Process gas compressor/gas turbine section

A process gas compressor/gas turbine section including a process gas compressor and a gas turbine which is coupled to the shaft of the process gas compressor in order to drive said compressor is provided. The process gas compressor is designed to compress combustible process gas and is equipped to seal the process gas compressor inner chamber from the atmosphere using a shaft seal which can be sealed with a seal gas and which has at least one leakage line. The leakage line can conduct leakage gas away from the shaft seal and is connected to the air inlet of the gas turbine such that the leakage gas together with the inlet air at the air inlet can be conducted into the gas turbine during the operation of the process gas compressor/gas turbine section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/EP2013/069921, having a filing date of Sep. 25, 2013, based on DE 102012219520.3 having a filing date of Oct. 25, 2012, the entire contents of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a process gas compressor/gas turbine section, in which the process gas compressor is provided to compress combustible process gas.

BACKGROUND

A process gas compressor has a housing and a rotor which is accommodated in the housing. The rotor has a shaft which is mounted at the longitudinal ends thereof outside the housing. As a result, the shaft passes at the longitudinal ends thereof through the housing, wherein the shaft is sealed there from the housing by a shaft seal. The inside of the process gas compressor is therefore separated from the atmosphere. The construction of the shaft seal is conventionally such that a gas separation is arranged first, followed by an oil separation, as viewed from the inside of the process gas compressor. The inside of the process gas compressor, the process side, is separated from the atmosphere by means of the shaft seal and from the bearing region by means of the oil separation. The shaft seal is constructed, for example, as a gas-lubricated rotating mechanical seal which is designed as a tandem seal.

A tandem seal is constructed from two gas-lubricated rotating mechanical seals which each have a sliding ring, which is fastened to the housing, and a counter ring, which is fastened to the shaft. Each sliding ring is arranged axially directly adjacent to the associated counter ring thereof, forming an axial gap. The rings are arranged in the tandem seal in such a manner that the process side is sealed from a flare pressure by the primary seal. The separation from the atmosphere is brought about with the secondary seal, wherein the secondary seal is additionally provided as redundancy to the primary seal in the event of failure of the primary seal. Seal gas which is used for sealing the axial gaps is introduced between the two counter rings. In order to separate the bearing region, a tertiary seal, for example, which can be constructed, for example, as a labyrinth seal or a carbon ring seal, is provided as the oil separation. The tertiary seal is acted upon with a seal gas, as a result of which the sealing of said tertiary seal is brought about.

Process gas can be used as the seal gas for the primary seal, and air or nitrogen can be used for the secondary seal. During the operation of the process gas compressor, leakage gas occurs because of a leakage of the primary seal and the secondary seal. The leakage gas is a gas mixture consisting of the process gas and the seal gas together with air, wherein the leakage gas is conventionally conducted away to the atmosphere or to a flare. These two variants are problematic for the environment by being associated with undesirable emissions to the surroundings. Although the provision of a system for separating the process gas from the leakage gas and for recycling the process gas into the process provides a remedy, such a system is, however, energy-intensive and is associated with high costs.

SUMMARY

An aspect relates to a process gas compressor/gas turbine section which has a low emission loading.

The process gas compressor/gas turbine section according to the embodiment of the invention has a process gas compressor and a gas turbine which is coupled to the shaft of the process gas compressor in order to drive said compressor, wherein the process gas compressor is designed to compress combustible process gas and is equipped to seal the process gas compressor inner chamber from the atmosphere with a shaft seal which can be sealed with a seal gas and which has at least one leakage gas line with which leakage gas can be conducted away from the shaft seal and which is connected to the air inlet of the gas turbine such that the leakage gas together with inlet air at the air inlet can be conducted into the gas turbine during the operation of the process gas compressor/gas turbine section.

The process gas compressor/gas turbine section is designed in such a manner that the leakage gas is supplied to the air inlet of the gas turbine. As a result, the leakage gas is mixed with the inlet air of the gas turbine and enters the compressor of the gas turbine. In the compressor, the air/leakage mixture is compressed and supplied to the combustion chamber of the gas turbine. The flame formed in the combustion chamber comes into contact with the leakage gas, and therefore the process gas portion in the leakage gas is burned in the combustion chamber. As a result, the process gas portion in the leakage gas is thermally utilized in the combustion chamber, and thus helps the driving power of the gas turbine. In addition, the leakage gas does not need to be supplied, for example, to a flare or to the atmosphere, and therefore the emission loading of the environment is reduced.

The shaft seal preferably has a process-side primary seal and an atmosphere-side secondary seal, wherein the primary seal and the secondary seal each have one of the leakage lines. The leakage line for the secondary seal preferably has an atmosphere line and a changeover member which is designed in such a manner that, during the normal operation of the shaft seal, the atmosphere line is connected in a fluid-conducting manner to the secondary seal for conducting leakage gas away from the secondary seal to the atmosphere, and, if the sealing effect of the secondary seal fails, the leakage line is connected in a fluid-conducting manner to the secondary seal for conducting leakage gas away from the secondary seal to the air inlet. It is preferred that the changeover member has a diaphragm in the atmosphere line and a bursting disk in the leakage line between the connection of the atmosphere line to the leakage line and the air inlet. Alternatively, it is preferred that the changeover member is a three-way directional control valve which is arranged at the connection of the atmospheric line to the leakage line.

The shaft seal is preferably a gas-lubricated rotating mechanical seal. It is preferred in this connection that the gas-lubricated rotating mechanical seal is realized in a tandem arrangement. In addition, it is preferred that the process gas compressor is a pipeline compressor.

DETAILED DESCRIPTION

As is apparent from the figures, a compressor/gas turbine section1has a process gas compressor2of turbocompressor design and a gas turbine3. The process gas compressor is, for example, a pipeline compressor for compressing natural gas. The gas turbine3has a compressor5for compressing inlet air, a turbine5for obtaining shaft output and a combustion chamber6. Furthermore, at the compressor inlet, the gas turbine3has an air inlet7via which ambient air is conducted to the compressor4. Exhaust gas is conducted away from the turbine5via an exhaust gas outlet8. The turbine5furthermore has a shaft9which is coupled by means of a coupling10to the shaft of the process gas compressor2and thereby drives the process gas compressor2.

The shaft of the process gas compressor2is mounted on both sides by means of bearings11. In order to seal the interior of the process gas compressor5from the atmosphere and from the bearings11, shaft seals12which are realized as gas-lubricated rotating mechanical seals in a tandem construction are provided on the shaft.

The shaft seals12each have a primary seal13, a secondary seal14and a tertiary seal15. The primary seal13seals off the process side of the process gas compressor2whereas the tertiary seal15seals off the bearing11. The secondary seal14is arranged between the primary seal13and the tertiary seal15and is provided as a support and protection of the primary seal13. If the primary seal13namely fails, the process pressure is first of all applied to the secondary seal14and not to the tertiary seal15which is conventionally formed by carbon rings and therefore because of the construction would not withstand the process pressure. In addition, the secondary seal14prevents the process gas from being able to enter the bearings11and therefore the atmosphere if the primary seal13fails.

The shaft seal furthermore has a process gas seal line16and a seal gas line17(the seal gas line differs from the process gas line because of the seal gas which does not have to be process gas and is preferably not process gas). The seal gas line can basically be operated with various gases, wherein inert gas (for example nitrogen) is preferred in some applications. In the process gas seal line16, process gas is present at a pressure which is somewhat higher than the process pressure present on the process side. In the seal gas line17, seal gas—optionally inert gas—is present at a pressure which is higher than the atmospheric pressure. The process gas seal line16is conducted onto the primary seal13, and therefore the primary seal13is sealed by the process gas. Analogously, the seal gas line17is conducted onto the tertiary seal15such that the tertiary seal15is sealed with the seal gas.

A primary leakage line18with which leakage of the primary seal13is conducted away from the shaft seal12is provided between the primary seal13and the secondary seal14. Owing to the fact that the primary seal13is acted upon with process gas, the leakage of the primary seal consists of process gas. Furthermore, a secondary leakage line19is provided between the tertiary seal15and the secondary seal14. With said secondary leakage line19, leakage of the secondary seal14and of the tertiary seal15is conducted away from the shaft seal12. Owing to the fact that the secondary seal is acted upon from the primary seal13with process gas, the leakage of the secondary seal14consists of process gas. In an analogous manner, the leakage of the tertiary seal15consists of inert gas. The leakage collected by the secondary leakage line19is therefore a mixture of process gas and inert gas.

The primary leakage lines18and the secondary leakage lines19are conducted to the air inlet7, and therefore the leakage flows in the primary leakage lines18and the secondary leakage lines19are supplied to the inlet air of the compressor4. The leakage gas flows are thereby mixed with the inlet air of the gas turbine3and pass into the compressor4. In the compressor4, the air/leakage mixture is compressed and supplied to the combustion chamber6. The flame formed in the combustion chamber6burns the process gas portion in the leakage gas. As a result, the process gas portion in the leakage gas is thermally utilized in the combustion chamber6and thus helps the driving power of the gas turbine3.

A shaft seal monitoring system26monitors and controls the operation of the shaft seals12, wherein the operating conditions can correspond to a design operating state or to an off-design operating state. Furthermore, the operation of the gas turbine3is monitored and controlled by a gas turbine monitoring system27. The gas turbine monitoring system27preferably has a gas analysis unit with which the composition of the air at the air inlet7can be measured. In principle, a gas analysis is not required because the shaft seal monitoring system26recognizes on the basis of the turbine load and the leakage at the shaft seals whether the leakage is still safe or not—as described below.

It is conceivable for the primary leakage lines18and the secondary leakage lines19to be connected to a flare20via a valve22. This creates the option that, by actuation of the valve22, the leakage flows in the primary leakage lines18and the secondary leakage lines19are not supplied to the air inlet7, but rather to the flare22. In the flare22, the process gas portion of the leakage flows is burned and the resulting combustion products are emitted into the atmosphere.

The conducting away of the leakage gas flows to the flare20is necessary, for example, whenever an ignitable mixture would form in the compressor4because of the introduction of the process gas leakage into the air inlet7. This should absolutely be avoided since there is the risk here of the flame penetrating from the combustion chamber6through the compressor4. For this purpose, the gas analysis unit with which the igniting risk in the air inlet7and in the compressor4can be measured is provided at the air inlet7. If, during the operation of the compressor/gas turbine section1, it is determined by the gas analysis unit that there is an impermissibly high ignition risk, the valve22is actuated by the gas turbine monitoring system27, as a result of which the leakage flows are conducted to the flare20instead of into the air inlet7.

It is conceivable that the secondary leakage lines19are additionally connected to a chimney21via a valve25as a changeover member by means of which the leakage gas flows in the secondary leakage lines19can be conducted away to the atmosphere. Downstream of the connection of the chimney21and before the air inlet7, a further valve24is installed as a further changeover member in the secondary leakage line19. Furthermore, an additional valve23is installed between the integration of the flare20into the primary leakage line18and the air inlet7.

The valves22to25are activated by the shaft seal monitoring system27such that leakages in the primary leakage line18and the secondary leakage line19can be supplied to the air inlet7in coordination with the currently prevailing operating state. The valves22and23and also the valves24and25can in each case be designed as a three-way directional control valve.

The valve24could be designed as a bursting disk and the valve25as a diaphragm. If the primary seal13and the secondary seal14fail, the process pressure penetrates to the secondary leakage lines19. Pressure dissipation via the chimney21is prevented by means of the diaphragm25, and therefore the bursting disk24bursts. The secondary leakage lines19are therefore connected to the air inlet, as a result of which the leakage gas flows in the secondary leakage lines19are supplied for thermal utilization not by the chimney21but rather to the air inlet7.

The fuel consumption of the process gas compressor3during use as a pipeline compressor for natural gas is typically 200 kg/MWH of natural gas. The fuel/air ratio is typically 1:10. The process gas leakage rate of the shaft seal is typically 5 to 10 kg/hour. The power of the gas turbine3is typically 10 MW, wherein the process gas portion in the air inlet flow is approx. 0.05%. The process gas compressor/gas turbine section1is typically switched off when the leakage rate of one of the shaft seals12is five times the value in relation to the normal operating state. In this case, the process gas portion in the air inlet flow is approx. 0.5%. For safety reasons, the process gas portion in the air inlet flow is monitored by the gas analysis unit.