Waste heat utilization system and method for liquid deslagging

Abstract

The invention relates to the technical field of liquid deslagging boilers, in particular to a liquid deslagging waste heat utilization system and method. According to the system, waste heat recovery is carried out through two parts, one part is that cold air conveyed by an air feeder exchanges heat with slag in a slag-air heat exchanger, and the cold air absorbing heat becomes high-temperature gas and then is fed into a coal economizer to be directly utilized; according to the method, the waste heat is recycled in two steps, the waste heat at different temperatures has different utilization values, the waste heat can be recycled, the waste heat can be recycled, the waste heat can be recycled, the waste heat can be recycled, the waste heat can be recycled, and the utilization rate of the waste heat can be improved. The waste heat utilization system adopts the energy gradient utilization principle and aims to comprehensively recover waste heat, heat in slag and flue gas is transferred to a working medium by designing an efficient system and method, the temperature of the working medium is increased, full and reasonable utilization of the waste heat is achieved, and the energy utilization efficiency of the whole system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid slagging boilers, and in particular to a system and method for utilizing waste heat of liquid slagging. Background Art

[0002] Liquid slag is extremely hot when discharged. Directly discharging the heat it contains would result in significant energy waste. Recovering the waste heat from the slag can reduce greenhouse gas emissions, such as carbon dioxide, generated by burning additional fuel. This helps lower the carbon footprint of the boiler system, complying with environmental protection requirements. Recovering the waste heat from the slag also reduces fuel usage, thereby lowering boiler operating costs and further improving economic efficiency.

[0003] The recovery of waste heat from liquid slag relies on a waste heat utilization system for liquid slag discharge. This waste heat recovery system typically sprays water onto the high-temperature liquid slag, quenching it with water. The large amount of steam generated during the quenching process is then fed into the boiler to recycle the waste heat. However, as the high-temperature liquid slag cools, its temperature drops rapidly, its viscosity increases dramatically, and its fluidity deteriorates, potentially even solidifying into lumps. This reduces the contact area between the liquid slag and water, lowering the heat transfer efficiency and, in turn, the utilization rate of the waste heat from the high-temperature liquid slag. Furthermore, the heat from the liquid slag is primarily transferred to the water through the cooling effect of the water, but this heat exchange method is inefficient. The short contact time and limited contact area between the liquid slag and water result in insufficient heat transfer and a reduced waste heat recovery rate. Therefore, the market lacks a waste heat utilization system for liquid slag discharge that significantly improves the recovery rate of slag waste heat, which is of great practical significance. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a system and method for utilizing waste heat from liquid slag discharge, aiming to solve the problems raised in the technical background and significantly improve the recovery rate of waste heat from slag.

[0005] By reducing the viscosity of the slag and improving its stable and reliable fluidity and thermal conductivity, the problem of slag treatment in liquid slag-discharging boilers can be effectively solved, the waste heat recovery efficiency can be greatly improved, environmental pollution can be reduced, the stability and reliability of system operation can be enhanced, and the progress of liquid slag-discharging boiler technology in the fields of energy utilization and environmental protection can be strongly promoted. It has extremely broad application prospects and significant economic and social benefits.

[0006] To solve the above technical problems, the present invention provides a waste heat utilization system for liquid slag discharge, comprising a collection device connected to a slag discharge boiler, and further comprising:

[0007] An additive supply unit, connected to the collecting device, for delivering the liquid slag removal additive into the collecting device;

[0008] The additive supply unit includes an additive storage bin, a metering device, and a delivery pipeline. The bottom of the additive storage bin is connected to the collection device via a delivery pipeline. The additive storage bin adopts a sealed structure made of carbon steel or stainless steel, which is moisture-proof and anti-caking. It can store a certain amount of additive.

[0009] The metering feeding device is installed on the pipeline between the additive storage bin and the additive feeding port. The additive feeding port is arranged at the connection between the furnace cold ash hopper outlet and the slag discharge port of the slag discharge boiler to ensure that the additive can be evenly mixed with the slag.

[0010] The metering feeding device uses a volumetric feeder, such as a screw feeder. This feeds the additive by controlling a fixed-volume cavity. The rotation of the screw blades transports the additive from the silo to the boiler. By adjusting the screw speed and pitch, the volume of the additive delivered can be measured and controlled, thus achieving precise metering.

[0011] The metering feeding device precisely controls the amount of additives added, adjusting the additive supply rate based on factors such as the amount of slag discharged from the liquid slag boiler and the properties of the slag, with a metering accuracy of ±1%. The delivery pipeline, constructed of high-temperature, wear-resistant alloy steel pipes or ceramic-lined steel pipes, transports the additives from the storage bin to the furnace or near the slag outlet of the liquid slag boiler, ensuring uniform mixing of the additives with the slag.

[0012] (1) Regulation based on slag discharge volume: When the slag discharge volume increases, it indicates that more slag is generated by combustion in the slag discharge boiler. In order to ensure that the slag can be discharged smoothly in liquid form, more additives are needed to lower the slag melting point and improve its fluidity. At this time, the control system will increase the additive supply rate based on the preset ratio between the additive supply amount and the slag. (2) Regulation based on slag properties: Slag properties mainly include melting point and viscosity. If the slag melting point is detected to be increased, it means that the current amount of additives used may be insufficient and cannot effectively lower the slag melting point. The control system will increase the additive supply rate. The slag melting point can be indirectly judged by detecting the fluidity of the slag at a specific temperature. For slag with higher viscosity, it is also necessary to increase the supply of additives to improve the fluidity of the slag and facilitate slag discharge.

[0013] The additive supply rate is a key control objective for metering feeders. Metering feeders operate based on additive supply rate instructions from the control system. For volumetric feeders, adjusting parameters such as screw speed and vibration frequency in vibrating feeders changes the amount of additive delivered per unit time, thereby achieving the desired supply rate.

[0014] The waste heat recovery unit includes a blower, a slag-air heat exchanger, an air preheater, an economizer, and a slag-water heat exchange pipe. The slag-air heat exchanger is located in the collection device. The blower is connected to the slag-air heat exchanger through a cold air supply pipe. The slag-air heat exchanger is connected to the economizer through a high-temperature gas conveying pipe so that high-temperature air is sent to the economizer to heat the slag discharge boiler feed water. The slag discharge boiler is connected to the air preheater through a flue gas conveying pipe so that high-temperature air is sent to the economizer to heat the slag discharge boiler feed water. A delivery pump is provided on the slag-water circulation heat exchange pipe. The slag-water circulation heat exchange pipe is partially located in the collection device and is also connected to the power generation circulation unit.

[0015] The slag discharged from the slag-discharging boiler 1 enters a collection device and first passes through a slag-air heat exchanger, where it is cooled to 700°C. The slag-water heat exchanger 10 is a shell-and-tube heat exchanger. The heat exchange tubes of this slag-water heat exchanger 10 can be copper or stainless steel tubes, with an inner diameter of 10 mm to 50 mm. Baffles are installed in the shell side of the slag-water heat exchanger 10 to enhance heat exchange. If the slag-water heat exchanger 10 is a plate heat exchanger, the heat exchange plates of the slag-water heat exchanger 10 are made of stainless steel or titanium plates, with a spacing between the plates between 5 mm and 20 mm. The corrugated shape of the heat exchange plates increases fluid disturbance and improves heat exchange efficiency.

[0016] The economizer 7 in the flue gas waste heat recovery unit adopts a fin-tube economizer with a fin height between 10mm and 30mm and a fin spacing between 5mm and 20mm, which improves the heat exchange efficiency between the flue gas and the feed water; the air preheater 6 can adopt a rotary air preheater or a tubular air preheater. The heat storage element of the rotary air preheater adopts corrugated plate or honeycomb ceramic, and the heat exchange tube of the tubular air preheater adopts carbon steel or stainless steel tube to improve the air preheating effect.

[0017] Multiple temperature sensors, multiple pressure sensors, and multiple flow sensors are respectively installed at the inlet and outlet of the slag-water heat exchange pipe, the inlet and outlet of the collection device, the inside of the slag discharge boiler, and the cold air supply pipe, the high-temperature gas delivery pipe, the flue gas delivery pipe, and the slag-water heat exchange pipe. Multiple solenoid valves or multiple electric regulating valves are installed on the cold air supply pipe, the high-temperature gas delivery pipe, the flue gas delivery pipe, and the slag-water heat exchange pipe;

[0018] The temperature sensor uses a thermocouple or a thermistor sensor with a measurement accuracy within ±0.5°C. The pressure sensor uses a piezoresistive sensor with a measurement accuracy within ±0.1%. The flow sensor uses an electromagnetic flowmeter or a turbine flowmeter with a measurement accuracy within ±0.5%. The data acquisition device uses a high-speed data acquisition card with a sampling frequency between 1 and 10kHz. The controller can be a programmable logic controller (PLC) or an industrial control computer (IPC).

[0019] The controller is connected to each temperature sensor, each pressure sensor, each flow sensor, a delivery pump, multiple solenoid valves or multiple electric control valves. The controller is used to control the speed of the delivery pump and the opening of each solenoid valve or each electric control valve according to the detection results of each temperature sensor, each pressure sensor and each flow sensor.

[0020] Preferably, the high-temperature gas delivery pipe is connected to the economizer and the air preheater through a purification device.

[0021] Preferably, the air preheater is connected to a flue gas-water heat exchanger.

[0022] Preferably, the liquid slag removal additive is a mixture of the following raw materials in percentage by mass: 40% to 50% flux, 20% to 30% dispersant and 20% to 30% heat transfer enhancer, wherein the flux is an alkali metal carbonate, the dispersant is a water-soluble functional polymer, and the heat transfer enhancer is a metal oxide.

[0023] Dispersants, heat transfer enhancers, and fluxes fundamentally improve the physical and chemical properties of slag through a synergistic mechanism of "homogenization, melting point reduction, and uniform heat transfer," effectively enhancing its fluidity. The flux lowers the melting point, the dispersant ensures uniform dispersion of components, and the heat transfer enhancer promotes uniform heat transfer. These three agents work together from different perspectives to comprehensively improve slag fluidity. The uniform dispersion effect of the dispersant maximizes the efficiency of the flux and heat transfer enhancer. The flux lowers the melting point, allowing the heat transfer enhancer to more easily maintain the liquid temperature of the slag, while the dispersant ensures the stability of the entire system, preventing fluidity loss caused by particle agglomeration. The dispersant reduces slag viscosity, the flux reduces the solids content, and the heat transfer enhancer maintains temperature uniformity. Together, these three agents significantly reduce the apparent viscosity of the slag, making it more fluid at high temperatures. This synergistic effect not only enhances the overall performance of the additives—increasing the thermal conductivity of the slag and enhancing its waste heat recovery potential—but also ensures the recovery and utilization of heat from liquid slag discharge.

[0024] Liquid deslagging additives are powdered solids at room temperature, making them easy to store and transport. With a melting point of 600°C to 800°C, they melt rapidly and mix thoroughly with the slag in the high temperatures of liquid deslagging boilers. After mixing with the slag, they can reduce its viscosity by 40% to 60%, significantly improving its fluidity and facilitating deslagging operations. Furthermore, they can increase the thermal conductivity of the slag by 30% to 50%, enhancing its waste heat recovery potential.

[0025] Preferably, the alkali metal carbonate is selected from sodium carbonate, potassium carbonate or a mixture of the two.

[0026] Alkali metal carbonates decompose at high temperatures to produce metal oxides and carbon dioxide gas, which react with acidic oxides in the slag (such as silica and alumina) to form low-melting-point compounds such as silicates and aluminates. For example, sodium oxide produced by the decomposition of sodium carbonate reacts with silica to form sodium silicate, which has a relatively low melting point. This lowers the overall melting point and viscosity of the slag, improving its fluidity and allowing it to flow more smoothly. This reduces slag accumulation and agglomeration at the furnace bottom, and increases heat recovery.

[0027] Preferably, the water-soluble functional polymer is selected from sodium polyacrylate, polyvinyl alcohol or a mixture of the two. Sodium polyacrylate, polyvinyl alcohol or a mixture of the two all have a long-chain structure, which can play a role of dispersion and stability in the slag, prevent the slag particles from agglomerating, and further improve the fluidity of the slag. Sodium polyacrylate can be adsorbed by its carboxyl functional group on the metal ions on the surface of the slag particles in the slag, so that the slag particles maintain a certain distance from each other to avoid agglomeration. For example, the carboxyl group of sodium polyacrylate can be adsorbed or ion exchanged with the metal ions on the surface of the slag particles, so that the surface of the slag particles is charged with the same charge, repelling each other, thereby preventing the slag particles from agglomerating. At the same time, the network structure formed by the long-chain molecules in the slag can separate the slag particles, further improve the dispersibility and fluidity of the slag, ensure that the additive can be evenly mixed with the slag, and improve the heat recovery rate.

[0028] Preferably, the metal oxide is selected from any one of aluminum oxide, titanium dioxide, and copper oxide, or a mixture of any two or all three. Aluminum oxide has high thermal conductivity and good thermal stability, and can be evenly dispersed in the slag, increasing the slag's thermal conductivity and improving the heat transfer efficiency between the slag and the heat exchange medium. Aluminum oxide has a thermal conductivity of approximately 30 W / (m·K), effectively enhancing the slag's heat transfer capacity.

[0029] Preferably, the particle size of the heat transfer enhancer is 50nm to 150nm. This particle size range is designed to achieve the best balance between heat transfer efficiency, dispersion stability, liquid-slag compatibility, and process feasibility. Smaller particle sizes can significantly increase the specific surface area of the heat transfer enhancer, making its contact area with the liquid slag larger, thereby improving heat transfer efficiency. However, if the particle size is too small, the van der Waals force between the particles is enhanced, making it easy to agglomerate and destroying the dispersibility; if the particle size is too large, it is easy to settle under the action of gravity, affecting the long-term stability of the additive. The particle size range of 50nm to 150nm is easier to achieve under existing granular material preparation technology, and the cost is relatively controllable.

[0030] The present invention also provides a waste heat utilization method of a waste heat utilization system for liquid slag discharge, comprising the following steps:

[0031] The additive supply unit feeds the additive into the collecting device to cause the additive to react physically and chemically with the slag, thereby increasing the fluidity of the slag in the collecting device;

[0032] When recovering waste heat from high-temperature flue gas, the blower sends cold air into the slag-air heat exchanger installed in the collection device. The cold air exchanges heat with the slag to generate high-temperature air. The high-temperature air is sent to the economizer through the high-temperature gas conveying pipe to heat the feed water of the slagging boiler. The high-temperature flue gas generated by the slagging boiler is sent to the air preheater, where it exchanges heat with the cold air. The generated high-temperature gas is sent to the slagging boiler as boiler combustion gas.

[0033] When the slag waste heat is recovered, the slag exchanges heat with the heat exchange medium in the slag-water heat exchange tube, so that the temperature of the heat exchange medium in the slag-water heat exchange tube increases, thereby providing heat for the power generation cycle unit;

[0034] Using multiple temperature sensors, multiple pressure sensors, and multiple flow sensors, respectively measure the temperature values, flow rate values, and pressure values at the inlet and outlet of the slag-water heat exchange pipe, the inlet and outlet of the collecting device, the inside of the slag discharge boiler, and the cold air supply pipe, the high-temperature gas delivery pipe, the flue gas delivery pipe, and the slag-water heat exchange pipe;

[0035] The controller receives the temperature, pressure and flow measurement values through the signal inlet, compares the temperature, pressure and flow measurement values with the corresponding temperature, pressure and flow setting values, and calculates the difference. Based on the calculated temperature, pressure and flow differences, the controller obtains control signals for controlling the operation of the delivery pump, multiple solenoid valves or multiple electric control valves.

[0036] Preferably, the differences of the temperatures, pressures and flows are calculated using a proportional-differential-integral method, which comprises the following steps:

[0037] The temperature difference, pressure difference and flow difference are calculated based on the measured values of temperature, pressure and flow obtained at the same time and the set values of temperature, pressure and flow;

[0038] The currently obtained temperature difference, pressure difference or flow difference is compared with the positive and negative values using the proportional operation method to obtain a temperature control signal, a pressure control signal or a flow control signal;

[0039] The currently obtained temperature difference, pressure difference or flow difference is differentiated using a differential operation method to obtain a temperature change rate signal, a pressure change rate signal or a flow change rate signal;

[0040] The currently obtained temperature difference, pressure difference or flow difference is respectively integrated using an integration operation method to obtain a temperature cumulative deviation signal, a pressure cumulative deviation signal or a flow cumulative deviation signal;

[0041] The signals obtained according to the above-mentioned proportional operation method, differential operation method and integral operation method are used to control the speed of the delivery pump, the opening degree of multiple solenoid valves or the opening degree of multiple electric control valves.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention integrates the waste heat recovery unit and the controller. Through collaborative work and precise control, it can more fully tap the waste heat resources of liquid slag discharge, achieve efficient energy utilization, reduce corporate energy costs, and reduce dependence on external energy. The waste heat utilization system of the provided liquid slag discharge additive improves the slag waste heat recovery rate. When the slag waste heat is recovered and utilized, the addition of the liquid slag discharge additive to the collection device through the additive supply unit significantly improves the fluidity of the slag, reduces the probability of the high-temperature liquid slag solidifying into agglomerates due to the increase in viscosity caused by the rapid drop in temperature during the cooling process, indirectly increases the contact area between the liquid slag and the heat exchange medium, and improves the heat exchange efficiency. In addition, the present invention recovers waste heat through two parts. One part is to make the cold air transported by the blower exchange heat with the slag in the slag-air heat exchanger. The cold air that absorbs heat becomes high-temperature gas and is sent to the economizer for direct use. The other part is that the slag after air heat exchange is again heat-exchanged with the water in the slag-water circulation heat exchange tube. The water after heat exchange is directly heated to water vapor for power generation in the power generation cycle unit, reducing the heat loss during transmission or conversion. The present invention divides waste heat recovery into two steps because it takes into account that waste heat at different temperatures has different utilization values. The waste heat utilization system adopts the principle of energy cascade utilization, aiming to fully recover waste heat. By designing efficient systems and methods, the heat in the slag and flue gas is transferred to the working fluid, the temperature of the working fluid is increased, the full and reasonable utilization of waste heat is achieved, and the energy utilization efficiency of the entire system is improved.

[0044] Compared with ordinary additives, the liquid slag discharge additive provided by the present invention further greatly improves the fluidity of liquid slag discharge slag through a unique combination of flux, dispersant and stabilizer ingredients, effectively solves the problem of poor slag discharge, reduces equipment maintenance costs and downtime, and improves the operating stability and reliability of liquid slag discharge boilers. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a diagram of the waste heat utilization system based on liquid slag removal additives of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 1. Slag discharge boiler; 2. Collection device; 3. Blower; 4. Slag-water heat exchange tube; 5. Additive supply unit; 6. Air preheater; 7. Economizer; 8. Purification device; 9. Power generation circulation unit; 10. Slag-air heat exchanger.

[0047] Figure 2 This is a schematic diagram of the PID algorithm control of the present invention. DETAILED DESCRIPTION

[0048] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0049] The inventors discovered that the operation of a liquid slag-discharging boiler produces large quantities of high-temperature slag and flue gas, which contain abundant thermal energy. Considering the varying utility value of waste heat at different temperatures, the waste heat utilization system employs a cascade energy utilization principle to comprehensively recover waste heat. By designing efficient systems and methods, the heat from the slag and flue gas is transferred to the working fluid, raising its temperature and achieving full and rational utilization of waste heat, thereby improving the energy efficiency of the entire system.

[0050] In view of this, the present invention provides a waste heat utilization system for liquid slag discharge, comprising a collecting device 2 connected to a slag discharge boiler 1, and further comprising:

[0051] The additive supply unit 5 is connected to the collecting device 2 and is used to feed the liquid slag removal additive into the collecting device 2;

[0052] The waste heat recovery unit includes a flue gas waste heat recovery unit and a slag waste heat recovery unit. The flue gas waste heat recovery unit includes a blower 3, a slag-air heat exchanger 10, an air preheater 6 and an economizer 7. The slag waste heat recovery unit includes a slag-water heat exchange pipe 4, wherein:

[0053] The slag-air heat exchanger 10 is disposed within the collection device 2. The blower 3 is connected to the slag-air heat exchanger 10 via a cold air supply pipe, and is used to exchange heat between cold air and high-temperature slag to generate high-temperature air. The slag-air heat exchanger 10 is connected to the economizer 7 via a high-temperature gas delivery pipe, so that the high-temperature air is delivered to the economizer 7 to heat the feed water of the slag discharge boiler 1. The slag discharge boiler 1 is connected to the air preheater 6 via a flue gas delivery pipe, so that the flue gas delivered after heating the feed water of the slag discharge boiler 1 heats the air in the air preheater 6 to obtain boiler combustion gas.

[0054] A delivery pump is provided on the slag-water circulation heat exchange pipe 4. The slag-water circulation heat exchange pipe 4 extends into the collection device 2 to exchange heat with the high-temperature slag. The slag-water heat exchange pipe 4 is also connected to the power generation circulation unit 9.

[0055] Multiple temperature sensors, multiple pressure sensors, and multiple flow sensors are respectively installed at the inlet and outlet of the slag-water heat exchange pipe 4, the inlet and outlet of the collecting device 2, inside the slag discharge boiler 1, and on the cold air supply pipe, the high-temperature gas delivery pipe, the flue gas delivery pipe, and the slag-water heat exchange pipe 4;

[0056] A controller is connected to each temperature sensor, each pressure sensor, each flow sensor, a delivery pump, multiple solenoid valves or multiple electric control valves. The controller is used to control the speed of the delivery pump and the opening of the multiple solenoid valves or multiple electric control valves according to the detection results of each temperature sensor, each pressure sensor, and each flow sensor.

[0057] Specifically, the high temperature gas delivery pipe is connected to the economizer 7 and the air preheater 6 through the purification device 8.

[0058] Specifically, the liquid slag removal additive is a mixture of the following raw materials in percentage by mass: 40% to 50% flux, 20% to 30% dispersant and 20% to 30% heat transfer enhancer, wherein the flux is an alkali metal carbonate, the dispersant is a water-soluble functional polymer, and the heat transfer enhancer is a metal oxide.

[0059] Fluxes (alkali metal carbonates) lower the ash melting point, allowing it to flow in a liquid state at relatively low temperatures, facilitating slag removal and improving slag fluidity. Dispersants (water-soluble functional polymers) prevent agglomeration and enhance compatibility with other ingredients. Heat transfer enhancers (metal oxides) improve thermal conductivity and effectively increase heat transfer efficiency within the furnace.

[0060] Flux (40% to 50%): If the flux content is too low, it will not be enough to significantly reduce the melting point of the slag and improve the fluidity, and it will not be able to effectively solve the slagging problem; if the content is too high, it may cause the slag to over-melt and become too fluid, affecting the overall performance of the additive. Dispersant (20% to 30%): If the dispersant content is too little, it will not be able to fully play its role in preventing the slag particles from agglomerating and stabilizing the system, affecting the slag discharge effect; if the content is too much, it may form an excessively thick adsorption layer on the surface of the slag particles, which will in turn affect the heat transfer and fluxing effects. Heat transfer enhancer (20% to 30%): If the proportion of heat transfer enhancer is too low, it will not be able to effectively improve the heat transfer efficiency, which is not conducive to the rapid melting and flow of the slag; if the proportion is too high, the overall synergistic effect will be affected due to the imbalance between the metal oxide and other components.

[0061] The liquid slag removal additive selects alkali metal carbonate, water-soluble functional polymer, and metal oxide as flux, dispersant, and heat transfer enhancer, respectively, and determines the above-mentioned proportion range in order to make the various components cooperate and work synergistically with each other in lowering the melting point of slag, improving fluidity, preventing agglomeration, and improving heat transfer efficiency, so as to achieve the best liquid slag removal effect, while taking into account multiple factors such as cost and equipment protection.

[0062] Specifically, the alkali metal carbonate is selected from sodium carbonate, potassium carbonate or a mixture of the two.

[0063] Specifically, the water-soluble functional polymer is selected from sodium polyacrylate, polyvinyl alcohol or a mixture thereof.

[0064] Specifically, the metal oxide is selected from any one of aluminum oxide, titanium dioxide, and copper oxide, or a mixture of any two of them, or a mixture of the three.

[0065] Specifically, the heat transfer enhancer has a particle size of 50 nm to 150 nm. Within this particle size range, the heat transfer enhancer has a larger specific surface area. A larger specific surface area increases the contact area with the heat transfer medium, enabling more efficient heat transfer. Heat transfer enhancers within this particle size range maintain good dispersibility and fluidity in the fluid. From the perspective of interfacial heat transfer, this particle size range helps reduce thermal resistance and effectively prevents agglomeration.

[0066] Specifically, the proportional-differential-integral operation is as follows: the proportional (P) link adjusts the control quantity proportionally according to the error value at the current moment, which can quickly respond to the error and reduce the deviation. The differential (D) link adjusts the control quantity according to the rate of change of the error. Its function is to predict the changing trend of the error, adjust the control quantity in advance, suppress the overshoot of the system, and make the system more stable. The integral (I) link integrates the error and accumulates past errors to eliminate the steady-state error of the system so that the measured value can eventually stabilize near the set value. Through the synergistic effect of these three links, the controller continuously adjusts the output of the control unit so that the measured values of temperature, pressure and flow gradually approach the set value, thereby achieving precise control of the boiler system. The difference between the temperatures, pressures and flows is calculated using the proportional-differential-integral method, which includes the following steps:

[0067] The temperature difference, pressure difference and flow difference are calculated based on the measured values of temperature, pressure and flow obtained at the same time and the set values of temperature, pressure and flow;

[0068] The currently obtained temperature difference, pressure difference or flow difference is compared with the positive and negative values using the proportional operation method to obtain a temperature control signal, a pressure control signal or a flow control signal;

[0069] The currently obtained temperature difference, pressure difference or flow difference is differentiated using a differential operation method to obtain a temperature change rate signal, a pressure change rate signal or a flow change rate signal;

[0070] The currently obtained temperature difference, pressure difference or flow difference is respectively integrated using an integration operation method to obtain a temperature cumulative deviation signal, a pressure cumulative deviation signal or a flow cumulative deviation signal;

[0071] The signals obtained according to the above-mentioned proportional operation method, differential operation method and integral operation method are used to control the speed of the delivery pump, the opening degree of multiple solenoid valves or the opening degree of multiple electric control valves.

[0072] Specifically, the high-temperature gas delivery pipe is connected to the economizer 7 and the air preheater 6 through the purification device 8 .

[0073] A waste heat utilization method of a waste heat utilization system comprises the following steps:

[0074] The additive supply unit 5 feeds the additive into the collecting device 2 to cause the additive to react physically and chemically with the slag, thereby increasing the fluidity of the slag in the collecting device 2;

[0075] When recovering waste heat from the high-temperature flue gas, the blower 3 sends cold air into the slag-air heat exchanger 10 disposed in the collection device 2. The cold air exchanges heat with the slag to generate high-temperature air. The high-temperature air is then sent to the economizer 7 through the high-temperature gas delivery pipe to heat the feed water of the slag discharge boiler 1. The high-temperature flue gas generated by the slag discharge boiler 1 is sent to the air preheater 6, where it exchanges heat with the cold air. The generated high-temperature gas is then sent to the slag discharge boiler as boiler combustion gas.

[0076] When the slag waste heat is recovered, the slag exchanges heat with the heat exchange medium in the slag-water heat exchange tube, so that the temperature of the heat exchange medium in the slag-water heat exchange tube 4 increases, thereby providing heat for the power generation cycle unit 9;

[0077] The temperature measurement values, flow measurement values, and pressure measurement values at the inlet and outlet of the slag-water heat exchange pipe 4, the inlet and outlet of the collecting device 2, the inside of the slag discharge boiler 1, the cold air supply pipe, the high-temperature gas conveying pipe, the flue gas conveying pipe, and the slag-water heat exchange pipe 4 are measured respectively by multiple temperature sensors, multiple pressure sensors, and multiple flow sensors.

[0078] The controller receives the temperature, pressure and flow measurement values through the signal inlet, compares the temperature, pressure and flow measurement values with the corresponding temperature, pressure and flow setting values, and calculates the difference. Based on the calculated temperature, pressure and flow differences, the controller obtains control signals for controlling the operation of the delivery pump, multiple solenoid valves or multiple electric control valves.

[0079] Example 1

[0080] The slag output of a liquid slag discharge boiler is 1.5m 3 / h, the temperature is 1400 ° C. The additives in the new liquid slag additive storage bin are mixed in a ratio of 40% by mass of sodium carbonate, 30% by mass of sodium polyacrylate, and 30% by mass of alumina micropowder.

[0081] The additive supply unit sets the additive addition rate to 50kg / h according to the slag output and properties, and transports the additive to the vicinity of the slag discharge port of the liquid slag discharge boiler through a conveying pipeline to mix with the slag.

[0082] The discharged slag enters a collection device and first passes through a slag-to-air heat exchanger 10, where it is cooled to 700°C. It then passes through a slag-to-water heat exchanger 4, a shell-and-tube structure with stainless steel tubes with an inner diameter of 30 mm and baffles installed within the shell. The slag exchanges heat with water at a flow rate of 4 m³ / h. After heat exchange, the water temperature rises from 20°C to 80°C. The resulting hot water is partially supplied to the steam generator, while the remainder is used for the plant's heating system.

[0083] Meanwhile, the flue gas generated by the slagging boiler 1 reaches a temperature of 900°C. The flue gas first enters the economizer 7, heating the boiler feed water from 20°C to 130°C, improving the boiler's thermal efficiency. The flue gas then enters the air preheater 6, preheating the combustion air from 20°C to 280°C, improving combustion conditions. Finally, the flue gas enters the flue gas-water heat exchanger, heating another water channel from 20°C to 50°C for process heating in industrial production.

[0084] The controller compares the temperature, pressure and flow measurement values received through the signal inlet with the temperature, pressure and flow set values respectively, and regulates the delivery pump speed, the opening of multiple solenoid valves or the opening of multiple electric regulating valves according to the temperature, pressure and flow signal values obtained by the proportional-differential-integral control algorithm, so that the measured values of the control parameters gradually approach the set values, thereby meeting the needs of improving the thermal efficiency of the boiler and the waste heat utilization efficiency of the entire system.

[0085] When the outlet water temperature of the slag-water heat exchange tube 4 is lower than 75℃, the controller increases the water flow rate to 4.5m3 by adjusting the water pump inverter. 3 / h, improving heat exchange efficiency. Through intelligent control, the entire system can operate stably and efficiently, achieving effective treatment of liquid slag and full recovery of waste heat, improving energy utilization efficiency and reducing environmental pollution.

[0086] Example 2

[0087] The only difference between Example 2 and Example 1 is that the additives in the liquid slag additive storage bin are mixed in a ratio of 40% by mass of sodium carbonate, 20% by mass of sodium polyacrylate, and 20% by mass of alumina fine powder.

[0088] Example 3

[0089] The only difference between Example 3 and Example 1 is that the additives in the liquid slag additive storage bin are mixed in a ratio of 50% by mass of sodium carbonate, 25% by mass of sodium polyacrylate, and 25% by mass of alumina fine powder.

[0090] In order to verify the recovery efficiency of liquid slag waste heat using the liquid slag additive, a specific verification implementation method is given:

[0091] 1. Experimental system construction

[0092] Two identical small-scale boiler experimental devices were established, ensuring consistency in structure, material, capacity, and initial performance to eliminate any interference from other factors. One set served as the experimental group and operated with a liquid slagging additive; the other, the control group, operated conventionally without any additives.

[0093] Temperature sensors (such as K-type thermocouples), pressure sensors (such as piezoresistive pressure sensors) and flow sensors (such as vortex flowmeters) are installed at key locations of the boiler, such as the furnace, flue, and heat exchanger inlet and outlet, to monitor and record various parameters during boiler operation in real time, including but not limited to fuel flow, air flow, steam production, flue gas temperature, flue gas pressure, feed water temperature, steam temperature and pressure, etc.

[0094] Calorimeters are installed before and after the heat exchanger in the waste heat recovery system to accurately measure the heat entering and leaving the system, thereby calculating the waste heat recovery efficiency. Calorimeters can use thermodynamic measurement methods, such as measuring the temperature change and flow rate of the working fluid and calculating the heat capacity of the working fluid.

[0095] 2. Experimental design

[0096] Select appropriate fuel to ensure that the fuel quality, composition and calorific value used in the two groups of liquid slagging boilers are exactly the same, and maintain a stable supply throughout the experiment.

[0097] Determine the experimental operating conditions, including boiler load levels (e.g., low, medium, and high), operating time, and number of starts and stops. These operating conditions should encompass typical conditions encountered by liquid slagging boilers in actual industrial production, allowing for a comprehensive assessment of the impact of liquid slagging additives on waste heat recovery efficiency under different operating conditions. For example, the operating time at each load level should be no less than four hours, with multiple switching between different loads to simulate load fluctuations in actual production.

[0098] In the experimental group of boilers, a liquid deslagging additive was added according to a predetermined ratio and method. The ratio should be optimized based on the additive's characteristics and the boiler's operating parameters. A preliminary range can be determined through preliminary pilot experiments or theoretical calculations, and then further optimized in this experiment. The additive can be added by direct injection into the furnace or premixed with the fuel to ensure uniform distribution throughout the combustion zone and sufficient contact and reaction with the coking material.

[0099] 3. Data collection and processing

[0100] During the experiment, a data acquisition system was used to collect and record data from various sensors installed on the boiler and waste heat recovery system in real time. The acquisition frequency was set to once per minute or higher to ensure that the dynamic changes in the system operating parameters could be captured. The collected data was preprocessed and analyzed to remove abnormal data points, and the data was smoothed through methods such as data fitting and filtering to improve data accuracy and reliability. The waste heat recovery efficiency was calculated based on the collected calorimeter data. The calculation formula for waste heat recovery efficiency is as follows:

[0101]

[0102] Among them, η is the waste heat recovery efficiency, Q rec is the actual amount of heat recovered by the waste heat recovery system, kJ, Q in Q is the total heat entering the waste heat recovery system, kJ. rec The mass flow rate m, specific heat capacity c and inlet and outlet temperature difference ΔT of the working fluid (such as water or air) in the waste heat recovery system can be measured, and the formula Q rec = mcΔT calculated; Q in This can be calculated through energy balance by measuring the flue gas temperature, flow rate and specific heat capacity before entering the waste heat recovery system, and combining it with parameters such as the calorific value and combustion volume of the fuel.

[0103] 4. Effect evaluation and comparative analysis

[0104] The waste heat recovery efficiency of the experimental group and the control group under different operating conditions were calculated respectively, and the curve of the waste heat recovery efficiency changing with time was drawn to intuitively show the difference between the two groups of experimental results.

[0105] Statistical analysis of the experimental data from the experimental and control groups, such as analysis of variance (ANOVA), is performed to determine whether the liquid slag additive has a significant effect on waste heat recovery efficiency. The statistical F value and the corresponding P value are calculated. If the P value is less than a pre-set significance level (e.g., 0.05), it can be considered that the additive has a significant effect on improving waste heat recovery efficiency.

[0106] In addition to waste heat recovery efficiency, other indicators related to energy waste can also be evaluated and compared, such as the thermal efficiency of the boiler, fuel consumption rate, exhaust gas temperature, and coking conditions. The coking condition can be quantitatively evaluated by regularly checking the coking degree inside the boiler (such as coking thickness, hardness, etc.) and combining image analysis or physical measurement methods. If the use of additives improves the thermal efficiency of the liquid slagging boiler, reduces the fuel consumption rate, drops the exhaust gas temperature, and significantly reduces the coking phenomenon, it further proves the effectiveness of the liquid slagging additive in recycling waste heat and reducing energy waste.

[0107] 5. Long-term stability test

[0108] In order to further verify the long-term stability and reliability of liquid slag additives in actual industrial applications, long-term operation experiments can be conducted. Based on the above experiments, the liquid slag boilers of the experimental and control groups are operated continuously for several weeks or months. According to the same experimental plan and data collection method, various operating parameters and performance indicators are regularly recorded and analyzed. During the long-term operation, it is observed whether the waste heat recovery efficiency of the experimental group after using the additive can continue to maintain a high level, whether other performance indicators are stable, and whether equipment corrosion, wear or other negative problems caused by the use of the additive occur. Through long-term stability testing, more powerful technical support and data basis can be provided for the actual industrial application of liquid slag additives.

[0109] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A waste heat utilization system for liquid slag discharge, comprising a collecting device (2) connected to a slag discharge boiler (1), characterized in that: Also includes: An additive supply unit (5) is connected to the collecting device (2) and is used to feed the liquid slag removal additive into the collecting device (2); The waste heat recovery unit comprises a blower (3), a slag-air heat exchanger (10), an air preheater (6), an economizer (7) and a slag-water heat exchange pipe (4). The slag-air heat exchanger (10) is arranged in the collecting device (2). The blower (3) is connected to the slag-air heat exchanger (10) through a cold air supply pipe. The slag-air heat exchanger (10) is connected to the economizer (7) through a high-temperature gas conveying pipe. The slag discharge boiler (1) is connected to the air preheater (6) through a flue gas conveying pipe. A conveying pump is provided on the slag-water circulation heat exchange pipe (4). Part of the slag-water circulation heat exchange pipe (4) is arranged in the collecting device (2). The slag-water circulation heat exchange pipe (4) is also connected to the power generation circulation unit (9). A plurality of temperature sensors, a plurality of pressure sensors, and a plurality of flow sensors are respectively arranged at the inlet and outlet of the slag-water heat exchange pipe (4), the inlet and outlet of the collecting device (2), inside the slag discharge boiler (1), and on the cold air supply pipe, the high-temperature gas delivery pipe, the flue gas delivery pipe, and the slag-water heat exchange pipe (4); and a plurality of solenoid valves or a plurality of electric regulating valves are arranged on the cold air supply pipe, the high-temperature gas delivery pipe, the flue gas delivery pipe, and the slag-water heat exchange pipe (4); The controller is connected to each temperature sensor, each pressure sensor, each flow sensor, a delivery pump, multiple solenoid valves or multiple electric control valves. The controller is used to control the speed of the delivery pump and the opening of each solenoid valve or each electric control valve according to the detection results of each temperature sensor, each pressure sensor and each flow sensor.

2. A waste heat utilization system for liquid slag discharge according to claim 1, characterized in that: The high-temperature gas delivery pipe is connected to the economizer (7) and the air preheater (6) through a purification device (8).

3. The waste heat utilization system for liquid slag discharge according to claim 1, characterized in that: The liquid slag removal additive fed into the collecting device (2) by the additive supply unit (5) is a mixture of the following raw materials in percentage by mass: 40% to 50% flux, 20% to 30% dispersant and 20% to 30% heat transfer enhancer, wherein the flux is an alkali metal carbonate, the dispersant is a water-soluble functional polymer, and the heat transfer enhancer is a metal oxide.

4. The waste heat utilization system of liquid slag discharge according to claim 3, characterized in that: The alkali metal carbonate is selected from sodium carbonate, potassium carbonate or a mixture of the two.

5. The waste heat utilization system of liquid slag discharge according to claim 3, characterized in that: The water-soluble functional polymer is selected from sodium polyacrylate, polyvinyl alcohol or a mixture of the two.

6. The waste heat utilization system for liquid slag discharge according to claim 3, characterized in that: The metal oxide is selected from any one of aluminum oxide, titanium dioxide, and copper oxide, or a mixture of any two of them, or a mixture of the three.

7. The waste heat utilization system for liquid slag discharge according to claim 3, characterized in that: The particle size of the heat transfer enhancer is 50nm to 150nm.

8. The waste heat utilization method of the waste heat utilization system of liquid slag discharge according to claim 1, characterized in that: The steps include: The additive supply unit (5) feeds the additive into the collecting device (2) to cause the additive to react physically and chemically with the slag, thereby increasing the fluidity of the slag in the collecting device (2); When the waste heat of the high-temperature flue gas is recovered, the blower (3) sends cold air into the slag-air heat exchanger (10) arranged in the collecting device (2), and the cold air exchanges heat with the slag to generate high-temperature air. The high-temperature air is sent to the economizer (7) through the high-temperature gas conveying pipe to heat the feed water of the slag discharge boiler (1). The high-temperature flue gas generated by the slag discharge boiler (1) is sent to the air preheater (6), and heat is exchanged with the cold air in the air preheater (6). The generated high-temperature gas is sent to the slag discharge boiler to serve as boiler combustion gas; when the waste heat of the slag is recovered, the slag exchanges heat with the heat exchange medium in the slag-water heat exchange pipe, so that the temperature of the heat exchange medium in the slag-water heat exchange pipe (4) is increased, thereby providing heat for the power generation cycle unit (9); Using a plurality of temperature sensors, a plurality of pressure sensors, and a plurality of flow sensors, temperature measurement values, flow measurement values, and pressure measurement values are respectively measured at the inlet and outlet of the slag-water heat exchange pipe (4), the inlet and outlet of the collecting device (2), the interior of the slag discharge boiler (1), and the cold air supply pipe, the high-temperature gas delivery pipe, the flue gas delivery pipe, and the slag-water heat exchange pipe (4); The controller receives the temperature, pressure and flow measurement values through the signal inlet, compares the temperature, pressure and flow measurement values with the corresponding temperature, pressure and flow setting values, and calculates the difference between the temperature, pressure and flow. Based on the calculated difference between the temperature, pressure and flow, the controller obtains the control signals for controlling the operation of the delivery pump, multiple solenoid valves or multiple electric control valves.

9. The method for utilizing waste heat from liquid slagging according to claim 8, characterized in that: The differences of the temperatures, pressures, and flows are calculated using a proportional-differential-integral method, which includes the following steps: The temperature difference, pressure difference and flow difference are calculated based on the measured values of temperature, pressure and flow obtained at the same time and the set values of temperature, pressure and flow; The currently obtained temperature difference, pressure difference or flow difference is compared with the positive and negative values using the proportional operation method to obtain a temperature control signal, a pressure control signal or a flow control signal; The currently obtained temperature difference, pressure difference or flow difference is differentiated using a differential operation method to obtain a temperature change rate signal, a pressure change rate signal or a flow change rate signal; The currently obtained temperature difference, pressure difference or flow difference is respectively integrated using an integration operation method to obtain a temperature cumulative deviation signal, a pressure cumulative deviation signal or a flow cumulative deviation signal; The signals obtained according to the above-mentioned proportional operation method, differential operation method and integral operation method are used to control the speed of the delivery pump, the opening degree of multiple solenoid valves or the opening degree of multiple electric control valves.

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