18.1.1 Energy Efficiency – The 5th fuel
Energy Efficiency – The 5th fuel
By Eric H Coffin, P.E., C.E.M.


Energy efficiency is considered the 5th fuel after coal, petroleum, nuclear, and alternative energy. Appliance efficiency in the home as well as motor and pump applications in the workplace can yield financial returns that exceed those of the famous investor Warren Buffett. Energy efficiency is often overlooked because of lack of understanding and let’s face it, it’s not sexy, or flashy. However, energy efficiency has the ability to allow us to exceed the carbon emission goals of the Paris Climate accord. All we need do is make use of existing technology and consider rate of return.

Your air conditioner is the largest consumer of energy in the typical Florida home amounting to 50% to 70% of your annual bill. Does your monthly bill always peak in the summer months? This paper will lay out the steps you can take to calculate an attractive rate of return.

Pumping equipment and it associated electricity consumption comprise the majority of the energy cost in the phosphate industry. A pro-forma cost-based computer model was developed to determine the savings associated with pump, motor, and power factor correction using a typical 100 hp motor. Rates of return of 37%, 42% and over 100% are typical of the improvements that await discovery by the process engineer.

18.1.2 Corrective Action and Grouting Plan to Seal Gypstack from Aquifer
Corrective Action and Grouting Plan to Seal Gypstack from Aquifer
David Jellerson, The Mosaic Company

In August 2016, Mosaic confirmed a loss of process water from the New Wales gypsum stack. It subsequently was determined that the water loss was the result of a sinkhole beneath the stack that compromised the geologic confining unit and the stack liner system. As a result of the event, Mosaic initiated recovery of water from the Floridan aquifer and commenced the project to restore the confining unit to seal the breach to the aquifer. This presentation will focus on the Corrective Action and Grouting Plan and the associated construction project.

18.1.3 Corrosion Resistant process equipment for hot phosphoric acid processes
Corrosion Resistant process equipment for hot phosphoric acid processes
W. Wayne Moroz, P.Eng - Mersen

The selection of materials of construction and design of equipment including heat exchangers, columns and vessels for hot phosphoric acid (and other hot acid) processes is a challenge due to the corrosive nature of many of these acids and processes. The “corrosion resistance” pyramid for materials of construction for hot acid processes is reviewed for “hot” acid conditions above 100 oC. For clean acid applications, many specialty metals and “lined” metallic or FRP equipment will work. Traditional heat exchange equipment for hot processes are typically metallic with noble “reactive” metals such as Tantalum and Niobium at the top of the pyramid, followed by high nickel content alloys. Glass lined, thermoplastic lined and fluoropolymer lined metallic or FRP vessels are at the top of the pyramid for reactors and columns that do not need to transfer heat. However, the presence of impurities, namely fluorides, that are found in many phosphoric acid plant applications limits the use of most metals and glass for materials of construction. Many times, one is left with only impregnated graphite or advanced ceramics like Silicon Carbide for the material of construction for heat exchangers. When fluorides are present, lined fluoropolymer equipment for reactors and columns are many times the material of choice. These materials are not traditional and special designs and configurations are required due to the material properties and methods of fabrication of equipment. Specific designs and applications for impregnated graphite and SiC heat exchangers as well as fluoropolymer lined vessel designs are discussed for hot phosphoric acid processes including evaporators, interchangers & defluorination processes.

18.1.4 Innovative Solutions for Cadmium and Arsenic Removal from Phosphoric Acid
Innovative Solutions for Cadmium and Arsenic Removal from Phosphoric Acid
Rajesh Raitani, Lei Zhang, Xueping Qiu, Jack Howley, John Carr, John Lampariello, - Solvay

A growing global population and higher caloric intake are leading to an increase in demand for phosphate based fertilizers and animal feeds. The phosphate rock used in production of these products often contains cadmium and other heavy metal impurities at concentrations which are considered to be toxic and mutagenic to humans. Existing and pending regulatory restrictions place limits on heavy metal content in finished fertilizers and feeds necessitating the removal of the impurities. This paper discusses the need for an efficient and cost-effective solution for heavy metal removal from fertilizer and feed products and provides a review of various decadmiation techniques currently available. It also introduces Solvay’s ACCO-PHOS® reagents and presents recent improvements to the technology that increase the efficiency of removal of heavy metals such as cadmium and arsenic from phosphoric acid.

18.1.5 Scale Inhibition for Evaporators in Phosphoric Acid Plants
Scale Inhibition for Evaporators in Phosphoric Acid Plants – an update for 2018
Paul Wiatr, Nalco Water

At AIChE 2016, Nalco Water presented its findings from a scale inhibition trial from a customer in Asia. In 2017, a second plant trial was performed, this time in North America. A similar approach was used, and the following results were observed:

• Length of the production campaign doubled
o Customer commented it could have gone longer
• Daily production of 54% acid increased
• Heat transfer coefficient values remained flat
• Input acid flow remained constant
• Evaporator cleaning time decreased

The purpose of the presentation is to update the audience on the specifics of the key performance indicators used by the customer to determine when to shut down the evaporator and how these measurements were affected by the scale inhibition program. These indicators were:

• Acid flow into the evaporator
• Heat transfer coefficient
• Steam flow
• Shell pressure
• Valve scale

An economic benefit analysis will also be presented.

The formation of scale in phosphoric acid plants has been a major problem in the industry for decades. The thinking for inhibition of scale formation on evaporators has been to maintain the heat exchange capacity longer and extend the acid production time, leading to less frequent shutdowns for cleaning. This presentation will also discuss an added benefit not foreseen, increased daily production.

Trials in plants in South America, North America and Asia are planned. If scheduling permits, the results of those trials, will be discussed as well.

18.1.6 How to Achieve the Expected Performance in your Agitated Slurry Tanks
How to Achieve the Expected Performance in your Agitated Slurry Tanks
Richard Grenville , Philadelphia Mixing Solutions

From the Beneficiary Plant to the Slurry Pipeline, to the Rock Slurry Tanks, to the Phosacid Plant understanding how to properly specify slurry characteristics will determine how often you will need to clean out your tanks and pipelines. Too often incorrect specifications lead to tanks sanding out, problems with the suction of pumps, or inconsistent solids concentrations being transferred downstream to the next step in the process. What may appear to be subtle differences in specification requirements can result in big differences in the successful operation of the plant. Getting this wrong will result in underperforming plants and poor reliability.

18.1.7 Reducing Stack Emissions from an Existing DAP Plant: Part 2 - Post Startup
Reducing Stack Emissions from an Existing DAP Plant: Part 2 - Post Startup
David Ivell, Jacobs and Om Agre, Dy., Zuari Agro Chemical Ltd. Goa

At the 2014 conference we presented a co-authored paper describing the plan to revamp an existing DAP/NPK plant for Zuari Agro Chemicals Ltd at their site in Goa, India. The objective of the revamp was to reduce the stack emissions to 35 mg/Nm3 (losses were as high as 500 mg/Nm3) while at the same time maximizing production rate (rates prior to the revamp were 1300-1400 mt/d).

The plant utilized a pipe reactor located in the dryer which produced MAP. No changes were planned to this arrangement. The plant utilized single stage scrubbing with the scrubbers operated at high mole ratio (1.3-1.4). The plan was to convert the scrubbing system to the dual mole ratio configuration along with replacing the old, corroded tail gas scrubber. The new scrubber was to be configured with two beds of fluidized packing.

The original plan was to have detailed engineering completed by October, 2015 and start-up by June, 2015. In the event, the implementation was delayed so that the dryer could be replaced during the shutdown. The modified plant started up in May, 2017.

The paper describes the problems faced during the initial operation in detail as well as the current performance.

18.1.8 Continuous Electrokinetic Dewatering of Phosphatic Clay
Continuous Electrokinetic Dewatering of Phosphatic Clay
Arthur P. Dizon and Mark E. Orazem, Department of Chemical Engineering, University of Florida

A dilute 2-3 wt.% suspension of phosphatic clay is produced as a waste stream in the beneficiation of phosphate ore. A typical Florida phosphate mining operation produces more than 100,000 gallons/min of phosphatic clay. The suspensions are pumped into large impoundments called clay settling areas (CSA) in which separation is achieved by hindered settling and self-consolidation. As it settles, the supernatant water is recycled for use in the beneficiation plant. A top crust is formed after a few years, but, after 25-50 years, the clay beneath the crust has a large water content and a pseudo-plastic character that limits the amount of weight the settling area can support. Methods that employ electrokinetic phenomena have been the subject of significant research as a possible means of accelerating the dewatering process.

Our previous work showed that batch electrokinetic dewatering processes could not be economically applied to an entire CSA. The objective of the present work was to overcome the economic hurdle through the development of continuous electrokinetic dewatering (EKD).1 The current prototype consists of a single unit which accepts a 10 wt.% suspension as a feed and produces up to a 38 wt.% cake. The most recent design can produce cake with a 35 wt.% solids content at a production rate of 4 kg/hr m2 on a dry-clay basis; whereas, our previous design could produce cake with a 35 wt.% solids at a rate of only 0.5 kg/hr m2 on a dry-clay basis. This comparison represents an 8-fold reduction in the electrode area required. As a result of these advances, the estimated cost for continuous electrokinetic dewatering was reduced by more than an order of magnitude. For a capital cost of $2000/m2, 10% interest, 20-year life, and an electrical cost of $0.062/kWh, the cost for dewatering a 10 wt.% feed to form a 35 wt.% cake is projected to be on the order of $10 per metric ton of dry clay produced. These cost projections do not include potential savings associated with obviating the need for construction of new clay settling areas.

1. R. Kong, A. P. Dizon, S. Moghaddam, and M. E. Orazem, “Development of Fully-Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions,” in Electrochemical Engineering: The Path from Discovery to Product, Volume XVIII of Advances in Electrochemical Science and Engineering, R. Alkire, editor, John Wiley & Sons, Hoboken, 2018, in press.

This work was supported by Mosaic Fertilizer LLC, Paul Kucera, program monitor.