formation of an acidic environment, which reduces the duration of the operation.

 When using a recycling plant for heating air, the heat transfer coefficient of the condensation and convective steps drops sharply. In this case, the areas of their heat transfer surface increase proportionally.

 The technical problem solved by the invention is to eliminate these disadvantages.

 The technical result is achieved by the fact that the air heater is represented by a U-shaped arrangement, where an evaporation stage is installed in its left branch in the direction of the exhaust gases, above which there are upper nozzles and pipelines for continuous and periodic blowing, and in the lower part there is a water-air heat exchanger located in the volume of the collector condensate having a cleaning pipe and connecting the evaporation stage with the lower nozzle leading in the right branch and the condensation stage, at the inlet of which by air Allowed second side fan conduits and injection of water vapor, the latter is also connected to the air heat exchanger and flash stage.

 The drawing shows an air heater, where 1 is a water-air heat exchanger, 2 is a water injection pipeline, 3 is an evaporation stage, 4 is a fan, 5, 13 are upper and lower nozzles, 6, 7, 12 are continuous, periodic blowdown and vapor deaerator pipes, 8 - overheating heat exchanger, 9 - smoke exhaust, 10 - chimney, 11 - condensation stage, 14 - condensate collector, 15, 16 - overflow and cleaning pipelines.

 Water-air heat exchanger 1, superheat heat exchanger 8, evaporative 3 and condensation 11 stages are calculated according to specific initial data. Based on the results of thermotechnical and aerodynamic calculations, their physical dimensions are determined.

 The upper 5 and lower 13 nozzles consist of elements in the form of Raschig rings.

 The pipelines of the vapor of the deaerator 12 of continuous 6 and periodic 7 purges are respectively connected to the outlet of the vapor after the vapor cooler with a continuous purge outlet pipe after the continuous purge cooler with a periodic purge discharge pipe before bubbling (not shown). Since there is always a certain vacuum at the point of supply of the vapor pipe 12 under the condition of normal operation, the process in the deaerator will not be disturbed. For the continuous purge to enter the heat recovery unit, the continuous purge separator and cooler must be placed higher than the continuous purge conduit 6.

 In the condensate collector 14, the upper level of condensate corresponds to the mark of the overflow pipe 15, under which a water-air heat exchanger 1 is placed.

 The proposed air heater can be installed immediately after the boiler or standard economizer. In both cases, it works as follows.

 The combustion products enter the overheating heat exchanger 3, in which they heat the exhaust gases so that there is no condensation of water vapor before leaving the chimney 10.

After the heat exchanger 3, the combustion products are irrigated with water from pipelines 6, 7. The upper nozzles 5 contribute to a more uniform distribution of the irrigated water and its partial evaporation. The process of water evaporation continues on the heat exchange surfaces of the evaporation stage 3, which leads to a sharp increase in the heat transfer coefficient from the gas side in comparison with purely convective heat transfer. Due to the fact that the discharged streams have a pH> 7, they neutralize in a certain way the influence of the formed acids upon dissociation with water of CO ₂ , SO ₂ , SO ₃ .

The flue gases enriched with water vapor in the evaporation stage 3 pass through the lower nozzle 13, in which they are additionally saturated with the evaporated condensate formed on the heat exchange surfaces of the condensation stage 11. The heat transfer in it from the side of the combustion products is as efficient as in the evaporation stage 3, since the reverse phase transition of water takes place there. Dehydrated products of combustion are removed with a temperature of 20-30 ^o C through the heat exchanger 8 of the exhaust fan 9 into the chimney 10.

Unevaporated water after the evaporation stage 3 and condensate draining from the condensation stage 11 enter the condensate collector 14 with a temperature above 80 ^o C. It is cooled below 50 ^o C by a water-air heat exchanger 1. The condensate from the condensate collector 14 is constantly drained through a water trap through a pipe 15 to the barbator. Through a pipe 16, the sludge is periodically removed to a bubbler.

 During heating, the air passes through the condensation stage 11, the water-air heat exchanger 11, and the evaporation stage 3. In series, a reduced pressure is created at the inlet of the fan 4 located at the inlet of the condensation stage 11, which ensures that the vapor comes out of the deaerator. It heats the flow of outdoor air. Metered water injections in front of each heat exchange surface create a liquid film that evaporates due to the transfer of heat from the flue gases. The phase transition of the liquid to the vapor state increases the heat transfer coefficient on the air side, which brings it closer to the value of the gas side.

 The presence of an increased amount of water vapor in the air supplied to the combustion, favorably affects the reduction of nitrogen oxides formed in the burner device.

 The proposed combined heat recovery device has the following advantages.

In addition to the beneficial use of low-potential heat of the flue gases, it is possible to utilize the boiler’s technological emissions in the form of steam and hot water,
- the proposed device for protection against low temperature corrosion uses technological emissions from the boiler room,
- the transition in the evaporation stage from a purely convective to convective-evaporative type of heat transfer allows you to reduce several times the area of the heat transfer surface,
- utilization of the heat of the technological emissions of the boiler room eliminates the supply of tap water for cooling them in a bubbler,
- injection of water into the heated air reduces several times the area of the heat transfer surface relative to the purely convective type of heat transfer from the air side,
- the supply of water vapor with air for combustion helps to reduce the formation of nitrogen oxides by 20%.

Claims (1)

 An air heater containing a condensation stage with a condensate collector and an overflow pipe connected under it, connected through an overheating heat exchanger with a smoke exhaust and a chimney, characterized in that it is represented by a U-shaped arrangement, where an evaporative stage is installed in its left branch in the direction of the exhaust gases, above which are located the upper nozzles and pipelines of continuous and periodic blowing, in the lower part there is a water-air heat exchanger placed in the volume of the condensate collector having ruboprovod purification stage and connects with the evaporator being in the right branch of the lower nozzle and the condensation stage, in which the inlet side of the air blower are arranged with pipes and injecting water vapor, the latter is also connected to the air heat exchanger and flash stage.