Turboexpander and method for using moveable inlet guide vanes at compressor inlet
A turboexpander-compressor system includes an expander configured to expand an incoming gas, a first set of moveable inlet guide vanes configured to control a pressure of the incoming gas, a compressor configured to compress a gas received from the expander, a shaft configured to support and rotate an expander impeller and a compressor impeller, a second set of moveable inlet guide vanes attached to the compressor and configured to control a pressure of the gas input into the compressor, and a controller configured to acquire information about a rotating speed of the shaft, a pressure and a temperature of the incoming gas, a pressure and a temperature of the gas output from the expander, and to control the second set of moveable inlet guide vanes to maximize a ratio between the rotating speed of the shaft and a drop of an enthalpy across the expander, in off-design conditions.
1. A turboexpander-compressor system, the system comprising:
an expander configured to expand an incoming gas and having an expander impeller;
a first set of moveable inlet guide vanes attached to the expander and configured to control a pressure of the incoming gas;
a compressor configured to compress a gas received from the expander and having a compressor impeller;
a shaft configured to support and rotate the expander impeller and the compressor impeller;
a compressor set of moveable inlet guide vanes connected to a compressor inlet and through which the gas output by the expander enters into the compressor;
a controller connected to the moveable inlet guide vanes and configured to:
acquire information about a rotating speed of the shaft, the pressure and a temperature of the incoming gas, and a pressure and a temperature of the gas output by the expander, and
compare a ratio between the rotating speed of the shaft and a drop of an enthalpy across the expander with a predetermined value, when determined that the turboexpander-compressor system functions in the off-design conditions; and
control a compressor set of moveable inlet guide vanes connected to a compressor inlet through which the gas output by the expander enters into the compressor, to adjust a pressure of the gas input into the compressor such as to bring the ratio closer to the predetermined value.
2. The turboexpander-compressor system of claim 1 , wherein an expander efficiency is related to the ratio of the rotating speed of the shaft and the drop of the enthalpy across the expander.
3. The turboexpander-compressor system of claim 1 , further comprising:
a first sensor configured to measure the rotating speed of the shaft;
a second sensor configured to measure the pressure of the incoming gas;
a third sensor configured to measure the temperature of the incoming gas;
a fourth sensor configured to measure the pressure of the gas output by the expander; and
a fifth sensor configured to measure the temperature of the gas output by the expander,
wherein the drop in the enthalpy is estimated using the information achieved from the first, second, third, fourth and fifth sensors.
4. The turboexpander-compressor system of claim 1 , further comprising: a sensor located at an inlet of the compressor, connected to the controller and configured to measure a pressure of the gas input in the compressor.
5. The turboexpander-compressor system of claim 1 , wherein the controller is configured to determine when the turboexpander-compressor system functions in off-design conditions.
6. The turboexpander-compressor system of claim 1 , wherein the controller is configured to control the first set of moveable inlet guide vanes to maintain the pressure of the incoming gas in a predetermined range.
7. The turboexpander-compressor system of claim 1 , wherein the controller is configured to estimate the drop of the enthalpy across the expander using a function of the pressure of the incoming gas, the temperature of the incoming gas, a composition of the incoming gas, and the pressure of the gas output by the expander.
8. The turboexpander-compressor system of claim 1 , further comprising:
a casing configured to hold the expander, the shaft and the compressor at predetermined locations.
9. A method of controlling a turboexpander-compressor system having an expander with an expander impeller connected via a shaft to a compressor impeller of a compressor that compresses a gas flow output by the expander, the method comprising:
receiving first information on a pressure and a temperature of an incoming gas entering the expander;
receiving second information on a pressure of a gas output by the expander;
receiving third information on a rotating speed of the shaft attached to the compressor impeller and the expander impeller;
determining when the turboexpander-compressor system functions in off-design conditions based on the received first, second and third information;
comparing a ratio between the rotating speed of the shaft and a drop of an enthalpy across the expander with a predetermined value, when determined that the turboexpander-compressor system functions in the off-design conditions; and
controlling a compressor set of moveable inlet guide vanes connected to a compressor inlet through which the gas output by the expander enters into the compressor, to adjust a pressure of the gas input into the compressor such as to bring the ratio closer to the predetermined value.
10. The method of claim 9 , wherein an expander efficiency is related to the ratio of the rotating speed of the shaft and the drop of the enthalpy across the expander.
11. The method of claim 9 , wherein receiving the first information, second information, and third information comprises the use of a first sensor configured to measure the rotating speed of the shaft; a second sensor configured to measure the pressure of the incoming gas; a third sensor configured to measure the temperature of the incoming gas; a fourth sensor configured to measure the pressure of the gas output by the expander; and a fifth sensor configured to measure the temperature of the gas output by the expander, wherein the drop in the enthalpy is estimated using the information achieved from the first, second, third, fourth and fifth sensors.
12. The method of claim 9 , wherein measuring a pressure of the gas input in the compressor comprises using a sensor located at an inlet of the compressor, and connected to the controller.
13. The method of claim 9 , further comprising determining when the turboexpander-compressor system functions in off-design conditions.
14. The method of claim 9 , wherein further comprising estimating the drop of the enthalpy across the expander using a function of the pressure of the incoming gas, the temperature of the incoming gas, a composition of the incoming gas, and the pressure of the gas output by the expander.
15. A controller configured to control a turboexpander-compressor system having an expander with an expander impeller, and a compressor with a compressor impeller, the expander impeller and the compressor impeller being rotated by a same shaft, and the compressor compressing a gas output by the expander, the controller comprising:
an interface configured to,
receive information on a pressure and a temperature of an incoming gas entering the expander, a pressure and a temperature of the gas output by the expander, and a rotating speed of the shaft, and
output commands to a compressor set of inlet vanes configured to control a pressure of the gas input in the compressor; and
a control unit connected to the interface and configured to,
receive the first, second and third information from the interface,
determine when the turboexpander-compressor system functions in off-design conditions,
generate the commands for the compressor set of moveable inlet guide vanes to maintain a ratio between the rotating speed of the shaft and a drop of enthalpy across the expander within a predetermined range, in off-design conditions; and
control the compressor set of moveable inlet guide vanes to adjust a pressure of the gas input into the compressor such as to bring the ratio closer to the predetermined range.
16. The controller of claim 15 , wherein an expander efficiency is related to the ratio of the rotating speed of the shaft and the drop of the enthalpy across the expander.
17. The controller of claim 15 , wherein the controller is configured to use of a first sensor configured to measure the rotating speed of the shaft; a second sensor configured to measure the pressure of the incoming gas; a third sensor configured to measure the temperature of the incoming gas; a fourth sensor configured to measure the pressure of the gas output by the expander; and a fifth sensor configured to measure the temperature of the gas output by the expander, wherein the drop in the enthalpy is estimated using the information achieved from the first, second, third, fourth and fifth sensors.
18. The controller of claim 15 , wherein to measure pressure, the controller is configure to measure a pressure of the gas input in the compressor comprises using a sensor located at an inlet of the compressor, and connected to the controller.
19. The controller of claim 15 , wherein the controller is configured to determine when the turboexpander-compressor system functions in off-design conditions.
20. The controller of claim 15 , wherein the controller is further configured to estimate the drop of the enthalpy across the expander using a function of the pressure of the incoming gas, the temperature of the incoming gas, a composition of the incoming gas, and the pressure of the gas output by the expander.