Combustion-supporting air preheating system for lithium bromide absorption furnace using rolling line waste steam

Abstract

The invention discloses a combustion-supporting air preheating system for a lithium bromide absorption furnace using rolling line waste steam, and relates to the technical field of heating furnace energy conservation. Comprising a steam-water separator, a filter and a switching valve, the input end of the steam-water separator is connected with a waste steam source, the output end of the steam-water separator is connected to the input end of the filter, and the output end of the filter is connected to the first input end of the switching valve; comprising a generator, a condenser, an evaporator, an absorber and a solution pump, the output end of a switching valve is sequentially connected with the generator, the condenser, the evaporator and the absorber, an air inlet in the condenser is connected with a combustion-supporting air source, an air outlet in the absorber is connected to a heating furnace, and the output end of the absorber is connected to the input end of the solution pump. The output end of the solution pump is connected to the backflow input end of the generator, and a dilution water adjusting valve is further arranged between the output end of the solution pump and the generator. The control system is used for detecting and adjusting system parameters in real time, and the PLC is electrically connected with the solution pump.

Description

Technical Field

[0001] This invention relates to the field of energy-saving technology for heating furnaces, specifically to a combustion air preheating system for a lithium bromide absorption furnace that utilizes waste steam from a rolling mill. Background Technology

[0002] The heating furnace is a core energy-consuming piece of equipment in the steel rolling process, accounting for 40% to 60% of the total energy consumption. Increasing the preheating temperature of the combustion air is a key technical means to reduce fuel consumption and optimize combustion efficiency in the heating furnace. However, existing combustion air preheating solutions in the steel rolling industry have significant limitations:

[0003] First, waste heat recovery and preheating of flue gas, such as regenerative heat exchangers and tubular heat exchangers, are affected by iron oxide scale dust blockage and temperature fluctuations (above ±20℃) in the steel rolling flue gas. The heat exchange efficiency decreases by 25%~35% with the running time, and the preheating temperature is generally ≤120℃, which is difficult to meet the high-efficiency combustion requirements of steel rolling heating furnaces for combustion air above 150℃.

[0004] Second, high-grade energy drives preheating, such as using high-pressure steam or electric heating in the plant. Although high-temperature preheating can be achieved, the operating cost is 50% to 70% higher than that of the flue gas waste heat solution, which does not meet the development requirements of energy conservation and carbon reduction in the steel rolling industry.

[0005] Thirdly, direct waste steam preheating is used. Some steel rolling mills have tried to use waste steam from the rolling line to directly heat the combustion air. However, because the steam comes from the vaporization cooling system of the rolling mill, the pressure (0.2~0.4MPa) and temperature (120~140℃) fluctuate greatly (±15℃), and it contains impurities such as iron oxide scale fragments and oil stains, which can easily lead to corrosion and leakage of the heat exchanger. The average fault interval of the system is less than 2 months, and it cannot operate stably.

[0006] Meanwhile, the vaporization cooling system in the steel rolling process (such as the rolling mill roller table and the water-cooled wall vaporization cooling of the heating furnace) generates a large amount of low-pressure waste steam: each ton of rolled material can generate 0.12~0.18 tons of waste steam with a pressure of 0.2~0.5MPa and a temperature of 120~150℃. If this type of waste steam is directly discharged, the annual loss of standard coal can reach 6%~10% of the total coal consumption of the steel rolling plant; if it is used for low-value purposes such as heating in the plant area, the energy utilization rate is only 20%~28%, and it is subject to seasonal limitations (the utilization rate is less than 8% in summer), forming a vicious cycle unique to the steel rolling process of "energy waste - thermal pollution - equipment corrosion".

[0007] The core bottleneck of existing technologies lies in the lack of coordination between waste steam recovery and combustion air preheating in the steel rolling process. On the one hand, the low-pressure waste steam in the rolling line is low in grade and contains many impurities, lacking a high-value recovery path suitable for the steel rolling scenario. On the other hand, the combustion air preheating of the steel rolling furnace relies on inefficient flue gas waste heat or high-cost external energy sources, failing to fully utilize the waste heat resources generated by the rolling line itself. This "separate management" energy model not only causes serious waste of waste heat resources in the steel rolling process but also increases the energy consumption of the heating furnace, which is seriously inconsistent with the steel rolling industry's transformation goal of "reducing costs and increasing efficiency, and green and low-carbon development".

[0008] Therefore, developing a lithium bromide absorption furnace combustion air preheating system for low-pressure waste steam in the steel rolling process is of urgent practical need and significant industrial value for overcoming existing technological bottlenecks in the steel rolling industry and achieving the dual goals of high-value recovery of waste steam from the rolling line and energy saving and consumption reduction in the furnace. This is precisely the core technical problem that this invention aims to solve. Summary of the Invention

[0009] To address these issues, embodiments of the present invention provide a combustion air preheating system for a lithium bromide absorption furnace that utilizes waste steam from a rolling mill, thereby resolving the problems existing in the aforementioned technologies.

[0010] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0011] A combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill includes:

[0012] An exhaust gas pretreatment unit includes a steam-water separator, a filter, and a switching valve; the input end of the steam-water separator is connected to an exhaust steam source, the output end of the steam-water separator is connected to the input end of the filter, and the output end of the filter is connected to the first input end of the switching valve.

[0013] A lithium bromide generator unit includes a generator, a condenser, an evaporator, an absorber, and a solution pump. The output of a switching valve is sequentially connected to the generator, condenser, evaporator, and absorber. The air inlet on the condenser is connected to a combustion air source, the air outlet on the absorber is connected to a heating furnace, the output of the absorber is connected to the input of the solution pump, the output of the solution pump is connected to the return input of the generator, and a dilution water regulating valve is also provided between the output of the solution pump and the generator, the dilution water regulating valve being connected to an external water source.

[0014] The control system includes a PLC controller, which is used for real-time detection and adjustment of system parameters. The PLC controller is electrically connected to the solution pump.

[0015] Optionally, it also includes a backup steam source, wherein the switching valve is an electric three-way switching valve, and the output end of the backup steam source is connected to the second input end of the three-way switching valve;

[0016] The control system includes a steam pressure sensor, which is installed on the steam output pipeline of the waste steam from the rolling mill. The steam pressure sensor and the electric three-way switching valve are electrically connected to the PLC controller.

[0017] Optionally, the control system further includes a concentration sensor, which is electrically connected to the PLC controller;

[0018] The concentration sensor is installed on the output pipe of the absorber.

[0019] Optionally, the control system further includes a temperature sensor, which is electrically connected to the PLC controller;

[0020] The temperature sensor is installed on the pipeline between the solution pump and the dilution water regulating valve.

[0021] Optionally, the control system further includes a steam flow regulating valve, which is electrically connected to the PLC controller;

[0022] The steam flow regulating valve is installed on the pipeline between the switching valve and the absorber.

[0023] Optionally, the control system further includes an air bypass valve, which is electrically connected to the PLC controller;

[0024] The condenser is provided with parallel heat exchange paths and bypass paths, and the air bypass valve is located in the bypass path to regulate the flow rate of the bypass path.

[0025] Optionally, the heat exchange channels of the condenser and absorber adopt a finned tube structure, and the heat exchange area allows the combustion air to be heated to above 150°C.

[0026] Optionally, the steam-water separator is a cyclone type structure used to remove more than 95% of liquid water droplets from the waste steam.

[0027] Optionally, the filter is a stainless steel filter screen, and the filtration accuracy of the stainless steel filter screen is greater than or equal to 10 μm.

[0028] The present invention has at least the following beneficial effects:

[0029] This invention utilizes a lithium bromide unit with a core of lithium bromide solution concentration circulation and refrigerant vapor phase change circulation. Through the coordinated operation of a generator, condenser, evaporator, and absorber, a dilute lithium bromide solution is pumped to the generator, where it is heated by high-temperature steam from the pretreatment unit and boils to produce refrigerant vapor, simultaneously concentrating into a concentrated lithium bromide solution. The refrigerant vapor enters the condenser, where it is condensed into liquid refrigerant, releasing condensation heat. The liquid refrigerant then enters the evaporator and evaporates into low-temperature refrigerant vapor, subsequently entering the absorber where it contacts the concentrated lithium bromide solution. The solution absorbs the refrigerant vapor, releasing heat. The dilute solution is pumped back to the generator to complete the cycle, and the condenser heats the combustion air. This utilizes the heat from the waste steam from the rolling mill to heat the furnace, improving resource utilization and reducing steel rolling costs. Attached Figure Description

[0030] To more clearly illustrate the prior art and the present invention, the accompanying drawings used in the description of the prior art and the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other drawings from the provided drawings without any creative effort.

[0031] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed herein.

[0032] Figure 1 This is a schematic diagram illustrating the principle structure of one embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0034] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," "fourth," etc. (if present), in the specification, claims, and accompanying drawings of this invention are intended to distinguish the objects referred to. For schemes with a sequential flow, this terminology need not be construed as describing a specific order or sequence; for schemes with device structures, this terminology does not distinguish between matters of importance or positional relationships.

[0035] Furthermore, the terms “comprising,” “having,” and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are expressly listed, but may also include other steps or units that are not expressly listed but are inherent to these processes, methods, products, or apparatuses, or steps or units added based on further optimizations of the inventive concept.

[0036] like Figure 1 As shown, the lithium bromide absorption furnace combustion air preheating system utilizing waste steam from rolling mills, as disclosed in this invention, includes:

[0037] The exhaust gas pretreatment unit includes a steam-water separator, a filter, and a switching valve; the input end of the steam-water separator is connected to the exhaust steam source, the output end of the steam-water separator is connected to the input end of the filter, and the output end of the filter is connected to the first input end of the switching valve.

[0038] The lithium bromide unit includes a generator, condenser, evaporator, absorber, and solution pump. The output of the switching valve is connected to the generator, condenser, evaporator, and absorber in sequence. The air inlet on the condenser is connected to the combustion air source, the air outlet on the absorber is connected to the heating furnace, the output of the absorber is connected to the input of the solution pump, the output of the solution pump is connected to the return input of the generator, and a dilution water regulating valve is also provided between the output of the solution pump and the generator. The dilution water regulating valve is connected to an external water source.

[0039] The control system includes a PLC controller, which is used for real-time detection and adjustment of system parameters. The PLC controller is electrically connected to the solution pump. The control system consists of the PLC controller and several sensors, actuators, etc. The specific structure will not be described in detail here.

[0040] The aforementioned waste steam pretreatment unit includes a steam-water separator, a filter, and an electric switching valve. The waste steam from the rolling mill first enters the cyclone-type steam-water separator to remove more than 95% of the liquid water droplets. Then it flows through a filter with a stainless steel filter screen with a filtration accuracy of ≥10μm to intercept impurities such as iron oxide scale and oil. The purified steam is then connected to the first input end of the switching valve.

[0041] The lithium bromide unit is based on a lithium bromide solution concentration cycle and a refrigerant vapor phase change cycle. The working medium is lithium bromide solution, and it works in concert through a generator, condenser, evaporator, and absorber. A dilute lithium bromide solution is pumped to the generator, where it is heated by high-temperature steam from the pretreatment unit and boils to produce refrigerant vapor, while simultaneously being concentrated into a concentrated lithium bromide solution. The refrigerant vapor enters the condenser, where combustion air is introduced. It condenses into liquid refrigerant through a finned tube heat exchange channel with cooling water, releasing condensation heat to heat the combustion air. The liquid refrigerant then enters the evaporator and evaporates into low-temperature refrigerant vapor, which then enters the absorber to contact the concentrated lithium bromide solution. The solution absorbs the refrigerant vapor and releases heat. The dilute solution is pumped back to the generator to complete the cycle, and the heated combustion air is discharged from the absorber's exhaust port. The heat exchange area of ​​the condenser and absorber is set according to the requirement of heating the combustion air to above 150°C. Under partial load (waste steam flow rate is 30% to 100% of the rated flow rate), the unit ensures a thermal efficiency of ≥80% by adjusting the speed of the solution pump and the opening of the flow regulating valve.

[0042] In a further embodiment, a backup steam source is also included, and the switching valve is an electric three-way switching valve, with the output end of the backup steam source connected to the second input end of the three-way switching valve;

[0043] The control system includes a steam pressure sensor, which is installed on the steam output pipeline of the waste steam from the rolling mill. The steam pressure sensor and the electric three-way switching valve are electrically connected to the PLC controller.

[0044] To ensure sufficient steam pressure when the waste steam supply is insufficient, a low-pressure backup steam source is set up. The switching valve is an electric three-way switching valve. The waste steam from the rolling mill is connected to the first input terminal of the electric three-way switching valve, the backup steam source is connected to the second input terminal of the electric three-way switching valve, and the output terminal of the electric three-way switching valve is connected to the generator.

[0045] A steam pressure sensor is installed on the waste steam conveying pipeline of the rolling mill to detect the pressure of the waste steam in real time and feed the pressure signal back to the PLC controller to control the electric three-way switching valve to automatically switch the steam source and ensure the stable temperature of the combustion air heating.

[0046] In a further specific embodiment, the control system also includes a concentration sensor, a temperature sensor, and a steam flow regulating valve, all of which are electrically connected to the PLC controller.

[0047] The concentration sensor is installed on the output pipeline of the absorber, the temperature sensor is installed on the pipeline between the solution pump and the dilution water regulating valve, and the steam flow regulating valve is installed on the pipeline between the switching valve and the absorber.

[0048] When the solution concentration is high, the PLC controller controls the dilution water regulating valve to open and replenish dilution water; when the concentration is below 50%, the solution pump speed is increased to increase the circulation volume and prevent crystallization; the temperature sensor feeds back the dilute solution temperature signal to the PLC controller, and the controller adjusts the opening of the steam flow regulating valve according to the signal to control the generator heating power.

[0049] In one specific embodiment, the control system further includes an air bypass valve, which is electrically connected to the PLC controller;

[0050] The condenser has parallel heat exchange paths and a bypass path. An air bypass valve is located in the bypass path to regulate the flow rate of the bypass path.

[0051] The aforementioned finned tube structure incorporates two parallel refrigerant vapor flow paths. One path connects directly to the heat exchange channel, while the other, separated from it, serves as a bypass channel. An air bypass valve is located within this bypass channel. When the combustion air outlet temperature falls below the set threshold, the PLC controller reduces the bypass valve opening, decreasing the refrigerant vapor bypass flow and extending the heat exchange time to raise the temperature. The bypass path flexibly adjusts the combustion air heating temperature through the refrigerant vapor diversion path, ensuring stable and efficient system operation under various conditions. The combustion air requires a temperature above 150°C to meet the high-efficiency combustion requirements of the heating furnace. However, the flow rate, pressure, and temperature of the waste steam from the rolling mill fluctuate due to the rolling production rhythm, leading to unstable refrigerant vapor production. Excessive refrigerant vapor can cause excessively high combustion air temperatures, affecting combustion efficiency and potentially damaging equipment; insufficient refrigerant vapor, on the other hand, will result in insufficient temperature. The bypass path acts as a "flow regulating valve," rapidly adjusting the intensity of heat exchange by changing the proportion of refrigerant vapor participating in heat exchange: when the temperature is insufficient, the bypass flow is reduced, allowing more refrigerant vapor to remain in the condenser and fully exchange heat with the combustion air, extending the heat exchange time and raising the temperature; when the temperature is too high, the bypass flow is increased, allowing some refrigerant vapor to bypass the heat exchange area, preventing the temperature from exceeding the limit.

[0052] Working principle: During system operation, the waste steam from the rolling mill is pretreated and then enters the generator to heat the lithium bromide solution to produce refrigerant steam. The refrigerant steam is liquefied in the condenser, releasing heat to heat the combustion air. The liquid refrigerant evaporates in the evaporator, and the refrigerant steam is absorbed by the solution in the absorber to form a dilute solution. The dilute solution is returned to the generator by the solution pump to complete the cycle. The heated combustion air flows through the evaporator and absorber and is connected to the heating furnace from the outlet of the absorber.

[0053] The above specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0054] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

[0055] The present invention has been described in detail above through general description and specific embodiments. It should be noted that, without departing from the concept of the present invention, various modifications and improvements can be made to these specific embodiments, all of which fall within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the appended claims.

Claims

1. A combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, characterized in that, include: An exhaust gas pretreatment unit includes a steam-water separator, a filter, and a switching valve; the input end of the steam-water separator is connected to an exhaust steam source, the output end of the steam-water separator is connected to the input end of the filter, and the output end of the filter is connected to the first input end of the switching valve. A lithium bromide generator unit includes a generator, a condenser, an evaporator, an absorber, and a solution pump. The output of a switching valve is sequentially connected to the generator, condenser, evaporator, and absorber. The air inlet on the condenser is connected to a combustion air source, the air outlet on the absorber is connected to a heating furnace, the output of the absorber is connected to the input of the solution pump, the output of the solution pump is connected to the return input of the generator, and a dilution water regulating valve is also provided between the output of the solution pump and the generator, the dilution water regulating valve being connected to an external water source. The control system includes a PLC controller, which is used for real-time detection and adjustment of system parameters. The PLC controller is electrically connected to the solution pump.

2. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 1, is characterized in that: It also includes a backup steam source, and the switching valve is an electric three-way switching valve, with the output end of the backup steam source connected to the second input end of the three-way switching valve; The control system includes a steam pressure sensor, which is installed on the steam output pipeline of the waste steam from the rolling mill. The steam pressure sensor and the electric three-way switching valve are electrically connected to the PLC controller.

3. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 2, is characterized in that: The control system also includes a concentration sensor, which is electrically connected to the PLC controller; The concentration sensor is installed on the output pipe of the absorber.

4. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 3, is characterized in that: The control system also includes a temperature sensor, which is electrically connected to the PLC controller. The temperature sensor is installed on the pipeline between the solution pump and the dilution water regulating valve.

5. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 4, is characterized in that: The control system also includes a steam flow regulating valve, which is electrically connected to the PLC controller. The steam flow regulating valve is installed on the pipeline between the switching valve and the absorber.

6. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 5, is characterized in that: The control system also includes an air bypass valve, which is electrically connected to the PLC controller; The condenser is provided with parallel heat exchange paths and bypass paths, and the air bypass valve is located in the bypass path to regulate the flow rate of the bypass path.

7. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 6, is characterized in that: The heat exchange channels of the condenser and absorber adopt a finned tube structure, and the heat exchange area allows the combustion air to be heated to above 150°C.

8. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 1, is characterized in that: The steam-water separator is a cyclone type structure used to remove more than 95% of liquid water droplets from waste steam.

9. The combustion air preheating system for a lithium bromide absorption furnace utilizing waste steam from a rolling mill, as described in claim 1, is characterized in that: The filter is a stainless steel filter screen, and the filtration accuracy of the stainless steel filter screen is greater than or equal to 10μm.

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