XI Международная студенческая научная конференция Студенческий научный форум - 2019

There are three main ways to save energy:

multiple-effect evaporation;

the use of thermal compression;

the use of mechanical compression.

Using one of these methods can significantly reduce energy consumption and improve energy efficiency of TP. It is often possible to combine these two methods to reduce capital and operating costs. In the most complex evaporation plants, all three methods can be used. In the development of Multihull evaporators (MBUS) it often happens that the available total useful temperature head on the MBUS is small, and the increase in the number of MBUS is limited by the inability to further reduce the temperature head on the body. For example, for Mbps used in the production of concentrates, the maximum temperature of the product in the first evaporator casing is in the range of 70-75 °C under the conditions of ensuring the quality of the concentrate, and the minimum temperature in the condenser is usually limited to 40 °with the use of recycled water as a refrigerant. In such cases, to increase the energy potential of secondary vapors can be used its compression, carried out in one way or another.

In practice, in order to increase the energy efficiency coefficient of evaporation plants, secondary steam compression by steam-jet compressors is used. Despite the fact that compressors of this type have low (25-30 %) thermodynamic efficiency, these devices are widely used, primarily due to the simplicity of design, small size, and therefore low price.

In these devices, the process of injection is carried out – the transfer of kinetic energy from one flow to another flow-by direct mixing. The flow of the working (active) medium, which has a large resting pressure, acquires due to this pressure in a special working nozzle a high speed (usually supersonic Laval nozzles are used).

The operation of jet compressors is characterized by the following main parameters: the compression ratio, the degree of expansion and the injection coefficient , i.e. the ratio of the mass flow of secondary and acute steam.

For fig.1the section of the steam-jet compressor is shown, which consists of three main parts: nozzle 4, suction chamber 3, and diffuser 6, 7, 8.

Fig. 1. Steam-jet compressor:

1-flange; 2-nozzle holder; 3-suction chamber; 4-nozzle; 5-flanges; 6,7,8-diffuser

The input part of the diffuser is called confusor or displacement chamber. Sharp steam with pressure P is fed to the nozzle 4. Passing through the skull nozzle, the steam expands, its pressure drops, and the speed increases to 1000 m/sec and above. Coming out of the nozzle at high speed, the steam flies through the suction chamber into the diffuser, dragging the secondary steam along the way. In the diffuser, the vapor velocity decreases, and its pressure increases, i.e. the compressor operates on the principle of converting potential energy into kinetic energy in the nozzle and Vice versa, kinetic energy into potential energy in the diffuser.

For fig. 2 shows the process of expansion of sharp steam in the nozzle and the process of its compression in the diffuser in the I-s diagram. Point A characterizes the initial parameters of the sharp vapor in front of the nozzle. On the AB line, equal to h, there is an adiabatic expansion of steam in the nozzle with a pressure drop to the pressure in the suction chamber. When the steam moves in the nozzle, part of the kinetic energy is lost to friction and converted into heat, so in reality the expansion of the steam is characterized by a polytropic AU line.In a medium-sized nozzle, the conversion of kinetic energy into thermal energy is 0,1 h , so, putting from the point b up 0.1 h , we obtain a point D. by Conducting a horizontal from the point D to the Isobaric P, we obtain a point C, the steam parameters in which correspond to the end of the expiration of the nozzle. The nozzle is supplied steam, but at the exit from the nozzle, the options change. Correct steam call work, then throughout the jet steam will match this name.

Secondary steam is supplied to the chamber usually perpendicular to the jet of the working steam and its speed is negligible, while the speed of the working steam at the outlet of the nozzle is huge. Therefore, the inelastic impact of the working steam jet on the secondary steam jet with the loss of kinetic energy and an increase in the heat content of the steam is inevitable. The compression process starts from point s, and above on isobare R from the point M. the Line MN=h characterizes the adiabatic compression process steam in the diffuser. In the diffuser, there will also be losses of kinetic energy for friction with an inevitable increase in the heat content of the steam, and the actual compression process will go along the MN line .

The disadvantages of steam-jet compressors (except for low thermodynamic efficiency) include the inevitable mixing of condensates of primary and secondary steam. In the vast majority of cases, the mixed condensate has a composition that does not allow it to be returned to the heat point without passing the water treatment stage, which increases the cost of heating steam. In addition, in order to achieve injection coefficients close to 2, even in a vacuum MVU, a vapor of sufficiently high pressure – over 1

MPa-should be available.

Jet compressors used to increase the parameters of secondary steam, in their properties occupy an intermediate value between the steam jet ejectors and injectors. They work in ranges of compression ratios of 1,2–2,5 and ratios of injection of 0.7–2 . Structurally, these are jet devices with a cylindrical mixing chamber, which can have an embarrassing section of one or another length.

Fig. 2. Compressor operation in I-s diagram

Another way to increase the energy potential of secondary steam is to compress it with a mechanical compressor of some type: piston, rotary or, more often, a turbocharger. These machines reach a sufficiently large thermodynamic efficiency: 80-85 % at a productivity of not less than 14 000 m /min. But at a lower performance efficiency loss (not more than 75 % for 1000 m /min). High efficiency of mechanical compressors with high performance evaporators allows them to be used even in combination with a single-hull evaporator.

Literature

Bezzubtsev M. M. Electrotechnology Electrotechnology and installation: a tutorial, 2012. – SPb.: Spbgau, 242 p.

Bezzubtseva M. M., Volkov V. S., Spirkin A. G., Fokin S. A. Power engineering of technological processes-textbook, 2011. – SPb.: Spbgau, 265 p.

Bezzubtsev M. M., Volkov V. S., Zubkov V. V., Applied the theory of heat and mass transfer processes in the system analysis of the energy intensity of production: – textbook, 2013. – SPb.: Spbgau, 131 p.

Bezzubtseva M. M., Karpov V. N., Volkov V. S. Energy security of agriculture-textbook, 2012. – SPb.: Spbgau, 242 p.

Bezzubtsev M. M., Volkov V. S., Kotov A. V. energy-Efficient electrotechnologies in agricultural and environmental management study guide, 2012. – SPb.: Spbgau. - 260 p. (in the library)

Bezzubtseva M. M., Kovalev M. E. Electrical engineering of processing and storage of agricultural products – textbook, 2012. – SPb.: Spbgau. - 242 p.

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