System for preparing high-temperature steam by utilizing boiler flue gas and using method thereof

Abstract

The invention discloses a system for preparing high-temperature steam by using boiler flue gas and a using method thereof.The system comprises a flue gas boiler, high-temperature flue gas is introduced into the flue gas boiler through a pipeline, a gas outlet of the flue gas boiler is connected with a gas inlet of a desulfurization and denitrification device, and the desulfurization and denitrification device is connected with a dust removal device; the tail end of the dust removal device is connected with the heat collecting device, an inlet and an outlet of the high-temperature heat pump are connected with the heat collecting device and the flash tank respectively, and the flash tank is connected with the steam compressor through a pipeline. The flue gas boiler is used for recovering heat of high-temperature flue gas to generate high-temperature steam, the heat collecting device is used for collecting heat of low-temperature flue gas, the high-temperature heat pump is used for extracting the collected heat to generate high-temperature hot water, flash evaporation steam is heated and pressurized through flash evaporation and the steam compressor, the enthalpy value and the steam grade of the steam are improved, and the energy consumption is reduced. The flue gas heat which is wasted originally is fully recycled, and the energy utilization rate is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of boiler flue gas utilization technology, and in particular to a system for producing high-temperature steam using boiler flue gas and a method of using the same. BACKGROUND

[0002] The flue gas generated by the fuel combustion of a factory boiler is generally directly discharged into the atmosphere after dust removal and desulfurization and denitrification. In some cases, the flue gas waste heat is recovered, and an ORC power generation device is used to generate power, or a coal economizer is used to preheat boiler feed water, or a waste heat boiler is used to recover heat from high-temperature flue gas to produce steam for use in other process sections.

[0003] The prior art directly discharges the treated boiler flue gas into the atmosphere, which results in a large amount of heat loss due to the large amount and high temperature of the flue gas, and is not conducive to green industrial production. The method of using an ORC power generation device to generate power can only be used in cases where the flue gas temperature is high, and has the problems of low waste heat recovery efficiency, low power generation efficiency, and long investment recovery period. The method of using a coal economizer to preheat boiler feed water has low energy grade of the recovered energy, and has the contradiction between high flue gas discharge temperature and low-temperature corrosion, resulting in low waste heat recovery efficiency. The method of using a waste heat boiler to recover heat from high-temperature flue gas to produce steam for use in other process sections is only suitable for high-temperature flue gas applications, and the end flue gas temperature is still high, resulting in large heat loss and low recovery efficiency.

[0004] Therefore, a system for producing high-temperature steam using boiler flue gas and a method of using the same are provided to solve the problems of the prior art. SUMMARY

[0005] The present application aims to provide a system for producing high-temperature steam using boiler flue gas and a method of using the same, which recovers the heat of high-temperature flue gas from a flue gas boiler to produce high-temperature steam, collects the heat of low-temperature flue gas using a heat collection device, and generates high-temperature hot water by extracting the collected heat using a high-temperature heat pump, increases the enthalpy and grade of the steam by flashing and using a steam compressor to increase the temperature and pressure of the flashed steam, fully recovers and utilizes the originally wasted flue gas heat, and further improves the energy utilization rate. To achieve the above-mentioned application purposes, the technical solutions adopted by the present application are as follows:

[0006] According to one aspect of the present application, a system for producing high-temperature steam using boiler flue gas is provided, comprising a flue gas boiler, a desulfurization and denitrification device, a dust removal device, a heat collection device, a high-temperature heat pump, a flash tank, and a steam compressor. High-temperature flue gas is introduced into the flue gas boiler through a pipeline. The gas outlet of the flue gas boiler is connected to the gas inlet of the desulfurization and denitrification device, and the desulfurization and denitrification device is connected to the dust removal device. The distal end of the dust removal device is connected to the heat collection device. The inlet and outlet of the high-temperature heat pump are connected to the heat collection device and the flash tank, respectively, and the flash tank is connected to the steam compressor through a pipeline.

[0007] Preferably, a water pump set is provided between the high-temperature heat pump and the flash tank.

[0008] Preferably, a shock wave soot blowing device is provided in the flue gas boiler to blow off the accumulated soot inside the flue gas boiler.

[0009] Preferably, a gas-water separation device is provided at the steam output position in the flash tank.

[0010] Preferably, the desulfurization and denitrification device and the dust removal device can be exchanged in position according to requirements.

[0011] A method for producing high-temperature steam using boiler flue gas is provided, comprising the following steps:

[0012] S1. High-temperature flue gas discharged from a boiler is introduced into a flue gas boiler through a pipeline. Low-temperature softened water entering the flue gas boiler is heated to generate high-temperature steam a. The generated high-temperature steam a is introduced into other process sections through a steam pipeline.

[0013] S2. After the high-temperature flue gas exchanges heat with the low-temperature softened water in the flue gas boiler, the temperature of the flue gas decreases, and the flue gas becomes sub-high-temperature flue gas. After passing through a desulfurization and denitrification device and a dust removal device, the flue gas enters a heat collection device. In the heat collection device, the flue gas exchanges heat with heat source water, and the temperature of the flue gas decreases to become low-temperature flue gas that does not condense, and the low-temperature flue gas is discharged through a chimney.

[0014] S3. Heat source water absorbs heat from the flue gas in the heat collection device and then enters a high-temperature heat pump. The high-temperature heat pump heats mixed softened water to form high-temperature hot water, which then enters a flash tank. The high-temperature hot water is flashed in the flash tank to generate micro-positive-pressure steam, which is introduced into a steam compressor through a pipeline. The steam compressor increases the temperature and pressure of the micro-positive-pressure steam generated by flashing to generate high-temperature steam b, which is then introduced into other process sections through a steam pipeline.

[0015] S4. The flash-condensed water inside the flash tank and the low-temperature softened water outside are transported to the inside of the high-temperature heat pump through a water pump set.

[0016] Preferably, in S1 and S2, the high-temperature flue gas discharged from the boiler is recovered, and the total heat energy Q Z (kWh) of the recovered flue gas can be calculated by the formula:

[0017]

[0018] Q1(kJ / h) is the heat exchange amount of high-temperature flue gas and low-temperature softened water, and its formula is

[0019] Q1=1000M1(H2-H1)

[0020] In the formula,

[0021] M1 is the flow of low-temperature softened water (t / h);

[0022] H1 is the specific enthalpy of low-temperature softened water entering the flue gas boiler for heat exchange (kJ / kg);

[0023] H2 is the specific enthalpy of high-temperature steam a (kJ / kg);

[0024] Q2(kJ / h) is the heat utilized by the high-temperature heat pump after the flue gas passes through the heat collection device and is exchanged, and its formula is

[0025] Q2=1000M0C3η1(T4-T5)

[0026] In the formula,

[0027] M0 is the mass flow of flue gas after desulfurization, denitration and dust removal;

[0028] C3 is the specific heat capacity of flue gas after desulfurization, denitration and dust removal (kJ / (kg·℃));

[0029] η1 is the efficiency of the final heat exchange of the dust-removed flue gas to the high-temperature heat pump;

[0030] T4 is the temperature of the dust-removed flue gas (℃);

[0031] T5 is the non-dew flue gas temperature (℃).

[0032] Preferably, in S3 and S4, the temperature and mass of the mixed softened water, the flash condensate water and the low-temperature softened water before and after the water pump set 8 meet the following relationship, which is adjusted according to specific parameters:

[0033] M4T8=M3T6+M2T7

[0034] In the formula,

[0035] M2 is the flow of low-temperature softened water entering the water pump set 8 (t / h);

[0036] M3 is the flow of flash condensate water (t / h);

[0037] M4 is the flow of mixed softened water (t / h);

[0038] T6 - flash condensate water and micro-positive pressure steam temperature (°C) ;

[0039] T7 - low temperature softened water temperature of water inlet pump group 8 (°C) ;

[0040] T8 - mixed softened water temperature (°C) ;

[0041] T9 (°C) is the high temperature hot water temperature into the flash tank, which is calculated by the following formula:

[0042]

[0043] wherein:

[0044] Q3 - heat quantity of high temperature heat pump transferred to mixed softened water (kJ / h) ;

[0045] C1 - specific heat capacity of low temperature softened water (kJ / (kg.°C)) ;

[0046] And the heat quantity Q3 (kJ / h) of high temperature heat pump transferred to mixed softened water can be calculated by the following formula:

[0047] Q3 = 3600P a5 η3

[0048] wherein:

[0049] P a5 - high temperature heat pump power (kW) ;

[0050] η3 - COP of high temperature heat pump.

[0051] Preferably, in S3, the distribution of materials and heat in the flash tank can be calculated by the following formula:

[0052] M4 = M5 + M3

[0053] M4H3 = M5H5 + M3H4

[0054] wherein:

[0055] M5 - flow rate of micro-positive pressure steam and steam inlet compressor (t / h) ;

[0056] H3 - specific enthalpy of high temperature hot water (kJ / kg) ;

[0057] H4 - specific enthalpy of flash condensate water (kJ / kg) ;

[0058] H5 - specific enthalpy of micro-positive pressure steam (kJ / kg).

[0059] Preferably, in S3, the steam compressor shaft power P a7 (kW) can be calculated by the following formula:

[0060]

[0061] In the formula:

[0062] P3 - flash tank flash and micro-positive pressure steam and steam compressor inlet pressure (kPa) ;

[0063] P4 - steam compressor outlet pressure (kPa) ;

[0064] η2 - polytropic efficiency of the steam compressor.

[0065] In summary, due to the adoption of the technical scheme, the beneficial effects of the present application are:

[0066] 1. The system and method for producing high-temperature steam using boiler flue gas, which recovers heat from high-temperature flue gas of a flue gas boiler to produce high-temperature steam, collects heat from low-temperature flue gas using a heat collection device, extracts the collected heat using a high-temperature heat pump to generate high-temperature hot water, and increases the enthalpy and grade of the steam by flashing and using a steam compressor to increase the temperature and pressure of the flashed steam, thereby fully recovering and utilizing the originally wasted flue gas heat and further improving energy utilization efficiency.

[0067] 2. The system and method for producing high-temperature steam using boiler flue gas, which discharges flue gas through a chimney at a temperature close to the dew point of the flue gas, thereby fully recovering and utilizing the originally wasted flue gas heat and further improving energy utilization efficiency.

[0068] 3. The system and method for producing high-temperature steam using boiler flue gas, which can simultaneously recover heat from both high-temperature flue gas and low-temperature flue gas, greatly improving the efficiency of flue gas heat recovery and producing high-grade steam heat energy for use in other process sections. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 is a flowchart of the present application;

[0070] In the drawings, 1 is a flue gas boiler, 2 is a desulfurization and denitrification device, 3 is a dust removal device, 4 is a heat collection device, 5 is a high-temperature heat pump, 6 is a flash tank, 7 is a steam compressor, and 8 is a water pump set. DETAILED DESCRIPTION

[0071] To make the purpose, technical scheme and advantages of the present application clearer and more apparent, the following preferred embodiments are described in detail with reference to the drawings. However, it should be noted that many details in the description are only intended to make the reader have a thorough understanding of one or more aspects of the present application, and the aspects of the present application can be realized even without these specific details.

[0072] Please refer toFigure 1 The application provides a system for preparing high-temperature steam by using boiler flue gas and a use method thereof.

[0073] The system comprises a flue gas boiler 1, a desulfurization and denitration device 2, a dust removal device 3, a heat collection device 4, a high-temperature heat pump 5, a flash tank 6 and a steam compressor 7. High-temperature flue gas is introduced into the flue gas boiler 1 through a pipeline. The gas outlet of the flue gas boiler 1 is connected with the gas inlet of the desulfurization and denitration device, and the desulfurization and denitration device is connected with the dust removal device 3. The tail end of the dust removal device 3 is connected with the heat collection device 4. The inlet and outlet of the high-temperature heat pump 5 are connected with the heat collection device 4 and the flash tank 6 respectively, and the flash tank 6 is connected with the steam compressor 7 through a pipeline. A water pump group 8 is arranged between the high-temperature heat pump 5 and the flash tank 6. A shock wave soot blowing device is arranged in the flue gas boiler 1 to blow off the accumulated ash in the flue gas boiler 1. A gas-water separation device is arranged at the steam output position in the flash tank 6. The desulfurization and denitration device 2 and the dust removal device 3 can be exchanged according to requirements.

[0074] Working process: The high-temperature flue gas discharged from a boiler is introduced into the flue gas boiler 1 through a pipeline. The low-temperature softened water entering the flue gas boiler 1 is heated to generate high-temperature steam a. The generated high-temperature steam a is introduced into other process sections through a steam pipeline. After heat exchange with the low-temperature softened water, the high-temperature flue gas is cooled and becomes secondary high-temperature flue gas. After passing through the desulfurization and denitration device 2 and the dust removal device 3, the secondary high-temperature flue gas enters the heat collection device 4. In the heat collection device 4, the flue gas after desulfurization, denitration and dust removal is heat-exchanged with heat source water, and then is cooled and becomes non-condensation low-temperature flue gas which is discharged through a chimney. The heat source water is heated by the heat collection device 4 and then enters the high-temperature heat pump 5. The mixed softened water is heated by the high-temperature heat pump 5 to form high-temperature hot water which enters the flash tank 6. The high-temperature hot water is flashed in the flash tank 6 to generate micro-positive-pressure steam which is introduced into the steam compressor 7 through a pipeline. The micro-positive-pressure steam is heated and pressurized to generate high-temperature steam b which is introduced into other process sections through a steam pipeline. The temperature of the above-mentioned non-condensation low-temperature flue gas discharged through the chimney is only about 3-5 ℃ higher than the dew point of the flue gas, so that the flue gas heat can be fully recovered and utilized, and the flue gas condensation and corrosion of the chimney can be prevented.

[0075]

[0076] The high-temperature flue gas and the low-temperature softened water heat exchange quantity Q1 (kJ / h) can be obtained by the following formula:

[0077] Q1 = 1000M1 (H2-H1)

[0078] The flue gas heat Q2 (kJ / h) utilized by the high-temperature heat pump after heat exchange through the heat collection device can be obtained by the following formula:

[0079] Q2 = 1000 M03 η1 (T4 - T5)

[0080] The temperature and mass of the mixed softened water, flash condensate water and low temperature softened water before and after the water pump group 8 satisfy the following relationships:

[0081] M4T8 = M3T6 + M2T7

[0082] For the adjustment according to specific parameters; the high temperature hot water temperature T9 (°C) entering the flash tank can be obtained by the following formula:

[0083]

[0084] Q3 = 3600P a5 η3

[0085] The distribution of materials and heat in the flash tank can be obtained by the following formula:

[0086] M4 = M5 + M3

[0087] M4H3 = M5H5 + M3H4

[0088] The shaft power of the steam compressor 7 can be obtained by the following relationship P a7 (kW)

[0089]

[0090]

[0091] The saturated steam at the outlet of the steam compressor is obtained by spraying condensate water, and the water spraying amount M6 (t / h) can be obtained by the following formula:

[0092]

[0093] The total amount of saturated steam generated by the steam compressor is M7 (t / h) which can be obtained by the following formula:

[0094] M7 = M5 + M6

[0095] Among them, C1 is the specific heat capacity of low-temperature softened water (kJ / (kg.℃)), C2 is the specific heat capacity of high-temperature flue gas (kJ / (kg.℃)), C3 is the specific heat capacity of flue gas after desulfurization, denitrification and dust removal (kJ / (kg.℃)), T0 is the high-temperature flue gas temperature (℃), T1 is the temperature of low-temperature softened water for heat exchange entering the flue gas boiler 1 (℃), T2 is the temperature of high-temperature steam a (℃), high-temperature steam a is saturated steam, and its pressure P1 (kPa) corresponds to temperature T2, T3 is the sub-high-temperature flue gas temperature (℃), T4 is the flue gas temperature after dust removal (℃), T5 is the non-condensing flue gas temperature (℃), T6 is the temperature of flash condensed water and slightly positive pressure steam (℃), T7 is the low-temperature softened water temperature of the water inlet pump group 8 (℃) (T7=T1), T8 is the mixed softened water temperature (℃), T9 is the high-temperature hot water temperature (℃), T 10 is the superheated steam temperature at the outlet of the steam compressor 7 (°C), P2 is the flue gas pressure after dust removal, corresponding to the flue gas dew point (kPa), P3 is the flash tank flash and slightly positive pressure steam and the steam compressor 7 inlet pressure (kPa), P4 is the steam compressor outlet pressure (kPa), η1 is the efficiency of the flue gas heat after dust removal and the final heat exchange to the high-temperature heat pump, η2 is the variable efficiency of the steam compressor 7, η3 is the high-temperature heat pump COP, H1 is the specific enthalpy of low-temperature softened water for heat exchange in the flue gas boiler (kJ / kg), H2 is the specific enthalpy of high-temperature steam a (kJ / kg), H3 is the specific enthalpy of high-temperature hot water (kJ / kg), H4 is the specific enthalpy of flash condensed water (kJ / kg), H5 is the specific enthalpy of slightly positive pressure steam (kJ / kg), and H6 is the specific enthalpy of superheated steam at the steam compressor outlet (kJ / kg) , H7 is the specific enthalpy of saturated steam (high-temperature steam b) corresponding to the outlet pressure (kJ / kg), H8 is the specific enthalpy of make-up water (kJ / kg), M1 is the low-temperature softened water flow rate (t / h), M2 is the low-temperature softened water flow rate of the water inlet pump group 8 (t / h), M3 is the flash condensed water flow rate (t / h), M4 is the mixed softened water flow rate (t / h), M5 is the slightly positive pressure steam and the flow rate of the steam compressor 7 (t / h), M6 is the make-up water amount (t / h), M7 is the total saturated steam flow rate generated by the steam compressor (t / h), Q1 is the heat exchange amount between high-temperature flue gas and low-temperature softened water (kJ / h), Q2 is the heat that the flue gas uses after heat exchange by the high-temperature heat pump after passing through the heat collection device (kJ / h), Q3 is the heat transferred to the mixed softened water by the high-temperature heat pump (kJ / h), P a5 is the high temperature heat pump power (kW), P a7 is the steam compressor shaft power (kW).

[0096] The specific heat capacity C2 of high-temperature flue gas, the specific heat capacity C3 of flue gas after desulfurization, denitrification and dust removal, the flue gas temperature T5 after desulfurization, denitrification and dust removal (3-5℃ higher than the dew point temperature), the heat exchanger parameters and the heat pump performance parameters are all known quantities. The various parameters are adjusted according to the material balance and energy balance of the entire system.

[0097] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A system for producing high temperature steam using boiler flue gas, characterized by, It comprises a flue gas boiler, a desulfurization and denitration device, a dust removal device, a heat collection device, a high-temperature heat pump, a flash tank and a steam compressor, the high-temperature flue gas is introduced into the flue gas boiler through a pipeline, the gas outlet of the flue gas boiler is connected with the gas inlet of the desulfurization and denitration device, the desulfurization and denitration device is connected with the dust removal device, the tail end of the dust removal device is connected with the heat collection device, the inlet and outlet of the high-temperature heat pump are connected with the heat collection device and the flash tank respectively, and the flash tank is connected with the steam compressor through a pipeline. A water pump group is arranged between the high-temperature heat pump and the flash tank.

2. The system for producing high-temperature steam using boiler flue gas according to claim 1, characterized in that: A shock wave soot blowing device is arranged in the flue gas boiler to blow off the accumulated ash in the interior of the flue gas boiler.

3. The system for producing high-temperature steam using boiler flue gas according to claim 1, characterized in that: A gas-water separation device is arranged at the steam output position in the flash tank.

4. The system for producing high-temperature steam using boiler flue gas according to claim 1, characterized in that: The desulfurization and denitration device and the dust removal device can be exchanged according to requirements.

5. The system for producing high-temperature steam using boiler flue gas according to claim 1, characterized in that: It comprises the following steps:

6. The use of claim 1-5, wherein the method is characterized in that, S1, the high-temperature flue gas discharged from a boiler is introduced into a flue gas boiler through a pipeline, low-temperature softened water entering the flue gas boiler is heated to generate high-temperature steam a, and the generated high-temperature steam a is introduced into other process sections through a steam pipeline; S2, after the high-temperature flue gas exchanges heat with the low-temperature softened water in the flue gas boiler, the temperature of the high-temperature flue gas is reduced to become secondary high-temperature flue gas, the secondary high-temperature flue gas enters a heat collection device after passing through a desulfurization and denitration device and a dust removal device, in the heat collection device, the flue gas after desulfurization and denitration and dust removal exchanges heat with heat source water to reduce the temperature and become low-temperature flue gas without dewing, and then is discharged through a chimney; S3, the heat source water absorbs the heat of the flue gas in the heat collection device, enters a high-temperature heat pump, heats mixed softened water in the high-temperature heat pump, forms high-temperature hot water, and then enters a flash tank, the high-temperature hot water is flashed in the flash tank to generate micro-positive pressure steam, the micro-positive pressure steam is introduced into a steam compressor through a pipeline, the micro-positive pressure steam is heated and pressurized to generate high-temperature steam b, and then is introduced into other process sections through a steam pipeline; S4, the flash condensate water in the flash tank and the low-temperature softened water outside are transported into the high-temperature heat pump through a water pump group. It is obtained that Q1 (kJ / h) is the heat exchange amount of the high-temperature flue gas and the low-temperature softened water, and the formula is Q1 = 1000M1 (H2-H1) 7. The method of using a boiler flue gas to produce high temperature steam of claim 6, wherein: In S1 and S2, the high-temperature flue gas discharged by the boiler is recovered, and the total heat energy Q of the recovered flue gas z (kWh) can be calculated by the formula: In the formula, M1 is the low-temperature softened water flow (t / h); H1 is the specific enthalpy of the low-temperature softened water entering the flue gas boiler (kJ / kg); H2 is the specific enthalpy of the high-temperature steam a (kJ / kg); Q2 (kJ / h) is the heat utilized by the high-temperature heat pump after the flue gas exchanges heat in the heat collection device, and the formula is Q2 = 1000M0C3η1 (T4-T5) In the formula, M0 is the mass flow of the flue gas after desulfurization and denitration and dust removal; C3 is the specific heat capacity of the flue gas after desulfurization and denitration and dust removal (kJ / (kg.℃)); η1 is the efficiency of the final heat exchange of the flue gas after dust removal to the high-temperature heat pump; T4 is the temperature of the flue gas after dust removal (℃); T5 is the temperature of the flue gas without dewing (℃). In S3 and S4, the temperature and mass of the mixed softened water, the flash condensate water and the low-temperature softened water before and after the water pump group meet the following relationship, and are adjusted according to specific parameters:

8. The method of using a boiler flue gas to produce high temperature steam of claim 6, wherein: M4T8 = M3T6 + M2T7 In the formula, M2 is the low-temperature softened water flow entering the water pump group (t / h); ​ M3 - the flow of flash condensate (t / h); M4 - the flow of mixed softened water (t / h); T6 - the temperature of flash condensate and micro-positive pressure steam (℃); T7 - the temperature of low-temperature softened water for the water pump set (℃); T8 - the temperature of mixed softened water (℃); T9 (℃) is the temperature of high-temperature hot water into the flash tank, which is calculated by the following formula: wherein: Q3 - the heat of high-temperature hot water transferred to mixed softened water (kJ / h); C1 - the specific heat capacity of low-temperature softened water (kJ / (kg.℃)); and the heat of high-temperature hot water transferred to mixed softened water Q3 (kJ / h) is calculated by the following formula: Q3 = 3600P a5 η3 wherein: P a5 - High temperature heat pump power (kW); η3 - the COP of high-temperature hot water pump.

9. The method of using a boiler flue gas to produce high temperature steam of claim 6, wherein: In S3, the distribution of materials and heat in the flash tank is calculated by the following formula: M4 = M5 + M3 M4h3 = M5H5 + M3H4 wherein: M5 - the flow of micro-positive pressure steam and steam compressor (t / h); H3 - the specific enthalpy of high-temperature hot water (kJ / kg); H4 - the specific enthalpy of flash condensate (kJ / kg); H5 - the specific enthalpy of micro-positive pressure steam (kJ / kg).

10. The method of using a boiler flue gas to produce high temperature steam of claim 6, wherein: In S3, the shaft power P of the vapor compressor a7 (kW) can be derived by the following equation: wherein: P3 - the pressure of flash tank flash and micro-positive pressure steam and steam compressor inlet (kPa); P4 - the pressure of steam compressor outlet (kPa); η2 - the polytropic efficiency of steam compressor.

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