Multi-stage high-temperature coal gas waste heat gradient recovery system

Abstract

The invention relates to a multi-stage high-temperature coal gas waste heat gradient recovery system which is divided into a first-stage high-pressure steam generation unit, a second-stage medium-pressure steam generation unit, a third-stage hot water ORC waste heat power generation unit and a fourth-stage heating medium water ORC waste heat power generation unit, and the system is divided into a high-temperature waste heat recovery section, a medium-temperature waste heat recovery section and a coal gas washing waste heat recovery section according to the coal gas temperature gradient; the primary high-pressure steam generation unit comprises a high-pressure steam pocket, a primary high-pressure evaporator, a primary high-pressure superheater, a secondary high-pressure superheater and a primary water supply preheater; the second-stage medium-pressure steam generation unit comprises a medium-pressure steam pocket, a second-stage medium-pressure evaporator, a third-stage medium-pressure evaporator, a first-stage medium-pressure superheater, a second-stage medium-pressure superheater and a second-stage water supply preheater. The waste heat recovery device has the beneficial effects that the high-temperature coal gas is recovered from 900-1200 DEG C to 90-100 DEG C, and the deep recovery of waste heat of flue gas with high ash content is also realized. The heat recovery efficiency of the system is improved by at least 20%, and energy consumption and emission are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of flue gas waste heat recovery, relates to the waste heat recovery of high-temperature coal gas, and particularly relates to a technology for deep recovery of waste heat from flue gas with large load and high ash content. Background Art

[0002] In recent years, energy conservation and emission reduction have been the key points of the national strategy, especially for high-energy-consuming industries. Industrial energy consumption in China accounts for more than 70% of the total energy consumption, and at least 50% of it is converted into industrial waste heat with different carriers and temperatures. Most of it can be recycled, but the current recovery rate of industrial waste heat resources in China is only about 30%, and the energy utilization efficiency is relatively low. Among them, flue gas waste heat accounts for 35% of the total waste heat energy contained, which is equivalent to 340 million tons of standard coal. However, the recovery rate of industrial flue gas waste heat in China is only 29%, which is 15% - 20% lower than the average level abroad. It is difficult to recover the waste heat of industrial high-temperature flue gas, and the total amount of flue gas emissions remains high. The main difficulties lie in the high flue gas temperature (about 1000°C), high dust content (≥100g / Nm 3 ), unclear ash deposition mechanism, large uncertainty in the process calculation of heat exchange equipment, serious problems such as ash blockage, wear, and corrosion on the surface area of heat exchange equipment, and it is difficult to achieve deep waste heat recovery. The high-temperature flue gas generated by the gasifier has great recovery value. Efficiently recovering this part of waste heat can not only reduce energy consumption but also reduce carbon emissions. However, due to its high temperature, high ash content, and complex composition, traditional recovery technologies are difficult to achieve deep recovery.

[0003] Therefore, a multistage high-temperature coal gas waste heat deep recovery system is designed, including a crude coal gas waste heat recovery process and a low-temperature high-efficiency waste heat power generation complete set process, to solve problems such as small flue gas recovery treatment volume, low recovered heat grade, and insufficient heat recovery depth, filling the domestic technical gap. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the existing waste heat recovery technology and provide a multistage high-temperature coal gas waste heat gradient recovery system to expand the depth of flue gas waste heat recovery.

[0005] The technical solution adopted by the present invention is: a multistage high-temperature coal gas waste heat gradient recovery system. According to the waste heat recovery method, the system is divided into a first-stage high-pressure steam generation unit, a second-stage medium-pressure steam generation unit, a third-stage hot water ORC waste heat power generation unit, and a fourth-stage heat medium water ORC waste heat power generation unit. According to the high-temperature coal gas temperature gradient, the system is divided into a high-temperature waste heat recovery section, a medium-temperature waste heat recovery section, and a coal gas water washing waste heat recovery section; The first-stage high-pressure steam generation unit includes: a high-pressure steam drum, a first-stage high-pressure evaporator, a first-stage high-pressure superheater, a second-stage high-pressure superheater, and a first-stage feed water preheater; the second-stage medium-pressure steam generation unit includes: a medium-pressure steam drum, a second-stage medium-pressure evaporator, a third-stage medium-pressure evaporator, a first-stage medium-pressure superheater, a second-stage medium-pressure superheater, and a second-stage feed water preheater; The high-temperature waste heat recovery section includes, arranged from top to bottom in the high-temperature waste heat recovery tower: a first-stage high-pressure evaporator, a second-stage medium-pressure evaporator, a first-stage high-pressure superheater, a second-stage high-pressure superheater, a first-stage medium-pressure superheater, a second-stage medium-pressure superheater, and a third-stage evaporator; the medium-temperature waste heat recovery section includes a first-stage feed water preheater, a second-stage feed water preheater, and a gas-liquid heat exchanger, arranged in sequence from top to bottom in the medium-temperature waste heat recovery tower; the coal gas washing waste heat recovery section consists of a third-stage hot water ORC waste heat power generation unit and a fourth-stage heat medium water ORC waste heat power generation unit. The flue gas flow is as follows: The flue gas first enters the tube side of the first-stage high-pressure evaporator and the second-stage medium-pressure evaporator. The recovered heat causes the shell side to produce saturated steam at the corresponding pressure. The flue gas after preliminary cooling sequentially passes through the shell side of the first-stage high-pressure superheater and the second-stage high-pressure superheater, then enters the shell side of the first-stage medium-pressure superheater and the second-stage medium-pressure superheater for heat exchange and is gradually cooled. Then, guided by the conical deflector plate, the flue gas enters the third-stage medium-pressure evaporator. After passing through the third-stage medium-pressure evaporator, the flue gas enters the bottom of the high-temperature waste heat recovery tower and is discharged from the outlet at a lower position. Then it enters the medium-temperature waste heat recovery section. The flue gas sequentially flows through the first-stage feed water preheater, the second-stage feed water preheater, and the gas-liquid heat exchanger for further cooling. After the flue gas is discharged from the gas-liquid heat exchanger, it is cleaned by the scrubbing tower and filtered by the filter, and then enters the fourth-stage heat medium water ORC waste heat power generation unit. The high-temperature steam generated on the shell side of the gas-liquid heat exchanger serves as the heat source for the third-stage hot water ORC waste heat power generation unit. The first-stage high-pressure evaporator can produce steam at 8 - 12 MPa; the second-stage medium-pressure evaporator and the third-stage medium-pressure evaporator can produce steam at 4 - 7 MPa; the first-stage high-pressure superheater and the second-stage high-pressure superheater can produce superheated steam at 8 - 12 MPa, and the first-stage medium-pressure superheater and the second-stage medium-pressure superheater can produce superheated steam at 4 - 7 MPa.

[0006] Through multi-stage cascade recovery, this system can recover flue gas at a temperature of 900 - 1200 °C to 90 - 100 °C, providing an efficient and environmentally friendly energy solution for enterprises, significantly improving energy utilization efficiency, and helping to achieve the goal of green and sustainable development.

[0007] The three-stage hot water ORC waste heat power generation unit includes: a second working fluid pump, a second evaporator, a second preheater, a second condenser, a steam turbine, a second generator, a second steam-water separator, and a second lift pump. The heat source sequentially enters the second evaporator and the second preheater to evaporate and preheat the working fluid respectively. After being discharged from the second preheater, it is re-transported back to the shell side of the steam-liquid heat exchanger by the second lift pump. The working fluid evaporated by the second evaporator enters the second steam-water separator. In the second steam-water separator, the gaseous working fluid is discharged from the top of the steam-water separator. The discharged high-temperature gaseous working fluid directly enters the steam turbine. The steam turbine converts thermal energy into mechanical energy, driving the second generator to convert mechanical energy into electrical energy. The exhaust steam discharged from the steam turbine enters the second condenser, and the condensed working fluid is re-transported to the second preheater by the second working fluid pump.

[0008] The four-stage heat medium water ORC waste heat power generation unit includes: a first working fluid pump, a first evaporator, a first preheater, a first condenser, an expander, a first generator, a first steam-water separator, and a first lift pump. The flue gas first enters the first evaporator and the first preheater for heat exchange to evaporate and preheat the working fluid respectively. Subsequently, it is discharged from the first preheater and transported by the first lift pump to the scrubbing tower as the water source for the spray water. The working fluid preheated by the first preheater enters the first evaporator to continue absorbing heat and vaporizing. The high-temperature working fluid vaporized by the first evaporator enters the first steam-water separator. In the first steam-water separator, the gaseous working fluid is discharged from the top of the steam-water separator. The high-temperature gaseous working fluid discharged from the top of the first steam-water separator directly enters the expander. The steam turbine converts thermal energy into mechanical energy, driving the first generator to convert mechanical energy into electrical energy. The exhaust steam discharged from the expander enters the first condenser, and the condensed working fluid is re-transported to the first preheater by the first working fluid pump.

[0009] The three-stage medium-pressure evaporator is designed with three folding processes. The two ends of the tube side use conical deflector plates and a smoke box for folding processes, and the shell side uses an annular baffle for folding. The conical deflector plate is arranged at the outlet of the secondary medium-pressure superheater and the inlet of the three-stage medium-pressure evaporator. An annular nitrogen nozzle is designed under the conical deflector plate. The smoke box is arranged at the bottom of the three-stage medium-pressure evaporator, and a valve is provided at the bottom of the smoke box. The flue gas is guided by the conical deflector plate at the inlet of the three-stage medium-pressure evaporator, flows along the inner tube bundle to the bottom of the evaporator, reaches the smoke box for a baffle, then turns back upward along the middle tube bundle, flows to the bottom of the conical baffle, and then, under the combined action of the conical deflector plate and the gas sprayed by the annular nitrogen nozzle, turns back downward along the outer tube bundle and flows out from the N2 port on the side of the lower tube box. The cold end of the shell side enters from ports T3 and T4, flows upward against the current through the conical deflector plate, and is discharged from ports T1 and T2. The annular nitrogen nozzle forms a high-speed nitrogen jet, which not only effectively disperses the particulate matter in the flue gas to prevent its deposition on the evaporator wall, but also reduces the dead zone of the flue gas flow caused by the conical deflector plate, further improving the heat transfer efficiency. The annular nitrogen nozzle is linked with the control system to dynamically adjust the spraying intensity according to the flue gas concentration and flow rate to ensure the long-term stable operation of the system.

[0010] Optionally, the applicable conditions for the high-temperature waste heat recovery section are as follows: the flue gas temperature is 900 - 1200 °C, the pressure is 4 - 6 MPa, and the ash content is 15 - 16 tons per hour.

[0011] The medium at the inlet of the shell side of the primary high-pressure evaporator comes from the liquid separated by the high-pressure steam drum. The steam at the outlet of the shell side enters the high-pressure steam drum, and the saturated steam in the high-pressure steam drum then enters the high-pressure superheater and the high-pressure superheater in sequence, finally generating high-pressure superheated steam.

[0012] The medium at the inlet of the shell side of the secondary medium-pressure evaporator comes from the liquid separated by the medium-pressure steam drum. The steam at the outlet of the shell side enters the medium-pressure steam drum; the medium at the inlet of the shell side of the tertiary medium-pressure evaporator comes from the liquid separated by the medium-pressure steam drum. The steam at the outlet of the shell side enters the medium-pressure steam drum; the saturated steam in the medium-pressure steam drum then enters the secondary medium-pressure superheater and the primary medium-pressure superheater in sequence, finally generating medium-pressure superheated steam.

[0013] The inlet flue gas temperature of the medium-temperature waste heat recovery section is 300 - 500 °C. The primary feed water preheater, the secondary feed water preheater, and the vapor-liquid heat exchanger all adopt high-efficiency internal finned tube bundles. The high-temperature steam generated by the primary feed water preheater is used to supplement the high-pressure steam drum; the high-temperature steam generated by the secondary feed water preheater is used to supplement the medium-pressure steam drum.

[0014] A nuclear level gauge is provided on the side of the smoke box. The nuclear level gauge detects the ash accumulation height in the smoke box to ensure timely ash cleaning and prevent excessive ash accumulation from affecting the system operation efficiency. The valve and the nuclear level gauge work in coordinated linkage to monitor the ash accumulation height in real time and automatically control the ash cleaning frequency according to the set ash accumulation height.

[0015] An actuator operation port X and an ash discharge port d are provided at the bottom of the tertiary medium-pressure evaporator for convenient ash cleaning operation.

[0016] The beneficial effects of the present invention: The present invention solves the problems of small treatment capacity of coal gas waste heat recovery, low recovered heat grade, and insufficient heat recovery depth, etc. This process design invention recovers high-temperature coal gas from 900 - 1200 °C to 90 - 100 °C, realizing the deep recovery of high-temperature coal gas waste heat. The heat recovery efficiency of the system is increased by at least 20%, reducing energy consumption and emissions. At the same time, the power generation efficiency is increased, achieving a win-win situation of environmental protection and economic benefits. In addition, through optimized design, the present system can also adapt to different scales of coal gas treatment requirements. Its modular components are convenient for installation and maintenance, making the system have a wide application prospect in different industrial application scenarios. Description of the Drawings

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0018] Figure 1 Schematic diagram of the multi-stage high-temperature coal gas waste heat gradient recovery system of the present invention; Figure 2 Structural diagram of the three-stage medium-pressure evaporator of the present invention; Figure 3 Distribution diagram of the tube bundles of the three-stage medium-pressure evaporator of the present invention.

[0019] Wherein: 1 - medium-pressure steam drum; 2 - high-pressure steam drum; 3 - first-stage high-pressure evaporator; 4 - second-stage medium-pressure evaporator; 5 - first-stage high-pressure superheater; 6 - second-stage high-pressure superheater; 7 - first-stage medium-pressure superheater; 8 - second-stage medium-pressure superheater; 9 - conical deflector; 10 - annular nitrogen nozzle; 11 - third-stage medium-pressure evaporator; 12 - smoke box; 13 - nuclear level gauge; 14 - first-stage feed water preheater; 15 - second-stage feed water preheater; 16 - steam-liquid heat exchanger; 17 - steam scrubbing tower; 18 - filter; 19 - first evaporator; 20 - first steam-water separator; 21 - expander; 22 - first generator; 23 - first condenser; 24 - first working fluid pump; 25 - first preheater; 26 - second lifting pump; 27 - second preheater; 28 - second evaporator; 29 - second steam-water separator; 30 - steam turbine; 31 - second generator; 32 - second condenser; 33 - second working fluid pump; 34 - first lifting pump; 35 - inner tube bundle; 36 - intermediate tube bundle; 37 - outer tube bundle; N1 - inlet of the tube side of the third-stage medium-pressure evaporator; N2 - outlet of the tube side of the third-stage medium-pressure evaporator; T3-4 - inlet of the shell side of the third-stage medium-pressure evaporator; T1-2 - outlet of the third-stage medium-pressure evaporator; X - actuator operation port; d - ash discharge port. Detailed implementation manners

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0021] To enable those skilled in the art of this technology to better understand the solution of the present invention, the present invention will be further described in detail below in conjunction with the drawings and specific implementation manners.

[0022] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated position or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0023] As Figure 1 shown, it is a schematic process flow diagram of a multi-stage high-temperature coal gas waste heat gradient recovery system according to the present invention. The system is divided into a first-stage high-pressure steam generation unit, a second-stage medium-pressure steam generation unit, a third-stage hot water ORC waste heat power generation unit, and a fourth-stage heat medium water ORC waste heat power generation unit according to the waste heat recovery method. The system is divided into a high-temperature waste heat recovery section, a medium-temperature waste heat recovery section, and a coal gas water washing waste heat recovery section according to the high-temperature coal gas temperature gradient.

[0024] As Figure 1 shown is a multi-stage high-temperature coal gas waste heat gradient recovery system, wherein the first-stage high-pressure steam generation unit includes: a high-pressure steam drum 2, a first-stage high-pressure evaporator 3, a first-stage high-pressure superheater 5, a second-stage high-pressure superheater 6, and a first-stage feed water preheater 14; the second-stage medium-pressure steam generation unit includes: a medium-pressure steam drum 1, a second-stage medium-pressure evaporator 4, a third-stage medium-pressure evaporator 11, a first-stage medium-pressure superheater 7, a second-stage medium-pressure superheater 8, and a second-stage feed water preheater 15; the third-stage hot water ORC waste heat power generation unit includes: a second working fluid pump 33, a second evaporator 28, a second preheater 27, a second condenser 32, a steam turbine 30, a second generator 31, a second steam-water separator 29, and a second lifting pump 26; the fourth-stage heat medium water ORC waste heat power generation unit includes: a first working fluid pump 24, a first evaporator 19, a first preheater 25, a first condenser 23, an expander 21, a first generator 22, a first steam-water separator 20, and a first lifting pump 34; the high-temperature waste heat recovery section includes, arranged in sequence from top to bottom in the high-temperature waste heat recovery tower: a first-stage high-pressure evaporator 3, a second-stage medium-pressure evaporator 4, a first-stage high-pressure superheater 5, a second-stage high-pressure superheater 6, a first-stage medium-pressure superheater 7, a second-stage medium-pressure superheater 8, and a third-stage evaporator 11; the medium-temperature waste heat recovery section includes a first-stage feed water preheater 14, a second-stage feed water preheater 15, and a gas-liquid heat exchanger 16, which are arranged in sequence from top to bottom in the medium-temperature waste heat recovery tower; the coal gas water washing waste heat recovery section includes: a steam washing tower 17, a filter 18, a first evaporator 19, a first preheater 25, and a first lifting pump 34.

[0025] The described multi-stage high-temperature coal gas waste heat gradient recovery system has the following flue gas flow: The flue gas first enters the tube sides of the primary high-pressure evaporator 3 and the secondary medium-pressure evaporator 4. The recovered heat causes the shell side to produce saturated steam at the corresponding pressure. The flue gas after preliminary cooling sequentially passes through the shell sides of the primary high-pressure superheater 5 and the secondary high-pressure superheater 6, and then enters the shell sides of the primary medium-pressure superheater 7 and the secondary medium-pressure superheater 8. The recovered heat respectively produces superheated steam at 8 - 12 MPa and 4 - 7 MPa. Then, the flue gas is guided by the conical deflector 9 into the tertiary medium-pressure evaporator 11, and the recovered heat produces steam at 4 - 7 MPa. After the flue gas passes through the tertiary medium-pressure evaporator 11, it enters the bottom of the high-temperature waste heat recovery tower and exits from the outlet at a lower position, and then enters the medium-temperature waste heat recovery section. The flue gas sequentially flows through the primary feed water preheater 14, the secondary feed water preheater 15, and the vapor-liquid heat exchanger 16, and is further cooled. After the flue gas exits from the vapor-liquid heat exchanger 16, it is cleaned by the steam scrubbing tower 17 and filtered by the filter 18, and then enters the fourth-stage heat medium water ORC waste heat power generation unit to heat and preheat the working medium of the power generation system respectively. The design of this system also considers the goals of minimizing heat loss and maximizing energy efficiency. For example, the primary high-pressure evaporator 3 and the secondary medium-pressure evaporator 4 adopt a specially designed shell-and-tube structure to enhance the heat exchange efficiency and reduce the heat loss during the heat transfer process; and adopt designs that prevent erosion, abrasion, and ash accumulation to maintain the stable operation of the equipment; the tertiary medium-pressure evaporator 11 ensures good heat conduction performance while withstanding high-temperature flue gas through optimized flow channel layout and material selection. The entire system adopts an advanced monitoring system to monitor the operating status of each part in real time to ensure the stable and efficient operation of the system, thereby providing a continuous and reliable energy supply for industrial production. The high-pressure steam generated on the shell side of the primary high-pressure evaporator 3 is connected to the high-pressure steam drum 2. The liquid separated by the high-pressure steam drum 2 is reconnected to the inlet of the shell side of the primary high-pressure evaporator 3 to form a cycle. At the same time, the gas separated by the high-pressure steam drum 2 sequentially enters the secondary high-pressure superheater 6 and the primary high-pressure superheater 5, and finally forms high-pressure superheated steam. The steam generated on the shell sides of the secondary medium-pressure evaporator 4 and the tertiary medium-pressure evaporator 11 is connected to the medium-pressure steam drum 1. The liquid separated by the medium-pressure steam drum 1 is respectively reconnected to the inlets of the shell sides of the secondary medium-pressure evaporator 4 and the tertiary medium-pressure evaporator 11 to form a cycle. The gas separated by the medium-pressure steam drum 1 sequentially enters the secondary medium-pressure superheater 8 and the primary medium-pressure superheater 7, and finally forms medium-pressure superheated steam. The high-temperature steam generated by the primary feed water preheater 14 is connected to the high-pressure steam drum 2, the medium-temperature vapor-liquid generated by the corresponding secondary feed water preheater 15 enters the medium-pressure steam drum 1, and the high-temperature steam generated on the shell side of the vapor-liquid heat exchanger 16 is used as the heat source for the third-stage hot water ORC waste heat power generation unit to realize the evaporation and preheating of the working medium.

[0026] The high-temperature waste heat recovery system shown has the primary high-pressure evaporator 3 and the secondary medium-pressure evaporator 4 both designed to resist erosion, withstand high temperatures and resist ash accumulation. Their internal structures are finely optimized to ensure efficient heat exchange in a high-temperature and high-ash environment, reduce thermal resistance and fouling, and maintain the long-term stable operation of the system.

[0027] The described tertiary medium-pressure evaporator 11 has a three-fold design, effectively reducing the overall length of the high-temperature waste heat recovery section and increasing the flow velocity of the flue gas in the tube pass. The two ends of the tube pass are respectively folded by the conical deflector 9 and the smoke box 12, and the shell pass uses the annular baffle 38 ( Figure 2 The alternating lengths in the middle represent alternating diameters to achieve the baffle effect) to improve the heat exchange effect. Among them, the tube pass process: a conical deflector 9 is designed at the outlet of the secondary medium-pressure superheater 8 and the inlet of the tertiary medium-pressure evaporator 11. An annular nitrogen nozzle 10 is designed on the lower side of the conical deflector 9, a smoke box 12 is designed at the bottom, a valve is designed at the bottom of the smoke box 12, and a nuclear level gauge 13 is designed on the side. The flue gas is guided by the conical deflector 9 at the inlet of the tertiary medium-pressure evaporator 11, flows along the inner tube bundle 35 to the bottom of the evaporator, reaches the smoke box 12 for baffle, then turns back upward from the middle tube bundle 36, and then turns back downward from the outer tube bundle 37 under the combined action of the conical deflector 9 and the gas ejected from the annular nitrogen nozzle 10, and flows out from the N2 port on the side of the lower tube box. Since the flow dead zone caused by the conical deflector 9 is likely to cause problems such as ash accumulation on the wall of the device and affect the heat exchange efficiency, an annular nitrogen nozzle 10 is provided on the lower side of the conical deflector 9. The high-speed jet of the annular nitrogen nozzle 10 can disperse the fly ash particles, prevent them from depositing on the wall of the device, and at the same time enhance the turbulence degree of the flue gas, further improving the heat exchange effect. This design effectively extends the service life of the equipment and ensures the efficient and stable operation of the system. The design of the annular nitrogen nozzle 10 also considers the optimization of the injection angle and flow velocity to ensure an appropriate ratio of nitrogen to flue gas and further reduce the risk of ash accumulation. The shell pass process: the cold end of the shell pass enters from ports T3 and T4, flows upward countercurrently through the annular baffle, and is discharged from ports T1 and T2. In addition, the smoke box 12 designed at the bottom, the valve at the bottom and the nuclear level gauge 13 on the side work together to monitor the dynamics of the flue gas and ash in real time, adjust the operating parameters in a timely manner, and ensure the self-cleaning ability of the smoke box 12 to prevent ash accumulation in the smoke box from affecting the heat exchange effect. The nuclear level gauge 13 detects the level through the attenuation characteristics of the γ-rays released by the radioactive isotope after penetrating the medium. It has the characteristics of being resistant to high temperatures and pressures, not being affected by dust, corrosion and adhesion, not requiring hole opening, not requiring wiring power supply, and having a long service life. An actuator operation port X and an ash discharge port d are designed at the bottom of the tube box for convenient ash cleaning operation.

[0028] The first-stage feedwater preheater 14, the second-stage feedwater preheater 15, and the vapor-liquid heat exchanger 16 all adopt high-efficiency internal finned tube heat exchangers to increase the convective heat transfer efficiency of vapor-liquid heat transfer and improve the flue gas waste heat recovery efficiency. In the low-temperature waste heat ORC power generation system, the first evaporator 19 and the second evaporator 28, and the second preheater 27 and the first preheater 25 all adopt composite high-efficiency heat exchange tubes, and the material is selected as nickel-based alloy to ensure long-term stable operation. Before the flue gas enters the four-stage heat medium water ORC waste heat power generation unit, it first passes through the steam scrubbing tower 17 and the filter 18 to remove impurities and particulate matter in the flue gas, ensure the cleanliness of the flue gas entering the system, reduce the corrosion and wear of the equipment, improve the heat transfer efficiency, and extend the service life of the system. The designs of the steam scrubbing tower 17 and the filter 18 fully consider the flue gas flow rate and composition to ensure the best treatment effect and provide a stable and reliable heat source for the subsequent power generation process.

[0029] Both the three-stage hot water ORC waste heat power generation unit and the four-stage heat medium water ORC waste heat power generation unit adopt non-azeotropic working fluids. The variable-temperature phase characteristics of non-azeotropic working fluids can improve the temperature matching degree between the cyclic endothermic / exothermic process and the heat source / cold source, and reduce the heat transfer exergy loss. It not only optimizes the thermodynamic cycle, but also reduces the sensitivity of the system to the ambient temperature and improves the system thermal efficiency. By precisely controlling the working fluid ratio, the system can maintain high-efficiency operation under different working conditions, further improving the energy utilization rate and economic benefits. According to different working conditions and requirements, the steam turbine 30 and the expander 21 are respectively used as power generation equipment. The steam turbine is used for high-parameter working conditions, and the expander is suitable for low-parameter working conditions. The combination of the two achieves a more efficient energy power generation efficiency.

[0030] In the four - stage hot - medium water ORC waste - heat power generation unit, the flue gas first enters the first evaporator 19 and the first pre - heater 25 for heat exchange. The recovered heat is used to vaporize and pre - heat the working fluid, and then it is discharged from the first pre - heater 25 and is transported by the first lift pump 34 to the steam scrubbing tower 17 as the water source for the spray water. The working fluid pre - heated by the first pre - heater 25 enters the first evaporator 19 to continue absorbing heat and vaporizing. The high - temperature working fluid vaporized by the first evaporator 19 enters the first steam - water separator 20, where vapor - liquid separation occurs. The gaseous working fluid is discharged from the top of the steam - water separator 20. The high - temperature gaseous working fluid discharged from the top of the first steam - water separator 20 directly enters the expander 21. The expander 21 converts thermal energy into mechanical energy, driving the first generator 22 to convert mechanical energy into electrical energy. The exhausted steam discharged from the expander 21 enters the first condenser 23, and the condensed working fluid is re - transported by the first working fluid pump 24 to the first pre - heater 25. In the three - stage hot - water ORC waste - heat power generation unit, the heat source sequentially enters the second evaporator 28 and the second pre - heater 27 to evaporate and pre - heat the working fluid respectively. After being discharged from the second pre - heater 27, it is re - transported by the second lift pump 26 back to the shell - side of the vapor - liquid heat exchanger 16. The working fluid evaporated by the second evaporator 28 enters the second steam - water separator 29. In the second steam - water separator 29, the gaseous working fluid is separated from the liquid. The high - temperature gaseous working fluid discharged from the top of the steam - water separator 29 directly enters the steam turbine 30. The steam turbine 30 converts thermal energy into mechanical energy, driving the second generator 31 to convert mechanical energy into electrical energy. The exhausted steam discharged from the steam turbine 30 enters the second condenser 32, and the condensed working fluid is re - transported by the second working fluid pump 33 to the second pre - heater 27. During the whole process, the system realizes the full utilization of waste heat through the efficient conversion of thermal energy and mechanical energy, achieving the effect of energy conservation and emission reduction. At the same time, the modular design of each component ensures the stability and flexibility of the system operation, facilitating rapid deployment and adjustment in different industrial scenarios.

Claims

1. A multi-stage high-temperature coal gas waste heat gradient recovery system, characterized in that: According to the waste heat recovery method, the system is divided into a primary high-pressure steam generation unit, a secondary medium-pressure steam generation unit, a third-level hot water ORC waste heat power generation unit and a fourth-level heat medium water ORC waste heat power generation unit. According to the temperature gradient of high-temperature coal gas, the system is divided into a high-temperature waste heat recovery section, a medium-temperature waste heat recovery section and a coal gas water washing waste heat recovery section. The first-stage high-pressure steam generating unit comprises: a high-pressure steam drum (2), a first-stage high-pressure evaporator (3), a first-stage high-pressure superheater (5), a second-stage high-pressure superheater (6) and a first-stage feedwater preheater (14); the second-stage medium-pressure steam generating unit comprises: a medium-pressure steam drum (1), a second-stage medium-pressure evaporator (4), a third-stage medium-pressure evaporator (11), a first-stage medium-pressure superheater (7), a second-stage medium-pressure superheater (8) and a second-stage feedwater preheater (15); The high-temperature waste heat recovery section includes: a first-stage high-pressure evaporator (3), a second-stage medium-pressure evaporator (4), a first-stage high-pressure superheater (5), a second-stage high-pressure superheater (6), a first-stage medium-pressure superheater (7), a second-stage medium-pressure superheater (8) and a third-stage evaporator (11), which are arranged in sequence from top to bottom of the high-temperature waste heat recovery tower; the medium-temperature waste heat recovery section includes a first-stage feed water preheater (14), a second-stage feed water preheater (15) and a gas-liquid heat exchanger (16), which are arranged in sequence from top to bottom in the medium-temperature waste heat recovery tower; the coal gas water washing waste heat recovery section is composed of a third-stage hot water ORC waste heat power generation unit and a fourth-stage heat medium water ORC waste heat power generation unit; The flue gas flow is as follows: the flue gas first enters the tube side of the first-stage high-pressure evaporator (3) and the second-stage medium-pressure evaporator (4), and the recovered heat causes the shell side to produce saturated steam of corresponding pressure as a by-product. After the initial cooling, the flue gas passes through the shell side of the first-stage high-pressure superheater (5) and the second-stage high-pressure superheater (6), and then enters the shell side of the first-stage medium-pressure superheater (7) and the second-stage medium-pressure superheater (8). The recovered heat produces superheated steam of 8-12MPa and 4-7MPa respectively. Then, the flue gas enters the third-stage medium-pressure evaporator (11) under the guidance of the conical guide plate (9), and the recovered heat produces 4-7MPa as a by-product. a steam, the flue gas passes through the three-stage medium-pressure evaporator (11), enters the bottom of the high-temperature waste heat recovery tower, is discharged from the lower outlet, and then enters the medium-temperature waste heat recovery section. The flue gas flows through the first-stage feed water preheater (14), the second-stage feed water preheater (15) and the vapor-liquid heat exchanger (16) in sequence to further cool down. After the flue gas is discharged from the vapor-liquid heat exchanger (16), it is cleaned by the steam washing tower (17) and filtered by the filter (18) before entering the fourth-stage heat medium water ORC waste heat power generation unit. The high-temperature steam generated in the shell side of the vapor-liquid heat exchanger (16) serves as the heat source of the three-stage hot water ORC waste heat power generation unit.

2. A multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 1, characterized in that: The three-stage hot water ORC waste heat power generation unit comprises: a second working fluid pump (33), a second evaporator (28), a second preheater (27), a second condenser (32), a steam turbine (30), a second generator (31), a second steam-water separator (29) and a second lift pump (26). The heat source sequentially enters the second evaporator (28) and the second preheater (27) to evaporate and preheat the working fluid respectively. After being discharged from the second preheater (27), the heat source is transported back to the shell of the steam-liquid heat exchanger (16) by the second lift pump (26). In the process, the working fluid evaporated by the second evaporator (28) enters the second steam-water separator (29), and in the second steam-water separator (29), the gaseous working fluid is discharged from the top of the steam-water separator (29). The discharged high-temperature gaseous working fluid directly enters the steam turbine (30), and the steam turbine converts thermal energy into mechanical energy, driving the second generator (31) to convert the mechanical energy into electrical energy. The exhaust steam discharged from the steam turbine (30) enters the second condenser (32), and the condensed working fluid is re-transported to the second preheater (27) by the second working fluid pump (33).

3. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 1, characterized in that: The four-stage heat medium water ORC waste heat power generation unit comprises: a first working fluid pump (24), a first evaporator (19), a first preheater (25), a first condenser (23), an expander (21), a first generator (22), a first steam-water separator (20) and a first lift pump (34). The flue gas first enters the first evaporator (19) and the first preheater (25) for heat exchange, whereby the working fluid is evaporated and preheated respectively. The flue gas is then discharged from the first preheater (25) and transported by the first lift pump (34) to a steam scrubber as a source of spray water. The working fluid preheated by the first preheater (25) enters the first evaporator (19) and the first preheater (25). The first evaporator (19) continues to absorb heat and vaporize. The high-temperature working medium vaporized by the first evaporator (19) enters the first steam-water separator (20). In the first steam-water separator (20), the gaseous working medium is discharged from the top of the steam-water separator (20). The high-temperature gaseous working medium discharged from the top of the first steam-water separator (20) directly enters the expander (21). The steam turbine converts thermal energy into mechanical energy, driving the first generator (22) to convert mechanical energy into electrical energy. The exhaust steam discharged from the expander (21) enters the first condenser (23). The condensed working medium is re-transported to the first preheater (25) by the first working medium pump (24).

4. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 1, characterized in that: The three-stage medium-pressure evaporator (11) is designed with three folds. The two ends of the tube side are folded by using a conical guide plate (9) and a smoke box (12) respectively. The shell side is folded by using an annular baffle. The conical guide plate (9) is arranged at the outlet of the second-stage medium-pressure superheater (8) and the inlet of the third-stage medium-pressure evaporator (11). An annular nitrogen nozzle (10) is designed on the lower side of the conical guide plate (9). The smoke box (12) is arranged at the bottom of the third-stage medium-pressure evaporator (11). A valve is provided at the bottom of the smoke box (12). The smoke is discharged from the third-stage medium-pressure evaporator (11). ) is guided by the conical guide plate (9) at the inlet, flows downstream from the inner tube bundle (35) to the bottom of the evaporator, reaches the smoke box (12) for deflection, then turns upward from the middle tube bundle (36), flows to the bottom of the conical deflector (9), and then turns downward from the outer tube bundle (37) under the combined action of the conical guide plate (9) and the gas sprayed by the annular nitrogen nozzle (10), flows out from the N2 port on the side of the lower tube box, enters the shell side cold end from ports T3 and T4, flows upward in countercurrent through the conical guide plate, and is discharged from ports T1 and T2.

5. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 1, characterized in that: The applicable conditions of the high-temperature waste heat recovery section are: flue gas temperature is 900-1200℃, pressure is 4-6MPa, and ash content is 15-16 tons / hour.

6. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 1, characterized in that: The shell side inlet medium of the first-stage high-pressure evaporator (3) comes from the liquid separated from the high-pressure drum (2). The steam at the shell side outlet enters the high-pressure drum (2). The saturated steam in the high-pressure drum (2) then enters the high-pressure superheater (6) and the high-pressure superheater (5) in sequence, ultimately generating high-pressure superheated steam.

7. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 1, characterized in that: The shell side inlet medium of the second-stage medium-pressure evaporator (4) comes from the liquid separated by the medium-pressure drum (1), and the steam at the shell side outlet enters the medium-pressure drum (1); the shell side inlet medium of the third-stage medium-pressure evaporator (11) comes from the liquid separated by the medium-pressure drum (1), and the steam at the shell side outlet enters the medium-pressure drum (1); the saturated steam in the medium-pressure drum (1) then enters the second-stage medium-pressure superheater (8) and the first-stage medium-pressure superheater (7) in sequence, and finally generates medium-pressure superheated steam.

8. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 1, characterized in that: The inlet flue gas temperature of the medium-temperature waste heat recovery section is 300-500°C. The primary feedwater preheater (14), the secondary feedwater preheater (15) and the steam-liquid heat exchanger (16) all use high-efficiency internal fin tube bundles. The high-temperature steam generated by the primary feedwater preheater (14) is used to supplement the high-pressure steam drum (2); the high-temperature steam generated by the secondary feedwater preheater (15) is used to supplement the medium-pressure steam drum (1).

9. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 4, characterized in that: A nuclear level meter (13) is provided on the side of the smoke box (12). The valve and the nuclear level meter work in coordination with each other to monitor the dust accumulation height in real time and automatically control the dust cleaning frequency according to the set dust accumulation height.

10. The multi-stage high-temperature coal gas waste heat gradient recovery system according to claim 4, characterized in that: The bottom of the three-stage medium-pressure evaporator (11) is provided with an actuator operation port X and an ash discharge port d.

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