Process for wet desulphurization of magnesium metal reduction slag and limestone

Abstract

The application discloses a magnesium metal reduction slag and limestone wet combined desulfurization process and belongs to the technical field of limestone desulfurization. The preparation method of the magnesium metal reduction slag and low-grade limestone wet combined desulfurization process comprises the following steps: S1, uniformly mixing the magnesium metal reduction slag with water to carry out hydration reaction, preparing a hydrated magnesium slag slurry, uniformly mixing the prepared hydrated magnesium slag slurry with prepared low-grade limestone slurry, and obtaining SO2 absorption liquid; S2, using the SO2 absorption liquid to carry out a desulfurization reaction on flue gas in an absorption tower, generating calcium sulfite, and blowing air into the absorption tower to make the generated calcium sulfite tend to be completely oxidized to obtain calcium sulfate; and S3, slowly cooling the slurry in the absorption tower with cooling water in the desulfurization reaction process, and making the obtained calcium sulfate form gypsum crystals. The desulfurization process has high desulfurization efficiency, little gypsum scale is generated in the desulfurization process, the magnesium metal reduction slag is effectively utilized, and the environment is prevented from being polluted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of limestone desulfurization, in particular to a combined desulfurization process of magnesium reduction slag and limestone by wet method. BACKGROUND

[0002] The low-grade limestone / gypsum wet desulfurization method is the most widely used desulfurization method at present, which has high desulfurization efficiency, can reach more than 95%, is mature in technology and low in cost. The low-grade limestone / gypsum wet desulfurization process uses low-grade limestone which is cheap and easy to obtain as a desulfurization absorbent. The low-grade limestone is crushed and ground into powder and mixed with water to prepare an absorption slurry. Alternatively, the low-grade limestone with a size of about 20mm can be directly ground into an absorption slurry by a wet ball mill. In the absorption tower, the absorption slurry is contacted with flue gas, and SO2 in the flue gas reacts with calcium carbonate in the slurry and the oxidized air to be removed, and the final reaction product is gypsum. However, scaling and plugging are very common in the absorption tower, especially in power plants burning high-sulfur coal.

[0003] During the Pidgeon process of smelting magnesium, about 5-8 tons of magnesium reduction slag are produced per ton of crude magnesium, so about 3.5-5.6 million tons of magnesium slag are produced per year. The chemical composition of the magnesium reduction slag mainly includes calcium oxide, silicon dioxide, magnesium oxide, a small amount of iron trioxide and aluminum trioxide, and the mass fraction of calcium oxide in the magnesium slag is about 56%. Due to the urgent need for energy, resources and environmental protection, the treatment and recycling of magnesium slag have become a key link to limit the sustainable development of the magnesium industry. At present, the recycling methods of magnesium slag at home and abroad mainly include road materials, cement additives, desulfurizers, silicon-calcium-magnesium fertilizers and refractory materials, but most of them are still in the research stage. A large amount of magnesium slag has not been effectively utilized and is still randomly discharged and stacked, which not only occupies a large amount of land resources, but also easily causes serious environmental pollution. Therefore, the rational utilization of magnesium slag is related to the strategic goal of whether the magnesium industry can achieve sustainable development. Therefore, how to use magnesium reduction slag for flue gas desulfurization and take measures to avoid or reduce scaling has become a research topic. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a combined desulfurization process of magnesium reduction slag and low-grade limestone by wet method, which has high desulfurization efficiency and produces little gypsum scale during the desulfurization process, and effectively utilizes the calcium oxide component in the magnesium reduction slag, turning waste into treasure and eliminating environmental pollution caused by improper treatment of the magnesium reduction slag.

[0005] The purpose of the present application is achieved by adopting the following technical solutions:

[0006] The combined desulfurization process of magnesium reduction slag and low-grade limestone by wet method comprises the following steps:

[0007] S1, the metal magnesium reduction slag is mixed with water uniformly to carry out hydration reaction, and magnesium slag slurry is prepared, the prepared magnesium slag slurry and prepared low-grade limestone slurry are mixed and stirred uniformly, and SO2 absorption liquid is obtained;

[0008] S2, the SO2 absorption liquid is used for desulfurization reaction of flue gas in an absorption tower, calcium sulfite is generated by reaction, air is blown into the absorption tower, and the generated calcium sulfite tends to be completely oxidized to obtain calcium sulfate;

[0009] S3, in the desulfurization reaction process, the slurry in the absorption tower is slowly cooled by cooling water, and the generated calcium sulfate is formed into gypsum crystals.

[0010] In S1, the prepared low-grade limestone slurry is prepared by using one of low-grade limestone, quicklime and slaked lime powder or a mixture thereof.

[0011] Further, the reduction magnesium slag is high-temperature reduction magnesium slag discharged from a reduction tank of a magnesium smelting plant, and the flue gas is coal-fired power plant flue gas.

[0012] Further, the mixing mass ratio of water to the metal magnesium reduction slag is 5:1-10:1.

[0013] Further, in S2, the concentration of the generated calcium sulfate in the slurry in the absorption tower is detected by sampling, and when the detected concentration of the generated calcium sulfate exceeds the saturation degree of the generated calcium sulfate, a descaling agent is added to the slurry in the absorption tower.

[0014] Further, the descaling agent is CLEANS-403.

[0015] Further, in S3, in the desulfurization reaction process, the slurry in the absorption tower is cooled multiple times by cooling water, and each cooling is carried out every 25 min, and each cooling lasts for 30 min.

[0016] Further, in S2, while air is blown into the absorption tower, N, N, N', N'-tetramethyl ethylenediamine solution is added to the slurry in the absorption tower, and the N, N, N', N'-tetramethyl ethylenediamine is used as a suspending agent to suspend the generated calcium sulfate in the slurry in the absorption tower.

[0017] Further, the stirring device is arranged in the absorption tower, and the stirring device stirs the slurry in the absorption tower, so that the calcium sulfate obtained by oxidation is uniformly dispersed in the slurry in the absorption tower.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] (1) The metal magnesium reduction slag and limestone wet combined desulfurization process provided by the present application realizes waste recycling, can utilize a large amount of waste slag of a magnesium smelting plant, has strong practical value and great environmental benefits, and has a simple process and is suitable for popularization and application in the field.

[0020] (2) The metal magnesium reduction slag and limestone wet combined desulfurization process provided by the present application further removes the scaling on the surface of the equipment by adding a descaling agent to the slurry in the absorption tower.

[0021] (3) The metal magnesium reduction slag and low-grade limestone wet combined desulfurization process provided by the present application is provided with a stirring device in the absorption tower, the stirring device is used to stir the slurry in the absorption tower, so that the calcium sulfate obtained by oxidation is uniformly dispersed in the slurry in the absorption tower, which is beneficial to the precipitation of the calcium sulfate on the crystal thereof, thereby avoiding the diffusion of the calcium sulfate and the calcium sulfate crystal in the slurry in the absorption tower to the wall surface of the absorption tower due to the concentration difference.

[0022] (4) In step S2, the metal magnesium reduction slag and low-grade limestone wet combined desulfurization process provided by the present application adds the N, N, N', N'-tetramethyl ethylenediamine solution to the slurry in the absorption tower while air is blown into the absorption tower, the N, N, N', N'-tetramethyl ethylenediamine acts as a suspending agent to suspend the calcium sulfate obtained by oxidation in the slurry in the absorption tower, thereby avoiding the precipitation of the calcium sulfate obtained by oxidation to the bottom of the absorption tower. DETAILED DESCRIPTION

[0023] The application will be further described below in conjunction with specific embodiments. It should be noted that the following described embodiments or technical features can be combined in any manner to form new embodiments without conflict.

[0024] The scale removal agent is CLEANS-403 purchased from Shandong Jiequan Environmental Protection Technology Co., Ltd. The scale removal agent mainly wets and penetrates the scale surface through a surfactant, and the novel chelating agent in the scale removal agent plays a role of solubilization, polymer chelation and dispersion, and the metal corrosion inhibitor in the scale removal agent plays a role of inhibiting corrosion. The scale removal agent has the advantages of fast scale removal speed at normal temperature (25℃), high scale removal efficiency, no secondary precipitation and deposition, easy operation, easy biodegradation, and good economic and environmental benefits.

[0025] N, N, N', N'-tetramethyl ethylenediamine is purchased from Hubei Ximingtai Chemical Co., Ltd., CAS number: 150-77-6, molecular formula: C10H24N2, and molecular weight: 172.31.

[0026] Example 1

[0027] The embodiment provides a preparation method of a magnesium reduction slag and limestone wet combined desulfurization process, and the specific steps are as follows: S1, uniformly mixing magnesium reduction slag and water in a reaction kettle according to a mass ratio of 5:1 to perform hydration reaction, in the reaction process, the temperature of the hydration reaction is kept at 65℃, the time of the hydration reaction is 2h, and the stirring speed in the reaction process is 30r / min, 500L of magnesium slag slurry is prepared, and the prepared magnesium slag slurry and prepared 100L of low-grade limestone slurry are uniformly mixed and stirred to obtain 600L of SO2 absorption liquid;

[0028] In this step, the temperature required for the hydration reaction is obtained from the sensible heat of the magnesium reduction slag. The magnesium reduction slag refers to the high-temperature waste slag of more than 1200℃ discharged from a reduction tank of a magnesium smelting plant.

[0029] S2, using the SO2 absorption liquid to perform a desulfurization reaction on flue gas in an absorption tower, to obtain calcium sulfite, and at the same time, air is blown into the absorption tower, so that the calcium sulfite generated in the reaction tends to be completely oxidized to obtain calcium sulfate, and the oxidation rate is higher than 90%, and in this embodiment, the oxidation rate reaches 92%, so that there is enough calcium sulfate in the slurry for crystal growth;

[0030] S3, in the desulfurization reaction process, the slurry in the absorption tower is cooled by cooling water for multiple times, and each cooling is performed every 25min, and each cooling lasts for 30min, so that the gypsum crystals formed by the calcium sulfate obtained by oxidation in the previous step continue to grow. Finally, compared with the SO2 concentration in the flue gas of a coal-fired power plant, the desulfurization efficiency in this embodiment reaches 82%.

[0031] Example 2

[0032] The embodiment provides a preparation method of a magnesium metal reduction slag and limestone wet combined desulfurization process, and specific steps are as follows: S1, magnesium metal reduction slag and water are uniformly mixed in a reaction kettle according to a mass ratio of 8:1 to perform hydration reaction, in the reaction process, the hydration reaction temperature is kept at 80 DEG C, the hydration reaction time is 1h, and the stirring speed is 20r / min in the reaction process; 500L of hydrated magnesium slag slurry is prepared, the prepared hydrated magnesium slag slurry and prepared 250L of low-grade limestone slurry are uniformly mixed and stirred, and 750L of SO2 absorption liquid is obtained;

[0033] In the step, the temperature required by the hydration reaction is obtained from the sensible heat of the magnesium metal reduction slag, the magnesium metal reduction slag refers to the high-temperature waste slag of more than 1200 DEG C discharged from a reduction tank of a magnesium smelting plant.

[0034] S2, the SO2 absorption liquid is used for desulfurization reaction on flue gas in an absorption tower, calcium sulfite is obtained by reaction, air is blown into the absorption tower, calcium sulfite obtained by reaction tends to be completely oxidized to obtain calcium sulfate, and the oxidation rate is higher than 90%, in the embodiment, the oxidation rate reaches 95%, and it is guaranteed that there is enough calcium sulfate in the slurry for crystal growth;

[0035] S3, in the desulfurization reaction process, the slurry in the absorption tower is cooled by cooling water for multiple times, every time cooling is performed every 25min, and the duration of each cooling is 30min, so that the gypsum crystals formed by the calcium sulfate obtained by oxidation in the above step continue to grow. Finally, compared with the SO2 concentration in the flue gas of a coal-fired power plant, the desulfurization efficiency in the embodiment reaches 85%.

[0036] Embodiment 3

[0037] The embodiment provides a preparation method of a magnesium metal reduction slag and limestone wet combined desulfurization process, and specific steps are as follows: S1, magnesium metal reduction slag and water are uniformly mixed in a reaction kettle according to a mass ratio of 8:1 to perform hydration reaction, in the reaction process, the hydration reaction temperature is kept at 80 DEG C, the hydration reaction time is 1h, and the stirring speed is 20r / min in the reaction process; 500L of hydrated magnesium slag slurry is prepared, the prepared hydrated magnesium slag slurry and prepared 250L of low-grade limestone slurry are uniformly mixed and stirred, and 750L of SO2 absorption liquid is obtained;

[0038] In the step, the temperature required by the hydration reaction is obtained from the sensible heat of the magnesium metal reduction slag, the magnesium metal reduction slag refers to the high-temperature waste slag of more than 1200 DEG C discharged from a reduction tank of a magnesium smelting plant.

[0039] S2, the SO2 absorption liquid is used for desulfurization reaction on the flue gas in the absorption tower, calcium sulfite is obtained by reaction, air is blown into the absorption tower, the calcium sulfite generated by reaction tends to be completely oxidized to obtain calcium sulfate, and the oxidation rate is higher than 90%, and in the embodiment, the oxidation rate reaches 98%, so that there is enough calcium sulfate in the slurry for crystal growth;

[0040] S3, in the desulfurization reaction process, the slurry in the absorption tower is cooled by cooling water for multiple times, each cooling is carried out every 25 min, and the duration time of each cooling is 30 min, so that the gypsum crystals formed by the calcium sulfate obtained by oxidation in the previous step continue to grow. Finally, compared with the SO2 concentration in the flue gas of the coal-fired power plant, the desulfurization efficiency in the embodiment reaches 92 %.

[0041] Embodiment 4

[0042] The embodiment provides a preparation method of a magnesium reduction slag and limestone wet combined desulfurization process, and the specific steps are as follows: S1, the magnesium reduction slag and water are uniformly mixed in a reaction kettle according to a mass ratio of 5:1 to carry out hydration reaction, in the reaction process, the hydration reaction temperature is kept at 65 DEG C, the hydration reaction time is 2h, and the stirring speed in the reaction process is 30r / min, 500L of hydrated magnesium slag slurry is prepared, the prepared hydrated magnesium slag slurry and prepared 100L of low-grade limestone slurry are uniformly mixed and stirred to obtain 600L of SO2 absorption liquid;

[0043] In this step, the temperature required for the hydration reaction comes from the sensible heat of the magnesium reduction slag, and the magnesium reduction slag refers to the high-temperature waste slag of more than 1200 DEG C discharged from a reduction tank of a magnesium smelting plant.

[0044] S2, the SO2 absorption liquid is used for desulfurization reaction on the flue gas in the absorption tower, calcium sulfite is obtained by reaction, air is blown into the absorption tower, the calcium sulfite generated by reaction tends to be completely oxidized to obtain calcium sulfate, and the oxidation rate is higher than 90%, and in the embodiment, the oxidation rate reaches 92%, so that there is enough calcium sulfate in the slurry for crystal growth; and in the desulfurization reaction process, the concentration of the calcium sulfate obtained by oxidation in the slurry in the absorption tower is detected, when the detected concentration of the calcium sulfate obtained by oxidation exceeds the saturation degree of the calcium sulfate obtained by oxidation, the descaling agent CLEANS-403 is added to the slurry in the absorption tower.

[0045] S3, in the desulfurization reaction process, the slurry in the absorption tower is cooled by cooling water for multiple times, each cooling is carried out every 25 min, and the duration time of each cooling is 30 min, so that the gypsum crystals formed by the calcium sulfate obtained by oxidation in the previous step continue to grow. Finally, compared with the SO2 concentration in the flue gas of the coal-fired power plant, the desulfurization efficiency in the embodiment reaches 82 %.

[0046] Example 5

[0047] The embodiment provides a preparation method of a magnesium metal reduction slag and limestone wet combined desulfurization process, and specific steps are as follows: S1, uniformly mixing the magnesium metal reduction slag and water in a reaction kettle according to a mass ratio of 5:1 to perform a hydration reaction, in the reaction process, the hydration reaction temperature is kept at 65 DEG C, the hydration reaction time is 2h, and the stirring speed in the reaction process is 30r / min, 500L of a hydrated magnesium slag slurry is prepared, the prepared hydrated magnesium slag slurry and prepared 100L of a low-grade limestone slurry are uniformly mixed and stirred to obtain 600L of SO2 absorption liquid;

[0048] In the step, the temperature required by the hydration reaction is obtained from the sensible heat of the magnesium metal reduction slag, and the magnesium metal reduction slag refers to a high-temperature waste slag of 1200 DEG C or above discharged from a reduction tank of a magnesium smelting plant.

[0049] S2, using the SO2 absorption liquid to perform a desulfurization reaction on flue gas in an absorption tower, generating calcium sulfite, at the same time, air is blown into the slurry in the absorption tower, N, N, N', N'-tetramethyl ethylenediamine solution is added into the slurry in the absorption tower, and a stirring device at the bottom of the absorption tower is started to stir the slurry in the absorption tower, so that the generated calcium sulfite tends to be completely oxidized to obtain calcium sulfate, and the oxidation rate is higher than 90%, in the embodiment, the oxidation rate reaches 92%, so that enough calcium sulfate in the slurry is ensured for crystal growth;

[0050] S3, in the desulfurization reaction process, the slurry in the absorption tower is cooled by cooling water for multiple times, every 25min, and the cooling time is 30min, so that the gypsum crystals formed by the calcium sulfate obtained by oxidation in the previous step continue to grow, and the stirring device at the bottom of the absorption tower is started to stir the slurry in the absorption tower, so that the calcium sulfate and the calcium sulfate crystals in the slurry in the absorption tower are uniformly dispersed in the slurry in the absorption tower, and the N, N, N', N'-tetramethyl ethylenediamine acts as a suspending agent, so that the calcium sulfate obtained by oxidation is suspended in the slurry in the absorption tower, and the calcium sulfate obtained by oxidation is prevented from being deposited at the bottom of the absorption tower. Finally, compared with the SO2 concentration in the flue gas of a coal-fired power plant, the desulfurization efficiency in the embodiment reaches 82%.

[0051] The above-mentioned embodiment is only a preferred embodiment of the present application, and cannot be used to limit the protection scope of the present application, and any non-essential change and replacement made by a person skilled in the art on the basis of the present application all belong to the protection scope of the present application.

Claims

1. A process for wet desulphurization of magnesium metal reduction slag and limestone, characterized in that, It comprises the following steps: S1, the metal magnesium reduction slag is mixed with water to carry out hydration reaction, magnesium slag slurry is prepared, the prepared magnesium slag slurry and prepared limestone slurry are mixed and stirred uniformly to obtain SO2 absorption liquid; S2, the SO2 absorption liquid is used to carry out desulfurization reaction on flue gas in an absorption tower, calcium sulfite is generated by reaction, air is blown into the absorption tower to make the generated calcium sulfite tend to be completely oxidized to calcium sulfate; in S2, while the air is blown into the absorption tower, N, N, N', N'-tetramethyl ethylenediamine solution is added to the slurry in the absorption tower, the N, N, N', N'-tetramethyl ethylenediamine acts as a suspending agent to make the oxidized calcium sulfate suspended in the slurry in the absorption tower; S3, in the desulfurization reaction process, the slurry in the absorption tower is slowly cooled by cooling water, so that the oxidized calcium sulfate forms gypsum crystals.

2. The process for combined desulphurization of magnesium metal reduction slag and limestone according to claim 1, characterized in that, The reduction magnesium slag is high-temperature reduction magnesium slag discharged from a reduction tank of a magnesium smelting plant; the flue gas is coal-fired power plant flue gas.

3. The process for combined desulphurization of magnesium metal reduction slag and limestone according to claim 1, characterized in that, The mixing mass ratio of water to the metal magnesium reduction slag is 5:1-10:

1.

4. The process for combined desulphurization of magnesium metal reduction slag and limestone as claimed in claim 1, wherein, In S2, the concentration of the oxidized calcium sulfate in the slurry in the absorption tower is detected by sampling, when the detected concentration of the oxidized calcium sulfate exceeds the saturation degree of the oxidized calcium sulfate, a descaling agent is added to the slurry in the absorption tower.

5. The process for combined desulphurization of magnesium metal reduction slag and limestone according to claim 4, characterized in that, The descaling agent is CLEANS-403.

6. The process for combined desulphurization of magnesium metal reduction slag and limestone as claimed in claim 1, wherein, In S3, in the desulfurization reaction process, the slurry in the absorption tower is cooled multiple times by cooling water, each cooling is carried out every 25 min, and each cooling lasts for 30 min.

7. The process for combined desulphurization of magnesium metal reduction slag and limestone as claimed in claim 1, wherein, In S1, the prepared limestone slurry is prepared by using one of limestone, quicklime and slaked lime powder or a mixture thereof.

8. The process for combined desulphurization of magnesium metal reduction slag and limestone as claimed in claim 1, wherein, In S1, the prepared magnesium slag slurry and the prepared limestone slurry are mixed according to a volume ratio of (3-5):1.