TECHNICAL FIELD

The present invention relates to a seal gas supply control method, a seal gas supply control apparatus, and a rotary machine.

Priority is claimed on Japanese Patent Application No. 2014-235452, filed on Nov. 20, 2014, the content of which is incorporated herein by reference.

BACKGROUND ART

In rotary machines such as a centrifugal compressor, there is a rotary machine in which an end portion of a rotary shaft protrudes outside a casing so as to input and output a rotation of the rotary shaft rotatably provided in the casing. In this rotary machine, it is necessary to prevent a working fluid inside the casing from leaking from a gap between the rotary shaft and a shaft insertion hole which is formed in the casing and through which the rotary shaft penetrates the inside and the outside of the casing to the outside of the casing and to prevent foreign matters or like from entering the inside of the casing from the outside. Accordingly, a configuration in which a dry gas seal portion is provided between the rotary shaft and the casing is used.

The dry gas seal portion includes a rotary ring and a stationary ring. The rotary ring is integrally provided with the rotary shaft on an outer periphery portion of the rotary shaft. The stationary ring is fixed to the casing and is provided to face the rotary ring in an axial direction of the rotary shaft. The stationary ring is pressed toward the rotary ring by a coil spring or the like. Accordingly, the stationary ring and the rotary ring abut on each other in a state where the rotary machine stops. Spiral grooves are formed on a surface of the rotary ring facing the stationary ring. If the rotary shaft rotates in a state where the rotary machine is operated and a seal gas is supplied, the seal gas is introduced into a portion between the rotary ring and the stationary ring through the spiral grooves. The stationary ring is pressed in the axial direction of the rotary shaft against a biasing force of the coil spring by a pressure of the seal gas. Accordingly, a minute clearance is generated between the rotary ring and the stationary ring. The seal gas flows from a supply portion side to which a supply pipe for supplying the seal gas to the inside of the machine through the clearance is connected toward the outside of the machine to which a vent for evacuating the seal gas is connected, and thus, a portion between the rotary shaft and the casing is sealed. In this case, the supply pressure is higher than an external pressure of the machine such that the seal gas flows from the supply portion side to the outside of the machine.

In the dry gas seal portion, the seal gas which flows from the supply portion side toward the outside of the machine through the clearance between the rotary ring and the stationary ring is evacuated from a flare (funnel) to the outside through the vent which is connected to the casing.

A gas or the like evacuated from a device installed in a plant in addition of the rotary machine is fed to the flare and may be evacuated to the outside along the seal gas. According to a kind of the gas, the gas may be combusted in the vicinity of an outlet of the flare. If the gas or the like is fed to the flare from the device in addition to the rotary machine or the gas is combusted, a pressure inside the vent increases. If the pressure inside the vent is higher than the supply pressure, the external pressure of the machine is higher than the supply pressure, the seal gas backflows in the clearance between the rotary ring and the stationary ring. As a result, in the dry gas seal portion, the clearance is not formed between the rotary ring and the stationary ring, and the rotary ring and the stationary ring are likely to come into contact with each other and to be damaged.

PTL 1 discloses a configuration which includes an accumulator which absorbs gas which backflows from a tip side of a flare when an increase in a pressure on the flare side occurs. Accordingly, it is possible to prevent a gas from flowing from the tip side of the flare to a dry gas seal portion.

A configuration is also adopted, which includes a vent pressure detection sensor which detects a pressure in a vent, a seal gas pressure detection sensor which detects a supply pressure, and a pressure adjustment valve which adjusts a pressure of a supplied seal gas.

In this configuration, in a case where the pressure in the vent is higher than the pressure on the supply portion side, an opening degree of the pressure adjustment valve is adjusted to increase the pressure of the supplied seal gas. Accordingly, the supply pressure increases, the supply pressure is higher than the external pressure (vent pressure) of the machine, and thus, the backflow of the seal gas in the dry gas seal portion is prevented.

CITATION LIST

Patent Literature

[PTL 1] US Unexamined Patent Application Publication No. 2007/0147988

SUMMARY OF INVENTION

Technical Problem

However, it is not understood how much the vent pressure due to other devices in addition to the rotary machine increases. For example, in a case where a safety valve is operated due to other devices such as a pressure container and a pressure is released, the increase in the vent pressure due to the gas fed into the flare through the safety valve becomes abrupt. In this case, even when the opening degree of the pressure adjustment valve is adjusted, the increase of the internal pressure of the machine is likely to be late for the increase in the vent pressure. As a result, the seal gas backflows, and the rotary ring and the stationary ring are likely to collide with each other.

The present invention provides a seal gas supply control method, a seal gas supply control apparatus, and a rotary machine in which it is possible to prevent the external pressure of the machine from being higher than the supply pressure and it is possible to increase reliability of the rotary machine even when an abrupt increase in the vent pressure occurs.

Solution to Problem

According to a first aspect of the present invention, there is provided a seal gas supply control method with respect to a dry gas seal portion which seals the inside and outside of a rotary machine by a seal gas. The seal gas supply control method includes: a step of detecting a pressure difference between an internal pressure of the rotary machine and a supply pressure of the seal gas with respect to the dry gas seal portion; a step of adjusting an opening degree of a seal gas supply valve which supplies the seal gas to the inside of the rotary machine on the basis of the detected pressure difference between the internal pressure and the supply pressure; and a step of detecting a pressure of a vent portion, which discharges the seal gas evacuated from the dry gas seal portion to the outside, on the outside of the rotary machine of the dry gas seal portion. In the seal gas supply control method, the seal gas supply valve fully opens when the detected vent pressure satisfies a predetermined condition.

In this case, in the case where the vent pressure satisfies the predetermined condition, the seal gas supply valve fully opens, and it is possible to cause the supply pressure of the seal gas to be the maximum. Accordingly, even when an abrupt increase in the vent pressure occurs, it is possible to reliably prevent backflow of the seal gas in the dry gas seal portion.

In the seal gas supply control method according to a second aspect of the present invention, in the first aspect, the predetermined condition may be a condition in which the pressure difference between the vent pressure and the supply pressure of the seal gas is less than a predetermined threshold value.

According to this configuration, in a case where the pressure difference of the seal supply pressure with respect to the vent pressure is small, that is, the vent pressure is high, the seal gas supply valve fully opens.

In the seal gas supply control method according to a third aspect of the present invention, in the first aspect, the predetermined condition may be a condition in which the vent pressure exceeds a predetermined threshold value.

According to this configuration, the seal gas supply valve fully opens if the vent pressure exceeds the predetermined threshold value without detecting the pressure difference between the vent pressure and the seal supply pressure.

According to a fourth aspect of the present invention, there is provided a seal gas supply control apparatus with respect to a dry gas seal portion which seals the inside and outside of a rotary machine by a seal gas. The seal gas supply control apparatus includes: seal gas differential pressure detection means for detecting a pressure difference between an internal pressure of the rotary machine and a supply pressure of the seal gas with respect to the dry gas seal portion; seal gas pressure adjustment means for adjusting an opening degree of a seal gas supply valve which supplies the seal gas to the inside of the rotary machine on the basis of the detected pressure difference between the internal pressure and the supply pressure; and vent pressure detection means for detecting a pressure of a vent portion, which discharges the seal gas evacuated from the dry gas seal portion to the outside, on the outside of the rotary machine of the dry gas seal portion. The seal gas supply control apparatus fully opens the seal gas supply valve when the detected vent pressure satisfies a predetermined condition.

According to a fifth aspect of the present invention, there is provided a rotary machine, including: a rotary shaft which penetrates the inside and outside of a casing and is rotatably provided; a rotary ring which integrally rotates with the rotary shaft; a stationary ring which is provided in the casing, abuts on the rotary ring over the entire periphery when the rotary shaft stops, and forms a seal clearance between the stationary ring and the rotary ring when the rotary shaft rotates; a seal gas supply path which supplies a seal gas to the seal clearance; a vent portion which discharges the seal gas evacuated from the seal clearance to the outside on the outsides of the rotary machine of the rotary ring and the stationary ring; a seal gas supply valve which adjusts a supply pressure of the seal gas in the seal gas supply path; and a controller which adjusts an opening degree of the seal gas supply valve. The controller detects a vent pressure which discharges the seal gas evacuated from the seal clearance to the outside and fully opens the seal gas supply valve when the detected vent pressure satisfies a predetermined condition.

Advantageous Effects of Invention

According to the above-described seal gas supply control method, seal gas supply control apparatus, and rotary machine, in the case where the vent pressure satisfies the predetermined condition, the seal gas supply valve fully opens, and it is possible to cause the supply pressure of the seal gas to be the maximum. Accordingly, even when an abrupt increase in the vent pressure occurs, it is possible to reliably prevent backflow of the seal gas in the dry gas seal portion.

