Harnessing lost power with pressure exchanger

Abstract

A system for recovering energy from steam undergoing a pressure-reducing process in an industrial let-down station includes a rotary pressure exchanger in a steam flow line. Excess steam pressure may be used to directly pressurize another process stream such as a stream of air. The pressure exchanger may be more energy efficient, e.g., than generating electricity with a turbine and using the electricity to run an electric air compressor to compress the air. The rotary pressure exchangers may include a cylindrical rotor with longitudinal ducts extending there through. First and second end covers may be disposed at opposing longitudinal ends of the cylindrical rotor, for permitting entry and discharge of the steam and air into the longitudinal ducts. Boiler feedwater may be introduced to the steam at various locations in the let-down station, e.g., at an exit of the rotary pressure exchanger, to lower a temperature of the steam.

Description

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates generally to steam regulation in industrial plants, and more particularly to efficiently harnessing power from steam passing through a let-down station, and using the power to drive other processes conducted within the industrial plant or remote from the industrial plant.BACKGROUND OF THE DISCLOSURE

[0002] Steam is employed in numerous industrial applications including HVAC (heating, ventilation, and air conditioning), power generation and chemical processing. In many of these applications, saturated or superheated steam is generated within a boiler or co-generation system, and subsequently, the pressure of the steam is reduced to meet the required conditions for use in downstream heat exchange, propulsion, supporting chemical reactions or other operations. Reducing the pressure of the steam ensures that a steady supply of steam at the correct pressure is available to carry out the desired processes, which protects the downstream equipment. However, as the pressure is reduced, a significant amount of energy can be lost.

[0003] Many industrial plants rely on let-down stations to manage steam pressure. These let-down stations, sometimes referred to as pressure-reducing stations, often use throttling valves to reduce the pressure in stages. A let-down station may additionally allow for the temperature of the steam to be reduced, but additional temperature reduction might be needed, which may occur by introducing water into the throttling valves. During a throttling process, a large amount of the potential energy in the steam may be unrecoverable as it is absorbed as internal energy, which may result in changes in steam temperature. Some industrial plants attempt to recover a portion of the lost energy using turbines to generate electricity. While these methods have shown some success, they are often complex, costly, and not always suitable for all industrial applications. Moreover, these solutions typically require significant capital investment and ongoing maintenance, which can be prohibitive for many industries. Inefficiencies in the use of the electricity generated by the turbines may also contribute to additional power losses.

[0004] Thus, more direct and efficient systems to manage steam pressure and recover energy losses from the steam may be desirable.SUMMARY OF THE DISCLOSURE

[0005] Various details of the present disclosure are hereinafter summarized to provide a basic understanding. This summary is not an extensive overview of the disclosure and is neither intended to identify certain elements of the disclosure, nor to delineate the scope thereof. Rather, the primary purpose of this summary is to present some concepts of the disclosure in a simplified form prior to the more detailed description that is presented hereinafter.

[0006] According to an embodiment consistent with the present disclosure, a let-down system for regulating steam pressure in an industrial plant includes a high-pressure steam header fluidly coupled to a steam generator to receive high-pressure steam from the steam generator, a source of water, a mixing chamber having a first inlet fluidly coupled to the high-pressure steam header to receive steam therefrom and a second inlet fluidly coupled to the source of water to receive water therefrom such that the water may be mixed with the steam to lower a temperature of the steam and a low-pressure steam header fluidly coupled to the mixing chamber to receive the steam therefrom. The system further includes a pressure exchanger fluidly coupled between the high-pressure steam header and the mixing chamber, the pressure exchanger operable to receive the steam from the high-pressure steam header and transfers energy from the steam to an incoming process stream to thereby compress the incoming process stream using the energy from the steam.

[0007] According to another embodiment consistent with the present disclosure, a method for harnessing lost energy from a let-down station in an industrial plant includes (a) integrating at least one pressure exchanger to the let-down station, (b) directing high-pressure steam from a high-pressure header of the let-down station to the at least one pressure exchanger, (c) introducing a low-pressure process stream into the at least one pressure exchanger, (d) transferring energy from the high-pressure steam to the low-pressure process stream within the at least one pressure exchanger, thereby forming a stream of low-pressure steam and compressing the process stream to pressurized process stream (e) discharging the low-pressure steam from the pressure exchanger, (f) mixing the low-pressure steam with water to thereby lower a temperature of the low-pressure steam and (g) discharging the pressurized process stream for industrial use within the industrial plant or other applications

[0008] Any combinations of the various embodiments and implementations disclosed herein can be used in a further embodiment, consistent with the disclosure. These and other aspects and features can be appreciated from the following description of certain embodiments presented herein in accordance with the disclosure and the accompanying drawings and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic illustration of a let-down station including a plurality of rotary pressure exchangers for harnessing the power of steam undergoing a pressure-reducing process, in accordance with one or more embodiments of the present disclosure.

[0010] FIGS. 2A and 2B are schematic illustrations of an example of one of the rotary pressure exchangers of FIG. 1 in disassembled and operational configurations, respectively.

[0011] FIG. 3A is a schematic view of two pressure-reducing pathways comparing a throttling valve with a pressure exchanger, in accordance with the present disclosure.

[0012] FIG. 3B is a tabular compilation of various operational characteristics of the pressure reducing pathways of FIG. 3A determined by simulating a flow of steam therethrough.DETAILED DESCRIPTION

[0013] Embodiments of the present disclosure will now be described in detail with reference to the accompanying Figures. Like elements in the various figures may be denoted by like reference numerals for consistency. Further, in the following detailed description of embodiments of the present disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the claimed subject matter. However, it will be apparent to one of ordinary skill in the art that the embodiments disclosed herein may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description. Additionally, it will be apparent to one of ordinary skill in the art that the scale of the elements presented in the accompanying Figures may vary without departing from the scope of the present disclosure.

[0014] Embodiments in accordance with the present disclosure generally relate to systems and methods for recovering energy from steam undergoing a throttling process in an industrial let-down station. Let-down stations in accordance with the present disclosure may include a rotary pressure exchanger upstream of a throttling valve in a steam flow line. Excess steam pressure may be used to directly pressurize another process stream. For example, the steam may be used to pressurize a compressed air stream within the pressure exchanger. This may be more energy efficient than, e.g., generating electricity with a turbine and using the electricity to run an electric air compressor. The rotary pressure exchangers may include a cylindrical rotor with longitudinal ducts extending there through. First and second end covers may be disposed at opposing longitudinal ends of the cylindrical rotor, wherein the first end cover includes a steam inlet and a steam outlet, wherein the second end cover includes an air inlet and an air outlet, and wherein the longitudinal ducts rotate between an intake position wherein the longitudinal ducts are aligned with the steam inlet and air inlet and a discharge position wherein the longitudinal ducts are aligned with the steam outlet and air outlet. Boiler feedwater may be introduced to the steam at various locations in the let-down station, e.g., at an exit of the rotary pressure exchanger, to lower a temperature of the steam.

[0015] FIG. 1 is a schematic illustration of an example let-down station 100, in accordance with one or more embodiments of the present disclosure. Generally, the let-down station 100 is typically used to reduce the pressure and temperature of steam in a controlled manner. The let-down station 100 may receive high-pressure steam from one or more steam generators 101 such as a boiler, reboiler, a chemical reactor, or other sources. The steam generator(s) 101 in an industrial plant may include, for example, water tube boilers, fire tube boilers, heat recovery steam generators, electric steam generators, nuclear steam generators, or any combination thereof. The steam generators 101 in any industrial plant are critical to the operation of many industrial processes, each designed to suit specific temperature, pressure and capacity requirements. However, the steam generators 101 may produce steam at higher temperatures and pressures than is required for downstream equipment and processes within the plant.

[0016] The high-pressure steam from the steam generator(s) 101 enters a steam header 102, which distributes the steam to various pressure-reducing pathways 103 extending through the let-down station 100. Each of the pressure-reducing pathways 103 may appropriately reduce the temperature and pressure of the steam and may extend to a low-pressure steam header 104. The low-pressure steam header 104 may collect the steam from the various pathways 103 and distribute the low-pressure steam to the various heating circuits or process streams within the plant or to other destinations.

[0017] Each of the pressure-reducing pathways 103 may extend through a pressure exchange section 105 of the let-down system 100. As described in greater detail below, the pressure exchange section 105 may receive the steam from the high-pressure steam header 102 and transfer excess energy from the steam to an incoming process stream 106. The incoming process stream 106 is compressed to a higher pressure with the excess steam energy and then exits the pressure exchange section 105 as a pressurized process stream 107. The pressure exchange section 105 may include a rotary pressure exchanger 108 in each of the pressure-reducing pathways 103 to reduce the pressure of the steam and pressurize the process stream 106, as described in greater detail below. In some embodiments, the incoming process stream 106 is a stream of atmospheric air that may be compressed using the excess energy from the steam.

[0018] The let-down station 100 also includes a source of water 109. The source of water 109 may be a source of boiler feed water that is also fluidly coupled to an inlet of the steam generator 101. The source of water 109 is fluidly coupled to a mixing station 110 of the let-down system 100. The mixing station 110 may include a plurality of mixing chambers 111 disposed within respective pressure reducing pathways 103, and in which the water may be mixed with the steam exiting the respective pressure exchanger 108. In some embodiments, the water and the steam are mixed in the mixing chamber 111 to cool the steam to a predetermined temperature.

[0019] Control valves 112 are fluidly coupled between the source of water 109 and the mixing chambers 111. The control valves 112 are operable to adjust an amount of water entering the mixing chambers 111 such that an appropriate amount of the water may be introduced to the steam to achieve the predetermined steam temperature. In some embodiments, introducing water into the mixing chambers 111 may further reduce the pressure of the steam therein. Thus, the control valves 112 may be operable to further adjust the pressure of the steam exiting the mixing chambers 111. The steam may then enter the low-pressure header 104 at a predetermined pressure and temperature and exit the let-down system as an output stream 113.

[0020] FIG. 2A is a schematic illustration of one example of one of the pressure exchangers 108 of FIG. 1. As illustrated, the pressure exchanger 108 is configured as a rotary pressure exchanger in which a cylindrical rotor 202 may be induced to rotate in the direction of arrow AO about a longitudinal axis X0. The rotor 202 includes a plurality of longitudinal ducts 204 extending therethrough, which are circumferentially (angularly) spaced from one another about the axis X0. The rotor 202 is illustrated displaced (exploded) from a pair of stationary end caps 206, 208 to reveal the longitudinal ducts 204. However, in an operational configuration, the rotor 202 will be aligned with the end caps 206, 208 and may rotate within a sleeve 210 extending between the end caps 206, 208. The sleeve 210 may form a fluid tight seal with the end caps 206, 208 such that the rotor 202 may rotate freely in a sealed environment.

[0021] A first end cap 206 may include an inlet 212 and an outlet 214. The inlet 212 and outlet 214 may be arranged within the pressure-reducing pathway 103 (FIG. 1) such that steam “S” may pass through the end cap 206 into and out of the pressure exchanger 108. Similarly, a second end cap 208 may include an outlet 216 and an inlet 218. The inlet 218 may be fluidly coupled to the incoming process stream 106 and the outlet 216 may be fluidly coupled to the pressurized process stream 107 (FIG. 1) such that air “A” or another fluid may pass through the end cap 208 into and out of the pressure exchanger 108. The inlets 212, 218 and the outlets 214, 216 may be aligned and unaligned (misaligned) with the longitudinal ducts 204 as the rotor 202 rotates. When the inlet 212 and the outlet 216 are aligned with a longitudinal duct 204, the high-pressure steam “S” may enter through the inlet 212 and form a fluid column 220 with the air “A” already present within the longitudinal duct 204. The steam “S” will pressurize the air “A” and displace the air “A” out through the outlet 216 with the same pressure as the steam “S”. A barrier fluid “B” may be maintained within the longitudinal ducts 204 such that the steam “S” and the air “A” do not mix within the fluid column 220. In some embodiments, the barrier fluid “B” may include portions of the steam “S” and the air “A” that are trapped within the longitudinal duct 204. The rotor 202 may then rotate the fluid column 220, which includes the steam “S” and the barrier fluid “B,” to be aligned with the outlet 214 and the inlet 218. Here, the air “A” will enter through the inlet 218 and displace the steam “S” through the outlet 214 with the pressure of the air “A”.

[0022] The rotor 202 may then rotate the fluid column 220 back to be aligned with the inlet 212 and the outlet 216 where the pressure exchanging process may repeat. The rotor 202 may rotate in response to the pressure of the fluids “S” and “A”. The rotational speed of the rotor 202 may be controlled by throttling valves 222, as described with reference to FIG. 2B below.

[0023] FIG. 2B illustrates the pressure exchanger 108 in an operational configuration with the rotor 202 (FIG. 2A) removed for clarity. High-pressure steam “S” enters the pressure exchanger 108 from the pressure-reducing pathway 103 through the inlet 212. Similarly, low pressure air “A” enters the pressure exchanger 108 from the incoming process stream 106 through the inlet 218.

[0024] The steam “S” and the air “A” form fluid columns 220 within respective longitudinal ducts 204 (FIG. 2A) while discharging the air “A” and steam “S” already present in the longitudinal ducts 204 (FIG. 2A) through the outlets 214, 216, as described above. The pressure of the steam “S” decreases and the pressure of the air “A” increases. As the longitudinal ducts 204 rotate to the outlets 214, 216, the lower pressure steam “S” and increased-pressure air “A” exit the pressure exchanger 108. The lower pressure steam “S” may continue along the pressure-reducing pathway 103 to a throttling valve 222 coupled therein and, similarly, the increased-pressure air “A” may continue along the pressurized process stream 107 to another throttling valve 222 coupled therein. The throttling valves 222 may ensure that the rotor 202 (FIG. 2A) is not rotating too quickly for an effective pressure exchange between the steam “S” and the air “A.” The throttling valves 222 may also ensure that the pressure of the increased-pressure air “A” and lower pressure steam “S” is a predetermined pressure suitable for downstream purposes.

[0025] The inlet 218 and the outlet 216 define curved (arcuate) paths corresponding to a portion of the rotation of the longitudinal duct 204. The curved paths illustrate the path traveled by the air “A” within the pressure exchanger 108. The increased-pressure air “A” exits the pressure exchanger 108 as pressurized process stream 107. In this way, the excess pressure from the steam “S” is transferred directly to the air “A” within the pressure exchanger 108.

[0026] Compressed air “A” is a critical process stream that is used in almost every industry. Mechanical air compressors may consume around 147 W per one SCFM of atmospheric air to compress the atmospheric air to desired pressure. The pressure exchanger 108 may similarly compress atmospheric air “A” with the energy that must be removed from the steam “S” to bring the steam “S” to an acceptable pressure for further downstream processes.EXAMPLE

[0027] FIG. 3A is a schematic view of one of the pressure-reducing pathways 103 as compared to a pressure-reducing pathway 303 where the pressure exchanger 108 is replaced with a throttling valve 308. When a fluid such as steam “S” flows through a restriction, such as the throttling valve 308, without any appreciable change in kinetic or potential energy, the primary results of the process is a pressure drop in the steam “S”. The process therefore occurs at constant enthalpy as indicated by equation (1) below.Δ⁢H=0,H1=H2(1)

[0028] High-pressure steam “S” may enter the pressure reducing pathway 303 at 750° F. and 650 PSIG. The low-pressure steam “S” leaving the throttling valve 308 after expansion will have a pressure of 65 PSIG, and due to the constant enthalpy condition, the low-pressure steam “S” will have a temperature of 681.3° F. Then, the low-pressure steam “S” is combined with boiler feedwater (BFW) in the mixing chamber 111 to reduce its temperature to 330° F. The pressure-reducing pathway 303 may have a flow rate of 543 LB / hr of steam “S” if the throttling valve 308 is fully open. Generally, the energy lost when throttling the steam “S” with a throttling valve may not be lost in the form of heat and may be inefficient to recover.

[0029] In order to calculate the amount of energy can be “recovered” and the reduction of BFW that can be achieved with the pressure reducing pathway 103 including the pressure exchanger 108, a thermodynamic analysis of an expander may be employed. The pressure exchanger 108 may be analyzed as an expander with a minimum efficiency of 60%. The thermodynamic equations of an expander are presented below as equations (2) and (3) below:W˙=m˙⁢Δ⁢H(2)η=W.W.(Isentropic)(3)Where {dot over (W)}s is the work can be extracted, m is the mass flowrate, η is the Pressure exchanger efficiency and {dot over (W)} (Isentropic) is the maximum work can be recovered from an adiabatic pressure exchanger 108.FIG. 3B is a tabular a compilation of various operational characteristics of a simulated steam flow through the pressure reducing pathways 103, 303 illustrated in FIG. 3A. The steam flow was simulated using Aspen HYSYS simulation software using the Peng-Robinson equation of state (EOS) as fluid package. The high-pressure input stream of steam “S” and the low-pressure output stream of steam “S” was identical for both pressure-reducing pathways 103, 303. From the simulation, it was determined that the amount of energy that can be recovered is 19.8 kW for each throttling valve 308 that may be replaced with the pressure exchanger 108 of the present disclosure. It was also determined that the amount of BFW that is needed to reduce the temperature of the steam “S” was reduced by 73.28% using the pressure-reducing pathway 103 compared to the amount required using pressure-reducing pathway 303.

[0031] Thus, it may be seen that using a rotary pressure exchanger 108 presents many benefits in industrial applications. For example, the pressure exchanger 108 serves as an efficient means to harness and redistribute pressure energy within fluid streams. By seamlessly transferring pressure from high-pressure steam “S” streams to low-pressure air “A” streams, energy utilization and cost-effectiveness may be improved in processes operating at elevated pressures. The pressure exchanger 108 minimizes mixing between fluid streams also since the barrier fluid “B” (FIG. 2A) may be captured within the longitudinal ducts 204. The selective transfer of pressure energy with the pressure exchanger 108 not only conserves resources (e.g., boiler feedwater) but also contributes to maintaining the distinct properties of each fluid stream, which is a critical aspect in numerous industrial processes.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, for example, the singular forms “a,”“an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “contains”, “containing”, “includes”, “including,”“comprises”, and / or “comprising,” and variations thereof, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0033] Terms of orientation are used herein merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized these terms could be used with reference to an operator or user. Accordingly, no limitations are implied or to be inferred. In addition, the use of ordinal numbers (e.g., first, second, third, etc.) is for distinction and not counting. For example, the use of “third” does not imply there must be a corresponding “first” or “second.” Also, if used herein, the terms “coupled” or “coupled to” or “connected” or “connected to” or “attached” or “attached to” may indicate establishing either a direct or indirect connection, and is not limited to either unless expressly referenced as such.

[0034] While the disclosure has described several exemplary embodiments, it will be understood by those skilled in the art that various changes can be made, and equivalents can be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation, or material to embodiments of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, or to the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.

Claims

1. A let-down system for regulating steam pressure in an industrial plant, the system comprising:a high-pressure steam header fluidly coupled to a steam generator to receive high-pressure steam from the steam generator;a source of water;a mixing chamber having a first inlet fluidly coupled to the high-pressure steam header to receive steam therefrom and a second inlet fluidly coupled to the source of water to receive water therefrom such that the water is mixed with the steam to lower a temperature of the steam;a low-pressure steam header fluidly coupled to the mixing chamber to receive the steam therefrom; anda pressure exchanger fluidly coupled between the high-pressure steam header and the mixing chamber, the pressure exchanger being operable to receive the steam from the high-pressure steam header and transfer energy from the steam to an incoming process stream to thereby compress the incoming process stream using the energy from the steam.

2. The system of claim 1, wherein the incoming process stream is a stream of atmospheric air.

3. The system of claim 2, wherein the pressure exchanger includes a rotating rotor with longitudinal ducts extending therethrough, each duct configured to transfer pressure energy from the high-pressure steam to the atmospheric air.

4. The system of claim 3, wherein the pressure exchanger further includes first and second end caps disposed at opposing longitudinal ends of the rotor, wherein the first end cover includes a steam inlet and a steam outlet, wherein the second end cover includes an air inlet and an air outlet, and wherein the longitudinal ducts rotate between an intake position, where the longitudinal ducts are aligned with the steam inlet and the air inlet, and a discharge position, where the longitudinal ducts are aligned with the steam outlet and the air outlet.

5. The system of claim 4, wherein the air inlet and the air outlet define curved paths corresponding to a portion of the rotation of the longitudinal ducts.

6. The system of claim 1, further comprising a sleeve extending about the rotor and forming a seal with the end caps.

7. The system of claim 1, wherein the source of water is a source of boiler feed water fluidly coupled to an inlet of the steam generator.

8. The system of claim 7, further comprising a control valve coupled between the source of boiler feed water and the mixing chamber, the control valve operable to adjust an amount of water entering the mixing chamber.

9. A method for harnessing lost energy from a let-down station in an industrial plant, the method comprising:directing high-pressure steam from a high-pressure header of the let-down station to at least one pressure exchanger;introducing a low-pressure process stream into the at least one pressure exchanger;transferring energy from the high-pressure steam to the low-pressure process stream within the at least one pressure exchanger, thereby forming a stream of low-pressure steam and compressing the process stream to a pressurized process stream;discharging the low-pressure steam from the at least one pressure exchanger;mixing the low-pressure steam with water and thereby lowering a temperature of the low-pressure steam; anddischarging the pressurized process stream for industrial use within the industrial plant or other applications.

10. The method of claim 9, wherein introducing the low-pressure process stream includes introducing atmospheric air into the at least one pressure exchanger.

11. The method of claim 10, wherein introducing the atmospheric air into the at least one pressure exchanger includes introducing the atmospheric air into a longitudinal duct of a rotating rotor of the at least one pressure exchanger, and wherein transferring energy from the high-pressure steam includes equalizing a pressure of the atmospheric air and the high-pressure steam within the longitudinal duct.

12. The method of claim 11, further comprising maintaining a barrier fluid between the atmospheric air and the high-pressure steam within the longitudinal duct to prevent mixing of the atmospheric air and the high-pressure steam.

13. The method of claim 9, wherein mixing the low-pressure steam with water includes diverting a stream of boiler feed water (BFW) to the low-pressure steam to lower the temperature of the low-pressure steam.

14. The method of claim 13, further comprising adjusting a control valve control to adjust an amount of the BFW introduced to the low-pressure steam.

15. The method of claim 9, wherein integrating the pressure exchanger into the let-down station includes replacing a throttle valve of the let-down station with the pressure exchanger.

16. The system of claim 1, further comprising a plurality of pressure-reducing pathways extending between the high-pressure steam header and the low-pressure steam header, each pressure-reducing pathway comprising:a respective pressure exchanger fluidly coupled between the high-pressure steam header and a respective mixing chamber, wherein the respective mixing chamber fluidly coupled to the low-pressure steam header.

17. The system of claim 1, further comprising a throttling valve disposed in a stream flow line downstream of the pressure exchanger and upstream of the mixing chamber, the throttling valve being configured to control a pressure of the steam discharged from the pressure exchanger.

18. The system of claim 3, wherein each longitudinal duct is partially filled with a barrier fluid comprising trapped portions of steam and air, the barrier fluid separating a steam portion of the duct from an air portion of the duct during rotation of the rotor.

Images