Successful fertilizer plant start-up

CONSTRUCTION & COMMISSIONING

Successful fertilizer plant start-up

What lessons can be learnt from the successful commissioning and start-up of major fertilizer industry construction projects? Recent case studies from the nitrogen, phosphate and potash industries provide some interesting answers.

NITROGEN: CFCL THIRD AMMONIA/UREA PROJECT, INDIA

KBR’s most energy efficient ammonia plant

In January 2019, Chambal Fertilisers and Chemical Ltd (CFCL) successfully commissioned its third ammonia-urea unit (G3AU Project). This 2,200 t/d capacity ammonia and 4,000 t/d capacity urea plant is located at Gadepan near the city of Kota in Rajasthan, India1 . Since its commissioning, CFCL’s Gadepan complex has become India’s largest urea production site (Nitrogen+Syngas 364, p34).

Due to the high cost of natural gas in India, CFCL specified that the new plant should have the lowest possible energy consumption. The plant also needed to be self-sufficient in medium pressure (MP) steam.

To meet these requirements, the plant was configured with a gas turbine driving the process air compressor with the hot exhaust gas from the turbine used as preheated combustion air for the primary reformer (Fig. 1). This configuration improves the thermal efficiency of the gas turbine from around 30 percent to over 95 percent. It provides steam export to the urea plant for its turbine-driven CO2 compressor, and also eliminates the need for a forced draft fan and combustion air preheater. The newly-commissioned ammonia plant, due to these unique features, has become the world’s most energy efficient plant using KBR’s Purifier™ ammonia technology.

Project execution

Japan’s Toyo was awarded the engineering, procurement and construction (EPC) contract for the entire CFCL ammonia-urea plant, including outside battery limits. Toyo, in turn, awarded contracts to KBR for the ammonia plant license, basic engineering design and the supply of proprietary equipment.

To guarantee safety and quality, and ensure consistency in overall plant design, KBR also supported Toyo/CFCL in other activities, including:

• The review of the critical documents
• Critical equipment inspections
• Participation in Hazop
• 3D model reviews
• Supervision during catalyst loading of the reformer, ammonia converter etc.

Challenges and lesson learned

Examples of several challenges faced during plant commissioning and start-up – and how these were overcome – are provided below:

Purifier hydrogen leak

No leakage was initially detected from the purifier during a pre-start-up check with syngas at 30 kg/cm2 pressure. Nevertheless, a minor hydrogen leak was subsequently observed after commissioning the purifier during routine leak checks at plant. This was issuing from the sample point of the expander duct.

The hydrogen concentration of approximately four percent was diluted to about two percent by increasing the nitrogen flow to the duct. Nitrogen was also introduced at the vent point to avoid an explosive mixture. The leak from the flange in the expander compartment was ultimately reduced by cutting the syngas compressor suction pressure by 1.0 kg/cm2, which had the effect of increasing the load on the syngas turbine.

Cooling water pressure drop

The plant uses a plate-type heat exchanger to cool lean solution. During commissioning, cooling water flow through the lean cooler was found to be below design specification due to high pressure drop across the plates. This was discovered to be due to the installation of the wrong type of plates. After discussion with the vendor, the problem was resolved by replacing these and fitting the correct type of plates instead, as well as installing 20 percent extra plates to add more cooling capacity.

Valve faults

Purifier outlet valve: During start-up, a load limitation was being created by a high pressure drop (5 kg/cm2 ) observed between the expander outlet pressure and syngas suction pressure. To resolve this, the purifier outlet valve was replaced with a manual isolation valve during a short shutdown of the plant.

On checking, the purifier outlet valve was found to be stuck at 40 percent open position, so causing a high pressure drop, because the disc had disconnected from the stem.

Expander bypass valve: This was not operating smoothly during stroke checking. An inspection check by the vendor found that the valve stem had bent due to the actuator weight. It was discovered that the support for the valve actuator had not been fitted properly during the valve’s installation, causing bending of the valve stem. The valve was returned to normal operation by replacing this stem.

Anti-surge valve malfunction: An open anti-surge valve caused the ammonia plant to trip due to low air flow to the secondary reformer actuation. This resulted in low process air flow to the secondary reformer and ultimately prompted a full plant trip due to MP steam header fluctuation. The root cause of this malfunction was a heat leak from the control valve body. This was rectified by proper insulation of the valve body to avoid the heat leak to instruments.

The CFCL plant was successfully commissioned and became the world’s lowest energy ammonia plant despite the problems listed above.

PHOSPHATE: SERRA DO SALITRE PROJECT, BRAZIL

Brazil’s growing phosphates supply/ demand deficit over the next decade will have to be met by more imports and/or increases in domestic production capacity. The latter is set to receive a substantial boost with completion of the Serra do Salitre project this year.

Flagship investment project

The BRL 2.6 billion ($470 million) flagship project is the largest ever private sector investment in Minas Gerais state and ideally located, being close to Brazil’s major fertilizer-consuming markets. The project, originally a joint venture between Yara International and Brazilian producer Galvani, has been 100 percent Yara-owned since October 2018 (Fertilizer International 488, p45).

The Salitre project represents a major commitment by Yara to the growing Brazilian market, and a significant expansion of its in-country operations. The company invested $229 million in the project in 2020 following similar substantial investments in 2018 and 2019.

“The Serra do Salitre Mining-Industrial Complex is one of the largest private investments underway in Brazil and will double Yara’s fertilizer production capacity. The project allows the country to replace the import of 950 thousand tons per year of phosphate fertilizers, thus reducing the dependence on imports and the deficit in the sector’s trade balance, in addition to generating jobs and income for the national industry and supporting food production,” commented Leonardo Silva, vice president of production at Yara.

Two project phases

The Serra do Salitre project is divided into two phases. The initial phase, which came onstream in 2018, involved the completion of a 1.2 million tonne capacity phosphate rock mine and associated beneficiation plant. This delivered its first 150,000 tonnes of mined rock in early 2018. A one million tonne capacity production plant for finished phosphate products is now scheduled to be completed during the second half of this year, as part of the project’s second phase.

Building a fully integrated fertilizer production plant in Brazil is a costly, complex and highly ambitious venture. Almost inevitably, there has been some slippage in the project’s timetable, partly due to the Covid-19 pandemic, with finished phosphate production originally due to start-up in the first-quarter of 2020. Nevertheless, the scale of the project is such that it will increase national P2 O5 production by around 20 percent when it finally starts up.

Once operational, Serra do Salitre will generate:

• 900,000 tonnes of sulphuric acid
• 1.2 million tonnes of phosphate rock
• 250,000 tonnes of phosphoric acid
• One million tonnes of granulated finished phosphate products
• More than 1.2 million tonnes of gypsum
• 1,500 jobs during the operational phase
• Around 29 MW of energy.

Output from Salitre’s mine and beneficiation plant will also ensure that Yara’s Paulínia production plant in Sao Paulo state is self-sufficient in P2 O5 by providing a dedicated supply of phosphate rock.

Successful completion of phase one

Salitre’s transition-to-operation (TTO) began in 2017. This set 20 milestones and was vital to ensuring the successful on-time delivery of phase one of the project (Figure 2). The project’s TTO required the achievement of the following critical and sequential objectives:

• Extraction of 150,000 tonnes of phosphate rock during the mine development stage
• The first ore drop at the homogenisation yard
• Commissioning of the dry processing route
• Obtaining a preliminary operating license
• Process plant start-up
• Tailings dam operation start-up
• Production of first tonnages of phosphate rock concentrate
• Storage of 10,000 tonnes of phosphate rock concentrate at the coarse phosphate rock silo
• First-ore-on-truck (FOOT) to Paulínia
• First-ore-in-Paulínia (FOIP) processed
• First fertilizer lot produced at Paulínia using Salitre rock.

With the completion of the first phase of the project, phosphate rock is now being extracted and upgraded using froth flotation to produce a phosphate concentrate. This is currently supplying Yara’s Paulínia production plant in Sao Paulo state.

Serra do Salitre’s phosphate mine has an estimated life of 25 years. Friable ore is extracted by excavators and transported using a fleet of five 30-tonne Volvo trucks and 13 35-tonne Mercedes-Benz trucks. The ore is crushed at the mine before being transported to the beneficiation plant via a two-kilometre belt conveyor. Apatite-bearing ore with a P2O5 content of 4.7 precent is then upgraded in the beneficiation plant to produce a high-grade phosphate concentrate containing 33 percent P2O5 .

Phase one of the project involved the successful installation and commissioning of a range of mineral processing equipment, including: crushers, conveyors, mills, pulp, water and vacuum pumps, hydrocyclones, flotation columns, magnetic separators, thickeners and a filter press.

Final stages of phase two

Following successful completion of the first phase in 2018, construction of the project’s second phase is now scheduled to finish in the second half of 2021. Once operational, Serra do Salitre will ramp-up to annual production of 1.2 million tonnes of phosphate concentrate and 1.5 million tonnes of finished phosphates (SSP equivalent). Its product mix will include diammonium phosphate (DAP), monoammonium phosphate (MAP), nitrophosphate (NP), single superphosphate (SSP) and triple superphosphate (TSP).

Phase two of the project is now approaching the final stages of completion with the fertilizer production complex expected to enter operations within the next six months. Construction peaked in August 2019 when 3,800 workers were engaged on the project.

The Serra do Salitre complex includes a sulphuric acid plant, phosphoric acid plant and a fertilizer granulation plant. This has required the installation of major items of complex and interlinked process equipment such as boilers, heat exchangers, reactors, absorption towers, cooling towers, granulators, dryers and belt conveyors.

The amount or piping alone provides some indication of the scale-up in construction work between phases one and two of the project. “To have an idea of how challenging the works in phase two are… in phase one, [mineral] processing consumed 700 tonnes of piping,” commented Gustavo Horbach, Yara’s former project director. “Now, in phase two, there are three thousand tonnes.”

Once operations begin later this year and production then ramps-up in 2022, granulated fertilizers will be stored on site in two purpose-built 180,000 tonne capacity warehouses constructed from treated eucalyptus wood and reinforced concrete. These conical shaped and 30 metre-deep structures are partly underground and feature a fully-automated loading and unloading system. Materials enter the upper part of each warehouses and exit at the base, via a conveyor built within an underground concrete tunnel.

POTASH: ESTERHAZY K3 EXPANSION PROJECT, CANADA

Mosaic operates one of the world’s largest potash mining sites at Esterhazy, Saskatchewan, Canada. The site, which has been in operation since 1961, consists of the K1 and K2 potash mines, their respective K1 and K2 mills, and the under development K3 mine shafts. The Esterhazy complex produces a range of muriate of potash (MOP) products, including crystal, ag white, granular, and standard. The end-users for these products are primarily agricultural, supplemented by some industrial customers.

Ambitious expansion plans

Mosaic’s large-scale expansion plans for Esterhazy have involved increasing plant capacity at the K1 and K2 sites and building the new underground K3 operations. Upon completion, the ambitious K3 development will create one of the largest underground potash mines in the world (Fertilizer International 490, p43).

The objective of the K3 expansion is to install massive hoisting capacity at Esterhazy’s operations – which in turn will enable production of finished potash products on a much greater scale. K3, which is scheduled to be fully operational in 2022, will eventually replace the older K1 and K2 mines (Figure 3).

Hatch has been Mosaic’s long-term engineering partner at Esterhazy, dating back to the original project to expand the capacity of the K1 and K2 mills. Mosaic engaged Hatch as their full engineering, procurement, and construction management (EPCM) services partner following Hatch’s successful completion of the scoping, prefeasibility, and feasibility studies for this project.

By 2013, the K1 and K2 expansion projects had been completed below budget, with minimal negative impact to operations and an excellent safety record. Successful advances were also made in process automation and new production controls.

Massive state-of-the art operations

The current phase of the Esterhazy expansion is the construction of K3. This highly ambitious engineering project involved sinking twin shafts to a depth of just over 3,280 feet, and slip-forming two headframes with a design height of over 380 feet.

Hatch has participated in the K3 project from its initiation in 2008, starting with scoping-level studies all the way through to project development. Indeed, Hatch will continue to partner with Mosaic until K3 is fully commissioned and operational in 2022.

The Mosaic Company approved the first stage of development at K3 in 2009. This gave the go-ahead for the detailed design and construction management of two production shafts, headframes, and hoisting systems.

The North K3 headframe, the tallest structure in the province, houses and operates the massive hoists and skips that will transport potash to the surface from more than half a mile underground.

Shaft sinking

Saskatchewan’s geology is complex and also features high water pressures at depth. Hatch and Mosaic addressed these challenging conditions by using unique shaft-linings techniques when sinking the two 20-foot diameter shafts through water-bearing geological formations.

To accomplish this, both shafts were frozen to hold back groundwater while the permanent liner was installed. “To control water inflow from the Blairmore formation, we used unique technology to freeze the ground surrounding the shafts to a depth of 1,600 feet,” explains Scott Williamson, Hatch’s shaft manager. “The shaft is lined with concrete and steel in various configurations based on the geology encountered.” The permanent shaft liner consisted of support concrete, as well as a composite steel liner to prevent water ingress, where required.

K3 has two shafts. The first is used for both production and service, while the second is dedicated to production. The two pairs of production skips each have a 60-ton payload.

Following shaft sinking, the next hurdle was the slip-forming and mechanical fitout of the North headframe. This structure towers more than 380 feet above the prairies and houses two massive hoists – the Koepe and Blair. The Koepe hoist moves potash to the surface from underground, while the Blair hoist carries a cage for people and equipment. Hatch’s globally-responsive team of experts from Canada, Australia, and South Africa – working closely with Mosaic – designed the overall hoisting systems. These use leading-edge technology, state-of-the-art automation, and unique hoists.

Construction in two stages

Construction at K3 – comprising foundations, an electrical substation, ground freezing, shaft sinking and hoists – was scheduled in two stages. The first construction stage included:

• Site preparations
• Sinking and lining of the two shafts
• Hoist equipment and systems in the North shaft
• Egress hoist and headframe, bottom steel, surface facilities
• Preliminary mine development.

This phase of the project was completed in 2018.

The ongoing second construction stage involves:

• Replacing the temporary sinking head-frame in the South with a production headframe and hoisting system
• Completing the underground development
• Debottlenecking the K2 mill to achieve the final desired capacity of the Ester-hazy complex.

Shaft construction was performed using an unusual working platform – a five-level, shaft-sinking Galloway (see photo). An excavator suspended from the Galloway removes blasted muck to large buckets, which were then hoisted to the surface. Also, to reduce underground construction time, the steelwork of the shaft load-in station was modularised. To reduce shaft hoisting times and assembly times underground, innovative work practices were also used to lower the large quantity of heavy mobile equipment and bulk material handling systems.

Meeting major milestones

Years of careful planning were finally realised in February 2017. This was the date when the team celebrated a crucial K3 project milestone – the shaft finally reaching potash at a depth of 3,350 feet (Figure 1). Other major project milestones have been achieved in the four years since.

In May 2017, the team broke through the connection drift between the North and South shafts, located some 450 feet apart. This achievement was followed shortly after by the completion of the North shaft potash-level station.

The completion of the South shaft potash station, including the equipment assembly bay and electrical substation excavation, was subsequently completed in July that year. Then, in October 2017, another significant project objective was attained – the lights were turned on underground and a new, fully-assembled drum miner chassis, weighing 60 tons, was lowered into the mine.

The hoisting systems in the North shaft were commissioned in May 2018. This enabled K3 to enter operations and the ramp-up of production to begin. The next stage during 2019 was to finalise the design of the South headframe and associated equipment, before starting construction to replace the temporary headframe.

The South headframe

In August 2020, contractor Hamon Custodis Cottrell Canada, Inc commenced a continuous slip-form concrete pour to construct K3’s 313-foot-tall South headframe. The new headframe replaced the smaller temporary structure previously used for shaft sinking and the installation of shaft bottom steel in the mine.

The continuous pour would take a massive 784 concrete trucks and 24 backto-back days to complete. Incredibly, the structure grew upwards at a rate of six and a half inches per hour. Concrete trucks arrived every 45 minutes – delivering a total of 4,350 cubic meters of concrete. The headframe also incorporated three million pounds of rebar (reinforcing steel).

Once the South headframe was completed, outfitting began to prepare it for operation, with a focus on the hoist infrastructure that would be required to raise millions of tonnes of potash ore from K3 to the surface. The South shaft is solely dedicated to hoisting potash ore, unlike its sister North shaft which moves both people and materials. Indeed, the South headframe will double hoisting capacity at K3 – from 36,000 tonnes to 72,000 tonnes – once it becomes fully operational in 2022.

Work continued on the South headframe during the latter part of 2020 to add a roof penthouse, internal stairways, wall covers and a permanent 65-tonne overhead bridge crane for servicing the Koepe hoist. Mosaic reported further progress on the South shaft headframe in April this year. This included outfitting with piping, electrical trays, cable, lighting and other components.

A priority during the first half of 2021 will be the massive 2,000 tonne steel floors required to support the Koepe hoist and the 60-tonne skips used to raise ore to the surface. These steel floor will be assembled at ground level in modules and then raised to their final position using a hydraulic jacking system. Concurrently, the Koepe hoist, elevator and all the electrical/mechanical infrastructure will also be installed.

The next big milestone will be rope-up and installation of the large 60-ton skips. This is scheduled for autumn of 2021, with commissioning to follow.

Ramping up production

K3 continues to break records – setting a new daily tonnage record in February this year. Mosaic is now consistently hoisting ore through the North shaft and expects the average daily tonnage to continue increasing as they move into the second half of the year.

Underground engineering to support the production ramp-up is continuing – including work on the south surge, coarse ore bins and the mainline conveyor systems. The sixth four-rotor mining machine commenced cutting underground at K3 in January, while the first two-rotor mining machine was also available to start development work in February. As well as a further new machine added in April, Mosaic expects to deploy three more mining machines to the K3 fleet when the South headframe becomes operational next year.

All these new mining machines can run autonomously. In fact, Esterhazy’s engineering team is working towards automating the entire ore flow process – tracking potash as it moves underground from mining machines to conveyors to bins, before being hoisted upwards to the surface and then moved by overland conveyor to the K1 and K2 mills. These operations will be monitored from a state-of-the-art Integrated Operations Center (IOC). Mine automation at K3 is a part of Mosaic’s wider plans to revolutionise its business by adopting digital technology.

References

1. Singh U, et al., 2020. Successful commissioning of KBR world’s lowest energy ammonia plant at CFCL, Gadepan, India. CRU Nitrogen+Syngas 2020 Conference, 17-19th February, The Hague, The Netherlands.