Mohammad Abutayeh & Scott W. Campbell, Department of Chemical Engineering, University of South Florida

A thermodynamic model was developed to predict the limits of distribution of phosphates between the liquid and the solid phases in a reactor used for extracting phosphoric acid from phosphate rock by the dihydrate process. A computer code based on the model was generated to carry out different simulations of the process using several inputs of temperatures and liquid phase content of sulfates and phosphates.

Experimental data of equilibrium constants were regressed and included in the model obtaining a more accurate representation of the thermodynamic equilibrium. In addition, the Edwards-Maurer-Newman-Prausnitz Pitzer based model was incorporated into the model to write the activity coefficients of all species, while published lime solubility data was used to find an expression for the self interaction parameter of phosphoric acid. The model was validated by comparing its predictions to experimental citrate soluble loss data yielding very compatible results. Simulation results for ionic strength, solution acidity, lime solubility, and citrate soluble loss were used to analyze temperature plus solution sulfate and phosphate content effects on the dihydrate process.

Decreasing temperature and increasing sulfate levels was found to raise the acidity and the ionic strength of the solution as well as minimize the citrate soluble loss.

Neil Beckingham & Charles Dyke, Hatch Ltd.

During the manufacturing of phosphate fertilizers, a spent process liquor is produced and subsequently stored in large ponds. Spent liquor, also called “pond water”, is a very low pH brine with a high total dissolved solids (TDS) content, containing high levels of phosphate, fluoride, sulphate, silicon, sodium, calcium, and ammonium. If necessary, it is can be treated by double liming to neutralize it and remove some of its mineral content. However, this method is relatively expensive, does not make the water suitable for discharge, and can cause other waste management issues, such as sludge disposal.

In 2004, Hatch partnered with Mosaic, one of the world’s leading fertilizer manufacturers, to develop a cost effective and sustainable treatment method for fertilizer plant spent liquor so that it could meet the requirements for discharge to Florida Class III waters. The project work ultimately resulted in the development of the Mosaic Spent Liquor Treatment Process (SLTP). The SLTP is a membrane-based treatment process that removes essentially all of the fluoride, ammonia, and phosphate from spent liquor, while reducing its TDS from 35,000 to below 500 mg/L. SLTP economics compare favorably to traditional methods of pond water treatment.

In 2008, Mosaic awarded Hatch a contract to build a 1.44 million-gallons-day (MGD) SLTP plant at Mosaic’s Bartow, FL, facility. Hatch performed engineering design, procurement, construction, and commissioning services for the Bartow SLTP, and operates the SLTP under an evergreen plant operations and maintenance (O&M) contract with Mosaic.

This project has been noteworthy for the following:
• The Bartow SLTP was constructed ahead of schedule, with no lost time incidents during construction. Commissioning began in June 2009, and the plant began treating spent liquor in September 2009.
• The plant is currently operating in an optimization mode leading to acceptance testing. During operation, contaminant levels in the treated water have been well below design discharge limits, and through April 2010 the SLTP has discharged over 100 million gallons (MG) of treated spent liquor.

Eric Coffin, P.E, Green Engineering, Inc.

Pumping equipment and energy costs comprise a large portion of the money that is both invested and spent as operating costs in the phosphate industry. This paper offers a pro-forma cost-based computer model that optimizes up-front investment with on-going operational costs to yield a minimum life cycle cost for the owner. Purchasing the smallest pump and piping system during engineering design and construction makes the project manager a cost savings hero. Operating such a high pressure drop system over ten years results in high energy costs and frequent maintenance for the utility manager and front line mechanics. The owner is left to struggle with operating profitability and a stranded non-performing asset if forced to shut the doors. Learn how to quantify the investment, risk, and life cycle operating costs of pumping systems to optimize your company’s capital costs and operating costs.

Dr. Tino Prado & Megan Ross, Prado & Associates, Prado Technology Corp

The phosphate industry as we know it today started in the United States about one hundred years ago. Initially the industry started in places like Tennessee but then shifted to Florida where the main deposits were located. Currently additional mining activity also takes place in North Carolina and Idaho. Nevertheless, the reality is that during the past forty years phosphate rock mining and the associated production of phosphate fertilizers has shifted out of the United States to various countries in Africa where major deposits exist.

While the recent focus of attention has been in places like Africa, there has been a quiet expansion of production capacity in South America. Because rock deposits in South América are smaller than those in Africa, most production is for local or domestic consumption only. Nevertheless, two major mining projects are currently underway in Perú, of them sponsored by a Brazilian company. Phosphate rock production in South America is expected to increase dramatically over the next few years, and we likely expect that phosphoric acid capacity will also increase. The purpose of this technical paper is to provide an overview of the phosphate industry in the continent of South América and its future prospects.

Leif Bouffard, Central Engineering

As concerns over the financial liability associated with the final closure of a Phosphate Fertilizer Facility and the ultimate disposition of the cooling pond continues Central Engineering is evaluating the use of Series Filtration (Double Filtration) of Phospho-gypsum and the Closed Loop Cooling Water System as a more economical and rational approach to solving the problem. Commercially proven technologies were selected as a means of reducing the cooling ponds volume and acidity while eliminating the loss of water soluble P2O5 to the Gypsum Stack. The process provides for an improved recovery of Phosphoric Acid (water soluble P2O5) which directly results in a lower P2O5 concentration in the cooling pond water. Phosphoric Acid is usually the highest concentration of acidic component of the cooling water which must be neutralized prior to closure. The improved recovery of P2O5 also leads to improved recovery or harvesting of Sulfuric Acid and Ammonia as well. Employing the Closed Loop Cooling Water System provides a P2O5 free transport fluid for stacking of Phospho-gypsum which drastically reduces the loss of water soluble P2O5 to the gypsum stack. This combination ultimately leads to the elimination of the Cooling Pond and recovers the valuable constituents which make the cooling ponds a financial liability.

Richard Harrison, Pegasus TSI

This paper describes the steps required to prepare a capital cost estimate for a project in the chemical processing industry.

Three different accuracies are usually prepared – the initial order of magnitude +/- 50% estimate, a second round +/- 30% estimate, and finally a +/- 10% estimate is completed.

Deliverables required to complete the estimate depend on the accuracy of the estimate, but can include the following:

• Process Description
• Process Flow Diagrams
• Feed & Product Stream Summary
• Equipment List
• P&IDs
• Instrument List
• Electrical One-line Diagram
• Piping Line Table
• Equipment Arrangement Drawings
• Pipe Route Drawings
• Demolition Drawings
• Material Take Offs
• Major Equipment Quotes
• Project Schedule
• Estimate Summary
• Itemized Estimate Detail Report

A few recent projects will be reviewed including a sulfuric acid plant converter replacement, a phosphoric acid digester addition, a phosphoric acid filter central valve replacement, a clarifier addition, an evaporator expansion, and an evaporator fluosilicic acid recovery retrofit.

Dr. Martin Dionne, Hatch Ltd.

The extraction of minerals from earth requires ore beneficiation as a first stage of refinement. The primary concentrate can then undergo a second stage of refinement that requires regrinding to release the remaining gangue which is followed by a separation/flotation process to increase the concentrate grade. The higher grade Flotation Concentrate slurry needs to be dewatered by a filtering process/media. Maintaining the filtering rate and filter efficiency constant as a function of time can be challenging due to progressive filter cloth blinding that usually results in process upsets that impact the Plant OPEX as well as its capacity.

In the current studied case, the blinding was severe and occurred during a period of 7 to 10 days of operation where the filtering efficiency rate loss was averaging -1% per day with maximum/peak value at -3% per day; i.e., an average productivity loss of 10% and up to 30% over a production period of 10 days. This caused the disc filters to be the primary Plant bottleneck followed by the Flotation Plant; both being in the critical path for the Plant capacity increase program.

A study was initiated with the objectives of 1) understanding, identifying and solving the filter cloth blinding problem and 2) identifying the Flotation Plant bottlenecks and recommend solution for immediate improvements. The developed approach was based on an R&D project model that included: internal and external literature review, Process Performance Assessment to establish the base case process KPI’s , historical and in-plant DOE for process parameters optimization, Flotation Plant Performance Audit, ARENA modeling, FACT-Sage for thermochemical calculations as well as advanced Microscopic Characterization techniques such as FEG-SEM coupled with x-ray EDS, Auger Microscopy, IFTR, XPS, and XRD.

Microscopic characterization enabled us to identify the cause of the filter cloths blinding and to propose practical solutions. Interestingly, a link was made with another problematic sector of the Plant where the screens were experiencing a similar blinding/clogging problem causing them to be this sector’s bottleneck. Process Performance Assessment combined with Design of Experiment allowed us to recommend parameter changes/adjustments for optimal/improved filtering efficiency for a possible filtering rate capacity increase of 5 to 10 %. The Flotation Plant Audit allowed us to establish the current flotation circuit capacity and identify the bottlenecks for capacity increase while establishing a list of recommendations for process control improvements. Finally, literature review generated some spin-offs. New flotation reagents that have been identified and tested at the laboratory scale might lead to Flotation Plant improvements while lowering the cost of reagents by 30 to 50%.

Syed Ali Zeeshan Gardezi, Babu Joseph, and John T. Wolan, Dept of Chemical & Biomedical Engineering, University of South Florida

Fischer Tropsch Synthesis (FTS) is a process for converting syngas (a mixture of carbon monoxide and hydrogen) into clean liquid fuel. Originating in Germany in the 1920’s, it is an alternate route for producing liquid fuel e.g. gasoline, diesel and aviation fuel. With the gradual rise in global energy requirements (60 % between 2002-2030 source: world energy handbook 2004) there is an urgent need for alternate renewable energy resources. Following the current energy trends and future predictions (expected fourfold rise in the use of biomass for transportation fuel source: world energy handbook 2004) we have designed a tunable catalyst for efficient conversion of synthesis gas produced from biomass into liquid fuels. An egg shell catalyst consisting of a silica support impregnated to a tailored depth with cobalt nanoparticles has been designed and synthesized in our laboratory for this purpose.

Egg shell catalyst design is an exceedingly innovative concept that overcomes mass transfer limitations inherent with conventional reactor catalyst systems. Production of long chain hydrocarbons in FT synthesis is rate limited due to the accessibility of active catalytic sites for diffusion of carbon monoxide. The tunable thickness of active catalytic surface area ensures that enough active sites are available for desired, highly selective hydrocarbon chain growth. In this way the required petroleum cut is obtained without any additional unit operations. Such a design has not been explored or exploited commercially as yet. Conventional reactors provide waxy product and additional unit operations are required to obtain the desired fractions. Additionally, the specific reactor design that we offer eliminates current heat transfer issues. FT synthesis is a highly exothermic process, if the evolved heat is not removed; catalytic sintering, decay and attrition are the net result. This problem has been a major stumbling block for commercial reactors and must be operated far below full capacity. We offer an innovative mixing an inert heat sink and catalyst along with inter-compartmentalization. Such a combination results in effective heat removal in the absence of an external cooling jacket.

Our eggshell catalyst is product specific; there is huge savings in operating cost because of less downstream equipments for product refining. Lab results indicate absence of aromatics and alcohols in the final product; a clean fuel will thus enhance engine performance. Almost all FTS reactors face the issue of downstream wax accumulations which is very difficult to resolve. With this technology, there is little to no chance of facing this issue, reducing the plant downtime due to reactor problems. The reactor design takes care of heat transfer issues, thus the reactor can be operated at optimal conditions giving higher conversion. Indications are that linear scaling up of this reactor will preserve the optimized bench-scale results.

At present, our initial target market is the Department of Defense (Air Force). The Air Force has a goal to obtain half of its fuel used in the continental US from renewable sources by the year 2016 (DOD Energy Security Task Force 2008). We intend to provide a clean, continuous, reliable and domestic supply of NATO JP-8 (Jet Propellant-8) grade, the highest of its kind, produced via biomass using our proprietary gasifier, catalyst and reactor designs. Liquid fuel is a strategic resource that has significant security, economic and geo-strategic implications. DOD’s fuel consumption varies from year to year in response to changes in missions and the tempo of operations. In FY 2000, fuel costs represented 1.2% of the total DOD spending, but by FY 2008 fuel costs had risen to 3% (DESC Fact Books 2008). The Defense Energy Support Center (DESC), under the command of Defense Logistics Agency (DLA), has the mission of purchasing fuel for all DOD services and agencies, both in continental US and outside US. The Air Force and the Army represent the primary consumers of JP-8 fuel whereas the Navy consumes JP-5. The majority of DESC’s bulk fuel purchases are for JP-8 jet fuel, which has ranged from 60 to 74 million barrels annually. A September 2009 report published by the Congressional Research Services indicated that in FY 2008 the DOD’s purchases for JP-8 fuel totaled 62.5 million barrels at $3.13 per gallon (Congressional Research Service, Department of Defense Fuel Spending, Supply, Acquisition and Policy- Sept 2009). According to the same report, the DOD spent almost $18 billion on acquiring fuels in FY 2008. With the ongoing operations in Iraq and Afghanistan to support the ground operations, the DOD’s demand for JP-8 jet fuel will continue to go up and will only put upward pressure on reaching the target of obtaining 50 % of its fuel supply from renewable sources by 2016.