Abstract:
A system and method for recuperation is provided including a boiler wherein air and exhaust gas recirculation pass through the boiler and are cooled by thermal transfer with a coolant. The system includes an expander receiving coolant from the boiler, a recuperator receiving coolant from the expander, a condenser receiving coolant from the recuperator; a pump pumping coolant from the condenser to a low temperature portion of the boiler, and a valve, which allows coolant to pass directly from the boiler to the recuperator.

Description:
BACKGROUND 
       [0001]    When a Rankine Cycle Waste Heat Recovery (RC-WHR) is applied to air systems (both clean air and EGR), it preferably delivers target air temperatures to be reached for engine emissions compliance. It also tries to achieve as high a cycle efficiency as possible for example to improve engine Brake Specific Fuel Consumption (BSFC). Additionally, recuperation is often desired to help increase the cycle efficiency, regardless, when very dry fluids with narrow P-h dome are used as coolant. However, with a recuperator for energy exchange between pump-out coolant and exhaust from expander in the conventional RC-WHR system, the amount of recuperation, which is limited by the coolant temperature flowing out of recuperator, is constrained by the target air temperature. This constraint limits the cycle efficiency and bsfc improvement from RC-WHR system. 
       SUMMARY 
       [0002]    One or more embodiments provide a system and method for recuperation including a boiler wherein air and exhaust gas recirculation pass through the boiler and are cooled by thermal transfer with a coolant. The system includes an expander receiving coolant from the boiler, a recuperator receiving coolant from the expander, a condenser receiving coolant from the recuperator, a pump pumping coolant from the condenser to a low temperature portion of the boiler, and a valve, which allows coolant to pass directly from the boiler to the recuperator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  illustrates a conventional recuperation system. 
           [0004]      FIG. 2  illustrates the recuperation system of  FIG. 1  in greater detail. 
           [0005]      FIG. 3  illustrates a modified recuperation system. 
           [0006]      FIG. 4  illustrates the modified recuperation system of  FIG. 3  in more detail. 
           [0007]      FIG. 5  illustrates the previous recuperator configuration operating at C100. 
           [0008]      FIG. 6  illustrates the new recuperator configuration operating at C100. 
           [0009]      FIG. 7  illustrates the new recuperator configuration operating at C100 and also at supercritical. 
           [0010]      FIG. 8  illustrates the prior recuperator configuration operating at B50. 
           [0011]      FIG. 9  illustrates the new recuperator configuration operating at B50. 
           [0012]      FIG. 10  illustrates the new recuperator configuration operating at B50 and also at supercritical. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  illustrates a conventional recuperation system  100 . The recuperation system  100  includes an air plus exhaust gas recirculation (EGR)  110 , a boiler  120 , an expander  130 , a recuperator  140 , a condenser loop  145 , a condenser  150 , a pump  160 , and an intake manifold  170 . 
         [0014]    In operation, air plus EGR  110  is fed into the boiler  120 . An expander  130  is in fluid connection with the boiler and a recuperator  140 . Coolant flows from the boiler  120  to the expander  130  and then to the recuperator  140 . Some coolant passes from the recuperator  140  into the condenser loop  145  where the coolant then passes through the condenser  150  and is pumped by pump  160  back to the recuperator  140 . Finally, coolant passes from the recuperator  140  back to the boiler  120 . The coolant in the boiler  120  acts to reduce the temperature of the air plus EGR  110  until the desired temperature at the intake manifold is achieved. 
         [0015]      FIG. 2  illustrates the recuperation system  100  of  FIG. 1  in greater detail.  FIG. 2  includes the boiler  120 , the expander  130 , the recuperator  140 , the air cooled condenser  150  and the pump  160  of  FIG. 1  and additionally includes a transmission  180 , an integrated starter generator (ISG)  182 , an Inverter and Control  184 , a turbogenerator  186 , a high temperature radiator  188 , an A/C condenser  190 , and an accumulator  192 . 
         [0016]      FIG. 3  illustrates a modified recuperation system  200 . The modified recuperation system  200  includes an air plus exhaust gas recirculation (EGR)  210 , a boiler  220 , an expander  230 , a recuperator  240 , a condenser loop  245 , a condenser  250 , a pump  260 , an intake manifold  270 , a multi-position three-way valve  265 , and an intake manifold  270 . The modified recuperation system  200  of  FIG. 3  provides the ability to apply Rankine Cycle-Waste Heat Recycling (RC-WHR) systems to the air system (both clean air and EGR) and develop a match between dry fluids and such a RC system is a new and developing area. 
         [0017]    More specifically, instead of plumbing or piping the coolant (or refrigerant) from the pump  260  directly to the recuperater  240 , the coolant is first directed to the low temperature section of heat exchanger (boiler)  220 . After heated up to a certain degree, the refrigerant is routed to recuperator  240  for recuperation, and then introduced back to boiler  220  for further heating. By piping the coolant in this way, the target temperature is not a constraint to recuperation any more. By adding a multi-position 3-way valve  265 , the target temperature may be easily assured. For example, the temperature in the intake manifold  270  may be measured using a temperature sensor  268 . Data from the temperature sensor  260  may be passed to a valve control  267  to determine the settings for the valve  265 , that is whether the valve should be opened more, closed more, or remain in the same setting so as to deliver the desired temperature at the intake manifold  270 . 
         [0018]    Consequently, by carefully designing the two sections of the boiler  120 , a larger amount of energy may be recuperated, thus increasing the cycle efficiency and providing a BSFC improvement. Additionally, the target intake manifold temperature and the better BSFC improvement may both be achieved in such a system. Stated another way, the target air temperature (fresh air+EGR) at the intake manifold may now be maintained more accurately and consistently under all operating conditions. 
         [0019]      FIG. 4  illustrates the modified recuperation system of  FIG. 2  in more detail. The modified recuperation system includes the boiler  220 , the expander  230 , the recuperator  240 , the condenser  250 , the pump  270  of  FIG. 3  and additionally includes a transmission  280 , an integrated starter generator (ISG)  282 , an Inverter and Control  284 , a turbogenerator  286 , a high temperature radiator  288 , an A/C condenser  290 , and an accumulator  292 . For some embodiments, the new heat exchanger (boiler) may replace the current air system coolers (EGR, Charge Air Cooler (CAC), and/or Inter-stage cooler (ISC) 
         [0020]    With regard to coolants, coolants having a dry, narrow and much skewed P-h dome lead to large portion of energy contained in dry exhaust from the expander. This constitutes a great potential for recuperation, even with little superheat. 
         [0021]    In the prior plumbing setup shown in  FIG. 1 , refrigerant from the pump first recuperates the exhaust energy from the expander and then goes to the boiler. The actual amount of recuperation is constrained by intake manifold temperature, IMT, resulting in still-high-temperature exhaust energy unused and more burden on the condenser, which limits overall BSFC improvement up to 5.5%. 
         [0022]    In the new setup shown in  FIG. 3 , the refrigerant from pump goes to the low temperature portion of boiler to ensure the IMT temperature is at target. After heating up to a certain degree, the refrigerant is directed to the recuperator, where a larger portion of exhaust heat can be recuperated. For example, up to 30% of boiler total heat transfer may take place in the low temperature portion of the boiler in the analysis below. Additionally, comparison of the new plumbing design (of  FIG. 3 ) to the conventional design (of  FIG. 1 ) shows that the new plumbing design results in a better cycle thermal efficiency (by approximately 20%) and BSCF improvement (by approximately 1%), compared to the original design at the same conditions. This is illustrated in  FIGS. 5-10 , which illustrate the conventional system of  FIG. 1  and the modified system of  FIG. 3  at different operating conditions. In particular, in the Figures and the following description, a first condition, referenced as C100, describes an engine operating point approximating that of undergoing heavy hauling and/or acceleration. Likewise, a second operating condition, referenced as B50, describes an engine operating point approximating that of an engine cruising on a highway 
         [0023]    Additionally, at supercritical conditions, where the coolant&#39;s temperature and pressure exceed a boundary point and take on properties between those of a liquid and a gas, additional changes occur. More specifically, supercritical conditions provide higher expansion ratio, and as anticipated, cycle efficiency is improved, but at much more moderate margin. The selection of maximum system pressure also requires evaluation of system weight. 
         [0024]      FIG. 5  illustrates the previous recuperator configuration  500  operating at C100.  FIG. 5  also shows the intake air and EGR  510 , boiler  520 , expander  530 , recuperator  540 , condenser  550 , and pump  560 . As shown in  FIG. 5 , the power recovered from the expander is 21.75 kW. Additionally, the ηthermal (thermal efficiency) is 9.85%, the Pinch is 10.0 C, and the BSFC increase is 5.26%. 
         [0025]      FIG. 6  illustrates the new recuperator configuration  600  operating at C100.  FIG. 6  also shows the intake air and EGR  610 , boiler  620 , expander  630 , recuperator  640 , condenser  650 , and pump  660 . However, as shown in  FIG. 6 , the power recovered from the expander is now 27.36 kW—up from 21.75 kW in FIG.  5 —an increase of more than 6 kW. Additionally, the ηthermal is 12.39%, the Pinch is 10.5 C, and the BSFC increase is 6.53%. 
         [0026]      FIG. 7  illustrates the new recuperator configuration  700  operating at C100 and also at supercritical.  FIG. 7  also shows the intake air and EGR  710 , boiler  720 , expander  730 , recuperator  740 , condenser  750 , and pump  760 . However, as shown in  FIG. 7 , the power recovered from the expander is now 28.8 kW—up from 21.75 kW in FIG.  5 —an increase of more than 7 kW. Additionally, the ηthermal is 12.72%, the Pinch is 10.6 C, and the BSFC increase is 6.69%. 
         [0027]      FIG. 8  illustrates the prior recuperator configuration  800  operating at B50.  FIG. 8  also shows the intake air and EGR  810 , boiler  820 , expander  830 , recuperator  840 , condenser  850 , and pump  860 . As shown in  FIG. 8 , the power recovered from the expander is 10.84 kW. Additionally, the ηthermal is 9.79%, the Pinch is 10.0 C, and the BSFC increase is 5.46%. 
         [0028]      FIG. 9  illustrates the new recuperator configuration  900  operating at B50.  FIG. 9  also shows the intake air and EGR  910 , boiler  920 , expander  930 , recuperator  940 , condenser  950 , and pump  960 . However, as shown in  FIG. 9 , the power recovered from the expander is now 12.88 kW—up from 10.84 kW in FIG.  8 —an increase of more than 2 kW. Additionally, the ηthermal is 11.66%, the Pinch is 10.5 C, and the BSFC increase is 6.44%. 
         [0029]      FIG. 10  illustrates the new recuperator configuration  1000  operating at B50 and also at supercritical.  FIG. 10  also shows the intake air and EGR  1010 , boiler  1020 , expander  1030 , recuperator  1040 , condenser  1050 , and pump  1060 . However, as shown in  FIG. 10 , the power recovered from the expander is now 14.2 kW—up from 10.84 kW in FIG.  8 —an increase of about 3.5 kW. Additionally, the ηthermal is 12.49%, the Pinch is 10.6 C, and the BSFC increase is 6.87%.