Phosphorus burning tower waste heat gradient utilization equipment with plate heat exchanger and hot water tank coupled

Abstract

The invention discloses a plate heat exchanger and hot water tank coupled phosphorus burning tower waste heat gradient utilization device which comprises a phosphorus burning tower body, a first-stage waste heat recovery unit, a second-stage waste heat recovery unit, a flue gas passage pipe and a control unit, and the phosphorus burning tower body is communicated with the first-stage waste heat recovery unit through the flue gas passage pipe; and the first-stage waste heat recovery unit is communicated with the second-stage waste heat recovery unit. The system has the beneficial effects that the waste heat utilization rate is high, the waste heat recovery rate is greatly increased through a cascade mode of first-stage high-temperature steam production and second-stage medium-temperature heat storage, and a three-stage dust removal structure of primary filtration through a first filter screen, sedimentation through a smoke dust collecting hopper and fine filtration through a second filter screen is adopted; temperature and smoke dust concentration parameters are monitored in real time, a control unit automatically adjusts flow and valves, an alarm is given when abnormity occurs, the manual inspection frequency is reduced, the size of a heat exchange box and the number of heat exchange water collecting pipes can be adjusted according to the phosphorus burning amount, the device is suitable for phosphorus chemical production lines of different scales, the transformation difficulty is low, and the cost recovery period is short.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phosphorus chemical industry energy-saving and environment-friendly equipment, in particular to a phosphorus combustion tower waste heat cascade utilization equipment coupled with a plate heat exchanger and a hot water tank. BACKGROUND

[0002] In the phosphorus chemical industry, the phosphorus combustion tower is the core equipment for producing phosphoric acid, phosphate and other products. During the combustion of phosphorus, high-temperature flue gas with a temperature of 800-1200°C is generated. The flue gas not only carries a large amount of waste heat (about 40%-60% of the total heat of combustion), but also contains harmful smoke such as phosphorus compounds and dust.

[0003] In the prior art, there are three major problems in the waste heat recovery of the phosphorus combustion tower:

[0004] 1. Low waste heat utilization rate: Most devices use single-stage heat exchange structure, which can only recover high-temperature section waste heat (such as flue gas with a temperature of >600°C), and the medium and low-temperature section waste heat (300-600°C) is directly discharged with the flue gas, causing energy waste; and the cascade utilization mode of "high-temperature steam generation and medium-temperature heating" is not formed, resulting in poor energy matching.

[0005] 2. Incomplete smoke treatment: The traditional equipment only sets a single-stage filter screen at the end of the exhaust gas, which cannot effectively intercept smoke dust of different particle sizes (especially PM2.5 grade phosphorus compound particles) in the flue gas, which easily leads to emission exceeding the standard and pollutes the environment.

[0006] 3. Running monitoring lag: There is no real-time monitoring of the temperature and smoke concentration during the heat exchange process, and the circulating pump, valve and other components are adjusted by manual inspection, which easily causes equipment failure due to abnormal parameters (such as local overheating and smoke blocking the filter screen), affecting the production stability.

[0007] Therefore, it is necessary to provide a phosphorus combustion tower waste heat cascade utilization equipment coupled with a plate heat exchanger and a hot water tank to solve the above technical problems. SUMMARY

[0008] The purpose of the present application is to provide a phosphorus combustion tower waste heat cascade utilization equipment coupled with a plate heat exchanger and a hot water tank.

[0009] To achieve the above purpose, the present application provides the following technical scheme:

[0010] A phosphorus combustion tower waste heat cascade utilization equipment coupled with a plate heat exchanger and a hot water tank, comprising a phosphorus combustion tower body, a first waste heat recovery unit, a second waste heat recovery unit, a flue gas passage pipe and a control unit, the phosphorus combustion tower body is communicated with the first waste heat recovery unit through the flue gas passage pipe, and the first waste heat recovery unit is communicated with the second waste heat recovery unit.

[0011] The tower wall of the phosphorus combustion tower body is provided with a cavity layer, the cavity layer is injected with circulating cooling liquid, and the cavity layer is connected to a circulating cooling tank through a first circulating pump.

[0012] The primary waste heat recovery unit comprises a first heat exchange tank, a gas pocket and a dust collecting hopper, the gas pocket is arranged at the upper part of the heat exchange tank, the gas pocket is communicated with the heat exchange tank through a gas pipe, the bottom of the heat exchange tank is provided with a plurality of dust collecting hoppers, and the first heat exchange tank is provided with a first heat exchange water collecting pipe.

[0013] The secondary waste heat recovery unit comprises a base plate, a second heat exchange tank, a water collecting tank and a second heat exchange water collecting pipe, the second heat exchange tank and the water collecting tank are mounted on the base plate, the second heat exchange water collecting pipe is arranged in the second heat exchange tank, the outlet of the second heat exchange water collecting pipe is communicated with the water collecting tank, the side of the second heat exchange tank is provided with an air inlet pipe and an air outlet pipe, the air inlet pipe is communicated with the air outlet of the first heat exchange tank, and the air outlet pipe is provided with a second filter screen.

[0014] The water collecting tank is provided with a flow equalizing plate and a water filter screen.

[0015] The gas passage pipe is provided with a second circulating pump and a first control valve, and the air inlet pipe is provided with a third circulating pump and a second control valve.

[0016] The first heat exchange tank is provided with a first temperature sensor and a first dust sensor, the second heat exchange tank is provided with a second temperature sensor and a second dust sensor, and the first circulating pump, the second circulating pump, the third circulating pump, the first temperature sensor, the second temperature sensor, the first dust sensor and the second dust sensor are electrically connected to a control unit.

[0017] The waste heat recovery heat transfer calculation of the phosphorus combustion tower body after combustion comprises theoretical combustion temperature calculation and flue gas emission temperature; the theoretical combustion temperature calculation formula is:

[0018] (1)

[0019] (2)

[0020] In the formula, T is the theoretical combustion temperature, is the heat release of phosphorus combustion, is the total mass of mixed flue gas, is the mass of phosphorus, is the heat of phosphorus combustion, is the average specific constant pressure heat capacity of flue gas, is the temperature of air entering the furnace;

[0021] ​The calculation formula of flue gas emission temperature is:

[0022] (3)

[0023] wherein is the heat flow rate; is the empirical coefficient or characteristic coefficient, is the indoor temperature; is the outdoor temperature; is the cubic non-linear effect of the indoor temperature; is the scaling item of the indoor and outdoor temperature difference, which is dimensionless or adjusted to a suitable order of magnitude; is the correction item of the indoor and outdoor temperature ratio, which is obtained by subtracting the empirical constant 1.18 from the temperature ratio, and A is the area;

[0024] Total heat release of mixed flue gas is

[0025] (4)

[0026] wherein is the flue gas emission temperature, is the total area of the combustion chamber, is the theoretical combustion temperature, is the corresponding specific constant pressure heat capacity of flue gas, is the total mass of mixed flue gas, is the flue gas emission temperature is the corresponding specific constant pressure heat capacity of flue gas, is a constant, which depends on the fuel type and the excess air coefficient, and is 2500 under the condition of the phosphorus tower according to experience.

[0027] wherein the heat exchange calculation steps of the first heat exchange header are:

[0028] S1, steam production D, heat released on the hot fluid side is:

[0029] (5)

[0030] is the mass flow rate of the gas, is the specific constant pressure heat capacity of the gas, represents the inlet temperature of the fluid, represents the outlet temperature of the fluid; according to the heat balance, the heat obtained by the cold side is: (6)

[0031] is the cooling heat flow rate; for saturated steam mass flow rate, for constant pressure saturated steam enthalpy, for feed water enthalpy, for specific constant pressure heat capacity of water, for outlet temperature of fluid, for saturated temperature; for latent heat of vaporization, steam production of heat pipe steam generator is, ;

[0032] S2, average temperature difference ,

[0033] (7), wherein maximum temperature difference is represented; minimum temperature difference is represented, natural logarithm function is represented;

[0034] S3, heat transfer coefficient, heat transfer mode of heat pipe flue gas side is mainly convective heat transfer, when flue gas transversely sweeps through light pipe bundle, heat transfer coefficient , , is constant, for cross-row pipe bundle C, 0.33 is taken, for straight-row pipe bundle C, 0.26 is taken, outer diameter of light pipe of heat pipe, thermal conductivity of flue gas at constant temperature, Reynolds number of flue gas side fluid, Prandtl number of flue gas,

[0035] S4, temperature of working medium in pipe ,

[0036] (8)

[0037] steam temperature of working medium in heat pipe, average temperature of hot fluid, cold fluid side heat pipe, heat transfer area of hot fluid side, cold fluid side; for heat transfer coefficient, cold side convective heat transfer coefficient is represented;

[0038] S5, pipe wall temperature, hot fluid side pipe wall temperature ,

[0039] (9)

[0040] cold fluid side pipe wall temperature ,

[0041] (10); wherein Tf is the bulk temperature of the hot fluid; h is the heat transfer coefficient, Tc is the bulk temperature of the cold fluid; hcc is the cold side convective heat transfer coefficient; Q is the heat transfer per unit area per unit time, R is the fouling resistance of the hot and cold fluids.

[0042] Wherein the first soot sensor and the second soot sensor both adopt a light scattering type algorithm, and a soot concentration calculation formula thereof is (11), C is a particle concentration, K is a calibration coefficient (obtained by calibrating a standard concentration gas when the sensor is shipped, and different K values correspond to different particle sizes (PM1.0 / PM2.5 / PM10)), V is the effective voltage output by the photodetector; Zero concentration voltage (baseline voltage when there is no particle, used to offset dark current and ambient light interference).

[0043] Compared with the prior art, the beneficial effects of the present application are:

[0044] 1. High waste heat utilization rate, through a cascade mode of primary high-temperature steam generation + secondary medium-temperature heat storage, covering the waste heat of the high-temperature section of 600-1000 DEG C and the medium-temperature section of 300-500 DEG C, the waste heat recovery rate is greatly improved, and the coal consumption is saved;

[0045] 2. Strong environmental protection, adopting a three-stage dust removal structure of first filter screen primary filtration + soot hopper settlement + second filter screen fine filtration, the soot emission concentration is ≤10 mg / m³;

[0046] 3. Stable and intelligent operation, real-time monitoring of temperature and soot concentration parameters, automatic adjustment of flow and valve by the control unit, alarm in abnormal condition, reduction of manual inspection frequency, and reduction of equipment failure rate by more than 60%;

[0047] 4. Wide adaptability, the heat exchange tank size and the number of heat exchange water collecting pipes can be adjusted according to the amount of phosphorus, which is suitable for different scales of phosphorus chemical production lines, has low transformation difficulty and short cost recovery period. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 It is a structural schematic diagram of the present application;

[0049] Figures 2 to 4 It is a structure diagram of a primary waste heat recovery unit of the present application;

[0050] Figure 5 It is an internal structure diagram of a primary waste heat recovery unit of the present application;

[0051] Figure 6The secondary waste heat recovery unit structure diagram of the present application;

[0052] Figure 7 The internal structure diagram of the secondary waste heat recovery unit of the present application;

[0053] Figure 8 The flow uniformizing plate structure diagram of the present application;

[0054] Figure 9 The control unit module block diagram of the present application;

[0055] Figure 10 The circulation ratio and circulation pump shaft power relationship diagram of the present application;

[0056] Figure 11 The trend diagram of the influence of the amount of phosphorus on the maximum combustion temperature of the present application;

[0057] Figure 12 The trend diagram of the influence of the amount of phosphorus on the flue gas emission temperature of the present application;

[0058] Figure 13 The trend diagram of the influence of the excess air coefficient on the flue gas emission temperature of the present application;

[0059] In the figure, the reference numerals are: 1, phosphorus combustion tower body; 2, primary waste heat recovery unit; 3, secondary waste heat recovery unit; 4, flue gas passage pipe; 5, control unit; 6, cavity layer; 7, first circulation pump; 8, circulation cooling box; 9, first heat exchange box; 10, gas pocket; 11, dust collecting hopper; 12, gas pipe; 13, first heat exchange water collecting pipe; 14, air inlet; 15, air outlet; 16, first filter screen; 17, base plate; 18, second heat exchange box; 19, water collecting box; 20, second heat exchange water collecting pipe; 21, air inlet pipe; 22, air outlet pipe; 23, second filter screen; 24, flow uniformizing plate; 25, water filter screen; 26, second circulation pump; 27, first control valve; 28, third circulation pump; 29, second control valve; 30, first temperature sensor; 31, first dust sensor; 32, second temperature sensor; 33, second dust sensor. DETAILED DESCRIPTION

[0060] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0061] As Figures 1 to 13As shown, a plate heat exchanger and hot water tank coupled with phosphorus tower waste heat cascade utilization equipment, including a phosphorus tower body 1, a first waste heat recovery unit 2, a second waste heat recovery unit 3, a flue gas passage pipe 4 and a control unit 5, the phosphorus tower body 1 is communicated with the first waste heat recovery unit 2 through the flue gas passage pipe 4, the first waste heat recovery unit 2 is communicated with the second waste heat recovery unit 3.

[0062] The tower wall of the phosphorus tower body 1 is provided with a cavity layer 6, the cavity layer 6 is injected with circulating cooling liquid, and the cavity layer 6 is circumscribed by a first circulating pump 7 connected to a circulating cooling tank 8.

[0063] The first waste heat recovery unit 2 includes a first heat exchange tank 9, a gas pocket 10 and a dust collecting hopper 11, the gas pocket 10 is arranged on the upper part of the first heat exchange tank 9, the gas pocket 10 is communicated with the first heat exchange tank 9 through a gas pipe 12, the bottom of the first heat exchange tank 9 is provided with a plurality of dust collecting hoppers 11, and the first heat exchange tank 9 is provided with a first heat exchange water collecting pipe 13; the gas inlet 14 of the first heat exchange tank 9 is communicated with the flue gas passage pipe 4, and the first filter screen 16 is arranged at the gas outlet 15 of the first heat exchange tank 9.

[0064] The second waste heat recovery unit 3 includes a base plate 17, a second heat exchange tank 18, a water collecting tank 19 and a second heat exchange water collecting pipe 20, the second heat exchange tank 18 and the water collecting tank 19 are both mounted on the base plate 17, the second heat exchange water collecting pipe 20 is arranged in the second heat exchange tank 18, the outlet of the second heat exchange water collecting pipe 20 is communicated with the water collecting tank 19, the side of the second heat exchange tank 18 is provided with a gas inlet pipe 21 and a gas outlet pipe 22, the gas inlet pipe 21 is communicated with the gas outlet 15 of the first heat exchange tank 9, and the gas outlet pipe 22 is provided with a second filter screen 23.

[0065] The water collecting tank 19 is provided with a flow equalizing plate 24 and a water filter screen 25.

[0066] The flue gas passage pipe 4 is provided with a second circulating pump 26 and a first control valve 27, and the gas inlet pipe 21 is provided with a third circulating pump 28 and a second control valve 29.

[0067] The first heat exchange tank 9 is provided with a first temperature sensor 30 and a first dust sensor 31, the second heat exchange tank 18 is provided with a second temperature sensor 32 and a second dust sensor 33, and the first circulating pump 7, the second circulating pump 26, the third circulating pump 28, the first temperature sensor 30, the second temperature sensor 32, the first dust sensor 31 and the second dust sensor 33 are all electrically connected to the control unit 5.

[0068] The waste heat recovery heat transfer calculation of the phosphorus tower body 1 after combustion includes theoretical combustion temperature calculation and flue gas emission temperature; the theoretical combustion temperature calculation formula is:

[0069] (1)

[0070] (2)

[0071] wherein in the formulae is the theoretical combustion temperature, is the phosphorus combustion heat release, is the total mass of the mixed flue gas, is the mass of the burning phosphorus, is the phosphorus combustion heat, is the average specific heat at constant pressure of the flue gas, is the temperature of the air entering the furnace;

[0072] The calculation formula of the flue gas emission temperature is:

[0073] (3)

[0074] wherein is usually the heat flow; is the empirical coefficient or characteristic coefficient, is the indoor temperature; is the outdoor temperature; is the cubic non-linear effect of the indoor temperature; is the scaling item of the indoor and outdoor temperature difference, which is dimensionless or adjusted to a suitable order of magnitude; is the correction item of the indoor and outdoor temperature ratio, which is obtained by subtracting the empirical constant 1.18 from the temperature ratio, and A is the area;

[0075] The total heat release of the mixed flue gas is

[0076] (4)

[0077] wherein in the formulae is the flue gas emission temperature, is the total area of the combustion chamber, is the theoretical combustion temperature is the corresponding specific heat at constant pressure of the flue gas, is the total mass of the mixed flue gas, is the flue gas emission temperature is the corresponding specific heat at constant pressure of the flue gas, is a constant, which depends on the fuel type and the excess air coefficient, and is 2500 under the condition of the phosphorus burning tower, which is more appropriate.

[0078] wherein the heat exchange calculation steps of the first heat exchange header are:

[0079] S1, steam production D, the heat released by the hot fluid side is:

[0080] (5)

[0081] is the mass flow rate of the gas, is the specific heat capacity at constant pressure of the gas, represents the inlet temperature of the fluid,

[0082] represents the outlet temperature of the fluid; according to the heat balance, the heat obtained by the cold side is: (6)

[0083] is the cooling heat flow rate; is the saturated steam mass flow rate, is the enthalpy of saturated steam at constant pressure, is the enthalpy of feed water, is the specific heat capacity at constant pressure of water, is the outlet temperature of the fluid, is the saturation temperature; is the latent heat of vaporization, and the steam production of the heat pipe steam generator is ;

[0084] S2, average temperature difference ,

[0085] (7), wherein represents the maximum temperature difference; represents the minimum temperature difference, represents the natural logarithm function;

[0086] S3, heat transfer coefficient, the heat transfer mode of the heat pipe flue gas side is mainly convective heat transfer, and the heat transfer coefficient , , is a constant, and the constant is 0.33 for the staggered tube bundle C and 0.26 for the in-line tube bundle C, is the outer diameter of the light tube of the heat pipe, is the thermal conductivity of the flue gas at the constant temperature, is the Reynolds number of the flue gas side fluid, is the Prandtl number of the flue gas,

[0087] S4, the temperature of the working medium in the tube ,

[0088] (8)

[0089] is the steam temperature of the working medium in the heat pipe, ​​​The average temperature of the heat pipe for the hot fluid side and the cold fluid side, The heat transfer area of the hot fluid side and the cold fluid side; The heat transfer coefficient of the hot fluid side and the cold fluid side, The heat transfer coefficient of the cold fluid side is represented by

[0090] S5, the pipe wall temperature, the pipe wall temperature of the hot fluid side ,

[0091] (9)

[0092] The pipe wall temperature of the cold fluid side ,

[0093] (10) wherein The bulk temperature of the hot fluid is represented by The heat transfer coefficient of the hot fluid side and the cold fluid side, The bulk temperature of the cold fluid is represented by The heat transfer coefficient of the cold fluid side is represented by The heat transfer amount per unit area per unit time, The fouling resistance of the hot fluid and the cold fluid.

[0094] Wherein the first smoke sensor and the second smoke sensor both adopt a light scattering type algorithm, and the smoke concentration calculation formula is (11), C is the particle concentration, K is the calibration coefficient (calibrated by standard concentration gas when the sensor is factory-calibrated, different particle sizes (PM1.0 / PM2.5 / PM10) correspond to different K values), The effective voltage output by the photodetector; Zero concentration voltage (baseline voltage when there is no particle, used to offset dark current and ambient light interference).

[0095] Compared with the prior art, the beneficial effects of the present application are:

[0096] 1. High waste heat utilization rate: through the cascade mode of "first high-temperature steam generation + second medium-temperature heat storage", covering the high-temperature section of 600-1000℃ and the medium-temperature section of 300-500℃ waste heat, the waste heat recovery rate is increased from the traditional 40%-50% to more than 80%, and 100-500 tons of standard coal are saved per year (calculated according to 50kg / h of burning phosphorus);

[0097] 2. Strong environmental protection: adopting the three-stage dust removal structure of "first filter screen primary filtration + smoke dust hopper settlement + second filter screen fine filtration", the smoke dust emission concentration is ≤10mg / m³;

[0098] 3. Stable operation and intelligence: Real-time monitoring of temperature and smoke concentration parameters, automatic adjustment of flow and valve by control unit, alarm in abnormal conditions, reducing the frequency of manual inspection, and reducing the equipment failure rate by more than 60%;

[0099] 4. Wide adaptability: The size of the heat exchange tank and the number of heat exchange water collection pipes can be adjusted according to the amount of phosphorus combustion, which is suitable for different scales of phosphorus chemical production lines, with low transformation difficulty and short cost recovery period.

[0100] Workflow

[0101] Start the device: Start the first circulating pump, the second circulating pump and the third circulating pump, initialize the sensors by the control unit, and circulate the cooling liquid in the cavity layer of the phosphorus combustion tower body. The water collection tank is filled with cold water;

[0102] Phosphorus combustion and flue gas transportation: Phosphorus is burned in the phosphorus combustion tower body to produce high-temperature flue gas with a temperature of about 800°C. The flue gas enters the first waste heat recovery unit through the flue gas passage pipe (driven by the second circulating pump and adjusted by the first control valve);

[0103] First heat exchange and primary dust removal: After the flue gas is filtered by the first filter screen, it enters the first heat exchange tank and exchanges heat with the cold water in the first heat exchange water collection pipe. The cold water absorbs heat (about 600 kJ / kg) and vaporizes to produce 0.8 MPa saturated steam, which is stored in the steam pocket. The temperature of the flue gas drops to 400°C, and the large-particle-size dust (>10 μm) settles in the dust collection hopper;

[0104] Second heat exchange and fine dust removal: The 400°C medium-temperature flue gas enters the second heat exchange tank through the inlet pipe (driven by the third circulating pump and adjusted by the second control valve) and exchanges heat with the cold water in the second heat exchange water collection pipe. The cold water is heated to 60°C and flows into the water collection tank (treated by the flow equalization plate and water filter screen). The temperature of the flue gas drops to 150°C, and after being fine filtered by the second filter screen (dust concentration ≤8 mg / m³), it is discharged from the outlet pipe;

[0105] Intelligent monitoring: The first temperature sensor monitors the flue gas temperature in the first heat exchange tank in real time (target 400-600°C). If it exceeds 600°C, the control unit will increase the opening of the first control valve to increase the flue gas flow. The first dust sensor monitors the dust concentration after primary filtration (target ≤30 mg / m³). If it exceeds 30 mg / m³, the first filter screen needs to be cleaned. When all parameters are abnormal, the touch screen will alarm and record the fault information.

[0106] Example 1: Adaptation to small and medium-sized phosphorus chemical production line (phosphorus combustion amount 20 kg / h)

[0107] Phosphorus combustion tower body, diameter 1.5 m, height 6 m; cavity layer thickness 40 mm, circulating cooling liquid is softened water; circulating cooling tank volume 5 m³, first circulating pump power 1.5 kW (flow 30 m³ / h);

[0108] Primary waste heat recovery unit, the first heat exchange tank size 2.5m x 1.8m x 1.8m; the first heat exchange water collecting pipe (stainless steel 304) pipe diameter 40mm, quantity 12; gas pocket volume 3m³; three dust hoppers (volume 0.3m³ each); the first filter screen is a metal woven screen (pore size 8μm);

[0109] Secondary waste heat recovery unit, the second heat exchange tank size 2m x 1.5m x 1.5m; the second heat exchange water collecting pipe pipe diameter 32mm, quantity 10; water collecting tank volume 5m³; flow distribution plate is a perforated stainless steel plate (pore size 8mm); water filter screen is a PP cotton filter screen (pore size 5μm); the second filter screen is a HEPA H13 filter screen (pore size 0.3μm);

[0110] Piping and control components, the second circulating pump power 2kW (flow rate 5000m³ / h), the third circulating pump power 1kW (flow rate 3000m³ / h); control valve is an electric butterfly valve (bore 150mm); control unit is a Siemens S7-1200 PLC with a 7-inch touch screen; temperature sensor range 0-1200℃, dust sensor range 0-100mg / m³.

[0111] Specific working process

[0112] Start-up phase: start all circulating pumps, control unit initializes sensors, circulating coolant flows in the cavity of the phosphorus combustion tower in a laminar flow, and the water collecting tank is filled with cold water (25℃).

[0113] Flue gas transportation and primary treatment: 20kg / h of phosphorus combustion generates about 800℃ high-temperature flue gas, which enters the first heat exchange tank through the flue gas passage pipe (driven by the second circulating pump), first passes through the first filter screen to intercept flue dust with a particle size >8μm (interception rate about 60%); the flue gas exchanges heat with the cold water in the first heat exchange water collecting pipe, the cold water vaporizes after absorbing heat, generating 0.6MPa saturated steam (steam production about 52kg / h), which is stored in the gas pocket for production line heating; the flue gas temperature drops to 420℃, and large-particle-size flue dust (>10μm) settles in the dust collecting hopper.

[0114] Secondary treatment and emission: 420℃ medium-temperature flue gas enters the second heat exchange tank through the inlet pipe (driven by the third circulating pump), exchanges heat with the cold water in the second heat exchange water collecting pipe, and the cold water warms up to 55℃ and flows into the water collecting tank (uniformly distributed by the flow distribution plate and filtered by the water filter screen); the flue gas temperature drops to 160℃, and is fine filtered by the HEPA H13 filter screen (total dust removal rate ≥96%), and the final emission dust concentration is about 8mg / m³, meeting environmental protection standards.

[0115] Intelligent control: If the first temperature sensor detects flue gas temperature > 450℃, the control unit automatically adjusts the first control valve opening (increases flue gas flow); if the first dust sensor detects a concentration > 35mg / m³, the touch screen will alarm to remind cleaning the first filter screen.

[0116] Example 2: Adapt to large-scale phosphorus chemical production line (phosphorus burning amount 100kg / h)

[0117] Phosphorus burning tower body, diameter 3m, height 10m; cavity layer thickness 60mm, circulating cooling liquid is softened water; circulating cooling tank volume 15m³, first circulating pump power 4kW (flow rate 80m³ / h);

[0118] Primary waste heat recovery unit, first heat exchange tank size 4m×3m×2.5m; first heat exchange water collecting pipe (stainless steel 316L) pipe diameter 65mm, number 30; gas pocket volume 10m³; 4 dust hoppers (volume 1m³ each); first filter screen is metal woven mesh (pore size 6μm);

[0119] Secondary waste heat recovery unit, second heat exchange tank size 3.5m×2.5m×2.2m; second heat exchange water collecting pipe pipe diameter 50mm, number 25; water collecting tank volume 15m³; flow equalizing plate is a perforated stainless steel plate (pore size 12mm); water filter screen is a PP cotton filter screen (pore size 3μm); second filter screen is a HEPA H14 filter screen (pore size 0.1μm);

[0120] Piping and control components, second circulating pump power 5.5kW (flow rate 15000m³ / h), third circulating pump power 3kW (flow rate 10000m³ / h); control valve is an electric butterfly valve (diameter 300mm); control unit is a Siemens S7-1500PLC with a 12-inch touch screen; a third temperature sensor (monitoring water temperature in the water collecting tank) is added, and all sensors support 485 communication and can be connected to the factory MES system.

[0121] Specific work flow

[0122] Start-up phase: circulating pumps are started in the order of "cooling first, flue gas second" (to avoid tower wall over-temperature), control unit is networked with factory MES system, and production plan is received synchronously (such as phosphorus burning amount adjustment signal).

[0123] Flue gas delivery and primary treatment: 100kg / h of phosphorus burning produces about 850℃ high-temperature flue gas, which enters the first heat exchange tank through the flue gas passage pipe, and the first filter screen intercepts flue dust with particle size > 6μm (interception rate about 65%); flue gas exchanges heat with cold water in the first heat exchange water collecting pipe, producing 1.0MPa saturated steam (steam production about 265kg / h), which is stored in the gas pocket for use in the phosphoric acid concentration process; flue gas temperature drops to 380℃, and large-particle-size flue dust settles in the dust collecting hopper (automatic ash removal every 24 hours).

[0124] Secondary treatment and emissions:380℃ medium temperature flue gas into the second heat exchanger tank, with the second heat exchanger water pipe in the cold water heat, cold water temperature to 70℃ after the flow into the water tank (flow plate to avoid local overheating to 80℃ or more); flue gas temperature dropped to 140℃, by HEPAH14 filter screen fine filter (total dust removal rate ≥99%), the final emission dust concentration of about 5mg / m³; water tank hot water for workshop bath, equipment cleaning (water temperature below 60℃ automatically heat).

[0125] Intelligent control: if the second temperature sensor detects flue gas temperature <350℃, control unit to reduce the opening of the second control valve (reduce the flow of flue gas, improve the efficiency of heat exchange); if the second dust sensor detects the concentration >10mg / m³, automatically switch to standby HEPA filter (avoid downtime); all parameters are uploaded to the MES system in real time, supporting remote monitoring.

[0126] As shown in Figure 10 , several groups of circulation ratio calculation found that: when the circulation ratio is low, the flow rate is close to the natural circulation flow rate, so the total pressure difference of the bottom system is small, and the power consumption of the circulating pump is correspondingly reduced, but the safety of the circulating system cannot be guaranteed at this time; when the circulation ratio increases, the forced circulation is obviously different from the natural circulation, the total pressure difference of the system increases, and the consumption of the pump also increases accordingly, and the safety of the system is guaranteed.

[0127] The combustion of phosphorus is a typical chain reaction, and its overall reaction formula can be expressed as: When the amount of phosphorus and air is in different proportions, different phosphorus oxides can be obtained. Therefore, when the air quantity is constant, in order to ensure the complete oxidation of phosphorus, a sufficient amount of molten phosphorus must be sprayed. The influence of the amount of phosphorus on the highest combustion temperature and the flue gas emission temperature under the condition of constant air quantity or excess air coefficient (α>1) can be obtained by comparing the calculation results of the above formula, as shown in Figure 11 and Figure 12 .

[0128] The oxidation reaction of phosphorus can only occur in a certain concentration of oxygen. When the oxygen partial pressure is lower than 66.7Pa or higher than 93.3kPa, the reaction rate tends to zero. In addition, when the excess air coefficient is low, phosphorus cannot be completely oxidized and only low-valence phosphorus oxides can be obtained. Therefore, the excess air coefficient in the production of hot process phosphoric acid is generally selected to be above 1.8. However, under the condition of constant amount of phosphorus, high excess air coefficient cannot strengthen the heat transfer of the phosphorus combustion tower. By means of numerical simulation, the relationship between flue gas emission temperature and excess air coefficient under the condition of fixed amount of phosphorus is analyzed, as shown in Figure 13 . Figure 13This is a curve showing the change in flue gas emission temperature with the excess air coefficient; it indicates that when the amount of phosphorus burned is constant, the flue gas emission temperature increases with the increase of the excess air coefficient. This is because when the amount of phosphorus injected remains constant, the heat released by phosphorus combustion also remains constant. Therefore, as the excess air coefficient increases, the maximum combustion temperature decreases, leading to a reduction in radiative heat release and an increase in flue gas emission temperature. Furthermore, the excess air coefficient also affects the thickness of the condensate film on the water-cooled wall of the phosphorus combustion tower. Generally, when the amount of phosphorus burned is constant, the smaller the excess air coefficient, the thinner the condensate film, i.e., the lower the thermal resistance and the better the heat transfer effect.

[0129] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A waste heat recovery system for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank, characterized in that: It includes a phosphorus combustion tower body (1), a primary waste heat recovery unit (2), a secondary waste heat recovery unit (3), a flue gas passage pipe (4), and a control unit (5). The phosphorus combustion tower body (1) is connected to the primary waste heat recovery unit (2) through the flue gas passage pipe (4), and the primary waste heat recovery unit (2) is connected to the secondary waste heat recovery unit (3).

2. The waste heat recovery equipment for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 1, characterized in that: The tower wall of the phosphorus combustion tower body (1) is provided with a cavity layer (6), the cavity layer (6) is filled with circulating coolant, and the cavity layer (6) is externally connected to the circulating cooling tank (8) through a first circulating pump (7).

3. The waste heat recovery equipment for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 2, characterized in that: The primary waste heat recovery unit (2) includes a first heat exchange box (9), an air manifold (10), and a dust collection hopper (11). The air manifold (10) is located on the upper part of the first heat exchange box (9). The air manifold (10) is connected to the inside of the first heat exchange box (9) through an air pipe (12). Several dust collection hoppers (11) are provided at the bottom of the first heat exchange box (9). A first heat exchange water collection pipe (13) is provided inside the first heat exchange box (9). The air inlet (14) of the first heat exchange box (9) is connected to the flue gas passage pipe (4). A first filter screen (16) is provided at the air outlet (15) of the first heat exchange box (9).

4. The waste heat recovery equipment of a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 3, characterized in that: The secondary waste heat recovery unit (3) includes a base plate (17), a second heat exchange box (18), a water collection box (19), and a second heat exchange water collection pipe (20). The second heat exchange box (18) and the water collection box (19) are both installed on the base plate (17). The second heat exchange water collection pipe (20) is located inside the second heat exchange box (18). The outlet of the second heat exchange water collection pipe (20) is connected to the water collection box (19). An air inlet pipe (21) and an air outlet pipe (22) are provided on the side of the second heat exchange box (18). The air inlet pipe (21) is connected to the air outlet (15) of the first heat exchange box (9). The air outlet pipe (22) is provided with a second filter screen (23).

5. A waste heat recovery system for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 4, characterized in that: The water collection tank (19) is equipped with a flow equalization plate (24) and a water filter screen (25).

6. The waste heat recovery equipment of a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 5, characterized in that: The flue gas passage pipe (4) is equipped with a second circulation pump (26) and a first control valve (27), and the inlet pipe (21) is equipped with a third circulation pump (28) and a second control valve (29).

7. A waste heat recovery system for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 6, characterized in that: The first heat exchange box (9) is equipped with a first temperature sensor (30) and a first dust sensor (31), and the second heat exchange box (18) is equipped with a second temperature sensor (32) and a second dust sensor (33). The first circulation pump (7), the second circulation pump (26), the third circulation pump (28), the first temperature sensor (30), the second temperature sensor (32), the first dust sensor (31) and the second dust sensor (33) are all electrically connected to the control unit (5).

8. A waste heat recovery system for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 7, characterized in that: The calculation of waste heat recovery and heat transfer after combustion in the phosphorus combustion tower includes the calculation of theoretical combustion temperature and flue gas emission temperature; the formula for calculating theoretical combustion temperature is: （1） （2） Where in the formula The theoretical combustion temperature, The heat released during the combustion of phosphorus The total mass of the mixed flue gas is . For the sake of phosphorus quality, The heat of combustion of phosphorus This is the average specific heat capacity at constant pressure of the flue gas. The temperature of the air entering the furnace; The formula for calculating the flue gas emission temperature is: （3） in This is usually used to represent heat flow; These are empirical coefficients or characteristic coefficients. Indoor temperature; Outdoor temperature; To describe the cubic nonlinear effect of indoor temperature; This is a scaling term for the indoor-outdoor temperature difference, making the temperature difference dimensionless or adjusting it to a suitable order of magnitude. This is a correction term for the indoor-outdoor temperature ratio, calculated by subtracting the empirical constant 1.18 from the temperature ratio; where A is the area. Total heat release of the mixed flue gas for （4） Among them, China The flue gas emission temperature, The total area of ​​the combustion chamber. Theoretical combustion temperature The corresponding flue gas specific heat capacity at constant pressure, The total mass of the mixed flue gas is . To be related to flue gas emission temperature The corresponding flue gas specific heat capacity at constant pressure, It is a constant, depending on the type of fuel and the excess air coefficient. Based on experience, a value of 2500 is more appropriate under the conditions of a phosphorus combustion tower.

9. A waste heat recovery system for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 8, characterized in that: The heat exchange calculation steps for the first heat exchange water collection pipe are as follows: S1, steam production rate D, heat released on the hot fluid side. for: （5） for gas mass flow rate, for Specific heat capacity at isobaric pressure of a gas Indicates fluid The inlet temperature, This represents the outlet temperature of the fluid; according to heat balance, the heat gained on the cold side is: (6) To represent cooling heat flow; This is the saturated steam mass flow rate. For constant pressure saturated vapor enthalpy, To supply water enthalpy, The specific heat capacity at constant pressure of water, The outlet temperature of the fluid. To represent the saturation temperature, To account for the latent heat of vaporization, the steam production rate of the heat pipe steam generator is: ; S2, average temperature difference , (7), of which Indicates the maximum temperature difference; Indicates the minimum temperature difference. Represent the natural logarithm function; S3, heat transfer coefficient: The heat exchange mode on the flue gas side of the heat pipe is mainly convection heat transfer. The heat transfer coefficient is as follows when the flue gas passes laterally across the bare tube bundle. , , As a constant, C is taken as 0.33 for staggered tube bundles and 0.26 for inline tube bundles. The outer diameter of the heat pipe is the bare tube diameter. Let be the thermal conductivity of the flue gas at the characteristic temperature. The Reynolds number of the flue gas side fluid. The Prandtl number of the flue gas. S4, temperature of the working fluid inside the pipe , （8） This refers to the vapor temperature of the working fluid inside the heat pipe. This represents the average temperature of the heat pipes on both the hot and cold fluid sides. For the heat transfer area on the hot fluid side and the cold fluid side; For the heat transfer coefficient, Indicates the convective heat transfer coefficient on the cold side; S5, pipe wall temperature, hot fluid side pipe wall temperature , （9） Cold fluid side pipe wall temperature , (10); among which To represent the main temperature of the hot fluid; For the heat transfer coefficient, This refers to the main temperature of the cold fluid. Indicates the convective heat transfer coefficient on the cold side; The amount of heat transferred per unit area per unit time. For fouling thermal resistance of hot and cold fluids.

10. A waste heat recovery system for a phosphorus combustion tower coupled with a plate heat exchanger and a hot water tank as described in claim 9, characterized in that: Both the first and second dust sensors employ a light scattering algorithm, and their dust concentration calculation formula is as follows: (11), C is the particle concentration, K is the calibration coefficient, This is the effective voltage output by the photodetector. The voltage is at zero concentration.

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