CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63/074,070, filed September 3, 2020, which is incorporated herein by reference. US Patent No. 10,465,983 and US Patent No. 10,514,202, which are incorporated herein by reference, are commonly assigned to Bechtel Energy Technologies & Solutions, Inc.

FIELD OF THE DISCLOSURE

[0002] The present disclosure generally relates to systems and methods for single-stage refrigeration. More particularly, the present disclosure relates to improving the efficiency of conventional single-stage ejector-based refrigeration systems by adjusting the ejector motive conditions without great economic expense.

BACKGROUND

[0003] Conventional single-stage refrigeration systems using vapor compression have been employed for the last century in various applications. In FIG 1, for example, a schematic diagram illustrates one embodiment of a conventional single-stage vapor compression refrigeration system. The system 100 includes a flash drum 108, a compressor 112, a condenser 114, an expansion valve 120 and an evaporator 124. Vapor refrigerant from the flash drum 108 passes through line 110 to the compressor 112 where it is compressed and then passes through line 113 to the condenser 114. The outlet pressure of the compressor 112 is dependent on the condensing medium’s temperature. After leaving the condenser 114, the refrigerant in line 102 is a liquid. The liquid refrigerant in line 102 then passes through the expansion valve 120 where it is vaporized and chilled at the same instance employing the Joule-Thomson effect. For propane refrigerant, this temperature is approximately -23°F. The vaporized-chilled refrigerant then passes through line 106 to the evaporator 124 and then passes through line 118 to the flash-drum 108.

[0004] The conventional single-stage vapor compression refrigeration system 100 in FIG. 1 may be improved by using an ejector. Referring now to FIG. 2, a schematic diagram illustrates one embodiment of a conventional single-stage ejector-based vapor compression refrigeration system. The liquid refrigerant in line 102 passes through an ejector 204 and is let-down to an intermediate pressure in line 205 while compressing vaporized refrigerant from line 118. Liquid refrigerant from the flash drum 108 passes through line 206 to an expansion valve 208 where it is let down and then passes through line 210 to the evaporator 124. The evaporator 124 evaporates the refrigerant and then passes through line 118 to the ejector 204. The ejector 204 serves to improve the energy efficiency of the system 200 by increasing the suction pressure of the compressor 112.

[0005] Conventional single-stage ejector-based vapor compression refrigeration system have traditionally encountered complications however, when ambient conditions vary or in very hot climates because ejectors are traditionally designed for a single operating condition. When there is significant variance from that operating condition, an ejector’s efficiency is reduced, which results in a reduced coefficient of performance and higher energy requirements for the system.

[0006] As a result, modifications have been developed to maintain ejector efficiency when there are significantly different ejector operating conditions. For example, one modification uses adjustable nozzle ejectors. While this modification enables the ejector 204 to operate within different ambient operating conditions, it does not enable the adjustment of the ejector motive conditions in line 102. As such, a higher intermediate flash stage pressure in the flash-drum 108 is precluded. The modification would also require an additional control mechanism to adjust the ejector 204. Another modification uses multiple ejectors to account for the different operating conditions, which are controlled by valves. However, this modification also does not enable the adjustment of the ejector motive conditions in line 102. A more recent modification uses a compressor to adjust the ejector suction in line 118. While this modification offers the benefit of adjusting the suction pressure of the ejector 204 to achieve a stable operation with variant ambient operating conditions, it also does not enable the adjustment of the ejector motive conditions in line 102 and requires additional equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The detailed description is described below with reference to the accompanying drawings, in which like elements are referenced with like reference numbers, in which:

[0008] FIG. 1 is a schematic diagram illustrating one embodiment of a conventional single- stage vapor compression refrigeration system.

[0009] FIG. 2 is a schematic diagram illustrating one embodiment of a conventional single- stage ejector-based vapor compression refrigeration system.

[0010] FIG. 3 is a schematic diagram illustrating one embodiment of a modified single- stage ejector-based vapor compression refrigeration system.

[0011] FIG. 4 is a schematic diagram illustrating another embodiment of a modified single- stage ejector-based vapor compression refrigeration system.

[0012] FIG. 5 is a scatter-plot chart comparing the coefficient of performance (CoP) for the conventional single-stage ejector-based vapor compression refrigeration system in FIG. 2 and the modified single-stage ejector-based vapor compression refrigeration system in FIG. 3 at different flash stage pressures. DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

[0013] The present disclosure overcomes one or more deficiencies in the prior art by providing systems and methods for improving the efficiency of single-stage ejector-based refrigeration systems by adjusting the ejector motive conditions.

[0014] In one embodiment, the present disclosure includes a single-stage ejector-based refrigeration system, comprising: i) an ejector connected to a liquid refrigerant line and a vapor refrigerant line; ii) a flash drum in fluid communication with the ejector for receiving a two-phase refrigerant, the flash drum connected to another vapor refrigerant line and another liquid refrigerant line; iii) a compressor connected to the another vapor refrigerant line and a compressed refrigerant line; iv) a condenser connected to the compressed refrigerant line and a condensed refrigerant line; and v) a liquid propulsion device connected to the condensed refrigerant line and the liquid refrigerant line for increasing a pressure for a liquid refrigerant.

[0015] In another embodiment, the present disclosure includes a method for single-stage ejector-based refrigeration, comprising: i) introducing a liquid refrigerant and a vapor refrigerant into an ejector; ii) separating a two-phase refrigerant from the ejector into another liquid refrigerant and another vapor refrigerant; iii) compressing the another vapor refrigerant into a compressed refrigerant; iv) condensing the compressed refrigerant into the liquid refrigerant; and v) increasing a pressure for the liquid refrigerant before introducing the liquid refrigerant into the ejector.

[0016] The subject matter of the present disclosure is described with specificity, however, the description itself is not intended to limit the scope of the disclosure. The subject matter thus, might also be embodied in other ways, to include different structures, steps and/or combinations similar to and/or fewer than those described herein, in conjunction with other present or future technologies. Although the term “step” may be used herein to describe different elements of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless otherwise expressly limited by the description to a particular order. Other features and advantages of the disclosed embodiments will be or will become apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional features and advantages be included within the scope of the disclosed embodiments. Further, the illustrated figures and dimensions described herein are only exemplary and are not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different embodiments may be implemented. The pressures and temperatures described herein thus, illustrate exemplary advantages and/or parameters of the various embodiments.

[0017] Referring now to FIG 3, a schematic diagram illustrates one embodiment of a modified single-stage ejector-based vapor compression refrigeration system. Vapor refrigerant from the flash drum 108 passes through line 110 to the compressor 112 where it is compressed and then passes through line 113 to the condenser 114. Because the outlet pressure of the compressor 112 is dependent on the condensing medium’s temperature, a propane refrigerant condensing with air at 80°F will yield a compressed refrigerant at approximately 176 psia. After being condensed in the condenser 114, the liquid refrigerant in line 102 is propelled to the ejector using a liquid propulsion device 302 such as, for example, an ejector or a pump. The liquid refrigerant is thus, propelled through line 303 to the ejector 204, which lets the refrigerant down to an intermediate pressure in line 205 while compressing vaporized refrigerant from line 118. The intermediate pressure may be further controlled through an expansion valve 304. A two-phase refrigerant from the expansion valve 304 then passes through line 305 to flash-drum 108. Liquid refrigerant from the flash drum 108 passes through line 206 to an expansion valve 208 where it is let down and then passes through line 210 to the evaporator 124. The evaporator 124 evaporates the refrigerant and then passes through line 118 to the ejector 204. [0018] Referring now to FIG 4, a schematic diagram illustrates another embodiment of a modified single-stage ejector-based vapor compression refrigeration system using a suction line (e.g. internal) heat exchanger. Vapor refrigerant from the flash drum 108 passes through line 110 to an intermediate heat exchanger 402, to the compressor 112 and then passes through line 113 to the condenser 114. Because the outlet pressure of the compressor 112 is dependent on the condensing medium’s temperature, a propane refrigerant condensing with air at 80°F will yield a compressed refrigerant at approximately 176 psia. After being condensed in the condenser 114, the liquid refrigerant in line 102 is propelled to the heat exchanger 402 through line 303 using a liquid propulsion device 302 such as, for example, an ejector or a pump. The cooled liquid refrigerant is then sent to ejector 204, which lets the refrigerant down to an intermediate pressure in line 205 while compressing vaporized refrigerant from line 118. The intermediate pressure may be further controlled through an expansion valve 304. A two-phase refrigerant from the expansion valve 304 then passes through line 305 to flash-drum 108. Liquid refrigerant from the flash drum 108 passes through line 206 to an expansion valve 208 where it is let down and then passes through line 210 to the evaporator 124. The evaporator 124 evaporates the refrigerant and then passes through line 118 to the ejector 204.

[0019] Results comparing the modified systems illustrated in FIGS. 3-4 with the conventional systems illustrated in FIGS 1-2, based on a Honeywell Uni Sim® model, are depicted in Tables 1-3 below using propane as the refrigerant. The Coefficient of Performance (COP) calculation is based on the Cooling Capacity divided by the Energy Consumed. The Energy Consumed is the total energy consumed by the compressor, liquid propulsion device (pump) and air cooler fan power. The air cooler fan power may be calculated using a proprietary model that references an industry-standard design practice. Flash Ejector Pump

% Energy Stage Discharge Discharge Cooling Chilling

Difference Consumed Pressure Pressure Pressure Capacity Temperature

Case Run in COP COP (kW) (kPa) (kPa) (kPa) (kW) (°F)

Conventional Ejector 1 34.5% i 55 13.72 260.00 263.00 21.28 -23.00

System Conventional 0.0% 1 ₁₅ 17 35 162.00 20.00 -23.00

Modified 1 29.6% 1 49 14 29 250.00 276.00 1,800.00 21.35 -23.00

^{SyStem 2 32} - ^4% 1.53 13.93 260.00 274.00 1,800.00 21.26 -23.00

3 34.9% _{1 56} 13.60 270.00 274.00 1,800.00 21.15 -23.00

4 32.9% ! 53 13.79 260.00 265.00 1,500.00 21.13 -23.00

5 32.4% ! 53 13.96 255.00 259.00 1,300.00 21.32 -23.00

^{6 6} - ⁵ % 1.23 17.77 170.00 287.00 1,800.00 21.82 -23.00

9 33.8% _{1 54} 13.75 285.00 290.00 3,500.00 21.21 -23.00

TABLE 1

[0020] Due to the flexibility provided by the pump and ejector, the modified systems can achieve a higher COP and lower energy consumption than the conventional systems. This results in a higher ejector discharge pressure. The modified systems are also superior to conventional systems due to the ability to increase the intermediate flash stage pressure at the flash-drum 108 with the liquid propulsion device 302. In FIG. 5, a scatter-plot chart illustrates a comparison of the coefficient of performance (COP) for the conventional single-stage ejector-based vapor compression refrigeration system in FIG. 2 and the modified single-stage ejector-based vapor compression refrigeration system in FIG. 3 at different simulated flash stage pressures. FIG. 5 demonstrates that increasing the intermediate flash stage pressure has a positive effect on COP. This can be observed when comparing the cluster of points to the left side of the chart between a flash stage pressure of 140-180 kPa and the cluster of points in the upper right section between 229 and 300 kPa flash stage pressure in FIG. 5. Each of them represents refrigeration systems operating with an ambient temperature of 80°F and cooling to -23°F. The lower right side of the chart with flash stage pressures between 260 to 320 kPa represents refrigeration systems operating at 100°F ambient temperature and cooling to -23°F. With the increase in flash stage pressure, the COP is increased, which results in reduced energy requirements for refrigeration. [0021] The modified systems disclosed herein also present additional benefits related to superior flexibility with handling ambient temperature conditions as depicted in Tables 2-3 below. At an ambient temperature of 100°F, the modified systems offer an improved COP over the conventional systems. This is achieved with a higher intermediate flash stage pressure and a higher discharge pressure from the liquid propulsion device.

Flash Ejector Pump

% Energy Stage Discharge Discharge Cooling Chilling

Difference Consumed Pressure Pressure Pressure Capacity Temperature

Case Run in COP COP (kW) (kPa) (kPa) (kPa) (kW) (°F)

Conventional Ejector 0.00% _{x 03 19 49 2} 70.00 271.00 20.05 -23.00

System 2

Modified 7 5.20% _x p8 18.00 320.00 325.00 3,000.00 19.48 -23.00

^System 88 66.88W3 /o j ₁₀ 19.30 285.00 290.00 3,500.00 21.21 -23.00

TABLE 2

[0022] At a high ambient temperature, the modified system can achieve a -23 °F chilling temperature that is comparable in performance to a conventional system in colder ambient conditions. With a high ambient temperature, the performance is maintained with a modified system as demonstrated by runs 8-9 in Table 3 below.

[0023] While the present disclosure has been described in connection with presently preferred embodiments, it will be understood by those skilled in the art that it is not intended to limit the disclosure of those embodiments. For example, the modifications described herein may be implemented in new ejector-based vapor compression refrigeration systems or retrofitted to a conventional ejector-based vapor compression refrigeration system. Further, the modifications described herein may be implemented in other ejector-based vapor compression refrigeration systems to achieve similar results. Although propane is used as exemplary refrigerant, it is not intended to preclude other refrigerants from being used. It is therefore, contemplated that various alternative embodiments and modifications may be made to the disclosed embodiments without departing from the spirit and scope of the disclosure defined by the appended claims and equivalents thereof.