Gas boiler flue gas desulfurization and deacidification and waste heat utilization system

Abstract

The invention provides a gas boiler flue gas desulfurization and deacidification and waste heat utilization system which is characterized in that a low-temperature economizer and a discharge device are sequentially arranged in the flowing direction of flue gas discharged by a gas boiler, and the system further comprises a dry type absorbent injection device which is arranged on the upstream of the low-temperature economizer in the flowing direction of the flue gas; spraying the dry absorbent into the flue to react with the acid gas; the flue gas subjected to acid gas removal enters the low-temperature coal economizer for waste heat recovery, and the flue gas subjected to waste heat recovery is discharged from a discharge device.

Description

Technical Field

[0001] The invention relates to the fields of industrial waste treatment, environmental protection and energy, and in particular to a flue gas desulfurization, deacidification and waste heat utilization system for a gas boiler. Background Art

[0002] Existing steel mills have a large amount of abundant blast furnace gas, coke oven gas and converter gas. In order to effectively utilize these gases, most steel mills will build gas boilers for power generation. Since there is a certain amount of SO2 and SO3 in the combustion flue gas, the acid dew point is relatively high. If the flue gas temperature is lower than the acid dew point, corrosion will occur. For this reason, the outlet flue gas temperature of the general gas boiler is designed to be 15-20℃ higher than the acid dew point temperature, reaching about 130-150℃. However, due to the deterioration of boiler operation, the actual outlet flue gas temperature will be further increased, which leads to a large amount of flue gas waste heat waste. At the same time, it also causes problems such as large flue gas volume under working conditions, increased investment in tail environmental protection devices, and high power consumption of induced draft fans.

[0003] In order to reduce exhaust losses, some projects have applied low-temperature waste heat recovery technology, that is, setting up low-temperature economizers for waste heat recovery. However, due to the acid dew point corrosion problem, low-temperature economizers need to use 2205 duplex stainless steel or higher anti-corrosion materials, resulting in very high device costs, long equipment recovery cycles, and poor economic benefits. For example, the utility model patent with publication number CN208779478U discloses a blast furnace gas boiler flue gas waste heat deep utilization device, which recovers waste heat by setting a low-temperature economizer downstream of the blast furnace gas boiler. However, in this solution, after the low-temperature economizer recovers waste heat, the temperature of the flue gas will drop below the acid dew point, causing corrosion of the low-temperature economizer.

[0004] The invention patent application with the patent application publication number CN112221332 A discloses a device and method for preventing the blockage and corrosion of low-temperature economizers. It proposes to spray an alkaline absorbent in front of the flue gas inlet of the low-temperature economizer to neutralize and remove SO3 in the flue gas, ensure that the low-temperature economizer is not blocked and corroded by ammonium bisulfate, reduce the operating risk of the low-temperature economizer, and ensure the environmental protection and energy-saving benefits of the low-temperature electrostatic precipitator. This patent can achieve the removal of SO3 and has a good protective effect on the low-temperature economizer, but it is not conducive to the recovery of waste heat from the flue gas, because the evaporation and reaction of the alkaline absorbent solution will cause the flue gas temperature to drop, which will cause a negative impact. Summary of the invention

[0005] The problem to be solved by the present invention is to provide a gas boiler flue gas desulfurization, deacidification and waste heat utilization system, which can protect the low-temperature economizer from corrosion while maintaining the flue gas temperature and the waste heat recovery effect.

[0006] In order to solve the above technical problems, the present invention provides a gas boiler flue gas desulfurization and deacidification and waste heat utilization system, which is provided with a low-temperature economizer and an emission device in sequence along the flow direction of the flue gas discharged from the gas boiler, and also includes a dry absorbent injection device, which is arranged upstream of the low-temperature economizer along the flow direction of the flue gas and injects the dry absorbent into the flue to react with the acid gas;

[0007] The flue gas after the acid gas is removed enters the low-temperature economizer for waste heat recovery; the flue gas after waste heat recovery is discharged from the emission device.

[0008] Some of the embodiments further include a dust collector, wherein the dust collector is disposed downstream of the low-temperature economizer.

[0009] In some of the embodiments, an induced draft fan is further included, and the induced draft fan is arranged downstream of the dust collector.

[0010] In some of the embodiments, the low-temperature economizer is connected to a waste heat utilization device to supply the recovered waste heat to the waste heat utilization device.

[0011] In some of the embodiments, the waste heat utilization equipment includes a condensate pump, a heater, and a deaerator. The heater extracts steam to heat the condensate of the condensate pump. The low-temperature economizer is connected to the heater of the waste heat utilization equipment through a pipeline, and the waste heat recovered by the low-temperature economizer is used to heat the condensate.

[0012] In some embodiments, the heater is divided into a low-pressure heater and a high-pressure heater. The condensate is heated by the low-pressure heater and then heated again by the high-pressure heater. The low-pressure heater is connected to the low-temperature economizer to utilize waste heat.

[0013] In some embodiments, the dry absorbent has a particle size of 2-10 microns.

[0014] In some embodiments, the specific surface area of ​​the dry absorbent is greater than or equal to 38 m 2 / g.

[0015] In some embodiments, the pore volume of the dry absorbent is greater than or equal to 0.2 cm 3 / g.

[0016] In some embodiments, the dry absorbent is slaked lime.

[0017] In some of the embodiments, the low-temperature economizer is made of ND steel or carbon steel.

[0018] In some of the embodiments, the dust collector inlet is connected to a vertical flue, and the low-temperature economizer is arranged in the vertical flue.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention arranges a dry absorbent upstream of the low-temperature economizer to remove acidic gases in advance, thereby reducing the acid dew point of the flue gas without causing a decrease in the flue gas temperature. This can achieve flue gas treatment while greatly reducing the corrosion risk of the low-temperature economizer, while maintaining the effect of waste heat recovery. The cooling of the low-temperature economizer helps to improve the efficiency of the dry absorbent in removing acidic gases. The low-temperature economizer can use ordinary anti-corrosion materials with low construction cost.

[0021] 2. In the system of the present invention, after the flue gas is recovered through the waste heat of the low-temperature economizer, the amount of flue gas in the working condition is reduced, the cost of the dust removal device is reduced, and good energy-saving and environmental protection benefits are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the flue gas desulfurization, deacidification and waste heat utilization system of the gas boiler of the present invention.

[0023] Figure numerals: 1 - gas boiler, 2 - dry absorbent injection device, 3 - low-temperature economizer, 4 - dust collector, 5 - induced draft fan, 6 - chimney, 7 - deaerator, 8 - high-pressure heater, 9 - low-pressure heater, 10 - condensate pump. DETAILED DESCRIPTION

[0024] 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; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0026] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] In the existing waste heat recovery system of gas boilers, the temperature of the flue gas after waste heat recovery by the low-temperature economizer is reduced to below the acid dew point. At this time, the acid gas in the flue gas condenses and is highly corrosive. Although energy saving can be achieved, the problem of corrosion of the low-temperature economizer will also occur. At present, the corrosion rate is mainly reduced as much as possible through the structure or material of the low-temperature economizer. The low-temperature economizer is manufactured with highly corrosion-resistant materials. The overall cost is high, the recovery cycle is long, and the economic benefits are poor. At present, there is a technical solution of removing SO3 by using liquid alkaline absorbent. Although it protects the low-temperature economizer, it also reduces the flue gas temperature at the same time, reducing the energy-saving effect of waste heat recovery.

[0028] To solve the above problems, refer to Figure 1 This embodiment provides a gas boiler flue gas desulfurization and deacidification and waste heat utilization system, wherein a dry absorbent injection device 2, a low-temperature economizer 3, a dust collector 4, an induced draft fan 5 and a chimney 6 as an emission device are sequentially arranged downstream of a gas boiler 1 along the flow direction of the flue gas discharged from the gas boiler;

[0029] The flue gas of 130-180°C in the gas boiler 1 enters the flue at the tail of the boiler. The dry absorbent injection device 2 is arranged upstream of the low-temperature economizer 3, i.e., in the flue at the tail of the boiler, and the dry absorbent is sprayed into the flue by means of compressed air pneumatic conveying to mix evenly with the flue gas and fully contact the flue. The dry absorbent reacts with acid gases such as SO3 and HCl in the flue gas to remove acid. After the acid gas is removed, the flue gas enters the low-temperature economizer 3 for waste heat recovery. The low-temperature economizer 3 is connected to the waste heat utilization equipment to supply the recovered waste heat to the waste heat utilization equipment for utilization.

[0030] The flue gas temperature after waste heat recovery from the low-temperature economizer 3 is reduced to less than or equal to 90°C, and the remaining dry absorbent that does not participate in the deacidification reaction further reacts with SO2 in the flue gas for desulfurization. The flue gas after SO2 removal enters the dust collector 4 for dust removal. The inlet of the dust collector 4 is connected to a vertical flue, and the low-temperature economizer 3 is arranged in the vertical flue. The clean flue gas is finally discharged into the atmosphere through the chimney 6 through the action of the induced draft fan 5.

[0031] In this embodiment, the dry absorbent uses slaked lime, so that the acidic gas and sulfide in the flue gas react with the calcium hydroxide of the slaked lime, thereby effectively removing the acidic gas, and can also efficiently remove SO2 at low temperature after waste heat utilization. In order to allow the dry absorbent to fully react with the gas, in this embodiment, the particle size of the dry absorbent is 2-10 microns, and the specific surface area of ​​the dry absorbent is greater than or equal to 38m 2 / g, the pore volume of the dry absorbent is greater than or equal to 0.2cm 3 / g.

[0032] In this embodiment, a dry absorbent injection device 2 is provided in the tail gas flue of the gas boiler 1 upstream of the low-temperature economizer 3 to spray dry absorbent to remove acidic gases. While the acidic gases are removed, the acid dew point of the flue gas is also reduced. Therefore, when the flue gas temperature drops below 90°C after waste heat recovery, it is still higher than the acid dew point of the flue gas, thereby preventing the condensation of acidic substances and causing corrosion to the low-temperature economizer at the rear end. At the same time, due to the use of dry absorbent, compared with liquid absorbent, the heat recovered from the waste heat of the low-temperature economizer 3 will not be lost due to the decrease in flue gas temperature caused by the evaporation of the absorbent. While achieving flue gas treatment, the risk of corrosion of the low-temperature economizer 3 is reduced.

[0033] Therefore, the low-temperature economizer 3 in this embodiment can be made of common corrosion-resistant steel, such as ND steel or carbon steel, instead of 2205 duplex stainless steel or higher corrosion-resistant materials, thereby reducing the cost of the device, saving costs and improving economic benefits.

[0034] In order to recycle the heat recovered from the waste heat of the low-temperature economizer 3, this embodiment also includes a waste heat utilization device, which includes a condensate pump 10, a low-pressure heater 9, a high-pressure heater 8, and a deaerator 7. The condensate at the outlet of the condensate pump 10 is 50-60°C, and after being heated by the low-pressure heater 9 and the high-pressure heater 8, it is sent to the deaerator 7. The low-pressure heater 9 and the high-pressure heater 8 need to extract steam to heat the condensate of the condensate pump 10. In this embodiment, the low-temperature economizer 3 is connected to the low-pressure heater 9 through a pipeline, and the waste heat recovered by the low-temperature economizer 3 is used to heat the condensate, thereby reducing the steam extraction amount of the low-pressure heater 9, so that this part of the steam continues to work in the steam turbine, increasing the power generation of the unit.

[0035] The gas boiler flue gas desulfurization, deacidification and waste heat utilization system of this embodiment organically combines flue gas desulfurization, deacidification and deep waste heat utilization, and adopts a high-efficiency dry absorbent. The dry absorbent injection device 2 provided in the tail gas flue of the gas boiler is sprayed into the flue gas in front of the low-temperature economizer 3 to remove the acidic gas in the flue gas, thereby greatly reducing the concentration of SO3 in the flue gas and the acid dew point of the flue gas, so that the risk of the low-temperature economizer 3 being corroded by the condensed acidic gas after the waste heat recovery is greatly reduced. The low-temperature economizer 3 can be made of ordinary anti-corrosion ND steel or carbon steel, and the cost is greatly reduced, which effectively shortens the recovery period. At the same time, the dry absorbent will not evaporate and cause the flue gas temperature to drop, and the heat of waste heat recovery will be lost, so the efficiency of waste heat recovery can be maintained and the economic benefits can be improved. And the cooling of the low-temperature economizer helps to improve the efficiency of the dry absorbent in removing acidic gases.

[0036] Furthermore, through the waste heat utilization equipment, the waste heat is absorbed and used to heat the condensed water, reducing the steam extraction amount of the low-pressure heater 9 and increasing the power generation of the unit. After the waste heat is recovered by the low-temperature economizer 3, the flue gas temperature is reduced by 40-100°C, and the rear-end flue gas volume is reduced by at least 10%, so a smaller dust collector 4 can be used, and the investment cost of the dust collector 4 can also be effectively reduced.

[0037] Taking a 300t / h high-temperature and high-pressure blast furnace gas boiler as an example, the flue gas temperature at the boiler outlet is 135°C. After the flue gas desulfurization, deacidification and waste heat utilization system of the gas boiler in this embodiment, the flue gas temperature is reduced to 90°C. Waste heat recovery can reduce the steam extraction of the steam turbine by about 20t / h, and the power generation on the steam turbine side is increased by about 1900kw, with significant economic benefits. At the same time, the working flue gas volume is reduced by 11%, so the size of the dust collector can be reduced by 11%.

Claims

1. A gas boiler flue gas desulfurization and deacidification and waste heat utilization system, wherein a low-temperature economizer and an emission device are sequentially arranged along the flow direction of the flue gas discharged from the gas boiler, characterized in that: It also includes a dry absorbent injection device, which is arranged upstream of the low-temperature economizer along the flue gas flow direction and injects the dry absorbent into the flue to react with the acid gas; The flue gas from which the acidic gas has been removed enters the low-temperature economizer for waste heat recovery, and the flue gas from which the waste heat has been recovered is discharged from the emission device.

2. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 1 is characterized in that: The utility model also comprises a dust collector, wherein the dust collector is arranged downstream of the low-temperature economizer.

3. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 1, characterized in that: It also includes an induced draft fan, which is arranged downstream of the dust collector.

4. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 1, characterized in that: The low-temperature economizer is connected to a waste heat utilization device to supply the recovered waste heat to the waste heat utilization device.

5. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 4, characterized in that: The waste heat utilization equipment includes a condensate pump, a heater, and a deaerator. The heater extracts steam to heat the condensate of the condensate pump. The low-temperature economizer is connected to the heater of the waste heat utilization equipment through a pipeline, and the waste heat recovered by the low-temperature economizer is used to heat the condensate.

6. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 5, characterized in that: The heater is divided into a low-pressure heater and a high-pressure heater. The condensate is heated by the low-pressure heater and then heated again by the high-pressure heater. The low-pressure heater is connected to the low-temperature economizer to utilize the waste heat.

7. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 1, characterized in that: The particle size of the dry absorbent is 2-10 microns.

8. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 1, characterized in that: The specific surface area of ​​the dry absorbent is greater than or equal to 38m 2 / g.

9. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 1, characterized in that: The pore volume of the dry absorbent is greater than or equal to 0.2 cm 3 / g.

10. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to claim 2, characterized in that: The dust collector inlet is connected to a vertical flue, and the low-temperature economizer is arranged in the vertical flue.

11. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to any one of claims 1 to 10, characterized in that: The dry absorbent is slaked lime.

12. The gas boiler flue gas desulfurization, deacidification and waste heat utilization system according to any one of claims 1 to 10, characterized in that: The low-temperature economizer is made of ND steel or carbon steel.

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