GB2042866A - Process for reducing grain dust explosibility - Google Patents

Abstract

A process for reducing the explosibility of grain dust by dispersing throughout an explosible mass of grain and grain dust an aqueous solution of an inorganic salt hydrate such that at least .0001 parts by weight of inorganic salt hydrate is dispersed per part of dust.

Description

SPECIFICATION Process for reducing grain explosibility This invention relates to a process for reducing the risk of explosion of dust in grain storage bins, and more particularly, it relates to such a process in which there is dispersed throughout the grain and grain dust mass an aqueous solution of an inorganic salt hydrate.

Since 1 958 an average of eight grain elevator explosions have occurred annually in the United States. Wherever grain is handled, particularly in large quantities, there is a hazard due to the possibility of an explosion of the grain dust. The dust content of grain may be as high as 1% by weight of the entire mass and each time the grain is handled it produces more dust. The explosibility of the dust depends on particle size, moisture content, quantity of dust, the presence of oxygen, a source of ignition, and a closed space to contain the dust, and other similar factors.

The usual approach for avoiding dust explosions has been to remove as much dust as possible from the grain usually by aspirators and dust collectors, and also attempting to eliminate all sources of ignition. Nevertheless, in spite of these precautions explosions continue to occur.

One proposal which has been described in the prior art for reducing the explosibility of the grain dust is to treat the grain with oil. This obviously has many undesirable side effects, such as additional cost, the introduction of an undesirable taste factor, difficulty in removing oil from the final product, etc.

In accordance with the present invention the explosibility of a mixture of grain and grain dust is materially reduced by dispersing throughout the mass of grain and grain dust an aqueous solution of an inorganic salt hydrate such that on a dry basis there is dispersed at least 0.0001, preferably from 0.0001 to 5.0, and more preferably 0.01 to 1.0 part by weight of the inorganic salt hydrate per part of dust. In one preferred embodiment of this invention the aqueous solution contains 1050% by weight of salt hydrate. In another preferred embodiment the aqueous solution additionally contains a 0.1 %-0.3% by weight of a surfactant.In still another preferred embodiment of this invention the aqueous solution additionally contains 0.1-10.0% by weight of paraffin oil and sufficient emulsifying agent to emulsify the oil into the aqueous solution.

The inorganic salt hydrate is preferably one which is acceptable as a food additive and thus need not be removed from grain which will eventually be included in a food product. The hydrate has the property of releasing all or a substantial part of this bound water when exposed to a source of heat or ignition, and this mechanism is effective in dampening any tendency to explode. The salt hydrate can be a solid salt but preferably it is a hygroscopic material that remains liquid and thereby can be effective in wetting the dust particles. Among the suitable salt hydrates are CaCI2 2H2O, CaCI2 6H2O, Na2SO4 1 0H20, MgCIz 6H20, Kal(SO4)2 1 2H20, NH4AI(SO4)2 1 2H20, Na2CO3 7H20, Na2C03.1 OH 20, and many others that are well known to chemists.It is also to be understood that an hydros salts are equally operable since they form hydrates when dissolved in water. Thus the term "salt hydrate" when used herein is intended to include both the hydrate and the anhydrous compound when used in the aqueous solution of this invention.

The manner in which the hydrate is applied to the dust and associated grain is not of any critical nature so long as the hydrate can be dispersed as widely as possible to affect the most number of dust particles. A convenient way of accomplishing this is to prepare a concentrated aqueous solution of the salt hydrate and apply that solution to the grain and grain dust mixture by spraying or other similar means. This increases the moisture content of the grain but not by any serious amount i.e. an average of about 0.5% by weight of moisture is normally encountered.

It has been found desirable in certain instances to include in the aqueous solution a small portion of a surfactant. It is believed that this helps to provide a more complete coverage of the dust particles by the solution. Suitable surfactants are the alkali metal and alkaline earth metal salts of carboxylic acids of 820 carbon atoms such as salts of acids such as stearic, oleic, palmitic, myristic, lauric, sebacic, dioctylsuccinic, and the like. Another common surfactant which is operable is a polysorbate. Other water-soluble types would also be useful for this purpose. Specific compounds include sodium stearate, potassium oleate, sodium dioctyl sulfosuccinate, and polysorbate. The amount of surfactant used should be from about 0.01% to about 1%, preferably from 0.1 to 0.3% by weight of the solution.

As mentioned previsously it has been found in the past that the incorporation of oil into grain dust provides some reduction in the explosibility of the dust and it has been found in certain embodiments of the present invention it may be advantageous to include along with the salt hydrate a small amount of oil emulsified into the aqueous solution that is sprayed onto the grain and grain dust. The amount of oil is relatively small, i.e. 0.110.0% by weight of the aqueous solution along with a sufficient amount of an emulsifying agent to cause the oil to emulsify completely into the water. Although any oil is suitable for this purpose paraffin oil is preferred. The emulsifying agent may be any that is commercially available such as the polysorbates.

It has been found preferable to treat a mass of grain and grain dust with an aqueous solution of the inorganic salt hydrate by spraying such a solution onto a moving mass of grain and grain dust. The salt hydrate should be as concentrated as conveniently possible in the aqueous solution, for example, from about 10 to about 50% by weight of salt hydrate in the aqueous solution. This solution is then sprayed onto the mass of grain and grain dust at the rate to apply at least 0.0001, preferably from 0.0001 to 5.0, more preferably 0.01 to 1.0 part by weight of inorganic salt hydrate (dry basis) per part of dust. In most situations a concentration of about 0.05 to 0.20 part by weight of inorganic salt hydrate per part of dust is sufficient to eliminate all normal possibilities of explosion.

The process of this invention can be illustrated by the following examples wherein parts and percentages are by weight unless otherwise specified. In many of these examples wheat starch or corn starch is employed rather than grain dust because it has been found in comparison testing that the explosibility of wheat starch or corn starch is even greater than that of grain dust which undoubtedly contains some portion of non-combustible material.Thus in order to provide better control over the experiments a commercial wheat starch (manufactured and sold by Nutritional Biochemicals of Cleveland, Ohio) ground to a particle size in which 311 particles were smaller than 74 microns and 90% of which were smaller than 44 microns was employed in most of the testing procedure and the results were compared against similar tests with actual grain dust and other similar explosible materials.

The testing was accomplished in laboratory apparatus which comprised a cylinder in which was placed a Nichrome wire filament activated with 28 voits of electricity to produce a red hot filament for ignition purposes. The top of the cylinder was covered with a paper clamped across the opening, and into the bottom of the cylinder there was a pipe inlet connected to a source of air pressure at 4.5 psig.

The paper employed is a typewriter quality paper of 25% cotton fiber ("Trojan Bond" sold by Brown Company of Holyoke, Mass.). A sample chamber in the compressed air line near the inlet in the bottom of the explosion chamber was provided for introducing a weighed amount of dust. The procedure was to activate the ignition filament for 40 seconds and then to open a solenoid valve in the compressed air line which permitted a sudden shot of air to blow the dust from the sample chamber into the bottom of the explosion chamber. If no explosion occurred or if such explosion occurred that the paper cover was not damaged the result was judged negative and assigned a value of 0. If there was an explosion sufficiently great to cause some damage to the paper cover it was judged either positive or weakly positive and given values of 1.0 or 0.5 respectively.Over a series of tests a calculation was made to judge the percentage incident of explosion by totalling the values assigned to the results and dividing by the number of tests involved. Thus, for example, if ten tests were run, nine of which showing positive and one of which showing negative results the percent incident of explosion would be 9.0/10 x 100 = 90%.

The following examples illustrate various embodiments of this invention.

EXAMPLE 1 As a comparative base there were run several experiments in which 100 parts of wheat starch were treated with various amounts of water as the sole agent to dampen the explosibility of the starch.

The following results were obtained.

Water No. % Incident Parts by Wt. Tests of Explosion 3.3 4 100 5.7 10 54 7.9 10 45 10.2 10 39 14.0 10 37 EXAMPLE 2 In order to determine the explosibility of different type of grain dust, samples were tested without any treatment other than sieving to different particle sizes. The unsieved starting material gave a negative result and each of the sieved samples (100,200,250, and 325 mesh) gave positive results.

EXAMPLES 3-1 5 In this series of experiments the salt hydrate, if one is employed, is CaCI2-2H2O. Each composition was prepared by adding the ingredients to a high speed mixer and stirring for 2 minutes. The composition was then sprayed onto wheat starch, and the sprayed wheat starch employed as the sample in the above described apparatus and procedure.The results are shown in Table % By Weight of % Incident Composition Applied No. of Composition of spray to Wheat Starch Tests Explosion Example Water Emulsifier Paraffin Salt Hydrate ml g Oil g ml 3 100 -- -- -- 3.0 3 100 4 100 -- -- 2.4 CaCl2.2H2O 3.0 6 50 5 100 0.1 -- 1.2 CaCl2.2H2O 3.0 6 86 6* 100 0.1 0.5 1.2 CaCl2.2H2O 3.0 3 0 7 100 0.1 -- -- 3.0 10 70 8 100 0.1 -- 1.2 CaCl2.2H2O 3.0 10 75 9* 100 0.1 0.5 1.2 CaCl2.2H2O 3.0 10 55 10 100 0.1 -- -- 3.2 13 73 11 100 0.1 0.5 -- 3.0 13 77 12* 10 0.1 0.5 1.2 CaCl2.2H2O 3.0 13 35 13 100 0.25 10.0 -- 3.0 5 0 14 100 0.2 -- 1.2 CaCl2.2H2O 3.0 3 66 15 100 0.2 1.0 1.2 CaCl2.2H2O 3.0 7 14 *Difference in results is attributed to differences in the order of addition of ingredients in preparing composition.In Example 6 the order was water, salt, emulsifier, and oil; in Example 9 water, emulsifier, salt, and oil; and in Example 12 water, emulsifier, oil and salt.

EXAMPLES 16-33 The procedures described with respect to Examples 3-15 was repeated employing other compositions, not including paraffin oil or emulsifier. The results are shown in Table II. TABLE II Composition of Spray % By Weight of % Incident Example Water Salt Hydrate Composition Applied No. of ml g to Wheat Starch Tests Explosion 16 3.0 1.0 CaCl2.6H2O 4.0 10 100 17 4.8 1.55 CaCl2.6H2O 6.35 10 50 18 7.0 2.2 CaCl2.6H2O 9.2 10 40 19 9.7 3.0 CaCl2.6H2O 12.7 10 20 20 13.6 4.1 CaCl2.6H2O 17.7 10 10 21 3.0 1.1 Na2SO4.10H2O 4.1 6 66 22 5.1 1.8 Na2SO4.10H2O 6.9 10 50 23 7.8 2.8 Na2SO4.10H2O 10.6 10 25 24 10.2 3.8 Na2SO4.10H2O 14.0 10 45 25 15.0 5.5 Na2SO4.10H2O 20.5 10 0 26 1.5 0.5 MgCl2.6H2O 2.0 6 75 27 3.3 1.1 MgCl2.6H2O 4.4 6 75 28 5.4 1.8 MgCl2.6H2O 7.2 6 33 29 7.5 2.5 MgCl2.6H2O 10.0 4 37 30 3.2 2.0 CaCl2.2H2O 5.2 5 100 31 5.0 5.0 CaCl2.2H2O 10.0 5 0 32 3.2 1.2 Na2SO4.10H2O 4.4 5 100 33 8.8 3.0 Na2SO4.10H2O 11.8 6 8 EXAMPLES 34 40 Corn starch was employed in this series of experiments rather than wheat starch.Otherwise the tests were run in the same manner as those of Examples 3-1 5. No emulsifier or paraffin oil was employed in these examples. The results are shown in Table 3.

TABLE III Composition of Spray % By Weight of % Incident Example Water Salt Hydrate Composition Applied No. of ml g to Com Starch Tests Explosion 34* -- -- -- 2 100 35** -- Na2SO4.10H2O 2.0 5 60 36 100 2.0 Na2SO4.10H2O 4.0 4 25 37 100 2.0 Na2SO4.10H2O 4.0 5 30 38** -- Na2CO2.10H2O 2.0 4 38 39 100 5.0 CaCl2.6H2O 5.0 4 0 40 100 2.0 Na2CO3.10H2O 6.0 2 0 *Cornstarch tested without treatment of any kind.

**Treatment is with salt hydrate in absence of any additional water.

EXAMPLE 41 In this example sodium stearate was added as a surface active agent to determine whether it provided any dampening affect. Wheat starch treated with 3.5% of an aqueous solution containing 0.25% sodium stearate produced 70% incident of explosion. When the solution also contained 1.1% by weight of Na2SO4 10H2O, the incident of explosion dropped to 50%.

EXAMPLE 42 Grain dust (wheat) sieved to 100 mesh was treated with salt hydrates in the absence of additional water and in each instance the explosibility was negative. The salt hydrates employed were: 3% KA (,SO4)12H20 3% Na3PO4 12H2O 5% CaCI2 2H2O Wheat starch was also treated with the first and third of the above salt hydrates and the results were also negative.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended

Claims (10)

claims. CLAIMS

1. A process for reducing the explosibility of grain dust which comprises dispersing throughout an explosible mass of grain and grain dust an aqueous solution of an inorganic salt hydrate such that on a dry basis there is dispersed at least 0.0001 parts by weight of inorganic salt hydrate per part of dust.

2. A process according to claim 1, wherein the weight proportion of inorganic salt hydrate is from 0.0001 to 5.0 parts per part of dust

3. A process according to claim 2, wherein the weight proportion of inorganic salt hydrate is 0.01 to 1.0 part per part of dust.

4. A process according to claim 1, 2 or 3, wherein the aqueous solution contains 1 0-50% by weight of salt hydrate.

5. A process according to any one of the preceding claims, wherein said inorganic salt hydrate is CaCl2.2H2O; CaCl2.6H2O; Na2SO4- 10H2O; MgCl2.6H20; KAI(SO4)2- 12H2O; NH4AI(SO4)2 12H2O; Na2CO3-7H2O; or Na2CO3 10H2O.

6. A process according to any one of the preceding claims, wherein the said solution additionally contains 0.1-0.3% by weight of a water-soluble surfactant,

7. A process according to claim 6, wherein sald surfactant is sodium stearate, potassium oleate, sodium dioctyl sulfosuccinate, or polysorbate.

8. A process according to any one of the preceding claims, wherein the aqueous solution additionally contains 0.1-10.0% by weight of a non-toxic oil emulsifled into the aqueous solution.

9. A process according to claim 8, wherein said oil is paraffin oil.

10. A process according to any one of the preceding claims, wherein the aqueous solution is dispersed by spraying it onto a moving mass of said grain and grain dust.