Control system and method for pressure-let-downs stations

A method for depressurizing a gas in a pipeline, comprising the following steps:

• delivering a gas through a heat exchanger and an expander;
• heating the gas in the heat exchanger by delivering thereto heat from a heat pump through a heat transfer fluid circulating in a heat transfer circuit and in heat ex-change relationship with the gas and with a working fluid processed by the heat pump;
• expanding the gas from a first pressure to a second pressure in the expander and generating mechanical power therewith;
• and
• modulating a flow rate of the heat transfer fluid in the heat transfer circuit to minimize a difference between a first temperature differential between the gas and the heat transfer fluid at a gas inlet side of the heat exchanger and a second temperature differential between the gas and the heat transfer fluid at a gas outlet side of the heat exchanger.

A system for depressurizing a gas in a pipeline, comprising:

• an expander configured and arranged for generating mechanical power by expanding gas from a first pressure to a second pressure, the first pressure being higher than the second pressure;
• a heat pump;
• a heat transfer circuit having a heat transfer fluid circulating therein to receive heat from the heat pump and deliver the heat to the gas through a heat exchanger;
• and
• a controller configured to modulate a flow rate of the heat transfer fluid circulating in the heat transfer circuit when a first temperature differential between the gas and the heat transfer fluid at a gas inlet side of the heat exchanger varies from a second temperature differential between the gas and the heat transfer fluid at a gas outlet side of the heat exchanger to minimize the difference between the first temperature differential and the second temperature differential.