Potash Project — Recovery Methods Report

This report details the proposed mechanical evaporation and crystallization process designed to recover potash (KCl) from sylvinite ore at a planned annual capacity of 300,000 tonnes.

Report context

This recovery methods report, dated to the original technical report, presents the preliminary process design for a proposed potash processing plant. The plant is designed to produce up to 300,000 tonnes of potash annually, based on the overall wellfield development, and two different standard products,crystal granular and white standard. The processing plant is scheduled to operate at up to 8,000 hours per year.

Processing route

Recovery method

Mechanical evaporation is the recovery method that will be used to recover KCl for the project. The recovery method was determined based on 300,000 mt/a (331,000 tons/a) of potash product. The sylvinite ore is predominantly water-soluble NaCl and KCl with minimal insoluble or carnallite.

Feed brine characteristics

A NaCl-saturated brine is heated to a temperature of 50°C and then injected into the wellfield at a rate of up to 250 m³/h. The brine, elevated in potassium, is returned through a production well, and then pumped to the triple-effect countercurrent evaporation system. The feed brine grade is 12.4 percent KCl, 19.4 percent NaCl, and 68.2 percent H₂O.

Triple-effect evaporation

Fresh wellfield brine and recycled brine from the crystallization stages are mixed and enter a train of eight triple-effect countercurrent evaporation systems (24 total units). Each individual evaporator (3 m [10 ft] diameter, 4.9 m [16 ft] high) is equipped with a 550 m² shell and tube heat exchanger. The system is capable of 203,600 kilograms per hour (kg/h) of water evaporation to meet the process requirements.

The brine is preheated by pumping through a primary steam condensate preheater, then sequentially enters the third effect evaporator, second effect evaporator, and first effect evaporator for concentration. Upon reaching target concentration (approximately 23 percent KCl, 17 percent NaCl), high-temperature material from the first evaporator is sent to a thickener, then to the 8 MT/h salt centrifuge for solid-liquid (concentrated brine) separation where NaCl solids are removed. The concentrated brine/mother liquor proceeds to cooling crystallization.

Steam for each of the eight evaporator circuits is produced in a 745 kilowatt (kW) (1,000 hp), 12,500 kilowatt-hour (kWh) (42 Million British Thermal Units per hour [MMBTU/hr]) steam boiler. Live steam enters the first evaporator shell side for heat exchange/condensation. The secondary steam from the first evaporator proceeds to the second evaporator's shell side and then the third evaporator's shell side. Secondary steam from the third evaporator is condensed in an indirect condenser and collected to mix with the precipitated NaCl solids from the solid-liquid separation to generate brine returning to the wellfield. Steam consumption through the circuit is estimated at 85,540 kg/h.

Crystallization

The concentrated brine enters the cooling crystallization circuit using three stages of crystallizers with external coolers. Each draft tube baffle crystallizer is 7.6 m (25 ft) in diameter and 7.9 m (26 ft) high, and is equipped with two 600 m² shell and tube heat exchangers. By controlling supersaturation, coarse KCl crystals accumulate at the bottom, and both halite and MOP are separated via two 28 MT/h pusher centrifuges to a target moisture content of 8 to 10 percent. Brine after the crystallization stage is returned to the feed tank to the evaporation stage to mix with the wellfield brine before being pumped to the evaporation stage.

Temperature and pressure are controlled to ensure a high-purity separation of NaCl and KCl solids and control the final product specification. The plant will produce three products based on different sizing standard constraints. The plant will also produce a granular product with a P50 of approximately 2.5 mm, a white standard MOP with a P50 of 0.5 mm, and then a fine product, which is the remaining potash that is 100 percent passing 0.3 mm. The fine product will be recirculated and recompacted to either the standard or granular products.

Fluidized bed dryer

Solid KCl separated from the centrifuges is delivered to the internal dust-removal fluidized bed dryer by a quantitative feeder to complete the drying process to a target 0.2 percent moisture for the dried KCl product. After, it enters the internal dust-removal and internal heat-exchange fluidized bed cooler for further cooling. The resulting KCl product is then screened and graded to one of two standard products,crystal granular and white standard.

The crystal granular product will have a mean particle size of 2.5 mm, with less than 0.5 percent passing 0.85 mm. The white standard will be the primary product and will have a mean particle size of 0.5 mm, and the fines will be 100 percent passing 0.3 mm.

Compaction, loadout, and product storage

Potash fines are compacted into flakes using high-pressure rolls, then granulated, screened, and polished to produce durable, dust-free granules suitable for use in fertilizer and other applications. Potash products are conveyed to loadout for direct shipping or to product storage. An anti-caking agent (a mixture of anti-cake and de-dusting oil) is added before being dispatched into product storage. Any material sent directly to loadout is treated with an anti-caking agent in loadout only. The product is held in the storage building until it is ready for loading into railcars for shipping.

Energy, water, and process materials

Thermal optimization has not been explored at this time. Energy requirements are estimated at 200 MBTU/h for natural gas, 40 MBTU/h for the boilers, and 160 MBTU/h for the dryers. Electric power for processing demand is expected to require an installed connected power of 15,900 kW, with a total site connected power demand of 24,000 kW.

Steam evaporation and fluid bed dryer venting are the primary sources of water losses. These streams will be condensed and collected as much as possible for reuse in the injection brine. Any fresh makeup water will come from the deep well(s) on the Property.

Very limited reagents are necessary for the proposed type of mechanical evaporation processing. The only reagents necessary are those for product polishing (e.g., anti-caking).

Key reported parameters

Technical qualifications

This report presents a preliminary process design for a proposed potash processing plant. All parameters, including annual capacity, product grade, plant recovery, and availability, are design basis values rather than historical operating data or testwork results. Thermal optimization has not been explored at this time. Energy requirements are estimates only. The flowsheet is a conventional evaporation and crystallization design that will make use of fluid bed dryers to dry the final potash product. Very limited reagents are necessary for the proposed type of mechanical evaporation processing. The report does not provide detailed flowsheet diagrams beyond a simplified block diagram (Figure 17-2) and general plant layout (Figure 17-1).

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*Source: Recovery Methods, Section 17.0, original technical report.*