Efficient comprehensive recovery process for chemical waste heat

Abstract

The invention discloses a chemical waste heat efficient comprehensive recovery process which is achieved through a recovery system, and the recovery system comprises a boiler, a steam turbine, three sets of low-pressure heater heat exchangers, a thermoelectric deoxidizing tank, a condenser and a liquid nitrogen washing device. The recovery process comprises the following steps: S1, producing dead steam; s2, heating desalted water; s3, deoxidizing in a deoxidizing tank; and S4, liquid nitrogen washing. According to the invention, waste heat generated by chemical urea preparation and mixed exhaust steam composed of other exhaust steam act on the low-pressure heater heat exchanger, and condensate of the low-pressure heater heat exchanger is recovered, so that double recovery of substances and energy is realized, desalted water is used as supplement water of the low-pressure heater heat exchanger, steam consumption of 1.5 MPaG of a deoxidizing tank is reduced, and the energy consumption of the deoxidizing tank is reduced. The external steam supply amount under the same load of the boiler is greatly improved, and the heat efficiency of the boiler is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat power system, in particular to a chemical industry waste heat efficient comprehensive recovery process. BACKGROUND

[0002] Waste heat, also known as residual heat, is the heat energy that is no longer used after being discharged after being produced and manufactured for some needs in human activities. With the energy shortage in the world, countries are working hard to save energy, reduce emissions and strive for sustainable development. Based on the fact of energy shortage, the problem of waste heat utilization has become an increasingly important direction of energy efforts, and countries are strengthening investment and research in this regard, hoping to gain greater and more benefits. There are various ways and methods of energy utilization, but the most important, most meaningful and most valuable utilization is power generation, but the technology of waste heat power generation, especially low-temperature waste heat power generation, restricts its further development.

[0004] The invention patent with the authorized announcement number CN112097542B discloses a wastewater concentration waste heat recycling device and method. The wastewater concentration waste heat recycling device includes a desulfurization unit and a wastewater concentration system in communication, the wastewater concentration system includes a wastewater pool, a wastewater heater, a flash tank and a condenser and a low-pressure heater condensate system in communication, the low-pressure heater condensate system is in communication with the wastewater concentration system, and the system includes a generator set, a condenser, a first low-pressure heater and a high-pressure heater. The heat discharged from the generator set can be used to heat the wastewater in the wastewater heater, the condensate at the outlet of the condenser is used as a coolant to recover the heat of the secondary steam, the heat is used in stages, through the wastewater concentration system, the heat is returned to the low-pressure heater condensate system, the heat required for desulfurization wastewater treatment is almost not lost in the process, the wastewater concentration is realized, and the disadvantages of high-quality heat energy consumption in the conventional route are solved. However, the waste heat utilization efficiency of the device or similar waste heat utilization device still needs to be improved. SUMMARY

[0005] In view of the above problems, the present application provides a chemical industry waste heat efficient comprehensive recovery process.

[0006] The technical scheme of the present application is as follows:

[0007] A chemical industry waste heat efficient comprehensive recovery process, comprising the following steps:

[0008] S1, producing exhaust steam: the hot steam produced by the boiler is introduced into the steam turbine, the steam turbine produces the first exhaust steam as the heat source of the low-pressure heater, and the second exhaust steam produced in the production of chemical urea is collected as the heat source of the low-pressure heater;

[0009] S2, desalted water heating: the desalted water at 50±2℃ is sequentially heated by three groups of low-pressure heaters in series, to obtain heated desalted water, wherein the first group of low-pressure heaters uses mixed exhaust steam at a total steam pressure of 0.35±0.05MPaG to exchange heat with the desalted water, to heat the desalted water to 90±5℃, the second group of low-pressure heaters uses mixed exhaust steam at a total steam pressure of 0.5±0.05MPaG to exchange heat with the desalted water, to heat the desalted water to 110±5℃, and the third group of low-pressure heaters uses mixed exhaust steam at a total steam pressure of 1±0.05MPaG to exchange heat with the desalted water, to heat the desalted water to 130±5℃, and the condensate of the three groups of low-pressure heaters is recovered by a condenser;

[0010] S3, oxygen removal in an oxygen removal tank: the heated desalted water is sent to a thermal-electric oxygen removal tank for oxygen removal, and at the same time, as make-up water of the thermal-electric oxygen removal tank, to reduce the steam consumption of the thermal-electric oxygen removal tank at 1.5±0.1MPaG, and the third exhaust steam produced by the thermal-electric oxygen removal tank is injected into the three groups of low-pressure heaters, and the first exhaust steam, the second exhaust steam and the third exhaust steam together form the mixed exhaust steam;

[0011] S4, liquid nitrogen washing: the first exhaust steam in S1 and the used mixed exhaust steam in S2 are introduced into a liquid nitrogen washing device to provide heat source for a reboiler in the liquid nitrogen washing device, and the liquid nitrogen washing device produces purified gas and raw material gas, and the raw material gas is introduced into a boiler as fuel.

[0012] Further, the steam turbine internally comprises a high-pressure cylinder, a small steam turbine, a reheater, a medium-pressure cylinder and a low-pressure cylinder connected in series, and the thermal-electric oxygen removal tank is connected with a high-pressure heater.

[0013] Further, in S1, the steam turbine performs six-stage steam extraction, wherein the first-stage exhaust steam is discharged from the high-pressure cylinder into the small steam turbine at a temperature of 320-380℃, the second-stage exhaust steam is discharged from the high-pressure cylinder into the high-pressure heater at a temperature of 280-350℃, the third-stage and subsequent exhaust steam is reheated by the reheater, wherein the third-stage exhaust steam is discharged from the medium-pressure cylinder into the high-pressure heater at a temperature of 250-320℃, the fourth-stage exhaust steam is discharged from the medium-pressure cylinder into the first group of low-pressure heaters at a temperature of 180-220℃, the fifth-stage exhaust steam is discharged from the low-pressure cylinder into the second group of low-pressure heaters at a temperature of 120-160℃, the sixth-stage exhaust steam is discharged from the low-pressure cylinder into the third group of low-pressure heaters at a temperature of 80-110℃, and the remaining exhaust steam is discharged from the low-pressure cylinder, condensed by the condenser, and then condensed water is obtained.

[0014] Description: By extracting the first steam from the steam turbine, the energy is used optimally, and the overall thermal efficiency is improved.

[0015] Preferably, in S2, the desalted water is obtained by hydrating the condensed water, and the hydrating process comprises the following steps: filtering the condensed water to remove solid particles greater than 10 microns, then removing metal ions by cation exchange in a strong acid cation bed at a flow rate of 20-30 m / h, then removing CO2 by a carbon remover, then removing acid radicals by anion exchange in a strong base anion bed, and then mixing treatment in a mixed bed of cation resin and anion resin to obtain the desalted water, the conductivity of the desalted water is ≤0.1 μS / cm, and the SiO2 content is ≤10 μg / L.

[0016] Description: By optimizing the standard of desalted water, the subsequent operation is ensured to proceed smoothly, and the subsequent device is protected.

[0017] Preferably, the ratio of cation resin to anion resin in the mixed bed of cation resin and anion resin is 1:2.

[0018] Description: By optimizing the ratio of cation resin to anion resin in the mixed bed of cation resin and anion resin, the required desalination effect and efficiency are ensured.

[0019] Further, the steam flow of the first steam is 10-12 t / h, the steam flow of the second steam is 7-8 t / h, the steam flow of the third steam is 12-15 t / h, the flow of the desalted water is 400-500 t / h, the steam required by the thermal power deoxidizing tank is the second steam and the first steam extracted from the fifth or sixth stage, the steam flow is 20-25 t / h, the total steam amount is 0.5-0.55 MPaG, the water temperature output by the thermal power deoxidizing tank is 140-158 ℃, and the oxygen content is <7 μg / L.

[0020] Description: By optimizing the steam flow of each steam source, the energy is more reasonably distributed, and the maximum utilization efficiency of the remaining energy is achieved.

[0021] Further, the liquid nitrogen washing device comprises a nitrogen washing tower, a cold box, a liquid nitrogen storage tank, an expander, a heat exchanger, and a reboiler connected in series.

[0022] Preferably, in S4, the gas source of the liquid nitrogen washing is the synthesis gas produced by the coal water slurry or dry powder gasification technology, the synthesis gas is introduced into the bottom of the nitrogen washing tower, the liquid nitrogen is sprayed from the top of the nitrogen washing tower, the H2 content in the produced purified gas is > 99%, the methane-rich liquid is collected at the bottom of the nitrogen washing tower, the methane-rich liquid is heated by using the reboiler, the first spent steam for the reboiler is the spent steam produced by the third or fourth stage extraction steam, when heating, the mixed spent steam and the first spent steam produced by the fourth stage extraction steam are preferentially used, when the energy of the first spent steam produced by the fourth stage extraction steam is insufficient, the first spent steam produced by the third stage extraction steam is used, and the standard for judging insufficient energy is that the temperature of the first spent steam produced by the fourth stage extraction steam is lower than 150 DEG C.

[0023] The CO / CH4 in the raw material gas is ≥8 or the CO content is ≥30%.

[0024] Description: By optimizing the standard for judging insufficient energy, energy can be supplemented in time, and the purpose is also to more reasonably allocate energy to maximize the utilization efficiency of surplus energy.

[0025] Further, the condensed liquid in S1 and S2 is recovered through a water collecting tank.

[0026] The beneficial effects of the present application are:

[0027] The present application is a kind of chemical waste heat efficient comprehensive recovery process, which utilizes the mixed spent steam composed of the waste heat produced by the preparation of chemical urea and other various spent steams to act on the low-pressure heater, and simultaneously recovers the condensed liquid of the low-pressure heater, so as to realize the double recovery of matter and energy, uses the desalted water as the make-up water of the low-pressure heater, reduces the steam consumption of the deaerator at 1.5 MPaG, greatly improves the external steam supply under the same load of the boiler, finally, the process is combined with the liquid nitrogen washing process, the produced raw material gas is sent to the boiler for combustion, saves a large amount of electric coal, about equivalent to 10000Nm 3 / h of raw material gas, the heat value is equivalent to about 2.3t of 5000Kcal of electric coal, greatly improves the thermal efficiency of the boiler, and the thermal efficiency of the boiler is improved from the original design of 89% to 93%. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The present application is a kind of chemical waste heat efficient comprehensive recovery process utilizing the overall structure of chemical waste heat.

[0029] Among them, 1-boiler, 2-turbine, 3-low-pressure heater, 4-thermal power deaerator, 5-condenser, 6-liquid nitrogen washing device, 7-high-pressure heater, 8-water collecting tank. DETAILED DESCRIPTION

[0030] Example 1

[0031] The application discloses a chemical waste heat efficient comprehensive recovery process, which is realized through a recovery system, and the recovery system comprises a boiler 1, a steam turbine 2, three groups of low-pressure heaters 3, a heat-electricity oxygen-removing tank 4, a condenser 5 and a liquid nitrogen washing device 6; the steam turbine 2 internally comprises a high-pressure cylinder, a small steam turbine, a reheater, a medium-pressure cylinder and a low-pressure cylinder which are connected in series; the heat-electricity oxygen-removing tank 4 is connected with a high-pressure heater 7; the liquid nitrogen washing device 6 comprises a nitrogen washing tower, a cold box, a liquid nitrogen storage tank, an expander, a heat exchanger and a reboiler which are connected in series; and each element of the recovery system is a commercially available product.

[0032] The recovery process comprises the following steps:

[0033] S1, producing waste steam: hot steam produced by the boiler 1 is introduced into the steam turbine 2, the steam turbine 2 produces first waste steam as a heat source of the low-pressure heater 3 through steam extraction, and second waste steam produced in the production of chemical urea is collected as a heat source of the low-pressure heater 3;

[0034] The steam turbine 2 performs six-stage steam extraction, wherein first waste steam produced by first-stage steam extraction is discharged through the high-pressure cylinder and introduced into the small steam turbine, the temperature is 350 DEG C; first waste steam produced by second-stage steam extraction is discharged through the high-pressure cylinder and introduced into the high-pressure heater 7, the temperature is 300 DEG C; first waste steam produced by third-stage and subsequent steam extraction is reheated through the reheater, wherein first waste steam produced by third-stage steam extraction is discharged through the medium-pressure cylinder and introduced into the high-pressure heater 7, the temperature is 300 DEG C; first waste steam produced by fourth-stage steam extraction is discharged through the medium-pressure cylinder and introduced into the first group of low-pressure heaters 3, the temperature is 200 DEG C; first waste steam produced by fifth-stage steam extraction is discharged through the low-pressure cylinder and introduced into the second group of low-pressure heaters 3, the temperature is 140 DEG C; first waste steam produced by sixth-stage steam extraction is discharged through the low-pressure cylinder and introduced into the third group of low-pressure heaters 3, the temperature is 90 DEG C; and the remaining first waste steam is condensed through the condenser 5 after being discharged through the low-pressure cylinder to obtain condensed water;

[0035] S2, heating desalted water: desalted water at 50 DEG C is continuously heated through the three groups of low-pressure heaters 3 in series, and heated desalted water is obtained, wherein the first group of low-pressure heaters 3 uses mixed waste steam with a total steam amount of 0.35 MPaG to heat the desalted water to 90 DEG C, the second group of low-pressure heaters 3 uses mixed waste steam with a total steam amount of 0.5 MPaG to heat the desalted water to 110 DEG C, and the third group of low-pressure heaters 3 uses mixed waste steam with a total steam amount of 1 MPaG to heat the desalted water to 130 DEG C; and the condensate of the three groups of low-pressure heaters 3 is recovered through the condenser 5;

[0036] The desalted water is obtained by hydrating the condensed water, and the hydrating process comprises the following steps: filtering the condensed water to remove solid particles with a size of ≥10 μm, then removing metal ions by cation exchange in a strong acid cation bed at a flow rate of 25 m / h, then removing CO2 by a carbon remover, then removing acid radicals by anion exchange in a strong base anion bed, and then mixing and treating in a cation resin-anion resin mixed bed, wherein the ratio of the cation resin to the anion resin in the cation resin-anion resin mixed bed is 1:2, the conductivity of the desalted water is 0.55 μS / cm, and the SiO2 content is 4 μg / L;

[0037] The condensed liquid in S1 and S2 is recovered through the water collecting tank 8;

[0038] S3, oxygen removal in an oxygen removal tank: the heated desalted water is sent to the heat-electricity oxygen removal tank 4 for oxygen removal, and at the same time, the desalted water serves as make-up water for the heat-electricity oxygen removal tank 4, thereby reducing the steam consumption of the heat-electricity oxygen removal tank 4 at 1.5 MPaG, and the third exhaust steam produced by the heat-electricity oxygen removal tank 4 is injected into the three groups of low-pressure heaters 3, the first exhaust steam, the second exhaust steam and the third exhaust steam together form mixed exhaust steam, the steam flow rate of the first exhaust steam is 11 t / h, the steam flow rate of the second exhaust steam is 7.5 t / h, the steam flow rate of the third exhaust steam is 13 t / h, the flow rate of the desalted water is 450 t / h, the exhaust steam required by the heat-electricity oxygen removal tank 4 is the second exhaust steam and the first exhaust steam produced by the fifth or sixth stage extraction steam, the steam flow rate is 22 t / h, the total steam amount is 0.52 MPaG, the water temperature produced by the heat-electricity oxygen removal tank 4 is 150 ℃, and the oxygen content is 4 μg / L;

[0039] S4, liquid nitrogen washing: the first exhaust steam in S1 and the used mixed exhaust steam in S2 are introduced into the liquid nitrogen washing device 6 to provide heat source for the reboiler in the liquid nitrogen washing device 6, the liquid nitrogen washing device 6 produces purified gas and raw material gas, the raw material gas is introduced into the boiler 1 as fuel, the gas source for the liquid nitrogen washing is water coal slurry or synthetic gas produced by dry powder gasification technology, the synthetic gas is introduced into the bottom of the nitrogen washing tower, liquid nitrogen is sprayed from the top of the nitrogen washing tower, the H2 content in the produced purified gas is 99.3%, the methane-rich liquid is collected at the bottom of the nitrogen washing tower, the methane-rich liquid is heated by using the reboiler, the first exhaust steam for the reboiler is the exhaust steam produced by the third or fourth stage extraction steam, the first exhaust steam produced by the mixed exhaust steam and the fourth stage extraction steam is preferentially used during heating, when the energy of the first exhaust steam produced by the fourth stage extraction steam is insufficient, the first exhaust steam produced by the third stage extraction steam is used, and the standard for judging insufficient energy is that:

[0040] The CO / CH4 in the raw material gas is ≥8 or the CO content is ≥30%.

[0041] Example 2

[0042] The difference between this example and example 1 is that:

[0043] In S1, the steam turbine 2 carries out six stages of steam extraction, wherein the first stage of steam extraction produces first exhaust steam which is discharged from the high-pressure cylinder into the small turbine at a temperature of 320°C, the second stage of steam extraction produces first exhaust steam which is discharged from the high-pressure cylinder into the high-pressure heater 7 at a temperature of 280°C, the third and subsequent stages of steam extraction produce first exhaust steam which is reheated by the reheater, wherein the third stage of steam extraction produces first exhaust steam which is discharged from the intermediate-pressure cylinder into the high-pressure heater 7 at a temperature of 250°C, the fourth stage of steam extraction produces first exhaust steam which is discharged from the intermediate-pressure cylinder into the first group of low-pressure heaters 3 at a temperature of 180°C, the fifth stage of steam extraction produces first exhaust steam which is discharged from the low-pressure cylinder into the second group of low-pressure heaters 3 at a temperature of 120°C, the sixth stage of steam extraction produces first exhaust steam which is discharged from the low-pressure cylinder into the third group of low-pressure heaters 3 at a temperature of 80°C, and the remaining first exhaust steam is discharged from the low-pressure cylinder and then condensed by the condenser 5 to obtain condensate water;

[0044] Corresponding to the temperature of the first exhaust steam produced in S1, the temperature parameters of each stage in S2 and S3 are also adjusted accordingly:

[0045] S2, desalted water heating: the desalted water at 48°C is sequentially heated by the three groups of low-pressure heaters 3 in series to obtain heated desalted water, wherein the first group of low-pressure heaters 3 uses mixed exhaust steam with a total steam quantity of 0.3 MPaG to exchange heat with the desalted water to heat the desalted water to 85°C, the second group of low-pressure heaters 3 uses mixed exhaust steam with a total steam quantity of 0.45 MPaG to exchange heat with the desalted water to heat the desalted water to 105°C, the third group of low-pressure heaters 3 uses mixed exhaust steam with a total steam quantity of 0.95 MPaG to exchange heat with the desalted water to heat the desalted water to 125°C, and the condensate of the three groups of low-pressure heaters 3 is recovered by the condenser 5;

[0046] S3, deaerating tank deaeration: the heated desalted water is sent to the thermal power deaerating tank 4 for deaeration, and at the same time, as the make-up water of the thermal power deaerating tank 4, the steam consumption of the thermal power deaerating tank 4 at 1.4 MPaG is reduced, and the third exhaust steam produced by the thermal power deaerating tank 4 is injected into the three groups of low-pressure heaters 3, the first exhaust steam, the second exhaust steam and the third exhaust steam together form the mixed exhaust steam, the steam flow of the first exhaust steam is 10 t / h, the steam flow of the second exhaust steam is 7 t / h, the steam flow of the third exhaust steam is 12 t / h, the flow of the desalted water is 400 t / h, the exhaust steam required by the thermal power deaerating tank 4 is the second exhaust steam and the first exhaust steam produced by the fifth or sixth stage of steam extraction, the steam flow is 20 t / h, the total steam quantity is 0.5 MPaG, the water temperature produced by the thermal power deaerating tank 4 is 140°C, and the oxygen content is 6 μg / L.

[0047] Example 3

[0048] The difference between this example and example 1 is:

[0049] In S1, the steam turbine 2 carries out six stages of steam extraction, wherein the first stage of steam extraction produces first exhaust steam which is discharged from the high-pressure cylinder into the small turbine at a temperature of 380°C, the second stage of steam extraction produces first exhaust steam which is discharged from the high-pressure cylinder into the high-pressure heater 7 at a temperature of 350°C, the third and subsequent stages of steam extraction produce first exhaust steam which is reheated by the reheater, wherein the third stage of steam extraction produces first exhaust steam which is discharged from the intermediate-pressure cylinder into the high-pressure heater 7 at a temperature of 320°C, the fourth stage of steam extraction produces first exhaust steam which is discharged from the intermediate-pressure cylinder into the first group of low-pressure heaters 3 at a temperature of 220°C, the fifth stage of steam extraction produces first exhaust steam which is discharged from the low-pressure cylinder into the second group of low-pressure heaters 3 at a temperature of 160°C, the sixth stage of steam extraction produces first exhaust steam which is discharged from the low-pressure cylinder into the third group of low-pressure heaters 3 at a temperature of 110°C, and the remaining first exhaust steam is condensed by the condenser 5 after being discharged from the low-pressure cylinder to obtain condensate water;

[0050] Corresponding to the temperature of the first exhaust steam produced in S1, the temperature parameters of each stage in S2 and S3 are also adjusted accordingly:

[0051] S2, desalted water heating: the desalted water at 52°C is sequentially and continuously heated by the three groups of low-pressure heaters 3 connected in series to obtain heated desalted water, wherein the first group of low-pressure heaters 3 uses mixed exhaust steam with a total steam quantity of 0.4 MPaG to exchange heat with the desalted water to heat the desalted water to 95°C, the second group of low-pressure heaters 3 uses mixed exhaust steam with a total steam quantity of 0.55 MPaG to exchange heat with the desalted water to heat the desalted water to 115°C, the third group of low-pressure heaters 3 uses mixed exhaust steam with a total steam quantity of 1.05 MPaG to exchange heat with the desalted water to heat the desalted water to 135°C, and the condensate of the three groups of low-pressure heaters 3 is recovered by the condenser 5;

[0052] S3, deaerating tank deaeration: the heated desalted water is sent to the thermal power deaerating tank 4 for deaeration, and at the same time, as the make-up water of the thermal power deaerating tank 4, the steam consumption of the thermal power deaerating tank 4 at 1.6 MPaG is reduced, and the third exhaust steam produced by the thermal power deaerating tank 4 is injected into the three groups of low-pressure heaters 3, the first exhaust steam, the second exhaust steam and the third exhaust steam together form the mixed exhaust steam, the steam flow of the first exhaust steam is 12 t / h, the steam flow of the second exhaust steam is 8 t / h, the steam flow of the third exhaust steam is 15 t / h, the flow of the desalted water is 500 t / h, the exhaust steam required by the thermal power deaerating tank 4 is the second exhaust steam and the first exhaust steam produced by the fifth or sixth stage of steam extraction, the steam flow is 25 t / h, the total steam quantity is 0.55 MPaG, the water temperature produced by the thermal power deaerating tank 4 is 158°C, and the oxygen content is 2 μg / L.

[0053] Example 4

[0054] The difference between this example and example 1 is that:

[0055] The desalted water is obtained by hydrating the condensate water. The steps of the hydration treatment are as follows: removing solid particles with a size of ≥10 μm from the condensate water by filtration, then removing metal ions by cation exchange in a strong-acid cation bed at a flow rate of 20 m / h, then removing CO2 by a carbon remover, then removing acid radicals by anion exchange in a strong-base anion bed, and then mixing and treating in a mixed bed of cation resin and anion resin to obtain the desalted water. The ratio of the cation resin to the anion resin in the mixed bed is 1:2. The conductivity of the desalted water is 0.05 μS / cm, and the SiO2 content is 7 μg / L.

[0056] Example 5

[0057] The difference between this example and Example 1 is that:

[0058] The desalted water is obtained by hydrating the condensate water. The steps of the hydration treatment are as follows: removing solid particles with a size of ≥10 μm from the condensate water by filtration, then removing metal ions by cation exchange in a strong-acid cation bed at a flow rate of 20 m / h, then removing CO2 by a carbon remover, then removing acid radicals by anion exchange in a strong-base anion bed, and then mixing and treating in a mixed bed of cation resin and anion resin to obtain the desalted water. The ratio of the cation resin to the anion resin in the mixed bed is 1:2. The conductivity of the desalted water is 0.05 μS / cm, and the SiO2 content is 7 μg / L.

[0059] Example 6

[0060] The difference between this example and Example 1 is that:

[0061] S4, liquid nitrogen washing: the first exhaust steam in S1 and the used mixed exhaust steam in S2 are introduced into the liquid nitrogen washing device 6 to provide a heat source for the reboiler in the liquid nitrogen washing device 6. The liquid nitrogen washing device 6 produces purified gas and raw material gas. The raw material gas is introduced into the boiler 1 as fuel. The gas source for the liquid nitrogen washing is the synthesis gas produced by the coal water slurry or dry powder gasification technology. The synthesis gas is introduced into the bottom of the nitrogen washing tower, and the liquid nitrogen is sprayed from the top of the nitrogen washing tower. The H2 content in the produced purified gas is 99.5%. The methane-rich liquid is collected at the bottom of the nitrogen washing tower, and the methane-rich liquid is heated by the reboiler. The first exhaust steam for the reboiler is the exhaust steam produced by the third or fourth stage extraction. When the energy of the first exhaust steam produced by the fourth stage extraction is insufficient, the first exhaust steam produced by the third stage extraction is used.

[0062] Example 7

[0063] The difference between this example and Example 1 is that:

[0064] S4, liquid nitrogen washing: the first exhaust steam in S1 and the mixed exhaust steam after use in S2 are passed into the liquid nitrogen washing device 6 to provide heat source for the reboiler in the liquid nitrogen washing device 6, the liquid nitrogen washing device 6 produces purified gas and raw material gas, the raw material gas is passed into the boiler 1 as fuel, the gas source for the liquid nitrogen washing is the synthesis gas produced by the coal water slurry or dry powder gasification technology, the synthesis gas is passed into the bottom of the nitrogen washing tower, the liquid nitrogen is sprayed from the top of the nitrogen washing tower, the H2 content in the produced purified gas is 99.6%, the methane-rich liquid is collected at the bottom of the nitrogen washing tower, the methane-rich liquid is heated by the reboiler, the first exhaust steam for the reboiler is the exhaust steam produced by the third or fourth stage extraction, the first exhaust steam produced by the mixed exhaust steam and the fourth stage extraction is preferentially used during heating, when the energy of the first exhaust steam produced by the fourth stage extraction is insufficient, the first exhaust steam produced by the third stage extraction is used.

[0065] Experimental example

[0066] Next, we test according to the method in example 1, compared with the mixed exhaust steam composed of the waste heat produced by the non-utilized chemical urea preparation and other various exhaust steams, the method in example 1 of the present application reduces the steam consumption of the deoxidizing tank by 1.5 MPaG, greatly improves the external steam supply amount of the boiler under the same load, finally, through the combination with the process of liquid nitrogen washing, the produced raw material gas is sent to the boiler for combustion, a large amount of electricity and coal is saved, about equivalent to 10000 Nm 3 / h of raw material gas, the calorific value is equivalent to about 2.3 t of 5000 Kcal of electricity and coal, greatly improves the thermal efficiency of the boiler, the thermal efficiency of the boiler is improved from the original design of 89% to 93%.

Claims

1. A high-efficiency comprehensive recovery process for chemical waste heat, characterized in that, Includes the following steps: S1. Producing exhaust steam: The hot steam produced by the boiler (1) is fed into the steam turbine (2). The steam turbine (2) produces the first exhaust steam by extracting steam as the heat source of the low-pressure heat exchanger (3). At the same time, the second exhaust steam produced during the production of chemical urea is collected as the heat source of the low-pressure heat exchanger (3). S2, Demineralized water heating: Demineralized water at 50±2℃ is continuously heated by passing it through three sets of series-connected low-temperature heat exchangers (3) to obtain heated demineralized water. The first set of low-temperature heat exchangers (3) uses mixed exhaust steam with a total steam volume of 0.35±0.05MPaG to exchange heat with the demineralized water and heats the demineralized water to 90±5℃. The second set of low-temperature heat exchangers (3) uses mixed exhaust steam with a total steam volume of 0.5±0.05MPaG to exchange heat with the demineralized water and heats the demineralized water to 110±5℃. The third set of low-temperature heat exchangers (3) uses mixed exhaust steam with a total steam volume of 1±0.05MPaG to exchange heat with the demineralized water and heats the demineralized water to 130±5℃. At the same time, the condensate from the three sets of low-temperature heat exchangers (3) is recovered through the condenser (5). S3, Deoxygenation in the deoxygenation tank: The heated demineralized water is sent to the thermoelectric deoxygenation tank (4) for deoxygenation and serves as makeup water for the thermoelectric deoxygenation tank (4), reducing the steam consumption of the thermoelectric deoxygenation tank (4) by 1.5±0.1MPaG. At the same time, the third exhaust steam produced by the thermoelectric deoxygenation tank (4) is reinjected into the three sets of low-pressure heat exchangers (3). The first exhaust steam, the second exhaust steam and the third exhaust steam together form mixed exhaust steam. S4, Liquid nitrogen washing: The first exhaust steam in S1 and the mixed exhaust steam after use in S2 are fed into the liquid nitrogen washing device (6) to provide a heat source for the reboiler in the liquid nitrogen washing device (6). The liquid nitrogen washing device (6) produces purified gas and raw material gas. The raw material gas is fed into the boiler (1) as fuel.

2. The efficient and comprehensive recovery process for chemical waste heat according to claim 1, characterized in that, The turbine (2) includes a high-pressure cylinder, a small steam turbine, a reheater, an intermediate-pressure cylinder, and a low-pressure cylinder connected in series. The thermoelectric deaerator (4) is connected to a high-pressure heat exchanger (7).

3. The efficient and comprehensive recovery process for chemical waste heat according to claim 2, characterized in that, In S1, the steam turbine (2) performs six stages of steam extraction. The first exhaust steam produced in the first stage is discharged through the high-pressure cylinder and enters the small steam turbine at a temperature of 320–380°C. The first exhaust steam produced in the second stage is discharged through the high-pressure cylinder and enters the high-pressure heat exchanger (7) at a temperature of 280–350°C. The first exhaust steam produced in the third stage and subsequent stages is reheated by the reheater. Specifically, the first exhaust steam produced in the third stage is discharged through the intermediate-pressure cylinder and enters the high-pressure heat exchanger (7) at a temperature of 250–320°C. The first exhaust steam produced by the fourth stage extraction is discharged through the intermediate pressure cylinder and enters the first low-pressure heat exchanger (3) at a temperature of 180-220℃. The first exhaust steam produced by the fifth stage extraction is discharged through the low-pressure cylinder and enters the second low-pressure heat exchanger (3) at a temperature of 120-160℃. The first exhaust steam produced by the sixth stage extraction is discharged through the low-pressure cylinder and enters the third low-pressure heat exchanger (3) at a temperature of 80-110℃. The remaining first exhaust steam is discharged through the low-pressure cylinder and then condensed by the condenser (5) to obtain condensate.

4. The efficient and comprehensive recovery process for chemical waste heat according to claim 3, characterized in that, In S2, the demineralized water is obtained by hydration treatment of the condensate. The hydration treatment steps are as follows: filtering the condensate to remove solid particles ≥10μm, then performing cation exchange to remove metal ions in a strong acid cation bed at a flow rate of 20-30m / h, then removing CO2 through a decarbonator, then performing anion exchange to remove acid radicals in a strong base anion bed, and finally mixing and treating in a cation-anion resin mixed bed to obtain demineralized water with a conductivity of ≤0.1μS / cm and a SiO2 content of ≤10μg / L.

5. The efficient and comprehensive recovery process for chemical waste heat according to claim 4, characterized in that, The ratio of cation resin to anion resin in the cation-anion resin mixed bed is 1:

2.

6. The efficient and comprehensive recovery process for chemical waste heat according to claim 1, characterized in that, The steam flow rate of the first exhaust steam is 10-12 t / h, the steam flow rate of the second exhaust steam is 7-8 t / h, the steam flow rate of the third exhaust steam is 12-15 t / h, the flow rate of the demineralized water is 400-500 t / h, the exhaust steam required by the thermoelectric deaerator (4) is the second exhaust steam and the first exhaust steam produced by the extraction of steam from the fifth or sixth stage, the steam flow rate is 20-25 t / h, the total steam volume is 0.5-0.55 MPaG, the temperature of the water produced by the thermoelectric deaerator (4) is 140-158℃, and the oxygen content is <7 μg / L.

7. The efficient and comprehensive recovery process for chemical waste heat according to claim 3, characterized in that, The liquid nitrogen washing device (6) includes a nitrogen washing tower, a cold box, a liquid nitrogen storage tank, an expander, a heat exchanger, and a reboiler connected in series.

8. The efficient and comprehensive recovery process for chemical waste heat according to claim 7, characterized in that, In S4, the gas source for liquid nitrogen washing is syngas produced by coal-water slurry or dry powder gasification technology. The syngas enters through the bottom of the nitrogen washing tower, and liquid nitrogen is sprayed from the top. The purified gas produced has an H2 content >99%. Methane-rich liquid is collected at the bottom of the nitrogen washing tower and heated using the reboiler. The first exhaust steam used in the reboiler is exhaust steam produced by the third or fourth stage extraction. During heating, mixed exhaust steam and the first exhaust steam produced by the fourth stage extraction are preferentially used. When the energy of the first exhaust steam produced by the fourth stage extraction is insufficient, the first exhaust steam produced by the third stage extraction is used. The criterion for insufficient energy is: The feed gas has a CO / CH4 ratio ≥ 8 or a CO content ≥ 30%.

9. The efficient and comprehensive recovery process for chemical waste heat according to claim 3, characterized in that, In S1 and S2, the condensate is recovered through the water collection tank (8).

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