Abstract:
An addition to the air compressor of a combustion turbine system is disclosed, which chills the inlet air on warm days. The same equipment with minimal modification is used to prevent inlet air icing conditions on cold days. Referring to FIG.  1 , inlet air conditioner heat exchanger  3  supplies conditioned (chilled or heated) air to the combustion turbine, and heat recovery unit  1  supplies turbine exhaust heat to ammonia absorption refrigeration unit  2 . Control valves  5, 6, 7 , and  8  selectively supply either chilling refrigerant liquid or heating vapor from AARU  2  to conditioning heat exchanger coil  3.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of U.S. Provisional Patent Application 60/965,691 filed on 21 Aug. 2007, which is hereby incorporated by reference in its entirely. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   Combustion turbines benefit substantially from chilling the inlet air on warm days. Both capacity and efficiency improve. The improvements are maximized by using turbine waste heat to supply the chilling, in lieu of mechanical power. Examples of this are found in U.S. Pat. Nos. 6,739,119; 6,457,315; and 5,782,093. 
   As the inlet air accelerates in the bellmouth, it experiences adiabatic cooling. At inlet temperatures below about 40° F., such cooling of the air can lead to potentially harmful icing whenever the relative humidity is above about 70%. Accordingly, high performance turbines advantageously have means for heating such cold, moist air. Only about 10 to 15° F. temperature increase is required to reduce the relative humidity from 100% to below 70% when the ambient temperature is 40° F. or lower. 
   Prior art turbine inlet air heaters have used electric resistance heating, compressor bleed air, steam heating, exhaust heated air, and the like, with attendant capital cost and operating cost. 
   BRIEF SUMMARY OF THE INVENTION 
   It has now been discovered that it is possible to minimally modify a thermally-activated inlet air chiller for the compressor of a combustion turbine system such that it can supply the inlet air heating as well. The same inlet air exchanger is used, and the same waste heat recovery exchanger is used. The same working fluid is also used. All that is required is one or more modified or additional control mechanisms, as disclosed below. The disclosure applies to intercooled combustion turbines as well as single compressor models, using either liquid or gaseous fuel. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is an overview of the combustion turbine plus the waste heat powered inlet air chiller, and including one preferred modification for converting the chiller to a heater when desired. 
       FIG. 2  presents details of one preferred configuration of the waste heat powered chiller. 
       FIG. 3  illustrates one preferred modification to the chiller to enable it to convert to heating mode. 
       FIG. 4  illustrates another preferred approach to changing to heating mode. 
       FIG. 5  illustrates an intercooled combustion turbine arrangement, wherein waste heat powered chilling is applied to either or both of the inlet air and the partially compressed intermediate pressure air, and the inlet air chiller is convertible to an inlet air heater. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   There are several ways the thermally powered compressor inlet air chilling system can be modified to add an air heating function, as shown by the following examples. 
     FIG. 1  is a schematic flowsheet of a combustion turbine system including a thermally activated inlet air chilling system. In addition to the compressor, combustor, and expansion turbine, the system is comprised of an exhaust heat recovery unit  1 , which supplies turbine exhaust heat to the thermally activated system  2 ; and an inlet air exchanger  3 , that chills the inlet air with refrigerant produced in the thermally activated system. A water separator and demister  4  is located at the outlet of the exchanger, to prevent water droplets from entering the compressor. In normal chilling operation, a liquid refrigerant supply valve  5 , e.g. an expansion valve, supplies liquid refrigerant to the cold end of the exchanger, and vapor from the warm end is routed back to the thermally activated system. On cold days, when the thermally powered chiller/heater unit is shifted to heating mode, the liquid supply  5  and vapor return  6  valves are shut. Higher pressure vapor is controllably supplied through an added vapor valve  7 , plus condensate is removed from the exchanger via a new liquid valve  8 . 
     FIG. 2  is a schematic flowsheet of one preferred arrangement of a turbine waste heat activated ammonia absorption refrigeration unit adapted to supply chilling to the turbine inlet air. The AARU is comprised of solution control valve  20 , heat recovery coil  21 , rectifier  22 , condenser  23 , refrigerant heat exchanger  24 , air heat exchange coil  25 , absorber  26 , solution pump  27 , solution heat exchanger  28 , and refrigerant expansion valve  29 .  FIG. 3  illustrates one preferred set of modifications to the  FIG. 2  flowsheet in order to provide in addition the inlet air heating capability. A vapor valve  31  interrupts the normal vapor path back to the absorber. A vapor control valve  32  supplies higher pressure vapor to the inlet air heat exchanger, at a pressure high enough to maintain the desired inlet air temperature (about 42° F. or about 10° F. above ambient, whichever is lower); and a liquid control valve  33  drains condensate from the exchanger back to the absorber. In chilling operation using ammonia as the refrigerant, the pressure in the exchanger will normally be maintained between 36 and 55 psig. During heating operation, the pressure may be as high as about 75 psig, to produce 42° F. air, whereas the pressure may be much lower on very cold days. 
   Provided the inlet air heating duty is never more than about 10 to 15% of the design chilling duty, there is an even simpler method of providing that heat with this thermally activated chilling apparatus. That is illustrated in  FIG. 4 . On cold days, the condensing temperature is regulated at very roughly 100° F. (or roughly 55° F. above the desired inlet air temperature, and corresponding to about 200 psig condenser pressure). That can be done, for example, by turning off the condenser fans, reducing the solution pump flow, and/or using a bypass damper to control the amount of heat entering the heat recovery unit. For heating mode, a liquid refrigerant valve  41  is provided which allows the refrigerant to bypass the refrigerant heat exchanger  44  (RHX), thus carrying all the sensible heat into the exchanger. The absorber pressure would be controlled at approximately 100 psig, i.e. the saturation pressure corresponding to 65° F. condensing temperature in the air exchanger, i.e. about 20 F above the desired inlet air temperature. Roughly 10% of the liquid refrigerant will flash as it goes through the expansion valve, and then that flash vapor will re-condense in the exchanger. With this embodiment, the condenser pressure is maintained as high as about 200 psig in the heating mode. Liquid refrigerant flow can be advantageously controlled by condenser receiver level or other means. 
   Referring to  FIG. 5 , an intercooled combustion turbine system is depicted comprised of first compressor section  51  and final turbine section  52 , plus a multi-component intercooler comprised of heat recovery section  53 , and heat rejection section  54 , the latter comprised of a cooling water cooled section  55  plus a chilled section  56 . Condensed moisture from the cooling and chilling is controllably removed from the chilled air by control  57 , and the chilled and compressed air is routed to second stage compressor  58 . The compressed air then enters combustor  59  where it supports combustion of the fuel (gaseous or liquid). The hot gas expands in hot turbine  60 , and then further expands in final turbine  52 , with at least one turbine providing useful work output (beyond compression duty) at generator  61 . The inlet air to compressor  51  is conditioned in inlet housing  62 , comprised of a chilling/heating coil  63 , a refrigerant distributor  64 , and a trap  65  for removal of condensed water. In chilling mode, the cold refrigerant vapor from coil  63  is warmed in subcooler  66  while precooling the liquid supply refrigerant, and then the warmed vapor is absorbed in absorber  67 . Absorbent liquid is supplied to absorber  67  via control valve  68 , after being cooled in solution heat exchanger  69 . After absorption, pump  70  sends the absorbed liquid to the overhead of distillation column  72 , via control valve  74 , and to heat recovery unit  53 , via control valve  76 . If insufficient heat is available in heat recovery unit  53  additional heat can be obtained from exhaust heat recovery unit  78 , by sending pumped solution to it via control valve  77 . Solution cooled rectifier  73  is a preferred means of supplying the necessary reflux liquid to column  72 , i.e. via non-adiabatic distillation, or heat exchange on the trays. The overhead ammonia vapor from column  72 , which has been rectified to only about 1 to 2% water vapor, is condensed to liquid in condenser  75 , which is cooled by cooling water (or other source of ambient cooling). The refrigerant liquid is then divided, with part going to the inlet chiller  63  via subcooler  66  and expansion valve  80 , and the remainder to interchiller  56 , via subcooler  71  and expansion valve  81 . 
   Water removal control valve  57  preferably is actuated by a water sensor such as a float mechanism whereby only water is removed, and compressed air is not allowed to escape. The two compressor sections and the two or three turbine sections can be configured in a variety of ways.  FIG. 5  depicts in essence a standalone turbocharger in front of the combustion turbine. However all components can be mounted on a single shaft, or on two concentric shafts, as known in the art, for example the LMS  100  gas turbine. When the compression ratio of the first stage compressor  51  is at least about 2.8, the usable heat available at recovery unit  53  is sufficient to chill either coil  56  or  63 , but not both, and hence supplementary heat is required, i.e. from recovery unit  78 . When the compression ratio of compressor  51  is above about 4.5, the heat from recovery unit  53  alone is sufficient to produce both chilling duties. Note that it is particularly desirable to obtain the necessary heat to power the chiller from unit  53 , as that heat needs to be removed anyway, and the higher pressure makes for a more compact heat exchanger with more allowable pressure drop. Also, it leaves all the exhaust heat for cogeneration or a bottoming cycle. On the other hand, for simple cycle arrangements, it may be desirable to obtain at least some of the heat from exhaust recovery unit  78 , as that will supply desirable cooling of the exhaust to protect the SCR catalyst from overtemperature. 
     FIG. 5  illustrates a preferred method of converting the inlet chilling function to inlet heating when necessary to preclude icing in the bellmouth. To enter the anti-icing mode, liquid control valve  80  is shut, and vapor valve  79  is opened. Then the cooling supply to absorber  67  is regulated to maintain the low side pressure downstream of coil  63 , whereby that coil becomes a condenser, heating the air to the desired temperature. For example, suppose the entering air is at 28° F., and it is desired to heat it to 38° F., and to do that the ammonia condensing temperature in coil  63  needs to be at 47° F. Then the absorber cooling would be regulated to maintain a low side pressure of about 84 psia (69 psig), which is the saturation pressure for ammonia condensing at 47° F. Note that it is desirable to provide excess ammonia vapor to coil  63 , such that some vapor returns to absorber  67 , providing better temperature and pressure control. In this heating mode, high side pressure should be maintained sufficiently above low side pressure to provide good vapor flow to the heating coil, e.g. 150 to 250 psig, and low side pressure as above, e.g. 50 to 100 psig. This very simple method of converting the chilling system to heating duty works especially well when the chilling coil is designed to be self-draining, i.e. does not have liquid upflow paths.