JPS5846337B2 - Composition containing lime or limestone and Graham's salt or MxPnO (↓3n↓+↓1) - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to novel compositions for use in removing oxides of sulfur from gases.

Generally speaking, the invention can be defined as follows.

A composition for use in removing sulfur oxides from a gas by contacting components containing water, calcium ions, and sulfite or bisulfite ions at 2 to 100° C. to form a sludge, the composition comprising: graham salt or a dissolved polymer having the general formula, and the weight ratio of Ca to graham salt in the formula or Ca to Mx
The weight ratio of the PnO (3n+, ,
and y is the valence of M.

The sludge obtained by the present invention is an improved sludge.

In general terms, the novel composition of the present invention can be defined as a novel composition comprising lime or limestone and Graham's salt or a water-soluble polymer of the formula II above, said new composition may also contain water. .

As discussed more fully below, the method of the present invention is particularly useful in connection with the removal of sulfur oxides in the field of flue gas desulfurization.

The sludge of the present invention is useful in that it has a faster initial hardening rate than a corresponding sludge formed without Graham's salt or a compound of formula (2).

The sludge produced in accordance with the present invention is also useful as a landfill material or as a raw material for oxidation into gypsum board.

The novel compositions containing lime or limestone and Graham's salt or compounds of formula (2) are useful as compositions for treating aqueous wastewater containing sulfites.

The new substance may also be formed by precipitating a calcium-containing sludge from a sulfite-containing wastewater or by contacting with flue gas containing oxides of sulfuric acid to form a calcium-containing sludge, or by forming a sludge containing sulfur. Useful as a base material diluted with water, or water and lime or limestone, for preparing an aqueous material for forming a calcium-containing sludge on contact with sodium-containing water that has already been contacted with flue gases. .

Such sodium-containing water is acceptable in two-stage alkaline processes of flue gas desulfurization.

It goes without saying that the compositions of the present invention can equally be used in the presence of sulfate ions together with sulfite or bisulfite ions.

The disposal of sludge containing calcium sulfite is one of the most significant environmental problems facing the United States today.

Such sludges occur in many industrial processes, such as the desulfurization of flue gases containing sulfur dioxide and other sulfur oxides.

Such sludges often contain both calcium sulfite hemihydrate and calcium sulfate trihydrate.

Many such sludges dewater very slowly and some contain large amounts of water even after conventional dewatering steps have been carried out.

Some are thixotropic.

Large amounts of land are wasted as lagoons to store such sludge, and environmentalists fear that the dammed sludge, which has a low solids content, will leak and contaminate surface and groundwater. There is.

Significant amounts of money are spent in industry and utilities related to the installation, operation and maintenance of sludge management systems.

Various methods have been proposed for dealing with and avoiding the sludge problem, but none are completely satisfactory.

Solutions tried in the prior art include expensive but expensive lining of the lagoon with concrete or plastic liners to prevent water leakage, and untreated landfilling (partial dewatering of the sludge takes a long time, in the desulfurization of flue gases to increase the ratio of calcium sulfate dihydrate to calcium sulfite hemihydrate (requiring large areas of land, and the land is often unusable for other purposes). Forced oxidation (which requires more capital invested equipment), discharging acid waste into the sea (rights curtailed by laws and regulations), expensive legal methods,
Draining waste into deep, unused wells (legally regulated and in most cases deep wells into which waste has been dumped become useless), draining untreated acid waste into running water ( methods (which tend to be banned in many countries), smearing untreated sludge onto land (which dries slowly and requires a lot of land), and stabilizing the sludge as a solid with expensive chemical fixatives. (which further increases the total volume of solids to be treated and permanently requires land for their storage), and methods of altering the crystal size by adjusting the physical processing conditions (the required physical conditions The equipment and processes to achieve this are usually very expensive).

The following are improvements of the present invention over the prior art.

The calcium-containing sludge obtained according to the invention has a faster initial settling rate than the corresponding sludge produced without Graham's salt or the compound of formula I.

Furthermore, the Graham salt or formula ■ described herein
Even when the lowest amount of the compound in the preferred range is used, the resulting calcium-containing sludge has a lower volume of solids than the corresponding calcium-containing sludge produced without the use of Graham's salt or the compound in The viscosity is low, the filtration rate is fast, and the density is high.

In some cases, the normal crystal morphology of calcium sulfite hemihydrate is distorted by agglomeration of the crystals into a more globose shape than usual;
It was observed at 2000x magnification that the morphology of calcium sulfate trihydrate crystals changed from needle-like to block-like.

This is due to the above-mentioned properties.

Since more water is removed from the sludge, fewer sludge lagoons are needed and land is saved.

The present invention can be implemented at relatively low cost since it is sufficient to use small amounts of inexpensive chemicals.

The method and novel composition of the present invention can be applied to the current neutralization of sulfites with lime or limestone using existing equipment with little modification or modification.

For example, Graham's salt or a compound of formula (II) may be applied to the lime or limestone in the wet or dry state prior to contacting the lime or limestone in the wet or dry state with the sulfite or bisulfite ions.

The water liberated from the sludge is treated by conventional means,
Recirculation or return to running water faster and in greater quantities reduces the risk of water contamination and also reduces the area required for sludge storage.

The increased density of the resulting sludge makes the material more economical to handle.

This is because the time and equipment required to move the reduced volume dense solids is reduced and smaller.

Additionally, increasing the density of the stored sludge reduces the risk of leaching and leakage.

The water is removed from the sludge before it is used as a landfill material or as a land plaster, so that the pollutants removed with the water can be treated biochemically or chemically with other wastewater instead of going to the soil.

The present compositions are suitable for both the fly ash normally found in flue gases and the small amounts of MgO that are sometimes used with lime or limestone water to neutralize flue gases, so-called It is also unaffected by the presence of sodium ions found in the two-step alkaline method.

Many other advantages will be apparent to those skilled in the art.

The invention will be described in more detail below.

It is important that the Graham salt or the compound of formula I be present in solution when the calcium ions are reacted with the sulfite or bisulfite ions.

Adding Graham's salt or a compound of formula I after forming a calcium-containing sludge does not provide advantageous results.

When using the composition of the invention, calcium ions are contacted with sulfite or bisulfite ions at a temperature of 2 to 100°C, preferably 2 to 60°C.

Sulfate ions may also be present. As used herein, the term lime refers to quicklime, hydrated lime, and hydraulic lime in its various chemical and physical transformations.

Graham's salt is a well-known, high molecular weight, water-soluble glass that can be prepared by several methods, including melting monosodium phosphate over an extended period of time and rapidly cooling the melt. .

This Graham's salt is also called sodium metaphosphate glass, and its composition is generally expressed as (NaPO3)n.

The amount of the Graham salt of the present invention or the compound of formula (2) is based on the amount of calcium present.

Usually 0.0015 to 0.2 parts of Graham's salt or 0.0 of PnO(3n+1) present in the compound of formula (1)
1 part calcium ion to 0.015 to 0.2 part is suitable, preferably 0.01 to 0.04 part Graham's salt or 1 part calcium salt to PnO(3n+t).

Parts of CaO for Graham's salt or PnO (3n+t) are based on dry weight.

However, the use of Graham's salt or the compound of formula (■) in the maximum amount within the aforementioned range is desirable in that it increases the initial settling rate compared to the corresponding calcium-containing sludge prepared without Graham's salt or the compound of formula (■). However, this is undesirable in that the final settling volume increases.

Graham's salt or Formula I to prevent an increase in final settling volume.
The amount of the compound is adjusted to a preferred range.

When heavy metal ions, such as iron, are present in large amounts, the use of large amounts of Graham's salt or the compound of Formula I provides desirable results.

Formula I includes compounds such as sodium pyrophosphate, sodium tripolyphosphate, potassium pyrophosphate, potassium tripolyphosphate, and there are also commercially available acids known to contain compounds of formula (II).

The compounds of formula I can be used in hydrated or anhydrous form.

The compositions of the present invention are useful in connection with removing oxides of sulfur from gases.

For example, flue gases produced from the combustion of fossil fuels contain and contain sulfur dioxide.

Contacting sulfur dioxide with ice produces sulfite, which ionizes to sulfite and bisulfite ions.

If sulfur trioxide is also present, it produces sulfuric acid on contact with water and ionizes to sulfate ions.

Wet scrubbing of the flue gas by direct contact with aqueous lime or aqueous limestone forms a slurry containing a calcium sulfite hemiaqueous phase, and if sulfur trioxide is present in the flue gas, the slurry is further contaminated with sulfuric acid. Contains calcium ions.

Before contacting the aqueous lime or aqueous limestone with flue gases,
By adding Graham's salt or a compound of formula (2) to aqueous lime or aqueous limestone, a calcium-containing sludge with the above-mentioned advantageous properties is produced.

The compositions of the invention are also suitable for so-called two-stage alkaline systems of flue gas desulfurization.

In such desulfurization, an aqueous sodium salt solution is first contacted with flue gas to form sodium sulfite, sodium bisulfite, and optionally sodium sulfate, and then with lime or limestone to form a calcium-containing sludge for recirculation. liberates sodium.

The composition of the present invention may also be used in a process known as forced oxidation, in which some of the sulfite ions are converted to sulfate ions, with or without supplying external air into the system.

In such methods, calcium ions are simultaneously or separately contacted with sulfite or bisulfite ions to form a sludge containing calcium sulfite hemihydrate.

The novel compositions of the present invention include lime or limestone and Graham's salt or a water-soluble polymer having the formula MxPnO (sH-h).

Such novel compositions may further contain water, M, x, y
and n are as defined above.

The components may be added in any order.

In particularly useful embodiments of such novel compositions, calcium versus Graham salt or PnO(3n+
1) The weight ratio of the components is 1:0.0015-0.2.

An example is shown below.

All parts in the examples are parts by weight unless otherwise specified.

The data presented in the table below was obtained from a curve obtained by plotting the height of the liquid/solid interface of the sludge under static conditions in a 10071 Ll graduated cylinder as a function of time.

As used herein, the term "initial sedimentation rate" refers to time t.

and tl divided by the time t1 of the first linear portion of the above-mentioned curve.

The term "final settling volume" as used herein refers to the volume of solids, including the sludge portion, below the liquid/solid interface after the height of the interface has remained essentially unchanged for 2 hours from the curves described above. means.

Example 1 A material containing 1 part calcium to 0.01 part Graham's salt was prepared by adding 501 parts of CaO to 0.3551 parts of Graham's salt and mixing.

Example 2 * * The material described in Example 1 was diluted with 100 yd of water at room temperature with stirring.

Example 3 50'f! By adding 6.24P of sodium pyrophosphate to CaCO3 of
A material containing 1 part calcium to 0.2 part nO(sn+1) was prepared.

Example 4 1001711 of water was added to the material of Example 3 and mixed.

Examples 5-29 In each of Examples 5-29, 80 g of lime or limestone as shown in column 2 of Table A below is placed in a beaker containing 10 g of
1 of water was mixed.

The temperature of each mixture was adjusted to the initial temperature shown in column 3 of Table A.

Then, add the compound shown in column 4 of Table A to each mixture so that the weight ratio of Ca to P nO (s n + 1) in Graham's salt or the compound in column 4 becomes the number shown in column 5 of the 1 to person table. Added just the right amount.

If column 4 of Table A shows 10-, neither Graham's salt nor the compound of formula (2) is used.

In examples using Ca(OH)2, pH 5.5 is reached; in examples using CaCO3, pH 3.
Sulfur dioxide gas was bubbled through each mixture while stirring until the temperature reached 0.

The contents of each beaker were stirred and transferred to a separate 100ml graduated cylinder and allowed to stand for 2 hours.

The "initial settling velocity" and "final settling volume" of each side were measured as described above, and the results are shown in columns 6 and 7 of Table A, respectively.

The abbreviations rG, S, J are used in the table below for Graham's salt, and the compound column 10- in the table indicates a control example in which neither Graham's salt nor a compound of formula (1) is used for comparison.

Examples 30-37 The procedure for Examples 30-370 is similar to the procedure for Examples 5-290 above except that air is bubbled into each mixture while stirring for about 2 hours after sulfur dioxide gas is bubbled into each mixture. .

Just as Table A relates to Examples 5 to 29, Table B relates to Examples 30 to 3.
7.

Examples 38-43 In each of Examples 38-43, 80 Sl' of water was adjusted to the temperature indicated for each side in column 3 of Table C.

In each water, the weight ratio of Ca to Graham's salt was 1:C.
Sufficient Graham's salt was added to reach the numbers shown in column 5 of the table.

Fine powder of CaCO3 and IOP were added to each water and mixed.

Introduce SO2 gas into each water while stirring, 1 minute after the start of SO2 introduction※※, and 5 minutes while introducing S02 for another 9 minutes.
0% H2SO42.02? was added to each water at a rate of 2 drops/30 seconds.

SO2 was turned off when pH reached 3.0.

The resulting slurry was mixed with air for 2 hours and then heated for another 100 min.
The mixture was placed in an m1 graduated cylinder and allowed to stand for 2 hours.

"Initial settling velocity" and "final settling volume" for each side
are shown in Table C below.

Examples 44-48 In Examples 44-48, the water of 801 was adjusted to the temperatures indicated for each side in column 3 of Table D below.

A sufficient amount of Graham's salt was added to each water to provide a weight ratio of Ca to Graham's salt used on each side of 1 to the number shown in column 5 of the table.

10f of fine powder of Ca(OH)2 was added to each Graham's salt aqueous solution.

Blow SO2 into each for 15 minutes, and 95.7% H2SO41,547? in 1 minute after starting to blow SO2. was added to each.

H2SO4 was supplied at a rate of 1 drop/30 seconds for 4 minutes and then at a rate of 1 drop/minute for 11 minutes.

The pH of the resulting slurry was 5.5.

The resulting slurries were individually mixed, transferred to another 100 ml graduated cylinder, and allowed to stand for 2 hours.

The results are shown in Table D below. Examples 49-50 In each of Examples 49-50, sufficient graham is added so that the weight ratio of Ca to graham salt used on each side is 1 to the number for graham salt shown in column 5 of Table E. 80' of water at 25℃ in a beaker containing salt? were mixed.

Fura※※Iatush 1i and Ca(OH)2 fine powder 10 from a commercially available coal-burning electric utility station
S' was added to each beaker with mixing.

Then, S until the pH of the obtained slurry reached 5.5.
Injected O2 gas.

Each slurry was poured into a 100ml graduated cylinder and allowed to stand for 2 hours.

The results are shown in Table E below.

Examples 51-52 In each of Examples 51-52, the IOP at 60°C
of Na H803 was dissolved in 90rrL of water in a beaker, and a sufficient amount of Graham's salt was added to obtain the weight ratio of Ca to Graham's salt as shown in column 5 of the 1:F table for Graham's salt. .

IOS' Ca(OH)2 was added and stirred for 20 minutes.

The resulting slurry was transferred to another 1007711 graduated cylinder and allowed to stand for 2 hours.

The results are shown in Table F below.

Examples 53-55 In each of Examples 53-55, 80 L of water at 25°C? were placed in separate beakers and mixed by adding sufficient amount of Graham's salt to each beaker to obtain the weight ratio of Ca to Graham's salt as shown in column 5 of Table G below 1: for Graham's salt. .

Add 0.531 MgO to each and mix, then 1
0i of Ca(OH)2 was added to each with mixing.

*SO2 gas was blown into each slurry while stirring until the pH of the resulting slurry reached 5.5.

Pour the slurry into another 100ml graduated cylinder and
I left it for a while.

Claims (1)

[Claims] 1 Lime or limestone and Graham's salt or the formula MxPnO(an+,) (where M is a cation, n is a positive integer greater than 1, X is (n+2)/y, and y is M A composition for removing sulfur oxides from gas or water, comprising a water-soluble polymer having a valence of . 2. In the composition according to claim 1, Ca
A composition in which the weight ratio of ions to Graham's salt or PnO(2n+1) is 1:O,0O15 to 0.2. 3. The composition according to claim 1, which also contains water. 4. The composition according to claim 2, which also contains water.