A boiler liquid slag waste heat recovery and utilization system and method based on a cascade transcritical CO2 power cycle

Abstract

The present application belongs to the technical field of high-temperature molten slag waste heat utilization of liquid slag discharge boiler, and particularly relates to a boiler liquid slag waste heat recovery and utilization system and method based on a complex transcritical CO2 power cycle. The boiler liquid slag waste heat recovery and utilization system comprises a molten slag buffering unit, a centrifugal granulation unit, a waste heat recovery unit and a complex transcritical CO2 power cycle power generation assembly; wherein the centrifugal granulation unit is connected with the molten slag buffering unit to receive high-temperature liquid molten slag and granulate the same into solid granulated slag; the waste heat recovery unit recovers the molten slag waste heat of the centrifugal granulation unit by taking air as the working medium, and delivers the recovered molten slag waste heat to the complex transcritical CO2 power cycle power generation assembly for utilization. The present application fully utilizes the advantages of the complex cycle in maintaining the top-level heat absorption process unchanged, additionally increases the output power of the bottom-level cycle to improve the thermodynamic characteristics of the cycle, so as to achieve the purpose of utilizing the waste heat of the power station liquid slag discharge boiler.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature molten slag waste heat utilization of liquid slag discharge boiler, and particularly relates to a boiler liquid slag waste heat recovery and utilization system and method based on a cascade transcritical CO2 power cycle. BACKGROUND

[0002] It is reported that the energy consumption of industrial industries in China accounts for about 70% of the total energy consumption of the whole society, and the energy utilization rate is only 33%. The potential of waste heat resources in China is huge, and the recoverable waste heat resources account for 10%-40% of the total energy consumption of industrial industries. A large amount of industrial waste heat is not effectively utilized, resulting in low energy utilization rate, wasting primary energy and generating a large amount of carbon emissions. The liquid slag discharge boiler is a boiler type with high combustion intensity, high slag capturing rate and small dust content in flue gas, which can effectively overcome the shortcomings of solid slag discharge boiler, such as slagging on water-cooled walls in the furnace, fouling of heating surfaces and the like when burning easy slagging coal. However, the liquid slag discharge boiler also has the problem of very large physical heat loss of ash and slag.

[0003] In order to solve the above technical problems, the main treatment methods for the liquid slag discharge of the boiler in the prior art are mainly divided into water quenching method and dry method. The water quenching method has a fast cooling rate, and slag particles with high glass content can be easily obtained. However, the liquid slag has a very high temperature, about 1400℃ or so. When it is rapidly cooled and granulated by the 25℃ or so of the slag flushing cooling water, a large amount of heat will be released, a large amount of water vapor will be generated, and a large amount of slag flushing water with a temperature of about 85-90℃ will be generated. For a long time, this part of heat cannot be reasonably utilized, but is wasted, and the generated large amount of water vapor and slag flushing water will cause environmental heat pollution after being discharged into the environment. Moreover, when the slag flushing water is recycled, with the gradual increase of the temperature of the recycled slag flushing water, the liquid slag granulation rate will inevitably decrease, the coking amount in the granulation tank will increase, and in severe cases, slag blocking will occur, resulting in the shutdown of the boiler. Therefore, a large amount of new water must be supplemented to reduce the temperature of the recycled slag flushing water, which will consume a large amount of water resources, especially in areas lacking water resources, which will cause serious social harm. The dry method is to first granulate the slag liquid and then recover the waste heat. According to different granulation methods, it can be divided into mechanical crushing, air quenching and centrifugal granulation technology. Among them, the centrifugal granulation combined with the moving bed waste heat recovery technology does not consume water, has low energy consumption, obtains small-sized and high-quality slag particles, has a fast cooling rate, and has a high waste heat recovery rate. It is the preferred scheme for the treatment of liquid high-temperature molten slag. However, in order to further apply it in industrial production, three technical difficulties still need to be solved, i.e. complex composition of molten slag, high temperature, large change of physical properties, complex granulation process; non-steady-state complex heat transfer process of phase change particles coupled with mineral phase evolution under complex conditions is difficult to describe; information transmission of multi-phase, multi-parameter and multi-process of granulation-waste heat recovery is difficult.

[0004] To this end, the application provides a boiler liquid slag waste heat recycling system and method based on a cascade transcritical CO2 power cycle. SUMMARY

[0005] In order to solve the above-mentioned deficiencies in the prior art and overcome the low efficiency of liquid slag boiler waste heat utilization, the application provides a boiler liquid slag waste heat recycling system and method based on a cascade transcritical CO2 power cycle. The application proposes a combination of a cascade transcritical CO2 power cycle and a centrifugal granulation technology to achieve efficient utilization of liquid slag furnace liquid slag waste heat, thereby reducing the ash heat loss of the boiler and improving the efficiency of the generator set.

[0006] The boiler liquid slag waste heat recycling system and method based on a cascade transcritical CO2 power cycle of the application is implemented through the following technical solutions:

[0007] The first object of the application is to provide a boiler liquid slag waste heat recycling system based on a cascade transcritical CO2 power cycle, which comprises a molten slag buffer unit, a centrifugal granulation unit, a waste heat recycling unit, and a composite transcritical CO2 power cycle power generation assembly.

[0008] The molten slag buffer unit is used to receive high-temperature liquid molten slag and temporarily store the high-temperature liquid molten slag.

[0009] The input end of the centrifugal granulation unit is connected to the output end of the molten slag buffer unit to receive the high-temperature liquid molten slag from the molten slag buffer unit and granulate the high-temperature liquid molten slag to process it into solid granular slag.

[0010] The waste heat recycling unit comprises a waste heat conveying flow line, which uses air as the working medium and recovers the molten slag waste heat through heat exchange with the centrifugal granulation unit; and the output end of the waste heat conveying flow line is connected to the composite transcritical CO2 power cycle power generation assembly to convey the recovered molten slag waste heat to the waste heat conveying flow line for utilization in the composite transcritical CO2 power cycle power generation assembly.

[0011] In order to ensure that the slag waste heat during the granulation process of the centrifugal granulation unit can be recycled through the waste heat recovery unit, in a preferred embodiment of the present application, the centrifugal granulation unit comprises a granulation bin, a moving bed and an air distribution device connected in sequence. The inner wall of the granulation bin is provided with a cooling interlayer, and the input end of the granulation bin is communicated with the output end of the slag buffer unit to receive the high-temperature liquid slag output by the slag buffer unit and cool and granulate it into solid particle slag. The moving bed is arranged at the output end of the granulation bin for further cooling and granulation of the obtained solid particle slag to obtain the final solid slag particles. The air inlet of the air distribution device is communicated with the air output end of the waste heat recovery unit, and the air outlet of the air distribution device is communicated with the air inlet of the moving bed, so that air is sequentially sent into the moving bed and the granulation bin through the air distribution device to form a waste heat conveying flow line, so as to realize the recycling of the slag waste heat.

[0012] In order to ensure that the slag waste heat during the granulation process of the centrifugal granulation unit can be recycled through the waste heat recovery unit, in a preferred embodiment of the present application, the centrifugal granulation unit comprises a granulation bin, a moving bed and an air distribution device connected in sequence. The inner wall of the granulation bin is provided with a cooling interlayer, and the input end of the granulation bin is communicated with the output end of the slag buffer unit to receive the high-temperature liquid slag output by the slag buffer unit and cool and granulate it into solid particle slag. The moving bed is arranged at the output end of the granulation bin for further cooling and granulation of the obtained solid particle slag to obtain the final solid slag particles. The air inlet of the air distribution device is communicated with the air output end of the waste heat recovery unit, and the air outlet of the air distribution device is communicated with the air inlet of the moving bed, so that air is sequentially sent into the moving bed and the granulation bin through the air distribution device to form a waste heat conveying flow line, so as to realize the recycling of the slag waste heat.

[0013] In order to achieve the above technical effects, in a preferred embodiment of the present application, the waste heat conveying flow line comprises waste heat conveying branch A, waste heat conveying branch B and waste heat conveying branch C, and the output ends of the waste heat conveying branch A, waste heat conveying branch B and waste heat conveying branch C are communicated. The waste heat conveying branch A uses air as the working medium, is conveyed to the moving bed through the air distribution device, exchanges heat with the slag particles in the moving bed, and then a part of the air is discharged from the air outlet of the moving bed to form high-temperature air A, so as to fully realize the recovery of the waste heat of the slag in the moving bed and improve the cooling and granulation efficiency of the slag. Another part of the air that has exchanged heat with the slag particles in the moving bed is slowly introduced into the granulation bin along the axial direction, exchanges heat with the high-temperature slag and the preliminarily cooled solid slag in the granulation bin, and then is discharged from the top of the granulation bin to form the waste heat conveying branch B, and the discharged air forms high-temperature air B, so as to fully realize the recovery of the waste heat of the slag in the granulation bin and the waste heat of the slag in the conveying process of the granulation bin and the moving bed, and further improve the cooling and granulation efficiency of the slag. The waste heat conveying branch C uses air as the working medium, exchanges heat with the cooling layer to form high-temperature air C, so as to realize the recovery of the waste heat of the slag outside the granulation bin and further improve the cooling and granulation efficiency of the slag. The high-temperature air A, high-temperature air B and high-temperature air C are combined and then introduced into a supercritical heater and a CO2 heat exchanger, so as to realize the further utilization of the recovered waste heat of the slag.

[0014] In order to further improve the waste heat utilization efficiency, the waste heat recovery unit further comprises an air bypass, so as to re-convey part of the combined high-temperature air to the moving bed through the air distribution device to recover the waste heat of the slag and improve the waste heat utilization efficiency.

[0015] In a preferred embodiment of the present application, the slag buffer unit is composed of a slag ladle and a downcomer, the input end of the downcomer is connected with the output end of the slag ladle, and the output end of the downcomer is connected with the input end of the centrifugal granulation module, so as to convey the high-temperature liquid slag temporarily stored in the slag ladle to the centrifugal granulation unit through the downcomer.

[0016] In a preferred embodiment of the present application, the composite transcritical CO2 power cycle power generation assembly comprises a supercritical CO2 conveying flow line, a working medium pump, a generator A and a generator B, the input end of the supercritical CO2 conveying flow line is connected with the output end of the working medium pump, the CO2 in the saturated liquid state is adiabatically compressed to the supercritical state by the working medium pump, forms CO2 supercritical fluid, and then enters the supercritical CO2 conveying flow line; and comprises supercritical CO2 conveying flow line A and supercritical CO2 conveying flow line B.

[0017] The supercritical CO2 delivery flow line A comprises a supercritical heater, a high-temperature turbine and a regenerator connected in sequence, a part of the supercritical CO2 fluid enters the supercritical heater to absorb heat from the waste heat provided by the waste heat delivery flow line, and then enters the high-temperature turbine in a supercritical state to perform adiabatic expansion and drive the generator A to do work, and the exhaust steam of the high-temperature turbine enters the regenerator in a superheated state;

[0018] The supercritical CO2 delivery flow line B comprises a regenerator, a low-temperature turbine and a cooler connected in sequence, another part of the supercritical CO2 fluid enters the regenerator to absorb heat from the exhaust steam output by the high-temperature turbine, and forms a medium-temperature supercritical CO2 fluid; the medium-temperature supercritical CO2 fluid enters the low-temperature turbine to perform adiabatic expansion and drive the generator B to do work; and the exhaust steam of the low-temperature turbine enters the cooler to be cooled.

[0019] In a preferred embodiment of the present application, a condenser is further included, the input end of the condenser is connected with the output end of the cooler and the output end of the regenerator respectively, and the cooler and the condenser both have a condensing backwater line, so that the exhaust steam of the high-temperature turbine output by the regenerator after absorbing heat and the exhaust steam of the low-temperature turbine output by the cooler after being cooled both enter the condenser to exchange heat with the condensing backwater line and are cooled to a saturated liquid state, so that the exhaust steam returns to the working medium pump in the form of saturated liquid CO2 to form a closed cycle.

[0020] In a preferred embodiment of the present application, the condensing backwater in the condensing backwater line comes from the condensing water of the steam turbine, is heated after heat exchange in the cooler and the condenser, and then enters the economizer as boiler feed water.

[0021] In order to avoid the fine ash entering the supercritical heater and affecting the working efficiency of the composite transcritical CO2 power cycle generating assembly, in a preferred embodiment of the present application, the outlet of the waste heat recovery unit is further provided with a gas-solid separation device, which is used to remove fine ash to prevent the fine ash from entering the supercritical heater.

[0022] In a preferred embodiment of the present application, the centrifugal granulation unit is arranged below the molten slag buffer unit, and a flow control unit is further arranged between the centrifugal granulation unit and the molten slag buffer unit, the flow control unit is connected with the molten slag buffer unit and the centrifugal granulation unit respectively to control the flow rate and speed of the high-temperature liquid molten slag output from the molten slag buffer unit to the centrifugal granulation unit.

[0023] In a preferred embodiment of the present application, the boiler liquid slag waste heat recovery system based on the superposed transcritical CO2 power cycle further comprises an air preheater connected with the waste heat conveying flow line, receiving the air working medium after absorbing heat in the supercritical heater, and participating in the combustion of the pulverized coal.

[0024] The present application also provides a boiler liquid slag waste heat recovery method based on a superposed transcritical CO2 power cycle, which is implemented by using the above-mentioned boiler liquid slag waste heat recovery system based on the superposed transcritical CO2 power cycle and comprises the following steps:

[0025] Step 1: delivering the high-temperature liquid molten slag to the molten slag buffering unit for temporary storage.

[0026] It should be noted that the present application considers that the temperature of the high-temperature liquid molten slag that needs to be temporarily stored is about 1400℃, so the melting point of the material of the molten slag buffering unit needs to be higher than that of the high-temperature liquid molten slag. In a preferred embodiment of the present application, the molten slag buffering unit is composed of a slag ladle and a downcomer, the input end of the downcomer is connected with the output end of the slag ladle, and the output end of the downcomer is connected with the input end of the centrifugal granulation module, so as to deliver the high-temperature liquid molten slag temporarily stored in the slag ladle to the centrifugal granulation unit through the downcomer. In order to ensure the safe storage of the liquid molten slag, refractory ceramics or heat-resistant alloys can be used as the manufacturing materials of the slag ladle and the downcomer, so as to ensure that they still have stable chemical stability and wear resistance at a high temperature of 1400℃.

[0027] Step 2: delivering the high-temperature liquid molten slag in the molten slag buffering unit to the centrifugal granulation unit for granulation treatment, so as to obtain molten slag particles and molten slag waste heat.

[0028] In order to improve the centrifugal granulation effect and make the high-temperature liquid molten slag in the molten slag buffering unit smoothly enter the centrifugal granulation unit, in a preferred embodiment of the present application, the centrifugal granulation unit is arranged below the molten slag buffering unit, so as to make the high-temperature liquid molten slag in the molten slag buffering unit smoothly fall into the centrifugal granulation unit.

[0029] It should be noted that the present application is designed to ensure the safe operation of the unit, so the flow rate and speed of the high-temperature liquid molten slag when delivered to the centrifugal granulation unit are controlled, and when the liquid slag boiler needs to be adjusted for peak shaving or a fault occurs, the flow rate of the liquid molten slag will change. The molten slag buffering unit can ensure that the waste heat power generation unit still has stable waste heat supply within a certain period of time when the boiler operating condition changes, thereby providing a buffer space for the shutdown of the waste heat power generation unit. In addition to the same buffering effect as the molten slag buffering unit, the flow control unit can also indirectly control the high-temperature air temperature of the supercritical CO2 heat exchange, so as to determine the output power of the waste heat power generation unit.

[0030] And in a preferred embodiment of the present application, in order to facilitate the control of the flow and speed of the high-temperature liquid slag when it is transported to the centrifugal granulation unit, the present application sets a flow control unit between the centrifugal granulation unit and the slag buffer unit, so that the flow control unit is connected with the slag buffer unit and the centrifugal granulation unit respectively, so as to control the flow and speed of the high-temperature liquid slag output from the slag buffer unit to the centrifugal granulation unit.

[0031] Step 3: After the waste heat recovery unit absorbs the slag waste heat with air as the working medium, the waste heat delivery flow line provides a heat source for the supercritical CO2 power cycle power generation assembly.

[0032] It should be noted that in order to improve the recycling effect of slag waste heat on the basis of ensuring the processing cost, the present application preferably uses air as the working medium for recycling waste heat, absorbs the slag waste heat in the centrifugal granulation process, and releases the absorbed waste heat in the supercritical heater to provide a heat source for the supercritical heater.

[0033] And the present application considers that the air releasing heat still has a relatively high temperature, in order to further utilize the heat in the air after releasing heat, in a preferred embodiment of the present application, an air preheater is also provided, which is connected with the waste heat delivery flow line, receives the air working medium after absorbing heat in the supercritical heater, and participates in the combustion of the pulverized coal.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] The present application fully utilizes the advantage of the bottom cycle in improving the thermodynamic characteristics of the cycle by additionally increasing the output power of the bottom cycle under the premise of maintaining the top heat absorption process unchanged, so as to achieve the purpose of utilizing the waste heat of the liquid slag discharge furnace of the power plant. The bottom cycle of the present application can be understood as a supercritical CO2 power cycle with heat recovery measures, which has additional working medium for low-temperature turbine power generation compared with a single cycle.

[0036] The present application fully recycles and utilizes the high-temperature sensible heat of the turbine exhaust steam of the top cycle by setting a bottom cycle in the superposed transcritical CO2 power cycle generator set, additionally outputs net power, and reduces the average heat release temperature of the cycle and improves the cycle thermal efficiency.

[0037] Compared with the cycle with heat recovery (including simple heat recovery, re-compression cycle, etc.), the top cycle heat absorption process of the superposed cycle maintains good heat exchange matching characteristics and high waste heat utilization.

[0038] The present application uses air as the working medium of waste heat recovery, absorbs the waste heat of molten slag in the centrifugal granulation process, releases the absorbed waste heat in the supercritical heater to provide heat source for the supercritical heater, and the air with high temperature after releasing heat enters the air preheater to participate in the combustion of pulverized coal, which meets the energy saving requirement.

[0039] The boiler feed water is heated in the condenser and the cooler, and then enters the economizer, thereby improving the energy utilization efficiency of the boiler.

[0040] The present application uses the centrifugal granulation technology to process the liquid slag of the boiler, and has the advantages of low energy consumption, small slag particle size, high quality, fast cooling rate and high waste heat recovery rate.

[0041] The present application uses the centrifugal granulation technology to process the liquid slag of the boiler, and has the advantages of low energy consumption, small slag particle size, high quality, fast cooling rate and high waste heat recovery rate.

[0042] The present application fully utilizes the high-temperature air heated by the centrifugal granulation technology, fully utilizes the high waste heat recovery efficiency of the centrifugal granulation, and obtains high-temperature air to avoid the supercritical CO2 approaching the near-critical region during heat exchange. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The present application is based on the structure of the boiler liquid slag waste heat recovery and utilization system of the present application.

[0044] Figure 2 The present application is based on the structure of the boiler liquid slag waste heat recovery and utilization system of the present application. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be described clearly and completely.

[0046] In order to further recover the medium-high temperature flue gas waste heat, the prior art proposes that the heat absorption process of supercritical CO2 can be matched with the large temperature drop heat release process of flue gas to realize the recovery of medium-high temperature flue gas waste heat. However, when the supercritical CO2 cycle technology is directly applied to the recovery of medium-high temperature flue gas waste heat, the following problems exist: the working medium only passes through expansion work once in a single-stage transcritical cycle, and the exhaust steam still has a relatively high temperature, and directly treating it as waste will cause great energy waste. Although the regenerative, recompression and other cycle forms can reuse the sensible heat of the exhaust steam by adding an additional turbine, the increase of the inlet temperature of the working medium in the heat absorption process and the like will reduce the waste heat utilization efficiency, and therefore the output power of the unit is not obviously improved, but the construction cost of the unit is increased.

[0047] Embodiment 1

[0048] Please refer to Figure 1 The embodiment provides a boiler liquid slag waste heat recovery and utilization system based on a complex transcritical CO2 power cycle, which comprises a molten slag buffering unit 1, a centrifugal granulation unit 2, a waste heat recovery unit and a complex transcritical CO2 power cycle power generation assembly 3.

[0049] The molten slag buffering unit 1 is used for receiving high-temperature liquid molten slag and temporarily storing the high-temperature liquid molten slag.

[0050] The centrifugal granulation unit 2 is connected with the molten slag buffering unit, and the high-temperature liquid molten slag of the molten slag buffering unit 1 enters the centrifugal granulation unit 2 for granulation treatment, so that the high-temperature liquid molten slag is treated into solid granular slag.

[0051] The waste heat recovery unit comprises a waste heat conveying flow line, and the waste heat conveying flow line takes air as a working medium and realizes the recovery of molten slag waste heat through heat exchange with the centrifugal granulation unit 2; and the waste heat recovery unit comprises a waste heat conveying flow line, and the waste heat conveying flow line provides waste heat for the complex transcritical CO2 power cycle power generation assembly 3.

[0052] In order to ensure that the waste heat of the molten slag in the granulation process of the centrifugal granulation unit 2 can be recovered through the waste heat recovery unit, in a preferred embodiment of the present application, please refer to Figure 2The centrifugal granulation unit 2 comprises a granulation bin 21, a moving bed 22 and an air distribution device 23 connected in sequence. The inner wall of the granulation bin 21 is provided with a cooling interlayer 24. The input end of the granulation bin 21 is communicated with the output end of the molten slag buffering unit 1 to receive the high-temperature liquid molten slag output by the molten slag buffering unit 1 and cool and granulate the high-temperature liquid molten slag into solid granular slag. The moving bed 22 is arranged at the output end of the granulation bin 21 to further cool and granulate the obtained solid granular slag to obtain the final solid molten slag particles. The air inlet of the air distribution device 23 is communicated with the air output end of the waste heat recovery unit, and the air outlet of the air distribution device 23 is communicated with the air inlet of the moving bed 22 to sequentially deliver air into the moving bed 22 and the granulation bin 21 through the air distribution device 23 to form a waste heat delivery flow line to realize the recovery of the molten slag waste heat.

[0053] In order to ensure that the centrifugal granulation unit 2 can realize the processing of the high-temperature liquid molten slag into solid granular slag, improve the full recovery of the molten slag waste heat of the centrifugal granulation unit 2 in the granulation process, and facilitate the efficient use of the recovered molten slag preheating, in a preferred embodiment of the present application, the delivery direction of the working air in the waste heat delivery flow line is opposite to the direction of the falling of the solid granular slag in the centrifugal granulation unit 2 to form a convection, and then the air and the molten slag waste heat are fully heat exchanged, the air is heated by the molten slag waste heat, and the heated air is collected, so that the full recovery and utilization of the molten slag waste heat are realized.

[0054] In order to realize the above technical effects, in a preferred embodiment of the present application, please refer to Figure 2The waste heat conveying flow line comprises waste heat conveying branch A, waste heat conveying branch B and waste heat conveying branch C, and the output ends of the waste heat conveying branch A, waste heat conveying branch B and waste heat conveying branch C are communicated. The waste heat conveying branch A takes air as the working medium, is conveyed to the moving bed 22 through the air distribution device 23, exchanges heat with slag particles in the moving bed 22, and then a part of the air is discharged from the air output end of the moving bed 22 to form high-temperature air A, so that the slag waste heat in the moving bed 22 is recovered and the slag cooling and granulation efficiency is improved. Another part of the air that exchanges heat with slag particles in the moving bed 22 through the air distribution device 23 slowly enters the granulation bin 21 along the axial direction, exchanges heat with high-temperature slag and preliminarily cooled solid slag in the granulation bin 21, is discharged from the top of the granulation bin 21 to form the waste heat conveying branch B, and the discharged air forms high-temperature air B, so that the slag waste heat in the granulation bin 21 and the slag waste heat in the conveying process of the granulation bin 21 and the moving bed 22 is recovered, and the slag cooling and granulation efficiency is further improved. The waste heat conveying branch C takes air as the working medium, exchanges heat with the cooling interlayer 24 to form high-temperature air C, so that the slag waste heat outside the granulation bin 21 is recovered, and the slag cooling and granulation efficiency is further improved. The high-temperature air A, high-temperature air B and high-temperature air C are combined and then enter the composite transcritical CO2 power cycle power generation assembly 3 to exchange heat with CO2, so that the recovered slag waste heat is further utilized.

[0055] In order to further improve the waste heat utilization efficiency, the waste heat recovery unit further comprises an air bypass 4, so that part of the combined high-temperature air is conveyed to the moving bed 22 through the air distribution device 23 to recover the slag waste heat and improve the waste heat utilization efficiency.

[0056] In a preferred embodiment of the present application, the slag buffer unit 1 is composed of a slag ladle and a descending pipe, the input end of the descending pipe is connected with the output end of the slag ladle, and the output end of the descending pipe is connected with the input end of the centrifugal granulation module, so that the high-temperature liquid slag temporarily stored in the slag ladle is conveyed to the centrifugal granulation unit 2 through the descending pipe.

[0057] In a preferred embodiment of the present application, the composite transcritical CO2 power cycle power generation assembly 3 comprises a supercritical CO2 conveying flow line, a working medium pump 31, a generator A 32 and a generator B 33, the input end of the supercritical CO2 conveying flow line is connected with the output end of the working medium pump 31, the CO2 in the saturated liquid state is adiabatically compressed to the supercritical state by the working medium pump 31, forms CO2 supercritical fluid and then enters the supercritical CO2 conveying flow line, and comprises supercritical CO2 conveying flow line A and supercritical CO2 conveying flow line B.

[0058] The supercritical CO2 delivery flow line A comprises a supercritical heater 34, a high-temperature turbine 35 and a regenerator 36 connected in sequence. A part of the supercritical CO2 fluid enters the supercritical heater 34 and absorbs heat from the waste heat provided by the waste heat delivery flow line, and then enters the high-temperature turbine 35 in a supercritical state to perform adiabatic expansion and drive the generator A 32 to work. The exhaust steam of the high-temperature turbine 35 enters the regenerator 36 in a superheated state.

[0059] The supercritical CO2 delivery flow line B comprises a regenerator 36, a low-temperature turbine 37 and a cooler 38 connected in sequence. Another part of the supercritical CO2 fluid enters the regenerator 36 and absorbs heat from the exhaust steam of the high-temperature turbine 35 to form a medium-temperature supercritical CO2 fluid. The medium-temperature supercritical CO2 fluid enters the low-temperature turbine 37 to perform adiabatic expansion and drive the generator B 33 to work. The exhaust steam of the low-temperature turbine 37 enters the cooler 38 to be cooled.

[0060] In a preferred embodiment of the present application, a condenser 39 is further included. The input end of the condenser 39 is connected with the output end of the cooler 38 and the output end of the regenerator 36 respectively. The cooler 38 and the condenser 39 both have a condensing backwater line, so that the exhaust steam of the high-temperature turbine 35 output by the regenerator 36 and the exhaust steam of the low-temperature turbine 37 output by the cooler 38 are both cooled to a saturated liquid state by heat exchange with the condensing backwater line in the condenser 39, so that the exhaust steam returns to the working fluid pump 31 in a saturated liquid state of CO2 to form a closed cycle.

[0061] In a preferred embodiment of the present application, the condensing backwater in the condensing backwater line comes from the condensing water of the steam turbine, is heated by heat exchange in the cooler 38 and the condenser 39, and then enters the economizer as boiler feed water.

[0062] In order to avoid the fine ash entering the supercritical heater 34 and affecting the working efficiency of the composite trans-critical CO2 power cycle generating assembly 3, in a preferred embodiment of the present application, the outlet of the waste heat recovery unit is further provided with a gas-solid separation device 5 for removing fine ash to prevent the fine ash from entering the supercritical heater 34.

[0063] In a preferred embodiment of the present application, the centrifugal granulation unit 2 is arranged below the molten slag buffering unit 1, and a flow control unit 6 is further arranged between the centrifugal granulation unit 2 and the molten slag buffering unit 1. The flow control unit 6 is connected with the molten slag buffering unit 1 and the centrifugal granulation unit 2 respectively to control the flow rate and speed of the high-temperature liquid molten slag output from the molten slag buffering unit 1 to the centrifugal granulation unit 2.

[0064] In a preferred embodiment of the present application, the boiler liquid slag waste heat recovery system based on the cascade transcritical CO2 power cycle further comprises an air preheater 7, which is connected with the waste heat delivery flow line and receives the air working substance after absorbing heat in the supercritical heater 34 and participates in the combustion of the pulverized coal.

[0065] Embodiment 2

[0066] The embodiment provides a boiler liquid slag waste heat recovery method based on a cascade transcritical CO2 power cycle, which is implemented by using the above boiler liquid slag waste heat recovery system based on the cascade transcritical CO2 power cycle and comprises the following steps.

[0067] Step 1, the high-temperature liquid molten slag is delivered to the molten slag buffer unit 1 for temporary storage.

[0068] Step 2, the flow control unit 6 arranged between the centrifugal granulation unit 2 and the molten slag buffer unit 1 is controlled to control the flow and speed of the high-temperature liquid molten slag output from the molten slag buffer unit 1 to the centrifugal granulation unit 2, so that the high-temperature liquid molten slag in the molten slag buffer unit 1 enters the centrifugal granulation unit 2 below the molten slag buffer unit 1 under the action of gravity, and the high-temperature liquid molten slag is processed into solid granular slag by the centrifugal granulation unit 2.

[0069] Step 3, after the waste heat recovery unit absorbs the molten slag waste heat by taking air as the working substance, the waste heat delivery flow line provides a heat source for the composite transcritical CO2 power cycle power generation assembly 3.

[0070] Obviously, the above-mentioned embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

Claims

1. A boiler slag waste heat recovery and utilization system based on a cascade transcritical CO2 power cycle, characterized in that, It includes a slag buffer unit (1), a centrifugal granulation unit (2), a waste heat recovery unit, and a composite transcritical CO2 power cycle power generation component (3); among which, The slag buffer unit (1) is used to receive high-temperature liquid slag and temporarily store the high-temperature liquid slag; The input end of the centrifugal granulation unit (2) is connected to the output end of the slag buffer unit (1) to receive the high-temperature liquid slag from the slag buffer unit (1) and granulate it to process the high-temperature liquid slag into solid granular slag. The waste heat recovery unit includes a waste heat conveying line, which uses air as the working fluid and recovers the waste heat of molten slag by exchanging heat with the centrifugal granulation unit (2); and the output end of the waste heat conveying line is connected to the composite transcritical CO2 power cycle power generation component (3) to transport the recovered waste heat of molten slag to the waste heat conveying line for utilization in the composite transcritical CO2 power cycle power generation component (3); The centrifugal granulation unit (2) includes a granulation chamber (21), a moving bed (22), and an air distribution device (23) connected in sequence. The inner wall of the granulation chamber (21) is provided with a cooling jacket (24), and the input end of the granulation chamber (21) is connected to the output end of the slag buffer unit (1) to receive the high-temperature liquid slag output by the slag buffer unit (1) and initially cool and granulate it into solid granules. The waste heat conveying flow line includes waste heat conveying branch line A, waste heat conveying branch line B and waste heat conveying branch line C, and the output ends of waste heat conveying branch line A, waste heat conveying branch line B and waste heat conveying branch line C are connected. The waste heat conveying branch line A uses air as the working medium and is conveyed to the moving bed (22) through the air distribution device (23). After exchanging heat with the molten slag particles in the moving bed (22), it is discharged from the air output end of the moving bed (22) to form high temperature air A. The waste heat conveying branch line B uses air as the working medium. After being conveyed to the moving bed (22) by the air distribution device (23) and exchanging heat with the molten slag particles, it slowly enters the granulation chamber (21) along the axial direction. After exchanging heat with the high-temperature molten slag and the initially cooled solid granules in the granulation chamber (21), it is discharged from the top of the granulation chamber (21) to form high-temperature air B. The waste heat conveying branch line C uses air as the working medium to exchange heat with the cooling jacket (24) to form high-temperature air C; The high-temperature air A, high-temperature air B and high-temperature air C are combined and then enter the composite transcritical CO2 power cycle power generation component (3) for utilization.

2. The boiler slag waste heat recovery and utilization system based on cascade transcritical CO2 power cycle as described in claim 1, characterized in that, The moving bed (22) is located at the output end of the granulation chamber (21) and is used to further cool and granulate the obtained solid granules to form molten slag particles; The air inlet of the air distribution device (23) is connected to the air output end of the waste heat recovery unit, and the air outlet of the air distribution device (23) is connected to the air inlet of the moving bed (22) so that air is sequentially transported to the moving bed (22) and the granulation chamber (21) through the air distribution device (23) to form a waste heat transport flow line to realize the recovery of slag waste heat.

3. The boiler slag waste heat recovery and utilization system based on cascade transcritical CO2 power cycle as described in claim 1, characterized in that, The waste heat recovery unit also includes an air bypass (4) to transport part of the combined high-temperature air back to the moving bed (22) via the air distribution device (23) to recover the waste heat of the molten slag.

4. The boiler slag waste heat recovery and utilization system based on cascade transcritical CO2 power cycle as described in claim 1, characterized in that, The composite transcritical CO2 power cycle power generation component (3) includes a supercritical CO2 transport line, a working fluid pump (31), a generator A (32), and a generator B (33). The input end of the supercritical CO2 transport line is connected to the output end of the working fluid pump (31). The saturated liquid CO2 is adiabatically compressed to a supercritical state by the working fluid pump (31) to form a supercritical CO2 fluid, which then enters the supercritical CO2 transport line. The component includes a supercritical CO2 transport line A and a supercritical CO2 transport line B. The supercritical CO2 transport line A includes a supercritical heater (34), a high-temperature turbine (35), and a regenerator (36) connected in sequence. A portion of the supercritical CO2 fluid enters the supercritical heater (34) and, after being heated by the waste heat provided by the waste heat transport line, enters the high-temperature turbine (35) in a supercritical state for adiabatic expansion and performs work to drive the generator A (32). The exhaust steam from the high-temperature turbine (35) enters the regenerator (36) in a superheated state. The supercritical CO2 transport line B includes a regenerator (36), a low-temperature turbine (37), and a cooler (38) connected in sequence. Another part of the supercritical CO2 fluid enters the regenerator (36) and absorbs heat from the exhaust steam output from the high-temperature turbine (35) in the regenerator (36) to form a medium-temperature supercritical CO2 fluid. The medium-temperature supercritical CO2 fluid enters the low-temperature turbine (37) for adiabatic expansion and performs work to drive the generator B (33). The exhaust steam from the low-temperature turbine (37) enters the cooler (38) for cooling.

5. The boiler slag waste heat recovery and utilization system based on cascade transcritical CO2 power cycle as described in claim 4, characterized in that, It also includes a condenser (39), the input end of which is connected to the output end of the cooler (38) and the output end of the regenerator (36), and both the cooler (38) and the condenser (39) have a condensate return water line so that the exhaust steam of the high-temperature turbine (35) after absorbing heat output from the regenerator (36) and the exhaust steam of the low-temperature turbine (37) after cooling output from the cooler (38) both enter the condenser (39) to exchange heat with the condensate return water line and cool to a saturated liquid state so that the exhaust steam returns to the working fluid pump (31) in a saturated liquid state of CO2, forming a closed loop.

6. The boiler slag waste heat recovery and utilization system based on cascade transcritical CO2 power cycle as described in claim 5, characterized in that, The condensate return water in the condensate return water line comes from the condensate water of the steam turbine.

7. The boiler slag waste heat recovery and utilization system based on cascade transcritical CO2 power cycle as described in claim 4, characterized in that, The outlet of the waste heat recovery unit is equipped with a gas-solid separation device (5) to prevent fine ash from entering the supercritical heater (34).

8. The boiler slag waste heat recovery and utilization system based on cascade transcritical CO2 power cycle as described in claim 1, characterized in that, The centrifugal granulation unit (2) is located below the slag buffer unit (1), and a flow control unit (6) is also provided between the centrifugal granulation unit (2) and the slag buffer unit (1). The flow control unit (6) is connected to the slag buffer unit (1) and the centrifugal granulation unit (2) respectively to control the flow rate and speed of the slag buffer unit (1) when it outputs high-temperature liquid slag to the centrifugal granulation unit (2).

9. A method for recovering and utilizing waste heat from boiler slag based on a cascaded transcritical CO2 power cycle, characterized in that, The system for recovering and utilizing waste heat from boiler slag based on a cascaded transcritical CO2 power cycle, as described in any one of claims 1-8, includes the following steps: The high-temperature liquid molten slag is transported to the slag buffer unit (1) for temporary storage; The high-temperature liquid slag in the slag buffer unit (1) is transported to the centrifugal granulation unit (2) for granulation treatment to obtain slag particles and slag waste heat; The waste heat recovery unit absorbs the waste heat of the molten slag using air as the working medium, and then provides a heat source for the composite transcritical CO2 power cycle power generation component (3) through the waste heat transport flow line.

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