Abstract:
A technique for cooling furnace walls in a multi-component working fluid power generation system is disclosed. In a first embodiment, the technique involves removing process heat from a furnace having an inner tubular wall and an outer tubular wall. In a second embodiment, the technique involves removing process heat from a furnace system utilizing a fluid combiner. In a third embodiment, the technique involves removing process heat from a furnace having tubular walls formed of a plurality of fluid tubes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application relates to pending U.S. patent application Ser. No. 09/231,165, filed Jan. 12, 1999, for “TECHNIQUE FOR CONTROLLING REGENERATIVE SYSTEM CONDENSATION LEVEL DUE TO CHANGING CONDITIONS IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/231,171, filed Jan. 12, 1999, for “TECHNIQUE FOR BALANCING REGENERATIVE REQUIREMENTS DUE TO PRESSURE CHANGES IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,364, filed Jan. 12, 1999, for “TECHNIQUE FOR CONTROLLING SUPERHEATED VAPOR REQUIREMENTS DUE TO VARYING CONDITIONS IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/231,166, filed Jan. 12, 1999, for “TECHNIQUE FOR MAINTAINING PROPER DRUM LIQUID LEVEL IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,629, filed Jan. 12, 1999, for “TECHNIQUE FOR CONTROLLING DCSS CONDENSATE LEVELS IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,630, filed Jan. 12, 1999, for “TECHNIQUE FOR MAINTAINING PROPER FLOW IN PARALLEL HEAT EXCHANGERS IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,631, filed Jan. 12, 1999; U.S. patent application Ser. No. 09/231,164, filed Jan. 12, 1999, for “WASTE HEAT KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,366, filed Jan. 12, 1999, for “MATERIAL SELECTION AND CONDITIONING TO AVOID BRITTLENESS CAUSED BY NITRIDING”; U.S. patent application Ser. No. 09/231,168, filed Jan. 12, 1999, for “REFURBISHING CONVENTIONAL POWER PLANTS FOR KALINA CYCLE OPERATION”; U.S. patent application Ser. No. 09,231,170, filed Jan. 12, 1999, for “STARTUP TECHNIQUE USING MULTIMODE OPERATION IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,632, filed Jan. 12, 1999, for “BLOWDOWN RECOVERY SYSTEM IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,368, filed Jan. 12, 1999, for “REGENERATIVE SUBSYSTEM CONTROL IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,363, filed Jan. 12, 1999, for “DISTILLATION AND CONDENSATION SUBSYSTEM (DCSS) CONTROL IN A KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/229,365, filed Jan. 12, 1999, for “VAPOR TEMPERATURE CONTROL IN A KALINA CYCLE POWER GENERATION SYSTEM”; 
     U.S. patent application Ser. No. 09/229,367, filed Jan. 12, 1999, for “A HYBRID DUAL CYCLE VAPOR GENERATOR”; U.S. patent application Ser. No. 09/231,169, filed Jan. 12, 1999, for “FLUIDIZED BED FOR KALINA CYCLE POWER GENERATION SYSTEM”; U.S. patent application Ser. No. 09/231,167, filed Jan. 12, 1999, for “TECHNIQUE FOR RECOVERING WASTE HEAT USING A BINARY WORKING FLUID”. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of power generation systems, and, more particularly, to a technique for cooling furnace walls in a multi-component working fluid power generation system. 
     BACKGROUND OF THE INVENTION 
     In recent years, industrial and utility concerns with deregulation and operational costs have strengthened demands for increased power plant efficiency. The Rankine cycle power plant, which typically utilizes water as the working fluid, has been the mainstay for the utility and industrial power industry for the last 150 years. In a Rankine cycle power plant, heat energy is converted into electrical energy by heating a working fluid flowing through tubular walls, commonly referred to as waterwalls, to form a vapor, e.g., turning water into steam. Typically, the vapor will be superheated to form a high pressure vapor, e.g., superheated steam. The high pressure vapor is used to power a turbine/generator to generate electricity. 
     Conventional Rankine cycle power generation systems can be of various types, including direct-fired, fluidized bed and waste-heat type systems. In direct fired and fluidized bed type systems, combustion process heat is generated by burning fuel to heat the combustion air which in turn heats the working fluid circulating through the systems&#39; waterwalls. In direct-fired Rankine cycle power generation systems the fuel, commonly pulverized-coal, gas or oil, is ignited in burners located in the waterwalls. In bubbling fluidized Rankine cycle power generation systems pulverized-coal is ignited in a bed located at the base of the boiler to generate combustion process heat. Waste-heat Rankine cycle power generation systems rely on heat generated in another process, e.g., incineration, for process heat to vaporize, and if desired superheat, the working fluid. Due to the metallurgical limitations, the highest temperature of the superheated steam does not normally exceed 1050° F. (566° C.) . However, in some “aggressive” designs, this temperature can be as high as 1100° F. (593° C.). 
     Over the years, efficiency gains in Rankine cycle power systems have been achieved through technological improvements which have allowed working fluid temperatures and pressures to increase and exhaust gas temperatures and pressures to decrease. An important factor in the efficiency of the heat transfer is the average temperature of the working fluid during the transfer of heat from the heat source. If the temperature of the working fluid is significantly lower than the temperature of the available heat source, the efficiency of the cycle will be significantly reduced. This effect, to some extent, explains the difficulty in achieving go further gains in efficiency in conventional, Rankine cycle-based, power plants. 
     In view of the above, a departure from the Rankine cycle has recently been proposed. The proposed new cycle, commonly referred to as the Kalina cycle, attempts to exploit the additional degree of freedom available when using a binary fluid, more particularly an ammonia/water mixture, as the working fluid. The Kalina cycle is described in the paper entitled: “Kalina Cycle System Advancements for Direct Fired Power Generation”, co-authored by Michael J. Davidson and Lawrence J. Peletz, Jr., and published by Combustion Engineering, Inc., of Windsor, Conn. Efficiency gains are obtained in the Kalina cycle plant by reducing the energy losses during the conversion of heat energy into electrical output. 
     A simplified conventional direct-fired Kalina cycle power generation system is illustrated in FIG. 1 of the drawings. Kalina cycle power plants are characterized by three basic system elements, the Distillation and Condensation Subsystem (DCSS)  100 , the Vapor Subsystem (VSS)  110  which includes the boiler  142 , superheater  144  and recuperative heat exchanger (RHE)  140 , and the turbine/generator subsystem (TGSS)  130 . The DCSS  100  and RHE  140  are sometimes jointly referred to as the Regenerative Subsystem (RSS)  150 . The boiler  142  is formed of tubular walls  142   a  and the superheater  144  is formed of tubular walls and/or banks of fluid tubes  144   a . A heat source  120  provides process heat  121 . A portion  123  of the process heat  121  is used to vaporize the working fluid in the boiler  142 . Another portion  122  of the process heat  121  is used to superheat the vaporized working fluid in the superheater  144 . 
     During normal operation of the Kalina cycle power system of FIG. 1, the ammonia/water working fluid is fed to the boiler  142  from the RHE  140  by liquid stream FS  5  and from the DCSS  100  by liquid stream FS  7 . The working fluid is vaporized, i.e., boiled, in the tubular walls  142   a  of the boiler  142 . The FS rich working fluid stream  20  from the DCSS  100  is also vaporized in the heat exchanger(s) of the RHE  140 . In one implementation, the vaporized working fluid from the boiler  142  along with the vaporized working fluid FS  9  from the RHE  140 , is further heated in the tubular walls/fluid tube bank  144   a of the superheater  144 . The superheated vapor from the superheater  144  is directed to and powers the TGSS  130  as FS vapor  40  so that electrical power  131  is generated to meet the load requirement. In an alternative implementation, the RHE  140  not only vaporizes but also superheats the rich stream FS  20 . In such a case, the superheated vapor flow FS  9 ′ from the RHE  140  is combined with the superheated vapor from the superheated vapor from the superheater  144  to form FS vapor flow  40  to the TGSS  130 . 
     The expanded working fluid FS extraction  11  egresses from the TGSS  130 , e.g., from an intermediate pressure (IP) or a low pressure (LP) turbine (not shown) within the TGSS  130 , and is directed to the DCSS  100 . This expanded working fluid is, in part, condensed in the DCSS  100 . Working fluid condensed in the DCSS  100 , as described above, forms feed fluid FS  7  which is fed to the boiler  142 . Another key feature of the DCSS  100  is the separation of the working fluid egressing from TGSS  130  into ammonia rich and ammonia lean streams for use by the VSS  110 . In this regard, the DCSS  100  separates the expanded working fluid into an ammonia rich working fluid flow FS rich  20  and an ammonia lean working fluid flow FS lean  30 . Waste heat  101  from the DCSS  100  is dumped to a heat sink, such as a river or pond. The rich and lean flows FS  20 , FS  30  respectively, are fed to the RHE  140 . Another somewhat less expanded hot working fluid FS extraction  10  egresses from the TGSS  130 , e.g., from a high pressure (HP) turbine (not shown) within the TGSS  130 , and is directed to the RHE  140 . Heat is transferred from the expanded working fluid FS extraction  10  and the working fluid FS lean stream  30  to the rich working fluid flow FS rich  20 , to thereby vaporize the rich flow FS  20  and condense, at least in part, the expanded working fluid FS extraction  10  and FS lean working fluid flow  3 Q, in the RHE  140 . As discussed above, the vaporized rich flow FS  20  is fed to either the superheater  144 , along with vaporized feed fluid from the boiler  142 , or is combined with the superheated working fluid from the superheater  142  and fed directly to the TGSS  130 . The condensed expanded working fluid from the RHE  140  forms part of the feed flow, i.e., flow FS  5 , to the boiler  142 , as has been previously described. 
     FIG. 2 details a portion of the RHE  140  of VSS  110  of FIG.  1 . As shown, the RHE  140  receives ammonia-rich, cold high pressure stream FS rich  20  from DCSS  100 . Stream FS rich  20  is heated by ammonia-lean hot low pressure stream FS  3010 . The stream FS  3010  is formed by combining the somewhat lean hot low pressure FS extraction stream  10  from TGSS  130  with the lean hot low pressure stream FS  30  from DCSS  100 , these flows being combined such that stream FS  30  dilutes stream FS  10  resulting in a desired concentration of ammonia in stream FS  3010 . 
     Heat energy  125 , is transferred from stream FS  3010  to stream FS rich  20 . As discussed above, this causes the transformation of stream FS  20  into a high pressure vapor stream FS  9  or the high pressure superheated vapor stream FS  9 ′, depending on the pressure and concentration of the rich working fluid stream FS  20 . This also causes the working fluid stream FS  3010  to be condensed and therefore serve as a liquid feed flow FS  5  to the boiler  142 . 
     As previously indicated, in one implementation the vapor stream FS  9  along with the vapor output from boiler  142  forms the vapor input to the superheater  144 , and the superheater  144  superheats the vapor stream to form superheated vapor stream  40  which is used to power TGSS  130 . Alternatively, the superheated vapor steam FS  9 ′ along with the superheated vapor output from the superheater  144  forms the superheated vapor stream FS  40  to the TGSS  130 . 
     FIG. 3 illustrates exemplary heat transfer curves for heat exchanges occurring in the RHE  140  of FIG. 2. A typical Kalina cycle heat exchange is represented by curves  520  and  530 . As shown, the temperature of the liquid binary working fluid FS  20  represented by curve  520  increases as a function of the distance of travel of the working fluid through the heat exchanger of the RHE  140  in a substantially linear manner. That is, the temperature of the working fluid continues to increase even during boiling as the working fluid travels through the heat exchanger of the RHE  140  shown in FIG.  2 . At the same time, the temperature of the liquid working fluid FS  3010  represented by curve  530  decreases as a function of the distance of travel of this working fluid through the heat exchanger of the RHE  140  in a substantially linear manner. 
     That is, as heat energy  125  is transferred from working fluid FS  3010  to the working fluid stream FS  20  as both fluid streams flow in opposed directions through the RHE  140  heat exchanger of FIG. 2, the binary working fluid FS  3010  loses heat and the binary working fluid stream FS  20  gains heat at substantially the same rate within the Kalina cycle heat exchangers of the RHE  140 . 
     In contrast, a typical Rankine cycle heat exchange is represented by curve  510 . As shown, the temperature of the water or water/steam mixture forming the working fluid represented by curve  510  increases as a function of the distance of travel of the working fluid through a heat exchanger of the type shown in FIG. 2 only after the working fluid has been fully evaporated, i.e.,, vaporized. The portion  511  of curve  510  represents the temperature of the water or water/steam mixture during boiling. As indicated, the temperature of the working fluid remains substantially constant until the boiling duty has been completed. That is, in a typical Rankine cycle, the temperature of the working fluid does not increase during boiling. Rather, as indicated by portion  512  of curve  510 , it is only after full vaporization, i.e.,, full phase transformation, that the temperature of the working fluid in a typical Rankine cycle increases beyond the boiling point temperature of the working fluid, e.g., 212 degrees Fahrenheit. 
     As will be noted, the temperature differential between the stream represented by curve  530 , which transfers the heat energy, and the Rankine cycle stream represented by curve  510 , which absorbs the heat energy, continues to increase during phase transformation. The differential becomes greatest just before complete vaporization of the working fluids. In contrast, the temperature differential between the stream represented by curve  530 , and the Kalina cycle stream represented by curve  520 , which absorbs the heat energy, remains relatively small, and substantially constant, during phase transformation. This further highlights the enhance efficiency of Kalina cycle heat exchange in comparison to Rankine cycle heat exchange. 
     As indicated above, the transformation in the RHE  140  of the liquid or mixed liquid/vapor stream FS  20  to vapor or superheated vapor stream FS  9  or  9 ′ is possible in the Kalina cycle because, the boiling point of rich cold high pressure stream FS  20  is substantially lower than that of lean hot low pressure stream FS  3010 . This allows additional boiling, and in some implementations superheating, duty to be performed in the Kalina cycle RHE  140  and hence outside the boiler  142  and/or superheater  144 . Hence, in the Kalina cycle, a greater portion of the process heat  121  can be used for superheating vaporized working fluid in the superheater  144 , and less process heat  121  is required for boiling duty in the boiler  142 . The net result is increased efficiency of the power generation system when compared to a conventional Rankine cycle type power generation system. FIG. 4 further depicts the TGSS  130  of FIG.  1 . As illustrated, the TGSS  13 Q in a Kalina cycle power generation system is driven by a high pressure superheated binary fluid vapor stream FS  40 . Relatively lean hot low pressure stream FS extraction  10  is directed from, for instance the exhaust of an HP turbine (not shown) within the TGSS  130  to the RHE  140  as shown in FIGS. 1 and 2. A relatively lean cooler, even lower pressure flow FS extraction  11  is directed from, for instance, the exhaust of an IP or LP turbine (not shown) within the TGSS  130  to the DCSS  100  as shown in FIG.  1 . As has been discussed to some extent above and will be discussed further below, both FS extraction flow  10  and FS extraction flow  11  retain enough heat to transfer energy to still cooler higher pressure streams in the DCSS  100  and RHE  140 . 
     FIG. 5 further details the Kalina cycle power generation system of FIG. 1 for a once through, i.e.,, non-recirculating, system configuration. As shown, working fluid FS  5  and FS  7  from the RHE  140  and DCSS  100  are combined to form a feed fluid stream FS  57  which is fed to the bottom of the boiler  142 . The working fluid  57  flows through the boiler tubes  142   a  where the working fluid  57  is exposed to process heat  123 . The working fluid is heated and vaporized in the boiler tubes  142   a , while cooling the boiler walls. Sufficient liquid working fluid must be supplied by feed stream FS  57  to provide an adequate flow to the boiler tubes  142   a  to ensure proper cooling during system operation. Without an adequate flow to the boiler tubes  142   a , the boiler tubes  142   a  can become overheated causing a premature failure of the boiler tubes  142   a , particularly in the combustion chamber, and requiring system shut-down for repair. The heated working fluid rises in the boiler tubes  142   a  and the fully vaporized working fluid stream is directed from the boiler tubes  142   a  as stream FS  8  and combined with the vapor stream FS  9  from the RHE  140 . The combined vaporized fluid stream FS  89  is directed to the superheater  144 , where it is exposed to process heat  122 . The high pressure superheated vapor flow FS  40  is directed from the superheater  144 . 
     The TGSS  130 , as shown, includes both a HP turbine  130 ′ and an IP turbine  130 ″. The superheated high pressure vapor stream FS  40  is directed first to the HP turbine  130 ′ of the TGSS  130  and then to the IP turbine  130 ″ of the TGSS  130 . The vapor flow FS  40  must be sufficient to provide the necessary energy to drive the turbines so that the required power is generated. The lower pressure hot working fluid exhausted from the HP turbine  130 ′ is split into a lower pressure vapor working fluid stream FS  40 ′ to the boiler  142  where it is reheated and then sent to the IP turbine  130 ″ and an extraction flow FS  40 ″ to the RHE  140 . Typically, approximately 50% of the exhaust flow from the HP turbine  130 ′ is split off as stream FS  40 ″ to the RHE  140 , although this may vary. The even lower pressure hot working fluid exhausted from the IP turbine  130 ″ is split into a working fluid stream FS  11  which is fed to the DCSS  100  and extraction flow FS  40 ′″ which is fed to the RHE  140 . It will be understood that the TGSS  130  could also include other turbines, e.g., a LP turbine to which a portion of the fluid flow from the IP turbine might be first directed before being directed from the TGSS  130  to the DCSS  100 . The lean hot working fluid extraction streams FS  40 ″ and FS  40 ′″from the TGSS  130  are combined to form stream FS  10 , which is further combined, as previously discussed, with lean hot working fluid stream FS  30  from the DCSS  100  to form a hot working fluid stream  3010 . Stream  3010  is directed on to the RHE  140 . 
     The RHE  140 , as previously described receives the hot stream FS  3010  and a rich cold fluid stream FS  20  from the DCSS  100 . Heat is transferred from the stream FS  3010  to vaporize stream FS  20 . During this process, the steam FS  3010  is condensed to form condensate  3010 ′ which is fed to the boiler  142  as liquid stream FS  5 . 
     FIG. 6 illustrates a furnace structure  146  incorporating both the boiler  142  and the superheater  144 . As shown, the furnace structure  146  has a primary (lower) section  146 ′, a secondary (upper) section  146 ″, and a backpass section  146 ″′. The boiler  142  is located in the lower section  146 ′ and the superheater  144  is located in the upper section  146 ″. The heat source  120 , which in this instance is shown to be a pair of direct-fired burners  124  located in the walls of the boiler  142  but, as previously described, may also be waste heat or a fluidized bed, generates process heat within the furnace structure  146 . The backpass section  146 ″′, which generally directs combustion and flue gases  147  to an exhaust stack (not shown), can also be used to support further heat exchange devices, which are typically operating at temperatures that are lower than the operating temperatures in either the boiler  142  or the superheater  144  due to the relatively lower temperature of the combustion and flue gases  147  passing through the backpass section  146 ″′. 
     As previously described, the boiler  142  is formed of tubular walls  142   a , and the superheater  144  is formed of tubular walls and/or banks of fluid tubes  144   a . The tubular walls  142   a  typically include a plurality of wall fluid tubes  142   a ′, and the tubular walls and/or banks of fluid tubes  144   a typically include a plurality of wall fluid tubes  144   a ′ and/or suspended fluid tubes  144   a ″ , respectively, as shown. The wall fluid tubes  142   a ′, the wall fluid tubes  144   a ′, and the suspended fluid tubes  144   a ″ are typically interconnected through headers (not shown) in the furnace structure  146 . 
     As also previously described, working fluid passes through the tubular walls  142   a  of the boiler  142  and the tubular walls and/or banks of fluid tubes  144   a of the superheater  144  so as to generate superheated vapor for powering the TGSS  130  and generating electrical power. However, the working fluid passing through the tubular walls  142   a  of the boiler  142  and the tubular walls and/or banks of fluid tubes  144   a of the superheater  144  also works to cool the walls of the furnace structure  146 , particularly in the boiler  142 , or wherever else the heat source  120  might be located. That is, the working fluid works to protect the walls of the furnace structure  146  from the high temperatures generated by the heat source  120  and thereby prevent material and/or structural damage to the furnace structure  146 . 
     During normal operation, the walls of the furnace structure  146  are generally protected from overheating by flows of the liquid working fluid stream FS  5  from the RHE  140 , the liquid working fluid stream FS  7  from the DCSS  100 , and, to a lesser degree, the vaporized working fluid stream FS  9  from the RHE  140 . However, during start-up and/or low-load operation there is typically insufficient vapor flow through the tubular walls  142   a  of the boiler  142  and the tubular walls and/or banks of fluid tubes  144   a  of the superheater  144  to cool the walls of the furnace structure  146 . Thus, the walls of the furnace structure  146 , particularly in the boiler  142 , or wherever else the heat source  120  might be located, are susceptible to being overheated and damaged during start-up and/or low-load operation. 
     Further, even during normal operation the flow rate through the tubular walls  142   a  of the boiler  142  and the tubular walls and/or banks of fluid tubes  144   a of the superheater  144  may be insufficient to cool the walls of the furnace structure  146 . That is, despite the fact that some working fluid may be flowing through the tubular walls  142   a  of the boiler  142  and the tubular walls and/or banks of fluid tubes  144   a  of the superheater  144 , the flow rate of such working fluid may be insufficient to cool the walls of the furnace structure  146 . For example, this may occur when the heat source  120  is generating very high process heat, and/or when the entire furnace structure  146  is operating as a superheater. Thus, the walls of the furnace structure  146 , particularly in the boiler  142 , or wherever else the heat source  120  might be located, are susceptible to being overheated and damaged even during normal operation. 
     One proposal to overcome an overheating problem in a furnace is described in U.S. Pat. No. 5,588,298 (&#39;298 patent), issued to Kalina et al. on Dec. 31, 1996, and hereby incorporated herein by reference. In the &#39;298 patent, Kalina et al. describe a furnace system having two independent combustion zones and two corresponding independent heat exchanger systems in a single furnace system. The two independent heat exchanger systems support two totally separate working fluid streams, which may or may not be combined in an external power system. 
     One supposed benefit of the furnace system described in the &#39;298 patent is that the temperature in each combustion zone can be independently controlled, thereby preventing excessive tube metal temperatures and subsequent damage to the walls of the furnace. However, there are also several disadvantages associated with the furnace system described in the &#39;298 patent. One such disadvantage is that there are two totally separate combustion systems, as well as two totally separate heat exchanger systems and working fluid streams, to maintain. Another disadvantage is that two separate control systems are required to control and coordinate the two totally separate combustion and heat exchanger systems. A further disadvantage is that temperature differences between the two totally separate combustion zones and corresponding independent heat exchanger systems can result in material expansion differences which can cause joint failures in the walls of the furnace system. The above-stated disadvantages are prevalent in any furnace system employing two or more combustion zones and/or two or more heat exchanger systems in a single furnace. 
     In view of the above, it is readily apparent that a satisfactory solution to the problem of furnace wall overheating in a Kalina cycle power generation system has yet to be discovered. Accordingly, it would be desirable to overcome the above-described problems and disadvantages and provide a technique for cooling furnace walls in a Kalina cycle power generation system. 
     OBJECTS OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a technique for cooling furnace walls in a multi-component working fluid power generation system. 
     It is another object of the present invention to provide a technique for removing process heat from a furnace having an inner tubular wall and an outer tubular wall. 
     It is another object of the present invention to provide a technique for removing process heat from a furnace system utilizing a fluid combiner. 
     It is another object of the present invention to provide a technique for removing process heat from a furnace having tubular walls formed of a plurality of fluid tubes. 
     Additional objects, advantages, novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to a preferred embodiment(s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a technique for cooling furnace walls in a multi-component working fluid power generation system is provided. In a first embodiment, the technique involves removing process heat from a furnace, wherein the process heat is provided within a heat zone such as, for example, a combustion zone, within the furnace. Typically, a fuel such as, for example, oil, gas or coal, is combusted so as to generate the process heat within the heat zone. In any event, the technique can be realized by providing a first multi-component working fluid such as, for example, a binary working fluid containing ammonia and water, to a first tubular wall of the furnace so as to absorb a first portion of the process heat. A second multi-component working fluid is provided to a second tubular wall of the furnace so as to absorb a second portion of the process heat. Preferably, the first tubular wall is located closer to the heat zone than the second tubular wall so as to shield some of the process heat from the second tubular wall. 
     In one aspect of the present invention, the first multi-component working fluid has a higher boiling point than the second multi-component working fluid. Consequently, the first multi-component working fluid, which is preferably provided in liquid form, is typically vaporized by the first portion of the process heat, while the second multi-component working fluid, which is preferably provided in vapor form, is typically superheated by the second portion of the process heat. Since the first multi-component working fluid is preferably provided in liquid form, a pump may be used to provide the first multi-component working fluid to the first tubular wall. 
     In another aspect of the present invention, the first multi-component working fluid transfers at least some of its absorbed process heat to the second multi-component working fluid. This transfer is preferably performed in a recuperative heat exchanger. 
     In a second embodiment, the technique involves removing process heat from a furnace system. Again, the process heat may be generated by combusting a fuel such as, for example, oil, gas or coal. However, the process heat may also be provided from waste heat or other heat sources. In any event, the technique can be realized by providing a first working fluid such as, for example, a binary working fluid containing ammonia and water, to a first set of fluid channels so as to absorb a first portion of the process heat. The first set of fluid channels are typically fluid tubes forming a first tubular wall of the furnace system. Preferably, the first fluid channels form a tubular wall of the furnace system. 
     The heated first working fluid from the first set of fluid channels is combined. That is, the heated first working fluid flowing from all of the first fluid channels is combined to form a single stream of heated first working fluid. This single stream of heated first working fluid is then combined with a second working fluid such as, for example, a binary working fluid containing ammonia and water. The combination of the heated first working fluid and the second working fluid are provided to a second set of fluid channels so as to absorb a second portion of the process heat. The second set of fluid channels are typically fluid tubes forming a second tubular wall of the furnace system. Preferably, the second fluid channels form an upper tubular wall of the furnace system. 
     The first portion of the process heat typically superheats the first working fluid, which is preferably provided in vapor form. Similarly, the second portion of the process heat typically superheats the combination of the heated first working fluid and the second working fluid, which is also preferably provided in vapor form. Further, the first working fluid preferably has a higher boiling point than the second working fluid. 
     In one aspect of the present invention, the first working fluid is beneficially preheated so as to vaporize the first working fluid before it is provided to the first set of fluid channels. On the other hand, the second working fluid is beneficially preheated so as to superheat the second working fluid before it is combined with the first working fluid. 
     In a third embodiment, the technique involves removing process heat from a furnace having tubular walls formed of a plurality of fluid tubes. Again, the process heat may be generated by combusting a fuel such as, for example, oil, gas or coal. The process heat may also be provided from waste heat or other heat sources. However, the technique is particularly beneficial when the process heat is provided directly to at least a portion of the plurality of fluid tubes. In any event, the technique can be realized by providing process heat within the furnace, and then providing a vaporized multi-component working fluid such as, for example, a binary working fluid containing ammonia and water, to the plurality of fluid tubes so as to absorb at least a portion of the process heat. 
     Due to the high temperatures of the process heat, and due to the fact that the vaporized multi-component working fluid is also in a heated form, at least some, if not all, of the plurality of fluid tubes should be fabricated of a high temperature tolerant metal such as, for example, INCONEL 800 or an equivalent. Also, the plurality of fluid tubes can be coated so as to prevent heat degradation such as, for example, fire-side corrosion, of the fluid tubes. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to facilitate a fuller understanding of the present invention, reference is now made to the appended drawings. These drawings should not be construed as limiting the present invention, but are intended to be exemplary only. 
    
    
     FIG. 1 depicts a simplified block diagram of a conventional Kalina cycle power generation system. 
     FIG. 2 partially details the RHE of the conventional Kalina cycle power generation system of FIG.  1 . 
     FIG. 3 illustrates the basic heat exchange between flow streams in the RHE detailed in FIG.  2 . 
     FIG. 4 partially details the TGSS of the conventional Kalina cycle power generation system of FIG.  1 . 
     FIG. 5 is a more detailed representation of the conventional Kalina cycle power generation system of FIG. 1 depicting a once-through flow configuration. 
     FIG. 6 illustrates a furnace structure incorporating the boiler and the superheater of the conventional Kalina cycle power generation system of FIG.  1 . 
     FIG. 7 illustrates a furnace system having a liquid fossil fuel-fired burner and a solid fossil fuel-fired burner in a primary section of a furnace structure in accordance with the present invention. 
     FIG. 8 illustrates a furnace system having a liquid fossil fuel-fired burner in a backpass section and a solid fossil fuel fired burner in a primary section of a furnace structure in accordance with the present invention. 
     FIG. 9 illustrates a multi-component working fluid power generation system incorporating the furnace system of FIG. 8 in accordance with the present invention. 
     FIG. 10 illustrates a furnace system having an inner tubular wall and an outer tubular wall in accordance with the present invention. 
     FIG. 11 illustrates a multi-component working fluid power generation system incorporating the furnace system of FIG. 10 in accordance with the present invention. 
     FIG. 12 illustrates a multi-component working fluid power generation system having a vapor recirculation system for providing furnace wall cooling during start-up and low-load operation in accordance with the present invention. 
     FIG. 13 illustrates a multi-component working fluid power generation system having a fluid separating/combining system for providing furnace wall cooling during start-up and normal operation in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 7 illustrates a furnace system  700  for use in a multi-component working fluid power generation system in accordance with the present invention. The furnace system  700  includes a furnace structure  701  comprising tubular walls  702  and a single bank of coal-fired burners  704 , which are located in the tubular walls  702 . The furnace structure  701  also comprises a liquid fossil fuel-fired burner  706  and one or more hanging superheat panels  708  formed of suspended fluid tubes  708 ′. The furnace structure  701  further comprises a vapor flow sensor  726  for sensing the vapor flow through the tubular walls  702  of the furnace structure  701 . The furnace structure  701  still further comprises one or more fluid entry tubes  710  for conveying a liquid binary working fluid  712  to the furnace structure  701 , and one or more fluid exit tubes  714  for conveying a superheated binary working fluid  716  from the furnace structure  701 . The liquid binary working fluid  712  typically flows to the furnace structure  701  from a regeneration subsystem (not shown) of a multi-component working fluid power generation system, and the superheated binary working fluid  716  typically flows from the furnace structure  701  to a turbine/generator subsystem (not shown) of a multi-component working fluid power generation system. 
     The furnace system  700  also includes a controller  730 , which includes a keyboard  732  for receiving information from a user and a monitor  734  for displaying information to a user. It should be understood that other types of input devices, e.g., a keypad, mouse, touch screen or other devices, and other types of output devices, e.g., a printer, voice synthesizer or other devices, could be substituted if desired for the keyboard  732  and monitor  734 , respectively. The controller  730  also includes logic  736 , which will typically be in the form of hardware logic devices or software logic stored on a medium, and a processor  738  for processing, in accordance with the logic  736 , information provided as an input by a user via the keyboard  732 . The processor  738 , in accordance with the logic  736 , also processes control signals received from the vapor flow sensor  726  via communications line  727 , and generates and directs the transmission of control signals to the solid fossil fuel-fired burners  704  via communications line  705  so as to control the operation of the liquid fossil fuel-fired burners  704 , and to the liquid fossil fuel-fired burner  706  via communications line  707  so as to control the operation of the liquid fossil fuel-fired burner  706 , as described in detail below. The logic  736  may include an algorithm or an access instruction to a look-up table having a burner index with preselected burner set points or other data stored in a memory  740  of the controller  730  which can be used to determine the appropriate level of operation for the burners  704 ,  706  based upon received vapor flow information from vapor flow sensor  726 . 
     During start-up operation, the liquid fossil fuel-fired burner  706  is brought on-line so as to perform evaporative duty on the liquid binary working fluid  712  as the liquid binary working fluid  712  flows into the furnace structure  701  from the regeneration subsystem through the fluid entry tubes  710 . The liquid fossil fuel-fired burner  706  is used to provide this initial evaporative duty for several reasons. First, the liquid fossil fuel-fired burner  706  can typically be brought on-line much quicker than most solid fossil fuel-fired burners, thereby decreasing the time required for start-up operation. Secondly, the liquid fossil fuel fired burner  706  can typically be operated so as to control the temperature of the process heat within the furnace structure  701  in a manner that is much more accurate than most solid fossil fuel fired burners. This prevents large temperature differences from occurring between the combustion gases and the binary working fluid, which can lead to substantial heat losses. Thirdly, the liquid fossil fuel-fired burner  706  typically operates much more efficiently than most solid fossil fuel-fired burners, particularly in smaller direct-fired duty applications such as the initial evaporative duty application required in a start-up operation. 
     The vapor that is generated during a start-up operation flows through the tubular walls  702  and through the suspended fluid tubes  708 ′ of the superheat panels  708 . The vapor eventually flows from the furnace structure  701  through the fluid exit tubes  714  to the turbine/generator subsystem and to the regeneration subsystem, where it is transformed back into a liquid and then fed back to the furnace structure  701  through the fluid entry tubes  710 . 
     After the initial vapor flow has been generated through the operation of the liquid fossil fuel-fired burner  706  during start-up operation, the solid fossil fuel-fired burners  704  are brought on-line to begin normal operation and to increase the rate of vapor flow through the furnace structure  701  and the entire multi-component working fluid power generation system. The solid fossil fuel-fired burners  704  typically generate very high temperature combustion gases. These high temperature combustion gases could easily damage the tubular walls  702  of the furnace structure  701  if the initial vapor flow that was generated through the operation of the liquid fossil fuel-fired burner  706  during start-up operation was not present. That is, the initial vapor flow that was generated through the operation of the liquid fossil fuel-fired burner  706  during start-up operation acts to cool the tubular walls  702  of the furnace structure  701  during the beginning stages of normal operation, thereby preventing any overheating and subsequent damage to the tubular walls  702  of the furnace structure  701  caused by the high temperature combustion gases generated by the solid fossil fuel-fired burners  704 . 
     During normal operation, the liquid fossil fuel-fired burner  706  is secured allowing the solid fossil fuel-fired burners to continue to perform evaporative duty on the liquid binary working fluid  712  as the liquid binary working fluid  712  flows into the furnace structure  701  from the regeneration subsystem through the fluid entry tubes  710 . The solid fossil fuel-fired burners  704  may also perform some evaporative duty on any of the liquid binary working fluid  712  that was not vaporized by the combustion gases generated by the liquid fossil fuel-fired burner  706 . However, since the liquid fossil fuel-fired burner  706  vaporizes a substantial portion of the liquid binary working fluid  712 , most of the process heat generated by the solid fossil fuel-fired burners  704  goes toward superheating duty. Thus, the superheat panels  708 , which are generally larger than typical superheat panels, are hung so as to extend down into the area of the solid fossil fuel-fired burners  704  where the process heat generated by the solid fossil fuel-fired burners  704  is at very high temperature levels and thereby conducive to superheating duty. The large superheat panels  708  also serve to cover the tubular walls  702  of the furnace structure  701 , thereby preventing any overheating and subsequent damage to the tubular walls  702  of the furnace structure  701  which may occur due to the high temperature combustion gases generated by the solid fossil fuel-fired burners  704  during normal operation. 
     The superheated binary working fluid  716  that is generated during normal operation flows from the furnace structure  701  through the fluid exit tubes  714  to the turbine/generator subsystem where the superheated binary working fluid  716  is typically used to generate electrical power. The binary working fluid is thereafter transformed back into a liquid in the regeneration subsystem and then fed back to the furnace structure  701  from the regeneration subsystem through the fluid entry tubes  710 . 
     FIG. 8 also illustrates a furnace system  800  for use in a multi-component working fluid power generation system in accordance with the present invention. The furnace system  800  includes a furnace structure  801  comprising tubular walls  802  and a single bank of solid fossil fuel-fired burners  804 , which are located in the tubular walls  802 . The furnace structure  801  also comprises a liquid fossil fuel-fired burner  806  and one or more hanging superheat panels  808  formed of suspended fluid tubes  808 ′. The furnace structure  801  further comprises a vapor flow sensor  826  for sensing the vapor flow through the tubular walls  802  of the furnace structure  801 . The furnace structure  801  still further comprises one or more fluid entry tubes  810  for conveying liquid binary working fluid  812  to the furnace structure  801 , and one or more fluid exit tubes  814  for conveying superheated binary working fluid  816  from the furnace structure  801 . The liquid binary working fluid  812  typically flows to the furnace structure  801  from a regeneration subsystem (not shown) of a multi-component working fluid power generation system, and the superheated binary working fluid  816  typically flows from the furnace structure  801  to a turbine/generator subsystem (not shown) of a multi-component working fluid power generation system. 
     The furnace structure  801  in FIG. 8 differs from the furnace structure  701  in FIG. 7 in that the liquid fossil fuel-fired burner  806  is located in the backpass section  818  of the furnace structure  801 , whereas the liquid fossil fuel-fired burner  706  is located in the boiler section of the furnace structure  701 . This is significant in that the solid fossil fuel-fired burners  804  in the furnace structure  801  can be used exclusively to perform superheating duty, as described in detail below. 
     The furnace system  800  also includes a controller  830 , which includes a keyboard  832  for receiving information provided as an input from a user and a monitor  834  for displaying information to a user. It should be understood that other types of input devices, e.g., a keypad, mouse, touch screen or other devices, and other types of output devices, e.g., a printer, voice synthesizer or other devices, could be substituted if desired for the keyboard  832  and monitor  834 , respectively. The controller  830  also includes logic  836 , which will typically be in the form of hardware logic devices or software logic stored on a medium, and a processor  838  for processing, in accordance with the logic  836 , information provided as an input by a user via the keyboard  832 . The processor  838 , in accordance with the logic  836 , also processes control signals received from the vapor flow sensor  826  via communications line  827 , and generates and directs the transmission of control signals to the solid fossil fuel-fired burners  804  via communications line  805  so as to control the operation of the solid fossil fuel-fired burners  804 , and to the liquid fossil fuel-fired burner  806  via communications line  807  so as to control the operation of the liquid fossil fuel-fired burner  806 , as described in detail below. The logic  836  may include an algorithm or an access instruction to a look-up table having a burner index with preselected burner set points or other data stored in a memory  840  of the controller  830  which can be used to determine the appropriate level of operation for the burners  804 ,  806  based upon received vapor flow information from vapor flow sensor  826 . 
     During start-up operation, the liquid fossil fuel-fired burner  806  is brought on-line so as to perform evaporative duty on the liquid binary working fluid  812  as the liquid binary working fluid  812  flows through the backpass section  818  of the furnace structure  801 . The vapor that is generated from this evaporative duty flows from the backpass section  818  of the furnace structure  801  to a primary section  822  of the furnace structure  801  through one or more fluid transfer tubes  820 . The vapor then flows through the tubular walls  802  and the suspended fluid tubes  808 ′ of the superheat panels  808 . The vapor eventually flows from the furnace structure  801  through the fluid exit tubes  814  to the turbine/generator subsystem and to the regeneration subsystem, where the vapor is transformed back into a liquid and then fed back to the furnace structure  801  through the fluid entry tubes  810 . 
     After the initial vapor flow has been generated through the operation of the liquid fossil fuel-fired burner  806  during start-up operation, the solid fossil fuel-fired burners  804  are brought on-line to begin normal operation and to increase the rate of vapor flow through the furnace structure  801  and the entire multi-component working fluid power generation system. As with the solid fossil fuel-fired burners  704  in the furnace structure  701  of FIG. 7, the solid fossil fuel-fired burners  804  typically generate very high temperature combustion gases. These high temperature combustion gases could easily damage the tubular walls  802  of the furnace structure  801  if the initial vapor flow that was generated through the operation of the liquid fossil fuel-fired burner  806  during start-up operation was not present. That is, the initial vapor flow that was generated through the operation of the liquid fossil fuel-fired burner  806  during start-up operation acts to cool the tubular walls  802  of the furnace structure  801  during the beginning stages of normal operation, thereby preventing any overheating and subsequent damage to the tubular walls  802  of the furnace structure  801  caused by the high temperature combustion gases generated by the solid fossil fuel-fired burners  804 . 
     During normal operation, the liquid fossil fuel-fired burner  806  is brought off-line since the solid fossil fuel-fired burners  804  generate enough process heat to evaporate the liquid binary working fluid  812  as the liquid binary working fluid  812  flows through the backpass section  818  of the furnace structure  801 . As in start-up operation, the vapor that is generated in the backpass section  818  of the furnace structure  801  during normal operation works to cool the tubular walls  802  of the furnace structure  801 . However, during normal operation, the vapor that is generated in the backpass section  818  of the furnace structure  801  also becomes superheated as the vapor flows through the tubular walls  802  of the furnace structure  801 . That is, during normal operation, the vapor that is generated in the backpass section  818  of the furnace structure  801  flows from the backpass section  818  of the furnace structure  801  to the primary section  822  of the furnace structure  801  through the fluid transfer tubes  820 . The vapor is then superheated by the process heat generated by the solid fossil fuel fired burners  804  as the vapor flows through the tubular walls  802  and the suspended fluid tubes  808 ′ of the superheat panels  808 . Thereafter, the superheated binary working fluid  816  flows from the furnace structure  801  through the fluid exit tubes  814  to the turbine/generator subsystem where the superheated binary working fluid  816  is typically used to generate electrical power. The superheated binary working fluid  816  is then transformed back into a liquid in the regeneration subsystem and then fed back to the furnace structure  801  from the regeneration subsystem through the fluid entry tubes  810 . 
     At this point it should be noted that since the primary section  822  of the furnace structure  801  is operating exclusively as a superheater during normal operation, the superheat panels  808  may not be required, thereby simplifying the design of the furnace structure  801 . 
     FIG. 9 illustrates a multi-component working fluid power generation system  900  incorporating some of the principles discussed above with reference to FIG. 8, and also incorporating some of the functions discussed above with reference to FIGS.  1 - 6 . The multi-component working fluid power generation system  900  comprises a furnace structure  901  which is similar to the furnace structure  801  in FIG. 8 by having tubular walls  902 , a single bank of solid fossil fuel-fired burners  904  in a primary section  922  of the furnace structure  901 , a liquid fossil fuel-fired burner  906  in a backpass section  918  of the furnace structure  901 , and one or more hanging superheat panels  908  formed of suspended fluid tubes  908 ′. The furnace structure  901  in FIG. 9 is also similar to the furnace structure  801  in FIG. 8 in that the primary section  922  of the furnace structure  901  is operating exclusively as a superheater during normal operation. Thus, similar to the superheat panels  808 , the superheat panels  908  may not be required, thereby simplifying the design of the furnace structure  901 . 
     The multi-component working fluid power generation system  900  also comprises one or more spray stations  924  for controlling the temperature of superheated working fluid flowing through the tubing of the furnace structure  901 , a vapor flow sensor  926 , a single input/dual output valve device  928 , and a controller  930 , which includes a keyboard  932  for receiving information provided as an input from a user and a monitor  934  for displaying information to a user. It should be understood that other types of input devices, e.g., a keypad, mouse, touch screen or other devices, and other types of output devices, e.g., a printer, voice synthesizer or other devices, could be substituted if desired for the keyboard  932  and monitor  934 , respectively. The controller  930  also includes logic  936 , which will typically be in the form of hardware logic devices or software logic stored on a medium, and a processor  938  for processing, in accordance with the logic  936 , information provided as an input by a user via the keyboard  932 . The processor  938 , in accordance with the logic  936 , also processes control signals received from the vapor flow sensor  926  via communications line  927 , and generates and directs the transmission of control signals to the spray stations  924  via communications line  925  so as to control the temperature of superheated working fluid flowing through the tubing of the furnace structure  901 , to the valve device  928  via communications line  929  so as to control the flow path of working fluid stream FS  20 , to the solid fossil fuel-fired burners  904  via communications line  905  so as to control the operation of the solid fossil fuel-fired burners  904 , and to the liquid fossil fuel-fired burner  906  via communications line  907  so as to control the operation of the liquid fossil fuel-fired burners  906 , as described in detail below. The logic  936  may include an algorithm or an access instruction to a look-up table having a flow index with preselected flow set points or other data stored in a memory  940  of the controller  930  which can be used to determine the appropriate flow path setting for the valve device  928  based upon received vapor flow information from vapor flow sensor  926 . Similarly, the logic  936  may include an algorithm or an access instruction to a look-up table having a burner index with preselected burner set points or other data stored in the memory  940  of the controller  930  which can be used to determine the appropriate level of operation for the burners  904 ,  906  based upon received vapor flow information from vapor flow sensor  926 . 
     As previously noted, the primary section  922  of the furnace structure  901  operates exclusively as a superheater during normal operation. The multi-component working fluid power generation system  900  allows for such operation by overcoming the fact that there would be insufficient vapor flow to cool the tubular walls  902  of the furnace structure  901  if the solid fossil fuel-fired burners  904  were brought on-line at the beginning of start-up operation. This lack of sufficient vapor flow through the furnace structure  901  would also result in a failure of the TGSS  130  to provide hot fluid streams to both the DCSS  100  and the RHE  140 , which would result in the failure of these subsystems to perform their designated regeneration functions. The multi-component working fluid power generation system  900  overcomes these potential failures through a reconfiguration process controlled by the controller  930 . More particularly, during start-up operation, the controller  930  configures the multi-component working fluid power generation system  900  such that the valve device  928  directs the liquid working fluid stream FS  20  along flow path  942  where the liquid working fluid stream FS  20  is combined with the liquid working fluid stream FS  5  and directed along flow path  944 . The combination of liquid working fluid stream FS  20  and liquid working fluid stream FS  5  is then combined with liquid working fluid stream FS  7  and directed along flow path  946  to the backpass section  918  of the furnace structure  901 . The controller  930  also brings the liquid fossil fuel-fired burner  906  on-line during start-up operation so as to perform evaporative duty on the combination of liquid working fluid stream FS  20 , liquid working fluid stream FS  5 , and liquid working fluid stream FS  7  as the combination of these three liquid working fluid streams flows through the backpass section  918  of the furnace structure  901 . The vapor that is generated from this evaporative duty flows from the backpass section  918  of the furnace structure  901  to the primary section  922  of the furnace structure  901  along flow paths  948  and  950 . The vapor then flows through the tubular walls  902  and the suspended fluid tubes  908 ′ of the superheat panels  908 . The vapor eventually flows from the furnace structure  901  as hot working fluid stream FS  40  to the TGSS  130  where hot working fluid streams FS  40 ″ and FS  40 ″′ are extracted and thereafter combined with hot working fluid stream FS  30  to form hot working fluid stream  3010 . As described below, hot working fluid stream  3010  is eventually used to vaporize cold working fluid stream FS  20  in the RHE  140 . 
     Throughout start-up operation, the vapor flow sensor  926  provides vapor flow information to the controller  930 . Once it is determined that a sufficient amount of initial vapor flow has been generated through the operation of the liquid fossil fuel-fired burner  906  during start-up operation, the controller  930  brings the solid fossil fuel-fired burners  904  on-line to begin normal operation and to increase the rate of vapor flow through the furnace structure  901  and the entire multi-component working fluid power generation system  900 . As with the solid fossil fuel-fired burners  804  in the furnace structure  801  of FIG. 8, the solid fossil fuel-fired burners  904  typically generate very high temperature combustion gases. These high temperature combustion gases could easily damage the tubular walls  902  of the furnace structure  901  if the initial vapor flow that was generated through the operation of the liquid fossil fuel-fired burner  906  during start-up operation was not present. That is, the initial vapor flow that was generated through the operation of the liquid fossil fuel-fired burner  906  during start-up operation acts to cool the tubular walls  902  of the furnace structure  901  during the beginning stages of normal operation, thereby preventing any overheating and subsequent damage to the tubular walls  902  of the furnace structure  901  caused by the high temperature combustion gases generated by the solid fossil fuel-fired burners  904 . 
     After the solid fossil fuel-fired burners  904  are brought on-line at the start of normal operation, the liquid fossil fuel-fired burner  906  is brought off-line since the solid fossil fuel-fired burners  904  generate enough process heat to evaporate the liquid working fluid flowing through the backpass section  918  of the furnace structure  901 . As in start-up operation, the vapor that is generated in the backpass section  918  of the furnace structure  901  during normal operation works to cool the tubular walls  902  of the furnace structure  901 . However, during normal operation, the vapor that is generated in the backpass section  918  of the furnace structure  901  also becomes superheated as the vapor flows through the tubular walls  902  of the furnace structure  901 . That is, during normal operation, the vapor that is generated in the backpass section  918  of the furnace structure  901  flows from the backpass section  918  of the furnace structure  901  to the primary section  922  of the furnace structure  901  along flow paths  948  and  950 . The vapor is then superheated by the process heat generated by the solid fossil fuel-fired burners  904  as the vapor flows through the tubular walls  902  and the suspended fluid tubes  908 ′ of the superheat panels  908 . At this point, the spray stations  924 , with input from liquid working fluid stream FS  7 , can be used to control the temperature of the superheated working fluid flowing through the tubing of the furnace structure  901 . Eventually, the superheated working fluid flows from the furnace structure  901  as superheated working fluid stream FS  40  to the TGSS  130  where the superheated working fluid is typically used to generate electrical power. 
     As previously described, hot working fluid streams FS  40 ″ and FS  40 ″′ are extracted from the TGSS  130  and thereafter combined with hot working fluid stream FS  30  to form hot working fluid stream  3010 . During start-up operation, the temperature of working fluid stream  3010  is generally not hot enough to vaporize the cold working fluid stream FS  20  in the RHE  140 . However, during normal operation, the temperature of working fluid stream  3010  is hot enough to vaporize the cold working fluid stream FS  20  in the RHE  140 . Therefore, during normal operation, the controller  930  reconfigures the multi-component working fluid power generation system  900  such that the valve device  928  directs the cold liquid working fluid stream FS  20  along flow path  952  to the RHE  140 . The cold liquid working fluid stream FS  20  can then be vaporized by the hot working fluid stream  3010  in the RHE  140 . Thereafter, this vaporized working fluid is directed along flow path  954 . During this same process, the hot working fluid stream  3010  is condensed by the cold liquid working fluid stream FS  20  in the RHE  140 , thereby forming condensate  3010 ′. Thereafter, the condensate  3010 ′ is directed, as liquid working fluid stream FS  5 , along flow path  944  where liquid working fluid stream FS  5  is combined with the liquid working fluid stream FS  7 . The combination of liquid working fluid stream FS  5  and liquid working fluid stream FS  7  is then directed along flow path  946  to the backpass section  918  of the furnace structure  901 , where this combination of two liquid working fluid streams is vaporized by the process heat generated by the solid fossil fuel-fired burners  904 . The vaporized working fluid that is generated in the backpass section  918  of the furnace structure  901  is then directed along flow path  948 , where this vaporized working fluid is combined with the vaporized working fluid that was generated in the RHE  140  and directed along flow path  954 . The combination of the vaporized working fluid from the RHE  140  and the vaporized working fluid from the backpass section  918  of the furnace structure  901  is then directed to the primary section  922  of the furnace structure  901  along flow path  950 , where this combination of vaporized working fluids is superheated by the process heat generated by the solid fossil fuel-fired burners  904 . 
     FIG. 10 illustrates another furnace system  1000  for use in a multi-component working fluid power generation system in accordance with the present invention. The furnace system  1000  includes a furnace structure  1001  comprising tubular walls  1002  and a single bank of solid fossil fuel-fired burners  1004 , which are located in the tubular walls  1002 . The furnace structure  1001  also comprises one or more hanging superheat panels  1008  formed of suspended fluid tubes  1008 ′. The furnace structure  1001  further comprises a vapor flow sensor  1026  for sensing the vapor flow through the tubular walls  1002  of the furnace structure  1001 . The furnace structure  1001  still further comprises one or more fluid entry tubes  1010  for conveying liquid binary working fluid  1012  to the furnace structure  1001 , and one or more fluid exit tubes  1014  for conveying superheated binary working fluid  1016  from the furnace structure  1001 . The liquid binary working fluid  1012  typically flows to the furnace structure  1001  from a regeneration subsystem (not shown) of a multi-component working fluid power generation system, and the superheated binary working fluid  1016  typically flows from the furnace structure  1001  to a turbine/generator subsystem (not shown) of a multi-component working fluid power generation system. 
     The furnace structure  1001  in FIG. 10 differs from the furnace structure  701  in FIG.  7  and the furnace structure  801  in FIG. 8 in that no liquid fossil fuel-fired burner is required to perform evaporative duty. Instead, the furnace structure  100  comprises an inner tubular wall  1024  formed of loose fluid tubes  1024 ′ located adjacent to the solid fossil fuel-fired burners  1004  for performing evaporative duty. This is significant in that the solid fossil fuel-fired burners  1004  in the furnace structure  1001  can be used to perform both evaporative and superheating duty at the same time, as described in detail below. 
     The furnace system  1000  also includes a controller  1030 , which includes a keyboard  1032  for receiving information provided as an input from a user and a monitor  1034  for displaying information to a user. It should be understood that other types of input devices, e.g., a keypad, mouse, touch screen or other devices, and other types of output devices, e.g., a printer, voice synthesizer or other devices, could be substituted if desired for the keyboard  1032  and monitor  1034 , respectively. The controller  1030  also includes logic  1036 , which will typically be in the form of hardware logic devices or software logic stored on a medium, and a processor  1038  for processing, in accordance with the logic  1036 , information provided as an input by a user via the keyboard  1032 . The processor  1038 , in accordance with the logic  1036 , also processes control signals received from the vapor flow sensor  1026  via communications line  1027 , and generates and directs the transmission of control signals to the solid fossil fuel-fired burners  1004  via communications line  1005  so as to control the operation of the solid fossil fuel-fired burners  1004 , as described in detail below. The logic  1036  may include an algorithm or an access instruction to a look-up table having a burner index with preselected burner set points or other data stored in a memory  1040  of the controller  1030  which can be used to determine the appropriate level of operation for the solid fossil fuel-fired burners  1004  based upon received vapor flow information from vapor flow sensor  1026 . 
     During start-up operation, the solid fossil fuel-fired burners  1004  are brought on-line at a low level so as to perform evaporative duty on the liquid binary working fluid  1012  as the liquid binary working fluid  1012  flows through the loose fluid tubes  1024 ′ of the inner tubular wall  1024 . The vapor that is generated from this evaporative duty flows from the inner tubular wall  1024  to a primary section  1022  of the furnace structure  1001  through one or more fluid transfer tubes  1020 . The vapor then flows through the tubular walls  1002  and the suspended tubular tubes  1008 ′ of the superheat panels  1008 . The vapor eventually flows from the furnace structure  1001  through the fluid exit tubes  1014  to the turbine/generator subsystem and to the regeneration subsystem, where the vapor is transformed back into a liquid and then fed back to the furnace structure  1001  through the fluid entry tubes  1010 . 
     After the initial vapor flow has been generated through the low level operation of the solid fossil fuel-fired burners  1004  during start-up operation, the level of operation of the solid fossil fuel-fired burners  1004  is gradually increased to begin normal operation and to increase the rate of vapor flow through the furnace structure  1001  and the entire multi-component working fluid power generation system. As with the solid fossil fuel-fired burners  704  in the furnace structure  701  of FIG.  7  and the solid fossil fuel-fired burners  804  in the furnace structure  801  of FIG. 8, the solid fossil fuel-fired burners  1004  typically generate very high temperature combustion gases at normal operation. These high temperature combustion gases could easily damage the tubular walls  1002  of the furnace structure  1001  if the initial vapor flow that was generated through the low level operation of the solid fossil fuel-fired burners  1004  during startup operation was not present. That is, the initial vapor flow that was generated through the low level operation of the solid fossil fuel-fired burners  1004  during start-up operation acts to cool the tubular walls  1002  of the furnace structure  1001  during the beginning stages of normal operation, thereby preventing any overheating and subsequent damage to the tubular walls  1002  of the furnace structure  1001  caused by the high temperature combustion gases generated by the solid fossil fuel-fired burners  1004 . It should also be noted that the inner tubular wall  1024  also serves to protect the tubular walls  1002  of the furnace structure  1001  by shielding the tubular walls  1002  from the solid fossil fuel-fired burners  1004 . 
     As in start-up operation, the vapor that is generated in the inner fluid walls  1024  during normal operation works to cool the tubular walls  1002  of the furnace structure  1001 . However, during normal operation, the vapor that is generated in the inner tubular walls  1024  also becomes superheated as the vapor flows through the tubular walls  1002  of the furnace structure  1001 . That is, during normal operation, the vapor that is generated in the inner tubular walls  1024  flows from the inner tubular walls  1024  to the primary section  1022  of the furnace structure  1001  through the fluid transfer tubes  1020 . The vapor is then superheated by the process heat generated by the solid fossil fuel-fired burners  1004  as the vapor flows through the tubular walls  1002  and the suspended fluid tubes  1008 ′ of the superheat panels  1008 . Thereafter, the superheated binary working fluid  1016  flows from the furnace structure  1001  through the fluid exit tubes  1014  to the turbine/generator subsystem where the superheated binary working fluid  1016  is typically used to generate electrical power. The superheated binary working fluid  1016  is then transformed back into a liquid in the regeneration subsystem and thereafter fed back to the furnace structure  1001  from the regeneration subsystem through the fluid entry tubes  1010 . 
     At this point it should be noted that since the primary section  1022  of the furnace structure  1001  is operating exclusively as a superheater during normal operation, the superheat panels  1008  may not be required, thereby simplifying the design of the furnace structure  1001 . 
     FIG. 11 illustrates a multi-component working fluid power generation system  1100  incorporating some of the principles discussed above with reference to FIG. 10, and also incorporating some of the functions discussed above with reference to FIGS. 1-6. The multi-component working fluid power generation system  1100  comprises a furnace structure  1101  which is similar to the furnace structure  1001  in FIG. 10 by having tubular walls  1102 , a single bank of solid fossil fuel-fired burners  1104  in a primary section  1122  of the furnace structure  1101 , an inner tubular wall  1124  formed of loose fluid tubes  1124 ′ located adjacent to the solid fossil fuel-fired burners  1104  for performing evaporative duty, and one or more hanging superheat panels  1108  formed of suspended fluid tubes  1108 ′. The furnace structure  1101  in FIG. 11 is also similar to the furnace structure  1001  in FIG. 10 in that the primary section  1122  of the furnace structure  1101  is operating exclusively as a superheater during normal operation. Thus, similar to the superheat panels  1008 , the superheat panels  1108  may not be required, thereby simplifying the design of the furnace structure  1101 . 
     The multi-component working fluid power generation system  1100  also comprises a vapor flow sensor  1126 , a steam drum  1156 , a fluid pump  1128 , and a controller  1130 , which includes a keyboard  1132  for receiving information provided as an input from a user and a monitor  1134  for displaying information to a user. It should be understood that other types of input devices, e.g., a keypad, mouse, touch screen or other devices, and other types of output devices, e.g., a printer, voice synthesizer or other devices, could be substituted if desired for the keyboard  1132  and monitor  1134 , respectively. The controller  1130  also includes logic  1136 , which will typically be in the form of hardware logic devices or software logic stored on a medium, and a processor  1138  for processing, in accordance with the logic  1136 , information provided as an input by a user via the keyboard  1132 . The processor  1138 , in accordance with the logic  1136 , also processes control signals received from the vapor flow sensor  1126  via communications line  1127 , and generates and directs the transmission of control signals to the fluid pump  1128  via communications line  1129  so as to control the flow of working fluid from the steam drum  1156  to the inner tubular wall  1124 , as described in detail below. The processor  1138 , in accordance with the logic  1136 , further generates and directs the transmission of control signals to the solid fossil fuel-fired burners  1104  via communications line  1105  so as to control the operation of the solid fossil fuel-fired burners  1104 , as described in detail below. The logic  1136  may include an algorithm or an access instruction to a look-up table having a flow index with preselected flow set points or other data stored in a memory  1140  of the controller  1130  which can be used to determine the appropriate flow setting for the fluid pump  1128  based upon received vapor flow information from vapor flow sensor  1126 . Similarly, the logic  1136  may include an algorithm or an access instruction to a look-up table having a burner index with preselected burner set points or other data stored in the memory  1140  of the controller  1130  which can be used to determine the appropriate level of operation for the solid fossil fuel-fired burners  1104  based upon received vapor flow information from vapor flow sensor  1126 . 
     As previously noted, the primary section  1122  of the furnace structure  1101  operates exclusively as a superheater during normal operation. The multi-component working fluid power generation system  1100  allows for such operation by utilizing the inner tubular wall  1124  as both a vessel for performing evaporative duty and a shield for protecting the tubular walls  1102  of the furnace structure  1101 . Both of these functions of the inner tubular wall  1124  act against the process heat generated by the solid fossil fuel-fired burners  1104 , as described in detail below. 
     During normal operation, the cold liquid working fluid stream FS  20  is vaporized, and possibly even superheated, by heat energy  125  in the RHE  140 . Thereafter, this vaporized working fluid is directed along flow path  1154  to the primary section  1122  of the furnace structure  1101  where this vaporized working fluid is superheated, or even further superheated, by the process heat generated by the solid fossil fuel-fired burners  1104  as it flows through the tubular walls  1102  and the suspended fluid tubes  1108 ′ of the superheat panels  1108 . However, due to the already elevated temperature of this vaporized working fluid, the tubular walls  1102  of the furnace structure  1101  proximate to the solid fossil fuel fired burners  1104  can not be sufficiently cooled by this vaporized working fluid. Instead, the inner tubular wall  1124  is provided to perform this function. 
     The inner tubular wall  1124  provides cooling to the tubular walls  1102  of the furnace structure  1101  by allowing the solid fossil fuel-fired burners  1104  to perform an evaporative duty on a lean liquid working fluid  1158  as this lean liquid working fluid  1158  flows through the loose fluid tubes  1124 ′ of the inner tubular wall  1124 . The lean liquid working fluid  1158 , which is supplied by the steam drum  1156 , is forced along flow paths  1160  and  1162  to the inner tubular wall  1124  by the fluid pump  1128 . The fluid pump  1128  further forces the lean liquid working fluid  1158  through the loose fluid tubes  1124 ′ of the inner tubular wall  1124  where this lean liquid working fluid  1158  is evaporated by the process heat generated by the solid fossil fuel-fired burners  1104 . The vapor that is generated from this evaporative duty flows along flow path  1164  back to the steam drum  1156  where a portion may be condensed back into the lean liquid working fluid  1158 . However, the majority of the vapor is directed along flow path  1166 , where this vapor is combined with the hot working fluid stream  3010  and directed along flow path  1168  to the RHE  140 . In the RHE  140 , the combination of the vapor and the hot working fluid stream  3010  transfers heat energy  125  to the cold liquid working fluid stream FS  20  which thereafter condenses to form condensate  3010 ′. The condensate  3010 ′ flows from the RHE  140 , as liquid working fluid stream FS  5 , and is combined with the liquid working fluid stream FS  7 . The combination of liquid working fluid stream FS  5  and liquid working fluid stream FS  7  is then directed along flow path  1170  to the steam drum  1156  to form the supply of lean liquid working fluid  1158 . 
     As previously noted, the inner tubular wall  1124  may also serve as a shield for protecting the tubular walls  1102  of the furnace structure  1101  from the high temperature combustion gases generated by the solid fossil fuel-fired burners  1104 . If such is the case, the fluid tubes  1124 ′ of the inner tubular wall  1124  may or may not be interconnected by fins depending upon the degree of shielding required. That is, the fluid tubes  1124 ′ of the inner tubular wall  1124  may be interconnected by fins so as to increase the amount of shielding that is provided to the tubular walls  1102  of the furnace structure  1101 . 
     FIG. 12 illustrates a multi-component working fluid power generation system  1200  having a vapor recirculation system for providing furnace wall cooling during start-up and low-load operation in accordance with the present invention. The multi-component working fluid power generation system  1200  comprises a furnace structure  1201  having tubular walls  1202 , a single bank of solid fossil fuel-fired burners  1204  in a primary section  1222  of the furnace structure  1201 , and one or more hanging superheat panels  1208  formed of suspended fluid tubes  1208 ′. The multi-component working fluid power generation system  1200  also comprises one or more spray stations  1224 , a vapor flow sensor  1226 , a single input/dual output valve device  1228 , a first conventional valve device  1272 , a second conventional valve device  1274 , a third conventional valve device  1276 , a start-up compressor  1278 , and a recirculation compressor  1280 . The multi-component working fluid power generation system  1200  further comprises a controller  1230 , which includes a keyboard  1232  for receiving information provided as an input from a user and a monitor  1234  for displaying information to a user. It should be understood that other types of input devices, e.g., a keypad, mouse, touch screen or other devices, and other types of output devices, e.g., a printer, voice synthesizer or other devices, could be substituted if desired for the keyboard  1232  and monitor  1234 , respectively. The controller  1230  also includes logic  1236 , which will typically be in the form of hardware logic devices or software logic stored on a medium, and a processor  1238  for processing, in accordance with the logic  1236 , information provided as an input by a user via the keyboard  1232 . The processor  1238 , in accordance with the logic  1236 , also processes control signals received from the vapor flow sensor  1226  via communications line  1227 , and generates and directs the transmission of control signals to the solid fossil fuel-fired burners  1204  via communications line  1205  so as to control the operation of the solid fossil fuel-fired burners  1204 , to the spray stations  1224  via communications line  1225  so as to control the temperature of superheated working fluid flowing through the tubing of the furnace structure  1201 , to the single input/dual output valve device  1228  via communications line  1229  so as to control the operation of the single input/dual output valve device  1228 , to the first conventional valve device  1272  via communications line  1273  so as to control the operation of the first conventional valve device  1272 , to the second conventional valve device  1274  via communications line  1275  so as to control the operation of the second conventional valve device  1274 , to the third conventional valve device  1276  via communications line  1277  so as to control the operation of the third conventional valve device  1276 , to the start-up compressor  1278  via communications line  1279  so as to control the operation of the start-up compressor  1278 , and to the recirculation compressor  1280  via communications line  1281  so as to control the operation of the recirculation compressor  1280 , as described in detail below. The logic  1236  may include an algorithm or an access instruction to a look-up table having a flow index with preselected flow set points or other data stored in a memory  1240  of the controller  1230  which can be used to determine the appropriate settings for the single input/dual output valve device  1228 , the first conventional valve device  1272 , the second conventional valve device  1274 , the third conventional valve device  1276 , the start-up compressor  1278 , and the recirculation compressor  1280  based upon received vapor flow information from vapor flow sensor  1226 . Similarly, the logic  1236  may include an algorithm or an access instruction to a look-up table having a burner index with preselected burner set points or other data stored in the memory  1240  of the controller  1230  which can be used to determine the appropriate level of operation for the solid fossil fuel-fired burners  1204  based upon received vapor flow information from vapor flow sensor  1226 . 
     During start-up operation, the controller  1230  first causes the first conventional valve device  1272  and the second conventional valve device  1274  to open, and then sets the single input/dual output valve device  1228  such that flow path  1228 ′ is entirely directed to flow path  1228 ″ , thereby totally disconnecting flow path  1228 ′ from flow path  1228 ″′ and the TGSS  130 . The controller  1230  then directs the start-up compressor  1278  to inject a non-condensing vapor into the multi-component working fluid power generation system  1200  along flow paths  1272 ′ and  1272 ″ at a specific pressure such as, for example, 300-500 psi. The injected non-condensing vapor may be one of a variety of non-condensing vapor types such as, for example, air or nitrogen. The injected non-condensing vapor is pressurized to reduce the power required by the recirculation compressor  1280 , as described in detail below. 
     After the non-condensing vapor is injected and the system  1200  is pressurized, the controller  1230  causes the first conventional valve device  1272  to close, thereby disconnecting flow path  1272 ′ from flow path  1272 ″ and sealing the injected non-condensing vapor within the system  1200 . At this point it should be noted that a vapor generated in an evaporator internal to the system  1200 , or a vapor generated in an evaporator external to the system  1200 , could alternatively be used as the injected vapor. 
     After the system  1200  is sealed, the controller  1230  directs the recirculation compressor  1280  to begin recirculating the injected non-condensing vapor throughout the system  1200 . That is, the recirculation compressor  1280  recirculates the injected non-condensing vapor through the tubular walls  1202 , the suspended tubular tubes  1208 ′ of the superheat panels  1208 , and the RHE  140 . At this point it should be noted that the third conventional valve device  1276  is in a closed state. 
     After the injected non-condensing vapor has begun to recirculate through the system  1200 , the controller  1230  brings the solid fossil fuel-fired burners  1204  on-line at a low level so as to increase the temperature of the injected non-condensing vapor. As the temperature of the injected non-condensing vapor increases, the pressure of the injected non-condensing vapor also increases. In fact, the process heat generated from the solid fossil fuel-fired burners  1204  can alternatively be used to initially pressurize the injected non-condensing vapor in the system  1200  instead of the start-up compressor  1278 . In any event, once the temperature of the injected non-condensing vapor reaches a predefined threshold such as, for example, 700 degrees Fahrenheit, a liquid binary working fluid is added to the injected non-condensing vapor. This liquid binary working fluid can be, for example, the liquid binary working fluid stream FS  7 , which is added at the spray stations  1224 . Alternatively, the liquid binary working fluid could be liquid working fluid stream FS  20  or liquid working fluid stream FS  30 . In any event, once the liquid binary working fluid comes into contact with the high temperature injected non-condensing vapor, the liquid binary working fluid is immediately vaporized. That is, the high temperature injected non-condensing vapor vaporizes the liquid binary working fluid as the liquid binary working fluid is added to the system  1200 . 
     More and more liquid binary working fluid is added to the system  1200  and vaporized by the high temperature injected non-condensing vapor. The combination of the injected non-condensing vapor and the working fluid vapor is recirculated through the system  1200  by the recirculation compressor  1280 . Some of the vapor combination is directed along flow paths  3012  and  3014  to the RHE  140  where additional working fluid vapor is generated. At some point, the controller  1230  causes the third conventional valve device  1276  to open, thereby allowing some of the vapor combination to travel along flow paths  1276 ′ and  1276 ″ to the DCSS  100 . The DCSS  100  includes a condenser  102  which condenses the working fluid vapor so as to form liquid working fluid stream FS  30 . The condenser  102  also vents off the injected non-condensing vapor  103  to the atmosphere. 
     Eventually, all of the injected non-condensing vapor will be vented off and the controller  1230  will again cause the third conventional valve device  1276  to be closed. At this point, the RHE  140  is generating a sufficient amount of binary working fluid vapor to safely cool the tubular walls  1202  of the furnace structure  1201 . The controller  1230  can then shut down the recirculation system by directing the recirculation compressor  1280  to stop recirculating the binary working fluid vapor, by causing the second conventional valve device  1274  to close, and by setting the single input/dual output valve device  1228  such that flow path  1228 ′ is entirely directed to flow path  1228 ″′, thereby totally disconnecting flow path  1228 ′ from flow path  1228 ″ . Heretofore, only a small amount of binary working fluid vapor (e.g., a bleed stream) was allowed to the TGSS  130  for warm-up purposes. 
     Throughout the above-described start-up process, the controller  1230  gradually increases the level of operation of the solid fossil fuel-fired burners  1204 . Thus, during normal operation, there is sufficient process heat generated by the solid fossil fuel-fired burners  1204  such that evaporative duty can be performed on binary working fluid stream FS  57  in the backpass section  1218  of the furnace structure  1201 . The vaporized binary working fluid stream FS  57 ′ is then combined with vaporized binary working fluid stream FS  20 ′ from the RHE  140  and directed to the primary section  1222  of the furnace structure  1201  for superheating duty. Thus, during normal operation, the primary section  1222  of the furnace structure  1201  operates exclusively as a superheater. Consequently, the superheat panels  1208  may not be required, thereby simplifying the design of the furnace structure  1201 . 
     FIG. 13 illustrates a multi-component working fluid power generation system  1300  having a fluid separating/combining system for providing furnace wall cooling during start-up and normal operation in accordance with the present invention. The multi-component working fluid power generation system  1300  comprises a furnace structure  1301  having lower tubular walls  1302 , upper tubular walls  1303 , a single bank of coal-fired burners  1304  in a primary section  1322  of the furnace structure  1301 , and one or more hanging superheat panels  1308  formed of suspended fluid tubes  1308 ′. The multi-component working fluid power generation system  1300  also comprises a vapor flow sensor  1326 , a fluid pump  1328 , a fluid separator  1382 , and a fluid combiner  1384 . The multi-component working fluid power generation system  1300  further comprises a controller  1330 , which includes a keyboard  1332  for receiving information provided as an input from a user and a monitor  1334  for displaying information to a user. It should be understood that other types of input devices, e.g., a keypad, mouse, touch screen or other devices, and other types of output devices, e.g., a printer, voice synthesizer or other devices, could be substituted if desired for the keyboard  1332  and monitor  1334 , respectively. The controller  1330  also includes logic  1336 , which will typically be in the form of hardware logic devices or software logic stored on a medium, and a processor  1338  for processing, in accordance with the logic  1336 , information provided as an input by a user via the keyboard  1332 . The processor  1338 , in accordance with the logic  1336 , also processes control signals received from the vapor flow sensor  1326  via communications line  1327 , and generates and directs the transmission of control signals to the solid fossil fuel-fired burners  1304  via communications line  1305  so as to control the operation of the solid fossil fuel-fired burners  1304 , to the fluid pump  1328  via communications line  1329  so as to control the operation of the fluid pump  1328 , and to a fluid combiner  1384  via communications line  1385  so as to control the operation of the fluid combiner  1384 , as described in detail below. The logic  1336  may include an algorithm or an access instruction to a look-up table having a flow index with preselected flow set points or other data stored in a memory  1340  of the controller  1330  which can be used to determine the appropriate settings for the fluid pump  1328  and the fluid combiner  1384  based upon received vapor flow information from vapor flow sensor  1326 . Similarly, the logic  1336  may include an algorithm or an access instruction to a look-up table having a burner index with preselected burner set points or other data stored in the memory  1340  of the controller  1330  which can be used to determine the appropriate level of operation for the solid fossil fuel-fired burners  1304  based upon received vapor flow information from vapor flow sensor  1326 . 
     During start-up operation, the controller  1330  first brings the solid fossil fuel-fired burners  1304  on-line at a low level, and sets the fluid combiner  1384  such that flow path  1384 ″ accepts fluid flows from only flow path  1382 ″′, thereby totally disconnecting flow path  1384 ′ from flow path  1384 ″. The controller  1330  then directs the fluid pump  1328  to force a lean liquid working fluid stream FS  57  along flow path  1357  to the backpass section  1318  of the furnace structure  1301  for preheating duty by the combustion gases generated by the solid fossil fuel-fired burners  1304 . The fluid pump  1328  then forces a preheated lean liquid working fluid stream FS  57 ′ along flow path  1386  to the primary section  1322  of the furnace structure  1301  for evaporative duty in the lower tubular walls  1302  of the furnace structure  1301 . 
     The lower tubular walls  1302 , have spiral fluid tubes  1302 ′ so as to provide a long flow path length for the preheated lean liquid working fluid stream FS  57 ′ as the preheated lean liquid working fluid FS  57  flows through the lower tubular walls  1302  for the evaporative duty. However, due to the low level operation of the solid fossil fuel-fired burners  1304 , and the high boiling point of the preheated lean liquid working fluid stream FS  57 ′, only a portion of the preheated lean liquid working fluid stream FS  57 ′ becomes vaporized in the lower tubular walls  1302  during start-up operation. The resulting vapor/liquid mixture is directed from the lower tubular walls  1302  along flow path  1382 ′ to the fluid separator  1382 , from which vapor is directed to the fluid combiner  1384  along flow path  1382 ″ and liquid is directed along flow path  1382 ″ where this liquid is combined with the preheated lean liquid working fluid stream FS  57 ′ and again forced along flow path  1386  to the primary section  1322  of the furnace structure  1301  for evaporative duty in the lower tubular walls  1302  of the furnace structure  1301 . The vapor that is directed to the fluid combiner  1384  along flow path  1382 ″ is, further directed along flow path  1384 ″ to the upper tubular walls  1303  for further evaporative duty. The upper tubular walls  1303  are shown having vertical fluid tubes  1303 ′, but other types of fluid tubes (e.g., spiral, ribbed, etc.) are also possible depending upon flow rate. 
     During start-up operation, the vapor that is generated in the upper tubular walls  1303 , and also in the suspended fluid tubes  1308 ′ of the superheat panels  1308 , eventually flows from the furnace structure  1301  as hot working fluid stream FS  40  to the TGSS  130  where hot working fluid streams FS  40 ″ and FS  40 ″′ are extracted and thereafter combined with hot working fluid stream FS to form hot working fluid stream  3010 . As described below, hot working fluid stream  3010  is eventually used to vaporize rich cold working fluid stream FS  20  in the RHE  140 . 
     At this point it should be noted that temperature differences can occur in different portions of the preheated lean liquid working fluid stream FS  57 ′ as it flows through the lower tubular walls  1302  for the evaporative duty. That is, some of the fluid tubes  1302 ′ in the lower tubular walls  1302  may become hotter than others depending upon the proximity of each individual fluid tubes  1302 ′ to the solid fossil fuel-fired burners  1304 . Thus, some portions of the preheated lean liquid working fluid stream FS  57 ′ flowing through fluid tubes  1302 ′ will absorb more heat than other portions, thereby resulting in temperature differences in different portions of the preheated lean liquid working fluid stream FS  57 ′ at the outputs of the fluid tubes  1302 ′. However, these fluid temperature differences are not carried over to the upper tubular walls  1303  since all of lean liquid working fluid stream FS  57 ′ is recombined and directed along flow path  1382 ′ to the fluid separator  1382 , from which vapor is directed to the fluid combiner  1384  along flow path  1382 ″′ and then to the upper tubular walls  1303  along flow path  1384 ″. Thus, a more uniform temperature is maintained in the upper tubular walls  1303 . 
     Throughout start-up operation, the vapor flow sensor  1326  provides vapor flow information to the controller  1330 . Once it is determined that a sufficient amount of initial vapor flow has been generated to cool the furnace walls, the controller  1330  increases the operation elevation of the solid fossil fuel-fired burners  1304  to begin normal operation and to increase the rate of vapor flow through the furnace structure  1301  and the entire multi-component working fluid power generation system  1300 . At this time, the controller  1330  also resets the fluid combiner  1384  such that flow path  1384 ″ accepts fluid flows from both flow path  1382 ′″ and flow path  1384 ′, which carries a rich vaporized working fluid stream FS  20 ′ that is preheated in the backpass section  1318  of the furnace structure  1301 . Thus, during normal operation, the vapor that is generated in the lower tubular walls  1302  of the furnace structure  1301  is combined with a preheated rich vaporized working fluid stream FS  20 ″ and then directed along flow path  1384 ″ to the upper tubular walls  1303  and the suspended fluid tubes  1308 ′ of the superheat panels  1308  for superheating duty. Eventually, the superheated working fluid flows from the furnace structure  1301  as superheated working fluid stream FS  40  to the TGSS  130  where this superheated working fluid is typically used to generate electrical power. 
     As previously described, hot working fluid streams FS  40 ″ and FS  40 ″′ are extracted from the TGSS  130  and thereafter combined with hot working fluid stream FS  30  to form hot working fluid stream  3010 . During start-up operation, the temperature of working fluid stream  3010  is generally not hot enough to vaporize the cold working fluid stream FS  20  in the RHE  140 . However, during normal operation, the temperature of working fluid stream  3010  is hot enough to vaporize the rich cold working fluid stream FS  20  in the RHE  140 , thereby generating rich vaporized working fluid stream FS  20 ′ which is directed along flow path  1384 ′ to the backpass section  1318  of the furnace structure  1301 . During this same process, the hot working fluid stream  3010  is condensed by the cold liquid working fluid stream FS  20  in the RHE  140 , thereby forming condensate  3010 ′. Thereafter, the condensate  3010 ′ is directed, as liquid working fluid stream FS  5 , along flow path  1388  where this liquid working fluid stream FS  5  is combined with the liquid working fluid stream FS  7  to form lean liquid working fluid stream FS  57 . As previously described, the controller  1330  then directs the fluid pump  1328  to force the lean liquid working fluid stream FS  57  along flow path  1357  to the backpass section  1318  of the furnace structure  1301 . 
     As the operation elevation of the solid fossil fuel-fired burners  904  is increased during normal operation, the process heat generated by the solid fossil fuel-fired burners  1304  is similarly increased, thereby causing the lean liquid working fluid stream FS  57  to be vaporized and the rich vaporized working fluid stream FS  20 ′ to be superheated in the backpass section  1318  of the furnace structure  1301 . The lean vaporized working fluid that is generated in the backpass section  1318  of the furnace structure  1301  is directed along flow path  1386  to the primary section  1322  of the furnace structure  1301  for superheating duty in the lower tubular walls  1302  of the furnace structure  1301 . The resulting lean superheated vapor is directed from the lower tubular walls  1302  along flow path  1382 ′ to the fluid separator  1382 , where this resulting lean superheated vapor is then directed to the fluid combiner  1384  along flow path  1382 ″′. That is, during normal operation, all of the fluid that is directed from the lower tubular walls  1302  to the fluid separator  1382  is directed to the fluid combiner  1384  since no liquid is present. 
     The lean superheated vapor that is generated in the lower tubular walls  1302  of the furnace structure  1301  and the rich superheated vapor that is generated in the backpass section  1318  of the furnace structure  1301  are combined in the fluid combiner  1384  and directed along flow path  1384 ″ to the upper tubular walls  1303  for further superheating duty. 
     As is apparent from the foregoing description, the primary section  1322  of the furnace structure  1301  operates exclusively as a superheater during normal operation. Consequently, the superheat panels  1308  may not be required, thereby simplifying the design of the furnace structure  1301 . 
     At this point it should be reiterated that vapor flow through the tubular walls of all of the above-described furnace structures provides much needed cooling to such tubular walls so as to prevent overheating and subsequent damage to the tubular walls. However, in some instances, vapor flow may still not provide adequate protection from the high temperature combustion gases which are generated for superheating duty. To provide further protection against damage and failure of the tubular walls, it may be useful to construct the tubular walls of special materials such as, for example, INCONEL 800 or an equivalent material. Such materials can withstand the high temperature combustion gases that are generated for superheating duty, particularly in the areas adjacent to a heat source whether it be a direct-fired burner, a fluidized bed, waste heat, or another heat source type. It should be noted that such materials can be beneficially coated so as to avoid adverse effects such as, for example, fire-side corrosion on the outside of the fluid tubes. 
     The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the present invention, in addition to those described herein, will be apparent to those of skill in the art from the foregoing description and accompanying drawings. Thus, such modifications are intended to fall within the scope of the appended claims.