Low-temperature flue gas power generation system and method

Abstract

The invention discloses a low-temperature flue gas power generation system which comprises a flue gas pressure boosting and equalizing device for receiving low-temperature flue gas, an evaporator connected with the flue gas pressure boosting and equalizing device, a screw power machine connected with the evaporator and a power generator connected with the screw power machine. According to the low-temperature flue gas power generation system, heat of low-temperature flue gas with the temperature lower than 200 DEG C can be converted into high-quality electric energy, low-temperature flue gas waste heat is fully recycled, and the purposes of energy conservation and emission reduction are achieved. The invention further discloses a low-temperature flue gas power generation method.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste heat power generation, and in particular, the present invention relates to a low-temperature flue gas power generation system and method. Background Art

[0002] Most of the flue gas after combustion in industrial enterprises is reused through different methods of waste heat and waste pressure, but flue gas with a temperature below 200℃ is difficult to be utilized due to its low thermal enthalpy. 3 The hot blast furnace of the blast furnace is pure blast furnace gas, and the flue gas volume is about 2.6×10 5 Nm 3 / h, the flue gas temperature coming out of the hot blast furnace combustion chamber is about 300℃, and the temperature of the flue gas after heat exchange through the double preheating system is about 140℃, and the flue gas at this time is discharged into the environment. The flue gas temperature discharged by the hot blast furnace is not high, but the volume is large, and the heat energy is seriously wasted.

[0003] Chinese patent application number 201710069521.6 discloses a converter flue gas waste heat power generation system, comprising a first vaporization and cooling flue, a second vaporization and cooling flue, a combustion and settling chamber, a third vaporization and cooling flue and a waste heat boiler connected in sequence along the flue gas flow direction from the flue gas outlet of the water-cooled elbow above the converter, the evaporator and the economizer in the waste heat boiler are arranged in sequence along the flue gas flow direction, and the flue gas waste heat utilization system is divided into a low-pressure steam-water system and a high-pressure steam-water system according to different working pressures, wherein the low-pressure steam-water system is used to cool the first vaporization and cooling flue and the furnace door of the combustion and settling chamber, and is supplied with water by a low-pressure drum-deaerator to generate low-pressure steam; and the high-pressure steam-water system is used to cool the second vaporization and cooling flue, the furnace cover of the combustion and settling chamber, the third vaporization and cooling flue, and the waste heat boiler, and is supplied with water by a high-pressure drum to generate high-pressure steam, and the steam output by the high-pressure drum is treated by a heat accumulator to drive a steam turbine to drive a generator to generate electricity. In the solution disclosed in this patent, the flue gas is high-temperature flue gas and a steam turbine is used to generate electricity.

[0004] The Chinese patent with application number 201711122813.8 discloses a power generation device suitable for generating electricity from industrial kiln exhaust gas, which belongs to the field of wind power generation technology. The power generation device includes a wind wheel, a mounting bracket, a generator, a speed increaser and a flue connection pipe. The mounting bracket is connected to the flue connection pipe, and the wind wheel is horizontally mounted in the mounting bracket above the flue connection pipe. The main shaft of the wind wheel is connected to the generator through the speed increaser; the length of the wind wheel penetrating into the flue connection pipe is one-third of the diameter of the flue connection pipe. The horizontal position of the bearing of the wind wheel main shaft is higher than the horizontal position of the outer wall of the flue connection pipe. The present invention sets the position of the wind wheel above the level of the flue connection pipe, and the depth of penetrating into the flue is one-third of the inner diameter of the flue connection pipe, which effectively solves the problem of clogging the wind wheel and its bearings by a large amount of dust. In the scheme disclosed in the patent, the flue gas residual pressure is used to generate electricity.

[0005] The Chinese patent application number 200920175614.8 discloses an electronic pressure switch, including a connecting pipe assembly and an impeller, characterized in that: it has a joint assembly, the joint assembly includes a flow regulating valve and a water inlet joint, the flow regulating valve is placed in the water inlet joint, and two identical through holes are correspondingly opened on the two side walls of the water inlet joint corresponding to the position of the flow regulating valve; it has a flow control switch, the flow control switch passes through the two side walls of the water inlet joint and the two identical through holes are correspondingly opened, and the flow regulating valve is fixed with the rotary cover. The innovation of the utility model is that the flow control switch and the flow regulating valve are assembled together. When used, the flow regulating valve is fixed and the flow control switch can be rotated, so as to achieve the purpose of controlling the water flow. The water pump uses the utility model, which allows users to better control the water pump and save energy. In the scheme disclosed in the patent, the heat exchange between flue gas and heat transfer oil is increased, and the heat transfer oil is then heat-exchanged with the ORC system and then generated by the turbine.

[0006] It is hoped to provide an improved low-temperature flue gas power generation system and method, particularly with regard to how to fully recover the waste heat of the low-temperature flue gas to achieve the goal of energy conservation and emission reduction. Summary of the invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a low-temperature flue gas power generation system, the purpose of which is to fully recover the waste heat of low-temperature flue gas and save energy and reduce emissions.

[0008] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a low-temperature flue gas power generation system, including a flue gas boost pressure equalizer for receiving low-temperature flue gas, an evaporator connected to the flue gas boost pressure equalizer, a screw power machine connected to the evaporator, and a generator connected to the screw power machine.

[0009] The temperature of the low-temperature flue gas received by the flue gas boosting and equalizing device is lower than 200°C.

[0010] The screw power machine is connected to a condenser, and the exhaust steam of the working medium discharged from the screw power machine enters the condenser.

[0011] The condenser is configured to reduce the temperature of the working medium exhaust steam to below 55°C.

[0012] The condenser is connected to a working fluid circulation pump, and the working fluid circulation pump is connected to the evaporator.

[0013] The flue gas boost pressure equalizer comprises an air intake section, a pressure boost section and a pressure equalizing section which are arranged in sequence. The pressure boost section is a gradually converging nozzle, and the diameter of the pressure boost section gradually decreases from one end to the other end.

[0014] The air intake section is provided with a first check valve, and the pressure equalizing section is provided with a second check valve.

[0015] The present invention also provides a low-temperature flue gas power generation method, comprising the steps of:

[0016] S1, low-temperature flue gas enters the booster equalizer for boosting;

[0017] S2, the low-temperature flue gas after pressure increase enters the evaporator;

[0018] S3. After the liquid working medium in the evaporator absorbs the waste heat of the flue gas, the formed working medium steam enters the screw power machine.

[0019] The temperature of the low-temperature flue gas entering the flue gas boosting and equalizing device is lower than 200°C.

[0020] The low-temperature flue gas power generation method further comprises the steps of:

[0021] S4, the exhaust steam of the working fluid discharged by the screw power machine enters the condenser;

[0022] S5. The liquid working medium discharged from the condenser enters the evaporator through the working medium circulation pump.

[0023] The low-temperature flue gas power generation system of the present invention can convert the heat of low-temperature flue gas with a temperature below 200°C into high-quality electrical energy, realize full recovery of the waste heat of the low-temperature flue gas, and achieve the purpose of energy saving and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] This specification includes the following drawings, which show the following contents:

[0025] Figure 1 It is a structural schematic diagram of the low-temperature flue gas power generation system of the present invention;

[0026] Figure 2 is a cross-sectional schematic diagram of a boost equalizer;

[0027] The following are marked in the figure: 1. Flue gas booster and equalizer; 2. Evaporator; 3. Screw power machine; 4. Generator; 5. Condenser; 6. Working fluid circulation pump. DETAILED DESCRIPTION

[0028] The specific implementation methods of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, with the aim of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention and facilitating their implementation.

[0029] It should be noted that, in the following embodiments, the “first” and “second” mentioned do not represent an absolute distinction in structure and / or function, nor do they represent a sequential order of execution, but are merely for the convenience of description.

[0030] like Figure 1 As shown, the present invention provides a low-temperature flue gas power generation system, including a flue gas pressure boosting and equalizing device 1 for receiving low-temperature flue gas, an evaporator 2 connected to the flue gas pressure boosting and equalizing device 1, a screw power machine 3 connected to the evaporator 2, and a generator 4 connected to the screw power machine 3. The flue gas pressure boosting and equalizing device 1 is used for pre-processing the low-temperature flue gas by pressure boosting and equalizing, so that the pressure of the flue gas entering the evaporator 2 is stable and the flow rate is uniform, thereby ensuring a stable and smooth heat exchange process with the working medium.

[0031] Specifically, the temperature of the low-temperature flue gas received by the flue gas booster and equalizer 1 is lower than 200°C. The present invention can convert the heat of the flue gas with a temperature lower than 200°C into high-quality electrical energy, thereby fully recovering the waste heat of the low-temperature flue gas and achieving the purpose of energy saving and emission reduction.

[0032] The screw power machine 3 mainly utilizes power sources such as steam, hot water, hot liquid or vapor-liquid two-phase fluid to convert thermal energy into power, which can drive the generator 4 to generate electricity, or can replace the electric motor to directly drive mechanical equipment or replace the expansion valve of a large refrigerator to recover power.

[0033] Compared with common steam turbines, the working fluid parameters and loads of screw compressors can adapt to the changes in the waste heat and residual pressure parameters of industrial and mining enterprises' production heat and electricity loads, and can maintain stable high efficiency, and operate smoothly, safely and reliably. The structural characteristics of the screw compressor enable it to have self-descale capabilities, so there is no special cleanliness requirement for gas and liquid working fluids. The working fluid does not need to undergo any thermal engineering treatment (such as flash expansion tanks, steam-water separators, superheaters, etc.) before entering the screw compressor, so the thermal system supporting it is relatively simple.

[0034] According to whether the heat source directly drives the screw machine to expand and work, the screw machine power generation system is divided into a conventional circulation system and an organic Rankine cycle system (ORC). The conventional circulation system is also called a single circulation system, which is to directly introduce the heat-containing fluid into the screw machine to expand and work. This type of system is relatively simple and suitable for energy recovery of high-temperature and high-pressure fluids. The organic Rankine cycle system is also called a double circulation system. The entire system includes: evaporator 2, screw power machine 3, generator 4, condenser 5, and liquid pump. The system circulation organic working fluid is selected from R123, R134a, R245fa, R600a and R601a. ​​When recovering waste heat, the heat-containing fluid heats the liquid organic working fluid when passing through the evaporator 2, and the high-temperature and high-pressure gaseous working fluid enters the screw machine, driving the screw machine to work and drive the generator 4 to generate electricity. The low-temperature and low-pressure working fluid discharged from the screw machine enters the condenser 5 to release heat to the outside world and condense into liquid, and then is pumped into the evaporator 2 by the liquid pump for evaporation, thereby completing a complete cycle.

[0035] like Figure 1 As shown, the screw power machine 3 is connected to the evaporator 2 through a pipeline, and the low-temperature flue gas is sent into the evaporator 2 after being boosted, buffered and pressure-equalized by the booster equalizer. The low-temperature flue gas with a stable flow rate is discharged to the outside after heat exchange with the liquid working medium in the evaporator 2.

[0036] After absorbing the waste heat of the flue gas, the liquid working medium in the evaporator 2 can be transformed into working medium steam according to the specific system operating pressure. The working medium steam can be in the states of wet steam (gas-liquid two-phase), saturated steam and superheated steam. The working medium steam in these states can enter the screw power machine 3. The working medium steam expands in the screw power machine 3 to do work and drive the generator 4 to generate electricity.

[0037] The basic principles for selecting screw compressor working fluids using low-temperature flue gas as heat source are: to ensure good heat transfer capacity, the temperature difference between the boiling point of the working fluid and the heat source should not be less than 50°C; to ensure safe operation of the system, the flue gas heat source temperature cannot be higher than the critical temperature of the working fluid; the thermal enthalpy of low-temperature flue gas is not high, so the latent heat and specific heat of the working fluid should be as small as possible.

[0038] According to the above background technology, the exhaust gas temperature of the hot blast furnace is about 140℃, and the physical and chemical parameters of different organic working fluids are consulted to determine pentafluoropropane (R245fa) as the working fluid of the screw power machine 3. The specific physical and chemical parameters of R245fa are as follows: standard boiling point: 58.5℃; solidification temperature: -160℃; critical temperature: 256.9℃; critical pressure: 4.64MPa; saturated liquid density: 82.7kg / m 3 ; Liquid specific heat: 0.33kJ / (kg·℃); Latent heat of vaporization: 147kJ / kg; Isobaric steam specific heat: 0.22kJ / (kg·℃).

[0039] like Figure 1As shown, the screw power machine 3 is connected to the condenser 5 through a pipeline, and the exhaust steam of the working medium discharged from the screw power machine 3 enters the condenser 5. After being cooled by the condenser 5, the working medium is completely converted into liquid working medium. The condenser 5 is connected to the working medium circulation pump 6 through a pipeline, and the working medium circulation pump 6 is connected to the evaporator 2 through a pipeline. After the working medium in the condenser 5 is completely liquefied, it re-enters the evaporator 2 after passing through the circulation pump to exchange heat with the low-temperature flue gas, thereby completing the working medium cycle.

[0040] In the background technology, the working medium entering the screw power machine 3 can be steam, hot liquid or vapor-liquid two-phase fluid. Therefore, after the liquid R245fa working medium absorbs the waste heat of the flue gas, it can become vapor-liquid two-phase flow (wet steam), saturated steam or superheated steam according to the specific system operating pressure.

[0041] In the present invention, the condenser 5 is configured to reduce the temperature of the exhaust steam of the working medium to below 55° C. The temperature of the exhaust steam of the working medium coming out of the screw power machine 3 after condensation through the condenser 5 is lower than the boiling point of the working medium. Since the system is under positive pressure, the working boiling point of the working medium is higher than the standard boiling point of 58.5° C., and the temperature of the exhaust steam of the working medium after condensation is lower than 55° C. to ensure complete liquefaction.

[0042] In the present invention, the pressure rating of the system pipeline is selected to be lower than the critical pressure of the working fluid 4.64MPa. Therefore, ordinary pipelines with a standard pressure rating of 3.0MPa can meet the system safety operation requirements, that is, the system operating pressure is lower than 3.0MPa.

[0043] Taking the flue gas from a hot blast furnace as an example, the pressure of the flue gas before it comes out of the hot blast furnace combustion chamber and enters the double preheating system is about 0.5 kPa. After heat exchange in the double preheating system, the pressure is slightly higher than the atmospheric pressure. In order to ensure stable heat exchange between the flue gas and the working fluid in evaporator 2, the flue gas must be processed by a booster pressure equalizer before entering evaporator 2.

[0044] like Figure 2 As shown, the flue gas boost pressure equalizer 1 includes an air intake section, a boost section and a pressure equalizing section which are arranged in sequence, and the low-temperature flue gas flows in sequence along the air intake section, the boost section and the pressure equalizing section, and the boost section is a tapered nozzle, and the diameter of the boost section gradually decreases from one end to the other end, and the boost section is used to increase the pressure of the low-temperature flue gas to about 0.55 kPa. One end of the boost section is a large diameter end, and the other end of the boost section is a small diameter end, and the diameter of the large diameter end is larger than the diameter of the small diameter end. The air intake section is connected to the large diameter end of the boost section, and the diameter of the air intake section is the same as the diameter of the large diameter end, and the pressure equalizing section is connected to the small diameter end of the boost section, and the diameter of the pressure equalizing section is the same as the diameter of the small diameter end.

[0045] like Figure 2As shown, the air intake section is provided with a first check valve, which is a one-way stroke valve. The pressure equalization section is provided with a second check valve, and the pressure equalization section after the booster nozzle provides a buffer pressure equalization space. The end of the pressure equalization section is the second check valve, and the check pressure of the second check valve is ≥0.5kPa.

[0046] There is a check valve at both ends of the flue gas boost pressure equalizer 1 to ensure the one-way flow of the flue gas, so that the low-temperature flue gas can only flow through the intake section, the boost section and the pressure equalization section in sequence. Between the two check valves of the flue gas boost pressure equalizer 1 is a boost nozzle and a buffer pressure equalization space, so that the flue gas enters the evaporator 2 with a stable pressure and uniform flow, ensuring stable operation of heat exchange with the working medium in the evaporator 2.

[0047] The present invention also provides a low-temperature flue gas power generation method, comprising the steps of:

[0048] S1, low-temperature flue gas enters the booster equalizer for boosting;

[0049] S2, the low-temperature flue gas after pressure increase enters evaporator 2;

[0050] S3, after the liquid working medium in the evaporator 2 absorbs the waste heat of the flue gas, the formed working medium steam enters the screw power machine 3;

[0051] S4, the exhaust steam of the working medium discharged from the screw power machine 3 enters the condenser 5;

[0052] S5. The liquid working medium discharged from the condenser 5 enters the evaporator 2 through the working medium circulation pump 6.

[0053] Through the low-temperature flue gas power generation system and method of the present invention, the waste heat of flue gas with a temperature below 200°C can be recovered and generate benefits. In the present invention, the flue gas inlet and outlet temperatures in the evaporator 2 are calculated as 140°C / 60°C, and the working medium inlet and outlet temperatures in the screw power machine 3 are calculated as 130°C / 70°C, then 1.0×10 5 Nm 3 / h low-temperature flue gas can be equipped with a 300kW screw expander generator set.

[0054] The present invention is described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention; or the above concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. Low temperature flue gas power generation system, characterized in that: The invention comprises a flue gas pressure-boosting equalizer for receiving low-temperature flue gas, an evaporator connected to the flue gas pressure-boosting equalizer, a screw power machine connected to the evaporator, and a generator connected to the screw power machine.

2. The low-temperature flue gas power generation system according to claim 1, characterized in that: The temperature of the low-temperature flue gas received by the flue gas boosting and equalizing device is lower than 200°C.

3. The low-temperature flue gas power generation system according to claim 1, characterized in that: The screw power machine is connected to a condenser, and the exhaust steam of the working medium discharged from the screw power machine enters the condenser.

4. The low-temperature flue gas power generation system according to claim 3, characterized in that: The condenser is configured to reduce the temperature of the working medium exhaust steam to below 55°C.

5. The low-temperature flue gas power generation system according to claim 3, characterized in that: The condenser is connected to a working fluid circulation pump, and the working fluid circulation pump is connected to the evaporator.

6. The low-temperature flue gas power generation system according to any one of claims 1 to 5, characterized in that: The flue gas boost pressure equalizer comprises an air intake section, a pressure increasing section and a pressure equalizing section which are arranged in sequence. The pressure increasing section is a tapered nozzle, and the diameter of the pressure increasing section gradually decreases from one end to the other end.

7. The low-temperature flue gas power generation system according to claim 6, characterized in that: The air intake section is provided with a first check valve, and the pressure equalizing section is provided with a second check valve.

8. A low-temperature flue gas power generation method, characterized in that: Includes steps: S1, low-temperature flue gas enters the booster equalizer for boosting; S2, the low-temperature flue gas after pressure increase enters the evaporator; S3. After the liquid working medium in the evaporator absorbs the waste heat of the flue gas, the formed working medium steam enters the screw power machine.

9. The low-temperature flue gas power generation method according to claim 8, characterized in that: The temperature of the low-temperature flue gas entering the flue gas boosting and equalizing device is lower than 200°C.

10. The low-temperature flue gas power generation method according to claim 8, characterized in that: Also includes the steps: S4, the exhaust steam of the working fluid discharged by the screw power machine enters the condenser; S5. The liquid working medium discharged from the condenser enters the evaporator through the working medium circulation pump.

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