Heat exchanger for cooling steam-gas mixture

FIELD: power engineering.

SUBSTANCE: heat exchanger comprises pipes with spiral-ring fins. The fins are provided with longitudinal slots. The pipes in the heat exchanger are arranged vertically.

EFFECT: enhanced efficiency.

3 dwg

 

The invention is intended for power and heating boilers burning gaseous fuel, and provides higher efficiency boilers at the expense of deeper cooling of the products of combustion and condensation of the contained water vapor.

In some industries use heat exchangers, made of pipes with spiral ring rolling or wound and welded edges [Kuntysh V.B. have been, N.M. Kuznetsov Thermal and aerodynamic calculation finned air cooling heat exchangers. Energoatomizdat, S.-Petersburg, 1988, 278 S.].

In recent times, such heat exchangers are used for deeper cooling of exhaust gases for steam and hot water boilers that burn natural gas [Kudinov A.A., Antonov V.A., Alekseev Y.A. analysis of the effectiveness of the condensing heat exchanger for steam boiler DE-10-GM//Industrial energy. - 1997, No. 8; the Hubbub VI, Presic GA, Navrotsky R.A. utilization of the heat of the flue gases with the use of surface (including condensation) and contact heat exchangers. In : “proceedings of the seminar “Modern boilers - efficiency, safety and environmental friendliness”” - Kiev, 1996, pp.31-37].

When used as a cooling agent is water having a temperature below temperaturethe dew, on the finned surface is condensed contained in the gas mixture of water vapor. While useful is not only “physical” heat of gases, but also the so-called “latent” heat of vaporization, the value of which is often more than physical warmth. Thus, by cooling the flue from the boiler combustion products of natural gas from 153 to 50°water with a temperature of 5-20°With, the quantity of heat obtained by cooling the dry gas is 2153 of kilo per cubic meter (normal) burnt gas, and the quantity of heat released by the condensation of water vapor, as well - 3320 kilojoules per cubic meter.

Due to water vapor condensation on the cooling surfaces, the gas in the cooling process is drained. Figure 1 shows the calculation scheme of the heat exchanger for cooling the gas-vapor mixture (in the diagram, the heat exchanger depicted in the form of six streamlined cross finned tubes) and obtained a formula that gives the dependence of the concentration of water vapour From the vapour mixture from the temperature T at a known concentration pairaboutand the temperature of the mixture Taboutat the entrance to the heat exchanger and a given temperature Tarticlesurface of the fins of the heat exchanger. The concentration of pairarticlein the immediate vicinity of the surface is equal to the concentration of saturated steam at the rate which the temperature T article.

The results of calculations using this formula are shown in figure 2 for the following values of the temperature of the mixture Taboutat the entrance to the heat exchanger and the temperature of the cooling surface (wall edges) Tarticle: 1 - Tabout=430 K, Tarticle=290 K; 2 - Tabout=430 K, Tarticle=280 K; 3 - Tabout=380 K, Tarticle=290 K; 4 - Tabout=430 K, Tarticle=280 K. the Line 5 gives the dependence of the saturated vapor concentration (in g/m3) from temperature (°). The calculations are performed for the combustion products of natural gas, containing at the entrance to the heat exchanger 17% water vapor by volume.

From figure 2 it is seen that when the cooling of the combustion products of natural gas until at least 40-50°With the remaining vapor is in the overheated state, that is, the saturation temperature of this steam (when its partial pressure) remains below the temperature (gas mixture). This eliminates the condensation on the cooled walls of the flues and chimney through which combustion products are cooled in the heat exchanger, are released into the atmosphere.

These considerations fair in the absence of entrainment of water droplets and spray with a heat exchange surface.

In the analogues described in the above references, the axis of the finned tubes are arranged in the heat exchanger horizontally, respectively, the ribs are in the vertical plane the parts, almost perpendicular to the axes of the pipes. In the tube bundle condensate formed on the edges of the overlying pipe, flows down in the form of drops on the underlying and with the tubes of the bottom row on the bottom of the metal enclosure of the heat exchanger. In this part of small droplets and splashes inevitably entrained by the gas stream.

Evaporation is carried out drops does not reduce the amount of heat received in the heat exchanger due to steam condensation, if it (evaporation) occurs after the heat exchanger. However, it increases the degree of saturation of the gas with water vapor as by increasing the amount of vapor in the gas and by reducing the gas temperature due to the cost of heat for evaporation. All this can lead to condensation on the inner walls of the flues and chimney.

Closest to the technical essence and the achieved result of the proposed design should be considered as a heat exchanger-the heat exchanger described in [Kudinov A.A., Antonov V.A., Alekseev Y.A. analysis of the effectiveness of the condensing heat exchanger for steam boiler DE-10-GM//Industrial energy. - 1997, №8], which is selected as a prototype.

This heat exchanger consists of a bimetallic tubes with knurled edges located in the convection pass of the boiler horizontally in the form of packets. Pipes pumped cold water temperaturas below the dew point temperature surrounding pipes products of combustion. Water vapor contained in the combustion products condenses on the vertical edges and flows down in the form of droplets from the upper edges of the rows on the bottom, with some drops and splashes blowin transverse horizontal directional flow of products of combustion. This is the disadvantage of the prototype.

The proposed solution eliminates drift and spray condensate formed on the surface of the finned tubes of the heat exchanger. The essence of the proposed technical solution (Fig.3-5) is that in the known device, representing a heat exchanger for cooling the gas-vapor mixture consisting of vertical pipes with spiral ribs, i.e. transverse to the axis of the pipe, along the axis of the pipe 3 all edges 1 is a longitudinal slot 4. The slot 4 may be performed, for example, using disk cutters are moved along the pipe. The metal carrier pipe 3 is not affected, so as not decreased structural strength, only the edges are cut and planted the pipe 2, which has been rolled edges.

Because screw the knurled or wrapped edges are slightly inclined to the pipe axis, the vertical position of the pipe they have an inclination relative to the horizon, thanks to that formed by the condensation under the action of capillary forces to flow to the slots in Ebre, and then on the cracks on the bottom pipe of the Board of the heat exchanger, which establishes the finned tube. This eliminates the flow of condensate in the form of droplets from a pipe on the pipe, and means, and drift.

Failure of a film of water with a horizontal surface washing its parallel stream of products of combustion begins according to [J.J. van Rossum Experimental investigation of horizontal liquid films//Chemical Engineering Science, 1959. V. 11. P. 35 - 52] at a flow rate of greater than 18 m/s, even when the film thickness of the condensate 2.5 mm With decreasing film thickness the marginal rate of breakdown increases. Such large velocity gas mixture in heat exchangers are not used because of the sharp increase in aerodynamic resistance of the bundle of finned tubes, which guarantees the absence of breakdown of the film with horizontal ribs.

In accordance with the proposed technical solution (figure 3), the pipe is fixed in the tube plate so that the slots 4 in the ribs was placed along the back with respect to the incident flow of gases 5 of the pipe. This reduces the probability of dynamic failure flowing down along the slots of the condensate.

The lower tubular lattice restricts the top of the camera that receives the cooling water flowing from this camera on finned tubes.

If the water has a temperature below the dew point of water vapor, soderjaschihsya gas mixture (and only in this case, the possible condensation of the steam in the heat exchanger), flowing from the pipe on the grill condensate to evaporate not. On the contrary, the steam from the steam-gas mixture will condense on the lattice as well as on finned tubes.

To ensure free drainage of condensate from the tube in the outlet, the grill must be tilted a few degrees to the horizon and to have a small flange which prevents the swelling around the perimeter of the grid.

The technical result of the invention is:

- get more heat when deep cooling of the combustion products of natural gas through condensation of the contained water vapor;

- obtaining of products of combustion of demineralized water (about 1 liter of 1 m3burned gas), which, after deaeration, can be used to power steam boilers or other purposes;

- water vapor remaining in the combustion products, is overheated (not saturated) state that preclude condensation on the inner surfaces of insulated flues and chimneys.

This design was tested in the boiler room of Experimental-industrial complex of Ural state technical University.

A heat exchanger for cooling the gas-vapor mixture, consisting of pipes with spiral ribs, characterized in that along the C pipes all the ribs are made of longitudinal slots, and pipes in the heat exchanger are arranged vertically.



 

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