Patent Application
20090033140
The present invention relates to methods of controlling the flow of gases in mine applications. The present invention is useful during mining operations such as during cutting of the wall to control the flow of gas.
The use of foam to suppress coal dust is known and it typically includes applying a foam composition to a falling mass of coal either at a mine face or at a conveyor transfer point. It is also known to use foam to provide a temporary barrier layer over a landfill to protect the atmosphere from odors and blowing trash. Certain foams, formulated with metal ion salts, can be used to control and minimize the generation of hydrogen sulphide. It is also known to use a foam in the control of abandoned mine fires where the foam can be pressure injected underground. The foam can displace combustion air and gases that are the products of combustion, can extinguish the active burning zones, can remove heat from the surrounding strata, and can deposit known chemical fire fighting ingredients.
While foam has been suggested for use in the above disparate applications, there has been no suggestion to use foam to control gas flow, i.e., to increase the resistance to gas flow in particular mine applications such as during the active mining operation. During the mining of coal, methane may be generated. Methane is explosive in the presence of about 12%-21% oxygen when the methane is present at a level from about 5% to about 15%. Thus, there is a need to control the relative amounts of gases (e.g., oxygen and methane) during active mining operations. Typically, the control is provided by ventilation systems. While ventilation systems are adequate, they are expensive and thus there is a desire for a lower cost method of controlling gases.
The present invention is directed to methods of using foam to control the flow of gas within particular areas of certain mine applications. In one aspect, the present invention relates to a method of increasing resistance to gas flow in a mine void space that comprises delivering a foam composition to a void space from one of a shortwall mining machine, a longwall mining machine, a pillar extractor, a portion of a shortwall mining machine, a portion of a longwall machine, and portion of a pillar extractor. The term “portion” is used to indicate any part of the machinery or any sub-component associated with the machinery.
In one aspect of the present invention, during the mining operation as the cutter device (the device that removes the in situ raw ore) traverses the panel, a gob is created. Seals are constructed behind the active face adjacent the gob to create a semi-sealed gob. The seal may be created at suitable cross cuts. The seal may be equipped with piping so that an inert gas such as nitrogen can be injected to depress the oxygen concentration. Foam may be delivered to the void area adjacent the seal to provide a barrier to flow of gas (e.g., methane from the gob or oxygen to the gob).
In another aspect, the cutting device may be equipped with one or more foam delivery devices such as a nozzle to direct foam according to the present invention adjacent the head gate or tail gate to provide a barrier to flow of gas (e.g., methane from the gob or oxygen to the gob).
In one aspect, the present invention contemplates reducing the methane content at a tailgate by at least 0.1% by weight. In this regard, the present invention contemplates reducing the methane content at a tailgate by an amount ranging from about 0.1% to about 1%, by weight. Additionally, the present invention contemplates reducing the methane content at a tailgate by an amount ranging from about 0.2% to about 0.8%, by weight, or from about 0.3% to about 0.6% and generally by an amount of about 0.4% to about 0.5%.
The foam is delivered at a rate and in an amount sufficient to fill the void created by the seal adjacent the gob. The foam is selected to have a dwell time suitable to achieve additional mining operations. For example, the foam will have a dwell time of at least several hours, or a day, or several days, or a week, or several weeks, or a month, or several months, or one year, or several years. Put another way, the dwell time should have a half-life (the time after which one-half the initial volume of foam remains) on the order of at least about 50 hours, desirably about 100 hours, suitably about 200 hours, although greater times such as 300, 400, 500, 600, 700, 1000 hours or more are contemplated.
While the method of the present application may be applicable to a variety of mining operations, it is believed that it will be effective for pillar extraction mining, shortwall mining and longwall mining operations. In these operations, the reserve 10 is divided into panels 12 as shown in
Referring more specifically to
While the direction of mining proceeds in the direction indicated by the arrow 19, production or ploughing of the coal always proceeds from the headgate 22 to the tailgate 24 in the direction shown by the arrow 25 for shortwall mining, and potentially in both directions for longwall systems as will be described below in more detail. A “three-entry” development system uses the three maingate entries 16a-c, collectively the maingate 16, the three headgate entries 22a-c, and the three tailgate entries 24a-c that are commonly used to provide the necessary airways, escapeways, and other functions. The system permits installation of a belt and travelway in the center entry, and may allow one outer entry to be used as a return airway. While the present invention is described in connection with a “three-entry” development system, one of skill in the art will necessarily understand that the present invention could likewise be used in other arrangements, as will become clearer below.
Upon completing development of the panels 12, the longwall, shortwall, or pillar extraction mining of the panel 20 commences as shown in
Referring now to
Referring back to
According to the principles of the present invention, the low oxygen content gas mixture used to inertize the space could also be used to generate the foam, which in turn could be used to fill the void space created and encountered during the mining process, including but not limited to cross cut volume. Before, during, or after the construction of ventilation control devices, specifically seals or stoppings, it might be useful to provide a temporary or semi-permanent obstruction to gas flow or infiltration into the void space that may be created or encountered during the mining process. Accordingly, the present invention contemplates providing a composition that can be caused to expand into a foam upon appropriate mixing with a gas such as a low oxygen content gas or nitrogen. The foam can be delivered in any suitable manner such that the foam is caused to expand and fill the void space between adjacent stoppings and thus, provide a barrier to the presence or flow of any gas.
In addition, as the gob forms, it would be desirable to reduce or prevent gas or gas mixtures from passing through or from the gob to the active mining area where people may be present. Accordingly, the present invention provides a method of increasing the resistance to the flow of gas through a gob by applying a foam into the void space of the gob as it is being formed. In this regard, at least one delivery nozzle could be fixed to one or more of the tail frame structure of the conveyor, the shield side, or the gob shield. Each nozzle could be configured to deliver the foam composition to create a “plug” or to create a blanket and thus create a resistance to gas flow or displace volume which could otherwise be filled by a gas or gas mixture.
In one example of the present invention, during a longwall mining operation or a shortwall mining operation, a foam composition is delivered from one of the conveyor system, the shortwall machinery, or the longwall machinery to the gob, where, upon delivery, the foam composition is caused to expand and provide a barrier or a resistance to the flow of gas from or through the gob pile to an active mining work place. Generally, a low oxygen content gas or an inert gas such as nitrogen is mixed with the foam composition to cause the composition to expand to form the desired foam. In addition, the resulting foam should be inert, flame resistant, and/or incombustible. In this regard, the foam can provide a barrier or resistance to flow of methane from the gob to areas adjacent the gob. Alternatively or simultaneously, the foam can provide a barrier or resistance to the main ventilation flow of gas to the gob area, which can aid in the efficiency of gob vent boreholes (GVB).
Referring now to
The cutting machine 100 is movable in a cutting direction 19. It possesses two cutting rolls 102, 104 to shear the face of the panel 20. The dislodged ore is loaded by the cutting machine 100, sometimes referred to as a “cutter-loader,” on a conveyor. The conveyor consists of a channel 106, in which an armored chain conveyor is moved along the panel face. The cutting machine 100 is adapted for moving along the panel face 20. The channel 106 is subdivided into individual units that are interconnected, but are capable of performing a movement relative to one another in the working or cutting direction 19. Each of the channel units connects to a support unit 110 (110a-110r, respectively by means of a cylinder-piston unit (advance piston) 112. Each of the support units 110 serves the purpose of supporting the wall. To this end, a further cylinder-piston unit (not shown) is used, which stays a base plate relative to a roof plate. At its front end facing the ore bed, the roof plate mounts a so-called ore face catcher (not shown). The catcher typically is a flap that can be lowered in front of the mined ore face. The ore face catcher must be raised ahead of the approaching cutting machine 100. Likewise to this end, a further cylinder-piston unit not shown is used. These operating elements are described only by way of example since these machines are known. Of course, additional operating elements are present, but they need not be mentioned and described for the understanding of the invention.
Typically, a mining shield control device 114 is associated to each of the supports 110. A control device 120 may be associated with a group of supports 110 or mining shield control devices 114. Control systems 122 include data acquisition, data storage, and programming.
The foam delivery device 200 includes a tank 202 for containing the foam composition or concentrate and a pump 210 for delivering the foam composition. The tank 202 includes an input line 204 for delivery of the foam composition or concentrate. An output 206 of the tank is fluidly connected to the input 208 of the pump 210. A water supply line 212 connects to one of the output of the tank 206 or the input of the pump 208. The water is supplied at a rate sufficient to dilute the foam composition or concentrate to the desired level. The pump 210 mixes the water and foam composition or concentrate and provides an output 212. The output 212 is directed to a foam generating apparatus 214, details of which are not provided since such are well known in the art. The tank 202 and pump 210 may be provided on a skid 220 so that the foam delivery device 200 can be transported or moved as the cutting machine 100 moves.
The foam generating apparatus 214 includes a gas supply 216 such that the gas is mixed with the pump output 212 to expand the liquid pump outlet and create the foam, which is then discharged through a nozzle 218. The foam may be generated using known methods, e.g., by agitating a foamable solution of the invention in the presence of a gas, and in particular an inert gas other than air, such as nitrogen. One apparatus for this purpose forces the foamable solution through a restricted passage at a high pressure and injects gas into the solution downstream of the restriction. The foam may then be sprayed onto the substrate through a nozzle 218.
At the time of foam production, the foamable solution may be pumped at, for example, 400 to 500 psig, through a flow controlling orifice at a pre-determined flow rate. Downstream of the liquid flow control orifice, the gas is injected and mixed with the liquid stream. This may be achieved by using a gas orifice to control the flow in the same manner as the liquid side of the system. After the two streams are combined, the mixture passes through an exit, such as a hose that may or may not have a distribution nozzle attached. The foam can then be distributed over the area to be covered, by manually or automatically (or remotely) directing the hose nozzle. Similarly, the output may be directed into a multiport manifold for distribution. The manifold depending upon its size and the flow rate of foam may be used to distribute the foam either manually or mechanically (i.e., remotely).
As can be seen from
Thus, the present invention further provides a foam generated by the methods of the invention. The resulting foam is particularly useful as a barrier layer. Desirably, a foam of the invention exhibits the following characteristics: the foam's dwell time is very long (slow) and can be extended by increasing the concentration (i.e., decreasing the dilution ratio); the foam's stiffness exhibits the capability of covering the vertical surface of the gob material or seal material, the foam's persistence is excellent.
The foam may be delivered at any suitable rate although it is desirable to deliver the foam rapidly. In this regard, the foam may be delivered at a rate between about 100 gallons per minute (gpm) to about 1200 gpm. In some aspects, the foam may be delivered at a rate between about 200 gpm to about 1000 gpm, or between about 400 gpm to about 800 gpm, or between about 500 gpm to about 700 gpm, and about 600 gpm.
The foam will have a dwell time of at least several hours, or a day, or several days, or a week, or several weeks, or a month, or several months, or one year, or several years. Put another way, the dwell time should have a half-life (the time after which one-half the initial volume of foam remains) on the order of at least about 50 hours, desirably about 100 hours, suitably about 200 hours, although greater times such as 300, 400, 500, 600, 700, 1000 hours or more are contemplated.
In one aspect, the present invention contemplates that during mining operations and after delivery of foam, the methane content at a tailgate may be reduced by at least 0.1% by weight. In this regard, the present invention contemplates reducing the methane content at a tailgate by an amount ranging from about 0.1% to about 1%, by weight. Additionally, the present invention contemplates reducing the methane content at a tailgate by an amount ranging from about 0.2% to about 0.8%, by weight, or from about 0.3% to about 0.6% and generally by an amount of about 0.4% to about 0.5%.
A variety of foam compositions are known and it is contemplated that many compositions will be suitable for the desired application. In general, the foam composition should be able to be delivered to the intended site, should have a sufficient stiffness to retain its integrity and continuity for a period of time required to serve the intended function and should have a desirably long dwell time so that vertical and non-horizontal surfaces can be covered. Typically, the foam should have a stiffness such that it will retain its integrity for at least several hours, or a day, or several days, or a week, or several weeks, or a month, or several months, or one year, or several years. It is also desirable that the foam be biodegradable or non-toxic so that when the mine is closed, or at some other time when the barrier is no longer required, the foam does not pose an undesirable environmental impact. The foam composition may be formulated to include chemical control agents for compounds such as hydrogen sulphide, which may be present or may be generated during the working of the mine. The foam may also be formulated in a manner to allow buffering of any acidity or alkalinity of any water that may be present.
Consistent with these objectives, several exemplary foam compositions will be described below. One of skill in the art, however, will understand that these compositions are simply exemplary and that the foam composition may have include a variety of ingredients so that the foam composition achieves the above objectives.
One example of a foam composition useful in the process of the present invention includes a foam prepared from an aqueous composition comprising, in an approximately 1:1 molar ratio, (A) an anionic surfactant and (B) a carboxylic acid salt, R2 COOM1, where R2 is an alkyl group containing from 8 to 30 carbon atoms and M1 is a monovalent cation. The anionic surfactant may be a sulfate having the formula
where —OR is an alkoxy, alkylenoxy or alkaryloxy group having from 10 to 20 carbon atoms or an alkyl polyether group
in which R′ is an alkyl group containing from 10 to 20 carbon atoms, R″ is H or an alkyl group containing up to 4 carbon atoms, such as H or CH3, and n is an integer from 1 to 12, preferably from 3 to 6; and where M is a monovalent cation. M may be an alkali metal ion, the ammonium ion or alkyl-substituted or hydroxyalkyl-substituted ammonium.
When M is an alkali metal it is sodium, potassium or lithium. When M is an alkyl or hydroxyalkyl group-substituted ammonium, it generally has up to six, and preferably up to 3 carbon atoms. Suitable alkyl groups include methyl, ethyl, isopropyl, etc. radicals. Suitable hydroxyalkyl groups include hydroxyethyl, hydroxypropyl, etc. radicals. Examples of substituted ammonium radicals are mono-, di- and tri-alkyl ammonium radicals containing 1-3 carbon atoms in each substituent group, and mono-, di- and trialkanolammonium groups having 2-3 carbon atoms in each substituent. Substituted ammonium groups include mono-, di- and triethanolammonium radicals.
Typical R′ constituents include alkyls, such as decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, etc.; alkenyl groups, such as 1-dodecenyl, 1-tetradecenyl, 2-hexadecenyl, etc.; and alkaryl groups such as dodecylbenzene, isopropylnaphthalene, hexadecyltetraethoxy, etc.
Alternatively, the anionic surfactant may be a sulfonate having the formula
where R1 is an alkyl, alkylene or alkaryl group containing from 10 to 20 carbon atoms, and where M is a monovalent cation as further described above. Typical R1 substituents include alkyls, such as decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, etc.; alkenyl groups, such as 1-dodecenyl, 1-tetradecenyl, 2-hexadecenyl, etc.; and alkaryl groups such as dodecylbenzenene, isopropylnaphthalene, etc.
Sulfonate surfactants that are desirable for use in the invention include potassium dodecyl sulfonate, sodium 1-dodecenyl sulfonate, sodium dodecylbenzenene sulfonate, ammonium isopropylnapthalene sulfonate etc. Desirably, sulfonates include sodium alpha-olefin sulfonate, a mixture comprised substantially of C12 and C14 alpha-olefin radicals.
Sulfate surfactants that are desirable for use in the invention include alkyl sulfates, such as sodium lauryl sulfate; alkenyl sulfates, such as potassium 1-dodecenyl sulfate: alkaryl sulfates, such as ammonium dodecylbenzene sulfate; and alkylpolyether sulfates, such as sodium octodecyltetraethoxy sulfate. Suitable sulfates include the alkylpolyether sulfates. Mixed sulfonates and/or sulfates, i.e. mixtures of sulfonates or mixtures of sulfates or mixtures of sulfonates and sulfates having different substituents may also be used.
For some applications, it may be desired to use sulfonates and/or sulfates having, as the R or R′ substituent, a heteroatom-containing radical. In addition to carbon and hydrogen atoms, oxygen may be present in the form of carboxyl, ester or ether groups. The anionic surfactant may be present in the compositions of the invention at concentrations in the range of about 10-30 percent, and generally about 15-25 percent, based on the total dry weight of the composition.
Foams prepared as described appear to have a long life as compared to aqueous foams in general, and possess a stiffness much like cotton candy. Thus, the foams can be applied to an irregular, rough or sloping surface, where they will retain their integrity and continuity.
One of the two main components of the foaming composition used according to one aspect of the present method is an anionic surface active sulfate or sulfonate having the respective formulae as set forth and defined above. R, R′ and R1 are relatively large groups containing 10 to 20 carbon atoms. Examples of alkyl groups for R, R′ and R1 are lauryl, myristyl, palmityl and stearyl. Examples of alkylene groups for OR and for R1 are C10-C16 alpha olefins. Examples of alkaryl groups for OR and R1 are decylbenzene, dodecylbenzene and propylnapthalene. Examples of alkyl polyether groups are
and those derived from commercial homolog mixtures wherein, for example, R′ may be mixtures of C10 and C12 or C12 and C14 alkyl groups and n may be various integers within the stated ranges. Preferred —OR groups are alkylenoxy groups, especially alpha olefins containing from 10 to 14 carbon atoms, and alkylbenzyloxy in which the alkyl group contains from 10 to 16 carbon atoms.
As for the carboxylic acid salt, R2 is preferably a straight chain alkyl group, and can be one having from 8 to 20 carbon atoms. Examples of alkyl groups for R2, are pelargonyl, lauryl, myristyl, palmityl, stearyl and the like.
M1 is a monovalent cation that provides water solubility, such as the alkali metals, such as sodium, potassium or lithium; ammonium or substituted ammonium. Sodium, potassium and ammonium are suitable for M1.
The mixture is prepared simply by bringing together the anionic surface active sulfate or sulfonate and the carboxylic acid salt in water. One or more of the components may be formed in situ. For example, the carboxylic acid salt may be formed in situ by adding the carboxylic acid and the desired base. Heating may be required to achieve solution conveniently.
The pH of the composition should be neutral to mildly alkaline, with a pH between about 7.5 and about 8.5. Combinations of sulfonate and sulfate may be employed, although generally one or the other is used.
From the standpoint of forming foam, the concentration of the combination in the water may range widely from as low as about 1%, by weight, up to about 30%, by weight. However, from the standpoint of storage and transportation, a concentrate is desirable to avoid handling larger amounts of water. The concentrate can then be diluted with water at the site of use. At the time of foam production, the concentration of the combined foaming agents, A and B, is preferably between about 1 and about 3%, by weight.
At the time of foam production, the liquid composition may be pumped at, for example, 400 to 500 psig, through a foam generating apparatus 214 such as a flow controlling orifice at a pre-determined flow rate. Downstream of the liquid flow control orifice, gas is injected and mixed with the liquid stream. This may be achieved by using an orifice to control the flow in the same manner as the liquid side of the system. A compressor may generate a regulated gas pressure. After the two streams are combined, the mixture passes through an exit, such as the end of a hose that may or may not have a distribution nozzle attached.
The foam can then be distributed over the area to be covered. Similarly, the output may be directed into a multiported manifold for distribution. This manifold depending upon its size and the flow rate of foam, may be used to distribute the foam.
The degree of hardness of the water used to produce foam according to the present method can have an effect on the life of the resulting foam. Accordingly, in situations where the degree of hardness of the water available for preparing the composition in concentrate form or at the site may have a deleterious effect on the desired foam, a water hardness control agent may be incorporated in the composition to bind the calcium and/or magnesium present in the water. Examples of suitable hardness control agents are ethylenediamine tetraacetic acid, sodium and potassium tripolyphosphate and polyacrylates. The amount of hardness control agent used will be dictated, as is well known, by the degree of hardness of the particular water available and the extent it is desired to diminish that degree of hardness. Potassium tripolyphosplate is an exemplary desired hardness control agent.
A thickener/dispersant may be incorporated in the composition to be converted into foam, and an example of suitable thickener/dispersants are polymeric acrylates sold as thickener/dispersants, like Acrysol ICS-1 and Acrysol A-3 of Rohm & Haas Company.
Another example of a composition that may be useful in preparing foam compositions for use in the present invention may include a hydrolysed keratin protein, a modified starch, a ferrous ion component, and a dispersant.
The protein component of the composition may include a hydrolyzed keratin protein. The hydrolyzed keratin protein may be dry, such as that which is available from, e.g., Industria Suma Ltda. (Brazil), or in solution from other sources, e.g., Croda Kerr (England), Angus Fire (Canada), National Foam (US). The keratin protein used in the compositions may be derived from animal hooves and horns. Although other suitable sources of protein may be readily determined and used.
The composition may also contain starch, such as starch that has been modified to remove its anionic characteristics. Starch in its natural anionic state may be undesirable because it contributes to the instability of the foaming composition by reacting with the other components, particularly the cationic ferrous ion component, discussed below, resulting in unsatisfactory foam generation and performance.
The modified starch of the invention may be characterized by having been hydroxyalkylated using known processes. This process has the effect of removing the anionic characteristics of the starch. Suitable hydroxyalkylated starches may be readily purchased from commercial sources, e.g., National Starch (Instant Pure-Flo F) or Cerestar (Instant Gelex). In one embodiment, the starch is hydroxypropylated.
Further, the starch of the invention is desirably characterized by having an amylopectin content that exceeds the amylose content, i.e., an amylopectin content of at least about 75%. Desirably, the starch contains between about 90% to about 100% amylopectin, and most desirably, at least about 99% amylopectin. Starch containing suitable amylopectin contents may be derived from waxy maize or waxy sorghum, obtained from commercial sources, e.g., National Starch & Chemical or Cerestar. Further, mixtures of one or more starches from these or other sources that provide starch of the appropriate amylopectin content may be utilized in the invention. For convenience, the starch is desirably pregelatinized, obviating high temperature, high pressure, cooking in order to obtain gelatinization or solubility.
The mixture of the invention may also contain a ferrous ion component. The ferrous ion may be in the form of ferrous sulfate (FeSO4). The ferrous sulfate may be obtained from commercial sources, and is preferably in the form of ferrous sulfate heptahydrate (FeSO4.7H2O). Other sources of ferrous ion or ferrous sulfate may be substituted, as desired.
Optionally, dispersants may be added to enhance the dispersion of the ingredients. Such dispersants are well known to those of skill in the art and are not a limitation of the present invention. Examples of suitable dispersants include sodium lignosulfonate and ammonium lignosulfonate, which are available commercially, e.g., sodium lignosulfonate (available commercially as Maraperse N-22 from Lignotech USA, Inc.). Alternatively, dry dispersants may be readily selected.
If desired, an odorant may be added to mask the odor associated with the protein utilized in the mixture. One example of an odorant is cinnamon that may be in the form of cinnamon oil dispersed on a solid substrate, e.g., polymeric beads. This odorant is commercially available, e.g., from Horizon Chemical, Newark, Del. (catalog #2620). Other suitable odorants that do not affect foam performance may be readily determined and substituted by one of skill in the art.
The composition may also contain an amount of a pH modifier sufficient to provide a concentrate, foamable solution and foam having a pH between about 6.25 to about 7, and more preferably about 6.5. As with the other ingredients described herein, an appropriate pH modifier may be readily selected by one of skill in the art, and may be added in dry form to the mixture described above, or in liquid form, to the aqueous concentrate or foamable solution described herein. A suitable pH modifier is ammonium hydroxide.
Optionally, a biocide may be added to prevent the decomposition of the mixture or concentrate by bacteria. Any number of biocides may be used such as Kathon (Rohm and Haas, Co.), Nipacide BK, Nipacide BCP or Nipacid MX (Nipa Laboratories). Suitable amounts of the biocide may be readily determined and adjusted by one of skill in the art.
Where desired, the flow characteristics of the foam can be modified by the addition of small amounts of foam boosters, allowing certain foam applications to be smoother and more effective without sacrificing aging performance. Suitable foam boosters are well known and may be readily selected by those of skill in the art. For example, a modifier may include glycol ethers, many of which are known to those of skill in the art and example of such is diethyleneglycol monobutylether.
In one aspect, the present invention provides a dry mixture that upon dilution, can be used to produce a concentrate of the invention. Alternatively, the dry mixture of the invention may be diluted and used directly for generation of a foam of the invention. Such a dry mixture is advantageous for a variety of reasons. For example, the dry mixture permits reducing storage volumes and shipping costs as compared to more dilute compositions.
The dry mixture of the invention contains the components described above. Suitably, the hydrolyzed keratin protein is present in an amount between about 15% to about 20%, by weight, and more desirably, about 19%, by weight, of the mixture. The modified starch is present in an amount between about 25% to about 50%, by weight, and more preferably, about 30%, by weight. The ferrous ion component is present in an amount between about 6% to about 8%, by weight. One of skill in the art can readily adjust these percentages as needed, depending upon the source of ferrous ion. For example, when the source is ferrous sulfate heptahydrate, it may be present in an amount between about 30% to about 40%, by weight, and, more preferably, about 37%, by weight. Generally, the dispersant is present in the dry mixture in an amount between about 10% to about 15%, by weight. The amount of dispersant, however, may be readily adjusted depending upon the compound or compounds selected. For example, where the dispersant is ammonium lignosulfonate or sodium lignosulfonate, the dispersant is preferably present in an amount of about 12%, by weight.
Appropriate amounts of the optional ingredients described above for inclusion in the dry mixture of the invention may be readily determined by one of skill in the art. Alternatively, one or more of these optional ingredients, e.g., a glycol ether, may be added as desired upon dilution of the dry mixture.
In another aspect, the present invention provides an aqueous concentrate that upon dilution with water results in a foamable solution useful for generating a foam of the invention. The modified starch component, when utilized in the aqueous concentrate of the invention, acts as a protective colloid that assists in protecting the ferrous ion component from oxidation during shipping and storage, even when exposed to atmospheric air. Thus, the concentrate of the invention is stable and well adapted for shipment and storage in aqueous form.
The concentrate of the invention contains, at a minimum, about 2% to about 8%, by weight, hydrolyzed keratin protein, about 1% to about 7.5%, by weight, modified starch as described herein; about 1% to about 4%, by weight of ferrous ion, and about 1% to about 10%, by weight, dispersant, and water. One of skill in the art can readily adjust these percentages depending upon the source of this component. The ferrous ion component is ferrous sulfate heptahydrate that is present in an amount of between about 5% to about 20%, by weight. The concentrate further contains sufficient amounts of a pH modifier to adjust the pH of the concentrate to between about 6.5 to about 7.0, and other desired optional components, as discussed above.
For example, when present in the concentrate, the odorant is present in an amount up to about 1%, by weight, and the biocide is present in an amount between about 0.1% to about 1%, by weight, of the concentrate. Generally, when present in the concentrate, any foam boosters utilized are present in an amount up to about 2%, by weight, and most desirably, about 0.75% to about 2%, by weight. These amounts may be readily adjusted as needed by those skilled in the art.
In order to prepare the foamable solution, the dry mixture or, alternatively, the aqueous concentrate, is diluted with an appropriate amount of water. Where desired, the formulation of the dry mixture or concentrate may be adjusted in accordance with the dilution to be utilized by the customer in generating the foam of the invention. Generally, a concentrate of the invention is diluted at a ratio of between 3 to 10 parts by weight water to 1 part by weight concentrate to obtain a foamable solution having an actives concentration of between about 1 to about 5%, by weight, and preferably about 2 to about 4 wt %. One of skill in the art can readily prepare other desired concentrates and dilutions, having been provided with the ranges and guidelines described.
In one embodiment, a concentrate of the invention is diluted with about 6.5 parts water to 1 part concentrate, resulting in a foamable solution of the invention. In another embodiment, the same concentrate as above is diluted with about 3.75 parts water to 1 part concentrate.
Another example of a composition that may be useful in the present invention is a mixture in water that includes (A) a sodium sulfonate having the general formula
where R is an alkyl, alkylene or alkaryl group containing from 10 to 20 carbon atoms; (B) a carboxylic acid R1 COOH where R1 is an alkyl group containing 8 to 30 carbon atoms; (C) potassium hydroxide; (D) potassium silicate, such that the proportion of C plus D to B is sufficient to substantially complete neutralization to form the potassium salt of B and the proportion of B to A provides a mol ratio of B to A greater than 1:1 and up to about 2:1; (E) a non-ionic, solid, organic, water-soluble material such as sucrose or urea, and (F) a hydroxylic solvent for the potassium salt of B. Where hard water is encountered, a water conditioner (G) such as potassium tripolyphosphate can be included.
The composition is the result of mixing components (A) through (F) in water so that, in the resulting composition, the identity of certain of the components as such may be lost through, for example, ion interchange and neutralization. Component A is a sodium sulfonate having the defined formula. It is the surfactant foaming agent. Preferably, A is a sodium alphaolefin sulfonate containing from 10 to 20 carbon atoms, especially a mixture containing principally 14 and 16 carbon atoms.
Carboxylic acid (component B) provides, upon neutralization to its potassium salt, the soap foaming agent. R is a straight chain alkyl group containing from 8 to 20 carbon atoms, especially stearic and palmitic acids. In such a mixture, the relative proportions of stearic acid to palmitic acid may be between about 45 and about 55%, by weight, of the former to between about 55 and about 45%, by weight, of the latter, preferably about 50:50.
To form the desired potassium ion content, two sources may be used: component C, potassium hydroxide, and component D, potassium silicate. For example, silicate is required for minimization of carboxylic acid salt precipitation. However, if potassium silicate is used as a source of neutralizing potassium ion, precipitation of a complex silicate occurs. As stated above, the proportion of C plus D to carboxylic acid (B) is sufficient for substantially complete neutralization to form the potassium salt of B. However, the proportion of C to D will be such as to provide between about 50% to 90% of the potassium base from the potassium hydroxide (C) and about 50% to 10% of the potassium base from the potassium silicate (D). The preferred mole ratio is 4 moles of potassium base from the potassium hydroxide (C) to 1 mole of potassium base from the potassium silicate (D).
To enhance the stiffness of the resulting foam by increasing the solids content without upsetting the ionic equilibrium of the composition, a solid, non-ionic water soluble material, such as sucrose or urea (component E) may be included. Sucrose is preferred because of dwell time, concentrate physical properties and foam stiffness.
The viscosity of the concentrate is preferably about 200-300 cps at 30° C. so that it can be handled easily in a bulk storage/dilution system. Hence, there is included component F, a solvent for the potassium salt of carboxylic acid (B). This will generally be a hydroxylic solvent such as methanol, isopropanol, ethylene glycol, propylene glycol, glycol ethers and the like. Of these, the glycol ethers are preferred, especially ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, particularly the latter.
The degree of hardness of the water used to produce the composition, both concentrate and diluted form, can have an effect on the persistence and quality of the resulting foam. In order to accommodate water of various degrees of hardness from differing sources available, a hardness control agent, component G, can be included. Hardness control agents such as ethylene diamine tetraacetic acid or potassium phosphates can be used, but potassium tripolyphosphate, a known dispersing agent, is preferred because it improves the physical characteristics of the concentrate. In the preparation of the concentrate, the hardness control agent (G) is preferably added to the water immediately following the addition of the sodium alphaolefin sulfonate (A).
Reference has been made above to proportional relationships among certain of the components. In general the proportions of the components, on a water-free basis and in terms of percent by weight based on the combined weight of components A through F are: (A) from about 15 to about 20%, preferably about 18-19%; (B) from about 25 to about 35%, preferably about 30-32%; (C) from about 2 to about 8%, preferably about 5-6%; (D) from about 2 to about 5%, preferably about 3-4%; (E) from about 15 to about 30%, preferably about 23-24%, and (F) from about 10 to about 15%, preferably about 13-14%.
In the preferred concentrate, potassium tripolyphosphate (G) is also included in an amount between about 3 and 7%, preferably about 5-6%, based on the combined weight of the components A-G.
Reference has also been made to preparation of the composition as a concentrate with subsequent dilution with water, usually at the site of use, for foam generation. The concentrate may have a concentration of components A through F by weight on a water-free basis of between about 10 and about 40%, preferably about 23 to 31%, based on the total weight of the concentrate. For generation of foam such concentrate may be diluted with about 7 to about 9 volumes of water per volume of concentrate to provide a concentration of components A through F by weight on a water-free basis of between about 1 and about 6%, preferably about 3 to 4%, based on the total weight of the diluted composition.
Foam is generated from the diluted composition by agitation in the presence of gas, desirably an inert gas other than air, such as nitrogen as described above.
Another example of a foam composition that may used in connection with the present method is a thixotropic composition that includes an anionic sulfonate- or sulfate-based surfactant, a fatty acid, a thixotropic thickener, an acrylic acid polymer and a base. The composition optionally contains a water softening agent.
The anionic surfactants are the alkyl, alkylene, alkaryl and alkylpolyether sulfonates and sulfates as described above. The fatty acids are those having 14 to 18 carbon atoms. The thixotropic thickeners are those comprised of acrylic acid-alkoxylated methacrylic esters and the bases are the alkanolamines.
The fatty acid component functions in combination with the surfactant to provide the foaming activity. Fatty acids may include any of those having about 8 to about 30 carbon atoms. Generally, the fatty acids having 10-20 carbon atoms and preferably 14-18 carbon atoms are desired. Typical fatty acids desirably used in the invention include decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, etc. The preferred fatty acids are myristic acid, palmitic acid and stearic acid. Combinations of fatty acids having carbon contents within the above range may also be used in the invention. A particularly preferred fatty acid is commercial grade stearic acid which is a mixture of fatty acids, and predominantly a mixture of palmitic acid and stearic acid.
The fatty acid is generally present in the compositions of the invention at concentrations of at least 5% and may be present in amounts as high as 30%, based on the total dry weight of the composition. The fatty acid concentration is preferably in the range of about 5 to about 25 weight percent and most preferably in the range of about 10-20 weight percent based on the total dry weight of the composition.
The thixotropic thickening agent is present to impart to the composition the ability to produce a thixotropic foam, i.e. one which can be easily pumped but which will not flow or sag significantly upon standing. In general, any of the thixotropic polymer thickeners available on the market can be used in the invention. However, the preferred thixotropic agents are those which contain a significant amount of acrylic structure and which are soluble in aqueous alkaline solutions. Suitable thixotropic thickeners include the copolymers of acrylic acid and acrylic esters. A preferred acrylic polymer thickening agent is a copolymer of acrylic acid and methacrylic ester, such as alkoxolated methacrylic ester. The most preferred thixotropic thickeners are those comprised of acrylic acid and ethoxylated methacrylic ester in which the ester moiety has about 12-20 ethoxy groups and the ethoxy linkage is terminated by an alkyl group having 12-20 carbon atoms. The molar ratio of acrylic acid units to ethoxylated methacrylic ester units in these compositions is desirably in the range of 6-10:1. A commercially available thixotropic thickener having the above description is Acrysol™ ICS-1.
The thixotropic thickener is present in the compositions of the invention at a relatively high concentration. It generally comprises at least 5, and can comprise as much as 25 weight percent, based on the total dry weight of the composition. In preferred embodiments of the invention the thixotropic thickener is present at a concentration in the range of about 10-20 weight percent, based on the total dry weight of the composition.
The compositions may include an acrylic acid polymer. Although the function and manner of operation of this component are not completely understood, it appears that the acrylic acid polymer serves as a processing aid and makes it possible to incorporate very high concentrations of the thixotropic thickener into the formulation without forming a gel. Preferred acrylic acid polymers include polyacrylic acid homopolymer and acrylic acid copolymers in which acrylic acid is present as the major constituent. Polyacrylic acids found suitable for use in the invention are those having moderate molecular weights, i.e. those in the range of about 30,000-100,000 as determined by weight average techniques, and preferably in the range of about 40,000-70,000. The most preferred polyacrylic acids have weight average molecular weights in the range of about 50,000-60,000. The acrylic acid polymer is generally present at a concentration of about 5-20 and preferably about 5-15 weight percent, based on the total dry weight of the composition.
The base present in the composition also plays a role. Since the components of the invention perform in the alkaline pH range, it is desirable to add sufficient base to neutralize the acidic components, i.e. the acid function of the fatty acid, the thixotropic thickener and the acrylic acid polymer.
The base may be any water soluble base that will not adversely affect the performance of the composition. Suitable bases are the water-soluble monovalent bases, including alkali metal hydroxides, ammonium hydroxide, amines and alkanolamines. Useable bases include sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, primary, secondary, and tertiary amines in which the alkyl groups have 1-3 carbon atoms, and mono- di-, and trialkanol amines having 2-3 carbon atoms in each alkanol group. Examples of suitable amines include methyl amine, diethylamine, triethylamine, isopropylamine, butylamine, etc. Examples of alkanol amines useable in the invention include diethanolamine, triethanolamine, monoisopropanolamine, etc. Mixtures of these compounds may also be used in the invention. Suitable bases for use in the invention are ammonium and the lower alkanolamines such as mono-, di-, and triethanolamines. For example, a suitable base includes triethanolamine and a mixture containing 75-95 weight percent of triethanolamine and 5-25 weight percent of diethanolamine.
The base is generally present in a amount sufficient to neutralize all of the acid components in the formulation and raise the pH of the composition to a value of at least about 7.5 and preferably to a value of about 8-10.
The water available for dilution of the foam producing concentrates is often hard due to the presence of calcium and magnesium salts. In this instance, it may be desirable to include a water softening agent in the composition to control hardness. Although any of the common water softening agents may be used, it has been found that polyphosphates salts are highly suitable for use in the compositions of the invention. Preferred polyphosphate salts are the alkali and ammonium polyphosphate salts. A particularly preferred softening agent is potassium tri-polyphosphate, because of its ability to function at low temperatures, such as those encountered in winter operations using cold water. The amount of water softening agent will depend upon the hardness of the water being used to produce the foam. The softening agent is generally present in an amount sufficient to substantially eliminate the hardness of the water.
In producing the concentrate it is usually preferable to avoid incorporating unnecessarily large amounts of water into the formulation as this increases the storage and transportation costs. In the concentrated formulations, water is generally present in amounts of about 40-90 percent based on the total weight of the concentrate. In diluting the concentrate for use in foam generating applications, sufficient water is added to the concentrate to produce a composition desirably containing about 95 to about 99 weight percent water and about 1 to about 5 weight percent non-water components.
The foam-producing compositions of the invention may be prepared as concentrates and mixed with water for use. The mixing is accomplished by combining the concentrate and water in a circulating system and forcing the mixture through a conduit having a small cross-sectional area at a relatively high linear velocity. To avoid premature foaming, the mixture is discharged from the small cross-sectional area conduit into one having a larger cross-sectional area, thereby reducing its velocity prior to its reintroduction into the main body of water contained in the mixing vessel.
The foam compositions useful in the present invention may be any of the many types of cellular foamed resins. Typical resins which may be foamed include styrene, acrylonitrile-butadiene-styrene, polyolefins, phenolics, silicones, urethanes and vinyls. This list is of course not meant to be limiting but merely illustrative. Descriptions of typical foamable resins are found widely throughout the literature; such descriptions of the above resins are for example found in the 1970-1971 Modern Plastics Encyclopedia beginning at page 237. Two other resin types of interest are the isocynurates (described in U.S. Pat. No. 3,814,659) and the carbodiimides (described in U.S. Pat. Nos. 3,502,722 and 3,891,578). Both open-cell and closed-cell foamed resins may be used. In view of the knowledge of those skilled in the art and the numerous descriptions in the literature, more detailed description of the further various material resins need not be given here.
Each of the foam compositions described above may contain a hydrogen sulphide scavenging or control agent. The scavenging or control agent could be an iron-based compound such as a ferric or ferrous ion coordinated with an anionic ligand such as a polyaminocarboxylic acid, like hydrolyzed protein foam components, ethylenediamintetraacetic acid (EDTA), hydroxyethylethylenediaminetetraacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), or nitrilotriacetic acid. Other hydrogen sulfide control agents such as nitrogen bases (amines) can also be used.
While certain foam compositions have been described above, it is believed that there exists other foam composition that would be useful in practicing the methods of the present invention. Other suitable foam compositions should be easy to deliver, should have a sufficiently high dwell time (slow), should exhibit a sufficient stiffness such that the foam can cover vertical (and substantially vertical) surfaces of the gob material or seal material, should exhibit a sufficient persistence to withstand the prevailing environmental conditions for a suitable period of time, and should exhibit a sufficient barrier to the flow of gas.
The present invention also contemplates the use of the above foams for blast suppression. In this instance, the foam may be delivered to areas near protective structures such as mine seals to provide a physical separation of undesired explosive gases and the protective structure. It is contemplated that providing a foam in such a location may function to reduce the blast load on the protective structure by explosion pressure depression.
The following are non-limiting examples of the present invention.
A cross cut was fitted with a seal in the form a Kennedy panel without doors to create a void of approximately 4000 ft3. A foam composition according to the present invention was created using nitrogen gas and injected into the void. The oxygen level in the head space was measured during the filing operation and as the foam decayed. At the start of the filling operation, the oxygen content was about 21%, as expected. When the void is was approximately 80% filled with foam, the oxygen content decreased to about 10% and when the void was filled, the oxygen content decreased to about 0%. After about 200 hours, the void still contained about 50% of the initial volume of foam.
The following investigated application of foam according to the present invention at the headgate. As is typical, the barometric pressure throughout a given time period such as a single day varies from a maximum and a minimum, which at the testing site occurred between about 0800 (8 am) to 1100 (11 am) and between about 1500 (3 pm) to about 1900 (7 pm), respectively. As a result, the volume of methane in the mine typically decreases with an increase in barometric pressure and vice versa. Typically, a volume of nitrogen is continuously passed from the headgate to the tailgate and the amount in relation to the barometric pressure to reduce the amount of oxygen from passing through the seals.
Foam was delivered using separate applications at the headgate commencing at about 0930 when the barometric pressure was near the maximum. The methane content was measured at the ISO (tailgate). Referring to
However, after the nitrogen flow was reduced and foam was added at 1600 and about 1800, it can be seen that the ISO sensor measured methane reductions of about 0.6% almost instantly and independently of the shear position (referred to as the shield, where the cutters are at one end or the other when plotted points are at a maximum or minimum).
Referring to
Although the present invention has been described with respect to specific embodiments, it should be understood that the invention contemplates other uses and methods. In that regard, other embodiments of the present invention will be apparent to those skilled in the art from a consideration of the specification. It is therefore intended that the specification be considered as illustrative only and that this invention is not limited to the particular embodiment described above.
This application claims priority to U.S. Application 60/952,946 filed Jul. 31, 2007, the entire contents of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60952946 | Jul 2007 | US |
