RU2230258C1 - Smoke suction jet-type air heater - Google Patents

Abstract

FIELD: heat-power engineering; supply of preheated air to boiler units and industrial furnaces. SUBSTANCE: proposed air heater includes gas duct, hollow heat-exchange chamber with perforated sheets built in its guards which are closed with boxes provided with cold and heated air inlet and outlet branch pipes; holes of perforated sheets are connected with air nozzles and hot air traps which form passages for inlet of hot gases and outlet of cooled flue gases. EFFECT: simplified construction; enhanced reliability and efficiency due to increased rate of heat exchange; reduced usage of metals; reduced aerodynamic resistance. 1 dwg

Description

The present invention relates to a power system, namely, to use the heat of the flue gases of boiler units and industrial furnaces when heating the air supplied to the combustion.

Known air heater containing a set of pipes installed in the flue connected to the ducts of cold and heated air, air temperature sensors, air flow regulators located at the inlet and outlet of the air [1].

The disadvantages of the known device include the low rate of heat transfer between air and flue gases, due to the regularity of heat transfer through the wall, high metal consumption and bulkiness of the installation, significant aerodynamic resistance and rapid corrosion of heat exchange surfaces.

Closer in technical essence to the present invention is an air heater containing interconnected and adjacent to the gas duct air chambers (hollow heat exchange chambers), each of which is connected to its feed manifold (cold air duct) through a perforated partition (board) installed along the working the chamber walls at a given distance with holes staggered [2].

The main disadvantages of the known device are the impossibility of using jet air distribution to increase the heat transfer rate by direct contact of air with flue gases and their radiation, as well as to reduce harmful impurities in flue gases, the creation by air chambers of an intermediate link between flue gases and the air supply system, the presence heat exchange surfaces, which increases the intensity and, accordingly, the corrosion of the metal, complicates the design of properties, increases aerodynamic drag, reduces its reliability and efficiency.

The technical problem to which the invention is directed is to simplify the design, increase the reliability and efficiency of the device.

The task is realized in a smoke-suction jet air heater containing a gas duct, a hollow heat exchanger chamber, a perforated cold air board built into the heat exchanger enclosure and closed by a cold air duct, the perforation of which is made in the form of rectangular slots parallel to the direction of movement of the flue gases connected to curved slotted air nozzles for supplying cold air to the heat exchange chamber, forming among themselves along the entire height of the horizon heat exchange chamber rectangular rectangular channels for the passage of hot flue gases into it, installed at the opposite end of the heat exchange chamber opposite each nozzle along the entire height, hot air traps formed by curved rectangular channels connected to the edges of rectangular openings parallel to the direction of movement of the flue gases, perforated hot air boards also built into the enclosure of the heat exchanger chamber, closed by a duct of hot air, and forming horizontally between each other along the entire height of the heat exchanger chamber on-line rectangular channels for the exit of cooled flue gases from it to the subsequent section of the gas duct.

The drawing shows the proposed smoke suction jet air heater (DVSVP).

ICE includes a gas duct 1, a hollow heat exchange chamber 2, a perforated board of cold air 3 embedded in its enclosure, closed by a cold air box 4 with a nozzle 5, the rectangular slots of which are made parallel to the direction of movement of the flue gases and are connected to curved slotted air ducts from the inside of the enclosure 2 nozzles 6, which serve to supply cold air to the heat exchange chamber 2 and forming horizontal rectangular channels 7 for the passage of hot flue gases into heat an exchange chamber 2 mounted opposite each nozzle 6 at the end of the heat exchange chamber 2 over its entire height of the hot air trap 8, which are curved channels of rectangular cross section, forming horizontal rectangular channels 9 between them along its entire height for the exit of the cooled flue gases from the heat exchange chamber 2 moreover, the channels of the traps 8 are connected to rectangular openings parallel to the direction of movement of the flue gases, the perforated board of hot air 10, also built into the enclosure of the chamber 2 and closed that duct of hot air 11 with a pipe 12.

The proposed ICE is based on the properties of a free flooded turbulent air stream, in particular a flat stream, which propagates in the direction of flow and is mixed along the boundary surface with the surrounding gas medium, the mixing being accompanied by the involvement of the mass of the gas medium in the air stream, and the communication of the peripheral part of the gas motion medium coinciding with the direction of the jet. In addition to the mixing of the boundary layers of the air stream and the gas medium, intense heat exchange occurs between them, significantly exceeding the rate of heat transfer through the wall, since in this case there is no thermal resistance of the wall with contaminants, convective heat transfer occurs directly between the air and gas particles and begins to play a significant the role of radiant heat transfer, which leads to a quick equalization of the temperature of the air stream and the gaseous medium [3, p. 326–339], [4, p. 50-60]. In addition, the partial mixing of the heated air with flue gases and the subsequent use of the resulting mixture for combustion can reduce the content of flue gases NO _x and SO _x [5, p. 457],

ICE works as follows Flue gases at a vacuum corresponding to the mode of operation of a boiler unit or industrial furnace, through a gas duct 1 through horizontal rectangular channels 7 enter the heat exchange chamber 2, where also a high-pressure fan from the pipe 5 through the cold air duct 4 and air slotted nozzles 6 , the number of which is selected on the basis of the conditions for creating stable plane jets with a step between them l, determined from the condition of non-intersection of two nearby jets, air with a speed exceeding the flue gas bump several times (20-30 m / s) enters the heat exchange chamber 2 in the form of parallel flat jets dividing the heat exchange chamber 2 into vertical parallel prismatic sections that simultaneously perform the functions of a smoke exhaust and heat exchanger in which flue gas flows carried away by air jets, the length of which X is determined from the condition of non-intersection of two nearby air jets and, at the same time, providing a given thermal range of the jet (i.e. ensuring air heating and cooling flue gases to predetermined temperatures). In parallel with the processes of partial mixing and involvement in the air jets of a certain part of the flue gases occurring in the boundary layers, acceleration of the movement of the peripheral mass of gases, an intensive convective and radiant heat exchange occurs directly between the particles of air and flue gases and, accordingly, rapid heating of the air jets and cooling of the flue flows gases moving between them. Air jets heated to the required temperature with some admixture of flue gases, the amount of which is set from the required recirculation, fall into the rectangular inlet openings of the channels of the hot air traps 8, whose height H is equal to the height of the heat exchange chamber 2, and the width δ is determined depending on the thickness of the jet and the quantity recirculation flue gases, from where through the holes of the perforated board 10, the duct of hot air 11 and the pipe 12 air is supplied for the combustion process in a boiler unit or industrial furnace, and the cooled flue gases through the horizontal channels 9 enter the next section of the gas duct 1 at a speed greater than at the entrance to the heat exchange chamber 2, which is due to the transfer of part of the energy of the air jets to them and a smaller living area of the horizontal channels 9.

Thus, the proposed DVSVP allows, due to the absence of heat exchange surfaces, to sharply increase the heat transfer rate, reduce the metal consumption of the structure, reduce the amount of correlated metal, reduce the aerodynamic resistance of the device, improve the environmental performance of flue gases, which ultimately simplifies the design, increases reliability and efficiency devices.

The effectiveness of the proposed DVA can be illustrated by the following example.

Initial data:

Rated power of the boiler unit N = 12 MW

Flue gas consumption V _G = 17000 m ³ / h

The flow rate of blast air V _in = 13000 m ³ / h

The temperature of the flue gases at the entrance to the ICE t _n = 250 ° C

The temperature of the flue gases at the exit of the ICE t _y = 150 ° C

The temperature of the air at the entrance to the ICE θ _n = 25 ° C

The temperature of the air at the exit of the ICE θ _k = 135 ° C

The height of the heat chamber 2 N = 1.0 m

Dimensions of the nozzle exit slit 6 l = 0.02 m

The velocity of air flow from the nozzle 6 V ₀ = 30 m / s

Decision

The living area of the nozzle 6:

f ₀ = 1.0 · 0.02 = 0.02 m ² .

Air flow through one nozzle 6:

V ₁ = V ₀ · f ₀ ;

V ₁ = 30 · 0.02 = 0.6 m ³ / s.

Number of nozzles 6:

n = 13000 / (0.6 · 3600) = 6 pcs.

The thermal range of the air stream (the length of the heat chamber 2) is found from the set temperatures of cold and heated air and hot and cooled flue gases according to the procedure [4, p. 50-60].

The average temperature of the flue gases in the heat exchange chamber 2:

t _avg = (250 + 150) / 2 = 200 ° C.

The average temperature of the air stream in the heat exchange chamber 2

θ _cp = (25 + 135) / 2 = 80 ° C.

The average excess temperature (temperature head) in the heat exchange chamber 2:

θ ₀ = 200-80 = 120 ° C.

Excess temperature at trap inlet 8:

θ _x = 135-80 = 55 ° C.

Thermal range of the jet (length of the heat exchange chamber 2):

where n = 2.49 - experimental coefficient for a flat jet;

2B = slot width of nozzle 6;

X = (2.49 ² · 120 ² · 0.02) / 55 ² = 0.6 m.

The thermal range of the jet is checked for non-intersection of two near-jet jets as follows.

The thickness of a plane jet at a distance X is found from the relation [3, T. 8.1]:

T = 2 · (2.4 · a · X / B ₀ +1) · B ₀ ,

where a = 0.09 is the turbulence coefficient for a plane jet;

T = 2 (2.4 · 0.09 · 0.6 / 0.01 + 1) · 0.01 = 0.28 m.

Hence the minimum step between nozzles 6 and, accordingly, traps 8:

l _min = 0.3 m

Minimum width of thermal chamber 2 DVSVP:

L _min = 6 · 0.3 = 1.8 m.

The refinement of the width L of the heat exchange chamber 2 and the determination of the width of the traps 8 are carried out taking into account the required concentration of flue gases in the blast air empirically.

The metal consumption for the manufacture of this ICE (2 mm thick steel sheet) will be 0.5 tons, while the mass of a steel tubular air heater with the corresponding parameters is an order of magnitude larger [6, p.227].

Sources of information

1. RF patent 2170883, M.cl. F 23 L 15/04, 1999.

2. A.S. USSR 964356, M.cl F 23 L 15/04, 1982.

3. A.D. Altshul et al. Hydrodynamics and aerodynamics. - M.: Stroyizdat, 1987, 415 p.

4. I.A. Shepelev. Aerodynamics of air flows indoors. - M.: Stroyizdat, 1978, 145 p.

5. G.N. Delyagin et al. Heat-generating installations. - M.: Stroyizdat, 1986, 560 p.

6.K.F. Roddatis, Ya.B. Sokolovsky. Handbook of low-capacity boiler plants. - M .: Energy, 1975, 368 p.

Claims (1)

Smoke-absorbing jet air heater, including a gas duct, a hollow heat exchange chamber, a perforated board of cold air built into its enclosure, closed by a box of cold air, characterized in that the perforation of the board is made in the form of slots parallel to the direction of air movement, connected to curved slotted air nozzles for supplying cold air into the heat exchange chamber, forming horizontal rectangular channels between each other over the entire height of the heat exchange chamber for the passage of hot smoke into it gas, installed at the opposite end of the heat exchanger chamber along its entire height opposite each air nozzle of the hot air trap, formed by curved rectangular channels connected to the edges of rectangular holes parallel to the direction of the flue gases of the perforated hot air board built into the heat exchanger enclosure and forming all its height, horizontal rectangular channels for the exit of cooled flue gases from the heat exchange chamber to the subsequent section of ha zhoda.