CN101157504B - Process for Softening Hard Water Using SO2 and CO2 in Tail Gas - Google Patents

Abstract

A process for softening hard water with SO2 and CO2 contained in exhaust gas comprises: allowing the SO2 and the CO2 contained in the exhaust gas to react with the hard water; stopping the reaction when the pH of the mixed solution is tested to be 2.5-3.3; adjusting the pH of the mixed solution after reaction with alkaline solution to be 6.5-7.5; performing filtration to obtain softened water andfilter residue. The hard water contains 0.6-0.7g/L of Ca<2+> and 50-100mg/l of Mg<2+> and the pH thereof is 9-11; the volume concentrations of the sulfur dioxide and the carbon dioxide in the exhaustgas are respectively 1-10 percent and 5-30 percent. The invention overcomes the defect of high cost of the prior hard water softening art and provides a novel process with the excellent effect of treating the waste with another and saving the cost.

Description

Process for Softening Hard Water Using SO2 and CO2 in Tail Gas

technical field

The invention belongs to the field of environmental protection, and in particular relates to a new process for softening hard water by utilizing SO ₂ and CO ₂ in tail gas.

Background technique

Non-ferrous enterprises often produce purified water with a calcium content of about 1000mg/L in the wastewater treatment process. Due to the high hardness of this purified water, its reuse value is limited. ". To ensure "zero discharge" of wastewater, the hardness of this purified water must first be reduced.

At present, the hard water softening methods at home and abroad mainly include heating and boiling method, chemical softening method, ion exchange method, adsorption method, distillation, reverse osmosis and so on. These methods mainly consume a lot of raw materials or energy, and the cost is relatively high, and all of them need to be improved and innovated.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the disadvantage of high cost of existing hard water softening treatment, and provide a new process to achieve "treat waste with waste" and save costs.

The technical solution adopted by the present invention to solve the problems of the technologies described above is:

Tail gas containing _SO2 and _CO2 is reacted with hard water in the absorption tower, and when the pH of the reaction mixture is detected to be 2.5-5.5, the reaction is stopped, and the reacted mixture is filtered to obtain demineralized water and filter residue; the hard water is The solution containing Ca ²⁺ concentration of 0.6-0.7g/L, pH of 9-11, and volume concentration of sulfur dioxide and carbon dioxide in tail gas containing SO ₂ and CO ₂ are 1-10% and 5-30% respectively.

The hard water also contains Mg ²⁺ concentration of 50-100mg/l.

Adjust the pH value of the reacted mixed solution to 6.5-7.5 with lye, and then filter to obtain demineralized water and filter residue.

The liquid-gas ratio in the absorption tower is controlled at 2-3l/m ³ .

The production principle of sulfur dioxide and carbon dioxide softening hard water:

SO ₂ +H ₂ O→H ₂ SO ₃ →H ⁺ +HSO ₃ ^- →2H ⁺ +SO ₃ ^2-

CO ₂ +H ₂ O→H ₂ CO ₃ →H ⁺ +HCO ₃ ^- →2H ⁺ +CO ₃ ^2-

Ca ²⁺ +SO ₃ ^2- →CaSO ₃

Ca ²⁺ +CO ₃ ^2- →CaCO ₃

Mg ²⁺ +SO ₃ ^2- →MgSO ₃

Mg ²⁺ +CO ₃ ^2- →MgCO ₃

SO ²⁺ CaCO ₃ →CaSO ₃ +CO ₂

SO ₂ +MgCO ₃ →MgSO ₃ +CO ₂

2CaSO ₃ +O ₂ +4H ₂ O→2CaSO ₄ 2H ₂ O

2MgSO ₃ +O ₂ →2MgSO ₄

The invention is a new process for softening hard water by utilizing SO ₂ and CO ₂ in tail gas. Sulfur dioxide in the tail gas reacts with hard water to generate SO ₃ ^2- , and SO ₃ ^2- reacts with Ca ²⁺ and Mg ²⁺ to form calcium sulfite and magnesium sulfite precipitates respectively; carbon dioxide in the tail gas reacts with hard water to generate CO ₃ ^2- , CO ₃ ^2- reacts with Ca ²⁺ and Mg ²⁺ to form calcium carbonate and magnesium carbonate precipitates respectively; calcium carbonate reacts with sulfur dioxide to form calcium sulfite. Reverse gas-liquid washing is used in the reaction process, washing temperature: normal temperature; pH value at the end of the reaction (outlet pH value): 2.5-5.5; the primary filtrate is Ca ²⁺ , Mg ²⁺ purification liquid, that is, softened water; the filter residue is sub Calcium sulfate, calcium sulfate, calcium carbonate, magnesium sulfite, magnesium sulfate, and magnesium carbonate precipitate.

The beneficial effects of the present invention are:

1. Provide a new process method for softening hard water.

2. It better solves the problems of high cost of hard water softening and difficult treatment of sulfur dioxide in tail gas.

3. The process of the present invention "uses waste to treat waste" not only solves the problems of waste gas treatment and hard water softening, but also has significant environmental, economic and social benefits.

Description of drawings

Fig. 1 is the process flow chart of embodiment 1 of the present invention

Detailed ways

Example 1:

With reference to accompanying drawing 1, first send certain concentration hard water (Ca ²⁺ 400mg/L; Mg ²⁺ 100mg/L) into the bubbling absorption tower. Use liquid sulfur dioxide to prepare a gas with a sulfur dioxide concentration of 1%, and the gas flow rate is about 20Nm ³ /h, and then controlled by a control valve to blow into a bubbling absorption tower (tower diameter Φ200mm, tower height 1m), due to air stirring, it can avoid suspension Subsidence. The reaction is carried out under the conditions of normal pressure and normal temperature, and the tail gas after the absorption reaction is discharged through the top of the absorption tower. After gas-liquid absorption for 1 minute, the pH value is 3, and the pH value of the absorption liquid is adjusted to 7 with lye to obtain a suspension. The solid-liquid separation in the sedimentation tank, the precipitation time is 30min, the filtrate is demineralized water, the Ca ²⁺ is 18mg/L; the Mg ²⁺ is 10mg/L.

The monitoring and analysis report shows that before the desulfurization treatment, the volume percentage of SO ₂ is 1%. After the desulfurization treatment, the volume percentage of SO ₂ is reduced to 0.01%, and the desulfurization rate reaches more than 90%.

Example 2:

First, a certain concentration of hard water (Ca ²⁺ 1000mg/L) is sent to the spray absorption tower at one time. A branch with a displacement of about 200m _N ³ /h is drawn from the exhaust gas of a certain factory pipeline. First, dust is removed by a bag filter, and then controlled by a control valve to blow into a bubbling absorption tower (tower diameter Φ400m, tower height 3m), absorbing The liquid (hard water) at the bottom of the tower is pumped out and circulated from the top, and the liquid at the bottom is stirred because the water pump is continuously pumped out and sent in to prevent the suspension from settling. The liquid-gas ratio is controlled at about 2-3l/ ^m3 . Under the conditions of normal pressure and normal temperature, the spray reaction is carried out, and the tail gas after the absorption reaction is discharged through the top of the absorption tower. After gas-liquid absorption for 1 minute, the pH value is 3, and the pH value of the absorption liquid is adjusted to 7 with lye to obtain a suspension. The solid-liquid separation in the sedimentation tank, the precipitation time is 30min, and the filtrate is demineralized water. Ca ²⁺ is 18mg/L; Mg ²⁺ is 10mg/L.

The monitoring and analysis report shows that before the desulfurization treatment, the volume percentage of SO ₂ is 1%. After the desulfurization treatment, the volume percentage of SO ₂ is reduced to 0.01%, and the desulfurization rate reaches more than 90%. The volume percentage of CO ₂ is 14%. After washing and decalcification treatment, the volume percentage of CO ₂ is reduced to 5.6%, and the removal rate of CO ₂ reaches about 60%.

Claims (4)

1. utilize SO in the tail gas ₂, CO ₂The technology of softening of water is characterized in that, will contain SO ₂, CO ₂Tail gas and hard water react in the absorption tower, and when the pH of detection reaction mixed solution was 2.5-5.5, stopped reaction filtered reacted mixed solution, obtains softening water and filter residue; Described hard water is for containing Ca ²⁺Strength of solution 0.6-0.7g/L, pH is 9-11, sulfurous gas and carbonic acid gas volumetric concentration are respectively 1-10%, 5-30% in the tail gas.

2. according to claim 1ly utilize SO in the tail gas ₂, CO ₂The technology of softening of water is characterized in that, described hard water also contains Mg ²⁺Concentration is 50-100mg/L.

3. according to claim 1ly utilize SO in the tail gas ₂, CO ₂The technology of softening of water is characterized in that, it is 6.5-7.5 that reacted mixed solution is adjusted the pH value with alkali lye, filters then, obtains softening water and filter residue.

4. according to claim 1ly utilize SO in the tail gas ₂, CO ₂The technology of softening of water is characterized in that, the liquid-gas ratio in the absorption tower is controlled at 2-3L/m ³

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