RANKINE CYCLE MID-TEMPERATURE RECUPERATION

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

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

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

FIG. 1 illustrates a conventional recuperation system.

FIG. 2 illustrates the recuperation system of FIG. 1 in greater detail.

FIG. 3 illustrates a modified recuperation system.

FIG. 4 illustrates the modified recuperation system of FIG. 3 in more detail.

FIG. 5 illustrates the previous recuperator configuration operating at C100.

FIG. 6 illustrates the new recuperator configuration operating at C100.

FIG. 7 illustrates the new recuperator configuration operating at C100 and also at supercritical.

FIG. 8 illustrates the prior recuperator configuration operating at B50.

FIG. 9 illustrates the new recuperator configuration operating at B50.

FIG. 10 illustrates the new recuperator configuration operating at B50 and also at supercritical.

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

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.

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)

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.

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%.

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

Additionally, at supercritical conditions, where the coolant'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.

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%.

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%.

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%.

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%.

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%.

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%.

Claims

1. A recuperation system including:

a boiler, wherein air and exhaust gas recirculation pass through the boiler and are cooled by thermal transfer with a coolant;

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, wherein the valve allows coolant to pass directly from the boiler to the recuperator.

2. The system of claim 1 wherein the valve is a three-way valve.

3. The system of claim 1 further including a temperature sensor detecting the temperature at the intake manifold.

4. The system of claim 3 further including a valve control controlling the valve.

5. The system of claim 4 wherein the valve control receives an indication of the temperature at the intake manifold from the temperature sensor.

6. The system of claim 5 wherein the valve control adjusts the position of the valve in response to the temperature at the intake manifold.

7. A recuperation method including:

cooling air and exhaust gas recirculation passing through a boiler by thermal transfer with a coolant;

receiving the coolant from the boiler at an expander;

receiving the coolant from the expander at a recuperator;

receiving the coolant from the recuperator at a condenser;

pumping coolant from the condenser to a low temperature portion of the boiler; and

actuating a valve to allow coolant to pass directly from the boiler to the recuperator.

8. The method of claim 7 wherein the valve is a three-way valve.

9. The method of claim 7 further including detecting the temperature at the intake manifold using a temperature sensor.

10. The method of claim 9 further including controlling the valve using a valve control.

11. The method of claim 10 wherein the valve control receives an indication of the temperature at the intake manifold from the temperature sensor.

12. The method of claim 11 wherein the valve control adjusts the position of the valve in response to the temperature at the intake manifold.