Rankine system with gravity-driven pump

Abstract

A gravity-driven pumping unit has an inlet valve connected to a condenser, an outlet valve connected to a boiler, and a staging zone between the inlet and outlet valves. The inlet valve, the outlet valve, the liquid line and entire path established between the condenser and boiler are oriented, sized and shaped to allow for the vapor refrigerant to freely move upward from the boiler to the condenser and to allow for the liquid refrigerant to freely drain downwards from the condenser to the boiler by gravity. A control system opens and closes the inlet and outlet valves in a proper sequence, which enables gravity-driven movement of liquid refrigerant from the condenser to the staging zone and then from the staging zone to the boiler, against a positive pressure differential between the boiler and condenser.

1 . A Rankine system comprising:
 a closed-loop refrigerant cycle having an expansion machine, at least one condenser unit, at least one gravity-driven pumping unit, at least one boiler unit, and a control system;   said boiler unit providing thermal contact and heat transfer interaction between a fluid carrying enthalpy of available thermal energy and a liquid refrigerant;   said condenser unit providing thermal contact and heat transfer interaction between a fluid to be heated and a refrigerant vapor to be condensed;   said gravity-driven pumping unit having an inlet valve, an outlet valve, and a staging zone between said inlet valve and said outlet valve; said inlet valve being connected to said condenser unit and; said outlet valve being connected to said boiler unit; one of said inlet valve and outlet valve being a normally open valve and the other being designed for bi-directional operation;   said condenser unit being disposed at a higher elevation than that of said boiling unit;   said inlet valve, said outlet valve, and the entire path between said condenser unit and said boiler unit being oriented downwardly to allow vapor refrigerant to freely move upward from said boiler unit to said condenser unit and to allow liquid refrigerant to freely drain by gravity downwards from said condenser unit to said boiler unit;   said control system facilitating operation of said gravity-driven pumping unit by opening and closing said inlet valve and said outlet valve in a sequence which enables gravity-driven movement of liquid refrigerant from said condenser unit to said staging zone and then from said staging zone to said boiler unit, against a positive pressure differential between said boiler unit and said condenser unit.   
     
     
         2 . A Rankine system with as recited in  claim 1  wherein said at least one gravity-driven pumping unit includes a liquid receiver positioned upstream of said inlet valve. 
     
     
         3 . A Rankine system as recited in  claim 1  wherein said control system is programmed to open said inlet valve, allow for a time interval to fill said staging zone with liquid refrigerant, close said inlet valve, allow a time delay prior to opening said outlet valve, open said outlet valve, allow for a time interval to discharge refrigerant from said staging zone, close said outlet valve, allow for a time delay prior to opening said inlet valve, and repeat the above sequence. 
     
     
         4 . A Rankine system as recited in  claim 3 , wherein said control system is further programmed to assign nominal values to said time to fill the staging zone with refrigerant and to said time to discharge refrigerant from said staging zone, assign nominal values to said time delay prior to opening said outlet valve and to said time delay prior to opening said inlet valve, to provide maximal pumping capacity; assign values different from said nominal values of said time to fill staging zone with refrigerant and said time to discharge refrigerant from said staging zone, assign values larger than said nominal values of said time delay prior to opening said outlet valve and to said time delay prior to opening said inlet valve, to decrease pumping capacity. 
     
     
         5 . A Rankine system as recited in  claim 1  wherein said control system is programmed to maintain superheat at an inlet to said expansion machine based on pressure and temperature monitored by a pressure sensor and a temperature sensor at said inlet to said expansion machine, and to accordingly decrease pumping capacity if superheat is decreased and increase pumping capacity if superheat is increased. 
     
     
         6 . A Rankine system as recited in  claim 1  wherein said control system is programmed to open said inlet valve and said outlet valve, in order to relieve excessive pressure from a high pressure side of said Rankine system to a low-pressure side of said Rankine system, when at least one pressure sensor positioned within the system indicates excessive pressure elevation. 
     
     
         7 . A Rankine system as recited in  claim 1  wherein said at least one gravity-driven pumping unit comprises a plurality of gravity driven pumps, with each gravity-driven pump housing an inlet valve, an outlet valve, and a staging zone. 
     
     
         8 . A Rankine system as recited in  claim 7  wherein said control system is programmed to regulate pumping capacity by engaging a different number of said gravity-driven pumps. 
     
     
         9 . A Rankine system as recited in  claim 1  wherein a number of boiling pressure levels is provided; said expansion machine has an inlet associated with a highest boiling pressure level, and a number of inlets introducing refrigerant streams into an expansion process associated with other boiling pressure levels; said boiler unit has a plurality of boilers connected in sequence, with respect to said fluid carrying enthalpy of available thermal energy; said gravity-driven pumping unit has a plurality of said gravity-driven pumping units; a number of said boiling pressure levels, a number of said boilers, total number of said inlets to said expansion machine, and a number of said gravity-driven pumps are the same; and each said gravity-driven pump feeds one boiler and one inlet to said expansion machine. 
     
     
         10 . A Rankine system as recited in  claim 1  wherein a number of boiling pressure levels is provided; said expansion machine has a plurality of expansion machines, said boiler unit has the same plurality of boilers connected in sequence, with respect to said fluid carrying enthalpy of available thermal energy; said gravity-driven pumping unit has the same plurality of said gravity-driven pumping units; a number of said boiling pressure levels, a number of said boilers, a number of said expansion machines, and a number of said gravity-driven pumps are same; and each said gravity-driven pump feeds one boiler and one expansion machine. 
     
     
         11 . A Rankine system as recited in  claim 10  wherein said plurality of expansion machines is connected in series. 
     
     
         12 . A Rankine system as recited in  claim 10  wherein said plurality of said expansion machines is connected in parallel. 
     
     
         13 . A Rankine system as recited in  claim 1  wherein said at least one condenser unit comprises a plurality of condensers connected in sequence, with respect to the fluid to be heated and with respect to refrigerant stream exiting said expansion machine; said gravity-driven pumping unit has the same plurality of said gravity-driven pumping units; each said condensers feeds one gravity-driven pumping unit with refrigerant liquid and feeds a next downstream condenser, if any, with refrigerant vapor. 
     
     
         14 . A Rankine system as recited in  claim 1  wherein said outlet valve is installed to stop refrigerant flow in both directions and said inlet valve is installed to stop refrigerant flow in a direction from said boiler unit to said condenser unit. 
     
     
         15 . A Rankine system as recited in  claim 14  wherein said inlet valve is a normally open flow control device and said outlet valve is a normally closed flow control device. 
     
     
         16 . A Rankine system as recited in  claim 14  wherein said inlet valve is a normally closed flow control device and said outlet valve is a normally open flow control device. 
     
     
         17 . A Rankine system as recited in  claim 14  wherein said outlet valve is a co-axial solenoid valve. 
     
     
         18 . A Rankine system as recited in  claim 14  wherein said outlet valve is a motorized valve. 
     
     
         19 . A Rankine system as recited in  claim 14  wherein said outlet valve is a modulation valve actuated by a stepper motor. 
     
     
         20 . A Rankine system as recited in  claim 1  wherein said inlet valve is installed to stop refrigerant flow in both directions and said outlet valve is installed to stop refrigerant flow in a direction from said boiler unit to said condense unit. 
     
     
         21 . A Rankine system as recited in  claim 20  wherein said inlet valve is a normally open flow control device and said outlet valve is a normally closed flow control device. 
     
     
         22 . A Rankine system as recited in  claim 20  wherein said inlet valve is a normally closed flow control device and said outlet valve is a normally open flow control device. 
     
     
         23 . A Rankine system as recited in  claim 20  wherein said inlet valve is a co-axial solenoid valve. 
     
     
         24 . A Rankine system as recited in  claim 1  wherein said inlet valve and said outlet valve are installed to stop refrigerant flow in both directions. 
     
     
         25 . A Rankine system as recited in  claim 24  wherein said inlet valve is a normally open flow control device and said outlet valve is a normally closed flow control device. 
     
     
         26 . A Rankine system as recited in  claim 24  wherein said inlet valve is a normally closed flow control device and said outlet valve is a normally open flow control device. 
     
     
         27 . A Rankine system as recited in  claim 24  wherein said inlet valve and said outlet valve are co-axial solenoid valves. 
     
     
         28 . A Rankine system as recited in  claim 14  wherein said outlet valve is an assembly of two solenoid valves; a first solenoid valve exposed to said inlet valve and installed to stop refrigerant flow in a direction from said condenser unit to said boiler unit and; a second solenoid valve exposed to said boiler unit and installed to stop refrigerant flow in a direction from said boiler unit to said condenser unit. 
     
     
         29 . A Rankine system as recited in  claim 28  wherein said inlet valve is a normally open flow control device and said second solenoid valve is a normally closed flow control device. 
     
     
         30 . A Rankine system as recited in  claim 20  wherein said inlet valve is a normally closed flow control device and said second solenoid valve is a normally open flow control device. 
     
     
         31 . A Rankine system as recited in  claim 14  wherein said outlet valve is an assembly of two solenoid valves; a first solenoid valve exposed to said inlet valve and installed to stop refrigerant flow in a direction from said boiler unit to said condenser unit and; a second solenoid valve exposed to said boiler unit and installed to stop refrigerant flow in a direction from said condenser unit to said boiler unit. 
     
     
         32 . A Rankine system as recited in  claim 13  wherein said condenser unit has a two condensation stages having a vapor inlet, an inlet header, an outlet header, a plurality of refrigerant channels extending between said inlet header and said outlet header and sealed inside said inlet and outlet headers, an intermediate liquid outlet, a liquid outlet, means to route refrigerant flow from said vapor inlet to said intermediate liquid and liquid outlets, a first condensation stage associated with one portion of said refrigerant channels, a second condensation stage associated with another portion of said refrigerant channels, and means to remove a condensed liquid portion after said first condensation stage. 
     
     
         33 . A Rankine system as recited in  claim 32  wherein said means to route refrigerant flow from said vapor inlet to said intermediate liquid and liquid outlets consist of at least one of a phase separator, a baffle, and a collector inside said inlet header and said outlet header. 
     
     
         34 . A Rankine system as recited in  claim 32  wherein said means to remove condensed liquid portion after said first condensation stage consist of at least one of a phase separator, a baffle, and a collector inside said inlet header and said outlet header. 
     
     
         35 . A Rankine system as recited in  claim 32  wherein said condensation stage has a plurality of coils, and a plurality of vapor inlets of said coils are connected to said vapor inlet of said condenser unit, a plurality of intermediate liquid outlets of said coils are connected to said intermediate liquid outlet of said condenser unit, and a plurality of liquid outlets of said coils are connected to said liquid outlet of said condenser unit. 
     
     
         36 . A Rankine system as recited in  claim 32  wherein said two-stage condenser unit has a plurality of two-stage condenser coils. 
     
     
         37 . A Rankine system as recited in  claim 1  and including a vapor compression system with a compressor wherein said expansion machine is connected at least to assist in driving said compressor and further wherein the capacity of said vapor compression system is regulated by the pumping capacity of said gravity-driven pumping unit. 
     
     
         38 . A Rankine system as recited in  claim 18  wherein said staging zone has a relief valve connected to a point outside said gravity-driven pumping unit. 
     
     
         39 . A Rankine system as recited in  claim 1  wherein said vapor compression system is a heat pump.