CN1386568A

CN1386568A - Desulfurizing agent based on modifying solid waste of fuel coal and its preparing process

Info

Publication number: CN1386568A
Application number: CN 02116303
Authority: CN
Inventors: 寇元; 尚洪山
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2002-03-22
Filing date: 2002-03-22
Publication date: 2002-12-25

Abstract

A desulfurizing agent is prepared from the solid waste generated after burning coal, and the modifier (the oxide, hydroxide, or carbonate of alkali metal or alkali-earth metal) through mixing them with water, reacting at 100-600 deg.C and 0.2-5 MPa for at least 6 hr, washing, filtering and drying. Its advatnages are high desulfurizing efficiency, low cost and less energy consumption.

Description

Desulfurizing agent based on modification of coal-fired solid waste and preparation method thereof

The technical field is as follows:

the invention belongs to the technical field of flue gas desulfurization, and particularly relates to the technical field of application of coal-fired solid waste as a silicon-aluminum compound adsorbent to flue gas desulfurization.

Background art:

currently, the desulfurizing agents mainly used for flue gas desulfurization are the following two types:

(1)CaC0₃，CaO，Ca(OH)₂and (4) preparing the system. The desulfurization process is classified into a dry method, a semi-dry method and a wet method. The wet desulphurization efficiency can reach more than 90 percent, but the water consumption is too large, and the wet desulphurization is low-temperature desulphurization; dry processThe desulfurization efficiency of the desulfurization zone is lower in the medium-temperature desulfurization zone; the semi-dry process is in between (see Sino-Dutch semi Clean coal chemical technology, 389.Beijing, 15-16 June, 1995).

(2)Na₂CO₃And (4) preparing the system. Single Na without carrier₂CO₃System, under dry method medium and low temperature, Na₂CO₃The utilization rate is only about 10-20%. The process adopts Al₂O₃As a carrier, the desulfurization efficiency is higher at the temperature of 160 ℃ and 400 ℃ when the loading is lower (5 percent or 20 percent). However, with Al₂O₃Is a carrier, has expensive price, limited source, complicated preparation process and high energy consumption.

The invention content is as follows:

the invention aims to provide a desulfurizer and a preparation method thereof, wherein the desulfurizer is cheap and easily available in raw materials, and is suitable for increasing SO to a greater extentunder the conditions of no water, medium temperature (200-800 ℃) and no contribution to gas-solid reaction₂The removal efficiency and the removal rate simplify the process and reduce the investment cost.

The technical scheme of the invention is as follows:

the desulfurizer of the invention is obtained by taking coal-fired solid waste as a matrix material and carrying out solid-state synthesis reaction with a modifier, namely oxide, hydroxide or carbonate of alkali metal or alkaline earth metal in the presence of a proper amount of water.

The coal-fired solid waste comprises fly ash and coal cinder.

The modifier is selected from NaOH and Na₂CO₃、KOH、K₂CO₃、Ca(OH)₂、CaO、MgCO₃InOne of (1) and (b).

The weight ratio of the coal-fired solid waste to the modifier is 1: 0.1-2; the water addition amount is 0.1-1 times of the total weight of the coal-fired solid waste and the modifier.

The preparation method of the desulfurization adsorbent sequentially comprises the following steps:

(1) mixing the coal-fired solid waste, water and modifier-oxide of alkali metal or alkaline earth metal, hydrogen and oxygen

Mixing the compound or carbonate to obtain a uniformly mixed reactant;

(2) the reactant reacts for more than 6 hours under the conditions of 0.2-5MPa and 100-600 ℃ to obtain the product.

When the modifier such as NaOH or KOH is selected to make the product alkaline, the product is obtained

Soaking and washing the resultant until the filtrate is nearly neutral, filtering and drying to obtain the desulfurizer.

In thepreparation method, the coal-fired solid waste comprises fly ash and coal cinder.

In the preparation method, the modifier is selected from NaOH and Na₂CO₃、KOH、K₂CO₃、Ca(OH)₂、CaO、MgCO₃One kind of (1).

In the preparation method, the weight ratio of the coal-fired solid waste to the modifier is 1: 0.1-2; the water addition amount is 0.1-1 times of the total weight of the coal-fired solid waste and the modifier.

The modification mechanism of the invention is that the surface morphology of the adsorbent can be improved and the specific surface area can be increased after the coal-fired solid waste is modified by the modifier; adjusting the pore distribution of the adsorbent to accelerate SO₂Diffusion in the product layer; the active ingredients of the adsorbent are increased, and the desulfurization efficiency is improved.

The modified desulfurizer of the invention is an amorphous silicon-aluminum material, has obvious desulfurization effect, greatly improves the desulfurization efficiency of the adsorbent, and greatly promotes the following reactions: (taking the reaction of NaOH and fly ash as an example)

The fly ash, coal slag and the like adopted by the invention are wastes of coal-fired power plants, are cheap, easily obtained and disposable raw materials, and have convenient and economic sources.

Compared with the traditional method, the modification preparation process of the desulfurizer has the advantages of simple process, easy operation, low energy consumption (such as no need of hydrothermal treatment, no need of stirringand the like) and relatively low investment cost; the potential value of the waste of the coal-fired power plant/boiler plant can be reasonably utilized, and a series of practical related desulfurizing agents and corresponding desulfurizing process procedures can be developed; the adsorbent is a desulfurizer which is suitable for removing SO2 effectively under the conditions of no water, medium temperature and flue gas unfavorable for gas-solid reaction, and has better desulfurization efficiency and desulfurization speed.

The following terms are defined:

penetration time: 100% removal of SO₂The time (min) for each gram of desulfurizing agent.

Penetration sulfur capacity: 100% removal of SO₂During the process, SO is removed from the desulfurizing agent per gram₂Amount (mg).

Saturation time: SO is not adsorbed by the desulfurizer any longer₂The time (min) taken per gram of desulfurizing agent.

Saturated sulfur capacity: SO is not adsorbed by the desulfurizer any longer₂During the process, SO is removed from the desulfurizing agent per gram₂Amount of (mg)

A comparative experiment proves that: according to the method, as shown in the embodiment, the modified silicon-aluminum desulfurizer obtained by the interaction of NaOH and fly ash has the one-time penetration time of 288 minutes/g adsorbent at the desulfurization temperature of 500 ℃; the disposable penetration and saturated sulfur capacity were 64.6 and 134.0mg SO, respectively₂Per gram of adsorbent; while the penetration time and penetration sulfur capacity of untreated fly ash are 0, and the saturated sulfur capacity is less than 1mg SO₂About/g adsorbent. The interaction between NaOH and fly ash proves that the desulfurizer is a quick desulfurizer suitable for the conditions of no water and medium temperature (200-800 ℃), and is beneficial to desulfurization of flue gas flowing in a reactor quickly.

Description of the drawings:

FIG. 1 is a desulfurization curve of fly ash and modified desulfurizing agent at 500 ℃. In the figure, a is a curve of fly ash, d is a curve of a modified desulfurizer, and the dosage of the desulfurizer is 0.5 g.

FIG. 2 is a desulfurization curve of the modified desulfurization agent at different temperatures. In the figure, d2 is a 200 ℃ curve, d3 is a 300 ℃ curve, d4 is a 400 ℃ curve, d5 is a 500 ℃ curve, and d6 is a 600 ℃ curve. The amount of the desulfurizer is 0.5 g.

FIG. 3 is a Scanning Electron Microscope (SEM) image of fly ash and modified desulfurization agent. In the figure, a is an image of fly ash, and d is an image of a modified desulfurizing agent.

FIG. 4 XRD (X-ray powder diffraction) spectra of fly ash and modified sorbent. In the figure, a is a spectrogram of fly ash, and d is a spectrogram of a modified desulfurizing agent.

Example (b):

preparing a sodium silicoaluminate desulfurization adsorbent by using a solid chemical synthesis method:

20g of fly ash (from Beijing China power plant), 20g of NaOH and 20ml of water are uniformly mixed at room temperature, and then the mixture is transferred into a sealed stainless steel autoclave, wherein the reaction temperature is 300 ℃. The pressure in the reaction kettle is adjusted by a valve on the reaction kettle to maintain the pressure at 1MPa (the adjustment time is about 20 minutes), and the reaction time is 2 days. And afterthe reaction is finished, soaking the mixture in water for 3 hours, filtering and washing until the filtrate is close to neutral, and drying to obtain the modified desulfurizer. The content of each main component, Na, in the modified desulfurizer₂O：13.49％，SiO₂：37.53％。Al₂O₃：22.45％。

Comparative experiment:

0.5 g of the modified desulfurizing agent prepared in the example was taken, and the following comparative experiment and analysis were respectively performed:

(one) desulfurization experiments compared to untreated fly ash

And (3) desulfurization conditions: at a temperature of 500 ℃ and SO₂In a concentration of 1960ppm and a carrier gas of N₂The gas flow is 40ml/min, and the reactor is a fixed bed reactor.

SO₂The gas was detected by FT-IR spectrometer (Vector22, Bruker).

The experimental results are as follows:

as shown in FIG. 1, the desulfurization effect of fly ash itself is poor, the breakthrough time and breakthrough sulfur capacity are 0, and the saturated absorption is rapidly reached. The penetration time of the modified desulfurizer is 288min/g, and the penetration sulfur capacity is 64.6 mg/g.

Therefore, the modified desulfurizer removes SO at 100%₂The desulfurization activity is greatly improved after the condition is kept for a long time, and the modified desulfurizer is proved to be a high-efficiency and quick desulfurizer and is beneficial to flue gas desulfurization in a quick flowing process.

And (II) comparing the desulfurization experimental results of the adsorbents at different temperatures.

And (3) desulfurization conditions: SO (SO)₂In a concentration of 1960ppm and a carrier gas of N₂The gas flow is 40ml/min, the reactor is a fixed bed reactor, and the temperature is 200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃ respectively.

SO₂The gas was detected by FT-IR spectrometer (Vector22, Bruker).

The experimental results are as follows:

as shown in FIG. 2, it was found that the breakthrough time of the modified desulfurization agent was gradually increased as the desulfurization temperature was increased, and when the desulfurization temperature reached 500 ℃, the breakthrough time reached the longest value of 288 minutes per gram of the desulfurization agent, and the desulfurization temperature continued to increase and the breakthrough time began to decrease. It is stated that the desulfurization agent does not have the optimum desulfurization temperature, i.e., 500 ℃, but has the penetration time longer as the desulfurization temperature is higher.

As can also be seen from the following Table 1, the penetrating desulfurization efficiency of the modified desulfurizing agent is the best at 500 ℃, 46.3%, and the penetrating sulfur capacity is the maximum, 64.6mg/g desulfurizing agent; the saturated desulfurization efficiency is the best, 96.6%, and the saturated sulfur capacity is the largest, and is 134.mg/g desulfurizer.

Table 1: desulfurization activity of modified desulfurizing agent at different temperatures

Temperature of	Penetration adsorption	Saturated adsorption
	Penetration adsorption	Saturated adsorption	Time sulfur capacity min/g mg/g	Time sulfur capacity min/g mg/g
	200 300 400 500 600	42 9.4 108 24.2 186 41.6 288 64.6 168 37.6	Time sulfur capacity min/g mg/g	Time sulfur capacity min/g mg/g	424 34.0 596 60.0 1410 102.0 1440 134.0 1530 100.0

Therefore, the modified desulfurizer of the invention is an ideal desulfurizer suitable for medium temperature and anhydrous conditions.

(III) analysis of chemical composition, chemical composition and specific surface area of modified adsorbent, pore structure

As shown in Table 2 below, the molar Si/Al ratio (Si/Al) of the fly ash was 1.87, and after modification, the Si/Al ratio was reduced to 1.42, while a large amount of Na was contained₂O entered the resulting sample. According to the ratio of the mol of silicon, aluminum and sodium, the main component of the modified product can be simply written as NaSi_1.42AlO_3.42(sodium silicon aluminum oxygen complex).

Table 2: chemical composition, specific surface area and pore structure characteristics of fly ash and modified desulfurizer

Na₂O SiO₂Al₂O₃Si/Al surface area pore volume pore diameter Code

(wt％) (wt％) (wt％) (mol/mol) m²/g m³/g nm a 0.93 52.46 23.86 1.87 3.21 0.0036 11.4 b 19.29 32.30 36.49 1.13 17.06 0.038 9.0 c 17.94 24.18 22.25 1.36 13.30 0.057 17.1 d 13.49 37.53 22.45 1.42 29.18 0.14 18.1

Meanwhile, as can be seen from table 2, the specific surface area, pore volume and pore diameter of the fly ash are relatively small, and after modification, the specific surface area, pore volume and pore diameter of the adsorbent are respectively greatly improved, wherein the specific surface area is improved by more than 8 times, the pore volume is improved by more than 37 times, and the pore diameter is improved by more than 0.5 time. It is demonstrated that the pore structure and specific surface area of the modified sorbent are greatly improved, and these changes can greatly promote the improvement of the desulfurization efficiency of the sorbent.

Amorphous character of (tetra) adsorbents

As can be seen from fig. 3, fly ash is a kind of spherical particles with micron-sized particles of different sizes, on which some fine particles are more or less adhered. Aftermodification, a sample which is irregular, finer in granularity and scattered in stacking is obtained, and the sample can be judged to be an amorphous product from the appearance.

As shown in fig. 4, XRD (X-ray powder diffraction) analysis found that the peak intensities of fly ash a were all weak, indicating that only a small amount of crystalline phase components, which mainly included quartz and mullite, were contained. After modification, the original crystal phase components of the fly ash can be found to disappear or be weakened. Although a high spectral peak appears at the left end of a spectrum of the modified desulfurizing agent d, all the spectral peak intensities are weaker than those of the fly ash, and the fact that the modified crystalline phase components are not obvious proves that the modified desulfurizing agent belongs to an amorphous product.

Claims

1. A modified desulfurizing agent is prepared from the solid waste of coal as matrix and modifier (alkali metal or alkaline-earth metal oxide, hydroxide or carbonate) through solid-state synthesizing reaction in the presence of water.

2. The modified desulfurizing agent according to claim 1, wherein said coal-fired solid waste comprises fly ash and cinder.

3. The modified desulfurization agent of claim 1, wherein the modifier is selected from the group consisting of NaOH and Na₂CO₃、KOH、K₂CO₃、Ca(OH)₂、CaO、MgCO₃One kind of (1).

4. The modified desulfurizing agent according to claim 1, wherein the weight ratio of the coal-fired solid waste to the modifying agent is1 to (0.1-2); the water addition amount is 0.1-1 times of the total weight of the coal-fired solid waste and the modifier.

5. A process for preparing the modified desulfurization agent of claim 1, comprising the following steps in sequence:

(1) mixing the coal-fired solid waste, water and a modifier, namely an oxide, a hydroxide or a carbonate of alkali metal or alkaline earth metal to obtain a reactant which is uniformly mixed;

(2) reacting the reactant for more than 6 hours at the temperature of between 0.2 and 5MPa and between 100 and 600 ℃ to obtain a product, soaking and washing the product if necessary until the filtrate is nearly neutral, filtering and drying to obtain the desulfurizer.

6. The method of claim 5, wherein the coal-fired solid waste comprises fly ash and coal slag.

7. The method of claim 5, wherein the modifier is selected from the group consisting of NaOH and Na₂CO₃、KOH、K₂CO₃、Ca(OH)₂、CaO、MgCO₃One kind of (1).

8. The method according to claim 5, wherein the weight ratio of the coal-fired solid waste to the modifier is 1: 0.1-2; the water addition amount is 0.1-1 times of the total weight of the coal-fired solid waste and the modifier.