Abstract:
A rankine cycle system, which includes a turbine for driving a generator by way of a gearbox having an oil sump, is adapted to have the oil heated relatively quickly by causing a mixture of hot refrigerant gases from the evaporator and the oil from the low portion of the turbine to be mixed in an eductor and flow to the oil sump for heating the oil.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to organic rankine cycle systems and, more particularly, to a method and apparatus for starting such a system without preheating the lubricant. 
     BACKGROUND OF THE DISCLOSURE 
     The well known closed rankine cycle comprises a boiler or evaporator for the evaporation of a motive fluid, a turbine fed with vapor from the boiler to drive the generator or other load, a condenser for condensing the exhaust vapors from the turbine, and the apparatus, such as a pump, for cycling the condensed fluid to the boiler. Such a system is shown and described in U.S. Pat. No. 3,393,515. 
     With the advent of the energy crisis, and the need to conserve and to more effectively use the available energies, rankine cycle systems have been used to capture the so called “waste heat” or the energy from naturally occurring sources such as methane gas flares or geo-thermal heat sources. A turbine as applied for this purpose is shown and described in U.S. Pat. No. 7,174,716 assigned to the assignee of the present invention. 
     In order to start such a refrigerant system, the oil used to lubricate the bearing of the turbine must be heated to bring the temperature above the point where refrigerant will condense and displace the oil. This has traditionally been accomplished by using a heater which is effective in maintaining the temperature once it has been achieved but takes a relatively long time to do so. It is therefore desirable to substantially reduce the time for starting up such an organic rankine cycle system and possibly eliminate the need for an oil heater. 
     DISCLOSURE 
     Briefly, in accordance with one aspect of the disclosure, hot refrigerant vapor is drawn from a point downstream of the evaporator and upstream of the turbine inlet valve and routed to the eductor to draw oil from the turbine suction housing and pump a mixture of refrigerant vapor and oil to the oil sump to thereby heat the oil in the sump. 
     In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the spirit and scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an organic rankine cycle system in accordance with the prior art. 
         FIG. 2  is a schematic illustration of the turbine and generator portion thereof with the flow of oil indicated in accordance with the prior art. 
         FIG. 3  is a schematic illustration thereof in accordance with the present disclosure. 
         FIG. 4  is a flow diagram of the method in accordance with the present disclosure. 
     
    
    
     DESCRIPTION 
     Shown in  FIG. 1  is an organic rankine cycle system of the type which is typically used for the purpose of using waste heat or natural occurring heat sources to generate electricity. It includes, in serial flow relationship, a pump  11 , an evaporator  12 , a turbine  13  and a condenser  14 . The working fluid can be any suitable refrigerant such as R-245fa. 
     The heat source for heating the boiler or evaporator  12  can be any suitable source such as the exhaust of a gas turbine engine, methane gas flares, or a geo-thermal heat source providing hot water to the evaporator  12  as shown. 
     The turbine  13  is mechanically connected by way of a gear box (not shown) to a generator  16  for generating electricity. A bypass orifice  18  is provided to bypass the turbine  13  during start up of the system so that the temperature and pressure of the refrigerant can first rise to the desired level to ensure proper operation of the turbine  13 . 
     The condenser  14  can be either air cooled or water cooled by way of a heat sink  19  as shown. 
     A portion of the organic rankine cycle system is shown in  FIG. 3  including the evaporator  12  and the turbine  13 . The turbine  13  includes a high pressure volute  21 , a suction housing  22  and an impeller  23  and may be of the type shown and described in U.S. Pat. No. 7,174,716 assigned to the assignee of the present application. A turbine inlet valve  24  fluidly interconnects the evaporator  12  to the high pressure volute  21 . 
     In operation, refrigerant vapor is passed from the evaporator  12  through the turbine inlet valve  24  to the high pressure volute  21  and then passes through nozzles  26  to impart motive force to the impeller  23  to drive a shaft  27  in a gear box  28 . The drive shaft  27  is then connected by gears  29  to drive a generator  31 . The gear box  28  includes an oil sump  32  and an oil pump  33  to pump oil up to the gears  29  and the bearings  34  prior to being passed to the oil cooler (not shown). 
     Within the refrigerant flow circuit, oil tends to become emulsified within the refrigerant to provide a mixture of the two substances. Thus, within the suction housing  22 , the oil tends to separate from the vapor and collect in the bottom portion of the suction housing  22  as shown. It is thus desirable to return this oil to the oil sump  32 . This is accomplished by way of an eductor  36  having a primary flow inlet  37  and a secondary flow inlet  38 . The primary flow inlet  37  is fluidly connected by line  39  to the high pressure volute  21 , and the secondary flow inlet  38  is fluidly connected by line  41  to the lower portion of the suction housing  22  as shown. 
     In operation, the high pressure refrigerant vapor from the high pressure volute  21  passes along line  39  to the primary flow inlet  37  of the eductor  36  to thereby cause the secondary flow of oil from the suction housing  22  to flow through line  41  and into the secondary flow inlet  38 , with the mixture then flowing along line  42  to the oil sump  32 . The refrigerant vapor then rises in the gearbox  28  and is caused by pressure gradient to move to the suction housing  22  so as to flow from the gearbox  28  to the suction housing along line  45 . 
     A mixture of refrigerant and oil also exists in the evaporator  12  with the oil passing along line  49  to the suction housing  22 . 
     Traditionally, at system start up the oil in the sump  32  is cold and therefore and not in a suitable condition for proper circulation within the system. Accordingly, this problem has traditionally been addressed by the use of heater  51  which is placed within the oil sump  32  as shown. In one form, the heater  51  is an electrical heater which is capable of heating the oil in a relatively short period of time. However it is desirable to eliminate the waiting period that is necessary for this function and, if possible, eliminate the heater  51  altogether. 
     Referring now to  FIG. 3 , it will be seen that the high pressure volute  21  is no longer being applied to the primary flow inlet  37 . Rather, hot refrigerant vapor is taken from line  52  at a point downstream of the evaporator  12  but upstream of the turbine inlet valve  24 . This hot refrigerant vapor is routed along line  53  to the primary flow inlet  37 . As before, the oil is drawn from the suction housing  22  and flows along line  41  to the secondary flow inlet  38 . However, because of the hot refrigerant gas, the mixture of oil and refrigerant that flows along line  42  to the oil sump  32  is substantially increased in temperature (i.e. in the range of -). Accordingly, oil in the sump  32  is heated much more quickly then in the case of the prior art, thereby allowing a system to be started much earlier than before. The oil heater  51  of the prior art can therefore be eliminated. 
     Considering now the manner in which the system is started, the sequence of events is shown in  FIG. 4 . First, the pump  11  is turned on to circulate refrigerant through the system as shown in block  54 . Then the geothermal heat source  16  is applied to heat the evaporator  12  as shown in block  55 . The oil temperature alarms can be disabled as shown in block  56  since, even though the oil is cold at this point, the present system allows for start up of the system with these features as described hereinabove. Since the system must be in operation for a period of time before the vapor is superheated for proper operation of the turbine  13 , the bypass orifice  18  is opened to allow circulation of the refrigerant through the system but around the turbine  13  as shown in block  57 . 
     The oil pump  33  is then turned on as indicated at block  58  to circulate the oil within the system (i.e. within the gearbox  28  and the generator  31 ). The high temperature refrigerant leaving the evaporator  12  goes through the eductor  36  heating the oil being pumped from the suction housing  22  and then flowing to the sump  32  to heat the oil there as indicated at block  59 . Once the oil reaches an appropriate temperature for the system to properly operate, the power plant is allowed to resume normal operation and switch to power generation mode as shown in block  61 . 
     While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.