PROCESSES AND METHODS FOR REMOVING POLYPHOSPHORIC ACID-CONTAINING SALTS AND SOLIDS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. provisional application number 63/054,940 filed on July 22, 2020, and U.S. provisional application number 63/109,604 filed on November 4, 2020, each of which is hereby incorporated herein by reference in its entirety.

BACKGROUND

Phosphoric acid can be produced by wet processes that include digesting phosphate rock with sulfuric acid. This can be conducted in tanks or pits, followed by steps to filter and purify the phosphoric acid. However, this process can also produce sludges and “scaling” that result from suspended solids such as remaining sulfate rock and calcium sulfate byproducts. Further, it is thought that the sludges and scaling ultimately result from the compression and “gluing” of these solid materials with a polyphosphoric acid byproduct. These solid sludges and scales historically require workers to enter a confined space to physically remove them, which creates an exposure risk for the workers. Accordingly, there remains a need to effectively remove such sludges and scaling while reducing worker exposure risks.

SUMMARY

The present disclosure relates to a method of reducing or removing sludge or scaling, comprising: identifying a mass of solid deposit material comprising polyphosphoric acid; and treating the mass of solid deposit material with a composition comprising an amount of phosphate salt. In some embodiments, the phosphate salt comprises a sodium phosphate. In some embodiments, the phosphate salt comprises a monosodium phosphate, a disodium phosphate, or trisodium phosphate. In some embodiments, the phosphate salt comprises trisodium phosphate. In some embodiments, phosphate salt comprises trisodium phosphate dodecahydrate.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to certain embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications, and such further applications of the principles of the disclosure as described herein being contemplated as would normally occur to one skilled in the art to which the disclosure relates. Additionally, in the detailed description below, numerous alternatives are given for various features. It will be understood that each such disclosed alternative, or combinations of such alternatives, can be combined with the more generalized features discussed in the Summary above, or set forth in the embodiments described below to provide additional disclosed embodiments herein.

In some embodiments, the present disclosure relates to methods for removing scaling and sludges comprising polyphosphoric acid, which can generally be referred to as a “solid deposit material.” In certain embodiments, such sludges and scaling are created during the wet production of phosphoric acid from phosphate rock and sulfuric acid. In certain embodiments, this production of phosphoric acid results in byproducts that include, but are not limited to, polyphosphoric acid, calcium sulfate, and undissolved phosphate rock. These resulting byproducts can accumulate into solid deposit materials, wherein the polyphosphoric acid acts as a “glue" material to create scaling and sludges comprising the undissolved phosphate rock and calcium sulfate.

Thus, in some embodiments, the present disclosure relates to a method of reducing or removing sludge or scaling, comprising: identifying a mass of solid deposit material comprising polyphosphoric acid; and treating the mass of solid deposit material with a composition comprising an amount of a phosphate salt. In some embodiments, the phosphate salt comprises a sodium phosphate. In some embodiments, the phosphate salt comprises a monosodium phosphate, a disodium phosphate, or trisodium phosphate. In some embodiments, the phosphate salt comprises trisodium phosphate or a hydrate thereof. In some embodiments, phosphate salt comprises trisodium phosphate dodecahydrate.

Without being bound to any particular theory, in certain embodiments, Applicant has surprisingly discovered that polyphosphoric acid-containing scaling and solids cannot be effectively removed using non-phosphate salts. For example, sulfate salts (e.g., sodium sulfate decahydrate) demonstrated little utility and produced undesirable sulfur oxides. Other sulfates (e.g., ferrous sulfate heptahydrate) showed some promise but produced too much heat through exothermics. Other types of salts (e.g., those producing divalent and multivalent cations) can react to form solids, which can compound the scaling problem.

Therefore, in certain embodiments, the solids can be contacted with a phosphate salt-containing composition. In some embodiments, the composition comprising the phosphate salt is an aqueous composition. In some embodiments, the amount of phosphate salt comprises about 50 to about 75 wt. % of said aqueous composition. In some embodiments, the phosphate salt can be added in its solid form (e.g., a “dry hydrate"). In some embodiments, the amount of phosphate salt represents about 5 to about 50 wt. % of the mass of solid deposit material. In some embodiments, the amount of phosphate salt represents about 8 to about 30 wt. % of the mass of solid deposit material. In some embodiments, the amount of phosphate salt represents about 10 to about 25 wt. % of the mass of solid deposit material. In some embodiments, the amount of phosphate salt represents about 15 to about 20 wt. % of the mass of solid deposit material, such as about 15 wt. %.

In certain embodiments, the solid deposit material comprises a plurality of byproducts resulting from the production of phosphoric add. For example, in certain embodiments the solid deposit material further comprises phosphate rock. In some embodiments, the solid deposit material further comprises calcium sulfate.

In certain embodiments, the benefits of the methods described herein include the ability to “dissolve ^,, or otherwise “de-aggregate” the solid deposit materials comprising polyphosphoric add. Breaking down and de-aggregating these materials may eliminate, in certain embodiments, the need for works to enter the vessel or chamber to remove accumulated solid deposit materials. In certain embodiments, these methods create a flowable deposit material that can be pumped out of the chamber or vessel, thereby removing the exposure risk to workers.

In order to promote a further understanding of the present invention and its various embodiments, the following specific examples are provided. It will be understood that these examples are illustrative and not limiting of the invention.

EXAMPLES

Example 1

Preparation and Scope

Materials and Methods:

A rubber lined tank to be cleaned is 28 feet in diameter and 28 feet high. The tank is expected to contain an estimated 10 feet of sludge or 35% of the tank volume and is estimated at 350 to 400 tons. All recoverable liquids may be removed prior to mobilization.

The following materials may be mobilized and set-up:

• Vacuum Truck and hoses

• Crew cabs

• Containments, pads, track mats and LLDPE liner

• Lined Mix Boxes Roll-off boxes (Est. 16)

Roll-Off Truck

Air compressor

Air diaphragm pumps (3)

Hoses, fittings, valves, etc.

Track hoe

Off-Road Telehandler

Scrubber SST-20 or PPT-24 with blower (if required)

Mix Tank for slurry preparation (may require 480V 3 Ph, 60 amp service) Confined Space Entry Equipment

PPE including Level B and C PPE (Breathing air system)

Tank Ventilation Equipment Pressure washer and Extend-a-wand Trisodium phosphate dodecahydrate Hydrated Lime

50% sodium hydroxide or caustic soda (if scrubber required)

Air mover Fuel Cell

Portable toilet and wash station

Misc. rope, pH probe and supplies, bright light, mirror, spare gaskets, infrared thermometers, HOPE pipe to fabricate slurry injection manifold and sparge pipes, air lines/water hoses, poly 55-gallong drums (4).

Also provided may be: · access to a water supply, water for treatment process

• Electricians to wire the mix tank

General Procedures

Generally speaking, the following steps may be taken to complete the sludge removal and treatment, and cleaning of phosphoric acid tank: • Caustic solution is placed on a scrubber reservoir. A 6” hose is connected to a top vent on the tank inlet to the scrubber to be used to scrub SO ₂ and HF vapors from the tank during trisodium phosphate (“TSP”) slurry addition.

• A 50% trisodium phosphate dodecahydrate slurry is prepared and added to the tank.

• The composition may be circulated in the tank until all sludge becomes liquefied. A slight temperature of reaction estimated to be around 50°C may be observed. It may take 2-5 days until the sludge becomes liquefied.

• Once the tank materials becomes pumpable, an estimated 10 cubic yards (CY) (about 2000 gallons) may be transferred to mix boxes for further treatment on a batch basis. Volumes may be adjusted.

• A 30-35% hydrated lime slurry may be added to the material from the tank slowly and incrementally over a period of hours to control heat of reaction temperatures, and maintain the temperature below 80°C. The slurry solution may be mixed with a track hoe and the treated material is expected to exhibit a pH in the range of about 4 to about 5. The blended material may be allowed to hydrate and complete reacting overnight.

• The treated material may be transferred to a lined roll-off box for transportation and disposal, and it is estimated that 1100 tons of total material may be generated.

• Once the sludge has been removed from the tank, the interior of the tank may be pressure washed with a hot water pressure washer. Walls may be rinsed as high as possible, but pressure washing may be performed to a maximum height of 12 feet.

• The equipment used may be decontaminated all of the equipment and be demobilized from the site. Wash water and decontamination water may be transported off site and treated.

• Acid gases are anticipated to be present, including hydrofluoric acid (“HF ^" ) and sulfur oxides. Mobilization and Site Set-up Operating Procedures

Proper personal protective equipment (“PPE”) may be worn as required by the task being performed. Mix boxes, trackhoe, and mix tanks may each be placed in temporary containments, and containments may be placed on a mat at the site. Track mats may be cut from a roll and placed inside the containments prior to placing equipment. After equipment is placed in the containments, the sides may be stood-up with the use of L-brackets. Mix boxes may be butted up to the tank dike wall, and visqueen plastic may be placed over the tank dike wall in the area of the mix boxes, down into the containments.

Spotters may be used when placing all equipment. A reinforced LLDPE liner may be placed beneath the track hoe containment and the roll-off box loading containment and areas between to cover the swing area, as the loading containment may need to be angled to allow safe backing and dropping of the box or live loading of the box.

Electricians may wire the mix tank, and proper mix blade rotation may be confirmed.

Visqueen plastic may be affixed around top manholes on mix tank to protect the mix tank from TSP and lime spillage on tank.

A SST-20 or PPT-24 scrubber is installed inside the tank containment. A forklift may be utilized with a man basket to connect a 6" corrugated hose to the tank vent on top of the tank, and the same may be connected to the scrubber inlet. A section of 6” corrugated hose may be placed on the outlet of a scrubber and run over a tank dike.

A welded HDPE 4” pipe spool may be fabricated to go over the side of a mix box through which the TSP treated sludge may be pumped into the mix boxes. Threaded connections may be used.

A polymer drum may be filled three-quarters full with water and placed in one of the containments between two mix boxes for temporary storage of discharge from HDPE pipes after filling mix boxes. Air diaphragm pumps may be set-up and 2" and 3” hoses may be placed on site during set-up. Hoses that run up a stairway may be tied off or otherwise secured to the stairway structure to prevent hose jump while pumping material to the top of the tank.

Water may be incrementally added to mix tanks up to 2000 gallons, 2500 gallons, 4000 gallons, and 5000 gallons and a float gauge on the tank exterior may be marked at leach level for future reference, and the time necessary to reach each level may be recorded.

A SO ₂ scrubber may be utilized, and if utilized may be installed on the SST-20 or PPT-24 scrubber and placed inside tank containment.

TSP and lime shipments may be off-loaded and stored on site and may be covered with a tarp to keep dry and protected from the elements. Empty roll-off boxes may be staged on site.

Example 3 Scrubber Operation

The scrubber reservoir may be filled with water and 135 gallons of a 50% sodium hydroxide solution to a total volume of 450 gallons. The pH of the scrubber may be monitored hourly and the pH measured. When the pH of the scrubber solution reaches 7, the scrubber solution may be changed. Spent scrubber fluid may be transferred to a mix tank for reuse.

TSP Slurry Preparation

Mixers may be turned on, for example after addition of water, during batch preparation. A telehandler may be utilized to add supersacks of TSP to the mix tank until a total of 20 tons of TSP is added to the mix tank. The generation of fugitive dust may be minimized during addition. Water is added, and the TSP is blended to a 50% slurry by weight.

Example 5 TSP slurry may be transferred to the phosphoric acid tank through the top manway using a 2” acid hose and a 2” air diaphragm pump, Sludge temperatures may be monitored with an infrared thermometer before and during TSP addition, and temperatures may be recorded. If the temperature of the sludge increases by 10°F, TSP slurry addition may be stopped and the temperature allowed to decrease.

A water hose may be used to flush residual solids once the level drops below mixer blades, and the total volume of TSP slurry added to the tank may be recorded.

A circulation system may be utilized using a 3” acid hose and a 3” air diaphragm pump in operation. Withdrawal and re-injection points on the tank may be used.

After circulation is established, additional batches of TSP may be prepared and used. Further, some TSP slurry may be set aside for addressing hard material that may not be exposed during circulation.

Circulation of TSP slurry in the tank may continue for 3 to 5 days and most of the solids have been liquefied. Circulation withdrawal and re-injection points may be periodically modified during circulation. Circulation may continue 24 hours-a-day, 7 days-a-week and a two-man night shift may be utilized to monitor the circulation during the night shift.

Once the majority of solids have been liquefied, the volume of the tank may be measured and recorded.

Example β

Transfer of TSP Treated Material to Mix Boxes Material is transferred from the tank through the HOPE pipe to minimize splashing of material to the mix boxes utilizing a 3” recirculation line. Pumping slowly, each mix box RO-95 may be filed to 20 inches, and each mix box ROD- 12 may be filled to 21 inches using a gauge stick. After pumping is complete, the HDPE pipe sections may be placed in a 55-gallon drum for storage. If used, a transfer hose may be disconnected and capped.

Example 7

Lime Slurry Preparation

4000 gallons of water may be added to a mix tank. A mixer may then be turned on and a telehandler used to add supersacks of lime to the mix tank while minimizing fugitive dust until about 9 tons of hydrated lime are added to prepare a 35% slurry by weight and mixed until the slurry is used.

Example 8

The lime slurry may be pumped with a 2" air diaphragm pump to mix boxes through a HDPE manifold used for transfer of eluded. During transfer, the air valve on the air diaphragm pump is opened slowly to get consistent flow and speed can be increased gradually. Splashing of the lime slurry in to the acidic material is avoided. Prior to complete addition of the lime slurry, the track hoe lower stick, bucket, and lower linkage may be sprayed with lime slurry.

The lime slurry may be split into 6 portions and may be equivalent to 827 gallons of slurry in each portion and may be equivalent to an 8" rise in level in a RO-95 mix box or a 9” rise in a ROD- 12 mix box. The level of the mix box may be determined using a gauge stick.

After addition of lime slurry, mixing may be performed using a track hoe bucket while avoiding curling the bucket into the sludge or submersing the boom arm stick and bucket linkage in the material.

Temperature of the composition during mixing may be observed and recorded. Mixing may continue until the composition is thoroughly blended and remixing may be used to assist with heat dissipation.

Once the composition of the mixture is less than 115°F, a sample is obtained for field pH analysis by placing approximately 10 grams in a plastic cup, adding 90 mL distilled water, mixing and recording the pH using a portable calibrated pH meter. Samples may also be collected for TCLP metals analyses, and the mix box is allowed to sit overnight. If rain is expected, the mix box may be covered with a tarp.

Example 9

Transferring Materials from Mix Boxes to Roll-Off Boxes A secure liner is placed in a roll-off box and a label is affixed to the roll-off box prior to moving into position for loading. A LLDPE line is placed on the ground covering the area above where a trackhoe arm may swing during loading and a visqueen plastic material is placed under the area where a loaded bucket of material would be above during the transfer process. A spotter may also be used during loading or unloading.

Once the composition located in a mix box has a temperature of 115°F and a pH of greater than 4, a track how may be used to carefully load materials from teh mix box into a roll off box for shipment.

Example 10 Acid Tank

A pneumatic air hammer may be used to remove the lower manway opening to the acid tank. Ventilation is added to the confined space to ensure that proper tank air turnover is achieved. Air monitoring equipment may be calibrated and its function checked before use, and the inside of the confined space may be tented and the composition of the air analyzed.

A hot water pressure washer may be used to wash any remaining solids and liquids from the acid tank and a vacuum truck may be used to collect the remaining solids and liquids from the acid tank. Plastic hand tools may be used inside the acid tank taking care not to damage the rubber liner inside the tank. The hot water pressure washing may be used to clean the walls of the confined space in the tank up to 12 feet high. The liquids used to wash the tank may be collected and place into a mix tank, and a sample may be collected of the acid tank liquids for analyses.

Once the liquids are removed from the acid tank, workers may exit the confined space, and dispose of PPE in a roll off box for disposal.

Example 11

Equipment Decontamination and De-Mobilization Equipment used in the process of removing polyphosphoric acid- containing salts and solids from the acid tank including, but not limited to, mix boxes, trackhoe, and containments may be decontaminated by pressure washing. Decontamination fluids may be consolidated in a mix tank, and the mix tank itself may be cleaned.

For example, a mix tank may be cleaned by adding ventilation to the confined space within the mix tank and ensuring that proper tank air turnover is achieved, and the space may be analyzed by air monitoring equipment that is calibrated and functional.

A hot water pressure water may be used to wash the mix tank, and any remaining liquids in the mix tank may be collected by using a vacuum truck. Used PPE may be placed into roll-off boxes for disposal.

Once the mix tank is empty, Litmus pH paper may be used to verify the contents are within a pH of 6-8, and flanges and manways are sealed shut after all workers have exited.

The uses of the terms "a" and "an” and "the" and similar references in the context of describing the disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-cl aimed element as essential to the practice of the disclosure.

While the present disclosure has been illustrated and described in detail in the drawings and the foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. In addition, all references cited herein are indicative of the level of skill in the art and are hereby incorporated by reference in their entirety.

Listing of Embodiments:

The following provides an enumerated listing of some of the embodiments disclosed herein. It will be understood that this listing is non-limiting, and that individual features or combinations of features (e.g. 2, 3 or 4 features) as described in the Detailed Description above can be incorporated with the below- listed Embodiments to provide additional disclosed embodiments herein.

1. A method of reducing or removing sludge or scaling, comprising: identifying a mass of solid deposit material comprising polyphosphoric acid; and treating the mass of solid deposit material with a composition comprising an amount of phosphate salt.

2. The method of embodiment 1, wherein the phosphate salt comprises a sodium phosphate or a hydrate thereof.

3. The method of any one of embodiments 1 to 2, wherein phosphate salt comprises trisodium phosphate or a hydrate thereof.

4. The method of any one of embodiments 1 to 3, wherein the phosphate salt comprises trisodium phosphate dodecahydrate.

5. The method of any one of embodiments 1 to 4, wherein composition comprising the phosphate salt is an aqueous composition.

6. The method of embodiment 5, wherein the amount of phosphate salt comprises about 50 to about 75 wt. % of said aqueous composition.

7. The method according to any one of embodiments 1 to 6, wherein the amount of phosphate salt represents about 5 to about 50 wt. % of the mass of solid deposit material.

8. The method according to any one of embodiments 1 to 7, wherein the amount of phosphate salt represents about 8 to about 30 wt. % of the mass of solid deposit material. 9. The method according to any one of embodiments 1 to 8, wherein the amount of phosphate salt represents about 10 to about 25 wt. % of the mass of solid deposit material.

10. The method according to any one of embodiments 1 to 5, wherein the amount of phosphate salt represents about 15 to about 20 wt. % of the mass of solid deposit material.

11. The method according to any one of embodiments 1 to 10, wherein the solid deposit material further comprises phosphate rock.

12. The method according to any one of embodiments 1 to 11, wherein the solid deposit material further comprises calcium sulfate.

13. The method according to any one of embodiments 1 to 12, wherein treating the mass of solid deposit material with a composition comprising an amount of phosphate salt creates a flowable deposit material.

14. The method of embodiment 2, wherein the sodium phosphate is selected from at least one of a monosodium phosphate, a disodium phosphate, or a trisodium phosphate.

15. The method according to embodiment 13, further comprising removing the flowable deposit material from the chamber or vessel.

16. The method according to embodiment 15, wherein the flowable deposit material is removed by a process that includes pumping.