RU2812878C2 - Reciprocating compressor stage - Google Patents

Abstract

FIELD: compressor technology.

SUBSTANCE: reciprocating compressor stage contains inlet and outlet valves, cooled suction and discharge cavities, a suction line pipe and discharge line pipe 3, a liquid-cooled heat exchange device in the form of tube bundle 5. A liquid-cooled heat exchange device in the form of tube bundle 5 is placed in the discharge cavity to provide additional cooling of the said cavity. The open cross-sectional area of the channels for the passage of gas through it must be no less than the area in the slot of the fully open exhaust valve.

EFFECT: improved isothermal efficiency of the stage.

1 cl, 2 dwg, 1 tbl

Description

The invention relates to compressor technology.

Compressors of static and dynamic compression are known. Dynamic compression compressors include axial and centrifugal ones, and static (volumetric) compression compressors include screw, membrane, rotary and piston (Dzitoev M.S., Penkov M.M. et al. Gas supply systems and vacuum technology: textbook. - St. Petersburg .: VKA named after A.F. Mozhaisky, 2010. - P. 23-36). A common disadvantage of existing positive displacement compressors is the insufficiently developed heat transfer surface from the compressed gases into the cooling system, for example, in the cylinder head.

In the field of low-flow compressors of high and medium pressure, the most widely used are volumetric compression compressors with liquid cooling, the main executive element of which is a stage containing a cylinder with adjacent suction and discharge cavities (see book M.I. Frenkel. Piston compressors / subtitle : Theory, design and fundamentals of design / 3rd ed., revised and supplemented L.: Mechanical Engineering 1969. - 744 pp., Fig. IV.2 (pages 112 and 113), Fig. IV.14 (page 122), Fig. VII.3 (p. 282), Fig. VII.5 (p. 284), Fig. VII.6 (p. 285), Fig. VII.23 e, h, and (p. 304) Fig. XI.4 (p. 630), Fig. XI. 17. (p. 652), Fig. XI. 18 (p. 654), Fig. XI.21 (p. 656)). In these figures, the suction and discharge valves are located on both the side and end surfaces of the cylinder.

The closest in technical essence (prototype) to the proposed device is the second stage of the hydrogen compressor, shown in Fig. XI. 17 (p. 652) in the book. Frenkel M.I. Piston compressors /subtitle: Theory, design and design principles /. 3rd ed., revised. and additional L.: Mechanical Engineering 1969. - 744 p.

The stage has inlet and outlet valves, cooled suction and discharge cavities, branch pipes of the suction and discharge lines, and a liquid-cooled heat exchange device in the form of a tube bundle.

The disadvantage of the prototype is the limited heat removal from the compressed gas in the injection cavity, which is completely determined by the area of its cooled surface. This leads to an increase in the mechanical work required to compress the gas.

In the stage, energy is supplied to the compressed gas in the form of work, and only part of the energy is removed from it in the form of heat. The work supplied to the gas can be determined by the relation

Cooling the gas as it is compressed during the cycle helps reduce mechanical work.

To assess the thermodynamic perfection of the stages of piston compressors with cooling, isothermal efficiency is used, the value of which is determined by the following relationship:

Where - specific work of isothermal compression;

- specific work of the actual compression process. If we neglect the friction forces in the stage and other factors influencing the irreversibility of the compression process, then the specific work of the actual compression process will be written as:

where C _p is the specific isobaric heat capacity of the compressible gas;

T _stn - gas temperature at the standard injection point;

_Тstv - gas temperature at the standard suction point.

Standard suction and discharge points are points located on the gas flow axis in the interface planes of the suction line branch pipe and the suction cavity and the discharge cavity and the discharge line branch pipe, respectively.

The gas temperature at the standard discharge point is one of the indicators of the technical perfection of the piston compressor stage.

From equation (3) it follows that as the gas temperature at the standard injection point T _stn decreases, the mechanical work will decrease and the isothermal efficiency will increase.

Thus, the value of the gas temperature at the standard discharge point is one of the indicators of the technical perfection of the piston compressor stage.

To reduce the gas temperature at the standard discharge point T _stn of the piston compressor stage, it is necessary to remove the heat generated during gas compression. This heat can also be removed through the walls of the injection cavity. In this case, the heat flow is formed due to the transfer of heat from the compressed gas to the walls of the injection cavity and then to the cooling system. Moreover, the greater the amount of heat transferred to the walls of the discharge cavity, the more efficiently the heat is removed from the compressed gas, and, consequently, the more the gas temperature at the standard discharge point of the piston compressor stage decreases.

The total heat flow from the compressed gas to the walls of the injection cavity can be expressed by the formula:

where F is the total area of the wall to which heat is supplied;

k - heat transfer coefficient;

T _OC is the temperature on the outside of the discharge cavity.

From formula (4) it is clear that the larger the area of the internal surface of the discharge cavity of the piston compressor stage, the greater the heat flow, and, consequently, the more efficiently heat is removed from the compressed gas.

By transforming formula (4), we can express the gas temperature at the standard discharge point T _stn of the piston compressor stage:

From formula (5) it is clear that the larger the heat exchange surface area in the discharge cavity, the lower the final gas temperature at the standard discharge point T _stn stage of the piston compressor.

The objective of the invention is to increase the isothermal efficiency of the stage by lowering the gas temperature at the standard discharge point T _STN of the piston compressor stage by developing a technical solution in the form of a device characterized by the following set of distinctive features.

The essential features common to the prototype are that the proposed stage of a piston compressor and the prototype have inlet and outlet valves, cooled suction and discharge cavities, suction and discharge line nozzles, and a liquid-cooled heat exchange device in the form of a tube bundle.

Distinctive essential features are: placement of a liquid-cooled heat exchange device in the form of a bundle of pipes in the discharge cavity (that is, directly behind the exhaust valve) to provide additional cooling of the specified cavity, while the open cross-sectional area of the channels for the passage of gas in this heat exchange device is not less than the area the slots of the fully open exhaust valve.

The combination of the listed essential features ensures obtaining a technical result, expressed in a decrease in the final gas temperature at the standard injection point of the 7 _STN stage of the piston compressor in the proposed device in comparison with the prototype.

The cause-and-effect relationship between the totality of the listed essential features and obtaining the specified technical result is as follows.

First, placing a liquid-cooled heat exchange device in the form of a tube bundle in the discharge cavity (that is, directly behind the exhaust valve) leads to an increase in the heat exchange surface area in the discharge cavity and to additional cooling of the gas entering this cavity from the cylinder through the exhaust valve . This increases the efficiency of heat removal from the gas in the injection cavity, since the heat flow from the compressed gas into the stage cooling system increases. As a result of these processes, the final gas temperature at the standard discharge point of the reciprocating compressor stage will decrease. As a result, in the discharge cavity, directly behind the stage exhaust valve, the gas density will increase and, as a result, its pressure will decrease. For this reason, provided that the pressure created by the stage piston in front of the exhaust valve remains unchanged, due to the simultaneous decrease in pressure behind the exhaust valve (due to its additional cooling), an increase in the pressure drop across this valve will occur. This will lead to an increase in isothermal efficiency, since to increase the pressure drop across the valve, the piston will not need to perform additional compression work. This circumstance helps to reduce the mechanical work on gas compression.

Secondly, the choice of the open cross-sectional area for the passage of gas in the channels of the mentioned liquid-cooled heat exchange device is not less than the area in the slot of a fully open exhaust valve, which allows minimizing gas-dynamic losses when the gas flow moves in the discharge cavity towards the discharge pipe of the given stage.

These circumstances also contribute to a reduction in mechanical work on gas compression.

The essence of the invention is illustrated by drawings - fig. 1 and fig. 2.

The positions on them indicate:

1 - cooled compression cavity;

2 - end cover;

3 - discharge line pipe;

4 - location of the standard injection point;

5 - heat exchange device with liquid cooling in the form of a bundle of pipes;

6 - coolant inlet;

7 - coolant outlet;

8 - gas inlet into the injection cavity.

In fig. Figure 1 shows the compression cavity of a compressor stage with cooled walls with a liquid-cooled heat exchange device placed in it in the form of a tube bundle. Arrows directed in the compression cavity from bottom to top indicate the movement of compressed gas. Horizontal arrows at the inlet and outlet of said heat exchange device, as well as arrows inside it, indicate the movement of the coolant.

In fig. Figure 2 shows a perspective view of a liquid-cooled heat exchange device in the form of a tube bundle. Vertical arrows indicate the movement of gas relative to the tubes of the bundle, horizontal arrows indicate the flow of coolant at the entrance to the heat exchange device and at the exit from it.

Let's consider the operation of the proposed piston compressor stage (Fig. 1). When the required compression pressure is reached, the exhaust valve opens and the compressed gas enters the injection cavity 1, where a liquid-cooled heat exchange device in the form of a tube bundle 5 is installed.

The compressed gas in the injection cavity passes through the annular space of the additional liquid-cooled device in the form of a bundle of pipes 5 and through the walls of its tubes releases heat into the coolant, which enters through the inlet 6 and exits through the output 7 of the liquid-cooled device in the form of a bundle of pipes 5, Next, the cooled compressed gas enters the injection line nozzle 3, at the center of the outlet of which there is a standard injection point 4.

The positive effect of the proposed device can be determined by comparing the final gas temperature at the standard discharge point of the piston compressor stage and the prototype stage.

To carry out the corresponding calculations, the KOMDET-VKA application program was used (Fundamentals of calculation and optimal design of piston compressors and expanders on unified bases: monograph / M.M. Penkov, I.K. Prilutsky, A.I. Prilutsky. - St. Petersburg: VKA named after A.F. Mozhaisky, 2020), based on mathematical modeling of work processes in compressor and expansion machines of positive displacement. This program has been comprehensively tested at a number of domestic enterprises and organizations. The calculation results are summarized in Table 1.

During the calculations, it was assumed that there were no external gas leaks through closed valves and no external leaks.

From Table 1 it can be seen that the final gas temperature at the standard injection point T _stn becomes significantly lower than that of the prototype.

Claims (1)

A stage of a piston compressor containing inlet and outlet valves, cooled suction and discharge cavities, branch pipes of the suction and discharge lines, a liquid-cooled heat exchange device in the form of a tube bundle, characterized in that the liquid-cooled heat exchange device in the form of a tube bundle is placed in the discharge cavity for providing additional cooling of the specified cavity, while the open cross-sectional area of the channels for the passage of gas in it must be no less than the area in the slot of the fully open exhaust valve.