Turbo-expander overspeed protection

A method for controlling a speed of a turbo-expander receiving a working fluid from an oxy-fuel combustor, the method comprising:

• using a first valve to modulate a flow of the working fluid through a first pipe, into the oxy-fuel combustor between a minimum working fluid flow rate and a maximum working fluid flow rate;
• holding a volume of the working fluid at an inlet pressure in the first pipe;
• detecting a condition where the turbo-expander accelerates above a maximum acceleration, above a maximum speed, or above both a maximum acceleration and a maximum speed;
• and
• responsive to detecting the condition, reducing a pressure differential across the turbo-expander using operations comprising:
• (i) sending an open signal to open a first diverter valve between the first pipe and a discharge chamber at an outlet pressure lower than the inlet pressure, and
• (ii) sending a close signal to close the first valve.

A system for preventing overspeed of a turbo-expander, comprising:

• an oxy-fuel combustor system comprising a first pre-combustor volume containing a working fluid stream, a second pre-combustor volume containing an oxidant stream, and a third pre-combustor volume containing a fuel stream, all connected to a combustor volume containing a combusting gas stream, the combustor volume connected to a turbo-expander volume containing a hot working fluid stream, wherein the oxy-fuel combustor system is configured to drive rotation of a shaft to drive a generator, wherein the pre-combustor volume is at a greater pressure than a dump volume, and wherein the dump volume is enclosed;
• a working fluid cut-off valve configured to control flow of the working fluid stream into the first pre-combustor volume;
• an oxidant cut-off valve configured to control flow of the oxidant stream into a second pre-combustor volume;
• a fuel cut-off valve configured to control flow of the fuel stream into a third pre-combustor volume;
• a first bypass valve configured to control flow of a working fluid vent stream from the first pre-combustor volume into the dump volume;
• and
• a controller configured to detect a load rejection and send a close signal to the working fluid cut-off valve, the fuel cut-off valve, and the oxidant cut-off valve to close, and send an open signal to the first bypass valve to open such that the working fluid is vented from the first pre-combustor volume to the dump volume, reducing a rotation speed of the shaft.

A method for preventing overspeed of a turbo-expander powered generator during load rejection, comprising:

• passing a working fluid stream through a working fluid cut-off valve, through a first pre-combustor volume, and into a combustor volume;
• passing an oxidant stream through an oxidant cut-off valve, through a second pre-combustor volume, and into the combustor volume;
• passing a fuel stream through a fuel cut-off valve, through a third pre-combustor volume, and into the combustor volume;
• mixing and combusting the working fluid stream, the oxidant stream, and the fuel stream in the combustor volume to create a hot working fluid stream;
• driving a turbine with the hot working fluid stream, the turbine driving a shaft at a rotation speed, the shaft driving a generator, and the generator generating electrical power;
• detecting a load rejection of the electrical power and sending an upset signal to a controller;
• sending a close signal from the controller to the working fluid cut-off valve, the oxidant cut-off valve, and the fuel cut-off valve;
• sending an open signal from the controller to a first bypass valve, the first bypass valve connecting the first pre-combustor volume to a dump volume, wherein the dump volume is at a lower pressure than the combustor volume;
• and
• venting the working fluid stream through the first bypass valve into the dump volume, reducing the rotation speed.

A system for preventing overspeed of a turbo-expander, comprising:

• an oxy-fuel combustor comprising a combustion output that provides a working fluid to a turbo-expander, where the combustor further comprising a fuel stream input port, an oxidant stream input port, and a working fluid stream input port
• where each of the fuel stream, the oxidant stream, and the working fluid stream ports are connected to a corresponding valve, such that the fuel stream valve, the oxidant stream valve, and the working fluid stream valve can modulate the flow of the respective fuel, oxidant, and working fluid streams entering the respective port between a minimum and maximum flow rate,
• and where a first piped connection between the working fluid stream valve and the working fluid stream port holds a volume of the working fluid stream;
• and where a second piped connection between the fuel stream valve and the fuel stream port holds a volume of the fuel stream;
• and where a third piped connection between the oxidant stream valve and the oxidant stream port holds a volume of the oxidant stream;
• wherein a pressure of the working fluid in the first piped connection prior to entry into the working fluid port is higher than a pressure at a discharge chamber;
• further comprising a diverter valve between the first piped connection and the discharge chamber where a controller detects a condition where the turbo-expander accelerates above a maximum acceleration, a maximum speed, or both, and the controller opens the diverter valve as the working fluid stream valve is closed, thereby reducing a pressure differential across the turbo-expander.

A method for preventing overspeed of a turbo-expander, comprising:

• providing an oxy-fuel combustor comprising a combustion output providing a working fluid to a turbo-expander, the oxy-fuel combustor further comprising a fuel stream input port, an oxidant stream input port, and a working fluid stream input port;
• modulating a flow of a fuel stream through the fuel stream input port via a fuel stream valve;
• modulating a flow of an oxidant stream through the oxidant stream input port via an oxidant stream valve;
• modulating a flow of a working fluid stream through the working fluid stream port via a working fluid stream valve;
• where the flows of the fuel stream, the oxidant stream, and the working fluid stream enter their respective port between a minimum and a maximum flow rate;
• and where a first piped connection between the working fluid stream valve and the working fluid stream port holds a volume of the working fluid stream;
• and where a second piped connection between the fuel stream valve and the fuel stream port holds a volume of the fuel stream;
• and where a third piped connection between the oxidant stream valve and the oxidant stream port holds a volume of the oxidant stream;
• wherein a pressure of the working fluid in the first piped connection prior to entry into the working fluid port is higher than a pressure at a discharge chamber;
• detecting a condition where the turbo-expander accelerates above a maximum acceleration, a maximum speed, or both, in a controller;
• and
• sending a signal via the controller to the diverter valve to open and the working fluid stream valve to close, thereby reducing a pressure differential across the turbo-expander.