Automated inlet steam supply valve controls for a steam turbine powered chiller unit

Abstract

A control system and method are provided for the controlling of steam supplies used by a steam turbine driven chiller unit. The steam turbine can receive steam from a high pressure steam source and/or a low pressure steam source depending on the operating mode of the steam turbine. The high pressure steam is used for operating at the steam turbine at rated speed and to provide the breakaway torque when starting the steam turbine. The low pressure steam is used for extending idling of the steam turbine that enables the steam turbine to transition more quickly to rated speed when desired.

1 . A method of starting a steam turbine driven chiller system having a high pressure steam supply and a low pressure steam supply, the method comprising the steps of:
 executing a starting sequence for the steam turbine;   initiating a slow roll of the steam turbine using the high pressure steam supply;   transitioning from the high pressure steam supply to the low pressure steam supply; and   slow rolling the steam turbine at a predetermined slow roll speed using the low pressure steam supply.   
   
   
       2 . The method of  claim 1  wherein the step of initiating a slow roll of the steam turbine includes opening a governor valve of the steam turbine. 
   
   
       3 . The method of  claim 2  wherein the step of initiating a slow roll of the steam turbine further includes opening a high pressure steam inlet supply valve in response to the governor valve being opened to a predetermined position. 
   
   
       4 . The method of  claim 1  wherein the step of transitioning from the high pressure steam supply to the low pressure steam supply includes operating the steam turbine using the high pressure steam supply for a predetermined time period. 
   
   
       5 . The method of  claim 4  wherein the step of transitioning from the high pressure steam supply to the low pressure steam supply further includes the steps of:
 opening a low pressure inlet steam supply valve in response to the predetermined time period expiring; and   closing a high pressure inlet steam valve in response to the low pressure steam inlet supply valve beginning to open.   
   
   
       6 . The method of  claim 5  wherein the step of slow rolling the steam turbine at a predetermined slow roll speed using the low pressure steam supply includes positioning the low pressure inlet steam supply valve to maintain the predetermined slow roll speed. 
   
   
       7 . The method of  claim 1  wherein the step of slow rolling the steam turbine at a predetermined slow roll speed using the low pressure steam supply includes slow rolling the steam turbine at a predetermined slow roll speed for a predetermined time period. 
   
   
       8 . The method of  claim 1  wherein the predetermined slow roll speed is about 500 rpm. 
   
   
       9 . The method of  claim 1  further comprising the step of operating the steam turbine at a predetermined operational speed using the high pressure steam supply. 
   
   
       10 . The method of  claim 9  wherein the step of operating the steam turbine at a predetermined operational speed includes transitioning from the low pressure steam supply to the high pressure steam supply. 
   
   
       11 . The method of  claim 10  wherein the step of transitioning from the low pressure steam supply to the high pressure steam supply includes the steps of:
 opening a high pressure inlet steam supply valve;   closing a low pressure inlet steam valve in response to the high pressure steam inlet supply valve beginning to open; and   slow rolling the steam turbine at the predetermined slow roll speed using the high pressure steam supply for a predetermined time period.   
   
   
       12 . A method of initiating an idling mode in a steam turbine driven chiller system having a high pressure steam supply and a low pressure steam supply, the method comprising the steps of:
 executing a transition sequence for the steam turbine, the steam turbine operating at a rated speed using the high pressure steam supply prior to the transition sequence;   initiating an unload cycle for the chiller system;   transitioning from the high pressure steam supply to the low pressure steam supply; and   slow rolling the steam turbine at a predetermined idling speed using the low pressure steam supply, the predetermined idling speed being less than the rated speed.   
   
   
       13 . The method of  claim 12  wherein the step of executing a transition sequence for the steam turbine includes initiating a predetermined controlled stop time period. 
   
   
       14 . The method of  claim 13  wherein the step of executing a transition sequence for the steam turbine further includes the steps of:
 closing a high pressure steam inlet valve from a fully open position during the predetermined controlled stop time period; and   controlling the high pressure steam inlet valve with a control system in response to the high pressure steam inlet valve being closed to a predetermined position.   
   
   
       15 . The method of  claim 14  wherein the step of initiating an unload cycle for the chiller system occurs in response to the control system controlling the high pressure steam inlet valve. 
   
   
       16 . The method of  claim 13  wherein the step of initiating an unload cycle for the chiller system includes the steps of:
 increasing a leaving chilled water setpoint temperature for an evaporator of the chiller system;   decreasing the speed of the steam turbine to a predetermined turbine speed to avoid a surge condition in a compressor of the chiller system;   closing pre-rotation vanes of the compressor; and   opening a hot gas bypass valve of the chiller system.   
   
   
       17 . The method of  claim 16  wherein the step of transitioning from the high pressure steam supply to the low pressure steam supply occurs in response to one of the expiration of the predetermined controlled stop time period or the hot gas bypass valve being open more than a predetermined hot gas bypass valve position. 
   
   
       18 . The method of  claim 12  wherein the step of transitioning from the high pressure steam supply to the low pressure steam further includes the steps of:
 closing a high pressure inlet steam valve; and   controlling turbine speed with a low pressure steam inlet valve in response to the high pressure inlet steam valve being closed and the speed of the turbine being less than a predetermined first turbine speed, the predetermined first turbine speed being less than the rated speed and greater than the predetermined idling speed.   
   
   
       19 . The method of  claim 18  wherein the step of transitioning from the high pressure steam supply to the low pressure steam supply further includes the steps of:
 opening a hot gas bypass valve of the chiller system in response to the speed of the turbine being less than the predetermined first turbine speed;   starting a vacuum pump to establish a vacuum in the steam turbine in response to the speed of the turbine being less than the predetermined first turbine speed; and   stopping evaporator water flow in the chiller system, reducing condenser water flow in the chiller system and closing pre-rotation vanes of a compressor of the chiller system in response to the turbine speed being less than a predetermined second turbine speed, the predetermined second turbine speed being less than the predetermined first turbine speed.   
   
   
       20 . The method of  claim 12  wherein the predetermined idling speed is about 500 rpm. 
   
   
       21 . A chiller system comprising:
 a steam system comprising a high pressure steam supply, a low pressure steam supply, a steam turbine and a steam condenser connected in a steam loop;   a refrigerant system comprising a compressor, a refrigerant condenser, and an evaporator connected in a refrigerant loop, wherein the compressor is driven by the steam turbine;   a control panel to control operation of both the steam system and the refrigerant system, the control panel comprising a control system to operate the steam system in an idling mode using the low pressure steam supply; and   wherein idling mode operation results in the steam turbine operating at a predetermined slow roll speed and no substantial output capacity from the refrigerant system.   
   
   
       22 . The chiller system of  claim 21  wherein the high pressure steam supply provides steam within a range of about 90 psi to about 200 psi and the low pressure steam supply provides steam within a range of about 10 psi to about 20 psi. 
   
   
       23 . The chiller system of  claim 21  wherein the control system comprises a control algorithm configured to automatically control opening and closing of at least one of a high pressure steam inlet valve, a low pressure steam inlet valve, a turbine steam ring drain valve and a turbine gland seal steam system supply valve. 
   
   
       24 . The chiller system of  claim 21  wherein the control system is configured to transition the steam system from the idling mode to an operational mode using the high pressure steam supply and to transition the steam system from an operational mode using the high pressure steam supply to the idling mode. 
   
   
       25 . The chiller system of  claim 21  wherein the steam system comprises a governor valve and the control system is configured to automatically control opening and closing of the governor valve, a high pressure steam inlet valve and a low pressure steam inlet valve during the idling mode of operation.