TWI795128B - System and method for using organic rankine cycle to recover electrolyte waste heat for electricity generation - Google Patents

Abstract

Disclosed in the present invention are a system and method for using an Organic Rankine Cycle to recover electrolyte waste heat for electricity generation. The system comprises at least one electrolyte cycle loop and at least one Organic Rankine Cycle loop, wherein an electrolyte heat exchanger is simultaneously located in the two cycle loops, and an electrolyte circulating stream flowing in the electrolyte cycle loop exchanges heat via the electrolyte heat exchanger with an organic working medium stream flowing in the Organic Rankine Cycle loop, during which the former stream is cooled and the later stream is vaporized. After being vaporized, the organic working medium stream does work via an expander, and drives a generator to generate electricity. The electrical energy generated can be incorporated into a power grid or converted to DC electricity and then inputted to an electrolysis apparatus.

Description

System and method for recovering electrolyte waste heat for power generation using organic rankine cycle

The invention belongs to the field of electrolysis, especially the field of waste heat recovery in electrolyzed water devices, and relates to a system and method for recovering waste heat of electrolyte and generating electricity by using an organic Rankine cycle.

The electrolysis of water to produce hydrogen and oxygen has many industrial applications. For example, high-purity oxygen and hydrogen are used in the semiconductor industry; hydrogen is used as a clean, efficient new energy source, and petrochemicals that use hydrogen as raw material. Since the phenomenon of electrolysis of water was observed in 1789, the technology of electrolysis of water has been continuously developed. At present, there are three different electrolyzers commonly used, namely alkaline electrolyzer, polymer film electrolyzer and solid oxide electrolyzer, and the electrolysis efficiency has also increased to 70%-90%.

Alkaline electrolyzer is the most mature, economical and easy-to-operate electrolyzer. The electrolyte used is generally 10 wt%-30 wt% potassium hydroxide solution (KOH). After direct current is passed through the electrolyzer, hydrogen is produced at the cathode and oxygen is produced at the anode. This process consumes a large amount of electric energy. For example, an electrolyser with a hydrogen production of 1000 Nm ³ /h requires about 5.0 MWh of electricity. Therefore, there is a need for methods that can increase electrolysis efficiency and/or reduce power consumption.

US Patent Publication US 2018/0171870 A1 discloses a system integrating an electrolyzer, a motor, an ORC and a generator. The hydrogen generated by the electrolysis of water is used as fuel to supply the engine, and the hot exhaust gas generated by the engine exchanges heat with the working medium in the organic Rankine cycle and evaporates it. The evaporated working fluid expands to do work to drive the generator to generate electricity, and the generated alternating current is converted into direct current and passed into the electrolytic cell. This system requires the use of additional engines to achieve energy conversion and utilization.

It can be seen that the electrolysis process, especially the energy recycling method in the electrolysis process, has not been fully researched and disclosed in the prior art.

In view of the above deficiencies in the prior art, the object of the present invention is to provide a system and method for converting waste heat contained in the electrolyte into electrical energy and utilizing it.

In one aspect, the present invention discloses a system for recovering waste heat from electrolyte, the system includes at least one electrolyte circulation loop and at least one organic Rankine cycle loop, wherein an electrolyte heat exchanger is located in the above two circulation loops at the same time , the electrolyte circulation stream flowing in the electrolyte circulation loop exchanges heat with the organic working medium stream flowing in the organic Rankine circulation loop through the electrolyte heat exchanger.

Optionally, the organic working fluid stream contains tetrafluoroethane or Freon.

Further, the electrolyte circulation loop in the present invention also includes an electrolytic tank and an electrolyte circulation pump, wherein the electrolyte circulation stream flowing out of the electrolytic tank is input into the electrolyte heat exchanger through the electrolyte circulation pump, and is heated in the organic The organic working medium stream flowing in the Ken circulation loop cools down and flows back to the electrolyzer, and the temperature after cooling is about 85-90°C.

Further, the organic Rankine cycle circuit in the present invention also includes a Rankine expander and an associated generator, a Rankine cycle economizer, a Rankine cycle condenser, a Rankine cycle pump and an electrolyte heat exchanger , wherein the organic working fluid stream is heated and gasified by the electrolyte circulation stream in the electrolyte heat exchanger to form a gaseous working fluid stream, which expands in the Rankine expander to perform work, and then in the Rankine cycle section The condensed working fluid stream is cooled in the heater, and is condensed by the cooling water in the Rankine cycle condenser to obtain the condensed working fluid stream, which is transported to the Rankine cycle by the Rankine cycle pump In the economizer, after being heated by the gaseous working fluid stream, it is input into the electrolyte heat exchanger again to form a cycle, and the generator linked with the expander converts the expansion work into electrical energy, and the electrical energy is converted into direct current and then input into the electrolysis trough or directly into the grid.

In another aspect, the present invention also discloses a method for recovering the waste heat of the electrolyte using the above system, providing at least one electrolyte circulation loop and at least one organic Rankine cycle loop, wherein an electrolyte heat exchanger is located at the two In a circulation loop, the electrolyte circulation stream flowing in the electrolyte circulation loop exchanges heat with the organic working substance stream flowing in the organic Rankine cycle through the electrolyte heat exchanger.

Further, in the electrolyte circulation loop, the electrolyte circulation stream flowing out of the electrolytic cell is input into the electrolyte heat exchanger through the electrolyte circulation pump, and is cooled by the organic working fluid stream flowing in the organic Rankine circulation loop. back to the electrolyzer.

Further, a Rankine expander and an associated generator, a Rankine cycle economizer, a Rankine cycle condenser and a Rankine cycle pump are also provided in the organic Rankine cycle circuit, wherein the organic working medium flow In the electrolyte heat exchanger, the stream is heated and gasified by the electrolyte circulation stream to form a gaseous working medium stream. The stream expands in the Rankine expander to perform work, and then is condensed in the Rankine cycle economizer to work. The mass stream is cooled, and is condensed by the cooling water in the Rankine cycle condenser to obtain the condensed working fluid stream, which is transported to the Rankine cycle economizer by the Rankine cycle pump, where After being heated up by the gaseous working medium stream, it is input into the electrolyte heat exchanger again to form a cycle, and the generator linked with the expander converts the expansion work into electrical energy, and the electrical energy is converted into direct current and then input to the electrolyzer or directly into the grid.

Compared with the prior art, the technical solution provided by the present invention has the following advantages: There is no need to make major changes to the existing electrolyte circulation circuit in the electrolytic cell, saving cost investment; In the prior art, the electrolyte stream is generally cooled by cooling water. The present invention replaces the cooling water with the organic working medium stream in the organic Rankine cycle, saving the use of cooling water.

In view of the low temperature of the electrolyte circulation stream (generally lower than 100°C) and low heat energy, the present invention adds a Rankine cycle economizer to the organic Rankine cycle to improve the efficiency of heat exchange.

By adopting the system and method of the present invention, the electric energy generated by the organic Rankine cycle is sent back to the electrolyzer, which can reduce the electric energy consumption by 3%-4% in the process of electrolyzing water.

The specific implementation manner of the present invention will be described in detail below in conjunction with the accompanying drawings. However, the present invention should be understood as not limited to such embodiments described below, and the technical idea of the present invention can be implemented in combination with other known technologies or other technologies having the same functions as those known technologies.

In the following descriptions of specific embodiments, in order to clearly demonstrate the structure and working methods of the present invention, many directional words will be used to describe, but "front", "rear", "left", "right", "outer ", "inwardly", "outwardly", "inwardly", "axially", "radially" and other terms are to be understood as terms of convenience and shall not be construed as terms of limitation.

In the following description of specific embodiments, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical ", "horizontal", "top", "bottom", "inner", "outer" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description , rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operate in a particular orientation, and thus should not be construed as limiting the invention.

The terms "upstream" and "downstream" refer to the relative positional relationship between several steps, equipment or parts of equipment. In the present invention, according to the process flow, the first step and the first used equipment are located upstream of the subsequent steps or equipment.

In the present invention, terms such as "installation", "connection", "connection" and "fixation" should be interpreted in a broad sense, for example, it can be a fixed connection or a detachable connection, unless otherwise clearly specified and limited. , or integrated; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediary, and it can be the internal communication of two components or the interaction relationship between two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

Each aspect or embodiment defined herein may be combined with any other aspect or embodiments or embodiment(s) unless clearly stated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

在陽極：4OH ^‐O ₂+ 2H ₂O + 4e ^‐；

在陰極：4H ₂O + 4e ^‐4OH ^‐+ 2H ₂

總反應：2H ₂O     2H ₂+ O ₂ An electrolysis device refers to a device that is connected to a DC power source and electrolyzes water to generate _O2 and _H2 . Various electrolysis devices, including alkaline electrolysis devices, acidic electrolysis devices, and proton exchange membrane electrolysis devices, are suitable for use in the present invention. Taking the alkaline electrolysis device as an example, 10%-30% KOH aqueous solution is used as the electrolyte, and the following reactions occur in the electrolytic cell:

At the anode: 4OH ^‐ O ₂ + 2H ₂ O + ^4e‐ ;

At the cathode: 4H ₂ O + 4e ^‐ 4OH ^‐ + 2H ₂

Total reaction: 2H ₂ O 2H ₂ + O ₂

The structure of a typical alkaline electrolysis unit is well known to those skilled in the art and comprises an electrolytic cell, electrolyte, cathode, anode and diaphragm. The diaphragm is generally composed of asbestos and mainly plays the role of separating gases. The electricity consumption per unit of gas production, ie the efficiency of the electrolyzer, depends on the electrolysis voltage and the impedance of the electrolyte. Since the higher the reaction temperature, the smaller the impedance of the electrolyte, in the prior art, the working temperature of the electrolytic cell is 70-95°C, more preferably 80-90°C.

In the alkaline electrolysis device, the steps of electrolyzing water to produce hydrogen and oxygen are as follows: the gas generated near the electrode and the electrolyte are passed through the pipeline into the cathode gas electrolyte separator and the anode gas electrolyte separator respectively. In each separator, the mixture of electrolyte and gas is heated to separate the gas from the mixture. The separated electrolyte is mixed with the desalted water added to supplement the water consumed by electrolysis, and then sent back to the electrolyzer for circulation through the electrolyte circulation pump, electrolyte cooler, and filter if necessary, for electrolysis. Electrolyte coolers use cooling water to control the temperature of the returning electrolyte.

The Organic Rankine Cycle (ORC for short) is a Rankine cycle using low-boiling point organic matter as a working fluid, and is more suitable for low-temperature waste heat recovery. In the previous technology, it is mainly composed of heat exchangers, expanders, condensers and working medium pumps. Its working principle is: the organic working medium absorbs heat from the waste heat flow in the heat exchanger to generate The temperature of the steam, the steam enters the expander to expand and do work, thereby driving the generator. The steam discharged from the expander releases heat to the cooling water in the condenser, condenses into a liquid state, and finally returns to the heat exchanger with the help of the working fluid pump, and the cycle continues in this way. Suitable working fluids are, for example, tetrafluoroethane or Freon.

In the present invention, the circulation stream of the electrolyte whose temperature does not exceed 100° C. is exchanged with the organic working medium, and the thermal product energy of this stream is relatively low. Therefore, in order to ensure the gasification of the organic working medium, different from the prior art, the present invention adds a Rankine cycle economizer (that is, a heat exchanger) after the expander and before the condenser. After expansion and before condensation, the organic working fluid stream exchanges heat with the condensed working fluid stream in the Rankine cycle economizer, and transfers part of the waste heat to the latter, increasing the temperature of the stream. It makes the subsequent gasification easier, and also reduces the amount of cooling water correspondingly.

The specific embodiment of the present invention will be described in detail below in conjunction with accompanying drawing 1 .

Figure 1 is a schematic diagram of the principle of using the organic Rankine cycle to recover waste heat from the electrolyte circulation loop and use it to generate electricity. FIG. 1 includes an electrolyte circulation loop 10 and an organic Rankine cycle loop 8 . In the electrolyte circulation loop 10 , three parallel electrolyzed water devices are schematically listed, and each device simply marks the electrolyzer ( E1 , E2 , E3 ), the electrolyte circulation pump ( P1 , P2 , P3 ) and electrolyte heat exchangers ( LE1 , LE2 , LE3 ), while omitting some other components familiar to those skilled in the art. In order to recover the waste heat in the electrolyte from the three electrolyzed water devices at the same time, the condensed working fluid stream 6 is heated by a Rankine cycle economizer ( EC ) and then divided into three streams, that is, the first organic working fluid stream 1 and the second The organic working fluid stream 2 and the third organic working fluid stream 3 enter the electrolyte heat exchangers LE1 , LE2 and LE3 respectively, and connect with the first electrolyte circulation stream 11 , the second electrolyte circulation stream 12 , the second electrolyte circulation stream The three electrolyte circulation streams 13 exchange heat respectively. The temperature of the first, second and third electrolyte circulation streams after cooling is between 85-90°C, and are transported back to the electrolytic cell by the electrolyte circulation pump to form a circulation. The three organic working fluid streams 1 , 2 , 3 absorbing the waste heat of the electrolyte circulating stream are evaporated and gasified and merged into the gaseous working fluid stream 4 , which enters the rankine expander EX to expand and do work, driving the linkage generator G The electricity generated by the generator G can be converted into direct current for electrolysis of water device, or connected to the grid. The expanded gaseous working fluid stream 4 transfers part of its heat to the condensed working fluid stream 6 in the Rankine cycle economizer EC , and becomes the cooled working fluid stream 5 itself. The cooled working fluid stream 5 is condensed by the cooling water 7 in the Rankine cycle condenser CD to become the condensed working fluid stream 6 , which is pumped into the Rankine cycle economizer ( EC ) by the Rankine cycle pump PO After heating, it is divided into three streams, that is, the first organic working fluid stream 1 , the second organic working fluid stream 2 and the third organic working fluid stream 3 , and the cycle continues like this. If necessary, a liquid storage tank ST is set between the Rankine cycle pump PO and the Rankine cycle condenser CD , and Rankine cycle control valves V1 , V2 , and V3 are respectively set on the first, second, and third organic working fluid streams. With the device and method of the present invention, the electricity generated by the generator G is equivalent to 3%-4% of the total electricity required by the water electrolysis device, and the economic benefits are very considerable.

What is described in this specification is only a preferred embodiment of the present invention, and the above embodiments are only used to illustrate the technical solution of the present invention rather than limit the present invention. All technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments according to the concept of the present invention should be within the scope of the present invention.

1: The first organic working fluid stream 2: The second organic working fluid stream 3: The third organic working fluid stream 4: Gaseous working fluid stream 5: Working fluid stream after cooling 6: Working fluid stream after condensation 7: cooling water 8: Organic Rankine Cycle 10: Electrolyte circulation loop 11: The first electrolyte circulation stream 12: The second electrolyte circulation stream 13: The third electrolyte circulation stream

The advantages and spirit of the present invention can be further understood through the following detailed description of the invention and the accompanying drawings.

[Fig. 1] is a schematic flow chart of the present invention.

The reference signs are as follows:

E1, E2, E3-represents 3 independent electrolyzers; P1, P2, P3-electrolyte circulation pump; LE1, LE2, LE3-electrolyte heat exchanger; V1, V2, V3-Rankine cycle control valve; EX-Rankine expander; G-generator; EC-Rankine cycle economizer; CD-Rankine cycle condenser; PO-Rankine cycle pump; ST-storage tank;

1, 2, 3-respectively the first, second and third organic working fluid streams; 4-gaseous working fluid streams; 5-cooled working fluid streams; 6-condensed working fluid streams; 7- Cooling water; 8-organic Rankine circulation loop; 10-electrolyte circulation loop; 11, 12, 13-respectively the first, second and third electrolyte circulation streams.

none

1: The first organic working fluid stream

2: The second organic working fluid stream

3: The third organic working fluid stream

4: Gaseous working fluid stream

5: Working fluid stream after cooling

6: Working fluid stream after condensation

7: cooling water

8: Organic Rankine Cycle

10: Electrolyte circulation loop

11: The first electrolyte circulation stream

12: The second electrolyte circulation stream

13: The third electrolyte circulation stream

Claims (10)

A system for recovering electrolyte waste heat, characterized in that the system includes at least one electrolyte circulation loop and at least one organic Rankine cycle, and the electrolyte circulation loop includes an electrolytic cell, an electrolyte circulation pump and an electrolyte heat exchange Electrolyte circulation stream flows in the electrolyte circulation loop, and the organic Rankine cycle loop includes a Rankine expander and an associated generator, a Rankine cycle economizer, and a Rankine cycle condenser , a Rankine circulation pump and an electrolyte heat exchanger, an organic working fluid stream flows in the organic Rankine circulation loop, wherein, the electrolyte circulation stream and the organic working fluid stream are passed through the electrolysis Liquid heat exchanger for heat exchange. The system according to claim 1, wherein the organic working fluid stream contains tetrafluoroethane or Freon. The system as described in claim item 1, is characterized in that, the electrolyte circulating stream flowing out from the electrolytic cell is input into the electrolyte heat exchanger through the electrolyte circulating pump, and is absorbed by the organic working fluid flowing in the organic Rankine cycle loop. After the strand cools down, it flows back to the electrolyzer. The system as described in Claim 3 is characterized in that the temperature of the electrolyte circulation stream after being cooled by the electrolyte heat exchanger is 85-90°C. The system as described in claim 1, is characterized in that the organic working fluid stream is heated and gasified by the electrolyte circulation stream in the electrolyte heat exchanger to form a gaseous working medium stream, and the stream is heated in the Rankine expander Expansion work in the middle, then the working fluid stream is cooled after being condensed in the Rankine cycle economizer, condensed by cooling water in the Rankine cycle condenser to obtain the condensed working fluid stream, and the condensed working fluid stream The stream is transported by the Rankine cycle pump to the Rankine cycle economizer, where it is heated by the gaseous working fluid stream, and then enters the electrolyte heat exchanger again to form a cycle, and the generator linked with the expander Convert expansion work into electrical energy. A method for recovering waste heat from electrolyte using the system described in claim 1, characterized in that at least one electrolyte circulation loop and at least one organic Rankine cycle loop are provided, and the electrolyte The circulation loop includes an electrolytic cell, an electrolyte circulation pump and an electrolyte heat exchanger, and the electrolyte circulation stream flows in the electrolyte circulation loop, and the organic Rankine circulation loop includes a Rankine expander and an associated Generator, Rankine cycle economizer, Rankine cycle condenser, Rankine cycle pump and electrolyte heat exchanger, organic working medium stream flows in the organic Rankine cycle loop, wherein, the electrolyte cycle The stream exchanges heat with the organic working medium stream through an electrolyte heat exchanger. The method according to claim 6, wherein the organic working fluid stream contains tetrafluoroethane or Freon. The method as described in Claim 6, characterized in that the temperature of the electrolyte circulation stream is 85-90° C. after being cooled by the electrolyte heat exchanger. The method as described in claim item 6, it is characterized in that, the electrolyte circulating stream flowing out from the electrolytic cell is input into the electrolyte heat exchanger through the electrolyte circulating pump, and is absorbed by the organic working fluid flowing in the organic Rankine cycle loop. After the strand cools down, it flows back to the electrolyzer. The method as described in claim item 7, is characterized in that, the organic working fluid stream is heated and gasified by the electrolyte circulation stream in the electrolyte heat exchanger to form a gaseous working medium stream, and the stream is heated in the Rankine expander Expansion work in the middle, then the working fluid stream is cooled after being condensed in the Rankine cycle economizer, condensed by cooling water in the Rankine cycle condenser to obtain the condensed working fluid stream, and the condensed working fluid stream The stream is transported by the Rankine cycle pump to the Rankine cycle economizer, where it is heated by the gaseous working fluid stream, and then enters the electrolyte heat exchanger again to form a cycle, and the generator linked with the expander Convert expansion work into electrical energy.

Images